Article pubs.acs.org/IECR
Desulfurization of Liquid Hydrocarbon Streams via Adsorption Reactions by Silver-Modified Bentonite Dezhi Yi, Huan Huang, Xuan Meng, and Li Shi* The State Key Laboratory of Chemical Engineering, East China University of Science and Technology, Shanghai 200237, People’s Republic of China ABSTRACT: Removal of organic sulfur compounds from its solution has been investigated by using adsorption. The purpose of this study is to investigate the removal of dimethyl disulfide (DMDS) in liquid hydrocarbon streams with bentonite modified by Ag+. The addition of Ag+ on the bentonite significantly enhanced the adsorption capacity of DMDS. The adsorbents were characterized by nitrogen adsorption, X-ray diffraction (XRD), and thermal analysis (TGA). Fourier transform infrared (FT-IR) spectroscopy showed that the type and number of surface acidic sites on the adsorbents could increase the adsorption capacity. Several factors that influence the desulfurization capability, including loading, reaction temperature, and calcination temperature, were studied. The maximum sulfur adsorption capacity was obtained at a silver loading of 6 wt %, and the optimum calcination temperature was 150 °C. Spectral shifts of the ν(C−S), ν(S−S), and ν(Ag−S) vibrations of the complex compound obtained by the reaction of Ag+ and DMDS were measured with the Raman spectrum. On the basis of complex adsorption reaction and hybrid orbital theory, the adsorption on modified bentonite occurred via multilayer intermolecular forces and S−M (σ) bonds.
1. INTRODUCTION Dimethyl disulfide (DMDS), with strong odors, is a volatile organic compound containing sulfur. DMDS is known to be produced in aerobic or anaerobic environments, mainly from natural sources, petroleum refining processes, the wood-pulping industry, sewage treatment, and energy-related activities. DMDS has a very low odor threshold concentration as low as 0.1 ppb,1 and DMDS may cause toxic effects if inhaled or absorbed through skin. Because the crude oil is getting much worse and heavier in recent years, the content of DMDS existing in the liquid hydrocarbon streams especially in low hydrocarbons is getting much higher.2 Methyl tertiary butyl ether (MTBE), which is added to gasoline to boost the octane number of gasoline, has become of higher content in sulfur. As is shown in Table 1, the MTBE contains various kinds of sulfur
production of on-board transportation fuels because of the high costs that will arise from compliance with such regulations.6 In conventional removal of sulfur compounds, hydrodesulfurization (HDS) processes are carried out, using Co−Mo/Al2O3 or Ni−Mo/Al2O3 catalysts at high temperature (300−340 °C) and pressure (20−100 atm of H2) conditions.7 However, HDS processes cannot meet the current sulfur level requirements, and the hydrogenation of olefins should be simultaneously minimized, because it reduces the octane number. Contrary to the above methods, the adsorptive desulfurization has the advantages that it does not require hydrogen addition and can be operated at room temperature and atmospheric pressure. There is an ongoing effort to develop new adsorbents to remove the sulfur compounds from commercial fuels via π-complexation,8−12 van der Waals’ and electrostatic interactions,13,14 and reactive adsorption by chemisorption at elevated temperatures.15,16 Deep desulfurization on various adsorbents such as activated carbons (ACs),17−19 modified composite oxide,20,21 and zeolite22 has already been studied. Wakita et al.23 have investigated the removal of dimethyl sulfide and t-butylmercaptan in the city gas using Na−Y, Na−X, H−β zeolite. They concluded that the adsorption site of Na−Y was the Na+ in the supercage and the concentration of dimethyl sulfide in the effluent gas increased rapidly after an hour. Lee et al.2 used ion-exchanged zeolites to remove DMDS from C4 hydrocarbon mixture and reported that ion exchanged zeolites were favorable adsorbents with high capacity for adsorptive removal of DMDS from gas hydrocarbon mixture at ambient conditions. For the removal of
Table 1. Sulfur Content Analysis in MTBE sulfur compound
concentration (ppm)
methyl mercaptan ethyl mercaptan butyl mercaptan thiophene DMDS diethyl disulfide
1.01
