U.S. patent application number 10/896905 was filed with the patent office on 2005-01-06 for process for the production of difluoromethane.
This patent application is currently assigned to AlliedSignal Inc.. Invention is credited to Bass, John Stephen, Clemmer, Paul Gene, Smith, Addison Miles, Tung, Hsueh Sung.
Application Number | 20050004408 10/896905 |
Document ID | / |
Family ID | 24114432 |
Filed Date | 2005-01-06 |
United States Patent
Application |
20050004408 |
Kind Code |
A1 |
Clemmer, Paul Gene ; et
al. |
January 6, 2005 |
Process for the production of difluoromethane
Abstract
The present invention provides a vapor phase process for the
production of difluoromethane, HFC-32. The process of this
invention provides for the preparation of BFC-32 by a process that
exhibits both good product yield and selectivity.
Inventors: |
Clemmer, Paul Gene;
(Williamsville, NY) ; Smith, Addison Miles;
(Amherst, NY) ; Tung, Hsueh Sung; (Getzville,
NY) ; Bass, John Stephen; (East Amherst, NY) |
Correspondence
Address: |
Colleen Szuch
Honeywell International, Inc.
101 Columbia Road
P.O. Box 2245
Morristown
NJ
07962
US
|
Assignee: |
AlliedSignal Inc.
|
Family ID: |
24114432 |
Appl. No.: |
10/896905 |
Filed: |
July 23, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10896905 |
Jul 23, 2004 |
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08959748 |
Oct 28, 1997 |
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08959748 |
Oct 28, 1997 |
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08530649 |
Sep 20, 1995 |
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5763708 |
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Current U.S.
Class: |
570/165 |
Current CPC
Class: |
C07C 17/206 20130101;
C07C 17/206 20130101; C07C 19/08 20130101 |
Class at
Publication: |
570/165 |
International
Class: |
C07C 017/08 |
Claims
1. A process for the production of difluoromethane comprising: (a)
contacting dichloromethane with hydrogen fluoride in the presence
of a fluorination catalyst to produce a product stream of
difluoromethane, monochloromonofluoromethane, and unreacted
starting materials and (b) separating difluoromethane from the
product stream from step (a) wherein sufficient hydrogen fluoride
is employed in the process such that during step (b) the molar
ratio of hydrogen fluoride to monochloromonofluorometh- ane is at
least about 100:1.
2. A process as claimed in claim 1, in which the molar ratio of
hydrogen fluoride to monochloromonofluoromethane is at least about
150:1.
3. A process as claimed in claim 1 in which additional hydrogen
fluoride is added to the process stream recovered from step (a) in
order to ensure that the required ratio of hydrogen fluoride to
HCFC 31 is achieved during step (b).
4. A process for the production of difluoromethane comprising (a)
contacting dichloromethane with hydrogen fluoride in the presence
of a fluorination catalyst to produce a product stream comprising
difluoromethane, monochloromonofluoromethane and unreacted starting
materials, (b) separating difluoromethane from the product stream
from step (a) and (c) recovering difluoromethane and recycling HCFC
31 to step (a), wherein sufficient hydrogen fluoride is employed in
the process such that during step (b) the molar ratio of hydrogen
fluoride to monochloromonofluoromethane is at least about
100:1.
5. A process as claimed in claim 1 in which the separation step (b)
comprises distilling the product stream from step (a) whereby to
separate a top stream comprising difluoromethane and hydrogen
chloride from a bottom stream comprising hydrogen fluoride, HCFC-31
and unreacted dichloromethane.
6. A process of as claimed in claim 1 in which the fluorination
catalyst comprises a metal oxide, metal fluoride or
oxyfluoride.
7. A process as claimed in claim 6 in which the metal of the oxide,
fluoride, or oxyfluoride is at least one of chromium, aluminum,
zinc, nickel, cobalt, copper and magnesium.
