Dimerization of isobutene over nickel modified zeolites to obtain isooctene
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Catalysis Letters Vol. 110, Nos. 1–2, August 2006 (Ó 2006) DOI: 10.1007/s10562-006-0092-0
Dimerization of isobutene over nickel modified zeolites to obtain isooctene Medina Gonza´lez Yaocı´ huatl,a,b Herna´ndez Luna Martı´ n,a and Alcaraz Cienfuegos Jorgea,* a
Departamento de Ingenierı´a Quı´mica, Laboratorio de Investigacio´n de Procesos, Universidad Nacional Auto´noma de Me´xico, Conjunto E, L-223 Facultad de Quı´mica, Circuito Institutos Ciudad Universitaria, Mexico DF, C. P. 04510, Mexico b Laboratoire de Chimie Agroindustrielle, UMR 1010 INRA/INP-ENSIACET, Ecole Nationale Supe´rieure des Inge´nieurs en Arts Chimiques et Technologiques, 118 route de Narbonne, F-31077 Toulouse Cedex, France
Received 22 February 2006; accepted 11 April 2006
Ni/H Zeolites catalysts were prepared by impregnation, starting from HY-Zeolite, Hb-Zeolite and H-mordenite with nickel precursor salts, NiCl2, NiSO4 and NiCO3. The total number, NTSA, and the acid strength were found dependent on the nickel precursor salt. High catalytic activity, selectivity and stability of the modified zeolites in isobutene dimerization was attributed to the acidic properties of nickel modified zeolites. HY-Zeolite modified with NiCO3 resulted more active and selective to dimerization reaction. The prepared catalysts were characterized by EDSX, SEM, and Adsorption/Desorption of N2 at 77 K, NH3 chemisorption and Ammonia Temperature-Programmed-Desorption (NH3-TPD) and FT-IR of adsorbed pyridine. NH3-TPD and isobutene adsorption revealed an acid sites a new distribution and apparition of acid sites not present in the protonated zeolites. Catalytic activity and reactor behavior were studied in a continuous downstream fixed bed reactor at 298 K, 27.6 kPa (4 psig), and WHSV = 0.27 h)1. KEY WORDS: isobutene dimerization; nickel modified zeolites; olefin oligomerization.
1. Introduction The clean air regulation in all countries concerning the contents of olefins, sulfur and aromatics, particularly benzene in gasoline will become increasingly strict. In addition, the removal of MTBE from gasolines in the US because of its negative environmental impact in ground water will further increase the need for high octane blending compounds in the gasoline pool. Hence, the diisobutenes can also be used as a feedstock to produce other high-octane components like isooctane or ethers like 2-methoxy-2,4,4- trimethyl-pentane and 2-ethoxy-2,4,4-trimethylpentane. Solid acid catalysts for dimerization and oligomerization of olefins have been known for many years [1–3], especially catalytic systems consisting mainly of nickel compounds supported on oxides, zeolites and organometallic nickel complexes have been used as dimerization catalysts and several processes have been commercialized [4,5] using these catalysts to obtain low molecular weight branched products from olefins dimerization, because they are suitable as gasoline blending components. Dimerization technologies available today were developed in anticipation of an impeding ban or
*To whom correspondence should be addressed.
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