Al改性MCM-41选择性吸附脱硫机制的研究

STUDY ON SELECTIVE ADSORPTIVE DESULFURIZATION MECHANISM ON ALUMINUM MODIFIED MCM-41ZEOLITE

以MCM-41分子筛为主体、AlCl3为客体,采用后嫁接法制备不同硅铝比的Al-MCM-41分子筛吸附剂;采用X射线衍射、N2吸附-脱附等表征其织构性质;采用动态吸附法,并联合气相色谱-硫化学发光检测器考察其对催化裂化汽油的吸附脱硫性能及硫化物动态变化趋势;利用氨气程序脱附法和吡啶原位吸附红外光谱法分析其吸附脱硫机制。研究结果表明:采用后嫁接法制备的Al-MCM-41分子筛中铝物种能很好地与表面硅羟基结合,并保持了良好的二维六方规则排列的孔道结构;铝物种的引入可以有效调控介孔分子筛的酸性质,其中L酸中心位数量提高较明显,同时伴有B酸中心的微弱增强;Al-MCM-41分子筛中与配位不饱和且无B酸性的铝物种有关的L酸活性中心对2,3,4-三甲基噻吩和C_4噻吩具有较强的吸附能力,进而可提高其对催化裂化汽油的吸附脱硫效果。

Al-MCM-41 zeolites with different molar ratio of Si and Al, used as absorbents,were prepared by post-grafting method with MCM-41 molecular sieves as a subject and AlC13 as an object and characterized by XRD,N2 adsorption-desorption techniques to investigate the textural properties of modified Al-MCM-41 zeolites. The adsorptive desulfurization performance of FCC gasoline on these molecu- lar sieves and the dynamic variation trend of sulfur compounds were investigated by dynamic adsorptive method,combined with GC-SCD technique. The adsorptive desulfurization mechanism of sulfur com- pounds on the molecular sieves was studied by NH3-TPD and Py-FTIR methods. The results show that Al species of Al-MCM-41 molecular sieves is well dispersed and combined with the silicon hydroxyls and the channel structure with 2D six-party rule arrangement is remained. The introduction of aluminum spe- cies can effectively modulate the acidic properties of mesoporous molecular sieves. The Lewis acid center is promoted obviously, while only a slightly increases of B acid center is found. The L acid centers related to the ligand unsaturated aluminum species without B acidity have a strong adsorption ability for 2,3,4- trimethylthiophene and C4 thiophenes,and promote the adsorption desulfurization efficiency.