Autocatalytic kinetic model for thermogravimetric analysis and composition estimation of biomass and polymeric fractions

Abstract

A comprehensive kinetic model of slow pyrolysis of biomass during a Thermogravimetric analysis (TGA) has been developed, including the simulation of variable heating rates, composition estimation and structural analysis of biomass.Biomass was assumed as a matrix of three solid global components (hemicellulose, cellulose and lignin) in which water and oil can be also present.Kinetics were based on an auto-catalytic model because it can simulate the degradation in cellulosic materials, as the cleavage of the biopolymers produce oligomers that accelerate the further depolymerisation. The reaction pathway followed the Waterloo's mechanism, which stablishes that all solid compounds decompose into volatiles and charcoal. This mechanism was completed by the vaporization of water and oil, and assuming that the formed charcoal can break into volatiles by a slow reaction. The set was solved by the 8 th Runge-Kutta's method and validated by the Simplex Nelder-Mead and Broyden-Fletcher-Goldfarb-Shanno's methods. The development of this model has a high interest because it can help to understand how the conversion from biomass to biochemicals takes place.To assess what parameters can affect the thermal degradation of biomass pure polymeric samples of hemicellulose, cellulose and lignin and complex samples (seeds and woody biomass) were studied and fitted. Two types of operations were consideredtoo. An isothermal degradation from 150ºC up to 350ºC with increments of 50ºC, and a non-isothermal decomposition with heating rate of 5ºC/min, 10ºC/min and 20ºC/min up to temperatures around 800ºC, depending on the studied sample. Average absolute deviations lower than 7% were obtained. It was deduced that there are some interactions between the three main biomass compounds. These interactions were observed by the variations in the kinetic parameters between complex and pure 2 samples, also they were perceived between the isothermal and no-isothermal way. On the other hand, an effect of the biomass structure has been reported by the differences between the kinetics of the seeds and of the woody samples. It is remarkable that the developed model could reproduce the cellulose decomposition with a variable heating rate using a unique set of kinetic parameters. This was possible by a no-Arrhenius' dependence with temperature. In the same way, it was used to predict the initial composition of the studied biomass with deviations lower than 7% for lignin and cellulose.

Drop-in biofuels from the co-pyrolysis of grape seeds and polystyrene

“…The results obtained for weight loss and rate of weight loss for both samples of GSs and PS are given in Figure 2. As it is a type of lignocellulosic biomass, GSs form a complex solid mainly composed of hemicellulose and cellulose, which consist of monomeric sugars, and lignin, a complex, cross-linked, threedimensional aromatic polymer made up of phenyl-propane units [30,31]. Also, minor fractions of extractives, such as fatty acids, simple sugars, waxes and sterols and inorganic mineral matter (inorganic compounds like alkali metals [32], will be present in these samples [33] and can affect the degradation profile [34].…”

Development of a microwave pretreatment for the extraction of active compounds from natural by products

“…Concerning char production and its volatilization, they were not modified by the pretreatment, probably because of the mild conditions used. These results have been compared with the ones reported by Cabeza et al (2015) in which grape seeds were hydrolysed at 250-340ºC, and with a work dealing with Brazilian gingseng treated with pressurized water at 60ºC (Cabeza et al, 2017). Despite the fact that the raw materials were not utterly equivalent, and neither the pretreatments, the conclusions were similar to the ones obtained in this work.…”

“…The model used to fit the experimental data was previously developed by Cabeza et al (2015). This model followed an autocatalytic kinetics and it was demonstrated to be a suitable option to reproduce the thermal degradation of biomass.…”

“…200ºC. This enhancement at mild pretreatment temperatures could be due to either the cellulose weakest part extraction, the likeable structural changes (Cabeza et al, 2017), or the loose of hemicellulose (which has been demonstrated to behave as a shield for cellulose thermal degradation (Cabeza et al, 2015)). At higher temperatures, the kinetics for the volatilization would be worsened since cellulose extraction would be significant at that condition.…”

Two-phase modelling and simulation of the hydrothermal fractionation of holm oak in a packed bed reactor with hot pressurized water

“…Regarding kinetics, a new formulation was incorporated too. An autocatalytic 118 model is considered because it was assessed, in a previous study about biomass 119 thermal degradation during a thermogravimetric analysis (Cabeza et al, 2015), that it 120 can reproduce the strong mass changes in biomass at certain times or temperatures. 121…”