Semi-solid electrolyte with layered heterometallic low-valent electron-mediator enabling indirect destruction of gaseous toluene.

The electrochemical degradation of air pollutants, particularly volatile organic compounds (VOCs), at their gaseous state is a promising method. However, it remains at an infant stage due to sluggish solid-gas electron transfers at room temperature. We established a triphase reaction condition using a semi-solid electrolyte layer between the electrode and membrane to enhance the electron transfer at room temperature. A polyvinyl alcohol (PVA) gel layer was inserted between a bimetallic layered CuNi(CN)4 complex coated Cu foam electrode (TCNi-Cu) and Nafion 324 membrane for the degradation of gaseous toluene. The cyclic voltammetry of TCNi-Cu using a sodium hydroxide-coated copper mesh electrode at a triphase showed Cu1+ and Ni1+ stabilization at -0.7 and -0.9 V, respectively, which was similar to the liquid phase electron transfer behavior. The degradation capacity of gaseous toluene without using electrogenerated TCNi-Cu + PVA gel was 0.54 mg cm2 min-1, whereas that of TCNi-Cu + PVA gel layers was 1.17 mg cm-2min-1, which revealed the mediation effect at a triphase condition. Toluene was converted into oxygen-containing products, such as butanol, propanol, and acetone (without reduction products), which revealed that indirect oxidation occurred at the cathode using an in-situ generated oxidant, such as OH˙ radical. As an electron-mediator, Cu1+ was used to form oxidants for the degradation of toluene at -0.7 V. The toluene removal rate reached 1.4 µmol h-1, with an energy efficiency of 0.15 Wh L-1. This study is the first attempt to describe a liquid-electrolyte-free cathodic half-cell in electrochemical application to VOCs degradation, highlighting the electron transfer at room temperature.

MgO modified zeolite facilitated low temperature chemisorptive removal of gaseous acetaldehyde into value added intermediate as desorption product.

The adsorptive removal of acetaldehyde is more compatible for real-world applications. However, it must be upgraded from simple adsorption to a high efficiency process with value added products. This study develops a modified zeolite with Mg2+ ions that possesses acid-base sites for the removal of acetaldehyde at room temperature. Through a modified procedure, MgO is coated on commercial zeolite (13x), achieving a porosity of 501 m2 g-1 with MgO particles of 100 nm and pore diameter of 2.6 nm, and high breakthrough capacity of 50.00 mg/g. The initial pH and concentration of Mg2+ ion 12.5 and 0.2 M, respectively, with a maximum breakthrough capacity of 12.72 mg/g at 10% humidity. Significant variations in breakthrough capacity with respect to humidity in the presence of H2S and NH3 demonstrate the effects of water and gases on adsorption efficiency. Desorptive oxidation of adsorbed acetaldehyde at 250 °C yielded a high molecular weight intermediate ethylene oxide formation. The oxidation is followed by aldol condensation and hydrogenation. The higher breakthrough capacity and the intermediate product yielded using the developed MgO-zeolite proves the acid-base reaction sites involved in acetaldehyde removal follows chemisorption and possible process scale-up.

Enhanced electro-reduction of NO to NH3 on Pt cathode at electro-scrubber.

Besides cheaper electrodes used in NH3 product formation during NO degradation by mediated electrochemical reduction (MER), a specific electrode that can perform direct electrochemical reduction (DER) and MER of NO is an added advantage. In the present study, a Pt electrode was used to examine NO degradation through NH3 formation during the electro-scrubbing process. Initially, the DER of NO was tested on a Pt electrode to determine if the DER of NO is possible. The NO degradation by only absorption, DER on Pt, and MER using electrogenerated [Ni(I)(CN)4]3- showed that a combination of DER and MER increased the NO degradation efficiency. In addition, the online FTIR spectra obtained under different conditions showed that the product formed was NH3, either from the DER or MER during electro-scrubbing. The feed gas flow rate and feed concentration results of NH3 formation revealed an additional chemical reaction that was influenced by the Pt electrode in addition to the DER and MER processes. Furthermore, the degradation efficiency of NO when using the Pt electrode increased to 90% compared to that of the Cu electrode (65%), which showed that Pt follows a combination of DER and MER processes. Based on the gas-phase FTIR results of NH3 formation during NO degradation, higher NH3 production (0.32 mg/h) was obtained when using a Pt electrode than that using a Cu electrode (0.21 mg/h), highlighting the specificity of the Pt electrode in NH3 formation during the degradation of NO gas.

Implementation of concurrent electrolytic generation of two homogeneous mediators under widened potential conditions to facilitate removal of air-pollutants.

Electro-scrubbing is being developed as a futuristic technology for the removal of air-pollutants. To date, only one homogeneous mediator for the removal of air pollutants has been generated in each experiment using a divided electrolytic flow cell in an acidic medium. This paper reports the concurrent generation of two homogenous mediators, one at the anodic half-cell containing an acidic solution and the other at the cathodic half-cell containing a basic solution. The concept was inspired by the change in pH that occurs during water electrolysis in a divided cell. A 10 M KOH electrolyte medium assisted in the electrochemical generation of low valent 14% Co1+ ([CoI(CN)5]4-) mediator formed from reduction of [CoII(CN)5]3- which was accompanied by a change in the solution 'oxidation reduction potential' (ORP) of -1.05 V Simultaneously, 41% of Co3+ was generated from oxidation of CoIISO4 in the anodic half-cell. No change in the solution ORP was observed at the cathodic half-cell when both half-cells contain 5 M H2SO4, and Co3+ was formed in the anodic half-cell. An electro-scrubbing approach based on the above principles was developed and tested on gaseous-pollutants, CH3CHO and CCl4, by Co3+ and Co1+, respectively, with 90 and 96% removal achieved, respectively.

