(44e) Comparative Thermogravimetry/Mass Spectrometry Study of Woody Residuals and an Herbaceous Biomass Crop Using Pca Techniques

Keywords: slow pyrolysis, thermogravimetry/mass spectrometry, Principal components analysis, pre-treatments.

Introduction

Ministers and Government Representatives from 154 countries gathered in Bonn1 acknowledge that renewable energies combined with enhanced energy efficiency, can significantly contribute to sustainable development, providing access to energy, mitigating greenhouse gas emissions, reducing harmful air pollutants, thereby creating new economic opportunities, and enhancing energy security through cooperation and collaboration. The increased exploitation of biomass materials different from the species usually investigated requires a better description of both the dynamics and the influence of the heterogeneities on biomass thermal decomposition. With the sight of studying the influences of feedstock properties, special attention has been given to the effects of pretreatments on the pyrolytic behavior. The different available industrial applications for biomass thermoconversion (e.g. the production of charcoal, activated carbon and liquid fuels) require a clear understanding of the variations in the original composition and the effects of the pretreatments, since the yields and the composition, structure, and other properties of the products are highly influenced by the properties of the feedstock.

In this work, we present a chemometric analysis of the mass spectrometric evolution of the main pyrolysis products from different type of biomasses. These feedstocks (carpentry residuals and an herbaceous energy crop) have not attracted yet sufficient attention in the biomass studies. The specific aim is to monitor the differences in the thermal behavior from the identification of main pyrolysis products. The range of the evaluated samples involves water-washed and ethanol-extracted samples as well as samples submitted to both water-washing and ethanol extraction. The purpose when submitting samples to those pre-treatments is to study the influences of inorganic ions and extractive materials on the pyrolytic behaviour and reaction pathways. Principal components analysis (PCA) is used as the chemometric tool.

Experimental procedure

The wood chips (pine and beech) were taken from Barcelona's region carpentry residuals, while the herbaceous sample (artichoke thistle) came from a specialized crop in the Spanish province of Soria. The MS experiments were performed using a Perkin-Elmer TGS-2 thermobalance connected to a Hiden HAL quadrupole mass spectrometer, using argon purge gas. The sample mass was about 4 mg. The samples were heated from 20 °C to 900 °C at a heating rate of 20 °C min-1 in a platinum sample pan. The MS ion intensities were integrated within the temperature range of decomposition. The MS integrals of the most significant products (H2, H2O, CO, and CO2) have been applied as input data for the PCA calculation.

Brief results and discussion The PCA method is useful for the acquisition of quick information about the similarities in a group of samples2,3. From the principal components space, the herbaceous and woody samples are clearly separated, and this separation is more pronounced than the one resulting from the differences between the pretreatments. However, distinction can also be made between them: groups of samples are determined by the water-washing in such a way the extracted and untreated samples are closer than the rest, indicating the very lower effect of the extraction pre-treatment.

The results can be interpreted by the different chemical composition of the wood and thistle. The high lignin content of thistle results in the formation of a high amount of char and methane during thermal decomposition. However, wood evolves more organic products (aldehydes, acids, ketones, furan derivatives, etc.) due to its higher polysaccharide content. Also, considerable differences have been found with regard to the extractives and inorganic components between the samples. The two woody samples behave rather similarly. In this case differences in the thermal decomposition can be mainly attributed to the difference in the amount of extractives.

Acknowledgment

This work was supported by the Ministerio de Educación Cultura y Deporte of Spain and by the Hungarian National Research Fund (OTKA T37705 and T37704). Financial support received from the European Community (Contract RFC-CR-04006) is also thankfully acknowledged.

References

1. Political Declaration. International Conference for Renewable Energies, Renewables 2004. Bonn June 1-4, 2004.

2. Jackson, J. E. A User's Guide to Principal Components; Wiley Series in Probability and Statistics J. Wiley Sons: Hoboken, New Jersey, 2003.

3. Mészáros, E.; Jakab, E.; Várhegyi, G.; Szepesváry, P.; Marosvölgyi, B. Comparative Study of the Thermal Behavior of Wood and Bark of Young Shoots Obtained from an Energy Plantation. J. Anal. Appl. Pyrolysis 2004, 72, 317 - 328.