Direct Contact Membrane Distillation Configuration Research Articles

Performance analysis of a single and multi-staged direct contact membrane distillation module integrated with heat recovery units

In the present work, a single and multi-staged Direct Contact Membrane Distillation (DCMD) module is designed with optimal flow configuration to get the best DCMD system performance. An energy-efficient system was developed by integrating the DCMD module with heat exchangers (HXs). The heat exchangers were used to recover energy carried by the outgoing streams. The water productivity and energy requirement for the integrated DCMD-HX system was evaluated for both single and multistage DCMD configuration having the same membrane surface area. It was observed that the multistage DCMD configuration yielded a maximum water productivity of 16.34 LMH. An optimization problem was also developed with an objective to maximize the gain output ratio (GOR) of the integrated process. The multistage DCMD configuration could achieve the maximum GOR of 0.942. The minimum specific thermal energy consumption achieved for the integrated DCMD-HX system is 1100 kWh/m3 and 800 kWh/m3 for single and multistage DCMD, which is in accordance with the literature [1,2]. With optimization, the STEC value reduces to 711 kWh/m3 and 670 kWh/m3, respectively for single and multistage DCMD. The proposed flat sheet DCMD-HX configuration is found to be more energy-efficient than earlier literature reported DCMD-HX configuration without optimization. Further, optimization result concludes that a Mixed Integer Non Linear Programming (MINLP) problem can be formulated to achieve maximum GOR and product water by manipulating the number of DCMD stage and module for fixed membrane area.

The effect of chemistry of nanoparticle modifier groups on the PVDF membranes for membrane distillation

Recently, the synthesis of nanoparticles including their hydrophobic modifications for the synthesis of membranes for membrane distillation has shown incredible improvements in the; intrinsic physical and morphological properties, transmembrane flux, rejection, and life of the membrane. This study evaluates the effect of three different hydrophobic nanoparticles on the morphological, physical, and hydrophobic characteristics of the PVDF membranes. The octadecyl dihydrogen phosphate modified calcium carbonate (OC), octadecylamine modified Montmorillonite (OM), and Heptadeca- fluoro-1,1,2,2-tetrahydrodecyl) triethoxysilane modified silica (HS) nanoparticles were incorporated into the polyvinylidene difluoride (PVDF) membrane matrix in different compositions. The real seawater desalination performance of the newly synthesized membranes was tested in direct contact membrane distillation configuration for desalting the Arabian Gulf Seawater as feed. The PVDF membrane comprised of HS filler was the top performer with the highest water vapor flux of 42.3 LMH owing its CF2 functional groups, small chain length, small size and high electronegativity of F atoms, a stable C–F bonding interaction, and a low surface energy C–F compared to OC and OM nanoparticles. Also, HS incorporated membrane witnessed the highest anti-wetting and reliability by rejecting >98.7% ions from seawater.

Analysis of process intensification and performance assessment for fermentative continuous production of bioethanol in a multi-staged membrane-integrated bioreactor system

The work analyses process intensification in production of fermentative biofuel (bioethanol) in a multi-staged membrane integrated bioreactor system from sugarcane juice (SCJ) using Saccharomyces cerevisiae (NCIM 3205). Membrane based clarification, sterilization and concentration of sugar cane juice could replace several energy-intensive and polluting steps of conventional production schemes. Integration of traditional bioreactor with membrane-based devices for downstream purification of bioethanol enabled the system for recycling of cells and residual sugars to the fermentation unit through largely fouling free cross flow microfiltration and nanofiltration membrane modules. The new process design is characterized by high yield (0.48 g/g), productivity (14.6 g/L/h) and concentration capability (97.6 g/L) using concentrated SCJ of 22 wt% under high cell density in a flexible, compact, eco-friendly and modular plant. The final membrane distillation stage concentrated ∼98% pure ethanol in a solar-driven direct contact membrane distillation configuration using PTFE/PET hydrophobic membrane with enhanced flux with vis-à-vis the existing processes. A rectangular flat sheet cross flow membrane module in counter-current flow mode of hot and cold streams was employed. The membrane-based system achieves quite high levels of process intensification essential to sustainable operation at industrial scale. The achieved process intensification in the new system has been analysed vis-a-vis the existing conventional systems in terms of eco-friendliness, flexibility, cost of equipment and production, consumption of energy and material, profitability, E-factor, atom efficiency and business sustainability.

Testing of three different PVDF membranes in membrane assisted-crystallization process: Influence of membrane structural-properties on process performance

Throughout the world an intensified use of desalination for reducing current and future water scarcity is observed. Despite the enormous benefits of desalination processes, improvements are still required in terms of lower desalted water cost, higher productivity, better water quality and enhanced eco-sustainability of the desalination process. Environmentally sensitive concentrate management is today recognized as a significant hurdle to extensive implementation of desalination technologies. Membrane assisted crystallization (MCr) offers a suitable solution for redesigning desalination process through the treatment of brine streams for the production of salts and water. In this work, three different Hyflon/polyvinylidene fluoride (PVDF) composite membranes were tested in MCr operations. The coating of PVDF membranes with Hyflon allowed increasing membrane surface hydrophobicity. The latter is the membrane essential characteristic when MCr is implemented according direct contact membrane distillation configuration like in the present work. The aim was to analyze the MCr performance in terms of membrane chemical–physical properties and process operating conditions.

