benzofurans and 2-dichlorobenzene

Gaseous 1,2-dichlorobenzene (1,2-DCBz) was catalytically decomposed in a fixed-bed catalytic reactor using composite copper-based titanium oxide (CuOx/TiO2) catalysts with different copper ratios. Carbon nanotubes (CNTs) were introduced to produce novel CuOx/TiO2-CNTs catalysts by the sol-gel method. The catalytic performances of CuOx/TiO2 and CuOx/TiO2-CNTs on 1,2-DCBz oxidative destruction under different temperatures (150-350 °C) were experimentally examined and the correlation between catalyst structure and catalytic activity was characterized and the role of oxygen in catalytic reaction was discussed. Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) generation during 1,2-DCBz catalytic oxidation by CuOx/TiO2-CNTs composite catalyst was also examined. Results indicate that the 1,2-DCBz destruction/removal efficiencies of CuOx (4 wt%)/TiO2 catalyst at 150 °C and 350 °C with a GHSV of 3400 h(-1) are 59% and 94% respectively and low-temperature (150 °C) catalytic activity of CuOx/TiO2 on 1,2-DCBz oxidation can be improved from 59 to 77% when CNTs are introduced. Furthermore, oxygen either in catalyst or from reaction atmosphere is indispensible in reaction. The former is offered to activate and oxidize the 1,2-DCBz adsorbed on catalyst, thus can be generally consumed during reaction and the oxygen content in catalyst is observed lost from 39.9 to 35.0 wt% after reacting under inert atmosphere; the latter may replenish the vacancy in catalyst created by the consumed oxygen thus extends the catalyst life and raises the destruction/removal efficiency. The introduction of CNTs also increases the Cu(2+)/Cu(+) ratio, chemisorbed oxygen concentration and surface lattice oxygen binding energy which are closely related with catalytic activity. PCDD/Fs is confirmed to be formed when 1,2-DCBz catalytically oxidized by CuOx/TiO2-CNTs composite catalyst with sufficient oxygen (21%), proper temperature (350 °C) and high concentration of 1,2-DCBz feed (120 ppm).

Topics: Adsorption; Benzofurans; Catalysis; Chlorobenzenes; Copper; Dibenzofurans, Polychlorinated; Nanotubes, Carbon; Oxidation-Reduction; Polychlorinated Dibenzodioxins; Temperature; Titanium

The photocatalytic film Ce doped VxOy/TiO2 was loaded on cordierite honeycomb (CHC), and this composite was prepared by sol-gel and dipping method, with Ce, oxides of V and TiO2 as dopant and key substances, respectively. Using gaseous 1,2-dichlorobenzene to replace dioxin as target pollutant, dual degradation experiments at 140-280 °C were carried out (thermal decomposition and photodegradation), and the effects of preparation conditions on catalytic activity were investigated: doping amount of Ce, dipping time in the gel, the concentration of ammonium metavanadate (NH4VO3) solution, dipping time in NH4VO3 solution, sintering temperature. The gaseous samples were taken before and after the reactor and analyzed by gas chromatography. According to the results, the optimal preparation conditions were determined, and the corresponding removal rate was above 95% after 90 min of degradation at 280 °C. The composite was examined by ultrasonic to analyze the adhesive strength between the film and CHC, and further characterized by XRD and SEM. Furthermore, flue gas from waste incinerator was chosen as target pollutant, which contained PCDD/Fs, the industrial sidestream degradation experiment was carried out and showed excellent removal efficiency of the composite, the removal rate of PCDD/Fs reached ca. 90% after 90 min of degradation.

Topics: Benzofurans; Catalysis; Ceramics; Cerium; Chlorobenzenes; Dioxins; Gases; Incineration; Polychlorinated Dibenzodioxins; Temperature; Titanium; Vanadium Compounds

Chlorobenzene (CBz) is the precursor of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/Fs) generated in the processes of waste incineration, and it is regarded as a good indicator of PCDD/Fs for realizing PCDD/Fs online monitoring, moreover, pentachlorobenzene (PeCBz) and Hexachlorobenzene (HxCBz) belong to Persistent Organic Pollutants (POPs). However, the emission control of CBz in waste incineration does not attract enough attention, so this study focused on the inhibition of the 3 CBz formation routes in waste combustion by ammonium sulfate and urea, including CB formation from fly ash, CB formation from 1,2-dichlorobenzene (1,2-DiCBz) and the combustion of model medical waste. The results showed that both ammonium sulfate and urea reduced CBz yield during these three thermal processes. For instance, the inhibition rates of tetrachlorobenzene (TeCBz), PeCBz and HxCBz were 66.8%, 57.4% and 50.4%, respectively, when 1% urea was co-combusted with medical waste. By comparing the effect of ammonium sulfate and urea on CBz formation by three routes, urea was considered as a comparatively stable inhibitor for CBz.

