ChemInform Abstract: Towards an Organic Chemistry of the Hydrogenation of Coal

Abstract

Coals consist of vitrinite, exinite and fusinite In British carboniferous coals vitrinite and exinite contain aJJcanes, alkyl benzenes, alkyl phenols and alkyl naphthalenes trapped in an organic matrix; alkyl naphthalenes and alkyl phenols being the predominant arorriatics in vitrinites and exinites respectively The vitrinite matrix consists of substituted aromatic nuclei linked through hydroarornatic groups whilst the exinite matrix is aliphatic with aromatic substituents When vitrinite is heated the trapped molecules generate small volumes of fluid within which hydro— gen is transferred so as to break C—C and C—O bonds in the matrix Hydro— aromatic compounds hydrogenate coal more readily than does hydrogen. The chemical reactions are rapid, the rate of pyrolysis is diffusion controlled. Pyrolysis of exinites ruptures the aliphatic matrix and about half of the material volatilises, In the liquefaction of coals the heart of the process is the transfer of hydrogen from a hydroaromatic solvent to the coal matrix, Evidence is adduced that this may be achieved by the continuous, rapid pyrolysis of an intimate mixture of coal with a relatively small quantity of hydroaromatic material, PERSPECTIVEAND AIMS Let us oversimplify. Aromatic chemistry started from Faraday's isolation of benzene from coal tar (Ref. 1) and burgeoned with the development of the coal tar, dyestuff industry. In Europe throughout the first half of the twentieth century, much of chemical engineering and technological organic chemistry continuedto be dorninated.y the carbonisation of coal, Subsequently, and particularly in America, the flowering of the oil industry created an aliphatic chemical engineering emphasising continuous, catalFtic processing, More recently, interest in the properties of living material, in heredity and in fermentation have combined to produce bioengin— eers who, in a very real sense, are inward looking, In terms of tonnage, however, their activities are peripheral, In this lecture I return to coal and I shall try to see to what extent a chemical engineering can be developed from its hydrogenation, Traditionally coal has been hydrogenated to produce substitutes for oil and natural gas. Continued study of the process is based on four postulates, that 1. As Table 1 shows, in terms of energy much of the world lives below the poverty line and demands for energy are therefore certain to increase 2, Reserves of coal permit its exploitation for many decades 3. In much of the world the price of a ton of oil is more than ten times the price of a ton of coal 4. In the beautiful future when we all get our energy from the sun there will still be a need for a cheap feedstock for organic chemicals, F.K.R. Bergius was awarded the Nobel Prize in 1931 for the invention of the high pressure autoclave and its application during the previous twenty years to the hydrogenation of a variety of materials including coal, The association of the extraction and hydrogenation of coal was reported by Pott and Broche in 1933 (Ref. 2). The most dramatic exploitation of these discoveries was tIe production of a petroleum substitute by Germany during the Second World War. TABLE 1. Energy consumption per head of population per year (Tons of coal equivalent) 197