Propylene Production from Propane (Moving-Bed Reactor)

Propane dehydrogenation (PDH) is an endothermic equilibrium reaction. The PDH process portrayed in this analysis is similar to the Oleflex process developed by UOP LLC and is suited to produce polymer-grade (PG) propylene from propane. This process is carried out in the presence of a platinum catalyst and achieves overall propylene yields of about 90 wt.%.

The industrial plant can be divided into two main sections: (1) reaction; and (2) product recovery.

Reaction. In the reaction section, after heavy impurities removal in the depropanizer column, propane is sent to the dehydrogenation reactors. The propylene yield in such reactors is favored by higher temperatures and lower pressures. However, temperatures that are too elevated will promote thermal cracking reactions that generate undesirable byproducts. Therefore, the PDH reaction usually occurs at temperatures above 600°C and near atmospheric pressures. In order to purge the coke accumulated on the catalyst surface during the reaction, a continuous catalyst regenerator (CCR) unit is required. The catalyst circulates in moving beds through the reactors, before being fed to the CCR unit, which operates independently of the reaction, burning off the coke and returning the catalyst to its reduced state.

Product recovery. The reactor effluent is compressed, dried and sent to the product recovery section. In this section, a hydrogen-rich stream is recovered and light hydrocarbons and hydrogen traces are removed in a de-ethanizer. The PG propylene product is further purified in a propane-propylene (P–P) splitter and leaves as the top product.