Hollow Fiber Membrane Contactor Research Articles

Direct air capture of CO2 using green amino acid salts

Direct air capture (DAC) of CO2 using liquid sorbent technology is gaining attention as a promising approach in tackling the looming climate crisis. Despite technical advancements, critical aspects such as contactor selection, energy efficiency, sustainability, and environmental compatibility still pose uncertainties. In this study, various green amino acid salts performances in a DAC system were explored using non-porous hollow fiber membrane contactors (HFMCs). Two DAC absorption and desorption apparatuses were developed. For the DAC-absorption unit, the thermodynamic and kinetic behavior of five types of aqueous amino acid salt solutions were evaluated in long-term operations. High absorption stability for most of the solutions in different solvent loadings (up to 80% CO2 solvent loaded) were observed and potassium glycinate (GlyK) was selected as the most suitable candidate for DAC. To enhance the CO2 separation efficiency, parametric analysis on air and solvent flow rates, solvent temperature and concentration were conducted using GlyK. Vacuum low-temperature desorption experiments were carried out with GlyK to evaluate the CO2 removal efficiency over a range of solvent temperatures and concentrations, CO2 loadings, vacuum pressures, and vacuum/sweep gas mode. The results successfully quantified the effect of each operational parameter under various conditions on CO2 removal in a DAC system. Finally, to investigate the impact of membrane characteristics on DAC absorption–desorption performance, a developed and validated model was used. Taken all together, hybrid technology of membrane modules and green amino acid salts is shown to be a viable pathway towards a sustainable DAC process.

Numerical modelling and process simulation of a post-combustion CO2 capture pilot plant based on a membrane contactor unit

Hollow fiber membrane contactors (HFMC) have gained prominence in post-combustion CO2 capture applications due to their potential for high mass transfer rates, compactness, modularity and versatility. In this work, two pilot plant design have been proposed, an innovative solution which foresees the membrane contactor as CO2 absorption reactor, and a conventional one based on a packed column absorber. A one-dimensional model based on the resistance-in-series method has been developed for the membrane module and validated against experimental data from literature. The other process units have been simulated in Aspen Plus V11. According to the model results the membrane contactor unit is able to guarantee same levels of CO2 removal rates with improved energy performances compared to the conventional packed column absorber. In particular, if the same reactor volume is considered for the two absorber configurations, a reduction in the specific reboiler duty (SRD) of 8.5% is estimated. On the other hand, if the same liquid-to-gas (L/G) ratio is applied, the HFMC is able to guarantee a required reactor volume almost halved (45% reduction). These substantial improvements of the CO2 capture process could lead to lower investment cost and better economic indicators of the CO2 capture plant.

High-level phenol bioproduction by engineered Pichia pastoris in glycerol fed-batch fermentation using an efficient pertraction system

This study aimed to establish a high-level phenol bioproduction system from glycerol through metabolic engineering of the yeast Pichia pastoris (Komagataella phaffii). Introducing tyrosine phenol-lyase to P. pastoris led to a production of 59 mg/L of phenol in flask culture. By employing a strain of P. pastoris that overproduces tyrosine—a precursor to phenol—we achieved a phenol production of 1052 mg/L in glycerol fed-batch fermentation. However, phenol concentrations exceeding 1000 mg/L inhibited P. pastoris growth. A phenol pertraction system utilizing a hollow fiber membrane contactor and tributyrin as the organic solvent was developed to reduce phenol concentration in the culture medium. Integrating this system with glycerol fed-batch fermentation resulted in a 214 % increase in phenol titer (3304 mg/L) compared to glycerol fed-batch fermentation alone. These approaches offer a significant framework for the microbial production of chemicals and materials that are highly toxic to microorganisms.

