US3679380A - Pour improvers for fuel oils - Google Patents

Abstract

MIDDLE DISTILLATE FUEL OIL COMPOSITIONS CONTAINING AN EFFECTIVE AMOUNT OF A POUR IMPROVER CONSISTING OF A SOLUBLE, SUBSTANTIALLY LINEAR, ETHYLENE COPOLYMER CONSISTING OF, ON A WEIGHT BASIS, 58 TO 68% POLUMERIZED ETHYLENE UNITS, 32 TO 42% POLYMERIZED PROPYLENE UNITS, AND UP TO 10% POLYMERIZED 1,4-HEXADIENE UNITS, SAID COPOLYMER HAVING AN INHERENT VISCOSITY IN TETRACHLOROETHYLENE AT 30*C. OF ABOUT 0.1 TO 0.45, A NUMBER AVERAGE MOLECULAR WEIGHT OF ABOUT 1,000 TO 10,000 AND A MOLECULAR WEIGHT DISTRIBUTION OF LESS THAN ABOUT 8.

Description

United States Patent O 3,679,380 POUR IMPROVERS FOR FUEL OILS Charles B. Biswell, Woodstown, N.J., and Thomas F. Johnston, Wilmington, Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del. No Drawing. Continuation-impart of application Ser. No. 785,376, Dec. 19, 1968. This application Mar. 1, 1971, Ser. No. 119,841

Int. Cl. C101 1/16 US. Cl. 44-62 8 Claims ABSTRACT OF THE DISCLOSURE CROSS-REFERENCE TO RELATED APPLICATION This is a continuation-in-part of application Ser. No. 785,376 filed Dec. 19, 1968 now abandoned.

BACKGROUND OF THE INVENTION The use of additives to reduce the pour points of fuel oils is well known. The pour point of an oil is defined as the lowest temperature at which the oil flows under specified conditions of chilling without disturbance. Some additives which are effective in reducing the pour points of oils adversely affect the flowability (sometimes called pourability or pumpability) of the oils at temperatures just below the original pour points.

The art recognizes another type of fuel oil additive known as a pour improver, that is, an additive which improves the low temperature fluidity or pourability of the oil. Representative of such additives are polyethylene and copolymers of ethylene and propylene or vinyl acetate. Unfortunately, known pour improvers do not achieve the same response in all middle distillate fuel oils. There is a need, therefore, for pour improvers which can be used with such fuel oils.

SUMMARY OF THE INVENTION It is an object of the present invention to provide middle distillate fuel oil compositions having improved low temperature flowability. Another object is to provide low temperature pour improvers for middle distillate fuel oils. It is a further object to provide such fuel oil compositions by adding to middle distillate fuel oils only very small quantities of a pour improver. It is a still further object to provide such fuel oil compositions containing a flowability improving additive which does not adversely affect the properties of the fuel oil. Other objects will be apparent hereinafter.

The above objects are realized by introducing into a middle distillate fuel oil whose flowability is to be improved an effective amount of a substantially linear ethylene copolymer which is soluble in said fuel oil and consists of, on a weight basis, 58 to 68% polymerized ethylene units, 32 to 42% polymerized propylene units, and up to 10% polymerized 1,4-hexadiene units, said copolymer having an inherent viscosity as a 0.1 weight percent solution in tetrachloroethylene at 30 C. of about 0.1 to 0.45, a number average molecular weight of about 1,000 to 10,000 and a molecular weight distribution of less than about 8.

DETAILED DESCRIPTION OF THE INVENTION The present invention resides in middle distillate fuel oil compositions having improved low temperature flowability. More particularly, the fuel oils of this invention comprise a middle distillate fuel having completely dissolved therein an effective amount of a substantially linear ethylene copolymer consisting of, on a weight basis, 58 to 68% polymerized ethylene units, 32 to 42% polymerized propylene units, and up to 10% polymerized 1,4- hexadiene units, said copolymer having an inherent viscosity as a 0.1 weight percent solution in tetrachloroethylene at 30 C. of about 0.1 to 0.45, a number average molecular weight of about 1,000 to 10,000 and a molecular weight distribution of less than about 8.

