Removal of Organochlorine from Model Oil Using Mg-Modified ZSM-5 Zeolite:Dechlorination Performance,Regeneration,and Thermodynamics

Various metal-modified ZSM-5 zeolite adsorbents prepared by the impregnation method were applied to the removal of organic chlorides from model naphtha.The adsorption performance and regeneration stability were investigated by static adsorption experiments.The morphologies,structural features,and physicochemical properties of the adsorbents were characterized by X-ray diffraction,Brunauer-Emmett-Teller analysis,NH3 temperature-programmed desorption,scanning electron microscopy,transmission electron microscopy,and pyridine adsorption infrared spectroscopy.The Mg/ZSM-5 zeolite adsorbent possessed a relatively high specific surface area and good metal dispersion and exhibited the best dechlorination and regeneration performance.The characterization results revealed that introduction of the metal exerted a significant influence on the acidic properties of the catalyst surface.A decrease in the ratio of Brønsted acidic sites to Lewis acidic sites and an increase in the amount of moderately acidic sites were confirmed to be responsible for the excellent adsorption performance of the Mg-modified ZSM-5 zeolite.Furthermore,the Langmuir adsorption isotherm model was applied to study the adsorption equilibrium and thermodynamics of the Mg/ZSM-5 adsorbent under mild conditions.The results revealed that the removal of 1,2-dichloroethane by the Mg/ZSM-5 adsorbent was endothermic,spontaneous,disordered,and primarily involved physical adsorption.

A review:Advances in microbial remediation of trichloroethylene (TCE)

Research works in the recent past have revealed three major biodegradation processes leading to the degradation of trichloroethylene. Reductive dechlorination is an anaerobic process in which chlorinated ethenes are used as electron acceptors. On the other hand, cometabolism requires oxygen for enzymatic degradation of chlorinated ethenes, which however yields no benefit for the bacteria involved. The third process is direct oxidation under aerobic conditions whereby chlorinated ethenes are directly used as electron donors by microorganisms. This review presented the current research trend in understanding biodegradation mechanisms with regard to their field applications. All the techniques used are evaluated, with the focus being on various factors that influence the process and the outcome.

Catalytic reductive dechlorination of p-chlorophenol in water using Ni/Fe nanoscale particles

Nanoscale bimetallic Ni/Fe particles were synthesized from the reaction of sodium borohydride （NaBH4） with reduction of Ni^2＋ and Fe^2＋ in aqueous solution. The obtained Ni/Fe particles were characterized by TEM （transmission electron microscope）, XRD （X-ray diffractometer）, and N2-BET. The dechlorination activity of the Ni/Fe was investigated using p-chlorophenol （p-CP） as a probe agent. Results demonstrated that the nanoscale Ni/Fe could effectively dechlorinate p-CP at relatively low metal to solution ratio of 0.4 g/L （Ni 5 wt%）. The target with initial concentration ofp-CP 0.625 mmol/L was dechlorinted completely in 60 rain under ambient temperature and pressure. Factors affecting dechlorination efficiency, including reaction temperature, pH, Ni loading percentage over Fe, and metal to solution ratio, were investigated. The possible mechanism of dechlorination ofp-CP was proposed and discussed. The pseudo-first- order reaction took place on the surface of the Ni/Fe bimetallic particles, and the activation energy of the dechlorination reaction was determined to be 21.2 kJ/mol at the temperature rang of 287-313 K.

Mechanochemical decomposition of pentachlorophenol by ball milling

The mechanochemical dechlorination of pentachlorophenol （PCP） was studied using CaO and SiO2 powder as additives. The effects of the milling time and additives on the dechlorination rate were investigated. The resulting product was characterized by X-ray diffraction （XRD）, Fourier transform infrared spectra （FT-IR）, thermogravimetric analysis （TG） and ion chromatography （IC）. It is found that grinding operation could dechlorinate PCP, with the formation of inorganic chloride and amorphous carbon. The addition of quartz to the grinding mixture facilitated dechlorination. On the basis of the experimental results, the decomposition mechanism was proposed. Decomposition predominantly proceeds through rupture of C-Cl bond in PCP molecule, followed by the formation of inorganic chlorides.

