US3201344A

US3201344A - Refining hydrocarbon lubricating oils

Info

Publication number: US3201344A
Application number: US241034A
Authority: US
Inventors: Donald B Broughton
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1962-11-29
Filing date: 1962-11-29
Publication date: 1965-08-17
Anticipated expiration: 1982-08-17

Description

United States Patent M of Delaware Filed Nov. 29, 1962, Ser. No. 241,034

No Drawing.

11 Claims. (Cl. 208- -143) This invention relates to a process for the treatment of a lubricating oil fraction of petroleum in a specific manner to separate those components of the oil having optimum lubricating properties. More specifically, this invention concerns a process for separating the cyclic hydrocarbon components containing one or more relatively long, straight chain nuclear alkyl substituents from a lubricating oil fraction of petroleum by selective adsorption of those components of the lubricating oil charge stock on a molecular sieve adsorbent of the X or 13X variety, the recovered adsorbate components of the oil having generally the lowest viscosity and the highest viscosity index for hydrocarbons of the particular molecular weight and volatility present in the lubricating oil charge stock.

it is well-known that lubricating oils have lubricity by virtue of their capacity to intercede between the bearings and the moving parts of machinery, preventing direct contact between these surfaces whereby the internal friction of the lubricant is substituted for the much greater friction between one metallic surface moving relative to another surface in contact therewith. Petroleum lubricating oils possess many of the desirable properties of an ideal lubricant because the oil not only has sufficient surface tension to penetrate between the generally close fitting, sliding metal surfaces of bearings, etc. and to adhere to the metal surface once applied, but hydrocarbon oils also have sufiicient viscosity to resist being squeezed from the space between the metal surfaces under pressure. However, much of the mechanical energy consumed in moving mechanical parts may be consumed and converted to heat in the bearing surfaces if the viscosity of the lubricant results in excessive internal friction between the hydrocarbon molecules comprising the lubricating oil as the temperature of the mechanical parts increases. When the oil is used under conditions closely contiguous to an internal source of heat, as in the case of an internal combustion engine, the boiling point of the lubricating oil components may be exceeded, resulting in excessive vaporization of the hydrocarbons into the ambient atmosphere and if such vaporization exceeds the flash point for the oil (the temperature at which the resulting vaporization results in the formation of a combustible mixture of air and hydrocarbons), vaporization of the lubricating oil components exceeds the limits of tolerance. It therefore becomes desirable from the standpoint of maximizing the temperature range over which the oil is useful to select oils of maximum molecular weight for lubricating purposes, these oils having low volatility and correspondingly lower flash points. However, as the molecular Weight and boiling point of the oil increases, its viscosity likewise increases, in conformity with the generally observed dependance of viscosity on molecular Weight for hydrocarbon mixtures comprising isomers and homologs. At the molecular weight level at which the oil has a sufiiciently elevated boiling point to provide a lubricant having the required elevated flash point, the viscosity of hydrocarbon lubricating oils of random composition comprising mixed isomers and structural types becomes excessive; accordingly, such oils lack optimum lubricity. It is evident, therefore, that two mutually antagonistic factors control the choice of a suitable lubricating oil, and generally one factor must be compromised to satisfy the other.

32%,344 Patented Aug. 17, 1955 Another desirable characteristic of a lubricating oil which determines its performance in lubricating metallic mechanical parts is the viscosity index of the oil which measures the ability of the oil to maintain its viscosity as the temperature of the oil is increased; lubricating oils of maximum effectiveness, therefore, preferably have a high viscosity index. Thus, instead of a reduction in the viscosity of the oil as the temperature of the oil is increased, lubricants having a high viscosity index remain at substantially the same viscosity they possess at low temperature over a wide range of temperatures, maintaining a constant viscosity and consequently, their lubricity as the temperature of the oil is increased.

In the present process for separating a product having enhanced lubricating qualities from a lubricating oil boiling range fraction the feed stock is contacted with a porous, zeolitic molecular sieve adsorbent in which the pores are of sufficient size to accommodate straight chain and cyclic hydrocarbons having mono-alkyl substituents or multiple alkyl groups on the same side of the ring, but which are not of suificient size to accept into the pore chambers of the adsorbent the branched chain and cyclic hydrocarbons containing multiple nuclear alkyl substituents on opposing sides of the ring nucleus. Branched chain hydrocarbons, polynuclear cyclic hydrocarbons and poly-alkyl-substituted cyclic hydrocarbons of the hedgehog structure in which the alkyl groups project from the nucleus in opposite directions and effectively increase the diameter of the cyclic molecule by the distance of the alkyl projections are excluded from the pore openings of the adsorbent and make up the raffinate efiluent of the separation step, comprising less desirable lubricating oil components. The raifinate components occupy the external interstitial spaces between the molecular sieve particles and are separately withdrawn as a fraction from the spent adsorbent particles containing the adsorbate portion of the charge stock. After Withdrawing the radiinate fraction from the separation zone, adsorbate which is the desired portion of the charge stock having enhanced lubricating qualities and consisting of normal paraflins (if any) and the normal alkyl and mono-alkyl-substituted cyclic hydrocarbon components is desorbed from the spent molecular sieve particles by displacement from the pores with a desorbent. If the feed stock is not prehydrogenated prior to the separation-adsorption step, the recovered adsorbate is hydrogenated at this stage of the process cycle to convert aromatics and olefins, if any, in the fraction to their saturated analogs. The resulting naphthenes containing singular nuclear alkyl substituents of straight chain structure or multiple nuclear substitucnts on the same side of the ring, together with any normal parafiins in the feed stock, making up the adsorbate (particularly if the 10X variety of molecular sieves are utilized as adsorbent in the separation stage of the process), are relatively slender molecules having mean crosssectional diameters of low value compared to the naphthenes containing multiple nuclear substituents on opposing sides of the naphthene nucleus, particularly when the alkyl groups are of branched chain structure. These alkyl substituents account for the presence of the hydrocarbons in the raffinate fraction, since the chain branching and the multiplicity of nuclear substitution on the ring of the cyclic components greatly increase the mean cross-sectional diameter of these hydrocarbons and prevent them from entering the pore openings in the molecular sieve adsorbent.

