The wood extracts from hot-water extraction consist of monomeric and low molecular-weight oligmers of sugars (hexoses and pentoses), acetic acid, degraded lignin, and other low molecular-weight extractable substances. Hydrolysis of oligmers to monomeric sugars can be achieved by allowing more residence time for the wood extracts at high temperature under acidic conditions or could be achieved enzymetically. Separation of sugars and acetic acid is a key step in the biorefinery process. Several methods for the separation have been considered, including filtration, distillation, centrifugation, and chemical separation (i.e. chemical reactions that bond certain compounds to other molecules that allow them to be separated more easily). Membrane separation (or filtration) has been focuses in this study.