Patent Description:
This disclosure relates to a method for α-olefin isomerization reduction during polymerization and to a system for accomplishing the same. In particular, this disclosure relates to a method for isomerization reduction during the production of polyolefins.

Alpha olefins (such as, for example, <NUM>-octene, <NUM>-hexene, and <NUM>-butene) are copolymerized with ethylene to manufacture a polyethylene copolymer. <FIG> is a depiction of an exemplary process <NUM> that is presently used for producing a polyethylene copolymer that contains ethylene and octene. The process <NUM> utilizes a reactor <NUM> into which reactants such as hydrogen, ethylene, octene, catalyst and solvent are added. During the reaction a portion of the octene added to the reactor is polymerized with the ethylene to form the copolymer which is then discharged along with any unreacted monomers and comonomers in a product stream to a heat exchanger <NUM> and a devolatilizer <NUM>. Only the <NUM>-octene isomer (instead of other isomeric forms) participates in the polymerization reaction.

A heat exchanger (HE) <NUM> disposed downstream of the reactor increases the temperature of the product stream before entering the devolatilizer <NUM>. However, during the heating step, the isomerization of octene results in the formation of <NUM>-octene, <NUM>-octene and <NUM>-octene isomers that are inert to the polymerization process. Water is added to the product stream upstream of the heat exchanger <NUM> and an anti-oxidant is added to the product stream downstream of the heat exchanger <NUM>. A devolatilizer <NUM> disposed downstream of the heat exchanger <NUM> removes any unreacted ethylene, solvent or octene and recycles it to the reactor <NUM> to undergo further polymerization. The isomerization of octene to <NUM>-octene, <NUM>-octene and <NUM>-octene isomers is undesirable because it reduces the yield of the copolymer.

It is therefore desirable to retain the octene in its <NUM>-octene isomeric form during the production of the polyethylene copolymer.

In a first aspect the invention is a method for reducing isomerization during the copolymerization of ethylene with an α-olefin comprising adding to a reactor a reaction mixture comprising hydrogen, ethylene, an α-olefin, a solvent and a catalyst; where the catalyst does not include a chain shuttling agent that comprises dialkyl zinc; where the reactor is operated at a temperature of <NUM> to <NUM>; heating the reactor to a first temperature to react the ethylene with the α-olefin to form a copolymer; discharging from the reactor a first product stream to a heat exchanger; where the product stream comprises the copolymer; adding to the product stream prior to the heat exchanger a first additive that is operative to reduce isomerization of the α-olefin; and discharging from the heat exchanger a second product stream; where the heat exchanger is operated at a higher temperature than the reactor; wherein the first additive is selected from the group consisting of aromatic species having one or more hydroxyl functionalities, amines, fluoropolymers, phosphates, fatty acids, salts of fatty acids, esters of fatty acids, or a combination thereof; and wherein the amines include primary amines, secondary amines, tertiary amines, cyclic amines, hindered amines or a combination thereof; and where a temperature of the second product stream is higher than a temperature of the first product stream.

In a further aspect there is provided the method of claim <NUM>.

Disclosed herein too is a method for reducing isomerization during the copolymerization of ethylene with <NUM>-octene comprising adding to a reactor a reaction mixture comprising hydrogen, ethylene, an α-olefin, a solvent, a first additive and a catalyst; where the catalyst does not include a chain shuttling agent that comprises dialkyl zinc; and where the first additive is operative to reduce isomerization of the α-olefin; heating the reactor to a first temperature to react the ethylene with the α-olefin to form a copolymer; discharging from the reactor a first product stream to a heat exchanger; where the product stream comprises the copolymer; and discharging from the heat exchanger a second product stream.

Disclosed herein too is a system comprising a reactor that is operative to react a reaction mixture comprising hydrogen, ethylene, a solvent, an α-olefin, and a catalyst to form a polyethylene copolymer; where the catalyst does not include a chain shuttling agent that comprises dialkyl zinc; and a heat exchanger that is operative to receive a product stream containing the polyethylene copolymer from the reactor in addition to receiving an additive that is operative to reduce isomerization of the α-olefin.

