Chemical reactors bioreactors

There is an increasing number of areas where bioreactors are serious alternatives to conventional chemical reactors, particularly when their mild conditions and high selectivity can be exploited. In the pharmaceutical industry micro-organisms and enzymes can be used to produce specific stereo-isomers selectively, a very desirable ability since it can be that only the one isomer (possibly an optical isomer) may possess the required properties. In such applications the limitations of bioreactors are clearly outweighed by the advantages in their use. The fact that the products are formed in rather dilute aqueous solution and at relatively low rates may be of secondary importance and it may then be economically feasible to employ multiple separation stages in their purification. 

In recent years, membrane bioreactors, bioreactors combined with membrane separation unit have established themselves as an alternative configuration for traditional bioreactors. The important advantages offered by membrane bioreactors are the several different types of membrane modules, membrane structures, materials commercially available. Membrane bioreactors seem particularly suited to carry out complex enzymatic/microbial reactions and/or to separate, in situ, the product in order to increase the reaction efficiency. The membrane bioreactor is a new generation of the biochemical/chemical reactors that offer a wide variety of applications for producing new chemical compounds, for treatment of wastewater, and so on. 

Classification by End Use Chemical reactors are typically used for the synthesis of chemical intermediates for a variety of specialty (e.g., agricultural, pharmaceutical) or commodity (e.g., raw materials for polymers) applications. Polymerization reactors convert raw materials to polymers having a specific molecular weight and functionality. The difference between polymerization and chemical reactors is artificially based on the size of the molecule produced. Bioreactors utilize (often genetically manipulated) organisms to catalyze biotransformations either aerobically (in the presence of air) or anaerobically (without air present). Electrochemical reactors use electricity to drive desired reactions. Examples include synthesis of Na metal from NaCl and Al from bauxite ore. A variety of reactor types are employed for specialty materials synthesis applications (e.g., electronic, defense, and other). 

Additional information on mechanically agitated gas-liquid-solid reactors can be obtained in van t Riet and Tramper (Basic Bioreactor Design, Marcel Dekker, 1991), Ramachandran and Chaudhari (Three-Phase Catalytic Reactors, Gordon and Breach, 1983), and Gianetto and Silveston (Multiphase Chemical Reactors, Hemisphere, 1986). Examples... 

Bioreactors In biotechnology, although single-phase reactors are used (e.g., see the enzyme reactor described above), multiphase reactors are predominant. There are characteristics of bioreactors that set them apart from the t) ical chemical reactors, such as, for example, the presence of biomass that can remain in suspension but can also form biofilms on any surface. Formation of biofilms can either be a desired or an unwanted side reaction, depending on the objective of the application. 

A bioreactor or fennenter is a chemical reactor in which microbes (e.g., bacteria or yeast) act on an organic material (referred to as a substrate) to produce additional microbes and other desired or undesired products. A schematic diagram of a bioreactor is - given in Fig. 15.9-1. Mass balances for a biochemical reactor or fermenter are slightly... 

A bioreactor is a reactor that utilizes either a living organism or one or more enzymes from a living organism to accomplish a certain chemical transformation. Bioreactors can be either CSTRs (in which case they are known as chemostats) or PFRs. 

Miniaturized bioreactors can be divided into two categories based on scale microreactors and nanoreactors. These bioreactors present several fundamental advantages and open new venues. Miniaturized reactors allow for bench-scale chemical and biochemical production, which can be used by researchers. They also allow for cost-effective production when smaller quantities of a chemical are required. Other larger bioreactors are often not feasible because the production is not cost effective if the product is not very valuable or if the production is not consistent or pure enough for higher value chemicals. Miniaturized bioreactors, however, provide a great deal of conpol over reaction kinetics and hydrodynamics. 

Corollary In warm-up examples 4 and 5 (chemical reactors), we had information about stoichiometry and conversion, and the proposed procedure was to construct a table to take into account the moles entering the reactor, moles reacting, and the moles leaving the reactors (reagents and products). This is a convenient procedure and facilitates the material balance in the reactor. On the other hand, in the bioreactor problems, we had information about the disappearance of the substrate (kinetics), and in that case it was easier just to formulate the mass balance like (8.6). 

To further familiarize you with chemical reactors and bioreactors and to solve problems with the strategy proposed, analyzed, and revised in Chap. 7, in the next section (Sect. 8.5) we will solve three more problems of chemical processes and bioprocesses. 

For some apphcations, tight level control is desirable. For example, a constant liquid level is desirable for some chemical reactors or bioreactors in order to keep the residence time constant. In these situations, the level controller settings can be specified using standard tuning methods. If level control also involves heat transfer, such as for a vaporizer or an evaporator, the controller design becomes much more comphcated. In such situations special control methods can be advantageous (Shinskey, 1994). 

Chapter 4 (Santucci, Tosti, Basile) is mainly focused on the development of membranes based on metals other than Pd, such as Ni, Nb, V and Ti, which are considered today promising substitutes for the Pd-alloys. Particular attention is given to the synthesis of these membranes as well as to the effect of alloying on their chemical-physical properties. The chapter also provides a description of two porous (ceramic and glass) membranes used as a support for the new metal alloys, in gas separation and in membrane reactors, respectively. The objective of Chapter 5 (Gugliuzza) is to document what is known about nanocomposite polymeric membranes and the procedures of fabrication. Their potentialities in catalytic membrane reactors, bioreactors and membrane operations for alternative power production are highlighted. 

Special reactors are required to conduct biochemical reactions for the transformation and production of chemical and biological substances involving the use of biocatalysts (enzymes, immobilised enzymes, microorganisms, plant and animal cells). These bioreactors have to be designed so that the enzymes or living organisms can be used under defined, optimal conditions. The bioreactors which are mainly used on laboratory scale and industrially are roller bottles, shake flasks, stirred tanks and bubble columns (see Table 1). 

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