Aromatics coal liquid fuels

Proof of the existence of benzene in the light oil derived from coal tar (8) first established coal tar and coal as chemical raw materials (see Feedstocks, coal chemicals). Soon thereafter the separation of coal-tar light oil into substantially pure fractions produced a number of the aromatic components now known to be present in significant quantities in petroleum-derived liquid fuels. Indeed, these separation procedures were for the recovery of benzene—toluene—xylene (BTX) and related substances, ie, benzol or motor benzol, from coke-oven operations (8) (see BTX PROCESSING). 

Comparison of Fuels. The separation data of Table II show immediately some gross differences and similarities among the various fuels analyzed. Both coal liquids have a considerable amount of low boiling material which is made up of saturates and aromatics in about equal... 

Synthetic liquid fuels derived from coal and shale will differ in some characteristics from conventional fuels derived from petroleum. For example, liquid synfuels are expected to contain significantly higher levels of aromatic hydrocarbons, especially for coal-derived fuels, and higher levels of bound nitrogen. These differences can affect the combustion system accepting such fuels in important ways. In continuous combustors, i.e. gas turbines, the increased aromatics content of coal-derived fuels is expected to promote the formation of soot which, in turn, will increase radiation to the combustor liner, raise liner temperature, and possibly result in shortened service life. Deposit formation and the emission of smoke are other potential effects which are cause for concern. Higher nitrogen levels in synfuels are expected to show up as increased emissions of N0X (NO+NO2) An earlier paper presented results of an experimental study on the effect of aromatics and combustor... 

The conversion of methanol into olefins is similar to the commercially proven methanol to gasoline (MTG) which was commercialised using natural gas as the feedstock in New Zealand. The variant generally uses similar catalysts to produce light olefins only, rather than the iso-paraffins and aromatics of the MTG process. This leads to the prospect of coal or gas conversion into resins (solids). These high value products may be easier to transport and sell than liquid fuels Figure 11.6 illustrates the basic unit operations for the process. 

Improvement of the atmosphere continues to be of great concern. The continual search for fossil fuel resources can lead to the exploitation of coal, shale, and secondary and tertiary oil recovery schemes. For instance, the industrialization of China, with its substantial resource of sulfur coals, requires consideration of the effect of sulfur oxide emissions. Indeed, the sulfur problem may be the key in the more rapid development of coal usage worldwide. Furthermore, the fraction of aromatic compounds in liquid fuels derived from such natural sources or synthetically developed is found to be large, so that, in general, such fuels have serious sooting characteristics. 

A recent paper by EIA (Energy Information Administration) within DOE (U.S. Department of Energy) indicates that CTL (coal-to-liquids) fuels, under the High Price B Case, could become a viable supplement to the petroleum liquids supply in U.S. by 2010 (1). CTL fuels made from the indirect liquefaction technology are free of sulfur and aromatics, and also have clean combustion properties. These fuels are compatible with the petroleum-based ultra-clean transportation fuels mandated by EPA (U.S. Environmental Protection Agency) for 2006 and beyond to help meet the new stringent specifications for vehicle emissions. The CTL fuels can be used either as a blending component or as neat fuel. 

The relationships among hydroconversion of the coal liquids, sulfur distribution, and other important fuel properties still need to be evaluated. They are part of the S W-Gulf development program now under study. This paper summarizes some of the preliminary investigations carried out as a prelude to the development program. Data on reactions by which aromatic molecules are converted to gas are reviewed and correlated consideration is also given to the formation of aromatic molecules during pyrolysis of hydrocarbons. 

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