Abstract:
The present invention relates to a process for decomposing an aromatic acylated compound.HF-BF 3  complex in preparing an aromatic acylated compound by decomposing an aromatic acylated compound.HF-BF 3  complex obtained by reacting an aromatic compound with an acylating agent in the presence of HF-BF 3  as a catalyst, which comprises subjecting the aromatic acylated compound.HF-BF 3  complex to thermal decomposition in the presence of at least one aromatic hydrocarbon (A.H.) selected from benzene, toluene and chlorobenzene and at least one saturated aliphatic hydrocarbon (S.H.) selected from pentane, hexane and cyclohexane, as a decomposing agent.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a process for decomposing an aromatic acylated compound.sup.. HF-BF 3  complex in preparing an aromatic acylated compound by decomposing an aromatic acylated compound.sup.. HF-BF 3  complex obtained by reacting an aromatic compound with an acylating agent in the presence of HF-BF 3  used as a catalyst. 
     It is already known to obtain an aromatic acylated compound by reacting an aromatic compound with an acylating agent in the presence of HF-BF 3  as a catalyst. For example, Japanese Patent Application Kokai (Laid-open) No. 54-135756 discloses a method of obtaining a 2-alkyl-6-acylnaphthalene by reacting a 2-alkylnaphthalene with an acylating agent in the presence of HF and BF 3 . EP-A-0215351 discloses a method which comprises first converting an acid anhydride into an acyl fluoride in an acylating agent synthesis step, and then obtaining an aromatic acylated compound in the presence of HF and BF 3  by using the isolated acylfluoride in an acylated compound synthesis step. 
     The reaction produced liquids obtained by these methods are each a HF solution of an aromatic acylated compound.sup.. HF-BF 3  complex. On heating the liquid, the linkage between the aromatic acylated compound and HF-BF 3  is decomposed and HF and BF 3  are recycled for use as catalyst. 
     For separation of the aromatic acylated compound and HF and BF 3  from the reaction produced liquid, the following methods have hitherto been proposed: 
     (1) a method comprising heating the liquid at 20°-40° C. under reduced pressure to decompose the aromatic acylated compound.sup.. HF-BF 3  complex and distilling HF and BF 3  away in the form of gas to effect separation, 
     (2) a method comprising adding to the liquid a nitrogen compound such as ammonia, monoethylamine, piperidine, acetonitrile, nitroaniline, and chloroaniline to form a molecular compound, separating the molecular compound, and then heating it or reacting it with sulfuric acid, etc. to separate HF and BF 3 . 
     (3) a method comprising adding a decomposing agent inert to HF and BF 3 , e.g. aromatic hydrocarbons or halogenated aromatic hydrocarbons such as benzene, toluene and chlorobenzene (these aromatic hydrocarbons are hereinafter referred to as A.H.) and heating the mixture under reflux of the agent to effect decomposition. 
     The aromatic acylated compound in the reaction produced liquid obtained by reacting an aromatic compound with an acylating agent using HF-BF 3  as catalyst is susceptible to deterioration by heating, so that the above-mentioned operations need to be carried out as rapidly as possible. The prior methods for decomposing aromatic acylated compound.sup.. HF-BF 3  complex have the following difficulties. 
     (1) In the method of heating under reduced pressure, the degree of pressure reduction is determined according to the boiling point of acetylated compound. Aliphatic acylated compounds such as acetyl fluoride, propionyl fluoride and isobutyryl fluoride have relatively low boiling points, so that HF-BF 3  can be separated at temperatures of 20°-40° C. under low degree of pressure reduction. However, since aromatic acylated compounds have high boiling points, a considerably high degree of vacuum (namely, degree of pressure reduction) is necessary to distil the compounds at said temperature, which requires much power. Further, HF and BF 3  are highly corrosive and can incur great danger if air leaks into the apparatus under high vacuum. Therefore, this method is difficult to practice on commercial scale. 
     (2) The method comprising adding nitrogen compounds to form molecular compounds and then decomposing the latter compounds newly requires operations of separating the molecular compounds. Accordingly, the catalyst recovery step becomes very complicated and the method is not suited to practical use. 
