making biodiesel experiment

8.2 The Reaction of Biodiesel: Transesterification

So, how do we make biodiesel?

The method being described here is for making FAMEs biodiesel. The reaction is called transesterification, and the process takes place in four steps. The first step is to mix the alcohol for reaction with the catalyst, typically a strong base such as NaOH or KOH. The alcohol/catalyst is then reacted with the fatty acid so that the transesterification reaction takes place. The first figure below shows the preparation of the catalyst with the alcohol, and the second figure shows the transesterification reaction.

The catalyst is prepared by mixing methanol and a strong base such as sodium hydroxide or potassium hydroxide. During the preparation, the NaOH breaks into ions of Na+ and OH-. The OH- abstracts the hydrogen from methanol to form water and leaves the CH 3 O- available for reaction. Methanol should be as dry as possible. When the OH- ion reacts with H+ ion, it reacts to form water. Water will increase the possibility of a side reaction with free fatty acids (fatty acids that are not triglycerides) to form soap, an unwanted reaction. Enzymatic processes can also be used (called lipases); alcohol is still needed and only replaces the catalyst. Lipases are slower than chemical catalysts, are high in cost, and produce low yields.

Once the catalyst is prepared, the triglyceride will react with 3 mols of methanol, so excess methanol has to be used in the reaction to ensure a complete reaction. The three attached carbons with hydrogen react with OH- ions and form glycerin, while the CH 3 group reacts with the free fatty acid to form the fatty acid methyl ester.

The figure below is a graphic of the necessary amounts of chemicals needed to make the reaction happen and the overall yield of biodiesel and glycerin. The amount of methanol added is almost double the required amount so the reaction goes to completion. With 100 lbs of fat and 16-20 lbs of alcohol (and 1 lb of catalyst), the reaction will produce 100 lbs of biodiesel and 10 lbs of glycerin. The reaction typically takes place at between 40-65°C. As the reaction temperature goes higher, the rate of reaction will increase, typically 1-2 hours at 60 °C versus 2-4 hours at 40°C. If the reaction is higher than 65°C, a pressure vessel is required because methanol will boil at 65°C. It also helps to increase the methanol-to-oil ratio. Doubling the ratio of 3 mols of alcohol to 6 mols will push the reaction to completion faster and more completely.

The following video shows a time-lapsed reaction of transesterification of vegetable oil into biodiesel. It also incorporates the steps after the reaction to separate out the biodiesel (9:44).

MARK HALL: Hello. I'm Mark Hall of the Auburn University Extension Renewable Energy Specialist. We're doing several of these things on energy options that you can do, several pieces that, each piece of the puzzle, that you can contribute to our energy independence by making ethanol, making biodiesel, being more energy efficient in how you operate your home. 

Today, we're going to talk about making biodiesel. And we have Lance Hall. Lance has been making biodiesel to run in his car. He bought a used Volkswagen off eBay and started making biodiesel. And he's liked it so much that he's bought a new diesel car. And he's been real successful doing this for a couple of years. 

Before we bring Lance in, I'd like to thank my friend and coworker Walter Harris, the county agent coordinator in Madison County, for filming us today. Lance, come in and show us what you've been doing. And congratulations. You've been successful doing this. 

I was talking to my daddy about my new job several years ago. And he said, well, Lance has been doing that for a long time. I said, what? I didn't know that. So Lance, show people how to make biodiesel. 

LANCE HALL: OK. A lot of people know about the biodiesel. They've read the stories. They've done some research. But, yet, they still don't have enough confidence in their ability to actually make a batch. So I'm going to show you today on how to make a batch of biodiesel, just small scale, but it's easy. 

OK. The first thing that we're going to do is start off with vegetable oil. Now, this will be 800 milliliters. And don't be confused between the milliliters and your normal units of measure. It's a simple conversion that anybody can do with a handheld calculator. 

So we've got 800 milliliters here. Well, first thing we want to do is heat it. Now, don't be concerned about this fancy piece of equipment, either. The main element of this is to heat it any way that you can safely. 

And these things here are magnetic stirrers. Again, don't be concerned with this. Just stir it while you're heating it to even things out. And we're going to heat this up to about 130 degrees Fahrenheit. 

MARK HALL: Lance, tell them about where you get this equipment. 

LANCE HALL: All of this equipment that I've got in my shop, all my lab stuff, eBay is a wonderful place to find a used lab supplies, lab glass. These are magnetic stirrer plates. These are really handy to have if you have the means to buy them. You don't have to have them, of course. But I like to use them. 

And this is also an electronic scale that comes in handy when you start weighing out your catalyst, doing anything that you want to measure a precise weight. That's worth the money there. And that's going to take a little while, so-- 

MARK HALL: Lance, is there any other sites, internet sites that you would recommend for people that are interested in making biodiesel? 

LANCE HALL: There are several sites out there. One of the most informative on what biodiesel is, where it's being used, is biodiesel.org. That's the National Biodiesel Board website, lots of good information there. It won't really tell you as much how to make it, but hopefully, this will be one of the more informative sites that you'll actually be able to see somebody make one, make a batch. 

OK. As our oil is heating up, we have to mix up our methanol potassium hydroxide mixture. So safety is paramount with the use of methanol or the strong caustic lye potassium hydroxide. Methanol can cause blindness or death, and it can be absorbed through the skin. And the potassium hydroxide will burn your skin if it gets on you. 

So here's what we're going to do. We're going to take our methanol and we're going to pour this into a container. Face shields are good, too. 

We're going to use 175 milliliters of the methanol. That's roughly 20% of the 800 milliliters of oil. You usually want to use about a 20% methanol volume compared to the veggie oil volume. 

OK. Our next ingredient is our potassium hydroxide. That's our lye. Now, we have to do a quick calculation on how much of this we need to mix with our methanol in order for the reaction to take place. 

I've got a nice spreadsheet that I like to use. It's the Biodiesel-o-matic. You can usually find it online from different biodiesel websites. I'm going to pull that up. 

OK. We want to use 7 grams of potassium hydroxide per each liter of veggie oil. So you take 7 divided by 0.8. And that gives you 6.4 grams. 

Double bag this stuff, or it will absorb moisture. And that will kill your process. 

So we're going to use our scale. We're going to zero the container. And then we're going to put 6.4 grams into it. Make sure you have your gloves on. 

OK. That's our 6.4 grams. Close this immediately. Keep it double-bagged. OK. Now, you're going to take your 6.4 grams of potassium hydroxide and put that into your 175 milliliters of methanol. 

Again, you want to stir this. It's not necessary to heat it, though. Just stir. And stir this until at least the potassium hydroxide is completely dissolved into the methanol. You don't want to see any chunks of white potassium hydroxide flakes. 

All right. Our potassium hydroxide is fully mixed into our methanol. We want to remove the stir bar. And then we're just going to slowly pour this into our oil as it's being stirred. 

Again, you don't have to have fancy equipment. Just pour it in as you're stirring it manually. But the key is to do it slowly. 

The figure below shows a schematic of the process for making biodiesel. Glycerol is formed and has to be separated from the biodiesel. Both glycerol and biodiesel need to have alcohol removed and recycled in the process. Water is added to both the biodiesel and glycerol to remove unwanted side products, particularly glycerol, that may remain in the biodiesel. The wash water is separated out similar to solvent extraction (it contains some glycerol), and the trace water is evaporated out of the biodiesel. Acid is added to the glycerol in order to provide neutralized glycerol.

Schematic of the biodiesel process using transesterification:

Oil, alcohol, and a catalyst undergo transesterification. From there they are mixed methyl esters from which crude glycerol is removed. The crude glycerol goes into a separator under heat and a vacuum in which alcohol is removed. It then goes through a water wash and is neutralized with acid to produce neutralized glycerol. The other remaining mixed methyl esters from transesterification go into a different separator which removes any alcohol. They then undergo an extraction using water and move into a second separator under heat and a vacuum that removes any water. This yields biodiesel.

As briefly discussed, the initial reactants used in the process should be as dry as possible. Water can react with the triglyceride to make free fatty acids and a diglyceride. It can also dissociate the sodium or potassium from the hydroxide, and the ions Na+ and K+ can react with the free fatty acid to form soap. The figure below shows how water can help to form a free fatty acid, and that free fatty acid can react with the Na+ ion to form soap. The sodium that was being used for a catalyst is now bound with the fatty acid and unusable. It also complicates separation and recovery. All oils may naturally contain free fatty acids. The refined vegetable oil contains less than 1%, while crude vegetable oil has 3%, waste oil has 5%, and animal fat has 20%. Animal fats are a less desirable feedstock.

Biomass - Creating Bio-Diesel

Matthew A. Brown, Raymond I. Quintana, National Renewable Energy Laboratory

This detailed chemistry lesson from the U.S. Department of Energy focuses on transforming vegetable oil into biodiesel through a process of transesterification. The process described offers a good model for many chemical reaction processes that are used to produce a viable product.

Notes from our reviewers

The CLEAN collection is hand-picked and rigorously reviewed for scientific accuracy and classroom effectiveness. Read what our review team had to say about this resource below or learn more about how CLEAN reviews teaching materials .

