IMPROVED PROCESS FOR PRODUCING ALKYLATED AROMATIC FLUIDS This invention relates to an improved process for alkylating aromatic compounds in the production of lubricant fluids. The invention particularly relates to an improvement in the production of monoalkyl aromatic alkylates prepared by zeolite catalysis that yields an essentially colorless lubricant fluid of superior thermal stability.

Alkylaromatic fluids are well known in the synthetic lubricant and specialty fluid arts where fluids having good thermal and oxidative stability are required. U. S. patent 4,714,794 describes monoalkylated naphthalenes as having excellent thermal and oxidative stability sufficient to allow their use as thermal medium oils. U. S. patents 4,211,665 and 4,238,343 describe the use of alkylaromatics as transformer oils.

The preparation of alkylaromatics of lubricant quality is carried out usually by alkylation of aromatics in the presence of an acidic Friedel-Kraft alkylation catalyst like aluminum trichloride as described in U. S. patents 4,211,665 and 4,238,343. The use of various zeolites including intermediate pore size zeolites such as ZSM-5 and large pore size zeolites including L and ZSM-4 for alkylation of various monocyclic aromatics such as benzene is disclosed in U. S. patent 4,301,316.

For many applications the preferred form of the alkylaromatic is the mono- substituted alkylaromatic. While monoaromatics are obtained in admixture with polysubstituted alkyaromatics when conventional Friedel-Kraft catalyst are used, U. S. patent 5,034,563 teaches that a high selectivity of monoalkyl substitution can be achieved when large pore size zeolites exemplified by zeolite Y are employed as alkylation catalyst to yield lube-range alkylates. However, when the zeolite alkylation catalyst is obtained directly from a catalyst supplier and used as such the liquid alkylaromatic products produced are often colored and of poor thermal-oxidative stability.

It is an objective of the present invention to provide a process to produce alkylaromatic fluids of consistently superior properties that are essentially colorless and of high thermal-oxidative stability using large pore zeolite catalysis wherein the

catalyst is commercially obtained as conventional, untreated zeolite from zeolite catalyst vendors.

A method has been discovered for alkylating aromatic compounds employing zeolite catalysts to produce essentially colorless, predominantly monoalkyl aromatic fluids useful as lubricants that exhibit improved thermal oxidative stability. Surprisingly, it has been found that the product color and poor thermal stability that typically results from aromatics alkylation reactions using preferably large pore acidic zeolite catalyst obtained from vendors is eliminated or substantially improved when the vendor's catalyst is pretreated to lower moisture content, hydration water content and absorbed-oxygen content before the alkylation reaction.

While customary practice using zeolite catalysis for aromatic alkylation teaches the need to have some water in the form of hydrated cations in the catalyst in order to activate the catalyst, the present discovery runs contrary to those teachings, yet consistently produces an improved product. Consequently, regardless of the source or prior custody of the zeolite catalyst, the process of the invention compels the pretreatment of zeolite alkylation catalysts to lower moisture content, water of hydration and absorbed oxygen and assure the production of an aromatics alkylate that is improved with respect to color and thermal stability.

The catalyst pretreatment step of the invention can be carried out by heating the catalyst in an inert atmosphere, preferably in contact with an inert gas purge stream or in vacuo, for a time sufficient to remove entrained water, water of hydration and absorbed oxygen. The time required depends on the vigor of the pretreatment step which can range from temperatures between 50°C and 500°C under subatmospheric, atmospheric or supraatmospheric pressure.

The alkylation process of the invention involves the alkylation of aromatic compound (s) with olefins as alkylating agent in contact with pretreated solid, acidic zeolite catalyst particles to produce thermally stable and essentially colorless aromatic compound (s) that are predominantly monoalkylated and useful as lubricant fluids.

