U.S. patent application number 09/925730 was filed with the patent office on 2002-03-28 for process for the preparation of epsilon-caprolactam.
Invention is credited to Agterberg, Frank P.W., Guit, Rudolf P.M, Haasen, Nicolaas F..
Application Number | 20020038022 09/925730 |
Document ID | / |
Family ID | 8239891 |
Filed Date | 2002-03-28 |
United States Patent
Application |
20020038022 |
Kind Code |
A1 |
Agterberg, Frank P.W. ; et
al. |
March 28, 2002 |
PROCESS FOR THE PREPARATION OF EPSILON-CAPROLACTAM
Abstract
Process for the preparation of .epsilon.-caprolactam comprising
treating 6-aminocaproic acid, 6-aminocaproate ester,
6-aminocaproamide, oligomers or polymers of these compounds or
mixtures comprising at least two of these compounds in a
cyclization reactor in the presence of superheated steam in which a
gaseous product stream comprising .epsilon.-caprolactam, lights and
heavies is obtained, wherein the product stream, after condensation
and at least partial removal of water and lights, is split into a
.epsilon.-caprolactam stream and a heavies stream containing
heavies and .epsilon.-caprolactam and the heavies stream is
recycled to a cyclization reactor.
Inventors: |
Agterberg, Frank P.W.;
(Nieuwstadt, NL) ; Haasen, Nicolaas F.; (Sittard,
NL) ; Guit, Rudolf P.M; (Maastricht, NL) |
Correspondence
Address: |
PILLSBURY WINTHROP LLP
1600 TYSONS BOULEVARD
MCLEAN
VA
22102
US
|
Family ID: |
8239891 |
Appl. No.: |
09/925730 |
Filed: |
August 10, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09925730 |
Aug 10, 2001 |
|
|
|
PCT/NL00/00068 |
Feb 3, 2000 |
|
|
|
Current U.S.
Class: |
540/538 |
Current CPC
Class: |
C07D 201/08
20130101 |
Class at
Publication: |
540/538 |
International
Class: |
C07D 223/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 12, 1999 |
EP |
99200411.9 |
Claims
1. Process for the preparation of .epsilon.-caprolactam comprising
treating 6-aminocaproic acid, 6-aminocaproate ester,
6-aminocaproamide, oligomers or polymers of these compounds or
mixtures comprising at least two of these compounds in a
cyclisation reactor in the presence of superheated steam in which a
gaseous product stream comprising .epsilon.-caprolactam, steam,
lights and heavies is obtained, characterized in that the product
stream, after condensation and at least partial removal of water
and lights, is split into a .epsilon.-caprolactam stream and a
heavies stream containing heavies and .epsilon.-caprolactam and the
heavies stream is recycled to a cyclisation reactor.
2. Process according to claim 1, characterized in that the heavies
stream is recycled to the cyclisation reactor from which the
product stream is derived.
3. Process according to any one of claims 1-2, characterized in
that the condensation and the at least partial removal of water,
lights and heavies from the product stream is conducted in the
following steps: a) the product stream is fed to a partial
condensation unit (2), and split in a top stream comprising steam
(2t) and a liquid bottom stream (2b) comprising
.epsilon.-caprolactam, water, lights and heavies; b) the bottom
stream (2b) is fed to a distillation column (3) of which the top
stream (3t) is mainly water and the bottom stream (3b) comprises
.epsilon.-caprolactam, lights and heavies; c) the bottom stream
(3b) is fed to a vacuum distillation column (4) of which the top
stream (4t) is mainly lights and the bottom stream (4b) comprises
.epsilon.-caprolactam and heavies; d) the bottom stream (4b) is fed
to a vacuum distillation column (5) of which the top stream (5t) is
the .epsilon.-caprolactam stream and the bottom stream (5b) is the
heavies stream.
4. Process according to any one of claims 1-3, characterized in
that the .epsilon.-caprolactam stream is purified using a
crystallization process.
5. Process according to claim 4, characterized in that the
purification of .epsilon.-caprolactam is conducted in the following
steps: e) the caprolactam stream (5t) is fed as a liquid
.epsilon.-caprolactam stream into a crystallizer (6), in which
conditions are set such that .epsilon.-caprolactam crystals and a
mother liquid are formed (stream (6a)), f) the stream (6a) from the
crystallizer is fed to a separator (7), and split to purified
.epsilon.-caprolactam (7a) and a mother liquid (7b), g) the mother
liquid (7b) is recycled to the crystallizer (6).