Liquid-liquid extraction of sinapic acid from a mustard seed by-product using a hollow fiber membrane contactor

This study focuses on the recovery of sinapic acid using liquid–liquid extraction (LLE) assisted by a hollow fiber membrane contactor (HFMC) from an aqueous feed obtained through the hydrolysis of mustard bran. The hydrolyste contains 230 ± 36 mg/L of sinapic acid, with a natural pH of 4. A screening was performed with solvents of different chemical nature (alcohol, ester, ketone, ether, cyclic ether). Data showed that all the solvents tested gave an extraction efficiency of more than 80 % for pH < 5, whereas the initial concentration of sinapic acid in the aqueous feed has little impact on the extraction efficiency. Four of the solvents tested were selected for use in the HFMC: two volatile (CPME, MIBK) and two non-volatile (octanol, octyl acetate). The solubility of the volatile solvents in the feed phase was found to be an important factor to consider in evaluating the HFMC (2.6 ± 0.5 % and 1.07 ± 0.05 % v/v with MIBK and CPME, respectively). Mass transfer coefficients with volatile solvents (25 ± 1 x10-6 and 15.3 ± 0.5 x10-6 m/s for MIBK and CPME, respectively) exceeded those of non-volatile solvents (4.1 ± 0.2 x10-6 and 4.5 ± 0.5 x10-6 for octanol and octyl acetate, respectively) by 4- to 6-fold. Extraction was intensified by increasing the initial concentration of sinapic acid in the feed phase and by increasing the feed-to-solvent ratio. CPME demonstrated optimal recovery efficiency at a phase ratio of 8:1 (v/v), yielding 0.9 g of sinapic acid per liter of CPME used.

Performance evaluation and optimization of hollow fiber membrane contactors for carbon dioxide absorption: A comparative study of ammonia, ethanolamine, and diethanolamine solvents

Membrane absorption is an emerging technology that amalgamates the merits of chemical absorption and membrane separation. However, the pivotal choice of solvent profoundly influences the overall performance of the membrane contactor. In this paper, a robust two-dimensional (2D) steady-state non-wetting mathematical and physical model of a hollow fiber membrane contactor (HFMC) was established. COMSOL software was used to solve the model equation of the membrane contactor. The impacts of ammonia, ethanolamine (MEA) and diethanolamine (DEA) on carbon dioxide absorption under different operating conditions and membrane geometry properties were simulated and compared. Results showed that the utilization of NH3 as the solvent in HFMC showcases performance akin to that of MEA, a substantial advantage over DEA. Notably, the performance disparity between ammonia and MEA might alter significantly in response to varying operating parameters. For instance, the CO2 removal performance of HFMC using aqueous ammonia surpasses that of MEA when the CO2 volume fraction exceeds 19 %. Moreover, hollow fibers featuring larger inner diameters and lengths endow a heightened effective mass-transfer area, thereby facilitating superior carbon dioxide removal performance.

Using machine learning techniques to predict ammonium concentration in membrane contactors for nitrogen recovery as a valuable resource

The availability of real-time measurements of primary quality water variables is one of the key challenges in the wastewater treatment industry. However, due to the cost and maintenance requirements of sensors and probes for on-line measurement of primary quality variables, the prediction of these variables via data-driven approaches using as inputs easy-to-measure process variables has attracted research interest. In this paper, different machine learning techniques: feed-forward artificial neural network, random forest, support vector machine, gaussian process regression and partial least squares were used to predict in real-time the total ammonium nitrogen concentration during the operation of a hollow fibre membrane contactor. This recently developed technology allows the recovery of nitrogen from nitrogen rich streams (i.e. supernatant of anaerobic digesters in wastewater treatment plants) as ammonium sulphate (a marketable fertilizer). These contactors are usually operated in batch mode, pumping the high nitrogen concentration feed from the storage tank, where the total ammonium nitrogen concentration decreases progressively as the fertilizer is produced. Knowing the real-time concentration of total ammonium nitrogen in the storage tank would enable the optimization of the process operation, avoiding its operation with conservative fixed-time batch duration. The pH is an easy-to-measure process variable usually available in wastewater treatment plants that was used as input of the tested data-driven models, together with two extracted features from this variable (its derivative and increments after each reagent dosing). The number of total ammonium nitrogen measurements in the collected database is 2350 data points (corresponding to 8 complete batches, which were divided into 6 for training the data-driven models and 2 for testing them), ranging from 987 to 2.5 mg NH4+-N/L which covers almost the complete range of total ammonium nitrogen concentration values in the membrane contactor. The predictive ability of the developed predictive models was evaluated on the test data set by four indices, namely: the root-mean-square error, the slope and the intercept of the linear fit between the measured and predicted concentrations and the determination coefficient. The results showed a strong predictive ability of the fitted ANN that outperformed the other approaches exhibiting a determination coefficient of 0.99 and the lowest root-mean-square error (19.87 mg/L) in the test set. Permutation variable importance demonstrated that all machine learning techniques depended mainly on the two variables extracted from the pH: its derivative and increments, which resulted to be more important than the pH itself to predict the total ammonium nitrogen concentration.

