Preparation And Adsorption Property Of Carbon Microspheres Surface Molecularly Imprinted Materials For Desulfurization

Benzothiophenes, the most important sulfur compound pollutants in gasoline, are difficult to remove by traditional desulfurization techniques because of their steric hindrance and structural stability. As a novel adsorptive desulfurization, the molecular imprinting technique offers a simple way to remove the refractory sulfur compounds under mild conditions without decreasing the octane value. Based on the molecular imprinting technique, three kinds of molecularly imprinted polymer (MIP) on the surface of modified carbon microspheres (CMSs) or porous-CMSs were prepared by using benzothiophenes as the template molecule. And the structure and adsorption behavior of the surface molecularly imprinted materials were characterized and detected. The main results are as follows:(1) Surface modification of CMSs. Uniform carbon microspheres (CMSs) were prepared from C2H2by chemical vapor deposition, and oxidized by a mixture of concentrated sulfuric acid and nitric acid in order to improve their surface activity. Then, the oxidized CMSs were silanized using the coupling agent p-(chloromethyl) phenyl trimethoxysilane (CMTMS) in order to introduce benzyl chloride onto the surface of the oxidized CMSs, and the effects of reaction time, coupling agent concentration and reaction temperature were investigated. CMTMS was grafted onto the surface of0.4g oxidized CMSs with5%coupling agent at80℃for4h, and the Iniferter was grafted onto the surface of silanized CMSs via benzyl chloride by reaction with sodium diethyl dithiocarbamate. Then, methyl acrylic acid (MAA) monomers were grafted onto the surface of modified CMSs. The influences of reaction time, amount of MAA and irradiation distance were investigated. Under UV irradiation, MAA was grafted uniformly on the surface of Iniferter-CMSs under the optimum parameters of reaction:Iniferter-CMSs0.2g, MAA dosage4mmol (0.34mL), reaction time3h and the distance of ultraviolet irradiation15cm.(2) Molecularly imprinted polymer on the surface of Iniferter-modified carbon microspheres (CMSs) was synthesized by using dibenzothiophene (DBT) as template molecule, MAA as functional monomer and ethylene glycol dimethacrylate (EDMA) as crosslinker. The structure and adsorption behaviors were detected. The adsorption results show MIP/CMSs possessed high binding capacity and good selectivity. At298K, the adsorption equilibrium of MIP/CMSs was achieved within3h and the maximum adsorption capacity towards DBT reached88.83mg/g, which was higher than non-imprinted polymers on CMSs (NIP/CMSs,44.52mg/g). In addition, the adsorption of DBT on MIP/CMSs followed the pseudo-second-order model and Langmuir-Freundlich isotherm. The thermodynamic parameters of negative values of the Gibbs free energy change, positive values of standard enthalpy change and entropy change reveal that the adsorption was a spontaneous, endothermic and entropically driven process during288-318K. From the regeneration experiments and the adsorption results in the real gasoline, the MIP/CMSs were found to have good recycling capability, making it ideal for possible use in deep desulfurization of fuel oils.(3) Double-template molecularly imprinted polymer (D-MIP) on the surface of CMSs, using benzothiophene (BT) and DBT as the template molecules, MAA as functional monomer and EDMA as crosslinker, was prepared for the removal of benzothiophene sulfides from fuel gasoline. The structure and adsorption behaviors were detected. The adsorption results show that the D-MIP/CMSs exhibited excellent selectivity toward BT and DBT with higher binding capacity in simulated gasoline compared to non-imprinted polymer (D-NIP/CMSs). The adsorption equilibrium of D-MIP/CMSs was achieved within90min, and the adsorption capacity reached57.16(BT) and67.19mg/g (DBT). The pseudo-second-order model and Langmuir-Freundlich isotherm well described the adsorption of benzothiophene sulfides on the D-MIP/CMSs. The D-MIP/CMSs were recycled for10times without significant loss in adsorption capacity (7.0%for BT and4.8%for DBT). Therefore, the D-MIP/CMSs could be used in real gasoline.(4) Porous carbon microspheres (P-CMSs) with rich pore structure were obtained by hydrothermal method using glucose as carbon source. The surface of P-CMSs, with300-400nm particle size,607.5m2/g specific surface area,0.205cm3/g pore volume and1.25nm pore sizes, has rich oxygen-containing functional groups. The MIP/P-CMSs was prepared by surface imprinting using DBT as template, MAA as the functional monomer, EDMA as the crosslinker and P-CMSs modified with silane coupling agent as carrier material. The adsorption results indicate that the adsorption equilibrium time of MIPs/CMSs was about150min and the maximum adsorption amount was123.70mg/g. The adsorption amount of MIP/P-CMSs was larger than that of MIP/CMSs because of the porous structure of PCMSs. The pseudo-second-order model and Langmuir-Freundlich isotherm well described the adsorption of DBT on the MIP/P-CMSs. In addition, the MIP/P-CMSs exhibited good regeneration and desulfurization effect in real oil. The MIP/P-CMSs provide a new material for deep desulfurization of fuel oils.