Recovery Of Hydrochloric Acid Research Articles

(Invited) Engendering Non-Noble Metal Catalysts for Electrolyzers: From Fundamentals to Devices

In memory of Prof. Sri Narayanan, this presentation will showcase the electrocatalysis of hydrogen evolution reaction (HER) and oxygen reduction in the context of oxygen depolarization cathode (ODC) for electrolyzer applications. Fundamentals of HER/HOR in alkaline pH will be presented in the context of various theories proposed to rationalize pH, cations, and structure effects. It will be shown that none of them can effectively explain all observations. In this presentation, four schools of thought for HER/HOR will be discussed, focusing on the strengths and shortcomings of each hypothesis and highlighting the magnitude of electrochemical interface structure in hydrogen electrocatalysis. Translation of these fundamental concepts into a durable electrocatalyst will be presented as a functionalized mono-metallic Ni catalyst concept. Durability results will be presented from both steady-state operation and uncontrolled shutdown conditions. These will be presented in conjunction with anion exchange membranes such as VersogenÒ, OrionÒ. Another cathodic process in the context of electrolysis is the oxygen-depolarized cathode, typically paired with anodic processes, such as chlorine generation. ODC cathode using coordinated Fe-N-C catalysts will be presented in the context of hydrochloric acid recovery, where activity and durability in the context of both fundamentals of oxygen reduction reaction mechanism and effects of uncontrolled shutdown will be presented.

Kinetics of silica-assisted pyro-hydrolysis of CaCl2 waste for the recovery of hydrochloric acid (HCl): Effect of interaction between CaCl2 and SiO2

Pyro-hydrolysis of CaCl2 waste for HCl acid regeneration is a circular process enabling the sustainable development of the critical energy mineral extraction industry. However, the lack of detailed kinetic information has posed challenges in implementing this technology. An acidic additive such as silica (i.e., SiO2) is essential to make this reaction thermodynamically available, yet its reaction kinetics are still unknown. This study aims to reveal the detailed reaction kinetics of the SiO2-assisted pyro-hydrolysis of CaCl2 under two typical industrial settings for the feeding of reactants, physical mixing of powders and spray feeding where CaCl2 solution is expected to initially undertake drying and subsequently deposit onto the solid silica powders for a close contact. The isothermal experiment results revealed that the HCl release rate is strongly temperature-dependent. Comparatively, the CaCl2-deposited silica demonstrated a significantly faster release of HCl than the physically mixed sample, achieving 92% HCl release within 30 min at 800 °C. SEM analysis confirmed a closer inter-particle contact for the CaCl2-deposited sample, which is responsive to the accelerated HCl release. In addition, the experimental results were successfully fitted by a variable activation energy model which discovered a steady increase of the activation energy with the progression of the HCl release for both feedstock modes. This is primarily due to the continuous change on the formation of intermediates. The model also confirmed a lower activation energy for the CaCl2-deposited sample than its physically mixed counterpart at any given conversion extent of CaCl2. In contrast, for the physically mixed sample, the loose inter-particle contact led to the formation of a stable intermediate, Ca(OH)Cl, which can readily reverse to CaCl2, thereby slowing down the overall HCl release rate.

A novel ion exchange-electrodialysis hybrid system to treat rare-earth oxalic precipitation mother liquid: Contamination reduction, efficient Y3+ recovery, and acid separation

A novel ion exchange process combined with selective electrodialysis (SED) process has been demonstrated to not only efficiently recover low concentration rare-earth elements (REEs) and separate hydrochloric acid, but also significantly reduce membrane fouling. Two resins with different functional groups were selected for pretreatment and recovery of Y3+ from Y rare-earth oxalic precipitation (Y REOP) mother liquor. CH-93 resin showed a Y recovery rate of over 94 %, and the Y recovery efficiency remained above 90 % after 5 cycles. The mother liquor treated with resin (R-T) and the untreated mother liquor (W-R-T) were subjected to acid separation via SED, and membrane fouling was systematically evaluated. Compared with W-R-T group, the hydrochloric acid recovery efficiency of R-T group increased by 21.01 % (12 V), and the unit energy consumption decreased by 54.30 % (12 V). The results of 3D fluorescence excitation-emission matrix (3D-EEM) and fluorescent region integration (FRI) showed the dissolved organic matter (DOM) on AEM and CEM in R-T group both decreased by >45 %. The AEM of W-R-T group showed the highest fluorescence intensity ratio in V region (36 %), indicating humic acid-like substances were the main cause of AEM fouling. Generally, this study provides a new approach for the resource utilization of REOP mother liquor.

