Hydrothermal liquefaction (HTL) is regarded as a promising technology for the production of biofuels from biomass and wastes. As such, there is a drive towards continuous-flow processing systems to aid process scale-up and eventually commercialization. The current study presents results from a novel pilot-scale HTL reactor with a feed capacity of up to 100 L/h and a process volume of approximately 20 L. The pilot plant employs a heat exchanger for heat recovery and a novel hydraulic oscillation system to increase the turbulence in the tubular reactor. The energy grass Miscanthus and the microalgae Spirulina, both representing advanced dedicated energy crops, as well as sewage sludge as high-potential waste stream were selected to assess the reactor performance. Biomass slurries with up to 16 wt% dry matter content were successfully processed. The heat recovery of the heat exchanger is found to increase with reactor run time, reaching 80% within 5–6 h of operation. The hydraulic oscillation system is shown to improve mixing and enhance heat transfer. Bio-crudes with average yields of 26 wt%, 33 wt% and 25 wt% were produced from Miscanthus, Spirulina and sewage sludge, respectively. The yields also appeared to increase with reactor run time. Bio-crude from HTL of Spirulina was mainly composed of palmitic acid, glycerol, heptadecane and linolelaidic acid, while biocrude from sewage sludge contained mainly palmitic acid, oleic acid and stearic acid. In contrast, biocrude from HTL of Miscanthus consisted of a large number of different phenolics. An energetic comparison between the three feedstocks revealed a thermal efficiency of 47%, 47% and 33% and energy return on investment (EROI) of 2.8, 3.3 and 0.5 for HTL of Miscanthus, Spirulina and sewage sludge, respectively.

Hydrothermal liquefaction is a promising technology for the conversion of a wide range of bio-feedstock into a biocrude; a mixture of chemical compounds that holds the potential for a renewable production of chemicals and fuels. Most research in hydrothermal liquefaction is performed in batch type reactors, although a continuous and energy-efficient operation is paramount for such process to be feasible. In this work an experimental campaign in a continuous bench scale unit is presented. The campaign is based on glycerol-assisted hydrothermal liquefaction of aspen wood carried out with the presence of a homogeneous catalyst at supercritical water conditions, 400 • C and 300 bar. Furthermore, in the experimental campaign a water phase recirculation step is incorporated to evaluate the technical feasibility of such procedure. In total, four batches of approximately 100 kg of feed each were processed successfully at steady state conditions without any observation of system malfunctioning. The biocrude obtained was characterized using several analytical methods to evaluate the feasibility of the process and the quality of the product. Results showed that a high quality biocrude was obtained having a higher heating value of 34.3 MJ/kg. The volatile fraction of the biocrude consisted mostly of compounds having number of carbon atoms in the C 6 -C 12 range similar to gasoline. In terms of process feasibility, it was revealed that total organic carbon (TOC) and ash significantly accumulated in the water phase when such is recirculated for the proceeding batch. After four batches the TOC and the ash mass fraction of the water phase were 136.2 [g/L] and 12.6 [%], respectively. Water phase recirculation showed a slight increase in the biocrude quality in terms on an effective hydrogen-to-carbon ratio, but it showed no effects on the product gas composition or the pH of the water phase. The successful operation demonstrated the technical feasibility of a continuous production of high quality biocrude.

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Hydrothermal liquefaction of biomass produces a complex bio-crude, which can be further upgraded to biofuel or chemicals, but there is a need for improved molecular understanding of product composition and reaction pathways. This study extensively characterizes semi-volatile compounds in bio-crudes from hydrothermal liquefaction (HTL) of microalgae (N. gaditana, C. vulgaris), macroalgae (L. hyperborea), residue (Dried Distillers Grains with Solubles), and lignocellulosic (M. x giganteus). The bio-crudes were analyzed using 2D gas chromatography coupled to time-of-flight mass spectrometry with in-situ silylation. A total of 73 fatty acids were detected of which C18 and C20 compounds were most diverse while palmitic acid was the single most abundant fatty acid. Multiple fatty acid amides were detected in bio-crude from N. gaditana while being almost absent in samples from other lipid and protein containing feedstocks. Several alkylated indoles and quinolines were observed in bio-crudes from protein containing feedstocks. Monoglycerides, indanones, and alkylated benzenediols and chromen-2-ones, which are typically not reported, were also detected. These results provide new knowledge of a bio-crude fraction, which is difficult to characterize.

