Patent Publication Number: US-4320227-A

Title: Process for producing methacrolein and methacrylic acid

Description:
DETAILED DESCRIPTION OF THE INVENTION 
     This invention relates to a process for producing methacrolein and methacrylic acid by oxidizing isobutyl aldehyde with molecular oxygen or molecular oxygen-containing gas in the vapor phase. 
     Many processes have been proposed for the production of methacrylic acid which is a raw material of methyl methacrylate. Most of the processes are those where isobutylene is used as a raw material and it is oxidized to methacrolein, and then methacrolein is oxidized to methacrylic acid. 
     The processes using isobutyl aldehyde as a raw material have been proposed too. However, most of the processes are those where isobutyl aldehyde is oxidized to isobutyric acid in the first step and then isobutyric acid is converted to methacrylic acid in the other step. 
     There are also some other proposed processes where isobutyl aldehyde is oxidized to methacrolein and methacrylic acid. But, in these processes, the yield of the product is not good and the life of the catalyst used in these processes is short. 
     The inventors of the present application have made an earnest study on eliminating the defects of the processes and accomplished this invention. 
     According to the present invention, methacrolein and methacrylic acid can be obtained from isobutyl aldehyde in high yield for a long time. Particularly, methacrylic acid can be obtained in high yield. The catalyst used in the present invention has high activity, high selectivity, as well as very long catalyst life. 
     This invention relates to a process for producing mathacrolein and methacrylic acid by oxidizing isobutyl aldehyde with molecular oxygen or molecular oxygen-containing gas in the vapor phase characterized by the use of a catalyst of heteropoly-acid or a mixture of heteropoly-acid and its salt which has the general formula: 
     
         Mo.sub.a V.sub.b P.sub.c X.sub.d Y.sub.e O.sub.f 
    
     wherein Mo, V, P and O represent respectively molybdenum, vanadium, phosphorus and oxygen, X represents one or more elements selected from the group consisting of copper, tin, thorium, aluminum, germanium, nickel, iron, cobalt, zinc, titanium, lead, rhenium, zirconium, cerium, chromium, bismuth and arsenic, Y represents one or more elements selected from the group consisting of potassium, rubidium, cesium and thallium and a, b, c, d, e and f represent the atomic ratio of the elements where, 
     a is 10, 
     b is a number of 6 or less than 6 excluding 0 and, preferably, 0.5 to 3, 
     c is a number of 0.5 to 6 and, preferably, 0.5 to 3, 
     d is a number of 3 or less than 3 excluding 0 and, preferably, 0.01 to 1.0, 
     e is a number of 0 to 0.8 and, preferably, 0 to 0.5, 
     f is a number determined depending on the valency and atomic ratio of other elements and is usually a number of 35 to 80. 
     In this invention, the preferred catalyst is the one represented by the following formula: 
     
         Mo.sub.a&#39; V.sub.b&#39; P.sub.c&#39; Cu.sub.d&#39; X&#39;.sub.e&#39; Y&#39;.sub.f&#39; O.sub.g&#39; 
    
