Process for producing lower olefinic hydrocarbons from methanol
RELATED APPLICATIONS 
     This is a continuation-in-part of application Ser. No. 030,297 filed Mar. 23, 1987, now abandoned, which is a continuation of application Ser. No. 762,955 filed Aug. 6, 1985, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a process for preparation of lower olefins from methanol. 
     More particularly, it relates to a process for preparation of lower olefins of 2 to 4 carbon atoms from methanol. 
     Indirect liquefaction method of coal and petrolium hydrocarbons via gasification has problems to be solved in efficiency of Fischer-Tropsch synthesis (FT synthesis) and selectivity to gasoline. 
     However, recently Mobil Oil Corp. has developed a technique to obtain olefins of C 2  -C 4  carbon atoms from methanol using a novel zeolite catalyst with high selectivity, from which are expected novel composite catalysts and improved results by use of these catalysts for synthesis of lower hydrocarbons. 
     DE No. 3215068 (DISTILLERS) and U.S. Pat. No. 4,403,044 disclose production of olefinic hydrocarbons from methanol using a catalyst of alumina-free silicalite. However, said catalyst is not satisfactory in selectivity and yield of olefinic hydrocarbons. 
     SUMMARY OF THE INVENTION 
     The inventor has discovered a process for producing lower olefins (C 2  -C 4  olefins) from methanol in high yield and with high selectivity in the presence of a metallosilicate catalyst (Si/Me wherein Me is Fe, Ni or Co). 
     It is an object of this invention to provide a process for producing lower olefins from methanol in a high yield and with a high selectivity. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In accordance with this invention, methanol is brought into contact with a metallosilicate catalyst (Si/Me wherein atomic ratio of Si/Me is 25 to 3200 and Me is Fe, Ni or Co) under reaction conditions of a reaction temperature: 250° C. to 400° C., preferably 280° C. to 350° C., a space velocity (GHSV): 2000 to 8000 hr -1  and a pressure: atmospheric pressure to 50 kg/cm 2 . 
     The process of this invention is to produce lower olefins of C 2  -C 4  carbon atoms from methanol at a high conversion and with a high selectivity. 
     Under conditions of a reaction temperature of lower than 250° C. and a space velocity (GHSV) of more than 8000 hr -1 , the conversion is liable to decrease, and under conditions of a reaction temperature of higher than 400° C. and a space velocity of less than 4000 hr -1 , decomposition products, mainly methane, and a gasoline component increase. 
     In order to keep high conversion and high selectivity, space velocity is small when reaction temperature is low, and large when reaction temperature is high. 
     Preparation of Catalyst 
     (1) The first step of preparing a gel mixture: 
     Solution A: An aqueous solution containing a salt of metal (Me), i.e., a di- or tri-valent nitrate, sulfate or chloride and preferably nitrate of Fe, Ni or Co, a quaternary alkyl ammonium cation, and an inorganic acid of nitric, sulfuric or hydrochloric acid. 
     Preferable salts of a metal in the solution A are Fe 2  (SO 4 ) 3 , CoSO 4  and NiSO 4 . The inorganic acid to be used has preferably the same anion as that of the metal salt above. 
     Solution B: An aqueous silicate solution. 
     Solution C: An aqueous solution of ion modifier (NaC1). 
     The solutions A and B are added to the solution C at a rate that pH of the solution C is kept at about 10, resulting to produce a gel mixture in the solution C. 
     An ion modifier of NaCl is added to the solution A and a quaternary alkyl ammonium cation with an inorganic acid and alkali hydroxide are added to the solution C at the time of the addition, in order to prevent each component in the solutions A, B and C from changing. 
     (2) The second step of grinding the resulting gel mixture. 
     (3) The third step of hydrothermal reaction: 
     The gel mixture is heated to a temperature from room temperature to 150°-190° C. at a constant speed followed by heating to 190°-220° C. at a constant speed or an exponential speed to obtain a precurser synthetic metalosilicate having the following chemical composition in molar ratio; 
     
