Solvents in membrane synthesis and their effect on NF/RO performance: from conventional organic solvents to ionic liquids

Membrane technology has grown significantly over the last decades and is used in a broad range of applications nowadays. Nanofiltration (NF) and reverse osmosis (RO) are applied for the separation of low molecular weight components (< 1000 Da) and salts from the feed stream. The main part of the commercial NF and RO membranes are either integrally skinned asymmetric (ISA) or interfacially polymerized thin film composite (TFC) membranes. Polyamide (PA) TFC membranes are the standard in aqueous NF and RO applications, thanks to their very thin, dense top layer, able to form hydrogen bonds with water. For solvent-resistant nanofiltration (SRNF) applications, mainly ISA membranes are applied currently, which are very simple and fast to prepare. Unfortunately, they often suffer from rather low solvent permeances, associated with their thicker selective layer compared to that of TFC membranes. Therefore, the application of TFC membranes in SRNF is currently intensively investigated. The solvents used in the synthesis and post-treatment of (SR)NF and RO membranes have an impact on several aspects of the preparation process, like monomer and polymer solubility, monomer diffusion coefficients, solvent exchange rate and degree of swelling of the membrane. Therefore, they largely influence the chemical and morphological properties of the resulting membranes, and can thus significantly improve their performance. However, in interfacial polymerization, very similar solvents have always been applied to prepare the top layer, limiting the potential to obtain an optimized performance. Solvent post-treatments are often applied to improve this performance after synthesis, but the mechanism behind these treatments is still largely unclear. Therefore, in this PhD, the importance of the solvent type in interfacial polymerization and in post-synthesis solvent treatments was investigated. This resulted in important improvements in both the synthesis procedures and in membrane performance. The first part of this thesis focused on the potential to use ionic liquids (ILs) as reaction medium in interfacial polymerization, by replacing either the standard hexane or aqueous phase by an IL. As the physicochemical properties of ILs differed largely from those of conventional solvents, their use affected top layer formation in several ways. The replacement of hexane by an IL led to multiple advantages in the synthesis process. Not only the concentration of the amine monomer used for top layer formation could be reduced drastically, also the addition of commonly used additives could be omitted. By recycling the IL for use in consecutive interfacial polymerization cycles, the mass intensity of the top layer formation process decreased with 64%, resulting in a 52% lower mass intensity compared to the conventional interfacial polymerization. Also the residual acyl chloride monomer in the IL after top layer formation could be recycled, as the IL protected it from hydrolysis by lowering the reactivity of dissolved water molecules. Since the top layers formed via the IL-based interfacial polymerization were thinner, smoother, more hydrophilic, and showed a higher free volume size, they obtained a higher permeance and a significantly lower colloidal and organic fouling tendency. In the second part of this research, post-synthesis solvent treatments of both TFC and ISA membranes were studied in detail to further enhance membrane performances. Solvent activation of TFC membranes is a frequently used technique to improve the RO and SRNF performance of this type of membranes. It generally results in a drastic increase in permeance, while no decrease in selectivity is observed. Despite the clear benefits of this solvent treatment, the mechanism behind it still has been unclear. In this work, the occurrence of PA oligomer leaching from the top layer during solvent activation was proven, and an attempt was made to further optimize the leaching process. Since a similar treatment could possibly have a comparable effect on other types of membranes than these TFC membranes, the influence of a solvent treatment on the morphology and performance of ISA polyimide (PI) membranes was also investigated. The membrane was first cross-linked chemically to enable the use of harsh organic solvents. As this type of membranes is totally composed of preformed, high molecular weight polymers, no oligomeric fragments could leach during the treatment, and therefore, no increase in permeance