Influence of alkali catalyst on product yield and properties via hydrothermal liquefaction of barley straw

• The effect of an alkali catalyst (K2CO3) on HTL (hydrothermal liquefaction) of barley straw was studied.
• High bio-crude yield (34.85 wt%) and energy recovery were achieved with K2CO3.
• Comprehensive analysis of bio-crude and solid have been performed.
• Bio-crude contained more phenolic compounds and less carboxylic acids with K2CO3.
• Deoxygenation reactions were enhanced with K2CO3.

Barley straw was successfully converted to bio-crude by hydrothermal liquefaction at temperature of 280–400 °C using an alkali catalyst (K2CO3) in our previous work, and the maximum bio-crude yield was obtained at 300 °C. This paper extends previous work on studying liquefaction behavior of barley straw without and with K2CO3 at 300 °C. The effect of alkali catalyst on product distribution was investigated, and a detailed analysis of characteristic properties of bio-crude and solid residue has been performed by an elemental analyzer, FTIR (Fourier Transform infrared spectroscopy), TGA (thermogravimetric analysis) and GC-MS. The addition of K2CO3 increased the bio-crude yield to 34.85 wt%, and inhibited solid residue formation. Moreover, the bio-crude produced in the presence of a catalyst had better properties, in terms of higher heating value and lower O/C. GC-MS analysis showed that the major compounds identified in bio-crude were carboxylic acids, phenolic compounds and ketones, irrespective of whether the catalyst was used. However, the distribution and relative content of these compounds were different. More phenolic compounds and less carboxylic acids were observed in the catalytic run. In addition, the carbon and energy recovery with the addition of K2CO3 were twice as high as that without catalyst, indicating an improvement in energy efficiency.