US3100695A

US3100695A - Middle distillate pour point depressants

Info

Publication number: US3100695A
Application number: US63245A
Authority: US
Inventors: Roman S Slysh; 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: 1963-08-13
Anticipated expiration: 1980-08-13
Also published as: GB940492A; DE1253508B

Description

Unite S tates 3,100,695 MIDDLE DISTILLATE POUR POINT DEPRESSANTS Roman S. Slysh, Scotch Plains, and William C. Hollyday, Jr., Plain'field, N.J., assignors to Esso Research and Engineering Company, a corporation of Delaware N Drawing. Filed Oct. 13, 1960, Ser. No. 63,245

6 Claims. (Cl. 44-62) The present invention relates to improving the flow at low temperatures and at 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, aviation, and other fuels that are subject to low temperatures. In accordance with the present invention, an improved class of pour depressants are utilized in conjunction with surface active agents in middle distil-lates. The preferred class of pour depressants are alkylated polystyrene compounds and copolymers of ethylene and vinyl acetate which copolymers have a molecular weight between 700 and 5,000. Preferred surface active agents for utilization in combination with these pour depressants comprise sulfonic acid and various salts of sulfonic acid. The preferred salts are those of Group II metals of the periodic table, particularly the alkaline earth metals and zinc. Very desirable metals are calcium and barium, particularly the calcium sulfonates,

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 fuels that have too high a pour point, resulting either in distributional or operating difliculties or both. For example, the distribution of heating oils by pumping or syphoning is rendered difiicult 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 po ly'merization of various kinds, are not satisfactory in service with middel 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 effec- 31,100,695 Patented Aug. 13, 1963 tive 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. The boiling ranges of these oils are generally about. 250 to ,750 F. The per troleum distillate fuels in which the additive materialsof the invention are employed consist of a major proportion, at least 95%, of liquid hydrocarbons boiling at temperatures between about F. and about 750 F. These fuels include gasolines such as aviation, marine and automotive or motor gasolines, aviation fuels such as JP-l, IP-4, and lP-S fuels, and diesel fuels such as marine, stationary and automotive diesel engine fuels, Aviation fuel consists of at least of a mixture volatile hydrocarbons. It is defined by U.S. Military Specifications MIL-F-56l6 and MIL-F-5624 C. Its. volatility is such that its end point does not exceed572 F. Its viscosity is between 0.5 and 1.5 centistokes at F.

Diesel fuels as referred to in connection with. the invention consist of at least 95% of a mixture of hydro carbons boiling between 250 F. and 750 F. either by ASTM Method D 86-56 when their end points do not exceed 600 F. or by ASTM Method D-l58-54. Diesel fuels are defined by ASTM Specification D975.-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 bet-ween 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.

As pointed out heretofore, one class of pour depressants to be used in conjunction with the sulfonic salts are certain alkylated polystyrene compounds. These alkylated polystyrene compounds are prepared with certain olefins and have a critical composition. The olefin should have a molecular weight in the range 200 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 to 280. The alkylates of interest have the following structure:

Polystyrene Pour Depressants, Inventor: William C. Hollyday, I r.

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 added dropwise and the reaction temperature selected is maintained by cooling :or heating as necessary. After the completion ofthe reaction, the alkylates are purified by well known techniques, among which is precipitation with methanol, dissolving in hexane and reprecipitating 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.

For obtaining the superior pour point depressants of thisinvention, it is desired that the polystyrene starting material have an intrinsic viscosity within a range of about 0.2 to 2.0, preferably 0.8 to 1.5. These viscosities correspond to molecular weights within a range of from about 10,000 to 75,000 preferably 30,000 to 60,000 Staudinger, if the constant for isobutylene polymers is as sumed to apply. 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 3,000; 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 groups.

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 dodecene-l" through eicosylene and cracked wax are used in the examples specifically detailing the instant invention, any olefinic material having the above requirements may be 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.

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 1.5. 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 cataylst in amounts varying between 10 and 20% by weight based on the weight of the polystyrene. The preferred catalyst modifier, nitrobenzene, is present in amounts so that the mol ratio of nitrobenzene to the catalyst is from 0.2 to 0.8. Reaction temperatures within a range of from 80 to 150 F. are used. These operable reaction conditions are so adjusted that in the relationship.

T 1+R K varies between 6.0 tand 15, where C equals the 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 be obtained.

