MIDDLE DISTILLATE FUEL CONTAINING ADDITIVE COMBINATION TO INCREASE LOW TEMPERATURE FLOWABILITY
United States Patent 3773478
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 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. The fuel oil also contains a polymeric additive, usually in a lesser amount than said high molecular weight paraffinic fraction, said polymeric additive being characterized by having an average of at least one long alkyl side chain for every four carbon atoms along the polymer chain. This additive combination is unique in that the polymeric additive does not interfere with the flow improving properties of the high molecular weight hydrocarbon, and the high molecular weight hydrocarbon does not interfere with the pour point depressing properties of the polymeric additive, whereas such interference is encountered when using other conventional polymeric pour depressants such as a copolymer of ethylene and an unsaturated ester.
US Patent References:
Method for producing very low pour oils from waxy oils having boiling ranges of 680 deg.-750 deg. f. by distilling off fractions and solvents dewaxing each fraction
Farmer et al. - September 1959 - 2906688
Diesel fuel
MacLaren - October 1939 - 2177732
Fuel oils
Hudson - December 1959 - 2917375
Hydrocarbon fuel oil of lowered pour point
Winterhalter - December 1953 - 2664388
Synergistic mixture of pour depressants for middle distillates
Wythe et al. - December 1962 - 3069245
Method for producing very low pour oils from waxy oils having boiling ranges of 680 deg.-750 deg. f. by distilling off fractions and solvents dewaxing each fraction
Farmer et al. - September 1959 - 2906688
Diesel fuel
MacLaren - October 1939 - 2177732
Fuel oils
Hudson - December 1959 - 2917375
Hydrocarbon fuel oil of lowered pour point
Winterhalter - December 1953 - 2664388
Synergistic mixture of pour depressants for middle distillates
Wythe et al. - December 1962 - 3069245
Application Number:
04/807965
Publication Date:
11/20/1973
Filing Date:
03/17/1969
View Patent Images:
Export Citation:
Assignee:
Esso Research and Engineering Company (Linden, NJ)
Primary Class:
Other Classes:
44/459
International Classes:
C10L1/14; C10L1/16; C10L1/18; C10L1/10; C10L1/18
Field of Search:
44/62,70 208/33,15 252/56
US Patent References:
Primary Examiner:
Wyman, Daniel E.
Assistant Examiner:
Smith, Mrs. Y. H.
Claims:
What is claimed is
1. A wax-containing petroleum distillate fuel having a boiling range within the limits of about 250° F. and 700° F. which has been improved with respect to its low temperature flow properties by adding thereto:
2. Fuel composition as defined by claim 1 wherein there are present from about 0.2 to 1 wt. % of said substantially normal-paraffin-hydrocarbon-free fraction and from about 0.01 to 0.1 wt. % of said polymeric pour point depressant.
3. Fuel composition as defined by claim 1 wherein the proportion of said substantially normal-paraffin-hydrocarbon-free fraction to said polymeric pour point depressant is within the range of 50:1 to 1:1, parts by weight.
4. Fuel composition as defined by claim 1 wherein said polymeric pour point depressant is an alkylated polystyrene.
5. Fuel composition as defined by claim 1 wherein said polymeric pour point depressant is a copolymer of alkyl fumarates and vinyl acetate.
1. A wax-containing petroleum distillate fuel having a boiling range within the limits of about 250° F. and 700° F. which has been improved with respect to its low temperature flow properties by adding thereto:
2. Fuel composition as defined by claim 1 wherein there are present from about 0.2 to 1 wt. % of said substantially normal-paraffin-hydrocarbon-free fraction and from about 0.01 to 0.1 wt. % of said polymeric pour point depressant.
3. Fuel composition as defined by claim 1 wherein the proportion of said substantially normal-paraffin-hydrocarbon-free fraction to said polymeric pour point depressant is within the range of 50:1 to 1:1, parts by weight.
4. Fuel composition as defined by claim 1 wherein said polymeric pour point depressant is an alkylated polystyrene.
5. Fuel composition as defined by claim 1 wherein said polymeric pour point depressant is a copolymer of alkyl fumarates and vinyl acetate.
Description:
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 fuel will 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 filters. 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.
