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.

Numerical simulation on the fluidized bed gasification and CaO dechlorination of refuse derived fuel

A three-dimensional numerical model verified by previous experimental data is developed to simulate the fluidized bed gasification of refuse derived fuel （RDF）. The CaO dechlorination model obtained by the thermal gravity analysis （TGA） is coupled to investigate the process of CaO dechlorination. An Eulerian-Eulerian method is adopted to simulate the gas-solid flow and self-developed chemical reaction modules are used to simulate chemical reactions. Flow patterns, gasification results and dechlorination efficiency are obtained by numerical simulation. Meanwhile, simulations are performed to evaluate the effects of Ca/Cl molar ratio and temperature on dechlorination efficiency. The simulation results show that the presence of bubbles in the gasifier lowers the CaO dechlorination efficiency. Increasing the Ca/Cl molar ratio can enhance the dechlorination efficiency. However, with the temperature increasing, the dechlorination efficiency increases initially and then decreases. The optimal Ca/Cl molar ratio is in the range of 3. 0 to 3. 5 and the optimal temperature is 923K.

Catalytic Dechlorination and Kinetics of o-Dichlorobenzene by Pd/Fe

o-Dichlorobenzene (o-DCB) was dechlorinated by Pd/Fe powder in water throughcatalytic reduction. The dechlorination reaction is believed to take place on the surface site ofthe catalyst via a pseuclo-first-order reaction. The final reduction product of o-DCB is benzene.The dechlorination rate increases with the increase of bulk loading of palladium due to the increaseof both the surface loading of palladium and the total surface area. Dechlorination efficiencyaccounts for 90% at Pd/Fe mass ratio 0.02% and metal to solution ratio about 53.3g · L^(-1) in 120minutes. Dechlorination is affected by the reaction temperature, pH, Pd/Fe ratio and the addition ofPd/Fe. E_a is found to be 102.5 kJ · mol^(-1) in the temperature range of 287—313 K.

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.

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.

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.

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.

Rapid dechlorination of chlorinated organic compounds by nickel/iron bimetallic system in water

Detoxification of chlorinated organic compounds via reaction with nickel/iron powder was implemented in aqueous solution. Compared to iron, nickel/iron bimetallic powder had higher hydrodechlorination activities for both atrazine (ATR) and p-chlorophenol (pCP); nickel/iron (2.96%, w/w) was shown to have the largest specific surface area and the optimum proportion for the dechlorination of both ATR and pCP. Electrochemical measurements showed that the adsorbed hydrogen atom on the nickel must have been the dominant reductive agent for the dechlorination of both ATR andpCP in this system.

Influence of blast furnace top gas composition and dust on HCl removal with low temperature Ca-based dechlorination agent

Using fixed-bed reaction method and changing the gas composition and dust content,the influence of blast furnace top gas composition and dust on HCl removal with low temperature Ca-based antichlor was studied.It was found that,when the content of CO2 in blast furnace top gas increased,the dechlorination efficiency was getting worse obviously;when the contents of CO and N2 increased,the dechlorination efficiency was getting better to a certain extent;when the content of H2 changed,the dechlorination efficiency got no significant change;as the content of dust increased,the dechlorination efficiency got better obviously when the content was less than 15 g/m3,but it would be got worse quickly when the content was more than 20 g/m3,and the best content was 15–20 g/m3;the suitable site of the process of dechlorination was after gravity dust collector and before bag dust collector.

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.

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.

Kinetics of 2,4-dichlorophenol dechlorination by Pd-Fe bimetallic nanoparticles in the presence of humic acid

The remediation of groundwater which contains chlorinated organic compounds (COCs) by nanoscale bimetallic catalysts has received increasing interest in recent years. This report presents the dechlorination of 2,4-dichlorophenol (2,4-DCP) by Pd-Fe bimetallic nanoparticles in the presence of humic acid (HA) to investigate the feasibility of using Pd-Fe for the in situ remediation of contaminated groundwater. Our experimental results indicated that HA had an adverse effect on the dechlorination of 2,4-DCP by Pd-Fe nanoparticles. The rate constant k values of 2,4-DCP dechlorination were 0.017, 0.013, 0.009, 0.006 and 0.004 min?1 for HA concentrations of 0, 5, 10, 15 and 20 mg/L, respectively. The relationship between HA dosage and k values can be described as a linear model.

Influence of Dechlorination Temperature on Propane Dehydrogenation over Pt-θ-Al2O3

Several Pt-θ-Al_2O_3 catalysts with similar ultra-low Cl contents were used to investigate the influence of dechlorination temperature on propane dehydrogenation reaction. The Pt-θ-Al_2O_3 catalyst treated at a highest dechlorination temperature showed a lowest propane rate and propylene selectivity. The scanning transmission electron microscopy showed that the dispersions of Pt nanoparticles decreased with an increasing dechlorination temperature. The temperature-programmed reduction analysis showed that higher dechlorination temperature could lead to strong interactions between the metal and support, making it difficult to reduce Pt nanoparticles. The temperature-programmed oxidation analysis implied that more coke was deposited on the metal for catalyst treated at higher dechlorination temperature. The Raman spectra and the H/C ratio showed that more side-reactions, such as cracking and severe deep dehydrogenation reactions, occurred on catalysts treated at higher dechlorination temperatures. Therefore, the lower the dispersion of Pt nanoparticles was, the stronger the metal-support interactions and increased side-reactions would be, resulting in lower catalytic activity for Pt-θ-Al_2O_3 treated with higher dechlorination temperature.