As pointed out heretofore, the pour depressant agents have a cryoscopic molecular weight in the range from about 700 to 3,000 and an intrinsic viscosity in the range from about 0.1 to 0.5. These compounds are used in a weight concentration of about 0.002 to 2.00. A somewhat more preferred concentration is in the range from about 0.005 to 0.25 weight percent. A very desirable concentration to be used is in the range from about .025 to 0.1 weight percent.

Another class of pour depressants to be used in conjunction with the sulfonic acid salts comprise an ethylenevinyl acetate copolymer. It is preferred that the parts by weight of ethylene in the copolymer be in the range from about 60 to as compared to parts by weight of vinyl acetate in the range from about 40 to about 1%. A very desirable ethylene-vinyl acetate copolymer contains about 15 to 40% 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 5,000, preferably in the range from about 1,500 to 4,000. The molecular weights are determined by K. Rasts method (Ber. 55, 1051, 3727 (1922)). The intrinsic viscosities fall in the range from 0.08 to 0.50.

The ethylene-vinyl acetate copolymer as described above is used in a concentration in the range fromabout .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 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. effective method for 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 A very desirable method is to conduct polymerization in a benzene solution using di-tertia ry-butyl-peroxide 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 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 unreacted vinyl acetate under vacuum.

The sulfonic acid and sulfon-ic acid salts which comprise the surface active agents of the present invention to be used inconjunction with the hereinbefore described pour depressants are prepared as follows:

The sulfonic acid from which the sulfonates were derived was prepared during the manufacture of a white oil from a lubricant base stock. The lubricant base stock had a viscosity of about 3.22 cs. at 210 F. and 14.4 cs. at 100 F. and an API gravity of 29.6, and was treated with a mixture of sulfuric acid and sulfur trioxide (80/20 by weight). During the sulfonation the temperature was kept between about and F. with cooling. The sulfonic acid was extracted from the unsulfonated hydrocarbon with a water and isopropyl alcohol mixture. The free sulfonic' acid was isolated by evaporating the isopropyl alcohol and water.

The sulfonic acid had a molecular weight of about 525 and an average composition corresponding to the formula C H (C H SO H. The actual composition of this and other sulfonates derived from petroleum base stocks is if quite complicated. The sulfonic acid is actually a mixture of materials containing naphthenic (saturated) as well as aromatic rings and various alkyl groups. Diiferent molecules may also contain more than one ring (which may or may not be condensed), and more than one alkyl group.

Various metal salts of the 'sulfonic acid were prepared by neutralizing the acid with hydroxides of metals. The sulfonic acid dissolved in kerosene readily took up the hydroxides from aqueous solutions or suspensions to give a solution of the metal sulfonate in kerosene.

Sodium, calcium, aluminum, and stannic sulfonates among othersjwere prepared in this way.

Various amounts of the pour depressants and the various sulfon-ates in'kerosene were blended into distillate fuels and tested for pour depressant activity. A typical dis-tillate fuel boiling in the range from 250 to 750 F. to which the present additives may be added are middle distillate heating oils. 1 These fuels are of commercial grade and have typical properties as follows:

The improvements obtained by adding the additives in accordance with the present invention are set forth in the following table. All pour points quoted hereafter were obtained by ASTM Method D97-47.

In a first series of tests, an alkylated polystyrene prepared as described and having an intrinsic viscosity of 0.122 and a molecular Weight of about 925 was added to a cracked heating oil stock from a Venezuelan crude which had a 25 F. pour point. The inspections of this cracked heating oil were as follows: boiling 'range 408- 660 F., API gravity 23.7, viscosity 3.62 cs. at 100 F. The salts used in the first series of tests comprised the calcium salts, the sodium salts, the aluminum salts, the stannic salts, and the acid itself. The results of these tests are shown in the following Table I wherein alkyl PS represents a-lkylated polystyrene.

From the foregoing, it is apparent that calcium sulfomate has an appreciable efiect in enhancing the pour depressant activity, in cracked stocks, of both the alkylated aromatic (Table I) and the ethylene-vinyl acetate copolymer (Table II). Its effect whenfu-tilized in straight run stocks is somewhat lessened (Table III).

i "In' a second series of tests, the sulfonic agents of the present invention were used in conjunction with a copolymer of ethylene and vinyl acetate prepared as hereinbefore described. The cop'olymer contained about 34 weightpercent vinyl acetate and had an intrinsic viscosity of 0.354 and a molecular weight of about 4,000. The base stock was a Venezuelan cracked heating oil similar to that described with [respect to the first series or tests.

