Abstract:
A process for production of neopentyl glycol by hydrogenation of hydroxypivaldehyde in the presence of a Pt-Ru-W catalyst. This catalyst exhibits high activity and selectivity, and further has a long life. Neopentyl glycol is an important intermediate for use in production of a wide variety of chemicals.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a process for producing neopentyl glycol. More particularly, it is concerned with a process for producing neopentyl glycol (2,2-dimethyl-1,3-propanediol) by hydrogenating hydroxypivaldehyde (2,2-dimethyl-3-hydroxy propanal) as obtained by the condensation of isobutyraldehyde and formaldehyde, in the presence of a three-component catalyst of platinum-ruthenium-tungsten (hereinafter abbreviated to &#34;Pt-Ru-W&#34;). 2. Description of Related Arts 
     Neopentyl glycol is a very important intermediate for industrial use and has a wide variety of applications; for example, it is used in production of various synthetic resins such as acrylic resins, polyester resins, polyurethane resins, alkyd resins and polycarbonate resins, a plasticizer, a synthetic lubricating oil, a synthetic drying oil, a fiber processing agent, or a surfactant. 
     Neopentyl glycol has been usually produced by the following two methods. 
     In accordance with one of the methods, isobutyraldehyde and formaldehyde are subjected to an aldol condensation reaction and then to a crossed Cannizzaro reaction in the presence of a strongly alkaline catalyst, e.g. caustic soda, caustic potash or calcium hydroxide to thereby obtain the desired neopentyl glycol. This method, however, has a disadvantage in that sodium formate is also produced in an equimolar amount to the desired product. Therefore, unless sodium formate is effectively utilized, the method is unsuitable for use in production of neopentyl glycol on a commercial scale. 
     In accordance with another method, hydroxypivaldehyde, as obtained by the reaction of isobutyraldehyde and formaldehyde, is hydrogenated in the presence of a catalyst to thereby produce the desired neopentyl glycol, which is not accompanied by the production of sodium formate. This method is disclosed in Japanese Patent Publication Nos. 33169/1974, 17568/1678, U.S. Pat. Nos. 1,048,530, 1,219,162, 3,920,760, 4,021,496, West German Patent No. 1,014,089, European Patent Nos. 44,421, 44,444. In these patents, Raney nickel, Ni-Cr, Cu-Zn, Cu-Al, Cu-Cr and Cr-Ba catalysts are disclosed as catalysts for use in the hydrogenation reaction. 
     These conventional catalysts suffer from problems in that catalytic activity is insufficient and thus the reaction must be carried out under high pressure conditions, and that catalytic activity cannot be maintained at a high level for a long period of time since it is decreased under the influences of small amounts of impurities contained in hydroxypivaldehyde as the starting material. In the case of the Raney nickel catalyst, various problems arise; for example, preparation and handling of the catalyst are not easy, catalytic activity is insufficient and furthermore it cannot be maintained for a long time, and since the catalyst is used in a slurry form, the process inevitably becomes complicated. 
     SUMMARY OF THE INVENTION 
     As a result of investigations to overcome the above problems encountered in production of neopentyl glycol through hydrogenation of hydroxypivaldehyde, it has been found that a three-component Pt-Ru-W catalyst exhibits excellent performance in the hydrogenation reaction. 
     An object of the present invention is to provide a process for producing neopentyl glycol with high catalytic activity and high selectivity. 
     Another object of the present invention is to provide a process for producing neopentyl glycol with high productivity for a long period of time. 
     The present invention relates to a process for producing neopentyl glycol which comprises hydrogenating hydroxypivaldehyde in the presence of a Pt-Ru-W catalyst. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The process of the present invention usually proceeds in aqueous solvent. The aqueous solvent includes water and a mixed solvent of water and alcohol such as water-methanol, water-ethanol, water-n-propanol, water-isopropanol, water-n-butanol and water-isobutanol. Hydroxypivaldehyde to be used in the process of the present invention can be easily obtained by the aldol condensation reaction of isobutyraldehyde and formaldehyde in the presence of a basic catalyst according to the usual method. For example, the condensation reaction of formaldehyde and isobutyraldehyde is carried out at 50° to 95° C. in the presence of a tertiary amine catalyst, e.g. trimethylamine or triethylamine, or is carried out at 15° to 40° C. in the presence of a strongly alkaline catalyst, e.g. caustic soda. In the condensation reaction, the molar ratio of isobutyraldehyde to formaldehyde is 0.8:1 to 1.3:1 and preferably 1.1:1 to 1.2:1. 
     As hydroxypivaldehyde to be used for the starting material in the process of the present invention, the reaction mixture resulting from the above aldol condensation reaction may be used as such or after separation of unreacted isobutyraldehyde and formaldehyde. In addition, a dimer of hydroxypivaldehyde as obtained by crystallization in water after the separation of unreacted isobutyraldehyde and formaldehyde can be used the starting material. The dimer is represented by the following formula. ##STR1## 
     The dimer can be used in the process of the present invention without any hidrance because it acts as a hydroxypivaldehyde monomer in the hydrogenation reaction. 
     In accordance with the process of the present invention, hydroxypivaldehyde is dissolved in a suitable amount of aqueous solvent such as water and is subjected to the hydrogenation reaction in the presence of the Pt-Ru-W catalyst. The aqueous hydroxypivaldehyde solution may contain not more than 5.0% by weight of impurities such as unreacted isobutyraldehyde, formaldehyde and tertiary amine, amine compounds and sodium formate. 
     If catalysts containing Pt and Ru, singly or in combination with each other, are used, problems arise in catalytic activity and service life of the catalyst. These problems can be overcome by using the Pt-Ru-W catalyst of the present invention. 
     The significant effect of the catalyst in the present invention is exhibited as long as Pt, Ru and W are present even if the relative proportion of one element is small. The preferable catalyst composition is such that the weight ratio of Ru to Pt is 0.1:1 to 10:1 and preferably 0.2:1 to 5:1 and the weight ratio of W to Pt is 0.005:1 to 5:1 and preferably 0.01:1 to 2:1. 
     As the starting materials for preparation of the catalyst of the present invention, inorganic acid salts of the above elements, e.g. chloride, nitrate, sulfate and carbonate; oxides; hydroxides; organic acid salts; oxyacid salts; carbonyl compound and complexes can be used. 
     Any method can be employed in preparation of the catalyst of the present invention as long as in the final catalytic state, the elementary combination and the atomic ratios are satisfied with the requirement described above, and the catalyst is in the state durable for practical use. A catalyst support can or can not be used. 
     A convenient method for preparing a catalyst deposited on a support will hereinafter be explained. 
     An aqueous mixture into which chloroplatinic acid, ruthenium trichloride and ammonium tungstate has been dissolved in a predetermined ratio, is added to a catalyst support. Water is evaporated by heating while stirring. The residue is dried at a temperature of about 120° C. and then calcined at decomposition temperatures of the salts used. 
     Supports which can be used in the present invention include silica, alumina, silica-alumina, zeolite, magnesium oxide, titanium oxide, zirconium oxide, diatomaceous earth, carbon, silicon carbide, and the like. 
     When a catalyst support is used, the amounts of the catalyst components, Pt, Ru and W, deposited on the support are each within the range of 0.005 to 10 wt% (calculated as metal), with the range of 0.01 to 5 wt% being particularly effective, although they vary with the kind of the support. The catalyst components can be deposited on the support by any suitable method such as a method in which the three catalyst components are deposited on the support at the same time or a method in which each of the catalyst components are deposited successively. In addition, irrespective of the presence or absence of the catalyst support, depending on the kind of the compound to be used, there can be employed a method in which an aqueous solution of the component mixture is neutralized with a suitable acid or base to precipitate a mixed metal salt, which is then filtered, washed and dried and, thereafter calcined, or when water-insoluble compounds are used, there can be employed a method in which a uniform slurry of the components is prepared, and then dried and calcined. 
     The catalyst of the present invention can be used in a powder form or a tablet form obtained by compression molding. It can be employed in any reaction system such as a fixed bed system or a fluid bed system. After activation through hydrogenation and hydrogen according to the ordinary method, the catalyst is used in the hydrogenation reaction of the present invention. 
     The process of the present invention will hereinafter be explained in detail. 
     Aqueous medium, especially water, as a reaction solvent is used in such an amount that the hydroxypivaldehyde concentration is within the range of 10 to 80% by weight, preferably 15 to 60% by weight. If the hydroxypivaldehyde concentration is less than 10% by weight, it is difficult to separate neopentyl glycol formed from water, and the energy load for evaporation to dehydration increases. On the other hand, if it is more than 80% by weight, Tishchenko reaction between the hydroxypivaldehydes themselves occurs, resulting in neopentyl glycol ester of hydroxypivalic acid as by-product, which is unsuitable for practical use. 
     For hydrogenation reaction of hydroxypivaldehyde according to the process of the present invention, the Pt-Ru-W catalyst is dispersed or suspended in the aqueous solution containing hydroxypivaldehyde as the starting material in the presence of hydrogen, or the aqueous solution containing the starting material is passed through a column packed with the catalyst in the presence of hydrogen to produce neopentyl glycol. 
     The hydrogenation reaction can be carried out continuously or batchwise. 
     The reaction temperature is 60° to 150° C. and preferably 80° to 130° C. 
     The reaction pressure is 1 to 50 kg/cm 2  and preferably 5 to 40 kg/cm 2 , and the pressure is maintained by introducing hydrogen. 
     Although the reaction can be carried out outside the above specified reaction condition ranges, it proceeds efficiently under the above reaction conditions. 
     Separation and recovery of the objective neopentyl glycol from the reaction mixture after completion of the reaction can be carried out by techniques such as distillation or solvent extraction. 
     In accordance with the process of the present invention, in production of neopentyl glycol through hydrogenation of hydroxypivaldehyde, sufficiently high catalytic activity and selectivity are exhibited, and a long and stabilized service life of the catalyst can be realized. Thus the present invention has great industrial significance. 
     The present invention is described in greater detail with reference to the following examples, although it is not limited thereto. All parts and percents (%) are by weight. The compound names were abbreviated as follows: 
     HPA: hydroxypivaldehyde, 
     NPG: neopentyl glycol 
     IBA: isobutyraldehyde, 
     TEA: triethylamine, and 
     HPNE: hydroxypivalic acid neopentyl glycol ester 
    