         ______________________________________                                    
Si/Me             25-3200                                                 
OH.sup.-- /SiO.sub.2                                                      
                 0.3-1.0                                                  
H.sub.2 O/SiO.sub.2                                                       
                  30-100                                                  
R/R + alkalimetal                                                         
                 0.05-0.15                                                
NaCl/H.sub.2 O   0.01-0.06                                                
______________________________________                                    
 
    
     Wherein 
     Me is Fe, Ni or Co, 
     R is a quaternary alkyl ammonium cation where alkyl is C 1-3  alkyl, and 
     alkali metal is sodium or potassium. 
     (4) The last fourth step is to calcine the precursor metallosilicate in (3). 
     Methanol in the gaseous form is brought into contact with a catalyst in a known manner. 
     
         ______________________________________                                    
Preparation of, for instance, Fe-silicate                                 
(Si/Fe = 3200) Catalyst                                                   
______________________________________                                    
solution (A)                                                              
Fe(NO.sub.3).sub.2 9H.sub.2 O                                             
                       0.04   g                                           
H.sub.2 SO.sub.4       6.2    g                                           
TPAB*                  5.72   g                                           
H.sub.2 O              60     cc                                          
NaCl                   11.95  g                                           
solution (B)                                                              
H.sub.2 O              45     cc                                          
Water Glass (No. 3)**  69     g                                           
solution (C)                                                              
H.sub.2 O              208    cc                                          
NaCl                   40.6   g                                           
H.sub.2 SO.sub.4       1.8    g                                           
TPAB                   2.16   g                                           
NaOH                   2.4    g                                           
______________________________________                                    
  *Tetrapropylammonium bromide                                            
  **SiO.sub.2 28.9%, Na.sub.2 O 9.3                                       
 
    
     Solutions (A) and (B) are added through microfeeds, respectively, to solution (C) over 10 minutes at pH about 10. The mixture obtained is centrifuged to separate gel from supernatant, the gel is milled for one hour and the milled product is mixed with the supernatant above. 
     Hydrothermal reaction 
     A product obtained above is treated in an autoclave with stirring (90 rpm) over 1.5 hours to raise temperature from room temperature to 160° C. The temperature is further raised from 160° C. to 210° C. with rate of 12° C./hour. 
     Washing, drying and calcining 
     Washing: water 
     Drying: 120° C.×24 hours 
     Calcining: 540° C.×3.5 hours under air stream (100 ml/min.) 
     Ion exchange treatment 
     One cycle is 1N NH 4  NO 3  aq. 80° C.×1 hour, before washing. 
     After two cycles, the same drying and calcining as above are carried out. 
     The following examples illustrate the present invention. 
     The metallosilicate catalyst prepared as above was tableted and then crushed to 10-20 meshes. This catalyst (0.5 g or 2 cc) was packed in a reaction tube (quartz) of 6 mm inner diameter and a mixed gas containing 20 volume % of methanol and 80 volume % of nitrogen was subjected to reaction under the conditions of atmospheric pressure and SV (GHSV) of 2000 hr -1-8000  hr -1  at prescribed reaction temperatures using an atmospheric flow reaction apparatus. 
     Components in conversion gas were analyzed by a gas chromatography with an integrator. 
     Assay conditions for products: 
     
         ______________________________________                                    
       total hydrocarbon                                                  
                       C.sub.4.sup.-  hydrocarbon                         
______________________________________                                    
Column   Shimazu GC-8APT   Shimazu 7APTF                                  
         silicon OV-101    VZ-10                                          
         (50 m × 0.2 mm diameter)                                   
                           (3 m × 3 mm                              
                           diameter)                                      
Detector Hydrogen flame    Shimazu 7APTF                                  
         ionization detector                                              
                           VZ-10                                          
                           (3 m × 3 mm                              
                           diameter)                                      
Carrier gas                                                               
         N.sub.2 1.85 Kg/cm.sup.2                                         
                           N.sub.2 120 ml/min                             
Temperature                                                               
         From room temperature                                            
                           50° C.                                  
         to 120° C. with raising                                   
         rate of 4° C./min.                                        
Vaporizer                                                                 
         150° C.    150° C.                                 
temperature                                                               
______________________________________                                    
 
