The present invention provides a process for removal of hydrogen fluoride from a
gas stream containing fluorocarbons.
BACKGROUND OF THE INVENTION
10 Fluorocarbons are important compounds and find applications as heat transfer
agents, refrigerants, foaming agents, solvents, cleaning agents, propellants, and fire
extinguishers, and are required in large amounts.
Generally, fluorocarbons are produced by fluorination that either uses or generates
hydrogen fluoride, which is normally removed by distillation.
15 European Patent No. 2247561 provides a process for separation of
tetrafluoropropene and hydrogen fluoride by azeotropic distillation, followed by
condensation.
U.S Patent No. 5895639 provide method for removing hydrogen fluoride from
1,1,1,3,3-pentafluoropropane using sulphuric acid. This method generates highly
20 corrosive hydrogen fluoride that is detrimental to the equipment used and thus
increase the manufacturing cost.
US Publication No. 20160107892 provides a process for separation of hydrogen
fluoride from halocarbons using ionic liquids. The ionic liquids are difficult to
handle at commercial scales and need to be removed from 1234yf after use, which
25 makes the process cumbersome and add to the cost of running such process.
Owing to corrosive nature of hydrofluoric acid, many applications require
fluorocarbons to be completely free of hydrogen fluoride. Therefore, there is a need
in the art to develop a process for continuously and efficiently removing hydrogen
fluoride from fluorocarbons.
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5 OBJECT OF THE INVENTION
The main object of the present invention is to provide a cost effective and
commercially viable process for removal of hydrogen fluoride from a gas stream
containing fluorocarbons using metal salts.
10 SUMMARY OF THE INVENTION
The present invention provides a process for removal of hydrogen fluoride from a
gas stream containing fluorocarbon, comprising a step of contacting the gas stream
with one or more metal salts.
15 DETAILED DESCRIPTION OF THE INVENTION
As used herein, fluorocarbon is selected from a group consisting of fluoroalkanes,
fluoroolefins, perfluoroacyl or alkane sulfonyl fluorides or the like. Examples of
fluoroalkanes include Difluoromethane (R32), Chlorodifluoromethane (R22),
monofluoroethane (R161), difluoroethane (R152a), chlorodifluoroethane (R142a,
20 R142b), trifluoroethane (R143a, R143b), tetrafluoroethane (R134, R134a),
pentafluoroethane (R125), hexafluoroethane, monofluoropropane, difluoropropane,
trifluoropropane, chlorotetrafluroopropane (R244cb, R244bb), tetrafluoropropane
(R254cb), pentafluoropropane (R245fa, R245ca), hexafluoropropane or the like.
Examples of fluoroolefins include difluoroethylene, trifluoroethylene, 1,1,1,2-
25 tetrafluroopropene, 1,3,3,3-tetrafluoropropene, 2-Chloro-3,3,3-trifluoropropene, 1-
Chloro-3,3,3-trifluoropropene, tetrafluorobutene, hexafluorobutene (R1336mzz),
or the like. Examples of acid fluoride includes as trifluoromethane sulfonyl fluoride,
trifluoroacetylfluoride, perfluoroacyl or alkane sulphonyl fluorides whose boiling
points are less than 10°C
30 As used herein, the fluorocarbon may be a mixture of different fluoroalkane and
fluoroolefins.
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5 As used herein, the metal salt is selected from a group consisting of a metal fluoride
selected from potassium fluoride, and sodium fluoride, or an inorganic sulphate
selected from potassium sulphate, potassium bisulphate or the like. The inorganic
sulphate is used in solid or liquid form.
The inorganic sulphate molecule absorbs 1-14 molecules of hydrogen fluorides
10 from a gas stream. An inorganic sulphate molecule may absorb 1-14 molecules of
hydrogen fluoride from a gas stream and on desorption may desorb greater than 10-
14 molecules of hydrogen fluoride and preferably desorbs 10-12 molecules of
hydrogen fluoride. The inorganic sulphate absorbs hydrogen fluoride and forms
inorganic sulphate hydrogen fluoride complex which can dissociate into free HF
15 and inorganic sulphate.
