US 3904702 A
A method is disclosed for alkenylating alkylbenzenes by reaction with conjugated alkadienes utilizing alkali metal as promoter in a manner to maximize production of mono-adduct product. This involves continuously passing a slurry of the alkylbenzene and particulate alkali metal through a series of substantially isolated reaction zones in each of which the slurry is independently agitated, continuously feeding a stream of diene to each zone at low rate and regulating the amount of total diene to all zones to less than 0.5 mole per mole of alkylbenzene, separating alkali metal from the mixture after the last reaction zone, recovering unreacted alkylbenzene from the alkenylated product, and recycling the unreacted alkylbenzene and, optionally, recovered alkali metal to the first reaction zone.
Description (OCR text may contain errors)
United States Patent 1 [111 3,904,702 Mitchell Sept. 9, 1975 REACTION OF ALKYLBENZENES WITH Primary ExaminerC. Davis CONJUGATED DIENES  Inventor: Richard E. Mitchell, Boothwyn, Pa.
Assignee: Sun Ventures, Inc., St. Davids, Pa.
Filed: Sept. 17, 1973 App]. No.: 398,112
Related U.S. Application Data Continuation-impart of Ser. No. 282,995, Aug. 23, 1972, abandoned.
9/1965 Williamson et a1. 260/671 B 10/1973 Shima ct a1. 260/668 B OTHER PUBLICATIONS Eberhardt et al., J. Org. Chem., Vol. 30, pp. 8284, Jan. 1965.
ALKYL- BENZENE FEED Attorney, Agent, or FirmGeorge L. Church; Donald R. Johnson; J. Edward Hess 5 7 ABSTRACT A method is disclosed for alkenylating alkylbenzenes by reaction with conjugated alkadienes utilizing alkali metal as promoter in a manner to maximize production of mono-adduct product. This involves continuously passing a slurry of the alkylbenzene and particulate alkali metal through a series of substantially isolated reaction zones in each of which the slurry is independently agitated, continuously feeding a stream of diene to each zone at low rate and regulating the amount of total diene to all zones to less than 0.5 mole per mole of alkylbenzene, separating alkali metal from the mixture after the last reaction zone, recovering unreacted alkylbenzene from the alkenylated product, and recycling the unreacted alkylbenzene and, optionally, recovered alkali metal to the first reaction zone.
18 Claims, 1 Drawing Figure 1 ALKALI METAL CATALYST /RECYCLE DISTILLATION MONO-ADDUCT PRODUCT Z 9 50 52 l a 2 D HIGHER ADDUCTS PATENTED SEP 91975 ALKALI METAL MONO-ADDUCT PRODUCT T HIGHER ADDUCTS ZOFEJJEQQ DIENE FEED CATALYST /RECYCLE ALKYL- BENZENE RECYCLE TANK CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of Ser. No. 282,995, filed Aug. 23, 1972 and now abandoned.
BACKGROUND OF THE INVENTION This invention relates to reactions of alkylbenzenes with conjugated alkadienes promoted by means of alkali metals. The invention particularly concerns a method for alkenylating an alkylbenzene by reacting it with a C -C conjugated alkadiene in the presence of an alkali metal in a manner to maximize the production of mono-adduct product, i.e., the one-to-one addition product of the alkylbenzene and diene.
The use of alkali metals for promoting the addition of alkadienes to alkylbenzenes is known in the prior art. This kind of reaction is shown for such reactants as toluene or xylene with butadiene or isoprene in the following US. patents: 1,934,123, issued Nov. 7, 1933, F. Hofmann et al.; and 2,603,655, issued July 15, 1952, D. E. Strain. Such alkenylation reactions have also been described by R. E. Robertson et al., CAN. J. RES, 26B, 657-667 1948). However the conditions disclosed in these references result in the production of large amounts of adducts of higher molecular weight than the monoadduct product. These references fail to provide conditions under which the mono-adduct product could be obtained in high yield.
