Two-Phase Flow Oxidation of Valeraldehyde with O₂ in a Microstructured Reactor

Abstract

Microstructured reactors are the ideal device for highly exothermic reactions. In this work, the highly exothermic two-phase reaction of valeraldehyde with oxygen to valeric acid was carried out in a microreactor. The used device from one-A Engineering Austria GmbH is designed for process development and intensification and can be applied in the scale-up process to small-scale commercial production. The atom economic oxidation of valeraldehyde is performed at 0 to 40 °C with a catalytic amount of manganese­(II) acetate. A continuous flow oxidation of aldehydes in such reactors can be a safe and beneficial alternative to commercial batch processes.

Aerobic oxidations in flow: opportunities for the fine chemicals and pharmaceuticals industries

“…Two different types of segmented flow reactors have been utilised for manganese-catalysed aerobic oxidation of aliphatic aldehydes to acids. The first was reported by Baumeister et al, 54 who used a 4.7 mL microstructured reactor (one-A Engineering, Austria) for the conversion of valeraldehyde (9a) to valeric acid (10a) with pure oxygen with catalytic manganeseIJII) acetate at 40°C (Scheme 7, eqn (1)). The addition of octanoic acid as a co-feed is essential to maintain higher productivity and selectivity.…”

Lattice-Boltzmann Simulation and Experimental Validation of a Microfluidic T-Junction for Slug Flow Generation

“…In this range, droplet flow is successfully used in liquid/liquid systems for extraction [8][9][10] and synthesis of fine chemicals and pharmaceuticals [11][12][13][14]. In gas/liquid systems, applications include membrane fuel cells [15] and chemical synthesis [16][17][18]. For liquid-liquid extraction (LLE) processes, flow chemistry offers the benefit of excellent control over interfacial exchange parameters.…”

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

“…According to the patent literature, the oxidation of 2-ethylhexanal 3 to 2-ethylhexanoic acid 1 is typically performed in a gas sparged stirred tank or gas lift bubble column reactors with air or enriched air as the gas phase using molecular oxygen as the terminal oxidant and with the optional presence of a catalyst. − However, this oxidation is strongly exothermic (Δ r H = −287 kJ/mol, adiabatic temperature rise of 1065 K for pure aldehyde) and proceeds via highly reactive free radical species; thus an efficient temperature control is claimed to be critical for the selectivity, the productivity, and the safety of the process. − This intrinsically fast reaction presents gas–liquid mass transfer limitation in most industrial reactors. − As a matter of fact, even at the lab scale, the productivities published in recent articles on aerobic oxidation are affected by the gas to liquid oxygen mass transfer rate. , In order to reach the chemical regime and improve the productivity, advanced microreactors can be used. They are known to provide better mass and heat transfers than classical vessels. − Thus, continuous flow micro- and millimetric reactors were demonstrated to be a valuable alternative for the safe and efficient chemical processing − and among them aerobic oxidation of aldehydes. , While this reaction could be performed without neither catalysts nor radical initiators, the reaction rate was greatly increased using metal ions as catalysts, such as Mn­(II) and pure oxygen, inside segmented flow reactors. , …”

“…The selectivity of the oxidation process is known to be highly dependent on the aldehyde structure. − While high selectivity was observed with linear aliphatic aldehyde, selectivity below 80% toward the corresponding carboxylic acid was obtained for the target reaction, i.e., the oxidation of 2-ethylhexanal 3 . ,,, The synergistic use of alkali metals salts (i.e., sodium 2-ethylhexanoate) or organic carboxylate salt (i.e., ionic liquid) and Mn­(II) as catalyst can improve the selectivity up to 98% while maintaining good productivity of the process. , Under these conditions, total conversion of the aldehyde 3 was achieved using flow chemistry, and the selectivity was kept high.…”