NL192268C - Method for lowering the pour point of a gas oil or a lubricating oil. - Google Patents

Description

1 192268

Method for lowering the pour point of a gas oil or a lubricating oil

The present invention relates to a process for dewaxing the pouring point of a gas oil or a lubricating oil containing n-alkanes and / or slightly branched paraffins by dewaxing, whereby the gas oil or lubricating oil is contacted with a crystalline silicate at a temperature of 285-595 ° C and under a subatmospheric pressure of up to 205 bar to form gaseous olefins under normal conditions.

Such a method is known from US patent 3,700,585 (= U.S. re-issue 28,398).

According to this reference, hydrocarbon feeds are dewaxed by contacting them with a crystalline zeolitic material at a temperature of 288-621 ° C (550-1150 ° F) and a pressure between subatmospheric pressure and several hundred bar, optionally in the presence of added hydrogen.

As the catalyst, ZSM-5 type and ZSM-8 type aluminosilicates are used, i.e. zeolites with an Al 2 O 3 / SiO 2 molar ratio of 1: 5-100.

Other chemically more blowing products, such as olefins, are obtained by other methods, however, lower pressures must be used there to prevent the olefins obtained from being hydrogenated. This is apparent, for example, from U.S. Patent 4,171,257, according to which olefins are obtained by dewaxing with H-ZSM-5 at low pressures.

U.S. Patent 3,941,871 (= U.S. Re-issue 29,948) describes crystalline silicates with an Al 2 O 3 / SiO 2 molar ratio greater than 1: 200, as well as the use of these catalysts in various hydrocarbon conversions, including catalytic cracking. However, the use of these catalysts to lower the pour point of hydrocarbon feeds is neither disclosed nor suggested.

U.S. Pat. No. 4,061,724 discloses a crystalline silica polymorphic product called "silicalite" and a method of preparation thereof. This catalyst is used to selectively absorb organic materials from an aqueous solution.

Anderson et al., J. Catalysis, 58,114-130 (1979) describe comparative catalytic reaction and sorption measurements performed with ZSM-5 and silicalite catalysts. As a food, a.o.

3-methylpentane used. However, the use of "silicalite" catalysts in the dewaxing of lubricating oil or gas oil has been described.

Flanigen et al. Discuss in Nature, 271, 512-516 (February 9, 1978) the physical and adsorption properties of silicalite. Bibby et al., Nature, 280, 664-665 (August 23, 1979) report the preparation of a crystalline silicate called "silicalite-2".

Benesi, et al. In Adv. in Catalysis, 27 (1978), 120-123 reviews the acidity and catalytic activity of silica gel. West, et al., In J. Catalysis 29, (1973), 486-493, discuss the catalytic activity of silica gel.

The object of the invention is to provide an improved method for lowering the pour point of lubricating oils and gas oils, in particular to provide a method that gives better results than the ZSM-5 and ZSM previously used in the art. -8 catalysts.

It has now been found that such an improved process can be provided by using crystalline silicates with a very high SiCVA / Oa ratio.

The present application therefore relates to a method of the type described in the preamble, characterized in that as the crystalline silicate a silicate with a molar SiO2AlgOg ratio of more than 200: 1, a relative density in calcined form from 1.50 to 2.10 g / cm3 and a refractive index from 1.3 to 1.5.

It has surprisingly been found in the process of the invention that, in addition to lowering the pour point of the lubricating oil and gas oil, significant amounts of olefins are also generated, even at high pressures and in the presence of hydrogen.

The figure illustrates the difference in activity of ZSM-5, silicalite and silica gel on the catalytic conversion of n-C36 alkanes.

The hydrocarbon feed used in the present invention can be any gas oil or lubricating oil, for example, a diesel fuel or a heating fuel.

Preferably, the feed contains at least 5 wt% unbranched and slightly branched alkanes, for example 5 to 40 wt% and more preferably at least 10 wt% unbranched and slightly branched alkanes, for example 10 to 30 wt. %.

When sulfur compounds are present in the feed, sulfur can react with the olefins produced to yield mercaptans. To reduce the possibility of mercaptans being formed, the feed may be subjected to an H 2 treatment to less than <192268 2 100 parts per million organic sulfur and preferably to less than 50 parts per million organic sulfur . The presence of organic nitrogen compounds has not been found to be harmful to the present process; therefore, the feed can have any nitrogen content, such as 300 or 500 ppm or more.

