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

Muthuraman, Govindan,Chung, Sang Joon,Moon, Il Shik Elsevier 2011 Journal of hazardous materials Vol.193 No.-

<P><B>Highlights</B></P><P>► Simultaneous removal of H<SUB>2</SUB>S and CH<SUB>3</SUB>SH was achieved at electro-reactor. ► Active catalyst Ag(II) perpetually regenerated in HNO<SUB>3</SUB> medium by electrochemical cell. ► CH<SUB>3</SUB>SH destruction follows two reaction pathways. ► H<SUB>2</SUB>S induced destruction of CH<SUB>3</SUB>SH has identified. ► Low concentration of active Ag(II) (12.5×10<SUP>−4</SUP>molL<SUP>−1</SUP>) is enough for complete destruction.</P> <P><B>Abstract</B></P><P>In this study, an electrocatalytic wet scrubbing process was developed for the simultaneous removal of synthetic odorous gases namely, methyl mercaptan (CH<SUB>3</SUB>SH) and hydrogen sulfide (H<SUB>2</SUB>S). The initial process consists of the absorption of CH<SUB>3</SUB>SH and H<SUB>2</SUB>S gases by an absorbing solution, followed by their mediated electrochemical oxidation using a low concentration of active Ag(II) in 6M HNO<SUB>3</SUB>. Experiments were conducted under different reaction conditions, such as CH<SUB>3</SUB>SH and H<SUB>2</SUB>S loadings, active Ag(II) concentrations and molar flow rates. The cyclic voltammetry for the oxidation of CH<SUB>3</SUB>SH corroborated the electro-reactor results, in that the silver in the 6M HNO<SUB>3</SUB> reaction solution significantly influences the oxidation of CH<SUB>3</SUB>SH. At a low active Ag(II) concentration of 0.0012M, the CH<SUB>3</SUB>SH removal experiments demonstrated that the CH<SUB>3</SUB>SH degradation was steady, with 100% removal at a CH<SUB>3</SUB>SH loading of 5gm<SUP>−3</SUP>h<SUP>−1</SUP>. The electro-reactor and cyclic voltammetry results indicated that the removal of H<SUB>2</SUB>S (100%) follows a mediated electrocatalytic oxidation reaction. The simultaneous removal of 100% of the CH<SUB>3</SUB>SH and H<SUB>2</SUB>S was achieved, even with a very low active Ag(II) concentration (0.0012M), 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<SUB>3</SUB>SH and H<SUB>2</SUB>S follows an H<SUB>2</SUB>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<SUB>3</SUB>SH and H<SUB>2</SUB>S.</P>

Development of a Biphasic Electroreactor with a Wet Scrubbing System for the Removal of Gaseous Benzene

Govindan, Muthuraman,Chung, Sang Joon,Moon, Hyun-Ho,Jang, Jae Wook,Moon, Il-Shik American Chemical Society 2013 ACS combinatorial science Vol.15 No.8

<P>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<SUP>–1</SUP> and 100 ppm, respectively, benzene removal efficiency is 75% in sustainable way. The trend of CO<SUB>2</SUB> 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.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/acsccc/2013/acsccc.2013.15.issue-8/co400046g/production/images/medium/co-2013-00046g_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/co400046g'>ACS Electronic Supporting Info</A></P>

Prototype membrane electrolysis using a MFI-zeolite-coated ceramic tubular membrane provides in-line generation of two active electron mediators by eliminating active species crossover

Govindan, Muthuraman,Adam Gopal, Ramu,Zhu, Bo,Duke, Mikel,Gray, Stephen,Moon, Il Shik Elsevier 2019 Journal of membrane science Vol.579 No.-

