University of Cincinnati

UNIVERSITY OF CINCINNATI DATE: July 5, 2002 I, Dinesh Kumar Palaniswamy , hereby submit this as part of the requirements for the degree of: Master of Science in: Environmental Engineering It is entitled: Electrochemical Reduction of 2,4,6-Trinitrotoluene Approved by: Dr.George Sorial Dr.Dionysios Dionysiou Dr.Makram Suidan ELECTROCHEMICAL REDUCTION OF 2,4,6 -TRINITROTOLUENE A thesis submitted to the Division of Research and Advanced Studies of the University of Cincinnati in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in the Department of Civil and Environmental Engineering of the college of Engineering 2002 by Dinesh Kumar Palaniswamy B.E., Civil Engineering, P.S.G College of Technology, Coimbatore, 1998 Committee Chair: Dr. George Sorial ABSTRACT 2,4,6-trinitrotoluene (TNT) is a major constituent of munitions contaminated wastewater. This research aims at studying the efficiency of electrochemical processes in reducing TNT. A laboratory scale reactor was designed and developed to electrochemically reduce TNT in simulated munition wastewater. Experiments simulating batch conditions were first conducted on the laboratory scale reactor to study the effect of various parameters including applied current, type of electrolyte and the molar concentration of the electrolyte in the feed solution on the reduction kinetics of TNT. The results showed that the reduction rates of TNT increased with an increase in applied current and molar concentration of electrolyte in feed. The rates of reduction leveled off at higher currents (250 & 300 mA). Mass transfer limitations were speculated for this flattening of rate constants at higher currents. Experimental studies were conducted with two types of electrolyte in the feed- sodium sulfate (Na2SO4) and lithium sulfate (Li2SO4), and the results indicated that there was no significant difference in the reduction rates for TNT. Based on the batch simulation experimental results, continuous flow experiments were conducted on the laboratory scale reactor using three different currents (150, 200, and 250 mA) and for two different concentrations of the electrolyte (6 and 9 mM). Sodium sulfite was used as electrolyte in the feed to maintain strict anoxic conditions in the reactor, thereby preventing the formation of solid dimers. An average TNT reduction efficiency between 82.5-85% was achieved for the three currents studied. A mole balance closure of 85-92% was achieved. 2,4,6-triaminotoluene (TAT) was observed as the only liquid phase intermediate. A 3-stage reactor in series was simulated and experimental studies were conducted to ascertain the combined reduction efficiency for TNT. The results showed that an overall reduction efficiency of over 99 % was achieved. Keywords: 2,4,6-trinitrotoluene (TNT), electrochemical reduction, munitions wastewater, laboratory scale reactor, 2,4,6-triaminotoluene (TAT), water treatment. ACKNOWLEDEGEMENTS I would like to thank my advisor, Dr. George Sorial for his constant guidance, support and valuable suggestions, without which this research effort would not have been possible. I would also like to thank Dr.Makram Suidan and Dr. Dionysios Dionysiou for serving on my committee and for their constant support and suggestions. I would also like to thank my past colleague and good friend, Rajesh Babu Doppalapudi for his encouragement, help and insights. I would also like to thank all the members of my research group for their help, suggestions and friendship. TABLE OF CONTENTS TABLE OF CONTENTS…………………………………………………………. i LIST OF FIGURES………………………………………………………………... iv LIST OF TABLES………………………………………………………………….vi 1. INTRODUCTION AND LITERATURE REVIEW………………………. 1 1.1 Introduction…………………………………………………………2 1.2 Literature Review…………………………………………………...3 1.2.1 Biological Treatment Processes…………………………….3 1.2.2 Physical/Chemical Treatment Processes……………………6 1.2.3 Electrochemical Treatment Processes………………………8 1.3 Objectives…………………………………………………………...11 1.4 References………………………………………………………… 13 2. ELECTROCHEMICAL REDUCTION OF 2,4,6-TRINITROTOLUENE - KINETIC STUDY………………………. 17 2.1 Abstract……………………………………………………………. 18 2.2 Introduction………………………………………………………... 19 2.2.1 Electrochemical Reduction………………………………… 19 2.2.2 Objectives…………………………………………………. 21 2.3 Materials and Methods……………………………………………. 22 2.3.1 Experimental Setup………………………………………... 22 2.3.2 Chemicals………………………………………………….. 23 i 2.3.3 Experimental Methods……………………………………...24 2.3.4 Monitored Parameters………………………………………25 2.3.5 Analytical Procedure………………………………………. 25 2.4 Results and Discussion…………………………………………….. 27 2.4.1 Reactions Mechanism……………………………………… 27 2.4.2 Batch Simulation Experiments…………………………….. 27 2.4.3 Intermediates and End Products…………………………….31 2.5 Conclusions…………………………………………………………33 2.6 References…………………………………………………………. 