Purifying Bio-Diesel After Transesterification

Given the current and projected world-wide energy demands, I have been seeing more literature, newsletter, and journal references to biomass derived energy sources to reduce demand for petroleum-based fuels and be better for the environment. One area of development is the production of biodiesel, but it has a serious downside. As a major ion exchange supplier, we are seeing substantial developments in the purification of biodiesel using specialized ion exchange resins.

Chemical Process:
The process to manufacture biodiesel requires transesterification of a vegetable based oil in the presence of a catalyst and methanol. What results are raw biodiesel (methyl ester), soap, catalyst, glycerol, and methanol. This raw biodiesel needs to be purified to applicable standards, EN14214 or ASTM D6751.

Problem:
The typical purification process uses as many as 8 successive water washings of the raw biodiesel. This transfers water soluble impurities soap, catalyst, glycerol, methanol, and some biodiesel to the water. This results in a huge amount of organic and catalyst contaminated wastewater. So for every gallon of biodiesel produced, you end up with 8 gallons of liquid waste. Not a very environmentally friendly byproduct of biodiesel production.

Solution:
A very elegant solution is available and being used extensively in Europe, a leader in biodiesel production. The raw biodiesel or once washed raw biodiesel is flowed through a tank of a special ion exchange resin. The resin readily removes the glycerol, soap, and catalyst, all corrosive to diesel engine components, and water from the raw biodiesel. It can take the glycerin from 500 ppm down to less than 10 ppm. This is significantly below the standard of 200 ppm. This potentially allows for higher concentration of biodiesel in blends with petroleum diesel.

Results:
From literature and papers published by several ion exchange manufacturers, depending upon the process, 1 lb of ion exchange resin can treat 900 - 2000 lbs of biodiesel. Work is being done to have a way to regenerate the resin to allow for reuse.