Continuous process for producing adducted EPM or EPDM oil solution

Abstract: The present invention provides a continuous process for producing an adducted derivatized EPM or EPDM oil solution in which a grafted ethylene polymer is adducted with an antioxidant diamine for formation of an adduct during holding.

Description: The present invention relates to a continuous process for the production of adducted, or capped, derivatized ethylene-propylene copolymer or terpolymer (EPM or EPDM) oil solution. Engine motor lubricant formulations are conventionally based upon dilute solutions of synthetic elastomers in oil. The addition of low molecular weight polymer constituents to the oil provides an improvement in the viscosity index (VI) over the oil itself, such that the desired lubricant viscosity is achieved and maintained over the operating temperature range of the motor. Polymeric viscosity index improvers for lubricants are known in the art. For instance, United States Patent No. 4,161,452 describes the grafting in solution of diacid or anhydride functional monomers to ethylene copolymers with recovery of the grafted product in solid form, to provide a viscosity index improver. According to that patent, the grafted batch product may then be incorporated into an oil system to provide the desired VI improvement. United States Patent No. 4,357,250 discloses the use in lubricants, as a dispersant and viscosity modifier, of derivatized ethylene copolymers prepared by Ene reactions. The reaction product of maleic anhydride with a saturated ethylene-propylene rubber of low molecular weight has been employed to produce a low molecular weight oil viscosity index improver, according to United States Patent No. 4,670,515. The continuous grafting of ethylene copolymers and terpolymers in solution with monomers to produce an oil solution including a dispersant olefin copolymer that also functions as a viscosity index improver is taught in United States Patent No. 4,340,689. European Patent Application No. 0050994 describes lubricating oil dispersant viscosity index improvers made by grafting, for example, maleic anhydride to an ethylene/α-olefin copolymer in a hydrogen-treated mineral oil solvent using a free radical and then reacting the grafted intermediate with an amine having the structure R ( NH-CH 2 CH 2 CH 2 ) n NH 2 wherein R is an aliphatic hydrocarbon group containing from 12 to 33 carbon atoms and n is an integer from 1 to 3. Use of hydrogen-treated mineral oil increases the effectiveness of the viscosity index improver. None of the foregoing, however, describes a continuous process for producing an adducted derivatized ethylene-propylene copolymer or terpolymer oil solution. A continuous process results in lower production costs over batch processes for producing similar products, and further provides a more consistent product over time. In addition, a continuous process is more energy efficient than alternative processes. It also has the environmental advantage of generating no waste streams, since raw materials and intermediate species are either recovered or incorporated into the end product. Moreover, an adducted product is particularly desirable for providing long term stabilization of the oil solution, in that oxidation of the oil solution is reduced or eliminated by the presence of an adducted species having antioxidant properties. The present invention now seeks to provide a process for producing a stable adducted EPM or EPDM oil solution having the advantage of lower production costs associated with the process that can be operated continuously, of generating no waste streams thereby producing no deleterious environmental effects, and of having lower energy costs associated with it. In accordance with the invention, there is now provided a continuous process for the production of an adducted EPM or EPDM oil solution, comprising the sequential steps of: interpolymerizing in solution ethylene and an olefinic hydrocarbon having from 3 to 16 carbon atoms to produce a polymer product; concentrating the polymer product in the solution; grafting the polymer with a grafting monomer selected from organic acids and anhydrides to produce a graft polymer; preparing an oil solution of the graft polymer; mixing the oil solution with an antioxidant polyamine composition in the presence of an aliphatic or phenolic alcohol ethoxylate solvent; and maintaining the resulting mixture at an elevated temperature to permit the formation of an imide adduct between the grafted polymer and the polyamine. The invention is described below in greater detail with reference to the accompanying