The middle distillate fuel oils used as the base oils in the improved compositions of this invention are liquid hydrocarbon fuel oils boiling above the gasoline range and include, for example, diesel fuels, domestic heating fuels and the like. The middle distillate ifuel oils used in this invention are further defined as having an atmospheric pressure boiling range of about 250750 F., and preferably about 300-650" F. Such fuel oils can be straight run distillates, thermally or catalytically cracked distillates, or mixtures thereof. Furthermore, the fuel oils can be treated according to well known oil treatment processes such as hydrogenation, caustic washing, solvent refining or clay treating.

The copolymer which is added to the middle distillate fuel oils, as hereinabove defined, to provide the improved compositions of this invention is a substantially linear ethylene copolymer which is soluble in the oil and which consists of, on a weight basis, 58 to 68% polymerized ethylene units, 32 to 42% polymerized propylene units, and up to 10% polymerized 1,4-hexadiene units, said copolymer having an inherent viscosity as a 0.1 weight percent solution in tetrachloroethylene at 30 C. of about 0.1 to 0.45, a number average molecular weight of about 1,000 to 10,000 and a molecular weight distribution of less than about 8. Said copolymer has a pendent index of about 10 to 17. The term pendent index is used to indicate the number of pendent groups per 100 carbon atoms of the backbone polymer chain. The copolymer used herein has alkyl, and optionally if 1,4-hexadiene is copolymerized, alkenyl pendent groups. The average pendent size, that is, the average size of the pendent groups, is not in excess of two carbon atoms, and preferably, it is 1 to 1.5 carbon atoms.

The preferred ethylene copolymer contains 58 to 65% polymerized ethylene units, 35 to 42% polymerized propylene units, and up to 4% polymerized 1,4-hexadiene units.

The preferred inherent viscosity, as defined above, is about 0.20 to 0.30. A definition of inherent viscosity is given in the Journal of Colloid Science, 1, 261-269 (1946). It is expressed as lnNr/c, that is, the natural logarithm of the viscosity of the solution relative to the viscosity of the solvent over the concentration in grams of solute per 100 ml. of solvent. For the operable copolymers herein, inherent viscosities of about 0.1 to 0.45 correspond to weight average molecular weights of about 1,000 to 18,000, as determined by light scattering in hexane at 0., when the molecular weight distribution is about 2. The preferred viscosities correspond to molecular weights of about 5,000 to 10,000 at this molecular weight distribution. The copolymers which are operable herein have number average molecular weights of about 1,000 to 10,000.

The preferred molecular weight distribution, i.e. the weight average molecular weight divided by the number average molecular weight, is about 2 to 6.

As is obvious from the above description, the copolymers employed herein are narrowly defined as to molecular structure, composition, molecular weight and molecular weight distribution. Copolymers falling within this narrow definition are soluble in the middle distillate fuel oils and provide the desired improvement in flowability. They can be prepared by a variety of techniques now well known in the art, such as by polymerizing the monomers with a coordination polymerization catalyst, as described in US. Patents 2,799,668; 2,933,480; and 2,975,- 159. Since the utilization of these catalysts can produce a variety of types of ethylene copolymers, it is important to select polymerization conditions which will yield amorphous polymers having the aforesaid requisite composition, molecular weight and molecular weight distribution. More specifically, it is advantageous to use a hydrocarbon-soluble vanadium compound, for example, vanadium trisacetylacetonate, in combination with an alkyl aluminum chloride as described in US. Patent 3,300,459 and in I. Polymer Science, 51, 4l1ff and 429ff ('1961). Use of this catalyst system, especially when used in a continuous polymerization process, results in the formation of an essentially amorphous copolymer which is soluble in middle distillate fuel oils. Since such copolymers exhibit substantially no crystallinity as evidenced by X-ray examination, a more precise measure of the amorphous character of the polymer is the aforesaid solubility. The control of molecular weight and/ or molecular weight distribution can be effected by the methods disclosed in J. Polymer Science, 34, 531ff (1959) or in US. Patent 3,051,690.

As is well known, the aforesaid catalysts must be used in the strict absence of oxygen, water or other reactive material. For this reason, the solvents in which they are used are greatly limited, the preferred ones being the saturated aliphatic and hydroaromat-ic hydrocarbons, and certain nonreactive halogen compounds such as tetrachloroethylene or a liquid chlorobenzene. Such solvents also serve as polymerization media, the polymerization usually being carried out in a dilute suspension of catalyst at normal temperatures and pressures, although elevated or reduced temperatures and pressures also can be used.