8. A process as claimed in claim 7 in which the catalyst comprises
zinc or a compound of zinc and a metal oxide, fluoride or
oxyfluoride in which the metal of the oxide, fluoride or
oxyfluoride is chromium or aluminum.
9. A process for producing difluoromethane comprising the steps of:
(A) preheating a composition comprising hydrogen fluoride and
dichloromethane to form a vaporized and superheated composition;
(B) reacting the preheated composition of step (A) in the presence
of a fluorination catalyst under conditions suitable to form a
product stream comprising difluoromethane, chlorofluoromethane,
hydrogen chloride, dichloromethane and hydrogen fluoride; (C)
recovering by distillation from the product stream of step (B) a
high boiling fraction comprising hydrogen fluoride,
dichloromethane, and chlorofluoromethane and a low boiling fraction
comprising difluoromethane, hydrogen chloride, hydrogen fluoride,
and reaction byproducts; and (D) recovering substantially pure
difluoromethane from the low boiling fraction of step (C).
10. The process of claim 9 wherein the hydrogen fluoride and
dichloromethane are present in a mole ratio from about 1:1 to about
10:1.
11. The process of claim 9 wherein the composition of step (A)
further comprises chlorofluoromethane.
12. The process of claim 9 wherein the hydrogen fluoride and the
chlorofluoromethane are present in the product stream in a mole
ratio of at least about 25:1 to at least about 300:1.
13. The process of claim 9 wherein the hydrogen fluoride and the
chlorofluoromethane are present in the product stream in a mole
ratio of at least about 50:1 to at least about 200:1.
14. The process of claim 9 wherein the hydrogen fluoride and the
chlorofluoromethane are present in the product stream in a mole
ratio of at least about 75:1 to at least about 150:1.
15. The process of claim 1 wherein the fluorination catalyst is a
pretreated fluorination catalyst.
16. The process of claim 15 wherein the fluorination catalyst is
chromium oxide.
17. The process of claim 9 wherein the high boiling fraction of
step (C) is recycled to step (A).
18. The process of claim 9 wherein step (D) further comprises the
substeps of: (E) treating the low boiling mixture of step (C) in an
HCl distillation column or an aqueous HCl absorption tower under
conditions suitable to remove HCl and trace HF to form a crude
HFC.32 product; (F) treating the crude HFC.32 product formed in
step (E) with a first caustic scrubber under conditions suitable to
form a neutralized product; (G) treating the neutralized product of
step (F) in a second caustic scrubber under conditions suitable to
form a substantially chlorine-free product; (H) treating the
substantially chlorine-free product of step (G) with a sulfuric
acid scrubber and subsequently with a solid desiccant to form a
substantially moisture-free product; and (I) distilling the
substantially moisture-free product of step (H) under conditions
suitable to produce substantially pure difluoromethane.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a vapor phase process for
the production of difluoromethane, HFC-32. In particular, this
invention provides a process for the preparation of HFC-32 that
exhibits good product yield and selectivity.
BACKGROUND OF THE INVENTION
[0002] It is well known in the art that HFC-32 may be used as a
replacement for environmentally disadvantageous chlorofluorocarbon
refrigerants, blowing agents, and aerosol propellants. A variety of
methods for the vapor phase production of HFC-32 are known.
[0003] For example, U.S. Pat. No. 2,745,886 discloses a vapor phase
process for fluorinating a variety of halohydrocarbons including
methylene chloride, HCC-30, which process utilizes a hydrated
chromium fluoride catalyst activated with oxygen. Similarly, U.S.
Pat. No. 2,744,148 discloses a halohydrocarbon fluorination process
in which an HF-activated alumina catalyst is used.
[0004] U.S. Pat. No. 3,862,995 discloses the vapor phase production
of HFC-32 by reacting vinyl chloride and HF in the presence of a
vanadium derivative catalyst supported on carbon. U.S. Pat. No.
4,147,733 discloses a vapor phase reaction for the production of
HFC-32 by HCC-30 with HF in the presence of a metal fluoride
catalyst.
