DD275154A3 - METHOD FOR REGULATING THE NEUTRALIZATION PROCESS IN THE PREPARATION OF ALKALI OR ERDALKALICANANESES - Google Patents

Abstract

The invention relates to a method for controlling the Alkalitaetsgehaltes for the neutralization process in the production of alkali and Erdalkalicyaniden. It has been found that there is a clear dependence between the alkalinity content and the free blue-acid content of the reaction product, that this blue-acid content can be measured in a simple and trouble-free manner and used as a control quantity for hydroxide and / or blue acid dosing. To carry out the process, the free blue-acid content of the reaction product is measured by placing a membrane acid-permeable membrane module in the reaction product stream which is permeated with a constantly metered amount of carrier gas or tracer liquid which takes up the blues acid. Subsequently, this stream is subjected to a blue acid determination. The process achieves an accuracy of 0.1% by mass of alkali content in the reaction product. Fig. 1

Description

Object of the invention

The object of the invention is to develop a method by means of which the neutralization process can be carried out while maintaining a predetermined alkalinity content.

Explanation of the essence of the invention

The invention has for its object to develop a method in which a measured variable is used, which is in clear connection with the Zielfunktior of the neutralization process, the alkalinity content, regardless of concentration fluctuations of the reaction and by-products and mother liquor recycling, with little effort and is easy to measure and thus allows a high quality control of the neutralization process.

It has now been found that there is a clear dependence between the alkalinity content and the free hydrocyanic acid content of the reaction product, this free hydrocyanic acid content can be measured in a simple and trouble-free manner and can be used for the addition of hydroxide and / or blue acid doses.

The method according to the solution according to the invention achieves an accuracy of ± 0.1 mass fraction in% alkalinity content in the reaction product. It can be advantageously used both for the discontinuous and for the continuous neutralization process.

The process is furthermore suitable both for the reaction of pure hydroxide solutions and for mixtures of mother liquors and risch liquor as well as for Nachneutrelisation of cyanide solutions and products with too high alkali contents, which may also be crystalline or even have suspension character.

Even with a washing process of NaCN crystals, such as in the centrifugation or filtration process, the addition of dilute hydrocyanic acid to the scrubbing liquid can be regulated when the process according to the invention is used via the alkalinity content of the resulting mother liquor, thereby improving the quality of the end product by post-neutralization.

To carry out the process, the free hydrocyanic acid content of the reaction product is measured by placing a blue-acid-permeable membrane module in the reaction product which is flowed through by a constant metered amount of a carrier gas or a carrier liquid which takes up the hydrocyanic acid. Subsequently, this stream is subjected to a hydrocyanic acid determination.

For example, dry nitrogen or dry air (for example, controlled air) may be used as the carrier gas.

To the carrier liquid are u. a. Diluted alkalis (caustic soda, potassium hydroxide solution) suitable.

In the practical application of the solution according to the invention, it is by no means necessary to determine the absolute value of the free hydrocyanic acid content, but the porportionale measurement signal of the hydrocyanic acid analyzer can be used directly as a measure of the alkalinity of the reaction product and thus as a controlled variable for the process.

As analyzers are e.g. polarographic cyanogenic cells suitable, but the invention is not bound to this analyzer system.

The relationship between the content of free hydrogen cyanide in the reaction product or an analog measurement signal (y) and the alkalinity (x) is sufficiently accurate for NaCN solutions in a wide Konzentraticnsbereich by a function of

- = a-x + b described, y

For the specific measuring arrangements, an experimental determination is favorable.

For N, triumcyanide, the following series of measurements was taken in a laboratory experiment and at a temperature of the reaction solution (NaCN) of 80 ° C.

Alkalinity Measured value Color of the solution

(Mass fractions in%) (uA)

2 45 colorless

1 80 colorless

0.5 147 colorless

0.1 495 dark brown

- = 0.01109 χ + 0.0095

This series of measurements proves that a particular advantage of the solution according to the invention in the increasing accuracy or safety against overrunning with decreasing setpoint specification is because the sensitivity increases sharply with low alkalinity values.

The torroratura flow to the required value can be compensated for by tempering the reaction product to a constant value or by automatic temperature compensation to the desired value.

The influence of temperature is determined by a function of the shape

Igy = -c- + d (y ° Conc. Of hydrocyanic acid or analog measurement signal)

described in the relevant temperature range of 35 ⁰ C-IOO ⁰ C. For a measuring arrangement according to the inventive method with amperometric blue acid detector z. B. for NaCN in the range of 35-100 ° C the following relationship:

Igy = - 1372 · γ +5.534

y = measured signal of the analyzer T-temperature inc

embodiments

The inventive method is shown in Figure 1 as a test scheme.

It has been tested both in the laboratory and in technical reactors (continuous and discontinuous), as the following examples show:

example 1

In a 9O ⁰ C warm NaCN reaction solution 1, a membrane module 4 was arranged. A constant carrier gas flow (nitrogen) 2, which is controlled by the amount display (7), is passed through the membrane module 4 and takes on the proportional to the free hydrocyanic acid content of the reaction solution by the membrane module 4 diffusing hydrocyanic acid.

The hydrogen cyanide-laden carrier gas 3 is analyzed in the downstream hydrocyanic acid analyzer 5, which then realizes the output signal for the quantitative metering 6 of one of the two reaction components.

