US2138166A - Solvent refining of petroleum oils - Google Patents

Description

Patented Nov. 29, 1938 UNITED STATES- PATENT OFFICE v 2,188,188 sonvsm asmmc. or rnraomuu oms Arthur W. Hixson, Leonia, N. 3., and Ralph Miller,

New York, N. Y., assignors to The Chemical Foundation, Incorporated, a corporation of Delaware No Drawing; Application November 0, 1937. Serial No. 113,194

15 Claims.

and fuel oil fractions. the same general complexity obtains, although the respective percent- 15 ages of the diii'erent groups in such commercial fractions may vary. Thus, a typical relatively high boiling range distillate, having'the characteristics of lubricating oil, contains parafflnic, naphthenic, and aromatic constituents and some 20 asphalt, the respective proportions of such constituents depending largely on the type or source of the crude 011. Thus, Pennsylvania'oil contains little or no asphalt and a relatively small amount of aromatics. The Coastal oil, con- 25 versely, has a relatively higher percentage of asphalt and aromatics than the Pennsylvania oil.

For certain uses, it is desirable to preferentially remove certain of these constituents from the 30 homogeneous mixture, either for the purpose of improving the residuum forsome special purpose or for utilizing the extracted fraction for another use. Thus, it is known that for most purposes the heavier paraflinic fractions constitute the 35 best lubricants, especially for high temperature lubrication such as is required in the modern internal combustion engine. On the other hand,

it is likewise known that the more paraflinic lighter fractions, in the gasoline range, present 40 a decidedly greater tendency to knock than do the more oleflnic gasolines. It is, therefore, sometimes desirable to treat, say, a vapor phase cracked Mid-Continent gasoline so as to preferentially extract the olefinic constituents so that 45 they may subsequently be employed to blend with other gasolines toincrease the octane rating of such gasolines.

It has been proposed heretofore to subject complex mixtures of these hydrocarbon oils in the 50 lubricating and gasoline range to the action of solvents whichhave a preferential amnity for the non-parafiinic constituents so as to obtain an extract and/or a ramnate respectively richer in the desired type of oil than the original stock.

55 It is known that (by choosingthe proper solvent) it is theoretically possible to preferentially dissolvethe naphthenic and aromatic constituents, to segregate the solvent with its dissolved nonparaiiins from the residual oil and separately to recover the residual oil or rafilnate of a relatively I higher paraflinicity, and an extract fraction of a relatively lower paramnicity, than the original 'oil which was treated.

This result, although theoretically quite possible, has been difficult to achieve on a commercially satisfactory basis. The workers in the art have been active on this problem for over a decade and although literally hundreds of solvents or solvent mixtures have been suggested but a very few have attained commercial use. 0f the greater number cfthese extractants that have been proposed, the only ones that have gone into any substantial commercial use are; nitrobenzene, aniline, phenol, sulphur dioxide and benzene, furi'ural, B B dichloroethyl ether, and mixtures of cresol, phenol and propane. Each of these solvents, or solvent mixtures, present certain advantages, but they also present inherent disadvantages.

The reason why such a relatively few number of solvents actually have been employed out of the vast number suggested lies in the fact that the criteria of commercial values are verydifficult to meet. In the nature of its use, the

quantity of the solvent employed runs into large figures and actually may be calculated on a tonnage basis. For this reason the price of the solvent is a factor of dominant importance; too high a solvent cost is positively inhibitive to commercial employment, whatever may be the theoretical emcacy of extraction and the theoretical recovery of the solvent, for, in actual plant operation, some solvent loss is inevitable. This factor of high cost rules out a great many otherwise satisfactory solvents, particularly the 40 more complex organic compounds.