     wherein, Mo, V, P, Cu and O represent respectively molybdenum, vanadium, phosphorus, copper and oxygen, X&#39; represents one or more elements selected from the group consisting of arsenic, thorium, aluminum, germanium, nickel, iron, cobalt, zinc, titanium, lead, rhenium, zirconium, cerium, bismuth, tin and chromium, Y&#39; represents one or more elements selected from the group consisting of potassium, rubidium, cesium and thallium and a&#39;, b&#39;, c&#39;, d&#39;, e&#39;, f&#39; and g&#39; represent the atomic ratio of the elements where, 
     a&#39; is 10, 
     b&#39; is a number of 6 or less than 6 excluding 0 and, preferably, 0.5 to 3, 
     c&#39; is a number of 0.5 to 6 and, preferably, 0.5 to 3, 
     d&#39; is a number of 3 or less than 3 excluding 0 and, preferably, 0.01 to 1.0, 
     e&#39; is a number of 3 or less than 3 excluding 0 and, preferably, 0.01 to 1.0, 
     d&#39;+e&#39; is a number of 3 or less than 3 excluding 0, 
     f&#39; is a number of 0 to 0.8 and, preferably, 0 to 0.5, 
     g&#39; is a number determined depending on the valency and atomic ratio of other elements and is usually a number of 35 to 80. 
     The basic structure of the catalyst of the present invention is phosphovanadomolybdic acid. In case Y element is not present, the catalyst of the present invention is a catalyst in which a part of the catalyst-structure formed by the phosphovanadomolybdic acid is occupied by X element. In case Y element is present, the catalyst of the present invention is a catalyst in which a part of the catalyst-structure formed by the coexistence of phosphovanadomolybdic acid and its Y-metal salt is occupied by X element. 
     As mentioned above, in case Y element is not present, the catalyst is heteropoly-acid composed mainly of phosphovanadomolybdic acid, and in case Y element is present, the catalyst is a mixture of heteropoly-acid composed mainly of phosphovanadomolybdic acid, and its Y-metal salt. X element occupies a part of the structure of heteropoly-acid and its salt, if present. 
     In the X-ray diffraction pattern of the catalyst used in the present invention, the peaks of 2θ=8.0°, 8.9°, 9.3°, etc. characteristic diffraction peaks of the heteropoly-acid are observed. Further, in case heteropoly-acid salt is present, the peaks of 2θ=26.6°, 10.8°, etc. characteristic diffraction peaks of the Y-metal salt of the heteropoly-acid are also observed. However, in the region of the catalyst in which the amount of coexisting salt is poor, only the peaks due to the acid are observable. The catalyst in which the amount of Y-component is too much, to the extent in that particularly only the peaks due to Y-salt of the heteropoly-acid are observed does not give good results. It is essential to control the amount of addition of Y-component within the range of the present invention. 
     Although the catalyst used in the present invention is heteropoly-acid or a mixture of heteropoly-acid and its salt, it may additionally contain other compounds such as oxides of the constituent element. 
     The catalyst of this invention is excellent for industrial use since it has high activity, high selectivity, as well as very long catalyst life. Further, according to this invention, the reaction can be conducted at a high space velocity, because the increase in the space velocity has no substantial effects on the results of the reaction where the catalyst of this invention is employed. The catalyst of this invention is water soluble, which provides additional advantages in that it can easily be carried on a carrier and regenerated also with ease by dissolving it again in water after being deactivated in a long use for the reaction. 
     While the catalyst of this invention can be prepared by general methods for preparing usual heteropoly-acid, and its Y-metal salt, it should particularly be noted to avoid the formation of a heteropoly-acid ammonium salt structure in the resultant catalyst. 
     The catalyst of this invention can be prepared, for example, in the following manner. The catalyst of this invention can be prepared by reacting the starting materials of the constituent elements in water or in an organic solvent, an evaporating to dryness. 
     Particularly preferred preparation methods include those such as dispersing or dissolving the starting material, for example, oxides or phosphates of the constituent elements into water, reacting the same under heating while optionally adding hydrogen peroxide, removing insoluble component if necessary, and then evaporating the solution to dryness, or reacting phosphovanadomolybdic acid with oxides, hydroxides, phosphates, carbonates and the like of other constituent elements. 
     Various substances can be used as the starting material for the constituent elements of the catalyst. 
     The starting materials usable for the molybdenum component include, for example, molybdenum trioxide, molybdic acid or its salt, heteromolybdic acid or its salts, molybdenum metal and the like. 
     The starting materials usable for the phosphorus component include orthophosphoric acid, phosphorous acid, hypophosphorous acid or the salts thereof, diphosphorus pentoxide and the like. 
     The starting materials usable for the vanadium component include vanadium pentoxide, vanadium oxalate, vanadium sulfate, vanadic acid or its salts, phosphovanadomolybdic acid or its salt, vanadium metal and the like. 
     The starting materials usable for the components X and Y include corresponding oxides, phosphates, nitrates, sulfates, carbonates, molybdates, salts of organic acids, halides, hydroxides, metals of the elements X and Y and the like. 
     While the catalyst according to this invention exhibits high catalytic activity as it is, preferable effects such as improvements in thermal stability and catalyst life and increase in yield of methacrolein and methacrylic acid can be expected by carrying it on a suitable carrier. Preferred carriers include silicon carbide, α-alumina, aluminum powder, diatomaceous earth, titanium oxide and the like. The active carriers which react with heteropoly-acid are not preferable. 
     The calcination process which is required in most cases is not required when preparing the catalyst of this invention. Therefore, the catalyst of this invention can be prepared with ease and the price of the catalyst can be reduced. 
     The reactants used for the oxidation reaction in this invention are isobutyl aldehyde and molecular oxygen or molecular oxygen-containing gas, wherein the molar ratio of oxygen to isobutyl aldehyde preferably lies between 0.5 and 20 and, more preferably, between 1 and 10. 
     It is preferable to add water vapor to the feed gas in an amount between 1 and 20 and, more preferably, between 2 and 15 by molar ratio based on isobutyl aldehyde. 
     The feed gas may further contain other inert gases, for example, nitrogen, carbon dioxide, saturated hydrocarbon or the like. 
     The reaction temperature is preferably between 250°-400° C., more preferably, 250°-370° C. 
     The amount of the feed gas is preferably between 100 and 6000 hr -1  and, more preferably, between 400 and 3000 hr -1  as space velocity (SV) based on the NTP standard. Since the increase in the space velocity (SV) has no substantial effect on the results of the reaction where the catalyst of this invention is employed, the reaction can be conducted at a high space velocity. 
     While the reaction of this invention can be effected at a pressure either above or below the atmospheric pressure, it is suitably effected generally at a pressure near the atmospheric pressure. The preferred pressure for the reaction in this invention lies between 1 and 5 atm. 
     The reaction of this invention can be effected in any desired type of reactor such as of a fixed bed, a fluidized bed or a moving bed type. 
    
    
     In the following examples, no particular references are made to the details of oxygen in the catalyst composition since they are determined in accordance with the atomic ratio and valency of other elements. 
     The conversion of isobutyl aldehyde, the yield of methacrolein, the yield of methacrylic acid and the selectivity to (methacrolein+methacrylic acid) are defined as follows: ##EQU1## 
     EXAMPLE A1 
     100 g of molybdenum trioxide, 6.3 g of vanadium pentoxide, 1.1 g of copper oxide and 8.0 g of orthophosphoric acid were dispersed or dissolved into 1000 ml of deionized water. The resultant mixture was boiled and refluxed with stirring for about 6 hours to produce a clear orange red solution. After removing a slight amount of insoluble contents, it was evaporated to dryness on a hot bath. The dried product thus obtained (catalyst) had a composition: Mo 10  V 1  P 1  Cu 0 .2 and was confirmed to be heteropoly-acid by the observation of X-ray diffraction peaks at 2θ=8.0°, 8.9°, 9.3° and the like. It was ground to 24-48 mesh and diluted with the same amount of quartz sands having the same size in mesh and then charged into a tubular reactor made of glass of 18 mm in inside diameter and the reactor was immersed in a fluidized bath. The feed gas of a composition wherein isobutyl aldehyde:oxygen:nitrogen:water vapour=1:2.5:10:7 (in molar ratio) was passed through the tubular reactor at SV=1000 hr -1  (NTP standard) and subjected to oxidation reaction at a reaction temperature of 325° C. for 60 days. The results are shown in Table A-1. 
     After the reaction of 60 days, X-ray diffraction anaysis of the catalyst was made and it was confirmed that molybdenum trioxide had not been formed and the structure of the catalyst has not changed. 
     EXAMPLES A2-A17 
     1.1 g of copper oxide in Example A1 was replaced in each of the examples with 1.6 g of tin oxide, 3.7 g of thorium oxide, 0.7 g of aluminum oxide, 1.4 g of germanium oxide, 1.0 g of nickel oxide, 1.1 g of iron oxide, 1.1 g of cobalt oxide, 1.1 g of zinc oxide, 1.1 g of titanium oxide, 3.2 g of trilead tetroxide, 3.4 g of rhenium oxide, 1.7 g of zirconium oxide, 2.4 g of cerium oxide, 1.4 g of chromium oxide, 3.2 g of bismuth oxide and 1.9 g of arsenic acid respectively and dried products (catalysts) having compositions as shown in Table A-1 were obtained. The dried products thus obtained were confirmed to be heteropoly-acid by the observation of X-ray diffraction peaks at 2θ=8.0°, 8.9°, 9.3° and the like. 
     A series of continuous reactions were conducted using the above catalysts under the same reaction conditions as in Example A1. The results are as shown in Table A-1. 
     After the reaction of 60 days, X-ray diffraction analysis of the catalysts was made and it was confirmed that the structure of the catalysts had not changed. 
     
