We have carried out pilot scale RO experiments on the mixtures and have discovered that we easily can achieve 20 wt% NMP in distilled water as a feed to the distillation column; we have also achieved 30% but large pilot scale duration experiments will  give definite answer how the system behaves during duration trials and possible cleaning scenarios of the membranes to ensure a sustainable operation of the RO. We have unfortunately had some problems with the pilot unit for duration tests– it was converted from NF conditions (40 bar) to handle brackish water conditions (high pressure 80 bars) and switch to a higher pressure pump has given problems. Converting this system to higher pressures is necessary to handle high osmotic pressures that occur at high NMP concentrations.
We will if all goes well receive the plot unit in Schijndel in the week of 8 June. 2 months of pilot have been planned to assess long time stability to our mixture. We will be able to present first results of the duration trial during the kick-off meeting of 22/23 June..
We have seen that we need to operate at lower temperature 25 C to ensure high selectivity of water at these low temperatures; at these temperatures NMP does not permeate. We also have high temperature membranes available that can operate at 70 C but this results in in permeation of NMP with water resulting in less effective washing of the NMP treated paraffin streams.
We also discovered that we get biological activity in our water streams at low temperatures (25 C) as NMP is a good material for bacteria to grow on. But as our water and NMP will see higher temperatures in our process (washing evaporation) we do not expect issues here although we will need to check this.
Obtained water (permeate) is very pure.
For distillation column design we can assume for now a 75/25 mix of water/NMP coming out of the membrane unit and an operating temperature of 25 C. Permeate of the RO unit will be free of NMP.
