Ni2+-ion-exchanged dealuminated clinoptilolite: A superior adsorbent for deep desulfurization

A superior adsorbent for the deep desulfurization of liquid fuels has been developed. Clinoptilolite zeolite exhibits a very favorable adsorption isotherm for thiophene, benzothiophene, dibenzothiophene and isopropyl mercaptan (iso-octane as solvent) upon dealumination with oxalic acid and further ion-exchange with Ni2+. This is while the raw zeolite and the Ni2+-ion-exchanged raw zeolite adsorb benzothiophene and dibenzothiophene molecules scarcely. The effect of oxalic acid molarity and time of reaction on the chemical composition, crystallinity and adsorption capacity of benzothiophene and dibenzothiophene has been investigated in the first step (screening tests). The treated samples have been characterized by X-ray diffraction, X-ray fluorescence, Fourier transform Infra-red, N-2 adsorption, transmission electron microscopy and thermal gravimetry analysis. The sample exhibiting optimal adsorption characteristics was used for obtaining the adsorption isotherms for the 4 type of sulfur compounds at 20 degrees C. The optimum sample shows an adsorption saturation capacity of 2.7 mg S g(-1) for large molecules like dibenzothiophene (molecular diameter > 8 angstrom), i.e. ca. 2 times that of the not-dealuminated Ni2+-ion-exchanged or raw zeolite. The enhancement achieved for the adsorptive characteristics has been discussed. The optimum sample shows an exceptional regenerability for benzothiophene and dibenzothiophene. (C) 2016 Elsevier Ltd. All rights reserved.