Tert-Butylation of diphenylamine over zeolite catalysts comparison of different alkylation agents and catalysts

Article abstract of DOI:10.1016/j.catcom.2011.12.005

tert-Butylation of diphenylamine (DPA) with different tert-butylation agents isobutylene (IB), tert-butanol (TBA), and C₄-fraction (C4-IB) in the liquid phase was studied over zeolite catalyst H-BEA (H-BEA CP 814E). This zeolite and acidic clay

Full text of DOI:10.1016/j.catcom.2011.12.005

Catalysis Communications 18 (2012) 176–181
Contents lists available at SciVerse ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
tert-Butylation of diphenylamine over zeolite catalysts comparison of different
alkylation agents and catalysts
a
a
a
a
a
Gabriel Kostrab a, , Martin Lovič , Andrej Turan , Pavol Hudec , Alexander Kaszonyi , Martin Bajus ,
⁎
Ján Uhlár b, Peter Lehocký b, Dušan Mravec a
Institute of Organic Chemistry, Catalysis and Petrochemistry, Faculty of Chemical and Food Technology, Slovak University of Technology, Radlinského 9, 812 37 Bratislava, Slovak Republic
a
b
VUCHT, a.s., Nobelova 34, 836 03 Bratislava, Slovak Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
tert-Butylation of diphenylamine (DPA) with different tert-butylation agents isobutylene (IB), tert-butanol (TBA),
and C4-fraction (C4-IB) in the liquid phase was studied over zeolite catalyst H-BEA (H-BEA CP 814E). This zeolite
and acidic clay catalysts Nobelin and Fulcat 22B were compared in tert-butylation of diphenylamine with isobu-
tylene and tert-butanol.
The study of the influence of tert-butylation agents in alkylation of DPA over H-BEA showed that isobutylene is
the most suitable in tert-butylation of diphenylamine over the particular H-BEA zeolite catalyst in terms of con-
version and selectivity to desired products.
Comparative study of catalyst type influence on tert-butylation of DPA with TBA and IB employed zeolite catalyst
H-BEA and two clay ones Nobelin and Fulcat 22B. The study showed that all catalysts perform well in alkylation
of DPA but H-BEA with the highest total acidity is the most active.
tert-Butylation of diphenylamine over H-BEA zeolite catalyst and acidic clays appears to be an environmental
alternative to other catalysts (e.g. Friedel-Crafts) in industrial preparation of tert-butylated diphenylamines.
© 2011 Elsevier B.V. All rights reserved.
Received 28 September 2011
Received in revised form 21 November 2011
Accepted 1 December 2011
Available online 10 December 2011
Keywords:
tert-Butylation
Diphenylamine
Zeolites
Clay catalyst
Para-selectivity
Antioxidants
1. Introduction
Zeolite catalysts have been successfully used for the production of
fine organic chemicals [16–18]. They have limited utilization for the
Alkylation of aromatics is an acid catalyzed reaction and it is an
important process in petrochemistry as well as in fine chemical syn-
theses [1,2].
Some alkylated diphenylamines are important additives for sta-
bilizing organic products that are subjected to oxidative, thermal,
and/or light-induced degradation. These organic products are widely
used in engineering, for example as lubricants, hydraulic fluids, metal-
working fluids, fuels, or polymers.
Alkylated diphenylamines are manufactured by alkylation of diphe-
nylamine with monomers or oligomers of isobutylene (IB), propylene
and with 1-nonene, styrene, α-methylstyrene (AMS) and others using
different acid catalysts (mostly classical Friedel-Crafts) to produce tert-
butylated, octylated, nonylated, styrenated and cumylated diphenyl-
amines which are the most important chemicals used in antioxidant
formulations [3] (Scheme 1).
Acidic clay catalysts reported in the patent literature are claimed
to be excellent in the production of various alkylated diphenylamines
[4–13]. Acid-treated and rare earth-modified clays have received con-
siderable attention as catalysts for this industrially important reaction
[14,15]. Acid-treated clays are especially active catalysts for the alkyl-
ation of DPA with α-methylstyrene as the alkylating agent [15].
transformations of large molecules due to diffusion limitations caused
by their restricted pore size. The question remains whether these lim-
itations can be considered as absolute or exceptions can be found.