                                           TABLE A-1                               
__________________________________________________________________________
                            Conversion   Yield of                         
                                               Selectivity to             
                Time on                                                   
                     Reaction                                             
                            of isobutyl                                   
                                  Yield of                                
                                         methacrylic                      
                                               (methacrolein +            
                stream                                                    
                     temperature                                          
                            aldehyde                                      
                                  methacrolein                            
                                         acid  methacrylic acid)          
Example                                                                   
     Catalyst composition                                                 
                (days)                                                    
                     (°C.)                                         
                            (%)   (%)    (%)   (%)                        
__________________________________________________________________________
A1   Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2                                 
                1    325    100   19.6   58.0  77.6                       
                60   325    100   19.7   59.2  78.9                       
A2   Mo.sub.10 V.sub.1 P.sub.1 Sn.sub.0.2                                 
                1    330    100   15.5   54.5  70.0                       
                60   330    100   15.2   54.8  70.0                       
A3   Mo.sub.10 V.sub.1 P.sub.1 Th.sub.0.2                                 
                1    330    100   19.5   53.5  73.0                       
                60   330    100   19.6   53.7  73.3                       
A4   Mo.sub.10 V.sub.1 P.sub.1 Al.sub.0.2                                 
                1    330    100   15.8   55.1  70.9                       
                60   330    100   16.0   55.4  71.4                       
A5   Mo.sub.10 V.sub.1 P.sub.1 Ge.sub.0.2                                 
                1    330    100   13.1   55.9  69.0                       
                60   330    100   13.0   56.5  69.5                       
A6   Mo.sub.10 V.sub.1 P.sub.1 Ni.sub.0.2                                 
                1    330    100   20.1   52.1  72.2                       
                60   330    100   21.1   53.1  74.2                       
A7   Mo.sub.10 V.sub.1 P.sub.1 Fe.sub.0.2                                 
                1    330    100   16.6   53.9  70.5                       
                60   330    100   16.7   53.9  70.6                       
A8   Mo.sub.10 V.sub.1 P.sub.1 Co.sub.0.2                                 
                1    330    100   17.2   53.0  70.2                       
                60   330    100   17.5   53.5  71.0                       
A9   Mo.sub.10 V.sub.1 P.sub.1 Zn.sub.0.2                                 
                1    335    100   18.1   51.5  69.6                       
                60   335    100   18.5   51.8  70.3                       
 A10 Mo.sub.10 V.sub.1 P.sub.1 Ti.sub.0.2                                 
                1    330    100   15.1   54.8  69.9                       
                60   330    100   15.3   55.0  70.3                       
 A11 Mo.sub.10 V.sub.1 P.sub.1 Pb.sub.0.2                                 
                1    330    100   13.2   54.6  67.8                       
                60   330    100   13.3   54.6  67.9                       
 A12 Mo.sub.10 V.sub.1 P.sub.1 Re.sub.0.2                                 
                1    330    100   16.5   55.3  71.8                       
                60   330    100   16.8   55.7  72.5                       
 A13 Mo.sub.10 V.sub.1 P.sub.1 Zr.sub.0.2                                 
                1    335    100   17.3   56.1  73.4                       
                60   335    100   17.5   56.4  73.9                       
 A14 Mo.sub.10 V.sub.1 P.sub.1 Ce.sub.0.2                                 
                1    330    100   18.2   54.1  72.3                       
                60   330    100   19.0   54.8  73.8                       
 A15 Mo.sub.10 V.sub.1 P.sub.1 Cr.sub.0.2                                 
                1    330    100   17.1   52.5  69.6                       
                60   330    100   17.8   53.0  70.8                       
 A16 Mo.sub.10 V.sub.1 P.sub.1 Bi.sub.0.2                                 
                1    330    100   18.1   55.8  73.9                       
                60   330    100   18.3   56.0  74.3                       
 A17 Mo.sub.10 V.sub.1 P.sub.1 As.sub.0.2                                 
                1    335    100   18.5   56.0  74.5                       
                60   335    100   18.5   56.6  75.1                       
__________________________________________________________________________
 
    
     EXAMPLES A18-A22 
     The dried products as shown in Table A-2 were prepared as in Example A1 and were confirmed to be heteropoly-acid by X-ray diffraction analysis. 
     The continuous reactions were conducted using the above catalysts in the same reaction conditions as in Example A1. The results are shown in Table A-2. 
     After the reaction of 60 days, X-ray diffraction analysis of the catalysts was made and it was confirmed that the structure of the catalysts had not changed. 
     
                                           TABLE A-2                               
__________________________________________________________________________
                            Conversion   Yield of                         
                                               Selectivity to             
                Time on                                                   
                     Reaction                                             
                            of isobutyl                                   
                                  Yield of                                
                                         methacrylic                      
                                               (methacrolein +            
                stream                                                    
                     temperature                                          
                            aldehyde                                      
                                  methacrolein                            
                                         acid  methacrylic acid)          
Example                                                                   
     Catalyst composition                                                 
                (days)                                                    
                     (°C.)                                         
                            (%)   (%)    (%)   (%)                        
__________________________________________________________________________
A18  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.5                                 
                1    320    100   16.1   53.5  69.6                       
                60   320    100   16.3   53.8  70.1                       
A19  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.1                                   
                1    310    100   13.2   51.5  64.7                       
                60   310    100   13.3   52.5  65.8                       
A20  Mo.sub.10 V.sub.2 P.sub.1 Cu.sub.0.3                                 
                1    340    100   14.8   55.1  69.9                       
                60   340    100   15.2   56.6  71.8                       
A21  Mo.sub.10 V.sub.0.5 P.sub.1 Cu.sub.0.2                               
                1    320    100   18.0   51.1  69.1                       
                60   320    100   18.0   51.3  69.3                       
A22  Mo.sub.10 V.sub.1 P.sub.3 Cu.sub.0.2                                 
                1    340    100   15.0   52.5  67.5                       
                60   340    100   15.5   53.1  68.6                       
__________________________________________________________________________
 
