Diffusion Dialysis Process Research Articles

Preparation of Polyvinyl Alcohol (PVA)-Based Composite Membranes Using Carboxyl-Type Boronic Acid Copolymers for Alkaline Diffusion Dialysis.

Carboxyl-type boronic acid copolymers (CBACs) were synthesized by a radical polymerization method and used for the preparation of polyvinyl alcohol (PVA)-based composite membranes via a solution mixture method. The as-prepared composite membranes exhibited a water uptake (WR) of 122.6–150.0%, an ion exchange capacity (IEC) of 0.0147–0.0518 mmol g−1, and excellent mechanical (elongation at break (Eb) of 103.8–148.4%, tensile strength (TS) of 38.7–58.6 MPa) and thermal stability. The alkali resistances of the as-prepared membranes were tested by immersing the samples into 2 mol L−1 NaOH solutions at 25 °C for 60 h, and the results were encouraging: the mass loss and swelling degree of the as-prepared membranes were in the ranges of 1.9–5.9% and 222.6–241.9%, respectively. The separation performances of the as-prepared membranes were evaluated by the diffusion dialysis (DD) process with an NaOH/Na2WO4 mixture at room temperature. The results demonstrated that the dialysis coefficients of hydroxide (UOH) were in the range of 0.0147–0.0347 m h−1, and the separation factors (S) were in the range of 29.5–62.6. The introduced carboxyl groups from CBACs and the –OH groups from PVA were both deemed to play significant roles in the promotion of ion transport: the –COO− groups formed negatively charged transport channels for Na+ by electrostatic attraction, and the –OH groups promoted the transport of OH− via hydrogen bonding.

Prepared poly(aryl piperidinium) anion exchange membranes for acid recovery to improve dialysis coefficients and selectivity

The diffusion dialysis (DD) process based on AEM is considered for the acid recovery from acid effluents. In this work, the novel self-organized nanostructured cross-linked AEMs based on poly (aryl piperidinium) are synthesized for acid recovery. The cross-linked AEMs are designed by introducing 2-bromoethanol and 1,6-dibromohexane into the hydrophobic poly (biphenyl piperidine)s backbone via Menshutkin reaction, and the self-assembled nanostructure is confirmed by TEM imagines. The acid flux is improved by constructing a micro-phase separation structure and hydrogen bond network. The H-bond networks and cross-linking structure improve the selectivity between the acid and salt system without sacrificing IEC values of AEM. The IEC values of PBP-OH-x AEMs are in the range of 2.18–2.21 mmol/g. The AEMs exhibit high H+ dialysis coefficients (UH), ranging from 0.045 to 0.053 m/h, and have good separation factors (S) in the range of 32–56. The prepared PBP-OH-x AEMs have better DD performance, comparing with the commercial membrane DF-120 (UH = 0.009 m/h, S = 18.5). The novel AEMs based on poly (aryl piperidinium) showed the potential to be used in acid recovery via DD.

Construction of two dimensional anion exchange membranes to boost acid recovery performances

Currently, the development of two dimensional (2D) lamellar membranes for acid recovery via the diffusion dialysis process is still in its infancy. In this work, we proposed the concept of 2D anion exchange membranes (AEMs) to synergistically improve the H+ dialysis coefficient and separation factor. The 2D AEMs were fabricated by layer by layer stacking the graphene oxide nanosheets decorated by imidazolium cations (Im-GO). Benefitting from the attachment of imidazolium cations, the Im-GO membrane exhibits higher hydrophilicity and wider interlayer channels compared with the original GO membrane, favorable of quicker H+ migration. Additionally, imidazolium cations serving as typical anion exchange sites help with rapid H+ transfer and better distinguishing H+ and Fe2+ via the electrostatic exclusion mechanism. The diffusion dialysis results show that the acid dialysis coefficients gained by Im-GO (5.9 × 10−3- 8.2 × 10−3 m h−1) are an order of magnitude higher than GO (0.7× 10−3 m h−1). Ideally, Im-GO also gives rise to higher separation factors (24–37) toward H+ and Fe2+ than GO (15). Moreover, after 10 times continuing acid recovery testing, Im-GO demonstrates no declines of dialysis coefficients and separation factors. We believe the engineering strategy reported here could act as a versatile method for modifying 2D membranes, to further extend their usage scope.

