Kaolinite supported metal chlorides as Friedel-Crafts alkylation catalysts

T.S.R. Prasada Rao and G. Murali Dhar (Editors) Recent Advances in Basic and Applied Aspects of Industrial Catalysis Studies in Surface Science and Catalysis, Vol. 113 9 1998 Elsevier Science B.V. All rights reserved

557

Kaolinite supported metal chlorides as Friedel-Crafts alkylation catalysts Rugmini Sukumar, K.R. Sabu, L.V. Bindu and M. Lalithambika Regional Research Laboratory (CSIR), Thiruvananthapuram -695 019, India Ideal kaolinites are ineffective as solid acid catalysts even after thermal and acid activation. The effect of impregnating ZnC12, FeC13, MnC12, SnC12 and A1C13 on the catalytic activity of a natural kaolinite and its activated form is examined. The process leads to catalysts with improved activity, the maximum being associated with FeC13 when employed in the FriedelCrafts alkylation of benzene with benzyl chloride. 1 g of supported FeC13 catalyst (1 mmol/g clay) gave 86 mole% conversion to diphenylmethane with 100% selectivity when 2 mole benzene is alkylated with 0.1 mole benzyl chloride. Supported A1C13 catalysts proved to be the least effective for the alkylation studied. 1. INTRODUCTION Supported reagents based on porous inorganic materials have been the subject of widespread coverage in literature, catalytic alkylation using solid acids being a particularly important goal (1-3). However, much of the earlier reported work related to clay minerals had largely relied on montmorillonite clays, 2:1 layer silicates (4-9). Among the clay-based solid acid catalysts, the development of 'clayzic', ZnC12 supported on acid treated montmorillonite K10 has received a great deal of attention [4,8]. Clayzic is reportedly effective in catalyzing Friedel-Crafts alkylation within minutes at room temperature. We have reported that natural kaolinites, 1:1 layer silicates having lattice transition metals exhibited remarkably high catalytic activity for the alkylation of benzene with benzyl chloride after suitable surface modification (10). However, ion-exchanging enhanced the catalytic activity of an otherwise inactive acid treated metakaolinite derived from an ordered kaolinite (11). In continuation of our studies, we felt it of particular interest to study the effect of supporting metal halides onto natural kaolinites and its modified forms. We report here the preparation of kaolinite supported catalysts and their catalytic activity for the liquid phase alkylation of benzene. 2. EXPERIMENTAL Natural kaolinite was obtained from M/s. English Indian Clays Ltd. (EICL), Thiruvananthapuram, India and was purified by sedimentation/wet sieving as has been described earlier to obtain E1-K(W) (10). Other materials used are AR grade hydrochloric acid, aluminium chloride, ferric chloride, stannous chloride, manganese chloride and zinc chloride (E.Merck), benzene and benzyl chloride (BDH), acetonitrile and butylamine (SD

558 fine chemicals). The natural kaolinite, EI-K(W) was calcined at 550~ and treated with hydrochloric acid to yield an acid activated clay, EI-K(A) (10). The preparative schedule of supported catalyst is shown schematically in Fig.1. W1, W2, W3, W4 and W5 stands for zinc chloride, ferric chloride, manganese chloride, stannous chloride and aluminium chloride supported on the kaolinite respectively and A1, A2, A3, A4 and As stands for I Natural Kaolin, EI-K(W); < 45 pm I

Calcination/acid activation

[EI-K(A)I Metal halide, MClx (ZnC12, FeC13, MnC12, SnCI2, A1C131 / in acetonitrile/methanol Rotovap

I MClx/EI-K(W)I

I MClx/EI-K(A]

Drying overnight at 120~ [Wl, W2, W3, W4, W5l

[ A1, A2, A3, A4, A5 ]

Fig. 1. Preparation of supported reagents these halides supported on the activated kaolinite. Metal halides were impregnated on to the support from acetonitrile/methanol medium (1 mmol/g clay) employing rotary evaporator as per Clark et al. (8). The catalyst was activated by heating the clay at 120~ overnight prior to use. Characterisation techniques involved wet chemical analysis, X-ray diffraction (XRD) (Rigaku, CuKct radiation), and surface area analysis by BET N2 adsorption at -196~ (Micromeritics Gemini 2360). Acidity measurements were carried out by potentiometric titration in aprotic solvent (12). Friedel-Crafts alkylation of benzene using benzyl chloride was chosen as the test reaction. Reaction products were analysed by GC. 3. RESULTS AND DISCUSSION Chemical and mineralogical characteristics of the natural kaolin, EI-K(W) are presented in Fig.2 and Table 1. XRD pattern clearly indicates that the major clay mineral present is reasonably ordered kaolinite with small amount of quartz as impurity. Our earlier studies have showaa that EI-K is more or less inactive for the alkylation of benzene with benzyl chloride (10). Thermal treatment did not impart any alkylating activity to EI-K. However, refluxing of 550~ calcined EI-K with 2M hydrochloric acid marginally enhanced