    
     EXAMPLE A23 
     100 g of molybdenum trioxide, 6.3 g of vanadium pentoxide, 1.1 g of copper oxide and 8.0 g of orthophosphoric acid were dispersed or dissolved in 1,000 ml of deionized water and after about 3 hours of heating and stirring of the mixture, 0.45 g of potassium hydroxide was added to the resultant solution. The mixture was refluxed for about 3 hours while boiling. The aqueous solution thus formed was evaporated to dryness on a water bath. The composition of the dried product (the catalyst) was Mo 10  V 1  P 1  Cu 0 .2 K 0 .1. In the X-ray diffraction pattern of the catalyst, diffraction peaks of 2θ=8.0°, 8.9°, 9.3°, etc. due to heteropoly-acid mainly composed of phosphovanadomolybdic acid and faint diffraction peaks of 2θ=26.6°, 10.8°, etc. due to the potassium salt of the heteropoly-acid were recognized. The fact shows that the catalyst obtained is a mixture of heteropoly-acid mainly composed of phosphovanadomolybdic acid and its potassium salt. 
     The continuous reaction was conducted using the above catalyst in the same reaction conditions as in Example A1. The results are shown in Table A-3. 
     After the continuous reaction, X-ray diffraction analysis of the catalyst was made and it was confirmed that the structure of the catalyst had not changed. 
     EXAMPLES A24-A26 
     0.45 g of potassium hydroxide in Example A23 was replaced in each of the examples with 0.7 g of rubidium hydroxide, 1.0 g of cesium hydroxide, 1.5 g of thallium hydroxide respectively and dried products (catalysts) having compositions as shown in Table A-3 were obtained. 
     In the X-ray diffraction pattern of the catalysts, diffraction peaks of 2θ=8.0°, 8.9°, 9.3°, etc. due to heteropoly-acid mainly composed of phosphovanadomolybdic acid and faint diffraction peaks of 2θ=26.6°, 10.8°, etc. due to the salt of the heteropoly-acid were recognized. The fact shows that each of the catalysts is a mixture of heteropoly-acid mainly composed of phosphovanadomolybdid acid and its salt. 
     A series of continuous reactions were conducted using the above catalysts under the same reaction conditions as in Example A1. The results are as shown in Table A-3. 
     After the continuous reactions, X-ray diffraction analysis of the catalysts was made and it was confirmed that the structure of the catalysts had not changed. 
     
                                           TABLE A-3                               
__________________________________________________________________________
                            Conversion   Yield of                         
                                               Selectivity to             
                Time on                                                   
                     Reaction                                             
                            of isobutyl                                   
                                  Yield of                                
                                         methacrylic                      
                                               (methacrolein +            
                stream                                                    
                     temperature                                          
                            aldehyde                                      
                                  methacrolein                            
                                         acid  methacrylic acid)          
Example                                                                   
     Catalyst composition                                                 
                (days)                                                    
                     (°C.)                                         
                            (%)   (%)    (%)   (%)                        
__________________________________________________________________________
A23  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 K.sub.0.1                       
                1    320    100   19.5   58.8  78.3                       
                60   320    100   19.5   60.0  79.5                       
A24  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Rb.sub.0.1                      
                1    320    100   18.1   58.3  76.4                       
                60   320    100   18.0   59.3  77.3                       
A25  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Cs.sub.0.1                      
                1    315    100   19.7   59.0  78.7                       
                60   315    100   19.9   59.5  79.4                       
A26  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Tl.sub.0.1                      
                1    320    100   18.5   58.5  77.0                       
                60   320    100   18.7   58.8  77.5                       
__________________________________________________________________________
 
    
     EXAMPLES A27-A42 
     The dried products (catalysts) as shown in Table A-4 were prepared as in Example A23. 
     In the X-ray diffraction pattern of the catalysts, diffraction peaks of 2θ=8.0°, 8.9°, 9.3°, etc. due to heteropoly-acid mainly composed of phosphovanadomolybdic acid and faint diffraction peaks of 2θ=26.6°, 10.8°, etc. due to the salt of heteropoly-acid were recognized. The fact shows that each of the catalysts is a mixture of heteropoly-acid mainly composed of phosphovanadomolybdic acid and its salt. 
     A series of continuous reactions were conducted using the above catalysts under the same reaction conditions as in Example A1. The results are as shown in Table A-4. 
     After the continuous reactions, X-ray diffraction analysis of the catalysts was made and it was confirmed that the structure of the catalysts had not changed. 
     
