**4. Pyrolytic product distribution analysis of plant fibers affected by chemical compositions and interactions among them**

Pyrolysis behaviors of coniferous, broadleaf, bamboo, flax, grass, and cotton fibers have been proven to be relevant with the biomass types and chemical compositions [5], showing different pyrolysis kinetic parameters because of varieties of cellulose and hemicellulose compositions in diverse plant fibers [27]. The distribution of pyrolysis products would also be largely restricted by the different chemical compositions of these fibers. The pyrolysis products and their contents of flax fiber, coniferous fiber, and broadleaf fiber at 350°C are shown in **Table 4** [36]. The main pyrolysis products of several plant fibers included alcohol, aldehyde, ketone (furanone), acid, ester, hydrocarbon, anhydrosugar, and CO2. Flax fiber contained a high proportion of cellulose (92.35%), hence, a high proportion of glucose molecular units and its ketone yield in the pyrolysis product is the highest (37.3%). The glucose ring could be easily broken at C1-O and C2-C3 confirmed by Piskorz et al. [37] based on bond energy analysis, forming fragments of two carbon atoms (C1/C2) and four carbon atoms (C3–C6), of which two-carbon fragments could form hydroxyacetaldehyde, while four-carbon fragments would generate hydroxyacetone and other products after thermal decomposition process. In addition, 1,3-dihydroxy-2-propanone mainly originates from the breaking of the cellulose chain during pyrolysis [38]. Compared with flax fiber, the cellulose contents of coniferous fiber and broadleaf fiber are significantly reduced, the hemicellulose contents are significantly increased, and their ketone yields after pyrolysis show significantly reduced, while the yields of aldehydes and hydrocarbons are enhanced. It could be related to the fact that the pyrolysis of five-carbon sugars (xylose and arabinose) tended to generate furfural, and the pyrolysis of six-carbon sugars (glucose, mannose, and galactose) tended to generate


**Table 4.** *Pyrolysis product distribution of flax fiber, coniferous fiber, and broadleaf fiber at 350°C [36].* 5-hydroxymethylfurfural [3, 39–41]. 5-hydroxymethylfurfural is mainly obtained through an acetal reaction between C-2 and C-5, furfural can be obtained through the hydroxymethyl elimination reaction of 5-hydroxymethylfurfural [38], or through the cyclization/dehydration reaction of xylose [39].

Hemicellulose and lignin of lobular seal could be obtained through step-by-step extraction by Xuefei Cao [42], the main components of water-soluble hemicellulose are β-D-glucan and a small amount of pectin. The main component of alcohol-soluble hemicellulose is poly arabinogalactose. The main pyrolysis range of cellulose and hemicellulose spans 200–400°C, and their pyrolysis products are mainly carbonyl compounds. The main pyrolysis range of lignin is 300–700°C, and its pyrolysis products are mainly aromatic compounds. Both glycosidic bonds of cellulose and hemicellulose and the C-C bonds on the sugar ring have low dissociation energy, which is easy to break during pyrolysis to produce low carbon and oxygen-containing small molecule products. The bond dissociation energies of the methyl group on methoxy group of lignin monomer, Cα-Cβ connection bond on side chains, as well as β-O-4′ ether bond and Cα-Cβ in lignin dimer connection are small, so the lignin pyrolysis is easy to produce phenolic products with short side chains.

Therefore, the distribution of fiber pyrolytic products is closely related to their differences in cellulose/hemicellulose composition, and maybe the interactions between them as well. The production and utilization of reconstituted tobacco leave based on component reconstruction involved the separation and reorganization/ reassembling of water-impregnated extracts, ethanol-impregnated extracts, etc. of tobacco biomass. We take a grass fiber as an experimental example, its water-soluble components, ethanol-soluble components, and residual solid-phase components could be obtained through a step-by-step extraction process. The actual pyrolysis product distribution of the grass fiber and the weighted pyrolysis product distribution based on its component distribution are investigated, and the comparison results confirm that there are interactions between the chemical components of the plant fiber during pyrolysis [43], in which the generation of CO2 is inhibited by the interactions, and the generation of furan, phenol, and toluene was promoted by the interactions between components to varying degrees.

### **5. Conclusions**

In this chapter, a method for the determination of arabinose, galactose, glucose, xylose, mannose, and other monosaccharides in plant fiber hydrolysate is established based on high-performance anion exchange chromatography integrated pulse amperometric technique. The acid hydrolysis monosaccharides in coniferous fiber, broadleaf fiber, bamboo fiber, flax fiber, grass fiber, and cotton fiber could be determined by this method, and cellulose, hemicellulose, and lignin contents of each plant fiber were further calculated. Plant fibers are complex polymers, and their pyrolysis process is very complex. Under inert atmosphere, the average apparent activation energies of coniferous fiber, broadleaf fiber, bamboo fiber, flax fiber, grass fiber, and cotton fiber with different chemical compositions in the conversion rate of 0.05–0.85 are 193.79, 173.30, 201.10, 184.77, 176.78 and 186.28 kJ/mol, respectively. The apparent activation energies of plant fibers pyrolysis in the oxygen atmosphere are lower than those in the nitrogen atmosphere. The oxygen atmosphere can promote the pyrolysis of plant fibers. The pyrolysis of flax fiber with high cellulose content tends to generate ketones, while coniferous fiber and broadleaf fiber with high hemicellulose contents

are more likely to generate aldehydes and hydrocarbons. Furthermore, taking a grass fiber as the experimental object, interactions between its chemical components have been captured during pyrolysis from the perspective of pyrolysis product distribution, which inhibits the pyrolysis to generate CO2, and promote the generation of furan, phenols, toluene, etc. to different degrees.