6. Process according to claim 5, characterized in that a part of
the mother liquid (7b) is purged and the purge is recycled to the
distillation column (3) or to the distillation column (4).
7. Process according to any one of claims 5-6, characterized in
that the separator (7) is a crystal wash column.
8. Process according to claim 7, characterized in that the crystal
wash column is a hydraulic wash column in which the purified
.epsilon.-caprolactam crystals are removed from the crystal bed,
subsequently molten by a heat exchanger and a part of the molten
.epsilon.-caprolactam is recycled to the washcolumn as washing
liquid.
9. Process according to any one of claims 1-8, characterized in
that, polycaprolactam processing waste, polycaprolactam carpet wast
and/or polycaprolactam extraction wash water is treated in the
cyclisation reactor.
Description
[0001] The invention relates to a process for the preparation of
.epsilon.-caprolactam comprising treating 6-aminocaproic acid,
6-aminocaproate ester, 6-aminocaproamide, oligomers or polymers of
these compounds or mixtures comprising at least two of these
compounds in a cyclisation reactor in the presence of superheated
steam in which a gaseous product stream comprising
.epsilon.-caprolactam, steam, lights and heavies is obtained.
[0002] Compounds having a higher boiling point than
.epsilon.-caprolactam are designated as heavies in this
specification. Examples are 6-aminocaproic acid, 6-aminocaproamide,
oligomers of these compounds, .epsilon.-caprolactam cyclic
oligomers N-substituted or C-substituted lactams and/or amides.
Compounds having a lower boiling point than .epsilon.-caprolactam
are designated as lights in this specification. Examples are
N-methyl-.epsilon.-caprolactam, hexanoic acid, 5-hexenoic acid,
valeric acid and valeramide.
[0003] Such a process is described in WO-A-9837063. This patent
publication describes a process to prepare .epsilon.-caprolactam by
treating 6-aminocaproic acid, 6-aminocaproate ester and/or
6-aminocaproamide with superheated steam at a temperature of
between 250-400.degree. C. and a pressure of between 0.5 and 2 MPa.
The crude .epsilon.-caprolactam obtained still contains impurities
and requires further purification. The crude .epsilon.-caprolactam
product stream obtained in the cyclisation process as described in
WO-A-9837063 also contains lights and heavies. The majority of
these lights and heavies need first to be removed in order to make
efficient purification of .epsilon.-caprolactam possible in the
subsequent purification steps. Lights and heavies are usually
separated from the .epsilon.-caprolactam product stream with
distillation. A disadvantage of the separation of the heavies from
the .epsilon.-caprolactam product stream is that it is almost
impossible or very difficult to quantitatively separate
.epsilon.-caprolactam from the heavies without degradation of
.epsilon.-caprolactam and/or fouling of the separation equipment.
Another disadvantage is that the valuable .epsilon.-caprolactam
precursors are not recovered. For a commercially interesting
process it is advantageous to recover the greatest part of
.epsilon.-caprolactam and .epsilon.-caprolactam precursors from the
heavies before the heavies are disposed off.
[0004] An object of the invention is to provide a simplified
process for the preparation of .epsilon.-caprolactam. Still another
object is to get a high yield of .epsilon.-caprolactam.
[0005] These objects are achieved in that the product stream, after
condensation and at least partial removal of water and lights is
split into a .epsilon.-caprolactam stream and a heavies stream
containing heavies and .epsilon.-caprolactam and the heavies stream
is recycled to a cyclisation reactor.
[0006] It has been found that with the process according to the
invention high yields to .epsilon.-caprolactam can be achieved.
Another advantage is that the separation of .epsilon.-caprolactam
from the heavies does not need to be quantitatively. In the process
according to the invention the distillative separation of
.epsilon.-caprolactam and heavies can be performed at a less
reduced pressure and/or temperature compared to a process in which
there is no recycle of the heavies stream for obtaining comparable
yields of .epsilon.-caprolactam.
[0007] Preferably the heavies stream is recycled to the cyclisation
reactor from which the product stream is derived. This is
advantageous from an economical/investment point of view because no
additional cyclisation reactor is needed.
