Membrane is the key to cheap, and green, solvents
15 Jan 2000
Researchers at a US government-funded laboratory have developed a new method for making an organic solvent which, they claim, could replace environmentally-unfriendly chlorinated solvents in many applications.
The process, based on membrane technology, makes ethyl lactate, which currently costs up to $2 per pound. The new process will cut the price to 'well below $1 per pound,' claims Jim Frank, who is directing the research at the Argonne National Laboratory in Illinois cheap enough to compete with chlorinated solvents.
Ethyl lactate is made from lactic acid, which is, in turn, obtained from a fermentation process. This produces an impure broth, which has to be purified; converted to the acid; reacted with alcohol, and dehydrated.
The Argonne process pumps the broth (which contains ammonium lactate) into a reactor equipped with a selective membrane which will allow water and aqueous salts through, but is impermeable to organic molecules. A combination of thermal and catalytic cracking converts the ammonium lactate into the acid; alcohol, added to the same reactor, converts the acid to the ester.
The membrane, which works by a pervaporation (permeation followed by evaporation) principle, removes the unwanted ions and the water from the broth, which both purifies the acid and drives the alcohol/acid/ester equilibrium towards the ester. This cuts the number of reaction steps, the amount of equipment needed, and the amount of waste produced. Moreover, it consumes just a tenth of the energy of the traditional process, claims Frank, which will allow the huge potential price cuts.
The process was successful at the lab scale, and is currently under test at pilot plant scale at a nearby company.