RELATED ART
It is taught in the application of Nicholas Feldman and Wladimir Philippoff entitled "Increasing Low Temperature Flowability of Middle Distillate Fuel", Ser. No. 807,953 filed simultaneously with the present application and subsequently issued on May 2, 1972 as U.S. Pat. No. 3,660,058, that a paraffinic hydrocarbon fraction that is substantially free of normal paraffin hydrocarbons i.e., contains no more than about 5 wt. %, and preferably no more than about 1 wt. % of normal paraffin hydrocarbons, and that has a number average molecular weight of from about 600 to about 3,000, when added to a middle distillate petroleum fuel oil in a concentration of about 0.01 to about 3 wt. % 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.
DESCRIPTION OF THE INVENTION
In accordance with the present invention, it has now been found that further improvement in the low temperature properties of a petroleum fuel oil can be obtained if there is employed in combination with the high molecular weight hydrocarbon fraction a particular type of polymeric pour point depressant which is characterized by having, on the average, at least one long dependent alkyl hydrocarbon group for every 4 carbon atoms of the backbone of the polymer. This combination of the hydrocarbon fraction and the polymer is unique in that if the aforesaid hydrocarbon fraction is employed in conjunction with most of the conventional polymeric pour point depressant additives, particularly those of the ester type or those comprising copolymers of ethylene and unsaturated esters, the improvement that would be obtained in filterability by the use of the hydrocarbon fraction alone, as well as the pour point depression that would be obtained by the polymeric additive alone, are often adversely affected. In some instances, while the filterability improvement contributed by the aforesaid hydrocarbon fraction is not adversely affected, and in some cases is even improved, the pour point depressing action of the polymeric additive is impaired. However, with the additive combination of the present invention, neither the improved filterability nor the pour point depressing action is adversely affected.
More specifically, there are added to a waxy middle distillate petroleum fuel from about 0.1 to about 3 weight %, preferably from about 0.2 to 1 wt. %, of said high molecular weight, substantially normal-paraffin-hydrocarbon-free hydrocarbon fraction, and from about 0.005 to about 1 weight %, preferably from about 0.01 to 0.1 weight % of the polymeric pour point depressant. The weight ratio of the two types of additive can vary from 50 parts of the added hydrocarbon fraction per part of polymeric pour point depressant to about equal parts of the two types of additive. Preferably, about 5 to about 30 parts of the added normal-paraffin-free hydrocarbon fraction will be used per part of polymeric pour point depressant.
The distillate fuel oils that can be improved by this invention include those having boiling ranges within the limits of about 250° F. to about 700° F. The distillate fuel oil can comprise straight run or virgin gas oil, 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 kerosine, diesel fuels, jet fuels and heating oils. Since jet fuels are normally refined 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 440° F., a 50 percent point no higher than about 520° F., and a 90 percent point of at least 540° F. and no higher than about 640° F. to 650° F., although some specifications set the 90 percent point as high as 675° F. 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 100° F. and a 90 percent distillation point between 540° F. and 640° F. (See ASTM Designations D-396 and D-975)
The pour point depressant used in this invention is a polymer or copolymer wherein the monomer relationship is represented by the formula:
(A) . (B) x
wherein x is an integer 0 to 3, B is an alpha, beta unsaturated ester of from 4 to 8 total carbon atoms, and A is an unsaturated compound of the generalized formula: ##SPC1##
wherein R and R 1 are hydrogen or methyl, R 2 is a C 8 to C 20 alkyl group connected to the designated unsaturated carbon atom through an aromatic hydrocarbon group or through an ester group, and R 3 is either hydrogen, a carboxyl group, or the same as R 2 . When R 3 is hydrogen or a carboxyl group, x does not exceed 2.
The polymer and copolymer pour point depressants used in this invention will have number average molecular weights within the range of about 800 to 50,000, preferably about 1,000 to 10,000. Molecular weights can be determined by cryoscopic methods or by vapor phase osmometry.
A polymer of a monomer arrangement as depicted above, wherein x is zero, and wherein in monomer A, R 1 and R 2 are alkyl groups connected to the unsaturated carbon atoms through aromatic hydrocarbon groups is exemplified by an alkylated polystyrene or an acylated polystyrene, as more fully described below.
Examples of monomer A wherein R 3 is hydrogen or a carboxyl group and R 2 is linked to the unsaturated carbon through an ester group include vinyl laurate, vinyl palmitate, C 8 Oxo alcohol acrylate, C 13 Oxo alcohol methacrylate, allyl stearate, palmityl alcohol ester of alpha methyl acrylic acid, mono C 13 Oxo alcohol ester of fumaric acid, etc.