Evaluation of a hollow fiber membrane contactor reactor for reactive extraction in biodiesel production

A polypropylene hollow fiber membrane contactor reactor (HF-MCR) was used to evaluate the performance of a reactive extraction process for biodiesel production. The process involved the transesterification of soybean oil with methanol, catalyzed by sodium hydroxide. The experimental methodology assessed the impact of oil flow rate and methanol/oil molar ratio on the biodiesel (FAME) production rate, triglyceride reaction rate, and glycerin concentration in the final biodiesel product. The results demonstrated that, by employing a countercurrent configuration, is possible to extract the glycerin from the biodiesel-rich phase with methanol, achieving both the reaction and the separation stages in the same equipment. The best results were obtained at a methanol/oil molar ratio of 4:1 and an oil flow rate of 0.4 L h−1, leading to a triglyceride conversion rate of 0.14 mol h−1 and a FAME production rate of 0.24 mol h−1, equivalent to 34 % conversion and 56 % yield, respectively. The final biodiesel product showed a low concentration of glycerin, measuring only 0.06 % wt. This investigation highlights the potential of employing membrane contactors technology for the biodiesel production process, reducing the processing time by eliminating the biodiesel/glycerol separation stage, and therefore bringing down the load of downstream purification operations.

Optimization of CO2 Capture Efficiency in a Flue Gas Treatment System: Assessing the Impact of Flow Rates, Absorbent Concentrations, Nanoparticles, and Temperature

This study focuses on improving the efficiency of flue gas purification systems for carbon dioxide (CO2) capture. The researchers investigated various factors, including flow rates, absorbent concentrations, nanoparticles, and temperature, to optimize the CO2 capture process. They conducted experiments using a polytetrafluoroethylene (PTFE) hollow fiber membrane contactor to separate CO2 from nitrogen. The presence of titanium dioxide and silica nanoparticles in a potassium carbonate solution facilitated the separation process. The findings indicate that optimizing flow rates and absorbent concentrations can enhance CO2 capture efficiency. The use of nanoparticles in the absorbent solution was found to improve material capture effectiveness. The study also revealed that higher temperatures contribute to increased CO2 capture efficiency. The research aims to advance CO2 capture techniques to mitigate the release of industrial greenhouse gases, particularly in flue gas treatment systems. The researchers determined optimal settings for CO2 capture in these systems, emphasizing the importance of absorbent concentration for stability and absorption, as well as the role of nanoparticles in enhancing reaction kinetics and CO2 collection. The objective of the analysis is to maximize removal efficiency, although specific lower and upper bounds and a target value were not provided. The proposed solution suggests specific values for the independent variables, including temperature, gas flow rate, liquid flow rate, and the concentrations of K2CO3, PZ, SiO2, and TiO2, to optimize CO2 capture.

Liquid-liquid extraction of phenolic wastewater through a surface modified poly(vinylidene fluoride-co-hexafluoropropylene) hollow fiber membrane contactor and process optimization

BackgroundStrict environmental regulations have been recognized for phenolic wastewater treatment due to toxicity of the phenolic compounds. In this study, solvent extraction of a phenolic wastewater was investigated via a liquid-liquid membrane contactor system. MethodsPorous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) hollow fiber membranes were modified by coating an ultra-thin layer of hydrophobic surface modifying macromolecule (SMM). The membranes were characterized by various tests such as SEM-EDS, nitrogen permeation, overall porosity, contact angle and critical water entry pressure (CEPw). Significant findingsFrom SEM, an open structure with combination of finger-like and sponge-like structure was produced. The membrane exhibited high surface hydrophobicity (water contact angle of 109°) with good wetting resistance, overall porosity of 82% and mean pore size of 18 nm. From response surface methodology (RSM), the maximum phenol extraction flux of 2.02 × 10−3 kg/m2s was estimated by the model at the optimum process variables as phenol concentration of 448 mg/L, feed temperature of 42 °C, aqueous phase flowrate of 196 mL/min and organic phase flowrate of 117 mL/min. The coefficient of determination (R2) of 0.972 showed a close proximity between the model and the experimental data. The membrane showed a reasonable flux that can be a favorable alternative for industrial phenolic wastewater treatment.

