CA2218216A1 - Solid catalyst and process for producing unsaturated glycol diester using the same - Google Patents

Abstract

A process for producing an unsaturated glycol diester is disclosed which comprises reacting a conjugated diene with a carboxylic acid and molecular oxygen in the presence of a solid catalyst, comprising an inorganic porous material with palladium and tellurium supported thereon as active ingredients, to thereby produce the corresponding unsaturated glycol diester. The solid catalyst, when analyzed with an X-ray microanalyzer (EPMA), has active-ingredient distributions in which: (a) at least about 80% of all palladium supported on the catalyst and at least about 75% of all tellurium supported on the catalyst are present in a surface layer extending from the outer surface of the support to a depth corresponding to about 30% of the radius of the support; and (b) at least about 50% of the palladium present in the surface layer extending from the support surface to a depth corresponding to about 30% of the radius of the support coexists with tellurium in a tellurium/palladium atomic ratio of from about 0.15 to about 0.35. This process is industrially advantageous in producing unsaturated glycol diesters while attaining a high catalytic activity.

Description

SOLID CATALYST AND PROCESS FOR PRODUCING
UNSATURATED GLYCOL DIESTER USING THE SAME

FIELD OF THE INVENTION
The present invention relates to a palladium/-tellurium solid catalyst and a process for producing an unsaturated glycol diester using the catalyst. More particularly, the present invention relates to a process in which a conjugated diene is reacted with a carboxylic acid and molecular oxygen in the presence of a solid catalyst comprising palladium and tellurium as active ingredients supported on a support with specific distributions to thereby produce the corresponding unsaturated glycol diester.
BACKGROUND OF THE INVENTION
Unsaturated glycol diesters such as butenediol diacetoxy ester are important intermediates in the production of 1,4-butanediol, which is useful as a starting material for engineering plastics, elastomers, elastic fibers, artificial leathers, etc., and tetrahydrofuran, which is useful as a high-performance solvent or a starting material for elastic fibers.
Many processes have been proposed for producing such butenediol diesters. Well known among these are processes in which a solid catalyst comprising palladium and tellurium, both supported on active carbon, is used to catalyze the reaction of butadiene with a carboxylic acid and molecular oxygen to produce a butenediol diester.

Specifically, one proposed method for producing an unsaturated glycol diester comprises reacting molecular oxygen and a carboxylic acid with a conjugated diene in the presence of a solid catalyst containing palladium and at least one of tellurium and selenium tsee JP-A-48-72090; the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Another proposed method for producing an unsaturated glycol ester comprises reacting molecular oxygen and a carboxylic acid with a conjugated diene in the presence of a solid catalyst cont~; n; ng palladium, at least one of antimony and bismuth, and at least one of tellurium and selenium (see JP-A-48-96513).
However, although the catalysts used in the above proposed methods exhibit some catalytic activity, they are not practical. In order to improve catalytic activity there has been proposed a method for producing an unsaturated glycol diester which comprises reacting molecular oxygen and a carboxylic acid with a conjugated diene in the presence of a solid catalyst cont~; n; ng palladium and at least one of antimony, bismuth, selenium and tellurium, supported on a support comprising active carbon having been processed with nitric acid (see JP-A-49-11812). Another proposed method for producing an unsaturated glycol diester comprises reacting molecular oxygen and a carboxylic acid with a conjugated diene in the presence of a solid catalyst in which palladium and at least one of antimony, bismuth, selenium and tellurium are supported on an active carbon support and the resulting mixture is reduced, processed in gas containing molecular oxygen at a temperature of 200~C or higher and again reduced (see JP-A-50-4011). Yet another proposed method for activating a catalyst comprises supporting palladium and at least one of antimony, bismuth, selenium and tellurium on an active carbon support. This catalyst is used for producing an unsaturated glycol diester from a conjugated diene, a carboxylic acid and molecular oxygen and is activated by a process which comprises reducing the catalyst with methanol gas and then oxidizing it with molecular oxygen, said reduction and oxidation being performed at least once;
bringing the catalyst into contact with acetic acid and molecular oxygen and reducing it with hydrogen gas (see JP-A-55-3856).
In order to reduce the deterioration of catalytic activity due to the lapse of time, there has been proposed a catalyst for diacyloxy substitution of a conjugated diene which comprises at least one noble metal selected from group VIII of the periodic table of elements, and at least one element selected from group IV, V or VI of the periodic table of elements (with the proviso that zirconium, niobium and molybdenum are excluded) supported on a support. The support is silica having a specific surface area of 200 m2/g or larger and an average pore diameter of 100 A or larger (see JP-A-56-130232). There has also been proposed a method for producing an unsaturated glycol diester which comprises reacting a conjugated diene with a carboxylic acid and molecular oxygen in the presence of a solid catalyst comprising palladium and tellurium as active ingredients supported on a solid support, characterized in that the volume of pores having a pore radius of from S to 50 nm accounts for at least 80% of the total volume of pores having a pore radius of from 1.8 to 10,000 nm (see JP-A-8-3110).
Although the drawbacks of solid catalysts are considerably mitigated by the various methods proposed in the prior art, the proposed processes are still insufficient for industrial production of target compounds. In addition, since the proposed processes use palladium, an expensive noble metal, it is necessary to increase the activity per unit of palladium.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for producing an unsaturated glycol diester in which a catalyst-having higher activity than prior art catalysts is used to react a conjugated diene with a carboxylic acid and molecular oxygen to there~y provide an industrially advantageous process for producing unsaturated glycol diesters.
As a result of intensive investigations made by the present inventors, it has been found that the distributions of palladium and tellurium, supported as active ingredients on a support, exert a considerable influence on catalytic performance. The present invention has been completed based on this finding.
According to one preferred aspect of the present invention, a solid catalyst is provided which comprises an inorganic porous material as a support and palladium and tellurium supported thereon as active ingredients, wherein said solid catalyst, when analyzed with an X-ray microanalyzer (EPMA), has active-ingredient distributions in which:
(a) at least about 80% of all palladium supported on the catalyst and at least about 75% of all tellurium supported on the catalyst are present in a surface layer of the support, extending from an outer surface of the support to a depth corresponding to about 30% of the radius of the support; and (b) at least about 50% of the palladium present in the surface layer of the support extending from the outer surface of the support to a depth corresponding to about 30% of the radius of the support, coexists with tellurium in a tellurium/palladium atomic ratio of from about 0.15 to about 0.35.
According to another aspect of the present invention, a process for producing an unsaturated glycol diester is provided which comprises reacting a conjugated diene with a carboxylic acid and molecular oxygen in the presence of the above solid catalyst to thereby produce the corresponding unsaturated glycol diester.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 (A) is a graphic representation of the average distribution of palladium in the catalyst obtained in Example 1.
Fig. 1 (B) is a graphic representation of the average distribution of tellurium in the catalyst obtained in Example 1.
Fig. 1 (C) is a histogram of palladium in the catalyst obtained in Example 1.
Fig. 2 (A) is a graphic representation of the average distribution of palladium in the catalyst obtained in Comparative Example 1.
Fig. 2 (B) is a graphic representation of the average distribution of tellurium in the catalyst obtained in Comparative Example 1.
Fig. 2 (C) is a histogram of palladium in the catalyst obtained in Comparative Example 1.
Fig. 3 (A) is a graphic representation of the average distribution of palladium in the catalyst obtained in Comparative Example 5.
Fig. 3 (B) is a graphic representation of the average distribution of tellurium in the catalyst obtained in Comparative Example 5.
Fig. 3 (C) is a histogram of palladium in the catalyst obtained in Comparative Example 5.

