A Continuous Reactive Separation Process for Ethyl Lactate Formation

Abstract

The continuous formation of ethyl lactate (L1E) from aqueous lactic acid solution and ethanol is carried out in a reactive separation column. Nearly complete conversion of lactic acid can be achieved with L1E yield exceeding 85%; byproduct lactate oligomer esters and acids formed can be further converted to additional L1E. Concentrated (88 wt % in water) lactic acid feedstock gives the best results, with as little as 40% excess ethanol required to achieve >95% conversion of lactic acid. Similar conversion can be obtained using 50 wt % lactic acid feed solution, but with much higher ethanol feed rates. Optimal column operation in both cases is observed with no reflux, so that operation is as a reactive stripping column. Limiting the quantity of ethanol added or vaporizing feed ethanol makes it possible to eliminate ethanol and water from the bottom stream of the column, thus simplifying recovery and purification of L1E product and facilitating the recycle of byproduct oligomers. Reaction of oligomeric byproducts with excess ethanol over Amberlyst 15 cationic exchange resin in a batch reactor gives a high yield of L1E, indicating that process yields of L1E approaching 100% are feasible.