Process for producing alkyl-substituted aromatic hydrocarbon using heteropolyacid salts
BACKGROUND OF THE INVENTION 
     The present invention relates to a process for producing an alkyl-substituted aromatic hydrocarbon. More specifically, it relates to a process for producing an alkyl-substituted aromatic hydrocarbon at high yields industrially advantageously. 
     An alkyl-substituted aromatic hydrocarbon is useful as an intermediate for the preparation of a polymer and medicaments. As a process for producing such an alkyl-substituted aromatic hydrocarbon, there are conventionally known the Friedel-Crafts reaction in which an aromatic hydrocarbon is alkylated in a liquid phase in the presence of anhydrous aluminum chloride as a catalyst, a gaseous-phase reaction in which an aromatic hydrocarbon is alkylated in the presence of a solid silica alumina as a catalyst, or the like. 
     Since, however, the Friedel-Crafts reaction generally produces a large amount of high-boiling compound(s) as a by-product, the intended alkyl-substituted aromatic hydrocarbon cannot be produced at high yields. The other gaseous phase reaction using a solid silica alumina catalyst requires a high temperature, and various side reactions occur. Therefore, the yield of the intended product is similarly low. 
     The Mar. 6, 1991 issue of Nikkan Kogyo Shinbun (The Business and Technology Daily News) reported that when an acidic catalyst prepared by partially replacing hydrogen in tungstophosphoric acid with cesium is used in the production of dodecylphenol from phenol, it exhibits 20 to 60 times greater activity than sulfuric acid (catalyst) per weight and 100 times higher activity than zeolite per weight. This report also said that even a potassium salt, too, is considered effective as catalyst. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an industrially advantageous process for producing an alkyl-substituted aromatic hydrocarbon. 
     It is another object of the present invention to provide a process for producing an alkyl-substituted aromatic hydrocarbon at high yields industrially advantageously by alkylating an aromatic hydrocarbon such as naphthalenes and alkyl naphthalenes with an alkylating agent in the presence of a catalyst while inhibiting the formation of high-boiling by-products under mild conditions. 
     The above objects and other objects and advantages of the present invention will be apparent from the following description. 
     According to the present invention, the above objects and advantages are achieved by a process for producing an alkyl-substituted aromatic hydrocarbon, which comprises alkylating an aromatic hydrocarbon with an alkylating agent in the presence of a heteropoly-acid or salt thereof as a catalyst. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pore distribution curve of the catalyst used in Example 32. 
     FIG. 2 is a pore distribution curve of the catalyst used in Example 38. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the present invention, the aromatic hydrocarbon as a raw material for the alkylation may be any one of monocyclic, polycyclic and fused-ring aromatic hydrocarbons of which the aromatic rings have a substitution position for the alkylation. The aromatic hydrocarbon includes monocyclic compounds such as benzene, polycyclic compounds such as biphenyl and diphenyl methane and fused-ring compounds such as naphthalene and anthracene. These compounds may have one or more substituents on the aromatic ring. The substituent includes, for example a halogen atom, an alkyl group and a haloalkyl group. 
     The halogen atom preferably includes, e.g., fluorine, chlorine and bromine. 
     The alkyl group may be linear or branched, and preferably includes those having 1 to 8 carbon atoms such as methyl, ethyl, n-propyl, iso-propyl, n-butyl and isobutyl. 
     The haloalkyl group preferably includes groups in which a halogen atom such as fluorine or chlorine is substituted on the above alkyl groups having 1 to 8 carbon atoms, such as fluoromethyl. 
     As an aromatic hydrocarbon, particularly preferred are naphthalenes. Such naphthalenes include naphthalene; methylnaphthalenes such as 1-methyl-naphthalenes and 2-methylnaphthalene; dimethylnaphthalenes such as 1,5-dimethylnaphthalene and 1,6-dimethylnaphthalene; ethylnaphthalenes such as 1-ethylnaphthalene and 2-ethylnaphthalene; diethylnaphthalenes such as 2,6-diethylnaphthalene and 2,3-diethylnaphthalene; trimethylnaphthalenes such as 1,3,6-trimethylnaphthalenes; isopropylnaphthalenes such as 1-isopropylnaphthalene and 2-isopropylnaphthalene; and naphthalenes having a combination of alkyl group members such as methylethylnaphthalene, methylisopropylnaphthalene, ethylisopropylnaphthalene, dimethylethylnaphthalene, methyldiethylnaphthalene, dimethyldiethylnaphthalene, dimethyldiisopropylnaphthalene, trimethylethylnaphthalene, trimethyldiethylnaphthalene and diethylisopropylnaphthalene. 
