US3270065A - Recovery from metal-free oxygenated alcohol products arising during mod- ified oxidation of aluminum alkyls - Google Patents

Description

United States Patent "ice 3,270,065 RECUVERY FROM METAL-FREE OXYGENATED ALQOHUL PRODUCTS ARESING DURING MOD- lllFlED OXIDATIUN 61F ALUMINUM ALKYLS Adolph A. Austin, Colonia, NJL, assignor to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed .lluly 6, 1961, Ser. No. 122,102 4 Claims. (Cl. 260-632) The invention relates to the oxidation of hydrocarbyl aluminum compounds, especially trialkyl aluminum compounds. More particularly, the invention concerns a process in which trialkyl aluminum compounds are oxidized in two stages with a stripping step between the oxidation stages.

It is known that high molecular weight aluminum hydrocarbons can be prepared by either growing an alpha olefin, such as ethylene, on an aluminum hydrocarbon, e.g. triethyl aluminum, or displacing one or all of the hydrocarbyl groups in an aluminum hydrocarbon compound with a mixture of higher alpha olefins. For instance, higher boiling alpha olefins can be reacted with triisobutyl aluminum to form aluminum hydrocarbons having organic moieties corresponding to the alpha olefins. These higher molecular weight aluminum hydrocarbons are useful in the preparation of alcohols. US. Patent 2,892,858 describes a method of oxidizing these aluminum compounds to form aluminum alcoholates which are then hydrolyzed to release the alcohol product. The aforementioned patent discloses that sometimes there are hydrocarbons in the olefin feed used to manufacture the aluminum hydrocarbons that are inert and therefore are not converted in the oxidation reaction. It is suggested that these hydrocarbons can be separated from the product by distilling the aluminum alcoholates under vacuum.

While the conventional methods for preparing straight chain primary alcohols from aluminum hydrocarbons are suitable where alcohol purity and yields are not critical, these processes have undesirable limitations where such things are important. It is an object of the present invention to increase the conversion of the hydrocarbon moieties in the organoaluminum feed to oxygenated compounds and to prevent the loss of oxygenated products when the hydrocarbon contaminants in the oxidation reaction mixture are stripped out. Another object of the invention is to improve the yield of alcohol product. Still another object is to prepare straight chain primary monohydric alcohols that are essentially free of hydrocarbon contaminants and which are highly useful in the manufacture of detergents and polymer plasticizers.

These and other objects, which will be apparent from the subsequent description of the invention, are accomplished by carrying out the oxidation reaction in two stages and stripping the partially oxidized aluminum hydrocarbons recovered from the first oxidation step prior to completing the oxidation in the second step. As mentioned above, the aluminum hydrocarbons prepared by the growth reaction or the displacement reaction (wherein a mixture of olefins is used) are usually contaminated with a small quantity of difiicult to remove hydrocarbons that are either in the olefin feed use dto make the aluminum compounds or are formed in the preparation of the higher molecular weight aluminum hydrocarbons. These hydrocarbons which consist mainly of olefins and some parafiins are essentially removed in the stripping step.

The hydrocarbon-free partially oxidized product is then further oxidized to avoid the formation of additional hydrocarbon impurities. The final oxidation product consists substantially of the alcoholate and other oxygenated products, particularly esters. The esters are easily converted into useful alcohols, preferably by hydrogenation after 3,278,865 Patented August 3@, 1966 the alcoholate has been hydrolyzed in accordance with any of the known methods.

One of the advantages of the present process over the prior art methods is that the hydrocarbon product recovered when the partially oxidized aluminum hydrocarbon is stripped consists of substantially pure alpha olefins which can be utilized in other reactions, such as the above-mentioned displacement reaction. Another advantage is that there is no loss of oxygenated products because the reaction mixture is stripped when there is no significant amount of free oxygenated non-metal compounds present in the mixture.

The aluminum hydrocarbon feed used in the process is preferably a trialkyl aluminum in which each alkyl group contains from 2 to about 20 carbon atoms. Usually the aluminum compounds contain various alkyl groups, that is, a mixture of alkyl groups containing even carbon numbers. Since the higher molecular weight alcohols are more useful in the mahufacture of detergents and plasticizers, it is preferred to use a trialkyl aluminum feed in which the major proportion of the alkyl groups have carbon numbers bet-ween 8 and 16. The alcohols used to prepare plasticizers usually contain 8 or 10 carbon atoms' while the alcohols most suitable for detergent manufacture contain 10 to 14 carbon atoms.

