Biodiesel Glossary

316 Stainless Steel is the dream material for homebrewers. Too expensive to use in most applications.


ABS - Acrylonitrile Butadiene Styrene - A common thermoplastic used in a wide variety of everyday products. Solvents will damage ABS. It has some resistance to most chemicals (except strong oxidizers) It has good strength and crack resistance.

Acetone - Chemical Formula: C3H6O - (also known as propanone, dimethyl ketone, 2-propanone, propan-2-one and beta-ketopropane) A solvent used in the soap test. It is the active ingredient in fingernail polish remover. It is the simplest form of a ketone.

Acid Number - In biodiesel it is the results of ASTM D 664. It is a titration test on finished biodiesel that is a direct measure of free fatty acids. Over time, as biodiesel degrades, the Acid number will increase.

Alkali Solution - In biodiesel production, an Alkali solution is used as the reagent in titration. It is made by mixing catalyst either, KOH or NaOH, with water in prescribed ratios.

Anhydrous - without water, dry.

Anaerobic - Life or biological processes that occur in the absence of oxygen.

Anaerobic Digestion - A biochemical process by which organic matter is decomposed by bacteria in the absence of oxygen, producing methane and other byproducts.

Autoignition Temperature - The temprature at which a substance will ignite and burn without a spark or other ignition source.

Azeotrope - a mixture of two or more liquids that can to be separated by distillation. Ethanol and water are azeotropic at ethanol to water ratios above 95%. You can not distill the last 5% of the water out of ethanol.


Base - An Alkali, NaOH and KOH are alkali or basic. Not an acid.

Benzene - Chemical Formula: C6H6 also called Benzol. A colorless and flammable liquid commonly used as a solvent and precursor to the production of plastics, drugs and a number of other products. In Biodiesel production it is used as a solvent to extract oil from oilseeds.

Biodiesel - a fuel that is comprised of mono-alkyl esters of long chain fatty acids and is derived from vegetable oils or animal fats. ASTM D 6751 defines the requirements needed to be met in order to be classified as a fuel. A strong organic solvent.

Biodiesel Recipe - A prescription or directions detailing the ratios of alcohol, oil and catalyst used in making biodiesel.

Bromophenol Blue - an indicator solution that is used in the soap test titration. This pH indicating solution changes color from yellow to blue as pH changes from 3.0 to 4.6

Bubble wash - A method of removing water soluble impurities by bubbling air in water below biodiesel. As the air bubble rises it retains a small layer of water around the air that rises to the top of the biodiesel releases the air and then falls back to the bottom of the tank.


Calcium Stearate - Soap Scum or soap containing one calcium atom and two fatty acid chains. It is sometimes formed when biodiesel is washed in hard water.

Canola - a trademarked hybrid of rape initially bred in Canada. Bred for low acid levels.

Carbonation - Combining with Carbon dioxide. When NaOH is left exposed to air CO2 from the air will form Sodium Carbonate from the Sodium Hydroxide making it useless for making biodiesel.

Catalyst - a substance that accelerates the rate of a chemical reaction without being consumed in the reaction. In biodiesel production NaOH and KOH are the catalyst for transesterfication. While they are used in the saponification side reaction, they are still considered a catalyst since without a strong metallic base, transesterfication would not take place.

Cavitation - the forming of bubbles inside a pump. In our case it when water or methanol droplets evaporate and recondense while passing through a pump. In diesel engines water in the fuel will cause an IP (Injector Pump) to cavitate. In biodiesel production, adding warm methanol to oil just before the pump can result in the methanol boiling inside the pump. Cavitation is evident by the dramatic increase in noise coming from the pump. Cavitation can cause pitting and scaring of wetted surfaces inside the pump. It is the mechanisim by which water damages Injector Pumps.

CPVC - Biodiesel melts CPVC. Chlorinated Polyvinyl Chloride is a commonly available thermoplastic pipe with improved heat resistance properties over PVC. It is available in pipe sizes from ¼" to 12" and in both schedule 40 and schedule 80. CPVC is rated at 400psi at 73ÚF and 100psi at 180ÚF.



