DL Membrane Research Articles

Green Separation by Using Nanofiltration of Tristerix tetrandus Fruits and Identification of Its Bioactive Molecules through MS/MS Spectrometry.

Membrane technology allows the separation of active compounds, providing an alternative to conventional methods such as column chromatography, liquid-liquid extraction, and solid-liquid extraction. The nanofiltration of a Muérdago (Tristerix tetrandus Mart.) fruit juice was realized to recover valuable metabolites using three different membranes (DL, NFW, and NDX (molecular weight cut-offs (MWCOs): 150~300, 300~500, and 500~700 Da, respectively)). The metabolites were identified by ESI-MS/MS. The results showed that the target compounds were effectively fractionated according to their different molecular weights (MWs). The tested membranes showed retention percentages (RPs) of up to 100% for several phenolics. However, lower RPs appeared in the case of coumaric acid (84.51 ± 6.43% (DL), 2.64 ± 2.21% (NFW), 51.95 ± 1.23% (NDX)) and some other phenolics. The RPs observed for the phenolics cryptochlorogenic acid and chlorogenic acid were 99.74 ± 0.21 and 99.91 ± 0.01% (DL membrane), 96.85 ± 0.83 and 99.20 ± 0.05% (NFW membrane), and 92.98 ± 2.34 and 98.65 ± 0.00% (NDX membrane), respectively. The phenolic quantification was realized by UHPLC-ESI-MS/MS. The DL membrane allowed the permeation of amino acids with the MW range of about 300~100 Da (aspartic acid, proline, tryptophan). This membrane allowed the highest permeate flux (22.10-27.73 L/m2h), followed by the membranes NDX (16.44-20.82 L/m2h) and NFW (12.40-14.45 L/m2h). Moreover, the DL membrane allowed the highest recovery of total compounds in the permeate during the concentration process (19.33%), followed by the membranes NFW (16.28%) and NDX (14.02%). Permeate fractions containing phenolics and amino acids were identified in the membrane permeates DL (10 metabolites identified), NFW (13 metabolites identified), and NDX (10 metabolites identified). Particularly, tryptophan was identified only in the DL permeate fractions obtained. Leucine and isoleucine were identified only in the NFW permeate fractions, whereas methionine and arginine were identified only in the NDX ones. Liquid permeates of great interest to the food and pharmaceutical industries were obtained from plant resources and are suitable for future process optimization and scale-up.

Polyelectrolyte multilayers modification of nanofiltration membranes to improve selective separation of mono- and multivalent cations in seawater brine

Nowadays, brine produced in the Reverse Osmosis (RO) seawater desalination plants is a significant and largely untapped source of critical minerals and metals, which is usually discharged into the seas as wastewater. As a front face stage in the brine mining process, nanofiltration (NF) membranes can be used to separate brine stream into monovalent and multivalent ion-rich streams. Since high separation factors are required in seawater RO brine, polyelectrolyte multilayers with Layer-by-Layer (LbL) technique were used in this study to modify commercial polyamide NF membranes and improve their performance. Two common polyelectrolytes, poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) were coated onto two poly-piperazine polyamide NF membranes (NF270 and Desal-5 DL). The effects of the bilayers number and the outer layer charge on membranes’ performance were studied using two crossflow filtration setups with two different membrane sizes to find the membrane with the higher monovalent/multivalent separation factor. Desal-5 DL membrane coated with 5.5 bilayers provided the highest selectivity factors for mono/multivalent cations (> 21), the highest average rejection of multivalent cations group (about 95.7%) for short-term experiments. Another interesting result was the increase in water permeance of the Desal-5 DL membrane after it was coated with 5.5 bLs (indicating more than 20% improvement in pure water permeance). In addition, the stability test with brines at 20 bar showed that this membrane was stable over an extended period of filtration (22 hours) with an even higher selectivity factor of 34 and multivalent cations rejection of 97.7% on average.

