US2096725A - Process of refining mineral oils - Google Patents

Description

Patented Oct. 26, 1937 UNITED STATES 2,096,725 rnocnss F BEFINING menu. o ns Chester E. Andrews, bverbrook, and Men-ell It. Fenske, State College, Pa, assignors to Riihm & Haas Company, Philadelphia, Pa.

No Drawing. Application June 13, 1935,

Serial No. 26,408

16 Claims.

least reactive, the naphthenes next'.and the aro-' matic and unsaturated hydrocarbons are the most reactive.

The value of the more viscous fractions of these oils depends more on the physical than on the chemical properties of the oil, the latter being only important in that they more 'or less determine the former. One of the principal uses of such oils is .in the lubrication of all kinds of machinery and-the value of the oil for this purpose depends on its viscosity and particularly on the temperature coemcient of the viscosity. An oil having a high temperature coeflicie t is not so good a lubricant over a wide temperature range as is one having a lower coemci ent. The numerical'value of this coeflicient varies with 'oils of various composition and those which have the greatest proportion of parafflnic hydrocarbons have the lowest coeflicients.

A practical method of expressing-the quality by means of the "viscosity index! which is afunction of the viscosities of the oil at 100 and 210."l (seeDean and Davis,""'Chem.and Met.

Eng. 36, 618, 1929).: According to this method an oil having a high viscosity index is more dcsirable and contains a larger proportion of paraffinic hydrocarbons.

The more viscous fractions of these oils often contain substantial amounts of paraflin wax which crystallizes at low temperatures of operation and these crystals interfere with the flow and lubricating properties of the oil at low temperatures. In order that the components of these fractions of lubricating oil retain at all times, under conditions of use, their mutual solubility, these lubricants are put through a so-called "dewaxing process. This consists of chilling the fraction down to a temperature where the wax separates out'and then filtering out the sepaeii'ect of these paraihns.

of a lubricating oil in terms of this coeiiicient is rated wax. Due to difliculties in operation, this dewaxing is an involved problem in petroleum refining and many diluents and selective solvents have been proposed as an aid to its solution. The effectiveness of any process for wax removal is 5 commonly determined by measuring the pour poin of the oils before and after treatment. This pour point of an oil is related to the temperature at which the oil ceases to flow, and those of low pour test are most desirable for winter lubrication.

The less viscous fractions of vthese oils are believed to contain the same types of hydrocarbons as the more viscous fractions, but of lower molec-'- ular weight. The gasoline fractions from crude oils of different origins contain varying proportions of the various hydrocarbon types just as the lubricating oil fractions do. Due to the excess'ive knocking which they cause in'the internal combustion engine, the'normal paraiiins are the least desirable constituents of a fuel suitable for automotive use. No method has as yet been devised for the removal of normal paraflins from ,I a motor fuel, but it hasbeen necessary to add anti-knock agents to those gasolines which contain high percentages of these straight chain hydrocarbons. Manyorganic compounds, including low boiling fractions from cracking operations. have been proposed and used to counteract the A high grade kerosene fraction is one which contains a high per cent. of, paraflin' hydrocarbons. The process or treating kerosene fractions with liquid sulfur dioxide for removal of aromatics is well known to the petroleum indus- It has now been found that such hydrocarbon mixtures may be separated into fractions by treatment with certain solvents, and in so doing, mixtures having enhanced physical or chemical 40 properties may be obtained.

" We have discovered that the lower amines of the aliphatic series, particularly the three methylamipes, either .alone or in mixtures among them- I selves or with ammonia, water, methanol, or other liquids, are very effective solvents for removing undesirable hydrocarbons fromipetroleum fractions, either by extraction or precipitation. Any type of hydrocarbon mixture from gasoline to the mostviscous lubricatingoil, whether previouslytreated with sulfuric acid or refined by any other method. may be subjected to treatment with the solvents mentioned above. In all cases the mixture so treated will be separated into fra tions having different chemical and physical properties.

