DD288503A7 - METHOD FOR CONTINUOUS PRODUCTION OF SODIUM CYANIDE SOLUTION - Google Patents

Abstract

The invention relates to a process for continuous sodium cyanide neutralization. The aim of the invention is to make the Prozesz at low equipment and energy expense durchfuehrbar and to reduce the environmental impact by the use of highly concentrated Natriumcyanidabwaesser. In accordance with the present invention, a heated reaction tube is fed with a sodium cyanide cycle solution in a vertical direction from above and below. At one or more discharge points sodium hydroxide solution and blue acid are metered against each other. To carry out the process, certain parameter ranges must be observed. This concerns the quantitative ratio of the sodium cyanide cycle solution. The process is also very suitable for the reconstruction of outdated NaCN plants. Fig. 1 {continuous reaction; Circulation mode; heated reaction tube; counterflowing blue-caustic-soda lye dosage}

Description

Field of application of the invention

The invention relates to a method for carrying out a neutralization process in the sodium cyanide production. The method is characterized by energetically favorable parameters and low equipment complexity.

Characteristic of the known state of the art The difficulties in the reaction of hydrocyanic acid with sodium hydroxide are known. They are particularly in the handling

the extremely toxic hydrocyanic acid, whose low boiling point of 25 ⁰ C and the risk of polymerization of hydrogen cyanide, if not at each contact point of the reaction components, an excess of alkali of at least 0.2 parts by mass is guaranteed in%.

In practice, therefore, for a long time outweighed the discontinuous procedure, wherein in a stirred tank Sodium hydroxide is introduced and up to a residual alkalinity of about 0.8-2 parts by weight in% liquid or gaseous hydrocyanic acid

is added.

The previously proposed continuous processes have some disadvantages. Thus, in the processes according to GB-PS 1012917 and DE-AS 1103905 with circulation ratios of 160 parts by mass / h Sodium cyanide solution to a mass / h sodium hydroxide solution and corresponding amount of hydrocyanic acid or 230 parts by mass / h Sodium cyanide solution to 1 part by mass / h hydrocyanic acid and a corresponding addition of sodium hydroxide solution are worked as out

the exemplary embodiments. Otherwise, d. H. in reducing the circulatory relationship occur in a liquid

Hydrocyanic addition partial evaporation, which in the reaction tube to inhomogeneous concentrations and ultimately too Polymerization phenomena lead. Furthermore, it comes at the introduction. * ~ '! ό of hydrogen cyanide in the sodium cyanide / sodium hydroxide solution, if concentrated with

bzvv. supersaturated solutions, the failure of sodium cyanide crystals, which occur in the cold spots of the

Attach reaction tube. The resulting blockages of the reaction tube or the hydrocyanic acid line are with

high failure rates associated with the system.

In plants on a production scale, significant pump capacities are already required for the above-mentioned circulating quantities

necessary. On the other hand, centrifugal pumps must be used, which results in volume fluctuations and thus one

Management of the process in narrow residual limits is impossible. The same disadvantages are found in DD-WP 246226. Either dilute solutions (hydrocyanic acid, sodium cyanide and caustic soda) must be used to prevent constipation and Prevent partial evaporation of hydrocyanic acid or it must with an additional circuit in o.g. Magnitude over that Reaction tube to be driven. The contained mother liquor cycle is far from sufficient. This is associated with either an increased water evaporation in the crystallizer or significant circulation pump services

as well as the o. g. Disadvantages in process control.

Object of the invention The object of the invention is to develop an economical and continuous process for the neutralization process,

that can be realized with little technical equipment effort.

In addition, a significant reduction in environmental impact is to be achieved. Explanation of the essence of the invention The object of the invention is to provide a continuous process for the neutralization of caustic soda with hydrocyanic acid. Here are the problems of the process control with respect to the temperature-concentration and flow conditions

be improved.