Effects of fluid flow on the rate limiting for CO2 capture by an AEEA containing membrane

The efficiency of CO2 capture using a hollow fiber membrane containing 2-(2-Aminoethylamino) ethanol (AEEA) from the emission gas in the Integrated Gasification Combined Cycle (IGCC) was investigated by density functional theory and fluid dynamics. A reaction path for CO2 sorption to AEEA involving two H2O molecules with three – proton transfer was found to give the low barrier of the reaction due to 6 intermolecular hydrogen bonds which make the transition state structure more stable. The activation energy in the reaction path for CO2 sorption to AEEA was 7.11 kcalmol−1 which is approximately 10 kcalmol−1 lower than that involving one H2O molecule with two – proton transfer discussed in our previous study (Higashino et al., 2023). Since the activation energy is much lower than those in the other reaction paths we have investigated, it can occur much more frequently than others when sufficient moisture is maintained in the membrane. The estimated reaction rate k = 3.407 × 108 s−1 indicates that CO2 becomes carbamate by reaction with AEEA as soon as reaching the surface of the membrane, and thus, CO2 attachment to AEEA cannot be the rate limiting. Since flow in the hollow fiber membrane can be laminar, simulated CO2 permeance for the temperature of 358 K and the pressure of 2.4 MPa has a range from 10−10 to 10−9 m3 (STP) m−2s−1Pa−1, which is a few orders smaller than that for the flat sheet membrane, flow over which is turbulent, i.e.10−8 to 10−7 m3(STP) m−2s−1Pa−1 (Higashino et al., 2023). Overall, the reaction rate of CO2 attachment to AEEA is sufficiently large, and hence, any one of mass transfer of CO2 induced by turbulence (turbulent flow), molecular diffusion of CO2 from feed gas to the membrane surface (laminar flow), and molecular diffusion of bicarbonate (HCO3-) from the feed side to the permeate side in the membrane can be the rate limiting depending on which type of membrane, e.g. a flat sheet membrane module, a spiral membrane module, a hollow fiber membrane contactor, etc., is used for CO2 capture.

Experimental and Numerical Analysis for Improving CO2 Mass Transfer Performance of Blended Solvents in Hollow Fiber Membrane Contactors

Experimental and Numerical Analysis for Improving CO₂ Mass Transfer Performance of Blended Solvents in Hollow Fiber Membrane Contactors

CFD simulation of osmotic membrane distillation using hollow fiber membrane contactor: Operating conditions and concentration polarization effects

Inorganic salts, when present in high concentrations, can disrupt the osmotic balance of aquatic organisms, leading to physiological and ecological harm. Osmotic membrane distillation (OMD) is an emerging technique for recovering inorganic salts from wastewater. The process involves the transfer of water vapor from a feed solution (FS) to a permeate stream due to the difference in vapor pressure across a hydrophobic membrane. It thus results in a concentrated solution at the feed outlet and purified water at the permeate side. OMD is preferred due to its straightforward scale-up and low energy requirements. In this research, a steady state 2-D axisymmetric computational fluid dynamics (CFD) model is developed to study the recovery of sodium carbonate (Na2CO3) from aqueous feed solution through OMD in a hollow fiber membrane contactor (HFMC). Aqueous sodium chloride (NaCl) solution was taken as an osmotic solution (OS). The numerical convection-diffusion mass, momentum transport, and Happel equations were scripted in COMSOL Multiphysics™ version 6.0 software. The model computed the water transport from FS to OS. Computed water flux well matched with the literature based experimental results. Simulations were carried out to investigate the parametric effects, including Reynold’s number, FS and OS concentration and the module geometrical parameters to establish an optimized operating conditions and module geometry and to achieve the desired FS concentration. Results showed that a 2-fold rise in OS concentration increased the transmembrane water flux 4-fold. However, the flow rates of both FS and OS did not significantly affect the flux. On the other hand, concentration polarization (CP) showed dependence on the FS concentration, tortuosity, and Reynolds number. A membrane tortuosity of 1.6, feed concentration of 75 g L−1, OS concentration of 300 g L−1, and a FS Reynolds number in the turbulent flow range can result in higher transmembrane flux and lower chances of CP development.

