Oligomerized ethylene zeolites

Figure 5. CP/MAS C-NMR spectrum of oligomerized ethylene on H-ZSM-5 zeolite at 295 K. (Reproduced with permission from Ref. 10. Copyright, 1981, Butterworth and Co.)...

Nickel containing MCM-36 zeolite was used as new catalyst in the ethylene oligomerization reaction performed in slurry semi-batch mode. This catalyst, with micro-mesoporous structure, mild acidity and well balanced Ni2+/acid sites ratio, showed good activity (46 g of oligomers/gcataLh) and selectivity (100% olefins with even number of carbon atoms). The NiMCM-36 behaviour was compared to those obtained with NiMCM-22, NiY, NiMCM-41 and NiMCM-48 catalysts. 

These data clearly indicate that the NiMCM-36 catalyst exhibits very interesting properties for ethylene oligomerization, by comparison with the microporous NiMCM-22 zeolite at both reaction temperatures (70 and 150°C, respectively). Compared with other catalysts, the NiMCM-36 behaviour is intermediate between Ni-exchanged dealuminated Y zeolite and Ni-exchanged mesoporous materials. Taking into account that the amount of Ni2+ sites is near the same for all samples (Table 1), in order to explain these differences in catalytic behaviors, two mains categories of properties could be considered (i) the concentration and strength of acid and nickel sites and (ii) the diffusional properties (determined by the size and the architecture of pores). 

GTG [gas to gasoline] A process for converting natural gas to gasoline by oxidative coupling. Ethylene, formed initially, is oligomerized to a gasoline-like distillate over a zeolite catalyst. Under development by the Arco Chemical Company in 1988. 

Conversion of Ethylene on H-ZSM-5 zeolite Ethylene was reacted in three distinct ways. First, it was oligomerized at room temperature on an activated (at 673 K) zeolite. Secondly, water was then adsorbed at 295 K and the sample steam-cracked at 573 K. 

Yamamura, M., Chaki, K., Wakatsuki, T., Okado, H., and Fujimoto, K. (1994) Synthesis of ZSM-5 zeolite with small crystal size and its catalytic performance in ethylene oligomerization. Zeolites, 14, 643-650. 

The oligomerization of light olefins such as ethylene for the production of synthetic fuels using zeolites as catalysts has been extensively studied.[25-28] In general, it has been found that the rate of oligomerization of ethylene over ZSM-5 zeolite is slower compared with other olefins and higher reaction temperatures are necessary. The catalytic performance of this reaction is related to the nature and number of acid sites of the zeolite. 

The role of Brpnsted acid sites in the oligomerization of ethylene over HZSM-5 has been studied.[30,31] Amin and Anggoro1311 concluded that dealumination of HZSM-5 led to higher ethylene conversion, but the gasoline selectivity was reduced compared with a nondealuminated HZSM-5 (Si/Al = 15) zeolite sample. 

Propylene and other olefins of higher molecular weight can be easily oligomerized over a wide range of zeolitic and nonzeolitic acid catalysts.[1114] However, in the case of ethylene only low conversions can be obtained over acidic catalysts. Transition metal catalysts, on the other hand, and particularly those based on Ni... 

Ethylene oligomerization over Ni and Pd zeolites has been reported by Lapidus and Krylova.[73] It was found that NiCaX exhibited high selectivity for ethylene dimerization at 508 K. The highest activity and selectivity were achieved with a sample with a Ni content of 2.5 wt%, trara.v-2-butcnc being the major product. PdCaX also shows excellent selectivity to trans-2-butene, giving 65 % selectivity for a total yield of the C4 fraction of 78 %. 

Kustov, L. M., Borovkov, V. Y. and Kazanskii, V. B. Study of ethylene oligomerization on Brpnsted and Lewis acidic sites of zeolites using diffuse reflectance IR spectroscopy. Stud. Surf. Sci. Catal., 1984, 18, 241-247. 

Lapidus, A. and Krylova, A. Ethylene oligomerization over Ni- and Pd-zeolites, DGMK Tagungsber., 2001, 2001-4, 245-251. 

Oberson de Souza, M. and de Souza, R. F. Ethylene oligomerization with Ni(MeCN)6(BF4)2 in homogeneous phase, immobilized in ionic liquids or heterogenized in zeolite. Current Top. Catal., 3, 2002, 267-273. 

Figure 4 shows that similar A1 ion sites can be produced on a ZSM-5 zeolite by high-temperature drying and that activity for ethylene oligomerization accompanies formation of such sites. These sites are evidently created on zeolites by removal of A1 from the crystalline framework at high temperatures, leading to the exposure of A1 ions, possibly as A10+, outside the framework. 

Figure 5 shows (on ZSM-5 completely exchanged with deuterium oxide and dried at 800 C) that readdition of water (D20) gave two new bands, possibly arising from hydration of A10+ ions to form A1(0D)2+ ions. This suggests that either hydrated or anhydrous complex A1 cations, held outside the zeolitic framework can be active for ethylene oligomerization. 

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