Novel application for palygorskite clay mineral: a kinetic and thermodynamic assessment of diesel fuel desulfurization

Abstract

Palygorskite (Pal) is a low-cost clay mineral material and was investigated in this study as a novel material for adsorptive desulfurization of petroleum refining fractions from the Clara Camarao Potiguar Refinery (RPCC) in Brazil. This clay mineral was characterized by X-ray fluorescence, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetry, zeta potential ($$\zeta$$) and N2 adsorption/desorption isotherm analyses. Palygorskite textural properties (specific surface area 156 m2 g−1, total pore volume 0.36 cm3 g−1) and specific surface chemistry activity with several metals were crucial to efficient adsorption, proposing that an interaction between adsorbate/adsorbent involves π-complexation mainly with Fe species. This material was used in raw and thermally activated forms to evaluate the adsorption capacity. Several kinetic and equilibrium models were used to assess the experimental data. The results showed high correlation to the pseudo-second order kinetic model for both adsorbents (R2 > 0.99), suggesting a chemisorption process as the determining step. Isotherm data were used to evaluate the equilibrium experimental data. Maximum adsorption capacity calculated from the Langmuir isotherm (R2 > 0.97) was 6.25 mg g−1 for raw-Pal at 318 K. The adsorption thermodynamic assessment of S-compounds indicated an endothermic process, and there was consequently an increase in spontaneity at higher temperatures. The adsorbent raw-Pal displayed good potential in the adsorption of sulfur compounds in real diesel fuel. Palygorskite stands out for being an abundant clay mineral in nature, environmentally safe, and with high possibility of its applications in adsorption and catalysis processes.