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Downstream Processing of Bacterial Polyhydroxyalkanoates using Supercritical Fluid Technology

Applicant Mazzotti Marco
Number 132499
Funding scheme Project funding (Div. I-III)
Research institution Institut für Verfahrenstechnik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Chemical Engineering
Start/End 01.01.2011 - 31.01.2013
Approved amount 213'400.00
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Keywords (10)

biopolymers; supercritical fluid technology; downstream processing; Polyhydroxyalkanoates; PHA; supercritical; extraction; carbon dioxide; biodegradable; biopolymer

Lay Summary (English)

Lay summary
Polyhydroxyalkanoates (PHA's) comprise a class of biopolymers produced by bacterial fermentation. Due to their good biocompatibility and -degradability, they have many potential applications. However, there is still a lack of cost-efficient manufacturing processes. This project focuses on the recovery and purification of PHA's from bacterial biomass, representing the raw material, using supercritical fluid technology.Biodegradable polymers obtained from renewable resources such as PHA's are a possible solution to a number of global problems, e.g. the dependency on increasingly scarce fossil fuels or the environmental damage caused by plastic littering. Their future success depends on the availability of manufacturing processes that are competitive as well as environmentally acceptable and sustainable. It is widely believed that processes relying on supercritical carbon dioxide (scCO2) can make a valuable contribution in this direction. ScCO2 combines favorable properties like being non-toxic, noninflammable and inert in many applications, with economic and ecological advantages like being cheap, abundant and environmentally benign.This work investigates the potential of scCO2 technology in the field of downstream processing of bacterial PHA, with the goal of developing an integrated scCO2-based process for the isolation and purification of bacterial PHA from fermentation biomass. A four-step process is proposed, namely first scCO2 drying of fermentation biomass, followed by high pressure homogenization of cells in liquid CO2 for cell disruption. The next step concerns the isolation and purification of PHA from homogenized biomass by extraction using modified scCO2, and finally the recovery of PHA from the organic solution by scCO2 anti-solvent precipitation is aspired.Costs for downstream processing contribute significantly to the overall PHA manufacturing costs, hence efficient downstream processing will make PHA cheaper and more competitive, thus increasing the range of possible applications. From an ecological point of view, it is favorable to replace non-biodegradable plastic commodities made of fossil fuels with biodegradable products from renewable resources. Hence, this technology could positively affect economic aspects of PHA manufacturing, leading to a reduced ecological impact for polymeric materials. As this goal has to be achieved in an environmentally acceptable way, an integrated scCO2 process seems to be a clearly favorable; it minimizes or avoids completely the consumption of solvents and additional chemicals in the process. Hence the implementation of the proposed technology in a truly sustainable manner seems feasible.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants



CO2-assisted high pressure homogenization: A solvent-free process for polymeric microspheres and drug–polymer composites
Kluge Johannes, Mazzotti Marco (2012), CO2-assisted high pressure homogenization: A solvent-free process for polymeric microspheres and drug–polymer composites, in International Journal of Pharmaceutics, 436 , 394-402.

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
10th International Symposium on Supercritical Fluids 16.05.2012 San Francisco, California, USA


Polyhydroxyalkanoate (PHA) biopolymers comprise a large class of biocompatible and biodegradable natural polyesters that may be synthesized by bacterial fermentation processes in the form of submicron solid inclusion bodies. The present proposal aims at developing an integrated and sustainable four-step process covering the whole range of PHA downstream processing, thus allowing the isolation and purification of PHA from wet fermentation biomass. The proposed process relies on using supercritical carbon dioxide (scCO2) as process fluid in all four steps.A first step aims at drying wet biomass slurry using a process combining scCO2 with a membrane separation process, i.e. an innovative combination that has not been described previously and may find many other applications in drying technology. In the second step, high pressure homogenization is used for cell disruption and release of PHA inclusion bodies. The aim here is to process suspensions in liquid CO2, an innovative approach that has not been described previously and will dramatically simplify the recovery of solids from the homogenized suspension. The third step concerns the isolation and purification of PHA from dry homogenized biomass by extraction using scCO2 modified with an organic solvent. This approach promises a drastic reduction of the organic solvent consumption in this step; however, optimal operating conditions need to be determined thatmaximize PHA recovery while minimizing solvent consumption. Tackling the thermodynamics of the involved supercritical three-component system remains a major scientific challenge. In step four, pure PHA is recovered from the solution by precipitation using scCO2 as antisolvent. The integrated four-step process represents thus an entirely novel piece of technology, and is expected to achieve at good yield and low cost the isolation and purification of PHA from wet concentrated biomass. An implementation of the proposed technology in a truly sustainable manner is possible by recovery and recycling of involved CO2 and organic solvent streams.PHA will be used in a large variety of applications as soon as a technology exists that allows for its production at competitive prices. While current research is often targeting high-priced medical applications in tissue engineering and drug delivery, PHA might ultimately be used on a much larger scale in the manufacturing of sustainable and biodegradable alternatives for simple commodities such as plastic bags. Hence, the development of competitive manufacturing processes for PHA may be considered a step towards the solution of global environmental problems such as the dependency on increasingly scarce fossil resources or the damage caused by plastic littering, and to a future with sustainable polymer products. However, compared to PHA biosynthesis and fermentation, littleprogress has been made in PHA recovery and purification, even though the cost of downstream processing has been recognized as a key problem for large-scale PHA production.The project will be carried out at the Separation Processes Laboratory (Institute of Process Engineering, ETH Zurich) of the main applicant; it will involve one post-doctoral student with a work load of 100% and a project duration of 2 years is scheduled. The process equipment required to realize this project is available.