Researchers Refines Filters for Greener Natural Gas

A scanning electron microscope image

A scanning electron microscope image, left, and a high-resolution transmission electron microscope image shows an activated, sulfur-containing porous carbon sample. The material created at Rice University can be tuned to balance carbon dioxide sequestration and methane selectivity. Credit: Barron Research Group/Rice University

Natural gas producers are set to draw methane from a well and sequester the carbon dioxide with the use of filters that optimise either the carbon capture or methane flow. So far, no single filter could do both, but the Rice University team of scientists, now know how to fine-tune sorbents for their needs.

According to Andrew Barron, Rice chemist, fine adjustments have been made during the manufacturing of the polymer-based carbon sorbent that makes the best-known material for capturing the greenhouse gas or balancing carbon capture with methane selectivity. The details are featured in a paper by Barron and Saunab Ghosh, Rice research scientist, in the Royal Society of Chemistry Journal, Sustainable Energy, and Fuels. Barron said that the challenge was to capture as much as carbon as possible while allowing the methane to flow through at typical wellhead pressures.

The previous work by the lab determined that the carbon filters optimally captured with a surface are of 2,800 square metres per gram and a pore volume of 1.35 cubic centimetres per gram. They also discovered that the best carbon capture material did not achieve the best trade-off between carbon and methane selectivity. Barron said that the new work gave avenues to knowing how to tune the material for one or the other.

The latest filters were created by heating a polymer precursor and then treating it with a chemical activation reagent of potassium, oxygen, and hydrogen (aka KOH). The polymer became full of nanoscale channels ready to trap carbon, when baked with KOH at temperatures over 5000C (9320 F), making it a highly porous filter.

During processing, the ratio of KOH to polymer turned to be the critical factor, which determined the final filter’s characteristics. The filters were made with a 3-to-1 ratio of KOH to the polymer at a surface area of 2,700 square metres per gram and maximised carbon dioxide uptake under pressures of 5 to 30 bars. There were filters which were made with a 2-to-1 ratio of KOH to polymer had less surface area of around 2,200 square metres per gram and a lower pore.

Barron said that their goal was to create a guide to design better materials. He added that these materials could be used for carbon dioxide separation from natural gas, which was the future direction of their research.

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