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.

Hydrothermal carbonization (in acronym, HTC) is a thermochemical conversion process through which it is possible to directly transform wet organic substrates into a carbonaceous material, referred as hydrochar. Hydrochar has chemical and physical characteristics that make it similar to fossil peats and lignite. Depending on the process conditions, mostly temperature and residence time, this material can be enriched in its carbon content, modifying its structure and providing it interesting characteristics that make it possible to be used for several applications, such as for energy production, as a soil conditioner and improver, for carbon dioxide sorption and sequestration, and some others reported in literature. HTC is a different process, if compared to other common thermochemical processes, such as pyrolysis, torrefaction, gasification, etc., because it works in wet conditions (humidity content higher than 60%). As a matter of fact, biomass is transformed into hydrochar because of the properties of hot pressurized water, that acts both as a reactant and as a catalyst. The HTC process has been studied from many years, although at present not all the chemical reactions that occur during the process are completely known. Moreover, the application of this quite new process to different substrates can bring to different results. Even though HTC can be applied to any kind of organic material (of both animal and vegetable derivation), the possible uses of hydrochar can strongly be influenced by the characteristics of the feedstock. This, for example, can be due to legislative constraints. In Chapter 1, an overview of the existing literature is presented. To get insights on this process, a small bench scale batch reactor has been designed and built at the Department of Civil, Environmental and Mechanical engineering of the University of Trento, Italy. This reactor has been tested, prior to be used with real substrates. In Chapter 2 the reactor and the preliminary tests done are described. In this work, the HTC process applied to three different substrates have been studied: grape marc, the EWC 19.05.03 residue and the EWC 19.12.12 residue. In Chapter 3 the three raw substrates are described. Grape marc is produced by the winery industries or by distilleries. This feedstock is composed by woody seeds and holocellulosic skins and it presents an average humidity content of about 60%. At present, it is used for the production of animal food or it is landfilled. In this case, the application of HTC can be an interesting alternative to these end uses because, through this process, grape marc can be recovered, for example, for energy production. The hydrochar produced from this feedstock could be even used as a soil conditioner. In Chapter 4 several analyses on the hydrochar, on the process water and on the gaseous phase obtained during the carbonization tests are presented. The EWC 19.05.03 residue is a by-product of the composting treatment applied to the organic fraction of municipal solid waste (MSW). In collaboration with Contarina S.p.A., a company that collects and treats MSW in the province of Treviso, in the North-East of Italy, this by-product was carbonized and tested both as a soil conditioner and for energy production. Results of the analyses on the solid, liquid and gaseous phases produced by the HTC process are reported in Chapter 5. The EWC 19.12.12 residue is a by-product of the refuse derived fuel (RDF) production, from the residual fraction of the MSW. This substrate was provided by Contarina S.p.A. and preliminary tests on the exploitability of the hydrochar for energy production are reported in Chapter 6, together with analyses on both the liquid and gaseous phases. A rigorous energy balance has been proposed in Chapter 8, based on the experimental data obtained for grape seeds. In this chapter, all the hypotheses and the assumptions taken to evaluate the enthalpy of the HTC reaction at different process conditions (namely, three different temperatures and three residence times) are described. In Chapter 8 a kinetic model is proposed, based on a two-step reaction mechanism. The activation energy and pre-exponential factor of the various degradation reactions were determined by means of least square optimization versus the experimental data of grape marc. A thermo fluid model is even proposed in this chapter. The model integrates mass, momentum and heat equations within the reactor domain by means of the finite volumes method (f.v.m.) approach. Convective and radiative exchange between the reactor and the fluid within the reactor have been implemented in the f.v.m. model. Under two strong assumptions (mono-component and mono-phase fluid, which fulfils the reactor), it was possible to estimate the behaviour of an equivalent fluid (eq_fluid), in terms of thermal properties of the fluid (thermal capacity, thermal conductivity and thermal diffusivity). Moreover, a simplified dynamic analytic model is also presented – based on lumped capacitance method – in order to simulate the thermal behaviour of the system, using the actual temperature profile imposed by the reactor external heater. A resistance-capacitance network was used to describe the system. Finally, the Henry’s law has been applied to assess the amount of gas really produced during the HTC process. In Chapter 9, the main conclusions of this work are reported.