Production of adsorbents derived from nut shells for H2S removal

Abstract

The goal of this study is to investigate the removal of H2S from biogas, a sustainable gas made from the anaerobic digestion of organic waste, using adsorbents deriving from organic waste materials as precursors. The elimination of H2S is a critical step in biogas cleaning since this component can cause premature equipment deterioration, sulphur emissions as SO2 upon combustion and requires a significant cost. Due to the high cost of activated carbon, the key goal is to identify low-cost novel adsorbents for desulphurization. To this aim, different kind of nut shells were individuated among the wastes of the food industry, and walnuts and almond shells were selected for their large availability and specific properties as precursors of adsorbent materials. These two precursors were chosen because of the great production amounts available in both Italy and Spain; due to the high production, a substantial quantity of shells suitable for use as adsorbents may be obtained. In this study, both almonds and walnuts are produced in Spain, in particular originating in the municipality of El Arenal (Avila), located in the autonomous community of Castile and Leon. The experimental study was carried out in the Department of Chemical and Environmental Engineering at the University of Seville (US). To produce adsorbents, initially a jaw mill and a blade mill were used to grind the shells; then, an electromagnetic sieve was utilized to get the desired grain size; and finally, a tubular furnace was used for the activation steps, leading to the production of the final adsorbents. A fixed bed column was employed for the adsorption experimental campaigns, having a height of 430 mm and a diameter of 30 mm. Experimental tests were carried out at room temperature and atmospheric pressure, aiming at testing the H2S adsorption capacity of the produced adsorbents, while selecting the best performance for desulphurization of a model biogas.