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Production of lactic acid and derivatives from grass using mixed populations

Way Cern Khor (2017)
abstract
Second generation biorefinery is a facility for biofuel and material production where both fuel and high value products are produced from waste feedstock such as lignocellulosic biomass. Hydroxycarboxylic acids such as lactic acid can be produced from lignocellulosic biomass, which can serve as precursor to its polymer polylactic acid (PLA), or precursor for aviation fuel. A widely abundant biomass feedstock which comes forth for this purpose is grass. To achieve this, the intermediary processes have to be thoroughly investigated. Before the biomass feedstock can be utilized, it has to be pretreated to improve its biodegradability. Hence, the first objective of this thesis was to perform pretreatment on the selected biomass – grass. Thermo-mechanical pretreatment with extrusion and chemical pretreatment using calcium hydroxide were employed to enhance the biodegradability of grass. The efficiency of the pretreatment was evaluated based on the methane production and chemical oxygen demand (COD) conversion through mesophilic anaerobic digestion. Once the pretreatment was confirmed to be effective in improving the biodegradability of biomass, storage tests was performed to investigate the effect of pretreatment on biomass storability. Adjacent to storage, a fermentation process was performed to obtain lactic acid. The native microbiome from grass involved in the fermentation was also investigated. Extraction of lactic acid is required after this fermentation process. Membrane electrolysis using anion exchange membrane was used to extract lactic acid from the fermentation broth. Through this process, the pH of the fermentation broth can be controlled without extra chemicals, and lactic acid can be extracted and concentrated into a clear solution. Due to the hydrophilic nature of lactic acid, a possible strategy is to convert lactic acid into a more hydrophobic product – caproic acid through microbial chain elongation which is also known as reverse beta oxidation. Caproic acid has a maximum water solubility of 11 g L-1 at 20 °C, which allows an easier product separation from the fermentation broth. The extracted caproic acid can be further upgraded to fuel by Kolbe electrolysis. For polymerization of lactic acid into PLA, further purification processes were needed. First esterification process was used to remove acetic acid from the extracted solution. Ion exchange resin was used to further remove impurities from the broth. Finally, pure lactic acid was obtained using diethyl ether extraction. Polycondensation was performed to polymerize the lactic acid into the biodegradable plastic PLA.
Please use this url to cite or link to this publication:
author
promoter
UGent and UGent
organization
alternative title
De productie van melkzuur en derivaten van gras met behulp van gemengde populatie
year
type
dissertation
publication status
published
subject
keyword
Grass, Pretreatment, Fermentation, Elongation, Extraction, Storage, Extrusion, Calcium hydroxide, Lactic acid, Caproic acid, Decane, Membrane electrolysis
pages
165 pages
publisher
Ghent University. Faculty of Bioscience Engineering
place of publication
Ghent, Belgium
defense location
Gent : Aula (Ceremoniezaal)
defense date
2017-03-20 16:00
ISBN
9789059899803
language
English
UGent publication?
yes
classification
D1
copyright statement
I have transferred the copyright for this publication to the publisher
id
8526345
handle
http://hdl.handle.net/1854/LU-8526345
date created
2017-07-04 12:53:12
date last changed
2017-07-05 07:14:57
@phdthesis{8526345,
  abstract     = {Second generation biorefinery is a facility for biofuel and material production where both fuel and high value products are produced from waste feedstock such as lignocellulosic biomass. Hydroxycarboxylic acids such as lactic acid can be produced from lignocellulosic biomass, which can serve as precursor to its polymer polylactic acid (PLA), or precursor for aviation fuel. A widely abundant biomass feedstock which comes forth for this purpose is grass. To achieve this, the intermediary processes have to be thoroughly investigated.
Before the biomass feedstock can be utilized, it has to be pretreated to improve its biodegradability. Hence, the first objective of this thesis was to perform pretreatment on the selected biomass -- grass. Thermo-mechanical pretreatment with extrusion and chemical pretreatment using calcium hydroxide were employed to enhance the biodegradability of grass. The efficiency of the pretreatment was evaluated based on the methane production and chemical oxygen demand (COD) conversion through mesophilic anaerobic digestion. 
Once the pretreatment was confirmed to be effective in improving the biodegradability of biomass, storage tests was performed to investigate the effect of pretreatment on biomass storability. Adjacent to storage, a fermentation process was performed to obtain lactic acid. The native microbiome from grass involved in the fermentation was also investigated. 
Extraction of lactic acid is required after this fermentation process. Membrane electrolysis using anion exchange membrane was used to extract lactic acid from the fermentation broth. Through this process, the pH of the fermentation broth can be controlled without extra chemicals, and lactic acid can be extracted and concentrated into a clear solution.
Due to the hydrophilic nature of lactic acid, a possible strategy is to convert lactic acid into a more hydrophobic product -- caproic acid through microbial chain elongation which is also known as reverse beta oxidation. Caproic acid has a maximum water solubility of 11 g L-1 at 20 {\textdegree}C, which allows an easier product separation from the fermentation broth. The extracted caproic acid can be further upgraded to fuel by Kolbe electrolysis. 
For polymerization of lactic acid into PLA, further purification processes were needed. First esterification process was used to remove acetic acid from the extracted solution. Ion exchange resin was used to further remove impurities from the broth. Finally, pure lactic acid was obtained using diethyl ether extraction. Polycondensation was performed to polymerize the lactic acid into the biodegradable plastic PLA.},
  author       = {Khor, Way Cern},
  isbn         = {9789059899803},
  keyword      = {Grass,Pretreatment,Fermentation,Elongation,Extraction,Storage,Extrusion,Calcium hydroxide,Lactic acid,Caproic acid,Decane,Membrane electrolysis},
  language     = {eng},
  pages        = {165},
  publisher    = {Ghent University. Faculty of Bioscience Engineering},
  school       = {Ghent University},
  title        = {Production of lactic acid and derivatives from grass using mixed populations},
  year         = {2017},
}

Chicago
Khor, Way Cern. 2017. “Production of Lactic Acid and Derivatives from Grass Using Mixed Populations”. Ghent, Belgium: Ghent University. Faculty of Bioscience Engineering.
APA
Khor, W. C. (2017). Production of lactic acid and derivatives from grass using mixed populations. Ghent University. Faculty of Bioscience Engineering, Ghent, Belgium.
Vancouver
1.
Khor WC. Production of lactic acid and derivatives from grass using mixed populations. [Ghent, Belgium]: Ghent University. Faculty of Bioscience Engineering; 2017.
MLA
Khor, Way Cern. “Production of Lactic Acid and Derivatives from Grass Using Mixed Populations.” 2017 : n. pag. Print.