Process for preparation of hydrobromic acid

Abstract

A process has been disclosed for preparation of hydrobromic acid from bromine, sulfur dioxide and water, which involves in situ generation of bromine from bittern for the production of hydrobromic acid and separation thereof from co-products, viz., sulfuric and hydrochloric acids. The invented process obviates the need for double distillation or precipitation step for removal of sulfate impurities. The concentration of the product obtained by the disclosed process is about 48% and it contains <15 ppm sulfate and chloride impurities.

Claims

1. A continuous process for manufacturing hydrobromic acid by separating hydrobromic acid from sulfuric acid and subsequently concentrating the hydrobromic acid, comprising: (i) filling a flash tank and a first re-boiler with a mixture of hydrobromic acid and sulfuric acid from a feed tank; (ii) heating the mixture of hydrobromic acid and sulfuric acid to 95-100 C. under reduced pressure by heating the first re-boiler so as to cause thermo-siphoning of said mixture from the first re-boiler to the flash tank; (iii) continuously adding the mixture of the hydrobromic acid and sulfuric acid from the feed tank to the flash tank, maintaining the temperature at 95-100 C.; (iv) condensing an azeotropic mixture of hydrobromic acid and water formed during step (iii) in a first heat exchanger and feeding it back to a hollow column which is fitted above the flash tank; (v) allowing hydrobromic acid from the azeotropic mixture of hydrobromic acid and water to drop into a reflux divider, which is fitted in the hollow column in step (iv); (vi) allowing hydrobromic acid to flow through a connecting pipe from the reflux divider to a second re-boiler, said second re-boiler maintained at 65-70 C.; (vii) allowing hydrobromic acid to flow from the bottom of the second re-boiler to a first storage tank via a second heat exchanger; and (viii) collecting sulfuric acid from the bottom of the flash tank into a second storage tank via a third heat exchanger by opening a valve when specific gravity of sulfuric acid is at least 1.45.

2. The continuous process for manufacturing hydrobromic acid as described in claim 1, wherein incidentally produced HCl and water are removed from a mixture containing hydrobromic acid, HCl and water by allowing HCl and water vapor to flow from the first heat exchanger to a first vertical heat exchanger, allowing them to condense in the first vertical heat exchanger and collecting in the third storage tank.

3. A continuous process for manufacturing hydrobromic acid as described in claim 1, wherein traces of HCl and water, which get carried to a second re-boiler along with the hydrobromic acid, are further removed from the hydrobromic acid by maintaining temperature of the second re-boiler at 65-70 C., thereby allowing HCl and water to evaporate and flow to the third heat exchanger and subsequently to the second vertical heat exchanger, allowing HCl and water vapor to condense in the second vertical heat exchanger, and collecting them in a storage tank.

4. The continuous process for manufacturing hydrobromic acid as described in claim 1, wherein HBr mist which gets carried away to the third heat exchanger is allowed to condense in the third heat exchanger and is fed back to the second re-boiler.

5. The continuous process for manufacturing hydrobromic acid as described in claim 1, wherein the mixture of hydrobromic acid and sulfuric acid is prepared by treatment of bittern with chlorine to generate bromine which is reacted in situ with SO2 and water to produce a mixture of hydrobromic acid and sulfuric acid.

6. The continuous process for manufacturing hydrobromic acid as described in claim 5, wherein incidentally produced HCl and water are removed from a mixture containing hydrobromic acid, HCl and water by allowing HCl and water vapor to flow from the first heat exchanger to a first vertical heat exchanger, allowing them to condense in the first vertical heat exchanger and collecting in the third storage tank.

7. A continuous process for manufacturing hydrobromic acid as described in claim 5, wherein traces of HCl and water, which get carried to a second re-boiler along with the hydrobromic acid, are further removed from the hydrobromic acid by maintaining temperature of the second re-boiler at 65-70 C., thereby allowing HCl and water to evaporate and flow to the third heat exchanger and subsequently to the second vertical heat exchanger, allowing HCl and water vapor to condense in the second vertical heat exchanger, and collecting them in a storage tank.