. Hydrothermal co-liquefaction of biomasses -quantitative analysis of bio-crude and aqueous phase composition. In Sustainable Energy & Fuels 1, pp 789-805. Keywords 6• Hydrothermal liquefaction 7• Biomass mixtures 8• Quantitative analysis 9• Principal component analysis Abstract 12Hydrothermal liquefaction (HTL) is a promising technology for conversion of wet biomasses to liquid fuels, 13 but considerable amounts of oxygen and nitrogen remain in the bio-crude, while large amounts of water-14 soluble organics are displaced to the aqueous phase (AqP). 15In this study the bio-crude and AqP from HTL of 11 different feedstocks of lignocellulosics, residues, 16 macroalgae, microalgae, and their mixtures were analyzed for elemental composition, total acid number, 17 total organic carbon (TOC), total nitrogen, and pH. Quantitative analysis of major compound classes present 18 in both bio-crudes and AqPs was achieved using gas chromatography coupled to mass spectrometry 19 employing prior derivatization of authentic standards. 20 A wide range of biochemical content was obtained through mixing of biomasses and quantitative analysis 21 showed particular interaction between carbohydrates and proteins with extended effect on lipids. The 22 ability of ammonia and amines to form Schiff bases was the key factor affecting elemental distribution and 23 the direction of reaction pathways involved in the formation of cyclic oxygenates, hydroxypyridines, 24 (M. х giganteus), willow wood, and poplar wood was supplied by Department of Agroecology, Aarhus 100 University (Denmark). Timothy white clover (Clover) was harvested in Scotland. Dried Distillers Grains with 101 Solubles (DDGS) was delivered from Lantmännen Agroetanol AB, Norrköping, Sweden. Microalgae included 102 Spirulina and Chlorella vulgaris (C. vulgaris) acquired from commercial sources, and Nannochloropsis 103 gaditana (N. gaditana) from Lgem, The Netherlands, macroalgae included Laminaria hyperborea (L. 104 hyperborea) from the Univeristy of Leeds (UK), and Laminari digitata (L. digitata) from the Danish 105 Technological Institute, Denmark. 106 2.2 Hydrothermal liquefaction 107 Biomass slurries were prepared by mixing 10 wt% biomass, 2 wt.% potassium carbonate, and 88 wt.% 108 demineralized water. Feedstocks consisted of 11 biomasses and eight mixtures; poplar, spirulina, and C. 109 vulgaris were mixed in binary and ternary mixtures. DDGS, M. x giganteus, and N. gaditana were also 110 prepared as separate binary and ternary mixtures. The biochemical composition of biomasses and mixtures 111 is presented in Table 1 on dry and ash free basis. HTL experiments were performed in 20 ml batch reactors 112 from Swagelok. Experiments were initiated by loading 10 ml of 10 wt% biomass slurry into the reactor. 113Reactors were sealed and lowered into an Omega Engineering FSB-4 fluidized sand bath (FSB) preheated to 114 350 ⁰C. A reaction time of 20 min was applied, after which the reactors were cooled to ambient 115 temperature in a water bath. The reactors were vented and the AqP...

Hydrothermal liquefaction (HTL) is a promising technique for conversion of wet biomasses containing varying amounts of carbohydrate, protein, lipid, and lignin. In this work, mixtures of these model compounds were subjected to HTL at 335 °C. As many as 67 compounds were quantitated in the aqueous phase, including small organic acids, cyclic oxygenates, fatty acids, nitrogenates, and oxygenated aromatics. The concentrations correlated with the ratio of the model compounds. Principal component analysis separated samples on the basis of their quantitative results which could be linked to their biochemical composition. Concentrations of the analytes were modeled with partial least squares regression, and high-quality predictions were made from quality control (QC) samples and to varying degrees from Dried Distillers Grains with Solubles (DDGS), Miscanthus x giganteus, and Chlorella vulgaris. Values for total organic carbon (TOC), total nitrogen (TN), and pH were also predicted from QC samples, DDGS, M. x giganteus, and C. vulgaris. Carbohydrate and lipid contents mainly influenced TOC values and could be used for minimizing loss of organics, for techno-economic analysis, and for assessing potential for anaerobic digestion and thermal gasification. Pyrazines were modeled using linear, exponential, and second-degree polynomial fits, depending on whether carbohydrate or protein was the limiting biochemical component, which could be a way of controlling nitrogen and carbon displacement to the aqueous phase. This work shows that TOC, TN, pH, and concentrations of single compounds in the aqueous phase from HTL can, in many cases, be predicted from HTL of mixtures of biomass constituents.

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The purpose of this paper is to give a comprehensive description of the construction and commissioning of a continuous reactor system for hydrothermal liquefaction of biomass. The basis is a newly established facility at Aarhus University. It is capable of handling viscous biomass slurries and features a novel induction-based heating method that facilitates well-defined reaction environments. Carbon balance closure is obtained as all product fractions are recovered and positively quantified. The paper includes a residence time distribution measurement and a 24 h proof-of-concept experiment conducted at 350°C, 250 bar, and 15 min reaction time. It is based on the biomass dried distillers grains with solubles, a waste product of the bioethanol industry. The experiment seeks to determine the steady-state characteristics of the continuous reactor system for use in future experimental studies. It was found that steady state occurs within 6 h. Furthermore, data sampling windows of 2.1 h were found to mask the intrinsic variations of the system while still exposing trends. At steady state, the oil mass yield was found to be 38.9 ± 3.2% and the higher heating value was 35.3 ± 0.28 MJ kg −1 .