Removal of antibiotics and estrogens by nanofiltration and reverse osmosis membranes

The separation behavior of a variety of emerging contaminants, including nine antibiotics and six estrogens commonly reported in natural environment, by four commercial nanofiltration and reverse osmosis (NF/RO) membranes at various water conditions (pH, concentration) was investigated. The contaminant rejection at pH 6.0 followed a decreasing trend of XLE (94%–100%) ≈ NF90 (88%–100%) ＞ NF270 (25%–85%) ＞ DL (16%–75%). The dense structures of NF90 and XLE reflected by their small effective pore radii (0.30–0.31 nm) contributed mainly to their high rejection, demonstrating the important role of size exclusion. For the negatively charged loose NF270 and DL membranes (0.40–0.45 nm), charge repulsion made additional contribution, which is markedly reflected by their greater rejection to charged antibiotics than neutral estrogens (45%–85% vs. 25%–60% by NF270). The correlation between rejection data and normalized molecular sizes at pH 4.0 and 9.0 intuitively demonstrated the individual role of size exclusion and charge repulsion. The adsorption by membranes was mainly responsible for the initial compound reduction in feedwater by 6%–25% within 3 h, while only 0.3%–5.6% was attributed to self-degradation. The adsorption capacity was determined, which might be mainly governed by hydrophobic interaction. The resolved controlling factors and mechanisms will contribute to the accurate prediction and membrane selection for trace contaminant removal by membrane process.

In-situ growth of poly(m-phenylenediamine) in polyethylene (PE) matrix for nanofiltration membranes enabling outstanding selectivity of both mono-/di-valent ions and dyes/salt mixtures with enhanced water flux

Membrane-based nanofiltration is a crucial technique for treating dyestuff-salts wastewater, owing to its excellent selectivity towards mono/multivalent ions and organic matter. In this study, a facile and highly practical method was employed to enhance the hydrophilicity of the PE matrix through in-situ growth of poly(m-phenylenediamine) on the PE fibrils via the chemical oxidative polymerization of MPD. The inclusion of the poly(m-phenylenediamine) on PE enables the formation of homogenous and defect-free PA layer showing a unique honeycomb-like Turing morphology with characteristic crater-belt structure. Furthermore, the pendant amine groups from the poly(m-phenylenediamine) chain promotes the formation of a PA layer with a smaller effective mean pore size and a sharper pore size distribution, resulting from the formation of an extra polyamide network (reaction of PMPD with TMC) within the PA layer. The as-prepared PE-based NF membrane exhibits a high pure water permeance of 17.7 LMH bar−1, exceptional Na2SO4 rejection of 99.3%, and a long-term stability for cross-flow filtration for over 10 days. The PE-based NF membrane exhibits the water flux 2.2 times higher than that of the commercially available DK and DL membranes while maintaining a high salt rejection. Additionally, the PE-based NF membrane demonstrates exceptional selectivity, with a value of 115 for the separation of NaCl/Na2SO4 and 339.8 for Cl-/SO42- in a binary salt mixture. Furthermore, the PE-based NF membrane shows ultra-high selectivity values of 990 for CR/NaCl and 1039 for MB/NaCl in the treatment of dye/salt mixtures, respectively, which are significantly higher than those of the DK and DL membranes. The findings of this study highlight the potential of the in-situ growth of poly(m-phenylenediamine) on PE fibrils as a simple and cost-effective method for the modulation of hydrophilicity to enhance the NF membrane performance.

Separation of ions with equivalent and similar molecular weights by nanofiltration: Sodium chloride and sodium acetate as an example

Wastewater containing equivalent and similar molecular weights (similar ions) generated from the production process have great recovery value. But effective separation is tough because of their similarities in chemical and physical properties. This work aims at comparing the potential for the separation of sodium acetate (NaAc) and sodium chloride (NaCl), which typically exists in pigment wastewater, through nanofiltration (NF) or reverse osmosis (RO) process. The effects of operational conditions such as pH, pressure, temperature, and feed concentration on the rejection of solutes for five commercial membranes were investigated. The DL membrane exhibited a higher separation factor than other NF and RO membranes. Under the optimum condition at 10 bar, pH = 10, and 25 °C, the DL membrane showed the best performance with the acetate rejection as high as 87.14% and the chloride rejection at only 0.98%. Other than common steric hindrance and Donnan exclusion, a synergic mechanism involving dehydration phenomenon and the apparent activation energy was proposed to explain the separation behavior of the similar ions. This work may provide new strategies to recycle valuable resources from wastewater or other complex mediums.

