Effect of Swelling Pretreatment on Properties of Cellulose-Based Hydrochar
Hydrothermal carbonization (HTC) has been demonstrated as an effective method for preparing hydrochar to realize efficient utilization of biomass resources. In this study, both trifluoroacetic acid (TFA) and phosphorous acid (PA) under low temperature were used as swelling solvents to disrupt the cellulose crystalline structure within 1 h with distinct physiochemical properties. After TFA and PA swelling pretreatment, by means of hydrothermal carbonization, two varieties of swollen cellulose-derived hydrochars were produced. The results showed that the TFA and PA swelling pretreatment significantly enhanced the dehydration and deoxidation of cellulose through an HTC process. The H/C value and O/C value of swelled cellulose are lower than nonswelled by more than 4% at 220 °C, which demonstrates that the dehydrogenation reaction is enhanced during the hydrothermal process of swollen cellulose. Particle size as well as microscopic arrangement of hydrochars were distinctly different due to swelling cellulose. The particle size of hydrothermal carbon microspheres increases by a swelling process at the same hydrothermal carbonazition temperature. TFA-HTC have an estimate diameter of 0.2 μm at 220 °C, which is equivalent to the size of CEL-HTC-280. This study illustrates the mechanism for hydrothermal carbonization of TFA and PA swollen cellulose and provides a novel route for directionally regulating hydrothermal carbon microspheres and developing carbon-based catalysts.
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