[0008] Before recycling the heavies stream to the cyclisation
reactor, the heavies stream is optionally first fed to another
separation unit in which the heavies stream is further split into a
.epsilon.-caprolactam stream and a second heavies stream. This
second heavies stream is subsequently recycled to the cyclisation
reaction. Examples of possible separation units are extractors and
stripper columns. A preferred separation unit is a stripper column.
More preferably a gaseous stream containing steam is fed to the
stripper column to strip .epsilon.-caprolactam from the heavies
stream resulting in a gaseous .epsilon.-caprolactam containing top
stream. The gaseous .epsilon.-caprolactam containing top stream can
easily be integrated in the purification section (described below)
of the product stream from the cyclisation reactor.
[0009] With a cyclisation reactor is meant a reactor in which an
open-chain compound is converted into a compound that contains a
ring, a process called cyclisation. In the process according to the
invention 6-aminocaproic acid, 6-aminocaproate ester and/or
6-aminocaproamide is cyclised into .epsilon.-caprolactam.
[0010] The process according to the invention can be performed in a
reactor which is provided with an inlet for the starting
compound(s), an outlet for the steam/.epsilon.-caprolactam product
and means for supplying steam such that the steam is contacted with
the starting material. The reactor is optionally equiped with a
heating device and optionally with a mixing device. To this reactor
the starting compound and the steam can be continuously fed. A
possible reactor is a fluidized bed reactor containing inert
particles in which the bed is kept fluidized by the steam. Another
example of a reactor is a horizontal tube reactor having a rotating
axis on which axis means for mixing and/or transport are present.
Also means are possible present which prevent fouling of the
interior vessel wall and which promote an optimal steam/substrate
contact area for mass-transfer.
[0011] Examples of suitable cyclisation reactors are a packed
tower-type reactor, one or multiple staged bubble columns or a
multi-tube reactor. In case the cyclisation reactor consists of two
or more reactor vessels in series, the heavies stream or bottom
stream from the stripper is preferably fed to the last reactor
vessel.
[0012] A possible process according to the invention is
schematically represented in FIG. 1 +L.
[0013] In the cyclisation reactor (1) the gaseous stream (1a)
comprising .epsilon.-caprolactam, steam, lights and heavies is
obtained.
[0014] The starting mixtures comprising 6-aminocaproic acid,
6-aminocaproate ester, 6-aminocaproamide, oligomers of these
compounds and/or polymers of these compounds can be obtained by
various processes. For example in U.S. Pat. No. 4,730,040 a process
is described in which an aqueous mixture is obtained containing
6-aminocaproic acid and some .epsilon.-caprolactam starting from
5-formylvalerate ester. Further in EP-A-729943 a process is
described in which an aqueous mixture is obtained containing
6-aminocaproic acid, 6-aminocaproamide and .epsilon.-caprolactam
also starting from a 5-formylvalerate ester. U.S. Pat. No.
5,068,398 describes a process in which an aqueous mixture is
obtained containing 6-aminocaproate ester and some
.epsilon.-caprolactam starting from a 5-formylvalerate ester.
[0015] Other examples of starting mixtures which can be used in the
process according to the invention are polycaprolactam processing
waste, polycaprolactam carpet waste and/or polycaprolactam
extraction wash water.
[0016] The starting compound or mixture of starting compounds which
are obtainable by the above described processes, are preferably
contacted with the superheated steam as a liquid, for example as a
melt.
[0017] Polycaprolactam waste is preferably fed to the reactor as a
melt. This feeding may be achieved by using an extruder, gear pump,
or other means known in the art.
[0018] Starting mixtures can also be obtained starting from
6-aminocapronitrile as for example described in WO-A-9837063.
[0019] The cyclisation is preferably performed as described in
WO-A-9837063.
[0020] The condensation and at least partial removal of water,
lights and heavies from the product stream can be conducted in the
following steps:
[0021] a) the product stream is fed to a partial condensation unit
(2), and split in a top stream comprising steam (2t) and a liquid
bottom stream (2b) comprising .epsilon.-caprolactam, water, lights
and heavies;
[0022] b) the bottom stream (2b) is fed to a distillation column
(3) of which the top stream (3t) is mainly water and the bottom
stream (3b) comprises .epsilon.-caprolactam, lights and
heavies;
[0023] c) the bottom stream (3b) is fed to a vacuum distillation
column (4) of which the top stream (4t) is mainly lights and the
bottom stream (4b) comprises .epsilon.-caprolactam and heavies;
[0024] d) the bottom stream (4b) is fed to a vacuum distillation
column (5) of which the top stream (5t) is the
.epsilon.-caprolactam stream and the bottom stream (5b) is the
heavies stream.
