Patent Application
20060138023
This invention relates to the hydroisomerization of waxy feeds including slack wax, slack wax isomerate, Fischer-Tropsch wax, Fischer-Tropsch hydroisomerate waxy raffinates, and waxy distillates to produce a lube oil basestock or blending stock. More specifically, this invention relates to the conversion of a waxy feed using a mixed catalyst having a preselected acidity capable of promoting the formation of a basestock having a predetermined (VI) within a range of VIs.
The performance criteria for lubricants such as those used in automatic transmission fluids and passenger car engine oils has become increasingly more severe with users requiring basestock that provide better wear protection, improved volatility and low temperature properties.
Waxy feeds can be converted to liquid products using well known catalytic dewaxing catalysts; however, in these instances the selective cracking of paraffms typically results in a loss of viscosity (VI) which is undesirable.
U.S. Pat. No. 4,428,865, Oleck, et al., claims a method to enhance the pour point and viscosity index of crude oils of high wax content by contacting the highly waxy feed with two different zeolites such as ZSM-5 and ZSM-35.
In contrast, isomerization of waxy feeds using molecular sieve based catalyst that have linear 1D pore structures produces lube basestocks without loss in VI. While these catalysts offer benefits over those used in catalytic dewaxing, there nonetheless remains a need for improved catalysts for converting waxy feeds to lube basestocks that can be tailored to produce basestocks having a predetermined quality and yield.
The presently disclosed invention is a method for hydroisomerizing a waxy feed to produce improved yield of a lube basestock which comprises:
In another embodiment of the present invention both the first and second component comprise at least one 8, 10 or 12 ring molecular sieve or a mixture thereof. Both the first and second component have a metal hydrogenation component dispersed thereon.
This and other embodiments of the invention will be discussed below.
The feed suitable in the practice of the present invention includes waxy hydrocarbon oils such as slack wax, slack wax isomerate, Fischer-Tropsch wax, Fischer-Tropsch isomerate waxy raffmates and waxy distillates. Typically, such feeds will have wax contents of 15% or more. The preferred feed will have a nitrogen and sulfur content each below about 20% or more. The preferred feed will have a nitrogen and sulfur content each below about 20 ppm by weight. Indeed, if the feed contains higher amounts of sulfur and nitrogen, the feed can be first subjected to hydrotreating under typical hydrotreating conditions to reduce the sulfur and nitrogen contents. Any of the conventional hydrotreating catalysts can be employed like Ni/Mo on alumina, Ni/W on alumina Co/Mo on alumina. In other words any of the Group VIB to Group VIII. (The groups referred to here and hereinafter are those metals of the Periodic Table of Elements; Sargent-Welch Scientific Co.) on metal oxide refractory supports may be employed. Non-limiting commercial examples of such are identified as HDN-30, KF-840, and KF-848, etc.
Hydrotreating is conducted so as to lower the sulfur and nitrogen contents to levels of 20 wppm or less nitrogen or 20 wppm or less sulfur especially 10 ppm less nitrogen and 10 ppm or less sulfur and most preferably to levels below 5 ppm for nitrogen and 5 ppm or less for sulfur.
Waxy feeds secured from natural petroleum sources contain quantities of sulfur and nitrogen compounds which are known to deactivate wax hydroisomerization catalysts. To prevent this deactivation it is preferred that the feed contain no more than 10 ppm sulfur, preferably less than 2 ppm sulfur and no more than 2 ppm nitrogen, preferably less than 1 ppm nitrogen.
To achieve these limits the feed is preferably hydrotreated to reduce the sulfur and nitrogen content.
Hydrotreating can be conducted using any typical hydrotreating catalyst such as Ni/Mo on alumina, Co/Mo on alumina, Co/Ni/Mo on alumina, e.g., KF-840, KF-843, HDN-30, HDN-60, Criteria C-411, etc. Similarly, bulk catalysts comprising Ni/Mn/Mo or Cr/Ni/Mo sulfides as described in U.S. Pat. No. 5,122,258 can be used.
Hydrotreating is performed at temperatures in the range 280° C. to 400° C., preferably 340° C. to 380° C. at pressures in the range 500 to 3000 psi, hydrogen treat gas rate in the range of 500 to 5000 SCF/bbl and a flow velocity in the range 0.1 to 5 LHSV, preferably 1 to 2 LHSV.