In our previous work [22] we have studied various zeolite catalysts
to evaluate their efficiency in tert-butylation of DPA with tert-butanol
in the liquid phase. After preliminary screening we have concluded
that H-BEA CP 814E showed the best results in conversion, selectivity
and dialkylation. Subsequently we have optimized reaction conditions
— temperature, TBA/DPA molar ratio and catalyst charge amount.
In the presented paper we have investigated the possibility of utili-
zation of zeolite catalyst H-BEA (CP 814E) and clay catalysts Nobelin
and Fulcat 22B in the alkylation of DPA with different tert-butylation
agents as tert-butanol, isobutylene and C4-fraction containing isobutyl-
ene. The influence of catalytic activity and selectivity of these catalysts
on alkylation of DPA with different tert-butylation agents is evaluated,
compared and discussed in this paper.
2. Experimental
2.1. Catalysts and chemicals
Commercially available zeolite catalyst H-BEA (CP 814E) from
Zeolyst Int. and clay catalysts Nobelin (Rudex s.r.o., Bratislava, Slovakia)
and Fulcat 22B (Rockwood Additives, UK) were used as alkylation
⁎
Corresponding author at: SLOVNAFT, a.s., Member of MOL Group, Slovak Republic.
E-mail address: gabriel.kostrab@slovnaft.sk (G. Kostrab).
1566-7367/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2011.12.005

G. Kostrab et al. / Catalysis Communications 18 (2012) 176–181
177
Table 2
Composition of the used industrial C4-fraction (C4-IB).
Component
wt.%
Propane
0.1
Propene
0.3
i-Butane
4.3
Scheme 1. tert-Butylation of diphenylamine.
n-Butane
7.3
trans-2-Butene
1-Butene
2-Methylpropene (isobutylene)
Cis-2-butene
1,3-Butadiene
Unidentified
8.4
28.4
44.9
5.9
Traces only
0.4
catalysts. Characteristic properties of these catalysts are in Table 1. All
clay catalysts were used as purchased. H-BEA was activated by calcina-
tion in a stream of dry air at 500 °C during 6 h. Clay catalysts without
thermal activation were chosen for the DPA alkylation because it was
proven during previous studies, that they are more active than activated
ones. During thermal activation (500 °C), they lose residual mineral
acid they were pretreated with, therefore losing part of their acidity.
Also clays during their thermal procedure are losing water and thus
changing their structure. All this leads to decreased acidity after thermal
procedure and subsequently to decreased catalytic activity.
gas was helium (0.5 ml/min). Temperature program: from 110 °C with
gradient 3 °C/min to 270 °C.
Reaction time 0 min is defined as the time when reaction temper-
ature is reached (180 °C).
All chemicals except IB containing C4-fraction (diphenylamine, tert-
butanol, isobutylene and n-heptane) were of analytical grade purity
purchased from Sigma-Aldrich GmbH, Germany. IB containing C4-
fraction was obtained from a local producer (Kaučuk Kralupy, Czech
Republic). Composition of IB containing C4-fraction is in Table 2. 1,3-
butadiene was removed from this industrial C4-fraction by extraction.
Calculations are based on following formulas: 4,4′-DTBDPA/4-
TBDPA = moles of 4,4′-di-tert-butyldiphenylamine/moles of 4-
tert-butyldiphenylamine,
S4-TBDPA =(4-TBDPA/Σ TBDPA)×100,
S
4,4′-DTBDPA =(4,4′-DTBDPA/Σ DTBDPA)×100.
3. Results and discussion
2.2. Apparatus, procedure and analysis
3.1. Comparison of alkylation agents over H-BEA
The alkylation of diphenylamine was carried out in the laboratory
autoclave reactor (100 ml) equipped with magnetic stirring and elec-
trical heating with temperature regulation. The weighted amount of
liquid isobutylene or C4-fraction was introduced to the reactor from
the special steel sampler through two needle valves after heating
the sampler to circa 90 °C. In a typical run, diphenylamine (20 mmol),
70 ml n-heptane as a solvent and 0.7 g of freshly calcined zeolite cata-
lyst kept at 200 °C after calcination were used in alkylation reactions.
