US3790359A - Middle distillate fuel having increased low temperature flowability - Google Patents

Abstract

The low temperature flowability of a middle distillate petroleum fuel oil boiling within the range of about 250* to about 700*F. at atmospheric pressure is improved by adding to the fuel oil from about 0.1 to about 3 weight percent of an essentially saturated hydrocarbon fraction which is substantially free of normal paraffinic hydrocarbons and which has a number average molecular weight in the range of about 600 to about 3,000, together with a flow-improving additive such as a copolymer of ethylene and an unsaturated ester, wherein said copolymer has less than six methyl terminating side branches per 100 methylene groups, the weight ratio of said saturated hydrocarbon fraction to said copolymer flow-improving additive being in the range of about 25:1 to 1:1.

Description

United States Patent [191 Feldman [.111 3,790,359 Feb. 5, 1974 [75] Inventor: Nicholas Feldman, Woodbridge,

[73] Assignee: Esso Research and Engineering Company, Linden, NJ.

22 Filed: Mar. 17,1969

21 Appl. No.: 807,966

[52] US. Cl 44/62, 44/70, 208/15 [51] Int. Cl Cll l/l8 [58] Field of Search 44/62, 70; 252/56; 208/45,

[56] References Cited UNITED STATES PATENTS 2,906,688 9/1959 Farmeret al. 208/33 3,132,083 /1964 Kirk 208/45 3,236,612 2/1966 llnycky 44/62 3,413,103 11/1968 Young et al. 44/70 3,341,309 9/1967 llnyckyj 44/62 3,507,776 4/1970 Hann 208/15 2,177,732 10/1939 MacLaren 44/80 2,917,375 12/1959 Hudson 44/62 2,906,688 9/1959 Farmer et al. 208/45 FOREIGN PATENTS OR APPLICATIONS 993,744 6/1965 Great Britain 44/62 1,223,976 9/ 1966 Germany 44/70 Primary ExaminerDaniel E. Wyman Assistant Examiner-Mrs. -Y..H. Smith Attorney, Agent, or FirmPearlman and Stahl; Byron O. Dimmick [5 7] ABSTRACT The low temperature flowability-of a middle distillate petroleum fuel oil boiling within the range of about 250 to about 700F..at atmospheric pressure is improved by adding to the fuel oil from about 0.1 to about 3 weight percent of an essentially saturated hydrocarbon fraction which is substantially free of normal parafimic hydrocarbons and which has a number average molecular weight in the range of about 600 to about 3,000, together with a flow-improving additive such as a copolymer of ethylene and an unsaturated ester, wherein said copolymer has less than six methyl terminating side branches per methylene groups, the weight ratio of said saturated hydrocarbon fraction to said copolymer flow-improving additive being in the range of about 25:1 to 1:1.

5 Claims, N0 Drawings FIELD OF THE INVENTION Heating oils and other middle distillate petroleum fuels, e.g., Diesel fuels, contain normal paraffin hydrocarbon waxes which, at low temperatures, tend to precipitate in large crystals in such a way as to set up a gel structure which causes the fuel to lose its fluidity. The lowest temperature at which the fuelwill still flow is generally known as the pour point. When-the fuel temperature reaches or goes below the pour point and the fuel is no longer freely flowable, difficulty arises in transporting the fuel through flow lines and pumps, as for example when attempting to transfer the fuel from one storage vessel to another by gravity or under pump pressure or when attempting to feed the fuel to a burner. Additionally, the wax crystals that have come out of solution tend to plug fuel lines, screens and lilters. This problem has been well recognized in the past and various additives have been suggested for depressing the pour point of the fuel oil. One function of such pour point depressants has been to change the nature of the crystals that precipitate from the fuel oil, thereby reducing the tendency of the wax crystals to set into a gel. Small size crystals are desirable so that the precipitated wax will not clog the fine mesh screens that are provided in fuel transportation, storage, and dispensing equipment. It is thus desirable to obtain not only fuel oils with low pour points, but also oils that will form small wax crystals so that the clogging of filters will not impair the flow of the fuel at low operating temperatures. I

