Increasing Feed Temperature Research Articles

A sustainable solution for fresh-water demand in mining sectors: Process water reclamation from POX effluent by membrane distillation

Direct contact membrane distillation (DCMD) was applied to the oxidation under pressure (POX) effluent treatment at different feed temperatures (50–70 °C) and recirculation flowrates (0.3–1.5 L/min). Two different commercial membranes made of poly(tetrafluoroethylene) (PTFE) and poly(vinylidenefluoride) (PVDF) were compared, including the contribution of an additional spacer, in terms of distillate recovery rate and retention efficiency. Lower wetting rates were obtained for lower feed temperatures and recirculation flowrate, which allowed for a greater permeate recovery rate. In contrast, an increase in both feed temperature and recirculation flowrate led to lower resistances. Among them, the resistance imposed by the membrane had the highest contribution to mass transfer resistance, whereas fouling resistance had negligible effects. Due to its lower hydrophobicity, PVDF membranes were more subjected to wetting if compared to PTFE membranes. Under the best conditions (PTFE with spacer, feed temperature of 60 °C and 0.3 L/min) the process had an average distillate flux of 6.82 L/m2 h and a permeate recovery rate of 33.91%, without compromising the permeate physicochemical quality. That corresponds to high values of metals and acidy retention, >95.7% and >99.9%, respectively, generating a permeate that can be used directly as reuse water in the mining plant. Regardless of that, both membranes maintained its rejection efficiency and distillate flux after 240 days exposed to the effluent under similar experimental conditions. Moreover, no significant changes were observed in their morphology or structure. Overall, DCMD was considered as a promising alternative for process water reclamation since the final temperature of this effluent can reach up to 80 °C, which corroborates the use of its residual heat as a driving force of DCMD, thus reducing the energy demand for the processing of this effluent.

Enhancing the pervaporation performance of PEBA/PVDF membrane by incorporating MAF-6 for the separation of phenol from its aqueous solution

Phenol is highly toxic and carcinogenic even at low concentrations. This study focused on preparing high-performance mixed matrix membranes (MMMs) for the pervaporation separation of phenol from its aqueous solution. A highly-efficient zeolitic metal azolate framework, RHO-[Zn(Heim)2] (MAF-6, Heim = 2-ethylimidazole) was incorporated into the polyether block amide (PEBA-2533) supported on the polyvinylidene fluoride (PVDF) ultrafiltration membrane. The MAF-6 was chosen as the filler due to its inherent hydrophobic surfaces and aperture size (7.6 Å), which is larger than the molecular kinetic diameter of phenol (6.6 Å). Effects of the casting solution concentration, active layer thickness, MAF-6 loading, operating temperature, and phenol concentration were systematically investigated. With the increase of the MAF-6 loading ratio X from 0 to 7, the phenol flux of the membrane was gradually enhanced, but the water flux was reduced. For 1000 ppm phenol aqueous solution at 80 °C, MAF-6–7@MMM displayed the optimal separation factor of 25.9 with a phenol flux of 89.2 g∙m−2∙h−1. The pervaporation separation index (PSI) of the MAF-6–7@MMM was 1317.7 kg∙µm∙m−2∙h−1 at 80 °C, which was much higher than the PEBA/PVDF membrane (787 kg∙µm∙m−2∙h−1). Impressively, an increasing feed temperature enhanced the phenol flux more prominently than water, owing to the hydrophobicity and porosity of MAF-6. Consequently, the resultant MAF-6-X@MMMs broke the trade-off limitation between phenol permeability and selectivity. The as-prepared membrane also exhibited exceptional long-term stability, suggesting its prospect of industrial application.

