HIGH PRESSURE DESORPTION OF HYDROGEN CHLORIDE GAS

Abstract

A method for producing a hydrogen chloride. A pressurized highly concentrated hydrochloric acid having a hydrogen chloride concentration of 35% by weight or above is fed into a high pressure desorption device, the high pressure desorption device is operated at a pressure P.sub.des of 2 bar or above and at a temperature T from 110 to 200° C. in the bottom of the high pressure desorption device, and the hydrogen chloride is desorbed in the high pressure desorption device.

Claims

1-15. (canceled)

16. A method for producing a hydrogen chloride, comprising: a pressurized highly concentrated hydrochloric acid having a hydrogen chloride concentration of 35% by weight or above is fed into a high pressure desorption device, operating the high pressure desorption device at a pressure P.sub.des of 2 bar or above and at a temperature T from 110 to 200° C. in the bottom of the high pressure desorption device, and desorbing the hydrogen chloride in the high pressure desorption device.

17. The method according to claim 16, wherein the highly concentrated hydrochloric acid has a hydrogen chloride concentration of 40 to 60% by weight.

18. The method according to claim 16, wherein P.sub.des is in a range from 6 bar to 20 bar.

19. The method according to claim 16, wherein the temperature T is in a range from 120 to 175° C.

20. The method according to claim 16, wherein at least part of the highly concentrated hydrochloric acid is formed in an absorption device, in which a hydrogen chloride containing gas is absorbed into a less concentrated hydrochloric acid.

21. The method according to claim 16, wherein the absorption device is operated at a pressure P.sub.abs which is lower than P.sub.des.

22. The method according to claim 20, wherein at least part of the hydrogen chloride containing gas that is absorbed into the less concentrated hydrochloric acid, is formed in a low pressure desorption device.

23. The method according to claim 22, wherein at least part of a liquid obtained in the bottom of the high pressure desorption device is recycled into the low pressure desorption device.

24. A unit for producing a hydrogen chloride, comprising a high pressure desorption device for desorbing a hydrogen chloride from a pressurized highly concentrated hydrochloric acid, wherein the high pressure desorption device comprises a high pressure inlet for feeding a pressurized highly concentrated hydrochloric acid into the high pressure desorption device, an upper high pressure outlet for a hydrogen chloride which can be desorbed in the high pressure desorption device, and a lower high pressure outlet for a liquid obtainable in the bottom of the high pressure desorption device; and a subunit which is connected to the high pressure inlet and to the lower high pressure outlet and which is capable of regenerating at least part of the pressurized highly concentrated hydrochloric acid to be fed via the high pressure inlet from at least part of the liquid obtainable through the lower high pressure outlet.

25. The unit according to claim 24, wherein the high pressure desorption device can be operated at a pressure exceeding the pressure in the surrounding atmosphere by at least 5 bar.

26. The unit according to claim 24, wherein the interior of the high pressure desorption device is corrosion resistant against pressurized highly concentrated hydrochloric acids having a hydrogen chloride concentration of at least 35% by weight at a temperature of 110° C.

27. The unit according to claim 24, comprising a pump, wherein the pump is capable of feeding the highly concentrated hydrochloric acid against the high backpressure from the high pressure desorption device being under a pressure of at least 2 bar.

28. The unit according to claim 25, wherein the unit does not comprise a compressor for maintaining a high pressure P.sub.des of at least 2 bar in the high pressure desorption device.

29. A hydrogen chloride supplying unit, comprising a high pressure desorption device for desorbing a hydrogen chloride from a pressurized highly concentrated hydrochloric acid, wherein the high pressure desorption device comprises a high pressure inlet for feeding a pressurized highly concentrated hydrochloric acid into the high pressure desorption device, an upper high pressure outlet for a hydrogen chloride which can be desorbed in the high pressure desorption device, and a lower high pressure outlet for a liquid obtainable in the bottom of the high pressure desorption device; and a hydrogen chloride filling device which is connected to the upper high pressure outlet.

30. A system for constructing a unit according to claim 24, the system comprises a high pressure desorption device for desorbing a hydrogen chloride gas from a pressurized highly concentrated hydrochloric acid, wherein the high pressure desorption device comprises a high pressure inlet for feeding a pressurized highly concentrated hydrochloric acid into the high pressure desorption device, an upper high pressure outlet for a hydrogen chloride gas which can be desorbed in the high pressure desorption device, and a lower high pressure outlet for a liquid obtainable in the bottom of the high pressure desorption device; an absorption device comprising an outlet for highly concentrated hydrochloric acid; wherein the system is designed for connecting the outlet for highly concentrated hydrochloric acid in such a way via a pump with the high pressure inlet, that a highly concentrated hydrochloric acid from outlet can be pressurized and fed via the high pressure inlet into the high pressure desorption device.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0043] The invention is illustrated with reference to the figures described in the following. The figures are for illustration only and do not limit the scope of the claims.

[0044] FIG. 1: simplified process flow diagram of a high pressure desorption device suitable for a method of the invention;

[0045] FIG. 2: simplified process flow diagram of a unit according to the invention;

[0046] FIG. 3A: graphs showing the boiling points at different hydrochloric acid concentrations (low concentration range); and

[0047] FIG. 3B: graphs showing the boiling points at different hydrochloric acid concentrations (high concentration range).

