Hydrodechlorination Process Research Articles

The catalytic hydro-dechlorination of 2, 4, 4’ trichlorobiphenyl at mild temperatures and atmospheric pressure

ABSTRACT Polychlorinated biphenyls (PCBs), including all 209 congeners, are designated as persistent organic pollutants (POPs) due to their high toxicity and bioaccumulation in human bodies and the ecosystem. The need for PCB remediation still remains long after their production ban. In this study, a catalytic hydro-dechlorination (HDC) method was employed to dechlorinate 2,4,4’-trichlorobiphenyl (PCB 28), a congener found ubiquitously in multiple environmental media. The HDC of PCB 28 was experimentally studied at mild temperatures viz. ~20, 50, and ~77°C and atmospheric pressure. Et3N (triethylamine) was added as a co-catalyst. The dechlorination rates increased with temperature as well as Et3N dosage, and the HDC pathway was hypothesized based on the product and intermediates observed. The less chlorinated intermediates suggested that the position of the chlorine strongly impacted HDC rates, and the preference of HDC at para positions can be orders of magnitudes higher than the ortho. The activation energy was estimated in the range of 12.4–13.9 kJ/mole, indicating a diffusion-controlled HDC system. Implications: The remediation need for polychlorinated biphenyls (PCBs) still remains long after their production ban around the world. The development of low-cost methods is highly desirable, especially for developing countries, in response to the Stockholm Convention. In this study, the dechorination of a ubiquitously present PCB congener was studied using a catalytic hydro-dechlorination (HDC) method in low temperatures up to ~77°C and was able to achieve near 100% dechlorination in 6 hr. Results indicated that the HDC process can be performed under mild temperatures and atmospheric conditions and can be a potential solution to real world PCB contamination issues.

Improvement of the conventional flat plate electrode: Application of filtered Pd@Ti electrode in the removal of toxic chlorinated PPCPs

In order to change the mass transfer efficiency of conventional flat plate electrodes in the catalytic process, a new filtered Pd@Ti electrode has been prepared. The results indicated that the filtered Pd@Ti electrode had the best removal efficiency of 99.59% on diclofenac (DCF) at the flux of 40.85 L/m2∙h-1. Compared to unfiltered Pd@Ti electrodes, the removal efficiency was 1.18 times higher, the current efficiency was 2.15 times higher and the cost of electricity was 69.05% lower. The electrocatalytic hydrodechlorination process of DCF by filtered Pd@Ti electrode mainly relies on indirect reductive dechlorination by H* adsorbed on the electrode surface. The removal efficiency of the filtered Pd@Ti electrode remained above 80% after six cycles. The removal mechanism and reaction pathway of filtered Pd@Ti electrode for dechlorination of different chlorinated PPCPs were proposed. Furthermore, the ecotoxicity of chlorinated PPCPs and their products were evaluated by using the toxicity estimation software tool (T.E.S.T.) model. This study confirmed the promising application of filtered Pd@Ti electrodes for the removal and detoxification of chlorinated PPCPs in wastewater.

Electronic structure engineering of bimetallic Pd-Au alloy nanocatalysts for improving electrocatalytic hydrodechlorination performance

Regulating the electronic structure of Pd catalyst for promoting electrocatalytic hydrodechlorination is promising but still challenging. Herein, we propose an electronic structure engineering for accelerating the hydrodechlorination process by desigining bimetallic Pd-Au alloy nanoparticles (ANs) with electron-rich Pd as high-efficiency electrocatalysts. The Pd7Au3 ANs exhibits the highest electrocatalytic hydrodechlorination activity, the 4-chlorophenol hydrodechlorination efficiency reaches 98.35 % within 4 h, and the mass activity is 0.47 h−1 mgPd−1, which is 7.83 times as high as that of pure Pd nanoparticles. The experimental characterization and theoretical calculation reveal that Pd atoms “obtain” electrons and gold atoms “lose” electrons in Pd-Au ANs, resulting in the formation of electron-rich Pd, which promotes the desorption of the dechlorination product phenol and accelerates the renewal of active sites. This work provides an electronic structure engineering strategy of Pd-based electrocatalysts for electrocatalytic hydrodechlorination, which opens a new opportunity for rational design and construction of high-performance hydrodechlorination catalysts.