An integrated electrocoagulation–nanofiltration process for carwash wastewater reuse

In the present work, advanced treatment of carwash wastewater with an integrated electrocoagulation–nanofiltration (EC–NF) process to reuse the treated wastewater as rinsing water was investigated. The wastewater was pretreated by EC process under various operating parameters such as temperature (25 °C, 35 °C, 45 °C), stirring speed (150 rpm, 250 rpm, 350 rpm), and electrode connection mode (MP-P, MP-S, BP-S) using Fe electrode. The best results were achieved at 25 °C, 250 rpm and MP-P connection mode for EC, considering both pollutant removals and energy consumptions. EC sludge was characterized scanning electron microscopy-energy dispersive index (ESEM–EDX) analysis. The pretreated carwash wastewater using EC process was further treated by NF process using NF 270 and Desal 5DL membranes. Desal 5 DL membrane provided the highest treatment performance for chloride (92%), conductivity (80%) and total hardness (90%) parameters for EC–NF process. Resistance in series model was used for a deeper discussion of the reasons for flux decline. In addition, Fourier transform infrared (FTIR) spectroscopy and contact angle measurements were conducted for membrane fouling characterization. The foulants mainly accumulated on the membrane surface forming a cake layer and lower extent of membrane fouling was occurred for both membranes. As a result, this study showed that the water quality for reuse in carwashing process could be achieved with an integrated EC–NF process.

Custom-Tailoring Loose Nanofiltration Membrane for Precise Biomolecule Fractionation: New Insight into Post-Treatment Mechanisms.

Loose nanofiltration (NF) membranes with diverse selectivity can meet the great demands in various bioseparation applications. Thus, a facile strategy to tune the properties such as pore size, surface charge, and hydrophilicity of the NF membrane is required to produce tailor-made loose NF membranes without changing the existing production line. Herein, we systematically investigated the post-treatment of the nascent poly(piperazine amide) NF membranes using different reagents (organic acids, weak bases, organic solvents and ionic liquid (IL)). Various characterizations revealed that the skin/separation layer became looser and permeance was promoted with the decrease of salt rejection in varying degrees. It was found that the O/N ratio did not rigorously represent the cross-linking degree of the skin layer, because besides the hydrolysis of the residual acyl chloride impeding the amido bond formation, the breaking of existing amido bonds and the grafting of free trimesoyl chloride molecules on the nascent membranes could also increase the O/N ratio during post-treatments. Then three mechanisms including hydrolysis, swelling rearrangement and capping reaction effects were proposed to better understand the membrane properties variations. All these effects resulted in larger pore size of the NF membrane, and the hydrolysis/capping effect might increase negative charge and hydrophilicity on the membrane, while the swelling rearrangement could produce less defective skin structure. These three effects might be involved together during a single treatment. Finally, the NF membrane post-treated by N-hexane could efficiently separate antibiotics and NaCl with the highest permeate flux, whereas the one post-treated by ionic liquid outperformed others for the decoloration of cane molasses (much more efficient than NF270, DL, and NTR7450 membranes). The long-term operating stability of the post-treated membranes selected was also confirmed by a continuous crossflow filtration for 15 h with regular alkaline cleaning.

Comparison of the bromate ions removal by nanofiltration membranes made from different polymers at different conditions

Bromate is toxic compound which represent the carcinogenic effect for human health, a serial research’s has been developed by the scientists for the efficient bromate removal methods from the water with low cost in order to obtain water to Bromate a maximum concentration level (10ppb). Bromate ions are formed as a result of the reaction between bromide ions and ozone used as a water disinfectant in membrane demineralization plants .Different technologies have been used for Bromate elimination from water such as ion exchange, adsorption, biofiltration, electrolysis and membrane technology. The aim of this work is to study the rejection of bromate ions by nanofiltration membranes (N30F from Nadir and DL from Osmonics) made from different polymers using bromate solution at different conditions (feed bromate concentration, transmembrane pressure, pH and ionic strength).The bromate rejection is related to the feed solution, pH and ionic strength and the nature of the membrane. At pH=8, bromate ions were removed by the DL membrane made from polyamide around with higher than those by the N30F made from polyethersulfone