DETAILED DESCRIPTION

[0048] The high pressure desorption device 10 shown in FIG. 1 is a high pressure PTFE lined desorption column comprising a high pressure inlet 13 for feeding a pressurized highly concentrated hydrochloric acid into device 10, a lower high pressure outlet 14 for a liquid obtainable in the bottom of device 10, and an upper high pressure outlet 15 for a hydrogen chloride gas which can be desorbed in device 10. The bottom is heated by high pressure reboiler 11. Water contained by the desorbed hydrogen chloride gas, which leaves the device via outlet 15 is condensed in high pressure condenser 12. The cooled hydrogen chloride gas leaves condenser 12 via line 18 while the condensed liquid is recycled into device 10. Although not all details are shown, FIG. 1 further indicates that the desorption device may contain column internals 16 (e.g. made of graphite or CFRC or CFRP (Sigrabond® Chemical product lines sold by SGL) and a liquid distributor 19. FIG. 1 is also simplified in that it does not show the means that confer the column’s high pressure and corrosion stability. The column can be operated for a long time at high bottom temperature T of 110 to 200° C. and at high pressure P.sub.des of up to 20 bar even when very corrosive pressurized and highly concentrated hydrochloric acid is fed into the column via inlet 13. It is therefore quite possible to carry out the method of the invention in the device as shown in FIG. 1.

[0049] FIG. 2 shows the high pressure desorption device 10 (as shown in FIG. 1) as a part of a unit according to the invention. This unit further comprises an absorption device 20 and a low pressure desorption device 30.

[0050] Absorption device 20 comprises a feed 21 for a less concentrated hydrochloric acid, an inlet 22 for a hydrogen chloride containing gas and an outlet 23 for the highly concentrated hydrochloric acid. The highly concentrated hydrochloric acid can be formed in the absorption device 20, in which hydrogen chloride containing gas fed via inlet 22 is absorbed into a less concentrated hydrochloric acid. After the highly concentrated hydrochloric acid has left the absorption device through outlet 23, it is pumped in order to transport the highly concentrated hydrochloric acid against the high pressure P.sub.des and preheated in a heat exchanger before it is fed via inlet 13 into the high pressure desorption device 10.

[0051] Low pressure desorption device 30 is preferably a desorption column and comprises a low pressure reboiler 31, a hydrogen chloride containing gas head product outlet 32, and a low pressure sump outlet 36. Low pressure desorption device 30 is further equipped with a flash vessel 33. Part of the liquid obtained in the bottom of the high pressure desorption device 10 is recycled via flash vessel 33 into the low pressure desorption device 30. In low pressure desorption device 30, the hydrogen chloride containing gas is formed and passed through gas head product outlet 32. The vapors formed in flash vessel 33 are fed into the hydrogen chloride containing gas and the hydrogen chloride containing gas is then fed via inlet 22 into absorption device 20. The bottoms are passed through outlet 36 and excess heat can be transferred from the bottoms in a heat exchanger to the pressurized highly concentrated hydrochloric acid, before the pressurized highly concentrated hydrochloric acid is fed via inlet 13 into device 10. “Low pressure” when used in connection with device 30 refers to a lower pressure as compared to the pressure in device 10. Nevertheless, the pressure in the low pressure desorption device 30 is typically well above the surrounding atmospheric pressure.

[0052] It is apparent that the low pressure desorption device and the absorption device as shown in FIG. 2 together can be considered as a subunit which is connected to the high pressure inlet 13 and to the lower high pressure outlet 14 and which is capable of regenerating at least part of the pressurized highly concentrated hydrochloric acid to be fed via inlet 13 from at least part of the liquid obtainable through outlet 14.

[0053] For carrying out a method of the invention, the unit as described in FIG. 2 can be operated, for example, under the following conditions:

[0054] Composition of feed 21: Hydrochloric acid (33% by weight of HCI in water)

[0055] The following table provides example parameters for operating devices 10, 20, and 30

TABLE-US-00001 Temperature [°C] P [bar] HCI content in the bottom [% by weight] head bottom high pressure desorption device 10: 73 144 11 (P.sub.des) 33 absorption device 20: 40 5 43 (P.sub.abs) low pressure desorption device 30: 140 158 5 18

[0056] The pump is capable of transporting the highly concentrated hydrochloric acid against the high pressure P.sub.des.

[0057] The weak acid released via low pressure sump outlet 36 contains 18% by weight of HCI. This weak acid could be treated by breaking the azeotrope, e.g. with a solution of a hygroscopic salts, such as CaCl.sub.2.

[0058] After removal of residual moisture from the hydrogen chloride gas released through outlet 15 by drying in high pressure condenser 12, it is possible to further remove residual droplets carried by the stream obtained from condenser 12 with a high pressure demister (not shown). This will result in very low residual water content.

[0059] In FIGS. 3A and 3B, the boiling points in °C (vertical axis) are shown for different hydrogen chloride mass contents of the HCI / H.sub.2O binary system (horizontal axis). The Figures show the boiling points at pressures of 2 bar (lower most curve), 5 bar (middle curve), 11 bar (top most curve). The arrows in FIGS. 3A, 3B refer to the thermal separation in low pressure desorption device 30 and high pressure desorption device 10, respectively. The arrows thus illustrate how the invention makes efficient use of a very sharp decline of boiling points of the HCI/H.sub.2O binary system at hydrogen chloride mass contents above 0.35, i.e. at HCI concentrations above 35% by weight.

TABLE-US-00002 List of reference numerals high pressure desorption device 10 high pressure reboiler 11 high pressure condenser 12 column inlet for a pressurized highly concentrated hydrochloric acid 13 lower high pressure outlet 14 upper high pressure outlet 15 column internals 16 line for cooled hydrogen chloride gas 18 liquid distributor 19 absorption device 20 feed for less concentrated hydrochloric acid 21 inlet for hydrogen chloride containing gas 22 outlet for highly concentrated hydrochloric acid 23 low pressure desorption device 30 low pressure reboiler 31 hydrogen chloride containing gas head product outlet 32 flash vessel 33 low pressure sump outlet 36