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

Abstract

Hydroxyaromatic carboxylic acids (HACAs) such as salicylic acids, hydroxynaphthoic acids and their halogenated derivatives are essential feedstocks for the pharmaceutical, dye, fragrance, cosmetic and food industries. Large-scale production of HACAs is currently based on the Kolbe-Schmitt reaction between CO2 and petroleum-based phenolic compounds. This batch reaction is carried out at ∼125 °C, ∼85 bar and reaction times of up to 18 hours to achieve high conversions (≈99%). The long reaction times and dependence on fossil-derived phenols have negative sustainability implications. However, as a CO2-based process, HACA production has the potential for large-volume anthropogenic CO2 sequestration and contributes to net zero. A big challenge is that the current global production capacity of HACAs uses only about 41 450 tonnes per year of CO2 which is just ≈0.00012% of the annual anthropogenic emissions. Therefore, significant efforts are needed to increase both the sustainable production and demand for such CO2-based products to enhance their economic and environmental sustainability. This review covers the basic kinetic and thermodynamic stability of CO2. Thereafter, a comprehensive coverage of early and current developments to improve the carboxylation of phenols to make HACAs is given, while discussing their industrial potential. Moreover, it covers new propositions to use biomass-derived phenolic compounds for sustainable production of HACAs. There is also a need to expand the uses and applications of HACAs and recent reports on the production of HACA-based recyclable vinyl polymers point in the right direction.