312
Anal. Cham. 1986, 58, 312-319
Integrated Separation Scheme for Coal-Derived Liquids Using Ion-Exchange and Adsorption Chromatography Michael
G. Strachan’ a n d R. B. Johns*
Department of Organic Chemistry, University of Melbourne, Parkville, 3052, Victoria, Australia
A separatlon scheme for coal-derived liquids has been developed that separates by functlonallty Into discrete compound classes using Ion-exchange resins; neutrals are further subdlvlded Into fractions differing In polarlty, structure, and molecular welght by adsorption chromatography. Sufflclent material can be separated to allow further characterlzatlon at both gross structural and molecular levels. I t gives excellent overall reproduclblllty (f4% ) and recovery (>97 % ). Removal of acldlc and base species prior to recovery of the llquefactlon solvent by dlstlllatlon Is a maJor advantage of the method because It leads to a reduction both In the loss of lower bolllng components and In the potential thermal alteratlsn of the sample. The selectlvlty and dlscrlmlnatlon Of the procedure are demonstrated for a Vlctorlan brown coal (Loy Yang field) liquefaction product as shown by spectroscopic and chemical analyses of Its malor fractions, The use of this method as a chemical probe can facllltate lnvestlgatlon of liquefaction rnechanlsms by enabllng a ready selection for analysis of components varylng according to a choice of parameters encornpasslng functlonallty, polarlty, and structure.
A number of schemes (1-20) for the chromatographic separation of coal-derivedliquids (CDL) have been proposed. The methods can be assigned broadly to two categories: (1)those that opt for rapidity of analysis and (2) those for detailed compound class separations. The former usually use either GPC (14-18) or adsorption chromatography (3-12) and the latter ion-exchange chromatography (1,2,13), with or without more extensive adsorption chromatography (3-12). The selection of a particular procedure is, therefore, a function of the type and nature of the information sought. The majority of CDL separation schemes operates on the product after the removal of the liquefaction solvent, which is, typically, tetralin, g,lO-dihydrophenanthrene,or in more complex cases, recycle solvent. These solvents are normally removed by distillation a t atmospheric pressure; such a step often requires still temperatures in excess of 250 O C and even higher if quantitative solvent recovery is attempted. This leads to a 2-fold problem: (1)the loss of CDL boiling below these temperatures (this “light oil”, which contains low molecular weight coal derived material is, commonly, regarded as recovered solvent) and (2) the possibility of thermal alteration of the sample, especially if the CDL contains a high proportion of polar and/or reactive components. Hence, the total oil (TO) may contain high molecular weight material wrongly assigned as a liquefaction product rather than as a procedural artifact. A distortion of the T O composition may result and be unrecognized in the assessment of a particular liquefaction experiment. Recently, Philip and Anthony (21) have used a GPC-HPLC fractionation procedure to avoid these problems. Their method concentrates the tetralin/naphthalene solvent into one Present address: Petroleum Geochemistry Group, School of Applied Chemistry, W.A.I.T., Kent St., Bentley, 6102, W.A., Australia.
fraction, while producing four other fractions, of differing functionality. The limitation of this approach is that, being on an analytical scale, it limits the methods of analysis that may be applied in further characterization of the products. This paper reports a separation procedure that utilizes various nonaqueous ion-exchange resins (in a particular sequence) combined with silica and alumina adsorption flash chromatography that overcomes or minimizes the problems associated with a liquefaction solvent distillation step, while giving fractions based on chemical functionality differences. Another advantage of the method is that the fractions obtained are of a large enough scale that they can be subjected to further gross structural, spectroscopic, and analytical characterization if required. Because the scheme gives discrete chemical class separations, a more detailed insight into the composition of the CDL and hence into the mechanisms of the liquefaction reactions can more readily be achieved. The selectivity and discrimination achieved in the fractionation scheme is exemplified by describing the analysis of a Loy Yang Victorian brown coalderived liquid. EXPERIMENTAL SECTION Coal-Derived Liquid Samples and Column Loading. The CDL was produced by the uncatalyzed hydrogenative liquefaction in tetralin of a Victorian brown coal from the Loy Yang field (bore 1277) and was a medium light lithotype: C (65.7%),H (4.5%), 0 (28.0%),N (0.8%), and ash (
