DD275155A3 - 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 partial pressure of the blue acid over the reaction product, and that this content of blue acid can be measured in a simple and trouble-free manner and used as a control to meter in hydroxide and / or blue doses. 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. 3

Description

the variables a and b, which are constant for a specific measuring arrangement, are determined in a preliminary test, and the resulting quantity dose correction for one of the reaction components is carried out by means of a controller in accordance with the predetermined alkalinity target value for the process.

2. The method according to claim 1, characterized in that the temperature dependence of the hydrocyanic acid content of the carrier gas (3) or of the hydrocyanic acid analog measurement signal (y) in the temperature range of 3! 5-10O ⁰ C by the relationship

1gy = -cy + d

where T is the temperature in K which is determined for a specific measuring arrangement of constant magnitudes c and in a preliminary test and the said relationship with the automatic temperature compensation is used.

3. Verfahien according to claims 1 and 2, characterized in that the separated partial flow of the carrier gas (3) is maintained at a temperature above the condensation temperature.

4. Process according to claims 1 and 2, characterized in that the separated partial stream of the carrier gas (3) with a gas stream (4) is mixed.

5. Process according to claims 1 and 2, characterized in that in the separated partial stream of the carrier gas (3) a blue-acid permeable membrane module (9) is arranged, which flows through a second carrier gas or a carrier liquid (6) and passed to the hydrocyanic acid analyzer (10) becomes.

6. Process according to claims 1 to 5, characterized in that the cyanide-containing product stream (1) has a solids content of 0-40 parts by mass in%.

For this 2 Soiten drawings

Field of application of the invention

The invention relates to a process for controlling the alkalinity content for the neutralization process in the preparation of alkali metal and alkaline earth metal cyanides, in particular also for alkali metal and alkaline earth metal cyanide production processes. MK mother liquor recycling from the postcrosslinked crystallization and separation stage to 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 orfordorlich in order to prevent the polymerization of hydrogen cyanide in the reaction solution (dark coloration) and in the further processing, the saponification of the cyanides to formate back to force in the neutralization. According to the technology of cyanide production and the predetermined qualities of the final product, it is advantageous to be able to determine the alkalinity content in a range of 2-0.2%, defined as oinstellone.

For ancestors with mother liquor recycling from the crystallization and separation stage, the usual physical methods such as density, viscosity or refractive index measurement (for example DE 1667735) are not applicable due to changing contents of reaction product and impurities. For example, metal / metal oxide electrodes are not suitable for pH measurements since an alkalinity borel of 0.2-2% is insufficient for technically reproducible values due to the buffering capacity of the system, MeUl electrodes have quoritivity to redoxsystomone and the glass electrodes have insufficient durability Jm have strong Alkäische range.

As a rule, the control continues to be carried out by classical titration methods. The use of automatic analyzers are the technical difficulties in conveying and dosing the highly concentrated, hot, partly containing crystals solution.

The same disadvantage has the solution described in DD-WP 248703 with a measuring reactor and the dosage of aqueous hydrocyanic acid solution. In addition, due to the cycle times, no continuous measuring signal is available and the handling of aqueous hydrocyanic acid during operation and maintenance of the device places increased demands on the safety technology.

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, in

clearly related to the objective function of the neutralization process, the alkalinity content is independent of

Concentration fluctuations of the reaction and by-products sowas and the mother liquor recycling is, with low Effort and to measure in a simple manner and thus allows a high quality control of the neutralization process. It has now been found that between the alkalinity of the reaction product and the hydrocyanic acid partial pressure above the Reaction product is a clear dependence, this hydrocyanic acid partial pressure in a simple and störunanfälliger Measure way and use as a controlled variable for hydroxide and / or Blsusäuredöslerung. The method according to the solution according to the invention achieves an accuracy of ± 0.1% by mass in%. Alkalinity content in the reaction product. It can be both discontinuous and continuous Neutralization process advantageously used, the. The process is furthermore suitable both for the conversion of pure hydroxide solutions and for mixtures of mother liquors and Fresh liquor as well as for the post-neutralization of cyanide solutions and products with excessively high alkali contents,

which may also be metal-containing or even have suspension character. Even with a washing process of NaCN-

Crystals, for example in the centrifuging or filtration process, when using the method according to the invention on the Alkalinity content of the resulting mother liquor, the addition of dilute hydrogen cyanide be regulated to the washing liquid and

in order to achieve a quality improvement of the final product by post-neutralization.

To carry out the method, that is to measure the hydrocyanic acid partial pressure of the gas phase over the Reaction product, in particular two methods are possible:

1. Direct measurement

A carrier gas stream (eg, nitrogen or air) is contacted with the reaction product. A constant St rc ~ this gas is withdrawn, so tempered that no condensation occurs and subjected to a hydrocyanic ^r ., Ne other variant to avoid condensation consists in the defined dilution of the withdrawn gas stream with a second gas stream.

2. Indirect measurement

It is also a Trägei gas passed through the reaction product and withdrawn a partial stream. In this sub-stream is a

Blue membrane permeable membrane module arranged, which in turn of a second quantitatively constant

Carrier gas flow odor a carrier liquid is flowed through, which receives the diffusing through the membrane hydrogen cyanide

and feeds it to an eluate acid analyzer.

As a carrier gas can be z. As nitrogen or air are used. To the carrier liquid are u. a. diluted alkalis

(Caustic soda, potassium hydroxide) suitable.