8. The continuous process for manufacturing hydrobromic acid as described in claim 5, wherein HBr mist which gets carried away to the third heat exchanger is allowed to condense in the third heat exchanger and is fed back to the second re-boiler.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram showing equipment employed for preparation of hydrobromic acid wherein the numbered components are as under:

(2) 1.Math.feed tank 2.Math.flash tank 3.Math.first re-boiler 4.Math.valve 5.Math.third heat exchanger 6.Math.second storage tank 7.Math.reflux divider 8.Math.main heat exchanger 9.Math.first vertical heat exchanger 10.Math.third storage tank 11.Math.second re-boiler 12.Math.second heat exchanger 13.Math.first storage tank 14.Math.third heat exchanger 15.Math.second vertical heat exchanger 16.Math.fourth storage tank

DETAILED DESCRIPTION

(3) Bittern contains 800-1000 ppm bromine as magnesium bromide (MgBr.sub.2). Upon treatment of acidified bittern (pH=3) with chlorine, oxidation followed by substitution reaction occurs, releasing bromine. Overall reaction is as under:
MgBr.sub.2+Cl.sub.2.fwdarw.MgCl.sub.2+Br.sub.2

(4) Some HCl is also generated during chlorination of bittern.

(5) Bromine thus generated is subjected to air-stripping and then it passes through absorption tower, where it reacts with SO.sub.2 and water to form hydrobromic acid and sulfuric acid.
Br.sub.2+SO.sub.2+2H.sub.2O.fwdarw.H.sub.2SO.sub.4+2HBr

(6) Strength of HBr obtained at this stage is 25-28% and that of H.sub.2SO.sub.4 is 15-20%.

(7) Flash tank (2) and re-boiler (3) are filled with mixture of HBr+H.sub.2SO.sub.4 obtained as stated above. It also contains some HCl. The flash tank (2) is made up of polymer material and it is connected via connecting pipes to the re-boiler (3) as shown in FIG. 1. The re-boiler (3) is made up of corrosion resistant material such as graphite. The acid mixture is heated to 95-100 C. by heating re-boiler (3). The system is maintained at a reduced pressure of 670-700 mm Hg and hence the mixture boils at 95-100 C. The mixture boils and starts thermo-siphoning from re-boiler (3) to flash-tank (2) through upper connecting pipe.

(8) Because of the difference in boiling points and specific gravity, H.sub.2SO.sub.4 tends to remain at the bottom of the flash tank (2). HBr, HCl and water vapourizes and tends to move towards the upper end of the flash tank (2). The upper end of the flash tank (2) is connected via a hollow glass column to the heat exchanger (8).

(9) Once the mixture starts thermosiphoning, HBr+H2SO4 mixture is added continuously into the flash tank (2) from the feed tank (1). HBr forms azeotropic mixture with water and it goes into heat exchanger (8). HBr condenses in the heat exchanger (8) and it is fed back to the upper part of the hollow glass column as shown in FIG. 1. HCl is low boiling and along with some water vapour it moves from heat exchanger (8) to vertical heat exchanger (9) where it condenses and is collected separately in tank (10).

(10) A reflux divider (7) is provided at the centre of the hollow glass column mentioned above. HBr which is fed back to the upper part of the hollow glass column falls on the lower part of the reflux divider. At this stage, the concentration of HBr is 41-45% and it still contains 500-800 ppm HCl. Hence it needs to be purified and concentrated further.

(11) Lower part of the reflux divider is at a comparatively higher temperature than the upper part. Due to this, when 41-45% HBr (containing 500-800 ppm HCl) falls on the lower part of the reflux divider, HCl and water remaining therein further evaporates from it and enters into the heat exchanger (8). Thus HBr gets further purified and concentrated.

(12) A connecting pipe is provided at the lower end of the reflux divider (7) which extends up to a glass column above the re-boiler (11). HBr flows from the bottom of the reflux divider (7) to re-boiler (11) via this connecting pipe.

