Improved catalytic performance for 1-butene epoxidation over the

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Improved catalytic performance for 1-butene epoxidation over the titanium silicalite-1 extrudates by using SBA-15 or carborundum as additives Yi Zuo, Min Liu, Mengtong Ma, Chunshan Song, and Xinwen Guo Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b01482 • Publication Date (Web): 19 Jun 2017 Downloaded from http://pubs.acs.org on June 22, 2017

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Industrial & Engineering Chemistry Research

Improved catalytic performance for 1-butene epoxidation over the titanium silicalite-1 extrudates by using SBA-15 or carborundum as additives Yi Zuo1, Min Liu1, Mengtong Ma1, Chunshan Song2, Xinwen Guo1,* 1

State Key Laboratory of Fine Chemicals, PSU-DUT Joint Center for Energy Research,

Department of Catalysis Chemistry and Engineering, Dalian University of Technology, Dalian 116024, P. R. China 2

EMS Energy Institute, PSU-DUT Joint Center for Energy Research and Department of Energy

& Mineral Engineering, Pennsylvania State University, University Park, PA 16802, USA *E-mail: [email protected] (X. Guo).

ACS Paragon Plus Environment

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ABSTRACT.

A

nano-sized

titanium

silicalite-1

(TS-1)

was

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synthesized

in

a

tetrapropylammonium hydroxide hydrothermal system, and was then extruded with silica and different additives (carborundum and SBA-15). The obtained TS-1 extrudates were characterized and evaluated in the epoxidation of 1-butene in a fixed-bed reactor. The catalytic performances are enhanced when carborundum and SBA-15 are introduced to the shaped catalysts, especially when using carborundum. The reasons for the deactivation of TS-1 and improvement of catalytic performance were studied. The mesopores in SBA-15 improve the diffusion property of substrates, leading to a higher catalytic activity. The high heat conductivity property of carborundum removes the exothermal rapidly, eliminating the side reactions and obtaining a higher stability.

KEYWORDS. TS-1, epoxidation of 1-butene, additive, extrudate, SBA-15, carborundum.


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1 INTRODUCTION Titanium silicalite-1 (TS-1) was first hydrothermally synthesized by Taramasso et al. in 1983.1 In the past three decades, the synthesis and applications of TS-1 attract much attention, due to its excellent catalytic performances for selective oxidation reactions under mild conditions, including the oxidation of alkanes,2,3 epoxidation of alkenes,4-7 hydroxylation of aromatics,8-10 ammoximation of ketones11-13 and other applications.14-16 The first industrial application of TS-1 is the hydroxylation of phenol with H2O2 to produce benzenediols (catechol and hydroquinone) by Enichem in 1986.17 The traditional manufactures of benzenediols are Rhone-Poulenc and Brichima routes, which often use strong acid or base as the catalyst, producing much pollution and corroding the equipment seriously.18 The new route is an environmentally friendly alternative. The conversion of phenol reaches 25% in the Enichem route, while those in the Rhone-Poulenc route and Brichima route are only 5% and 10%, respectively. In recent years, the HPPO (hydrogen peroxide to propene oxide) route was commercialized by BASF/Dow Chemical and Evonik/Uhde in Belgium and South Korea, respectively.19,20 Some institutes also tried this route in pilot plants.21,22 Compared with the traditional routes, the HPPO route provides environmental and economic benefits. Propene oxide (PO) is one of the most important ramifications of propene, which is primarily used in the producing of polyether polyol and thus polyurethane. Therefore, many researchers focus on exploring the new route and relevant catalysts. The kinetics of propene epoxidation was also studied to provide theoretical guidance for industrial production.23,24


