Glossary

• Acetic Acid - An acid with the structure of C2H4O2. Acetyl groups are bound through an ester linkage to hemicellulose chains, especially xylans, in wood and other plants. The natural moisture present in plants hydrolyzes the acetyl groups to acetic acid, particularly at elevated temperatures.
• Acid - A solution that has an excess of hydrogen ions (H+)
• Acid Detergent Fiber (ADF) - organic matter that is not solubilized after 1 hour of refluxing in an acid detergent of cetyltrimethylammonium bromide in 1N sulfuric acid. ADF includes cellulose and lignin. This analytical method is commonly used in the feed and fiber industries.
• Acid Hydrolysis - The treatment of cellulosic, starch, or hemicellulosic materials using acid solutions (usually mineral acids) to break down the polysaccharides to simple sugars.
• Acid Insoluble Lignin - Lignin is mostly insoluble in mineral acids, and therefore can be analyzed gravimetrically after hydrolyzing the cellulose and hemicellulose fractions of the biomass with sulfuric acid. ASTM E-1721-95 describes the standard method for determining acid insoluble lignin in biomass. See lignin and acid soluble lignin.
• Acid number (acid value) - Acid number, also referred to as acid value, is a measure of the amount of mineral acids and free fatty acids in a sample. It is expressed as mg KOH required to neutralize 1g of biodiesel. ASTM D664 describes test conditions. The maximum acid number for biodiesel must be no more than 0.8 mg KOH/g. High fuel acidity is linked with corrosion and deposit formation in engines.
• Acid Soluble Lignin - A small fraction of the lignin in a biomass sample is solubilized during the hydrolysis process of the acid insoluble lignin method. This lignin fraction is referred to as acid soluble lignin and may be quantified by ultraviolet spectroscopy[1]. See lignin and acid insoluble lignin.
• Agricultural Residue - Agricultural crop residues are the plant parts, primarily stalks and leaves, not removed from the fields with the primary food or fiber product. Examples include corn stover (stalks, leaves, husks, and cobs); wheat straw; and rice straw. With approximately 80 million acres of corn planted annually, corn stover is expected to become a major biomass resource for bioenergy applications.
• Alcohol - An alcohol is an organic compound with a carbon bound to a hydroxyl group. Examples are methanol, CH3OH, and ethanol, CH3CH2OH.
• Aldoses - Occur when the carbonyl group of a monosaccharide is an aldehyde[
• Alkali Lignin - Lignin obtained by acidification of an alkaline extract of wood.
• Aquatic Plants - The wide variety of aquatic biomass resources, such as algae, giant kelp, other seaweed, and water hyacinth. Certain microalgae can produce hydrogen and oxygen while others manufacture hydrocarbons and a host of other products. Microalgae examples include Chlorella, Dunaliella, and Euglena.
• Arabinan - The polymer of arabinose with a repeating unit of C5H804[2]. Can be hydrolyzed to arabinose.
• Arabinose - A five-carbon sugar C5H1005. A product of hydrolysis of arabinan found in the hemicellulose fraction of biomass.
• Aromatic - A chemical that has a benzene ring in its molecular structure (benzene, toluene, xylene). Aromatic compounds have strong, characteristic odors.
• Ash - Residue remaining after ignition of a sample determined by a definite prescribed procedure.
• ASTM INTERNATIONAL - ASTM International, originally known as the American Society for Testing and Materials, is one of the largest voluntary standards development organizations in the world. The society is a reliable source for technical standards for materials, products, systems and services. Best in class practices are used for standards development and delivery. ASTM standards are developed by more than 30,000 ASTM members who are technical experts representing producers, users, consumers, government and academia from more than 100 countries. Participation in ASTM International is open to all with a material interest anywhere in the world.

