Is it feasible to blend isobutanol and diesel? | Explained

The story so far: On September 11, Union Transport Minister Nitin Gadkari said the Automotive Research Association of India (ARAI) was exploring the possibility of blending isobutanol with diesel. Isobutanol is an alcoholic compound with inflammable properties and is used as a solvent in several industries, including painting. Mr. Gadkari said ARAI was studying the possibility of blending isobutanol with diesel, after efforts to blend ethanol with diesel was unsuccessful.

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Is isobutanol better suited for diesel?

The discussion on the potential use of isobutanol primarily stems from the assumption that the alcoholic compound blends better with diesel, and after the blending experiment with diesel and ethanol failed. Ethanol, however, is available in surplus; as a biofuel, it is being seen as an important contributor to the government’s objective of scaling the net-zero emission target by 2070. At the annual conclave of the India Sugar and Bio-Energy Manufacturers Association (ISMA), Reji Mathai, director of ARAI, explained how isobutanol blended better with diesel compared with ethanol. “There was no need to add any complement [for efficiency], and isobutanol’s properties are better than ethanol for blending diesel. This is one [area] where studies are to be taken up,” he said.

More importantly, as Mr. Mathai pointed out, the flash point, or the lowest temperature at which isobutanol yields a vapour igniting a momentary flash, is higher than ethanol. A lower flash point was among the reasons that ethanol was not considered ideal for blending with diesel. Fuels with lower flash points are more volatile and entail a higher risk of catching fire. The other aspect relates to diverting some of the raw material required to produce ethanol to make isobutanol, as there is already a surplus of ethanol. According to an ISMA note, even after catering for industrial use in different States, the potential for ethanol supply is “more than 50% of the requirement” for the one-fifth blending with petrol. In addition to this, the sugar manufacturers’ association has also urged the government to revise the procurement prices for ethanol produced from cane juice/syrup or B-heavy molasses. The prices have not been changed since Ethanol Supply Year (ESY) 2022-23, while the Fair and Remunerative prices (FRP), or the minimum price sugar mills are required to pay farmers for sugarcane has increased by 16.5% during the period. “This imbalance has eroded economic viability, discouraged ethanol production and risked a build-up of surplus sugar in the domestic market,” it stated. Thus, the proposed blending also opens another avenue for the surplus production to be used.

How economical is it to make isobutanol?

Isobutanol can be produced from the same feedstock required to produce ethanol, such as sugarcane syrup and molasses and grains, among others. ISMA’s Director General Deepak Ballani explained the process to The Hindu, “Natural sugars are fermented by specially designed microbes under sterile conditions, unlike conventional yeast that produces ethanol; these engineered microbes are tuned to produce isobutanol.” On the aspect of costs, Mr. Ballani, taking the example of a sugar refinery, pointed out that producing isobutanol from biomass would require retrofitting a fermentation tank, and a distillation tank to separate ethanol from isobutanol. “A plant with a production capacity of 150 kilo litres per day (klp/d) can easily produce 125 klp/d of ethanol and 20 klp/d of isobutanol without a lot of changes to the overall infrastructure,” he stated.

What are some of the issues to consider?

Mathew Abraham, an automobile consultant and researcher who has previously worked with blending fuel types, noted two potential concerns emanating from isobutanol’s significantly lower cetane number compared with diesel, and about flash points. At the foremost, according to Mr. Abraham, isobutanol and diesel may have issues on miscibility (ability of two substances to mix to form a homogenous mixture) though it can be sorted out by mixing biodiesel to the blend. The latter refers to the fuel manufactured from non-edible vegetable oils, used cooking oil and/or animal fat.

Further, another point to note is the impact of the blend on the cetane number, which is a measure of combustion quality. An ideal combustion translates to rapid ignition and the fuel combusting completely to produce the necessary energy. Mr. Abraham notes the alcoholic compound’s significantly lower cetane number compared with the base fuel, diesel, would reduce the blend’s overall cetane number.

Also, a lower cetane number raises concerns about ‘[diesel] knock’ which can result in reduced power and can potentially damage engines. ‘Knocking’ occurs when the fuel burns unevenly and/or prematurely in the vehicle’s fuel cylinder, also generating an audible sound. However, Mr. Abraham added that the cetane value can be restored through proper additives which would entail incremental costs.

Mr. Abraham further stated that the proposed blend would have an impact on reducing emission and help with import substitution, but the riders must be addressed, and proper studies should be initiated encompassing varied vehicle classes and types. More importantly, he emphasised, “No more than 10% blending [of isobutanol] should be considered, else it could have an impact on engines.”

The blending paradigm is still being studied and the pilot project would take about 18 months to complete, according to Mr. Mathai. If successful, India would be the first country to have blended isobutanol with diesel.