Continuous, Fast, and Safe Aerobic Oxidation of 2-Ethylhexanal: Pushing the Limits of the Simple Tube Reactor for a Gas/Liquid Reaction

Abstract

A continuous-flow microreactor is applied for the selective aerobic neat oxidation of 2-ethylhexanal. Under 7.5 bar of O 2 and 10 ppm of Mn(II) as catalyst, a production of up to 130 g/h of 2-ethylhexanoic acid can be obtained with a PFA tubing of 7 m (Ø 1.65 mm, reactor volume ca. 15 mL). The synergistic use of alkali metal salts and Mn(II) as catalyst improve the selectivity up to 94% under those conditions. We show that the productivity of this simple tube microreactor is limited by the thermal management.

Let the substrate flow, not the enzyme: Practical immobilization of d‐amino acid oxidase in a glass microreactor for effective biocatalytic conversions

“…This could be overcome by using either gas‐liquid multiphase flow systems (Bolivar et al, ; Karande et al, ), or a liquid phase strongly enriched in molecular oxygen (Gemoets et al, ). In particular, the microchannel flow reactor represents an apparatus appropriate and safe for high‐pressure process operation to enhance the O 2 concentration in solution under single‐phase flow conditions (Keybl and Jensen, ; Vanoye et al, ; Verboom, ).…”

Organic oxidations promoted in vortex driven thin films under continuous flow

“…30 Its green chemistry credentials notwithstanding, oxygen (as a gas) is often difficult to handle and can present risks for fire when used with organic substrates and flammable solvents. 31,32 These risks are exacerbated at elevated temperatures and pressuresconditions that also introduce an energy penalty to the process. Therefore, it is useful to devise methods to carry out aerobic oxidations at atmospheric pressure, room temperature, and with non-flammable solvents.…”

A flow reactor setup for photochemistry of biphasic gas/liquid reactions

“…The efficiency of chemical reactions can be greatly enhanced over common batch processes and new approaches to the optimization of established reaction protocols and the execution of hitherto unfeasible processes can be enabled due to the inherent properties of micro/flow reactors: high mass-transfer rates [8], spatial separation of reagent addition and mixing, high reagent dispersion, high energy efficiency, improved irradiation [9–11], ease of upscaling, low hazard potential and multidimensional parameter control [7,9,11–12]. Over the past decade, various reactor types and technical specifications have been developed to address the intricate challenges of many chemical reactions, including the handling of hazardous [13–14] or explosive [15–16] reagents, advanced concentration and temperature gradients [17], multiphasic reactions including solid-phase protocols [18], addition of gaseous reagents [19], high-pressure conditions [20], cascade conversions without intermediate work-up operations [21], as well as thin film, falling film [22], micro-channel [23], and tube-in-tube reactors [24–25] for reactions between gaseous and liquid components. The high energy efficiency, low hazard potential, and precise control of reaction parameters have also prompted several adoptions of microflow techniques in technical manufactures of fine chemicals, polymers [26], and pharmaceutical intermediates [27–30].…”