Bioreactors Project 1, Study Guides, Projects, Research of Biochemistry

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Name : Xolani Paulos

Surname : Mfundisi

Student number : 219087865

Course : Biotechnology

Course code : ABFTT2A

Task : Assignment 1

Lecturer : Mr. N.Laloo

1. CSTR- CONTINOUS STIRRED TANK REACTORS

Continuous stirred tank reactors (CSTR) are the most basic of the continuous reactors used in chemical processes. Continuous stirred-tank reactors (CSTRs) are open systems, where material is free to enter or exit the system and operate on a steady-state basis, where the conditions in the reactor don't change with time. Reactants are continuously introduced into the reactor, while products are continuously removed. CSTRs are very well mixed, so the contents have relatively uniform properties such as temperature, density, etc.. Also, conditions in the reactor's exit stream are the same as those inside the tank. Systems connecting several CSTRs are used when the reaction is too slow. Multiple CSTRs can also be used when two immiscible liquids or viscous liquids are present and require a high agitation rate. CSTRs consist of a tank, usually of constant volume, and a stirring system to mix reactants together. Feed and exit pipes are present to introduce reactants and remove products. Pictured below is a CSTR that has had a portion of its side removed to show the interior. Stirring blades, also called agitators, are used to mix the reactants (Pfaudler Inc., Rochester, NY) A CSTR can also function as a loop reactor when a heated, pressurized fluid is injected into the system to facilitate the stirring. This allows for higher heat and mass transfer rates while simplifying maintenance because there is no agitator. An initial amount of cells are placed in the fibrous-bed basket. A nutrient rich medium is continuously fed into the reactor, and products are harvested. As the cells grow, they

(Scott. 2016) Disadvantages  Good temperature control is easily maintained  Cheap to construct  Reactor has large heat capacity  Interior of reactor is easily accessed Advantages  Conversion of reactant to product per volume of reactor is small compared to other flow reactors  Deadzones, where no mixing occurs, can develop  Reactants can bypass if outlet placed improperly

2. BUBBLE COLUMN REACTORS Bubble columns are intensively used as multiphase contactors and reactors in chemical, biochemical and petrochemical industries. They provide several advantages during operation and maintenance such as high heat and mass transfer rates, compactness and low operating and maintenance costs. Three-phase bubble column reactors are widely employed in reaction engineering, i.e. in the presence of a catalyst and in biochemical applications where microorganisms are utilized as solid suspensions in order to manufacture industrially valuable bioproducts. Investigation of design parameters characterizing the operation and transport phenomena of bubble columns have led to better understanding of the hydrodynamic properties, heat and mass transfer mechanisms and flow regime characteristics ongoing during the operation. Moreover, experimental studies are supported with computational fluid dynamics (CFDs) simulations and developed mathematical models to describe better the phenomena taking place in a bubble column reactor. This review focuses on bubble column reactors, their description, design and operation, application areas, fluid dynamics and regime analysis encountered and parameters characterizing the operation are presented together with the findings of published studies. In the bubble column bioreactor, the air or gas is introduced at the base of the column through perforated pipes or plates, or metal micro porous spargers. The flow rate of the air/gas influences the performance factors —O 2 transfer, mixing. The bubble column bioreactors may be fitted with perforated plates to improve performance. The vessel used for bubble column bioreactors is usually cylindrical with an aspect ratio of 4-.