     Of the above naphthalenes, particularly preferred in the present invention are naphthalene and mono- or dialkylnaphthalenes having one or two alkyl group members selected from methyl, ethyl and isopropyl. Specific examples of such naphthalenes include methylnaphthalenes, ethylnaphthalenes, dimethylnaphthalenes and isopropylnaphthalenes in addition to naphthalene. 
     Examples of the alkylating agent includes α-olefins such as C 2  -C 20  monoolefins, e.g. ethylene and propylene; aliphatic lower alcohols such as ethanol and isopropyl alcohol; lower alkyl ethers such as ethyl ether and isopropyl ether; acetic acid lower alkyl esters such as ethyl acetate and isopropyl acetate; and alkyl halides such as methyl chloride and isopropyl chloride, particularly lower alkyl chlorides generally used for alkylation; and polyalkylbenzenes such as diethylbenzene, triethylbenzene, tetraethylbenzene, diisopropylbenzene, triisopropylbenzene, tetraisopropylbenzene and mixtures of these used for transalkylation. 
     Of the above alkylating agents, particularly preferred are α-olefins. 
     In the process of the present invention, a heteropoly-acid or a salt thereof is used as a catalyst when the above aromatic hydrocarbon is alkylated with the above alkylating agent. 
     The heteropoly-acid or the salt thereof preferably includes, e.g., phosphorus tungstic acid, phosphorus molybdic acid, silicotungstic acid, silicomolybdic acid, and a compound obtained by replacing part or all of protons of any one of these acids with metals belonging to the group Ia of the periodic table (alkali metals) or metals belonging to the group IIa of the periodic table (alkaline earth metals). 
     Examples of the alkali metals are cesium, sodium, potassium, rubidium and lithium. Examples of the alkaline earth metals are magnesium, calcium, strontium and barium. 
     Of these catalysts, phosphorus tungstic acid, silicotungstic acid and salts of these are more preferably used. 
     As a phosphorus tungstic acid or a salt thereof, preferred is a compound of the formula (1), 
     
         M.sub.x H.sub.3-x PW.sub.12 O.sub.40                       (1) 
    
     wherein M is a metal belonging to the group Ia of the periodic table, and x is a number of 0 to 2.8. 
     A compound of the formula (1) in which x is 0.5 to 2.8 is more preferred, and a compound of the formula (1) in which x is 1.0 to 2.5 is particularly preferred. As a metal M belonging to the group Ia of the periodic table, preferred is potassium, rubidium or cesium. 
     The salt of phosphorus tungstic acid may include a complex salt obtained by replacing hydrogen atoms of phosphorus tungstic acid with a plurality of the above metals which are different from each other in kind. 
     Phosphorus tungstic acid or a salt thereof often contains crystal water. In the present specification, the description of such crystal water is omitted. That is, the description of no crystal water in the present specification does not necessarily mean the absence of crystal water. 
     Such a metal salt of phosphorus tungstic acid can be obtained by adding a stoichiometric amount of a carbonate of metal(s) belonging to the group Ia of a the periodic table to an aqueous solution of phosphorus tungstic acid with stirring and then subjecting the mixture to evaporation and solidification, e.g., at 50° C. 
     Further, the present inventors&#39; study has showed that the catalyst obtained by bringing an aqueous solution of phosphorus tungstic acid and solid potassium carbonate to contact with each other particularly exhibits excellent activity. 
     For the preparation of the above metal salt of phosphorus tungstic acid, the aqueous solution of phosphorus tungstic acid as a H 3  PW 12  O 40  preferably has a concentration of 10 to 150 g/100 cc, more preferably 30 to 100 g/100 cc. 
     The solid potassium carbonate may be any one of 1.5-hydrate or dihydrate. 
     An aqueous solution of phosphorus tungstic acid and solid potassium carbonate may be brought into contact with each other, e.g., by any one of a method in which solid potassium carbonate is added to an aqueous solution of phosphorus tungstic acid and a method in which an aqueous solution of phosphorus tungstic acid is added to solid potassium carbonate. Preferred is the method in which solid potassium carbonate is added to an aqueous solution of phosphorus tungstic acid. 
