Process issues of disproportionation isomerization
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I have recently come into contact with the process of xylene isomerization, and there are a few questions I would like someone to help me answer. Specifically, does the amount of recycled hydrogen decrease after it passes through the heat exchanger and then the reactor? Another question is: why is the temperature difference between the beginning and the end of the process sometimes over 60 degrees? Is this due to instability in the operating conditions? Should the design be based on the conditions at the beginning or at the end of the process? Please ask those with expertise to help. This post was last edited by DAC The army rules the world on 2009-3-29 at 17:52
Having been in this unit, the amount of circulating hydrogen definitely decreases, as the reaction consumes hydrogen; there is also some cracking and hydrogenation reactions, mainly involving the branching of benzene rings, but not in large amounts. In our unit, the hydrogen content was maintained at around 75%, I think; I can’t remember exactly. It’s been 3 years since I last dealt with this issue； As for changes in the reaction temperature, it should be low at the initial stage and higher later on. This is because, in the initial phase, the catalyst has high activity, which leads to numerous cracking reactions and the formation of a large amount of carbon deposits; hence, the feed temperature needs to be low. As carbon deposits gradually form on the surface over time, the catalyst’s activity decreases, and therefore the reaction temperature must be increased. As for what design to use, well, it’s definitely not the initial stage; it should be the later stage you mentioned, provided by that later stage you refer to means continuous normal operation. Furthermore, in practice, due to capacity adjustments and changes in the feed composition (such as variations in the ratio of xylene to ethylbenzene), the reaction temperature also changes. This post was last edited by unsj on 2009-3-27 17:13]
LZ, I’m not sure whether the toluene disproportionation process you are familiar with is carried out at atmospheric pressure or under pressure. After reviewing relevant information, I feel that the diameter of the pipelines used for atmospheric pressure disproportionation is relatively large, making it difficult to scale up the production capacity to over 100,000 tons. I’m not sure if this is indeed the case; if so, what measures are generally taken to address this issue?