466898 Mesoporous Catalysts for Conversion of 2,3-Butanediol to Butene

Tuesday, November 15, 2016: 1:50 PM
Franciscan B (Hilton San Francisco Union Square)
Quanxing Zheng1, Jason Grossardt1, Haider Almkhelfe1, Jiayi Xu1, Brian P. Grady2, Placidus B. Amama1 and Keith L. Hohn1, (1)Department of Chemical Engineering, Kansas State University, Manhattan, KS, (2)Chemical, Biological and Materials Engineering, University of Oklahoma, Norman, OK

2,3-butanediol has significant potential as a platform chemical for production of renewable fuels and chemicals since it can be produced with high productivity via fermentation and provides a C4 building block for further synthesis. Previous work has shown that Cu/ZSM-5 can convert 2,3-butanediol to butene with high selecitivty (~70%) [1]. This study expands on these results by investigating the role of pore size in 2,3-butanediol conversion to butene. Three different types of mesoporous materials (Al-MCM-48, Al-SBA-15 and meso-ZSM-5) were loaded with ~20wt% CuO and tested in the conversion of 2,3-butanediol to butene. Mesoporous aluminosilicate molecular sieves Al-MCM-48 with different SiO2/Al2O3 ratios of 23, 50, 100 and 200 were synthesized at room temperature by using N-Hexadecyltrimethylammonium bromide (CTAB) as the surfactant, tetraethyl orthosilicate (TEOS) and aluminum isopropoxide (Al(iProx)3) as Si and Al source [2]. Mesoporous aluminosilicate Al-SBA-15 with different SiO2/Al2O3 ratios of 23, 50, 100 and 200 were prepared by the “pH-adjusting” method [3], using triblock copolymer Pluronic 123 surfactant (EO20PO70EO20) as the structure-directing agent in a strong acidic HCl solution (2M), TEOS and Al(iProx)3 as Si and Al source. Meso-ZSM-5 was prepared by using a simple NaOH treatment of parent HZSM-5 zeolite [4]. Al-MCM-48 and Al-SBA-15 materials were characterized by small-angle X-ray scattering (SAXS), nitrogen adsorption and transmission electron microscopy (TEM), which clearly showed that the obtained Al-MCM-48 and Al-SBA-15 materials have highly ordered three-dimensional (3D) Ia3d cubic and two-dimensional (2D) p6mm hexagonal mesostructure, respectively. The pore (mesopore) size of Al-MCM-48, Al-SBA-15 and meso-ZSM-5 are about 2 nm, 10 nm and 20 nm, respectively, which is determined by the pore size distributions derived from the N2adsorption-desorption isotherms using BJH method. It should be noted that, apart from the mesopores, micropores with diameter of 0.5 nm were observed on meso-ZSM-5 zeolite, which is typical for the conventional ZSM-5.

Reactions were performed over reduced catalysts at the same reaction conditions (feed rate of 2,3-butanediol of 3.0 mL/h, hydrogen to 2,3-butanediol molar ratio of 5, reaction temperature 250 oC). The catalytic results demonstrated that 20%CuO/Al-SBA-15(50) exhibited the highest initial selectivity of butenes, which is 76.6% at 10 min of reaction. In addition, the results showed that the existence of mesopores on the catalysts (Al-MCM-48 and Al-SBA-15 types) could decrease the selectivities of products from cracking reactions, especially C3= and C5=- C7=, by comparison with the previous report on the catalyst 20%CuO/ZSM-5(280) [1]; meanwhile, the selectivity of C8= was found to increase with increasing pore size of the catalyst. However, the activities of the catalysts with MCM-48 and SBA-15 types were decreased dramatically over time. With respect to CuO/meso-ZSM-5(280) catalyst, it can be seen that the catalyst has the composited performance of both CuO/ZSM-5(280) catalyst and mesoporous copper catalysts (CuO/Al-MCM-48 and CuO/Al-SBA-15). Cu/meso-ZSM-5(280) is displayed high activity on the cracking reaction (C3=, C5=~C7=), and the oligomerization (C8=) as well. Interestingly, Cu/meso-ZSM-5(280) showed an excellent catalytic stability; the selectivity of butenes dropped from 71% to 61% in 670 min of reaction, which is much better than the catalyst with Cu loaded on the conventional ZSM-5(280), the selectivity of butenes dropped from 71% to 50% in 550 min.

[1] Q. Zheng, M.D. Wales, M.G. Heidlage, M. Rezac, H. Wang, S.H. Bossmann, et al., Conversion of 2,3-butanediol to butenes over bifunctional catalysts in a single reactor, J. Catal. 330 (2015) 222–237. doi:10.1016/j.jcat.2015.07.004.

[2] K. Schumacher, C.D.F. Von Hohenesche, K.K. Unger, R. Ulrich, a. Du Chesne, U. Wiesner, et al., The Synthesis of Spherical Mesoporous Molecular Sieves MCM-48 with Heteroatoms Incorporated into the Silica Framework, Adv. Mater. 11 (1999) 1194–1198.

[3] S. Wu, Y. Han, Y.C. Zou, J.W. Song, L. Zhao, Y. Di, et al., Synthesis of Heteroatom Substituted SBA-15 by the “pH-Adjusting” Method, Chem. Mater. 16 (2004) 486–492. doi:10.1021/cm0343857.

[4] J.C. Groen, J. a. Moulijn, J. Perez-Ramirez, Desilication: on the controlled generation of mesoporosity in MFI zeolites, J. Mater. Chem. 16 (2006) 2121. doi:10.1039/b517510k.

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