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Butene oxide (BO) is a homolog of PO and is also an important chemical intermediate, which is often used in the organic synthesis and polymer preparations. In industry, BO is mainly manufactured from the byproduct of Chlorohydrin route preparing propene oxide.25 This route produces much waste residue and water. Therefore, it is necessary to explore a new method. Based on the experience of HPPO route, it is easy to feed 1-butene in the epoxidation reaction instead of propene to produce BO. Actually, the epoxidation of 1-butene over TS-1 has already been studied by some researchers.26-28 However, the catalytic activity and stability of the TS-1 for 1-butene epoxidation are much poorer than that for propene. One more methylene in 1-butene than propene leads to a significant difference for the catalytic performance. Many efforts have been made to improve the catalytic performance, including decreasing the particle size of TS-1,27 treating with alkaline28 and eliminating the generation of extra-framework Ti.29 However, the effects are not so excited. Thus, new methods should be explored for improving the catalytic performance of 1-butene epoxidation. The epoxidation of alkenes often occurs in a fixed-bed reactor in industry, the catalysts of which should be shaped. Extrusion is one of the most commonly used shaping methods.30 Containing a large amount of active component is the advantage of this method. However, the heat conductivity property of the extrudates are not satisfactory, especially for strongly exothermal reactions such as epoxidation of alkenes. The accumulation of exotherm not only threatens the safety, but also promotes the generation of byproducts, which is considered as the main factor for the deactivation of TS-1.31 Therefore, we provide a method for enhancing the catalytic performance of 1-butene epoxidation over TS-1 extrudates by taking into account of rapid diffusion of substances or removing of exotherm, which is adding the additives with larger


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pore diameter or higher heat conductivity property in extrusion. In addition, the reasons for the improvement were discussed by analyzing the characterization and catalytic performance results.

2 EXPERIMENTAL SECTION 2.1 Preparation of TS-1 extrudates The powdery TS-1 was prepared in a tetrapropylammonium hydroxide (TPAOH) hydrothermal system referred to the literature.32 Tetraethyl orthosilicate and tetrabutyl titanate were used as silicon and titanium sources, respectively. Tetrapropylammonium hydroxide (TPAOH) was the template and base. The silicon and titanium sources were hydrolyzed separately, and then were mixed in a flask, followed by heating at 90 °C for 40 min to remove the alcohols. The synthesis gel with a molar composition of SiO2 : TiO2 : TPAOH : H2O = 1 : 0.25 : 0.3 : 57, was transferred to a Teflon-lined autoclave and crystallized at 170 °C for 48 h. The obtained suspension was separated by centrifugation. The solid was washed with distilled water, dried at 80 °C over night and calcined at 540 °C for 6 h. The above synthesized TS-1 powder was extruded with colloidal silica (30 wt%) as the agglomerant.33 SBA-15 and carborundum (smaller than 100 mesh) were introduced as the additives, which was prepared according to the method reported by Zhao et al.34 and was bought from Henan Ming Maite New Material Technology Co., Ltd., respectively. The extrusion process was mixing the TS-1 powder, pore-forming agent (Sesbania powder), additive, agglomerant and water in sequence, extruding the wet mixture, drying the wet extrudates at room temperature, and calcining them at 540 °C for 6 h. Finally, the obtained extrudates were cut to 2


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mm × 2 mm particles for using in the evaluation. The weight composition of the wet mixture is TS-1 : Sesbania powder : additive : SiO2 : H2O = 100 : 5 : 3 : 30 : 70. Three TS-1 extrudates using SBA-15, carborundum and both of the two as the additives were denoted as TS1/SiO2/SBA-15, TS-1/SiO2/SiC and TS-1/SiO2/SBA-SiC, respectively. The weight ratio of SBA15 to carborundum in TS-1/SiO2/SBA-SiC is 1 : 1. A sample prepared without any additive was introduced for comparison, and denoted as TS-1/SiO2. 2.2 Characterization of TS-1 extrudates X-ray powder diffraction (XRD) patterns were recorded on a Rigaku Corporation SmartLab 9 X-ray diffractometer equipment using Cu Kα radiation. Fourier transform infrared (FTIR) spectra were collected on a Bruker EQUINOX55 spectrometer from 4000 to 400 cm-1, and the KBr pellet technique was used. Ultraviolet visible diffused reflectance (UV/vis) spectra were obtained on a Jasco UV-550 spectrometer from 190 to 500 nm, and pure BaSO4 was used as a reference. Nitrogen physisorption measurements were performed at liquid nitrogen temperature on a Quantachrome QUADRASORB SI physical sorption apparatus. Total surface area and pore volume

were

calculated

according

to

the

BET

and

t-plot

method,

respectively.

