*Editorial* **Hydrothermal Carbonization**

**M. Toufiq Reza**

Department of Biomedical and Chemical Engineering and Sciences, Florida Institute of Technology, 150 West University Blvd, Melbourne, FL 32901, USA; treza@fit.edu

Over the past decade, hydrothermal carbonization (HTC) has emerged as a promising thermochemical pathway for treating and converting wet wastes into fuel, materials, and chemicals. Many of the earlier studies have been carried out to understand HTC reaction mechanisms and reaction kinetics using model compounds [1,2]. More recently, HTC studies have shifted from model compounds to researching lignocellulosic biomasses [3–5]; however, these works remain focused on solid biofuel production in the form of hydrochar. Perhaps the real potential for HTC lies in wet wastes (such as sewage sludge, agricultural wastes, animal wastes, etc.) and their conversion to fertilizer, high value materials, and sustainable chemicals [1]. However, the kinetics and reaction mechanism of the real wet wastes often deviate from those of the model compounds [6]. Therefore, studying the reaction kinetics of real wet waste is an important step towards revealing the viability of HTC in the commercial process.

This Special Issue titled, "Hydrothermal Carbonization" has invited researchers from around the World to contribute to these issues in the field of HTC research. Including the editorial, ten papers are listed in this Special Issue. Researchers from eight different countries have contributed their research to this Special Issue. The highlights of the Special Issue are as follows:


**Citation:** Reza, M.T. Hydrothermal Carbonization. *Energies* **2022**, *15*, 5491. https://doi.org/10.3390/en15155491

Received: 19 July 2022 Accepted: 27 July 2022 Published: 29 July 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the author. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

light ash fraction type [14]. This paper reported that the HTC of waste products can be performed and the hydrochar can be used to enhance the pelletization of clean corn stover.


Overall, HTC has shown tremendous potential toward commercialization. We hope that readers will find this Special Issue informative and inspiring. The editor is thankful to the authors for submitting their HTC research. The *Energies* editors and the reviewers are also acknowledged for reviewing the manuscripts, which have made significant improvements to this Special Issue.

**Funding:** The work is partially funded by USDA NIFA AFRI grant no. 2019-67019-31594 and grant no. 2021-67022-34487.

**Conflicts of Interest:** The author declares no conflict of interest.