Examples of monomer A where R 3 is the same as R 2 , and both are linked to the unsaturated carbons through ester groups include didecyl maleate, di- C 13 Oxo alcohol fumarate, di- C 16 linear Oxo alcohol maleate (see U.S. Pat. No. 3,417,021), etc.
Examples of monomer B include vinyl acetate, dimethyl fumarate, isopropyl acrylate, ethyl methacrylate, di-isopropyl maleate, allyl acetate, vinyl butyrate, etc.
The Oxo alcohols used in preparing the esters mentioned above are isomeric mixtures of branched chain aliphatic primary alcohols prepared from olefins, such as polymers and copolymers of C 3 to C 4 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 400° F., under pressures of about 1,000 to 3,000 psi., to form aldehydes. The resulting aldehyde product is then hydrogenated to form the Oxo alcohol, the latter being recovered by distillation from the hydrogenated product.
Examples of specific copolymers useful in this invention include a copolymer of one mole of di-lauryl fumarate and two moles of isopropyl methacrylate, a copolymer of one mole of stearyl acrylate and 2.5 moles of vinyl butyrate, and a copolymer of one mole of vinyl palmitate and 1.8 moles of vinyl acetate.
Particularly useful polymeric pour point depressants for use in this invention comprise alkylated polystyrenes, acylated polystyrenes and mixtures thereof. Especially preferred are alkylated polystyrenes prepared from essentially straight chain olefins having from about 10 to 20 carbonat atoms, e.g. decene-1, hexadecene-1, octadecene-1, eicosylene, and cracked paraffin wax, as well as acylated polystyrenes prepared from aliphatic acylating agents, e.g. acid halides, of 8 to 20 carbon atoms in a straight chain, e.g. stearoyl chloride or lauroyl chloride.
Alkylation of polystyrene can be conducted by the process described in U.S. Pat. No. 2,756,265 of William C. Hollyday, Jr.
Typically, the process comprises the steps of dissolving polystyrene in an inert solvent such as monochlorobenzene, and heating the mixture until the polystyrene is completely in solution. The mixture is then cooled to the selected reaction temperature (usually in the range of about 80° to 150° F.) at which time nitrobenzene and a Friedel-Crafts catalyst are added. The alkylating agent is then added dropwise and the reaction temperature is maintained by cooling or heating as necessary. After the completion of the reaction, the alkylates are purified by well known techniques.
Acylated polystyrenes are prepared by reaction of polystyrene with an acid chloride. See U.S. Pat. No. 3,069,245 of S. L. Wythe and W. C. Hollyday, Jr.
Typically, the method of acylation comprises dissolving the polystyrene in a suitable solvent, such as chlorobenzene, o-dichlorobenzene, or tetrachloroethylene and adding to the solution an equimolar quantity of carboxylic acid chloride/aluminum chloride complex at temperatures of 30° to 70° C. (preferably 40° to 60° C.), with provision for carrying away the evolved hydrogen chloride. After all the acid chloride/aluminum chloride complex has been added (one mole per mole of phenyl groups in the polystyrene, plus a slight excess) and hydrogen chloride evolution has stopped, the catalyst is destroyed with water or alcohol, the acylate is taken up in a suitable solvent, such as heptane or kerosene and washed with water and alkaline solutions. The resinous product may be isolated as the pure material by evaporating all solvents, or it may be used in solution for making blends in middle distillates.
The fractions of essentially saturated hydrocarbons that are used in accordance with the present invention in conjunction with the polymeric pour point depressants are generally amorphous solid materials having melting points within the range of about 80° to 140° F. 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 as a fuel oil flow improver in accordance with this invention can be obtained by deasphalting a residual petroleum fraction 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 semi-solid amorphous material by precipitation at low temperatures, followed by filtration. The residual oil fractions from which the desired amorphous hydrocarbons are obtained will have viscosities of at least 125 SUS at 210° F. Most of these residual oils are commonly referred to as bright stocks.
In some instances products obtained by this procedure will be naturally low in normal paraffin hydrocarbons and can be used in the present invention without further treatment. For example, by low temperature propane treatment of a deasphalted residual oil from certain Texas coastal crudes a precipitated high molecular 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. Removel 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 heptane or preferably a ketone such as 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 soem 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 a pressure 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.
