No abstract

This work presents a proof of concept for a green cyclodextrin derivatisation method that uses low-boiling epoxide reagents in a high-energy ball mill (HEBM). The simplified preparation and purification of low substitution-degree common (2-hydroxy)propylated β- and γ-cyclodextrins (β/γ-CDs) has been realised. The intelligent use of propylene oxide has also facilitated the more effective synthesis of highly substituted γ-CD. Epichlorohydrin-crosslinked CD-polymers (CDPs) have also been effectively prepared in the ball mill. The unoptimised preparations of soluble and insoluble CDPs displayed very small particle size distributions, while the prepared polymers currently have different complexation properties to those of their classically prepared analogues.

In the search for a more sustainable future, the biorefinery approach can help by replacing fossil feedstocks with renewable sources. When biorefineries meet circular economy, the production of new platform chemicals from residual lignocellulosic biomasses becomes the joint goal. In this frame, the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) has gained increasing interest, with the aim of producing intermediates for the chemical industry. Enabling technologies, particularly microwaves, have proven to be an efficient tool for process intensification, as they can reduce the reaction time and the formation of byproducts. In this work, MW-assisted processes with heterogeneous Ru-based catalysts were exploited for the reduction of LA both with H 2 and 2-PrOH as reductants. Different metal loadings and supports were considered, such as a commercial active carbon (Ru/AC) and titania (Ru/TiO 2 ). Among the different hydrogen sources, molecular hydrogen led to milder reaction conditions, enabling the complete flash conversion of LA in only 2 min without any solvent. In terms of catalytic activity, AC showed slightly better performances as support. In addition, flow MW-assisted processes were tested using a multiphase reactor, reaching complete conversion in only 8 min in an open loop system for both the tested catalysts. Performance enhancement and material reuse support the suitability of flow approach, paving the way for a sustainable and scalable process.

: Cyclodextrin (CD) polymers are covalently linked hollow structures that are a network of less flexible macrocycles. They can be divided into two main groups: a) soluble (CDPS); and b) insoluble (CDPIS) polymers. These two types are generally prepared in a similar reaction, and the CD/reagent ratio determines the final properties of the reaction product. Changing this ratio of the generally bifunctionalized crosslinking agent and reaction conditions can lead to CDPS or CDPIS. The classical synthetic way in solution often leads to partial reagent(s) degradation, which frequently results in poorly reproducible products. At the same CD/reagent ratio, the reaction in solution yielded soluble CD polymers, whereas the reaction under mechanochemical conditions produced insoluble CD polymers. Usually, further derivatization of CDPIS or polymerization of derivatized CDs can be difficult or even impossible. The reactivity of hydroxyl groups in methylated CDs is limited so that reactions generally require high-boiling solvents and/or a large excess of reagent. This paper presents an economical, reproducible, and well-scalable synthetic method for producing some insoluble CD polymers. The physicochemical and adsorption properties of CDPIS prepared in a planetary ball mill are also compared.

Over the last decade, enabling technologies and sustainable catalysis have become appealing options for biodiesel preparation because of their impressive process intensification and energy savings. The present review will compare the most innovative protocols that have been developed and improved to use non-conventional energy sources and catalysts that are performed, in particular, using continuous-flow methods. Although this account cannot be comprehensive, it will, however, provide a good overview of the reaction-rate improvements and catalyst activation that is provided by microwaves, ultrasound, hydrodynamic cavitation, flow reactors and even hybrid techniques. Advantages and limitations are discussed together with industrial scalability.