The shape and structure of the parafiin and naphthene molecules comprising the lubricating oil fraction are also' closely associated with other lubricating qualities of the oil and the ability of the hydrocarbon components of the fraction to enter the pores of the molecular sieves is thus :2) inherently correlated to the substantive physical properties of the components which determine their desirability as lubricants. Thus, hedgehog cyclic hydrocarbons containing multiple nuclear alkyl substituents occupying positions on opposite sides of the nuclear ring, such as hydrocarbons of the following structure:

have greater maximum cross-sectional dimensions than cyclic hydrocarbons in which the alkyl substituents occupy nuclear positions on the same side of the ring such as hydrocarbons having the following structure:

R t R R l ]R charge stock, a physical response shared in common with the branched chain paraffins. Thus, viscosity and viscosity index is related more directly to molecular shape than to such physical properties as flash point, boiling point and molecular weight. The correlation of lubricity with molecular shape is believed to arise from the fact that straight chain molecules do not contain alkyl groups projecting from the skeletal nucleus of the molecule which would, if present, interfere with the side-by-side movement of adjacent molecules past each other, developing internal friction from the resistance to such movement, Such internal friction would be present to a maximum degree in the raffinate components, as demonstrated by a comparison of the viscosity index of the rafiinate and adsorbate fractions separated from the lubricating oil charge stock.

One of the essential steps of the present combination process is the hydrogenation of the aromatic hydrocarbons present in the initial feed stock fraction or in the adsorbate product recovered from the separation stage of the process, either alternative source of charge stock to the hydrogenation stage providing a means for ultimately saturating the olefinic and aromatic double bonds in the hydrocarbons comprising the adsorbate portion of the lubricating oil. Thus, the initial feed stock lubricating oil fraction is, in accordance with one of the alternative flow arrangements provided herein, initially subjected to hydrogenation prior to the separation of adsorbate to thereby eliminate any olefinic and aromatic components present in the starting material by conversion to their corresponding parafiins and naphthenes. A particular advantage of this method of operation is that all aromatics in the charge stock are subjected to such prehydrogenation, eliminating from the charge stock any aromatics which may be adsorbed on the surface of the molecular sieve adsorbent by electrostatic adsorption. Thus, the selectivity of the adsorbent for the desired naphthene isomers having optimum lubricating qualities is thereby enhanced, although hydrogenation of the entire feed stock, rather than the select adsorbate fraction thereof provided by the present alternative process modification increases the demand and consumption of hydrogen by the process. The adsorbent, hereinafter more fully characterized, which is a metal aluminosilicate has the specific capacity to ad sorb into its porous structure only those parafiinic, naphthenic and aromatic components which are relatively slender, as determined by the mean cross-sectional diameters of the openings into the internal pore chambers of the adsorbent, being within the limits of from about 10 to about 13 Angstrom units, for which the molecular sieves specified herein are specific. Being metal aluminosilicates, however, these molecular sieves also have surface adsorptivity which is characteristic of aluminosilicates as a class. Hence, when the feed stock to the adsorption stage of the process is the nonhydrogenated stock containing aromatic components generally (whether the alkyl groups residing in these aromatics have a branched chain or straight chain structure and whether the alkyl groups are substituted in single or multiple nuclear positions), the molecular sieves will adsorb many of the aromatic components on the surface of the adsorbent at the same time that the components having the required slender structure will enter the pores of the adsorbent; in other words, if the cyclic components are present as aromatics, non-selective adsorption will take place and many cyclic hydrocarbons containing branched chain alkyl substituents and multiple nuclear substituents will be included in the adsorbate product, even though the undesirable branched chain paraflins will be excluded. On the other hand, if the starting material is prehydrogenated prior to contact ing the molecular sieve adsorbent, only the desirable straight chain, alkyl-substituted naphthenes monoand poly-alkyl-substituted naphthenes in which the alkyl groups are on the same side of the ring, and the normal or slightly branched chain paraflins will enter the pore openings of the adsorbent and make up the desired adsorbate product.

run petroleum distillate.

The scope of the present invention includes both types of operation; that is, adsorptive separation of the feed stock before and after hydrogenation; substantial improvement of the lubricating oil charge stock is realized in both instances, although prehydrogenation of the stock before separation is preferred, since such operation results in maximum improvement in lubricating properties and greatest beneficiation in the viscosity index of the stock. However, in both instances rem-oval of branched chain paraffins and poly-nuclearly substituted alkyl aromatics and alkyl naphthenes, considered to be the least desirable lubricating oil components, is effected by the separation step; prehydrogenation of the feed stock prior to the separation step, however, increases the selectivity.

of the separation step and further limits the adsorbate to only those naphthenes containing single nuclear alkyl substituents or multiple nuclear substituents on the same side of the ring, a selectivity which also limits the proportion of the initial charge stock entering the adsorbate fraction and hence, the yield of product. The adsorbate recovered from the process in which hydrogenation precedes the separation step, however, contains those components only which have superior qualities as lubricants and accordingly the latter embodiment of this invention is utilized when the production of a lubricating oil product having optimum lubricity is preferred over a product of lesser viscosity index, but in greater yield.

