- Bappi Paul, a scientist with the National Forensic Sciences University in Ahmedabad, was recently awarded the Vigyan Yuva-Shanti Swarup Bhatnagar for the catalytic conversion of carbon dioxide to ethanol, among other innovations.
- The catalytic conversion of carbon dioxide to methanol is a well-established technology, but one that is still new in India.
- Carbon capture and utilisation has an important role to play in decarbonising energy systems, but its technology is still too futuristic.
In 2005, Nobel Laureate and Hungarian-American chemist George A. Olah proposed, with two others, that the world embrace a “methanol economy” – a future where the economy depends not on fossil fuels, but on methanol and dimethyl ether (DME)-based fuels. The methanol economy, through the recycling of carbon dioxide, “will eventually free mankind from dependence on diminishing natural fossil fuels,” Olah wrote.
Over two decades later, the world’s economy continues to be steeped in fossil fuel use. But Olah’s work and vision has motivated newer innovations in renewable fuels. Bappi Paul, a scientist with the National Forensic Sciences University in Ahmedabad, was recently awarded the Vigyan Yuva-Shanti Swarup Bhatnagar for leapfrogging by using carbon dioxide to directly produce not methanol, but ethanol. The Vigyan Yuva-Shanti Swarup Bhatnagar is a government award that recognises young scientists who have made “exceptional contributions to science and technology.”
Both methanol and ethanol are alcohol-based, biodegradable fuels, but one of the key differences between them is that methanol has just one carbon atom while ethanol has two. Methanol has uses as both a fuel and a chemical, but is toxic and volatile to store. Ethanol, by comparison, is more energy dense and amenable to blending with petroleum. India, for example, has a target of blending 20% of ethanol with petroleum by 2025-26 to reduce greenhouse gas emissions released on fuel combustion.
But it’s the additional carbon atom in ethanol that has made its direct production from carbon dioxide particularly challenging. “Both carbon dioxide and methanol have one carbon atom. Normally, making ethanol from carbon dioxide has been a multi-step process, but we’ve developed a catalyst that can reduce the step to just one, enabling a direct conversion,” said Paul, who was also awarded a patent for this innovation.
Making fuel from carbon dioxide
One way to make methanol (chemical formula CH₃OH) involves the catalytic reaction of carbon dioxide with hydrogen. The process is made renewable when the carbon dioxide is captured and recycled from industrial emissions, and the hydrogen is generated by the electrolysis of water from renewable sources (which has fewer emissions compared to electricity from fossil sources). The first commercial-scale, renewable methanol plant was established in 2010 in Iceland, and named after George Olah.
The direct production of ethanol from carbon dioxide is still in the early stages of development. Ethanol is conventionally sourced from the fermentation of starch based crops like maize and barley or from sugarcane molasses. As of December 2023, India has an ethanol production capacity of 1380 crore litres, out of which about 875 crore litres is molasses based and about 505 crore litres is grain based.
However, using biomass to make ethanol has thrown up its own set of problems. The decision to use grain-based sources for ethanol production comes with a perpetual trade-off between food and fuel. Sourcing ethanol this way is also water intensive, and can have negative environmental impacts if discharge from ethanol plants is not properly disposed of. Sugarcane and starchy crops are also exposed to market fluctuations and erratic weather, all of which impact supply.
According to Paul, using captured carbon dioxide to produce methanol is becoming a more attractive option to players in the petroleum industry. “Continuously growing sugarcane will inevitably lead to some degradation, either in yield or in the environment. With this type of technology, oil refineries can capture the carbon dioxide they produce and directly use it in ethanol or methanol production. This could earn them carbon credits in the future for reducing their emissions.”
A report by the Ministry of Petroleum and Natural Gas said that public sector oil and gas companies are increasingly embracing carbon capture and storage technologies (CCUS) for various applications, including renewable fuel production.