Recovery of rare earth elements from electronic waste by diffusion dialysis

Recycling rare earth elements (REEs) contained in electronic waste is of utmost importance due to their ever-increasing use in the high-tech sector. In this context, the use of non-polluting techniques represents a real challenge for scientists. In this work, we demonstrated that a clean and energy-efficient process, diffusion dialysis, has great potential for the recovery of neodymium (Nd) and praseodymium (Pr), contained in the Nd-Fe-B magnets of end-of-life computer hard disk drives (HDDs). Four kinds of polymer membranes were prepared by blending cellulose triacetate (CTA) and polyethylenimine (PEI) with the addition of di-(2-ethylhexyl) phosphoric acid (D2EHPA), tridodecylamine (TDDA), trioctylamine (TOA) or trioctylphosphine oxide (TOPO). The membranes were first characterized by several techniques such as water uptake, contact angle, ATR-FTIR, SEM, XRD and zeta potential. They were further implemented in diffusion dialysis experiments in which diluted HDDs leachates were used as feed solutions. The relevance of the diffusion dialysis process for the recovery of REEs was demonstrated as it was possible to extract up to 15% of the boron by spontaneous diffusion through the CTA/PEI/TOA membrane in 6 h with a lab-scale cell operating in batch mode. All membranes were positively charged under the operating conditions and then, REEs (present mainly in the form of trivalent cations Nd3+ and Pr3+) were strongly rejected. A fairly good correlation was found between the membrane water uptake and boron transfer, with boric acid molecules passing more easily through the more hydrated membranes. The selectivity factor between boron and REEs resulted from the interplay between the membrane structure, its water uptake ability and surface charge. It was also found to be dependent on the leachate composition. The CTA/PEI/TDDA membrane was found to exhibit the greatest B/REE selectivity factors, with values reaching up to 3706 and 140 for Nd and Pr, respectively. The lower selectivity towards Pr was explained by the weaker Gibbs energy of hydration of Pr3+ cations compared with Nd3+.

Diffusion Dialysis for Acid Recovery from Acidic Waste Solutions: Anion Exchange Membranes and Technology Integration.

Inorganic acids are commonly used in mining, metallurgical, metal-processing, and nuclear-fuel-reprocessing industries in various processes, such as leaching, etching, electroplating, and metal-refining. Large amounts of spent acidic liquids containing toxic metal ion complexes are produced during these operations, which pose a serious hazard to the living and non-living environment. Developing economic and eco-friendly regeneration approaches to recover acid and valuable metals from these industrial effluents has focused the interest of the research community. Diffusion dialysis (DD) using anion exchange membranes (AEMs) driven by an activity gradient is considered an effective technology with a low energy consumption and little environmental contamination. In addition, the properties of AEMs have an important effect on the DD process. Hence, this paper gives a critical review of the properties of AEMs, including their acid permeability, membrane stability, and acid selectivity during the DD process for acid recovery. Furthermore, the DD processes using AEMs integrated with various technologies, such as pressure, an electric field, or continuous operation are discussed to enhance its potential for industrial applications. Finally, some directions are provided for the further development of AEMs in DD for acid recovery from acidic waste solutions.

