Gas to liquids is a refinery process to convert natural gas or other gaseous hydrocarbons into longer-chain hydrocarbons such as gasoline or diesel fuel. Methane-rich gases are converted into liquid fuels either via direct conversion or via syngas as an intermediate, for example using the Fischer Tropsch or Mobil processes.
The process has three steps.
Making synthesis gas
In the gasifier at around 2,200-2,650°F (1,400-1,600°C) the methane and oxygen are converted into a mixture of hydrogen and carbon monoxide known as synthesis gas, or syngas.
The reaction produces heat, which is recovered to produce steam for power.
Making liquid waxy hydrocarbons
The synthesis gas enters one of 24 reactors. Each reactor holds a large number of tubes containing a Shell proprietary catalyst. The catalyst serves to speed up the chemical reaction in which the synthesis gas is converted into long-chained waxy hydrocarbons and water.
The catalyst consists of tiny granules, just millimetres long with microscopic holes, containing minute metal particles.
The synthesis process generates a lot of heat, which is also used to produce steam that in turn powers the GTL plant via steam turbines.
All water in the GTL process is purified and reused in the utilities system of the plant to generate steam.
Making GTL (gas to liquids) products
The plant creates a range of products from natural gas that would otherwise be produced from oil.
Using a catalyst, the long hydrocarbon molecules from the GTL reactor are contacted with hydrogen and cut (cracked) into a range of smaller molecules of different length and shape. Distillation separates out the products with different boiling points.
GTL Naphtha is used as a chemical feedstock for plastics manufacture.
GTL Kerosene can be blended with conventional Jet Fuel (up to 50%) for use in aviation – known as GTL Jet Fuel – or used as a home heating fuel.
GTL Normal paraffins are used for making more cost-effective detergents.
GTL Gasoil is a diesel-type fuel that can be blended into the global diesel supply pool.
GTL Base oils are used to make high-quality lubricants.
- Better Control over the final products, means that you produce no by products
- The products are much cleaner than their traditional counterparts
- Reduces dependence on oil
- The capital costs are much higher than normal refinery costs