Sulfur Removal from Heavy Crude Oils Based on the Adsorption Process Using CuO- and AgO-Modified SiO₂-Based Nanomaterials: Experimental and Theoretical Study

This work presents the development and validation of a highly sulfur-selective nanomaterial based on silica doped with active metal phases for the desulfurization of heavy crude oils. Initially, various transition element oxide nanoparticles (Fe₃O₄, NiO, ZnO, MoO₃, CuO, and AgO) were synthesized and screened for sulfur adsorption in batch mode. AgO and CuO exhibited the highest removal efficiencies─24% and 21%, respectively─at an adsorbent-to-crude oil ratio of 2:40 (g/g). These were then used to modify silica supports through incipient wetness impregnation to obtain seven materials: SiCu2, SiAg2, SiCu4, SiAg4, SiAg2Cu2, SiAg1.32Cu1.32, and SiAg1.5Cu1.4. Among them, SiAg1.5Cu1.4 showed the best performance, achieving an adsorption capacity of ∼390 mg of S·g^-1, significantly outperforming the undoped SiO₂ (∼80 mg of S·g^-1). Adsorption isotherms were constructed at 25, 35, and 55 °C and fitted using both the Freundlich and Solid-Liquid Equilibrium (SLE) models. The isotherms indicated multilayer adsorption with a type III behavior (IUPAC classification), and thermodynamic analysis confirmed the process was spontaneous and exothermic at all tested temperatures. Dynamic adsorption tests using a fixed-bed column demonstrated high performance for SiAg1.5Cu1.4, with a breakthrough time of ∼350 min and complete saturation reached at 425 min. Numerical simulation of the breakthrough curve using Aspen Adsorption showed strong agreement with experimental data (maximum relative error = 5.0%). The model was further applied to evaluate scale-up scenarios by varying flow rates and bed dimensions, achieving projected treatment capacities of up to 3280 barrels in 57 h for a bed 5 m tall and 1.25 m in diameter. These results establish a scalable framework for sulfur removal from heavy crude oils using engineered bimetallic nanoadsorbents.