Course: BFM 202 Biodiesel Production

Lecture

Ion Exchange
Credits
BFM 202 Biodiesel Production Unit 5 Lecture has been adapted from "ENGY 131 Unit 5 Commentary Catalysis" by Southeastern Illinois College.

ENGY 131 Biodiesel Production course content by Southeastern Illinois College is licensed under a Creative Commons Attribution 3.0 Unported License. Except where indicated otherwise.

Ion Exchange

Once the transesterification process is completed, two product layers exist.
Crude biodiesel floats to the top while the crude glycerin settles to
the tank's bottom. Separation may be accelerated through the use of a
centrifuge.

Both the biodiesel and glycerin contain excess amounts of methanol,
fatty acid salts, water, and soap and are cleaned using a process known
as washing.

Once separated from glycerin, biodiesel can contain as much as 3%
methanol which acts as a solvent, collecting soap and other contaminants
suspended in the biodiesel.

Crude biodiesel will also contain residual catalyst and feedstock
impurities. If they remain in the fuel, it would ultimately foul fuel
injection systems and poison exhaust after-treatment systems.
ASTM EN 14109 dictates the concentrations of potassium and sodium while
ASTM EN 14105 dictates glycerol quality.

Dry Washing Biodiesel

In drywash methods, methanol is evaporated or distilled into a
flammable, toxic gas during the purification process. After separation,
distillation or flash evaporation removes the remaining methanol from
the biodiesel. This excess methanol can be recycled back into the
production process.

Water Washing Biodiesel

Water washing is a common method of cleaning biodiesel. It uses
aggressive power wash methods that can take a few hours or less
aggressive washes that take significantly longer. There are several
water wash processes that use water-to-biodiesel ratios of 1:1 or as
much as 5:1.

Water soaks up methanol releasing its impurities and washing them away
with the waste water. Spent wash water is treated and can be used for
irrigation or emitted as an effluent, adding costs to the process.
Depending upon the feedstock, the wash water can be a hazardous waste
that's difficult to dispose.

The water-wash method has limitations. Decreased yields occur because of the:
- methyl ester loss due to high soap levels causing emulsification
- high effluent treatment and disposal costs
- time and cost associated with drying methyl esters

Water washing requires heated and conditioned water and does not remove
insoluble water impurities. Environmental and sustainability issues can be
overcome through the use of water recycle systems.