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 obtained
from anaerobic digestion of cow dung and market wastes. The gas was stored in tubes or urine bag
before upgrading. Natural zeolite rocks, maize cobs, steel wire, desulphurizer, and worn-out tyres
were used as the upgrade materials. The composition of biogas was recorded before and after
upgrading using a GP180 portable biogas analyzer from Henan, China. The measured level of raw
biogas was 0.0227% H₂S, >20% CO₂ and 52-56% CH₄. The most efficient upgrade materials were
zeolite rocks with upgrade levels of 89–93% methane. The total removal using zeolite was
observed to be 75% CO₂ and 95.34% H2S. The morphological structures of zeolitic rocks account
for its higher upgrading properties compared to other materials. In addition, the porosity in these
rocks 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 and
CO₂.

Keywords: Biogas, Upgrading, Natural zeolite, Bio-methane