Torrefaction of patula pine under air conditions: A chemical and structural characterization

• Published in: Industrial crops and products 2018-08, Vol.118, p.302-310
• Main Authors: Ramos-Carmona, Sergio, Martínez, Juan Daniel, Pérez, Juan F.
• Format: Article
• Language: English
• Subjects: Biomass torrefaction; Morphological and chemical characterization; Oxidative atmosphere; Patula pine wood chips
• ISSN: 0926-6690; 1872-633X
• DOI: 10.1016/j.indcrop.2018.03.062

•Structure and morphology of a torrefied wood under an air atmosphere are studied.•Torrefaction under air at low temperature enhances porosity and reactivity.•The fibrous nature of biomass cell-walls disappears with torrefaction temperature.•Oxidation reactions were favored at 240 °C.•Lignin and aromaticity of biomass increase with the torrefaction severity. In this work, chemical properties and structure of patula pine wood chips torrefied under air atmosphere are studied. Oxidative conditions instead of inert environment are an interesting way to reduce torrefaction operating costs. In this way, the torrefaction process was carried out in a batch rotary kiln by varying temperature (180, 210, and 240 °C) and residence time (30, 75 and 120 min). Sample amount (∼50 g), heating rate (10 °C/min), airflow (1 slpm), and particle size (between 10 and 20 mm) were fixed. Proximate, ultimate, and heating value analyses, as well as the contents of hemicellulose, cellulose and lignin of raw and torrefied biomasses were determined. Similarly, changes in thermal behavior by DTG, chemical structure by FTIR, surface area by BET, and cell-wall structure by SEM were analyzed. A severe degradation of both hemicellulose and cellulose was found at 240 °C, and a char-like material rich in lignin with high LHV is obtained. At this temperature, oxidation reactions are favored leading to highest specific surface area (174.95 m2/g) at 75 min. In addition, the reactivity of torrefied biomasses were higher than the raw material; particularly, those produced at 180 and 210 °C. Likewise, their structure exhibited a higher aromaticity with torrefaction severity. Therefore, torrefaction under air conditions upgrades the quality of patula pine wood as a solid biofuel for further thermochemical processing such as combustion or gasification.