The combinations of flow improving additives and pour point depressants herein described may constitute the sole additives that are incorporated in the fuel oil compositions, or they can be employed in conjunction with other additives commonly used in distillate fuels, including rust inhibitors, antioxidants, sludge dispersants, demulsifying agents, dyes, haze suppressors, etc.
The nature of this invention and the manner in which it can be practiced will be more fully understood when reference is made to the following examples, which include a preferred embodiment.
EXAMPLE 1
Fuel oil blends were prepared using either of two middle distillate fuel oils consisting of mixtures of cracked distillates and heavy virgin naphtha. These middle distillate fuel oils are further characterized as follows: (Percentages are by volume)
Oils Tested:
Oil A: 80% cracked oil, FBP 630° F.
20% heavy virgin naphtha Cloud Point +6° F. Pour Point -5° F.
Oil B: 85% cracked oil, FBP 660° F.
15% heavy virgin naphtha Cloud Point +12° F. Pour Point -5° F.
Comparative blends were prepared using each of the fuel oils to which had been added either a copolymer of vinyl acetate and ethylene; a terpolymer of ethylene, vinyl acetate, and an alpha olefin; an alkylated polystyrene; a copolymer of fumarate esters and vinyl acetate; a solid hydrocarbon fraction more fully described below; or combinations of this solid hydrocarbon fraction with each of the separate polymeric pour depressants mentioned above. Each blend was prepared by simple mixing of the additives with the respective fuel oil, using heat if necessary. Some of the additives were in the form of concentrates, e.g. a 45 wt. % solution in kerosine; however, in the tabulated data the concentrations given are of each actual ingredient. The ASTM pour points of these various blends were measured and each of the 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 4° F. per hour until a temperature of 0° F. is reached, this being the temperature at which the flow test is conducted. The oil is then filtered through a U.S. 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 90 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, the pour point of each blend and the low temperature filterability test results are given in Tables I and II which follow.
TABLE I
Effect of Additives on Low Temperature Properties of Fuel Oil A
Additives Used ASTM % Recov- Pour Amorphous Polymeric ery in Point Hydrocarbon Pour Depressant Flow of Blend Test °F. None 0.01 wt. % EVAOL 1 -35 None 0.01 wt. % APS 1 -30 0.5 wt. % None 95 -15 0.5 wt. % 0.01 wt. % EVAOL 1 -15 0.5 wt. % 0.01 wt. % APS 95 -30 EVAOL -- Ethylene-Vinyl Acetate-Olefin Copolymer APS -- Alkylated Polystyrene
TABLE II
Effect of Additives on Low Temperature Properties of Fuel Oil B
Additives Used ASTM % Recov- Pour Amorphous Polymeric ery Point Hydrocarbon Pour Depressant in Flow of Blend Test °F. None 0.02 wt. % EVA 3 -50 None 0.02 wt. % APS 5 -30 None 0.03 wt. % FUVA 1 -25 0.4 wt. % None 100 -10 0.4 wt. % 0.02 wt. % EVA 100 -20 0.4 wt. % 0.02 wt. % APS 100 -40 0.4 wt. % 0.03 wt. % FUVA 100 -25 EVA -- Ethylene-Vinyl Acetate Copolymer APS -- Alkylated Polystyrene FUVA -- Fumarate Ester -- Vinyl Acetate Copolymer
The added hydrocarbon fraction was an amorphous material having a melting point of 111°F. that was obtained by propane precipitation from the deasphalted residuum of a Texas coastal crude oil. This hydrocarbon fraction was found by mass spectographic analysis and gas chromatography to contain no more than a trace of normal paraffin hydrocarbons and consisted of 5 wt. % of isoparaffins, 22 wt. % of aromatic hydrocarbons and 73 wt. % of cycloparaffins. The numer average molecular weight of this material was about 775 as determined by osmometry. The distillation characteristics of this solid hydrocarbon fraction were as follows:
Distillation Vapor Temp. (ASTM Vapor Temp. Converted to D-1160) at 5 mm Hg Atmospheric Pressure Initial BP 442°F. 754°F. 5% 590 926 10% 636 978 20% 686 1034 24% 689 1037 Only 24% would distill over There were 75% bottoms, and 1% loss
The ethylene, vinyl acetate, alpha-olefin copolymer (EVAOL) was prepared by the copolymerization of a mixture of about 10 wt. % of alpha-olefins in the C 12 - C 16 range, about 25 percent of vinyl acetate and about 65 percent of ethylene. The copolymer had a number average molecular weight of about 3,450 as determined by osmometry.