The hydrotreated waxy oil is stripped to remove ammonia and H2S and then is subjected to the hydroisomerization process of the present invention.
The catalyst employed in the hydroisomerization of waxy feeds in accordance with the present invention is a unitized mixed powdered pellet catalyst.
The term “unitized” as used here and in the claims means that each pellet is one made by mixing together a powdered first component with a powdered second component and pelletizing the mixture to produce pellets each of which contain all of the powder components previously recited.
The unitized catalyst can be prepared by starting with individual finished powdered components pulverizing and powdering such individual finished components, mixing the powdered materials together to form a homogeneous mass, then compressing/extruding and pelleting thus producing the unitized pellet catalysts. Pulverizing and powdering is to a consistency achievable using a ball mill or other such conventional powdering means to a particle size less than 100 microns.
The first component is a catalytic dewaxing component including crystalline 8, 10 and 12 ring molecular sieves. Crystalline molecular sieves include alumino silicates and alumino phosphates. Examples of crystalline alumino silicates include zeolites such as erionite, chabazite, ZSM-5, ZSM-11, ZSM-12, Theta-1 (ZSM-22), ZSM-23, ZSM-35, natural and synthetic ferrierites, ZSM-48, ZSM-57, SSZ-31, beta, mordenite, offretite, ECR-42, MCM-71, and ITQ-13. Examples of crystalline aluminum phosphates include SAPO-11, SAPO-41, SAPO-31, MAPO-11 and MAPO-31. Preferred molecular sieves include ZSM-5, ZSM-22, ZSM-23, ZSM-48, ferrierites, SSZ-31, SAPO-11, ECR-42, MCM-71, and ITQ-13. The most preferred molecular sieves are ZSM-48, ECR-42, MCM-71, SSZ-31, and ITQ-13.
The second isomerization component can be any of the typical isomerization catalyst such as those comprising amorphous refractory metal oxide support base (e.g., alumina, silica, zirconia, titania, silica-magnesia, silica-alumina, etc.) on which has been preferably deposited a catalytically active metal selected from Group VI B, Group VII B, Group VIII metals and mixtures thereof, preferably at lease one Group VIII metal, more preferably at least one noble Group VIII metal, most preferably Pt, Pd, and mixtures thereof, and optionally including a promoter or dopant such as halogen, phosphorus, boron, yttria, magnesia, etc., preferably halogen, yttria or magnesia, most preferably fluorine. The catalytically active metals are present in the range 0.1 to 5 wt %, preferably 0.1 to 3 wt %, more preferably 0.1 to 2 wt %, most preferably 0.1 to 1 wt %. The promoters and dopants are used to control the acidity of the isomerization catalyst. Thus, when the isomerization catalyst employs an acidic material such as silica-alumina, acidity of the resultant catalyst is reduced by addition of a basic material such as yttria or magnesia or by controlling the ratio of silica:aluminum in the silica-alumina.
The metal hydrogenation component can be deposited on either the first dewaxing component, the second isomerization component or preferably on both the first and second components. The metal is selected from at least one of Group VIB and Group VIII, preferably Group VIII, more preferably Pt, Pd and mixtures thereof. The amount of metal can range from 0.1 to 30 wt %, based on catalyst. If the metal is Pt or Pd., the preferred amount is from 0.1 to 5 wt %, based on catalyst. In order to maximize catalyst utilization, it is preferred that the metal dispersion be at least 0.3 (on a scale where 100% metal dispersion is 1.0) if the metal is only on one component. If the metal is on both components, then it is preferred that the metal dispersion (D) times the metal concentration (C) (i.e., D×C) on one of the components be at least 0.08.
The first and second components are combined in a ratio sufficient to promote wax isomerization and naphthene destruction without substantial decrease in VI. The zeolite to amorphous inorganic oxide ratios for catalysts according to the invention range from about 1:1 to 1:20 by weight, subject to the MCH test described below.
One technique for determining the proper ratio of first and second components in the catalyst is based on an evaluation of the combined components containing about 0.5 wt % Pt in converting methylcyclohexane (MCH) to various cyclopentane compounds. Catalyst that at 320° C. provide a ratio of trans 1,2-dimethylcyclopentane to trans-1,3-dimethylcyclopentane (trans-1,2/trans-1,3 DMCP) in the range of less than 1 have been found to promote maximum yields of basestocks whereas ratios in the range of greater than about 1 promote maximum VI.
