The microalgae Phaeodactylum tricornutum was processed by hydrothermal liquefaction in order to assess the influence of reaction temperature and reaction time on the product and elemental distribution. The experiments were carried out at different reaction times (5 and 15 min) and over a wide range of temperatures (275-420 °C) using a batch reactor system. All fractions were quantified and analyzed in terms of specific elemental concentrations. The highest bio-oil yield (39 %) was obtained at 350 °C when using a reaction time of 15 min. Under these conditions 82 % of the algal calorific value was recovered in the bio-oil fraction. The higher heating value of the bio-oil increased with reaction temperature and reaction time. The elemental analysis was used to map the distribution of elements in the obtained fractions with increasing temperature. Generally, most of the potassium, sodium, nitrogen, phosphorus, and sulfur were recovered in the aqueous fraction. The solid residue was found to primarily consist of a calcium phosphate compound.

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 .

Hydrothermal liquefaction is a promising technique for the production of bio-oil. The process produces an oil phase, a gas phase, a solid residue, and an aqueous phase. Gas chromatography coupled with mass spectrometry is used to analyze the complex aqueous phase. Especially small organic acids and nitrogen-containing compounds are of interest. The efficient derivatization reagent methyl chloroformate was used to make analysis of the complex aqueous phase from hydrothermal liquefaction of dried distillers grains with solubles possible. A circumscribed central composite design was used to optimize the responses of both derivatized and nonderivatized analytes, which included small organic acids, pyrazines, phenol, and cyclic ketones. Response surface methodology was used to visualize significant factors and identify optimized derivatization conditions (volumes of methyl chloroformate, NaOH solution, methanol, and pyridine). Twenty-nine analytes of small organic acids, pyrazines, phenol, and cyclic ketones were quantified. An additional three analytes were pseudoquantified with use of standards with similar mass spectra. Calibration curves with high correlation coefficients were obtained, in most cases R (2) > 0.991. Method validation was evaluated with repeatability, and spike recoveries of all 29 analytes were obtained. The 32 analytes were quantified in samples from the commissioning of a continuous flow reactor and in samples from recirculation experiments involving the aqueous phase. The results indicated when the steady-state condition of the flow reactor was obtained and the effects of recirculation. The validated method will be especially useful for investigations of the effect of small organic acids on the hydrothermal liquefaction process.

Understanding the condensation of the dimeric thiostannate­(IV) [Sn2S6]4– to SnS2 is of key importance for the development of solution processing of advanced tin­(IV) sulfide based electronic devices such as photovoltaics (e.g., Cu2ZnSnS4, CZTSSe) and thin-film transistors. Here, we report the crystal structure of tetraammonium thiostannate­(IV) trihydrate ((NH4)4Sn2S6·3H2O), which can be used as a more environmentally friendly alternative to the hydrazinium analogue in solution processed advanced tin­(IV) sulfide based electronic devices, e.g., CZTSSe. Hirshfeld surface analysis shows that crystal bound water molecules play a significant role in the structure and interact strongly with the sulfur atoms in the dimeric thiostannate­(IV) complex [Sn2S6]4–. The thermal decomposition and corresponding condensation of ((NH4)4Sn2S6·3H2O) to SnS2 have been studied by TG/DSC-MS and solid-state 119Sn MAS NMR. It involves the formation of the relatively more condensed thiostannate­(IV) complex [Sn4S10]4– at 90 °C via evaporation of ammonia, hydrogen sulfide, and water from the structure. With increasing temperature, more tin is transformed from tetrahedral to octahedral coordination, and at 220 °C, crystalline SnS2 is formed. In an aqueous ammonium sulfide based solution, the structure of dimeric [Sn2S6]4– is retained, and aqueous solutions of (NH4)4Sn2S6·3H2O can be spin coated and thermally decomposed to form crystalline SnS2 thin films. X-ray scattering techniques show that the solution processed SnS2 thin film is highly textured with the ab plane parallel to the substrate. Furthermore, AFM and TEM reveal that the thin film is continuous and with an inherent porous surface structure from the gaseous formation byproducts.

The effect of recycling the aqueous phase in a continuous hydrothermal liquefaction process was investigated in terms of product yield distribution, carbon balance, and composition of all main fractions. Using a custom-built continuous reactor system, a long-term experiment was conducted at 350 °C and 250 bar with a feedstock of dried distiller’s grains with solubles. In two consecutive recycle experiments, the aqueous phase of the preceding experiment was used as dispersion medium for the feedstock preparation. In these recycle-experiments a significant increase in biocrude yields was observed with a maximum increase in the first recycle experiment. However, the recycling of the aqueous phase also resulted in lower heating values and higher water contents in the oil fraction. Based on these findings, recycling the aqueous phase is a trade-off between improved yields and reduced burn qualities of the biocrude. That said, recycling also lowers carbon discharge to the aqueous fraction, which may contribute significantly to reducing the environmental footprint of an industrial HTL plant.