• Teaching Tips An undergraduate Chemistry background should be sufficient for the teacher to proceed with leading this experience. Teachers with less Chemistry experience could lead this experiment after first running through it themselves, and with careful attention to safety precautions.
• About the Science Well-presented and comprehensive lab. Students make a fuel that is quite safe to handle, and safety precautions are thoroughly addressed. Students are given a list of vocab words and a background on biodiesel history, potential benefits, and current global usage facts as it pertains to passenger cars. Introduces advanced chemistry topics, such as esterification, and basic topics, such as titration, and applies them to making an actual fuel. Biofuels do have environmental impacts, including the release of formaldehyde other aldehydes into the environment when produced and burned. See: [http://en.wikipedia.org/wiki/Issues_relating_to_biofuels#Pollution] Biofuels can have drawbacks in terms of the energy it takes to produce them. This science is emerging, so educators should find current information about this aspect, if needed. This project was written by two DOE ACTS Fellows under the direction of scientists and education programs staff at NREL. Comments from expert scientist: Scientifically this resource is very sound and relevant, as 1 billion gallons of biodiesel per year are produced from soybean oil. The resource introduces the concept of biofuels/renewable fuels and 6 exercises are given to illustrate why biofuels are useful and being researched, as well as how to make biodiesel from vegetable oil.
• About the Pedagogy Students first practice the chemical process to create bio-diesel with new oil, then use a series of tests to determine the correct proportions to work with used oils, providing a well-scaffolded, authentic learning experience. Well-written lab activity with cross-curriculum connections to Tech Ed classes a good way to integrate learning about renewable energy into an existing chemistry curriculum.
• Technical Details/Ease of Use Necessary materials may need to be ordered ahead of time. Takes quite a bit of time and effort; in some cases it is a time-intensive activity. Although the fuel is not dangerous, the idea of making a fuel in a school may not be well received. Biodiesel bottles will need to be left for a week to separate.

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Learning about materials: making biodiesel, part one

The Learning about materials resources collection presents educational resources about materials in the form of teacher’s notes and photocopiable worksheets. This resource contains instructions for practical work on a) making a biodiesel and b) comparing it to fossil diesel, as well as a comprehension exercise, and a team exercise.

Making biodiesel

Making biodiesel - teacher's notes, learning about materials - introduction.

• 14-16 years
• Practical experiments
• Teacher notes
• Industrial processes
• Natural resources
• Sustainability

Specification

• Biodiesel is produced by reacting vegetable oils with methanol in the presence of a catalyst.
• 14. understand the use of alternative fuels, including biodiesel and alcohols derived from renewable sources such as plants, in terms of a comparison with non-renewable fossil fuels
• (a) social, economic and environmental impact of chemical synthesis and the production of energy
• 2.5.10 describe the incomplete combustion of alkanes to produce carbon monoxide and water and sometimes carbon (soot – equations for the production of soot are not required);
• 2.5.28 demonstrate knowledge that the combustion of fuels is a major source of atmospheric pollution due to: combustion of hydrocarbons producing carbon dioxide, which leads to the greenhouse effect causing sea level rises, flooding and climate change;…
• 2.5.26 demonstrate knowledge that the combustion of fuels is a major source of atmospheric pollution due to: combustion of hydrocarbons producing carbon dioxide, which leads to the greenhouse effect causing sea level rises, flooding and climate change…
• 2. Research different energy sources; formulate and communicate an informed view of ways that current and future energy needs on Earth can be met.
• 10. Appreciate the role of science in society; and its personal, social and global importance; and how society influences scientific research.

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Projects from Make: Magazine

Backyard biodiesel.

Convert vegetable oil into a liter of biodiesel fuel.

• Time Required!: Six hours over three days
• Print this Project

By Rob Elam

It’s easy to make a small batch of biodiesel that will work in any diesel engine, from a model airplane engine to the family car. You don’t need any special equipment — an old juice bottle will serve as the “reactor” vessel — and on such a small scale you can quickly refine your technique and perform further experiments. After a few liters’ worth of experience, you’ll know if you’ve been bitten by the biodiesel bug.

The principle behind biodieseling is to take vegetable oil (either new or used), and process it into a fuel that’s thin enough to spray from a regular diesel engine’s fuel-injection system. This is done chemically, by converting the oil into two types of compounds: biodiesel, which shares the original oil’s combustibility, and glycerin, which retains the oil’s thick, viscous properties. Drain away the glycerin, and you’re left with a fuel that you can pour into any diesel vehicle with no further modification.

Once you get to the far side of the learning curve, making biodiesel is very much like cooking. In fact, a commercial biodiesel production plant shares more in common with a large-scale bakery than a petroleum refinery. There’s organic chemistry involved in baking a cake, but most bakers wouldn’t consider themselves organic chemists.

Project Steps

Biodiesel homebrewing safety.

While biodiesel is safe to handle and store, the homebrewing process involves flammable, poisonous, and caustic chemicals, alcohols, and lye.

Keep all chemicals clearly labeled, sealed, and out of reach of children and pets. When handling methanol and lye, wear long sleeves, safety glasses, and gloves made out of nitrile — or, even better, PVC.

Wash the gloves after each use, and be careful not to touch your skin or eyes. Keep a water hose nearby in case of skin contact. Methanol can be absorbed through the skin, so wash immediately with water if contact occurs. Immediately flush lye off skin with water or vinegar.

Methanol fumes are poisonous, so wear a mask, or hold your breath while pouring, and work outside or with good ventilation.

Filter and De-water your oil

If you’re using new oil, you can skip to Step #5. But if you’re starting with waste oil from a restaurant fryer, it will contain food particles, water, and free fatty acids (FFAs) — contaminants that you need to remove or adjust for. The FFAs make the oil more acidic, (a.k.a. rancid), which counters the effect of the lye.

You can compensate for this by adding more lye into the main reaction later, but you need to perform a titration test beforehand in order to determine how much extra lye you’ll need.

Start with more than one liter of oil, since the following steps will slightly reduce your oil’s volume.

Warm the oil to about 95ºF in a pot on an electric hot plate (don’t use a gas burner, here or anywhere else in this project), then filter it through a few layers of cheesecloth in a funnel (or use a coffee filter).

Heat the oil to 140ºF and maintain the temperature for 15 minutes.

The water will fall to the bottom, so you’ll risk steam explosions if the temperature gets too high. Pour the oil into a bottle or other vessel and let it settle for at least 24 hours. This removes water, which would produce soap in your batch. If you see water at the bottom (it will be dirty, not clear), don’t pour it back out with the oil.

Test your oil to determine its acidity

Dissolve one gram of lye in one liter of distilled water (0.1% lye solution), or use an equivalent ratio to make a smaller amount.

This is your reference test solution, which you can store sealed and re-use for later batches.

In a small jar, dissolve 1ml of slightly warm oil in 10ml of isopropyl alcohol.

Stir until clear, then add two drops of phenolphthalein solution.

Using a graduated syringe or dropper, add your reference test solution drop-by-drop into the oil/alcohol solution, keeping track of how much you’re using. The more acidic the oil, the more you’ll need to add.

Stir constantly, and continue adding solution until the mixture stays pink for ten seconds.

Note the number of milliliters of lye solution you used; this is the number of extra grams of lye you’ll need to add per liter of oil.

This process is called “titration,” and it’s a standard method of determining a solution’s acidity.

Process the oil

This is the main chemical reaction that produces the biodiesel.

First, calculate how much lye you need.

If you’re using new oil, use 5 grams of NaOH or 7 grams of KOH per liter.

With used oil, use these amounts plus one gram for every milliliter of solution you used in the titration step 7.

For example, if it took 1.5ml of lye solution to turn the mixture pink, use 6.5g of NaOH or 8.5g of KOH.

Measure your lye into a clean Mason jar.

Add 220ml of methanol, cover securely, and tip the jar to make sure the lid doesn’t leak.

Then swirl or shake the jar gently until the lye dissolves fully. This will take a few minutes, and the jar will become slightly warm in the process.

This mixture is the methoxide solution, and it’s dangerous stuff; you’ll need to wash the Mason jar lid after you’re done with your batch, or its seal will dissolve. (Some regular homebrewers prepare methoxide ahead of time and store it in #2 HDPE plastic.)

Warm a liter of your oil up to 130ºF. Let it cool down if the temperature gets too high.

Pour the oil into a large bottle, add the methoxide solution, cap tightly, and shake like crazy for about five minutes.

The contents might change color a couple of times.

Set this mixture aside, and admire.

In half an hour or so, you should see a darker, dirty, glycerin layer start to sink toward the bottom, and a larger, lighter, biodiesel layer rise to the top. This is a good time to clean up.

If you’re sure your bottle won’t leak, you may want to let it settle upside-down, so you can drain the glycerin out by cracking the bottle cap. Or you can lay it sideways to make it easier to pour off the biodiesel.

Let the liquids continue to settle overnight.

Separate, wash, and dry your biodiesel

Your bottle now contains biodiesel, glycerin, mono- and di-glycerides, soap, methanol, lye, and possibly a little leftover oil (triglycerides). The glycerides are all oil-soluble, so they’ll reside predominantly in the upper, biodiesel layer. The thin layer of glycerin, which is water-soluble, will sink.

Depending on the oil and catalyst you used, it might be either liquid or solid. Soap, methanol, and lye, which are also water soluble, will be mixed throughout both layers — although some of the soap can sometimes form its own thin layer between the biodiesel and glycerin.

If you see more than two layers, or only one, then something’s wrong — possibly excessive soap or monoglyceride formation. These are both emulsifiers, and in sufficient quantities they will prevent separation. In this case, check your scales, measurements, and temperatures. You can reprocess the biodiesel with more methoxide, or try again with fresher oil (or new oil). If you can, shake the bottle even harder next time.