For example, it is preferable that the content of organic nitrogen compounds is less than about 25 and more preferably less than about 10 parts by weight per million.

The feed is contacted with the crystalline silicate at standard cracking conditions, i.e. an elevated temperature, usually from about 290 ° C to about 595 ° C, and preferably from about 340 ° C to about 480 ° C, a subatmospheric pressure pressures up to about 20,500 kPa and preferably from atmospheric to about 14,000 kPa and more preferably from atmospheric to about 3,500 kPa and a space velocity from about 0.1 to about 50 hours, preferably about 0.5 to 25 hours and more preferably from about 1 to about 10 h ~ 1.

If desired, the process of the present invention can be carried out in the presence of hydrogen or hydrogen can be added at a system pressure of 20,500 kPa and preferably from 1,400 to 20,500 kPa. The hydrogen can be dissolved in the feed or can be present as a gas at 15 partial pressures up to about 10,000 kPa or more, or at hydrogen to hydrocarbon volume ratios of 350 to 3650 liters of hydrogen per liter of liquid hydrocarbon feed. Very surprisingly, significant amounts of olefins are generated even in the absence of hydrogen at pressures at which olefins will usually be hydrogenated, even in the absence of a specific metal hydrogenation catalyst. This unusual advantage due to the use of the crystalline silicates and low sodium crystalline silicates makes it possible during refining that a low pressure reactor need not be included in the process scheme of the olefin preparation. Using the present process, olefins can be obtained without first decreasing and then increasing the pressure and without separating hydrogen from the process stream.

Apart from whether hydrogen is present, the following general relationship can be observed in the contact zone: The higher the molecular weight of the paraffins in the feed, the lower the required temperature and pressure for satisfactory conversion and olefin preparation.

"Crystalline silicate," as used herein, refers to silicates having a rigid, three-dimensional network of SiO 4 tetrahedrons, in which the tetrahedrons are cross-linked by sharing oxygen atoms. The crystalline silicates are substantially free of alumina, but they may contain minor amounts of alumina from impurities in the starting products or impurities from the reaction vessels. The silica / alumina mole ratio of the crystalline silicates is greater than about 200: 1, preferably greater than about 500: 1, and most preferably greater than about 1000: 1. The crystalline silicates further have densities in the calcined form of 1.50 to 2.10 g / cm3 and a refractive index of 1.3 to 1.5.

As previously destroyed, crystalline silicates which can be used in the method of the present invention have been reported in the literature. Silicalite (U.S. Patent 4,061,724) as prepared has a density at 25 ° C of 1.99 ± 0.05 g / cm3 as measured by displacement. In the calcined form (600 ° C in air for one hour), silicalite has a density of 1.70 ± 0.05 g / cm3. Regarding the average refractive index of silicalite crystals, values obtained by measuring the form prepared as such and the calcined form (600 ° C in air for one hour) have been obtained from 1.48 ± 0.01 and 1.39 ± 0, respectively. 01.

The X-ray powder diffraction pattern of silicalite (600 ° C calcination in air for one hour) has as its six strongest lines (ie interplanar spaces) the lines listed in Table A ("S" - strong and "VS" - very strong): 45

TABLE A

d-nm Relative intensity 50 1.11 ± 0.02 vs 1.00 ± 0.02 vs 0.385 ± 0.007 vs 0.382 ± 0.007 s 0.376 ± 0.005 s 55 0.372 ± 0.005 s 3 192 268

Table B shows the X-ray powder diffraction pattern of a conventional silicalite formulation containing 51.9 moles SiO 2 per mole (TPA) 20 prepared according to the procedure of U.S. Patent 4,061,724 and calcined in air at 600 ° C for one hour.

5 TABLE B

d-nm Relative intensity 1.11 100 10 1.002 64 0.973 6 0.899 1 0.804 0.5 0.742 1 15 0.706 0.5 _0.668 ___ 5_______________________ __ g 0.598 14 0.570 7 20 0.557 8 0.536 2 0.511 2 0.501 4 0.988 5 25 0.486 0.5 0.460 3 0.444 0.5 0.435 5 0.425 7 30 0.408 3 0.400 3 0.385 59 0.382 32 0.374 24 35 0.371 27 0.364 12 0.359 0.5 0.348 3 0.344 5 40 0.334 11 0.330 7 0.325 3 0.317 0.5 0.313 0 .5 45 0.305 5 0.298 10

Silicalite crystals both in the form prepared as such and in the calcined form are orthorhom-50 and have the following unit cell parameters: a = 2.005 nm, b = 1.986 nm, c = 1.336 nm (all values ± 0.01 nm).