Enhanced CO2 removal in hollow fiber membrane contactors using amine-based nanofluids

Increasing the mass transfer coefficient, improving the rheological properties of the liquid, reducing the possibility of wetting, and reducing the consumption of the absorbent are among the significant effects of using nanofluids in membrane contactors as chemical absorbents. The use of nanofluids allows the system to use higher transmembrane pressures and higher liquid flow rates. In this work, stable amine-based nanofluid were prepared by adding different amounts (0–0.4 wt%) of three nanoparticles (Al2O3, Fe3O4, and MWCNT-COOH) to MEA aqueous solution. Amine-based nanofluids were then used in a membrane contactor to remove CO2 from the gas mixtures. The influence of effective parameters on the separation performance was evaluated in order to better understand how NPs affect CO2 removal. The findings of this work show that the use of nanofluids can improve CO2 removal performance by 5% and thus reduce adsorbent consumption by 20%. The effect of nanoparticle dispersion on mass transfer flux was evaluated using a new enhancement factor (Rnano). Numerical methods were used to provide a suitable equation for Rnano so that it can be combined with general mass transfer equations. The Rnano values obtained for the NPs used in this work were in the range of 0.03–0.05.

New upstream solution for mercury removal from petroleum condensate via HFMC: Thermodynamics, kinetics, DFT and mass transport

This work presents a new solution for the removal of mercury from petroleum condensate via hollow fiber membrane contactor (HFMC), which follows the principles and practices of solvent extraction. Results demonstrate that mercury can be successfully removed from petroleum condensate feed by the synergistic mixture solution of HCl and thiourea as extractant. Under equal circulating flow rates of 1.67 cm3 s−1 of feed and the synergistic extractant (0.5 mol dm−3 HCl and 1.5 mol dm−3 thiourea) at 323.15 K, the percentage of mercury removal reached 98.4%. The values of ∆H° (120 kJ mol−1), ∆S° (0.37 kJ mol−1) and ∆G° (−1.15 kJ mol−1) indicate that the reaction is endothermic, irreversible and spontaneous at 323.15 K, respectively. The results of Fourier-transform infrared spectroscopy (FTIR) confirm that mercury has been removed and is consistent with the obtained reaction mechanism from density functional theory (DFT). To describe the mass transport through HFMC, two mass transport mathematical models corresponding to reaction flux and diffusion flux are considered. The reaction flux model is seen to fit in well with the experimental results. The mass transfer coefficients in the membrane phase (km) and shell side (ks) are 7.45 × 10−6 cm s−1 and 2.09 × 10−5 cm s−1, respectively indicating that the mass transfer in the membrane phase is the controlling step.

The role of solvent temperature and gas pressure on CO2 mass transfer during biogas upgrading within porous and dense-skin hollow fibre membrane contactors

Biogas upgrading uniquely requires pressurisation of hollow fibre membrane contactors (HFMC) to be competitive with classical water absorption, and when complemented with an ambient industrial temperature range, these conditions will determine CO2 mass transport phenomena that are distinct dependent upon whether microporous or nonporous membranes are used. This study therefore examines the independent and concomitant role of temperature and pressure in determining CO2 mass transport, and selectivity, within microporous and nonporous HFMC. At low solvent temperatures, higher CO2 flux was achieved which indicates that solvent solubility is more critical than CO2 diffusivity to enhancing mass transport. Low temperatures also favoured mass transfer within the microporous membrane, explained by the reduction in solvent vapour pressure which limited pore wetting by condensation. In contrast, the nonporous membrane exhibited poorer mass transfer at low temperatures due to a decline in dense polymer permeability. Crucially in this study, neither wetting of the microporous membrane or plasticisation of the nonporous membrane were observed following pressurisation. Consequently, CO2 flux increased in proportion to the applied pressure for both membrane types, emphasising the critical role of pressurisation in augmenting process intensification for biogas upgrading which is typically facilitated at pressures of 7–10 bar. Resistance-in-series analysis illustrated how pressurisation reduced gas-phase resistance, and subsequently enhanced selectivity. Consequently, an outlet gas quality of 98% methane could be achieved within a single microporous module at 4.5 bar, meeting the industrial standard for biomethane whilst reducing solvent requirements, separation energy and methane losses. Comparable behaviour was observed during pressurisation of the nonporous membrane, but with a less significant benefit to CO2 mass transfer and selectivity, ostensibly due to the resistance imparted by the dense polymer. When considered collectively, low solvent temperature and high gas pressure enhance process intensification subsequently reducing process size (e.g., membrane area) and separation energy, while also advancing selectivity to deliver a gas product at the composition required for biomethane with minimum methane losses, which are critical factors in demonstrating microporous HFMC as an industrially competitive solution for biogas upgrading.