Silica-assisted pyro-hydrolysis of CaCl2 waste for the recovery of hydrochloric acid (HCl): Reaction pathways with the evolution of Ca(OH)Cl intermediate by experimental investigation and DFT modelling

The chlorine evolution mechanism remains unclear during the thermal treatment of CaCl2/Ca(OH)Cl-containing solid waste. In this paper, we have conducted both experimental investigation and density functional theory (DFT) calculation to elucidate the mechanism of pyro-hydrolysis of CaCl2 with and without SiO2 in the temperature ranges of 400–900 °C. It was determined that pyro-hydrolysis of CaCl2 alone generated a maximum of 12% HCl by decomposition into Ca(OH)Cl, which is a stable intermediate that can be reverted to CaCl2 at 800 °C. Upon the addition of SiO2 at an equimolar ratio to CaCl2, the HCl release extent was accelerated to 50% at 900 °C. Both experiments and DFT calculations prove that the added SiO2 can promote the dissociation of water molecules which provides hydroxyl ions that enable the conversion of CaCl2 into Ca(OH)Cl at low temperatures. The resulting Ca(OH)Cl can also quickly react with SiO2 to form Cl-bearing silicates such as Ca2SiO3Cl2 and Ca3SiO4Cl2 with weakened CaCl bond that are relatively easy to cleave into Cl-free CaSiO3 and HCl(g) from 800 °C.

Recovery of Hydrochloric Acid from Industrial Wastewater by Diffusion Dialysis Using a Spiral-Wound Module.

In the present study, the possibility of using a spiral-wound diffusion dialysis module was studied for the separation of hydrochloric acid and Zn2+, Ni2+, Cr3+, and Fe2+ salts. Diffusion dialysis recovered 68% of free HCl from the spent pickling solution contaminated with heavy-metal-ion salts. A higher volumetric flowrate of the stripping medium recovered a more significant portion of free acid, namely, 77%. Transition metals (Fe, Ni, Cr) apart from Zn were rejected by >85%. Low retention of Zn (35%) relates to the diffusion of negatively charged chloro complexes through the anion-exchange membrane. The mechanical and transport properties of dialysis FAD-PET membrane under accelerated degradation conditions was investigated. Long-term tests coupled with the economic study have verified that diffusion dialysis is a suitable method for the treatment of spent acids, the salts of which are well soluble in water. Calculations predict significant annual OPEX savings, approximately up to 58%, favouring diffusion dialysis for implementation into wastewater management.

Clathrate-based material recovery of hydrochloric acid (HCL) from spent acids

The increasingly strict rules concerning acid discharging and metals into the environment, and the growing demand on recycling via materials recovering with appropriate treatments have focused the attention of research communities to develop new techniques of acids recovery and metals from the waste of industries. Different technologies have been utilized to recover spent acids that include electrochemistry, precipitation, adsorption, membrane filtration, and ion exchange. Although the advantages of these methods, the operational, costs are still high and may make the resulting pollution caused by adding chemical materials. This work conducts hydrate formation experiments on the guest liquid for different samples to extract Hydrochloric acid (HCL). Each sample consisting of distilled water, cyclopentane, and spent acids. The volume ratios of cyclopentane to water were (6:1, 4: 1, 3:1, and 2:1) with five initial amounts (12.5%, 10%, 7.5%, 5%, 2.5%) of Hydrochloric acid (HCL).). It was found that the hydrate method was effective in recovering spent acids from Hydrochloric acid with a maximum efficacy of 95.4% at the proportion of cyclopentane/water (6:1) and the amount of Hydrochloric acid 12.5%. Hydrate formation was also inspected by increasing the time of hydrate formation by (60, 80, 100, and 120) minutes with the decreased water volume proportion of cyclopentane by (6: 1, 4: 1, 3: 1, 2: 1) respectively. It can be concluded that the increase in volume proportion leads increasing in removal efficacy while reducing the yield percentage, and enriched factor.

