Development of a new production process for N-vinyl-2-pyrrolidone

Article abstract of DOI:10.1246/bcsj.81.449

We describe the first continuous production process for N-vinyl-2-pyrrolidone (NVP). The starting materials are γ-butyrolactone (GBL) and monoethanolamine (MEA). The process consists of two stages: the synthesis of N-(2-hydroxy-ethyl)-2-pyrrolidone (HEP) from GBL and MEA, and the vapor-phase dehydration of HEP to NVP. The key features of this technology are the dehydration catalyst and the vapor-phase reaction system. The catalyst is of very simple composition, being alkali (or alkaline earth) metal oxides-SiO ₂. Though its acid and base strengths are very weak, its catalytic performance is high. We presume that the excellent catalytic performance is due to the selective adsorption of HEP to the catalyst. Moreover, an IR spectroscopic study of the HEP-adsorbed catalyst indicated that the isolated silanol of the catalyst surface plays an important role. This account describes the progress made from the laboratory study to the industrial process, along with the experimental results and discussion.

Full text of DOI:10.1246/bcsj.81.449

ꢀ 2008 The Chemical Society of Japan
Bull. Chem. Soc. Jpn. Vol. 81, No. 4, 449–459 (2008)
449
Award Accounts
The Chemical Society of Japan Award for Technical Development for 2006
Development of a New Production Process for N-Vinyl-2-pyrrolidone
ꢀ1
Yuuji Shimasaki, Hitoshi Yano,2 Hideto Sugiura,3 and Hideyuki Kambe4
1Catalyst Research Center, Nippon Shokubai Co., Ltd., Aboshi-ku, Himeji 671-1292
2Process Technology Center, Nippon Shokubai Co., Ltd., Aboshi-ku, Himeji 671-1292
3Kawasaki Plant, Nippon Shokubai Co., Ltd., Kawasaki-ku, Kawasaki 210-0865
4Specialty Chemicals Business Unit, Nippon Shokubai Co., Ltd., Chuo-ku, Osaka 541-0043
Received June 29, 2007; E-mail: yuji shimasaki@shokubai.co.jp
We describe the first continuous production process for N-vinyl-2-pyrrolidone (NVP). The starting materials are ꢀ-
butyrolactone (GBL) and monoethanolamine (MEA). The process consists of two stages: the synthesis of N-(2-hydroxy-
ethyl)-2-pyrrolidone (HEP) from GBL and MEA, and the vapor-phase dehydration of HEP to NVP. The key features of
this technology are the dehydration catalyst and the vapor-phase reaction system. The catalyst is of very simple com-
position, being alkali (or alkaline earth) metal oxides–SiO2. Though its acid and base strengths are very weak, its cata-
lytic performance is high. We presume that the excellent catalytic performance is due to the selective adsorption of HEP
to the catalyst. Moreover, an IR spectroscopic study of the HEP-adsorbed catalyst indicated that the isolated silanol of
the catalyst surface plays an important role. This account describes the progress made from the laboratory study to the
industrial process, along with the experimental results and discussion.
is normally used and a continuous-flow system is difficult to
employ. In addition, separation of the product from a reaction
mixture is difficult, and the waste, which contains the catalyst,
must be treated. Accordingly, the development of a vapor-
phase heterogeneous catalytic system to replace a liquid-phase
stoichiometric reaction system is desirable with respect to
productivity and environmental concerns. An efficient vapor-
phase production process is absolutely dependent on the
development of an excellent catalyst. Many studies designed
to improve the process and the catalyst have been done, both
in academia and industry. Among various types of catalysts,
acidic or basic metal oxide catalysts have been extensively
studied. However, most of the catalysts studied have been
solid acid catalysts or solid base catalysts. These promote
the desired reactions, but their selectivity and catalytic life
are often not practical for industrial use, probably because
their active sites are too strong to work for long periods
without deactivation. It should be possible to develop practical
catalysts among those that possess both weakly acidic sites and
weakly basic sites although there have been few studies of
the development of bifunctional acid–base catalysts for
industrial use.
1. Introduction
Since the 1980s, when people began to increasingly think
about environmental problems due to growing concerns, the
environment has been considered more and more in most
global societal activities to enable realizing a sustainable soci-
ety. This consideration has included the chemical industry,
which has been required to design products and processes such
that the processes do not consume large amounts of energy or
produce large amounts of by-products.
Although continual efforts have been made in the chemical
industry to improve production processes, some processes
still consume large amounts of energy and raw materials and
produce large amounts of waste. These processes should be
replaced as soon as possible with environmentally friendly
ones. One of the key means of designing an environmentally
friendly process is catalytic technology, which can transform
a stoichiometric reaction into a catalytic reaction. The use of
catalysis can minimize the production of by-products, which
are inevitable in a stoichiometric process. There are two types
of catalytic reaction system: homogeneous and heterogeneous.
Heterogeneous catalytic reaction systems are superior to homo-
geneous ones as green processes. The use of heterogeneous
catalysts eases both the separation of the products from the
catalyst and reuse of the catalyst. In particular, vapor-phase
heterogeneous catalytic systems are advantageous because
they can be operated in solvent free, continuous-flow systems.
In contrast, in a homogeneous catalytic reaction system solvent
We have been studying new production processes that
use reactive monomers from hydroxyethyl compounds (de-
rivatives of ethylene oxide) by vapor-phase dehydration. In
1991, we industrialized a new process for producing ethyl-
eneimine by the vapor-phase dehydration of monoethanol-
amine (MEA) with an acid–base catalyst.1 We later (1994) de-
Published on the web April 10, 2008; doi:10.1246/bcsj.81.449

450 Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
AWARD ACCOUNTS
veloped excellent catalysts for the production of vinyl com-
pounds from hydroxyethyl compounds by vapor-phase de-
hydration.