drawings, in which: FIG. 1 is a process flow diagram illustrating graphically the steps of the process of the present invention; and FIG. 2 is a graph showing the variation in weight percent of stored polyamine over time during holding of the adducted EPM or EPDM oil solution made according to the present invention. The continuous process of the present invention incorporates a number of steps including the formation of the derivatized EPM or EPDM along with the steps producing the adducted EPM or EPDM oil solution, as shown in FIG. 1. As described in United States Patent No. 4,340,689 ("the '689 patent"), the continuous grafting of ethylene copolymers in solution with monomers to produce an oil solution including a dispersant olefin copolymer that also functions as a viscosity index improver. The preferred EPM copolymer is produced by interpolymerization in solution of monomers of ethylene and one or more higher mono-olefins having from 3 to 16 carbon atoms, preferably propylene. The reaction is carried out in solution in the presence of a Ziegler catalyst, e.g. , a vanadium compound activated by an alkyl aluminum chloride. If EPDM is to be produced, one or more polyenes are also added to the interpolymerization reaction mixture described above. Suitable polyene monomers may be selected from branched chain monomers, straight or branched chain polyene or cyclic polyenes containing 4 to 20 carbon atoms and preferably 5 to 10 carbon atoms and two carbon-carbon double bonds. Useful polyenes include the alkylidene norbornenes, and specifically 5-ethylidene-2-norbornene. The EPM or EPDM polymerization is carried out on a continuous basis in an agitated first reaction vessel 100 into which monomer, catalyst and polymerization accelerators have been continuously supplied, and from which reaction products are continuously withdrawn. A cement of the polymerized reaction products is then prepared by concentrating the reaction products in a second vessel 110. Such concentration is desirable for increasing efficiency of a subsequent grafting reaction, and for reducing the likelihood of producing unwanted byproducts during the grafting reaction. The cement thus produced is advanced to a mixer or mixers 120, 130 where it is mixed with a grafting monomer and a peroxide catalyst to achieve a desired grafting reaction. The peroxide catalyst is one having a half life (T 1/2 ) of 10-20 minutes at the reaction vessel temperature of 121-177°C (250-350°F), and is preferably one having T 1/2 of 12-17 minutes at 149-163°C (300-325°F). Examples of such catalysts include DICUP® (Hercules, Inc.), which is dicumyl peroxide, and VAROX® (R.T. Vanderbilt Co.), which is 2,5-dimethyl-2,5-di(tertbutyl peroxy) hexane. The resulting mixture is then passed from the first reaction vessel to a third reaction vessel 140, which may preferably be a plurality of reactors connected in series for continuous operation as shown in FIG. 1. After reaction, solvent is removed according to steps set forth in the '689 patent, and the oil solution is made. With respect to the present invention, the process of the '689 patent is used to graft an organic acid or anhydride to the EPM copolymer having the generalized structure in which R is an alkylene group having 0-4 carbon atoms; Y is hydrogen or a branched or straight chain alkyl group, a halogen group such as chlorine, bromine or iodine, or a heterocyclic or other organic group having 1-12 carbon atoms; and X is a hydroxy, alkoxy or aryloxy group, but at least one X group is hydroxy. The structure is such as to permit formation of an imide upon reaction with the amine composition described below. For EPM, the grafted group is preferably maleic anhydride. The amount of graft will vary depending upon the particular characteristics desired in the final product. In the preferred embodiment, an amount of 0.5-1.5 weight percent maleic anhydride in the grafted EPM is employed. The oil solution production process described above and disclosed in the '689 patent is adjusted to produce an effluent end stream composed of between 10 and 20 percent by weight grafted EPM and about 80-90 weight percent paraffinic oil. In the present invention, a second stream is added to this end stream, consisting of an antioxidant polyamine composition, R-(NH 2 ) n in which n is at least two and R is an organic group containing three or more carbon atoms in organic solution. Effective compositions for the amine are such that a first, or primary, amine group is separated from a secondary amine group (or tertiary amine group, if more than too amine groups are provided) by at least three or more carbon