Published August 2002
Due to the higher annual growth rates of propylene compared to ethylene, the highest possible propylene to ethylene ratios (P/E) in steamcrackers is very desirable. Steamcrackers are still the main propylene source accounting for 70% share of primary production. In the cracking furnaces, the achievable P/E is limited to a value of approx. 0.65, since at higher ratios the total olefins yield (i.e. the sum of ethylene and propylene) drops to an uneconomically low level.
In order to overcome this situation, different approaches have been made to comply with the challenge of higher propylene production in steamcrackers. These secondary propylene production routes include:
- Recycling of C4 and C5 after di-olefins and in most cases olefins saturation
- Metathesis unit, reacting ethylene with C4 olefins to form propylene.
- Integration of C4/C5 fluidized catalytic cracking - Superflex process.
- Integration of C4/C5 fixed bed catalytic cracking - Propylur® process.
This review examines the integration of a fixed bed catalytic cracking unit into a steamcracking facility using the Propylur® process that has been developed by Lurgi. This process is exclusively available through Linde for application in steamcrackers. The Propylur® process is a low pressure and high temperature, catalytic and adiabatic process for converting C4 to C7 olefins to propylene, along with co-production of ethylene and C5+ gasoline. The driving force behind this process is to adjust the propylene to ethylene production ratio. Since propylene demand has been strong this process provides a means of increasing the propylene production and eliminating some of the other less desirable co-products coming from the ethylene plant. In general the process is highly integrated with the fractionation section of the olefin plant. In this analysis we have looked at the process on a nearly stand alone basis, which lowers the return on capital investment. The Propylur® process can be applied to refinery and any other source of C4+ olefins such as conversion of MTBE and TAME plants. This particular analysis is focused toward C4+ olefins as produced in a steam cracker environment. This process can also be used to process the C4/C5 olefins produced in a FCC unit.