Numerical study on performance and efficiency of batch submerged vacuum membrane distillation for desalination

Harvesting clean water from seawater is widely studied in thermal-driven vacuum membrane distillation (VMD) application. Although the conventional VMD promotes excellent flux due to the deaeration by means of vacuum, the external heat supply of the system suffers the heat loss during pumping high feed volume. The batch submerged VMD (S-VMD) which has internal heat supply was introduced in this work to provide uniform feed temperature in the feed tank. This simple and space-saving design makes it particularly suitable to supply water for small community with space limitation. To evaluate the energy efficiency of the S-VMD in desalinating seawater, the performance of the system had been simulated and verified with the experimental results. The effects of main operating parameters including feed temperature and its circulation rate, heat transfer coefficient, vacuum degree on permeate side, packing density of membrane and temperature polarization on the membrane permeation flux using saline water feed had been experimentally investigated. Energy efficiency in terms of gained output ratio (GOR) and thermal loss of the heat supply had also been examined. The simulated results showed that the flux enhanced with the increase of feed temperature, circulation rate, vacuum degree and packing density of membrane. The combination of feed temperature with circulation flow and packing density of membrane played dominant role to improve permeate flux and GOR of the system. This finding is important for the future implementation of S-VMD system in space-constraint remote area. The simulation results were in good agreement with experimental results, recording less than 5% error.

Understanding the effects of operational conditions on the membrane distillation process applied to the recovery of water from textile effluents

This study analyzed the influence of operational conditions on the Direct Contact Membrane Distillation for synthetic effluents containing reactive and disperse dyes. Results of the permeate flux demonstrated different behavior of the process according to the class of dye. It was found a higher dependence of feed temperature to reactive dye and the analysis of temperature gradient between feed and permeate demonstrated the possibility of operation with higher temperatures in both streams to increase the permeate flux for both dyes. Feed flow rate influenced more the process with reactive dye, while the permeate flow rate determined this behavior for disperse dye. Energy factors showed that the gain output rate and energy efficiency enhanced with the increase of feed temperature, and the energy efficiency increased only with the permeate flow rate (and not with feed flow rate). The water distillation recovery rate was 97.3 % for reactive and 98.7 % for disperse dye; the color rejection of the dyes was over 98 %. These results indicated the adequate functionality of the process for water recovery of textile wastewater, providing an adequate permeate for possible reuse.

Alkaline stable thermal responsive cross-linked anion exchange membrane for the recovery of NaOH by electrodialysis

We report synthesis of acrylonitrile-vinylimidazole copolymer (PVACN) as novel cross-linking agent, for the fabrication of highly conducting stable and thermal responsive cross-linked polysulfone based anion exchange membrane (AEM) for the recovery caustic soda from industrial waste by electrodialysis. Reported cross-linker (PVACN) showed synergised properties aliphatic carbon chain and grafted ionic groups, while structural features of cross-linked AEM impart conductive and stable nature. Cross-linked architecture of the AEM also formed tight and dense structure. Reported PSCr (cross-linked polysulfone) AEMs possessed imidazolium quaternized groups to avoid Hoffmann elimination reaction (E2), while relatively less number of OH− attacking sites also showed membrane stability under alkaline medium. Suitable optimized PSCr/3 AEM exhibited 1.21 meq g−1 ion-exchange capacity (IEC), 5.5 × 10−2 S/cm ionic conductivity along with 21.7% swelling ratio, and assessed to be highly suitable for alkali recovery by electrodialysis. Electrodialytic recovery of NaOH was performed by increasing the concentrations about 5-times, while about 80% of treated water was also recovered as spin-off. Electro-dialyzer showed 1.33 kWh/kg energy consumption, 75.7% current efficiency at 35 °C, which were significantly improved with increase in feed temperature. Reported AEM provides sustainable and feasible alternative for applying ED for alkali separation/recovery from the industrial waste water.

Simulation Study on Direct Contact Membrane Distillation Modules for High-Concentration NaCl Solution.