Novel poly (ionic liquid)-based anion exchange membranes for efficient and rapid acid recovery from industrial waste

Owing to the less energy consumption, positive impact on the environment, and prospect of providing clean water resources, anion exchange membranes (AEMs) are promising materials for acid recovery from various industrial wastewater/effluent. Based on the diffusion dialysis process, AEMs selectively allow rapid proton permeation while efficiently retaining metal ions. To enhance the efficiency of the acid recovery process, precise control of macromolecular architecture and chemical composition that enables high hydrophilicity, proton conductivity through the membrane, and ion exchange capacity is required. In this direction, we report on the one-step fabrication of novel poly (ionic liquids)-based AEMs by the free radical polymerization of 1-butyl-3-vinyl imidazolium bromide, acrylic acid, styrene, and acrylonitrile under sunlight. The effect of monomer composition in an AEM matrix on the structural, physicochemical, surface, thermal, and proton conductivity is investigated. The experimentally determined acid dialysis coefficient (UH+) obtained with synthesized poly (ionic liquid) based membranes PILM-1 and PILM-2 were 7.3 ± 2 and 9.2 ± 2 mh−1 at room temperature (25 °C), while separation factors (SF) were 88.9 ± 3 and 50.1 ± 2, respectively. Both the UH+ (>700 times) and SF (>4 times) are significantly values higher compared to the commercial AEM DF-120 (0.009 mh−1 and 18.8 for UH+ and SF, respectively). Thus, this study demonstrates the potential of the prepared AEMs as an alternate to deliver cost-effective, scalable, and rapid acid recovery compared to the currently existing technology.

In-situ crosslinked AEMs with self-assembled nanostructure for acid recovery

The highly selective anion exchange membranes (AEMs) for acid recovery were invented via cationic functionalization of bromo poly(2, 6-dimethyl-1, 4 phenylene oxide). The quantity of tris(2-(2-methoxyethoxy) ethyl) amine (TDA) was precisely adjusted to obtain hydrophilic ion transport channels in the membrane structure. The vinyl part of 2-(dimethylamino) ethyl methacrylate (DMAEMA) was in-situ crosslinked to achieve high selectivity. The cationic groups being efficiently produced by TDA and DMAEMA were responsible for high flux, while the crosslinked nature of the membrane restricted the active transport of Fe2+ ion. The self-assembled nanostructure AEMs showed an excellent selectivity from 49 to 1391 and H+ dialysis coefficients up to 0.0325 m h−1, respectively at 25 °C, which is superior as compared with a commercial DF-120 membrane and some recently reported dense membranes. The representative membranes exhibited better operational stability for 10 consecutive cycles during the entire diffusion dialysis process.

Recovery of H2SO4 from wastewater in the presence of NaCl and KHCO3 through pH responsive polysulfone membrane: Optimization approach

Through the phase inversion technique, asymmetric flat sheet pH-responsive Polysulfone (PSF) membrane was prepared and utilized for recovering H2SO4 in the presence of NaCl and KHCO3 from wastewater. Hydrophilic and pH-responsive characteristics were incorporated within the membrane by blending Polyethylene glycol methyl ether (PEGME) and Humic acid (HA). The modification in membrane morphology with pH was characterized by Field Emission Scanning Electron Microscopy (FESEM), Differential scanning calorimetry (DSC) and Fourier Transform Infrared Studies (FTIR) method. The ion exchange capacity of the prepared pH-responsive membrane increased from 0.145 to 0.25 mmol/g when compared to the pristine PSF membrane. Pure water flux (PWF) of 113.8–46.8 L/m2h, water uptake of 25.9%–6.8% were obtained for pH-responsive membrane when pH varied from 4 to 12. Recovery of H2SO4 was optimized by design expert software 9.0 TRIAL and was found to be a maximum of 76.57 ± 1.5% in the presence of 0.32 M NaCl and 0.5 M KHCO3 at pH ~8.4, through the pH-responsive PSF membrane by diffusion dialysis process. The influencing parameters (pH, NaCl (M) and KHCO3 (M)) were optimized and acid recovery modeling was performed through response surface methodology (RSM) and central composite design (CCD). F value of 6573.40 through ANOVA study indicated the significance of the quadratic model chosen, whereas an insignificant lack of fit (prob > F = 0.0519) confirmed the goodness of fit between the model and obtained experimental data's.