In addition to this important factor of initial cost, there are other factors of a chemical or physicochemical nature which characterize the ideal selective solvent and which are extremely diflicult to discover embodied in a commercially available compound. For example, certain solvents suggested in the past, although possessing a. satisfactory high .selectivity, present a low solubility for the constituents which are desired to be removed. In these circumstances, in order to extract such non-parafilnic constituents, a large and commercially excessive amount of such solvent must be employed. Yet again, certain solvents may possess a satisfactory selectivity and' teristic which militates against their use. For

example, such a solvent may have adensity which is so close to that of the oil being treated that segregation or stratification is'dimcult and costly. Other factors which characterize the ideal solvent are: a desirably low melting point, a relatively low boiling point, a marked tendency to stratify from the paraffinic fraction at separation temperatures, a low solubility in water and an amenability to recovery, preferably by simple physical methods such as low temperature fractional distillation. It will thus be seen that, in

the very nature of this technical use, the field from which a, satisfactory selective solvent may be chosen is quite constricted.

As intimated above, one of the factors of major importance in the choice of a selective solvent is a low initial solvent cost. For refinery operations, such initial cost should, of course, be as low as possible and, in any'event, should' not exceed a price of the order of 9 to 10 cents a pound. Such solvent should, in conformity with the norm indicated above, have a selectivity which is as high as possible and which is at least comparable to that of the solvents now employed. Such solvent also should have a relatively high density as compared with the oils to be treated, such as a lubricating oil fraction. Additionally, the solvent should have a high miscibility temperature, a boiling point not materially exceeding 200 C. and should be substantially insoluble in water and stable under the conditions of use. A selective solvent which would satisfy these criteria would be superior to any now in commercial employment.

With the above outlined stringent requirements in mind, the prior workers naturally investigated the simple, readily available aliphatic compounds. Considered as a class, however, such compounds were found to be unsuitable. Similarly, the simpler, less expensive benzene derivatives were studied, but as indicated above, with but a very few exceptions, these were found to be ineffective. While a multitude of the more complicated derivatives have been suggested in the literature, it is apparent to those skilled in the art that the price requirement in this field is a definite limitation which rules out any such expensive synthetic derivatives.

In view of these considerations, it is apparent that if a synthetic compound is to be employed as a selective solvent, it must be produced from a starting material or mother substance that is relatively cheap and that, with this requirement, for all practical purposes the benzene derivatives, except for the simpler substitution products, are ruled out. It is also quite apparent that as an inexpensive source material petroleum products would be decidedly more preferable. In recent years the potentialities of the parafiin hydrocarbons as a source material for the production of substituted aliphatics has received considerable attention. For example, Haas and his colleagues (Ind. Chem. Soc, 28,339 (1936) and U. S. Patent 1,967,667) describe a vapor phase nitration of paraffin hydrocarbons for the production of nitro paraffins and indicate that such end productsselective solvent for the fractionation of mineral oils. The potentialties of such compounds for use as selective solvents has previously been considered andthe patent literature describes the use of nitro substituted parafilns as selective solvents. An investigation of the characteristics of these simpler substitution products, however, indicates their unsuitability for the purpose at hand. As a typical example, the behavior of nitromethane is a case in point. When nitromethane (B. P. 101 C.) is mixed with an equal quantity'of Mid-continent oil having aviscosity of 48 Saybolt seconds at 210 F. and a viscosity index of 57, and the mixture was heated in an attempt to insure miscibility, it was-found that the solvent boiled before complete miscibility was obtained, in fact, hardly any of the oil dissolved in the solvent. This characteristic of too low a'boiling point substantially precludes the use of this compound for the extraction of lubricating oils.

It might appear, theoretically, that the higher members of the series would operate, due to their higher boiling point and longer chain structure. However, this does not prove to be the case for, as the length of the chain increases, there is a corresponding decrease in density so that, while the higher homologues may satisfy the requirement as to boiling point and miscibility with the oil to be processed, the differential in density which obtains is too small to insure the necessary rapid stratification.