One object of this invention, therefore, is to prepare an improved hydrocarbon lubricant utilizing a starting material comprising the lubricating oil fraction of a straight Another object of this invention is to separate from a lubricating oil fraction the components having the lowest viscosity and highest viscosity index from the various isomers and structural types of hydrocarbons represented by a particular molecular weight or range of molecular weights. Still another object of this invention is to recover the components having maximum viscosity index and minimum viscosity from a mixture of hydrocarbons having substantially the same volatility.

In one of its embodiments this invention relates to a process for recovering the components of lowest viscosity from a hydrocarbon mixture boiling in the lubricating oil range which comprises contacting said mixture with a dehydrated, zeolitic, metal aluminosilicate molecular sieve containing pores which permit the entry of hydrocarbons having a mean molecular diameter of from about to about 13 Angstrom units, withdrawing from the resulting molecular sieve containing selectively sorbed adsorbate component a raffinate comprising nonsorbed hydrocarbon component of the mixture, contacting said molecular sieve particles containing adsorbate with a desorbent for the sorbed hydrocarbon component at desorption conditions whereby said adsorbate is displaced from said molecular sieve, said process being further characterized in that one of said fluids selected from the group consisting of said mixture and the recovered desorbed adsorbate is reacted with hydrogen at hydrogenation reaction conditions suflicient to saturate all unsaturated bonds in the hydrocarbon components of said fluid.

Charge stocks which are suitable starting materials for use in the present process are preferably separated from straight run petroleum distillates, comprising the lubricating oil boiling range components of crude petroleum. Depending upon the source of the original crude petroleum and the prior treatment of the petroleum, the lubricating oil fraction is generally separated from the residue remaining after removal of the gasoline, kerosene and gas oil fractions of lower boiling point and'is usually separated from the crude oil residue remaining after distilling the aforementioned overhead fractions by distillation at a subatmospheric pressure, generally at absolute pressures of 10 pounds per square inch or less to thereby minimize cracking or other decomposition of the hydrocarbons in the still residue as the temperature of the latter is raised to vaporize the lubricating oil components therefrom. Thus, at about 3 mm. Hg absolute, the lubricating oil fraction boils within or encompasses the range of from about 300 to 500 F. and is the overhead condensate of the distillation at this pressure. The foregoing boiling range corrected to atmospheric pressure is within the range of from about 500 to about 800 F. Other methods of separation for recovering the lubricating oil fraction of a petroleum crude may be utilized, including solvent extraction which involves mixing the residue of a crude oil remaining after distilling off the gasoline, kerosene and gas oil cuts, with a solvent such as liquefied propane, butane and/or pentane, or with a chlorinated hydrocarbon such as 2,2-dichloroethylene, or with other chlorinated hydrocarbon solvents which selectively dissolve the lubricating oil components from the waxy and residual asphaltic components of the crude oil, separated from the solvent as a non-extracted rafiinate.

The composition of the lubricating oil fraction will vary depending upon the source of the oil (that is, the geographic location of its origin). Pennsylvania crudes which are referred to in the petroleum refining art as paraffin base crudes generally contain larger proportions of paraifinic and naphthenic hydrocarbons than lube oil fractions derived from Southwestern asphalt-base crude oils. A typical Oklahoma asphalt-base crude oil, for example, may contain from 15 to 25 percent by weight of aliphatic paraffins, 40 to 50 percent by weight of alkyl naphthenes containing from 1 to 3 rings per molecule, and 20 to 25 percent by weight of alkyl aromatics containing from 2 to 4 rings and from 5 to 10 percent by weight of nonvolatile asphaltenes which are largely aromatic in character. Pennsylvania crudes, on the other hand, contain much larger proportions of paraffinic hydrocarbons, up to 50 ercent by weight of the entire lube oil fraction. A large proportion of the C to C aliphatic parafiins may be removed from the lubricating oil starting material prior to use in the present process as a crystalline wax by channeling the lubricating oil through refrigerated tubes which cool the oil to temperatures of from 40 to 0 F. and cause the precipitation of the crystalline wax constituents which may thereafter be filtered from the remaining oil.

The hydrogenation stage of the present process utilizing as charge stock the lubricating oil in its entirety or, more preferably in some cases, the adsorbate fraction thereof separated from the lubricating oil in a preceding separation stage is contacted with hydrogen at hydrogenation reaction conditions sufficient to substantially saturate the aromatic and/ or olefinic components of the fraction to the corresponding naphthenes and parat rins. Hydrogenation is preferably effected in the presence of a catalyst which usually reduces the temperature required to effect the reaction, enhances the speed of the reaction or promotes specific conversions not otherwise occurring in the absence of a catalyst, such as ring saturation. Typical useful hydrogenation catalysts for this purpose include the Group VIII metals of the Periodic Table, their oxides or sulfides, generally composited with a suitable refractory support, such as alumina, silica, silica-alumina, silicarnagnesia, silica-zirconia, and other metal oxides or metal oxide mixtures calcined or otherwise heat treated to form a refractory support. Of the Group VIII metals, metal oxides ad metal sulfides, the iron group metals, particularly nickel and cobalt, and the so-called noble metals: platinum and palladium, are the preferred members of this group. The metal is composited with the support by methods well-known in the art and in some cases certain modifying components may be added to the catalyst composition, as in the case of nickel or cobalt sulfide, which when combined with molybdenum oxide, forms a nickel or cobalt thiomolybdate. The latter derivatives are especially active hydrogenation catalysts when composited with a refractory metal oxide carrier or support such as alumina. The most active, and therefore, the preferred hydrogenation catalysts are the supported nickel and platinum or palladium catalysts composited with refractory metal oxide supports such as alumina, silica or an aluminosilicate which may be prepared synthetically with various proportions of alumina and silica or may be derived from mineral sources, such as kieselguhr clay, bauxite, Attapulgus clay, cracking catalyst composites, etc. In the case of the nickel and cobalt supported catalysts, the active metallic component is present in the composite in amounts up to about 20 percent by weight, and more preferably, from about 2 to about 10 percent by weight of the catalyst composition. Platinum and palladium supported catalysts generally contain from 0.01 to about 1 percent by weight of the active metallic component preferably composited with the refractory support in a finely divided crystalline form which enhances the activity of the composite for hydrogenation purposes.

