U.S. patent application number 10/211808 was filed with the patent office on 2003-07-31 for continuous hydrolysis process for the preparation of 2-hydroxy-4-methylthiobutanoic acid.
This patent application is currently assigned to Novus International, Inc.. Invention is credited to Blackburn, Thomas F., Hsu, Yung C., Kranz, Allen H., Pellegrin, Paul F., willock, James M..
Application Number | 20030144547 10/211808 |
Document ID | / |
Family ID | 23897286 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030144547 |
Kind Code |
A1 |
Hsu, Yung C. ; et
al. |
July 31, 2003 |
Continuous hydrolysis process for the preparation of
2-hydroxy-4-methylthiobutanoic acid
Abstract
A continuous process for the preparation of
2-hydroxy-4-methylthiobutanoic acid which includes introducing
sulfuric acid into a first reactor including a continuous stirred
tank reactor and introducing 2-hydroxy-4-methylthiobutanenitrile
into the first reactor. 2-hydroxy-4-methylthiobutanenitrile is
continually hydrolyzed within the first reactor to produce an
intermediate aqueous hydrolysis solution containing
2-hydroxy-4-methylthiobutanamide. The intermediate aqueous
hydrolysis solution is continuously introduced into a plug flow
reactor. 2-hydroxy-4-methylthiobutanamide is continually hydrolyzed
within the plug flow reactor to produce an aqueous hydrolyzate
product solution containing 2-hydroxy-4-methylthiobutanoic acid.
2-hydroxy-4-methylthiobut- anoic acid is recovered from the aqueous
hydrolyzate product solution.
Inventors: |
Hsu, Yung C.; (Chesterfield,
MO) ; Blackburn, Thomas F.; (Chesterfield, MO)
; Pellegrin, Paul F.; (St. Louis, MO) ; Kranz,
Allen H.; (St. Charles, MO) ; willock, James M.;
(Ballwin, MO) |
Correspondence
Address: |
SENNIGER POWERS LEAVITT AND ROEDEL
ONE METROPOLITAN SQUARE
16TH FLOOR
ST LOUIS
MO
63102
US
|
Assignee: |
Novus International, Inc.
|
Family ID: |
23897286 |
Appl. No.: |
10/211808 |
Filed: |
August 2, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10211808 |
Aug 2, 2002 |
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09748067 |
Dec 22, 2000 |
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6458997 |
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09748067 |
Dec 22, 2000 |
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09165806 |
Oct 2, 1998 |
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6166250 |
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09165806 |
Oct 2, 1998 |
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08876011 |
Jun 13, 1997 |
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5998664 |
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08876011 |
Jun 13, 1997 |
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08477768 |
Jun 7, 1995 |
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Current U.S.
Class: |
562/512 |
Current CPC
Class: |
B01J 19/1881 20130101;
B01J 2219/00063 20130101; B01J 19/2435 20130101; C07C 319/18
20130101; B01J 2219/0011 20130101; B01J 2219/00166 20130101; B01J
2219/185 20130101; B01J 19/245 20130101; B01J 2219/00033 20130101;
B01J 2219/00103 20130101; A23K 20/105 20160501; B01J 2219/00099
20130101; B01J 19/18 20130101; B01J 19/24 20130101; B01J 14/00
20130101; C07C 319/20 20130101; B01J 19/1862 20130101; B01J
2219/00013 20130101; B01J 19/243 20130101; B01J 2219/00094
20130101; B01J 19/1837 20130101; C07C 319/20 20130101; C07C 323/52
20130101; C07C 319/20 20130101; C07C 323/60 20130101; C07C 319/18
20130101; C07C 323/52 20130101; C07C 319/18 20130101; C07C 323/60
20130101 |
Class at
Publication: |
562/512 |
International
Class: |
C07C 323/52 |
Claims
We claim:
1. A process for the preparation of 2-hydroxy-4-methylthiobutanoic
acid comprising: introducing sulfuric acid into a first reactor
comprising a continuous stirred tank reactor; introducing
2-hydroxy-4-methylthiobutane- nitrile into said first reactor;
continuously hydrolyzing 2-hydroxy-4-methyl-thiobutyronitrile
within said first reactor to produce an intermediate aqueous
hydrolysis solution containing 2-hydroxy-4-methylthiobutanamide;
continuously introducing water and the intermediate aqueous
hydrolysis solution into a plug flow reactor; and continuously
hydrolyzing 2-hydroxy-4-methylthiobutanamide within said plug flow
reactor to produce an aqueous hydrolyzate product solution
containing 2-hydroxy-4-methylthiobutanoic acid.
2. The process as set forth in claim 1 wherein sulfuric acid is
introduced into said first reactor in an acid stream having a
strength of between about 50% by weight and about 70% by weight
sulfuric acid.
3. The process as set forth in claim 1 wherein sulfuric acid is
introduced into said first reactor in an acid stream having a
strength of between about 70% by weight and about 99% by weight
sulfuric acid, and the acid stream is continuously introduced to
the first reactor concurrently with a water stream to form sulfuric
acid having a strength of between about 50% by weight and about 70%
by weight on an organic-free basis within the first reactor.
4. The process as set forth in claim 1 wherein at least about 90%
of 2-hydroxy-4-methylthiobutanenitrile is converted to
2-hydroxy-4-methylthiobutanamide within the first reactor.
5. The process as set forth in claim 1 wherein the molar ratio of
sulfuric acid to 2-hydroxy-4-methylthiobutanenitrile introduced
into the first reactor is between about 0.7 and about 1.5.
6. The process as set forth in claim 1 wherein the molar ratio of
sulfuric acid to 2-hydroxy-4-methylthiobutanenitrile introduced
into the first reactor is between about 0.9 and about 1.2.
7. The process as set forth in claim 5 wherein the molar ratio of
sulfuric acid to 2-hydroxy-4-methylthiobutanenitrile introduced
into the first reactor is between about 1.0 and about 2.0 during
the period between start up of the process until steady state
conditions are established in the plug flow reactor, and thereafter
said molar ratio of sulfuric acid to
2-hydrxy-4-methylthiobutanenitrile is between about 0.7 and about
1.5.
8. The process as set forth in claim 6 wherein the molar ratio of
sulfuric acid to 2-hydroxy-4-methylthiobutanenitrile introduced
into the first reactor is between about 1.0 and about 1.5 during
the period between start up of the process until steady state
conditions are established in the plug flow reactor, and thereafter
said molar ratio of sulfuric acid to
2-hydroxy-4-methylthiobutanenitrile is between about 0.9 and about
1.2.
9. The process as set forth in claim 1 wherein the ratio of the
rate of sulfuric acid flow into said plug flow reactor to the rates
of 2-hydroxy-4-methylthiobutanamide and
2-hydroxy-4-methylthiobutanenitrile flow into said plug flow
reactor is controlled to provide an excess of at least 5% by weight
sulfuric acid than is stoichiometrically equivalent to 2-hydroxy
-4-methylthiobutanamide and 2-hydroxy-4-methylthiobutanenitrile
introduced into the plug flow reactor.
10. The process as set forth in claim 9 wherein sulfuric acid and
2-hydroxy-4-methylthiobutanenitrile are introduced into said first
reactor at relative rates effective to provide said excess in said
plug flow reactor.
11. The process as set forth in claim 1 wherein the intermediate
aqueous hydrolysis solution comprises up to about 11 wt. %
2-hydroxy-4-methylthiobutanoic acid, up to about 8 wt. % ammonium
bisulfate, at least about 10 wt. % water, at least about 35 wt. %
amide and up to about 2 wt. % nitrile.
12. The process as set forth in claim 1 wherein the aqueous
hydrolyzate product solution produced under steady state conditions
at the exit of the plug flow reactor comprises at least about 36
wt. % 2-hydroxy-4-methylthiobutanoic acid, at least about 30 wt. %
ammonium bisulfate, at least about 25 wt. % water, up to about 0.05
wt. % amide and up to about 0.05 wt. % nitrile.
13. The process as set forth in claim 12 wherein the aqueous
hydrolyzate product solution produced upon start up of the process
comprises up to about 0.05 wt. % amide and up to about 0.05 wt. %
nitrile.
14. The process as set forth in claim 1 wherein the water and the
intermediate aqueous hydrolysis solution are continuously
introduced into a mixer to form a diluted intermediate hydrolysis
solution, and the diluted intermediate hydrolysis solution is
continuously introduced into the plug flow reactor such that the
hydrolysis of 2-hydroxy-4-methyl-thio- butyramide is completed as
the diluted intermediate hydrolysis solution flows through the plug
flow reactor.
15. The process as set forth in claim 14 wherein the molar ratio of
sulfuric acid to 2-hydroxy-4-methylthiobutanenitrile added to the
first reactor is between about 0.7 and about 1.5, and the flow of
the diluted intermediate hydrolysis solution through said plug flow
reactor is turbulent.
16. The process as set forth in claim 14 wherein the water stream
is heated before being introduced into the mixer to prevent liquid
phase separation and precipitation of ammonium bisulfate in said
plug flow reactor.
17. The process as set forth in claim 14 wherein said plug flow
reactor comprises a packed column reactor and the diluted
intermediate aqueous hydrolysis solution flows through the packed
column reactor at or above the threshold velocity of the packed
column reactor.
18. The process as set forth in claim 14 wherein said plug flow
reactor comprises a pipeline reactor and the diluted intermediate
aqueous hydrolysis solution moves through the pipeline reactor in
turbulent flow.
19. The process as set forth in claim 18 wherein said plug flow
reactor is operated at a Reynolds number greater than about
3,000.
20. The process as set forth in claim 18 wherein said plug flow
reactor is operated at a Reynolds number greater than about
5,000.
21. The process as set forth in claim 1 wherein the plug flow
reactor is operated at a Peclet number of at least 50, a peak
temperature of about 90 to about 120.degree. C. and a residence
time between about 30 and about 90 minutes.
22. The process as set forth in claim 1 wherein the plug flow
reactor operates substantially adiabatically.
23. The process as set forth in claim 1 wherein the plug flow
reactor operates substantially isothermally.
24. The process as set forth in claim 1 wherein the plug flow
reactor operates adiabatically and autothermally.
25. The process as set forth in claim 1 further including
recovering 2-hydroxy-4-methylthiobutanoic acid from the aqueous
hydrolyzate product solution.
26. The process as set forth in claim 1 wherein
2-hydroxy-4-methylthiobuta- noic acid is recovered by extracting
2-hydroxy-4-methylthiobutanoic acid from the aqueous hydrolyzate
product solution.
27. The process as set forth in claim 1 wherein 2-hydroxy
-4-methylthiobutanoic acid is recovered by neutralizing the aqueous
hydrolyzate product solution to form an organic phase containing
2-hydroxy-4-methylthiobutanoic acid and an aqueous phase, and
separating the organic phase and the aqueous phase to recover
2-hydroxy-4-methylthiobutanoic acid.
28. The process as set forth in claim 1 wherein vapor emissions
from the process are not greater than about 0.5 scf per 1000 lbs.
product 2-hydroxy-4-methylthiobutanoic acid.
29. The process as set forth in claim 28 wherein vapor emissions
from the process,are not greater than about 0.3 scf per 1000 lbs.
2-hydroxy-4-methylthiobutanoic acid.
30. A process for the preparation of 2-hydroxy-4-methlthiobutanoic
acid comprising: introducing sulfuric acid into a first reactor
comprising a continuous stirred tank reactor; introducing
2-hydroxy-4-methylthiobutane- nitrile into said first reactor;
continuously hydrolyzing 2-hydroxy-4-methyl-thiobutanenitrile
within said first reactor to produce an intermediate aqueous
hydrolysis solution containing 2-hydroxy-4-methylthiobutanamide;
continuously introducing the intermediate aqueous hydrolysis
solution exiting said first reactor and a water stream into a
second continuous stirred tank reactor such that a substantial
portion of 2-hydroxy-4-methylthiobutanamide contained in said
intermediate solution is hydrolyzed in the second continuous
stirred tank reactor to form a finishing reaction solution;
continuously introducing the finishing reaction solution into a
plug flow reactor; and continuously hydrolyzing
2-hydroxy-4-methylthiobutanamide within said plug flow reactor to
produce an aqueous hydrolyzate product solution containing
2-hydroxy-4-methylthiobutanoic acid.
31. The process as set forth in claim 30 wherein sulfuric acid is
introduced into said first reactor in an acid stream having a
strength of between about 50% by weight and about 70% by weight
sulfuric acid.
32. The process as set forth in claim 30 wherein sulfuric acid is
introduced into said first reactor in an acid stream having a
strength of between about 70% by weight and about 99% by weight
sulfuric acid, and the acid stream is continuously introduced to
the first reactor concurrently with a water stream to form sulfuric
acid having a strength of between about 50% by weight and about 70%
by weight on an organic-free basis within the first reactor.