Membrane distillation technology, as a new membrane-based water treatment technology that combines the membrane technology and evaporation process, has the advantages of using low-grade heat, working at atmospheric pressure with simple configuration, etc. In this study, heat and mass transfer were coupled at the membrane surfaces through the user-defined function program. The effects of feed temperature, feed velocity and permeate velocity on temperature polarization were mainly investigated for a high-concentration NaCl solution. The temperature polarization was increased with the increase of feed temperature and the decrease of feed and permeate velocity. The effects of temperature, inlet velocity and solution concentration on the evaporation efficiency of the membrane module for co- and counter-current operations were investigated in detail. The counter-current operation performed better than co-current operation in most cases, except for the condition where the NaCl concentration was relatively low or the module length was long enough. In addition, the optimal membrane thickness for both PVDF and PTFE was studied. The optimal membrane thickness was found in the range of 10 to 20 μm, which corresponded to the highest permeate flux for the selected materials, pore size distribution, and operation conditions. Membrane material with lower thermal conductivity and larger porosity was prone to get higher permeate flux and had larger optimal membrane thickness. Increasing feed velocity or feed temperature could decrease the optimal membrane thickness.

Behavior of volatile compounds in membrane distillation: The case of carboxylic acids

Thanks to its unique features, membrane distillation (MD) has been particularly applied for desalination but also for niches applications with feed solutions containing a mixture of volatile molecules. For such solutions, the complex interplay of the solutes and solvent physicochemical and operating parameters makes it challenging to predict the separation efficiency by MD. There is thus a need for a better understanding of the behavior of volatile compounds in MD as well as the influence of their physicochemical environment. This study aimed at investigating the influence of different operating parameters on rejection efficiency of air-gap MD towards carboxylic acids (formic, acetic and succinic acids). Acid rejection was found to be highly dependent on the carboxylic acid structure. In addition, it increased with the acid concentration, which could be related to the formation of acid dimers in the feed solution. This behavior is opposite to what is classically observed for pressure-driven membrane processes thus suggesting that MD can be a suitable alternative to these techniques for the concentration/separation of carboxylic acids. On the other hand, acid rejection decreased with the increase of feed temperature which could be explained by the calculation of the apparent energies of activation of both the water and carboxylic acids using an Arrhenius-type model. Finally, the acid dissociation rate played a key role in the acid rejection. Taking advantage of this observation, it was demonstrated how a simple pH adjustment can be used to successfully achieve the selective separation of ethanol (compared to acetic acid) from an acetic acid/ethanol aqueous mixture.

Vacuum membrane distillation multi-component numerical model for ammonia recovery from liquid streams

In this work, a modelling research on the separation of ammonia gas from liquid streams via vacuum membrane distillation (VMD) is conducted. An experimentally validated multi-component simulation model of a flat sheet VMD module is developed by implementing heat and mass balances through the feed, membrane and permeate channels. Continuous removal of the gases transferred through the membrane at a constant pressure in the permeate channel is assumed. The transport mechanisms through the pores under VMD conditions for both volatiles are discussed. Under studied VMD conditions and the typical concentration range in waste waters (i.e. 1-10 g TAN l-1), it is observed that none of the two volatile components (ammonia and water) is preferentially transported. The resulting VMD performance is simulated and evaluated in terms of total transmembrane flux, ammonia flux, ammonia selectivity and thermal energy consumption. The model was validated experimentally and showed good agreement, with an average relative error <10%. The experiments were performed with a solution of (NH4)2SO4 in a laboratory set up under controlled conditions. The simulation, as well as the experimental results, emphasize the existing trade-off between the flux (JNH3) and selectivity (SNH3) of ammonia. Increasing feed temperature and decreasing vacuum pressure results in higher JNH3 but lower SNH3. Moreover, those parameters that enhance the heat transfer through the membrane (i.e. feed temperature, pore size, porosity, vacuum pressure, etc.) promote the water flux over ammonia. While those parameters that enhance mixing and the ammonia mass transfer in the feed (i.e. feed velocity, spacer geometry, pH, ammonia feed concentration, etc.) promote the ammonia flux over water. The only operating parameter which enhances simultaneously the JNH3 and SNH3 is the feed velocity, indicating that the spacer geometry can play an important role in designing VMD modules for ammonia separation. VMD can extract and concentrate ammonia on the permeate side at a low specific thermal energy consumption. However, the JNH3 is greatly limited by the feed ammonia concentration which will ultimately determine the cost-effectiveness of the recovery. The trends described by the model are in agreement with other authors’ observations and give insight into the mechanisms dominating ammonia separation via VMD and its performance limits.