O
O
O
NH
+
H2O
+
NH3
The catalysts’ performance was high in the following
dehydrations, which include dehydration of glycol ethers to
vinyl ethers (eq 1),2,3 dehydration of glycol thioethers to
vinyl thioethers (eq 2),4 dehydration of N-(2-hydroxyethyl)-
cyclic amides to N-vinyl-cyclic amides (eq 3),5 dehydration
of N-(2-hydroxyethyl)-cyclic imides to N-vinyl-cyclic imides
(eq 4),6 and dehydration of N-(2-hydroxyethyl)-aromatic
amines to N-vinyl-aromatic amines (eq 5).7 R represents
an alkyl group, an aryl group, or an aralkyl group in the
eqs 1 and 2.
GBL
2-Pyrrolidone
ð6aÞ
O
O
N
+ C2H2
ð6bÞ
NH
2-Pyrrolidone
NVP
Meanwhile, various processes using no acetylene have been
disclosed that use HEP as a raw material, as follows:
OH
OH
+
+
ð1Þ
ð2Þ
H2O
H2O
RO
RO
RS
O
O
RS
O
SOCl2
OH
Cl
N
N
O
CEP
HEP
ð3Þ
ð7aÞ
OH
+
H2O
O
N
N
N
N
-HCl
N
O
O
O
O
NVP
OH
+
+
ð4Þ
ð5Þ
N
H2O
H2O
O
O
Ac2O
OAc
OH
N
N
OH
N
HEP
AEP
(Ac: CH3CO)
ð7bÞ
We found that SiO2, modified by the addition of an alkali
(or alkaline earth) metal oxide, exhibited high catalytic per-
formance in the vapor-phase dehydration of hydroxyethyl
compounds to the corresponding vinyl compounds. The newly
developed catalysts produced vinyl ethers, vinyl thioethers,
N-vinyl lactams, N-vinyl cyclic imides, and N-vinyl aromatic
amines with high yields. In particular, N-vinyl-2-pyrrolidone
(NVP) was produced in very high yield.
NVP, CAS [88-12-0], is a clear, colorless liquid that is mis-
cible in all proportions with water and most organic solvents.
The known properties of NVP are as follows:8 mol wt. 111;
boiling point at 53.3 kPa, 193 ꢁC; freezing point, 13.5 ꢁC;
specific gravity (25/4 ꢁC), 1.04.
O
N
-AcOH
NVP
The process described in eq 7a is a dehydrochlorination
of N-(2-chloroethyl)-2-pyrrolidone (CEP) obtained by the re-
action of HEP with thionyl chloride.11 The process described
in eq 7b is an elimination of acetic acid from N-(2-acetoxy-
ethyl)-2-pyrrolidone (AEP) obtained by the reaction of HEP
with acetic anhydride.12 These processes also present various
problems: the sub-raw material is used in an amount equiva-
lent to HEP, the cost of intermediate production is large, and
by-products are generated from the sub-raw material in large
amounts. Consequently, these processes are not well suited
to industry.
NVP is a useful reactive monomer and is used principally
for the production of homopolymers and copolymers. These
polymers are used as the raw materials for pharmaceuticals,
adhesives, paints, cosmetics, and many other chemical
products.
NVP has been produced by the vinylation of 2-pyrrolidone,
which is produced from ꢀ-butyrolactone (GBL) and ammonia,
with acetylene as the only industrial process (the Reppe pro-
cess) since 1940 (eq 6).9,10 This process presents some prob-
lems, such as the explosion risk of acetylene, necessary restric-
tion of the plant location to sites close to acetylene production
plants, and the exhaust of large amounts of alkaline waste
and solvents.
The above problems would be solved if the vapor-phase de-
hydration of HEP (eq 8a), which is produced from GBL and
MEA, to NVP (eq 8b) were to efficiently proceed through
the use of heterogeneous catalysts. Various oxides have been
reported as the catalyst, including active alumina;13 cerium
oxide, zinc oxide, and chromium oxide;14 zirconium oxide and
thorium oxide;15 lanthanum oxide and neodymium oxide;16
acidic heterogeneous catalysts other than the oxides of metals

Y. Shimasaki et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
451
of group 12, 13, 14, and 16;17 a mixed oxide of group 4 and 14
elements, or an oxide of group 4 and 14 elements that has been
modified by group 1 or group 2 elements.18
ethyl)-4-hydroxybutanamide (HEBA) from GBL and MEA,
and the second reaction is the formation of HEP by the intra-
molecular dehydration of HEBA.
Among them, zirconium oxide showed the highest catalytic
performance (HEP conversion = 88.6%, NVP selectivity =
92.6%) in the patent.15 However, in the experiment conducted
by the authors using zirconium oxide under the reaction condi-
tions of the present study, the conversion of HEP was as high
as 84.9% but the selectivity of transformation to NVP, at
67.3%, was not sufficiently high to be used for a commercial
process (eqs 8a and 8b).
O
O
NHCH2CH2OH
OH
O + H2NCH2CH2OH
GBL
HEBA
MEA
ð9aÞ
O
O
O
O
OH
NHCH2CH2OH
OH
+
H2O
OH
N
+
H2O
+
H2NCH2CH2OH
MEA
O
N
GBL
HEP
HEP
HEBA
ð8aÞ
ð9bÞ
2.1 Synthesis of HEBA from GBL and MEA (the First Re-
action). The equivalents of GBL and MEA were put into a
glass flask (capacity 50 mL) and stirred at 100 ꢁC for 4 h. The
products were analyzed by gas chromatography.
O
O
OH
+
H2O
N
N
The conversion of MEA and the selectivity to HEBA based
on MEA were defined as follows: conversion (mol %) =
100 ꢂ (mole of consumed MEA)/(mole of fed MEA); selec-
tivity (mol %) = 100 ꢂ (mole of produced HEBA)/(mole
of consumed MEA). The conversion of GBL and the selectiv-
ity to HEBA based on GBL were defined as follows: conver-
sion (mol %) = 100 ꢂ (mole of consumed GBL)/(mole of
fed GBL); selectivity (mol %) = 100 ꢂ (mole of produced
HEBA)/(mole of consumed GBL).
Table 1 shows the effect of water on the conversion of MEA
and the selectivities to HEBA in the first reaction. The reaction
temperature was initially 25 ꢁC and rose to 92 ꢁC due to the
heat of reaction. The MEA was completely consumed in 4 h.
Water did not influence this reaction.