The alkylation reaction between the aromatic compound and the alkylating agent is carried out in the presence of a pretreated zeolite having a pore size of at least 5 to permit the relatively bulky alkylated product to be released from the catalytic site within the zeolite pore. Large pore size pretreated zeolite catalysts are the most useful catalysts for the purpose although less highly constrained intermediate pore size zeolites may also be used. The large pore size zeolite are zeolites such as faujasite, synthetic faujasites (zeolite X and Y), zeolite L, ZSM-4, ZSM-18, ZSM-20, mordinite and offretite which are characterized by the presence of a 12-membered oxygen ring system in the molecular structure as described in Chen et al,"Shape- Selective Catalysis in Industrial Applications", Chemical Industries Vol. 36, Marcel Dekker Inc., New York, 1989. The large pore zeolites may also be characterized by a "Constraint Index"of not more than 2, in most cases not more than 1. Zeolite beta is included in this class although it may have a"Constraint Index"approaching the upper limit of 2. The method for determining Constraint Index is described in U. S. patent 4,016,218 together with values for typical zeolites and the significance of the Index is described in U. S. patent 4,816,932 to which reference is made for a description of the test procedure and its interpretation.

A highly useful large pore zeolite for the production of monoalkylated aromatics of the invention is pretreated zeolite Y in the ultrastable form, usually referred to as USY. Zeolite USY or zeolite Y, unpretreated by the method of this invention, is a material of commerce, available in large quantities as a catalyst for the cracking of petroleum. Zeolite Y may be bound with silica, alumina, silica-alumina or other metal oxides. It may have a SiO2-to-AI203 ratio of from 3-500, and be partially exchanged with rare earth elements, with ammonium cation or other cations. Reference is made to Wojoiechowski,"Catalytic Cracking: Catalysts, Chemistry and Kinetics", Chemical Industries Vol. 25, Marcel Dekker, New York, 1986, for a description of zeolite USY, its preparation and properties. Large pore zeolites also include Zeolite X, zeolite L, ZSM-4, ZSM-18, ZSM-20, mordenite and Offretite.

Zeolite MCM-22 is also a useful catalyst for this reaction. MCM-22 is described in U. S. Patent 4,954,325 to M. K. Rubin and P. Chu.

Zeolite catalysts of the invention, such as the preferred zeolite Y, are article of commerce and may be obtained from catalyst manufactures. As so obtained they can be used as catalyst for aromatics alkylation to produce lube range alkylates with high selectivity for mono-alkylates as described in U. S. patent 5,034,563. However, the lube alkylate of such a process using zeolite catalyst obtained directly from the catalyst suppliers often is colored and exhibits very poor thermal oxidative stability.

This limitation of the alkylation process is overcome by the catalyst pretreatment step of the present invention.

The pretreatment step of the present invention flows from the inherent discovery that zeolite aromatic alkylation catalysts that are low in moisture content, water-of-hydration content and absorbed-oxygen content consistently produce lube alkylates that have improved color and excellent oxidative and thermal stability. These catalysts produce these unexpected improved results while maintaining high productivity of lubes rich in monoalkylated aromatics of preferred viscometrics.

Commercially obtained zeolite aromatics alkylation catalyst have been found to be relatively rich in moisture content, water-of-hydration content and absorbed-oxygen content. Reducing the moisture content, water-of-hydration content and absorbed- oxygen content of commercially obtained zeolite catalyst by the pretreatment step of the invention has been found to yield a superior lube product.

Zeolite alkylation catalyst is pretreated by heating the solid catalyst particles for a time sufficient to lower the catalyst water content, water-of-hydration and absorbed oxygen content. Preferably and conveniently, the solid catalyst is heated in a vessel in bulk form but it is within the scope of the present invention to suspend the catalyst in an otherwise unreactive and inert liquid, with or without stirring, to enhance heat transfer to the solid catalyst and accelerate the pretreatment step. Vapor of the inert liquid may be removed periodically to carry off water vapor and oxygen from the catalyst. However, the zeolite alkylation catalyst is pretreated preferably by heating the solid catalyst in an inert gaseous environment at a temperature and for a time sufficient to lower the catalyst water content, water-of-hydration and absorbed oxygen content. Most preferably, the pretreatment is carried out in a vessel employing a moisture-free inert gas purge stream such as nitrogen or Group VIII gases of the

Periodic Table to remove water vapor and oxygen from the vessel. Optionally, the pretreatment may be carried out by heating the catalyst in vacuo in a closed vessel.

To those skilled in the chemical engineering arts, other means are well known to essentially dry solid particles by continuous or batchwise methods. These methods are included within the scope of the present invention to the extent that they can be applied to remove water, water-of-hydration and absorbed oxygen from solid zeolite alkylation catalyst particles. Zeolite alkylation catalyst can be pretreated by the process of the invention in a fixed bed, fluid bed or batchwise. Rather than employing a vessel, the solid catalyst particles can be transported through a column containing an inert liquid at an appropriate temperature or the solid can be carried through a heated or inert liquid-containing column by gas ebullition.

