Amorphous aluminosilicate catalysts for hydroxyalkylation of aniline and phenol

Amorphous aluminosilicate catalysts for hydroxyalkylation

of aniline and phenol

C. Perego *, A. de Angelis, A. Carati, C. Flego, R. Millini, C. Rizzo, G. Bellussi

EniTecnologie, via Maritano 26, I-20097 San Donato Milanese, Italy

Available online 18 April 2006

Abstract

Amorphous aluminosilicates with controlled porosity in the region of micro-pores (ERS-8, SA) and meso-pores (MCM-41, HMS and MSA)

have been compared as catalysts in the hydroxyalkylation of phenol with acetone and of aniline with formaldehyde. The comparison has also

included two commercial silica–alumina gels and H-Beta.

In the hydroxylakylation of phenol with acetone to bisphenol A (BPA), the catalysts have been compared by batch test in terms of activity and

selectivity. In the hydroxylakylation of aniline with formaldehyde, also the catalyst life has been investigated. As a general behavior, mesoporous

aluminosilicates have evidenced better catalytic activity, selectivity and longer catalyst life than both microporous ones and commercial silica–

alumina gels. In the hydroxyalkylation of aniline to methylenedianiline (MDA), mesoporous MSA have shown similar performances of H-Beta in

term of MDA yields, but lower catalyst life.

# 2006 Elsevier B.V. All rights reserved.

Keywords: Amorphous; Aluminosilicates; Catalysts

www.elsevier.com/locate/apcata

Applied Catalysis A: General 307 (2006) 128–136

1. Introduction

The condensation of molecules containing carbonyl groups,

such as aldehydes and ketones, with aromatic compounds is

known as hydroxyalkylation. This reaction is widely applied in

the chemical industry to produce important commodities (e.g.

bisphenol A (BPA) and methylenedianiline (MDA)) and several

fine chemicals [1].

Industrial hydroxyalkylation processes are usually catalyzed

by strong mineral acids (HCl, H2SO4 and H3PO4), having

several drawbacks concerning handling, safety, corrosion and

waste disposal. In addition, because the reagents are mixed with

the acid catalyst, the separation of the products from the

catalyst is often a difficult and energy-consuming process. In

order to avoid these problems, many efforts have been devoted

to the search of solid acid catalysts, which should be safer and

environmentally friendly than mineral acids.

Different solid acid catalysts have been proposed as

substitutes of mineral acids in hydroxyalkylation reaction.

Among them, the most important belong to the classes of

* Corresponding author.

E-mail address: [email protected] (C. Perego).

0926-860X/$ – see front matter # 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.apcata.2006.03.013

zeolites and zeotypes, heteropolyacids, exchange resins, clays

and amorphous silica–aluminas. In particular for the synthesis

of MDA and BPA, according to the large dimension of the

molecules involved, large pore zeolites (e.g. Beta, mordenite,

ZSM-12) have been preferred as catalysts [1]. In order to reduce

the diffusion limitation in the micropores of zeolitic catalyst for

MDA synthesis, Corma et al. have recently claimed the use of

delaminated zeolites (e.g. ITQ-2, ITQ-6 and ITQ-18) [2].

The application amorphous silica–alumina was described

since 1968: gels of the type used in commercial catalytic

cracking were claimed to be active catalysts for MDA synthesis

[3]. These silica–alumina gels were characterized by a broad

pore size distribution with pores ranging in diameter from few

to a few hundred Angstroms. According to Thomas, these

characteristics of silica–alumina gels ‘‘make them less than

ideal catalysts’’ [4].

Later on new families of aluminosilicates were described.

Their high surface area (larger than 500 m2/g) and ordered pore

distribution open new opportunities for acid catalyzed reactions.

In 1992, a new mesoporous aluminosilicates designed as MCM-

41 [5] was discovered. MCM-41 has a hexagonal array of

uniform mesopores, which can vary approximately from 15 to

100 A in size. Several amorphous aluminosilicates, prepared as

MCM-41 by surfactant micelle templated syntheses and

mailto:[email protected]

http://dx.doi.org/10.1016/j.apcata.2006.03.013

C. Perego et al. / Applied Catalysis A: General 307 (2006) 128–136 129

Table 1

Reagent mixture and product compositions

Samples Gelling agent (R) Reagent mixture molar ratio Product composition (SiO2/Al2O3)

