Bio-oil produced via pyrolysis

Pyrolysis is the chemical and physical separation of solid biomass into different molecules at high temperatures and in the absence of oxygen. Hemicelluloses, celluloses, and lignin in the biomass degrade at different temperatures, rates and by different pathways. Lignin is more termically stable and decomposes over a wider temperature range compared to cellulose and hemicellulose (Bridgewater et al. 1999). After decomposition of the chemical bonds the molecules recombine to new compounds. A part of the biomass is reduced to carbon, while other parts are oxidized and hydrolyzed to carbohydrates, alcohols, phenols, aldehydes, ketones, or carboxylic acids (Uddin 2018). The received products have different characteristics than the raw material. Pyrolysis produces three different fractions after cooling down the pyrolysis vapours:

•     Liquid phase (pyrolysis oil)
•     Gasous phase (e.g hydrogen, methane, carbon monoxide, nitrogen)
•     Solid phase (char)

Pyrolysis takes place in a temperature range from 200 to 600°C and in two steps. First, below 400°C organic molecules are cracked into smaller fractions and primary vapors and char are occuring. Above 400°C secondary reactions form aromatics from char particles. The temperature and the residence time of the biomass in the reactor influences the range (pyrolysis oil, syngas or char), yield and distribution of the received products (see figure below).