Synthesis of ε-caprolactam from cyclohexanone oxime using zeolites Hβ, HZSM-5, and alumina pillared montmorillonite

Article abstract of DOI:10.1002/jccs.200100025

The Beckmann rearrangement of cyclohexanone oxime (CHO) to ε-caprolactam (ε-C) was studied in a plug flow reactor at 300-400°C under atmospheric pressure by using Hβ, ZSM-5, and alumina pillared montmorillonite. With Hβ(X)Y zeolites, raising the SiO₂/Al₂O₃ molar ratio (X) results in the enhancement of catalyst acid strength with concomitant decrease of the total acid amount. Increasing the calcination temperature (Y) causes remarkable diminution of catalyst surface area, acid strength, and acid amount. A similar trend was found for AIPMY catalysts. In the reaction of CHO, the initial catalytic activity correlates well with the total acid amount of various catalysts except for Hβ(10)Y (Y > 600°C). The reaction proceeds on both Broensted and Lewis acid sites and the catalyst deactivation most likely occurs at the strong Broensted acid sites. The effect of solvents in the feed on the catalytic results was also investigated; it was found that polar solvents such as ethanol or n-butanol give high ε-C yield and longer catalyst lifetime. In the reaction of CHO/C₂H₅OH over Hβ(10)800 at 400°C and W/F 74.6 g·h/mol, the CHO conversion and ε-C yield remain 100% and 92%, respectively, for at least 20 h time-on-stream. The reaction paths and the mechanism for ε-C formation are proposed.

Full text of DOI:10.1002/jccs.200100025

JournaloftheChineseChemicalSociety, 2001, 48, 137-144
137
Synthesis of -Caprolactam from Cyclohexanone Oxime Using Zeolites
H ,HZSM-5,andAluminaPillaredMontmorillonite
Kuang-Hao Ouyang (
), Chih-Wei Chen (
) and An-Nan Ko* (
)
DepartmentofChemistry,TunghaiUniversity,Taichung,Taiwan,R.O.C.
The Beck mann re ar range ment of cyclohexanone oxime (CHO) to -caprolactam ( -C) was stud ied in a
plug flow re ac tor at 300-400 CunderatmosphericpressurebyusingH , ZSM-5, and alu mina pil lared mont-
morillonite.WithH (X)Y zeolites, rais ing the SiO2/Al2O3 molarratio(X)resultsintheenhancementofcata-
lyst acid strength with con com i tant de crease of the to tal acid amount. In creasing the cal cinationtemperature
(Y)causesremarkablediminutionofcatalystsurfacearea,acidstrength,andacidamount.Asimilartrendwas
foundforAlPMYcatalysts.InthereactionofCHO,theinitialcatalyticactivitycorrel ates well with the to tal
acid amount of var i ous cat a lysts ex cept for H (10)Y (Y 600 C). The re ac tion pro ceeds on both Brönsted
andLewisacidsitesandthecatalystdeactivationmostlikelyoccursatthestrongBrönsted acid sites. The ef-
fectofsolventsinthefeedonthecatalyticresultswasalsoinvestigated;itwasfoundthatpolarsolventssuch
as eth a nol or n-butanol give high -Cyieldandlongercatalystlifetime.InthereactionofCHO/C2H5OH over
H (10)800 at 400 C and W/F 74.6 g h/mol, the CHO con ver sion and -C yield re main 100% and 92%, re-
spec tively, for at least 20 h time-on-stream. The re ac tion paths and the mech a nism for -C for ma tion are pro-
posed.