Tuning the Stability of Membrane Protein Dimerization by Changing the Lipid Solvent

In cell membranes, proteins encounter a unique problem where the solvent is a mixture of diverse chemical composition. The question arises, how do changes in lipid composition affect a simple reaction such as protein association? Previously, we experimentally measured the equilibrium dimerization reaction of the CLC-ec1 Cl−/H+antiporter in a synthetic mimic of the E. colimembrane - 2:1 POPE/POPG comprised of C16:0/C18:1 acyl chains (Chadda et al., eLife 2016). In this condition, the free energy of association is −11 kcal/mole, one of the strongest membrane protein complexes studied so far. Examination of the dimerization interface shows that the monomer introduces a region of hydrophobic mismatch ∼10 Å shorter than the surrounding membrane. Coarse-grained molecular dynamics (MD) simulations show that C16:0/C18:1 lipids adopt constrained configurations at the dimerization interface that introduce an energetic penalty in the dissociated state. Based on this, we hypothesized that short chain lipids, e.g. 2:1 DLPE/DLPG with C12:0 acyl chains, could solvate the shorter interface without penalty, and thus stabilize the dissociated state. Chloride transport function was measured in the DL membranes demonstrating that the protein is folded. On the other hand, dimerization stability is shifted, with a gradual increase in monomeric population for DL < 1%, and a complete shift to monomers at higher DL. Small-angle neutron scattering experiments were carried out on the mixed DL/PO membranes, showing a reduction in bilayer thickness from 0 - 40% DL that correlates strongly with the changes in dimerization. MD simulations of mixed PO/DL membranes show preferential accumulation of short-chain lipids along the dimerization interface. Altogether, these results indicate that short-chain lipids modulate CLC dimer stability by local hydrophobic matching, with preferential solvation capable of tuning the reaction across a wide-range of compositions.

Fabrication and characterization of phosphorylated chitosan nanofiltration membranes with tunable surface charges and improved selectivities

Phosphorylated chitosan (PCS) with tailored amount of phosphate groups was synthesized, and novel composite nanofiltration membranes (NFMs) with tunable surface charges were prepared by coating PCS onto polyacrylonitrile (PAN) supporting layer and subsequently cross-linked by glutaraldehyde (GA). Chemical structures and compositions of PCS and NFMs, along with morphologies, surface charges, and performance of NFMs were represented by using FTIR, TG, ATR-IR, SEM-EDX, AFM, streaming potential analyzer, and cross-flow flat permeation test, respectively. The effect of different phosphorous abundance of PCS precursors on the surface charge and permselectivity of NFMs was investigated systematically. It was illustrated that the incorporation of phosphate group with high-substitute degree did enhance the surface charge and selectivity of NFM, respectively, while retaining its permeability. The resultant membrane showed a zeta potential of −77.6 mV at 1 mol·m−3 KCl electrolyte solution and pH 7.0, significantly more superior than that of the commercial DL membrane. For the feedwater (Na2SO4 + MgCl2, 1.0 g·L−1), the mass ratio of SO42−/Cl− and Mg2+/Na+ decreased from initial 0.5:1 in the feed to 1.58 × 10−2 and 0.254 in the permeate after filtration by the optimal NF membrane. Anionic dyes removal tests also confirmed the existence of negative charge characteristics from the prepared membranes, and pivotal role of the Donnan exclusion in separating performance. In addition, NFM4 exhibits good chemical stability in the long-term operation.