The alkylated polystyrene (APS) was prepared by the methods outlined in U.S. Pat. No. 2,756,265, e.g. Example 8, using as the alkylating material a mixture of C 12 to C 18 olefins averaging about C 16 . The alkylated polystyrene had an intrinsic viscosity of about 0.25, corresponding to a number average molecular weight of about 1,200.
The copolymer of fumarate esters and vinyl acetate (FUVA) was prepared by polymerizing 0.4 mole of vinyl acetate with 0.16 mole of mixed dialkyl fumarates in which the alcohols used in making the fumarate esters were mixed C 12 - C 13 linear primary alcohols. The polymerization was conducted in heptane solution at 85° C. using benzoyl peroxide catalyst. The copolymer was recovered by flash evaporation of the volatile components and the copolymer was found to have a number average molecular weight of about 15,400 as determined by vapor phase osmometry.
The copolymer of ethylene and vinyl acetate (EVA) had a mole ratio of ethylene to vinyl acetate of about 4.2 and an average molecular weight as determined by vapor phase osmometry of about 1,740. Polymerization was conducted at a temperature of about 180° F. in the presence of di-lauroyl peroxide catalyst.
It will be seen from the test data that although all of the polymeric materials were effective pour point depressants in each of the fuel oils, only the fumarate-vinyl acetate copolymer and the alkylated polystyrene were as effective pour point depressants in the presence of the amorphous hydrocarbon flow improver as in its absence, and neither one interfered with the low temperature flow improving properties of the added amorphous hydrocarbon material. Both of these materials fit the definition of suitable additives for the present invention. The ethylene vinyl acetate copolymer and the ethylene, vinyl acetate, alpha-olefin terpolymer are pour point depressants that are outside of the scope of the present 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 fuel will 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 filters. 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.
RELATED ART
It is taught in the application of Nicholas Feldman and Wladimir Philippoff entitled "Increasing Low Temperature Flowability of Middle Distillate Fuel", Ser. No. 807,953 filed simultaneously with the present application and subsequently issued on May 2, 1972 as U.S. Pat. No. 3,660,058, that a paraffinic hydrocarbon fraction that is substantially free of normal paraffin hydrocarbons i.e., contains no more than about 5 wt. %, and preferably no more than about 1 wt. % of normal paraffin hydrocarbons, and that has a number average molecular weight of from about 600 to about 3,000, when added to a middle distillate petroleum fuel oil in a concentration of about 0.01 to about 3 wt. % 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.
DESCRIPTION OF THE INVENTION
In accordance with the present invention, it has now been found that further improvement in the low temperature properties of a petroleum fuel oil can be obtained if there is employed in combination with the high molecular weight hydrocarbon fraction a particular type of polymeric pour point depressant which is characterized by having, on the average, at least one long dependent alkyl hydrocarbon group for every 4 carbon atoms of the backbone of the polymer. This combination of the hydrocarbon fraction and the polymer is unique in that if the aforesaid hydrocarbon fraction is employed in conjunction with most of the conventional polymeric pour point depressant additives, particularly those of the ester type or those comprising copolymers of ethylene and unsaturated esters, the improvement that would be obtained in filterability by the use of the hydrocarbon fraction alone, as well as the pour point depression that would be obtained by the polymeric additive alone, are often adversely affected. In some instances, while the filterability improvement contributed by the aforesaid hydrocarbon fraction is not adversely affected, and in some cases is even improved, the pour point depressing action of the polymeric additive is impaired. However, with the additive combination of the present invention, neither the improved filterability nor the pour point depressing action is adversely affected.
More specifically, there are added to a waxy middle distillate petroleum fuel from about 0.1 to about 3 weight %, preferably from about 0.2 to 1 wt. %, of said high molecular weight, substantially normal-paraffin-hydrocarbon-free hydrocarbon fraction, and from about 0.005 to about 1 weight %, preferably from about 0.01 to 0.1 weight % of the polymeric pour point depressant. The weight ratio of the two types of additive can vary from 50 parts of the added hydrocarbon fraction per part of polymeric pour point depressant to about equal parts of the two types of additive. Preferably, about 5 to about 30 parts of the added normal-paraffin-free hydrocarbon fraction will be used per part of polymeric pour point depressant.