Figure 1 shows the relationship between the conversion of
MEA and the reaction time in the presence of excess GBL
(GBL/MEA = 39.0, molar ratio). The conversion of MEA
increased with the reaction time and then reached saturation.
Figure 2 shows the relationship between the conversion of
GBL and the reaction time in the presence of excess MEA
(MEA/GBL = 38.3, molar ratio). In this case, the reaction
was very fast, in contrast to that depicted in Figure 1. The con-
version of GBL reached an upper limit in 10 min.
HEP
NVP
ð8bÞ
We looked for catalysts that perform better than ZrO2, and
found that SiO2 modified by the addition of alkali (or alkaline
earth) metal oxides exhibits higher catalytic activity and selec-
tivity.19–21
No industrial processes for the production of HEP existed
until this new process to produce NVP was developed because
HEP had no particular use. However, demand for HEP has in-
creased, and the development of a process to produce it has be-
come important. We investigated the reaction conditions in de-
tail for the purpose of developing an industrial process for HEP
production, and succeeded in developing a continuous-flow
production system for HEP.
We also studied the purification of NVP and HEP, as well as
the development of catalysts, and successfully tested the total
process in the pilot plant. Based on these studies, our new
commercial process for NVP synthesis was initiated at Nippon
Shokubai’s Kawasaki plant in 2001.
2. Development of a Continuous-Flow
HEP Production System
We think the reaction rate is faster under this condition
because this reaction involves a nucleophilic attack by MEA
on GBL. We tested the gradual addition of GBL to MEA in
A patent disclosed that HEP can be produced from GBL and
MEA, and that the HEP yield is improved by the addition of
water to the reaction system beforehand.22 However, no exam-
ple of a continuous-flow reaction was given, as all the exam-
ples in the patent were done batchwise. Also not reported
was the purification process for HEP.
Table 1. Effect of Water on the 1st Reactiona)
Time
/h
H2O
/wt %
MEA Conv.
/mol %
HEBA Sel.
/mol %
The preference was to use a continuous-flow system for the
reaction and purification of HEP because we used such a sys-
tem for the vapor-phase dehydration and purification of NVP.
Hence, we developed a total continuous-flow process, from the
introduction of starting materials to the storage of NVP.
The reaction of GBL and MEA conversion to HEP is shown
in eq 8a. This reaction comprises two successive reactions
(eq 9). The first reaction is the formation of N-(2-hydroxy-
0.5
4.0
0.5
4.0
84
100
84
100
100
100
100
10
10
100
a) Reaction conditions: MEA/GBL = 1/1 (molar ratio);
temperature, 25 ꢁC.

452 Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
AWARD ACCOUNTS
Table 2. Effect of Water on the Second Reactiona)
100
80oC
H2O
/wt %
HEBA Conv.
/mol %
HEP Sel.
/mol %
60oC
80
40oC
60
40
20
0
0
10
50
96.2
98.4
99.8
82.8
90.2
92.9
a) Reaction conditions: reactor; 25-mL vessel, temperature;
250 ꢁC, time; 1 h.
0
50
100
150
200
250
300
350
400
450
Table 3. Effect of Temperature in the Presence of Water on
the Second Reactiona)
time/min
Figure 1. Relationship between the conversion of MEA
and the reaction time in the presence of excess GBL. Re-
action condition: GBL/MEA = 39.0, molar ratio.
Temperature H2O
/ꢁC
Max. pressure HEBA Conv. HEP Sel.
/mol %
/wt %
/MPa
/mol %
250
270
250
10
10
30
1.6
2.1
2.5
93.7
94.7
93.1
90.1
91.1
93.9
100
80oC
60oC
80
a) Reaction conditions: reactor, 100-mL autoclave; tempera-
ture, 250 ꢁC; time, 1 h.
60
40
20
0
Table 4. Effect of MEA on the Second Reaction
HEBA/MEA Temperature Time HEBA Conv. HEP Sel.
/ꢁC
(molar ratio)
/h
/mol %
/mol %
0
50
100
150
200
250
time/min
HEBA only
10/5
250
250
3
3
100
100
87
97
Figure 2. Relationship between the conversion of GBL and
the reaction time in the presence of the excess MEA.
Reaction condition: MEA/GBL = 38.3, molar ratio.
Table 5. Comparison of the Reaction Methoda)
Reaction method Max. pressure H2O HEBA Conv. HEP Sel.
bench-scale experiments (described in Section 2.4) in the ex-
pectation that it would have advantages as a practical method.
2.2 Synthesis of HEP from HEBA (the Second Reaction).
HEBA was placed in a stainless steel reaction vessel and
heated. The reaction was carried out in the temperature range
of 200–250 ꢁC. The products were analyzed by gas chroma-
tography.
/MPa
/wt %
/mol %
/mol %
1-step reaction
2-step reaction
1.9
1.6
10
10
100
100
88
84
a) Reaction conditions: MEA/GBL = 1, molar ratio; reactor,
100-mL autoclave; temperature, 250 ꢁC; time, 1 h.
The conversion of HEBA and the selectivity to HEP were
defined as follows: conversion (mol %) = 100 ꢂ (mole of con-
sumed HEBA)/(mole of fed HEBA); selectivity (mol %) =
100 ꢂ (mole of produced HEP)/(mole of consumed HEBA).
Table 2 shows the effect of water on the second reaction.
The addition of water dramatically increased the selectivity
to HEP. The principal by-product was the condensed product
of HEBA.
O
CH2CH2OH
NHCH2CH2OH
OH
(1-n) H2O
N
n
HO
H
n
O
Polymer
O
HEBA
ð10Þ
-n H2O
OH
n
N
More detailed effects of temperature and water were exam-
ined by use of a 100-mL autoclave, as shown in Table 3. The
effect of temperature was small. The amount of water influ-
enced the selectivity to HEP. The addition of a large amount
of water increased the selectivity to HEP, but lessened the
productivity because it increased the load on the purification
system.
The side reaction is the condensation of HEBA to form
a by-product, as shown in eq 10. Water probably suppresses
this side reaction. This condensation is presumably an equi-
librium reaction, but the reaction of HEBA to HEP is not an
equilibrium reaction. Thus, the condensation product (poly-
mer) is converted back to HEBA by water, and is then convert-
ed to HEP.
