- Email: [email protected]
Side chain methylation of toluene and ethylbenzene with dimethyl-carbonate over alkaline X-zeolite
Studies in Surface Science and Catalysis 130 A. Corma, F.V. Melo, S. Mendioroz and J.L.G. Fierro (Editors) 9 2000 Elsevier Science B.V. All fights reserved.
2645
Side chain methylation of toluene and ethylbenzene with dimethylcarbonate over alkaline X-zeolite Rajaram Bal and S. Sivasanker National Chemical Laboratory, Pune 411 008, India.
Side chain methylation of toluene and ethylbenzene using dimethylcarbonate has been studied at atmospheric pressure in the temperature range 673K- 773K in a fixed bed reactor over Na, K and Cs exchanged X-type zeolite. Methylation of toluene produces ethylbenzene and i-propylbenzene as the main products while n- and i-propylbenzenes are the major alkylated products from ethylbenzene. The Cs exchanged sample is the most active, the catalyst prepared by exchanging with alkali hydroxide being more active than that prepared from the chloride. The influences of process parameters such as duration of run, temperature and contact time on conversion and product yields have been investigated. Tentative mechanisms for the formation of the various products are proposed. 1. INTRODUCTION While, alkylation occurs mainly at the side chain over basic catalysts, acidic catalysts induce substitution at the aromatic ring [1]. The side chain methylation of toluene to ethylbenzene (EB) and EB to propylbenzenes with methanol over alkaline zeolites has been reported by earlier workers [2,3]. Itoh et. al [4,5] reported that basic and weak acid sites present in the zeolite are required for side chain alkylation. According to Engelhardt et al [6] the selectivity for side chain alkylation increases with increase in the size of the alkali cation ( Na < K < Cs), the catalyst exchanged with alkali hydroxides being more selective than those exchanged with chloride solutions. On the basis of laser Raman and diffuse reflectance UVvis studies, Unland and Freeman [7] have concluded that side chain reaction selectivity is influenced by electrostatic fields experienced by the aromatic nucleus [8]. These interactions, primarily through perturbation of the electrons, increase with cation loading level or with increasing cationic size in a particular zeolite. The influence of acidity and basicity of the zeolite on selectivity in the alkylation of aromatic molecules has been determined by Giordano et. al [9]. We now report the use of dimethylcarbonate (DMC) to alkylate toluene to EB and EB to both i- and n-propylbenzenes over alkaline X-zeolite catalysts. 2. EXPERIMENTAL 2.1. Material and catalyst
Toluene, EB and DMC (>99% purity) were obtained from Aldrich, USA. Zeolite-X was synthesized using the gel composition 4.54Na10 9 3.44SIO1 9 A1203 9 180H20 following a reported procedure [ 10]. Ion-exchange was carried out using both hydroxide and chloride
2646 solutions of K and Cs, six exchanges being carried out at 353K with 1M solution (50ml/g) on each sample. The ion-exchanged zeolites were washed well with deionised water and dried at 373K overnight.
2.2. Apparatus and procedure The reaction was carried out in a fixed bed down-flow glass reactor (i.d. 1.5cm) at atmospheric pressure using a 2g charge of catalyst. The zeolite products were pelleted without any binder, crushed, sized (8-14 mesh) and activated at 773K for 12h in air and 3h in N2 before the reaction. The mixture of reactants was then feed into the reactor using a syringe pump. The liquid products were cooled in an ice trap and were collected periodically for analysis. Analysis of the gas and liquid products was carried out by gas chromatography (HP5880A) using a methyl silicon gum capillary column (0.2mm X 50m) with FID and TCD. 3. RESULTS AND DISCUSSION
3.1. Characterization of the catalysts X-ray diffraction measurements were carried out using Ni-filtered CuKa radiation. XRD revealed that all the samples were highly crystalline. Though the specific BET surface area apparently decrease with exchange of heavier ions (Table 1), it is found to be nearly constant (1050 + 65 m2/g) when adjusted for the additional mass of the heavier ions. The intermediate electronegativity (Sint) of the samples calculated [ 11 ] on the basis of Sanderson's electronegativity decrease (as expected) with increasing basicity of the cation (Table 1); NaX > KX > CsX. Sint has been used by earlier workers to define the basicity of the catalyst [ 9]. Table 1 Physical properties of the catalysts Catalyst Si/A1 a % exchange Sinb NaX 1.34 3.28 KX (C1) 1.34 82 3.1 KX (OH) 1.34 88 3.09 CsX (CI) 1.34 51 3.08 CsX (OH) 1.34 52 3.07 a Unit cell composition of NaX is Na82A182Sil100384. b Sint = Intermediate electronegativity [ 11 ]. c BET surface area was calculated from nitrogen sorption.
