Propylene Recovery for Production of Polypropylene (PP)
The Application
During the production of polypropylene (PP) one typical process step is the degassing of PP resin in the resin bin in order to purge out non-reacted propylene monomer. Typically nitrogen is used and continuous purge streams containing substantial content of monomer have to process to minimise the loss of profit and the required flare gas capacities:
Substantial loss of propylene monomer;
Increased flare gas streams and therefore secondary emissions to the atmosphere.


Our Solution

The BORSIG Propylene Recovery technology is an easy add-on system and can be considered in existing and new process installations. The purge gas stream compressed and condensed in the downstream condenser stage, which might be cooled with cooling agent or liquid propylene. For some PP production licenses an additional dryer system must be installed prior to condensation. After separating the condensate the remaining purge gas is fed into the membrane system, while the permeate side of the membrane separation stage is fed back to compressor’s suction side. By means of the resulting pressure difference and the hydrocarbon selective membrane material, the purge gas stream is separated into the purified nitrogen stream and the recycled propylene-rich permeate stream. A small part of the separated stream is sent to the flare to prevent accumulation of lighter components.
The process system consists beside the required membrane stage, mainly of compressor and condensation unit, fully de-signed as package unit with dedicated PLC. Sometimes dryers and transfer liquid pumps are installed to meet specific client’s requirements.

The Benefits

Recovery rates > 95% Propylene and purity > 99 mol.% Nitrogen;
Short payback periods in order of 1-3 years;
Safe operation, high reliability, low maintenance;
Tailor-made design to specific plant’s conditions and local regulations;
Quick installation and easy implementation through package unit design;
Feasibility for adaptation into existing plants (retrofit design).