    
     EXAMPLE 1 
     1.5 parts of powdered HPA (purity:99.8%), 10 parts of water and 0.5 parts of a 0.4%Pt-0.3%Ru-0.01%W catalyst deposited on active carbon were placed in a 100-milliliter stainless steel autoclave, which was then closed. After thorough purging with hydrogen, hydrogen was introduced under pressure into the autoclave to maintain the hydrogen partial pressure at 9.8 kg/cm 2 . 
     The autoclave was placed on an agitator. While agitating the autoclave, the reaction was carried out by raising the temperature of the contents from room temperature to 120° C. over a period of 15 minutes and then maintaining at 120° for 15 minutes by the use of an external heater. 
     After the reaction was completed, the autoclave was cooled to room temperature. At this time, the pressure was decreased to 5.2 kg/cm 2 . 
     After separation of the catalyst, 11.5 parts of a reaction solution was obtained. A gas chromatographic analysis showed that the reaction solution had the following composition: 
     HPA: 0%, 
     NPG: 13.26%, 
     HPNE: 0%, 
     H 2  O: 86.74%. 
     The conversion of HPA was 100%, and the selectivity into NPG was 100%. Thus it can be seen that the objective product could be obtained quantitatively. 
     EXAMPLES 2 TO 11 
     In the same manner as in Example 1 except that the recovered catalyst was used repeatedly, HPA was hydrogenated under the reaction conditions shown in Table 1. 
     As a result, NPG was quantitatively obtained as shown in Table 1. 
     