The clay catalysts (Nobelin and Fulcat 22B), were used as received with-
out activation procedure because higher temperature has negative in-
fluence on the clay structure and its catalytic activity decreases. For
reusabitity test, used zeolite catalyst was filtered from reaction mixture,
washed with n-heptane and methanol and calcined to remove any
trapped organics. Clay catalyst was washed with n-heptane and metha-
nol and dried at 120 °C. As to alkylating agents, tert-butanol, isobutylene
or isobutylene containing C4-fraction were introduced into autoclave
reactor in amount of 40 mmol. The amount of isobutylene containing
C4-fraction was calculated to meet IB content of 40 mmol. The reactor
was flashed thrice with nitrogen to replace air before adding the alky-
lating agent. Alkylation reactions were carried out at 180 °C and at the
autogenous pressure at stirring 1000 min−1 (see Ref. [22]).
The influence of different tert-butylation agents on tert-butylation
of diphenylamine (DPA) was studied over commercially available
zeolite catalyst H-BEA. The reaction conditions were as optimized
in Ref. [22].
The main reaction products have been identified by GC–MS and 1H-
NMR as 4-tert-butyldiphenylamine and 4,4′-di-tert-butyldiphenyla-
mine () in all cases. Other reaction products were identified as mono-
octylated diphenylamines, isomers of mono- and di-tert-butylated
diphenylamines and isomers of tert-butyl octyl diphenylamine. The
main desired reaction products are 4-tert-butyldiphenylamine and
4,4′-di-tert-butyldiphenylamine (para- or para, para′-isomers).
2-tert-butyldiphenylamine or other ortho-alkylated diphenylamines
(mono or dialkylated) were not present in the final reaction mixture
(1H-NMR). Free electron pair on N activates ortho- and para-positions
of DPA aromatic ring. This fact influences tert-butylation to these posi-
tions. tert-Butyl group on aromatic ring of DPA activates ortho- and
para-positions on the second aromatic ring. The formation of ortho- or
ortho, ortho′-isomers is hindered by the position of –NH in Ph–NH–Ph
and bulky tert-butyl group. As to theoretically possible N-alkylation
of diphenylamine, there was not any presence of N-tert-butylated
diphenylamine in the reaction mixture (1H-NMR) probably due to
sterical hindrance of –NH and given reaction conditions which, as
we assume, prefer N-dealkylation and further shift of alkyl from N-
to aromatic ring of DPA.
The samples of the reaction mixture were withdrawn periodically
from the closed reactor and were analyzed on CHROMPACK 9002 gas
chromatograph equipped with CP Sil 5 CB column (25 m×0.53 mm)
and FID detector. The temperature program of the chromatographic
analysis was: 110 °C (5 min), from 110 °C to 275 °C with a slope of
3 °C/min.
Fig. 1 shows the influence of alkylating agents on the conversion
of DPA. The highest conversion of DPA was obtained using IB. After
120 min the conversion reached 99% and then slowly decreased. In
the case of IB containing C4-fraction, the conversion of DPA was
continuously increasing throughout reaction time interval reaching
its maximum at 95%. The lowest conversion of DPA was achieved
using TBA as alkylating agent; the local maximum was 94% at
120 min and slowly decreasing to 91% at 480 min of reaction time.
The small formal decrease of conversion can be probably ascribed
to secondary reactions, namely dealkylation i.e. splitting of IB from
tert-butyl DPA and formation of isobutylene dimer. The dimerisation
of IB decreases its concentration and shifts alkylation equilibrium to
a higher concentration of DPA. In all alkylations with IB, where for-
mal decrease of conversions of alkylated compound was observed,
an increased formation of diisobutylene was detected [19–22]. IB
The reaction products were identified on GC/MS QP5000 (Shimadzu)
with EI and capillary column (HP-1, 50 m×0.2 mm×0.33 μm), carrier
Table 1
Characteristic properties of catalysts.
Catalyst
SBET
Vmicro,t
Smeso t
,
Aciditya
(m2/g)
(cm3/g)
(m2/g)
(mmol/g)
H-BEA (12.5) CP 814 E
Fulcat 22B
Nobelin
707
240
164
0.196
0.015
0.007
309
205
148
1.03
0.242
0.183
a
Total acidity was determined by standard TPDA method.

