Hydrothermal conversion of woody biomass with disodium octaborate tetrahydrate and boric acid

Abstract

In this study, Scotch pine (Pinus sylvestris L.) was used as a woody biomass in the form of sawdust. Hydrothermal conversion of the biomass was carried out in the absence and presence of disodium octaborate tetrahydrate and boric acid at the temperatures of 250, 300 and 350°C. The effects of temperature and catalysts on the product distributions and bio-oil compositions were investigated. The highest total bio-oil yield obtained at 300°C with disodium octaborate tetrahydrate was 34.9wt%, whereas the total bio-oil yields from the non-catalytic run and the run with H3BO3 at 300°C were 24.6wt% and 19.1wt%, respectively. Although the composition of bio-oils was similar in all runs, some compounds such as furfural and furfural derivatives were not observed in the light and heavy bio-oils produced from the non-catalytic run and the run with disodium octaborate tetrahydrate at 300°C. The light bio-oils from all runs contained mainly oxygenated hydrocarbons. The major compounds in HBOs were the following: 4-methyl-3-penten-2-one and 4-hydroxy-4-methyl-2-pentanone for disodium octaborate tetrahydrate, 4-hydroxy-4-methyl-2-pentanone and (Z,Z)-9,12-octadecadienoic acid for the non-catalytic run and (Z,Z)-9,12-octadecadienoic acid for the run with boric acid. The maximum heating values for the LBO and HBO were estimated to be about 25 and 28MJ/kg, respectively, and they were obtained with disodium octaborate tetrahydrate. SEM analysis of the bio-char obtained from the non-catalytic run at 250°C showed a semi-char formation. An increase in temperature from 250 to 300°C led to the formation of regular channels on the surface of the bio-char. These open channels closed when the temperature was increased from 300 to 350°C.