Fig. 4 (A) is a graphic representation of the average distribution of palladium in the catalyst obtained in Example 7.
Fig. 4 (B) is a graphlc representation of the average distribution of tellurium in the catalyst obtained in Example 7.
Fig. 4 (C) is a histogram of palladium in the catalyst obtained in Example 7.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
(I) Solid Catalyst for Acyloxy Substitution In the solid catalyst for use in the present invention, the palladium and tellurium supported as active ingredients have respective distributions which satisfy requirements (a) and (b) described above.
The distribution of an active ingredient supported on a support in a solid catalyst is influenced by all the factors involved in catalyst preparation (e.g., the properties of the support, the kind of salt from which the active ingredient is derived, the properties of a solution of the salt, infiltration method, drying method, etc.). It is therefore impossible to unconditionally specify a technique capable of giving a specific distribution of a supported ingredient. Even when any of the disclosed prior art techniques is used for catalyst preparation, the obtained catalysts do not have the same distribution of supported ingredients as those described below in the Examples and Comparative Examples. For example, catalysts prepared using different starting tellurium salts differ considerably in the distribution of supported tellurium, even when such catalysts are prepared under the same conditions. For example, see Example 4 and Comparative Example 10. In these examples in which tellurium metal, as a tellurium salt, is used under the conditions employed therein, the active ingredient is densely deposited in a surface layer of the support. In addition, catalysts prepared from the same starting materials (support, palladium salt, and tellurium salt) can differ from each other in the distribution of each supported ingredient merely when produced using different drying methods (see Comparative Example 10 and Examples 1 and 7) or produced under slightly modified conditions (see Example 3 and Comparative Example 1) .
In view of the above, the present inventors have made intensive investigations concerning the influence on catalytic performance of the distributions of palladium and tellurium supported as active ingredients in a solid catalyst. As a result, they have found that the distribution of ingredients in catalysts obtained, using an extremely large number of combinations of catalyst preparation conditions, is a crucially important factor which influences the catalytic performance, although preferred catalyst preparation conditions cannot be specified. They have further found that a solid catalyst, in which supported active ingredients have specific distributions, is exceedingly active.
For determining the distributions of supported ingredients, an EPMA is generally used. However, even catalysts prepared by the same method do not have identical distributions of supported ingredients. Even catalyst products produced in the same lot have some degree of fluctuation from particle to particle. It is therefore difficult to accurately determine the distribution of a supported ingredient based on an examination of only one particle. In many particles, the distribution of a supported ingredient fluctuates to some degree within each particle.
This does not mean that the distribution of a supported ingredient in a catalyst particle varies merely as a function of distance from the center of the particle, but rather that in any section of a catalyst particle which, for example, is spherical, different straight lines passing through the center of the section have distributions of supported ingredients which differ from one another along their lengths. It is therefore difficult to accurately express the distribution of a supported ingredient in a particle through a mere examination along one line. In the case where no such fluctuations are found in supported-ingredient distribution in a catalyst particle, the distribution of the supported ingredient in the particle can be represented by the results of an examination of the distribution along any center line, assuming the support is spherical. However, in the case of supports of irregular shape, it is difficult to accurately express the distribution of a supported ingredient from only the results of an analysis along center lines through the particle. Therefore, it is very difficult to obtain a distribution of a supported ingredient which accurately represents the distributions in all catalyst particles.
Under these circumstances, the present inventors used the method described below to determine the distribution of a supported ingredient which represents all distributions of the ingredient in the catalyst.
Ten catalyst particles are arbitrarily selected. For each selected particle, the section having the largest area is ex~m;ned with an EPMA along the longest straight line extending from one point to another on the circumference of the section. Hereinafter, this straight line is referred to as the ~major diameter line"; the length thereof is referred to as the "diameter in the major diameter direction"; the center of the major diameter line is referred to as the "center in the major diameter direction"; and half of the diameter is referred to as the "radius in the major diameter direction.
For each selected particle, the longest straight line which meets the major diameter line at right angles is also examined by EPMA. Hereinafter, this straight line is referred to as the "minor diameter line"; the length thereof is referred to as the ~'diameter in the minor diameter direction"; the center of the minor diameter line is referred to as the ~center in the minor diameter direction"; and half of the diameter is referred to as the "radius in the minor diameter direction". The major and minor diameter lines are each examined by EPMA at intervals of 20 ~m. The results obtained are corrected using equations (1) to (5), which will be described later. Thus, supported-ingredient distributions for ten major diameter lines and supported-ingredient distributions for ten minor diameter lines are obtained. In the case where the support is spherical, the section of the particle is examined only along a major diameter line, based on the assumption that the support is a true sphere. The supported-ingredient distribution determined from the results is regarded as being representative of all distributions in the catalyst. In the case where the support is cylindrical, the axis (the major-diameter-direction center line in a rectangular section) is regarded as a major diameter line and a straight-line which meets the major diameter line at its center at right angles is regarded as the minor diameter line, based on the assumption that the support is a true cylinder. In the case of a support of any other shape, the section is regarded as an ellipse having its major axis and minor axis equal to the respective major diameter line and minor diameter line of the section, and the solid body formed by rotating the ellipse about the major axis is regarded as the shape of the catalyst particle. In addition, with respect to the supported-ingredient distributions along the major diameter line, the positions of both ends of the major diameter line (which are located on the surface of the catalyst particle) are each taken as 0% and the position of the center of the major diameter line is taken as 100%, to determine the positions (%) of the individual examination sites. Furthermore, the major diameter lines for each of the ten particles is divided at its center into two parts, thereby obtaining supported-ingredient distributions for twenty major-diameter-line radii. The twenty distributions are averaged with respect to each position (%) to thereby obtain an average supported-ingredient distribution for the major-diameter-line radii. In a similar manner, supported-ingredient distributions for the twenty minor-diameter-line radii and an average supported-ingredient distribution for the minor-diameter-line radii are determined.
For the actual determination of distributions by EPMA, it is- preferred to employ the ZAF correction method.
The ZAF correction method is a technique for deter~ining the correction factor for atomic number effect (Z), absorption effect (A), and fluorescent excitation effect (F).
Specifically, the f~F in the following equation is determined:

Cu~k/Cstd = (Iunk/Istd)xf~Fxf other ( 1 ) wherein Cunk is the concentration of an element in the catalyst being examined, Cstd is the concentration of the element in a standard sample, IUnk is the found intensity of the element in the catalyst, Istd is the found intensity of the element in the standard sample, fzAF is the correction factor obtained by the ZAF correction method, and f other is other correction factors.
This correction method is described in detail in, for example, Hiroyoshi Soejima, "Electron Beam Microanalysisl', Nikkan Kogyo Shinbun-sha. In the case of porous support materials, such as in the catalysts of the present invention, fOther is not negligible because of the density effect, etc.
Therefore, the standard sample for use in ex~mining such a porous catalyst is preferably one consisting of the same support as that of the catalyst being examined and an active ingredient supported thereon homogeneously in a known concentration. The term llhomogeneously" as used above means that the active ingredient is homogeneously distributed in the region where incident electrons diffuse, the region where specific X rays generate, and the passageways through which the X rays exit, on the order of about 10 nm; namely, the whole standard sample is homogeneous on the order of a nanometer. However, since such a standard sample is difficult to prepare, the present inventors used a standard -sample containing palladium metal for determining the distribution of palladium in the catalyst, tellurium metal for determining the distribution of tellurium in the catalyst, and a support on which no active ingredient is supported as a standard sample for the elements constituting the support. The supported-ingredient distributions were measured by the ZAF method and determined through the following calculations. In the case where the catalyst particle is spherical, the palladium concentration IrW (wt%) at each examination site is determined using the following equations:
Vfr = r~3-(r-20)~3 (2) WCalC = ~ ( Irxvfr ) /~ Vfr fwt = (Wanlxn)/(total of the Wcalc values for all particles examined) IrW = Irxfwt wherein Vfr is the volume correction factor for each examination site; r is the distance (~m) from the center of the straight line along which examination was made to an ex~min~tion site, provided that r is regarded as 20 when r<20; WCalc is the palladium concentration (wt~) in each sample determined from the results of an EPMA ~X~inAtion; Ir is the palladium concentration (wt%) at each ex~min~tion site determined by the ZAF correction method for each sample; ~ is total over the range of the diameter of each straight line along which an ~X~m; nation was made; fWt is the supporting percentage correction factor, and corresponds to f other in equation (1); Wanl is the palladium supporting percentage (wt%) of the catalyst; n is the number of samples examined;
and IrW is the corrected palladium concentration (wt%) at each examination site in each sample.
In the case of cylindrical catalyst particles, the following equations (2-bl) and (2-b2) are used in place of the above equation (2) for the major diameter direction and minor diameter direction, respectively, to determine the respective values of Vfr. From each Vfr value, fWt is determined using equations (3) and (4). The average of the two values of fWt thus obtained is used as the fWt of the catalyst to calculate IrW using equation (5).
Vfr = 1 (2-bl) Vfr = r~2-(r-20)~2 provided that r=20 when r<20. (2-b2) In the case of supports of other shapes, equation (2-c) is used in place of equations (2-bl) and (2-b2).
Otherwise, the calculations for supports of other shapes are made in the same manner as in the case of cylindrical supports.
Vfr = (ra~xrbl~2)-(ra2xrb2~2) (2-c) When the above equation is used for a calculation for the major diameter direction, ra, is the distance (~m) between the center of the major-diameter-direction straight line along which ex~m;nation was made and an ex~min~tion site, and ra2, rb1, and rb2 are determined using the following equations.
ra2 = ral 20 provided that ra1=20 when ra1<20 (2-c-al) rbl = (ra1/Da)xDb (2-c-a2) rb2 = (ra2/Da)XDb (2-c-a3) When equation (2-c) is used for a calculation for the minor diameter direction, rb1 is the distance (~m) between the center of the minor-diameter-direction straight line along which examination was made and an examination site, and rb2, ral, and ra2 are determined using the following equations.
rb2 = rb1 20 provided that rbl=20 when rbl<20 (2-c-bl) ral = (rbl/Db)XDa (2-c-b2) ra2 = (rb2/Db)XDa (2-c-b3) In the above equations, Da is the length (~m) of the major diameter line, and Db is the length (~m) of the minor diameter line.
With respect to tellurium, an average distribution along the radii is determined in the same manner as described above for palladium.
The proportion of each active ingredient present in the surface layer of the support, extending from the support surface to a depth corresponding to about 30% of the radius of the support, to the total amount of the active ingredient CA 022l82l6 l997- lO- l4 supported in the catalyst was calculated as follows from the average supported-ingredient distribution along the radii determined by the method described above. In the case where the solid catalyst is spherical, the proportion of the palladium present in the range of from r1 to r2, in terms of distance from the catalyst surface, to all palladium supported in the catalyst, Cra (%), is determined using the following equations:
Vfr = (R-rl)~3-(R-r2)~3 (6) Cr = ( IrwXVfr/ ( ~ ( IrWXVfr ) ) ) x l O 0 ( 7 ) Cra = (total of the Cr values for all samples)/n (8) wherein Vfr is volume correction factor for each examination site; R is radius; Cr is the proportion (%) of the palladium present in each sample in the range of from rl to r2, in terms of distance from the catalyst surface, to all palladium contained in the catalyst; IrW is the corrected palladium concentration (wt%) at each examination site in each sample;
~ is total over the range from the catalyst surface to the center of each sample; and n is the number of samples.
Consequently, the proportion of the palladium supported in the range from the catalyst surface to the depth corresponding to about 30% of the radius, to all palladium, Cr30 (%), is defined as follows.