Effect of residual commercial antiscalants on gypsum scaling and membrane wetting during direct contact membrane distillation

Membrane distillation (MD) is considered as a promising technology for reverse osmosis (RO) brine treatment, but application of MD is significantly hampered by gypsum scaling and subsequent membrane wetting. As antiscalants are widely used in RO desalination, it is of interest to understand effects of residual antiscalants on membrane scaling during RO brine treatment using MD. In this work, MDC220, PTP-0100 and SHMP were adopted to study effects of residual antiscalants on water vapor flux, distillate conductivity and scale growth using a direct contact membrane distillation (DCMD) device. Feed temperature and antiscalant dose were investigated in ranges of 40–60 °C and 0–10 mg L−1, respectively. Moreover, morphological characterization of scale layers in the presence of antiscalants were performed using a field emission scanning electron microscopy. The results show that all the antiscalants neither decreased feed surface tension nor worsened distillate quality. The presence of antiscalants effectively retarded flux decline and distillate conductivity increase; SHMP and MDC220 outperformed PTP-0100 in restricting gypsum scaling. The performance of antiscalants was temperature dependent, and increased feed temperature adversely affected scaling inhibition performance. The dose of antiscalants played a significant role in gypsum scaling restriction and the inhibition performance was superb at a MDC220 dose not less than 5 mg L−1.

Moisture Content Throughout the Pelleting Process and Subsequent Effects on Pellet Quality

This experiment was designed to evaluate the effects of steam addition to the condi­tioner on moisture content throughout the pelleting process and subsequent effects on pellet quality. Treatments consisted of diets pelleted with no steam and steam added to achieve conditioning temperatures of 145 and 190°F. Conditioner retention time was set at 30 s and diets were pelleted with a ¼ × 2 ½ inch pellet die. Pellet samples were collected and immediately placed in an experimental counterflow cooler for 15 min. All treatments were replicated at 3 separate time points to provide 3 replicates per treatment. Mash, conditioned mash, hot pellets, and cooled pellet samples were collected for moisture content analysis, and cooled pellets for pellet durability index (PDI). Data were analyzed with pelleting run as the experimental unit and time period as the blocking factor. Moisture samples were analyzed as a 3 × 4 factorial of steam-conditioning and sample location. There was a steam-conditioning × sample interaction (P < 0.01) for moisture. Moisture in mash samples was similar for all treatments. For the no steam treatment, there was no difference in moisture content between the mash, conditioned mash, and hot pellets; however, moisture decreased in cooled pellets. For the 145°F treatment, there was an increase in moisture from mash to conditioned mash, followed by a decrease in both hot pellets and cooled pellets. For the 190°F treatment, moisture increased from mash to conditioned mash, and decreased in hot pellets and cooled pellets. Increasing conditioning temperature from no steam to 190°F increased (P < 0.01) PDI from 3.3, 59.1, to 91.1%, respectively. In conclusion, increasing feed temperature from 97.2 to 190°F via steam addition increased the conditioned mash moisture content by 4.2%, resulting in improved pellet quality.

Comparative evaluation of the radioactivity removal efficiency of different commercially available reverse osmosis membranes

Reverse osmosis (RO) is a water purification process that uses a semi-permeable membrane to remove ions from potable water. It has high rejection throughput, low energy consumption, and negligible pollution load when compared to conventional treatment methods. Comparative percentage salt rejection (SR) efficiency for surrogates of cesium and molybdenum was performed using commercially available membranes. Polyamide, polysulfone, polyamide–polysulfone composite, and cellulose acetate were subjected to various operating conditions in a domestically developed high-pressure membrane test cell. Five different concentrations of surrogate salts ranging from 100 to 500 ppm and varied pressures of 15–17 kg/cm2 combined with varying temperatures of the feed solution from 25°C to 45°C were used in this experimental work. It was found that the %SR efficiency of these membranes increased with the increase in salt concentration and feed temperature. However, a significant decrease in SR was observed with increasing pressure. A comparative study of these commercially available RO membranes was also performed against short-lived radioisotope Technetium-99m, and was determined by activity counts of feed and filtered samples using a well counter. The results suggest that the rejection efficiency was found to be highest in the case of polyamide–polysulfone composite, followed by polysulfone, polyamide, and cellulose acetate.

