New membrane material could make purification of gases significantly more efficient

Industrial processes for chemical separations, including natural gas purification and the production of oxygen and nitrogen for medical or industrial uses, are collectively responsible for 15 percent of the world's energy use. They contribute to the world's greenhouse gas emissions. A new kind of membranes has been developed by researchers at MIT and Stanford University.

There is a tradeoff between how fast gases can penetrate through the material and the ability to let the desired molecule go. The new family of materials, based on carbon ladder, provides both high permeability and extremely good selectivity.

The findings are reported in a paper by a group of people, including an associate professor of chemistry at Stanford, an assistant professor of chemical engineering at MIT, and a professor at King Abdullah University of Science and Technology.

Gas separation is an important and widespread industrial process that can be used to remove unwanted compounds from natural gas, remove oxygen and nitrogen from air for medical and industrial purposes, and separate carbon dioxide from other gases for carbon capture. The performance of such separation processes could be improved by the new ladder polymer membranes. The new membranes have five times the selectivity and 100 times the permeability as the existing ones. They are 100 times more impermeable and three times more effective at separating methane from hydrogen gas.

The Xia lab has developed a new type of polymers called ladder polymers, which are formed from double strands connected by rung-like bonds, and they have a high degree of rigidity and stability. The Xia lab developed a chemistry called CANAL which stitches readily available chemicals into ladder structures with hundreds or even thousands of rungs. A thin sheet with sub-nanometer-scale pores can be made with the help of industrially available casting processes. The chemistry and choice of chemical building blocks allowed us to make very rigid ladder polymers with different configurations.

The collaboration used the expertise of both Xia and Smith to apply the CANAL polymers to the membranes. It took us eight years to find the right structures for the high separation performance.

Over the past several years, the Xia lab has varied the structures of CANAL to understand how they affect their separation performance. Adding more kinks to their original CANAL polymers improved the mechanical robustness of their membranes and boosted their selectivity without losing their permeability of the more permeable gas. As the material ages, the selectivity improves. The combination of high selectivity and high permeability makes these materials perform better in gas separations.

Smith says that 15 percent of global energy use goes into chemical separations, and these separation processes are often based on century-old technologies. Most of these processes require high temperatures for boiling and reboiling solutions, and these are the hardest processes to replace.

He says that the separation of oxygen and nitrogen from air only has a small difference in size. It is incredibly difficult to make a filter that can separate them efficiently without decreasing throughput. The razor-thin sieve needed to access this type of size is not an issue in some cases. Smith says that the new materials have the highest combination of permeability and selectivity of all known materials.

CANAL polymers are strong and can be scaled for industrial use within a few years. An MIT spinoff company called Osmoses, led by authors of this study, recently won the MIT $100K entrepreneurship competition and has been partly funded by The Engine to commercialise the technology.

Smith says that the separation of carbon dioxide from other gas mixtures is a form of emissions reduction that could be done with these materials. The purification of the fuel made from agricultural waste products is a possibility. Hydrogen separation can be carried out efficiently, helping with the transition to a hydrogen-based economy.

The close-knit team of researchers is continuing to refine the process to facilitate the development from laboratory to industrial scale and to better understand the details on how the macromolecular structures and packing result in the ultrahigh selectivity. Smith expects platform technology to play a role in multiple decarbonization pathways, starting with hydrogen separation and carbon capture, because there is a pressing need for these technologies in order to transition to a carbon-free economy.

Jun Myun Ahn is the chief executive officer at Osmoses, and he was part of the research team.

More information: Holden W. H. Lai et al, Hydrocarbon Ladder Polymers with Ultrahigh Permselectivity for Membrane Gas Separations, Science (2022). DOI: 10.1126/science.abl7163. www.science.org/doi/10.1126/science.abl7163 Journal information: Science Citation: New membrane material could make purification of gases significantly more efficient (2022, March 24) retrieved 24 March 2022 from https://phys.org/news/2022-03-membrane-material-purification-gases-significantly.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.