The distillate fuel oils that can be improved by this invention include those having boiling ranges within the limits of about 250° F. to about 700° F. The distillate fuel oil can comprise straight run or virgin gas oil, 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 kerosine, diesel fuels, jet fuels and heating oils. Since jet fuels are normally refined 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 440° F., a 50 percent point no higher than about 520° F., and a 90 percent point of at least 540° F. and no higher than about 640° F. to 650° F., although some specifications set the 90 percent point as high as 675° F. 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 100° F. and a 90 percent distillation point between 540° F. and 640° F. (See ASTM Designations D-396 and D-975)
The pour point depressant used in this invention is a polymer or copolymer wherein the monomer relationship is represented by the formula:
(A) . (B) x
wherein x is an integer 0 to 3, B is an alpha, beta unsaturated ester of from 4 to 8 total carbon atoms, and A is an unsaturated compound of the generalized formula: ##SPC1##
wherein R and R 1 are hydrogen or methyl, R 2 is a C 8 to C 20 alkyl group connected to the designated unsaturated carbon atom through an aromatic hydrocarbon group or through an ester group, and R 3 is either hydrogen, a carboxyl group, or the same as R 2 . When R 3 is hydrogen or a carboxyl group, x does not exceed 2.
The polymer and copolymer pour point depressants used in this invention will have number average molecular weights within the range of about 800 to 50,000, preferably about 1,000 to 10,000. Molecular weights can be determined by cryoscopic methods or by vapor phase osmometry.
A polymer of a monomer arrangement as depicted above, wherein x is zero, and wherein in monomer A, R 1 and R 2 are alkyl groups connected to the unsaturated carbon atoms through aromatic hydrocarbon groups is exemplified by an alkylated polystyrene or an acylated polystyrene, as more fully described below.
Examples of monomer A wherein R 3 is hydrogen or a carboxyl group and R 2 is linked to the unsaturated carbon through an ester group include vinyl laurate, vinyl palmitate, C 8 Oxo alcohol acrylate, C 13 Oxo alcohol methacrylate, allyl stearate, palmityl alcohol ester of alpha methyl acrylic acid, mono C 13 Oxo alcohol ester of fumaric acid, etc.
Examples of monomer A where R 3 is the same as R 2 , and both are linked to the unsaturated carbons through ester groups include didecyl maleate, di- C 13 Oxo alcohol fumarate, di- C 16 linear Oxo alcohol maleate (see U.S. Pat. No. 3,417,021), etc.
Examples of monomer B include vinyl acetate, dimethyl fumarate, isopropyl acrylate, ethyl methacrylate, di-isopropyl maleate, allyl acetate, vinyl butyrate, etc.
The Oxo alcohols used in preparing the esters mentioned above are isomeric mixtures of branched chain aliphatic primary alcohols prepared from olefins, such as polymers and copolymers of C 3 to C 4 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 400° F., under pressures of about 1,000 to 3,000 psi., to form aldehydes. The resulting aldehyde product is then hydrogenated to form the Oxo alcohol, the latter being recovered by distillation from the hydrogenated product.
Examples of specific copolymers useful in this invention include a copolymer of one mole of di-lauryl fumarate and two moles of isopropyl methacrylate, a copolymer of one mole of stearyl acrylate and 2.5 moles of vinyl butyrate, and a copolymer of one mole of vinyl palmitate and 1.8 moles of vinyl acetate.
Particularly useful polymeric pour point depressants for use in this invention comprise alkylated polystyrenes, acylated polystyrenes and mixtures thereof. Especially preferred are alkylated polystyrenes prepared from essentially straight chain olefins having from about 10 to 20 carbonat atoms, e.g. decene-1, hexadecene-1, octadecene-1, eicosylene, and cracked paraffin wax, as well as acylated polystyrenes prepared from aliphatic acylating agents, e.g. acid halides, of 8 to 20 carbon atoms in a straight chain, e.g. stearoyl chloride or lauroyl chloride.
Alkylation of polystyrene can be conducted by the process described in U.S. Pat. No. 2,756,265 of William C. Hollyday, Jr.