Tubular membrane used in continuous and semi-continuous diffusion dialysis

Tubular membrane is firstly developed from the polyvinyl alcohol based casting solution. The membrane is compact with the diameter of 1.27–1.72 cm and the length of 30–60 cm, which is like a piece of “sieve tube” or “blood vessel” from bionic aspect. The membrane can be used in the static and continuous diffusion dialysis (DD) processes to separate an acidic liquor containing HCl and glyphosate (Gly). The acidic liquor is filled or pumped into the tubular membrane, while the membrane is immersed in the matrix solution of water. The matrix solution can also be static while the acidic liquor is continuous to form a semi-continuous process.Static DD process shows that the recovery ratio (RH) can reach up to 70.2% with the Gly rejection of 95.3% after 1 h. Continuous process shows that the water osmosis coefficient (UH2O) is in the range of 1.54–3.09 × 10−4 m h−1. The RH increases from 64% to 74% as the water flow rate increases. The Gly productivity is 43–72% after precipitation from the residual liquor. Finally, semi-continuous process shows high feed flow rate of 1.86 L m−2 h−1, stable RH values of 71.1–75.5%, and high Gly productivity of 65.1–87.9%.

Application and modeling of pressure-concentration double-driven diffusion dialysis

Diffusion dialysis (DD) is an ion exchange membrane separation process driven by concentration differences. DD is simple to operate and has excellent stability, low energy consumption, and a low installation cost. To overcome the limitations of the traditional DD process, such as low processing capacity and serious water osmosis, the authors propose a pressure-concentration double-driven (PCDD) DD process. This novel DD is double driven because the concentration difference is the main mass transfer force, and the pressure difference is the assistant mass transfer force. The common FeSO4/H2SO4 mixed solution system is used to investigate the PCDD DD process. Our first area of interest is the operating parameters' effects (the pressure difference as well as the initial H2SO4 and FeSO4 concentrations in feed) on the PCDD DD process performance. Results show that the high pressure difference can significantly promote the increment of the H+ dialysis coefficient from 0.0012 to 0.0039 m/h and the Fe2+ dialysis coefficient from 1.25 × 10−5 to 5.95 × 10−5 m/h. Pressure differences in high value can also change the direction of water osmosis (from the dialysate to diffusate). All these are employed to maintain the separation factor in an acceptable range (∼65). Moreover, the increment of the initial FeSO4 concentration in the feed can improve the H+ dialysis coefficient and reduce the Fe2+ dialysis coefficient to increase the separation factor further. However, increasing the initial H2SO4 concentration in the feed is not a commonly accepted method to improve the PCDD DD process performance. A mathematical model based on non-equilibrium thermodynamics is established to quantify the PCDD DD mass transfer process. Notably, the fitting results of the calculated fluxes based on the model and the experimental fluxes are very satisfactory. The research presented here indicates that the PCDD DD process can increase the DD's processing capacity, maintain a good separation effect, and inhibit the water osmosis simultaneously.

Preparation and properties of polyvinyl alcohol (PVA) / mesoporous silica supported phosphotungstic acid (MS-HPW) hybrid membranes for alkali recovery

