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To understanding the biomass pyrolysis process in depth, the pyrolysis mechanism of cellulose was investigated based on the combination of gas and liquid product releasing behavior with the structure evolution of solid product at 200–600 °C. In particular, the transformation process of the chemical functional group of solid char was explored with two-dimensional perturbation correlation infrared spectroscopy (2D-PCIS). It was found that at a lower temperature (<350 °C), it was mainly the dehydration and keto alcohol isomerization of cellulose and the char was mainly composed of aromatic and alicyclic compounds rich in CO structures. With temperature increasing (350–450 °C), glycosidic bonds were rapidly broken, with volatiles increasing greatly, and formed network structure containing low-order fused rings (2–5 rings). At a higher temperature (450–600 °C), the accelerated etherification of pyran rings resulted in a continuous increase of LG and solid char went to higher-order fused rings (2 × 2–4 × 4 rings). These mechanistic insights are helpful for the understanding of the biomass pyrolysis process.

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Quality and energy efficiency are two critical concerns associated with the production of biomass pellets. This study elaborates methods to improve the quality of biomass pellets by using a new additive solution (carboxymethyl cellulose (CMC)) and its influence on pellet physical and mechanical properties during the densification of three types of agricultural waste (cotton stalks, wheat straw, and rape straw). Simultaneously, the cohesion and binding mechanisms were analyzed with attenuated total reflectance infrared spectra (ATR-FTIR) and light microscopy (LM). The results show that adding CMC lowers the energy consumption and increases the pellet quality by improving relaxed density, compressive strength, and durability for cotton stalks and wheat straw. However, adding CMC to rape straw decreased the pellet quality. Our results showed that addition of CMC leads to electrostatic forces among the particles that might be responsible for the cohesion strength of biomass pellets, which may be attributed to the formation of polyelectrolytes. The electric dipole from water molecule in biomass and OH groups on the CMC formed the hydrogen bond. In addition, strong bonds, similar to solid bridges, were formed at the interfaces between CMC and biomass solid particles. These interactions enhance interparticle bonding in the pellets, thereby improving the product quality and providing an efficient means to convert agricultural waste into biomass energy.