Internally cross-linked poly (2,6-dimethyl-1,4-phenylene ether) based anion exchange membrane for recovery of different acids by diffusion dialysis

Acid recovery from acidic waste is a critical issue to be focused on nowadays. Chemical approaches for recovery are not commercially viable and energy intensive to save the environment. Here, we report internally cross-linked poly (2,6-dimethyl-1,4-phenylene ether) (PPE) based anion exchange membranes (AEMs) for acid recovery by diffusion dialysis, prepared via quick grafting of N-methyl-4-piperidone using ultrasonication. The prepared AEMs are assessed for their physicochemical parameters and depicted water uptake (WU) and ion-exchange capacity (IEC) in the range 22.00%–31.00% and 0.64 meq/g–2.18 meq/g respectively for Cl−1, NO3− and SO42− ions. AEMs were investigated for recovery of hydrochloric acid (HCl), nitric acid (HNO3) and sulphuric acid (H2SO4) from simulated effluent based on their proton diffusion coefficient (UH+), separation factor (S) and recovery efficiency (Ƞ). These membranes illustrated the proton diffusion coefficient as high as 0.065 m h−1 and enhanced separation factor values up to 132 at 27 °C. Recovery performance for different acids is corroborated based on unique self-organized membrane structure, studied using AFM phase imaging and cumulative influence of bulk diffusion coefficient, ion-exchange capacity, and hydration radii of Cl−1, NO3− and SO42− ions. The acid recovery efficiency illustrated the trend HCl > HNO3 > H2SO4. The hydrate (–OH) functionality with a non-overlapping set of lone pairs on oxygen enhances the proton mobility via Grotthuss mechanism inside the membrane matrix and provides a cradle-like pathway for high proton mobility. The results are pronounced for fabricated membranes compared to commercially available standards for acid recovery via diffusion dialysis.

Crosslinked terpolymer anion exchange membranes for selective ion separation and acid recovery

Anion exchange membrane (AEM) is useful for the removal of salts via electrodialysis (ED) process. AEM is also used for the recovery of acid from an aqueous feed containing acid and metal ion through diffusion dialysis (DD). However, for the selective separation of monovalent and divalent ions, special type of AEM is required. Herein, we report the preparation of poly(acrylonitrile-co-n-butyl acrylate-co-polydimethylamino ethyl methacrylate) (PAN-co-PnBA-co-PDMA) terpolymer-based crosslinked AEMs for the separation of monovalent ion from bivalent ion via ED process and recovery of hydrochloric acid (HCl) from aqueous feed of HCl and FeCl2 through DD. The slowing down the movement of bivalent anion under electrical potential, and hindering the diffusion of metal ion are the key factors for the optimization of the membranes. The tuning the polarity of the microenvironment of quaternized nitrogen (from DMA moieties) of the terpolymer by changing the length of alkyl chain gave membranes with different monovalent to bivalent anions selectivity, and separation factor for acid recovery. AEM-TP-C1, AEM-TP-C4 and AEM-TP-C10 membranes were prepared by quaternizing the DMA moieties (C1 to C10 denote length of alkyl) of the terpolymer followed by crosslinking. The AEM-TP-C10 membrane exhibited best selectivity (4.76) during desalination of sodium chloride and sodium sulfate mixture (0.01 M, 0.01 M) via ED process. Best performance in terms of acid recovery was obtained with AEM-TP-C4 membrane with dialysis coefficient of 0.031 m/h and separation factor of 38 during acid recovery. The length of alkyl and the hydrophobicity of the environment of the quaternized nitrogen is a governing factor for deciding the performance of the AEMs. This work provides an insight to design crosslinked AEMs for selective separation and acid recovery. The tertiary amine presence in the terpolymer may be quaternized with varieties of halide compounds to further correlate the structure of quaternized amine and property of the AEMs.

