Sweeping Gas Membrane Distillation Process Research Articles

Performance and exergy analysis of vacuum-assisted sweeping air membrane distillation and bubble column dehumidifier

This study provides a comprehensive theoretical analysis of an integrated Sweeping Gas Membrane Distillation (SGMD) and Bubble Column Dehumidifier (BCD) system for cost-effective water desalination. Analytical investigations on this novel system are not available in the literature which represents a knowledge gap. The current analytical study offers insights into the efficiency of the integrated SGMD-BCD system, identifies optimal operational conditions, and provides benchmark data for future scaling-up and commercialization. The theoretical model, based on solving heat and mass transfer equations, is validated against the experimental data. An exergy analysis of the integrated SGMD-BCD is considered to explore the possible improvements in the design and operation for enhanced performance. Results reveal a peak GOR of 0.41 under maximal tested feed flow rates and temperatures, coupled with minimal air flow rates and air channel pressures. The BCD achieves maximum effectiveness in the range of 0.95–0.98 at feed temperature of 90 °C. Exergetic efficiency reaches its peak at 3.25%, observed at the lowest feed flow rate (1 L/min) and temperature (40 °C). Notably, the SGMD process exhibits 18 to 20 times the exergy destruction compared to the BCD at a 90 °C feed temperature, highlighting the need for improvements in its design and operation.

Surface modified porous polyetherimide hollow fiber membrane for sweeping gas membrane distillation of dyeing wastewater

Highly porous polyetherimide (PEI) hollow fiber membranes were prepared through a spinning process. The membranes were modified by a dip-coating method using polydimethylsiloxane (PDMS) to increase surface hydrophobicity. The membranes were used in a sweeping gas membrane distillation (SGMD) process for separation of methylene blue (MB) solutions. From FESEM examination, an open structure with large finger-like cavities was observed in the membrane structure. The PEI-PDMS membrane presented a high surface porosity with N2 permeance of 15300 GPU and mean pore size of 72 nm. Formation of an ultra-thin PDMS coated layer resulted in an improved surface hydrophobicity with water contact angle of around 104º. Moreover, the coated layer resulted in the increment of critical water entry pressure from 250 to 400 kPa. The PEI and PEI-PDMS membranes indicated pure water flux of 26.2 and 22.5 kg/m2 h, respectively, through the SGMD process at feed temperature of 60 °C. During 5 days of the SGMD process, the PEI and PEI-PDMS showed an approximate permeation flux reduction of 42% and 19%, respectively. The PEI-PDMS membrane showed a good antifouling property with flux recovery ratio of about 89.4%. Adsorption of MB on the outer surface of the membranes was confirmed by studying the variation of fouling factor vs. MB concentration in the feed solution. The improved PEI-PDMS membrane demonstrated a high permeation flux and antifouling properties which are promising parameters for a prolonged membrane distillation operation.

Utilization of Bidirectional Cation Transport in a Thin Film Composite Membrane: Selective Removal and Reclamation of Ammonium from Synthetic Digested Sludge Centrate via an Osmosis-Distillation Hybrid Membrane Process.

Selective removal and resource recovery of ammonium nitrogen (NH4+-N) from high-strength ammonium waste streams is of practical importance for biological wastewater treatment and environmental protection. In this study, we demonstrate the simultaneous removal and reclamation of ammonium from synthetic digested sludge centrate via a novel osmosis-distillation hybrid membrane (ODHM) process. Using NaHCO3 as the draw solute, ammonium diffuses from the synthetic centrate to the draw solution by utilizing the bidirectional cation transport nature of the thin film composite (TFC) membrane. Then, NH4+ is converted to gaseous NH3 at 60 °C and recovered by a sweeping gas membrane distillation (SGMD) process. Herein, the bidirectional transport of monovalent cations in the osmotic process, selectivity of TFC membranes for different cations, and recovery of the draw solution following the extraction of ammonia through the SGMD process were systematically investigated. The removal of NH4+-N from the synthetic centrate achieved 21.34% during a 6-h continuous operation of the ODHM system, with ammonium fluxes through the TFC and SGMD membranes at 1.39 and 0.57 mol m-2 h-1, respectively. A secondary interfacial polymerization was proposed to further enhance ammonium transport through the TFC membrane. Results reported here highlight the potential of the ODHM process for the selective removal and reclamation of ammonium from ammonium-rich waste streams.

Computational study of sweeping gas membrane distillation process – Flux performance and polarization characteristics

Computational fluid dynamics simulations were conducted in a three-dimensional sweeping gas membrane distillation (SGMD) desalination module. The module flux performance and polarization characteristics were investigated for a wide range of flow rates spanning the laminar and turbulent flow regime in the feed and permeate channel. The membrane was treated as a functional surface with zero thickness, and the membrane permeability was determined by a combination of Knudsen and molecular diffusion using the Dusty Gas model. The mathematical model and numerical method was validated against existing experimental work. It was shown that low membrane thickness, high porosity, and low tortuosity yield high vapor flux. It was demonstrated that high vapor flux can be achieved in a SGMD module by increasing the permeate flow rate to avoid temperature and moisture polarization in the permeate channel. By increasing the feed flow rate, the flux also increased, and temperature and concentration polarization decreased. It was shown that the SGMD process, as effective as other MD processes, could be used as an alternative method for water desalination. The model developed here can be utilized for design and optimization of full-scale SGMD modules.