<P><B>Abstract</B></P> <P>Active ion crossover is a major obstacle in membrane electrolysis, which reduces the efficiency of the active mediator and increases operational cost. Using a prototype tubular cell divided with a MFI-zeolite-coated (shell side) ceramic tubular membrane, two active mediators, Co<SUP>3+</SUP> (Co<SUB>2</SUB>(SO<SUB>4</SUB>)<SUB>3</SUB>) in 5 M H<SUB>2</SUB>SO<SUB>4</SUB> at the anodic half-cell and Ni<SUP>1+</SUP> ([Ni(CN)<SUB>4</SUB>]<SUP>3-</SUP>) in 9 M KOH at the cathodic half-cell, were produced. The rate of Co<SUP>3+</SUP> production increased from 5.74 × 10<SUP>−3</SUP> M min<SUP>−1</SUP> to 7.11 × 10<SUP>−3</SUP> M min<SUP>−1</SUP> when the use of 9 M KOH at the cathodic half-cell instead of 5 M H<SUB>2</SUB>SO<SUB>4</SUB> at both half-cells and controlled migration due to the pH change. The absence of a UV–visible spectral peak for cobalt or nickel ions in the other side of the electrolyzed solution supports the lack of active metal ion crossover by the MFI-zeolite-coated ceramic membrane. In high acid and base electrolyte pH, the 5.6 fold higher resistance (5.13 Ω cm<SUP>−2</SUP>) than in high acid electrolytes in both half-cells (0.91 Ω cm<SUP>−2</SUP>) prevented proton and active mediator ion crossover. SEM-EDS and XRD data profiles found no cobalt or nickel ions on the membrane, which also supports the lack of migration, whereas the Al ion concentration decreased on the lumen side (9 M KOH containing the cathodic half-cell), demonstrating the dissolution of Al<SUB>2</SUB>O<SUB>3</SUB> in the KOH medium (uncoated MFI). The MFI-coated tubular membrane can be a good choice for the effective generation of two mediators by membrane electrolysis using high end pH electrolytes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> MFI type zeolite membrane achieved for effective minimization of active ion crossover by pH variation. </LI> <LI> Two electron mediators have generated concurrently with high generation rate at each half-cells. </LI> <LI> No active ions migration evidenced by UV–visible analysis that were tested even during electrolysis. </LI> <LI> More than 1000 h operation in highly acid and base conditions confirm the effective stability of zeolite coating. </LI> </UL> </P>

Simple Technical Approach for Perpetual Use of Electrogenerated Ag(II) at Semipilot Scale: Removal of NO and SO₂ as a Model System

Govindan, Muthuraman,Chung, Sang-Joon,Moon, Il-Shik American Chemical Society 2012 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.51 No.6

<P>The sustainable applicability of Ag(II)/Ag(I) redox mediator was studied in a semipilot-scale system for treatment of model artificial flue gases containing NO and SO<SUB>2</SUB>. Various discontinuous current supplies were tested for their effect on sustainable use of the electrogenerated mediator. Current density, cell volume, number of flow-through cell, and feed flow rates were varied in electrochemical thin layer cells to improve the applicability of the proposed current supply method. Discontinuing current flow every (5/5) min on–off (<I>i</I><SUB>DC5</SUB>) resulted in improved regeneration capacity of Ag(II) after 15 h. After extended operation (24 h), removal efficiencies of 62% NO and 100% SO<SUB>2</SUB> were achieved by mediated electrochemical oxidation both individually and simultaneously using the proposed discontinuous current supply, demonstrating the sustainable use of the mediator. This study will be taken as a pretest for long-term sustainability testing of the mediator, Ag(II), during industrial scaling up.</P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ie2015813'>ACS Electronic Supporting Info</A></P>

Co3+ homogeneous mediator generation efficiency in a divided tubular electrochemical reactor with MFI-type zeolite membrane

Muthuraman Govindan,Bo Zhu,Mikel Duke,Stephen Gray,문일식 한국공업화학회 2017 Journal of Industrial and Engineering Chemistry Vol.52 No.-

