(30c) Effect of Hydrothermal Treatment Temperature on Surface Morphology and Oxygen Functionality of Hydrochar Produced from Cellulose

Hydrothermal treatment (HTT) of biomass is one such method that has been used to produce fuel, fertilizers, adsorbents, and countless other products. Hydrothermal carbonization (HTC) is mild HTT where wet biomass or wastes are treated at 180-260°C to produce hydrochar. Increasing HTT temperature to near-critical conditions (260-374°C) is commonly referred to as hydrothermal liquefaction (HTL), as the desired product is biocrude and a substantial amount hydrochar as byproduct. HTT above critical point (374°C, commonly up to 420°C) is known as supercritical water gasification (SCWG), which converts biomass to gaseous fuel and hydrochar as byproduct.

Regardless of the HTT condition, hydrochar results from different reactions that occur during these HTT processes. Due to those reactions, hydrochar grows outward with different types of oxygen-containing functional groups attached to the hydrochar. These functional groups including surface morphology play a vital role in their applications. In the past years, researchers have been working on HTC, HTL, and SCWG of different feedstocks and characterized the hydrohcar properties. To the best of authors’ knowledge, no study has been reported how the hydrochar properties change with HTT temperature from sub-to-supercritical conditions.

In this study, the main goal was to understand the hydrochar formation at a wide range of HTT temperatures. To achieve this goal, hydrochars were produced from a model compound (cellulose), at various HTT temperatures ranging from 220-420°C. Boehm titration including with FTIR analysis was carried out to determine the surface functionality. Furthermore, the XRD and SEM analyses were conducted to investigate the crystallinity and particle size distribution of the hydrochar, respectively. Results showed that oxygen-containing acidic functional groups reached the highest (1495±25 µmol/g) at 260°C and reduced afterward with the increase of temperature. The particle sizes of the hydrochars increased with the temperature in the subcritical region but decreased in the supercritical region.