Search

Cellulose is one of the major components of biomass. The study on its pyrolysis process will be beneficial to the in-depth understanding of biomass pyrolysis mechanism. In this work, in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFT) combined with two-dimensional perturbation correlation infrared spectroscopy (2D-PCIS) was first used to characterize the evolution process of the functional groups in cellulose during pyrolysis. The results showed that the degradation of carbon skeleton was prior to the dehydration of free hydroxyls after the destruction of hydrogen bond networks during pyrolysis. The thermal stability of C O in cellulose followed by the order of glycosidic bond

The in-depth study of the cleavage behaviors of linkages in biomass is important for the better understanding of biomass pyrolysis mechanism. This study aimed to clarify the pyrolysis mechanism of the typical ether linkages in biomass including β-1,4-glycosidic bond, α-O-4 bond and methoxyl using cellobiose, benzylphenyl ether and guaiacol as the model compounds. Combining the detection of the key intermediates, especially radicals by SVUV-PIMS and the evaluation of the reaction pathways by density functional theory (DFT) quantum chemical calculations, it was found that the concerted cleavage of β-1,4-glycosidic bond was more kinetically favorable than homolytic cleavage and heterolytic cleavage, and the ring opening of cellobiose via the breakage of C1′-O was likely to occur before the cleavage of glycosidic bond. The α-O-4 bond in benzylphenyl ether was mainly cleaved by Cα-O homolysis, and it was easy for the formed radicals to recombine with each other to yield phenolic dimers. In the initial evolution process of methoxyl in guaiacol, homolytic demethylation was the most important unimolecular reaction, while demethoxylation and radical-induced rearrangement reactions were difficult to occur due to their high energy barriers. In the presence of the formed methyl radicals from homolytic demethylation reaction, these two reactions would occur since their energy barriers were significantly reduced at this condition. [ABSTRACT FROM AUTHOR]

This study proposed a sequential and coupling method to determine the comprehensive kinetic models for pyrolysis of cellulose, hemicellulose and lignin. Isoconversional method was employed to find the correlation between activation energy and conversion rate. Cellulose pyrolysis could be interpreted by one-step global reaction model, while pyrolysis of hemicellulose and lignin could be divided into three stages and two stages, respectively, in which competitive parallel reactions occurred. Coats-Redfern method and Kissinger method were subsequently used to obtain the reaction model f(α). Particularly, a new mean reaction model f′(α) was introduced to deal with the complex competitive parallel reactions. It was proposed that pyrolysis of cellulose followed Avrami-Erofeev (m = 2) nucleation model, while pyrolysis of hemicellulose and lignin could be described by reaction-order model. The other kinetic parameters and the contribution of each parallel reaction to devolatilization were further analyzed based on the modified distributed activation energy models. And the detailed kinetic models for pyrolysis of biomass components were finally obtained. [ABSTRACT FROM AUTHOR]