The second factor is when the catalyst, impregnated with about 0.5 wt % Pt and evaluated in converting methylcyclohexane to various cyclopentane compounds at 10% conversion, exhibits a selectivity for ethylcyclopentane (ECP) formation above at least 50%.
This technique is further explained as follows. The reaction of MCH over the catalyst to various cyclopentane products is shown in
The key factors are summarized as follows: (1) total conversion of MCH for a given catalyst weight at 320° C. is an indication of the relative number of acid sites; (2) selectivity to ECP, at 10% conversion, is a measure of the relative acid strength wherein high ECP selectivity values indicates low acid strength and low ECP selectivity values indicates high acid strength; and (3) the ratio of trans-1,2-DCMP to trans-1,3-DCMP correlates with the constraint at the catalyst active site wherein a high ratio (>1) indicates little or no physical constraint at the active site and a low ratio (<1) indicates a physical constraint at the active site.
In the present process, to produce a catalyst that will give high yield, the ratio of trans-1,2-DCMP to trans-1,3-DCMP is adjusted to less than about 1 predominantly by controlling both the number and strength of the amorphous isomerization component. It is preferred to use lower acid strength amorphous components such as alumina.
Conversely, a catalyst that will maximize VI is produced by increasing the acid strength of the amorphous phase. In this case it is preferred to use higher acid strength amorphous components such as silica-aluminas or modified silica-aluminas. Another way of making such a catalyst is by changing the ratio of the microporous component to the amorphous component such that the unitized catalyst has a trans-1,2/trans-1,3 DMCP ratio of >1.
The hydroisomerization process utilizing the catalyst of the present invention is conducted at temperatures between about 200° C. to 400° C., preferably 250° C. to 380° C., and most preferably 300° C. to 350° C. at hydrogen partial pressures between about 350 to 5,000 psig (2.41 to 34.6 mPa), preferably 1,000 to 2500 psig (7.0 to 17.2 mPa), a hydrogen gas treat ratio of 500 to 10,000 SCF H2/bbl (89 to 1780 m3/m3), preferably 2,000 to 5,000 SCF H2/bbl (356 to 890 m3/m3) and a LHSV of 0.1 to 10 v/v/hr, preferably 0.5 to 5 v/v/hr, and more preferably 1 to 2 v/v/hr.
In an alternate embodiment of the present invention the waxy feed is first subject to solvent dewaxing to a pour point of the order of +10° C. or lower.
The dewaxing solvent used may include the C3-C6 ketones such as methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), mixtures of MEK and MIBK, aromatic hydrocarbons like toluene, mixtures of ketones and aromatics like MEK/toluene, ethers such as methyl t-butyl ethers and mixtures of same with ketones or aromatics. Similarly, liquefied, normally gaseous hydrocarbons like propane, propylene, butane, butylene, and combinations thereof may be used as the solvent. Preferably the solvent employed will be an equal volume mixture of methyl ethyl ketone and methyl isobutyl ketone. Typically the isomerate to solvent ratio will range between 1 to 10 and preferably will be about 1:3. The dewaxed feed is then subjected to hydroisomerizing as described hereinabove.
It is also contemplated herein that both the first and second components be at least one crystalline 8, 10 or 12 ring molecular sieves. It is also contemplated that both the first and second components be a mixture of 8, 10 or 10 ring molecular sieves. Thus, both the first and second components can be selected from any of the 8, 10 and 12 ring molecular sieves listed above, and mixtures thereof. It is preferred that the first component be ITQ-13 and the second component be selected from ZSM-48, ZSM-35, ZSM-22, ZSM-23, ZSM-57, SSZ-31, and mixtures thereof. It is more preferred that the first component be selected from ITQ-13, ZSM-57, and mixtures thereof, and the second component be selected from ZSM-22, ZSM-23, ZSM-35, ZSM-48, SSZ-31, and mixtures therof.
The metal hydrogenation component can be deposited on either the first dewaxing component, the second isomerization component or preferably on both the first and second components. The metal is selected from at least one of Group VIB and Group VIII, preferably Group VIII, more preferably Pt, Pd, and mixtures thereof. The amount of metal can range from 0.1 to 30 wt. %, based on catalyst. If the metal is Pt, Pd or a mixture thereof, the preferred amount is from 0.1 to 5 wt. %, based on catalyst. In order to maximize catalyst conversion, it is preferred that the metal dispersion be at least 0.3 if the metal is only on one component. If the metal is on both components, then it is preferred that the dispersion on one of the components be at least 0.3.