     (3) In the method of using inert decomposing agents, usually a decomposition-distillation column provided with a heater at the column bottom is used to effect the separation of catalyst as rapidly as possible. The inert agents used are the above-mentioned A.H. The aromatic acylated compound.sup.. HF BF 3  complex is rapidly decomposed by contact with the A.H. vapor and is distilled, while HF and BF 3  are separated from the column top. However, a part of A.H. is entrained with HF and BF 3  and is distilled out from the column top along with HF and BF 3 . HF and BF 3  are cooled in a condenser together with A.H. vapor, HF and A.H. are condensed, and BF 3  is separated as non-condensable gas. The condensate is separated in a separator into HF and A.H.. The separated HF contains A.H. associated with the non-condensable gas (BF 3 ), dissolved therein. When the concentration of A.H. in HF is high, alkylated products and acylated products of said A.H. are formed by side reactions in the acylating agent synthesis step using recovered HF, resulting in decrease in yields in the acylating agent synthesis step and in the synthesis step of intended acylated compounds. Further, since the alkylated products of A.H., e.g. tetraisopropylbenzene, is insoluble in HF, they can cause blockages of piping, etc. Thus, the A.H. becomes an obstacle to the recycling of HF and BF 3  of the catalyst. Although there is further known, to separate A.H. dissolved in HF, a method comprising subjecting the HF solution after separation of non-condensable gas (BF 3 ) to redistillation, this method requires a separate distillation column which requires a considerably large number of stages and reflux ratio. Therefore, the construction cost becomes high and energy consumption for redistillation is large. 
     SUMMARY OF THE INVENTION 
     The present inventors have made extensive studies on the process for decomposing aromatic acylated compound.sup.. HF-BF 3  complexes, which has had difficulties as described above. As the result, it has been found that when the HF-BF 3  complex is distilled by using, as a decomposing agent, a liquid mixture of said A.H. with at least one saturated hydrocarbons selected from pentane, hexane and cyclohexane, which has a lower boiling point than that of A.H., (these saturated hydrocarbons being hereinafter referred to as S.H.), the A.H. concentration in the decomposing agent at the column top decreases markedly and the A.H. concentration in recovered HF also decreases and that resultant side reactions in the acylating agent synthesis step which uses recovered HF and in the acylated compound synthesis step are suppressed, the yields of the acylating agent and acylated compound are improved, and recycling of catalyst is facilitated, and thus attained the present invention. 
     Thus, according to the present invention, there is provided a process for decomposing an aromatic acylated compound.sup.. HF-BF 3  complex in preparing an aromatic acylated compound by decomposing an aromatic acylated compound.sup.. HF-BF 3  complex obtained by reacting an aromatic compound with an acylating agent in the presence of HF-BF 3  as a catalyst, which comprises subjecting the aromatic acylated compound.sup.. HF-BF 3  complex to thermal decomposition in the presence of at least one aromatic hydrocarbon (A.H.) selected from benzene, toluene and chlorobenzene and at least one saturated aliphatic hydrocarbon (S.H.) selected from pentane, hexane and cyclohexane, as a decomposing agent. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows an example of a decomposition-distillation column used in the present invention for decomposing an aromatic acylated compound.sup.. HF-BF 3  complex and separating the aromatic acylated compound from HF-BF 3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The aromatic compounds used for obtaining the acylated compounds according to the present invention include, for example, alkylbenzenes such as toluene, xylene, cumene, and butylbenzene, naphthalene, alkyl naphthalenes such as methylnaphthalene and the like, phenols and naphthols, and aromatic ethers such as anisol and phenyl ether. 
     The acylating agents include, for example, acyl fluoride such as acetyl fluoride, propionyl fluoride, isobutyryl fluoride, ethylmethylacetyl fluoride, and benzoyl fluoride, carboxylic acids such as acetic acid, propionic acid and butyric acid and the esters thereof, and acid anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride. 
     The amount of the acylating agent to be used is 1.3 or less, preferably 0.8-1.0, in terms of molar ratio relative to the starting aromatic compound. When the acylating agent is in excess, the agent will remain in the reaction produced liquid and exert an undesirable influence at the time of catalyst separation. 
     The amount of HF to be used is 5 times by mole or more, preferably 10-15 times by mole, to the amount of acylating agent. BF 3  is preferably used in an equivalent amount to the acylating agent or in slight excess. 
