US3520796A - Making lubricating oils by hydrotreating and dewaxing - Google Patents

Description

United States Patent ice US. Cl. Edi h-33 6 @laims ABSTRACT Ell THE BESLSURE A process for producing a finished lubricating oil of enhanced quality, e.g. reduced pour point, from lubricating oil base stocks comprising substantially components boiling below 800 F. and containing more than 0.75 percent by weight sulfur by subjecting such base stock to hydrofinishing and then dewaxing the hydrofinished base stock.

This application is a continuation-in-part of our copending application Ser. No. 533,450, filed Mar. 11, 1966 and now abandoned.

Our invention relates to an improved process for producing lubricating oils from certain high sulfur content stocks.

It has previously been suggested in the art to prepare lubricating oils by subjecting crude lubricating oil stocks to a variety of treatments including deasphalting, solvent extraction, comparatively severe hydrogen treatment sometimes called hydrotreating, solvent dewaxing, acid treatment, clay contacting and more recently, mild hyrogen treatment sometimes called hydrofinishing. This last mentioned mild hydrofinishing operation in many instances is employed in lieu of acid treatment and clay contacting and is employed mainly in the treatment of lubricating oil base stocks, as distinguished from crude lubricating oils, in order to remove odor and color forming materials which are considered to be objectionable in the final lubricating oil product. All of the abovementioned operations contribute to the production of the final finished lubricating oil from the crude lubricating oil stock by removing undesirable constituents and/or hydrocarbon types from either the crude lubricating oil stock or the intermediate lubricating oil base stock. Generally, the prior art does not suggest any preferred order in which these various operations are to be conducted other than that dictated by economic or engineering expediencies such as, for example, employing previously a treating technique which is effective to remove materials deleterious to subsequent treatment steps or which reduces the quantity of material to be treated in a subsequent step, the operation of which is more expensive.

One of the required characteristics or properties of a finished lubricating oil is that it have a low pour point. The desired level of the pour point of a finished lubricating oil varies, dependent upon the type of finished lubricating oil desired as a product and its intended employment. Usually, however, a pour point of +10 F. or lower is required. In some instances the desired pour point may even be as low as F. or even lower. In most instances, however, a finished lubricating oil having a pour point of about 5F. to about F. is satisfactory. The art has recognized for many years that the pour point of a lubricating oil is generally related to the quantity of wax present in the material and a variety of dewaxing techniques have been suggested to lower the Wax content of lubricating oils and concomitantly 3,520,796 Patented July 14:, 1970 lower the pour point thereof. Fresently, the technique employed widely in the art is a solvent dewaxing operation. Even though present day solvent dewaxing techniqucs are generally considered to be somewhat of an improvement over techniques previously employed in the art, the solvent dewaxing treatments are still beset by the traditional problem in the dewaxing field, i.e. the wax cannot be removed from the lubricating oil without cooling the material being treated to an extremely low temperature usually lower than the desired pour point of the finished product. Thus, the limiting factor in most solvent dewaxing operations is the refrigeration capacity of the unit and any technique which would permit obtaining the desired pour point of the treated material but permitting employment of a dewaxing temperature even a few degrees above what might otherwise be required, results in a substantial improvement and enhancement of the process from an economic view point.

In many instances this desirable characteristic of a low pour point in a lubricating oil can be obtained when employing a solvent dewaxing treatment in combination with any one or more of the treating techniques mentioned previously. A typical example of the prior art operation includes solvent dewaxing an intermediate lubricating oil base stock followed by acid and clay contacting of the dewaxed base stock. In more modern refinery operations this scheme would require solvent dewaxing of a lubricating oil base stock followed by hydrofinishing of the dewaxed material to yield the finished lubricating oil. While this sequence of operations may in some instances be entirely satisfactory to yield a lubricating oil having the desired pour point in an economical manner, it has been found that in many instances this sequence is not advantageous.