Cr30 = (total of the Cra values for all examination sites in the range of from a depth of 0% to a depth of about 30~) (9) For a catalyst which is not spherical, Cr30 is determined for each of the average distributions for major-diameter-line radii and the average distributions for minor-diameter-line radii, and the average thereof is taken as the Cr30 of the catalyst. In the case of cylindrical supports, equation (6-bl) is used in place of equation (6) to calculate the average supported-ingredient distribution for the major-diameter-line radii, while equation (6-b2) is used in place of equation (6) to calculate the average supported-ingredient distribution for the minor-diameter-line radii.
Vfr = 1 (6-bl) Vfr = (R-rl)~2-(R-r2)~2 (6-b2) In the case of supports of any other shape, equation (6-cl) is used in place of equation (6) to calculate the average supported-ingredient distribution for major-diameter-llne radll:
Vfr = ((R-r1)x(R~-rl')~2)-((R-r2)x(R~-r2')~2) (6-cl) wherein R' is the radius of minor diameter line; rl' =
(rl/R)xR'; and r2' = (r2/R)xR'.
For the calculation of the average supported-ingredient distribution for minor diameter lines, equation (6-c2) is used in place of equation (6):

Vfr = ((R-rl)~2x(R'-rl'))-((R-r2)~2x(R'-r2')) (6-c2) wherein R' is the radius of major diameter line; rl' =
(r1/R)xR'; and r2' = (rz/R)xR'.
With respect to tellurium, the value of Cr30 is determined in the same manner as described above for palladium.
For the active ingredients supported in the range from the catalyst surface to a depth corresponding to about 30% of the radius, the tellurium/palladium atomic ratio, Xr, for each examination site in each sample is determined using the following equation:
Xr = (Irw(Te)/l27.6l)/(Irw(pd)/lo6-4) (10) wherein IrW(Te) is the corrected tellurium concentration (wt%) for each ex~mination site in each sample, and IrW(pd) is the corrected palladium concentration (wt%) for each examination site in each sample.
Consequently, the proportion, Ctp (%), of the palladium which has been supported on the layer extending from the catalyst surface to a depth corresponding to about 30% of the radius, and which has a tellurium/palladium atomic ratio Xr in the range of from about O.lS to about 0.35, to all the palladium supported on that layer, is determined using the following equation.
C~p = ((total, in all examination radii, of Cr wherein the palladium present in the layer extending from a depth corresponding to 0% of the radius to a depth corresponding to about 30% of the radius has an Xr of from about 0.15 to about 0.35)/((major-diameter-direction Cr30 x n)+(minor-diameter-direction Cr30 x n)))xlO0 (11) In the case of spherical catalyst particles, however, the following equation (11') is used in place of equation (11) for determining the Ctp.
Ctp = ((total, in all examination radii, of Cr wherein the palladium present in the layer extending from a depth corresponding to 0% of the radius to a depth corresponding to about 30% of the radius has an Xr of from about 0.15 to about 0.35)/(Cr30 x n))xlO0 (11') Although reasons explaining the high activities of catalysts having specific supported-ingredient distributions according to the present invention are not known, the following explanations are possible. The reaction process can be divided into the following steps: (1) substrates enter pores of the catalyst; (2) the substrates diffuse within the pores; (3) the substrates are adsorbed onto active sites in the pores where active ingredients are supported; (4) a reaction occurs at the adsorption sites; (5) the reaction products are desorbed from the active sites; (6) the reaction products diffuse within the pores; and (7) the reaction -products are released from the pores. In the case where the time required for step (2) or for steps (2) and (6) is longer than that required for the other steps, higher reaction rates are attained when the distance over which the substrates or reaction products must move within the pores is shorter, that is, when a greater proportion of the active ingredients are present in areas close to the inlets of the catalyst pores (a surface layer portion of the catalyst). However, when that distance becomes shorter than a given value, the difference between the time required for step (2), or for steps (2) and (6), and the time required for the other steps becomes smaller and the influence on reaction rate is reduced.
Consequently, the area where active ingredients are present in a large amount need not be limited to the surface of the support, and therefore the active ingredients may be present in a layer extending to some depth. Specifically, a catalyst in which at least about 80% of all supported palladium and at least about 75% of all supported tellurium are present in a surface layer extending from the outer surface of the support to a depth corresponding to about 30% of the radius, as in the present invention, has high activity.
For the acyloxy substitution reaction, the proportion of tellurium to palladium supported as active ingredients is important. If the proportion of supported tellurium to supported palladium is too small, palladium is released from the support and enters the reaction mixture during the acyloxy substitution reaction. If the proportion of tellurium is too large, tellurium enters the reaction mixture. In either case, the catalytic activity is reduced.
Generally, it is particularly preferred that the proportion of supported tellurium to supported palladium in a catalyst be from about 0.05 to about 5.0 in terms of the ratio of number of gram-atom of supported tellurium atoms per gram-atom of supported palladium. It should however be noted that in many catalysts, the supported-palladium distribution and the supported-tellurium distribution are not completely the same, but differ from each other in some degree. Therefore, the supported palladium and tellurium are not present in a constant atomic ratio. When the relationship between the amount of palladium and the tellurium/palladium atomic ratio in a catalyst is expressed by means of a histogram and the histogram distribution has too great a width, then the catalyst is undesirable because palladium or tellurium will be released therefrom as described above. However, an exceedingly narrow histogram distribution is not essential.
The acyloxy substitution reaction according to the present invention can be satisfactorily conducted even when the tellurium/palladium atomic ratio varies to some degree.
Therefore, the histogram distribution may have some degree of width.
However, the importance of the tellurium/palladium atomic ratio does not apply to the whole catalyst. It is only the active ingredients present in the layer extending from the support surface to a depth corresponding to about 30% of the radius, as in the present invention, which are limited in the width of the histogram distribution.
Specifically, a catalyst in which at least about 50% of the palladium, present in a surface layer of the support extending from the support surface to a depth corresponding to about 30~ of the radius of the support, coexists with tellurium in a tellurium/palladium atomic ratio of from about 0.15 to about 0.35 was found to have exceedingly high activity.
The support employed in the catalyst for the acyloxy substitution of a conjugated diene according to the present invention is preferably an inorganic, porous material which undergoes substantially no change under the reaction conditions. Preferred examples of supports include active carbon, oxides such as silica, alumina, titania, and zirconia, and mixed oxides thereof. Especially preferred is silica. The support is not particularly limited in shape.
However, support particle diameters which are too large result in reduced catalyst particle surface areas, while support particle diameters which are too small result in increased pressure losses in a packed catalyst layer. The preferred industrially effective range of support size is therefore from about l to about 8 mm. The support is preferably porous, and preferably has an average pore -diameter of from about 10 to about 50 nm.