SiO2/Al2O3 R/SiO2 H2O/SiO2 EtOH/SiO2

MCM-41 (CH3)3C16H33NOH 100 0.11 10 8 39

HMS C12H25NH2 100 0.27 10 5 75

MSA (C3H7)4NOH 100 0.09 8 8 100

ERS-8 (C6H13)4NOH 100 0.08 8 8 100

SA HNO3 100 0.01 20 – 100

Grade J639 Grace commercial sample 100

MS 13/110 Grace commercial sample 11.4

Beta Sample prepared according to [17] 22

characterized by a narrow pore size distribution in mesopore

region, have been described by several research groups: FSM-16

[6], HMS [7], SBA [8], MSU [9] and KIT-1 [10]. Other

amorphous aluminosilicate families obtained by cluster tem-

plated sol–gel syntheses in basic medium have been described:

MSA [11] and ERS-8 [12], (micro)/meso- and micro-porous

materials with controlled pore size distribution, respectively.

Mesoporous aluminosilicates, like MCM-41, are good

catalysts even better than large pore zeolites for acid catalyzed

reactions requiring mild acidity and involving bulky reactants

and products (e.g. Friedel–Crafts alkylation 2,4-di-tert-butyl-

phenol with cinnamyl alcohol [13]). Al/MCM-41 aluminosi-

licate showed higher catalytic activity in the hydroxyakylation

of 2-methoxynaphtalene and naphthalene with paraformalde-

hyde than that of some acidic zeolites (e.g. Y, mordenite, ZSM-

5) and amorphous silica–alumina gel [14].

In a recent patent, some mesoporous aluminosilicates,

selected among the previous described families, were patented

by us as active catalysts for MDA synthesis [15].

In order to better understand the role of porosity and acidity,

aluminosilicates with controlled porosity in the micro-region

(ERS-8), meso-region (MCM-41, HMS) and (micro)-meso-

region (MSA)1 were synthesized and evaluated in the

hydroxyalkylation of aniline and phenol. All the catalysts

were prepared by sol–gel synthesis in alkali-free medium via a

polymeric gel route involving alkoxide hydrolysis and

condensation, catalyzed by a proper basic organic gelling

agent. Also a microporous silica–alumina (SA) prepared in

acidic medium without organic gelling agent was used as

catalyst. The comparison to two commercial silica–alumina

gels and to a zeolite Beta completes the catalytic study.

2. Experimental

2.1. Catalyst preparation

All samples were prepared as described in Ref. [16] from

silicon and aluminum alkoxide (Si(OC2H5)4 (Dynasil A,

Nobel), Al(i-OC3H7)3 or Al(sec-OC4H9)3 (Fluka)). Ethyl

alcohol (EtOH) and/or water were used as solvents. The gel

formation was catalyzed by basic aqueous alkali-free gelling

1 MSA is mainly mesoporous with a lower contribution of micropores [16].

agent (selected among: cetyltrimethylammonium hydroxide

(CTMA-OH), tetrapropylammonium hydroxide (TPA-OH),

tetrahexylammonium hydroxide (THA-OH), dodecylamine

(DDA)), or by acid (HNO3). The synthesis parameters are

summarized in Table 1.

All the syntheses gave initially rise to a clear solution. In the

case of MCM-41 and HMS, a progressive flocculation was then

observed. After 15 h ageing at room temperature, the samples

were filtered, washed and dried at 100 8C.

Homogeneous gels without separation of liquid solution

were instead formed for other syntheses: the gel was opalescent

for MSA and transparent for ERS-8 and SA samples. After 15 h

ageing at room temperature, the gels were dried at 100 8C.

All the samples were calcined for 8 h in air at 550 8C.

The synthesized catalysts were compared to two commercial

silica–alumina gels supplied by Grace (J639 and MS 13/110)

and to a zeolite Beta in acidic form, prepared in our laboratories

according to [17].

2.2. Physico-chemical characterization

The textural properties of these catalysts were determined by

nitrogen isotherms at liquid nitrogen temperature by using a

Micromeritics ASAP 2010 apparatus (static volumetric

technique). Before determination of adsorption–desorption

isotherms the samples (�0.2 g) were outgassed for 16 h at

350 8C under vacuum.

The specific surface area was determined from the BET

equation three parameters fit in the range p/p8 0.01–0.20. The

total pore volume (VT) was evaluated by Gurvitsch rule. Mean

pore size (dDFT) was calculated using DFT method (Micro-

meritics’ DFT Plus1 software) for all materials with the

cylindrical pores in oxide surface model.

The acidity was determined by the pyridine adsorption–

desorption method, followed by FT-IR spectroscopy. Self-

supported wafers of 15–20 mg/cm2 thickness were evacuated in

situ (500 8C, 1 h, 10�4 mbar, dynamic vacuum) in a pyrex cell

with KBr windows, contacted with pyridine at 200 8C(13.3 mbar) and stepwise evacuated at increasing temperature

(200–500 8C) in dynamic vacuum, as already described [18].