HEP
Table 4 shows the effect of MEA on the second reaction.
MEA did not inhibit the second reaction. MEA increased the
selectivity to HEP as well as water did. It is likely that MEA
acts as a base to promote the hydrolysis of the condensation
product by the produced water.
2.3 One-Step Reaction. A one-step reaction was carried
out by heating the crude product of the first reaction without
the isolation of HEBA, as shown in Table 5. The selectivity
to HEP was higher than that observed in the two-step reaction
method. We consider this to be due to the effect of co-existing
MEA because the second reaction proceeds in the presence of

Y. Shimasaki et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
453
Control
Valve
100
95
90
85
80
Cooler
260oC
HEP
CW
250oC
Heating Medium
H2O
0.5
1
1.5
2
2.5
3
MEA
GBL
Residence time / h
Figure 4. Selectivity to HEP vs. the residence time. Reac-
tion conditions: GBL/MEA/H2O = 1/1/1 (molar ratio);
temperature, 250 ꢁC.
Figure 3. Model flow sheet of the new process of HEP pro-
duction.
influence the synthesis of HEBA from GBL and MEA (first
reaction). Second, the first reaction reaches completion in a
shorter time when GBL is gradually added to MEA. Third,
the addition of water increases the selectivity to HEP dramat-
ically in the synthesis of HEP from HEBA (second reaction).
Fourth, water probably suppresses the side reaction (conden-
sation of HEBA). Fifth, the one-step reaction method, which
combines the first and the second reactions, is more productive
for HEP synthesis. Sixth, we have developed a productive
method for HEP production by use of a continuous-flow reac-
tion system.23
Table 6. Results of the Continuous-Flow Reactiona)
Temperature Back pressure Residence time MEA Conv. HEP Sel.
/ꢁC
/MPa
/h
/mol %
/mol %
250
3.7
0.99
1.08
1.3
100
100
100
100
100
100
100
100
89.3
90.5
91.6
93.4
93.2
92.0
93.8
93.9
1.76
2.8
260
4.1
1.08
1.38
1.71
3. Development of a Process for Vapor-Phase
Dehydration HEP to NVP
a) Reaction conditions: GBL/MEA/H2O = 1/1/1 (molar ratio);
temperature, 250 ꢁC.
3.1 Preparation of the Catalysts for Laboratory Experi-
ments. To be of practical use, a catalyst must be physically
strong enough to withstand the stresses it experiences within a
reactor, for example, during moving and loading. Hence, in-
dustrial catalysts are made in various shapes, such as cylinders,
tubes, and beads. They are shaped by molding, impregnation,
or coating on a support. Molding usually reduces catalytic per-
formance because the molding force changes properties of the
catalyst, such as its pore size, pore volume, and density. To
avoid these changes, additives that control the catalyst’s phys-
ical properties and improve its strength are used. Our industrial
catalyst was molded with careful consideration of the additive
and molding conditions.
the unreacted MEA in the two-step reaction.
2.4 Bench-Scale Production. Bench-scale production was
carried out by use of a stainless steel reactor (capacity 100 L).
An equivalent of GBL was added dropwise to MEA for 2.8 h
without heating. The temperature increased as the reaction pro-
ceeded. The maximum reaction temperature was 76 ꢁC. Next,
water (30 wt %) was added to the reactor and stirred for 1 h at
250 ꢁC. The reaction proceeded smoothly to completion, with
no unusual elevation of temperature. The maximum pressure
was 2.4 MPa. The conversion of MEA was 100%, and the
selectivity to HEP was 94%.
2.5 Continuous-Flow Reaction. The continuous-flow re-
action was carried out using the apparatus shown in Figure 3.
The reactor was a stainless steel tube with an inside diameter
of 16.2 mm and a length of 500 cm with structured packing in-
side. GBL, MEA, and water were fed into the reactor, and this
mixture then passed through the reactor with a residence time
of 0.99–2.8 h. The reactor was heated to the reaction tempera-
ture by use of a heating medium. Table 6 and Figure 4 show
the results of the reaction.
However, the catalysts for laboratory experiments were pre-
pared by a simple method as follows.
3.1.1 Mono-Metal Oxide Catalysts:
Silicon oxide
(Sylysia 350, Fuji Silysia Chemical Ltd.) and ZrO2 (Tokyo
Chemical Industry Co., Ltd.) were used as starting materials.
These oxides in powder form were first kneaded with water
to form slurries. The slurries were dried at 120 ꢁC for 20 h to
form solids. The obtained solids were crushed into particles
of 9–16 mesh and calcined at 500 ꢁC for 2 h in air.
The MEA conversion and the HEP selectivity values were
very similar to those of the bench-scale production. The selec-
tivity to HEP increased with the residence time. Raising the
temperature shortened the residence time required to attain
the upper limit of the yield of HEP, as shown in Figure 4.
The continuous-flow reaction probably yielded the same result
as the bench-scale reaction because high temperature does not
inhibit the first reaction.
3.1.2 Metal Oxide Catalysts Modified with Alkali or
Alkaline-Earth Metal Oxide: A mixture containing various
metal oxides and hydroxides (or carbonates) of alkali or alka-
line earth metals were kneaded with water. Each mixed oxide
catalysts was prepared in a manner similar to the mono-metal
oxide catalysts described above. All metal oxides (TiO2,
La2O3, and WO3) were purchased from Tokyo Chemical
Industry Co., Ltd.
2.6 HEP Production: Conclusions. First, water does not
3.2 Reaction Procedures. The vapor-phase dehydration

454 Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
AWARD ACCOUNTS
Table 8. Catalytic Performance of Alkali or Alkaline Earth
Metal Oxide-Added SiO2 Catalystsa)
HEP
Catalyst
(molar ratio)
Reaction temp HEP conversion NVP selectivity
/ꢁC
/mol %
/mol %
Condenser
N2
SiO2
400
400
370
370
370
370
400
400
400
16.3
59.2
57.0
85.9
89.8
96.5
51.1
58.9
50.8
94.2
99.2
98.7
95.1
94.2
88.8
85.2
89.2
99.8
Li2O/SiO2 (1/20)
Na2O/SiO2 (1/20)
K2O/SiO2 (1/20)
Rb2O/SiO2 (1/20)
Cs2O/SiO2 (1/20)
CaO/SiO2 (1/10)
SrO/SiO2 (1/10)
BaO/SiO2 (1/10)
Preheat zone
Purge
Cat. zone
a) Reaction conditions: HEP gas concentration, 10 vol % (balanced
by N2); GHSV, 2000 hꢃ1; catalyst, calcined at 500 ꢁC for 2 h.