Radiolysis of pentachlorophenol (PCP) in aqueous solution by gamma radiation

Steady-state radiolysis experiments were performed to investigate the γ-irradiation treatment of pentachlorophenol (PCP) in aqueous solution. The e?ect of initial concentration on the PCP degradation was also investigated. The experimental results showed that γirradiation was able to degrade PCP in aqueous solution successfully, and the radiolytical degradation process of PCP could be described by the first-order kinetic model. When the initial concentration of PCP was 25 and 50 mg/L and the radiation dose ...

Rapid treatment of atrazine-contaminated water by nickel/iron bimetallic system

The utility of nickel/iron in the remediation of atrazine-contaminated water was investigated. The experimental results showed that nickel/iron had effective catalytic activity in dechlorinating atrazine under acidic conditions. The dechlorination reaction approximately followed the first-order kinetics under the experimental conditions(nickel/iron:1.0 g/250 ml;C atrazine=20.0 mg/L), the reaction rate increased with decreasing pH value of the reaction solution and increasing the proportion of Ni:Fe within 2.95%. For condition with 2.95% nickel/iron, the reaction rate constants were 0.07518(R=0.9927), 0.06212(R=0.9846) and 0.00131 min -1(R=0.9565) at pH=2.0, 3.0 and 4.0, respectively. HPLC analysis was used to monitor the decline of atrazine concentration.

Kinetics and Mechanism of Dechlorination of o-Chlorophenol by Nanoscale Pd/Fe

Nanoscale Pd/Fe bimetallic particles were synthesized with an efficient method to dechlorinate o-chlorophenol. The nanoscale Pd/Fe particles were determined by transmission electron microscopy and BET specific surface area analysis. Most of the particles are in the size range of 20—100 nm. The BET specific surface area of synthesized nanoscale Pd/Fe particles is 12.4 m 2/g. In contrast, a commercially available fine iron powder(<100 mesh) has a specific surface area of 0.49 m 2/g. Batch studies demonstrated that the nanoscale particles can effectively dechlorinate o-chlorophenol. The dechlorination reaction takes place on the surface of synthesized nanoscale Pd/Fe bimetallic particles in a pseudo-first order reaction. The surface-area-normalized rate coefficients(k_ SA) are comparable to those reported in the literature for chlorinated ethenes. The observed reaction rate constants(k_ obs) are dominated by the mass fraction of Pd and the mass concentration of the nanoscale Pd/Fe particles.

A novel use of TiO_2 fiber for photocatalytic ozonation of 2,4-dichlorophenoxyacetic acid in aqueous solution

More efficient oxidation methods are needed to degrade especially newly emerging recalcitrant organic contaminants at low concentrations in the water environment. Reduced photonic efficiency of immobilized TiO2 is a major challenge in TiO2-assisted advanced oxidation processes (AOP). Mineralization of 2,4-dichllorophenoxyacetic acid (2,4-D) in low aqueous solution by O3/UV/TiO2 using the world’s first high-strength TiO2 fiber was investigated and compared with O3, UV/TiO2, and O3/TiO2 in laboratory batch ex...

Dechlorination of disinfection by-product monochloroacetic acid in drinking water by nanoscale palladized iron bimetallic particle

Nanoscale palladized iron(Pd/Fe)bimetallic particles were prepared by reductive deposition method.The particles were characterized by X-ray diffraction(XRD),X-ray fluorescence(XRF),scanning electron microscope(SEM),transmission electron microscope(TEM),and Brunauer-Emmett-Teller-nitrogen(BET-N_2)method.Data obtained from those methods indicated that nanoscale Pd/Fe bimetallic particles containedα-Fe^0.Detected Pd to Fe ratio by weight(Pd/Fe ratio)was close to theoretical value. Spherical granules with diame...

Catalytic Dechlorination of Chlorobenzene in Water by Pd/Fe System

Chlorobenzene was dechlorinated by Pd/Fe bimetallic system in water through catalytic reduction. The dechlorination rate increases with increase of bulk loading of Pd due to the increase of both the surface loading of the Pd and the total surface area. For conditions with 0.005% Pd/Fe, 45% dechlorination efficiency was achieved within 5 h. The dechlorinated reaction is believed to take place on the bimetal surface in a pseudo-first-order reaction, with the rate constant being 0.0043 min-1.

