Kinetics and mechanism of oxidation of tetrachloroethylene with permanganate

The kinetics, reaction pathways and product distribution of oxidation of tetrachloroethylene (PCE) by potassium permanganate (KMnO4) were studied in phosphate-buffered solutions under constant pH, isothermal, completely mixed and zero headspace conditions. Experimental results indicate that the reaction is first-order with respect to both PCE and KMnO4 and has an activation energy of 9.3+/-0.9 kcal/mol. The second-order rate constant at 20 degrees C is 0.035+/-0.004 M(-1) s(-1), and is independent of pH and ionic strength (I) over a range of pH 3-10 and I approximately 0-0.2 M, respectively. The PCE-KMnO4 reaction may proceed through further oxidation and/or hydrolysis reaction pathways, greatly influenced by the acidity of the solution, to yield CO2(g), oxalic acid, formic acid and glycolic acid. Under acidic conditions (e.g., pH 3), the further oxidation pathway will dominate and PCE tends to be directly mineralized into CO2 and chloride. Under neutral (e.g., pH 7) and alkaline conditions (e.g., pH 10), the hydroxylation pathway dominates the reaction and PCE is primarily transformed into oxalic acid prior to complete PCE mineralization. Moreover, all chlorine atoms in PCE are rapidly liberated during the reaction and the rate of chloride production is very close to the rate of PCE degradation.     

Secondary organic aerosol production from aqueous photooxidation of glycolaldehyde: Laboratory experiments

Organic particulate matter (PM) formed in the atmosphere (secondary organic aerosol; SOA) is a substantial yet poorly understood contributor to atmospheric PM. Aqueous photooxidation in clouds, fogs and aerosols is a newly recognized SOA formation pathway. This study investigates the potential for aqueous glycolaldehyde oxidation to produce low volatility products that contribute SOA mass. To our knowledge, this is the first confirmation that aqueous oxidation of glycolaldehyde via the hydroxyl radical forms glyoxal and glycolic acid, as previously assumed. Subsequent reactions form formic acid, glyoxylic acid, and oxalic acid as expected. Unexpected products include malonic acid, succinic acid, and higher molecular weight compounds, including oligomers. Due to (1) the large source strength of glycolaldehyde from precursors such as isoprene and ethene, (2) its water solubility, and (3) the aqueous formation of low volatility products (organic acids and oligomers), we predict that aqueous photooxidation of glycolaldehyde and other aldehydes in cloud, fog, and aerosol water is an important source of SOA and that incorporation of this SOA formation pathway in chemical transport models will help explain the current under-prediction of organic PM concentrations.     

Degradation of anti-inflammatory drug ketoprofen by electro-oxidation: comparison of electro-Fenton and anodic oxidation processes

The electrochemical degradation of the nonsteroidal anti-inflammatory drug ketoprofen in tap water has been studied using electro-Fenton (EF) and anodic oxidation (AO) processes with platinium (Pt) and boron-doped diamond (BDD) anodes and carbon felt cathode. Fast degradation of the parent drug molecule and its degradation intermediates leading to complete mineralization was achieved by BDD/carbon felt, Pt/carbon felt, and AO with BDD anode. The obtained results showed that oxidative degradation rate of ketoprofen and mineralization of its aqueous solution increased by increasing applied current. Degradation kinetics fitted well to a pseudo-first-order reaction. Absolute rate constant of the oxidation of ketoprofen by electrochemically generated hydroxyl radicals was determined to be (2.8?±?0.1)?×?10⁹ M^?1 s^?1 by using competition kinetic method. Several reaction intermediates such as 3-hydroxybenzoic acid, pyrogallol, catechol, benzophenone, benzoic acid, and hydroquinone were identified by high-performance liquid chromatography (HPLC) analyses. The formation, identification, and evolution of short-chain aliphatic carboxylic acids like formic, acetic, oxalic, glycolic, and glyoxylic acids were monitored with ion exclusion chromatography. Based on the identified aromatic/cyclic intermediates and carboxylic acids as end products before mineralization, a plausible mineralization pathway was proposed. The evolution of the toxicity during treatments was also monitored using Microtox method, showing a faster detoxification with higher applied current values.     

