Microporous polypropylene membrane prepared via TIPS using environment-friendly binary diluents and its VMD performance

Performance investigation of poly(vinylidene fluoride-cohexafluoropropylene) membranes containing SiO2 nanoparticles in a newly designed single vacuum membrane distillation system

The current study focuses on the development of a superhydrophobic poly(vinylidene fluoride-cohexafluoropropylene) nanocomposite membrane suitable for vacuum membrane distillation by incorporating SiO2 nanoparticles. At loading hydrophobic nano-SiO2 particle concentration (0.50-1.50 wt.%), the developed nanocomposite membranes are optimized in terms of vacuum membrane distillation performance. The influence of temperature, vacuum pressure, and feed water flow is studied for desalinating high-salinity brine. The results show that the developed vacuum distillation membrane is capable of 95% salt rejection during the treatment of a highly saline feed (65,000 ppm) at fixed flow rates of 120 L/h saline feed and different operating conditions consisting of feed inlet temperatures ranging from 40°C to 70°C and distillate inlet temperatures of 7-15°C. The vacuum membrane distillation process achieves 0.38-1.66% water recovery with increasing concentration factor, meaning that recovery is increased, and shows a specific electrical energy consumption of 5.16-23.90 kWh/m3 for product water. Overall, the newly designed membrane demonstrates suitability for a vacuum membrane distillation system. PRACTITIONER POINTS: Desalinate high-salinity brine (TDS > 35,000 ppm) using a vacuum membrane distillation system. A hydrophobic PVDF-HFP/SiO2 nanocomposite membrane development for vacuum membrane distillation. A newly designed single vacuum membrane distillation system for RO brine treatment.

Polypropylene Hollow-Fiber Membrane Made Using the Dissolution-Induced Pores Method

The efficient preparation of hydrophilic polypropylene membranes has always been a problem. Here, a twin-screw extruder was used to melt-blend ethylene-vinyl alcohol copolymer and polypropylene; then, hollow fibers were extrusion-molded with a spinneret and taken by a winder; after this, dimethyl sulfoxide was used to dissolve the ethylene-vinyl alcohol copolymer of the fiber to obtain a polypropylene hollow-fiber membrane. This procedure was used to study the effects of different contents and segment structure of ethylene-vinyl alcohol copolymer on the structure and filtration performance of the membranes; furthermore, the embedded factor and blocked factor were used to evaluate the ethylene-vinyl alcohol copolymer embedded in the matrix without dissolving and or being completely blocked in the matrix, respectively. The results show that the increase in ethylene-vinyl alcohol copolymer could reduce the embedded factor and increase the blocked factor. The increase in the polyethylene segments of ethylene-vinyl alcohol copolymer could increase both the embedded factor and blocked factor. The water permeation of the membrane reached 1300 Lm⁻²·h⁻¹·bar⁻¹ with a 100% rejection of ink (141 nm) and the elongation at break reached 188%, while the strength reached 22 MPa. The dissolution-induced pores method provides a completely viable alternative route for the preparation of polypropylene membranes.

Green Approaches for Sustainable Development of Liquid Separation Membrane

Water constitutes one of the basic necessities of life. Around 71% of the Earth is covered by water, however, not all of it is readily available as fresh water for daily consumption. Fresh water scarcity is a chronic issue which poses a threat to all living things on Earth. Seawater, as a natural resource abundantly available all around the world, is a potential water source to fulfil the increasing water demand. Climate-independent seawater desalination has been touted as a crucial alternative to provide fresh water. While the membrane-based desalination process continues to dominate the global desalination market, the currently employed membrane fabrication materials and processes inevitably bring adverse impacts to the environment. This review aims to elucidate and provide a comprehensive outlook of the recent efforts based on greener approaches used for desalination membrane fabrication, which paves the way towards achieving sustainable and eco-friendly processes. Membrane fabrication using green chemistry effectively minimizes the generation of hazardous compounds during membrane preparation. The future trends and recommendations which could potentially be beneficial for researchers in this field are also highlighted.