The catalyst water content, water-of-hydration and absorbed oxygen content of the zeolite catalyst particles can be effectively lowered by heating the catalyst at a temperature between 50°C and 250°C, but preferably at a temperature of 100°C.

One-half hour to twenty-four hours is a sufficient time to heat the catalyst, usually 1-5 hours; however, at a preferred temperature of 100°C in a vessel in the presence of a nitrogen purge stream four hours of heating has been found sufficient to pretreat the catalyst particles sufficiently to catalyze the preparation of a superior lube product.

The alkylation process of the invention is carried out by contacting the aromatic compound, alkylating agent and pretreated zeolite catalyst in a suitable alkylating reaction zone which may be a fixed catalyst bed, fluid bed or stirred reactor vessel.

Alkylating conditions include temperature between 50°C and 300°C, pressure from 0.2 to 250 atmospheres, fixed bed feed weight hourly space velocity from 0.1 hr~1 to 1 Ohr- 10 and an alkylatable aromatic compound to alkylating agent mole ratio from 0.1: 1 to 50: 1, preferably from 2: 1 to 1: 2.

Useful alkylatable aromatic hydrocarbons for the present invention include benzene, toluene, biphenyl, o, m, p-xylene, hemimellitene, pseudocumene, ethylbenzene, n-propylbenzene, cumene, n-butylbenzene, isobutylbenzene, sec- butylbenzene, tert-butylbenzene, p-cymene, biphenyl, diphenylmethane, triphenyl

methane, 1,2-diphenylethane and similarly alkyl substituted naphthalenes and anthracenes; also derivatives of aromatic hydrocarbons including phenol, hindered phenols such as 2,6-dimethyl phenol, catechol, acylphenol such as acetylphenol, carbonate esters such as phenyl methyl or ethyl carbonate and diphenyl carbonate, alkylphenol such as anisole, chloro and bromobenzene, aniline, acyl aniline such as acetanilide, methyl and ethylbenzoate, thiophenol and acylated thiophenol, nitrobenz- ene, diphenylether, diphenylsulfide and similarly substituted naphthalenes and anthracenes, in particular naphthols such as mono and dihydroxy naphthalene.

Useful olefinic alkylating agents for the present invention include C2-C20 linear or branched olefins, preferably C2-C20 linear or branched alpha olefins or vinylidene olefins such as t-butene, 2-methyl-1-pentene, 2,4,4-trimethyl-1-pentene and the like.

The most preferred olefins are alpha olefins such as 1-hexene, 1-octene, 1-decene, 1- dodecene and 1-hexadecene.

The zeolite catalyst pretreatment process of the present invention, the alkylation step and the properties of the lubricant fluids prepared by the process of the present invention are described in the following nonlimiting Examples 2-5 and compared with alkylation control Example 1 carried out without a zeolite catalyst pretreatment step.

EXAMPLE 1 (control-no catalyst pretreatment) Alkvlation Charge diphenylether (260gms, 1.5 mole), 1-hexadecene (112gms, 0.5 mole) and 11.3 gms (0.3wt%) of solid, calcine Ultrium x5210x1 catalyst particles (40% zeolite USY, alpha value 199, unit cell size 24.688) into a 500cc round bottom flask equipped with a magnetic stirrer, a thermocouple, a nitrogen-vacuum line and a sampling tube. Evacuate the system with vacuum to remove air and refill with nitrogen. Repeat this procedure for a total of three times and leave under nitrogen atmosphere. Heat the reaction mixture with stirring to 200°C. After 4 hours at reaction temperature take a sample and analyze on gas chromatograph (gc). Turn off the heat after 8 hours at reaction temperature and let the mixture cool down under nitrogen atmosphere. When the mixture has cooled down to room temperature remove the

catalyst by filtration of the reaction mixture through a glass fiber filter paper. Analyze the filtrate by gc. Conversion of 1-hexadecene is typically greater than 98%. Distill the filtrate at 90°C/<1 millitorr vacuum using a short path Kugelrohr apparatus to remove all unreacted diphenyl ether (2 hours). Cool the sample down under vacuum to room temperature. Analyze the lube product by gc to confirm complete distillation (<0.5% starting material). Repeat distillation if >0.5% SM. The lube product has a light orange-brown color and a hot-tube test rating at 305°C of 5 with heavy deposits.

