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

Abstract

Significant process intensification was achieved for the continuously operated Kolbe-Schmitt synthesis of 2,4-dihydroxybenzoic acid (b-resorcylic acid) on laboratory scale by using different approaches opening novel process windows. The results of the optimal process variant, both from the economic and ecological view, were scaled up to the pilot scale. In a first step, the synthesis from resorcinol in aqueous potassium hydrogen carbonate solution was transferred from the capillary reactor to a tailor-made electrically heated microstructured reactor comprising 40 microchannels and enabling a 25-fold increase of the capacity. In a second step, a pilot plant comprising three of such reactors operated in parallel was built and successfully tested with the same reaction.

A critical review of the production of hydroxyaromatic carboxylic acids as a sustainable method for chemical utilisation and fixation of CO2

“…Since the Kolbe-Schmitt reaction was first reported in 1884 [10], numerous investigations have focused on overcoming either the two-pot, high pressure or batch mode nature of the industrially applied carboxylation process. This has led to the development of various carboxylation methodologies, categorised by the use of novel activation/carboxylation agents [53,55], heterogeneous catalysts [48][49][50][51][52]and homogeneous stoichiometric reagents [35,53,54] as shown in Table 1. These new developments attempt to reduce the long reaction times and high CO 2 pressures that characterise the conventional Kolbe-Schmitt reaction.…”

“…This enabled space-time yields up to at product yield of 32%. Despite 28,800 𝑘𝑔 𝑚 -3 ℎ -1 low yields, the space-time yields were significantly improved due to reduced reaction times from hours to a few seconds [54].…”

“…One of the added CO 2 moieties performs an electrophilic attack on the benzene ring, whereas the old CO 2 moiety becomes a molecule of solvent. 58 development of various carboxylation methodologies, categorised by the use of novel activation/carboxylation agents, 53,55 heterogeneous catalysts [48][49][50][51][52] and homogeneous stoichiometric reagents 35,53,54 as shown in Table 1. These new developments attempt to reduce the long reaction times and high CO 2 pressures that characterise the conventional Kolbe-Schmitt reaction.…”

Conversion of carbon dioxide to resorcylic acid under ultrasonication by Kolbe–Schmitt reaction

“…The Kolbe-Schmitt synthesis is a traditionally used carboxylation reaction for phenolic cores, which enables the introduction of a carboxylic group by an electrophilic substitution and KolbeSchmitt reaction remains the standard commercial method for the preparation of aromatic hydroxy acids [4,5]. An example of important industrial synthesis under conventional conditions is the aqueous Kolbe-Schmitt synthesis of b-resorcylic acid.…”

Phenols to Pores to Adsorption. A Potential Route Towards New Methods for Extracting Value From Shale Oil Side Stream

“…3,5-Dihydroxybenzoic acid has been subjected to the Kolbe-Schmitt reaction to get dihydroxyterephthalic acid directly [10,11]. These high surface area compounds are extremely versatile materials, being useful as gas separation or storage media, adsorbents to various organic molecules [12], and chemical sensors or catalysts for many chemical processes [13]. Some of said porous materials can be used to remove sulfur containing organic compounds from fuels [14][15][16].…”