Diffusion dialysis (DD) separation process is shackled by the ion flux and selectivity. To solve this problem, the development of membrane materials is very important. In this study, mesoporous silica has been synthesized first and then phosphotungstic acid was adsorbed in the mesopores under vacuum condition. The obtained functionalized mesoporous silica materials (MS-HPW) have been then blended with pre-crosslinked polyvinyl alcohol (PVA) solution to prepare a series of hybrid membranes. The as-prepared membranes possess ion exchange capacities (IECs) of 0.015–0.030 (mmol/g) and water uptake (WR) of 98.3%–196.6%, as well as good thermal and mechanical stability. Alkali resistance of the hybrid membranes has been tested in 2 M NaOH solution at 25 °C and the results are acceptable: swelling degree is in the range of 134.3%–160.2% and mass loss is in the range of 3.2%–12.2%. The as-prepared membranes have been used for alkaline diffusion dialysis (DD) process of NaOH/Na2WO4 system and the results are encouraging: PVA/MS-HPW hybrid membranes exhibit higher ion flux and selectivity than that of PVA and PVA/MS membranes. The mesoporous structure and OH− adsorption ability of MS-HPW material are considered to play important roles during the ion transport.

Selective removal of chloride from the adipate formation bath in foil industry by diffusion dialysis

Aluminum electrode foils are the most essential components inside electrolytic capacitors, which are widely used in diverse electronic systems. The production involves the usage of various chemicals, and it generates a huge amount of exhausted bath solution consisting of highly-concentrated ammonium adipate and trace Cl− impurity. The loss of these expensive chemicals is a heavy burden for the foil manufacturers. The current work innovatively applies diffusion dialysis (DD) to selectively remove the chloride from this abandoned solution, which makes the reuse of these chemicals possible. In the process, Cl− ion presents a superior permeability compared with adipate2− ion, and a high permselectivity of 6 is obtained by using conventional anion exchange membranes. The effects of flow intensity and chloride concentration on the selective dechlorination performance have been thoroughly studied, respectively. Furthermore, the long-term stability of the membranes has been carefully investigated, and their performance is unchanged during a six-month period. The overall economics of this new process is very encouraging, and a stunningly short pay-off period (43 days) is achieved. This work not only solves the problem of reusing the exhausted adipate bath solution, but also further demonstrates the great potential of the DD process in selective ion separation applications.

Evonik Industries opens new precipitated silica production unit in the US

Aluminum electrode foils are the most essential components inside electrolytic capacitors, which are widely used in diverse electronic systems. The production involves the usage of various chemicals, and it generates a huge amount of exhausted bath solution consisting of highly-concentrated ammonium adipate and trace Cl− impurity. The loss of these expensive chemicals is a heavy burden for the foil manufacturers. The current work innovatively applies diffusion dialysis (DD) to selectively remove the chloride from this abandoned solution, which makes the reuse of these chemicals possible. In the process, Cl− ion presents a superior permeability compared with adipate2− ion, and a high permselectivity of 6 is obtained by using conventional anion exchange membranes. The effects of flow intensity and chloride concentration on the selective dechlorination performance have been thoroughly studied, respectively. Furthermore, the long-term stability of the membranes has been carefully investigated, and their performance is unchanged during a six-month period. The overall economics of this new process is very encouraging, and a stunningly short pay-off period (43 days) is achieved. This work not only solves the problem of reusing the exhausted adipate bath solution, but also further demonstrates the great potential of the DD process in selective ion separation applications.

Fabrication and characterization of pyridinium functionalized anion exchange membranes for acid recovery

In the present work, the fabrication of pyridinium functionalized anion exchange membranes (AEMs) for acid recovery using diffusion dialysis (DD) processes was developed using brominated poly (2,6-dimethyl-1,4-phenylene oxide) (BPPO) as a polymer backbone and 4-methylpyridine (MP) as an ion exchange element. The electrochemical and physiochemical properties of the developed AEMs were tested under various concentration of MP into the polymer matrix. Water uptake (WR) of 17.18% to 30.55%, ion exchange capacity (IEC) of 1.94–2.24 mmol/g and linear swelling ratio (LSR) of 6.87–14.89% were obtained. In addition, the new membranes exhibited dense morphology, higher thermal and chemical stability in addition to dimensional and mechanical sturdiness. Acid dialysis coefficient (UH) in the range of 0.011–0.066 m/h was obtained. In addition the developed AEMs had a separation factor (S) in range of 24.87–77.61 resulting in enhanced DD performance compared to commercial membrane DF-120B under comparable experimental conditions. The new prepared membranes showed potential for successful application in acid recovery via diffusion dialysis.

