BORSIG Membrane Technology GmbH
Bottroper Str. 279
D-45964 Gladbeck / Germany
Phone +49 (0) 2043 / 4006-01
Fax +49 (0) 2043 / 4006-6299


BORSIG Nitrogen Recovery Unit

The BORSIG Nitrogen Recovery Unit is an easy add-on system and can be considered for existing and new process installations. The purge gas stream is compressed and condensed in the downstream condenser stage being cooled with a cooling agent or liquid propylene. A degassing vessel downstream of the propylene separator may prove useful to reduce the amount of inert gases solved in the recovered propylene. The recovered propylene can be provided in a liquid or gaseous state at battery limit. 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. In some cases a hydrogen-selective membrane stage is used in order to meet the requirements of the highly purified nitrogen. In principal this stage is installed downstream of the hydrocarbon-selective membrane stage.

The benefits

  • Recovery rates > 95% propylene and purity > 99 mol% nitrogen
  • Short return on investment periods (1-3 years)
  • Safe operation, high reliability, low maintenance
  • Tailor-made design
  • Quick installation and easy implementation by package unit design
  • Adaptation to existing plants (retrofit design) feasible



Nitrogen- and Monomer Recovery Unit