Kinetic study of the removal of dimethyl phthalate from an aqueous solution using an anion exchange resin

Phthalate acid esters are becoming an important class of pollutants in wastewaters. This study addresses the kinetics of removal of dimethyl phthalate (DMP) using the anion exchange resin D201-OH from an aqueous solution. The effects of various factors on the removal rate and efficiency were investigated. An overall initial removal rate (OIRR) law and a pseudo first-order kinetic (PFOK) model were also developed. The internal diffusion of DMP within the resin phase of D201-OH is the rate-controlling step. Optimization of the particle size and pore structure of the resin D201-OH, the DMP concentration, and the reaction temperature can improve the DMP removal rate. The hydrolysis reaction of DMP catalyzed by D201-OH indicates an overall reaction order of 1.76, a value that is between the first order and the second order. The apparent activation energy of the reaction is 34.6 kJ/mol, which is below the homogeneous alkaline hydrolysis activation energy of 44.3 kJ/mol. The OIRR law can quantify the initial removal rate under different conditions. The results also show that the theoretical DMP removal efficiency predicted by the PFOK model agrees well with the experimentally determined values. Our research provides valuable insights into the primary parameters influencing the kinetic process, which enables a focused improvement in the removal or hydrolysis rate for similar processes.     

丙烯酸废水超临界水氧化动力学研究

用H2O2作为氧化剂,对丙烯酸生产废水进行超临界水氧化研究.得到了反应速率方程表达式.COD、H2O2和水的反应级数分别为1、0和0,指前因子A为4.97 s-1,反应活化能Ea为20.64 kJ/mol,诱导时间为8 s左右.     

Atmospheric oxalic acid and SOA production from glyoxal: Results of aqueous photooxidation experiments

Aqueous-phase photooxidation of glyoxal, a ubiquitous water-soluble gas-phase oxidation product of many compounds, is a potentially important global and regional source of oxalic acid and secondary organic aerosol (SOA). Reaction kinetics and product analysis are needed to validate and refine current aqueous-phase mechanisms to facilitate prediction of in-cloud oxalic acid and SOA formation from glyoxal. In this work, aqueous-phase photochemical reactions of glyoxal and hydrogen peroxide were conducted at pH values typical of clouds and fogs (i.e., pH=4–5). Experimental time series concentrations were compared to values obtained using a published kinetic model and reaction rate constants from the literature. Experimental results demonstrate the formation of oxalic acid, as predicted by the published aqueous phase mechanism. However, the published mechanism did not reproduce the glyoxylic and oxalic acid concentration dynamics. Formic acid and larger multifunctional compounds, which were not previously predicted, were also formed. An expanded aqueous-phase oxidation mechanism for glyoxal is proposed that reasonably explains the concentration dynamics of formic and oxalic acids and includes larger multifunctional compounds. The coefficient of determination for oxalic acid prediction was improved from 0.001 to >0.8 using the expanded mechanism. The model predicts that less than 1% of oxalic acid is formed through the glyoxylic acid pathway. This work supports the hypothesis that SOA forms through cloud processing of glyoxal and other water-soluble products of alkenes and aromatics of anthropogenic, biogenic and marine origin and provides reaction kinetics needed for oxalic acid prediction.     

Haloacetic acid removal by sequential zero-valent iron reduction and biologically active carbon degradation

An innovative haloacetic acid (HAA) removal process was developed. The process consisted of a zero-valent iron (Fe⁰) column followed by a biologically active carbon (BAC) column that were efficient in degrading tri- and di-HAAs, and mono- and di-HAAs, respectively. The merit of the process was demonstrated by its performance in removing trichloroacetic acid (TCAA). An empty bed contact time of 10 min achieved nearly complete removal of 1.2 μM TCAA and its subsequent products, dichloroacetic acid (DCAA) and monochloroacetic acid (MCAA). HAA removal was a result of chemical dehalogenation and biodegradation rather than physical adsorption. Preliminary kinetic analyses were conducted and the pseudo-first-order rate constants were estimated at ambient conditions for Fe⁰ reduction of TCAA and biodegradation of DCAA and MCAA by BAC. This innovative process is highly promising in removing HAAs from drinking water, swimming pool water, and domestic or industrial wastewater.     

