Time-average synthesis rate

As the period increases, the time-average synthesis rate falls towards the space-mean, quasi steady state value as expected. At large periods, the steady state is approached in each portion of the cycle. The quasi-steady state line in... 

Figure 3 was calculated from steady-state measurements. Curvature of the rate vs composition relation causes the quasi steady-state rate to be well below the steady-state reactor performance. This emphasizes the very large effect of cycling frequency on the time average synthesis rate. 

The effect of feed composition cycling on the time-average rate and temperature profile was explored in the region of integral conversion in a laboratory fixed bed ammonia synthesis reactor. Experiments were carried out at 400°C and 2.38 MPa over 40/50 US mesh catalyst particles. The effect of various cycling parameters, such as cycle-period, cycle-split, and the mean composition, on the improvement in time-average rate over the steady state were investigated. 

Monomer concentrations Ma a=, ...,m) in a reaction system have no time to alter during the period of formation of every macromolecule so that the propagation of any copolymer chain occurs under fixed external conditions. This permits one to calculate the statistical characteristics of the products of copolymerization under specified values Ma and then to average all these instantaneous characteristics with allowance for the drift of monomer concentrations during the synthesis. Such a two-stage procedure of calculation, where first statistical problems are solved before dealing with dynamic ones, is exclusively predetermined by the very specificity of free-radical copolymerization and does not depend on the kinetic model chosen. The latter gives the explicit dependencies of the instantaneous statistical characteristics on monomers concentrations and the rate constants of the elementary reactions. 

The reaction conditions are constrained. In other words, there is usually a strict upper and lower limit for each reaction parameter. In the case of the synthesis described above, for example, the lower temperature is set by the need to provide sufficient thermal energy to initiate the reaction and the upper temperature by the need to remain below the decomposition temperature of the glue (see Section 2). The lower and upper limits on the total flow rate meanwhile are determined, respectively, by the maximum length of time one is prepared to allow for a single reaction and the minimum reaction time needed to produce crystals of nanometer dimensions. In this work, we select minimum and maximum total flow rates of 2 and 40 il min 1 which, for the typical chip volumes we use ( 16.6 il), correspond to average residence times of about 500 and 25 s, respectively. 

In a continuation of some studies on acyl migrations in model compounds related to aminoacyl-S-RNA, a technique has been developed using NMR to determine the rate of acyl migration in some 3 -0-acyl ribonucleo-sides. It was estimated that the half-time of equilibration into 2 and 3 -isomers of an averag e aminoacyl-S-RNA derivative in H 7 buffer at 37° is 2 X 10 sec. It was concluded that equilibration of an average aminoacyl-S-RNA would most likely be much faster than peptide bond synthesis. 

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