Emulsion – A mixture of biodiesel and water milky white in color that is sometimes difficult to separate. Emulsions in the wash water are caused ways. Excessive agitation during washing can cause the soap in the biodiesel to mix with water. Also, incompletely reacted biodiesel containing FFAs can hydrolyze causing an emulsion when water is added.

E.P.D.M. EPDM is a terpolymer elastomer made from ethylenepropylenediene monomer. Biodiesel melts it.

Esters - a product of the reaction of acids (usually organic) and alcohols. Fatty Acid Methyl Esters (FAME) are the product of the reaction of methanol and long chain fatty acids and are commonly called Biodiesel.

Esterfication - The process of attaching an alcohol molecule to a Free Fatty Acid. The acid process for making biodiesel uses esterfication.

Ethanol - Chemical Formula: C2H5OH - Also known as ethyl alcohol or grain alcohol. It is not commonly used in the production of biodiesel due to its expense, regulatory issues, and the difficulty in getting the glycerin byproduct to separate from the ethyl esters.

Ethyl Ester - Biodiesel made using Ethyl Alcohol.


Feedstock - The input to a reaction. In Biodiesel the feedstock is vegetable oil.

FLUOROCARBON (FKM) (VITON®) (FLUOREL®) - Fluorocarbon elastomers. Many variants exist with most being resistant to biodiesel. A few expensive variants exist that are resistant to both biodiesel and methanol.

Free Fatty Acids (FFA) - Fatty acids not attached to alcohol molecules like glycerin in vegetable oil or methanol in biodiesel. In the single stage base method of making biodiesel, FFAs are converted to soap. In an acid esterfication stage the FFA is converted directly to biodiesel.


Glycerin - Chemical Formula: C3H8O3 - also known as glycerine, and glycerol. It is an alcohol and is found in animal and plant fats and oils (glycerides). It is a byproduct of making biodiesel. It is used in wide variety of products from antifreeze to fabrics.

Glycerol - Chemical Formula: C3H8O3 - also known as glycerine, and glycerin. It is an alcohol and is found in animal and plant fats and oils (glycerides). It is a byproduct of making biodiesel. It is used in wide variety of products from antifreeze to fabrics.


HDPE (high density polyethylene) HDPE is resistant to a wide range of chemicals. It has several uses including being the material carboys are made from.

Hydrogenated Oil - Oil that has been chemically altered to improve shelf life. It is solid at room temperature and makes biodiesel with a high gel point temperature.

Hygroscopic - Absorbs water from the air.


Indicator solution - A chemical suspended in either water or alcohol that changes color with pH. As an example, phenolphthalein is an indicating solution that changes from colorless to pink as pH changes from 8.5 to 10.0. Other chemicals change colors at different pH. A few drops of indicating solution are used in titration tests.

Isopropyl alcohol - Chemical Formula: CH3CHOHCH3. - Also known as isopropanol, 2-Propanol and propan-2-ol. It is the main ingredient in rubbing alcohol and is used in titrating WVO. It is also used as a dewatering additive for gasoline. Commonly available in drugstores as rubbing alcohol.




LDPE - typical uses are plastic bottles and cone bottom tanks.

Linoleic acid - Chemical Formula: C18H32O2 or more specifically CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH) - An 18 carbon polyunsaturated fatty acid with two double bonds (C18:2). If the OH protion of the molecule is replaced with methanol it becomes Methyl Linoleic or one of the chemical components of biodiesel. It is found naturally in vegetable based oil attached to a glycerin molecule (glyceride).

Linolenic acid - Chemical Formula: C18H32O2 or more specifically CH3(CH2CH=CH)3CH2(CH2)7COOH - An 18 carbon polyunsaturated fatty acid with three double bonds (C18:3). If the OH portion of the molecule is replaced with methanol it becomes Methyl Linolenic or one of the chemical components of biodiesel. If the OH portion of the molecule is replaced with a glycerin molecule then it becomes a glyceride or one of the chemical components of vegetable oil.

Litmus paper - Paper impregnated with litmus powder and used as a pH indicator. It changes to red with increasing acidity and blue with increasing basicity.

