This scanning electron microscope image shows micropores in carbon capture material derived from common asphalt. Image: Tour Group/Rice University.
This scanning electron microscope image shows micropores in carbon capture material derived from common asphalt. Image: Tour Group/Rice University.

A Rice University laboratory has improved its method for turning plain asphalt into a porous material that can capture greenhouse gases from natural gas. In research detailed in Advanced Energy Materials, Rice researchers showed that a new form of the material can sequester carbon dioxide until it makes up 154% of its weight at the high pressures that are common at gas wellheads.

Raw natural gas typically contains between 2% and 10% carbon dioxide and other impurities, which must be removed before the gas can be sold. This clean-up process is complicated and expensive, and often involves flowing the gas through fluids called amines that can soak up and remove about 15% of their own weight in carbon dioxide. This amine process also requires a great deal of energy to recycle the fluids for further use.

“It’s a big energy sink,” said Rice chemist James Tour, whose lab developed a technique last year to turn asphalt into a tough, sponge-like substance that could be used in place of amines to remove carbon dioxide from natural gas as it’s pumped from ocean wellheads. Initial field tests in 2015 found that pressure at the wellhead made it possible for the asphalt material to adsorb, or soak up, 114% of its weight in carbon at ambient temperatures.

According to Tour, the new, improved asphalt sorbent is made in two steps from a less expensive form of asphalt, which makes it more practical for industry. “This shows we can take the least expensive form of asphalt and make it into this very high surface area material to capture carbon dioxide,” he said. “Before, we could only use a very expensive form of asphalt that was not readily available.”

The lab heated a common type asphalt known as Gilsonite at ambient pressure to eliminate unneeded organic molecules. They then heated it again in the presence of potassium hydroxide for about 20 minutes to synthesize oxygen-enhanced porous carbon with a surface area of 4200m2 per gram, much higher than that of the previous material.

The Rice lab’s initial asphalt-based porous carbon collected carbon dioxide from gas streams under pressure at the wellhead and released it when the pressure dropped. The carbon dioxide could then be repurposed or pumped back underground, while the porous carbon could be reused immediately.

In the latest tests with its new material, Tour’s group showed that its new sorbent could remove carbon dioxide at 54 bar pressure. One bar is roughly equal to atmospheric pressure at sea level, and the 54 bar measure in the latest experiments is characteristic of the pressure levels typically found at natural gas wellheads, Tour said.

This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.