The operable copolymers are dissolved in the middle distillate fuel oils by any suitable method, for example, by agitating the desired amount of polymer in the oil at ordinary or ambient temperatures. If desired, the rate of solution can be increased by employing elevated temperatures. The copolymers can be dissolved in an aliphatic,-

aromatic or cycloaliphatic hydrocarbon solvent, for example, hexane, benzene, toluene, cyclohexane or kerosene, or in the fuel oil itself, to form a concentrate containing 15 to 75 weight percent copolymer. The concentrate subsequently can be diluted with the fuel oil to the desired effective concentration.

The concentration of coplymer in the middle distillate fuel oil compositions of this invention is dependent upon the base oil characteristics. It is well known that the responsiveness of fuel oils to flowability additives varies with the fuel oil itself. This variation of responsiveness precludes the setting of absolute concentration values for the copolymer additives of this invention. Other variables which atfect the amount of additive employed in- .clude the nature of the copolymer, the pour point of the base oil, and the extent of the desired improvement in flowability, the latter including a consideration of the minimum temperature at which fiowability is to be im proved. Most of the middle distillate fuel oil compositions of this invention contain 0.002 to 0.5 weight percent, and preferably 0.01 to 0.1 weight percent, of the copolymer, although it must be recognized that in order to achieve the maximumdesirable effect of the copolymer, it may be necessary to select a narrow concentration rangewithin the aforesaid ranges.

The fuel oil compositions of this invention can contain other additives commonly used in fuel oils, such as rust and corrosion inhibitors, dispersants, stabilizers, antioxidants, haze inhibitors, smoke suppressors, dyes and introduce the other additives into the concentrate which has been described above so that all of the additives are introduced into the base oil at the same time.

The following examples, illustrating the inventive compositions disclosed herein, are given without any intention that the invention be limited thereto. All parts and percentages are by weight unless otherwise indicated. The procedure used to demonstrate the improvement in the low temperature flow properties of middle distillate fuel oils containing the copolymers described herein is the Enjay Fluidity Test which correlates more closely with actual use conditions than does the American Society of Testing Materials Test Method D-97.

EXAMPLE 1 An ethylene/propylene/1,4-hexadiene copolymer was prepared in a continuous, exaporatively-cooled reactor in solution in hexane in the presence of a coordination catalyst made in situ by combining vanadium 'tris-(acetylacetonate) and diisobutylaluminum chloride. The reactor eflluent was freed from residual monomers in a flasher, washed with an equal volume of 1% sulfuric acid and then twice with equal volumes of water, and finally pan dried in a vacuum oven. The reactor conditions used are tabulated below. The aforesaid monomers and catalyst reactants are designated '15, P, H, V and Al, respectively. Hydrogen was used to control molecular weight.

Polymer 1 2 3 Liquid volume (liters) 0. 792 0. 792 0. 792 Residence time (minutes) 30 36 27. 6 Temperature 0.). 30 30 30 V (millimols/liter 0. 356 0. 72 0.64 Al (millimolsflliter) 5. 3 10. 6 9. 6 Mols P/mols E (in vapor phase). 2. 5 3. 0 3. 2 Mol percent H: (in vapor phase) 25 21. 8 61 P feed (lb./hr.) 0.100 0. 26 0. 32 H teed (lb./hr.) 0.014 0. 037 0.022 Polymer produetlon (lb./hr.) 0. 08 0. 22 0. 38

The copolymers prepared above were characterized as follows:

Percent E P H 1, inh MWD l Polymer:

MW D =Molecular weight distribution 1741i. (wt. average M.W; determined by light scattering in n-hexane at 90 0.; number average M.W. determined by boiling point elevation in n-hexane).

EXAMPLE 2 The copolymers of Example 1 were evaluated as pour improvers for middle distillate fuel oils using the Enjay Fluidity Test. The test unit consisted of a vertical cylinder divided into an upper section and a lower section with a glass capillary connecting the two sections. The test involved adding 40 ml. of fuel oil containing copolymer to the lower section and cooling the appartus in a cold bath at 35 F. for 1% hours, resulting in a final fuel oil temperature of -25 F. The test unit was withdrawn from the bath, slowly inverted, and replaced in the cold bath. After one minute the top cap on the cylinder was removed, allowing any fuel which was still fluid to flow into the bottom half of the cylinder. The volume of fuel which had flowed through the capillary tube into the lower section of the cylinder after three minutes was recorded. A recovery of (32 ml.) of the original oil is considered good. Values less than this may still reflect an improvement in flowability over the unmodified oil.