DESCRIPTION OF TI-IEPRIOR ART It is known in the prior art to employ a copolymer pour point depressantor flow improver of the type comprising a copolymer of ethylene with another ethylenically unsaturated monomer, such as an unsaturated ester or another alpha olefin, wherein the ethylene forms a backbone along which there are randomly distributed side chains consisting of hydrocarbon groups or of oxysubstituted hydrocarbon groups of up to 16 carbon atoms. The use of copolymers, of ethylene and other monomers such as vinyl'esters, acrylate estersor methacrylate esters, and the like to lower the pour point and improve the flowability of middle distillate fuels at low temperature is well known in the art. See

for example, US. Pat. Nos. 3,037,850, 3,048,079,

3,069,245, 3,093,623 and 3,236,612.

REFERENCE TO COPENDING APPLICATION It is taught in the application of Nicholas Feldman and Wladimir Philippoff, Ser. No. 807,953, having the same filing date as the present application, and subsequently issued on May 2, 1972 as US. Pat. 3,660,058 that an amorphous, normally solid, essentially saturated hydrocarbon fraction, obtained-from a residual petroleum oil, said fraction being substantially free of that type of hydrocarbon that is used as one component of the additive combination of the present invention.

DESCRIPTION OF THE INVENTION In accordance with the present invention, it has been found that the low temperature flow properties of the petroleum middle distillate fuel oil can be improved by incorporating into the fuel oil a small concentration of an ethylene copolymer type pour point depressant and a small concentration of an essentially saturated hydrocarbon fraction that is substantially free of normal paraffinic hydrocarbons, the hydrocarbon fraction having a number average molecular weight in the range of about 600 to about 3,000. The ethylene copolymer is further characterized by being a random copolymer of from 3 to moles of ethylene and 1 mole of an unsaturated ester, wherein the copolymer has less than 6 methyl-terminating side branches per 100 methylene groups, and the copolymer has a number average molecular weight of about 1000 to 50,000. More specifically, there are added to a waxy middle distillate petroleum fuel, from about 0.1 to about 3 weight percent, preferably about 0.2 to 1 weight percent, of the said high molecular weight hydrocarbon fraction, together with from about 0.005 to about 1 weight percent, generally about 0.0l to 0.1 weight percent, of ,the ethylene copolymer pour depressant. The weight ratios of the two types of additives can vary from equal parts to as little as 1/25th as much of the ethylene copolymer pour depressant as the high molecular weight hydrocarbon fraction.

The distillate fuel oils that can be improved by this invention include those having boiling ranges within the limits of about 250F. to about 700F. The distillate fuel oil can comprisestraight run or .virgin gas'oil or cracked gas oil or a blend in any proportion of straight run and thermally and/or catalytically cracked distillates.

The most common petroleum middle distillate fuels are kerosene, diesel fuels, jet fuels and heating oils. Since jet fuels are normallyrefined to very low pour points, there will be generally no need to apply the present invention to such fuels. The low temperature flow problem is most usually encountered with diesel fuels and with heating oils. A representative heating oil specification calls for a 10 percent distillation point no higher than about 440F., a 50 percent point no higher than about 5 20F., and a percent point of at least 540F. and no higher than about 640F. to 650F., although some specifications set the 90 percent point as high as 675F. Heating oils are preferably made of a blend of virgin distillate, e. g., gas oil, naphtha, etc., and cracked distillates, e.g., catalytic cycle stock. A representative specification for. a diesel fuel includes a minimum flash point of F. and a 90 percent distillation point between 540F. and 640F. (See ASTM Designations D396 and D-975.) I i The copolymer flow-improving additive that is used in this invention is a copolymer formed from about 3 to about 40 molar proportions of ethylene, and one normal paraffmic hydrocarbons and having a number average molecular weight within the range of about 600 to 3,000, when added to a middle distillate petroleum fuel oil in a concentration of about 0.01 to about 3 weight percent, will depress the pour point of the fuel oil to some extent and will'also improve the low temperature flowability of the said petroleum fuel oil. Itis mole of at least one second unsaturated monomer. The polymer is oil-soluble and is characterized by having less than six methyl terminating side branches on the polyethylene backbone per 100 methylene groups of the said backbone. Such polymers are preparedby free radical catalysis in a solvent at temperatures of less than C. in order to minimize ethylene branching,

