Propylene oligomerization, conversion

A wide variety of acid-catalyzed reactions besides those described above have been investigated with heteropoly compounds as catalysts. Al203-supported H3PW12O40 (probably decomposed) catalyzed propylene-ethylene codimerization at 573 K to form pentenes with a selectivity of 56% (butenes 17%, hexenes 27%) (224). Propylene oligomerization proceeded on various kinds of salts of H3PWl204o (225). The activities of the salts decrease in the order A1 > Co > Ni, NH4 > H, Cu > Fe, Ce > K. The A1 salt gave trimers with 90% conversion at 503 K. The selectivities to trimer are about 40% for Al, Ce, Co, and Cu, while that of the acid form is 25%. 

With ligands 10 (R = H), Ni(II) complexes of fonnula [NiCl2(10)] were prepared and investigated for ethylene and propylene oligomerization catalysis and revealed interesting structural transformations [21], The mononuclear complex was found in equilibrium with the dinuclear, chloride-bridged strucmre and could be isolated on crystallization below 253 K. Conversely, the latter regenerates the mononuclear form at room temperature, either in solution or in the solid state (Scheme 14.17). 

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... 

Due to the accumulation of the oligomerized products of PO and carbonate-derived intermediates, the propylene conversion tended to decrease sharply soon after the reaction and then after 10-20 min, it gradually decreased with time onstream. Quasi-steady-state conversions were usually obtained after 30-60 min. The selectivity to PO and hydrogen conversion reached steady state much earlier. The used catalysts could be almost completely recovered by treating at 523 K in a stream of air, which allowed repeated experiments. 

Dimerization of isobutene with a catalyst of Si02/Al203 molar ratio of 102, NiO/Si02 molar ratio 0.021 in autoclave at 60 °C, 15 min and conversion 44% oligomerization of propylene with the above formula for catalyst, space velocity 2.87h , 3.08 MPa, 94 C, conversion 79%... 

According to Olah s investigations the conversion of methyl alcohol over bifunctional acidic-basic catalyst after initial acid-catalyzed dehydration to dimethyl ether involves oxonium ion formation catalyzed also by the acid functionality of the catalyst. This is followed by basic site catalyzed deprotonation to a reactive surface-bound oxonium ylide, which is then immediately methylated by excess methyl alcohol or dimethyl ether leading to the crucial - 2 conversion step. The ethyl methyl oxonium ion formed subsequently eliminates ethylene. All other hydrocarbons are derived from ethylene by known oligomerization-fragmentation chemistry. Propylene is formed via a cyclopropane intermediate. The overall reaction sequence is depicted in Scheme 19. 

Zeolite ZSM-58 (and its coimterpart Sigma-1) have been foimd useful in the conversion of methanol to mainly lower olefins [16,18] and for the oligomerization of propylene [17]. Moreover, it has been shown that shape selective... 

From a fundamental and a practical point of view it is quite important to give an accurate definition of the conditions in which given selectivities have been obtained, because chemical selectivities may be partly, or even entirely masked by kinetics artifacts caused by consecutive reactions. This can be illustrated by the curves of Figure 1, giving the yield of dimers versus conversion in the oligomerization of propylene by a nickel based catalyst. 

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