Electrochemical Regeneration Process Research Articles

Techno-economic analysis of bromine mediated propane oxidative dehydrogenation to produce propylene

The production of propylene from propane is becoming increasingly important. Catalytic propane dehydrogenation (PDH) is the major on-purpose propylene production process today. The conventional PDH process has a relatively high energy consumption (6.1–9.4 kWh/kg C3H6) which results in high direct CO2 emissions and modest propylene yield (0.8–0.9 kg C3H6/kg C3H8). A bromine-mediated propane oxidative dehydrogenation process (Br-ODH) is evaluated in this techno-economic study which can potentially improve both the process energy efficiency and product yield. To investigate the Br-ODH process feasibility, a heat integrated process model was designed using Aspen Plus® V12 for a 450 kta propylene facility using reaction data from the literature. The partial oxidation of propane under bromine limited conditions selectively produces a propylbromide intermediate which can be readily separated from propane. Propylbromide undergoes dehydrobromination under relatively mild conditions to produce the propylene product in a second step. Bromine is regenerated by conversion of the hydrogen bromide byproduct either thermochemically or electrochemically. Due to the current interest in use of renewable electricity in chemical processes, the electrochemical regeneration process was evaluated in this study. Based on the model, the Br-ODH process can achieve approximately 10% higher propylene yield with 37% lower utilities than conventional PDH. However, the use of high-cost electrolyzers resulted in the capital investment increasing by approximately 11%. Capital cost was also increased due to the requirements of high alloy materials of construction for the potentially corrosive halogen containing equipment. The sensitivity analysis showed that the production cost was most sensitive to the propane price. For the electrolyzer-based regeneration process the capital cost was found to be key parameter that might limit competition with conventional PDH; however, the development of a commercial thermochemical HBr oxidation process analogous to the Deacon process for chlorine would likely bring significant cost savings.

Introducing Nanoscale Electrochemistry in Small-Molecule Detection for Tackling Existing Limitations of Affinity-Based Label-Free Biosensing Applications.

Electrochemical sensing techniques for small molecules have progressed in many applications, including disease diagnosis and prevention as well as monitoring of health conditions. However, affinity-based detection for low-abundance small molecules is still challenging due to the imbalance in target-to-receptor size ratio as well as the lack of a highly sensitive signal transducing method. Herein, we introduced nanoscale electrochemistry in affinity-based small molecule detection by measuring the change of quantum electrochemical properties with a nanoscale artificial receptor upon binding. We prepared a nanoscale molecularly imprinted composite polymer (MICP) for cortisol by electrochemically copolymerizing β-cyclodextrin and redox-active methylene blue to offer a high target-to-receptor size ratio, thus realizing "bind-and-read" detection of cortisol as a representative target small molecule, along with extremely high sensitivity. Using the quantum conductance measurement, the present MICP-based sensor can detect cortisol from 1.00 × 10-12 to 1.00 × 10-6 M with a detection limit of 3.93 × 10-13 M (S/N = 3), which is much lower than those obtained with other electrochemical methods. Moreover, the present MICP-based cortisol sensor exhibited reversible cortisol sensing capability through a simple electrochemical regeneration process without cumbersome steps of washing and solution change, which enables "continuous detection". In situ detection of cortisol in human saliva following circadian rhythm was carried out with the present MICP-based cortisol sensor, and the results were validated with the LC-MS/MS method. Consequently, this present cortisol sensor based on nanoscale MICP and quantum electrochemistry overcomes the limitations of affinity-based biosensors, opening up new possibilities for sensor applications in point-of-care and wearable healthcare devices.