178
G. Kostrab et al. / Catalysis Communications 18 (2012) 176–181
effective the combination of catalyst and particular alkylation agent
is in the production of dialkylated DPA. The highest 4,4′-DTBDPA/4-
TBDPA ratio (2.2) was achieved using IB, significantly lower ratio
was observed with C4-IB (0.88) and the poorest result was obtained
with TBA (0.62). We suppose that the achieved ratio of di/mono alky-
lated derivatives is a question of chemical equilibrium, which is shifted
by the concentration of free IB. In C4-fraction, IB is diluted by the other
hydrocarbons. In TBA, it is chemically bonded. Moreover, water formed
by alkylation with TBA depresses the evolution of IB from TBA and
formation of reactive carbcation. Ratio of 4,4′-/4-isomers is a mirror
of reactivity of different alkylation agents because of consecutive
alkylation reactions. The decrease of this ratio with time for pure
IB is connected to the partial dealkylation of tert-butylated DPA and
di-tert-butylated DPA. H-BEA zeolites are the most acidic from the
tested range of catalysts (Table 1), and dealkylation of 4,4′-di-tert-
butyl DPA is preferred as a consequence of decreasing concentration
of IB removed by dimerisation.
The study of the influence of tert-butylation agents in the alkyl-
ation of DPA over H-BEA with TBA, IB and C4-IB revealed that all
mentioned agents are good in tert-butylation of diphenylamine in
terms of conversion and selectivity to desired products. Depending
on specific demand for certain tert-butylated DPA product (mono-
or di-tert-butylated DPA) and availability of tert-butylating feed one
can decide which agent could be utilized. For example, in the case of
high 4,4′-DTBDPA demand, IB can be beneficially used because with IB
one can obtain 2.2 times higher 4,4′-DTBDPA yield at 97% conversion
of DPA with 88% selectivity to 4,4′-DTBDPA.
Fig. 1. The influence of the alkylation agent on conversion of DPA over H-BEA (for re-
action conditions see Section 2.2).
in C4-fraction is diluted other hydrocarbons and dimerisation of IB
is depressed. In the case of TBA, water formed by dehydration of
TBA can react with IB to form back TBA and part of IB can form
dimer, so conversion of DPA formally decreases with time.
Fig. 2 shows the influence of alkylating agent on selectivity to 4-
TBDPA and 4,4′-DTBDPA in tert-butylation of DPA over H-BEA. It can
be clearly seen from Fig. 2 that all tert-butylation agents used in the
DPA alkylation screening perform well. Selectivity to 4-TBDPA and
also to 4,4′-DTBDPA is high and the obtained results do not differ
much within studied range of tert-butylation agents. Para-selectivity
(4-TBDPA and 4,4′-DTBDPA) is a result of activation of ortho- and
para-positions of DPA molecule but due to steric reasons alkylation
to the ortho-position is very problematic. So the differences in selec-
tivities between alkylation agents are small.
3.2. Zeolite versus clay catalysts
3.2.1. Zeolite versus clay catalysts (TBA as alkylation agent)
Clay catalysts reported in the patents are claimed to be excellent
and cheap catalysts in the production of various alkylated diphenyl-
amines [4–12]. Acid treated and rare earth-modified clays have also
received considerable attention as acid catalysts for this industrially
important reaction [14,15].
Fig. 3 shows the influence of alkylating agent on 4,4′-DTBDPA/4-
TBDPA ratio in the tert-butylation of DPA. It can be seen from Fig. 3
that alkylation agents used in the screening generate different, with
reaction time increasing 4,4′-DTBDPA/4-TBDPA ratio. It shows how
The influence of two acidic clay catalysts — Nobelin and Fulcat 22B
on tert-butylation of DPA with TBA is shown in this paragraph. The
catalytic performance of these clay catalysts is compared to the zeo-
lite H-BEA, which was considered as the very suitable one among a
wider range of zeolite catalysts as concluded in Ref. [22].
