US2115704A - Treatment of hydrocarbon oils - Google Patents

Description

Patented May 3, 1938 PATENT oFFIcE TREATMENT OF HYDROGARBON OILS Eugene R. Browns'combe, Aidan, Pa., assignor to The Atlantic Refining Company, Philadelphia, Pa., a corporation of Pennsylvania No Drawing.

4 Claims.

The present invention relates to the art of min eral oil refining, and has particular reference to the separation of crude petroleum or petroleum products into fractions of different chemical composition while of approximately thesame distillation range.

In accordance with my invention, crude petroleum or'petroleum products, particularly oils of substantial viscosity, are separated into various fractions by extraction with a mixture of solvents, and more particularly with selective solvents such as nitrobenzene, nitrotoluene, benzaldehyde, dichloro ethyl ether, cresylic acid and furfural, to which has been added an organic acid anhydride such as, for example, acetic, succinic, maleic, phthalic anhydrides, and the homologues thereof.

It is recognized in the art that mineral oils, such as petroleum, comprise essentially a mixture of hydrocarbons of various groups or homologous series of compounds, such for example, as paraffins of the'general formula CnH2n-I-2, olefines of the general formula CnHZn, hydroaromatics and polymethylenes of the same empirical formula, and various other series of compounds of chain and/or ring structures in which the hydrogen to carbon ratio is less than in the foregoing series. A large number of individual compounds of each series and of differing boiling points are present in petroleum.

The various types of crude petroleum, which are generally classified into three groups, namely, paraffinicbase, naphthenic or asphaltic base, and mixed base,'contain the Variousseries of hydrocarbons mentioned heretofore in different proporare obtained from the Mid-Continent oil fields,

contain hydrocarbons in proportions intermediate between these two extremes.

The paraflin base oils and their distillates are said to be more parafiinic than the mixed base oils and their distillates and these in turn are more paraffinic than the naphthene base oils and their distillates. Conversely the naphthene base oils are more naphthenic than the mixed base oils and these in turn more naphthenic than the paraffin base oils. The usual criteria of the de- Application April 25, 1925, Serial No. 18,261

gree of paraffinicity or naphthenicity of an oil are the viscosity-gravity constant and the vis cosity index. The viscosity-gravity constant is a constant relating viscosity and specific gravity and is described in an article entitled The vis- 5 cosity-gravity constant of petroleum lubricating oils by J. B. Hill and H. B. Coates which will be found in vol. 20, page 641 et seq., of Industrial and Engineering Chemistry. Viscous oils resulting from the distillation of Pennsylvania type crudes have viscosity-gravity constants ranging from about .805 to about .828 and in most instances are below .820. Those resulting from the distillation of Mid-Continent crudes have viscosity-gravity constants ranging from about .835 to about .855, whereas those from naphthenic crudes are generally higher than .860. The viscosity index is a. coefficient based on the change of viscosity with temperature and is described by Dean and Davis in vol. 36, page 618 of Chemical and Metallurgical Engineering. The more paraffinic oils are characterized by low viscosity-grew ity constants and high viscosity indices, whereas the more naphthenic oils are characterized by higher viscosity-gravity constants and lower viscosity indices.

My invention is based upon the discovery that oils containing both the parafiinic series of hydrocarbons and the various naphthenic series may be fractionally extracted with a selective solvent in admixture with an organic acid anhydride. The various series of hydrocarbons possess a differential solubility in such solvent mixture, the naphethenic hydrocarbons being much more soluble therein than the paraffinic hydrocarbons. By means of extraction with such solvent mixture, it is therefore possible to effect a partial separation of the naphthenic hydrocarbons from the parafiinic, and to obtain from an oil containing both classes of hydrocarbons, an oil which is much more parafiinic than the original oil and one which is much more naphthetic. By my invention, for example, it is possible to produce an oil of the quality normally obtained from Appalachian crudes, from crudes of the mixed base type from the Mid-Continent area or from those of the naphthenic base type and, conversely, to obtain oils from mixed base crudes or paraffinic base crudes such as are normally obtained from the naphthenic oils of the Gulf coast area. In 5 general, from oils from any source there may be obtained by my process, oils which are respectively more parafiinic and more naphthenic than the oils normally obtained from such source by distillation.