Disclosed herein too is a system comprising a reactor that is operative to react a reaction mixture comprising hydrogen, ethylene, a solvent, an α-olefin, an additive and a catalyst to form a polyethylene copolymer; where the catalyst does not include a chain shuttling agent that comprises dialkyl zinc; and where the additive is operative to reduce isomerization of the α-olefin; and a heat exchanger that is operative to receive a product stream containing the polyethylene copolymer from the reactor.

Disclosed herein is a method for reducing the amount of isomerization of α-olefins that occur during the polymerization with ethylene to produce and ethylene copolymer. More specifically, disclosed herein is a method for reducing the amount of octene that is converted into <NUM>-octene, <NUM>-octene and <NUM>-octene obtained during the production of a polyethylene copolymer. The method comprises adding an additive upstream of the reactor and/or upstream of the heat exchanger that reduces octene isomerization and hydrogenation. The additive is added upstream of the heat exchanger and downstream of the reactor to reduce the isomerization of the α-olefin during the manufacturing of the ethylene copolymer.

<FIG> is a depiction of an exemplary embodiment of a process <NUM> for reducing the amount of undesirable α-olefin isomers. The system <NUM> comprises a reactor <NUM> that is operative to receive reactants that produce a polyethylene copolymer. The reactants are hydrogen, ethylene, an α-olefin, a catalyst and a solvent. The catalyst is a molecular catalyst that does not include a chain shuttling agent that comprises zinc. The catalyst is a molecular catalyst that does not include a chain shuttling agent that comprises dialkyl zinc.

A first additive that is operative to minimize isomerization of the α-olefin is also added to the reactor <NUM>. The system <NUM> further comprises a heat exchanger (HE) <NUM> and a devolatilizer <NUM> both of which lie downstream of the reactor <NUM> and are in fluid communication with the reactor <NUM>. The heat exchanger <NUM> is operated at a higher temperature than the reactor <NUM>. The devolatilizer <NUM> lies downstream of the heat exchanger <NUM> and is in fluid communication with it. The heat exchanger <NUM> receives a first product stream that comprises a copolymer of ethylene and α-olefin along with unreacted reactants and other byproducts from the reactor <NUM>.

Water and a second additive are added downstream of the reactor <NUM> and upstream of the heat exchanger <NUM>. The second additive is operative to reduce isomerization of the α-olefin during the heating in the heat exchanger <NUM>. The devolatilizer <NUM> receives a second product stream from the heat exchanger. The term "second product stream" is used to distinguish the "first product stream" from the "second product stream" and is not meant to indicate that the devolatilizer <NUM> receives two product streams from the heat exchanger <NUM>. As noted above, the temperature of the product stream leaving the heat exchanger <NUM> is greater than the temperature of the product stream entering the heat exchanger <NUM>.

In an embodiment, the first additive may be the same as the second additive or different from it. Both the first additive and the second additive reduce isomerization of the α-olefin during the polymerization process.

In an embodiment, a third additive may be added downstream of the heat exchanger <NUM>. The third additive may be the same or different from the first additive and the second additive. In an embodiment, the first additive, the second additive and the third additive are the same additive and function to reduce isomerization of the α-olefin during the polymerization process.

The α-olefins that undergo isomerization in the absence of the additive are <NUM>-butene, <NUM>-hexene, <NUM>-octene, <NUM>-decene, <NUM>-dodecene, <NUM>-tetradecene, <NUM>-hexadecene, <NUM>-octadecene, or a combination thereof. In an embodiment, a preferred α-olefin is <NUM>-octene.

It is desirable for the additives that are added to the reactor <NUM> and the heat exchanger <NUM> to comprise moieties that reduce isomerization of the α-olefins during the polymerization process. Examples of such moieties are hydroxyls, amines, carboxylic acids, esters of carboxylic acids, phosphates, fluorine, or a combination thereof. Preferred additives that may be added to the reactor and/or to the product stream prior to or after the heat exchanger are aromatic species having one or more hydroxyl functionalities, amines (e.g., primary amines, secondary amines, tertiary amines, cyclic amines, and hindered amines), fluoropolymers, fatty acids (e.g., stearic acids), salts of fatty acids (e.g., stearates), esters of fatty acids, or a combination thereof. It is desirable for the additives to avoid catalyst deactivation and participating in the polymerization of the ethylene with the α-olefins and thus becoming part of the copolymer.

