The processes for production of specific chemicals from coal are typically proprietary systems using specialized process systems. In the following discussion, some of the processes for important chemicals such as formaldehyde, olefins, etc. are presented. Methanol (MeOH) is of course another important primary chemical made from coal syngas; however, it is also a liquid fuel in its own right particularly in certain markets (China). See detailed discussion of methanol synthesis and use under discussion of liquid fuels on the main portal in Gasifipedia. Carbon Monoxide Figure 2 shows a simplified cryogenic partial condensation CO/H2 purification scheme. Syngas feed is first pre-treated with molecular sieves to remove carbon dioxide (CO2) and water before being chilled to approximately -300°F in the cold box by heat exchange against exit gases. Refrigeration is supplied by the cold product streams and by flashing the final CO liquid product stream exiting the stripping tower. Separation of CO/H2 and purge gas is accomplished by a series of condensation/depressurization steps, of which, depending on the operating pressure cycle, the overall heat exchange/recovery and refrigeration streams may vary and can become very complex. Figure 2 shows a simple configuration of a condensation process. It includes a molecular sieve adsorber station, a cold box containing the plate fin heat exchangers to pre-cool the feed syngas against the product streams. Acetic Acid and Derivatives
The rhodium catalyzed process is highly selective (>98% acetic acid) and operates under mild reaction pressure (~ 500 psia) in a liquid phase reactor. Technology licensors include Monsanto/BP, Celanese, BP, and Chiyoda, the latter three vendors represent an improved version of the original Monsanto/BP technology. Figure 3 shows a simplified block flow diagram (BFD) of the Eastman Chemicals' coal-to-chemicals facility producing MeOH from coal derived syngas, followed by converting MeOH into acetic acid and its derivatives of methyl acetate and acetic anhydride. With the Eastman facility, acetic acid is reacted with MeOH to form methyl acetate (CH3COOCH3), which is further reacted with CO to produce acetic anhydride ([CH3CO]2O). The catalytic reactions for these additional derivatives are shown in Figure 4. Formaldehyde
Equilibrium conversion and potential side reactions are highly temperature dependent. The overall reaction temperature is controlled by the quantity of air (oxygen) used, and the addition of inerts, such as water and/or nitrogen. Figure 5 shows a typical flow scheme of a MeOH oxidative dehydrogenation process producing commercial grade formaldehyde. A mixture of methanol and water is mixed with air and recycled gas, and the total feed mixture is vaporized by heat exchange against hot reactor effluent. The vaporized feed mixture is fed into the catalytic reactor to form formaldehyde. Excess reaction heat is removed by generating steam. The reactor effluent, after cooled by heat exchanging with incoming feed, is scrubbed with water in the absorber to remove the formaldehyde product as a 55% solution. Water can be added to produce commercial grade formaldehyde at 37% concentration. A portion of the product gas leaving the top of the absorber is recycled, and the remainder is incinerated. Typical overall formaldehyde yield is in the range of 92 to 95%. Olefins Figure 6 shows a simplified flow diagram of UOP/HYDRO's MTO process. Other technology licensers include ExxonMobil and Lurgi, using different types of catalyst systems and process know-how. Per Figure 6, fresh MeOH feed is combined with recycled water and fed to a fluidized-bed catalytic reactor, equipped with a catalyst regeneration and recycle reactor as shown. The reactor operates at typically 350°C and at 30 psig. With UOP/HYDRO’s proprietary catalyst system, claimed methanol conversion is quite high, and the process is 80% selective for ethylene and propylene. The produced ethylene/propylene ratio can be altered from 1.5 to 0.6, depending on operation conditions.
Chemicals
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