A review on common adsorbents for acid gases removal: Focus on biochar

Abstract

Biochar, a product of pyrolysis of biomass, represents an attractive alternative to non-renewable or unsustainably sourced biomass as an adsorbent material for treating gaseous effluents. Biomass from residues associated with agricultural and forestry operation, otherwise considered waste material or a storage issues, represents a potential sustainable source of adsorbent. There are several adsorbents for removal of contaminants from gases including carbon based, silica based, and metal oxide based adsorbents; however, availability of feedstock, low cost, and potential high adsorption capacity distinguish biochar from other adsorbents. This review includes common sorbents for removal of contaminants from gas, biochar production methods, and compares biochar with activated carbon as one of the most common commercial adsorbents. Adsorption isotherms, mechanisms, and process systems for removal of acid gases such as CO2 and H2S by biochars have been comprehensively reviewed. The application of molecular modeling to describe adsorption by activated carbons and possible extension to biochar were studied. There is still a lack of published information in the molecular modeling of biochars, and using these models to understand the complex adsorbent mechanisms on the very heterogeneous surfaces of biochar (relative to commercial adsorbent materials such as activated carbons). Therefore, further research needs to fill these gaps to identify all potentials of this promising adsorbent.