Mirella - Biochem Eng Flashcards
Why are cells/enzymes not widely used in chemical processing?
There is an inability to conduct the desired step
Rates & yields are often low compared to chemistry
Requirements for low product or substrate concentration
Instability at operating conditions
What’s upstream and downstream bio processing?
Upstream - everything regarding reagents and design of reactor
Downstream - separation and recovery of product of interest. This varies more greatly between processes depending on the specification of the final product.
Lec 1 Group activity 1 answers:
1) High purity insulin
2) Upstream is the fermentation process
3) Downstream is more challenging - more stages (depending on the specification of the final product) Downstream is complex since upstream insulin yield is very low and insulin is intracellular.
4) Upstream must be efficient for downstream to function.
Lec 1 Group Activity 2 answers:
1) pH, concentration of biomass, temperature, pressure, mixing speed, air/oxygen
2) Remove the water (reduce the volume), start with easy separation, break the cells, most difficult/expensive separation at the end. Only do most expensive separation method when dealing with smaller volumes.
3) Level of purity of product, multiple separation steps (hence low yield)
Why may the kinetics of immobilised enzymes differ from those of soluble enzymes?
1) Conformational effects - conformation of the enzyme may be altered by immobilisation
2) Electrostatic and partitioning effects - concentration of chemical species in the immediate enzyme environment may differ from that of the bulk solution due to his physio-chemical properties of the support.
3) Diffusional or mass transfer effects - kinetics may be limited by the rate of substrate diffusion to the external surface of the support or by the rate of substrate diffusion through pores of the support
What does Km tell you?
Km (k-1 / k1) suggests the affinity for the enzyme to substrate. The lower the Km value, the less substrate needed to reach V max, and hence, the greater the affinity.
(Lower Km is better)
What are typical assumptions made for bioreactor modelling?
Growth rate of biomass is greater than death rate, rx»_space; rd
Steady flows
Monod kinetics apply
Perfect mixing
No P, S, or X in gas outlet stream
No X or P in the inlet streams
Negligible CO2 in the gas inlet stream
No CO2 in liquid
What is the key difference / difficulty with modelling fed-batch reactors?
The volume is constantly changing / is not constant.
Describe feedforward control:
Feedforward control: measures one or more inputs of a process, calculates the required value of the other inputs and then adjusts it.
Feedforward control has to predict the output as it does not measure output. So, it is sometimes called as PREDICTIVE CONTROL.
Feedforward control does not check how the adjustments of inputs worked in the process. So, it is referred to as OPEN LOOP CONTROL.
Feedforward control is not self-correcting.
Feedforward control takes corrective action before the disturbances entering into the process.
The feedforward control requires to measure and control more inputs. The process has to be stimulated quickly in order to predict the process output for effective control which demands sophisticated equipment. The additional instruments and control equipment makes it expensive.
The feedforward control does not affect the stability of the system. A stable system without feedforward control would remain stable even after including it.
Describe feedback control:
Feedback control measures the output of a process, calculates the error in the process and then adjusts one or more inputs to get the desired output.
The feedback control reacts only to the process error (the deviation between the measured output value and set point). So, it is called as REACTIVE CONTROL.
Feedback control measures the output and verifies the adjustment results. So, it is called as CLOSED LOOP CONTROL
If the input adjustments failed to produce correct output, then the feedback control can identify the error and make further adjustments accordingly. This process will continue till the desired output is achieved. Therefore, feedback control is self-correcting.
Feedback control takes corrective action only after the disturbances has affected the process and generated an error.
As there is no need for any simulation of process and measurement of inputs, the feedback control requires less measuring instruments and control equipment comparatively. The expense is also less.
The feedback control may create instability of the system.
What do we consider when deciding upon the most effective nutrients to use in a bioprocess?
Cost
Potential pathways / lead to unwanted products
How easy it is to break down the nutrient (hence how much O2 is needed to do so)
Pros and cons of feedforward control:
Pros:
• Compensates for the disturbance before the control variable is affected
• Does not affect the stability of the control system
Cons:
• Cannot eliminate steady-state offset
• Requires a sensor and model for each disturbance
Pros and cons of feedback control:
Pros:
Provides zero steady-state offset
Effective for all disturbances
Improved stability
Cons:
Complex
How may the volumetric mass transfer coefficient, kla, by controlled and regulated?
By controlling agitation, airflow, and pressure within the vessel.
How may (oxygen) mass transfer be improved?
1) Increase agitation (mixing) rate: → greater surface area between gas and liquid → greater mass transfer → larger values of kLa → more oxygen being supplied
2) Increase gas flow rate → more potential oxygen → smaller bubbles → greater surface area between gas and liquid → greater mass transfer → larger values of kLa → more oxygen being supplied
