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Hydrothermal liquefaction of microalgae: influence of volatile salts form the culture water on the mass balances

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Abstract
Background : The interest in microalgae as source of biofuels has significantly increased in recent years, because of their higher photosynthetic efficiency and faster growing rates than terrestrial biomass. Hydrothermal liquefaction (HTL), also called subcritical water extraction, is a promising technology that converts wet microalgae into an organic liquid energy carrier, usually called bio-crude oil. Much focus is currently set on lipid-rich strains, as they are believed to produce more biocrude oil via HTL. However, these strains are usually slow growing organisms, thus reducing the overall productivity of the process. Aim : This work aims to study the suitability of several microalgae species as feedstock for biofuel via HTL under practical conditions for industrial operation. The species were cultivated, harvested and converted to biofuels in a single chain. Strains with high biomass productivity (non-lipid-rich) were selected. Methods : The selected strains had great differences in strain-specific parameters (i.e. biochemical composition, cell structure or growth environment), and they all presented a robust growth and a high biomass productivity. They were characterized in terms of biochemical and elemental composition. Special focus was paid on the accurate characterization of the feedstock and the fate of salts from the culture medium during the HTL process. Two temperatures were tested (250 and 375 ºC) with a reaction time of 5 min, in autoclaves of 43 mL. Results : A sound characterization of the organic content of the HTL feedstock is critical for a correct mass balance closure. The presence of volatile inorganic salts from the culture medium can significantly affect the mass balances. At 250 ºC, these salts are mixed with the biocrude oil and aqueous phases obtained after HTL, while these phases appear to be entirely organic when 375 ºC are used. This is related to the change in the polarity of water at subcritical conditions. Regarding the production of biofuels, the type of strain appeared to affect HTL at 250 ºC, especially the cell wall, leading to noteworthy differences in the biocrude oil yields. These differences appear to be scarcer at 375 ºC. Harsher conditions seem to make the process less sensitive to strain-specific parameters. Summary/conclusions : This works shows that the volatile inorganic salts accumulated in the algae pastes after harvesting significantly affect the HTL process. These salts are mixed with the biocrude oil and aqueous phases obtained from HTL at 250 ºC, while at 375 ºC they crystallize and precipitate, separating from the biocrude oil. A correct management of these salts (directly linked with the cultivation and harvesting techniques) appears to be critical for an industrial implementation of the HTL technology. With regard to the production of biofuels, fast growing species with high biomass productivity seem to be the best option for making microalgae HTL a successful technology.

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Chicago
López Barreiro, Diego, Wim Brilman, Frederik Ronsse, and Wolter Prins. 2013. “Hydrothermal Liquefaction of Microalgae: Influence of Volatile Salts Form the Culture Water on the Mass Balances.” In Chemical Engineering, 9th European Congress, Abstracts.
APA
López Barreiro, D., Brilman, W., Ronsse, F., & Prins, W. (2013). Hydrothermal liquefaction of microalgae: influence of volatile salts form the culture water on the mass balances. Chemical Engineering, 9th European congress, Abstracts. Presented at the 9th European congress of Chemical Engineering (ECCE-9).
Vancouver
1.
López Barreiro D, Brilman W, Ronsse F, Prins W. Hydrothermal liquefaction of microalgae: influence of volatile salts form the culture water on the mass balances. Chemical Engineering, 9th European congress, Abstracts. 2013.
MLA
López Barreiro, Diego, Wim Brilman, Frederik Ronsse, et al. “Hydrothermal Liquefaction of Microalgae: Influence of Volatile Salts Form the Culture Water on the Mass Balances.” Chemical Engineering, 9th European Congress, Abstracts. 2013. Print.
@inproceedings{3206792,
  abstract     = {Background : The interest in microalgae as source of biofuels has significantly increased in recent years, because of their higher photosynthetic efficiency and faster growing rates than terrestrial biomass. Hydrothermal liquefaction (HTL), also called subcritical water extraction, is a promising technology that converts wet microalgae into an organic liquid energy carrier, usually called bio-crude oil. Much focus is currently set on lipid-rich strains, as they are believed to produce more biocrude oil via HTL. However, these strains are usually slow growing organisms, thus reducing the overall productivity of the process.
Aim : This work aims to study the suitability of several microalgae species as feedstock for biofuel via HTL under practical conditions for industrial operation. The species were cultivated, harvested and converted to biofuels in a single chain. Strains with high biomass productivity (non-lipid-rich) were selected.
Methods : The selected strains had great differences in strain-specific parameters (i.e. biochemical composition, cell structure or growth environment), and they all presented a robust growth and a high biomass productivity. They were characterized in terms of biochemical and elemental composition. Special focus was paid on the accurate characterization of the feedstock and the fate of salts from the culture medium during the HTL process. Two temperatures were tested (250 and 375 {\textordmasculine}C) with a reaction time of 5 min, in autoclaves of 43 mL.
Results : A sound characterization of the organic content of the HTL feedstock is critical for a correct mass balance closure. The presence of volatile inorganic salts from the culture medium can significantly affect the mass balances. At 250 {\textordmasculine}C, these salts are mixed with the biocrude oil and aqueous phases obtained after HTL, while these phases appear to be entirely organic when 375 {\textordmasculine}C are used. This is related to the change in the polarity of water at subcritical conditions.
Regarding the production of biofuels, the type of strain appeared to affect HTL at 250 {\textordmasculine}C, especially the cell wall, leading to noteworthy differences in the biocrude oil yields. These differences appear to be scarcer at 375 {\textordmasculine}C. Harsher conditions seem to make the process less sensitive to strain-specific parameters.
Summary/conclusions : This works shows that the volatile inorganic salts accumulated in the algae pastes after harvesting significantly affect the HTL process. These salts are mixed with the biocrude oil and aqueous phases obtained from HTL at 250 {\textordmasculine}C, while at 375 {\textordmasculine}C they crystallize and precipitate, separating from the biocrude oil. A correct management of these salts (directly linked with the cultivation and harvesting techniques) appears to be critical for an industrial implementation of the HTL technology. With regard to the production of biofuels, fast growing species with high biomass productivity seem to be the best option for making microalgae HTL a successful technology.},
  author       = {L{\'o}pez Barreiro, Diego and Brilman, Wim and Ronsse, Frederik and Prins, Wolter},
  booktitle    = {Chemical Engineering, 9th European congress, Abstracts},
  language     = {eng},
  location     = {The Hague, The Netherlands},
  title        = {Hydrothermal liquefaction of microalgae: influence of volatile salts form the culture water on the mass balances},
  url          = {http://www.eventure-online.com/eventure/publicAbstractView.do?id=222053\&congressId=6293},
  year         = {2013},
}