Aromatic species having one or more hydroxyl functionalities may be used as the additive. Aromatic species having the following structure shown in the formula (<NUM>) can be used:
<CHM>
where one or more of R<NUM> through R<NUM> is a hydroxyl group, with the remainder of R<NUM> through R<NUM> being independently a hydrogen, a substituted or unsubstituted C<NUM> - C<NUM> alkyl group, a substituted or unsubstituted C<NUM> - C<NUM> cycloalkyl group, a substituted or unsubstituted C<NUM> - C<NUM> ester group, or a halogen group.

Examples or the aromatic species of the formula (<NUM>) that may be used as the additive are phenol, dihydroxybenzene (e.g., catechol, resorcinol and hydroquinone), trihydroxybenzene (e.g., hydroxyquinol, phloroglucinol, and pyrogallol), tetrahydroxybenzene (e.g., benzenetetrol), alkylphenol (e.g., cresols, xylenols, propylphenol, butylphenol, amylphenol, heptylphenol, octylphenol, nonylphenol, dodecylphenol and related "long chain alkylphenols" (LCAPs)), or a combination thereof.

Bisphenol-type dihydroxy aromatic compounds may also be used as the additive and may include some of the following: <NUM>,<NUM>'-dihydroxybiphenyl, <NUM>,<NUM>-dihydroxynaphthalene, <NUM>,<NUM>-dihydroxynaphthalene, bis(<NUM>-hydroxyphenyl)methane, bis(<NUM>-hydroxyphenyl)diphenylmethane, <NUM>,<NUM>-bis(<NUM>-hydroxyphenyl)ethane, <NUM>-(<NUM>-hydroxyphenyl)-<NUM>-(<NUM>-hydroxyphenyl)propane, bis(<NUM>-hydroxyphenyl)phenylmethane, <NUM>,<NUM>-bis(<NUM>-hydroxy-<NUM>-bromophenyl)propane, <NUM>,<NUM>-bis(hydroxyphenyl)cyclopentane, <NUM>,<NUM>-bis(<NUM>-hydroxyphenyl)cyclohexane, <NUM>,<NUM>-bis(<NUM>-hydroxyphenyl)isobutene, <NUM>,<NUM>-bis(<NUM>-hydroxyphenyl)cyclododecane, trans-<NUM>,<NUM>-bis(<NUM>-hydroxyphenyl)-<NUM>-butene, <NUM>,<NUM>-bis(<NUM>-hydroxyphenyl)adamantine, (alpha, alpha'-bis(<NUM>-hydroxyphenyl)toluene, bis(<NUM>-hydroxyphenyl)acetonitrile, <NUM>,<NUM>-bis(<NUM>-methyl-<NUM>-hydroxyphenyl)propane, <NUM>,<NUM>-bis(<NUM>-ethyl-<NUM>-hydroxyphenyl)propane, <NUM>,<NUM>-bis(<NUM>-n-propyl-<NUM>-hydroxyphenyl)propane, <NUM>,<NUM>-bis(<NUM>-isopropyl-<NUM>-hydroxyphenyl)propane, <NUM>,<NUM>-bis(<NUM>-sec-butyl-<NUM>-hydroxyphenyl)propane, <NUM>,<NUM>-bis(<NUM>-t-butyl-<NUM>-hydroxyphenyl)propane, <NUM>,<NUM>-bis(<NUM>-cyclohexyl-<NUM>-hydroxyphenyl)propane, <NUM>,<NUM>-bis(<NUM>-allyl-<NUM>-hydroxyphenyl)propane, <NUM>,<NUM>-bis(<NUM>-methoxy-<NUM>-hydroxyphenyl)propane, <NUM>,<NUM>-bis(<NUM>-hydroxyphenyl)hexafluoropropane, <NUM>,<NUM>-dichloro-<NUM>,<NUM>-bis(<NUM>-hydroxyphenyl)ethylene, <NUM>,<NUM>-dibromo-<NUM>,<NUM>-bis(<NUM>-hydroxyphenyl)ethylene, <NUM>,<NUM>-dichloro-<NUM>,<NUM>-bis(<NUM>-phenoxy-<NUM>-hydroxyphenyl)ethylene, <NUM>,<NUM>'-dihydroxybenzophenone, or a combination comprising at least one of the foregoing dihydroxy aromatic compounds.