The pore diameter of silicalite is about 0.6 nm and its pore volume is 0.18 cm3 / g as determined by adsorption. Silicalite adobs neopentane (0.62 nm kinetic diameter) slowly at ambient temperature. The uniform pore structure imparts size selective molecular sieve properties to the composition and the pore size allows for the separation of p-xylene from o-xylene, m-xylene and ethylbenzene, as well as separations of compounds with quaternary carbon atoms from those with carbon-carbon bonds of lower value (e.g. unbranched and slightly 192268 4 branched alkanes).

The crystalline silicates of U.S. RE Patent 29,948 are described in the anhydrous state having the following composition: 0.9 ± 0.2 [xR2O + (1-xjM ^ O]: <0.005 Al2 O3:> 1 SiO2 where M is a metal is different from a Group IIIA metal, n is the dignity of the metal, R is an alkyl ammonium group, and x is a number greater than 0 but no greater than 1. The organosilicate is characterized by the X-ray diffraction pattern of Table C.

TABLE C

Interplanar space d (nm): Relative intensity Ί5 - __Vil______s___________ 1.00's 0.74 w 0.71 w

0.63 W.

0.64) W.

0.597) 0.556 w

0.501 W.

25 0.460 W.

0.425 W.

0.385 -------------------- USA

0.371 S.

0.304 W.

30 0.299 W.

0.294 W.

The crystalline silicate polymorph of U.S. Pat. No. 4,073,865 is described with a density of 1.70 ± 0.05 g / cm3 and an average refractive index of 1.39 ± 0.01 after calcination in air at 600 ° C, such as prepared by a hydrothermal process, incorporating fluoride anions in the reaction mixture. The crystals, which can be 200 micrometers, exhibit a substantial absence of infrared adsorption in the hydroxyl stretching region and also an extraordinary degree of hydrophobicity.

They have the X-ray diffraction pattern of Table D.

40

TABLE D

d (nm) Intensity 45 1.114. 91 1.001 100 0.975 17 0.899 1 0.804 0.5 50 0.744 0.5 0.708 0.2 0.669 4 0.636 6 0.599 10 55 0.571 5 0.557 5 5 192 268 TABLE D (continued) d (nm) Intensity 5 0.537 1 0.533 1 0.521 0 .3 0.512 1.5 0.502 3 10 0.497 6 0.492 0.6 0.472 0.5 0.462 2 0.447 0.6 15 0.436 3 0.425 4 Ö> 13 “0.5 0.408 1.5 0.400 3 20 0.385 44 0.382 25 0.371 21 0.365 5 0.362 5 25 0.359 1 0.348 1.5 0.345 3 0.344 3 0.335 3 30 0.331 5 0.325 1.5 0.323 0.8 0.322 0.5 35

The literature describes the following process for the preparation of the crystalline silicate, which is called "silicalite-2" (Nature, August 1979):

The silicalite-2 precursor is prepared using only tetra-n-butylammonium hydroxide, although addition of ammonium hydroxide or hydrazine hydrate as a source of additional hydroxyl ions greatly increases the rate of reaction. A successful preparation is mixing 8.5 moles SiO 2 as silica (74% SiO 2), 1.0 moles tetra-n-butylammonium hydroxide, 3.0 moles NH 4 OH and 100 moles water in a steel pressure vessel and heating for 3 days at 170 ° C. The precursor crystals have an oval shape, about 2-3 micromillimeters in length and 1-1.5 micromillimeters in diameter. The precursor of the silicalite-2 is reported as non-forming when Li, Na, K, Rb or Cs ions 45 are present, in which case the precursor of the silicalite of U.S. Pat. No. 4,061,724 is formed . The size of the tetraalkylammonium ion is said to be critical since replacement of the tetra-n-butylammonium hydroxide with other quaternary ammonium hydroxides (such as tetraethyl, tetrapropyl, triethylpropyl and triethylbutyl hydroxide) results in amorphous products. The precursor of silicalite-2 is stable at longer reaction times in the hydrothermal system. The amount of Al present in 50 silicalite-2 depends on the purity of the starting products and is reported as less than 5 ppm.

