Separation of Small Organic Compounds Derived from Aldol-Condensation by Membrane Processes

The separation of C3-carbohydrates (DL-glyceraldehyde and dihydroxyacetone) present after the aldol-condensation of formaldehyde and glycolaldehyde was examined using the membrane processes nanofiltration (NF) and reverse osmosis (RO), which exemplifies the crucial problem area of the retention of small organic compounds. Two RO- and one NF-membrane were tested in order to obtain two fractions, namely a C3-enriched and a fraction containing mainly formaldehyde, methanol, and formic acid for a subsequently repeated aldol-condensation. In the case of a RO-process, operated until a volumetric concentration factor of 4 and two sequenced diafiltration steps, approximately 80% of formaldehyde, methanol, and formic acid were removed. Meanwhile, only about 40% of C3-carbohydrates were found in the permeate.