We have discovered that when treating certain types of lubricating oil base stocks the sequence of solvent dewaxing followed by hydrofinishing or of hydrofinishing a substantially wax-free lubricating oil base stock either produces a finished lubricating oil having a pour point which is higher than desired or requires a dewaxing operation employing an increased refrigeration capacity in order to obtain a sufficiently low dewaxing temperature and thus obtain a finished product having the desired pour point. Further, we have discovered that when treating lubricating oil base stocks of this particular type, it is necessary to hydrofinish the base stock and then to subject the hydrofinished stock to a solvent dewaxing treatment.

The particular materials to which the process of our invention is applicable can be described as comparatively low boiling, high sulfur content lubricating oil base stocks. By the term lubricating oil base stock is meant a fraction or group of fractions usually produced at an intermediate point in the production of a lubricating oil which lacks but the final finishing operations, such as, for example, hydrofinishing, acid treatment or clay contacting, before being classed as a finished lubricating oil. Generally, such lubricating oil base stocks can be obtained from crude lubricating oil stocks, i.e. untreated materials boiling in the general range of lubricating oils, by atmospheric and vacuum distillation followed by deasphalting, such as propane deasphalting, solvent extraction, treatment in a Duo-Sol process, comparatively severe hydrogen treatment, i.e. hydrotreating, etc. or any combination of one or more of these treatments or none, depending upon the type of crude lubricating oil stock being considered and the type of finished lubricating oil desired as product.

Generally, the lubricating oil base stocks treated in accordance with our invention are comprised substantially of components boiling below about 800 F. Lubricating oil base stocks having a 90 percent point of about 830 F. or lower are quite suitable. Lubricating oil base stocks having a 90 percent point of less than about 800 F. can be treated in accordance with the process of our invention with particularly advantageous results. These comparatively low boiling lubricating oil base stocks will generally be found to have an average molecular weight of less than about 375 and will usually have an average molecular weight of about 350 or even lower.

The lubricating oil base stocks treated in accordance with our invention must also have a sulfur content of at least about 0.75 percent by weight. Usually these materials will be found to have a sulfur content of at least 1.0 percent by weight.

The process of our invention is suitable for treatment as an entity of the entire spectrum of lubricating oil base stocks meeting the above description as well as treatment of individual lubricating oil base stock fractions. These individual fractions generally have a range from about 90 to about 120 F. between their percent and 90 percent points and are usually considered as having a nominal spread of about 100 F. between their 10 percent and 90 percent points. The process of our invention can also treat the lubricating oil base stocks described above either alone or in admixture with other lubricating oil base stocks.

It is believed that these lower boiling lubricating oil base stocks which also have a comparatively high sulfur content initially, i.e. before hydrofinishing, comprise certain sulfur containing molecules which upon hydrofinishing and the removal of sulfur therefrom either form waxy components themselves, are converted to certain compounds which although are generally not considered to be waxes have the same deleterious effect on the pour point as do waxes, or are converted to non-sulfur containing compounds which lack the solubilizing effect upon waxes which the corresponding sulfur containing materials have. This phenomenon appears to be borne out by the fact that lubricating oil base stocks having a comparable boiling range but having a comparatively low sulfur content do not exhibit this effect upon hydrofinishing.

Of the three major types of hydrogen treating operations generally associated with the lubricating oil field, i.e. hydrocracking, hydrotreating and hydrofinishing, the hydrogen treating operation employed in our invention is termed hydrofinishing. Generally, hydrocracking is an extremely severe operation wherein comparatively high boiling hydrocarbons, e.g. stocks containing components boiling above the general lubricating oil range or above 1000 F., are treated so as to effect somewhat random severing of carbon-to-carbon bonds, thereby resulting in a substantial overall reduction in molecular weight and boiling point of the treated material while concomitantly effecting a substantial increase in API gravity in order to produce large quantities of materials boiling below about 600 F. and a somewhat lesser quantity of materials boiling in the lubricating oil range from about 600 to about l000 or 1100 F. In hydrocracking, at times, the production of lubricating oils can be merely incidental to the production of gasoline and furnace oil.