The spectra were registered at 20 8C with a mod. 2000 (Perkin-

Elmer) FT-IR spectrometer, taken the resolution of 1 cm�1. The

density of the acid sites was evaluated from the peak area of the

IR signals at 1455 (Lewis type) and 1545 cm�1 (Brønsted type),

C. Perego et al. / Applied Catalysis A: General 307 (2006) 128–136130

taking the extinction coefficient calculated by Take et al. [19].

The error in peak area determination was around 15%. After

desorption at 200 8C, the ‘‘total’’ density of the sites was

measured.

2.3. Catalytic tests: apparatus, procedure and analysis

The catalytic tests were carried either batchwise or by a

continuous flow, fixed bed microreactor.

2.3.1. Hydroxyalkylation of phenol with acetone to BPA

The tests were performed loading 1 g of catalyst, 9 g of

phenol and 1.16 g of acetone in an autoclave (phenol/acetone

molar ratio = 5). The autoclave was closed, stirred and heated at

150 8C for 6 h. Unreacted phenol was evaporated under vacuum

and the sample analysed through GC–MS.

2.3.2. Hydroxyalkylation of aniline with formaldehyde to

MDA—batch tests

Aminal (aminoacetal), product of non-catalyzed condensa-

tion of two molecules of aniline with one molecule of

formaldehyde was produced adding dropwise 22.4 g of aqueous

formaldehyde (37.5%, 0.27 mol) to 100 ml of aniline

(1.096 mol). The organic phase containing the aminal and

unreacted aniline was separated and dried over Na2SO4.

Residual water content was about 1000 ppm.

The tests were performed loading the catalyst (0.25 or 1 g),

4 g of aminal and 10 g of aniline in an autoclave (aniline/

formaldeyde molar ratio, including aminal = 14.7). The

autoclave was closed, stirred and heated at 150 8C for 6 h.

Unreacted aniline was evaporated under vacuum, and the

sample analysed through HPLC [20].


MDA—continuous tests

The continuous reactor was a standard laboratory assembly,

built up around a SS tubular microreactor (13 mm i.d., 25 cm

long) equipped with a 1.6 mm o.d. axial thermowell and heated

by an oil bath. The reactor was charged with 3 g of catalyst,

crushed from 5 t pelletized wafers of 3.9 cm diameter and

sieved to 20–40 mesh particles. The catalyst was then flushed in

slowly flowing dry nitrogen while heating up to 180 8C for 3 h.

The stability tests were performed with MSA, SA, Grace

J639 and H-Beta at the following reaction conditions: 3.8 MPa

Table 2

Textural properties of ERS-8, SA, MSA, MCM-41, HMS, Grace J639 and MS 13

Samples Isotherm

MCM-41 Type IV without hysteresis loop

HMS Type IV with a hysteresis loop at

high relative pressure ( p/p8 > 0.8)

MSA Type IV + (I) with a H2 hysteresis loop

ERS-8 Type I

SA Type I

Grace J639 Type IV with a H1 hysteresis loop

MS 13/110 Type IV with a H1 hysteresis loop

a Interparticle void.

total pressure; T = 180 8C; aniline/formaldehyde = 42.5/1;

liquid hourly space velocity (LHSV) = 2–6–10–40 h�1 referred

to the reaction mixture. LHSV was increased every 48 h of time

on stream (tos). In the case of H-Beta, the life test was repeated

with a larger concentration of aminal, corresponding to aniline/

formaldehyde = 7.2/1 and LHSV = 2 h�1.

The samples were collected and analyzed as above

described.

3. Results and discussion

3.1. Catalyst preparation and characterization

The chemical composition of the catalysts is reported in

Table 1. MCM-41 and HMS samples, whose syntheses

comprise a solid phase separation, show a lower SiO2/Al2O3

molar ratio than the reagent mixture, in agreement with the

higher silica solubility at high pH.

By contrast, the materials obtained by gelation (MSA, ERS-

8, SA) show the same SiO2/Al2O3 as the reagent mixtures,

according to the complete hydrolysis of the alkoxides and to the

absence of phase separation during the preparation.

Therefore, the aluminum content in the catalysts decreases

in the order MCM-41 > HMS > MSA = ERS-8 = SA.

Textural properties are reported in Table 2.

Between the two microporous aluminosilicates, ERS-8,

synthesized in basic medium, shows higher surface area and

pore volume than SA, prepared in acidic medium.

