(38c) An Integrated Bromine Mediated Process for Biomethane Conversion to Gasoline

Methane will remain abundant from both fossil resources and renewable biological sources into the foreseeable future. A chemical process ?platform? for the selective partial oxidation of methane and other alkanes based upon use of bromine for C-H bond activation and novel process steps for bromine recovery and reuse. The overall alkane conversion occurs in a three-step process involving, i) bromination under bromine limiting concentrations, ii) reaction of alkylbromide intermediates to form products, and iii) recovery of the bromine with a catalyst/metal oxide solid reactant. The process does not utilize a synthesis gas intermediate and is tolerant to common methane contaminants including high concentrations of carbon dioxide present in biomethane. Process optimization and reaction engineering allows us to use relatively non-selective thermal bromination at modest temperatures ~ 400 oC for methane activation with conversions in excess of 75%. Methyl-Br has many reactivity features in common with Methyl-OH and thus the wide variety of products available with methanol feeds (e.g. MTO, MTP, MTG) can also be made with methyl bromide. The molecular weight of the alkylbromides provide a chemical handle for ease of separation. Use of adiabatic reactors and other process options allow minimization of the requirements for costly structures with expensive metallurgy though proper choice of the materials of construction is critical. A key feature of the process is the potential use of a solid-reactant for recovery of the bromine that minimizes bromine or hydrobromic acid inventories and facilitates efficient recovery of the halogen. Bromine has fundamental advantages over chlorine and advanced reactor designs utilizing moving or switched bed zone reactors offer significant process cost reduction options. Preliminary engineering-economic models and pilot facility operation show the process to have particular promise as a commercial route to production of liquid transportation fuels from biomethane derived from byproducts of existing commercial processes.