A Novel Route to Produce 4-T-Butyltoluene by T-Butylation of Toluene with T-Butylalcohol Over Mesoporous Al-MCM-41 Molecular Sieves M

Applied Catalysis A: General 286 (2005) 44–51 www.elsevier.com/locate/apcata

A novel route to produce 4-t-butyltoluene by t-butylation of toluene with t-butylalcohol over mesoporous Al-MCM-41 molecular sieves M. Selvaraj a,*, S.H. Jeon a, J. Han b, P.K. Sinha c, T.G. Lee a,** a Research Institute of New Energy and Environmental System, Yonsei University, Seoul 120-749, South Korea b Environment & Process Technology Division, KIST, Seoul 136-791, South Korea c CWMF, BARC Facilities, Govt. of India, Kalpakkam 603102, India

Received 16 August 2004; received in revised form 16 February 2005; accepted 23 February 2005 Available online 8 April 2005

Abstract

t-Butylation of toluene with t-butylalcohol (t-BuOH) as alkylating agent was conducted under liquid phase reaction conditions over Al- MCM-41 with different Si/Al ratios for highly selective synthesis of 4-t-butyltoluene. For the reactions, the inﬂuences of various reaction parameters such as reaction temperature, time and t-BuOH to toluene ratio are discussed. With increasing the Si/Al ratios of Al-MCM-41 catalysts from 21 to 104, the conversion of toluene, and the yield and selectivity of 4-t-butyltoluene decreased because the number of Brønsted acid sites in Al-MCM-41catalysts is found to decrease almost linearly with increasing ratios of Si/Al. The conversion and selectivity is increased in Al-MCM-41(21) with each cycling of reaction. The Si/Al ratio of 21 is found to be more suitable for the t-butylation of toluene to highly selective synthesis of 4-t-butyltoluene. Thus the selectivity of 4-t-butyltoluene is higher in Al-MCM-41(21) than that in other Al- MCM-41 samples. # 2005 Elsevier B.V. All rights reserved.

Keywords: Al-MCM-41; Catalytic activity; Brønsted acidity; Conversion of toluene; Selectivity of 4-t-butyltoluene

1. Introduction Ioffe et al. [9] studied different catalytic systems such as AlCl3,AlCl3–CH3NO2, sulfuric acid and polyphosphoric The alkylations of aromatic hydrocarbons with olefins/ acid in the liquid phase for alkylation of toluene by C4- different types of alcohols are applied on a large scale in the alcohols. By the above reaction, low yield and selectivity chemical industry [1]. Among para-dialkylated aromatics, of para isomer was obtained. These alkylations are still p-xylene, p-diisopropylbenzene, p-ethyltoluene, p-dietyl- performed with catalysts in chemical industries. Often benzene, p- and m-cymenes and 4-tert-butyltoluene are very such catalysts are strong mineral acids or Lewis acids (e.g. important in fine chemical and petrochemical industries [2– HF, H2SO4,andAlCl3), which are highly toxic and 6]. The above products are alkylated-aromatic products. 4-t- corrosive. They are dangerous to handle and to transport as Butyltoluene is produced by alkylation of toluene with they corrode storage and disposal containers. Often the anyone alkylating agent such as isobutylene, diisobutylene, products need to be separated from the acid with a difficult MTBE or t-BuOH. The product has been used as an and energy consuming process. Finally, it occurs fre- intermediate product to produce 4-t-butylbenzoic acid and quently that these acids are neutralized at the end of the 4-t-butylbenzaldehyde; they are especially used in perfum- reaction and, therefore, the correspondent salts have to be ery and in the fields of plastics and resins [7,8]. disposed. Similar problems arise when free bases are used as catalysts. In order to avoid these problems many efforts have been * Corresponding author. Tel.: +82 2 2123 5751; fax: +82 2 312 6401. devoted to the search of solid acid catalysts that are more ** Co-corresponding author. E-mail addresses: [email protected] (M. Selvaraj), selective, safe, environmentally friendly, regenerable, and [email protected] (T.G. Lee). reusable and which do not have to be destroyed after reaction.

