Decoupled temperature and pressure hydrothermal synthesis of carbon sub-micron spheres from cellulose

TLDR

Hydrothermal batch reactors normally couple temperature and pressure, limiting process control. The authors designed a decoupled temperature‑pressure hydrothermal system that keeps pressure constant while lowering cellulose degradation temperature, enabling rapid formation of carbon sub‑micron spheres. High‑pressure water in the system cleaves cellulose hydrogen bonds and promotes dehydration, driving carbonization at lower temperatures. This approach produces carbon sub‑micron spheres without isothermal time and, per a life‑cycle assessment, markedly cuts carbon emissions, delivering a carbon‑negative material.

Abstract

Abstract The temperature and pressure of the hydrothermal process occurring in a batch reactor are typically coupled. Herein, we develop a decoupled temperature and pressure hydrothermal system that can heat the cellulose at a constant pressure, thus lowering the degradation temperature of cellulose significantly and enabling the fast production of carbon sub-micron spheres. Carbon sub-micron spheres can be produced without any isothermal time, much faster compared to the conventional hydrothermal process. High-pressure water can help to cleave the hydrogen bonds in cellulose and facilitate dehydration reactions, thus promoting cellulose carbonization at low temperatures. A life cycle assessment based on a conceptual biorefinery design reveals that this technology leads to a substantial reduction in carbon emissions when hydrochar replacing fuel or used for soil amendment. Overall, the decoupled temperature and pressure hydrothermal treatment in this study provides a promising method to produce sustainable carbon materials from cellulose with a carbon-negative effect.