Oxidation Of Monochlorobenzene Research Articles

Cysteine enhanced degradation of monochlorobenzene in groundwater by ferrous iron/persulfate process: Impacts of matrix species and toxicity evaluation in ISCO

Monochlorobenzene (MCB), a solvent and synthetic intermediate, has been widely detected in groundwater at industrial contaminated sites. Cysteine (Cys) enhanced Fe2+/persulfate (Fe2+/Cys/PS) process with high degradation efficiency of organic pollutants has the potential for in-situ chemical oxidation of MCB. In this study, we systematically explored the impacts of common anions (CO32−, HCO3−, SO42−, NO3−, NO2−, PO43−, HPO42−, H2PO4−, Cl−, Br−), cations (NH4+, Mg2+, Al3+, Mn2+, Cu2+) and natural organic matter (NOM) on the degradation kinetics of MCB by the novel Fe2+/Cys/PS process and evaluated the ecotoxicity. The results showed that the removal of MCB in absence of matrices was enhanced by Cys due to its reduction and complexation ability. All of the anions inhibited the MCB degradation through the scavenging of SO4•− and HO•, though the inhibition degree of SO42−and NO3− was slight. Cations such as NH4+, Mg2+ and Al3+ hardly interfered with the reaction. Low concentrations of Cu2+ and NOM promoted the MCB oxidation, but the promotion strength weakened and turned into inhibition with the increased concentration of Cu2+ and NOM. The toxicity assessment of the transformation products (TPs) in the presence of Cl− and Br− based on the quantitative structure-activity relationships model showed the potentially higher toxicity of some TPs than their parent MCB. These results indicate that groundwater matrices may interfere with the MCB oxidation process. To accurately evaluate the effects of groundwater matrices on Fe2+/Cys/PS process for MCB oxidation and its potential toxicity, the field tests should be carried out in the future.

Synthesis of W-Nb-O solid acid for catalytic combustion of low-concentration monochlorobenzene

WO3-Nb2O5 mixed oxides were prepared by citric acid based sol-gel method, and were tested for catalytic combustion of 1000 ppmv monochlorobenzene (MCB), as a typical chlorinated aromatic hydrocarbon in air pollution. Research results for the structure-function relationship revealed that the physicochemical properties of WO3-Nb2O5 were notably promoted than single component metal oxide, due to the strong electron interaction between W, Nb and O elements, which were confirmed by the techniques of H2-TPR, positron lifetime spectra and XPS characterization. WO3-Nb2O5 were amorphous, in which W and Nb elements were homogeneous dispersed. The functionalized materials contributed to the improvement of adsorption, activation, cracking and deep oxidation of MCB on the catalyst surface, and only non-negligible production of CO byproduct was detected. Both the acid property and oxidative property played important roles in the catalytic degradation process, and their cooperative catalytic effect could be optimized by the catalyst composition and preparation process. 2W1Nb (W/Nb = 2:1, molar ratio) displayed the largest acid amount and the best redox property, and thus it displayed the highest catalytic degradation performance, and 50% conversion of MCB was achieved at 280 °C with the GHSV of 9000 mL gcat−1 h−1. Besides, in the 120 h continuous reaction, only slight decrease (from 91% to 86%) for the catalytic activity of 2W1Nb was observed in initial 7 h, showing that it was desired towards the demanding conditions (such as resistance to water adsorption, chlorine poison and carbon deposition). Moreover, the WO3-Nb2O5 materials also satisfied the environment-friendly and low-cost needs for environmental catalysis, which could be a promising alternative for traditional V2O5-WO3/TiO2 catalyst system.

Hydrochemistry indicating groundwater contamination and the potential fate of chlorohydrocarbons in combined polluted groundwater: a case study at a contamination site in North China.

