The Research On Degradation Of Cellulose With Catalytic Method

Mn/ZSM-5 which has relatively catalytic activity was prepared with the metal support by incipient impregnation method. Mn/ZSM-5 participated in the degradation of cellulose under the solution and the phosphoric acid media were investigated in this paper. The average degree of polymerization of cellulose (DP) was determined using method of pulp viscosity determination in cupri-ethylenediamine (CED) solution as described in ISO standard (ISO5351-1:1991). The characteristic comparison of functional groups of cellulose before and after degradation was conducted by FT-IR spectra with KBr pressed pellet method. Then X-ray diffraction measurements of Mn/ZSM-5 catalyst and cellulose were performed on X-ray diffractometer. Morphologies of the catalyst and cellulose have been studied using SEM. The filtrate was purified by column chromatography (eluent: petroleum ether/ ethyl acetate=3/1, stationary phase: silica gel GF254) to give the pure products from the cellulose degradation, which were characterized with NMR spectra and quantitatively measured by HPLC. In the experiments, the effects of phosphoric acid concentration, reaction time, reaction temperature, H₂O₂ and catalyst dosages on degradation of cellulose were investigated.Mn/ZSM-5 which had catalytic activity was prepared by optimal condition: weight ratio of manganese chloride: ZSM-5 zeolite =0.2:1, calcinations temperature 650°C, calcinations time 6h.The optimal conditions on Mn/ZSM-5 participated in degaradation of cellulose in the solution are as follows: pH value is 3, reaction time and temperature are 6h and 60℃respectively, H2O2 and catalyst Mn/ZSM-5 dosage are 2mL and 0.4g. After the degradation, the DP and crystalline of cellulose were decreased sharply. Significant changes on the surface were obvious as the surface cover on cotton linters was removed, and many terraces, steps, and kinks form after degradation. Some soluble sugar was obtained.This paper also studied the heterogeneous catalyst Mn/ZSM-5 participated Fenton-like reaction in degradation of cellulose under the phosphoric acid medium. Cellulose can be degraded to small molecular chemicals such as 5-HMF, LA and others. The effects of reaction factors on the molar yield of 5-HMF is discussed. The cellulose degradation process can be divided into three steps: 1). breakage of inter and intra molecular hydrogen bond resulting in the destruction of aggregation state of the cellulose; 2). activation effect of Fenton-like regent for catalytic cleavage ofβ-1-4-glucosidic bonds in cellulose generating soluble sugars and partly degraded cellulose with much lower DP which lead to a sharp drop in DP; 3). dehydrations of glucose going along with formation of low molecular weight species such as 5-HMF and LA which are separated and characterized in this paper.