Recovery of hydrochloric acid using positively-charged nanofiltration membrane with selective acid permeability and acid resistance

An acid-recovering nanofiltration (NF) membrane with both acid resistance and selective acid permeability was fabricated via a water-based coating process for the recovery of hydrochloric acid. To achieve this, a thermally cross-linked branched-polyethyleneimine (b-PEI) layer was introduced to a loose polyethersulfone NF membrane by dip-coating of b-PEI and an epoxy linker and heat treatment in a sealed oven with a high-humidity atmosphere. The resulting membrane displayed a positive surface charge with a zeta potential, and exhibited a rejection performance order of MgCl2> MgSO4> NaCl > Na2SO4 characteristic of positive-charge-separation membranes. Mg rejection and Cl permeation experiments showed that the selective permeation of hydrochloric acid was achieved with Mg rejection above 95% and Cl permeation above 70%, and this allowed the acid to be recovered by obtaining permeate at the same pH as the feed. Moreover, the NF membrane maintained selective separation performance and flow rate for a month.

Experimental and theoretical study on the behaviour of a pickling solution: The role of ferrous ions

Abstract The existence of ferrous ions plays an important role in the performance of pickling liquor as well as the recovery of hydrochloric acid from waste pickling liquor. The promotion mechanism and the interaction between ferrous ions and hydrogen chloride molecules have remained largely unsolved. In this research, the fundamental aspects of a simulated hydrochloric acid pickling solution with different concentrations of ferrous ions were experimentally and theoretically studied. The experimental results showed that the existence of ferrous ions in the pickling liquor effectively inhibited the volatilisation of hydrogen chloride from solution and that the inhibition of volatilisation enhanced with an increase in concentration of ferrous ions. To understand the interaction between ferrous ions and hydrogen chloride molecules, the structure and thermodynamic properties of possible hydration structures were obtained by using molecular simulation. The results showed that a new type of cluster, hydrogen chloride-ferrous ion-water, was formed in the presence of ferrous ions, which made the hydrogen chloride molecules in the pickling liquor more stable compared to the same condition without ferrous ions. The existence of ferrous ions in pickling liquor benefits the pickling process from an economic and environmental aspect.

Experimental investigation and modeling of diffusion dialysis for HCl recovery from waste pickling solution

Hydrochloric acid recovery from pickling solutions was studied by employing a batch diffusion dialysis (DD) laboratory test-rig equipped with Fumasep membranes. The effect of main operating parameters such as HCl concentration (0.1–3 M) and the presence of Fe2+ (up to 150 g/l) was investigated to simulate the system operation with real industrial streams. The variation of HCl, Fe2+ and water flux was identified. When only HCl is present, a recovery efficiency of 100% was reached. In the presence of FeCl2, higher acid recovery efficiencies, up to 150%, were observed due to the so-called “salt effect”, which promotes the passage of acid even against its concentration gradient. A 7% leakage of FeCl2 was detected in the most severe conditions. An original analysis on water flux in DD operation has indicated that osmotic flux prevails at low HCl concentrations, while a dominant “drag flux” in the opposite direction is observed for higher HCl concentrations.A comprehensive mathematical model was developed and validated with experimental data. The model has a time and space distributed-parameters structure allowing to effectively simulate steady-state and transient batch operations, thus providing an operative tool for the design and optimisation of DD units.

Green synthesis of benzonitrile using ionic liquid with multiple roles as the recycling agent.

Preparation of benzonitrile from benzaldehyde and hydroxylamine hydrochloride is one of the most advantageous approaches. Nevertheless, it suffers from various constraints such as longer reaction time, corrosion and recovery of hydrochloric acid, the use of metal salt catalysts and their separation. For these reasons, a novel green benzonitrile synthetic route was proposed with ionic liquid as the recycling agent in this study. The results indicated that hydroxylamine 1-sulfobutyl pyridine hydrosulfate salt ((NH2OH)2·[HSO3-b-Py]·HSO4) was an expert alternative to hydroxylamine hydrochloride. Meanwhile, the ionic liquid [HSO3-b-Py]·HSO4 exhibited the multiple roles of co-solvent, catalysis and phase separation, thus the use of metal salt catalyst was eliminated, and no additional catalyst was needed. Hence, the separation process was greatly simplified. When the molar ratio of benzaldehyde to (NH2OH)2·[HSO3-b-Py]·HSO4 was 1 : 1.5, the volume ratio of paraxylene to [HSO3-b-Py]·HSO4 was 2 : 1, the benzaldehyde conversion and benzonitrile yield were both 100% at 120 °C in 2 h. Even better, the ionic liquid could be recovered easily by phase separation, and recycled directly after reaction. Additionally, this novel route is applicable to the green synthesis of a variety of aromatic, heteroaromatic and aliphatic nitriles with excellent yields.

