What Are The Benefits of Biodiesel?
What Are The Benefits of Biodiesel?
What Are The Benefits of Biodiesel?
Biodiesel Production
As mentioned above biodiesel can be produced from straight vegetable oil, animal oil/fats, tallow
and waste oils. There are three basic routes to biodiesel production from oils and fats:
Base catalyzed transesterification of the oil.
Direct acid catalyzed transesterification of the oil.
Conversion of the oil to its fatty acids and then to biodiesel.
Almost all biodiesel is produced using base catalyzed transesterification as it is the most economical
process requiring only low temperatures and pressures and producing a 98% conversion yield. For
this reason only this process will be described in this report.
The Transesterification process is the reaction of a triglyceride (fat/oil) with an alcohol to form
esters and glycerol. A triglyceride has a glycerine molecule as its base with three long chain fatty
acids attached. The characteristics of the fat are determined by the nature of the fatty acids attached
to the glycerine. The nature of the fatty acids can in turn affect the characteristics of the biodiesel.
During the esterification process, the triglyceride is reacted with alcohol in the presence of a
catalyst, usually a strong alkaline like sodium hydroxide. The alcohol reacts with the fatty acids to
form the mono-alkyl ester, or biodiesel and crude glycerol. In most production methanol or ethanol
is the alcohol used (methanol produces methyl esters, ethanol produces ethyl esters) and is base
catalysed by either potassium or sodium hydroxide. Potassium hydroxide has been found to be more
suitable for the ethyl ester biodiesel production, either base can be used for the methyl ester. A
common product of the transesterification process is Rape Methyl Ester (RME) produced from raw
The products of the reaction are the biodiesel itself and glycerol.
A successful transesterification reaction is signified by the separation of the ester and glycerol
layers after the reaction time. The heavier, co-product, glycerol settles out and may be sold as it is
or it may be purified for use in other industries, e.g. the pharmaceutical, cosmetics etc.
Straight vegetable oil (SVO) can be used directly as a fossil diesel substitute however using this fuel
can lead to some fairly serious engine problems. Due to its relatively high viscosity SVO leads to
poor atomisation of the fuel, incomplete combustion, coking of the fuel injectors, ring
carbonisation, and accumulation of fuel in the lubricating oil. The best method for solving these
problems is the transesterification of the oil.
The engine combustion benefits of the transesterification of the oil are:
Lowered viscosity
Complete removal of the glycerides
Lowered boiling point
Lowered flash point
Lowered pour point
Production Process
An example of a simple production flow chart is proved below with a brief explanation of each step.
(ref 1)
removed with a flash evaporation process or by distillation. In others systems, the alcohol is
removed and the mixture neutralized before the glycerin and esters have been separated. In either
case, the alcohol is recovered using distillation equipment and is re-used. Care must be taken to
ensure no water accumulates in the recovered alcohol stream.
Glycerin Neutralization
The glycerin by-product contains unused catalyst and soaps that are neutralized with an acid and
sent to storage as crude glycerin. In some cases the salt formed during this phase is recovered for
use as fertilizer. In most cases the salt is left in the glycerin. Water and alcohol are removed to
produce 80-88% pure glycerin that is ready to be sold as crude glycerin. In more sophisticated
operations, the glycerin is distilled to 99% or higher purity and sold into the cosmetic and
pharmaceutical markets.
Methyl Ester Wash
Once separated from the glycerin, the biodiesel is sometimes purified by washing gently with warm
water to remove residual catalyst or soaps, dried, and sent to storage. In some processes this step is
unnecessary. This is normally the end of the production process resulting in a clear amber-yellow
liquid with a viscosity similar to petrodiesel. In some systems the biodiesel is distilled in an
additional step to remove small amounts of color bodies to produce a colorless biodiesel.
Product Quality
Prior to use as a commercial fuel, the finished biodiesel must be analyzed using sophisticated
analytical equipment to ensure it meets any required specifications. The most important aspects of
biodiesel production to ensure trouble free operation in diesel engines are:
Complete Reaction
Removal of Glycerin
Removal of Catalyst
Removal of Alcohol
Absence of Free Fatty Acids