US3431194A - Process for lowering the pour point of a middle distillate - Google Patents

Description

United States Patent ABSTRACT OF THE DISCLOSURE A process for lowering the pour point of a middle distillate in which said distillate is fractionated into light and heavy fractions. The heavy fraction is hydroisomerized and reblended with the light fraction.

13 Claims This is a continuation-in-part of our application, Ser. No. 512,521, filed Dec. 8, 1965, entitled, Improved Hydroisomerization Catalyst, now abandoned.

This invention relates to an improved combination process wherein a middle distillate is both isomerized and desulfurized. More particularly, this invention pertains to a method for the simultaneous pour and cloud point reduction as well as desulfurization of middle distillates. This may be done selectively with only minor side effects on the middle distillate. Only slight changes in characteristics such as specific gravity of the middle distillate are noted. This is accomplished by dividing the middle distillate into two fractions, a lower boiling fraction and a higher boiling fraction. The higher boiling fraction is then contacted with an acidic solid support containing an impregnated or otherwise dispersed and reduced group VIII metal. Optionally, the acidic support which contains the impregnated reduced group VIII metal may also contain oxides or sulfides of mixtures of group VIII and VII) metals, such as nickel, cobalt, tungsten and molybdenum impregnated therein. These metal sulfides may be added to promote the activity of the acid supported group VIII metal for hydroisomerization and desulfurization of middle distillates containing high levels of sulfur. Such high levels of sulfur are thought to poison group VIII metal such as platinum severely when used alone.

The high pour and cloud points of the various waxy middle distillate fractions make their use unattractive as diesel fuels, heating oils, etc., in various cold climate locations. Since high pour and cloud points are correlated with the normal paraffin wax content of such distillates, a process for converting the normal parafiins into the corresponding branched isomers would be very desirable. However, the conversion of the normal parafiins into their branched isomers must be done selectively. Waxy normal paraffins are those which start at a weight of C If these long chain normal paraflins are cracked into small or intermediate sized fragments, product quality specifications would not be met since the specific gravity and boiling range (i.e. molecular weight) of the distillate fraction must be maintained. A process which resulted in substantial cracking of the long parafiin chains would be totally unacceptable for that purpose.

A variety of methods for reducing the pour point of middle distillates have been proposed. However, they have all met with only limited success. One of the more widely used methods is the addition of a pour depressant to the middle distillate. In the past, it has been found that pour point reduction by additives has only been effective for certain types of responsive oils and the cloud points of all distillates remainvirtually unaffected by the pour point depressant. Since the low temperature flow problems do not correlate with pour alone, but rather with both cloud and pour, a process is needed which would reduce both of them. Use of pour point depressant is not such a process.

Other methods have also been tried. Among them is the use of a molecular sieve to separate the waxy normal parafiins from the middle dis'tillates. This technique has met with some limited success but still presents several severe problems. Included among them is sieve deactivation after repeated cycles. Additionally, there is the problem of impurities, such as sulfur, being adsorbed along with the normal paraflins and contaminating the parafiins so that they may not be used without further processing. It is, of course, also true that the selective physical removal of the normal paraflins from the waxy upper boiling fraction would serve to affect the reblended specific gravity of a total distillate so that this too is unsatisfactory. In the same fashion, urea adduction in which the waxy straight chain paraflins form adducts with urea and are then preferentially removed from the upper boiling fraction of middle distillate is also unsatisfactory. As in the case of molecular sieving, the use of urea adducts serves to remove the heavy long chain normal paraflins from the middle distillate and this, as is mentioned above, is unsatisfactory. Furthermore, conventional molecular sieving and urea adduction require much more elaborate and expensive processing than simple catalytic hydrotreating which may be done in conjunction with existing hydrodesul-furization plants.

