Heterogeneously catalyzed coal hydroliquefaction: Screening of catalysts and characterization

Abstract

This project is centred upon the study of the activities of different catalysts in one-step coal liquefaction processes. A series of alumina supported catalysts was prepared by multistep impregnation, including a conventional CoMo/Al2O3 and other preparations containing Zn as a second promoter, and the alumina was acidified with different fluorine contents. These catalysts were extensive physicochemically characterized and their hydrodesulphurization (HDS) and hydrogenation (HYD) activities were tested using a model compound (thiophene). The results obtained indicate that partial substitution of Co by Zn does not affect the HDS and HYD activities and that fluorination diminishes these activities because of textural changes of the carrier. The prepared catalysts were tested in coal liquefaction and their activities were compared to those of cheap iron containing dispersion catalysts such as red mud, Fe2O2 aerosol, and Cottrell and pyrite ashes (by-products of the sulphuric acid industry). Most of the liquefaction tests were carried out in a magnetically stirred laboratory autoclave for 1 h, at 400 rpm, in the 673 K (400°C) − 748 K (475°C) temperature range, at 17 ± 1 MPa operating pressure, with two different solvents; tetralin and anthracene oil, and using mainly 2/1 and 3/1 solvent/coal ratios. The liquefaction products were fractionated into oils, asphaltenes and preasphaltenes, using pentane, toluene and tetrahydrofurane (THF) as extractive solvents. Prior to the study and comparison of the catalyst activities and exploration of the influence of various operating conditions (temperature, tetralin/coal ratio, type of solvent and operating pressure) on catalytic and non-catalytic coal liquefaction was performed. The coal used in most of the experiments was a Spanish subbituminous A coal. Additionally in order to contrast results a comparison of all the catalysts was carried out with a standard high volatile (HV) bituminous coal (140 FR 36) from the European Centre for Coal Specimens Stichting Steenkoolbank Nederland (SBN). Supported catalysts present higher activities than iron-based catalysts. Among these catalysts, red mud proved to be the most active. Catalytic experiments using anthracene oil as solvent and CoZnMo/fluorinated alumina catalysts present maximum yields indicating that Zn as second promoter and carrier acidification to be beneficial in coal liquefaction with solvents similar to those used in real plants.