     The precipitate of potassium phosphorus tungstate obtained by the contact of an aqueous solution of phosphorus tungstic acid and solid potassium carbonate is concentrated, preferably concentrated under reduced pressure, to form potassium phosphorus tungstate. 
     The temperature for bringing an aqueous solution of phosphorus tungstic acid and solid potassium carbonate into contact with each other is preferably between 5° C. and 50° C. 
     The present inventors&#39; study has also showed the following: According to a method in which potassium carbonate in the form of a solid or an aqueous solution is gradually added to an aqueous solution of phosphorus tungstic acid and the reaction mixture is subjected to dehydration by distillation under reduced pressure, there can be obtained a catalyst having numerous pores having an average pore radius of 100 to 600 Å, preferably 200 to 500 Å, and this catalyst also exhibits remarkably superior activity. 
     As a heteropoly-acid or the salt thereof in the present invention, silicotungstic acid or an acid thereof is also used. As silicotungstic acid or an acid thereof, preferred is a compound of the formula (2), 
     
         M.sub.x H.sub.4-x SiW.sub.12 O.sub.4                       (2) 
    
     wherein M and x are as defined above. 
     A compound of the formula (2) in which x is 0.5 to 2.8 is more preferred, and a compound of the formula (2) in which x is 1.0 to 2.5 is particularly preferred. In the formula (2), potassium, rubidium or cesium is preferred as a metal (M) belonging to the group Ia of the periodic table. 
     The salt of silicotungstic acid includes complex salts obtained by replacing hydrogen atoms of silicotungstic acid with a plurality of the above metals which are different from each other in kind. 
     Silicotungstic acid or a salt thereof often contains crystal water. In the present specification, the description of such crystal water is omitted. That is, the description of no crystal water in the present specification does not necessarily mean the absence of crystal water. 
     Such a metal salt of silicotungstic acid can be obtained by adding a stoichiometric amount of carbonate of metal(s) belonging to the group Ia of the periodic table to an aqueous solution of silicotungstic acid with stirring and then subjecting the mixture to evaporation and solidification, e.g., at 50° C. 
     The heteropoly-acid or the salt thereof as a catalyst may be used in an as-produced state as a catalyst. Meanwhile, the heteropoly-acid or the salt thereof may be supported, e.g., on silica gel, activated carbon, silica-alumina, alumina, saponite, montmorillonite, acid clay, activated clay, or titania. Further, the heteropoly-acid or salt thereof may be dried by heating it to 100° to 300° C. to increase its alkylating catalyst activity. 
     In the process of the present invention, the above-described heteropoly acids or salts thereof may be used alone or in combination. 
     For the alkylation, the amount of the potassium phosphorus tungstate as an anhydride per part of the aromatic compound as a raw material is preferably 0.0001 to 0.5 part by weight, more preferably 0.001 to 0.1 part by weight. The alkylation can be carried out by any method such as a continuous flow method and a batch method. The reaction conditions are suitably selected depending upon an aromatic compound as a raw material and the kind of an alkylating agent. For example, when olefins are used as an alkylating agent, the reaction is generally carried out in a liquid phase under pressure in the presence or absence of a solvent. The solvent is preferably selected, for example, from saturated hydrocarbons such as decalin, cyclodecane, hexane, heptane, octane, nonane, decane, undecane and dodecane; halogenated aliphatic hydrocarbons such as dichloromethane and 1,2-dichloroethane; halogenated aromatic hydrocarbons such as chlorobenzene, dichlorobenzene, bromobenzene and dibromobenzene; ethers such as diethyl ether and tetrahydrofuran; and carbon disulfide. Of the above solvents, particularly preferred are saturated hydrocarbons. The reaction temperature is preferably between 100° C. and 300° C., more preferably  150° C. and 250° C. The reaction pressure (olefin pressure) is preferably 1 to 500 kg/cm 2 .G, more preferably 1 to 300 kg/cm 2 .G. 
     The reaction time depends on aromatic hydrocarbon as a raw material, a catalyst, amounts of the raw material and the catalyst and a reaction temperature. In general, however, the reaction time is 1 minute to 24 hours, preferably 30 minutes to 10 hours. 
     After the reaction is carried out in the liquid phase as described above, the catalyst is, for example, separated from the reaction mixture by filtration and the solvent is distilled off, whereby the intended alkyl-substituted aromatic hydrocarbon can be obtained. The alkyl-substituted aromatic hydrocarbon is further treated by distillation, extraction, recrystallization, etc., as required. 