In an engine, glycerin droplets in biodiesel will clog fuel filters, soap can form ash that will damage injectors, and lye can also abrade fuel injectors. Meanwhile, methanol has toxic and combustible fumes that make biodiesel dangerous to store. You don’t want any of these contaminants in your biodiesel. If you left your biodiesel to settle undisturbed for several weeks, these water-soluble impurities would slowly fall out of the biodiesel (except for the methanol). Washing your biodiesel with water removes the harmful impurities, including the methanol, much faster.

Unfortunately, washing will not remove the invisible, oil-soluble mono- and di-glycerides. These are a problem in rare instances when large amounts of certain types of monoglycerides crystallize. This can clog fuel filters and injectors, and cause hard starts, especially in cold weather. High-quality, commercial biodiesel has very low levels of mono- and di-glycerides, which is the ideal for biodiesel homebrewing.

You can roughly test for the presence of mono- and di-glycerides in your own batch by processing it a second time, as if it were vegetable oil, starting with step 2 again. If more glycerin drops out, then your first reaction left some unfinished business behind.

Pour the biodiesel layer off the top, into another bottle.

Don’t pour off any of the glycerin, as it makes washing difficult; better to leave a little biodiesel behind.

If you let the bottle settle upside-down, drain the glycerin from the bottom.

Gently add some warm distilled water to the biodiesel.

Rotate the bottle end over end, until the water starts to take on a little bit of white soapiness, which may take a few minutes.

Do not shake the bottle. You want to bring water and biodiesel into contact, without mixing it too vigorously. The biodiesel contains soap, and if you overdo the agitation, the soap, biodiesel, and water will make a stable emulsion that won’t separate.

Turn the bottle upside-down, crack the cap, and drain away the soapy water.

If you’re using a soft drink bottle with a narrow neck, you can plug the opening with your thumb instead of using the cap.

Add more warm water and keep repeating the sloshing and draining process. Each time there will be less soap, and you can mix a little more vigorously.

If you go too far and get a pale-colored emulsion layer between the biodiesel and white, soapy water, don’t drain it away; it’s mostly biodiesel. Just keep washing and diluting until the water becomes clear and separates out quickly.

It takes a lot of water. But if the emulsification layer persists, try applying heat, adding salt, and adding vinegar, in that order.

After draining the last wash water away, let the biodiesel sit to dry in open air until it’s perfectly clear, which may take up to a couple of days. In general, the better your washing, the faster the fuel will clear.

If you’re in a hurry, you can dry the fuel faster by heating it at a low temperature. As with the evaporation method, the fuel is done when it clears.

If you can read a newspaper through the biodiesel, it’s dry and ready to pour into a vehicle. Congratulations — you’re done!

Biodiesel Chemistry (background information)

Vegetable oil is a triglyceride, which means that its molecule consists of a glycerin “backbone” with three fatty acids attached, forming a shape like a capital letter E. To make biodiesel, we add lye and methanol. The highly caustic lye breaks the three fatty acid branches off of the glycerin backbone. These free fatty acids then bond with the methanol, which turns them into fatty acid methyl esters — otherwise known as biodiesel. The freed glycerin, which is heavier, sinks to the bottom, leaving the fuel (and lye) on top. Wash the lye out of the upper layer, and you have pure biodiesel.

But it’s not that simple. With some triglyceride molecules, only one or two fatty-acid branches break off, which leaves mono- or di-glyceride molecules (shaped like capital Ts or Fs), rather than free glycerin. At the same time, mixing methanol and lye produces some water — and oil, water, and lye mixed together make soap. With all of these incomplete and competing chemical reactions, your batch will inevitably contain soap, water, leftover lye, methanol, and mono- and di-glycerides, along with the nice biodiesel and glycerin. Mono- and di-glycerides are emulsifiers, so they prevent mixed liquids from separating, making it harder to extract biodiesel. The picture gets even muddier when you use waste vegetable oil rather than pure oil, since it contains free fatty acids, water, and countless random contaminants from all those French fries.

These by-products are bad for an engine, potentially causing micro-abrasions that damage fuel injectors or clog fuel filters. But you can remove them by washing or cooking the biodiesel in various ways, or by processing the incompletely converted biodiesel again, as if it were vegetable oil. In extreme cases, you’ll end up with a thick, soapy mass that never separates. All biodieselers wind up with a batch of this glop sooner or later. Fortunately, you can use it to make a good, grease-cutting soap — which is something that all biodiesel homebrewers need to have on hand.

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How to Make Biodiesel From Vegetable Oil

Juanmonino / Getty Images

• Ph.D., Biomedical Sciences, University of Tennessee at Knoxville
• B.A., Physics and Mathematics, Hastings College

Biodiesel is a diesel fuel that is made by reacting vegetable oil (cooking oil) with other common chemicals. Biodiesel may be used in any diesel automotive engine in its pure form or blended with petroleum-based diesel. No modifications are required, and the result is a less-expensive, renewable, clean-burning fuel.

Here's how to make biodiesel from fresh oil. You can also make biodiesel from waste cooking oil, but that is a little more involved, so let's start with the basics.

Materials for Making Biodiesel

• 1 liter of new vegetable oil (e.g., canola oil, corn oil, soybean oil)
• 3.5 grams (0.12 ounces) sodium hydroxide (also known as lye). Sodium hydroxide is used for some drain cleaners. The label should state that the product contains sodium hydroxide ( not calcium hypochlorite, which is found in many other drain cleaners).
• 200 milliliters (6.8 fluid ounces) of methanol (methyl alcohol). Heet fuel treatment is methanol. Be sure the label says the product contains methanol (Iso-Heet, for example, contains isopropyl alcohol and won't work).
• Blender with a low-speed option. The pitcher for the blender is to be used only for making biodiesel. You want to use one made from glass, not plastic because the methanol you will use can react with plastic.
• Digital scale to accurately measure 3.5 grams, which equals 0.12 ounces
• Glass container marked for 200 milliliters (6.8 fluid ounces). If you don't have a beaker, measure the volume using a measuring cup, pour it into a glass jar, then mark the fill-line on the outside of the jar.
• Glass or plastic container that is marked for 1 liter (1.1 quarts)
• Widemouthed glass or plastic container that will hold at least 1.5 liters (2-quart pitcher works well)
• Safety glasses, gloves, and an (optional) apron

You do not want to get sodium hydroxide or methanol on your skin, nor do you want to breathe the vapors from either chemical. Both are toxic. Please read the warning labels on the containers for these products. Methanol is readily absorbed through your skin, so do not get it on your hands. Sodium hydroxide is caustic and will give you a chemical burn. Prepare your biodiesel in a well-ventilated area. If you spill either chemical on your skin, rinse it off immediately with water.

How to Make Biodiesel

• You want to prepare the biodiesel in a room that is at least 70 degrees F because the chemical reaction will not proceed to completion if the temperature is too low.
• If you haven't already, label all your containers as "Toxic—Only Use for Making Biodiesel." You don't want anyone drinking your supplies, and you don't want to use the glassware for food again.
• Pour 200 milliliters methanol (Heet) into the glass blender pitcher.
• Turn the blender on its lowest setting and slowly add 3.5 grams sodium hydroxide (lye). This reaction produces sodium methoxide, which must be used right away or else it loses its effectiveness. (Like sodium hydroxide, it can be stored away from air/moisture, but that might not be practical for a home setup.)
• Mix the methanol and sodium hydroxide until the sodium hydroxide has completely dissolved (about 2 minutes), then add 1 liter of vegetable oil to this mixture.
• Continue blending this mixture (on low speed) for 20 to 30 minutes.
• Pour the mixture into a widemouthed jar. You will see the liquid start to separate out into layers. The bottom layer will be glycerin. The top layer is biodiesel.
• Allow at least a couple of hours for the mixture to fully separate. You want to keep the top layer as your biodiesel fuel. If you like, you can keep the glycerin for other projects. You can either carefully pour off the biodiesel or use a pump or baster to pull the biodiesel off of the glycerin.

Using Biodiesel

Normally, you can use pure biodiesel or a mixture of biodiesel and petroleum diesel as a fuel in any unmodified diesel engine. There are two situations in which you definitely should mix biodiesel with petroleum-based diesel:

• If you are going to be running the engine at a temperature lower than 55 degrees Fahrenheit (13 degrees C), you should mix biodiesel with petroleum diesel. A 50:50 mixture will work in cold weather. Pure biodiesel will thicken and cloud at 55 degrees Fahrenheit, which could clog your fuel line and stop your engine. Pure petroleum diesel, in contrast, has a cloud point of -10 degrees Fahrenheit (-24 degrees C). The colder your conditions, the higher the percentage of petroleum diesel you will want to use. Above 55 degrees Fahrenheit, you can use pure biodiesel without any problem. Both types of diesel return to normal as soon as the temperature warms above their cloud point.
• You will want to use a mixture of 20% biodiesel with 80% petroleum diesel (called B20) if your engine has natural rubber seals or hoses. Pure biodiesel can degrade natural rubber, though B20 tends not to cause problems. If you have an older engine (which is where natural rubber parts are found), you could replace the rubber with polymer parts and run pure biodiesel.

Biodiesel Stability and Shelf Life

You probably don't stop to think about it, but all fuels have a shelf life that depends on their chemical composition and storage conditions. The chemical stability of biodiesel depends on the oil from which it was derived.

Biodiesel from oils that naturally contain the antioxidant tocopherol or vitamin E (e.g., rapeseed oil) remain usable longer than biodiesel from other types of vegetable oils . According to Jobwerx.com, stability is noticeably diminished after 10 days, and the fuel may be unusable after two months. Temperature also affects fuel stability in that excessive temperatures may denature the fuel.

