The FT-i.r. and 'H n.m.r. spectroscopic analyses of oils or maltenes from a Spanish lignite (Utrillas, Teruel), are reported. These oils were obtained by depolymerization with alkyl aromatic ethers (anisole, 3-methyl anisole and1,3-dimethoxybenzene) catalyzed by Lewis acids ZnCI,, AICI,, SbCI, and BF, (as, boron trifluoride etherate), at atmospheric pressure and temperatures <220X. Bands due to aromatic ethers in the i.r. and n.m.r. spectra of the oils obtained by depolymerization indicate solvent incorporation. Oils obtained by direct lignite extraction showed 25% aromatic H and some H, (%3%) without OH groups. These appeared in some oils obtained by depolymerization with AICI, and were due to secondary reactions with the aromatic extract. Oils derived from processes with good yields showed increases in aromaticity. The extent of substitution of aromatic rings in oils obtained by depolymerization was less than for oils directly extracted. All the oils studied show a low degree of condensation. (Keywords: lignite; coal-derived oils; instrumental methods of analysis) Catalyscd depolymerization is a liquefaction process with pressure and under mild temperatures (0.1 MPa, 220°C).
The process causes breakage of the coal molecule and later alkylation of an aromatic substrate by the active fragments generated, thus increasing the proportion of low molecular weight compounds. This treatment increases the solubility of coal in a variety of organic solvents1-3 and yields liquid products (maltenes or oils and asphaltenes), which closely resemble parts of original molecule. This is because the reaction conditions used degrade the coal by breaking existing bonds without altering its structure.
Combined i.r. and 'H n.m.r. spectroscopy provide much information about the oil structure. 1.r. spectroscopy provides information on the mix of functional groups, and 'H n.m.r. allows a calculation, using certain assumptions, such structural parameters as aromaticity (f,), degree of substitution (a) and degree of condensation (H,JC,J for such mixtures4s5.
These parameters have been widely used. Brooks and Stevens6 successfully applied the Brown-Ladner equations to fractions of a low-temperature tar and found that ~50% of each fraction was predominantly aromatic. Oelert' used these formulae, with parameters obtained by i.r. spectroscopy, and applied them to shock-heating products of coal and tar fractions*. De Ruiter and Tschamler' have also applied a combined structural scheme to coal extracts. Friedel and Retcofsky" performed the same analysis using pyridine and carbon disulphide as extraction solvents. More recently, the present authors have conducted an in-depth investigation into the use of the Brown-Ladner equations in coal research". This method has also been used to determine the structural units of hydrogenation products" from oils and asphaltenes and of products from lignite solubilization' 3.
Maltenes from a variety of solubilizations by depolymerization I4 have been studied. These oils were 0016-2361/85/0303164,5%3.00 @ 1985 Butterworth & Co. (Publishers) Ltd