INTRODUCTION
As an important raw ma te rial for 6-nylon, -capro-
hours.7 B2O3/ZrO2 was re ported to be a highly ac tive and se-
lectivecatalystforthesynthesisof -C at 300-320 Cduring
8 h time-on-stream; the -Cyieldwasfoundtoassociatewith
thenumberofintermediatestrongacidsites.8 Borate-pillared
lay ered dou ble hy drox ides (LDH) were shown to ex hibit a
lower de cay rate than pure boria and was at trib uted to the sta-
bi li za tion of boria in the interlayer of LDH.10 Thereaction
paths and ki net ics in the gas phase re ar range ment of CHO
over HNaY were also stud ied; Brönsted sites of strength pka
1.5 were pro posed to be the ac tive sites re spon si ble for the
formationof -C.11 For ultrastable HY ze o lite, dif fer ent de-
cay mod els have been dis cussed andtherelatedkinetic pa-
ram e ters were cal cu lated ac cord ing to the time-on-stream
theory.12 H-USY cat a lysts with SiO2/Al2O3 ra tios of 27 and
62 were re ported to give ex cel lent cat a lytic re sults by us ing
1-hexanolasdiluent.13 On the other hand, for bo ron MFI ze o-
lite, re duc ing tem per a ture and pres sure re sulted in an en-
hance ment of -C se lec tiv ity at the ex panse of the cat a lyst
lifetime.Nevertheless,apromotiveeffectonthecatalyststa-
bil ity oc curs with ad di tion of wa ter up to 6 mol per mol
CHO.18 On the highly si li ceous ZSM-5 ze o lite, however,
silanolnestsontheexternalsurfacewereproposedtobemost
suitablefortheCHOrearrangement.24 The ef fect of sol vent
dur ing CHO re ac tion on silicalite-1 has also been stud ied;
ethanolandmethanolwerefoundtobethemosteffectivesol-
vents.25 Com paring the re ac tion over H-MCM-41 and H-
FSM-16 dur ing ini tial time-on-stream (6 h), H-MCM-41 ex-
lactam ( -C) is com mer cially made by a Beck mann re ar-
range ment of cyclohexanone oxime (CHO). Tra di tionally,
theprocessutilizesconcentratedsulfuricacidcatalystand
wascarriedoutintheliquidphase. Thedisadvantagesofthis
methodincludecorrosionhazards,safetyproblemsandasub-
stantialamountofammoniumsulfateformedduringneutral-
izationofoleum. Asaresult, greatefforthasbeenfocusedon
-C syn the sis via va por-phase re ac tion over solid-acid cat a-
lystsduringthepastthreedecades.1 Avarietyofdifferentcat-
alystshavebeeninvestigated, viz. silica-alumina,2tantalum
oxide,3 sil ica-supported boria,4 alu mina-supported boria or
other species,5-7 zirconia-supported boria,8 metal ox-
ide-supportedsilica,9 borate-pillaredlayereddoublehydrox-
ides10 as well as zeolites such as HY, 11-14 Pd/Y,14 ZSM-5,15-17
[B]-ZSM-5,18,19 Beta,20-22 [Al]-and [B]-Beta,23 silicalite-124,25
andmesoporousmolecularsieves.26-28
For the reaction of CHO over silica- or alumina-
supportedboria,catalystspreparedbyvapordecomposition
us ing ethyl bo rate as agent were found to ex hibit better cat a-
lyticperformancethanthatbytheconventionalimpregnation
method, pre sum ably due to the more uni form dis per sion of
B2O3 onto SiO2 or Al2O3 for the for mer method.4,6 For B2O3/
Al2O3, the catalystactivitydecreasedwithtime-on-stream,
whereas -Cselectivityremainedstableduringthefirstfive

138 J. Chin. Chem. Soc., Vol. 48, No. 2, 2001
Ouyang et al.
hib ited a better per for mance us ing 1-hexanol as dil u ent.26
How ever, the -C se lec tiv ity of FSM-16 can be im proved by
supportingAl2O3, ZnO and CdO.27 Excellentcatalystperfor-
mance was ob served on Al-MCM-41 by us ing eth a nol in the
feed; the highly ef fi cient ca tal y sis is at trib uted to the large
sur face area, uni form mesopores as well as the weak and me-
diumacidityofthecatalyst.28
and HZSM-5 zeolites with SiO2/Al2O3 mol ra tio of X that was
cal cined at Y C for 6 h. Alu mina pil lared mont mo ril lo nite
was pre pared as fol lows: so dium hy drox ide so lu tion was
added dropwise at a rate of 2 mL/min into a 0.1 M alu mi num
chloridesolutiontoobtainafinalmolarratioOH-/Al of 2.0.