Thus, a process is needed which will result in the lowering of pour and cloud points but will not affect the specific gravity of the total middle distillate. Hydroisomerization of the waxy normal parafiins has been suggested, however, the sulfur present in the middle distillate has presented a significant problem. Group VII metal catalysts dispersed on acidic solids, such as nickel on silica-alumina, platinum on alumina, are deactivated in use with straight run sulfur-containing feedstocks because the active metal sites which provide a hydrogenationdehydrogenation functionality are converted into the relatively inactive sulfides. It is a generally accepted concept that a minimum hydrogenationdehydrogenation functionality is required for an n-paraflin hydroisomerization catalyst. In part, this may be needed for the generation of olefinic intermediates which are capable of undergoing skeletal isomerization over the active acidic sites of the catalyst support and, in another part, to minimize catalyst deactivation by coking in an atmosphere of hydrogen gas. Thus, the presence of sulfur in a middle distillate may cause severe deactivation of some isomerization catalysts. There are also catalysts which are sulfurtolerant. They include group VIII and VII) metal sulfides which are supported on acidic solids. Unfortunately, these catalysts that are sulfur-tolerant are rather inactive for normal parafiin hydroisomerization.

According to this invention, it has unexpectedly been discovered that the use of the unique processing scheme enables one to satisfactorily hydroisomerize the waxy normal paraflins of a middle distillate without facing the problem of severe catalyst deactivation. It has been found that if the middle distillate is split into two fractions, a lighter boiling fraction and a heavier higher boiling fraction, only the higher boiling fraction will require pour reduction treatment since the lighter fraction is already capable of pouring at the temperatures of 20 to 20 R, which are required in colder climates. The higher boiling fraction may be contacted directly with an acidic support such as alumina onto which a noble metal has been impregnated. These noble metals are selected from group VIII of the Perodic Table and the most preferred noble metals are platinum and palladium. It is an important concept of the instant invention that no prior desulfurization is needed before the heavy higher boiling stream is contacted with the isomerization catalyst. In a particular embodiment of the invention, it may be desirable to mildly desulfurize the heavier stream down to a level of about .4 wt. percent sulfur. This is not essential to the instant invention although it may be desirable to hydrotreat down to a .4 wt. percent of sulfur level since certain fuel specifications require this to be the maximum sulfur content which is tolerable. In addition, this hydrotreating serves as a general clean up of the feedstock and may be desirable in that aspect. It should be emphasized that the catalyst of the instant invention will operate successfully at the sulfur levels which are present in the middle distillate stream. Should a hydrotreating step be necessary, a commercial Nalco-Esso cobalt molybdate on alumina catalyst may be employed with typical process conditions of 600 -750 F. temperature, 400 800 p.s.i.g. pressure, space velocities between 0.5 and 2.0 v./hr./v. and hydrogen gas rates between 500 and 2000 s.c.f. per barrel of oil to be processed. The lower boiling fraction will in all probability not require any type of hydrotreating treatment.

In a more specific embodiment of this invention, the acidic support is impregnated with a group VIII metal such as platinum or palladium and, in addition, oxides or sulfides of other group VIII and VIb metals, such as nickel, cobalt, molybdenum, and tungsten. In this manner, both the pour and cloud points of the middle distillate can be reduced while simultaneously the noble metal component may be somewhat protected from deactivation caused by sulfur poisoning. This will only be needed in certain cases and it should be emphasized that the noble metal, acidic support catalyst is satisfactory for almost all occasions.

The acidic support may be any of a great number of such supports, all well-known in the art. They include alumina, halogen-treated alumina, silica-alumina, boriaalumina as well as wide pore sieves such as type X and type Y molecular sieves. It should be noted that any molecular sieve adsorbent with pore sizes of 8 to A. units would be satisfactory. Those molecular sieves classified as type X are described generally in US. Patent No. 2,882,244. Molecular sieves designated as type Y are described generally in US. Patent No. 3,130,007. The acidic support may be any one or a combination of those mentioned above as well as the other widely known acidic supports for hydroisomerization. The catalysts may be prepared by impregnation of the support, by coprecipitation of the catalyst components, by cationic exchange in case of crystalline zeolitic supports, by preparing intimate mixtures of the two catalysts components, or by combinations of these techniques, e.g. using mixtures of platinum supported on alumina with nickel-tungsten sulfide on silica-alumina. Preferably, a nickel sulfide or nickel-tungsten sulfide catalyst supported on the acidic solid, e.g. alumina, is impregnated with a platinum salt solution and after drying and calcining, the platinum metal is reduced in a hydrogen atmosphere. In this manner, noble metal sites are made available for normal paraffin dehydrogenation. This is a preferred embodiment.

