Aqueous Phase Recirculation Research Articles

Impact of nitrogenous alkaline agent on continuous HTL of lignocellulosic biomass and biocrude upgrading

Continuous hydrothermal liquefaction (CHTL) of lignocellulosic biomass with subsequent hydrotreating is carried out to study the effect of NH3 versus NaOH as alkaline HTL catalyst. Product analysis include Py-GCxGC–MS, simulated distillation and fractional distillation. Ammonia enhances biocrude quality slightly in terms of H/C ratio, density and HHV, but a significant coke formation of 11wt.% is observed. Furthermore, ammonia pollutes the biocrude with 2.7wt.% nitrogen, which is observed to inhibit hydrotreating conversion. In comparison, CHTL with NaOH is associated with a 43wt.% yield of a hydrotreatable biocrude, stable TOC levels during aqueous phase recirculation and mass, carbon and energy balance closure. Hydrotreating eliminates the TAN, reduces oxygen to 2–3wt.% and produces a promising fuel bio-blendstock with ultra-low sulphur and a diesel fraction equal to 43%.

Hydrothermal liquefaction of barley straw to bio-crude oil: Effects of reaction temperature and aqueous phase recirculation

Hydrothermal liquefaction (HTL) of barley straw with K2CO3 at different temperatures (280–400°C) was conducted and compared to optimize its process conditions; the aqueous phase as a co-product from this process was recycled to explore the feasibility of implementing wastewater reuse for bio-crude oil production. Results showed that low temperature favored the formation of bio-crude oil, with a maximum yield of 34.9wt% at 300°C. Contrarily, at high temperature, the bio-crude oil had better qualities in terms of less oxygen content and higher heating values (HHVs). The compounds identified in bio-crude oil were mainly phenolics, carboxylic acids, aldehydes and alcohols, among which the relative contents of phenolics and carboxylic acids decreased with increasing temperature. In the recirculation studies, bio-crude yield was enhanced gradually with aqueous phase addition at 300°C, and reached 38.4wt% after three cycles. The HHVs of bio-crude oil from HTL with aqueous phase were 28.4–29.4MJ/kg, slightly higher than those from HTL with fresh water. While no obvious differences in elemental distribution can be found after aqueous phase recirculation. In conclusion, this study gives a detailed insight into the HTL behavior of barley straw, and offers potential opportunities and benefits for bio-crude oil production through the reuse of aqueous phase.