Biphasic Epoxidation Reaction in the Absence of Surfactants—Integration of Reaction and Separation Steps in Microtubular Reactors

Abstract

This paper presents a paradigm shift with respect to the current direction of bi-phasic reactions in surfactant-free emulsions: herein, the contact area between both phases is simply sustained by the reactor design (i.e. diameter of the tubular reactor) compared to the current trend of using reversible/switchable emulsions where the addition of an external agent (e.g. bi-stable surfactant, magnetic particles, etc.) is required. In this way, temporally stable phase dispersions using micro-tubular reactors facilitate the integration of reaction and separation steps in bi-phasic systems without the need for energy-intensive downstream separation steps. In this study, we demonstrate this innovative tool in the epoxidation reaction of sunflower oil with hydrogen peroxide. Using a combination of mechanistic and kinetic studies, we demonstrate that the poor solubility of the catalytic species in the oil phase may be used advantageously, allowing ready recyclability of catalyst (and oxidant) in consecutive runs.

Direct valorisation of waste cocoa butter triglycerides via catalytic epoxidation, ring‐opening and polymerisation

“…However, at temperatures above 150°C decomposition of hydrogen peroxide dominates and the reaction yield is significantly reduced compared with the batch, lower‐temperature, process. A more recent study reported a lower temperature epoxidation of sunflower oil in an unstable two‐phase flow regime using surfactant‐less biphasic H 2 O 2 epoxidation catalysed by a W‐based system . The reaction system was not optimised for high per‐pass conversion, but the ease of phase separation after the reaction allowed simple re‐circulation to reach higher conversion in a loop‐reactor mode.…”

“…Epoxidation of cyclooctene using a sacrificial aldehyde reactant in the Mukaiyama epoxidation was performed in a segmented continuous flow microreactor, reporting 100% selectivity to the epoxide at a short residence time of 2 min . However, there are only two examples of epoxidation of triglycerides under flow conditions, the epoxidation of soybean oil and of sunflower oil …”

Epoxidation of methyl oleate in a TiO2 coated-wall capillary microreactor

“…This result very common for the reaction in microreactor, because lower average flow velocity turn weakens the mass transfer [35] and therefore lower oxirane yields are obtained. It is worth to note that the residence time of 2.7 min is much smaller than that of the conventional batch which required several hours [1,5,6] and is in similar order to micro-flow reactor using homogeneous catalyst (6.7 min [17] and 10.6 min [12]). …”

“…Moreover, a microreactor could operate under continuous flow operation and is easy to scale-up. Microreactor has been applied in many reactions and in both homogeneous [10][11][12][13] and heterogeneous [14][15][16] catalytic systems. Recently, He et al [17] investigated biphasic epoxidation reactions in a microreactor.…”

“…However, the reaction rates seem to be independent on contact area as comparable rate could be observed between with and without surfactant. The hypothesis is that potential mass transfer limitations may overcome by sustaining the phase dispersion by the microreactor itself [12]. However, limited study of heterogeneous catalytic in microreactor has been reported in the literature; such as microporous titaniumsilicalite heterogeneous catalyst (TS-1) in microreactor for epoxidation of alkene [18][19][20].…”