The effect of storage duration on biooil properties and hydrodeoxygenation of biooil using a palladium on carbon catalyst

Abstract

Biooil produced through the fluidized fast pyrolysis of yellow poplar wood (Liriodendron tulipifera) was stored in sealed glass bottles at 23°C for two, four, six, eight, or ten weeks to investigate the effect storage time had on biooil properties, including viscosity, pH, water content, and heating value. Biooil viscosity increased as the storage duration increased, while pH, water content, and heating value were unchanged. Thirty-three components were identified in the biooils and were classified into five sub-groups: aldehydes and ketones from carbohydrates, aliphatic phenols, phenolic aldehydes, and phenolic ketones from lignin. The concentrations of the sub-groups, especially the carbohydrate-derived ketones and lignin-derived compounds, gradually decreased with prolonged storage. The yield of pyrolytic lignin extracted from the biooils increased with storage duration from 13.2 wt% (fresh biooil; control) to 24.3 wt% (10 weeks). The average molecular weight of pyrolytic lignin also increased from 872 g mol-1 (control) to 1161 g mol-1 (10 weeks). The amounts of phenolic hydroxyl and methoxyl groups decreased from 11.2 wt% (control) to 8.0 wt% (10 weeks) and 11.9 wt% (control) to 8.6 wt% (10 weeks), respectively. In addition, biooil was hydrodeoxygenated to overcome disadvantages like storage instability. The hydrodeoxygenation (HDO) of yellow poplar wood biooil II was performed under different temperature ranges (250-370°C), reaction times (40-120 minutes), and Pd/C catalyst loading (0-6 wt%) in supercritical ethanol under a hydrogen atmosphere. After the HDO, a gas; char; and liquid (light and heavy oil) phase, illustrated that the distribution of these products was heavily influenced by the HDO temperature, reaction time, and catalyst loading. The highest yield of heavy oil was approximately 48.4 wt% (wet basis), with the HDO conditions at 250°C, 60 minutes of reaction time, and 4 wt% of the catalyst. However, in this condition, the degree of deoxygenation was strikingly low, resulting in a lower heating value (28.7 MJ/kg). The upgraded oils were less acidic and contained less water than the raw biooil. The water contents of the light and heavy oils at different conditions were 48.5 wt%-62.4 wt% and 0.4 wt%-1.9 wt%, respectively. Higher heating values of heavy oil were estimated to be between 28.7 MJ/kg and 37.4 MJ/kg, which is about twice the heating value of biooil. The elemental analysis of the liquid products showed that the heavy oil had a lower O/C ratio, which ranged from 0.17 to 0.36 (original biooil: 0.71). The H/C ratio of heavy oil decreased from 1.50 to 1.32 with the increase in temperature, 250°C and 370 °C, respectively, and increased slightly from 1.26 to 1.42 during a longer reaction time, 40 minutes and 90 minutes, respectively.