From Water Rejection to Oil Affinity: Comparative Adsorption of Petroleum Liquids, Water, and Xylene on Modified Sawdust

Abstract

This study evaluated hardwood sawdust (USDM) chemically modified with 0.5 M succinic acid (0.5MSD) as a low-cost sorbent for the selective removal of organic liquids from water. The specific gravities of the tested adsorbates decreased in the order water > lube oil > m-xylene > diesel > kerosene > gasoline. Batch adsorption and Foster swelling tests were carried out on the adsorbents with the adsorbates. On UMSD, equilibrium capacities (mg g⁻¹) followed DPK ≈ PMS (0.23 and 0.227) > xylene (0.15) > water (0.14) > AGO ≈ lube oil (0.09 and 0.089). Modification of sawdust with succinic acid enhanced hydrocarbon uptake while preventing water sorption: the adsorbates DPK, PMS, xylene, AGO, lube oil, and water were identified to be adsorbed to the treated adsorbents with batch adsorption values of 0.32, 0.29, 0.28, 0.27, 0.26, and −0.07 mg g⁻¹, respectively. The kinetic test with xylene adsorption showed that the 0.1–0.5 M prepared concentration exhibited rapid initial uptake reaching equilibrium in ~40–50 min; percentage removal decreased from ~88–89% at 0.1–0.2 M to ~79–81% at 0.5 M due to site saturation. The selectivity shift observed for the swelling test showed that UMSD swelled most in water, whereas 0.5MSD exhibited increased swelling in hydrocarbons, especially under agitation. The treated biomass was improved by the successful replacement of surface hydroxyl groups via an esterification reaction. The reaction induces carbonyl and ester functionalities, which reduce hydrophilicity and promote organophilic wetting; mild microstructural changes aid film and capillary uptake of viscous oils.