Representative of the type of aluminum trial kyls in the feed are hexyl octyl dodecyl aluminum, butyl didecyl aluminum, hexadecyl tetradecyl dodecyl aluminum, etc. It is understood that the foregoing compounds merely indicate kinds of aluminum hydrocarbons that may be found in the mixed feeds.

The aluminum trialkyls can be prepared, as mentioned above, by reacting intermediate or high molecular weight olefins, such as a C to C alpha olefin fraction, with a relatively low molecular weight aluminum alkyl, e.g. aluminum trialkyl, under superatmospheric pressure and at an elevated temperature. Among the low molecular weight aluminum alkyl compounds that may be used in the displacement reaction are triisopropyl aluminum, diethyl aluminum hydride, ethyl aluminum dihydride, diethyl butyl aluminum and tri-n-butyl aluminum. The displacement reaction is illustrated by the following equation:

Another method of preparing aluminum hydrocarbons which can be converted into straight chain alcohols is by the so-called growth reaction. In this reaction a low or intermediate molecular weight aluminum alkyl is reacted with a low molecular weight alpha olefin to effect the addition or growth of the olefin in the alkyl radicals attached to the aluminum. In some cases a displacement reaction occurs before the growth reaction takes place.

Aluminum alkyls that can be utilized in the growth reaction preferably contain alkyl groups having 2 or 4 carbon atoms, although aluminum compounds containing alkyl radicals up to 8 carbon atoms can also be used. The aluminum alkyl is reactive with a low molecular weight olefin, preferably ethylene, at temperatures of to C. and pressures of 200 to 5000 p.s.i.g. Sometimes it is useful to employ an inert hydrocarbon diluent, such as n-hexane or benzene, in order to facilitate the reaction. The growth product comprises mainly aluminum hydrocarbons in which the alkyl radicals are different. Representative compounds have already been described herein.

The first stage of the oxidation of the aluminum hydrocarbon is usually effected under relatively mild conditions by means of a suitable molecular oxygen-containing oxidizing agent, such as air or dilute oxygen.

Oxygen itself can be used but this is not necessary because the reaction is exothermic and takes place without difficulty by simply bubbling air through the liquid reaction mixture. Because the reaction is highly exothermic it is necessary to cool the mixture as the oxidation proceeds in order to maintain the temperature below the decomposition temperature of the aluminum hydrocarbons (above about 150 C.). The reaction can be carried out at room temperature, but it is preferred to utilize moderately high temperatures, that is, about 50 to 100 C., because the aluminum alkyls are usually fluid at these temperatures and there is no need to use a diluent. If a diluent is necessary, any inert hydrocarbon liquid, such as a C to C aliphatic or cyclic hydrocarbon, can be employed. Typical :of the useful hydrocarbon diluents are n-hexane, cyclochexane and benzene. Sufficient diluent should be used to make the aluminum compounds fluid at the reaction temperature. The amount of diluent necessary to achieve this result varies bet-ween about and 50 wt. percent of the aluminum compound.

The molecular oxygen, which is preferably in the form of air, is bubbled through the liquid reaction mixture until approximately 0.8 mole of oxygen per mole of aluminum trialkyl has been taken up by the feed. The best results are obtained when about one-half to two-thirds of the oxidizable alkyl groups in the aluminum hydrocarbons are oxidized in the first step. This point is reached when about 0.7 to 1 mole of oxygen per mole of aluminum compound has reacted. The oxidation reaction is stopped at this point in order to avoid the formation of significant amounts of free oxygenated materials that would be lost in the stripping step. Depending upon the temperature, flow of oxygen and other conditions, the desired level of oxidation will be reached in from a few minutes to 3 or 4 hours. At temperatures of 50 to 100 C. and oxygen rates of about 2 to 5 liters per minute per mole of aluminum trialkyl, the reaction generally has reached the desired point after about 20 minutes to an hour.

From the above, it is apparent that time is not an important factor. Neither is pressure a critical condition because the reaction can satisfactorily be effected at substantially atmospheric pressure. Superatmospheric pressure, e.g., up to 5 atmospheres, can be used to prevent volatilization of lower boiling diluents when high oxidation temperatures are utilized.

Following the partial oxidation of the aluminum hydrocarbon feed, the hydrocarbon contaminants in the liquid reaction mixture are removed, usually by stripping at reduced pressures to avoid degradation of the partially oxidized aluminum compounds. While the oxidized aluminum hydrocarbons are more stable than the corresponding unoxidized compounds, they tend to decompose at temperatures above about 400 C. If a hydrocarbon diluent is not used in the oxidation reaction, the volatilized hydrocarbons consist principally of alpha olefins which can be used to make other chemicals. This is one reason why it is preferred to effect the oxidation reaction in the absence of diluents.