MSA, MCM-41 and HMS aluminosilicates are characterized

by a high surface area and a mean pore size centered in the region

of mesopores. Compared to the commercial silica–alumina gels

(Grace J639 and MS 13/110) the surface areas are larger and the

mean pore size lower. Besides, these aluminosilicates obtained

by surfactant micelle templated syntheses or by cluster templated

sol–gel syntheses are characterized by a narrower pore size

distribution than commercial silica–alumina gels [11,21].

The results of adsorption–desorption of pyridine are

reported in Table 3, together with the acidity of zeolite Beta,

taken as a reference in the catalytic reaction.

The total density of acid sites is almost comparable for all

the amorphous aluminosilicates, except for MCM-41, showing

the largest density of both Brønsted and Lewis sites according

to its larger Al content. For the same reason also the silica–

alumina gel Grace MS 13/110 shows the highest density of

/110

SBET(3p) (m2/g) VT (ml/g) dDFT (A)

1140 0.83 21

948 0.96 19 (936)a

928 0.74 32

1196 0.62 16

509 0.24 13

318 1.44 207

480 1.02 94


Table 3

Brønsted and Lewis acid site density (mmol/g)

Samples SiO2/Al2O3 Al content

(mmol/g)

Total acid site

density (mmol/g)

Lewis Brønsted

ERS-8 100 333 108 38

SA 100 333 94 19

MSA 100 333 101 47

MCM-41 39 854 173 120

HMS 75 444 77 37

Grace J639 100 333 59 27

Grace MS 13/110 11.4 2920 258 25

H-Beta 22 1514 340 280

Scheme 1.

Lewis acid sites, but in this case the Brønsted site density is very

low. Zeolite Beta is a very acidic material with respect to both

amorphous aluminosilicates and silica–alumina gels, as already

reported in literature [22–24].

3.2. Hydroxyalkylation reaction

The aim of the present report is to provide a comparison of

the catalytic activity of amorphous aluminosilicates with

controlled porosity and H-Beta in the hydroxyalkylation of

aniline and phenol. Hydroxyalkylation is a variant of the

Friedel–Crafts aromatic alkylation in which the alkylating

agent is a carbonylic compound, rather than an alkene, alcohol

or alkylhalide. This reaction is known to require an acid catalyst

in order to activate the carbonyl group enhancing its ability as

electrophile towards an electron-rich aromatic ring. In the case

of acidic zeolites, the first stage of reaction is usually reported

as the formation of an anionic lattice-associated carbenium ion,

by the attack of a proton on a carbonylic group (>C O). This

carbocation is then attacked by a free or weakly adsorbed

Scheme

aromatic. However, the adsorbed conjugate acid of the carbonyl

reactant has also a strong tendency to react with another

carbonylic compound, giving rise to competitive side reaction

(e.g. aldol condensation). The hydroxyalkylation usually does

not stop at the first step and the alcohol initially produced (1:1

adduct) reacts with another molecule of aromatic compound to

form bisarylalkanes (2:1 adducts), according to Scheme 1. As

reported by Venuto [25], the molecular weight and the steric

requirements of 1:1 adduct may be rather great. Besides, the 1:1

adduct then comprises a bulky alkylating agent for condensa-

tion with a second aromatic molecule, generating a very large

product. Therefore, both porosity and acidity are expected to

play a significant role.

3.2.1. Hydroxyalkylation of phenol with acetone to BPA

Bisphenols are formed by the acidic condensation of 1 mol

of ketone (or aldehyde) with 2 mol of phenols. The bisphenol

most largely produced in the chemical industry is bisphenol A

(BPA) ( p,p0-isopropylidenediphenol), which derives from the

acid catalyzed condensation of 2 mol of phenol with 1 mol of

acetone. The industrial production of BPA is performed using

hydrochloric acid or sulphonic resins as catalysts [1]. The

reaction proceeds according to the Scheme 2. The main

2.


Table 4

Product molar composition (%)

Catalyst Acetone conversion (%) Bisphenol p,p0-Bisphenol (BPA) o,p0-Bisphenol BPX Chromans Mesytil oxide

ERS8 72.47 62.28 36.19 26.09 8.23 1.93 27.56

MSA 64.7 68.22 29.73 38.49 8.40 11.73 11.65

MS 13/110 71.08 58.99 38.74 20.25 8.49 3.23 29.29

H-Beta 100 76.27 48.97 27.3 23.7 0.01< 0.01<

reaction produces BPA together with relevant quantities of the

o,p0-isopropylidenediphenol (o,p0/p,p0 ratio up to 1:2). Both

isomers can undergo to further condensation producing small

amounts of heavier by-products: trisphenols (BPX) and

chromans. Besides acetone by aldol condensation produces

small amount of mesytil oxide.