Topics: Ammonium Sulfate; Benzofurans; Chlorobenzenes; Coal Ash; Dioxins; Hexachlorobenzene; Incineration; Polymers; Urea

The discrepancies between polychlorinated dibenzo-p-dioxin to polychlorinated dibenzofuran (PCDD to PCDF) ratios in laboratory and field studies in the exhaust of combustion sources are not fully explained by available formation models. In this paper we present the results of experimental studies of the surface mediated formation of PCDD/F at the conditions mimicking the combustion cool zone from a mixture of 1,2-dichlorobenzene (1,2-DCBz) and 2-monochlorophenol (2-MCP) over a model surface consisting of 5% CuO/Silica. The PCDD to PCDF ratio was found to be strongly dependent on the ratio of chlorinated benzenes to chlorinated phenols and oxygen content. The higher the 1,2-DCBz to 2-MCP ratio, the lower the PCDD to PCDF ratio. PCDFs are formed predominantly from chlorinated benzenes, while chlorinated phenols are responsible for majority of PCDDs. These laboratory results are in general agreement with full-scale measurement and can be used to improve predictive models of PCDD/F formation.

Topics: Benzofurans; Chlorobenzenes; Chlorophenols; Copper; Dibenzofurans, Polychlorinated; Halogenation; Polychlorinated Dibenzodioxins; Silicon Dioxide

Formation of polychorinated dibenzo-p-dioxins (PCDDs) has been demonstrated to occur via surface-mediated reactions of chlorinated phenols. However, polychlorinated dibenzofurans (PCDFs) are observed in much lower yields in laboratory studies than in full-scale combustors where PCDFs are in higher concentrations than PCDDs. This has led to the suggestion that at least PCDFs are formed from elemental carbon in the de novo process. However, the potential for PCDF formation from reactions of chlorinated benzenes has been largely overlooked. In this study, we investigated the potential contribution of chlorinated benzenes to formation of PCDD/Fs using 1,2-dichlorobenzene as a surrogate for reactions of other chlorinated benzenes and CuO/silica (3 wt % Cu) as a surrogate for fly ash. Results were similar for oxidative and pyrolytic conditions with a slight increase in more chlorinated products under oxidative conditions. Reaction products included chlorobenzene, polychlorinated benzenes, phenol, 2-monochlorophenol (2-MCP), dichlorophenols, and trichlorophenols with yields ranging from 0.01 to 2% for the phenols and from 0.01 to 10% for chlorinated benzenes. 4,6-Dichlorodibenzo furan (4,6-DCDF) and dibenzofuran (DF) were observed in maximum yields of 0.2% and 0.5%, respectively, under pyrolytic conditions and 0.1% and 0.3%, respectively, under oxidative conditions. In previous studies of the pyrolysis of 2-MCP under identical conditions, 4,6-DCDF and dibenzo-p-dioxin (DD) were observed with maximum yields of ∼0.2% and ∼0.1%, respectively, along with trace quantities of 1-monochlorodibenzo-p-dioxin (1-MCDD). Under oxidative conditions, 1-MCDD, DD, and 4,6-DCDF were observed with maximum yields of 0.3%, 0.07% and 0.1%, respectively. When combined with the fact that measured concentrations of chlorinated benzenes are 10-100× that of chlorinated phenols in full-scale combustion systems, the data suggest surface-mediated reactions of chlorinated benzenes can be a significant source of PCDD/F emissions.

Topics: Benzofurans; Chlorobenzenes; Copper; Dibenzofurans, Polychlorinated; Incineration; Oxidation-Reduction; Phenols; Polychlorinated Dibenzodioxins

Soots were prepared from flame combustion of benzene and o-dichlorobenzene (ODCB), creating one soot without carbon-chlorine bonds (benzene soot) and one with such bonds (ODCB soot). ODCB soot was tested for PCDD/F formation between 277 and 600 degrees C without additional chlorine, but levels were very low. Copper and Cu2O were added as potential catalysts for ODCB soot oxidation, but levels of PCDD/F observed were even lower than without these additives. Both benzene soot and ODCB soot produced PCDD/F after adding CuCl2 to the reaction mixtures, suggesting that a (volatile) metal chloride was needed in order for PCDD/F formation to take place. Under the various conditions of [Cu2+], time, and temperature tested, ODCB soot was always more reactive than benzene soot in forming PCDD/F. It seemed plausible that, despite the fact that CuCl2 was very effective in creating C-Cl bonds in benzene soot, the C-Cl bonds created in ODCB soot during preparation were of a reactivity so as to make this soot especially prone to PCDD/F formation. High temperature (gas phase) chlorination of soots by HCI or other chlorinating agents, followed by deposition of these soots and condensed metal chlorides on the ducts and walls of the postcombustion zone, could create an effective mechanism for de novo formation of PCDD/F.

Topics: Benzene; Benzofurans; Chlorobenzenes; Dibenzofurans, Polychlorinated; Incineration; Insecticides; Polychlorinated Dibenzodioxins; Soil Pollutants; Volatilization