Biphenyl-based covalent triazine framework-incorporated polydimethylsiloxane membranes with high pervaporation performance for n-butanol recovery

Biphenyl-based covalent triazine framework (CTF) particles, as a new class of organic porous materials, were incorporated into polydimethylsiloxane (PDMS) for the fabrication of a high performance pervaporation membrane for n-butanol (n-BtOH) recovery. Increasing the CTF loading remarkably enhanced both the flux and the separation factor of the membrane. This was ascribed to the strongly hydrophobic, highly porous and mesoporous structure of CTF providing highly permeable and preferential pathways for n-BtOH. Importantly, compared to other reported PDMS-based mixed matrix membranes containing conventional microporous particles, our CTF-incorporated PDMS (CTF/PDMS) membrane exhibited a significantly higher flux and excellent separation factor. Increasing feed temperature and n-BtOH concentration further enhanced pervaporation performance. As a result, the maximum n-BtOH recovery performance (total permeate flux: 2816 ± 118 g m−2 h−1, separation factor: 62.8 ± 1.5 and permeate n-BtOH concentration: 71.5 ± 2.7 wt%) was attained when the CTF/PDMS membrane containing 12.5 wt% CTF was operated with a 4 wt% n-BtOH feed solution at 60 °C. Our proposed strategy provides an effective method to prepare high performance membranes for pervaporation and gas and organic solvent separation.

Effect of different conditions on pervaporation dehydration in CA/NYL66 blend membrane

In this study, cellulose acetate (CA) / nylon66 (NYL66) (95/5) blend membranes with different thicknesses were prepared by a solvent evaporation method. The effects of membrane thickness (almost 7-25 micrometre), feed concentration (70- 95 wt.% isopropanol), and feed temperature (30-60 C) were investigated on the performance of membrane in the separation of isopropanol-water mixtures. With regard to the results of sorption experiments, it was found that the increase of feed temperature enhanced the overall sorption while by increasing feed concentration, the overall sorption passed through a maximum value at 70 wt. % isopropanol (IPA) . The best separation factor 3080.51 was gained at high isopropanol concentration 95 wt.%, low feed temperature 30 C, and high membrane thickness 24.62 micrometre. Regarding the pervaporation separation index, the obtained results showed that proper values for the thickness of membrane, feed temperature, and isopropanol concentration in feed were 24.62 micrometre, 40 C, and 70 wt.%, respectively.

A highly selective sorption process in POSS-g-PDMS mixed matrix membranes for ethanol recovery via pervaporation

Incorporating nanofillers into polymer matrix to construct mixed matrix membranes (MMMs) is an effective approach to improve either sorption selectivity or diffusion selectivity or both. In this contribution, octa-vinyl polyhedral oligomeric silsesquioxanes (V-POSS) particles were chemically incorporated into polydimethylsiloxane (PDMS) matrix to fabricate POSS-g-PDMS MMMs. POSS-g-PDMS MMMs exhibited a homogeneous phase and achieved good integration between V-POSS and PDMS. Compared with pure PDMS membrane, POSS-g-PDMS MMMs possessed higher crosslinking density and gel content as well as enhanced ethanol affinity and hydrophobicity, which contributed to the significant improvement of ethanol sorption selectivity with a little sacrifice of diffusion selectivity. The chemical incorporation of V-POSS into PDMS matrix significantly enhanced both separation factor and permeation flux, which showed reversal trade-off effect. The best pervaporation performance of POSS-g-PDMS MMMs was achieved at 5 wt% POSS loading, with separation factor of 17.7 and permeation flux of 536 g/(m2 h), increased by 130% and 260% compared with pure PDMS membrane, respectively. An excessive POSS loading sharply depressed the fast transport of small molecules and finally led to the decline of diffusion selectivity and separation factor. The sorption and diffusion selectivity results suggested selective sorption was a major contributor to the high separation factor of MMMs at 5 wt% POSS loading, and diffusion was a rate-controlling process. The effect of variation of external driving forces and intrinsic membrane properties induced by increasing feed temperature and ethanol concentration on pervaporation performance was also investigated in detail. This work may provide useful insights of PDMS based mixed matrix membranes, especially those with covalent bonding between organic and inorganic phases for pervaporation recovery applications.

