C4 reprocessing

Same question: assuming a process capacity of 600,000 tons per year, how much more olefin can be recovered by adding C4 reprocessing? And what is the increase in energy consumption?

I’ve always had a question: if the catalyst is still from the SAPO series, can it handle C4? The C4 reprocessing used in oil refining relies on Z5 components. Several senior experts have doubts about this reprocessing method employed by the Da Hua Research Institute – as to whether it can be implemented, whether it is feasible, and whether anyone is aware of this situation

Well, this must be the type of catalyst in question. What’s unclear now is whether the use of SAPO for reprocessing will cause any problems in terms of energy and material consumption. Based on the structure of molecular sieves and various experimental data, SAPO has a lower ability to facilitate C4 rereaction compared to Z5, due to its pore structure and acidity; this might lead to issues such as an excessively high circulation rate.

This post was last edited by fossil-zhang on 2011-8-17 at 17:21. Reply to 4#: The purpose of reprocessing C4 in coswave C4 is to increase the selectivity for C3. Moreover, C4 is mixed with the feed and then sent back to the reverse reaction system; therefore, the existing SAPO-34 catalyst is naturally used. If a different catalyst were used, how would the process need to be adjusted? Although MTO and FCC are similar, they are still different; the feed composition for C4 reprocessing in catalytic cracking differs from that in MTO, and the requirements for catalysts also vary. One can take a look at some of the patents applied for by Liu Zhongmin regarding the production of propylene or the improvement of propylene selectivity. Furthermore, since C4 can be produced as a product, it can also return to the pores of SAPO-34 as a reactant; thus, there is no issue with mass transfer resistance. As for acidity, the reprocessing of C4 involves the reaction C2 + C4 = C3, and its effect is not very different from that of the ZSM-5 series. Liu Zhongmin has been working with this catalytic reaction system for over 20 years, so I think his choice will be fine – he has conducted numerous experiments to verify it. He also said that in fact, C4 doesn’t necessarily have to be reprocessed; it might be better to use it to produce other products. The key factor is still market demand.

Thank you. When developing projects in the past, I carried out comparisons in this area; based on the actual test results, it is quite difficult to refine C4 using SAPO. However, from your answer, it seems that Liu Zhongmin and his team may indeed have made some technical breakthroughs. In terms of catalysis, Da Hua’s capabilities are beyond doubt; it is hoped that they will indeed manage to make breakthroughs in several technologies, not only to remain at the forefront in academic circles but also to achieve advancements in the industrial sector as well.

Reply to 6# coswave: Liu Zhongmin is one of the few individuals in China’s catalysis academic community who are able to transform technology into advanced production capabilities on a large scale. He is also quite low-key in his approach. In China’s catalysis field, many people simply publish articles in high-tier academic journals as a routine practice; it’s inevitable, given the current conditions in China’s research community. Behind DMTO’s industrial success today lies the strong research capabilities of Dahuaxian, the support of senior scientists, as well as over 20 years of dedicated effort. I’ve heard Liu Zhongmin talk about the difficulties he faced back then in using DMTO technology to find investors and funds for pilot tests – there wasn’t enough money for such tests, and few companies were willing to invest. Even after overcoming various obstacles, not many people were interested in supporting the project. At that time, people had a high regard for UOP’s technology and didn’t believe that Chinese companies could develop it. But UOP was too arrogant and set exorbitant prices; if Shaanxi Chemical Industry Group hadn’t been willing to fund the project, it likely would have failed from the start. So it’s not anyone else’s fault – it’s only their own failure to seize the opportunity. Now that the Dahuai DMTO project has been a success, it’s Liu Zhongmin’s turn to face difficulties; many people come to him with cash, including those companies that used to ignore him back then. So, those who work in technology sometimes really need to be able to tolerate loneliness. When Liu Zhongmin gives a presentation, he usually places on the first page of the PPT the flags of the countries from which the technologies for each stage of the DMTO process originate; the only flag there is the Chinese Five-Star Red Flag, which represents the MTO process. Those who see it feel both proud and sad. I truly admire Professor Liu Zhongmin; he has taken the process of advancing catalytic technology from research to industrial application to its absolute limit.