In the present work a tubular electrochemical cell with MFI-type zeolite coated membrane (TZM) wasengineered and evaluated using Co2+ oxidation efficiency in high acid medium. Electrolysis of Co2+ wascarried out at room temperature (20 3 C) in 4 M H2SO4 at anodic half-cell, and showed 42% Co2+oxidation with 0.3 V higher cell voltage than the commonly used Nafion324 membrane in planararrangement. Further, the TZM membrane was robust when operated in the cell at different temperatures(10, 30 and 50 C) as no noticeable change in surface morphology was observable by SEM analysis. Furthertesting showed Co2+ oxidation efficiency decreased with temperature and increased with current density,suggesting stable operation of the TZM but structural change in cobalt precursor. The TZM membraneshowed less resistance 0.91 V cm2 (at 10 C) than Nafion324, which is decreased with increasingtemperature from 10 C to 50 C. A 72 h test of the TZM at slightly elevated current density (70 mA cm2)showed increased oxidation efficiency of Co2+ to 57% compared to the traditional planar cell withNafion324 (43%). Therefore, the engineered tubular electrochemical reactor with TZM is robust forgeneration of homogeneous mediators towards environmental pollution removal.

A review on an electrochemically assisted-scrubbing process for environmental harmful pollutant’s destruction

Govindan Muthuraman,문일식 한국공업화학회 2012 Journal of Industrial and Engineering Chemistry Vol.18 No.5

Mediated electrocatalytic oxidation (MEO) has been used for 150 years. Recently, the process was combined with scrubbing technology to allow the effective treatment of industrial air pollution. This review focuses on the development and applications of the MEO-assisted scrubbing process for the treatment of environmental air pollution. Particular focus was given to MEO using metal ions as mediators, influencing factors, such as electrolytes, electrode, flow method and rate, and the scrubbing column. More than 200 related publications were reviewed with 174 cited. Electro-scrubbing is considered as an advanced technology with possible further developments. Active electrodes, such as titanium-based Pt, DSA(RuO2/IrO2) film electrodes result in the complete mineralization of air pollutants in the MEO process. Air pollutants are removed with the assistance of electrogenerated high energy metal ions, such as Ag(II), Co(III) and Ce(IV), as well as by ozone and chlorine, as mediators in an acidic medium.

Co³⁺ homogeneous mediator generation efficiency in a divided tubular electrochemical reactor with MFI-type zeolite membrane

Govindan, Muthuraman,Zhu, Bo,Duke, Mikel,Gray, Stephen,Moon, Il Shik Elsevier 2017 Journal of industrial and engineering chemistry Vol.52 No.-

<P><B>Abstract</B></P> <P>In the present work a tubular electrochemical cell with MFI-type zeolite coated membrane (TZM) was engineered and evaluated using Co<SUP>2+</SUP> oxidation efficiency in high acid medium. Electrolysis of Co<SUP>2+</SUP> was carried out at room temperature (20±3°C) in 4M H<SUB>2</SUB>SO<SUB>4</SUB> at anodic half-cell, and showed 42% Co<SUP>2+</SUP> oxidation with 0.3V higher cell voltage than the commonly used Nafion324 membrane in planar arrangement. Further, the TZM membrane was robust when operated in the cell at different temperatures (10, 30 and 50°C) as no noticeable change in surface morphology was observable by SEM analysis. Further testing showed Co<SUP>2+</SUP> oxidation efficiency decreased with temperature and increased with current density, suggesting stable operation of the TZM but structural change in cobalt precursor. The TZM membrane showed less resistance 0.91Ωcm<SUP>2</SUP> (at 10°C) than Nafion324, which is decreased with increasing temperature from 10°C to 50°C. A 72h test of the TZM at slightly elevated current density (70mAcm<SUP>2</SUP>) showed increased oxidation efficiency of Co<SUP>2+</SUP> to 57% compared to the traditional planar cell with Nafion324 (43%). Therefore, the engineered tubular electrochemical reactor with TZM is robust for generation of homogeneous mediators towards environmental pollution removal.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Engineered and operated a divided tubular electrochemical reactor with MFI-type zeolite membrane. </LI> <LI> Co<SUP>3+</SUP> generation efficiency by TZM found competitive with Nafion324 with plate and frame type. </LI> <LI> Limited Co<SUP>2+</SUP> migration occurs by its structural change not by TZM structural change. </LI> <LI> No change in TZM structure was found after all electrolysis experiments in 5M H<SUB>2</SUB>SO<SUB>4.</SUB> </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Initial Assessment of Membrane Divided Cathodic Half-cell Cell for Gas Phase Removal of Air Pollutants: Gas Phase Removal Study on Dichloromethane

