Hydrothermal carbonization and torrefaction of grape pomace: a comparative evaluation

Area of Science:

• Biomass Conversion
• Renewable Energy Technologies
• Waste Valorization

Background:

• Grape pomace is a high-moisture winery waste with potential for energy recovery.
• Conventional drying methods for biomass are energy-intensive.
• Sustainable valorization of lignocellulosic waste is crucial for a circular economy.

Purpose of the Study:

• To compare hydrothermal carbonization (HTC) and torrefaction for converting grape pomace into solid biofuel.
• To characterize the fuel properties, morphology, structure, and combustion behavior of the produced chars.
• To evaluate the potential of the HTC aqueous phase for valuable compounds.

Main Methods:

• Grape pomace was subjected to hydrothermal carbonization (175–275°C) and torrefaction (250–300°C).
• Solid products (chars) were analyzed for mass yield and energy densification.
• Fuel properties, morphological/structural characteristics, and combustion behavior were evaluated.
• The aqueous phase from HTC was assessed for antioxidant activity.

Main Results:

• Mass yields ranged from 47% to 78%, with energy densification ratios between 1.15 and 1.42.
• Hydrothermal carbonization produced chars with higher energy density and combustion reactivity compared to torrefaction.
• Torrefied chars exhibited greater aromaticity than HTC chars.
• The aqueous phase from hydrothermal carbonization demonstrated significant antioxidant activity.

Conclusions:

• Hydrothermal carbonization is a promising process for valorizing high-moisture winery waste like grape pomace into energy-rich chars.
• HTC offers advantages in terms of energy density, combustion reactivity, and the production of valuable co-products.
• Both HTC and torrefaction represent viable pathways for converting grape pomace into solid biofuels, with HTC showing unique benefits.