was observed here. Instead, the permeance drastically decreased and the retention increased after immersion in DMF, caused by densification of the membrane skin layer. The degree of densification was related to the polymer-solvent affinity, resulting in a varying degree of swelling and subsequent reorganization of the polymer chains. Besides the possibility to establish more energetically favorable interchain interactions during this reorganization, densification was also driven by extra cross-linking during immersion, due to a facilitated contact between the solvated, flexible polymer chains and partly unreacted cross-linker molecules. This simple treatment could transform ultrafiltration membranes into highly permeable membranes with selectivities in the (SR)NF range, showing an up to 400% higher solvent permeance compared to commercial SRNF membranes.CHAPTER 1 Introduction and scope of the thesis 1 1.1 Membrane technology 2 1.1.1 Classification 2 1.1.2 Performance 3 1.2 Pressure-driven membrane processes 4 1.2.1 Classification 4 1.2.2 Transport mechanism 4 1.2.3 Applications 5 1.3 Preparation of thin film composite membranes 6 1.3.1 Phase inversion 6 1.3.2 Cross-linking 7 1.3.3 Interfacial polymerization 8 1.3.4 Post-treatments 13 1.4 Characterization of the interfacial polymerization mechanism and top layer properties 14 1.4.1 In-situ techniques 14 1.4.2 Simulations 14 1.4.3 Post-synthesis characterizations 15 1.5 Ionic liquids 16 1.5.1 Properties 16 1.5.2 Synthesis 17 1.5.3 Applications 18 1.6 Thesis objectives and outline 18 CHAPTER 2 Preparation of high-performance thin film composite membranes using ionic liquids as the organic reaction medium Fundamental study 21 2.1 Introduction 23 2.2 Experimental 24 2.2.1 Materials 24 2.2.2 Membrane synthesis 25 2.2.3 Membrane performance 25 2.2.4 Membrane characterization 26 2.2.5 MPD mass transfer 27 2.2.6 MPD solubility in the organic phase 27 2.3 Results and discussion 28 2.3.1 Influence of synthesis conditions 28 2.3.2 Further top layer characterization 38 2.3.3 RO performance and fouling tendency 41 2.4 Conclusions 43 2.5 Acknowledgements 44 CHAPTER 3 Preparation of high-performance thin film composite membranes using ionic liquids as the organic reaction medium Optimization 45 3.1 Introduction 47 3.2 Experimental 48 3.2.1 Materials 48 3.2.2 Membrane synthesis 49 3.2.3 Membrane performance 49 3.2.4 Membrane characterization 49 3.2.5 Other measurements 50 3.2.6 Mass and solvent intensity 50 3.3 Results and discussion 50 3.3.1 Ionic liquid drying 50 3.3.2 Reaction time 52 3.3.3 Rinsing time 54 3.3.4 TFC membrane drying 55 3.3.5 Ionic liquid recycling 57 3.3.6 Mass and solvent intensity 62 3.4 Conclusions 62 3.5 Acknowledgements 63 CHAPTER 4 Preparation of high-performance thin film composite membranes by replacing the aqueous phase in interfacial polymerization by an ionic liquid 65 4.1 Introduction 67 4.2 Experimental 68 4.2.1 Materials 68 4.2.2 Membrane synthesis 69 4.2.3 Membrane performance 70 4.2.4 Membrane characterization 70 4.2.5 TMC mass transfer 70 4.3 Results and discussion 70 4.3.1 Determination of the optimal monomer concentrations 71 4.3.2 Position of the reaction zone 71 4.3.3 Further top layer characterization 75 4.3.4 Improvement of the performance 79 4.4 Conclusions 82 4.5 Acknowledgements 83 CHAPTER 5 Solvent activation on interfacially polymerized SRNF membranes: elucidation of the mechanism 85 5.1 Introduction 87 5.2 Experimental 88 5.2.1 Materials 88 5.2.2 Membrane synthesis 88 5.2.3 Membrane performance 89 5.2.4 Membrane characterization 89 5.2.5 Characterization of PA oligomers 90 5.3 Results and discussion 90 5.3.1 Fundamental understanding 90 5.3.2 Optimization of solvent activation effect 96 5.4 Conclusions 99 5.5 Acknowledgements 99 CHAPTER 6 Transformation of cross-linked polyimide UF membranes into highly permeable SRNF membranes via solvent annealing 101 6.1 Introduction 103 6.2 Experimental 104 6.2.1 Materials 104 6.2.2 Membrane synthesis 104 6.2.3 Membrane performance 104 6.2.4 Membrane characterization 105 6.2.5 Interaction parameters 105 6.3 Results and discussion 106 6.3.1 Principle 106 6.3.2 Solvent type 107 6.3.3 Immersion time 112 6.3.4 Degree of cross-linking 113 6.3.5 Formation of nanofiltration membranes 115 6.4 Conclusions 117 6.5 Acknowledgements 117 CHAPTER 7 General conclusions and perspectives 119 7.1 General conclusions 120 7.1.1 ILs as solvent in interfacial polymerization 120 7.1.2 Post-synthesis solvent treatments 121 7.2 Future prospects and challenges 123 7.2.1 RO applications 123 7.2.2 SRNF applications 124nrpages: 166status: publishe

