Chlorination Rate Research Articles

Catalytic oxidation of chlorobenzene over Pd/perovskites

The catalytic performances of pre-reduced palladium catalysts supported on lanthanum based perovskites LaBO3 (B=Co, Mn, Fe, Ni) were investigated for the total oxidation of chlorobenzene (PhCl; 1000ppmv) in air. The catalysts were prepared using a wet impregnation technique and Pd-nitrate was used as a palladium precursor. The catalytic performances were compared to those of a reference palladium catalyst supported on a conventional support, namely γ-Al2O3. Easiness of chlorobenzene destruction was found to follow the sequence based on the T50 values (temperature at which 50% of chlorobenzene was converted into products): Pd/LaMnO3+δ (243°C)>Pd/LaFeO3 (270°C)>Pd/Al2O3 (348°C)>Pd/LaCoO3 (360°C)>Pd/LaNiO3 (408°C). Complete conversion of chlorobenzene is reached at ca. 320–500°C, but at those temperatures substantial amounts of polychlorinated benzenes are formed. Quasi in situ XPS studies were monitored on Pd/LaCoO3 and Pd/LaFeO3 after each stage of the global process, namely after calcination, reduction and exposure to the flowing reactive mixture (1000ppmv PhCl in air) from room temperature to 230 and 310°C (Pd/LaFeO3) and to 280°C (Pd/LaCoO3). It was shown that the calcination treatment leads to a palladium which a BE higher than that of PdO and to a (B/La)XPS<1 which attests of a lanthanum enrichment at the XPS surface. After H2 treatment it was shown that palladium is totally reduced while the B cation is either unreduced (Fe3+) or reduced (Co3+ into Co2+ and Co0). In the reactive atmosphere, Pd0 is progressively (oxi)chlorined while the perovskite network is reconstructed with productions of LaOCl and Co3O4. The pre-reduced Pd/LaBO3 are more active than the perovskite alone for PhCl transformation but substantially increase the chlorination rate of PhCl. Among the different catalysts Pd/LaFeO3 shows the best compromise between PhCl oxidation and chlorination rates.

Myeloperoxidase-catalyzed chlorination: The quest for the active species

Myeloperoxidase (MPO) is a dominating enzyme of circulating polymorphonuclear neutrophils that catalyzes the two-electron oxidation of chloride, thereby producing the strong halogenating agent hypochlorous acid (ClO(-)/HOCl). In absence of MPO the tripeptide Pro-Gly-Gly reacts with HOCl faster than the amino acid taurine (2-aminoethanesulfonic acid, Tau), while the MPO-mediated chlorination shows reverse order. A comparative study of the enzymatic oxidation of both substrates at pH 4.0-6.0, varying H2O2 concentration is presented. Initial and equilibrium rates studies have been carried on, reaction rates in the latter being slower due to the chemical equilibrium between MPO-I and MPO-II-HO2. A maximum of chlorination rate is observed for Pro-Gly-Gly and Tau when [H2O2] approximately 0.3-0.7 mM and pH approximately 4.5-5.0. Several mechanistic possibilities are considered, the proposed one implies that chlorination takes place via two pathways. One, for bulkier substrates, involves chlorination by free HOCl outside the heme cavity; ClO(-) is released from the active center, diffuses away the heme cavity, and undergoes protonation to HOCl. The other implies the existence of compound I-Cl(-) complex (MPO-I-Cl), capable of chlorinating smaller substrates in the heme pocket. Electronic structure calculations show the size of Pro-Gly-Gly comparable to the available gap in the substrate channel, this tripeptide being unable to reach the active site, and its chlorination is only possible by free HOCl outside the enzyme.

Chlorination of Titanium Oxycarbide Produced by Carbothermal Reduction of Rutile

Titanium oxycarbide was produced by carbothermal reduction of rutile. Mixtures of titania and graphite with different carbon to titania molar ratio were pressed into pellets and heated under argon atmosphere at 1450 °C. Titanium oxycarbide was chlorinated in a horizontal tube furnace. Effects of furnace temperature, chlorine partial pressure, gas flow rate, and particle size on the rate and extent of chlorination were examined. The chlorination was ignited at 150 °C to 200 °C. Chlorine partial pressure and gas flow rate strongly affected the chlorination rate, while the effect of particle size was insignificant. Best chlorination results were obtained for titanium oxycarbide produced with carbon to titania molar ratio 2.5, and chlorination was close to 100 pct in 30 minutes.

