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The interest in third generation biofuels from microalgae has been rising during the past years. Meanwhile, it seems not economically feasible to grow algae just for biofuels. Co-products with a higher value should be produced by extracting a particular algae fraction to improve the economics of an algae biorefinery. The present study aims at analyzing the influence of two main microalgae components (lipids and proteins) on the composition and quantity of biocrude oil obtained via hydrothermal liquefaction of two strains (Nannochloropsis gaditana and Scenedesmus almeriensis). The algae were liquefied as raw biomass, after extracting lipids and after extracting proteins in microautoclave experiments at different temperatures (300-375°C) for 5 and 15min. The results indicate that extracting the proteins from the microalgae prior to HTL may be interesting to improve the economics of the process while at the same time reducing the nitrogen content of the biocrude oil.

The interest in third generation biofuels from microalgae has been rising during the past years. Meanwhile, it seems not economically feasible to grow algae just for biofuels. Co-products with a higher value should be produced by extracting a particular algae fraction to improve the economics of an algae biorefinery. The present study aims at analyzing the influence of two main microalgae components (lipids and proteins) on the composition and quantity of biocrude oil obtained via hydrothermal liquefaction of two strains (Nannochloropsis gaditana and Scenedesmus almeriensis). The algae were liquefied as raw biomass, after extracting lipids and after extracting proteins in microautoclave experiments at different temperatures (300-375°C) for 5 and 15min. The results indicate that extracting the proteins from the microalgae prior to HTL may be interesting to improve the economics of the process while at the same time reducing the nitrogen content of the biocrude oil.

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.

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.

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.

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.

Abstract Hydrothermal treatment of sewage sludge is considered to be a promising environmentally friendly technology which can transform the organic matter in sludge into clean energy. However, the char and tar produced by side reactions will inhibit reaction. Five model compounds (humic acid, glutamic acid, glycerol, guaiacol, glucose) representing the main organic components (humus, proteins, lipids, lignin, and carbohydrates) in sewage sludge were treated in an autoclave at 300–400 °C for 30 min, the influence of the organic component on char/tar formation was studied. The char yield of humic acid was highest, up to 69.8(±3.1)%, followed by glucose. The tar yield of glycerol and guaiacol was highest in subcritical water and supercritical water, respectively. To further evaluate the utilization value of char/tar or to give a reasonable strategy for char/tar inhibition, the char/tar was characterized by elemental analysis, fourier transform infrared spectroscopy, thermosgravimetric analyzer, scanning electron microscope, and gas chromatography-mass spectrometer. The char/tar arising from the different model compounds exhibit differences in properties such as calorific value, thermal stability, and surface structure, which were due to the different pathways involved in their formation. The results provide the underlying insights needed to guide follow-up treatments or utilization of the char and tar produced during hydrothermal treatment of sewage sludge.

Abstract Hydrothermal treatment of sewage sludge is considered to be a promising environmentally friendly technology which can transform the organic matter in sludge into clean energy. However, the char and tar produced by side reactions will inhibit reaction. Five model compounds (humic acid, glutamic acid, glycerol, guaiacol, glucose) representing the main organic components (humus, proteins, lipids, lignin, and carbohydrates) in sewage sludge were treated in an autoclave at 300–400 °C for 30 min, the influence of the organic component on char/tar formation was studied. The char yield of humic acid was highest, up to 69.8(±3.1)%, followed by glucose. The tar yield of glycerol and guaiacol was highest in subcritical water and supercritical water, respectively. To further evaluate the utilization value of char/tar or to give a reasonable strategy for char/tar inhibition, the char/tar was characterized by elemental analysis, fourier transform infrared spectroscopy, thermosgravimetric analyzer, scanning electron microscope, and gas chromatography-mass spectrometer. The char/tar arising from the different model compounds exhibit differences in properties such as calorific value, thermal stability, and surface structure, which were due to the different pathways involved in their formation. The results provide the underlying insights needed to guide follow-up treatments or utilization of the char and tar produced during hydrothermal treatment of sewage sludge.