Thermogravimetry (TG) curves were performed on a Mettler-Toledo TGA/SDT851e instrument with a nitrogen flow rate of 60 mL/min. The used samples were heated from room temperature to 800 °C at 10 °C/min. The heat conductivity coefficients of the samples were provided on a Netzsch LFA 427 Laser Flash Analysis Equipment by a professional determination organization (Guangzhou Chemical Union Quality Testing Technology Co., Ltd). A standard test method for thermal diffusivity of solids by the flash method (ASTM E1461) was used to determine the data.


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2.3 Epoxidation of 1-butene The epoxidation of 1-butene was carried out in a fixed-bed reactor. The loading of the cut catalyst particles was 7.0 g. The typical reaction conditions were: temperature 40 °C; pressure 3.2 MPa; molar ratio of 1-butene : H2O2 3 : 1; WHSV of 1-butene 0.87 h-1; methanol as solvent; concentration of H2O2 1.4 mol/L. The residual H2O2 was checked by iodometric titration. The products were analyzed on a Tianmei 7890F gas chromatograph with a FID and a PEG-20M capillary column (30 m × 0.25 mm × 0.5 µm). BO was the main product, and butanediol (BD) and its monomethyl ethers (MME) were the byproducts. The conversion of H2O2 (X(H2O2)), selectivity of BO (S(BO)) and conversion of 1-butene (X(BE)) were calculated with equations (1), (2) and (3), respectively: X(H2O2) = ( n0(H2O2) - n(H2O2) ) / n0(H2O2)

(Eq. 1)

S(BO) = n(BO) / ( n(BO) + n(MME) + n(BD) )

(Eq. 2)

X(BE) = ( n(BO) + n(MME) + n(BD) ) / ( n0(H2O2) × 3 )

(Eq. 3)

The n0(H2O2) and n(H2O2) represent the initial and final molar numbers of H2O2, respectively. The n(BO), n(MME) and n(BD) stand for the molar numbers of BO, MME and BD, respectively.

3 RESULTS AND DISCUSSION Figure 1 shows the XRD patterns of the TS-1 extrudates prepared with different additives. All the samples have five characteristic peaks of MFI topology, which are located at the 2θ of 7.8°, 8.8°, 23.0°, 23.9° and 24.4°.35 However, different additives lead to distinct relative crystallinities


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(RCs). The RCs were calculated by choosing the sample with the strongest total intensity of the five characteristic peaks, signing its RC as 100% and comparing the total intensities of other samples with the strongest one. The RCs of TS-1/SiO2/SBA-15, TS-1/SiO2/SiC and TS1/SiO2/SBA-SiC are lower than that of TS-1/SiO2, but the reason for the decrease of RCs may not be the same. The slightly decreased RC of TS-1/SiO2/SBA-15 is mainly due to the relative lower content of TS-1, while those of TS-1/SiO2/SiC and TS-1/SiO2/SBA-SiC are also probably accounted for the addition of carborundum with small ununiformed particle size destroying part of the framework in the calcination process and blocking some channels of TS-1. Furthermore, in the pattern of TS-1/SiO2/SiC, a characteristic peak of carborundum is clearly observed at the 2θ of 35°. The pattern of carborundum used in the work is shown in Fig. S1 of Supporting Information. The nitrogen physisorption isotherms of the TS-1 extrudates are shown in Fig. 2. All the TS-1 extrudates have a type I isotherm, which shows an uptake at the low relative pressure (p/p0 < 0.1). This indicates that micropores are primary in the samples. However, the isotherms at the high p/p0 (0.6-1.0) are quite different. A small hysteresis loop appears in the isotherm of TS1/SiO2, which is accounted for the irregular pores formed by the removing of pore-forming agent (Sesbania powder) during the extrusion process. A larger hysteresis loop and a stronger increase at the p/p0 of 0.8-1.0 in the isotherm of TS-1/SiO2/SiC suggests that the addition of SiC promotes the formation of more irregular macropores, which is probably helpful for the diffusion of reactants, products and exotherm, and thus benefits the epoxidation of 1-butene. In the isotherm of TS-1/SiO2/SBA-15, typically regular mesopores are formed, i.e. an uptake and a hysteresis loop appears at the p/p0 of ~0.6, due to the introduction of mesoporous material SBA-15. The