[0005] In practice, these processes for HFC-32 production suffer
from a variety of problems including low product yield and
selectivity as well as operational difficulties such as feed
decomposition. The process of this invention provides for the
production of HFC-32 by a process that overcomes some of the
disadvantages of the known processes.
DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
[0006] The present invention provides a method for HFC-32
production in good yield and selectivity. In general, the process
of this invention comprises contacting HCC-30 and HF in the
presence of a fluorination catalyst to produce a product stream of
difluoromethane, chlorofluoromethane ("HCFC-31"), hydrogen
chloride, dichloromethane, and hydrogen fluoride and separating
HFC-32 from the product stream. In a preferred embodiment, the
invention comprises the steps of:
[0007] (A) preheating a composition comprising hydrogen fluoride
("HF") and HCC-30 and, optionally, HCFC-31, to form a vaporized and
superheated composition,
[0008] (B) reacting the preheated composition of step (A) in the
presence of a fluorination catalyst under conditions suitable to
form a product stream comprising HFC-32, HCFC-31 and hydrogen
chloride and unreacted HCC-30 and HF;
[0009] (C) recovering by distillation from the product stream of
step (B) a high boiling fraction comprising HF, HCC-30, and HCFC-31
and a low boiling fraction comprising HFC-32, HCl, HF, and reaction
byproducts; and
[0010] (D) recovering substantially pure HFC-32 product from the
low boiling fraction of step (C).
[0011] In step (A) a composition comprising HF and HCC-30 is
preheated in at least one vaporizer. By "preheating" is meant to
vaporize and superheat the composition. The composition is heated
to a temperature of from about 125.degree. C. to about 400.degree.
C., preferably 150.degree. C. to about 300.degree. C., more
preferably from about 175.degree. C. to about 275.degree. C. and
most preferably 200.degree. C. to about 250.degree. C. The
vaporizer, as well as the other vessels used in this process, may
be made of any suitable corrosion resistant material.
[0012] Although fresh HF and HCC-30 may be used in step (A),
preferably the composition of step (A) contains recycled material
from step (C) as described below. When the process is run without
continuous recycle, the mole ratio of HF to organic, specifically
the mole ratio of HF to HCC-30, is from about 1:1 to about 10:1,
preferably from about 1:1 to about 4:1. Optionally, fresh HCFC-31
may be added to the composition of step (A).
[0013] Alternatively, a continuous recycle stream of the high
boiling fraction obtained in step (C) is recycled to step (A) in
which case a large excess of HF to organics is used. In the process
of this invention, the higher the HF:organics mole ratio, the
higher the yield and selectivity for HFC-32. Correspondingly, a
large excess of HF will result in-the reduction of HCFC-31 produced
as well as the concentration of unreacted HCC-30. Additionally, the
use of a large excess of HF will decrease catalyst deactivation
rates and result in less decomposition in preheaters and
vaporizers, especially when the reaction is conducted at pressures
in excess of 3 atmospheres. Generally, a ratio of HF to HCFC-31, as
measured after separation of HFC-32 from the product stream, of at
least about 25:1 to at least about 300:1, preferably at least about
50:1 to at least about 200:1, and more preferably at least about
75:1 to at least about 150:1 is used.
[0014] The preheated composition of step (A) is reacted in step (B)
in a vapor phase fluorination reaction to form a product stream
mixture. The reaction may proceed in one or more isothermal or
adiabatic reactors. When more than one reactor is used, the reactor
arrangement is not critical, but a sequential arrangement is
preferred. Inter-reactor heating or cooling may be used to obtain
the best reactor performance.