    
     A. Effects of reaction temperature on production of lower olefins 
     Reactions were carried out at reaction temperatures of 295° C., 330° C. and 350° C. using the metallosilicate catalyst (atomic ratio of Si/Fe=3200) and relation between reaction temperature and composition of the conversion gas was examined. The results are shown in Table 1. 
     
                                           TABLE 1                                 
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Reaction temperature (°C.)                                         
               295° C.                                             
                       330° C.                                     
                               350° C.                             
GHSV (hr.sup.-1)                                                          
               8000    8000    8000                                       
MeOH concentration (Vol %)                                                
               20      20      20                                         
Pressure (Kg/cm.sup.2)                                                    
               1       1       1                                          
MeOH conversion (C wt %)                                                  
                After                                                     
                   After                                                  
                       After                                              
                           After                                          
                               After                                      
                                   After                                  
               1 hour                                                     
                   3 hours                                                
                       1 hour                                             
                           3 hours                                        
                               1 hour                                     
                                   3 hours                                
               33.5                                                       
                   22.8                                                   
                       68.2                                               
                           59.5                                           
                               81.7                                       
                                   76.6                                   
HC-selectivity (C wt %)                                                   
               51.0                                                       
                   59.0                                                   
                       86.2                                               
                           80.8                                           
                               95.2                                       
                                   91.8                                   
DME selectivity (C wt %)                                                  
               49.0                                                       
                   41.0                                                   
                       13.8                                               
                           19.2                                           
                                4.8                                       
                                    8.2                                   
C.sub.2 -C.sub.4 olefins (C wt %)                                         
               97.6                                                       
                   95.3                                                   
                       60.2                                               
                           62.7                                           
                               60.8                                       
                                   60.2                                   
C.sub.5.sup.+ Aliphatics (C wt %)                                         
                1.2                                                       
                    0.2                                                   
                       30.8                                               
                           28.0                                           
                               33.2                                       
                                   33.6                                   
Aromatics (C wt %)                                                        
               --  --   5.8                                               
                            6.3                                           
                                3.8                                       
                                    4.1                                   
STY of C.sub.2 -C.sub.4 olefins                                           
               11.9                                                       
                    9.2                                                   
                       25.3                                               
                           21.5                                           
                               33.8                                       
                                   30.2                                   
(C mol/l · hr)                                                   
__________________________________________________________________________
 HC: Hydrocarbon                                                          
 DME: Dimethyl ether                                                      
 STY: Space time yield                                                    
 
    
     Table 1 shows that with increase in reaction temperature, STY (space time yield) of C 2  -C 4  olefins increased. 
     B. Effects of space velocity on production of lower olefins 
     Effects of space velocity on production of lower olefins were examined using metallosilicate catalyst (atomic ratio of Si/Fe 3200) at 300° C. and space velocities (GHSV) of 2,000, 4000 and 8000. 
     The results are shown in Table 2. 
     