Hydrogenation is effected by contacting the feed stock with the hydrogenation catalyst in the presence of a molar excess of hydrogen, sufficient to saturate all of the unsaturated double bonds in the aromatic and olefinic (if any) components. Although the catalyst may be conveniently stirred into the oil in the presence of an atmosphere of hydrogen above the oil surface, the preferred procedure comprises passing a flowing stream of the oil at the conversion temperature over a fixed bed of the hydrogen catalyst particles in the presence of hydrogen supplied at the required pressure. For this purpose the oil contacted with the catalyst in liquid phase is supplied at a temperature of from about 80 to about 250 C. and more preferably at a temperature of from about 125 to about 200 C. and at a superatmospheric pressure, preferably within the range of from about 5 to about 50 atmospheres. Hydrogenation proceeds at a relatively rapid rate, particularly at elevated temperatures and particularly in the presence of one of the hydrogenation catalysts specified above. Reaction periods of from 5 minutes to 1 hour or liquid hourly space velocities (in the presence of a catalyst) of from 0.1 to 2.5 volumes of oil per volume of catalyst per hour are generally sufllcient to hydrogenate all of the aromatic double bonds in the lubricating oil feed stock, whether the entire lubricating oil fraction or the previously separated adsorbate fraction is utilized as charge stock. Since the oil is a material of relatively high viscosity the feed stock is preferably diluted with from 1 to l to about 5 to 1 volumes of an inert diluent such as a lower paraffin prior to being charged into the hydrogenation reactor. Paraffins of C to C carbon content, which are readily separated from the hydrogenated product by distillation are especially suitable diluents.

In the separation stage of the present process whereby an adsorbate fraction composed of hydrocarbons having a specific slender structure is recovered from the lubrieating oil charge stock, either before or after hydrogenation of the stock, is contacted with a solid, particular adsorbent herein referred to as a molecular sieve adsorbent capable of distinguishing between poly-alkyl-substituted cyclic hydrocarbons of the hedgehog type in which the alkyl radicals are distributed around the nucleus or composite sides of the ring) and cyclic hydrocarbons containing a single, relatively straight chain alkyl substituent (i.e., in the boiling range of the lubricating oil fraction used as feed stock) or poly-alkyl-substituted hydrocarbons in which all of the alkyl substituents are on one side of the ring nucleus. All of these hydrocarbon types are generally present in the lubricating oil fraction, in addition to aliphatic components of varying degrees of branched chain structure. Contact between the charge stock and the molecular sieve adsorbent is made under conditions whereby separation between the foregoing structural types is effected. If aliphatic paraflins are present in the particular charge stock utilized (as in the case of certain Pennsylvannia crudes) the present separation will selectively segregate in the present adsorbate frac tion those components having a relatively straight chain configuration (i.e., a central carbon atom skeleton cont aining no alkyl substituents or at most methyl groups as substituents) from the more highly branched chain isomers and homologs (i.e., containing multiple ethyl, propyl, etc. radicals along the central carbon atom skeleton of the pararlin molecule). These aliphatic, relatively straight chain paraffins are also highly desirable lubricatoil components, raving high viscosity indices and thermal refractivity.

Solid, particulate substances which have the required molecular sieve properties useful in the above indicated separation are the dehydrated alkali metal and alkaline earth metal aluminosilicates prepared synthetically by special procedures disclosed in the prior art. These compositions are referred to broadly as dehydrated, zeolitic molecular sieves of the 10X and 13X variety. These adsorbents, of which the 10X species is generally preferred, as hereinafter described, are formed by combining certain molecular proportions of an alumina-bearing reactant with a silica-bearing reactant in th presence of certain minimum proportions of water and an alkali base, such as an alkali metal hydroxide, carbonate, or other watersoluble source of the alkali metal. Zeolite X molecular sieves have compositions which, in general, correspond to the following empirical formula:

Ill 2 O ZAlgOgIXSlOzZYHgO wherein M represents an alkali or alkaline earth metal, n is a whole number from one to two, depending upon the valence of the metal M, X has a value of 2.5:L-0.5, and Y has an average value in the above formula for the hydrated Zeolite X (i.e., the present zeolite X prior to activation by dehydration) from about 6 to about 7. The empirical formula for the 13X molecular sieves, as specified herein, which are prepared initially and provide the starting material from which the 10X species are prepared have the following specific formula in their hydrated form (in which form they are initially recovered from the zeolite-forming reaction mixture):

(where M is an alkali metal such as sodium). The 10X species of molecular sieves specified herein are prepared from the aforementioned 13X variety by ion exchange of the alkali metal from the composition of the 13X species, for example, by replacement with an alkaline earth metal; the resulting 10X molecular sieves contain an appreciable proportion (generally from 25 to percent by weight) of the alkaline earth metal. An appreciable proportion of the ion-exchanged zeolite has the following empirical formula:

5M0 6Al O 1 SSiO 6.2-8H O (where M is an alkaline earth metal, such as calcium). When activated by dehydration, both the 10X and 13X molecular sieves are useful adsorbents in the present process.

