Technology About Gas

Improved filters for greener natural gas

 By Robin Wylie
About gas

A newly created material with the highest-known carbon absorptivity could improve the green credentials of natural gas even further…

In its untreated state, natural gas contains various impurities, including CO2 and other gases, which are routinely removed in a process known as natural gas sweetening. Removing such gases—primarily CO2—is important to reduce the environmental pollution associated with natural gas burning, but also serves to reduce the infrastructure corrosion that they can also cause.
Some of the most effective materials used for removing CO2 from natural gas are activated porous carbons (PCs) because of their high surface area and large pore volumes. But scientists are constantly pushing the carbon absorptivity of PC materials.

The most recent breakthrough, announced earlier this year, was made by researchers from Rice University, Texas, who managed to maximize the carbon-absorbing efficiency of a PC material by tweaking the microstrcuture of its pores. The research leader, Saunab Ghosh, had last year published a study which discovered that there was a limit to increasing the carbon absorptivity of PC materials by increasing their surface area and pore volume. But in the new study, the researchers managed to show that by altering the size of the micro-pores within a PC material, rather than increasing their total volume, the carbon absorptivity of the material could be increased to its highest level yet. The researchers achieved this by treating a PC material with various amounts of a chemical reagent, potassium hydroxide, and selecting the iteration which optimized its carbon absorptivity.

Gas flare

Importantly, Ghosh and his co-author discovered that this optimum material owed its world-best CO2 absorption not to the total volume of its pores, but instead to its ratio of micro-pores, with diameters of less than 2 nanometers, to meso-pores, with diameters of 2 nm and above. This discovery offers a possible way to improve the efficiency of natural gas sweetening, and thus to reduce the environmental impact of natural gas. But it also provides an important clue to improving the process even further. Previous studies had suggested that the most important criterion for designing PC materials for CO2 absorption was that they should primarily be rich in extremely small micropores. But Ghosh’s work shows that the situation is a little more nuanced by proving that it’s the size of the particles, rather than their total volume, which really controls the process.

SEE MORE: Natural gas and microgrids by Andrew Burger

about the author
Robin Wylie
Freelance earth/space science journalist. Currently finishing off a PhD in volcanology at University College London.