Exemplary phenols are Irganox <NUM> commercially available from BASF and IRGANOX <NUM> commercially available from Ciba.

Primary amines have one of three hydrogen atoms in ammonia is replaced by an alkyl or aromatic. Examples of primary amines include methylamine, ethanolamine, octylamine, aniline, or a combination thereof.

Secondary amines have two organic substituents (alkyl, aryl or both) bound to the nitrogen atom of ammonia together with one hydrogen (or no hydrogen if one of the substituent bonds is a double bond). Examples of secondary amines include dimethylamine and methylethanolamine, diphenylamine, or a combination thereof.

In tertiary amines, all three hydrogen atoms are replaced by organic substituents. Examples include trimethylamine, triphenylamine, trioctylamine, or a combination thereof.

Cyclic amines are either secondary or tertiary amines. Examples of cyclic amines include the <NUM>-member ring aziridine and the six-membered ring piperidine. N-methylpiperidine and N-phenylpiperidine are examples of cyclic tertiary amines.

Some of the aromatic secondary and tertiary amines listed above are termed hindered amines. Examples of hindered amines are n,n'-bis(<NUM>,<NUM>-dimethylpentyl-p-phenylenediamine), alkylated diphenylamines, <NUM>,<NUM>'-bis(alpha, alphadimethylbenzyl)diphenylamine, diphenyl-p-phenylenediamine, mixed di-aryl-p-phenylenediamines, <NUM>,<NUM>-bis(dimethylamino)naphthalene, N',N',N',N'-tetramethyl-<NUM>,<NUM>-naphthalenediamiine, or a combination thereof. Examples of hindered amines are CHIMASSORB <NUM>, CHIMASSORB <NUM>, CHIMASSORB <NUM>, and CGL <NUM> commercially available from BASF Plastic Additives.

Additives that comprise carboxylic acid functional groups are useful for reducing the isomerization. Fatty acids are a useful group of additives for use in the reactor and/or in the heat exchanger. A fatty acid is a carboxylic acid with a long aliphatic tail (chain), which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from <NUM> to <NUM>. Examples of saturated fatty acids are caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, or a combination thereof. Examples of unsaturated fatty acids are myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linoelaidic acid, arachidonic acid, eicosapentaenoic acid, erucic acid, docosahexaenoic acid, or a combination thereof. Without being limited to theory, the carboxylic acid groups present in the fatty acids can reduce isomerization of the α-olefin in the heat exchanger. A preferred fatty acid for use in minimizing isomerization of α-olefins is stearic acid.

Salts and esters of fatty acids may also be used as additives. Fatty acid salts of Group I and II metals are useful for reducing isomerization of the α-olefins. Preferred salts of fatty acids are lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba) salts, or a combination thereof.

Potassium, sodium, calcium and magnesium salts of the fatty acids are more preferred. In an embodiment, potassium, sodium, calcium and magnesium salts of stearic acid are preferred. Sodium stearate, potassium stearate, magnesium stearate, calcium stearate or a combination thereof are especially preferred as additives for minimizing the isomerization of α-olefins. Preferred esters of fatty esters are fatty acid alkyl esters. Fatty acid methyl esters and fatty acid ethyl esters are preferred.

Fluoropolymers may also be used as additives for minimizing the isomerization of α-olefins. Examples of fluoropolymers are polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, polyhexafluoropropylene, polyperfluoropropylvinylether, polyperfluoromethylvinylether, or a combination thereof. The fluoropolymers may be homopolymers, block copolymers, random copolymers, star block copolymers, alternating copolymers, or combinations thereof. Combinations of the foregoing fluoropolymers can include blends of the fluoropolymers that are not reactively bonded to each other.

