Controlled precipitation and purification of hemicellulose from DMSO and DMSO/water mixtures by carbon dioxide as anti-solvent

Anti-solvent precipitation of xylans and mannans from dimethylsulfoxide (DMSO) or DMSO/water mixtures, and subsequent drying with supercritical carbon dioxide (scCO2) were developed into a useful technique for preparing spherical hemicellulose micro-particles. Depending on the type of hemicellulose, water content of DMSO, precipitation pressure and temperature, the particle size can be adjusted within a wide range from less than 0.1 to more than 5 μm. For example, fast super-saturation which can be achieved by applying supercritical conditions results in the formation of very small particles as mass transfer between the solvent DMSO and anti-solvent scCO2 is reduced to a minimum. Anti-solvent precipitation from aqueous DMSO (e.g., 10% water) allows for processing distinctly larger amounts of hemicelluloses compared to pure DMSO without the necessity of increasing the precipitation pressure. The formation of an additional inert aqueous phase increases the mass transfer resistance, which results in the formation of larger, stable agglomerates. Curiepoint pyrolysis GC/MS, gel permeation chromatography (GPC) and analysis of the monosaccharide composition of both the parent hemicellulosic material and the corresponding precipitates demonstrated that hemicelluloses can be purified from residual lignin by supercritical anti-solvent precipitation with carbon dioxide without altering the structure of the biopolymers.