Required Membrane Area Research Articles

Factors that influence the membrane area of a multistage microfiltration process required to produce a micellar casein concentrate

The objective of the work reported in this paper was to develop a theoretical model to determine the effect of type of microfiltration (MF)-process feed, number of stages, and flux on the minimization of the MF membrane area required to produce a 95% serum protein–reduced micellar casein concentrate. The MF feed, number of stages, and flux were all factors that had an effect on the MF membrane area and should be taken into consideration when designing a MF system to produce a 95% serum protein–reduced micellar casein concentrate. Feeding the MF process with a diluted ultrafiltration retentate (DUR) diluted to the protein concentration of skim milk, as opposed to skim milk, reduced the required membrane area by 36% for a 5-stage process. When DUR was the MF feed, feed protein concentration, which depended on the number of MF stages, was optimized. The DUR protein concentration that minimized the required MF membrane area was 2.47, 3.85, 4.77, and 5.41% for a 2-, 3-, 4-, or 5-stage MF process, respectively. For a 5-stage process, increasing the protein concentration of the feed from 3.2 to 5.4% decreased the required MF membrane area by 10%. It was also found that as the number of stages increased from 2 to 5, the required MF membrane area decreased by 39%, when the MF feed was DUR at the optimal feed protein concentration. Finally, increasing the flux from 50 to 60kg/m2 per hour decreased the required MF membrane area by 17% when the MF feed was DUR at the optimal MF feed protein concentration. Overall, using DUR as a feed for MF could reduce the amount of MF membrane area required to make a 95% serum protein–reduced micellar casein concentrate.

Innovative use of membrane contactor as condenser for heat recovery in carbon capture.

The gas-liquid membrane contactor generally used as a nonselective gas absorption enhancement device is innovatively proposed as a condenser for heat recovery in liquid-absorbent-based carbon capture. The membrane condenser is used as a heat exchanger to recover the latent heat of the exiting vapor from the desorber, and it can help achieve significant energy savings when proper membranes with high heat-transfer coefficients are used. Theoretical thermodynamic analysis of mass and heat transfer in the membrane condensation system shows that heat recovery increases dramatically as inlet gas temperature rises and outlet gas temperature falls. The optimal split mass flow rate is determined by the inlet gas temperature and the overall heat-transfer coefficient in the condensation system. The required membrane area is also strongly dependent on the overall heat-transfer coefficient, particularly at higher inlet gas temperatures. Mass transfer across the membrane has an insignificant effect on heat transfer and heat recovery, suggesting that membrane wetting may not be an issue when a membrane condenser is used for heat recovery. Our analysis provides important insights into the energy recovery performance of the membrane condensation system as well as selection of operational parameters, such as split mass flow rate and membrane area, thickness, and thermal conductivity.

Modeling and Simulation of a Hybrid Process (Pervaporation+Distillation) using MATLAB

This paper reports the modeling and simulation of a hybrid process, based on the combination of distillation and pervaporation, for the separation of azeotropic mixture of alcohol and ether. Pervaporation has emerged as one of the most active areas in the membrane research, and the pervaporation process has been shown to be an indispensable component for chemical separations. Pervaporation is more suitable for the separation of azeotropic or constant boiling mixtures which otherwise are difficult to separate by ordinary distillation. Although distillation is the most widely used technique for the separation of liquid mixtures, however the distillation separation of the mixtures with an azeotropic composition or close boiling mixtures is energetically expensive. A hybrid process exploits the advantages of pervaporation and distillation, while the negative aspects are minimized. Simulation tasks were carried out with MATLAB and the results of alternative process configurations that result from the relative location of separation technologies have been compared on the basis of the required membrane area.

Technical optimization of an integrated UF/NF pilot plant for conjoint batch treatment of two-phase olives and olive oil washing wastewaters

The membrane plant dimension and fouling control strategy of an integrated batch UF and NF membranes-in-series process is addressed for the simultaneous treatment of the two main effluents generated in olive mills operating with the two-phase technology, in particular wastewater derived from the washing of the olives (OWW) and from the olive oil washing during the vertical centrifugation (OOW). Beforehand, the raw effluent, that is, 1:1v/v mixture of OWW and OOW, called OWMW2, was pretreated by pH–temperature flocculation stand-alone or followed by photocatalysis with TiO2 nanoparticles under UV irradiation. The proposed model is able to predict the permeate flux performance of the selected membranes at a given time as a function of the applied pressure and organic matter load of the feedstock accurately. Moreover, working upon threshold conditions provides significant and stable fluxes, 15.5Lh−1m−2 on the UF membrane and 22.2Lh−1m−2 on the NF one, minor fouling build up (28.6–33.3% reduction) as well as required membrane area, 170.3 and 61m2, respectively. Finally, the treatment line just comprising UF preceded by pH–T flocculation and UV/TiO2 photocatalysis provides an effluent compatible for irrigation and permits the minimum membrane plant dimension (only 6 total modules).