Methods for supporting active ingredients on an inorganic porous material in the catalyst of the present invention are not particularly limited, as long as the active ingredients supported on the catalyst have the specific distributions described above. Some preferred techniques for supporting active ingredients on the surface of a catalyst according to the invention include: a method in which an aqueous solution containing the active ingredients is infiltrated into a porous support in the presence of urea (see JP-A-51-40392); a method in which an inorganic support is impregnated with a solution-containing polyethylene glycol and the active ingredients (see JP-B-55-33381; the term "JP-B" as used herein means an "examined Japanese patent publication"); a method in which a hydrocarbon is added to a solution of salts of the active ingredients in at least one solvent selected from ketones, esters, and alcohols to form a resultant mixed solution having lower polarity than acetone, which is then infiltrated into an inorganic porous support (see JP-B-57-5578); and a method in which a solution of the active ingredients is sprayed over a heated support to deposit the active ingredients on the surface of the support (see JP-A-3-293036). Other preferred techniques comprise supporting the active ingredients around the surface of a support, for example a method in which small amounts of the active ingredients are first supported on a support, and then further amounts of the active ingredients are added, to result in a necessary amount of the active ingredients being supported on the support (see JP-B-54-8638). Still other techniques comprise those in which the active ingredients are supported in regulated positions, such as the competitive adsorption method (see, e.g., JP-B-52-23920 and JP-B-52-30475). Other preferred examples of techniques in which the active ingredient is supported in regulated positions include: a method comprising adsorbing the active ingredients onto a surface layer of a support under conditions in which tenacious adsorption occurs, followed by drying the support to fix the active ingredients; a method comprising infiltrating a solution of the active ingredients into a support under conditions in which the active ingredients are not adsorbed onto the support, followed by rapidly drying the support to thereby deposit large amounts of the active ingredients on a surface layer of the support; and a method comprising hydrophobizing a support, for example by a surface treatment which comprises infiltrating an aqueous solution containing the active ingredients into only a surface layer of the support, and then drying the support to fix the active ingredients. Any of the above methods may preferably be used to support the active ingredients on a support. Although the mechanism by which specific distributions of active ingredients are produced is unclear, one particularly preferred method for supporting the active ingredients on a support comprises infiltrating an aqueous solution containing the active ingredients into a support and then drying the support. Drying may preferably be conducted in a kiln, wherein hydrogen gas is introduced while fluidizing the catalyst to thereby conduct drying and reduction simultaneously. Alternatively, the impregnated support may preferably be dried with superheated steam.
The catalyst with the active ingredients supported thereon is preferably reduced prior to use. It may also be preferred to subject the catalyst to drying or burning prior to reduction, for example in circumstances where the catalyst has been dried insufficiently or where it is desired to decompose a supported salt to some degree prior to use. Salt decomposition may be preferred where one of the ingredients is a nitrate, to thereby reduce the amount of NOx generated upon reduction. Salt decomposition may also be preferred to reduce heat generation during reduction. The drying or burning of the catalyst may be conducted repeatedly if desired.
Methods for drying, burning, and reduction are not particularly limited, so long as they do not inhibit the attainment of the specific supported-ingredient distributions in the catalyst according to the present invention.
Preferred examples of drying methods include: fluidized-bed vacuum drying using a rotary evaporator or a conical blender;
stationary drying using a vacuum dryer, a stacked-shelf type dryer, or the like; fluidized-bed drying using a kiln dryer or the like; and drying in a stream of nitrogen, air, hydrogen, steam, etc. Any of these preferred drying methods may be used. Preferred examples of burning methods include:
a method comprising heating the catalyst in a stream of, e.g., nitrogen, air, or a mixture thereof using a fixed bed or a fluidized bed, such as in a kiln; and a method in which the catalyst is heated without passing a gas therethrough.
Either of these preferred burning methods may be used.
Preferred examples of reduction methods include: vapor-phase reduction with, e.g., hydrogen gas or methanol gas; and liquid-phase reduction with a liquid such as hydrazine or formalin.
A palladium compound is preferably used for preparing the catalyst. Preferred examples thereof include palladium oxide; palladium salts of inorganic acids, such as palladium nitrate, palladium chloride, and palladium sulfate; palladium salts of organic acids, such as palladium acetate; complex palladium salts such as tetraamminepalladium chloride; and organometallic palladium compounds such as palladium acetylacetonate. It may also be preferred to use palladium metal. The concentration of palladium supported on the support is preferably within the range of from about 0.1 to about 20% by weight of the catalyst, more preferably from about 0.5 to about 10% by weight of the catalyst. If the palladium concentration is below the lower limit of about -0.1% by weight, the catalyst is reduced in activity per unit weight thereof and may be unsuitable for practical use. If the palladium concentration exceeds the upper limit of about 20% by weight, not only is the catalyst reduced in activity per unit of palladium, but the catalyst cost is also increased because palladium is expensive. Therefore, the use of either too much or too little palladium is economically undesirable.
A tellurium compound is preferably also used for preparing the catalyst. Preferred examples thereof include tellurium halides such as tellurium(II) chloride and tellurium(IV) chloride; tellurium oxides such as tellurium(IV) oxide and tellurium(VI) oxide; telluric acid (H6TeO6) and salts thereof; tellurous acid (H2TeO3) and salts thereof; tellurium metal; sodium hydrogen telluride (NaHTe);
and organotellurium compounds such as diphenyl ditelluride ([PhTe]2). The total amount of tellurium supported in the catalyst is not particularly limited, as long as at least about 50% of the palladium, present in a surface layer of the support extending from the outer surface of the support to a depth corresponding to about 30% of the radius of the support, coexists with tellurium in a tellurium/palladium atomic ratio of from about 0.15 to about 0.35, as described above.
(II) Production of Unsaturated Glycol Diester The conjugated diene, e.g., butadiene, used as a -starting material in producing an unsaturated glycol diester using the catalyst described above, is not necessarily pure.
It may contain an inert gas such as nitrogen; a saturated hydrocarbon, e.g., methane, ethane, or butane; or an unsaturated hydrocarbon, e.g., butene. Besides butadiene, examples of other preferred conjugated dienes include isoprene, alkyl-substituted butadienes such as 2,3-dimethylbutadiene and piperylene, and cyclic dienes such as cyclopentadiene.
Preferred examples of the carboxylic acid used as the other starting material include lower monocarboxylic acids such as acetic acid, propionic acid, and butyric acid.
Acetic acid is particularly preferred due to its high reactivity and low cost. The carboxylic acid may preferably serve not only as a starting material, but also as a solvent.
It may also be preferred to carry out the reaction in the presence of an inert organic solvent such as a saturated hydrocarbon or an ester. However, it is preferred that the carboxylic acid starting material comprises at least about 50% by weight of the solvent in which the reaction is conducted. Furthermore, the amount of carboxylic acid is preferably in the range from the stoichiometric amount to about 60 mol per mol of the conjugated diene.
The molecular oxygen used in the process of the present invention need not be pure oxygen, and may preferably be diluted with an inert gas, e.g., nitrogen. For example, air may be used as the molecular oxygen. The amount of oxygen is not particularly limited as long as it is not less than the stoichiometric amount. However, from the standpoint of safety in industrial production, the amount of oxygen is preferably in a range which does not result in an explosive composition.
The process of the present invention, in which a conjugated diene is reacted with a carboxylic acid and molecular oxygen to produce the corresponding unsaturated glycol carboxylic diester, can be carried out either batch-wise or continuously. Although the reaction may preferably be carried out by a fixed-bed, fluidized-bed, or suspension type process, the fixed-bed type process is more preferred as an industrial process. The reaction is preferably conducted at a temperature of about 20~C or higher. However, a more preferred reaction temperature range is from about 40 to about 120~C from the standpoints of reaction rate, by-product generation, etc. The reaction may be preferably conducted either at ordinary pressure or at elevated pressure.
Although elevated pressure is more preferred from the standpoint of heightening the reaction rate, it also results in increased equipment cost. Therefore, the most preferred pressure range is from about atmospheric pressure to about 100 kgf/cm2.

