Rate-determining step, pressure effects, high

For several of these ligands the reaction is first order in ethene and thus it was suggested that the insertion of ethene in the titanacyclopentane ring is the rate-determining step, as was also found for the triazacyclohexane catalyst [13], Turnover numbers of the titanium catalyst are very high, but since some of the chromium catalysts have a second order dependency in ethene a comparison cannot be made at higher pressure these chromium catalysts will be more effective [7,17],... 

In kinetically labile simple systems it may be assumed that the regularity reflected by the above examples (i.e., that the rate-determining step is the solvent substitution) is of fairly general validity. The high rates of most of these reactions make their investigation difficult this is the reason why reliable experimental data have become available for the interpretation of the solvent effect in this field only since the spreading of the fast kinetic methods (stopped flow, T-jump, pressure jump, etc.). 

At high pressure and with some ammonia in the gas, the effect is to have only one rate-determining step. Figure 28.6 gives some indication of the production rate as a function of pressure. Most systems are designed for 2000 to 5000 psi. 

The value of the monomer partition coefBcient between the CO2 and the water phase indirectly determines the ratio between the effect of enhanced polymerization and the effect of extraction on the reduction of residual monomer. Depending on the process conditions, i.e. temperature, pressure, and the phase behavior of the system involved, this ratio between enhanced polymerization and extraction may vary for different latex systems. With respect to the PMMA latex, the high partition coefBcient m2 as shown in Section 14.4, causes extraction to be the predominant effect as compared to conversion of the monomer. Therefore, a preliminary process design has been developed based on C02-extraction. For this purpose, a mass transfer model has been set up to determine the rate-limiting step in the extraction process. In addition, a process flow diagram, including equipment sizing has been developed. Finally, an economic evaluation has been performed to study the viability of this technique for the removal of residual monomer from latex-products. 

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