I preferably using free radical catalysts or initiators that wherein R is hydrogen or methyl; R is a OOCR or COOR group wherein R is hydrogen or a C to C preferably a C to C straight or branched chain alkyl group; and R is hydrogen or COOR.,. The monomer,

when R and R are hydrogen and R is OOCR., includes vinyl alcohol esters of C to C monocarboxylic acids, preferably C to C monocarboxylic acids. Examples of such esters include vinylacetate, vinyl isobutyrate, vinyl laurate, vinyl myristate, vinyl palmitate, etc. When R is COOR.,, such esters include methyl acrylate, methyl methacrylate, lauryl acrylate, palmityl alcohol ester of alpha-methylacrylic acid, C Oxo alcohol esters of methacrylic acid, etc. Examples of monomers where R is hydrogen and R and R are COOR., groups, include monoand diesters of unsaturated dicarboxylic acids such as: mono-C Oxo fumarate, di-C Oxo fumarate, diisopropyl maleate; di-lauryl fumarate, ethyl methyl fumarate; etc.

The Oxo alcohols used in preparing the esters mentioned above are isomeric mixtures of branched chain aliphatic, primary alcohols prepeared from olefms, such as polymers and copolymers of C to C, monoolefins, reacted with carbon monoxide and hydrogen in the presence of a cobalt-containing catalyst such as cobalt carbonyl, at temperatures of about 300 to 400F., under pressures of about 1000 to 3000 psi,.to form a1- dehydes. The resulting aldehyde product is then hydrogenated to form the 0x0 alcohol, the latter being recovered by distillation from the hydrogenated product.

As previously mentioned, about 3 to 40 moles of ethylene will be used per mole of other monomer, which other monomer is preferably an ester as hereinbefore defined, or a mixture of about 30 to 99 rnole percent ester and 70 to 1 mole percent ofa C to C preferably C to C branched or straight chain alpha monoolefin. Examples of such olefins include propylene, n-octenel,n-decene-1, etc.

In general, the polymerizations can be carried out as follows: Solvent and a portion of the unsaturated ester, e.g., 0-50, preferably to 30 weight percent, of the total amount of unsaturated ester used in the batch, are charged to a stainless steel pressure vessel which is equipped with a stirrer. The temperature of the pressure vessel is then brought to the desired reaction temperature and pressured to the desired pressure with ethylene. Then catalyst, preferably dissolved in solvent so that it can be pumped, and additional amounts of unsaturated ester are added to the vessel continuously, or at least periodically, during the reaction time, which continuous addition gives a more homogeneous copolymer product as compared to adding all the unsaturated ester at the beginning of the reaction. Also during this reaction time, as ethylene is consumed in the polymerization reaction, additional ethylene is supplied through a pressure controlling regulator so as to maintain the desired reaction pressure fairly constant at all times. Following the completion of the reaction, the liquid phase in the pressure vessel is distilled to remove the solvent and other volatile constituents of the reacted mixture, leaving the polymer as residue.

Usually, based upon 100 parts by weight of copolymer to be produced, about 100 to 600 parts by weight of solvent, and about lto 20 parts by weight of catalyst or initiator will be used.

The solvent can be any non-reactive organic solvent for furnishing a liquid phase reaction which will not poison the catalyst or otherwise interfere with the reaction, and preferably is a hydrocarbon solvent such as benzene, hexane, cyclohexane, dioxane, or t'ert-butyl alcohol.

