Efficient liquid-phase ethylation of benzene with ethylene over mesoporous MCM-22 catalyst

Microporous and Mesoporous Materials 179 (2013) 63–68

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Efficient liquid-phase ethylation of benzene with ethylene over mesoporous MCM-22 catalyst Bin Zhang a,b, Zhendong Wang b, Peng Ji a, Yueming Liu a, Hongmin Sun b, Weimin Yang b, Peng Wu a,⇑ a Shanghai Key Laboratory of Green Chemistry and Chemical Processes, Department of Chemistry, East China Normal University, North Zhongshan Rd. 3663, Shanghai 200062, PR China b Shanghai Research Institute of Petrochemical Technology, SINOPEC, North Pudong Rd. 1658, Shanghai 201208, PR China

a r t i c l e

i n f o

Article history: Received 13 December 2012 Accepted 3 May 2013 Available online 11 May 2013 Keywords: Mesoporous zeolites MCM-22 Carbon templating Liquid-phase alkylation Ethylbenzene

a b s t r a c t Mesoporous MCM-22 zeolites with Si/Al ratios of 15–45 were hydrothermally synthesized through a hard template technique by carbon black particles. The physicochemical properties of mesoporous MCM-22 were characterized by XRD, SEM, N2 adsorption, TEM, XPS, ICP, TGA-DTA and NH3-TPD techniques. In comparison with conventional MCM-22, mesoporous MCM-22 showed an obvious hysteresis loop in N2 adsorption–desorption isotherm, and possessed 4–10 nm mesopores as well as a larger external surface area. The presence of mesopores was beneficial to increase the accessibility of zeolitic acid sites and to decrease the mass transfer limitations of bulky molecules. When employed to liquid-phase ethylation of benzene with ethylene, mesoporous MCM-22 exhibited higher ethylene conversion, higher selectivity to ethylated benzenes and better stability than conventional MCM-22, potentially serving as a solid-acid catalyst in petrochemical industry. Ó 2013 Elsevier Inc. All rights reserved.

1. Introduction Alkylation of benzene with ethylene is one of major industrial processes for the production of ethylbenzene, which in turn is an important raw material for styrene manufacture [1,2]. A variety of zeolites, such as ZSM-5 [3,4], Beta [5,6] and MCM22 [7,8], have been used as catalysts in commercial processes for ethylbenzene manufacture, since these crystalline porous materials possess the micropores of molecular dimensions and exhibit outstanding shape selectivity for ethylbenzene. However, the mass transfer limitation of reactants and products has been demonstrated to playing an important role in the efficiency of this process [9]. To overcome the diffusion limitation and increase the accessibility of catalytic active sites to molecules, introducing mesopores into these zeolites has been gaining much attention. Various post treatment techniques, including desilication with alkaline leaching, hydrothermal and chemical treatments [10– 14], have been developed to endow zeolites with inhomogeneous distributed mesoporosity coming from defect domains. Currently, hard template-directing synthesis using carbon materials as porogens is one of the most widely used methods for introducing mesopores into zeolite crystals. The intracrystal or intercrystal mesopore are formed when removing the hard tem-

⇑ Corresponding author. Tel./fax: +86 21 62232292. E-mail address: [email protected] (P. Wu). 1387-1811/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.micromeso.2013.05.004