Studies on Effective Generation of Mediators Simultaneously at Both Half-Cells for VOC Degradation by Mediated Electroreduction and Mediated Electrooxidation.

Of the several electrochemical methods for pollutant degradation, the mediated electrooxidation (MEO) process is widely used. However, the MEO process utilizes only one (anodic) compartment toward pollutant degradation. To effectively utilize the full electrochemical cell, an improved electrolytic cell producing both oxidant and reductant mediators at their respective half-cells, which can be employed for treating two pollutants simultaneously, was investigated. The cathodic half-cell was studied first toward maximum [CoI(CN)5]4- (Co+) generation (21%) from a [CoII(CN)6]3- precursor by optimizing several experimental factors such as the electrolyte, cathode material, and orientation of the Nafion324 membrane. The anodic half-cell was optimized similarly for higher Co3(SO4)2 (Co3+) yields (41%) from a CoIISO4 precursor. The practical utility of the newly developed full cell setup, combining the optimized cathodic half-cell and optimized anodic half-cell, was demonstrated by electroscrubbing experiments with simultaneous dichloromethane removal by Co+ via the mediated electroreduction process and phenol removal by Co3+ via the MEO process, showing not only utilization of the full electrochemical cell, but also degradation of two different pollutants by the same applied current that was used in the conventional cell to remove only one pollutant.

Effective identification of (NH4)2CO3 and NH4HCO3 concentrations in NaHCO3 regeneration process from desulfurized waste.

This work describes the quantitative analysis of (NH4)2CO3 and NH4HCO3 using a simple solution phase titration method. Back titration results at various (NH4)2CO3-NH4HCO3 ratios demonstrated that 6:4 ratio caused a 3% error in their differentiation, but very high errors were found at other ratios. A similar trend was observed for the double indicator method, especially when strong acid HCl was used as a titrant, where still less errors (2.5%) at a middle ratio of (NH4)2CO3-NH4HCO3 was found. Remaining ratios with low (NH4)2CO3 (2:8, 4:6) show high +ve error (found concentration is less) and high (NH4)2CO3 (7:3, 8:2, and 9:1) show high -ve error (found concentration is higher) and vice versa for NH4HCO3. In replacement titration using Na2SO4, at both higher end ratios of (NH4)2CO3-NH4HCO3 (2:8 and 9:1), both -ve and +ve errors were minimized to 75% by partial equilibrium arrest between (NH4)2CO3 and NH2COONH4, instead of more than 100% observed in back titration and only double indicator methods. In the presence of (NH4)2SO4 both -ve and +ve error% are completely reduced to 3±1 at ratios 2:8, 4:6, and 6:4 of (NH4)2CO3-NH4HCO3, which demonstrates that the equilibrium transformation between NH2COONH4 and (NH4)2CO3 is completely controlled. The titration conducted at lower temperature (5 °C) in the presence of (NH4)2SO4 at higher ratios of (NH4)2CO3-NH4HCO3 (7:3, 8:2,and 9:1) shows complete minimization of both -ve and +ve errors to 2±1%, which explains the complete arresting of equilibrium transformation. Finally, the developed method shows 2±1% error in differentiation of CO3(2-) and HCO3(-) in the regeneration process of NaHCO3 from crude desulfurized sample. The developed method is more promising to differentiate CO3(2-) and HCO3(-) in industrial applications.

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.

A single catalyst of aqueous CoIII for deodorization of mixture odor gases: a development and reaction pathway study at electro-scrubbing process.

A constant generation of aqueous Co(III) active catalyst and its utility on various odor gases deodorization at electro-scrubbing process is the primary investigation. The Co(III) activation and regeneration for continuous use is established by electrochemical undivided cell in H2SO4 medium. The generated aqueous Co(III) is then applied to simultaneous deodorization of simulated odor gases, namely, ammonia, trimethylamine, hydrogen sulfide, methyl mercaptan, and acetaldehyde, for municipal waste treatment plant emissions. The electro-scrubbing process results indicated that deodorization is almost complete at a low gas flow rate of 30 L min(-1). FTIR and pH studies demonstrated that amine compounds are removed via complex formation with H2SO4 and Co(III). In the case of sulfur compounds, deodorization of methyl mercaptan and hydrogen sulfide are removed by the Co(III)-MEO (Co(III)-mediated electrocatalytic oxidation) process via the formation of acetic acid as intermediate and SO4(2-) as a product. Also, acetaldehyde deodorization results obtained by pH, total acidity and CO2 analyses evidence the process follow Co(III)-MEO. The constant generation of aqueous active Co(III) and an electro-scrubbing process offers promise as a means of removing odorous waste gases from gaseous emissions.

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.