Thus, some solid acid catalysts are used for t-butylation of catalysts for the higher selectivity of 4-t-butyltoluene toluene. produced by the alkylation of toluene using t-BuOH as the t-Butylation of toluene reaction was carried out using alkylating reagent. Owing to its low cost and extensive use toluene with MTBE, t-BuOH and t-butyl chloride in the in industries, t-BuOH was chosen instead of isobutene. The presence of activated clay, silica-alumina and iron sulphate effects of reaction temperature, time and t-BuOH to catalysts under liquid phase reaction conditions [10,11]. toluene ratio on the selectivity of 4-t-butyltoluene were The 4-t-butyltoluene was synthesized over NiY zeolite as investigated. catalyst, but, by the above reactions, the yield and selectivity of the products ( p, m and o-isomers) were very low because the activity of the catalysts is very low 2. Experimental [12]. From the above solid acid catalysts, low yield and selectivity of para isomer was obtained, because all the 2.1. Materials catalysts have small surface areas along with different structures. The performance of the zeolite is also limited The syntheses of Al-MCM-41 materials were carried out by diffusional constraints associated with smaller pores. by hydrothermal method using sodium metasilicate (Na2 These materials suffer from limited thermal stability as SiO3Á5H2O), cetyltrimethylammonium bromide (C16H33 + well as negligible catalytic activity due to framework (CH3)3N Br), aluminum sulphate (Al2(SO4)3Á18H2O), sul- neutrality. Moreover, the need for present day hetero- furic acid (H2SO4). In order to study the formation of 4-t- geneous catalysts in processing hydrocarbons with high butyltoluene by t-butylation of toluene, the reagents t-BuOH molecular weights has made researchers search for better ((CH3)3–C–OH), toluene (C7H8O) and decane were used. systems. These limitations were overcome after the All chemicals (AR grade) were purchased from Aldrich & discovery of mesoporous materials [13,14]. Co., USA. Incorporation of aluminum [15] and other metals [16,17] into their mesoporous structure has therefore been inves- 2.2. Synthesis and characterization of Al-MCM-41 tigated in order to introduce solid-state acidity and thereby catalytic function. The typical characteristics of Al-MCM- Al-MCM-41 with Si/Al ratios equal to 21, 42, 62, 83 and 41, viz. highly ordered mesoporosity, large surface area, 104 were synthesized and characterized; acidity measure- high thermal stability and mild acidity, give the possibility of ments were done according to the published method [22– applying these materials as catalysts in the synthesis and 24]. conversion of large molecules. Corma et al. [15] first reported the details of synthesis 2.3. t-Butylation of toluene—experimental procedure for and characterization of aluminum incorporating mesopor- liquid phase catalytic reaction ous materials. However, the catalytic activity of the material was low in comparison to the usual silica-alumina The Al-MCM-41 catalyst (0.2 g freshly calcined catalyst and also the thermal stability was poor. Busio et al. catalystkeptat4008C was used) was added into a [18] also reported synthesis and characterization of the Al- mixture of t-BuOH/toluene (various mmol ratios) with MCM-41, wherein incorporation of an excess of aluminum 100 ml of decane as solvent. Each reaction was carried out (Si/Al = 10) formed an impure crystal-phase tridimite, and in a stirred batch autoclave reactor (100 ml, Autoclave the Lewis acid site prevailed because of the octahedral Engineers) at reaction temperatures between 125–200 8C non-framework aluminum, accompanied with the collapse for different times (h). The reactor was flushed twice with of the structure. Selvaraj et al. [2,3,19–23] reported the nitrogen to replace air. Alkylation reactions were carried details of synthesis and characterization of some meso- out at the autogeneous pressure. The reactor was cooled porous solid acid catalysts. These have been used for down to 0 8C and the reaction products were recovered isopropylation of toluene, ethoxylation of b-naphthol, self- from the reactor. condensation of acetophenone and intermolecular cycliza- The samples of the reaction mixture were withdrawn tion of ethanolamine; from those reactions, good conver- periodically from the closed reactor and analysed on a sion and product selectivity are obtained. Particularly, CHROMPACK 9002 gas chromatograph equipped with a alkylation of toluene was carried out over mesoporous CP Sil 5 CB column (25 m Â 0.53 mm) and an FID detector. solid acid catalysts by the best candidates [3,5,6]. We have The temperature program was held at 60 8C (5 min), applied the mesoporous catalysts for highly selective increased from 60 to 220 8C with a slope of 5 8C/min and synthesis of 4-t-butyltoluene. held at 220 8C during 5 min isothermally. In the present study, Al-MCM-41 with Si/Al ratios The products of the reaction were identified on a GC/MS equal to 21, 42, 62, 83 and 104 were synthesized and QP5000 (Shimadzu) with EI and capillary column (HP-1, characterized according to the published method [22–24] 50 m Â 0.2 mm Â 0.33 mm); carrier gas was helium (1 ml/ using cetyltrimethylammonium bromide as template under min). Temperature program: from 50 8C with a gradient of hydrothermal conditions. The materials have been used as 5 8C/min to 240 8C was used. 46 M. Selvaraj et al. / Applied Catalysis A: General 286 (2005) 44–51

