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

• Ni form dealuminated clinoptilolite has been used for deep desulfurization.
• Different dealumination extents using different oxalic acid molarities are studied.
• An optimum dealumination procedure has been developed.
• The optimum sample shows an adsorption capacity of 10.1 mg S g−1 for iso-propyl mercaptan.
• The optimum sample shows an exceptional regenerability in cyclic operation.

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 iso-propyl 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, N2 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 °C. The optimum sample shows an adsorption saturation capacity of 2.7 mg S g−1 for large molecules like dibenzothiophene (molecular diameter > 8 Å), 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.

Screening experiments for the assessment of percent sulfur removal for an initial liquid solution containing a constant amount of sulfur compound (77 mg S L−1 for BT and 74 mg S L−1 for DBT) as a function of Si/Al molar ratio. The error in the measurement of the sulfur removal is maximum ±1 (%).Figure optionsDownload as PowerPoint slide