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Study of Continuous Dehydrogenation of Cyclohexane under Multi-phase Reaction Conditions

Author: ZhiZunOu
Tutor: XuGuoHua
School: Zhejiang University
Course: Chemical Engineering
Keywords: Cyclohexane Multiphase Continuous dehydrogenation Raney-Ni Catalyst Deactivation
CLC: TQ203
Type: Master's thesis
Year: 2011
Downloads: 32
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Abstract


Hydrogen has a clean, renewable and utilization of the advantages of one of the hot new field of energy research. Hydrogen volumetric energy density is very low, looking for a suitable hydrogen storage carrier volume energy density, and resolve the reservoir of good hydrogen storage carrier, hydrogen technology is an important topic of hydrogen towards practical engineering applications. Liquid organic hydrocarbons hydrogen storage having a high hydrogen storage capacity, transport, reactant and product may be repeated cycles of use, etc., is a potential vehicle storage technology, benzene - cyclohexane system is one of the typical representatives. Benzene - cyclohexane hydrogen storage technology (benzene hydrogenation) of the hydrogen storage system is relatively mature, but its dehydrogenation technology (cyclohexane dehydrogenation), especially car dehydrogenation technology is not yet resolved as the hydrogen storage system technical bottlenecks engineering applications, for cyclohexane the car dehydrogenation technology research has important significance. Thesis the multiphase state conditions of the continuous dehydrogenation of cyclohexane reaction experimental device using self-designed, with Raney-Ni as a catalyst, under conditions of no additional purge gas in cyclohexane multiphase state the continuous dehydrogenation under the reaction conditions, to get the optimum conditions of the reaction system parameters. On this basis, there is investigated for a long time under the reaction conditions for continuous dehydrogenation of cyclohexane behavior, and the deactivation of the catalyst and its mechanism of the exploratory research. The thesis consists of the following three parts. The first part of this paper continuous multiphase conditions dehydrogenation of cyclohexane in experimental feasibility study. The study shows that a self-designed experimental apparatus, Raney-Ni as a catalyst, under conditions of no additional purge gas, cyclohexane continuous dehydrogenation reaction can be carried out smoothly, and the salt bath temperature, cyclohexane feed rate and The amount of catalyst generated hydrogen production rate of the reaction system, the purity of the hydrogen and cyclohexane dehydrogenation conversion rate can have a significant impact. When the salt bath temperature of 370 ° C, cyclohexane feed rate of 25 ml h-1, the amount of catalyst, 3 g cyclohexane continuous dehydrogenation system optimal overall performance, the hydrogen production rate of up to 27 ml-min-1, the hydrogen purity of 88%, the dehydrogenation of cyclohexane conversion rate was 9.4%. Feed rate of 25 ml · h-1, the amount of catalyst 5 g ,290-410 ℃ salt bath temperature cyclohexane consecutive the dehydrogenation apparent reaction kinetics studies have shown that the apparent activation energy of the reaction is about 12.57 kJ · mol-1. The second part of cyclohexane in the multiphase state conditions for 6 hours long continuous dehydrogenation performance. Found that when the salt bath temperature of 360 ° C, the feed rate of 28 ml · h-1, the amount of catalyst, 3 g cyclohexane continuous dehydrogenation system better overall performance, the initial hydrogen production rate of up to 37ml · min-1, 6-hour average hydrogen production rate of approximately 25 ml · min-1, the hydrogen purity more than 95% can be achieved. Was found that there is an obvious phenomenon of catalyst deactivation during the course of the reaction. The feed rate of 55 ml-h-1, the amount of catalyst 3 g cyclohexane dehydrogenation reaction under ,300-360 ° C salt bath temperature and catalyst deactivation rate analysis showed that the deactivation of the catalyst series is 4, The catalyst deactivation rate is substantially independent of the influence of the reaction temperature, can be expressed as: rd = 0.289 · (3.0 .289 · t 1) -4 / 3. The third part of the thesis studies the causes and mechanisms of the deactivation of the catalyst during the reaction. Found around the particle size distribution of the catalyst in the reaction showed no significant change, but the catalyst has a specific surface area after the reaction than the fresh catalyst is increased by about 70%, and surface adsorption of a large number of substances; different pretreatment and reaction conditions the catalyst surface morphology of scanning electron microscopy and energy dispersive analysis of the results showed that the fresh Raney-Ni surface is smooth, flat, and the surface of the catalyst after the reaction there is a lot of coke deposits in the surface of the catalyst is the main reason for the catalyst deactivation. Experimental studies have shown that prolonged heating process does not impact on the activity of the catalyst and the macro, micro structure, washed using ethanol catalyst pretreatment mode will make the surface of the catalyst in the subsequent heating process produce coke and reduce its activity.

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