Preferred embodiments of the present invention will now be described below in more detail by reference to Examples. ~owever, the invention should not be construed as being limited to these preferred Examples. To express the distributions of supported active ingredients in the catalysts of the following Examples and Comparative Examples, the following terms are used. The proportion of active ingredient present in the surface layer of the support extending from the outer surface of the support to a depth corresponding to about 30% of the radius, to the total amount of the active ingredient supported in the catalyst, i.e., the proportion determined using equation (9), is referred to as ~proportion A~ (%); while the proportion of palladium which has been supported on the surface layer of the catalyst extending from the outer surface of the support to a depth corresponding to about 30% of the radius, and which has a tellurium/palladium atomic ratio of from about 0.15 to about 0.35, to all the palladium present in that surface layer, i.e., the proportion determined using equation (11), is referred to as "proportion B" (%).
The results of the reactions are described using the following terms. The term "activity" is used to express the total number of millimoles of 3,4-diacetoxy-1-butene, 3-hydroxy-4-acetoxy-1-butene, 1-acetoxycrotonaldehyde, 1,4-diacetoxy-2-butene (1,4-DABE), l-hydroxy-4-acetoxy-2-butene, 1,4-dihydroxy-2-butene, diacetoxyoctatriene, and triacetoxybutene, among various other reaction products, yielded per kg of catalyst per hour. The term "1,4-DABE

selectivity" means the proportion (mol%) of 1,4-diacetoxy-2-butene which is produced, relative to the total amount of the above-listed reaction products and other reaction products such as furan, acrolein, monoacetoxybutene, butanol, and monoacetoxy-1,3-butadiene.

Into a 50-ml measuring flask was introduced 0.843 g of tellurium metal (manufactured by NE Chemcat Corp.). 20 g of 35 wt% aqueous nitric acid solution was added to dissolve the metal. To this solution was added 27.05 g of 10.0 wt%
aqueous palladium nitrate solution (manufactured by NE
Chemcat Corp.), followed by sufficient 35 wt% aqueous nitric acid solution to adjust to the total volume of the contents to 50 ml. To the resultant solution was added 25.05 g of a spherical silica support (manufactured by Fuji Silysia Chemical, Ltd., Japan and sold under the trademark, CARiACT-Q-15; particle diameter, 1.7-3.36 mm; hereinafter referred to as "CARiACT-Q-15"). After the support was immersed in the solution at-room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 56.05 g. A
28.0-g portion of the thus-obtained catalyst was placed in a horizontal kiln (inner diameter, 3 cm; effective sectional area, 7.1 cm2). The kiln contents were heated from room temperature to 150~C over a period of 1 hour and then kept at 150~C for 2 hours, while rotating the kiln at 30 rpm and passing hydrogen gas therethrough at a rate of 4.2 Nl/min.
Thus, drying and reduction were conducted simultaneously.
The contents were then cooled in a nitrogen stream to obtain 13.39 g of an activated catalyst. The activated catalyst contained 5.0 wt% palladium and 1.56 wt% tellurium.
4 g of the catalyst was then packed into a stainless-steel reaction tube having an inner diameter of 12 mm (effective sectional area, 1.005 cm ). 1,3-Butadiene, acetic acid, and nitrogen containing 6% oxygen were introduced into the reaction tube at rates of 0.15 mol/hr, 2.5 mol/hr, and 100 Nl/hr, respectively, and the reaction was continuously conducted for 7 hours at a pressure of 60 kgf/cm2 and a temperature of 80~C. A portion of the reaction mixture withdrawn between 4 hours and 5 hours after initiation of the reaction, and a portion of the reaction mixture withdrawn between 6 hours and 7 hours after initiation of the reaction, were quantitatively analyzed by gas chromatography to determine the reaction products. The results of these analyses were averaged to determine the activity and selectivity, and are shown in Table 1.
Distributions of supported ingredients were determined as follows. Ten catalyst particles were arbitrarily selected from the catalyst obtained above. With respect to each selected particle, the section having the largest area was examined with an EPMA (JXA-8600M, manufactured by JEOL Ltd., Japan) along the longest straight line extending from one point to another on the circumference of the section, the examination being conducted at intervals of 20 ~m along this line. With respect to each examination site, ZAF correction and supporting percentage correction were conducted. Thus, supported-ingredient distributions for 20 radii and an average supported-ingredient distribution for the radii were determined with respect to each of palladium and tellurium. Values of proportion A were determined from the average supported-ingredient distributions for the radii, while proportion B was determined from the supported-ingredient distributions for the 20 radii. The results obtained are shown in Table 1. Figs. 1 (A) to (C) show supported-ingredient distributions and a histogram, with respect to the tellurium/palladium atomic ratio, of palladium present in a layer ranging from the surface of the catalyst particles to a depth of 30%.

A catalyst was prepared in the same manner as in Example 1, except that the flow rate of hydrogen gas during the drying and reduction step was changed to 0.26 Nl/min.
The diacetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 1. The results obtained are shown in Table 1.

- 34 _ Into a 50-ml measuring flask was introduced 1.244 g of tellurium dioxide (manufactured by Mitsuwa Chemical Co., Ltd., Japan). 28 g of a 35 wt% aqueous nitric acid solution was added to dissolve the tellurium compound. To this solution was added 20.89 g of 10.0 wt% aqueous palladium nitrate solution, followed by sufficient 35 wt% aqueous nitric acid solution to adjust the total volume to 50 ml. To the resultant solution was added 20.81 g of a spherical silica support (manufactured by Shell Chemical Co., Ltd., Japan; sold under the trademark, S980G; particle diameter, 2.4-3.4 mm). After the support was immersed in the solution at room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 49.10 g. The catalyst was packed into a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm2). The catalyst was dried first at 90~C for 2 hours and then at 150~C for 2 hours, while passing nitrogen gas through the tube at a rate of 6.7 Nl/min. Subsequently, while introducing hydrogen in place of nitrogen at a rate of 0.42 Nl/min, the dried catalyst was heated at a rate of 50~C/hr to 400~C and kept at this temperature for 2 hours. The contents of the tube were then cooled in a nitrogen stream to obtain 22.23 g of an activated catalyst. The activated catalyst contained 4.4 wt%

palladium and 1.98 wt% tellurium. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 1, except that the catalyst prepared in this Example was used. The results obtained are shown in Table 1.

27.2 g of tellurium metal was dissolved in 735.6 g of a 35 wt% aqueous nitric acid solution. 758.8 g of 10.0 wt%
aqueous palladium nitrate solution was added thereto, followed by sufficient 35 wt% aqueous nitric acid solution to adjust the total volume to 1,400 ml. To the resultant solution was added 950 g of a spherical silica support (CARiACT-Q-15). After the support was immersed in the solution at room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 2,145.5 g. The catalyst was packed into an SUS reaction tube having an inner diameter of 8 cm (effective sectional area, 50.2 cm2). The catalyst was dried first at 90~C for 2 hours and subsequently at 150~C for 2 hours while passing dry air through the tube at a rate of 317 Nl/min, and then removed from the reaction tube. Thus, 1,024.1 g of dried catalyst was obtained. Into an SUS reaction tube having an inner diameter of 5.2 cm (effective sectional area, 21.2 cm2) was packed 268.4 g of the dried catalyst. The contents of the tube were heated to 150~C while passing nitrogen gas through the tube at a rate of 5.2 Nl/min. Subsequently, while introducing hydrogen in place of nitrogen at a rate of 5.2 Nl~min, the contents were heated at a rate of 50~C/hr to 400~C and kept at this temperature for 4 hours. Thereafter, the contents of the tube were cooled in a nitrogen stream to obtain 260.5 g of an activated catalyst. The activated catalyst contained 4.9 wt%
palladium and 1.76 wt% tellurium. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 1, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1.

