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Biocrudes derived from hydrothermal liquefaction (HTL) and lipid extraction (EXT) of the high-lipid Scenedesmus were hydrotreated to investigate the influences of the feedstock on the profiles of the hydrotreating biofuels. For HTL and EXT biocrudes, similar yields were obtained (52.87% and 49.06%, wt%) but with different fatty acid (60.53% and 66.92%), C (60.28% and 74.40%), H (9.55% and 10.96%), O (26.99% and 13.81%) and N (3.19% and 0.85%) contents (wt%), HHVs (29.19 and 38.33 MJ kg−1) and chemical constituents (fatty acids and triglycerides), respectively. After hydrotreatment, 0.45 g HTL and 0.42 g EXT biofuels were obtained from 1 g Scenedesmus, with different heteroatoms (9.14% and 1.01%) and HHVs (42.77 and 48.85 MJ kg−1), respectively. However, a certain number of heavy products, such as C30+ hydrocarbons and C31+ esters, were found in both biofuels. By adjusting the reaction conditions, including the temperature and catalyst loading, the content of heavy products decreased from a maximum of 26.24% to a minimum of 1.30% at 350 °C with a 50% catalyst loading. Based on the hydrotreating model fatty acids and esters, the proposed reaction mechanism demonstrated that the formation of heavy products could be inhibited using EXT biocrude instead of HTL biocrude as the feedstock. [ABSTRACT FROM AUTHOR]

This study explored the effect of the Maillard reaction on the Co-Hydrothermal Liquefaction (HTL) of two different microalgae strains for bio-crude production. Model compounds, glucose and soya protein were mixed at different ratios and HTL was run at different temperatures to investigate the mechanism of the Maillard reaction. Pure Nannochloropsis (Nan), Spirulina (Spi) and the mixture of the two microalgae strains at the ratio of 1 : 1 (oven dry weight basis) were hydrothermally converted under the same reaction conditions for comparison. The mixtures of model compound and microalgae were also subjected to HTL to investigate the effects of chemical compounds on bio-crude yield. The Co-HTL for Nan and Spi exhibited lower bio-crude yield than that of HTL for individual microalgae. A high protein content has a negative effect on the fatty acid recovery. The dosage of glucose could enhance the bio-crude yield during HTL because of the Maillard reaction with protein. In addition, the results of elemental analysis indicated that the glucose dosage had promoted the energy recovery during HTL; FTIR and GC-MS spectra of bio-crudes revealing that tailoring the ratio between glucose and protein could elevate the quality of bio-crude from microalgae, especially for the microalgae with a low lipid content. [ABSTRACT FROM AUTHOR]

In this study, hydrothermal liquefaction (HTL) experiments of Nannochloropsis and Spirulina were carried out at different temperatures (220–300 °C) to explore the effects of temperature on bio-crude yield and properties. The optimal temperature for bio-crude yield was around 260–280 °C. Transfers of element and chemical compounds in bio-crude were discussed in detail to deduce the reaction mechanism. The hydrogen and carbon recoveries were consistent with the results of bio-crude yields at every temperature point. The relative percentage of fatty acid in bio-crude decreased and the amine and amide increased for both microalgae with temperature rising. The N-heterocyclic compounds in bio-crude increased with temperature rising for Nannochloropsis , while decreased when temperature increased from 220 °C to 280 °C for Spirulina. Bio-crude gained at higher temperature or from microalgae with high protein content may contain high heteroatom compounds. [ABSTRACT FROM AUTHOR]

The high nitrogen-containing compounds in bio-crude restricted the further upgrading of hydrothermal liquefactions (HTL) of microalgae. In order to optimize the process of microalgal HTL and improve the quality of bio-crude, flash heating HTL of Nannochloropsis was investigated and the bio-crudes were separated by filtration instead of dichloromethane extraction which caused nitrogen-containing compounds in bio-crude. The highest bio-crude yield of flash heating HTL was 31.4%, which is almost the same with that of conventional HTL (30.2%). Bio-crude with high HHV (38.32 MJ/kg) and low nitrogen content (3.32%) was achieved by isolated aqueous extract. Lipids in microalgae can be efficiently converted into bio-crude at low reaction temperature of 200 °C, the increasing of bio-crude yield at higher temperature of 275 °C was mainly contributed by heteroatom compounds. The aqueous extract yield was around 2.6–4.3%, composed of nitrogen-heterocycles (17.9%), DKP derivatives (67.7%), and oxygen-containing compounds (20.7%), resulted in low Carbon Recovery and high Nitrogen Recovery in aqueous extract. By isolating aqueous extract, the quality of bio-crude can be improved with few losses of valuable compounds. Image 1011 • High yield with high HHV biocrude by flash heating HTL. • Less DKP derivatives and N-heterocycles compounds in biocrude. • Less Maillard reaction in flash heating HTL. • More nitrogen in aqueous extract while less nitrogen in biocrude. [ABSTRACT FROM AUTHOR]