Groundwater contamination characteristics and the potential fate of chlorohydrocarbons were investigated at a combined polluted groundwater site in North China. Groundwater chemistry and (2)D and (18)O isotope compositions indicated that high salination of groundwater was related with chemical pollution. The elevated salinity plume was consistent with the domain where typical chlorohydrocarbon contaminants occurred. The concentrations of heavy metals, oxidation-reduction potential, and pH in organic polluted areas significantly differed from those in peripheral (background) areas, indicating modified hydrochemistry possibly resulting from organic pollution. Under the presented redox conditions of groundwater, monochlorobenzene oxidation may have occurred when the trichlorohydrocarbons underwent reductive dechlorination. These findings suggested that inorganic hydrochemistry effectively indicated the occurrence of chemical contamination in groundwater and the potential fate of chlorohydrocarbons.

Heterogeneous Fenton-like oxidation of monochlorobenzene using green synthesis of iron nanoparticles

Iron nanoparticles (Fe NPs) were synthesized using tea extracts as a catalyst for the Fenton-like oxidation of monochlorobenzene (MCB), where 69%, 53%, and 39% of MCB were, respectively, degraded by Fe NPs synthesized using green tea extracts, oolong tea extracts, and black tea extracts. Fe NPs synthesized using green tea extracts (GT-Fe NPs) demonstrated the best degradation since green tea contains a high concentration of caffeine/polyphenols used as both reducing and capping agents in the synthesis of Fe NPs. This was confirmed by SEM image, EDS, and XRD pattern of GT-Fe NPs. In addition, batch experiments show that the oxidation of MCB and the removal of chemical oxygen demand (COD) using GT-Fe NPs were 81% and 31%, respectively, at optimal conditions, where dosages were 0.6g/L GT-Fe NPs, 0.045mol/L H2O2, and initial pH of 3.0. Compared to homogeneous Fenton oxidation of MCB, GT-Fe NPs as a heterogeneous catalyst indicate that Fe2+ and Fe3+ leached from GT-Fe NPs nanoparticles and consequently reduced the formation of iron sludge. Finally, GT-Fe NPs were successful in removing MCB from wastewaters, and the possible Fenton-like oxidative mechanism of MCB was proposed. The proposition was based on adsorption of MCB on the surface of GT-Fe NPs, decomposition of H2O2, generation of hydroxyl radicals, and oxidation of MCB.

Oxidative treatment of aqueous monochlorobenzene with thermally-activated persulfate

The oxidation of aqueous monochlorobenzene (MCB) solutions using thermally-activated persulfate has been investigated. The influence of reaction temperature on the kinetics of MCB oxidation was examined, and the Arrenhius Equation rate constants at 20°C, 30°C, 40°C, 50°C, and 60°C for MCB oxidation performance were calculated as 0, 0.001, 0.002, 0.015, 0.057 min−1, which indicates that elevated temperature accelerated the rate. The most efficient molar ratio of persulfate/MCB for MCB oxidation was determined to be 200 to 1 and an increase in the rate constants suggests that the oxidation process proceeded more rapidly with increasing persulfate/MCB molar ratios. In addition, the reactivity of persulfate in contaminated water is partly influenced by the presence of background ions such as Cl−, HCO3−, SO42−, and NO3−. Importantly, a scavenging effect in rate constant was observed for both Cl− and CO32− but not for other ions. The effective thermally activated persulfate oxidation of MCB in groundwater from a real contaminated site was achieved using both elevated reaction temperature and increased persulfate/MCB molar ratio.

