Liquefaction of Victorian Brown Coal with Continuous Reactors (IV)
Effect of Preheating Conditions on Liquefaction Yields
1998 Volume 77 Issue 2 Pages 139-147
Details
1998 Volume 77 Issue 2 Pages 139-147
The effect of preheating conditions on the liquefaction reaction of Victorian brown coal (Yallourn) was investigated using a process development unit (PDU) with three stirred tank reactors and three preheaters connected in series. Four kinds of solvents (RS, RS +CLB, RS+HDAO and RS+CLB +HDAO) were used for liquefaction to examine the relationship between the solvent properties and the effect of the preheating conditions. RS, CLB, HDAO were the recycled solvent fraction (b. p.180-420°C), heavy liquefaction product derived from the brown coal (coal liquid bot-tom, b. p.>420°C) and coal liquid product further hydrogenated over Ni-Mo catalyst (b. p.<250°C), respectively. For all experiments, the liquefaction was carried out in the presence of iron-sulfur catalyst (Fe2O3, S/Fe atomic ratio 1.2) under the conditions of temperature 450°C and pressure 14.7 MPa.
When the feed slurry was preheated up to 410°C for- 2 min. with hydrogen gas of 10 wt. % on daf coal, the distillate yield (b.p.<420°C) decreased 5-13 wt.% on daf coal for all kinds of the solvent in comparison with the case where reaction at the pre-heating stage was negligible. The decrease in the distillate yield resulted from the sup-pression of the conversion of the heavy fraction (CLB) into the solvent fraction (180-420°C). At the preheating stage, CO2 and H2O evolved and the coal of 20-30 wt % converted to preasphaltenes (benzene insoluble-pyridine solubles). The oxygen-contain-ing functional groups decomposed rapidly at more than 350°C, resulting in the formation of many radicals in the coal (Plorg.). Since the greater part of the coal remained as pyridine insolubles (Plorg.), the retrogressive reaction caused by the radicals in the Plorg. was considered to reduce the conversion of the heavy fraction into the distillate at the liquefaction stage.
Based on these results, it is concluded that the usual preheating conditions of the liquefaction process decreased the liquedaction performance. This indicates that the distillate yield increases if the retrogressive reaction at the preheating stage is suppres-sed by controlling the preheating conditions and solvent quality such as hydrogen donor ability and catalyst activity.