Fig. 4 compares the influence of H-BEA and clay catalysts on con-
version of DPA in tert-butylation of DPA with TBA. As seen in the pic-
ture, the highest, almost 97% conversion of DPA was observed over
Fulcat 22B, comparable conversion (96%) was achieved over Nobelin
but only after 480 min. H-BEA zeolite was more active (it is the most
Fig. 2. The influence of alkylation agent on selectivity to 4-TBDPA and 4,4′-DTBDPA
Fig. 3. The influence of alkylation agent on 4,4′-DTBDFA/4-TBDFA ratio over H-BEA
over H-BEA (for reaction conditions see Section 2.2).
(multiplied by 100, for reaction conditions see Section 2.2).

G. Kostrab et al. / Catalysis Communications 18 (2012) 176–181
179
Fig. 6. The influence of H-BEA and clay catalysts on selectivity to 4,4′-DTBDPA with TBA
as alkylating agent (for reaction conditions see Section 2.2).
Fig. 4. The influence of H-BEA and clay catalysts on conversion of DPA with TBA as
alkylating agent (for reaction conditions see Section 2.2).
4,4′-DTBDPA and so such high selectivity to para- and para,para′-
isomers is not a question of shape-selectivity but of thermodynamic
stability of tert-butylated groups in the para- and para,para′-positions
on the aromatic rings of DPA.
Fig. 6 shows the influence of H-BEA and clay catalysts on selectiv-
ity to 4,4′-DTBDPA in the tert-butylation of DPA with TBA. It is seen,
that 4,4′-selectivity is after 6 h comparable for all studied catalysts.
Probably it is also a matter of thermodynamic stability of 4,4′-isomer,
not the matter of catalysts.
From Figs. 5 and 6 it is evident that mono- and di-alkylated DPA
are transformed to the thermodynamically more stable isomers.
Fig. 7 shows the influence of H-BEA and clay catalysts on 4,4′-
DTBDPA/4-TBDPA ratio in the tert-butylation of DPA with TBA indi-
cating the catalyst efficiency in producing more valuable dialkylated
DPA (4,4′-DTBDPA). It can be clearly seen from Fig. 7 that catalysts
utilized have different with time increasing 4,4′-DTBDPA/4-TBDPA
ratio. The highest 4,4′-DTBDPA/4-TBDPA ratio was achieved over H-
BEA and Fulcat 22B (more reactive catalysts), significantly lower was
observed over Nobelin, which is not as reactive — has lower total acid-
ity. The most active catalyst (the highest acidity) has the highest ratio of
4,4′-/4-isomers, because of consecutive reactions from mono- to di-tert-
butyl DPA. Fulcat 22B and Nobelin need longer time to achieve higher
4,4′-/4-isomers ratio.
acidic) because the highest conversion was obtained after 120 min and
after that time we can see a conversion decrease because of dealkylation
and DPA formation and diisobutylene formed from IB. Clays are not as
active (they are not as acidic as H-BEA) and so their reactivity is lower
also for back (dealkylation) reactions and so conversion of DPA is in-
creasing (Fig. 4).
The most part of H-BEA acidity is inside pores, which are easily
achievable for IB. However for DPA and its tert-butyl derivatives the
transport inside narrow pores is hindered. Thus acidic sites inside
narrow pores increase the rate of IB dimerisation and allow dealkyla-
tion of DPA after achieving the chemical equilibrium between DPA, IB
and alkylderivatives of DPA. Nobelin and Fulcat 22B do not have a sig-
nificant part in the acidic sites, which are differently achievable for IB
and DPA. Also these clays are not as acidic as H-BEA zeolite.
Fig. 5 shows the influence of H-BEA and clay catalysts on selectiv-
ity to 4-TBDPA. The obtained selectivities over all catalysts are higher
than 90%, especially in the case of Nobelin, almost 100% and Fulcat
22B, having 99% selectivity to 4-TBDPA after 480 min. The selectivity
to 4-TBDPA over H-BEA (99%) is comparable to both clay catalysts.
Nobelin is the least acidic and so dealkylation of 4-tert-butyl DPA is
not significant as for more acidic catalysts (H-BEA and Fulcat 22B).
