# Temperature and Agitation Are Highly Influential on Yield and Monodispersity of Self-Generated Carbon (SGC) Formed in Hydrothermal Carbonization Filtrate

## TL;DR

This study shows that temperature and agitation strongly affect the production of self-generated carbon from hydrothermal carbonization filtrate, influencing yield and particle uniformity.

## Contribution

The study identifies temperature and agitation as critical factors for optimizing the yield and monodispersity of self-generated carbon from HTC filtrate.

## Key findings

- SGC yield increased by 102% at 50°C compared to 20°C after 26 days.
- Agitated samples showed a 260% yield increase at 20°C and produced more uniform particles.
- SEM imaging revealed distinct morphology differences, with no spherical SGC at 4°C.

## Abstract

Hydrothermal carbonization
(HTC) offers significant potential for
converting residual waste streams into advanced carbon materials with
diverse applications. However, a key challenge in scaling up HTC is
managing the large volumes of organic-rich filtrate produced during
the process. Through a resting process, the filtrate can be repurposed
to produce self-generated carbon (SGC). The spontaneously formed SGC
exhibited a spherical morphology and low ash content, even when derived
from complex, ash-rich precursors such as anaerobic digestate. SGC
production from HTC filtrate may open up a new valorization route
for industrial and municipal side-streams. In this study, we investigate
how temperature, time, and agitation influence SGC yield, morphology,
and particle size distribution. The cumulative yield was measured
at intervals (days 2, 5, 7, 9, 26). The average cumulative yield after
26 days increased by 102 % at 50 °C compared to 20 °C, but
decreased by 42 % at 4 °C. Agitated samples had the highest yield,
increasing by over 260 % at 20 °C. The products showed variations
in morphology and size distribution, with agitated samples producing
more uniform and smaller particles. SEM imaging indicated a distinct
product at 4 °C, with no visible spherical material being generated.
Our results imply that changes in temperature and agitation are highly
influential in the formation of SGC and may be used in optimizing
product yield, sphere size and uniformity. The consistent formation
rate over the 26-day period suggests that extending the experimental
duration could further increase material yield. This is supported
by mass balance calculations.