Towards an industrial synthesis of diamino diphenyl methane (DADPM) using novel delaminated materials: A breakthrough step in the production of isocyanates for polyurethanes

Article abstract of DOI:10.1016/j.apcata.2011.03.026

Delaminated materials ITQ-2, ITQ-6 and ITQ-18 are very efficient catalysts of zeolitic nature for the synthesis of diamino diphenyl methane (DADPM), the polyamine precursor in the production of MDI for polyurethanes. The exfoliation process results in excellent accessibility of their active sites to reactant molecules as well as fast desorption of products. These catalysts present higher activity and slower rates of deactivation than their corresponding zeolites. Moreover, the topology of the delaminated structure imposes a precise control of the isomer distribution, offering an additional flexibility in the synthesis of DADPM. By optimizing the process conditions it is possible to achieve final DADPM crude under industrial production specifications with ITQ-18. This catalyst represents a real chance for replacing HCl in the industrial production of DADPM.

Full text of DOI:10.1016/j.apcata.2011.03.026

Applied Catalysis A: General 398 (2011) 143–149
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Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Towards an industrial synthesis of diamino diphenyl methane (DADPM) using
novel delaminated materials: A breakthrough step in the production of
isocyanates for polyurethanes
P. Botellaa, A. Cormaa,∗, Robert H. Carrb, Christopher J. Mitchellb
a Instituto de Tecnología Química (UPV-CSIC), Universidad Politécnica de Valencia, Consejo Superior de Investigaciones Científicas, Avenida de los Naranjos s/n, 46022, Valencia, Spain
b HUNTSMAN Polyurethanes, Everslaan 45, B-3078 Everberg, Belgium
a r t i c l e i n f o
a b s t r a c t
Article history:
Delaminated materials ITQ-2, ITQ-6 and ITQ-18 are very efficient catalysts of zeolitic nature for the syn-
thesis of diamino diphenyl methane (DADPM), the polyamine precursor in the production of MDI for
polyurethanes. The exfoliation process results in excellent accessibility of their active sites to reactant
molecules as well as fast desorption of products. These catalysts present higher activity and slower rates
of deactivation than their corresponding zeolites. Moreover, the topology of the delaminated structure
imposes a precise control of the isomer distribution, offering an additional flexibility in the synthesis of
DADPM. By optimizing the process conditions it is possible to achieve final DADPM crude under indus-
trial production specifications with ITQ-18. This catalyst represents a real chance for replacing HCl in the
industrial production of DADPM.
Received 4 February 2011
Received in revised form 11 March 2011
Accepted 14 March 2011
Available online 21 March 2011
Keywords:
Aniline–formaldehyde condensation
Aminal
Diamino diphenyl methane
Solid acids
© 2011 Elsevier B.V. All rights reserved.
Delaminated zeolites
1. Introduction
ortho-isomers). Besides DADPM, higher molecular weight species
(basically triamines and tetramines) are also present in the product
Diamino diphenyl methane (DADPM, also named methylene-
dianiline, MDA) is the precursor of MDI (methylene diphenylene
diisocyanate), an important monomer for the synthesis of
polyurethanes and thermoplastics. Polyurethanes are used in the
production of flexible and rigid foam products, coatings, adhesives,
sealants, elastomers and binders, which have application in a wide
variety of industries like automotive, footwear, refrigeration, con-
struction and furniture [1]. In the USA alone, the 2003 production
of polyurethanes and related products was 4.9 million tonnes, with
a 2.8% growth increase over 2002 [2].
Commercially, DADPM is obtained by acid catalyzed conden-
sation of 2 molecules of aniline with 1 molecule of formaldehyde
at 60–80 ◦C. The reaction mixture is then heated at 100–160 ◦C to
complete the reaction. A sub-stoichiometric quantity of hydrochlo-
ric acid is normally used to catalyze the process, which after the
condensation has to be neutralized with NaOH giving an equivalent
amount of NaCl. The final mixture separates in two layers, organic
and aqueous. The former phase is distilled to recover the unreacted
aniline and crude DADPM is obtained [3,4]. This usually contains
more than 60% of 4,4ꢀ-DADPM (the para-isomer) and small amounts
(3–5%) of the other diamines, 2,4ꢀ-DADPM and 2,2ꢀ-DADPM (named
mixture (20–25%). The product distribution is strongly influenced
by the process variables and a high quality 4,4ꢀ-DADPM crude
is preferentially obtained by working at mild temperatures and
high aniline to formaldehyde (A/F) molar ratio. The recovered
DADPM product may then be used to produce MDI by reac-
tion with phosgene or conversion to isocyanate by non-phosgene
routes.