• B20 - A mixture of 20% biodiesel and 80% petroleum diesel based on volume.
• Bacteria - A small single-cell organism. Bacteria do not have an organized nucleus, but they do have a cell membrane and protective cell wall. Bacteria can be used to ferment sugars to ethanol.
• Bark - The outer protective layer of a tree outside the cambium comprising the inner bark and the outer bark. The inner bark is a layer of living bark that separates the outer bark from the cambium and in a living tree is generally soft and moist. The outer bark is a layer of dead bark that forms the exterior surface of the tree stem. The outer bark is frequently dry and corky.
• Base - A solution that has an excess of hydroxide ions (OH-)in aqueous solution.
• Benzene - An aromatic component of gasoline, which is a known cancer-causing agent.
• Biodiesel - A biodegradable transportation fuel for use in diesel engines that is produced through the transesterfication of organically- derived oils or fats. It may be used either as a replacement for or as a component of diesel fuel.
• BIODIESEL - Biodiesel is a renewable fuel for diesel engines. It is comprised of mono-alkyl esters of fatty acids which can be derived from vegetable oils, animal fats and algae. Biodiesel is defined in the European Union in the technical regulation EN 14214 or in the United States in ASTM D6751-02. Government regulations define biodiesel as Fatty Acid Methyl Esters (FAME), which is the result of reaction of fatty acids with methyl alcohol. There is some debate to modify the definition to include other products, such as Fatty Acid Ethyl Esters (FAEE), where the methanol can be replaced by bioethanol, giving a product that is fully biological. Biodiesel is an oxygenated fuel. It may be blended with petroleum diesel or used in pure form.
• BIODIESEL BLENDS - Biodiesel can be used alone (B100) or blended with petroleum diesel in any proportion. The most popular biodiesel blend is B20 (20 percent biodiesel), which is in compliance with Energy Policy Act of 1992. The American Society of Testing and Materials (ASTM) has approved a standard for biodiesel when used in blends at 20 percent by volume or lower: ASTM D6751 Standard Specification for Biodiesel Fuel Blend Stock for Distillate Fuels. Any diesel engine can operate on these blends with few or no modifications. Blends of up to B20 can meet the ASTM D975 standard. When used in low-level blends of 5 percent biodiesel (B5) or below, biodiesel functions the same as petroleum diesel. When B20 is used, a 1 – 2 percent decrease in power, torque and fuel economy may be experienced; however, these changes are usually not noticeable by the user. Each percent of biodiesel in petroleum diesel increases the cloud point (defined later) by about 0.15°C (1°F/4% biodiesel).
• Biofuels - Biomass converted to liquid or gaseous fuels such as ethanol, methanol, methane, and hydrogen.
• Biomass - An energy resource derived from organic matter. These include wood, agricultural waste and other living-cell material that can be burned to produce heat energy. They also include algae, sewage and other organic substances that may be used to make energy through chemical processes.
• Biomass - Any plant-derived organic matter. Biomass available for energy on a sustainable basis includes herbaceous and woody energy crops, agricultural food and feed crops, agricultural crop wastes and residues, wood wastes and residues, aquatic plants, and other waste materials including some municipal wastes. Biomass is a very heterogeneous and chemically complex renewable resource.
• Biomass Processing Residues - Byproducts from processing all forms of biomass that have significant energy potential. For example, making solid wood products and pulp from logs produces bark, shavings and sawdust, and spent pulping liquors. Because these residues are already collected at the point of processing, they can be convenient and relatively inexpensive sources of biomass for energy.
• BQ-9000 - BQ-9000, or the National Biodiesel Accreditation Program, is a voluntary program for the accreditation of producers and marketers of biodiesel fuel. The program is a combination of the ASTM standard for biodiesel (ASTM D6751) and a quality systems program that includes storage, sampling, testing, blending, shipping, distribution and fuel management practices. BQ-9000 is open to any biodiesel manufacturer, marketer or distributor of biodiesel and biodiesel blends in the United States and Canada. BQ-9000 helps companies improve their fuel testing and greatly reduce any chance of producing or distributing inadequate fuel. More information on BQ-9000 can be found at www.bq-9000.org.
• By-product - Material, other than the principal product, generated as a consequence of an industrial process or as a breakdown product in a living system.

