Methane from coal conversion

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,... 

Another important use of methane is its conversion into synthesis gas (or syn-gas), a mixture of hydrogen gas and carbon monoxide as shown in Figure 17.1. Syn-gas can also be derived from coal. When this occurs, it is called water gas. Interestingly, the reaction of methane giving carbon monoxide and hydrogen can be reversed so that methane can be produced from coal through this route. 

The current two-step industrial route for the synthesis of methanol, from coal or methane to synthesis gas and then from synthesis gas to methanol, has certain drawbacks. The economic viability of the whole process depends on the first step, which is highly endothermic. Thus a substantial amount of the carbon source is burned to provide the heat for the reaction. It would be highly desirable, therefore, to replace this technology with a technically simpler, single-step process. This could be the direct partial oxidation of methane to methanol, allowing an excellent way to utilize the vast natural-gas resources. Although various catalysts, some with reasonable selectivity, have been found to catalyze this reaction (see Sections 9.1.1 and 9.6.1), the very low methane conversion does not make this process economically feasible at present. 

Product distribution data (Table V) obtained in the hydrocracking of coal, coal oil, anthracene and phenanthrene over a physically mixed NIS-H-zeolon catalyst indicated similarities and differences between the products of coal and coal oil on the one hand and anthracene and phenanthrene on the other hand. There were differences in the conversions which varied in the order coal> anthracene>phenanthrene coal oil. The yield of alkylbenzenes also varied in the order anthracene >phenanthrene>coal oil >coal under the conditions used. The alkylbenzenes and C -C hydrocarbon products from anthracene were similar to the products of phenanthrene. The most predominant component of alkylbenzenes was toluene and xylenes were produced in very small quantities. Methane was the most and butanes the least predominant components of the gaseous product. The products of coal and coal oil were also found to be similar. The most predominant components of alkylbenzenes and gaseous product were benzene and propane respectively. The data also indicated distinct differences between products of coal origin and pure aromatic hydrocarbons. The alkyl-benzene products of coal and coal oil contained more benzene and xylenes and less toluene, ethylbenzene and higher benzenes when compared to the products from anthracene and phenanthrene. The gaseous products of coal and coal oil contained more propane and butanes and less methane and ethane when compared to the products of anthracene and phenanthrene. The differences in the hydrocracked products were obviously due to the differences in the nature of reactants. Coal and coal oil contain hydroaromatic, naphthenic, heterocyclic and aliphatic structures, in addition to polynuclear aromatic structures. Hydrocracking under severe conditions yielded more BTX as shown in Table VI. The yields of BTX obtained from coal, coal oil, anthracene and phenanthrene were respectively 18.5, 25.5, 36.0, and 32.5 percent. Benzene was the most... 

The most important route for the conversion of methane to petrochemicals is via either hydrogen or a mixture of hydrogen and carbon monoxide. The latter material is known as synthesis gas. The manufacture of carbon monoxide-hydrogen mixtures from coal was first established industrially by the well-known water-gas reaction ... 

Synthesis of DME from coal-bed methane consists of three reactions, namely, methane reforming, methanol synthesis, and methanol dehydration. Water produced by the methanol dehydration reaction participates in the water-gas shift reaction, which in turn produces hydrogen that can be utilized for methanol synthesis. In case the CO shift conversion reaction is slow, DME is synthesized by the methanol synthesis reaction and the methanol dehydration reaction. 

A high heating value product gas ( 850 Btu/scf, C02-free) can be produced directly from coal-steam reactions using a single-stage reactor in conjunction with a multiple catalyst. The conversion ( 60%) is carried out at 2 atm and 650°C. The multiple catalyst consists of potassium carbonate and a nickel methanation catalyst. The influence of each catalyst on the coal-steam reactions is combined in the integrated system. Potassium carbonate increases the total gas production and rate while the nickel catalyst hydrocracks the evolved liquids and methanates the carbon oxides. 

Tn synthesizing low sulfur fuels from coal the Stone Webster process A uses the step-by-step addition of hydrogen to coal under conditions which minimize coke production. The first step involves the conversion of solid coal to a liquid by mild hydrocracking in the presence of a recycle solvent. In the next step these liquids react further with hydrogen under more severe conditions to produce methane, ethane, and aromatics. 

The use of an MHTGR was studied for methanol synthesis from coal without CO2 production. Besides coal and steam, the process requires a supplemental hydrocarbon feed or ideally hydrogen, also methane could be used, plus a non-combustion source of high-temperature heat which is ideally an HTGR. Based on coal with 60 % carbon content and a conversion rate of 80 %, a balance of the process was predicted such that with an input of 162 t/h of coal and 69.4 t/h of methane and an electric power of 300 MW yields 347 tb of methanol [64]. 

FIGURE 17.12 Routes to coal conversion. BTU refers to British thermal units, a measure of the heat energy that can be obtained from a fuel. Methanation means synthesis of CH4 gas. Hydrogenation and hydrotreating refer to reaction with elemental Hj gas. 

In order to produce methanol the catalyst should only dissociate the hydrogen but leave the carbon monoxide intact. Metals such as copper (in practice promoted with ZnO) and palladium as well as several alloys based on noble group VIII metals fulfill these requirements. Iron, cobalt, nickel, and ruthenium, on the other hand, are active for the production of hydrocarbons, because in contrast to copper, these metals easily dissociate CO. Nickel is a selective catalyst for methane formation. Carbidic carbon formed on the surface of the catalyst is hydrogenated to methane. The oxygen atoms from dissociated CO react with CO to CO2 or with H-atoms to water. The conversion of CO and H2 to higher hydrocarbons (on Fe, Co, and Ru) is called the Fischer-Tropsch reaction. The Fischer-Tropsch process provides a way to produce liquid fuels from coal or natural gas. 

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