33. The process as set forth in claim 30 wherein at least about 90%
of 2-hydroxy-4-methylthiobutanenitrile is converted to
2-hydroxy-4-methylthiobutanamide within the first reactor.
34. The process as set forth in claim 30 wherein the molar ratio of
sulfuric acid to 2-hydroxy-4-methylthiobutanenitrile introduced
into the first reactor is between about 0.7 and about 1.5.
35. The process as set forth in claim 30 wherein the molar ratio of
sulfuric acid to 2-hydroxy-4-methylthiobutanenitrile introduced
into the first reactor is between about 0.9 and about 1.2.
36. The process as set forth in claim 34 wherein the molar ratio of
sulfuric acid to 2-hydroxy-4-methylthiobutanenitrile introduced
into the first reactor is between about 1.0 and about 2.0 during
the period between start up of the process until steady state
conditions are established in the plug flow reactor, and thereafter
said molar ratio of sulfuric acid to
2-hydroxy-4-methylthiobutanenitrile is between about 0.7 and about
1.5.
37. The process as set forth in claim 35 wherein the molar ratio of
sulfuric acid to 2-hydroxy-4-methylthiobutanenitrile introduced
into the first reactor is between about 1.0 and about 1.5 during
the period between start up of the process until steady state
conditions are established in the plug flow reactor, and thereafter
said molar ratio of sulfuric acid to
2-hydroxy-4-methylthiobutanenitrile is between about 0.9 and about
1.2.
38. The process as set forth in claim 30 wherein the ratio of the
rate of sulfuric acid flow into said plug flow reactor to the rates
of 2-hydroxy-4-methylthiobutanamide and
2-hydroxy-4-methylthiobutanenitrile flow into said plug flow
reactor is controlled to provide an excess of at least 5% by weight
sulfuric acid than is stoichiometrically equivalent to
2-hydroxy-4-methylthiobutanamide and
2-hydroxy-4-methylthiobutanenitrile introduced into the plug flow
reactor.
39. The process as set forth in claim 38 wherein sulfuric acid and
2-hydroxy-4-methylthiobutanenitrile are introduced into said first
reactor at relative rates effective to provide said excess in said
plug flow reactor.
40. The process as set forth in claim 30 wherein the intermediate
aqueous hydrolysis solution comprises up to about 11 wt. %
2-hydroxy-4-methylthiobutanoic acid, up to about 8 wt. % ammonium
bisulfate, at least about 10 wt. % water, at least about 35 wt. %
amide and up to about 2 wt. % nitrile.
41. The process as set forth in claim 30 wherein the finishing
reaction solution comprises at least about 32 wt. %
2-hydroxy-4-methylthiobutanoic acid, at least about 25 wt. %
ammonium bisulfate, at least about 25 wt. % water, up to about 5
wt. % amide and up to about 1 wt. % nitrile.
42. The process as set forth in claim 30 wherein the aqueous
hydrolyzate product solution produced under steady state conditions
at the exit of the plug flow reactor comprises at least about 36
wt. % 2-hydroxy-4-methylthiobutanoic acid, at least about 30 wt. %
ammonium bisulfate, at least about 25 wt. % water, up to about 0.05
wt. % amide and up to about 0.05 wt. % nitrile.
43. The process as set forth in claim 42 wherein the aqueous
hydrolyzate product solution produced upon start up of the process
comprises up to about 0.05 wt. % amide and up to about 0.05 wt. %
nitrile.
44. The process as set forth in claim 30 wherein at least about 80%
of 2-hydroxy-4-methylthiobutanamide formed in said first reactor is
converted to 2-hydroxy-4-methylthio-butyric acid within the second
continuous stirred tank reactor.
45. The process as set forth in claim 30 wherein the molar ratio of
sulfuric acid to 2-hydroxy-4-methylthiobutanenitrile added to the
first reactor ranges from about 0.7 to about 1.5, and the second
continuous stirred tank reactor is operated at a temperature
ranging from about 70.degree. C. to about 120.degree. C.
46. The process as set forth in claim 45 wherein said plug flow
reactor comprises a packed column reactor and the finishing
reaction solution flows through the packed column reactor at or
above the threshold velocity of the packed column reactor.
47. The process as set forth in claim 45 wherein said plug flow
reactor comprises a pipeline reactor and the finishing reaction
solution moves through the pipeline reactor in turbulent flow.
48. The process as set forth in claim 47 wherein said plug flow
reactor is operated at a Reynolds number greater than about
3,000.
49. The process as set forth in claim 47 wherein said plug flow
reactor is operated at a Reynolds number greater than about
5,000.
50. The process as set forth in claim 30 wherein the plug flow
reactor is operated at a Peclet number of at least 50, a peak
temperature of about 90 to about 120.degree. C. and a residence
time between about 30 and about 90 minutes.
51. The process as set forth in claim 30 wherein the plug flow
reactor operates substantially adiabatically.
52. The process as set forth in claim 30 wherein the plug flow
reactor operates isothermally.
53. The process as set forth in claim 30 wherein the plug flow
reactor operates adiabatically and autothermally.
54. The process as set forth in claim 30 wherein the molar ratio of
sulfuric acid to 2-hydroxy-4-methylthiobutanenitrile added to the
first reactor is between about 0.7 and about 1.5, and the flow of
the finishing reaction solution through said plug flow reactor is
turbulent.
55. The process as set forth in claim 30 further including
recovering 2-hydroxy-4-methylthiobutanoic acid from the aqueous
hydrolyzate product solution.
56. The process as set forth in claim 30 wherein
2-hydroxy-4-methylthiobut- anoic acid is recovered by extracting
2-hydroxy-4-methylthiobutanoic acid from the aqueous hydrolyzate
product solution.
57. The process as set forth in claim 30 wherein
2-hydroxy-4-methylthiobut- anoic acid is recovered by neutralizing
the aqueous hydrolyzate product solution to form an organic phase
containing 2-hydroxy-4-methylthiobutano- ic acid and an aqueous
phase, and separating the organic phase and the aqueous phase to
recover 2-hydroxy-4-methylthiobutanoic acid.
58. The process as set forth in claim 30 wherein vapor emissions
from the process are not greater than about 0.5 scf per 1000 lbs.
product 2-hydroxy-4-methylthiobutanoic acid.
59. A process for the preparation of 2-hydroxy-4-methylthiobutanoic
acid comprising: concurrently introducing
2-hydroxy-4-methylthiobutyanenitrile- , concentrated sulfuric acid
stream having a strength of between about 70% by weight and about
99% by weight, and water into a vessel in which
2-hydroxy-4-methylthiobutanenitrile is hydrolyzed; hydrolyzing
2-hydroxy-4-methylthiobutanenitrile within said vessel to produce
an intermediate aqueous hydrolysis solution containing
2-hydroxy-4-methylthiobutanamide; and hydrolyzing
2-hydroxy-4-methylthiob- utanamide to produce an aqueous
hydrolyzate product solution containing
2-hydroxy-4-methylthiobutanoic acid.
60. The process as set forth in claim 59 wherein the vessel is a
first reactor comprising a continuous stirred tank reactor,
2-hydroxy-4-methylthiobutanenitrile is continuously hydrolyzed
within the first reactor, the intermediate aqueous hydrolysis
solution is introduced into a plug flow reactor, and
2-hydroxy-4-methylthiobutanamide is continuously hydrolyzed within
the plug flow reactor.
61. The process as set forth in claim 59 wherein the vessel is a
first reactor comprising a continuous stirred tank reactor,
2-hydroxy-4-methylthiobutanenitrile is continuously hydrolyzed
within the first reactor, the intermediate aqueous hydrolysis
solution is introduced into a second continuous stirred tank
reactor, 2-hydroxy-4-methylthiobuta- namide is continuously
hydrolyzed within the second continuous stirred tank reactor to
form a finishing reaction solution, the finishing reaction solution
is introduced into a plug flow reactor, the hydrolysis of
2-hydroxy-4-methylthiobutanamide is completed as the finishing
reaction solution flows through the plug flow reactor.
62. The process as set forth in claim 59 further including
recovering 2-hydroxy-4-methylthiobutanoic acid from the aqueous
hydrolyzate product solution.
63. An apparatus for use in a process for the preparation of
2-hydroxy-4-methylthiobutanoic acid, comprising a first continuous
stirred tank reactor for the continuous hydrolysis of
2-hydroxy-4-methylthiobutanenitrile in the presence of sulfuric
acid to produce an intermediate aqueous hydrolysis solution
containing 2-hydroxy-4-methylthiobutanamide, and a plug flow
reactor for the continuous hydrolysis of
2-hydroxy-4-methylthiobutanamide with sulfuric acid to produce an
aqueous hydrolyzate product solution containing
2-hydroxy-4-methylthiobutanoic acid.
64. The apparatus as set forth in claim 63 further including a
second continuous stirred tank reactor for receiving water and the
intermediate aqueous hydrolysis solution exiting the first
continuous stirred tank reactor, such that a substantial portion of
2-hydroxy-4-methyl-thiobutyra- mide contained in the intermediate
hydrolysis solution is hydrolyzed in the second continuous stirred
tank reactor to form a finishing reaction solution, and the
hydrolysis of 2-hydroxy-4-methylthiobutanamide is completed as the
finishing reaction solution flows through the plug flow
reactor.
65. The apparatus as set forth in claim 63 further including a
mixer for mixing water and the intermediate aqueous hydrolysis
solution exiting the first continuous stirred tank reactor to form
a diluted intermediate hydrolysis solution, and discharging the
diluted intermediate hydrolysis solution mixture to the plug flow
reactor such that the hydrolysis of
2-hydroxy-4-methylthiobutanamide is completed as the diluted
intermediate hydrolysis solution flows through the plug flow
reactor.
66. The apparatus as set forth in claim 63 wherein the plug flow
reactor is insulated for adiabatic operation.
67. The apparatus as set forth in claim 63 wherein said first
reactor comprises an inlet for 2-hydroxy-4-methylthiobutanenitrile,
an inlet for concentrated sulfuric acid, an inlet for water, and
means within the reactor for mixing
2-hydroxy-4-methylthiobutanenitrile, concentrated sulfuric acid and
water in proportions suited for hydrolysis of
2-hydroxy-4-methylthiobutanenitrile to
2-hydroxy-4-methylthiobutanamide.
68. The apparatus as set forth in claim 67 further including means
for removing heat generated by dilution of sulfuric acid and
reaction of 2-hydroxy-4-methylthiobutanenitrile. and water in order
to maintain a reaction temperature for hydrolysis of
2-hydroxy-4-methylthiobutanenitril- e.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of U.S. Ser. No. 09/165,806, filed Oct.
2, 1998, which is a divisional of U.S. Ser. No. 08/876,011, filed
Jun. 13, 1997, which is a filewrapper continuation of U.S. Ser. No.
08/477,768, filed Jun. 7, 1995 (now abandoned).
BACKGROUND OF THE INVENTION
[0002] This invention relates to the preparation of
2-hydroxy-4-methylthiobutanoic acid and more particularly to an
improved process for preparing an aqueous solution comprising
2-hydroxy-4-methylthiobutanoic acid.
[0003] 2-hydroxy-4-methylthiobutanoic acid, commonly referred to as
the hydroxy analog of methionine and also known as
2-hydroxy-4-methylthiobuty- ric acid or HMBA, is an analog of the
essential amino acid methionine. Methionine analogs such as HMBA
are effective in supplying methionine for nutritional uses,
particularly as a poultry feed supplement. To efficiently produce
feed supplements containing HMBA, the hydrolysis must be
sufficiently complete.
[0004] HMBA has been manufactured by various processes involving
hydrolysis of 2-hydroxy-4-methylthiobutanenitrile (also known as
HMBN or 2-hydroxy-4-methylthiobutyronitrile and hereinafter "HMBN"
or "nitrile"). HMBA has been produced as a racemic D,L-mixture by
hydrolyzing HMBN with a mineral acid, precipitating the acid
residue by addition of an alkaline earth hydroxide or carbonate,
and recovering a salt of HMBA from the aqueous phase by evaporative
crystallization, as described, for example, in Blake et al U.S.
Pat. No. 2,745,745.
[0005] British Patent No. 915,193 describes a process for the
preparation of the calcium salt of HMBA in which HMBN is hydrolyzed
to HMBA in a continuous back-mixed reactor using a dilute sulfuric
acid solution, and HMBA is separated from the reaction liquor by
extraction with an ether. Because of the use of a continuous
back-mixed reaction system, the process of the British patent may
not achieve complete conversion of HMBN or amide intermediate to
HMBA. The presence of unreacted material is undesirable where a
liquid HMBA product is to be made.
[0006] Recently, HMBA has been commercially produced by hydrolyzing
HMBN with sulfuric acid to form a high quality hydrolyzate
containing HMBA, extracting HMBA from the hydrolyzate, and
recovering the HMBA from the extract as described by Ruest et al.