                                           TABLE 2                                 
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Reaction temperature (°C.)                                         
               300     300     300                                        
GHSV (hr.sup.-1)                                                          
               2000    4000    8000                                       
MeOH concentration (Vol %)                                                
               20      20      20                                         
Pressure (kg/cm.sup.2)                                                    
               1       1       1                                          
MeOH conversion (C wt %)                                                  
               After                                                      
                   After                                                  
                       After                                              
                           After                                          
                               After                                      
                                   After                                  
               1 hour                                                     
                   3 hours                                                
                       1 hour                                             
                           3 hours                                        
                               1 hour                                     
                                   3 hours                                
               81.7                                                       
                   74.7                                                   
                       55.8                                               
                           21.0                                           
                               47.6                                       
                                   41.7                                   
HC-selectivity (C wt %)                                                   
               92.9                                                       
                   85.6                                                   
                       58.7                                               
                           53.2                                           
                               61.9                                       
                                   56.0                                   
DME selectivity (C wt %)                                                  
                7.10                                                      
                   14.4                                                   
                       41.4                                               
                           46.8                                           
                               38.1                                       
                                   44.0                                   
C.sub.2 -C.sub.4 olefin (C wt %)                                          
               51.7                                                       
                   52.2                                                   
                       76.7                                               
                           89.3                                           
                               87.2                                       
                                   96.0                                   
C.sub.5.sup.+ aliphatics (C wt %)                                         
               32.6                                                       
                   32.2                                                   
                       11.4                                               
                            0.67                                          
                                6.3                                       
                                    1.3                                   
Aromatics (C wt %)                                                        
               11.0                                                       
                   11.8                                                   
                        8.9                                               
                           --   3.0                                       
                                    1.0                                   
STY of C.sub.2 -C.sub.4 olefins                                           
                7.0                                                       
                    6.0                                                   
                        9.0                                               
                            3.4                                           
                               18.4                                       
                                   16.0                                   
(C mol/l · hr)                                                   
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     Table 2 shows that the STY of C 2  -C 4  olefins increases at temperatures within the range of 250°-350° C. as GHSV increases. 
     C. Effects of Si/Me ratio on production of lower olefins 
     Effects of Si/Me ratio on production of lower olefins were examined using metallosilicate catalysts (atomic ratios of Si/Ni 400, 3200: Si/Co 40, 3200 and Si/Fe 40, 400) at about 300° C. and space velocities (GHSV) of 2000 and 8000 respectively. 
     The results are shown in Tables 3 and 4. 
     Tables 3 and 4 show that hydrocarbon selectivity reaches about 100 % in Fe-silicate catalyst at the temperature of about 300° C. 
     As described hereinbefore, the metallosilicate catalysts containing metal Fe, Ni or Co prepared above is suitable for synthesis of olefins from metanol. It is assumed to owe to uniformity in crystal structure and acid property of the metallosilicate catalyst. 
     
