Research On New Process Of Upgrading Bio-oil By Catalytic Esterification

Bio-oil is a potential alternative fuel to replace diminishing fossil resources in the future. However, due to the negative effects of acids and aldehydes in bio-oil, it has to be upgraded before its application as a high-graded fuel. Catalytic esterification is a mild upgraded method, which was investigated to reduce the acid number and improve stability of bio-oil. In addition, the products(such as esters, alcohols and ethers) themselves are good oxygenated liquid fuels.The upgrading process, esterification and water removal of light distillate bio-oil over Amberlyst-36 ion-exchange resin, was executed at 100℃. The results showed that the optimum upgrading conditions were alcohol-oil ratio 1.5, 15wt% catalyst dosage and 4 h. under this operation factors, the acid number of upgraded bio-oil was reduced from 72.23 mgNaOH/g to 3.98 mgNaOH/g, water content was decreased from 53.06% to 3.34%. And upgraded bio-oil was relatively stable and the physical and chemical properties were improved significantly, but crude bio-oil was extremely unstable and viscosity was increased observably from 3.21 mm2/s to 48.24 mm2/s after keeping for three months. It was also found labile acids, aldehydes of crude bio-oil could transform to stable oxygenated compounds, and the total relative content of esters, alcohols and ethers reached up to 74.70%. Moreover, distilled water and dichloromethane were mixed adequately to extract sugars and their derivatives, they can almost completely separate from upgrading bio-oil.Because bio-oil contains significant amounts of aldehydes and the acetals are relatively unstable, alkylation reaction of 2-methylfuran and aldehydes was introduced in this study. Four cases were carried out to upgrade crude bio-oil, which were catalytic esterification, catalytic esterification and water removal, catalytic esterification alkylation, catalytic esterification alkylation and water removal, respectively. The results showed that water content and acid number of the upgraded bio-oil with water removal was only 20% and less than 50% of the upgraded bio-oil without water removal, respectively. The properties were improved more obviously. Furthermore, more stable and higher boiling point products of long carbon chain were obtained by alkylation of 2-methylfuran.Catalytic esterification alkylation and water removal was the optimal upgraded case and was investigated to optimize technical parameters. The results showed that the optimum upgrading conditions were 12wt% catalyst dosage, alcohol-oil ratio 1 and 10 g 2-methyfuran. Under this operation conditions, acetalization reaction was effectively suppressed and the higher relative content of alkylation products and esters could be realized, and the total relative content of stable target products, such as esters, alcohols and ethers, reached up to 84.44%. Furthermore, GC-MS analysis and upgrading mechanism indicated that labile components of crude bio-oil, like acids, aldehydes, ketones and lower alcohols, could be transform to stable target products. At the same time, levoglucosan in bio-oil not only can be converted to the value-added levulinic acid and esters under acid-treatment, but also can be transform to more stable beta.-D-Glucopyranoside, butyl by glycosidation. TG/DTG and ~1H NMR spectra analysis also demonstrated the transformation of the volatile components in bio-oil. However, Amberlyst-36 ion exchange resin lost some activity in esterification process due to the H~+ exchange with the metal ions and blocking of organics in the inner pores. Thus, in order to remain initial activity of catalyst, the pre-treatment of the cruded bio-oil has to be proceeded before its catalytic upgrading.