[0025] The condensation of the product stream (step a)) is
preferably performed at a temperature of 80-200.degree. C., more
preferably at a temperature of 100-170.degree. C.
[0026] The distillation in step b) is for example performed at a
temperature of 60-160.degree. C., preferably at a temperature of
80-140.degree. C.
[0027] The distillation in step c) and d) is preferably performed
at a pressure lower than 10 kPa, more preferably at a pressure
lower than 5 kPa. The temperature of the distillation in step c)
and d) is preferably between 110.degree.-170.degree. C., more
preferably between 120-150.degree. C.
[0028] Preferably a part of the residue in the cyclisation reactor
and/or a part of the heavies stream (5b) is purged (stream (5c))
and the rest is recycled to a cyclisation reactor, preferably to
the cyclisation reactor from which the product stream is
derived.
[0029] The .epsilon.-caprolactam streams resulting from the process
according to the invention can be purified according to
conventional techniques. Advantageously the caprolactam is purified
by a crystallisation process.
[0030] The purification of .epsilon.-caprolactam by crystallisation
can be conducted in the following steps:
[0031] e) the .epsilon.-caprolactam stream (5t) is fed as a liquid
.epsilon.-caprolactam stream into a crystallizer (6), in which
conditions are set such that .epsilon.-caprolactam crystals and a
mother liquid are formed (stream (6a)),
[0032] f) the stream (6a) from the crystallizer is fed to a
separator (7), and split to purified .epsilon.-caprolactam (7a) and
a mother liquid (7b),
[0033] g) the mother liquid (7b) is recycled to the crystallizer
(6).
[0034] Preferably, a part of the mother liquid (7b) is purged and
the purge is recycled to the distillation column (3) or to the
distillation column (4).
[0035] The crystallizer (6) is operated such that crystallization
of .epsilon.-caprolactam occurs through cooling. In the
crystallizer (6) relatively pure .epsilon.-caprolactam crystals are
formed (solid phase) and a mother liquid, which comprises
.epsilon.-caprolactam, impurities and optionally solvent (liquid or
melt phase). The solid phase in the crystallizer can have a
different appearance, depending on the way the crystallization is
performed. The crystallization in the crystallizer (6) can be
performed for example either by cooling via a heat exchanging
surface (suspension or layer crystallization) or by adiabatic
cooling by evaporation of part of the contents of the crystallizer,
for instance a solvent, under reduced pressure (crystallization in
suspension). The method of crystallization induced by reduced
pressure cooling is preferred, since no crystallization on inner
surfaces of the crystallizer occurs. In reduced pressure cooling
the condensed vapour from the crystallizer may or may not be
returned, totally or partially to the contents of the crystallizer.
Preferably the crystallizer is operated by evaporating the solvent
under reduced pressure.
[0036] Preferably solvent is present in the mixture in the
crystallizer, although crystallization can also be conducted
without solvent. Many solvents are suitable. Examples of suitable
solvents are water, alkanes (like n-hexane, n-heptane, iso-octane,
cyclohexane), alcohols (like methanol, ethanol, n-propanol,
butanol), aromatic hydrocarbons (like benzene, toluene, o-xylene,
m-xylene, p-xylene), ammonia, chlorinated hydrocarbons (like
tetrachloromethane, chloroform or ethylchloride), ketones like
acetone or methylethyl keton) and esters (like ethyl acetate).
Preferably water and aromatic hydrocarbons are used as solvent,
since these solvents give large crystals. Most preferred as solvent
is water. The solvent will act as a freezing point depressor for
the melt in the crystallizer.
[0037] The concentration of solvent in the melt in the crystallizer
is dependent on the solvent, the amounts of impurities in the feed
.epsilon.-caprolactam and the way the cooling in the crystallizer
is performed. With the preferred solvent water and reduced pressure
cooling the concentration of water in the melt is usually below 20
weight %, preferably 1-15 weight % and more preferred 2-10 weight
%.
[0038] A solvent stream may be directly fed to the crystallizer
and/or is mixed with the liquid crude .epsilon.-caprolactam feed
stream prior to being fed to the crystallizer.
