Insight in the thin-film pollyamide membrane structure after compaction

Identifier:  TDX:2477

Handle: https://hdl.handle.net/20.500.11797/TDX2477

Authors:  Blazheska, Jasna

Abstract:
Reverse osmosis (RO) is the finest level of membrane-technology available and one of the most promising technologies to overcome the problem of global clean water scarcity. The RO membrane market is dominated by thin-film composite (TFC) polyamide membranes. When operated at high temperature (max 45˚C) and high pressure (max 82 bar) membranes can suffer compaction, which results in reduced permeate production (>30%) so that the feed pressure has to be increased to meet the design parameters. Ultimately these translate into an increase in the cost of the water produced and substantially lower membrane product life-time. The objective of this study was to gain fundamental understanding on the compaction phenomena and its implication to the transport mechanism. With that purpose a series of analyses were conducted with the aim of characterizing: (1) the membrane morphology and thickness of each layer in the membrane from cross sectional images as a result of high temperature and pressure operation (2) the polyamide chemical content after process operation (3) the portions of permeability flow loss due to compaction of the polyamide and support layer, separately, and their contribution to the total membrane flow loss by applying the series resistance model, and (4) the pore size (free-volume hole size) of the polyamide layer in dry and swollen hydrated state. In total 11 different techniques were applied attempting to reveal complete information. Several observations were identified that might be attributed to the permeability loss of the membrane after the operation. Moreover the results indicated that there is a sizable portion (~50%) of added resistance coming from the polyamide layer to the total flow loss of the entire composite membrane, which leads to irreversible changes in the membrane performance. The root cause for these observations might be the changes in the polyamide structure that most probably occurs during the operation at combined conditions of high pressure and high temperature.