atoms. Two effective antioxidant polyamine groups are N,N-dimethyl, 1,3-diaminopropane and N-phenyl, 1,4-phenylene diamine (NPPDA), the latter of which is preferred. The amine composition is provided in stoichiometric quantities based upon the amount of grafted monomer present in the EPM or EPDM oil solution, so that the grafted functionality is completely adducted by the amine and the organic solvent. In the preferred embodiment, this ratio will be 0.6-1.2 amine-containing molecules per grafted anhydride group. The organic solvent employed is selected to be compatible with the compositions in the first stream and includes the family of aliphatic or phenolic alcohol ethoxylates as shown by the structure below: wherein x is a number from 1-10, and R is either an aliphatic group having from 7 to 20 carbons or an aryl group such as phenyl and substituted derivatives thereof, the substitution being an alkyl group having from three to 20 carbons. Useful examples include SURFONIC® N-40 or N-60 (Texaco, Inc.), which are the reaction products of nonyl phenol with ethylene oxide, and SURFONIC® L46-7, which is the reaction product of C 12 -C 19 aliphatic alcohols with ethylene oxide. Other organic solvents useful in the practice of this invention include the reaction products of other alkyl phenols and or C 7 -C 20 aliphatic alcohols with ethylene oxide. The first and second streams are fed together into a mixer 150, e.g. , a static mixer, of sufficient size and mixing capacity to permit complete mixing of the two streams. Thorough mixing permits formation of an adduct between the amine functional group and the anhydride. Thus, the adduct formed is an imide: or an acid amide: in which the reactant R-NH 2 as shown is the antioxidant polyamine composition described above. It is also hypothesized that, in the first stream, there will be present small quantities of maleic anhydride oligomer formed from excess maleic anhydride monomer during the grafting reaction. This species is also adducted according to reaction (III), with the resulting product believed to contribute to the chelating/dispersant performance of the oil solution. The resultant adducted mixture is advanced to a holding tank 160, where it is preferably held at adduct forming temperatures to drive reaction (I) and maintain the presence of adduct imide in the solution. Such temperatures are in the range of 49-177°C (120-350°F), with the range of 149-177°C (300-350°F) being preferred. It has also been determined that a greater capping efficiency results when the capping reaction occurs under a nitrogen atmosphere, rather than a vacuum. Thus, the mixed product is preferably held under a nitrogen atmosphere to provide increased capping efficiency. It has been observed that holding the adducted mixture at the adduct forming reaction temperature results in an increasing amount of adducted EPM or EPDM. This is shown by the data set forth in Table I. FIG. 2 is a theoretical graph showing the variation in weight percent of stored polyamine (NPPDA) over time during holding of the adducted EPM or EPDM oil solution made according to the present invention. Table II shows similar data for several different samples of adducted derivatized EPM or EPDM. HOLDING TIME (hr) NPPDA (wt%) 1 0.25 1.36 0.75 1.39 1.25 1.39 1.75 1.47 2.25 1.58 2.75 1.61 3.75 1.60 4.75 1.62 5.75 1.61 Total Target NPPDA (wt%) |------Analyzed NPPDA (wt %)------| Reaction Time (hours) 3 6 24 72 Final 6.8 Bound 1.31 --- 1.92 2.11 ---- Total 8.74 --- 9.54 9.39 ---- 6.8 Bound 1.63 1.73 1.82 1.95 ---- Total 6.67 7.03 7.67 7.85 ---- 4.5 Bound 1.35 1.39 1.65 1.59 ---- Total 4.45 4.52 4.55 4.60 ---- 4.5 Bound 1.17 1.27 1.39 1.49 1.48 Total 4.59 4.49 4.47 4.23 4.56 4.5 Bound 1.11 1.26 1.36 1.63 1.50 Total 3.64 3.99 4.28 4.18 4.40 4.5 Bound 1.23 1.28 1.44 1.60 1.55 Total 4.97 5.05 5.12 5.05 5.02 The advantages of the continuous capping process of the present invention as applied in a continuous graft cement production system, as compared to a batch capping process, are shown in Table III, which includes comparative data for batch capped oil solution and continuously capped oil solution. In the batch capping process, the cement, oil and amine solution are combined in a sealed vessel, and the hexane strapped off with stirring by raising the temperature of the mixture to about 188°C (370°F) under a vacuum. The data shown in Table III illustrates the superiority of products produced according to the present invention, in which the cement is produced continuously and capped continuously, as compared to products wherein either the cement production or the capping process is a batch