Catalytic preparation of tertiary butyl alcohol by decomposition of tertiary butyl hydroperoxide
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the catalytic decomposition of tertiary butyl hydroperoxide. More particularly, this invention relates to a method for the preparation of tertiary butyl alcohol by the catalytic decomposition of tertiary butyl hydroperoxide. Still more particularly, this invention relates to a method wherein the substantially selective decomposition of tertiary butyl hydroperoxide to tertiary butyl alcohol is accomplished in the presence of a phthalocyanine catalyst, a mercaptan and a free radical inhibitor. 
     2. Prior Art 
     It is known to react isobutane with oxygen, either thermally or catalytically, to form a peroxidation reaction product wherein the principal peroxide that is formed is tertiary butyl hydroperoxide. It is also known to thermally or catalytically decompose the tertiary butyl hydroperoxide to form tertiary butyl alcohol. 
     The metal phthalocyanines are known compounds, described for example in the ACS Monograph Series by F. H. Moser and A. L. Thomas entitled &#34;Phthalocyanine Compounds&#34; (Rhinehold Publishing Corp.). 
     Williams et al. U.S. Pat. No. 3,816,548 is directed to a liquid phase oxidation process for oxidizing an isoparaffin hydrocarbon such as isobutane to an alcohol such as tertiary butyl alcohol in the presence of certain metal phthalocyanine catalysts. 
     Klein in U.S. Pat. No. 3,472,876, discloses the use of cobalt diimine chelates to catalyze the reaction of oxygen with an olefin to form an olefin epoxide. 
     Quin U.S. Pat. No. 2,854,487 discloses a process wherein isopropyl benzene hydroperoxides are catalytically decomposed to form carbinols in the presence of hydrogen and a catalyst composed of palladium supported on activated alumina. 
     Grane U.S. Pat. No. 3,474,151 discloses that tertiary butyl alcohol starts to dehydrate at 450° C. and to decompose at a &#34;rapid rate&#34; at temperatures above 475° F. Grane discovered, however, that residual quantities of hydroperoxide contaminants present in tertiary butyl alcohol could be thermally decomposed by heating the contaminated tertiary butyl alcohol at a temperature of 375° to 475° F. for about 1 to 10 minutes. Heating tertiary butyl alcohol containing small amounts of peroxides at high temperatures for even short periods of time to remove the peroxides produces undesirable products such as isobutylene. 
     Grane et al. U.S. Pat. No. 4,294,999 discloses a process wherein isobutane is oxidized in a pressured reactor in the presence of a solubilized molybdenum catalyst to provide a mixture of tertiary butyl alcohol, tertiary butyl hydroperoxide, methanol, acetone, and other oxygen-containing compounds. The tertiary butyl hydroperoxide is thermally decomposed under pressure at about 280° F. to provide a tertiary butyl alcohol product containing only residual quantities of tertiary butyl hydroperoxide which are then decomposed in accordance with Grane U.S. Pat. No. 3,474,151 by heating the tertiary butyl alcohol at 375° to 475° for about 1 to 10 minutes. 
     Grane et al. U.S. Pat. No. 4,296,262 discloses a related process wherein isobutane is reacted with oxygen in a reaction zone for a residence time of about 1 to 10 hours at a temperature of about 240° to about 340° F. and a pressure of about 100 to about 1000 psig. in the presence of a catalytically effective amount of a soluble molybdenum catalyst. A liquid stream comprising tertiary butyl alcohol is recovered from the reaction mixture and fed to a decomposition zone wherein the tertiary butyl hydroperoxide contained therein is decomposed by &#34;hot aging&#34; at 250°-350° F. at a pressure lower than the pressure in the oxidation zone. The tertiary butyl alcohol can be further subjected to a cleanup treatment at 375°-475° F. for 1 to 10 minutes. Worrell et al. in U.S. Pat. No. 4,296,263 disclose a related process wherein the feedstock is a mixture of normal butane with isobutane and wherein the oxidation catalyst is a soluble form of chromium, cobalt, nickel, manganese, molybdenum, or a mixture thereof. 
