• Energy Research

Abstract The microalgae species Nannochloropsis gaditana (marine) and Scenedesmus almeriensis (freshwater) were subjected to hydrothermal liquefaction (HTL) at 350 °C in small microautoclaves for 15 min to study the separation of the aqueous and biocrude oil products, either by gravity or assisted by an organic solvent (dichloromethane). The vast majority of the research available for microalgae HTL determines the product yields by separating the HTL phases with an organic solvent. This study shows that its utilization affects the product distribution, increasing the amount of biocrude oil produced and reducing the concentration of organic molecules in the aqueous phase. The increase in the biocrude oil yield comes at the expense of a higher nitrogen and oxygen content. This harms the quality of the biocrude oil in view of its application as biofuel, due to undesired emissions upon combustion. The results herewith presented indicate that the yields of the HTL products strongly depend on the separation method applied. As the use of large amounts of organic solvents for separating the products at industrial scales is unlikely, their use is also discouraged in laboratory experimentation in order to forestall creating false expectations about the biocrude oil yields obtained by means of microalgae HTL.

Aim of the work is the implementation of a low temperature reforming (LT reforming) unit downstream the Haloclean pyrolyser in order to enhance the heating value of the pyrolysis gas. Outside the focus of this work was to gain a synthesis gas quality for further use. Temperatures between 400 °C and 500 °C were applied. A commercial pre-reforming catalyst on a nickel basis from Sudchemie was chosen for LT reforming. As biogenic feedstock wheat straw has been used. Pyrolysis of wheat straw at 450 °C by means of Haloclean pyrolysis leads to 28% of char, 50% of condensate and 22% of gas. The condensate separates in a water phase and an organic phase. The organic phase is liquid, but contains viscous compounds. These compounds could underlay aging and could lead to solid tars which can cause post processing problems. Therefore, the implementation of a catalytic reformer is not only of interest from an energetic point of view, it is generally interesting for tar conversion purposes after pyrolysis applications. By using a fixed bed reforming unit at 450–490 °C and space velocities about 3000 l/h the pyrolysis gas volume flow could be increased to about 58%. This corresponds to a decrease of the yields of condensates by means of catalysis up to 17%, the yield of char remains unchanged, since pyrolysis conditions are the same. The heating value in the pyrolysis gas could be increased by the factor of 1.64. Hydrogen concentrations up to 14% could be realised.

AbstractFor chemical recycling of plastic refuses a cascade of cycled‐spheres reactors has been developed combining separation and decomposition of polymer mixtures by stepwise pyrolysis at moderate temperatures. In low‐temperature pyrolysis, mixtures of poly(vinyl chloride), polystyrene and polyethylene or polystyrene, polyamide 6 and polyethylene have been separated into hydrogen chloride, styrene and polyamide 6 and aliphatic compounds from polyethylene decomposition. Compared with the low‐temperature pyrolysis of the single components, some interactions between the polymers are found when pyrolyzing mixtures. Some mechanistic aspects of these interactions are discussed.

Abstract With the rapid growth in population and urbanization, a development in sustainable treatment of sewage sludge has become an urgent environmental concern globally. Lipid extraction has been investigated in order to valorize waste sewage sludge treatment through a pathway that leads to biodiesel. In this work, an integrated approach that combines lipid extraction of sewage sludge with hydrothermal liquefaction of the lipid-extracted sludge was studied in order to maximize valorization. The hydrothermal process was performed at temperatures ranging from 250 to 350 °C with 20 min. Regarding the bio-crude: below 300 °C, similar values are found with and without lipid-extraction, with the former variant containing more nitrogenated compounds stemming from Maillard reactions, while the latter more hydrocarbons; at 350 °C, higher bio-crude is obtained from raw sewage sludge owning to the conversion of lipids. Palmitic acid was selected as a model lipid to elucidate the role of lipids during the process, as well as to provide an improved understanding of the reaction network. Energy recovery reached values of 85.4% for hydrothermal liquefaction of sewage sludge and 98.3% for integrated approach considering the whole range of biofuel products. The energy consumption ratio was applied to estimate energetic efficiency for the combined process, making it possible to estimate the breakeven point of the process, plus the efficiency of both the hydrothermal process on its own in comparison with the combined option.

The complex nature of the hydrothermal liquefaction (HTL) of lignin product downstream requires an effective separation strategy. In this study, the use of adsorption separation was undertaken using deep eutectic solvent (DES)-modified amberlite XAD-4 adsorbents to achieve this goal. XAD-4 was modified with a choline chloride: ethylene glycol DES and characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and the Brunauer–Emmett–Teller (BET) test. In addition, the HTL product was characterized using Gas Chromatography with Flame Ionization Detection (GC-FID). The performance of unmodified and DES-modified adsorbents was initially tested on the model compounds of guaiacol, phenol and catechol, followed by the HTL product in a batch adsorption system. The Freundlich model best described the model compound adsorption system with a preferential affinity for guaiacol (kf = 12.52), outperforming phenol and catechol. Adsorption experiments showed an increase in capacity and selectivity for all species when the DES-modified adsorbents were used at all mass loadings. GC-FID analytics showed the DES-modified XAD-4 (300 mg) as having the highest selectivity for guaiacol, with an equilibrium concentration of 121.45 mg/L representing an 85.25% uptake, while catechol was the least favorably adsorbed. These results demonstrate the potential of DES-functionalized XAD-4 adsorbents in selectively isolating high-value aromatics from the HTL of the lignin product stream.