• Carbohydrate - A class of organic compounds including sugars and starches. The name comes from the fact that many (but not all) carbohydrates have the basic formula CH2O.
• Carbon dioxide - (CO2) A colorless, odorless gas produced by respiration and combustion of carbon-containing fuels. Plants use it as a food in the photosynthesis process.
• Carbon monoxide - (CO) A colorless, odorless, poisonous gas produced by incomplete combustion.
• Catalyst - A substance that alters the rate of a chemical reaction, without being consumed or produced or affected by the reaction. Enzymes are catalysts for many biochemical reactions.
• Cellulase - A family of enzymes that break down cellulose into glucose molecules.
• Cellulose - The carbohydrate that is the principal constituent of wood and other biomass and forms the structural framework of the wood cells. It is a polymer of glucose with a repeating unit of C6H10O5 strung together by ß-glycosidic linkages. The ß-linkages in cellulose form linear chains that are highly stable and resistant to chemical attack because of the high degree of hydrogen bonding that can occur between chains of cellulose (see below). Hydrogen bonding between cellulose chains makes the polymers more rigid, inhibiting the flexing of the molecules that must occur in the hydrolytic breaking of the glycosidic linkages. Hydrolysis can reduce cellulose to a cellobiose repeating unit, C12H22O11, and ultimately to glucose, C6H12O6. Heating values for cellulose may be slightly different based upon the feedstock. Example values are shown below (higher heating value [HHV] at 30°C, dry basis).
• Cetane Number - The Cetane Number (CN) is a measure of ignition properties of a diesel fuel. The fuel quality test ASTM D613-05 determines the rating of diesel fuel in terms of an arbitrary scale of CN using a standard single-cylinder, four-stroke cycle, variable compression ratio, indirect-injected engine. CN relates to the delay between when fuel is injected into the cylinder and when ignition occurs. Cetane, a long-chain hydrocarbon with 16 carbon atoms, does not require a pilot flame or an ignition spark and ignites well under high temperature and high pressure conditions. Therefore, it is the ideal fuel for diesel engines. Cetane was assigned a CN of 100 and used as the reference fuel. The higher the CN of a diesel fuel, the better the ignition and combustion. Petroleum-based diesel fuels have a CN of 50 – 52, and the addition of ignition accelerators can increase the range to 53 – 54. Biodiesel compares well with these fuels with regard to its ignition qualities. The CN of biodiesel is directly related to its fatty acid composition. The longer the fatty acid carbon chains and the more saturated the molecules, the higher the CN. Examples of CN for biodiesel (methyl esters) derived from vegetable oils are as follows: peanut 54, soybean 45, palm 62, sunflower 49. Biodiesel standards require a minimum CN of 47. This easily complies with the requirements of engine manufacturers for high-quality fuel with good ignition qualities without the need for additives.
• Chips - small fragments of wood chopped or broken by mechanical equipment. Total tree chips include wood, bark, and foliage. Pulp chips or clean chips are free of bark and foliage.
• Cloud Point - The cloud point is the temperature at which the smallest observ­able cluster of hydrocarbon crystals first occurs upon cooling under defined conditions. The standard test, ASTMD 2500-05, describes cloud point determination for diesel fuels. A specific value for the cloud point requirements of diesel fuel has not been set. However, it is suggested the cloud point be no more than 6°C higher than the 10th percentile minimum ambient temperature for the month the fuel will be used. The 10th percentile temperature corresponds to the minimum temperature that would be reached no more than 3 days out of 30 for the month. For example, 10th percentile temperature for the month of December is -12°C in Oklahoma. At low temperatures, biodiesel will gel or crystallize into a solid mass that cannot be filtered or pumped. The engine cannot run at these temperatures. Typical cloud points for biodiesel (methyl esters) derived from vegetable oils are as follows: peanut 5°C, soybean 1°C, palm 13°C, sunflower 1°C.
• Cold Filter Plugging Point - The low-temperature performance of diesel fuels also is evalu­ated with the Cold Filter Plugging Point (CFPP) tests. The method is published as a European standard, ENII6:1981, and it is a national standard in various countries around the world. The CFPP measures the highest temperature at which wax separating out of a sample can stop or seriously reduce the flow of fuel through a standard fuel filter under standard test conditions. The CFPP does not correlate well with low-temperature performance of North American fuels in North American equipment, and it is not included in the ASTM Book of Standards.
• Combustion - A chemical reaction between a fuel and oxygen that produces heat (and usually, light).
• Corrosion Test - Some compounds in diesel fuel, especially sulfur compounds and residual catalyst, can be corrosive. Corrosion is readily caused by copper compounds. Hence, copper is used as an indicator of the tendency of the fuel to cause corrosion. ASTM D130-04 uses pol­ished copper strips soaked in the fuel to characterize the tendency to corrode metals.

• E-10 - A mixture of 10% ethanol and 90% gasoline based on volume.
• E-85 - A mixture of 85% ethanol and 15% gasoline based on volume.
• Elemental Analysis - The determination of carbon, hydrogen, nitrogen, oxygen, sulfur, chlorine and ash in a sample. See Ultimate Analysis.
• Energy crop - A crop grown specifically for its fuel value. These include food crops such as corn and sugarcane, and nonfood crops such as poplar trees and switchgrass.
• Enzyme - A protein or protein-based molecule that speeds up chemical reactions occurring in living things. Enzymes act as catalysts for a single reaction, converting a specific set of reactants into specific products.
• Ester - An ester is a compound formed from the reaction between an acid and an alcohol. In esters of carboxylic acids, the -COOH group of the acid and the -OH group of the alcohol lose a water and become a -COO- linkage.
• Esterification - Carboxylic acids (fatty acids) react readily with alcohols in the presence of a catalyst (mineral acids) to yield compounds called esters. The process is called esterification.Oil or fat used in alkaline transesterification reactions should contain no more than 1 percent free fatty acids (FFA). Low-quality feedstocks often contain significant quantities of free fatty acids and water, which make them unsuitable for homogeneous alkaline-catalyzed processes. Neutralization of FFAs can be carried out by the addition of excess alkali, but this leads to the formation of soaps and post-reaction separation problems. Thus, a preferred pretreat­ment process for used cooking oils is an esterification process that commonly uses a strong liquid acid catalyst, such as sulfuric acid.
• Ethanol - (CH3CH2OH) A colorless, flammable liquid produced by fermentation of sugars. Ethanol is used as a fuel oxygenate. Ethanol is the alcohol found in alcoholic beverages.
• Extractives - Any number of different compounds in biomass that are not an integral part of the cellular structure. The compounds can be extracted from wood by means of polar and non-polar solvents including hot or cold water, ether , benzene, methanol, or other solvents that do not degrade the biomass structure. The types of extractives found in biomass samples are entirely dependent upon the sample itself.