(13) As the temperature of re-boiler (11) is maintained at 65-70 C., traces of HCl and water vapour present in HBr evaporates and goes into the heat exchanger (14) along with some HBr-mist. HBr-mist condenses in the heat exchanger (14) and flows back to re-boiler (11). HCl and water vapour goes from upper end of heat exchanger (14) to vertical heat exchanger (15) where it condenses and it is collected in the storage tank 16.

(14) Because of high specific gravity, HBr collects at the bottom of the re-boiler (11), from where it flows through the heat exchanger (12) and ultimately flows to the storage tank (13). The concentration of HBr collected in the storage tank (13) is about 48%. It contains <15 ppm sulfate and <15 ppm chloride.

(15) H.sub.2SO.sub.4 is collected from the bottom of the flash-tank (2) by opening the valve (4). Collection is started when specific gravity of H.sub.2SO.sub.4 is at least 1.45, preferably at least 1.5. Rate of drain-out of H.sub.2SO.sub.4 is adjusted in proportion with the rate of addition of the HBr+H.sub.2SO.sub.4 mixture in the flash-tank (2).

EXAMPLE-1

(16) As per an embodiment of the invention, bittern containing about 1000 ppm bromine as magnesium bromide (MgBr.sub.2) was acidified with sulfuric acid to pH 3. Acidified bittern was sprayed from the top of a stripping tower. Chlorine gas (3-4% in excess to stoichiometric amount of bromine content of the bittern) and air were injected from the bottom of the stripping tower. It generated bromine as per the following reaction:
MgBr.sub.2+Cl.sub.2.fwdarw.MgCl.sub.2+Br.sub.2

(17) Bromine thus generated was fed from the bottom of an absorption tower in which SO.sub.2 (about 5% in excess to stoichiometric amount) and water were introduced from the top. Bromine reacted with SO2 and water to obtain HBr (28%) and H.sub.2SO.sub.4 (20%).

(18) HBr+H.sub.2SO.sub.4 mixture obtained as above was filled in flash tank (2) and re-boiler (3). It was heated to 95 C. by heating re-boiler. The system was maintained at about 670 mm Hg. After the mixture started boiling and thermo-siphoning, gradual addition of HBr+H.sub.2SO.sub.4 mixture into the flash tank was started.

(19) H.sub.2SO.sub.4 formed was collected from the bottom of the flash tank (2) by opening the valve (4). Collection was started when specific gravity of H.sub.2SO.sub.4 was 1.51. Rate of drain-out of H.sub.2SO.sub.4 was adjusted in proportion with the rate of addition of the HBr+H.sub.2SO.sub.4 mixture in the flash-tank (2).

(20) HBr formed azeotropic mixture with water and was condensed in heat exchanger (8). It was fed back to the upper part of the hollow glass column in which a reflux divider (7) was fitted. HBr was then allowed to flow from the bottom of the reflux divider (7) to re-boiler (11) via a connecting pipe. Temperature of the re-boiler (11) was maintained at 65-70 C. HBr collecting at the bottom of the re-boiler (11) was allowed to flow via heat exchanger (12) to the storage tank (13). Concentration of HBr collected in the storage tank (13) was about 48% and it contained <15 ppm chloride and sulfate impurities. Incidentally produced HCl and water were removed from the mixture containing hydrobromic acid, HCl and water by allowing HCl and water vapour to flow from heat exchanger (8) to vertical heat exchanger (9), allowing them to condense in vertical heat exchanger (9) and collecting in tank (10).

(21) Traces of HCl and water which was carried to re-boiler (11) along with hydrobromic acid were further removed from hydrobromic acid by maintaining temperature of re-boiler (11) at 65-70 C., thereby allowing HCl and water to evaporate and flow to heat exchanger (14) and subsequently to vertical heat exchanger (15), allowing HCl and water vapour to condense in vertical heat exchanger (15), and collecting them in the storage tank (16).

(22) HBr mist which was carried away to heat exchanger (14) was allowed to condense in the heat exchanger (14) and was fed back to re-boiler (11).