Hydrodechlorination and deep hydrogenation on single-palladium-atom-based heterogeneous catalysts

Halophenols are widely present in wastewater and groundwater, which threaten global water safety and human health. Importantly, hydrodechlorination (HDC) via heterogeneous catalysis is efficient and environmentally friendly. To further improve the catalytic performance and atomic economy, Pd-based single atom catalysts (SACs) were prepared through electrostatic attraction and used in the catalytic HDC for the first time. By substituting different defect-rich supports, the coordination environments of atomically dispersed Pd-atoms were mediated with different catalytic performance. The results demonstrate that the Pd/CeO2 SACs have the highest HDC activity and remain stable during cycle tests. The moderately intensive metal-support interactions (MIMSI) effect was identified as a critical factor for the higher activity of SACs, unlike the traditional strong metal-support interaction effect. The HDC process on Pd SACs was further investigated by combining kinetic experiments with density functional theory calculations, which facilitated the recognition of HDC intermediates and an understanding of the reaction mechanism.

Effect of unimodality and bimodality of Pd nanoparticles on the catalytic activity of Pd/SiO2 in the removal of diclofenac from water

In this work, we investigated the catalytic performance of uni- and bimodal Pd/SiO2 catalysts in the aqueous phase hydrodechlorination (HDC) of diclofenac – a very popular nonsteroidal anti-inflammatory drug. Unimodality and bimodality was confirmed by temperature-programmed hydride decomposition (TPHD) and TEM. The highest activity and 100% efficiency in batch and flow mode were observed for bimodal Pd NPs. This outstanding efficiency could be attributed to the close coexistence of small and large metal nanoparticles with different affinity to hydrogen and chloroorganic compound. The obtained results encourage discussion on the necessity to strive for perfect unimodal catalysts for the HDC processes.

Theoretical and Applied Aspects of Hydrodechlorination Processes—Catalysts and Technologies

The commercial implementation of hydrodechlorination processes will be an essential step in resolving the problem of environmentally sound organochlorine wastes processing. By now, there is a number of fundamental, applied, and process elaborations of such processes, in which chlorine is almost completely removed from wastes. The review article contains a significant number of results including basic regularities of thermal hydrodechlorination, comprehensive and selective catalytic hydrodechlorination. It discusses thermodynamics, kinetics, and catalysts of gas and liquid phase processes. Considerable attention is paid to hydrodechlorination of vinyl chloride production wastes and utilization of tetrachloromethane, which is the ozone-depleting substance. It also discusses hydrodechlorination of mono- and (poly)chlorobenzenes. The important examples of liquid phase data include hydrogenation using complex hydrides of elements. It also includes several flow sheets of hydrodechlorination processes.

The Preparation of Pd/Foam-Ni Electrode and Its Electrocatalytic Hydrodechlorination for Monochlorophenol Isomers

Noble metal palladium modified foamed nickel electrode (Pd/foam-Ni) was prepared by electrodeposition method. The fabricated electrode showed better catalytic performance than the Pd/foam-Ni prepared by conventional electroless deposition. The catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Electrocatalytic activity of the Pd/Ni was studied for the hydrodechlorination of monochlorophenol isomers. The Pd/Ni exhibited good catalytic activity for 3-chlorophenol (3-CP). Complete decomposition of chlorophenol isomers could be achieved within 2 h, and the hydrodechlorination process conformed to the pseudo-first-order kinetic model. It showed a supreme stability after recycling for 5 times. The Pd/Ni exhibited a promising application prospect with high effectiveness and low Pd loading.

Sepiolite-carbon nanocomposites doped with Pd as improving catalysts for hydrodechlorination processes

Abstract The present work introduces a new type of improved catalysts based on sepiolite-carbon nanocomposites anchoring Pd nanoparticles. The nanocomposites are prepared by assembly in aqueous media of graphene nanoplatelets (GNP) and the nanofibrous sepiolite under a sonomechanical treatment. The methodology allows the co-assembly of other nanomaterials such as multiwall carbon nanotubes (MWCNT) and Pd nanoparticles, these last ones in situ generated from PdCl2 and further treatment with NaBH4. The presence of silanol groups at the external surface of sepiolite favors the growth and assembly of Pd NP which exhibit a quite narrow size distribution independently of the composition of the prepared sepiolite-carbon nanocomposite. The electrical conductivity of the prepared sepiolite-carbon/Pd materials depends of the composition, being lower in materials with higher content in sepiolite. However, the presence of the clay mineral improves textural properties of the resulting materials. The prepared sepiolite-carbon/Pd nanocomposites were tested as catalysts in the hydrodechlorination (HDC) of 4-chlorophenol (4-CPh) under H2 flux, showing all of them an exclusive selectivity towards phenol, though their catalytic activity depends on their composition. Sepiolite is able to neutralize the evolved HCl, favoring the catalytic process. In addition, the good balance between textural and electrical properties achieved in some of the prepared materials enhances the contact between the catalyst surface and the reagents and also favors the electronic transfer, making this new type of sepiolite-carbon/Pd systems very promising. In fact, the concept here reported could be extended to other catalytic applications where the supported metal acting as active center requires the presence of heat and water resistant conductive supports.