The results of the second series of tests are shown in the following Table II.

Table II EFFECT OF SURFACE ACTIVE AGENTS ON POUR DEPRESSANT ACTIVITY OF ETHYLENE/VINYL ACE- TATE COPOLYMER 1 Copolymer Calcium sulfonate Combination blendsPour blends blends point, F., blends with copolymer plus sulfonate Weight Pour Weight Pour percent point, percent Point copoly- F. calcium F. 0211- Alumi- Stannic met sulfonate cium num 1 In a cracked heating oil stock from Venezuela crude, +25 F. original pour point.

In the third series of tests, the calcium sulfonate was used in conjunction with \both classes of the pour depressants utilizing a straight run stock. The stock had a boiling range of 354 to 624 R, an API gravity of 37.6 and a viscosity of 2.35 cs. at 100 F.

35 The results .ofthese tests are illustrated 1n the followlng Table III;

Table III EFFECT OF SURFACEACTIVE'AGENT ON POUR 40 DEPRESSANT ACTIVITY 1 t 1 Pour point, F., with additive indicated Weight Pour depressant percent polymer Polymer Polymer plus on y ea e um l l i sulfonate Z Alkylated polystyrene; 0. 01 -20 -20 0.02 25 35 0.03 -30 35 0 0.05 35 -40 Ethylene/vinyl acetate copolymen--- 0.01 -15 -20 0.02 -25 35 0.03 30 40 0.05 +30 60 1 In a straight run heating oil stock from Venezuela crude, +10 F. original pour. point.

2 Calcium sulfonate added equal to polymer.

Table 1 EFFECT OF SURFACE ACTIVE AGENTS ON THE POUR DEPRESSANT ACTIVITY OF ALKYLATED POLYSTYRENE 1 Alkyl polystyrene Calcium sulionate Combination blends-Pour point, F. blends with alkyl blends blends PS plus sulfonate Weight Pour Weight Pour percent point, percent 2 point, Calcium Acid Sodium Aluminum Stanmc alkyl .PS F. calcium F.

sulfonate 1 In a cracked heating 011 stock from Venezuela crude, 4-25 F. original pour point.

2 Also weight percent other salts.

In a fourth series of tests,v calcium sulfonate was used in conjunction with both classes of polymers wherein the base stock was a mixed straight run and cracked stock froma Venezuelan crude. This stock had a boiling range of 408-660 R, an API gravity of 33.0 and a viscosity of 3.70 cs. at 100 F.

The results of these tests are shown in the following Table IV...

In a mixed straight run/cracked (50/40) heating oil stock from Venezuela crude, +10 F. original pour point.

2 Constant amount (0.05 weight percent) calcium sulfonate in each blend. 7 p .p

From the above, it is apparent that in mixed cracked/ straightrun stocks, calcium sulfonate has a desirable effect on the copolymer and a lesser effect on thealkylated aromatic. In a fifth series of (tests, a mixed heating oil from a Canadian crude was utilized using the various surface active agents. The base stock had a boiling range of 316 to 685 F. andan'API gravity of 28.3. g

The results of these tests are shown in the following Table V.

Table V Table VI EFFECT OF SURFACE ACTIVE AGENT N POUR DEPRES- S ANT ACTIVITY Pour point, F.,with additive indicated Heating oil test stock Weight 7 percent polymer 2 Polymer Polymer+ only calcium sulionate 3 Cracked (+25 F. original four point). 0. 01 +20 0 0.03 -30 -40 0.05 740 -45 0.10 -45 -65 Straight run (+10 F. original pour point) 0. 01 30 0.03 -25 -35 0.05 25- -35 0.10 -35 -40 Mixed F. original pour polnt) 0. 01 +5 5 i 0.03 0.05 -25 0; 10 -40 -40 1 In heating oil stocks from Venezuela crudes.