BET surface area c, (m2/g) 1025 915 900 817 824
3.2. Alkylation of toluene and ethylbenzene The activity of the catalysts were nearly constant upto 2h on stream and then decreased slowly with process time (studied upto 6h). The data reported in this paper were collected at a time on stream (TOS) of 2h.
3.2.1. Influence of basicity of the catalyst The activity of the different catalysts at various temperatures in the alkylation of toluene and EB with DMC are presented in Fig. l(a) and (b), respectively. The product distributions (at 698K for toluene and at 723K for EB) are presented in Fig. 2 (a) and (b). The activities of the catalysts (based on toluene and EB conversion) increase with increase in
2647 //
~
zs ~,~, (b) --ffi =673K e - - 698K ~ 7 2 3 K --*--- 748K 773K
~x,j,
15
//
(a)
~"
. . . . . // ' 3.28 16 t CsX(CI)~KX(C1) S "-" CsX(OH) KX(OH) int
,, \ ~ \ ~r
= 673K ---- 698K ~723K ~ - ~ 748K ~ X~,~'- ,,,,* 773K
Z0 * ~
3.06 /'CsX(Cl)''~ KX(CI)' '//
CsX(OH) KX(OH)
' S l ~t
3~28
Fig. 1. Influence of basicity: (a) Toluene conversion (Toluene/DMC (mole), 5; W/F (g.h.mole-1), 30) (b) EB conversion ( EB/DMC (mole), 5; W/F (g.h.mole-1), 60).
~-. (a) ""
- - m ~ Benzene _-w xylenes EB m v w i-PrBZ
10
H
%+. (b)
- - - - - Methane --~ BZ + Tol -A-- xylenes - - v m Styrene 9 i-PrBZ
~~ .
\,
r )
~ A
,=i 5
I--------
o~~~~.. I 3.1]
Bz
~
~
I
~
~
~//
i// CsX(C1)\ KX(CI) CsX(OH) KX(OH)
I
I
I
i//
~
3.28 S
int
=
3"061 CsX(CI)~XKX(C1) CsX(OH) KX(OH)
3.28 S
int
Fig. 2. Product yields over the catalysts: (a) Toluene methylation (Temp., 698K; Toluene/DMC (mole), 5; W/F (g.h.mole -1, 30; TOS, 2h)
(b) EB methylation (Temp.,
723K; EB/DMC (mole), 5; W/F (g.h.mole-1), 60; TOS, 2h).
2648
~,~,
14 (a)
9
~ Benzene ----4--- Xylenes
(b)
EB
12
i-PrBZ l
~
.o 2
m ~ m ~ n ~ m O----~----O~---_____,__O~ 660 " 680 ' 700 " 720 " 740 ' 760 " 780
660 " 680 ' 700 " 720 ' 740 ' 760 " 780
Temperature (K)
T e m p e r a t u r e (K)
Fig. 3. Product yields over C s X ( O H ) : 5; W / F ( g . h . m o l e -1, 30) _ _ n ~ Methane;
(a) T o l u e n e methylation: ( T o l u e n e / D M C (mole),
(b) EB methylation: ( E B / D M C (mole), 5; W / F (g.h.mole-]) = 60;
__.mBZ+Tol; ~
15
X y l e n e s ; - - v m Styrene;
.....~_.___--~
(a)
:
i-PrBZ; - - + ~
n-PrBZ).