Niter bath
Figure 5. Laboratory-scale experimental equipment.
catalysts showed greater than 90% selectivity to NVP. The
major by-products observed were 2-pyrrolidone and acetalde-
hyde.
Table 7. Conversion and Selectivity in HEP Dehydration
on Various Metal Oxidesa)
With the SiO2 catalyst itself, the selectivity to NVP was
very high, while the conversion of HEP was low. The conver-
sion was improved by the addition of a small amount of Na2O
to the SiO2. The conversion obtained with this catalyst, Na2O/
SiO2 (molar ratio 1/20), was much higher than that with SiO2
alone, despite its lower reaction temperature, and the selectiv-
ity to NVP was also improved by the addition of Na2O. Addi-
tion of alkali or alkaline-earth metal oxides to the metal oxides
other than SiO2 did not result in good catalytic performance.
3.4 Catalytic Performance of SiO2 Modified with Alkali
or Alkaline-Earth Metal Oxide. Table 8 shows the catalytic
performance of SiO2 enhanced with various kinds of alkali
(or alkaline earth) metal oxides. The conversion of HEP was
markedly improved by the addition of any type of alkali or
alkaline-earth metal oxide to SiO2. In general, alkali metal
oxides were more effective in improving the activity than
alkaline earth metal oxides.
Catalyst
(molar ratio)
Reaction temp HEP conversion NVP selectivity
/ꢁC
/mol %
/mol %
SiO2
Na2O/SiO2 (1/20)
ZrO2
400
370
370
370
350
370
370
370
370
370
350
380
380
16.3
57.0
84.9
97.3
98.8
13.2
82.4
40.4
18.5
19.7
69.8
5.0
94.2
98.7
67.3
23.6
20.5
44.2
12.7
82.1
76.4
61.9
9.2
Na2O/ZrO2 (1/20)
Cs2O/ZrO2 (1/20)
Na2O/TiO2 (1/20)
Cs2O/TiO2 (1/20)
CaO/TiO2 (1/10)
BaO/TiO2 (1/10)
Na2O/La2O3 (1/10)
Cs2O/La2O3 (1/10)
Na2O/WO3 (1/20)
Cs2O/WO3 (1/20)
75.0
71.8
9.2
a) Reaction conditions: HEP gas concentration, 10 vol % (balanced by
N2); GHSV, 2000 hꢃ1; catalyst, calcined at 500 ꢁC for 2 h.
The relationship between the catalytic performance and
the ionization potential of the added alkali metal elements is
shown in Figure 6. The conversion of HEP decreased and
the selectivity to NVP increased with the decrease in the ion-
ization potential of the alkali metal elements. The basicity of a
metal oxide becomes stronger as the ionization potential of the
metal elements decreases. The strength of basicity of alkali
metal oxides is estimated to be in the order Cs2O > Rb2O >
K2O > Na2O > Li2O. This order may also hold when they
are supported on SiO2. We suggest that Cs2O/SiO2 has the
highest activity because it has the strongest basicity among
the SiO2–alkali metal oxide mixtures.
was carried out in a fixed-bed flow-type reactor under atmo-
spheric pressure.
Laboratory-scale experimental equipment is shown in
Figure 5. Crushed catalysts (9–16 mesh, 5 cm3) were placed
in a stainless-steel reaction tube having an inside diameter of
10 mm, and heated to the reaction temperature in a molten-salt
bath. The reactant gas of 10 vol % HEP in nitrogen was passed
through the catalyst bed at a gas hourly space velocity (GHSV)
of 2000–6000 hꢃ1. The reaction was carried out at 350–400 ꢁC.
After the reactant gas was fed for 1 h, the products were
analyzed by gas chromatography.
3.3 Catalytic Performance of Various Metal Oxides.
Table 7 shows the conversions of HEP and the selectivities
to NVP in the presence of the metal oxides and various metal
oxides loaded with alkali or alkaline earth oxides in the vapor-
phase dehydration of HEP. The conversion of HEP and
the selectivity to NVP were defined as follows: conversion
(mol %) = 100 ꢂ (mole of consumed HEP)/(mole of fed
HEP); selectivity (mol %) = 100 ꢂ (mole of produced NVP)/
(mole of consumed HEP).
The low activities of the alkaline-earth metal oxide-added
SiO2 as compared to those of alkali metal oxide-added SiO2
might be due to the weaker basicity of the former. However,
it is not necessarily true that the stronger the basic sites, the
higher the activity, as described later in Section 3.8.1 on the
basis of indicator color changes.
3.5 Effect of the Cs2O Content of the Cs2O/SiO2 Cata-
lyst. The effects of the amount of Cs2O in the Cs2O/SiO2
catalyst on the conversion of HEP and the selectivity to NVP
are shown in Figure 7. The conversion increased steeply as the
amount of added Cs2O increased to a Cs2O/SiO2 molar ratio
of 0.0025, where the conversion was almost saturated. The
All the catalysts studied yielded NVP, though the conver-
sion and selectivity changed depending on the type of catalyst
(Table 7). Among them, both SiO2 itself and modified SiO2

Y. Shimasaki et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
455
100
80
60
40
20
0
100
80
60
40
20
380°C
370°C
Sel.
↑
Rb
↑
Cs
↑
K
Conv.
↑
Na
360°C
↑
Li
0
3.5
4
4.5
5
5.5
0
200
400
600
800
1000
Ionization potential/eV
Contact time(1/GHSV)/ms
Figure 6. Relationships between ionization potential of
alkali element added to SiO2 and catalytic activity and
selectivity. Reaction conditions: catalyst, alkali metal
oxide/SiO2 = 1/20 (molar ratio); HEP gas concentration,
10 vol % (balanced by N2); GHSV, 2000 hꢃ1; reaction
temperature, 370 ꢁC; ionization potential: 5.39 eV/Li,
5.12 eV/Na, 4.32 eV/K, 4.16 eV/Rb, and 3.88 eV/Cs
(Ref. 24).
