Isobutanol Explained: How This 4-Carbon Alcohol Matches Petrol's Performance

With the exception of its primary use as an industrial solvent, isobutanol is a four-carbon alcohol that is becoming a promising next generation biofuel. Isobutanol stands in contrast to traditional biofuels like ethanol, with its physical characteristics closer to those of petroleum, providing superior performance, energy density and compatibility with current fuel infrastructure.

What Makes Isobutanol Different?

Alcohols with less carbon atoms are mostly used. For example, alcohol (ethanol) contains two carbon atoms and isopropyl alcohol, which is a common sanitiser and cleaning agent, contains three. However, isobutanol has four carbon atoms, which creates properties that are much more similar to conventional petroleum fuels.

It has a higher carbon content, is not easily water-absorbent and has a more oil-like behavior than other materials. It has these properties and is a better prospect for transport fuels than first generation biofuels like ethanol.

How Is Isobutanol Produced?

There are two production ways for isobutanol, which can be produced flexibly according to resources and industrial infrastructure.

The biological method uses special strains of yeast or bacteria that convert plant sugars. Bio-isobutanol is produced from raw materials like sugarcane syrup, corn mash, molasses and agricultural residues. Many of the existing plants are suitable for producing isobutanol with minor modifications, one of the major advantages of this approach.

The second approach is the petrochemical process, in which isobutanol is synthesized directly from petroleum via traditional refining processes.

Why Is It Blended With Diesel?

Using an isobutanol/diesel blend offers some benefits for engineers and policy makers. The most important advantage is the reliance on imported crude oil can be decreased and the agricultural sectors can be supported by producing a demand for raw materials from different farms.

Compared to ethanol, isobutanol has a higher energy content per litre, which will help keep vehicles fuel economy and mileage close to what they get from conventional diesel. It also helps minimize water absorption, enabling it to be better mixed with diesel without separating.

Another key benefit is safety. It is relatively less volatile in transport and storage due to its relatively high flash point. It can also be transported via existing fuel storage facilities, pumps and pipelines without resulting in corrosion, avoiding the need for expensive infrastructure improvements.

How Countries Around The World Use Bio-Mixed Fuels

The introduction of bio-based fuels to transport sectors is also underway in several countries, with various approaches.

The U.S. is using a mixture of bio-isobutanol and ethanol in petrol, especially in specialized marine engines and for passenger cars.

Brazil continues to be a world leader in ethanol use with up to 27 per cent of petrol being ethanol; Brazil is also promoting biodiesel.

To reduce emissions from diesel fuel based transport, countries across Europe have started to use more Hydrotreated Vegetable Oil (HVO) and biodiesel.

Indonesia has the world's largest mandatory blending programme of biodiesel, B35, in which palm oil is imported from the local industry, to cut dependence on fossil fuels and bolster its energy security.