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MINISTRY OF EDUCATION MINISTRY OF NATIONAL TRAINING DEFENCE ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY TRAN VAN CONG RESEARCHING HIGH VOLTAGE ELECTROCHEMICAL ENGINEERING OF APPLIED ELECTRODIC PLASMA GENERATION FOR DECOMPOSITION OF 2,4-DICHLOROPHENOXYACETIC ACID AND 2,4,5-TRICHLOROPHENOXYACETIC ACID IN WATER ENVIRONMENT Specialization : Chemical engineering Code : 52 03 01 SUMMARY OF DOCTORAL THESIS IN CHEMICAL ENGINEERING Ha Noi - 2022 THE SCIENTIFIC RESEARCH WAS COMPLETED AT ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY, MINISTRY OF NATIONAL DEFENCE Scientific supervisors: Prof.Dr.Sci Nguyen Duc Hung Dr Nguyen Van Hoang Reviewer 1: Reviewer 2: Reviewer 3: Thesis is defended at the doctoral evaluating Council at Institute level, held at the Academy of Military Science and Technology at :…hour…minute, day…month…year 2022 Thesis can be found at: - Library of Academy of Military Science and Technology - Vietnam National Library INTRODUCTION Necessity of the thesis Toxic compounds of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) are decomposed of agent orange dioxin residues in Vietnam In addition, in agriculture, the use of 2,4-D chemicals to kill weeds for a long time also causes serious environmental pollution that need to treat Direct current high voltage electrochemical engineering to create plasma is one of the high effective treatment methods for aromatic ring compounds contain chlorine atom that difficult to decompose and cause polluted environment Therefore, PhD student selected the subject "Researching high-voltage electrochemical engineering of applied electrodic plasma generation for decomposition of 2,4-dichlorophenoxy acetic acid and 2,4,5-trichlorophenoxyacetic acid in water environment” to address the pollutted problem that mentioned above Research objectives Researching on using electrode plasma engineering to treat 2,4-D, 2,4,5-T contaminant compounds in water environment The polluted substances after treatment are completely decomposed Subjects and scope of the thesis Thesis studies the use of direct current high voltage electrochemical engineering in the voltage range from to 20 kV to perform an electrochemical reaction to create a gaseous environment on the electrode for the plasma formation process with the aim to decompose polluted compounds 2,4-D, 2,4,5-T in water environment Research content Investigating the factors affecting the plasma appearance on the electrode and the formation of active agents Investigating the factors affecting the decomposition efficiency, kinetics, mechanism, intermediate compounds of decomposition process Investigating treatment efficiency through environmental index such as COD, TOC Assessment of environmental criteria after treatment Research methods Thesis uses the theoretical method overview combined with experiment to conduct the research content Scientific and practical significance of the thesis Thesis results clarify the factors affecting the formation of plasma in water environment and ability to form active agent Evaluation of the treatment efficiency of 2,4-D, 2,4,5-T by electrochemical plasma engineering and applicability in practice Thesis layout The content of the thesis is presented in the regulation structure including: Introduction; Chapter Overview; Chapter Research subjects and methods; Chapter Results and discussion; Conclusion; References; Appendix, as follows: Introduction: Outline of 2,4-D and 2,4,5-T pollutants, the necessity in researching the use of electrochemical plasma engineering to treat pollutants Chapter 1: Overview Introduction feature of electrochemical plasma and some treatmental