[0015] The reactor or reactors used in this process are filled with
a fluorination catalyst and the organic and HF vapor is allowed to
contact the catalyst under conditions suitable to form a reaction
mixture. The reactor temperature is maintained at from about
125.degree. to about 425.degree. C., preferably 150.degree. C. to
about 300.degree. C., more preferably 175.degree. C. to about
275.degree. C. and most preferably 200.degree. C. to about
250.degree. C. Reactor pressure may be atmospheric, subatmospheric,
or superatmospheric. Preferably reactor pressure is maintained at
from about 0 psig to about 250 psig. Contact time, the time
required for the reactants to pass through the catalyst bed
assuming a 100% void catalyst bed, is typically from about 1 to
about 120 seconds, preferably from about 2 to 60 seconds, more
preferably from about 4 to about 50 seconds, and most preferably
from about 5 to about 30 seconds.
[0016] Any known vapor phase fluorination catalyst may be used in
the process of this invention. Exemplary catalysts include, without
limitation, chromium, copper, aluminum, cobalt, magnesium,
manganese, zinc, nickel and iron oxides, hydroxides, halides,
oxyhalides and inorganic salts thereof,
Cr.sub.2O.sub.3/Al.sub.2O.sub.3, Cr.sub.2O.sub.3/AlF.sub.3,
Cr.sub.2O.sub.3/carbon, CoCl.sub.2/Cr.sub.2O.sub.3/Al.sub.2O.sub.3,
NiCl.sub.2/Cr.sub.2O.sub.3/Al- .sub.2O.sub.3, CoCl.sub.2/AlF.sub.3
and NiCl.sub.2/AlF.sub.3. Additionally, supported metal catalysts
such as nickel, cobalt, zinc, iron, and copper supported on
chromia, magnesia, or alumina may be used. Chromium oxide/aluminum
oxide catalysts are described in U.S. Pat. No. 5,155,082 which is
incorporated herein in its entirety. Preferably, chromium oxide, a
commercially available catalyst, is used. The chromium oxide may be
crystalline or amorphous. Preferably, amorphous chromium oxide is
used. The catalyst is used in an amount effective to drive the
reaction.
[0017] The fluorination catalyst may be, and is preferably,
pretreated prior to the introduction of the reaction feed stock. By
"pretreat" is meant to chemically or physically alter the catalyst
in order to create active sites on the catalyst at which the
reaction may occur. The catalyst is pretreated by calcining under a
flow of inert gas such as nitrogen at a temperature from about
200.degree. C. to about 450.degree. C. for at least about 1 hour.
The catalyst is then exposed to HF alone or in combination with up
to about 5 to about 99 weight percent of an inert gas at a
temperature from about 200.degree. C. to about 450.degree. C. for
at least about 1 hour. Preferably, the catalyst then undergoes a
third pretreatment step in which it is contacted with chlorine gas.
Preferably, the chlorine is diluted with from about 60 to about 75%
HF and/or from about 20 to about 30% of an inert gas. The chlorine
may be passed over the catalyst at a total volume chlorine to total
volume catalyst of about 1:3,000 v/v, preferably about 10:1,000
v/v, more preferably about 50:500 v/v. Exposure time may be from
about 1 to about 200 hours, preferably 5 to 70 hours, more
preferably 10 to 30 hours. The chlorine exposure may be conducted
at any temperature and pressure convenient to the fluorination
reaction.
[0018] The flow of chlorine is discontinued after pretreatment is
complete and the feed HF and HCC-30 introduced. A small amount of
chlorine, from about 0.1 to about 10 mol percent based on organic
content, preferably from about 2 to about 8 mol percent, may be
added to the reactor, preferably while the fluorination reaction
proceeds, for periods of time from about 1 to about 200 hours,
preferably from about 5 to about 70 hours, and more preferably from
about 10 to about 25 hours, should the catalyst become deactivated
to restore activity.
[0019] The product stream produced in step (B) contains reaction
products which are HFC-32, HCFC-31, and HCl as well as unreacted
feed stock such as HF and HCC-30. The product stream of step (B) is
fed into a recycle column in step (C). The recycle column may be
any standard distillation column known in the art. The high boiling
fraction, or bottom stream, from the recycle column is composed of
unreacted HF and HCC-30 and intermediate reactant HCFC-31.
