Development of a monolithic carbon xerogel-metal composite for crude oil removal from oil in-saltwater emulsions: Evaluation of reuse cycles

This study aims to evaluate the reuse capacity of carbon xerogels-Ce/Ni composite (XCeNi) during crude oil adsorption from O/W emulsions and subsequent regeneration through the oxidation process using air as an oxidant agent for six cycles. For the six cycles of evaluation, batch adsorption experiments were done at different temperatures and modeled using the solid-equilibrium model (SLE). In contrast, catalytic tests were performed under non-isothermal and isothermal heating. To estimate the change in the sample's surface composition, X-ray photoelectron spectroscopy (XPS) analysis was carried out during each regeneration cycle. According to batch adsorption experiments and SLE fitting, the XCeNi sample presents a high affinity for hydrocarbons and a similar maximum adsorption capacity during six regeneration cycles. Crude oil was also successfully decomposed under non-isothermal heating (100-800 degrees C), reducing the main decomposition peak from 250 to 150 degrees C for all the evaluated cycles. Under isothermal heating at 150, 200, and 250 degrees C, conversions of 100% were obtained for all cycles evaluated. At the first cycle the time required to decompose 100% of adsorbed crude oil at 60 min, whereas, after the 6 cycle, it is achieved at 120 min. The gaseous analysis of the products involved in the oxidation of the crude oil in each cycle was considered, finding an increase in the production of light hydrocarbons and reducing gas emissions such as CO2, NOX, and SOX during all reuses. The activation energy increases from 10.1 to 18.7 kJ mol(-1) during the six cycles due to the reduction of the content of Ce3+. The Ce3+ concentration is reduced to 0 after each adsorption cycle. Apparently, the ability of the xerogel to decompose the adsorbed crude during all cycles may be associated with the increase in Ce3+ during the adsorption process, and then during the oxidation treatment is transformed to Ce(OH)(2)(2+). Also, the influence of Ni2+ on XCeNi is noted. Through the regeneration, the Ni2+/Ni3+ ratio varies, which shows the continuous redox processes that have taken place in this sample.