Wet torrefaction of alkali lignin - Effects of experimental conditions on the nano structure of char
Y. O. Donar., Bilge S., Sınağ A.
Ankara University, Department of Chemistry 06100 Beşevler Ankara TURKEY
E-mail: sinag@science.ankara.edu.tr

In recent years, hydrothermal carbonization (HTC) which is also called hydropyrolysis or wet torrefaction of biomass has been investigated by some researchers, with the objective of transforming the material into a more suitable feedstock for subsequent thermal conversion processes, such as combustion and gasification[5]. Hydrothermal carbonization (HTC) process indicate significantly advantages in that it can generate a variety of low-cost and sustainable carbonaceous materials with attractive nanostructure and functionalization patterns for a wide range of application [1]. 

In this study alkali lignin was hydrothermally carbonized in a stainless steel autoclave. Effect of three main reaction parameter; reaction temperature, reaction time and substrate concentration on hydrochar quality was investigated in detail. 

The hydrothermal carbonization experiments were carried out in, a autoclave under different reaction conditions changing the temperature (180, 220, 260 °C), reaction time (2, 4, 6 hours) and the lignin concentration (50, 100, 200 g/L). The hydrochars were characterized by X-ray diffraction (XRD), Raman spectroscopy, 13C CP-MAS NMR, XPS, FTIR and SEM techniques.

Obtained results show that low temperatures are not sufficient to carbonize lignin hydrothermally as expected but these findings demonstrate that carbonization takes place at 220 °C partially. However main carbonization occurs at 260 °C giving between 40 to 46 % of hydrochar yield. Obtained hydrochar consists of mainly C and O atoms. Aromatic skeleton and lots of oxygen functionalities were present on the surface. 

1. Donar Y.O., Çağlar E., Sınağ A., Preparation and characterization of agricultural waste biomass based hydrochars //Fuel -2016, -183.-P. 366-72.

Acknowledgement
This work was financially supported by TUBİTAK under the contract number “113Z635”. The authors thank TÜBİTAK for their financial support.