Efficient Oxidative Dehydrogenation of Lactate to Pyruvate Using a Gas−Liquid Micro Flow System

Abstract

An efficient production of pyruvate by the oxidative dehydrogenation of lactate is achieved using a micro flow system based on gas−liquid slug flow. In this micro flow system, oxidizing agents and acetonitrile solutions of lactates and vanadium species are used, and lactate is converted into the corresponding pyruvate. For reasons of atom economy and enhanced mass transfer of oxygen into the liquid phase, due to internal circulation flow within slugs, molecular oxygen is the preferred agent. In a catalyst screening, vanadium oxytrichloride (VOCl3) gave the highest pyruvate yield. A continuous system is developed, consisting of the following two processes using T-shaped mixers: the mixing of an acetonitrile solution of lactate with that of VOCl3 and the injection of oxygen gas into the solution mixture. Compared with the conventional batch system, the oxidative dehydrogenation of lactate to the corresponding pyruvate proceeds more effectively using this micro flow system.

Catalytic Transformation of Biomass Derivatives to Value‐Added Chemicals and Fuels in Continuous Flow Microreactors

“…Due to the strong shear force generated by centrifugal forces in the CCCS, liquid-liquid mixing is enhanced considerably, accelerating reactions with fast kinetics that are limited by mass transfer. [134] Typically, microreactors have been used for single liquid phase and biphasic (gas-liquid or liquid-liquid) catalytic transformation of biomass derivatives to valuable products using homogeneous or heterogeneous catalysts (e. g., the (biphasic) synthesis of furans from sugars, [135][136][137][138][139][140][141][142][143][144] (aerobic) oxidation, [144][145][146][147][148][149] and hydrogenation of biomass derivatives [144,[150][151][152][153] ). [126] Another intensified reactor configuration for multiphase (gasliquid or liquid-liquid) catalytic biomass transformation is the spinning disc reactor, consisting of a rotating disc around which fluids are fed.…”

“…[53] An issue in this route is the fast decarboxylation of lactic acid (e. g., to acetaldehyde), thus mild reaction conditions and low amounts of oxidant are required for a selective production of pyruvic acid. [148] The solid VOCl 3 catalyst was mixed as a slurry with the substrate in an acetonitrile solvent. [146] In the microreactor, the oxygen mass transfer could be regulated accurately by slug flow operation before entering the packed bed, which resulted in a more selective reaction due to the prevention of unwanted side reactions (e. g. decarbonylation).…”

“…Furthermore, the incorporation of these in microreactors might be done without the requirement of difficult immobilization procedures (e. g., use of dense packing filters). [148] [106] An alternative method for the incorporation of solid catalysts into multiphase microreactors is by dispersing catalyst particles in the liquid droplet or slug ( Figure 10).…”

“…Many reactions have potential for intensification in microreactors, [133] and they hold great promises for improving (certain types of) biomass transformations. [134] Typically, microreactors have been used for single liquid phase and biphasic (gas-liquid or liquid-liquid) catalytic transformation of biomass derivatives to valuable products using homogeneous or heterogeneous catalysts (e. g., the (biphasic) synthesis of furans from sugars, [135][136][137][138][139][140][141][142][143][144] (aerobic) oxidation, [144][145][146][147][148][149] and hydrogenation of biomass derivatives [144,[150][151][152][153] ). Furthermore, biodiesel synthesis by the (trans)esterification of triglycerides and fatty acids derived from plant oils, waste cooking oils and animal fats has been extensively studied in microreactors using inorganic [154][155][156] or enzymatic catalysts.…”

“…VOCl 3 catalyzed oxidation of different alkyl (i. e. methyl, ethyl, isopropyl, n-butyl) lactates to their corresponding pyruvates was conducted in a microreactor (d C = 0.5 or 1.0 mm). [148] The solid VOCl 3 catalyst was mixed as a slurry with the substrate in an acetonitrile solvent. The liquid slurry was mixed with pure O 2 to generate a pseudo gas-liquid slug flow in the microreactor.…”