The main drawback of the homogenous process is the disposal of
the large amount of salt water liberated in the neutralization of HCl
that contains traces of aromatic amines which have to be removed
by biological treatment before discharging the residual water.
Substitution of HCl by a suitable solid acid will minimize the
generation of polluting water and it could allow the re-use of the
catalyst, resulting in a simpler process [3]. Many solid acid cata-
lysts have been evaluated over the past 30 years for the synthesis
of DADPM, as recently revisited by de Angelis et al. [4]. Among
them, ion-exchange resins have shown excellent selectivity to the
para-isomer, although their specific activity is low and the final
recovery and regeneration of the used catalyst has not been solved
[5,6]. Very recently the researchers from Dow Global Technologies
Inc. have obtained high yield in the production of 4,4ꢀ-DADPM and
its polymeric derivatives over an ion exchange resin based in a
styrene–divinylbenzene co-polymer but, unfortunately, this sys-
tem presents the same serious limitations for the re-use of the
expended catalyst [7].
∗
Corresponding author. Fax: +34 96 3877809.
E-mail address: acorma@itq.upv.es (A. Corma).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.03.026

144
P. Botella et al. / Applied Catalysis A: General 398 (2011) 143–149
Different salts of tungsten have also been tested (borides, sili-
crude DADPM to industrial production specifications, both in batch
and continuous flow reactor systems.
cides and sulfides) [8,9]. They present very mild acidity and their
activities are low even at high reaction temperatures (200 ◦C).
Acidic clays [10–13] and diatomaceous earth [12] have also shown
moderate activity for this process, which then requires high reac-
tion temperatures, favoring ortho-substitution and the formation
of polymeric DADPM. Silica–alumina has been claimed as an
active catalyst for DADPM synthesis [14–16], but also with low
yields of primary amines. However, recently Perego et al. have
proposed the use of several amorphous aluminosilicates charac-
terized by a narrow pore size distribution in the mesopore region
[17–19]. These materials show high activity in the conversion of an
aniline–formaldehyde condensate (aminal) to DADPM with a very
high ratio 4,4ꢀ-DADPM/(2,2ꢀ + 2,4ꢀ-DADPM) (5.99–6.71). Unfortu-
nately, they exhibit a relatively short catalyst life and some partial
destruction of the pore structure during thermal regeneration.
Despite the results obtained with other inorganic solid acids,
the best performance ever achieved in DADPM production used
zeolitic materials. Zeolite Y pre-treated with a fluorinated agent
[20], and Beta zeolite [17,21–25] in particular, have shown clear
improvements in catalyzing the reaction. There are three main
advantages of microporous materials as catalyst for this process:
(i) high acid site density, thus, improving catalytic activity and
catalyst life; (ii) a shape selectivity effect due to confined molecular
diffusion. (The work of researchers from Eni Tecnologie is partic-
ularly relevant, as by modifying the pore aperture and channel
diameter of Beta zeolite through a silylation treatment, they
were able to increase the ratio 4,4ꢀ-DADPM/(2,2ꢀ + 2,4ꢀ-DADPM)
in the range 2.2–5.8 [4,23]. A similar effect was also observed
upon treatment of the zeolite with boric acid (H3BO3) or with
orthophosphoric acid (H3PO4) as free acids or as ammonia salts
[24]; (iii) a moderate water resistance is claimed for some zeolites,
with a maximum tolerance of 3% H2O in the feed.
2. Experimental
2.1. Catalysts
ITQ-2, ITQ-6 and ITQ-18 catalysts have been prepared by expan-
sion and subsequent exfoliation of the corresponding laminar
precursors, respectively, of the MWW structure, Ferrierite (FER)
and Nu-6 [27–29]. In the case of ITQ-18, two samples of this mate-
rial were prepared with different levels of delamination. A further
sample of ITQ-18 was prepared as extrudates (1.6 mm diameter
with 20% w/w alumina binder). For the purpose of comparison, the
corresponding zeolitic materials MCM-22 [32], FER [33] and Nu-6
[34] were also synthesized.
Al content in all samples was monitored by atomic absorption
spectroscopy (Varian spectrAA-10 Plus). Powder X-ray diffrac-
tion patterns (not shown) were collected using a Philips XꢀPert
diffractometer equipped with a graphite monochromator, oper-
ating at 40 kV and 45 mA and employing nickel-filtered Cu-K␣
radiation (ꢀ = 0.1542 nm). Materials crystallite size was estimated
from TEM micrographs in a Philips CM-10 microscope operating at
100 kV. Acidity of samples was measured by the standard pyridine
adsorption–desorption method [35]. We are aware that this deter-
mination only distribution in some zeolites with narrow pores, like
Nu-6 and FER. However, this situation does not happen in the case
of delaminated materials, where most of their acid sites are fully
accessible to the probe. Surface area of catalysts was calculated by
the BET/BJH method with N2 adsorption/desorption performed at
77 K in a Micromeritics ASAP 2000 instrument. The most relevant
physicochemical properties of these catalysts are summarized in
Table 1.
