US3037850A

US3037850A - Middle distillate pour point depressants

Info

Publication number: US3037850A
Application number: US63244A
Authority: US
Inventors: Stephen L Wythe; Jr William C Hollyday
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1960-10-18
Filing date: 1960-10-18
Publication date: 1962-06-05
Anticipated expiration: 1979-06-05
Also published as: DE1232784B; GB940491A

Description

3,037,850 MIDDLE DISTILLATE PGUR PGINT DEPRESSANT S Stephen L. Wythe, Westfield, and William C. Hollyday, Jr., Plainfield, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Oct. 18, 1960, Ser. No. 63,244 Claims. (Cl. 4462) The present invention is concerned with improving the flow of fuels at low temperatures and improving pour point characteristics of middle distillates. More particularly, the invention relates to the preparation of improved low cold test hydrocarbon fuels, in particular heating oils and diesel fuels, kerosene, aviation turbo-jet fuels, and other fuels that are subject to low temperatures. The preferred class of pour depressants are alkylated polystyrene compounds utilized in conjunction with copolymers of ethylene and vinyl acetate. 7

With the increase in the use of hydrocarbon fuels of all kinds, a serious problem has arisen in areas frequently subject to low temperatures in the cold test characteristics of fuels. Particularly, serious problems have been encountered by heating oils and diesel and jet fuels that have too high a pour point, resulting either in distributional or operating difiiculties or both. For example, the distribution of heating oils by pumping or syphoning is rendered diflicult or impossible at temperatures around or below the pour point of the oil. Furthermore, the flow of the oil at such temperatures through the filters cannot be maintained, leading to the failure of the equipment to operate.

It is, of course, well known to add pour depressants to lubricating oils to lower the pour point. These lube oil additives, mostly high molecular weight organic compositions formed by alkylation of benzene or naphthalene or derivatives thereof or by polymerization of lower molecular weight methacrylates, or by condensation polymerization of various kinds, are not satisfactory in service with middle distillate and lighter fuels. Poor performance of these additives might possibly result from the structural differences between waxes occurring in lubricating oils and so-called middle distillates.

A wide variety of compounds have been found to be effective as pour point depressants for lubricating oil. Among the best known are Paraflow, Santopour and Acryloid and their modifications. They are prepared either by condensing aromatic compounds with long chain parafiins, such as wax, or by condensing olefinic esters. It is generally considered that these pour depressants are effective in that in cooling an additive-containing oil, the hydrocarbon chain of the additive becomes incorporated into the crystal lattice of the separated wax, while the other part of the pour depressant molecule prevents the crystals from adhering together to form a gel structure. The failure of these additives to be effective in middle distillates may at least in part be due to the basic difference in the composition between the wax in lubricating oils and that in middle distillate fuels.

It is, therefore, the principal object of the present invention to set forth an improved pour depressant for middle distillate and lighter fuels. these oils are generally about 250 to 750 F.

The petroleum distillate fuels in which the additive materials of the invention are employed consist of a major proportion, at least 95%, of liquid hydrocarbons boiling at temperatures between about 70 F. and about 750 F. These fuels include gasolines such as aviation, marine and automotive or motor gasolines, aviation turbo-jet fuels such as JP-l, JP-4 andJP 5 fuels, and diesel fuels such as marine, stationary and automotive diesel engine fuels.

Aviation turbo-jet fuel consists of at least 95% of a 3,037,850 Patented one 5, 1 962 'r ce mixture of volatile hydrocarbons. It is defined by US. Military Specifications MIL-:F-5616 and MIL- -F-S 624 C. Its volatility is suchthat its endpoint does not exceed 572 F. Its viscosity is between 0.5 and 1.5 centistokes at 100 F. 7

Diesel fuels as referred to in connection with the invention consist of at least 95% of a mixture of hydrocarbons boiling between 250 F. and 750 F. either by ASTM Method D-8656 when their end points do not exceed 600 F. or by ASTM Method D-158-54. Diesel fuels are defined byEASTM Specification D-975-53T and fall into grades 1D, 2D and 4D, in all of which the additive materials of the invention may be used. They have viscosities between 1.4 and 26.4 centistokes.

The liquid fuels in which the additive materials may be incorporated thus comprise at least 95% by weight of a mixture of hydrocarbons having a boiling range between the limits of 75 F. and 750 F. and a viscosity between the limits of 0.264 and 26.4 centistokes at 100 F.