Maxwell–Stefan modeling of high flux tubular silicalite-1 membranes for CO2 removal from CO2/H2 gas mixtures

In this work, a Maxwell–Stefan model for high flux tubular silicalite-1 membranes for separation of CO2 from a CO2/H2 mixture was developed. The model concerns tubular membranes operating in a counter flow module and includes transport through flow-through defects in the silicalite-1 film and pressure drop over the graded alumina support. Adsorption and diffusion parameters for perfect silicalite-1 crystals were taken from the literature. The flux and selectivity predicted by the model were in reasonably good agreement with experimentally observed data for a ZSM-5 membrane without any fitting of the model. However, the CO2 flux and selectivity measured experimentally for the ZSM-5 membrane were higher than that predicted by the model for a silicalite-1 membrane.The model was used to investigate a case with a 20,000Nm3/d feed comprised of a 50/50 mixture of CO2/H2 at pressure of 25bar and a membrane temperature of 296K. The permeate pressure was 1bar and 90% of the CO2 permeated the membrane. In this case, the membrane permselectivity and CO2 flux varied along the length of the tubes between 20–26 and 950–396kg/(m2h), respectively. Further, both defects and pressure drop over the support were shown to have an adverse effect on the selectivity, which indicates that membrane selectivity can be improved by reducing the flow-through defects and/or by preparing supports with less flow resistance. For a one-stage process, the required membrane area is as small as ca. 0.85m2 and the hydrogen loss through the membrane was 12.4%. For a two-stage process the required membrane area almost doubled to 1.6m2, however the hydrogen loss through the second membrane is reduced to as little as 2.5%. In summary, this work shows that high flux zeolite membranes may be an interesting option for CO2 removal from synthesis gas.

Thermodynamic analysis of a stand-alone reverse osmosis desalination system powered by pressure retarded osmosis

In this study, a methodology is developed to assess the feasibility of a reverse osmosis (RO) desalination system powered by a stand-alone salinity driven pressure retarded osmosis (PRO) technology. First, the proposed hybrid RO–PRO system is analysed as a thermodynamic cycle and its feasibility is mathematically interpreted using a feasible condition (FC) number, several dimensionless operational variables and a number of constraints to represent the objective of zero brine discharge. Then, a study of the stand-alone feasibility of a hybrid seawater RO–PRO system is carried out. The results show that lower RO water recovery and higher dimensionless flow rate improve the stand-alone feasibility of the system. A subsystem, a look inside the PRO, is developed to study the applied pressure and the required membrane area to achieve the operations with optimum FC numbers. It is found that the optimum applied hydraulic pressure is inversely proportional to the dimensionless flow rate in the feasible range of stand-alone operations and more area of membrane is required by a larger FC number. Finally, a case study of a selected operation is presented based on its energy performance, and two influencing factors, the inefficiency of the components and the salinity concentration of the feed water.

Modelling of osmotic energy from natural salt gradients due to pressure retarded osmosis: Effects of detrimental factors and flow schemes

In this investigation, a simplified pressure retarded osmosis (PRO) model incorporating the detrimental effects of internal polarization concentration (ICP), external polarization concentration (ECP) and reverse salt permeation (RSP) is proposed and verified using published data. The results demonstrate the accuracy of the model to address decreased water flux and power density due to the performance limiting effects. Based on the model, the discharge behaviour of a PRO process is reported with respect to different applied pressures on the draw solution and two flow schemes, co-current and counter-current flows. In the co-current flow PRO process, from the flow profiles in the draw and feed channels, it is found that the adverse effects on the process dynamics, such as water flux and power density, and required membrane area, can be regarded as a further retardation by applying ‘an extra applied pressure’ on the draw solution. In addition, the capacity of extractable energy of the full scale PRO discharge is significantly reduced due to the ICP, ECP and RSP effects. Furthermore, the termination conditions of the PRO discharge and its effects on the dynamics of the PRO process are also investigated in the case of the counter-current flow PRO process.