Figure 8. Variations of the conversion as a function of
the contact time (1/GHSV) at different temperatures over
the Na2O/SiO2 (1/20 molar ratio).
were not linear, indicating that the rates have positive-order
kinetics with respect to HEP. The 0-order kinetics mean that
only HEP was adsorbed to the catalyst. The positive-order
kinetics mean that other reactants of HEP were also adsorbed
to the catalyst. The amount of by-products acetaldehyde and
2-pyrrolidone increased at higher temperature. Equation 11
shows the side reaction. NVP is hydrolyzed to 2-pyrrolidone
and acetaldehyde via N-(1-hydroxyethyl)-2-pyrrolidone (1-
HEP). Using the pulse method, we observed that 2-pyrrolidone
was adsorbed strongly to the catalyst. We believe that the posi-
tive-order kinetics are due to the adsorption of 2-pyrrolidone to
the catalyst. Based on the initial rates at different temperatures,
100
Conv.
80
Sel.
60
the activation energy is calculated to be 153.3 kJ molꢃ1
.
40
20
0
O
O
OH
+
H2O
N
N
ð11Þ
1-HEP
0.00
0.01
0.01
0.02
0.02
O
Cs2O/SiO2/molar ratio
NH
+
CH3CHO
Figure 7. Effects of the amount of Cs in the Cs2O/SiO2
catalyst on the conversion and the selectivity. Reaction
conditions: HEP gas concentration, 10 vol % (balanced
by N2); GHSV, 2000 hꢃ1; reaction temperature, 380 ꢁC.
3.7 The Change of Catalytic Performance with Time on
Stream. Figure 9 shows our one example of a change in
catalytic performance with time on stream. The conversion
of HEP gradually decreased with time on stream. The cause
of the decrease in conversion was coke deposition on the cat-
alyst’s surface. The conversion was recovered by the regener-
ation of the catalyst. Catalyst regeneration was carried out by
heating at the reaction temperature in the presence of synthetic
air. The degree of recovery attainable by regeneration is nearly
steady with long time on stream. However, it eventually grad-
ually decreases with very long continuous use. This deactiva-
tion is due to the sintering of the catalyst. The selectivity to
NVP was almost constant with time on stream.
selectivity to NVP increased slightly with the addition of Cs2O
to a Cs2O/SiO2 molar ratio of 0.001, and gradually decreased
with further increases in the amount of Cs2O.
3.6 Effects of Reaction Conditions. Figure 8 shows the
effects of GHSV and reaction temperature on the conversion
of HEP in the presence of the catalyst Na2O/SiO2 (1/20 molar
ratio) and a HEP concentration of 10 vol % in N2. At 360 ꢁC,
the conversion increased linearly with the contact time, indi-
cating that the reaction rate was 0 order with respect to
HEP. As discussed later, the catalyst surfaces should be fully
covered with HEP at this temperature, and little NVP remains
on the surfaces. At 370 and 380 ꢁC, however, the relationships
The industrial catalyst maintained steady performance for
over 1 year, and 1 kg of the catalyst produced more than 15
tons of NVP per year.

456 Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
AWARD ACCOUNTS
100
Sel.
80
60
NEP
Conv.
40
After regeneration
20
NVP
0
0
100
200
300
400
500
600
700
800
900
Time on stream/h
Figure 9. Change in catalytic performance with time on
stream. Reaction conditions: catalyst, Na2O/P2O5/SiO2 =
5/1/100 (molar ratio), calcined at 600 ꢁC for 3 h; HEP gas
concentration, 10 vol % (balanced by N2); GHSV, 4000
HEP
h
ꢃ1; reaction temperature, 380 ꢁC.
1.0
1.5
2.0
2.5
3.0
3.5
Retention time/min
3.8 Features of the Catalysts and the Reaction Mech-
anism.
The properties of the catalyst were investigated
through measurements of their acid and base strengths, the
adsorption and desorption behaviors of some reactants on the
catalyst, and the temperature-dependent IR spectra of the
HEP-adsorbed catalyst. We applied the results to an analysis
of the reaction mechanism.
Figure 10. Desorption peaks of each reagent in the pulse
ꢀ
adsorption method. HEP peaks were magnified 5 times.
Vacuum
KBr window
Outlet gas
Heating unit
3.8.1 Acid and Base Strengths of Catalysts: The acid and
base strengths of the catalysts were measured by the indicator
method.25 The indicators used were p-dimethylaminoazo-
benzene (pKa ¼ þ3:3), 4-phenylazo-1-naphthylamine (pKa ¼
IR
þ4:0), neutral red (pKa ¼ þ6:8), bromothymol blue (KBH
¼
þ7:2), phenolphthalein (KBH ¼ þ9:4), and 2,4,6-trinitroani-
line (KBH ¼ þ12:2).
The maximum acid strength of SiO2 itself was H0 ¼ þ3:3.
In contrast, the alkali metal oxide-added SiO2 catalysts did not
change the colors of all the indicators used; namely, the acid
strength is weaker than H0 ¼ þ6:8 and the base strength is
HEP
N2
Figure 11. Variable temperature IR unit.
weaker than H ¼ þ7:2. This result is reasonable because this
alyst. In contrast, the intensities of the desorption peaks of
NEP corresponded to the injection amount regardless of the
pulse number, and lacked long tails. These results indicate that
NEP is not strongly adsorbed to the catalyst. During the reac-
tion of HEP, the surface active sites are fully covered with
HEP; NVP is desorbed immediately after it is formed by the
dehydration of HEP. The adsorption behavior of NVP is sim-
ilar to that of NEP, indicating that NVP is also adsorbed weak-
ly to the catalyst. Considering the strong adsorption of HEP
and weak adsorption of NEP, we suggest that the strong ad-
sorption of HEP is due to the interaction of its OH group with
the surface of the catalyst.
