EP0323759A2

EP0323759A2 - Olefin polymerization process with product viscosity and pour point control

Info

Publication number: EP0323759A2
Application number: EP88312436A
Authority: EP
Inventors: Henry Ashjian; Quang Ngoc Le; William Everett Garwood
Original assignee: Mobil Oil Corp
Current assignee: ExxonMobil Oil Corp
Priority date: 1988-01-06
Filing date: 1988-12-30
Publication date: 1989-07-12
Also published as: AU2771389A; EP0323759A3; ZA89141B; JPH01247490A

Abstract

This invention relates to conversion of light neutral viscosity range decene oligomers from a BF₃ polymerization process to higher viscosity products by reaction with ditertiary butyl peroxide. The products have reduced pour point and increased viscosity compared to products not utilizing ditertiary butyl peroxide. The process of the present invention eliminates the need for alkyl aluminum chloride or esters thereof.

Description

This invention relates to olefin polymerization processes; more particularly, this invention relates to olefin polymerization processes with product viscosity and pour point control.
At present, there is a trend to more severe service ratings for IC lubricants; for example, the SAE service ratings of SD and SF are obsolescent because more engine manufacturers specify an SF rating and it is expected that even more severe ratings will need to be met in the future as engine core temperatures increase in the movement toward greater engine efficiency. This progressive increase in service severity dictates a need to develop better lubricants; for example, lubricants with improved resistance to oxidation at high temperatures and higher VI requirements to ensure that the lubricants will have adequate viscosity at high temperatures without excessive viscosity when the engine is cold. In part, improved performance may be obtained by improved additive technology, but significant advances are needed in basestock performance to accommodate more severe service requirements.
It is known from US 3149178 and 3382291 to utilize BF₃ and AlCl₃, as catalyst, to polymerize olefins useful for producing synthetic lubricants.
The use of aluminium alkyl halide compounds is described in U.S. 4,041,098 and 4,469,910. The alkyl aluminium halide catalyzed process presents environmental problems and disposal problems considering the catalyst being utilized. Furthermore, the process is complicated.
The use of peroxide treatment for modifying the viscosity of various lubestocks including distillates and hydrocracked resids has been described in U.S. 3,128,246 and 3,594,320. Other peroxide treatment processes are described in U.S. 4,594,172 and 4,618,737. Peroxide treatment has not, however, previously been proposed for use with light neutral viscosity range decene oligomers from a BF₃ polymerization process.
The invention seeks to provide a process which eliminates the need for such alkyl aluminum chloride or esters thereof while providing a significant advance in the art by further reduction in pour point and increase in viscosity without significant change in viscosity index.
The present invention provides a process for producing a high viscosity index, low pour point synthetic lubricant from a 1-olefin feed, which process comprises:

(i) feeding to a reaction zone a stream (1) of a 1-olefin, having from 5 to 20 carbon atoms, saturated with BF₃ and a stream (2) of BF₃ complexed, in a 1:1 molar ratio, with a promoter, the BF₃ and the BF₃ complexed with a promotor being the sole catalyst system;
(ii) commingling streams (1) and (2) in a reaction zone under polymerization reaction conditions;
(iii) controlling the relative rate of addition of streams (1) and (2) to charge from 0.006 mole to 0.01 mole promotor per l00 g of 1-olefin;
(iv) recovering an oily liquid polymer; and
(v) subjecting the polymer to treatment with an organic peroxide compound to increase the viscosity and lower the pour point of the oily liquid polymer.

Figure 1 shows a schematic depiction of an alkylaluminum chloride process; and
Figure 2 shows a schematic depiction of a BF₃ catalyzed process.

