Flow Chemistry of the Kolbe‐Schmitt Synthesis from Resorcinol: Process Intensification by Alternative Solvents, New Reagents and Advanced Reactor Engineering

Abstract

The Kolbe-Schmitt synthesis from resorcinol was exemplarily investigated to figure out the process intensification potential of continuous processing in the milli and micro scale, alone and combined with additional intensification means like alternative solvents, new reagents and an advanced reactor design. The oil bathheated synthesis was investigated for capillary reactors of different dimensions, using aqueous solutions of KHCO 3 and reactive ionic liquids. Already the first case led to space-time yields (STY) of 15,500 kg/(m 3 h) at 37 % yield. Synthesis with different CO 2 -donating salts showed that KHCO 3 has the highest activity and that hydrogen carbonates are better than carbonates. The replacement of KHCO 3 by reactive ionic liquids led to a substantial increase, both in yield (58 %) and STY (69,900 kg/(m 3 h)). The application of scCO 2 did not significantly increase the yield despite an even more substantial change of the reaction medium. Using an electrically heated microstructured reactor resulted in a tenfold higher productivity (0.75 t/a) compared to the capillary reactor and does much better ensure scalability of the reaction.

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

“…However, a kinetic and thermodynamic study of the aqueous Kolbe-Schmitt synthesis of 2,4-DHBA was performed at the Ecole Polytechnique Fédérale de Lausanne (EPFL) and recently published [16]. The developed model was validated against own and literature experimental data, inter alia against the experimental data published previously by the authors [7,10]. All literature data were around the model predictions with a standard deviation of maximal ± 30 %.…”

“…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]. Here, they will be summarized only briefly in view of the illustration of the process development strategy from lab to pilot scale.…”

“…Furthermore, tailored microreactors were designed and manufactured for microwave heating and direct electric heating. The results of these investigations have been reported in detail elsewhere [9][10][11]. Finally, for verification of the scale-up concept, a mobile pilot plant was designed, constructed, and applied.…”

“…Subsequent to the reactor, the reaction was rapidly thermally quenched by using a microstructured cross-flow heat exchanger (type CRMH, Institut für Mikrotechnik Mainz GmbH). The constant pressure in the system was controlled by a diaphragm sensing back pressure regulator (type KBP, Swagelok) [10].…”

“…Although in principle it is possible to achieve scale-up by parallel operation of a large number of small capillaries with one or more meters of length (simple numberingup), this path would cause several problems in, e.g., equal distribution and manufacture. Larger diameters, however, lead to smaller yield and space-time yield as well as increased byproduct formation due to the radial temperature gradient and the reduced surface-to-volume ratio [10]. For this reason, with the development of a tailor-made microreactor an alternative approach was followed: scale-out by "smart dimensioning".…”