Hydrothermal Conversion Of Biomass. II. Conversion Of Wood, Pyrolysis Oil, And Glucose In Hot Compressed Water

In part I of this work, hydrothermal conversion (HTC) of glucose has been studied. In this part 11 of the study, the investigation is extended to two other feedstocks: wood and pyrolysis oil. The effects of residence time (0-60 min) and feedstock concentration (0-45 wt %) oil product yields are studied at 350 degrees C. For all three investigated feedstocks: (i) oil, char, and gas are formed with two distinct rates (fast rates in the first 10 min, followed by slow rates after this time), (ii) deoxygenation proceeds via both dehydration and decarboxylation. Dehydration is an initial reaction (first 5 min) and leads to undesired lowering of the H/C ratio of the oil product. Two types of char have clearly been identified for HTC of wood: primary char (nonliquefied remainder of biomass) and secondary char (polymerization product). Only a small amount of primary char is formed, while at longer residence times, typically practiced in pilot and demonstration plants, the majority of char is produced in polymerization reactions in the liquid phase (reaction order > 1). Several catalysts have been tested for their ability to increase decarboxylation yield and reduce char formation. The Ru/TiO2 catalyst is able to convert WSIS (char) to gas, while leaving the oil product practically unaltered with respect to composition and yield. Visual observations have revealed that a single liquid phase appears to exist at the HTC reaction conditions and that phase splitting into an oil and a water phase occurs in the temperature range of 180-220 degrees C. The engineering reaction path model, proposed for glucose in part I of this work, is extended for use with solid biomass and pyrolysis oil.