NanoMembrane – Nanoporous ceramic membranes for use in sustainable closed-cycle water- and solvent-saving methods
Within the NanoMembrane project, new ceramic nanofiltration membranes (NF) with reduced cut-offs and improved chemical stability were developed and tested in different applications. Whereas such testing served to check on the membranes’ stability and separation performance under conditions of use, it also provided clear definitions of the requirements to be met by membranes and hence contributed directly to optimising separation properties during development. The scientific/technical objectives comprised:
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- Development of nanofiltration membranes with cut-offs of 200g/mol
- Development of pH-stable nanofiltration membranes
- Development of organophilic nanofiltration membranes
- Setup and adaptation of test facilities
- Laboratory and pilot tests with solvents and sewage from the chemical, textile, metal and paper industries
- Life cycle assessment/integrated life cycle assessment
Within the NanoMembrane project, ceramic nanofiltration membranes with cut-offs of approximately 200g/mol were synthesised for the first time at a specific water flow of 9 l/(m2•h•bar). The systematic assessment of the pH stability was carried out with two hours of filtration with hydrochloric acid and sodium hydroxide followed by a subsequent rinsing with water and determination of the retention with PEG-200 and revealed a stability of the NF-membranes in HCl of up to 2mol/l (7.2%) at 25°C and in NaOH of up to 4mol/l (16%) at 60°C. In organic solvent, the investigated NF-membranes, depending on the type of solvent used, showed very different, not yet describable behaviours. The best retentions were found to be achieved in THF with a cut-off of 350g/mol at a specific flow of 3,5 l/(m2•h•bar).
The fabrication of the novel ceramic NF-membranes was transferred from the laboratory (0.0055m2) to the technical scale (0.25m2). Ten different laboratory facilities and pilot plants for membrane characterisation and testing were used within the project. Besides, a filtration test plant for organic solvents was developed, set up and then used by Merck for pilot tests after approval by a relevant authority.
Application tests in the chemical, metalworking, textile finishing as well as paper and pulp industries confirmed the improved retention of dissolved molecules, dyes, surface-active agents, and multivalent salts as compared to previously used commercial membranes. The studies revealed approaches to an efficient and cost-effective use of membranes during the treatment of rinsing baths for cleaning metal parts and during preparation of bleaching solutions from pulp production.
Within integrated life cycle assessment, the use of ceramic nanofiltration membranes for treatment of liquid wastes or sewage proved to be of ecological benefit. Analysing concrete examples and attempting to generalise the different statements, basic know-how has been created which in the future will enable to draw up company- and application-specific life cycle assessments for use of ceramic nanofiltration membranes.