Electrochemical dechlorination of chloroacetic acids (CAAs) using hemoglobin-loaded carbon nanotube electrode

Hemoglobin (Hb) was immobilized on carbon nanotube (CNT) electrode to catalyze the dechlorination of chloroacetic acids (CAAs), and the electrocatalytic behaviors of the Hb-loaded electrode for the dechlorination of trichloroacetic acid (TCAA) were studied by cyclic voltammetry and constant-potential electrolysis technique. An Hb-loaded packed-bed flow reactor was also constructed for bioelectrocatalytic dechloriantion of CAAs from drinking water. The results showed that the reduced heme of Hb immobilized on CNT electrode was easily regenerated, and Hb exhibited a stable and high activity for reductive dechlorination of CAAs with significant lowering of overpotential. TCAA could be reduced at -0.450 V (vs. saturated calomel electrode (SCE)) with catalysis of Hb-loaded electrode and its dechlorination was stepwise, following the pathway of TCAA-->dichloroacetic acid (DCAA)-->monochloroacetic acid (MCAA)-->acetic acid. It was also found that all CAAs, e.g., TCAA, DCAA and MCAA, could be dechlorinated completely at -0.450 V. The removal of 30.0 mM TCAA and DCAA is ca. 40% and 31%, respectively, with electrolysis for 100 min at -0.600 V (vs. SCE) using the Hb-loaded packed-bed flow reactor. The dechlorination activities of CAAs follow the decreasing order: TCAA>DCAA>MCAA, and the average current efficiency is over 90%.     

Gas phase naphthalene chlorination

Chlorination of naphthalene by Cl atoms has been studied in the gas phase. The chlorinating agent was produced by γ-radiolysis of tetrachloromethane. At low conversions only monosubstituted products are observed. Both isomers are formed, the yield of 1-chloronaphthalene exceeding that one of its isomer. The extent of the addition reaction increases with the temperature. The relative Arrhenius plot of observed rate constants is linear over the temperature range investigated (60–120 °C) and its slope corresponds to a difference of 11.0 kJ/mol between the activation energies of 2-chloronaphthalene and 1-chloronaphthalene.     

Oxidation of industrial dyeing wastewater by supercritical water oxidation in transpiring-wall reactor.

Industrial dyeing wastewater was oxidized in supercritical water in a transpiring-wall reactor, using hydrogen peroxide as an oxidant. Experiments were performed at 595 to 704 K and 18 to 30 MPa, with an oxidant dosage ratio ranging from 0.6 to 2.0. A chemical oxygen demand (COD) removal of more than 98.4% was achieved at 704 K and 28 MPa, with a retention time less than 35 seconds, which increased with the temperature, pressure, and oxidant. A modified first-order rate expression was regressed from experimental data, taking into account the influence of induction time. The resulting pre-exponential factor, A, and activation energy, Ea, were 1.07 seconds(-1) and 12.12 kJ x mol(-1), respectively, while the reaction order for feed wastewater (based on COD) and oxidant were assumed to be 1 and 0, respectively. Gas chromatography/mass spectrometry analysis for effluents indicated that carbon dioxide, carbon monoxide, and nitrogen were the main reaction products, and phenol; benzenecarboxylic acid; 1, 2-benzenedicarboxylic acid; and isoquinoline were detected as intermediates.     

Pyrolysis kinetics and residue characteristics of petrochemical industrial sludge

This study investigated the pyrolysis characteristics of sludge from wastewater treatment plants in the petrochemical industry and focused on the pyrolysis kinetics, elemental composition of residue, and volatile organic compounds (VOCs) of exhaust gas. As pyrolysis temperature increased to 773 K, the increasing rate of crude oil production tended to a stable condition. The result indicated that the optimal temperature of crude oil and water mixed production was 773 K. When pyrolysis temperature increased from 673 to 973 K, carbon, oxygen, nitrogen, and hydrogen concentrations of residue decreased and the sulfur concentration of residue increased. The concentrations of benzene, toluene,ethylbenzene, and styrene increased by the increasing pyrolysis temperature. We found that the reaction order of sludge pyrolysis was 2.5 and the activation energy of the reaction was 11.06 kJ/mol. We believe that our pyrolysis system is transitional between devolatilization and combustion.     