plates from the zeolite crystals or matrix by calcination. Jacobsen et al. used nanosized carbon particles as hard templates to produce mesoporous ZSM-5 zeolites, in which the carbon was encapsulated and embedded in zeolite crystals and the mesopores were generated from the voids as removing the carbon by calcination [15]. They also investigated the formation of mesoporous ZSM-5 with 12–30 nm mesopores by impregnating the synthesis gel components with multiwall carbon nanotubes [16,17]. Tao et al. synthesized uniform mesopore-containing ZSM-5 and Y zeolites using carbon aerogel templating technique [18,19]. Christensen et al. reported that mesoporous ZSM-5 single crystal exhibited significantly improvement in catalytic activity and selectivity as compared to conventional ZSM-5 catalysts in the alkylation of benzene with ethylene [20]. The improvement of catalytic performances was attributed to more accessibility of large molecules to the catalytic active sites located inside the mesopores. However, there is still no report on the hard-templating synthesis of mesoporous MCM-22, which is an important catalyst for the production of ethylbenzene or cumene via benzene alkylation with ethylene or propylene. In the present work, carbon black particles were introduced into the synthesis system of MCM-22 as porogen to synthesize mesopore-containing MCM-22 zeolites. The obtained mesoporous MCM-22 zeolites with different Si/Al molar ratios were employed as catalyst in liquid-phase alkylation of benzene with ethylene and the comparison of catalytic performance was carried out.

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2. Experimental

of 10 K min 1 from 373 K to 873 K under a helium flow (30 cm3 min 1).

2.1. Synthesis of conventional MCM-22 2.5. Catalytic reactions Conventional MCM-22 zeolites with different Si/Al molar ratios were hydrothermally synthesized following the procedures reported previously [21]. Silica sol (40 wt.%) and Al2(SO4)3
18H2O were used as silicon and aluminum sources, respectively, while hexamethyleneimine (HMI) was used as the structure-directing agent (SDA). The typical composition of the synthetic gels was 1.0 SiO2: 1/n Al2O3: 0.10 NaOH: 0.45 HMI: 20.0 H2O, where n was 30, 40, 60 or 90. The crystallization was carried out in Teflon-lined stainless autoclaves under rotation (200 rpm) at 423 K for 3 days. The products were filtered, washed with deionized water and dried at 373 K overnight to obtain the 2-dimensional (2D) lamellar precursors. Then they were calcined at 823 K for 5 h in air to remove the organic species occluded, resulting in the formation of conventional MCM-22 zeolite with 3D MWW structure. 2.2. Synthesis of mesoporous MCM-22 Carbon black M1400 (ASTM D-3249) with an average particle diameter of 13 nm supplied by Cabot Corporation was used as hard template for synthesizing mesoporous MCM-22. Other sources were the same as that for conversional MCM-22 mentioned above. The gel composition was 1.0 SiO2: 1/n Al2O3: 0.10 NaOH: 0.45 HMI: 20.0 H2O: 1.0 M1400, where n was 30, 40, 60 or 90. Through the crystallization and product treatment procedures same as conventional MCM-22, mesoporous MCM-22, denoted as MCM-22-CB, was obtained after burning off the SDA species and the carbon black.

The H-MCM-22 and H-MCM-22-CB catalysts were pressed into self-supported tablets under the pressure of 20 MPa using an electric tablet machine. They were then scrapped to collect the granules with a griddle of 10–20 mesh. The shaped tablets were tested in the reaction of liquid-phase alkylation of benzene with ethylene in a fixed bed reactor. In a typical catalyst evaluation, 1.0 g of catalyst was loaded on the middle of the stainless reactor (750 mm length, 10 mm diameter), and activated at 723 K under nitrogen flow to eliminate any adsorbed water. The reactor was then brought to the reaction temperature of 473 K where the alkylation was operated continuously at 4.5 MPa, benzene to ethylene molar ratio of 2.0 and weight hourly space velocity (WHSV) of 6.0 h 1 for ethylene. In poisoning experiment, 2,4-dimethylquinoline (2,4-DMQ), employed as the agent poisoning selectively the acid sites located on the external surface of the zeolites, was cofed with benzene into the reactor at a rate of 100 lL h 1. The reaction products were analyzed on-line with an Agilent 7890 gas chromatograph (GC) equipped with a flame ionization detector and a HP-FFAP (50 m ⁄ 0.32 mm ⁄ 0.25 lm) capillary column. The esterification of acetic acid with ethanol was carried out using 0.1 g of catalyst at ethanol to acetic acid molar ratio of 3.0 and feeding rate of loaded 2 mL h 1. The products were off-line analyzed by GC. In poisoning experiment, 2,4-DMQ was co-fed into the reactor continuously at a rate of 50 lL h 1 together with acetic acid and ethanol. 3. Results and discussion

The calcined MCM-22 and MCM-22-CB were ion-exchanged twice in 1 M NH4NO3 solution at room temperature for 5 h. They were calcined at 723 K for 5 h to obtain the proton-type samples, denoted as H-MCM-22 and H-MCM-22-CB, respectively.

