(90f) Hydrothermal Liquefaction of Wastewater Treatment Microalgae in a Pilot-Scale Continuous Flow Reactor

Hydrothermal
liquefaction (HTL) is considered as one of most promising techniques for
valorization of whole, wet algae biomass. HTL uses subcritical water (270-350 ºC
and 8-18 MPa) to convert the organic biomass constituents into an energy-rich bio-crude oil that can be upgraded into
liquid fuels. To date, many studies have used batch reactor; shifting to
continuous reactors is necessary for progressing to commercial-scale processes
due to the higher productivity and lower operating costs of steady-state,
continuous systems.

This
study reports the modification and preliminary testing of a pilot-scale continuous
flow reactor (CFR) for hydrothermal liquefaction of wastewater microalgae at
low solids loadings. The goal of this reactor is to perform continuous (>30 liters
or >8 hours) HTL on algae slurries with solid algal contents up to 10 wt.%,
and to produce char-free bio-crude oils using a dual high-pressure cylinder
filter system with blow-down pots to remove solids. CFR systems must address several
challenges: smooth flow of homogenous biomass slurry through unit operations,
clogging, solid-liquid-gas separation/filtration, multiple unit operations, and
process safety and control. Here we report on the progress of the reactor
development relative to bio-crude oil production, reaction residence time, and
operational stability. In addition to reactor development, HTL product
characterization was also conducted using Fourier transform ion cyclotron
resonance mass spectroscopy (FT-ICR MS) and fatty acid methyl ester (FAME)
analysis by gas chromatography mass spectroscopy (GC/MS for bio-crude oil
quality, and oxy-combustion calorimetry and elemental analysis (CHNS) for mass
and energy balances.