Separation of Sucrose and Reducing Sugar in Cane Molasses by Nanofiltration

Recovery of sugars from cane molasses is a promising approach to increase the added value of molasses and reduce its environmental pollution. In this work, for the first time, nanofiltration (NF) was used for the separation of sucrose and reducing sugar in cane molasses by a cascade diafiltration-concentration process. The retention difference between sucrose and reducing sugar by all the tested NF membranes was not distinct at 25 °C, while due to the thermal-induced pore size change and enhanced solute diffusivity, the NF retention behavior changed significantly at 60 °C, and the DL membrane with a sucrose retention of 96% and a reducing sugar retention 5% was selected for the process optimization and modeling. High temperature (55–60 °C), low permeate flux (below 15 Lm−2 h−1), and high sugar concentration resulted in a low retention of reducing sugar due to the dominant diffusive mass transfer, which was desirable for the molasses separation by NF. Mathematical modeling could well predict the diafiltration and concentration processes if using right sugar retention data. The deviations between prediction lines and experimental data in the cross-flow filtration of real solution were mainly caused by the permeate flux variation rather than membrane fouling. After diafiltration, the ratio of sucrose in total molasses sugar increased from 76.1 to 87.9%, while in the permeate of the second concentration step, the ratio of sucrose was only 2.4%. Thus, the retentate of diafiltration could be directly used for sucrose crystallization to avoid the accumulation of reducing sugar and salts, and the permeate of the second concentration step could be concentrated by NF270 at room temperature to produce syrup drinking.

Scaling of nanofiltration membranes used for chromium(III) ions recovery from salt solutions.

The effect of membranes' structure on the efficiency of chromium(III) ions recovery from salt solution at low pH and the efficiency of chemical cleaning of these membranes were analyzed in this work. The nanofiltration membranes (DL and HL) used in this study were provided by GE Osmonics. The DL membrane had an irregular, dense support layer structure, while the HL membrane had a loose one. In the case of the DL membrane, it was found that, under tested solutions, the layer of mineral scale formed on the surface gradually decreases the membrane permeability coefficient. In the case of the DL membrane, the scaling was observed only on the surface. On the other hand, a small roughness (118Å) and low density charge (zeta potential at level -4) of the HL membrane causes an uneven growth in deposits and, consequently, irregular nature of the surface structure which hinders the removal of accumulated sediment from the tested membranes' surface. Additionally, the loose structure of the support layer of HL membrane contributes to its internal scaling. Consequently, the permanently loose structure of the HL membrane permeability coefficient was observed.

Nanofiltration: a Final Step in Industrial Process Water Treatment

We report here a proposed process water treatment design guide: selection of nanofiltration membrane, membrane test for model solutions and test for pre-treated industrial process water. We also suggest a complex evaluation method, which can help in decision-making process. Membrane selection experiments showed that high flux coupled with high enough rejection is favored to shorten treatment time and perform acceptable rejection. The effect of composition was studied during constant total salt concentration and it was revealed that the DL membrane had stable flux and high rejection. In case of pre-treated industrial process water a more complex effect could be observed: the counter ions present in the feed solution, moreover the complexing agents as well as other properties of the feed could lower the membrane’s rejection, simultaneously decreasing the flux. Nanofiltration though still showed advantages, which allowed its implementation into an existing industrial scale technological chain. At a recovery rate of 0.2-0.5 all the environmental requirements could be fulfilled, and the permeate leaving the technology could be fed into the city sewer system.

Performances of some NF and RO membranes for desalination of MBR treated wastewater

In recent years, because of both lowered discharge limits and reduction of usable water sources, reutilization of water became inevitable. This situation makes the application of advanced water treatment technologies compulsory. In this study, applicability of nanofiltration (NF) and reverse osmosis (RO) methods was investigated for reuse of industrial wastewater treated with advanced treatment method at organized industrial zone. For this purpose, two NF (HL-GE and DL-GE) and one RO (AG-BWRO) membranes were used at 10bar of applied pressure. Permeability test revealed that HL membrane exhibited the highest permeability with 7.22±0.79L/m2hbar of permeability constant followed by AG membrane with a permeability constant of 6.03±0.25L/m2hbar. Less permeable membrane was DL with a permeability constant of 2.08±0.11L/m2hbar. In terms of rejection performance, conductivity, salinity, chemical oxygen demand (COD), total organic carbon (TOC), color, divalent ions (Ca2+, Mg2+ and SO42−) and monovalent ions (Na+, K+, Cl− and HCO3−) were rejected by HL membrane with an average rejection of 37.2±2.1%, 38.6±2.5%, 72.5±5.5%, 79.9±6.1%, 85.4±1.2%, 86.0±0.5%, 88.8±0.3%, 99.9±0.0%, 46.0±0.9%, 27.0±0.3% 17.9±1.1%, 64.3±2.8%, respectively. The respective rejections by DL membrane were 31.1±0.8%, 31.2±1.1%, 36.8±16.4%, 68.2±7.3%, 81.0±4.0%, 77.9±0.7%, 84.7±07%, 99.9±0.0%, 41.0±04%, 18.4±1.7%, 14.0±1.3%, and 45.2±2.7%. On the other hand, higher water quality was obtained with AG-BWRO membrane. AG-BWRO achieved conductivity, salinity, COD, TOC and color rejections of 96.8±0.2%, 96.9±0.1%, 74.7±2.8%, 90.5±4.8% and 87.6±1.9%, respectively. Divalent ions and monovalent ions were rejected by AG-BWRO membrane with an average rejection of higher than 94%. In conclusion, AG-BWRO membrane was found to be the best membrane considering both product water quality and quantity. DL membrane was found to be the worst one among the three membranes investigated in this work.

