Abstract:
This invention relates to a process for producing mono-ortho-tert-butyl-aniline in high security selectivity and at high conversion using a silica-containing catalyst. The reaction is carried out using a fixed bed reactor. Di-tert-butyl derivatives are avoided by maintaining preselected mole ratios of isobutylene to aniline, preselected temperatures and preselected reaction times.

Description:
TECHNICAL FIELD 
     This invention pertains to a process for producing mono-ortho-tert-butyl-aniline at high selectivity and at high conversion using a silica-alumina catalyst. 
     BACKGROUND OF THE INVENTION 
     The alkylation of aromatic amines by the reaction of the aromatic amine with an olefin in the presence of a catalyst system is known. Patents which illustrate aromatic amine alkylation processes using a heterogeneous catalyst system comprising silica-alumina catalysts are as follows: 
     British Patent No. 421,791 discloses the reaction of N-alkylated aromatic amines to ring alkylated aromatic amines by effecting isomerization in the presence of activated hydrosilicates. 
     French Patent No. 1.406,739 discloses ring alkylation of aromatic amines and other aromatic compounds by contacting the aromatic amine with an olefin in the presence of a crystalline alumino-silicate. Aniline and diphenylamine are represented as examples of aromatic hydrocarbon suited for alkylation. 
     Canadian Patent No. 663,698 discloses para-alkylation of aromatic amines, typically aniline derivatives, by contacting aniline with an olefin in the presence of a silica-alumina-type catalyst. Anilineisobutylene reactions are carried out at temperatures from about 200°-330° C. with temperatures of 240°-260° C. being preferred. 
     U.S. Pat. No. 4,351,951 discloses a process for preparing aromatic amines by reacting the aromatic amine with the primary or secondary alcohol in the presence of a catalyst containing iron oxides. 
     British Patent No. 846,226 discloses a process for the alkylation of aniline and phenyl amines by reaction with isobutylene in liquid phase at temperatures between 150° and 300° C. in the presence of activated, substantially neutral bleaching earths of the montmorillonite type. 
     Lavroski, et al., in an article Catalytic Alkylation of Aniline by n-Butene shows the reaction of aniline with n-butene in the presence of a silica-alumina catalyst. 
     U.S. Pat. No. 2,194,079 shows the reaction of diphenylamine with cyclohexene in the presence of an acid-activated bleaching earth. 
     SUMMARY OF THE INVENTION 
     This invention relates to an improved process for producing mono-tert-butyl aniline by the alkylation of aniline with isobutylene in the presence of a silica-alumina catalyst system. As noted in the prior art, aromatic amines, including aniline, have been alkylated with olefins using silica-alumina catalyst systems. However, a mixed reaction product effluent was obtained. The improvement for producing mono-tert-butyl aniline as opposed to di-tert-butyl aniline in the form of ring di-tert-butyl derivatives as well as a mixture of ring and N-alkylated di-tert-butyl aniline derivatives involves careful reaction control to minimize by-product formation in the form of di-tert-butyl derivatives of aniline and carrying out the reaction in a fixed bed catalytic reactor. The reaction is carried out by contacting a feedstock of aniline and isobutylene where the molar ratio of aniline to isobutylene is from 2 to 10:1. The temperature is maintained from 160° to 180° C. and the pressure is maintained from 500 to 1500 pounds per square inch. The reaction is carried out in a fixed bed reactor, in contrast to a stirred, tank reactor, and the space velocity based upon aniline feed to the reactor is from 0.05 to 0.5 cc&#39;s per hour per cc volume catalyst (LSHV). 
    