Conditions more favorable for securing good yields of the mono-adduct product in such alkenylation reactions have been described by G. G. Eberhardt et al., in J. ORG. CHEM., 30, 82-84 1965) and Eberhardt US. Pat. No. 3,244,758, issued Apr. 5, 1966. The conditions described in these references include utilizing a granular support on which the alkali metal is distended and slowly adding the conjugated diene to the alkyl aromatic reactant while vigorously agitating the mixture. While these conditions result in good yields of the mono-adduct, nevertheless substantial amounts of higher adducts are formed. For example, in the reaction of o-xylene with butadiene in the disclosed manner, the alkenylated product typically contains 80-85% by weight of mono-adduct (i.e., o-tolylpentene) with the remainder being mainly di-adducts resulting from the combination of two butadiene molecules with one of o-xylene.
As shown in the above-cited Eberhardt references, the alkenylation of alkylbenzenes can be used as a route for preparing various alkylnaphthalenes by following the alkenylation reaction with a ring closure step to form an alkyltetralin and then a dehydrogenation step to produce the corresponding alkylnaphthalene. For example, the reaction of butadiene with toluene gives l-phenylpentene which upon ring closure forms l-methyltetralin which can be dehydrogenated to l-methylnaphthalene. Other examples of analogous conversions are l,5-dimethylnaphthalene from oxylene and l,7-dimethylnaphthalene from p-xylene. These dimethylnaphthalenes can be isomerized, respectively, to the 2,6 and 2,7-isomers, as described by G. Suld et al., J. ORG. CHEM., 29, 2936-2946 (1964); and the 2,6- and 2,7-isomers can be oxidized to the corresponding diacids useful for making polyester resins, as disclosed in US. Pat. No. 3,293,223, issued Dec. 20, 1966, Irl N. Duling.
SUMMARY OF THE INVENTION The present invention provides an improved method for carrying out the alkenylation of alkylbenzenes by 5 means of conjugated alkadienes in the presence of alkali metal, whereby higher selectivities for producing the mono-adduct product are achieved.
The method is applicable to any alkylbenzene having l-4 alkyl substitutents which collectively contain at least three benzylic non-tertiary hydrogen atoms, and
the alkenylating agent can be any C -C conjugated alkadie ne. The method comprises:
A. forming a slurry of the alkylbenzene and an alkali metal in particulate form, said alkali metal being potassium, sodium or a potassium-sodium mixture;
B. continuously. passing the slurry under alkenylation conditions through a series of successive reaction zones substantially isolated from each other while continuously and independently mixing the slurry in each zone;
C. continuously feeding a separate stream of the C -C conjugated alkadiene to each of said reaction zones and dispersing same into the slurry within the zone at a rate to maintain a low concentration of the diene in the slurry, the amount of total diene to all zones being controlled to provide less than 0.5 mole diene per mole of alkylbenzene feed;
D. passing the resulting reaction mixture from the last of said zones to a separation zone and therein separating alkali metal from the bulk of the hydrocarbon phase;
E. separating unreacted alkylbenzene from the alkenylated product;
F. and recycling the unreacted alkylbenzene to Step BRIEF DESCRIPTION OF THE DRAWING One embodiment of the invention is illustrated in the accompanying drawing which is a diagrammatic flowsheet of the process with certain parts shown broken away for illustrating internal arrangement of equipment.
DESCRIPTION The alkylbenzene reactant for the present process can have one to four alkyl groups, and it should contain at least three benzylic non-tertiary hydrogen atoms per molecule. The term benzylic hydrogen refers to a hydrogen atom attached to a carbon atom which is directly attached to the benzene ring. Thus toluene or diethylbenzene meets the requirement of containing at least three benzylic non-tertiary hydrogen atoms, but
having three benzylic hydrogen atoms, also does not since they are tertiary hydrogen atoms. The size and configuration of the alkyl substituents on the benzene ring are immaterial as long as three or more benzylic hydrogen atoms which are non-tertiary are present. Generally the number of carbon atoms in each alkyl group will be in the range of l-lO and usually 1-2.
The following are illustrative examples of suitable alkyla'rornatics which can be alkenylated in an improved manner by means of the present process: toluene; o-, rnor p-xylcne; mesitylene; pseudocumene; hemimellitene; 'durene; isodurene; prehnitene; methylethylben- Zenes; cymenes; di-n-propylbenzenes; tri-nethylbenzene does not. Triisopropylbenzene, while hexylbenzenes; ethyldecylbenzenes; butylbenzenes; and the like.
