Upgrading/Deacidification of Biofuels (Gasoline, Kerosene, and Diesel-like Hydrocarbons) by Adsorption Using Activated Red Mud-Based Adsorbents

This study explored the adsorption of carboxylic acids, especially free fatty acids (FFA), present in biofuel (distilled fractions of bio-oil such as gasoline-like hydrocarbons, kerosene-like hydro-carbons and diesel-like hydrocarbons) using red mud-based adsorbents. The red mud was ther-mally activated (at 40 °C and 600 °C) and chemically activated with HCl (0.25M, 1M, and 2M). Analytical techniques were used to characterize the adsorbents' properties. At the same time, the study examined factors like feed type, adsorbents, FFA content, adsorbent percentage, activation temperature, acid solution concentration and contact time to assess adsorption efficiency. The characterization results indicated that chemical activation with 0.25M HCl significantly in-creased the surface area to 84.3290 m²/g, surpassing thermally activated samples (35.2450 m²/g at 400 °C). Adsorption experiments demonstrated that all chemically activated samples, with 5% adsorbent, adsorbed over 2000 mg FFA per gram of adsorbent, with CARM – 1M HCl achieving 100% removal of acids from gasoline-like hydrocarbons. Kinetic modeling showed that the pseudo-second-order model best represented the adsorption data, as evidenced by high R² values and close agreement between experimental and calculated qe values. Therefore, adsorption with chemically activated red mud efficiently deacidifies biofuels, providing a cost-effective and promising approach for their upgrading.