     According to the present invention, a heteropoly-acid or a salt thereof is used as a catalyst as described above in the production of an alkyl-substituted aromatic hydrocarbon by alkylating an aromatic hydrocarbon with an alkylating agent. Therefore, the intended alkylation can be carried out with high selectivity under mild conditions while inhibiting side reactions of the aromatic hydrocarbon as a material and olefins as an alkylating agent in particular, and the intended alkyl-substituted aromatic hydrocarbon can be obtained at high yields. 
     The present invention will be explained further in detail hereinafter. However, the present invention shall not be limited to these Examples. 
     EXAMPLE 1 
     An autoclave having a capacity of 50 ml was charged with 700 mg of naphthalene, 2 ml of n-hexane together with 60 mg of phosphorus tungstic acid which had been preliminarily dried under heat at 200° C. for 3 hours. Then, ethylene was introduced into the autoclave under pressure until the ethylene pressure in the autoclave became 60 kg/cm 2  G, and the autoclave was closed. The mixture was allowed to react with stirring at 180° C. for 3 hours. 
     The reaction results are as follows: Naphthalene conversion 100%, selectivity to diethylnaphthalenes 14%, selectivity to triethylnaphthalenes 33%, selectivity to tetraethylnaphthalenes 31%, selectivity to pentaethylnaphthalenes 15%, and tar formation ratio 7%. 
     EXAMPLE 2 
     An autoclave having a capacity of 50 ml was charged with 700 mg of naphthalene, 4 ml of a hexane mixture together with 50 mg of phosphorus tungstic acid which had been preliminarily dried under heat at 200° C. for 3 hours. Then, ethylene was introduced into the autoclave under pressure until the ethylene pressure in the autoclave became 30 kg/cm 2  G, and the autoclave was closed. The mixture was allowed to react with stirring at 170° C. for 2 hours. 
     The reaction results are as follows: Naphthalene conversion 72%, selectivity to monoethylnaphthalenes 29%, selectivity to diethylnaphthalenes 42%, selectivity to triethylnaphthalenes 18%, and tar formation ratio 2%. 
     EXAMPLE 3 
     Example 2 was repeated except that the phosphorus tungstic acid was replaced with 200 mg of a catalyst in which 25% by weight of phosphorus tungstic acid was supported on silica (Wako Gel C-200), and which had been preliminarily dried under heat at 200° C. for 3 hours. 
     The reaction results are as follows: Naphthalene conversion 58%, selectivity to monoethylnaphthalenes 20%, selectivity to diethylnaphthalenes 51%, selectivity to triethylnaphthalenes 18%, and tar formation ratio 2%. 
     EXAMPLE 4 
     Phosphorus tungstic acid (H 0 .5 Cs 2 .5 PW 12  O 40 ) in which protons were partially replaced with cesium was prepared according to the method described in J. Catal., 83, 121 (1983), and this phosphorus tungstic acid was dried under heat at 200° C. for 3 hours. 
     Then, Example 2 was repeated except for the use of the above phosphorus tungstic acid substituted partially with cesium. 
     The reaction results are as follows: Naphthalene conversion 67%, selectivity to monoethylnaphthalenes 22%, selectivity to diethylnaphthalenes 46%, selectivity to triethylnaphthalenes 21%, and tar formation ratio 3%. 
     EXAMPLE 5 
     Example 2 was repeated except that the phosphorus tungstic acid was replaced with phosphorus molybdic acid which had been preliminarily dried under heat at 200° C. for 3 hours and that the reaction temperature was changed to 220° C. 
     The reaction results are as follows: Naphthalene conversion 54%, selectivity to monoethylnaphthalenes 19%, selectivity to diethylnaphthalenes 50%, selectivity to triethylnaphthalenes 22%, and tar formation ratio 5%. 
     EXAMPLE 6 
     Example 5 was repeated except that the phosphorus molybdic acid was replaced with 70 mg of silicotungstic acid which had been preliminarily dried under heat at 200° C. for 3 hours. 
     The reaction results are as follows: Naphthalene conversion 48%, selectivity to monoethylnaphthalenes 20%, selectivity to diethylnaphthalenes 48%, selectivity to triethylnaphthalenes 18%, and tar formation ratio 3%. 