techniques of 2,4-D, 2,4,5-T, application of cold plasma technology to treat pollutants in Vietnam and the world Chapter 2: Research subjects and methods Research subjects are the factors affecting the plasma formation and the decomposition efficiency of 2,4-D, 2,4,5-T Research method is based on experiment, analysis, evaluation and conclusions with the decomposition of 2,4-D, 2,4,5-T compounds Chapter 3: Results and discussion Identifying some results as factors affecting plasma formation, active agents, decomposition efficiency, studying kinetics and mechanism of decomposition process of 2,4-D, 2,4,5-T Chapter OVERVIEW 1.1 Overview of plasma x Formation of plasma Matter exists mainly in three forms, solid, liquid and gases In the gaseous state, if energy is continued to be supplied, the collision between particles in the gases is so strong that they break into pieces, creating charged particles which are ions and electrons or the plasma state The expanded plasma concept considers plasma including particles such as electrons and ions and neutral particles such as atoms and molecules as well as free radicals and photons x Classification of plasma Plasma can be classified according to temperature into two types: thermal plasma and cold plasma or classification based on physicalchemical properties into plasma chemistry or plasma physics 1.2 Electrochemical plasma x Electrochemical plasma generation engineering Electrochemical plasma is formed in the solution at high voltage, the electrolysis process generates H2, O2, continues providing energy enough strong to form plasma state that generates OHx free radicals, H2O2 and particles nano x Formation of active agents in electrochemical plasma OH• free radical is formed through several mechanisms: Dissociation: H2O + e- Hx + OHx + eIonization: H2O + e- H2O+ + 2eH2O+ + H2O2 H3O+ + OHx The emission of UV rays when plasma occurs also contributes to the breaking of O-O bonds leading to the formation of OH• free radical: H2O2 + hv 2OHx H2O2 is one of the oxidizing agents that generate during plasma formation process in solution according to the following reactions: OHx + OHx H2O2 2H2O H2O2 + H2 Electrochemical reactions such as electrode corrosion, metal ion reduction to nanoparticles occur according to the following reaction: Me Men+ Men+ + (n/2)H2 Meo(nano) + nH+ x Catalysis of OHx free radical generation in electrochemical plasma Gaseous catalysis: Oxygen gases bubbling in the plasma combined with electron creating superoxide free radical (xO2-) leading to the formation of H2O2 and OHx free radical according to reaction mechanism: e- + O2 xO22 xO2- + 2H+ H2O2 + O2 H2O2 + e- + H+ OHx + H2O Metal catalysis: OH• free radical is formed in the presence of Fe2+ ion in solution via the Fenton reaction: Fe2+ + H2O2 OHx + OH- + Fe3+ Fe3+ + H2O2 H+ + Fe2+ + HOx2 The zero-valent iron nanoparticles catalyze for the formation of OH• free radicals according to the reaction: Fe0 + O2 +2H+ Ѝ Fe2+ + H2O2 Fe0 + H2O2 +2H+ Ѝ Fe2+ + 2H2O Fe2+ + H2O2 Ѝ Fe3+ + OHx + OHx 2,4-D, 2,4,5-T pollution in Vietnam Toxic acid 2,4-D, 2,4,5-T are a decomposition component of agent orange dioxin that is still present at some airports and 2,4-D is also commonly used causing pollutant the environment and ecosystem, so this substance is currently banned use according to decision 278 of Ministry of agriculture and rural development Chapter RESEARCH SUBJECTS AND METHODS 2.1 Research subjects Research subjects include: factors affecting plasma formation, efficiency, mechanism, kinetics of 2,4-D, 2,4,5-T decomposition process Investigate of pollution index such as COD, TOC, TDS, Cl-, pH 2.2 Electrochemical plasma generator x High voltage direct current