Enhanced extraction of natural substances using microwave energy
- Autores: Katalin Sólyom
- Directores de la Tesis: Rafael B. Mato Chain (dir. tes.), María José Cocero Alonso (codir. tes.)
- Lectura: En la Universidad de Valladolid ( España ) en 2013
- Idioma: español
- Tribunal Calificador de la Tesis: Juan Monzó Cabrera (presid.), Alexander Navarrete Muñoz (secret.), Georgios Stefanidis (voc.), Volker Gaukel (voc.), Juan García Serna (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: UVADOC
- Resumen
Motivation: Nowadays, in numerous industrial extraction processes, technologies that can save the time, space, energy and solvent are welcome in order to achieve production intensification. This is of particular importance in those cases where complex natural raw materials are involved, and the biological cell wall disruption step is blamed for the slow kinetics and low throughput in the process.
Among several mechanical, chemical, physical or physicochemical treatments of natural raw materials, the possibility of using microwaves has emerged. Due to the electromagnetic irradiation of the material, rapid heating up and evaporation of intracellular water can be achieved, and the resulting pressure gradient may lead to cell wall damage. Thus, the intracellular compounds of interest become more accessible after an efficient pre-treatment, and faster kinetics can be achieved in the subsequent conventional process.
Objectives: In this Doctoral Thesis, three different raw materials and processes were studied in order to explore the effects of microwave pre-treatment on extraction process kinetics.
Firstly, microorganisms were used, such as wastewater sludge, in order to intensify biogas production by liberating any intracellular material, which thus became accessible for anaerobic bacteria in the digestion process. Due to the large cell variety present in wastewater sludge, the specific study of the cell structure becomes difficult to elucidate, although the overall process kinetics can be upgraded, just as in a conventional thermal pre-treatment.
Secondly, unicellular microalgae were chosen as better candidates for this purpose. Also, lipid extraction for biodiesel production, and high added value algal pigment extraction are at the centre of attention in the field of continuously developing sustainable process engineering. The study on different microalgae and extraction techniques presented here showed that microwave pre-treatments have the potential to improve extraction kinetics, and also higher extraction yields may be obtained.
Finally, the abundant viticulture in the region of Castile and Leon suggested the study of wine making by-products (grape marc) in order to obtain valuable compounds (polyphenols) with antioxidant capacity, via solid-liquid extraction. Compared to the two former raw materials, grape marc represents higher-level cell organization, where different cell wall types may have diverse responses to pre-treatments. Microwave pre-treatments were studied both in the presence and in absence of an extracting solvent. Only solvent assisted microwave irradiation led to the successful intensification of kinetics in the performed comparative study. As a competing novel technique, the use of ultrasounds was also assessed through these studies, and similar results were found when compared with microwave assisted extractions. Both pre-treatment techniques were able to overcome the long extraction times and large solvent stocks required in the industrial extraction process. The possible thermal degradation of these valuable compounds was considered.
Besides the study of these processes and the analysis of the effect of microwave irradiation on different raw materials, special importance has been devoted to the determination of the energy absorbed by the materials and solvents during the processes. The fraction of electromagnetic microwave energy absorbed by the sample is subsequently dissipated as heat. This heat can be described using an energy balance, which takes into account the sensible heat, by the temperature increment in the system, the latent heat, by solvent evaporation, and finally the heat loss to the environment. Unfortunately, results from published literature on the aforementioned topics are hard to compare with each other due to the lack of this data. Information about absorbed energy would facilitate the obtaining of comparable results in different experimental conditions, which are indispensable for scaling up.
Conclusions: Based on the results discussed in this dissertation, further research can be performed in order to develop an industrial scale microwave assisted extraction process of grape marc polyphenols. Furthermore, the deeper study of the microwave effect on different cell structures and the role of the solvent in the microwave assisted extraction seem to be interesting issues to follow in the future.