The XRD patterns of conventional MCM-22 and mesoporous MCM-22 precursors with different Si/Al ratios are shown in Fig. 1. In the low angle region, the precursors showed typical

B 310

310

101

100

A

d

d

c

c

b

b a 30

a 5

310

100 101 102

C

10 15 20 25 2Theta (degree)

d

30

D 310

10 15 20 25 2Theta (degree)

001 002 100 101 102

5

Intensity (a.u.)

X-ray powder diffraction (XRD) patterns were collected on a Bruker D8 Advance diffractometer equipped with a rotating anode and Cu–Ka radiation (k = 1.5405 Å), from 2–35° with a scan rate of 2° min 1. The crystallinity was determined by measuring the intensity of the diffraction peaks appearing at 2h = 7–10° and 24– 26°. N2 adsorption–desorption isotherms were measured at 77 K on a BELSORP-MAX analyzer after the samples were degassed under vacuum at 383 K for 4 h and then at 623 K for 6 h. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were performed on a FEI Nova NanoSEM 450 microscope and a FEI Tecnai G2 F30 S-Twin microscope, respectively. TGA and DTA profiles were collected out with a Q600 thermogravimetric analyzer of TA Instruments. X-ray photoelectron spectroscopy (XPS) measurements were performed on ESCALAB 250 (VG) using Al Ka (hm = 1486.6 eV) radiation. The Si/Al molar ratios were determined by inductively coupled plasma (ICP) elemental analyses on a Varian 725-ES optical emission spectrometer. The acid-site distribution was measured with ammonia temperature programmed desorption (NH3-TPD) on an apparatus equipped with a thermal conductivity detector. A sample of 150 mg was activated in helium flow at 873 K for 1 h. It was then cooled to 373 K where adsorption of NH3 and desorption physically adsorbed NH3 were preformed. The NH3-TPD profile was recorded by heating the sample at a rate

Intensity (a.u.)

2.4. Characterization methods

102

3.1. Synthesis and physicochemical properties of mesoporous MCM-22 zeolites

001 002 100 101 102

2.3. Preparation of H-MCM-22 and H-MCM-22-CB catalysts

d c

c b

b a 5

10 15 20 25 2Theta (degree)

30

a 5

10 15 20 25 2Theta (degree)

30

Fig. 1. XRD patterns of MCM-22 precursors (A), calcined MCM-22 (B), MCM-22-CB precursors (C), and calcined MCM-22-CB (D). The samples were hydrothermally synthesized at Si/Al ratio of 15 (a), 20 (b), 30 (c) and 45 (d), respectively.