     EXAMPLE 7 
     A 50 ml autoclave was charged with 700 mg of naphthalene and 2 ml of n-hexane together with 60 mg of a commercially available phosphorus tungstic acid (not dried under heat). Then, ethylene was introduced into the autoclave under pressure until the ethylene pressure in the autoclave became 30 kg/cm 2  G, and the autoclave was closed. The mixture was allowed to react with stirring at 190° C. for 3 hours. 
     The reaction results are as follows: Naphthalene conversion 37%, selectivity to monoethylnaphthalenes 62%, selectivity to diethylnaphthalenes 22%, selectivity to triethylnaphthalenes 11%, and tar formation ratio 3%. 
     EXAMPLE 8 
     Example 7 was repeated except that naphthalene was replaced with 720 mg of 2-methylnaphthalene. 
     The reaction results are as follows: 2-Methylnaphthalene conversion 54%, selectivity to methylethylnaphthalenes 30%, selectivity to methyldiethylnaphthalenes 41%, selectivity to methyltriethylnaphthalenes 22%, and tar formation ratio 3%. 
     EXAMPLE 9 
     Example 7 was repeated except that naphthalene was replaced with 730 mg of 2-ethylnaphthalene. 
     The reaction results are as follows: 2-Ethylnaphthalene conversion 60%, selectivity to diethylnaphthalenes 31%, selectivity to triethylnaphthalenes 30%, selectivity to tetraethylnaphthalenes 21%, and tar formation ratio 4%. 
     EXAMPLE 10 
     Example 7 was repeated except that naphthalene was replaced with 750 mg of 2-isopropylnaphthalene. 
     The reaction results are as follows: 2-Isopropylnaphthalene conversion 56%, selectivity to isopropylethylnaphthalenes 32%, selectivity to isopropyldiethylnaphthalenes 29%, selectivity to isopropyltriethylnaphthalenes 20%, and tar formation ratio 4%. 
     EXAMPLE 11 
     Example 7 was repeated except that naphthalene was replaced with 730 mg of 2,6-dimethylnaphthalene. 
     The reaction results are as follows: 2,6-Dimethylnaphthalene conversion 71%, selectivity to dimethylethylnaphthalenes 24%, selectivity to dimethyldiethylnaphthalenes 45%, selectivity to dimethyltriethylnaphthalenes 23%, and tar formation ratio 3%. 
     EXAMPLE 12 
     Example 11 was repeated except that the phosphorus tungstic acid was replaced with 200 mg of a catalyst in which 20% by weight of phosphorus tungstic acid was supported on activated carbon and which had been preliminarily dried under heat at 200° C. for 3 hours. 
     The reaction results are as follows: 2,6-Dimethylnaphthalene conversion 80%, selectivity to dimethylethylnaphthalenes 22%, selectivity to dimethyldiethylnaphthalenes 46%, selectivity to dimethyltriethylnaphthalenes 25%, and tar formation ratio 2%. 
     EXAMPLE 13 
     Example 11 was repeated except that the phosphorus tungstic acid was replaced with 200 mg of a catalyst in which 40% by weight of phosphorus tungstic acid was supported on activated clay and which had been preliminarily dried under heat at 200° C. for 3 hours. 
     The reaction results are as follows: 2,6-Dimethylnaphthalene conversion 84%, selectivity to dimethylethylnaphthalenes 21%, selectivity to dimethyldiethylnaphthalenes 48%, selectivity to dimethyltriethylnaphthalenes 26%, and tar formation ratio 2%. 
     EXAMPLE 14 
     A 50 ml autoclave was charged with 10 g of naphthalene (special-grade reagent, supplied by Wako Jun-yaku Kogyo K. K.) and 10 ml of decane together with 850 mg of potassium phosphorus tungstate having a composition shown in Table 1, and the autoclave was closed. Then, a gas phase inside the autoclave was replaced with ethylene gas, and the mixture was allowed to react with stirring under an ethylene pressure of 30 kg/cm 2  G at a temperature of 200° C. for 2 hours. After the reaction, the catalyst was separated by filtration, and the resultant reaction mixture was analyzed on its contents by gas chromatography. Table 1 shows the results. 
     EXAMPLES 15-17 
     Example 14 was repeated except for the use of a metal salt of phosphorus tungstic acid having a composition shown in Table 1. Table 1 shows the results. 