Study on commercial membranes and sweeping gas membrane distillation for concentrating of glucose syrup

In this work, sweeping gas membrane distillation (SGMD) process was used for concentrating of glucose syrup. The main questions in this work include: is SGMD process practical for concentrating of glucose solution prior the fermentation step in bioethanol process?. and are the commercially available hydrophobic membranes sufficient enough to develop the SGMD process in pilot scale for this issue?. To answer these questions, SGMD process was performed using three commercial membranes made of PP, PVDF and PTFE. All membranes characterized using scanning electron and atomic force microscopes for their morphological and topographical features. Important operating parameters including feed temperature (45-65O C), feed flow rate (400-800 mL/min), feed concentration (10-50 g/L), and gas flow rate (0.113-0.453 N.m3 /h) were studied for their effects on the permeate flux and the optimized parameters were then reported. Moreover, the influence of three flow arrangements of SGMD module (co-current, counter-current and cross-current) on the permeate flux was studied. The best performance (the highest permeate flux and rejection) was achieved when the PTFE membrane (0.22 µm) was used under the optimum operating conditions (feed temperature: 65o C; feed flow rate: 600 mL/min; gas flow rate: 0.453 N.m3 /h; feed flow channel depth: 2 mm; and the cross-current flow arrangement). Results indicated that SGMD process is a promising option for concentrating of the sugar syrup prior the fermentation step in the bioethanol production process.

Concentrating of Sugar Syrup in Bioethanol Production Using Sweeping Gas Membrane Distillation.

Membrane distillation (MD) is a relatively new and underdeveloped separation process which can be classified as a green technology. However, in order to investigate its dark points, sensitivity analysis and optimization studies are critical. In this work, a number of MD experiments were performed for concentrating glucose syrup using a sweeping gas membrane distillation (SGMD) process as a critical step in bioethanol production. The experimental design method was the Taguchi orthogonal array (an L9 orthogonal one) methodology. The experimental results showed the effects of various operating variables, including temperature (45, 55, and 65 °C), flow rate (200, 400, and 600 ml/min) and glucose concentration (10, 30, and 50 g/l) of the feed stream, as well as sweeping gas flow rate (4, 10, and 16 standard cubic feet per hour (SCFH)) on the permeate flux. The main effects of the operating variables were reported. An ANOVA analysis showed that the most and the least influenced variables were feed temperature and feed flow rate, each one with 62.1% and 6.1% contributions, respectively. The glucose rejection was measured at 99% for all experiments. Results indicated that the SGMD process could be considered as a versatile and clean process in the sugar concentration step of the bioethanol production.

Sweeping Gas Membrane Distillation (SGMD) as an Alternative for Integration of Bioethanol Processing: Study on a Commercial Membrane and Operating Parameters

This article considers the application of the sweeping gas membrane distillation process (SGMD) for direct separation of ethanol-water using a flat sheet PTFE membrane. It also studies the effect of operating parameters including feed concentration, feed temperature, feed flow rate, and sweeping gas flow rate on the permeation flux and selectivity of ethanol/water. The results showed that the increase in feed temperature increases in permeate flux and selectivity. Selectivities of 18.5 to 25 were achieved using dilute feeds within the temperature range of 35 to 55°C. However, by increasing the feed concentration by more than 5 wt.%, the selectivity was decreased. The increase in permeation flux and ethanol selectivity at higher feed flow rates was mainly due to the reduction of polarization effects. Moreover, the PTFE membrane was characterized by AFM. The results showed that the present process could be used as a stand-alone technique for bioethanol process integration.

Artificial neural network model for desalination by sweeping gas membrane distillation

Sweeping gas membrane distillation process (SGMD) has been used for desalination and its performance index, defined as the product of the distillate flux and the salt rejection factor, has been modeled using artificial neural network (ANN) methodology. A feed-forward ANN has been developed for prediction of the performance index based on a set of 53 different experimental SGMD tests. A feed solution of 30g/L sodium chloride was used in all experiments and the salt rejection factors were found to be greater than 99.4%. The individual and interaction effects of the input variables, namely the feed inlet temperature, the feed flow rate or the feed circulation velocity, and the air flow rate or the air circulation velocity, on the SGMD performance index have been investigated. The optimum point was determined by means of Monte Carlo simulation. The obtained optimal conditions were a feed inlet temperature of 69°C, an air flow rate of 34.5L/min (i.e. 2.02m/s air circulation velocity) and a feed flow rate of 160L/h (i.e. 0.155m/s liquid circulation velocity). Under these operating conditions a performance index of 1.493×10−3kg/m2.s has been achieved experimentally being the maximal SGMD performance index obtained inside the region of experimentation.

