Procesos integrados de biotransformación y separación de interés industrial en líquidos iónicos y disolventes eutécticos profundos

Abstract

Sustainability of the processes is one of the most important challenges that industrial development has to face and it is included in the twelve Principles of Green Chemistry. The application of these principles is essential for the construction of a cleaner and more sustainable industry, with the least risk and environmental impact. Thus, the main aim of this PhD memory has been to develop integral protocols for the synthesis/separation of products with high value in the industry. Specifically, the biocatalytic synthesis of many compounds of interest in the cosmetic, food and pharmaceutical industry (panthenyl monoacyl esters and flavour esters) and biodiesel from renewable sources has been developed. The methodology used to achieve this aim is genuinely original, because it combines the high activity and selectivity of enzymes with the excellences of the non-aqueous reaction media employed: ionic liquids (ILs) and deep eutectic solvents (DESs). The main conclusions obtained with the experimental activities carried out are: 1) Two methodologies for producing panthenyl monoacyl esters (pro-vitamin B5) have been developed. The first one was based on the combination of a lipase with different ILs to carry out the selective synthesis of these compounds by two approaches: direct esterification of fatty acids with panthenol and through transesterification, using different acyl donors. High product yields and selectivities in the panthenyl monoacyl ester synthesis were obtained when IL based on the combination between imidazolium cation alkyl derivatives ([Xmim]+) with [BF4]- and [NTf2]- anions as reaction media were used. However, the ability of panthenol to form eutectic mixtures with fatty acids it was also demonstrated. This way, a single-phase liquid system was obtained for the first time from the mixture of the two solid substrates (fatty acid and panthenol) after melting at temperatures close to 60 °C. Additionally, the suitability of these new liquid reaction media, which were exclusively composed of the reaction substrates themselves, was demonstrated in the biocatalytic synthesis of panthenyl monoacyl esters, since high yields (>80%) and selectivities (>93%) were obtained and the enzyme was active and stable during seven operational cycles of reuse. 2) A methodology for the biocatalytic síntesis/separation of sixteen flavour esters in sponge-like ionic liquids (SLILs) has been developed. For this purpose, immobilized lipases and different SLILs were evaluated for the esterification of carboxylic acid with aliphatic and/or aromatic alcohols. Besides, a separation protocol based on the centrifugation after cooling the solid SLIL/flavour ester mixture through nylon membranes was successfully designed, obtaining high extraction yields (>95%) and recovering the biocatalyst/SLIL system, which could be reused for six consecutive operational cycles. 3) An integral protocol for the direct extraction and biocatalytic transformation of microalgae oil into biodiesel without prior isolation has been developed, including both the biodiesel final separation and the biocatalyst/ILs system recovery. For this purpose, different binary mixtures composed of SLILs with [Bmim][Cl] were evaluated for the extraction of microalgae oils from Chlorella vulgaris or Chlorella protothecoides microalgae and the in situ biodiesel biosynthesis. The fast and efficient biodiesel synthesis was obtained when a [C16tma][NTf2]:[Bmim][Cl] (95:5 v/v) mixture was employed. In addition, the algae biodiesel was separated from the IL/biocatalyst system through an easy cooling/centrifugation protocol at controlled temperatures. This PhD memory proposes original, efficient and simple protocols, since they integrate highly selective biocatalytic transformation of subtracts obtained from renewable sources and the separation of products without using any organic solvent. These contributions constitute an important guarantee towards the construction of a more sustainable chemical industry, because they require low energy consumption and avoid the generation of by-products, maximizing the atom economy of the processes. Finally, and for all the proposed strategies developed, the reaction/separation systems based on the combination of the biocatalyst/IL, were easily recovered and reused during different operational cycles.