65

3 -1

[0 0 1] and [0 0 2] diffractions due to the layer stacking of the MWW sheets (Fig. 1A and C). After calcination at 823 K in a muffle furnace for 5 h, the organic species and carbon black were removed completely. Meanwhile, interlayer dehydroxylation and condensation took place. The XRD patterns of the calcined products then showed well-resolved characteristic peaks of 3D MWW topology in the range of 2h = 2–35° without the presence of peaks of other crystalline phases and amorphous phase (Fig. 1B and D). This confirmed the formation of MCM-22 zeolites with high crystallinity [22,23]. More importantly, the XRD patterns showed little difference between conventional MCM-22 and mesoporous MCM-22 after calcination, indicating that the addition of carbon black particles had little influence on the crystallinity of MCM-22 structure. The SEM images of the conventional MCM-22 and mesoporous MCM-22 before and after calcination are shown in Fig. 2. All the samples exhibited the same typical flaky morphology of the MCM-22 zeolite, approximately 0.05–0.1 lm in thickness and 0.2–0.5 lm in length, indicating no obvious difference in morphology between conventional MCM-22 and mesoporous MCM-22 [24,25]. Fig. 3 illustrates the nitrogen adsorption–desorption isotherms of H-MCM-22 and H-MCM-22-CB as well as the corresponding BJH pore size distribution plots calculated according to the method reported by Li and Jaroniec [26]. Distinct differences can be identified in the shapes of the isotherms between H-MCM-22 and H-MCM-22-CB. In contrast to a typical type I isotherm of H-MCM-22, the isotherm of H-MCM-22-CB possessed a type IV behavior with a hysteresis loop at P/P0 > 0.6. This is usually due to a multilayer adsorption of nitrogen molecules inside mesopores [27]. Moreover, the H-MCM-22-CB sample showed a more obvious hysteresis loop of type H1 than that of H-MCM-22, which may stem from the mesopores created by removing the spherical carbon black particles. As the adsorption and desorption branches of the isotherm of H-MCM-22-CB were almost vertical, the size of mesopores was relatively uniform. The existence of mesopores was evidenced by the BJH pore size distribution at 4–10 nm, which was absent for conventional MCM-22. Since there was little difference in the XRD patterns and SEM images between conventional MCM-22 and mesoporous MCM22, a series of characterizations were further carried out to make

Adsorption amount (cm g )

B. Zhang et al. / Microporous and Mesoporous Materials 179 (2013) 63–68

1000 800 b

600 400

a 5 10 15 20 25 Pore diameter (nm)

200 0 0.0

a 0.2 0.4 0.6 0.8 Relative presure P/P0

1.0

Fig. 3. N2 adsorption–desorption isotherms at 77 K on H-MCM-22 (a) and H-MCM22-CB (b). Inset shows the BJH pore size distributions.

clear how carbon black particles affect the formation or structure of mesopores in MCM-22. As shown in the TEM investigation (Fig. 4), both MCM-22 and MCM-22-CB showed well ordered but not interrupted arrangement of the MWW sheets. Intracrystal mesopores were not observed for MCM-22-CB. These results suggest that the addition of carbon black may only influence the aggregation of zeolite crystals and carbon particles were not embedded within the crystals. The mesopores formed were irregular ones existing in intercrystal or interparticle positions but not inside the crystals. The textural properties of H-MCM-22 and H-MCM-22-CB synthesized with Si/Al molar ratios of 15 and 20 were listed in Table 1. It was noteworthy that on the basis of the slopes and intercepts of the nitrogen adsorption–desorption isotherms, the external surface areas of the H-MCM-22-CB samples (195.6 and 154.4 m2 g 1) were much higher than those of MCM-22 (130.8 and 103.1 m2 g 1) when compared at the same Si/Al ratios. This could be ascribed to the mesopores created by assistance of carbon black particles. Moreover, the addition of the carbon black particles may make the MCM-22 crystals arranged in a disordered manner, thus leading to a high external surface area. Fig. 5 showed the TGA and DTA curves of as-synthesized MCM22 and MCM-22-CB precursors dried at 373 K. The DTA curves implied there were three kinds of desorption temperature-dependent weight loss (Fig. 5B). In the case of conventional MCM-22

A

B

500 nm

500 nm C

500 nm

b

D

500 nm

Fig. 2. SEM images of MCM-22 precursor (A), MCM-22-CB precursor (B), calcined MCM-22 (C) and calcined MCM-22-CB (D) synthesized at Si/Al ratio of 30.

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B

A

Fig. 4. TEM images of MCM-22 (A) and MCM-22-CB (B) after calcination.