The solvent used may be a pure amine, a mixture of amines, and mixtures of these with other liquids such as water, ammonia, methanol and other alcohols, monoethyl ether of ethylene glycol, aniline, aromatic hydrocarbons etc. The process is carried out in a closed system, if necessary under pressure, and at a temperature low enough to keep the solvent in the liquid state and to permit the formation of at least two phases. In certain types of operation it may be desirable to cool the mixture of solvent and oil. By lowering the pressure on the system a certain amount of the amines or ammonia will evaporate, thus causing a lowering of the temperature. The solvent thus evaporated can be condensed in a suitable apparatus and returned to the system or used in a subsequent treatment. This internal refrigerating action is advantageous in the procass for removal of wax.

These solvents also have the advantage that their selective solubility can be varied to fit any "hydrocarbon mixture by changing the percentage extraction apparatus, such as a series of mixing and settling tanks or in a, suitable contacting tower by a counter-current method. In the process for wax removal, any of the conventional types of apparatus may be used with the amines .ous hydrocarbon producing a sharper and easier separation of oil from wax.

Whatever the nature of the extraction process, the mixture of hydrocarbons and amines will separate into two liquid phases, one of which will contain a higher proportion of amines than the other. Likewise, one phase will contain a higher proportion of certain hydrocarbon types than the other because in no case is there a-sharp line of demarcation in the solubilities of the varitypes in the different amine mixtures. I V

It is also possible to dissolve practically all of the material being treated in the solvent and then by changing the temperature, pressure or composition of the solvent to cause the formation of two phases in which the relative proportions of the various types of hydrocarbon are different.

The two phases which appear are separated, and each is subjected to a distillation processor an equivalent process in order to remove the amines and-other solvent in case amixture is used. The amines with or without the other solvent'are 'then brought back to the liquid state in order to be available for later use with another batch of hydrocarbon. It may be necessary to warm the oil somewhat in order to completely remove the amines, and carrying out this step at reduced pressures also facilitates the complete removal. By washing the oil containing amine with a suitable solvent such as water, methanol and the like, the removal of amine from the oil may also be effected. It is advantageous to remove the amines at somewhat elevated temperatures under pressures sufiicient to condense them at temperatures of ordinary cooling water in order to avoid the use of compressors or condensing liquids other than water.

The proportion of solvent to oil used in this process may be varied within very wide limits and will depend on the nature of both solvent and oil, the proportion of material that isv to be removed, and the temperature. The same is true of the temperature, specific amine mixture or mixture of amine with other liquids. The composition of the solvent can also be changed so as to meet any desired operating conditions such as temperature, pressure, density etc., as well as to give a product of any predetermined characteristics.

Liquids which may be used with the amines in order to bring about these results are ammonia, water, methanol, isopropanol, ethanol, and other alcohols, aniline, monoethyl ether of ethylene glycol etc. In fact, any solvent which in combination with amines and oil will produce two phases, is more or less suitable. It is-immaterial whether the extracted oil exists as a separate phase containing a small percentage of solvent or whether a solvent mixture is used which is not completely miscible and the oil is added and I allowed to partition itself between the two solvents according to their selectivity for the various types.

This method is applicable to the entire range of distillates and still residues obtained in the ordinary refining of Pennsylvania, Mid-Continent, California, Texas, Mexico etc. oils, and in every case fractions of varying composition and properties are obtained.

We have also found that lubricating oils which have been extracted by the methylamines respond more readily to clay treatment for color improvement than the unextracted oil even though they may appear to be darker. For a corresponding color improvement there is, therefore, less clay needed for an extracted oil than'for an unextracted oil.

The following tables show the results of various extractions with widely varying solvent mixtures on all types of these oils. Increase in viscosity index is accompanied by improvement in many of the other physical properties such asConrad- 7 cases where a pressure is recorded it is absolute pressure, and where no pressure is given, it

merely means that it was not measured for that particular extraction.