Preferably, this mixture is recycled to step (A) after recovery.
Further in step (C), a low boiling fraction, or top stream, of
HFC-32, HCl, HF, and reaction byproducts is recovered.
[0020] Alternatively, step (C) may be performed in two parts. In
the first part, the product stream of step (B) is quenched. By
"quenching" is meant that the temperature of the reaction mixture
is reduced to below its dew point. Quenching may be conducted in a
packed column containing any suitable corrosion resistant packing
material and a suitable refluxing liquid such as HF, HCC-30, and/or
HCFC-31 after which the quenched product is fed into the recycle
column.
[0021] In step (D), substantially pure HFC-32 is recovered from the
low boiling fraction of step (C) by any method well known in the
art. Preferably step (D) is performed by a series of substeps
including step (E), treating the gaseous mixture in an HCl
distillation column or aqueous HCl absorption tower under
conditions suitable to remove HCl and trace HF. The crude HFC-32
product of step (E) is then treated in step (F) with a first
caustic scrubber under conditions suitable to form a neutralized
product by neutralizing residual acidity. Typically, the caustic
scrubber contains water, sodium hydroxide, or potassium hydroxide.
Step (F) is followed by step (G) in which the step (F) product is
treated in a second caustic scrubber, preferably comprising sodium
hydroxide together with a sulfite, such as sodium sulfite under
conditions suitable to remove residual chlorine and form a
substantially chlorine-free product. In step (H), the step (G)
product is treated with a sulfuric acid scrubber followed by a
solid desiccant, such as any suitable, commercially available,
molecular sieve that absorbs residual moisture from the gas stream
to form a substantially moisture-free product. This is followed by
step (I) in which the step (H) product is conducted through a
plurality of distillation columns under conditions sufficient to
remove the residual impurities and produce substantially pure
HFC-32, greater than 99.97 weight percent. Any residual HCFC-31
removed in step (I) may be recycled to step (A).
[0022] The following non-limiting examples will serve to clarify
and exemplify the process of this invention.
EXAMPLES 1 AND 2
[0023] In a 1/2 inch Monel pipe reactor, about 110 ml
Cr.sub.2O.sub.3/Al.sub.2O.sub.3 (40/60 wt %) co-extruded catalyst
were packed. The catalyst was dried/calcined at about 400.degree.
C. for about 16 hours using air at 2-3 liters per minute. Then, the
temperature was lowered to 200.degree. C. and air was replaced with
nitrogen at about 0.5-1.5 liters per minute. Anhydrous HF was
pumped into the reactor at about 1-2 ml/min until exotherm passed
through the reactor. Subsequently, temperature was raised at
25.degree. C. every half hour until the temperature was about
350-400.degree. C. and held there for 8 hours. Temperature was then
lowered to the desired reaction temperature. HF and HCC-30 were fed
into the reactor at a molar ratio of 4:1 (HF:HCC-30). The mixture
of HF and HCC-30 passed through two preheaters, the first of which
was at about 100-185.degree. C. and the second at about
200-275.degree. C. The pressure was 50 psig and reactor temperature
was 275.degree. C. for Example 1 and 300.degree. C. for Example 2.
For Example 1, contact time was 16 seconds resulting in 82%
conversion and 89.3% HFC-32 selectivity. The productivity was 10
lbs HFC-32/hr/ft.sup.3. Contact time for Example 2 was 10 seconds
and HCC-30 conversion decreased to 77%. HFC-32 productivity for
Example 2 was 13.6 lbs/hr/ft.sup.3 and HFC-32 selectivity was about
85%. The results of these examples are summarized on Table I.