• Fat - Fats are a mixture of triacylglycerides and usually solid under ambient conditions.
• Fatty Acid - Fatty acid is an organic compound consisting of a hydrocarbon chain and a carboxylic acid group. Long chain fatty acids (more than 8-10 carbon atom on the hydrocarbon chain) are most commonly present in oils and fats. These fatty acids usually have an even number of carbon atoms and unbranched chains. Fatty acids may be “saturated,” which means there is no double bonds on the hydrocarbon chain, or “unsaturated” with one or more double bonds. If a fatty acid contains two or more double bond in the structure, it is “polyunsaturated.”
• Fermentation - A biochemical reaction that breaks down complex organic molecules (such as carbohydrates) into simpler materials (such as ethanol, carbon dioxide, and water). Bacteria or yeasts can ferment sugars to ethanol.
• Fixed Carbon - The carbon remaining after heating in a prescribed manner to decompose thermally unstable components and to distill volatiles. Part of the proximate analysis group.
• Flash Point - Flash point is the lowest temperature at which the vapor of a combustible liquid can be made to ignite momentarily in air. The flash point test method is described by ASTM D-93. All No. 2 die­sel fuels have high flash points (54°C, minimum; 71°C, typical). According to ASTM regulations, biodiesel must have a flash point minimum of 130°C (266 F), while No. 2 petroleum diesel is required to have a flash point above 52°C (125 F). The U.S. Department of Transportation considers a material with a flash point of 93°C or higher to be nonhazardous. A low flash point in biodiesel can indicate residual methanol remaining from the conversion process. A high flash point can mean the oil conversion reaction has not proceeded to completion. A low flash point in biodiesel can result in premature ignition, causing irregular timing, excessive fuel blow-by into the crankcase oil and excessive emissions. A high flash point can lead to poor ignition, resulting in inconsistent firing and variable engine performance. It also can indicate potential clogging of fuel lines, filters and injector clogging in cold climates.
• Forestry Residues - Includes tops, limbs, and other woody material not removed in forest harvesting operations in commercial hardwood and softwood stands, as well as woody material resulting from forest management operations such as precommercial thinnings and removal of dead and dying trees.
• Fossil Fuel - A carbon or hydrocarbon fuel formed in the ground from the remains of dead plants and animals. It takes millions of years to form fossil fuels. Oil, natural gas, and coal are fossil fuels.
• Free Fatty Acids (UNESTERIFIED FATTY ACIDS) - - Free fatty acids are not bound or attached to other molecules such as glycerol. The unesterified fatty B139acids may come from the breakdown of a triglyceride into its components (fatty acids and glycerol). They also may arise from incomplete conversion or hydrolysis during storage of feedstock. Free fatty acids are very soluble in biodiesel and can further compromise oxidative stability during storage. Biodiesel with high fatty acid number can increase deposits in the fueling system. Free fatty acids must be removed during edible-oil processing because they reduce the smoke point in frying fats and rapidly oxidize to give rancid flavors. Food-grade oils usually contain less than 0.05 percent free fatty acids.
• Fungi - Fungi are plant-like organisms with cells with distinct nuclei surrounded by nuclear membranes, incapable of photosynthesis. Fungi are decomposers of waste organisms and exist as yeast, mold, or mildew.

• Galactan - The polymer of galactose with a repeating unit of C6H10O5. Found in hemicellulose it can be hydrolyzed to galactose.
• Galactose - A six-carbon sugar with the formula C6H1206. A product of hydrolysis of galactan found in the hemicellulose fraction of biomass.
• Global Warming - A term used to describe the increase in average global temperatures due to the greenhouse effect. Scientists generally agree that the Earth's surface has warmed by about 1 degree Fahrenheit in the past 140 years.
• Glucan - The polymer of glucose with a repeating unit of C6H10O5. Cellulose is a form of glucan. Can be hydrolyzed to glucose.
• Glucose - (C6H12O6) A six-carbon fermentable sugar.
• Glycerin - (C3H8O3) A liquid by-product of biodiesel production. Glycerin is used in the manufacture of dynamite, cosmetics, liquid soaps, inks, and lubricants.
• Glycerol (GLYCERIN) - Glycerol, the simplest trihydric alcohol [C3H5(OH)3], is a byproduct of the biodiesel process. It is a water soluble/miscible, colorless, sweet tasting and viscous liquid. In com­merce, it is usually called glycerin, sometimes spelled glycerine. In general “glycerol” refers to the pure compound, whereas “glycerin” is used for lower-purity products. One important property of glycerol is that it is safe for human consumption. Therefore, it is used in foods, syrups, ointments, medicines and cosmetics.
• Greenhouse Effect - The heat effect due to the trapping of the sun's radiant energy, so that it cannot be reradiated. In the earth's atmosphere, the radiant energy is trapped by greenhouse gases produced from both natural and human sources.
• Greenhouse Gas - A gas, such as water vapor, carbon dioxide, tropospheric ozone, methane, and low level ozone, which contributes to the greenhouse effect.
• Guaiacyl - A chemical component of lignin. It has a six-carbon aromatic ring with one methoxyl group attached. It is the predominant aromatic structure in softwood lignins. See syringyl.