     When isobutane is reacted with molecular oxygen, the principal products of the reaction are tertiary butyl alcohol and tertiary butyl hydroperoxide. However, minor amounts of other peroxides, including ditertiary butyl peroxide are also formed. Generally speaking, from about 10 to about 100 parts of tertiary butyl hydroperoxide are formed per part of ditertiary butyl peroxide. Minor quantities of other contaminants are also formed. 
     In addition, a minor amount of water will be formed, which will normally amount to about 0.5 to 1 wt. % of the reactor effluent. The amount of byproduct water that is produced is a function of the severity of the reaction conditions employed and will tend to increase as the severity of the reaction conditions is increased. 
     A listing of the components present in a representative reaction product from the reaction of isobutane and their nominal boiling points is given in Table A. 
     
                       TABLE A                                                     
______________________________________                                    
Component           NBP (°C.)                                      
______________________________________                                    
Isobutane           -11.7                                                 
Methyl formate      31.8                                                  
Acetone             56.3                                                  
Isobutylene oxide   60.0                                                  
Isobutyraldehyde    64.1                                                  
Methanol            64.7                                                  
Methyl-t-butyl peroxide                                                   
                    74.2                                                  
Isopropyl alcohol   82.3                                                  
Tertiary butyl alcohol                                                    
                    82.4                                                  
Ditertiary butyl peroxide                                                 
                    111.0                                                 
Tertiary butyl hydroperoxide                                              
                    118.9                                                 
t-butyl-i-pr-peroxide                                                     
                    124.0                                                 
Tertiary butyl formate                                                    
                    163.8                                                 
______________________________________                                    
 
    
     The minor by-products are sometimes difficult to remove. For example, tertiary butyl formate has a higher boiling point than ditertiary butyl peroxide but tends to distill overhead, which suggests that it forms a minimum boiling azeotrope with another component or components. 
     As indicated, tertiary butyl hydroperoxide is useful as a raw material for the manufacture of tertiary butyl alcohol. The tertiary butyl alcohol can be formed by catalytic decomposition of the tertiary butyl hydroperoxide. In the Williams et al. process disclosed in U.S. Pat. No. 3,472,876, an oxygen-containing gas was charged to a reactor containing isobutane and an oxidation catalyst to provide a reaction mixture comprising tertiary butyl alcohol, tertiary butyl hydroperoxide, acetone, and tertiary butyl ether. The reported results in the patent indicate that there was a comparatively low rate of conversion and a comparatively poor selectivity of the reaction to tertiary butyl alcohol. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, isobutane is reacted with oxygen in an oxidation zone to provide an oxidation product comprising a solution of tertiary butyl hydroperoxide in tertiary butyl alcohol and unreacted isobutane. A catalyst may be present to catalyze the reaction of the oxygen with the isobutane if desired. 
     A suitable feedstock is used, such as one prepared by the oxidation of isobutane with molecular oxygen to provide an oxidation reaction product containing a solution of tertiary butyl hydroperoxide in tertiary butyl alcohol and unreacted isobutane. The feedstock may comprise tertiary butyl hydroperoxide dissolved in tertiary butyl alcohol which is recovered from the oxidation reaction product. The feedstock is charged to a catalytic decomposition zone wherein the tertiary butyl hydroperoxide is decomposed in the presence of a catalyst composition of the present invention to provide a decomposition reaction product characterized by a comparatively high conversion rate and a comparatively high selectivity of tertiary butyl hydroperoxide to tertiary butyl alcohol. 
     The tertiary butyl alcohol will not be the only decomposition product that is formed. A minor amount of ditertiary butyl peroxide will also be formed together with other oxygen-containing materials such as those listed above. 
     The tertiary butyl alcohol that is recovered from the decomposition reaction mixture will be contaminated with ditertiary butyl peroxide and other oxygenated impurities. 
     The ditertiary butyl peroxide can be recovered, if desired, by a process such as the process disclosed in copending Sanderson et al. U.S. patent application Ser. No. 06/945,628, filed Dec. 23, 1986, and entitled &#34;Recovery of Purified Ditertiary Butyl Peroxide&#34; or the process disclosed in copending application Ser. No. 06/945,629, filed Dec. 23, 1986 by Sanderson et al., and entitled &#34;Ditertiary Butyl Peroxide Recovery&#34;, now U.S. Pat. No. 4,810,809. 