The next most severe hydrogen treating operation is termed hydrotreating and is generally considered to be intermediate hydrocracking and hydrofinishing in its severity. Thus, hydrotreating effects a significant amount of molecular rearrangement, while not effecting the excessive and random breakdown of molecules effected in hydrocracking. Generally hydrotreating is primarily employed for the saturation of aromatics but is still sufficiently severe so as to effect, at times, a significant reduction in boiling range of the treated material.

Finally, the least severe hydrogen treating operation, termed hydrofinishing, operates primarily for the removal of minor quantities of contaminants and colorforming bodies found in lubricating oils or lubricating oil base stocks. Thus, hydrofinishing is effective, for example, to reduce the sulfur content of the materials treated along with other contaminants and color-forming bodies but does not result in any significant increase in API gravity or any significant reduction in the boiling range of the treated material. Usually any increase in API gravity effected by hydrofinishing will be less than about 5 API. Furthermore, at times it would even appear that the boiling range of the treated material has even been increased somewhat as indicated by a slight increase in the ASTM 10 percent and even 30 percent points. Moreover, inasmuch as hydrofinishing does not effect any noticeable severing of carbon-to-carbon bonds which is essential to an extensive degree, in hydrocracking and which, at times, can be obtained in hydrotreating, hydrofinishing does not result in any reduction in the pour point of the material treated. Additionally, bydrofinishing does not effect any significant amount, if any, of saturation, such as, for example, saturation of aromatics.

In the hydrofinishing operation of our process the operating conditions employed can include a temperature from about 400 to about 850 F. and preferably from about 600 to about 750 F., a pressure in the range from about 800 to about 3000 p.s.i.g. and preferably from about 1000 to about 2000 p.s.i.g., a liquid hourly space velocity in the range from about 0.1 to about 10.0 and preferably from about 1.0 to about 4.0 volumes of lubricating oil base stock per volume of catalyst per hour and a hydrogen circulation rate in the range from about 1000 to about 20,000 s.c.f./b. and preferably from about 2000 to about 7000 s.c.f./b. The catalyst employed in the hydrofinishing operation in accordance with our invention can be any of the hydrogenating catalysts wellknown in the art such as, for example, Group VI and Group VIII metals, their oxides and sulfides, or mixtures thereof, either alone or supported on a suitable carrier. These suitable carriers generally include materials which have extremely low cracking activity, if any, and can be described as having a cracking activity significantly below 35 on the Kellogg cracking activity scale. Usually such materials will have a Kellogg cracking activity of less than about 25 and preferably less than about 20. Examples of catalysts which we have found to be advantageous for use in our invention are combinations of nickel, cobalt and molybdenum on an alumina support such as, for example, a catalyst of the type described in US. Pat. 2,880,171, and a combination of nickel and tungsten on alumina. Catalysts such as these can also contain a small quantity of silica such as, for example, less than about 5 percent by weight or even lower.

In the solvent dewaxing treatment of our invention we have found that any of the well-known solvents employed in the art to effect dewaxing are quite satisfactory. Generally, we prefer to employ methylethylketone and toluene in about a 50-50 mixture as the solvent. The particular temperature employed in the solvent dewaxing treatment in accordance with our invention is usually about 5 F. or more above that required when not employing our processing sequence or is about the same as that temperature which would be required to provide a product having the desired pour point, usually about +10 F. or lower, when treating a low sulfur content material.

In order to illustrate our invention in greater detail, reference is made to the following examples.

EXAMPLE I In this example several crude lubricating oil fractions obtained from a reduced Kuwait crude having substantial components boiling above about 700 F. were separately subjected to solvent extraction treatment after which the raffinates were combined and subjecting to finishing operations including solvent dewaxing and hydrofinishing. One portion of the rafiinate was subjected to solvent dewaxing-followed by hydrofinishing of the dewaxed raffinate, while another portion of the rafiinate was first subjected to hydrofinishing and then the hydrofinished rafiinate was subjected to a solvent dewaxing treatment. The inspection data for the light neutral lubricating oil base stock fraction of the raffinate is shown in Table I below.