U.S. Pat. No. 4,524,077. In the process, HMBN is mixed with
sulfuric acid having a strength of between about 50% and about 70%
by weight on an organic-free basis at a temperature of between
about 25.degree. C. and about 65.degree. C. To control the rate of
reaction, the HMBN is preferably added to the acid over a period of
about 30 to about 60 minutes. Under the preferred conditions,
substantial conversion of the nitrile to
2-hydroxy-4-methylthiobutanamide (also known as
2-hydroxy-4-methylthiobut- yramide and hereinafter "amide") takes
place in a period of between about one-half hour and about one and
one-half hours. Thereafter, the amide is converted to HMBA by
further hydrolysis at a temperature within the range of between
about 70.degree. C. and 120.degree. C. Final hydrolysis of the
amide to the acid is carried out in sulfuric acid having an initial
strength of between about 30% and about 50% by weight on a
organic-free basis. To provide the preferred acid strength, the
acid phase is diluted by adding water before heating the reaction
mixture. Under conditions of relatively dilute acid strength and
increased temperature, the amide is converted to the acid within a
period of approximately one and one-half to three hours. In
carrying out the hydrolysis, approximately one mole of sulfuric
acid per mole of the HMBN feed is used, with an acid excess of 0 to
10%, preferably 0 to 5%, providing satisfactory results. Ruest et
al. describe a batch process and state that a batch process is
preferred to ensure that the hydrolysis reaction is carried
substantially to completion. If a continuous reaction system is
utilized, Ruest et al. describe that it should be designed and
operated to assure essentially complete conversion. For example,
continuous operation could be implemented in a plug flow tubular
reactor or cascaded stirred tank system. A single back-mixed
reactor is described by Ruest et al. as providing adequate
conversion only at residence times that would generally be
considered unacceptable for commercial production.
[0007] Hernandez et al. U.S. Pat. No. 4,912,257 describes a process
in which HMBA is produced by sulfuric acid hydrolysis of HMBN in a
single step. HMBN is fed to an acidification vessel where it is
mixed with 98% sulfuric acid at an acid/nitrile molar ratio between
0.5 and 2 to form a reaction mixture containing 20-50% by weight
sulfuric acid. The mixture is agitated and cooled to 50.degree. C.
in a continuous addition loop for 30-60 minutes as the reaction
mixture is produced batchwise. The reaction mixture is then fed to
a hydrolysis reactor and heated to a temperature of between
60.degree. C. and 140.degree. C. for five minutes to six hours
while applying a slight vacuum to the reactor. The process
described by Hernandez et al. is said to produce HMBA by hydrolysis
of the acidified HMBN solution in a single step unlike the two step
hydrolysis processes known in the art.
[0008] In order to provide a high quality hydrolyzate solution
containing maximum HMBA and minimal nitrile and amide components,
high conversion of HMBN and 2-hydroxy-4-methylthio-butyramide to
HMBA must be obtained. Batch production of HMBA generally provides
high conversion. However, conventional batch processes for
producing HMBA have several drawbacks. The productivity of a batch
process is limited by batch turnaround time. Additionally, the
quality of HMBA hydrolyzate can deviate between batches because
reaction conditions can vary as each batch is produced. Filling and
emptying of the batch reactor and non-steady state conditions cause
vapor emissions which must be treated before release. The equipment
required for the prior art processes is costly. Sulfuric acid and
water are mixed in an acid dilution tank to form diluted sulfuric
acid feed. A heat exchanger is required to remove the heat of
dilution that is generated within the tank. The tank, heat
exchanger, pump and recirculation loop must be of corrosion
resistant construction.
SUMMARY OF THE INVENTION
[0009] Among the several objects of the present invention are the
provision of an improved process for the preparation of HMBA; the
provision of such a process which can be operated in a continuous
mode; the provision of such a process which can be operated with
high productivity; the provision of such a process which can
significantly reduce capital and maintenance costs as compared to
conventional processes; the provision of such a process which
affords improved control of reaction conditions as compared to
conventional batch hydrolysis systems; the provision of such a
process which reduces the vapor emissions as compared to
conventional batch systems; the provision of such a process which
eliminates the need for separate sulfuric acid dilution, in
particular, the provision of such a process which can be operated
using a concentrated sulfuric acid feed stream without prior
dilution; and the provision of such a process which can produce
HMBA of consistent quality for use in the preparation of animal
feed supplements.
[0010] These and other objects are obtained through a process for
the preparation of HMBA including introducing sulfuric acid into a
first reactor comprising a continuous stirred tank reactor, and
introducing 2-hydroxy-4-methylthiobutanenitrile into the first
reactor. 2-hydroxy-4-methylthiobutanenitrile is continually
hydrolyzed within the first reactor to produce an intermediate
aqueous hydrolysis solution containing
2-hydroxy-4-methylthiobutanamide. The intermediate aqueous
hydrolysis solution is continuously introduced into a plug flow
reactor. 2-hydroxy-4-methylthiobutanamide is continuously
hydrolyzed within the plug flow reactor to produce an aqueous
hydrolyzate product solution containing
2-hydroxy-4-methylthiobutanoic acid. 2-hydroxy-4-methylthiobut-
anoic acid is recovered from the aqueous hydrolyzate product
solution.
[0011] In another embodiment of the invention,
2-hydroxy-4-methylthiobutan- oic acid is produced by a process in
which 2-hydroxy -4-methylthiobutanenitrile, concentrated sulfuric
acid having a strength of between about 70% by weight and about 99%
by weight, and water are concurrently introduced into a vessel in
which 2-hydroxy-4-methylthiobuta- nenitrile is hydrolyzed.
2-hydroxy -4-methylthiobutanenitrile is hydrolyzed within the
vessel to produce an intermediate aqueous hydrolysis solution
containing 2-hydroxy-4-methylthiobutanamide.
2-hydroxy-4-methylthiobutanamide is hydrolyzed to produce an
aqueous hydrolyzate product solution containing
2-hydroxy-4-methylthiobutanoic acid. 2-hydroxy-4-methylthiobutanoic
acid is recovered from the aqueous hydrolyzate product
solution.
[0012] Yet another embodiment of the present invention is directed
to an apparatus for use in a process for the preparation of HMBA.
The apparatus includes a first continuous stirred tank reactor for
the continuous hydrolysis of 2-hydroxy-4-methylthiobutanenitrile in
the presence of sulfuric acid to produce an intermediate aqueous
hydrolysis solution containing 2-hydroxy-4-methylthiobutanamide.
The apparatus also includes a plug flow reactor for the continuous
hydrolysis of 2-hydroxy-4-methylthiobutanamide with sulfuric acid
to produce an aqueous hydrolyzate product solution containing
2-hydroxy-4-methylthiobutanoic acid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic flowsheet of the process of the
invention, illustrating continuous manufacture of HMBA from HMBN,
water and sulfuric acid;
[0014] FIG. 2 is a schematic flowsheet of a process of the
invention in which 2-hydroxy-4-methylthiobutanamide exiting a first
reactor is converted to HMBA in a continuous stirred tank reactor
and a plug flow reactor operated in series;
[0015] FIG. 3 is a schematic illustration of a continuous stirred
tank reactor adapted for conversion of HMBN to
2-hydroxy-4-methylthiobutanamid- e while a concentrated sulfuric
acid stream is introduced into the reactor;
[0016] FIG. 4 is a schematic flowsheet of a bench-scale continuous
hydrolysis process in which 2-hydroxy-4-methylthiobutanamide
exiting a first recirculating reactor is converted to HMBA in a
second recirculating reactor and a plug flow reactor operated in
series;
[0017] FIG. 5 is a plot showing amide concentration, nitrile
concentration, and Gardner color for the hydrolyzate product as a
function of acid/nitrile molar ratio fed to the first reactor and
temperature within the plug flow reactor based on bench scale
experiments; and
[0018] FIG. 6 is a schematic flowsheet of a bench-scale continuous
hydrolysis process in which 2-hydroxy-4-methylthiobutanamide
exiting a first reactor is introduced into a plug flow reactor and
hydrolyzed to produce HMBA.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0019] In accordance with the present invention, a process for the
preparation of HMBA is provided in which HMBN is continuously
hydrolyzed in the presence of sulfuric acid to form
2-hydroxy-4-methylthiobutanamide (hereinafter referred to as
"nitrile hydrolysis"), and the amide is continuously hydrolyzed to
form HMBA (hereinafter "amide hydrolysis"). The process is
implemented utilizing an apparatus which comprises a first
continuous stirred tank reactor (hereinafter "CSTR") for nitrile
hydrolysis and a plug flow reactor (hereinafter "PFR") for
subsequent amide hydrolysis. The nitrile hydrolysis generates
substantial exothermic heat and is, therefore, most efficiently
conducted in a CSTR back mixed for heat transfer and temperature
control. The amide hydrolysis is less exothermic yet must be
brought to completion in order to achieve desired product quality
and yield. A PFR has been found to be well suited for the amide
hydrolysis because it can be configured to operate without
substantial back-mixing, yet provide adequate residence time for
the reaction without requiring excessive pressure drop. For
example, it has been found that an industrial scale pipeline
reactor can be operated at a Reynolds number in excess of about
5000 without excessive pressure drop through the reactor, while
producing a hydrolyzate containing less than about 0.1% amide and
less than about 0.1% nitrile on an HMBA basis.
[0020] More particularly, the invention is directed to an apparatus
including a first reactor comprising a first CSTR for receiving
sulfuric acid and HMBN feed streams. It has been discovered that
concentrated sulfuric acid, water, and HMBN can be concurrently
introduced into the first CSTR in order to produce within the CSTR
a more dilute effective sulfuric acid strength suitable for
hydrolysis of HMBN. Despite the disparate density and viscosity of
sulfuric acid and HBMN and the high heat of dilution released when
sulfuric acid is diluted with water, HMBN, water and concentrated
sulfuric acid can be simultaneously fed into the first CSTR without
hindering the hydrolysis of HMBN. The dilution of sulfuric acid
within the reactor eliminates the need for separate acid dilution
as used in a conventional batch process, reducing cost and
maintenance of the hydrolysis system. As the HMBN reacts with water
within the CSTR, an intermediate aqueous hydrolysis solution
containing 2-hydroxy-4-methylthiobutanamide is formed. The
intermediate aqueous hydrolysis solution is then mixed with a
heated water stream to provide water for amide hydrolysis and
prevent liquid phase separation within the PFR and precipitation of
ammonium bisulfate. The diluted intermediate hydrolysis solution
may be continuously fed to a second CSTR. Alternatively, the
intermediate aqueous hydrolysis solution and the heated water
stream can be introduced directly to the second CSTR. A substantial
portion of the amide is converted to HMBA in the second CSTR by
further hydrolysis to form a finishing reaction solution. The
finishing reaction solution is further hydrolyzed in a PFR located
downstream of the second CSTR to form an aqueous hydrolyzate
product solution containing HMBA. Alternatively, the second CSTR
can be bypassed such that the diluted intermediate hydrolysis
solution is continuously fed directly to the PFR and hydrolyzed to
form the hydrolyzate product solution. It has been discovered that
the process of the invention may be operated at high productivity
in one or more CSTRs in series together with a PFR finishing
reactor. Thus, the capital costs of implementing the process
compare favorably with the batch processes previously considered
necessary in the art to provide adequate conversion at high
productivity.
[0021] It has been found that such a continuous hydrolysis process
can provide efficient conversion of HMBN to HMBA to produce a high
quality hydrolyzate product containing trace amounts of HMBN and
2-hydroxy-4-methylthiobutanamide. In order to produce quality feed
supplements containing HMBA, the process of the invention may be
operated at high productivity to produce an aqueous hydrolyzate
product solution comprising at least about 36 wt. % HMBA, at least
about 30 wt. % ammonium bisulfate, at least about 25 wt. % water,
up to about 0.05 wt. % amide and up to about 0.05 wt. % nitrile.
The HMBA within the aqueous hydrolyzate product solution includes
HMBA monomer as well as dimers. In a particularly preferred
embodiment of the invention, high conversion is achieved during
start up as well as at steady state so that the above described
product composition may be consistently produced throughout all
process operations.
[0022] Ordinarily, the hydrolyzate product produced before steady
state conditions are established, for example, during start up,
could contain more amide and nitrile than is desired in a high
quality HMBN product. It has been discovered that such composition
fluctuations can be prevented by operating at a higher acid to
nitrile molar ratio during start up in order to establish steady
state conditions very rapidly. Presumably, all the acid and HMBA
are introduced into the first CSTR reactor, but it would be
feasible to divide the acid stream and introduce one portion
directly into the PFR. Broadly speaking, therefore, the acid to
nitrile molar ratio is based on the cumulative rates at which acid
and nitrile are introduced into the process as a whole. Operation
at a higher acid to nitrile ratio is achieved by controlling the
rate of sulfuric acid flowing into the plug flow reactor so that it
is at least stoichiometrically equivalent to the sum of the nitrile
and acid flowing into that reactor. For effective control, the acid
rate is preferably at least 5% in excess of the rate equivalent to
the sum of nitrile and amide. The acid to nitrile molar ratio is
between about 1.0 and about 2.0 from start up of the process until
steady state is established, preferably between about 1.0 and about
1.5, and most preferably between about 1.15 and about 1.25. After
steady state is reached, the acid to nitrile molar ratio is between
about 0.7 and about 1.5, preferably between about 0.9 and about
1.2, and most preferably between about 0.95 and about 1.05.