The mix ture was then aged at 60 C for 12 h. Con se quently,
theresultantsolutionAcontainedaluminumpolyoxycation
[Al13O4(OH)24(H2O)127 +].35 Sodiummontmorillonite(Na-M)
clay (10 g, Kunipia-F, Kunimine In dus tries Co., Ltd.) was
added into de-ionized wa ter (100 mL) and then stirred for 24
h. Sub se quently, a de sired amount (4 mmol Al/g Na-M) of so-
lu tion A was added into this so lu tion. The mix ture so lu tion
was stirred for 6 h, fil tered and washed with de-ionized wa ter.
The solid sam ple was then dried at 110 C for 12 h and cal-
cined at Y C (Y 300, 400or500)toobtainaluminapillared
montmorillonite(AlPMY).
Alu mi num con tain ing Beta ze o lite is known as an ef-
fectivecatalystfortheBeckmannrearrangementofCHOus-
ing higher al co hols as sol vents; how ever, the dealumination
of Beta zeolite tends to deteriorate the catalytic per for-
mance. 20 Poor cat a lytic re sults were ob tained us ing ben zene
assolventforthesamereaction.21 Intheliquidphasereaction
over the Beta ze o lite with out silanol groups but con tain ing
frame work Al, very high con ver sion and se lec tiv ity were
found.22 With [Al]- and [B]-Beta zeolites, both cat a lysts ex-
hib ited very high ini tial ac tiv ity; how ever, this was also ac-
companiedbyrapiddeactivationandthuscatalystregenera-
tionwasnecessaryforindustrialapplications.23 The Beta ze-
o lite dis plays both the Brönsted and the Lewis acid ity. This
has been shown to de pend strongly on the cal ci na tion con di-
tions and the pre treat ment meth ods in a va ri ety of re ac tions
such as the Meerwein – Ponndorf – Verley re duc tion of ke-
tones and Friedel Crafts re ac tions.29-32
Up to now, dif fer ent re sults have been re ported on the
natureofactivesitesthatareresponsiblefortheformationof
-C from CHO, such as strong Brönsted acid ity,11 weak or in-
termediate Brönsted acid sites,7,33,34 and neutral silanol
groups on the ex ter nal sur face of the zeolites.16 However,the
possiblecauseforcatalystdeactivationstillremainsunclear.
In this work, the Beck mann re ar range ment of CHO to -C
wasstudiedusingzeolitesH ,HZSM-5andaluminapillared
montmorillonite(AlPM).ByutilizingH and HZSM-5 with
differentSiO2/Al2O3 mol ra tios as well as var i ous cat a lyst
calcinationtreatments,thenatureofcatalystacidity,viz.acid
type, acid strength, and acid amount, was al tered and its ef-
fect on the cat a lytic re sult was ex am ined. The in flu ence of
sol vents in the feed on the cat a lyst per for mance was also
studied.Inaddition,thereactionpathsandthemechanismfor
-Cformationareproposed.
Catalyst Characterization
The XRD pow der pat terns of var i ous sam ples were ob-
tained by an X-ray diffractometer using CuK radiation
(Shimadzu XD-5). The BET sur face ar eas of cat a lysts were
mea sured with a sorp tion an a lyzer (Quantachrome Quantasorb).
The cat a lyst acid ity was ob tained from the peak area of tem-
perature-programmeddesorptionplots, inassociationwith
calibrationdataasdescribedintheliterature.36 The na ture of
acidic sites on H ze o lite was de ter mined with a FT-IR spec-
trometer(Perkin-Elmer2000)usingaMCTmid-IRdetector.
The H sam ple was pressed into a disk (~20 mg cm-2 ).Before
adsorptionwithpyridinevapor, thewaferwasevacuatedat1
10-4 torr and 400 C for 2 h. The FT-IR spec tra were re-
cordedatroomtemperature.
