Keith Holmes of Dunedin asks :-

Is it true that during the Second World War Germany and South Africa made transport fuels from coal? If so, what is the process and is it feasible today

Greg Visser, a chemical engineer with Solid Energy, responded.

The process you refer to is called gasification. It was originally developed in the 1800s to produce town gas for cooking and lighting. With the addition of the Fischer-Tropsch (F-T) process in the 1930s, it was further refined for the production of synthetic fuels. The process was later perfected by Germany during World War II and more than 90 per cent of Germany's aviation fuel and half its total petroleum during the war had come from coal. At its peak in early 1944, the German synfuels effort produced more than 124,000 barrels per day from 25 plants. Later, South Africa commercialised the process and now have the world's largest coal-to-transport fuel plants producing close to 180,000 barrels per day.

Gasification is a process that converts coal into carbon monoxide and hydrogen by reacting the coal at high temperatures and pressures with a controlled amount of oxygen and water (in the form of steam). The resulting gas mixture is called synthesis gas or syngas and can be used as a fuel itself. The syngas may be burned directly in internal combustion engines, used to produce methanol and hydrogen, or converted via the F-T process into transport fuels (petrol, jet fuel and diesel).

Before the syngas is introduced to the F-T process, the hydrogen/carbon monoxide ratio is adjusted for optimum F-T performance (generally a ratio of 2:1). As the syngas passes through the F-T reactor, it comes into contact with a proprietary iron or cobalt catalyst and forms long-chain paraffin hydrocarbons (waxes) ranging from C1 to C100+ along with some oxygenates such as water and alcohols. The waxes and oxygenates are separated by fractionation and the waxes are then processed through conventional refining methods to yield the finished transport fuel products.

A coal-to-liquids plant is very feasible with today's prevailing energy prices. World gasification capacity is projected to grow by more than 70 per cent by 2015. New Zealand has a globally significant coal resource in the form of lignite (low rank, high moisture coal) in Southland. Solid Energy is currently in the assessment phase of a project looking to convert the lignite into high value transport fuels for the domestic market by using the gasification technology.