Table 1 A comparison of physicochemical properties between H-MCM-22 and H-MCM-22-CB with Si/Al ratio of 15 and 20. Sample

H-MCM-22(15) H-MCM-22CB(15) H-MCM-22(20) H-MCM-22CB(20)

d

c

2

673 K

Gel Bulk Si/Al Si/Ala

Surface Vmicro Si/Alb (cm3 g

15

14.9 14.8

14.8 14.7

0.17 0.15

471.1 340.3 130.8 482.5 286.9 195.6

19.8 19.7

19.7 19.5

0.17 0.15

455.3 352.2 103.1 477.9 323.5 154.4

20

SSA (m g

)

1

)

Stotal

Smicro

Sexternal

a

Given by ICP. Given by XPS. c Micropore volume was calculated by t-plot method. d SSA, specific surface area. Stotal was calculated by BET method. Smicro was obtained by t-plot method. Sexternal = Stotal Smicro.

Weight (%)

A

90 80 70

22.7 % 34.6 %

a

b

Deriv. weight (a.u.)

b

100

488 K

1

B b

a b

400

500 600 700 800 Desorption temp. (K)

Fig. 6. NH3-TPD profiles of H-MCM-22 (a) and H-MCM-22-CB (b) synthesized at Si/ Al ratio of 15.

MCM-22 zeolite. The peaks at around 488 K and 668 K were assigned to the desorption of ammonia adsorbed on weak acid sites and strong acid sites, respectively [30,31]. It was seen that with the addition of carbon black particles in H-MCM-CB sample, the peak area for both acid sites were decreased simultaneously, which indicated the amount of acid sites also decrease. This is probably caused by a relatively lower crystallinity of MCM-22-CB. Actually, it was shown that H-MCM-22-CB possessed a smaller micropore volume than H-MCM-22 did (Table 1), suggesting that the addition of carbon black particles affected slightly the crystallization of MCM-22 zeolite.

a 60

400 600 800 1000 1200 Temp. (K)

400 600 800 1000 1200 Temp. (K)

Fig. 5. TGA (A) and DTA (B) curves of MCM-22 precursor (a) and MCM-22-CB precursor (b) synthesized at Si/Al = 30.

precursor, the weight loss below 473 K is attributed to adsorbed water, whereas the weight loss in the range of 473–1073 K is mainly due to the removal of HMI molecules and interlayer dehydroxylation. It was reported that the decomposition of HMI molecules occluded in interlayer voids occurred in a lower temperature region of 473–643 K, while the decomposition of HMI molecules from the intralayers of 10-MR sinusoidal channels occurs in a higher temperature region of 643–1073 K [28,29]. When carbon black particles were added into the synthesis gels, the weight loss of the MCM-22-CB precursor was increased to 35.6%, compared with 22.7% weight loss of MCM-22 precursor shown in TGA analysis (Fig. 5A). Moreover, the peak intensity of MCM-22-CB precursor at about 900 K in DTA analysis increased sharply, indicating the existence of carbon particles in MCM-22-CB precursor indeed. The NH3-TPD profiles of H-MCM-22 and H-MCM-22-CB were showed in Fig. 6. They exhibited typical desorption peaks of

3.2. Catalytic properties of mesoporous MCM-22 in alkylation of benzene with ethylene Mesoporous zeolites were reported to be more effective than conventional zeolites in catalytic reactions. For example, mesoporous ZSM-5 showed higher ethylene conversion and ethylbenzene selectivity than conversional ZSM-5 owing to increased products diffusion contributed by mesopores [15,20]. Mesoporous Zr-MFI containing intercrystal mesopores showed drastically improved activity for the reduction of cyclohexanone by 2-propanol, which was predominantly attributed to the contribution of the mesopores supplying an easier accessibility to the catalytic active sites for bulky molecules [32]. Herein, the successful synthesis of mesoporous MCM-22 encouraged us to investigate its catalytic behaviors in the liquid-phase alkylation of benzene with ethylene, an useful and important method for producing ethylbenzene. The benzene alkylation with ethylene reaction has been postulated to occur essentially on the active sites of external 12-memered ring (MR) half cups or side pockets on the crystal surface of MCM-22 zeolite [33]. H-MCM-22-CB possessing additional mesopores and a larger external surface area is thus expected to exhibit a superior catalytic performance.

