Development of a biphasic electroreactor with a wet scrubbing system for the removal of gaseous benzene.

An efficient, continuous flow electroreactor system comprising a scrubbing column (for absorption) and a biphasic electroreactor (for degradation) was developed to treat gas streams containing benzene. Initial benzene absorption studies using a continuous flow bubble column containing absorbents like 40% sulfuric acid, 10% silicone oil (3, 5, 10 cSt), or 100% silicone oil showed that 100% silicone oil is the most suitable. A biphasic batch electroreactor based on 50 mL of silicone oil and 100 mL of activated Co(III) (activated electrochemically) in 40% sulfuric acid demonstrated that indirect oxidation of benzene is possible by Co(III). Combined experiments on the wet scrubbing column and biphasic electroreactor (BP-ER) were performed to determine the feasibility of benzene removal, which is reside in the silicone oil medium. In semidynamic scrubbing with BP-ER experiments using an aqueous electroreactor volume of 2 L, and an inlet gas flow and a gaseous benzene concentration were 10 Lmin(-1) and 100 ppm, respectively, benzene removal efficiency is 75% in sustainable way. The trend of CO2 evolution is well correlated with benzene recovery in the BP-ER. The addition of sodiumdodecyl sulfate (SDS) enhanced the recovery of silicone oil without affecting benzene removal. This process is promising for the treatment of high concentrations of gaseous benzene.

Mineralization of gaseous acetaldehyde by electrochemically generated Co(III) in H2SO4 with wet scrubber combinatorial system.

Electrochemically generated Co(III) mediated catalytic room temperature incineration of acetaldehyde, which is one of volatile organic compounds (VOCs), combined with wet scrubbing system was developed and investigated. Depending on the electrolyte's type, absorption come removal efficiency is varied. In presence of electrogenerated Co(III) in sulfuric acid, acetaldehyde was mineralized to CO2 and not like only absorption in pure sulfuric acid. The Co(III) mediated catalytic incineration led to oxidative absorption and elimination to CO2, which was evidenced with titration, CO2, and cyclic voltammetric analyses. Experimental conditions, such as current density, concentration of mediator, and gas molar flow rate were optimized. By the optimization of the experimental conditions, the complete mineralization of acetaldehyde was realized at a room temperature using electrochemically generated Co(III) with wet scrubber combinatorial system.

Nano-Ag-Nafion modified Pt electrode for oxidation of volatile organic compounds: an electrochemical study.

In this work, we describe Nano-Ag-Nafion coated pt electrode for oxidation of volatile organic compound (VOC), here acetaldehyde. Electrochemically synthesized Nano-Ag-Nafion film on Pt was analyzed by electrochemically in various electrolyte solutions like nitric acid, sulfuric acid, potassium nitrate, and potassium hydroxide for its stability. High stability of Nano-Ag-Nafion film appeared in potassium hydroxide medium among electrolyte solutions studied. Electrocatalysis of acetaldehyde was occurred only in acid and neutral medium. A catalytic oxidative peak during cathodic voltammetric reduction scan was observed at 1.75 V, which, unusual redox behavior, follows EC' reaction path way between electrogenerated Ag(II) and acetaldehyde. For Nano-Ag potential applicability, a calibration plot was drawn from various concentration range of acetaldehyde to check the maximum concentration level of acetaldehyde degradation in air.

The combined removal of methyl mercaptan and hydrogen sulfide via an electro-reactor process using a low concentration of continuously regenerable Ag(II) active catalyst.

In this study, an electrocatalytic wet scrubbing process was developed for the simultaneous removal of synthetic odorous gases namely, methyl mercaptan (CH(3)SH) and hydrogen sulfide (H(2)S). The initial process consists of the absorption of CH(3)SH and H(2)S gases by an absorbing solution, followed by their mediated electrochemical oxidation using a low concentration of active Ag(II) in 6M HNO(3). Experiments were conducted under different reaction conditions, such as CH(3)SH and H(2)S loadings, active Ag(II) concentrations and molar flow rates. The cyclic voltammetry for the oxidation of CH(3)SH corroborated the electro-reactor results, in that the silver in the 6M HNO(3) reaction solution significantly influences the oxidation of CH(3)SH. At a low active Ag(II) concentration of 0.0012 M, the CH(3)SH removal experiments demonstrated that the CH(3)SH degradation was steady, with 100% removal at a CH(3)SH loading of 5 gm(-3) h(-1). The electro-reactor and cyclic voltammetry results indicated that the removal of H(2)S (100%) follows a mediated electrocatalytic oxidation reaction. The simultaneous removal of 100% of the CH(3)SH and H(2)S was achieved, even with a very low active Ag(II) concentration (0.0012 M), as a result of the high efficiency of the Ag(II). The parallel cyclic voltammetry results demonstrated that a process of simultaneous destruction of both CH(3)SH and H(2)S follows an H(2)S influenced mediated electrocatalytic oxidation. The use of a very low concentration of the Ag(II) mediator during the electro-reactor process is promising for the complete removal of CH(3)SH and H(2)S.