The sodium form of zeolite X which provides the starting material from which the alkaline earth metal derivative is prepared to form the 10X zeolite is by mixing together a source of silica gel such as colloidal silica, sodium silicate or a hydrolyzed alkyl orthosilicate with a source of alumina gel, such as sodium aluminate, activated alumina, etc. and a certain minimum quantity of alkali metal hydroxide (such as caustic soda) and water. The preferred ratios of the various reactants utilized in the preparation of the 13X zeolite are such that the following ratios of oxides are provided in the reaction mixture:

3 to 5 Na O/SiO 1.2 [0 1.5 H O/Na O 30 to 65 The mixture of zeolite-forming reactants is then heated to a temperature of about C., preferably in a closed container to prevent loss of moisture, for a reaction period 9 suilicient to obtain maximum formation of a resulting crystalline product (generally within less than 6 hours). The finely divided crystals of hydrated zeolite X precipitated from the aqueous phase are separated from the mother liquor by filtration or other means of separation. Because the crystals are of such small size, not readily adapted to liquid phase contacting procedures, particularly for use with feed stocks having the viscosity of lubricating oils, the crystals are preferably mixed with a porous clay binder with which the crystals are compatible, shaped into suitably sized pellets (for example, by compressing a mixture of the zeolite crystals and clay in a pilling machine) and thereafter the pills are heated to a temperature above the boiling point of water to dehydrate the composition and thereafter to a temperature of from about 200 to about 500 C. to activate the zeolite X crystals in the pellets.

The 10X Variety of molecular sieves, comprising the alternative zeolitic molecular sieves utilizable in the present separation process, are synthesized by ion exchanging the crystals of 13X alkali metal aluminosilicates, prepared as indicated above, preferably prior to dehydration, with an aqueous solution of an alkaline earth metal salt, such as calcium chloride, magnesium chloride, etc., to replace at least a portion of the alkali metal ions in the 13X molecular sieves with the corresponding alkaline earth metal ions. Such ion exchange is conveniently effected by mixing the finely divided crystals of alkali metal aluminosi-licate or, less preferably, with the pilled form of the molecular sieves, as desired, with an aqueous solution of the alkaline earth metal salt. The ion exchange process may be eflected by intimate contact between the alkaline earth salt solution, for example by permitting a solution of the alkaline earth metal salt to continuously drain through a column of the crystals, by mixing the alkali metal zeolite with an aqueous solution of the alkaline earth metal salt and repeating the procedure until the supernatant solution no longer contains an appreciable proportion of alkali metal ions. The resulting ion-exchange zeolite crystals are pilled, dehydrated and activated by essentially the same procedure as described above for the 13X form of zeolite.

Zeolite X molecular sieves of the 10X variety which contain pore openings of about 10 Angstrom units in cross-sectional diameter absorb a smaller, although a more select, proportion of the lubricating oil constituents than the 13X variety of molecular sieves, which contain pore openings having a mean cross-sectional diameter of from 10 to about 13 Angstrom units and such selectivity is directly correlatable with the desirable lubricating qualities of the recovered absorbate. Thus, 10X molecular sieves permit cyclic hydrocarbons having only relatively straight chain alkyl substituents on the nucleus of the hydrocarbon ring and cyclic hydrocarbons having not more than 2 rings per molecule to enter the internal structure of the molecular sieve, whereas the 13X molecular sieve variety of zeolite not only accepts all of the hydrocarbons which the 10X variety of absorbent accepts, but also certain poly- =alkyl-substituted isomers and homologs of somewhat less than optimum lubricity in which the alkyl substituents are of more branched chain structure, as well as polycyclics containing 3 condensed rings per molecule. Zeolite 13X, however, does not absorb poly-alkyl-substituted cyclic hydrocarbon-s of the hedgehog type (i.e., in which the alkyl groups are substituted on opposite sides of the nucleus) or highly branched chain alkyl-substituted cycli-cs, the latter hydrocarbons which make up the raflinate fraction having a substantially higher viscosity and lower viscosity index than the desired absorbate recovered as the present product. The straight chain alkyl-substituted cyclic hydrocarbons are not as prevalent in lubricating oil fractions as the branched chain and poly-alkylsubstituted cyclic hydrocarbons; hence, the yield of absorbate product recovered from the process when the initial lubricating oil fed stock is contacted with a 10X molecular sieve absorbent is of substantially lesser quantity than the yield of product recovered by treatment of the hydrogenated lubricating oil stock with 13X molecular sieves. The quantity of recovered absorbate product is also greater when the feed stock is the nonhydrogenated initial feed stock in which many of the cyclic hydrocarbon components are of aromatic structure because of the aforementioned tendency of zeolitic molecular sieves (of aluminosilicate composition) to absorb hydrocarbons containing aromatic unsaturation via super ficial or electrostatic adsorptive forces, in addition to pore adsorption. The preferred products having the lowest viscosity at a particular boiling point and the greatest viscosity index is the portion of the hydrogenated lubricating oil stock recovered by the 10X variety molecular sieves; nevertheless, even the adsorbate product recovered by contacting the prehydrogenated (or even the non-prehydrogenated) lubricating oil fraction with 13X molecular sieves has substantially better lubricating qualities than the charge stock, either hydrogenated or prior to hydrogenation.

The ratfinate fraction recovered from the present process and comprising cyclic hydrocarbons of the hedgehog structure as Well as aliphatic and cyclic components in which the aliphatic chain or the substituent alkyl groups are highly branched are least desirable as lubricating oil components and are either discarded from the present process or subjected to a subsequent isomerization whereby these hydrocarbons are isomerized to less branched chain aliphatic hydrocarbons or cyclics containing fewer alkyl substituents or alkyl groups of straighter alkyl chain configuration; the isomerized product may be recycled as feed stock to the separation stage, if desired.