Ammonium recovery and concentration from synthetic wastewater using a poly(4-methyl-1-pentene) (PMP) liquid–liquid membrane contactor: Flux performance and mass transport characterization

Hollow fiber membrane contactors are a promising technology for the removal and recovery of ammonia from liquid effluents. However, a better understanding of the process engineering (e.g. mass transport of ammonia over water) and performance optimization is required. In this study, the performance of a hollow fibre liquid–liquid membrane contactor (HF-LLMC), incorporating a new polymer chemistry (i.e., poly (4-methyl-1-pentene (PMP) and an asymmetric fibre structure, for the recovery and concentration of ammonium from synthetic aqueous solutions, was investigated. The influence of the feed and acid flow rates was evaluated experimentally by determining the overall mass transfer coefficient (kov), the ammonium recovery as a function of time and the acid consumption. In addition, the experimental results were fitted to a mathematical model to determine the membrane permeabilities to ammonia (PNH3) and water (Pw) and identify the mass transfer resistance regime. The highest kov values experimentally obtained were in the range of 3·10–3 to 3.51·10–3 m/h with corresponding ammonia recovery rates of 94 and 96.2% after 10 h, operating at a feed and acid flow rates of 180 L h−1 and 500 L h−1, respectively, which are in the upper range of the HF-LLMC literature. The overall results of this study were not only the upper range of the HF-LLMC ammonia recovery literature but a much-lower water transport was confirmed indirectly by the concentration factor (CF) values obtained experimentally. The remarkable selectivity of the membrane towards ammonia over water (i.e., PNH3 = 87–180 L m–2h−1 bar−1 and Pw = 1.2–1.4·10–3 L m−2 h−1 bar−1 at NTP conditions) is attributed to the asymmetrical membrane structure and the polymer chemistry (i.e., PMP). The proven high ammonia selectivity of the HF-LLMC makes it a promising technology for the recovery and concentration of ammonium from urban (e.g. wastewaters) and industrial (e.g. soda ash and fertilizers production) diluted streams.

Book Review Hollow Fiber Membrane Contactors: Module Fabrication, Design and Operation, and Potential Applications

The latest developments and applications of hollow fiber membrane contactors (HFMCs) were discussed in this recent published book. Membrane contactor provides gas–liquid or liquid–liquid contact without dispersion of one phase in another, which gives a higher mass transfer coefficient compared to the conventional contactors. Using a microporous hydrophobic or hydrophilic membrane, one of the fluids is immobilized in the pores where the mass transfer is occurred based on the concentration gradient. HFMC technology has been implemented in various applications including gas separation, fermentation, pharmaceuticals, wastewater treatment, chiral separation, semiconductor manufacturing, carbonation of beverages, metal ion extraction, protein extraction, VOC removal from waste gas, and osmotic distillation.