[0023] Referring to FIG. 1, 2-hydroxy-4-methylthiobutanamide is
continuously generated by the hydrolysis of HMBN in a CSTR 10. At
start up of the process, a sulfuric acid feed stream is introduced
into the reactor 10 and circulated therein. The sulfuric acid has a
strength of between about 50% by weight and about 70% by weight,
preferably between about 60% by weight and about 70% by weight.
HMBN is then introduced into the circulating sulfuric acid stream
where it reacts with water to form the amide within the aqueous
hydrolysis solution. Continuous nitrile hydrolysis occurs as the
HMBN and sulfuric acid streams are continuously fed to the aqueous
hydrolysis solution within the reactor 10. Sulfuric acid serves as
a catalyst and is not consumed in the nitrile hydrolysis reaction.
The residence time during which the intermediate aqueous hydrolysis
solution is contained within the reactor 10 is between about 20
minutes and about 60 minutes, preferably between about 25 minutes
and about 45 minutes. The intermediate aqueous hydrolysis solution
produced in the reactor comprises up to about 11 wt. % HMBA, up to
about 8 wt. % ammonium bisulfate, at least about 10 wt. % water, at
least about 35 wt. % amide and up to about 2 wt. % nitrile. The
intermediate aqueous hydrolysis solution preferably comprises
between about 5 and about 10 wt. % HMBA, between about 4 and about
8 wt. % ammonium bisulfate, between about 10 and about 15 wt. %
water, between about 35 and about 50 wt. % amide and up to about 2
wt. % nitrile, and more preferably, comprises between about 5 and
about 8 wt. % HMBA, between about 4 and about 5 wt. % ammonium
bisulfate, between about 12 and about 13 wt. % water, between about
40 and about 50 wt. % amide and up to about 1 wt. % nitrile.
[0024] The reaction is carried out at a temperature between about
40.degree. C. and about 70.degree. C., preferably between about
60.degree. C. and about 65.degree. C., and at a total pressure of
between about 0 and about 15 psig. A pump 11 circulates reacting
solution between CSTR 10 and an external heat exchanger 12, in
which exothermic heat of reaction is removed by transfer to a
coolant. The reactor 10 may also be jacketed to provide additional
cooling capacity, and also to provide for heating the contents of
the reactor if required during start up.
[0025] The liquid level within the reactor 10 is maintained
constant by a level controller. Although the liquid level can also
be controlled by gravity overflow from the reactor, the hydrolysis
system is more easily designed if positive level control is
utilized. A level controller is also preferred because the
intermediate hydrolysis solution is viscous. Moreover the
availability of a level controller allows the working volume and
residence time of the reactor be varied at the operator's
selection, e.g., to adapt to changes in throughput.
[0026] As the intermediate aqueous hydrolysis solution is
generated, it exits the reactor 10 and is mixed with a heated water
stream in an in-line mixer 14 to form a diluted aqueous hydrolysis
solution. The water stream is heated to a temperature of between
about 60.degree. C. and about 100.degree. C., preferably between
about 70.degree. C. and about 90.degree. C., and, most preferably
between about 75.degree. C. and about 80.degree. C. The
intermediate aqueous hydrolysis solution is mixed with the heated
water stream to prevent separation of the organic and aqueous
phases or precipitation of ammonium bisulfate within the PFR. The
water stream also further dilutes sulfuric acid within the
solution, provides water to be consumed during amide hydrolysis,
and reduces the viscosity of the solution. The water stream is
introduced at a rate which provides sulfuric acid strength in the
diluted aqueous hydrolysis solution of between about 30% and about
50% by weight on an organic-free basis, preferably between about
35% to about 45% by weight, more preferably about 43% by
weight.
[0027] If the temperature of the diluted aqueous hydrolysis
solution is too low for adequate amide conversion, the solution may
be brought to the requisite temperature in a preheater 23.
Preheating the solution may be necessary, for example, when ambient
heat losses are significant. The diluted aqueous hydrolysis
solution enters a PFR 16 either directly from the mixer or after
being preheated. In the PFR, the small amount of residual HMBN is
hydrolyzed to form additional amide and the amide is hydrolyzed to
form HMBA. Preferably, the molar ratio of water to amide fed to the
PFR is between about 5 and about 10. To maintain turbulence within
the PFR and minimize axial backmixing therein, the flow rate of the
diluted aqueous hydrolysis solution is operated to maintain
suitable velocity within the PFR.
[0028] As indicated above, at a given residence time in the PFR, it
has been found that conversion may be substantially increased by
increasing the acid/nitrile molar ratio in the feed. Experience has
shown that in some instances steady state is obtained in about two
hours during start up when the acid/nitrile molar ratio is 1.0, yet
steady state conditions, and complete conversion, may be obtained
almost immediately when the acid/nitrile molar ratio is 1.2. Rapid
establishment of steady state conditions enables consistent
production of a high quality hydrolyzate product which comprises up
to about 0.05 wt. % amide and up to about 0.05 wt. % nitrile upon
leaving the PFR 16.
[0029] The expense of the excess acid, however, may be prohibitive
if an increased acid/nitrile molar ratio is maintained during
routine operation of the process after steady state conditions are
established. Thus, it is preferable to use an acid/nitrile molar
ratio of between about 1.0 and about 1.5, preferably between about
1.15 and about 1.25, only from initial start up until steady state
conditions are established in the PFR in order to avoid preparation
of off-specification hydrolyzate product during start-up. Such a
molar ratio is obtained when the amount of excess sulfuric acid
added to the CSTR 10 is between about 10 and about 50% by weight,
preferably between about 15 and about 25% by weight, over that
stoichiometrically equivalent to the amide and HMBN introduced to
the PFR. After steady state is established, the acid/nitrile molar
ratio can then be adjusted to, and maintained at, a more cost
effective molar ratio of between about 0.7 and about 1.15,
preferably between about 0.95 and about 1.05. The preferred steady
state molar ratio is obtained when the amount of excess sulfuric
acid added to the CSTR 10 is between about 0 and about 15% by
weight, preferably between about 0 and about 5% by weight, over
that stoichiometrically equivalent to the amide and HMBN introduced
to the PFR. The water feed rate into the mixer 14 may be increased
to avoid liquid phase separation of organic and aqueous phases when
an acid/nitrile molar ratio below 1.0 is used. It has been
discovered that operation of the PFR at a high acid/nitrile molar
ratio during start up improves conversion of amide to HMBA within
the PFR without darkening the color of the hydrolyzate product.
Despite the increased severity of reaction conditions provided by a
high acid/nitrile ratio, it has unexpectedly been discovered that
acid/nitrile molar ratio does not significantly affect hydrolyzate
color. Moreover, the high acid to nitrile molar ratio also allows
PFR operation at a lower temperature during steady state operation,
therefore producing a light colored hydrolyzate product.
[0030] The hydrolyzate product leaving the PFR has a light color of
between about 5 to about 10, preferably between about 5 to about 7,
as measured using a Gardner calorimeter. Color is adversely
affected by excessive PFR temperatures and residence time within
the PFR. The PFR operates at a temperature between about 70.degree.
C. and about 120.degree. C. When the PFR is operated adiabatically,
the temperature rises along the flow path as the reaction product
absorbs the adiabatic heat of reaction, reaching a point on the
flow path (hot spot) at which the temperature reaches a plateau,
and beyond which it may drop slightly if conditions are less than
perfectly adiabatic. The peak temperature in the reactor is
preferably between about 90.degree. C. and about 120.degree. C.,
more preferably between about 90.degree. C. and about 105.degree.
C. The residence time of the finishing reaction solution within the
PFR is between about 30 minutes and about 100 minutes, preferably
between about 50 minutes and about 70 minutes. When the PFR is
operated at a temperature above 110.degree. C., a dark hydrolyzate
may be produced. However, a PFR temperature below 90.degree. C. may
result in incomplete amide hydrolysis unless a high acid to nitrile
molar ratio is employed. Darkening of the hydrolyzate product can
also occur if the residence time exceeds about 120 minutes. A light
colored hydrolyzate product is produced when an acid/nitrile molar
ratio of between about 1.1 and about 1.5 is used during start up
and normal operation when the PFR 16 is operated at a moderate
temperature of between about 70 and about 95.degree. C., preferably
between about 80.degree. C. and about 90.degree. C. The PFR
temperature can be reduced when it is operated adiabatically by
lowering the temperature of the heated water stream entering the
mixer 14. If the diluted aqueous hydrolysis solution is introduced
into the preheater 23 (FIG. 1) before it is introduced to the PFR,
the heat applied to the preheater can be reduced to lower the PFR
operating temperature. Alternatively, cooling and/or heating may be
provided to control the PFR temperature when the PFR is operated
isothermally. When a second CSTR 24 precedes the PFR 16 as shown in
FIG. 2, a darkened hydrolyzate product may be produced if the
operating temperature of the second CSTR is too high. A light
colored hydrolyzate product is produced when the above described
acid/nitrile molar ratio is used and the second CSTR is operated at
a moderate temperature of between about 70 and about 95.degree. C.,
preferably between about 80.degree. C. and about 90.degree. C.
[0031] The PFRs best suited for use in the amide hydrolysis process
of the invention are configured for operation at a Peclet number of
at least 50 at a PFR operating temperature of at least 90.degree.
C. The Peclet number (Pe) is a measure of axial backmixing within
the PFR as defined by the following equation:
Pe=uL/D
[0032] where: u=velocity, L=length, and D=axial dispersion
coefficient. The Peclet number of a PFR is inversely proportional
to axial back-mixing. Axial backmixing is effectively minimized
when the Peclet number is at least 50, preferably between about 50
and about 200 or more, and residence time is between about 40 and
about 100 minutes, preferably between about 50 and about 60
minutes.
[0033] The PFR 16 of the present invention may be pipeline PFR or a
packed column PFR filled with a packing material. The amide
hydrolysis reaction is non-zero order, but the kinetics of reaction
have been found sufficiently favorable that high conversion may be
realized within the relatively modest residence times noted above,
and without substantial pressure drop. More particularly, it has
been found that, where the nitrile has been substantially converted
to amide, and the nitrile concentration is not greater than about
2% by weight in the stream entering the plug flow reactor, the
residual amide and nitrile concentrations may each be reduced to
not greater than about 0.2% by weight on an HMBA basis in a
pipeline reactor that is operated with a velocity of the reacting
solution in the turbulent flow range regime, for example, at a
Reynolds number of at least about 3000, preferably at least about
5000. Provided that the nitrile/amide ratio of the solution
entering the reactor is not greater than about 1% by weight in the
stream entering the PFR, the amide and nitrile concentrations in
the reaction product may each be reduced to not greater than about
0.1% by weight, HMBA basis. For the relatively modest residence
time required to achieve such conversion, a PFR reactor operated
may be operated at turbulent velocity without excessive pressure
drop. Moreover, it has been found that the desired conversion may
be attained at a modest operating temperature, in the range of
between 90.degree. C. and about 105.degree. C., which does not
require a high pressure reactor, and which allows the preparation
of a product having a light color.
[0034] Alternatively, a packed column PFR may be used to carry out
the final hydrolysis reaction. By use of structured packing, a
packed column reactor may be operated at a significantly lower
velocity than a pipeline reactor without significant backmixing due
to wall effects or channeling. The packing promotes turbulence and
radial mixing, and minimizes axial backmixing, dead spots and
channelling of flow so that all fluid elements travel through the
PFR in about the same residence time. Thus, a packed column reactor
may have a substantially greater diameter and a more compact
configuration than a pipeline reactor. It is particularly
advantageous where reactants or products are of high viscosity.
[0035] However, for the process of the invention, it has been found
that a pipeline reactor, i.e., an elongate tubular reactor
substantially devoid of internal packing or other internal flow
obstructions, is preferred. While a slightly greater degree of
axial backmixing per unit length may be incurred in a pipeline
reactor, the kinetics of the nitrile and amide hydrolysis have been
discovered to allow nearly quantitative conversion with the modest
residence times and low pressure drops described above. Because of
low pressure drop incurred even at high velocity in a reactor
suitable for the process of the invention, a pipeline reactor may
be configured, i.e., with a high L/D (length to diameter) ratio, to
operate at a very high Peclet number, typically in excess of 200,
and readily in excess of 2000. Additionally, a pipeline reactor for
the process of the invention can be constructed of relatively
inexpensive materials of construction, e.g., teflon-lined carbon
steel pipe. For a packed column reactor, more exotic materials of
construction may be required. A pipeline reactor also affords
greater flexibility since it can be operated at a much greater
turndown ratio than a packed column, in the latter of which
conversion declines sharply below a well defined threshold
velocity. Threshold velocity in a packed column is attained in the
transition between laminar and turbulent flow.