The separation stage of the present process in which the lubricating oil fraction (either before or after prehydrogenation) is contacted with one of the aforementioned prescribed zeolitic molecular ieve to recover the desired adsorbate portion of the feed stock components is effected at a temperature and pressure which maintains the feed stock in essentially liquid phase and which reduces the viscosity of the feed stock sufliciently to enable the oil to flow readily into the pore openings of the molecular sieves. The latter effect may be enhanced by mixing the lubricating oil feed stock with a more fluid hydrocarbon having generally a lower viscosity than the lubricating oil stock but which, on the other hand, does not enter the pore openings'of the molecular sieve adsorbent prior to the entry of the adsorbate components of the feed stock into the pores. Thus, any diluent suitable for this purpose must itself be essentially inert to the molecular sieve adsorbent so that the .adsorbate components of the feed stock are not precluded from entering the pores of the zeolite. Typical diluent hydrocarbons suitable for the in the present separation stage of the process are the tertiary hydrocarbons of lower molecular weight (and accordingly of lower boiling point) than the lubricating oil stock, such as 2,2-dimethylpropane, 2,3-diethyl-2,3 dimethylbutane, 2,2,4,4-tetramethyl-3,3-di-tert.-butyl-pentane, 3,3-diethylpentane, 3,3,4,4-tetraethylhexane, etc., or a poly-alkyl-substituted cyclic hydrocarbon, such as 3 ethylhydr-ocumene, 2,5-diethylhydrocumene, 3,5-diethylethylbenzene, etc., the latter diluent hydrocarbons being readily separable by distillation from the efiluent railinate or adsorbate product streams for recycling in the process.

After completion of the adsorption stage of the process the raffinate residue occupying the interstitial spaces between the particles of adsorbent is preferably flushed therefrom prior to the subsequent desorption-recovery stage of the process to thereby preclude contamination of the .desorbate product with interstitial ralfinate left in the mass of adsorbent particles. A suitable fluid usable for flushing purposes may be selected from the aforementioned diluents or other inert wash fluids.

The desired extract or adsorbate portion of the lubricating oi'l adsorbed by the zeolitic molecular sieves during the separation stage of the process is recovered therefrom by displacement with an adsonbate-type compound preferentially adsorbed by the zeolite or by an essentially inert hydrocarbon charged into the adsorption zone at a higher temperature than the temperature at which the adsorption separation initially took place or by an adsorbate-type hydrocarbon of lower molecular weight than the adsorbate hydrocarbon and supplied to the adsorption zone during the desorption stage in a substantially greater molar excess than the adsorbate present in the pores of the molecular sieve. Of the above alternate procedures available for effecting desorption of the adsorbate, the generally preferred procedure comprises suffusing the spent molecular sieve particles with an adsorbate type hydrocarbon of substantially lower molecular weight than the lowest molecular weight component of the feed stock, preferably a normal paraffin hydrocarbon containing from about 4 to about carbon atoms per molecule, the desorbent being supplied to the desorption zone containing spent molecular sieve particles in sufiicient quantity to substantially surround each of the molecular sieve particles with desorbent and in greater molar excess than the adsonbate present in the pores of the spent adsorbent. The fluid phase in the interstitial space thereby contains a desorbent to adsorbate molar ratio greater than 1 to 1, particularly when a flowing stream of desorbent is charged into one end of the desorption zone and a mixed desorbentadsorbate effluent is withdrawn from the other end of the unit. A displacement action occurs by virtue of the mass action effect of the excess desorbent in the interstitial space relative to adsorbate inside of the pores. This type of desorption is enhanced by charging the desorbent in countercurrent relationship to the spent molecular sieve particles whereby the adsorbent particles of the most advanced state of desorption are contacted with freshest desorbent containing the least adsorbate. The desorbent stream containing the highest proportion of desorbate is withdrawn from the process flow for recovery of the desired adsor-bate from desorbent which may the recycled in the process.

Countercurrent methods of separation Which include both the adsorption .and desorption stages may be adapted to continuous processing techniques by providing two separate vessels packed with molecular sieve adsorbent particles, in one of which adsorption takes place as feed stock is charged into the vessel, while in the other vessel desorption simultaneously takes place as desorbent is charged into the vessel containing spent adsorbent. The adsorption and desorption stages are switched at regular intervals to provide an essentially continuous swing react-or method of operation, feed stock adsorbate readily displacing adsorbed desorbent at less than molar ratios because of the preferential adsorption of feed stock adsorbate during the separation stage of the process cycle.

The adsorption stage of the present separation process is conveniently operated at a temperature of from about to about 200 C., and more preferably at temperatures of from about 50 to about 150 C., the pressure being suificiently superatmospheric to maintain the diluent (if utilized) in substantially liquid phase. Desorption may be effected at the same temperature as the adsorption stage to provide an economically operated isothermal process, although desorption is more rapid and other advantages accrue to the process when the desorption stage is operated at a somewhat higher temperature than the adsorption stage, more preferably at temperatures of from about 100 to about 300 C. The particular process conditions utilized in .any specific operation will depend to a large extent upon the feed stock and desorbent charged to the process, since the two stages of the separation process are mutually dependent and the effluent streams from the process equipment are generally mixtures of desorbent, rafiinate and extract components.

This invention is further illustrated with respect to several of its specific embodiments in the following examples which, however, are not intended to limit the generally broad scope of the invention necessarily in accordance therewith.

In the following examples mixtures of known composition are subjected to separation in accordance with the process herein provided, providing an indication of trends and operating principles prevalent in the instant process.