The tests of the hydroxyalkylation of phenol with acetone

were performed with three different amorphous catalysts: two

ordered microporous (ERS-8) and mesoporous (MSA) alumi-

nosilicates and a commercial silica–alumina gel (Grace MS 13/

110). The results are reported in Table 4 together with that

obtained with H-Beta.

The amorphous aluminosilicates are able to activate the

hydroxyalkylation with comparable catalytic activities. Con-

cerning the selectivity the main differences between ERS-8 and

MSA (i.e. less chromans, higher p,p0/o,p0 and more mesytil

oxide) are probably due to the different pore dimension. In fact,

these two aluminosilicates show similar acidity but different

porosity. The lower pore diameter of ERS-8 with respect to

MSA (16 A versus 32 A) likely hampers the formation of bulky

products like o,p0-BPA and chromans, while favoring the

formation of p,p0-BPA and mesytil oxide having a low steric

hindrance. However, neither ERS-8 nor MSA evidence peculiar

performances with respect to the commercial silica–alumina

gel. Finally, all amorphous aluminosilicates show a lower

hydroxylation activity and selectivity with respect to H-Beta.

The zeolite Beta produces more BPA and practically no mesytil

oxide and chromans. The lower activity of amorphous

aluminosilicates with respect H-Beta can be reasonably

attributed to their lower acidity (particular the Brønsted one)

and lower resistance to the water produced during BPA

synthesis. Being less consumed by hydroxyalkylation, a larger

concentration of acetone is available for aldol condensation to

mesytil oxide, by a second order reaction rate with respect to

acetone. Both acid sites and porosity result play a role in the

reaction, affecting the activity and the selectivity, respectively.


MDA

Methylenedianiline (MDA), product of condensation of

2 mol of aniline with 1 mol of formaldehyde, is used as

precursor, through phosgenation, of methylenediisocianate

(MDI). This important chemical commodity is nowadays

largely produced by adding formaldehyde to stoichiometric

amount of hydrochloric acid and aniline at 60–80 8C in agitated

reactor. The reaction mixture is then heated at 100–160 8C for

about 1 h to complete the condensation. The reaction mixture is

then neutralized with an excess of NaOH, producing almost

stoichiometric amount of sodium chloride [1].

The reaction can also be performed in two steps according to

Scheme 3, by the non-catalytic condensation of aniline and

formaldehyde to produce aminal (anilinoacetal), followed by

the rearrangement of aminal to MDA catalyzed by acids. In this

procedure, the water produced in the first step is removed,

taking advantage in the catalytic activity for the rearrangement

[26]. The acid catalyzed rearrangement of aminal first produces

benzylamines, by the eletrophilic substitution on an aromatic

ring carrying a strong activating group, e.g. –NH2, which is

para–ortho orientating. This reaction is relatively rapid and the

formation of p-bonded benzylamines is favored according to

the lower steric hindrance of p position versus o position. Than

the dissociation of benzylamines follows, giving rise to the

formation of a benzylic carbenium ion, which reacts with

aniline forming MDA (see Scheme 3). This reaction is

considered to be the rate-determining step [27]. Beside aniline,

the carbenium ion can also react with MDA, forming

oligomeric amines (triamines and tetraamines). 2,20- and

2,40-MDA are more reactive than 4,40-MDA because of the

availability of p positions for further reactions. An undesirable

side reaction produces small amounts of N-methyl MDA.

The variables affecting the product distribution are aniline

concentration, catalyst concentration (e.g. HCl) and tempera-

ture. The higher the excess of aniline the higher is the

concentration of diamines (MDA isomers) in the reaction

mixture. According to the steric hindrance p isomer (4,40-MDA) is favored at low temperature. However, 4,40-MDA can

isomerize to 2,40- and 2,20-isomers at high temperatures via an

acid catalyzed protodealkylation [28]. At 190 8C in HCl, the

isomer equilibrium composition is 4,40:2,40:2,20 = 49:49:2 [27].

Finally, triamines and tetraamines can react with the

excess of aniline giving back MDA enriched in the 2,40-isomer

[28]. This transalkylation is supposed to involve an initial

C-protonation, followed by loss of the benzyl cations [28]

(Scheme 4).

The results of the aminal rearrangement catalyzed by

amorphous aluminosilicates are reported in Tables 5 and 6.