The main drawback of zeolites is the strong limitation to molec-
ular diffusion imposed by a structure built of narrow geometrical
channels. Even in the case of a tri-dimensional zeolite with twelve-
ring (12-ring) pores, e.g., Beta, the process is controlled by diffusion,
which becomes evident as a reduction of the crystallite size gives
a significant enhancement of the primary amines production [26].
Moreover, restrictions to diffusion of reactants and products can
be even worse in the case of medium-pore size zeolites (e.g.,
ZSM-5, ERB-1) [21,22] or unidimensional structures (e.g., SSZ-59)
[26].
2.2. Reaction procedure
2.2.1. Synthesis of the aminal
To prepare the neutral A/F condensate 50.00 g of aniline (Aldrich,
99+% purity) were heated at 50 ◦C at autogeneous pressure in
a 100 ml two-necked flask with stirring. Formaldehyde (Aldrich,
37 wt% aqueous solution) was added with a syringe pump at
1.00 g min−1, until the mixture achieved an A/F molar ratio 3.0
(M). After complete condensation the mixture was distilled in a
rotavapor until less than 2 wt% of water was left (Karl-Fisher test).
As has been shown elsewhere, the accessibility of acid sites in
zeolitic materials can be drastically enhanced by delamination of a
given structure [27–30]. The exfoliation process can produce single
2.2.2. Batch testing
layered structures with large external surface areas (≥300 m2 g−1
)
4.00 g of the A/F mixture was introduced in a 25 ml flask, with
a reflux condenser and nitrogen inlet. The mixture was heated to
reaction temperature in a silicon bath and then the appropriate
amount of catalyst (typically 1.00 g) was added. After 60–120 min
the reaction was stopped by cooling the mixture in an ice bath. Then
the crude product was analyzed by gas chromatography (GC) and
1H NMR analysis (CDCl3, 300 MHz).
and very little, if any, microporosity. As a consequence, active sites
are highly accessible through the external surface and, at the same
time, reactant diffusion and product desorption are faster, as the
process takes place basically on the outer shell [31]. This produces
catalysts that are more active than their corresponding zeolites
for reactions controlled by the diffusion into the micropores. On
this basis, several delaminated zeolitic materials have been pro-
posed as suitable catalysts for the synthesis of DADPM [26], with
higher performance than large pore zeolites and with a much lower
rate of deactivation and superior resistance to water content in the
feed (up to 5%). Nevertheless, the amines distribution seems to be
strongly affected both by the process conditions and the topology
of the delaminated material. In the present contribution we explore
the keys for the efficient preparation of DADPM with delaminated
materials ITQ-2, ITQ-6 and ITQ-18. After presenting the reaction
scheme corresponding to a process catalyzed by solid acids, the
catalytic behavior of delaminated materials will be compared with
their corresponding zeolite precursors. Furthermore, we provide
optimized process conditions to accomplish the manufacture of
2.2.3. Fixed-bed testing
3.20 g of catalyst pelletized to 0.42–0.59 mm were charged in
a stainless-steel reactor (160 mm length, 10.5 mm ID) and the sys-
tem was pressurized at 4 bar with nitrogen. The neutral condensate
(A/F = 3.0 M; <1% H2O) was fed at 2.7–9.4 g h−1 with a Gilson 306
HPLC pump. Reaction at 160 ◦C was followed with time on stream
(TOS) by GC and 1H NMR.
In a second fixed bed test, 60 g of ITQ-18 extrudates were
charged in a stainless-steel reactor (22 cm length, 25 mm ID). Neu-
tral condensate (A/F = 4.0 M; ∼1.5% H2O) was fed at 1.0 g min−1 with
a HPLC pump. Reaction at 125 ◦C was followed with TOS by GC and
1H NMR.

P. Botella et al. / Applied Catalysis A: General 398 (2011) 143–149
145
Table 1
Physico–chemical characteristics of zeolites and delaminated materials tested in the present work.
c
d
Sample
Si/Al (M)a
Crystal (␮m)b
SEXT (m2 g−1
)
SMICRO (m2 g−1
)
Acidity (␮mol py)e
Brønsted
Lewis
250
250
350
400
350
400
MCM-22
ITQ-2
FER
ITQ-6
Nu-6
15
15
30
30
45
45
45
0.1
0.1
0.1
0.1
0.1
0.1
0.1
141
234
53
413
34
312
367
225
79
44
209
8
56
69
19
15
5
48
60
15
9
5
9
33
31
4
7
3
23
33
3
10
3
20
22
3
9
2
20
14
1
6
2
ITQ-18
ITQ-18B
610
892
16
14
4
3
7
19
6
13
6
10
6
a
As-made ratio determined by atomic absorption spectrophotometry.
