US2712518A - Pour-point reduction - Google Patents

Description

United States Patent POUR-POINT REDUCTION Samuel Clyde Vaughn, Berkeley, Calif., assignor to Tide Water Associated Oil Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application October 25, 1951, Serial No. 253,201

14 Claims. (Cl. 196-1) This invention relates to the treatment of hydrocarbon oils for the reduction of pour-point. It is particularly adapted for the reduction of the pour-point of gas-oils, especially those intended for use as fuels for diesel engines, though other oils may be treated in accordance therewith.

Briefly, the invention comprises dissolving hydrogenated castor oil in the oil to be treated at elevated temperature, cooling the solution to precipitate the hydrogenated castor oil, and separating treated oil from the precipitated hydrogenated castor oil. Depending upon the amount of hydrogenated castor oil used, the pourpoint of the treated oil may be reduced 40 or more Fahrenheit degrees below that of the original oil. It is believed that the pour-point reduction is due to the removal of petroleum wax from the oil, though it may be due wholly or in part to unknown reactions between the hydrogenated castor oil and petroleum wax contained in the oil.

In the operation in cold climates of diesel engines using hydrocarbon fuels having boiling ranges between approximately 350" F. and 700 F. difiiculties are encountered with many otherwise satisfactory fuels due to the precipitation of wax from the oil at low temperatures. The precipitated wax at times causes plugging of the fuel lines and even prevents flow of oil from the fuel tank. Since the more parafiinic types of gas oils are preferred for diesel engine fuels because of their better combustion characteristics, as indicated by high cetane numbers, and since the more parafiinic oils have the greater tendency to precipitate wax, the situation is of major importance in the manufacture of quality diesel fuelsv Similar troubles, however, are encountered in furnace oils, and the like, as well as with other oils. Accordingly, a maximum pour-point specification is commonly employed in the purchase of oils intended to be usedin cold weather, the pour-point being that'temperature at which the oil ceases to how as determined by ASTM method D97-47.

To produce oils having required low-pour points from stocks of high pour-point, two general procedures are in common use, employed either singly or in combination with each other. In one, the oil is refrigerated to a point where sufiicient of the wax precipitates that it can be removed by filtration, thus lowering the pour-point of the filtrate oil. In the second method, certain additives are incorporated in the oil which tend to prevent precipitation of the wax.- Both these'methods have great disadvantages in the treatment of gas oils, such a diesel fuels. The refrigeration method requires expensive equipment and high operating costs to reduce the temperature of the oil sufiiciently for the required amount of de-' waxing. Such costs make this procedure economic only with high priced oils. On the other hand, the common pour-point depressant additives have not proven effective in lowering the pour-point of gas oils and diesel oils to the extent required. I

Thepreseht' invention'provides' a means whereby the I ice pour-point of gas oils may be effectively reduced without resort to refrigeration. The practice of the invention depends upon the solubility of hydrogenated castor oil in the gas oil, or other oil to be treated. At temperatures in the neighborhood of F., hydrogenated castor oil is practically insoluble in hydrocarbon oils, the solubility in most gas oils being less than 0.1% at these tempera tures. At temperatures above the melting point of the hydrogenated castor oil, it appears to be completely miscible with most hydrocarbon oils, at least sufliciently so to permit solution of upwards of 20%. In accordance with the invention, an amount of hydrogenated castor oil, depending upon the degree of pour-point reduction required, is dissolved in the oil to be treated at elevated temperature. The homogeneous solution is then cooled to a temperature where the hydrogenated castor oil precipitates from the oil. The precipitated hydrogenated castor oil is then removed from the oil by filtration, centrifuging, or other means, leaving a treated oil of lowered pour-point. If desired, the separated hydrogenated castor oil may be recovered for use in treating subsequent batches of oil by removal of occluded oil and wax by steam and/ or vacuum stripping or by extraction with a suitable solvent. The oil so removed may be used as desired, for example as feed stock for catalytic or thermal cracking.

Depending upon the character of the oil to be treated, the character and amount of wax in the oil, and the degree of pour-point reduction required, the amount of hydrogenated castor oil used in the process may vary from less than 1% to over 20%, based on the Weight of the oil. With any given oil, the higher rates have been found to give greater reduction in pour-point. On the other hand, the higher rates give lower yields of treated oil due to greater volumes of oil being occluded by the precipitated hydrogenated castor oil. For this reason, it is preferred to use from 1 to 10 parts (by weight) of hydrogenated castor oil per parts of oil when treating diesel fuel oils having, before treatment, pour-points of from 10 to 40 F.