SEPARATION OF XYLOSE FROM GLUCOSE USING PILOT SCALE SPIRAL WOUND COMMERCIAL MEMBRANE

Xylose is an intermediate product in xylitol production and glucose interferes in the process of separation. Thus the aim of this study is to investigate the performance of pilot scale commercial spiral wound NF membrane namely Desal-5 DK, Desal-5 DL and NF90 for separation of xylose from glucose. Separation of xylose and glucose model solutions was done in a pilot scale cross-flow system, using a commercial nanofiltration (NF) membrane with molecular weight cut off (MWCO) ranging from 150 to 1000 g/mol. The model solution consists of 1:1 ratio of xylose to glucose at 10 g/L each diluted in ultrapure water. The filtration was operated in total recycled mode at 10 bar. The sugar concentration was analyzed using high performance liquid chromatography (HPLC). From this study, the pure water permeability (PWPs) of the Desal-5 DK membrane was considerably higher at 6.78 ± 0.06 than PWPs of the Desal-5 DL and NF90 membranes at 1.28 ± 0.24 and 1.33 ± 0.05, respectively. The Desal-5 DK also gave the higher xylose separation factor at 1.17 as compare to Desal-5 DL (0.81) and NF90 membranes (0.84). This indicates that membrane Desal-5 DK was the most selective membrane to separate xylose form glucose. Overall, it can be concluded that the spiral wound nanofiltration membrane offers cost-effective and easy-maintenance, which has a potential in xylose-glucose separation.

Recovery of bioactive compounds from artichoke brines by nanofiltration

In this work a membrane-based process for the fractionation of artichoke brines was investigated in order to separate flavonoids and caffeoylquinic acids from salt compounds. Therefore, the performance of different spiral-wound nanofiltration (NF) membranes in the treatment of clarified artichoke brines was evaluated in terms of productivity and selectivity towards bioactive compounds in selected operating conditions. Membranes with different polymeric material (polyethersulphone, polyammide) and molecular weight cut-off (MWCO) (from 200 to 1000Da) were tested. NF membranes of 200Da produced better results in terms of recovery and concentration of compounds of interest. A better separation of salt compounds from caffeoylquinic acid derivatives was reached by using Filmtec-Dow NF 200 and Desal DL membranes. For these membranes a low rejection towards dry residue (between 14% and 18%) was observed, while rejections towards total caffeoylquinic acids, flavonoids and cynarin were higher than 92%.According to the obtained results the NF permeate, enriched in salt compounds, can be reused in the working cycle for the preparation of new acidulated brines through the adjustment of the standard salt concentration; the concentrated stream, enriched in phenolic compounds, is a good source of possible ingredients to functionalize foodstuffs.

