446792 High-Temperature Membrane Reactors: An Effective Approach for Equilibrium-Limited Reactions
Reaction and separation are considered as two of the most crucial steps in chemical plants. Performance of each of these two steps can strongly affect the profitability of a given process by affecting its raw materials and energy demand and consumption. In an effort to improve the overall performance of the process, reaction and separation can be combined into a multifunctional Membrane Reactor (MR) that offers a platform for simultaneously carrying out the reaction and separation steps in one single stage. Such reactors typically consist of a catalyst bed in contact with a high-temperature membrane that either enables the removal in situ of one or more products (extractive MR) from the system or the controlled dosing of one or more of the reactants (contactor MR). Replacing the conventional two-stage reaction and separation systems with such a multifunctional reactor increases the process synergy, reduces the by-product formation as well as amount of reactants consumed. Additionally, a considerable reduction in the overall energy costs is to be expected [Sanchez and Tsotsis, 2002; Soltani et al., 2013]. While there are several reports on the applications of MR for both gas and liquid phase reactions, further studies are still required to characterize and optimize their performance, and to move towards commercialization of these multifunctional reactors [Sanchez and Tsotsis, 2002; Soltani et al., 2013].
In this talk, we will present two different examples of high-temperature MR currently under investigation by our Group. The first is a extractive MR that is used for methanol (MeOH) synthesis, and the other a contactor MR that is used for carbon (CO2) capture and utilization (CCU). Synthesis of MeOH from syngas is a severely equilibrium-limited reaction, which means that a large fraction of the unreacted syngas feed, must be recycled to make this equilibrium-limited process economically feasible. The ability of MR to increase the per-pass yield makes them a optimal choice for process intensification [Soltani et al., 2013], particulalry for coal-deruved and biomass-derived syngas from air-blown gasifiers that contains considerable amounts of inert N2.
Power plants are responsible for a large fraction of the man-made carbon-dioxide emissions, and are major contributors to the green house effect. Thus, reducing the amount of CO2 emissions from such plants is of the utmost importance. The key challenge here is the dilute CO2 concentration in the flue-gas, which make the conventional approaches such as direct sequentration technically as well as economically inefficient. Coupling of reaction and separation in a contactor MR, provides the driving force for the separation which moderates the challenge of separating dilute CO2 from flue-gas, and can also produce valuable products (e.g., synthetic natural gas, alcohols, etc.) which can be used as fuels to reduce the overall energy demand of the plant, and to improve its efficiency.
During our talk, we will present the two multifunctional reactor configurations that are being presently experimentally investigated, and will discuss the influence of reaction conditions and separation efficiency on the final yield of the reaction. The different types of high-temperature membranes that have been investigated will be described, and the influence of membrane characteristcs on overall system performance will be described. Efforts to optimize MR performance both experimentally and numerically will be furher outlined.
- Sanchez Marcano, J.G., and Tsotsis, T. T., “Catalytic Membranes and Membrane Reactors,” Wiley VCH, 2002.
- Soltani, S., Sahimi, M., and Tsotsis T.T., “Catalytic Membrane Reactors: A Brief Overview”, Encyclopedia of Membrane Science and Technology, Eric. M.V. Hoek and Volodymyr V. Talabar Editors, John Wiley & Sons, 2013.