The
objective of this study was to elucidate the effect of adding
acid and alkali to hydrothermal liquefaction (HTL) of two waste biomass
feedstocks: manure digestate and carbohydrate-rich food waste. HTL
reactions were conducted at 300 °C for 60 min, with and without
the addition of acid or base. We measured the quantity and characterized
the quality of the three main HTL products: oil, aqueous and hydro-char.
For both feedstocks, carbon recovery distributions had wide ranges
among (1) biocrude oil (26–61 wt %), (2) aqueous product (9–49
wt %) and (3) hydro-char (1–36 wt %). The addition of acid
affected HTL reactions for manure more than for food waste. For the
aqueous phase, the addition of acid decreased the recovery of C1–4
carboxylic acids and increased the production of cyclic furan compounds.
GC–MS analysis of the biocrude oil suggested that dehydration
reactions were enhanced by adding acid to the HTL media. FTIR spectroscopy
coupled with principal component analysis showed that hydro-char samples
cluster according to acid-modified and base-modified reactions, based
on distinct chemical structures. This study clarifies the role of
pH during HTL and its effect on chemical pathways and carbon distribution
among products.
A contribution to biomass conversion into sugars and lignin using a compact reactor that is easy to scale-up was made. Wheat bran was continuously fractionated under supercritical water conditions.
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