(b)
12
9
--=-*~ -A ~v~
'~ 6 m
BZ Xylene EB
4
i-PrBZ o~
10
20
30
4'0
'
5'0
2'0 ' 3'0 ' 4'0 ' 5'0 ' 6'0 ' 7'0 ' 8'0
W/F (g.h.mole "1)
W / F (g.h.mole "1)
Fig. 4. I n f l u e n c e of contact time over C s X ( O H (a) T o l u e n e methylation: (Temp., 698K; T o l u e n e / D M C (mole), 5) (b) EB methylation: (Temp., 723K; E B / D M C (mole), 5; - - = - - Methane;
---- BZ+Tol; ~
Xylenes; ~ v - -
i-PrBZ;
*,
n-PrBZ;--§
Styrene
2649 basicity (decrease in Sint) as found by earlier workers [6]. The K and Cs containing samples prepared from the alkali hydroxides are more active than those prepared from the chloride salts. Interestingly, unlike in the case of methanol [2], alkylation of toluene with DMC produces also the dialkylated product, i-propylbenzene.
3.2.2. Influence of temperature Conversion is found to go through a maximum (- 698K for toluene and -723K for EB) with temperature over all the catalysts (Fig. 3 (a) and (b)). Many factors such as equilibrium constraints, changes in the nature of the catalyst with temperature, changes in adsorption coefficient of the reactants and rapid decomposition of the alkylating agent at higher temperatures could be responsible for the observed behaviour. Earlier workers have also reported a similar behaviour in the side chain alkylation of toluene over basic catalysts and have attributed it to the decomposition of the alkylating agent (methanol) [2] and passivation of the active centres [12]. We believe that the rapid decomposition of the alkylating agent and lower adsorption coefficient of the active alkylating species at higher temperatures are probably responsible for the observed behaviour. The yields of the various products also pass through similar maxima. 3.2.3. Influence of contact time The influence of contact time (W/F, g.h.mole-1; W = catalyst, g; F = feed rate, mole.h -l) on the reaction is presented in Fig. 4 (a) and (b). An increase in contact time increases conversion and product yield over all the catalysts. Plots of product yields over CsX(OH) as a function of conversion are presented in Fig. 5 (a) and (b). It is noticed that the yields of many of the products produced in the alkylation of toluene and benzene are extrapolatable to the origin suggesting these to be formed primarily from the starting alkylbenzenes. 3.2.4. Reaction mechanisms The side chain alkylation of toluene with methanol has been suggested to occur over basic sites in alkali exchanged zeolites [2.6,13]. A co-operative action of the acidic and basic sites has also been proposed for side chain alkylation, the basic site activating the side chain and the acidic site adsorbing the benzene ring [14]. While alkylation using methanol has been suggested to take place through the intermediate HCHO, DMC has been reported to aklylate through CH3+[ 15]. The alkylation of toluene to EB with DMC is shown below: C6HsCH3 + (CH3)3CO3 ~ C6HsC2H5 + CH3OH + CO2. The formation of i-propylbenzene probably occurs by the reaction of EB with methanol as shown below in (c) [3]. The alkylation of EB with DMC may occur by the various steps shown below: a) Activation of EB on a basic site, C6HsCHECH3 + B -~ C6HsCHECH2 + BH (B, basic site); b) Formation or n-propylbenzene, C6HsCHECH2 + (CH3)2CO3 + BH -~ C6HsCHECHECH3 + CH3OH + CO2. c) Formation of i-propylbenzene may occur as shown below [3]: CH3OH --~ HCHO + H2 C6HsCH2CH3 + HCHO --~ C6HsC(CH3)=CH2 + H20 C6HsC(CHa)=CH2 + H2 ~ C6HsCH(CH3)2
2650
15
(a) ./A,t
Benzene "- Xylenes EB - - v - - i-PrBZ
10
Methane ---*-- BZ + Tol --4,--- Xylenes - - v m i-PrBZ 9 n-PrBZ - - + m Styrene
4-
(b) v /A
2-
.+J+.f~
/r" v~ .
o
9
"
10
15
Conversion (wt%)
20
o
.
.
.
.