Sodium-alginate-laden MXene and MOF systems and their composite hydrogel beads for batch and fixed-bed adsorption of naproxen with electrochemical regeneration

Sodium alginate (SA)-laden two-dimensional (2D) Ti3C2Tx MXene (MX) and MIL-101(Fe) (a type of metal–organic framework (MOF)) composites were prepared and used for the removal of naproxen (NPX), following the adsorption and electrochemical regeneration processes. The fixed-bed adsorption column studies were also conducted to study the process of removal of NPX by hydrogels. The number of interactions via which the MX-embedded SA (MX@SA) could adsorb NPX was higher than the number of pathways associated with NPX adsorption on the MIL-101(Fe)-embedded SA (MIL-101(Fe)@SA), and the MX and MIL-101(Fe) composite embedded SA (MX/MIL-101(Fe)@SA). The optimum parameters for the electrochemical regeneration process were determined: charge passed and current density values were 169.3 C g−1 and 10 mA cm−2, respectively, for MX@SA, and the charge passed and current density values were 16.7 C g−1 and 5 mA cm−2, respectively, for both MIL-101(Fe)@SA and MX/MIL-101(Fe)@SA. These parameters enabled excellent regeneration, consistent over multiple adsorption and electrochemical regeneration cycles. The mechanism for the regeneration of the materials was proposed that the regeneration of MX@SA and MIL-101(Fe)@SA involved the indirect electrooxidation process in the presence of OH radicals, and the regeneration of MX/MIL-101(Fe)@SA involved the indirect oxidation process in the presence of active chlorine species.

Adsorption and electrochemical regeneration of 2D magnetic MXene nanosheets loaded with tetracycline

A delaminated Ti3C2Tx MXene nanosheet–Fe3O4 nanoparticle composite (DLMX-Mag) was synthesized using a facile batch fabrication method and applied to an adsorption and electrochemical regeneration process for the removal of tetracycline (TC) from aqueous solutions. The addition of magnetite to the delaminated Ti3C2Tx MXene nanosheets produced a composite with magnetic properties, a larger surface area, and more functional groups attached to its surface. These characteristics are beneficial for magnetic solid–liquid separation and act to increase the adsorption capacity of the material. The experimental data of TC adsorption on DLMX-Mag were best described by the Elovich kinetic model, and the Freundlich isotherm model. Physical and chemical characterization revealed that the adsorption occurred via a surface complexation mechanism. Optimization of the electrochemical parameters resulted in 100% regeneration being achieved for DLMX-Mag. After the fifth cycle of electrochemical treatment, the physicochemical analysis results indicated that the crystallinity of the materials was slightly reduced; however, the addition of new functional groups had the effect of ensuring that the adsorptive capacity was retained. These findings demonstrate that the synthesized magnetic nano-adsorbents should be useful for industrial wastewater treatment.

Hybrid process of adsorption and electrochemically based green regeneration of bentonite clay for ofloxacin and ciprofloxacin removal.

Removal of emerging contaminants, such as antibiotics, from wastewater by adsorption is a simple, low-cost, and high-performance process; however, regeneration and reuse of the exhausted adsorbent are necessary to make the process economically viable. This study aimed to investigate the possibility of electrochemical-based regeneration of clay-type materials. For this, the calcined Verde-lodo (CVL) clay was saturated with the antibiotics ofloxacin (OFL) and ciprofloxacin (CIP) in one-component systems by an adsorption process and then subjected to photo-assisted electrochemical oxidation (0.45 A, 0.05 mol/L NaCl, UV-254 nm, and 60 min), which promotes both pollutant degradation and adsorbent regeneration. The external surface of the CVL clay was investigated by X-ray photoelectron spectroscopy before and after the adsorption process. The influence of regeneration time was evaluated for the CVL clay/OFL and CVL clay/CIP systems, and the results demonstrate high regeneration efficiencies after 1 h of photo-assisted electrochemical oxidation. Clay stability during regeneration was investigated by four successive cycles in different aqueous matrices (ultrapure water, synthetic urine, and river water). The results indicated that the CVL clay is relatively stable under the photo-assisted electrochemical regeneration process. Furthermore, CVL clay was able to remove antibiotics even in the presence of natural interfering agents. The hybrid adsorption/oxidation process applied here demonstrated the electrochemical-based regeneration potential of CVL clay for the treatment of emerging contaminants, since it can be operated quickly (1h of treatment) and with lower consumption of energy (3.93 kWh kg-1) than the traditional method of thermal regeneration (10 kWh kg-1).