3.8.3 Variable-Temperature IR: The IR spectra were
measured at different temperatures. The variable-temperature
IR unit we used is shown in Figure 11.
The IR spectrum of the fresh catalyst, from which the ad-
sorbents were desorbed at 400 ꢁC under flowing N2, shows
the absorption peak of the single silanol at 3740 cmꢃ1. This
peak was almost absent from the spectrum of the HEP-
adsorbed catalyst, which was treated at 100 ꢁC, as shown in
Figure 12. This peak increased only slightly when the temper-
ature was raised to 200 ꢁC, demonstrating that some of the
ꢃ
catalyst can be considered to be the salt (cesium silicate)
formed by the neutralization of CsOH and silicic acid. It
is probable that these weak active sites are strong enough to
effect the dehydration of HEP under high temperature.
3.8.2 Adsorption and Desorption Behaviors of Various
Reactants: This experiment was performed using the pulse
method as follows: the catalyst (Na2O/SiO2, 50 mg, 1/20
molar ratio), was fixed by quartz wool in the center of a stain-
less-steel reaction tube having an inside diameter of 4 mm and
a length of 10 cm. Nitrogen gas was passed through the cata-
lyst, which was kept at 300 ꢁC. A constant quantity (0.3 mL)
of the reactant was injected successively into the nitrogen
stream ahead of the catalyst. The outlet gases were monitored
by mass spectrometry. HEP, NVP, and N-ethyl-2-pyrrolidone
(NEP) were used as the reactants. NEP was used to investigate
the effect of the hydroxy group alone, since a hydroxy group in
HEP is replaced by hydrogen in NEP.
As shown in Figure 10, the desorption peak intensity of
HEP increased with the pulse number for the initial four pulses
and then leveled off after the fifth pulse. Each HEP peak had a
long tail, suggesting that HEP is strongly adsorbed to the cat-

Y. Shimasaki et al.
Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
457
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
alone Si-OH
HEP adsorbed Catalyst (200 °C)
↑
↑
↑
HEP adsorbed Catalyst (100 °C)
↑
Catalyst
3900
3400
2900
Wavenumber/cm-1
Figure 12. IR spectrum of the HEP-adsorbed catalyst. Catalyst: Cs2O/SiO2 (1/20 molar ratio), Calcined at 500 ꢁC for 2 h.
2400
1900
1400
3.9 Dehydration of HEP to NVP: Conclusions. First,
SiO2 to which a small amount of alkali metal oxide was added
exhibited pronounced catalytic activity in the intramolecular
dehydration of HEP to NVP in the vapor phase. Second, the
conversion of HEP decreased and the selectivity to NVP in-
creased with an increase in the ionization potential of the alkali
metal element added to SiO2. Third, for a catalyst to be effi-
cient, the acid strength should be weaker than H0 ¼ þ6:8
Pyr
H C
H
H
H
H
H C
H O
H C C Pyr
O H
H2O
O- M+
O- M+
H O
Si O Si
(I)
Si O Si
(II)
and the base strength weaker than H ¼ þ7:2. Fourth, it
ꢃ
is presumed that HEP is adsorbed to acid–base pairs on the
catalyst through the interaction of the hydroxy group in the
molecule with those sites, forming NVP by intramolecular
dehydration.
NVP
HEP
H O
O-
M+
O
Si O Si
(III)
(Pyr:
N )
4. The Process of NVP Production from MEA and GBL
Figure 13. Reaction mechanism proposed for the dehydra-
tion of HEP to NVP.
The total process consists of four parts: the HEP reaction
system, the HEP purification system, the NVP reaction system,
and the NVP purification system. A model flow sheet of the
new process of NVP production is shown in Figure 14.
Each system was established through an escalation from
a laboratory scale to a bench and a pilot scale process. We si-
multaneously developed the process for producing the practi-
cal catalyst.
Both higher quality and lower cost relative to other NVP
syntheses currently in use were necessary for a foray into the
market. Many factors were optimized, including influences
on stability and the cost of storage, as well as differences in
the new products’ reaction behavior from that of the current
NVP. Fortunately, the very high performance of the catalyst
enabled the use of simple purification systems and attainment
of the desired quality and cost.
4.1 Process of HEP Production. The reaction of GBL and
MEA to form HEP is carried out in the HEP tube reactor,
which contains structured packing. Water is simultaneously
fed to the reactor. This reaction is controlled by the composi-
tion of the reactants, the residence time, and the temperature.
HEP is purified by water stripping, removal of the heavy by-
product, and recovery of the GBL. GBL is formed by the de-
composition of the heavy by-product at the bottom of the HEP
recovery column. Both GBL and water are recycled.
4.2 Process of NVP Production. The NVP production
process consists of the vapor-phase reaction system, the trap-
ping system, and the purification system.
HEP was converted to NVP and desorbed from the catalyst.
This result suggests that HEP is adsorbed to the silanol group
on the catalyst.
3.8.4 Reaction Mechanism: The adsorption of HEP and
the successive reactions are proposed as shown in Figure 13.
From the fact that this reaction occurred on SiO2 alone, as seen
in Table 7, it seems possible that the active sites are acidic and
basic sites of the hydroxy group on SiO2. This hydroxy group
can remain on the alkali metal oxide/SiO2 catalyst because the
amount of alkali metal oxide is not large enough to cover the
SiO2 surface. The acidic sites presumably interact with the O
atom of the OH group in HEP. HEP is first adsorbed to the
silanol of the catalyst surface by the dehydration involving
the OH group of HEP and silanol (I). The basic site, which
is strengthened by the electron donation of Cs, pulls a proton
from the ꢁ-carbon atom, and vinylation occurs (II).
The comparison of the catalytic performance of SiO2 with
that of SiO2 enhanced with alkali or alkaline-earth metal oxide
in Table 8 indicates that acidic catalysts have low activity
while basic catalysts have much higher activity. The selectivity
to NVP is almost unchanged, regardless of the activity. This
tendency is not clear for the catalysts other than SiO2. The
acidic sites, proton of silanol and/or alkali metal cation of sil-
icate, probably play an important role in determining catalytic
performance.

