Siloxane removal for biogas purification by low cost mineral adsorbent

Abstract

The potential use of raw and expanded perlite as low-cost adsorbents for biogas purification has been investigated. The thermal expansion of perlite causes a reduction in the density of silanol groups from 2515.43 to 653.75 OH/nm2; in contrast, the specific surface area of perlite increased two-fold due to the thermal expansion. To determine the equilibrium adsorption capacity and the adsorption kinetics batch experiments were conducted. The adsorption capacities are in the following order: activated carbon (6.8 mg/g) > silica gel (6.6 mg/g) > expanded perlite (5.8 mg/g) > raw perlite (5.6 mg/g) when compared at the same experimental conditions. The equilibrium adsorption data showed that perlite can be used to reduce the octamethylcyclotetrasiloxane concentration below 28 mg/m3, as recommended by leading manufacturers. The adsorption kinetics of octamethylcyclotetrasiloxane onto raw and expanded perlite followed the Linear-Driving Force model suggesting that the mass transfer is the rate-controlling step. In addition to its low cost, expanded perlite has the advantage of requiring lower desorption temperature (200 °C) for regeneration in comparison to the reported values for activated carbon (>400 °C) and fast desorption kinetics (20 min), which could contribute to a cleaner production of biogas.