Destruction of commercial pesticides by cerium redox couple mediated electrochemical oxidation process in continuous feed mode.

Mediated electrochemical oxidation was carried out for the destruction of commercial pesticide formulations using cerium(IV) in nitric acid as the mediator electrolyte solution in a bench scale set up. The mediator oxidant was regenerated in situ using an electrochemical cell. The real application of this sustainable process for toxic organic pollutant destruction lies in its ability for long term continuous operation with continuous organic feeding and oxidant regeneration with feed water removal. In this report we present the results of fully integrated MEO system. The task of operating the continuous feed MEO system for a long time was made possible by continuously removing the feed water using an evaporator set up. The rate of Ce(IV) regeneration in the electrochemical cell and the consumption for the pesticide destruction was matched based on carbon content of the pesticides. It was found that under the optimized experimental conditions for Ce(III) oxidation, organic addition and water removal destruction efficiency of ca. 99% was obtained for all pesticides studied. It was observed that the Ce(IV) concentration was maintained nearly the same throughout the experiment. The stable operation for 6h proved that the process can be used for real applications and for possible scale up for the destruction of larger volumes of toxic organic wastes.

Experimental aspects of combined NOx and SO2 removal from flue-gas mixture in an integrated wet scrubber-electrochemical cell system.

The objective of this work was to study the effect of some operating conditions on the simultaneous removal of NO(x) and SO2 from simulated NO-SO2-air flue-gas mixtures in a scrubber column. The gaseous components were absorbed into 6M HNO3 electrolyte in the scrubber in a counter-current mode, and were oxidatively removed by the Ag(II) mediator oxidant electrochemically generated in an electrochemical cell set-up. The integration of the electrochemical cell with the scrubber set-up ensured continuous regeneration of the Ag(II) mediator and its repeated reuse for NO(x) and SO2 removal purpose, thereby avoiding: (1) the usage of chemicals continuously for oxidation and (2) the production of secondary waste. The influences of packing material (raschig glass rings, raschig poly(vinylidene) fluoride rings, Jaeger tri-pack perfluoroalkoxy spheres), feed concentrations of NO and SO2 (100-400 ppm NO and 100-400 ppm SO2), superficial gas velocity (0.061-0.61ms(-1)) and liquid velocity (0.012-0.048 ms(-1)) were investigated. The raschig glass rings with high surface area provided highest NO removal efficiency. NO and NO(x) showed decreasing abatement at higher feed concentrations. The removal of nitrogen components was faster and also greater, when SO2 co-existed in the feed. Whereas the gas flow rate decreased the removal efficiency, the liquid flow rate increased it for NO and NOx. The flow rate effects were analyzed in terms of gas/liquid residence time and superficial liquid velocity/superficial gas velocity ratio. SO2 removal was total under all conditions.

Novel process for simultaneous removal of NO(x) and SO2 from simulated flue gas by using a sustainable Ag(I)/Ag(II) redox mediator.

The objective of this work is to develop a sustainable process for simultaneous removal of waste gases such as NO, NO2, and SO2 by an electrochemically generated Ag(I)/Ag(II) redox mediator system. High removal efficiency was achieved for NO and SO2 by the wet scrubbing method at room temperature and atmospheric pressure. This removal is achieved through oxidation and absorption by contacting the gaseous stream with redox mediator ions that offer specific or selective solubility for the solute gases to be recovered in a wet scrubber. The process parameters such as gas velocity, liquid velocity, Ag(I) concentration, and HNO3 concentration were investigated to explore the possibility of complete removal of waste gases. The Ag(I)/Ag(II)-based mediated electrochemical oxidation process proved to be quite effective for simultaneous removal of NO, NO(x), and SO2 from the simulated flue gas mixtures containing NO and SO2 over a wide concentration range of 100-400 ppm. Studies were carried out with individual gas components for the mixture, and the effect of input NO and input SO2 concentrations on the NO(x) and SO2 removal efficiencies at 20 degrees C was examined. Complete oxidation of NO to NO2 with 100% NO removal efficiency and 92% NO(x) removal efficiency was achieved along with 100% SO2 removal efficiency, highlighting a potentially far greater efficiency of the Ag(I)/Ag(II)-based system in functionality and selectivity. Active research work in this direction is anticipated in the near future.

Studies on electrochemical recovery of silver from simulated waste water from Ag(II)/Ag(I) based mediated electrochemical oxidation process.