     If desired, the ditertiary butyl peroxide and other contaminants may be removed from the tertiary butyl alcohol product by a catalytic purification process such as, for example, the purification process disclosed in copending Sanderson et al. U.S. patent application Ser. No. 06/836,798, filed Mar. 6, 1986, and entitled &#34;Removal of Peroxide Contaminants from Tertiary Butyl Alcohol Using a Nickel Catalyst&#34;, now abandoned or by a purification process disclosed in copending Sanderson et al. U.S. patent application Ser. No. 06/926,159, filed Nov. 3, 1986, and entitled &#34;Catalytic Removal of Peroxide Contaminants from Tertiary Butyl Alcohol&#34;, now U.S. Pat. No. 4,742,179, issued May 3, 1988, or by the process disclosed in copending Sanderson et al. application Ser. No. 06/932,822, filed Nov. 20, 1986, and entitled &#34;Catalytic Decomposition of Impurities in Tertiary Butyl Alcohol&#34;, now U.S. Pat. No. 4,705,903, issued Nov. 10, 1987, or, as yet another example, by the process disclosed in copending Sanderson et al. U.S. patent application Ser. No. 07/004,508, filed Jan. 30, 1987, and entitled &#34;Catalyst for Removing Peroxide Contaminants from Tertiary Butyl Alcohol&#34;, now U.S. Pat. No. 4,873,380. 
     DESCRIPTION OF THE PROCESS OF THE PRESENT INVENTION 
     The starting materials for the process of the present invention are tertiary butyl hydroperoxide, a metal phthalocyanine catalyst, a mercaptan, free radical inhibitor and a solvent. 
     The solvent to be used in practicing the process of the present invention may be any suitable organic solvent in which tertiary butyl hydroperoxide is soluble at least to an extent sufficient to provide a solution containing from about 5 to about 50 wt. % of tertiary butyl hydroperoxide. A preferred solvent is isobutane and a still more preferred solvent is tertiary butyl alcohol or a mixture thereof with isubutane. In accordance with the most preferred embodiment of the present invention, the charge material for the process will comprise about a 5 to about a 30 wt. % solution of tertiary butyl hydroperoxide and tertiary butyl alcohol. 
     The yield and selectivity are improved if the catalyst composition also contains an appropriate mercaptan and/or an appropriate free radical inhibitor. Mercaptans and free radical inhibitors are well known classes of catalyst modifiers that are discussed in greater detail, for example, in texts such as W. A. Pryor, &#34;Free Radicals&#34;, McGraw Hill, New York, 1966. 
     The metal phthalocyanine catalyst used in this invention is suitably a phthalocyanine of a heavy metal selected from the Group IB, Group VIIB, or Group VIIIB of the Periodic Table. 
     Phthalocyanine itself is: ##STR1## 
     The two hydrogens in the center of the molecule are replaced by metals from these groups. The metals may be in a high oxidation state or a lower oxidation state. For example, Ferric (Fe +++ ) or Ferrous (Fe ++ ) may be used. In addition, from 1 to 16 of the peripheral hydrogen atoms on the 4 benzene rings may be replaced with halogen atoms and by numerous organic and inorganic groups. Suitable phthalocyanines include cobalt phthalocyanine, copper phthalocyanine, chloroferric phthalocyanine, ferrous phthalocyanine, manganese phthalocyanine, and ruthenium phthalocyanine. 
     A free-radical inhibitor is a compound which will scavenge free-radicals. These inhibitors may react with radicals to produce another radical either too stable to react or reactive in some new pathway. Phenols, amines, quinones and other similar materials with active hydrogen are inhibitors. 
     Examples of inhibitors are: phenol, hydroquinone, 2,3-dihydroxynapthalene, quinone, N,N&#39;-diphenylphenylenediamine, etc. 