• Hardwood - One of the botanical groups of dicotyledonous trees that have broad leaves in contrast to the conifers or softwoods. The term has no reference to the actual hardness of the wood. The botanical name for hardwoods is angiosperms. Short-rotation, fast growing hardwood trees are being developed as future energy crops. They are uniquely developed for harvest from 5 - 8 years after planting. Examples include: Hybrid poplars (Populus sp.), Hybrid willows (Salix sp.), Silver maple (Acer saccharinum), and Black locust (Robinia pseudoacacia).
• Heating Value - Higher heating value (HHV) is the potential combustion energy when water vapor from combustion is condensed to recover the latent heat of vaporization. Lower heating value (LHV) is the potential combustion energy when water vapor from combustion is not condensed. See also higher heating value and lower heating value.
• Hemicellulose - Hemicellulose consists of short, highly branched chains of sugars. In contrast to cellulose, which is a polymer of only glucose, a hemicellulose is a polymer of five different sugars. It contains five-carbon sugars (usually D-xylose and L-arabinose) and six-carbon sugars (D-galactose, D-glucose, and D-mannose) and uronic acid. The sugars are highly substituted with acetic acid. The branched nature of hemicellulose renders it amorphous and relatively easy to hydrolyze to its constituent sugars compared to cellulose. When hydrolyzed, the hemicellulose from hardwoods releases products high in xylose (a five-carbon sugar). The hemicellulose contained in softwoods, by contrast, yields more six-carbon sugars.
• Herbaceous Energy Crops - Perennial non-woody crops that are harvested annually, though they may take 2 to 3 years to reach full productivity. Examples include: Switchgrass (Panicum virgatum), Reed canarygrass (Phalaris arundinacea), Miscanthus (Miscanthus x giganteus), and Giant reed (Arundo donax).
• Herbaceous Plants - Non-woody species of vegetation, usually of low lignin content such as grasses.
• Heterogenous Catalysis - Heterogeneous catalysis involves the use of a catalyst in a dif­ferent physical phase than the reactants. Typical examples involve a solid catalyst with liquid or gaseous reactants. The main advantage of a heterogeneous catalyst is that the catalyst is easily separated from the reactants and products. A common approach is to pack a reaction vessel with catalyst particles and stream reactants through the packed bed. Currently, research is being conducted on numer­ous heterogeneous catalysts for biodiesel production. Axens, a Paris-based refining, petrochemical and natural gas market-focused company, has already developed a commercial biodiesel produc­tion technique (Esterfip-H) based on heterogeneous catalysis. This system eliminates water washes, and the product-separation scheme is simple and clean with less effluent to treat and dispose. Further­more, the reaction byproduct glycerin is 98 percent pure. Esterfip-H requires slightly higher operating temperatures to perform, but the stability of the catalyst and simplified downstream processing reduce conventional biodiesel production costs.
• Hexose - Any of various simple sugars that have six carbon atoms per molecule (e.g. glucose, mannose, and galactose.)
• Higher Heating Value (HHV, also known as Gross Heat of Combustion) - The heat produced by combustion of one unit of substance at constant volume in an oxygen bomb calorimeter under specified conditions. The conditions are: initial oxygen pressure of 2.0-4.0 MPa (20-40 atm), final temperature of 20°-35°C, products in the form of ash, liquid water, gaseous CO2 and N2, and dilute aqueous HCl and H2SO4. It is assumed that if significant quantities of metallic elements are combusted, they are converted to their oxides. In the case of materials such as coal, wood, or refuse, if small or trace amounts of metallic elements are present, they are unchanged during combustion and are part of the ash.
• Holocellulose - The total carbohydrate fraction of wood — cellulose plus hemicellulose.
• Homogeneous catalysts - Homogeneous catalysis involves the use of a catalyst in the same physical phase as the reactants. The majority of current biodiesel processes use homogeneous catalysts, such as a strong acid like sulfuric or hydrocholoric acid or strong base-like sodium or potassium hydroxide or methoxide dissolved in alcohol. Hence, oil, alcohol and catalyst are all in the liquid phase.
• Hydrocarbon (HC) - An organic compound that contains only hydrogen and carbon. In vehicle emissions, these are usually vapors created from incomplete combustion or from vaporization of liquid gasoline. Emissions of hydrocarbons contribute to ground level ozone.
• Hydrolysis - A chemical reaction that releases sugars, which are normally linked together in complex chains. In ethanol production, hydrolysis reactions are used to break down the cellulose and hemicellulose in the biomass.