Effect of reducing agent on catalytic hydrodechlorination of aqueous-phase OCDD/F

Removal/destruction of aqueous-phase octachlorodibenzo-p-dioxin (OCDD) and octachlorodibenzofuran (OCDF) via hydrodechlorination process (HDC) is experimentally evaluated over palladium/activated carbon (Pd/AC) catalyst. Pd catalyst is mainly used as active component for effectiveness in removing dioxin from wastewater. Studies on the removal of PCDD/Fs accomplished with HDC reaction in aqueous phase are limited and the influencing factors have not been clarified. In this study, high-concentration OCDD/F are selected as targets, and the effects of solvent and operating temperature on dechlorination efficiency are investigated via experimental tests. The results indicate that the highest hydrodechlorination efficiency is achieved with isopropanol as solvent. The OCDD/F removal efficiency achieved with the solution of 80% isopropanol is higher than that of 50% isopropanol, whereas the destruction efficiency of OCDD/F reveals the opposite trend. Generally, the removal and destruction efficiencies of PCDFs are higher than those of PCDDs. In addition, the activation energies of OCDD and OCDF are calculated with the Arrhenius equation as 24.8 and 23.1 kJ/mol, respectively. Stability tests are conducted with three cycles. Overall, the results indicate that a high performance (≥99%) can be achieved by combining hydrodechlorination with Pd/AC at a temperature range of 303–353 K, demonstrating that Pd/AC has good potential for removing PCDD/Fs from wastewater.

Catalytic hydrodechlorination of triclosan using a new class of anion-exchange-resin supported palladium catalysts

We prepared a new class of anion-exchange-resin supported Pd catalysts for efficient hydrodechlorination of triclosan in water. The catalysts were prepared through an initial ion-exchange uptake of PdCl42− and subsequent reduction of Pd(II) to Pd(0) nanoparticles at ambient temperature. Two standard strong-base anion exchange resins (IRA-900 and IRA-958) with different matrices (polystyrene and polyacrylic) were chosen as the supports. SEM and TEM images showed that Pd(0) nanoparticles were evenly attached on the resin surface with a mean size of 3–5 nm. The resin supported Pd catalysts (Pd@IRA-900 and Pd@IRA-958) were able to facilitate rapid and complete hydrodechlorination of triclosan. At a Pd loading of 2.0 wt.%, the observed pseudo first-order rate constant (kobs) was 1.25 ± 0.06 and 1.6 ± 0.1 L/g/min for Pd@IRA-900 and Pd@IRA-958, respectively. The catalysts were more resistant to Cl− poisoning and natural organic matter fouling than other supported-Pd catalysts. The presence of 10 mM NaCl suppressed the kobs value by 31% and 23% for Pd@IRA-900 and Pd@IRA-958, whereas the presence of humic acid at 30 mg/L as TOC lowered the rates by 28% and 27%, respectively. The better performance of Pd@IRA-958 was attributed to the polymeric matrix properties (i.e., hydrophobicity, pore size, and surface area) as well as Pd particle size. GC/MS analyses indicated that very low concentrations of chlorinated intermediates were detected in the early stage of the hydrodechlorination process, with 2-phenoxyphenol being the main byproduct. The catalysts can be repeatedly used in multiple operations without significant bleeding. The catalysts eliminate the need for calcination in preparing conventional supported catalysts, and the resin supports conveniently facilitate control of Pd loading and material properties.

