Supercritical Technologies for the Valorization of Wine Industry By-Products

This study aim at the valorization of wine industry by products; particularly on the extraction and characterization of grape seeds oil using supercritical CO2 (SC-CO2) and polyphenols from grape skins and defatted grape seeds using subcritical water (SW) and then, modeling of the kinetics of extractions and process economic analysis. The overall objective of the work is to develop recovery strategies for wine-making wastes in order to reduce their environmental impact and to valorize them in order to provide wine-makers with the possibility of selling by-products at a profitable price. To address the objectives, the work is divided into seven Chapters. In Chapter 1, some general overview and the fundamental of SC-CO2 and SW technologies along with emerging areas of applications are presented. Special emphasis is given to the work in the field of valorization of agro-industrial by-products. Then, the Chapter ends by stating the general and specific objectives of the thesis. The second Chapter is devoted to the characterization of grape seeds oil. To make the result more holistic, grape seeds from six grape cultivars were extracted using SC-CO2 in two subsequent harvesting years and the resulting oils were characterized. Comparative extractions were also performed by utilizing conventional solvent extraction using n-hexane and by mechanical press. The results testify the potentiality of grape seed oil as a source of unsaturated fatty acids and tocols. Moreover, they offers a clear picture of the similarities and differences among oils from different grape cultivars and obtained through different extraction techniques. The third Chapter is dedicated to compare the effectiveness of the models used to evaluate the kinetic of SC-CO2 extraction curves. Particularly, three models, the broken and intact cells (BIC), the shrinking core (SC), and the bridge (combined BIC-SC) models are critically analyzed. The objective of the Chapter is to objectively choose the best model that can be used in the subsequent Chapters. In order to model the kinetics of SC-CO2 extraction, one of the very important parameter is the solute solubility. But solubility data (especially of grape seed oil) is very scares in the literature. The bulk majority of the scientific works estimate the value of solubility of solute in SC-CO2 from theoretical models. So, the fourth Chapter is devoted to experimental determination of solubility of grape seed oil in SC-CO2 over a range of pressure and temperature of practical importance and the data were modeled by different models to compare their effectiveness. The fifth Chapter is aimed to study the effect of the main process variables affecting the SC-CO2 extraction of oil from grape seeds, both experimentally and through modeling. The dependency of the extraction kinetics on the variables more tested in the literature (pressure, temperature, particle size and solvent flow rate) was confirmed, and original trends were obtained for the less investigated variables, such as the bed porosity (ε), the extractor diameter to length ratio (D/L), the extractor free volume and the type of cultivars. In the sixth Chapter the attention is moved to the valorization of grape skins and defatted grape seeds by using SW. The results show that, both skins and defatted seeds contain significant concentration of polyphenols and SW is a potential green solvent for extracting valuable polyphenols from wine-making by-products. The extraction kinetics was also simulated by a simple model available in the literature. In the seventh and last Chapter, a preliminary economic feasibility study was investigated for the establishment of SC-CO2 extraction plant for the extraction of grape seeds oil. The result shows that, a SC-CO2 extraction plant is technically viable and economically feasible for the extraction of grape seed oil with estimated rate of return on investment at 8.5% and payback period of 5 year at current minimum retail selling price of grape seed oil in the market. The project has an attractive socio-economic and environmental benefit and generates substantial revenue for the local government in the form of tax and will allow wine-makers to sell wet grape marc at a price of up to US$ 10/ton.