Investigation of biomass pyrolysis by thermogravimetric analysis and differential scanning calorimetry

Abstract

The influence of sample size on the pyrolysis of wheat straw and three types of cellulose has been investigated by simultaneous thermogravimetric analysis and differential scanning calorimetry. Samples between 2 and 20 mg were pyrolyzed to a maximum temperature of 600°C at a heating rate of 40°C min −1. It was found that sample size had a large effect on the pyrolysis of Avicel cellulose; the mass loss peak was shifted to higher temperatures at higher sample mass. However, the effect of sample mass on the pyrolysis of wheat straw was insignificant. In wheat straw samples washed in water to reduce the KCl content, the influence of sample size was between that of cellulose and straw, but closer to straw. A model for the TGA/DSC-system has been developed, which includes heat transfer by both convection and radiation to the two crucibles and the sample. Simulations with the model showed that the sample mass had a large influence on the pyrolysis at high heat of reaction and in agreement with data, the pyrolysis peak shifts to higher temperatures at higher sample mass. The recommendation found in the literature that samples should be no larger than 1 mg in TGA measurements must be limited to biomass samples with a high heat of reaction such as cellulose.