Transformation of cross-linked polyimide UF membranes into highly permeable SRNF membranes via solvent annealing

A simple method for the preparation of highly permeable solvent-resistant nanofiltration (SRNF) membranes was developed. By applying a solvent treatment to cross-linked polyimide ultrafiltration membranes, polymer chain flexibility increased and the matrix rearranged into a more dense structure, creating highly selective SRNF membranes with exceedingly high ethanol permeance. This densification was driven by the ability of the membrane to lower its free energy while in the solvated state via the establishment of extra favorable interactions, like hydrogen bonds and π interactions. Moreover, further reaction of only partly reacted cross-linker molecules was completed during the treatment, thus enhancing the cross-linking degree. The extent of densification depended on the type of solvent, the immersion time and the initial cross-linking degree of the membrane, all influencing the degree of solvation and chain rearrangement. By altering the synthesis conditions, a membrane with equal selectivity to Duramem 300 but showing a 400% higher ethanol permeance was obtained. This demonstrates the high potential of the technique to be applied as novel method for the preparation of SRNF membranes with exceptionally high solvent permeance.status: publishe

Sustainable Process for the Preparation of High-Performance Thin-Film Composite Membranes using Ionic Liquids as the Reaction Medium

A new form of interfacial polymerization to synthesize thin-film composite membranes realizes a more sustainable membrane preparation and improved nanofiltration performance. By introducing an ionic liquid (IL) as the organic reaction phase, the extremely different physicochemical properties to those of commonly used organic solvents influenced the top-layer formation in several beneficial ways. In addition to the elimination of hazardous solvents in the preparation, the m-phenylenediamine (MPD) concentration could be reduced 20-fold, and the use of surfactants and catalysts became redundant. Together with the more complete recycling of the organic phase in the water/IL system, these factors resulted in a 50 % decrease in the mass intensity of the top-layer formation. Moreover, a much thinner top layer with a high ethanol permeance of 0.61 L m(-2)  h(-1)  bar(-1) [99 % Rose Bengal (RB, 1017 Da) retention; 1 bar=0.1 MPa] was formed without the use of any additives. This EtOH permeance is 555 and 161 % higher than that for the conventional interfacial polymerization (without and with additives, respectively). In reverse osmosis, high NaCl retentions of 97 % could be obtained. Finally, the remarkable decrease in the membrane surface roughness indicates the potential for reduced fouling with this new type of membrane.status: publishe

Verworven kinderafasie: een systematisch onderzoek van de literatuur

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Simplified synthesis route for interfacially polymerized polyamide membranes

A simplified method for the synthesis of thin film composite (TFC) membranes via interfacial polymerization was studied. Traditionally, the porous support layer is synthesized by phase inversion and subsequently impregnated with an aqueous amine solution before contacting it with an organic acyl chloride solution. In this simplified method, the phase inversion step and the impregnation with the amine monomer are carried out simultaneously by adding the amine to the coagulation bath before immersing the cast polymer film in it. This way, a two step process was successfully simplified into one step, combining both phase inversion and monomer impregnation of the support. Variation of synthesis parameters showed that a good membrane performance was achieved by adding 2 wt% m-phenylenediamine (as a monomer), triethylamine and sodium dodecyl sulfate (as a base/acylation catalyst and surfactant, respectively) to the coagulation bath. These synthesis conditions accord with the ones used in the traditional method. However, the polysulfone concentration, used for the synthesis of the support layer, could be lowered in the simplified method, without compromising in membrane performance. This method could lead to a more efficient, time and material saving synthesis of TFC membranes, which is of potential interest from a commercial and environmental point of view.publisher: Elsevier articletitle: Simplified synthesis route for interfacially polymerized polyamide membranes journaltitle: Journal of Membrane Science articlelink: http://dx.doi.org/10.1016/j.memsci.2013.10.005 content_type: article copyright: Copyright © 2013 Elsevier B.V. All rights reserved.status: publishe