                                           TABLE A-4                               
__________________________________________________________________________
                            Conversion   Yield of                         
                                               Selectivity to             
                Time on                                                   
                     Reaction                                             
                            of isobutyl                                   
                                  Yield of                                
                                         methacrylic                      
                                               (methacrolein +            
                stream                                                    
                     temperature                                          
                            aldehyde                                      
                                  methacrolein                            
                                         acid  methacrylic acid)          
Example                                                                   
     Catalyst composition                                                 
                (days)                                                    
                     (°C.)                                         
                            (%)   (%)    (%)   (%)                        
__________________________________________________________________________
A27  Mo.sub.10 V.sub.1 P.sub.1 Sn.sub.0.2 K.sub.0.1                       
                1    325    100   16.7   54.8  71.5                       
                60   325    100   16.9   55.0  71.9                       
A28  Mo.sub.10 V.sub.1 P.sub.1 Th.sub.0.2 K.sub.0.1                       
                1    330    100   15.5   55.1  70.6                       
                60   330    100   15.8   55.3  71.1                       
A29  Mo.sub.10 V.sub.1 P.sub.1 Al.sub.0.2 K.sub.0.1                       
                1    330    100   16.0   56.1  72.1                       
                60   330    100   16.2   56.3  72.5                       
A30  Mo.sub.10 V.sub.1 P.sub.1 Ge.sub.0.2 K.sub.0.1                       
                1    325    100   15.5   56.2  71.7                       
                60   325    100   15.8   56.6  72.4                       
A31  Mo.sub.10 V.sub.1 P.sub.1 Ni.sub.0.2 K.sub.0.1                       
                1    325    100   17.5   54.8  72.3                       
                60   325    100   17.0   55.5  72.5                       
A32  Mo.sub.10 V.sub.1 P.sub.1 Fe.sub.0.2 K.sub.0.1                       
                1    325    100   16.8   54.0  70.8                       
                60   325    100   16.9   54.5  71.4                       
A33  Mo.sub.10 V.sub.1 P.sub.1 Co.sub.0.2 K.sub.0.1                       
                1    325    100   17.0   54.5  71.5                       
                60   325    100   17.3   54.8  72.1                       
A34  Mo.sub.10 V.sub.1 P.sub.1 Zn.sub.0.2 K.sub.0.1                       
                1    330    100   18.5   52.1  70.6                       
                60   330    100   18.7   52.3  71.0                       
A35  Mo.sub.10 V.sub.1 P.sub.1 Ti.sub.0.2 K.sub.0.1                       
                1    325    100   17.0   54.9  71.9                       
                60   325    100   17.5   55.1  72.6                       
A36  Mo.sub.10 V.sub.1 P.sub.1 Pb.sub.0.2 K.sub.0.1                       
                1    325    100   14.5   54.5  69.0                       
                60   325    100   14.8   54.8  69.6                       
A37  Mo.sub.10 V.sub.1 P.sub.1 Re.sub.0.2 K.sub.0.1                       
                1    325    100   15.8   56.5  72.3                       
                60   325    100   16.0   57.0  73.0                       
A38  Mo.sub.10 V.sub.1 P.sub.1 Zr.sub.0.2 K.sub.0.1                       
                1    330    100   17.5   56.5  74.0                       
                60   330    100   17.0   57.3  74.3                       
A39  Mo.sub.10 V.sub.1 P.sub.1 Ce.sub.0.2 K.sub.0.1                       
                1    325    100   18.5   54.5  73.0                       
                60   325    100   18.6   55.0  73.6                       
A40  Mo.sub.10 V.sub.1 P.sub.1 Cr.sub.0.2 K.sub.0.1                       
                1    325    100   17.3   53.5  70.8                       
                60   325    100   17.5   53.7  71.2                       
A41  Mo.sub.10 V.sub.1 P.sub.1 Bi.sub.0.2 K.sub.0.1                       
                1    325    100   19.5   55.8  75.3                       
                60   325    100   19.4   56.1  75.5                       
A42  Mo.sub.10 V.sub.1 P.sub.1 As.sub.0.2 K.sub.0.1                       
                1    330    100   19.8   56.2  76.0                       
                60   330    100   19.5   57.0  76.5                       
__________________________________________________________________________
 
    
     EXAMPLES A43-A45 
     The dried products (catalysts) as shown in Table A-5 were prepared as in Example A1 and were confirmed to be heteropoly-acid by X-ray diffraction analysis. 
     The continuous reactions were conducted using the above catalysts in the same reaction conditions as in Example A1. The results are shown in Table A-5. 
     After the continuous reactions, X-ray diffraction analysis of the catalysts was made and it was confirmed that the structure of the catalysts had not changed. 
     EXAMPLES A46-A52 
     The dried products (catalysts) as shown in Table A-5 were prepared as in Example A23 and were confirmed to be a mixture of heteropoly-acid mainly composed of phosphovanadomolybdic acid and its salt by X-ray diffraction analysis. 
     The continuous reactions were conducted using the above catalysts in the same reaction conditions as in Example A1. The results are shown in Table A-5. 
     After the continuous reactions, X-ray diffraction analysis of the catalysts was made and it was confirmed that the structure of the catalysts had not changed. 
     
                                           TABLE A-5                               
__________________________________________________________________________
                              Conversion   Yield of                       
                                                 Selectivity to           
                  Time on                                                 
                       Reaction                                           
                              of isobutyl                                 
                                    Yield of                              
                                           methacrylic                    
                                                 (methacrolein +          
                  stream                                                  
                       temperature                                        
                              aldehyde                                    
                                    methacrolein                          
                                           acid  methacrylic acid)        
Example                                                                   
     Catalyst composition                                                 
                  (days)                                                  
                       (°C.)                                       
                              (%)   (%)    (%)   (%)                      
__________________________________________________________________________
A43  Mo.sub.10 V.sub.1 P.sub.1 Ge.sub.0.2 Sn.sub.0.2                      
                  1    330    100   17.1   55.5  72.6                     
                  60   330    100   17.0   55.8  72.8                     
A44  Mo.sub.10 V.sub.1 P.sub.1 Fe.sub.0.2 Zr.sub.0.1                      
                  1    330    100   18.0   56.3  74.3                     
                  60   330    100   17.5   56.9  74.4                     
A45  Mo.sub.10 V.sub.1 P.sub.1 Ni.sub.0.2 As.sub.0.2                      
                  1    330    100   18.7   56.6  75.3                     
                  60   330    100   18.6   57.1  75.7                     
A46  Mo.sub.10 V.sub.1 P.sub.1 Bi.sub.0.1 As.sub.0.2 K.sub.0.2            
                  1    325    100   19.9   56.6  76.5                     
                  60   325    100   20.0   57.0  77.0                     
A47  Mo.sub.10 V.sub.1 P.sub.1 Fe.sub.0.2 Zr.sub.0.1 K.sub.0.1            
                  1    320    100   18.0   56.5  74.5                     
                  60   320    100   17.5   58.1  75.6                     
A48  Mo.sub.10 V.sub.1 P.sub.1 Fe.sub.0.2 Ce.sub.0.1 K.sub.0.1            
                  1    325    100   18.7   54.8  73.5                     
                  60   325    100   18.5   55.5  74.0                     
A49  Mo.sub.10 V.sub.1 P.sub.1 Ni.sub.0.2 As.sub.0.2 K.sub.0.1            
                  1    325    100   20.2   56.9  77.1                     
                  60   325    100   20.5   57.1  77.6                     
A50  Mo.sub.10 V.sub.1 P.sub.1 Sn.sub.0.2 As.sub.0.2 Cs.sub.0.1           
                  1    325    100   19.8   56.5  76.3                     
                  60   325    100   19.7   56.9  76.6                     
A51  Mo.sub.10 V.sub.1 P.sub.1 Zr.sub.0.2 As.sub.0.2 Cs.sub.0.2           
                  1    325    100   19.5   57.1  76.6                     
                  90   325    100   19.0   57.8  76.8                     
A52  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 K.sub.0.1 Cs.sub.0.1            
                  1    320    100   19.9   59.5  79.4                     
                  60   320    100   19.5   60.0  79.5                     
__________________________________________________________________________
 
    
     EXAMPLE A53 
     The oxidation of isobutyl aldehyde was carried out in a similar manner as in Example A1 except that the reaction temperature was changed. The results are shown in Table A-6. 
     