In C4 reprocessing, energy consumption increases – that’s certain. In fact, in the chemical industry, it’s common to add additional units in order to achieve a higher selectivity for the desired product, which in turn leads to increased energy consumption. Professor Liu Zhongmin also said that if C4 has better alternatives, it is reasonable to choose not to recycle it. Reprocessed C4 still consists mainly of olefins; oligomerization can also be an option. It’s just that the system settings are more complex. The reprocessing of C4 is aimed at improving the selectivity of C3. Let’s discuss this reaction: C2= + C4= ——— 2 C3=. This reaction can take place without the involvement of any other reactants; it is somewhat similar to an olefin disproportionation reaction. Theoretically, this reaction is subject to thermodynamic limitations, and especially at higher reaction temperatures, the extent of the reaction is reduced. I don’t know what the actual situation is? Is the reaction depth of C4 large? From the perspective of thermodynamic limitations, C4 reprocessing is acceptable; reprocessing at the C5 level or above is theoretically meaningless. Additionally, I have a question: based on the composition of the products, the acidity difference between SAPO-34 and ZSM-5 should be significant. Yet SAPO-34 is still capable of carrying out the aforementioned reaction. From a catalytic perspective, could catalysts from other series, such as those used in Fischer-Tropsch synthesis, also enable this reaction? As I understand it, in catalysts that are not of the molecular sieve type, molecular reformation reactions basically do not occur, so reactions between olefins do not take place. Is this understanding correct? But if I were to say that the aforementioned reaction also occurs in the Fischer-Tropsch synthesis system, would that be incorrect, or rather far-fetched? Please give some suggestions.

I have listened to the presentations given by several senior colleagues from Dahuake, and they were indeed very thorough. It can be said that Liu Zhongmin built upon the foundations laid by those seniors, thus fulfilling their wishes as well. In fact, not only in Dahuazhong, but many research institutions in China encounter the same situation when developing new projects: they have to turn to manufacturers to carry out pilot tests and experiments. There’s nothing that can be done about this, as manufacturers prefer stability over change. I have also heard about what you mentioned regarding seeking help from a company in Shanghai for pilot testing. When I communicated with them, their chief engineer said that he was very supportive of this idea, but many people in the company were unwilling to get involved. In China, there is a tendency to rely on foreign technology; since he was about to retire, he didn’t proceed with it. Now they have to turn to others for help, which is really unfortunate.

When discussing C4 cracking, people generally consider the disproportionation reactions of C2 and C4. In fact, there is another reaction in C4 cracking: C4 dimerizes to form C8, which is then cracked into C2 and C3. The mechanism for this reaction has already been established. The principle used in the current production of propylene from the C4 components in liquefied gas is exactly this one; it works without problems with Z5, but I’m not entirely sure about its effectiveness with SAPO. In my opinion, as long as there is an active center, the reaction will proceed, provided that the thermodynamic conditions are met. However, since it is not a molecular sieve catalyst, the product distribution cannot be controlled through shape selection, and therefore the composition differs.

The acidity of SAPO-34 and ZSM-5 is not on the same level as that of Fischer-Tropsch catalysts; compared to the former two, the acidity of Fischer-Tropsch catalysts can be considered virtually non-existent. Of course, this is a relative comparison – some acidity does exist, but it is very low, and it originates mainly from the carrier or oxide additives. From a catalytic perspective, due to both the weak acidity and the low reaction temperature, the disproportionation reactions between olefins mentioned earlier basically do not occur under Fischer-Tropsch conditions. If you write an article explaining experimental phenomena in this way, it is likely to be rejected by the reviewers. Actually, if you look at the products of the Fischer-Tropsch reaction, it’s clear that there is usually less C2; however, the amount of C4 does not decrease significantly, nor does the amount of C3 increase significantly. Have you observed similar results using ordinary carriers? Unless a more acidic carrier is used at relatively high reaction temperatures, as Wang Ye from Xiamen University discovered when using microporous acidic molecular sieves (similar to ZSM) as carriers for catalysts, gasoline selectivity and the isomerization ratio increase. However, this is also caused by the acidity of the carrier and the selectivity of the molecular sieve, rather than the Fert process itself. We are currently working on encapsulating SAPO-34 within an iron catalyst to see if this can improve the selectivity for low-carbon olefins at high temperatures, by taking advantage of the acidity and stereoselectivity of the molecular sieve.