[0036] The PFR 16 is insulated to compensate for heat losses to the
atmosphere. The heat of reaction generated during the amide
hydrolysis is sufficient for autothermal operation under adiabatic
conditions. Advantageously, the diluted aqueous hydrolysis solution
can enter the PFR at a temperature below the reaction temperature
for the amide hydrolysis. During autothermal operation, the heat of
reaction generated by amide hydrolysis increases the temperature
within the PFR, lessening the likelihood that a hot spot will form
therein. The temperature profile in the PFR can be monitored
through several temperature sensors T (FIGS. 1 and 2) along the
length of the reactor. The hot water feed temperature can be
adjusted to achieve the desired temperature profile in the PFR by
increasing or decreasing the heat supplied to the water feed stream
by the water heater 18 before it enters the mixer 14 to form the
diluted aqueous hydrolysis solution. Additionally, the temperature
of the diluted aqueous hydrolysis solution exiting the mixer 14 can
be raised through the use of preheater 23 to increase the PFR
operating temperature.
[0037] Although residual nitrile hydrolyzes in the inlet portion of
the PFR, the nitrile hydrolysis should proceed sufficiently to
completion in the CSTR 10 so that the exothermic reaction heat from
the nitrile hydrolysis does not create a hot spot in the PFR that
degrades hydrolyzate product quality and disrupts adiabatic
autothermal operation of the PFR. Although hot spot temperatures of
as much as 110.degree. C. to about 120.degree. C. can be tolerated
within the PFR, the hydrolyzate product can darken significantly
under such conditions.
[0038] The PFR operates at a total pressure of between about 0 and
about 15 psig. A pressure control valve at the outlet of the PFR
provides up to 15 psig back pressure to avoid boiling in the
reactor system when the PFR operates at a temperature higher than
105.degree. C.
[0039] Advantageously, hydrolysis solution samples may be withdrawn
from sample valves S (FIGS. 1 and 2) and analyzed via gas
chromatography to determine the hydrolysis solution composition
profile along the length of the PFR. Once steady state conditions
are established, a hydrolyzate sample can be removed from the PFR
outlet every eight to twelve hours and quantitatively analyzed to
monitor product quality.
[0040] The aqueous hydrolyzate product solution exiting the PFR 16
flows through a cooler 20 before being stored in a hydrolyzate
product surge tank 22. The CSTRs, PFRs and the hydrolyzate product
surge tank utilized in the processes of the present invention are
operated under the same overhead pressure (preferably about 10
psig) by employing a common vent header which is blanketed with
nitrogen and controlled by a pressure controller which relieves
pressure by venting gases to an incinerator header when pressure
exceeds about 15 psig. Venting may remove volatile organic sulfur
compounds such as methyl sulfide, methyl disulfide, and
methylmercaptan, which are by-products of the reaction. The vapor
emissions are less than 0.5 scf per 1000 lbs. HMBA product, usually
less than 0.3 scf per 1000 lbs. product. Emissions of 0.2 scf/1000
lbs. HMBA and even lower are readily achievable, especially where
only a single CSTR is used.
[0041] The HMBA can be recovered from the aqueous hydrolyzate
product solution by neutralization with ammonium hydroxide, or by
extraction methods such as that described by Ruest et al. U.S. Pat.
No. 4,524,077 which is incorporated herein by reference.
[0042] FIG. 2 illustrates an embodiment of the present invention
wherein the amide hydrolysis is conducted in the PFR 16 and a
second CSTR 24 upstream of the PFR. The second CSTR enables easy
handling of the viscous amide, thoroughly mixes the hydrolysis
solution, and controls the temperature and water content of the
finishing reaction solution, resulting in a relatively low
viscosity of the latter solution as introduced into the PFR. The
nitrile hydrolysis takes place in CSTR 10 and the intermediate
aqueous hydrolysis solution and a heated water feed stream are
introduced into the second CSTR 24 wherein a substantial portion of
the amide is hydrolyzed to HMBA. For purposes of the present
invention, a substantial portion of the amide is hydrolyzed when
more than 50% by weight, preferably between about 50% and about 80%
by weight, of the amide is hydrolyzed to HMBA. The residence time
during which the diluted aqueous hydrolysis solution is contained
within the second CSTR 24 is between about 30 minutes and about 80
minutes, preferably between about 40 minutes and about 60 minutes.
The liquid level in the second CSTR can be controlled by gravity
overflow to the PFR 16 or by level control as previously
described.
[0043] The amide hydrolysis reaction is initiated in the second
CSTR at a temperature between about 70.degree. C. and about
120.degree. C., preferably between about 90.degree. C. and about
105.degree. C., and at a total pressure of between about 0 and
about 15 psig. Conversion to HMBA is generally improved by
operating the second CSTR at an elevated temperature between about
90.degree. C. and about 110.degree. C. The second CSTR 24 is
provided with a steam heated jacket in order to maintain the
operating temperature. If the temperature sensors T (FIG. 2) detect
a hot spot within the PFR, the operating temperature of the second
CSTR can be lowered.
[0044] The amide hydrolysis reaction is substantially carried out
in the second CSTR, producing a finishing reaction solution which
is introduced into the PFR 16. The finishing reaction solution
comprises at least about 32 wt. % HMBA, at least about 25 wt. %
ammonium bisulfate, at least about 25 wt. % water, up to about 5
wt. % amide and up to about 1 wt. % nitrile. Preferably, the
finishing reaction solution comprises between about 31 and about 42
wt. % HMBA, between about 20 and about 30 wt. % ammonium bisulfate,
between about 20 and about 30 wt. % water, between about 2 and
about 5 wt. % amide and up to about 1 wt. % nitrile. The amide
hydrolysis is then completed within the PFR as described above for
FIG. 1.
[0045] FIG. 3 illustrates a preferred embodiment of the invention
wherein the CSTR 10 can be adapted in the processes shown in FIGS.
1 and 2 to receive concentrated sulfuric acid, HMBN, and water feed
streams. When the streams are simultaneously fed to the reactor,
sulfuric acid is diluted in the reactor as the nitrile hydrolysis
reaction occurs. A separate acid dilution system is not required
and associated installation and maintenance costs are avoided. The
concentrated sulfuric acid introduced into the CSTR 10 has a
strength of between about 70% by weight and about 99% by weight,
preferably between about 90% by weight and about 98% by weight. The
aqueous hydrolysis solution within the CSTR 10 has a strength of
between about 50% by weight and about 70% by weight, preferably
between about 60% by weight and about 70% by weight of sulfuric
acid on an organic-free basis. The aqueous hydrolysis solution is
continuously pumped through an external heat exchanger 12 at a high
circulation rate to remove heat of reaction. A pump 11 circulates
reacting solution between CSTR 10 and an external heat exchanger
12, in which exothermic heat of reaction is removed by transfer to
a coolant. The heat exchanger also removes the heat generated by
dilution of sulfuric acid when concentrated sulfuric acid is fed
directly to reactor 10.
[0046] The process of the present invention provides an improved
method for preparing HMBA. High productivity can be achieved using
such a process because it can be operated continuously to provide
greater throughput than a conventional batch process. The process
significantly reduces capital and maintenance costs associated with
batch processes, for example, by eliminating the need for separate
sulfuric acid dilution when concentrated sulfuric acid is
introduced to a reactor without prior dilution. The process also
affords improved control of reaction conditions as compared to
conventional batch hydrolysis systems. Such improved control of the
hydrolysis reactions enables production of a hydrolyzate solution
of consistently high quality. The process vent emissions are
significantly reduced as compared to conventional batch systems
because filling and emptying of tanks and operation at non-steady
state conditions is eliminated.
[0047] The following examples are presented to describe preferred
embodiments and utilities of the present invention and are not
meant to limit the present invention unless otherwise stated in the
claims appended hereto.
EXAMPLE 1
[0048] Bench scale equipment as shown in FIG. 4 was used to
demonstrate the continuous hydrolysis process.
[0049] Nitrile (2-hydroxy-4-methylthiobutanenitrile) and 65%
aqueous sulfuric acid were continuously pumped at rates of 1.01
g/min and 1.167 g/min, respectively, into a well-mixed
recirculating reactor 26 having a liquid volume of 42.1
milliliters. The reaction temperature was controlled at 65.degree.
C. through cooling jackets provided on the recirculating reactor
loop, which removed the heat released from the nitrile hydrolysis
reaction. A pump 28 recirculated the aqueous hydrolysis solution in
the reactor loop. The residence time of the reactor 26 based on the
total feed rate was 25.4 minutes. At the outlet of the reactor, a
sample was periodically removed during steady state conditions. All
sampling ports are designated with an S in FIG. 4. The sample was
analyzed by a gas chromatographic method to determine the
hydrolyzate product composition leaving the reactor. The gas
chromatography result showed that practically all nitrile feed was
hydrolyzed and converted to amide and approximately 15% of the
formed amide was further hydrolyzed in this reactor to form HMBA,
the final hydrolysis product.
[0050] The amide rich hydrolyzate leaving the recirculating reactor
26 was fed continuously into the second recirculating reactor 30
which is similar to the first recirculating reactor 26 but has a
liquid volume of 119.3 milliliters. A water feed at 0.57 g/min was
also introduced into the second well-mixed reactor which provided a
residence time of 52.6 minutes. The temperature of this reactor
loop was maintained at 102.degree. C. via a heating fluid jacket
provided on the recirculating reactor loop. A pump 32 recirculated
the hydrolyzate in the reactor loop. An outlet sample from the
reactor 30 was obtained and analyzed by gas chromatography which
revealed that approximately 94.5% of the feed amide was hydrolyzed
to HMBA.
[0051] The outlet from the second recirculating reactor 30
continuously entered the final finishing reactor which was
constructed of a series of four coils 34 of Teflon tubing. The
finishing reactor was placed inside a constant temperature oven 36
for preventing heat losses to the ambient, thus maintaining a
temperature of 102.degree. C. throughout the reactor coils 34. This
isothermal PFR having a total liquid volume of 91 milliliters and a
corresponding 43 minutes residence time was designed to assure
completion of the amide hydrolysis. In this case, the hydrolysis of
amide was completed at the outlet of the third coil 38. The
hydrolyzate product taken from the outlet of the PFR was analyzed
and contained 35% HMBA, with the remaining material being water and
by-product ammonium bisulfate. The color of the hydrolyzate product
was 6-7 on the Gardner color scale.
EXAMPLES 2-9
[0052] The same continuous bench scale equipment as used in Example
1 was also used to determine the effect of residence time and
reaction temperature on conversion. The acid to nitrile feed ratio
of each example was maintained at approximately a 1.0 molar
stoichiometric ratio. At the outlet of each recirculating reactor
and the end of each coil of the PFR, a sample (indicated as RECIRC
and S, respectively, in Tables 1-8 below) was removed during steady
state conditions and was analyzed by a gas chromatographic method
to determine the hydrolysis solution composition leaving the
reactor or coil. The hydrolysis solution composition and the
temperature and residence time in each reactor or coil are shown in
Tables 1-8 below. The remainder of the product included water and
ammonium bisulfate. The results, based on various feed rates
(1.01-2.33 grams/min. nitrile feed) and temperatures (60-65.degree.
C. for nitrile hydrolysis and 90-120.degree. C. for amide
hydrolysis) illustrate that increasing residence time and reaction
temperatures improves the conversion of both hydrolysis reactions.
However, increasing temperatures also resulted in an increase in
product color.
EXAMPLE 2
[0053] Nitrile at 1.01 g/min was fed to the first recirculating
reactor, along with 1.15 g/min 64.7% sulfuric acid, giving a 0.99
acid/nitrile molar ratio. A water feed at 0.55 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 1 below.
1 TABLE 1 RECIRC-I RECIRC-II S1 S2 S3 Temperature 64 103 104 104
104 (.degree. C.) Residence Time 25 53 11 11 11 (min) Hydrolysis
Solution Composition (wt. %) Nitrile 0.11 trace trace trace trace
HMBA 8.3 34 33 35 33 Amide 38 2.7 0.70 0.12 0.03 Hydrolyzate
Product Color: 6-7 on Gardner scale
EXAMPLE 3
[0054] Nitrile at 1.01 g/min was fed to the first recirculating
reactor, along with 1.16 g/min 64.7% sulfuric acid, giving a 0.99
acid/nitrile molar ratio. A water feed at 0.54 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 2 below.