CatalyticReaction
Thecatalyticreactionwasperformedat300-400 C un-
der at mo spheric pres sure by us ing a plug flow re ac tor. Prior
tothereaction,thecatalystwasactivatedwithflowingdryair
(60 mL/min) at 400 C for 2 h and then cooled to the re ac tion
tem per a ture with ni tro gen gas (99.99%, 60 mL/min). The
feed was pre pared by dis solv ing CHO in var i ous sol vents (1
mol/l), viz. benzene, cyclohexane, methanol, ethanol, n-
butanol, and butyl ether. It was in jected via a microfeeder
(Stoelting) into the re ac tor (1 cm I. D. 34 cm), con tain ing
0.1~0.6gcatalystsample.Nitrogenwasutilizedasthecarrier
gas (60 mL/min). The value of W/F re fers to the weight of
cat a lyst (g) over the feed rate of CHO (mol/h). The effluents
were col lected with a con denser. The liq uid prod ucts were
iden ti fied with a GC-MS (HP 5989B) and were pe ri od i cally
analyzedwithaGC(ChinaChromatographyCo.)fittedwith
a FID and a megabore col umn DB-1 (J&W, 0.544 mm 30
EXPERIMENTALSECTION
Catalyst Preparation
Both zeolites H and HZSM-5 were ob tained from PQ
Corp. The samples were heated to various temperatures
(400-1000 C) at a rate of 6 C/min and cal cined for 6 h. The
symbolsH (X)YandHZSM-5(X)Y,respectively,denoteH

-CaprolactamSynthesis
J. Chin. Chem. Soc., Vol. 48, No. 2, 2001 139
m). The flow rate of ni tro gen gas was 10 mL/min. The oven
temperaturewasprogrammedasfollows:theinitialtempera-
ture of 80 C for 2 min., fol lowed by heat ing with a rate of 20
C/min. to the fi nal tem per a ture of 220 C.
X re sults in a de crease of acid amounts but with con com i tant
en hance ment of rel a tive in ten sity of strong to weak acid ity.
Raising the cal ci na tion tem per a ture of AlPMY causes a sig-
nificant diminution of the catalyst acidity. For HZSM-
5(X)500samples,37 the vari a tion of acid i ties with X val ues
was sim i lar to that of H (X)500 sam ple. Fig. 4 shows the
TPD of am mo nia pro files from H (10)Y sam ples. The cat a-
RESULTSANDDISCUSSION
Catalyst Properties
Fig. 1 shows the pow der X-ray dif frac tion pat terns of
the H (10)Y sam ples. Two main peaks ap pear at 2 equal to
7.9 and 22.5 forallsamplesexceptforH (10)1000,indicat-
ing the col lapse of crys tal line struc ture af ter cal ci na tions at
elevatedtemperature(1000 C).Therelativeintensitiesof
these two peaks slightly in crease with cal ci na tion tem per a-
tures from 400 to 900 C. Fig. 2 shows the pow der X-ray dif-
frac tion pat terns of AlPMY sam ples. The d(001) basal spac-
ings are 18.2, 17.7 and 17.4 Å for AlPM300, AlPM400 and
AlPM500, respectively. Accordingly, the corresponding
interlayer dis tances are 8.6, 8.1 and 7.8 Å.Intercalationof
Na-M clays with alu mina causes a no ta ble in crease of the
interlayerdistance.
Fig. 3 dis plays the TPD of am mo nia pro files from var i-
ous H (X)500 and AlPMY sam ples. In creasing the value of
Fig. 2. XRD pow der pat terns of var i ous AlPMY sam-
ples.
Fig. 1. XRD powder pat terns of var i ous H (10)Y
samples.
Fig. 3. TPD of am mo nia pro files from H (X)500 and
AlPMYsamples.

140 J. Chin. Chem. Soc., Vol. 48, No. 2, 2001
Ouyang et al.