The diene reactant is a C -C conjugated alkadiene, viz. 1,3-butadiene, 1,3-pentadiene and isoprene.
Both reactants should be substantially free of water, sulfur compounds or other impurities capable of reacting with alkali metals, as otherwise excessive loss of the alkali metal promoter will occur. Water can conveniently be removed from the feed materials by treatment with a molecular sieve adsorbent.
Alkenylation of the alkylbenzene by reaction with the diene is promoted by means of potassium, sodium or a potassiumsodium mixture. Preferably the alkali metal promoter is composed of a major proportion of sodium and a minor proportion of potassium on a weight basis, such as 7598 parts sodium to 2-25 parts potassium. Normally only a small proportion of alkali metal to the alkylbenzene reactant is employed, such as 0.0l5.0 g. moles alkali metal per liter of alkylbenzene and preferably 0.1 to 1.0 g. mole per liter.
The catalyst for the alkenylation reaction, however, is not considered to be the alkali metal per se but rather the metallo-organic product resulting from reaction of at least part of the alkali metal with the alkylbenzene. For instance, in the alkenylation of toluene employing potassium as promoter, the effective catalyst is believed to be the reaction product, benzyl potassium, which forms when a dispersion or slurry of molten potassium in heated toluene stands. Thus in order to obtain the catalyst, the alkali metal needs to be in contact with the alkylbenzene at a temperature above the melting point of the metal for enough time to permit substantial reaction. The respective melting points of K and Na are 623C. and 975C. but alloys of these metals exhibit lower melting points. For example, a 50:50 by weight mixture of the two has a melting point of C. However, since the reaction between the metal and alkylbenzene is slow at low temperatures, it is advantageous to maintain the temperature of the dispersion at least above 50C. to form the metallo-organic catalyst. The latter is slightly soluble in the aromatic hydrocarbon but mainly will be present as a dispersed solid.
The accompanying drawing illustrates the improved method of alkenylating alkylbenzenes in accordance with the invention. For purpose of describing the process, the reactants are considered to be o-xylene and butadiene. The desired reaction for producing the mono-adduct product is illustrated by the following equation (hydrogen atoms being omitted for simplicity):
methyl-t- As shown, the desired product from these reactants is 5-o-tolylpentene-2, which can be converted to 1,5-dimethyltetralin by treatment with an acid catalyst. During this reaction substantial amounts of higher adducts tend to form due to the reaction of more than one mole of butadiene per mole of o-xylene reacted. Reaction of the additional butadiene can occur in several ways to produce higher adducts of various structures.
The present method minimizes the formation of these higher adducts by carrying out the alkenylation reaction-in a series of independently mixed reaction zones through which the dispersion of alkali metal in o-xylene flows continuously. The butadiene feed, however, is divided into separate streams and one stream thereof is fed to each reaction zone. This procedure results in substantially higher selectivity in conversion of the oxylene to the desired mono-adduct than otherwise can be secured.
Referring now to the drawing, a mixture of the oxylene feed from line 10 and recycled o-xylene from line 11 passes mainly through lines 12 and 13 to heater 14 wherein it is heated to the desired reaction temperature. This generally is in the range of 50170C. and more preferably 90l C. A minor proportion of the o-xylene is diverted through line 17 and heater 18 to a catalyst preparation tank 19. Alakli metal which is maintained in molten condition in supply tank 20 by means of heating coils 21 is drawn through line 22 to catalyst preparation tank 19. The latter is provided with a motorized stirrer 23 for effectively dispersing the alkali metal in the hydrocarbon. The temperature in tank 19 is also usually held in the range of 50l70C., more preferably 90l40C., to facilitate reaction of the alkali metal and o-xylene and form the metalloorganic catalyst.