2 TABLE 2 RECIRC-I RECIRC-II S1 S2 S3 Temperature 62 98 102 102 102
(.degree. C.) Residence Time 25 53 11 11 11 (min) Hydrolysis
Solution Composition (wt. %) Nitrile 0.22 0.05 0.05 trace 0.035
HMBA 7.8 33 38 38 39 Amide 35 3.5 0.81 0.18 0.09 Hydrolyzate
Product Color: 5-6 on Gardner scale
EXAMPLE 4
[0055] Nitrile at 1.43 g/min was fed to the first recirculating
reactor, along with 1.65 g/min 64.7% sulfuric acid, giving a 0.99
acid/nitrile molar ratio. A water feed at 0.76 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 3 below.
3 TABLE 3 RECIRC-I RECIRC-II S1 S2 S3 Temperature 65 105 105 105
105 (.degree. C.) Residence Time 18 36 7.7 7.7 7.7 (min) Hydrolysis
Solution Composition (wt. %) Nitrile 0.36 0.06 0.05 trace trace
HMBA 6.7 34 36 37 38 Amide 39 3.1 0.79 0.28 trace Hydrolyzate
Product Color: 6-7 on Gardner scale
EXAMPLE 5
[0056] Nitrile at 1.45 g/min was fed to the first recirculating
reactor, along with 1.69 g/min 64.7% sulfuric acid, giving a 1.0
acid/nitrile molar ratio. A water feed at 0.78 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 4 below.
4 TABLE 4 RECIRC-I RECIRC-II S1 S2 S3 S4 Temperature 65 90 90 90 90
90 (.degree. C.) Residence Time 18 37 7.7 7.7 7.7 7.3 (min)
Hydrolysis Solution Composition (wt. %) Nitrile 0.37 trace trace
trace trace trace HMBA 6.1 32 36 37 36 37 Amide 40 5.8 2.1 0.99
0.60 0.40 Hydrolyzate Product Color: 4 on Gardner scale
EXAMPLE 6
[0057] Nitrile at 2.0 g/min was fed to the first recirculating
reactor, along with 2.33 g/min 65% sulfuric acid, giving a 1.01
acid/nitrile molar ratio. A water feed at 1.09 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 5 below.
5 TABLE 5 RECIRC-I RECIRC-II S1 S2 S3 S4 Temperature (.degree. C.)
65 105 105 105 105 105 Residence Time (min) 13 26 5.4 5.4 5.4 5.2
Hydrolysis Solution Composition (wt. %) Nitrile 0.45 0.09 trace
0.04 trace 0.06 HMBA 5.3 34 36 36 36 37 Amide 40 3.3 0.84 0.28 0.12
0.07 Hydrolyzate Product Color: 6-7 on Gardner scale
EXAMPLE 7
[0058] Nitrile at 1.42 g/min was fed to the first recirculating
reactor, along with 1.65 g/min 65% sulfuric acid, giving a 1.01
acid/nitrile molar ratio. A water feed at 0.795 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 6 below.
6 TABLE 6 RECIRC-I RECIRC-II S1 S2 S3 Temperature 60 120 120 120
120 (.degree. C.) Residence Time 18 36 7.5 7.5 7.5 (min) Hydrolysis
Solution Composition (wt. %) Nitrile 0.23 0.05 trace trace trace
HMBA 5.2 36 35 36 36 Amide 39 1.5 trace trace trace Hydrolyzate
Product Color: 17 on Gardner scale
EXAMPLE 8
[0059] Nitrile at 1.43 g/min was fed to the first recirculating
reactor, along with 1.66 g/min 65% sulfuric acid, giving a 1.0
acid/nitrile molar ratio. A water feed at 0.78 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 7 below.
7 TABLE 7 RECIRC-I RECIRC-II S1 S2 S4 Temperature 65 100 100 100
100 (.degree. C.) Residence Time 18 36 7.6 7.6 7.3 (min) Hydrolysis
Solution Composition (wt. %) Nitrile 0.26 0.10 NA NA trace HMBA 7.0
34 NA NA 37 Amide 36 3.7 NA NA 0.05 Hydrolyzate Product Color: 6 on
Gardner scale
EXAMPLE 9
[0060] Nitrile at 1.04 g/min was fed to the first recirculating
reactor, along with 1.15 g/min 65% sulfuric acid, giving a 0.96
acid/nitrile molar ratio. A water feed at 0.57 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 8 below.
8 TABLE 8 RECIRC-I RECIRC-II S1 S2 S3 S4 Temperature (.degree. C.)
65 100 100 100 100 100 Residence Time (min) 25 52 11 11 11 11
Hydrolysis Solution Composition (wt. %) Nitrile 0.36 0.08 0.05 0.05
0.04 trace HMBA 8.7 35 37 36 35 34 Amide 39 3.6 0.89 0.37 0.17 0.05
Hydrolyzate Product Color: 6 on Gardner scale
EXAMPLES 10-20
[0061] The effect of acid/nitrile feed molar ratio on the reaction
conversion, as well as the coupling effect of this ratio with
reaction temperature was determined. In these examples, the nitrile
feed rate was essentially constant and the water feed rate was
adjusted for various 65% sulfuric acid feeds to assure the same
water content of the final hydrolyzate from each run. At the outlet
of each reactor and the end of each coil of the PFR, a sample was
removed during steady state conditions and was analyzed by a gas
chromatographic method to determine the hydrolyzate product
composition leaving the reactor or coil. The hydrolysis solution
composition and the temperature and residence time in each reactor
or coil are shown below. The remainder of the hydrolyzate included
water and ammonium bisulfate. Based on the range of the variables
that were analyzed, i.e., acid/nitrile molar ratio from 0.6 to 1.2
and amide hydrolysis temperature from 90-120.degree. C., an optimum
range of conditions were derived as shown in FIG. 5 for the fixed
residence (or nitrile feed rate) tested. Within the range of
90-101.degree. C. and 1.0-1.2 acid/nitrile ratio, any combination
of temperature and acid/nitrile molar ratio will result in a
satisfactory product containing up to 0.05% by weight amide, up to
0.05% by weight nitrile and having a color of between 5 and 7 on a
Gardner scale.
EXAMPLE 10
[0062] Nitrile at 1.02 g/min was fed to the first recirculating
reactor, along with 1.03 g/min 64.75% sulfuric acid, giving a 0.88
acid/nitrile molar ratio. A water feed at 0.53 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 9 below.
9 TABLE 9 RECIRC-I RECIRC-II S1 S2 S3/S4 Temperature 65 105 105 105
105 (.degree. C.) Residence Time 27 53 11 11 11 (min) Hydrolysis
Solution Composition (wt. %) Nitrile 0.80 0.31 0.35 0.40 NA HMBA
8.3 35 41 49 NA Amide 41 3.7 1.7 0.96 NA Hydrolyzate Product Color:
6-7 on Gardner scale
EXAMPLE 11
[0063] Nitrile at 0.99 g/min was fed to the first recirculating
reactor, along with 0.70 g/min 65% sulfuric acid, giving a 0.62
acid/nitrile molar ratio. A water feed at 0.94 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 10 below.
10 TABLE 10 RECIRC-I RECIRC-II S1 S2 S3 S4 Temperature 65 90 90 90
90 90 (.degree. C.) Residence Time 32 53 11 11 11 11 (min)
Hydrolysis Solution Composition (wt. %) Nitrile 5.2 2.2 2.4 2.5 2.5
2.5 HMBA 7.9 25 27 29 30 30 Amide 45 9.5 7.4 5.9 5.2 4.6
Hydrolyzate Product Color: 5 on Gardner scale
EXAMPLE 12
[0064] Nitrile at 1.01 g/min was fed to the first recirculating
reactor, along with 1.37 g/min 64.75% sulfuric acid, giving a 1.19
acid/nitrile molar ratio. A water feed at 0.53 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 11 below.
11 TABLE 11 RECIRC-I RECIRC-II S1 S2 S3 S4 Temperature 65 90 90 90
90 90 (.degree. C.) Residence Time 23 50 10 10 10 10 (min)
Hydrolysis Solution Composition (wt. %) Nitrile trace trace trace
trace trace trace HMBA 7.7 31 35 34 35 35 Amide 33 2.8 0.72 0.17
0.03 trace Hydrolyzate Product Color: 5 on Gardner scale
EXAMPLE 13
[0065] Nitrile at 1.01 g/min was fed to the first recirculating
reactor, along with 0.70 g/min 65% sulfuric acid, giving a 0.60
acid/nitrile molar ratio. A water feed at 0.90 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 12 below.
12 TABLE 12 RECIRC-I RECIRC-II S1 S2 S3 S4 Temperature 65 120 120
120 120 120 (.degree. C.) Residence Time 32 52 11 11 11 10 (min)
Hydrolysis Solution Composition (wt. %) Nitrile 6.0 2.6 2.7 2.2 2.7
2.3 HMBA 7.7 27 32 29 34 31 Amide 44 5.4 4.0 1.4 1.8 1.4
Hydrolyzate Product Color: 10 on Gardner scale
EXAMPLE 14
[0066] Nitrile at 1.0 g/min was fed to the first recirculating
reactor, along with 1.37 g/min 64.75% sulfuric acid, giving a 1.19
acid/nitrile molar ratio. A water feed at 0.513 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 13 below.
13 TABLE 13 RECIRC-I RECIRC-II S1 S2 S3 S4 Temperature 65 120 120
120 120 120 (.degree. C.) Residence Time 23 50 10 10 10 10 (min)
Hydrolysis Solution Composition (wt. %) Nitrile trace trace trace
trace trace trace HMBA 8.5 34 34 35 35 34 Amide 31 0.44 trace trace
trace trace Hydrolyzate Product Color: 12+ on Gardner scale
EXAMPLE 15
[0067] Nitrile at 1.0 g/min was fed to the first recirculating
reactor, along with 1.05 g/min 64.75% sulfuric acid, giving a 0.91
acid/nitrile molar ratio. A water feed at 0.67 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 14 below.
14 TABLE 14 RECIRC-I RECIRC-II S1 S2 S3 S4 Temperature (.degree.
C.) 65 105 105 105 105 105 Residence Time (min) 27 53 11 11 11 11
Hydrolysis Solution Composition (wt. %) Nitrile 0.39 0.11 0.11 0.11
0.10 0.09 HMBA 8.9 34 34 37 38 38 Amide 37 4.0 1.5 0.71 0.32 0.20
Hydrolyzate Product Color: 6 on Gardner scale
EXAMPLE 16
[0068] Nitrile at 1.02 g/min was fed to the first recirculating
reactor, along with 0.71 g/min 64.75% sulfuric acid, giving a 0.6
acid/nitrile molar ratio. A water feed at 0.93 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 15 below.
15 TABLE 15 RECIRC-I RECIRC-II S1 S2 S3 S4 Temperature 65 120 120
120 120 120 (.degree. C.) Residence Time 32 52 11 11 11 10 (min)
Hydrolysis Solution Composition (wt. %) Nitrile 5.7 2.5 2.7 2.6 2.6
2.5 HMBA 8.5 29 33 34 35 35 Amide 45 6.2 4.3 2.6 2.0 1.5
Hydrolyzate Product Color: 6 on Gardner scale
EXAMPLE 17
[0069] Nitrile at 1.02 g/min was fed to the first recirculating
reactor, along with 0.69 g/min 65% sulfuric acid, giving a 0.59
acid/nitrile molar ratio. A water feed at 0.90 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 16 below.
16 TABLE 16 RECIRC-I RECIRC-II S1 S2 S3 S4 Temperature 65 90 90 90
90 90 (.degree. C.) Residence Time 32 53 11 11 11 10 (min)
Hydrolysis Solution Composition (wt. %) Nitrile 6.0 3.4 3.2 3.2 3.3
3.3 HMBA 8.2 25 27 28 29 30 Amide 44 12 8.0 7.5 6.6 5.7 Hydrolyzate
Product Color: 5 on Gardner scale
EXAMPLE 18
[0070] Nitrile at 1.02 g/min was fed to the first recirculating
reactor, along with 1.38 g/min 65% sulfuric acid, giving a 1.18
acid/nitrile molar ratio. A water feed at 0.54 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 17 below.
17 TABLE 17 RECIRC-I RECIRC-II S1 S2 S3 S4 Temperature 65 90 90 90
90 90 (.degree. C.) Residence Time 23 50 10 10 10 10 (min)
Hydrolysis Solution Composition (wt. %) Nitrile trace trace trace
trace trace trace HMBA 7.2 31 35 35 35 36 Amide 34 2.9 0.75 0.24
trace trace Hydrolyzate Product Color: 5 on Gardner scale
EXAMPLE 19
[0071] Nitrile at 1.03 g/min was fed to the first recirculating
reactor, along with 1.39 g/min 65% sulfuric acid, giving a 1.17
acid/nitrile molar ratio. A water feed at 0.52 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 18 below.
