Aqueous Kolbe−Schmitt Synthesis Using Resorcinol in a Microreactor Laboratory Rig under High-p,T Conditions

Abstract

The aqueous Kolbe−Schmitt synthesis using resorcinol to yield 2,4-dihydroxy benzoic acid was performed in a microreactor rig. This small-scale plant was equipped initially with one capillary reactor and one microstructured cooler only. Later, two upgraded versions were constructed, having in addition a microstructured cooler and a microstructured mixer, respectively. The chemical protocol was significantly varied as compared to standard laboratory operation as described in the literature. Higher temperatures (up to 220 °C) and pressures (up to 74 bar) were employed in a facile manner, termed high-p,T processing. In this way, the reaction time could be shortened by orders of magnitude, from about 2 hours to less than one minute, in some cases to some seconds. This resulted in a remarkable increase of the space-time yield by a factor of 440 at best. Productivity was in the L/h range and yielded at best 111 g/h product, corresponding to 4 t/a. Scale-out solutions are indicated. Drawbacks of the microreactor operation were also identified such as high sensitivity to fouling and delicate regulation of the system pressure, leading to partly unstable plant operation. Possibly even a considerable part of the product was rearranged to 2,6-dihydroxybenzoic acid and then thermally decomposed under the harsh reaction conditions. Solutions to overcome or at least diminish these restrictions are envisaged, and in the hope that this may be achieved, a process innovation and business perspective for the high-p,T microreactor processing is depicted.

Kolbe‐Schmitt Flow Synthesis in Aqueous Solution – From Lab Capillary Reactor to Pilot Plant

“…Details of the investigations on the lab-scale had been reported previously [7,[9][10][11]17]. Here, the promising process intensification results were transferred from the lab scale to pilot scale by applying methods like smart dimensioning as well as internal and external numbering-up without a considerable loss of performance.…”

“…Although the KolbeSchmitt synthesis for a long time has been industrially applied to produce pharmaceuticals like Aspirin®, antimicrobials, or fine chemicals [3][4][5][6], especially the variant carried out in solution was regarded to have high potential for process intensification. Encouraged by the results of preliminary investigations at IMM [7][8][9], a research project had been carried out in the framework of the funding cluster Novel Process Windows of the Deutsche Bundesstiftung Umwelt (DBU) focusing on transferring the best lab-scale results to the pilot scale. The results of the detailed investigation of several aspects concerning the process intensification potentials have already been reported [9][10][11].…”

Sustainability lessons from practice: how flow intensification can trigger sustainability and modular plant technology in EU projects

“…The fine chemical considered here is 2,4-dihydroxybenzoic acid, because there has been vast research performed to develop a respective flow process [40][41][42] and cost data were available. The reaction for this process is shown as follows:…”

A View Through Novel Process Windows

“…[31,35,36] In comparison with a batch reaction carried out in a flask, the spacetime yield in a capillary reactor was increased by a factor of 1000. This process has been combined with the use of reactive ionic liquids for solvent-free operation, which could further improve the space-time yield of the capillary reactor.…”