Additive-Gas Effects on Cl2 Plasma-Based Copper-Etch Process and Sidewall Attack

The influence of the additive gas in plasma-based copper etch and sidewall attack was investigated. The additive gas, such as Ar, , and , drastically changed the plasma-phase chemistry, i.e., the Cl radical concentration, and the ion-bombardment energy, which resulted in changes of the copper chlorination rate and the sidewall roughness. The addition of Ar increased the Cl concentration, which increased the copper chlorination rate and the sidewall attack. The addition of enhanced ion bombardment, which increased the copper chlorination rate. Meanwhile, the addition of diluted the Cl concentration and formed a copper nitride passivation layer, which protected the sidewall and reduced roughness. The addition of induced a fluorocarbon passivation layer, which decreased the copper chlorination rate in the vertical direction but protected the sidewall from vigorous Cl attack and resulted in a smooth sidewall surface. Therefore, the additive gas not only affected the Cu chlorination rate but also influenced sidewall roughness.

The kinetics and mechanism of selective iron chlorination of an ilmenite ore

The kinetics of the ilmenite chlorination was studied between 600 and 850°C. The ilmenite chlorination rate was determined by monitoring the mass changes using a thermogravimetric system of high resolution. Non-isothermal and isothermal runs were performed. The influence of temperature, chlorine flow and sample mass in the reaction rate was established. The thermal decomposition of ilmenite previous to the chlorination was taken into account. The formation of intermediate titanates during the chlorination reactions was found. The dependence of the reaction rate with temperature was analysed, and apparent activation energy of 186 kJ mol−1 was obtained for the chlorination process. A global mechanism was proposed involving: rupture of the ilmenite structure, formation and subsequent decomposition of pseudorutile and chlorination of hematite.

Behaviour of Rare Earth Elements in Molten Salts in Relation to Pyrochemical Reprocessing of Spent Nuclear Fuels

The kinetics of chlorination of lanthanide oxides (by Cl2 and HCl) and precipitation of lanthanide phosphates was studied by in situ electronic absorption spectroscopy in 3LiCl-2KCl and NaCl-KCl melts at 400-750 oC. Products of the chlorination are the corresponding hexachlorospecies, LnCl63-, and the rate of chlorination increases with increasing temperature. Composition of the precipitated phosphates depends on the melt composition and 1.5-5 fold excess of phosphate, depending on the nature of lanthanide, is needed for the complete removal of the lanthanides from the melt. Over three hours are required for completing the reaction of phosphate precipitation.

Myeloperoxidase-catalyzed taurine chlorination: Initial versus equilibrium rate

Myeloperoxidase (MPO) catalyzes the two-electron oxidation of chloride, thereby producing hypochlorous acid (HOCl). Taurine (2-aminoethane-sulfonic acid, Tau) is thought to act as a trap of HOCl forming the long-lived oxidant monochlorotaurine [( N-Cl)–Tau], which participates in pathogen defense. Here, we amend and extend previous studies by following initial and equilibrium rate of formation of ( N-Cl)–Tau mediated by MPO at pH 4.0–7.0, varying H 2O 2 concentration. Initial rate studies show no saturation of the active site under assay conditions ( i.e. [H 2O 2] ⩾ 2000 [MPO]). Deceleration of Tau chlorination under equilibrium is quantitatively described by the redox equilibrium established by H 2O 2-mediated reduction of compound I to compound II. At equilibrium regime the maximum chlorination rate is obtained at [H 2O 2] and pH values around 0.4 mM and pH 5. The proposed mechanism includes known acid–base and binding equilibria taking place at the working conditions. Kinetic data ruled out the currently accepted mechanism in which a proton participates in the molecular step (MPO-I + Cl −) leading to the formation of the chlorinating agent. Results support the formation of a chlorinating compound I–Cl − complex (MPO-I–Cl) and/or of ClO −, through the former or even independently of it. ClO − diffuses away and rapidly protonates to HOCl outside the heme pocket. Smaller substrates will be chlorinated inside the enzyme by MPO-I–Cl and outside by HOCl, whereas bulkier ones can only react with the latter.