The temperature used'during the reaction will be in the range of to 130 C., preferably to 125 C. Preferred free radical catalysts or initiators are those which decompose rather rapidly at the prior noted reaction temperatures, for example, those that have a half-life of about an houror less at 130C. preferably. In general, this will include the acyl peroxides of C to C branched or unbranched, carboxylic acids such as di-acetyl peroxide (half-life of 1.1 hours at C.); dipropionyl peroxide (half-life of 0.7 hour at 85C.); dipelargonyl peroxide (half-life of 0.25 hour at 80C.); di-lauroyl peroxide (half-life of 0.1 hour at C.), etc. The lower peroxides such as di-acetyl and dipropionyl' peroxide are less preferred because they are shock sensitive, and as a result the higher peroxides such as di-lauroyl peroxide are especially preferred. The short half-life catalysts. also include various azo free radical initiators such as azodiisobutyronitrile (half-life, 0.12 hour at 100C.); azobis-Z- methylheptonitrile and azobis-2-methyl-valeronitrile. In contrast to the preceding, 'di-tert. butyl peroxide, which has been used extensively in the prior art, has a half-life of about 180 hours at 100C. and a half-life of about 7 hours at C., and does not produce the desired low degree of branching. For example, nuclear magnetic resonance studies indicate that a copolymer of 6 to 6.5 moles of ethylene per mole of vinyl acetate has an average of about 3.5 methyl-terminating side branches on the polyethylene backbone per 100 methylene groups of the'backbone if the copolymer is prepared at 105C. and900-950 psig pressure using lauroyl peroxide catalyst or initiator, but has an average of about 10 to 1 1 such branches if prepared at C. and

900-950 psig and using tert.butyl peroxide catalyst or initiator.

The pressures employed can range between $00 and 30,000 psig. However, relatively moderate pressures of 700 to about 3,000 psig will generally suffice with vinyl esters such as vinyl acetate. In the case of esters having a lower reactivity to ethylene, such as methyl methacrylate, then somewhat higher pressures, such as 3,000 to 10,000 psi have been found to give more optimum results than lower pressures. ln general, the pressure should be at least sufficient to maintain a liquid phase medium under the reaction conditions, and to maintainthe desired concentration of ethylene in solution in the solvent. i

The time of reaction will depend upon, and is interrelated to, the temperature of the reaction, the choice of catalyst, and the pressure employed. In general, however, 05 to 10, usually 2 to 5 hours will complete the desired reaction.

The fractions of essentially saturated hydrocarbons that are used in accordance with thepresent invention in conjunction with the copolymer pour point depressants, are generally amorphous solid materials having melting points within the range of about 80 to 140F. and having number average molecular weights within the range of about 600 to about 3,000. This molecular weight range is above the highest molecular weight of any hydrocarbons that are naturally present in the fuel oil.

An amorphous hydrocarbon fraction that is useful in accordance with this invention can be obtained by deasphalting a residual petroleum fraction and then adding a solvent such as propane to the deasphalted residuum, lowering the temperature of the solvent-diluted residuum, and recovering the desired solid or semisolid amorphous material by precipitation at a low temperature followed by filtration. The residual oil fractions from which the desired hydrocarbons are obtained will have viscosities of at least 125 SUS at 210F.

Most of these residual oils are commonly referred to as bright stocks.

' lecular weight amorphous fraction can be obtained which has only a trace of normal paraffins, about 5 percent of isoparaffins, about 73 percent of cycloparaffins and about 22 percent of aromatic hydrocarbons. In other instances it is necessary to treat the high molecular weight fraction in some manner to reduce its content of normal paraffins. Removal of normal paraffins from an amorphous hydrocarbon mixture can be effected by complexing with urea, as will be illustrated hereinafter in one of the examples. Solvent extraction procedures can also be used, but in many instances they are not as effective as complexing techniques. Thus the amorphous hydrocarbon mixture can be dissolved in a ketone, e.g., methyl ethyl ketone, at its boiling point and then when the solution is cooled to room temperature the normal paraffins will be predominantly precipitated and the resultant supernatant solution will give a mixture containing some normal paraffins but predominating in cycloparaffins and isoparaffins.

Vacuum distillation can also be used for the removal of normal paraffin hydrocarbons from a high molecular weight paraffinic fraction, but such a procedure requires a very high vacuum, i.e., less than 5 mm Hg. absolute pressure, preferably apressure below 3 mm Hg,

absolute, e.g., 2 mm. or 120 microns. If the pressure used is 5 mm or higher, the necessary temperature for the distillation is high enough to cause cracking of the constituents, which is undesirable.