EXAMPLE I The separation is efiected in two adsorption columns, approximately 30 inches in length having a cross-sectional, internal diameter of 2.2 inches, each column being packed with molecular sieve particles, one column containing 10X molecular sieves supplied by the Linde Company, and the other column being packed with Linda 13X molecular sieve particles. The 10X molecular sieves are a pelleted mixture of clay and calcium aluminosilicate crystals (the sodium derivative ion-exchanged with a calcium salt) pressed into pellets of approximately 14 mesh size. The 13X molecular sieves consist of a mixture of clay and the sodium derivative of the aluminosilicate prepared initially, also approximately 14 mesh in size.

The following pure hydrocarbons are each mixed with 300 volumes of 3,3-diethylpentane diluent (i.e., to form a 25 percent by volume solution of sample) and the mixture charged into each of two adsorption columns packed with fresh molecular sieve pellets, one containing the 10X variety and the other 13X molecular sieves:

(l) Chrysene (a tetracyclic, condensed-ring aromatic hydrocarbon).

(2) Hydrogenated chrysene (hydrogenated by passing the hydrocarbon in admixture with normal octane over an alumina-supported nickel catalyst in the presence of hydrogen at C. and at 400 p.s.i.g. pressure).

(3) Dodecyl benzene (n-dodecylene alkylate of benzene).

(4) Dodecyl cyclohexane.

(5) 1,3,5-tri-isopropy1 benzene.

(6) 1,3,5-tri-isopropyl cyclohexane.

(7) 1,4,7-triethyl naphthalene.

(8) 1,4,7-triethy1 decahydronaphthalene.

(9) Methylnaphthalene.

(10) Methyl decahydronaphthalene.

Each of the foregoing feed stocks are charged into the column containing the 10X molecular sieves, and a separate stream of the feed stock is separately charged into the column containing the 13X molecular sieves, both feed streams being charged into the bottom of the columns containing the molecular sieve particles at 15 C. and 200 p.s.i.g. All streams are allowed to flow upwardly through the mass of particles and nonadsorbed raffinate is withdrawn from the top of the column for analysis. In each instance 30 ccs. of charge stock (exclusive of diluent) is pumped into the column, followed by 200 ccs. of 3,3-diethylpentane which is not adsorbed by the molecular sieves, but removes nonadsorbed raffinate out of the column into the overhead receiver. The diethylpentane elutriant is charged into the column at the same temperature and pressure that the feed stock enters the column; that is, at 15 C. and at 200 p.s.i.g. pressure.

Following the removal of railinate components from the column as overhead, as indicated by the change of the refractive index and infrared spectrum of the overhead stream to that of diethylpentane, the flow of elutriant is discontinued, followed by charging a desorbent stream consisting of n-pentane at 400 F. and 600 p.s.i.g. pressure into the bottom of the column and collecting the overhead efiluent from the column in a separate receiver. The composition of the desorbate overhead and the degree of desorption effected is measured by refractive index and infrared spectroscopic examination of the efiluent stream. The following table presents the data relating to the composition of the fractions recovered from each of the above feed stocks.

13 Table I ADSORPTION AND DESORPTION OF HYD ROCARBONS ON X AND 13X MOLECULAR SIEVES 1 DEP; 3,3-Diethylpentane.

2 Residue after evaporation of pentane.

3 Nil sample content.

4 Percent of total charged into column.

6 Remainder is net loss, representing column holdup.

EXAMPLE II In the following run the apparatus and procedure specified in the foregoing Example I is duplicated for a charge stock consisting of a light lubricating oil fraction of a Pennsylvania crude oil which has been dewaxed by chilling to 30 C., followed by separating the non-crystallized portion (rafiinate) of the lube oil fraction from the solidified portion (filtrate). As initially prepared, this fraction consists of hydrocarbons in the C C range and as indicated by adsorption on an activated silica gel, elution of the adsorbate and infrared spectroscopic examina tion of the adsorbate, the mixture contains about 45% by weight of aromatic components. Infrared spectroscopic examination of the lubricating oil fraction as a whole indicates that the cyclic hydrocarbons comprise monocyclic, di-cyclic, tri-cyclic and tetra-cyclic condensed ring naphthenic and aromatic components, and in addition, mono-cyclic compounds containing from 1 to 4 nuclear alkyl substituents. The lubricating oil cut in one series of runs is subjected to the present adsorption separation procedure in its as-received form and, in a second series of runs, after prehydrogenation suh'icient to convert the aromatic components to naphthenes, each of the foregoing feed stocks (that is, the as-received and hydrogenated lube oil fraction) being contacted with 10X and 13X molecular sieves at 60 C. in separate contacting columns, as described in Example I above. Following the adsorptive separation stage, the mass of molecular sieve particles is washed with several volumes of 3,3-diethylpentane, followed by desorption of the adsorbate with n-pentane at 160 C. and :at 600 lbs/in. pressure. In each case, light components of the efliuent streams (3,3-diethylpentane and n-pentane) are distilled overhead from the raflinate and adsorbate streams. The following Table II indicates the change in properties of the recovered adsorbate and raffinate products separated by contact with the molecular sieve adsorbents. Viscosities of these product streams are measured at C., 40 C. and at 60 C., viscosity index being a calculated value, as indicated below in footnote 3.

Cyclic hydrocarbons having nuclear Table II SEPARATION OF LUBRICATING OIL FRACTION BEFORE AND AFTER HYDRO GENATION BY ADSORPTIVE CON- TAOT WITH MOLECULAR SIEVE ADSORBENTS Ratlmate Adsorbate Sample From From From From 10X 13X 10X 13X Lubricating oil, as received: 1

Volume percent of charge 71 49 29 51 Viscosity Index 3 78 .71 93 88 Lubricating oil, prehydrogenated: 2

Volume percent of charge 76 57 24 43 Viscosity Index 78 79 1. 18 l. 08

Hydrocarbon types in fraction 1 Viscosity index of lubricating oil, as received and as used as feed stock 0 85 2 Viscosity of hydrogeneated lubricating oil used as feed stock: 0.87.