From these results it is seen that “shape-selective” H-BEA and two
non-shape-selective clays have very near selectivity to 4-TBDPA and
H-BEA 814E
Nobelin
Fulcat 22B
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0
200
400
time (min)
Fig. 7. The influence of H-BEA and clay catalysts on 4,4′-DTBDPA/4-TBDPA ratio with
TBA as alkylating agent (for reaction conditions see Section 2.2, 4,4′-DTBDPA/4-TBDPA
ratio multiplied by 100).
Fig. 5. The influence of H-BEA and clay catalysts on selectivity to 4-TBDPA with TBA as
alkylating agent (for reaction conditions see Section 2.2).

180
G. Kostrab et al. / Catalysis Communications 18 (2012) 176–181
H-BEA 814E
Fulcat 22B
Nobelin
Fulcat 22B
H-BEA 814E
Nobelin
120
100
80
100
80
60
40
20
60
40
0
200
400
600
time (min)
20
0
200
400
600
Fig. 10. The influence of H-BEA and clay catalysts on selectivity to 4,4′-DTBDPA with IB
as alkylating agent (for reaction conditions see Section 2.2).
time (min)
Fig. 8. The influence of H-BEA and clay catalysts on conversion of DPA with IB as alkylating
agent (for reaction conditions see Section 2.2).
Fig. 10 shows the influence of H-BEA and clay catalysts on selectiv-
ity to 4,4′-DTBDPA in tert-butylation of DPA with IB. The highest, 94%
selectivity to 4,4′-DTBDPA was achieved over Fulcat 22B but after
480 min. Lower selectivity to 4,4′-DTBDPA was obtained over both H-
BEA and Nobelin (88 and 80%, respectively). DFA, as has been previously
mentioned, is activated to ortho-, and para-position on aromatic ring for
electrophilic substitution reaction, but due to sterical hindrance para-/
para,para′-position is preferred for mono/disubstituted DFA.
Fig. 11 shows the influence of H-BEA and clay catalysts on 4,4′-
DTBDPA/4-TBDPA ratio in the tert-butylation of DPA with IB indicat-
ing the catalyst efficiency in producing more valuable dialkylated
DPA (4,4′-DTBDPA). It can be clearly seen from Fig. 11 that the used
catalysts allow different 4,4′-DTBDPA/4-TBDPA ratio. The highest
4,4′-DTBDPA/4-TBDPA ratio was achieved over Fulcat, significantly
lower was observed over H-BEA (more acidic and thus more active
for dealkylation) and even worse result was obtained over Nobelin
which acidity is the lowest.
3.2.2. Zeolite versus clay catalysts (IB as alkylation agent)
Fig. 8 shows the influence of studied catalysts on conversion of
DPA in tert-butylation of DPA with IB. As it is seen in the picture,
the highest (almost 100%) maximal conversion of DPA was observed
over H-BEA and Fulcat 22B (after 120 min), slightly lower (97%) was
achieved over Nobelin (but after 480 min). Nobelin with the lowest
acidity was the least active.
Fig. 9 shows the influence of H-BEA and clay catalysts on selectiv-
ity to 4-TBDPA. The obtained selectivities over all catalysts are higher
than 90%, especially in the case of H-BEA and Fulcat 22B. The slightly
lower selectivity to 4-TBDPA was achieved after 480 min over the
least Nobelin (96%) which is also excellent. H-BEA started with selec-
tivity to 4-TBDPA at 97% and even increased it during whole period of
reaction time. Fulcat started at 91% and its selectivity increased to al-
most 100%. Acidities of Fulcat 22B and Nobelin are lower than H-BEA
and the formation of 4-tert-butyl DPA is slower. In comparison with
H-BEA, the dealkylation of alkylated DPA is also slower.
Fulcat 22B catalyzes DPA alkylation slower than H-BEA due to its
significantly lower acidity. Lower acidity also explains lowed contri-
bution of secondary reactions, namely dealkylation, which is also sig-
nificantly lower than in the case of H-BEA. Dealkylation reaction
produces IB, which can form DIB, thus lowering IB concentration in
H-BEA 814 E
Nobelin
Fulcat 22B
105
100
95
H-BEA 814E
Nobelin
Fulcat 22B
20
15
10
5
90
85
80
0
0
200
400
600
0
200
400
600
time (min)
time (min)
Fig. 9. The influence of H-BEA and clay catalysts on selectivity to 4-TBDPA with IB as
Fig. 11. The influence of H-BEA and clay catalysts on 4,4′-DTBDPA/4-TBDPA ratio with
alkylating agent (for reaction conditions see Section 2.2).
