Green and efficient epoxidation of propylene with hydrogen peroxide (HPPO process) catalyzed by hollow TS-1 zeolite: A 1.0 kt/a pilot-scale study

doi:10.1016/j.cej.2016.02.072

Chemical Engineering Journal

Volume 295, 1 July 2016, Pages 370-375

https://doi.org/10.1016/j.cej.2016.02.072 Get rights and content

Highlights

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Hollow TS-1 zeolite is an good catalyst for HPPO process at pilot scale.
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Increasing the solubility of propylene favors fast conversion rate.
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Shortening the residence time of H₂O₂ insider benefits high PO selectivity.
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The lifetime of hollow TS-1 zeolite in HPPO process is very long.

Abstract

The propylene epoxidation catalyzed by hollow TS-1 zeolite with 30 wt% H₂O₂ solution as oxidant at 1.0 kt/a pilot plant has been examined. Rising reaction temperature is in favor of increasing TOF of H₂O₂ but reduces the selectivity of PO, due to the promotion of major and side reactions at the same time. Enhancing the CH₃OH amount and the WHSV of H₂O₂ is preferential to improving the TOF of H₂O₂ and the selectivity of PO, but increase capital and energy consumption as well. Taking all into consideration, the optimized epoxidation has been confirmed: T is 40–50 °C; molar ratio of CH₃OH/H₂O₂ is 5–15, and the WHSV of H₂O₂ is more than 1.2 h⁻¹. When the epoxidation of propylene carried out over 6000 h, the TOF of H₂O₂ is 30.9–32.2 mmol g⁻¹ h⁻¹ and the PO selectivity is 96–99%, respectively. The final PO product from this plant is at 99.97% purity, which has been used as an intermediate to synthesize kinds of chemicals.

Introduction

Propylene oxide (PO) is one of key propylene based chemical intermediates for producing fine chemicals, such as polyurethane plastics, polyglycol esters, unsaturated resins and surfactants [1], [2], [3]. As the fast development of material and environmental technologies, the demand of PO is continuously growing in the world, for example, the global PO market is over 7.5 million tons in 2010. Several of synthetic methods have been exploited for producing PO in academic and industrial sections, i.e. chlorohydrin process, styrene monomer propene oxide (PO/SM) process, tert-butyl alcohol (PO/TBA) process, cumene hydroperoxide (CHP) process and hydrogen peroxide propene oxide (HPPO) process [4], [5], [6], [7], [8], [9]. Compared with other four routes, HPPO route is much more environmental-friendly, without the generation of toxic by-products and wastes. HPPO process is based on titanium silicate (TS-1) zeolite as catalyst, [10], [11], [12], [13] low concentration (30–50 wt%) aqueous H₂O₂ solution as oxidant under mild conditions (usually lower than 70 °C) [14], [15]. The first commercial HPPO propylene epoxidation plant at 100 kt/a capacity was launched by Evonik and SKC at Korea in 2008 [16]. Then, several more HPPO process units were set up gradually in Belgium by BASF and DOW (300 kt/a, 2009), [17] in China by Evonik and Uhde (230 kt/a, 2013), [18] and in Thailand by DOW (390 kt/a, 2012) [19]. In HPPO process, PO is produced directly from propylene in a one-step reaction, as illustrated in Fig. 1. However, epoxidation is a cascade reaction, and these side products lower the yield of PO via secondary reaction. Among them, propylene glycol monomethyl ethers (MME, with two isomers, as shown in Fig. 1) and 1,2-propylene glycol (PG) are the two main byproducts, which are formed by ring-opening reactions of PO with CH₃OH and H₂O. Thus, it is of ultra-importance to optimize the operating parameters, such as reaction temperature, CH₃OH concentration, and weight hourly space velocity (WHSV) of H₂O₂, to avoid these side reactions occurred.

However, the conversional TS-1 zeolite usually has poor catalytic activity and reproducibility, due to the mismatch of hydrolysis and crystallization rates between Si and Ti species under hydrothermal conditions [20]. To solve these problems, the hollow TS-1 zeolite was produced by post-synthesis method in the presence of TPAOH solution at high temperature [21], [22], [23]. Compared with conventional TS-1, hollow TS-1 zeolite is of abundant intracrystalline cavities and high framework Ti species content. In our previous working, hollow TS-1 zeolite exhibits higher catalytic performances and stability in several oxidation reactions with aqueous H₂O₂ solution as oxidant, such as cyclohexanone ammoxidation, aromatic oxidation, phenol hydroxylation at industrial scale and propylene epoxidation in lab. Herein, the epoxidation of propylene catalyzed by hollow TS-1 zeolite has been carried out at 1.0 kt/a pilot scale. Thus the effects of several major important parameters on epoxidation reaction have been systemically investigated, for obtaining the optimized reaction conditions to support the even larger pilot scale test [24].

Section snippets

Synthesis of hollow TS-1 zeolite catalyst

Hollow TS-1 zeolite was synthesized as previously published method [25], [26]. In a general procedure, tetrapropylammonium hydroxide (TPAOH) was selected as organic structure directing agent (OSDA) for synthesis of the TS-1 zeolite, as described in ENI method. The molar ratio of SiO₂:TiO₂:TPAOH:H₂O is 1:0.04:0.36:40, the hydrothermal synthesis temperature is 170 °C, under the autogenous pressure. Firstly, the tetraethyl orthosilicate (TEOS) and tetrabutyl orthotitanate (TBOT) was dissolved in

Characterization of hollow TS-1 zeolite

Multiple characterization results of hollow TS-1 zeolite are illustrated in Fig. 3. From the result of XRD pattern, five diffraction peaks between 22° and 25° are apparently detected, which indicates that this material is of typical MFI topology and in high crystallinity [27], [28]. Meanwhile from high magnification SEM image, we can observe that the hollow TS-1 zeolite particle is of aggregate morphology, and the crystal size ranges from 250 to 300 nm. AS shown in TEM image, hollow TS-1 zeolite

Conclusion

The epoxidation of propylene catalyzed by hollow TS-1 zeolite based catalyst at 1.0 kt/a pilot scale, operating in a fixed-bed reactor and under mild conditions, has been investigated. Hollow TS-1 zeolite, which is of abundant intracrystalline mesopores and high framework Ti species, presents high catalytic activity and long lifetime (over 6000 h) in this process. Rising reaction temperature accelerates the major epoxidation, H₂O₂ decomposition and ring-opening reactions at the same time,

Acknowledgments

This work was financially supported by the National Basic Research Program of China (973 Program, 2006CB202508), China Petrochemical Corporation (SINOPEC Group 20673054). Changjiu Xia thanks Swedish Research Council (VR) and Swedish Governmental Agency for Innovation Systems (VINNOVA) and the Göran-Gustafsson Foundation for Natural Sciences and Medical Research.

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Green and efficient epoxidation of propylene with hydrogen peroxide (HPPO process) catalyzed by hollow TS-1 zeolite: A 1.0 kt/a pilot-scale study

Highlights

Abstract

Introduction

Section snippets

Synthesis of hollow TS-1 zeolite catalyst

Characterization of hollow TS-1 zeolite

Conclusion

Acknowledgments

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Chem. Eng. J.

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Catal. Commun.

Microporous Mesoporous Mater.

Stud. Surf. Sci. Catal.

J. Catal.

Chin. J. Catal.

Chin. J. Catal.

Chem. Eng. J.

J. Catal.

Fluid Phase Equilib.

Catal. Today