While the reaction mixture can be stripped at atmospherie pressure in some cases, in most instances it is necessary to utilize pressures below about 200 mm. of mercury absolute pressure and preferably not exceeding about 50 mm. of mercury. A convenient pressure at which the stripping can be carried out is between about mm. and 50 mm. The temperature and pressure utilized in this portion of the process are governed by those conditions which cause substantial decomposition of the partially oxidized material. While temperatures ranging from room temperature up to 400 C. can be used, it is preferred to effect the stripping at pot temperatures of 100 to 325 C., and, most advantageously, at temperatures of 200 to 300 C.

The stripping is continued until no more hydrocarbon is removed from the partially oxidized liquid reaction mixture. Usually the vapor taken overhead represents about 5 to 10 wt. percent of the total weight of the aluminum trialkyl feed.

The oxidation of the aluminum hydrocarbons is then completed in a second stage at a rapid rate. It is advantageous to carry out the second oxidation step in a short period of time because it has been found that the kind and amount of impurities in the final oxidation product depend mainly on the rate of oxidation during the last one-third or one-fifth of the oxidation reaction. Therefore it is important to use efficient agitation and large quantities of molecular oxygen in order to oxidize the last alkyl group in the aluminum trialkyl molecule as quickly as possible to the alcoholate, -i.e., Al(OR) The temperatures used in the second oxidation stage can be substantially the same as those employed in the first stage. Preferably, the final oxidation is effected at temperatures of 50 to C. under atmospheric or moderate pressures, e.g., up to 5 or 10 atmospheres. Pure oxygen or large amounts of air are rapidly bubbled through and admixed with the reactants in the liquid phase, preferably for periods not exceeding about an hour. If, for example, about 10 to 20 liters of oxygen per minute per mole of aluminum trialkyl are passed through the reaction mixture maintained at about 50 to 100 C., the oxidation will be completed in about 10 to 20 minutes. Completion of the oxidation is indicated when the off gas has the same composition as the inlet gas.

By using excess oxygen, i. e., 10 to 100% excess, little or no free hydrocarbon is formed in the second oxidation stage and more alcohols are prehydrolyzed than when mild conditions are used, e.g., a low oxygen rate. The vehicle used for the oxygen is not important and, therefore, air or oxygen diluted with nitrogen can be used in place of pure oxygen. The ester content of the final aluminum alcoholate product increases with an increased oxygen input rate. For example, increasing the oxygen rate from 0.2 to 20 liters per minute per mole of aluminum trialkyl causes the saponification number of the product to go from 2 to 7.

The final alcoholate product is hydrolyzed to release the alcohol product. The hydrolysis can be effected according to conventional processes with water, dilute acid or base. A preferred method comprises mixing the alcoholates with about 1 to 10 volumes of a dilute mineral acid solution at a slightly elevated temperature, e.g., about 30 to 70 C. It is generally best to carry out the hydrolysis with a tWo or threefold excess of dilute inorganic acid at an elevated temperature with good agitation. These conditions promote the hydrolysis reaction so that it is substantially complete in about 0.5 to 1 hour. Lower temperatures, for example room temperature, and stoichiometric amounts of the aqueous acid solution may be used if time is not an important factor.

Upon completion of the hydrolysis reaction, the freed alcohols separate into a distinct liquid layer which can be easily recovered from the lower aqueous layer by simply drawing off the latter layer or decanting the upper layer. The separated crude alcohol mixture contains about 5 to 10 wt. percent non-alcohol oxygenated materials, e.g., esters, which can be converted into alcohols by hydrogenation or saponification. It is preferred to hydrogenate the crude alcohols because more alcohols are recovered by this method.

The hydrogenation is suitably effected in the presence of a catalyst in the liquid phase, e.g., by the trickle process, at hydrogen pressures of 500 to 5000 p.s.i.g. and temperatures above 200 C. If a fixed catalyst bed is used, it will be found that space velocities in the order of 0.2 to 0.5, or as high as 2, volumes of liquid feed per volume of catalyst space per hour (v./v./hr.) are satisfactory at temperatures of 250 to 500 C., preferably 240 to 300 C., and hydrogen pressures of 1000 to 4000 p.s.i.g. Among the catalysts that can be used in the hydrogenation step are sulfated molybdenum oxide, cobalt and copper chromite catalysts. The catalysts usually contain about to 50 wt, percent of an inert carrier such as charcoal, kieselguhr, etc. The preferred catalyst is sulfated molybdenum oxide on charcoal. The liquid phase hydrogenation also reduces the concentration of carbonyl compounds in the alcohols and thus makes them more suitable for the manufacture of high quality plasticizers. Water, e.g., 5 to 10 wt. percent based on the feed, can be added to the reaction mixture to improve the selectivity.