Dechlorination of pentachlorophenol by grinding at low rotation speed in short time

In order to apply grinding method for degradation of pentachlorophenol(PCP) to an industrial scale,the proportion of different materials[CaO,SiO_2 and CO(NH_2)_2]and the size of grinding balls were examined.For saving energy and increasing dechlorination efficiency,the rotation speed and grinding time were maintained at relatively low values.At a mass ratio of grinding balls to materials(40:1),PCP was added into a big steel jar(300 ml) with other materials to grind at 300 r ·min^(-1)for 5 h.The results indicated that when PCP was mixed with CaO and SiO_2in a molar ratio of 1:60:60,the best dechlorination of 58.4%was achieved.CO(NH_2)_2 could not be used as hydrogen donor in the dehalogenation by mechanochemical reaction,since it restrained the dechlorination process.The size of grinding balls has significant effect on the reaction.The experiment with 5 mm steel balls indicates that the weight is too light to provide appropriate energy for the reaction,while steel balls of 10 and 15 mm could give better dechlorination reaction.It indicates that dechlorination depends on the mass of balls and fill rate.

Study on Reductive Dechlorination of PCBs in Groundwater by Fe/Zn Bimetal

[Objective] The research aimed to study reductive dechlorination effect of PCBs in groundwater by Fe/Zn bimetal. [Method] Fe/Zn bi- metal as reduction system, PCBs degradation ratio as inspected index, degradation effect of PCBs by Fe/Zn bimetallic system when adding self- made hydroxypropyl-β-cyclodextdn （HP-β-CD） was studied. Meanwhile, we investigated the influences of loading ratio and Fe-Zn dosage on PCBs dechlorination. [ Result] PCBs was significantly solubilized by the synthesized HP-β-CD. With increase of the HP-β-CD concentration, the apparent solubility of PCBs increased linearly, forming 1：1 inclusion complex. When Fe-Zn dosage was 10 g, and mass fraction of Zn was 7%, the dechlori- nation efficiency of 321 μg/L PCBs was 47.6% after degrading for 7 d at 10 ℃. [ Condusion] The research provided theoretical guiding for in situ remediation of the qroundwater contaminated bv PGBs.

Cathodic Hydrogen as Electron Donor in Enhanced Reductive Dechlorination

In situ capping is an attractive and cost-effective method for remediation of contaminated sediments,but few studies on enhancing contaminant degradation in sediment caps have been reported,especially for chlorinated benzenes.Electrically enhanced bioactive barrier is a new process for in situ remediation for reducible compounds in soil or sediments.The primary objective of this study is to determine if electrodes in sediment could create a redox gradient and provide electron acceptor/donor to stimulate degradation of chlorinated contaminant.The results demonstrate that graphite electrodes lead to sustainable evolution of hydrogen,displaying zero-order kinetics in the initial stages with different voltages.The constant rates of hydrogen evolution at 3,4,and 5 V are1.05,2.54,and 4.3 nmol·L 1·d 1,respectively.Even higher voltage can produce more hydrogen,but it could not keep long time because the over potentials on electrode surfaces prevent its function.The study shows that 4 V is more appropriate for hydrogen evolution.The measured and evaluated concentration of 1,2,3,5-tetrachlorobenzene in pore water of sediment and concentration of sulfate show that dechlorination is inhibited at higher concentration of sulfate.

Catalytic dechlorination of o-chlorophenol by nanoscale Pd/Fe

Transformation of chlorophenols by nanoscale bimetallic particles represents one of the latest innovative technologies for environmental remediation. Nanoscale Pd/Fe bimetallic particles were synthesized in the laboratory for treatment of o-chlorophenol. Most of the nanoscale particles are in the size range of 20—100 nm. BET specific surface area of the nanoscale Pd/Fe particles is 12.4 m2/g. In comparison, a commercially available Fe powder(<100 mesh) has a specific surface area of just 0\^49 m2/g. Batch experiments demonstrated that the nanoscale Pd/Fe bimetallic particles can effectively dechlorinate o-chlorophenol. Dechlorination efficiency is affected by the mass fraction of Pd in the bimetal, nanoscale Pd/Fe mass concentration and mixing intensity.

Dechlorination by combined electrochemical reduction and oxidation

Chlorophenols are typical priority pollutants listed by USEPA (U.S. Environmental Protection Agency). The removal of chlorophenol could be carried out by a combination of electrochemical reduction and oxidation method. Results showed that it was feasible to degrade contaminants containing chlorine atoms by electrochemical reduction to form phenol, which was further degraded on the anode by electrochemical oxidation. Chlorophenol removal rate was more than 90% by the combined electro- chemical reduction and oxidation at current of 6 mA and pH 6. The hydrogen atom is a powerful reducing agent that reductively dechlorinates chlorophenols. The instantaneous current efficiency was calculated and the results indicated that cathodic reduction was the main contributor to the degradation of chlorophenol.