Binary mixtures of semicrystalline polymers with low-molecular-mass compounds: thermal behaviour and phase structure

The results of phase equilibrium studies in mixtures of semicrystalline polymers with low-molecular-mass compounds are summarized and analyzed. A new classification of phase diagrams for such mixtures is proposed. Alternative points of view on the phase composition of semicrystalline polymers are presented. The phase structure evolution during the thermally induced phase separation of mixtures is monitored and the morphology of the forming capillary porous bodies as precursors of polymeric membranes is described. The general regularities concerning the influence of the nature of mixture components, polymer molecular mass, temperature scanning rate and other factors on the topology of phase diagrams are considered. Experimental methods used to construct the phase diagrams of mixtures and to study features of their phase structure are compared.

The bibliography includes 203 references.

Analysis of the Thermal Behavior of Polypropylene-Camphor Mixtures for Understanding the Pathways to Polymeric Membranes via Thermally Induced Phase Separation

An experimental phase diagram of the isotactic polypropylene-camphor system is constructed using an original optical method. It considerably deviates from the dynamic diagram, which can be obtained using conventional differential scanning calorimetry (DSC), and contains an additional boundary line that describes camphor solubility in the polymer. An accurate phase diagram makes it possible to perform a detailed and consistent thermodynamic analysis of the DSC, optical, and scanning electron microscopy data on the cooling of prehomogenized mixtures of different compositions, which leads to the formation of capillary-porous bodies via thermally induced phase separation. The removal of camphor results in the formation of polypropylene membranes, the morphology and functional properties of which, such as the total pore volume, mean pore size, permeability coefficient, and breaking stress, appear to be highly dependent on the composition of the initial binary system. It is shown that thermally induced phase separation induces the formation of microscopic cracks in the studied membranes. The crack density decreases with the polymer content in the initial system, but at 53 wt % of polypropylene, the membrane becomes completely impermeable to isopropanol despite the presence of large ∼4 μm pores, thus questioning the perspectives of its practical use. In general, the study makes it possible to achieve a deeper understanding of the membrane formation process via thermally induced phase separation in the mixtures of semicrystalline polymers with low molar mass substances.

Fabrication of PP hollow fiber membrane via TIPS using environmentally friendly diluents and its CO2 degassing performance

CO₂ removal is an essential water purification process in many fields, such as petrochemical production and thermal power generation. It is challenging to remove low concentrations of CO₂ from RO effluent water. The core component of the membrane degassing technique is a high-performance hydrophobic microporous membrane. Polypropylene (PP) membranes were prepared with environmentally friendly binary diluents via thermally induced phase separation. Firstly, the effects of PP concentration on the phase diagram, flat sheet membrane structure and mechanical properties were studied to optimize the PP content for a hollow fiber membrane (HFM). The PP HFM showed a sponge-like cross-sectional structure without any dense skin layer, a large loading force and breaking elongation, and a narrow pore size distribution with a mean pore size of 0.16 μm. The as-fabricated PP HFM module was applied for CO₂ removal from RO effluent water from a petrochemical plant. A higher water temperature and vacuum degree facilitated CO₂ removal. Increasing the effective membrane length enhanced degassing efficiency. Increasing the water flow rate increased CO₂ degassing flux, but simultaneously decreased degassing efficiency. When the water flow rate increased from 20 mL min⁻¹ to 63 mL min⁻¹, although the effective membrane length increased from 3 m to 4.8 m for the best degassing efficiency of 88%, the amount of treated water increased by 3.15 times. The declined CO₂ concentration in the outlet water was 1.6 mg L⁻¹.

A PP membrane prepared via TIPS using CO/SO as environmentally friendly binary diluents to remove low-concentration CO₂ from RO effluent water.