To efiect solution of the hydrogenated castor oil in the hydrocarbon oil a temperature of at least about F. will be found necessary. A temperature of about 200 F. is recommended to insure complete solution. Higher temperatures may be used when desired if care is taken to prevent overheating and consequent partial decomposition of the hydrogenated castor oil. In efiecting the solution, the oil may be first heated and the hydrogenated castor oil may be mixed therewith either in the solid or molten state. Alternately, the hydrogenated castor oil may be added to the cold hydrocarbon oil and the mixture heated with sufficient agitation to produce a homogeneous solution.

The temperature to which the oil solution of hydrogenated castor oil is cooled should be below about 100 F. to insure substantially complete separation 01' the hydrogenated castor oil. A temperature of about 75 F. has been found entirely satisfactory in the treatment of diesel fuels. However,- still lower temperatures may be found to be convenient or desirable in some instances.

Various techniques are known to the art for separating suspended solid matter from liquids. Any of these may be found suitable, in the practice of the invention, for

separating the precipitated hydrogenated castor oil from the hydrocarbon oil. Filtration is preferred, though centrifuging is also effective. Likewise, the technique of washing filter cake -with suitable wash liquid to remove occluded filtrate is well known. Though not necessary in the practice of the invention, such washing of the precipitated hydrogenated castor oil may be used as desired. By choice of suitable wash liquid the recovered occluded oil may be found to have a pour-point approximating that of the filtered oil.

' hydrogenated castor oil may be effected by steam stripping, preferably with the aid of vacuum to prevent overheating. In any event, the separation may be effected by extraction with a solvent incapable of dissolving the hydrogenated castor oil, for example benzol. V g

While a particular embodiment of. the present inven= tion relates to the reduction of pour-point of low boiling hydrocarbon materials,'such as gas oils and diesel fuel, other uses will be readily apparent to those skilled in the art. 7 For example, the pour-point of heavier oils may also advantageously be lowered by means of the present process. In this connection, whentreating oils heavier than gas oils, the base oil should be predhuted with a low boiling hydrocarbon or hydrocarbon fraction, such as .pentane, octane, or naphtha. For example, in cases involving waxy lubricating oils, dilution in an amount of 1:1 or more has been found to be desirable. The type of. material the pour-point of which is to be lowered will in a large measure determine the amount of hydrogenated castor oilto be added. K

Hydrogenated castor oil suitable for the practice of the V invention, consists primarily I or glyceryl 12-hydroxystearate, the commercial grades of which contain minor Example IV The procedure of Example I was followed using 4-00 parts diesel fuel and 1 part hydrogenated castor oil. Complete solution was obtained at about 175 F., and

precipitation did not begin until a few degrees above the final cooling temperature of 105F. The filtered oil had a pour-point of 5 F.

Example V Repetition of Example Iusing 1000 parts diesel fuel and 1 part hydrogenated castor oil and cooling to 95 F. gave no reduction in the pour-point of the filtered oil.

Example VI To 100 parts by'weight of a 30 F. pour-point gas oil, cut from Ventura crude oil, there were added 8 parts hydrogenated castor 'oil and the mixture heated to 210 F., effecting complete solution of the hydrogenated castor oil'in the gas oil. The resulting mixture was cooled, without stirring, to about 70 F. over a period of about hours, during which time the: hydrogenated castor oil precipitated. The resulting mixture was filtered, yielding 70 parts of gas oil having a pour-point of F. The filter cake from the filtration was washed, with about 100 parts of pentane. The pentane V was evaporated from the washings, yielding parts of quantities of mixed glycerides of dihydroxystearic and stearic acids as well as other impurities. 'The invention contemplates the use of either the pure compound or the commercial product, though the latter is preferred.

Following are examples of the invention applied to V the treatment of gas oils and diesel fuels, using a commercial grade of hydrogenated castor oil having the following specifications;

Specific gravity, F; 0.98 to 1.00

Melting point (ASTM D87 2), F 183 to 188 Acid number 20 Ash, percent below 0.005

Saponification number 175 [0185 xample l T05 parts by weight of a finished summer grade diesel fuel having a pour-point of 10 F. there was added 1 part of solid hydrogenated castor oil. The mixture was heated with mechanical stirring- Atabout 175 F. the mixture became homogeneous. After a temperature of 210 F. was reached, the heating was discontinued and the mixture cooled, with continued stirring, to a temperature of about F. During the cooling hydrogenated caster oil began to precipitate from the oil at about to F. and the mixture became mushy at about 120 F. The period of cooling was about two hours. The cooled'mix ture was filtered, and the filtrate oil was found to have apour-point of -45 F. V I 0 Example '11 I V The procedure of Example I wasv followed using 25 7 parts diesel'fuel and 2 parts h drogenated castor oil. excep't that the final cooling temperature was about 95 F.

