Why does the CATOFIN process not require a SHP unit for propane dehydrogenation?
Thread Content
I have been researching the propane dehydrogenation process recently. Side reactions occur during the PDH dehydrogenation reaction, resulting in the formation of acetylene and MAPD. The UOP OLEFLEX process features a selective hydrogenation SHP unit that is used to selectively remove MAPD from the C3 fraction at the bottom of the deethanizer, as well as from MAPD that accumulates in the propylene distillation column; this is because MAPD can affect the performance of PT/SN catalysts. The CATOFIN process of LUMMUS does not feature a selective hydrogenation SHP unit. The main reason for this is that CR-based catalysts can tolerate certain amounts of olefins and alkynes; as a result, the MAPD produced in the reaction returns to the reactor along with the recycled propane in the propylene distillation tower. This continuous generation and recycling leads to an increasing amount of MAPD in the system – so how is it removed?
The CATOFIN process uses CR series catalysts, which possess high selectivity and tolerance, enabling the suppression of the formation of by-products such as alkynes (MAPD). Since CR catalysts can tolerate alkynes and alkenes to a certain extent, the CATOFIN process does not require an SHP unit to specifically remove MAPD. In practical operation, the CATOFIN process handles the continuously generated and recycled MAPD by strictly controlling reaction conditions (such as temperature and pressure) and periodically regenerating the catalyst, thereby maintaining the stable operation of the system and the activity of the catalyst, and reducing the need for SHP units. .
Could someone who doesn’t have a PDH device explain this?
The CATOFIN process indeed does not have a selective hydrogenation unit (SHP), as the CR series catalysts it uses provide excellent control over the formation of by-products. During the operation, the formation of alkynes can be minimized by optimizing the reaction conditions. Furthermore, the impact of by-products can be further reduced through periodic catalyst regeneration and appropriate reactor design. If by-products such as alkynes accumulate to the point where they affect catalyst performance, removal mechanisms are incorporated into the process flow, such as the recycling of diluents and the regeneration or replacement of catalysts, in order to maintain production efficiency and product quality. .
Thank you for your answers. It is understandable that CR catalysts have better tolerance to impurities as well as olefins and alkynes compared to PT catalysts. What I don’t quite understand is why side reactions can only be reduced but not eliminated. A certain amount of MAPD will always be generated, but no mechanism for removing MAPD is present in the process flow. Even if the amount produced is small, it will accumulate over time during continuous operation; no matter how much it is diluted, it remains within the system. Could MAPD be removed from the reactor through coking and carbon formation, followed by regeneration and burning, thereby achieving equilibrium?