Upgrading biogas using Eburru zeolitic rocks and other adsorbent materials to remove carbon dioxide and hydrogen sulphide

Abstract

The trace amounts of carbon dioxide and hydrogen sulfide in raw biogas lower its calorific value,cause corrosion and make it hard to compress biogas into the cylinder. Raw biogas was obtainedfrom anaerobic digestion of cow dung and market wastes. The gas was stored in tubes or urine bagbefore upgrading. Natural zeolite rocks, maize cobs, steel wire, desulphurizer, and worn-out tyreswere used as the upgrade materials. The composition of biogas was recorded before and afterupgrading using a GP180 portable biogas analyzer from Henan, China. The measured level of rawbiogas was 0.0227% H2S, >20% CO2 and 52-56% CH4. The most efficient upgrade materials werezeolite rocks with upgrade levels of 89–93% methane. The total removal using zeolite wasobserved to be 75% CO2 and 95.34% H2S. The morphological structures of zeolitic rocks accountfor its higher upgrading properties compared to other materials. In addition, the porosity in theserocks mean that CO2 and H2S were adsorbed resulting in high CH4 levels in the upgraded biogas.Other adsorbents showed upgrading properties with removal rates above 70% for both H2S andCO2. Keywords: Biogas, Upgrading, Natural zeolite, Bio-methane