Synthesis from coal gasification

Synthesis gas is obtained either from methane reforming or from coal gasification (see Coal conversion processes). Telescoping the methanol carbonylation into an esterification scheme furnishes methyl acetate directly. Thermal decomposition of methyl acetate yields carbon and acetic anhydride,... 

Ammonia from coal gasification has been used for fertilizer production at Sasol since the beginning of operations in 1955. In 1964 a dedicated coal-based ammonia synthesis plant was brought on stream. This plant has now been deactivated, and is being replaced with a new faciUty with three times the production capacity. Nitric acid is produced by oxidation and is converted with additional ammonia into ammonium nitrate fertilizers. The products are marketed either as a Hquid or in a soHd form known as Limestone Ammonium Nitrate. Also, two types of explosives are produced from ammonium nitrate. The first is a mixture of fuel oil and porous ammonium nitrate granules. The second type is produced by emulsifying small droplets of ammonium nitrate solution in oil. 

Hydrocarbons from Synthesis Gas and Methanol. Two very important catalytic processes in which hydrocarbons are formed from synthesis gas are the Sasol Eischer-Tropsch process, in which carbon monoxide and hydrogen obtained from coal gasification are converted to gasoline and other products over an iron catalyst, and the Mobil MTG process, which converts methanol to gasoline range hydrocarbons using ZSM-5-type 2eohte catalysts. 

Conventional Transportation Fuels. Synthesis gas produced from coal gasification or from natural gas by partial oxidation or steam reforming can be converted into a variety of transportation fuels, such as gasoline, aviation turbine fuel (see Aviation and other gas turbine fuels), and diesel fuel. A widely known process used for this appHcation is the Eischer-Tropsch process which converts synthesis gas into largely aHphatic hydrocarbons over an iron or cobalt catalyst. The process was operated successfully in Germany during World War II and is being used commercially at the Sasol plants in South Africa. 

Synthesis gas consists of a nonhydrocarhon mixture (H2,CO) ohtain-ahle from more than one source. It is included in this chapter and is further noted in Chapter 5 in relation to methane as a major feedstock for this mixture. This chapter discusses the use of synthesis gas obtained from coal gasification and from different petroleum sources for producing gaseous as well as liquid hydrocarbons (Fischer Tropsch synthesis). 

The purge gas from the methanol synthesis unit contains mainly methane. Depending upon the size of the plant, this stream may be reformed to supplement the synthesis gas produced from coal gasification. 

The SMDS process, as shown in Figure 12.15, produces high-quality diesel fuel from natural gas. Although synthesis gas generated from coal gasification would, presumably, be equally suitable, it is a process being considered in many GTL processes in oil production. 

Derivation (1) Air oxidation of ethylene followed by hydration of the ethylene oxide formed (2) ace-toxylation (3) from carbon monoxide and hydrogen (synthesis gas) from coal gasification (4) Oxirane process. 

Although copper-based catalysts have long been known to have good WGS activities, sensitivity of those catalysts to poisons that were present in the coal-derived gas precluded them from being employed industrially. It is only due to a massive change from coal gasification to hydrocarbon steam reforming which produces much purer synthesis gas, that copper-based catalysts entered the scene of WGS processes. Since... 

Table 11-1. Composition op Crude Synthesis Gas from Coal Gasification with Steam and Oxygen...

Tjeed gases, CO and H2, for the Fischer-Tropsch synthesis obtained from coal gasification contain sulfur compounds that have been acknowledged as catalyst poisons. Since the early work of Fischer and Tropsch (I), the need for scrupulous removal of sulfur compounds from reactant gas streams has been stressed. Hence to date, little work has... 

The steam boiler plants are preferably fired with sulfur-fiee or low-sulfur fuels from the plant itself, for instance purge gas from methanol synthesis or flash gas from coal gasification and gas scrubbers. Wherever this heat supply is insufficient, it may be supplemented by firing natural gas, if available, or coal. The latter often requires complex desulfurization systems so that in certain cases even the production of low-sulfur fuel gas by coal gasification with air and subsequent desulfurization of the gas may be considered as an alternative to coal-fired systems. 

Ammonia is the basis for industrial fertilizer production and, therefore, the most important bulk chemical in the world. About one-quarter comes from coal gasification [1]. It is produced by the Haber-Bosch synthesis, which takes place at 90-180 bar and 400-530°C using the following reaction [28] ... 

Figure 13-18. Flow diagram for the production of synthesis gas for methanol or synthetic natural gas (SNG) from coal gasification product gas. Udengaardand Berzins, 1985. Reproduced with permission from Acid and Sour Gas Treating Processes, edited by S. A. Newman, copyright 1985, Gulf Publishing Company...

The Selexol process has found a very wide range of applications. It was originally used to remove CO2 from an ammonia plant in Nebraska, followed soon after by H2S and CO2 removal from natural gas in the U.S. and in Europe. Other applications include desulfurization and CO2 removal from synthesis gas derived from the partial oxidation of heavy petroleum stocks and from coal gasification. Natural gas treating applications include several, where in addition to production of pipeline specification gas, a relatively pure stream of carbon dioxide is produced for reinjection into oil formations, so-called enhanced oil recovery or EOR. A relatively new use for the process dating back to 1979 is the purification of landfill gas drawn from the biological degradation of municipal waste in sanitary landfills. This application is characterized by the occurrence of chlorinated and aromatic hydrocarbons as impurities in the landfill gas. 

Complete and simultaneous removal of CO2, H2S and organic sulfur, NH3, hydrogen cyanide, gumformers, higher hydrocarbons and other impurities from coal gasification crude gas to produce gas for synthesis or pipeline transmission. ... 

The gasification plant is equipped with two Texaco gasifiers, each capable of producing all of the synthesis gas required for operation of the complex. Eastman chose an entrained-bed gasification process for the Chemicals from Coal project because of three attractive features. The product gas composition using locally available coal is particularly suitable for production of the desired chemicals. Also, the process has excellent environmental performance and generates no Hquids or tars. EinaHy, the process can be operated at the elevated pressure required for the downstream chemical plants. 

Partial oxidation of heavy Hquid hydrocarbons requires somewhat simpler environmental controls. The principal source of particulates is carbon, or soot, formed by the high temperature of the oxidation step. The soot is scmbbed from the raw synthesis gas and either recycled back to the gasifier, or recovered as soHd peUetized fuel. Sulfur and condensate treatment is similar in principle to that required for coal gasification, although the amounts of potential poUutants generated are usually less. 

---