According to the invention, sodium cyanide cycle solution and sodium hydroxide solution are fed to a reaction tube. The minimum pressure in the Reaction tube is 0.2 MPa. At one or more points of discharge, hydrocyanic acid is metered in at a minimum temperature of 35.degree. C., additionally directly

at the discharge point z. B. by double jacket the reaction tube with low voltage steam <0.4 MPa or hot water> 5O ⁰ C is heated.

The maximum temperature of liquid hydrocyanic acid may be a minimum of 5 ⁰ C below the boiling point at the selected Do not fall below reaction pressure. Furthermore, it is necessary to control the speed of the blue acid side stream at the discharge point in a range of 3-7 m / s

to maintain a good mixing. Speeds> 7 m / s no longer produce a positive effect for the mixing, but can lead to negative effects due to the increased negative pressure at the point of introduction

Crystallize the sodium cyanide and partial evaporation of the hydrocyanic acid in the reaction tube lead. In addition, to avoid partial evaporation, a minimum ratio of 3: 1 between sodium cyanide Circulatory stream and sodium hydroxide necessary, with the sodium cyanide cycle also in the further process, ζ. B. in the Centrifugation resulting sodium cyanide solution can be added. The regulation of the Restalkaiigehaltes at the desired level can in a known manner by a stoichiometric Metering of the sodium hydroxide solution and the hydrocyanic acid take place. More advantageous is a blue acid dosage based on a Restalkalitätsmessung. The addition of the sodium hydroxide to the sodium cyanide solution should be carried out before the first discharge point of the hydrocyanic acid. As even more favorable for the reaction, a counter dosing of sodium hydroxide solution and hydrogen cyanide has proven. A particularly advantageous apparatus for realizing the solution according to the invention is shown in FIGS. 1 and 2. In this case, sodium cyanide circulation solution 1, sodium hydroxide solution 3 and hydrogen cyanide 2 at the illustrated end of the reaction tube

metered against each other, wherein perpendicularly from above and vertically from below sodium cyanide solution is introduced while

Sodium hydroxide solution and hydrocyanic acid flow in a horizontal direction against each other. embodiment The invention will be explained in more detail with reference to an example and two drawings.

Fig. 1: shows a front view of a reaction tube Fig. 2: shows a side view of a reaction tube

A sodium cyanide solution 1, about 42% by weight of 4t / h, becomes a reaction tube of the embodiment shown in FIG

driven in the circulation. By throttling behind the reaction section, a pressure of 0.23 MPa is set. Furthermore, 1 t / h of sodium hydroxide solution 3 45 parts by mass in% and about 0.3 t / h hydrogen cyanide 2 are metered against each other, the

Hydrochloric acid in the pressure line of the metering pump is heated to a temperature of 38 ⁰ C and the hydrogen cyanide inlet a Diameter of 6mm ν «4m / s. The discharge point is heated with 0.35MPa steam. The control of the amount of hydrocyanic acid is carried out via a known per se determination of residual alkalinity. A stoichiometric dosage is not advantageous in this case, since a reused mother liquor, which in its Cyanide content varies greatly, and concentrated effluents of the sodium cyanide cycle solution are fed. As much sodium cyanide solution is removed from the process and fed to the subsequent process stages that the Ratio of 4: 1 between the sodium cyanide cycle and the caustic soda remains.

Claims (1)

A process for the continuous production of a sodium cyanide solution by neutralization of caustic soda with hydrocyanic acid in a reaction tube in a Kreislauffahrweise a portion of the sodium cyanide formed, one or more discharge of the hydrocyanic acid at a discharge of 3-7 m / s in a heated with steam or hot water reaction tube and a ratio of the sodium cyanide cycle solution to the sodium hydroxide of ^ 3: 1, characterized in that the system pressure in the reaction tube is greater than 0.2 MPa and the hydrocyanic acid (2) in a temperature range of 35 ⁰ C to a maximum of 5 ⁰ C below its boiling point is initiated at the selected system pressure. For this 1 page drawings