                                           TABLE 1__________________________________________________________________________                        Reaction Conditions       Charging Conditions     Time (min)              Amount                   H.sub.2     (raising                                     Results              of   Partial     time/ HPA   NPG Repeating       HPA          Water              Catalyst                   Pressure                        Temperature                               maintaining                                     Conversion                                           SelectivityNo.   Number       (g)          (g) (g)  (kg/cm.sup.2)                        (°C.)                               time) (mol %)                                           (mol %)__________________________________________________________________________Example 2 1     2.1          16.9              2.0  40.0  95    25/45 100   10Example 3 2     4.1          25.0              2.0  25.0  85    40/20 100   10Example 4 3     1.5          10.0              1.0  9.9  120    15/30 100   10Example 5 4     1.5          10.0              0.5  8.5  120    10/20 100   10Example 6 5     1.5          10.0              0.5  8.8  120    15/25 100   10Example 7 6     4.0          23.4              2.0  25.0 110    30/15 100   10Example 8 7     4.1          25.7              2.0  25.0  80    30/18 100   10Example 9 8     1.5          10.0              1.0  9.8  120    15/25 100   10Example 10 9     2.0          16.6              2.0  40.0  90    25/60 100   10Example 11 10    1.5          10.0              0.5  8.0  120    10/20 100   10__________________________________________________________________________ 
    
