Hydrogen transfer reactions in solvent augmented coal liquefaction

Samples of Point of Ayr (POA) coal were dissolved in a solvent mixture of either tyre pyrolysis oil (TPO) and hydrogenated anthracene oil (HAO), or hydrogenated tyre pyrolysis oil (HTPO) and HAO. The addition of TPO caused an apparent reduction in percentage dissolution and introduced coking problems even at relatively moderate conditions. Analysis of the coal liquids by isotopic mass balance suggested the values of actual percentage dissolution calculated by ash balance were corrupted by coking of TPO. When a catalyst activated coal, produced by depositing iron sulphide on POA coal, was used with TPO under various hydrogen overpressures, coking was reduced, with dissolution increasing with increasing hydrogen overpressure. Samples of HTPO were produced by hydrogenating TPO in either a spinning/falling basket autoclave or a trickle bed reactor. The HTPO samples produced from the trickle bed reactor generally were not as effective in dissolving POA coal due to overproduction of saturates; however, the HTPO samples from the autoclave contained a higher proportion of > 450 degrees C boiling point material, indicating underhydrogenation of the TPO feed. Addition of HTPO from the autoclave caused coal dissolution to increase with increasing HTPO content and no coking was observed. Measurements of H-donor contents by a chemical test procedure using sulphur as a hydrogen acceptor, suggested that the increase was probably the result of the introduction of compounds more active towards initiating cleavage of bonds between aromatic centres, rather than differences in the total H-donor contents. (C) 1998 Elsevier Science Ltd. All rights reserved.