:0 1'5 2'0 Conversion (wt%)
2'5
Fig. 5. Product yields at different conversions over CsX(OH): (a) Toluene conversion (Toluene/DMC (mole), 5; Temp., 698K) (b) EB conversion (Temp., 723K; EB/DMC (mole), 5). 4. CONCLUSIONS Alkylation of toluene and ethylbenzene with dimethylcarbonate is promoted by alkali exchanged zeolite-X. Maximum toluene and ethylbenzene conversion and side chain alkylated product formation are observed at -698K and -723K (respectively) for the two feeds. Side chain alkylation activity increases with the basicity of the catalyst. Alkylation of toluene with dimethylcarbonate produces also the dialkylated product, i-propylbenzene. REFERENCES H. Pines and J. T. Arrigo, J.Am. Chem. Soc., 101 (1979) 6783. T. Yashima, K. Sato, T. Hayasaka and N. Hara, J. Catal., 26 (1972) 303. C. S. Huang and A. -N. Ko., Catalysis Lett., 19 (1993) 319. H. Itoh, T. Hattori, K. Suzuki and Y. Murakami, J.Catal., 79 (1983) 21. H. Itoh, T. Hattori, K. Suzuki and Y. Murakami, J.Catal., 72 (1913) 170. J. Englehardt, J. Szanyi and J. Valyon, J.Catal., 107 (1987) 296. J. J. Freeman and M. L. Unland, J. Catal., 54 (1978) 183. M. L. Unland and J. J. Freeman, J. Phys. Chem., 82 (1978) 1036. N. Giordano, L. Pino, S. Cavallaro, P. Vitarelly and B. S. Rao, Zeolites, 7 (1987) 131. F. Polak, Int. Chem. Eng., 11 (1971) 449. W.J. Mortier, J. Catal., 55 (1978) 138. A.N. Vasiliew and A. A. Galinsky, React. Kinet. Catal. Lett., 51 (1993) 253. A.E. Palomares, G. Eder-Mirth and J. A. Lercher, J. Catal., 168 (1997) 442. H. Itoh, A. Miyamoto and Y. Murakami, J. Catal., 64 (1980) 284. 15. Z.-Hua Fu and Y. Ono, J.Catal., 145 (1994) 166. .
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
2645
Side chain methylation of toluene and ethylbenzene with dimethylcarbonate over alkaline X-zeolite Rajaram Bal and S. Sivasanker National Chemical Laboratory, Pune 411 008, India.
Side chain methylation of toluene and ethylbenzene using dimethylcarbonate has been studied at atmospheric pressure in the temperature range 673K- 773K in a fixed bed reactor over Na, K and Cs exchanged X-type zeolite. Methylation of toluene produces ethylbenzene and i-propylbenzene as the main products while n- and i-propylbenzenes are the major alkylated products from ethylbenzene. The Cs exchanged sample is the most active, the catalyst prepared by exchanging with alkali hydroxide being more active than that prepared from the chloride. The influences of process parameters such as duration of run, temperature and contact time on conversion and product yields have been investigated. Tentative mechanisms for the formation of the various products are proposed. 1. INTRODUCTION While, alkylation occurs mainly at the side chain over basic catalysts, acidic catalysts induce substitution at the aromatic ring [1]. The side chain methylation of toluene to ethylbenzene (EB) and EB to propylbenzenes with methanol over alkaline zeolites has been reported by earlier workers [2,3]. Itoh et. al [4,5] reported that basic and weak acid sites present in the zeolite are required for side chain alkylation. According to Engelhardt et al [6] the selectivity for side chain alkylation increases with increase in the size of the alkali cation ( Na < K < Cs), the catalyst exchanged with alkali hydroxides being more selective than those exchanged with chloride solutions. On the basis of laser Raman and diffuse reflectance UVvis studies, Unland and Freeman [7] have concluded that side chain reaction selectivity is influenced by electrostatic fields experienced by the aromatic nucleus [8]. These interactions, primarily through perturbation of the electrons, increase with cation loading level or with increasing cationic size in a particular zeolite. The influence of acidity and basicity of the zeolite on selectivity in the alkylation of aromatic molecules has been determined by Giordano et. al [9]. We now report the use of dimethylcarbonate (DMC) to alkylate toluene to EB and EB to both i- and n-propylbenzenes over alkaline X-zeolite catalysts. 2. EXPERIMENTAL 2.1. Material and catalyst
Toluene, EB and DMC (>99% purity) were obtained from Aldrich, USA. Zeolite-X was synthesized using the gel composition 4.54Na10 9 3.44SIO1 9 A1203 9 180H20 following a reported procedure [ 10]. Ion-exchange was carried out using both hydroxide and chloride
2646 solutions of K and Cs, six exchanges being carried out at 353K with 1M solution (50ml/g) on each sample. The ion-exchanged zeolites were washed well with deionised water and dried at 373K overnight.