Typically, the process comprises the steps of dissolving polystyrene in an inert solvent such as monochlorobenzene, and heating the mixture until the polystyrene is completely in solution. The mixture is then cooled to the selected reaction temperature (usually in the range of about 80° to 150° F.) at which time nitrobenzene and a Friedel-Crafts catalyst are added. The alkylating agent is then added dropwise and the reaction temperature is maintained by cooling or heating as necessary. After the completion of the reaction, the alkylates are purified by well known techniques.
Acylated polystyrenes are prepared by reaction of polystyrene with an acid chloride. See U.S. Pat. No. 3,069,245 of S. L. Wythe and W. C. Hollyday, Jr.
Typically, the method of acylation comprises dissolving the polystyrene in a suitable solvent, such as chlorobenzene, o-dichlorobenzene, or tetrachloroethylene and adding to the solution an equimolar quantity of carboxylic acid chloride/aluminum chloride complex at temperatures of 30° to 70° C. (preferably 40° to 60° C.), with provision for carrying away the evolved hydrogen chloride. After all the acid chloride/aluminum chloride complex has been added (one mole per mole of phenyl groups in the polystyrene, plus a slight excess) and hydrogen chloride evolution has stopped, the catalyst is destroyed with water or alcohol, the acylate is taken up in a suitable solvent, such as heptane or kerosene and washed with water and alkaline solutions. The resinous product may be isolated as the pure material by evaporating all solvents, or it may be used in solution for making blends in middle distillates.
The fractions of essentially saturated hydrocarbons that are used in accordance with the present invention in conjunction with the polymeric pour point depressants are generally amorphous solid materials having melting points within the range of about 80° to 140° F. 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 as a fuel oil flow improver in accordance with this invention can be obtained by deasphalting a residual petroleum fraction 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 semi-solid amorphous material by precipitation at low temperatures, followed by filtration. The residual oil fractions from which the desired amorphous hydrocarbons are obtained will have viscosities of at least 125 SUS at 210° F. Most of these residual oils are commonly referred to as bright stocks.
In some instances products obtained by this procedure will be naturally low in normal paraffin hydrocarbons and can be used in the present invention without further treatment. For example, by low temperature propane treatment of a deasphalted residual oil from certain Texas coastal crudes a precipitated high molecular 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. Removel 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 heptane or preferably a ketone such as 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 soem 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 a pressure 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.
The combinations of flow improving additives and pour point depressants herein described may constitute the sole additives that are incorporated in the fuel oil compositions, or they can be employed in conjunction with other additives commonly used in distillate fuels, including rust inhibitors, antioxidants, sludge dispersants, demulsifying agents, dyes, haze suppressors, etc.
The nature of this invention and the manner in which it can be practiced will be more fully understood when reference is made to the following examples, which include a preferred embodiment.
EXAMPLE 1
Fuel oil blends were prepared using either of two middle distillate fuel oils consisting of mixtures of cracked distillates and heavy virgin naphtha. These middle distillate fuel oils are further characterized as follows: (Percentages are by volume)
Oils Tested:
Oil A: 80% cracked oil, FBP 630° F.
20% heavy virgin naphtha Cloud Point +6° F. Pour Point -5° F.
Oil B: 85% cracked oil, FBP 660° F.
15% heavy virgin naphtha Cloud Point +12° F. Pour Point -5° F.
Comparative blends were prepared using each of the fuel oils to which had been added either a copolymer of vinyl acetate and ethylene; a terpolymer of ethylene, vinyl acetate, and an alpha olefin; an alkylated polystyrene; a copolymer of fumarate esters and vinyl acetate; a solid hydrocarbon fraction more fully described below; or combinations of this solid hydrocarbon fraction with each of the separate polymeric pour depressants mentioned above. Each blend was prepared by simple mixing of the additives with the respective fuel oil, using heat if necessary. Some of the additives were in the form of concentrates, e.g. a 45 wt. % solution in kerosine; however, in the tabulated data the concentrations given are of each actual ingredient. The ASTM pour points of these various blends were measured and each of the 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 4° F. per hour until a temperature of 0° F. is reached, this being the temperature at which the flow test is conducted. The oil is then filtered through a U.S. 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 90 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, the pour point of each blend and the low temperature filterability test results are given in Tables I and II which follow.