Threshold performance of a spiral-wound reverse osmosis membrane in the treatment of olive mill effluents from two-phase and three-phase extraction processes

A reverse osmosis (RO) treatment stage was examined for the complete depuration of the different effluents exiting the olive mill factories (OMW) working with diverse extraction procedures, that is, the two-phase and the three-phase extraction processes, respectively. In the present work, the modelization of batch RO purification of OMW by means of the relevant equations of the threshold flux theory for fouling control and plant dimension is addressed. Results show that higher threshold flux values (20.2–22.1% increase) and major feed recovery rates (80.2–85.0%) as well as very significant reduction of the long-term fouling index (27.3–52.7%) were achieved by using as pretreatment steps the following series of processes: pH-T flocculation, UV/TiO2 photocatalysis, UF and NF in series. This leads to both lower energy and capital costs, in particular a reduction of the required membrane area in case of batch membrane processes equal to 22.3–44.8%. Accurate prediction of the rejection behavior was attained by the used leaky solution-diffusion model in all cases, with reflection coefficients (σCOD) ranging from 0.86 to 1.0. The purified effluent streams are finally compatible with irrigation water quality standards (COD values below 1000mgL−1).

Theoretical analysis of a reverse osmosis desalination system driven by solar-powered organic Rankine cycle and wind energy

The utilization of renewable energy for desalination can solve the problems of energy crisis and fresh water shortage. In this study, a reverse osmosis (RO) desalination system driven by solar-powered organic Rankine cycle (ORC) and wind energy is proposed, which is different from the current desalination system driven by single energy source. In order to ensure the continuous production, energy storage units are employed. A mathematical model is established to simulate the overall system which mainly consists of a solar collector subsystem, an ORC subsystem, a wind power subsystem and a RO desalination subsystem. The sensitive analysis of some key parameters, namely turbine inlet pressure, condenser temperature of ORC, feed water pressure and the water salinity, is conducted to determine the relationship between parameters and fresh water output. The result shows daily fresh water output increases with the increase in the turbine inlet pressure under the given conditions. The condenser temperature has a significant effect on daily fresh water output. With the increase in feed water pressure, the fresh water output and the required membrane area both decreases. The fresh water output is also sensitive to the water salinity, while the required membrane area is less sensitive to it.

Oxygen-selective membranes integrated with oxy-fuel combustion

The perovskite-type oxide SrCo0.8Fe0.2O3−δ (SCF), a highly oxygen-permeable material, is restricted for application in the membrane-integrated oxy-fuel combustion process by its low tolerance to CO2. In the present work, we found that the CO2 tolerance of SCF is improved by increasing the oxygen partial pressure in the CO2-containing gas. Long term oxygen permeation experiments, at 950°C, show that mixing 5% of oxygen into the CO2 sweep gas effectively prevents degradation of the SCF membrane. X-ray photoelectron spectroscopy indicates that the increase in CO2 tolerance of SCF is caused by a decrease in basicity of the material with increasing oxygen partial pressure. Based on these experimental results, a modified oxy-fuel combustion process is proposed. Calculation of the required membrane area for operating a 50MW coal-fired power plant showed that the modified process comprises a viable option.

A cascaded pervaporation process for dehydration of acetic acid

Pervaporation is advantageous in separating close-boiling point mixtures, azeotropes, thermally sensitive compounds and purification of chemicals. However, one pervaporation unit may not be economically feasible to simultaneously provide a high purity of compounds in both the retentate and the permeate streams. In this study, a cascaded pervaporation method is developed aiming to dehydrate 85wt% acetic acid solution from a basis feed of 100kg/h. First, pervaporation experiments were performed using lab-made PPSU membranes. In pervaporation, the separation factor depends on the intrinsic properties of the membrane and on the operating conditions. These aspects cause a variation of the separation factor in pervaporation from 2 to 24. The process with one pervaporation unit, a cascaded PV system, and a cascaded PV with recycle stream is evaluated. This study demonstrates an efficient dewatering of acetic acid from an initial feed of 85wt% acetic acid, obtaining 99.7wt% acetic acid at rate of 72.8kg/h using a cascaded PV with recycle stream. The large membrane area requirement in PV due to the low flux may be the main limitation for PV. Therefore, the development of new membranes exhibiting a high flux and a high selectivity are vital to decrease the membrane area, which may improve the potential for realizing these processes on a commercial scale.

