The torrefaction bio-oil is composed of a number of chemical compounds with low concentrations, which results in a low efficiency of its application. To improve the concentrations of high-value chemicals such as furfural in the torrefaction bio-oil, four metal chlorides and hydrochloric acid were investigated as catalysts in the torrefaction of Douglas fir by microwave heating. The number of chemical compounds in the attained bio-oil was significantly reduced with introducing MgCl2, FeCl3, and AlCl3 being into the process of torrefaction. The bio-oil obtained with these three catalysts were dominated by furfural with the concentration over 20 mg/g with the torrefaction temperature, time, and catalyst/reactant ratio of 250 °C, 10 min, and 8 wt.%, respectively. The effects of torrefaction conditions on product yield were investigated by selecting MgCl2 as the catalyst, and the results indicated that the yield of torrefied biomass decreased significantly with the increase of reaction temperature, time, and catalyst loading while the yield of bio-oil collected simultaneously was increased. Further analysis for the bio-oil suggested that low temperature, long reaction time, and high catalyst loading favored furfural production. The analysis for non-condensable gas suggested that high reaction temperature and catalyst loading promoted the methane and carbon monoxide production during torrefaction. According to bio-oil and non-condensable gas analysis, a reaction pathway was proposed to explain biomass catalytic torrefaction using MgCl2.
Bibliographical noteFunding Information:
This work was partially supported by The Agriculture and Food Research Initiative of National Institute of Food and Agriculture, United States Department of Agriculture (Award Numbers: 2016-67021-24533 and 2018-67009-27904), and Pacific Northwest National Laboratory . The authors also thank the scientists of Pacific Northwest National Laboratory (PNNL), Alan Zacher and Todd Hart, for their contributions and assistance on non-condensable gases analysis.
- Catalytic torrefaction
- Metal chloride