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Make Biodiesel!

Introduction: Make Biodiesel!

Step 1: Safety

Step 2: Necessary Supplies

Step 3: filter the wvo.

Step 4: Titrate Your Oil

Step 5: Prep the Oil

Step 6: Methoxide Mixing and Introduction to the WVO

Step 7: draining the glycerin.

Step 8: What's Next?

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Making biodiesel from dirty old cooking oil just got way easier

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Researchers have developed a powerful, low-cost method for recycling used cooking oil and agricultural waste into biodiesel, and turning food scraps and plastic rubbish into high-value products.

The method harnesses a new type of ultra-efficient catalyst that can make low-carbon biodiesel and other valuable complex molecules out of diverse, impure raw materials.

Waste cooking oil currently has to go through an energy-intensive cleaning process to be used in biodiesel, because commercial production methods can only handle pure feedstocks with 1-2% contaminants.

The new catalyst is so tough it can make biodiesel from low-grade ingredients, known as feedstock, containing up to 50% contaminants.

It is so efficient it could double the productivity of manufacturing processes for transforming rubbish like food scraps, microplastics and old tyres into high-value chemical precursors used to make anything from medicines and fertilisers to biodegradable packaging.

The catalyst design is reported in a new study from an international collaboration led by RMIT University, published in Nature Catalysis.

Co-lead investigator Professor Adam Lee, RMIT, said that conventional catalyst technologies depended on high purity feedstocks and required expensive engineering solutions to compensate for their poor efficiency.

“The quality of modern life is critically dependent on complex molecules to maintain our health and provide nutritious food, clean water and cheap energy,” Lee said.

“These molecules are currently produced through unsustainable chemical processes that pollute the atmosphere, soil and waterways.

“Our new catalysts can help us get the full value of resources that would ordinarily go to waste – from rancid used cooking oil to rice husks and vegetable peelings – to advance the circular economy.

“And by radically boosting efficiency, they could help us significantly reduce environmental pollution from chemical manufacturing and bring us closer to the green chemistry revolution.”

Catalyst sponge: advancing green chemistry

To make the new ultra-efficient catalyst, the team fabricated a micron-sized ceramic sponge (100 times thinner than a human hair) that is highly porous and contains different specialised active components.

Molecules initially enter the sponge through large pores, where they undergo a first chemical reaction, and then pass into smaller pores where they undergo a second reaction.

It’s the first time a multi-functional catalyst has been developed that can perform several chemical reactions in sequence within a single catalyst particle, and it could be a game changer for the $US34 billion global catalyst market.

Co-lead investigator Professor Karen Wilson, also from RMIT, said the new catalyst design mimicked the way that enzymes in human cells coordinated complex chemical reactions.

“Catalysts have previously been developed that can perform multiple simultaneous reactions, but these approaches offer little control over the chemistry and tend to be inefficient and unpredictable,” Wilson said.

“Our bio-inspired approach looks to nature’s catalysts – enzymes – to develop a powerful and precise way of performing multiple reactions in a set sequence.

“It’s like having a nanoscale production line for chemical reactions – all housed in one, tiny and super-efficient catalyst particle.”

DIY diesel: supporting distributed biofuel production

The sponge-like catalysts are cheap to manufacture, using no precious metals.

Making low-carbon biodiesel from agricultural waste with these catalysts requires little more than a large container, some gentle heating and stirring.

It’s a low-technology, low-cost approach that could advance distributed biofuel production and reduce reliance on fossil fuel-derived diesel.

“This is particularly important in developing countries where diesel is the primary fuel for powering household electricity generators,” Wilson said.

“If we could empower farmers to produce biodiesel directly from agricultural waste like rice bran, cashew nut and castor seed shells, on their own land, this would help address the critical issues of energy poverty and carbon emissions.”

While the new catalysts can be used immediately for biodiesel production, with further development they could be easily tailored to produce jet fuel from agricultural and forestry waste, old rubber tyres, and even algae.

The next steps for the RMIT School of Science research team are scaling up the catalyst fabrication from grams to kilograms and adopting 3D printing technologies to accelerate commercialisation.

“We’re also hoping to expand the range of chemical reactions to include light and electrical activation for cutting-edge technologies like artificial photosynthesis and fuel cells,” Lee said.

“And we’re looking to work with potential business partners to create a range of commercially available catalysts for different applications.”

The research was supported through funding from the Australian Research Council (Discovery, Linkage, Industrial Transformation Training Centres).

‘ A spatially orthogonal hierarchically porous acid-base catalyst for cascade and antagonistic reactions ’, with collaborators from University College London, University of Manchester, University of Western Australia, University of Plymouth, Aston University, Durham University and University of Leeds, is published in Nature Catalysis (DOI: 10.1038/s41929-020-00526-5).

Story: Gosia Kaszubska

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Farm Energy

Biodiesel Production Principles and Processes

Introduction.

The process to make biodiesel involves a chemical reaction. This means that the biodiesel industry is a chemical industry. Those involved in making biodiesel must have a good understanding of the underlying chemistry to ensure they are making quality fuel in a safe manner.

Biodiesel is an alternative fuel for diesel engines that is produced by chemically reacting a vegetable oil or animal fat with an alcohol such as methanol or ethanol. In words, the reaction is:

The photo shows a bottle of biodiesel and glycerin (also called glycerol). The biodiesel is the lighter-colored layer at the top. The darker-colored crude glycerin has settled to the bottom.

It is important to realize that unmodified vegetable oil, sometimes called straight vegetable oil (SVO) or waste vegetable oil (WVO), is not biodiesel. Some people have used SVO or WVO in diesel engines with varying degrees of success. The primary problem is the high viscosity and low volatility of the unmodified vegetable oils. Without exception, U.S. engine manufacturers have recommended against the use of SVO and WVO. More discussion of SVO and WVO can be found here .

Biodiesel is usually preferred over SVO and WVO because the chemical reaction converts the oil or fat into compounds that are closer to the hydrocarbons found in regular diesel fuel.

The chemical reaction that converts a vegetable oil or animal fat to biodiesel is called “transesterification.” This is a long name for a simple process of combining a chemical compound called an “ester” and an alcohol to make another ester and another alcohol. Oils and fats are included in the ester family. When they react with methanol or ethanol, they make methyl or ethyl esters and a new alcohol called glycerol or, more commonly, glycerin.

The vegetable oils and animal fats used to make biodiesel can come from virtually any source. All of these products consist of chemicals called triglycerides, so biodiesel can be made from soybean oil, canola oil, beef tallow, and pork lard, and even from such exotic oils as walnut oil or avocado oil.

Even used cooking oil or waste oil can be used to make biodiesel. However, these oils present special challenges for biodiesel production because they contain contaminants such as water, meat scraps, and breading that must be filtered out before the oil is converted to biodiesel.

Methanol is the most common alcohol used for making biodiesel. It is sometimes called methyl alcohol or wood alcohol. It is very toxic, and swallowing as little as a spoonful can cause blindness or even death. Dangerous exposure can also occur from breathing methanol vapors or absorbing methanol through skin contact. In the United States, ethanol is usually more expensive than methanol, so it is used less frequently to make biodiesel. It is the alcohol that is found in alcoholic drinks, so it is not toxic in small amounts. However, it is subject to very challenging government regulations because of the tax requirements associated with alcoholic beverages.

The chemical reaction used to make biodiesel requires a catalyst. A catalyst is usually a chemical added to the reaction mixture to speed up the reaction. Since the catalyst is not consumed in the reaction, it will be left over at the end in some form. In biodiesel production, the actual compound that catalyzes the reaction is called methoxide. One common way to make methoxide is to dissolve sodium hydroxide or potassium hydroxide in methanol. Large producers buy a solution of sodium methoxide in methanol that is much safer to work with.

High-quality biodiesel is defined by compliance with the American Society for Testing and Materials (ASTM) specification D6751. Fuel testing to verify compliance can be expensive, especially for small producers, but it is the most reliable way to ensure that fuel consumers will have access to high-quality fuel.

More Topics on Biodiesel Production

Oilseed crops for biodiesel production, oilseed handling for biodiesel production, used and waste oil and grease for biodiesel, feedstock pretreatment in biodiesel production, safe chemical handling in biodiesel production, commercial and large scale biodiesel production systems, small scale biodiesel production systems, mobile biodiesel production systems, reactors for biodiesel production, equipment for biodiesel production systems, controls and instrumentation for biodiesel production, biodiesel fuel quality, transportation and storage of biodiesel, processor capacity for biodiesel production, post-treatment in biodiesel production, waste management in biodiesel production, methanol recovery during small scale biodiesel production, saponification in biodiesel production, methoxide catalysts in biodiesel production, new uses for crude glycerin from biodiesel production, for additional information.

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Contributors to This Article

• Jon Van Gerpen, Professor, Department of Biological and Agricultural Engineering, National Biodiesel Education Program , University of Idaho

Peer Reviewers

• Joe Thompson, Research Support Scientist, Department of Biological and Agricultural Engineering, National Biodiesel Education Program , University of Idaho
• Cole Gustafson , Biofuels Economist, North Dakota State University

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Article Contents

Introduction, edible sources—virgin oil, nonedible sources, algae-based biodiesel, conclusions, acknowledgments.

