Biogas is a vital renewable energy source that could play an effective role in fulfilling the world’s energy demand, not only in heat and power generation but also as a vehicle fuel in the future. Unfortunately, due to impurities, biogas requires a series of upgrading steps, which affects its economics and sustainability. Hydrogen sulfide (H₂S) is one of the impurities that economically and environmentally hinder the biogas utilization as a source of energy. H₂S removal from biogas using different technologies was extensively studied and established. One of such technology is adsorption. Adsorption by solid sorbents is considered as a suitable removal technique for toxic gases such as H₂S because of its simplicity, easy handling, and environmental friendly sorbents. In this review, the utilization of waste material-based sorbent for H₂S removal was appraised. Other gaseous components of biogas such as siloxanes, CO₂, etc., are out of the scope of this work. The potential and effectiveness of the waste-derived sorbents, either raw waste or modified waste, were summarized in terms of its characteristics, suitability, and sustainability. The review provides an insightful analysis of different types of wastes such as sewage sludge, food waste, forestry waste, fly ash, and industrial wastes as an alternative to commercial adsorbents to adsorb H₂S gas. Based on the analysis, it was concluded that if these sorbents are to be successfully commercialized, its economic analysis, regeneration conditions, and potential utilization of the spent sorbents has to be further exploited. Nevertheless, there is a great prospectus in the future for these waste materials to be utilized as sorbents for H₂S removal.

Chicken eggshell (ES) is a waste from the food industry with a high calcium content produced in substantial quantity with very limited recycling. In this study, eco-friendly sorbents from raw ES and calcined ES were tested for sulfur dioxide (SO₂) and hydrogen sulfide (H₂S) removal. The raw ES was tested for SO₂ and H₂S adsorption at different particle size, with and without the ES membrane layer. Raw ES was then subjected to calcination at different temperatures (800 °C to 1100 °C) to produce calcium oxide. The effect of relative humidity and reaction temperature of the gases was also tested for raw and calcined ES. Characterization of the raw, calcinated and spent sorbents confirmed that calcined eggshell CES (900 °C) showed the best adsorption capacity for both SO₂ (3.53 mg/g) and H₂S (2.62 mg/g) gas. Moreover, in the presence of 40% of relative humidity in the inlet gas, the adsorption capacity of SO₂ and H₂S gases improved greatly to about 11.68 mg/g and 7.96 mg/g respectively. Characterization of the raw and spent sorbents confirmed that chemisorption plays an important role in the adsorption process for both pollutants. The results indicated that CES can be used as an alternative sorbent for SO₂ and H₂S removal.

In recent decades, economic growth and the growing demand for limited resources have prompted a global search for more environmentally friendly and sustainable raw materials for the production of chemicals, materials, and fuels. Compared with traditional fossil fuel feedstocks, whose upgrading features high temperature, high pressure and sever greenhouse gas footprint, the upgrading of biomass-derived platform molecules with various functional groups are achievable at room temperature and ambient pressure with the emerging electrocatalytic hydrogenation (ECH) technology. The selectivity and conversion rate of ECH can be manipulated by adjusting and optimizing the electrode material and the composition of the electrolyte. This review summarizes the progress made in the ECH of various biomass platform molecules with different functional groups (such as 5-hydroxymethylfurfural, furfural, and levulinic acid) into chemicals and fuels across different electrocatalytic systems. It introduces the two mechanisms of ECH reaction and systematically reviews those on both noble metal electrocatalysts (Pt, Pd, Ag, Ru, etc.) and non-noble metal electrocatalysts (Cu, Pb, Sn, etc.). Finally, the current challenges and unresolved issues for the ECH of biomass-derived platform molecules are presented. This review will provide useful insights and guideline for the rational design of high-performance electrocatalysts for selective ECH of biomass platform molecules.