Process for preparing propylene oxide and acetic acid
This is a continuation, of application Ser. No. 884,644, filed Mar. 8, 1978 now abandoned. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a process for preparing propylene oxide and acetic acid which are useful in chemical, light industries, food production, as starting material for the manufacture of polymeric, synthetic fibres and solvents. 
     BACKGROUND OF THE INVENTION 
     Known in the art is a process for preparing propylene oxide and acetic acid the oxidation of propylene and acetaldehyde with an oxygen-containing gas in a liquid phase in the presence of a homogeneous catalyst at a temperature within the range of from 150 to 250° C. As the homogeneous catalyst, use is made of salts of cobalt, manganese, ruthenium. Selectivity of the formation of propylene oxide as calculated for the reacted acetaldehyde is 35 molar percent. 
     This prior art process has a disadvantage because of a low selectivity of the formation of propylene oxide as calculated for the reacted acetaldehyde. 
     Known in the art is also a process for preparing propylene oxide and acetic acid the oxidation of propylene and acetaldehyde with an oxygen-containing gas in the presence of a heterogeneous catalyst such as silver oxide at a temperature of from 70 to 150° C. under a pressure of from 2 to 60 atm. Selectivity of the formation of propylene oxide as calculated for the reacted acetaldehyde does not exceed 70 molar percent (cf. USSR Inventor&#39;s Certificate No. 334825). This prior art process is objectionable because there is an insufficient selectivity of the formation of propylene oxide as calculated for the reacted acetaldehyde. 
     OBJECT OF THE INVENTION 
     It is an object of the present invention to increase the selectivity of the formation of propylene oxide as calculated for the reacted acetaldehyde. 
     BRIEF SUMMARY OF THE INVENTION 
     This object is accomplished by a process for preparing propylene oxide and acetic acid by subjecting propylene and acetaldehyde to oxidation with an oxygen-containing gas in a liquid phase at a temperature within the range of from 70 to 100° C. under a pressure of from 40 to 50 atm. Boron compounds of the formula BE, wherein E is a metal selected from Group IV, V and VI of the periodic system and nitrogen are catalysts for the process of the present invention. In accordance with the present invention, the catalyst used is a boride of tantalum, molybdenum, zirconium or nitrogen. It is advisable to use the catalyst in the process according to the present invention in an amount of from 0.1 to 0.2% by weight of the reaction mixture. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The process for preparing propylene oxide and acetic acid in accordance with the present invention is performed in the following manner. 
     Into a metallic reactor there are charged the liquified starting components and a powder-like catalyst is introduced i.e., a boride of tantalum, molybdenum, zirconium or nitrogen in an amount within the range of from 0.1 to 0.2% by weight of the reaction mixture; the pressure is increased to 40-50 atm and the temperature is maintained within the range of from 70 to 100° C., whereafter the oxygen-containing gas having an oxygen content of from 10 to 100% by volume, is passed into the reaction mixture at a rate of from 10 to 12 l/hr. The reaction is conducted for 1-1.5 hours. On completion of the reaction, the desired products are separated by rectification. It is preferable to use, as the oxidizing gas, air and perform the reaction at a temperature of from 70° to 80° C. under the pressure of 40 atm. The catalyst is produced in a conventional manner as by way of a high temperature synthesis from the appropriate elements. 
     The use of a boride of tantalum, molybdenum, zirconium or nitrogen as the catalyst in the process according to the present invention makes it possible to increase the selectivity of the formation of propylene oxide up to 93 molar percent as calculated for the reacted acetaldehyde. 
    
    
     For a better understanding of the present invention the following Examples are given hereinbelow by way of illustration. 
     EXAMPLE 1 
     Into a 200 cm 3  metallic reactor there are charged 40 ml (24 g) of liquified propylene, 10 ml (7.5 g) of acetaldehyde and 40 ml (35 g) of benzene (solvent) and 0.1 g of tantalum boride is added thereto. The reactor is sealed, air is supplied thereinto at a pressure of 40 atm and the temperature is elevated to 70° C. Thereafter, air is bubbled through the reactor at the rate of 10-12 l/hr. After 1.25 hours the oxidation is discontinued, the pressure is released and the unreacted propylene is evaporated at room temperature. 
     From the remaining liquid portion, i.e., the oxidized portion, propylene oxide and acetic acid are recovered by rectification. The distillation residue is subjected to analysis. 
     Given hereinbelow are data identifying the contents of the oxidized composition and the yields of propylene oxide and acetic acid. 
     
