Studies On Hydrolysis Of Chitosan In Supercritical And Near-Critical Water

Because supercritical and near-critical water have special solubility, high ion product, low surface tension and high diffusion coefficient, chitosan can be degraded into soluble chitooligosaccharide rapidly. So, supercritical and near-critical water degradation, a new degradation method for chitosan, is put forward first time here.In this thesis, functions and uses of chitosan and chitooligosaccharide were introduced first, methods for degrading chitosan that have already existed at present were summarized in succession. And then properties of supercritical fluid and supercritical water were expatiated, and the applications of supercritical water in the recycling of waste bio-resources were also summed up. Lastly, process conditions for the supercritical and near-critical hydrolyzing of chitosan in batch reactor were discussed in detail.Supercritical and near-critical hydrolyzing of chitosan was studied under following conditions: temperature 200~380℃, pressure 20~35MPa, reaction time l~15min, initial concentration of chitosan 10g/L and acetic acid concentration 0.125%. Products were analyzed by IR and TLC, and main products were monosackcharide and oligosaccharide with degree of polymerization under six.At the range of operation condition, the relationships between the yield of chitooligosaccharide and the operationparameters such as pressure, temperature and reaction time were investigated. The process conditions of discoloring using active carbon were also discussed, and the appropriated conditions were 0.5g active carbon/100ml solution. From quadrature analysis we can get the result that for the hydrolysis of chitosan in supercritical and near-critical water, pressure had the biggest contribution, reaction time and temperature were posterior, the optimal process conditions are operating pressure 35MPa, reaction temperature 250C , residence time 10min.Xu Liangfeng (Applied Chemistry) Directed by Professor Chen Kaixun...