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US005959044A [ii] Patent Number: 5,959,044  Date of Patent: *Sep. 28,1999
 METHOD OF CONTROLLING CONTINUOUS ETHYLENE-LIMITED METALLOCENECATALYZED COPOLYMERIZATION SYSTEMS
 Inventor: Juan Carlos Villar, 36 Martin La., Westbury, N.Y. 11590
[ * ] Notice: This patent issued on a continued prosecution application filed under 37 CFR 1.53(d), and is subject to the twenty year patent term provisions of 35 U.S.C. 154(a)(2).
 Appl. No.: 08/676,720  Filed: Jul. 8, 1996
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Primary Examiner—David W. Wu  ABSTRACT
A process for continuously producing copolymer comprising moieties derived from ethylene and an a-olefin in the presence of a metallocene catalyst system, said process comprising continuously supplying into a liquid-phase reaction zone a feed of ethylene, a feed of liquefied a-olefin, a feed of diluent, a feed of metallocene catalyst system, and continuously drawing out a reactor effluent produced thereby; and in accordance with a procedure comprising (a) setting the rate of metallocene system feed to a fixed molar rate; (b) introducing said ethylene feed at a fixed rate as required to produce the desired molar quantity of copolymer product per unit time; (c) setting the total rate of all feeds and the volume of said liquid-phase reaction zone to a fixed residence time, said residence no less than the minimum required to substantially eliminate molecular ethylene from said effluent; (d) performing an isokathic adjustment of the ethylene/a-olefin ratio of said feeds so as to produce product containing the desired ratio of ethylene to a-olefin moieties; and (e) adjusting the reaction zone temperature so as to produce copolymer of the desired molecular weight. The process of the invention described herein is particularly suited to in-line analysis of molecular weight and composition by virtue of the relationship
wherein -d[E]/dt is the total rate at which ethylene concentration vanishes from said reaction zone by reason of incorporation into said copolymer product, [Ef] is the concentration of ethylene in the total feed, and x-1 is the inverse of said residence time.
20 Claims, 1 Drawing Sheet
METHOD OF CONTROLLING CONTINUOUS ETHYLENE-LIMITED METALLOCENECATALYZED COPOLYMERIZATION SYSTEMS
BACKGROUND OF THE INVENTION
The present invention relates to a method of controlling metallocene-catalyzed continuous processes for the copolymerization of olefins in the solution-phase, that is to say systems that utilize diluent.
More particularly, this invention relates to continuous systems in which all ethylene entering the reactor vessel is consumed in the copolymerization reactions therein. Such systems are herein referred to as efhylene-limited copolymerizations because the flow of ethylene into the reactor is limiting to all reaction mechanisms that consume molecular ethylene.
DESCRIPTION OF THE RELATED ART
In continuous solution copolymerizations, the molecular weight and composition of the product can vary quite broadly, even unpredictably, depending on the reaction parameters, namely the concentration of the individual reactants in the total feed, the nature of the catalyst system employed, the catalyst concentration, the residence time, and the reaction temperature. In efhylene-limited systems as described herein, the relationship between the reaction parameters and the copolymer properties can even appear chaotic. Application of traditional theory can result in meaningless calculations, such as negative reaction rates. When the practitioner changes a reaction parameter in an attempt to alter a particular product property, he usually finds that multiple product properties are altered. The industry has generally avoided solution-phase copolymerizations in favor of gas phase and high pressure pure feed systems.
It is an object of this invention to provide a method for controlling the properties of ethylene/a-olefin produced by efhylene-limited continuous copolymerizations in the solution phase.
SUMMARY OF THE INVENTION
Disclosed herein is a method of controlling an efhylenelimited metallocene-catalyzed olefin copolymerization system. Such a system is characterized as a process for continuously producing copolymer of monomer moieties derived from ethylene and an a-olefin in the presence of a metallocene catalyst system and in a liquid-phase reaction zone by supplying a continuous monomer feed or feeds comprising ethylene, at least one a-olefin, a diluent, and a metallocene catalyst system into the liquid-phase reaction zone of a reactor under conditions effective in producing a copolymer product while continuously withdrawing the copolymer produced from the reactor. Such a system is further characterized in that the actual mechanical introduction of ethylene feed into the reaction zone is the ratelimiting step for all reactions within the reaction zone that consume ethylene. Efhylene-limited systems can be identified by the absence of ethylene in the reactor effluent.
The method of the present invention comprises (a) setting the rate of metallocene system feed to a fixed molar rate; (b) introducing said ethylene stream at a fixed rate as required to produce the desired molar quantity of copolymer product per unit time; (c) setting the total rate of all feeds and the volume of said liquid reaction zone to a fixed residence time, said residence no less than the minimum required to com
pletely eliminate molecular ethylene from said effluent stream; (d) performing an isokathic adjustment of the ethylene/a-olefin ratio of said total feed streams so as to produce product containing the desired ratio of ethylene to a-olefin moieties; and (e) adjusting the reaction zone temperature so as to produce copolymer of the desired molecular weight.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram of a boiler reactor embodiment of the present invention.