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Biodiesel production—current state of the art and challenges

• Article contents
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Palligarnai T Vasudevan, Michael Briggs, Biodiesel production—current state of the art and challenges, Journal of Industrial Microbiology and Biotechnology , Volume 35, Issue 5, 1 May 2008, Page 421, https://doi.org/10.1007/s10295-008-0312-2

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Biodiesel is a clean-burning fuel produced from grease, vegetable oils, or animal fats. Biodiesel is produced by transesterification of oils with short-chain alcohols or by the esterification of fatty acids. The transesterification reaction consists of transforming triglycerides into fatty acid alkyl esters, in the presence of an alcohol, such as methanol or ethanol, and a catalyst, such as an alkali or acid, with glycerol as a byproduct. Because of diminishing petroleum reserves and the deleterious environmental consequences of exhaust gases from petroleum diesel, biodiesel has attracted attention during the past few years as a renewable and environmentally friendly fuel. Since biodiesel is made entirely from vegetable oil or animal fats, it is renewable and biodegradable. The majority of biodiesel today is produced by alkali-catalyzed transesterification with methanol, which results in a relatively short reaction time. However, the vegetable oil and alcohol must be substantially anhydrous and have a low free fatty acid content, because the presence of water or free fatty acid or both promotes soap formation. In this article, we examine different biodiesel sources (edible and nonedible), virgin oil versus waste oil, algae-based biodiesel that is gaining increasing importance, role of different catalysts including enzyme catalysts, and the current state-of-the-art in biodiesel production.

JIMB 2008: BioEnergy—special issue.

Biodiesel is a clean-burning fuel currently being produced from grease, vegetable oils, or animal fats. Its chemical structure is that of fatty acid alkyl esters. Biodiesel is produced by transesterification of oils with short-chain alcohols or by the esterification of fatty acids. The transesterification reaction consists of transforming triglycerides into fatty acid alkyl ester, in the presence of an alcohol, such as methanol or ethanol, and a catalyst, such as an alkali or acid, with glycerol as a byproduct [ 20 ]. Chemical reaction at supercritical conditions without the use of a catalyst has also been proposed [ 36 ].

In the United States, oil is the fuel of transportation. Coal, nuclear, hydropower, and natural gas are primarily used for electric power generation. The United States with 5% of the world’s population, consumes 25% of the world’s petroleum, 43% of the gasoline, and 25% of the natural gas. According to Oil and Gas Journal (O&GJ) estimates, worldwide reserves at the beginning of 2004 were 1.27 trillion barrels of oil and 6,100 trillion cubic feet of natural gas. These are proven recoverable reserves. At today’s consumption level of about 85 million barrels per day of oil and 260 billion cubic feet per day of natural gas, the reserves represent 40 years of oil and 64 years of natural gas.

Thus, because of diminishing petroleum reserves and the deleterious environmental consequences of exhaust gases from petroleum diesel, biodiesel has attracted attention during the past few years as a renewable and environmentally friendly fuel. Since biodiesel is made entirely from vegetable oil or animal fats, it is renewable and biodegradable. Biodiesel also contains very little sulfur, polycyclic aromatic hydrocarbons, and metals. Petroleum-derived diesel fuels can contain up to 20% polycyclic aromatic hydrocarbons. For an equivalent number of carbon atoms, polycyclic aromatic hydrocarbons are up to three orders of magnitude more soluble in water than straight chain aliphatics. The fact that biodiesel does not contain polycyclic aromatic hydrocarbons makes it a safe alternative for storage and transportation.

Like petroleum diesel, biodiesel operates in compression-ignition engines. Biodiesel is most often blended with petroleum diesel in ratios of 2% (B2), 5% (B5), or 20% (B20). It can also be used as pure biodiesel (B100). Biodiesel fuels can be used in regular diesel vehicles without making any changes to the engines, although older vehicles may require replacement of fuel lines and other rubber components. (Biodiesel has similar materials compatibility to ultralow sulfur diesel (ULSD); so vehicles built to run on that should be compatible with pure biodiesel.) It can also be stored and transported using diesel tanks and equipment. Since biodiesel is oxygenated, it is a better lubricant than diesel fuel, increasing the life of engines, and is combusted more completely. Indeed, many countries are introducing biodiesel blends to enhance the lubricity of low-sulfur diesel fuels [ 1 ]. The higher flash point of biodiesel makes it a safer fuel to use, handle, and store. With its relatively low emission profile, it is an ideal fuel for use in sensitive environments, such as heavily polluted cities.

There are several technical challenges that need to be addressed to make biodiesel profitable. First, the high cost of virgin vegetable oil as the source of triglycerides plays a large role in process profitability. To reduce production costs and make it competitive with petroleum diesel, low cost feedstocks, such as nonedible oils, waste frying oils, and animal fats, could be used as raw materials. However, the relatively higher amounts of free fatty acids and water in this feedstock results in the production of soap in the presence of alkali catalyst. Thus, additional steps to remove any water and either the free fatty acids or soap from the reaction mixture are required. In fact, commercial processors often employ an acid-catalyzed esterification reactor to process excess free fatty acids prior to base-catalyzed transesterification.

Considerable research has been done on biodiesel made from virgin vegetable oils (e.g., soybean oil, sunflower oil, rapeseed oil) using alkali catalysts. The majority of biodiesel today is produced by alkali-catalyzed (e.g., NaOH, KOH) transesterification with methanol, which results in a relatively short reaction time [ 16 ]. However, the vegetable oil and alcohol must be substantially anhydrous and have a low free fatty acid content, because the presence of water or free fatty acid or both promotes soap formation. The soap formed lowers the yield of esters and renders the downstream separation of the products difficult [ 16 ], requiring additional processing.

In this review article, we examine different biodiesel sources (edible and nonedible), virgin oil versus waste oil, algae-based biodiesel that is gaining increasing importance, the role of different catalysts including enzyme catalysts, and the current state-of-the-art in biodiesel production.

Biodiesel production from soybean oil is very popular. Researchers have focused on different catalyst systems, different solvents, and different acyl acceptors. Soybean oil has five fatty acids: approximately equal amounts of palmitic acid, oleic acid, and linolenic acid (about 13% each), linoleic acid (approximately 55%), and stearic acid (approxmately 4%). The average US production of soybean oil from 1993 to 1995 was 6.8 billion kg, and in 2002, soybeans were harvested from more than 30 million ha across the United States, which accounts for 40% of the total world soybean output [ 26 ]. This production capacity accounts for more than 50% of the total available biobased oil for industrial applications. A useful industrial application of soybean oil is in biodiesel blends. According to Kinney and Clemente [ 26 ], soybean oil-derived biodiesel possess enhanced biodegradation, increased flashpoint, reduced toxicity, lower emissions, and increased lubricity. However, oxidative instability and cold flow in northern climates limit the usefulness of a soybean oil-derived biodiesel as a fuel. The tools of biotechnology could be utilized to modify the fatty acid profile of soybean for performance enhancement, which may increase the attractiveness of biodiesel derived from this commodity crop [ 26 ]. There is still some disagreement in the literature over the oxidative stability of biodiesel, and in particular how well the “iodine value” characterizes its stability. The iodine value is a measure of the level of “unsaturation” of the fatty acids in the oil, with more saturated fatty acids being less susceptible to oxidation. However, other factors also significantly affect the stability, such as the level of natural antioxidants (such as vitamin E) in the fuel [ 15 ].

Soybean oil has a high iodine value compared to many other biodiesel feedstocks (indicating a relatively low level of saturation compared to other oils, such as rapeseed and canola), but Mushrush et al. [ 30 ] conducted storage stability tests and found soybean biodiesel (in concentrations up to 20%) to be stable in the “stable” fuel and to reduce the instability in the “unstable” fuel significantly. In addition to fuel storage stability, fuel solubility, and oxidative stability, seawater stability should also be taken into consideration in water environments [ 31 ].

According to Mushrush et al. [ 31 ], US Navy shipboard fuel tanks compensate for diminishing fuel by the addition of seawater to the fuel tank. The authors found that this can lead to “fuel instability problems such as filter stoppage and other serious engine damage.” Presence of trace fatty acids in the oil and seawater led to the formation of a soapy emulsion at the interphase. When using recycled oil, care should be taken to remove all acidic components or the biodiesel will not be stable [ 32 ].

Freedman et al. [ 16 ] have investigated the effect of the molar ratio of the alcohol to oil, type of catalyst (base vs acid), temperature and degree of refinement of the oil on the yield of biodiesel. They reported a 98% yield of biodiesel in 1 h using alkali catalysts such as sodium hydroxide or sodium methoxide with alcohols such as methanol, ethanol, and iso-butanol [ 17 ]. For the alkali-catalyzed reaction, the effect of alcohol to oil ratio was found to be the most important variable affecting the yield, while temperature had a significant effect on the initial reaction rate. Their study also shows that acid catalysts would be more effective when the degree of refinement of oil was low, and for oils that had a high free fatty acid content.

Enzyme catalysts

Biocatalysts are gaining more attention nowadays and have the potential to outperform chemical catalysts for biodiesel production in the future. New biochemical routes to biodiesel production, based on the use of enzymes, have become very interesting [ 6 , 9 , 18 , 27 , 33 , 37 , 39 ]. Most of the articles published have used a variety of substrates such as rice bran oil, canola, sunflower oil, soybean oil, olive oil, and castor oil. Several lipases from microbial strains, including Pseudomonas fluorescens [ 22 , 40 ], Pseudomonas cepacia [ 10 ], Rhizomucor miehei [ 40 ], Rhizopus oryzae [ 28 ], Candida rugosa [ 7 ], Thermomyces lanuginosus [ 48 ], and Candida antarctica [ 27 ], have been reported to have transesterification activity.