LLDPE - Linear low density PE, also called Medium Density PE (MDPE)

Lye - common term for Sodium Hydroxide (NaOH)


Magnesium Stearate -Soap scum or soap made with magnesium as the metal. This soap contains one magnesium atom and two fatty acid chains. This soap will sometimes be formed when washing biodiesel with hard water. It can have the appearance of snow flakes in the biodiesel or a thin emulsion layer. Given time it will settle into the water layer below the biodiesel.

Methane - Chemical Formula: CH4 - Also know as natural gas. It is mined from wells as a petrochemical. It is also produced as a byproduct of biological activity. It is used as the raw material by industry to produce methanol.

Methanol - Chemical Formula: CH3OH - also known as methyl alcohol or wood alcohol. It is the most common alcohol used for transesterfication of WVO into Biodiesel. It is also used in the titration test. Methanol is toxic and will burn without a visible flame. Care must be taken with working with methanol to prevent fires and limit exposure.

Methyl Ester - An acid combined with methyl Alcohol. Methyl Esters made from long chain Fatty Acids are commonly called Biodiesel.

Methoxide - In chemistry Sodium Methoxide or Sodium Methylate is a chemical made by dissolving Sodium Metal in methanol and is sometimes used in commercial biodiesel production. In home-brewing it is commonly used to refer to the mixture of Sodium Hydroxide and methanol or the mixture of Potassium Hydroxide and Methanol.

Mist wash - A method of removing water soluble impurities by spraying a fine mist of water over the top of an open container of biodiesel. As the small droplets of water fall into and through the biodiesel they attract any water soluble impurities and collect on the bottom of the tank.

Molecular Sieve - A material with small uniform pores that trap specific molecules or atoms. Silica-gel and zeolite are two materials used as a molecular sieve. Molecular sieves are not often used in biodiesel due to the intensive energy needed to regenerate them.


NITRILE (NBR) - (BUNA-N) is a general purpose oil-resistant polymer known as nitrile rubber



Partially Hydrogenated Oil - Oil that has been chemically altered to improve shelf life. It is liquid at room temperature, but freezes solid just below room temperature.

Ph Test Strips - Paper strips impregnated with a chemical that changes color with pH.

Phenol Red - Chemical Formula: C19H14O5S -This pH indicating solution changes color from yellow to red as the pH changes from 6.6 to 8.0. It can be used as the indicating solution when titrating WVO.

Phenolphthalein - Chemical Formula: C20H14O4 - This pH indicating solution changes color from colorless to pink as the pH changes from 8.5 to 10.0. It can be used as the indicating solution when titrating WVO.

Polyethylene is a semi-crystalline material with excellent chemical resistance. They provide good resistance to organic solvents and degreasing agents.

Polymerization - When used to refer to biodiesel it is the oxidation of the fatty acid chain. When unsaturated oils are used to make biodiesel the double bond is prone to oxidation under certain conditions. Polymerization creates short chain fatty acids that increase acidity, alcohols that reduce flash point, and aldehydes that smell bad. Severe polymerization of biodiesel causes filter plugging.

Potassium Hydroxide - (KOH) a strong base that is sometimes used to make biodiesel. Dissolves in methanol easier than NaOH and the soaps are liquid rather than the solid soaps formed when using NaOH.

Potassium Stearate - A liquid soap containing one Potassium Molecule and one fatty acid. It is formed when using KOH as the catalyst for making biodiesel.

PP (polypropylene) Polypropylene is a thermoplastic polymer. Its strength and brittleness are between LDPE and HDPE. It has good chemical resistance to solvents, acids and bases. It has numerous uses in biodiesel production.

Processor - (also see reactor) The vessel used to hold the WVO, methanol and catalyst while it chemically reacts and changes WVO into biodiesel. The Appleseed uses a hot water heater as the Processor.

P.V.C. (Polyvinyl chloride) a polymer of vinyl chloride. PVC loses 78% of its strength when heated to 140ÚF. It can be used in unheated applications and has excellent chemical resistance properties.

PVDF (polyvinylidene fluoride), is used for chemical waste drainage systems. It is highly resistant to chemicals and heat. Joints are made using heat-fusion with a special tool or by mechanical joints using stainless steel couplings and clamps. This plastic is not used often in making biodiesel due to the expense as well as the difficulty in making joints.