     EXAMPLE 18 
     Example 14 was repeated except that the raw material was changed to purified naphthalene (supplied by Kawasaki Steel Corp.), that catalyst was replaced with 10 mg of potassium phosphorus tungstate having a composition shown in Table 1, and further that the reaction temperature was changed to 260° C. Table 1 shows the results. 
     EXAMPLE 19 
     Example 14 was repeated except that the raw material was changed to 10 g of 2-ethylnaphthalene and that the catalyst was changed to 200 mg of potassium phosphorus tungstate having a composition shown in Table 1. Table 1 shows the results. 
     EXAMPLE 20 
     Example 14 was repeated except that the alkylating agent was changed to propylene, that the catalyst was changed to 200 mg of potassium phosphorus tungstate having a composition shown in Table 1, and that the reaction temperature was changed to 170° C. Table 1 shows the results. 
     EXAMPLE 21 
     A 50 ml autoclave was charged with 10 g of naphthalene (desulfurized, purified product, supplied by Kawasaki Steel Corp.) and 10 ml of decane together with 200 mg of potassium phosphorus tungstate having a composition shown in Table 1, and the autoclave was closed. Then, air inside the autoclave was replaced with ethylene gas, and the mixture was allowed to react with stirring under an ethylene pressure of 30 kg/cm 2  G at a temperature of 180° C. for 1 hour. After the reaction, the catalyst was separated by filtration, and the resultant reaction mixture was analyzed on its contents with gas chromatography using a capillary column (DB-1). Table 1 shows the results. 
     EXAMPLES 22-24 
     Example 14 was repeated except for the use of a metal salt of phosphorus tungstic acid having a composition shown in Table 1 (Examples 22 and 23) or phosphorus tungstic acid having a composition shown in Table 1 (Example 24). Table 1 shows the results. 
     
                                           TABLE 1                                 
__________________________________________________________________________
              Catalyst                                                    
                   Reaction                                               
                          Raw material                                    
                                 Selectivity                              
              amount                                                      
                   temperature                                            
                          conversion                                      
                                 to alkylation      Alkylating            
Example                                                                   
     Catalyst (mg) (°C.)                                           
                          (%)    reactions (mol %)                        
                                          Raw material                    
                                                    agent                 
__________________________________________________________________________
14   K.sub.2.2 H.sub.0.8 PW.sub.12 O.sub.40                               
              850  200    55     95       naphthalene                     
                                                    ethylene              
15   Cs.sub.2.2 H.sub.0.8 PW.sub.12 O.sub.40                              
              850  200    52     93       naphthalene                     
                                                    ethylene              
16   K.sub.2 HPW.sub.12 O.sub.40                                          
              850  200    61     95       naphthalene                     
                                                    ethylene              
17   KH.sub.2 PW.sub.12 O.sub.40                                          
              850  200    50     91       naphthalene                     
                                                    ethylene              
18   K.sub.2 HPW.sub.12 O.sub.40                                          
               10  260    63     89       naphthalene                     
                                                    ethylene              
19   K.sub.2 HPW.sub.12 O.sub.40                                          
              200  200    48     92       2-ethylnaphthalene              
                                                    ethylene              
20   K.sub.2 HPW.sub.12 O.sub.40                                          
              850  170    65     97       naphthalene                     
                                                    propylene             
21   K.sub.2.3 H.sub.0.7 PW.sub.12 O.sub.40                               
              200  180    69     97       naphthalene                     
                                                    ethylene              
22   K.sub.2.5 H.sub.0.5 PW.sub.12 O.sub.40                               
              200  180    67     95       naphthalene                     
                                                    ethylene              
23   K.sub.2.8 H.sub.0.2 PW.sub.12 O.sub.40                               
              200  180    59     98       naphthalene                     
                                                    ethylene              
24   H.sub.3 PW.sub.10 O.sub.40                                           
              850  200    43     85       naphthalene                     
                                                    ethylene              
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 Note)                                                                    
 Selectivity to alkylation reactions stands for the total of selectivities
 to mono, di, tri and tetraalkylated products, and descriptions of crystal
 water of catalysts are omitted (this note also applies to Tables 2, 3 and
 4 to be described later).                                                
 
    
     EXAMPLE 25 
     A 50 ml autoclave was charged with 10 g of naphthalene (purified naphthalene, supplied by Kawasaki Steel Corp.) and 10 ml of decane together with 850 mg of potassium silicotungstate having a composition shown in in Table 2, and the autoclave was closed. Then, air inside the autoclave was replaced with ethylene gas, and the mixture was allowed to react with stirring under an ethylene pressure of 30 kg/cm 2  G at a temperature of 200° C. for 2 hours. After the reaction the catalyst was separated by filtration, and the resultant reaction mixture was analyzed on its contents by gas chromatography. Table 2 shows the results. 