Lipase has been shown to be effective in the transesterification of sunflower oil in a solvent-free medium [ 2 ]. One problem that arose was the inhibition of the enzyme due to glycerol formation. A number of different acyl acceptors have shown to be effective with lipase as the catalyst. Methanol and ethanol are the most commonly used alcohols. Longer chain alcohols have also been shown to be effective, but they provide lower yields than methanol. Recent studies using methyl acetate as the acyl acceptor and soybean oil show that the use of this acyl acceptor does not lead to inhibition of the enzyme [ 11 ]. Also, since no glycerol is produced in the process, this method is very convenient for recycling the catalyst, and byproduct triacetylglycerol shows no negative effect on the fuel property [ 47 ].

The results of biodiesel production by transesterification of olive oil using lipase as a catalyst were recently reported [ 37 ]. The final conversion and yield of biodiesel were unaffected by initial enzyme concentrations above 500 U/ml olive oil. The optimum reaction temperature was 60 °C.

The effect of different solvents and three different acyl acceptors on the transesterification of triolein (as a model compound) has been recently investigated [ 8 ]. The yield of biodiesel (methyl or ethyl ester) was monitored as a function of time. The yield of the product was also determined in a solvent-free system for two different modes of stirring. The results indicated that the highest yield was obtained in a solvent-free system with mechanical stirring. Methyl acetate was also effective as a solvent and acyl acceptor.

Other catalyst systems

In an attempt to reduce the problems with separation and soap formation, some nonenzymatic heterogeneous catalysts have been investigated. ZrO 2 , ZnO, SO 4   2− /SnO 2 , SO 4   2− /ZrO 2 , KNO 3 /KL zeolite, and KNO 3 /ZrO 2 are some solid catalysts that were studied in the transesterification of palm and coconut oil [ 23 ]. The reaction was carried out at 200 °C, 50 bar, 3 wt% catalyst, and a 6:1 molar ratio of methanol to oil. All the solid catalysts exhibited some activity for both palm and coconut oil. The sulfonated metal catalysts gave the highest fatty acid methyl ester yields overall. ZrO 2 gave an 86.3% yield for coconut oil and 90.3% yield for palm oil. The study shows that SO 4   2− /ZrO 2 is deactivated quickly but can easily be regenerated.

Other sulfonated solid catalyst can be used to catalyze the transesterification reaction. Recently, one of the more interesting sulfonated solid catalysts was derived from amorphous carbon [ 42 ]. Carbon rings present in compounds such as starches and sugars provide a large number of sites available for sulfonation. Studies were performed using glucose and sucrose as carbon sources. The carbon source was pyrolyzed at low temperatures resulting in carbon rings. The sheets were then sulfonated by sulfuric acid. The result is an inexpensive solid catalyst that has properties similar to Nafion ® . The authors show that it is an effective catalyst for the esterification of oleic and stearic acid. They claim an activity greater than half that of sulfuric acid and greater than regular solid catalysts at 80 °C. If true, this catalyst offers an inexpensive alternative to immobilized enzyme catalysts. However, studies carried out in our laboratory both with virgin oil and waste oil showed substantially lower yields compared to enzyme catalysts. In these studies, the catalyst was made by a similar technique, which involved pyrolizing the sugar first and then sulfonating it. Sucrose was placed in test tubes in a tube furnace and was heated to 375 °C for a period of 15 h. The result was a black powder, which was ground using a mortar and pestle. The black powder was combined with 150 mL of 96 wt% sulfuric acid and was heated to 150 °C for 15 h. The solution was then vacuum-filtered using glass wool filters. The solid was washed with distilled/deionized water until the pH of the wash water was near neutral. Experiments were run with triolein, olive oil, and used olive oil as the source. The reactions were carried out at 85 °C with 0.05 g of the sugar catalyst. An 8:1 molar ratio of methanol to triolein was used. The yields in all cases were very small compared to Novozym 435. A high temperature was used, because runs at 40 °C showed an even smaller yield.

Other catalyst systems have also been investigated. Xie and Huang [ 46 ] have reported the synthesis of biodiesel from soybean oil using KF/ZnO catalyst. The catalyst with 15% KF loading and that calcined at 873 K showed the optimum activity. The results showed that the activity of the catalysts correlated well with their basicity. Wang and Yang [ 44 ] investigated the transesterification of soybean oil with nano-Mgo in supercritical and subcritical methanol. The authors report an increase in the transesterification rate when nano-MgO was added from 0.5 to 3 wt%.

Other recent advances

Recently, Fabbri et al. [ 14 ] reacted soybean oil with di-Me carbonate (DMC), which avoided the coproduction of glycerol. The main difference between the biodiesel like material, which the authors call DMC-BioD, and biodiesel produced from vegetable oil and methanol (MeOH-biodiesel) was the presence of fatty acid glycerol carbonate monoesters (FAGCs) in addition to FAMEs. The authors report that the presence of FAGCs influenced both fuel and flow properties, while the distribution of main pyrogenic compounds, including polycyclic aromatic hydrocarbons (PAHs), was not affected.

Dubé et al. [ 12 ] have developed a membrane reactor to produce biodiesel from canola oil and methanol via both acid- and base-catalysis. Several tests, using food-grade canola oil, were performed in the semibatch two-phase membrane reactor at various temperatures, catalyst concentrations, and initial feed loadings. The novel two-phase membrane reactor was particularly useful in removing unreacted canola oil from the fatty acid methyl ester product yielding a high purity biodiesel. In a recent article [ 5 ], canola oil was transesterified using methanol and caustic in a reactor with membranes of varying pore sizes. It was shown that all the membranes could retain the canola oil in the reactor, which indicated that the oil droplets present in the reactor were larger than all the pore sizes tested.

Other vegetable oils that have been used in biodiesel production include corn, sunflower, cottonseed, peanuts, canola, and rapeseed. However, expanding the use and production of a particular feedstock must be evaluated in terms of the environmental and economic impacts. According to a recent United Nations report, the global rush to switch from oil to energy derived from plants will drive deforestation, push small farmers off the land, and lead to serious food shortages and increased poverty unless carefully managed. The United Nations report points to crops like palm oil, maize, sugar cane, and soya and urges governments to beware of their human and environmental impacts, some of which could have irreversible and damaging consequences. Thus, it makes sense to examine biodiesel production from waste oil and other nonedible sources. This will be done in the following sections.

Several studies have been done on the production of biodiesel from waste oils or animal fats [ 45 ] describing the feasibility of making quality biodiesel from this feedstock while identifying the problems with the free fatty acids present in the raw materials. The presence of free fatty acids and water in this feedstock results in the production of soap in the presence of alkali catalyst. Thus, additional steps to remove any water and either the free fatty acids or soap from the reaction mixture are required. Despite the lower reaction rate associated with sulfuric acid-catalyzed transesterification processes, this approach has several advantages over the base-catalyzed method [ 4 ]: it employs a one-step process as opposed to a two-step process; it can handle feedstock with a high free fatty acid content; downstream separation of the biodiesel is straightforward; and a high quality glycerol byproduct is produced.

The acid-catalyzed process suffers from a number of drawbacks. In addition to the low reaction rate, a drawback of the acid-catalyzed process is the requirement for the reactor to withstand an acidic environment. Yet another drawback to the acid-catalyzed process is that high alcohol-to-oil ratios are necessary to promote the conversion of oil to fatty acid alkyl ester [ 17 ]. In their study on acid-catalyzed transesterification of soybean oil, Canakci and Van Gerpen [ 4 ] found that water strongly inhibits the ester-formation reaction. They recommended that the concentration of water in the reaction mixture should be less than 0.5%. Therefore, water formed by the esterification of free fatty acid would limit the presence of free fatty acid in oil to 5%. However, this is highly dependent on the amount of alcohol present.

The use of insoluble solid catalysts (such as immobilized enzymes) facilitates its removal from the glycerol and fatty acid alkyl ester products and leads to a reduction in waste material requiring disposal. The biggest advantage of enzyme catalysts is the absence of soap formation. Aside from enzymes, several researchers have attempted to use acid or alkali solid catalysts (e.g., zinc and calcium oxides, calcium and barium acetates, hydrotalcite, NaX faujasites, titanosilicate structure-10, calcium carbonate rock, tungstated zirconia-alumina) [ 19 ]. Almost all the catalysts require temperatures in excess of 200 °C to achieve conversions greater than 90% within the time scale of the experiment. Recently, mesoporous silica multifunctionalized with both organosulfonic acid and hydrophobic organic groups such as allyl and phenyl was shown to be effective in esterifying free fatty acids while excluding water, a byproduct that inhibits the reaction, from the proximity of the active sites [ 29 ]. Such a catalyst seems promising because of its relatively high surface area, flexible pore size, and its potential for controlling catalytic functionalities at the molecular level.

One of the authors, Vasudevan and his student Xiangping Shen, have recently investigated biodiesel production by transesterification of waste olive oil with methanol and Novozym ® 435. Experiments were carried out to investigate the influence of the molar ratio of methanol to triolein, mode of methanol addition, reaction temperature, and mixing speed on biodiesel yield.

For waste olive oil, the experiments results indicated that a molar ratio of 9:1 for methanol to triolein resulted in the highest biodiesel yield. This ratio is higher than the stoichiometric ratio of 3:1 probably due to the presence of other fatty acids in the feed and due to the fact that waste oil was used. At ratios higher than 9:1, the yield became lower due to enzyme deactivation by methanol.

