Preparation and analysis of straw activated carbon synergetic catalyzed by ZnCl2-H3PO4 through hydrothermal carbonization combined with ultrasonic assisted immersion pyrolysis.

In this paper, wheat straw (WS), corn straw (CS) and sorghum straw (SS) were used as raw materials. ZnCl2 and H3PO4 were used as catalysts. Hydrothermal carbonization combined with pyrolysis were used to co-activate with the ultrasonic auxiliary impregnation method in order to prepare straw activated carbon (SAC). Methylene blue adsorption value and iodine value were used as the main evaluation index to optimize the process conditions. The activation process was analyzed and the optimum preparation conditions were obtained. The results showed that it was feasible to combine hydrothermal carbonization with ultrasonic assisted immersion pyrolysis using ZnCl2 and H3PO4 as catalysts for preparing SAC. WS, CS and SS showed similar characteristics in the preparation of SAC. The best preparation conditions of hydrothermal temperature and the impregnation ratio of ZnCl2 were 200 °C and 2:1. The optimum pyrolysis condition was at a heating rate of 5 °C/min and an impregnation ratio of H3PO4 equal to 2:1 with 1 h of pyrolysis at 500 °C. The temperature and time of ultrasonic auxiliary conditions were 40 °C and 30 min. For WSHUPC, CSHUPC and SSHUPC, the MB adsorption values were 165, 166 and 164 mg/g and the iodine values reached 764, 725 and 701 mg/g. It was demonstrated the three kinds of straws were highly efficient precursor for the preparation of activated carbon used to remove dyes from wastewater. The preparation method in this study combines the advantages of physical and chemical activation.