In Situ Electro-Synthesis and Resynthesis of Redox Actives in Aqueous Organic Redox Flow Batteries

Aqueous anthraquinone redox flow batteries (AARFBs) offer a safe and potentially inexpensive solution to the problem of storing massive amounts of electricity produced from intermittent renewables and are especially well-suited for large-scale stationary deployment.1,2 However, production cost of anthraquinone-based electrolytes and molecular decomposition are the two major challenges preventing them from being commercialized.3,4 We report electrochemical approaches to both these problems: anthraquinone electrosynthesis from lower-cost anthracene feedstock, and the electrochemically-induced reversal of decomposition.We demonstrate the electrochemical oxidation of an anthracene derivative to a redox-active anthraquinone at room temperature in a continuous flow cell without the use of hazardous oxidants or noble metal catalysts. The anthraquinone, generated in situ, was used as the active species in a flow battery electrolyte without further modification or purification.5,6 Utilizing 2,6-dihydroxy-anthraquinone (DHAQ) without further structural modification, we demonstrate that the regeneration of the original molecule after decomposition represents a viable route to achieve low-cost, long-lifetime AARFBs. We used in situ (online) NMR and EPR and complementary electrochemical analyses to show that the decomposition compounds 2,6-dihydroxy-anthrone (DHA) and its tautomer, 2,6-dihydroxy-anthranol (DHAL), can be recomposed to DHAQ electrochemically through two steps: oxidation of DHA(L)2− to the dimer (DHA)2 4− by one-electron transfer followed by oxidation of (DHA)2 4− to DHAQ2− by three-electron transfer per DHAQ molecule. This electrochemical regeneration process also rejuvenates the positive electrolyte – rebalancing the states of charge of both electrolytes without introducing extra ions.7

Covalent Immobilization of Dehydrogenases on Carbon Felt for Reusable Anodes with Effective Electrochemical Cofactor Regeneration.

This study presents the immobilization with aldehyde groups (glyoxyl carbon felt) of alcohol dehydrogenase (ADH) and formate dehydrogenase (FDH) on carbon-felt-based electrodes. The compatibility of the immobilization method with the electrochemical application was studied with the ADH bioelectrode. The electrochemical regeneration process of nicotinamide adenine dinucleotide in its oxidized form (NAD+ ), on a carbon felt surface, has been deeply studied with tests performed at different electrical potentials. By applying a potential of 0.4 V versus Ag/AgCl electrode, a good compromise between NAD+ regeneration and energy consumption was observed. The effectiveness of the regeneration of NAD+ was confirmed by electrochemical oxidation of ethanol catalyzed by ADH in the presence of NADH, which is the no active form of the cofactor for this reaction. Good reusability was observed by using ADH immobilized on glyoxyl functionalized carbon felt with a residual activity higher than 60 % after 3 batches.

Electrocatalytic oxidation of antidiabetic drug metformin adsorbed on intercalated MXene

Two-dimensional (2D) Ti3C2Tx transition metal carbide (MXene) nanosheets intercalated with sodium ions (SI–Ti3C2Tx MXene) were used in the adsorption and electrochemical regeneration process for removal of the antidiabetic drug metformin (MF) as a model emerging pollutant. After MF adsorption, SI–Ti3C2Tx MXene oxidized the MF on its surface through its electrocatalytic activity at very low current density and cell potential. For complete oxidation the optimum parameters were 0.525 C g−1, 0.005 mA cm−2, and pH 6 in absence of NaCl or 26.25 C g−1 and 0.5 mA cm−2 in the presence of 2.5 w/v% NaCl. The overall regeneration of SI–Ti3C2Tx is governed by a combined mechanism, i.e., desorption followed by degradation. The degradation mechanism, such as direct electron transfer or indirect oxidation, depends on the applied operating conditions. Thus, the investigation suggests that these 2D sheets are good nanoadsorbents as well as good electrocatalysts and proves their usefulness in practical water-treatment applications.

