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1268 KiB

Open AccessArticle

Hydrophobic Ceramic Membranes for Water Desalination

by Joanna Kujawa, Sophie Cerneaux, Wojciech Kujawski and Katarzyna Knozowska

Appl. Sci. 2017, 7(4), 402; https://doi.org/10.3390/app7040402 - 15 Apr 2017

Cited by 44 | Viewed by 8604

Hydrophilic ceramic membranes (tubular and planar) made of TiO₂ and Al₂O₃ were efficiently modified with non-fluorinated hydrophobic grafting molecules. As a result of condensation reaction between hydroxyl groups on the membrane and reactive groups of modifiers, the hydrophobic surfaces [...] Read more.

Hydrophilic ceramic membranes (tubular and planar) made of TiO₂ and Al₂O₃ were efficiently modified with non-fluorinated hydrophobic grafting molecules. As a result of condensation reaction between hydroxyl groups on the membrane and reactive groups of modifiers, the hydrophobic surfaces were obtained. Ceramic materials were chemically modified using three various non-fluorinated grafting agents. In the present work, the influence of grafting time and type of grafting molecule on the modification efficiency was evaluated. The changes of physicochemical properties of obtained hydrophobic surfaces were determined by measuring the contact angle (CA), roughness (RMS), and surface free energy (SFE). The modified surfaces were characterized by contact angle in the range of 111–132°. Moreover, hydrophobic tubular membranes were utilized in air-gap membrane distillation to desalination of sodium chloride aqueous solutions. The observed permeate fluxes were in the range of 0.7–4.8 kg·m⁻²·h⁻¹ for tests with pure water. The values of permeate fluxes for membranes in contact with NaCl solutions were smaller, within the range of 0.4–2.8 kg·m⁻²·h⁻¹. The retention of NaCl in AGMD process using hydrophobized ceramic membranes was close to unity for all investigated membranes. Full article

(This article belongs to the Special Issue Membrane Distillation)

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2954 KiB

Open AccessArticle

Increasing the Performance of Vacuum Membrane Distillation Using Micro-Structured Hydrophobic Aluminum Hollow Fiber Membranes

by Chia-Chieh Ko, Chien-Hua Chen, Yi-Rui Chen, Yu-Hsun Wu, Soon-Chien Lu, Fa-Chun Hu, Chia-Ling Li and Kuo-Lun Tung

Appl. Sci. 2017, 7(4), 357; https://doi.org/10.3390/app7040357 - 04 Apr 2017

Cited by 25 | Viewed by 6648

Abstract

This study develops a micro-structured hydrophobic alumina hollow fiber with a high permeate flux of 60 Lm⁻²h⁻¹ and salt rejection over 99.9% in a vacuum membrane distillation process. The fiber is fabricated by phase inversion and sintering, and then modified [...] Read more.

This study develops a micro-structured hydrophobic alumina hollow fiber with a high permeate flux of 60 Lm⁻²h⁻¹ and salt rejection over 99.9% in a vacuum membrane distillation process. The fiber is fabricated by phase inversion and sintering, and then modified with fluoroalkylsilanes to render it hydrophobic. The influence of the sintering temperature and feeding temperature in membrane distillation (MD) on the characteristics of the fiber and MD performance are investigated. The vacuum membrane distillation uses 3.5 wt % NaCl aqueous solution at 70 °C at 0.03 bar. The permeate flux of 60 Lm⁻²h⁻¹ is the highest, compared with reported data and is higher than that for polymeric hollow fiber membranes. Full article

(This article belongs to the Special Issue Membrane Distillation)

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2844 KiB

Open AccessFeature PaperArticle

Exergy Analysis of Air-Gap Membrane Distillation Systems for Water Purification Applications

by Daniel Woldemariam, Andrew Martin and Massimo Santarelli

Appl. Sci. 2017, 7(3), 301; https://doi.org/10.3390/app7030301 - 20 Mar 2017

Cited by 16 | Viewed by 5512

Abstract

Exergy analyses are essential tools for the performance evaluation of water desalination and other separation systems, including those featuring membrane distillation (MD). One of the challenges in the commercialization of MD technologies is its substantial heat demand, especially for large scale applications. Identifying [...] Read more.

