DE2166413B2 - Process for the production of hydrochloric acid - Google Patents

Description

The invention relates to a process for the production of hydrochloric acid from an aqueous iron (IIl) chloride solution by heating the solution to higher temperatures.

Hydrochloric acid is used for this. Pickling steel to remove the oxide coating from the base metal. To the Refreshing the pickling liquids is usually an acid with a concentration of 20 to 30% used, acids of higher strength being preferred. A waste material is used in the pickling plant formed, which is referred to as hydrochloric waste pickling liquid will. This waste pickling liquid contains about 18 to 25 percent by weight in addition to water Iron (IH) chloride (FeCb), less than 1 percent by weight Iron (III) chloride (FeCb) as well as variable but small amounts of free HCl and small amounts of organic inhibitors, which reduce the attack of the acid on the base metal.

For cost reasons and because of environmental pollution efforts are made to recover the hydrochloric acid from the pickling solutions. The recovery according to DE-PS 3 67 766, iron pickling liquors are added before they are decomposed into hydrochloric acid oxidized in order to convert the divalent iron contained in the pickling liquor into trivalent iron. Afterward thermal decomposition of the aqueous iron (III) chloride solution then takes place. As for thermal decomposition Moisture is required, which can be in the form of water or water vapor, is at the known method provided the water by body, which water only at higher temperatures give up the ability to bring in, z. B. by calcium chloride. From DE-PS 6 68 138 the production of hydrochloric acid and iron oxides is still from Chlorides known by the thermal reaction of the chlorides with water vapor, whereby the one to be decomposed chloride-containing solution in a thin layer less than 5 mm thick only as long as exposed to the decomposition temperature, as is necessary to the To obtain metal oxides or hydrochloric acid. For the decomposition of ferric chloride, a temperature of about 300T applied while other chlorides require even higher temperatures.

The object of the (invention is, in the production of Hydrochloric acid from an aqueous solution of ice (III) chloride by heating the solution to higher To improve the temperatures of this process economically by simplifying the equipment required and chemicals and lowering the temperatures required for decomposition. This task is achieved by the method according to claim 1.

An aqueous solution of iron (III) chloride is used as the starting product. Since the acidic pickling solutions iron in

ίο contain bivalent form, this will contain iron initially oxidized, this oxidation in the usual way at higher temperatures with oxygen z. B. the oxygen in the air, and wherein the oxidation promoting catalysts are present or added.

The iron (III) -chIorid solution is then heated to a temperature from 121.1 to 204 ⁰ C and at the top a stream of water vapor and HCl is detached. An aqueous iron oxide slurry remains as the residue. The decomposition of iron (III) chloride takes place under reduced pressure, whereby this reduced pressure can be generated by applying a vacuum to the decomposition vessel, or by injecting hot gases into the solution

by means of an immersion burner. Surprisingly, decomposition under reduced pressure enables use at lower temperatures than at normal or overpressure, with still good degrees of conversion be achieved.

Starting solutions which contain even larger amounts of dissolved iron (III) chloride are preferably cooled beforehand in order to precipitate iron (III) chloride from the solution.
The temperature which is required for the rapid decomposition of the aqueous iron (III) chloride solution is considerably reduced by the decomposition under reduced pressure. With a vacuum of 686 to 711 mm Hg, the temperature is 121.1 to I26.7 ° C. Under atmospheric pressure one would need a decomposition temperature that is about 37.8 ° C higher.

It is preferred to introduce the inert gas into the decomposition solution in order to generate the necessary heat To provide the necessary to maintain the decomposition reaction, thereby reducing the Eliminates the need for indirect heaters and the associated corrosion problems will. Hot submerged combustion gases provided by a submerged burner are the preferred source of hot inert gas.

When the hot submerged combustion gas is used for heating, the generated gas occurs Hydrogen chloride not only with the accompanying water vapor, but also with the non-condensable Gases that are formed during combustion. It is necessary to steam and remove the HCl from this Wash out gas stream with water, thereby obtaining a lower concentration of the hydrochloric acid product is, as by decomposition processes, which a

fco include indirect heating of the ferric chloride solution,

A preferred embodiment of the recovery of hydrochloric acid from a hydrochloric waste liquor is described below:

h5 Burnt pickling liquid, which is about 22% dissolved Contains iron (II) chloricl and some free HCI, is mixed with finely divided iron oxide particles in an amount which is sufficient. to deal with the free HCI

to implement. The pickling liquid is in buckets at 104 ° C Concentrated evaporator, with enough water removed to make a concentrated treated Produce waste pickling liquid, which contains about 40% dissolved ferrous chloride

The hot ferrous chloride liquid is added used to extract the aqueous sludge bottoms from the decomposer for the aqueous ferric chloride solution.