[0039] The temperature of the mixture in the crystallizer is
dependent on the presence and concentration of solvent and
impurities in the mixture, but at most 69.degree. C., being the
melting temperature of pure .epsilon.-caprolactam. Preferably the
temperature of mixture in the crystallizer is 20-69.degree. C.,
more preferable 35-67.degree. C. The crystallizer can be operated
in batch or in continuous mode. Preferably the crystallizer is
operated in a continuous mode.
[0040] The separator (7) may be any separator that is capable of
separating crystals from the mother liquid, e.g. a filter working
under forces like gravity, reduced pressure, increased pressure or
a centrifuge. Various types of filters and centrifuges can be used.
In these separators during or after separation washing of the
crystals is possible and preferred. The separator (7) is for
instance a horizontal vacuum belt filter. This type of solid-liquid
separator has an excellent washing efficiency. Another example of a
separator is a crystal washcolumn, in which the crystals are
compacted into a packed bed which bed is transported with gravity,
hydraulic pressure or a mechanical means. An example of a crystal
washcolumn in which the crystal bed is transported with a
mechanical means is a Niro screw-type wash column system as for
example described in `European Chemical News`, Jun. 30-Jul. 6,
1997, page 23. A crystal washcolumn has the advantage that an
effective separation of the .epsilon.-caprolactam crystals from the
mother liquid is achieved and simultaneously very effective washing
of the crystals is performed. A more preferred crystal washcolumn
is the so-called TNO-Thijssen hydraulic wash column as described in
"Improved procedures for separating crystals for the melt", D.
Verdoes, G. J. Arkenbout et al., Applied Thermal Engineering, 17
(8-10), 1997, 879-888.
[0041] In the TNO-Thijssen hydraulic wash column, the purified
.epsilon.-caprolactam crystals are removed from the crystal bed and
subsequently molten by a heat exchanger. A part of the molten
.epsilon.-caprolactam crystals is recycled to the crystal
washcolumn as washing liquid. The .epsilon.-caprolactam washing
liquid finally crystallizes on the surface of .epsilon.-caprolactam
crystals present in the so-called washfront. This is advantageous
because, with a minimum quantity of washing liquid, a very
effective separation of the .epsilon.-caprolactam crystals from the
mother liquid and simultaneously a high washing efficiency of the
.epsilon.-caprolactam crystals is achieved. In the TNO-Thijssen
hydraulic wash column the purified .epsilon.-caprolactam is
obtained as a liquid melt (stream 7a).
[0042] Advantageously the purified .epsilon.-caprolactam (7a) from
the separator (7) is further purified in a second crystallization
step (crystallizer (8)) followed by a second separation/washing
step (separator (9)) of the .epsilon.-caprolactam crystals. This
second crystallization step may be performed in a similar way as
the first crystallization step. The separation and effective
washing of the .epsilon.-caprolactam crystals from the mother
liquid can be performed in a solid-liquid separation equipment as
described for separation/washing step (7). Preferably stream (8a)
leaving from the second crystallizer (8) comprising
.epsilon.-caprolactam crystals and a mother liquid, is fed to a
second crystal wash column (9) and split to a mother liquid and
purified .epsilon.-caprolactam. The mother liquid is recycled to
crystallizer (8). Preferably a part of the mother liquid is
recycled to the first crystallizer (6). If necessary additional
crystallization steps and separation/washing steps are
possible.
[0043] The invention will be elucidated by the following examples,
however these are not intended to limit the scope of the invention
in any way.
EXAMPLE I
[0044] A 500 ml autoclave having a turbine mixer was continuously
fed with a concentrated organic substrate mixture of
.epsilon.-caprolactam precursors and steam. The composition of the
organic feed mixture was (wt %) 33.9% of .epsilon.-caprolactam,
10.9% of 6-aminocaproic acid, 38.3% of 6-aminocaproic amide, 13.6%
of Nylon-6-oligomers and 3.3% of water. The autoclave was initially
charged with 61 grams of the same organic feed mixture. After
flushing with nitrogen and adjusting the pressure valve such that
the pressure in the reactor was 1.2 MPa, the temperature was raised
to 300.degree. C. At the same time the continuous feed of the
organic mixture was started at a rate of 38 g/hr and the steam feed
at a rate of 222 g/hr. The .epsilon.-caprolactam content of the
product phase was continuously analyzed. After approximately 10
hours a steady-state was reached at a .epsilon.-caprolactam
concentration in the condensate of 12.9 wt %. The reactor contents
at steady state amounted to approximately 100 grams, present as
oligomers of .epsilon.-caprolactam and 6-aminocaproic acid.
