Carbonaceous adsorbent from waste oil fly ash: surface treatments and hydrogen sulfide adsorption potential

The aim of this research was to prepare carbonaceous adsorbent from waste oil fly ash (OFA) as an alternative to commercial activated carbon for desulfurization of model natural gas at atmospheric temperature. OFA was treated with a mixture of acids (HNO3 & H3PO4) followed by its surface treatment with CO2 and different hydroxide (i.e., NH4OH, NaOH & KOH) solutions to enhance surface characteristics of material for H2S adsorption application. Surface area, spectroscopic, microscopic and thermogravimetric analyses were used for the diagnosis of carbonaceous adsorbent. Scanning electron microscopy confirms the textural alteration on the adsorbent surface after hydroxide treatment. The uptake capacity of carbonaceous adsorbent was greatly influenced by porosity and surface functional groups changing. Characterizations showed the highly porous texture and thermally stable adsorbent. Fixed bed adsorption tests for hydrogen sulfide removal from natural gas revealed that the adsorbent modified with KOH gave highest adsorption capacity, i.e., 4.5 mg/g while the adsorbent without any surface treatment showed only 0.06 mg/g capacity. Three well-known kinetic models namely Yoon–Nelson, Thomas and Zhang & Cheng model were fitted to experimental breakthrough data. Zhang & Cheng model was in appropriate agreement with experimental packed bed data for all samples. Isotherm modeling reveals that Freundlich isotherm model best describes the adsorption data. The obtained results and their analysis showed that the adsorbent with high desulfurization capability could be prepared from waste oil fly ash.