Ethanol

Q: What is ethanol?

A: Ethanol, also called grain alcohol or ethyl alcohol, can be made from any starch- or sugar-based feedstock. Corn is the most common feedstock used in the United States, whereas sugar cane is the preferred feedstock in Latin America. The energy content of ethanol is approximately two-thirds that of gasoline by volume. For that reason, and because of its higher cost, ethanol is typically used as a gasoline additive. Approximately one out of every eight gallons of gasoline sold in the U.S. contains 8% to 10% ethanol. All reciprocating engine vehicles can use ethanol blends in small quantities (up to 20%, or denoted as E20), and with slight alterations can accommodate ethanol blends as high as 85% (E85). It is also possible to run engines on pure ethanol.

Q: How is ethanol produced?

A: There are two different methods for producing ethanol, both based on breaking down plant matter into simple sugars and starches and then fermenting them to produce alcohol. Ethanol is primarily made through a distilled ethanol process whereby the sugars and starches from the feedstock are boiled and concentrated into grain alcohol (basically "moonshine," although ethanol is denatured to prevent the fuel from being consumed). The process can also use microbe fermentation (with a byproduct of CO2) or a wet-milling procedure that also yields high-fructose corn sweetener. The fermentation process can easily break down simple sugars in the fruits or edible portions of plants; examples of commonly-used feedstocks include corn kernels, sugar cane, milo, cheese whey, and potato waste. New technologies are emerging that can break down the more complex sugars that compose other parts of plants, such as the fibrous stalks, husks, grasses, and wood. Converting these sources of cellulosic and hemicellulosic biomass into ethanol opens up a new avenue for fuel supplies, since this waste biomass is readily available and renewable in large quantities. What are essentially agricultural wastes will soon commonly be converted into a usable energy source.

Q: Pros and cons of ethanol:

Pros: Ethanol reduces levels of carbon monoxide and other toxic air pollutants. The biomass used for ethanol absorbs carbon dioxide (CO2) when it is grown, so it adds no net CO2 to the atmosphere. It can be used to boost the octane in gasoline to prevent engine knocking, and it increases gasoline's lubricity. It also takes only six months to harvest a substantial crop of fuel. Ethanol is an oxygenate that reduces ground-level ozone. Since ethanol can be produced locally, it has the potential to add to the local economy, particularly in the agricultural sector, and help reduce the importation of oil.

Cons: Depending on the ethanol/gasoline blend, ethanol may raise levels of nitrogen oxides produced as gasoline emissions. Because of its lower energy content relative to gasoline, ethanol also reduces mileage per gallon. Corn-based ethanol production is energy intensive, and in some instances uses nearly as much energy to produce (including the energy needed for farming and making fertilizers) than it supplies, although new technologies are improving the efficiency of production.

Biodiesel

Q: What is biodiesel?

A: Biodiesel is a combustible fuel that is physically similar to petroleum diesel but made from natural, renewable sources. As with every transportation and stationary fuel, biodiesel is processed to meet ASTM standards. A blend of 20 percent biodiesel with 80 percent petroleum (B20) can be used in all diesel-burning equipment, including compression-ignition engines and oil heat boilers, without modification. Higher blends, including pure biodiesel, can be used in many engines made after 1994, but slight modifications are necessary.

Q: How is biodiesel produced?

A: Biodiesel, otherwise known as fatty acid alkyl esters, can be made from any vegetable oil or animal fat. In the U.S., roughly half of biodiesel production uses soybean oil, and most of the remaining half is recycled from restaurants' cooking oil. The fats and oils are combined with an alcohol, commonly methanol, and a catalyst, commonly sodium or potassium hydroxide, to produce a chemical reaction giving off fatty acid methyl esters and a glycerol co-product. Many esterification technologies can be used to produce biodiesel; all involve basic fats, an alcohol, and a catalyst.

Q: What are the pros and cons of biodiesel?

Pros: When blended with standard transportation diesel, biodiesel helps to extend the energy capacity of the diesel. Biodiesel can also be used as a home heating oil. Because biodiesel is produced from natural sources, it generally releases as much carbon dioxide as it uses growing. A blend of 20 percent biodiesel will reduce carbon dioxide (CO2) emissions by 15 percent, and adding biodiesel also reduces the amount of particulates (PM), carbon monoxide (CO), and sulfur dioxide (SO2) released as emissions. Biodiesel is less combustible than petroleum, making it safer to store and transport. In addition, if biodiesel spills, it is biodegradable and breaks down roughly four times faster than petroleum diesel.

Cons: Use of biodiesel results in increased levels of harmful nitrogen oxide (NOx) emissions when used in diesel engines, although not usually in residential heating equipment. Also, in and of itself biodiesel releases the same amount of hydrocarbon (or soluble carbon) emissions when burned as regular diesel. Furthermore, pure biodiesel has a high "clouding" point, meaning that liquid biodiesel begins to thicken into a solid at low temperatures. Because of its higher clouding point, biodiesel is more difficult to store and transport in cold climates, which adds to its cost.

Biomass and Biomass Gasification

Q: What is biomass?

A: Biomass is generally made up of woody plant residue and complex starches. The largest percentage of biomass used to create energy is wood, but other bioproducts, such as fast-growing switchgrass, are being investigated as sources of energy. The three largest sources of biomass used for fuel are cellulose, hemicellulose, and lignin. Biomass processing results in the end-products biochemicals, biofuels, and biopower, all of which can be used as fuel sources. Biochemicals involve converting biomass into chemicals to produce electricity; biofuels are biomass converted into liquids for transportation; and biopower is made by either burning biomass directly (as with a wood-burning stove) or converting it into a gaseous fuel to generate electric power. Currently, production of electricity from biomass constitutes 3.3 percent of the United States' energy supply.

Q: What is biomass gasification?

A: Biomass gasification uses a high-temperature process to convert biomass (such as wood pulp) into a synthesis gas (syngas) that consists mainly of carbon monoxide (CO), carbon dioxide (CO2), and hydrogen (H2). The gas can either be used to produce heat or electricity, which can then be used for other purposes (such as production of hydrogen fuel cells), or anaerobic bacteria can be added to the gas to create ethanol and other fuel liquids. One type of gasification process currently being developed for large-scale use by the United States Environmental Protection Agency (EPA) in conjunction with the forest products industry involves black liquor, a biomass byproduct of the timber industry. The gas produced is cycled into a turbine to create heat and electricity, and waste solids are siphoned off for use in the pulping process. The forest products industry is a large producer of cogenerated electricity from wood-derived fuels: it produces 41 percent of the United States' self-generated electricity through cogeneration.

Q: What are the pros and cons of biomass gasification?

Pros: Production of electricity and heat from biomass has the potential for widespread use in the United States, as the gasification process uses many diverse and plentiful feedstocks. Although biomass releases carbon dioxide (CO2) into the atmosphere when combusted, the amount of CO2 released is equal to or less than the amount that the crop absorbs while growing (net emissions of CO2 are zero). Also, production of biomass feedstocks creates jobs in the domestic agricultural sector. In the case of the paper products industry, biomass gasification may eliminate the need to purchase electricity while reducing some of the industry's chemical use and improving waste management.

Cons: At present, the technology to produce electricity from biomass in large quantities is not economically viable; however, research is being done in many areas of biomass production, and this will likely change. Even though net CO2 emissions are zero, other pollutants such as SOx and NOx are released during combustion.