The first and second components are combined in a ratio sufficient to promote wax isomerization and naphthene destruction without substantial decrease in VI. The zeolite to amorphous inorganic oxide ratios for catalysts according to the invention range from about 1:1 to 1:20 by weight, subject to the MCH test described below.
One technique for determining the proper ratio of first and second components in the catalyst is based on an evaluation of the combined components containing about 0.5 wt. % Pt in converting methylcyclohexane (MCH) to various cyclopentane compounds. Catalyst that at 320° C. provide a ratio of trans 1,2-dimethylcyclopentane to trans 1,3-dimethylcyclopentane (t-1,2/t-1,3 DMCP) in the range of less than about 1 have been found to promote maximum yields of basestocks.
The second factor is when the catalyst, impregnated with about 0.5 wt. % Pt and evaluated in converting methyl cyclohexane to various cyclopentane compounds at 320° at 10% conversion, exhibits a selectivity for ethylcyclopentane (ECP) formation above at least 50%.
This technique is further explained as follows. The reaction of MCH over the catalyst to various cyclopentane products is shown in
The key factors are summarized as follows: (1) conversion of MCH at 320° C. is an indication of relative catalyst activity; (2) selectivity to ECP, at 10% conversion, correlates with catalyst acidity wherein high ECP selectivity indicates low catalyst acidity and low ECP selectivity indicates high catalyst acidity, and (3) the ratio of trans-1,2-DCMP to trans-1,3-DCMP correlates with the constraint at the catalyst active site wherein a high ratio (>1) indicates little or no constraint at the active site and a low ratio (<1) indicates a constrained geometry at the active site.
In the present process, the ratio of trans-1,2-DCMP to trans-1,3-DCMP is adjusted to less than about 1 predominantly by controlling the acidity of the amorphous isomerization component. It is preferred to use weakly acidic amorphous components such as alumina. Increasing the acidity of the amorphous phase generally increases the above-cited ratio.
The hydroisomerization process utilizing the catalyst of the present invention is conducted at temperatures between about 200° C. to 400° C., preferably 250° C. to 380° C. and most preferably 300° C. to 350° C. at pressures between about 500 to 5,000 psig (3.55 to 34.6 mPa), preferably 1,000 to 2000 psig (7.0 to 13.9 mPa), a hydrogen gas treat ratio of 500 to 10000 SCF H2/B (89 to 1780 m3/m3), preferably 2,000 to 5,000 SCF H2/B (356 to 890 m3/m3) and a LHSV of 0.5 to 5 v/v/hr, preferably 1 to 2 v/v/hr.
In an alternate embodiment of the present invention the wax feed is first subject to solvent dewaxing to a pour point on the order of +10° C. or lower.
The dewaxing solvent used may include the C3-C6 ketones such as methyl-ethyl ketone (MEK), methyl isobutyl ketone (MIBK), mixtures of MEK and MIBK, aromatic hydrocarbons like toluene, mixtures of ketones and aromatics like MEK/toluene, ethers such as methyl t-butyl ethers and mixtures of same with ketones or aromatics. Similarly, liquified, normally gaseous hydrocarbons like propane, propylene, butane, butylene, and combinations thereof may be used as the solvent. Preferably the solvent employed will be an equal volume mixture of methyl ethyl ketone and methyl isobutyl ketone. Typically the isomerate to solvent ratio will range between 1 to 10 and preferably will be about 1:3. The dewaxed feed is then subjected to hydrodewaxing as described hereinabove.
The present invention is demonstrated below in the non-limiting examples.
This example illustrates the yield -VI trade-off on a hydrocracker distillate (Feed A) for catalysts with different degrees of acidity in the amorphous component. The physical properties of the hydrocracker distillate (Feed A) are shown in Table 1.
The catalyst in Table 2 (column B) was made by combining the zeolite theta-1 (TON) in the powder form with alumina (BET Surface Area 190 m2/m3) in the powder form followed by intimate mixing so as to form a homogeneous powdered mixture and then forming into catalyst pellets by pressing in a die and sizing to the required mesh size. Both the TON and the alumina had been loaded with palladium in the powdered form using aqueous palladium tetraamine dinitrate (at pH=10) and palladium dichloride respectively before being intermixed.