DETAILED DESCRIPTION OF THE
Disclosed herein is a method of continuous production of copolymer comprising moieties derived from ethylene and an a-olefin in the presence of a metallocene catalyst system, said process comprising continuously supplying into a liquid-phase reaction zone a feed of ethylene, a feed of liquefied a-olefin, a feed of diluent, a feed of metallocene catalyst system, and continuously drawing out a reactor effluent produced thereby; and in accordance with a procedure comprising:
a) setting the rate of metallocene system feed to a fixed molar rate;
b) introducing said ethylene stream at a fixed rate as required to produce the desired molar quantity of copolymer product per unit time;
c) setting the total rate of all feeds and the volume of said liquid reaction zone to a fixed residence time, said residence no less than the minimum required to completely eliminate molecular ethylene from said effluent stream;
d) performing an isokathic adjustment of the ethylene/aolefin ratio of said total feed streams so as to produce product containing the desired ratio of ethylene to a-olefin moieties; and
e) adjusting the reaction zone temperature so as to produce copolymer of the desired molecular weight.
The traditional theory set forth herein is derived from Odian, Principles of Polymerization, John Wiley & Sons (3rd Ed. 1991), the relevant contents of which are incorporated herein by reference.
The composition of a copolymer is always almost different than, though dependent upon, the composition of the reaction feed. In calculation fractions of monomers A and B in the final product, we follow the traditional approach in assuming four reaction mechanisms, each having a rate constant dependent upon the terminal moiety at the propagating end of the growing copolymer chain and upon the identity of the monomer:
The rates of disappearance of the monomers from the molecular weight of the incorporated monomers. The propareaction mixture are given by: gation rate is the rate at which monomer moieties are added
to the growing copolymer chain. The initiation rate is the rate at which copolymer growth is terminated. The ratio -3[A]/3f=*1JA»][A]+A21[fl»IA] (2a) 5 jyR. yields the degree of polymerization, Xn, from which
the number average molecular weight is easily derived if the composition of the copolymer is known. A steady-state assumption is made that the rates of Initiation
teady-state assumption is made that the rates of interconversion are equal: The initiation rate is traditionally given by
k21[B*\A\=k12[A*JB] (3) ^-[^Ffei+IBKftfl (9)
and a pair of parameters and r2 are defined, such that: where W is the concentration of catalyst, or initiator, I The
equation represents the total sum of the rates at which the monomers join with catalyst to initiate new propagating chains. At equilibrium, the initiation rate is equal to the termination rate—the rate at which growing copolymer Dividing equations (2a) and (2b) and substituting (3) and chains terminate their growth, either through side reactions (4) into the result obtains: 20 or ^ the 1uench used to halt ^polymerization in the
n =kn/kl2 r2 = k22/k2l (4)
The degree of polymerization, Xn, is obtained by dividing the propagation rate by the initiation rate:
MWWMMiiJWW^ (5) where SR is the molar ratio of the monomer moieties (i.e.,
the composition) of the final product, equal to the relative 9c „ _ ,,r.lrn, ,nT„, .
rates of incorporation of the two monomers. Ihe equation
can be rearranged in linear form as: The average number molecular weight is then given by:
or expressed as the mole fraction, FA or FB, of monomer in where MWA and MWB are the molecular weights of each the final product' individual moiety of A and B, respectively.
rdA]2 + 2[A][B] + r2[B]2 This invention relates to the special case of ethylene
limited copolymerizations, that is, copolymerizations in which all molecular ethylene entering the reaction zone is r2[B]2 + [A][B] completely consumed in the process of copolymerization
B ~ n[A]2 +2[A][B] + r2[B]2 40 such that none survives to appear in the reactor effluent.
Ethylene-limited continuous copolymerizations are therefore easily assayed by the absence of unreacted ethylene in By executing successive runs of the copolymerization the reactor effluent> that is to say that [EoiJ=0, where [EOIJ reaction at constant temperature, the parameters 9t, [A], and is the concentration of ethylene in the reactor effluent. Of [B] may be measured experimentally and the values and course> with sophisticated enough equipment, one may well r2 derived by linear regression or other statistical analysis. detect insignificantly small quantities of molecular ethylene Several sets of such analysis executed at varying tempera- m the effluent, but this is not significant to the invention and, tares will permit experimental derivation of the temperature for the purposes 0f this invention, "absence" of ethylene in dependencies of r1 and r2 through an additional application the effluent comprises a substantial absence of such ethylof linear regressions using the equations: ^ ene what is significant is that the rate-limiting step for all
reaction mechanisms that consume molecular ethylene is the rate at which ethylene is actually introduced into the reaction zone. Reaction rates are traditionally reported in the rate of ln(r2)=ln(K2)-E2iRT (7b) change of concentration of a reactant with respect to time. If,
55 then, [Ey] is the concentration of ethylene in moles/liter in where T is the absolute temperature in degrees Kelvin, R is the feed stream and <£ is the flow rate, or volumetric flux, of the Universal Gas Constant, Et is the sum of the Arrhenius the feed stream in liters/second, then [Ey]<P is the rate in activation energies for equations (la) and (lb), E2 is the sum moles/second that ethylene enters the reaction vessel. If the of the Arrhenius activation energies for equations (lc) and volume of the reaction zone is given to be V, then the rate (Id), and Kt and K2 are constants. A regression analysis m of change per unit time of the ethylene concentration in the yields the E and K values as the slopes and intercepts, reaction zone attributable to the feed is given by: respectively.
Molecular Weight -a^at^Ef&lv^Efc-1 (12)
The number average molecular weight, Mn, of a copoly- 65 wherein -d[E]/dt is the rate at which ethylene concentration mer may be expressed as the ratio of the propagation rate, vanishes from the reaction zone by reason of incorporation R^, to the initiation rate, R;, multiplied by the average into copolymer product, [Ef] is the concentration of ethylene