Table 1. Catalyst Properties and Catalytic Results. Reaction Conditions: Atmospheric Pressure; 300 C; Feed, CHO/C6H6 1 mol/l;
W/F, 74.6 g·h/mol
Selectivity (mol%)a, b
BET surface
Area (m2/g)
Acid amount Conversion
(mmol NH3/g)
Catalyst
(mol%)a
-C
HEN
HAN
CHA
CHE
AN
H (10)500
628
631
603
630
583
539
469
—
0.973
0.906
0.464
0.980
0.665
0.259
0.181
0.026
0.996
0.810
0.532
0.313
0.318
0.226
97.1 44.5 39.3 74.9 7.8 3.8
89.4 40.1 44.6 70.9 7.7 4.1
72.3 20.2 55.2 66.0 6.3 4.7
95.4 35.9 47.4 72.7 6.8 4.8
85.7 39.2 27.7 74.2 10.2 3.7
96.9 46.9 29.6 70.7 7.0 3.6
89.0 49.5 25.8 70.7 7.4 3.7
24.0 3.7
16.7 5.8
13.6 3.6
25.0 4.0
28.8 3.4
33.3 5.6
26.3 4.7
10.1 5.6
6.6 4.6
23.4 14.2
25.2 15.8
20.9 20.6
16.1 15.1
27.3 14.9
24.8 16.9
33.5 17.4
1.6 2.8 3.8 0.5
2.0 3.0 3.8 0.4
3.0 4.2 1.0 1.9
0.9 2.7 3.7 0.5
2.0 3.4 4.0 0.4
H (25)500
H (75)500
H (10)400
H (10)600
H (10)800
0
2.4 5.4 0.8
H (10)900
1.9 2.4 5.1 1.1
H (10)1000
HZSM-5(31)500
HZSM-5(51)500
HZSM-5(75)500
AlPM300
62.0 6.8
39.7 57.1 9.7 8.2
28.8 29.1 10.1
0
1.5
0
0
0
0
0
0
0
430
423
430
258
250
214
95.3 23.9 72.6 87.0 3.0 2.8
95.5 17.0 77.3 84.5 3.8 3.8
8.5 2.6
7.0 5.6
7.0 7.8
3.5 3.0 5.8
3.6 2.0 1.7
3.8 2.5 1.1
6.6 4.1
6.3 4.0
67.7 9.2
30.2 2.4
21.1 2.3
17.2 1.8
76.5 81.4 5.3 4.2
63.2 66.5 3.4
66.2 73.2 3.0
49.2 71.7 3.9
0
0
0
18.9 12.0 11.7 21.5
17.0 8.4 12.2 18.4
27.7 12.3 16.5 16.0
1.0
0
0
0
0
0
1.6
1.7
2.6
AlPM400
AlPM500
a Time-on-stream = 8 min. (left) and 112 min. (right).
b
-C, -caprolactam; HEN, 5-hexenitrile; HAN, hexanenitrile; CHA, cyclohexanone; CHE, 2-cyclohexen-1-one; AN, aniline.
lyst acid amount di min ishes mark edly with the cal ci na tion
tem per a ture Y. Ta ble 1 in di cates the BET sur face area and
the acid amount of var i ous cat a lysts. ForH (X)Y zeolites,
the sur face area ex hib its only a small change with the SiO2/
Al2O3 mol ra tio, whereas it de creases no ta bly with the cal ci-
nationtemperature.Theacidamountdiminishesapparently
with both the val ues of X and Y. In the case of HZSM-
5(X)500 zeolities, rais ing the val ues of X low ers the acid
amount, whilethesurfacearearemainsnearlyconstant. With
AlPMY sam ples, both the sur face area and the acid amount
decreaseasthecalcinationtemperatureincreases.
CatalyticResults
In the Beck mann re ar range ment of CHO over var i ous
cat a lysts, the ma jor prod uct is -C and the side prod ucts in-
clude cyclohexanone (CHA), cyclohexen-1-one (CHE),
hexanenitrile (HAN), 5-hexenenitrile (HEN) and aniline
(AN) that is con sis tent with other stud ies.18,26 The CHO con-
versionandtheproductselectivityarecalculatedwithrespect
to the mols of CHO con verted. Dif fer ent sol vents were used
as dil u ents for CHO in the feed. For the cat a lytic re ac tion of
CHO us ing ben zene as sol vent at 300 C and at mo spheric
pressure,theCHOconversionandtheproductselectivityare
listedinTable1.Theinitialcatalyticactivitiesexhibitthefol-
lowing orders: H (10)500
H (25)500
H (75)500;
H (10)400 H (10)500 H (10)600; HZSM-5(31)500
HZSM-(51)500 HZSM-5(75)500 and AlPM300 AlPM400
AlPM500. Such a trend is in ac cor dance with the rel a tive
to tal acid amounts of these cat a lysts as il lus trated in Fig. 5.
