What is Gas to Liquids?

The conversion of natural gas into liquid fuels is an attractive option to commercialise abundant gas reserves. Gas to Liquids (GTL), with virtually unlimited markets, offers a new way to unlock remote gas reserves, complementary to other traditional technologies such as Liquefied Natural Gas (LNG) and pipelines.

GTL conversion is an umbrella term for a group of technologies that can create liquid synthetic fuels from a variety of feedstocks.

View video: Shell's Gas to Liquids State of the Art Technology.

The basic technology was developed in Germany in the 1920s, and is known as the Fischer-Tropsch process after its inventors. In essence it uses catalytic reactions to synthesise complex hydrocarbons from simpler organic chemicals. This process can create identical liquids from a variety of feedstocks, although the technical challenges are greater for biomass and coal.

There are two main categories of natural gas-based Fischer-Tropsch process technology: the high and the low temperature versions.

Shell is one of several companies that have developed low-temperature Fischer-Tropsch GTL technology. Shell’s proprietary GTL process, also known as Shell Middle Distillate Synthesis - SMDS, uses a much more active and selective catalyst than earlier processes, which enables the production of a range of finely tailored liquid fuels in a fully commercialised system. There are three main stages:

• In the first, natural gas is partially oxidized at high temperature and pressure in the Shell Gasification Process (syngas manufacture step).
• The second stage, Heavy Paraffin Synthesis (Fischer-Tropsch synthesis step), is the heart of the process. Here the gas is converted into liquid hydrocarbons.
• Finally, the Heavy Paraffin Conversion (hydrocracking step) reactor is used to fine-tune the product by selective cracking and fractionation to separate the desired middle distillate products.

The products from Fischer-Tropsch GTL plants includes middle distillates such as GTL Fuel for transport use, naphtha for chemical feedstocks, normal paraffin for detergent feedstocks and lubricant base oils.  In addition, there could also be condensates and LPG production from treating of wellstream gas. Shell GTL products comprise primarily of clean GTL Fuel (gasoil) and naphtha. There is flexibility to vary the proportions of these products, depending on the intensity of the Fischer-Tropsch GTL cracking process and other operating conditions. Specialist products from GTL plants are lower volume streams, such as normal paraffin (detergent feedstock) and lubricant base oils, which are sold into high-value markets of limited size.

Shell has pioneered the development of Gas to Liquids technology and has operated a medium scale GTL plant at Bintulu, Malaysia since 1993, that has current capacity of 14,700 bbl/day. With a decade of operating experience at the Bintulu plant, Shell technologists have the confidence to scale up to a worldscale 140,000 bbl/day GTL plant planned to be operational in Qatar towards the end of the decade.