Patent Publication Number: US-4056577-A

Title: Separation of acid-hydrocarbon emulsions and alkylation process utilizing said separation

Description:
This invention relates to an improved process for the separation of HF acid-hydrocarbon emulsions and to the production of high quality alkylate. In accordance with another aspect, this invention relates to an improved recovery system following alkylation for the separation of a hydrocarbon liquid phase and an HF acid catalyst liquid phase comprising the addition of a tetralkylammonium iodide coalescing promoter to decrease the time for effecting phase separation of the alkylation effluent. In accordance with another aspect, this invention relates to minimizing the time a hydrocarbon phase separating from an alkylation reaction mass is in contact with an HF acid phase by addition of a controlled amount of a tetraalkylammonium iodide as a coalescing promoter to the reaction effluent. In accordance with a further aspect, this invention relates to the HF alkylation of isoparaffins with olefin(s) by adding to the alkylation effluent a controlled amount of a tetraalkylammonium iodide coalescing promoter followed by separation of the reaction mass into a hydrocarbon liquid phase and an HF acid catalyst liquid phase in a relatively short period of time due to the presence of the coalescing promoter during phase separation. 
     It is known in the art to react alkylatable hydrocarbons with alkylating hydrocarbons in the presence of an HF acid catalyst to produce alkylate. The alkylation reaction effluent normally is subjected to gravity separation wherein the mass is allowed to separate in a suitable settling zone into a hydrocarbon liquid phase and an HF acid catalyst liquid phase. The hydrocarbon phase recovered from the settling zone is conventionally subjected to fractionation to recover alkylate, unreacted hydrocarbon, and residual HF. One of the problems encountered in the usual alkylation process is the presence of heavy materials which reduce the quality of the alkylate yielded. The heavy materials produced ordinarily are caused by prolonged contact of the hydrocarbon phase and HF acid phase following alkylation. The present invention overcomes this problem by minimizing the time that the hydrocarbon separating from the reaction mass is allowed to be in contact with the HF phase in the settling zone so that the separating liquid hydrocarbon phase is in contact with the HF acid catalyst after removal from the alkylation zone a very short period of time. 
     Accordingly, an object of this invention is to provide an improved process for effecting separation of HF acid-hydrocarbon emulsions. 
     Another object of this invention is to provide an improved process for alkylation. 
     Another object of this invention is to provide an improved process for the rapid separation of an alkylation effluent into separate hydrocarbon and acid phases. 
     Other objects, aspects, and the several advantages of this invention will be apparent to those skilled in the art upon a study of the disclosure and the appended claims. 
     In accordance with the invention, a process is provided for achieving rapid separation of HF acid-hydrocarbon emulsions into separate HF acid and hydrocarbon phases by addition of up to about 700 ppm of a tetraalkylammonium iodide coalescing promoter to the emulsion. 
     In accordance with another embodiment of the invention, an improved process for the production of high quality motor fuel alkylate is provided which comprises reacting an alkylatable hydrocarbon with an olefin in the presence of an HF acid catalyst, adding to the alkylation effluent a finite amount of up to about 700 ppm of a tetraalkylammonium iodide as a coalescing promoter to minimize the time for the hydrocarbon phase to separate from the alkylation reaction mass, and allowing the alkylation separation effluent to separate into an HF acid phase and a hydrocarbon phase. 
     In accordance with a specific embodiment of the invention, a process for alkylation recovery of high octane motor fuel alkylate is provided comprising reacting isobutane with butylenes in the presence of an HF acid catalyst under alkylation conditions, adding to the alkylation reaction mass effluent a finite amount of up to about 700 ppm of tetrabutylammonium iodide to decrease the time to effect phase separation of the alkylation effluent, passing the alkylation effluent into a phase separation zone, and allowing the effluent to separate into an upper hydrocarbon phase and a lower acid phase, both of which can be separately withdrawn and passed to further processing as desired. 
     The conditions for carrying out the alkylation reaction of the present invention are well known in the art. The present invention is directed to improved separation of the alkylation reaction mass by decreasing the time for separation of the hydrocarbon phase and the catalyst phase in a separation zone following alkylation. 
     In general, any of the conventional catalytic alkylation reactions can be carried out by the method and with the apparatus of the present invention. Thus, the alkylation reaction can comprise the reaction of an isoparaffin with a butylene with the reaction being carried out in the presence of HF acid as the alkylation catalyst. Such conventional alkylation is taught in U.S. Pat. No. 3,213,157. 
     The alkylation reaction is carried out with the hydrocarbon reactants in the liquid phase; however, the reactants need not be normally liquid hydrocarbons. The reaction conditions can vary in temperature from, say, about -40° F (-40° C) to as high as 150° F (66° C) and carried out under sufficient pressure to maintain liquid phase conditions. While generally applicable to the alkylation of hydrocarbons, the present invention is particularly effective for the alkylation of saturated branched chain paraffins such as isobutane and/or isopentane with butylenes in the presence of hydrofluoric acid. In the alkylation of isoparaffins with butylenes, a substantial molar excess of isoparaffin to butylenes is employed, usually to provide the feed ratio in excess of 1:1, usually from 4:1 to about 20:1, and preferably from about 10:1 to about 15:1. The reaction zone is maintained under sufficient pressure to insure that the hydrocarbon reactants and alkylation catalyst are in the liquid phase. The volume ratio of HF to total hydrocarbons will be in the range of 0.2 to 1 to about 20 to 1. 
     In accordance with the invention, it has been found that rapid separation of HF acid-hydrocarbon emulsions into separate liquid HF acid and liquid hydrocarbon phases can be achieved by adding to the emulsion a finite amount of up to about 700 ppm of a tetraalkylammonium iodide as a coalescing promoter. Suitable iodide compounds that can be employed include those having alkyl groups from about 4 to about 20 carbon atoms with lower alkyl-substituted compounds (4 to 8 carbon alkyls) presently preferred. Representative examples of suitable tetraalkylammonium iodide compounds include tetrabutylammomium iodide, tetrapentylammonium iodide, tetraoctylammonium iodide, tetrahexadecylammonium iodide, tetraeicosylammonium iodide, tetradodecylammonium iodide, and the like, including mixtures thereof. Presently preferred is tetrabutylammonium iodide and other lower alkylammonium iodides, wherein the alkyl group has 4 to 8 carbon atoms. 
     The amount of tetraalkylammonium iodide added to the HF acid-hydrocarbon emulsion will be a sufficient finite amount of up to about 700 ppm, based on HF acid present in the emulsion, to cause rapid separation of the HF acid-hydrocarbon emulsion into separate HF acid and hydrocarbon phases. It is presently preferred that the amount of coalescing promoter ranges from about 200 to about 700 ppm with about 700 ppm being preferred when tetrabutylammonium iodide is employed. 
     In actual operation, in connection with facilitating the separation of an HF acid-hydrocarbon emulsion obtained as by the effluent of an alkylation reaction, the tetraalkylammonium iodide is preferably added to the effluent prior to introduction into a phase separation zone such as a gravity settling or separation zone. If desired, the tetraalkylammonium iodide can be added to the alkylation reaction so as to decrease the time for causing separation between the hydrocarbon and acid phases. Ordinarily, alkylation effluent comprising HF acid catalyst, alkylated hydrocarbons, and unreacted hydrocarbons is passed to a phase separation zone such as a gravity separator wherein the separate hydrocarbon and HF acid phases can form. The coalescing promoter is added to the alkylation reaction effluent ordinarily prior to introduction into the settling zone. As demonstrated by the specific working example hereinbelow, the time for effecting phase separation between the HF acid and hydrocarbons can be decreased by about 40 to about 70 percent using tetraalkylammonium iodide in an amount of up to about 700 parts per million by weight of the HF acid catalyst in the alkylation reaction effluent. 
    
