DE69103598T2 - Process for the production of lubricants with low pour point and high viscosity index by solvent dewaxing. - Google Patents

Description

Solvent dewaxing of waxy lubricating oils has long been known. It is also known that lighter oils, oils with lower boiling point and VI (viscosity index) of about 90 to 105/110 are more easily miscible with dewaxing solvents of a given composition than oils with higher VI. It is also generally accepted that good yields of dewaxed oils are obtained when the dewaxing process is carried out under miscible oil/solvent conditions. To date, solvent-to-oil ratios, dewaxing temperatures and solvent/cosolvent ratios have been adjusted to obtain oil/solvent miscibility at the dewaxing temperature (filter temperature). However, all too often a compromise must be made between dewaxed oil yield and pour point. This means that low pour points are achieved at the expense of product yield or, conversely, high yields are achieved at the expense of higher pour points.

US-A-3 365 390 describes a lubricating oil production process in which a heavy oil feedstock is hydrocracked, the hydrocracked wax is separated from a hydrocracked lubricating oil portion of the products, and the hydrocracked wax is hydroisomerized using an active reforming catalyst. An isomerized lubricating oil fraction thus produced can be separately dewaxed to obtain isomerized ultra-high VI lubricating oil, or the isomerized lubricating oil fraction is co-isomerized with a hydrocracked lubricating oil fraction. When the isomerizate is dewaxed in combination with a hydrocracked lubricating oil fraction, the recovered paraffin is a mixture of hydrocracked paraffin and isomerized paraffin and the properties of the recovered lubricating oil are upgraded due to the presence of the isomerizate lubricating oil fraction.

High boiling, high VI wax isomers and natural waxy oil distillates are difficult to dewax to achieve a pour point in the range of about -20ºC and below. Such oils, when solvent dewaxed at low temperatures, typically exhibit oil/solvent miscibility problems, leading to poor dewaxed oil yields.

It has been found that high boiling, high VI oils can be solvent dewaxed to a low pour point under miscible conditions using dewaxing solvents with low miscibility, e.g., C3 to C6 ketone based dewaxing solvents such as methyl ethyl ketone, methyl isobutyl ketone, acetone, etc., and mixtures thereof such as MEK/MIBK, by combining a quantity of low boiling, conventional VI waxy oil with the high boiling, high VI oil and processing the mixture together under conventional solvent dewaxing conditions. The addition of the low boiling, conventional VI waxy oil to the high boiling, high VI oil allows the dewaxing to be carried out under miscible conditions, resulting in the production of acceptable yields of low pour point dewaxed oil. It has also been found that the dewaxed low pour point oil blend can be subsequently fractionated into fractions having specifications very close to those of the original materials in terms of boiling point and VI, and that both of these fractions have the low pour point of the blend. After normalizing the yields, it has been found that the yield of high boiling high VI low pour point oil obtained by the co-processing method is higher than that obtained when the high boiling high VI oil is dewaxed alone.

Figure 1 compares the miscibility of heavy, high-boiling paraffin isomer oil with high VI with that of a mixture of this heavy oil with a light oil in a ratio of 2:1 in ketone dewaxing solvents with varying proportions at different temperatures.

Figure 2 shows the yield of dewaxed oil with a pour point of -21ºC derived from Fischer-Tropsch isomerize, where the yield is normalized to 100 barrels of Fischer-Tropsch isomerize feed based on both pure Fischer-Tropsch isomerize and a Fischer-Tropsch isomerize/150N blend to the dewaxer.

Heavy, high VI, paraffinic oils, whether obtained by wax isomerization or from conventional oils such as deasphalted, hydrocracked 600N oil or bright stocks, can be dewaxed with typical low miscibility dewaxing solvents such as C3 to C6 ketones at the low dewaxing temperatures used when low target pour points of -21°C or below are to be achieved, using conventional solvents under miscible conditions (e.g., a filter temperature of not less than about -35°C so as to have a pour point/filter ΔT of about 3 to 4°C or less) to a pour point of -21°C and below, preferably about 124°C, most preferably about -27°C. solvent dewaxed by adding a quantity of the lower boiling conventional VI paraffinic oil distillate to the heavy, high boiling paraffinic oil and processing this mixture according to the solvent dewaxing process under miscible conditions.