The fluoropolymers have weight average molecular weights (Mw) of <NUM> to <NUM>,<NUM>, preferably <NUM>,<NUM> to <NUM>,<NUM> and more preferably <NUM>,<NUM> to <NUM>,<NUM> grams per mole (g/mole). An exemplary commercially available fluoropolymer is DYNAMAR 5920A commercially available from <NUM> Advanced Materials.

Phosphates may also be used as an additive to reduce isomerization. Phosphates are salts of phosphoric acid H<NUM>PO<NUM>.

Phosphate salts having the structure of formula (<NUM>) may be used
<CHM>.

In an embodiment, in the formula (<NUM>), two of the R groups (i.e., any two of R<NUM>, R<NUM> or R<NUM>) and may be joined together to provide a cyclic group, for example, diphenyl pentaerythritol diphosphate. Other suitable phosphates can be aromatic phosphates, such as, for example, phenyl bis(dodecyl)phosphate, phenyl bis(neopentyl)phosphate, phenyl bis(<NUM>,<NUM>,<NUM>'-trimethylhexyl)phosphate, ethyl diphenyl phosphate, <NUM>-ethylhexyl di(p-tolyl)phosphate, bis(<NUM>-ethylhexyl)p-tolyl phosphate, tritolyl phosphate, bis(<NUM>-ethylhexyl)phenyl phosphate, tri(nonylphenyl)phosphate, bis(dodecyl)p-tolyl phosphate, dibutyl phenyl phosphate, <NUM>-chloroethyl diphenyl phosphate, p-tolyl bis(<NUM>,<NUM>,<NUM>'-trimethylhexyl)phosphate, or <NUM>-ethylhexyl diphenyl phosphate.

Polymeric phosphates can also be used as additives. Di- or polyfunctional aromatic phosphorus-containing compounds are also useful, for example, compounds of the formulas below:
<CHM>
<CHM>
or
<CHM>
wherein each R<NUM> is a hydroxyl, a hydrocarbon having <NUM> to <NUM> carbon atoms; a hydrocarbonoxy having <NUM> to <NUM> carbon atoms and n is <NUM> to <NUM>. Examples of suitable di- or polyfunctional aromatic phosphorus-containing compounds include the bis(diphenyl) phosphate of hydroquinone and the bis(diphenyl)phosphate of bisphenol-A ( and respectively, their oligomeric and polymeric counterparts, or a combination thereof.

The additives can be added in amounts of up to <NUM>,<NUM> parts per million (ppm), preferably <NUM> to <NUM>,<NUM> ppm and more preferably <NUM> to <NUM>,<NUM> ppm based on a total weight of the copolymer manufactured.

In order to manufacture a copolymer of ethylene and α-olefin at a high yield, reactants such as hydrogen, ethylene, α-olefin, a catalyst, and a solvent are added to the reactor. The reactor is operated at a temperature of <NUM> to <NUM>. An optional additive such as, for example, one of those listed above may be added to the first reactor along with the reactants.

Upon conversion of a portion of the ethylene and α-olefin to the copolymer in the reactor, unreacted reactants along with the desired product (the copolymer of ethylene and octene) and other byproducts are charged to the heat exchanger to be heated further. The heat exchanger is generally operated at a higher temperature than the reactor in order to facilitate devolatilization of solvent and other small molecules in the devolatilizer. The heat exchanger is generally operated at a temperature of <NUM> to <NUM>. To the product stream emanating from the reactor is added the additive along with water. A product stream from the heat exchanger is charged to the devolatilizer. Additional additive may optionally be added to the product stream being charged to the devolatilizer. The copolymer product along with any undesirable byproducts are removed from the devolatilizer while unreacted reactants are recycled back to the reactor to undergo further processing.

By adding the additive to the product stream at a point between the reactor and the heat exchanger instead of downstream of the heat exchanger, the amount of α-olefin isomerization is reduced by <NUM> to <NUM> percent, preferably by <NUM> to <NUM> weight percent as compared with a process where the additive is added downstream of the heat exchanger, all other factors remaining unchanged.

The process and the system detailed herein are exemplified by the following example.