In accordance with the present invention, a synergistic efiect is secured by utilizing two different classes of pour depressants in conjunction with each other. The first class of pour depressants comprises alkylated polystyrene compounds while the second class of pour depressants to be utilized in conjunction with the first class of pour depressants comprises copolymers of ethylene and vinyl esters, particularly vinyl acetate. V

The first class of pour depressants comprising alkylated polystyrene compounds are prepared with certain olefins and have a critical composition. The olefin should have a molecular weight in the ranget200 to 250 and if it is a mixture at least- 95 mole percent of the olefins should have molecular weights individually in the range of 170 to 280. The alkylates of interest have the following structure:

The boiling ranges of R is an alkyl group, straight or branched, containing 9 carbon atoms or less while R is a straight-chainalkyl group containing 10 carbon atoms or more, x is the number from 3 to 15 inclusive and y is 0.75 to 2.00.

All products were made under the reaction conditions of solvent, temperature, catalyst and finishing procedure as described in U.S. Patent No. 2,756,265 assigned to Esso Research and Engineering Company, entitled Alkyl- 'ated Polystyrene Pour Depressants, inventor; William C. Hollyday,Jr. V

Broadly, the process comprises the steps of dissolving the desired polystyrene in an inert solvent and heating the mixture until the polystyrene is completely in solution. The mixture is cooled to the desired reaction temperature at which time the nitrobenzene and the Friedel- Crafts catalyst is added. The alkylating agent is then groups.

added dropwise and the reaction temperature selected is maintained by cooling or heating as necessary. After the completion of the reaction, the alkylates are purified by well known techniques, among which is precipitation with methanol, dissolving'in' hexane and reprecitating several times with methanol or isopropanol. If desired, the

alkylated material may be dissolved in oil, washed with alkaline solutions, and the oil solution then steam stripped to result in the final product. i For obtaining the superior pour point depressants of this invention, it is desired that the polystyrene starting material have an intrinsic viscosity within a range of about 0.2 to 1.0, preferably 0.8 to 1.5. These viscositiescorrespond to molecular weights within a range of from about 10,000 to 75,000, preferably 30,000 to 60,000 Staudinger. Since the amounts of the other reactants are based on the weight of the polystyrene, the amount of polystyrene used will depend upon restrictions such as equipment capacity, etc. 'The cryoscopic molecular Weight after alkylation was about 700 to 5,000; the intrinsic viscosity about 0.1 to 0.5.' The 700 molecular weight comprises, in essence, a trimer containing three alkylated phenyl groups, whereas, the 3,000 molecular weight comprises, in essence, about eight alkylated phenyl The alkylation agent chosen for the preparation of the improved pour point depressants of this invention will be olefinic in nature and will preferably contain from 14 to :18 carbon atoms in a straight chain. Although dodecene1 through eicosylene and cracked Wax are used, any olefinic material having the above requirements maybe used. It is preferred that equimolar quantities of polystyrene and the alkylating agent be used, however, from 0.80 to 2.00 mols of alkylation agent per mol equivalent of polystyrene is operable. p

' These alkylated polystyrenes should be prepared wherein the olefin mixture has a molecular weight of about 224 (that of n-hexadecene). The polystyrenes should have a molecular weight within a range of from about 10,000 to 75,000, preferably 30,000 to 60,000 Staudinger. These molecular weights correspond to intrinsic viscosities within the range of from 0.2 to 2.0, preferably 0.8 to 1.0. The alkylating agent contemplated contains 12 to 20 carbon atoms in a straight chain. A chlorinated aromatic hydrocarbon is used as a solvent and a Friedel- Crafts catalyst in amounts varying between and by weight based on the weight of the polystyrene. The preferred catalyst modifier, nitrobenzene, is present in junction with the first class of pour depressants so as to secure synergistic results are copolymers of ethylene and a vinyl acetate. It is preferred that the parts by weight of ethylene in the copolymer be in the range from about 60 to 99% as. compared to parts by weight of vinyl ace: tate in'the range from about 40 to'about 1%. A very desirable ethylene-vinyl acetate copolymer contains from about 15 to 25% by weight of vinyl acetate, as for example, about 20% parts by weight of vinyl acetate.

The molecular weights of the ethylene-vinyl acetate copolymer are critical and should be in the range from about 1,000 to 3,000, preferably, in the range from about 1,500 to 2,200. The molecular weights are determined by K. Rast s method (Ber. 55, 1051, 3727 (1922)).