     EXAMPLE 12 
     In a 2 liter four-necked round bottom flask equipped with a condenser, a thermometer, a nitrogen gas inlet nozzle and stirrer, 595 parts of IBA, 657 parts of 37% formalin and 33 parts of TEA were added through the dropping funnel over a period of 10 minutes while stirring at 30° C. in a nitrogen stream. The temperature of the reaction mixture rose to 60° to 65° C. in 7 to 8 minutes, and within the range of 65° to 73° C., IBA vigorously reflexed for about 10 minutes. 
     At the point that the refluxing was coming to an end, heating with an external heater was started, and when the temperature of the reaction mixture reached 90° C., the reaction was stopped. Twenty minutes were required for this process, and 1,285 parts of a reaction solution was obtained. This solution was diluted with an equal amount of water to prepare a solution to be hydrogenated. 
     The results of a gas chromatographic analysis of the solution to be hydrogenated are shown in the left column of Table 2. 
     
                       TABLE 2______________________________________(Unit: %)        Solution to be                    HydrogenatedComponents   Hydrogenated                    Solution______________________________________HPA          31.2        0.1IBA          0.4         traceTEA          0.9         traceCH.sub.3 OH  0.8         0.9HPNE         1.2         1.7Water        63.2        63.4Unknown      1.7         3.5NPG          0.6         30.4______________________________________ 
    
     The hydrogenation reaction was carried out as follows. 
     200 parts of the above solution and 20 parts of a 0.9% Pt-0.5%Ru-0.01%W catalyst deposited on active carbon were placed in a 0.3-liter stainless steel autoclave equipped with a reflux condenser, a feed introduction tube, a hydrogen introduction tube, and a stirring apparatus, and hydrogen was introduced in the autoclave at a constant hydrogen partial pressure of 8.0 kg/cm 2 . The reaction was carried out batchwise with stirring for 40 minutes. 
     Then, the above solution was introduced continuously into the reaction system at a rate of 80 g/hr and at the same time hydrogen was continuously supplied while maintaining the hydrogen partial pressure at 8.0 kg/cm 2 . Simultaneously, the reaction mixture was continuously withdrawn from the bottom of the autoclave while maintaining the liquid in the system at a constant level. The reaction was carried out under stationary conditions continuously for 25 hours to obtain 2,200 parts of a reaction solution. The results of a gas chromatographic analysis of the reaction solution are shown in Table 2. The conversion of HPA was 99.7 mol %, and the selectivity into NPG was 95.6 mol %. 
     EXAMPLE 13 
     The feed solution obtained in the same manner as in Example 12 was hydrogenated in a packed layer type reaction tube having an inner diameter of 30 mm and a column length of 500 mm. The reaction tube was packed with 300 ml of a 0.5%Pt-0.4%Ru-0.02%W catalyst deposited on active carbon. The feed solution was continuously introduced at a flow rate of LHSV (Liquid Hourly Space Velocity) about 0.7 hr -1 , and hydrogen was supplied simultaneously while maintaining the partial pressure at 9.5 kg/cm 2  by automatic control. The hydrogenation reaction was carried out continuously for 28 days. The results are shown in Table 3. 
     
                                           TABLE 3__________________________________________________________________________Operating Feed Temperature (°C.)                      HPA   NPG   AmountDays  Amount      Top Middle              Bottom                  LHSV                      Conversion                            Selectivity                                  of NPG(days) (kg) Stage          Stage              Stage                  (hr.sup.-1)                      (mol %)                            (mol %)                                  (kg)__________________________________________________________________________ 5     25.6      101 110 106 0.71                      100   100    7.910     50.8      105 110 107 0.68                      100   100   19.315     76.0      103 118 116 0.70                      100   100   23.420    101.6      100 109 107 0.69                      99.7  100   31.325    127.2      110 119 120 0.73                      99.2  100   39.228    142.6      109 120 118 0.71                      100   100   43.9__________________________________________________________________________ Common Conditions Catalyst: 0.5% Pt0.4% Ru0.02% W deposited on active carbon Bulk Density: 0.45 g/ml Catalyst Packed Layer: 30 mm (diameter) × 500 mm (length) Amount of Catalyst: 300 ml Hydrogenation Conditions: Column liquid type Temperature (middle stage): 106 to 120° C. Pressure: 9.5 kg/cm.sup.2 LHSV: 0.68 to 0.73 hr.sup.-1 
    
     During the process, absolutely no decrease in catalytic activity was observed, and NPG was formed quantitatively. 
     142.6 kg of the total reaction mixture was mixed together. A 5 kg portion of the mixture was subjected to dehydration under reduced pressure in a packed column type distillation column (number of plates: 10; Sulzer pack filler produced by Sumitomo Jukikai Co., Ltd.), and subsequently, purification distillation was carried out to obtain 1.44 kg of NPG. 
     Dehydration and purification distillation conditions are shown in Table 4, and the quality of NPG is shown in Table 5. It was found that the NPG obtained was of high quality. 
     