As-estimated from the TEM images.
External surface area.
b
c
d
e
Micropore area.
Determined from the infrared spectra of adsorbed pyridine after evacuation at 250, 350 and 400 ◦C.
2.2.4. Product characterization
3. Results and discussion
3.1. Production of DADPM with zeolitic materials
For GC analysis, reaction samples were diluted with methanol
(1/10 v/v; Aldrich, 99.9+% purity). 1 ␮l of diluted sample was
injected in a Varian 3900 GC apparatus, equipped with a 30 m HP-
5 column and a FID detector. Nitrobenzene (Aldrich, 99+% purity)
was used as internal standard to calculate the content in free aniline
and the distribution of diamines and triamines. For 1H NMR anal-
ysis samples were exchanged several times with D2O in order to
remove all the labile protons (–NH2 and HOH signals). Spectra were
registered in a 300 MHz Varian Gemini spectrometer using CDCl3
as solvent (Aldrich, 99.9 atom %D). Chemical shift is expressed in ı
(ppm) relative to the tetramethylsilane used as internal standard.
Typically, four different groups of compounds can be quantified by
this technique (see Fig. 1): primary amines (1H NMR ı: 3.7, s, 2H, Ph-
CH2-Ph), secondary amines (1H NMR ı: 4.2, s, 2H, Ph-NH-CH2-Ph),
quinazolines (mainly 3-phenyl-3,4-dihydroquinazoline, 1H NMR ı:
4.8, s, 2H, Ph-CH2-NR2), and N-methylated derivatives (basically
N-methyl-DADPM, 1H NMR ı: 2.7–2.6, s, 3H, Ph-NH-CH3).
During the reaction, tar-like products were formed in the cat-
alyst, and this became dark-brown. Used catalysts were extracted
in a micro-soxhlet with CHCl3 for 24 h [36]. The solvent was evap-
orated and the remaining organic material was weighed, diluted
with CDCl3 and analyzed by GC–MS and 1H NMR. These frac-
tions were added to the amines content previously determined in
the liquid phase. Residual carbon content was quantified by ele-
mental analysis in order to estimate the non-extractable organic
deposit.
As commented before, the current industrial production of
DADPM is carried out through a homogeneous process in a sin-
gle step, where the aniline reacts with aqueous formaldehyde in
an agitated tank in the presence of hydrochloric acid. After separa-
tion of the organic layer, this is distilled to recover the aniline and
crude DADPM is obtained. However, when the process is catalyzed
by zeolitic materials this single step reaction is not feasible. The
main limitation comes from the organic/aqueous two-phase sys-
tem (aniline–water) present, which strongly hinders mass transfer
processes within the microstructure of the catalyst. As a conse-
quence, incomplete conversion of the neutral aminal is achieved.
In this sense, the preparation of DADPM over zeolites (in gen-
eral, over solid acids) works better through a two-step process
[4,10–24], as shown in Scheme 1: (i) synthesis of the aminal (I)
under neutral conditions by condensation of 2 mol of aniline with
1 mol of formaldehyde (aqueous solution), followed by removal
of the aqueous phase; here, an expensive distillation process can
be avoided if catalyst used in the next step shows resistance to
small amounts of water in the organic layer; (ii) isomerization
of the aminal into DADPM in the presence of a solid acid mate-
Fig. 1. 1H NMR characterization of the reaction showing the different groups of
products. Chemical shift is expressed in ı (ppm) relative to the tetramethylsilane
used as internal standard.
Scheme 1. General reaction scheme for the isomerization of the neutral aminal to
DADPM over zeolitic materials. Processes (1) and (2) involve several steps.

146
P. Botella et al. / Applied Catalysis A: General 398 (2011) 143–149
Table 2
DADPM synthesis on ITQ-2 and ITQ-6 in a batch reactor and comparison with their corresponding zeolitesa.