IB as alkylating agent (for reaction conditions see Section 2.2).

G. Kostrab et al. / Catalysis Communications 18 (2012) 176–181
181
Table 3
and utilized industrial acid catalyst. As it was proven, tert-butylation
of DPA produces mainly para- and para,para′-tert-butylated DPA as
final alkylation products what is the result of activation of para- and
para,para′-positions in DPA.
Studied DPA alkylation reaction is important industrial process.
4-tert-butyldiphenylamine and 4,4′-di-tert-butyldiphenylamine are
antioxidants with the utilization in lube oil formulations and polymer
materials.
Reusability of zeolite and clay catalysts.
Catalyst
XDPA (%)
S4-TBDPA (%)
S4,4′-DTBDPA (%)
H-BEA
91
89
86
97
94
93
99
99
99
99
98
99
90
89
90
89
87
90
H-BEA 1x
H-BEA 2x
Nobelin
Nobelin 1x
Nobelin 2x
5. Nomenclature
DPA
TBA
IB
C4-IB
XDPA
DIB
diphenylamine
tert-butanol
isobutylene
C4-fraction isobutylene
conversion of DPA
diisobutylene
the reaction mixture. This is the reason why dealkylation of 4,4′-
DTBDPA on Fulcat 22B is suppressed and 4,4′-DTBDPA/4-TBDPA ratio
significantly increases.
The length of di-tert-butyl DPA molecule is circa 0.8 nm and its
width circa 0.45 nm. Size of DPA, tert-butyl DPA and di-tert-butyl
DPA allows these molecules to move in pores and channels of H-
BEA zeolite. In the alkylation of DPA over H-BEA, external and internal
acid sites are catalyzing the reactions. The acidic sites inside pores of
H-BEA are more easily accessible for IB than for DPA, leading to more
intense dimerisation of IB by H-BEA in comparison with Fulcat. In the
case of clays, only accessible acid sites on the external surface are
catalyzing the reaction, including residual mineral acids, clays were
pretreated with (Fulcat 22B with sulphuric acid, Nobelin with hydro-
chloric acid). Here the accessibility of acid sites on the external surface
is nearly the same for IB and DPA, thus dimerisation of IB is not
preferred.
Acknowledgments
This work was supported by the Slovak Research and Development
Agency under the contract no.: APVV-0446-07 and the VEGA Scientific
Grant Agency of the Slovak Republic under Research Project No. 1/
0012/09. IB containing C4-fraction was obtained from local industrial
producer Kaučuk Kralupy, Czech Republic. Its contribution is gratefully
acknowledged.
3.3. Zeolite reusability
References
The crucial issue concerning zeolite usage on the industrial scale is
their reusability. The activity of zeolite catalysts tends to decrease
sharply after few runs. Blocking of zeolites pores by coke formation
is the culprit of drastic decrease of catalytic activity. Table 3 presents
data on reusability of used zeolite and clay catalysts. Both catalysts
activity decreased, but remained high after few runs.
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4. Conclusion
tert-Butylation of diphenylamine over zeolite catalyst H-BEA and
acid clays showed the possibility to utilize clay catalyst Fulcat 22B
as an environmental alternative to the other classical catalysts in
preparation of tert-butylated diphenylamines (Friedel-Crafts types
or mineral acids). It also showed its potential to be a cheaper substi-
tute for H-BEA.
tert-Butylation of diphenylamine was studied using three possible
tert-butylation agents. It was proven that isobutylene is the most
suitable tert-butylation agent. The highest conversion and selectivity
to desired products — 4-tert-butyldiphenylamine and 4,4′-di-tert-
butyldiphenylamine were achieved when isobutylene was used as
tert-butylation agent, regardless on catalyst used.
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Within the studied range of catalysts, the most active catalysts
were H-BEA zeolite and acid clay Fulcat 22B, which is well known