3. Results and discussion protonated by the catalyst to form t-butyl carbocation (Eq. (2)). The carbocation further reacts with toluene in The synthesized Al-MCM-41 catalysts have been used the presence of the catalyst to form 4-t-butyltoluene and for t-butylation of reaction with t-BuOH to highly selective 3-t-butyltoluene Eq. (3). Either 4-t-butyltoluene or 3-t- synthesis of t-butyltoluene. The reaction mechanism is butyltoluene reacts with the carobocation over the catalyst discussed. to form 3,5-di-t-butyltoluene (Eq. (4)). Excess isobutylene further reacts with each molecule over the catalyst to 3.1. Mechanism of t-butylation of toluene form oligomers (Eq. (5)) while the oligomers (R-alkyl groups) react with excess toluene in the presence of the The t-butylation of toluene with t-BuOH is an electro- catalyst to form alkyltoluenes with longer alkyl chains philic substitution reaction on the aromatic ring. t- (Eq. (6)). The remaining oligomers further react with Butylation reactions catalyzed by acids or solid acid zeolites water over the catalyst to form alcohols (Eq. (7)). All the are commonly considered to proceed via carbenium ion above products (all equations) are obtained with respect to mechanisms [3]. the catalytic properties along with optimal reaction t-BuOH reacts with solid acid catalyst to form isobutene, conditions. The reaction of toluene with t-BuOH is given along with removal of water (Eq. (1)). Isobutene is in Fig. 1.

Fig. 1. Reaction scheme of t-butylation of toluene. M. Selvaraj et al. / Applied Catalysis A: General 286 (2005) 44–51 47

In all cases, the main reaction products have been high aluminum content, the high hydrothermal stability and identified as 4-t-butyltoluene and 3-t-butyltoluene. 2-t- also the higher number of Brønsted acid sites from creation Butyltoluene was present in the reaction products only in of negative charges on the pore walls, which is attributed to trace amounts. The main product is logically 4-t-butylto- the incorporation of Al trivalent ions in place of tetrahedral luene because para-position is favored by the influence of Si in the structure. The number of acid sites for the the steric hindrance of the methyl group on one side and different catalysts follow the order; Al-MCM-41(21) > Al- voluminous t-Bu group due to the structure of mesoporous MCM-41(42) > Al-MCM-41(62) > Al-MCM-41(83) > Al-MCM-41 catalysts. Al-MCM-41(104), as obtained from TPD and FTIR- The formation of 2-t-butyltoluene is hindered by ortho- pyridine treatment. This reaction is activated on the m- position of methyl and voluminous t-Bu group. The same and the p-positions by the presence of the methyl group. The steric effect allows only the formation of 3,5-di-t- selectivity of 4-t-butyltoluene is higher than those of 3-t- butyltoluene, where all alkyl groups are in the meta- butyltoluene, 2-t-butyltoluene and 3,5-di-t-butyltoluene due position. 3,5-Di-t-butyltoluene was also found in the to steric hindrance of the methyl group at the para-position. reaction products, but only in trace amounts obtained over The 3-t-butyltoluene and 3,5-di-t-butyltoluene are thermo- Al-MCM-41 catalysts. The other products have been dynamically more stable [3]. Thus, the conversion of toluene identified by GC–MS as alkyltoluenes with longer alkyl and selectivity of 4-t-butyltoluene are higher in Al-MCM- chains. These products were formed by alkylation of toluene 41(21) than in the other Al-MCM-41 catalysts. The results with lower oligomers of isobutene (preferentially by are shown in Table 1. dimers). The effects of various parameters on the t- butylation of toluene reaction are discussed. 3.3. Variation of reaction time with different Si/Al ratios of Al-MCM-41 3.2. Selectivity of 4-t-butyltoluene The liquid phase reaction of t-butylation of toluene was The reaction of t-butylation of toluene was carried out in carried out at various reaction times with 2:1 mmol ratio of t- the presence of various Si/Al ratios of Al-MCM-41 catalysts. BuOH to toluene and 100 ml of decane as solvent at 175 8C Maximum conversion of toluene to the extent of 86.2 and reaction temperature, in the presence of Al-MCM-41 with 92.3% 4-t-butyltoluene selectivity was obtained when the different Si/Al ratio catalysts. Lower reaction time (<1h) reaction was carried out in the presence of Al-MCM-41(21). does not favor the formation of 4-t-butyltoluene because The conversion of toluene and selectivity of 4-t-butyltoluene surface activity of the catalysts is insufficient to react with in the presence of Al-MCM-41(21) are higher, due to the reactants. Then conversion of toluene, yield and selectivity