“Liquid inorganic sulphate” refers to a solution of inorganic sulphate in hydrogen
fluoride. The absorption of hydrogen fluoride from a gas stream using inorganic
sulphate, converts solid inorganic sulphate to a liquid solution comprising inorganic
sulphate and hydrogen fluoride. The hydrogen fluoride may be present in the range
20 of 2-5 molecules of hydrogen fluoride per inorganic sulphate molecules. The liquid
inorganic sulphate salt is also used for removal of hydrogen fluoride.
As used herein, the outlet gas stream refers to the gas stream obtained after passing
inlet gas stream through metal salt. The outlet gas stream may contain hydrogen
fluoride in the range from 0.001 to 5%
25 As used herein, the inlet gas stream-1 refers to the product stream containing
fluorocarbon and hydrogen fluoride. The inlet gas stream may contain hydrogen
fluoride in the range from 0.1-99%.
The outlet stream may contain some content of hydrogen fluoride and can be passed
repeatedly through the metal salt till the concentration of hydrogen fluoride reaches
30 <2% complete removal of hydrogen fluoride may require 2-5 absorption cycles.
In an embodiment of the present invention, the inlet gas stream is contacted with
inorganic sulphate at a temperature range of -10 to 40°C and more preferably at a
temperature of 0-30°C.
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5 In a specific embodiment, the inlet gas stream comprising hydrogen fluoride is
contacted with a solid potassium hydrogen sulphate bed at 30°C to obtain outlet gas
stream.
In an embodiment, the present invention provides a process for recovering hydrogen
fluoride from a gas stream, comprising the steps of:
10 a) contacting an inlet gas stream comprising hydrogen fluoride with a metal salt to
obtain an outlet gas stream and metal salt-hydrogen fluoride complex; and
b) heating the complex of step a) to recover hydrogen fluoride.
The present invention is economic, as hydrogen fluoride may easily be recovered
and recycled
15 The outlet gas stream may contain hydrogen fluoride in the range from 0.001-5%
and more preferably 0.001-2%.
The metal salt can be activated for reuse after several absorption cycles by heating
at a temperature range from 60-300°C.
The inorganic sulphate can be activated for reuse after several absorption cycles by
20 heating at a temperature range from 60-90°C and more preferably in the range 70-
90°C.
The metal fluoride can be activated for reuse after several absorption cycles by
heating at a temperature range from 200-300°C and more preferably in the range
200-280°C.
25 In another embodiment of the present invention, the fluorocarbon contaminated
with hydrogen fluoride may be passed sequentially passed through metal fluoride
followed by inorganic sulphate.
In another embodiment of the present invention, the fluorocarbon contaminated
with hydrogen fluoride may be passed sequentially passed through inorganic
30 sulphate followed by metal fluoride.
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5 The outlet gas stream is passed through water or alkali scrubber and adsorbent to
further eliminate hydrogen fluoride and moisture from it.
The absorbent for present invention may be selected from alumina, carbon and
molecular sieves.
The size of molecular sieves used for present invention is selected in the range from
10 3 to 10 Å and preferably in the range of 3-5 angstrom and more preferably in the
range 3 to 4 Å.
In a specific embodiment, first gas stream is contacted with water scrubber and
molecular sieves of size 3-4 Å to obtain third gas stream.
Unless stated to the contrary, any of the words “comprising”, “comprises” and
15 includes mean “including without limitation” and shall not be construed to limit any
general statement that it follows to the specific or similar items or matters
immediately following it.
Embodiments of the invention are not mutually exclusive but may be implemented
in various combinations. The described embodiments of the invention and the
20 disclosed examples are given for the purpose of illustration rather than limitation of
the invention as set forth in the appended claims.
The following example is given by way of illustration and therefore should not be
construed to limit the scope of the present invention.
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5 EXAMPLES
Example 1: Recovery of hydrogen fluoride.
A gas stream comprising hydrogen fluoride was contacted with potassium hydrogen
sulphate at 30°C to obtain first stream. Later, desorption of potassium hydrogen
sulphate obtained after absorption of HF, was carried out at 80°C to recover
10 hydrogen fluoride.
Recovery % of HF: 99%.
Example 2: Recovery of hydrogen fluoride.
A gas stream comprising hydrogen fluoride was contacted with sodium fluoride at
30°C to obtain outlet stream. Later, desorption of sodium fluoride obtained after
15 absorption of HF, was carried out at 250°C to recover hydrogen fluoride.
Recovery % of HF: 99%.
Example 3: Purification of R1234yf.