2.2. Apparatus and procedure The reaction was carried out in a fixed bed down-flow glass reactor (i.d. 1.5cm) at atmospheric pressure using a 2g charge of catalyst. The zeolite products were pelleted without any binder, crushed, sized (8-14 mesh) and activated at 773K for 12h in air and 3h in N2 before the reaction. The mixture of reactants was then feed into the reactor using a syringe pump. The liquid products were cooled in an ice trap and were collected periodically for analysis. Analysis of the gas and liquid products was carried out by gas chromatography (HP5880A) using a methyl silicon gum capillary column (0.2mm X 50m) with FID and TCD. 3. RESULTS AND DISCUSSION
3.1. Characterization of the catalysts X-ray diffraction measurements were carried out using Ni-filtered CuKa radiation. XRD revealed that all the samples were highly crystalline. Though the specific BET surface area apparently decrease with exchange of heavier ions (Table 1), it is found to be nearly constant (1050 + 65 m2/g) when adjusted for the additional mass of the heavier ions. The intermediate electronegativity (Sint) of the samples calculated [ 11 ] on the basis of Sanderson's electronegativity decrease (as expected) with increasing basicity of the cation (Table 1); NaX > KX > CsX. Sint has been used by earlier workers to define the basicity of the catalyst [ 9]. Table 1 Physical properties of the catalysts Catalyst Si/A1 a % exchange Sinb NaX 1.34 3.28 KX (C1) 1.34 82 3.1 KX (OH) 1.34 88 3.09 CsX (CI) 1.34 51 3.08 CsX (OH) 1.34 52 3.07 a Unit cell composition of NaX is Na82A182Sil100384. b Sint = Intermediate electronegativity [ 11 ]. c BET surface area was calculated from nitrogen sorption.
BET surface area c, (m2/g) 1025 915 900 817 824
3.2. Alkylation of toluene and ethylbenzene The activity of the catalysts were nearly constant upto 2h on stream and then decreased slowly with process time (studied upto 6h). The data reported in this paper were collected at a time on stream (TOS) of 2h.
3.2.1. Influence of basicity of the catalyst The activity of the different catalysts at various temperatures in the alkylation of toluene and EB with DMC are presented in Fig. l(a) and (b), respectively. The product distributions (at 698K for toluene and at 723K for EB) are presented in Fig. 2 (a) and (b). The activities of the catalysts (based on toluene and EB conversion) increase with increase in
2647 //
~
zs ~,~, (b) --ffi =673K e - - 698K ~ 7 2 3 K --*--- 748K 773K
~x,j,
15
//
(a)
~"
. . . . . // ' 3.28 16 t CsX(CI)~KX(C1) S "-" CsX(OH) KX(OH) int
,, \ ~ \ ~r
= 673K ---- 698K ~723K ~ - ~ 748K ~ X~,~'- ,,,,* 773K
Z0 * ~
3.06 /'CsX(Cl)''~ KX(CI)' '//
CsX(OH) KX(OH)
' S l ~t
3~28
Fig. 1. Influence of basicity: (a) Toluene conversion (Toluene/DMC (mole), 5; W/F (g.h.mole-1), 30) (b) EB conversion ( EB/DMC (mole), 5; W/F (g.h.mole-1), 60).