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isotherm of TS-1/SiO2/SBA-SiC shows a comprehensive but weaker trend of those containing SBA-15 and carborundum singly. The surface areas and pore volumes of the TS-1 extrudates calculated based on the nitrogen physisorption isotherms are listed in Table 1. The addition of SBA-15 and carborundum leads to an obvious decrease of the microporous surface area, which may be caused by the relatively increased mesopores in the samples prepared with SBA-15, and the destroying of the framework and blocking of pores by carborundum in those with carborundum (proved by XRD). The total surface areas of all the TS-1 extrudates prepared with additives are larger than that of TS-1/SiO2. The largest total surface area is obtained on the TS-1/SiO2/SBA-15, probably due to the introduction of regular mesopores with large surface area. The FTIR and UV/vis spectroscopies can provide us the information of the coordination states of titanium.36 In the FTIR spectra of TS-1 extrudates (Fig. 3), there are five characteristic bands of the MFI topology, which are sited at the λ = 450, 550, 800, 1100 and 1225 cm-1. There is usually a band at 960 cm-1 in the spectrum of TS-1. Most researchers believe that it belongs to the stretching vibration of Si-O bond affected by the titanium ion in the neighborhood.37 In other words, the appearance of this band can be considered as an indirect proof of titanium inserting to the MFI framework. Therefore, the relative intensity of the bands at 960 to 800 cm-1 (I960/800) is often used for determining the relative content of framework Ti.38 The data of I960/800 are listed in Table 1. The effect of additive on the I960/800 is similar to that on the RC, that is, the I960/800 of TS1/SiO2/SiC and TS-1/SiO2/SBA-SiC are obviously lower than those of the other two samples. This phenomenon can be explained by the destroying of the TS-1 framework leading to the loss of framework Ti.


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Figure 4 shows the UV/vis spectra of the TS-1 extrudates prepared with different additives. There are mainly three bands in the UV/vis spectrum of TS-1, which are sited at 210-220, 240280 and 310-330 nm.39 The three bands are assigned to the tetrahedrally coordinated Ti (framework Ti), octahedrally coordinated Ti (extraframework Ti) and anatase TiO2.40 The band intensity of TS-1/SiO2/SiC and TS-1/SiO2/SBA-SiC at 210-220 nm is not weaker, but is similar to that of the other two extrudates, probably due to the influence of carborundum in the two samples showing a wide absorption from 210 nm to 390 nm. There are weak bands at ~260 nm and ~320 nm in the TS-1/SiO2 and TS-1/SiO2/SBA-15, proving the existence of a small amount of octahedrally coordinated Ti and anatase TiO2 in the two samples. A wide band between 300 nm and 400 nm appears in the spectra of TS-1/SiO2/SiC and TS-1/SiO2/SBA-SiC, which is also assigned to the absorption of carborundum. The catalytic performances of the four TS-1 extrudates were evaluated in the epoxidation of 1butene in a fixed-bed reactor, the data of which were shown in Fig. 5. The selectivity of BO over the four samples are similar and are all higher than 95%. Nevertheless, we do not believe that the data reflect the actual results, i.e. the actual selectivities are not so similar. Some byproducts are preserved in the catalysts (discussed below). On the other hand, the H2O2 conversion over the samples are quite different. After 60 h reaction, the conversion of H2O2 over TS-1/SiO2 decreased sharply from 80% to 40%. The initial conversion over TS-1/SiO2/SiC, TS1/SiO2/SBA-15 and TS-1/SiO2/SBA-SiC are higher than that of TS-1/SiO2. The stabilities of the formers are also better than that of the latter. SBA-15 is a mesoporous material. Compared with the pure amorphous silica support free of regular porosity, the addition of SBA-15 to the support will take the place of silica in the neighborhood of TS-1. Thus, the mesopores will enhance the diffusion property of the extrudates. As a result, the catalytic activity and stability of TS-