A gas mixture containing 1234yf and hydrogen fluoride (5%) was passed through a
sodium fluoride bed to obtain a stream containing mainly of 1234yf. The absorption
20 cycle was repeated 3 times to get HF content of outlet stream: 0.45%.
Example 4: Purification of R1234yf.
A gas mixture containing 1234yf and hydrogen fluoride (5%) was passed through a
potassium hydrogen sulphate scrubber or liquid potassium hydrogen sulphate
(KHSO4.xHF complex) to obtain a stream containing mainly of 1234yf. The
25 absorption cycle was repeated 3 times to get HF content of outlet stream: 0.43%.
Example 5: Purification of R1234yf.
A gas mixture containing 1234yf and hydrogen fluoride (5%) was passed through a
potassium hydrogen sulphate scrubber or liquid potassium hydrogen sulphate
(KHSO4.xHF complex) to obtain first gas stream. The first gas stream obtained was
30 passed through a sodium fluoride bed to obtain second stream comprising mainly
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5 of 1234yf. The absorption cycle was repeated 3 times to get HF content of outlet
stream: 0.3%.
Example 6: Purification of R32.
A gas mixture R32 and hydrogen fluoride (5%) was passed through a sodium
fluoride bed to obtain an outlet stream containing R32. The absorption cycle was
10 repeated 3 times to get HF content of outlet stream: 0.42%.
Example 7: Purification of R32.
A gas mixture containing R32 and hydrogen fluoride (5%) was passed through a
liquid potassium hydrogen sulphate (potassium hydrogen sulphate HF complex)
scrubber to obtain first gas stream. The first gas stream obtained was passed through
15 a sodium fluoride bed to obtain second stream containing R32. The absorption cycle
was repeated 3 times to get HF content of outlet stream: 0.28%
Example 8: Purification of R134a.
A gas stream comprising R134a, hydrogen fluoride (5%) was passed through a
potassium hydrogen sulphate bed to obtain outlet gas stream. The absorption cycle
20 was repeated 3 times to get HF content of outlet stream: 0.48%.
Example 9: Purification of R134a.
A gas stream comprising R134a, hydrogen fluoride (5%) was passed through a
potassium hydrogen sulphate bed to obtain outlet gas stream-1. The outlet gas
stream-1 obtained was passed through a water scrubber and alumina bed to remove
25 left hydrogen fluoride and to obtain outlet gas stream-2 containing R134a. The
absorption cycle was repeated 3 times to get HF content of final outlet stream2:
0.21%.
Example 10: Purification of R245fa.
A gas stream comprising R245fa, hydrogen fluoride (5%) was passed through a
30 potassium hydrogen sulphate bed to outlet gas stream containing R245fa. The
absorption cycle was repeated 3 times to get HF content of outlet stream: 0.48%.
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WE CLAIM:

1. A process of removing hydrogen fluoride from a gas stream containing
fluorocarbon and hydrogen fluoride, comprising a step of contacting the gas stream
with one or more metal salts.
2. The process as claimed in claim 1, wherein the metal salt is a metal fluoride
10 selected from a group consisting of sodium fluoride and potassium fluoride or an
inorganic sulphate selected from a group consisting of potassium sulphate and
potassium bisulphate or a combination thereof.
3. The process as claimed in claim 1, wherein the fluorocarbon is selected from a
group consisting of fluoroalkanes, fluoroolefins, perfluoroacyl or alkane sulfonyl
15 fluorides or a mixture thereof.
4. The process as claimed in claim 1, wherein the gas stream containing
fluorocarbon and hydrogen fluoride is sequentially contacted with one metal salt
followed by another metal salt.
5. The process as claimed in claim 1, wherein the gas stream containing
20 fluorocarbon and hydrogen fluoride is first contacted with a metal fluoride followed
by an inorganic sulphate.
6. The process as claimed in claim 1, wherein the process additionally involves
recovering hydrogen fluoride.
7. The process as claimed in claim 6, wherein the hydrogen fluoride is recovered by
25 heating metal salt-hydrogen fluoride complex formed by the contact of metal salt
and hydrogen fluoride at a temperature of 60-300°C.
8. The process as claimed in claims 1, wherein fluorocarbon obtained has hydrogen
fluoride content in the range of 0.001-5%.
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5 9. The process as claimed in claim 1, wherein the gas stream contains hydrogen
fluoride in the range of 0.1-99%.