The alkali metal, which is added to supply tank 20 in any suitable manner as indicated by dashed line 23, can be potassium or sodium or any mixture or alloy of these two metals. The effective catalyst tends to form more readily when potassium is used than when sodium alone is employed and the selectivity for mono-adduct production appears to be somewhat better. However mixtures of sodium and potassium containing even as much as 95% or more sodium are about as effective as potassium alone. In view of the fact that sodium usually is less expensive than potassium it is distinctly preferred that the alkali metal utilized be composed of a major proportion of sodium and a minor proportion of potassium on a weight basis. Within the zone where the alkenylation reaction occurs, it is desirable to maintain the Na:K proportion within the range of :25 to 98:2 and a proportion of about :5 is preferred. At this weight proportion the loss of alkali metals from the system due to solubility of their derivatives in the hydrocarbon phase generally involves roughly twice as much sodium as potassium. Accordingly, about a two-to-one Na:K ratio needs to be maintained for the alkali metals added as make-up through line 22 in order to maintain the 95:5 preferred proportion in the system.
The proportion of alkali metal to alkylbenzene in catalyst preparation tank 19 is not critical and can vary widely, Generally from 5 to 20 parts by weight of the alkylbenzene per part of alkali metal are used in preforming the catalyst dispersion. The minimum residence time in tank 19 for forming the catalyst will vary with temperature, decreasing as higher temperatures are employed. Typically, for a temperature level of l 10C., a residence time of 0.52.0 hours is employed.
The catalyst dispersion flows from tank 19 through line 24 to line 15 where it meets the main stream of oxylene from heater 14. The rate of addition of dispersion from line 24 to the main o-xylene stream typically is such that the resulting slurry contains 0.0l-5.0 gram moles of alkali metal (combined and uncombined) per liter of o-xylenc, more preferably 0.05l.0 gram mole per liter. The mixture flows into horizontal tank 16 which is divided into several independently stirred reaction zones. The number of such zones can vary, for example, from 2-10 but preferably is in the range of 36. As illustrated in the drawing, five independent zones, designated by A, B, C, D and E, are utilized. The zones are separated by baffles 25, 26, 27 and 28 each of which is somewhat spaced from the top of tank 16 to permit overflow of the reaction mixture to the next zone. The zones are provided with motorized stirrers 29, 30, 31, 32 and 33 and with spargers 34,35, 36, 37 and 38 for independently admitting a continuous stream of butadiene from feed line 39 to each reaction zone.
Effective mixing conditions are maintained in each of zones A, B, 'C, D and E by the respective motorized mixers, and the butadiene is fed relatively slowly through the sparger provided in each zone. The butadiene in each zone is thus immediately dispersed into the slurry at a rate whereby a low concentration of the diene therein is maintained. Preferably each zone has about the same volumetric capacity and the rates of butadiene addition to the zones are approximately the same. although this is not essential for practicing the invention. The amount of total diene to all five zones is controlled so as to provide less than 0.5 mole diene per mole of alkylbenzene feed. Best results are usually obtained by holding this ratio in the range of 0.05-0.30 mole diene per mole of alkylbenzene fed through line to tank 16. The slurry of catalyst in o-xylene passes from the inlet end of tank 16 successively through the series of reaction zones, flowing over the baffles 25, 26, 27 and 28 from one zone to the next. The final slurry from reaction zone E passes out of tank 16 via line 40.
The foregoing arrangement involving several independently stirred reaction zones with separate butadiene feed streams, as compared with a single reaction zone to which both reactants are fed continuously, permits a substantial increase in selectivity for monoadduct production. In other words, this arrangement materially reduces the percentage of the reacted oxylene that is converted to di-adducts and other higher adducts. This comes about because the average concentration of mono-adducts in the slurry for the serially arranged reaction zones is less than the mono-adduct concentration would be for a single stage reaction system. In the latter the final mono-adduct concentration is also the concentration always maintained in the reactor; whereas in the present system the final monoadduct concentration is only that in zone E and the average concentration thereof for all zones is considerably less. Since the amount of higher adducts formed is proportional to the concentration of mono-adducts in the hydrocarbon phase as the butadiene is contacted with it, the use of a plurality of stages in the manner described substantially improves selectivity for the desired product. The following tabulation gives representative selectivity values that can be obtained in varying the number of reaction stages from one to six when reacting butadiene with o-xylene in a once-through operation. Selectivity for the present purpose is defined as the weight of mono-adducts divided by the weight of total adducts formed times 100.