     The temperature of acylation is -20°˜+30° C., preferably -10°˜+20° C. Elevating the temperature results in increase in reaction velocity but also in increase in side-reaction velocity. The reaction temperature should be determined also in consideration of the melting points of raw materials. 
     The reaction is carried out, under usual conditions, at a slightly applied pressure of from normal pressure to 5 kg/cm 2  G. The pressure is determined according to the molar ratio of the catalyst used and the reaction temperature. 
     Since the reaction proceeds in a homogeneous liquid phase, it requires no vigorous stirring. 
     The reaction produced liquid thus obtained is a HF solution of an aromatic acylated compound.sup.. HF-BF 3  complex, HF-BF 3  is decomposed from the complex by heating, and HF and BF 3  can be vaporized and separated. 
     The catalyst separation needs to be operated as rapidly as possible to avoid thermal deterioration of the reaction product. Although it is already known that using A.H. as a decomposing agent inert to HF-BF 3  is effective for thermal decomposition of the complex to proceed smoothly, it has been further found that the use of a liquid mixture of A.H. and S.H. lowers the concentration of A.H. in the decomposing agent accompanying HF-BF 3 , and hence is advantageous in operations of catalyst recycling. 
     As to the mixing proportion of A.H. and S.H., the amount of S.H. is 0.1-0.8 times by weight, preferably 0.2-0.5 times by weight, relative to A.H. When the proportion of S.H. to A.H. is too small, the amount of A.H. associated with HF and BF 3  increases, which results in such difficulties as causing decrease in yields and blockages of piping in the acylating agent synthesis step and the acylated compound synthesis step. On the other hand, when the proportion of S.H. to A.H. is too large, the solubility of the aromatic acylated compound in the decomposing agent decreases, resulting in deposition of the acylated compounds in the distillation column, packed column, or piping and leading to the risk of blocking. 
     The amount of the decomposing agent to be used is 0.2-1.5 times by weight, preferably 0.5-1.0 times by weight, relative to the amount of reaction liquid. When the amount of the decomposing agent used is too large, energy consumption necessary for heating increases. When the amount is too small, it results in a risk of causing blockages in pipelines etc. since the solubility of the acylated compound is decreased. 
     An example of apparatuses used for decomposition of an aromatic acylated compound.sup.. HF-BF 3  complex using a liquid mixture of A.H. and S.H. and separation of the aromatic acylated compound from HF and BF 3  is a distillation apparatus as shown in FIG. 1. In FIG. 1, the reaction produced liquid is introduced through a passage 1 into a distillation column 2. A liquid mixture of A.H. and S.H., the decomposing agent, is introduced through a passage 3. A packed column or a plate column is used for the distillation column 2. To increase the efficiency of separation of HF and BF 3  from the aromatic acylated compound, the packed column, when it is used, is divided into an upper packed part 4, middle packed part 5 and lower packed part 6, and the reaction produced liquid is supplied between the upper packed part 4 and the middle packed part 5, and the decomposing agent between the middle packed part 5 and the lower packed part 6. 
     Heating at a reboiler 7 yields the vapor of HF, BF 3  and the decomposing agent from the top of the distillation column. In a primary condenser 8, mainly a part of the decomposing agent and an azeotropic composition of three components, namely HF, BF 3  and water, are condensed. In a primary separator 9, the decomposing agent and the azeotropic composition separate into two layers owing to density difference. The decomposing agent is withdrawn through a passage 10 and refluxed to the distillation column. The azeotropic composition containing HF, BF 3  and water is withdrawn through a passage 12. From a passage 11, are separated the vapors of HF and BF 3  and of the decomposing agent containing a low concentration of A.H., and further condensed in a secondary condenser 13. From a secondary separator 14, BF 3  vapor is recovered through a passage 16 and, as to the condensed decomposing agent and HF, HF is recovered through a passage 15 based on the difference in density, and the decomposing agent is refluxed through a passage 17 to the distillation column. At the column bottom, a liquid containing the aromatic acylated compound and the decomposing agent is obtained through a passage 18. The liquid is sent to the purification step of the aromatic acylated compound, where the decomposing agent is separated and recycled to the distillation column. 
     The catalyst separation described above is favorably operated under normal or slightly applied pressure from the viewpoint of process advantage. It requires heating at 100°-180° C. at the column bottom. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
     The present invention will be described further in detail below with reference to Examples. However, the invention is in no way limited by the Examples. 