The extraction takes up the accelerator, which is dissolved and suspended in the bottom products of the decomposer, the ferrous chloride and any remaining ferrous chloride present. A small amount of the finely divided iron oxide which is formed in the decomposer is also taken up, whereby the finely divided iron oxide particles are made available, which are expediently at the beginning of the Oxidation are present in the oxidation reactor. If desired, the entire bottom product of the The decomposer must be mixed with the hot concentrated ferrous chloride liquid, since the iron oxide is the Oxidation reaction does not interfere

The hot concentrated liquid at 104.4 ° C and the bottom product of the decomposer, which is also approximately at this temperature, are transferred to an oxidation vessel, which is preferably a glass-lined vessel provided with an air inlet and mechanical stirring device, in order to achieve an intimate or vigorous mixing in the oxidation device. The hot concentrated liquid contains about 3 parts by weight of ammonium chloride accelerator and about 1 part by weight of copper (II) chloride K ^ accelerator, each per 100 parts by weight of the hot concentrated liquid , 9 bar. The contents of the oxidation device are ^{heated to a temperature of approximately 149 °} C. and this temperature is maintained by removing a stream of water vapor.

After about an hour, the oxidizer contains iron oxide from the conversion of iron (II) ions into iron (III) ions and a liquid, aqueous one Solution of iron (III) chloride and dissolved ammonium and copper (II) ions. Under these conditions about 98% iron (II) ions are converted into iron (IH) -iores.

The material contained in the oxidizer is transferred to a filter where the iron oxide particles are removed. The retained iron oxide like this is washed with water. Part of the iron oxide is used to reduce the free HCl content of the Neutralize waste pickling liquid starting solution.

The aqueous iron (IU) chloride solution including the dissolved, unconverted iron (II) chloride and the accelerator, as well as the washing water, are transferred to the decomposition vessel for the iron (III) chloride. The conditions for the filtration are set so that the charge for the decomposer has approximately the desired decomposition temperature in the region of 121.degree. The decomposer is kept at the desired temperature and the stripping conditions are maintained by an immersion burner heated with natural gas and air.

It is convenient to continuously withdraw a stream of slurry from the decomposer and this through a decanting vessel with a conical Direct soil. This decanter gives a Bottom product of the decomposer as an aqueous suspension of iron oxide and dissolved ammonium and copper (II) ions. This aqueous slurry is mixed with the hot concentrated liquid that formed by the evaporator, mixed The separated solution is transferred to the oxidizer returned

The decomposer is continuously fed in via K.ipf Stream taken off that contains HCl gas, water vapor, nitrogen, carbon dioxide, oxygen and other combustion gases The water vapor stream flowing in the oxidation device is formed, is combined with the overhead flow and then transferred to an adiabatic absorber. In this absorber, a water flow absorbs the HCl gas. Nitrogen and other gases as well as water vapor are led out of the absorber Hydrochloric acid obtained from the bottom product.

It can be seen that in the invention In the process, essentially the entire chlorine content of the waste pickling liquid used can be recovered as hydrochloric acid. The iron oxide obtained is in essentially pure and it is suitable for making steel. The accelerator system is recycled

The parts mentioned in the example are based on weight.

example

The decomposition vessel used was one with a mechanical stirrer, a water-cooled condenser, and a A flask fitted with a receiving vessel was used. A vacuum pump was connected to the condenser. A small flask was connected to the decomposer by means of a pipe. This little flask served as a Trap for the E; .sen (III) oxide slurry. The test solution filled the trap and connection line when the solution was brought into the disintegrator. The connecting line remained open during the entire experiment.

The test solution contained the dissolved iron ions to about 85% in the trivalent form and about 15% in the bivalent form.

The vacuum pump was put into operation ^ ". And 500 ml of the test solution placed in the decomposer at room temperature. The temperature of the solution in the Decomposer increases. The overhead product from the decomposer was condensed and collected.

As the contents in the decomposer became more concentrated and the temperature and vacuum increased, it became wider Test solution added to maintain the liquid level in the decomposer.

After the temperature in the decomposer increased to 126.7 ° C, the vacuum was 686 bis 711 mm Hg. The condensate had a concentration of 30% hydrochloric acid.

The iron oxide and solids in the decomposer settled in the pipeline along the way Fall away.

The experiment could go on indefinitely by removing the trap if it were by the precipitated solids is filled, and further test solution is added to the decomposer in order to maintain the liquid level therein, the condensate having a hydrochloric acid concentration of 30%.

Ψ: 5

Comparative experiment

If one works as in the previous example, but without applying a vacuum, a temperature becomes from 182 to 188 ° C is required, with a 33% Hydrochloric acid is obtained.

Claims (2)

Patent claims: 1. A process for the preparation of hydrochloric acid from an aqueous solution of iron (III) chloride, by heating the solution to higher temperatures, characterized in that the iron (III) chloride solution to a temperature of about 121.1 to 204 ^° C. and that a stream of steam and HCl gas is taken off overhead, with heating being carried out under reduced pressure. 2. The method according to claim 1, characterized in that the liquid aqueous iron (III) chloride solution before heating, cools to precipitate a solid phase that the solids separated from the cooled liquid aqueous iron (III) chloride solution and that the cooled separated liquid iron (III) chloride solution then subjected to heating.