Abstract
Despite the huge amounts of grape marc generated in Tunisia from the wine industry, very few efforts have been exerted to manage this harmful waste. Therefore, thermal processes may contribute to an environmental friendly management and also help winemakers to create new economic profitable circuits in an increasingly competitive context. Among the various thermochemical conversion process, pyrolysis is suitable for the recovery of food processing residues, due to their high minerals content and ability to create high added values of the derived products (biochar, bio-oil and syngas). In this context, the aim of this work is to optimize the pyrolysis process in order to benefit from the grape marc potential for achieving highest product yields. Therefore, physico-chemical and energy characteristics of grape marc issued from a Tunisian wine cooperative were determined according to international standards. Thermogravimetric analyzes were also performed to predict the grape marc behavior during degradation under an inert atmosphere. The profile of the mass loss rate shows two decomposition peaks corresponding to the cellulose and lignin decomposition. These peaks are shifted to lower temperatures comparing to several lignocellulosic biomass feedstocks due to high content of minerals that may play a catalytic role in the thermal degradation process. The biochar yield was about 40%, which was never met in literature for agricultural biomass in slow pyrolysis. Such behavior may be attributed to high lignin content in grape marc. Activation energies were calculated using integral Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose methods and differential Friedman method. The obtained values were 226.8, 224.2 and 229.5 kJ/mol, respectively. Such kinetics data are crucial in the design of the pyrolyzer for Tunisian grape marc recovery.
Highlights
Grape is one of the most important fruit crops in the world with over 74 million tons produced annually [1]
Activation energies decrease, which may be explained by an overlapping of cellulose and lignin continuing degradation as well as by char rearrangement through secondary and more complex reactions, which was found in literature [52,53,54,55]. In these times, where the circular economy is at the service of the economic actors, the slow pyrolysis of grape marc can be an advantage in the wine industry and distilleries on more than one level, especially in the Tunisian context
As better environmental management of grape marc is increasingly necessary, this study is required to achieve a better understanding of the economics of grape marc pyrolysis for bio-fuel production and for resolving issues related to the capabilities of this technology in practical applications
Summary
Grape is one of the most important fruit crops in the world with over 74 million tons produced annually [1]. Pressing grapes give juice, which is mostly for fermentation, and marc, which is called pomace (solid product) [2], containing skins, seeds and stalks [3]. The pressing grape method depends strongly on the type of wine (white or red), Toscano et al [3] described a general process giving the following proportions of grape products: 73% of juice and 27% of grape marc. Grape marc may be processed further in distilleries in order to extract alcohol and the generated waste is called the exhausted grape marc residues. Wine cave (fresh grape marc) and alcohol distilleries (exhausted grape marc) produce large amounts of wastes, which are estimated at 7 million tons worldwide per year [4]
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