JP3196181B2 - Reaction endpoint control method using ORP electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, when chlorinating milk of lime to obtain calcium hypochlorite,
The present invention relates to a method for performing automatic management using an ORP electrode meter instead of analyzing the liquid composition of a reaction solution.

[0002]

2. Description of the Related Art To control the end point of a reaction for producing highly bleached powder by chlorinating lime milk, analysis of the concentration of residual alkali in a conventional reaction solution or observation of the crystal state of calcium hypochlorite in the reaction solution by a microscope. And so on. If too much alkali is left, insoluble residues increase in the final product, whereas if the alkali becomes completely zero, calcium hypochlorite will decompose. Therefore, it is desirable that the residual alkali be 0.8 ± 0.1% at the end of the chlorination reaction.

On the other hand, end point management methods using ORP electrodes have been studied in recent years, but have not been fully utilized. Generally, in the production reaction of calcium hypochlorite, the indicated value of the ORP electrode increases as the reaction proceeds. However, in this case, it is difficult to find a correlation between the absolute value of the ORP electrode potential and the calcium hypochlorite concentration. that is,
Potential fluctuation range due to calcium hypochlorite concentration is several tens of meters
In contrast to V, fluctuations of several mV to several tens mV occur due to changes in other ion species, liquid flow velocity, temperature, and the like. Therefore, it has been difficult to put the ORP electrode into practical use even with great care in managing the ORP electrode.

[0004]

SUMMARY OF THE INVENTION The present invention relates to an ORP
It is intended to provide a method for reliably managing the end point of the reaction using an electrode.

[0005]

Means for Solving the Problems The present inventors have noticed that the rate of change of the ORP electrode indicated value increases as the chlorination reaction end point is approached. In other words, when the blowing rate of chlorine is kept constant, the residual alkali concentration decreases near the end point of the reaction and the pH decreases.
The rate of change in the potential of the RP electrode rapidly increases and reaches a peak. This rate of change is not affected by the relative shift of the ORP electrode potential. If the relationship between the potential change rate and the remaining alkali concentration is determined in advance, the end point of the chlorination reaction can be easily managed only by measuring the ORP electrode potential change rate. That is, the point at which the rate of change reaches the maximum value or the prescribed value of the rising phase is set as the end point. Further, an appropriate aging time may be provided starting from this point.

[0006]

The present invention will be described in more detail with reference to the following examples. However, the scope of the present invention is not limited by the following examples. In addition, the unit described in an Example represents a weight unit unless there is particular notice.

[EXAMPLE] 28 parts of water was added to 10 parts of calcium hydroxide having a purity of 97%, and a chlorination reaction was carried out by passing chlorine gas at a rate of 50 g / Hr while maintaining the temperature at 25 ° C. ORP electrode (Model OR8E manufactured by Yokogawa Electric Corporation)
FG-PT-05-TT1), and the potential and the rate of change of the potential were recorded with an indicator recorder (model R100 manufactured by Yokogawa Electric Corporation). The unit time was 10 seconds. When the potential change rate reaches an arbitrary value in the rising process, chlorine is stopped, and the change rate and residual alkali determined by liquid composition analysis are shown in the following table (5 each).
Times). When approaching the end point, the rate of change, which had been constant until then, suddenly rises. The rate of change reaches a peak at 6.5 mV / 10 sec, decreases, and reaches a constant value. After the peak of the rate of change, the remaining alkali becomes substantially zero, and calcium hypochlorite starts to decompose.

Next, an experiment was conducted in which actual end point management was performed using the results. From the table, it can be seen that in order to obtain a desirable residual alkali in the calcium hypochlorite production reaction, the time when the rate of change becomes 6 mV / 10 sec should be the end point. An experiment was conducted under these end point control conditions, and the composition of the reaction solution at the end point was analyzed.
Was 0.196. From this result, it was found that the end point management which was sufficiently satisfactory could be performed.

[0009]

[Comparative Example] Salification was performed in the same manner as in the above-mentioned embodiment, and an end point control experiment using a generally indicated ORP electrode potential value was performed. When the ORP electrode potential reached a specified value, the end point was determined, the composition of the reaction solution was analyzed, and the remaining alkali was measured. The specified value of the ORP electrode potential is 650, 700, 720,
725, 730, 750, and 760 mV and seven levels were used, and each was performed five times. The results are shown in the table below. In view of this, the set potential may be set to around 723 mV, but the dispersion of the remaining alkali is large, and the reliability of the endpoint management method is lacking. The reason for this is, as described above, that the ORP electrode potential fluctuates by several tens of mV due to factors other than the remaining alkali in the reaction solution.

Table: End point management method based on ORP electrode potential indication value 終 End point ORP electrode potential Remaining Alkali mV Average% Minimum% Maximum% ──────────────────────────────── 650 7.09 6.98 7.26 700 3.93 3.37 4.54 720 1.47 1.35 1.67 725 0.61 0.36 0.98 730 0.24 0.10 0.63 750 0.13 *** 0.44 760 *** *** 0.17 ──────────────────────────────── *** Alkaline remaining 0 (over Caused chlorine decomposition)

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yoshinori Kamado 950, Fujisawa, Nakago-mura, Nakakubijo-gun, Niigata Prefecture Nihon Soda Co., Ltd. Nihongi Plant (56) References JP-A-4-134390 (JP, A) ( 58) Field surveyed (Int.Cl. ⁷ , DB name) G01N 27/416 C01B 11/06 G01N 27/26 341

Claims (1)

(57) [Claims] 1. A method for controlling the end point of a chlorination reaction, wherein a change rate (differential coefficient, gradient) of an ORP electrode potential is used.