The Influence of Torrefaction Temperature on Hydrophobic Properties of Waste Biomass from Food Processing

Abstract

The annual potential of waste biomass production from food processing in Europe is 16.9 million tonnes. Unfortunately, most of these organic wastes are utilized without the energy gain, mainly due to the high moisture content and the ability to the fast rotting and decomposition. One of the options to increase its value in terms of energy applications is to valorize its properties. Torrefaction process is one of the pre-treatment technology of raw biomass that increases the quality of the fuel, especially in the context of resistance to moisture absorption. However, little is known about the influence of torrefaction temperature on the degree of valorization of some specific waste biomass. The aim of this paper was to analyze the influence of the temperature of the torrefaction on the hydrophobic properties of waste biomass, such as black currant pomace, apple pomace, orange peels, walnut shells, and pumpkin seeds. The torrefaction process was carried out at temperatures of 200 °C, 220 °C, 240 °C, 260 °C, 280 °C, and 300 °C. The hydrophobic properties were analyzed using the water drop penetration time (WDPT) test. The torrefied waste biomass was compared with the raw material dried at 105 °C. The obtained results revealed that subjecting the biomass to the torrefaction process improved its hydrophobic properties. Biomass samples changed their hydrophobic properties from hydrophilic to extremely hydrophobic depending on the temperature of the process. Apple pomace was the most hydrophilic sample; its water drop penetration was under 60 s. Black currant and apple pomaces reached extremely hydrophobic properties at a temperature of 300 °C, only. In the case of orange peels, walnut shells, and pumpkin seeds, already at the temperature of 220 °C, the samples were characterized by severely hydrophobic properties with a penetration time over 1000 s. At the temperature of 260 °C, orange peels, walnut shells, and pumpkin seeds reached extremely hydrophobic properties. Furthermore, in most cases, the increase of torrefaction temperature improved the resistance to moisture absorption, which is probably related to the removal of hydroxyl groups and structural changes occurring during this thermal process.