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

Abstract

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, CO 2 , and H 2 O) 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.

Syngas Production from Pyrolysis of Nine Composts Obtained from Nonhybrid and Hybrid Perennial Grasses

“…Composting reduces the content of two of the major biomass components, namely, cellulose and hemicellulose, while increasing the content of lignin [ 10 , 23 , 24 ]. These changes are of particular importance, since lignin is the component responsible for the highest H 2 and CH 4 formation, hemicellulose is responsible for the highest CO 2 emission, and cellulose is responsible for the highest CO release [ 28 – 31 ]. Yang et al [ 29 ] examined pyrolysis characteristics of lignin, cellulose, and hemicellulose and concluded that the main source of H 2 release was lignin.…”

Effect of composting on the production of syngas during pyrolysis of perennial grasses

“…The release of H 2 can be primarily attributed at lower temperatures to cracking of CAH bonds of lignin, and at higher temperatures to pyrolytic reactions of lignin due to its higher content of aromatic rings (i.e. cracking and deformation of C@C and CAH bonds) and as previously mentioned to charring reactions [10,12]. As pointed out by Barneto et al [13,15] lignin increases char production seven-and tenfold compared to hemicellulose and cellulose, and composting enhances this effect even greater (by another 19.5%).…”

“…hemicellulose [6,8]. Lignin is responsible for the highest H 2 and methane (CH 4 ) formation, cellulose for the highest carbon monoxide (CO) release, and hemicellulose for the highest carbon dioxide (CO 2 ) emission [9][10][11][12]. As pointed out by Yang et al [10] lignin releases four times more H 2 than cellulose and three times more than hemicellulose.…”

Analytical Techniques as a Tool to Understand the Reaction Mechanism

“…Numerous kinetic calculations can be found in the literature for the thermogravimetric experiments of biomass samples with very diverse results [28][29][30][31][32][33][34]. The kinetic models generally assume that the isothermal gas or liquid phase models can be applied for the dynamic experiments.…”