Sweeping gas membrane distillation of sucrose aqueous solutions: Response surface modeling and optimization

Response surface methodology and desirability function approach have been applied for modeling and multi-response optimization of sweeping gas membrane distillation process used for concentration of sucrose aqueous solutions. Response surface models have been developed to predict the permeate flux and the sucrose concentration rate. The models have been statistically validated by ANOVA. The sucrose rejection factor was found to be greater than 98.9% and therefore the response surface model can not be developed for this response. The models have been used to perform the overall desirability function. In addition, the overlap contour plots have been drawn to study the interaction effects between operating parameters on both the permeate flux and the sucrose concentration rate, to identify the desirability zone and to determine the optimal point. The optimal operating conditions were found to be 70.9 °C feed temperature, 2.09 m/s air circulation velocity and an initial sucrose concentration of 223 g/L. Under these conditions the measured permeate flux 1.077 × 10 −3 kg/m 2 s and the sucrose concentration rate 4.686 g/L h were found to be the highest values in this study confirming the validity of the applied sweeping gas membrane distillation optimization procedure.

Modeling and optimization of sweeping gas membrane distillation

A central compositional orthogonal design has been applied for modeling and optimization of sweeping gas membrane distillation process. The effects of the operational parameters, liquid temperature, gas temperature, liquid flow rate and gas flow rate and their binary interactions on the membrane distillate flux (i.e. permeate flux) have been investigated. The developed model has been statistically validated by analysis of variance and further used to predict the distillate flux. The optimum operating conditions have been determined by Monte Carlo method finding a liquid inlet temperature of 71.6°C, a gas inlet temperature of 17.3°C, a water circulation velocity of 0.16m/s (i.e. flow rate of 165L/h) and a gas circulation velocity of 2.11m/s (i.e. flow rate of 36L/min). Under these optimal conditions the measured water distillate flux was 2.789×10−3kg/m2.s, while the predicted distillate flux was only 2% higher confirming the developed model. Desalination experiments were performed under the optimum conditions using a feed 30g/L NaCl solution and Mediterranean seawater. The obtained distillate fluxes were 2.31×10−3kg/m2.s and 2.05×10−3kg/m2.s for NaCl solution and seawater, respectively; and the salt rejection factors were 99.94% for 30g/L NaCl solution and 99.48% for seawater.

Numerical simulation and experimental studies on heat and mass transfer using sweeping gas membrane distillation

A plate-and-frame membrane module has been used in sweeping gas membrane distillation process. Both numerical simulation and experimental studies have been carried out. The numerical simulation focuses on modelling heat, mass and momentum transport through the three parts of the sweeping gas membrane distillation system, namely: feed, membrane and permeate side. The model is based on Navier-Stokes equations coupled with the Darcy-Brinkman-Forcheimer formulation in transient regime in two-dimensions. A strong solver based on a compact Hermitian method has been used for solving partial derivative equations. The whole parts of the system are represented by only one domain of resolution instead of considering multi-domain approach but using non-regular discretization. The numerical simulations were conducted for different operational parameters at the module inlets such as the feed temperature, the permeate temperature, the sodium chloride feed concentration, the feed velocity and the permeate velocity. The results were validated in comparison with experimental results. Good agreements between the numerical simulation and the experimental permeate fluxes have been found.

Pollutants removal from wastewaters through membrane distillation

The Sweeping Gas Membrane Distillation process is considered for the treatment of wastewaters containing volatile organic compounds such as acetone and ethanol. The separation technique is based on the use of microporous hydrophobic membranes under conditions of non wettability, in which the membrane separates an aqueous phase from a stripping gas. A wide experimental investigation is performed to study the role of temperature, composition and flow rate of the liquid phase and the influence of the sweeping gas flow rate. Performances of flat PTFE membranes are studied in the case in which dry nitrogen is used as stripping agent. Liquid feed flow rate as well as nitrogen flow rate are identified as the major design quantities since they greatly affect the separation efficiency. A simplified mathematical model is developed to describe multicomponent mass transfer in the gas phases, in which a pseudo-binary diffusion approach is assumed; molecular diffusion is considered as the prevailing transport mechanism through the membrane. The results obtained are compared with the experiments and the validity range of the model is defined.

Thermal boundary layers in sweeping gas membrane distillation processes

AbstractThe sweeping gas membrane distillation process was analyzed in a plate and frame membrane module, and a method clarifying the contribution of each boundary layer separately was developed. The temperature polarization coefficients of the fluid phases as well as the overall one have been defined, and their effects on the permeate flux were studied. Also studied is the influence of experimentally relevant parameters, such as the inlet temperatures or circulation velocities of the fluids. Results from two porous and hydrophobic membranes in different experimental conditions were interpreted on the basis of a combined Knudsen/molecular diffusion flow model. The theory agreed well with the experiment.