law of the polyreaction r p ¼ k p [C*][M], the quantity [C*] is a function of the two
equilibrium constants (K 1 and K 2 ) and the concentration of the charged components
(Ti and Al), i.e., [C*] ¼ f(K 1 , K 2 , [Ti] 0 , [Al] 0 ). Hence, we intensively concentrated
our experimental efforts on determining the exact conditions of the two equilibrium
steps, their thermodynamic data, and the detection of the kinetic sigmoid curve!
2.1 Kinetic Analysis by Means of a Half Continuous Stirred
Tank Reactor: Ethylene Polymerization with an In Situ
Start [11]
Figure 3 shows a flow chart of the polymerization plant with the injection system,
on-line registration of the polymerization rate, temperature course and pressure,
and the stirrer tachometer. The injection system allows the immediate in situ start
of the reaction, and the flow meters enable measurement of the true initial rates
(monomer consumption in dependence on time). With this very rapid technique it is
also possible to pursue strong unsteady polymerizations versus time courses.
Figure 4 shows the dependence of polymerization rates (v p ) on time; the third
parameter is the ratio Al/Ti, which is marked on the maxima of the curves. Note
the strong unsteady polymerization courses and the strong changes with increasing
Al concentration. The arrows in Fig. 4 identify that time (or rather interval)
from which the clear reaction solution becomes cloudy through precipitating
polyethylene. This precipitation divides the reaction into two phases: a homogeneous phase and a heterogeneous phase. The homogeneous initial part of Fig. 4
shows a significant behavior dependence on the ratio Al/Ti: the polyreaction
starts immediately and, the higher the ratio Al/Ti, the faster the initial rate
(intersection point with the ordinate).
Figure 5 demonstrates the kinetic evaluation of these results. On the lefthand side, the initial velocity v p (intersection points with the ordinate) is plotted
versus the concentration of the Al component while the Ti concentration was kept
constant. The result is the Al isothermal curve of the second equilibrium reaction
generating the active species. It demonstrates in the initial part the demanded
sigmoid curve course according to the location of the two successive equilibria.
This induction period is enlarged in Fig. 6. It can be clearly seen how sensitively
the initial polymerization rate responds to the ratio Al/Ti. With a ratio >1
(i.e., here [AlEtCl 2 ] > 3Â10
À3 mol L
À1 ), the formation of the active species
increases drastically.
Figure 5 additionally demonstrates on the right-hand side the kinetic counterexperiment. Again the initial polymerization rate is plotted, but now versus the
concentration of the titanium component while the Al concentration is kept constant.
The result is the Ti isothermal curve with the expected inverse characteristic.
The important message here is that if the active species is formed in only one
single equilibrium reaction, the course of the Ti isotherm has to show the same
Contributions to the Ziegler–Natta Catalysis: An Anthology
7
equilibrium constants (K 1 and K 2 ) and the concentration of the charged components
(Ti and Al), i.e., [C*] ¼ f(K 1 , K 2 , [Ti] 0 , [Al] 0 ). Hence, we intensively concentrated
our experimental efforts on determining the exact conditions of the two equilibrium
steps, their thermodynamic data, and the detection of the kinetic sigmoid curve!
2.1 Kinetic Analysis by Means of a Half Continuous Stirred
Tank Reactor: Ethylene Polymerization with an In Situ
Start [11]
Figure 3 shows a flow chart of the polymerization plant with the injection system,
on-line registration of the polymerization rate, temperature course and pressure,
and the stirrer tachometer. The injection system allows the immediate in situ start
of the reaction, and the flow meters enable measurement of the true initial rates
(monomer consumption in dependence on time). With this very rapid technique it is
also possible to pursue strong unsteady polymerizations versus time courses.
Figure 4 shows the dependence of polymerization rates (v p ) on time; the third
parameter is the ratio Al/Ti, which is marked on the maxima of the curves. Note
the strong unsteady polymerization courses and the strong changes with increasing
Al concentration. The arrows in Fig. 4 identify that time (or rather interval)
from which the clear reaction solution becomes cloudy through precipitating
polyethylene. This precipitation divides the reaction into two phases: a homogeneous phase and a heterogeneous phase. The homogeneous initial part of Fig. 4
shows a significant behavior dependence on the ratio Al/Ti: the polyreaction
starts immediately and, the higher the ratio Al/Ti, the faster the initial rate
(intersection point with the ordinate).
Figure 5 demonstrates the kinetic evaluation of these results. On the lefthand side, the initial velocity v p (intersection points with the ordinate) is plotted
versus the concentration of the Al component while the Ti concentration was kept
constant. The result is the Al isothermal curve of the second equilibrium reaction
generating the active species. It demonstrates in the initial part the demanded
sigmoid curve course according to the location of the two successive equilibria.
This induction period is enlarged in Fig. 6. It can be clearly seen how sensitively
the initial polymerization rate responds to the ratio Al/Ti. With a ratio >1
(i.e., here [AlEtCl 2 ] > 3Â10
À3 mol L
À1 ), the formation of the active species
increases drastically.
Figure 5 additionally demonstrates on the right-hand side the kinetic counterexperiment. Again the initial polymerization rate is plotted, but now versus the
concentration of the titanium component while the Al concentration is kept constant.
The result is the Ti isothermal curve with the expected inverse characteristic.
The important message here is that if the active species is formed in only one
single equilibrium reaction, the course of the Ti isotherm has to show the same
Contributions to the Ziegler–Natta Catalysis: An Anthology
7