• Kinematic Viscosity - Viscosity is a measure of a fluid’s resistance to flow. Kinematic viscosity can be obtained by dividing the absolute viscosity of a fluid by its mass density. The greater the viscosity, the less readily the liquid flows. Viscosity decreases strongly with increasing tem­perature. Biodiesel is more viscous than No. 2 diesel fuel, but only by a small amount. ASTM D445 is a standard test procedure for determining the kinematic viscosity of liquids. According to ASTM standards, kinematic viscosity is measured at 40°C and should be between 1.9 and 6.0 mm2/s.
• Klason Lignin - Lignin obtained from wood after the non-lignin components of the wood have been removed with a prescribed sulfuric acid treatment. A specific type of acid-insoluble lignin analysis.

• Lignin - The major noncarbohydrate, polypenolic structural constituent of wood and other native plant material that encrusts the cell walls and cements the cells together. It is a highly polymeric substance, with a complex, cross-linked, highly aromatic structure of molecular weight about 10,000 derived principally from coniferyl alcohol (C10H12O3) by extensive condensation polymerization. Higher heating value (oven dry basis): HHV=9111 BTU/LB (5062 CAL/G, 21178 J/G)[3].
• Lignin Pseudo-Molecule for Modeling - The n Lignin ratio of methoxy groups to phenylpropanoid groups (MeO:C9) is used to calculate an ultimate analysis for the lignin pseudo-molecule and then this ultimate analysis is used to estimate other properties of the molecule, such as its higher and lower heating values.
• Lignin Ratio of MeO to C9 - Lignin empirical formulae are based on ratios of methoxy groups to phenylpropanoid groups (MeO:C9). The general empirical formula for lignin monomers is C9H10O2 (OCH3)n, where n is the ratio of MeO to C9 groups. Where no experimental ratios have been found, they are estimated as follows: 0.94 for softwoods; 1.18 for grasses; 1.4 for hardwoods. These are averages of the lignin ratios found in the literature. Paper products, which are produced primarily from softwoods, are estimated to have an MeO:C9 ratio of 0.94.
• Lignocellulose - Refers to plant materials made up primarily of lignin, cellulose, and hemicellulose.
• Lower Heating Value (LLV also known as Net Heat of Combustion) - The heat produced by combustion of one unit of a substance, at atmospheric pressure under conditions such that all water in the products remains in the form of vapor. The net heat of combustion is calculated from the gross heat of combustion at 20°C by subtracting 572 cal/g (1030 Btu/lb) of water derived from one unit mass of sample, including both the water originally present as moisture and that formed by combustion. This subtracted amount is not equal to the latent heat of vaporization of water because the calculation also reduces the data from the gross value at constant volume to the net value at constant pressure. The appropriate factor for this reduction is 572 cal/g[3].

• Mannan - The polymer of mannose with a repeating unit of C6H10O5[2]. Can be hydrolyzed to mannose.
• Mannose - A six-carbon sugar C6H1206. A product of hydrolysis of mannan found in the hemicellulose fraction of biomass.
• Mass Closure (%) - The percent by weight of the total samples extracted from the biomass sample compared to the weight of the original sample. It is a sum of the weight percent of moisture, extractives, ash, protein, total lignin, acetic acid, uronic acids, arabinan, xylan, mannan, galactan, glucan, and starch. This is a good indicator of the accuracy of a complete biomass compositional analysis.
• Moisture - This is a measure of the amount of water and other components that are volatilized at 105°C present in the biomass sample[6].
• Moisture Free Basis - Biomass composition and chemical analysis data is typically reported on a moisture free or dry weight basis. Moisture (and some volatile matter) is removed prior to analytical testing by heating the sample at 105°C to constant weight. By definition, samples dried in this manner are considered moisture free.
• Monosaccharide - a simple sugar such as a five-carbon sugar (xylose, arabinose) or six-carbon sugar (glucose, fructose). Sucrose, on the other hand is a disaccharide, composed of a combination of two simple sugar units, glucose and fructose.
• municipal solid waste (MSW) - Any organic matter, including sewage, industrial, and commercial wastes, from municipal waste collection systems. Municipal waste does not include agricultural and wood wastes or residues.
• Municipal Wastes - Residential, commercial, and institutional post-consumer wastes contain a significant proportion of plant-derived organic material that constitutes a renewable energy resource. Waste paper, cardboard, construction and demolition wood waste, and yard wastes are examples of biomass resources in municipal wastes.

• Native Lignin - The lignin as it exists in the lignocellulosic complex before separation.
• Neutral Detergent Fiber (NDF) - Organic matter that is not solubilized after one hour of refluxing in a neutral detergent consisting of sodium lauryl sulfate and EDTA at pH 7. NDF includes hemicellulose, cellulose, and lignin.
• Nitrogen Oxides (NOx) - A product of photochemical reactions of nitric oxide in ambient air, and the major component of photochemical smog.
• Non-renewable Resource - A non-renewable energy resource is one that cannot be replaced as it is used. Although fossil fuels, like coal and oil, are in fact fossilized biomass resources, they form at such a slow rate that, in practice, they are non-renewable.

