(654f) Replacing Methanol By Methyl Bromide: Highly Efficient Conversion Of Methane To Light Hydrocarbons

The direct bromination of methane offers a very selective (>98%) route [1] towards methane activation but shifts the problem of fuel production to converting and handling methyl bromide. The direct conversion of methyl bromide, at about 200 °C, into light hydrocarbons can be catalyzed under pressure by AlBr3 resulting in the formation of propane or butane-rich mixtures of light hydrocarbons, carbonaceous deposits, and HBr. After releasing the gaseous products, the addition of hydrogen at about 260 °C allows a quantitative conversion of the carbonaceous deposits into the same range of light hydrocarbons. These second-stage products efficiently contribute to the overall process yield while enabling a full regeneration of the catalyst's activity [2]. This oxygen-free process [3] is compared to the conversion of methyl bromide on zeolites and the currently used methanol-to-gasoline (MTG) process in terms of product distributions, apparent energy of activation and overall energy requirements. A detailed chemical analysis of the intermediates revealed the presence of a carbon pool consisting of highly substituted benzene and cyclopentadiene derivatives, as observed on zeolites used in the MTG process. This similarity suggests that the currently used oxygen based syngas/MTG process for methane conversion may be extended to a bromine-mediated process by using methyl bromide as an intermediate instead of methanol (Figure 1). The results are discussed in terms of possible large-scale implementation and estimated energy requirements.

Fig. 1: Process diagram for the conversion of methane to higher hydrocarbons using methyl bromide as an intermediate.

References:

[1] G. A. Olah, B. Gupta, M. Farina, J. D. Feldberg, W. M. Ip, A. Husain, R. Karpeles, K. Lammertsma, A. K. Melhotra, N. J. Trivedi, Journal of the American Chemical society 1985, 107, 7097.

[2] N. Osterwalder, W.J. Stark, Direct Coupling of Bromine-Mediated Methane Activation and Carbon-Deposit Gasification, ChemPhysChem, 8(2), 297-303 2007.

[3] N. Osterwalder and W. J. Stark, European Patent Application EP 06 005 927.6 and US provisional application 2006.