| Biofuel | How made | Notes |
|---|---|---|
| SUBSTITUTES FOR PETROLEUM DIESEL | ||
| Biodiesel ester | Lye is combined with alcohol, then mixed with vegetable oil (fresh or used). Glycerin is produced as a by-product. | No engine modifications required. More viscous than petroleum diesel (but less so than SVO); may not work in cold weather. Biggest source of vegetable oil in the US is soybeans; despite their poor yield. |
| Straight Vegetable Oil (SVO) biodiesel | Could be just filtered vegetable oil, but it's better to remove water and free fatty acids to prevent corrosion. | Requires engine modifications: different fuel pump, injectors, and glow plugs. Very viscous; may not work in cold weather even with engine modifications. Instead of modifying the engine, many people simply add a second fuel tank for the SVO, and switch from petroleum diesel to SVO once the engine is warmed up (and back to petroleum diesel a few minutes before shutting the engine off). |
| Biodiesel from algae | The algae in question may contain over 50% oil and grow in warm salty water. Efficient harvesting of the algae and extraction of the oil are unsolved problems. | http://www.unh.edu/p2/ biodiesel/article_alge.html, http://www.valcent.net/s/Ecotech.asp |
| Fischer-Tropsch | Can use any source of carbon; including natural gas, coal, or biomass
(cellulose). The carbon source is heated with steam to produce
syngas; a mixture of hydrogen and carbon monoxide:
Reforming of methane from natural gas or biogas: Syngas from carbon is enriched in hydrogen by reacting it with additional steam (this is the shift reaction): 3CO + 3H2 + H2O ---> CO2 + 2CO + 4H2 producing syngas with the ideal 2:1 ratio of hydrogen:carbon monoxide. Passing the syngas through a cobalt or iron catalyst produces a mixture of hydrocarbons; from which a synthetic diesel fuel can be produced. |
Invented in the 1920s in Germany. Germany used this process during World War II and South Africa uses it today. Both countries have lots of coal but no oil. The US Air Force is using this process to make jet fuel from coal. |
| SUBSTITUTES FOR PETROLEUM GASOLINE | ||
| Ethanol from grain | Starchy grain (usually corn in the US) is ground, mixed with water and enzymes (alpha amylase and glucoamylase), and cooked. This process (mashing) converts the starch into simple sugars. The fiber- and protein-rich residue is used as animal feed. The sugar solution is extracted and fermented by yeast into carbon dioxide and a weak (10%) ethanol solution. The ethanol is extracted and concentrated to 95% by distillation; forming hydrous ethanol. If the ethanol is to be mixed with gasoline (nearly all of it is in the US), the remaining water is removed by chemical dehydration. | Pure ethanol has 69% of the energy of gasoline. Because E85; which is 85% ethanol and 15% gasoline, has 75% of the energy of gasoline, it gives ¾ the miles per gallon (MPG) of gasoline. No engine modifications are required for gasoline with up to 10% ethanol. Flex-fuel vehicles (FFVs) can use E85 as fuel. Despite the lower energy content of ethanol, it's possible to build a high-compression engine that gets the same MPG from ethanol that a conventional gasoline engine gets from gasoline. Contrary to what many ethanol opponents believe; the EROEI of grain ethanol is somewhat greater than 1. Ethanol can not be transported in pipelines meant to carry gasoline. |
| Ethanol from sugar cane, sorghum, or sugar beets | Same as ethanol from grain but no 'mashing' step is required | Yield of alcohol per acre can be higher than for ethanol from grain. Brazil makes a great deal of ethanol from sugar cane. |
| Cellulosic ethanol via methanol | Biomass (or fossil carbon) is converted to syngas, then to methanol
(see below). The methanol is reacted with additional syngas over an
iron carbonyl catalyst to form ethanol: CH3OH + 2CO + H2 ---> C2H5OH + CO2 Note that the overall process uses hydrogen and carbon monoxide in a 1:1 ratio. |
http://www.rangefuels.com/our-first-plant |
| Cellulosic ethanol via bacterial conversion of syngas | Biomass (or fossil carbon) is converted to syngas, which is then fermented into ethanol using Clostridium carboxidivorans | http://www.Coskata.com/ |
| Enzymatic cellulosic ethanol | Cellulose is converted into starches and sugars by the action of enzymes (cellulase); then processed as with ethanol from grain. | http://www.iogen.ca/company/ technology/cellulose_ethanol.html |
| Cellulosic ethanol via acid hydrolysis | Cellulose is degraded into simple sugars by the action of a strong mineral acid. The resulting carbohydrates are processed as with ethanol from grain. | |
| Methanol | Like the Fischer-Tropsch process, methanol can be made from any
source of carbon via syngas. Syngas is passed through a
copper catalyst
to convert it into methanol:
CO + 2H2 ---> CH3OH |
Methanol is poisonous by ingestion and to a lesser degree by inhalation and contact. It corrodes or dissolves many materials: lead, magnesium, copper (including alloys), zinc (including galvanized steel), aluminum, cork, and natural rubber. Pure methanol has 60% of the energy of gasoline. Conversion of natural gas to methanol is one example of a gas-to-liquid (GTL) process. |
| Alcohol-derived gasoline (ADG) | Heated ethanol or methanol is passed through an HZSM-5 zeolite catalyst; which converts it into a mixture of water and liquid hydrocarbons suitable for use as gasoline. | Also called methanol-to-gasoline (MTG) or the Mobil process. No engine modifications are required to use the resultant 'gasoline'; which is rich in high-octane aromatic chemicals. Benzene in ADG is a known carcinogen. |
| Butanol | Starchy grain is fermented into butanol (via butyric acid) using bacteria from the genus Clostridium | The original ABE process produces large quantities of acetone and ethanol as by-products. Newer processes may increase yield and reduce the amount of by-products produced. Supposedly, butanol requires no engine modifications and does not corrode gasoline pipelines like ethanol. |
| OTHER PROCESSES | ||
| Thermal depolymerization (TDP) | Plastic or organic waste is combined with water and subjected to heat and pressure; converting it into light crude oil. This is approximately the process by which petroleum is created in nature; sped up by a factor of a billion or so. |
http://www.changingworldtech.com/, NIMBY in Carthage, MO |
| Hydrogen homestead | Electricity from wind or sunlight is used to power a home and electrolyze water into hydrogen and oyxgen. The hydrogen is compressed, stored, and used in the home (for cooking, home heat, clothes dryer, etc.) and as motor vehicle fuel. | (Hydrogen is not really a biofuel, but shares some of the benefits of biofuels.) Nearly all of the technology here -- photovoltaic panels, electrolyzers, safe storage of compressed hydrogen, fuel cells -- is hideously expensive. Hydrogen's very poor volume energy density makes it an inferior motor vehicle fuel. |