    
     SPECIFIC EXAMPLE 
     Several emulsions were prepared, each with 100 ml of liquid isooctane and 100 ml of liquid HF acid. The two liquids were agitated together by shaking in a closed container for about 60 seconds at room temperature (about 76° F) for runs below. The agitation was stopped and the time was observed for substantially complete liquid phase separation to occur. 
     The base runs were made without any additive. 
     The invention runs were made using tetrabutylammonium iodide (TBAI). 
     
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Tetrabutylammonium Iodide                                                 
                     Phase Separation                                     
(about 76° F) Time, Seconds                                        
______________________________________                                    
Base Runs:                                                                
(a) - (1)            28                                                   
(b) - (1)            30                                                   
(c) - (1)            30                                                   
(d) - (2)            30                                                   
Invention Runs:                                                           
(d) - (3) with 0.07 gms TBAI                                              
                      9                                                   
(e) - (3) with 0.07 gms TBAI                                              
                     11                                                   
(f) - (3) with 0.07 gms TBAI                                              
                     12                                                   
(g) - (4) with 0.07 gms TBAI                                              
                     17                                                   
(h) - (4) with 0.07 gms TBAI                                              
                     17                                                   
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 (1) First base sample checked three times.                               
 (2) Second base sample tested only once.                                 
 (3) First invention sample checked three times.                          
 (4) Second invention sample checked twice.                               
 
    
     Looking at the runs above, it is seen that phase separation time was decreased by about 40 to 70 percent using TBAI in an amount of about 700 parts per million by weight of the HF acid (catalyst).