**Non-Energy Valorization of Residual Biomasses via HTC: CO2 Capture onto Activated Hydrochars**

#### **Katia Gallucci \*, Luca Taglieri, Alessandro Antonio Papa, Francesco Di Lauro, Zaheer Ahmad and Alberto Gallifuoco**

Industrial Engineering Department, University of L'Aquila, Monteluco di Roio—67100 L'Aquila, Italy; luca.taglieri@univaq.it (L.T.); alessandroantonio.papa@graduate.univaq.it (A.A.P.); francesco.dilauro@student.univaq.it (F.D.L.); zaheer.ahmad@graduate.univaq.it (Z.A.); alberto.gallifuoco@univaq.it (A.G.)

**\*** Correspondence: katia.gallucci@univaq.it

Received: 13 February 2020; Accepted: 5 March 2020; Published: 10 March 2020

**Abstract:** This study aims to investigate the CO2 sorption capacity of hydrochar, obtained via hydrothermal carbonization (HTC). Silver fir sawdust was used as a model material. The batch runs went at 200 ◦C and up to 120 min. The hydrochar was activated with potassium hydroxide impregnation and subsequent thermal treatment (600 ◦C, 1 h). CO2 capture was assayed using a pressure swing adsorption (PSA) process. The morphology and porosity of hydrochar, characterized through Brunauer-Emmett-Teller, Barrett-Joyner-Halenda (BET-BJH) and scanning electron microscopy (SEM) analyses, were reported and the sorbent capacity was compared with traditional sorbents. The hydrochar recovered immediately after the warm-up of the HTC reactor had better performances. The Langmuir equilibrium isotherm fits the experimental data satisfactorily. Selectivity tests performed with a model biogas mixture indicated a possible use of hydrochar for sustainable upgrading of biogas to bio-methane. It is conceivably a new, feasible, and promising option for CO2 capture with low cost, environmentally friendly materials.

**Keywords:** hydrochar; hydrothermal carbonization; biogas upgrading; CO2 capture; pressure swing adsorption