Stepwise addition of methanol resulted in higher yields of biodiesel probably due to less inhibition of the enzyme by methanol. Higher yields of biodiesel were also obtained at a reaction temperature of 60 °C, which resulted in higher reaction rates and lower inhibition of the enzyme active sites by methanol. Mixing speed in the range 100–400 rpm had relatively little effect on the yield. The effect of different acyl acceptors or solvents or both on biodiesel yield was also evaluated. The highest yields were obtained when tert -butanol and methanol were both present as solvent/acyl acceptor perhaps due to the synergy that resulted as a result of better dispersion of the oil in the mixture.

The efficacy of Novozym ® 435 was also determined by reusing the enzyme after washing it with a solvent. The results showed that enzyme was very stable and still retained a high activity after several runs.

Wang et al. [ 43 ] investigated lipase-catalyzed alcoholysis of soybean oil deodorizer distillate (SODD) for biodiesel production. In this system, free fatty acids and glycerides were converted to biodiesel simultaneously. Butanol was adopted as the reaction medium in which the negative effects caused by excessive methanol and byproduct glycerol were eliminated. There was no obvious loss in lipase activity even after 120 cycles. Studies by Vasudevan and Shen have not demonstrated such high enzyme stability.

The addition of a cosolvent to generate a homogeneous reaction mixture has been discussed [ 3 ]. While this enhances reaction rate significantly, the cosolvent must eventually be separated from the biodiesel and this requires additional processing. Another issue that has an adverse effect on biodiesel production is the removal of residual triglycerides and glycerol from the biodiesel product. The employment of multiple water wash steps creates an environmental challenge due to the need to treat the wastewater. The presence of unreactable materials in waste oil leads to poor flow properties of the biodiesel in cold weather. The use of homogeneous base catalysts coupled with the presence of free fatty acids and the chemical nature of the reaction components serve to yield a low quality glycerol byproduct.

If the goal is to reduce or eliminate the formation of soap and/or to process more waste oil and produce high quality biodiesel and glycerol, then enzyme catalysis is very attractive. Unfortunately, the process is not economically viable. In 2005, Novozymes (Bagsværd, Denmark) in conjunction with National Renewable Energy Labs (NREL) announced a 30-fold enzyme cost reduction in the conversion of pretreated corn stover to ethanol. The cost of the enzyme was approximately $0.10/gal of ethanol. A similar reduction in the cost of lipase would make enzymatic transesterification/esterification process economically very viable. In fact, current research in our laboratory and other laboratories is focused on ways to minimize inactivation of the enzyme by methanol. This can be achieved by utilizing different acyl acceptors and solvents (such as tert -butanol or higher alcohols), which in turn will increase the number of times the enzyme can be regenerated and reused. Thus, if better solvents are developed that minimize enzyme deactivation and/or if better enzymes are made through directed evolution resulting in an increase in the number of regenerations, then the cost of the enzyme can be proportionally higher. Elimination of solvents and the use of a single acyl acceptor-solvent will also lead to a reduction in costs.

There is also renewed focus on finding alternate uses for the byproduct glycerol or to convert glycerol to more useful products (including methanol or ethanol) via fermentation. Focus should also be on technologies to improve the conventional process for biodiesel production by perhaps utilizing membrane reactors to handle waste oil.

Nonedible oils, like Jatropha, Pongamia, Argemone, Castor, Sal, etc., can be used for the production of biodiesel. Jatropha curcas has tremendous potential for biodiesel production. A tropical plant that grows in low to high rainfall areas (rainfall as little as 25 cm per year) can be used to reclaim marginal soil.

Shah et al. [ 38 ] have investigated three different lipases ( Chromobacterium viscosum, Candida rugosa , and Porcine pancreas ) for transesterification of Jatropha oil in a solvent-free system to produce biodiesel; only lipase from Chromobacterium viscosum was found to give appreciable yield. Immobilization of lipase ( Chromobacterium viscosum ) on Celite-545 enhanced the biodiesel yield to 71% with a process time of 8 h at 40 °C.

Tiwari et al. [ 41 ] optimized the three important reaction variables in biodiesel production—methanol quantity, acid concentration, and reaction time for reduction of free fatty acid (FFA) content of Jatropha curcas oil. The optimum combination for reducing the FFA of Jatropha curcas oil from 14% to less than 1% was found to be 1.43% v/v H 2 SO 4 acid catalyst, 0.28 v/v methanol-to-oil ratio, and 88-min reaction time at a reaction temperature of 60 °C. This process gave an average yield of biodiesel of more than 99%. The fuel properties of Jatropha biodiesel were found to be comparable to that of diesel.

Karmee and Chadha [ 24 ] have investigated biodiesel production from the nonedible oil of Pongamia pinnata by transesterification of the crude oil with methanol and KOH as catalyst. A maximum conversion of 92% (oil to ester) was achieved using a 1:10 molar ratio of oil to methanol at 60 °C. When tetrahydrofuran was used as cosolvent, the conversion increased to 95%. Important fuel properties of methyl esters of Pongamia oil biodiesel compared well with ASTM standards.

There is growing interest in algae-based biodiesel especially as more states in the United States mandate blending biodiesel with petroleum diesel. In the following paragraphs, we examine the pros and cons of algae-based biodiesel. It is important to keep in mind that any biofuel is ultimately a means of collecting solar energy and storing it in an energy dense chemical. To make such a system as efficient as possible, it is beneficial to understand the entire process from beginning to end.

Photosynthesis begins with a photon being captured by a 2p electron in a ring of conjugate double bonds within a pigment molecule (with the 2p electron being part of a conjugate pi bond), causing a π–π* excitation (where the energy level of this excitation determines the wavelength of light that can be “harvested,” with the pigments in photosynthetic organisms allowing the capture of photons with wavelengths from 400 to 700 nm). Recently published research [ 13 ] appears to finally explain the near 100% efficiency with which this captured energy is transmitted to the reaction center of a chloroplast. Their observation of coherent electronic oscillations between donor and acceptor pigment molecules (classically viewed as exchanging energy through virtual photon emission and absorption) demonstrates the wavelike behavior of the excitation energy transfer through the chromophore, accounting for almost loss-less energy transmission.

A crude analysis of the quantum efficiency of photosynthesis can be done without getting into the details of the Calvin cycle; rather simply by looking at the photon energy required to carry out the overall reaction and the energy of the products. The Z-scheme, well-established in photosynthesis research, indicates that eight photons must be absorbed to split one CO 2 and two H 2 O molecules, yielding one base carbohydrate (CH 2 O), one O 2 molecule, and one H 2 O (which, interestingly, is not made of the same atoms as either of the two input H 2 O molecules).

With the average energy of “photosynthetically available radiation (PAR)” photons being roughly 217 kJ, and a single carbohydrate (CH 2 O) having an energy content taken to be one-sixth that of glucose [(CH 2 O) 6 ], or 467 kJ/mole, we can make a rough maximum efficiency of 26.9% for converting captured solar energy into stored chemical energy. With PAR accounting for 43% of incident sunlight on earth’s surface, the quantum limit (based on eight photons captured per CH 2 O produced) on photosynthetic efficiency works out to roughly 11.6%.

In reality, most plants fall well below this theoretical limit, with global averages estimated typically between 1 and 2%. The reasons for such a difference generally revolve around rate limitations due to factors other than light (H 2 O and nutrient availability, for example), photosaturation (some plants, or portions of plants receive more sunlight than they can process while others receive less than they could process), and Rubisco (the protein that serves ultimately as a catalyst for photosynthesis) also accepting atmospheric O 2 (rather than CO 2 ), resulting in photorespiration, releasing some of the already captured carbon.

In the United States, the average daily incident solar energy (across the entire spectrum) reaching the earth’s surface ranges from 12,000 to 22,000 kJ/m 2 (varying primarily with latitude). If the maximum photosynthetic efficiency is 11.6%, then the maximum conversion to chemical energy is around 1,400–2,550 kJ/m 2 /day, or 3.8 × 10 12  J/acre-year in the sunniest parts of the country. Assuming the heating value of biodiesel to be 0.137 GJ/gal, the maximum possible biodiesel production in the sunniest part of the United States works out to be approximately 28,000 gal/acre-year, assuming 100% conversion of algae biomass to biodiesel, which is infeasible.

It is important to keep in mind that this is strictly a theoretical “upper limit” based on the quantum limits to photosynthetic efficiency, and does not account for factors that decrease efficiency and conversion, or the efficiency with which algae convert carbohydrates into triglycerides (which is not well quantified at this point, and is dependent on many environmental factors). Based on this simple analysis though, it is clear that claims of algal biodiesel production yields in excess of 40,000 gal/acre-year or higher should be viewed with considerable skepticism. While such yields may be possible with artificial lighting, this approach would be ill-advised, as at best only about 1% of the energy used to power the lights would ultimately be turned into a liquid fuel (clearly, one needs to look at the overall efficiency).

This upper limit also allows us to assess how truly inefficient many crops are when viewed strictly as biofuel producers. With soybeans yielding on average 60 gal of oil (and hence biodiesel) per acre-year, the actual fuel production is staggeringly small in comparison to the amount of solar energy available. This should further make it clear that using typical biofuels for the purpose of electricity generation (as opposed to the transportation sector) is an inefficient means of harnessing solar energy. Considering that photovoltaic panels currently on the market achieve net efficiencies (for solar energy to electrical energy) of the order of 15–20%, with multilayer photovoltaics and solar thermal-electric systems achieving efficiencies twice that in trial runs, biomass to electricity production falls far behind (considering typical plant photosynthetic efficiencies of 1–2%), with conversion of that biomass energy to electrical energy dropping the net efficiency to well under 1%.