These catalytic tests were performed batchwise, at the same

reaction conditions (aniline/formaldeyde = 14.7, T = 150 8C,

reaction time = 6 h), but different catalyst amount (i.e. 1 and

0.25 g, respectively). Data reported in Table 5 show that the

aminal completely rearranged with all catalysts. Also

benzylamine was always completed rearranged, but for SA.

Accordingly the overall amines production (MDA and

oligomeric amines) is always close to 100%, with the exception

of SA. In order to better evidence differences in catalytic

activity, the tests were repeated for some catalysts lowering the

catalyst amount (i.e. 0.25 g) at the same conditions (Table 6).

Again, all catalysts are able to completely rearrange


Scheme 3.

Scheme 4.


Table 5

Condensation of aniline with formaldehyde in a batch reactor at 150 8C, 1 g of catalyst, after 6 h. reaction time

Catalyst Amines

(%)

Benzylamines

(%)

N-Methylated

(%)

Diamines

(MDA) (%)

Oligomeric amines

(triamines and tetraamines) (%)

MDA isomer ratio 4,40-MDA/(2,40- + 2,20-MDA)

MSA 98.84 0 1.16 73.21 25.63 5.99

MCM 41 99.14 0 0.86 74.06 25.08 4.98

HMS 99.07 0 0.93 76.05 21.14 5.58

SA 94.6 4.49 0.91 60.23 34.37 6.38

ERS 8 99.18 0 0.82 80.82 18.36 5.41

J 639 99.12 0 0.88 76.05 23.07 5.55

Rearrangement of the aminal obtained in the neutral condensation of aniline with formaldehyde.

Table 6

Condensation of aniline with formaldehyde in a batch reactor at 150 8C, 0.25 g of catalyst, after 6 h reaction time

Catalyst Amines

(%)

Benzylamines

(%)

N-Methylated

(%)

Diamines

(MDA) (%)

Oligomeric amines

(triamines and tetraamines) (%)

MDA isomer ratio 4,40-MDA/(2,40- +2,20-MDA)

MSA 99.18 0 0.82 73.49 25.68 5.99

HMS 99.3 0 0.7 56.74 40.17 6.71

SA 52.73 46.8 0.47 7.43 45.3 6.51

ERS 8 99.27 0 0.73 75.29 23.98 5.50

J 639 99.61 0 0.39 73.51 26.1 6.53

MS13-110 99.31 0 0.69 78.44 20.86 6.37

H-Beta 99.57 0 0.43 83.98 15.53 2.55

Rearrangement of the aminal obtained in the neutral condensation of aniline with formaldehyde.

Fig. 1. Aminal to MDA in fixed bed reactor (3.8 MPa; 180 8C; aniline/

formaldehyde = 42.5/1).

benzylamine, with the exception of SA for which the

concentration of unconverted benzylamine sensibly increases

from 4.49 to 46.8%. With the other aluminosilicates, the amines

production is practically the same in both the tests, while some

differences can be evidenced in the distribution between

diamines and oligomeric amines.

Lowering the amounts of catalysts results in an increase of

oligomeric amines with respect to diamines (i.e. the ratio

oligomeric amines/diamines increases). This increase is largest

for SA and reduces in the order SA > HMS > ERS-

8 > J639 > MSA. Hence, the larger the increase the lower is

the transalkylation activity. MSA behavior is practically not

affected by the catalyst loading; a higher stability of MSA with

respect tootheramorphous aluminosilicatescan behypothesized.

Concerning the MDA isomers, 4,40-MDA prevails on 2,20-and 2,40-MDA for all amorphous aluminosilicates and the

isomer distribution is practically the same for all of them and

independent on catalyst amount. Lowering the catalyst amount

also results in a reduction of N-methylated, this trend being

confirmed for all aluminosilicates.

Comparing the results of amorphous aluminosilicates with

that of H-Beta, two main behaviors are evidenced. Zeolite Beta

produces the lowest amount of oligomeric amines and the

lowest MDA isomer ratio 4,40/(2,40 + 2,20) = 2.55. Hence, H-

Beta shows the largest isomerization activity with respect to

amorphous aluminosilicates, though the ratio is still far from

the equilibrium one (�1).