Alternatively, the esters in the crude alcohol product can be saponified with a strong caustic aqueous solution, such as wt. percent sodium hydroxide. The saponification reaction can be carried out at 20 to 100 C. and atmospheric pressure over a period of 0.5 to 4 hours.

After the hydrogenation or saponification of the crude alcohols, they are recovered by conventional methods, such as decantation, and fractionally distilled into narrow cuts. The quality of the alcohols recovered by this process is similar to the best oxo alcohols that are commercially available. In addition to producing high quality alcohols, the process results in a substantial increase in alcohol yield. Yields up to 96% have been obtained by the present process as opposed to yields of 80 to 85% in prior art processes. Another advantage of the process is that the total oxidation time is decreased about 70% relative to the oxidation times reported in the prior art processes.

The invention further illustrated in the following specific examples.

Example 1 In a well mixed reactor, 250 g. of a growth aluminum trialkyl prepared by reacting ethylene with aluminum triethyl was oxidized with air at the rate of 1.3 l./min. for minutes at C. and atmospheric pressure until 7 liters of oxygen reacted with the mixed alkyls. The growth alkyls contained 7.7 wt. percent free hydrocarbon (olefins and paraflins) impurities and had an average alkyl chain length of 11.1 carbon atoms. The alkyl distribution in the aluminum trialkyl was as follows:

C No. of alkyl groups: Wt. percent of trialkyl 2 0.90 4 11.32 6 5.18 8 9.34 10 12.73 12 15.30 14 15.01 16 12.15 18 8.95 20 5.45 22 3.17 24 2.29 26 0.57

After the partial oxidation was completed, the reaction mixture was severely stripped at reduced pressure (down to 0.5 mm.) and 250 C. (pot temperature), thereby removing 19.5 g. of hydrocarbon overhead. The bottoms or residue from the stripping operation was then further oxidized at 50 C. and atmospheric pressure with 1.3 liters of pure oxygen/min. for minutes to rapidly finish the oxidation. No further oxygen pickup was noted after 30 minutes. The crude product (239.3 g.) contained mainly mixed aluminum alcoholates and other oxygenated compounds. The crude alcoholate mixture was hydrolyzed by mixing it with 5 wt. percent HCl solution at 40 C. for 30 minutes, and thereafter the crude alcohols were decanted from the aqueous layer, Analyses of the crude alcohols showed the product to consist mainly of straight chain alcohols with no more than 1 to 2 wt. percent hydrocarbon, and about 5 to 10 wt. percent esters and carbonyl compounds; ester and carbonyl numbers were 6.4 and 5.5, respectively. The mixed crude alcohols were hydrogenated in a rocking unit over a sulfated molybdenum oxide-charcoal (100:50 parts by weight) catalyst at 3000 p.s.i.g. at 240 C. and a v./v./hr. of 0.3 The liquid hydrogenated mixture was separated from the solid catalyst and it was found that the ester and carbonyl numbers were reduced to 2.5 and 0.5, respectively. Further analyses showed that these oxygenated products were converted to primary alcohols.

Example 2 Example 1 is repeated with the exception that the mixed crude alcohols are hydrogenated over a fixed bed of cobalt-kieselguhr (100250 parts by weight) catalyst.

Example 3 Example 1 is repeated except the crude alcohol mixture is admixed with about 10 grams of 20 wt. percent sodium hydroxide solution at room temperature and the alcohols are recovered from the saponfication mixture by decantation and distilled to further purify them.

It is not intended to restrict the present invention to the foregoing examples which are merely given to demonstrate some of the embodiments of the invention. It should only be limited to the appended claims in which it is intended to claim all of the novelty inherent in the invention as well as the modifications and equivalents coming within the scope and spirit of the invention.