Table 1 t-Butylation of toluene: variation of reaction time with different Si/Al ratios of Al-MCM-41 Catalysts Time (h) Conversion of toluene (%) Yield of the products (%) 4-t-BT selectivity 4-t-BT 3-t-BT Others Al-MCM-41(21) 1 74.3 65.3 5.1 3.9 87.88 2 86.2 79.6 5.3 1.3 92.34 4 93.4 56.7 30.4 6.3 60.70 8 96.2 52.4 37.0 6.8 54.46 Al-MCM-41(42) 1 69.2 59.8 5.0 4.4 86.41 2 81.0 74.1 5.1 1.8 91.48 4 88.7 51.2 29.6 7.9 57.72 8 90.8 46.9 35.3 8.6 51.65 Al-MCM-41(62) 1 63.1 53.3 4.8 5.0 84.46 2 74.8 66.6 4.9 3.3 89.03 4 81.8 45.7 28.4 7.7 55.86 8 84.4 41.4 34.8 8.2 49.05 Al-MCM-41(83) 1 56.0 44.8 4.6 6.6 80.00 2 67.6 57.1 4.7 5.8 84.46 4 74.5 40.2 28.1 6.2 53.95 8 77.0 35.9 33.4 7.7 46.62 Al-MCM-41(104) 1 47.9 36.3 4.4 7.2 75.78 2 59.4 45.8 4.5 9.1 77.10 4 66.2 34.7 27.7 3.8 52.41 8 68.6 30.4 31.1 7.1 44.31 Reaction conditions: 0.2 g of catalyst; reaction temperature (T) = 1758C; 1:2 mmol ratio of t-butylalcohol to toluene; 100 ml of n-decane; 4-t-BT, 4-t- butyltoluene; 3-t-BT, 3-t-butyltoluene; others—2-t-butyltoluene, 2,5-di-t-butyltoluene and oligomers. 48 M. Selvaraj et al. / Applied Catalysis A: General 286 (2005) 44–51

Table 2 t-Butylation of toluene: variation of reaction temperature with different Si/Al ratios of Al-MCM-41 Catalysts Temperature (8C) Conversion of toluene (%) Yield of the products (%) 4-t-BT selectivity 4-t-BT 3-t-BT Others Al-MCM-41(21) 125 66.7 55.4 4.8 6.5 83.05 150 75.3 65.3 5.2 4.8 86.71 175 86.2 79.6 5.3 1.3 92.34 200 90.3 58.4 23.5 8.4 64.67 Al-MCM-41(42) 125 61.4 49.7 4.5 7.2 80.94 150 70.1 59.7 4.7 5.7 85.16 175 81.0 74.1 5.1 1.8 91.48 200 84.9 52.6 22.1 10.2 61.95 Al-MCM-41(62) 125 54.9 42.0 4.4 8.5 76.50 150 63.8 52.1 4.6 7.1 81.66 175 74.8 66.6 4.9 3.3 89.03 200 78.3 44.8 21.5 12.0 57.21 Al-MCM-41(83) 125 47.5 32.3 4.2 11.0 68.0 150 56.5 42.5 4.3 9.7 75.22 175 67.6 57.1 4.7 5.8 84.46 200 70.8 35.2 20.8 14.8 49.71 Al-MCM-41(104) 125 40.1 22.9 3.9 13.3 57.10 150 49.2 32.9 4.1 12.2 66.86 175 59.4 45.8 4.5 9.1 77.10 200 63.0 25.5 19.7 17.8 40.47 Reaction conditions: 0.2 g of catalyst; reaction time = 2 h; 1:2 mmol ratio of t-butylalcohol to toluene; 100 ml of n-decane; 4-t-BT, 4-t-butyltoluene; 3-t-BT, 3-t- butyltoluene; others—2-t-butyltoluene, 2,5-di-t-butyltoluene and oligomers. of 4-t-butyltoluene increase with increasing reaction time up because the acid sites on the catalyst surface are decreased to 2 h over different Al-MCM-41 (different Si/Al ratios) with decreasing aluminum content. The results are shown in catalysts in the same reaction conditions. But the conversion, Table 1. When the reaction time is increased (>3 h), the yield and selectivity decrease with increasing Si/Al ratios, conversion of toluene increased, but the yield and selectivity

