Abstract
This is the first study of cellulose carbonization in the interior of cell walls. Cotton cellulose was pyrolyzed under nitrogen or in aromatic solvents (benzophenone, diphenyl sulfide, and 1,3-diphenoxybenzene) at 280 °C, and cross sections of the cell walls were examined using ultraviolet (UV) microscopy. After pyrolysis under nitrogen, UV absorption caused by carbonization appeared inside the cell walls. The absorptivity of the cell interiors was homogeneous and slightly lower than that of the cell surfaces. The UV spectra had maximal absorption at ca. 250 nm. The spectra of model compounds and Py-GC/MS analysis data suggested that furanic and polycyclic aromatic structures were present in the carbonized products. The use of aromatic solvents decreased the yields of solid carbonized products and the UV absorptivity, which remained homogeneous throughout the cross sections. The mechanism of cellulose carbonization in cell walls is discussed along with the influence of aromatic solvents.
Highlights
Cellulose is the major component of the cell walls of plants
Each residue was embedded in epoxy resin, and the samples were cut into 0.5 mm thick sections using a diamond knife mounted on a Leica Reichert Supernova Microtome (Buffalo Grove, IL, USA)
In our previous study we found that the IR spectra of hydrolysis residue obtained under nitrogen and in aromatic solvent were similar.[16]
Summary
Cellulose is the major component of the cell walls of plants. Thermochemical conversion technologies such as pyrolysis are promising ways to convert cellulose into renewable fuels, chemicals, and materials. Based on the fragment structure, they reported that as carbonization progressed, the chemical structure of char changed from carbohydrate / furan / benzene Furanoic compounds such as furfural and 5-hydroxymethylfurfural (5-HMF) have subsequently been proposed as important intermediates in the hydrothermal carbonization of reducing sugars.[13,14,15] In our previous paper, a negative relationship was observed between the yield of 5-HMF and solid carbonized product (cellulose char hydrolysis residue) in the pyrolysis of cellulose in nitrogen and various aromatic solvents, which can stabilize thermal degradation products (intermediates) by forming OH–p hydrogen bonds and breaking intermolecular hydrogen bonding.[16] These results indicate that 5-HMF is an important intermediate in cellulose carbonization under pyrolysis conditions. The mechanism by which aromatic solvents suppress carbonization is discussed by using three aromatic solvents reported in our previous study,[16] focusing on the action inside the cell wall
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