Use of Thermogravimetry/Mass Spectrometry Analysis to Explain the Origin of Volatiles Produced during Biomass Pyrolysis

Pyrolysis of alternative biomasses, which contributes to the recovery of arid soils and does not compete with alimentary biomass, could increase use of biomass as feedstock in energy production facilities. In this sense, in order to optimize this thermal process and gain better insight the origin and evolution of the main produced volatiles, nonisothermal thermogravimetry coupled to mass spectrometry (TG/MS) has been applied for samples of two biomasses [Leucaena Leucocephala (Leucaena) and Chamaecytisus Palmensis (Tagasaste)], which find application as energy crops and contribute to soil restoration. In a first stage, autocatalytic kinetics has been used in order to obtain the mass loss rate profiles (DTG) of each biomass pseudocomponent (hemicellulose, cellulose, lignin, and extractives) during pyrolysis. In a second stage, the experimental mass spectrometry signals of the main volatiles (CO, CO2, and H2O) have been simulated using a linear combination of the previously calculated DTG profiles. The accurate fitting obtained, explains the origin of these volatiles from a simple volatization process, mainly from lignin. In a third stage, in order to simulate the hydrogen signal, it has been necessary to consider the char produced during the volatization process. According to the model, the charring process explains close to 77 wt % of the total hydrogen obtained during pyrolysis. Considering the specific char production of each biomass pseudocomponent, it is possible to measure their individual contributions to hydrogen production: hemicellulose, 27.5; cellulose, 9.7; and lignin, 60.9 wt %, for Leucaena. Taking into account the composition of the samples, the relation between the specific hydrogen productions of the single pseudocomponents (hemicellulose:cellulose:lignin) can be calculated: 3.4:1.0:7.6.