The improved synthetic lubricants of the present invention are suitably produced from 1-decene, or from a mixture of 1-olefins, having between about 6 and about 12 carbon atoms, having a mean value of the olefin chain length of about 10 carbon atoms, although the 1-olefin charge can be any normally liquid 1-olefin having between about 5 and about 20 carbon atoms or mixtures of such 1-olefins. Examples of the 1-olefin charge are 1-pentene; 3-methyl-1-butene; 1-hexene; 3,3-dimethyl-1-butene; 2,3-dimethyl-1-butene; 1-heptene; 1-octene; 2,3,3-trimethyl-1-pentene; 2-ethyl-1-hexene; 1-decene; 1-undecene; 1-dodecene; 1-tetradecene; 1-hexadecene; 1-octadecene; and 1-eicosene, with 1-decene being preferred.
In accordance with this process, a 1-olefin charge is saturated with BF₃, suitably at room temperature, before it is charged to the reaction zone. The second stream that is charged to the reactor is a 1:1 molar complex of BF₃ and a promotor compound. This complex, upon contacting the first stream in the reactor, effects the polymerization reaction.
The promoter compound used to form BF₃-promoter catalyst complexes include, by way of example, water; alcohols, such as octanol and 1-decanol; acids, such as acetic acid, propionic acid, and butyric acid; ethers, such as diethyl ether; acid anhydrides such as acetic acid anhydride and succinic anhydride; esters, such as ethyl acetate and methyl propionate; ketones, such as acetone; and aldehydes, such as benzaldehyde. The rate of addition of stream (2) is conveniently expressed in terms of moles of promoter per weight unit of olefin. This rate will be between 0.006 mole promoter and 0.01 mole promoter per 100 g. of 1-olefin charge.
The reaction temperature employed is generally below 60°C and preferably between 0°C and 35°C. The reaction can be carried out at atmospheric pressure, but moderate pressures from about 1 psig up to about 500 psig are preferred.
The present process is suitably used with neutral lube feeds, that is, a vacuum stripped bottoms fraction of the oily liquid polymer, ranging from light neutrals, that is, from 100 SUS at 100°F to heavy neutrals, that is, 700 SUS at 100°F. Typical light to medium neutral stocks may have an IBP below 650°F (about 345°C) (ASTM D-2887) and the end point may be below 1000°F (about 540°C). Heavier neutrals will generally boil in the range 650°F to 1050°F (about 345°C to 565°C, ASTM D-1160, 10 mm Hg), typically from 750°F to 1050°F (about 400°C to 565°C, ASTM D-1160).
Figure 2 schematically depicts the process of the invention. The first step is the BF₃ polymerization process. The oligomers formed (oily liquid polymer) includes the light neutral viscosity range oligomers. This synthetic lubrication product can be washed as shown, using conventional techniques.
Figure 2 further shows a stripping step used to separate the light neutral viscosity range oligomer. It can occur in an autoclave under vacuum. The peroxide treatment can precede or follow the distillation step. Treatment before stripping is preferred.
Depending upon the quantity of residual unsaturation in the distillate product, it may be desirable to carry out a final hydrotreatment to remove at least some of these unsaturates and to stabilize the product.
Conventional hydrotreating catalysts and conditions are suitably used. Catalysts typically comprise a base metal hydrogenation component such as nickel, tungsten, cobalt, nickel-tungsten, nickel-molybdenum or cobalt-molybdenum, on a inorganic oxide support of low acidity such as silica, alumina or silica-alumina, generally of a large pore, amorphous character. Typical hydrotreating conditions use moderate temperatures and pressures, e.g. 100°-400°C (about 212°-750°F), typically 150°-300°C (about 300°-570°F), up to 20,000 kPa (about 3000 psig), typically about 2125-14000 kPa (about 300-2000 psig) hydrogen pressure. Space velocities of about 0.3-2.0, typically 1 LHSV, with hydrogen circulation rates typically about 600-1000 n.l.l.⁻¹ (about 107 to 5617 SCF/Bbl) usually about 700 n.l.l.⁻¹ (about 3930 SCF/Bbl).
As shown in Figure 2, the catalyst can be filtered after hydrogenation is complete.
The oily liquid polymer product is subjected to treatment with an organic peroxide compound at elevated temperature to affect a coupling between the polymer components to increase the viscosity of the lubricant. The treatment preferably occurs before stripping but can occur afterwards. The treatment can be repeated.
The preferred class of organic peroxides are ditertiary alkyl peroxides represented by the formula ROOR¹ where R and R¹, which may be the same or different, each represent tertiary alkyl groups, preferably lower (C₄ to C₆) tertiary alkyl groups. Suitable peroxides of this kind include ditertiary butyl peroxide, ditertiary amyl peroxide and tertiary butyl, tertiary amyl peroxide. Other organic peroxides may also be used including dialkyl peroxides with one to ten carbon atoms such as dimethyl peroxide, diethyl peroxide, dipropyl peroxide, di-n-butyl peroxide, dihexyl peroxide and acetylperoxides such as dibenzoylperoxide.
