Coal has been the feedstock used originally in the industrial production of syngas. It is still widely used in South Africa and China for the production of ammonia and methanol, and was expected for years to become the preferred route for large scale syn-gas generation in the United States, because of existing huge domestic coal reserves. Syn-gas is produced from coal by gasification, a process combining partial oxidation and steam treatment, according to the following reactions:
Different coal gasification processes have been developed and commercialized over the years. The selection of a particular design depends greatly on the characteristics of the coal used: lignite, sub-bituminous, hard coal, graphite, water content, ash content, levels of impurities, etc. Due to the low H/C ratio of coal, the obtained syn-gas is rich in carbon oxides (CO and CO2) and deficient in hydrogen.
Before being sent to the methanol unit, the syn-gas must thus be subject to the WGS reaction to enhance the amount of hydrogen formed. Some of the CO2 produced must also be separated and any H2S removed to avoid poisoning of the very sensitive methanol synthesis catalyst. Whilst sulfur must be removed to protect the catalyst, some of the cost of this operation may be offset by its commercialization for the preparation of chemicals such as sulfuric acid.
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