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1/SiO2/SBA-15 are higher than TS-1/SiO2. The high stability of TS-1/SiO2/SiC is primarily attributed to the high heat conductivity coefficient (kx) and fast heat conductivity rate (kc) of carborundum, leading to a faster exotherm removal. The deactivation of TS-1 in the epoxidation of alkenes are mainly due to the blocking of channels by the oligomers of epoxides.31 It is clear that the main and side reactions of 1-butene epoxidation are all exothermal in Scheme 1. The reaction enthalpies (∆H0) were calculated based on the data in the reference.41 The exothermal amount of the main reaction is the highest, indicating that a low reaction temperature is in favor of the main reaction. A slow heat conductivity rate will aggravate the side reactions, producing oligomers. Hence, the slightly increased kx and kc (see Table 1) will decrease the occurrence of side reactions and prolong the lifetime. The stability of TS-1/SiO2/SBA-SiC is similar to that of TS-1/SiO2/SiC, which is probably due to the function of carborundum. The TG curves of the used TS-1 extrudates are shown in Fig. 6. The weight loss in different temperature ranges calculated according to the curves are settled in Table 2. The total weight loss of the used TS-1/SiO2 is similar to that of TS-1/SiO2/SBA-15, and is more than those of TS1/SiO2/SiC and TS-1/SiO2/SBA-SiC. The weight loss in the temperature range of 100-300 °C is attributed to the MMEs and 1,2-butanediol, while that in the range of 300-500 °C shows a same trend with the stability of the samples except for TS-1/SiO2/SBA-15. The weight loss in this range is assigned to the oligomers of ethers, diol or BO, which can block the channels of TS-1 and is considered as the main factor for its deactivation. The weight loss of TS-1/SiO2/SBA-15 in this range is clearly more than those of the other three samples, indicating its largest carbon storage capacity from the mesopores. In addition, the difference in the weight loss of the used samples proves that the similarly high selectivity obtained by the four samples is probably due to the storage of large byproducts in the TS-1 or support channels.


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The total and microporous surface area data calculated based on the isotherms of used TS-1 extrudates are also listed in Table 2. It is clear that the microporous surface areas decrease after the reactions, indicating that some channels of TS-1 were blocked. However, the total surface area seems unchanged after the reactions. We found that some agglomerant would be leached during the reaction, exposing some external surface of TS-1.22 The increase of external surface area and the decrease of microporous surface area leads to a nearly unchanged total surface area.

4 CONCLUSIONS Different additives (SBA-15 and carborundum) were used to prepare TS-1 extrudates for improving the catalytic performance of 1-butene epoxidation. The catalytic activity and stability of the obtained samples were enhanced when SBA-15 or carborundum were introduced as the additive. The mesopores of SBA-15 can improve the diffusion property and deposited carbon storage capacity. The high heat conductivity coefficient and heat conductivity rate of carborundum promotes the removal of exotherm and reduces the occurrence of side reactions. ASSOCIATED CONTENT Supporting Information. The XRD pattern of carborundum, NH3-TPD profiles, and SEM and TEM images of the TS-1 extrudates prepared with different additives. AUTHOR INFORMATION Corresponding Author *X. Guo. Tel.: +86 411 84986133; fax: +86 411 84986134; E-mail: [email protected].


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ACKNOWLEDGMENT We acknowledge the financial supporting of the National Key Research and Development Program of China (2016YFB0301704), the National Natural Science Foundation of China (21506021) and the Fundamental Research Funds for the Central Universities (DUT16RC(4)11). REFERENCES (1) Taramasso, M.; Perego, G.; Notari, B. Preparation of porous crystalline synthetic materials comprised of silicon and titanium oxides. U.S. Patent 4,410,501, 1983. (2) Huybrechts, D. R. C.; De Bruycker, L.; Jacobs, P.A. Oxyfunctionalization of alkanes with hydrogen peroxide on titanium silicalite. Nature 1990, 345, 240. (3) Wang, J.; Zhao, Y.; Yokoi, T.; Kondo, J.N.; Tatsumi, T. High-performance titanosilicate catalyst obtained through combination of liquid-phase and solid-phase transformation mechanisms. ChemCatChem 2014, 6, 2719. (4) Clerici, M. G.; Bellussi, G.; Romano, U. Synthesis of propylene oxide from propylene and hydrogen peroxide catalyzed by titanium silicalite. J. Catal. 1991, 129, 159. (5) Kuwahara, Y.; Nishizawa, K.; Nakajima, T.; Kamegawa, T.; Mori, K.; Yamashita, H. Enhanced catalytic activity on titanosilicate molecular sieves controlled by cation−π interactions. J. Am. Chem. Soc. 2011, 133, 12462. (6) Wu, M.; Song, H.; Chou, L. Preparation, characterization and catalytic performance study of La-TS-1 catalysts. RSC Adv. 2013, 3, 23562.


