Characterization of Product Fractions from Hydrothermal Liquefaction of Nannochloropsis sp. and the Influence of Solvents

Abstract

We collected and analyzed the gas, crude bio-oil, dissolved aqueous solids, and insoluble residual solids product fractions arising from hydrothermal liquefaction of Nannochloropsis sp. at 350 °C for 60 min. Most of the carbon and hydrogen in the algal biomass appears in the crude bio-oil product, as desired. A majority of the original nitrogen appears as ammonia in the aqueous phase. We also determined how the solvent used to recover the crude bio-oil affected the yields and compositions of the product fractions. We used both nonpolar solvents (hexadecane, decane, hexane, and cyclohexane) and polar solvents (methoxycyclopentane, dichloromethane, and chloroform). Hexadecane and decane provided the highest gravimetric yields of bio-oil (39 ± 3 and 39 ± 1 wt %, respectively), but these crude bio-oils had a lower carbon content (69 wt % for decane) than did those recovered with polar solvents such as chloroform (74 wt %) and dichloromethane (76 wt %). We quantified the amount of 19 different individual molecular components in the crude bio-oil for the first time. Fatty acids were the most abundant components, but some aromatic and sulfur- and nitrogen-containing compounds were also quantified. The amount of free fatty acids in the crude bio-oil significantly depended on the solvent used, with polar solvents recovering more fatty acids than nonpolar solvents. The bio-oil recovered with chloroform, for example, had a fatty acid content equal to 9.0 wt % of the initial dry algal biomass.

Life cycle comparison of hydrothermal liquefaction and lipid extraction pathways to renewable diesel from algae

“…Many aspects of HTL have been studied including reaction temperature, pressure, retention time, feedstock species, influence of solvents, effects of catalysts, elemental distribution in products, and energy recovery. That work indicates that high temperatures (250°C to 350°C) and high pressures (approximately 10 to 20 MPa) are required and that the HTL oil can contain substantial amounts of nitrogen incorporated from the algal biomass (Alba et al 2012;Biller and Ross 2011;Brown et al 2010;Duan and Savage 2011;Minowa et al 1995;Valdez et al 2011;Vardon et al 2011;Yu et al 2011). From a life cycle perspective considering total energy demand and total emissions, these aspects suggest net energy demand may be higher than for lipid-extracted pathways because heat will be needed to establish the process conditions.…”

“…The HTL yield is defined here to be the mass of HTL oil recovered per dry mass of algae processed, sometimes written as a percentage. Numerous studies are reported in the literature and each reports different yields for the various fractions (Table 1) and different distributions of solids between oil and aqueous phases (Alba et al 2012;Biller and Ross 2011;Brown et al 2010;Duan and Savage 2011;Minowa et al 1995;Valdez et al 2011;Vardon et al 2011;Yu et al 2011). The product distribution may be influenced by many factors, including chemical composition of the algae, reaction temperature, retention time, feedstock solid content, and catalyst usage.…”

“…Experimenters subtracted these dry masses and the gas mass from the dry feed to compute the dry solids in the aqueous phase. Brown et al (2010) and Valdez et al (2011) assayed the gas fraction by GC-MS relative to a standard loaded at the start of the experiment without opening the reactor. Their gas values do not include gases still dissolved in the product liquids and thus likely underestimate the gas yield.…”

Hydrothermal Conversion of Lipid-Extracted Microalgae Hydrolysate in the Presence of Isopropanol and Steel Furnace Residues

“…Whilst for conventional HTL there is currently no consensus whether the increase in bio-oil yields justifies the additional costs of the solvent extraction procedure [29], it is clear that the HTL of the algae cake in the presence of IPA appears to be only feasible if the water phase is subsequently extracted to recover IPA and the organic reaction products. Consequently, this approach was applied to all subsequent experiments.…”

Climate Implications of Next Generation Biofuels Produced from Algae

“…Under steady state conditions, biocrude can be recovered from the aqueous phase using organic solvents (53) and subsequently blended with petroleum crude to produce a variety of drop in fuels in conventional refineries (54). Nutrients in the aqueous phase can be recovered to recycle along with CO 2 in the gas phase (55).…”