Effect of additives on hydrothermal liquefaction of polysaccharides

We investigated the effect of added K₂CO₃ (alkali) and HCOOH (acid) on the product yields and compositions from isothermal and fast hydrothermal liquefaction (HTL) of polysaccharides abundant in food waste. Added K₂CO₃ increased the biocrude yields from isothermal HTL of cellulose, starch, amylose, and amylopectin but had no positive effect on biocrude yields from HTL of pectin and chitin under these conditions. Lower biocrude yields were obtained with added K₂CO₃ after fast HTL of all the polysaccharides tested. The addition of HCOOH led to no notable increase in biocrude yields during isothermal HTL. However, after fast HTL, there was a decrease in biocrude yields. Adding either K₂CO₃ or HCOOH gave biocrudes with higher quality after isothermal HTL. HTL with the additives produced biocrudes with a higher fraction of lower boiling compounds. Biocrudes from fast HTL with K₂CO₃ had a lower proportion of furan derivatives suggesting a decrease in acid-catalyzed dehydration reactions. With added HCOOH the biocrude composition remained similar to the control run.