The data collected with these kinds of tests do not allow to

evidence significant differences among amorphous aluminosi-

licates and commercial silica–alumina gels. Only SA evidenced

a limited catalytic activity that seems to be due to both its

porosity and its acidity. In fact, among amorphous alumino-

silicates SA has the smaller pore diameter and pore volume and

the smaller Brønsted acid site density. The role of porosity and

acidity was further investigated by continuous test. Micro-

porous (SA), mesoporous (MSA) and silica–alumina gel (Grace

J639) having the same SiO2/Al2O3 molar ratio have been

selected for these tests. The tests were performed so to collect

information also on catalyst life. The results are reported in

Fig. 1, where conversion includes the rearrangement of aminal

to all products (diamines, oligomeric amines, N-methylated),

but benzylamine. In fact, for all catalysts the rearrangement of

aminal is always complete and the deactivation is revealed by

the appearance of benzylamine.

The difference of catalysts life among aluminosilicates is

relevant. In fact, while SA quickly deactivates, probably


Fig. 2. Product distribution for the continuous rearrangement of aminal in fixed

bed reactor (3.8 MPa; 180 8C; aniline/formaldehyde = 42.5/1) with MSA.


bed reactor (3.8 MPa; 180 8C; aniline/formaldehyde = 7.2 /1) with H-Beta.

because of its small pore diameter, pore volume and Brønsted

acid site density. MSA has a relevant life and Grace J639

behaves in between. With respect to MSA, Grace J639 is

characterized by a broader pore size distribution [16] and a

smaller surface area. These can be the reason of a lower

stability, together with the smaller acid site density.

According to space velocity and yield, the catalyst life of

MSA corresponds to a productivity of around 120 g MDA/g

catalyst. Figs. 2 and 3 report the selectivity for MSA and H-

Beta during the life tests. At the beginning of the stability test,

the distribution between diamines and oligomeric amines is

constant and comparable for both MSA and H-Beta. On the

contrary the MDA isomer ratio, after an initial decrease,

constantly increases. However, the MDA isomer ratio is always

lower for H-Beta than MSA. Besides, the smallest value for H-

Beta (�1.4) approaches the equilibrium one, indicating that the

fresh H-Beta has a good isomerization activity, larger than that

of amorphous aluminosilicates. A similar behavior was already

reported for the isomerization of o-, p- and m-cymene and

attributed to the larger strong acid site density of the Brønsted

type of H-Beta with respect to MCM-41 and MSA [29].

In the stability test with MSA just before the deactivation,

which was evidenced by the appearance of benzylamine at

around 120 h, diamines progressively reduce in favor of

oligomeric amines. Simultaneously the MDA isomer ratio


bed reactor (3.8 MPa; 180 8C; aniline/formaldehyde = 42.5/1) with H-Beta.

increases more rapidly. The increase of oligomeric amines and

of 4,40-MDA isomer evidences a reduction of transalkylation

and isomerisation activity of MSA along with the time,

probably related to the progressive deactivation of the Brønsted

acid sites. In fact, the MDA isomerization and oligomeric

amine transalkylation, both proceeding via protodealkylation

[28], are more acid demanding than aminal and benzylamines

rearrangements. In case of H-Beta, even over 200 h,

benzylamine is never detected. Repeating the stability test

with a larger aminal concentration (58% corresponding to

aniline/formaldehyde = 7.23, with respect to the 42.5 of the

previous tests). Benzylamine appears after around 130 h t.o.s.,

with a global productivity of around 300 g MDA/g catalyst. The

selectivity is summarized in Fig. 4. As for MSA, to the

deactivation corresponds a progressively decrease of diamines

in favor of oligomeric amines and the increase of MDA isomer

ratio.

The longer stability of H-Beta with respect to the

mesoporous aluminosilicate MSA may be due to the larger

acid side density.

4. Conclusion

Amorphous aluminosilicates with narrow pore size dis-

tribution, prepared by surfactant micelle templated syntheses

(e.g. MCM-41, HMS) or by cluster templated sol–gel syntheses

(e.g. MSA, ERS-8) proved to be suitable catalysts for the

hydroxyalkylation of phenol and aniline, with performances

depending on porosity and acidity.

In the hydroxylakylation of phenol with acetone to

bisphenol, the catalytic activities of microporous (ERS-8)

and mesoporous (MSA) are similar and comparable with that of

a commercial silica–alumina gel (Grace MS 13/110). MSA is a

little more selective to bisphenol. However, H-Beta shows a

better activity and selectivity with respect to amorphous

aluminosilicates, probably related to its higher acidity and

higher resistance to the water produced during condensation.

In the case of rearrangement of the aminal, obtained by not

catalyzed condensation of aniline and formaldehyde, only the

microporous silica–alumina SA shows insufficient catalytic

activity and stability. The mesoporous MSA evidences a larger


catalytic stability than other amorphous silica–aluminas. This

has been confirmed by stability tests with MSA and a

commercial silica–alumina gel with the same SiO2/Al2O3

ratio. This may be due to its larger surface area and narrower

pore size distribution. The selectivity to diamines (MDA) and

oligomeric amines is comparable with that of H-Beta. However,

H-Beta is more stable than MSA, with an overall productivity

more than double (300 g versus 120 g MDA/g catalyst).