458 Bull. Chem. Soc. Jpn. Vol. 81, No. 4 (2008)
AWARD ACCOUNTS
Waste
Water
Waste
Water
HEP
Recovery
Column
HEP
Evaporator
NVP
Reactor
HEP
Reactor
H2O
Strip
Column
Crystallizer
H2O
Strip
Colum
GBL
Recovery
Column
NVP
NVP
Collector
NVP
Recovery
Column
H2O
MEA
Heavy
Waste
GBL
Recoveried HEP
Figure 14. Model flow sheet of the new process of NVP production.
The vapor-phase reaction system is the core of this new
NVP production process. In general, an inert carrier gas, such
as nitrogen, is fed to a reactor to control the partial pressure
of the raw material and to carry out a continuous vapor-phase
catalytic reaction. It usually requires a large-scale absorption
column as well as a large amount of solvent to condense the
reaction products. Moreover, large volumes of inert carrier
gas have to be treated for recycling. In the new process,
HEP is fed to a fixed-bed-catalyst reactor equipped with a shell
and tube heat exchanger, with no carrier gas, under reduced
pressure. Consequently, the reaction products are easily con-
densed upon cooling, without any losses.
4.2.1 Vapor-Phase Reaction System: The following is a
practical example. HEP was evaporated and fed to a reactor at
a pressure of 10 kPa, a GHSV of 135–200 hꢃ1, and a reaction
temperature of 360–380 ꢁC. The selectivity of NVP was 98–
99%, and the conversion of HEP was 85%. The by-products,
aside from water, were small amounts of acetaldehyde and
2-pyrrolidone.
If the catalyst has carbon deposits, it can be reactivated
quickly by aeration at the reaction temperature. As a result,
the catalyst has a considerably long life and the reaction can
be run stably for long periods.
4.3 NVP Purification System. The high selectivity of
NVP in the vapor-phase dehydration allows us to produce
highly pure NVP (above 99.9%), as it is easy to remove the
water from the condensed reaction products by distillation
and then separate the NVP from unreacted HEP by distillation.
Unreacted raw material (HEP) can be recycled.
The distilled NVP contains small amounts of by-products.
These impurities could cause problems in the polymerization
of some kinds of polymers, so a further purification step, such
as crystallization, is required to purify distilled NVP.
4.4 Features of the New Process. The new process can be
operated continuously, from HEP production to NVP purifica-
tion, by several operators. The production yield of the process
is much higher than that of the conventional Reppe process.
The process produces high-purity NVP with small amounts
of wastes, which are composed mainly of water. It is thus
the most environmentally friendly process for NVP produc-
tion, overcoming the drawbacks of the Reppe process, and is
particularly suitable for mass production.
The authors thank Mr. Ariyoshi, Dr. Kurus, Mr. Ugamura,
Mr. Yamaguchi, and Mrs. Kondo for their continued support
in the development of catalyst and process. The authors also
thank the staff of the technical development and manufacture
departments in the Kawasaki plant for their support in the in-
dustrialization of this process, and the staff of the catalyst man-
ufacture department in the Himeji plant for the development
and production of the commercial catalyst. The authors also
thank Mr. Nakayama for obtaining the IR spectra.
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Yuuji Shimasaki was born in 1958 in Kochi, Japan. After graduating Tokyo University of Agri-
culture and Technology in 1980, he entered Graduate School of Nagoya Institute of Technol-
ogy. After he received a master’s degree from Nagoya Institute of Technology in 1982, he joined
Nippon Shokubai Chemical Industry. He was engaged in studies on methacrylic acid synthesis
catalyst during 1982–1984. After that he has been studied a solid acid–base catalysts and
vapor-phase organic syntheses up to 2004. During that he wrestled with the development of eth-
yleneimine production process and catalyst from 1984 to 1990, and the development of N-
vinyl-2-pyrrolidone production process and catalyst from 1991 to 2001. In 1992 he received
the 41st Chemical Society of Japan Award for Technical Development, and the Catalyst Society
of Japan Award in Technical Division. He has been a General Manager of Process Technology
Center of Nippon Shokubai Co., Ltd during 2004–2007. Now, he is a General Manager of
Catalyst Research Center of Nippon Shokubai Co., Ltd.
Hitoshi Yano was born in 1962 in Wakayama, Japan. After graduating Kyoto University
of in 1984, he entered graduate school of the same university. After he received a master’s degree
from Kyoto University in 1986, he joined Nippon Shokubai Chemical Industry. He was
engaged in the development of ethyleneimine production process and catalyst from 1986 to
1990, development of ethylene sulfide production process and catalyst from 1991 to 1995 and
the development of N-vinyl-2-pyrrolidone production process and catalyst from 1995 to 2001.
He is a General Manager of Process Technology Center of Nippon Shokubai Co., Ltd from April
2007.
Hideto Sugiura was born in 1972 in Kanazawa, Japan. After graduating School of Engineering,
Nagoya University in 1995, he entered graduate school of same university. After he received
a master’s degree from Graduate School of Engineering, Nagoya University in 1997, he
joined Nippon Shokubai Co., Ltd. He was engaged in remodeling of ethylene oxide process in
Kawasaki Chidori Plant during 1997–1999. After that he has been designed N-vinyl-2-pyrrolidone
production process up to 2006. During that he has been designed poly(vinylpyrrolidone)
production process from 2003 to 2006. From 2006, he has been engaged in remodeling of ethyl-
ene oxide process in Kawasaki Ukishima Plant. Now, he belongs to Technology Department of
Kawasaki Plant of Nippon Shokubai Co., Ltd.
Hideyuki Kambe was born in 1964 in Hyogo, Japan. After graduating Himeji Institute of Tech-
nology in 1987, he entered graduate school of Osaka university. After he received a master’s de-
gree from Osaka University in 1989, he joined Nippon Shokubai Chemical Industry. He was en-
gaged in the studies of a solid acid–base catalysts and vapor-phase organic syntheses from 1989 to
2001. He devoted himself to the development of N-vinyl-2-pyrrolidone production process and
catalyst during 1995–2001. Now, he is a Manager of Performance Chemical Business Division
of Nippon Shokubai Co., Ltd.