The catalyst used in our process may comprise an acidic support which is a refractory oxide and a hydrogenation component. The acidic support will be of a type similar to that used in the preparation of catalytic agents for hydrocarbon conversion reactions and will contain hydroxyl groups distributed over the surface thereof, said surface preferably comprising a rather large area, for example, from about 50 to about 1000 square meters per gram. The acidic support is a solid and may be selected from diverse high surface area refractory oxides which are not necessarily equivalent for use as socalled supports in preparing these catalysts. Among suitable acidic supports are such various substances as silica,

alumina, titanium dioxide, zirconium dioxide, zinc oxide, silica alumina, silica-magnesia, silica-alumina-magnesia, chroma-alumina, alumina-boria, silica-zirconia, silicaalumina-zirconia, etc., and also various naturally occurring acidic supports of differing degrees of purity such as bauxite, kaolin or clay (which may or may not have been acid treated), diatomaceous earths such as kieselguhr, montmorillonites, spinels such as magnesium oxidealumina spinels or zinc oxide spinels, etc. Of the abovementioned refractory oxides, alumina is preferred and particularly preferred is synthetically prepared gammaalumina of a high degree of purity.

All of these above-mentioned supports, whether synthetically prepared or naturally occurring, contain both chemically combined and physically absorbed water. By various well-known techniques such as drying and/or calcination, the water content of these refractory oxides can be lowered or minimized While at the same time a surface can be developed, which surface is useful either by itself or in combination with other materials as a site for accelerating reactions, such as catalyzed hydrocarbon conversion reactions. It is well known that excessive temperatures can destroy these surfaces and thus must be avoided. In the drying and/or calcination of a suitable refractory oxide, such as alumina, physically absorbed water is first removed therefrom. Then at still higher temperatures chemically combined hydroxyl groups begin to escape from the surface. This is accomplished by the combination of two hydroxyl groups, for example, to form one molecule of water and a new oxide bond. In the case of alumina, the complete elimination of chemically combined hydroxyl groups from the surface thereof results, under conditions of calcination, in conversion of the alumina to the well-known anhydrous alpha-alumina which is generally unsatisfactory or inert as a catalyst support. These unsatisfactory or inert properties have previously been attributed to the low surface area of alphaalumina but they are now considered to be additionally related to the loss of chemically combined hydroxyl groups. Thus, as set forth hereinabove, while many refractory oxides are suitable for supports for the catalysts of the process of the present invention, these refractory oxides are characterized by the presence on the surface thereof of chemically combined hydroxyl groups. The presence of such chemically combined hydroxyl groups can be determined by treatment of these refractory oxides after drying and/ or calcination with anhydrous hydrogen chloride which tends to react with said hydroxyl groups with the elimination of water and the substitution of chlorine atoms for hydroxyl groups. Then the chlorine content of such refractory oxides can be readily determined by known analytical techniques. This chlorine content can then be specified as equal to the hydroxyl equivalents on the surface of said refractory oxides.

In the catalysts used in the process of the present invention, the above-described acidic supports have composited therewith a hydrogenation component. Suitable hydrogenation components include metals of subgroup V112 and group VIII of the Periodic Table including chromium, molybdenum, tungsten, iron, cobalt, nickel, platinum, palladium, ruthenium, rhodium, osmium and iridium. These metals are not necessarily equivalent as bydrogenation components in the catalysts utilized in the process of the present invention and of these metals platinum and palladium are preferred and platinum metal is particularly preferred.

These hydrogenation components may be composited with the above-mentioned acidic supports in any desired manner, such as by impregnation, coprecipitation, etc. Impregnation techniques are well-known and in one such method a compound of the desired hydrogenation component, such as the platinum compound chloroplatinic acid, is dissolved in a suitable solvent and the refractory oxide is contacted therewith, followed by drying and calcination. When synthetically prepared refractory oxides of high degrees of purity are utilized, it is sometimes desirable or preferable to coprecipitate the platinum group metal along with the refractory oxide. Following such coprecipitation, the resultant composite is dried and calcined. As set forth hereinabove, of the metals which may be composited with a refractory oxide, platinum and palladium are preferred, and platinum is particularly preferred. As hereinabove described, the composite of platinum group metal and refractory oxide prepared by impregnation, coprecipitation, etc., is next dried and calcined. This calcination is normally carried out under carefully controlled conditions to remove therefrom physically absorbed solvents such as water but under sufficiently mild conditions so that chemically combined hydroxyl groups are not completely eliminated or lost. Calcination temperatures ranging from about 350 C. to about 700 C. are usually satisfactory. As stated previously, the presence of these chemically combined hydroxyl groups in such platinum group metal-refractory oxide composites is a necessary prerequisite for preparation of the catalytic agents for use in the process of the present invention.