As these catalysts possess both Brönsted and Lewis acid
sites, they should all ex hibit cat a lytic ac tiv ity re gard less of
their acid strengths. In ad di tion, the de cay rate of H (X)Y,
HZSM-5(X)500, and AlPMY di min ishes with de creas ing X
or in creas ing Y val ues. These re sults im ply that the cat a lyst
de ac ti va tion oc curs mainly on the strong acid sites (Fig. 3
Fig. 4).
However,itisnoteworthythattheH (10)Y zeolites (Y
600) show quite high ini tial activites in spite of their much
lower acid amounts. In ad di tion, the cat a lytic de cay rates of
Fig. 4. TPD of am mo nia pro files from H (10)Y sam-
ples.

-CaprolactamSynthesis
J. Chin. Chem. Soc., Vol. 48, No. 2, 2001 141
H (10)800 ze o lite are dra mat i cally smaller than those of
other sam ples. To ex plain the pos si ble rea sons for these re-
sults, thenatureofacidicsiteswasstudiedbyFT-IRspectros-
copy on H (10)400 and H (10)800samplesafteradsorption
with pyridine va por as shown in Fig. 6. The bands at 1445,
1489, and 1597 cm-1 are as cribed to Lewis acid sites, whereas
those at 1548, 1489, and 1597 cm -1 are due to Brönsted acid
sites. It is no tice able that Brönsted acid sites (1548 cm-1) al-
most dis ap pear while Lewis acid sites (1445 cm-1) are still
presentaftercalcinationofH (10) at 800 C. There fore, it is
pro posed that Lewis acid sites on H (10)800zeolitearemore
effectivethanBrönstedacidsitesincatalyzingthisreaction.
Furthermore, catalyst deactivation occurs mainly on the
strong Brönsted acid sites that re sults in much lower de cay
rate of H (10)800zeolite.Consequently,thezeoliteH (10)800
ischosenforfurtherstudiesonitscatalyticperformance.The
se lec tiv ity data in Ta ble 1 re veals that the -Cselectivityin-
creaseswithtime-on-stream, whereasthereversephenomena
are ob served for the selectivities of the ma jor side prod ucts,
CHA and HAN. These re sults are prob a bly due to the con tin-
u ous for ma tion of cokes on the cat a lyst acid sites dur ing the
re ac tion and thus hin ders fur ther re ac tions to yield the side
prod ucts. It is known that ze o lite beta is more tol er a ble to
cok ing than ZSM-5 in spite of the fact that the amount of coke
depositspresentintheformerare, ingeneral, greaterthanthe
lat ter, re gardlessofthe conversionlevel. Thus, the observed
trend for cat a lytic per for mance fol lows the se quence: H
methanol, ethanol, n-butanolandbutyletherwereutilizedas
solventsforCHO.Table2indicatestheeffectsofsolventson
the cat a lytic re sults at 300 C over the H (10)800catalyst.
Apparently, allsolventsexhibitsimilarCHOconversionat
short time-on-stream of 0.5 h. How ever, the de cay rate is
much slower with po lar sol vents, es pe cially for eth a nol and
n-butanol. Fig. 7comparesthecatalyticresultsat400 C over
H -10-800 by us ing ben zene and eth a nol as sol vents. With
CHO/C6H6, the CHO con ver sion drops from 100% to 81%
dur ing 16 h time-on-stream and the -Cselectivityremains
nearly a con stant value of 89%. If eth a nol is used, com plete
conversionand -Cselectivityof92%areattainedforatleast
20 h time-on-stream. The rea sons are ex plained as fol lows:
thealcoholdehydratestoalkene,dialkyletherandwaterover
H (10) 800 cat a lyst. Dur ing the re ac tion, both al co hol and
thecontinuouslyproducedwatersuppresstheformationof
polymersandcokeonthecatalystsurface.Consequently,the
ex tent of de ac ti va tion of sur face ac tive sites is re duced. To
verifythisargument,waterwasfedtogetherwithbenzeneor
dibutyl ether (sol vent/wa ter mo lar ra tio 1) into the re ac tor
andthedecayratebecomessignificantlydiminished(Table
2). Thepositiveeffectofwateronpreventingdeactivation
was also proposed in the CHO reaction using B-MFI
HZSM-5
AlPM(Table1).