Study on vacuum membrane distillation coupled with mechanical vapor recompression system for the concentration of sulfuric acid solution

This paper presents a new vacuum membrane distillation (VMD) coupled with mechanical vapor recompression system for the concentration of sulfuric acid solution; the mathematical models based on the mass and energy balances in each part of the system are established. The influences of the corresponding operating parameters including feed concentration, feed temperature, feed velocity and permeate-side absolute pressure on membrane flux are investigated and discussed. The membrane flux increases with the increase in feed temperature and velocity, but it decreases with the increase in feed concentration and permeate-side absolute pressure. Furthermore, the energy consumption of the proposed system is explored through analyzing the influences from key factors, including boiling point elevation, temperature and concentration polarization and heat transfer temperature difference of heat exchanger on power consumption of compressor. Compared with the conventional VMD system and multi-effect MD system, the proposed system can save 77.6% and 20.4% energy due to a significant improvement in thermal efficiency by recovering the latent heat of vaporization. Eventually, an economic evaluation of the proposed system is performed comprehensively and the most optimized compression ratio of compressor can be obtained, which can guarantee the lowest energy consumption and total annual cost. Therefore, these results can provide significant references for the implementation and further optimization of the proposed system in the future.

Removal of dyes by poly(p‐phenylene terephthamide)/polyvinylidene fluoride hollow fiber in‐situ blend membranes

ABSTRACTIn order to obtain the compatible poly(p‐phenylene terephthalamide) (PPTA)/polyvinylidene fluoride (PVDF) blend membranes, the casting solution was synthesized via the in situ polycondensation process and flat sheet blend membranes were successfully prepared through the immersion precipitation phase inversion method in our previous study. In this study, the polycondensation solution was directly used as the spinning dope to fabricate PPTA/PVDF hollow fiber in‐situ blend membrane by the dry‐wet spinning technique. Hollow fiber membranes were employed to remove the dyes including Congo red (CR) and methylene blue (MB) from the dyeing liquor. Effects of operation conditions on dye rejection and membrane water flux were investigated. With the increase of operation pressure, feed concentration and feed temperature, dye rejection rates gradually decreased, but the rejection value of CR and MB still remained above 99.5%. On the contrary, the permeation water flux basically increased. During the continuous dye filtration of 300 min, hollow fiber membrane can maintain high dye rejection rates and stable water flux. The combination method of physical backwashing and chemical cleaning can effectively alleviate membrane fouling and recover membrane water flux. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48569.

Kapok Fibre as Membrane Distillation for Humic Acid Wastewater Treatment

Membrane distillation (MD) is a process of combining membrane with thermal desalination where it operates at two different temperatures which are hot and cold. A vapour pressure resulted between the temperature differences of two sides of the membrane is called permeate flux. In this study, kapok fibre, which provides hydrophobic properties, has been chosen as an alternative solution for synthetic membrane in the MD process. Therefore, the primary purpose of this research is to investigate the effect of feed temperature ranging from 40 to 70℃ towards the separation of pure water from humic acid (HA) wastewater. An experimental investigation for the performance of vacuum membrane distillation (VMD) system was performed to treat the HA wastewater to produce pure water. The experimental set up of VMD was set with kapok fibre acting as a barrier that separates the collected pure water from HA wastewater, which is conducted for four hours. Based on this study, the increase in the amount of calculated permeate flux correlates to the increase of feed temperature. The calculated permeate flux is 0.237 kgh-1m-2 at the temperature of 40℃. The amount of calculated flux increases steadily to 0.4 and 0.6 kgh-1m-2 respectively for every 10℃ increments. Furthermore, the physical properties of kapok fibre were analysed by using a scanning electron microscope (SEM). Surface morphology of the kapok fibre at the condition of before and after the MD process were studied without subjecting any chemical treatment on it. Accordingly, the physical properties of the kapok fibre were seen different after the MD process conducted. Additionally, the hydrophobic properties of the kapok fibre were evaluated by using an absorption test. The absorption test was conducted at varies temperature, which results in the highest percentage of absorptivity 4.823 % at 60℃. The hydrophobic kapok fibre has shown excellent properties that can be applied in the MD process and utilised in wastewater treatment.