                       TABLE 4______________________________________                    Purification           Dehydration                    Distillation______________________________________Temperature (°C.)             65 to 70/80                        140 to 145/(Top/Bottom)                 150 to 160Degree of Vacuum (mm Hg)             300/400    48/60(Top/Bottom)Reflux Ratio      4          2______________________________________ 
    
     
                       TABLE 5______________________________________Molten Color (APHA):  5Melting Point (°C.):                 130.1Acid Content (%) (as HCOOH):                 0.001Ester Content (%):    0.1Water Content (%):    0.05Ash Content (%):      0.01______________________________________ 
    
     EXAMPLE 14 TO 16 
     Hydrogenation was carried out in the same manner as in Example 1 except that the amount of each component deposited was changed in the Pt-Ru-W catalyst deposited on active carbon. 
     The results are shown in Table 6, and NPG was formed quantitatively. 
     
                       TABLE 6______________________________________  Deposited   HPA        NPG  Amount (%)  Conversion SelectivityNo.      Pt    Ru     W      (mol %)  (mol %)______________________________________Example 14    1     1       0.005 99.5     100Example 15    5     1      0.01   98.6     100Example 16    5     3      0.01   99.7     100______________________________________ 
    
     EXAMPLES 17 TO 21 
     Hydrogenation was carried out in the same manner as in Example 1 except that alumina, silica, silica-alumina, titania or graphite carbon was used as the support in the Pt-Ru-W catalyst, 
     The results are shown in Table 7. 
     
                       TABLE 7______________________________________      Deposition               HPA       NPG      Amount (%)               Conversion                         SelectivityNo.     Support  Pt    Ru  W    (mol %) (mol %)______________________________________Example 17   Alumina  1     1   0.01 97.2    95.5   pelletExample 18   Silica   1     1   0.01 95.3    91.2Example 19   Silica   1     1   0.01 93.5    90.1   aluminaExample 20   Titania  1     1   0.01 81.1    74.2Example 21   Graphite 1     1   0.01 92.0    85.4   carbon______________________________________ 
    
     COMPARATIVE EXAMPLES 1 TO 3 
     Hydrogenation was carried out in the same manner as in Example 1 except that a catalyst comprising 0.5% Ru deposited on active carbon was used as the catalyst. 
     The results are shown in Table 8. 
     Although the selectivity into NPG at the first reaction was satisfactory, when the reaction was repeated two or three times, the selectivity into NPG dropped unsatisfactorily. 
     
                       TABLE 8______________________________________    Repeating HPA Conversion                           NPG SelectivityNo.      Number    (mol %)      (mol %)______________________________________Comparative    1         98.2         96.8Example 1Comparative    2         96.5         67.8Example 2Comparative    3         92.0         49.1Example 3______________________________________ 
    
     COMPARATIVE EXAMPLES 4 TO 6 
     Hydrogenation was carried out in the same manner as in Example 1 except that a catalyst comprising 0.5% Pt deposited on active carbon was used as the catalyst. 
     The results are shown in Table 9. 
     
                       TABLE 9______________________________________    Repeating HPA Conversion                           NPG SelectivityNo.      Number    (mol %)      (mol %)______________________________________Comparative    1         100          53.0Example 4Comparative    2         92.5         50.0Example 5Comparative    3         97.0         41.0Example 6______________________________________ 
    
     The selectivity into NPG at the first reaction was low, and when the reaction was repeated two or three times, the selectivity dropped more. 
     COMPARATIVE EXAMPLES 7 TO 9 
     Hydrogenation was carried out in the same manner as in Example 1 except that a catalyst comprising 0.5% Pt-0.5% Ru deposited on active carbon was used as the catalyst. 
     The results are shown in Table 10. 
     
                       TABLE 10______________________________________    Repeating HPA Conversion                           NPG SelectivityNo.      Number    (mol %)      (mol %)______________________________________Comparative    1         100          97.6Example 7Comparative    2         99.5         91.6Example 8Comparative    3         99.6         63.5Example 9______________________________________ 
    
     The catalyst comprising a combination of Pt and Ru is superior in performance to those comprising Pt or Ru alone, but is inferior to the catalyst of the present invention.