     EXAMPLE 1 
     In FIG. 1, a distillation column 55 mm in inner diameter and 1,300 mm in hight was packed with 1/2B Raschig rings, the upper packed part being filled in a depth of 0.3 m, the middle packed part in a depth of 0.3 m, and the lower packed part in a depth of 0.4 m, and a HF-BF 3  complex was decomposed therein. 
     The reaction liquid fed to the distillation column contained about 16% by weight of 2-isobutyryl-6-methylnaphthalene (hereinafter abbreviated as BMN) obtained by acylation of 2-methylnaphthalene using isobutyryl fluoride as an acylating agent. The liquid feed rate was 2855 g/hr. The decomposing agent used was a liquid mixture of benzene (Bz) and hexane (Hx) of a weight ratio of 80:20. The amount and the composition of the reaction produced liquid, operation conditions for the distillation column, etc. are shown in Table 1. The concentration of benzene in HF recovered from the column top was found to be 2.2% by weight. 
     EXAMPLE 2 
     An experiment was conducted in the same manner as in Example 1 except that a reaction produced liquid containing about 20% by weight of BMN was fed at a rate of 4000 kg/hr. The amount and the composition of the reaction produced liquid, operation conditions for the distillation column, etc. are shown in Table 1. The concentration of benzene in HF recovered from the column top was found to be 2.0% by weight. 
     EXAMPLE 3 
     An experiment was conducted in the same manner as in Example 1 except that a liquid mixture of benzene and hexane in a weight ratio of 70:30 was used as a decomposing agent and a reaction liquid containing about 21% by weight of BMN was fed at a rate of 3653 kg/hr. The amount and the composition of the reaction produced liquid, operation conditions for the distillation column, etc. are shown in Table 1. The concentration of benzene in HF recovered from the column top was found to be 0.3% by weight. 
     EXAMPLE 4 
     An experiment was conducted in the same manner as in Example 3 except that a reaction produced liquid containing about 25% by weight of BMN was fed at a rate of 3342 kg/hr. The amount and the composition of the reaction produced liquid, operation conditions for the distillation column, etc. are shown in Table 1. The concentration of benzene in HF recovered from the column top was found to be 0.9% by weight. 
     EXAMPLE 5 
     An experiment was conducted in the same manner as in Example 1 except that a reaction produced liquid containing about 29% by weight of 1-isobutyryl-2,4-dimethylbenzene (hereinafter abbreviated as BDMB) obtained by acylation of m-xylene using isobutyl fluoride as an acylating agent was fed at a rate of 1776 g/hr. The amount and the composition of the reaction produced liquid, operation conditions for the distillation column, etc. are shown in Table 1. The concentration of benzene in HF recovered from the column top was found to be 2.1% by weight. 
     EXAMPLE 6 
     The procedures in Example 1 were repeated except that a reaction produced liquid containing about 29% by weight of 2,4&#39;-dimethyl-butyrophenone (hereinafter abbreviated as DMBP) obtained by acylation of toluene using ethylmethylacetyl fluoride as an acylating agent was fed at a rate of 2,200 g/hr. The amount and the composition of the reaction produced liquid, operating conditions for the distillation column, etc. are shown in Table 1. The concentration of benzene in HF recovered from the column top was found to be 2.0% by weight. 
     EXAMPLE 7 
     The procedures in Example 1 were repeated except that a liquid mixture of toluene (T1) and hexane was used as a decomposing agent and a reaction produced liquid containing about 32% of BMN was fed at a rate of 2600 g/hr. The amount and the composition of the reaction liquid, operation conditions for the distillation column, etc. are shown in Table 1. The concentration of toluene in HF recovered from the column top was found to be 1.8% by weight. 
