Key end products from coal gasification include hydrogen (and synthetic natural gas as a closely related product), electric power, fuels (mainly diesel fuel and gasoline), and fertilizer (which hinges on the large quantities of ammonia produced from gasification). In the context of liquid fuels, methanol can be added as an end product; in some locations (China in particular) methanol is a heavily-used fuel blending stock and feedstock for methyl tert-butyl ether (MTBE) manufacture and commands a large market. At the same time, methanol and ammonia are important not only as fuel/fuel additive/feedstock for gasoline production and fertilizer feedstock, respectively, but they are important as key building blocks for further chemical synthesis; many such chemicals are high-value products and gasification provides the option of using relatively inexpensive coal to produce them.
Historically, producing chemicals from coal through gasification has been used since the 1950s and, as such, has already carved out a share of the chemicals market. According to the Gasification & Syngas Technologies Council's (GSTC) Worldwide Syngas Database, a survey of current and planned gasifiers, from 2004 to 2007 chemical production increased its gasification product share from 37% to 45%. From 2008 to 2010, 22% of new gasifier additions were to be for chemical production. In October 2014, summary statistics of the GSTC Worldwide Syngas Database clearly illustrate the predominance of operating, under construction and planned gasification capacity for chemicals production over fuels and electricity end uses, as shown in Figure 1. (For more on the markets for other gasification products and in general, see markets in Introduction to Gasification.) It should be noted that a sizeable fraction of the chemicals production as described in the Worldwide Syngas Database includes ammonia and fertilizers, which are discussed in more detail separately.
Because the slate of chemical products that can be made via coal gasification can in general also use feedstocks derived from natural gas and petroleum, the chemical industry tends to use whatever feedstocks are most cost-effective. Therefore, interest in using coal tends to increase for higher oil and natural gas prices and during periods of high global economic growth that may strain oil and gas production. Also, production of chemicals from coal is of much higher interest in countries like South Africa, China, India and the United States where there are abundant coal resources. Judging by the Worldwide Syngas Database and the preponderance of coal to chemicals plants which are located in China, it is readily apparent that the abundance of coal combined with lack of natural gas resources in China is strong inducement for the coal to chemicals industry pursued there (see additional discussion below about the market for chemicals production from coal). In the United States, the best example of the industry is Eastman Chemical Company which has been successfully operating a coal-to-chemicals plant at its Kingsport, Tennessee, site since 1983. Similarly, Sasol has built and operated coal-to-chemicals facilities in South Africa.
To put chemicals production from coal/petcoke into context, refer to Figure 2, which shows the many potential products that can be produced from coal gasification derived syngas. Shown in dark green in the figure, primary chemicals that are produced directly from the syngas include methanol (MeOH), hydrogen(H2) and carbon monoxide (CO), which are the chemical building blocks from which a whole spectrum of derivative chemicals can be manufactured, including olefins, acetic acid, formaldehyde, ammonia, urea and others. As a relevant example, the Eastman Chemical plant uses two primary products of CO and MeOH as intermediate chemicals to make acetic acid via a carbonylation reaction; acetic acid can react with additional MeOH to produce methyl acetate, which after further carbonylation forms the final product of acetic anhydride, a raw material to convert cellulose into cellulose acetate, a component for photographic film and coating materials, fibers and other plastic products. Figure 2 also shows methanol being converted to formaldehyde (about 40% of methanol produced follows this route); formaldehyde is widely used in manufacture of plastics, plywood, paints, explosives, and textiles.
Globally, much of ammonia production goes towards synthesis of fertilizers such as urea and ammonium nitrate, as discussed elsewhere, but Figure 2 shows that ammonia also serves as an intermediate chemical for acrylonitrile, used in manufacture of plastics and synthetic rubber.