Low-Temperature Catalytic Oxidation of Monochlorobenzene by Ozone over Silica-Supported Manganese Oxide

In this study, we investigated the use of a silica-supported manganese oxide prepared through the impregnation method for the low-temperature (<150 °C) ozone catalytic oxidation (OZCO) of gaseous monochlorobenzene (MCB). Moreover, the effects of various operating parameters including the reaction temperature, ozone concentration, and space velocity (SV) on MCB removal were also evaluated. In the absence of ozone, MCB conversion achieved over 10 wt % MnOx/SiO2 was only 15% at 250 °C; the conversion increased to 90.4% over 10 wt % MnOx/SiO2 when 900 ppm of ozone was added at 120 °C and SV = 300 000 h–1. In the kinetic analysis, the power-rate law feasibly describes the data of MCB oxidation via OZCO reaction. For temperatures lower than 120 °C, the activation energy and frequency factor were 10.5 kJ mol–1 and 8.05 × 102 L1.187 mol–0.187 g–1 s–1, respectively. Furthermore, the economic feasibility analysis conducted by comparing the cost of the OZCO process relative to that of general catalytic oxidation using V2O5-based catalysts indicates that the OZCO process is more cost-effective for the removal of MCB from flue gas.

Enhancement of the biodegradability of aromatic groundwater contaminants.

Groundwater (GW) from the Bitterfeld industrial region, Central Germany, is contaminated mainly with monochlorobenzene (MCB). Accordingly, current research addresses the development of feasible in situ groundwater remediation technologies. Although easily degradable under aerobic conditions, MCB persists in the essentially anaerobic Bitterfeld aquifer. Therefore, we focused on primary oxidation of MCB and the subsequent anaerobic biodegradability of MCB oxidation products by the indigenous microbial community. In groundwater microcosms, most efficient MCB removal was observed upon treatment with Fenton's reagent (H2O2 + Fe2+), which produces the highly reactive hydroxyl radical and Fe3+ simultaneously. Phospholipid fatty acid analysis following different treatments suggested respective shifts of the microbial community compositions, and indicated that Fenton's reagent had a rather beneficial than an adverse effect on biomass development. Potential metabolites of hydroxyl radical attack on MCB such as chlorohydroquinone, hydroquinone, catechol, resorcinol, and phenol were anaerobically degraded by the groundwater microbial community under Fe3+ -reducing conditions.

Cytochrome P450 catalyzed oxidation of monochlorobenzene, 1,2- and 1,4-dichlorobenzene in rat, mouse, and human liver microsomes

We studied metabolism of monochlorobenzene (MCB), 1,2-dichlorobenzene (1,2-DCB) and 1,4-DCB in liver microsomes from untreated male and female Wistar rats and B6C3F1 mice or in those after the induction of CYP3A or 2E1 as well as in human male liver microsomes. MCB and 1,2-DCB were oxidised mainly by rat and human CYP2E1. It was found that 1,4-DCB was oxidised by rat and human CYP2E1 at a several-fold lower rate than 1,2-DCB, but a greater part to covalently binding products. In contrast to previous studies showing rat CYP3A1 as the main CYP form oxidising both DCBs, our experiments indicate only a certain role of rat and human CYP3A in MCB, 1,2-DCB and 1,4-DCB oxidation to covalently bound products. The relative roles of human liver CYP2E1 and 3A4 in the metabolism of 1,4-DCB seem to be individually different. Metabolic rates of MCB, 1,2-DCB and 1,4-DCB correlated with CYP2E1 immunochemical level in microsomes from 11 different human livers and with metabolic rates of CYP2E1 substrates. These rates in different human livers were up to 10-fold different and were generally several-fold higher than those in untreated rats or mice. Metabolic activation of MCB and 1,2-DCB to products binding covalently to microsomal proteins and to calf-thymus DNA, respectively, mostly corresponded to production of water-soluble metabolites. Significant species and sex differences in the oxidation of MCB, 1,2-DCB and 1,4-DCB were reflected in a markedly higher oxidation in male mice than male rats and higher oxidation in male than female mice. The formation of covalently bound products generally corresponded to production of soluble metabolites, but female rats formed significantly less covalently bound products of 1,4-DCB (and also of 1,2-DCB and MCB) than male rats and mice of both sexes, in possible reflection of the fact that 1,4-DCB is not carcinogenic in female rats despite its carcinogenicity for male rats and both sexes of mice.