Vanadium (IV) benzenedicarboxylate: A novel adsorbent for selective separations
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Vanadium (IV) benzenedicarboxylate: A novel adsorbent for selective separations Lumei Liu, Xiqu Wang, and A.J. Jacobsona) Department of Chemistry, University of Houston, Houston, Texas 77204-5003 (Received 3 November 2008; accepted 18 February 2009)
The crystal structure of VOBDC (BDC = 1,4-benzenedicarboxylate) has a 1-dimensional ˚ , and shows remarkable flexibility upon channel system with apertures of 8 A adsorption/desorption of various guest molecules in the channels. VOBDC can selectively and rapidly adsorb organic molecules containing sulfur on exposure to a 5% CH4/He stream with different contents of thiophene or dimethyl sulfide at ambient temperature. Selective uptake of thiophene from liquid octane with thiophene concentrations from 2000 ppmw down to 100 ppmw is also observed. X-ray crystallographic data show that the adsorbed thiophene molecules adopt a herringbone packing arrangement within the channels of VOBDC while adsorbed dimethyl sulfide molecules are disordered among several positions in the channels with the sulfur atoms pointing toward the channel walls. The observed adsorptive capacities for thiophene and dimethyl sulfide are 155 mg and 208 mg sulfur per gram of VOBDC, respectively, consistent with the crystal structure data. I. INTRODUCTION
Natural gas and coal-derived gas contain sulfurbearing odorants, for example, thiophenes and methylsulfide.1 Transportation fuels also contain organic sulfur compounds typically 300 ppmw in gasoline, 500 ppmw in diesel, and 3000 ppmw in jet fuel.2 The U.S. Environmental Protection Agency announced new regulations that require the reduction of sulfur levels to 30 ppmw in gasoline and 15 ppmw in diesel.3 For fuel cell applications, the sulfur concentration in the fuel should be below 0.2 ppmw, because the sulfur compounds contaminate the anode electrocatalysts and degrade performance.4 Current hydrodesulfurization processes cannot remove the refractory sulfur compounds to this level and are not practical for small-scale residential units or for transportation systems. New processes and sorbents for sulfur removal are needed, therefore, in petroleum refining and for fuel cell applications. Several deep desulfurization adsorbents using mixed oxides or zeolites, such as transition metal ion-exchanged a)
Address all correspondence to this author. e-mail: [email protected] This paper was selected as an Outstanding Symposium Paper for the 2008 International Materials Research Conference, Symposium A. To maintain JMR’s rigorous, unbiased peer review standards, the JMR Principal Editor and reviewers were not made aware of the paper’s designation as Outstanding Symposium Paper. DOI: 10.1557/JMR.2009.0230 J. Mater. Res., Vol. 24, No. 6, Jun 2009
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Y zeolites,5 CuCl/g-Al2O3,6 an oxidation process coupled with a Fe(III)/activated carbon adsorbent,4 and TDA SulfaTrap Sorbent,1 have been developed to meet the stringent, lower sulfur level requirements, but further improvements are needed.7–9 The recently developed
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