                                           TABLE 3                                 
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Reaction temperature (°C.)                                         
                 291° C.                                           
                     291° C.                                       
                         291° C.                                   
                                291° C.                            
GHSV (hr.sup.-1) 8000                                                     
                     8000                                                 
                         8000   8000                                      
Si/Me            Si/Ni                                                    
                     Si/Ni                                                
                         Si/Co  Si/Fe                                     
                 3200                                                     
                     400 3200                                             
                             40 400 40                                    
MeOH concentration (Vol %)                                                
                 58.9                                                     
                     57.5                                                 
                         58.8                                             
                             65.7                                         
                                97.7                                      
                                    100                                   
Hydrocarbon selectivity (C wt %)                                          
                 39.3                                                     
                     34.1                                                 
                         51.2                                             
                             80.0                                         
                                99.3                                      
                                    100                                   
DME selectivity (C wt %)                                                  
                 60.7                                                     
                     65.9                                                 
                         48.8                                             
                             30.6                                         
                                 0.7                                      
                                     0.0                                  
C.sub.1 - hydrocarbon (C wt %)                                            
                  4.4                                                     
                      4.1                                                 
                          4.7                                             
                              5.9                                         
                                 0.4                                      
                                     0.6                                  
C.sub.2 -C.sub.4 hydrocarbons (C wt %)                                    
                  0.0                                                     
                      0.0                                                 
                          0.0                                             
                              0.8                                         
                                 6.7                                      
                                    12.8                                  
C.sub.2.sup.= -C.sub.4.sup.=  hydrocarbons (C wt %)                       
                 91.4                                                     
                     91.6                                                 
                         91.2                                             
                             88.4                                         
                                55.1                                      
                                    38.8                                  
C.sub.5.sup.+ aliphatics (C wt %)                                         
                  2.6                                                     
                      2.8                                                 
                          0.3                                             
                              0.3                                         
                                33.6                                      
                                    40.7                                  
Aromatics (C wt %)                                                        
                  1.6                                                     
                      1.5                                                 
                          3.8                                             
                              4.6                                         
                                 4.2                                      
                                     7.1                                  
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                                           TABLE 4                                 
__________________________________________________________________________
Reaction temperature (°C.)                                         
                 300° C.                                           
                       300° C.                                     
                             300° C.                               
                                      300° C.                      
GHSV(hr.sup.-1)  2000  2000  2000     2000                                
Si/Me            Si/Ni 3200                                               
                       Si/Ni 400                                          
                             Si/Co 3200                                   
                                   40 Si/Fe 400                           
MeOH concentration (Vol %)                                                
                 92.8  86.6  87.8  99.8                                   
                                      100                                 
Hydrocarbon selectivity (C wt %)                                          
                 98.9  97.1  97.2  99.2                                   
                                      100                                 
DME selectivity (C wt %)                                                  
                  1.1   2.9   2.8   0.5                                   
                                       0.0                                
C.sub.1 - hydrocarbon (C wt %)                                            
                  0.2   0.8   0.0   0.3                                   
                                       0.6                                
C.sub.2 -C.sub.4 hydrocarbons (C wt %)                                    
                  4.9   6.3   3.8   4.3                                   
                                      10.4                                
C.sub.2.sup.= -C.sub.4.sup.= hydrocarbons (C wt %)                        
                 47.3  49.6  52.4  47.0                                   
                                      47.5                                
C.sub.5.sup.+ aliphatics (C wt %)                                         
                 35.5  37.5  33.3  36.1                                   
                                      27.0                                
Aromatics (C wt %)                                                        
                 12.1   5.8  10.5  12.3                                   
                                      14.4                                
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     D. Effects of Me-free catalyst on Production of lower olefins 
     The Production of the lower olefins was examined using a Me-freesilicate catalyst. Said catalyst was prepared in the similar manner to the above mentioned without metal salt in the solution A. 
     The result is shown in Table 5. 
     
                       TABLE 5                                                     
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Reaction temperature (°C.)                                         
                     300                                                  
GHSV (hr.sup.-1)     2,000                                                
Metal free catalyst  Silicate                                             
MeOH concentration (Vol %)                                                
                     100                                                  
Hydrocarbon selectivity (C wt %)                                          
                     100                                                  
DME selectivity (C wt %)                                                  
                     0                                                    
C.sub.1 - hydrocarbon (C wt %)                                            
                     0.5                                                  
C.sub.2 -C.sub.4 hydrocarbon (C wt %)                                     
                     14.3                                                 
C.sub.2.sup.= -C.sub.4.sup.=  hydrocarbon (C wt %)                        
                     31.8                                                 
C.sub.5.sup.+  aliphatics (C wt %)                                        
                     33.5                                                 
Aromatics (C wt %)   19.9                                                 
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     Table 5 shows that productin of the C 2   =  -C 4   =   olefins is smaller than that of the metallosilicate catalyst. 
     E. Comparison of the present catalyst and the catalyst of DE No. 3215068 (referred to as &#39;068) 
     
         ______________________________________                                    
Preparation of the catalyst of DE &#39;068                                    
Si/Fe = 3200                                                              
______________________________________                                    
solution (A)                                                              
Fe(NO.sub.3).sub.2 9H.sub.2 O                                             
                       0.04   g                                           
H.sub.2 SO.sub.4       6.2    g                                           
TPAB*                  7.53   g                                           
H.sub.2 O              60     cc                                          
solution (B)                                                              
H.sub.2 O              45     cc                                          
Water Glass (No. 3)**  69     g                                           
solution (C)                                                              
H.sub.2 O              104    cc                                          
NaCl                   26.27  g                                           
______________________________________                                    
 *Tetrapropylammonium bromide                                             
 **SiO.sub.2 28.9%, Na.sub.2 O 9.3%                                       
 