Turkey: Evonik & Ege Kimya – precipitated silica

Aluminum electrode foils are the most essential components inside electrolytic capacitors, which are widely used in diverse electronic systems. The production involves the usage of various chemicals, and it generates a huge amount of exhausted bath solution consisting of highly-concentrated ammonium adipate and trace Cl− impurity. The loss of these expensive chemicals is a heavy burden for the foil manufacturers. The current work innovatively applies diffusion dialysis (DD) to selectively remove the chloride from this abandoned solution, which makes the reuse of these chemicals possible. In the process, Cl− ion presents a superior permeability compared with adipate2− ion, and a high permselectivity of 6 is obtained by using conventional anion exchange membranes. The effects of flow intensity and chloride concentration on the selective dechlorination performance have been thoroughly studied, respectively. Furthermore, the long-term stability of the membranes has been carefully investigated, and their performance is unchanged during a six-month period. The overall economics of this new process is very encouraging, and a stunningly short pay-off period (43 days) is achieved. This work not only solves the problem of reusing the exhausted adipate bath solution, but also further demonstrates the great potential of the DD process in selective ion separation applications.

Composite Cationic Exchange Membranes Prepared from Polyvinyl Alcohol (PVA) and Boronic Acid Copolymers for Alkaline Diffusion Dialysis.

Boronic acid copolymers with a large number of functional groups were obtained via a free radical polymerization method. The corresponding composite membranes for alkaline diffusion dialysis (DD) were prepared by a crosslinking reaction between polyvinyl alcohol (PVA) and the as-obtained boronic acid copolymers. The composite membranes possessed water uptake (WR) of 122.1–194.4%, ion exchange capacities (IECs) of 0.79–1.17 mmol/g, as well as both good mechanical stability (tensile strength of 40.7–49.9 MPa and elongation at break of 52.1–121.1%) and thermal stability. The as-prepared membranes were stable in 2 M NaOH solution at 65 °C with a swelling degree and mass loss of as-prepared membranes in the range of 305–368% and 9.2–22%, respectively. A NaOH/Na2WO4 mixture was used to investigate the separation properties of as-prepared membranes via the DD process. Results indicated that the dialysis coefficients of OH− (UOH) were in the range of 0.0079–0.0150 m/h, while the separation factors (S) were in the range of 26.6–53.2. The functional groups from boronic acid copolymer and –OH from PVA were demonstrated to promote the ion transport synergistically.

Significantly enhanced dehalogenation selectivity in near-neutral zinc sulfate electrolytes by diffusion dialysis

For industries around the world, the hydrometallurgical roast–leach–electrowin process is the most common means of producing zinc metal. Dechlorination from the highly-concentrated zinc sulfate electrolyte is of vital importance to the zinc industry. In a recently published work, we innovatively employed diffusion dialysis (DD) to selectively remove Cl- and F- from a highly-acidic spent electrolyte, which extended the application of DD from acid recovery to selective ion separation. In the current paper, we greatly enhance the dechlorination selectivity by adjusting the acidity of feed electrolytes. The Cl-/SO42- permselectivity increases from 2.56 to 42.8 when the acidity is reduced from 160 to 0 g/L as free H2SO4, and meanwhile the removal ratio of Cl- impurity is basically retained (from 55.1% to 46.6%). The competitive permeation of different ions and the interplay between anions and cations are carefully investigated. It is believed that the distinct diffusivity of anions (Cl-, F-, HSO4- and SO42-) originates from their different hydrated sizes. This excellent selectivity observed here is unprecedented and has never been observed in any practical DD processes. It not only remarkably improves the cost-effectiveness of the dechlorination process in zinc production, but also puts forward a new possibility to regulate the permselectivities between ions with the same charge sign and provides new insights into the DD process in the selective ion separation.

