Design of An Airlift Reactor with Multi-Net Draft Plates and Its Application in Production of Chitosan

• Main Authors: Ting-Kuo Huang, 黃定國
• Other Authors: Wen-Teng Wu
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/38728975084153646110

碩士 === 國立清華大學 === 化學工程學系 === 87 === ABSTRACTSince 1970s, the continuous progress in biotechnology, it has become the important technology in the world. Fermentation engineering of biotechnology deal with the use of living microorganism to produce biotechnological products. In fermentation engineering, bioreactor is the most important part for industrialization of biotechnology. Bioreactor with better liquid mixing and higher oxygen transfer are very important for microorganism. Bubble columns and airlift reactors are the two main kinds of pneumatic bioreactors. Because of many operational advantages, such as simple structure, low shear stress, low operational cost and ease to maintain, they are commonly employed in bioprocess and wastewater treatment. Despite many advantages, the commercial applications of conventional pneumatic bioreactors in biotechnology is still quite limited due to oxygen transfer and liquid mixing in the bioreactors. The purpose of this study was focus on bioreactor design for fermentation engineering. In the present study, we developed a novel bioreactor - airlift reactor with mulit-net draft plates. The novel bioreactor was investigated in the air-water hydrodynamic system and applied to production of chitosan. Other bioreactors including bubble column, airlift reactor, airlift reactor with double net draft tubes[Tung et al., 1997] and agitated reactor are also employed for comparison. For air-water system, the novel bioreactor has properties of both gas-liquid draft flow and gas-liquid dispersion that overcome the disadvantage of poor gas-liquid mixing of conventional bubble column. In liquid mixing, the novel bioreactor shorten the liquid mixing time of bubble column about 40%, about 30% for airlift reactor and about 10% for airlift reactor with double net draft tubes. And the novel bioreactor also has the ability of bubble slicing that slice bubbles into smaller ones and increase the interfacial area of gas bubbles. In oxygen mass transfer, the novel bioreactor had higher volumetric oxygen transfer coefficient ( kLa ) than other pneumatic bioreactors. The kLa in the novel biorector was up to 50% higher than that in the bubble column, 60% higher than airlift reactor and 10% higher than airlift reactor with double net draft tubes. The novel bioreactor has special properties of gas-liquid draft flow and bubble slicing that improve those disadvantages of conventional pneumatic bioreactors. Hence, both oxygen transfer and liquid mixing of the novel bioreactor were better than those of conventional bubble column and airlift reactor. For production of chitosan by fermentation, the novel bioreactor - airlift reactor with 3 net draft plates was chosen for production of chitosan by fermentation. Cultivation of A. coerulea was carried out in agitated reactor, bubble column and airlift reactor with double net draft tubes for comparison. The experiment results showed that shear stress of agitated reactor damaged microorganism. In the pneumatic bioreactors with expulsion shear stress, the ability of oxygen mass transfer of bioreactors had important effect on metabolism of microorganism. We proposed correlation equations that the volumetric oxygen transfer coefficient ( kLa ) of pneumatic bioreactors versus those maximum productivity of biomass and chitosan in the form of : DCW max. = 0. 4899*kLa - 59.166 CHITOSAN max. = 0.0425*kLa - 4.718Above equations correlated the kLa of pneumatic bioreactors with the maximum productivity of biomass and chitosan of microorganism may be useful with regard to information of scale up. The concluded results demonstrated that since the novel bioreactor had higher oxygen mass transfer rate and lower shear stress in comparison with bubble column, airlift reactor with double net draft tubes and agitated reactor, the novel bioreactor had higher productivity of biomass（39.52g/L） and chitosan （3.92g/L）. Furthermore, properties of chitosan including weight-averaged molecular weight （1600~1200 KDa）and degree of deacetylation （95~94%）in the novel bioreactor were higher than that in bubble column, airlift reactor with double net draft tubes and agitated reactor. These experimental facts suggests strongly that the novel bioreactor is excellent candidate for applied to aerobic fermentation engineering.keywords : bioreactor design; chitosan; fermentation; Absidia coerulea