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The aqueous fraction generated from hydrothermal liquefaction (HTL) of algae contains approximately 20 to 35% of the total carbon present in the algal feed. Hence, this aqueous fraction can be utilized to produce liquid fuels and/or specialty chemicals for economic sustainability of HTL on an industrial scale. In this study, aqueous fractions produced from HTL of freshwater and saline-water algal cultures were analyzed using a wide variety of analytical instruments to determine their compositional characteristics. Organic chemical compounds present in eight aqueous fractions were identified using two-dimensional gas chromatography equipped with time-of-flight mass spectrometry. Identified compounds include organic acids, nitrogen compounds and aldehydes/ketones. Conventional gas chromatography and liquid chromatography methods were utilized to quantify the identified compounds. Inorganic species in the aqueous stream from HTL of algae also were quantified using ion chromatography and inductively coupled plasma optical emission spectroscopy. The concentrations of organic chemical compounds and inorganic species are reported. The amount quantified carbon ranged from 45 to 72 % of the total carbon in the aqueous fractions.

Hydrothermal liquefaction (HTL) is a viable thermochemical process for converting wet solid wastes into biocrude that can be hydroprocessed to liquid transportation fuel blendstocks and specialty chemicals. The aqueous byproduct from HTL contains significant amounts (20–50%) of the biogenic feed carbon, which must be valorized to enhance economic sustainability of the process on an industrial scale. In this study, aqueous fractions produced from HTL of food industry wastes, municipal wastes, and biomass cultivated on wastewater were characterized using a wide variety of analytical approaches. Organic species present in these aqueous fractions were identified using two-dimensional gas chromatography equipped with time-of-flight mass spectrometry. Identified compounds include organic acids, nitrogen compounds, alcohols, aldehydes, and ketones. Conventional gas chromatography coupled with flame ionization detection and liquid chromatography utilizing refractive index detection were employed to quantify the identified compounds. Inorganic species in the aqueous streams were also were quantified using ion chromatography and inductively coupled plasma optical emission spectroscopy. The concentrations of organic compounds and inorganic species are reported, and the significance of these results are discussed in detail.

Catalytic fast pyrolysis (CFP) has been considered as a very promising approach for converting lignocellulosic biomass into higher-quality bio-oils followed by hydrotreating to produce fuel-range products. A reactive, robust, and low-cost catalyst is required to drive the CFP process. Red mud, a side-product produced during the refining of bauxite to alumina, appears to be an effective catalyst for in situ CFP of biomass. In this paper, we report the impact of CFP reaction temperature on the conversion of a pinyon juniper feedstock to bio-oils using red mud as the catalyst and then to fuel-range hydrocarbons by hydrotreating of the produced bio-oil. The yield and quality of the CFP bio-oil produced and the yield and quality of hydrotreated final products were determined. When the CFP process temperature was lowered from 450 to 400 °C, the bio-oil yield increased with minimal differences in the oxygen content, hydrogen-to-carbon ratio, water content, etc. In addition, CFP bio-oils at both temperatures were processed in a single-stage continuous hydrotreater without reactor plugging during the testing period (i.e., ∼100 h on stream). The yield of hydrocarbon fuel from CFP bio-oil produced at 400 °C was lower than that of at 450 °C. However, the overall yield, from biomass to hydrocarbon fuel, was still higher for CFP processing at 400 °C than for processing at 450 °C. This indicates such a low-cost catalyst can enable production of bio-oil with much improved stability and consequently enable hydrotreating with a much simplified process and the potential for enhancing overall carbon efficiency by further tuning the CFP parameters. Detailed analysis of bio-oil and hydrotreated products showed a lower content of lignin-derived species in both samples from lower CFP temperature, suggesting more cellulose derived products staying in bio-oil which led to a higher bio-oil yield. Furthermore, CFP processing of three different biomass feedstocks corroborated red mud catalyst development for producing improved quality bio-oil and, when combined with hydrotreating, for the production of fuel range hydrocarbons.