Hydrothermal carbonization of macrophyte Potamogeton lucens for solid biofuel production: Production of solid biofuel from macrophyte Potamogeton lucens

Abstract

Hydrothermal carbonization (HTC) was used to convert macrophyte Potamogeton lucens into solid biofuel-hydrochar. HTC was carried out in a high pressure reactor with and without chemical additives under subcritical temperatures (240–320°C), residence times (10–40min) and biomass to water dilution ratios varying from 1:4 to 1:12. Hydrochar produced in HTC with chemical additives viz. KOH, Na2CO3 and acetic acid had improvement in higher heating value (HHV) and energy density (Ed) in comparison to non-additive HTC from level of sub-bituminous coal to bituminous coal. As reflected by Van Krevelen diagram, HTC with additives had also improvement in H/C and O/C atomic ratios. Enhancement in HHV by utilization of additives followed order; acetic acid>Na2CO3>KOH. Hydrochar yield of 39% obtained in non additive process decreased to 36% (both with KOH, Na2CO3) and 37% (with acetic acid). However at same time Ed was enhanced from a value of 1.69 in non-additive HTC to 1.72, 1.76 and 1.84 with KOH, Na2CO3 and acetic acid respectively. The hydrochar produced has thus huge potential to serve as an alternate fuel. The study also expresses yield (Y), HHV, Ed and energy yield (Ey) in terms of temperature, residence time and biomass to water dilution ratio by linear and nonlinear laws.