Preparation of Iron Oxide Red with High Titanium Slag Recovery Dust

High titanium slag production will generate a lot of dust containing some ferrotitanium resources. To make full use of the resources, the high titanium slag recovery dust is used to prepare the iron oxide red in the experimental study. The high titanium slag dust is treated by hydrochloric acid leaching heated under constant-pressure, and then hydrolytic acid leaching filtrate is heated under constant pressure to prepare iron oxide red and recover hydrochloric acid. The impacts of hcl concentration, acid leaching temperature and time, and hydrolysis concentration time on the productivity of iron oxide red are studied, and the analytical characterization is carried out for the product with XRF, XRD and IR. The results show that: 90% iron oxide red containing Fe2O3 can be obtained under the conditions i.e. HCl concentration of 6mol/L, reaction temperature of 90℃, acid leaching time of 5h, and hydrolysis concentration time of 1.5h, and the hydrochloric acid recovery rate exceeds 80%.

Recovery of hydrochloric acid from galvanizing industrial effluents

ABSTRACTThe recovery of hydrochloric acid and its separation from iron, zinc and minor elements, in the galvanizing pickling baths, were studied by solvent extraction (SX) and distillation and by distillation and crystallization. Several extractants were tested, the tri-isooctyl amine, Alamine 308, the primary aliphatic amine Primene JM-T and the mixture of four trialkylphosphine oxides, Cyanex 923. Only Cyanex 923 enabled distillation. The results indicated the feasibility of the processes to treat a real effluent using Cyanex 923 and to obtain high HCl concentrations in the distillate (256–330 g/L).

Engendering anion immunity in oxygen consuming cathodes based on Fe-Nx electrocatalysts: Spectroscopic and electrochemical advanced characterizations

Oxygen reduction reaction (ORR) is the key reaction utilized for several potentially promising technologies such as in energy conversion (fuel-cells) or as oxygen depolarized cathodes (ODC) in anodic evolution of bulk chemicals such as chlorine. In the latter case elimination of one volt out of a theoretical maximum of 1.34V (in case of hydrogen evolution electrode) provides very significant energy savings. Here we report iron based Fe-Nx catalyst with promising activity compared to state of the art noble metal catalysts (RhxSy) for hydrochloric acid recovery systems. A combined electrochemical and synchrotron-based spectroscopic approach is used to probe the structural and elec tronic properties of the active centers. The surface sensitive delta-mu (Δm) analysis of the near edge X-ray absorption fine structure (NEXAFS), supported by first-principles calculations, reveals the immunity of the Fe-Nx-Cy active centers to chloride poisoning. Initial stability studies show that even after a harsh corrosive treatment, the catalyst ORR activity remains comparable to the current state of the art precious based material. Our study opens up promising avenues for developing affordable and robust oxygen consuming electrodes.

Selective Yield of the Distorted Fe-N4-Cx Active Site with Immunity for Anion Poisoning for Oxygen Depolarized Cathode Applications