Catalyst
Amines
(%)b
Diamines
(%)c
Triamines
(%)c
Sec. Amines
(%)b
N-methylated
(%)b
Quinazolines DADPM distribution (%)c
(%)b
DADPM-isomer ratio
4,4ꢀ/(2,2ꢀ + 2,4ꢀ)
2,2ꢀ
2,4ꢀ
4,4ꢀ
MCM-22
ITQ-2
FER
95.9
98.4
60.3
98.1
79.3
83.8
53.7
79.9
16.6
14.6
6.6
3.1
0.3
36.9
0.8
1.0
1.1
2.0
0.8
0
1.1
3.8
0
14.8
37.7
8.9
63.4
42.3
44.8
46.3
4.3
1.0
5.0
1.4
0.2
1.0
0.3
ITQ-6
18.2
2.8
30.8
a
Experimental condition: A/F = 3.0 M (<1% H2O); T = 150 ◦C; 20 wt% catalyst; TOS = 60 min.
b
c
Determined by 1H NMR.
Determined by GC.
rial. The second step comprises several sequential reactions. The
acid catalyzed rearrangement of aminal takes place rapidly in the
presence of an aniline excess, producing secondary amines, mainly
aminobenzylanilines (ABAs) (II), by the electrophillic substitution
on an aromatic ring with a strong para–ortho orientating amino
group. The reaction is quantitative, even at low catalyst concentra-
tions, and is followed by the dissociation of ABA to give a benzylic
carbenium ion, which reacts with aniline to form DADPM (III).
Besides aniline, the carbenium ion can also react with DADPM
to give oligomeric amines (triamines and tetramines). The rear-
rangement takes place over Brønsted acid sites [19] and concerns
the slower step of the reaction, thus, being limited by pore diffu-
sion [37]. A catalyst suitable for industrial purposes will be able
to transform ABAs into the corresponding DADPMs with a final
concentration of secondary amines in the crude below 5000 ppm.
However, depending on the process conditions (e.g., reaction tem-
perature and A/F molar ratio) the product distribution can change.
The higher the excess of aniline the higher the concentration of
diamines in the product mixture. For steric reasons, 4,4ꢀ-DADPM
will be favored at low temperature. However, the para-isomer can
also isomerize to 2,4ꢀ and 2,2ꢀ-DADPM at high reaction temper-
atures via an acid catalyzed protodealkylation. Moreover, in the
presence of an excess of aniline, triamines and tetramines can
follow a transalkylation process to give back DADPM enriched in
the 2,4ꢀ fraction [38]. The physico–chemical characteristics of the
solid acid catalyst (essentially the strength and distribution of acid
sites), can bring about the formation of several by-products, which
decrease the quality of the final crude. The most important ones
are quinazolines (IV) and N-methylated products (V). These last
are particularly undesirable because they cannot be transformed
into isocyanate groups through reaction with phosgene. Although
in the homogeneous process N-methylation takes place through
the Plöchl reaction [39], in our case, as the condensation step occurs
in neutral conditions, this is not feasible. We hypothesize that N-
methylated derivatives can be formed by rearrangement of the ABA
intermediate by strong acid sites (see Scheme 1). Suitable DADPM
crude will have less than 1% of N-methylated compounds, prefer-
ably, less than 0.5%.
4,4ꢀ-DADPM decreases significantly in the case of ITQ-2, with a
4,4ꢀ-DADPM/(2,2ꢀ + 2,4ꢀ-DADPM) ratio about 1 (higher than 4 for
MCM-22). The large dimensions (14.6 × 7.4 × 4.6 A) of the aminal
˚
molecule give rise to a strong steric hindrance to diffusion through
the 10-ring channels. Therefore a shape selectivity effect within
the zeolitic structure is expected, which favors the production of
the linear isomer 4,4ꢀ-DADPM. Conversely, the aminal molecules
can easily be accommodated in the large opened cavities of the
external surface. In this sense, as the internal volume accessible is
limited, the reaction takes place on the outer surface of the catalyst
where no shape selectivity effect will be evident with ITQ-2. The
reaction only takes place on the external surface, and the product
distribution is controlled by the thermodynamics of the process (at
150 ◦C the reaction in hydrochloric acid yields 56.0% 4,4ꢀ-DADPM,
35.2% 2,4ꢀ-DADPM and 8.8% 2,2ꢀ-DADPM) [40].
The effect of the exfoliation process on the catalytic behavior
is also seen for ITQ-6 and its corresponding zeolitic precursor FER
(both with a Si/Al molar ratio of 30). ITQ-6 presents a surface with
opened cavities of 10-ring with a large increase of the external
surface area (Table 1). Although ITQ-6 shows a somewhat lower
concentration of Brønsted acid sites than FER due to some dea-
lumination inherent to the delamination process, these are more
accessible to bulky molecules. This was formerly demonstrated by
our group by measuring the adsorption of 2,6-di-tert-butylpyridine
(DTBPy) that certainly cannot penetrate in the 10-ring pores of
FER [28]. The results showed that a much higher amount of DTBPy
is adsorbed on ITQ-6 (90% accessibility) than on FER (∼5% acces-
sibility). Therefore, the superior catalytic activity offered by the
delaminated material in the synthesis of DADPM is not surprising
(Table 2). Again the delamination process involves the loss of the
shape selectivity effect inherent to the zeolitic structure, and ITQ-6
presents a 4,4ꢀ-DADPM/(2,2ꢀ + 2,4ꢀ-DADPM) ratio of 1.4, whereas in
FER this ratio is 5.0.