Schematic illustration of an example of a bubble column reactor

3. AIRLIFT REACTORS Bioreactors of the airlift type are a promising design for aerobic fermentations. The basic knowledge required for understanding and predicting the performance of these reactors is only now beginning to emerge. In this review we present our observations and those of other investigators in an attempt to build up a coherent picture of airlift devices. All the major aspects, mixing and hydrodynamics, mass and heat transfer—in these reactors are considered. Comparisons between bubble columns and airlift systems are made where analogies, similarities and/or differences between them provide insight into airlift systems. Throughout, the areas of particular concern and those in need of further research in this field are mentioned. Extensive work on all forms of airlift reactors, particularly in non-Newtonian media- homogeneous and suspensions-remains to be done. Current knowledge does not permit airlift reactor design with a high degree of confidence. However, the technical feasibility of all types of fermentations —plant cell, tissue culture, bacterial, fungal, and those utilizing yeasts—in airlift vessels has been demonstrated. In the airlift bioreactors, the medium of the vessel is divided into two interconnected zones by means of a baffle or draft tube. In one of the two zones referred to a riser, the air/gas is pumped. The other zone that receives no gas is the down comer. The dispersion flows up the riser zone while the down flow occurs in the down comer. There are two types of airlift bioreactors. Internal-loop airlift bioreactor (has a single container with a central draft tube that creates interior liquid circulation channels. These bioreactors are simple in design, with volume and circulation at a fixed rate for fermentation. External loop airlift bioreactor possesses an external loop so that the liquid circulates

Advantages  High conversion rate per weight of catalyst.  Easy to build.  More contact between reactant and catalyst than in other types of reactors.  More product is formed due to increased reactant/catalyst contact.  Low cost of construction, operation, and maintenance.  Effective at high temperatures and pressures. Disadvantages  Difficult temperature control.  Temperature gradients may occur.  Catalyst difficult to replace.  Channeling of gas stream can occur, leading to ineffective regions in the reactor.  Side reactions possible.  Heat transfer to or from reactor can be difficult. (Slideserve.com: Kellsie Mason)

5. FLUIDISED-BED BIOREACTORS

Before the reactor is started the catalyst pellets lie on a grate at the bottom of the reactor. Reactants are pumped into the reactor through a distributor continuously, causing the bed to become fluidized. The bed's behavior after initial fluidization depends on the state of the reactant. If it is a liquid the bed expands uniformly with increased upward flow of the reactant. This is called homogenous fluidization. If the reactant is a gas the bed will be non-uniform because the gas forms bubbles in the bed, resulting in aggregative fluidization. Sometimes these bubbles in coarse materials can grow larger than two-thirds of the bed's diameter, which can cause slugging. Slugging can result in variable pressures, vibrations in the bed, and heat transfer reductions. Increasing the velocity of the gas leads to a turbulent regime, as shown below. In the fast fluidization regime the bed surface starts to disappear. Increasing the gas velocity further results in pneumatic transport, in which the bed is completely removed and the particles are uniformly spaced in the fluid. During this process the reactants react due to the presence of the catalyst pellets, forming products that are removed continuously. Fluidized bed reactors are mainly used for large-scale applications , they can also be used for laboratory or bench-scale tests of a catalyst. If small catalyst particles are placed in a packed bed, severe pressure drop problems can be encountered, especially if higher gas flow rates are used. This problem can be circumvented by the use of a fluidized bed reactor. In such a system, the catalyst particles are placed in a vessel that has a porous plate at the bottom through which the reactant gases pass, as shown in Fig. 6.8. Figure 6.8. Schematic representation of a fluidized bed reactor. The reactor can be operated with or without a through flow of catalyst; the latter mode is used if gradual deactivation of the catalyst occurs. Fluidized bed reactors are heterogeneous catalytic reactors in which the mass of catalyst is fluidized. This allows for extensive mixing in all directions. A result of the mixing is excellent temperature stability and increased mass-transfer and reaction rates. Fluidized bed reactors are capable of handling large amounts of feed and catalyst, and FBR used for treating aniline-and nitrobenzene-contaminated wastewater.

6. PHOTOBIOREACTORS

Fogler, Scott H. Elements of Chemical Reaction Engineering. 3rd ed. Englewood Cliffs, NJ: Prentice- Hall, 1998 "Chemical Reactors." CIEC Promoting Science at the University of York, York, UK. University of York, 18 Mar. 2013. Web. http://www.essentialchemicalindustry.org Fogler, Scott H. Elements of Chemical Reaction Engineering. 5th ed. Englewood Cliffs, NJ: Prentice- Hall, 2016. Nigar. Kantarcia., Fahir., Borak Kutlu O.Ulge. 2005. Science direct. Bubble column reactors. https://doi.org/10.1016/j.procbio.2004.10.004. 29 Apr 20