In the Ag(II)/Ag(I) based mediated electrochemical oxidation (MEO) process, the spent waste from the electrochemical cell, which is integrated with the scrubber columns, contains high concentrations of precious silver as dissolved ions in both the anolyte and the catholyte. This work presents an electrochemical developmental study for the recovery of silver from simulated waste water from Ag(II)/Ag(I) based MEO process. Galvanostatic method of silver deposition on Ti cathode in an undivided cell was used, and the silver recovery rate kinetics of silver deposition was followed. Various experimental parameters, which have a direct bearing on the metal recovery efficiency, were optimized. These included studies with the nitric acid concentration (0.75-6M), the solution stirring rate (0-1400 rpm), the inter-electrode distance between the anode and the cathode (2-8 cm), the applied current density (29.4-88.2 mA cm(-2)), and the initial Ag(I) ion concentration (0.01-0.2M). The silver recovered by the present electrodeposition method was re-dissolved in 6M nitric acid and subjected to electrooxidation of Ag(I) to Ag(II) to ascertain its activity towards Ag(II) electrogeneration from Ag(I), which is a key factor for the efficient working of MEO process. Our studies showed that the silver metal recovered by the present electrochemical deposition method could be reused repeatedly for MEO process with no loss in its electrochemical activity. Some work on silver deposition from sulfuric acid solution of different concentrations was also done because of its promising features as the catholyte in the Ag(II) generating electrochemical cell used in MEO process, which include: (i) complete elimination of poisonous NO(x) gas liberation in the cathode compartment, (ii) reduced Ag(+) ion migration across Nafion membrane from anolyte to catholyte thereby diminished catholyte contamination, and (iii) lower cell voltage and hence lesser power consumption.

Destruction of organic pollutants by cerium(IV) MEO process: a study on the influence of process conditions for EDTA mineralization.

The mediated electrochemical oxidation (MEO) process with cerium(IV) and nitric acid as the oxidizing medium was employed for the destruction of various model organic pollutants in continuous organic feeding mode. A near complete destruction was observed for all the organics studied. The effects of various experimental conditions were evaluated with respect to EDTA mineralization. The key parameters varied in the process were concentration of EDTA (67-268 mM), temperature (70, 80 and 95 degrees C), concentrations of Ce(IV) (0.7, 0.8 and 0.95 M), nitric acid (2, 3 and 4M) and duration of organic addition (30 and 120 min). Under the experimental conditions of 80 degrees C and 0.95 M Ce(IV) in 3 M nitric acid, nearly 90% destruction was achieved based on CO(2) production and 95% based on TOC analyses for all the organic compounds studied. The in situ regeneration of mediator ion by the electrochemical cell was found to be good during the organic destruction within the range of experimental conditions studied. In the case of long term organic feeding (120 min) the destruction was calculated after the CO(2) evolution attained the steady state and under this condition the destruction efficiency was found to be 85% based on CO(2) evolution.

Mineralization of phenol by Ce(IV)-mediated electrochemical oxidation in methanesulphonic acid medium: a preliminary study.

The mediated electrochemical oxidation (MEO) process using cerium(IV) in methanesulphonic acid (MSA) as the oxidizing medium was employed for the mineralization of phenol in batch and continuous feeding modes. Although nitric acid was an extensively studied electrolyte for organic mineralization reactions in MEO processes it does possess the problem of NO(x) gas production during the reduction of nitric acid in the cathode compartment of the electrochemical cell. This problem could be circumvented by proper choice of the electrolyte medium such as MSA. The mediator cerium in MSA solution was first oxidized to higher oxidation state using an electrochemical cell. The produced Ce(IV) oxidant was then used for the destruction of phenol. It was found that phenol could be mineralized to CO2 by Ce(IV) in MSA. The evolved CO2 was continuously measured and used for the calculation of destruction efficiency. The destruction efficiency was observed to be 85% based on CO2 evolution for 1000 ppm phenol solution at 80 degrees C in continuous feed mode.

Destruction of EDTA using Ce(IV) mediated electrochemical oxidation: a simple modeling study and experimental verification.

Mediated electrochemical oxidation (MEO) is a recent development in the environmental research field for the complete destruction of organic pollutants. This study presents the destruction of EDTA by cerium(IV) MEO process in nitric acid medium. The destruction reaction was carried out in a continuous stirred tank reactor under various conditions. A simple kinetic model was developed to analyze and simulate the organic destruction in the MEO process. The model was based on the calculation of the total mass balance, the component mass balance, and the energy balance in the reactor and also in the heating jacket. The sensitivity to key operating conditions such as the initial EDTA concentration (50-200 mM), EDTA feeding time (30-180 min), reaction temperature (323-363 K), and the rate laws corresponding to zero-, first-, second-, and third-order reaction were analyzed. It was found that the model simulated agreed well with the experimental data for EDTA oxidation. The results obtained showed the suitability of the MEO process for the effective mineralization of high concentrations of EDTA.