Into a 50-ml measuring flask was introduced 1.244 g of tellurium dioxide. 28 g of 35 wt% aqueous nitric acid solution was added to dissolve the tellurium compound. To this solution was added 22.09 g of 10.0 wt% aqueous palladium nitrate solution, followed by sufficient 35 wt% aqueous nitric acid solution to adjust the total volume to 50 ml. To the resultant solution was added 20.56 g of a spherical silica support (trademark CARiACT-15, manufactured by Fuji Silysia Chemical, Ltd. (old name: Fuji-Davison Chemical, Ltd.), particle diameter, 2.4-4.0 mm). After the support was immersed in the solution at room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 45.39 g. The catalyst was packed into a pyrex glass tube having an inner diameter of 2.S cm (effective sectional area, 4.9 cm2). The catalyst was dried first at 90~C for 2 hours and then at 150~C for 2 hours, while passing nitrogen gas through the tube at a rate of 6.7 Nl/min. Subsequently, while introducing hydrogen in place of nitrogen at a rate of 0.42 Nl/min, the dried catalyst was heated at a rate of 50~C/hr to 400~C and kept at this temperature for 2 hours.
The contents of the tube were then cooled in a nitrogen stream to obtain 21.89 g of an activated catalyst. The activated catalyst contained 4.9 wt% palladium and 1.18 wt%
tellurium. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 1, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1.

Into a 50-ml measuring flask was introduced 0.955 g of tellurium metal. 20 g of 35 wt% aqueous nitric acid solution was added to dissolve the metal. To this solution was added 26.51 g of 10.0 wt~ aqueous palladium nitrate solution, followed by sufficient 35 wt% aqueous nitric acid solution to adjust the total volume to 50 ml. To the resultant solution was added 20.78 g of a spherical silica support (CARiACT-Q-15). After the support was immersed in -the solution at room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 45.97 g. The catalyst was packed into a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm2). The catalyst was dried first at 90~C for 3 hours and then at 150~C for 2 hours, while passing nitrogen gas through the tube at a rate of 1.7 Nl/min. Subsequently, while introducing hydrogen in place of nitrogen at a rate of 0.42 Nl/min, the dried catalyst was heated at a rate of 50~C/hr to 400~C and kept at this temperature for 2 hours. The contents of the tube were then cooled in a nitrogen stream to obtain 22.26 g of an activated catalyst. The activated catalyst contained 4.9 wt% palladium and 1.76 wt% tellurium. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 1, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1.

To 56 g of a spherical silica support (manufactured by Shell Chemical Co., Ltd.; trademark, S980G; particle diameter, 2.4-3.4 mm) were added 57 g of 10 wt% aqueous palladium nitrate solution and 140 g of an aqueous solution obtained by dissolving 2.6 g of tellurium dioxide in nitric acid. This mixture was kept at 30~C for 2 hours, subsequently allowed to cool for S hours, and then filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain 136 g of a catalyst. The catalyst was packed into a pyrex glass tube having an inner diameter of 4.6 cm (effective sectional area, 16.6 cm2). The catalyst was dried first at 65~C for 6 hours and then at 100~C for 2 hours, while passing nitrogen gas through the tube at a rate of 2.3 Nl/min. Thereafter, the dried catalyst was heated to 150~C. While passing hydrogen gas through the tube at a rate of 330 Nl/hr, the dried catalyst was further heated at a rate of 50~C/hr to 300~C and kept at this temperature for 4 hours. The contents of the tube were then cooled in a nitrogen stream to obtain 60 g of an activated catalyst. The activated catalyst contained 4.86 wt% palladium and 1.76 wt~ tellurium. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 1, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1. Figs. 2 (A) to (C) show supported-ingredient distributions and a histogram, with respect to the tellurium/palladium atomic ratio, of palladium present in a layer ranging from the surface of the catalyst particles to a depth of 30%.

_ 40 -A catalyst was prepared in the same manner as in Comparative Example 1, except that CARiACT-15 (trademark) having a particle diameter of 2.4-4.0 mm, manufactured by Fuji Silysia Chemical, Ltd. (old name: Fuji-Davison Chemical, Ltd.), was used as a catalyst support, and the amount of tellurium dioxide was reduced to 1.3 g. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 1, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1.

To 40 g of a molded peat carbon (manufactured by Norit N.V., Holland; trademark, Sorbnorit-2X; cylindrical form having a diameter of 2 mm and a length of 6 mm) as a catalyst support were added 60 g of water and 60 g of a 60 wt% aqueous nitric acid solution. After this mixture was kept at 90-to 94~C for 3 hours, it was cooled and then filtered to remove the solution. Active carbon treated with nitric acid was thus obtained. To this active carbon were added 20 g of 10.0 wt% aqueous palladium nitrate solution and 120 g of an aqueous solution obtained by dissolving 0.55 g of tellurium metal in 35 wt% nitric acid. After this mixture was kept at 30~C for 3 hours, it was allowed to cool for 5 hours and then filtered to remove the solution. The residue was dried for 8 hours under a reduced pressure of 240 Torr at a maximum temperature of 140~C to obtain a catalyst having supported thereon 4.2 wt% palladium and 0.78 w% tellurium. A
30-ml portion of the catalyst was packed into a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm ). The contents of the tube were heated to 350~C at a rate of 50~C/hr and then kept at this temperature for 4 hours, while passing nitrogen containing 8 vol%
methanol through the tube at a rate of 39 Nl/hr. The contents of the tube were then allowed to cool to room temperature in a nitrogen stream. Subsequently, the contents of the tube were heated to 300~C and kept at this temperature for 10 hours, while passing nitrogen containing 2 vol% oxygen through the tube at a rate of 39 Nl/hr, before being allowed to cool to room temperature in a nitrogen stream.
Thereafter, the contents of the tube were heated to 350~C at a rate of 50~C/hr and kept at this temperature for 15 hours, while passing nitrogen containing 8 vol% methanol through the tube at a rate of 39 Nl/hr, before being allowed to cool to room temperature in a nitrogen stream. Subsequently, the contents of the tube were heated to 300~C and kept at this temperature for 4 hours, while passing nitrogen cont~in;ng 2 vol% oxygen through the tube at a rate of 39 Nl/hr, before being allowed to cool to room temperature in a nitrogen stream. Thereafter, the contents of the tube were heated to 350~C at a rate of 50~C/hr and kept at this temperature for 4 hours, while passing hydrogen through the tube at a rate of 39 Nl/hr, before being allowed to cool to room temperature in a nitrogen stream. Subsequently, the contents of the tube were heated to 300~C and kept at this temperature for 15 hours, while passing nitrogen containing 2 vol% oxygen through the tube at a rate of 39 Nl/hr, before being allowed to cool to room temperature in a nitrogen stream.
Thereafter, the contents of the tube were heated to 350~C at a rate of 50~C/hr and kept at this temperature for 4 hours, while passing hydrogen through the tube at a rate of 39 Nl/hr, before being allowed to cool to room temperature in a nitrogen stream. The catalyst thus prepared through the activation treatment, comprising repetitions of oxidation and reduction, contained 4.7 wt% palladium and 0.87 wt% tellurium supported thereon. The acetoxylation reaction of butadiene was conducted in the same manner as in Example 1, except that the catalyst prepared according to this Example was used.
The results obtained are shown in Table 1. Since the support used was cylindrical, supported-ingredient distributions were determined as follows. Ten catalyst particles were arbitrarily selected from the catalyst obtained above. With respect to each selected particle, the section having the largest area was ex~mined with an EPMA (JXA-8600M, manufactured by JEOL Ltd.) along the major diameter line, which is the axis (the major-diameter-direction center line in the rectangular section), and along the minor diameter line, which is a straight line meeting the major diameter line at its center at right angles, the examination being conducted at intervals of 20 ~m along these lines. With respect to each examination site, ZAF correction and supporting percentage correction were conducted. Thus, supported-ingredient distributions for 20 major-diameter-line radii, an average supported-ingredient distribution for the major-diameter-line radii, supported-ingredient distributions for 20 minor-diameter-line radii, and an average supported-ingredient distribution for the minor-diameter-line radii, were determined. Values of proportion A were determined from the average supported-ingredient distribution for the major-diameter-line radii and that for the minor-diameter-line radii, while proportion B was determined from the supported-ingredient distributions for the 40 radii in total (20 major diameter radii and 20 minor diameter radii). The results obtained are shown in Table 1.