power supply High voltage direct current power from to 20 kV, P = 15kVA x Structure of reaction vessel and electrode Reaction vessel is made of heat resistant glass, including double layer The inner layer contains the reaction solution, the outer layer is circulating water through the thermostatic bath Metal anode and cathode electrodes are made of cylindrical shape, wrapping around with epoxy to create an electrode area in contact with the solution Figure 2.4 Diagram of electrochemical plasma generation process treating 2,4-D, 2,4,5-T 2.3.Chemicals for research 2,4-D, 2,4,5-T acid, Sigma Aldrich and other necessary chemicals 2.4.Research methods Researching the factors affecting the decomposition process of 2,4-D, 2,4,5-T are evaluated through the decomposition efficiency with the formula: Decomposition efficiency: H(%) = C0 C t u100% C0 Where as: H(%) : decomposition efficiency after t minutes ; C0: initial concentration, mg/L; Ct: concentration at time t, mg/L 2.5.Analytical equipment and methods Analyzing 2,4-D, 2,4,5-T by HPLC 1100, Agilent Analyzing degradation products by GC-MS 6890-5975, Agilent Analyzing H2O2, OHx free radical by UV-Vis, UH 5300, Hitachi Analyzing of particle size, Zeta potential by SZ-100, Horiba Analyzing of particle size, Zeta potential by SZ-100, Horiba Analyzing metal by ICP-MS 7800/7850, Agilent Analyzing total organic carbon in solution by TOC-5000A, Shimadzu Measure electrical conductivity by HI 8733 instrument, Hanna Measure pH value by HI 8314 instrument, Hanna Chapter RESULTS AND DISCUSSION 3.1 Factors affecting plasma formation on electrode Researching plasma appearance conditions showed that the plasma appearance depends on factors such as voltage (Figure 3.2), distance between two electrodes (Figure 3.3), electrical conductivity (Figure 3.4.) , solution temperature (Figure 3.5), electrode size and pH value (Table 3.2) 120 15 kV-Cu 15 kV-Fe 15 kV-W 10 kV-Cu 10 kV-Fe 10 kV-W kV-Cu kV-Fe kV-W 100 Plasma appearance I(m A) 80 60 40 20 0 20 40 60 80 100 120 Time (min) Figure 3.2 Plasma appearance on copper, iron and tungsten electrodes depends on the voltage at T= 30 oC, h = 200 mm, pH = 7, EC = 1.4 µS/cm 110 200 200 200 220 220 220 230 230 230 300 300 300 100 90 Plasma appearance 80 I(m A) 70 60 50 40 30 mm-Cu mm-Fe mm-W mm-Cu mm-Fe mm-W mm-Cu mm-Fe mm-W mm-Cu mm-Fe mm-W 20 10 0 20 40 60 80 100 120 Time (min) Figure 3.3 Appearance plasma on copper, iron, and tungsten electrodes depends on the electrode distance at T=30 oC, V=15 kV, pH=7, EC=1.4 µS/cm 160 20 µS-Cu 20 µS-Fe 20 µS-W 30 µS-Cu 30 µS-Fe 30 µS-W 50 µS-Cu 50 µS-Fe 50 µS-W 100 µS-Cu 100 µS-Fe 100 µS-W 150 µS-Cu 150 µS-Fe 150 µS-W Plasma xuҩt hiӋn 140 I (m A) 120 100 80 60 40 20 50 100 150 200 250 300 t (giây) Figure 3.4 Appearance plasma on copper, iron and tungsten electrodes depends on the electrical conductivity at T=30 oC, V=15 kV, pH=7, h=200 mm 250 20 20 20 30 30 30 40 40 40 50 50 50 Plasma appearance 200 I(m A) 150 100 50 o C C C o C o C o C o C o C o C o C o C o C o o Cu Fe W Cu Fe W Cu Fe W Cu Fe W 0 20 40 60 80 100 120 Time (min) Figure 3.5 Appearance plasma on copper, iron and tungsten electrodes depends on the solution temperature at V=15 kV, pH=7, h=200 mm, EC=1.4 µS/cm Table 3.2 Influence of factors on plasma appearance EC U(kV)T( C) h(mm) pH Ø (mm) (µS/cm) o 30 200 1,4 10 30 200 1,4 15 30 200 1,4 15 30 220 1,4 15 30 230 1,4 15 30 300 1,4 15 30 200 20 15 30 200 30 15 30 200 50 15 30 200 100 15 30 200 150 15 20 200 1,4 15 40 200 1,4 15 50 200 1,4 15 30 200 120 15 30 200 69 15 30 200 52 15 30 200 40 15 30 200 60 15 30 200 10 110 15 30 200 11 150 15 30 200 1,4 (-): Plasma not appearance,
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