Stirred Reactors Selectivity,
The data show that for five stages, as illustrated in the drawing, an increase of about 7% in selectivity over that for a single stage can be secured. This represents a distinct improvement for a commercial operation. The data also indicate that little further improvement would be achieved by employing more than six stages.
The reaction in tank 16 is exothermic. By way of example, if the butadiene is added at the same temperature as the o-xylene in amount to convert 30% of the o-xylene, the following approximate increases in temperature in an adiabatic system would be typical:
In order to avoid such temperature increases. tank 16 can, if desired, he provided with cooling coils or other heat removal means (not shown) to keep the temperature constant from inlet to outlet. The process can also be conducted, however, by introducing the slurry through line 15 at somewhat below the average desired temperature and allowing the temperature to rise above the average level the mixture flows to outlet line 40.
The reaction mixture next passes through cooler 41 to settler 42 wherein the alkali. metal, including that in the form of undissolved metallo-organic catalyst, is allowed to settle from the bulk of the hydrocarbon phase. A concentrate of the alkali metal solid material in a minor portion of the hydrocarbon phase is removed from the bottom of settler 42 and recycled through lines 43 and 15 to reaction tank 16. As an alternative to using a settler in this step, a cyclone separator can be employed to recover the alkali metal for reuse. Catalyst recycle is not an essential feature of the invention as in some cases, where very small amounts of catalyst are employed, it will be more economical to discard the catalyst rather than recycle it. On the other hand recycle of unreacted alkylbenzene (discussed hereinafter) is essential as the process is not economical without it.
From the upper part of settler 42 the hydrocarbon phase is withdrawn through line 44 and sent to fractional distillation tower 45. The unreacted o-xylene is removed overhead via line 46, cooled in condenser 47 and passes to recycle tank 48. The recovered o-xylene is recycled for reuse through line ll. The bottoms from tower 45 pass through line 49 to a second distillation column 50 from which the desired mono-adduct product is recovered via overhead line 51. The higher adduct material, obtained in minor proportion as bottoms through line 52, is composed principally of di-adduct with lesser amounts of triadduct and higher material.
The following is a specific example of a continuously operating 5-stage reaction system, as shown in the drawing. for preparing the mono-adduct 5-0- tolylpentene-Z) from o-xylene and butadiene. This example is expressed on a weight basis with 1000 parts of o-xylene per unit time being fed to the system (line 10). The fresh o-xylene at this rate admixes with 7398 parts of recycled o-xylene from line 11 and most of the mixture passes through heater 14, where the temperature is raised to 100-1 15C., and then to reactor tank 16. About 36 parts of o-xylene is diverted through line 17 and heated to lO-l 15C. in heater 18 and is then admixed in tank 19 with 4 parts sodium and 2 parts potassium. After an average residence time of about one hour in tank 19, the resulting catalyst dispersion in amount of 42 parts per unit time flows through line 24 to reactor tank 16. The latter preferably is provided with cooling means to prevent the temperature from rising above 125C. as the reaction occurs and also preferably is of a size such that the total residence time in the tank is 2-3 hours. The slurry leaving reactor 16 through line 40 and amounting to 9941 parts passes through cooler 41 to settler 42, or to a cyclone separator, whereby the alkali metal components are separated from the bulk of the hydrocarbon phase. A stream totaling 970 parts, composed of 747 parts o-xylene, 138 parts mono-adduct, 16 parts higher adducts, and 73 and 2 parts, respectively, of Na and K (combined plus uncombined forms), is recycled through line 43. The hydrocarbon phase, amounting to 8965 parts and containing 4 parts Na and 2 parts K in soluble forms, is dis tilled in column 45, from which 7412 parts of 0-xylene distillate is recovered for recycling. The bottoms from column 45 is composed typically of 15 parts o-xylene, 1370 parts mono-adduct. 162 parts higher adducts, 4 parts Na and 2 parts K, giving a total of 1553 parts. This material is distilled in column 50 to yield an overhead product composed of 1368 parts mono-adduct and 15 parts o-xylene. The bottoms from column 50 consists of 169 parts composed of 2 parts monoadduct, 161 parts higher adducts and 6 parts alkali metal (combined form).
The foregoing specific operation of the process provides a selectivity, as previously defined, of nearly 90%, which is substantially better than would be obtainable employing a single mixing stage in the reactor.