In situ electrochemical recomposition of decomposed redox-active species in aqueous organic flow batteries

Aqueous organic redox flow batteries offer a safe and potentially inexpensive solution to the problem of storing massive amounts of electricity produced from intermittent renewables. However, molecular decomposition represents a major barrier to commercialization-and although structural modifications can improve stability, it comes at the expense of synthetic cost and molecular weight. Now, utilizing 2,6-dihydroxy-anthraquinone (DHAQ) without further structural modification, we demonstrate that the regeneration of the original molecule after decomposition represents a viable route to achieve low-cost, long-lifetime aqueous organic redox flow batteries. We used in situ (online) NMR and electron paramagnetic resonance, and complementary electrochemical analyses to show that the decomposition compound 2,6-dihydroxy-anthrone (DHA) and its tautomer, 2,6-dihydroxy-anthranol (DHAL) can be recomposed to DHAQ electrochemically through two steps: oxidation of DHA(L)2- to the dimer (DHA)24- by one-electron transfer followed by oxidation of (DHA)24- to DHAQ2- by three-electron transfer per DHAQ molecule. This electrochemical regeneration process also rejuvenates the positive electrolyte-rebalancing the states of charge of both electrolytes without introducing extra ions.

Regenerative Electrocatalytic Redox Cycle of Copper Sulfide for Sustainable NH3 Production under Ambient Conditions

Electrochemical nitrogen reduction reaction (NRR) is a promising method for energy-efficient and low-emission NH3 production. Herein, we report electrochemical NH3 production using a copper sulfide-based electrocatalyst. A solid-state synthesis is employed to prepare the Cu9S5 catalyst for artificial N2 fixation in a neutral aqueous electrolyte. Despite an excellent NRR activity of 10.8 ± 0.4 μg/hcm2 at −0.5 VRHE, however, the catalyst itself is reductively degraded during the NRR. To achieve continuous electrochemical NH3 production, a regenerative electrochemical sulfur cycle is introduced that revives the Cu9S5 crystal structure and NRR activities. The electrochemical regeneration process reconstructing the metal–sulfur bond in between sequential NH3 production processes restores the NRR activity. Importantly, catalytic surfaces providing a labile sulfhydryl functional group attached to the N2-adsorption metal center are required to achieve efficient NRR activity under ambient conditions.

Adsorption of Reactive Black 5 Dye from Aqueous Solutions by Carbon Nanotubes and its Electrochemical Regeneration Process

: Removal of Reactive Black 5 (RB5) dye from aqueous solutions was investigated by adsorption onto Multi-walled Carbon Nanotubes (MWCNTs) and Single-walled Carbon Nanotubes (SWCNTs). A Taguchi orthogonal design including pH, initial RB5 concentration, contact time, and CNTs dose, was used in 16 experiments. The results showed that all four factors were statistically significant, and the optimum conditions for both adsorbents were as follows: pH of 3, adsorbent dose of 1000 mg/L, RB5 concentrations of 25 mg/L, and contact time of 60 min. An equilibrium study by Isotherm Fitting Tool (ISOFIT) software showed that Langmuir isotherm provided the best fit for RB5 adsorption by CNTs. The maximum predicted adsorption capacities for the dye were obtained as 231.84 and 829.20 mg/g by MWCNTs and SWCNTs, respectively. The results also indicated that the adsorption capacity of SWCNTs was about 1.21 folds higher than that of MWCNTs. Studies of electrochemical regeneration were conducted, and the results demonstrated that RB5-loaded MWCNTs and SWCNTs could be regenerated (86.5% and 77.3%, respectively) using the electrochemical process. Adsorbent regeneration was mostly due to the degradation of the dye by the attack of active species such as chlorate, H2O2, and, •OH, which were generated by the electrochemical oxidation process with Ti/RuO2-IrO2-TiO2 anodes. The results of Gas Chromatography-Mass Spectrometry (GC-MS) analysis showed that acetic acid, 3-chlorobenzenesulfonamide, and 1,2-benzenedicarboxylic acid were produced after adsorbent regeneration by the electrochemical process in the solution of regeneration. The adsorption and regeneration cycles showed that the electrochemical process with Ti/RuO2-IrO2-TiO2 and graphite is a good alternative method for the regeneration of CNTs and simultaneous degradation of the dye.