     EXAMPLE 26 
     Example 25 was repeated except for the use of potassium silicotungstate having a composition shown in Table 2. Table 2 shows the results. 
     EXAMPLE 27 
     Example 25 was repeated except that the catalyst was changed to 10 mg of silicotungstate having a composition shown in Table 2 and that the reaction temperature was changed to 260° C. Table 2 shows the results. 
     EXAMPLE 28 
     Example 25 was repeated except that the raw material was changed to 10 g of 2-ethylnaphthalene, that the catalyst was changed to 100 mg of potassium silicotungstate having a composition shown in Table 2. Table 2 shows the results. 
     EXAMPLE 29 
     Example 25 was repeated except for the use of 200 mg of cesium silicotungstate. Table 2 shows the results. 
     EXAMPLE 30 
     Example 25 was repeated except that the alkylating agent was changed to propylene, that the catalyst was changed to 200 mg of potassium silicotungstate having a composition shown in Table 2 and that the reaction temperature was changed to 170° C. Table 2 shows the results. 
     EXAMPLE 31 
     Example 25 was repeated except for the use of 850 mg of silicotungstungstic acid having a composition shown in Table 2. Table 2 shows the results. 
     
                                           TABLE 2                                 
__________________________________________________________________________
             Catalyst                                                     
                  Reaction                                                
                         Raw material                                     
                                Selectivity                               
             amount                                                       
                  temperature                                             
                         conversion                                       
                                to alkylation      Alkylating             
Example                                                                   
     Catalyst                                                             
             (mg) (°C.)                                            
                         (%)    reactions (mol %)                         
                                         Raw material                     
                                                   agent                  
__________________________________________________________________________
25   KH.sub.3 SiW.sub.12 O.sub.40                                         
             850  200    45     97       naphthalene                      
                                                   ethylene               
26   K.sub.2 H.sub.2 SiW.sub.12 O.sub.40                                  
             850  200    60     94       naphthalene                      
                                                   ethylene               
27   K.sub.2 H.sub.2 SiW.sub.12 O.sub.40                                  
              10  260    35     91       naphthalene                      
                                                   ethylene               
28   K.sub.2 H.sub.2 SiW.sub.12 O.sub.40                                  
             100  200    57     96       2-ethylnaphthalene               
                                                   ethylene               
29   Cs.sub.2 H.sub.2 SiW.sub.12 O.sub.40                                 
             200  200    58     94       naphthalene                      
                                                   ethylene               
30   K.sub.2 H.sub.2 SiW.sub.12 O.sub.40                                  
             200  170    53     98       naphthalene                      
                                                   propylene              
31   H.sub.4 SiW.sub.12 O.sub.40                                          
             850  200    29     89       naphthalene                      
                                                   ethylene               
__________________________________________________________________________
 
    
     EXAMPLE 32 
     A 500 ml round-bottomed flask was charged with 50 g of phosphorus tungstic acid (H 3  PW 12  O 40 .27H 2  O), and 100 g of water, and the phosphorus tungstic acid was dissolved in the water at room temperature. 2.0 Grams of potassium carbonate (special-degree reagent) was added to the solution with stirring. Thereafter, the mixture was subjected to an evaporation operation under reduced pressure with a rotary evaporator over a hot water bath at a temperature of 50° C. to give 45.6 g of potassium phosphorus tungstate. 
     FIG. 1 shows the pore distribution of the above potassium phosphorus tungstate. In FIG. 1, the ordinate axis shows the pore radius (r), and the abscissa axis shows the ratio (dv/d(log)r) of the infinitesimal change (dv) in pore volume to the infinitesimal change (d(log)r) in pore radius. The pore distribution was determined on the basis of the isothermal desorption curve of nitrogen gas at a liquid nitrogen temperature. 
     The above-obtained potassium phosphorus tungstate was used as a catalyst for the following reaction. 