Removal of benzothiophenes from model diesel/jet oil fuel by using pervaporation process: Estimation of mass transfer properties of the different membranes and dynamic modeling of a scale-up batch process

Removal of benzothiophenes is a crucial step in order to reduce sulfur content in transportation fuels up to the desired levels. In this study, pervaporation process is investigated for the removal of benzothiophenes from model diesel/jet fuels (benzothiophene/n dodecane mixtures). Values of different mass transfer parameters were estimated for different sulfur selective membranes by using reported experimental results. These parameters were then used to compare the membrane selectivity for benzothiophene. Polyimide membrane prepared from 2,3,5,6-tetramethyl-1,4-phenylenediamine showed the highest selectivity (1.99) towards benzothiophene at 393 K feed temperature. Membrane selectivity towards benzothiophene increased with increasing feed temperature for all membranes.Later, a mathematical model was developed for a scale-up batch pervaporation unit. The model was simulated to reduce the sulfur concentration from 303 PPM mole to 30.3 PPM mole in 100 liters of model diesel/jet fuel by using a 5 m2 spiral wound module. Simulations showed that all membranes are able to reduce the sulfur content up to the desired limit (303 PPM mole to 30.3 PPM mole). Polyimide/POSS hybrid membrane took 11.17 h to reduce sulfur concentration; however, the product recovery was low (7.05%). Moreover, polyimide membranes synthesized from 2,3,5,6-tetramethyl-1,4-phenylenediamine gave the highest product recovery 35.81% and took 21.33 h to reduce the sulfur concentration.

Flux enhanced water gap membrane distillation process-circulation of gap water

A New process and design of flux-enhanced and energy-efficient water gap membrane distillation (WGMD) module is experimentally tested and evaluated. The gap water is circulated in a separate closed loop to enhance the heat and mass transfer characteristics inside the MD module. A fundamental investigation is conducted to compare the performance of WGMD system with and without gap circulation at different operating conditions. Results showed that circulation of the gap water increases the system flux by 80 to 96% compared to without gap circulation, at the expense of some increase in energy consumed as indicated by the changes in feed and coolant water temperatures through the module. With gap circulation, a reduction in the electric specific energy consumption (SEC) between 15% and 25% was measured, associated with an increase in the gain output ratio (GOR) between 5 and 22%, compared to the case of no gap circulation. The energy utilization efficiency increase with increasing feed temperature. Higher circulation flow rates enhanced the flux while gap width showed marginal effects with circulation due to dominating forced convection inside the gap.

Experimental investigation of energy consumption and model identification of reverse osmosis desalination system fed by hybrid renewable energy source under different operating conditions

AbstractIn this article, the specific energy consumption (SEC) and water production cost (Cw) of a reverse osmosis (RO) desalination plant are investigated experimentally under different working conditions. The plant is fed by a hybrid renewable energy source. The frequency of the high‐pressure pump motor is changed from 35 to 50 Hz using a variable frequency drive. In addition, the feed water temperature and the reject control valve are controlled. This article investigates the effects of SEC, Cw, permeate salt concentration, and plant productivity. The results show that both SEC and Cw are reduced by increasing the frequency up to 45 Hz before rising thereafter. Also, SEC and Cw decrease with increasing feed temperature and reduced reject valve opening. As a result, the optimum values of SEC and Cw are found at 45 Hz and 40 °C with 25% valve opening, representing 4.5 kWh/m3 and 0.55 $/m3, respectively. Then, a model is proposed for the RO plant using the Matlab identification toolbox. The model is validated by comparing the simulation results with the experimental data. Based on the best fit ratio, the model presents good results for verification, which can be used for a process control design. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.