Energy & Fuels 1989, 3, 268-272
268
Investigation of Liquefactioi . Mechanisms with Molecular Pro 3es+,S B. C. Bockrath,* K. T. Schroeder, and M. R. Smith Pittsburgh Energy Technology Center, U.S. Department of Energy, Pittsburgh, Pennsylvania 15236 Received October 19, 1988. Revised Manuscript Received December 27, 1988
Coal conversion in the presence of a petroleum resid solvent has been investigated by using 1,3dimethylnaphthalene and decalin as mechanistic probes. Total free radical activity, as measured by the decalin isomerization, increases with added coal or resid. In the case of an Illinois No. 6 coal and a Maya atmospheric tower bottom, the total radical activity of some mixtures is greater than expected from a simple sum of effects. Hydrogen atom activity, as measured by the demethylation of dimethylnaphthalene, also increases with added coal or resid. Of the four fossil-derived materials studied, Illinois No. 6 coal produces the most selective hydrogen atom donors.
Introduction In the investigation of mechanisms, it is extremely valuable to know the nature of the chemical environment of the reaction in as much detail as possible. In the case of liquefaction mechanisms, our knowledge is limited because the extreme conditions of temperature and pressure restrict the use of sensitive instrumental probes. One strategy to circumvent this problem is to use chemical probes that may be added to reaction mixtures and then recovered after completion of the liquefaction experiment. Analysis of the reaction products might then be used to deduce something about the nature of the reaction snvironment as witnessed by these “reporter” molecules. In this study, the mechanisms of coal liquefaction have been investigated by using 1,3-dimethylnaphthalene and decalin as molecular probes. These two pure compounds have been added to various mixtures composed of a coal, a liquefaction solvent, and a high molecular weight alkane. In all cases, the amount of the probes added to the reaction mixture of coal, solvent, and alkane is small enough that the probes themselves are unlikely to perturb the reaction chemistry to a measurable degree. The mixtures were heated in small autoclaves to liquefaction conditions and the products recovered for analysis by quantitative gas chromatography. From the analysis of the products from the added probes, it is possible to draw conclusions about the relative amount and kind of intermediates that were created by the liquefaction conditions. For example, cis-decalin is transformed to an equilibrium mixture of the cis and trans isomers by the abstraction of hydrogen from either tertiary position by a free radical.’P2 The extent to which the equilibrium has gone to completion is then a measure of the exposure of decalin to radicals of sufficient reactivity to abstract the tertiary hydrogen. In the case of 1,3-dimethylnaphthalene, it is the monomethyl products that are of particular interest. Dealkylation of aromatic compounds is known to proceed under liquefaction conditions by the attack of free ‘Preliminary communication in: Prepr. Pup.-Am. Chem. SOC., 325-332. Reference in this report to any specific commercial product, process, or service is to facilitate understanding and does not necessarily imply its endorsement or favoring by the U.S. Department of Energy. f Presented at the Symposium on Coal Liquefaction, 196th National Meeting of the American Chemical Society, Los Angeles, CA, Sept 25-30, 1988.
Diu.Fuel C h e m . 1988, 33(3),
Table I. Analyses of Coal and Residua Illinois Wyodak Maya ATB No. 6 Proximate Analysis (wt % ) (As Received) moisture volatile matter fixed carbon ash
6.5 32.6 38.1 22.9
7.8 41.8 40.2 10.2
North Slope VTB