559 its catalytic activity for the alkylation of benzene with benzyl chloride, giving 20 mole% conversion of the latter to diphenylmethane at 80~ within a reaction time of 3 h. At the same time, disordered natural kaolinitic clays such as PBK-K and PBL-K are found to be better alkylation catalysts in the dried (110~ state, calcined state and calcined/acid activated forms (10). Calcination of these two kaolinitic clays followed by activation with 2M HC1 gave 75-85 mole% conversion of benzyl chloride to diphenylmethane with 100% selectivity to the latter. Later studies have shown that exchanging Fe(III) or AI(III) on acid activated metakaolinite of EI-K resulted in enhancement of alkylating activity (11). Fe(III) exchanged variety was efficient for alkylating benzene with benzyl chloride giving 92 mole% conversion (11). Metakaolinisation of EI-K at 550~ followed by activation with hydrochloric acid produced a substrate with suitable pore geometry and exchange sites for the effective exchange of Fe(III) or AI(III). Depending on the extent of further heat treatment, the exchanged Fe(III) or AI(III) could have acted as Bronsted or Lewis acid site in initiating the benzylation. Table 1. Properties of natural kaolin, EI-K(W) % SI.No. Property 1 A1/Si 1.08 1.08 0.34 2 Fe203 14.34 3 Loss on ignition (at 1025+25~ 5.10 4 pH (at 27+2~ 5 Surface area (m2/g) 13.00 6 Minerals present Kaolinite (major) Quartz (minor) 68.00 Particle size (<2 ~m) 0.0.82 Crystallinity index (from XRD)

K

I 2 3 4

K K

EI-K(W) W2 EI-K(A) A2

>~ Z [--,

i

10

1

15 20 2~ (CuK) o~

i

I

25

30 =

.

1

1

35

40

Fig.2. X-ray diffractograms of supports and supported reagents K - Kaolinite, Q - Quartz

560 Ideal kaolinites are known to possess a rigid 1:1 layer structure without isomorphous substitution and only small number of acid sites (even though strong) and hence are not effective as solid acid catalyst without any modification. In the present study, it was seen from XRD that the process of supporting of metal halides on EI-K(W) did not change the structure of the support. This is illustrated in Fig.2 by taking the case of FeC13. The surface area of supported system is slightly higher than that of the support except In the case of SnCl2 as shown in Table 2. The considerable decrease in surface area observed in the case of SnC12 cannot be explained with the present set of data. Thermal and acid treatment of clays are proven methods of activation prior to supporting which reportedly enhances its porosity, surface area and surface acidity (13,14). The acidity distribution patterns of these supported samples shown in Fig.3 & 4 show that they have considerably higher total acidity than EIK(W) or EI-K(A). From this it can be depicted that there exists a synergistic interaction between the support and the Lewis acid halide supported. Table 2. Surface area, total audit), and catalytic activi~ of supported reagents

Sample code

EI-K(W) W1 W2 W3 W4 W5 EI-K(A) A1 A2 A3 A4 A5

Surface area (m2/g)

Total acidity* (m2/g)

Reaction time (min)

% conversion # to diphenylmethane (mole")

13.0 16.12 17.62 13.29 5.25 16.23 15.00 30.04 28.04 15.83 7.20 16.06

0.13 0.34 2.22 0.80 1.75 0.45 0.13 1.77 2.25 0.71 2.07 1.51

180 180 45 170 120 45 180 300 45 180 365 45

nil 68 85 60 38 06 09 71 86 66 62 07

*meq.of n-butylamine/g #0.1 mole benzyl chloride/2 mole benzene/lg catalyst The order of total acidity values are different when EI-K(W) and EI-K(A) are used as support. In the former case it is ZnC12 < AICI3 < MnC12 < SnC12 < FeC13 and in the latter case it is MnC12 < A1C13 < ZnCI2 < SnC12 < FeC13. Figs.3 & 4 show that the acidity distribution pattern of each supported samples are different from one another. Since the kaolinite layers are rigidly interwoven due to hydrogen bonding, only highly polar molecules such as HCHO, DMSO and DMF can penetrate them and hence can intercalate. Therefore it could be envisaged that the metal halides spread over untreated kaolinite results in a metal halide-kaolinite structure in which only the surface hydroxyls and broken edge hydroxyls interact with the metal halide through weak forces of attraction. In the case of acid activated metakoalinites, numerous mesopores may be created in which the Lewis acid halides can

561 congregate. This congregated metal halides can act as extremely effective Lewis acid centres. In the case of clayzic, it is known that ZnCI2 when supported occupies both the surface of the support as well as mesopores (14). Evaluation of acidity of supported halides described in the present paper shows that the acidity of FeC13 and ZnCI2 supported on EI-K(A) and FeC13 and SnC12 supported on EI-K(W) are comparable. 600 L . . . . . . . . . .

