Instantaneous conversion

STEAM EXPLOSION Ovetpressure associated with the rapid expansion in volume on instantaneous conversion of water to steam. 

In batch operations, mixing takes place until a desired composition or concentration of chemical products or solids/crystals is achieved. For continuous operation, the feed, intermediate, and exit streams will not necessarily be of the same composition, but the objective is for the end/exit stream to be of constant composition as a result of the blending, mixing, chemical reaction, solids suspension, gas dispension, or other operations of the process. Perfect mixing is rarely totally achieved, but represents the instantaneous conversion of the feed to the final bulk and exit composition (see Figure 5-26). 

Bauer et al. describe the use of a noncontact probe coupled by fiber optics to an FT-Raman system to measure the percentage of dry extractibles and styrene monomer in a styrene/butadiene latex emulsion polymerization reaction using PLS models [201]. Elizalde et al. have examined the use of Raman spectroscopy to monitor the emulsion polymerization of n-butyl acrylate with methyl methacrylate under starved, or low monomer [202], and with high soUds-content [203] conditions. In both cases, models could be built to predict multiple properties, including solids content, residual monomer, and cumulative copolymer composition. Another study compared reaction calorimetry and Raman spectroscopy for monitoring n-butyl acrylate/methyl methacrylate and for vinyl acetate/butyl acrylate, under conditions of normal and instantaneous conversion [204], Both techniques performed well for normal conversion conditions and for overall conversion estimate, but Raman spectroscopy was better at estimating free monomer concentration and instantaneous conversion rate. However, the authors also point out that in certain situations, alternative techniques such as calorimetry can be cheaper, faster, and often easier to maintain accurate models for than Raman spectroscopy, hi a subsequent article, Elizalde et al. found that updating calibration models after... 

The instantaneous conversion of each monomer was calculated from the amount of unreacted monomers determined by GC, which was found to be higher than 90% during the course of semi-continuous polymerization and to increase slightly as the polymerization proceeded. The ratio of instantaneous conversion between the two... 

Figure 2. Changes in conversion ratio CMma/CMaa during semicontinuous polymerization of MMA-MAA comonomer system (CMma) instantaneous conversion of MM A (C mm a) instantaneous conversion of MAA ((A) SP-28 (90/10) (d) SP-26 (85/15) (O) SP-27 (80/20))...

The other parameters are the same as for the FFB model. Similar to the FFB model, Equations 30-32 give the instantaneous conversion to obtain time averaged values, integration is required for X (Equation 23) and T ... 

Clearly, in cases in which only BH + or B is excited (and no instantaneous conversion takes place before the steady state is set up), (15) and (16) are considerably simplified by setting x0 = 0 or y0 = 0. In specific cases the use of justifiable simplifications about the magnitudes of the components of a and a can simplify the expressions still further. For example, if y0 = 0 and the pH is high enough for k2 to be very small compared with all the other rate... 

A number of aliphatic hydrazones (374) are slowly transformed into the solid hexahydro-1,2,4,5-tetrazines (375) when left at room temperature. Addition of acetic acid/acetate buffer (pH = 5.5) to the hydrazone causes almost instantaneous conversion of the hydrazone into the hexahydrotetrazine. This acceleration of the rate of dimerization suggests the intermediacy of a protonated hydrazone (376) (77TL3155, 73ACS779, 72TL949, 71AJC1859, 70TL2199,63 AG 1204). In acidic media there is an equilibrium between the hexahydrotetrazines and the hydrazones (70HCA251). The hydrazones (374) are also intermediates in the preparation of the hexahydrotetrazines from aldehydes and hydrazines. 

In general, silyl compounds present a contrast to their methyl analogues in that they more readily enter into reactions in which the respective group retains its identity. This is exemplified in the instantaneous conversion of the silyl halides by water into disilyl ether, and in their rapid reaction with silver salts. The principal causes of this reactivity are (i) the case with which the co-ordination number of the silicon atom rises from four to six ... 

Raw and filtered experimental data far the reforming of methanol. The jagged trace in each case is the result of calculating instantaneous conversion at each analysis. The smooth curves underlying the experimental data are the result ofapplying a ID filter to data from each run in turn. This leaves unsmoothed any errors between curves. Such errors can arise from flow controller inaccuracies, temperature variations and other causes and will lead to a bumpy conversion surface if left untreated... 

The instantaneous conversion of EG or any other organic to CO2 would be characterized by the absence of chemical intermediates in the anolyte and a linear conversion-time (CO2 evolution) curve. In such a case, conversion would increase linearly with time to a maximum of 100%. Contrary to expectations, nonlinearity (curvature) was found to be one of the most obvious features of actual conversion-time data. A simple model has been formulated to explain thisnonlinear behavior by taking into account the sequential oxidation of known and suspected chemical intermediates [13]. 

An excellent in situ preparation of diborane results from the reaction of boron trichloride (BCI3) or boron trifluoride (BF3) with sodium borohydride in the presence of alkenes, as shown above. This reagent gave virtually instantaneous conversion of an alkene to a trialkylborane at ambient temperatures, when done in a ether solvent. When diborane was isolated and purified it also reacted with alkenes, rapidly and quantitatively in ether solvents. 

As long as the potential is sufficiently positive (for oxidations) or negative (for reductions) to force the instantaneous conversion of analyte to product, then... 

It is possible that equilibrium morphology is not obtained because the movement of the polymer chains is not fast enough to reach that equilibrium within the time-frame of the reaction this is kinetic control of morphology. The kinetic parameters influence the rate of formation of a certain morphology [27, 28], which is basically determined by the interfacial tensions [29]. The parameters of importance are the rate of formation of the polymer (parameters are propagation rate coefficient, and the local monomer and radical concentrations) and the rate of diffusion of the polymer chains (parameters are viscosity in the locus of polymerization, molar mass and topology of the polymer chain). Both the rate of formation and the rate of diffusion of a polymer chain are, for example, affected by the mode of addition of the monomer and initiator. An increased rate of addition of the monomer will lead to a lower instantaneous conversion and thus a lower viscosity in the particle, which in turn increases the rates of diffusion and leads to different morphologies. 

In copolymerisations (70, 408), the copolymer composition may be controlled by the relative rates of monomer addition. In this way, any large differences in the comonomer reactivity ratios or water solubilities can be overcome to produce a copolymer with uniform composition. In order to maintain control of the monomer concentration in the polymer particles, the polymerisation may have to be performed under monomer-starved conditions. This means that the polymer particles are not saturated with monomer, but are being polymerised at an instantaneous conversion of 90% or greater. If the monomer addition rate is greater than the polymerisation rate, the reactor will be operating under flooded conditions, and control over the copolymer composition is lost. 

Chemical reactions take place by individual processes, each of which involves the almost instantaneous conversion of one or more molecules of reactant into one or more molecules of product. In order to predict the course of a chemical reaction, we need to be able to predict the way in which these basic conversions take place and the frequency with which they take place under any given set of conditions. 

In this work (41), a mathematical model was developed for co-pol3nnerization systems with different reactivity ratios based on the mass balances of the system and the assumption that the overall rates of monomer addition are smaller than the overall rates of polymerization in the corresponding batch polymerization the overall conversion was based on a curve-fitting method the instantaneous conversion and conversion at time were based on the mass balances of the system, which are related to the overall conversion. 

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