~-. (a) ""
- - m ~ Benzene _-w xylenes EB m v w i-PrBZ
10
H
%+. (b)
- - - - - Methane --~ BZ + Tol -A-- xylenes - - v m Styrene 9 i-PrBZ
~~ .
\,
r )
~ A
,=i 5
I--------
o~~~~.. I 3.1]
Bz
~
~
I
~
~
~//
i// CsX(C1)\ KX(CI) CsX(OH) KX(OH)
I
I
I
i//
~
3.28 S
int
=
3"061 CsX(CI)~XKX(C1) CsX(OH) KX(OH)
3.28 S
int
Fig. 2. Product yields over the catalysts: (a) Toluene methylation (Temp., 698K; Toluene/DMC (mole), 5; W/F (g.h.mole -1, 30; TOS, 2h)
(b) EB methylation (Temp.,
723K; EB/DMC (mole), 5; W/F (g.h.mole-1), 60; TOS, 2h).
2648
~,~,
14 (a)
9
~ Benzene ----4--- Xylenes
(b)
EB
12
i-PrBZ l
~
.o 2
m ~ m ~ n ~ m O----~----O~---_____,__O~ 660 " 680 ' 700 " 720 " 740 ' 760 " 780
660 " 680 ' 700 " 720 ' 740 ' 760 " 780
Temperature (K)
T e m p e r a t u r e (K)
Fig. 3. Product yields over C s X ( O H ) : 5; W / F ( g . h . m o l e -1, 30) _ _ n ~ Methane;
(a) T o l u e n e methylation: ( T o l u e n e / D M C (mole),
(b) EB methylation: ( E B / D M C (mole), 5; W / F (g.h.mole-]) = 60;
__.mBZ+Tol; ~
15
X y l e n e s ; - - v m Styrene;
.....~_.___--~
(a)
:
i-PrBZ; - - + ~
n-PrBZ).
(b)
12
9
--=-*~ -A ~v~
'~ 6 m
BZ Xylene EB
4
i-PrBZ o~
10
20
30
4'0
'
5'0
2'0 ' 3'0 ' 4'0 ' 5'0 ' 6'0 ' 7'0 ' 8'0
W/F (g.h.mole "1)
W / F (g.h.mole "1)
Fig. 4. I n f l u e n c e of contact time over C s X ( O H (a) T o l u e n e methylation: (Temp., 698K; T o l u e n e / D M C (mole), 5) (b) EB methylation: (Temp., 723K; E B / D M C (mole), 5; - - = - - Methane;
---- BZ+Tol; ~
Xylenes; ~ v - -
i-PrBZ;
*,
n-PrBZ;--§
Styrene
2649 basicity (decrease in Sint) as found by earlier workers [6]. The K and Cs containing samples prepared from the alkali hydroxides are more active than those prepared from the chloride salts. Interestingly, unlike in the case of methanol [2], alkylation of toluene with DMC produces also the dialkylated product, i-propylbenzene.
