Efficient removal of nickel and vanadium porphyrins drom petroleum oil using chitosan-modified zeolite X composite derived from coal fly ash

Abstract

The increasing worldwide demand for oil as a primary energy source has led to a rapid decline in light crude reserves, prompting the investigation of heavy crude as a viable alternative. One of the critical challenges facing the heavy crude oil industry is the high metal content, especially nickel and vanadium, which exist in the form of porphyrin complexes. The presence of nickel and vanadium porphyrins causes equipment corrosion and the poisoning of catalysts, in addition to environmental damage. Therefore, there is an urgent need to remove these detrimental elements and prevent their buildup in feedstocks. The synergistic combination of the unique characteristics of zeolite and chitosan presents promising opportunities for diverse applications, particularly in crude oil demetallization operations. The main objective of this study is to remove nickel and vanadium porphyrins from crude oil using a composite of chitosan (CHS) modified with zeolite-X (ZX) derived from Malaysian coal fly ash (CFA) as a new demetallization agent. The synthesis of ZX began with the pretreatment of CFA. This process included separating the magnetic fraction and acid washing to remove impurities. Next, the treated CFA was transformed into ZX through an alkaline fusion-hydrothermal method under different synthesis conditions. The synthesized ZX was characterized using a vibrating sample magnetometer (VSM), X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), N2 adsorption-desorption isotherm, infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). Under optimal conditions, ZX derived from treated CFA efficiently eliminated Ni2+ and V5+ ions from aqueous solutions, achieving maximum adsorption capacities of 41.55 mg/g for Ni2+ and 32.38 mg/g for V5+, respectively. However, the prepared zeolite exhibited a low affinity for metal porphyrins in the organic medium. The CHS/ZX composite was fabricated by immersing as-synthesized zeolite particles into the chitosan-gelling solution, and the matrix formulation was optimized via response surface methodology (RSM). The model's reliability in predicting the removal of metal porphyrins using the values of the established variables was excitedly validated with a reasonable accuracy error of 0.5%. The systematic characterization shows that synthesizing the CHS/ZX composite successfully combines the mesoporous structure with the functional groups of both ZX and CHS. The adsorption and desorption mechanisms of metal porphyrins by the CHS/ZX composite were investigated using a model solution containing vanadyl and nickel tetraphenyl porphyrin (VO-TPP and Ni-TPP) in toluene. The efficacy of CHS/ZX compounds in removing metal porphyrins doubled compared to the removal rates achieved by the parent components individually. The impact of qualitative and quantitative variables on the recovery of metal porphyrins from saturated CHS/ZX composites was explored and studied. Under optimized conditions, 27.07 mg/g of the VO-TPP and 28.02 mg/g of the Ni-TPP adsorbed by the CHS/ZX composite were successfully recovered. The results indicate that CHS/ZX effectively removed 3.00 mg/g nickel and 7.68 mg/g vanadium from heavy Basrah crude oil, and 0.83 mg/g nickel and 5.54 mg/g vanadium from medium Basrah crude oil under optimal conditions. Overall, CHS/ZX composites show promising potential to be developed for crude oil demetallization, leading to improved refining processes in the petrochemical industry.