Can the variance in membrane performance influence the design of organic solvent nanofiltration processes?
Graphical abstract
Introduction
Taking membrane research from its initial phase of concept development, material and membrane design into process development requires substantial resources and time. This is not special but true for many innovations starting with an innovation trigger. This is also known as the Gartner Hype Cycle [1]. Judgment of the quality of the innovation trigger occurs often through reproducibility and applications studies and generally also creates - after a peak of inflated expectations - a trough of disillusion. In membrane research, the innovation trigger is assumed to occur through the availability of new materials and membranes made thereof. Yet, it is often not well known how statistically significant the mass transport properties of new membrane materials and new membrane products are. In a recent meta-study for example [2], published in this journal with more than 3000 references, the authors pose the fundamental questions (a) whether there is an average proton conductivity for Nafion membranes, (b) how the proton conductivity due to Nafion modification has evolved over past 10 years, (c) which additives really contribute to a conductivity increase, (d) how temperature or humidity affect conductivity. While such questions are not scientifically inspiring and do not initiate a new hype cycle, such questions are important in order to understand and judge the significance of a new material or membrane type. Here we pose similar questions with respect to the statistical significance and comparability of characterization methods to quantify mass transport properties for membranes used in organic solvent nanofiltration. As opposed to the meta-study, we have chosen to engage different labs and research groups with comparable analytical infrastructure, to use a round robin test evaluating the results of a developed standard experimental procedure. This leads to conclusions on standard deviations in flux and retention values in a complex parameter space for different membrane materials in various solvent/solute systems.
Section snippets
Background
Organic solvent nanofiltration (OSN) became a new member of the family of pressure-driven membrane processes by the discovery of solvent resistant membranes. Up to now, a great number of various applications were developed since the production and reactions in organic solvents comprises a wide range [3], [4]. Although OSN is still in the focus of industry as an energy-efficient separation process, there are only a few established plants [5], [6], [7]. However, the progress in the investigation
Materials and categorization
An appropriate categorization usable for test systems has to be as simple as possible and as accurate as necessary. Following this maxim, we decided to categorize the solvents in protic and non-protic solvents. In protic solvents, we extended the category with two degrees of polarity and for non-protic solvents with three degrees of polarity. Therefore, the normalized polarity index of Reichardt [32] supplies the values. The same as the polarity, in this way a wide range of the
Statistical analysis and evaluation
While it is often stated that comparable results have been obtained in different studies, these statements are qualitative and therefore subjective. To avoid such subjectivity and allow for a meaningful quantitative reference, we considered a statistical evaluation of the results. Thus, we defined a degree of congruence. The difference between a random sample and a reference or confidence intervals compared to each other are typically used. Confidence intervals should give the precision of an
Results and discussion
Considering the spent effort devoted to the standardized experimental procedure and the validation of the analytic methods, it can be concluded that the obtained results of the round robin test are a best case representative for the diversity of measurements in diverse laboratories. Differences are quite normal since locations, set-ups, measurement devices, analytic methods, time of measurements and experimenter vary from each other. The contributors endeavored to operate as equal as possible
Conclusion
The data quality of results from membrane characterizations has never been stated as a basis for the OSN users. This uncertainty hinders the progress in finding one or more reasonable standard systems for OSN membrane characterization. Such standardized procedure can simplify the assessment of membrane performance and their applicability in real separation processes. As a result, the process design of a OSN plant in industrial scale would be less difficult and troublesome. In this study, we
Acknowledgment
The authors wish to acknowledge the German Federal Ministry for Economic Affairs and Energy (BMWi) for financial support via the project “Energieeffiziente Stofftrennung in der chemischen und pharmazeutischen Industrie durch Membranverfahren - ESIMEM” (03ET1279E).
References (46)
- et al.
An overview of the proton conductivity of nafion membranes through a statistical analysis
J. Membr. Sci.
(2016) - et al.
2.05 - nanofiltration operations in nonaqueous systems
- et al.
Experimental observations of nanofiltration with organic solvents
J. Membr. Sci.
(2001) - et al.
Important factors influencing molecular weight cut-off determination of membranes in organic solvents
J. Membr. Sci.
(2012) - et al.
Solvent dependent solute solubility governs retention in silicone based organic solvent nanofiltration
J. Membr. Sci.
(2016) - et al.
Characterisation of organic solvent nanofiltration membranes in multi-component mixtures: membrane rejection maps and membrane selectivity maps for conceptual process design
J. Membr. Sci.
(2013) - et al.
Solvent-membrane-solute interactions in organic solvent nanofiltration (osn) for grignard functionalised ceramic membranes: explanation via spiegler-kedem theory
J. Membr. Sci.
(2016) - et al.
Observations on the permeation performance of solvent resistant nanofiltration membranes
J. Membr. Sci.
(2006) - et al.
On negative retentions in organic solvent nanofiltration
J. Membr. Sci.
(2013) - et al.
Molecular weight cut-off determination of organic solvent nanofiltration membranes using poly(propylene glycol)
J. Membr. Sci.
(2017)
Organic solvent resistant poly(ether-ether-ketone) nanofiltration membranes
J. Membr. Sci.
In search of a standard method for the characterisation of organic solvent nanofiltration membranes
J. Membr. Sci.
Solvent resistant nanofiltration for acetonitrile based feeds: a membrane screening
J. Membr. Sci.
Characterisation of organic solvent nanofiltration membranes in multi-component mixtures: process design workflow for utilising targeted solvent modifications
Chem. Eng. Sci.
Will ultra-high permeance membranes lead to ultra-efficient processes? Challenges for molecular separations in liquid systems
J. Membr. Sci.
Performance of spiral-wound membrane modules in organic solvent nanofiltration - fluid dynamics and mass transfer characteristics
J. Membr. Sci.
{PMMA polymethylmethacrylate}
Model-based structural optimization of seawater desalination plants
Desalination
Structural optimization of membrane-based biogas upgrading processes
J. Membr. Sci.
Optimization of membrane based nitrogen removal from natural gas
J. Membr. Sci.
Solvent dependent membrane-solute sensitivity of osn membranes
J. Membr. Sci.
Understanding gartner’s hype cycles, Strategic Analysis Report No. R-20-1971
Molecular separation with organic solvent nanofiltration: a critical review
Chem. Rev.
Cited by (31)
Solvent and thermally stable polymeric membranes for liquid molecular separations: Recent advances, challenges, and perspectives
2023, Journal of Membrane ScienceSynergizing machine learning, molecular simulation and experiment to develop polymer membranes for solvent recovery
2023, Journal of Membrane ScienceSolutes in solvent resistant and solvent tolerant nanofiltration: How molecular interactions impact membrane rejection
2023, Journal of Membrane ScienceFrom academia to industry: Success criteria for upscaling nanofiltration membranes for water and solvent applications
2023, Journal of Membrane ScienceSustainable organic solvent nanofiltration membranes
2023, Green Membrane Technologies towards Environmental Sustainability