EXAMPLE 2 (invention-catalyst pretreatment) Pretreatment Charge 11.3 gms (0.3wt%) of solid, calcined Ultrium x5210x1 catalyst particles (40% zeolite USY, alpha value 199, unit cell size 24.688) into a 500cc round bottom flask equipped with a magnetic stirrer, a thermocouple, a nitrogen-vacuum line and a sampling tube. Start a steady stream of nitrogen flow through the reactor. Heat the reactor to 100°C. Water starts to appear at the nitrogen exit line. Continue to purge the catalyst and reactor system with nitrogen at 100°C for at least 3 to 4 hours. When the hot purge is finished, no moisture is observed in the reactor system. Turn off the heat and let the reactor cool down overnight with a continued nitrogen purge.

Alkylation The next day, combine diphenyl ether and 1-hexadecene into a narrow mouth bottle and purge the mixture with nitrogen for half an hour. Immediately after the purge is complete, pour the organic liquid quickly into the round bottom flask containing dried catalyst. Evacuate the system with vacuum and refill with nitrogen to remove air. Repeat three times. Heat the reaction mixture with stirring to 200°C. After 4 hours at reaction temperature take a sample and analyze on gas chromatograph (gc). Turn off the heat after 8 hours at reaction temperature and let the mixture cool down under nitrogen atmosphere. When the mixture has cooled down to room temperature remove the catalyst by filtration of the reaction mixture through a glass fiber filter paper. Analyze the filtrate by gc. Conversion of 1-hexadecene is typically greater than 98%. Distill the filtrate at 90°C/<1 millitorr vacuum using a short path Kugelrohr apparatus to remove all unreacted diphenyl ether (2 hours). Cool the sample down under vacuum to room temperature. Analyze the lube product by gc to

confirm complete distillation (<0.5% starting material). Repeat distillation if >0.5% SM.

The lube product is colorless and has a hot-tube test rating at 305°C of 1-2.

EXAMPLE 3 (invention-catalyst pretreatment) Example 3 is a duplication of Example 2 and produces the same result, thus establishing reproducibility of the process of the invention.

EXAMPLE 4 (MCM-22 zeolite catalyst) Example 4 is the same as Example 2 except 1 wt% of a crushed MCM- 22/AI203 zeolite catalyst is used. The product basestock had a hot-tube test rating at 305°C of 1-2 with very low deposit formation.

EXAMPLE 5 (MCM-22 zeolite catalyst-no pretreatment) Example 5 is the same as control Example 1, except 1 wt% of a crushed MCM- 22/AI203 zeolite catalyst is used. The product basestock has a hot-tube test rating at 305°C of 7-8 with very low deposit formation.

Examples 1,2 and 3 show that pretreatment of catalyst and feed improved the lube product quality. Examples 4 and 5 show that pretreatment of catalyst and feed improved the product quality achieved by MCM-22 catalyst.

The following Table summarizes the results of Examples 1-5 showing that catalyst pretreatment following the process of the present invention leads to an increase in the preferred monoalkyl alkylation product, a colorless lubricant fluid and a significant improvement in thermal oxidative stability.

TABLE Example 1 Example 2 Example 3 Example 4 Example 5 no pre-catalyst & catalyst & catalyst & no pre- treatment feeds were feeds were feeds were treatment pretreated pretreated pretreated Reaction Time, hrs 8 8 8 6 8 1-C conversion, wt% >98 >98 >98 >98 >98 Lube Product Composition, wt% Mono alkyl 93.05 98.85 98.6 82.4 87.7 Di-alkyl 2.11 0.98 1.2 16.6 11.9 Others 4.84 0.17 0.2 1.0 0.4 Lube color Light Colorless Colorless Colorless Colorless Hot Tube Rating 5 1-2,2 1-2,1 1-2.2 7-8 @ 305°C (a) (a) Hot tube test was conducted at 305°C with oil feed rate at 0.35 cc/hr, air feed rate at 10cc/min., test duration 16 hours. Higher rating means heavier deposit. 1 is almost completely clean. 9 is heavy black carbon deposits.