Purpose of sulfur and chlorine injection in the propane dehydrogenation unit
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In recent years, a large number of propylene production units via propane dehydrogenation (PDH) have come online in China, impacting the polypropylene market. The main processes for PDH are as follows: (1) UOP’s Olefex process, which uses platinum-based catalysts ； (2) LUMMUS’ Catofin process uses chromium-based catalysts. It is understood that in China, aside from Tianjin Bohua which uses LUMMUS’ Catofin process, all other companies use UOP’s Olefex process. Question: Do both of these processes require the addition of sulfur, water, and chlorine during production? What is the principle behind sulfur injection, water injection, and chlorine injection? Is this the same principle as injecting water, sulfur, and chlorine into the reforming catalyst?
Sulfur injection is done to passivate the reactor walls, while chlorine injection is used during catalyst regeneration on the ceramic balls that ensure uniform dispersion of platinum
The purpose of sulfuring is to passivate the metal, preventing it from catalyzing the thermal cracking of reactants at high temperatures to form small olefins; this would reduce the yield of reaction products and increase coking on the catalyst. Chlorine plays an important role in the dispersion of platinum on the catalyst; this chlorine is specially treated so that it no longer exhibits acidic properties during dehydrogenation reactions. Recharging chlorine is intended to disperse the agglomerated platinum metal again after catalyst regeneration, thereby restoring the catalyst’s activity.
Sulfur injection generally involves the use of DMDS, and both processes require it; UOP uses a larger amount, with 3 injection points, aimed at passivating the metal on the inner walls of the pipes to prevent it from falling off and clogging the catalyst mesh. Chlorine injection is required only in the UOP process, with the purpose of restoring the catalyst’s activity. Neither of them has water injection; only aromatic washing oil is used before the compressor
Thank you; I am currently conducting laboratory research in this area, and your post is very useful. The reaction tubes currently in use are made of 304SS, 310SS, and 904L stainless steel, and there are indeed some differences between them. Could you please provide some guidance? Is it necessary to continue adding sulfur throughout the process? How long does it take to inject, and under what reaction conditions should it be injected? Thank you
Thank you; I am currently conducting laboratory research in this area, and your post is very useful. The reaction tubes currently in use are made of 304SS, 310SS, and 904L stainless steel, and there are indeed some differences between them. Could you please provide some guidance? Is it necessary to continue adding sulfur throughout the process? How long does it take to inject, and under what reaction conditions should it be injected? Thank you
At 400°C, DMDS decomposes in large amounts to produce H2S; therefore, the Oleflex process begins continuous sulfur injection at 400°C
So where does all this injected sulfur end up? Does the C4 extract from the depropanization tower contain sulfur?
I would like to ask everyone: What is the basis for adjusting the sulfur injection amount? Is it the sulfur partial pressure or the hydrogen sulfide content in the reaction effluent? How to understand the equilibrium phase diagram of metal sulfides?
The C4 at the bottom of the depropanization tower should be free of sulfur; the reaction effluent passes through a desulfurization bed, the regeneration gas from this bed goes through an alkali scrubber, and the waste alkaline solution is subjected to wet oxidation.