Economic Evaluation of Off-gas Recycle Pressure Swing Adsorption (PSA) in Industrial Scale Poly(3-hydroxybutyrate) Fermentation

The use of high purity oxygen as a feeding gas in microbial fermentation has recent gained huge attention in industrial scale process due to its advantageous effect to increase viable cell density as well as target metabolite productivity. However, usage of highly pure oxygen is currently too expensive for industrialization. To overcome this limitation, off-gas recycle pressure swing adsorption (PSA) was employed which assist in continuous production of high purity oxygen during fermentation process. The off-gas from fermentation process contained about 70~80% oxygen which was re-utilized as the input gas in PSA, whereas conventional PSA process utilized air with 21% oxygen content. This difference in the oxygen content of the input gas decreased the size of PSA, resulting in reduction of equipment costs. Using the characteristics of off-gas recycle PSA, we analyzed and compared the economic feasibility of a highly pure oxygen supplying strategy for the production of poly(3-hydroxybutyrate) (PHB) by Ralstonia eutropha based on previously reported data, using both air and highly pure oxygen. To achieve annual production of 3,630 tonnes of PHB the aforementioned method was adopted, by doing so the production cost of PHB was significantly reduced to 4.2 $/kg. While, the conventional process (utilizing air as the feeding gas) resulted in the highest cost (5.9 $/kg). The low cost of off-gas recycle PSA was due to reduction of fixed capital cost, which was about 3 times lower than that of the conventional fermentation process. Therefore, the production cost of fermentation was considerably decreased by using a highly pure oxygen supplying strategy based on off-gas recycle PSA.