On-line Determination Method Of High Concentration Chlorine Dioxide Gas

Chlorine dioxide gas is unstable and explosible. Concentration of ClO₂ during production must be diluted within the safe concentration, generally less than 10%. by entering air. However, the concentration of ClO₂ gas can not be too small. Otherwise, it can not reach the using instructions. Conventional analytical methods are too complicated and time-consuming to meet the detecting demand for ClO₂. According to a large number of experiments, this dissertation has set up two kinds of on-line determination methods for high concentration ClO₂ gas. which are simple and convenient.These two methods employ water to absorb ClO₂ gas, and then the concentration of ClO₂ gas can be determined indirectly by measuring the concentration of ClO₂ solution using the photometer. Therefore, the shortcoming that ClO₂ gas will decompose in light is overcome. In addition, no chemical reagent is needed, and no waste is generated. The brief descriptions of these two applicable methods are as follows:1. The first method is the absorption membrane-tube spectrophtometry. Chlorine dioxide gas diffuses through the capillary ventilative membrane tube and dissolves in the water flowing in the tube in succession. The concentration of ClO₂ solution is detected by the photometer at wavelength of 370-375 nm and the concentration of ClO₂ gas is obtained indirectly. The results of the absorbent membrane-tube spectrometry show that:(1) The optimum measurement conditions: a light-emitting diode (LED) with wavelength about 370-375 nm was chosen as the light source of the photometer; a 30cm long silicon tube was used as the absorbing pipeline; absorption temperature was 40℃; Gas flow rate had no influence on determination, but different liquid flow rate could result in different concentration of ClO₂ solution, so the liquid flow ratemust be controlled accurately; pH within 5.0-9.0 showed no influence.(2) Under the aforementioned conditions, the detection range of CIO2 gas was 0.43-12.3%. When concentration was higher than this range, we could regulate the liquid flow rate to change the concentration of CIO2 solution so as to ensure absorbance in the linear range of the photometer.(3) The response time of this method was 30-50 s and it reduced with the increasing of the liquid flow rate.(4) This method was used for on-line determination of the CIO? from the generator. It is quick, simple, reliable, interference-free and better precise. There was no significant difference (PO.01) between this method and the continuous iodimetry.2. The second method is the absorption coil spectrophotometry. Chlorine dioxide gas diffuses into water of circular motion in the coiled pipe and then equilibrium of CIO2 is formed. The concentration of the equilibrium is detected by the photometer at wavelength of 410-420 nm and the concentration of CIO2 gas is achieved indirectly. The results of the absorbent coil spectrophotometry show that:(1) The optimum measurement condition: a LED with wavelength of 410-420 nm was used as the luminous source of the photometer; a coil of 0.4 cm diameter, 30 cm helix diameter and 60 cm length was selected as the mixing pipeline; absorption temperature was 40°C; there was no need to control the gas flow rate and liquid flow rate accurately under the condition that the flow rate ratio of gas and liquid was over 1000; pH within 5.0-9.0 had no influence.(2) Under above-mentioned conditions, the detection range of CIO2 gas was 0.14-11.1%. When concentration was higher than this range, we could dilute the equilibrium of CIO2 to the linear range of the photometer, but the detection range was doubled according to the dilution multiple.(3) The response time of this method was 15³0s, and it reduced with the increasing of the gas flow rate and the liquid flow rate.(4) This method was used for on-line determination of chlorine dioxide from the generator. It is quick, simple, reliable, interference-free and better precise. There was no significant difference (PO.01) between this method and the continuous iodimetry.