[0045] After 29 hours the feed rate was increased to 57 g/hr of the
organic feed and 333 g/hr of steam. At that point of the continuous
run the overall conversion of the .epsilon.-caprolactam precursors
fed to the reactor was approximately 91%.
[0046] After another 10 hours, the .epsilon.-caprolactam
concentration in the condensed steam was 12.9 wt % indicating that
steady-state was reached again. The reactor contents in the new
steady-state conditions was approximately 140 grams. The reaction
was continued for a total of 54 hrs. The overall conversion of
.epsilon.-caprolactam precursors fed in total was 94.4% at the end
of the run.
[0047] Subsequently the substrate feed was stopped and the run was
continued in batch-mode at a steam-feed of 390 g/hr. After 7 hours
the condensed steam contained approximately 120 gram of
.epsilon.-caprolactam. The autoclave contained 7 grams of residue,
corresponding to an overall conversion of 99.7% of the organic
feed. Overall 17700 gram of an aqueous product mixture was obtained
which contained approximately 12.9 wt % .epsilon.-caprolactam.
Subsequently the excess of water was evaporated using a rotary
evaporator at a pressure of 10.5 kPa and a water bath temperature
of 60.degree. C., yielding 3130 gram 72.8 wt % aqueous
.epsilon.-caprolactam solution. The composition of this product was
analyzed using HPLC and GC-MS methods. Excluding water, the product
contained 98.0 wt % .epsilon.-caprolactam. Approximately 0.9 wt %
of light impurities and 1.1 wt % of heavy impurities were
present.
[0048] Subsequently residual water, lights and heavies were
successively removed by batch distillation of the product in three
separate distillation stages using a laboratory vigreux column.
[0049] During the first stage mainly water was removed at a column
pressure that was gradually reduced from 8 to 0.2 kPa and the
bottom temperature increased from 62 to 85.degree. C. In the second
stage the lights fraction was distilled off at a column pressure of
0.3 kPa and a bottom temperature that gradually increased from 91
to 122.degree. C. At the end of this stage approximately 3% of the
.epsilon.-caprolactam was collected in the light fractions.
[0050] In the third stage 2150 gram (95.1%) of the
.epsilon.-caprolactam was distilled over the top at a pressure of
0.1 kPa and a bottom temperature gradually raising from 120 to
140.degree. C. At the end of this stage 68 grams of residue was
collected. According to the mass-balance 1.7% of the original
amount of .epsilon.-caprolactam ended up in this heavies residue,
corresponding to approximately 60% of the total weight of this
residue fraction. Subsequently, the heavies residue was used as
substrate in the following batch experiment:
[0051] A 500 ml autoclave having a turbine mixer was filled with
the heavies residu. The autoclave was substantially flushed with
nitrogen and a pressure valve was adjusted such that the pressure
in the reactor was maintained at 1.2 MPa. When the temperature
reached 300.degree. C. a steam flow was started at a rate of 300
g/hr. The steam containing .epsilon.-caprolactam leaving the
reactor was condensed and analyzed. After 5 hours the condensed
steam contained approximately 62 grams of .epsilon.-caprolactam,
which corresponds to a practically complete conversion of
.epsilon.-caprolactam precursors to .epsilon.-caprolactam.
[0052] The resulting approximately 2 grams of residue did not yield
any more caprolactam upon extended reaction.
EXAMPLE II
[0053] Example I was repeated, except that the feed consisted of
nylon-6 spin-chips. 100.1 grams of nylon-6 spin-chips (type GL
1030, size 2.0.times.3.0 mm (d.times.L)) was charged to the
autoclave. The autoclave was subsequently flushed with nitrogen and
a pressure valve was adjusted such that the pressure in the reactor
was maintained at 1.2 MPa. When the temperature reached 300.degree.
C. a steam flow was started at a rate of 260 g/hr. The steam
containing .epsilon.-caprolactam leaving the reactor was condensed
and analyzed. After 5 hours the condensed steam contained a total
of 98 g .epsilon.-caprolactam, corresponding to 98% yield. The
autoclave was virtually empty on visual inspection.
* * * * *