3 Slope of curve in plot of viscosity versus temperature, determined at 10 0., 40 C. and 80 C. r

4 Based upon Infrared and X-ray spectrographic analysis.

5 Poly-cyclic.

6 Mono and di-cyclic, long chain alkyl.

7 Mouo-, diand tri-cyclic.

The above data indicate that components flowing through the column packed with 13X molecular sieves are primarily cyclic hydrocarbons containing 2 to 4 condensed rings, whereas the components flowing through the column packed with 10X molecular sieve adsorbent particles consist predominantly of monocyclic hydrocarbons, including a small proportion of poly-cyclic constituents. After hydrogenation which saturates the aromatic nuclei, eliminating surface adsorption effects, both 10X and 13X molecular sieves adsorb a lower proportion of the charge stock, but a more select portion having a higher viscosity index.

The results thus establish the remarkable change in viscosity of the adsorbate product as the adsorbent is shifted to the 10X molecular sieves and as the feed stock is subjected to prehydrogenation prior to adsorptive separation, the less desirable, low viscosity index components of the fraction tending to concentrate in the rafiinate fraction in each instance.

I claim as my invention:

1. A process for recovering the components of lowest viscosity from a hydrocarbon mixture boiling in the lubricating oil range which comprises reacting said hydrocarbon mixture with hydrogen at hydrogenation reaction conditions sufiicient to saturate substantially all unsaturated bonds in the hydrocarbon components thereof, thereafter contacting said mixture with a dehydrated, zeolitic, metal aluminosilicate molecular sieve containing pores which permit the entry of hydrocarbons having a mean molecular diameter of from about 10 to about 13 Angstrom units, withdrawing from the resulting molecular sieve containing selectively sorbed adsorbate component a raifiuate comprising nonsorbed hydrocarbon component of the mixture, and contacting said molecular sieve particles containing adsorbate with a desorbent for the sorbed hydrocarbon component at desorption conditions whereby said adsorbate is displaced from said molecular sieve.

2. The progress of claim 1 further characterized in that said hydrocarbon mixture subjected to hydrogenation is mixed with a liquid solvent for the hydrocarbon components of the mixture, said solvent having a boiling point less than the lowest boiling components of said hydrocarbon mixture prior to said hydrogenation reaction.

3. The process of .claim 1 further characterized in that said hydrogenation stage of the process cycle is effected in the presence of a hydrogenation catalyst comprising a refractory solid selected from the group consisting of the metals and the oxides and sulfides of the metals of Group VIII of the Periodic Table.

4. The process of claim 3 further characterized in that said metal of Group VIII of the Periodic Table is nickel and said catalyst comprises a support for said nickel consisting of alumina.

5. The process of claim 1 further characterized in that said desorbent is a normal paraffinic hydrocarbon of lower molecular weight than the adsorbate component of said mixture.

6. The process of claim 5 further characterized in that said normal parafiinic hydrocarbon contains from 4 to about 10 carbon atoms per molecule.

'7. The process of claim 5 further characterized in that said desorption is effected at a temperature of from about 100 C., to about 300 C. and at a pressure sufiicient to maintain said desorbent in substantially liquid phase during the period of contact between the desorbent and the molecular sieve containing adsorbate.

8. The process of claim 1 further characterized in that the mass of molecular sieve particles is flushed with a liquid which is substantially inert to the molecular sieve adsorbent prior to contacting the molecular sieve particles containing adsorbate with desorbent, the mass of molecular sieve particles being flushed for a period sufficient to remove interstitial raffinate from said mass of particles.

component of the lubricating oil mixture and a sufficient cross-sectional diameter that precludes its adsorption in the pores of the molecular sieve adsorbent.

11. The process of claim 10 further characterized in that said flush hydrocarbon is 3,-3-diethylpentane.

References Cited by the Examiner UNITED STATES PATENTS 2,744,053 5/56 Kay et al. 208-2l1 2,938,864 5/60 Fleck et al. 20831O 3,112,259 11/63 Grawitz 208264 ALPHONSO D. SULLIVAN, Primary Examiner.

Claims

1. A PROCESS FOR RECOVERING THE COMPONENTS OF LOWEST VISCOSITY FROM A HYDROCARBON MIXTURE BOILING IN THE LUBRICATING OIL RANGE WHICH COMPRISES REACTION SAID HYDROCARBON MIXTURE WITH HYDROGEN AT HYDROGENATION REACTION CONDITIONS SUFFICIENT TO SATURATE SUBSTANTIALLY ALL UNSATURATED BONDS IN THE HYDROCARBON COMPONENTS THEREOF, THEREAFTER CONTACTING SAID MIXTURE WITH A DEHYDRATED, ZEOLITIC, METAL ALUMINOSILICATE MOLECULAR SIEVE CONTAINING PORES WHICH PERMIT THE ENTRY OF HYDROCARBONS HAVING A MEAN MOLECULAR DIAMETER OF FROM ABOUT 10 TO ABOUT 13 ANGSTOM UNITS, WITHDRAWING FROM THE RESULTING MOLECULAR SIEVE CONTAINING SELECTIVELY SORBED ADSORBATE COMPONENT A RAFFINATE COMPRISING NONSORBED HYDROCARBON COMPONENT OF THE MIXTURE, AND CONTACTING SAID MOLECULAR SIEVE PARTICLES CONTAINING ADSORBATE WITH A DESORBENT FOR THE SORBED HYDROCARBON COMPONENT AT DESORPTION CONDITIONS WHEREBY SAID ADSORBATE IS DISPLACED FROM SAID MOLECULAR SIEVE.