Research on the explosion characteristics of chlorine dioxide gas

Availableonlineatwww.sciencedirect.comCHINESEScience DirectCHEMICALLETTERSELSEVIERChinese Chemical Letters 19(2008)1375-1378Research on the explosion characteristics of chlorine dioxide gasRi Ya Jin, shuang Qi Hu, Ying Hao Zhang, Tao BoCollege of Chemical Environmental Engineering, North University of China, Taiyuan 030051, ChinaReceived 26 February 2008AbstractThe explosion characteristics of chlorine dioxide gas have been studied for the first time in a cylindrical exploder with a shellcapacity of 20 1. The experimental results have indicated that the lower concentration limit for the explosive decomposition ofchlorine dioxide gas is 9.5%(ICIO2V[air]), whereas there is no corresponding upper concentration limit. The maximum pressure ofexplosion relative to the initial pressure was measured as 0.024 MPa at 10% ClO2 and 0. 641 MPa at 90% CIO2. The induction timethe time from the moment of sparking to explosion) at 10% ClO2 was 2195 ms, but at 90% ClO2 the induction time was just msThe explosion reaction mechanism of C1O is of a degenerate chain-branching type involving the formation of a stable intermediate(Cl2O3), from which the chain branching occursC 2008 Ri Ya Jin. Published by Elsevier B V. on behalf of Chinese Chemical Society. All rights reservedKeywords: Chlorine dioxide gas; Explosive decomposition; Pressure of explosion; Explosion limitChlorine dioxide has attracted significant commercial attention as a novel neutral oxy-chlorine species acting as apowerful oxidant and disinfectant [1-5]. In its pure state, chlorine dioxide is unstable and can decompose into chlorineand oxygen upon heating or irradiation. CIO2 cannot be compressed or stored commercially because it decomposeswith time and is highly explosive at high concentrations. Therefore, ClO2 is generated on-site. The explosivedecomposition of chlorine dioxide at spontaneous process has been studied over the pressure and temperature ranges267-5332 Pa and54134C[6The explosion limit and pressure of explosion of chlorine dioxide gas have not been reported during the past fewdecades. The research reported herein concerns the explosion characteristics of chlorine dioxide, including theexplosion limit, the induction time prior to explosion, and the maximum pressure of explosion relative to the initialpressure. These parameters have been measured by igniting chlorine dioxide gas with an ignition electrode1. ExperimentalChlorine dioxide was synthesized as needed by mixing NaC1O2 with 20%(w/w)hydrochloric acid at about 50CThe ClO2 was passed through Drierite, which removed most of the H2O, and then it was transferred to the exploder; thepercentage relative humidity is 35% in it. The purity of the gas was checked by measuring its infrared spectrum. Noimpurities were ever found. Preparations and handling operations were all carried out in darknesss Corresponding authorE-mail address: jryal968@TYH中国煤化工001-8417/S-see front matter 2008 Ri Ya Jin. Published by Elsevier B V onCNMHGrights reserveddoi:10.1016 j cclet.200809.001376R Y Jin et al./Chinese Chemical Letters 19(2008)1375-1378An apparatus for studying chlorine dioxide gas explosions was constructed entirely from stainless steel alloy, itonsisted of a 20 I cylinder explosion tank and a vacuum system with an absolute pressure of <5 kPa which could beattained by means of a mechanical pump. The temperature was controlled at 25+2C by means of a bimetalthermoregulator, and this controlled relay in turn activated an electric heaterThe preset parameters for control tests were as follows: test specification of pressure 0-5 MPa, sensitivity shift11.37 mV/105 Pa, sampling frequency 10.00 kHz, sampling length 50 K, sampling time5 K, triggering level0.0156 V, filter frequency of the electric amplifier 0.3-100 kHz, and ignition voltage output 8 kV. When theconcentration of chlorine dioxide gas was below 50%(IC1O2 airD), the voltage range selected was +I V; when theconcentration of chlorine dioxide gas was greater than 60%0, the voltage range selected was +2 VThe percent by volume of chlorine dioxide gas admitted into the tank was controlled through the partial pressureThe delay time from admission into the tank was 500 ms prior to autoignition2. Results and discussionWhen the concentration of chlorine dioxide gas was 10%, in a series of five experiments, a signal intensity indicati(24.414 m v)of explosion was obtained only once after ignition, but in the other cases no detonator signal was obtainedWhen the concentration of chlorine dioxide gas was 9.5%0, no signal waves indicative of an explosion were obtainedafter ignition in any of a series of five batch experimentsWhen the concentration of chlorine dioxide gas was greater than 20%0, the dependences of the induction time(orensitive time) and the maximum pressure of explosion were relative to the initial pressure on the concentration ofchlorine dioxide. The higher the concentration of chlorine dioxide, the greater the pressure of explosion, and theshorter the induction time. When the concentration of C1O, was increased from 10% to 80%, the induction time wasreduced from 2195 ms to 8 ms. but it did not decrease further on increasing the concentration of clo, to 90% whenhe concentration of ClO2 was increased from 10%o to 90%, the maximum pressure of explosion relative to the initialpressure increased from 0.024 MPa to 0.641 MPa(as shown in Fig. 1 ). It is apparent that there is no upperconcentration limit for the explosion of chlorine dioxide gasWhen chlorine dioxide gas was ignited by an electrode, explosive