The amount of peroxy compound used in the process is determined by the increase in viscosity which is desired in the treatment. In general, the increase in viscosity is related to the amount of peroxide used with greater increases resulting from greater amounts of peroxide. As a general guide, the amount of peroxide catalyst used will be from 1 to 50, preferably from 4 to 30 weight percent of oil. There is an essentially exponential relationship between the proportion of peroxide used and the viscosity increase, both with batch and continuous reaction. The presence of hydrogen may decrease peroxide utilization slightly, but significant increases in viscosity may still be obtained without other lube properties being significantly affected. The exception to this statement is that pour point is reduced.
It is practicable to cascade the effluent from a catalytic hydrotreating unit directly to a peroxide treatment reactor, permitting the hydrogen to remain in the stream. The coupling of components out of the lube boiling range would, in this case, increase lube yield and for this reason may represent a preferred process configuration.
The reaction between the lubricant component and the peroxide is carried out at elevated temperature, suitably at temperatures from 50°C to 300°C and in most cases from 100°C to 200°C. The treatment duration will normally be from 1 hour to 6 hours. There is no fixed duration because various starting materials will vary in their reactivity and amenability to coupling by this method. The pressure used depends upon the temperature and upon the reactants and, in most cases, needs to be sufficient only to maintain the reactants in the liquid phase during the reaction. Space velocity in continuous operation will normally be from 0.25 to 5.0 LHSV (hr⁻¹).
The peroxide is converted during the reaction primarily to an alcohol whose boiling point will depend upon the identity of the selected peroxide. This alcohol by-product may be removed during the course of the reaction by simple choice of temperature and pressure. Accordingly, temperature and pressure may be selected together to ensure removal of this product. The alcohol may be converted back to the peroxide in an external regeneration step and recycled for further use. If ditertiary butyl peroxide is used, the tertiary butyl alcohol formed may be used directly as a gasoline octane improver. Alternatively, it may be readily converted back to the original ditertiary butyl peroxide by reaction with butyl hydroperoxide in the presence of a mineral acid, as described in U.S. 2,862,973, with the butyl hydroperoxide being obtained by the direct oxidation of isobutane, as described in U.S. 2,862,973.
The reaction may be carried out batchwise or continuously. In either case, it is preferable to inject the peroxide compound incrementally to avoid exotherms and production of lower quality products associated with high reaction temperatures. If the reaction is carried out in a continuous tubular reactor, it is preferred to inject the peroxide compound at a number of points along the reactor to achieve the desired incremental addition.
The effect of the peroxide treatment is principally to increase the viscosity of the lubricant and reduce pour point without affecting a significant reduction in viscosity index or significant increase in cloud point. The increase in viscosity implies an increase in molecular weight. It is thought that the action of the peroxide is by the removal of hydrogen atoms to form free radicals in non-terminal positions which then combine with each other to form branched chain dimers which are capable of reacting even more rapidly than the monomer. Thus, the viscosity of the treated material increases rapidly in the presence of additional amounts of peroxide which generate new free radicals. The greater reactivity perceived with the initial dimer may be attributed to reactive tertiary hydrogens which are present in the dimers and higher reaction products but not on the paraffins present in the starting material. The greater reactivity of the dimers indicates that the incremental addition of successively smaller amounts of peroxide, particularly in continuous tubular reactor synthesis, will produce relatively greater progressive increases in viscosity. The reactivity also ensures that the range of molecular weights in the product will be narrower and that product quality will be more consistent.
The products of the present process are characterized by a high viscosity index coupled with a low pour point. Viscosity indices of at least 130, for example, 140 or 150 are characteristic of the products but with low pour points indicating a significant quantity of iso-paraffinic components. Pour points below 10°F for the base stock (that is, without pour point improvers or other additives) and in most cases below 5°F are readily obtained, for example, 0°F with correspondingly low Brookfield viscosities, for example, less than 2500b at -20°F. Use of the present viscosity and pour point modification process enables product viscosity to be increased from that of a light neutral to that of a heavy neutral or a bright stock with little or no adverse effect on viscosity index. Concurrently, pour point is reduced to generally less than -65°F and in general, less than -85°F. Thus, the present lubricant base stocks have an extremely good combination of properties making them highly suitable synthetic lubricants.
The following Examples illustrate the invention.

