Enhancing Carbon Dioxide Conversion to Methane through Membrane Reactor Properties: An Investigation

Climate change, accelerated by human activities, has emerged as a significant environmental issue in the current era. Governments and organizations worldwide are progressively taking substantial steps to address this challenge.

An important initiative in this direction involves the development of innovative technologies that can capture and convert low-concentration carbon dioxide into valuable products.

Recently, scientists have put forth carbon dioxide methanation in a membrane reactor as a promising method. Distribution-type membrane reactors, in particular, are attractive due to their ability to enhance catalyst activity by mitigating hotspot formation.

While the effectiveness of membrane reactors has been demonstrated, the efficiency of membrane properties and the heat transfer characteristics of membrane materials still pose uncertainties.

In a recent study, a team of researchers led by Professor Mikihiro Nomura from Shibaura Institute of Technology in Japan, along with Yuka Shimizu from the same institute and Marcin Moździerz, Grzegorz Brus, and Elzbieta Fornalik-Wajs from AGH University of Krakow in Poland, has showcased the novelty of distribution-type membrane reactor for carbon dioxide utilization.

Their findings have been published in Catalysis Today.

“Through a dual-degree program between Shibaura Institute of Technology and AGH University of Krakow, we assessed heat transfer in membrane components, allowing us to highlight the specific advantages of the membrane reactors discussed in our research,” explained Prof. Nomura.

Subsequently, the team managed to regulate the reaction rate within the reactor by distributing reactant feeding through the membrane. They then conducted precise thermal conductivity evaluation of the porous alumina (Al₂O₃) membrane, with detailed physical and chemical structural features analyzed through laser flash analysis measurements.

The researchers observed a 36.4% lower thermal conductivity in the solid part of the sample compared to non-porous alumina.

Furthermore, the team employed a catalytic membrane with a silica separation layer, exhibiting a hydrogen gas permeance of 1.4 × 10⁻⁶ mol m⁻² s⁻¹ Pa^{−1> and a hydrogen-to-carbon dioxide selectivity of 35.9, in the distributor-type membrane reactor test. They achieved a high carbon dioxide conversion rate of 92.3% at 350 ℃.}

Building on these outcomes, the team conducted simulations using Ansys Fluent software to investigate the impact of membrane thermal conductivity and permselectivity.

By setting carbon dioxide permeance of the membrane at 3.91 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ for all scenarios, the team found that a carbon dioxide permselective membrane with a high selectivity of 35.9 produced approximately 1.4 times more methane compared to a hydrogen permselective membrane with a low selectivity of 0.10. Additionally, a higher thermal conductivity of the membrane helped in suppressing temperature rise in the reactor.

“Membrane reactors offer the advantage of spatially distributed reactant feeding within the reactor, allowing for better control over reaction rates and temperature profiles in both the axial (flow) and radial (membrane surface) directions,” noted Prof. Nomura.

“This distinctive capability and membrane design make them ideal for deployment in small-scale facilities. Therefore, implementing membrane reactors in small-scale carbon dioxide emission sources—commonly owned by numerous small- and medium-sized enterprises with limited resources—will accelerate the realization of a carbon-neutral society.

“Specifically, we foresee their application in small combustion devices like boilers, an area that has received minimal attention in the fight against global warming.”

These findings can also provide insights into other exothermic processes, such as hydrocarbon partial oxidation in membrane reactor systems, bolstering sustainable technologies.