                       TABLE A-6                                                   
______________________________________                                    
Reaction                                                                  
       Conversion                                                         
                 Yield of Yield of                                        
                                  Selectivity to                          
temper-                                                                   
       of isobutyl                                                        
                 methac-  methacrylic                                     
                                  (methacrolein +                         
ature  aldehyde  rolein   acid    methacrylic acid)                       
(°C.)                                                              
       (%)       (%)      (%)     (%)                                     
______________________________________                                    
325    100       19.6     58.0    77.6                                    
300    100       36.0     44.5    80.5                                    
275    100       60.2     25.2    85.4                                    
240    100       81.0     6.7     87.7                                    
______________________________________                                    
 
    
     EXAMPLE B1 
     100 g of molybdenum trioxide, 6.3 g of vanadium pentoxide, 1.1 g of copper oxide, 8.0 g of orthophosphoric acid and 1.9 g of arsenic acid were dispersed or dissolved into 1000 ml of deionized water. The resultant mixture was boiled and refluxed with stirring for about 6 hours to produce a clear orange red solution. After removing a slight amount of insoluble contents, it was evaporated to dryness on a hot bath. The dried product thus obtained (catalyst) had a composition: Mo 10  V 1  P 1  Cu 0 .2 As 0 .2  and were confirmed to be heteropoly-acid by the observation of X-ray diffraction peaks at 2θ=8.0°, 8.9°, 9.3° and the like. It was ground to 24-48 mesh and diluted with the same amount of quartz sands having the same size in mesh and then charged into a tubular reactor made of glass of 18 mm in inside diameter and the reactor was immersed in a fluidized bath. The feed gas of a composition wherein isobutyl aldehyde:oxygen:nitrogen:water vapour=1:2.5:10:7 (in molar ratio) was passed through the tubular reactor at SV=1500 hr -1  (NTP standard) and subjected to oxidation reaction at a reaction temperature of 330° C. for 60 days. The results are shown in Table B-1. 
     After the reaction of 60 days, the X-ray diffraction analysis of the catalyst was made and it was confirmed that molybdenum trioxide had not been formed and the structure of the catalyst had not changed. 
     EXAMPLES B2-B16 
     1.9 g of arsenic acid in Example B1 was replaced in each of the examples with 3.7 g of thorium oxide, 0.72 g of aluminum oxide, 1.4 g of germanium oxide, 1.0 g of nickel oxide, 1.1 g of iron oxide, 1.1 g of tricobalt tetroxide, 1.1 g of zinc oxide, 1.1 g of titanium oxide, 3.2 g of trilead tetroxide, 3.4 g of rhenium heptoxide, 3.2 g of zirconium oxide, 2.4 g of cerium oxide, 3.2 g of bismuth oxide, 2.1 g of tin oxide and 1.4 g of chromium oxide respectively and dried products (catalysts) having compositions as shown in Table B-1 were obtained. The dried products thus obtained were confirmed to be heteropoly-acid by the observation of X-ray diffraction peaks at 2θ=8.0°, 8.9°, 9.3° and the like. 
     The continuous reactions were conducted using the above catalysts under the same reaction conditions as in Example B1. The results are as shown in Table B-1. 
     After the reaction of 60 days, X-ray diffraction analysis of the catalysts was made and it was confirmed that the structure of the catalysts had not changed. 
     
                                           TABLE B-1                               
__________________________________________________________________________
                            Conversion   Yield of                         
                                               Selectivity to             
                Time on                                                   
                     Reaction                                             
                            of isobutyl                                   
                                  Yield of                                
                                         methacrylic                      
                                               (methacrolein +            
                stream                                                    
                     temperature                                          
                            aldehyde                                      
                                  methacrolein                            
                                         acid  methacrylic acid)          
Example                                                                   
     Catalyst composition                                                 
                (days)                                                    
                     (°C.)                                         
                            (%)   (%)    (%)   (%)                        
__________________________________________________________________________
B1   Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 As.sub.0.2                      
                1    330    100   19.1   64.1  83.2                       
                60   330    100   19.5   64.9  84.4                       
B2   Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Th.sub.0.2                      
                1    330    100   19.6   61.8  81.4                       
                60   330    100   19.3   62.2  81.5                       
B3   Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Al.sub.0.2                      
                1    330    100   18.5   62.9  81.4                       
                60   330    100   18.8   63.5  82.3                       
B4   Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Ge.sub.0.2                      
                1    325    100   19.8   61.8  81.6                       
                60   325    100   20.2   62.2  82.4                       
B5   Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Ni.sub.0.2                      
                1    325    100   19.3   61.8  81.1                       
                60   325    100   19.0   62.9  81.9                       
B6   Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Fe.sub.0.2                      
                1    325    100   18.3   62.7  81.0                       
                60   325    100   17.5   64.0  81.5                       
B7   Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Co.sub.0.2                      
                1    325    100   18.1   62.4  80.5                       
                60   325    100   18.0   62.9  80.9                       
B8   Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Zn.sub.0.2                      
                1    330    100   19.9   61.0  80.9                       
                60   330    100   19.9   61.4  81.3                       
B9   Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Ti.sub.0.2                      
                1    325    100   18.6   62.3  80.9                       
                60   325    100   19.0   62.7  81.7                       
B10  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Pb.sub.0.2                      
                1    325    100   18.3   62.7  81.0                       
                60   325    100   18.0   63.7  81.7                       
B11  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Re.sub.0.2                      
                1    325    100   19.7   62.0  81.7                       
                60   325    100   19.5   63.0  82.5                       
B12  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Zr.sub.0.2                      
                1    330    100   19.1   62.2  81.3                       
                60   330    100   19.0   63.0  82.0                       
B13  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Ce.sub.0.2                      
                1    325    100   19.6   61.9  81.5                       
                60   325    100   19.5   62.5  82.0                       
B14  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Bi.sub.0.2                      
                1    325    100   18.5   62.5  81.0                       
                60   325    100   18.0   63.7  81.7                       
B15  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Sn.sub.0.2                      
                1    325    100   19.6   62.0  81.6                       
                60   325    100   19.9   61.4  81.3                       
B16  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Cr.sub.0.2                      
                1    325    100   19.0   61.8  80.8                       
                60   325    100   19.2   63.1  82.3                       
__________________________________________________________________________
 
