Methanol synthesis in South Africa

Dr Garth Cambray

Methanol is an essential ingredient in the production of biodiesel, a fuel which can potentially help reduce the amount of fossil carbon released into the atmosphere. SASOL, a world leader in fuel technologies, is the only producer of methanol in South Africa. This article looks at how this important chemical is synthesized in South Africa.

Methanol is the simplest of all alcohols. It consists of a singe carbon atom with 3 hydrogen atoms attached to it, and then one alcohol group - an oxygen and hydrogen. Hence the formula for methanol is CH3OH. It differs from methane, the simplest alkane gas, by having an OH instead of a 4th hydrogen. Methane is CH4.

The SASOL plant at Sasolberg produces 140 000 tons per year of methanol as a highly marketable co-product of the SASOL wax division. During the production of waxes and methanol, methane is reformed to synthesis gas in autothermal reformers.

The autothermal reaction is a crafty way of reacting the methane in natural gas to produce synthesis gas by combining two reactions, one which produces heat with another which requires heat. The first reaction, which requires heat, involves the reaction of methane with water to produce carbon monoxide and hydrogen gas.

CH4 + H2O ->CO + 3H2

The second reaction, which generates heat, involves the reaction of a certain amount of oxygen with methane to produce carbon monoxide and hydrogen.

2CH4+ O2 -> 2CO + 4H2

In the SASOL process, most of this synthesis gas is taken to other reactors to produce products ranging from waxes to fuels. A small percentage is diverted to the synthesis of alcohols such as methanol at SASOL solvents.

Various catalysts are used to react carbon monoxide with hydrogen to produce methanol. The basic reaction is as follows:

CO + 2H2 -> CH3OH

The methanol produced is of high purity and is used by most small and large biodiesel producers in South Africa. To produce biodiesel, approximately 200ml of methanol are required to produce 1 liter of biodiesel - hence the South African demand for methanol stands to increase quite dramatically in the next few years as more environmentally friendly fuel targets are reached.

 

June 2007