The light, lower boiling, low VI paraffinic oil added to the heavy, high boiling, high VI paraffinic oil is such that it can be easily separated from the heavy oil by distillation, therefore it is characterized by having a 90% boiling point that is about 50 to 300°F, preferably 50 to 100°F, lower than the 10% boiling point of the heavy oil. The majority of the light oil is substantially lighter and boils lower than the majority of the heavy oil.

The light oil is added to the heavy oil in an amount sufficient to make the mixture miscible in the low miscibility dewaxing solvent used at a filter temperature that allows the waxy oil to have a pour point of at least -21°C, preferably about -24°C, and most preferably about -27°C. The amount of light oil added can range from about 5 to 50%, preferably about 20 to 40%, by volume of the oil mixture.

The solvent dewaxing process that is advantageously operated with the two-component waxy feedstock is any typical solvent dewaxing process including those referred to as indirect cooling processes with dilution, direct cooling processes with predilution, or simply direct cooling processes.

Indirect cooling methods include, for example, scraped surface cooling methods in which the waxy oil batch is diluted with solvent to produce a solution that is passed through the scraped surface cooler in which a coolant is passed through the outer shell of the heat exchanger while a rotating scraper blade prevents wax buildup on the inner surface of the cooler.

Direct cooling processes can operate either without dilution or with pre-dilution of the paraffin-containing charge. The diluted or undiluted paraffin-containing charge is then cooled by injecting cold solvent directly into the paraffin-containing charge.

A preferred embodiment of cooling with dilution is the DILCHILL process in which the wax-containing charge is passed through a cooling tower divided into stages and cold solvent is injected into several of these stages. In these stages into which cold solvent is injected, a high degree of mixing is maintained so that essentially instantaneous mixing of the cooling solvent and the wax-containing oil is achieved, thereby achieving a harmful shock cooling is avoided. This process is described in more detail in US-A-3,773,650. In an alternative embodiment, the waxy oil is cooled in the apparatus described above to a temperature of about 35°F above the filter temperature, with cooling down to the filter temperature being carried out in a subsequent scraped surface cooler. This embodiment is described in US-A-3,775,288.

The low miscibility dewaxing solvents typically used in solvent dewaxing processes, which are the same solvents used in the process of the present invention, include C3 to C6 ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK) and mixtures thereof such as MEK/MIBK.

The heavy, high boiling, high VI paraffinic oil can be the material obtained by isomerizing paraffin, either as synthetic paraffin obtained from the Fischer-Tropsch process or as natural paraffin obtained from dewaxing hydrocarbon oils, commonly called slack wax, or a natural petroleum material such as hydrocracked oil, deasphalted 600N or bright stock oil. When the paraffinic oil to be dewaxed is a heavy, high boiling, high VI isomerizate, it is preferred that the entire oil fraction boiling in the lubricating oil boiling range (i.e., about 330°C and above, preferably about 370°C and above) be the feed to the dewaxing process of the present invention, i.e., utilizing the addition of a light oil fraction to facilitate dewaxing under miscible conditions. In general, heavy, high-boiling, high VI materials, whether they are isomerizates, natural oils or hydrocracked oils, are those materials having a viscosity in the range of 6 to 12 cSt (6 to 12 mm²/s) at 100ºC, preferably 8 to 10 cSt (8 to 10 mm²/s) at 100ºC, a mean liquid volume % boiling point of 450 to 550ºC, preferably 475 to 525ºC and a VI of at least 120, preferably at least 140.

The light, lower boiling, lower VI oil has a viscosity of about 3 to 7 cSt (3 to 7 mm²/s) at 100°C, preferably 4 to 6 cSt (4 to 6 mm²/s) at 100°C, a 90% boiling point of about 0 to 300°F (0 to 166.7°C) below the 10% boiling point of the heavy oil, and a VI of less than about 110, preferably less than about 100.

In the process of the invention, the heavy oil is mixed with a volume of the light oil to permit operation of the solvent dewaxing process under miscible conditions at a filter temperature low enough to produce an oil having a pour point of at most -21°C.

After processing the blended oil feedstock using the solvent dewaxing process, the resulting dewaxed oil product is fractionated into fractions that closely resemble the original source material (i.e., a light oil fraction with conventional VI and a heavy oil fraction with very high VI). Each of these fractions has a pour point of at least about -21ºC, the pour point of the blend. The yield of heavy oil with a pour point of -21ºC obtained by this co-processing process is higher than that possible by processing the heavy oil alone.