The six middle distillate fuel oils used in these tests were chosen because of their variable response to known pour improvers. The oils used, arranged in decreasing order of response to known additives, are the following.

Fuel A: Commercially available No. 2 fuel oil, a blend of straight run and cracked stocks, boiling range 397-618 F.

Fuel B: Commercially available blend of 25% No. 1 straight run and 75% No. '2 straight run distillate stocks, unhydrogenated, boiling range 334-602 F.

Fuel C: Commercially available hydrogenated No. 2 fuel oil, boiling range 302-639 F.

Fuel D: Commercially available No. 2 fuel oil, blend of cracked stocks, unhydrogenated, boiling range 413- 612 F.

Fuel E: Commercially available No. 2 diesel fuel oil, boiling range 408-603 F.

Fuel F: Commercially available No. 2 fuel oil, boiling range 320-612" F.

The effectiveness of the copolymers of Example 1 with respect to the above middle distillate fuel oils is shown in the following table.

FLUIDITY F MIDDLE DISTILLATE FUEL OILS WITH ADDI'IIVE Ml. recovered Wt. percent Fuel oil additive Polymer 1 Polymer 2 Polymer 3 The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A middle distillate fuel oil composition having low temperature flowability and containing an effective amount of a soluble, substantially linear, ethylene copolymer consisting of, on a weight basis, 58 to 68% polymerized ethylene units, 32 to 42% polymerized propylene units, and up to 10% polymerized 1,4-hexadiene units, said copolymer having an inherend viscositty as a 0.1 weight percent solution in tetrachloroethylene at 30 C. of 0.1 to 0.45, a number average molecular weight of about 1,000 to 10,000, a molecular weight distribution of less than 8, a pendent index of 10 to 17 and an average pendent size of not greater than 2 carbon atoms.

2. The composition of claim 1 wherein the concentration of copolymer is 0.002 to 0.5 weight percent.

3. The composition of claim 1 wherein the middle distillate fuel oil has a boiling point of 300650 F.

4. The composition of claim 1 wherein the oil is a heating fuel.

5. The composition of claim 1 wherein the oil is a diesel fuel.

6. The composition of claim 1 wherein the concentration of copolymer is 0.01 to 0.1 weight percent and the copolymer consists of 58 to polymerized ethylene units, 35 to 42% polymerized propylene units, and up to 4% polymerized 1,4-hexadiene units, has an inherent viscosity of 0.20 to 0.30, a molecular weight distribution of 2 to 6 and an average pendent size of 1 to 1.5 carbon atoms.

7. An additive for improving the low temperature flowability of middle distillate fuel oil compositions, which additive comprises kerosene containing 15 to weight percent of a soluble, substantially linear, ethylene copolymer consisting of, on a weight basis, 58 to 58% polymerized ethylene units, 32 to 42% polymerized propylene units, and up to 10% polymerized 1,4-hexadiene units, said copolymer having an inherent viscosity as a 0.1 weight percent solution in tetrachloroethylene at 30 C. of 0.1 to 0.45, a number average molecular weight of about 1,000 to 10,000, a molecular weight distribution of less than 8, a pendent index of 10 to 17 and an average pendent size of not greater than 2 carbon atoms.

8. The additive of claim 7 wherein the copolymer consists of 58 to 65% polymerized ethylene units, 35 to 42% polymerized propylene units, and up to 4% polymerized 1,4-hexadiene units, has an inherent viscosity of 0.20 to 0.30, a molecular weight distribution of 2 to 6 and an average pendent size of 1 to 1.5 carbon atoms.

References Cited UNITED STATES PATENTS 3,507,636 4/1970 Sweeney 44-62 DANIEL E. WYMAN, Primary Examiner W. J. SHINE, Assistant Examiner US. Cl. X.R. 4480 rio-wao UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION mm No. 3, 79,380 Dated July 25, 1 2

humor) Charles Biswell and Thomas E. Johnston.

It is certified that error appeara in the above-identified patent and that said Letters Patent are hereby corrected as ahown below:

in Col. 1, line 3 "Thomas should read Thomas E. Col. 6, line 30, 5895" shouldread 68% r Signed and sealed this 23rd day of January 1973.

(SEAL) Attest;

EDWARD M.FLETCHER,JR. I Q ROBERT GOTTSCHALK Attestlng Officer Commissioner of Patents