Calorimetric study of quinoline interaction with o-phenylphenol and coal-derived asphaltenes

Abstract

A calorimetric method is presented for the simultaneous evaluation of equilibrium constant, K, and molar enthalpy, ΔH o , for 1:1 adduct formation of quinoline (Qu) with coal-derived asphaltenes in solvent benzene. Asphaltene ( A), together with its acid/neutral ( AA), and base ( BA) fractions used in this study were isolated from a centrifuged liquid product ( CLP) sample prepared from Kentucky hvAb coal at 27.6 MPa hydrogen pressure and 723 K, with reactor charged with glass pellets. The computed K values for the interaction of Qu and A, AA, and BA are, within experimental error, the same, 18–19 dm 3 mol −1; whereas there is large variation in the ΔH o values (Qu- A, −16.92 ± 0.21 kJ mol −1; Qu- AA, −14.74 ± 0.04 kJ mol −1; Qu- BA, −11.76 ± 0.04 kJ mol −1). For Qu- A and Qu- AA systems, hydrogen-bonding occurs between the aromatic phenols (present in A and AA) and quinoline, which is a strong hydrogen-bond acceptor, in addition to other molecular interactions. The hydrogen-bonding interaction in the Qu- BA system is lacking because both Qu and BA are hydrogen-bond acceptors. Since asphaltenes are really mixtures, we have taken a pure compound, o-phenyl-phenol (OPP), and obtained thermodynamic parameters for its interaction with quinoline (Qu). OPP was chosen to represent the aromatic phenols found in coal liquefaction products. Results obtained are: K (dm 3 mol −1): 10.4 (in CS 2), 6.2 (in CCl 4); ΔH o (kJ mol −1): −31.40 ( in CS 2) −27.80 ( in CCl 4). The solvent effect is apparent. By using o-phenylanisole as a model non-hydrogen-bonding donor (Dietz Blaha, Li J. Chem. Thermodynamics, 1977, 9, 783), the relative contribution of H-bond to π-interactions in the total enthalpy change for the OPP—Qu system is estimated to be 3:1.