The precursor contains trapped tetraalkylammonium salts, which due to their size are only removed by thermal decomposition. Thermal analysis and mass spectrometry show that the tetraalkylammonium ion decomposes at about 300 ° C and disappears as the tertiary amine, olefin and water. This is in contrast to the normal theimical decomposition at 200 ° C of the same tetraalkylammonium salt in 55 air.

The Nature article further states that the main differences between the patterns of silicalite and silicalite-2 are that peaks at 9.06,13,9,15,5,16,5,20,8,21,7,22 , 1, 24.4, 26.6 and 27.0 degrees 2Θ (CuK

192268 6 alpha radiation) in the silicalite x-ray diffraction pattern are not present in the silicalite-2 diagram. Also peaks at 8.8,14,8,17,6, 23,1,23,9 and 29,9 degrees are singlets in the silicalite-2 pattern instead of doublets as in the silicalite pattern. These differences are reported as the same as found between the diffraction patterns of aluminosilicates, orthorhombic ZSM-5 and tetragonal ZSM-11. Unit-5 cell dimensions reported as calculated on the assumption of quadrangular symmetry for silicalite-2 are a = 2.004 nm; b = 2.004 nm and c = 1.338 nm. The measured densities and refractive indices of silicaiite-2 and its precursor are reported as 1.82 and 1.98 g / cm3 and 1.41 and 1.48, respectively.

The preparation of crystalline silicates generally involves the hydrothermal crystallization of a reaction mixture containing water, a source of silicon dioxide and an organic forming compound at a pH of 10 to 14. Representative molding moieties include quaternary cations such as XR4, wherein X is phosphorus or nitrogen and R is an alkyl group containing 2 to 6 carbon atoms, e.g.

When the organic forming compound is supplied to the system in the hydroxide form in an amount sufficient to establish a basicity equivalent at the pH of 10 to 14, the reaction mixture must contain only water and a reactive form of silica as additional ingredients. In those cases where the ph must be increased above 10, ammonium hydroxide or alkali metal hydroxides may be suitably used for that purpose, especially the hydroxides of lithium, sodium and potassium. It has been found that no more than 6.5 moles of alkali metal oxide per mole of organic forming species are required for this purpose, even when none of the forming compounds are provided in the void of the hydroxide.

The source of silicon dioxide in the reaction mixture may be in whole or in part an alkali metal silicate, but should not be used in amounts greater than which would change the molar ratio of alkali metal to organic forming compound, as mentioned above. Other silica sources include solid reactive amorphous silica, for example, fumed silica, silicon dioxide, silica gel, and organic orthosilicates. Since the nature of the reaction system is beneficial for the inclusion of alumina as an impurity in the crystalline silica product, care should be taken in choosing the source of silica to minimize the alumina content as an impurity. Commercially available silicon dioxide oxides can usually contain from 500 to 700 ppm of Al2Oa, while smoked silicon dioxide can contain from 80 to 2000 ppm of Al2 O3 impurity. Ethyl orthosilicate is a preferred source of silicon oxide since it can be obtained with very low alumina contents. Small amounts of AI2Oa present in the crystalline silicate product do not materially alter the essential properties. However, large amounts of alumina, as used in the preparation of the ZSM-5 zeolite from Argauer et al., Produce a product which is not widely used in olefin-producing reactions of the crystalline silicates. The amount of silicon dioxide in the reaction system should generally be from about 13 to 50 moles SiO 2 per mole ion organic forming compound. Water should generally be present in an amount of 150 to 700 moles per mole ion of the organic forming compound or of the quaternary cation. The reaction preferably takes place in an aluminum-free reaction vessel, which is resistant to attack by alkali or base, for example teflon.

When alkali metal hydroxides are used in the reaction mixture, alkali metal cations appear as impurities in the crystalline product. These impurities can be present in the crystalline mass in an amount of about 1% by weight. It is preferable to reduce the concentration of the alkali metal components in the crystalline mass by ion exchange or with another suitable removing agent to less than 0.1 wt% alkali metal, preferably less than 0.03 wt% and more preferably less than 0.01 wt% alkali metal. When the alkali metal concentration is very low, less than about 0.1% by weight, surprisingly large amounts of olefins are produced.