Adsorption and electrochemical regeneration of intercalated Ti3C2Tx MXene for the removal of ciprofloxacin from wastewater

Two-dimensional Ti 3 C 2 T x MXene nanosheets intercalated with sodium ions (SI-Ti 3 C 2 T x ) was synthesized by a facile batch fabrication method and applied for Ciprofloxacin (CPX) removal in the adsorption and electrochemical regeneration process. The successful synthesis and properties of the synthesized nanosheets were evaluated with X-ray diffraction (XRD), FE-scanning electron microscopy (SEM), FE-transmission electron spectroscopy, Zeta-potential analyses, and X-ray photoelectron spectroscopy. After intercalation, the surface terminations and the spacing between the layers of SI-Ti 3 C 2 T x MXene were increased which enhanced the adsorption capacity of nanosheets in terms of fast kinetics and higher removal rates. As a result, 10 mg L −1 CPX was reduced to approximately 1 mg L −1 in just 15–20 min, which is an extraordinary kinetic behavior in CPX adsorption. Elovich kinetic model and the Redlich-Peterson isotherm model fitted the experimental data with the highest correlation coefficient. SI-Ti 3 C 2 T x could be completely regenerated through an electrochemical regeneration approach within 5 min. Even after the subsequent adsorption and regeneration cycles, the removal rate enhanced up to ~99.7%. After the electrochemical treatment, the results of XRD and SEM indicated the stability of the material. Results obtained herein suggest that this type of nanoadsorbent will be useful in practical water treatment applications. • Sodium intercalated Ti 3 C 2 T x (SI-Ti 3 C 2 T x ) MXene nanosheets were fabricated using a simple batch reaction method. • The SI-Ti 3 C 2 T x MXene provided better CPX adsorption performance than pristine Ti 3 C 2 T x MXene. • An increase in spacing between layers and higher surface terminations collectively enhanced the adsorption capacity. • The electrochemical technique along with complete regeneration improved the adsorption capacity. • SI-Ti 3 C 2 T x was found to be stable for five regeneration cycles.

Evaluation of electrolytic reactor configuration for the regeneration of granular activated carbon saturated with methylene blue

Abstract The performance of an electrochemical process for the regeneration of granular activated carbon (GAC) was evaluated using boron-doped diamond (BDD) anodes. Three different configurations were tested in the reactor: fluidized bed, packed bed with a divided cell and packed bed with an undivided cell. The GAC used was previously saturated with a synthetic solution of methylene blue (MB). The effects of three operational parameters were evaluated: current density, initial pH and reaction time, and NaCl as the electrolyte. Regeneration efficiencies (REs) of up to 76 % ± 2 were achieved with a current density of 6 mA cm−2 during 24 h of reaction, and a specific electric energy consumption of 1530 kW h ton-1 of GAC was obtained. The best results were obtained using the packed bed reactor with a divided cell and the GAC in the cathodic compartment. The present results were attributed to an improvement in the desorption caused by the local alkaline pH in the cathodic compartment, to the contribution of the electrochemical oxidation by the hydroxyl radical, and, in parallel, to the chemical oxidation of the organic compounds by the oxidizing species formed from the chloride ion. It was also found that the electrochemical regeneration process has a negative effect on the GAC integrity after three cycles of continuous regeneration.

Design, Fabrication, and Testing of Electrolytic Cell for Minimizing Simulated Active Waste

The main objective of this work is to see the feasibility of using an electrochemical ion-exchange process in line with decontamination for removal of radioactive metal ions from simulated decontaminated solution/metal ion–loaded cation-exchange resin. This could extend the service period of resin, and the volume of radioactive resin (organic) waste generation could be minimized. Simulated decontamination solutions/spent resins were used in the middle section of a three-compartment cell separated by cation-permeable Nafion membranes. Metal ions from this central compartment permeated through the membrane and got deposited on the cathode by application of potential. Process parameters like applied voltage, interelectrode distance, pH, decontamination formulations, and type of membrane were optimized for efficient transport of metal ions. The resin life was observed to be extended by 5 h by an electrochemical regeneration process with Nafion membrane N115. The transport process, as monitored by the change in metal ion concentration in the cathodic compartment, was observed to pass through a maximum. Maximum metal ion removal was observed with formic acid/formate formulation indicating that the presence of acidity in the anodic compartment has a synergistic effect on the transport process. The cathodic compartment deposit was characterized by X-ray diffraction, laser Raman spectroscopy, scanning electron microscopy, and energy dispersive X-ray analysis.