Efficient synthesis of interfacially polymerized membranes for solvent resistant nanofiltration

Thin film composite (TFC) membranes are used worldwide in aqueous applications. They mostly consist of a polyamide top-layer put on a polysulfone support via interfacial polymerization. Due to their thin and dense selective layer, these membranes are also interesting for filtrations in organic solutions. Polysulfone should then be replaced by a more solvent resistant material. The synthesis of solvent resistant nanofiltration TFC membranes via a newly developed method is reported: phase inversion, crosslinking and impregnation of a polyimide support are combined by adding amines to the aqueous coagulation bath. Next, a thin polyamide top-layer is formed on the support via interfacial polymerization. Several amines are tested as crosslinker for the support and as monomer for top-layer formation. The use of an amine mixture is also explored. Membrane stability, time in the coagulation bath, effect of solvent activation and mass & solvent intensity of the process are investigated. This novel synthesis method minimizes the use of (hazardous) materials, thus requires less reagents and creates less waste. Moreover, time and effort are saved during the synthesis process, which is of great interest for membrane producers and from an environmental point of view.publisher: Elsevier articletitle: Efficient synthesis of interfacially polymerized membranes for solvent resistant nanofiltration journaltitle: Journal of Membrane Science articlelink: http://dx.doi.org/10.1016/j.memsci.2014.11.046 content_type: article copyright: Copyright © 2014 Elsevier B.V. All rights reserved.status: publishe

Cerebellar cognitive affective syndrome associated with topiramate.

The cerebellar cognitive affective syndrome (CCAS) represents a spectrum of cerebellar-induced neurocognitive and affective disturbances. In this report a patient is described who developed CCAS under a treatment with standard daily dose of the anti-epileptic drug topiramate (TPM). Cognitive disturbances consisted of impaired visuo-spatial memory, concentration deficits and executive dysfunctions. Behavior and affect were characterized by marked mood-swings and several disinhibited symptoms. After a gradual discontinuation of treatment with topiramate, a complete remission of the cognitive and affective symptoms was observed within 6 weeks. Functional neuroimaging studies by means of SPECT were conducted 2 weeks and 8 months following TPM discontinuation. This case report seems to suggest that functional disruption of the cerebello-cerebral circuitry, leading to CCAS, can follow treatment with topiramate.Case ReportsJournal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Changes in Metabolism as a Diagnostic Tool for Lung Cancer: Systematic Review

Lung cancer is the leading cause of cancer-related mortality worldwide, with five-year survival rates varying from 3–62%. Screening aims at early detection, but half of the patients are diagnosed in advanced stages, limiting therapeutic possibilities. Positron emission tomography-computed tomography (PET-CT) is an essential technique in lung cancer detection and staging, with a sensitivity reaching 96%. However, since elevated 18F-fluorodeoxyglucose (18F-FDG) uptake is not cancer-specific, PET-CT often fails to discriminate between malignant and non-malignant PET-positive hypermetabolic lesions, with a specificity of only 23%. Furthermore, discrimination between lung cancer types is still impossible without invasive procedures. High mortality and morbidity, low survival rates, and difficulties in early detection, staging, and typing of lung cancer motivate the search for biomarkers to improve the diagnostic process and life expectancy. Metabolomics has emerged as a valuable technique for these pitfalls. Over 150 metabolites have been associated with lung cancer, and several are consistent in their findings of alterations in specific metabolite concentrations. However, there is still more variability than consistency due to the lack of standardized patient cohorts and measurement protocols. This review summarizes the identified metabolic biomarkers for early diagnosis, staging, and typing and reinforces the need for biomarkers to predict disease progression and survival and to support treatment follow-up

Posterior fossa syndrome: a follow-up neuropsychological and neuroimaging study

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The cerebellum and language: a review

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