Suitable ion exchange materials include those which are decomposable to hydrogen by calcination and are known in the art, for example ammonium nitrate or those metal cations or metal cation complexes, which exhibit little or no hydrogenation or cracking activity, such as calcium, strontium, barium, zinc, silver or the rare earth metals. As used herein, "hydrogenation activity" refers to the ability to absorb and dissociate molecular hydrogen.

The alkali metal remaining in the product can also be removed by washing with an aqueous acidic solution of sufficient strength, for example hydrochloric acid. The crystal structure is otherwise unaffected by contact with strong mineral acids even at elevated temperatures due to the lack of acid soluble components in its crystal structure.

The crystalline silicate may be in any suitable form that may be required for ordinary use in a fixed bed, fluidized bed or suspension. Preferably, the crystalline silicate in a fixed bed reactor and in a composition with a porous inorganic binder or such matrix is in such proportions that the product obtained is 1 to 95% by weight and preferably 10 to 70% by weight of silicate. contains the final composition.

The preferred crystalline silicates are the silicates as disclosed in U.S. Patent 4,061,724 and U.S. RE Patent 29,948.

The terms "" matrix "and" "porous matrix" include inorganic preparations with which the silicate can be combined, dispersed, or otherwise thoroughly mixed, the matrix being non-catalytically active in the hydrocarbon cracking phrase, i.e., virtually no acid sites and has substantially no hydrogenation activity. The porosity of the matrix may be inherent in a particular material or may be caused by a mechanical or chemical method. Representative examples of satisfactory matrices include pumice stone, refractory stone, diatomaceous earth and inorganic oxides. Representative inorganic oxides include alumina, silicon dioxide, naturally occurring and conventionally processed clays, for example bentonite, kaolin, sepiolite, attapulgite and halloysite. The preferred matrices have few or no acid sites and therefore have little or no cracking activity. Silicon dioxide and alumina are particularly preferred. The use of a non-acidic matrix is preferred to maximize the olefin preparation.

The assembly of the crystalline silicate with an inorganic oxide matrix can be carried out by any suitable known method, whereby the silicate is thoroughly mixed with the oxide, while the latter is in an aqueous state, e.g. as an aqueous salt, hydrogel, moist gelatinous precipitate, or in a dry state, or combinations thereof.

A suitable method is the preparation of an aqueous mono or poly oxide gel or ball using an aqueous solution of a salt or mixture of salts, for example aluminum sulfate and sodium silicate. Ammonium hydroxide carbonate or a similar base is added to the solution in an amount sufficient to precipitate the oxides in aqueous form. After washing the precipitate to remove most of any water-soluble salt present in the precipitate, the silicate in finely divided state is mixed with the precipitate together with added water or lubricant in an amount sufficient to form the mixture by extrusion to facilitate 30.

Surprisingly, it has been found that the yield of olefins, especially olefins having 2 to 4 carbon atoms, was substantial even in the presence of hydrogen at 1400 kPa or more, however, this advantage is diminished when the matrix itself is acidic. These olefins are particularly desirable and valuable for many known applications in petroleum and chemical processing techniques, while their chemically less reactive alkane counterparts are much less desirable products. The olefin yield will vary depending on the particular feed composition, the shape of the silicate and the reaction conditions employed. As used herein, "substantially olefin fraction" means that the converted hydrocarbons contain at least 10 wt% olefins, preferably at least 20 wt% olefins, more preferably at least 30 wt% olefins, even more preferably at least 40 wt.% olefins and most preferably contain at least 50 wt.% olefins. "Converted Hydrocarbons" means that portion of the hydrocarbon product that is boiling below the initial boiling point of the feed.

The silicalite used in the invention was prepared by dissolving 90 g of (C3H7) 4NBr in 30 ml of water and adding the solution to 39.6 g of fumed silica in 100 ml of water. A solution of NaOH in 37 g of water (9.2% NaOH) was then added to the synthesis mixture with stirring. The silicate product was obtained by crystallizing the synthesis mixture at 200 ° C for 70 hours.

Example I

A catalyst was prepared containing 25% by weight of silicalite as prepared above, which was incorporated into a high alumina silica-alumina matrix. The final catalyst contained 3 wt% cobalt, 7 wt% nickel and 20 wt% molybdenum and had a surface area of 200 m 2 / g and an average pore diameter of 8.1 nm.