34 3. ELECTROCHEMICAL REDUCTION OF 2,4,6-TRINITROTOLUENE - CONTINUOUS FLOW STUDY………... 45 3.1 Abstract……………………………………………………………..46 3.2 Introduction…………………………………………………………47 3.2.1 Biological Treatment Processes…………………………….47 3.2.2 Physical/Chemical Treatment Processes……………………48 3.2.3 Electrochemical Treatment Processes………………………49 3.2.4 Objectives………………………………………………… 51 3.3 Materials and Methods……………………………………………...52 3.4 Results and Discussion…………………………………………….. 54 3.4.1 Performance of Reactor……………………………………. 54 3.4.2 Continuous Versus Batch Simulation……………………… 56 3.4.3 Electrochemical Reactors in Series…………………………57 ii 3.4.4 Intermediates and End Products…………………………….58 3.4.5 General Discussion………………………………………… 58 3.5 Conclusions…………………………………………………………61 3.6 References…………………………………………………………..62 4. RECOMMENDATIONS…………………………………………………...70 4.1 Recommendations…………………………………………………..71 4.2 References…………………………………………………………..73 APPENDIX…………………………………………………………………A1 Batch Simulation Experiments for Reduction of TNT…………….. A2 Continuous Flow Experiments with TNT…………………………..A30 III- Stage Reactor Study for Reduction of TNT…………………… A36 iii LIST OF FIGURES 2.1 Setup of the Laboratory Scale Electrochemical Reactor……………………36 2.2 Batch Simulation Experiments: TNT Reduction using 3.53 mM Na2SO4 as Electrolyte in Feed …………………………………...37 2.3 Batch Simulation Experiments: TNT Reduction using 3.53 mM Li2SO4 as Electrolyte in Feed. …………………………………..38 2.4 Batch Simulation Experiments: Comparison of Rate Constants versus Applied Current For 3.53 mM Li2SO4 and Na2SO4 as Electrolytes in Feed………………………………...39 2.5 Batch Simulation Experiments: TNT Reduction in the Absence of Electrolyte in Feed …………………………………………….40 2.6 Batch Simulation Experiments: TNT Reduction using 1.77 mM Na2SO4 as Electrolyte in Feed …………………………………..41 2.7 Batch Simulation Experiments: TNT Reduction using 6mMNa2SO4 as Electrolyte in Feed ……………………………………...42 2.8 Batch Simulation Experiments: TNT Reduction using 9mMNa2SO4 as Electrolyte in Feed. ……………………………………..43 2.9 Batch Simulation Experiments: Variation of Rate Constant with Applied Current for Different Molar Concentrations of Na2SO4 Electrolyte in Feed…………………………………………….…..44 3.1 Reactor Performance with Time in Continuous Flow Mode……………….66 iv 3.2 Batch Simulation Experiment: Variation of TNT Concentration with Time for 200 mA Applied Current and for 9 mM Electrolyte in Feed.…….67 3.3 Three Stage Electrochemical Reactor Performance for TNT Reduction…...68 3.4 Proposed Mechanism for Reduction of TNT……………………………….69 v LIST OF TABLES 3.1 Mole Balance of TNT for Continuous Flow Experiments………….………65 vi 1. INTRODUCTION AND LITERATURE REVIEW 1 1.1 Introduction Environmental contamination of soil, surface water and ground water by hazardous and toxic chemicals has a detrimental effect on human health and the natural ecosystem. Energetic compounds are substances containing molecules that undergo exothermic reactions at a very high rate and are primarily associated with munitions manufacturing and processing industry. Organic energetic compounds are found as contaminants in soils, sub surface and surface water at sites where these compounds were processed and produced. 2,4,6- trinitrotoluene (TNT) is a major constituent of organic energetic compounds that are found in munitions production wastewater. The United States Department of Defense (DOD) has identified more than 1000 sites with explosive contamination of which more than 95 % were contaminated with TNT and 87% exceeded permissible ground water levels (Walsh et al. 1993). TNT has three structural isomers: 2,3,5-TNT, 2,4,6-TNT and 2,4,5-TNT. The symmetrical isomer 2,4,6-TNT is the most commonly found form of the three. In this thesis, the acronym TNT refers to 2,4,6-Trinitrotoluene. TNT finds wide use as a high explosive because of its low melting point (80.1o C) stability and low sensitivity. It is produced by nitration of toluene to nitrotoluene, dinitrotoluene (DNT) and finally to TNT using a mixture of nitric and sulfuric acids (Palmer et al. 1996). TNT is used in bombs and explosives, in a binary mixture with a primary explosive to trigger the detonation. TNT is reported to be toxic to both humans and animals. TNT may be absorbed through the skin and mutation data had been reported. The orl-rat LD 50 value for TNT is 795 mg/kg (Sax and Lewis 1989). The United States Environmental Protection Agency 2 (USEPA) has set a drinking water limit of 20 µg/L as the life time exposure limit for TNT (EPA 1989). Munitions wastewater is mainly of two types: red water and pink water. The process water resulting from purifying operation of the crude TNT is called “Red Water” and is a major environmental problem associated with TNT manufacturing processes. Another

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