' Tithe following examples, the essentially saturated weight percent of aromatic hydrocarbons, 73 weight percent of cycloparaffins, and no more than a trace of normal paraffin hydrocarbons. The number average molecular weight of this material was about 775 as determined by osmometry. The distillation characteristics of this solid amorphous hydrocarbon fraction were as follows:

(ASTM Vapor Temp. Vapor Temp. D-l l60) at 5 mm Hg. Converted to Atmospheric Pressure Initial BP 442F. 754F. 5% 590 926 10% 636 978 20% 686 I034 24% 689' Only 24% would distill over. There wee percent bottoms, and 1 percent loss.

This invention will be further understood when reference is made to the following examples which include preferred embodiments of the invention. 7

EXAMPLE -1 Fuel oil blends-were prepared using a middle distillate fuel oil consisting of volume percent of cracked distillates having a final boiling point of 660F. and 15 volume percent of heavy virgin naphtha, the fuel oil having a cloud point of +l2F. and a pour point of 5F. To separate portions of this fuel oil there were added various percentage concentrations of the amorphous solidhydrocarbon fraction, essentially free of normal paraffin hydrocarbons, described above. To. other portions of the fuel oil there were added various concentrations of the copolymer of ethylene and vinyl acetate described above. To still other portions of the fuel oil there wereadded both the solid hydrocarbon fraction and the pour point depressant. Each of the resulting fuel oil blends was subjected to a low temperature filterability test which is run as follows:

A 200 milliliter sample of the oil is cooled at a controlled rate of 2F. per hour until a temperature of 0F. is reached, this being the temperature at which the flow test is conducted. The oil is then filtered through a US. 40 mesh screen at the test temperature, and the volume percentage of oil that passes through the screen at the end of 25 seconds is then measured. If at least percent of the oil has gone through the'screen in no more than 25 seconds, the oil is considered to pass the test. The composition of each blend and the low temperature filterability test results are given in Table I, which follows.

TABLE I EFFECT OF SOLID AMORPHOUS HYDROCARBON AND COPOLYMER POUR DEPRESSANT ON LOW TEMPERATURE PROPERTIES OF FUEL OIL Additive Solid Recovery in ASTM Pour Hydrocarbon Copolymer Filterability Point of Blend Test "F 0.4% None l 0"" WW" 0.3% None 5 None 0.02 3 -50 None 0.05 30 None 0.06 36 75 0.4 0.02 100 0.3 0.015 100 20 0.2 0.01 100 0.1 0.015 100 -40 Percentages are by weight.

The data in Table I demonstrate that the combination of the amorphous solid hydrocarbon fraction and the ethylene-vinyl acetate copolymer more effectively improved low temperature flow properties of the fuel than did either additive alone. Thus while it required 0.4 weight percent of the solid hydrocarbon to attain 100 percent recovery in the flow test, only 0.1 weight percent of the added hydrocarbon was needed for 100 percent when 0.0l5 weight percent of the copolymer was present, and yet even four times as much of the copolymer when used alone was not highly effective in improving filterability.

The copolymer flow improver that was used in this example was a copolymer of ethylene and vinyl acetate having a mole ratio of ethylene to vinyl acetate of about 4.2 and having an average molecular weight as determined by vapor phase osmometry of about 1740. A typical preparation of this pour depressant is as follows:

A three-liter stirred autoclave was charged with 850 ml. of benzene as solvent and 40 ml. of vinyl acetate. The vapor space of the autoclave was first purged with a stream of nitrogen and then with a stream of ethylene. The autoclave was then heated to 180F. while ethylene was pressured into the autoclave until the pressure was raised to 750 psig. Then, while maintaining a temperature of 180F. and said 750 psig pressure, 100 mL/hour of vinyl acetate and 160 ml./hour of solution consisting of 12 parts by weight of di-lauroyl peroxide dissolved in'88 parts by weight of benzene, were continuously pumped into the autoclave at an even rate. A

total of 250 ml. of vinyl acetate was injected over 2 hours and minutes, while 440 ml. of the peroxide solution (or about 55 grams of peroxide) were injected into the reactor over a period of two hours and 45 minutes from the start of the injection. After the last of said peroxide was injected, the batch was maintained at 180F. for an additional 15 minutes. Then, the temperature of the reactor contents was lowered to about 140F., the reactor was depressurized, and the contents were discharged from the autoclave. The emptied reactor was rinsed with one liter ofwarm benzene (about 120F.) which was added to the product. The product mixture was then stripped of the solvent and unreacted monomers by blowing nitrogen through it while it was heated on a steam bath. This final stripped product consisted of about 325 grams of copolymer of ethylene and vinyl acetate.