Analogous results can be obtained in the alkenylation of other alkylbenzenes by conjugated diolefins by the procedure of the invention. Other particularly useful alkenylations are the reaction of toluene with butadiene to give phenylpentene and the reaction of other xylenes with butadiene to yield other tolylpentenes, viz. m-toly1pentene-2 from m-xylene or p-tolylpentene-2 from p-xylene.
The invention claimed is:
1. Method of reacting an alkylbenzene having 1-4 alkyl substituents collectively containing at least three benzylic non-tertiary hydrogen atoms with a C conjugated alkadiene to produce mono-adduct product which comprises:
A. forming a slurry of said alkylbenzene and an alkali metal in particulate form, said alkali metal being potassium, sodium or a potassium-sodium mixture;
B. continuously passing the slurry under alkenylation conditions through a series of successive reaction zones substantially isolated from each other while continuously and independently mixing the slurry in each zone;
C. continuously feeding a separate stream of .the
C -C conjugated alkadiene to each of said reaction zones and dispersing same into the slurry within the zone at a rate to maintain a low concentration of the diene in the slurry, the amount of total diene to all zones being controlled to provide less than 0.5 mole diene per mole of alkylbenzene feed;
D. passing the resulting mixture from the last of said zones to a separation zone and therein separating alkali metal from the bulk of the hydrocarbon phase;
E. separating unreacted alkylbenzene from the alkenylated product;
F. and recycling the unreacted alkylbenzene to Step (A), said series of reaction zones in step (B) being effective to reduce the formation of by-product diadduct which is formed by the addition of a mole of alkadiene to at least two alkyl groups of said alkylbenzene.
2. Method according to claim 1 wherein said series consists of 2-10 successive reaction zones and said slurry contains 0.0 l-5.0 gram moles of alkali metal per liter of alkylbenzene.
3. Method according to claim 2 wherein said series consists of 3-6 successive reaction zones. the slurry contains 0.05l.0 gram mole of alkali metal per liter of alkylbenzene and said alkenylation conditions include a temperature in the range of -l40C.
4. Method according to claim 3 wherein said alkylbenzene is toluene, said conjugated alkadiene is butadiene and said alkenylated product mainly comprises phenylpentene.
5. Method according to claim 4 wherein the amount of butadiene to all zones provides 0.05-0.30 mole butadiene per mole of toluene.
6. Method according to claim 3 wherein said alkylbenzene is xylene, said conjugated alkadiene is butadiene and said alkenylated product mainly comprises tolylpentene.
7. Method according to claim 6 wherein the amount of butadiene to all zones provides 0.05-0.30 mole butadiene per mole of xylene.
8. Method according to claim 1 wherein said alkylbenzene is toluene or a xylene, said alkadiene is butadiene and said series consists of 3-6 successive reaction zones.
9. Method according to claim 8 wherein the slurry contains 0.01-5.0 gram moles of alkali metal per liter of alkylbenzene, said alkenylation conditions include a temperature in the range of 90-l40C., and the amount of butadiene to all zones provides 0.05-0.30 mole butadiene per mole of alkylbenzene.
10. Method according to claim 9 wherein said alkylbenzene is o-xylene and said alkenylated product mainly comprises o-tolylpentene-2.
11. Method according to claim 9 wherein said alkylbenzene is m-xylene and said alkenylated product mainly comprises m-tolylpentene-2.
12. Method according to claim 9 wherein said alkylbenzene is p-xylene and said alkenylated product mainly comprises p-tolylpentene2.
13. Method according to claim 1 wherein said slurry is formed by dispersing the alkali metal in a minor proportion of the alkylbenzene to be reacted to form a relatively concentrated slurry, holding said slurry at a temperature above the melting point of the alkali metal and below C. until substantial reaction between the alkali metal and alkylbenzene has occurred, and then admixing said concentrated slurry with a large 16. Method according to claim 13 wherein the alkali metal is potassium.
17. Method according to claim 13 wherein the alkali metal is composed of a major proportion of sodium and a minor proportion of potassium on a weight basis.
18. Method according to claim 1 wherein recovered alkali metal is also recycled to Step (A).