Govindan Muthuraman,Youngyu Choi,Daekeun Kim 한국대기환경학회 2021 한국대기환경학회 학술대회논문집 Vol.2021 No.10

Apart from many other reasons of electrochemical removal of VOCs at liquid phase, its solubility in aqueous medium limits the removal process. Gas phase electrochemical removal of VOCs are in infant stage and many devoid to be filled either fundamental or engineering aspects. In the present investigation, a membrane divided cathodic half-cell was optimized for the gas phase removal of dichloromethane (DCM) by catalytic reductive method. First, 3D foam electrode modified with suitable mediator (Ex.: Ni(II) (CN)₄<SUP>2-</SUP>) and suitable gel (Ex.:sodium silicate and PVA + NaOH) optimized between membrane and electrode. Initial parameters such as cell potential, cyclicvoltammetry (CV) and impedance analyses were carried out under gas flow conditions to understand the electron transfer process under gas phase. Finally, gas phase reductive removal of DCM validated with combination of ex-situ gas chromatography (GC) under different feed concentrations, flow rate and applied current densities. A possible current efficiency correlation with removal of DCM was optimized towards the scale up process.

Na-β-Alumina as a Separator in the Development of All-Vanadium Non-Aqueous Tubular Redox Flow Batteries: An Electrochemical and Charging-Discharging Examination Using a Prototype Tubular Redox Flow Cell

Muthuraman, Govindan,Boyeol, Lee,Il-Shik, Moon The Electrochemical Society 2018 Journal of the Electrochemical Society Vol.165 No.9

<P>The non-aqueous redox flow battery (N-ARFB) is in the development stages with aim to produce high power density storage systems. In addition to the development of N-ARFBs, this study examined the applicability of a sodium beta alumina (Na-beta-Al2O3) membrane in the development of a N-ARFB through an analysis of the electrochemical processes, redox active species migration, and charging/discharging at room temperature (25 +/- 3 degrees C). Through impedance analysis, the ionic conductivity of the Na-beta-Al2O3 was 2.97 x 10(-2) S cm(-1) which is slightly higher than the literature value. UV-Visible analysis showed no migration of the vanadium acetylacetonate (V(acac)(3)) ion from one compartment to another, either during the charging or discharging process. In addition, the lack of a change in the morphology of the spent membrane revealed not only stability, but also confirmed no permeation of V(acac)(3) species. The maximum applied current density for charging and discharging was 0.01 mA cm(-2) and 0.0015 mA cm(-2), respectively. The charging/discharging of V(acac)(3) enables voltage and current efficiencies of almost 16% and 11% respectively, at the state of charge of 15%. This demonstrates that the Na-beta-Al2O3 membrane can be improved for use in N-ARFB after optimizing the conditions. (C) The Author(s) 2018. Published by ECS.</P>

Mineralization of Gaseous Acetaldehyde by Electrochemically Generated Co(III) in H₂SO₄ with Wet Scrubber Combinatorial System

Govindan, Muthuraman,Chung, Sang-Joon,Moon, Il-Shik American Chemical Society 2012 ACS combinatorial science Vol.14 No.6

<P>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 CO<SUB>2</SUB> and not like only absorption in pure sulfuric acid. The Co(III) mediated catalytic incineration led to oxidative absorption and elimination to CO<SUB>2</SUB>, which was evidenced with titration, CO<SUB>2</SUB>, 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.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/acsccc/2012/acsccc.2012.14.issue-6/co300012a/production/images/medium/co-2012-00012a_0011.gif'></P>