Augmenting acid recovery from different systems by novel Q-DAN anion exchange membranes via diffusion dialysis

Abstract In this study, a series of novel anion exchange membranes composed of polyvinyl alcohol (PVA) and various amount of synthesized anion exchange precursor were successfully prepared and used for acid recovery by DD process. The anion exchange precursor (Q-DAN) was synthesized through reaction of 1,5-diaminonaphthalene (DAN) and 2,3-epoxypropyltrimethylammonium chloride (EPTC) which was confirmed by proton NMR. The dosage of Q-DAN inside membrane matrix played an important role to determine the electrochemical and physicochemical properties of Q-DAN AEMs. Influences of Q-DAN and multivalent metal ions on acid recovery were elaborated in detail. Acid dialysis coefficients (UH) values for FeCl2-HCl system were in the range of 0.0194–0.0295 m/h and separation factors were ranged from 27.84 to 52.60 at 25 °C. Furthermore, acid dialysis coefficient (3.28 times) and separation factor (2.84 times) were much greater than commercial membrane DF-120 (UH and S = 0.009 m/h and 18.5), respectively. Moreover, Q-DAN-4 membrane was selected to investigate the effects of multivalent metal ions on diffusion dialysis. The results showed that the presence of different metal salts in hydrochloric acid solution effect the membrane diffusivity and selectivity in diffusion dialysis process due to complexation of metal ions and acid.

An optimized process for treating sodium acetate waste residue: Coupling of diffusion dialysis or electrodialysis with bipolar membrane electrodialysis

The sodium acetate waste residue produced by insecticide factories contains mostly CH3COONa (∼76.6wt%) and other organic impurities, and had been treated by bipolar membrane electrodialysis (BMED) to generate CH3COOH and NaOH. Nevertheless, the energy consumption was high (22.3kWh/kg for CH3COOH and 29.7kWh/kg for NaOH) and the purity of products was insufficient, as the total organic carbon (TOC) was 1.61g/L and 0.16g/L in acid and base compartments respectively. Accordingly, the BMED was coupled with diffusion dialysis (DD) or electrodialysis (ED) here to obtain an optimized process. The DD or ED was used to purify the waste residue, which had the advantage of low energy consumption or high capacity. Then the purified solution was taken for BMED to produce CH3COOH and NaOH.The coupled process showed that the product purities were improved, and the apparent energy consumption (Eapp) was reduced. Coupling of BMED with DD process could have the output of 0.33mol/L CH3COOH and 0.35mol/L NaOH, current efficiency of 85.5% for CH3COOH and 93.7% for NaOH. The TOC values were 0.52g/L and 0.04g/L in acid and base compartments respectively, and the Eapp for BMED process was reduced to 11.7kWh/kg CH3COOH and 16.0kWh/kg NaOH. Meanwhile, the BMED process after coupling with ED had Eapp of 7.4kWh/kg CH3COOH and 10.4kWh/kg NaOH, and could yield products with TOC values of 0.13g/L and 0.01g/L in acid and base compartments respectively. In summary, the optimized DD-BMED or ED-BMED process for treating sodium acetate waste residue has significant advantages as compared with direct BMED process.

Continuous dialysis of hydrochloric acid and sodium chloride mixture

ABSTRACTUsing a two-compartment counter-current dialyzer with single passes, the simultaneous transport of hydrochloric acid and sodium chloride through an anion-exchange membrane Neosepta-AFN was studied at steady state. The diffusion dialysis process was quantified by four membrane mass transfer coefficients, which were correlated with the hydrochloric acid and sodium chloride concentrations in the feed. These characteristics were calculated from the experimental data on dialysis using a two-step procedure combining the numerical integration of the basic differential equations and a multivariable optimization. The second step of this procedure ensured the best agreement between the experimental and calculated data.