Comparative Example 1

A light neutral viscosity range lube is made from 1-decene as described in U.S. 3,382,291. Properties before and after hydrogenation are as follows:

	After Hydrogenation	Before Hydrogenation
Gravity, API	39.9	38.0
Specific	0.8256	0.8348
Pour Point, °F	less than -65	less than -65
K.V. 40°C, cs	28.54	27.98
K.V. 100°C, cs	5.55	5.47
K.V. 100°F, cs	31.1	30.5
K.V. 210°F, cs	5.67	5.58
SUS 100°F	147	144
SUS 210°F	44.8	44.5
Viscosity Index	135.9	135.1

Example 2

100 g. of hydrogenated stock from Example 1 is placed in a 500 ml round bottom flask equipped with a stirrer, thermometer, water condenser, condenser liquid take-off and dropping burette. The flask is heated to 150°C, and 20 g DTBP is added dropwise from the burette over a one hour period. The temperature is held at 150°C for an additional three hours, then raised to 185°C in the next two hours. The contents are then cooled to room temperature and topped first at atmospheric pressure to a pot temperature of 300°C, then under a vacuum of 0.1 mm pressure to a pot temperature of 190°C to remove any DTBP decomposition products not condensed in the take-off during the reaction period.

The 99.6 g of lube product had the following properties:

Gravity, °API	37.2
Specific	0.8388
Pour Point, °F	less than -65
KV at 40°C, cs	68.8
KV at 100°C, cs	10.55
KV at 100°F, cs	75.9
KV at 210°F, cs	10.86
SUS at 100°F	352
SUS 210°F	62.1
Viscosity Index	141.1

Example 3

100 g of stock from Example 1, which is not hydrogenated, is reacted with 20 DTBP in the same manner as described in Example 2. The 98.8 g of lube product had the following properties:

Gravity, °API	35.0
Specific	0.8499
Pour Point, °F	-65
KV at 40°C, cs	98.8
KV at 100°C, cs	13.6
KV at 100°F, cs	110.0
KV at 210°F, cs	14.0
SUS at 100°F	508
SUS at 210°F	74.0
Viscosity Index	138.5

The viscosity of this product charging the unhydrogenated oligomer is higher than that of Example 2, 508 vs. 352 SUS at 100°F.

Example 4

50 g of the lube product from Example 3 is reacted with 10 g DTBP in the same manner as described in Example 2. The 49.8 g of lube product had the following properties:

Gravity, °API	32.2
Specific	0.8639
Pour Point, °F	-40
KV at 40°C, cs	385.5
KV at 100°C, cs	38.5
KV at 100°F, cs	435
KV at 210°F, cs	39.7
SUS at 100°F	2012
SUS at 210°F	187
Viscosity Index	147.7

Example 5

The experiment in this example is carried out in a two gallon autoclave. 4934 g of stock (unhydrogenated oligomers as in Example 3) and 1233 g. of DTBP are added together to the autoclave. After purging with nitrogen, the autoclave is sealed with nitrogen at room pressure and gradually heated up to 150°C while stirring at 200 RPM. After heating at 150°C for three hours, the total liquid product is flashed at 150°C for 0.5 hour followed by nitrogen purging at 125°C for two hours to remove all by-products (alcohol and acetone). The lube product is then cooled to room temperature and discharged. The lube product had the following properties:

Specific Gravity	0.854
Pour Point, °F	-55
KV at 40°C, cs	210.4
KV at 100°C, cs	24.09
KV at 100°F, cs	235
KV at 210°F, cs	24.8
SUS at 100°F	1091
SUS at 210°F	119
Viscosity Index	142.5

The autoclave experiment shows much higher viscosity compared to the glassware experiment in Example 3 (1091 vs 508 SUS at 100°F and 143 vs 138.5 VI) although the DTBP dosage used is only slightly higher (20 wt% vs 16.7 wt% DTBP). Thus, the peroxide utilization is improved with the closed autoclave experiment because of better contact and the elimination of peroxide loss due to evaporation.