As the result of considerable experimentation in this field, it has been found that such cheap source material, that is to say, the parafiin hydrocarbons or their simpler derivatives, may be utilized for the production of substituted aliphatics which serve admirably as selective solvents. It has been found that as a broad proposition, while nitro substituted paraffins are unsuitable, certain derivatives are eminently suitable. Considered more specifically, it has been found that the introduction of another substituent, particularly a halogen, in the nucleus, modifies the physical characteristics of the original compound so as to render it most effective for the function of selec tive extraction. It was found that, when a hydrogen of a nitroparaffin was replaced with a chlorine atom, the resulting nitrochloroparaffin possessed a higher density and a higher boiling point than the corresponding nitroparaflin, and that the modification of these characteristics was of such a degree as to comply with the described criteria established for an effective selective solvent. The comparison between nitropropane, for example, and its analogue, nitrochloropropane, clearly illustrates this beneficial modification of the physical characteristics which are so important in this particular use. Whereas nitropropane has a boiling point of 131 C. and a density of 1.002 (25 C.) nitrochloropropane, on the other hand, has a boiling point of 1723 C. and a density of 1.224 (30 C.) Similarly, whereas nitrobutane has a boiling point of 139 C'. and a density of substantially .98, its analogue, nitrochlorobutane, has a boiling point of 181-8 C. and a density of 1.187 (20 C.). a

It is thus clear that the marked increase in the boiling point and density is a constitutive property of the halogenated nucleus and serves to sharply differentiate the nitrochloroparaflins from the corresponding nitroparafiins in respect of their availability and utility as selective solvents.

As is known to those skilled in the art, the property of selectivity or preferential solubility Fifty grams ofnitrochloropropane'were added to 50 grams of a Mid-continent neutral oil having a viscosity of 268 Saybolt seconds at 100' I". and a viscosity index of 57.7. The mixture was heated above the miscibility temperature of 96 C. After complete miscibility had been obtained, the solution was allowed to cool, with occasional agitation, in an oven maintained at C., at which temperature the two layers were separated. Each layer was then subjected to vacuum distillation.

Upon' analysis (using an all-glass Fitsimmons suspended level viscometer and calculating the yield on the weight basis). it was found that 86 per cent. of the original oil was in the raiilnate and that such rafilnate had a viscosity of 239.9 Saybolt seconds at 100 F. and 46.1 Saybolt seconds at 210 F. and a viscosity index of 69.1. The oil layer contained but 16 per cent. of the solvent.

It is luminously obvious that these results show that'nitrochloroparaflins possess the property of marked selectivity as well as the other beneficial properties such as satisfactory boiling points,

density and miscibility, which determine their commercial utility. It will be noted, in passing, that in the illustrative experiment, the yields are given in weight. Since the rafiinate has a lower, and the extract a higher specific gravity than the original oil, a comparison calculated on a volume basis will be numerically more favorable.

The series of compounds whichhave herein been described as selective solvents may be produced in any efiective or approved manner. The procedure may be by two diflerent general methods, each utilizing the parafilns as a source material. Such parafiins may be nitrated and the resulting nitroparaflins then halogenated. Again, the parafilns may be chlorinated and the chloroparaflins may be nitrated. Then again, if desired, the compounds mentioned herein may be produced with a synthesis starting from the nitrdtilcohols.

For example, according to one method (see Konawalofl, Russian Journal of Physical Chemistry, 36, 22 (1904)) isobutyl chloride may be reacted with dilute nitric acid in a sealed tube at '70 to 80 C., from 12 to lfihours and the unreacted chlorobutane separated and treated with additional amounts of nitric acid. The formed nitrochlorobutane may be removed by fractional distillation. Or again, the nitrochloroparaffin may be prepared by the method outlined by Henry (Bul. Societe Chemique de Paris, 3rd Series, 13, 999 (1885)); which consists essentially in producing anitro alcohol by condensation of the corresponding aldehyde with a nitromethane group in the presence of a small amount of potassium carbonate, followed by the treatment of the nitro alcohol with phosphorus pentachloride to produce the nitrochloroparaflin.