decomposition reactions were observed asopposed to a slow spontaneous process. In an explosion, the rate of decomposition of chlorine dioxide was greatlyaccelerated, and the pressure of explosion increased rapidly at first and then reached a maximum, It could beconcluded that ignition by an electric spark gave rise to a branched-chain reaction. This explosive decompositioncannot be thermal in nature or of the ordinary chain-branching typeIn order to confirm the explosive products ignited C1O2, infrared spectrum analysis of the expleignited ClO2 determined that the intermediate were Cl2O, and Cl2O6, and the IR spectra of gaseous and matrix-isolated Cl2O6 and Cl2O3 were recorded in the range 1500-300 cm by using the FtiR spectrometer: FTS 3000 bydigilab of America, with the infrared spectrogram shown in Figs. 2 and 3, respectively. It can be seen from Fig. 2, thethree bands are observed in the region of the asymmetric stretching modes of the CIO2 and ClO3 groups(1200-1100 cm ) respectively, and the other two bands are also found in the region of the symmetric stretching modes of兰-0.6The sensitive time of explosive/T(ms)中国煤化工10Fig. 1. The maximum pressure of explosion curve for CIO2 gas relative to the initial atmeCNMHGof explosive at differentconcentration ([CiO2airD)R Y Jin et al./Chinese Chemical Letters 19(2008)1375-137811259eFig. 2. Infrared spectrum of explosive products ignited ClO2 determined that the intermediate was ClOggh0.2Fig. 3. Infrared spectrum of explosive products ignited ClO2 determined that the intermediate was Cl2Othe ClO2 and CiO3 groups (1000-900 cm ) respectively. Furthermore, the bands at 628 and 566 cm shouldcorrespond to the stretching modes of asymmetry in the two groups, as is agreement with the spectra of Cl2O observedby Jansen et al. [7]. So the Cl2O6 was determined in the explosive products. On the other hand, the most importantthree vibrational frequencies of Cl2O3, from Fig 3, the 1 126.0 and 975.0cm can be approximately described as theantisymmetric and symmetric stretching of Cl-O of ClO 2 group, respectively, the 487.3 cm as the stretching modeof Cl-O of ClO2 group, as was almost accordance with the spectra of Cl2O3 observed by Muller and Willner [8] andBurkholder et al. [9], in which the corresponding values were 1203. 1, 1060 and 506 cm respectively. Thus, theCl2O3 was also confirmed in the explosive productsSo, it belongs to a special case in which the reactant forms a stable intermediate(Cl2O3). A mechanism applicableto the CiO2 explosion after ignited the initiation reaction is believed to be:2ClO2→ClO+ClO3ClO2+Clo→Cl2O3As the concentration of the ClO3 built up, its reaction with the chain carrier CIO became increasingly importantThe most reasonable way for this reaction to occur would be as followsCIO+Cl2O3-ClO2+ClOOCl(3)Thus the dissociation reactions believed to occur are as follows:中国煤化工CIOOCI1→ClOO+C1CNMHGClOo→Cl+O21378R Y Jin et al. /Chinese Chemical Letters 19(2008)1375-1378Once Cl atoms are produced, the branching reactionCl+ClO2→2ClOis expected to occur.The dominant termination reactions under the conditions of this study wereCl+ClO2→Cl2+OCl→知C2In fact, Gray and IP [10, 11] have already investigated the spontaneously explosive decomposition of gaseoushlorine dioxide with helium, hydrogen, methane, ethane, propane, ethyle and butadiene as diluents, and they foundthat it was branched-chain rather than thermal in character, which is supported indirectly by the pressure-timehistories and by the induction periods observed the explosion of mixtures of chlorine dioxide. Moreover, Green et al[12]observed that the photolysis of CIO 2 could lead to the formation of Cl2O3 as a result of the addition of the CIo atlow temperatures in 2004. Furthermore, Croce et al. [13] reported that the products Cl2O4, Cl2O6, Cl and O2 wereformed under the photochemical decomposition of 5-80 torr gaseous ClO2 at 293 and 303 K in 2008. In particular,Davis and Lee [14] used photo fragment translational energy spectroscopy to study the dissociation dynamics of arange of electronically excited OCIO vibrational states, and they observed that for all levels studied, the dominantproduct(>96%)was CIO+O, accompanied by the production of Cl +O2 with a quantum yield of up to 3. 9+.8%Compared with the results mentioned above, it can be seen that our explosion reaction mechanism in this paper iseliable3. Conclusionse. There is no upper concentration limit for the explosion of chlorine dioxide gas, but the low concentration limit forplosion has been found to be 9.5%( air). Thus, when the concentration of chlorine dioxide gas in air isbelow 9.5%o it does not present an explosion hazardThe induction time and the maximum pressure of explosion relative to the initial pressure are dependent on theconcentration of chlorine dioxide gas, and the higher the concentration of chlorine dioxide gas, the greater the pressureof explosion, and the shorter the induction times. The explosive decomposition of CIO2 is of a degenerate chainbranching type involving the formation of a stable intermediate(C12O3), from which chain branching occurs. Chaininitiation takes place at the point of ignition, and termination takes place on the inner walls of the exploderAcknowledgmentsThis work was supported by the National Natural Science Foundation of China(No. 50774068)and ShanxiProvincial Science and Technology Department, China.References[1] C.Y. Chang, Y.H. Hsieh, S.S. Hsu, J. Hazard. Mater. B79(2000)89[2]J Du, Y. Han, R.H. Linton, Food Microbiol. 20(2003)5833] T.w. Chien, H. 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