Decomposition of hexachlorobenzene over Al_2O_3 supported metal oxidecatalysts

Decomposition of hexachlorobenzene(HCB)was investigated over several metal oxides(i.e.,MgO,CaO,BaO,La2O3,CeO2,MnO2, Fe2O3,and Co3O4)supported on Al2O3,which was achieved in closed system at a temperature of 300°C.Catalysts were prepared by incipient wetness impregnation with different metal oxides loading and impregnating solvents.The decomposition effciency of different catalysts for this reaction depends on the nature of the metal oxide used,and Al2O3 supported La2O3 was found to be the most active one.Pe...

Coupled anaerobic/aerobic biodegradation of 2,4,6 trichlorophenol

Degradation of 2, 4, 6 trichlorophenol(TCP) with co immobilizing anaerobic granular sludge and isolated aerobic bacterial species was studied in coupled anaerobic/aerobic integrated reactors. The synergism of aerobes and anaerobes within co immobilized granule might facilitate degrading the TCP and exchange of anaerobic metabolites 4 CP, which promoted system organic removal efficiency and recovered from organic shock loads more quickly. The biomass specific activities experiment further confirmed that strict anaerobes be not affected over the course of this experiment by the presence of an oxic environment, aerobic activity predominated in the outer co immobilized granule layers, while the interior was characterized by anaerobic activity. The co immobilized granule could thus enable both aerobic and anaerobic microbes function in the same reactor and thereby integrate the oxidative and reductive catabolism.

Catalytic dechlorination of chlorobenzene in water by Pd/Fe bimetallic system

Catalytic reductive dechlorination of monochlorobenzene(MCB) was carried out in the palladium/iron system. With low Pd loading(0 005%), 45% dechlorination efficiency was achieved within 5 h. Pd as catalyst accelerated the reductive dechlorination reaction. Dechlorination mechanism and kinetics were discussed. The reaction took place on the bimetal surface in a pseudo first order reaction, with the rate constant being 0 0071 min -1 ( K SA =8 0×10 -3 L/(m 2·h). The reduction product for MCB was benzene.

Electrochemical dechlorination of chloroform in neutral aqueous solution on palladium/foam-nickel and palladium/polymeric pyrrole film/foam-nickel electrodes

Electrochemical dechlorination of chloroform in neutral aqueous solution was investigated using palladium-loaded electrodes at ambient temperature. Palladium/foam-nickel （Pd/foam-Ni） and palladium/polymeric pyrrole film/foam-nickel （Pd/PPy/foam-Ni） composite electrodes which provided catalytic surface for reductive dechlorination of chloroform in aqueous solution were prepared using an electrodepositing method. Scanning electron microscope （SEM） micrographs showed that polymeric pyrrole film modified the electrode-surface characteristics and resulted in the uniform dispersion of needle-shaped palladium particles on foam-Ni supporting electrode. The experimental results of dechlorination indicated that the removal efficiency of chloroform and current efficiency in neutral aqueous solution on Pd/PPy/foam-Ni electrode could be up to 36.8% and 33.0% at dechlorination current of 0.1 mA and dechlorination time of 180 min, which is much higher than that of Pd/foam-Ni electrode.

PVP-Supported Palladium-Cadmium Bimetallic Catalyst for the Hydrogen Transfer Dechlorination of Aryl Chlorides

PVP-supported bimetallic catalyst, PVP-PdCl2-CdCl2, exhibits extremely high catalytic activity for the hydrogen transfer dechlorination of aryl chlorides in neutral environment. The yields of dechlorination products are high under mild reaction conditions and the operation is simple.

Removal of chloride from simulated acidic wastewater in the zinc production

The removal of chloride from the zinc electrolyte produced during hydrometallurgical zinc production is challenging. The ion-exchange method is a promising way to remove chloride if the resin washing wastewater can be recycled. This paper focuses on chloride removal from resin washing wastewater to enable its reuse. Various processing factors including the oxygen gas velocity, temperature, and reaction time were investigated systematically. The results show that the optimal conditions for dechlorination are an oxygen gas velocity of 0.5 L-min^-1, a reaction temperature of 80 ℃, and a reaction time of 30 min. A dechlorination efficiency of 80% with a residual chloride ion concentration less than 200 mg-L^-1 was achieved, which meets the requirements for the recycling of wastewater. The presence of manganese accelerates the dechlorination by forming a Mn^2+- MnO^2-MnO4^-Mn^2+ redox cycle. In this process, about 15 kg of the MnO2 and all of the zinc can be recovered from 100 m^3 wastewater, and the wastewater can be reused, which makes the ion-exchange method a promising technique for chloride removal.

