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Bài giảng Kỹ thuật phản ứng sinh học: Chương 5 - Bùi Hồng Quân

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Bài giảng Kỹ thuật phản ứng sinh học: Chương 5 Quá trình truyền khối khí lỏng, cung cấp cho người học những kiến thức như: Khái niệm cơ bản; Tính toán quá trình truyền khối khí lỏng. Mời các bạn cùng tham khảo!

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Nội dung Text: Bài giảng Kỹ thuật phản ứng sinh học: Chương 5 - Bùi Hồng Quân

http://buihongquan.com Chương 5. Quá trình truyền khối khí lỏng  5.1. Khá i niệ m cơ bả n  5.2. Tính toá n quá trình truyề n khó i khí lỏ ng 12/23/2018 Bioreaction engineering. 198
http://buihongquan.com BIOREACTORS 12/23/2018 Bioreaction engineering. 199
http://buihongquan.com Contents 1. Introduction 2. O2 uptake and Stoichiometry 3. Surface aeration 4. Methods of aeration 5. Mechanically stirred bioreactors 6. Bubble driven bioreactors 7. Airlift bioreactors 8. Packed bed and trickle flow bioreactors 9. Fluidized bed bioreactors 12/23/2018 Bioreaction engineering. 200
http://buihongquan.com Bioreactors- Introduction Importance of considering process engineering factors when culturing cells. Biological factors include the characteristics of the cells, their maximum specific growth rate, yield coefficient, pH range and temperature range. The productivity of a fermentation is determined by the mode of operation of the fermentation process; eg. the advantages of fed-batch and continuous fermentations over batch fermentations. 12/23/2018 Bioreaction engineering. 201
http://buihongquan.com Bioreactors-- Introduction Bioreactors The oxygen demand of an industrial process is generally satisfied by aeration and agitation Productivity is limited by oxygen availability and therefore it is important to the factors that affect a fermenters efficiency in supplying O2 O2 requirement, quantification of O2 transfer and factors influencing the transfer of O2 into solution 12/23/2018 Bioreaction engineering. 202
http://buihongquan.com Bioreactors- Introduction Mass transfer, in particular, oxygen transfer are important factor which determined how a reactor must be designed and operated. Cost was also described as an important consideration. The larger the reactor or the faster the stirrer speed, the greater the costs involved. 12/23/2018 Bioreaction engineering. 203
http://buihongquan.com MASS TRANSFER and PHASES The rate of oxygen transfer = driving force / resistance. E.g resistance to mass transfer from medium to mo`s are complex and may arise from;  Diffusion from bulk gas to gas/liquid interface  Solution of gas in liquid interface  Diffusion of dissolved gas to bulk of liquid  Transport of dissolved gas to regions of cell  Diffusion through stagnant region of liquid surrounding the cell  Diffusion into cell  Consumption by organism (depends on growth/respiration kinetics) 12/23/2018 Bioreaction engineering. 204
http://buihongquan.com The following diagram serves to illustrate the different phases and material that are relevant in general transport processes associated with fermentation technology; M AS S TR AN S FE R Solid and D is p e rs e d g a s e s Dis s olv ed n u tr i e n ts Im m i s c i b l e liquid n u tr i e n ts P r o d u c ts i n w a te r Ce l l s Fl o c 12/23/2018 Bioreaction engineering. 205
http://buihongquan.com Phases present in bioreaction / bioreactor Non aqueous phase Aqueous phase Solid phase (Reactants / products) Dissolved reactants / Reaction products Gas (O2, CO2, CH4 etc) Cells Liquids (e.g oils) Sugars Organelles Solid (e.g particles of Minerals Enzymes substrate) Enzymes ......... 1   2 .......... 1 = reactant supply and utilisation 2 = product removal and formation 12/23/2018 Bioreaction engineering. 206
http://buihongquan.com Mass Transfer • One of the most critical factors in the operation of a fermenter is the provision of adequate gas exchange. •The majority of fermentation processes are aerobic • Oxygen is the most important gaseous substrate for microbial metabolism, and carbon dioxide is the most important gaseous metabolic product. • For oxygen to be transferred from a air bubble to an individual microbe, several independent partial resistance’s must be overcome 12/23/2018 Bioreaction engineering. 207