3.3. Production of DADPM with ITQ-18
Another delaminated zeolitic material developed by our group
is ITQ-18, the exfoliated form of Nu-6 zeolite [29]. Its framework
structure has been recently solved [30] and is characterized by the
existence of 1D straight eight- ring (8-ring) channels developing
along the [0 1 0] direction and two non-equivalent sets of 8-ring
channels alternating along the crystallographic c direction.
We have tested Nu-6 and ITQ-18 samples, both with a Si/Al
molar ratio of 45, for the synthesis of DADPM in a batch reactor
and the results are presented in Table 3. They show the exfoliation
process leads to a significant increase in the production of primary
amines and a lower production of N-methylated impurities, which
is in agreement to that observed in ITQ-2 and ITQ-6 materials.
However, ITQ-18 presents a catalytic behavior clearly different to
the other delaminated samples. On one hand, ITQ-18 is less active
than ITQ-2 and ITQ-6, and needs more severe process conditions
(i.e., higher reaction temperature and/or higher catalyst loading)
to achieve full conversion of secondary amines. According to the
3.2. Production of DADPM with ITQ-2 and ITQ-6
ITQ-2 comes from the exfoliation of the layered precursor
of MCM-22 [26]. The delamination treatment makes accessible
large cavities on the surface corresponding to twelve-ring (12-
˚
ring) pores of about 7 A diameter, whereas in the original zeolite
only the ten-ring (10-ring) channels are accessible to the reac-
tant molecules. As a consequence, a significant increase in the
external surface area is achieved (Table 1). In the delaminated
material better accessibility of the acid sites and lower limita-
tions to molecular diffusion are expected. This is reflected by the
superior activity of ITQ-2 versus MCM-22 (as determined by the
content of primary amines in the reaction mixture), both with a
Si/Al molar ratio of 15 (Table 2). Nevertheless, the selectivity to

P. Botella et al. / Applied Catalysis A: General 398 (2011) 143–149
147
Table 3
DADPM synthesis on ITQ-18 samples and comparison with the corresponding zeolite Nu-6a.
Catalyst
Amines
(%)b
Diamines
(%)c
Triamines
(%)c
Sec. Amines
(%)b
N-methylated
(%)b
Quinazolines
(%)b
DADPMdistribution (%)c
DADPM-isomer ratio
4,4ꢀ/(2,2ꢀ + 2,4ꢀ)
2,2ꢀ
2,4ꢀ
4,4ꢀ
Nu-6
ITQ-18
ITQ-18B
74.7
90.7
89.3
64.9
71.8
71.3
9.8
18.9
18.0
22.0
7.7
8.6
2.3
1.3
1.8
1.0
0.3
0.3
0
0.6
0.6
11.3
12.8
12.9
53.6
58.3
57.8
4.7
4.4
4.3
a
Experimental condition: A/F = 3.0 M (<1% H2O); T = 150 ◦C; 20 wt% catalyst; TOS = 60 min.
b
c
Determined by 1H NMR.
Determined by GC.
standard pyridine adsorption–desorption method (Table 1), ITQ-
18 possesses a smaller population of medium strength Brønsted
acid sites, which are those active in the isomerization reaction,
as a consequence of its lower Si/Al molar ratio. The importance
of the acid site density and strength in the catalytic performance
has been reported for amorphous aluminosilicates [19]. Unfortu-
nately, it has not been possible to synthesize the ITQ-18 structure
with a higher framework Al content. On the other hand, it is sur-
prising that ITQ-18 retains the selectivity to para-substitution of
the parent zeolite Nu-6. This can be rationalized through con-
sideration of the 8-ring channels of Nu-6 which are very narrow
˚
(4.5 × 2.6 A). This precludes the internal diffusion of the aminal
molecule, which means that the isomerization into DADPM takes
place mostly on the outer surface. A preliminary study of diffu-
sion within the pore structure by MonteCarlo Simulation and of
adsorption within pores by Molecular Dynamics Simulation [41],
has reported that the large opened cavities present on the surface
of ITQ-2 and ITQ-6 materials are deep enough to allow the ortho-
substitution in the isomerization reaction. Conversely, the same
study revealed that the interaction of 4-ABA and the substitution
in the 4-position are favored in the shallow cavities present on the
surface of Nu-6 and ITQ-18.