The wax that is isomerized can come from any source. Synthetic waxes from Fischer-Tropsch processes, as well as waxes obtained from solvent or self-cooling dewaxing, and mixtures of these waxes can be used. Waxes from the dewaxing of conventional hydrocarbon oils are commonly referred to as slack waxes and usually contain a significant amount of oil. The oil content of these slack waxes can range anywhere from 0 to 45% or more, usually 5 to 30% oil. For the purpose of this invention, the heavy waxes obtained from the dewaxing of bright stocks and the heavy Fischer-Tropsch waxes are the feedstocks of choice.

Hydrogenative isomerization (hydroisomerization) can be carried out over any of the standard hydroisomerization catalysts containing a hydrogenation metal selected from Group VIB and Group VIII and mixtures thereof, preferably the Group VIII metals, especially the Group VIII noble metals, most preferably platinum. The metal loading is in the range of between 0.1 and 5.0 wt.% metal, preferably 0.1 to 1.0 wt.% metal, most preferably 0.2 to 0.6 wt.% metal.

The hydrogenation metal component is supported on a refractory support of inorganic metal oxide, preferably alumina or silica-alumina, most preferably the transition aluminas, e.g. gamma-alumina. Preferably the support is halogenated. The halogen is usually chlorine or fluorine or a mixture thereof, preferably fluorine, the net halogen content being in the range of 1 to 10 wt.%, preferably 2 to 8 wt.%.

The isomerization is carried out under temperature conditions between about 250 and 400°C, preferably 270 to 360°C, pressures of 500 to 3000 psi H₂, preferably 1000 to 1500 psi H₂, hydrogen gas rates of 1000 to 10,000 SCF/bbl and a volume flow rate in the range of 0.1 to 10 V/V/hr, preferably 1 to 2 V/V/hr.

Preferred catalysts are the subject of US-A-4,959,337, US-A-4,906,601 and US-A-4,900,707.

The use of these catalysts to produce a lubricating oil base stock or base blend by the isomerization of paraffin is the subject of US-A-4,929,795, US-A-4,923,588 and US-A-4,937,399, respectively.

A most preferred catalyst is the subject of US-A-4,906,601. The use of this catalyst for paraffin isomerization is the subject of US-A-4,923,588.

This catalyst comprises a Group VIII noble metal on a refractory metal oxide base with small particle size and low fluoride content. The catalyst is characterized in that it has a fluoride content in the range of 0.1 up to, but less than, 2 wt.%, preferably 0.1 to 1.5 wt.%. particularly 0.2 to 1.0 wt.%, a particle diameter of less than 1/16 inch and a preferred noble metal loading in the range of 0.1 to 2.0 wt.%. The preferred fine particle support is 1/20 inch trilaminate alumina.

As expected, noble metal isomerization catalysts are extremely susceptible to deactivation by the presence of heteroatom compounds (i.e., N, O, or S compounds) in the paraffin feedstock, so care must be taken to remove such heteroatom materials from the paraffin feedstock batches. When working with high purity paraffins, such as synthetic Fischer-Tropsch paraffins, such precautions may not be necessary. In such cases, it may be sufficient to subject such paraffins to a very mild hydrogen treatment to ensure protection of the isomerization catalyst. On the other hand, paraffins obtained from natural petroleum sources contain amounts of heteroatom compounds, as well as significant amounts of oil containing heteroatom compounds. In such cases, the slack waxes should be hydrotreated to reduce the level of heteroatom compounds to levels commonly considered in the industry as tolerable for feedstocks subjected to isomerization catalysts. Such levels are typically an N content of about 1 to 5 ppm and an S content of about 1 to 20 ppm, preferably 2 ppm or less nitrogen and 5 ppm or less sulfur. Similarly, such slack waxes should be deoiled to an oil content in the range of 0 to 35% oil, preferably 5 to 25% oil, prior to hydrotreating. The hydrotreating step employs a typical hydrotreating catalyst such as Co/Mo or Ni/Mo on alumina under standard conditions recognized in the art, e.g. B. a temperature of 280 to 400ºC, a volume flow rate of 0.1 to 2.0 V/V/h, a pressure of 500 to 3,000 psig H₂, and hydrogen gas rates of 500 to 5,000 SCF/bbl.

The present invention will be more readily understood by reference to the following non-limiting examples.