Exergy analyses are essential tools for the performance evaluation of water desalination and other separation systems, including those featuring membrane distillation (MD). One of the challenges in the commercialization of MD technologies is its substantial heat demand, especially for large scale applications. Identifying such heat flows in the system plays a crucial role in pinpointing the heat loss and thermal integration potential by the help of exergy analysis. This study presents an exergetic evaluation of air-gap membrane distillation (AGMD) systems at a laboratory and pilot scale. A series of experiments were conducted to obtain thermodynamic data for the water streams included in the calculations. Exergy efficiency and destruction for two different types of flat-plate AGMD were analyzed for a range of feed and coolant temperatures. The bench scale AGMD system incorporating condensation plate with more favorable heat conductivity contributed to improved performance parameters including permeate flux, specific heat demand, and exergy efficiency. For both types of AGMD systems, the contributions of the major components involved in exergy destruction were identified. The result suggested that the MD modules caused the highest fraction of destructions followed by re-concentrating tanks. Full article

(This article belongs to the Special Issue Membrane Distillation)

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5794 KiB

Open AccessFeature PaperArticle

Improving Liquid Entry Pressure of Polyvinylidene Fluoride (PVDF) Membranes by Exploiting the Role of Fabrication Parameters in Vapor-Induced Phase Separation VIPS and Non-Solvent-Induced Phase Separation (NIPS) Processes

by Faisal Abdulla AlMarzooqi, Muhammad Roil Bilad and Hassan Ali Arafat

Appl. Sci. 2017, 7(2), 181; https://doi.org/10.3390/app7020181 - 14 Feb 2017

Cited by 50 | Viewed by 10018

Abstract

Polyvinylidene fluoride (PVDF) is a popular polymer material for making membranes for several applications, including membrane distillation (MD), via the phase inversion process. Non-solvent-induced phase separation (NIPS) and vapor-induced phase separation (VIPS) are applied to achieve a porous PVDF membrane with low mass-transfer [...] Read more.

Polyvinylidene fluoride (PVDF) is a popular polymer material for making membranes for several applications, including membrane distillation (MD), via the phase inversion process. Non-solvent-induced phase separation (NIPS) and vapor-induced phase separation (VIPS) are applied to achieve a porous PVDF membrane with low mass-transfer resistance and high contact angle (hydrophobicity). In this work, firstly, the impacts of several preparation parameters on membrane properties using VIPS and NIPS were studied. Then, the performance of the selected membrane was assessed in a lab-scale direct-contact MD (DCMD) unit. The parametric study shows that decreasing PVDF concentration while increasing both relative humidity (RH) and exposure time increased the contact angle and bubble-point pore size (BP). Those trends were investigated further by varying the casting thickness. At higher casting thicknesses and longer exposure time (up to 7.5 min), contact angle (CA) increased but BP significantly decreased. The latter showed a dominant trend leading to liquid entry pressure (LEP) increase with thickness. Full article

(This article belongs to the Special Issue Membrane Distillation)

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3290 KiB

Open AccessArticle

Wetting Resistance of Commercial Membrane Distillation Membranes in Waste Streams Containing Surfactants and Oil

by Lies Eykens, Kristien De Sitter, Chris Dotremont, Wim De Schepper, Luc Pinoy and Bart Van Der Bruggen

Appl. Sci. 2017, 7(2), 118; https://doi.org/10.3390/app7020118 - 25 Jan 2017

Cited by 56 | Viewed by 8779

Abstract

Water management is becoming increasingly challenging and several technologies, including membrane distillation (MD) are emerging. This technology is less affected by salinity compared to reverse osmosis and is able to treat brines up to saturation. The focus of MD research recently shifted from [...] Read more.

Water management is becoming increasingly challenging and several technologies, including membrane distillation (MD) are emerging. This technology is less affected by salinity compared to reverse osmosis and is able to treat brines up to saturation. The focus of MD research recently shifted from seawater desalination to industrial applications out of the scope of reverse osmosis. In many of these applications, surfactants or oil traces are present in the feed stream, lowering the surface tension and increasing the risk for membrane wetting. In this study, the technological boundaries of MD in the presence of surfactants are investigated using surface tension, contact angle and liquid entry pressure measurements together with lab-scale MD experiments to predict the wetting resistance of different membranes. Synthetic NaCl solutions mixed with sodium dodecyl sulfate (SDS) were used as feed solution. The limiting surfactant concentration was found to be dependent on the surface chemistry of the membrane, and increased with increasing hydrophobicity and oleophobicity. Additionally, a hexadecane/SDS emulsion was prepared with a composition simulating produced water, a waste stream in the oil and gas sector. When hexadecane is present in the emulsion, oleophobic membranes are able to resist wetting, whereas polytetrafluoretheen (PTFE) is gradually wetted by the feed liquid. Full article

(This article belongs to the Special Issue Membrane Distillation)

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1739 KiB

Open AccessFeature PaperArticle

Membrane Operations for Process Intensification in Desalination

by Enrico Drioli, Aamer Ali and Francesca Macedonio

Appl. Sci. 2017, 7(1), 100; https://doi.org/10.3390/app7010100 - 20 Jan 2017

Cited by 36 | Viewed by 7109

Abstract

Process intensification strategy (PIS) is emerging as an interesting guideline to revolutionize process industry in terms of improved efficiency and sustainability. Membrane engineering has appeared as a strong candidate to implement PIS. The most significant progress has been observed in desalination where substantial [...] Read more.