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The catalytic activity and product distribution were compared between H-MCM-22 and H-MCM-22-CB synthesized at the same Si/Al ratio of 15. The alkylation of benzene with ethylene was operated in liquid-phase phase at 4.5 MPa and 473 K. The reaction products were made up of ethylbenzene (EB), xylenes (Xys), para-diethylbenzene (p-DEB), ortho-diethylbenzene (o-DEB), meta-diethylbenzene (m-DEB), triethylbenzenes (TEB), C9–C11 and other by-products. These two catalysts have very comparable bulk Si/Al ratios but different surface Si/Al ratios as evidenced by XPS analysis (Table 1). Although H-MCM-22 was richer in surface Al content than H-MCM-22-CB, the latter gave a higher ethylene conversion (Table 2). Fig. 7 further compares the ethylene conversion between conventional MCM-22 and MCM-22-CB prepared at various Si/Al molar ratios (15, 20, 30 and 40). It was obviously that mesoporous MCM-22 samples possessed higher ethylene conversions than conventional MCM-22 samples. The increase of ethylene conversion became less with decreasing Al content, i.e. increasing Si/Al ratio. Meanwhile, the ethylated benzenes (EBs, including ethylbenzene, diethylbenzenes and triethylbenzenes) selectivity was also enhanced to a certain degree on mesoporous MCM-22 zeolites (not shown). To check the stability of mesoporous MCM-22 in duration and lifetime, the reaction time was prolonged to time on stream (TOS) of 60 h. As shown in Fig. 8, two sets of catalysts with Si/Al molar ratios of 15 and 20 were compared. Generally, the reactions took about 15 h to reach the highest catalytic activity and a stable reaction level at initial stage. The selectivity of EBs was always maintained around 98.5%. In industrial ethylbenzene process, high EB yield is finally achieved through transalkylation of diethylbenzenes and triethylbenzenes to ethylbenzene. Thus, in addition to EB selectivity, the total selectivity to EBs is also an important parameter evaluating the alkylation selectivity of the zeolites. Mesoporous MCM-22 showed not only higher ethylene conversion but also more durable than conventional MCM-22, especially the sample with Si/Al molar ratio of 15 (Fig. 8A). The ethylene conversion merely decreased from 70% to 53% during 60 h of TOS at a relatively high space velocity for ethylene (WHSV = 6.0 h 1). Furthermore, poisoning experiments were carried out to investigate the reaction space for benzene alkylation on MCM-22 using 2,4-dimethylquinoline (2,4-DMQ). With a too large molecular dimension, 2,4-DMQ is believed not to enter into the intracrystal 10-MR pores of MWW, but to poison selectively the acid sites located on the external surface [34]. When the reactions were carried out in the absence of 2,4-DMQ, the ethylene conversion was 57% for H-MCM-22 and 72% for H-MCM-22-CB (Si/Al ratio of 15) (Fig. 9A). When the 2,4-DMQ was co-fed into the reactor with benzene, the alkylation reaction gave an extremely low ethylene conversion. On the other hand, the esterification of acetic acid with ethanol, that is, a reaction involving only linear molecules for both reactants and product (ethyl acetate), was hardly affected by the addition of 2,4-DMQ, as both H-MCM-22 and H-MCM-22-CB showed no obvious change in the conversion of acetic acid (Fig. 9B). These results indicated that 2,4-DMQ may poison selectively the acid sites on the external surface but not those located in the 10-MR channels, and that the ethylation of benzene involving both bulky reactant and product molecules takes place essen-

80

Ethlene conv.(%)

b 60 a

40 20 0 0

1 2 3 4 5 6 7 -2 Al/(Al + Si) ratio *10

Fig. 7. Dependence of ethylene conversion of benzene ethylation on the Al content of H-MCM-22 (a) and H-MCM-22-CB (b) reaction conditions: cat. 0.5 g; temp., 473 K; pressure, 4.5 MPa; benzene/ethylene molar ratio, 2.0; ethylene WHSV, 6.0 h 1.