In the tables Vol. means the ratio of the volumes of amine solvent used per volume of oil being treated. fV. I. indicates Viscosity Index.

The original oils had'the following characteristics:

Viscosity 45. l 185. 5 95 55. 3 577 15. 2 157. 2 2692 95. 4 Residual 011 B"; 107.4 1820 72. 5

fffifffff 65 Residual oil A-Continued -4a 5a. a

Texas solar California distillate Methan0l Dlmethylamine Methanol.. Dimethylamjnn Original OiL- Methanol... Dimethylaminn .MethanoL. Dimethylmninn Original 0"- Complete inspection data Percent e v w Pre G t V IG p. SS. [8V1 [EV- Solvent mine Vol. V. I. Yield an Sp. Gr. constant 001:

210 F. I? F.

Distillate Oil A V Percent Methanol 56 25 2, 100. 0 45.0 180. 2 94 1. 30. 4 0. 8739 0. 819 4% Monomethy ine 22.0 50.9 415 19.9 0.9343 0.882 8+ Ammonia 75 25 2. 1 101. 0 45. 1 179. 7 85 7. 0 30. 4 0. 8744 0. 819 4% M yman 05.0 46.6 243 25.2 0. 9029 0.851 8+ Residual oil A Ammonia 25 2.1 96.5 159.9 2724 25.2 0.9034 0.814 7% Monomethylam ne 58 121. 5 2618 8+ Methanol 25 2. 0 97- 3 158. 2 2639 I 25. 4 0. 0000 0. 809 Monomethylaminn Methanol 25 2.0 98.1 162. a 2124 25. a. 0.9016 n. 811' m Monomgthylaminn 65. 0 115. 8 2251 21. 8 0. 9223 0. 845 8+ Original distillate A Original residual A From these tables it is obvious that awide choice of conditions is open to the operator, in every instance a lubricating oil of'increased viscosity index is obtained. Thus, the operator can choose any particular set of conditions consistent with the desired result.

A sample of. gasoline from which the light naphthahad been removed was extracted with a water-monomethylamine mixture containing 50 volume per cent. amine The extract portion had a refractive index of 1.4554, and the rafllnate of 1.4388. Since it is generally known that the straight chain parafiins are the most undesirable constituents of a superior or high knock rating motor fuel,- and further, that for a given boiling point the normal .paraffins are among the compounds having the lowest refractive index it is obvious that a motor fuel of improved knock rating has been produced in the extract portion. Since gasoline is a relatively volatile hydrocarbon,mixture, we prefer to use an amine-ammonia solvent mixture in order to facilitate the removal of solvent by distillation at low temperatures thus preventing the loss of gasoline. We have also found that the presence of the methylamines, particularly dimethylamine'and monomethylamine in gasoline in small quantities greatly increases or improves the knock rating of the fuel. by extracting a gasoline with a mixture off dimethylamine and ammoniaand by removing not quite all of the solvent, a fraction-loan be produced that has been improved on two counts, namely, it will contain a smaller proportion of hydrocarbons of poor detonating qualities and will also contain an active anti-knock agent.

A sample of kerosene was extracted with a methanol-monomethylamine mixture yielding an extract having a refractive index of 1.4741 and a raflinate with one of 1.4474. As in the case of the extraction of gasoline, an improved kerosene is recovered from the raflinate portion since it has a lower refractive index and, therefore, a

higher content of paraflin type hydrocarbons.

A mixture containing 49 wt. per cent toluene.

butand 51% methylcyclohexane was extracted with an 87 volume per cent monon'iethylamine-l3% water mixture. The extract portion was 63.5% toluene and the rafiinate portion was 46% toluene.

A cyclohexane-benzene mixture containing 16.5% of the former on extraction with a mixture of methylamines and water gave an extract analyzing 11% 'cyclohexarie and a rafiinate analyzing 21% cyclohexane.