• Oil - Oils are liquid at atmospheric conditions. More than 90 percent of oils consist of triacylglycerides.
• Organic Compound - An organic compound contains carbon chemically bound to hydrogen. Organic compounds often contain other elements (particularly O, N, halogens, or S).
• Oxygenate - An oxygenate is a compound which contains oxygen in its molecular structure. Ethanol and biodiesel act as oxygenates when they are blended with conventional fuels. Oxygenated fuel improves combustion efficiency and reduces tailpipe emissions of CO.
• Ozone - A compound that is formed when oxygen and other compounds react in sunlight. In the upper atmosphere, ozone protects the earth from the sun's ultraviolet rays. Though beneficial in the upper atmosphere, at ground level, ozone is called photochemical smog, and is a respiratory irritant and considered a pollutant.

• Particulates - A fine liquid or solid particle such as dust, smoke, mist, fumes, or smog, found in air or emissions.
• Petroleum - Any petroleum-based substance comprising a complex blend of hydrocarbons derived from crude oil through the process of separation, conversion, upgrading, and finishing, including motor fuel, jet oil, lubricants, petroleum solvents, and used oil.
• Photosynthesis - A complex process used by many plants and bacteria to build carbohydrates from carbon dioxide and water, using energy derived from light. Photosynthesis is the key initial step in the growth of biomass and is depicted by the equation: CO2 + H2O + light + chlorophyll = (CH2O) + O2
• Polymer - A large molecule made by linking smaller molecules (monomers) together.
• Polysaccharide - A carbohydrate consisting of a large number of linked simple sugar, or monosaccharide, units. Examples of polysaccharides are cellulose and starch.
• Pour Point - Pour point is the temperature at which the fuel ceases to flow. One drawback of biodiesel is that it has higher cloud and pour points than petroleum diesel, which could lead to engine problems during winter in much of the United States. The pour point always is lower than the cloud point.
• Protein - A protein molecule is a chain of up to several hundred amino acids and is folded into a more or less compact structure. Because about 20 different amino acids are used by living matter in making proteins, the variety of protein types is enormous. In their biologically active states, proteins function as catalysts in metabolism and to some extent as structural elements of cells and tissues[7]. Protein content in biomass (in mass %) can be estimated by multiplying the mass % nitrogen of the sample by 6.25.
• Proximate Analysis - The determination, by prescribed methods, of moisture, volatile matter, fixed carbon (by difference), and ash. The term proximate analysis does not include determinations of chemical elements or determinations other than those named[7]. The group of analyses is defined in ASTM D 3172.

• Reaction - A chemical reaction is a dissociation, recombination, or rearrangement of atoms.
• Renewable Energy Resource - An energy resource that can be replaced as it is used. Renewable energy resources include solar, wind, geothermal, hydro and biomass. Municipal solid waste (MSW) is also considered to be a renewable energy resource.
• Residues, Biomass - Byproducts from processing all forms of biomass that have significant energy potential. For example, making solid wood products and pulp from logs produces bark, shavings and sawdust, and spent pulping liquors. Because these residues are already collected at the point of processing, they can be convenient and relatively inexpensive sources of biomass for energy.

• Saccharide - A simple sugar or a more complex compound that can be hydrolyzed to simple sugar units.
• Softwood - Generally, one of the botanical groups of trees that in most cases have needle-like or scale-like leaves; the conifers; also the wood produced by such trees. The term has no reference to the actual hardness of the wood. The botanical name for softwoods is gymnosperms.
• Specific Gravity - The specific gravity is defined as the ratio of a given volume of a sample material at 25°C to the weight of the same volume of water at 25°C. Specific gravity is determined by ASTM D-287. No. 2 diesel exhibits a specific gravity of 0.85. Biodiesel specific gravity varies between 0.86 and 0.90 depending on the feedstock used.
• Stability - In regards to biodiesel, the term “stability” refers to thermal sta­bility under both hot and cold temperatures, resistance to oxidation, polymerization, water absorption and microbial activity. The main source of instability in biodiesels is unsaturated fatty acid chains. Stability also can be affected by metals and plastics in contact with biodiesel. The presence of water in biodiesel can cause rust formation and corrosion. The presence of water also promotes microbial growth. Water and sediment analysis in biodiesel is described by ASTM D2709. According to ASTM D6751-06, the maximum allowable water and sediment is 0.05 percent by volume. Oxidation stability of diesel fuel is measured by ASTM D2274. Oxidation of biodiesel leads to the formation of hydro peroxides, which can polymerize to form insoluble gums and cause plugging in fuel systems and filters.
• Starch - A molecule composed of long chains of a-glucose molecules linked together (repeating unit C12H16O5 ). These linkages occur in chains of a-1,4 linkages with branches formed as a result of a-1,6 linkages (see below). This polysaccharide is widely distributed in the vegetable kingdom and is stored in all grains and tubers. A not-so-obvious consequence of the a linkages in starch is that this polymer is highly amorphous, making it more readily attacked by human and animal enzyme systems and broken down into glucose. Gross heat of combustion: Qv(gross)=7560 Btu/lb (4200 cal/g,17570 J/g)[3].
• Stover - The dried stalks and leaves of a crop remaining after the grain has been harvested.
• Structural Chemical Analysis - The composition of biomass reported by the proportions of the major structural components; cellulose, hemicellulose, and lignin.
• Syringyl - A component of lignin, normally only found in hardwood lignins. It has a six-carbon aromatic ring with two methoxyl groups attached. See guaiacyl.

