Membranes for Olefin/Paraffin Separation

The use of membranes as a new means for olefin/paraffin separation has attracted the attention of many researchers due to the low operating cost. Although a number of polymeric membranes have been investigated, it was not surprising that some rather low separations were obtained due to the similar physical properties of olefins and paraffins. Other advanced polymeric membranes such as polyimides showed improved separations; however, the performance seemed to decrease dramatically for gas mixtures due to the plasticization effect. On the other hand, the use of facilitated transport membrane techniques exhibited high performances due to the incorporation of a carrier for olefins. However, these processes still suffered from stability issues due to the loss of the carrier and/or membrane degradation caused by the weak chemical stability of most polymeric materials. Nowadays, PVDF and PTFE polymers have been emerging as strong candidates for membranes materials due to the superior properties, which make them an attractive option for membrane contactors. The long term stability of PVDF and PTFE membrane contactors for propylene/propane separation using AgNO3 as a carrier was investigated for a period of two months. The results revealed that the performance of PTFE remained invariable with time, while PVDF exhibited a linear decrease in the separation performance owing to membrane wetting. Characterization of the membranes revealed the formation of defects on PVDF due to the membrane’s incompatibility with Ago particles, whereas PTFE only suffered from the physical deposition of Ago. As a consequence, the use of ceramic membrane contactors was explored instead due to its robust nature and excellent chemical and thermal properties. Ceramic hollow fibres were developed by the phase inversion-sintering technique, followed by the modification with silane solutions to promote its hydrophobicity, and finally examined for propylene/propane separation. The ceramic membrane module proved to be stable throughout continuous experiments up to a period of six months where no decline in the performance was observed. However, beyond this stage the extensive Ago deposition on the membrane surface seemed to have had an influence as evident by the slight drop in performance. However, by exposing the advantages of ceramic membranes over their polymeric counterparts, a novel regeneration method was developed where the membrane module encountered extensive treatments with strong HNO3 to remove silver depositions, followed by the re-modification of the membranes to restore its hydrophobicity. The performance of the regenerated membrane module was confirmed to be entirely recovered once more.Open Acces