Non-polar ben zene and cyc lo hex ane as well as po lar
100
80
60
40
20
0
0.0
0.2
0.4
0.6
0.8
1.0
Acid amount (mmol/g)
Fig. 5. In flu ence of cat a lyst to tal acid ity on CHO con-
versions.Reactionconditions:CHO/C6H6; 300
C; W/F, 74.6 g h/mol; Time-on-stream, 8 min.
( ) H (X)500; ( ) H (10)400, H (10)600; ( )
HZSM-5(X)500; ( ) AlPMY.
Fig. 6. FT-IR trans mis sion spec tra of H (10) zeolites.
H (10)400: (a) blank; (b) pyridine va por ad-
sorption;H (10)800: (c) blank; (d) pyridine va-
poradsorption.

142 J. Chin. Chem. Soc., Vol. 48, No. 2, 2001
Ouyang et al.
Table 2. Effect of Solvents on Catalytic Results over H (10)800 Catalyst. Reaction Conditions: Atmospheric
Pressure; 300 C; Feed, CHO/Solvent 1 mol/l; W/F, 74.6 g·h/mol
Selectivity (mol%)a
Conversion
Solvent
(mol%)a
-C
HEN
HAN
CHA
CHE
AN
C6H6
C6H6/H2O
C6H12
CH3OH
C2H5OH
n-C4H9OH
(C4H9)2O
(C4H9)2O/H2O
83.9 22.7
89.2 33.1
90.6 25.4
80.1 25.7
90.1 43.9
89.0 42.3
93.5 30.9
94.2 39.0
68.5 83.7
68.9 79.6
66.2 81.1
75.7 86.7
86.0 90.7
78.6 86.8
65.6 72.5
64.8 67.4
3.0 2.5
2.5 2.0
2.7 2.3
2.5 2.4
2.2 2.0
2.7 2.8
3.6 4.1
3.1 4.9
8.8 3.4
6.6 2.2
9.2 3.2
11.5 5.5
5.1 2.6
6.8 3.8
8.5 3.0
7.1 2.2
16.6 9.0
16.8 12.2
18.7 12.0
7.8 5.4
4.8 3.3
9.4 6.6
1.9 1.3
3.7 4.0
2.0 1.5
1.3
1.5
1.4
1.5
0
0
0
0
1.0
1.0
1.6
0
0
0
0.9 0.5
1.0
1.1
1.4
0
0
0
19.9 18.3
20.9 22.3
1.5 2.0
2.7 3.2
a Time-on-stream = 0.5 h (left) and 3.5 h (right)
zeolites18 and Al-MCM-41.28 The -Cselectivityisremark-
ably higher for both eth a nol and n-butanol. In ad di tion, it in-
creases with time-on-stream. It is note wor thy that other sol-
vents, viz, benzene, cyclohexaneandbutylether, exhibitsig-
nif i cantly larger CHA se lec tiv ity, that de clines with time-
on-stream. The selectivities of CHE and AN are small and lit-
tlevariationoccurswithtime-on-stream.
Fig. 8 shows the prod uct yields as a func tion of con tact
time for the re ac tion over H (10)800 at 300 C. Due to cat a-
lyst de ac ti va tion, the data at ini tial time-on-stream (8 min)
areutilized.Asthecontacttimeincreases,the -C yield raises
rap idly from 7.4% to 68% and there af ter in creases slightly.