But the faith in the conversion of carbon dioxide to fuels like methanol and ethanol must be tempered by the fact that the technology is energy and capital intensive, said Sebastian C. Peter, a professor at the Jawaharlal Nehru Centre for Advanced Scientific Research and head of the National Centre of Excellence in Carbon Capture & Utilization in Bengaluru. “Even though it is relatively easier to convert carbon dioxide to methanol compared to carbon dioxide to ethanol, it’s still a very thermodynamically charged process. The conversion requires very high levels of compression and energy consumption. This means there’s a high energy input, which pushes up the cost,” he said.
The importance of a catalyst
Trained as a chemist from the National Institute of Technology Silchar in Assam, Paul worked as a researcher in the CSIR-Indian Institute of Petroleum after completing his PhD and then travelled to Japan on a postdoctoral fellowship. He then returned to India as a Ramanujan Fellow and is currently an associate professor at the National Forensic Sciences University. Along the way, he developed an expertise in the role catalysts play in organic reactions.
The breakthrough in the carbon dioxide to ethanol conversion was thanks to a catalyst. “Some of the challenges with this carbon dioxide reaction is that a lot of unwanted byproducts can be made, like carbon monoxide or formic acid. But the main advantage of the catalyst that I have developed is that it gives around 96% selectivity towards ethanol.”
The catalyst in question is a transition metal mixed oxide which facilitates the direct conversion of carbon dioxide to ethanol through hydrogenation. The catalyst comprises synthesised rhodium nanoparticles supported on nanostructured iron silica oxide.
So far, Paul has managed to create small batches of ethanol using this method, and is in the midst of researching how to make its production a continuous process. One batch produces a miniscule amount of ethanol – 120 minimoles. A mole is a unit that measures large quantities of atoms, molecules, and other small particles. “What we’ve done is show that the pathway for this reaction is possible. More studies are required to see how we can increase the yield,” Paul said.
The limits of CCU
Even the more well-established technology of converting carbon dioxide to methanol is under continuous development for improvements in efficiency, said Peter. “Our lab has designed a catalyst that reduces the amount of pressure needed to convert carbon dioxide to methanol, from over 100 bars to 50 bars,” he said.
Only a handful of plants capturing carbon dioxide for conversion to fuels are operational in India, mostly on a pilot basis or at a small scale. Last year, coal giant NTPC installed a flue gas to methanol plant for the conversion of carbon dioxide to methanol. The Indian Institute of Technology, Delhi is also experimenting with the technology with Pune-based Thermax Global, an energy and environment solutions company, to set up a plant with a capacity of 1.4 tonnes of methanol per day.
The direct conversion of carbon dioxide to ethanol is newer still, and a futuristic technology whose commercial viability will need to be seen. “This is not something that can be decentralised, and as of now, it’s a very capital intensive process that requires specialised reactors,” said Paul.
Carbon capture and utilisation has an important role to play in decarbonising energy systems, but the confidence demonstrated by the fossil fuel industry that these technologies can work at scale has been called premature. “To say that carbon capture and storage technology will allow the oil and gas industry to continue with the current trends and at the same time bring emissions down in line with the Paris targets is, in our view, pure fantasy,” said Fatih Birol, executive director of the International Energy Agency.
The reliance on carbon capture technology has also sparked concerns that it will enable the continued use of fossil fuels at a time when the scientific consensus is that they should be phased out.
According to Paul, finding ways to productively use carbon dioxide and prevent its release into the atmosphere is “today’s need.”
“In an ideal situation, we’d have a fuel that doesn’t emit any carbon, such as hydrogen. But our energy systems are still very dependent on fossil fuels, and even producing hydrogen is a carbon intensive process. Our fossil fuel reserves are limited and we need to have a different source of energy, but till those systems are developed, using, capturing, and converting carbon dioxide and keeping it in a loop is necessary,” said Peter.
Banner image: A flame from burning ethanol. Image by SirVir at Polish Wikipedia via Wikimedia Commons [CC BY-SA 3.0].