    
     The solutions (A) and (B) are added to the solution (C) over 10 minutes at pH about 10. 
     Hydrothermal reaction 
     The product obtained above is treated in an autoclave with stirring (90 rpm) over 1.5 hours to raise the temperature from a room temperature to 160° C., and the temperature (160° C.) is held for 20 hours. Washing, drying, calcining and ion exchange treatment are effected in the similar manner to that mentioned above. 
     
         ______________________________________                                    
 Conversion conditions                                                    
______________________________________                                    
Reaction tube   6 mm inner diameter quartz                                
Catalyst        2 cc                                                      
Feed            Methanol 20% (volume) in                                  
                N.sub.2 gas as a carrier                                  
Pressure        atmospheric                                               
______________________________________                                    
                the present                                               
                          DE &#39;068                                         
______________________________________                                    
Temperature °C.                                                    
                 300       420                                            
GHSV/hr.sup.-1  2000      2000                                            
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     The results are in Table 6. 
     
                       TABLE 6                                                     
______________________________________                                    
          the present      DE &#39;068                                        
          Si/Fe =                                                         
                 Si/Ni =  Si/Co =  Si/Fe =                                
          3200   3200     3200     3200                                   
______________________________________                                    
MeOH conversion                                                           
            81.7     92.8     87.8   100                                  
(c wt %)                                                                  
Hydrocarbon 92.9     98.9     97.2   15                                   
Selectivity                                                               
(c wt %)                                                                  
DMS*         7.1      1.1      2.8   86                                   
Selectivity                                                               
(c wt %)                                                                  
Product                                                                   
(c wt %)                                                                  
C.sub.2 -C.sub.4 olefins                                                  
            51.7     47.3     52.4   8.6                                  
C.sub.5.sup.+  Aliphatics                                                 
            32.6     35.5     33.3   7.2                                  
Aromatics   11.0     12.1     10.5   --                                   
______________________________________                                    
 
    
     Selectivity of the present catalyst is superior to that of DE &#39;068. 
     The present metallosilicate catalyst has acid properties suitable for preparing olefin. The acid properties have two, i.e., weak acid and strong acid. The strong acid property, in particular, attributes to production of olefin. Too strong acidity in the strong acid induces an aromatization or cyclization of dimethyl ether (herein referred to as DME), intermediate, and hydrogen produced reacts with lower olefin to produce lower paraffin. Too low acidity in the strong acid gives no hydrocarbon from DME. Suitable acidity in the strong acid induces production of olefin from DME, and further produces oligomer. Quantitative formation of olefin is effected, because the catalyst has no ability for cyclization and dehydrogenation. 
     Suitable acidity of the strong acid is attained when metal is Fe, Ni or Co, but too strong acidity when metal is Al. No lower olefin but lower paraffin is obtained when metal is Al as stated above. 
     The present metallosilicate catalyst has fine and uniform crystals, because the time for preparing catalyst is very short. The fine and uniform crystals making staying time of reaction gas uniform in crystals, until desired olefin is able to produce with high selectivity by controlling conditions. The fines and unformity in crystals improves reaction activity and makes it possible to effect a reaction at lower temperature. Hydrocarbon once produced is not decomposed because the hydrocarbon is not subjected to high temperature. C 2  and/or C 3  olefin are taken out of the reaction system as soon as they are produced. This favors an improvement in selectivity and in life of catalyst. 
     Furthermore, process for preparing the present catalyst gives a catalyst a Fe, Ni or Co richcore and an Si-rich coating. Shape selectivity serves to effect no reaction in the coating layer which is non-selective but in the core which has selective.