"--"+~.

---

wl

-+-

W2

-

a

i

W4

-

0.0

"

-10~753"

11.5

38:2 8'0.4 187.1 222.1 EQ. OF n - B U T Y L ~ I N N X 0 . 0 1

MILLI

Fig.3. Acidity distribution pattern of EI-K(W) supported reagents 600

>

-o- AI - * - A2 * A3

400

E

ZOO 0.0 -I00 _..l_L I 0.53 MILLI

[,.

I

1

1_ I

I

I

I

I

I

9

1

!

l

i

!

I

I

1

!

l

I

I

[

I

J

1

z

!

l

z

12.7 33.3 83.4 151.9 EQ. O F n--BUTYLAMINE X 0.01

l

1

!

228.4

Fig.4. Acidity distribution pattem of EI-K(A) supported reagents The mole% conversion of benzyl chloride to diphenylmethane in the alkylation of benzene on each supported catalyst is shown in Table 2. EI-K(W) is inactive and EI-K(A) is marginally active. A1C13 supported on EI-K(W) and EI-K(A) is less active than the EI-K(A). This may probably be attributed to the poisoning effect of moisture on the supported A1C13. Out of the ten supported catalysts studied, FeC13 on EI-K(W) and FeC13 on EI-K(A) proved to be the most active. Supported ZnC12 catalysts have shown comparable activity. Clark et al. obtained very poor conversions (< 6%) in the benzylation of benzene in the case of FeC13, A1C13, MnCI2 and SnCI2 supported on activated montmorillonite K 10 (4). They reported the highest conversion in the case of supported ZnCI2 which was attributed to the high local concentration of Zn ions residing in the structural mesopores of the support. Such Zn ions are described to be highly polar. Variation in catalytic activity of similar reagents cannot be

562 explained based on surface area and acidity values alone as there are too many factors governing the activity of a supported catalyst such as pore structure of the support, percentage loading of the halide and drying temperature. 4. CONCLUSION Impregnation of metal chlorides on to natural kaolinites and its modified forms results in efficient Friedel-Crafts alkylation catalysts. A synergistic interaction between the halide and the surface of support as well as mesopore surface of the support is possible. The present study shows that kaolinite and its metakaolinised acid activated forms are efficient support material with comparable performance to the existing commercial montmorillonite K 10. ACKNOWLEDGEMENT The authors are thankful to Dr. A.D. Damodaran, former Director, and Dr. G.Vijay Nair, Director, RRL(T) for their constant encouragement and guidance. REFERENCES 1. P. Laszlo, ed., Preparative Chemistry using Supported Reagents, Academic Press, Inc. 1987. 2. K. Tanabe, M. Misono, Y. Ono and H. Hattori, New Solid Acids and Bases. Their Catalytic Properties; Studies in Surface Science and Catalysis, V.51, Kodansha, Tokyo/Elsevier, Amsterdam, 1989. 3. K. Smith, ed., Solid Supports and Catalysts in Organic Synthesis, Ellis Horwood, Chichester, 1992. 4. J.H. Clark, A.P. Kybett, D.J. Macquarrie, S.J. Barlow and P. Landon, J. Chem. Sot., Chem. Commun. (1989) 1353. 5. S.J. Barlow, T.W. Bastock, J.H. Clark and S.R. Cullen, J. Chem. Sot., Perkin Trans., 2 (1994)411. 6. J.H. Clark, A.P. Kybett and D.J. Macquarrie, Supported Reagents, Preparation, Analysis and Applications, VCH, New York, 1992. 7. C.N. Rhodes, M. Franks, G.M.B. Parkes and D.R. Brown, J. Chem. Sot., Chem. Commun. (1991 ) 804. 8. P.D. Clark, A. Kirk and R.A. Kydd, Catal. Lett., 25 (1994), 163. 9. P. Laszlo, Pure and Appl. Chem., V.62, No.19 (1990) 2027. 10. K.R. Sabu, R. Sukumar and M. Lalithambika, Bull. Chem. Soc. Jpn., 66 (1993) 3535. 11. R. Sukumar, O.K. Shinamma, K.R. Sabu, M. Lalithambika and A.D. Damodaran, Catalysis; Modern Trends, N.M. Gupta and D.K. Chakraborty (eds.), Narosa Publishing House (1995) 486. 12. R. Cid and G. Pecchi, Appl. Catal., 18 (1985) 15. 13. C.N. Rhodes and D.R. Brown, J. Chem. Soc., Farady Trans., 95, 15 (1992) 2269. 14. J.H. Clark and in part S.R. Cullen, S.J. Barlow and T.W. Bastock, J. Chem., Soc. Perkin Trans., 2 (1994) 1117.