The reaction of methane and bromine is a mildly exothermic and exergonic example of free radical alkane activation. We show here that the reaction of methane and bromine (CH4:Br2 > or = 1) may yield either a kinetically or a thermodynamically determined bromomethane product distribution and proceeds in two main phases between 450 and 550 degrees C under ambient pressure on the laboratory time scale. This is in contrast to the highly exothermic methane fluorination or chlorination reactions, which give kinetic product distributions, and to the endergonic iodination of methane, which yields an equilibrium distribution of iodomethanes. The first phase of reaction between methane and bromine is a relatively rapid consumption of bromine to yield a kinetic methane bromination product distribution characterized by low methane conversion, low methyl bromide selectivity, and higher polybromomethane selectivity. In the second slower phase CHxBr(4-x) reproportionation leads to significantly higher methane conversion and higher methyl bromide selectivity. For methane bromination at 525 degrees C, CH4 conversion and CH3Br selectivity reach 73.5% and 69.5%, respectively, after ample (60 s) time for reproportionation. The high selectivity and simple configuration make this pathway an attractive candidate for scale-up in halogen-mediated methane partial oxidation processes.

We have developed a mathematical model to track facets appearing and disappearing during the evolution of crystal shape. The model also gives the crystal shape at steady state that is consistent with the predictions from the Wulff-Chernov approach (Chernov, A. A. Sov. Phys. Crystallogr. 1963, 7, 728). We show that under constant growth rate conditions, the steady state shape of a crystal is unique, stable, and independent of the seed crystal shape. The predicted shape of solution grown succinic acid is shown to be in excellent agreement with experimentally grown shapes. This model explains the experimentally observed uniqueness of the steady-state shape of crystals with respect to the random seed shapes.

The attainable region approach for reaction-mixing systems was applied to systems with simultaneous reaction and separation. A model de®eloped for a countercurrent cascade of two-phase CSTRs can be considered as a surrogate for the stripping or rectifying sections of a reacti®e distillation column. An o®erall composition ®ector defined satisfies the same geometric properties as the reaction ®ector. The necessary conditions for the reaction-mixing attainable region were applied to the cascade of two-phase CSTRs. This article focuses only on the countercurrent cascade of two-phase CSTRs; therefore, the region identified is a feasible region, which is a subset of the attainable region for reaction-separation systems. For consecuti®e reactions, the boundary of the feasible region is gi®en by the trajectory for a cocurrent cascade of two-phase CSTRs. The o®erall composition ®ector for the cocurrent cascade of two-phase CSTRs is tangent to the trajectory. For single re®ersible reactions, the attainable region for single-phase reactors is significantly expanded by using a countercurrent cascade of ®apor-liquid CSTRs. Two examples used are transalkylation of toluene and the synthesis of isopropyl acetate.

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As an alternative to the partial oxidation of methane to synthesis gas followed by methanol synthesis and the subsequent generation of olefins, we have studied the production of light olefins (ethylene and propylene) from the reaction of methyl bromide over various modified microporous silico-aluminophosphate molecular-sieve catalysts with an emphasis on SAPO-34. Some comparisons of methyl halides and methanol as reaction intermediates in their conversion to olefins are presented. Increasing the ratio of Si/Al and incorporation of Co into the catalyst framework improved the methyl bromide yield of light olefins over that obtained using standard SAPO-34.

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