The catalyst was contacted with an Arabian light vacuum gas oil with the properties listed in Table E at a temperature of 416 ° C, a pressure of 16,900 kPa, a space velocity of 55 1.0, and a hydrogen to hydrocarbon volume ratio of 1780 (10,000 SCFB) . An inspection of the product indicated that 44.8 wt% of the feed having a boiling point above 316 ° C had been converted to a product having a boiling point below 316 ° C with a recovery of 87.6 wt% of hydrocarbons with 192 268 8 5 carbon atoms.

TABLE E

5 Arabian light vacuum gas oil

Density, ° API 22.9

Sulfur, wt% 2.19 N, total, wppm 887

10 Pour point, ° C 29 ° C

ASTM D-1160 Dest.

initial kpt / 10%, ° C 339/380 30/50%, ° C 413/447 70/90%, ° C 468/503 15 final boiling point, ° C 536

Example II

A trial was conducted to compare the activity of the hydrocarbon conversion of silicalite, ZSM-5 and silica gel for long chain n-alkanes. Individual samples of silicalite, H-ZSM-5 and an amorphous silica were introduced into barrels together with measured amounts of non-branched hydrocarbons of 36 carbon atoms and subjected to theimical gravimetric analysis. The samples were heated at 10 ° C / minute; an expansion of the weight of residual normal alkanes with 36 carbon atoms against the temperature is shown in Figure 1. As can be seen from Figure 1, the degree of weight loss, i.e. the hydrocarbon conversion activity, for the crystalline silicate and for amorphous silica is greatest between 300 ° -350 ° C, while for ZSM-5 it is greatest between 200-250 ° C .

30

Example III

An experiment was conducted to compare the catalytic activity of silicalite and ZSM-5 for dewaxing gas oil feeds. The feed of Table E was contacted with three compositions: 25 wt% silicalite placed in a silica-alumina matrix having a high alumina content, 25 wt% H-ZSM-5 placed in the same matrix and the matrix alone. The reaction conditions and an analysis of the products obtained are listed in Table F.

TABLE F

40 Reaction conditions Silicalite H-ZSM-5 Matrix

Temperature, ° C 404 404 404

Printing ink 16370 16360 16370

Space velocity h-1 1.0 1.0 1.0 45 Total, conversion, wt% feed 36.0 54.2 43.2

Total n-alkane conversion, wt% 41.5 78.9 8.9 feed

Product analysis 50 - n-alkane content Supply Silicalite H-ZSM-5 Matrix n-C18 0.12 0.48 0.18 0.44 n-C1B 0.17 0.42 0.02 0.52 55 n-Cjjo 0 , 30 0.34 0.02 0.71 n-C21 0.47 0.58 0.07 0.34 9 192 268 TABLE F (continued)

Reaction conditions Silicalite H-ZSM-5 Matrix 5 IVC22 0.55 0.43 0.05 0.68 n-CjKj 0.55 0.38 0.31 0.58 n-C24 0.53 0.34 0.05 0 .58 RV-Cas 0.51 0.30 0.12 0.45 n-Cae 0.51 0.19 0.03 0.41 10 n-C27 0.49 0.11 0.08 0.25 n- Cae 0.45 0.17 0.15 0.21 n-Ca »0.43 0.09 0.24 0.11 n-Cgo 0.39 0.03 0.07 0.20 n-C31 0.30 0.00 0.00 0.15 15 n-Cga 0.28 0.00 0.00 0.08 ------- n-Cga -------- 0.28 0.00 0 .00 0.00 nG * θ [Ϊ6 0.00 -Όφθ ---— 0.00 _________ n — C35 0.12 _ _ -

Total n-alkanes wt% feed 6.61 3.86 1.39 6.01 20 -

The product analyzes listed in Table F show that silicalite preferably allows cracking from higher molecular weight n-alkanes to lower molecular weight n-alkanes, as indicated by the conversion of 68% of nCas-nC ^ alkanes, but only one 8% reduction in nC18 - nC24 25 alkanes. In contrast, the ZSM-5 removed 77% of the nC2 - nC2 alkanes and 81% of the nC18 - nC24 alkanes, while the matrix removed only 36% of the nC2S - nC2 alkanes and generated 19% additional nC18 - nC24 alkanes. Therefore, silicalite is more selective for the conversion of high molecular weight n-alkanes to intermediate molecular weight alkanes than ZSM-5 or the matrix. This is a highly desirable advantage for a dewaxing catalyst, since the long chain waxes are preferably cracked to shorter chain branched alkanes, while the highly active ZSM-5 tends to crack intermediate chain alkanes to gases.