Kinetics for chlorination of maleic anhydride grafted polypropylene

AbstractPreparation of Chlorinated maleic anhydride grafted polypropylene (Cl‐PP‐g‐MAH) by free radical process was carried out using carbon tetrachloride (CCl4) as the solvent and benzoperoxide (BPO) as the initiator. Effects of reaction temperature, concentrations of PP‐g‐MAH and BPO on the rate of chlorination were studied. The experimental results showed the actual rate constant for chlorination of maleic anhydride grafted polypropylene followed the Arrhenius law and the total apparent activation energy was 19.7 kJ mol−1. The kinetic model for chlorination of maleic anhydride grafted polypropylene was found to be R = K[BPO]0.53[C]0.93. The properties of chlorination of maleic anhydride grafted polypropylene were better than those of maleic anhydride grafted polypropylene. The products were characterized by Fourier transform infrared spectroscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Experimental study of mass transfer and H 2S removal efficiency in a spray tower

The aim of this study was to characterise the mass transfer parameters and H 2S removal efficiency in a laboratory-made spray tower designed for deodorisation. In order to study mass transfer, the volumic interfacial area ( a) and the volumic mass transfer coefficient ( k L a) were estimated. The influences of both superficial liquid and gas velocities were quantified ( U L from 4.1 × 10 −5 to 4.6 × 10 −4 m s −1, U G from 9.4 × 10 −3 to 2.8 × 10 −2 m s −1). It could be shown that the superficial liquid velocity has a slight influence on the mass transfer parameters whereas the variation of the superficial gas velocity influences them much more. Then H 2S removal efficiency was studied at pH 10 in the presence or not of an oxidant, sodium hypochlorite. The results demonstrated that as soon as the chlorination rate reached 0.5 g Cl 2 L −1, more than 99% of the hydrogen sulphide is removed.

Kinetics of reactions between chlorine or bromine and the herbicides diuron and isoproturon

AbstractThe chemical oxidation of two herbicide derivatives of the phenylurea group—diuron and isoproturon—has been carried out by means of chlorine, in the absence and in the presence of bromide ion. Apparent second‐order rate constants for the reactions between chlorine and the herbicides were determined to be below 0.45 L mol−1 s−1. Hypobromous acid reacts faster with the investigated herbicides, especially with isoproturon (kapp = 24.8 L mol−1 s−1 at pH 7). While pH exerts a negative effect on the bromination rate, the maximum chlorination rate was found to be at circumneutral pH. In a second stage, the oxidation of each compound was conducted in different natural waters, in order to simulate the processes which take place in water purification plants. Again, chlorine was used as an oxidant, and bromide ion was added in some experiments with the aim of producing the more reactive HOBr oxidant. The herbicide oxidation rate was inversely proportional to the organic matter content of the natural water. However, the formation of trihalomethanes (THMs) was directly proportional to the organic matter content and constitutes a limitation for the application of chlorine during drinking water treatment. Finally, the evolution of herbicide concentration was modeled and predicted by applying a kinetics approach based on the rate constants for the reactions between the herbicides and the active oxidants. Copyright © 2007 Society of Chemical Industry

Ａｒ‐Ｃｌ２‐Ｏ２雰囲気におけるＰｂＯ‐ＰｂＣｌ２の塩化および蒸発挙動

It is quite important to know the reactivity and behavior of Pb contained in steelmaking dust, or bottom ash and fly ash generated from municipal solid waste incineration process with chlorine. In the present study, chlorination and evaporation kinetics of PbO-PbCl2 melt have been investigated in Ar-Cl2-O2 atmosphere from 1023 to 1123K. The weight of PbO specimen increased first and then decreased in Ar-Cl2-O2 stream during experiments, which phenomena mean that produced PbCl2 by PbO chlorination formed liquid oxychloride phase of PbO-PbCl2 system and then PbCl2 evaporated. Increase of partial pressure of chlorine increased the initial chlorination rate, however no effect on the latter evaporation rate was observed. Decrease of maximal weight gain of specimen and the slight increase of evaporation rate were observed with increasing partial pressure of oxygen. Apparent activation energies of chlorination and evaporation of PbO-PbCl2 melt in the steady state were 35 kJ/mol and 156 kJ/mol, respectively. Evaporation rate of PbO-PbCl2 was also investigated at 1073K in Ar-O2 atmosphere, however the change of evaporation rate with changing partial pressure of oxygen was within experimental error. Measured evaporation rate strongly depended on the composition of melt. Composition dependency of evaporation rate estimated from the activity of PbCl2 for the PbO-PbCl2 system generally represented the same trend, however the measured evaporation rate was larger than estimated one in the whole composition range. This result indicates that the formation of oxychloride melt affects the evaporation rate. Chlorination mechanisms and removal efficiency of Pb by chlorination have been discussed based on the present results.