Effect of extended exposure to alkaline cleaning chemicals on performance of polyamide (PA) nanofiltration membranes

Abstract This study aimed to increase the knowledge on the influence of alkaline cleaning on performance of polyamide based nanofiltration membranes. In the experiments the Desal-5 DL, XN45 and NF270 membranes were exposed to alkaline conditions at temperatures of 40, 50, 60 and 70 °C and the influence of the extended alkaline exposure to the membrane permeability, glucose and MgSO 4 retention was measured. The characteristic features of the experimental kinetic data for permeability were a rapid increase in permeability after a short time exposure and a subsequent steady increase when the exposing time was continued while the characteristic features for the retention data were a rapid decrease in retentions of glucose and MgSO 4 after a short time exposure and a subsequent steady decrease when the exposing time was continued. The model developed in this study described well the both rapid and slow changes and it can be used to predict the performance of the tested membranes at the temperature range between 40 and 60 °C. The increase in exposure temperature accelerated the changes in membrane performance. The alkali induced changes caused at the 70 °C exposure could not be described with the simple rate law. However, only minor changes in chemical structure of the membranes were noticed in IR spectra after the exposure to alkaline conditions at 70 °C. This indicates that changes observed in permeability and retention could mainly be linked to conformational changes occurring in the polymeric matrix of the membrane skin layers. It was also shown that after a relatively long recovery time (144.5 h) the alkali induced changes in membrane performances were at least partly recovered.

Effect of interaction between anionic surfactants and poly(piperazine-amide) nanofiltration membranes used for chromium(III) recovery from saline solution.

The effect of the anionic surfactant on the permeation properties of the nanofiltration (NF) membranes used for chromium(III) recovery from saline solution at low pH have been presented in this paper. The membrane surface layer performance periodically modified by sodium dodecyl sulphate (SDS) solution has been studied with measurements of zeta potential, atomic force microscopy (AFM) and permeability coefficient of tested membranes. It was found that the membrane surface layer modification by SDS caused a substantial reduction in the possibility of separation of loose NF membrane characterized by a high density of positively charged groups activating under the effect of the low pH of the saline solutions (HL membrane). On the other hand, in the case of dense NF membranes characterized by a strong negatively charged surface (DL membrane) constituting used the SDS improves the separation of chloride and chromium(III) ions. In this case, the surfactant solution also provides a high membrane permeability coefficient behavior over a long period of use. DL membrane modification by SDS allowed both to retain the stable membrane working for a long period and to limit the frequency of the chemical cleaning of this membrane.

Two-stage nanofiltration process for high-value chemical production from hydrolysates of lignocellulosic biomass through hydrothermal liquefaction

Two-stage nanofiltration (TSNF) process was proposed for recovering high-value chemicals, including monophenols, cyclopentenones, glucose and acetic acid, from hydrolysates of lignocellulosic biomass (rice straw) through hydrothermal liquefaction (HTL). The separation performances of three single nanofiltration (NF) processes and three TSNF processes were studied. Results showed that at the first stage of (DL+DK) TSNF process, DL membrane had high glucose rejection of 97.12%, and lower acetic acid rejection as well as lower aromatics rejections than DK membrane. At the second stage, DK membrane had rather low acetic acid rejection of 5.04% to ensure acid separation from aromatics. Unlike glucose or acetic acid, aromatics were unable to be recovered into one fraction due to scattered rejections of different aromatic compounds on NF membrane. The (DL+DK) TSNF process was proved to be a feasible way to fractionate hydrolysates into three parts: glucose concentrate, monophenols and cyclopentenones concentrate, and acetic acid permeate.

Nanofiltration of glucose: Analysis of parameters and membrane characterization

Membrane characterization and modeling of nanofiltration processes of uncharged solutes are of special interest for the food industry. In this work two commercial membranes, DK and DL, were used to concentrate glucose solutions. Membranes were characterized according hydrophobicity, thickness, porosity, and hydraulic permeability. The influence of pressure and concentration of glucose on the permeate flux and rejection were studied. Both membranes presented a great potential for the food industry due to their high rejection of glucose. The osmotic pressure model was combined with film theory and the real driven force was calculated taking into account the osmotic pressure and the concentration polarization. Both phenomena influenced the process (concentration polarization only in the most dilute solutions at low pressure) and the permeability for glucose solutions was similar to the hydraulic permeability. A mathematical model based on the Donnan-Steric Pore Model was used to determine the pore radius and the effective thickness of both membranes. As the concentration inside the pore (needed for the calculations) is difficult to measure experimentally, various alternatives were proposed. The average of the concentration at the interface and permeate best fitted the experimental data. The model was applied successfully; the maximum error was 8% within the range of concentrations (5–100g/L) for the DL membrane and 5% for the DK membrane up to 50g/L.