HCL RECOVERY UNIT

Abstract

A unit for recovering hydrogen chloride from an aqueous liquid which includes hydrogen chloride and is contaminated with compounds of low or no volatility, the unit having an evaporation unit for forming, from the liquid, a vapour which contains hydrogen chloride and a liquid concentrate which is contaminated with the compounds of low or no volatility, a first distillation unit for separating the hydrogen-chloride-containing vapour into a first top product and a first bottom product, and a second distillation unit for separating a hydrogen-chloride-containing aqueous fluid into a second top product and a second bottom product, one of these two distillation units being configured to be able to implement therein a distillation above the ambient pressure, and the other of these two distillation units being configured to be able to implement therein a distillation below the ambient pressure.

Claims

1-15. (canceled)

16. A unit for recovering hydrogen chloride from an aqueous liquid which comprises hydrochloric acid and is contaminated with compounds of low or no volatility, said unit comprising: an evaporation unit for forming, from the liquid, a vapour which contains hydrogen chloride and a liquid concentrate that is contaminated with the compounds of low or no volatility, a first distillation unit for separating the hydrogen-chloride-containing vapour into a first top product and a first bottom product, and a second distillation unit for separating a hydrogen-chloride-containing aqueous fluid into a second top product and a second bottom product, wherein one of these two distillation units is configured to be able to implement therein a distillation above the ambient pressure and the other of these two distillation units is configured to be able to implement therein a distillation below the ambient pressure, and the first distillation unit is in fluid-conducting communication with the second distillation unit such that at least part of the first bottom product is able to form at least part of the hydrogen-chloride-containing aqueous fluid.

17. The unit according to claim 16, having a first distillation unit for separating a fluid which can be returned into the distillation unit and the hydrogen-chloride-containing vapour into the first top product and the first bottom product, wherein the second distillation unit is in fluid-conducting communication with the first distillation unit in such a way that at least part of the second bottom product is able to form at least part of the returnable aqueous fluid.

18. The unit according to claim 16 for recovering hydrogen chloride from an aqueous liquid which comprises hydrochloric acid and is contaminated with compounds of low or no volatility and for recovering hydrogen chloride from a hydrogen-chloride-containing gas, further comprising: an absorption unit for absorbing hydrogen chloride gas from the gas into an absorbent so as to obtain a hydrogen-chloride-enriched absorbent and a hydrogen-chloride-depleted gas.

19. The unit according to claim 18, wherein at least one of the distillation units is in fluid-conducting communication with the absorption unit such that at least part of at least one of the two bottom products is able to serve as an absorbent in the absorption unit.

20. The unit according to claim 19, wherein the second distillation unit is in fluid-conducting communication with the absorption unit such that at least part of the second bottom product is able to serve as an absorbent in the absorption unit.

21. The unit according to claim 18, wherein the second distillation unit is in fluid-conducting communication with the first distillation unit via the absorption unit such that the second bottom product is able to function as an absorbent and the hydrogen-chloride-enriched absorbent is able to form at least part of the returnable aqueous fluid.

22. The unit according to claim 20, wherein the absorption unit is integrated into a bottom circulation of the second distillation unit such that part of the second bottom product is able to function as an absorbent.

23. The unit according to claim 18, wherein the absorption unit is in fluid-conducting communication with the distillation unit which is configured to be able to implement therein a distillation below the ambient pressure such that the hydrogen-chloride-depleted gas can be withdrawn from the absorption unit into this distillation unit.

24. The unit according to claim 16, wherein the first distillation unit is configured to be able to implement therein a distillation above the ambient pressure and the second distillation unit is configured to be able to implement therein a distillation below the ambient pressure.

25. The unit according to claim 16, wherein the second distillation unit is configured to be able to implement therein a distillation above the ambient pressure and the first distillation unit is configured to be able to implement therein a distillation below the ambient pressure.

26. A method for recovering hydrogen chloride from an aqueous liquid which comprises hydrochloric acid and is contaminated with compounds of low or no volatility, comprising: a vapour which contains hydrogen chloride and a liquid concentrate that is contaminated with compounds of low or no volatility are formed from the liquid in an evaporation unit, the hydrogen-chloride-containing vapour is separated in a first distillation unit into a first top product and a first bottom product, a hydrogen-chloride-containing aqueous fluid is separated in a second distillation unit into a second top product and a second bottom product, wherein a distillation above the ambient pressure is implemented in one of these two distillation units and a distillation below the ambient pressure is implemented in the other of these two distillation units, and the first bottom product forms at least part of the hydrogen-chloride-containing aqueous fluid.

27. The method according to claim 26, for recovering hydrogen chloride from an aqueous liquid which comprises hydrochloric acid and is contaminated with compounds of low or no volatility and for recovering hydrogen chloride from gas containing hydrogen chloride, wherein the hydrogen-chloride-containing gas is brought into contact with an absorbent in an absorption unit.

28. A use of hydrochloric acid for the absorption of hydrogen chloride from a hydrogen-chloride-containing gas formed during a thermal decomposition.

29. The use according to claim 28, wherein the thermal decomposition comprises a thermal decomposition of aluminium chloride hexahydrate.