18 TABLE 18 RECIRC-I RECIRC-II S1 S2 S3 S4 Temperature 65 120 120
120 120 120 (.degree. C.) Residence Time 23 50 10 10 10 10 (min)
Hydrolysis Solution Composition (wt. %) Nitrile trace trace trace
trace trace trace HMBA 7.1 33 33 34 34 48 Amide 35 0.39 trace trace
trace trace Hydrolyzate Product Color: >18 on Gardner scale
EXAMPLE 20
[0072] Nitrile at 1.02 g/min was fed to the first recirculating
reactor, along with 1.05 g/min 65% sulfuric acid, giving a 0.90
acid/nitrile molar ratio. A water feed at 0.63 g/min was also
introduced into the second recirculating reactor. The hydrolysis
solution composition and the temperature and residence time in each
reactor or coil are shown in Table 19 below.
19 TABLE 19 RECIRC-I RECIRC-II S1 S2 S3 S4 Temperature (.degree.
C.) 65 105 105 105 105 105 Residence Time (min) 27 53 11 11 11 11
Hydrolysis Solution Composition (wt. %) Nitrile 0.38 0.06 0.09 0.06
0.09 0.09 HMBA 8.9 28 39 31 41 38 Amide 40 2.5 0.97 0.31 0.18 0.10
Hydrolyzate Product Color: 7 on Gardner scale
EXAMPLE 21
[0073] The bench scale equipment used in the preceding examples was
modified by replacing the second recirculating reactor 30 with a
small mixing loop 40 with negligible volume used for mixing the
water feed and the hydrolysis soltuion leaving the first loop
reactor 26. The diluted aqueous hydrolysis solution was
recirculated through the mixing loop by a pump 42. The mixer loop
40 was heated in a hot water bath 44 in order to heat the diluted
aqueous hydrolysis solution before it entered the PFR in which the
amide hydrolysis reaction occurred. The modified bench scale
equipment is shown in FIG. 6.
[0074] Nitrile at 0.73 g/min was fed to the first recirculating
reactor, along with 0.83 g/min 65% sulfuric acid, giving a 0.99
acid/nitrile molar ratio. The temperature in the reactor loop was
60.degree. C. and the residence time was estimated as 36.8 minutes.
Analysis of the reactor outlet sample revealed that nitrile was
essentially hydrolyzed to amide with less than 0.1% unreacted
nitrile remaining in the outlet stream. The temperature of the
hydrolysis solution at the outlet of the mixer loop was 75.degree.
C. and the residence time in the mixer loop was 1.5 minutes. The
PFR coils were maintained at 100 to 101.degree. C. The residence
time in each of the first three coils was 16 minutes and that in
the last coil was 15.2 minutes. Amide hydrolysis was completed in
the last PFR coil.
EXAMPLE 22
[0075] The equipment used in the continuous hydrolysis process as
shown in FIG. 2 consists of two CSTRs and one packed column type
PFR. The first CSTR was devoted for the nitrile hydrolysis while
the second CSTR and PFR were for the amide hydrolysis. The PFR is
an 8 inch diameter teflon lined carbon steel pipe packed with Koch
SMVP Teflon packing. The PFR was manufactured by Koch Engineering.
The threshold velocity for the SMVP packing is 0.95 mm/sec.
[0076] 105 lbs/hr of nitrile and 121 lbs/hr of 65% sulfuric acid
were continuously fed to the first 20 gallon CSTR in which 13
gallons of liquid were maintained by a level controller controlling
the reactor outlet flow. The reactor was maintained at 65.degree.
C. by an external cooler in a product recirculating loop. The
residence time based on the total feed rate and the reactor liquid
volume was 38 minutes. The outlet hydrolyzate sample, based on a
gas chromatographic analysis, was found to contain less than 0.1%
nitrile, 34.9% amide, and 11.2% HMBA. The outlet stream was
introduced to the second 30 gallon CSTR having a liquid volume of
27.7 gallons. An 80.degree. C. hot water stream was also fed to the
second CSTR at a rate of 60.5 lbs/hr. The reactor temperature was
105.degree. C. and the residence time was 91 minutes. The
hydrolyzate from the reactor contained 1.9% amide, indicating that
more than 90% of incoming amide was converted to HMBA in this
vessel. The second CSTR outlet stream then entered the packed
column reactor containing structure packing and having a total
liquid volume of 25 gallons. From the various samples obtained
along the length of the column reactor, the amide hydrolysis
reaction was found to have approached completion at 70% of the
length of the reactor. The temperature profile of the adiabatic
column reactor ranged from 100 to 102.degree. C. and the residence
time in the PFR was 52.9 minutes. The final product contained less
than 0.1% nitrile, less than 0.1% amide, and 48% HMBA. The major
by-product of the hydrolysis process, ammonium bisulfate, can be
separated from the product by conventional means. cl EXAMPLE 23
[0077] The equipment as used in Example 22 was used for the
following hydrolysis process except that the second CSTR was
bypassed such that the packed column reactor was the sole reactor
for the amide hydrolysis reaction (FIG. 2).
[0078] The feed rates to the first CSTR were as described in
Example 22. However, the temperature in the first CSTR was
60.degree. C. Analysis of the outlet sample revealed that the
intermediate hydrolysis solution contained 0.2% nitrile, 39.4%
amide, and 9.5% HMBA. The lower CSTR operating temperature resulted
in a slightly higher nitrile concentration but a lower HMBA
concentration. The intermediate hydrolysis solution was mixed with
a hot water stream (60.5 lbs/hr) in an in-line static mixer. The
diluted aqueous hydrolysis solution entered the PFR which
maintained a steady state temperature profile from 80.degree.C. at
the inlet, reaching a peak temperature of 105.degree. C. at the
middle and dropping to 102.degree. C. at the outlet of the packed
column. Although the column walls were heat traced and insulated,
some heat losses were encountered. The residence time in the column
reactor was 52.9 minutes. The final hydrolyzate at the outlet of
the column reactor contained less than 0.1% nitrile, 0.1% amide and
40.8% HMBA, the balance being by-product ammonium bisulfate and
water.
EXAMPLE 24
[0079] The equipment as utilized in Example 23 was used in the
following hydrolysis except that concentrated sulfuric acid was fed
directly to the first CSTR (FIG. 3) without pre-dilution to 65%
sulfuric acid with water. A water stream was also fed to the
reactor. Thus, both the heat of dilution of the acid and the heat
of hydrolysis were removed via the external circulating cooler. The
second CSTR was by-passed.
[0080] Nitrile (72 lbs/hr), 96% sulfuric acid (56.2 lbs/hr) and
dilution water (26.7 lbs/hr) were simultaneously fed to the first
CSTR where nitrile hydrolysis was occurring. The operating liquid
volume was 10 gallons, which provided 42.5 minutes of residence
time based on the total sum of the three feed rates. The reaction
temperature was controlled at 55.degree. C. The gas chromatographic
analysis of the intermediate hydrolysis solution showed that it
contained 0.5% nitrile, 40.6% amide, and 5.7% HMBA. The
intermediate hydrolysis solution was mixed with 41.3 lbs/hr hot
water in the in-line static mixer. The diluted aqueous hydrolysis
solution entered the packed column reactor in the same fashion as
described in Example 23, except that the adiabatic reaction
temperatures in the column reactor were slightly higher, probably
due to additional heat release from the higher unreacted nitrile
content leaving the CSTR which was operated at a lower temperature.
From the samples withdrawn from the column reactor, the amide
hydrolysis was determined to have been completed at 70% of the
column height from the bottom inlet.
EXAMPLES 25-38
[0081] Hydrolysis solution samples were taken at the outlet of each
CSTR, the PFR inlet (S1), the PFR outlet (S6), and at four sampling
ports along the length of the PFR (S2 through S5) as shown in FIG.
2. The samples were removed during steady state conditions and were
analyzed by a gas chromatographic method to determine the
hydrolysis solution composition when leaving the CSTRs and when
flowing through the PFR. The hydrolysis solution composition and
the temperature and residence time in each CSTR and within each
section of the PFR are shown below. The remainder of the hydrolysis
solution included water and ammonium bisulfate. Examples which do
not indicate CSTR-II data involved equipment wherein the second
CSTR was bypassed such that a diluted aqueous hydrolysis solution
flowed from the in-line mixer directly to the PFR.
[0082] The data demonstrate that conversion is affected by
temperature, acid/nitrile ratio and the degree of axial backmixing
in the plug flow reactor. Backmixing is in turn a function of the
velocity at which the reacting mixture flows through the reactor.
In the instances in which backmixing affected conversion, the
reactor was operated at less than its threshold velocity of 1.0
mm/sec., resulting in a lower average driving force, i.e., amide
concentration integrated along the length of the reactor, for this
non-zero order reaction. In some instances, it was possible to
compensate for operation below threshold velocity using relatively
higher temperature and/or acid/nitrile ratio. Further discussion of
the relationship of velocity to axial back-mixing and the resultant
effect on conversion is set forth at the end of Example 38.
EXAMPLE 25
[0083] Nitrile at 105.00 lbs/hr was fed to the first CSTR, along
with 120.95 lbs/hr 65% sulfuric acid, giving a 1.03 acid/nitrile
molar ratio. A water feed at 60.50 lbs/hr was also introduced into
the second CSTR. The hydrolysis solution composition for each
sample and the temperature and residence time for each location are
shown in Table 20 below.
20 TABLE 20 CSTR-I CSTR-II S1 S2 S3 S4 S5 S6 Volume (gal) 13 27.7
17.5 (total PFR) Temperature 65 104 101 103 102 103 103 102
(.degree. C.) Residence Time (min) PFR Velocity = 1.0 mm/sec.
Hydrolysis Solution Composition (wt. %) Nitrile 0.02 0.02 0.01 0.01
0.01 trace trace trace HMBA 12 41 34 39 39 39 41 40 Amide 34 2.0
0.5 0.27 0.04 0.02 0.02 0.02 Hydrolyzate Product Color: 11-12 on
Gardner scale
EXAMPLE 26
[0084] Nitrile at 105.00 lbs/hr was fed to the first CSTR, along
with 120.95 lbs/hr 65% sufuric acid, fiving a 1.00 acid/nitrile
molar ratio. A water feed at 60.50 lbs/hr was also introduced into
the second CSTR. The hydrolysis solution composition for each
sample and the temperature and residence time for each location are
shown in Table 21 below.
21 TABLE 21 CSTR-I CSTR-II S1 S2 S3 S4 S5 S6 Volume (gal) 13 27.7
17.5 (total PFR) Temperature 65 105 101 102 102 102 102 101
(.degree. C.) Residence Time (min) PFR Velocity = 1.0 mm/sec.
Hydrolysis Solution Composition (wt. %) Nitrile 0.01 trace trace
trace trace trace trace 0.01 HMBA 11 36 37 29 26 30 31 47 Amide 35
1.9 1.1 0.21 0.05 0.05 0.05 0.05 Hydrolyzate Product Color: 6-7 on
Gardner scale
EXAMPLE 27
[0085] Nitrile at 105.00 lbs/hr was fed to the first CSTR, along
with 145.14 lbs/hr 65% sulfuric acid, giving a 1.21 acid/nitrile
molar ratio. A water feed at 57.4 lbs/hr was also introduced into
the second CSTR. The hydrolysis solution composition for each
sample and the temperature and residence time for each location
arre shown in Table 22 below.
22 TABLE 22 CSTR-I CSTR-II S1 S2 S3 S4 S5 S6 Volume (gal) 13 27.7
17.5 (total PFR) Temperature 65 93 90 93 92 92 92 91 (.degree. C.)
Residence Time (min) PFR Velocity = 1.0 mm/sec. Hydrolysis Solution
Composition (wt. %) Nitrile trace trace trace trace trace trace
trace trace HMBA 11 33 34 35 36 36 38 33 Amide 31 1.8 1.3 0.14 0.02
0.01 0.01 0.01 Hydrolyzate Product Color: 9-10 on Gardner scale
EXAMPLE 28
[0086] Nitrile at 72.00 lbs/hr was fed to the first CSTR, along
with 82.94 lbs/hr 65% sulfuric acid, giving a 1.0 acid/nitrile
molar ratio. A water feed at 41.30 lbs/hr was also introduced into
the in-line mixer. The hydrolysis solution composition for each
sample and the temperature and residence time for each locaation
are shown in Table 23 below.
23 TABLE 23 CSTR-I S1 S2 S3 S4 S5 S6 Volume (gal) 10 19.9 (total
PFR) Temperature (.degree. C.) 65 80 96 97 97 97 97 Residence Time
(min) PFR Velocity = 0.69 mm/sec. Hydrolysis Solution Composition
(wt. %) Nitrile 0.13 0.03 0.02 0.01 0.01 0.01 0.02 HMBA 14 22 28 24
27 25 44 Amide 40 19 3.3 1.6 1.7 1.4 1.2 Hydrolyzate Product Color:
3 on Gardner scale
EXAMPLE 29
[0087] Nitrile at 72.00 lbs/hr was fed to the first CSTR, along
with 82.94 lbs/hr 65% sulfuric acid, giving a 1.0 acid/nitrile
molar ratio. A water feed at 41.30 lbs/hr was also intrduced into
the in-line mixer. The hydrolysis solution composition for each
sample and the temperature and residence time for each location are
shown in Table 24 below.
