A Kinetics Study on Hydrothermal Liquefaction of High-diversity Grassland Perennials

Abstract

Modeling of the liquefaction reaction kinetics for the low-input high-diversity mixtures of native grassland perennials was studied. The highest liquid yield of 82% was achieved within a short residence time of 1 minute at 374°C and 22.1 MPa. Seven possible reaction schemes and kinetic models were developed and compared. The unknown kinetic parameters of each model were estimated by nonlinear least square method. Model 3, assuming that biomass first decomposes to condensable hydrocarbons or tars (liquid products), gaseous products, and solid chars via three competitive reactions and then tars are subjected to a second cracking reaction producing gases, is found to be the best one closely matching the experimental yield data obtained from liquefaction of prairie grasses. The effects of temperature on reaction rate constants for all the reactions except the biomass conversion to char were best described by Arrhenius-type equations. The model developed here in addition to helping better understand the fundamentals of reaction kinetics of biomass liquefaction is also helpful for prediction of three lumped products—liquid products, gaseous products, and solid chars, and rough design of biomass liquefaction reactors and subsequent techno-economic analysis of the process.

Keywords:

• biomass
• bio-oil
• hydrothermal liquefaction
• kinetic model
• low input high diversity perennials
• prairie grass