It has been known heretofore to separate hydrocarbon oils into fractions by means of solvents such as sulfur dioxide, iurfural, and others. Such separation is accomplished by agitating the oil with the solvent and bringing the mixture to such a temperature, below the temperature of complete miscibility of the oil and solvent, that the mixture separates into two layers, one of which is the undissolved and more parafiinic portion of the oil containing some dissolved solvent and the other of which is solvent containing dissolved naphthenic constituents of the oil. These two layers are separated at this separation temperature and the solvent may subsequently be removed from each. I have found it highly advantageous to eifect such separation by employing a mixture of a selective solvent and an organic acid anhydride. In particular, the aromatic nitro solvents, for example, nitrobenzene, are highly selective but usually require a separation temperature below, for example, 60 F., due to their relatively low miscibility temperature with the hydrocarbon oils. The separation temperatures employed are, in general, about 45 F. below the miscibility temperature of the oil and solvent. By employing a suitable mixture of a selective solvent and an organic acid anhydride, I am able to separate hydrocarbon oils into fractions at temperatures considerably above those which could be employed with the selective solvent alone. For example, 100 parts by volume, of a medium viscosity lubricating oil distillate from Winkler (W. Texas) crude oil was mixed with 200 parts, by volume, of nitrobenzene, and the miscibility temperature was found to be 79 F. In general, this would indicate that the extraction should be carried out at temperatures not higher than about 35 F. When 109 parts of the same oil were admixed with 200 parts of a solvent composed of by volume of nitrobenzene and 5% by volume of maleic anhydride, the miscibility temperature was found to be 104 F., indicating that an extraction could be carried out satisfactorily at a temperature of the order of 60 F. When parts, by volume, of the same oil were mixed with 200 parts, by volume, of solvent composed of 90% by volume of nitrobenzene and 10% by volume of maleic anhydride, the miscibility temperature was found to be 129 R, which would permit of extraction at temperatures as high as about 85 F. It will be understood, of course, that the quality of the undissolved or more parafiinic oil fraction produced by means of the solvent mixture will frequently be somewhat lower than that of a similar fraction produced with nitrobenzene alone. In general, greater yields are obtained and higher operating temperatures may be employed when a mixture of a selective solvent and an organic acid anhydride is utilized. In any event, an economic balance must be struck between the yield and quality of the refined oil, and the cost of producing the same.

Furthermore, in accordance with my invention, I am able to separate hydrocarbon oils into fractions with my solvent mixture, which oils could not be economically treated with a selective solvent alone. For example, it is not practical to employ a solvent, such as nitrobenzene, in treating very asphaltic oil stocks such as those derived from some California crude oils, for the reason that the miscibility temperature of the oil and solvent is very low, excessive refrigeration is required, and in certain cases the nitrobenzene may crystallize before separation of fractions can be effected. However, by adding to the selective solvent, e. g., nitrobenzene, a suitable quantity of an organic acid anhydride, for example 5% or 10% of maleic anhydride, I am able to treat in a satisfactory manner, even the very asphaltic California oils.

In accordance with my invention, I first mix the oil to be treated with a suitable-proportion of a mixture of a selective solvent and an organic acid anhydride at a temperature such that complete solution is effected and a homogeneous liquid obtained. I then cool the solution to a temperature at which separation of the liquid into a two-layer system will take place. One layer will contain a relatively small amount of the solvent mixture dissolved in the paraffinic portion of the oil, while the other layer Will contain the more naphthenic portion of the oil dissolved in the major quantity of the solvent mixture. Or, I may agitate the mixture of solvent and organic acid anhydride with the oil at temperatures at which the liquids are-only partially miscible, and thereby effect solution of the naphthenic portion of the oil in the solvent mixture. In either of the above procedures I may take advantage of the principles of countercurrent extraction.