    
     EXAMPLE B17 
     100 g of molybdenum trioxide, 6.3 g of vanadium pentoxide, 1.1 g of copper oxide, 1.9 g of arsenic acid and 8.0 g of orthophosphoric acid were dispersed or dissolved in 1000 ml of deionized water and after about 3 hours of heating and stirring of the mixture, 0.45 g of potassium hydroxide was added to the resultant solution. The mixture was refluxed for about 3 hours while boiling. The aqueous solution thus formed was evaporated to dryness on a water bath. The composition of the dried product (the catalyst) was Mo 10  V 1  P 1  Cu 0 .2 As 0 .2 K 0 .1. In the X-ray diffraction pattern of the catalyst, diffraction peaks of 2θ=8.0°, 8.9°, 9.3°, etc. due to heteropoly-acid mainly composed of phosphovanadomolybdic acid and faint diffraction peaks of 2θ=26.6°, 10.8°, etc. due to the potassium salt of the heteropoly-acid were recognized. The fact shows that the catalyst obtained is a mixture of heteropoly-acid mainly composed of phosphovanadomolybdic acid and its salt. 
     The continuous reaction was conducted using the above catalyst in the same reaction conditions as in Example B1. The results are shown in Table B-2. 
     After the continuous reaction, X-ray diffraction analysis of the catalyst was made and it was confirmed that the structure of the catalyst had not changed. 
     EXAMPLES B18-B20 
     0.45 g of potassium hydroxide in Example B17 was replaced in each of the examples with 0.7 g of rubidium hydroxide, 1.0 g of cesium hydroxide, 1.5 g of thallium hydroxide respectively and dried products (catalysts) having compositions as shown in Table B-2 were obtained. 
     In the X-ray diffraction pattern of the catalysts, diffraction peaks of 2θ=8.0°, 8.9°, 9.3°, etc. due to heteropoly-acid mainly composed of phosphovanadomolybdic acid and faint diffraction peaks of 2θ=26.6°, 10.8°, etc. due to the salt of the heteropoly-acid were recognized. The fact shows that each of the catalysts is a mixture of heteropoly-acid mainly composed of phosphovanadomolybdic acid and its salt. 
     The continuous reactions were conducted using the above catalysts under the same reaction conditions as in Example B1. The results are shown in Table B-2. 
     After the continuous reactions, X-ray diffraction analysis of the catalysts was made and it was confirmed that the structure of the catalysts had not changed. 
     
                                           TABLE B-2                               
__________________________________________________________________________
                              Conversion   Yield of                       
                                                 Selectivity to           
                  Time on                                                 
                       Reaction                                           
                              of isobutyl                                 
                                    Yield of                              
                                           methacrylic                    
                                                 (methacrolein +          
                  stream                                                  
                       temperature                                        
                              aldehyde                                    
                                    methacrolein                          
                                           acid  methacrylic acid)        
Example                                                                   
     Catalyst composition                                                 
                  (days)                                                  
                       (°C.)                                       
                              (%)   (%)    (%)   (%)                      
__________________________________________________________________________
B17  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 As.sub.0.2 K.sub.0.1            
                  1    325    100   19.1   64.6  83.7                     
                  60   325    100   19.6   65.0  84.6                     
B18  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 As.sub.0.2 Rb.sub.0.1           
                  1    325    100   18.9   64.9  83.8                     
                  60   325    100   18.5   65.7  84.2                     
B19  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 As.sub.0.2 Cs.sub.0.1           
                  1    320    100   19.1   65.3  84.4                     
                  60   320    100   19.0   65.9  84.9                     
B20  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 As.sub.0.2 Tl.sub.0.1           
                  1    325    100   18.3   64.8  83.1                     
                  60   325    100   18.1   65.2  83.3                     
__________________________________________________________________________
 
    
     EXAMPLES B21-B25 
     The dried products (catalysts) as shown in Table B-3 were prepared as in Example B17 and were confirmed to be a mixture of heteropoly-acid mainly composed of phosphovanadomolybdic acid and its salt by X-ray diffraction analysis. 
     The continuous reactions were conducted using the above catalysts in the same reaction conditions as in Example B1. The results are shown in Table B-3. 
     After the continuous reactions, X-ray diffraction analysis of the catalysts was made and it was confirmed that the structure of the catalysts had not changed. 
     
                                           TABLE B-3                               
__________________________________________________________________________
                                   Conversion   Yield of                  
                                                      Selectivity         
                     Time on                                              
                           Reaction                                       
                                   of isobutyl                            
                                         Yield of                         
                                                methacrylic               
                                                      (methacrolein +     
                     stream                                               
                           temperature                                    
                                   aldehyde                               
                                         methacrolein                     
                                                acid  methacrylic acid)   
Example                                                                   
     Catalyst composition                                                 
                     (days)                                               
                           (°C.)                                   
                                   (%)   (%)    (%)   (%)                 
__________________________________________________________________________
B21  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Sn.sub.0.1 Al.sub.0.1 K.sub.0.1 
     7               1     330     100   19.5   61.7  81.2                
                     60    330     100   19.4   62.5  81.9                
B22  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Ni.sub.0.1 Ge.sub.0.1 K.sub.0.1 
                     1     325     100   19.0   62.6  81.6                
                     60    325     100   19.0   63.1  82.1                
B23  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 As.sub.0.1 Re.sub.0.1 K.sub.0.1 
                     1     330     100   19.3   64.3  83.6                
                     60    330     100   19.7   64.8  84.5                
B24  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Sn.sub.0.1 K.sub.0.1 Cs.sub.0.1 
                     1     320     100   19.7   61.7  81.4                
                     60    320     100   19.6   62.0  81.6                
B25  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 Co.sub.0.1 Cs.sub.0.1 Rb.sub.0.1
     .               1     320     100   19.2   61.8  81.0                
                     60    320     100   19.0   62.5  81.5                
__________________________________________________________________________
 
    
     EXAMPLES B26-B29 
     The dried products (catalysts) as shown in Table B-4 were prepared as in Example B1 or Example B17. 
     The continuous reactions were conducted using the above catalysts in the same reaction conditions as in Example B1. The results are shown in Table B-4. 
     