A

Ethylene conv. (%)

Si/Al = 15 60

b

40 a

100

Ethylene sel. to EBs (%)

80

20

b

98

a

97 96

20

40 TOS (h)

60

80 60 b 40 a

20

20

40 TOS (h)

60

100

C

Si/Al = 20

0

Ethylene sel. to EBs (%)

0

Ethylene conv. (%)

B

Si/Al = 15 99

D

Si/Al = 20 99

b

98

a

97 96

0

20

40 TOS (h)

60

0

20

40 TOS (h)

60

0

a

b 1.40 a

a

b 1.40 a

H-MCM-22-CB + 2,4-DMQ

H-MCM-22-CB

20

H-MCM-22

40

0

b

B

60

H-MCM-22 + 2,4-DMQ

H-MCM-22-CB + 2,4-DMQ

20

H-MCM-22-CB

40

H-MCM-22

60

Conv. of acetic acid (%)

A

80

H-MCM-22 + 2,4-DMQ

Conv. of ethylene (%)

Fig. 8. Ethylene conversion (A, C) and EBs selectivity (B, D) as a function of time on stream in the ethylation of benzene over H-MCM-22 (a) and H-MCM-22-CB (b) synthesized at Si/Al ratio of 15 or 20 reaction conditions: cat. 0.5 g; temp., 473 K; pressure, 4.5 MPa; benzene/ethylene molar ratio, 2.0; ethylene WHSV, 6.0 h 1.

b

Fig. 9. Alkylation of benzene with ethylene (A) and esterification of acetic acid with ethanol (B) on H-MCM-22 and H-MCM-22-CB without addition (a) or in the presence of 2,4-DMQ (b).

Table 2 Catalytic activity and product distribution in the liquid-phase alkylation of benzene with ethylene on H-MCM-22 and H-MCM-22-CBa. Catalyst

H-MCM-22 H-MCM-22-CB a

Ethylene conv. (%)

57.09 72.05

Product distribution (%) EB

Xys

m-DEB

p-DEB

o-DEB

C9–C11

TEB

Others

82.58 83.42

0 0

4.28 4.21

3.94 3.87

6.36 6.25

0.36 0.31

0.38 0.34

2.1 1.6

Reaction conditions: cat. 0.5 g; temp., 473 K; pressure, 4.5 MPa; benzene/ethylene molar ratio, 2.0; ethylene WHSV, 6.0 h

1

; TOS = 15 h.

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tially on the acid sites located on the crystal surface. Thus, possessing mesopores and an opener external surface area, H-MCM-22-CB is benefit to the bulky reactions like benzene ethylation. 4. Conclusions Mesoporous MCM-22 with Si/Al ratios of 15–45 have been hydrothermally synthesized with the presence of carbon black particles. In comparison with conventional MCM-22, MCM-22-CB possesses larger intercrystal mesopores which are beneficial to increase the accessibility of catalytic sites to bulky molecules by decreasing mass transfer limitations. This endows the MCM-22CB catalysts with higher ethylene conversion as well as catalytic stability in the liquid-phase alkylation of benzene with ethylene in comparison to conventional MCM-22.

[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20]

Acknowledgements

[21] [22]

This project was supported by the National Science Foundation of China (20925310, U1162102), Ph.D. Programs Foundation of Ministry of Education (2012007613000), Ministry of Science and Technology (2012BAE05B02), STCSM (12JC1403600), Shanghai Municipal Education Commission (13zz038) and Shanghai Leading Academic Discipline Project (B409).

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