Extracting liquid fertilizer from ammonia-laden pharmaceutical wastewater using Hollow fiber membrane contactors

Production of certain pharmaceuticals generates wastewater with a high ammonia load, posing economic and environmental burdens. Recovering ammonia as a nitrogen fertilizer can alleviate these burdens and is vital from a circular economy perspective. For this purpose, this study, jointly performed by a research university and a large pharma company, evaluated the use of Hollow fiber membrane contactors (HFMC). The experiments were conducted using real pharmaceutical wastewater in two separate laboratories at two process scales (bench and pilot) and two operating modes (batch and continuous). The study evaluated the effect of feed concentration, flow rate, and process configuration and described the results using a single-parameter (mass transfer coefficient K) mathematical model. We then used the model to design scaled-up batch and continuous processes, based on which we performed a detailed economic assessment. A robust and consistent ammonia removal and recovery were obtained for all the experimental conditions tested. The model adequately described the empirical results, and K was similar across all the experiments in this study, which were conducted in practically relevant conditions. Both batch and continuous process designs were found feasible, increasing process flexibility. The economic evaluation revealed that acid and base consumption, rather than the initial investment, is the most significant expense. The cost of membranes, although relatively high, had little contribution to the overall expenses. Revenues from selling the recovered nitrogen as ammonium-sulfate fertilizer reduces the evaluated net cost of the novel treatment to a minimum of $3.76 per kgN - a potential cost savings of up to 29% relative to the current treatment ($5.28). Therefore, applying HFMC to recover nitrogen from pharmaceutical wastewater is promising from both economic and environmental viewpoints.

Non-dispersive solvent extraction as an alternative for sulfuric acid and copper recycling from membrane distillation concentrate of gold mining wastewater

The wastewater from the pressure oxidation process is a complex stream enriched in sulfuric acid and dissolved metallic species, conventionally treated by neutralization, a technique that does not allow for by-product recovery. Previous studies focused on water recovery from the wastewater by membrane distillation and the concern related to concentrate production after water is recovered is now addressed by using hollow-fiber membrane contactors in non-dispersive solvent extraction processes intended for sulfuric acid and copper recycling. Tris(2-ethylhexyl)amine (TEHA), Aliquat 336, and Lix 84-I were used as extractants, the first two for acid recovery and the latter for copper. It was investigated the contribution of different organic phases flow rate (4–12 cm3/s), organic phase composition (5–15 wt%), and temperature (30–60 °C) on the performance of hollow fiber membrane contactors, with an in-depth disclosure of mass transfer phenomena limiting the extraction efficiency. For both acid and copper recovery, a reduction in viscosity forces prevails over the decrease in inertial forces, improving the flow regime. Even so, the predominant mechanism was the diffusive transport of both solutes into the fluid, across the membrane pores, rather than being carried along by the aqueous phase flow. The acid and copper recovery from membrane distillation concentrate achieved values greater than 91%, which represents an acid stream containing 5.86 g-H2SO4/L and an aqueous copper solution with a concentration of 269.0 mg/L, both at high purity. It was discussed different opportunities for their reuse within the gold ore processing circuit and challenges related to their external commercialization. Preliminary economic analysis suggested that the mineral acid would present slightly higher costs than currently practiced (0.54 US$/kgH2SO4; market prices: 0.03–0.11 US$/kgH2SO4), although the operational costs related to copper were comparable with market prices (11.58 US$/kgCu; market prices: 10.31 US$/kgCu). In a broad context, the opportunity for acid and sulfuric acid recycling has the potential to extend sustainability in the mining sector.

Efficient CO2 absorption through wet and falling film membrane contactors: insights from modeling and simulation

The release of excessive carbon dioxide (CO2) into the atmosphere poses potential threats to the well-being of various species on Earth as it contributes to global working. Therefore, it is necessary to implement appropriate actions to moderate CO2 emissions. A hollow fiber membrane contactor is an emerging technology that combines the advantages of separation processes and chemical absorptions. This study investigates the efficacy of wet and falling film membrane contactors (FFMC) in enhancing CO2 absorption in a monoethanolamine (MEA) aqueous solution. By analyzing factors such as membrane surface area, gas flow rate, liquid inlet flow rates, gas–liquid contact time, and solvent loading, we examine the CO2 absorption process in both contactors. Our results reveal a clear advantage of FFMC, achieving an impressive 85% CO2 removal efficiency compared to 60% with wet membranes. We employ COMSOL Multiphysics 6.1 simulation software and finite element analysis to validate our findings, demonstrating a close agreement between predicted and experimental values, with an average relative error of approximately 4.3%. These findings highlight the significant promise of FFMC for applications in CO2 capture.