The ethylene-vinyl acetate copolymer as described above is used usually in a concentration in the range from about .001 to .5% by weight, preferably, in a concentration in the range from about .005 to .1% by weight. The low molecular weight copolymers may be prepared by any peroxide process. In some instances, it may be desirable to first prepare a higher average molecular weight polymerization product and then recover from that product material having a molecular weight within the range between about 1,000 and about 3,000. Since such polymerization products normally consist of a smear of polymers whose molecular weights vary over a wide range, an eifective methodifor recovering the 1,000 to 3,000 molecular weight portion therefrom is to extract the product with a solvent such as normal heptane or methyl-ethyl ketone. Other methods for obtaining the low molecular weight materials include thermal degradation of the high molecular weight polymer or treatment of the high molecular weight polymer with ozone in order to break the polymer chains. Still other methods also useful will be apparent to those skilled in the art.

A very desirable method is to conduct polymerization in a benzene solution using di-tertiary-butyl-perox- .ide as an initiator at a temperature in the range from about 280 to 340 F. The preferred temperature is about 300 F. The pressure is in the range from about 700 to-2,000 pounds, preferably, at about 800 pounds. The autoclave or similar equipment containing the solvent, initiator and vinyl acetate is purged about three times with nitrogen twice with ethylene and then charged with a sufficient amount of ethylene to yield the desired pressure when heated to the reaction temperature.

' During the polymerization, additional ethylene is added amounts so that the mol ratio of nitrobenzene to the cat- K varies between 6.0 and =15, where C equalsthe weight ratio of catalyst to polystyrene, T is the temperature F., and R is the ratio of mols of catalyst modifier to mols of aluminum chloride. By this particular process advantageous yields of an alkylated polystyrene pour depressant having an overall activity in a wide range of lubricating oils may he obtained.

As pointed out heretofore, the pour depressant agents have a cryoscopic molecular weight in the range from about 700 to 3,000 to 5,000 and an intrinsic viscosity in the range from about 0.1 to 0.5. These compounds are used a weight concentration of about 0.002 to 0.20. A somewhat more preferred concentration is inthe range from about 0.005 to 30.05 weight percent. A very desirable concentration to 'be used is in the range from about whenever the pressure drops by about p.s.i.g. Polymerization is considered complete when it is less than 50 p.s.i.g. pressure drop per hour. The product is stripped free of solid and untreated vinyl acetate under vacuum. Various amounts of the pour depressants of the present invention and the various salts were utilized in distillate fuels. A typical distillate fuel boiling in the range from 250 to 750 F. to which the present additives were added are middle distillate heating oils. These fuels are of commercial grade and have typical proper'tie's as follows: r a

TABLE I Synergistzc Pour Depressant Activity of Pour Depressant Mixtures Pour Pt., F., with Additive Indicated Total Wt. Test Oil Description Per- 50/50 (B)Ethcent, (A) Mixylene/ Poly- Alkyl ture Vinyl mer Poly- (A) Acetate styrene (B) Copolymer l-Stralght Run, Venezuela Crude, 0.01 20 15 15 10 F. Pour Point 0.02 20 25 25 0. 03 20 35 30 0. 01 +20 +20 +15 2-Cracked, Venezuela Crude, 0. 02 +20 ---25 +15 25 F. Pour Point 0. 03 +15 30 --26 0.05 5 40 0.10 20 45 3-Mixed (Straight Run Crack- 0. 01 +10 +5 +5 ed), Venezuela Crude, 10 F. 0.02 10 l5 Pour Point .4 0.03 --15 -15 0.05 20 25 15 0. -35 40 30 0. 01 15 15 A-Mixed, Venezuela Louisiana 0.02 30 -20 Crudes, 0 F. Pour Point 0.03 35 25 0. 05 -35 -35 35 0.10 -40 45 40 0. 01 +15 +15 0 fi-Mixed, Canadian Crude, 20 0.02 +5 0 10 F. Pour Point 0. 03 0 -20 0.05 30 60 0. 10 30 75 -66 The inspections of the above-identified base oils are as follows:

The practical importance of this synergistic action is illustrated in Table H where the actual amounts of polymer needed to reach a given pour point in each of the five middle distillates (listed in Table I) are compared. It will be seen that in every case a considerable saving in total polymer can be realized by using a mixture of polymers instead of either polymer separately. The savings in total polymer required for a given pour point ranges from 33 to 67%, with a corresponding savings in treating cost, since the polymers intrinsically cost about the same.