What is claimed is:

1. A process for preparing an alcohol from a mixture of normally liquid aluminum trialkyls contaminated with hydrocarbon which comprises oxidizing a trialkyl aluminum in which each alkyl group contains from 2 to 20 carbon atoms with molecular oxygen until about 0.7 to 1 mole of oxygen per mole of aluminum trialkyl has reacted,

. stripping the hydrocarbon contaminant from the partially oxidized aluminum trialkyl at reduced pressure and temperatures of below 400 C., subjecting said partially oxidized aluminum trialkyl to a further rapid oxidation at a temperature of 50 to C. with a 10 to 100% molar excess of molecular oxygen per mole of unoxidized aluminum trialkyl thereby forming an alcoholate having the formula: Al(OR) wherein each R is a C to C alkyl group, hydrolyzing said alcoholate and byproduct esters, subjecting the alcoholate and byproduct esters to hydrolysis thereby forming a mixture of alcohols and esters, reacting said mixture with a material selected from the group consisting of hydrogenation agents and saponification agents to convert at least a part of the esters to alcohols and recovering the alcohols formed as a result of said hydrolysis and conversion.

2. A process in accordance with claim 1 in which the esters are converted to alcohols by reaction with hydrogen at elevated temperatures and pressures.

3. A process in accordance with claim 1 in which the esters are converted to alcohols by saponification of said esters with an aqueous solution of a strong caustic.

4. A process for preparing an alcohol from a mixture of normally liquid aluminum trialkyls contaminated with about 5 to 10 wt. percent hydrocarbons which comprises contacting an aluminum trialkyl containing from 2 to 20 carbon atoms per alkyl group with oxygen at temperatures up to 100 C. until about 0.8 mole of oxygen per mole of said aluminum trialkyls has reacted, stripping the hydrocarbon contaminant from the partially oxidized aluminum trialkyls at below about 200 mm. absolute pressure and temperatures below 400 C., subjecting the stripped, partially oxidized aluminum trialkyls to a further rapid oxidation at up to 100 C. with a 10 to 100% molar excess of molecular oxygen per mole of unoxidized taluminum trialkyl thereby forming an alcoholate having the formula: Al(OR) wherein each R is a C to C alkyl group and byproduct esters, subjecting the alcoholate and byproduct esters to hydrolysis thereby forming a mixture of alcohols and esters, hydrogenating said esters at about 250 to 550 C. and 500 to 5000 p.s.i.g. of hydrogen to convert them to alcohol and recovering the alcohol formed as a result of said hydrolysis and hydrogenation.

(References on following page) 7 8 References Cited by the Examiner FOREIGN PATENTS UNITED STATES PATENTS 642,149 6/1962 Canada- 1,302,011 4/1919 Jens 260-638 LEON ZITVER, Primary Examiner.

2,892,858 6/1959 Ziegler 260632X 5 A, H. sUTTo, M, B. ROBERTO H.GMOORE, J. E. 3,017,438 1/1962 AtWOOd 2 2 EVANS, Assistant Examiners.

Claims (1)

1. A PROCESS FOR PREPARING AND ALCOHOL FROM A MIXTURE OF NORMALLY LIQUID ALUMINUM TRIALKYLS CONTAMINATED WITH HYDROCARBON WHICH COMPRISES OXIDIZING A TRIALKYL AMUMINUM IN WHICH EACH ALKYL GROUP CONTAINS FROM 2 TO 20 CARBON ATOMS WITH MOLCULAR OXYGE UNTIL ABOUT 0.7 TO 1 MOLE OF OXYGEN PER MOLE OF ALUMINUM TRIALKYL HAS REACTED, STRIPPING THE HYDROCARBON CONTAINMINANT FROM THE PARTIALLY OXIDIZED ALUMINUM TRIALKYL AT REDUCED PRESSURE AND TEMPERATURES OF BELOW 400*C., SUBJECTING SAID PARTIALLY OXIDIZED ALUMINUM TRIALKYL TO A FURTHER RAPID OXIDATION AT A TEMPERATURE OF 50* TO 100*C. WITH A 10 TO 100% MOLAR EXCESS OF MOLECULAR OXYGEN PER MOLE OF UNOXIDIZED ALUMINUM TRIALKYL THEREBY FORMING AN ALCOHOLATE HAVING THE FORMULA: AI(OR)3 WHEREIN EACH R IS A C2 TO C20 ALKYL GROUP, HYDROLYZING SAID ALCOHOLATE AND BYPRODUCT ESTERS TO HYDROL SUBJECTING THE ALCOHOLATE AND BYPRODUCT ESTERS TO HYDROLYSIS THEREBY FORMING A MIXTURE OF ALCOHOLS AND ESTERS, REACTING SAID MIXTURE WITH A MATERIAL SELECTED FROM THE GROUP CONSISTING OF HYDROGENATION AGENTS AND SAPONIFICATION AGENTS TO CONVERT AT LEAST A PART OF THE ESTERS TO ALCOOHOLS AND RECOVERING THE ACOHOLS FORMED AS A RESULT OF SAID HYDROLYSIS AND CONVERSION.