Reactor - (also see processor) The vessel used to contain the reaction converting WVO into biodiesel.


Saponification - The process of making soap from esters of fatty acids.

Saturated Fat - Oils that are saturated with hydrogen. These are naturally occurring in animal fats and make high gel point biodiesel. They are solid at room temperature. They are chemically different from trans fatty acids in structure, but similar in gel point temperatures.

Smoke Point - The temperature at which vegetable oils and fats will first start smoking. It is the temperature at which oil will start to thermally degrade into low flashpoint components and become a fire hazard. Restaurants will throw out oil when it starts to smoke at normal cooking temperatures.

Soap Test - a test used to determine the amount of soap present in oil, glycerin or unwashed biodiesel. It is a titration test using hydrochloric acid solution as a reagent, bromophenol blue as an indicator (.04% in water), and acetone or isopropyl alcohol as a solvent.

Sodium Hydroxide - (NaOH) A strong base used in making biodiesel. Soaps formed during biodiesel production when using NaOH are solid. Sodium Hydroxide is available in both bead and flake forms. The bead form is slightly safer since it does not send dust flying into the air when disturbed.

Sodium Stearate - Soaps containing one sodium molecule and one fatty acid molecule. It’s the soap we make when using NaOH as the catalyst for making biodiesel.

Static wash -A method of removing water soluble impurities by putting biodiesel and water in the same tank without any agitation. Over time, water soluble impurities will move from the biodiesel layer to the water layer.

Stir wash - A Method of washing biodiesel that can cause instant emulsion if there is soap in the biodiesel. Basically, you pour water in fresh unwashed biodiesel and strongly agitate with some mixing devise. If you have high conversion fuel, and low soap content biodiesel and no free glycerine, it will supposedly create a short lived emulsion that quickly separates.

SVO - Straight Vegetable Oil


TEFLON® (PTFE) - Polytetrafluoroethylene TEFLON® was developed by Dupont and is Dupont’s brand name for Polytetrafluoroethylene (PTFE) It is now made by several manufactures and has excellent high temperature and chemical resistant properties.

Titration - A chemical test used in biodiesel production to determine how much catalyst is needed to turn all the Free Fatty Acids (FFAs) in Waste Vegetable Oil (WVO) to soap. It uses an Alkali solution made from your chosen catalyst as a reagent, phenolphthalein, phenol red or turmeric as an indicator, and isopropyl alcohol as a solvent.

Trans Fatty Acids - Hydrogenated and Partially Hydrogenated oils. These are made from vegetable oils to improve shelf life and make the oils more solid at room temperature.

Transesterfication - The process of exchanging one alcohol for another. The Base process for making biodiesel exchanges one glycol in the triglyceride molecule (one glycol attached to three Fatty Acids) for three methanol molecules each attached to a Fatty Acid (Methyl Ester or biodiesel.

Turmeric - A spice that can be used as a ph indicator. It changes from yellow to red as pH changes from 8.0 to 9.0. Ground turmeric can be found in the spice section of your local grocery.


Unsaturated Fat - Oil that is not saturated with hydrogen and contains one or more double bonds in the fatty acid chain. Unsaturated oil is liquid at room temperature and below. Biodiesel made from unsaturated fat is also low in gel point. Unsaturated oils go rancid faster than saturated oils or trans fatty acids. .


Viscosity - The thickness of biodiesel. It is measured by timing how long it takes for a volume of liquid to flow through a restriction. It is a resistance to flow of a liquid.

Viton® - a fluoroelastomer developed by DuPont. Viton® is a registered trademark of DuPont Performance Elastomers. It is resistant to organic solvents and many aggressive chemicals. The material used in gaskets and tubing and is the most often recommended material for replacing natural rubber fuel lines damaged by biodiesel.


WVO - Waste Vegetable Oil




Zeolite - A type of molecular sieve. A porous material that traps certain types of atoms in the pores on a molecular level. They can be used to remove methanol or water from biodiesel. They are regenerated by heating. Their use in biodiesel is limited due to the high cost of the material and the large amount of energy needed to regenerate it.

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