Solution polymerization process

A continuous solution polymerization process comprising:

• i) injecting ethylene, a process solvent, a single site catalyst formulation, optionally one or more α-olefins and optionally hydrogen into a first reactor to produce a first exit stream containing a first ethylene interpolymer in said process solvent;
• ii) passing said first exit stream into a second reactor and injecting into said second reactor, ethylene, said process solvent, a first heterogeneous catalyst formulation, optionally one or more α-olefins and optionally hydrogen to produce a second exit stream containing a second ethylene interpolymer and said first ethylene interpolymer in said process solvent;
• iii) passing said second exit stream into a third reactor and optionally injecting into said third reactor, ethylene, process solvent, one or more α-olefins, hydrogen and a second heterogeneous catalyst formulation to produce a third exit stream containing a third ethylene interpolymer, said second ethylene interpolymer and said first ethylene interpolymer in said process solvent;
• iv) phase separating said third exit stream to recover an ethylene interpolymer product comprising said first ethylene interpolymer, said second ethylene interpolymer and said third ethylene interpolymer;
• wherein said third reactor is a tubular reactor;
• wherein, the production rate is increased at least about 9% relative to a continuous solution polymerization process wherein said first heterogeneous catalyst formulation is replaced with said single site catalyst formulation, wherein production rate is measured in kilograms of said ethylene interpolymer product produced per hour;
• wherein said single site catalyst formulation comprises:
• a) a component (i) defined by the formula
• (LA)aM(PI)b(Q)n
• wherein LA is selected from the group consisting of unsubstituted cyclopentadienyl, substituted cyclopentadienyl, unsubstituted indenyl, substituted indenyl, unsubstituted fluorenyl and substituted fluorenyl;
• M is a metal selected from titanium, hafnium and zirconium;
• PI is a phosphinimine ligand;
• Q is independently selected from the group consisting of a hydrogen atom, a halogen atom, a C1-10 hydrocarbyl radical, a C1-10 alkoxy radical and a C5-10 aryl oxide radical;
• wherein each of said hydrocarbyl, alkoxy, and aryl oxide radicals may be unsubstituted or further substituted by a halogen atom, a C1-18 alkyl radical, a C1-8 alkoxy radical, a C6-10 aryl or aryloxy radical, an amido radical which is unsubstituted or substituted by up to two C1-8 alkyl radicals or a phosphido radical which is unsubstituted or substituted by up to two C1-8 alkyl radicals;
• wherein a is 1;
• b is 1;
• n is 1 or 2;
• and (a+b+n) is equivalent to the valence of the metal M;
• b) an alumoxane co-catalyst;
• c) an boron ionic activator, and;
• d) optionally, a hindered phenol;
• wherein said first and said second heterogeneous catalyst formulation comprises a metal compound defined by the formulas M(X)n or MO(X)n, wherein M is selected from the group comprising titanium, zirconium and hafnium, 0 represents oxygen, X represents chloride or bromide and n is an integer that satisfies the oxidation state of the metal M;
• and
• wherein the production rate, for comparison purposes, is determined using a continuous solution polymerization process using methylpentane as process solvent, reactors arranged in series, a first reactor volume of 3.2 gallons, a second reactor volume of 5.8 gallons, the third reactor being a tubular reactor having a volume of 0.58 gallons, the pressure in the first reactor of from about 14 MPa to about 18 MPa, the pressure in the second reactor being lower than the pressure in the first reactor, an average residence time of the solvent in the first reactor of about 61 seconds, an average residence time of the second reactor of about 73 seconds, an average residence time in the third reactor of about 7.3 seconds, and adjusting all other conditions to provide an ethylene interpolymer product having a melt index of about 1 (ASTM D1239, 2.16 kg load, 190° C.) and density of about 0.917 g/cm3 (ASTM D792).