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 about 15 percent of the world’s energy use. They also contribute a corresponding amount to the world’s greenhouse gas emissions. Now, researchers at MIT and Stanford University have developed a new kind of membrane for carrying out these separation processes with roughly 1/10 the energy use and emissions.
Using membranes for separation of chemicals is known to be much more efficient than processes such as distillation or absorption, but there has always been a tradeoff between permeability — how fast gases can penetrate through the material — and selectivity — the ability to let the desired molecules pass through while blocking all others. The new family of membrane materials, based on “hydrocarbon ladder” polymers, overcomes that tradeoff, providing both high permeability and extremely good selectivity, the researchers say.
[...] The new type of polymers, developed over the last several years by the Xia lab, are referred to as ladder polymers because they are formed from double strands connected by rung-like bonds, and these linkages provide a high degree of rigidity and stability to the polymer material. [...] The sizes of the resulting pores can be tuned through the choice of the specific hydrocarbon starting compounds. “This chemistry and choice of chemical building blocks allowed us to make very rigid ladder polymers with different configurations,” Xia says.
[...] Today, 15 percent of global energy use goes into chemical separations, and these separation processes are “often based on century-old technologies,” Smith says. “They work well, but they have an enormous carbon footprint and consume massive amounts of energy. The key challenge today is trying to replace these nonsustainable processes.” Most of these processes require high temperatures for boiling and reboiling solutions, and these often are the hardest processes to electrify, he adds.
For the separation of oxygen and nitrogen from air, the two molecules only differ in size by about 0.18 angstroms (ten-billionths of a meter), he says. To make a filter capable of separating them efficiently “is incredibly difficult to do without decreasing throughput.” But the new ladder polymers, when manufactured into membranes produce tiny pores that achieve high selectivity, he says. In some cases, 10 oxygen molecules permeate for every nitrogen, despite the razor-thin sieve needed to access this type of size selectivity. These new membrane materials have “the highest combination of permeability and selectivity of all known polymeric materials for many applications,” Smith says.
Journal Reference:
Holden W. H. Lai, Francesco M. Benedetti, Jun Myun Ahn et al., Hydrocarbon ladder polymers with ultrahigh permselectivity for membrane gas separations, Science, 375, 6587.
DOI: 10.1126/science.abl7163
(Score: 0) by Anonymous Coward on Tuesday April 19 2022, @03:48PM (2 children)
These wonder materials all pay the price in countries that obey patent laws.
(Score: 1, Funny) by Anonymous Coward on Tuesday April 19 2022, @04:32PM (1 child)
Captain Underpants approves this message.
(Score: 1, Funny) by Anonymous Coward on Tuesday April 19 2022, @05:13PM
Underpants for the win! They need to make underwear out of this stuff. Let the clean methane out, trap the stink.
(Score: 0) by Anonymous Coward on Tuesday April 19 2022, @09:02PM (2 children)
If I understand what they're saying, they are making mechanical sieves where they have such good process control that they can make them such that they can have"holes" big enough to pass O2 and small enough to stop N2, or whatever--pick your two favorite molecules.
(Score: 0) by Anonymous Coward on Wednesday April 20 2022, @11:08AM
Did they re-invent an Inogen?
(Score: 2, Interesting) by Anonymous Coward on Wednesday April 20 2022, @08:46PM
You understand correctly. This won't replace all gas distillation since 90% purity (1 nitrogen for 10 oxygen cited in summary) isn't nearly good enough for many industrial processes, but it's plenty for breathing oxygen. The biggest questions are how much these new filters cost and how long they last.