                                           TABLE B-4                               
__________________________________________________________________________
                             Conversion   Yield of                        
                                                Selectivity               
                 Time on                                                  
                      Reaction                                            
                             of isobutyl                                  
                                   Yield of                               
                                          methacrylic                     
                                                (methacrolein +           
                 stream                                                   
                      temperature                                         
                             aldehyde                                     
                                   methacrolein                           
                                          acid  methacrylic acid)         
Example                                                                   
     Catalyst composition                                                 
                 (days)                                                   
                      (°C.)                                        
                             (%)   (%)    (%)   (%)                       
__________________________________________________________________________
B26  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.5 As.sub.0.5 K.sub.0.1            
                 1    340    100   20.3   60.8  81.1                      
                 60   340    100   20.1   61.1  81.2                      
B27  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.1.0 As.sub.0.8 K.sub.0.1            
                 1    330    100   21.1   59.9  81.0                      
                 60   330    100   21.1   60.0  81.1                      
B28  Mo.sub.10 V.sub.0.5 P.sub.1 Cu.sub.0.2 As.sub.0.2                    
                 1    335    100   18.9   64.8  83.7                      
                 60   335    100   18.8   65.1  83.9                      
B29  Mo.sub.10 V.sub.1 P.sub.3 Cu.sub.0.2 As.sub.0.2 K.sub.0.3            
                 1    330    100   19.7   61.3  81.0                      
                 60   330    100   19.5   62.0  81.5                      
__________________________________________________________________________
 
    
     EXAMPLES B30-B31 
     With use of the catalyst of Example B17 the oxidation of isobutyl aldehyde was carried out in a similar manner as in Example B1 except that the space velocity (SV) was changed. The results are shown in Table B-5. These results show that the increase in the space velocity (SV) has no substantial effect on the results of the reaction. 
     
                                           TABLE B-5                               
__________________________________________________________________________
                            Conversion   Yield of                         
                                               Selectivity                
                     Reaction                                             
                            of isobutyl                                   
                                  Yield of                                
                                         methacrylic                      
                                               (methacrolein +            
                 SV  temperature                                          
                            aldehyde                                      
                                  methacrolein                            
                                         acid  methacrylic acid)          
Example                                                                   
     Catalyst composition                                                 
                 (hr.sup.-1)                                              
                     (°C.)                                         
                            (%)   (%)    (%)   (%)                        
__________________________________________________________________________
B30  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 As.sub.0.2 K.sub.0.1            
                  500                                                     
                     315    100   18.2   64.9   83.1                      
B31  Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 As.sub.0.2 K.sub.0.1            
                 3000                                                     
                     340    100   18.5   63.8   82.3                      
__________________________________________________________________________
 
    
     COMPARATIVE EXAMPLE 1 
     Dried product having a composition Mo 10  V 1  P 1  was obtained in the same manner as in Example A1 but with no addition of 1.1 g of copper oxide and using the above catalyst the continuous reaction was carried out in a similar manner as in Example A1. The results are shown in Table C-1. 
     COMPARATIVE EXAMPLE 2 
     A catalyst was prepared in the same manner as in Example A23, however, instead of 0.45 g of potassium hydroxide, 9 g of potassium hydroxide was used to obtain a catalyst of the composition of Mo 10  V 1  P 1  Cu 0 .2 K 2 . Oxidation of isobutyl aldehyde was carried out using the catalyst thus obtained under the same conditions as in Example A1. The results are shown in Table C-1. Since activity of the catalyst was low, it was necessary to raise a reaction temperature, and the yield was low. Examination of the catalyst by X-ray diffraction showed that the potassium salt of heteropoly-acid predominated in the catalyst. 
     COMPARATIVE EXAMPLE 3-4 
     The dried products (catalysts) as shown in Table C-1 were prepared as in Comparative Example 2 and the continuous reactions were conducted in the same reaction conditions as in Example A1. The results are shown in Table C-1. 
     
                                           TABLE C-1                               
__________________________________________________________________________
                              Conversion   Yield of                       
                                                 Selectivity to           
                  Time on                                                 
                       Reaction                                           
                              of isobutyl                                 
                                    Yield of                              
                                           methacrylic                    
                                                 (methacrolein +          
Comparative       stream                                                  
                       temperature                                        
                              aldehyde                                    
                                    methacrolein                          
                                           acid  methacrylic acid)        
Example                                                                   
       Catalyst composition                                               
                  (days)                                                  
                       (°C.)                                       
                              (%)   (%)    (%)   (%)                      
__________________________________________________________________________
1      Mo.sub.10 V.sub.1 P.sub.1                                          
                  1    340    100   15.8   45.0  60.8                     
                  30   340    100   17.0   42.5  59.5                     
2      Mo.sub.10 V.sub.1 P.sub.1 Cu.sub.0.2 K.sub.2                       
                  1    350    100   17.1   48.8  65.9                     
                  30   350    100   18.8   45.1  63.9                     
3      Mo.sub.10 V.sub.1 P.sub.1 Ge.sub.0.2 Cs.sub.2                      
                  1    350    100   20.2   39.8  60.0                     
                  30   350    100   21.8   36.1  57.9                     
4      Mo.sub.10 V.sub.1 P.sub.1 Ni.sub.0.2 As.sub.0.2 K.sub.2            
                  1    350    100   19.7   42.1  61.8                     
                  30   350    100   21.1   38.3  59.4                     
__________________________________________________________________________