Figure 1 shows how the miscibility of a Fischer-Tropsch isomer fraction of 8.7 cSt (8.7 mm²/s) at 100ºC boiling in the range of 550 to 575ºC (approximately corresponding to a viscosity grade of 250N) can be improved by about 10ºC by adding 33% of a conventional 150N base stock. Filtration studies were carried out on this combined feedstock and compared with evaluations of the base case, the pure Fischer-Tropsch paraffin isomer fraction of 8.7 cSt (8.7 mm²/s) at 100ºC. The isomerizate was prepared by isomerizing a 150% Fischer-Tropsch paraffin feed over an isomerization catalyst comprising 0.6% Pt/5.6% F/Al2O3 at a temperature between 365 and 375°C, a pressure of 1000 psig, a H2 flow rate of 7500 SCF/bbl and a liquid hourly flow rate (LHSV) of 1. The dewaxing values are given in Table 1.

In an effort to achieve the target pour point of -21ºC, the solvent composition of the MEK/MIBK system was lowered to 10% MEK and dewaxing of the 100% Fischer-Tropsch wax isomerizate at 8.7 cSt (8.7 mm²/s) at 100ºC was carried out at a filter temperature just below miscibility (degree of miscibility: -3). Typically for immiscible dewaxing, the process gave low spread at pour point filter temperature and high filter rates. However, as normally expected in immiscible dewaxing, the efficiency of the two liquid phase wash is very poor and the resulting low yield of 15.7% is unacceptable. Although not directly measured, it was calculated, based on typical values of immiscible dewaxing of isomerizate, that the product had a VI of about 158 and a viscosity at 100ºC of about 8.0 cSt (8.0 mm²/s). It has been observed that when moving from miscible dewaxing to immiscible dewaxing, miscible dewaxing, an increase in viscosity is common, while the VI shows very little change.

Switching to miscible dewaxing, as done in the second case, by increasing the filter temperature, increased the yield to acceptable levels, but the achievable pour point was increased to only -10ºC.

Using a blend of conventional 150N oil and Fischer-Tropsch paraffin isomerizate at 8.7 cSt (8.7 mm²/s) at 100ºC, the filter temperature can be reduced below the target pour point without immiscibility occurring. Low pour points (-21ºC) have been obtained with good yields. The low filtration rate of 5.2 m³/m²/day is not necessarily a cause for concern because plants operating with 600N feedstocks are typically designed for filtration rates of 4 to 6 m³/m²/day and techniques for managing these rates are known.

As one might expect, the product from the dewaxer is a mixture of conventional and non-conventional lubricant. Critical to the process is the successful separation of the light dewaxed oil from the heavy dewaxed oil, e.g. the light conventional oil from the heavier isomerized oil. Although any separation process (distillation, extraction, membranes, etc.) can be considered, the simplest and most straightforward process is distillation. For this reason, low boiling conventional lubricants are processed together with the relatively high boiling isomerized oils. It is interesting to note that this does not involve a large difference in viscosity qualities. Due to the highly paraffinic nature of the isomerized oil, it has a much higher boiling point than conventional feedstocks of the same viscosity. This difference in viscosity/boiling point relationship makes the separation of a 150N oil at 5.0 cSt and a Fischer-Tropsch paraffin isomerizate at 8.7 cSt quite feasible, as shown in Table 2.

The dewaxed oil product from the co-processing was separated into fractions which were then re-blended to largely the same specifications as individually processed dewaxed oil fractions would have (see Table 2).

Using the 40% to final boiling point blend, a product of 9.2 cSt (9.2 mm²/s), 148 VI, pour point -22ºC was made, leaving a conventional material of 4.7 cSt (4.7 mm²/s), 102 VI, pour point -22ºC. These specifications are very close to the source materials. Surprisingly, it has been found that not only is the dewaxing of the heavy oil fraction made easier by the process of dewaxing a heavy oil/light oil blend, but the yield of the dewaxed heavy oil is also higher. Thus, while 100 barrels of Fischer-Tropsch isomerize can be dewaxed to yield 15.7 barrels of oil with a pour point of -21ºC (15.7 LV%, see Table 1), when these same 100 barrels of Fischer-Tropsch isomerize are mixed with 50 barrels of 150N oil (to yield a total of 150 barrels of oil to be dewaxed), a total yield of dewaxed oil of 49.3% is obtained (74 barrels of DWO (dewaxed oil) based on 150 barrels of mixture), and it was found that after fractionation, 60% or 44.4 barrels (60% of 74 barrels) constituted the amount of oil with a VI, viscosity and pour point equivalent to the 15.7 barrels obtained when dewaxing the Fischer-Tropsch isomerize. alone. This increases the yield of high-quality, high-VI oil and at the same time makes dewaxing easier (see Figure 2).