     A 50 ml autoclave was charged with 10 g of naphthalene (desulfurized, purified product, supplied by Kawasaki Steel Corp.), 10 ml of decane and 200 mg of the above potassium phosphorus tungstate, and the autoclave was closed. Then, air inside the autoclave was replaced with nitrogen gas, and the mixture was allowed to react under an ethylene pressure of 30 kg/cm 2  G at a temperature of 180° C. for 1 hour. After the reaction, the catalyst was separated by filtration, and the resultant reaction mixture was analyzed to determine its components by gas chromatography. Table 3 shows the results. 
     EXAMPLES 33-35 
     Example 32 was repeated except for the use of a potassium phosphorus tungstate which had been prepared in the same manner as in Example 32 and had a composition shown in Table 3. Table 3 shows the results. 
     EXAMPLES 36-38 
     A potassium carbonate aqueous solution having a concentration shown in Table 3 was added to phosphorus tungstic acid aqueous solution to give a catalyst of potassium phosphorus tungstate shown in Table 3. Then, the reaction was carried out in the same manner as in Example 32. Table 3 shows the results. FIG. 2 shows the pore distribution of the catalyst used in Example 38. 
     
                       TABLE 3                                                     
______________________________________                                    
                                     Amount of                            
      Potassium phos-       Naphthalene                                   
                                     ethylation*                          
Ex-   phorus tungstate      conversion                                    
                                     (mmol/g ·                   
ample (catalyst)   K.sub.2 CO.sub.3                                       
                            (%)      cat)                                 
______________________________________                                    
32    HK.sub.2 PW.sub.12 O.sub.40                                         
                   solid    65       360                                  
33    H.sub.0.7 K.sub.2.3 PW.sub.12 O.sub.40                              
                   solid    69       404                                  
34    H.sub.0.5 K.sub.2.5 PW.sub.12 O.sub.40                              
                   solid    71       419                                  
35    H.sub.0.2 K.sub.2.8 PW.sub.12 O.sub.40                              
                   solid    59       328                                  
36    HK.sub.2 PW.sub.12 O.sub.40                                         
                   2%       58       313                                  
                   aqueous                                                
                   solution                                               
37    HK.sub.2 PW.sub.12 O.sub.40                                         
                   10%      61       327                                  
                   aqueous                                                
                   solution                                               
38    H.sub.0.5 K.sub.2.5 PW.sub.12 O.sub.40                              
                   2.5%     67       377                                  
                   aqueous                                                
                   solution                                               
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     COMPARATIVE EXAMPLE 1 
     Example 1 was repeated except that the phosphorus tungstic acid was replaced with 200 mg of H +  -ZSM5 which had been preliminarily dried under heat at 200° C. 
     The reaction results are as follows: Naphthalene conversion 0.1%, and selectivity to monoethylnaphthalenes 99%. 
     COMPARATIVE EXAMPLE 2 
     A 50 ml autoclave was charged with 700 mg of naphthalene, 100 mg of aluminum chloride and 2 ml of 1,2-dichloroethane. Then, ethylene was introduced into the autoclave under pressure until the ethylene pressure became 60 kg/cm 2  G, and the mixture was allowed to react with stirring at 30° C. for 5 hours. 
     The reaction results are as follows: Naphthalene conversion 49%, Selectivity to monoethylnaphthalenes 29%, selectivity to diethylnaphthalenes 18%, selectivity to triethylnaphthalenes 6%, and tar formation ratio 43%. 
     COMPARATIVE EXAMPLE 3 
     An attempt was made to repeat Example 1 by the use of 100 mg of p-toluenesulfonic acid in place of phosphorus tungstic acid. However, no reactions took place. 
     COMPARATIVE EXAMPLES 4-6 
     Example 14 was repeated except for the use of a catalyst shown in Table 4 and employment of the conditions shown in Table 4. Table 4 shows the results. 
     
                                           TABLE 4                                 
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            Catalyst                                                      
                 Reaction                                                 
                        Raw material                                      
                               Selectivity                                
            amount                                                        
                 temperature                                              
                        conversion                                        
                               to alkylation   Alkylating                 
Example                                                                   
     Catalyst                                                             
            (mg) (°C.)                                             
                        (%)    reactions (mol %)                          
                                        Raw material                      
                                               agent                      
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4    AlCl.sub.3                                                           
              50 100    27     87       naphthalene                       
                                               ethylene                   
5    Silica alumina                                                       
            3,000                                                         
                 200     8     --       naphthalene                       
                                               ethylene                   
6    H--Y zeolite                                                         
            3,000                                                         
                 200    53     80       naphthalene                       
                                               ethylene                   
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