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(24) Wu, G.; Wang, Y.; Wang, L.; Feng, W.; Shi, H.; Lin, Y.; Zhang, T.; Jin, X.; Wang, S.; Wu, X.; Yao, P. Epoxidation of propylene with H2O2 catalyzed by supported TS-1 catalyst in a fixed-bed reactor: Experiments and kinetics. Chem. Eng. J. 2013, 215-216, 306. (25) Kirk, R. O.; Dempsey, T. J. Kirk-Othmer Encyclopedia of Chemical Technology; Wiley: New York, 1982. (26) Li, H.; Wang, W.; Lin, R. W.; He, C.; Wu, X.; Gao, J.; She, X. Method for synthesizing 1,2-epoxy butane. CN Patent 200,710,034,925.8, 2007. (27) Ma, S.; Li, G.; Wang, X.; Jin, C.; Liu, M.; Guo, X. 1-Butylene epoxidation over various titanosilicate molecular sieves. J. Fuel. Chem. Technol. 2005, 33, 509. (28) Zuo, Y.; Liu, M.; Jiang, H.; Guo, X. Epoxidation of 1-butene over tetrapropylammonium hydroxide treated TS-1. Acta Petrol. Sinica (Petrol. Proc. Sec.) 2015, 31, 611. (29) Zhang, T.; Zuo, Y.; Liu, M.; Song, C.; Guo, X. Synthesis of titanium silicalite-1 with high catalytic performance for 1-butene epoxidation by eliminating the extraframework Ti. ACS Omega 2016, 1, 1034. (30) Zuo, Y.; Liu, M.; Hong, L.; Wu, M.; Zhang, T.; Ma, M.; Song, C.; Guo, X. Role of supports in the tetrapropylammonium hydroxide treated titanium silicalite‑1 extrudates. Ind. Eng. Chem. Res. 2015, 54, 1513. (31) Thiele, G. F.; Roland, E. Propylene epoxidation with hydrogen peroxide and titanium silicalite catalyst: Activity, deactivation and regeneration of the catalyst. J. Mol. Catal., A 1997, 117, 351.


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FIGURE CAPTIONS Figure 1. XRD patterns of the TS-1 extrudates prepared with different additives. Figure 2. Nitrogen physisorption isotherms of carborundum and the TS-1 extrudates prepared with different additives. Figure 3. FTIR spectra of the TS-1 extrudates prepared with different additives. Figure 4. UV/vis spectra of the TS-1 extrudates prepared with different additives. Figure 5. Catalytic performance of 1-butene epoxidation in a fixed-bed reactor over the TS-1 extrudates prepared with different additives. Figure 6. TG curves of the used TS-1 extrudates prepared with different additives.

SCHEMES TITLE Scheme 1. The main and side reactions in the epoxidation of 1-butene.


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Table 1. Physicochemical properties of the TS-1 extrudates prepared with different additives. AT(a) cat.

AM

VT

VM I960/800

(b)

kx(c)

kc

(W/(m·°C))

(cm2/s)

(m2/g)

(m2/g)

(cm3/g) (cm3/g)

TS-1/SiO2

344

312

0.38

0.10

1.53

0.29

0.0032

TS-1/SiO2/SBA-15

409

277

0.42

0.10

1.52

0.29

0.0031

TS-1/SiO2/SiC

368

222

0.35

0.07

1.38

0.31

0.0036

TS-1/SiO2/SBA-SiC

401

233

0.39

0.10

1.29

0.30

0.0035

(a)

AT and AM represent the total and microporous surface areas, respectively. VT and VM stand for the total and microporous volumes, respectively. (b)

I960/800 represents the relative intensity of the bands at 960 to 800 cm-1 in the FTIR spectra.

(c)

The kx and kc are the heat conductivity coefficient and heat conductivity rate, respectively.


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Table 2. Weight loss in different temperature ranges and surface areas of the used TS-1 extrudates. Cat.

Weight loss amount / %

AT

AM

Improved catalytic performance for 1-butene epoxidation over the

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