It is believed that non-branched chain hydrocarbons and slightly branched chain hydrocarbons are adsorbed within the pores of the silicalite and held there for a sufficient time for cracking to take place. The adsorbed alkane cracked to an alkane 35 and a lower molecular weight olefin. It is believed that alkanes are retained in the pores for further cracking, while the olefin is expelled through the hydrophobic surface of the silicate. In contrast, the olefin is believed to be retained by a ZSM-5 zeolite and hydrogenated. The more branched chain hydrocarbons and hydrocarbons of other forms that are not adsorbed by the silicate pass through the reaction zone. This theory is not intended to limit the invention.

Example IV

A crystalline silicate preparation containing 400 parts by weight of sodium, mixed in the ratio 1 part by weight of silicalite 45 to 2 parts by weight of aluminum oxide. The preparation was tested for hydrocarbon conversion with a hydrocarbon fraction of 391 ° C + with the properties listed in Table G.

TABLE G

50 Supply Light neutral lubricating oil 'Boiling range 10/50/90%, ° C 391/403/432 ppm N / ppm S 1.2 / 6.1

Pour point eC> +29 55 Viscosity index 112 192 268 10

The reaction conditions include a temperature of 405 ° C and of 416 ° C, a dmk of 7000 kPa and a space velocity of 2 and 1780 L Hg / L oil (10,000 SCF / B). The analysis of the obtained liquid products yielded the following results:

5 TABLE H

Yields, wt% Test A 405 ° C Test B 416 ° C

C, 0 0 10 C2 = 0.1 0.1 C2 0 1.1 C3 = 1.7 1.9 C3 1.1 1.3 C4 = 3.0 4.1 15 C4 1.4 1.7 CS -82 ° C 9.1 11.5 ________________ _82 = 499¾- 2.5 3J ~~~ 199-371 ° C 2.7 4.0 371 eC + 78.4 71.6 20 Pour point, ° C +7 -4

Viscosity index 98 92

The hydrocarbon conversion over the crystalline silicate therefore significantly lowers the pour point and also produces a C4 hydrocarbon product containing a very substantial amount of olefins, about 65% by weight.

Comparative Example 30 An experiment was conducted with the feed of Example IV, Table G, to compare the behavior of ZSM-5 with silicalite while processing to comparable pour points (Runs B of Example IV and this Comparative Example) and to comparable yields (tests A of examples IV and this comparative example). The ZSM-5 composition was prepared in an aluminum oxide matrix with 1 part of ZSM-5 to 2 parts of alumina. The reaction conditions were: pressure 7000 kPa, space velocity 2, and 1780 L H2 / L oil (10,000 SCF / B).

TABLE I

Yields, wt% Test A 291 ° C Test B290 ° C

40 - C4 0 0.1 C2 = 0 0 C2 0.2 0.1 C3 = o o 45 C3 3.9 3.0 C4 = 0.3 0.2 C4 6.3 4.9

Cg-82 ° C 8.8 7.1 82-199 ° C 2.3 1.9 50 199-371 ° C 0.2 0.2 371 ° C + 78.0 82.5

Pour point, ° C -10 +15 '

Viscosity index 86 92

Claims (3)

Comparing the data of this comparative example with that of example IV shows that even when there is considerable pressure and hydrogen is present, silicalites surprisingly produce olefins, while ZSM-5 does not. 1. A method of lowering the pour point of a gas oil or lubricating oil containing n-alkanes and / or slightly branched alkanes by dewaxing, contacting the gas oil or lubricating oil with a crystalline silicate at a temperature of 285- 595 ° C and under a subatmospheric pressure of up to 205 bar to form gaseous olefins under normal conditions, characterized in that as the crystalline silicate a silicate having a SiO 2 / Al 2 O 3 molar ratio of more than 200: 1, a relative density in calcined form of 1.50 to 2.10 g / cm3 and a refractive index of 1.3 to 1.5. 2. Process according to claim 1, characterized in that the crystalline silicate used is silicalite. 3. A method according to claim 1 or 2, characterized in that a partial hydrogen pressure of at most 10,000 kPa is applied.