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Title: Extraction and purification of green polymers using aqueous two-phase extraction (ATPE)
Author: Leong, Yoong Kit
ISNI:       0000 0004 7430 1906
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2018
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Due to the increasing concern towards depleting petroleum resource and pollutions done by conventional plastics, polyhydroxyalkanoates (PHAs) which have diverse structure variability and rapid biodegradation have gained increasing attentions as potential replacement for plastics. However, PHAs have a much higher production cost compared to that of conventional plastics due to expensive carbon source and downstream processing. Aqueous two-phase extraction (ATPE) outshines other PHAs purification techniques by having the advantages of providing a mild environment for bioseparation, being green and non-toxic, and easily scaled-up. Henceforth, this research aimed to study on the purification and recovery of PHAs using thermoseparation-based ATPE. Firstly, cloud point extraction technique which based on thermoseparating polymers (TSP)/water two phase system was employed. The recovery yield of 94.8 % and purification factor (PF) of 1.41 fold was achieved under the conditions of 20 wt/wt % ethylene oxide-propylene oxide (EOPO) with 3900 g/mol MW and 10 mM of NaCl addition at thermoseparating temperature of 60 °C. TSPs have also been coupled with ammonium sulfate to form a two-phase system. Under the condition of 14 wt/wt % of both EOPO 3900 and (NH4)2SO4 at pH 6, yield and purity up to 72 % and 60 % can be achieved. Without the need of additional TSPs top-up, recycling and reutilization of phase-forming polymers can be done at least twice with satisfying yield and PF. Using two-level full factorial design, the statistical analysis demonstrated that the phosphate and thermoseparating polymer concentration are the most significant parameters due to their individual influence and synergistic interaction between them on all response variables. Utilizing the two significant parameters, the purification and recovery of PHAs were further optimized using central composite design and achieved recovery yield as high as 99.9 %. The optimum PF of 1.431 fold was obtained at 17.12 wt/wt % of phosphate salts and 18.52 wt/wt % of EOPO 3900. Using the addition of fresh phase-forming components, a total of 4 successive purification cycles with satisfying yield and PF were demonstrated. Utilizing the carbon source screened by the preliminary integrated economic and environmental assessment developed, the feasibility of extractive bioconversion of PHAs under the influence of different parameters was studied. The strategy successfully achieved a yield and PF of 97.6 % and 1.36 fold respectively under the condition of 5 wt/wt % EOPO 3900 concentration, 30 °C fermentation temperature and pH 6. The scaling-up to 2 L bioreactor proved that the scale-up of ATPE can be predicted reliably from laboratory-scale experimental data. In the final section, the evaluation of economic and environmental performance of two processes (which are with and without thermoseparating ATPE as primary purification step) were performed. With the basis of 9,000 tons PHAs production per year and 7,920 operating hours, the process with thermoseparating ATPE as primary purification step standout in terms of both economic and environmental performance. PHA production cost of 5.77 US$/kg with a payback period of fewer than 4 years and ROI of 25.2 % was achieved. The research proved that thermoseparating ATPE is a powerful and potential technique for PHAs purification and recovery as the technique showed a much higher PHAs recovery yield (approximately 2 times) in comparison with the literature (Divyashree and Shamala, 2010). In conclusion, this opens promising standpoints for utilizing thermoseparating ATPE as the primary step in the isolation and purification of PHAs from fermented broth.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TP Chemical technology