The analyzer 5 provides a following series of measurements

Alkalinity (mass fractions in%) 0.2 0.4 0.6 1.2 2.0 Measured value (Skt) A scale division 62 49 38 24 17 1 / measured value 10 * 1.62 2.04 2.60 4.15 5.90

Example 2

A membrane module 4 is placed in a NaCN reaction solution 1 of 4O ⁰ C and from 0.5 l / h carrier liquid (0.2 η sodium hydroxide solution) flows through, which is subjected to the hydrocyanic acid determination:

Alkalinity (mass fractions in%) 0.4 1.2 1.6 Measured value (Skt) 67 29 22 1 / measured value / O ² 1.49 3.45 4.54

Example 3

In a technical neutralizer, 592 kg / h of aqueous sodium hydroxide solution, 960 kg / h of mother liquor from the crystallization process downstream centrifugal stage and 155 kg / h hydrogen cyanide were reacted. In the outgoing NaCN reaction solution 1, a membrane module 4 was used.

The constant carrier gas flow (nitrogen) 2 flowing through the membrane module 4 was fed to the hydrocyanic acid analyzer 5.

The set point of the associated controller that controlled the hydrodewatering metering pump was set to 5099 divisions, corresponding to an alkalinity of 0.8 mass%. The NaCN reaction solution 1 arose at different times

Alkalinity analyzed.

t (h) 1 2 3 5 Alkali diet (% by mass) 0.82 0.85 0.75 0.88

Average value: 0.82% by weight in%

Example 4

A carrier gas stream 2 of 15 l / h is passed through a membrane module 4 in the NaCN reactant solution 1.

The NaCN reaction solution 1 had a cyanide content of 42.5 mass% and an alkalinity of 0.3 mass%.

At different temperatures, the following values were obtained:

T ( ⁰ C) measured value (Skt)

(1 g measured value "-1372 γ + 5.534)

19 40 60 80 90 7 13 28 46 54

Claims (3)

1. A method for controlling the neutralization process in the preparation of alkali or Erdalkalicyaniden by reacting hydrocyanic acid or hydrocyanic gases or liquids with alkali or alkaline earth metal hydroxides, in which the setting of the predetermined for the process Alkalitätssollwertes by adjusting the amount of dosage of one of the reaction components, characterized characterized in that a blue-acid-permeable membrane module (4) is arranged in the NaCN reaction solution (1) to be controlled, through which a constant amount of carrier gas or carrier liquid (2) flows, which is proportional to the free hydrocyanic acid content of the product flow through the membrane module (4). passing through this cyanogenic acid and this charged carrier stream (3) is fed to a hydrocyanic acid analyzer (5), the hydrocyanic acid content determined in the analyzer (5) or the measurement signal (y) of the hydrocyanic acid analyzer (5) analogous to the hydrocyanic acid content being the measure of the acidity old (x) represents the Prodiiktotrorvies, this relationship is expressed in the following relationship the variables a and b, which are constant for a specific measuring arrangement, are determined in a preliminary test and the controller is used to carry out the corresponding metering dose correction for one of the reaction components via a controller in accordance with the preset alkali value for the process. 2. The method according to claim 1, characterized in that the temperature dependence of the free hydrocyanic acid content of the reaction solution or of the HCN content analog measurement signal (γ) in the temperature range of 35-100 ⁰ C by the relationship Ig y = _C 1 + d is given that »T is the temperature in K, which are determined for a concrete measuring arrangement of constant magnitudes c and d in a preliminary test and the said relationship is used for automatic temperature compensation. 3. The method according to claim 1 and 2, characterized in that the NaCN reaction solution (1) has a solids content of 0.1-40 parts by mass in%. For this 1 page drawing Field of application of the invention The invention relates to a method for Regdung the Alkalitätsgehaltes for the neutralization process in the production of alkali and Erdalkalicyaniden, especially for alkali and Erdalkalicyanidherstellungsverfahren with mother liquor recycling from the downstream crystallization and separation stage in the neutralization process. Characteristic of the known state of the art In the preparation of alkali and Erdalkalicyaniden a certain alkalinity content of the reaction is required in the neutralization stage to prevent the polymerization of hydrogen cyanide in the reaction solution (dark coloration) and push back in saponification of the cyanides in formate in further processing. According to the technology of cyanide production and the predetermined qualities of the final product, it is advantageous to be able to set the alkalinity content in a range of 2-0.2% in a defined manner. For processes with mother liquor recycle from the crystallization and separation stage, the usual physical methods such as density, viscosity or refractive index measurement (e.g., DE 1667785) are not applicable due to varying levels of reaction product and impurities. For example, Me / metal oxide electrodes are not suitable for pH measurements, since an alkalinity range of 0.2-2% does not allow for the potential difference due to the buffering capacity of the system for reproducible values, metal electrodes have cross sensitivities to redox systems and the gas electrodes have insufficient endurance in the strong alkaline range. Usually, the control is still carried out by classical titration methods. The use of automatic analyzers is the technical difficulties in conveying and dosing the highly concentrated, hot, partly containing crystals entgegon. The same disadvantage has the solution described in DD-WP 248703 with a measuring reactor and the dosage of aqueous hydrogen cyanide solution. In addition, due to the cycle times, no continuous measuring signal is available and the volume with aqueous hydrocyanic acid during operation and maintenance of the device places increased demands on the safety technology.