Table 3 t-Butylation of toluene: variation of mmol ratio (t-butylalcohol/toluene) with different Si/Al ratios of Al-MCM-41 Catalysts t-BA/toluene mmol ratio Conversion of toluene (%) Yield of the products (%) 4-t-BT selectivity 4-t-BT 3-t-BT Others Al-MCM-41(21) 1:1 40.4 29.4 8.4 2.6 72.77 2:1 86.2 79.6 5.3 1.3 92.34 1:2 89.9 63.3 18.4 8.2 70.41 1:4 72.3 49.5 10.4 12.4 68.46 Al-MCM-41(42) 1:1 35.1 25.5 7.2 2.4 72.64 2:1 81.0 74.1 5.1 1.8 91.48 1:2 84.8 59.7 17.2 7.9 70.40 1:4 67.1 44.8 10.2 12.1 66.76 Al-MCM-41(62) 1:1 28.9 19.9 6.8 2.2 68.85 2:1 74.8 66.6 4.9 3.3 89.03 1:2 78.7 55.0 16.2 7.5 69.88 1:4 60.9 39.5 9.6 11.8 64.86 Al-MCM-41(83) 1:1 21.6 13.2 6.5 1.9 61.11 2:1 67.6 57.1 4.7 5.8 84.46 1:2 71.5 49.5 14.7 7.3 69.23 1:4 53.6 33.0 9.1 11.5 61.56 Al-MCM-41(104) 1:1 13.4 7.3 4.4 1.7 54.47 2:1 59.4 45.8 4.5 9.1 77.10 1:2 63.2 42.3 13.8 7.1 66.93 1:4 45.3 24.6 9.5 11.2 54.30 Reaction conditions: 0.2 g of catalyst; reaction temperature (T) = 1758C; reaction time = 2 h; 100 ml of n-decane; 4-t-BT, 4-t-butyltoluene; 3-t-BT, 3-t- butyltoluene; others—2-t-butyltoluene, 2,5-di-t-butyltoluene and oligomers. M. Selvaraj et al. / Applied Catalysis A: General 286 (2005) 44–51 49

Fig. 2. Variation of reaction time with (a) conversion of toluene (%) and (b) Fig. 3. Variation of reaction time with (a) conversion of toluene (%) and (b) selectivity of 4-t-butyltoluene (%) at different temperature over Al-MCM- selectivity of 4-t-butyltoluene (%) on different mmol ratio (t-butanol/ 41(21) material. toluene) over Al-MCM-41(21) material. of 4-t-butyltoluene decreased, because 4-t-butyltoluene is 3.4. Variation of reaction temperature with different gradually transformed to 3-t-butyltoluene, while the other Si/Al ratios of Al-MCM-41 by-products, namely 2-t-butyltoluene, 3,5-di-t-butyltoluene and oligomers slightly increased. The conversion The t-butylation of toluene was carried out at various of toluene and selectivity of 4-t-butyltoluene are higher in reaction temperatures with 2:1 mmol ratio of t-BuOH to Al-MCM-41(21) than those of other Al-MCM-41 cata- toluene and 100 ml of decane as solvent for 2 h reaction time lysts due to the greater chemisorption of reactants on the in the presence Al-MCM-41 with different Si/Al ratio catalyst surface pores due to the higher number of catalysts. The results are shown in Table 2. When the Brønsted acid sites at 175 8C for 2 h; the results are shown temperature was increased up to 175 8C at the same reaction in Table 1. So the optimum reaction time was found to be conditions, the conversion of toluene, yield and selectivity of 2 h for the highly selective synthesis of 4-t-butyltoluene. 4-t-butyltoluene increased. After the reaction temperature of Such higher yield and selectivity of 4-t-butyltoluene 175 8C, the conversion increases, but the yield and and conversion of toluene using Al-MCM-41(21) depict selectivity of 4-t-butyltoluene decrease, because the its superiority in performance compared to other Al- selectivity of 3-t-butyltoluene and of other by-products MCM-41. namely 2-t-butyltoluene, 3,5-di-t-butyltoluene and oligo- 50 M. Selvaraj et al. / Applied Catalysis A: General 286 (2005) 44–51