A normal heptane-toluene mixture, containing 42 mol. per cent of theformer on extraction with a mixed methylamine-water mixture, yielded an extract containing 10.5 mol. per cent heptane and a rafiinate containing 43.3 mol. per cent heptane.

Similarly the amine solvent mixtures have a selective'solubility for olefins over parafilns.

Besides separating hydrocarbon mixtures according to. type, the amine solvent mixtures also produce separation according to molecular weight or viscosity. When a sample of oil is vaporized during a distillation, separation is brought about according to molecular weight or viscosity. This v is because, in general, the higher the boiling point, the higher is the viscosity and molecular weight. 1-Iowe ver, separation according to type does not usually occur to any degree by distilla tion in the case of an extremely complex hydrocarbon mixture such as a lubricating oil. This fact is shown by measuring the viscosity index of a Pennsylvania neutral and bright stock. It will be found that they are practically identical.

A mixture of normal parafllns in the range of approximately 16-18 carbon atoms permolecule, and an equal volume of normal heptane was extracted with a mixed amine-water solvent. The extract portion contained 35% of the high molecular weight paraflins, and the raflinate 55% of the high molecular weight. compounds. This property of the amine solvent mixtures to produce separation according to molecular-weight we have termed a fractionating process.

The following examples show how the methylamines aid as a diluent, internal refrigerant, and selective solvent for oil in a dewaxing process:

The solubility of paraflin wax in naphtha, in benzene-acetone solution containing 65% benzene, and in dimethylamine, was determined at 7 C. The first two solvents have been used for dewaxing purposes cormnercially. The wax was found to be six times as soluble in the naphtha and three times as soluble in the benzene-acetone solution as it was in the dimethylamine. The methylamines also possess the advantage of being less dense so that when they are added to the oil, the specific gravity of the solution is greatly reduced and the Wax can settle out more easily. In the case of the first two solvents the cooling was brought about by the use of externalrefrigerants, but with the dimethylamine its internal refrigerating action caused by evaporation was used to maintain the desired temperature.

A sample of Pennsylvania cylinder stock having a pour point of 70 F. yielded oils on treatment with dimethylamine having pour points of 45 F., 35 F., 25 F., and 15 F., depending on the amount of dimethylamine present and the temperature to which the mixture was cooled.

Similar treatment on a Pennsylvania wax distillate of 70 F. pour point produced easily oils of 5 F. pour. We have found that with monomethylamine alone the'mixture of solvent and Wax distillate on suificient cooling separates into one solid and two liquid phases. We prefer to keep the concentration of the diand trimethylamines in the solvent or diluent sufliciently high so that only one liquid phase is formed on cooling thlus facilitating the removal of the wax from the o1 The foregoing data are given by way of illustration only and not as a limitation, since the invention may be otherwise practiced within the scope of the appended claims.

In the claims, the term methylamine is employed to include monomethylamine, dimethylamine and trimethylamine, mixtures of any two of. them or mixtures of all three or mixtures of these andsuitable proportions of other liquids. By suitable proportions we mean the addition of quantities of other liquids to the methylamines to obtain the desired operating conditions, such as temperature, solvent to hydrocarbon ratio,- density, pressure, etc., and to obtain products with the desired properties, such as hydrocarbon type or molecular weight, viscosity, volatility, gravity, viscosity index, carbon residue, oxidation characteristics, color, knock rating, fagur point, melting point, penetration and the The liquids used with the methylamine consist of a variety of substances, which, mixed together with the amines and the mixture to.be treated,

produce two phases under any practical operating conditions and do not react with themethylamine or the mixture to be treated. Thus it is seen that a variety of substances which in themselves have insufficient solvent action selective characteristics to be used alone, may now be used along with the amines as efl'ective solvents.