The impact of the hydrodechlorination process on the physicochemical properties of bimetallic Ag-CuBeta zeolite catalysts

Beta zeolites with two Si/Al ratios of 17 and 1300 were used for synthesis of Ag2.0Cu2.0HAlBeta and Ag2.0Cu2.0SiBeta zeolites by conventional wet impregnation and two-step postsynthesis methods, respectively. The calcination of Ag2.0Cu2.0HAlBeta and Ag2.0Cu2.0SiBeta at 773 K for 3 h in air led to formation of C-Ag2.0Cu2.0HAlBeta and C-Ag2.0Cu2.0SiBeta. After reduction at 873 K for 3 h in flowing 10% H2/Ar, red-C- Ag2.0Cu2.0HAlBeta and red-C-Ag2.0Cu2.0SiBeta were obtained and investigated as the catalysts in gas phase hydrodechlorination of 1,2-dichloroethane at atmospheric pressure, at relatively low reaction temperature (523 K). The state of silver and copper in catalysts at different stages of their biography was characterized by low-temperature N2 sorption, temperature – programmed reduction (TPR), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and temperature-programmed hydrogenation (TPH). We have shown that the state of silver and copper species change under HDC conditions. After catalytic run both agglomeration of metal particles and their re-dispersion took place. According to TPH, XRD and XPS measurements we postulate that the cause of this phenomenon is the formation of chlorine containing species in spent zeolite catalysts.

Hydrodechlorination of (CH3)3SiCHCl2 over Pd, Ni, Co and Fe supported on AlF3

Gas phase hydrodechlorination (HDC) process of Me3SiCHCl 2 was studied in a flow reactor at 200 ∘C using a 2% metal loading (w/w) of four different monometallic catalysts (Pd/AlF 3, Ni/AlF 3,Co/AlF 3 and Fe/AlF 3). The catalysts were prepared by sol-gel method and structurally examined by BET method, FT-IR and XPS techniques. The XPS technique showed that Ni II, Fe III and Co III exist as oxides. The major products in the HDC process of Me 3SiCHCl 2 were identified by GC and GC-MS and found to include Me 3SiCH 2Cl, Me 3SiCl, and Me 4Si. The effect of these catalysts on the quantitative conversion, selectivity and conversion rates are reported. Gas phase hydrodechlorination process of Me3SiCHCl2 was studied in a flow reactor at 200°C using a 2% metal loading (w/w) of four different monometallic catalysts (Pd/AlF3, Ni/AlF3, Co/AlF3 and Fe/AlF3). The XPS technique showed that NiII, FeIII and CoIII exist as oxides. The major products in the process of Me3SiCHCl2 were identified to include Me3SiCH2Cl, Me3SiCl, and Me4Si

Exploring the role of the catalytic support sorption capacity on the hydrodechlorination kinetics by the use of carbide-derived carbons

This work aims at evaluating the effect of the catalytic support sorption capacity on the hydrodechlorination (HDC) process. Carbide-derived carbons (CDCs) have been selected for such goal as their high purity and tunable pore structure makes them a suitable carbon model material. CDCs were synthesized from TiC by chlorination at different extraction temperatures (800–1300°C) in order to selectively modify their pore structure and crystallinity. Afterwards, the catalysts were produced using a three step process of sulfuric acid treatment, ion-adsorption of palladium precursor and gas phase reduction. Pd/TiC-CDC (1% wt.) catalysts were tested in the HDC of 4-chlorophenol (4-CP) in both aqueous and organic phases under ambient conditions (30°C, 1atm, [4-CP]0=2.9mmolL−1, [Pd-TiC-CDC]=1gL−1, 50NmL H2min−1). The experimental results were successfully fitted by an expanded kinetic model which accounts for consecutive reaction and sorption processes in parallel, allowing to deduce true HDC kinetic constants.The sorption capacity of the support was found to determine the HDC rates in aqueous phase. In this sense, those catalysts showing the highest surface areas and lowered ordered structures led to higher HDC rates, confirming that a high surface density of 4-CP onto the catalyst surface enhances significantly the HDC reaction. The optimum catalyst (Pd/TiC-CDC-1000) led to the complete conversion of 4-CP in 15min at a HDC rate of 4.1×10−2Ls−1gcat−1.

Influence of the postsynthesis preparation procedure on catalytic behaviour of Ag-loaded BEA zeolites in the hydrodechlorination of 1,2-dichloroethane into value added products

Two silver-containing BEA zeolites prepared by a two-step postsynthesis method (Ag2.0SiBEA) and a conventional wet impregnation (Ag2.0HAlBEA) showed a high activity in the conversion of 1,2-dichloroethane (1,2-DCE) into value added products with 100% selectivity into ethylene and 100% selectivity into vinyl chloride, respectively. The role of the silver in two kinds of studied catalysts was different. The HRTEM, STEM with EDS elemental mapping showed that the excellent activity of silver containing catalyst, prepared by two-step postsynthesis method, in hydrodechlorination of 1,2-DCE was strongly related to the presence of very small (<3nm) metallic nanoparticles, resistant for the deactivation by chlorine poisoning. On the other hand, introduction of Ag ions into the HAlBEA zeolite led to a decrease of the coke formation during hydrodechlorination process on red-C-Ag2.0HAlBEA zeolite catalyst. As a result, it was observed lower drop of activity of red-C-Ag2.0HAlBEA catalyst than HAlBEA over HDC reaction with maintaining 100% selectivity to vinyl chloride.