TABLE I
Effect of Additives on Low Temperature Properties of Fuel Oil A
Additives Used ASTM % Recov- Pour Amorphous Polymeric ery in Point Hydrocarbon Pour Depressant Flow of Blend Test °F. None 0.01 wt. % EVAOL 1 -35 None 0.01 wt. % APS 1 -30 0.5 wt. % None 95 -15 0.5 wt. % 0.01 wt. % EVAOL 1 -15 0.5 wt. % 0.01 wt. % APS 95 -30 EVAOL -- Ethylene-Vinyl Acetate-Olefin Copolymer APS -- Alkylated Polystyrene
TABLE II
Effect of Additives on Low Temperature Properties of Fuel Oil B
Additives Used ASTM % Recov- Pour Amorphous Polymeric ery Point Hydrocarbon Pour Depressant in Flow of Blend Test °F. None 0.02 wt. % EVA 3 -50 None 0.02 wt. % APS 5 -30 None 0.03 wt. % FUVA 1 -25 0.4 wt. % None 100 -10 0.4 wt. % 0.02 wt. % EVA 100 -20 0.4 wt. % 0.02 wt. % APS 100 -40 0.4 wt. % 0.03 wt. % FUVA 100 -25 EVA -- Ethylene-Vinyl Acetate Copolymer APS -- Alkylated Polystyrene FUVA -- Fumarate Ester -- Vinyl Acetate Copolymer
The added hydrocarbon fraction was an amorphous material having a melting point of 111°F. that was obtained by propane precipitation from the deasphalted residuum of a Texas coastal crude oil. This hydrocarbon fraction was found by mass spectographic analysis and gas chromatography to contain no more than a trace of normal paraffin hydrocarbons and consisted of 5 wt. % of isoparaffins, 22 wt. % of aromatic hydrocarbons and 73 wt. % of cycloparaffins. The numer average molecular weight of this material was about 775 as determined by osmometry. The distillation characteristics of this solid hydrocarbon fraction were as follows:
Distillation Vapor Temp. (ASTM Vapor Temp. Converted to D-1160) at 5 mm Hg Atmospheric Pressure Initial BP 442°F. 754°F. 5% 590 926 10% 636 978 20% 686 1034 24% 689 1037 Only 24% would distill over There were 75% bottoms, and 1% loss
The ethylene, vinyl acetate, alpha-olefin copolymer (EVAOL) was prepared by the copolymerization of a mixture of about 10 wt. % of alpha-olefins in the C 12 - C 16 range, about 25 percent of vinyl acetate and about 65 percent of ethylene. The copolymer had a number average molecular weight of about 3,450 as determined by osmometry.
The alkylated polystyrene (APS) was prepared by the methods outlined in U.S. Pat. No. 2,756,265, e.g. Example 8, using as the alkylating material a mixture of C 12 to C 18 olefins averaging about C 16 . The alkylated polystyrene had an intrinsic viscosity of about 0.25, corresponding to a number average molecular weight of about 1,200.
The copolymer of fumarate esters and vinyl acetate (FUVA) was prepared by polymerizing 0.4 mole of vinyl acetate with 0.16 mole of mixed dialkyl fumarates in which the alcohols used in making the fumarate esters were mixed C 12 - C 13 linear primary alcohols. The polymerization was conducted in heptane solution at 85° C. using benzoyl peroxide catalyst. The copolymer was recovered by flash evaporation of the volatile components and the copolymer was found to have a number average molecular weight of about 15,400 as determined by vapor phase osmometry.
The copolymer of ethylene and vinyl acetate (EVA) had a mole ratio of ethylene to vinyl acetate of about 4.2 and an average molecular weight as determined by vapor phase osmometry of about 1,740. Polymerization was conducted at a temperature of about 180° F. in the presence of di-lauroyl peroxide catalyst.
It will be seen from the test data that although all of the polymeric materials were effective pour point depressants in each of the fuel oils, only the fumarate-vinyl acetate copolymer and the alkylated polystyrene were as effective pour point depressants in the presence of the amorphous hydrocarbon flow improver as in its absence, and neither one interfered with the low temperature flow improving properties of the added amorphous hydrocarbon material. Both of these materials fit the definition of suitable additives for the present invention. The ethylene vinyl acetate copolymer and the ethylene, vinyl acetate, alpha-olefin terpolymer are pour point depressants that are outside of the scope of the present invention.