Montmorillonite and vanadia—montmorillonite catalysts for aniline alkylation

JOURNAL OF

MOLECULAR CATALYSIS ELSEVIER

Journal of Molecular Catalysis 88 (1994) L271-L276

Letter

Montmorillonite and vanadia-montmorillonite catalysts for aniline alkylation Sankarasubbier Narayanan*, Kiranmayi Deshpande, Boppana P. Prasad Catalysis Sectton, Indzan Institute of Chemwal Technology. Hyderabad-500 007. India

(Received September 21, 1993; accepted November 19, 1993)

Abstract

An efficient aniline alkylating property of montmorillonite and vanadia-montmorillonite is discussed in the light of acidity. Key words: alkylation; anihne" montmorillonlte;vanadla

Smectite clay minerals have layer structures in which two-dimensional oxy anions are separated by layers of exchangeable hydrated cations. These clays can be used as catalysts and support; the catalytic activity and selectivity are due to the acidity and the pore structure of the material [ 1,2]. Montmorillonite and pillared montmorillonites are both used as catalysts and as matrices for rare earth exchanged zeolite-Y molecular sieves for catalytic cracking of heavy oils [ 3 ]. One of the problems of using montmorillonite as catalyst is that it deactivates, and at high temperatures the structural collapse can occur, leading to decrease in surface area and catalytic cracking activity [ 3]. Very little information is available on the use of clay material especially montmorillonite for reactions such as disproportionation [ 4] and alkylation [ 5-7]. Pillared synthetic saponite has been reported to be a good toluene alkylation catalyst for producing high yields of p-xylene [ 5]. We have earlier reported an enhanced aniline alkylation activity of silica supported vanadia catalyst over simple oxides [8]. Alkylation of aniline is an industrially important reaction. In this communication we report a preliminary account of the efficient alkylating ability of montmorillonite clay in the vapour phase aniline alkylation reaction. The influence of vanadia as an additive is *Corresponding author. 0304-5102/94/$07.00 © 1994 Elsevier Science B.V. All nghts reserved SSDI0304-5 102(93) E0294-Q

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discussed. A correlation between acidity variation of montmorillonite and vanadia-montmorillonite with aniline alkylation is also presented. Montmorillonite is of commercial origin ( Fluka, K 10, an acid activated clay) with surface area 220-270 m 2 g - ~ and bulk density 300-370 g - i. Vanadia (V205) was prepared by air calcination of a m m o n i u m metavanadate (NHaVO3) at 773 K for 6 h. Different weight percentages of vanadia-loaded montmorillonite were prepared by wet impregnation of montmorillonite with an aqueous solution of the required quantity of ammonium metavanadate in oxalic acid. The dried sample was calcined at 773 K for 6 h. Samples were used in powdered form for surface area measurement and for catalysis experiments, The BET surface area was measured by nitrogen adsorption at 77 K on sample which was degassed at 623 K for 2 h. Catalysis experiments were carried out at atmospheric pressure on ca. 500 mg of catalyst taken in a tubular down-flow glass reactor (40 cm X 1.5 cm). Aniline-ethanol mixture ( 1 : 5 w t / w t ) was fed from the top using a calibrated motorised syringe. Experiments were carded out at different feed rates of aniline in the temperature range 523-723 K. The liquid products were collected after 60 to 90 min. During this period there was no deactivation of catalysts and the activity remained steady. The products were analyzed by a gas chromatograph with a SS column (3 m × 3 mm) 10% Apiezon-L treated with 2% KOH on chromosorb A W ( 8 0 / 1 0 0 ) . The products identified were N-ethylaniline ( N E A ) , N , N ' diethylaniline ( N N ' D E A ) and others, mostly C-alkylated products. In Table 1 aniline conversion and the product selectivity for reactions carried out on montmorillonite, vanadia and vanadia-loaded montmorillonite are given along with the surface area. Vanadia has the lowest surface area of 33 m 2 g - 1 and montmorillonite has the highest, nearly 220 m 2 g - 1. Addition of vanadia decreases the surface area of montmorillonite almost linearly. Vanadia shows the least activity with only 35% conversion. Montmorillonite shows a relatively high conversion of 77% when compared with vanadia. Addition of 5 wt.% of V:O5 has no significant effect on the conversion when compared to montmorillonite even though there is a decrease of nearly 44 m 2 g - i in the surface area. Addition of 10 wt.% of V205 to montmorillonite, however, increases the conversion substantially in spite of the decrease in surface area of montmorillonite by 95 m 2 g - 1. Further addition of vanadia not only decreases the surface area of montmorillonite but also the Table 1 Anihneconversionover montmonlloniteand V20~-montmorilloniteat 673 K, 1 bar and 12 cm3h-~ g-~ cat. No.

1 2 3a 4 5 6 7

Catalyst

K10 5V-KI0 10V-KI0 15V-KI0 20V-K10 25V-KI0 100V

V205 (wt.%)

Nil 5 10 15 20 25 100

BET surface area (m2g -1 )

Conversion (%)

220 176 125 116 96 68 33

77 76 97 (85) 68 52 57 35

aThe values m parenthesesare for 10% V2Os-SiO2 [9].