Synthesis and characterization of green agents coated Pd/Fe bimetallic nanoparticles

The low stability and mobility of nanoparticles in liquid phase is one of the biggest challenges for the application of zero-valent iron (ZVI) technology. In this research, three green agents, polyethylene glycol (PEG), starch, and guar gum were coated on Pd/Fe bimetallic nanoparticles (NPs) to enhance the stability and reactivity of Pd/Fe NPs. The modified NPs (PEG-Pd/Fe, Starch-Pd/Fe, and Guar gum-Pd/Fe NPs) were characterized in terms of specific surface area, particle size, shape, morphology, and structural feature, etc. The results show that the diameters of modified Pd/Fe NPs are in the range of 60–100 nm. Compared with the pristine unmodified Pd/Fe NPs, the aggregations of modified Pd/Fe NPs were successfully reduced. XRD patterns indicate that modified Pd/Fe NPs remained the body centered cubic crystal structure, and the modification process contributed to improve the antioxidant ability. 2,4-Dichlorophenol (2,4-DCP) dechlorination experiments show that physico-chemical properties of the three modifiers have different effects on the reactivity of modified Pd/Fe NPs. The initial pH value of the reaction system had complex effects on the dechlorination of 2,4-DCP by using modified Pd/Fe NPs. Activation energies of pristine, PEG-Pd/Fe, Starch-Pd/Fe, and Guar gum-Pd/Fe NPs were calculated to be 39.47 kJ/mol, 38.66 kJ/mol, 36.59 kJ/mol, and 33.88 kJ/mol, respectively, implying that the modification process can enhance the dechlorination rate of Pd/Fe NPs, and that catalytic hydrodechlorination process of 2,4-DCP with modified Pd/Fe NPs is a surface-controlled chemical reaction.

Design of a Bimetallic Au/Ag System for Dechlorination of Organochlorides: Experimental and Theoretical Evidence for the Role of the Cluster Effect

The experimental study of dechlorination activity of a Au/Ag bimetallic system has shown formation of a variety of chlorinated bimetallic Au/Ag clusters with well-defined Au:Ag ratios from 1:1 to 4:1. It is the formation of the Au/Ag cluster species that mediated C–Cl bond breakage, since neither Au nor Ag species alone exhibited a comparable activity. The nature of the products and the mechanism of dechlorination were investigated by ESI-MS, GC-MS, NMR, and quantum chemical calculations at the M06/6-311G(d)&SDD level of theory. It was revealed that formation of bimetallic clusters facilitated dechlorination activity due to the thermodynamic factor: C–Cl bond breakage by metal clusters was thermodynamically favored and resulted in the formation of chlorinated bimetallic species. An appropriate Au:Ag ratio for an efficient hydrodechlorination process was determined in a joint experimental and theoretical study carried out in the present work. This mechanistic finding was followed by synthesis of molecular bimetallic clusters, which were successfully involved in the hydrodechlorination of CCl4 as a low molecular weight environment pollutant and in the dechlorination of dichlorodiphenyltrichloroethane (DDT) as an eco-toxic insecticide. High activity of the designed bimetallic system made it possible to carry out a dechlorination process under mild conditions at room temperature.

Hydrodechlorination of polychlorinated biphenyls in contaminated soil from an e-waste recycling area, using nanoscale zerovalent iron and Pd/Fe bimetallic nanoparticles

Soil pollution by polychlorinated biphenyls (PCBs) arising from the crude disposal and recycling of electronic and electrical waste (e-waste) is a serious issue, and effective remediation technologies are urgently needed. Nanoscale zerovalent iron (nZVI) and bimetallic systems have been shown to promote successfully the destruction of halogenated organic compounds. In the present study, nZVI and Pd/Fe bimetallic nanoparticles synthesized by chemical deposition were used to remove 2,2',4,4',5,5'-hexachlorobiphenyl from deionized water, and then applied to PCBs contaminated soil collected from an e-waste recycling area. The results indicated that the hydrodechlorination of 2,2',4,4',5,5'-hexachlorobiphenyl by nZVI and Pd/Fe bimetallic nanoparticles followed pseudo-first-order kinetics and Pd loading was beneficial to the hydrodechlorination process. It was also found that the removal efficiencies of PCBs from soil achieved using Pd/Fe bimetallic nanoparticles were higher than that achieved using nZVI and that PCBs degradation might be affected by the soil properties. Finally, the potential challenges of nZVI application to in situ remediation were explored.