The filtered oil had a pour.-point.of.. .35 a

' Exci lr'zple Ill 7 The procedure of Example i was followed using 100 parts diesel fuel and 1 part hydrogenated castor oil. Complete solution wasobtained during the heating step at about 175 F. and, during the cooling, precipitationbe gan at about 120 F. The filtered oil had a pour-point f 00 1 7 1 I.

additional gas oil having a pour-point of 10 F.

Example VII A 35 F. pour-point gas oil cut from mixed San Joaquin Valley waxy crude oils was treated in accordance with the procedure'of Example VI. The resulting yields were comparable with those of Example VI. The combined recovered gas oil had a pour-point of l0v F.

Example VIII The filter cake produced in a procedure the same as Example VI, except Without the pentane washing, was subjected to steam distillation at atmospheric pressure, the temperature in the still reaching 580 F. The distillate was a high pour-point waxy oil which had properties excellently adapted for catalytic cracking charge stock. The residue from the distillation was primarily hydrogenated castor oil which was found suitable for treating a subsequent batch of oil.

In the above examples, and elsewhere in the specifications and claims, the term diesel fuel is used to denote a fuel suitable for use in high speed diesel engines composed primarily of gas oil. This is in contrast to heavier.

hydrocarbon fuels designed for use in low speed diesel engines. The term gas oil is used, as commonly employed by the petroleum arh to denote. oils having boiling ranges above about 350 F. and below about I claim: a

1. A process for reducing the pour-point of hydro carbon oils which comprises dissolving glyceryl-l2 hydroxy-stearate in a hydrocarbon oil, cooling the-resulting solution sufiiciently to precipitate said glyceryl-l2-v hydroxy-stearate, and separating oil' of lowered pour. point from the resulting precipitate; said cooling and I separation of oil being conducted at a temperature above the pour-point of the oil being treated' V 2. A process as of claim 1 in which the hydrocarbon oil is a petroleum fraction having a boiling range above about 350 F, and below about 750 F.

3. A process as of claim 2 .in whichthe petroleum fraction is a straight-run petroleum fraction.

4. A process as of claim l in which the dissolving step is conducted at a temperature above about F;

5. A process as of claim 4 in which the solution is cooled to below about 105 F. to precipitate the glyceryll2-hydroxy-stearate. V

A r s as of s im 1 n whist e We ghts glyceryl-12-hydroxy-stearate is between about 1% and about 20% of the weight of the oil.

7. A process as of claim 1 in which the glyceryl-l2- hydroxy-srearate is hydrogenated castor oil.

8. A process asof claim 1 in which the separation step is conducted by filtration.

9. A process as of claim 1 in which the separation step is conducted by centrifuging.

10. A cyclic process of removing wax from hydrocarbon oils which comprises dissolving glyceryl-lZ- hydroxy-stearate in a waxy petroleum oil at a temperature above the solution temperature of said stearate in said oil, cooling the resulting solution to a temperature at which said stearate substantially entirely precipitates but above the pour-point of said waxy oil, separating oil of reduced wax content from the resulting precipitate, removing wax and occluded oil from said precipitate, and cycling the remainder of the precipitate to the process to treat a subsequent batch of oil.

11. A process as in claim wherein the occluded oil is removed at least in part by washing with a solvent for the oil incapable of dissolving a substantial amount of the glyceryl-12-hydroxy-stearate.

12. A process as in claim 10 wherein the wax is removed from the precipitate by distillation at reduced partial pressure.

13. A process as in claim 10 wherein the wax is removed from the precipitate by extraction with a waxsolvent incapable of dissolving a substantial amount of the glyceryl-IZ-hydroXy-stearate.

14. A process as of claim 1 in which the temperature to which the oil-stearate solution is cooled and at which the lowered pour-point oil is separated is between about F. and about F.

References Cited in the file of this patent UNITED STATES PATENTS 2,023,996 De Groote et al Dec. 10, 1935 2,034,175 Chase at al Mar. 17, 1936 2,050,923 De Groote et al. Aug. 11, 1936 2,100,915 Pevere Nov. 30, 1937 2,100,916 Pevere et al Nov. 30, 1937 2,196,374 Wasson et al. Apr. 9, 1940 2,229,659 Carr Jan. 28, 1941 2,261,801 Frolich et al. Nov. 4, 1941

Claims (1)

1. A PROCESS FOR REDUCING THE POUR-POINT OF HYDROCARBON OILS WHICH COMPRISES DISSOLVING GLYCERYL-12HYDROXY-STEARATE IN A HYDROCARBON OIL, COOLING THE RESULTING SOLUTION SUFFICIENTLY TO PRECIPITATE SAID GLYCERYL-12HYDROXY-STEARATE, AND SEPARATING OIL OF LOWERED POURPOINT FROM THE RESULTING PRECIPITATE; SAID COOLING AND SEPARATION OF OIL BEING CONDUCTED AT A TEMPERATURE ABOVE THE POUR-POINT OF THE OIL BEING TREATED.