The Influence of Talc Addition on the Performance of Polypropylene Membranes Formed by TIPS Method

The effect of talc addition on the morphology of capillary membranes formed by a thermally induced phase separation (TIPS) method was investigated in the presented work. The usability of such formed membranes for membrane distillation was evaluated. Two types of commercial capillary polypropylene membranes, fabricated for microfiltration process, were applied in the studies. A linear arrangement of polymer chains was obtained in the walls of membranes formed without a talc addition. In the case of membranes blended with talc, the linear structure was disordered, and a more porous structure was obtained. The changes in morphology enhanced the mechanical properties of blended membranes, and their lower thermal degradation was observed during 350 h of membrane distillation studies. Long-term studies confirmed the stability of talc dispersion in the membrane matrix. A leaching of talc from polypropylene (PP) membranes was not found during the membrane distillation (MD) process.

Capillary Polypropylene Membranes for Membrane Distillation

Only nonwetted porous membranes can be used in membrane distillation. The possibility of application in this process the capillary polypropylene membranes manufactured by thermally-induced phase separation was studied. The performance of a few types of membranes available commercially was presented. The resistance of the membranes to wetting was tested in the continuous process of water desalination. These studies were carried out for 1000 h without module cleaning. The presence of scaling layer on the membranes surface was confirmed by Scanning Electron Microscope observations. Both the permeate flux and distillate conductivity were almost not varied after the studied period of time, what indicates that the used membranes maintained their nonwettability, and the negative influence of scaling was limited. The role of surface porosity on the pore wetting and influence of membrane wettability on the quality of the distillate obtained were discussed.

Fabrication of a loose nanofiltration candidate from Polyacrylonitrile/Graphene oxide hybrid membrane via thermally induced phase separation

It is still a challenge to design and fabricate a robust nanoporous membrane in large scale and of fundamental importance for practical application. Here, a robust three/two-dimensional polyacrylonitrile/graphene oxide (PAN/GO) homogeneous nanoporous membrane is fabricated in large scale via thermally induced phase separation method, which guarantees the membrane with high mechanical strength and selective separation properties. Differing from conventional nanofiltration (NF) membrane with high rejection to both salt and dye, the resulting hybrid membrane is relative loose, which shows outstanding performances, i.e. high dye rejection and low salt rejection, high permeability and antifouling properties, acting as a promising candidate for dye/salt fractionation. The incorporation of 0.2 wt% GO endows membrane with excellent performance, where high tensile strength, high water permeability (33 L⋅ m^-2⋅ h^-1⋅ bar^-1), selectivity (100% to methyl blue, 99.8% to acid red 18, 26.7% to magnesium sulfate and 10.9% to sodium chloride and flux recovery ratio of 84.4%) are perfectly balanced. Its homogeneous structure and high strength guarantee long term use without the peeling of thin active layer as encountered by conventional NF membranes. The successful fabrication of such a hybrid membrane provides an attractive opportunity for loose NF membrane preparation with performance enhancement in a feasible way for practical application.

The Effect of Diluent Mixture with Upper Critical Solution Temperature on Membrane Formation Process, Microstructure, and Performance of PVDF Hollow Fiber Membrane by TIPS Process

Thermally induced phase separation (TIPS) is a technique to prepare commercial membrane. However, the quick polymer crystallization during the quenching process will bring about a dense and thick skin layer and thus decrease permeability markedly. In this paper, a diluent mixture with upper critical solution temperature (UCST) was used to prepare polyvinylidene fluoride (PVDF) hollow fiber membrane. That is, the separation between diluent (propylene carbonate (PC)) and non-diluent (dioctyl terephthalate (DOTP)) occurred during the quenching process when the temperature of the dope was lower than 110 °C. The effects of separation between PC and DOTP and the resulting coalescence of DOTP on the PVDF crystallization process, microstructure, and the permeability of the membranes were analyzed. The results showed that the suitable PC/DOTP weight ratio reduced the thickness of the skin layer near the outer surface markedly and resulted in a porous outer surface, and the microstructure evolution process was proposed. The maximum pure water flux for the prepared membrane is up to 128.5 L·m-2·h-1 even in a dry mode without using a hydrophilizing agent. The rejection rate of the carbonic particle is nearly 100%. This study presents a novel and simple way to fabricate the microporous membrane with the interconnected pore structure.