Elevated temperatures and pressures will be utilized during the hydroisomerization-hydrodesulfurization process. This serves to prevent catalyst deactivation. Space velocities and hydrogen recycle rates may also be widely varied within the scope of this invention.

With more particularity, this invention pertains to the hydroisomerization of middle distillates which are utilized as automotive and marine diesel oils, domestic heating oils, light fuel oils, etc. These middle distillates boil between 300 and 800 F., preferably 350 and 750 F. They contain about 100 ppm. to 3 wt. percent sulfur. As a general rule, waxy middle distillates will pour between -l and 70 F. and have a cloud point of to 75 F. The reason for this high pour point is the large amount of C plus normal parafiins contained within the middle distillate. A middle distillate to be treated by the process of the instant invention will contain about 3 to 30 wt. percent of C plus normal parafiins. Specific gravity of the middle distillates to be treated by the instant invention will vary between 0.82 and 0.88; specific gravity levels of below 0.81 are usually unacceptable for application as fuels. Particular middle distillates to be treated by the process of the instant invention are those derived from the following crudes: Brega, Aramco, Safaniya, Iranian, Kuwait, Eastern Mediterranean Iraq, Louisiana-Mississippi and middle distillates derived from synthetic crude sources, e.g. oil shale, tar sands or coal.

The middle distillate is separated into at least two components, a lighter fraction boiling between 300 and 700 F., particularly between 375 and 600 F., containing about 50 to 95 by weight of the entire middle distillate, preferably 70 to 90% by weight. A heavier fraction boiling between 500 and 800 F., particularly between 550 and 700 F., contains about 0.1 to 4% by Weight of sulfur and represents 5 to 50% by weight of the middle distillates. This sulfur level is unacceptable by contrast to the lighter fraction which contains about 100 to 10,000 parts per million of sulfur. The heavier fraction also contains between 50 and 95% of the C plus normal parafiins which are contained in the middle distillate.

Consequently, the lighter fraction need not be sub jected to the hydroisomerization process of the instant invention. That is to say, the lower fraction already meets the desired sulfur and pour levels and so only the heavier fraction which boils between 500 and 800 F. need be treated by hydroisomerization.

As mentioned previously, the preferred acidic support for the hydroisomerization is alumina, or an alumina derivative such as alumina promoted with halogen, silicaalumina, boria-alumina, zeolitic crystalline alumino-sili cates which are molecular sieves. The acidic support is then impregnated with a group VIII metal, preferably platinum or palladium. In a preferred embodiment along with the platinum or palladium, the acidic support is impregnated also with oxides or sulfides of other group VIII and VIb metals, such as cobalt, nickel, molybdenum and tungsten. This may be done by well-known conventional means.

The splitting of the feedstock into a lighter and heavier boiling fraction is an important aspect of the instant invention. If desired, mild hydrotreating of the heavier fraction may take place but this would not be required and, in addition, if utilized should be no longer than a .4 wt. percent level. Needless to say, the invention will operate satisfactorily at lower sulfur levels but it is desirable to avoid the additional expense of obtaining these levels when the catalyst will perform in a completely satisfactory fashion when higher sulfur levels are present.

The pour and cloud points of the hydrotreated higher boiling fraction are then reduced by means of the contacting with an acidic support onto which a noble metal cata lyst has been impregnated. Following this, the treated heavier fraction may then be reblended with the untreated lower boiling fraction. The combined fraction now has satisfactory pour and cloud points, sulfur levels. In a particular embodiment, higher boiling fraction is contacted with an acidic support containing a noble metal and a desulfurization type catalyst, successful results are also obtained. Alternatively, the entire middle distillate may be treated with the combined desulfurization noble metal catalyst with no separation into lighter and heavier boiling fractions.

The desulfurization catalyst may also serve to enhance the hydroisomerization reaction. This may be accomplished by the contribution of additional metal sites needed for the hydroisomerization process. This would allow the contacting of the entire middle distillate with an acidic support having noble metal impregnated therein along with desulfurization catalyst.