In practical application, the solution according to the invention, it is by no means necessary, the absolute value of the Determine hydrocyanic partial pressure, but the HCN partial pressure proportional measurement signal of the hydrocyanic acid analyzer

can directly serve as a measure door the alkalinity content of the reaction product and thus as a controlled variable for the process. When

Analyzers are z. B. polarographic cyanogenic, but the invention is not to this Bound analyzer system. The influence of temperature is determined by a function of the shape Ig y «= -c · - + d (y = P _H cn or analogue signal)

described in the temperature range of interest. For a measuring arrangement with membrane module in the liquid phase and amorphometrischon hydrocyanic acid analyzer, for example, for NaCN solutions in the range 35-100 ⁰ C (membrane module in the gas phase) following Rozelchnungen was determined:

Ig · / * -1721 · - + 6.30174 I = measurement signal of the analyzer T = temperature in K

The relationship between the hydrocyanic acid partial pressure of the reaction product or an analog measurement signal (y) and the alkalinity content (x) becomes sufficiently accurate for NaCN solutions in a wide concentration range by a function of the form

1 V ⁼

described.

For concrete measuring arrangements, an experimental determination is favorable. For sodium cyanide in a laboratory experiment and a temperature of 20 ° C, a gas space above the NaCN solution, the following well reproducible Meßreihn was added.

Degree of conversion d. Lye (% by mass) Alkalinity (mass fractions in%) Measured value (uA) Color d. solution 90 95 98 99 99.8 5.5 2.75 1.1 0.54 0.11 0.93 1.85 4.6 9.2 39.7 colorless colorless colorless colorless dark brown This gives numerically following appearance for the function mentioned above: - = 0.1955x + 3.7054 * 10 " ³ y

This series of measurements shows that a particular advantage of the solution according to the invention lies in the increasing accuracy or safety against overrunning with decreasing setpoint specification, since the sensitivity rises sharply with low alkalinity values.

Exemplary embodiments

The process according to the invention was tested both in the laboratory and in industrial reactors (continuous and discontinuous). The invention will be explained in more detail with reference to three drawings and four Qeispiolen.

Fig. 1: shows the experimental scheme of direct measurement of the hydrocyanic acid partial pressure. Fig. 2: shows the experimental scheme of the direct measurement of the hydrocyanic acid partial pressure with dilution of the measurement gas. Fig. 3: shows the experimental scheme of the indirect measurement of the hydrocyanic acid partial pressure via a blue acid-permeable module. example 1 A carrier gas stream 2 of 50 l / h was in a static mixer 7 with a cyanide-containing product stream 1 in contact

brought and a part of the loaded carrier gas 3 separated from the solution, in which by means of a

Blue acid analyzer 10, which was added to the hydrocyanic acid proportional measurement. The determined series of measurements had the following picture: Alkalinity (% by weight) 0.3 0.5 1.0 2.0 Measured value (Skt) = scale divisions 100 87 58

- - 10 ² 1 1,15 1,72 2,78

measurement

According to the requirements of the process, the process variable was defined. Example 2 The series of measurements was taken for the following conditions: A carrier gas stream 2 of 50 l / h wurdo passed through a 9O ⁰ C warm cyanide-containing product stream 1, a loaded Carrier gas 3 was separated to prevent condensation with an additional diluent gas 4 in the ratio 1: 5

brought together and the hydrocyanic acid content measured.

Alkalinity (% by weight) 0.5 1.0 1.5 Measured value (Skt) 50 31

1 test word

• 10 '2.00 3, «2 4.54

Example 3

A Trägorgasstrom 2 of 50 l / h was passed through a cyanide laiiigon product stream 1 of 81 ⁰ C. In the withdrawn Toilmonge the gas whose temperature einpogelte at 80 ⁰ C, a membrane module 9 eingebrachi was introduced through which a further Trigergae β with 30l / h the hydrocyanic acid analyzer 10.

The well reproducible series had the following appearance:

Alkalinity 0.2 0.4 0.6 1.2 2.0

Measured value (Skt) 105 71 51 24

Moßwert

• 10 '0.95 1.41 1.96 4.16 5.55

Example 4

In a 4O ⁰ C warm, continuous, cyanide-containing product stream 1 50 l / h carrier gas 2 are passed and separated again in the gas separator 8 in the loaded carrier gas 3, a HCN permeable membrane module 9, which is 0.5 l / h TrSgerftüssigkeit (0 , 5 η NaOH) 6 is flowed through. After adjusting the equilibrium blue-acid pressure, this leaves as loaded carrier liquid 5, the membrane module 9 and enters the analyzer 10, which provides the hydrocyanic acid adequate output signal for the quantitative metering of one of the two reaction components 12. The separated in the gas separator 8 1 .Trägergas 3 leaves as excess gas via the line 11, the system. To control the carrier gas and Flüosijkeitsströme serve the quantity 13th

The measured values displayed in the HCN analyzer 10 are shown in the following table: Alkalinity (% by mass) 0.4 1.2 1.6

Measured value (Skt) 49 24 20

measurement

10 ² 2.04 4.17 5.00

Claims (1)

1. A method for controlling the neutralization process in the production of alkali or Erdalkalicyaniden by reacting hydrocyanic acid or hydrocyanic gases or liquids with alkali or alkaline earth metal hydroxides, in which the adjustment of the value specified for the process Alkalitätswertes by adjusting the quantity dosage of the reaction components, characterized characterized in that a carrier gas stream (2) passed through the cyanidhal'iigen product stream (1), a part of the gas (3) and subjected to a hydrocyanic acid analysis, wherein the determined hydrocyanic acid content or the hydrocyanic acid analog measurement signal (y) of the analyzer the measure for the alkalinity content (x) of the product stream (1), this relationship is expressed in the following relation -J-ax + b.