Specific product formation rate

Here, n, v, and p represent a specific growth rate, a specific substrate consumption rate, and a specific product formation rate, respectively. and are the mean values of data used for regression analysis and a, bp and C are the coefficients in the regression models that are determined based on selected operating data in a database. This model was linked with the dynamic programming method and successfully applied to the simulation and onhne optimization of glutamic acid production and Baker s yeast production. 

In Eq. (8.11), Sf is the substrate feed rate, and FSf consequently is the molar flow into the fermenter (there is no flow out of the fermenter). Yx/s and YpyS are the two empirical yield coefficients of cell X or product P on substrate S [g (g substrate)-1] and qp is the specific production formation rate [g product (g cells)-1 h-1] (qp-X = rp, the product formation rate [g product h 11). 

It is important to emphasize the general character of this definition for the volumetric productivity (Py), since it includes all phases of a production cycle in a bioreactor, allowing an evaluation of the impact of bioreactor preparation time and duration of growth and production phases on productivity. As can be observed from Equations 19 to 22, for an industrial bioreactor with a given volume and operation mode, the volumetric productivity depends basically on cell concentration in the production phase and on the specific product formation rate (qp). 

Note that will be negative for nutrients that are consumed by the cells and positive for products. In order to obtain positive values for all of the metabolic quotients, it is customary to speak in terms of the specific substrate (nutrient) consumption rate and the specific product formation rate p ... 

PRODUCT FORMATION Specific product formation rate... 

The characteristic parameter for product formation is the specific product formation rate, q. Equations 4.2.31-4.2.34 and the methods of analysis introduced for metabolic byproducts also apply to secreted protein products. 

Certain factors and product precursors are occasionally added to various fermentation media to iacrease product formation rates, the amount of product formed, or the type of product formed. Examples iaclude the addition of cobalt salts ia the vitamin fermentation, and phenylacetic acid and phenoxyacetic acid for the penicillin G (hen ylpenicillin) and penicillin V (phenoxymethylpenicillin) fermentations, respectively. Biotin is often added to the citric acid fermentation to enhance productivity and the addition of P-ionone vastly iacreases beta-carotene fermentation yields. Also, iaducers play an important role ia some enzyme production fermentations, and specific metaboHc inhibitors often block certain enzymatic steps that result in product accumulation. 

Frequently, the specific byproduct formation rate is presented as a function of specific substrate consumption rate and substrate-to-product yield (see Equation 12), but other structures can be assumed. The specific production rate can be limited by a precursor substrate and modeled by a Monod-type expression, as in Equation 73, or it may be inhibited by a substrate that is not, in principle, linked to its production, as in Equation... 

Recently, many batch operations have been transformed into fed-batch (semicontinuous) operations by the gradual introduction of nutrient into the reactor. The rationale is to control the feed optimally to maximize a composite performance index. For the case of penicillin fermentation, for example, for which the specific growth rate and the specific penicillin formation rate are mutually disposed, the optimal feed policy is carried out in two phases. During the first phase, cell biomass is quickly built up to the allowable maximum level. During the second product formation phase, the feed is controlled such that... 

For the influence of the specific surface area of the semiconductor powder on the rate of product formation, two opposite effects are of major importance [81], One is concerned with the rate of electron-hole recombination, which increases linearly with surface area, and accordingly the reaction rate should decrease. The other is a linear increase of the IFET rate due to increasing concentration of adsorbed substrates per unit volume, which should also increase the product formation rate. It is therefore expected that, depending on the nature of semiconductor and substrates, the reaction rate, or p, may be constant, increase, or decrease with increasing surface area. This is nicely reflected by the CdS/Pt catalyzed photoreduction of water by a mixture of sodium sulfide and sulfite. The highest p values are observed at small surface areas and are constant up to 2 m /g. From there a linear decrease to almost zero at a specific surface area of 6 m /g takes... 

Control. A mechanism may be designed for control (regulation) of various functions control of concentrations (homeostasis), of rates, of specific product formation, of temperature, and so on. We shall see some examples later. 

Specific alterations of the relative reactivity due to hydrogen bonding in the transition state or to a cyclic transition state or to electrostatic attraction in quaternary compounds or protonated azines are included below (cf. also Sections II, B, 3 II, B, 5 II, C and II, F). A-Protonation is often reflected in an increase in JS and therefore the relative reactivity can vary with the significance of JS in controlling the reaction rate. Variation can also result from rate determination by the second stage of the SjjAr2 mechanism or from the intervention of thermodynamic control of product formation. Variation in the rate and in the reactivity pattern of polyazanaph-thalenes will result when nucleophilic substitution [Eq. (10)] occurs only on a covalent adduct (408) of the substrate rather than on its aromatic form (400). This covalent addition is prevented by any 4-... 

Rate of product formation, g-11 - h 1 j Specific growth rate, h 1... 

Measurements of overall reaction rates (of product formation or of reactant consumption) do not necessarily provide sufficient information to describe completely and unambiguously the kinetics of the constituent steps of a composite rate process. A nucleation and growth reaction, for example, is composed of the interlinked but distinct and different changes which lead to the initial generation and to the subsequent advance of the reaction interface. Quantitative kinetic analysis of yield—time data does not always lead to a unique reaction model but, in favourable systems, the rate parameters, considered with reference to quantitative microscopic measurements, can be identified with specific nucleation and growth steps. Microscopic examinations provide positive evidence for interpretation of shapes of fractional decomposition (a)—time curves. In reactions of solids, it is often convenient to consider separately the geometry of interface development and the chemical changes which occur within that zone of locally enhanced reactivity. 

Phenomenological evidence for the participation of ionic precursors in radiolytic product formation and the applicability of mass spectral information on fragmentation patterns and ion-molecule reactions to radiolysis conditions are reviewed. Specific application of the methods in the ethylene system indicates the formation of the primary ions, C2H4+, C2i/3+, and C2H2+, with yields of ca. 1.5, 1.0, and 0.8 ions/100 e.v., respectively. The primary ions form intermediate collision complexes with ethylene. Intermediates [C4iZ8 + ] and [CJH7 + ] are stable (<dissociation rate constants <107 sec.-1) and form C6 intermediates which dissociate rate constants <109 sec. l). The transmission coefficient for the third-order ion-molecule reactions appears to be less than 0.02, and such inefficient steps are held responsible for the absence of ionic polymerization. 

The cells can be grown at high dilution rates in the first fermenter, usually under the limitation of a growth substrate which triggers poly(3HB) synthesis, to obtain cells at the beginning of the poly(3HB) accumulation phase when entering the second fermenter. Product formation in the second vessel can then take place at high specific velocity. 

---