Valorization of raspberry seed cake by flash and slow pyrolysis: Product yield and characterization of the liquid and solid fraction

• Raspberry seed cake has a pyrolytic behavior similar to lignocellulosic biomass.
• Flash pyrolysis at 450 °C shows highest liquid yield and best liquid properties.
• Pyrolysis liquid can be a source of levoglucosan or high-value phenolic compounds.
• The organic liquid fraction from slow pyrolysis has promising fuel properties.
• Solid residue from flash and slow pyrolysis has potential as solid energy carrier.

The valorization of raspberry seed cake by flash and slow pyrolysis is investigated in this study. During flash pyrolysis, temperature significantly affects the yield and properties of the products. The highest liquid yield (53.6 wt%) is found at 450 °C. This liquid has a water content (26.2 wt%), a HHV (18.6 MJ/kg) and a pH-value (3.2) that are comparable to those of pyrolysis liquids produced by flash pyrolysis of lignocellulosic biomass. In terms of added-value chemicals, levoglucosan and phenols are interesting compounds because of their high economic value. The solid residue has potential as solid energy carrier at industrial scale because of its high energy content (24.5 MJ/kg). Pyrolysis liquid from slow pyrolysis of raspberry seed cake is collected in three fractions as a function of pyrolysis temperature. Fraction 1 (220–320 °C) and fraction 2 (320–350 °C) are single-phased and have a high water content. In contrast, fraction 3 (350–450 °C) spontaneously separates in two fractions. The organic fraction (12.1 wt%), mainly composed of phenols, is promising as renewable fuel because of its relatively high calorific value (27.0 MJ/kg) and its relatively low water content (9.3 wt%). The aqueous fraction (10.2 wt%) has a high water content (67.4 wt%), but also contains a high amount of levoglucosan. The solid residue can be valorized as solid energy carrier because of its high calorific value (30.9 MJ/kg) or as precursor in the production of activated carbon.