Hydrogen is passed in conjunction with the middle distillate over the acidic supported noble metal and desulfurization catalyst containing catalytic agent. The

presence of the hydrogen serves to prevent coke formation, initiate dehydrogenation and aid in the formation of active chemical intermediates which are essential to the process. The temperature over the catalyst zone has been found to be important. Results of a satisfactory nature have been achieved with temperatures in the range of 550 to 1000 F. However, it is most preferred to use temperatures of 800 F. or higher. In fact, superior results are achieved with temperatures of 800 F. up to about 1000 F. A distinct improvement in pour point and cloud point is achieved when temperatures of 800 to 1000 F. are utilized. In addition, the specific gravity of the middle distillate obtained is substantially improved with temperatures in the range of 80 to 1000 F. utilized over the hydroisomerization zone. Pressure may vary between 50 and 1000 p.s.i.g., preferably 200 to 800 p.s.i.g.; space velocities may also vary widely. A range of 0.2 to 10 v./hr./v. may be utilized, preferably 0.5 to 10 v./hr./v. The hydrogen recycle rate may vary between 500 and 15,000 s.c.f. per barrel of oil, preferably it may vary between 1000 and 10,000 s..c.f. per barrel of oil, most preferably the hydrogen recycle rate will vary between 2000 and 10,000 s.c.f per barrel of oil.

Typically, about between 20 and 80% by weight of the C plus normal parafiins will be isomerized. Following the hydroisomerization with the catalyst described herein, the heavier fraction is blended with the lighter fraction again. The combined fractions now have a pour point of -20 to 30 F. as opposed to the l0 to F. pour point the original middle distillate had. In addition, the specific gravity of the midde distillate now varies between 0.810 and 0.88 which is substantially the same as the specific gravity of 0.820 to 0.880 it had originally. Further, the cloud point of the middle distillate is now -l5 to 35 F. This also compares favorably with the 5 to F. cloud point it originally had.

In a specific embodiment of the instant invention, a middle distillate boiling between 375 and 685 F. derived from a Zelten-light Arabian crude oil is separated into two fractions, a lighter and a heavier one. The middle distillate prior to separation contains 4000-7000 parts per million of sulfur; this is an acceptable level for the instant invention and no hydrotreating is necessary. Additionally, the middle distillate contains 7-10% by weight of C plus normal paraffins, has a specific gravity of 0.8 to 0.9 and a cloud point of -15 F. The lighter fraction boiling between 375585 F. constituted 60-80% by weight of the total middle distillate. The lighter fraction had a pour point of to -30 F., a cloud point of to F. and contained 3000-4000 parts per million of sulfur. These are acceptable levels. The heavier fraction contained over 11,000 parts per million of sulfur and had a pour point of 3050 F. As indicated previously, it has unexpectedly been discovered that successful operations can be carried on at this sulfur level too. The lighter fraction is stored for subsequent reblending. The heavier fraction is contacted with the hydroisomerization catalyst of the instant invention, In this embodiment, the hydroisomerization catalyst comprises an acidic support which is alumina; impregnated onto this support is a platinum or palladium salt solution. The composition of the catalyst may vary widely. About 0.1 to 1.0 wt. percent of platinum or palladium is adsorbed onto the support.

The heavier fraction is passed over the hydroisomerization catalyst at a space velocity of 0.5 to 10 v./hr./v. and a hydrogen recycle rate of 1000 to 10,000 s.c.f. per barrel of oil. Temperature over the hydroisomerization zone may vary between 850l000 F., preferably between 875-950 F., and pressure between 1000 p.s.i.g. Subsequent to this treatment the heavier fraction is recombined with the lighter fraction. The combined middle distillate now has a pour point of 20 to 0 F., a cloud point of 18 to 2 F. and contains substantially the same amount of sulfur. Additionally, the specific gravity of the middle distillate is substantially the same as it was prior to the treatment of the heavier fraction. The C plus normal paraffin content of the middle distillate has now been reduced from 8.6% by weight to about 3 to 6.5% by weight. The middle distillate would now be acceptable for colder climates.

