This review revises the advances in the chemocatalytic processes for producing renewable carboxylic acids for the synthesis of bio-based polymers and proposes the actions to overcome the problems threatening their technical and economic viability.

Lactic acid and ester derivatives, which are important precursors of a wide variety of products, can be prepared via retro-aldol sugar condensation in the presence of Sn-containing zeolites. However, the preparation of these materials is often complex and requires zeolitic structures that are difficult to obtain on a commercial scale, hindering the access to this technology at the industrial level. In the present study, a comparative investigation was conducted on the preparation of a faujasite zeolite functionalized with Sn and Al species from a commercial USY material using simple post-synthetic methods. The Sn–Al-USY zeolite displayed poor selectivity towards methyl lactate when the methanolic solutions of glucose were treated with it; however, alkaline ion-exchange switched the catalytic activity of this zeolite, enhancing its performance in retro-aldol condensation and inhibiting the dehydration pathway towards methyl levulinate. The catalytic activities of these materials have been correlated to their acid–base properties and the interaction of the supported tin species with alkali metals. Na and K-exchanged Sn–Al-USY demonstrated high catalytic activity in the transformation of glucose into methyl lactate, providing yields above 40% from glucose as well as good stability and reusability.

The effects of the nature and strength of surface acid sites on the properties of the catalyst used for the one-pot conversion of levulinic acid to valeric biofuels have been investigated. The acid supports were prepared from a commercial beta zeolite (HBEA) modified by partial substitution of Al by Zr atoms. This procedure enables changes in the nature and strength of the acidic sites of the starting zeolite. A constant amount of Pd (2 wt%) was incorporated on these acid supports by the incipient wetness impregnation method. These catalysts were tested in liquid phase reactions and the Pd/HBEA catalyst showed the best catalytic performance, achieving an 80% yield of valeric biofuel after 2 h of the reaction. The fresh catalysts were characterized by DRIFT spectroscopy using pyridine, CD₃CN, and CO as probe molecules and by XRD to explain the differences in catalytic performance. The presence of strong Brønsted acid sites (BAS) was shown to be critical for reaching high ethyl valerate yields since the differences in catalytic behavior and the concentration of these acid sites parallel each other. Up to three types of Lewis acid sites (LAS) of different strengths were also identified. These LAS have also been shown to be active, although their intrinsic activities decrease as they are weaker. Reutilization tests of the Pd/HBEA catalyst were also carried out and mild deactivation was observed. The spent catalyst underwent a simple calcination treatment at 773 K and this was adequate for the recovery of the surface acidity, but the reducibility of the Pd species was affected. This prevented complete recovery of catalytic activity.

The synthesis of dimethyl adipate (DAP), a stable configuration of adipic acid, from biomass-derived cyclopentanone (CPO) and dimethyl carbonate (DMC) constitutes an attractive greener route than petroleum-based industrial processes. Solid basic catalysts such as MgO, Mg₅(CO₃)₄(OH)₂·4H₂O, KOCH₃ and Ca(OCH₃)₂ have been used achieving a DAP yield up to 30% at 533 K. In addition to the type of catalyst, other operating conditions such as the substrate, reaction time, temperature and CPO concentration have been studied. The methylation of DAP and CPO and the self-aldol condensation of CPO to form dimers and oligomers are reactions that occur in parallel with the production of DAP. It has been established that the main challenge is the self-aldol condensation of CPO. It has been identified that at short reaction times, to prevent methylation, and at dilute concentrations, to avoid CPO self-condensation, the DAP formation rate is much higher than these other competitive reactions. Finally, it should be noted that a DAP productivity up to 3.45 g·gcat⁻¹·h⁻¹ has been achieved under mild conditions.