As the exfoliation process involves a large increase in the acces-
sibility to reactant molecules of the catalytically active hydroxyl
bridging groups, and then an increase in the production of primary
amines, one could think that the way to increase the specific activ-
ity of ITQ-18 could be to extend the process of delamination as
much as possible. This has been done by synthesizing another sam-
ple through a prolonged treatment in the ultrasound bath (Table 1,
ITQ-18B). This material presented an increase of about 50% in the
external surface area and a similar distribution of acid sites as
standard ITQ-18. However, no improvement in the catalytic per-
formance was achieved (Table 3), showing that all catalytic sites
are accessible in both samples.
Fig. 2. Production of secondary amines and amine distribution over ITQ-18 sample
vs. the catalyst load in the rearrangement of the neutral condensate (A/F = 3.0 M;
<1% H2O) in a batch reactor. Symbols: Secondary amines (ꢀ); diamines/triamines
(wt/wt) ratio (ꢁ); 4,4ꢀ-DADPM/(2,2ꢀ + 2,4ꢀ-DADPM) (wt/wt) ratio (ꢁ). Experimental
conditions as in Table 4.
in neither the 4,4ꢀ-DADPM/(2,2ꢀ + 2,4ꢀ-DADPM) ratio, nor in the tri-
amines production. When increasing the reaction temperature in
the range 110–160 ◦C there is a dramatic reduction of the sec-
ondary amines content in the final crude (respectively, from 31.5%
to less than 0.1%), although such temperature increases result in
an increase in the degree of ortho-substitution [4]. Therefore, an
increasein the concentration of ortho–para and ortho–ortho isomers
is observed and the 4,4ꢀ-DADPM/(2,2ꢀ + 2,4ꢀ-DADPM) ratio drops
from 6.9 to 3.6 (Table 4 entries 2, 4–6, Fig. 3). Furthermore, the
higher reaction temperature favors DADPM oligomerization, which
is reflected by an increase in the triamines fraction.
3.4. Catalytic deactivation of ITQ-18 in a continuous flow
fixed-bed reactor
Nonetheless, complete conversion of the aminal (as measured
by the total disappearance of secondary amines in the mixture),
can be achieved over ITQ-18 by moving to more severe process
conditions. By increasing the catalyst loading in the range 16–24%
at 150 ◦C (Table 4, entries 1–3, Fig. 2), the percentage of aminoben-
zylanilines decreases from 10.8% to 0.6% with no substantial change
As commented before, the main limitation for the application
of zeolites as catalysts in the synthesis of DADPM is their fast
deactivation. During the reaction strongly basic compounds (e.g.,
quinazolines) can be irreversibly adsorbed on acid sites, leading to
Table 4
DADPM synthesis on ITQ-18 in a batch reactor: effect of the catalyst loading and the reaction temperaturea.
T (◦C)
Weight
(%)
Amines
(%)b
Diamines
(%)c
Triamines
(%)c
Sec. Amines
(%)b
N-methylated
(%)b
Quinazolines
(%)b
DADPM distribution (%)c
DADPM-isomer ratio
4,4ꢀ/(2,2ꢀ + 2,4ꢀ)
2,2ꢀ
2,4ꢀ
4,4ꢀ
150
150
150
110
130
160
16
20
24
20
20
20
86.8
90.7
98.2
67.4
86.3
99.5
71.0
71.8
80.9
60.0
72.6
73.7
15.4
18.9
17.3
7.4
13.7
26.3
10.8
7.7
0.6
31.5
12.4
<0.1
2.1
1.3
1.2
0.8
1.0
0.5
0.3
0.3
<0.1
0.3
0.3
<0.1
0.7
0.6
1.6
0
0
1.1
13.4
12.8
14.9
7.6
10.7
15.0
56.9
58.3
64.3
52.4
61.9
57.6
4.0
4.4
3.9
6.9
5.8
3.6
a
Experimental condition: A/F = 3.0 M (<1% H2O); TOS = 120 min.
Determined by 1H NMR.
Determined by GC.
b
c

148
P. Botella et al. / Applied Catalysis A: General 398 (2011) 143–149
Fig. 3. Production of secondary amines and amine distribution over ITQ-18
samples vs. the reaction temperature in the rearrangement of the neutral conden-
sate (A/F = 3.0 M; <1% H2O) in a batch reactor. Symbols: Secondary amines (ꢀ);
Diamines/triamines (wt/wt) ratio (ꢁ); 4,4ꢀ-DADPM/(2,2ꢀ + 2,4ꢀ-DADPM) (wt/wt)
ratio (ꢁ). Other experimental conditions as in Table 4.