Example 6

An alkyl aluminum chloride polymerization process is used to make the following high viscosity lube stocks from 1-decene. This process is described in U.S. Patent Nos. 4,041,098 and 4,469,910. A schematic presentation appears in Fig. 1.

Pour Point, °F	-50	-30
KV at 40°C, cs	80.4	390.7
KV at 100°C, cs	11.7	38.8
KV at 100°F, cs	89	440
KV at 210°F, cs	12	40
SUS at 100°F	42.5	2038.1
SUS at 210°F	66.4	188.0
Viscosity Index	138.0	147.3

These properties compare with those with about the same viscosity from the combination BF₃-DTBP process as follows:

	Alkyl		Alkyl
Process	Aluminum Chloride	BF₃-DTBP	Aluminum Chloride	BF₃-DTBP
Example	6	3	6	4
KV at 40°C, cs	80.4	98.8	390.7	385.5
KV at 100°C, cs	11.7	13.6	38.8	38.5
Viscosity Index	138.0	138.5	147.3	147.3
Pour Point, °F	-50	-65	-30	-40

The results show that in all comparisons the combination BF₃-DTBP process gives a lower pour point and the same or higher viscosity index.
The combination of BF₃-DTBP process eliminates the need for alkyl aluminum chloride to make higher viscosity polyalpha olefin lubricants which cannot be made with BF₃ alone. Additionally, because the need for alkyl aluminum chlorides is avoided, the process of the present invention avoids environmental and disposal problems incurred in the use of the alkyl aluminum chloride process. Thus, environmental problems in disposing of the alkyl aluminum chloride heel are avoided. Moreover, corrosion of vessels and lines and a complicated process utilizing extensive washing necessary with the alkyl aluminum chloride process are avoided.
The DTBP step can be integrated into the BF₃ process preferably before the vacuum stripping step. Product yield for the combined BF₃-DTBP process will still be 99% compared to 90 to 93% for the alkyl aluminum chloride process.

Claims

1. A process for producing a high viscosity index, low pour point synthetic lubricant from a 1-olefin feed, which process comprises:

(i) feeding to a reaction zone a stream (1) of a 1-olefin, having from 5 to 20 carbon atoms, saturated with BF₃ and a stream (2) of BF₃ complexed, in a 1:1 molar ratio, with a promoter, the BF₃ and the BF₃ complexed with a promotor being the sole catalyst system;

(ii) commingling streams (1) and (2) in a reaction zone under polymerization reaction conditions;

(iii) controlling the relative rate of addition of streams (1) and (2) to charge from 0.006 mole to 0.01 mole promotor per 100 g of 1-olefin;

(iv) recovering an oily liquid polymer; and

(v) subjecting the polymer to treatment with an organic peroxide compound to increase the viscosity and lower the pour point of the oily liquid polymer.

2. A process according to Claim 1, wherein the peroxide comprises a ditertiary alkyl peroxide.

3. A process according to Claim 2, wherein the peroxide comprises ditertiary butyl peroxide.

4. A process according to any preceding claim, wherein the polymer is treated with the peroxide at a temperature from 100° to 300°C.

5. A process according to any preceding claim, wherein the amount of peroxide used to treat the polymer is from 1 to 50 weight percent of the polymer.

6. A process according to any preceding claim which further comprises washing the polymer prior to treatment with the peroxide compound.

7. A process according to any preceding claim which further comprises stripping the polymer prior to treatment with the peroxide compound to recover a light neutral viscosity range oligomer.

8. A process according to any preceding claim which further comprises stripping the polymer, after treatment with the peroxide compound, to recover a light neutral viscosity range oligomer.

9. A process according to Claim 7 or 8 which further comprises hydrogenating the light neutral viscosity range oligomer.

10. A process according to any preceding claim, wherein the 1-olefin comprises 1-decene.

11. A process according to any preceding claim which further comprises repeating the organic peroxide compound treatment.

12. A process according to any preceding claim, wherein the polymer is treated with organic peroxide compound in an autoclave under vacuum.