1 TABLE I Example 1 Example 2 Catalyst
Cr.sub.2O.sub.3/Al.sub.2O.sub.3 Cr.sub.2O.sub.3/Al.sub.2O.s- ub.3
(40/60 wt %) (40/60 wt %) Pressure 50 psig 50 psig HF/HCC-30 4 4
Temperature .degree. C. 275 300 Contact Time (sec.) 16 10
Conversion % CH.sub.2Cl.sub.2 82 77 Selectivity (%): HFC-32 89.3
84.7 HCFC-31 10.6 15.2 HCC-40 0.1 0.1 Productivity
(lbs/hr/ft.sup.3): HFC-32 10.3 13.6
EXAMPLES 3-6
[0024] In the pipe reactor of Examples 1 and 2, about 100-110 ml
Cr.sub.2O.sub.3/Al.sub.2O.sub.3 catalyst of 78/22 weight percent
ratio was packed. The catalyst was dried/calcined and HF-treated
using the same procedure as for Examples 1 & 2. HF and HCC-30
were fed into the reactor at a 4:1 (HF/HCC-30) ratio. A mixture of
HF and HCC-30 was passed through the same preheaters indicated in
Examples 1 & 2. Pressures, contact times, and the results are
shown on Table II.
2 TABLE II Example 3 Example 4 Example 5 Example 6 Catalyst
Cr.sub.2O.sub.3/Al.sub.2O.sub.3 Cr.sub.2O.sub.3/Al.sub.2O.sub.3
Cr.sub.2O.sub.3/Al.sub.2O.sub.3 Cr.sub.2O.sub.3/Al.sub.2O.sub.3
(78/22 wt %) (78/22 wt %) (78/22 wt %) (78/22 wt %) Pressure (psig)
50 200 225 225 HF/CH.sub.2Cl.sub.2 4 4 4 4 mole ratio Temperature
275 275 275 275 (.degree. C.) Contact Time 11 36 40 26 (sec)
Conversion (% CH.sub.2Cl.sub.2) 71 70 70 61 Selectivity: HFC-32 82
81 81 77 HCFC-31 18 19 19 23 HCC-40 0.05 0.05 0.05 0.05
Productivity (lbs/hr/ft.sup.3): HFC-32 12 12 12 15
EXAMPLE 7
[0025] A 4 inch diameter Monel 400 reactor was charged with 4
liters of chromium oxide catalyst. The catalyst was dried under 20
slpm nitrogen flow at a temperature of 350.degree. C. for 8 hours.
After reducing the catalyst bed temperature to 250.degree. C.,
anhydrous HF was added to the flowing nitrogen at a flow rate of
0.2 lbs/hr. The HF flow rate was gradually increased to 1.0 lb/hr
and the temperature increased to 350.degree. C. and held for 4
hours. The catalyst bed temperature was then decreased to
250.degree. C. and chlorine introduced to the HF/N.sub.2 mixture at
a rate of 500 sccm for a period of 24 hours.
[0026] After this pretreatment procedure, the chlorine and nitrogen
flows were discontinued and HCC-30 was mixed with HF and passed
though a preheater at 185.degree. C. The vaporized HCC-30 and HF
mixture was fed to the reactor at a pressure of 45 psig the
effluent from the reactor was quenched using a heat exchanger and
fed into a distillation column maintained at 50 psig. The low
boiling distillation components, HCFC-31, HF, and HCC-30 were
recycled back to mix with fresh HF and HCC-30 feed stream and were
fed to the preheater, and the reactor at a flow rate of 4.6 lbs/hr.
The recycle stream contained a molar ratio of HF:HCFC-31 of 360:1.
The recycle material was mixed with additional HF and HCC-30 at
flow rates of 0.5 and 1.0 lbs/hr, respectively, before being passed
over the catalyst. The resulting contact time was 12 seconds. The
low boiling components separated in the distillation column, HCl
and HFC-32, were passed through a caustic scrubber containing 10%
KOH where HCl was removed. The purified HFC-32 was dried and
collected. The resulting HCC-30 conversion was 90% with 90%
selectivity to HFC-32 and 9% selectivity to HCFC-31.
* * * * *