METHOD FOR MEASURING ACID CONCENTRATION

Abstract: A method for measuring acid or alkali concentration by measuring the moisture content and electric conductivity of a sample and deriving the acid or alkali concentration of the sample from a predetermined relationship between electric conductivity corresponding to the moisture content and acid or alkali concentration.

Description: SPECIFICATION Method for Measuring Acid or Alkali Concentrations Technical Field: The present invention relates to a method for measuring acid or alkali concentrations. Background Art: Acids and alkalis play important roles in various industrial fields. Concentrations of acid or alkali, therefore, are very strictly controlled according to the manner of their uses. There have been proposed and put into practice various analyzing methods therefor. The most popular method is the titration method. The titration method has been used for various process control systems because of its high precision and relatively easy use. The titration method, however, presents serious problems in efficiency and safety in process control in fields in which a slight change in acid or alkali concentration greatly affects chemical reactions since it requires relatively long time for analysis. Disclosure of the Invention An object of the present invention is to provide a method of measuring an acid or alkali concentration with high precision in a short time. The method of measuring an acid or alkali concentration according to the present invention is characterized in that the acid or alkali concentration in a sample is determined by accurately measuring the water content and the electric conductivity in the sample, and then determining the acid or alkali concentration from the results of the above measurements using the correlation between the acid or alkali concentration and the electric conductivity in relation to the water content in the sample. Brief Description of the Drawing The deawing is a graph showing the correlation between the concentration of sulfuric acid and the electric conductivity in realation to the water content in samples. Best Mode for Carrying Out the Invention - The measuring system according to this invention comprises a water content measuring system and an electric conductivity measuring system. As the water content measuring system, any system which is suitable for the property of a sample may be selected from available chemical, optical or electrical measuring methods. All of these systems are modified in practice to obtain quick results, continuous measurements or recordings so that they can be used in online process control systems in industrial plants. For example, in the method of optically measuring water content by utilizing the principle that the energy of a predetermined discontinuous wavelength which is generated in the nearinfrared region is absorbed by the water, an infrared spectrum transmitted through a thin layer of water presents four absorption bands, i.e., 1.2 , 1.45 , 1.93 ij and 2.95 p. The water content in various substances can, therefore, be determined with high precision by conducting the transmission or reflection suitable for a sample at any of the above wavelengths. The values obtained by chemical, optical or electrical measurement are converted into electrical signals, recorded in a form suitable for the purpose, or transmitted to a control system. In this invention, it is preferable to transmit the values as signals to a measuring system for electric conductivity which has a memory for the correlation between the acid or alkali concentration and the electric conductivity in relation to the water content. An explanation will now be given of the measurement system for electric conductivity according to this invention. The concentration and the electric conductivity of a solution generally have a correlation under predetermined conditions. In the present invention, using the above principle, the acid or alkali concentration is determined by obtaining the correlation between the electric conductivity and the concentration of acid or alkali in realtion to various water contents, storing the calibration curve in a memory in advance, and measuring the electric conductivity. As the electric conductivity of a solution varies by temperature, it is desirable to maintain the temperature of a sample solution constant or minimize its variation and to conduct temperature compensation operations. The method according to the present invention is applicable to the measurement of an acid or alkali concentration in various types of solutions containing not only water and an acid or alkali but also in samples containing organic solvents. For example, it can be applied to the measurement of a sulfuric acid concentration in a reaction mixture obtained by decomposing cumene hydroperoxide (which is described hereinafter) under the presence of sulfuric acid to obtain phenol and acetone. In the case that the object of measurement is an acid or alkali organic solvent solution, it is necessary to prepare the sample to be analyzed by adding water to the sample taken out of the solution. The method according to this invention can be incorporated in an online process control system for industrial plants and can achieve process control of acid or alkali effectively since it can determine the concentration of acid or alkali with high precision in a short time by measuring the water content and the electric conductivity, and since the operator is free from the danger of directly contacting acids or alkalis that is often encountered in titration or other methods. An example of the present invention is shown below. Example: Sulfuric acid is used as a catalyst in a reaction to obtain phenol and acetone by decomposing cumene hydroperoxide. The concentration of sulfuric acid should be strictly controlled in order to prevent side reactions and improve yield. A sample was taken out of a reactor to which cumene hydroperoxide, sulfuric acid and acetone which is used for removing the reaction heat and contains about 1% of water were continuously fed, to optically determine the water content of the sample by Pier optical water analyzer (manufactured by Nippon Yak in Kagaku Kogyo Co., Ltd.). The correlation between the sulfuric acid concentration and the electric conductivity in relation to each water content was obtained in advance. The results are shown in the graph. In the graph, the symbols al, a2, a3 and a4 indicate water content and the progression al > a2 > a3 > a4. The correlation was stored in advance in the memory of the control system which was programmed so that when the data concerning the water content and the electric conductivity were transmitted, the sulfuric acid concentration was calculated and at the same time signals were transmitted to the feeding system of the sulfuric acid concentration. As a result, the concentration of sulfuric acid was maintained precisely at a predetermined level and the time required for measurement was shorter than the titration method, thereby preventing side reactions and remarkably improving the yield of phenol.

Claims: Claims: 1. A method for measuring the concentration of acid or alkali in a sample which comprises having water content present in the sample, precisely determining said water content, measuring the electric conductivity of said sample, and obtaining from the above results the acid or alkali concentration using the correlation between the acid or alkali concentration and the electric conductivity in relation to the water content. 2. The method as claimed in Claim 1 wherein the results of the measurements are stored in a memory system for the correlation between the acid concentration and the alkali concentration in relation to each water content, thereby determining the acid or alkali concentration.

Inventors: HAMAMOTO, TOSHIHARU, KOSHIBE, MINORU, YAMANO, NOBUYUKI
Applicants: MITSUI TOATSU CHEMICALS, INCORPORATED
Application year: 1983
Main classification: G01N27
IPC codes: G01N27