Fouling control by threshold flux measurements in the treatment of different olive mill wastewater streams by membranes-in-series process

This paper deals with the measurement of the critical and threshold flux for modelization, prediction and control of the fouling issues of batch membranes-in-series processes, in detail ultrafiltration (UF) followed by nanofiltration (NF) and reverse osmosis (RO), for the reclamation of olive mill wastewater (OMW-2). Results suggest the existence of threshold flux values for both UF and NF membranes, with minimum constant fouling attained on the latter, that is 54.5% lower. UF+NF in series after pH–T flocculation process followed by photocatalysis with ferromagnetic-core titanium dioxide under ultraviolet irradiation (UV/TiO2) as pretreatment to inhibit fouling issues guarantees COD values in the permeate of 1.3gL−1. This value complies with irrigation water quality standards. Moreover, the adoption of this treatment sequence helps reducing the required membrane area, equal to 104.6m2 and 81.4m2 for the UF and NF membranes, respectively, leading to a limited need of overdesign of the membrane plant. In addition, especially the use of the applied UV/TiO2 photocatalysis process not only enhances the productivity but also ensures minimization of the constant fouling build-up on both membranes. This latter effect sensibly increases the longevity of the membranes, reducing the capital and operating costs of the treatment.

Performance Modeling and Cost Analysis of a Pilot-Scale Reverse Osmosis Process for the Final Purification of Olive Mill Wastewater

A secondary treatment for olive mill wastewater coming from factories working with the two-phase olive oil production process (OMW-2) has been set-up on an industrial scale in an olive oil mill in the premises of Jaén (Spain). The secondary treatment comprises Fenton-like oxidation followed by flocculation-sedimentation and filtration through olive stones. In this work, performance modelization and preliminary cost analysis of a final reverse osmosis (RO) process was examined on pilot scale for ulterior purification of OMW-2 with the goal of closing the loop of the industrial production process. Reduction of concentration polarization on the RO membrane equal to 26.3% was provided upon increment of the turbulence over the membrane to values of Reynolds number equal to 2.6 × 104. Medium operating pressure (25 bar) should be chosen to achieve significant steady state permeate flux (21.1 L h−1 m−2) and minimize membrane fouling, ensuring less than 14.7% flux drop and up to 90% feed recovery. Under these conditions, irreversible fouling below 0.08 L h−2 m−2 bar−1 helped increase the longevity of the membrane and reduce the costs of the treatment. For 10 m3 day−1 OMW-2 on average, 47.4 m2 required membrane area and 0.87 € m−3 total costs for the RO process were estimated.

Design and performance evaluation of reverse osmosis desalination systems: An emphasis on fouling modeling

Sensitivity analysis was performed on different design and performance factors of a reverse osmosis system. In general, the most important design and performance parameter was the feed pressure and feed concentration, respectively. From the design point of view, it seems that, if newer technologies move toward decreasing the feed pressure to possibly save on pumping power requirement, the required membrane area may become much more sensitive to the feed pressure. In terms of performance, it was found that increasing the salt concentration of the feed for the range investigated, almost doubled the sensitivity of permeate concentration and water permeate flux to it. A model is proposed for predicting the normalized decrease in permeate flux due to fouling with two constants that have a robust interpretation. Results indicate that the model can predict the behavior accurately.

Post-combustion Carbon Capture with a Gas Separation Membrane: Parametric Study, Capture Cost, and Exergy Analysis

A systematic method that integrates process simulation, capture cost estimation, and exergy analysis is applied to evaluate a gas separation membrane process for post-combustion carbon capture in a coal power plant. The influences of membrane performance and process configuration on the energy consumption, required membrane area, and capture cost have been studied. The results indicate that the energy consumption decreases with the increase of CO2/N2 selectivity, but a larger membrane area is required, while for a high CO2 permeance, the membrane area can be significantly reduced. The carbon capture ratio influences the specific energy consumption as well, which should be a trade off. For a two-stage membrane process, the capture load distribution between the first and second stage affects the separation performance greatly, and the optimal range varies with the other parameters. Under the assumptions in this work, the profiles of capture cost related to membrane parameters show that the optimal CO2/N2 selectivity is 70–90. The exergy analysis indicates that the main energy bottleneck of a membrane technology is located in the membrane unit operation, which has relatively low exergy efficiency. On the other hand, CO2 compression has less potential for energy savings because it has already had very high exergy efficiency.

Dehydration of natural gas using membranes. Part II: Sweep/countercurrent design and field test

Membrane technology is an attractive alternative to conventional glycol dehydrators for natural gas dehydration. While membranes with high water/methane selectivity are available, the separation performance of membrane systems is restricted by the moderate feed-to-permeate pressure ratio encountered in this application, resulting in high membrane area requirement and high methane loss. This paper (Part II of a two-part study) addresses that challenge by evaluating suitable process designs to overcome the limitations of feed-to-permeate pressure ratio, using a process simulation package. A design with a dry gas on the permeate side as a countercurrent sweep shows the best combination of low methane loss and minimum membrane area requirement. The design was experimentally evaluated by field testing a spiral-wound module that incorporates countercurrent operation, at a natural gas processing plant. The use of a dry sweep gas on the permeate side significantly increased water vapor flux across the membrane. For example, as sweep/feed flow rate ratio increased from 0% to 5.9% at a permeate pressure of 4.8bar, water flux increased by 2.5 times, from 0.13slpm/m2 (standard liter per minute per m2 membrane area) to 0.47slpm/m2. The measured water flux reached about 80% of the value calculated with the process simulation package for a perfect sweep/countercurrent module, confirming the suitability of the spiral-wound modules with countercurrent configuration for natural gas dehydration.