Example 1 In this example, a middle distillate derived from a one-third Zelten-two-thirds light Arabian mixed crude boiling between 375 and 685 F. was treated with the process hereindescribed. The middle distillate had a specific gravity of 0.832 and a sulfur level of 0 .66 wt. percent. It contained about 9.6 wt. percent of C plus normal parafiins and had a pour point of 10 F. and a cloud point of 14 F. The middle distillate was divided into two fractions, a lighter fraction constituting about 69% of the total middle distillate and boiling between 375 and 585 F. and a heavier fraction boiling between 585 F. and 685 F. and constituting about 31% by weight of the total middle distillate. The lighter fraction constituted about 4.7 barrels of middle distillate and the heavier fraction constituted about 2.0 barrels of middle distillate.

The lighter fraction was stored and a sample of the heavier fraction was hydrotreated mildly at a temperature of 650 F., a pressure of 400 p.s.i.g. over a Co-Mo/Al O catalyst until a sulfur level of 0.4 wt. percent was obtained. Following this, the heavier fraction was contacted with a hydroisomerization catalyst.

The catalyst employed was a commercial Ketjen platinum on alumina reforming catalyst. It contained 0.61 wt. percent Pt and 0.72 wt. percent C1. The catalyst was prepared in the form of /s of an inch diameter pellets made by grinding and pilling the inch extrudate supplied by Ketjen. The original extrudate had a surface area of 172 M. g. The Ketjen catalysts were prepared by chloroplatinic acid impregnation of gamma-alumina.

The heavier fraction was then passed over the platinum catalyst at a rate of 1.3 w./hr./w. and a hydrogen recycle rate of 13,000 set". per barrel of middle distillate was used. Temperature over the zone was 800 F. and pressure was 200 p.s.i.g. The results obtained are indicated in Table I. As expected, the catalyst deactivated markedly in the presence of the high sulfur-containing feedstock at 800 F.

At the end of 30 hours, the temperature was raised to 900 F. The surprisingly high and stable activity achieved is illustrated in Table II. Thus, operation at about 900 F. is critical for useful activity levels when using a high sulfur content feedstock.

The above tables, Tables I and II, contain data with respect to the heavier fraction following treatment. It is apparent that a substantial reduction in cloud point has been achieved by operation at 900 F. Reblending the heavier fraction which was treated at 900 F. with the lighter refraction results in a middle distillate having a pour point of 20 F. and a cloud point of 18 F. This represents a major improvement over the original pour and cloud points of 10 F. and 14 F. The specific gravity of the middle distillate was now 0.830. Upon analysis, it was discovered that normal paraffins of C constituted only 3.4 wt. percent of the middle distillate as opposed to the original 9.6 wt. percent. This indicates the success of the instant process in reducing the pour and cloud points without disturbing other characteristics of the middle distillate. Reblending the fraction which was treated at 800 F. with the lighter fraction resulted in a middle distillate with a pour point of 0 F. and a cloud point of 4 F. Specific gravity in this case was 0.827 and the normal paraffins of C constituted 7.1% of the middle distillate.

Example 2 In this example, the exact feedstock is again treated only there is no mold hydrotreating and the feedstock which is passed over the catalyst of the instant invention contains about 1.2 wt. percent sulfur. Temperature of 900 F. during the sulfur contacting is utilized. It should be emphasized that there is no hydrotreating prior to the contacting of the portion of the middle distillate with the catalyst of the instant invention. Substantially identical results to those obtained in Example 1 are achieved. Pour point is now 20 F. and cloud point is 18 F. as compared to an original pour point of 10 F. and an original cloud point of 14 F. Specific gravity is now 0.830 and about 3.4 wt. percent of C normal paraffins are present.

Although this invention has been described with some degree of particularity, it is intended to be limited only by the attached claims.

What is claimed is:

1. An improved process for hydroisomerizing and thereby lowering the pour point of a middle distillate boiling between 300 and 800 F. which comprises separating the middle distillate into a lighter fraction boiling between 300 and 700 F. and a heavier fraction boiling between 500 and 800 F., contacting the said heavier fraction with a catalyst, said catalyst comprising an acidic support impregnated with a noble metal, reblending said heavier fraction and said lighter fraction whereby the pour point of the middle distillate is substantially reduced.