EXAMPLE 2 A copolymer of ethylene, vinyl acetate, and di-C Oxo alcohol fumarate ester is prepared at 900 psig and dure as in the preparation of the vinyl acetate and ethylene copolymer of Example 1. The initial charge is 670 ml. of benzene and 32 ml. of vinyl acetate. A mixture of weight percent of vinyl acetate and 20 weight percent of fumarate esters is injected at the rate of 80 ml. per hour for 145 minutes along with 64 ml. per hour of a solution of 23 weight percent lauroyl peroxide in 77 weight percent of benzene for a total of 155 minutes. A yield of 200 grams of polymer is obtained. A 47 wt. percent solution of the polymer in kerosene has a kinematic viscosity at F. of 42 centistokes. The base fuel oil of Example 1 is improved in low temperature properties by adding thereto 0.02 weight percent of the terpolymer and 0.2 weight percent of the amorphous solid, substantially normal-paraffinhydrocarbon-free fraction used in Example 1.

What is claimed is: l. A wax-containing petroleum distillate fuel having a boiling range within the limits of about 250F. and 700F. which has been improved with respect to its low temperature flow properties by adding thereto:

from about 0.1 to about 3 weight per cent of a flowimproving, amorphous, normally solid essentially saturated hydrocarbon fraction that is substantially free of normal paraffin hydrocarbons, said fraction having a number average molecular weight of from about 600 to about 3000 and having been obtained from a residual petroleum oil, and from about 0.005 to about 1 weight per cent ofa wax-modifying random copolymer of ethylene and an unsaturated ester, said random copolymer having an aveage molecular weight of from about 1,000 to 50,000 and comprising from about 3 to 40 molar proportions of ethylene per molar proportions of other monomers, said copolymer having less than 6 methyl-terminating side branches on the polyethylene backbone per 100 methylene groups of the said backbone, unsaturated ester having the general formula:

l i ii R; R3

wherein:

a. R, is selected from the group consisting of hydrogen and methyl radicals;

b. R, is selected from the group consisting of OOCR and COOR. groups. c. R is selected from the group consisting of hydrogen and -COOR and i d. R, is selected from the group consisting of hydrogen and C, C alkyl groups.

2. Fuel composition as defined by claim 1 wherein the weight ratio of said substantially normal-paraffinhydrocarbon-free hydrocarbon fraction to said random copolymer is from about 1:1 to about 25:1.

3. Fuel composition as defined by claim 1 wherein said copolymer has been prepared in an inert solvent by free radical catalysis at a temperature of about 70to C. using a catalyst having a half life at 130C. under 1 hour.

4. Fuel composition as defined by claim 1 wherein said copolymer is a copolymer of ethylene and vinyl acetate.

5. Fuel composition as defined by claim 1 wherein said copolymer is a terpolymer of ethylene, vinyl acetate, and aliphatic alcohol diester of fumaric acid.

Claims (4)

1. 2. Fuel composition as defined by claim 1 wherein the weight ratio of said substantially normal-paraffin-hydrocarbon-free hydrocarbon fraction to said random copolymer is from about 1:1 to about 25:1.
2. 3. Fuel composition as defined by claim 1 wherein said copolymer has been prepared in an inert solvent by free radical catalysis at a temperature of about 70* to 130*C. using a catalyst having a half life at 130*C. under 1 hour.
3. 4. Fuel composition as defined by claim 1 wherein said copolymer is a copolymer of ethylene and vinyl acetate.
4. 5. Fuel composition as defined by claim 1 wherein said copolymer is a terpolymer of ethylene, vinyl acetate, and aliphatic alcohol diester of fumaric acid.