Optimization of CO2 concentration captured by membrane technology - Possibility of reduction in CO2 capture energy and cost -

The influence of specific power requirements and the membrane area on the CO2 recovery ratio and the CO2 concentration is investigated for CO2 membrane separation from a pressurized gas stream. Three different membrane configurations of a simple single stage, a single stage with permeate recycle, and an ideal two-cascade are considered. A feed gas containing 40% H2 and 60% CO2 and having a total pressure of 2.5MPa is used. In the cases of a simple single stage and a single stage with permeate recycle, a higher CO2 recovery ratio leads to a larger membrane area and higher energy consumption for the gas recycle. In addition, a higher CO2 concentration needs a larger membrane area and considerable power. An ideal two-cascade reduces the compressor power requirement as compared to a single stage with permeate recycle; however, it increases the membrane area. A lower CO2 concentration in the recovered CO2 stream implies a smaller membrane area and lower power requirement in the CO2 capture from the pressurized gas stream.

A parametric study of the impact of membrane materials and process operating conditions on carbon capture from humidified flue gas

Membranes are among a suite of technologies being considered for post-combustion carbon capture. Recent studies have shown the importance of process design in optimizing membrane system performance and setting guidelines for membrane materials development. In this study, the simulated performance of membranes based on a rubbery poly(ethylene oxide) block copolymer, a polyvinylamine/polyvinyl alcohol blend that shows facilitated CO2 transport, and a glassy thermally-rearranged polybenzimidazole is compared for a single-stage membrane operation treating humidified flue gas. Parametric studies were conducted to investigate the impact of different operating modes and conditions. For all cases, high membrane CO2 permeance minimizes membrane area requirements, while high CO2/N2 selectivity improves the CO2 purity and reduces the energy needed for CO2 purification. The benefits of higher selectivity are accentuated at higher feed-to-permeate pressure ratios, at the expense of increased energy cost. The advantages of higher permeance are most pronounced at a lower pressure ratio. The effects of water vapor in flue gas on CO2 capture with membranes can be complex depending on possible interactions of sorbed water with the membrane. From a process standpoint, a slight positive sweep effect is generated from the co-permeation of water vapor which increases the CO2 separation degree at a fixed membrane area.

Simulation of membrane-based CO2 capture in a coal-fired power plant

A two-stage membrane process is designed for CO2 capture from coal-fired power plants. Vacuum operation on the permeate side of the membrane is the preferred option to reduce the power demand for compressing the huge feed volume. The energy recovered from the CO2-depleted emission stream and the energy consumed for post-capture CO2 liquefaction are considered in this simulation study. A numerical modeling of the membrane process and a brief description on assessing both the capital and operating costs of the process are provided. It is found that the membrane area requirement is dominated by recovery of the lower concentrations of CO2 in the tail portion of the flue gas stream. Process optimizations allowing the minimal CO2 capture cost or minimal power demand indicate that current membrane technology is promising for flue gas CO2 capture, assuming a permeance of 1000 GPU and CO2/N2 selectivity of 30. The potential of membrane technology for CO2 capture was also explored by using membranes with a CO2/N2 selectivity of 50 and 200.

Mathematical Modeling of CO2/CH4 Separation by Hollow Fiber Membrane Module Using Finite Difference Method

Removal of CO2 in landfill gas recovery processes and fractured wells as well as its application in enhanced oil recovery and its environmental aspects are of interest. Also separation of CO2 from CH4 in Ethylene Oxide plant is an environmental policy of Marun Petrochemical Company. In the present work, a shell-fed hollow fiber module was modeled mathematically for CO2 separation from CH4. Finite difference method was used for solving the equations. Comparison between co-current and counter-current flow patterns showed that for all conditions, counter current pattern had better efficiency for CO2/CH4 separation. Influence of operating parameters such as feed pressure, permeate pressure, feed flow rate, fiber length and CO2 concentration of feed on separation efficiency of CO2/CH4 mixture was investigated. Also the effect of feed and permeate pressures on required membrane area showed that the membrane area increases by increasing permeate pressure and decreases by increasing feed pressure. The modeling offers valuable data about feasibility study and economical evaluation of a gas separation unit operation as a helpful unit in the industry.