     
                                           TABLE 1__________________________________________________________________________Example No.    1    2   3   4   5   6   7   8   9    Comp.                                                     Comp. 2Acylated compound          BMN  BMN BMN BMN BDMB                               DMBP                                   BMN BMN BMN  BMN  BMN__________________________________________________________________________Feed rate of reaction          2855 g/H               4000                   3653                       3342                           1776                               2200                                   2600                                       4300                                           2900 2085 3600produced liquid HF       1600 1750                   1900                       1470                           670 907 1100                                       1700                                           1450 1005 1850 BF3      450  796 366 539 446 487 503 881 519  335  660 Break- Acylated 456  782 759 829 517 628 831 1415                                           767  560  961 compounddown  Unreacted          235  369 389 322  63  25  66 169  74   92   13 material Others   114  303 239 182  80 153 100 135  90   93  116Decomposing agent          Bz/Hx               Bz/Hx                   Bz/Hx                       Bz/Hx                           Bz/Hx                               Bz/Hx                                   T1/Hx                                       T1/Pn                                           CB/CH                                                Bz   T1Mixing ratio   80:20               80:20                   70:30                       70:30                           80:20                               80:20                                   80:20                                       80:20                                           70:30                                                100  100Feed rate      1420 g/H               1336                   1220                       1545                           650 650 1402                                       1402                                           1818 1405 1560Decomposition operationconditionsPressure       4.0 K/G               4.0 4.0 4.0 4.0 4.0 4.0 4.0 2.0  4.0  4.0Temperature    150° C.                158                    156                        155                           158 158 170 165 165  155  173Overhead withdrawal rateBF.sub.3        444 g/H               788 344 513 444 450 495 859 503  329  652HF             1592 1732                   1890                       1465                           666 899 1056                                       1666                                           1431 996  1806Decomposing agent           100  120                   24   43  50 117 160 198  70   59   60A.H. concentration in HF          2.2 wt %               2.0 0.3 0.9 2.1 2.0 1.8 1.6 1.5  5.9  4.7Bottom withdrawal rateAcylated compound           449 g/H               762 744 817 509 575 814 1394                                           744  550  894Decomposing agent          1320 1216                   1196                       1502                           600 533 1242                                       1204                                           1748 1346 1500Unreacted material          122  228 265 183  15  5   26 126  17   60   20Others         248  490 467 364 142 271 209 255 205  150  228__________________________________________________________________________ 
    
     EXAMPLE 8 
     The procedures in Example 1 were repeated except that a liquid mixture of toluene and pentane (P n ) was used as a decomposing agent and a reaction liquid containing about 33% by weight of BMN was fed at a rate of 4300 g/hr. The amount and the composition of the reaction produced liquid, operation conditions for the distillation column, etc. are shown in Table 1. The concentration of toluene in HF recovered from the column top was found to be 1.6% by weight. 
     EXAMPLE 9 
     The procedures in Example 1 were repeated except that a liquid mixture of chlorobenzene (CB) and cyclohexane (CH) was used as a decomposing agent and a reaction produced liquid containing about 26% by weight of BMN was fed at a rate of 2900 g/hr. The amount and the composition of the reaction produced liquid, operation conditions for the distillation column, etc. are shown in Table 1. The concentration of chlorobenzene in HF recovered from the column top was found to be 1.5% by weight. 
     COMPARATIVE EXAMPLE 1 
     The procedures in Example 1 were repeated except that benzene alone was used as a decomposing agent in place of the liquid mixture of benzene and hexane, and a reaction produced liquid containing about 27% by weight of BMN was fed at a rate of 2085 g/hr. The amount and the composition of the reaction liquid, operation conditions for the distillation column, etc. are shown in Table 1. The concentration of benzene in HF recovered from the column top was found to be 5.9% by weight. 
     COMPARATIVE EXAMPLE 2 
     The procedures in Example 1 were repeated except that toluene alone was used as a decomposing agent and a reaction liquid containing about 27% by weight of BMN was fed at a rate of 3600 g/hr. The amount and the composition of the reaction produced liquid, operation conditions for the distillation column, etc. are shown in Table 1. The concentration of toluene in HF recovered from the column top was found to be 4.7% by weight. 
     EFFECT OF THE INVENTION 
     As shown in respective Examples, when a liquid mixture of A.H. and S.H. is used as a decomposing agent, the amount of A.H. contained in recovered HF and BF 3  as catalyst has advantages in that aromatic compounds can be easily acylated by simple operations and at low pressure and that HF-BF 3  can be recycled for use as catalyst. According to the present invention, the acylation process is further improved and the yields in the acylating agent synthesis step and the acylated compound synthesis step are improved. Thus, the present invention is of great industrial importance.