生物工艺学教学课件：Chapter 04 Mass Transport in Bioreactor

1、Chapter 4Mass Transport in BioreactorO2O2 4.1. The oxygen demandThe oxygen demand4.2. The oxygen transportOTR-The oxygen transfer rate(mol m-3 h-1) A-surface (m2) -thickness (m) C-the concentration difference over the film (mol m-3) D- the diffusivity of the gas in the film (m2 h-1)OTR=KL a (C*-C)1.

2、 D 2.C-The force( mol m-3)a-The specific interface area(m-1)By substituting eqs.2-4 into eq.1 , OTR is given by:eq1eq2eq3 eq4OTR=KL a (C*-C) KL air, stirrer and speed, viscosity A small gas bubble C* oxygen carrier temperature and pressureC recombinent DNAParameters that influence oxygen transfer ca

3、pacity of a bioreactor 4.3. Control of oxygen transfer rateFermenter design: Medium: Stirrers Oxygen solubility Baffles Viscosity Sparger Surface active compounds Liquid height: width ratioOrganism: Controlled parameters: Morphology Stirrer speed (RPM) Air liquid interface adsorption Aeration rate (

4、VVM) Oxygen partial pressure (pO2) How do they influence oxygen transfer capacity and how do we make use of them? OTR influenced by oxygen solubilityLeft: OTR influenced by the viscosity of the mediumRight: OTR influenced by the surface of the medium OTR influenced by the mediumOTR influenced by sti

5、rrer rate and aerotion rateOTR influenced by the partial pressure of oxygen(PO2) increase of the aeration rate increase the oxygen concentration in the inlet air PO2 can be manipulated in two ways :Change = Input from gas phase Consumption dC/dt = KL(C*-C) - roThere are oxygen electrodes readily ava

6、ilable to measure the dissolved oxygen tension DOT (% air saturation)4.4. Analysis of the oxygen transfer capacity The dissolved oxygen concentration depends on the partial pressure of oxygen according to Henrys law:Determination of oxygen transfer capacity1. sulphite oxidation methods2. Dynamic met

7、hods3. Gas mass balance methodsWill they get the same value?2Na2SO3 + O2 2Na2SO4 Sulphite oxidation method Dynamic method Gassing out methodThe dynamic method Dynamic method Where dC/dt is expressed in kg m-3 h-1 , V is the medium volume(m3), Cg (kg m-3), is the oxygen concentration is the gas, Q is

8、 the gas flow rate (m3 h-1), and ro is the volumetric oxygen consumption rate (kg m-3 h-1). Subscripts i and o of Q and Cg refer to inlet and outlet gas, respectively The gas mass balance method Qi(100-CO2,i-CCO2,i-CW,i)=Qo(100-CO2,o-CCO2,o-CW,o)4.5. Internal diffusion in solid phase biocatalystsD i

9、s the effective diffusivity (m2 h-1) of the substrate in the solid phase ; Sr is the concentration (Kg m-3) of the substrate in the solid phase at the distance; rp (m) from the sphere centre, V”max is the maximum specific reaction rate per sphere volume unit (kg m-3 sphere h-1) at non diffusion limiting conditions and Ks id the saturation constant (kg m-3) of the unrestricted biocatalyst.The effectiveness factor ( )When the effectiveness factor is known, the volumetr