Based on the molecular distillation results, a scheme of the process combining molecular distillation separation with bio-oil upgrading is proposed. The light fraction rich in carboxylic acids and other light components could be used for esterification, catalytic cracking, and steam reforming, to produce ester fuel, hydrocarbons, and hydrogen, respectively. For the middle fraction, steam reforming at high temperature or hydrodeoxygenation at high pressure could efficiently convert this fraction into hydrogen or hydrocarbons. The heavy fraction, which consisted mainly of pyrolytic lignin and sugar oligomers, could be emulsified with diesel to obtain emulsion fuel with a relatively high heating value. On the other hand, the extraction of some valuable chemicals can benefit the overall economy of this process.

Recently, some further research has been performed, aiming at investigating some characteristics of the distilled fractions and devising more promising upgrading methods. Thermal decomposition processes and the pyrolysis products of crude bio-oil and distilled fractions were investigated by means of TG-FTIR by Guo (Guo et al., 2010a). The light

fraction (LF) was completely evaporated at 30-150 °C, with the maximum weight loss rate at about 100 °C due to the volatilization of water and compounds of lower boiling point. The middle fraction (MF) and heavy fraction (HF) contained more lignin-derived compounds, and these decomposed continuously over a wide temperature range of 30-600 °C, leaving a final residue yield of 25-30%. Upgrading of the distilled fraction rich in carboxylic acids and ketones was carried out by Guo (Guo et al., 2011). Carboxylic acids accounted for 18.39% of the initial fraction, with acetic acid being the most abundant. After upgrading, the carboxylic acid content decreased to 2.70%, with a conversion yield of 85.3%. The content of esters in the upgraded fraction increased dramatically from 0.72% to 31.1%. The conversion of corrosive carboxylic acids into neutral esters reduced the corrosivity of the bio-oil fraction.

Figure 6. A scheme of the process combining molecular distillation separation with bio-oil upgrading.

Author details

Shurong Wang Zhejiang University, China

Acknowledgement

The author acknowledges the financial support from the Program for New Century Excellent Talents in University, the International Science & Technology Cooperation Program of China (2009DFA61050), Zhejiang Provincial Natural Science Foundation of China (R1110089), the Research Fund for the Doctoral Program of Higher Education of

China (20090101110034), the National Natural Science Foundation of China (50676085) and

the National High Technology Research and Development Program of China

(2009AA05Z407). The author also highly appreciates the kind support from Mr. Zuogang

Guo, Mr. Qinjie Cai, Mr. Long Guo and Miss Yurong Wang, who have been involved in the

experimental research and the preparation of this chapter.