Synthetic Fuels
Liquid transportation hydrocarbon fuels and various other chemical products can be produced from syngas via the well-known and established catalytic chemical process called Fischer-Tropsch (FT) synthesis, named after the German inventors, Franz Fischer and Hans Tropsch in the 1920s. The FT process requires a syngas with a H2/CO ratio of 2:1. The syngas is converted into hydrocarbons of various molecular weights according to the following equation:
(2n+1) H2 + nCO → Cn H(2n+2) + nH2O
where n is an integer. For the production of liquid fuels, the FT process conditions are chosen to maximize the formation of higher molecular weight liquid hydrocarbon products. In the FT reactor, the primary components include waxes, hydrocarbon condensate, tail gas, and reaction water. The waxes are further processed in an upgrading unit by hydrocracking with H2; this chemically splits the waxes into lower molecular weight liquid hydrocarbons. A H2 recovery unit extracts the required quantity of H2 needed from the tail gas or from the inlet syngas stream. The reaction products, along with the products from the upgrading section, are fractionated into the final products of diesel, naphtha, and other light liquids, depending on the desired product or mix of products.
In some countries, natural gas is a very expensive energy source, especially when it is imported in the form of liquefied natural gas (LNG). When relatively inexpensive feedstocks are available, such as petroleum coke, they can be converted to syngas via gasification. The syngas, which is a mixture of CO and H2, is then cleaned to remove contaminants and sulfur compounds (which would poison the catalyst), and then converted to methane (CH4) via the catalytic methanation process.
The Substitute Natural Gas (SNG) can be produced and treated so that it meets the strict requirements of natural gas pipelines. This requires the use of syngas cleanup systems and an AGR system for sulfur and CO2 removal. Below is an example of an SNG process.
