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Kinetics and Microbiology of Biological Processes
Published in Jay J. Cheng, Biomass to Renewable Energy Processes, 2017
In glucose-to-ethanol fermentation process, the growth of yeast cells may be inhibited by the product (ethanol), especially at a high ethanol concentration. The phenomenon is called product inhibition. A commonly used model for the kinetics of the yeast growth under product inhibition is as follows: μμm[S]KS+[S][1−〈[P][P]*〉n]
Industrial Integration of Biotechnological Processes from Raw Material to Energy Integration
Published in Farshad Darvishi Harzevili, Serge Hiligsmann, Microbial Fuels, 2017
Grégoire Léonard, Andreas Pfennig, Ayse Dilan Celebi, Shivom Sharma, François Maréchal
In biotechnological processes, product inhibition is frequently encountered, or the product is even toxic to the microorganisms. As a consequence, the product needs to be removed continually, ensuring a relatively low concentration in the fermenter. This can, for example, be realized by a pump-around, from which the product is removed in a separation step, preferably without the need to separate the microorganisms first. If a low product concentration in the fermenter is required, this will lead to a large flow rate of the pump-around and, correspondingly, large equipment for the separation step. Thus, while the separation may be feasible in principle, the equipment dimensions in such a case may not be. Thus, it cannot be overemphasized that in the evaluation of process options, the overall feasibility of process realization and equipment size on the desired technical scale needs to be taken into account for each option as well. Simple balances may help at this stage to gain significant insight, for example, on the flow rates required to keep product concentrations sufficiently low to avoid product inhibition at the production rate of the microorganisms.
The Reductions of 2-Methyl-2-alkenoic Acids with Ruthenium (BINAP) Catalysts
Published in Mike G. Scaros, Michael L. Prunier, Catalysis of Organic Reactions, 2017
David J. Ager, Diane E. Froen, Scott A. Laneman
A second explanation is also possible: There appears to be an equilibrium between the coordination of the catalyst and the substrate and the catalyst and the product. At the point where there is more product than substrate, product inhibition occurs which slows down the reaction. In our examples, inspection of the hydrogen uptake over time shows an inflection point at about 50% of the theoretical uptake amount.
Interactions of mixing and reaction kinetics of depolymerization of cellulose to renewable fuels
Published in Chemical Engineering Communications, 2018
A novel strategy of introducing both low and high mixing at regular intervals was also attempted to show the effect of mixing on the hydrolysis process. For a batch process, reactants were mixed initially for few hours (0–8 h), following which the mixing was terminated and then the reaction was continued without any mixing for 72 h. It was observed that when no glucose and cellobiose accumulate in the reactor, product inhibition was suppressed and better mixing accelerates the reaction by enhancing convective mass transfer between the enzymes, substrate, and intermediate complexes. After a certain mixing period, the inhibitors (glucose and cellobiose) start dominating the reaction kinetics and slow down the reaction rates and production of glucose and reducing sugar (Pal and Chakraborty, 2013). The phenomena can be explained based on the mass transfer theory. As seen in the previous literature, convective and diffusional mass transfer resistances exist in series at the solid–liquid interface. These two resistances are also in series with the intraparticle diffusional resistance and the reactive resistance offered by the solid cellulosic structure. Thus, the convective mass transfer resistance when increased to a certain level, it increases the effective resistance of the system (Chakraborty et al., 2014). The restricted contact of the product with the substrate and the enzyme increases the effective resistance of the cellulose–cellulase system. This results in increased product inhibition and decreased product yield of the process. Hence, it was seen that the initial rates of glucose and reducing sugar formations were greater for continuous mixing compared to no mixing conditions (Chakraborty et al., 2014). But, as the reaction time progresses, the rates of product formation decreases significantly at continuous mixing and produces more glucose and reducing sugars at no mixing. It was also seen that when using the optimal mixing strategy, i.e., 4 h of initial mixing for 2% substrate loading, glucose and reducing sugar yield increase significantly as compared to no mixing as well as continuous mixing throughout (Chakraborty et al., 2014).