Article pubs.acs.org/EF
Reaction Kinetics Study on the Heating Stage of the Shenhua Direct Coal Liquefaction Process Xiangen Shan,†,‡ Kejian Li,‡ Xuwen Zhang,‡ Hongbo Jiang,*,† and Huixin Weng† †
Research Institute of Petroleum Processing, East China University of Science and Technology, Shanghai 200237, China National Engineering Laboratory for Direct Coal Liquefaction, Shanghai 201108, China
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ABSTRACT: Direct coal liquefaction in the heating stage of Shenhua Shendong bituminous coal was carried out in a 0.01 t/d continuous tubular facility with iron catalyst and hydrogenated anthracene and wash oil as solvent at a residence time (t) of 3.5− 6.5 min and a reaction temperature (T) of 340−450 °C. The results show that when t = 3.5 min and T = 340 °C, a cracking reaction of coal occurs, while the oil yield was almost zero. As the residence time and temperature each increase, coal conversion and product yield exhibit different change patterns. Especially when t = 6.5 min and T = 450 °C: under these conditions, the coal conversion and oil yield reached 83.67 and 52.27 wt %, respectively. To investigate the liquefaction kinetics, a 8-lump reaction kinetic model which follow first-order irreversible reactions (r = ki dC/dt) was developed to estimate the rate constants. The results indicated that the model is perfectly valid for the heating stage, and the yield of oil and gas were mainly from coal other than preasphaltene (PAA).
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models.4−8 In this work, Shendong bituminous coal was hydroliquefied in a 0.01 t/d continuous experimental apparatus to investigate the liquefaction mechanism of the heating stage. The gas holdup were calculated using a “gas shut-down method” and the liquefied product of different reaction conditions were obtained by Soxhlet extraction. Finally, the 8-lump kinetic model was developed for direct coal liquefaction in the heating stage, and the DCL reaction kinetics data of different reaction conditions were simulated by optimization algorithm.
INTRODUCTION Direct coal liquefaction (DCL) is an advantageous approach for the clean and effective utilization of coal, but also a complex combination of physical and chemical processes. In DCL process, coal is cracked and hydrogenated to produce largermolecule extractable materials, oils and gases. The research of kinetics of DCL focus on reaction rate and its influencing factors, which, in turn, is helpful for reactor design and process optimization. Until now, many works have been carried out for experiment and kinetics study of DCL, and various kinetic models have been developed. Li et al.1 used a 5-lump model to investigate the kinetics of both heating and isothermal stages, which concluded that the rate-controlled process is the reaction of preasphaltene to oil and gas. Kidoguchi et al.2 studied the initial reaction kinetics of Wandoan coal in an autoclave, with temperatures of 200−450 °C and reaction times of 0−65 min. The reactions from coal to preasphaltene (PAA), oil, and gas were taken into consideration, while further hydrogenation from preasphaltene was neglected. Compared with traditional kinetic experiments carried out in a batch autoclave reactor, the use of a continuous testing device is a effective means to conduct reaction kinetics of DCL, because of its quick heating rate. Besides, there are few differences between a continuous testing device and a commercial reactor that has the same hydromechanics behavior and operating conditions. Zhu et al.3 employed a 0.01 t/d continuous facility and used a 1-L autoclave as a reactor to study kinetics of Shendong coal at temperatures of 410−450 °C. Equations were established that related the different product yields and temperature. Gertenbach et al.4 adopted a bench-scale continuous coal liquefaction unit to study the reaction kinetics of Kentucky No. 9 coal at temperatures of 360, 400, and 440 °C. They established a reaction kinetic model that incorporated both series/parallel and reversible reactions. Different ranks, different petrographic compositions, and different mineral components of coal mean different kinetic © 2015 American Chemical Society
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EXPERIMENTAL SECTION
2.1. Raw Materials. 2.1.1. Coal. Shenhua Shengdong coal sample was ground to particles