Synthesis of Novel Graphene Composite Adsorbent for Water Treatment By Adsorption and Electrochemical Regeneration

One of the efficient and cost effective ways to remove organic contaminants from water is adsorption coupled with electrochemical oxidation. Graphite intercalated compounds (GIC) and activated carbons (AC) are among the common adsorbents for the adsorption - electrochemical regeneration process; nevertheless, they have significant shortcomings, i.e. GIC has low adsorptive capacity, whereas AC requires long regeneration time and high energy consumption associated with low current efficiency and high cell voltages. Owing to their huge surface area and high electrical conductivity, graphene-based materials are promising candidates as adsorbents suitable for electrochemical regeneration. This results in higher adsorptive capacity and current efficiency compared to AC and GIC. In this study, we prepared different types of graphene-based materials, namely graphene foam and magnetite reduced graphene oxide (rGO). The synthesized materials were characterized and tested for adsorption and electrochemical regeneration. Our findings revealed that, in addition to high current efficiency (greater than 80 %), these materials had a good adsorptive capacity compared to GIC. However, during the regeneration, graphene was oxidized and corroded after only a few cycles, contaminating the treated water. In the case of graphene foam, the integrity of the foam was lost after electrochemical regeneration. In order to overcome this corrosion problem and increase the current efficiency, a new composite was developed that is resistant to oxidation. The composite was characterized using scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman spectroscopy. Methylene blue was employed as a model adsorbate in synthetic wastewater samples. Regeneration was carried out in an electrolytic cell operated at a constant current. In spite of the slight reduction in adsorptive capacity compared to the pure graphene, the composite facilitated the oxidation of the organics to an extent in which a current efficiency of around 100 % was achieved. TEM images indicated that the composite was not significantly corroded during the electrochemical treatment. Even after ten cycles of adsorption and regeneration, no reduction in the adsorptive capacity and no contamination of the treated water was observed. In brief, the results of the current study introduce graphene composites as efficient materials for the adsorption - electrochemical regeneration process.

Electrochemical regeneration of phenol-saturated activated carbon – proposal of a reactor

ABSTRACTAn electrochemical process was used to investigate the activated carbon regeneration efficiency (RE) saturated with aromatics. For this purpose, an electrochemical reactor was developed and the operational conditions of this equipment were investigated, which is applied in activated carbon regeneration process. The influence of regeneration parameters such as processing time, the current used, the polarity and the processing fluid (electrolyte) were studied. The performance of electrochemical regeneration was evaluated by adsorption tests, using phenol as adsorbate. The increase in current applied and the process time was found to enhance the RE. Another aspect that indicated a better reactor performance was the type of electrolyte used, showing best results for NaCl. The polarity showed the highest influence on the process, when the cathodic regeneration was more efficient. The electrochemical regeneration process developed in this study presented regeneration capacities greater than 100% when the best process conditions were used, showing that this form of regeneration for activated carbon saturated with aromatics is very promising.

Electrochemical regeneration of a graphite adsorbent loaded with Acid Violet 17 in a spouted bed reactor

A novel spouted bed reactor is evaluated for water treatment by an adsorption and electrochemical regeneration process. The adsorbent is a bisulphate graphite intercalation compound with low specific surface area but high electrical conductivity, suitable for adsorption of contaminants and simultaneous electrochemical regeneration within a single unit. The effects of current density and liquid flow rate on Acid Violet 17 removal were investigated. The hydrodynamic behaviour of the liquid spouted bed reactor was characterised by a flow regime map. A four-parameter model has been developed to describe the adsorption and electrochemical regeneration process in the liquid spouted bed reactor. It was found that the experimental data of dye removal agrees well with the modelled simulations.