A modification of the Henry method was utilized with good results. Under the Henry synthesis, in the first stage of the reaction, the nitro 3 dry pyridine and utilizing this" chloride 'as the chlorinating agent. When utilizing this modified reaction, it is advisable to add the chloride slowly to the boiling mixture. The reaction products are preferably purified by washing with water It will be understood that the methods given are merely suggestive and are not given-as necessarily related to the actual extraction of the oil. The invention is available for employment with the described class oicompounds, or their equivalents, however such compounds may be produced.

It will be appreciated that within the broad concept of the invention a relatively largenumber of diiferent specific compounds may be used, the choice of which will depend on the conditions of the particular extraction operation and/or on the characteristics of the oil fraction which is to be treated. The different solvents comprehended herein may be used alone or in admixture with each other or with specifically different solvents. Again. the improved solvents described herein may be used in conjunction with other known solvents for sequential extractions.

It is particularly to be observed that the improved results disclosed herein are obtainable with the broad class of compounds described and are not limited to the particular compound cited in the example. As examples of other characteristic members of-the group may be mentioned, chioronitromethane, bromo nitromethane, a achloronitroethane, a b-chloronitroethane', a a adibromonitroethane, a a-chloronitropropane, a a-bromonitropropane, a-chloro-b-nitropropane,

leum oils containing parafllnic and non-parafiinic constituents, the step consisting in separating the constituents by extracting with a nitrochloroparaflin.

2. The process of solvent refining of petroleum oils containing parafflnic and non-parafllnic constituents, which comprises selectively extracting the non-parafllnic constituents with a halogen substituted nitroparafiln.

3. The process of solvent refining of petroleum oils containing para'iiinic and non-parafilnic constituents which comprises, separating such constituents by extracting the oil with a halogenated nitrogen-containing paraflin.

4. In the process of solvent refining of petroleum oils containing paramnic and non-parafiinic constituents the step consisting in separating the constituents by extracting with a halogenated mononitroparafiin. e

5. The process of solvent refining of petroleum oils containing paraifinic and non-parafiinic constituents which comprises separating such constituents by extracting the oil with a chlorinated nitros'en-containing parafiin.

6. The process of solvent refining of petroleum 75 oils containing parafiinic and non-parafiinic constituents which comprises, separating such constituents by extracting the oil with a chlorinated mononitroparafiln.

. I. The process 01' solvent refining oi petroleum oils containing parafiinic and non-parafllnic constituents which comprises separating such constituents by extracting the oil with a halogenated nitrcethane.

8. The process of solvent refining of petroleum oils containingparafilnic and non-parafiinic constituents which comprises separating such constituents by extracting the oil with a halogenated nitropropane.

9. The'process of solvent refining of petroleum oils containing parafiinic and non-paramnlc constituents which comprises separating such constituents by extracting the oil with a halogenated nitrobutane.

10. The process of solvent refining of petroleum oils containing parafiinic and non-parafilnic constituents which comprises, separating such constituents by extracting the oil with chloronitroethane.

11. The process of solvent refining oi petroleum oils containing parafiinic and, non-parafiinic constituents which comprises separating such constituents by extracting the i1 with chloronitropropane. I

12. The process 01' solvent refining of petroleum oils containing paramnic and non-parafilnic constituents which comprises, separating such constituents by extracting the oil with chloronitrobutane.

13. The process of solvent refining of petroleum oils containing parafiinic and non-paraffinic constituents which comprises, separating such constituents by extracting the oil with B-chloro l.- nitro propane.

14. The process oi solvent refining of pyrogenetically produced oil fractions containing paraflinic and non-paramnic constituentswhichcomprises, selectively extracting the non-parafiinic constituents with a chloronitroparaflln.

15. In the process of solvent refining oi pyrogenetically produced oil fractions containing parafiinic and non-parafiinic constituents the step consisting in separating the constituents by extracting with a selective solvent containing a nitrcchloroparafiin.

ARTHUR W. HIXSON. RALPH MIILER...