30. A set for setting up a unit according to claim 16; comprising the evaporation unit, having an inlet, an outlet, and a liquid draw-off, the first distillation unit, having an inlet, an upper outlet, and a lower outlet, the second distillation unit, having an inlet, an upper outlet, and a lower outlet wherein one of these two distillation units is configured to be able to implement therein a distillation above the ambient pressure and the other of these two distillation units is configured to be able to implement therein a distillation below the ambient pressure, and the set is designed to interconnect the evaporation unit and the two distillation units to form a unit.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0075] The invention is illustrated by means of the following figures, without being restricted thereto.

[0076] FIG. 1 shows an embodiment of the unit according to the invention for recovering HCl.

[0077] FIG. 2 shows an embodiment of the unit according to the invention for recovering HCl.

[0078] FIG. 3 shows an embodiment of the unit according to the invention for recovering HCl.

DETAILED DESCRIPTION

[0079] FIG. 1 shows a unit 1 for recovering hydrogen chloride from an aqueous liquid 31 which comprises hydrochloric acid and is contaminated with compounds of low or no volatility (in this case dissolved aluminium and other metals). The unit 1 has an evaporation unit 30 for forming a hydrogen-chloride-containing vapour 32 and a liquid concentrate 33 from the liquid 31. Details of the evaporation unit, such as the heating unit for providing the heat required for evaporation, a phase separator for returning entrained metal-containing liquid droplets, are not shown. The unit 1 also has a first distillation unit 10 for separating the hydrogen-chloride-containing vapour 32 into a first top product 12 and a first bottom product 13. The unit 1 also has a second distillation unit 20 for separating a second hydrogen-chloride-containing aqueous fluid 21 into a second top product 22 and a second bottom product 23. The hydrogen-chloride-containing aqueous fluid 21 is formed from the first bottom product 13, wherein a substream 19 of the first bottom product 13 is discharged in order to counteract an accumulation of metal contaminants in the distillation units. The fluid 11 returned into an upper region of the first distillation unit 10 is formed from the second bottom product 23. The distillation units 10, 20 shown in the figures are columns. For the sake of simplicity, heating units for heating the column bottoms and cooling units for cooling the column tops are not shown. In the example illustrated here, the first distillation unit 10 is configured to be able to implement therein a distillation above the ambient pressure. The second distillation unit 20 is configured to be able to implement therein a distillation below the ambient pressure. The pump 18 conveys the bottom product 23 against a pressure gradient. The seals, wall thicknesses and column materials required for the particular operating pressure of the relevant column are not indicated. The linings of the various units, which are resistant to the action of hydrochloric acid or hydrogen chloride gas, are also not shown. Tanks and heat exchangers are also not shown.

[0080] In FIGS. 2 and 3, the same reference signs have the same meaning as in FIG. 1. The units 1 according to the invention shown in FIGS. 2 and 3 for recovering hydrogen chloride also have an absorption unit 40. The absorption unit serves to absorb hydrogen chloride from a gas 41 containing hydrogen chloride (e.g. roasting gas) into an absorbent 42 so as to obtain a hydrogen-chloride-enriched absorbent 43 and a hydrogen-chloride-depleted gas 44.

[0081] In the unit 1 of FIG. 2, the second distillation unit 20 is in fluid-conducting communication with the absorption unit 40 in such a way that the second bottom product 23 serves as an absorbent 42 in the absorption unit 40. The absorption unit 40 is in fluid-conducting communication with the first distillation unit 10 so that the hydrogen-chloride-enriched absorbent 43 forms the returned fluid 11. A part of the second bottom product 23 that has not transitioned into the hydrogen-chloride-depleted gas 44 in the absorption unit 40 therefore forms a part of the returned aqueous fluid 11, wherein the fluid 11 also includes absorbed portions of the hydrogen-chloride-containing gas 41. In the absorption unit 40, the absorbent 42 is conducted from top to bottom in countercurrent to the rising gas 41.

[0082] In the unit 1 of FIG. 3, the absorption unit 40 is integrated in the bottom circulation of the second distillation unit 20 in such a way that part of the second bottom product 23 acts as an absorbent 42. The hydrogen-chloride-depleted gas 44 is extracted in the second distillation unit 20, which—as described above for FIG. 1—is configured to be able to implement therein a distillation below the ambient pressure.

LIST OF REFERENCE SIGNS

[0083] unit for recovering hydrogen chloride 1

[0084] first distillation unit 10

[0085] returnable fluid 11

[0086] first top product 12

[0087] first bottom product 13

[0088] pump 18

[0089] substream 19

[0090] second distillation unit 20

[0091] hydrogen-chloride-containing aqueous fluid 21

[0092] second top product 22

[0093] second bottom product 23

[0094] evaporation unit 30

[0095] aqueous liquid which comprises hydrochloric acid and is contaminated with compounds of low or no volatility 31

[0096] hydrogen-chloride-containing vapour 32

[0097] liquid concentrate 33

[0098] absorption unit 40

[0099] hydrogen-chloride-containing gas 41

[0100] absorbent 42

[0101] hydrogen-chloride-enriched absorbent 43

[0102] hydrogen-chloride-depleted gas 44