24 TABLE 24 CSTR-I S1 S2 S3 S4 S5 S6 Volume (gal) 10 19.9 (total
PFR) Temperature (.degree. C.) 60 81 103 103 101 101 100 Residence
Time (min) PFR Velocity = 0.69 mm/sec. Hydrolysis Solution
Composition (wt. %) Nitrile 0.19 0.01 trace trace trace trace trace
HMBA 8.8 20 38 37 39 47 54 Amide 38 22 1.4 0.59 0.34 0.33 0.06
Hydrolyzate Product Color: 6-7 on Gardner scale
EXAMPLE 30
[0088] Nitrile at 150.00 lbs/hr was fed to the first CSTR, along
with 172.79 lbs/hr 65% sulfuric acid, giving a 1.04 acid/nitrile
molar ratio. A water feed at 86.40 lbs/hr was also introduced into
the second CSTR. The hydrolysis solution composition for each
sample and the temperature and residence time for each location are
shown in Table 25 below.
25 TABLE 25 CSTR-I CSTR-II S1 S2 S3 S4 S5 S6 Volume (gal) 10 27.7
25.0 (total PFR) Temperature 65 104 100 102 102 102 102 101
(.degree. C.) Residence Time (min) PFR Velocity = 1.4 mm/sec.
Hydrolysis Solution Composition (wt. %) Nitrile 0.26 0.03 0.01
trace trace trace trace trace HMBA 8.1 35 37 39 37 37 39 38 Amide
38 3.0 1.5 0.21 0.03 0.02 0.02 0.02 Hydrolyzate Product Color:
10-11 on Gardner scale
EXAMPLE 31
[0089] Nitrile ate 150.00 lbs/hr was fed to the first CSTR, along
with 172.79 lbs/hr 65% sulfuric acid, giving a 1.02 acid/nitrile
molar ratio. A water feed at 86.40 lbs/hr was also introduced into
the second CSTR. The hydrolysis solution composition for each
sample and the temperature and residence time for each location are
shown in Table 26 below.
26 TABLE 26 CSTR-I CSTR-II S1 S2 S3 S4 S5 S6 Volume (gal) 10 27.7
25.0 (total PFR) Temperature 65 102 100 103 103 104 103 102
(.degree. C.) Residence Time (min) PFR Velocity = 1.4 mm/sec.
Hydrolysis Solution Composition (wt. %) Nitrile 0.13 0.01 0.03 0.03
0.02 0.02 0.02 0.01 HMBA 7.0 36 37 39 39 40 41 40 Amide 40 3.2 2.4
0.84 0.23 0.18 0.16 0.13 Hydrolyzate Product Color: 8-9 on Gardner
scale
EXAMPLE 32
[0090] Nitrile at 105.00 lbs/hr was fed to the first CSTR, along
with 120.95 lbs/hr 65% sufuric acid, giving a 102 acid/nitrile
molar ratio. A water feed at 60.50 lbs/hr was also introduced into
the second CSTR. The hydrolysis solution composition for each
sample and the temperature and residence time for each location are
shown in Table 27 below.
27 TABLE 27 CSTR-I CSTR-II S1 S2 S3 S4 S5 S6 Volume (gal) 10 27.7
17.5 (total PFR) Temperature 63 105 101 103 103 103 103 101
(.degree. C.) Residence Time (min) PFR Velocity = 1.0 mm/sec.
Hydrolysis Solution Composition (wt. %) Nitrile 0.36 0.03 0.01 0.01
0.01 trace trace trace HMBA 9.1 38 38 40 40 41 39 40 Amide 39 2.7
1.8 0.32 0.08 0.05 0.05 0.03 Hydrolyzate Product Color: 10-11 on
Gardner scale
EXAMPLE 33
[0091] Nitrile at 72.00 lbs/hr was fed to the first CSTR, along
with 82.94 lbs/hr 65% sulfuric acid, giving a 1.0 acid/nitrile
molar ratio. A water feed at 41.30 lbs/hr was also introduced into
the in-line mixer. The hydrolysis solution composition for each
sample and the temperature and residence time for each location are
shown in Table 28 below.
28 TABLE 28 CSTR-I S1 S2 S3 S4 S5 S6 Volume (gal) 10 19.9 (total
PFR) Temperature (.degree. C.) 60 84 103 105 105 105 103 Residence
Time (min) PFR Velocity = 0.69 mm/sec. Hydrolysis Solution
Composition (wt. %) Nitrile 0.41 0.02 0.01 0.01 0.01 0.01 0.01 HMBA
9.5 23 26 23 23 23 47 Amide 43 17 2.3 0.63 0.62 0.61 0.72
Hydrolyzate Product Color: 5-6 on Gardner scale
EXAMPLE 34
[0092] Nitrile at 90.60 lbs/hr was fed to the first CSTR, along
with 103.80 lbs/hr 65% sulfuric acid, giving a 1.03 acid/nitrile
molar ratio. A water feed at 51.90 lbs/hr was also introduced into
the in-line mixer. The hydrolysis solution composition for each
sample and the temperature and residence time for each location are
shown in Table 29 below.
29 TABLE 29 CSTR-I S1 S2 S3 S4 S5 S6 Volume (gal) 12.6 25.0 (total
PFR) Temperature (.degree. C.) 59 82 104 105 105 105 104 Residence
Time (min) PFR Velocity = 0.86 mm/sec. Hydrolysis Solution
Composition (wt. %) Nitrile 0.39 0.03 0.01 0.01 0.01 0.01 0.01 HMBA
9.1 23 33 30 31 31 38 Amide 41 18 2.0 0.92 0.79 0.71 0.76
Hydrolyzate Product Color: 8-9 on Gardner scale
EXAMPLE 35
[0093] Nitrile at 90.60 lbs/hr was fed to the first CSTR, along
with 124.80 lbs/hr 65% sulfuric acid, giving a 1.20 acid/nitrile
molar ratio. A water feed at 49.40 lbs/hr 65% was also introduced
into the in-line mixer. The sydrolysis solution composition for
each sample and the temperature and residence time for each
location are shown in Table 30 below.
30 TABLE 30 CSTR-I S1 S2 S3 S4 S5 S6 Volume (gal) 12.6 25.0 (total
PFR) Temperature (.degree. C.) 45 86 107 107 107 107 105 Residence
Time (min) PFR Velocity = 0.86 mm/sec. Hydrolysis Solution
Composition (wt. %) Nitrile 0.07 0.01 trace trace trace trace trace
HMBA 8.1 23 35 33 39 37 37 Amide 36 12 1.0 trace trace trace 0.01
Hydrolyzate Product Color: 11-12 on Gardner scale
EXAMPLE 36
[0094] Nitrile at 90.60 lbs/hr was fed to the first CSTR, along
with 124.80 lbs/hr 65% sufuric acid, giving a 1.20 acid/nitrile
molar ratio. A water feed at 49.40 lbs/hr was also intrduced into
the in-line mixer. The hydrolysis solution composition for each
sample and the temperature and residence time for each location are
shown in Table 31 below.
31 TABLE 31 CSTR-I S1 S2 S3 S4 S5 S6 Volume (gal) 12.6 25.0 (total
PFR) Temperature 58 82 105 103 103 103 101 (.degree. C.) Residence
Time (min) PFR Velocity = 0.86 mm/sec. Hydrolysis Solution
Composition (wt. %) Nitrile trace trace trace trace trace trace
trace HMBA 8.3 20 38 37 38 38 39 Amide 31 18 0.96 trace trace trace
trace Hydrolyzate Product Color: 11-12 on Gardner scale
EXAMPLE 37
[0095] Nitrile at 90.60 lbs/hr was fed to the first CSTR, along
with 103.80 lbs/hr 65% sulfuric acid, giving a 1.0 acid/nitrile
molar ratio. A wate feed at 51.90 lbs/hr was also introduced into
the in-line mixer. The hydrolysis solution composition for each
sample and the temperature and residence time for each location are
shown in Table 32 below.
32 TABLE 32 CSTR-I S1 S2 S3 S4 S5 S6 Volume (gal) 12.6 25.0 (total
PFR) Temperature (.degree. C.) 59 88 109 109 109 109 107 Residence
Time (min) PFR Velocity = 0.86 mm/sec. Hydrolysis Solution
Composition (wt. %) Nitrile 0.09 0.01 trace 0.01 trace trace 0.01
HMBA 8.8 26 38 69 38 40 41 Amide 37 13 0.30 0.02 0.01 0.01 trace
Hydrolyzate Product Color: 11-12 on Gardner scale
EXAMPLE 38
[0096] Nitrile at 105.00 lbs/hr was fed to the first CSTR, along
with 120.95 lbs/hr 65% sulfuric acid, giving a 1.0 acid/nitrile
molar ratio. A water feed at 60.50 lbs/hr was also introduced into
the in-line mixer. The hydrolysis solution composition for each
sample and the temperature and residence time for each location are
shown in Table 33 below.
33 TABLE 33 CSTR-I S1 S2 S3 S4 S5 S6 Volume (gal) 14.6 25.0 (total
PFR) Temperature (.degree. C.) 60 80 103 104 105 104 102 Residence
Time (min) PFR Velocity = 1.0 mm/sec. Hydrolysis Solution
Composition (wt. %) Nitrile 0.22 0.02 0.01 0.01 0.01 0.01 0.01 HMBA
9.5 24 39 45 45 42 41 Amide 39 21 2.5 0.19 0.20 0.28 0.11
Hydrolyzate Product Color: 8-9 on Gardner scale
[0097] As noted above, certain of the conversions obtained in a
packed column PFR were not sufficient to meet target residual amide
concentrations in the product hydrolyzate. These lower conversions
were attributable to lower reaction temperature or acid/nitrile
ratio, excessive axial backmixing, or some combination of these
factors. Based on studies conducted on reactors operated at
velocity adequate to provide a Peclet number greater than about 50,
it was determined that residual amide concentration in the
hydrolyzate could be consistently reduced to less than about 0.03%
at reaction temperatures and acid/nitrile ratios in the preferred
ranges discussed above for steady state operations. But where the
Peclet number was significantly below 50, lower conversions were
generally found unless temperature and/or acid/nitrile ratio were
increased to compensate.
[0098] To investigate the effect of velocity on back-mixing in a
packed column PFR, residence time distribution tests were conducted
at varying velocities using a pulse of salt as a tracer injected at
the bottom of a column in which tap water was caused to flow
upwardly. At the top outlet of the reactor a conductivity probe was
inserted for measuring the conductivity of the outlet flow, from
which tracer response data, in terms of salt (NaCl) concentration
vs. time, were obtained. Following conventional methods,
calculations based on the response data were made to determine the
mean residence time (the first moment of distribution), the
variance (the second moment of distribution), the Peclet number,
and the equivalent number of stirred tanks in series. For the
reactor tested, the flow rate (gpm), mean residence time (.THETA.),
dimensionless variance (.sigma..sup.2) , Peclet number (Pe), and
number of equivalent stirred tank reactors (j), are set forth in
Table 34.
34 TABLE 34 gpm .THETA. .sigma. Pe j 0.95 29.5 0.0393 50.9 25.5
0.47 66.3 0.0681 29.4 14.7 0.90 25.1 0.0749 26.7 13.4* *Based on
injection of tracer at a port spaced above the bottom of the
reactor. Adjusted for this factor, j = 20.5 and Pe = 41.
[0099] These data demonstrate a critical velocity threshold in the
range of 0.5 gpm for the packed column that was used in these
tests.
[0100] Based on kinetic calculations on the amide hydrolysis
reaction, the relationship between the number of equivalent stirred
tank reactors and the residual amide concentration was calculated.
Computations were also made of the correlation between the number
of equivalent stirred tank reactors and: (a) the ratio of
(requisite reactor length for a given degree of conversion) to
(requisite length for the same degree of conversion under perfect
plug flow conditions) (L/L.sub.p); and (b) the ratio between
(residual amide concentration for a given length of reactor) vs.
(residual amide concentration for the same length reactor under
perfect plug flow conditions) (C/C.sub.p). These calculations are
set forth in Table 35.
35 TABLE 35 j L/L.sub.p C/C.sub.p C (% amide out) 15 1.236 2.66
0.0581% 20 1.177 2.25 0.0491 25 1.141 2.00 0.0436 30 1.178 1.83
0.0399 40 1.088 1.62 0.0353 .infin. 1.000 1.00 0.0218
[0101] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and have been described herein in
detail. It should be understood, however, that it is not intended
to limit the invention to the particular form disclosed, but on the
contrary, the intention is to cover all modifications, equivalents
and alternatives falling within the spirit and scope of the
invention as defined by the appended claims.
* * * * *