After the extraction proper, I effect separation of the two layers which form, by any suitable procedure, as for example, by decantation. I then remove from each of the separated layers,

the portion of the solvent mixture which each contains, by suitable procedure, such as by vacuum distillation, thereby to obtain two oils of similar distillation ranges but of different chemical composition and different physical characteristics.

Before removing the solvent mixture from the undissolved or more paramnic layer, I may add a further quantity of the solvent mixture and repeat the extraction, thereby to remove additional naphthenic constituents from said layer. The extraction step may be repeated any desired number of times, each repetition producing an oil of higher parafiinicity as evidenced by its lower viscosity-gravity constant.

A countercurrent relationship in these successive extractions may be established in the conventional manner by employing the partially spent solvent mixture containing dissolved naphthenic oil from the succeeding stages of the extraction system to extract additional quantities of oil in the preceding stages. In the event that the miscibility temperature of the oil with the selective solvent in the latter stages of the system is sufficiently high, the organic acid anhydride may be introduced at any desired preceding stage, in order to lessen or eliminate the refrigeration required in the earlier stages.

Where substantial quantities of waxy hydrocarbons belonging to the true paraflin series (CnH2n+2) are present, such hydrocarbons remain in the undissolved or more paraflinic layer and may cause such layer to be solid or semisolid, after the removal of the solvent mixture therefrom. In some cases, the extraction and separation of the layers may be effected at tempertures above the melting point of the waxy hydrocarbons, so that substantial entrainment of oil in the molten or liquid wax is avoided. Such layer may be separated into solid and liquid hydrocarbons by any of the well-known dewaxing processes, such as by cold-settling, filtering, or by centrifuging. In many instances, it may be advantageous to dewax the oil prior to extraction. However, it is to be understood that in accordance with my invention, dewaxing may be effected either prior or subsequent to extraction.

My invention will be further understood from the following specific examples:

I. 100 parts by volume of a residuum from at Gulf Coast crude oil having a viscosity of 518 1 seconds Saybolt universal at 210 F., a specific gravity of 0.9759 at 60 FL, and a viscosity-gravity constant of 0.894 were mixed with 200 parts by volume of a solvent consisting of by volume of nitrobenzene and 10% by volume of acetic anhydride, and heated to slightly above the temperature of complete miscibility, i. e., about 115 F. The homogeneous liquid which resulted was cooled, with agitation, to about 68 F,, and allowed to settle, whereupon a two-layer system was formed. After separation, the layers were each freed of solvent by vacuum distillation. The resulting undissolved oil fraction comprising 40.3% of the stock had a viscosity of 221 seconds Saybolt universal at 210 F., a specific gravity of 0.9212, and a viscosity-gravity constant of 0.836. The initial Gulf Coast residuum had a miscibility temperature of 91 F., with nitrobenzene alone, and would have required extraction at temperatures below 46 F., to effect a satisfactory separation of oil fractions.

II. parts by volume of a Barbers Hill lubricating oil distillate having a viscosity of seconds Saybolt universal at 210 F., a specific gravity of 0.926 at 60 F., and a viscosity-gravity constant of 0.854, were mixed with 200 parts by volume of a solvent consisting of 90% by weight of nitrobenzene and 10% by weight of phthalic anhydride, and heated to slightly above the temperature of complete miscibility, i. e., about 144 F. The homogeneous liquid which resulted was cooled, with agitation, to about 95 F., and allowed to settle, whereupon a two-layer system formed. After separation, the layers were each freed of solvent by vacuum distillation. The resulting undissolved fraction comprising 56.0% of the stock had a viscosity of 91 seconds Saybolt universal at 210 F., a specific gravity of 0.9013, and a viscosity-gravity constant of 0.825. The initial lubricating oil distillate had a miscibility temperature of 110 F., with nitrobenzene alone, and would have required extraction at temperatures below 65 F., to effect a satisfactory separation of oil fractions.

refined oil fraction had a viscosity of 84 seconds Saybolt universal at 210 F., a specific gravity of 0.8911, and a viscosity-gravity constant of 0.813. miscibility temperature of 110 F., with nitrobenzene alone, and would have required extraction at temperatures below 65 F., to effect a satisfactory separation of the oil into fractions.