Selectivity(%) NEA

NN'DEA

Others

64 64 48 (85) 59 86 84 70

25 28 37 (5) 27 14

11 8 15 (10) 14

16

20

10

S. Narayanan et al. / Journal of Molecular Catalyszs 88 (1994) L271-L276

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aniline conversion. In Fig. 1 the influence of temperature (523-723 K) on conversion and selectivity of both pure montmorillonite and 10% V2Os-loaded montmorillonite is given. It may be noticed that at low conversion levels the selectivity is only for N-ethylaniline. As the temperature of reaction increases, the total conversion increases with the formation of NN'DEA and C-alkylated products in the temperature region studied. V205 seems to favour N-ethylaniline compared to pure montmorillonite. The selectivities of the catalyst are compared at constant conversion levels (Table 2 and 3). Analysis of selectivity data for aniline alkylation at low conversion level indicates that NEA is a primary product ( Table 2). Inspection of Table 3 reveals that at a given conversion level the selectivity of the products remains more or less the same. Generally, at high conversion levels the secondary products namely N,N'-diethylaniline and C-alkylated products are formed. The formation of secondary products is at the expense of the primary

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Table 2 Product selectivity at nearly constant conversion at 673 K, I bar, 60 cm ~ h - ~ g No.

I 2 3 4 5

Catalyst

KI0 10V-KI0 15V-KI0 20V-KI0 25V-KI0

Conversion

27 27 16 13 14

Selecuv~ty 1% ) NEA

NN'DEA

82 70 100 100 100

18 30 -

Table 3 Product selectw~ty at nearly constant conversion, at 673 K, 1 bar, 24 cm ~ h J g No

1 2 3 4 5

Catalyst

KI0 10V-K10 15V-KI0 20V-KI0 25V-KI0

Conversion

69 73 75 73 71

J cat.

Others

~ cat.

Selectivity ( ck ) NEA

NN'DEA

Others

56 63 57 53 61

32 28 36 39 32

12 9 7 8 7

product, viz. N-ethylaniline. The sequential formation of NEA, NN'DEA and others have already been explained [8-10] and it is only further confirmed by this work. The addition of 10 wt.% of V205 favours conversion. This may be compared with the enhanced aniline alkylation activity of I0 wt.% V2Os-silica catalyst at 673 K (Table 1). This has been attributed to a fine dispersion of vanadia and the possible formation of V-O-Si compound resulting in active V 4÷ species [9]. It is known that the catalytic activity of montmorillonite is mainly due to its acidic nature [ 1-4]. Therefore, it would be of interest to study the influence of vanadia addition on acidity and aniline alkylation activity of montmorillonite. Non-aqueous n-butylamine titration with bromothymol blue as indicator (pKa = 7) is used in the acidity measurement of the catalyst sample. In Fig. 2 the almost linear increase in acidity of montmorillonite catalyst with increasing addition of vanadia is shown. Vanadia shows highest acidity with least conversion. V2Os-montmorillonite shows less acidity and more activity than pure V205. A similar decrease in aniline alkylation activity with increase in acidity of supported vanadia catalyst, compared to pure oxides has been reported [9]. In the case of alumina, the aniline alkylation activity has been explained as being due to the hydroxyl group population attached to the AI atom which are responsible for acidity [ 10]. In the case of montmorillonite, the BrOnsted hydroxyl group which contributes to the strong acid site may be responsible for aniline alkylation. Addition of a small amount of V205 favourably affects the reaction in terms of conversion although product selectivity is disturbed. The mechanism by which it affects the alkylation reaction is not clear. The choice of acidity measurement by n-butylamine titration may not be the best one, however, it is still possible to correlate

S Narayanan et al /Journal oJ Molecular Catalysts 88 (1994) L271-L276

L275

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aniline alkylation activity of montmorillonite and vanadia-loaded montmorillonite with a measure of acidity. Further work on the establishment of acidity index by temperature programmed desorption (TPD) of ammonia and by cumene dealkylation are in progress. A real picture of the dependence of aniline alkylation on acidity will then emerge. Nevertheless this is a first report on the vapour phase aniline alkylation over montmorillonite and V2Os-montmorillonite.

Acknowledgement

One of us (KD) wishes to thank the Council of Scientific & Industrial Research (CSIR), New Delhi for Junior Research Fellowship. References [ 1] [2] [3] [4] [5] [6] [ 7] [8] [9] [ 10]

F. Figueras, Catal. Rev-Scl Eng., 30 (1988) 457 M. Frenkel, Clays and Clay Minerals, 22 (1974) 435. J. Sterte and J.E. Otterstedt, Appl Catal., 38 (1988) 131. T. Matsuda, M. Asanuma and E. Klkuchi. Appl. Catal.. 38 ( 1988 ) 289 K. Urabe, H. Sakurai and Y. Izumu J Chem. Soc., Chem C o m m u n , (1986) 1074. M. Horio, K. Suzuki, H. Masuda and T Moil. Appl. Catal., 72 ( 1991 ) 109. J.R. Butruille and T.J. Pinnavam, Catal. Today, 14 (1992) 141. S Narayanan and B P. Prasad, J. Chem Soc., Chem. Commun., (1992) 1204. S. Narayanan, B.P. Prasad and V. Vishwanathan, React. Kinet. Catal. Lett., 48 ( 1992 ) 497. S. Narayanan, B.P. Prasad and V. VIshwanathan, React. Kmet. Catal. Lett., 48 (1992) 561