The liquid phase reaction of t-butylation of toluene was carried out at various reaction times with 2:1 mmol ratio of t- BuOH to toluene and 100 ml of decane as solvent at different reaction temperatures in the presence of Al-MCM-41(21). When the reaction time was increased to 2 h at the temperature from 125 to 175 8C in the same reaction conditions, the conversion of toluene increases while the yield and selectivity of 4-t-butyltoluene increases, but, after 2 h, the yield and selectivity decreased. The results are shown in Fig. 2. When the reaction time (>4 h) along with temperature (>175 8C) are increased, selectivity of 3-t- butyltoluene increased and yields of other by-products as 2- t-butyltoluene and 3,5-di-t-butyltoluene also increased, because of debutylation of 4-t-butyltoluene with formation of toluene and isobutylene.

3.5. Variation with t-butanol to toluene ratio

The t-butylation of toluene was carried out at 175 8C reaction temperature with various mmol ratios of t-BuOH to toluene and 100 ml of decane as solvent for 2 h reaction time in the presence Al-MCM-41 with different Si/Al ratio catalysts; the results are shown in Table 3. The conversion of toluene, yield and selectivity of t-butyltoluene decreased at 1:1 mmol ratio of t-BuOH to toluene. This may be due to the t-BuOH is insufﬁcient to react with toluene. As the 2 mmol of t-BuOH is increased to 1 mmol of toluene, the conversion of toluene, yield and selectivity of 4-t-butyltoluene increase. This may be due to equilibrating of the two reactants on the Brønsted acid sites of the inner side surface of catalyst. As the 2 mmol of toluene is increased to 1 mmol of t-BuOH, the conversion increased, but the yield and selectivity of 4-t- butyltoluene the 3-t-butyltoluene decreased, while other by- products slightly increased. When 4 mmol of toluene was combined with 1 mmol of t-BuOH, the conversion of toluene, yield and selectivity of 4-t-butyltoluene and 3-t- butyltoluene decreased, but the other products of oligomers Fig. 4. Variation with run of the catalysts with (a) conversion of toluene (%) and (b) selectivity of 4-t-butyltoluene (%) in the presence of different Al- increased. In all the cases, 4-t-butyltoluene was obtained as MCM-41 materials. the major product along with small amounts of 3-t- butyltoluene products. In addition, trace amounts of other mers increase by transalkylating of 4-t-butyltoluene, while alkylated products like 3,5-di-t-butyltoluene, 2-t-butylto- the 4-t-butyltoluene has low thermodynamical stability at luene and oligomers were also observed. At a reaction higher reaction temperature (>175 8C). The conversion of temperature of 175 8C for reaction time at 2 h over different toluene, yield and selectivity of 4-t-butyltoluene are higher Si/Al ratios of Al-MCM-41 catalysts, the highest conversion over Al-MCM-41(21) than that the values of other Al- of toluene and highest selectivity of 4-t-butyltoluene were MCM-41 catalysts due to the increased catalytic activity obtained at t-BuOH to toluene ratio of 2:1, while the along with the higher number of Brønsted acid sites on the conversion and yield and selectivity increased with high surface of the catalyst while most of converted reactants are aluminum content such results are shown in Table 3. favored into 4-t-butyltoluene at 175 8C for 2 h. So the Generally, as the molar ratio of toluene is increased with t- optimum reaction temperature was found to be 175 8C for BuOH, the conversion of toluene decreased, and as the molar the highly selective synthesis of 4-t-butyltoluene. When the ratio of t-BuOH is increased with toluene, the conversion of reaction temperature is further increased to 200 8C, the toluene decreased. This may be due to coking of the catalyst conversion of toluene