In addition to these features,.these methylamine solvents have many other desirable properties, such as low boiling point, low freezing point, low density, low viscosity, solubility in organic as well as in inorganic substances, availability, chemical stability, non-corrosive to ordinary materials of construction, easy detection and estimation, etc. The low boiling point per mits easy removal, the avoidance of the high temperatures and possible thermal decomposition of the products; the low density and viscosity permit easy and rapid separation of the phases; the low freezing allows them to be used over a. wide temperature range for a great variety of purposes; the easy solubility in various substances permits the removal of amines by washing, and facilitates handling .and storage; their chemical stability insures low losses, as well as the avoidance of contamination; their inertness to ordinary materials of construction permits low cost of plant installation and operation and their ready analysis and detection avoids losses in han dling, storage and processing.

The use of the methylamines in dewaxing petroleum oils is claimed in our application Serial No. 155,432 filed July 24, 1937.

We claim:

1. The process of separatingmixtures of hydrocarbons into fractions of different compositions comprising mixing said hydrocarbon mixture with methylamine so that at least two phases form, separating the phases and removing the methylamine from said phases.

2. The process of separating mixtures of hydrocarbons into fractions of different compositions comprising mixing said hydrocarbon mixture with liquid methylamine in a closed system so that at least two phases form, separating the phases and removing the methylamine from said phases.

3. The process of separating mixtures of hydrocarbons intcr fractions of different compositions comprising mixingsaid hydrocarbon mixture with a solvent containing methylamine and ammonia in a closed system so that at least two phases form, separating the phases and removing the methylamine and ammonia from said phases. I I

4. The process of separating mixtures of hydrocarbons into fractions of different compositions comprising mixing said hydrocarbon mixture with a solvent containing methylamine and.

a liquid which is not a solvent for the hydrocarbons so that at least two phases form, separating the phases and removing the solvent from the phases. v

5. The process of separating mixtures of hydrocarbons into fractions of difierent compositions comprising mixing said hydrocarbon mixture with a solvent containing methylamine and water so that at least two phases formQseparating the phases and removing the solvent from the 'phases.

6. The process of separating mixtures of hydrocarbons into fractions oi diflferent compositions comprising mixing said hydrocarbon mixture with a solvent containing methylamine and a liquid which is a solvent for the hydrocarbons Y I fractions having different chemical and physical properties which comprises mixing said petroleum oils with methylamine so that two phases form, separating the phases'and removing the methylamine.

9. The process of separating petroleum oils into fractions having different chemical and physical properties which comprises mixing said petroleum oils with a.- solvent containing methylamine and ammonia so that two phases form, separating the phases and removing the methylamine and ammonia.

10. The process of separating lubricating oils into fractions-one of which has a higher viscosity index and the other a lower viscosity index than the original oil which comprises mixing the oil with methylamine so that two phases are formed, separating the phases and removing the methylamine.

11. The process of separating lubricating oils into fractions one of which has a higher viscosity index and the other a lower viscosity index than the original oil which comprises mixing the oil with a solvent containing methylamine and ammonia so that two phases are formed, separating the phases and removing the methylamine and ammonia.

12. The process of separating lubricating oils into fractions one of which has a higher'viscosity index and the other a lower viscosity index than -the original oil which comprises mixing the oil with a solvent containing methylamine and a liquid which is not a solvent for the lubricating oil so that two phases are formed, separating the phases and removing the solvent.

than the, original oil which comprises mixing the oil'with-a' solvent containing methylamine and methanol so that two phases are formed, separating the phases and removing the methylamine.

15; The process of separating kerosene into fractions having different chemical and physical properties, which comprises mixing said kerosene with methylamine so that at least two phases form, separating the phases and removing the methylamine from said phases.

16. The process; of' separating gasoline into fractions having d'riferent chemical and physical properties, which comprises mixing said gasoline with methylamine so'that at least two phases form, separating the-{phases andremovi'ng the methylamine jrom said phases.

.AQHESTVER E; ANDREWS. man a. R. FENSKE.