Comparison of reductive dechlorination of p-chlorophenol using Fe 0 and nanosized Fe 0

Chlorophenols, as a kind of important contaminants in groundwater, are toxic and difficult to biodegrade. Laboratory tests were conducted to examine zero-valent iron as an enhancing agent in the dechlorination of chlorinated organic compounds. Nanoscale iron particles were synthesized from common precursors KBH 4 and FeSO 4. Batch experiments were performed to investigate the reduction of p-chlorophenol (4-CP) by both common Fe 0 and nanoscale Fe 0. Comparison of 300 mesh/100 mesh/commercial reductive iron powders showed that size of iron particles played an important role in reduction process. Initial concentration and pretreatment of iron particles also influenced the chlorination rate. Nanoscale Fe 0 offered much more advantages for treatment of 4-CP compared with common iron particles, such as stability and durability. And they can be used to treat contaminants in groundwater over a long time. Among different parts of synthesized nanoscale iron particle solution, the very fine particles were the major agent for treatment of pollutants. As for preservation of nanoscale Fe 0, ethanol was recommended.

Chlorination of MgOHCl with HCl gas

Chlorination of MgOHCl particles with HCl gas was examined and complete conversion to MgCl2 was observed within 60 min in the temperature range 325–525°C. X-ray diffraction analysis of samples treated for varying times revealed that MgOHCl was directly converted into MgCl2 without first decomposing into MgO. Such behaviour was observed even at temperatures significantly higher than the equilibrium decomposition temperature of MgOHCl under ambient atmosphere. The results also showed that the rate of chlorination of MgOHCl was independent of temperature.

Chlorination kinetics of ZnO with Ar-Cl2-O2 gas and the effect of oxychloride formation

The chlorination rate of ZnO with Ar-Cl2-O2 gas was measured from 1023 K to 1273 K and the effects of temperature and partial pressures of chlorine and oxygen were investigated. The rate-determining step of chlorination was considered to be the dissociation of intermediate between ZnO and Cl2 from linear relationship between reciprocal values of reaction rate and partial pressure of chlorine. The activation energy of chlorination was 58.2±2.5 kJ/mol. This comparatively low activation energy as a chemically controlled reaction was consistent with estimated rate-determining step of the dissociation of unstable compound. Increasing the partial pressure of oxygen slightly increased the chlorination rate, and this effect is considered to be caused by the increase in the formation rate of zinc oxychloride. To clarify the formation of zinc oxychloride, the equilibrium between Ar-Cl2-O2 gas and ZnO was investigated by the transpiration method at 1073 K. Calculated partial pressures of ZnOCl from experimental results were in the same order with or one order of magnitude larger than those estimated from reported Gibbs energy of formation of ZnOCl. Zinc oxychloride formation in ZnO chlorination must be taken into consideration as well as ZnCl2 and Zn2Cl4 formation.

Chlorination Kinetics of ZnFe&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;4&lt;/SUB&gt; with Ar-Cl&lt;SUB&gt;2&lt;/SUB&gt;-O&lt;SUB&gt;2&lt;/SUB&gt; Gas

Chlorination rate of ZnFe2O4 with Ar-Cl2-O2 gas was measured at 1023 to 1123 K by gravimetry. The effects of temperature, partial pressures of chlorine and oxygen on the rate were investigated. Zinc oxide contained in ZnFe2O4 specimen was selectively chlorinated and evaporated in gas, while iron oxide remained as oxide in a chlorinated residue. Chlorination rate increased with increasing partial pressure of chlorine. On the other hand, chlorination rate slightly decreased with increasing partial pressure of oxygen and chlorination of iron oxide was prevented. Since the order of chlorination rate with respect to partial pressure of chlorine was approximately 0.5, the rate-determining step of chlorination is considered to be the dissociative adsorption of chlorine gas on the surface of solid ZnFe2O4. Decrease of chlorination rate with the increase of partial pressure of oxygen could be explained by the occupation of adsorption sites of chlorine atoms by oxygen and the chlorination rate was expressed as functions of partial pressures of chlorine and oxygen as r=k·(P_Cl2^1/2/1+K_OP_O2^1/2) The activation energy of chlorination was 35.1±2.2 kJ/mol which is relatively small compared to that of ZnO chlorination reaction (58.2 kJ/mol). It is considered that this low activation energy is due to the weak adsorption of chlorine atom on the adsorption site.

Removal of Zn and Pb from Fe2O3–ZnFe2O4–ZnO–PbO Mixture by Selective Chlorination and Evaporation Reactions

Selective chlorination and evaporation reactions could become one of the useful methods for the treatment of steelmaking dust containing zinc and lead. In the present study, chlorination rate of Fe2O3–ZnFe2O4–ZnO–PbO mixture with Ar–Cl2–O2 gas (PCl2=0.5×104 to 2.0×104 Pa, PO2=1.0×104 to 5.1×104 Pa) has been measured at 1 073 K by gravimetry and the effects of partial pressures of chlorine and oxygen on the chlorination and evaporation rates have been investigated. Zinc oxide and lead oxide contained in the oxide mixture were selectively chlorinated and zinc and lead chlorides evaporated to gas phase, while iron oxide remained as oxide in a chlorinated residue. By chlorinating with Ar–Cl2 gas, over 99% of zinc and lead could be removed from oxide mixture and approximately 3% of iron has been lost by chlorination and evaporation reactions simultaneously. To decrease the loss of iron oxide and improve the efficiency of selective chlorination and evaporation reactions, chlorination by using Ar–Cl2–O2 gas has been conducted and the enrichment of oxygen gas effectively depressed the chlorination of iron oxide, while the removal efficiency of zinc and lead was maintained.