Mild hydrolysis of 2-trifluoromethylphenol: kinetics, mechanism and environmental relevance

2-Trifluoromethylphenol was hydrolysed in a phosphate buffer at neutral pH. At mild temperatures ranging from 34 degrees C to 69 degrees C this compound liberates consecutively fluorine anions to form salicylic acid. This process is energetically driven by the hydration of the fluorine anions. No intermediates have been detected by HPLC and (19)F-NMR and this was confirmed by computer calculations which favor the first step in the whole reaction sequence being rate-limiting. Accordingly, the reaction energy of the first dehalogenation of the trifluoromethyl anion is 28.4 kcal mol(-1) higher than for the second dehalogenation. The pseudo-first-order kinetic was determined and from an Arrhenius diagram an activation energy of E(a)=25.1 kcal mol(-1) has been estimated. At 37 degrees C and a pH of 7.4 the half-life was 6.9 h. The rate of hydrolysis was favored at higher pH and it was not influenced by oxygen, sunlight or trace elements found in natural water. The latter was shown by incubations with lake water instead of distilled water.     

Evaluation of photolysis and hydrolysis of atrazine and its first degradation products in the presence of humic acids

Relative importance of hydrolysis and photolysis of atrazine and its degradation products in aqueous solutions with dissolved humic acids (HA) has been assessed under exposure to sunlight and under UV irradiation. Quantum yield for direct photolysis of atrazine at 254 nm was 0.037 mol photon(-1), the reaction order was 0.8. Atrazine, desethylatrazine and desisopropylatrazine converted to their 2-hydroxy analogs with rate constants 0.02-0.08 min(-1) in clear solutions, while addition of HA (300 mg L(-1)) caused a 10-fold increase in rate constants. Hydroxyatrazine was not degraded. No evidence of photo-Fenton reaction was found. Under exposure to solar light, atrazine, desethylatrazine and desisopropylatrazine were converted to 2-hydroxy analogs only at pH 2 because of acid hydrolysis and possible contribution of photolysis. At lower HA concentration, only their light-shielding effect was noticed, while at higher concentrations, HA-catalysed hydrolysis prevailed. Hydroxyatrazine concentration diminished at all pH values in solutions without HA exposed to sunlight.     

DFT M06-2X investigation of alkaline hydrolysis of nitroaromatic compounds

The nitroaromatic compounds 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT) and 2,4-dinitroanisole (DNAN) are potential environmental contaminants and their transformations under a variety of environmental conditions are consequently of great interest. One possible method to safely degrade these nitrocompounds is alkaline hydrolysis. A mechanism of the initial stages of this reaction was investigated computationally. Simulations of UV-VIS and NMR spectra for this mechanism were also produced. The results obtained were compared to available experimental data on the alkaline hydrolysis of TNT and suggest that the formation of Meisenheimer complexes and an anion of TNT are potential first-step intermediates in the reaction path. As the reaction proceeds, computational results indicate that polynegative complexes dominate the degradation pathway, followed by cycles of carbon chain opening and breaking. A second possible pathway was identified that leads to polymeric products through Janovsky complex formation. Results from this study indicate that the order of increasing resistance to alkaline hydrolysis is TNT, DNT and DNAN.     

污水中溶解游离氨基酸和结合氨基酸测定方法研究

采用邻苯二甲醛作为柱前衍生化试剂，结合反相高效液相色谱，对污水中溶解游离氨基酸（dissolvedfreeami．nOacid，DFAA）进行定性和定量分析，探讨了污水样品有无前处理对DFAA分析的影响，并采用气相酸水解方法对污水中总溶解氨基酸（dissolvedtotalaminoacid，DTAA）进行了分析。结果表明，污水经过pH调节和N，流清洗后，可以明显去除氨和挥发性胺的干扰，色谱峰更加清晰；前处理后的水样经RP—HPLC分析，能够快速检测出14种氨基酸，各氨基酸在一定线性范围内呈现良好的线性关系，相应的线性相关系数（R^2）均大于0．99，加标回收率为92％～102％。污水处理厂进水和出水中氨基酸主要以溶解结合氨基酸（dissolvedcombinedaminoacid，DCAA）为主，与进水相比，出水中DFAA含量减少了0．22μmol／L，DTAA由5．68μmol／L降至3．08μmol／L。     

Bioavailability and mass balance studies of a commercial pentabromodiphenyl ether mixture in male Sprague-Dawley rats

