Study On Hydrolysis Of Cellulose By Polyoxometalate

With the rapid consumption of non-renewable resources and the growing of energy crisis, the utilization of renewable resources, instead of non-renewable ones, is attracting more and more attention all over the world. In recent years, Cellulose, the most abundant source of biomass, has been investigated for potential applications, especially, as a promosing alternative to fossil resources for the sustainable production of chemicals. In this paper, the potential of polyoxometalates to catalyze the hydrolysis of cellulose under acidic conditions was explored. The experiment solved many drawbacks, such as environmental pollution, corrosion risk and so on. In addition, the paper has a certain theoretical significance and economic value for the research and development of new and efficient catalysts. The main results of this paper are as follows:1. A solid acid 12-tungstophosphoric acid was synthesized and applied for the hydrolysis of cellulose in aqueous phase. A study to optimize the reaction conditions, such as the amount of catalyst, reaction time, temperature, the amount of cellulose used, and reusability of the catalyst, was performed. The results showed that the optimal conditions were: 0.1g of cellulose, 5mL of distilled water, catalyst amount 0.08mmol, reaction temperatur 180℃, reaction time 2h, the highest conversion could reach 54.7%, while the total reducing sugars (TRS) and glucose yields reached a maximum of 54.0 and 50.5%, respectively. After the reaction, the catalyst H3PW12O40 was extracted by diethyl ether form the aqueous solution to reuse. All the results illustrated that H3PW12O40 is a high-efficiency, reusable, environmentally benign solid acid catalyst for the hydrolysis of cellulose.2. A series of insoluble heteropolytungstate salts, Cs_xH_3-xPW₁₂O₄₀ (x=0.5, 1.0,1.5, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 3), which was characterized by using infrared spectra, elemental analysis and X-ray powder diffraction, were prepared and applied for the hydrolysis of cellulose in aqueous phase. When using Cs_0.5H_2.5PW₁₂O₄₀ as the catalyst, a study to optimize the reaction conditions, such as the amount of catalyst, reaction time, temperature, and the amount of cellulose used, was performed. The results showed that the optimal conditions were: 0.1g of cellulose, 5mL of distilled water, catalyst amount 0.06mmol, reaction temperatur 160℃, reaction time 6h, the highest conversion could reach 60.2%, while TRS and glucose yields reached a maximum of 37.1 and 35.8%, respectively. In addition, in the optimal conditions, the effect of cesium content on the catalytic performance of cellulose hydrolysis by solid acid catalyst Cs_xH_3-xPW₁₂O₄₀ (x=0.5, 1.0, 1.5, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 3), was performed. The results showed that among the tested catalysts, Cs_0.5H_2.5PW₁₂O₄₀ with the strong protonic acid site, showed the best catalytic performance for cellulose hydrolysis. After the reaction, the Cs_xH_3-xPW₁₂O₄₀ catalyst could be collected by centrifuge. All the results illustrated that Cs_0.5H_2.5PW₁₂O₄₀ with strong acidity is an environmentally benign B-acid catalyst for the hydrolysis of cellulose.