blocking of the micropores and rapid deactivation. To avoid this,
researchers working with zeolites have carried out the reaction
with very high aniline to formaldehyde ratios, which requires the
use of large reactors and the distillation and recycling of a large vol-
ume of aniline. At the end of the reaction, the partially exhausted
zeolite catalyst can be regenerated, which is usually performed by
burning of the organic deposit in air or oxygen, although it can
also be suggested that regeneration can be achieved by washing
the catalyst with aniline [42]. In the case of delaminated mate-
rials, one would expect that the large external surface area and
the absence of microporosity will preclude a fast deposition of the
reaction products on the catalyst surface. To demonstrate this, the
rearrangement of aminal (A/F = 3.0 M; <1% H2O) has been carried
out in a continuous flow fixed-bed reactor working at 160 ◦C, 4 bar
and a contact time (W/F) of 0.34 h. The results presented in Fig. 4
Fig. 5. Rearrangement of the neutral condensate (A/F = 3.0 M; <1% H2O) in
a
continuous flow fixed-bed reactor over ITQ-18 fresh sample and after four
reaction-regeneration cycles. (a) Production of primary and secondary amines; (b)
4,4ꢀ-DADPM/(2,2ꢀ + 2,4ꢀ-DADPM) (wt/wt) ratio. Symbols: Fresh ITQ-18 (ꢀ,ꢁ); regen-
erated catalyst (ꢁ,᭹). Experimental conditions: W/F = 0.34 h; T = 150 ◦C; P = 4 bar.
show that delaminated ITQ-18 material displays a slow decay over
the 8 h duration of the experiment, after which it retains 94% of
the initial activity. Under similar process conditions, Beta zeolite
shows the same initial activity but a much higher rate of deacti-
vation, and after 8 h of TOS the catalyst barely achieves 30% of the
initial activity [26]. Moreover, if the contact time is increased to
1 h, ITQ-18 shows no sign of catalytic decay over the same dura-
tion of the experiment, with no production of secondary amines
and a constant 4,4ꢀ-DADPM/2,2ꢀ + 2,4ꢀ-DADPM) ratio about 80% of
the para-isomer (Fig. 4). This is in agreement with former results
published by our group on the stability of the catalytic behavior of
ITQ-2 during the isomerization of the aminal, as a consequence of
the improved molecular diffusion and faster desorption of products
inherent to a process that takes place mainly on the outer shell of
the catalyst [26].
Even if catalytic deactivation occurs slowly, sooner or later
catalyst regeneration is needed. Here, ITQ-18 exhibits excellent
performance after thermal regeneration in air (540 ◦C, 24 h). Fig. 5
shows the results obtained in the acid rearrangement of the ami-
nal (A/F = 3.0 M; <1% H2O) in a continuous flow fixed bed reactor
(T = 150 ◦C, P = 4 bar, W/F = 0.34 h) with catalyst fresh and after
4 reaction-regeneration cycles. No significant change in amines
production neither in the product distribution is observed. The
complete burning of the organic deposit in the regenerated cat-
alyst was confirmed by elemental analysis, with carbon content of
about 0.1 wt%.
The benefits of using a delaminated material are also demon-
strated at
a significantly larger technical scale, where the
rearrangement of aminal (A/F = 4.0 M; ∼1.5% H2O) has been car-
ried out using ITQ-18 extrudates in a continuous flow fixed-bed
reactor working at 125 ◦C, 4 bar and a contact time (W/F) of 1 h. The
results presented in Fig. 6 show that delaminated ITQ-18 extrudates
display little decay over the 72 h duration of the experiment. Over
this same period the 4,4ꢀ-DADPM/(2,2ꢀ + 2,4ꢀ-DADPM) ratio remains
constant at ∼4.3. Overall levels of N-methylated impurities were
Fig. 4. Rearrangement of the neutral condensate (A/F = 3.0 M; <1% H2O) over ITQ-
18 sample in a continuous flow fixed-bed reactor. (a) Production of primary and
secondary amines; (b) 4,4ꢀ-DADPM/(2,2ꢀ + 2,4ꢀ-DADPM) (wt/wt) ratio. Symbols:
W/F = 0.34 h (ꢁ,᭹); W/F = 1.17 h (ꢀ,ꢁ). Other experimental conditions: T = 160 ◦C;
P = 4 bar.

P. Botella et al. / Applied Catalysis A: General 398 (2011) 143–149
149
Acknowledgements
The authors thank Huntsman Polyurethanes and CICYT
(MAT2006-14274-C02-01), Project Prometeo from Generalitat
Valenciana, Project MULTICAT (Consolider-Ingenio 2010) and Fun-
dación Areces for financial support.
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4. Conclusions
Delaminated materials ITQ-2, ITQ-6 and ITQ-18 are active and
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