From the above examples it will be noted that by extraction of an oil with a solvent mixture comprising a selective solvent, such as nitrobenzene, and an organic acid anhydride, there may be obtainedoil fractions which are respectively more paraifinic and more naphthenic than the original oil. By repetition of the extraction process upon the undissolved fraction, oils of even greater paraffinicity will result. The quantity of 1 organic acid anhydride to be employed in conjunction with the selective solvent will vary, depending upon the character of the selective solvent, the temperature at which the extraction is to be carried out, and the quality of refined oil desired. In general, the quantity of organic acid anhydride employed will be of the order of from about 5% to about 10% of the selective solvent. However, more or less of the organic acid anhydride may be employed, depending upon the temperature at which the extraction is to be carried out.

While, in the above examples, I have shown the use of a selective solvent such as nitrobenzene in admixture with various organic acid anhydrides, I do not intend to limit myself thereto, but may employ various selective solvents in conjunction with the organic acid anhydrides. The following table illustrates the effect upon the miscibility temperature of oil with various selective solvents to which have been added small quantities of an organic acid anhydride. The miscibility temperatures were determined by heating 1 volume of lubricating oil stock with 2 volumes of selective solvent or solvent mixture, to a temperature such that complete solution of oil and solvent was obtained, and thereafter cooling the solution until the formation of a haze was noted, thus indicating the separation of two liquid phases.

III. The same Barbers Hill lubricating oil distillate as shown in Example II was continuously extracted in a 3stage countercurrent system with 200% by volume of a solvent comprising 90% by volume of nitrobenzene and 10% by volume of maleic anhydride, at a temperature of about 131 F., or about 43 below the temperature of miscibility, i. e., 174 F. The resulting undissolved oil fraction, after removal of solvent by vacuum distillation, comprised 45.2% of the oil stock charged to the extraction system. This My process is practically independent of the particular nature or source of the crude oil or oil fraction to be extracted. There may be produced by my process oil products of desired characteristics from oil which by distillation will not produce such products. Moreover, it will be understood, that in accordance with my invention, an important aspect thereof is the increase of the miscibility temperature of the oil and naphthenic solvent by reason of the presence of the organic acid anhydride, regardless of any selective sol- The initial lubricating oil stock had a 1 the oil is of substantial viscosity, i.

vent action the anhydride itself may have upon the oil.

When, in the appended claims, oil is referred to as being viscous, it is to be understood that e., of the order of 50 seconds Sayboit universal at 100 F.,

or more.

What I claim is:

1. In the process of decreasing the viscositygravity constant of a viscous mineral oil, the step of extracting the oil with nitrobenzene containing maleic anhydride in sufficient quantity to substantially increase the miscibility temperature of said nitrobenzene with said oil.

2. In the process of decreasing the viscositygravity constant of a'viscous mineral oil, the step of extracting the oil with nitrobenzene containing phthalio anhydride in suificient quantity to substantially increase the miscibility temperature of said nitrobenzene with said oil.

3. In the process of decreasing the viscositygravity constant of a viscous mineral oil, the step of extracting the oil with nitrobenzene containing acetic anhydride in sufficient quantity to substantially increase the miscibility temperature of said nitrobenzene with said oil.

4. In the process of decreasing the viscositygravity constant of a viscous mineral oil, the step of extracting the oil with nitrobenzene containing an organic acid anhydride from the group consisting of acetic anhydride, maleic anhydride, and phthalic anhydride, said anhydride being present in sufficient quantity to substantially in crease the miscibility temperature of said nitrobenzene with said oil.

EUGENE R. BROWNSCOMBE.