Experimental and simulation study of peanut shell-derived activated carbon and syngas production via integrated pyrolysis-gasification technique

Abstract

Carbonaceous materials are among the most appropriate and widely used materials in the field of energy production, conversion, and storage. According to recent studies, biochar-based catalytic supports and adsorbents have shown great potential in the fields of energy production and the adsorption and storage of various gases due to their adjustable surface chemistry and porosity. In the present study, the pyrolysis of peanut shell to produce activated carbon as a precursor for catalyst support was investigated. Acid washing pretreatment was performed on raw biomass before pyrolysis to remove metals and impurities and reduce the ash content of the biomass. Before pyrolysis, thermogravimetric analysis was performed to determine the temperature range of biomass thermal decomposition. Pyrolysis was carried out at temperatures of 300, 400, and 500 °C to study the effect of pyrolysis temperature on biochar yield. KOH-activation on biochar was followed by subsequent pyrolysis at 650 °C to produce activated carbon. To study the effect of pyrolysis temperature and KOH activation on the structural and physiochemical characteristics of biochar, nitrogen adsorption/desorption and FTIR analyses were conducted. The pore size of the activated carbon surface changed from mesoporous to microporous with increasing the pyrolysis temperature and subsequent KOH activation, and the biochar specific surface area increased from 3.5 to 363.1 m2 g-1. In order to evaluate and optimize the operating conditions of the biochar and syngas production processes on larger scales, the integrated pyrolysis and gasification processes were simulated in Aspen Plus software. The effects of temperature, pressure, and air to biomass ratio on biochar production rate and H2/CO ratio were evaluated. A temperature of 650 °C, a pressure of 1 bar and an air to biomass ratio of 0.1 were selected as optimum operating conditions to simultaneously achieve maximum biochar production and maintain the quality of synthetic gas. The findings of the experimental and simulation sections of this study could provide a useful guide for the industrial-scale production of biochar and activated carbon as a catalytic support in various chemical production processes, as well as a water polutant adsorbent and gas adsorbent for various gas purification and storage processes.