The catalyst in Table 2 (column C) was made by combining the zeolite TON with silica-alumina (Si—Al) using the same technique as used in column A to produce a homogeneous powdered catalyst before forming into pellets. In this case, the palladium was loaded (as palladium tetraamine dinitrate) on to the finished unitized catalyst by incipient wetness.
Table 2 shows a comparison of activity and selectivity of these two catalysts for hydrodewaxing versus solvent dewaxing (column A). The acidity differences of each catalyst component and the corresponding finished unitized catalysts is also shown using the reaction of methylcyclohexane at 320° C. The table clearly shows the higher acidity (greater number and acid strength) silica-alumina catalyst (column C) gives lower yield but much higher VI compared with the very low acidity associated with alumina (column B) which results in high yield but a debit in VI.
This example further illustrates the yield-VI trade off and shows a comparison of activity and selectivity of two catalysts for hydrodewaxing a hydrocraker distillate (Feed B) versus solvent dewaxing. The physical properties of the hydrocracker distillate (Feed B) are shown in Table 3.
The methods of making two of these catalysts (columns B and C) were described in Example 1.
Columns B and C in Table 4 allow a comparison of the yields and VI's obtained by both catalysts. Again the least acidic catalyst (column B) exhibits higher yields with lower VI's compared with the higher acidic catalyst (column C).
This example further illustrates the yield-VI trade and shows a comparison of activity and selectivity of two catalysts for hydroisomerization a hydrocraker distillate (Feed B) versus solvent dewaxing. This example illustrates that by changing the relative amounts of microporous component to amorphous component the overall acidity of the unitized catalyst an be tailored to maximize yield or VI.
Table 5 compares two unitized catalysts both of which have been made by combining the powdered ZSM-5 (Si/Al ratio 110) with the powdered amorphous component in different ratios and then loading platinum by incipient wetness using platinum tetraamine dichloride. Table 5 shows a comparison of activity and selectivity for these catalysts for dewaxing hydrocracker Distillate B, the physical properties of which are shown in Table 3, with solvent dewaxing. The catalyst in column B which has a 1,2/1,3 DMCP ratio of <1 shows higher yield but lower VI than the catalyst in column C which has a 1,2/1,3 DMCP ratio >1.
This example illustrates that good hydrogenation metal dispersion is required for maximum catalyst conversion. However, the metal in a mixed powdered catalyst can be dispersed on the microporous component or on the amorphous component.
The catalysts in Table 6 were made by combining the zeolite theta-1 (TON) in the powder form with alumina (BET Surface Area 190m2/m3) in the powder form followed by intimate mixing so as to form a homogeneous powdered mixture and then forming into catalyst pellets by pressing in a die and sizing to the required mesh size.
The TON in the catalyst in column A had been loaded with platinum tetramine dinitrate before being intermixed with alumina.
The TON in the catalyst in column B had been loaded with palladium in the powdered form using aqueous palladium tetraamine dinitrate (at pH=10) before being intermixed with alumina.
The TON in the catalyst in column C had been loaded with palladium in the powdered form using aqueous tetramine dinitrate (at pH=10) before being intermixed with platinum loaded (as platinum dichloride) alumina.
The catalyst in column D was made as described in Example 1.
Table 6, columns A and B, compares the activity of two TON zeolite/alumina mixed powder catalysts in which the noble metal has been loaded only on the TON zeolite component. The Pd TON/alumina catalyst (column B), which has 12% metal dispersion, is shown to have much lower activity for pour point reduction than the Pt TON/alumina catalyst (column A) which has 65% metal dispersion.
Loading additional Pt or Pd on the alumina component (Column C, and Column D, respectively) improves the activity of the catalyst to the level of that observed in Column A.
Comments:
Good metal dispersion on zeolite - excellent catalyst activity.
Poor metal dispersion on zeolite - poor catalyst activity.
Poor metal dispersion on zeolite, good metal dispersion on support - good catalyst activity.
Dispersion of metal on support can be less than 50% and still give good initial catalyst activity.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US02/36521 | 11/12/2002 | WO | 11/28/2005 |