Into a 50-ml measuring flask was introduced 0.887 g of tellurium metal. 20 g of 35 wt% aqueous nitric acid solution was added to dissolve the metal. To this solution was added 28. 46 g of 10.0 wt% aqueous palladium nitrate solution, followed by sufficient 3~ wt% aqueous nitric acid solution to adjust the total volume to 50 ml. To the resultant solution was added 20.21 g of a spherical silica support (CARiACT-Q-15). After the support was immersed in the solution at room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 44.62 g. The catalyst was packed into a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm2). The catalyst was dried first at 90~C for 3 hours and then at 150~C for 2 hours, while passing nitrogen gas through the tube at a rate of 1.7 Nl/min. The dried catalyst was placed in a cylindrical vessel having an inner diameter of 9.5 cm.
An 80 wt% solution of hydrazine monohydrate was sprayed over the catalyst until all the catalyst particles were immersed in the solution, while rotating the vessel at 20 rpm.
Thereafter, rotation of the vessel was stopped, and the vessel was allowed to stand for 18 hours. The catalyst was then washed with water and placed in a horizontal kiln (inner diameter, 3 cm; effective sectional area, 7.1 cm2). The contents of the kiln were dried first at room temperature for 1 hour and-then at 150~C for 1 hour, while rotating the kiln at 30 rpm and passing nitrogen gas therethrough at a rate of 6.7 Nl/min. Subsequently, the dried catalyst was placed in a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm2). The contents of the tube were heated to 150~C over a period of 30 minutes, while passing nitrogen gas through the tube. Thereafter, while introducing hydrogen in place of nitrogen at a rate of 0.42 Nl/min, the contents of the tube were heated at a rate of 50~C/hr to 400~C and kept at this temperature for 2 hours.
The contents of the tube were then cooled in a nitrogen stream to obtain 21.65 g of an activated catalyst.
The activated catalyst contained 5.1 wt% palladium and 1.59 wt% tellurium. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 1, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1.
COMPARATIVE EXAMPLE S
Into a 50-ml measuring flask was introduced 0.897 g of tellurium metal. 20 g of 35 wt% aqueous nitric acid solution was added to dissolve the metal. To this solution was added 26.70 g of 10.0 wt% aqueous palladium nitrate solution, followed by sufficient 35 wt% aqueous nitric acid solution to adjust the total volume to 50 ml. To the resultant solution was added 20.46 g of a spherical silica support (CARiACT-Q-15). After the support was immersed in the solution at room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 44.92 g. The catalyst was then placed in a 200-ml round bottom flask, and dried first at 80~C for 12 hours and then at 150~C for 3 hours, while rotating the flask at 30 rpm and introducing nitrogen gas into the flask at a rate of 0.08 Nl/min.
Subsequently, the catalyst was placed in a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm ). The contents of the tube were heated to 150~C over a period of 30 minutes, while passing nitrogen gas through the tube. Thereafter, while introducing hydrogen in place of nitrogen at a rate of 0.42 Nl/min, the contents of the tube were heated at a rate of 50~C/hr to 400~C and kept at this temperature for 2 hours. The contents were then cooled in a nitrogen stream to obtain 21.86 g of an activated catalyst.
The activated catalyst contained 4.8 wt% palladium and 1.61 wt% tellurium. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 1, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1. Figs. 3 (A) to (C) show supported-ingredient distributions and a histogram, with respect to the tellurium/palladium atomic ratio, of palladium present in a layer ranging from the surface of the catalyst particles to a depth of 30%.

Into a 50-ml measuring flask was introduced 1.062 g of tellurium metal. 20 g of 35 wt% aqueous nitric acid solution was added to dissolve the metal. To this solution was added 28.55 g of 10.0 wt~ aqueous palladium nitrate solution, followed by sufficient 35 wt% aqueous nitric acid solution to adjust the total volume to 50 ml. To the resultant solution was added 20.28 g of a spherical silica support (CARiACT-Q-15). After the support was immersed in the solution at room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 44.40 g. The catalyst was placed in a 200-ml round bottom flask, and dried first at 80~C for 4 hours and then at 150~C for 3 hours, while rotating the flask at 30 rpm and introducing nitrogen gas into the flask at a rate of 6.7 Nl/min. Subsequently, the catalyst was placed in a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm2). The contents of the tube were heated to 150~C over a period of 30 minutes, while passing nitrogen gas through the tube.
Thereafter, while introducing hydrogen in place of nitrogen at a rate of 0.42 Nl/min, the contents of the tube were heated at a rate of 50~C/hr to 400~C and kept at this temperature for 2 hours. The contents of the tube were then cooled in a nitrogen stream to obtain 21.79 g of an activated catalyst. The activated catalyst contained 5.1 wt% palladium and 1.82 wt% tellurium. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 1, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1.

Into a 50-ml measuring flask was introduced 1.008 g of tellurium metal. 20 g of 35 wt% aqueous nitric acid solution was added to dissolve the metal. To this solution was added 27.10 g of 10.0 wt% aqueous palladium nitrate solution, followed by sufficient 35 wt% aqueous nitric acid solution to adjust the total volume to 50 ml. To the resultant solution was added 25.11 g of a spherical silica support (CARiACT-Q-15). After the support was immersed in the solution at room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 54.28 g. A
28.2-g portion of the catalyst was placed in a horizontal kiln (inner diameter, 3 cm; effective sectional area, 7.1 cm2), and dried first at 60~C for 5 hours and then at 150~C
for 2 hours, while rotating the kiln at 30 rpm and introducing nitrogen gas into the kiln at a rate of 4.3 Nl/min. Subsequently, the catalyst was placed in a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm ). The contents of the tube were heated to 150~C over a period of 30 minutes, while passing nitrogen gas through the tube. Thereafter, while introducing hydrogen in place of nitrogen at a rate of 0.27 Nl/min, the contents of the tube were heated at a rate of 50~C/hr to 400~C and kept at this temperature for 2 hours. The contents of the tube were then cooled in a nitrogen stream to obtain 13.98 g of an activated catalyst. The activated catalyst contained 5.0 wt% palladium and 1.86 wt% tellurium. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 1, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1.

Into a 50-ml measuring flask was introduced 0.988 g of tellurium metal. 20 g of 35 wt% aqueous nitric acid solution was added to dissolve the metal. To this solution was added 26.52 g of 10.0 wt% aqueous palladium nitrate solution, followed by sufficient 35 wt% aqueous nitric acid solution to adjust the total volume to 50 ml. To the resultant solution was added 20.47 g of a spherical silica support (CARiACT-Q-15). After the support was immersed in the solution at room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 45.27 g. The catalyst was packed into a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm2). The catalyst was dried first at 90~C for 40 hours and then at 150~C for 2 hours, while passing nitrogen gas through the tube at a rate of 0.017 Nl/min. Subsequently, while introducing hydrogen in place of nitrogen at a rate of 0.42 Nl/min, the contents of the tube were heated at a rate of 50~C/hr to 400~C and kept at this temperature for 2 hours.
The contents of the tube were then cooled in a nitrogen stream to obtain 21.91 g of an activated catalyst. The activated catalyst contained 4.9 wt% palladium and 1.81 wt%
tellurium. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 1, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1.