Reductive degradation of chlorinated organic pollutants-contaminated water by bimetallic Pd/Al nanoparticles: Effect of acidic condition and surfactants

The Pd/Al nanoparticles (NPs) prepared by aqueous cementation were employed to probe hydrodechlorination (HDC) efficiencies of 4-chlorophenol (4-CP) in aqueous solution and 2-chlorobiphenyl (2-PCB) in surfactant solution. Major factors affecting HDC performance were investigated including acidic types, pH conditions, and surfactant types and their concentrations. Among HCl, H2SO4, H3PO4, formic acid, and acetic acid, only HCl was the proper pH adjustor to initiate HDC reaction of 4-CP with Pd/Al NPs at pH 3.0 due to the particular penetration function of active Cl− on the compact oxide film of Al. Aqueous pH states obviously influenced HDC efficiency and its values stable at pH 3–4 were the optimum range for HDC with HCl adjustor. 0.389mM of 4-CP could be almost completely dechlorinated into phenol after 30-min reaction using 2g/L of Pd/Al NPs with 1.2wt.% of Pd loading. In addition, the effect of surfactants on HDC process of highly hydrophobic 2-PCB was explored, which were employed for its better solubilization. The addition of surfactants including SDS, CTAB, Tween 80, or Brij 30 had adverse effect on HDC activity of Pd/Al NPs due to their inhibiting effect on Al corrosion. The adverse effect was closely related with the concentrations of surfactants especially for each CMC level and molecular structures.

Comparison for thermal decomposition and product distribution of chloroform under each argon and hydrogen reaction atmosphere

Thermal reaction studies of diluted mixture (1%) of chloroform (CHCl3) under each argon (Ar) and hydrogen (H2) reaction atmosphere have been investigated to examine the effect of reaction atmosphere on decomposition of CHCl3 and product distributions. The experimental results were obtained over the temperature range 525–900 °C with reaction times of 0.3–2.0 sec. at 1 atm by utilizing an isothermal tubular flow reactor. Complete destruction (>99%) of the parent reagent, CHCl3 was observed near 675 °C under H2 reaction atmosphere (CHCl3/H2 reaction system) and 700 °C under Ar reaction atmosphere (CHCl3/Ar reaction system) with 1 sec reaction time. The CHCl3 pyrolysis yielded more conversion in H2 atmosphere than in Ar atmosphere. Major products in CHCl3/Ar reaction system were C2Cl4, CCl4, C2HCl3 and HCl over a wide temperature range. Hydrocarbon was not found in CHCl3/Ar reaction system. Major products of CHCl3/H2 reaction system observed were CH2Cl2, CH3Cl, CH4, C2Cl4, C2HCl3, C2H2Cl2, C2H3Cl and HCl at 600 °C with 1 sec. reaction time. Non-chlorinated hydrocarbons such as CH4, C2H4 and C2H6 were the major products at above 850 °C. Product distributions were distinctly different in Ar and H2 reaction atmospheres. The H2 gas plays a key role in acceleration of reagent decay and formation of non-chlorinated light hydrocarbons through hydrodechlorination process. The important reaction pathways, based on thermochemical and kinetic principles, to describe the features of reagent decay and intermediate formation under each Ar and H2 reducing reaction atmosphere were investigated.

Complete Reduction of Polychlorinated Biphenyls by Acid-Etched Steel Wool in Supercritical Carbon Dioxide

Inexpensive household steel wool was used as a reducing agent for the reductive dechlorination of polychlorinated biphenyls (PCBs) in supercritical carbon dioxide (scCO2). Untreated steel wool does not produce significant results. Steel wool treated with 6 N HCl, however, showed complete reduction of the PCBs (Aroclor 1254) used. Scanning electron microscopy (SEM) reveals the formation of nanoscale pits (nanopits) on the surface of steel wool after etching with HCl. These nanopits are responsible for the high efficiency of the hydrodechlorination process.