process, or both. Graft Cement Type Capping Process Type NPPDA/Total MAH Ratio (molar) Bound NPPDA (wt %) Engine Test Performance Sequence VE Batch Batch 0.43 0.47 Failed Batch Batch 0.55 1.28 Good Batch Continuous 0.55 1.17 Excellent Batch Continuous 1.0 1.60 Not tested Continuous Batch 0.48 0.83 Not tested Continuous Continuous 1.1 1.95 Excellent Continuous Continuous 0.74 1.65 Excellent Continuous Continuous 0.77 1.48 Excellent The effects of holding under a nitrogen atmosphere as compared to holding under a vacuum are illustrated by the data shown in Table IV. There, it is shown that substantially higher efficiencies of capping are produced as a result of adduct formation in holding under a nitrogen atmosphere as compared to holding and adduct formation under a vacuum, where the composition is formed according to the present invention. Capping Efficiencies Under Different Atmospheres Reaction Time (hrs) Atmosphere Total NPPDA Bound NPPDA Theoretical Bound NPPDA Capping Efficiency 8 Nitrogen 1.67 0.74 1.24 0.60 17 Nitrogen 1.80 0.65 1.24 0.52 17 Nitrogen 2.28 1.17 1.24 0.94 20 Nitrogen 2.89 1.32 1.24 1.06 18 Nitrogen 2.99 0.92 1.24 0.74 18 Nitrogen 2.84 0.96 1.24 0.77 18 Nitrogen 2.27 1.16 1.24 0.94 8 Vacuum 1.66 0.60 1.24 0.48 8 Vacuum 1.80 0.71 1.35 0.53 8 Vacuum 1.47 0.51 1.20 0.43

Claims: A continuous process for the production of adducted EPM or EPDM oil solution comprising the sequential steps of: interpolymerizing in solution ethylene and an olefinic hydrocarbon having from 3 to 16 carbon atoms to produce a polymer product; concentrating the polymer product in the solution; grafting the polymer with a grafting monomer selected from organic acids and anhydrides to produce a grafted polymer; preparing an oil solution of the grafted polymer; mixing the oil solution with an antioxidant polyamine composition in the presence of an aliphatic or phenolic alcohol ethoxylate solvent; and maintaining the resulting mixture at an elevated temperature to permit the formation of an imide adduct between the grafted polymer and the polyamine. The process according to claim 1, wherein the olefinic hydrocarbon is propylene. The process according to claim 1 or claim 2, wherein the interpolymerization mixture comprises also at least one polyene. The process according to claim 3, wherein the polyene is 5-ethylidene-2-norbornene. The process according to any preceding claim wherein the grafting monomer has the structure in which R is omitted or is C 1 to C 4 alkylene; Y is hydrogen, branched or straight chain alkyl, halogen or C 1 to C 12 heterocyclic or other organic group having 1-12 carbon atoms; and one X is hydroxy, and the other X is hydroxy, alkoxy or aryloxy or both X together are oxygen. The process according to claim 5, wherein the grafting monomer is maleic anhydride. The process according to any preceding claim, wherein the grafted polymer contains between 0.5 and 1.5 weight percent of grafting monomer. The process according to any preceding claim, wherein the polyamine includes at least two amine groups separated by three or more carbon atoms. The process according to claim 8, wherein the antioxidant polyamine composition is NPPDA. The process according to any preceding claim, wherein the amount of polyamine is between 0.6 and 1.2 amine-containing molecules per grafted monomer. The process according to any preceding claim, wherein the aliphatic or phenolic alcohol ethoxylate solvent is a reaction product of one or more alkyl phenols or C 12 -C 19 alkyl alcohols with ethylene oxide. The process according to any one of claims 1 to 10, wherein the aliphatic or phenolic alcohol ethoxylate solvent is the reaction product of one or more C 7 -C 20 aliphatic alcohols with ethylene oxide. The process according to any preceding claim, wherein the mixture is maintained at a temperature between 50°C and 180°C to permit adduct formation. The process according to claim 13, wherein the mixture is maintained at a temperature between 150°C and 180°C. The process according to any preceding claim, wherein the grafting step comprises also a peroxide catalyst. The process according to claim 15, wherein the peroxide catalyst is dicumyl peroxide or 2,5-dimethyl-2,5-di(tertbutyl peroxy) hexane. The process according to any preceding claim, wherein the oil solution is based upon a paraffinic oil.

Inventors: CAINES TONY L, JUNKER MICHAEL L, CAINES, TONY L., JUNKER, MICHAEL L.
Applicants: DSM COPOLYMER INC, ETHYL ADDITIVES CORP, DSM COPOLYMER, INC., ETHYL ADDITIVES CORPORATION
Application year: 1991
Main classification: C08F8
IPC codes: C08L51, C08F8, C10N70, C08F255, C10M149, C10N40, C10N30