Engendering anion immunity has tremendous implications in electrocatalysis in aqueous acidic electrolytes. This is specially exemplified by oxygen reduction reaction and its connotations with application for energy conversion (phosphoric acid), oxygen depolarized cathodes (ODC) (HCl recovery) and metal air batteries. For ODC cathodes used for chlorine generation, it is noteworthy that an energy saving of ~700 kWh per ton of chlorine gas (up to 30%) can be realized. Need for immunity for anion poisoning is particularly manifest as a result of dependence on costly and rare platinum group metal (PGM) catalysts considering their vulnerability to impurities such as halides. In this abstract we will demonstrate a new class of pyrolyzed M-Nx-C (M=Fe and/or Co) catalysts, which are immune to anion poisoning and are the leading non-platinum group metal (non-PGM) catalysts for ORR owing to their high activity and stability. Unique aspect of these emanates from the use of metal organic framework (MOF) precursors such as Zn based zeolitic imidizolate framework (ZIF, a subclass of metal organic framework) as a sacrificial template1. Herein, we report a facile, low cost and scalable synthetic process of ZIF-8 using a reactive ball-milling approach. A highly active Fe-based ORR catalyst using the as-synthesized ZIF-8 as precursor is demonstrated in hydrochloric acid electrolysers. The ZIF-8 derived catalyst shows a prominent ORR activity with an on-set potential of 0.92 V and a half wave potential of 0.78 V in 0.1 M HClO4 electrolyte in the rotating disk electrode (RDE). The high ORR activity can be partly attributed to the ultra-high surface area as it is closely related to the high density of active sites and the intrinsically improved mass transport properties of the MOF. In addition, combined x-ray adsorption spectroscopy (XAS) and Mössbauer spectroscopy reveal that this catalyst contains high concentration of the distorted Fe-N4-Cx moiety featured with a large Fe out-of-plane displacement and elongated Fe-N bond distance, which is shown to exhibit high intrinsic activity toward ORR owing to the moderate Fe-O binding energy and high Fe2+/3+ redox transition potential.2 Remarkably, the highly active ORR catalyst sustains its activity even in presence of high concentrations of Cl- (Fig. 1), thereby opening up promising avenues for the application of Fe-Nx-C catalysts such as ODCs in hydrochloric acid recovery electrolyzers (Fig. 2). Acknowledgement The authors gratefully acknowledge financial support from the Massachusetts Clean Energy Council via their catalyst award (2013). The authors also gratefully acknowledge the financial support from Denora North America (2014). Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Use of Beamline 2-2 at SSRL was partially supported by the National Synchrotron Light Source II, Brookhaven National Laboratory, under U.S. Department of Energy Contract No. DE-SC0012704. Use of the beamline 9-BM in Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. MRCAT operations are supported by the Department of Energy and the MRCAT member institutions. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

Preparation of diffusion dialysis membrane for acid recovery via a phase-inversion method

Herein, the preparation of anion exchange membrane (AEM) from brominated poly(2,6-dimethyl 1,6-phenylene oxide) BPPO and dimethylaniline (DMA) by phase-inversion process is reported. Anion exchange membranes (AEMs) are prepared by varying the DMA contents. Prepared AEMs show high thermal stability, water uptake (WR) around 202% to 226%, dimensional change ratios of 1.5% to 2.6% and ion exchange capacities (IECs) of 0.34 mmol/g to 0.82 mmol/g with contact angle of 59.18° to 65.15°. These membranes are porous in nature as confirmed by SEM observation. The porous property of membranes are important as it could reduce the resistance of transportation of ions across the membranes. They have been used in diffusion dialysis (DD) process for recovery of hydrochloric acid (HCl) from the mixture of HCl and ferrous chloride (FeCl2). Presence of ¯N+(CH3)2C6H5Br &$175;as a functional group in membrane matrix facilitates its applications in DD process. The dialysis coefficients of hydrochloric acid (UH) of the membranes are in range of 0.0016 m/h to 0.14 m/h and the separation factors (S) are in range of 2.09 to 7.32 in the HCl/FeCl2 system at room temperature. The porous membrane structure and presence of amine functional group are responsible for the mechanism of diffusion dialysis (DD).