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Propylene oxide in the oxidized composition                               
                            4.6 g                                         
Acetic acid in the oxidized composition                                   
                            5.0 g                                         
Acetaldehyde in the oxidized composition                                  
                            4.0 g                                         
Conversion degree for the acetaldehyde                                    
                            49%                                           
Conversion degree for the propylene                                       
                            13.8%                                         
Selectivity of the formation of propylene                                 
oxide as for acetaldehyde   93 mol.%                                      
Selectvity of the formation of acetic acid                                
as for acetaldehyde         96 mol.%                                      
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     EXAMPLE 2 
     The procedure for the preparation of propylene oxide and acetic acid is carried out in accordance with the procedure in the foregoing Example 1. 
     As the catalyst, use is made of nitrogen boride. The oxidized composition and the yields of propylene oxide and acetic acid are given hereinbelow. 
     
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Content of propylene oxide in the oxidized composition                    
                            4.5 g                                         
Content of acetic acid in the oxidized composition                        
                            4.9 g                                         
Content of acetaldehyde in the oxidized composition                       
                            4.2 g                                         
Conversion degree for the acetaldehyde                                    
                            46%                                           
Conversion degree for the propylene                                       
                            13.5%                                         
Selectvity of the formation of propylene oxide                            
as calculated for acetaldehyde                                            
                            93%                                           
Selectivity of the formation of acetic acid                               
as calculated for acetaldehyde                                            
                            98%                                           
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     EXAMPLE 3 
     The procedure for the preparation of propylene oxide and acetic acide is conducted in a manner similar to that described in Example 1 hereinbefore. 
     As the catalyst, molybdenum boride is used and the oxidation reaction is conducted for 1.5 hours. 
     The oxidized composition and the yields of propylene oxide and acetic acid are given hereinbelow. 
     
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Content of propylene oxide in the oxidized composition                    
                            3.2 g                                         
Content of acetic acid in the oxidized composition                        
                            4.2 g                                         
Content of acetaldehyde in the oxidized composition                       
                            4.8 g                                         
Conversion degree for the acetaldehyde                                    
                            38%                                           
Conversion degree for the propylene                                       
                            8.7%                                          
Selectivity of the formation of propylene oxide                           
as calculated for acetaldehyde                                            
                            80 mol.%                                      
Selectivity of the formation of acetic acid as                            
calculated for acetaldehyde 95 mol.%                                      
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     EXAMPLE 4 
     The procedure for the preparation of propylene oxide and acetic acid is conducted in a manner similar to that described in the foregoing Example 1. 
     As the catalyst zirconium boride is used and the oxidation reaction is carried out over a 1.5 hour. 
     The oxidized composition and the yields of propylene oxide and acetic acid are given hereinbelow. 
     
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Content of propylene oxide in the oxidate                                 
                            3.6 g                                         
Content of acetic acid in the oxidized compostion                         
                            4.7 g                                         
Content of acetaldehyde in the oxdized composition                        
                            4.1 g                                         
Conversion degree for the acetaldehyde                                    
                            47%                                           
Conversion degree for the propylene                                       
                            10.9%                                         
Selectivity of the formation of propylene oxide as                        
calculated for acetaldehyde 78 mol.%                                      
Selectivity of the formation of acetic acid as                            
calculated for acetaldehyde 95 mol.%                                      
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     EXAMPLE 5 
     Into a 200 cm 3  metallic reactor there are charged 40 ml (24 g) of liquified propylene, 10 ml (7.5 g) of acetaldehyde and 40 ml (35 g) of benzene (solvent) and 0.2 g of tantalum boride is introduced into the reactor. The apparatus is sealed, air is passed thereinto at a pressure of 50 atm and heated to the temperature of 100° C. Thereafter, air is bubbled through the reactor at a rate of from 10 to 12 l/hr After one hour the oxidation is discontinued, the pressure is released and the unreacted propylene is evaporated at room temperature. 
     From the remaining liquid portion (oxidized composition) propylene oxide and acetic acid are recovered by rectification. The remaining liquid portion (oxidized composition) is subjected to analysis The data identifying the contents of the oxidized composition and the yields of propylene oxide and acetic acid are given hereinbelow. 
     
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Content of propylene oxide in the oxidized composition                    
                            4.7 g                                         
Content of acetic acid in the oxidized composition                        
                            5.1 g                                         
Conversion degree for the acetaldehyde                                    
                            50%                                           
Conversion degree for the propylene                                       
                            14.0%                                         
Selectivity of the formation of propylene oxide as                        
calculated for acetaldehyde 75 mol.%                                      
Selectvity of the formation of acetic acid as                             
calculated for acetaldehyde 92 mol.%                                      
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