2 Polymer is a 50/50 mixture of alkylatcd polystyrene and ethylene/ vinyl acetate copolymer. For example, 0.01 weight percent polymer equalls 0.005 weight percent alkyl polystyrene plus 0.005 weight percent copo ymer. m (Eionstant amount (0.05 weight percent) calcium sulionate in each copolymers of ethylene and vinyl acetate in combination with a surface active agent present in a concentration in the range from about .005 to .25 by weight selected from the class consisting of petroleum sulfonic acids and salts of petroleum sulfonic acids, said copolymer be- EFFECT OF SURFACE ACTIVE AGENTS 0N POUR DEPRESSANT ACTTVITY 1 Pour point, F., blends of polymer with added agent indicated 1 Weight Iour Depressant percent v polymer High Zinc Barium Polymer alkaline di-alkyl Calcium alkyl only Ba thio- PzS /HC 4 phenate sulionate 3 phosphate Alkylated polystyrene 0. 01 +15 +10 +15 +15 +15 0.03 0 -10 -10 0 -5 0. 05 -25 -25 -35 -25 0. 10 -30 -35 -45 -45 -45 Ethylene/vinyl acetate copolymer 0. 01 +15 +5 +5 +10 +15 0. 03 -20 -15 -20 -30 -45 0. 05 35 -50 35 0. 10 -65 -75 -75 75 75 1 In a mixed straight run/cracked heating oil stock from Canadian crude, +20 F. original pour point. 2 Surface active agent added equal to polymer, on active ingredient basis.

a Colloidal barium carbonate dispersed in calcium sulfonate solution.

4 Product from treatment of 780 molecular weight polybutene with weight percent 3PzS5, then neutralized with high alkalinity calcium sulfonate.

In a sixth series of tests, a /50 mixture of an alkylated polystyrene was used in conjunction with a copolymer of ethylene/vinyl acetate in various base stocks. The cracked stock had a boiling range of 408-660 -F.,

'an API gravity of. 23.7, and a viscosity of 3.62 cs. at

100 F. The straight mun stock had a boiling range of 354-624 R, an API gravity of 37.6, and a viscosity of 2.35 cs. at 100 F. The mixed stock had a boiling range V of 408-660 R, an API gravity of 33.0 and aviscosity of 3.70 cs. at 100 F.

The results of these tests are shown in the following Table VI.

ing characterized by having a molecular weight in the petroleum sulfonic acid has a molecular-weight of about 525.and an average composition corresponding to the 3. The composition as idefined vby claim 1 wherein 6. The composition as defined by claim 1 wherein said petroleum sulfonic acid salts are salts of metals of Said Petroleum sflllfonic acid Salt is calcium onate. Group 110i the Pericldic tabie- References Cited in the file of this patent 4. The composition as defined by claim 1 wherein said petroleum sulfonic acid salts are alkaline earth 5 UNITED STATES PATENTS i 2,499,723 Coifman et al Mar. 7, 1950 me 2,703,817 Serniuk Mar. s, 1955 5. The COIHPOSLHOH as defined lay claim 1 wherein 2,756,265 Hollyday July 24, 1956 said petroleum sulfonic acid salt is zinc sulfonate- 2,917,378 Vitalis Dec. 15, 1959

Claims

1. A PETROLEUM DISTILLATE FUEL COMPOSITION HAVING AN IMPROVED POUR WHICH CONSISTS ESSENTIALLY OF 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 .001 TO 5% BY WEIGHT OF A POUR DEPRESSANT SELECTED FROM THE CLASS CONSISTING OF ALKYLATED POLYSTYRENES AND COPOLYMERS OF ETHYLENE AND VINYL ACETATE IN COMBINATION WITH A SURFACE ACTIVE AGENT PRESENT IN A CONCENTRATION IN THE RANGE FROM ABOUT .005 TO 25% BY WEIGHT SELECTED FROM THE CLASS CONSISTING OF PETROLEUM SULFONIC ACIDS AND SALTS OF PETROLEUM SULFONIC ACIDS, SAID COPOLYMER BEING CHARACTERIZED BY HAVING A MOLECULAR WEIGHT IN THE RANGE FROM ABOUT 1,000 TO 3,000 AND BEING FURTHER CHARACTERIZED BY CONTAINING FROM ABOUT 1% TO 40% BY WEIGHT OF VINYL ACETATE IN THE COPOLYMER, SAID ALKYLATED POLY-STYRENE BEING CHARACTERIZED BY HAVING A MOLECULAR WEIGHT IN THE RANGE FROM ABOUT 700 TO 3,00 AND BEING FURTHER CHARACTERIZED BY HAVING ABOUT ONE ALKYL GROUP CONTAINING FROM ABOUT 14 TO 18 CARBON ATOMS PER RING.