TG, TG-MS, AND FTIR CHARACTERIZATION OF HIGH-YIELD BIOMASS CHARCOALS

The pyrolysis and combustion characteristics of various high-yield cha rcoals manufactured in a process development unit were studied by ther mogravimetry (TG), thermogravimetry-mass spectrometry (TG-MS), and Fou rier transform infrared spectrometry (FTIR), Charcoals resulting from two runs with a macadamia nutshell feedstock and one run with a eucaly ptus wood feedstock are compared. The peculiarities of devolatilizatio n, oxygen gasification (temperature-programmed combustion), and the fo rmation of nitrogen oxides are discussed. Small sample sizes (0.2-4 mg ) were employed to minimize the effects of heat and mass transfer limi tations; nevertheless the results offered a reliable characterization of kilograms of charcoal. Samples produced in different runs or taken from different parts of the reactor behaved similarly with only minor differences that we attribute to reactor inhomogeneities and variation s in feedstock composition. In the presence of oxygen, two partial pro cesses were detected. The lower temperature weight loss may be due to devolatilization of the char and oxidation of the volatile matter that results in a carbonized residue. The residue burns off around 450-500 degrees C. The rate of both processes evidenced strong dependence on oxygen concentration, indicating an unexpected influence of oxidation on the low-temperature devolatilization processes. The intensity of th e mass-spectrometric ion signal for NO+, which represents the formatio n of nitrogen oxides, did not follow the overall mass loss rate curves (DTG). The peak temperatures of the NO+ and DTG curves differed by 3- 9 degrees C. These differences were influenced by the feedstock compos ition but did not depend on such operating conditions as the heating r ate and oxygen concentration. Elevated pressure thermogravimetry revea led that a very high partial pressure of CO2 in the carrier gas (577 k Pa) has only negligible influence on the rate of the temperature-progr ammed combustion.