3.2.2. Influence of temperature Conversion is found to go through a maximum (- 698K for toluene and -723K for EB) with temperature over all the catalysts (Fig. 3 (a) and (b)). Many factors such as equilibrium constraints, changes in the nature of the catalyst with temperature, changes in adsorption coefficient of the reactants and rapid decomposition of the alkylating agent at higher temperatures could be responsible for the observed behaviour. Earlier workers have also reported a similar behaviour in the side chain alkylation of toluene over basic catalysts and have attributed it to the decomposition of the alkylating agent (methanol) [2] and passivation of the active centres [12]. We believe that the rapid decomposition of the alkylating agent and lower adsorption coefficient of the active alkylating species at higher temperatures are probably responsible for the observed behaviour. The yields of the various products also pass through similar maxima. 3.2.3. Influence of contact time The influence of contact time (W/F, g.h.mole-1; W = catalyst, g; F = feed rate, mole.h -l) on the reaction is presented in Fig. 4 (a) and (b). An increase in contact time increases conversion and product yield over all the catalysts. Plots of product yields over CsX(OH) as a function of conversion are presented in Fig. 5 (a) and (b). It is noticed that the yields of many of the products produced in the alkylation of toluene and benzene are extrapolatable to the origin suggesting these to be formed primarily from the starting alkylbenzenes. 3.2.4. Reaction mechanisms The side chain alkylation of toluene with methanol has been suggested to occur over basic sites in alkali exchanged zeolites [2.6,13]. A co-operative action of the acidic and basic sites has also been proposed for side chain alkylation, the basic site activating the side chain and the acidic site adsorbing the benzene ring [14]. While alkylation using methanol has been suggested to take place through the intermediate HCHO, DMC has been reported to aklylate through CH3+[ 15]. The alkylation of toluene to EB with DMC is shown below: C6HsCH3 + (CH3)3CO3 ~ C6HsC2H5 + CH3OH + CO2. The formation of i-propylbenzene probably occurs by the reaction of EB with methanol as shown below in (c) [3]. The alkylation of EB with DMC may occur by the various steps shown below: a) Activation of EB on a basic site, C6HsCHECH3 + B -~ C6HsCHECH2 + BH (B, basic site); b) Formation or n-propylbenzene, C6HsCHECH2 + (CH3)2CO3 + BH -~ C6HsCHECHECH3 + CH3OH + CO2. c) Formation of i-propylbenzene may occur as shown below [3]: CH3OH --~ HCHO + H2 C6HsCH2CH3 + HCHO --~ C6HsC(CH3)=CH2 + H20 C6HsC(CHa)=CH2 + H2 ~ C6HsCH(CH3)2
2650
15
(a) ./A,t
Benzene "- Xylenes EB - - v - - i-PrBZ
10
Methane ---*-- BZ + Tol --4,--- Xylenes - - v m i-PrBZ 9 n-PrBZ - - + m Styrene
4-
(b) v /A
2-
.+J+.f~
/r" v~ .
o
9
"
10
15
Conversion (wt%)
20
o
.
.
.
.
:0 1'5 2'0 Conversion (wt%)
2'5
Fig. 5. Product yields at different conversions over CsX(OH): (a) Toluene conversion (Toluene/DMC (mole), 5; Temp., 698K) (b) EB conversion (Temp., 723K; EB/DMC (mole), 5). 4. CONCLUSIONS Alkylation of toluene and ethylbenzene with dimethylcarbonate is promoted by alkali exchanged zeolite-X. Maximum toluene and ethylbenzene conversion and side chain alkylated product formation are observed at -698K and -723K (respectively) for the two feeds. Side chain alkylation activity increases with the basicity of the catalyst. Alkylation of toluene with dimethylcarbonate produces also the dialkylated product, i-propylbenzene. REFERENCES H. Pines and J. T. Arrigo, J.Am. Chem. Soc., 101 (1979) 6783. T. Yashima, K. Sato, T. Hayasaka and N. Hara, J. Catal., 26 (1972) 303. C. S. Huang and A. -N. Ko., Catalysis Lett., 19 (1993) 319. H. Itoh, T. Hattori, K. Suzuki and Y. Murakami, J.Catal., 79 (1983) 21. H. Itoh, T. Hattori, K. Suzuki and Y. Murakami, J.Catal., 72 (1913) 170. J. Englehardt, J. Szanyi and J. Valyon, J.Catal., 107 (1987) 296. J. J. Freeman and M. L. Unland, J. Catal., 54 (1978) 183. M. L. Unland and J. J. Freeman, J. Phys. Chem., 82 (1978) 1036. N. Giordano, L. Pino, S. Cavallaro, P. Vitarelly and B. S. Rao, Zeolites, 7 (1987) 131. F. Polak, Int. Chem. Eng., 11 (1971) 449. W.J. Mortier, J. Catal., 55 (1978) 138. A.N. Vasiliew and A. A. Galinsky, React. Kinet. Catal. Lett., 51 (1993) 253. A.E. Palomares, G. Eder-Mirth and J. A. Lercher, J. Catal., 168 (1997) 442. H. Itoh, A. Miyamoto and Y. Murakami, J. Catal., 64 (1980) 284. 15. Z.-Hua Fu and Y. Ono, J.Catal., 145 (1994) 166. .
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.