     An alkyl thiol or alkyl mercaptan (R-S-H) where R=alkyl group with C 1  to C 18 . For example, methane thiol (methyl mercaptan), butane thiol, pentane thoil, octane thiol, and dodecane thiol (dodecyl mercaptan). 
     A catalytically effective amount of a metal phthalocyanine should be used (e.g., from about 0.001 to about 5 wt. %, based on the weight of the tertiary butyl hydroperoxide charge). From about 0.2 to about 5 parts by weight of chain transfer agent per part of chloroferric phthalocyanine may be used, as may from about 0.2 to about 5 parts by weight of mercaptan, per part of chloroferric phthalocyanine catalyst. From about 1 to about 1.5 parts by weight, per part of the chloroferric phthalocyanine, of 2,3-dihydroxynaphthalene and about 1 to about 20 parts by weight, per part of 2,3-dihydroxynaphthalene of a C 1  -C 18  alkyl thiol may be employed. 
     The process of the present invention may be conducted batchwise in kettles or by continuously passing the reactants through a reactor. 
     The solvent solution of tertiary butyl hydroperoxide that is charged to the reaction zone should also have dissolved or slurried therein from about 0.001 to about 5 wt. %, based on the weight of the tertiary butyl hydroperoxide, of a metal phthalocyanine catalyst, from about 0.2 to about 5 parts by weight, per part of phthalocyanine catalyst, of a mercaptan and about 0.2 to 5 parts by weight of a free radical inhibitor per part of phthalocyanine catalyst. 
     The catalytic decomposition of the tertiary butyl hydroperoxide is preferably conducted at a temperature within the range of about 20° to about 125° C. and, more preferably, at a temperature within the range of about 30° to about 60° C. The reaction is preferably conducted at autogeneous pressure although superatmospheric pressures up to about 1000 psig. may be used, if desired. 
     Flow rates of the charge solution to the reaction zone should be adjusted in order to provide an appropriate contact time within the reactor. In a batch process, the holding time may suitably be from about 0.5 to about 10 hours. 
     In accordance with the most preferred embodiment of the present invention, isobutane is reacted with oxygen in an oxidation zone under oxidation reaction conditions including a temperature of about 135° to about 155° C., a pressure of about 300 to about 800 psig., and a holding time of about 0.5 to about 5 hours to provide an initial oxidation reaction product comprising unreacted isobutane, tertiary butyl hydroperoxide, and some tertiary butyl alcohol. The oxidation reaction product is fractionated in any appropriate manner (e.g., by distillation in a distillation zone) to remove the isobutane therefrom for recycle and to provide a solution of tertiary butyl hydroperoxide and tertiary butyl alcohol which will normally contain from about 5 to about 30 wt. % of tertiary butyl hydroperoxide. The charge stock may comprise a solution of t-butyl hydroperoxide in t-butyl alcohol containing from about 2 to about 90 weight percent of t-butyl hydroperoxide. If the tertiary butyl hydroperoxide concentration is excessive, additional tertiary butyl alcohol may be added. 
     The solvent solution of tertiary butyl hydroperoxide in organic solvents (e.g., tertiary butyl alcohol solvent solution of tertiary butyl hydroperoxide) is then charged to a catalytic hydroperoxide decomposition zone where it is brought into contact with a metal phthalocyanine catalyst, a chain transfer agent and a free radical inhibitor to substantially selectively convert the tertiary butyl hydroperoxide to tertiary butyl alcohol with high yields and selectivities. 
     The reaction product from the tertiary butyl hydroperoxide decomposition step may then be fractionated in any suitable manner, such as, for example, in the manner shown in the process disclosed in above identified copending U.S. patent application Ser. No. 06/945,628 filed Dec. 23, 1986. In accordance with a process recovery sequence of this nature, both the tertiary butyl alcohol and the ditertiary butyl peroxide will be recovered in purified form as products of the reaction. 
     Alternately, a crude tertiary butyl alcohol product stream contaminated with ditertiary butyl peroxide and other contaminants may be obtained which will then be further treated either thermally, in accordance with the process of the Grane et al. U.S. patents, or catalytically by one of the processes disclosed in the copending Sanderson et al. patent applications to convert the ditertiary butyl peroxide to tertiary butyl alcohol and to otherwise significantly reduce the level of contamination of the other oxygen-containing impurities. 