The yield increase is much greater than would be obtained by simply mixing fractions of separately dewaxed Fischer-Tropsch isomerizate and 150N oil. Linear mixing of such fractions to give a final product with a VI of 148 would require a mixture of 84 LV% Fischer-Tropsch isomerizate/16 LV% 150N. This mixture would give a yield of only 18.7%, compared to the approximately 44% of product with a VI of 148 obtained by coprocessing. The oil product obtained by linear blending would also be of a different quality. While coprocessing would yield 44.4% of material with a VI of 148, 55.21 cSt (55.2 mm²/s) at 40ºC, 9.19 cSt (9.19 mm²/s) at 100ºC, linear blending would yield 18.7% of product with a VI of 148, 44.78 cSt (44.78 mm²/s) at 40ºC, 7.9 cSt (7.9 mm²/s) at 100ºC. Furthermore, co-processing followed by fractionation yields a light oil with a VI of 102 and a viscosity of 5, which is obviously superior to the 150N base oil fraction, which when dewaxed separately yielded a dewaxed oil with a VI of 90 and a viscosity of 5. Table 1 Evaluation of NCL/Conventional Co-Processed Dewaxing Feed Composition, % Fischer-Tropsch Isomerizate 8.7 cSt Solvent Composition, % Filter Temperature, ºC Degree of Miscibility, ºC Feed Filter Rate, m³/m²/day Wax Cake Liquid/Solid, V/V Dewaxed Oil Yield, wt.% (Wash-Filter Time) Dewaxed Oil Pour Point, ºC 1 cSt = 1 mm²/s Table 2 Dewaxed oil tests Fischer-Tropsch paraffin isomerizate/150N 2/1 dewaxed to -25ºC Distillate fraction tests Total remixture calculated by weight Distillate fraction, LV% Temperature, ºC Wt.% Act. Auto-pour point, ºC Cloud point (microtube), ºC API gravity at 60ºF Density at 15ºC Viscosity at cSt Refractive Index at 75ºC Blend Investigations Sample Dewaxed Oil Fischer-Tropsch Paraffin High VI fraction with viscosity of 9 from dewaxing the combined feed Low VI fraction with viscosity of 5 from dewaxing the combined feed Distillation fraction, LV% Viscosity at cSt Density at 15ºC Refractive index at 75ºC Pour point of dewaxed oil (auto pour point), ºC Cloud point of dewaxed oil (microtubes), ºC approx. 40 to final boiling point

Claims (4)

1. A process for producing high boiling dewaxed oils having a high viscosity index (VI) and a pour point of -21°C or below by solvent dewaxing under miscible conditions using dewaxing solvents having low miscibility, which comprises combining a low boiling waxy oil having a conventional VI with the high boiling high VI oil and processing the mixture together under conventional miscible solvent dewaxing conditions using dewaxing solvents having low miscibility selected from a C3 to C6 ketone or a mixture of two or more C3 to C6 ketones, wherein the high boiling high VI oil is any natural petroleum oil, hydrocracked oil or oil obtained by the isomerization of wax, the oil having a viscosity in the range of 6 to 10 cS (6 to 10 um²/s) at 100°C, an average liquid volume (LV) % boiling point of 450 to 550°C and a VI of at least about 120 and the low boiling conventional VI paraffinic oil has a viscosity of 3 to 7 cS (3 to 7 um²/s) at 100°C, a 90% boiling point that is 0 to 300°F (0 to 166.7°C) lower than the 10% boiling point of the high boiling high VI oil, and a VI of less than about 110, wherein the amount of the low boiling conventional VI oil added to the high boiling high VI oil is in the range of 5 to 50 vol.%. 2. The process of claim 1 wherein the high boiling high VI oil has a viscosity in the range of 8 to 10 cS (8 to 10 um2/s) at 100°C, an average LV% boiling point of 475 to 525°C, and a VI of at least 140. 3. The process of claim 1 or claim 2 wherein the low boiling conventional VI oil has a viscosity of 4 to 6 cS (4 to 6 µm²/s) at 100°C, a 90% boiling point that is 50 to 100°F (27.8 to 55.6°C) lower than the 10% boiling point of the high boiling high VI oil, and a VI of less than about 100. 4. A process according to any one of claims 1 to 3, wherein the amount of low boiling conventional VI oil added to the high boiling high VI oil is in the range of 20 to 40 vol.%.