Electrochemical Regeneration of Zn-Saturated Granular Activated Carbon from Electroplating Wastewater Plant

An electrically assisted regeneration (EAR) process was used to assess the effectiveness of regenerating exhausted granular activated carbon (GAC) preloaded with electroplating wastewater containing hyper Zn concentration at a concentration of 950.5 mg L −1 (1.45 × 10 −2 mol L −1 ). The electrochemical rege-neration process supplied with direct current was controlled at a constant voltage of 5.0 V. Two regeneration methods were tested and compared: first, acid washing (pH 1.0) and, second, electrically assisted acid washing. Results showed that the Zn adsorption capacity of GAC regenerated by EAR was significantly higher than that of GAC regenerated by acid washing. The effectiveness of the Zn desorbing efficiency from GAC was enhanced by electric current in the electrochemical regeneration process. Using the EAR method, a regeneration efficiency of 88.3% was observed for GAC, whereas using acid regeneration, the efficiency was only 25.3%. These observations reveal that EAR could be a potential alternative to acid washing for the regeneration of GAC saturated with Zn.

Sustainable Electrochemical Regeneration of Copper-Loaded Ion Exchange Media

An electrochemical method for regenerating copper-loaded ion exchange media was investigated. The method involved circulating a moderate pH regenerant solution between a bed of ion exchange media and an electrochemical cell. The electrochemical regeneration process eliminates more than 99% of the acid and base use associated with conventional regeneration, consumes no water, produces metallic copper, and eliminates the production of a copper-laden sludge. Experiments were performed measuring copper plating rates as a function of the aqueous copper concentration, cell current, and flow rate. Experiments were also performed to determine the equilibrium partitioning of copper ions between the solution and the ion exchange media under loading and regeneration conditions. A mathematical model was developed and calibrated using experimental data, to provide guidance for the design of electrochemical ion exchange regeneration systems. The model incorporates the plating kinetics, the stripping of copper from the resin, and the equilibrium isotherm and predicts aqueous and adsorbed copper concentrations during the regeneration process. The model indicates that, in 789 min, 90% of copper can be removed from a resin loaded with 50 mg(Cu)/g(resin). An economic analysis indicates that energy costs for plating are less than 1% of chemical costs for conventional ion exchange regeneration.

Physicochemical Properties of Alkaline Aqueous Sodium Metaborate Solutions

Background: The transition to a hydrogen fuel economy is hindered by the lack of a practical storage method and concerns associated with its safe handling. Chemical hydrides have the potential to address these concerns. Sodium borohydride (sodium tetrahydroborate, NaBH4), is the most attractive chemical hydride for H2 generation and storage in automotive fuel cell applications, but recycling from sodium metaborate (NaBO2), is difficult and costly. An electrochemical regeneration process could represent an economically feasible and environmentally friendly solution. Method of Approach: We report a study of the properties of concentrated NaBO2 alkaline aqueous solutions that are necessary to the development of electrochemical recycling methods. The solubility, pH, density, conductivity, and viscosity of aqueous NaBO2 solutions containing varying weight percentages (1, 2, 3, 5, 7.5, and 10wt.%) of alkali hydroxides (NaOH, KOH, and LiOH) were evaluated at 25°C. The precipitates formed in supersaturated solutions were characterized by x-ray diffraction and scanning electron microscopy. Results: All NaBO2 physicochemical properties investigated, except solubility, increased with increased hydroxide ion concentration. The solubility of NaBO2 was enhanced by the addition of KOH to the saturated solution, but decreased when LiOH and NaOH were used. The highest ionic conductivity (198.27S∕m) was obtained from the filtrate of saturated aqueous solutions containing more than 30wt.%NaBO2 and 10wt.% NaOH prior to filtration. At 10wt.% hydroxide, the viscosity of the NaBO2 solution was the highest in the case of LiOH (11.38 cP) and lowest for those containing NaOH (6.37 cP). The precipitate was hydrated, NaBO2 for all hydroxides, but its hydration level was unclear. Conclusions: The use of KOH as the electrolyte was found to be more advantageous for the H2 storage and generation system based on NaBO2 solubility and solution half-life. However, the addition of NaOH led to the highest ionic conductivity, and its use seems more suitable for the electroreduction of NaBO2. Further investigations on the impact of KOH and NaOH on the electroreduction of NaBO2 in aqueous media have the potential to enhance the commercial viability of NaBH4.