Cyanogenic glycosides are common plant toxins. Toxic hydrogen cyanide originating from cyanogenic glycosides may affect soil processes and water quality. In this study, hydrolysis, degradation and sorption of dhurrin (4-hydroxymandelonitrile-beta-d-glucoside) produced by sorghum has been studied in order to assess its fate in soil. The log K(ow) of dhurrin was -1.18+/-0.08 (22 degrees C). Hydrolysis was a first-order reaction with respect to dhurrin and hydroxyl ion concentrations. Half lives ranged from 1.2h (pH 8.6; 25 degrees C) to 530d (pH 4; 25 degrees C). The activation energy of hydrolysis was 112+9kJ. At pH 5.8 and room temperature, addition of humic acids (50gl(-1)) increased the rate of hydrolysis tenfold, while addition of kaolinite or goethite (100-250gl(-1)) both decreased the rate considerably. No significant sorption to soil components could be observed. The degradation rates of dhurrin in top and subsoils of Oxisols, Ultisols, Alfisols and Mollisols were studied at 22 degrees C (25mgl(-1), soil:liquid 1:1 (w:V), pH 3.8-8.1). Half-lives were 0.25-2h for topsoils, and 5-288h in subsoils. Hydrolysis in solution explained up to 45% of the degradation in subsoils whereas the contribution in topsoils was less than 14%, indicating the importance of enzymatic degradation processes. The highest risk of dhurrin leaching will take place when the soil is a low activity acid shallow soil with low content of clay minerals, iron oxides and humic acids.     

Pyrolysis Kinetics and Residue Characteristics of Petrochemical Industrial Sludge

ABSTRACT

This study investigated the pyrolysis characteristics of sludge from wastewater treatment plants in the petrochemical industry and focused on the pyrolysis kinetics, elemental composition of residue, and volatile organic compounds (VOCs) of exhaust gas. As pyrolysis temperature increased to 773 K, the increasing rate of crude oil production tended to a stable condition. The result indicated that the optimal temperature of crude oil and water mixed production was 773 K. When pyrolysis temperature increased from 673 to 973 K, carbon, oxygen, nitrogen, and hydrogen concentrations of residue decreased and the sulfur concentration of residue increased. The concentrations of benzene, toluene, ethylbenzene, and styrene increased by the increasing pyrolysis temperature. We found that the reaction order of sludge pyrolysis was 2.5 and the activation energy of the reaction was 11.06 kJ/mol. We believe that our pyrolysis system is transitional between devolatilization and combustion.     

废铅酸蓄电池铅膏柠檬酸浸出动力学研究

通过研究废铅酸蓄电池铅膏柠檬酸-柠檬酸钠浸出过程中PbSO4转化率随时间变化,考查了物料粒度、搅拌速度和浸出温度对转化率的影响,建立了反应的动力学方程,并计算了浸出反应表观活化能。结果表明,减小物料粒度、提高浸出温度和适当提高搅拌速度,均可提高硫酸铅转化率。浸出反应表观活化能为67.82 kJ/mol,浸出反应受化学反应步骤控制。     

卡马西平降解菌的筛选分离及其降解机理

药品污染物日益成为新兴污染物研究的重点,药品卡马西平因具有多种药效被广泛使用,在环境中频繁被检出,且浓度较高,不易去除,通常作为环境中药品污染状况的指示化合物。本研究从长期用于去除药品废水的曝气生物滤池中分离出一株细菌YK-6,其能以卡马西平为惟一碳源、氮源和能源生长,通过生理生化以及16S rDNA基因序列分析鉴定并命名为Pseudomonas putida YK-6。该菌株YK-6在pH为7.2、温度30℃、卡马西平初始浓度为20 mg/L、摇床振荡速率为160 r/min的生长条件下培养5 d,对卡马西平的降解率可达54.66%。菌株YK-6对卡马西平的可能降解途径为首先通过生物的氧化作用,将CBZ氧化成CBZ-EP,CBZ-EP经过水解作用转化为CBZ-DiOH,CBZ-DiOH经丙酮酸氧化脱羧及在NADH还原性辅酶的作用下,裂解成苯胺和邻苯甲酸,苯胺和邻苯甲酸再经进一步氧化,直至最终矿化。     

超声波光催化协同降解对甲基苯磺酸水溶液的机理研究

采用超声波与光催化联合法对模拟废水中难生物降解的对甲基苯磺酸(4-TSA)进行降解实验研究,借助紫外光谱、红外光谱、质谱、气相色谱、高效液相色谱、化学需氧量和总有机碳的检测结果对反应机理进行了初步探讨.实验结果表明:超声波和光催化之间存在着协同效应;当溶液初始质量浓度30 mg/L,光催化剂TiO2投加量为100 mg...