SynopsisThe rate of isomerization during the polyesterification of maleic acid or maleic anhydride depends on the structure of the glycol used: the longer the chain of the glycol, the lower the isomerization rate. The rate constants differ greatly from one case to another. Thus, the difference in the reaction rate constants depends mainly on the steric effects caused by the different types of glycols used in the polycondensation. The isomerization approaches a constant value, ;which after a certain time depends on the structure of the glycol and the temperature of the condensation. The activation energies calculated from the rate constants would fall at about 20 f 4 kcal./mole. This value for the activation energy corresponds to that reported in the literature for the transformation of maleic acid into fumaric acid. The reaction apparently follows secondorder kinetics due to the catalytic effect of the maleic acid on the isomerization.
A nickel phthalocyanine complex (NiPc) supported on bentonite clay (Bihar, India) was used as a selective catalyst for the dehydrogenation of ethylbenzene to styrene. Maximum activity was observed for the catalyst sample containing 1.0 wt% NiPc/bentonite. A higher loading of complex (> 1.4 wt%) exhibited no activity and resembled polycrystalline NiPc. The texture of the studied catalyst and the mode of surface dispersion of the supported NiPc were investigated through the adsorption of N 2 and O 2 , respectively. The activity of the diluted samples could be attributed to the presence of separate highly dispersed molecules of NiPc on the bentonite surface without having a marked effect on its pore system for most active samples. The selectivity towards styrene was found to depend strongly on the NiPc surface area and the degree of dispersion. The activity was a function of the whole structure including modifications of both acid sites through different interactions and of the pore system through a penetration mechanism.
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