Reaction pathways of monomers and oligomers during hydrothermal liquefaction of lignin

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Eutectic solvents for the valorisation of the aqueous phase from hydrothermally liquefied black liquor

The potential valorisation of the aqueous phase obtained after the hydrothermal liquefaction of Kraft black liquor by means of liquid-liquid extraction with new generation solvents was analysed for the first time ever. For this purpose, hydrophobic eutectic solvents (ES), based on combinations of menthol or thymol with octanoic, decanoic or dodecanoic acid, were tested to recover phenolic compounds from this wastewater. All of them showed high affinity for phenolic compounds and ethanol, but low affinity for the rest of the compounds, leaving a more biodegradable raffinate. Regarding phenolic compounds, the average extraction yields ranged from 66% to 91% with menthol-based ES and from 34% to 98% with thymol-based ES. The best solvent in terms of recovery and selectivity for phenolic compounds was 1:1 Menthol:Octanoic acid, with separation factors of 104.2 and 29.2 for phenolic compounds to volatile fatty acids and alcohols, respectively. In this regard, the results obtained open the simultaneous valorisation of the extract as a source of phenolic compounds, regenerating the ES, and the raffinate as a sustainable feedstock for further fermentation or catalytic processes

Valorisation of the residual aqueous phase from hydrothermally liquefied black liquor by persulphate-based advanced oxidation

Hydrothermal liquefaction of Kraft black liquor is a promising method for the production of valuable organic chemicals. However, the separation of the biochar and biocrude leaves a residual aqueous phase in large volumes, which needs to be properly managed to make the process profitable. In this work, the persulphate-based advanced oxidation was assessed, for the first time ever, as a pretreatment of this aqueous phase to reduce its content of phenolic compounds and alcohols, which hinder further valorisation strategies. Results revealed that the phenolic compounds and the alcohols were oxidised in presence of low persulphate anion concentrations (<50 mM), mainly to quinone-like compounds and organic acids. At higher oxidant concentrations, these intermediates were subsequently oxidised to valuable acetic acid. When Fe (II) was added as the catalyst, low concentrations (<9 mM) enhanced the degradation of both phenolic compounds and alcohols due to the increase of the sulphate radicals, consequently reducing persulphate requirements for their removal. Nevertheless, higher Fe (II) doses produced the sequestration of sulphate radicals, thus decreasing the oxidation performance and generating undesired parallel reactions

Experimental Results and Simulations of a Lab-Scale Hydrogen Storage Tank based on NaAlH4

Experimental results of absorption and desorption reactions of cerium-doped NaAlH4 in an air-heated tank are presented. With a hydrogenation pressure of 100 bars a maximum capacity of 3.5 wt% is reached after 4 h during absorption experiments. For desorption, after 5 h reaction a capacity of 3.5 wt% is reached at a pressure of 4 bars and 150°C. Additionally, the kinetics of the material and the tank geometry have been modelled and the influence of cooling heat transfer and inlet hydrogen temperature are analyzed

Simulations and Experimental Results of a Lab-Scale Hydrogen Storage Tank Based on Sodium Alanate (NaAlH4)

Absorption and desorption reactions of cerium-doped NaAlH4 have been performed in a lab-scale hydrogen storage tank. The experiments show a maximum rate of reaction for a temperature of 145°C at the outside of the air-cooled tank. Using an optimal heat management by adjusting the cooling-air temperature during the experiment, 3.5 wt% hydrogen can be absorbed within 1 hour and a total gravimetric capacity of 4.1 wt% hydrogen can be reached in 3 hours

Experimental study of powder bed behavior of sodium alanate in a lab-scale H2 storage tank with flow-through mode

Chemical hydrogen storage in complex hydrides offers the potential of high gravimetric storage densities compared to intermetallic hydrides, and is therefore a promising technology for mobile applications. The main challenge for mobile application is still the required high refuelling rate of the hydrogen storage tanks. Since hydrogen is bonded by an exothermal chemical reaction in complex hydrides, appropriate storage tanks require high heat transfer rates for the cooling of the tank. Hydride tanks that are state of the art rely on an indirect cooling and are additionally equipped with e.g. finns, foams, etc. to improve the heat transfer rate. For the present study, an improved laboratory tank, which allows for indirect as well as direct cooling by excess H2 gas (flow-through mode), has been designed and built. This laboratory tank is filled with 87 g of NaAlH4 (doped with 2 mol% CeCl3) and equipped with 8 thermocouples as well as two pressure sensors. Experimental results presented in this paper show a significant influence of the cooling by gaseous excess H2 on the flow-directional temperature profiles at the part of the reaction bed close to the inlet. Considering the overall conversion, this influence is rather small due to the low heat capacity flux (r cp)H2. Furthermore, it is shown that changes in material properties, attributed to the effects of heat and mass transport as well as intrinsic reaction kinetics, can be measured and assessed by the temperature and pressure sensors. After about 10 complete charging and discharging cycles, the initial permeability K of the bed has decreased by 50% to 1.6$1012 m2. In the same time, the initial thermal conductivity has increased by a factor of 1.3 to values reported in literature (0.67 Wm1 K1) and remains constant during further cycles. Additionally, it is observed that the reaction rate of the second absorption step improves, even after a total of 36 cycles

Experimental Results of an air-cooled lab-scale H2 storage tank based on sodium alanate

One possibility to store hydrogen in fuel-cell driven automobiles is the storage in solid state hydrides. Sodium alanate (NaAlH4) is a well-known hydride desorbing up to 5 wt.% H2 with reasonable rates at temperatures above 120°C. Therefore a high temperature PEM fuel cell (HT-PEM FC) system with exhaust temperatures of about 180°C can be used to provide the required enthalpy of reaction. In this study, the absorption and desorption behaviour of a lab-scale tank containing 304 g cerium-doped NaAlH4 is studied using (exhaust) air as cooling medium. For absorption reactions an optimal temperature for maximal reaction rates is identified. Additionally, the importance of an adapted heat management is shown for the present tank. For desorption experiments different operation procedures are used and the constraints in temperature and air-flow given by the HT-PEM are considered. For all 25 experiments a good cycling stability has been measured with a stabilized material capacity of more than 3.7 wt.% H2