Transformation of Pyrene in Aqueous Chlorination in the Presence and Absence of Bromide Ion: Kinetics, Products, and Their Aryl Hydrocarbon Receptor-Mediated Activities

To assess the endocrine-disrupting activity stemming from the presence of pyrene in drinking water, the kinetics of chlorination of pyrene was investigated at room temperature, the products of its aqueous chlorination with and without bromide ion were identified, and their aryl hydrocarbon receptor (AhR)-mediated activities were determined. It was found that the presence of bromide ion greatly promoted the reaction rate of chlorination of pyrene accompanied with the formation of brominated products. While the main product was 1-Cl-pyrene without the addition of bromide ion, di-Br-pyrene and 1-Br-pyrene became the main products in the presence of bromide ion. GC-MS and NMR analysis identified three structures of dibromopyrene in chlorination with the addition of bromide ion as 1,3-di-Br-pyrene, 1,6-di-Br-pyrene, and 1,8-di-Br-pyrene, and their molar ratio was determined to be approximately 0.3:1:1. Finally, 1-Br-pyrene, 1,3-di-Br-pyrene, a mixture of 1,6-di-Br-pyrene and 1,8-di-Br-pyrene (di-Br-pyrene), 1-Cl-pyrene, and a mixture of 1,6-di-Cl-pyrene and 1,8-di-Cl-pyrene (di-Cl-pyrene) were fractionated by HPLC, and their AhR-mediated activities were assessed by a yeast assay. It was found that the effective molar concentrations (or mass concentration) showing half-maximal transcriptional response, EC50, for pyrene, 1-Br-pyrene, 1-Cl-pyrene, di-Cl-pyrene, and di-Br-pyrene were 5632 (1.14), 3089 (0.86), 1942 (0.46), 597.2 (0.21), and 147.3 (0.04) nM (mg/L), respectively.

Kinetics of MgO chlorination with HCl gas

The kinetics of chlorination of MgO particles with HCl gas in the temperature range from 450 °C to 650 °C were measured and analyzed in terms of the shrinking core model. The MgO particles were produced by the thermal decomposition of MgOHCl manufactured in-house and were found to have a d50 of 510 nanometers. Over 90 pct of the MgO was converted to MgCl2 within 30 minutes at 650 °C. Analysis of the data indicated that the chlorination process was initially controlled by the kinetics of the chemical reaction between MgO and HCl, but as the thickness of the MgCl2 product layer increased as the chlorination progressed, the rate of chlorination became controlled by the diffusion of HCl through the MgCl2 ash layer surrounding a MgO core in the particles. A mathematical model that predicted the shrinkage of the MgO core with time was found to be in good agreement with the measurements over the range of temperatures studied. The ash layer thickness for the onset of the diffusion control regime was found to increase linearly with temperature. The apparent rate constant for chlorination in the initial reaction-controlled regime was well described by the Arrhenius equation: k (m/s)=0.0787 exp (−7596/T).

Kinetics of Low-Temperature Oxidative Chlorination of Benzene in Aqueous Acetic Acid

The kinetics of chlorination of benzene with a mixture of sodium peroxide with hydrochloric acid in aqueous acetic acid at 298 K was studied. The chlorination rate is the highest when the AcOH concentration in the binary solvent is 49.4-40.6 mol % and the ratio of the initial cocentrations of water and sodium peroxide, 18.5–20.2. The linear dependences of logk app on the AcOH concentration and [H2O]0/[Na2O2]0 ratio were obtained.

Nonaqueous Chlorination of Uranium Metal in Tributyl Phosphate

Low-temperature chlorination of uranium metal in the TBP-TCE-Cl2 systems was studied. Dissolution of uranium in the dipolar aprotic solvent proceeds with formation of U(IV) compounds. The activation energy of this process is 31.24 kJ mol−1, and relative reaction order with respect to Cl2 is 2. The effect of TBP concentration on chlorination was examined. The chlorination rate sharply increases at a water content in the TBP-TCE system of 0.2–0.6 vol %.