References

[1] A. de Angelis, P. Ingallina, C. Perego, Ind. Eng. Chem. Res. 4 (2004) 1169.

[2] A. Corma, P. Botella, C. Mitchell, J. Chem. Soc., Chem. Commun. (2004)

2008.

[3] F.E. Bentley, US Patent 3,362,979 (1968).

[4] J.M. Thomas, Sci. Am. (April) (1992) 112.

[5] J.S. Beck, J.C. Vartuli, W.J. Roth, M.E. Leonoswicz, C.T. Kresge, K.D.

Schmitt, C.T.-W. Chu, D.H. Olson, E.W. Sheppard, S.B. McCullen, J.B.

Higgins, J.L. Schlenker, J. Am. Chem. Soc. 114 (1992) 10834.

[6] S. Inagaki, Y. Fukushima, K. Kuroda, J. Chem. Soc., Chem. Commun.

(1993) 680.

[7] A. Tuel, S. Gontier, Chem. Mater. 8 (1996) 114.

[8] Q. Huo, D.I. Margolese, G.D. Stucky, Chem. Mater. 8 (1996) 1147.

[9] S.A. Bagshaw, E. Prouzet, T.J. Pinnavaia, Science 269 (1995) 1242.

[10] R. Ryoo, J.M. Kim, C.H. Shin, J.Y. Lee, Stud. Surf. Sci. Catal. 105 (1997) 45.

[11] G. Bellussi, C. Perego, A. Carati, S. Peratello, E. Previde Massara, G.

Perego, Stud. Surf. Sci. Catal. 84 (1994) 85.

[12] G. Perego, R. Millini, C. Perego, A. Carati, G. Pazzuconi, G. Bellussi,

Stud. Surf. Sci. Catal. 105 (1997) 205.

[13] E. Armengol, M.L. Cano, A. Corma, H. Garcia, M.T. Navarro, J. Chem.

Soc., Chem. Commun. (1995) 519.

[14] A. Corma, H. Garcia, J. Miralles, Microporous Mesoporous Mater. 43

(2001) 161.

[15] C. Perego, A. de Angelis, O. Farias, A. Bosetti, Belgian Patent 1013456A6

(2002).

[16] C. Rizzo, A. Carati, M. Tagliabue, C. Perego, Stud. Surf. Sci. Catal. 128

(2000) 613.

[17] I. Kiricsi, C. Flego, G. Pazzuconi, W.O. Parker Jr., R. Millini, C. Perego,

G. Bellussi, J. Phys. Chem. 98 (1994) 4627.

[18] C. Flego, I. Kiricsi, C. Perego, G. Bellussi, Catal. Lett. 35 (1995) 125.

[19] J. Take, T. Yamaguchi, K. Miyamoto, H. Ohyama, M. Misono, Stud. Surf.

Sci. Catal. 28 (1986) 495.

[20] P. Falke, R. Tenner, H. Knopp, J. fur Prakt Chem. 328 (1) (1986) 142.

[21] A. Corma, Chem. Rev. 97 (1997) 2373.

[22] R. Savidha, A. Panduragan, Appl. Catal. A 276 (2004) 39.

[23] M.A. Ali, T. Tatsumi, T. Masuda, Appl. Catal. A 233 (2002) 77.

[24] B. Dragoi, A. Gervasini, E. Dumitriu, A. Auroux, Thermochim. Acta 420

(2004) 127.

[25] P. Venuto, Microporous Mater. 2 (1994) 297.

[26] F. P. Recchia, H. Ulrich, process for preparing di(aminophenyl)-methane,

US Patent 3,676,497 (1972).

[27] H. Ulrich, Chemistry and Technology of Isocianates, Wiley, Chicester,

2001.

[28] P.J. Whitman, F.F. Frulla, G.H. Temme, F.A. Stuber, Tetrahedron Lett. 17

(1986) 1887.

[29] C. Perego, S. Amarilli, A. Carati, C. Flego, G. Pazzuconi, C. Rizzo, G.

Bellussi, Microporous Mesoporous Mater. 27 (1999) 345.

Amorphous aluminosilicate catalysts for hydroxyalkylation of aniline and phenol

Documents

Transcript of Amorphous aluminosilicate catalysts for hydroxyalkylation of aniline and phenol