TABLE I Pour point, F. 75 Sulfur, percent by wt 0.8 Distillation, vacuum, percent at F.:

The operating conditions employed in the solvent dewaxing treatment and in the hydrofinishing treatment in both the conventional solvent dewaxing followed by hydrofinishing sequence and the hydrofinishing followed by solvent dewaxing treatment sequence of our invention were substantially the same with but one exception. Thus, the conditions employed in the hydrofinishing operation included a pressure of 1650 p.s.i.g., a temperature, measured at bed outlet of about 700 F. and a liquid hourly space velocity of 3.0. In the solvent dewaxing treatment the solvent employed was a methylethylketone-toluene blend consisting of 55 percent methylethylketone. The solvent to oil ratio for dilution was from about 4.1 to about 4.3 and for the wash was 2.0. The one important variation in operating conditions between the two operations was in the temperature employed in the solvent dewaxing treatments. In the conventional sequence a filtration temperature of F. was employed to provide a dewaxed light neutral fraction having a pour point of 0 E, while in the solvent dewaxing operation in accordance with our invention, i.e. after hydrofinishing, the filtration temperature employed was only -10 F. The following Table II shows the inspection data for the finished light neutral lubricating oils obtained from the two processing sequences described above.

TABLE II Finished lubricating oil Dewaxing Hydrofinishing before hydrofollowed by 6 From a comparison of the inspection data in Table II above it will be noted that in all other physical properties excepting pour point the two finished light neutral lubricating oils are substantially identical. Significantly, however, the lubricating oil produced in accordance with the process of our invention has a pour point 5 F. lower than that of the material produced in accordance with the more conventional operation. It will also be noted that this lower pour point was obtained when dewaxing at a temperature 5 F. higher than that employed with the more conventional operation. Thus, quite unexpectedly, it will be seen that finished products having a lower pour point are obtained when employing a higher filtration temperature in the solvent dewaxing treatment in accordance with our invention. To express it in another manner, this data would indicate that when treating a low boiling, high sitfur content lubricating oil base stock and dewaxing such base stock prior to hydrofinishing, a filtration temperature must be employed which is at least about 25 F. lower than the desired pour point of the finished product whereas in operating in accordance with the process of our invention a filtration temperature of only 15 F. lower than the desired pour point of the finished product can be employed. This constitutes a 10 F. savings in refrigeration capacity.

EXAMPLE II In this example a blend of light neutral distillates obtained from an Ordovician crude and a Delta lube mixture, which blend had the inspection data shown in Table III below, was subjected to a furfural extraction and the rafiinate from the extraction was then subjected to a solvent dewaxing treatment. In the solvent dewaxing treatment the solvent employed was a methylethylketone-tolu ene blend consisting of percent methylethylketone. The solvent to oil ratios for the initial and secondary dilutions were 0.6 and 1.4, respectively, while the solvent to oil ratio for the wash was 1.0. A filtration temperature of 6 F. was employed. This solvent dewaxing treatment provided a hydrofinishing charge stock having the inspections also shown in Table III. After hydrofinishing, the dewaxed and hydrofinished product was analyzed and the inspection data obtained is shown in Table III. For purposes of comparison, the inspection data for the raffinate of Eaxmple I as well as the inspection data for the finished lubricating oil obtained by dewaxing and hydrofinishing such rafiinate in Example I are also shown in Table III.

TABLE III Dewaxed Dewaxed and hyand hydrofinishdrofinish- Rafifinate ed rafilnate Dewaxed ed rafififrom Exfrom Ex- Charge Rafiflnate rafilnate nate ample I ample I Gravity, AII 29. 3 33. 8 33.1 33.0 32. 3

i SUS at- FSO F 103. 3

150 F 55. 0 53. 4 210 F 30. 8 39.6 30. 7 Viscosity index 87 114 102 Pour point, F. 0 Color, D 1500 L 3.0 L 1. 5 L 1.0 Sulfur, percent by weight 0.20 0. 08 O. 08 Distillation, vacuum, F.:

7 From the inspection data shown in Table III above for the solvent extracted ratfinate, it will be seen that the intermediate lubricating oil base stock obtained from the blended crude lubricating oil stock, although having a 90 percent boiling point of 795 F., has a sulfur content substantially below 0.75 percent; to wit 0.20 percent. From an examination of the data shown for the hydrofinished product obtained from this raffinate after dewaxing, it will be seen that a satisfactory pour point of F. was obtained and that a dewaxing temperature of only about 6 F. was required to produce this pour point in the finished lubricating oil. A comparison of the results obtained in this example with the resultant product obtained from the high sulfur content material of Example I when employing the same operating sequence, as shown in the last two columns of Table III, demonstrates that when treating a feed stock having a very similar boiling range but having a high sulfur content, i.e. above about 0.75 percent, even more severe dewaxing conditions, e.g. a filtration temperature of F., is not capable of producing a finished lubricating oil having an equally low pour point.

EXAMPLE III In this example a lubricating oil base stock comparable to that described as the raffinate in Example II is subjected to hydrofinishing under mild hydrogenating conditions in the presence of a hydrogenating catalyst. Subsequently, the hydrofinished base stock is subjected to a solvent dewaxing treatment employing a methylethylketone-toluene blend as the solvent and a filtration temperature in the range from about -l0 F. to about 5 F. Inspection of the finished lubricating oil obtained by hydrofinishing and then dewaxing this comparatively low boiling, low sulfur content lubricating oil base stock shows that the pour point of the product is not substantially different from that obtained when employing the operating sequence of Example II. It will be seen, therefore, that the process of our invention, requiring dewaxing subsequent to hydrofinishing, is operable when treating a comparatively low boiling, high sulfur content stock but that when treating a comparatively low boiling, low sulfur content stock there does not appear to be any advantage to be gained regarding the pour point of the finished product through employment of our inventive process.

We claim:

1. An improved process for the production of a finished lubricating oil from a lubricating oil base stock 8 comprised substantially of components boiling below about 800 F. and containing at least about 0.75 percent by weight sulfur which comprises subjecting the lubricating oil base stock to hydrofinishing by contacting it with hydrogen in the presence of a hydrogenation catalyst comprising a hydrogenating component selected from the group consisting of (a) nickel, cobalt and molybdenum and (b) nickel and tungsten supported on a carrier having a cracking activity on the Kellogg scale of less than about 25 under hydrofinishing conditions of pressure, space velocity and a temperature from about 600 to about 750 F. thereby effecting removal of color-forming bodies from the lubricating oil base stock without any significant reduction in boiling point, saturation of aromatics or reduction of pour point and then subjecting the hydrofinished base stock to a solvent dewaxing treatment.

2. The process of claim 1 wherein the lubricating oil base stock has a percent boiling point of less than about 830 F.

3. The process of claim 1 wherein the lubricating oil base stock has a 90 percent boiling point of less than about 800 F.

4. The process of claim 2 wherein the lubricating oil base stock is a fraction having a range from about 90 F. to about 120 F. between its 10 percent boiling point and its 90 percent boiling point.

5. The process of claim 3 wherein the lubricating oil base stock is a fraction having a range from about 90 F. to about 120 F. between its 10 percent boiling point and its 90 percent boiling point.

6. The process of claim 1 wherein the lubricating oil base stock contains more than about 1.0 percent by weight sulfur.

References Cited UNITED STATES PATENTS 2,787,582 4/1957 Watkins et al. 208-58 3,142,634 7/1964 Ireland et al 208- 3,012,963 12/ 1961 Archibald 208-264 3,285,848 11/1966 Donaldson et al. 208-212 3,293,173 12/1966 McCall 208212 3,318,800 5/1967 Ringler 208-18 HERBERT LEVINE, Primary Examiner US. Cl. X.R.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 i 520. 796 Dated Julv 14 L 1970 n H. C. Murphy Jr. J. R. Murphy and H. C. Stauffer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 66, "+50 F. should be +5F.--

Column 4 line 73 "subjecting" should be subjected-.

SIGNED AND SEALED 0C? 6 Attest:

Edward m. much i van-nun 1:. sum. .13- L Attesung Officer oomissioner of Patents