Catalytic Degradation of Chitosan by Supported Heteropoly Acids in Heterogeneous Systems

Yimin Song,Xuecheng Zhang,Zhipeng Ma,Ru Zhang,Hang Zhang,Yunpeng Min,Huiru Wang

doi:10.3390/catal10091078

Abstract

Several kinds of composite materials with phosphotungstic acid (PTA) as the catalyst were prepared with activated carbon as support, and their structures were characterized. According to the Box–Behnken central combination principle, the mathematical model of the heterogeneous system is established. Based on the single-factor experiments, the reaction temperature, the reaction time, the amount of hydrogen peroxide and the loading capacity of PTA were selected as the influencing factors to study the catalyzed oxidation of hydrogen peroxide and degradation of high molecular weight chitosan. The results of IR showed that the catalyst had a Keggin structure. The results of the mercury intrusion test showed that the pore structure of the supported PTA catalyst did not change significantly, and with the increase of PTA loading, the porosity and pore volume decreased regularly, which indicated that PTA molecules had been absorbed and filled into the pore of activated carbon. The results of Response Surface Design (RSD) showed that the optimum reaction conditions of supported PTA catalysts for oxidative degradation of high molecular weight chitosan by hydrogen peroxide were as follows: reaction temperature was 70 ℃, reaction time was 3.0 h, the ratio of hydrogen peroxide to chitosan was 2.4 and the catalyst loading was 30%. Under these conditions, the yield and molecular weight of water-soluble chitosan were 62.8% and 1290 Da, respectively. The supported PTA catalyst maintained high catalytic activity after three reuses, which indicated that the supported PTA catalyst had excellent catalytic activity and stable performance compared with the PTA catalyst.

Highlights

Chitosan is the deacetylated product of chitin, which is abundant in nature
The results show that chitosan molecules are easy to carry out in a homogeneous system, the degradation reaction is uniform, the chitosan fragments with uniform molecular weight can be obtained effectively and the production cost is low
Compared to unsupported phosphotungstic acid (PTA) under different catalyst dosage conditions, the low molecular weight chitosan (LWCS) obtained by the supported PTA catalyst had a higher yield and lower average molecular weight, which indicated that supported PTA could significantly improve the degradation efficiency of chitosan (Figure 1A,B)

Summary

Introduction

Chitosan is the deacetylated product of chitin, which is abundant in nature It is widely distributed in the crusts of marine arthropods, such as shrimps and crabs, fungi, insects, algae cell membranes and cell walls of higher plants. High molecular weight chitosan has a strong hydrogen bond and a tight crystal structure. It is insoluble in ordinary solvents and can only be dissolved in some acidic media. Low molecular weight chitosan has high solubility and is easy to absorb in vivo. It has anti-bacterial and anti-tumor functions and Catalysts 2020, 10, 1078; doi:10.3390/catal10091078 www.mdpi.com/journal/catalysts

Methods

Results

Conclusion