Viewed in this light, it becomes clear that biofuels must offer some other benefits in addition to fuel production, to be energetically (or economically) appealing, in terms of how efficiently we can harness an energy source (solar energy) and turn it into a higher value form. Corn and soy, which dominate US agriculture, have long been grown for producing animal feed. The emerging ethanol and biodiesel industries, which have primarily relied on these crops, are ultimately a coproduct from crops grown as a food source for humans and animals. But, the relatively low net photosynthetic efficiency of the crops, and low total fuel yields, means that neither is a desirable approach if our goal is producing more fuel than that could be produced from those crops as a coproduct of animal feed production.

As the search for other feedstocks continues, it would be desirable to look for crops that can give a high net conversion of solar energy to energy in the form of fuel, while providing additional side benefits (coproducts, for example), since the net efficiency for harnessing solar energy through photosynthesis into liquid fuels is rather low.

Aquatic species such as microalgae have become appealing because of the potential for significantly higher average photosynthetic efficiency than with typical land crops, due to their aquatic environment providing them with better access to water, CO 2 , and nutrients (depending on the system they are grown in). Additionally, while land crops may require substantial energy inputs for irrigation, planting, fertilization, and harvesting, these can be greatly minimized with an aquatic crop, with a well-designed system. Unfortunately, there are significant challenges to making this an economically viable energy crop.

While any form of biomass can be processed into a liquid fuel through various thermochemical processes (such as pyrolysis or gasification and Fischer-Tropsch synthesis), the energy and economic requirements of such processes are substantially greater than is required for transesterifying plant oils into biodiesel. Therefore, it is desirable to have a higher oil content to minimize processing costs (energetic and economic).

The storage of energy as oil rather than as carbohydrates slows the reproduction rate of any algae; so, higher oil strains generally grow slower than low oil strains. The result is that an open system (such as open raceway ponds) is readily taken over by lower oil strains, despite efforts to maintain a culture of higher oil algae. Attempts to grow higher oil extremophiles, which can survive in extreme conditions (such as high salinity or alkalinity) that most other strains cannot tolerate, have yielded poor results, in terms of the net productivity of the system. While an extremophile may be able to survive in an extreme condition, that does not mean it can thrive in such conditions.

Many research groups have therefore turned to using enclosed photobioreactors of various designs as a means of preventing culture collapse or takeover by low oil strains, as well as decreasing the vulnerability to temperature fluctuations. The significant downside is the much higher capital cost of current photobioreactor designs. While such high costs are not prohibitive when growing algae for producing high value products (specialty food supplements, colorants, pharmaceutical products, etc.), it is a significant challenge when attempting to produce a low value product such as fuel. Therefore, substantial focus must be placed on designing much lower cost photobioreactors and tying algae oil production to other products (animal feed or fertilizer from the protein) and services (growing the algae on waste stream effluent to remove eutrophying nutrients, or growing nitrogen fixing algae on power plant emissions to remove NO x emissions).

An additional challenge, when trying to maximize oil production with algae, is the unfortunate fact that higher oil concentrations are achieved only when the algae are stressed—in particular due to nutrient restrictions. Those nutrient restrictions also limit growth (thus limiting net photosynthetic efficiency, where maximizing that is a prime reason for using algae as a fuel feedstock). How to balance the desire for high growth and high oil production to maximize the total amount of oil produced is no small task. One of the goals of DOE’s well-known Aquatic Species Program was to maximize oil production through nutrient restriction; however, their study showed that while the oil concentration went up, there was a proportionally greater drop in reproduction rate, resulting in a lower overall oil yield.

One approach to balancing these issues has been successfully tested on a small commercial scale (2 ha) by Huntley and Redalje [ 21 ], using a combination of photobioreactors and open ponds. The general approach involves using large photobioreactors for a “growth stage,” in which an algal strain capable of high oil content (when nutrient restricted) is grown in an environment that promotes cell division (plentiful nutrients, etc.)—but which is enclosed to keep out other strains. After the growth stage, the algae enter an open raceway pond with nutrient limitations and other stressors, aimed at promoting biosynthesis of oil. The nutrient limitations discourage other strains from moving in and taking over (since they also require nutrients for cell division).

The economic picture Huntley and Redalje [ 21 ] presented is perhaps rosy due to the inclusion of substantial revenue from selling a high-value carotenoid coproduct, astaxanthin. Producing coproducts is perfectly fine and desirable; unfortunately, the potential market for a carotenoid is far smaller than the potential market for biodiesel—so, it could only help out with the economics of fuel production until that market is saturated. Since carotenoid synthesis increases with oil synthesis, the same conditions can be employed though to maximize total yield of each (resulting in an average oil yield of 25% of dry weight, using Haematococcus pluvialis ).

The average biomass energy production reported by Huntley and Redalje [ 21 ] of 763 GJ/ha/year at their site in Hawaii works out to a net photosynthetic efficiency of just over 1%, based on an assumed average daily solar radiation of 19,300 kJ/m 2 (or 70,445 GJ/ha/year, calculated by NREL based on the National Solar Radiation Database). Unfortunately, this is not substantially different from what is routinely achieved with typical land crops. However, the average oil yield reported was 422 GJ/ha/year, roughly 0.6% of incident solar energy, equating to over 1,200 gal of biodiesel per acre-year—far better than conventional oil bearing crops.

While their trials can be counted a success by many measures, it is worth pointing out how low the yield is in terms of comparison to the potential yield based on the quantum limits of photosynthetic efficiency, as well as compared to other means for harnessing solar energy. It should be no surprise though that their yield achieved came well short of the potential yield, since nutrient depletion in the open pound phase greatly limits cell division and hence biomass production (ultimately limiting photosynthetic efficiency for converting sunlight to chemical energy). An open pond system probably could be useful in cultivating high oil algaes either through the approach taken by Huntley and Redalje [ 21 ], in which nutrient restriction in the pond prevents any form of algae from growing well (thus preventing takeover) and forcing oil concentration in the algae cultivated in a nutrient-rich photobioreactor stage, or through the use of an oil-rich “extremophile” algae that can survive in an extreme environment (such as very high salinity) that other strains cannot tolerate. One form of this approach would be engineering algae to be resistant to an inhibitor that would be dumped into an open pond to keep other strains out, but this is likely to be controversial.

It may also be possible to increase algal biosynthesis of oil by identifying the enzyme that regulates lipid production and attempting to increase its activity through genetic engineering. Acetyl-CoA carboxylase (ACCase) catalyzes the carboxylation of acetyl-CoA to maloynl-CoA, believed to be the rate-limiting step in fatty acid synthesis in plants and animals [ 25 ]. While efforts focused on genetic manipulation to increase the activity of ACCase have been going on for at least 15 years, and certainly much has been learned in that time, the research has not yet reached the stage of actually being able to substantially increase the net oil yield from algae (and thus increase the commercial viability). Most of the research has focused on developing a detailed knowledge of the enzymatic pathways for lipid biosynthesis, before beginning to pursue genetic modification. NREL has identified a gene that plays a large role in controlling ACCase activity, and has studied naturally occurring genetic mutations in algae strains that affect oil synthesis [ 35 ].

Another area where genetic engineering of microalgae could prove useful would be reducing the size of pigment antenna. Algae tend to have long pigment antennas for absorbing incident sunlight, to allow individual cells to thrive in low-light conditions. This also results in individual algae “harvesting” more energy (photons) in individual photosystems than the metabolic processes can handle, with excess energy being radiated as heat or fluorescence. In high light conditions, without good agitation to rotate the algae nearest the surface, up to 80% of incident sunlight can be wasted through this photosaturation [ 34 ]. Maximizing efficiency in high sunlight would require either physical agitation or other means to rotate algae to the solar exposure region, or shortening (through selective breeding or genetic manipulation) of the pigment antennae to reduce the amount of light harvested by each algae.

Overall, while there is significant interest in algal biodiesel; it is important to keep in mind that this is still years away from being ready for actual commercial implementation. If we want to grow high oil algaes, two approaches appear possible—the use of an “extremophile” that can tolerate extreme conditions, and therefore be grown in an open pond under those conditions (which other strains cannot tolerate), or the use of photobioreactors for keeping invasive strains out, and optimizing the growth environment. The biggest challenge with the latter approach is the capital cost of current photobioreactors. Unfortunately, the focus does not appear to be in developing lower cost photobioreactors to bring down the capital cost for building a “photobioreactor farm,” which ultimately will present a barrier to commercialization. Many current designs use vertical tube systems, which require expensive metal support structures. Economic viability will likely require much simpler, less expensive systems that can be placed on the ground—such as simple troughs covered with plastic film.

Biodiesel is a clean-burning fuel that is renewable and biodegradable. A recent United Nations report urges governments to beware of the human and environmental impacts of switching to energy derived from plants. There should a healthy debate about turning food crops or animal feed into fuel and the consequences of the switch to biofuels needs to be carefully thought out. The focus of biodiesel production needs to be on sources like waste oil and grease, animal fats, and nonedible sources. It is important to ascertain a priori what quantities of these materials may be annually collectible, and what proportion of transportation-fuel needs could these sources supply. Current research has focused on these areas as well as on algae-based biofuels. Many technical challenges remain and these include development of better and cheaper catalysts, improvements in current technology for producing high quality biodiesel, use of solvents that are nonfossil-based, conversion of the byproducts such as glycerol to useful products such as methanol and ethanol, and development of low cost photobioreactors.

One of the authors, PTV, acknowledges his former and current students involved in biodiesel research: Fernando Sanchez, Robert Coggon, Xiangping Shen, and Vassili Vorotnikov.

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