Behavior and control of chlorine in dyestuff residue incineration

Dyestuffresidue, a type of hazardous waste, is incinerated in the tubular furnace, and thermodynamic equilibrium model is used to calculate and analyze the chlorine behavior. The HCI emission and its effects on the behaviors of heavy metals are studied. Meanwhile, the effects of three dechlorine reagents are predicted at a high temperature. Results show that HCI emission is dependent on incineration temperature. The HCl evaporated mainly derives from the organic chlorine. Under the working condition of 500-- 900℃, the main products of rig, Pb, Cu, Ni, Zn, and Mn in reaction with HCl are HgCl2 （g）, PbCl4（g）, PbCI2 （g）, （CuCl）3 （g）, NiCl2 （s）, NiCl2 （g）, ZnCl2 （s）, ZnCl2 （g）, Zn （g）, MnCl2 （s）, and MnCl2 （g）, respectively. Among the three dechlorine reagents, CaCO3 is optimal to remove chlorine at high temperature, little of HCl is released below 800℃, whereas Fe3O4 is unstable at high temperature.

Optimization of Fenton pretreatment for 2-chlorophenol solution

Fenton oxidation was used as the pretreatment of 2-chlorophenol wastewater with the objective of dechlorination, as it was considered that after breakage of aryl—Cl bond, the generated intermediates may be easily biodegraded. Hence, the optimization of pH and the low Fenton reagent doses for dechlorination was investigated. More than 99% dechlorination is obtained at the optimal pH 4 and the Fenton reagent doses of 86 mmol/L H2 O2 and 2.87 mmol/L Fe2+. The corresponding 2-chlorophenol is degraded completely, 80.02% COD is also removed, and the biodegradability, evaluated in terms of the BOD5 /COD ratio, is increased up to 0.41. To test the effect of this pretreatment, the pretreated 2-chlorophenol wastewater was fed to a sequencing batch reactor(SBR). The results show that complete mineralization is achieved. It is demonstrated that, for the treatment of recalcitrant compounds like 2-chlorophenol, the Fenton pretreatment could be quite effective and economical for enhancing the biodegradability in a Fenton-biological coupled system.

Self-regeneration of activated carbon modified with palladium catalyst for electrochemical dechlorination

Catalyst regeneration and the retention of high catalytic activity are still the critical issues in environmental application. A novel fluidized gas-liquid-solid electrochemical reactor was developed to simultaneously remove chlorinated pollutants and in situ regenerate the spent catalyst. Activated carbon modified with palladium catalyst （AC-Pd） was prepared for electrochemical dechlorination. For the 4-chlorophenol wastewater of initial concentration 200 mg· L^- 1, the removal efficiency could nearly reach 100% in less than 30 rain. Catalytic activity of AC-Pd catalyst was preserved effectively even in consecutive cycling run without special regeneration. OH radicals, generated by electrochemical reaction, played a critical role in self-regeneration of AC-Pd. High catalytic activity of spent AC-Pd catalyst provided an attractive alternative in wastewater treatment.

STUDY ON THE PYROLYSIS AND RECYCLING OF PVC WASTE AS AN ENERGY SOURCE

The pyrolysis dechlorination of PVC (polyvinyl chloride) has been carried out by batch operation under atmospheric pressure. The kinetics involved in the PVC thermal decomposition was studied by using thermogravimetric technique. Several tests were carried out at the heating rate of 5-10℃/min, the yields of products and the distribution of chlorine were also studied. The kinetic parameters such as activation energies, reaction orders and preexponential factors under nitrogen atmosphere were calculated by applying Friedman’s method. The results showed that the PVC thermal degradation is substantially a two-step process. The first step mainly involves dechlorination of the polymers. HCI is the main volatile product and this reaction can be seen as a first-order reaction. A kinetic model for the thermal dechlorination of PVC has been developed.