• Total Lignin - The sum of the acid soluble lignin and acid insoluble lignin fractions.
• Total Solids - The amount of solids remaining after all volatile matter has been removed from a biomass sample by heating at 105°C to constant weight.
• Toxics - As defined in the 1990 Clean Air Act Amendments, toxics include benzene, 1,3 butadiene, formaldehyde, acetaldehyde, and polycyclic organic matter.
• Transesterification - Transesterification is the general term used to describe the important class of organic reactions where an ester is transformed into another through interchange of the alkoxy moiety. In biodiesel production process, transesterification refers to the reaction of a lipid (triacylglyceride) with an alcohol (short-chain alcohols such as methanol, ethanol or buthanol) to form fatty acid esters (biodiesel) and a byproduct – glycerol. The reaction is reversible. Usually, an excess of alcohol is used to force the equilibrium to the product side. The stoichiom­etry mole ratio for the reaction is 3:1 alcohol to lipids. However, in practice, this is usually increased to 6:1 to raise the product yield. If methanol is used in this process, it is called methanolysis. The presence of a catalyst (a strong base or acid enzyme) accelerates the conversion. Most biodiesels are currently synthesized using an alkaline catalyst, because the transesterification reaction by an acid catalyst is much slower.
• Triacylglycerol (Triacylglyceride) - A triacylglyceride is a compound formed from one unit of glycerol and three units of fatty acids. In simple triacylglycerides, all three fatty acids are iden­tical. In mixed triacylglycerides, two or three different fatty acids may be present. Fats and oils are physical mixtures of many different triacylglycerides. The blue section on the figure represents a glycerol molecule, and the red section is esterified fatty acids to a glycerol molecule. R, R’ and R” symbolize hydrocarbon chains on fatty acids.
• Triglyceride - A triglyceride is an ester of glycerol and three fatty acids. Most animal fats are composed primarily of triglycerides.

• Ultimate Analysis - The determination of the elemental composition of the organic portion of carbonaceous materials, as well as the total ash and moisture. Determined by prescribed methods. See elemental analysis.
• Uronic Acid - A simple sugar whose terminal -CH2OH group has been oxidized to an acid, COOH group. The uronic acids occur as branching groups bonded to hemicelluloses such as xylan.

• Volatile - A solid or liquid material that easily vaporizes.
• Volatile Matter - Those products, exclusive of moisture, given off by a material as a gas or vapor, determined by definite prescribed methods that may vary according to the nature of the material. One definition of volatile matter is part of the proximate analysis group usually determined as described in ASTM D 3175.

• Whole Tree Chips - Wood chips produced by chipping whole trees, usually in the forest. Thus the chips contain both bark and wood. They are frequently produced from the low-quality trees or from tops, limbs, and other logging residues.
• Willstatter Lignin - Lignin obtained from the lignocellulosic complex after it has been extracted with fuming hydrochloric acid.
• Wood - A solid lignocellulosic material naturally produced in trees and some shrubs, made of up to 40%-50% cellulose, 20%-30% hemicellulose, and 20% -30% lignin.

• Xylan - A polymer of xylose with a repeating unit of C5H804, found in the hemicellulose fraction of biomass. Can be hydrolyzed to xylose. Gross heat of combustion: Qv(gross)=17751.9 Jg-1.
• Xylose - A five-carbon sugar C5H1005. A product of hydrolysis of xylan found in the hemicellulose fraction of biomass.

• Yeast - Any of various single-cell fungi capable of fermenting carbohydrates.
• Yellow, Brown and Trap Grease - Yellow grease is produced from vegetable oil or animal fat that has been heated and used for cooking. Renderers filter out the solids and heat the spent cooking oil to drive out moisture until it meets industry specifications for yellow grease. Yellow grease is required to have a free fatty acid (FFA) level of less than 15 percent. If the FFA level exceeds 1 percent, it is called brown grease. This grease may be sold at a discount or blended with low FFA material to meet yellow grease specifications. Trap grease is material that is collected in special traps in restaurants to prevent the grease from entering the sanitary sewer system where it could cause blockages. Many rendering plants will not process trap grease because it is usually contaminated with cleaning agents. Yellow grease, brown grease and trap grease can be used to produce biodiesel.