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Kinetics, Catalysis, and Reaction Engineering
Reaction Engineering Studies of the Epoxidation of Fatty Acid Methyl Esters with Venturello Complex Swarup K Maiti, William Kirk Snavely, Padmesh Venkitasubramanian, Erik Hagberg, Daryle H. Busch, and Bala Subramaniam Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b05977 • Publication Date (Web): 22 Jan 2019 Downloaded from http://pubs.acs.org on January 26, 2019
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Industrial & Engineering Chemistry Research
Reaction Engineering Studies of the Epoxidation of Fatty Acid Methyl Esters with Venturello Complex
S.K. Maiti,1 W.K. Snavely,1 P. Venkitasubramanian,2 E. C. Hagberg,2 D.H. Busch1, 3 and B. Subramaniam1, 4* 1
Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, KS 2 3
Archer Daniels Midland Company, Decatur, IL
Department of Chemistry, 4Department of Chemical and Petroleum Engineering, University of Kansas, Lawrence, KS
*To whom correspondence should be addressed. E-mail:
[email protected]; Phone: 785-864-2903; Fax: 785-884-6051
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ABSTRACT Atom economical and safe epoxidations of a variety of FAMEs (methyl oleate, methyl linoeate, methyl linoleate and methyl soyate) under near-isothermal conditions are demonstrated using tungsten-based Venturello catalyst and H2O2 as oxidant under solvent-free conditions. By systematically optimizing substrate/catalyst ratio, stirring rate, H2O2 addition rate and external cooling rate, safe operation with minimal temperature rise was demonstrated in a semi-batch rector for each of the substrates with total selectivity toward the epoxides at complete conversion. In the case of methyl oleate epoxidation which produces only one epoxide as product, intrinsic conversion/selectivity data obtained under near-isothermal (± 0.1 °C) conditions were regressed with suitable kinetic and reactor models to obtain an activation energy of 85 ± 6.8 kJ/mol. These results provide valuable guidance for the rational design, scaleup and safe operation of FAME epoxidation reactors.
KEYWORDS: Epoxidation, FAMEs, homogeneous tungsten catalyst, kinetics
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Industrial & Engineering Chemistry Research
1. INTRODUCTION The development of resource-efficient and inherently safe processes for the functionalization of oils and fats of plant origin to produce epoxides (for various applications such as lubricants, plasticizers, polyurethanes, polycyanates and detergents) has received renewed interest as an alternative to petroleum-based feedstocks.1 Current industrial processes for epoxidation of fatty acids and fatty esters are based on the Prileshajev peracid process,2 which suffers from drawbacks such as low epoxide selectivity, waste generation, safety and corrosion. To overcome these problems, the development of safe and atom-economical catalytic processes for the epoxidation of fatty acid methyl esters (FAMEs) or vegetable oils has received increased attention in recent years. Indeed, several types of heterogeneous and homogeneous systems have been reported for FAME epoxidation. Heterogeneous catalysts include resins, 3-5 metal oxides,6,7 polyoxometalates,8-11 alumina,7, 12 Ti-substituted Zeolites including TS-1,13 and Ti-b,14,15 amorphous silica supported Ti,16-18 Ti incorporated mesoporous silica,19-21 and CoCuAl layered double hydroxides.22 Among chemoenzymatic epoxidation processes23,24 utilizing H2O2, the commercial biocatalyst Novozyme 435 formed by immobilizing lipase B from candida antartica on polyacrylate is one of the most efficient and stable catalysts. Satyarthi et al. epoxidized methyl soyate (MS) using MoOx/γ-Al2O3 catalyst and TBHP as oxidant, with total double bond conversion of 90.1 % in 6 h at 100 °C.25 While these catalysts in general show good selectivity toward the epoxide, they suffer from drawbacks such as low activity and/or H2O2 decomposition. Homogeneous catalysts, in general, exhibit high catalytic activity and product selectivity. Aerts et al. epoxidized methyl oleate (MO) and methyl linoleate (ML) using stoichiometric amounts of meta-chloroperbenzoic acid (mCPBA) as oxidant, with conversion and epoxide selectivity,
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respectively, of 42% and 96% (MO) and 53% and 100% (ML).26 Piazza et al. epoxidized ML and methyl linolenate (MLn) with immobilized oat seed peroxygenase catalyst, using tertbutylhydroperoxide as oxidant.27 The total epoxide yields were 89 % and 92.6 % for ML and MLn, respectively, after 24 h. Du et al. epoxidized MLn using methyl trioxorhenium, pyridine and H2O2 for an overall epoxides yield of ~77 % in 6 h at room temperature.28 Tungsten-based catalysts, including polyoxometalates (POM), have been reported to show high epoxidation selectivity.29-31 Specifically, the Venturello catalyst (“Tetrakis”) using methyl trioctyl ammonium chloride as phase transfer reagent and H2O2 as oxidant is reported to be very effective for MO epoxidation.32,33 In addition, two different strategies for separating and recovering Venturello catalyst from the product mixture have been recently reported.34,35 High catalytic activity combined with the high exothermicity result in temperature excursions, which could result in thermal runaway and unsafe conditions. Reliable knowledge of intrinsic reaction kinetics is therefore required for rational reactor design, scale-up and safe operation of FAME epoxidations. Relatively few studies focus on reaction engineering aspects. Wu et al. reported iodine value of ~4 % and epoxy value of ~6 % during MO epoxidation using H2O2 and formic acid at 60 °C and 8 hours reaction time, with rapid addition of H2O2 addition (