TABLE II Polymer Savings Due to Synergzstic Actzon Wt. Percent Polymer Required Percent Depressed Polymer Test Oil No. Pour (B) Eth- Saved in Table I Point, (A) Alkyl ylene/ 50/50 with Poly- Vinyl (A) (A) styrene Acetate (B) (B) Copolymer The alkylated polystyrene used in the examples given had one C (average) alkyl group per group and an intrinsic viscosity of about 0.124. Intrinsic viscosities in the range 0.100 to 0.600 are suitable. The ethylene/vinyl acetate copolymer contained about 34 weight percent vinyl acetate and had an intrinsic viscosity of 0.350. About 18 to 38% vinyl acetate and intrinsic viscosities in the range 0.100 to 0.600 are suitable.

The present invention is concerned with the utilization of two classes of pour depressants in combination with each other. The amount of one pour depressant as compared to the other may vary from 25-75% to -25% although it is preferred that the ratio weight percent of one pour depressant as compared to the other vary from about 60-40 weight percent to 40-60 weight percent.

What is claimed is:

1. A petroleum distillate fuel composition having an improved pour which comprises essentially a petroleum distillate fuel boiling in the range between about 250 F. and about 750 F. which has been improved with respect to pour point by the incorporation therein of a pour depressing efiective amount in the range from about .002 to .2% by weight of a pour depressant which consists in combination an alkylated polystyrene plus a copolymer of ethylene and vinyl acetate, said copolymer being characterized by having a molecular weight in the range from about 1000 to 3000 and being further characterized by containing from about 1% to 40% by weight of vinyl acetate in the copolymer, said alkylated polystyrene being chanacter'ized by having a molecular weight in the range from about 700 to about 3000 and being further characterized by having about one alkyl group containing from 12 to 20 carbon atoms per ring.

2. Composition as defined by claim 1 wherein the weight percentage of alkylated polystyrene present varies in the range from about .03 to .1 and wherein the amount of copolymer present varies in the range from about .03 to .05% by weight.

3. Composition as defined by claim 1 wherein the amount of said alkylated polystyrene as compared to said copolymer varies in the range from about 40 to 60% by weight.

4. Composition as defined by claim 1 wherein the pour depressant comprises about 50% by weight of said alkylated polystyrene and 5 0% by weight of said copolymer.

5. Composition as defined by claim 1 wherein the amount of said pour depressant added is in the range from about .01 wt. percent to .03 wt. percent.

References Cited in the file of this patent UNITED STATES PATENTS 2,499,723 Oofiman et a1. Mar. 7, 1950 2,703,817 Serniuk Mar. 8, 1955 2,756,265 Hollyday July 24, 1956

Claims

1. A PETROLEUM DISTILLATE FUEL COMPOSITION HAVING AN IMPROVED POUR WHICH COMPRISES ESSENTIALLY A PETROLEUM DISTILLATE FUEL BOILING IN THE RANGE BETWEEN ABOUT 250* F. AND ABOUT 750*F. WHICH HAS BEEN IMPROVED WITH RESPECT TO POUR POINT BY THE INCORPORATION THEREIN OF A POUR DEPRESSING EFFECTIVE AMOUNT IN THE RANGE FROM ABOUT .002 TO .2% BY WEIGHT OF A POUR DEPRESSANT WHICH CON SISTS IN COMBINATION AN ALKYLATED POLYSTYRENE LPUS A COPOLYMER OF ETHYLENE AND VINYL ACETATE, SAID COPOLYMER BEING CHARATERIZED BY HAVING A MOLECULAR WEIGHT IN THE RANGE FROM ABOUT 1000 TO 3000 AND BEING FURTHER CHARACTERIZED BY CONTAINING FROM ABOUT 1% TO 40% BY WEIGHT OF VINYL ACETATE IN THE COPOLYMER, SAID ALKAYLATED POLYSTYRENE BEING CHARACTERIZED BY HAVING A MOLECULAR WEIGHT IN THE RANGE FROM ABOUT 700 TO ABOUT 3000 AND BEING FURTHER CHARATERIZED BY HAVING ABOUT ONE ALKYL GROUP CONTAINING FROM 1I TO 20 CARBON ATOMS PER RING.