    
     DRAWING 
     The drawing is a plot of product ratio versus reaction temperature for the reaction of isobutylene with aniline. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the alkylation of aniline with isobutylene, a variety of products are produced which include N,N-alkylated anilines to ring alkylated aniline derivatives to a combination of N and ring alkylated aniline derivatives or polyalkylated ring aniline derivatives. The mono-tert-butyl derivatives of aniline, where the tert-butyl group is ortho to the amino group, has excellent utility as an antioxidant. Because isobutylene is readily reacted with aniline, and a variety of products are produced by the reaction, there is a need to maximize the amount of mono-tert-butyl-aniline where the tert-butyl group is ortho to the amine without generating other by-products. The N-alkylated derivatives are difficult to separate from the ring-alkylated aniline derivatives and the di-tert-butyl derivatives of aniline must be decomposed in order to recover reactants. 
     It has been found in the practice of this invention that minimal amounts of di-tert-butyl derivatives of aniline can be produced by the reaction of isobutylene with aniline in the presence of a silica-alumina catalyst and when the reaction is carried out in a fixed bed reactor. The catalyst system is highly acidic and a catalyst having a silica content from 70 to 85% by weight should be utilized. Although other oxides can be present in the catalyst system, e.g., magnesia, a catalyst system having essentially silica and alumina is preferred as such catalyst has the highest acidity. To enhance catalytic activity of the silica-alumina the catalyst can also be activated by removing alkali or alkaline earth metal oxides from the catalyst systems. That technique is referred to as activation and such activations can be accomplished by contacting the catalyst system with acid and recovery undissolved silica-alumina catalysts. 
     To effect high conversion at high selectivity, the reaction is carried out in a fixed bed catalytic reactor. A high rate of flow is maintained through the catalyst bed to minimize the effect of temperature excursion in the bed which may result in higher levels of di-tert-butyl derivatives of aniline in the reaction product. A liquid hourly space velocity of from 0.05 to 0.5 hours -1  is maintained and preferably the liquid hour space velocity is from 0.1 to 0.25 hours -1 . The reaction temperature in the catalyst bed is maintained from 130° to 180° C. When the temperature falls below about 150° C., insufficient conversion of aniline to ring alkylated aniline derivative is produced leaving unreacted aniline or higher concentrations of N-tert-butyl aniline in the reactor effluent. When the temperature above about 200° C. is employed or there are temperature excursions within the fixed bed catalytic reactor which results in localized temperatures above about 200° C., one may experience higher productions of para-tert-butyl aniline. 
     The mole ratio of isobutylene to aniline in the initial reaction zone is maintained at a level from about 2 to 10 moles aniline per mole isobutylene. This mole ratio permits conversion to be carried out at a level from about 40 to 90 based upon the moles of aniline present in the reactor feed. (N-tert-butyl derivatives of aniline being equivalent to 1 mole of unreacted aniline.) When the mole ratio falls below about 2 there is insufficient conversion of the aniline to product and when the mole ratio is above about 10 to 1 there is a tendency to convert some of the aniline to di-tert-butyl aniline. 
     The following examples are provided to illustrate various embodiments of the invention and are not intended to restrict the scope thereof. 
     EXAMPLE 1 
     Aniline and isobutylene were pumped as liquids over a catalyst bed of silica and alumina held in a tube reactor and reacted. The bed contained 12 cc of catalyst and the catalyst contained 87% silica and 13% alumina. 
     Table 1 provides reaction conditions and analytical analysis of the reaction product. In Table I, N-T-BU refers to N-tert-butyl-aniline; 2-T-BU refers to 2-tert-butyl-aniline; di-T-BU refers to di-tert-butyl-aniline (either N,N., N,ring-; or ring,ring- and O/P refers to the ortho/para ratio. 
     
                                           TABLE 1__________________________________________________________________________Aniline/isobutylene over 13% Al.sub.2 O.sub.3 /SiO.sub.2   Temp.  Pres.      Ratio          LHSV              % Conv.                   % Sel.                        % Sel.                             % Sel.                                  % Sel.                                       o/p Ring/NRun   C.  PSIG      N/R (HR-1)              Aniline                   N-T-BU                        2-T-BU                             4-T-BU                                  DI-T-BU                                       Ratio                                           Ratio__________________________________________________________________________1  100 910 0.1 0.25              2.53 71.38                        9.80 0.00 0.00 --  0.142  150 910 0.1 0.25              40.99                   84.92                        8.85 1.62 0.57 5.46                                           0.123  200 972 0.1 0.25              36.60                   86.89                        9.25 1.70 0.86 5.44                                           0.124  200 972 0.1 0.25              83.13                   7.04 35.88                             11.58                                  38.71                                       3.10                                           6.745  200 977 0.1 0.25              83.65                   6.81 34.54                             11.08                                  37.23                                       3.11                                           6.706  250 977 1.1 0.25              96.91                   0.21 1.77 58.59                                  37.82                                       0.03                                           287.437  250 992 1.1 0.25              97.64                   0.16 1.38 57.94                                  38.80                                       0.02                                           370.70__________________________________________________________________________ As can be seen from the data, increased conversion to dit-butyl-aniline occurs at temperatures of 200° C. Further, the ortho/para ratio decreases. 
    
     
                                           TABLE 2__________________________________________________________________________Aniline/isobutylene over H-- Y zeolite   Temp.  Pres.      Ratio          LHSV              % Conv.                   % Sel.                        % Sel.                             % Sel.                                  % Sel.                                       o/p Ring/NRun   C.  PSIG      N/R 1/H Aniline                   N-T-BU                        2-T-BU                             4-T-BU                                  DI-T-BU                                       Ratio                                           Ratio__________________________________________________________________________1  100 887 0.25          0.125              12.76                   47.78                        40.84                             4.40 0.00 9.28                                           0.952  150 894 0.25          0.125              42.69                   53.90                        37.80                             5.13 0.27 7.37                                           0.803  128 898 0.25          0.125              43.40                   54.15                        38.55                             5.20 0.28 7.41                                           0.814  128 899 0.25          0.060              59.42                   50.08                        37.03                             4.96 0.63 7.47                                           0.845  128 900 0.25          0.060              57.43                   52.78                        39.67                             5.36 0.67 7.40                                           0.856  127 907 1.00          0.060              50.77                   49.84                        39.57                             5.31 0.94 7.45                                           0.907  152 888 1.00          0.060              64.39                   28.56                        57.01                             9.36 3.01 6.09                                           2.328  152 896 1.00          0.060              73.07                   27.87                        55.76                             9.10 3.13 6.13                                           2.339  165 300 1.00          0.120              65.10                   2.99 45.62                             28.59                                  21.44                                       1.60                                           24.8210 165 300 1.00          0.120              65.10                   4.83 65.89                             20.23                                  9.04 3.26                                           17.83__________________________________________________________________________ As can be seen from the data, increased conversion to dit-butyl-aniline occurs at temperatures of 200° C. Further, the ortho/para ratio decreases.