How can waste carbon dioxide be used?

Louise Smyth

What if you could take the world’s most pressing challenge and turn it into opportunity? That’s the kind of thinking happening right now in Qatar. Researchers have developed a way of taking CO2 out of the process of energy production and turning it into carbon nanotubes (CNT). Essentially a rolled sheet of graphene, sometimes called the ‘miracle material’, CNTs are being planned for use in a huge array of applications from photovoltaics to batteries storing renewable energy. 

Qatar is one of the world’s top producers of natural gas — and unfortunately, also the carbon dioxide that comes with processing it into usable products. But a novel process developed by Texas A&M University at Qatar researchers could help Qatar process its wealth of natural gas while reducing the country’s carbon footprint. And quite possibly give birth to an entirely new industry in Qatar of producing high-quality industrial materials feeding a range of vital industries.

Developed in Qatar, the CARGEN reactor technology was conceived and designed by Professor Nimir O. Elbashir and his research team at Texas A&M’s Qatar campus in collaboration with Professor Mahmoud M. El-Halwagi and his co-worker Dr Debalina Sengupta from the Artie McFerrin Department of Chemical Engineering at Texas A&M’s main campus in College Station, Texas. This technology is believed to be the first of its kind that processes natural gas (methane) and captured carbon dioxide to produce both syngas, a valuable precursor to numerous hydrocarbon feedstocks that drive Qatar’s economy, and high-quality solid carbon nanotubes. And unlike conventional processes, all without releasing more CO2 into the atmosphere. 

Elbashir’s research focuses on converting natural gas into valuable hydrocarbon products, including ultraclean fuels or useful chemicals, in a process called gas-to-liquid conversion (GTL). A major drawback of GTL processing is that it produces a lot of CO2, which increases Qatar’s carbon footprint and has led to the tiny country being named the world’s leading producer of CO2 per capita. 

Under the umbrella of the Texas A&M University Engineering Experiment Station (TEES) Gas and Fuels Research Centre (GFRC) headquartered at Qatar Foundation, Elbashir and researchers at both campuses have focused on how to reduce CO2 emissions and reduce Qatar’s carbon footprint. Elbashir directs the GFRC, one of the largest TEES research centres and a major initiative, bringing together 32 multidisciplinary scientists and professors from Texas A&M’s campuses in Texas and Qatar, all working in the same area but from different angles to speed up technology development in natural gas processing.

The CARGEN technology was developed to advance the dry reforming of natural gas, which is especially attractive as it converts methane and CO2 (both greenhouse gases) through a reactor to produce syngas, a mixture of carbon monoxide and hydrogen that is then processed to make liquid hydrocarbons and ultraclean fuels. This process, however, requires a lot of heat to drive the chemical reactions. This heat – the necessary reactions happen at more than 1,000 degrees Celsius – usually comes from burning fuels, which emits even more CO2.

Elbashir’s team has designed the novel CARGEN — or CARbon-GENerator — reactor, a second reactor added to the reforming process, along with a catalyst to drive the chemical reactions to produce expensive carbon nanotubes and syngas from CO2 and methane. These high-quality carbon nanotubes can be used in several industries in Qatar, including steel and cement, while the syngas can be turned into ultra-clean fuels and value-added products. The process can be driven by either electric or solar power, eliminating the need to burn fuel and thereby resulting in much lower CO2 emissions than conventional technologies.  

“We are making Qatar COemissions into two products that are important to the economy in Qatar and will broaden the role of hydrocarbons in Qatar’s manufacturing facilities,” Elbashir said. “CNTs are very expensive and extremely versatile, and can be used to manufacture products such as computers and other high-quality materials. And at the same time, we are also producing syngas, which can then be used to make the chemicals Qatar’s processing industries rely on.”

The CARGEN reactor is a result of a nearly $5 million Exceptional Proposal grant from the Qatar National Research Fund’s National Priorities Research Program, said Ph.D. student Mohamed Sufiyan Challiwala, who has been a significant contributor to the project. Challiwala started working on the project as a master’s student in chemical engineering at Texas A&M at Qatar before pursuing his Ph.D. through the main campus and beginning his doctoral research in Qatar. 

Challiwala said, “CARGEN provides a new perspective on the implementation of natural gas reforming technology. Rather than considering carbon or ‘coke’ formation as a process challenge, CARGEN treats it as an opportunity to convert at least 65 per cent of CO2 per pass with 50 per cent lower energy requirements. Most importantly, it produces CNTs and fibres that are considered to be next-generation materials with tremendous applications. Because of its uniqueness, this process is now patented with the support of Qatar Foundation.”

Dr Hanif Choudhury, a research scientist in Elbashir’s research group, said, “The CARGEN concept of CNT generation has been validated at the micro-, milli- and gram scales, with the quality of the carbon nanotubes controlled and preserved at every scale.” 

The next step is partnering with industry collaborators to scale up the technology even further. 

What are the possible uses of carbon nanotubes?

Carbon nanotubes are hollow cylinders made of graphite carbon atoms much smaller than the width of a human hair. Discovered more than 50 years ago, it’s only now that their potential to revolutionise the way we make – well, everything – is starting to be realised. So how could CNTs be used? 

for computing, researchers have found ways to ‘unzip’ CNTs into atom-thick sheets of graphene. Like silicon, graphene is a semi-conductor. With their nanoscale size, they can pack much more computing power in one place – or even use CNTs as ‘quantum wires’ able to switch a single electron – to make computing more powerful. 

Because of their properties interacting with electrons, researchers have been exploring ways to use CNTs to significantly increase the efficiency of photovoltaic cells. In addition, a team at the Massachusetts Institute of Technology pioneered a way to use CNTs to store energy from solar thermal systems that could store 10,000 times more energy than previous methods. 

Also biotechnology researchers have been finding ways to exploit CNTs to inject drugs or genes into individual cells. And in one study, CNTs were injected into kidney tumours in mice and then aimed a near-infrared laser at the cancer cells, making the CNTs vibrate. In the mice getting the highest ‘dose’ of CNTs and exposed to 30 seconds of laser light, the tumours disappeared in 80 per cent of the cases.