2. The process of claim 1 wherein said acidic support is alumina.

3. The process of claim 1 wherein said noble metal is selected from the group consisting of platinum and palladium.

4. An improved process for lowering the pour point and cloud point of a middle distillate boiling between 300 and 800 F. by means of hydroisomerization which comprises dividing the said middle distillate into two fractions, a lighter boiling fraction boiling between 300 and 700 F. which comprises about 50 to 90% by weight of the total middle distillate and a higher boiling fraction boiling between 500 and 800 F. which comprises to 50 wt. percent of the middle distillate, contacting said heavier fraction in the presence of hydrogen with a catalyst, said catalyst comprising an acidic support impregnated with a group VIII metal, reblending the lighter and heavier fractions subsequent to the contacting of the heavier fraction with the said catalyst and thereby recovering a middle distillate substantially reduced in pour point and sulfur content.

5. The process of claim 4 is selected from the group alumina derivatives and said group VIII metal is selected from the group consisting of platinum and palladium.

6. An improved process for lowering the pour point of a middle distillate fraction, said fraction boiling between 300 and 800 F. and having a pour point of -l0 to 70 F. which comprises separatin the said middle distillate into two fractions, a lighter fraction boiling between 300 and 700 F. and a heavier fraction boiling between 500 and 800 F., contacting said heavier fraction with a catalyst in the presence of hydrogen at a temperature of at least about 900 F., said catalyst comprising an acidic support selected from the group consisting of alumina, silica-alumina and alumina derivatives impregnated with a group VIII metal selected from the group consisting of platinum and palladium, reblending said higher boiling fraction with said lighter boiling fraction after said higher boiling fraction is contacted with said catalyst whereby the said reblended middle distillate has a substantially lower pour point.

7. An improved process for desulfurizing and hydroisomerizing a middle distillate fraction, said fraction boiling between 300 and 800 F. and having a pour point of -l0 to 70 F. which comprises dividing said middle distillate fraction into two fractions, a lighter fraction boiling between 300 and 700 F. and a heavier fraction boiling between 500 and 800 F., contacting said heavier fraction in the presence of hydrogen at a temperature of at least about 900 F. with a catalyst, said catalyst comprising an acidic support selected from the group consisting of alumina, halogen-treated alumina, silica-alumina,

wherein said acidic support consisting of alumina and 10 boria-alumina and wide pore molecular sieves, impregnated on said acidic support a group VIII noble metal, removing said heavier fraction from said catalyst Zone and reblending said heavier fraction with said lower boiling fraction whereby a middle distillate is obtained with a lower pour point.

8. An improved process for lowering the pour point and sulfur content of a middle distillate, said middle distillate boiling between 300 and 800 F. which comprises separating said middle distillate into two fractions, a lighter fraction comprising 50 to by weight of the middle distillate and boiling between 300 and 700 F. and a heavier fraction comprising 10 to 50% by weight of the middle distillate and boiling between 500 and 800 F., hydrotreating said heavier fraction to a maximum level of about .4 wt. percent, contacting said hydrotreated fraction with a catalyst comprising an acidic support impregnated with a group VIII noble metal, said contacting taking place in the presence of hydrogen, removing said heavier fraction from said catalyst zone and reblending it with said lighter fraction whereby a middle distillate is obtained having a substantially lower pour point.

9. The process of claim alumina.

10. A process for lowering the pour point and sulfur content of a middle distillate boiling between 300 and 800 P. which comprises dividing the middle distillate into two fractions, a lighter fraction boiling between 300 and 700 F. and a heavier fraction boiling between 500 and 800 F., separating the two fractions, contacting the said heavier fraction with a catalyst at a temperature of 900 to 1000 F. in the presence of hydrogen, said catalyst comprising an acidic support selected from the group consisting of alumina, halogen-treated alumina, silica-alumina, boria-alurnina, and wide pore molecular sieves, said acidic support being impregnated with .01 to 1.0 wt. percent of a metal selected from the group consisting of platinum and palladium and .1 to 20 wt. percent of a desulfurizing agent whereby said heavier fraction is reduced in pour point and sulfur content, reblending said heavier and said lighter fractions.

11. The process of claim 10 wherein the pressure during said contacting is 500 to 1000 p.s.i.g.

12. The process of claim 10 wherein said heavier fraction is passed over said catalyst at a velocity of 0.5 to 10 v./hr./v.

13. The process of claim 10 wherein said hydrogen is passed over said catalyst and recycled at a rate between 1000 and 10,000 s.c.f. per barrel of oil.

8 wherein acidic support is References Cited UNITED STATES PATENTS