    
    
     SPECIFIC EXAMPLES 
     The invention will be further illustrated by the following specific examples which are given by way of illustration and not as limitations on the scope of this invention. 
     Procedure 
     A 100 ml three-necked flask equipped with a water-cooled condenser, thermometer and magnetic stirrer was suspended in a water bath. The flask was charged with the catalyst(s) shown in the table and then 20.0 g of 18.43% TBHP in TBA. The contents were vigorously stirred and 1 ml aliquots withdrawn at the times indicated. Analysis was by GC. 
     
                                           TABLE I                                 
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Decomposition of TBHP to TBA                                              
Notebook                                                                  
      Time                                                                
         Temp                                                             
             FePCYCl.sup.a                                                
                   2,3-DiHy.sup.b                                         
                         DT.sup.c                                         
                            Weight %            Exo-                      
Number                                                                    
      (Hr)                                                                
         (°C.)                                                     
             (g)   Napth (g)                                              
                         (g)                                              
                            TBHP                                          
                                TBA                                       
                                   Acetone                                
                                        MeOH                              
                                            DTBP                          
                                                therm                     
__________________________________________________________________________
6274-67                                                                   
      1.0                                                                 
         30.0                                                             
             0.05  0     2.54                                             
                            0.034                                         
                                93.03                                     
                                   0.94 2.26                              
                                            0.88                          
                                                Yes                       
6274-70                                                                   
      4.0                                                                 
         26.0                                                             
             0.05  0.10  0  2.10                                          
                                94.00                                     
                                   0.52 &lt;0.1                              
                                            0.21                          
                                                No                        
6274-72                                                                   
      1.0                                                                 
         26.0                                                             
             0.05  0.05  0  0.36                                          
                                95.12                                     
                                   0.66 &lt;0.1                              
                                            3.36                          
                                                No                        
6274-74                                                                   
      0.5                                                                 
         33.0                                                             
             0.05  0.05  0.84                                             
                            0.39                                          
                                94.81                                     
                                   1.10 0.81                              
                                            1.30                          
                                                Yes                       
6274-75                                                                   
      0.5                                                                 
         33.0                                                             
             0.05  0.05  0.14                                             
                            0.06                                          
                                96.11                                     
                                   0.97 0.05                              
                                            2.15                          
                                                Yes                       
6274-76                                                                   
      0.5                                                                 
         31.0                                                             
             0.05  0.07  0.07                                             
                            0.14                                          
                                95.97                                     
                                   0.79 &lt;0.1                              
                                            2.57                          
                                                Yes                       
6274-77                                                                   
      0.5                                                                 
         31.0                                                             
             0.05  0.20  0.84                                             
                            9.34                                          
                                88.37                                     
                                   0.34 0.89                              
                                            0.73                          
                                                Yes                       
6274-44                                                                   
      1.0                                                                 
         40.0                                                             
             0.01  0     0  3.89                                          
                                92.96                                     
                                   0.67 &lt;0.1                              
                                            2.11                          
                                                Unk                       
Starting Material           18.43                                         
                                81.02                                     
                                   0    0   0.06                          
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 .sup.a Chloroferric phthalocyanine                                       
 .sup.b 2,3Dihydroxynaphthalene                                           
 .sup.c Dodecane Thiol                                                    
 
    
     Discussion of Results in Table 
     Experiment No. 6274-74 which was conducted in the presence of Fe(III)PCYCl and dodecane thiol (DT) shows high conversion of TBHP and good selectivity to TBA. It may be compared to 6274-44 which had no DT added. In the presence of DT, the DTBP dropped from 2.11 to 0.88. The presence of the inhibitor 2,3-dihydroxy naphthalene lowers the percent TBHP conversion but does not lower the percent DTBP formed. (See Exp. No. 6274-70 and Exp. No. 6274-72). In the presence of both inhibitor and DT, the DTBP remains low. In fact, the percent DTBP formed appears to be proportional to the amount of DT added. (See Exp. No. 6274-76 and Exp. No. 6274-77).