http://buihongquan.com Stoichiometry of respiration To consider the Stoichiometry of respiration the oxidation of glucose may be represented as; C6H12O6 + 6O2 = 6H2O + 6CO2 Atomic weight of Carbon 12 Hydrogen 1 Oxygen 16 Molecular weight of glucose is 180 How many grams of oxygen are required to oxidise 180g of glucose? Answer 192g 12/23/2018 Bioreaction engineering. 208
http://buihongquan.com Solubility of Oxygen  Both components oxygen and glucose must be in solution before they become available to microorganisms  Oxygen is 6000 times less soluble in water than glucose  A saturated oxygen solution contains only10mg dm-3 of oxygen  Impossible to add enough oxygen to a microbial culture to satisfy needs for complete respiration  Oxygen must be added during growth at a sufficient rate to satisfy requirements 12/23/2018 Bioreaction engineering. 209
http://buihongquan.com Comparison of conc. driving forces and uptake rates for glucose and oxygen by yeast Problems encountered in oxygen transport can be illustrated by comparing transport of glucose vs oxygen; 1% Sugar (glucose) Broth O2 sat @ 25oC Conc. in bulk broth 10,000 ppm approx. 7 ppm Critical conc . 100 ppm 0.8 ppm (growth stops) Rate of demand 2.8 mmoles/ g cells /h 7.7 mmoles/ g cells /h 12/23/2018 Bioreaction engineering. 210
http://buihongquan.com MASS TRANSFER and RESPIRATION (a) Mass balance Stoichiometry of respiration e.g glucose; C6H12O6 + 6O2  6H2O + 6 CO2 Oxidation of 180 gms Glucose requires 192 gms O2 Compare with a hydrocarbon (i.e 6 CH2) 12/23/2018 Bioreaction engineering. 211
http://buihongquan.com The Oxygen requirements of industrial fermentations  Oxygen demand dependant on conversion of Carbon (C) to biomass  Stoichiometry of conversion of oxygen, carbon and nitrogen into biomass has been elucidated  Use these relationships to predict the oxygen demand for a fermentation  Darlington (1964) expressed composition of 100g of dry yeast C 3.92 H 6.5 O 1.94 12/23/2018 Bioreaction engineering. 212
http://buihongquan.com O2 Requirements 6.67CH2O + 2.1O2 = C 3.92 H 6.5 O 1.94 + 2.75CO2 + 3.42H2O 7.14CH2 + 6.135O2 = C 3.92 H 6.5 O 1.94 + 3.22CO2 + 3.89H2O where CH2 = hydrocarbon CH2O = carbohydrate From the above equations to produce 100g of yeast from hydrocarbon requires three times the amount of oxygen than from carbohydrate 12/23/2018 Bioreaction engineering. 213
http://buihongquan.com Compare solubility of Oxygen vs Glucose ( e.g. oxygen = 9.0 mg/l @ 20oC, 11.3 mg/l @ 10oC) Thus must consider; Requirement for oxygen important in biotechnological processes Quantification of oxygen transfer (to avoid rate limiting step) important  Factors influencing rate of transfer (e.g. viscosity) important 12/23/2018 Bioreaction engineering. 214
http://buihongquan.com FACTORS AFFECTING OXYGEN DEMAND  Rate of cell respiration  Type of respiration (aerobic vs anaerobic)  Type of substrate (glucose vs methane)  Type of environment (e.g pH, temp etc.)  Surface area/ volume ratio large vs small cells (bacteria v mammalian cells) hyphae, clumps, flocks, pellets etc.  Nature of surface area (type of capsule etc) 12/23/2018 Bioreaction engineering. 215
http://buihongquan.com Methods of Aeration  A bioreactor is a reactor system used for the culture of microorganisms. They vary in size and complexity from a 10 ml volume in a test tube to computer controlled fermenters with liquid volumes greater than 100 m3. They similarly vary in cost from dollars to a few million dollars.  In the following sections we will compare the following reactors  Standing cultures  Shake flasks  Stirred tank reactors  Bubble column and airlift reactors  Fluidized bed reactors 12/23/2018 Bioreaction engineering. 216
http://buihongquan.com Standing cultures In standing cultures, little or no power is used for aeration. Aeration is dependent on the transfer of oxygen through the still surface of the culture. 12/23/2018 Bioreaction engineering. 217

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