The best material to capture carbon dioxide (CO2) from natural gas wells could be in a cheap derivative of asphalt, a material primarily used to build roads, Rice University scientists have found.
Chemist James Tour said a substance derived from asphalt appears to provide a compound matched to battle CO2 emissions, and the material could be made cheaply in a few steps. The findings were published in the American Chemical Society journal Applied Materials and Interfaces. Tour's research team tried several grades of asphalt, some costing only 30 cents/pound.
Apache Corp. funded the research. Schlumberger Ltd. unit MI SWACO and Prince Energy LLC provided the asphalt samples.
The asphalt substance "provides an ultra-inexpensive route to a high-value material for the capture of carbon dioxide from natural gas streams," Tour said. "Not only did we increase its capacity, we lowered the price substantially."
The findings build on a discovery by Tour's team last year of a carbon capture material for sequestration at the wellhead. The first discovery sequestered CO2 at ambient temperature, with pressure provided by the wellhead. In the latest discovery, the "best" version is a powder that holds 114% of its weight in CO2. Like the initial discovery, the porous carbon materials capture CO2 molecules at room temperature, while letting the desired methane natural gas flow through.
The basic compound, asphalt-porous carbon (A-PC), is able to capture CO2 as it leaves a wellhead under pressure, which is supplied by the rising gas at about 30 atmospheres, or 30 times atmospheric pressure at sea level. When the pressure is relieved, A-PC spontaneously releases the CO2, which then may be piped to storage, pumped back downhole or repurposed for uses such as enhanced oil recovery.
The goal of the research was to simplify the process of capturing carbon from wellheads at sea, where there's limited room for bulky equipment, Tour said. The ability of A-PC to capture and release CO2 without degrading it over several cycles makes it practical, he said.
Finding a way to efficiently capture CO2 is a goal for many exploration and production companies, some of which are working on research with universities and with private entities, including the Environmental Defense Fund. Reducing wellsite emissions also is a goal of the Obama administration's newly announced plan to cut methane emissions from new and modified sources by 40-45% below 2012 levels by 2025 (see Daily GPI, Jan. 14).
The A-PC was formulated by the researchers by mixing asphalt with potassium hydroxide at high temperature. Researchers turned the material into a porous carbon with a large surface area: 2,780 square meters/gram. That material captured 93% of its weight in CO2. Additional experiments showed that processing A-PC with ammonia and then hydrogen increased capacity to 114%.
The Rice lab continues to tweak the material, but it already is better for carbon capture than other materials now in use, according to Tour.
"Amine-based materials now used by industrial facilities like power plants to absorb CO2 are expensive and corrosive and can only capture about 13% CO2 by weight," he said. "Materials in development based on metal organic frameworks are far more expensive to produce and don't show as great a selectivity for CO2 over methane.”
Lead authors were postdoctoral associate Almaz Jalilov and graduate student Gedeng Ruan. Co-authors were Rice graduate students Chih-Chau Hwang, Desmond Schipper, Yilun Li, Huilong Fei and Errol Samuel, and lab assistant Josiah Tour.
Other Rice researchers are working on different ways to control CO2 emissions from gas wells. In a proof-of-concept study published late last year, chemist Andrew Barron and his lab reported that amine-rich compounds were effective at capturing CO2 when combined with carbon-60 molecules, also known as buckminsterfullerenes, or in layman’s terms, buckyballs (see Daily GPI, Dec. 5, 2014). Researchers now are looking for ways to improve the compound's capacity and rate of absorption.