Process intensification strategy (PIS) is emerging as an interesting guideline to revolutionize process industry in terms of improved efficiency and sustainability. Membrane engineering has appeared as a strong candidate to implement PIS. The most significant progress has been observed in desalination where substantial reduction in overall energy demand, environmental footprint, and process hazards has already been accomplished. Recent developments in membrane engineering are shaping the desalination industry into raw materials and energy production where fresh water will be produced as a byproduct. The present study discusses the current and perspective role of membrane engineering in achieving the objectives of PIS in the field of desalination. Full article

(This article belongs to the Special Issue Membrane Distillation)

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1778 KiB

Open AccessFeature PaperArticle

Improving Nanofiber Membrane Characteristics and Membrane Distillation Performance of Heat-Pressed Membranes via Annealing Post-Treatment

by Minwei Yao, Yun Chul Woo, Leonard D. Tijing, Cecilia Cesarini and Ho Kyong Shon

Appl. Sci. 2017, 7(1), 78; https://doi.org/10.3390/app7010078 - 12 Jan 2017

Cited by 30 | Viewed by 5867

Abstract

Electrospun membranes are gaining interest for use in membrane distillation (MD) due to their high porosity and interconnected pore structure; however, they are still susceptible to wetting during MD operation because of their relatively low liquid entry pressure (LEP). In this study, post-treatment [...] Read more.

Electrospun membranes are gaining interest for use in membrane distillation (MD) due to their high porosity and interconnected pore structure; however, they are still susceptible to wetting during MD operation because of their relatively low liquid entry pressure (LEP). In this study, post-treatment had been applied to improve the LEP, as well as its permeation and salt rejection efficiency. The post-treatment included two continuous procedures: heat-pressing and annealing. In this study, annealing was applied on the membranes that had been heat-pressed. It was found that annealing improved the MD performance as the average flux reached 35 L/m²·h or LMH (>10% improvement of the ones without annealing) while still maintaining 99.99% salt rejection. Further tests on LEP, contact angle, and pore size distribution explain the improvement due to annealing well. Fourier transform infrared spectroscopy and X-ray diffraction analyses of the membranes showed that there was an increase in the crystallinity of the polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) membrane; also, peaks indicating the α phase of polyvinylidene fluoride (PVDF) became noticeable after annealing, indicating some β and amorphous states of polymer were converted into the α phase. The changes were favorable for membrane distillation as the non-polar α phase of PVDF reduces the dipolar attraction force between the membrane and water molecules, and the increase in crystallinity would result in higher thermal stability. The present results indicate the positive effect of the heat-press followed by an annealing post-treatment on the membrane characteristics and MD performance. Full article

(This article belongs to the Special Issue Membrane Distillation)

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Review

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2748 KiB

Open AccessFeature PaperReview

Fouling in Membrane Distillation, Osmotic Distillation and Osmotic Membrane Distillation

by Mourad Laqbaqbi, Julio Antonio Sanmartino, Mohamed Khayet, Carmen García-Payo and Mehdi Chaouch

Appl. Sci. 2017, 7(4), 334; https://doi.org/10.3390/app7040334 - 29 Mar 2017

Cited by 76 | Viewed by 10540

Abstract

Various membrane separation processes are being used for seawater desalination and treatment of wastewaters in order to deal with the worldwide water shortage problem. Different types of membranes of distinct morphologies, structures and physico-chemical characteristics are employed. Among the considered membrane technologies, membrane [...] Read more.

Various membrane separation processes are being used for seawater desalination and treatment of wastewaters in order to deal with the worldwide water shortage problem. Different types of membranes of distinct morphologies, structures and physico-chemical characteristics are employed. Among the considered membrane technologies, membrane distillation (MD), osmotic distillation (OD) and osmotic membrane distillation (OMD) use porous and hydrophobic membranes for production of distilled water and/or concentration of wastewaters for recovery and recycling of valuable compounds. However, the efficiency of these technologies is hampered by fouling phenomena. This refers to the accumulation of organic/inorganic deposits including biological matter on the membrane surface and/or in the membrane pores. Fouling in MD, OD and OMD differs from that observed in electric and pressure-driven membrane processes such electrodialysis (ED), membrane capacitive deionization (MCD), reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), microfiltration (MF), etc. Other than pore blockage, fouling in MD, OD and OMD increases the risk of membrane pores wetting and reduces therefore the quantity and quality of the produced water or the concentration efficiency of the process. This review deals with the observed fouling phenomena in MD, OD and OMD. It highlights different detected fouling types (organic fouling, inorganic fouling and biofouling), fouling characterization techniques as well as various methods of fouling reduction including pretreatment, membrane modification, membrane cleaning and antiscalants application. Full article

(This article belongs to the Special Issue Membrane Distillation)

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