This example was conducted to demonstrate the advantages of adding the additive upstream of the heat exchanger instead of downstream of the heat exchanger. In a pilot plant, a mixture of <NUM>-octene, Isopar-E (solvent) was fed to the reactor and subsequent heat exchanger without addition of catalyst or co-catalyst to create a baseline (see run <NUM> in Table <NUM> below). Hydrogen was then added to measure the increased octene isomerization and hydrogenation based on mass balance and gas chromatography (GC) analysis (see run <NUM> in Table <NUM>). The same conditions as for run <NUM> were used to produce a baseline before the addition of each additive (see runs <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> in Table <NUM> respectively). The additives were mixed with Isopar-E and added at a total flow rate of <NUM> pounds per hour. Shown in parenthesis is the actual flow rate for each additive in grams per hour (g/h). In the additive tank, water is also present to give a water flow rate of <NUM>/h for all runs.

For all additives and combinations of additives tested, the octene losses due to hydrogenation and isomerization were reduced from <NUM> to <NUM> weight percent compared to the baseline experiments. The results are shown in the Table <NUM> below.

This set of examples were performed in a laboratory in a stainless steel vessel. For all experiments <NUM> milliliters (ml) of dry octene was added to a <NUM> stainless steel vessel inside a nitrogen padded glove box along with the additives described. The vessel was sealed inside the glove box. If hydrogen was used, it was added to pressurize the vessel to <NUM> psi. The vessel was then removed from the glove box and placed in an oven heated to the desired temperature for <NUM> hours. After heating, the vessel was opened and the octene sampled in a gas chromatograph. The isomer level in the final material was compared to the isomer level in the original octene sample to determine the % octene isomerized.

Experiment <NUM> - these experiments were conducted in the presence of nickel catalyst. It was found that small amounts of granular nickel would isomerize the octene, most notably in the presence of hydrogen. A variety of different additives were found to decrease the amount of isomerization in the nickel/hydrogen system by levels between <NUM> and <NUM>%. The results are shown in the Table <NUM> below.

These results show that the inclusion of an additive in either the reactor and/or the heat exchanger reduces the isomerization of <NUM>-octene from <NUM> to <NUM>, preferably <NUM> to <NUM> weight percent when compared with a reaction conducted using the same reactants but without the additive. The addition of these additives has been shown to also reduce isomerization when molecular sieves are present in the reactor.

It will be understood that, although the terms first, second, third, and the like may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. Thus, first element, component, region, layer or section discussed below could be termed second element, component, region, layer or section without departing from the teachings of the present invention.

As used herein, the singular forms "a," "an" and "the" are intended to comprise the plural forms as well, unless the context clearly indicates otherwise.

Furthermore, in describing the arrangement of components in embodiments of the present disclosure, the terms "upstream" and "downstream" are used. These terms have their ordinary meaning. For example, an "upstream" device as used herein refers to a device producing a fluid output stream that is fed to a "downstream" device. Moreover, the "downstream" device is the device receiving the output from the "upstream" device. However, it will be apparent to those skilled in the art that a device may be both "upstream" and "downstream" of the same device in certain configurations, e.g., a system comprising a recycle loop.

Claim 1:
A method for reducing isomerization of α-olefins during the copolymerization of ethylene with an α-olefin comprising:
adding to a reactor a reaction mixture comprising hydrogen, ethylene, an α-olefin, a solvent and a catalyst; where the catalyst does not include a chain shuttling agent that comprises dialkyl zinc; where the reactor is operated at a temperature of <NUM> to <NUM>;
heating the reactor to a first temperature to react the ethylene with the α-olefin to form a copolymer;
discharging from the reactor a first product stream to a heat exchanger; where the product stream comprises the copolymer;
adding to the product stream prior to the heat exchanger a first additive that is operative to reduce isomerization of the α-olefin; and
discharging from the heat exchanger a second product stream;
where the heat exchanger is operated at a higher temperature than the reactor;
wherein the first additive is selected from the group consisting of aromatic species having one or more hydroxyl functionalities, amines, fluoropolymers, phosphates, fatty acids, salts of fatty acids, esters of fatty acids, or a combination thereof; and wherein the amines include primary amines, secondary amines, tertiary amines, cyclic amines, hindered amines or a combination thereof; and
where a temperature of the second product stream is higher than a temperature of the first product stream.