Innovative hydrophobic coating of perfluoropolyether (PFPE) on commercial hydrophilic membranes for DCMD application

Innovative hydrophobic coated membranes have been prepared and characterised in Direct Contact Membrane Distillation (DCMD) for potential water treatment applications. A UV-curable perfluoropolyether (PFPE) hydrophobic compound (Fluorolink® AD 1700) was used as coating material to tailor the surface of commercial microfiltration hydrophilic polyamide (PA) membranes with different pore sizes.The coated membranes consisted of a top thin hydrophobic porous layer overlying the hydrophilic commercial membrane support. Produced membranes were fully characterised in terms of surface and cross-section morphology, water contact angle, porosity, pore size and liquid entry pressure. The innovative coated hydrophobic membranes were tested in DCMD configuration, using deionized water and salty solution 0.6M (NaCl) as feed. In particular, the effect of the coating concentration on the permeate fluxes was investigated for different hydrophilic pore size commercial membranes (0.1–0.22–0.45μm). The measured permeate fluxes ranged between 4.56–22.81kg/m2h at different feed temperatures (40–50–60°C) keeping constant the permeate temperature at 14°C, for deionized water, whereas an average value of 11kg/m2h, at 50°C was found in case of the salty solution.

Effect of non-solvent additives on the morphology, pore structure, and direct contact membrane distillation performance of PVDF-CTFE hydrophobic membranes

Four common types of additives for polymer membrane preparation including organic macromolecule and micromolecule additives, inorganic salts and acids, and the strong non-solvent H2O were used to prepare poly (vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) hydrophobic flat-sheet membranes. Membrane properties including morphology, porosity, hydrophobicity, pore size and pore distribution were investigated, and the permeability was evaluated via direct contact membrane distillation (DCMD) of 3.5g/L NaCl solution in a DCMD configuration. Both inorganic and organic micromolecule additives were found to slightly influence membrane hydrophobicity. Polyethylene glycol (PEG), organic acids, LiCl, MgCl2, and LiCl/H2O mixtures were proved to be effective additives to PVDF-CTFE membranes due to their pore-controlling effects and the capacity to improve the properties and performance of the resultant membranes. The occurrence of a pre-gelation process showed that when organic and inorganic micromolecules were added to PVDF-CTFE solution, the resultant membranes presented a high interconnectivity structure. The membrane prepared with dibutyl phthalate (DBP) showed a nonporous surface and symmetrical cross-section. When H2O and LiCl/H2O mixtures were also used as additives, they were beneficial for solid–liquid demixing, especially when LiCl/H2O mixed additives were used. The membrane prepared with 5% LiCl+2% H2O achieved a flux of 24.53kg/(m2·hr) with 99.98% salt rejection. This study is expected to offer a reference not only for PVDF-CTFE membrane preparation but also for other polymer membranes.

Comparison of hollow fiber membranes in direct contact and air gap membrane distillation (MD)

Hollow fiber microporous membranes was used for seawater desalination in direct contact membrane distillation (DCMD) and air gap membrane distillation (AGMD) configurations. The efficiencies of hollow fiber membranes with different membrane materials and pore size were compared in a laboratory-scale DCMD system. The water flux and salt rejection were shown to be different depending on the membrane properties. The apparent permeabilities for water vapor and NaCl ion were estimated to determine the optimum membrane distillation (MD) membranes. A novel AGMD membrane module utilizing hollow fiber membranes was designed, and its prototype was fabricated using a 3D printer. Using this AGMD module, the performance of the hollow fiber membrane was examined and compared with the results from DCMD experiments. The water flux in AGMD configuration was less than 40% of that in DCMD configuration due to high mass transfer resistance and insufficient cooling plate area. However, it holds promise for practical applications of hollow fiber MD due to the higher thermal efficiency of AGMD than that of DCMD.

Direct contact membrane distillation for anaerobic effluent treatment

This study was conducted using direct contact membrane distillation configuration for treating effluent from a thermophilic anaerobic membrane bioreactor. The effluent was taken as feed to better understand the effect of treating anaerobic wastewater (with and without biomass) on the flux and fouling interaction on membrane distillation in batch mode. While treating the effluent without biomass, permeate fluxes varied from 1.41 to 9.22L/m2h at a temperature of (40–70°C) and cross flow velocities of 0.005, 0.008, 0.01, 0.012 and 0.014m/s. The COD and ammonia rejection at the stage was greater than 90%. In conditions where biomass was introduced in the feed at 6 and 12g/L MLVSS, it was observed that permeate flux decreased from 2 to 0.6L/m2h after 72h operation at 12g/L MLVSS wastewater, thus maximum observable fouling was also at 12g/L. Fouling investigation concluded that the major foulant on the MD membrane surface was removable fouling, accounting for 71–77.5% of the total fouling at a loading rate of 6 and 12g/L MLVSS, respectively. After cleaning, the membrane could recover 96% of the initial flux.

Exploring the spinning and operations of multibore hollow fiber membranes for vacuum membrane distillation

Hollow fiber membranes with a multibore configuration have demonstrated their advantages with high mechanical strength, easy module fabrication, and excellent stability for membrane distillation (MD). In this work, the microstructure of multibore fibers was optimized for vacuum MD (VMD). A microstructure consisting of a tight liquid contact surface and a fully porous cross‐section is proposed and fabricated to maximize the wetting resistance and VMD desalination performance. The new membrane exhibited a high VMD flux of 71.8 L m−2 h−1 with a 78°C model seawater feed. Investigations were also carried to examine various effects of VMD operational conditions on desalination performance. The 7‐bore membrane showed higher flux and superior thermal efficiency under the VMD configuration than the direct contact MD configuration. Different from the traditional single‐bore hollow fiber, the VMD flux of multibore membrane at the lumen‐side feed configuration was higher than that of the shell‐side feed due to the additional evaporation surface of multibore geometry. © 2013 American Institute of Chemical Engineers AIChE J, 60: 1078–1090, 2014