Liquefaction reactivity enhancement of coal by mild alkylation and solvent swelling techniques

Utilization of coal pretreatment techniques, including mild alkylation and solvent swelling, has been investigated to determine the effect of these procedures on the reactivity of coal. Alkylation recipes investigated have included both selective (O-methylation, Liotta) and non-selective (Sternberg) techniques, in which the reaction conditions are adjusted to bring about a minimal alkylation extent. The degree of reactivity enhancement has been evaluated under both direct hydroliquefaction and coal/oil co-processing conditions, and at both low and high severity reaction conditions. Pretreatment and liquefaction experiments have been carried out using two coals, Illinois no. 6 hvB and Wyodak subbituminous from the Argonne Premium Coal Collection sample bank. All experiments were conducted in tubing bomb microautoclave reactors utilizing dihydrophenanthrene for the direct hydroliquefaction experiments and Cold Lake resid for co-processing runs. Coal conversion was determined based on THF solubility. Results of these experiments have indicated that alkylation is a beneficial pretreatment step for enhancing the reactivity of coal. The effect is greatest at low severity reaction conditions (350 °C, 5 min), and for the low rank (high oxygen) coal which was selectively O-methylated. Oxygen alkylation was not effective for the high rank (Illinois no. 6 hvB) coal under all reaction conditions studied. Non-selective methylation was found to be ineffective for reactivity enhancement of the low rank coal (Wyodak subbituminous), but effective in the case of high severity co-processing reaction conditions for the high rank coal. Preliminary results on liquefaction of coals pre-swollen in acetone have shown that this procedure is also very effective in terms of promoting additional conversion, with a marked increase found in the yield of hexane solubles for the swollen coals.