The re sults im ply that -C is a pri mary prod uct. For CHA and
HEN, the yields of both prod ucts in crease to a max i mum
valueandthendecline, indicatingthesecompoundstobepri-
mary un sta ble prod ucts. The yields of CHE and AN are quite
low at small con tact time so that they be long to sec ond ary
prod ucts. As the con tact time in creases, the HAN yield en-
hances from a quite small value to a mark edly large one, im-
plyingHANtobeasecondarystableproduct.Scheme il lus-
trates the possible reaction paths. Isomerization of CHO
leads to the for ma tion -C(pathI).Dehydrationandhydroly-
sis of CHO pro duce HEN and CHA (paths II & III), re spec-
tively. Hy dro ge na tion and dehydrogenation of HEN yield,
re spec tively, HAN and AN (paths IV & V). CHE is pro duced
via dehydrogenation of CHA (path VI). The rel a tive ini tial
for ma tion rates of -C, CHA and HEN are 26.3:1.6:1.0 as is
estimatedfromthereactiondataobtainedatW/F1.6g h/mol
and 8 min. time-on-stream. The cor re spond ing ra tios were
Fig. 7. Cat a lytic re sults at 400 C and W/F 74.6 g h/
mol over H (10)800 ze o lite. CHO/C2H5OH:
( ) CHO conversion; (l) -C selectivity;
CHO/ C6H6: ( ) CHO con ver sion; (s) -C se-
lectivity.
Fig. 8. Prod uct yields as a func tion of con tact time. Re-
actionconditions:H (10)800; CHO/C2H5OH;
300 C; Time-on-stream, 8 min.

-CaprolactamSynthesis
J. Chin. Chem. Soc., Vol. 48, No. 2, 2001 143
Scheme I
11.0:2.1:1.0 for re ac tions over HNaY-4 ze o lite with 99.07%
pro ton ex change at 335 C.12 Fig. 9 il lus trates the pro posed
reactionmechanismfortheformationof -C from CHO. For
the re ac tion via Brönsted acid sites (Fig. 9a), it involves
protonation (step I), de hy dra tion and ring en large ment (step
II), hydration (step III), and deprotonation, fol lowed by bond
shift (steps IV V). With Lewis acid sites (Fig. 9b), the re ac-
tionfollowsthesequenceofcoordinatebondformation,ring
en large ment (step I), and bond shift (steps II III).
CONCLUSIONS
Inthisstudy,thefollowingconclusionsareobtained:
1. For H (X)Y zeolites, an in crease of X re sults in the
en hance ment of acid strength with con com i tant de crease of
acid amounts, whereas the sur face area ex hib its only small
variation. RaisingYvaluescausesapparentdiminutionof
sur face area, acid strength and acid amount. A sim i lar trend
was found for AlPMY sam ples.
2. The ini tial cat a lytic ac tiv ity is par al lel to the to tal
acid amount of cat a lysts ex cept for H (10)Y (Y 600 C).
ThereactionproceedsviabothBrönsted and Lewis acid sites
ofallacidstrength.Thecatalystdeactivationismainlyattrib-
uted to the strong Brönsted acid sites.
Fig. 9. Re ac tion mech a nisms for -C for ma tion from
CHO on (a) Brönsted acid sites (B.A.); (b)
Lewis acid sites (L.A.).
form HAN and AN, re spec tively.
3. Solvents with large polarity, viz. ethanol and n-
butanol, ex hibit good cat a lytic per for mance, i.e., high -C
yield and lon ger cat a lyst life time. In the re ac tion of CHO/
C2H5OH over H (10)800 at 400 C, and W/F 74.6 g h/mol
un der at mo spheric pres sure, the CHO con ver sion and -C
yieldremain100%and92%, respectively, duringatleast20h
processtime.
ACKNOWLEDGEMENTS
We grate fully ac knowl edge fi nan cial sup port by the
Na tional Sci ence Coun cil of the Re pub lic of China (NSC
88-2113-M-029-004). We also thank Kunimine In dus tries
Co., Ltd. for sup ply ing Kunipia-F.
4. CompetitivereactionsofCHOproduce -C, CHA,
and HEN as pri mary prod ucts. Dehydrogenation of CHA
yields CHE. Hy dro ge na tion and dehydrogenation of HEN
Received January 10, 2001.

144 J. Chin. Chem. Soc., Vol. 48, No. 2, 2001
Ouyang et al.
Key Words
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T. Catal.Today 1997, 37, 353.
20. Dai, L.-X.; Hayasaka, R.; Iwaki, Y.; Koyano, A.; Tatsumi,
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