Cellulose Hydrolysis And Catalytic Performance Of ZnCaFe Hydrotalcites In The Hydrolysis

Efficient utilization of cellulose is a significant method to solve problems like energy crisis and greenhouse effect, and high-selectivity hydrolysis of cellulose into glucose is the key technology. Extensive research about efficient hydrolysis of pretreated cellulose with hydrotalcite-like solid catalysts overcame shortcomings such as high cost of cellulose hydrolysis, difficult separation of catalyst from acid hydrolysis and hardly achievement of hydrolysis of cellulose by using supercritical water, etc. Therefore, this study has significant importance for industrialized production of cellulose hydrolysis.Pretreating cellulose is the main method to obtain high-selectivity cellulose hydrolysate. According to high efficiency of ball milling treatment and low energy consumption of ultrasonic treatment, this study firstly report the method of treating cellulose by combining these two treatments: pre-ball-milled for 12h, the cellulose samples then be repretreated under the ultrasonic for 60min, and the crystallinity degree of cellulose could be reduced by 20%, and the water retention value be increase by 96%, while the energy consumption could be reduced by 50%, and the conversion of cellulose and the yield of glucose in the hydrolysis could be enhance by 12% and 60% respectively. The treatment of cellulose under different times and methods was characterized by means of X-ray diffraction (XRD), electron microscopy (SEM), infrared spectroscopy (IR) and thermo gravimetric-differential thermal analyzer (TG-DTA). Changes of crystal structure, morphology, group and thermogravimetric analysis of cellulose samples were observed and reasons for high cellulose conversion and the yield of glucose in the hydrolysis were fully explained.The study synthesized a series of different metal ions in hydrotalcite-like catalyst by co-precipitation synthesis with urea as a precipitator and screened the Zn-Ca-Fe hydrotalcite like compounds (Zn-Ca-Fe LDH) with high efficiency and high selectivity under the reaction of cellulose hydrolysis. Under the reaction condition of temperature 155 oC, reaction time 20 h, stirring speed 200 r/min, H₂O 50 mL, cellulose dosage 2.0 g and Zn-Ca-Fe LDH catalyst dosage 1g, the catalyst can make the conversion ratio of cellulose and glucose yield reached 42.56% and 93.2% respectively. And the Zn-Ca-Fe LDH catalyst can be reused for 5 times under the above condition without obvious deactivation. The Zn-Ca-Fe LDH catalyst samples which used in different times were characterized by XRD, IR, Inductively coupled plasma atomic emission spectrometer (ICP-AES) and CO₂-TPD. Changes of sample's crystal structure, morphology, content of metal ions, and the high catalytic activity of catalyst and the cause of inactivation after recycling utilization were sufficiently analyzed.