and yield and selectivity of 4-t- by unsaturation of reactant and catalyst pores; then there butyltoluene decreased. This may be due to the debutylation would be fast diffusion without reaction from the catalyst of 4-t-butyltoluene with formation of toluene and isobuty- active sites. Hence the optimal molar ratio of t-BuOH to lene. toluene is 2:1. Thus, the optimum conditions for obtaining M. Selvaraj et al. / Applied Catalysis A: General 286 (2005) 44–51 51 maximum conversion of toluene (86.2%) and highest higher in recyclable Al-MCM-41(21) than the values of selectivity of 4-t-butyltoluene (92.3%) can be summarized other Al-MCM-41 catalysts due to no loss of catalytic as follows: Catalyst, Al-MCM-41 with Si/Al = 21; reaction activity after the recycling process. Thus, a higher yield and temperature = 175 8C, time = 2 h and t-BuOH to toluene selectivity of 4-t-butyltoluene and conversion of toluene ratio = 2:1. using Al-MCM-41(21) depicts its superiority in perfor- The liquid phase reaction of t-butylation of toluene was mance compared to other Al-MCM-41 catalysts. carried out at various reaction times with different mmol ratios of t-BuOH to toluene and 100 ml of decane as solvent at 175 8C in the presence Al-MCM-41(21); the results are Acknowledgement given in Fig. 3. The conversion of toluene and selectivity of 4-t-butyltoluene increase but the yield and selectivity The authors gratefully acknowledge the Korea Research decrease with different time in the series 1:1 < Foundation for sponsoring this work (KRF-2003-005- 1:4 < 1:2 < 2:1 mmol ratios of t-BuOH to toluene. The D00002). conversion and selectivity are higher in 2:1 mmol ratios for 2 h than those of other mmol ratios due to equilibrium of the reactants with the greater chemisorption on the Brønsted acid sites of catalyst surfaces. The yields of other products References such as oligomers in 1:1 mmol ratio, 3-t-butyltoluene and 2,5-di-t-butyltoluene in 1:2 and 1:4 ratios are slightly higher [1] H.G. Franck, J.W. Stadelhofer, Industrial Aromatic Chemistry, Springer, Berlin, 1988. than those of 2:1 mmol ratio due to the favorable catalyst [2] M. Selvaraj, A. Pandurangan, K.S. Seshadri, P.K. Sinha, V. Krishna- surface and reaction conditions. samy, K.B. Lal, J. Mol. Catal. A: Chem. 186 (2002) 173. [3] M. Selvaraj, A. Pandurangan, K.S. Seshadri, P.K. Sinha, K.B. Lal, 3.6. Recyclability Appl. Catal. A: Gen. 242 (2003) 347. [4] A.B. Halgeri, J. Das. Catal. Today 73 (2002) 65. [5] C. Perego, S. Amarilli, A. Carati, C. Flego, G. Pazzuconi, C. Rizzo, G. All Al-MCM-41 catalysts were reused for the t- Bellussi, Micropor. Mesopor. Mater. 27 (1999) 345. butylation of toluene at 175 8C with 2 h reaction time and [6] J. Cejka, A. Krejei, N. Zilkova, J. Dedecek, J. Hanika. Micropor. 2:1 mmol ratio of t-BuOH to toluene for the highly selective Mesopor. Mater. 44–45 (2001) 499. synthesis of t-butyltoluene; the results have been depicted in [7] G.W. Hearne, T.W. Evans, V.W. Buls, C.G. Schwarzer, Ind. Eng. Fig. 4. No loss of catalytic activity was observed after 4 runs. Chem. 47 (11) (1995) 2311. [8] N. Kusano, T. Kobayashi, H. Miyajima, JP 61145130 (1986). Instead, its conversion of toluene, yield and selectivity of t- [9] B.V. Ioffe, R. Lemann, B.V. Stoljarov, Neftekhimija 9 (3) (1969) 386. butyltoluene increased with each cycling in Al-MCM- [10] N. Kusano, T. Kobayashi, H. Miyajima, JP 61145130 (1986). 41(21). But the conversion, yield and selectivity decreased [11] M. Hino, K. Arata, Chem. Lett. 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Mesopor. t-butyltoluene increased in only Al-MCM-41(21) with each Mater. 74 (2004) 157. cycling. The conversion and selectivity of t-butyltoluene are [24] M. Selvaraj, Ph.D. thesis, Anna University, Tamil Nadu, India (2003).