Preparation And Characterization Of Sulfonated Crosslinked Chitosan-SiO₂ Composite Solid Acid Catalysis

Resin-based solid acid catalyst is a kind of the solid acid catalysts are widely used, have many advantages of low activation temperature, high selectivity, especially for low-temperature catalytic reaction below 150 ℃ compared to others. C urrently, commercial resin-based solid acid catalysts have shortcomings of expensive, difficult to degrade. Chitosan have many advantages of cheap, extensive sources, environmental friendly, and its derivatives of sulfonated crosslinked chitosan solid acid catalyst exhibit excellent catalytic activity, with good prospects, but the acid contents and thermal stability of catalyst is still needs further improvement in order to expand its applications. In this paper, preparation of sulfona ted crosslinked chitosan-Si O2 composite solid acid catalyst, so as to achieve synergy of two solid acids to improve the catalytic activity and thermal stability of sulfonated crosslinked chitosan solid acid catalyst.Firstly, preparation of nanosilica as ethyl silicate raw material by sol-gel method, secondly, preparation of amino functional nanosilica by 3-aminopropyl triethoxysilane as modifier, thirdly, preparation of two kinds of sulfonated crosslinked chitosan-Si O2 composite solid acid as chitosan and prepared nanoparticles raw material, finally, the catalytic properties, chemical stability, mechanical strength and other physical and chemical properties of them were characterized, and sulfonated crosslinked chitosan resin-based solid acid catalyst for comparison.FT-IR spectroscopy confirmed that Si-OH stretching vibration peak of the amino functional nanosilica is weaker than nanosilica, and amino functional nanosilica have weak-CH2- and N-H vibration peak, indicating that the successful introduction of aminopropyl(-(CH2)3NH2) on the surface of nanosilica. Two kinds of composite solid acid have Si-O-Si and Si-O vibration peak, respectively, indicating that they contain nanosilica, and have S=O and C-O-S stretching vibration, respectively, indicating they are reaction with sulfuric acid successfully.Sulfur contents and acid contents of sulfonated crosslinked chitosan-Si O2 are higher than sulfonated crosslinked chitosan-Si O2-NH2, and either of them is higher than sulfonated crosslinked chitosan. Adding nanosilica particles in solid acid increase the degree of swelling in distilled water and dilute hydrochloric acid, and amino functional nanosilica particles reduce the degree of swelling in dilute hydrochloric acid, dilute sodium hydroxide and distilled wate r. Quality and sulfur retention rate of sulfonated crosslinked chitosan-Si O2 are higher than sulfonated crosslinked chitosan-Si O2-NH2, and either of them is higher than sulfonated crosslinked chitosan. Comparison of sulfur retention rate per unit mass, sulfonated crosslinked chitosan-Si O2 is higher than sulfonated crosslinked chitosan, but sulfonated crosslinked chitosan-Si O2-NH2 and sulfonated crosslinked chitosan almost the same. Maximum thermal decomposition temperature of two kinds of sulfonated crosslinked chitosan-Si O2 are higher than sulfonated crosslinked chitosan, so adding nanosilica can improve the thermal stability of solid acid, and no better thermal stability by amino modification of composite solid acid.The solid acid prepared for catalytic esterification of citric acid and n-butanol synthesis of tributyl citrate, results showed that the composite solid acid catalyst exhibits higher catalytic activity than sulfonated crosslinked chitosan catalyst. When first used, the esterification rate of sulfonated crosslinked chitosan-Si O2 and sulfonated crosslinked chitosan-Si O2-NH2 can reach 95% and 96%, respectively, and high 2.2% and 3.2% compared with sulfonated crosslinked chitosan. After reused seven times, the esterification rate of sulfonated crosslinked chitosan-Si O2 and sulfonated crosslinked chitosan-Si O2-NH2 can be maintained 93.8% and 94.5%, respectively, and high 2.6% and 3.4% compared with sulfonated crosslinked chitosan.