Recovery of hydrochloric acid and glycerol from aqueous solutions in chloralkali and chemical process industries by membrane distillation technique

Membrane distillation (MD) is a rapidly advancing process for separation of azeotropic and close boiling liquid mixtures besides dewatering of high boiling solvents. Recovery of hydrochloric acid (HCl) from a chloralkali industrial effluent and dehydration of glycerol/water mixture was performed using MD technique. HCl was recovered using chemically resistant polytetrafluoroethylene (PTFE) membrane of 0.22μm pore size and 78% porosity. The effluent feed contained 32.8wt.% of aqueous HCl with color forming Fe compounds and heavy hydrocarbon (C9–C14) impurities that gave an oily appearance. Permeate obtained was colorless aqueous HCl (33wt.%) at a high flux with negligible impurity levels. An increase in permeate pressure from 5 to 15mmHg resulted in a gradual reduction in flux from a high value of 8.57kg/m2/h to a moderate 1.02kg/m2/h at ambient temperature of 28°C. Effect of feed composition in terms of acid and inorganic salt contents besides feed temperature (25–60°C) on flux and separation efficiency was demonstrated at a constant downstream vacuum of 8–10mmHg. Dehydration of glycerol was performed using novel indigenously synthesized ultraporous hydrophobic polystyrene (PS) membrane of 0.72μm pore size. Permeate was found to contain pure water due to the low vapor pressure and larger molecular size of glycerol which cannot penetrate PS as it does not get wetted by water. This indicated a selectivity of infinity (∞) which is associated with a reasonable water flux in the range 0.56–0.02kg/m2/h at a vacuum of 5mmHg for feed glycerol concentration varying from 10 to 90wt.%. PS membrane was characterized by SEM, FTIR, XRD and TGA to assess surface and cross-sectional morphologies, structural elucidation, crystallinity and thermal stability of the membrane, respectively. A detailed economic estimation of HCl recovery for a feed effluent capacity of 2m3/h is presented. The study showed that commercial grade HCl and glycerol could be recovered from aqueous streams at a reasonable price by employing MD technique.

Recovery of hydrochloric acid from simulated chemosynthesis aluminum foils wastewater: An integration of diffusion dialysis and conventional electrodialysis

Abstract Diffusion dialysis (DD) and conventional electrodialysis (CED) were integrated to recover hydrochloric acid from simulated chemosynthesis aluminum foil wastewater. Effects of dialysate flow rate, DD pre-running duration ( t 1 ), CED current were investigated. Results showed that the integration of DD and CED was a feasible and effective approach to recover the hydrochloric acid. The dialysate flow rate and CED current are adjustable to achieve a compatibility and operational uniformity between DD and CED. When the dialysate flow rate was 0.60 L/(h m 2 ), t 1 was 10 min, and CED current was 2 A, the average acid recovery ratio and average aluminum leakage ratio were 74.9% and 12.2% respectively, while the energy consumption was only 0.41 kw h. The results confirm that such integration process is not only a cost-effective process compared with an individual DD process, but also an environment friendly process with little water consumption. Especially, due to the concentrating by CED, the recovered acid can be reused in the productive cycle directly.

Recovery of hydrochloric acid from simulated chemosynthesis aluminum foil wastewater by spiral wound diffusion dialysis (SWDD) membrane module

Recovering hydrochloric acid from simulated chemosynthesis aluminum foil wastewater by spiral wound diffusion dialysis (SWDD) membrane module was studied. Effects of flow rate intensity, diffusate flow rate intensity, dialysate flow rate intensity, and initial feed composition (HCl and AlCl 3 concentration) on diffusion performance were investigated. The results showed that the acid recovery ratio and aluminum leakage ratio decreased with an increase in the flow rate intensity. And for a diffusion dialysis process, an appropriate flow rate intensity ratio (diffusate:dialysate) was found to be approximately 1.0. The HCl concentration in the feed was observed to have little influence on the diffusion performance of SWDD membrane module, while the acid recovery ratio and aluminum leakage ratio increased as the AlCl 3 concentration in the feed increased. More than 95% HCl were recovered from the simulated wastewater which contained 2.12 mol/L HCl and 0.8 mol/L AlCl 3 at the flow rate intensity of 0.48 L/(m 2 h). When compared with plate-and-frame diffusion dialysis (PFDD) membrane module, the SWDD membrane module has a higher acid recovery ratio, lower metal leakage ratio, higher loading density, and similar time to reach the equilibrium. Preliminary economic evaluation revealed that an investment in this process could be recovered within 16.5 months.