Towards cheaper gasoline from methanol
Globally, the transportation sector accounts for a quarter of all energy-related carbon dioxide emissions and its share will only increase in future, with economic growth currently under way in most developing countries.
Measures like promoting electric vehicles and blending fossil fuels with biofuel can help reduce carbon intensity to a considerable extent.
Even though solar and wind energy production is ever increasing, there is a need to explore bio energy options. Converting biofuels into high-quality fuels such as high-octane petrol or advanced jet fuels is plausible technologically but the existing technologies are rather expensive as they involve conversion processes that are costly.
This is where a team of researchers from the US achieved a breakthrough recently. They have found a way a cheaper one at that to convert methanol harvested from biomass sources into high-performance fuels.
Researchers from the National Renewable Energy Laboratory, a US Department of Energy lab, have developed a novel catalyst whose use can drive down the costs involved in the biorefining process significantly. The NREL scientists reported the new technique in a recent issue of Nature Catalysis journal.
“We have developed a catalyst, a solid material that helps to convert matter from one form to another just as nature would but much faster, that converts a common chemical into high-performance gasoline (petrol),” said Jesse Hensley, a scientist with NREL’s National Bioenergy Center and a co-author of the study.
“This common chemical (methanol) can be produced from renewable sources like biomass and gases from wastewater treatment facilities, which means we can produce a gasoline that is better than what we get from oil, without using oil,” Hensley said.
The problem with existing technologies is that the conversion cost of doing so is prohibitively expensive as it relies on multi-step processes requiring high temperatures. Besides, they produce low-grade fuel, that too in small amounts, compared to petroleum-based fuel.
“With the previously reported technology, the conversion cost from methanol to the desired fuel product is about $1 a gallon (nearly 3.8 litres),” said Daniel Ruddy, main author of the paper and a colleague of Hensley, in a statement. With their new catalyst, the NREL scientists managed to bring down the cost considerably. According to Ruddy, their best-case scenario was 10 US cents (₹7) a litre.
Explaining the process, Hensley said biomass gasification produces carbon monoxide, carbon dioxide and hydrogen gases. These gases are the same ones produced by steam reforming or partial oxidation of natural gas. Carbon monoxide, carbon dioxide and hydrogen are converted to methanol first. The methanol is next converted to dimethyl ether (DME) to remove oxygen, present in carbon monoxide and carbon dioxide gases.
“Both methanol and dimethyl ether produce gasoline when reacted over our catalyst. The dimethyl ether gives a better yield of gasoline in our process than methanol,” Hensley explained.
Copper does it
But when they set out to do, they found that it wasn’t an easy solution. The process developed by the NREL scientists at first ran into the problem of hydrogen deficiency. Hydrogen is a key component of hydrocarbons, which are necessary for fuels.
The researchers then hypothesised that using a transition metal would solve that problem. The addition of copper to the catalyst solved that problem. The researchers estimate the copper-infused catalyst resulted in 38 per cent more yield and 29 per cent less cost.
Moreover, they realised that they hit a jackpot. They found that the fuel that they had produced was high-quality high carbon efficient fuel. They realised that even if the cost savings were minimal, the resulting product would have higher value.
With petroleum prices being low currently, the new process may not be commercially viable yet.
“But if and when oil becomes more expensive, because we can produce methanol from any carbon source, this process will be cheaper. If one includes the environmental cost, this process is probably cheaper if starting with biocarbon,” said Hensley.
The biggest takeaway from the study is that high-performance synthetic fuels are still a possibility. “Secondly, this is a way to integrate bio and fossil carbon into the same process to begin to wean ourselves off petroleum,” Hensley said.