Into a 50-ml measuring flask was introduced 1.536 g of telluric acid (H6TeO6; manufactured by Mitsuwa Chemical Co., Ltd.). 16 g of water was added to dissolve the tellurium compound. To this solution was added 28.45 g of 10.0 wt% aqueous palladium nitrate solution, followed by sufficient water to adjust the total volume to 50 ml. To the resultant solution was added 25.58 g of a spherical silica support (CARiACT-Q-15). After the support was immersed in the solution at room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 53.64 g. The catalyst was dried in a stream of 250~C superheated steam (2 m/sec) for 15 minutes. The dried catalyst was packed into a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm ). The catalyst was heated to 150~C over a period of 30 minutes, while passing nitrogen gas through the tube. Subsequently, while introducing hydrogen in place of nitrogen at a rate of 0.51 Nl/min, the catalyst was heated at a rate of 50~C/hr to 400~C and kept at this temperature for 2 hours. The contents of the tube were then cooled in a nitrogen stream to obtain 27.42 g of an activated catalyst. The activated catalyst contained 5.2 wt%
palladium and 1.56 wt% tellurium. A 6-g portion of the activated catalyst was packed into a glass tube having an inner diameter of 12 mm. 1,3-Butadiene, acetic acid, and nitrogen containing 9% oxygen were introduced into the glass tube at rates of 6.4 g/hr, 12 ml/hr, and 1.8 Nl/hr, respectively, and the reaction was continuously conducted for 7 hours at atmospheric pressure and a temperature of 80~C. A
portion of the reaction mixture withdrawn between 5 hours and 6 hours after initiation of the reaction, and a portion of the reaction mixture withdrawn between 6 hours and 7 hours after initiation of the reaction, were quantitavely analyzed by gas chromatography to determine the reaction products.
The results of these analyses were averaged to determine the activity and selectivity, and are shown in Table 1.
Distributions of supported ingredients were determined in the same manner as in Example 1, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1. Figs. 4 (A) to (C) show supported-ingredient distributions and a histogram, with respect to the tellurium/palladium atomic ratio, of palladium present in a layer ranging from the surface of the catalyst particles to a depth of 30~.

A catalyst was prepared in the same manner as in Example 7, except that drying with superheated steam was conducted at 150~C. The diacetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 7, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1.

5.44 g of trimethylsilyl chloride was dissolved in 100 ml of n-hexane, and 20.01 g of a spherical silica support (CARiACT-Q-15) was added thereto. This mixture was allowed to stand for 18 hours with occasional shaking and then filtered to remove the solution. The residue was washed with 100 ml of n-hexane five times and then vacuum-dried at 80~C
for 3 hours. To this hydrophobized silica support was added 50 ml of an aqueous solution containing 1.535 g of telluric acid and 28.5 g of 10.0 wt% aqueous palladium nitrate solution. After the support was immersed in the solution at room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 42.68 g. The catalyst was packed into a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm ). The catalyst was dried first at 90~C for 2 hours and then at 150~C for 2 hours, while passing nitrogen gas through the tube at a rate of 1.7 Nl/min. Subsequently, while introducing hydrogen in place of nitrogen at a rate of 0.42 Nl/min, the dried catalyst was heated at a rate of 50~C/hr to 400~C and kept at this temperature for 2 hours. The contents of the tube were then cooled in a nitrogen stream to obtain 21.95 g of an activated catalyst. The activated catalyst contained 5.0 wt%
palladium and 1.51 wt~ tellurium. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 7, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1.

Into a 50-ml measuring flask was introduced 1.535 g of telluric acid. 16 g of water was added to dissolve the tellurium compound. To this solution was added 28.44 g of 10.0 wt% aqueous palLadium nitrate solution, followed by sufficient water to adjust the total volume to 50 ml. To the resultant solution was added 26.09 g of a spherical silica support (CARiACT-Q-15). After the support was immersed in the solution at room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 54.62 g. The catalyst was placed in a vacuum dryer (DP-32, manufactured by Yamato Scientific Co., Ltd., Japan), and dried under vacuum (below 50 Torr) first at 60~C for 2 hours, subsequently at 80~C for 5 hours, and then at 150~C for 2 hours. The dried catalyst was packed into a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm2). The catalyst was heated to 150~C over a period of 30 minutes, while passing nitrogen gas through the tube. Subsequently, while introducing hydrogen in place of nitrogen at a rate of 0.54 Nl/min, the catalyst was heated at a rate of 50~C/hr to 400~C and kept at this temperature for 2 hours. The contents of the tube were then cooled in a nitrogen stream to obtain 27.96 g of an activated catalyst. The activated catalyst contained 5.1 wt% palladium and 1.53 wt% tellurium. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 7, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1.

Into a 25-ml measuring flask was introduced 0.768 g of telluric acid. 8 g of water was added to dissolve the tellurium compound. To this solution was added 14.21 g of 10.0 wt% aqueous palladium nitrate solution, followed by sufficient water to adjust the total volume to 25 ml. To the resultant solution was added 12.75 g of a spherical silica support (CARiACT-Q-15). After the support was immersed in the solution at room temperature for 1 hour, the mixture was filtered to remove the solution. Thereafter, the excess solution was removed from the support with a centrifuge to obtain an impregnated support in an amount of 26.60 g. The catalyst was packed into a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm2). The catalyst was dried first at 90~C for 2 hours and then at 150~C for 2 hours, while passing dry air through the tube at a rate of 4.3 Nl/min. Subsequently, while introducing hydrogen in place of dry air at a rate of 0.27 Nl/min, the dried catalyst was heated at a rate of 50~C/hr to 400~C and kept at this temperature for 2 hours. The contents of the tube were then cooled in a nitrogen stream to obtain 13.68 g of an activated catalyst. The activated catalyst contained 5.0 wt% palladium and 1.52 wt% tellurium. The acetoxylation reaction of butadiene and the determination of supported-ingredient distributions were conducted in the same manner as in Example 7, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 1.

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COMPARATIVE EXAMPLE 11 (Example 1 in JP-B-59-51850) A silica support obtained by heating Silica Gel ID
(trademark), manufactured by Fuji Silysia Chemical, Ltd. (old name: Fuji-Davison Chemical, Ltd.), at 500~C in air for 1 hour was used as a catalyst support. To 10.02 g of this support was added a solution obtained by dissolving 0.1750 g of palladium chloride (manufactured by NE Chemcat Corp.) and 0.0536 g of tellurium dioxide (manufactured by Mitsuwa Chemical Co., Ltd.) in 40 ml of 6 N hydrochloric acid. After the support was immersed in the solution at room temperature for 24 hours, the mixture was heated on a water bath under vacuum first at 60~C for 2 hours and then at 80~C for 3 hours to evaporate the volatile ingredients to dryness.
Subsequently, this solid was packed into a pyrex glass tube having an inner diameter of 2.5 cm (effective sectional area, 4.9 cm2). The contents were dried at 150~C for 3 hours while passing nitrogen through the tube at a rate of 1.9 Nl/min, and were then kept first at 200~C for 3 hours and then at 400~C for 2 hours while passing nitrogen saturated at room temperature with methanol through the tube at a rate of 1.9 Nl/min. Thereafter, the contents of the tube were cooled in a nitrogen stream to obtain 10.17 g of an activated catalyst.
The activated catalyst contained 1.03 wt% palladium and 0.42 wt% tellurium.
The acetoxylation reaction of butadiene was conducted in the same manner as in Example 1, except that the catalyst prepared according to this Example was used. The results obtained are shown in Table 2. Since the support comprised irregularly shaped particles formed by crushing, supported-ingredient distributions were determined as follows. Ten catalyst particles were arbitrarily selected from the catalyst obtained above. With respect to each selected particle, the section having the largest area was examined with an EPMA (JXA-8600M, manufactured by JEOL Ltd.) along the major diameter line, which was the longest straight line in the section, and along the minor diameter line, which was the longest straight line meeting the major diameter line at right angles, the examination being conducted at intervals of 20 ~m along these lines. With respect to each examination site, ZAF correction and supporting percentage correction were conducted. Thus, supported-ingredient distributions for 20 major-diameter-line radii, an average supported-ingredient distribution for the major-diameter-line radii, supported-ingredient distributions for 20 minor-diameter-line radii, and an average supported-ingredient distribution for the minor-diameter-line radii, were determined. Values of proportion A were determined from the average supported-ingredient distribution for the major-diameter-line radii and that for the minor-diameter-line radii, while proportion B
was determined from the supported-ingredient distributions for the 40 radii in total (20 major diameter radii and 20 minor diameter radii). The results obtained are shown in Table 2. For the purpose of comparison, the results obtained in Example 1 are also shown in Table 2. Since the palladium concentration of the catalyst used in Comparative Example 11 was about 1/5 of that of the catalyst used in Example 1, the values of activity given in Table 2 have been converted to activities per g of palladium per hour.

Table Z

Results of High-pressure Proportion Supported . Reaction A (%) Ingredlent Proportion Pd Te/Pd Activity *2 Selectlvlty Pd Te B (%) (%) Ex. 1 5.0 0.26 161 . 88.3 87.2 87.1 94.4 Comp. Ex. 11 1.0 0.34 117 80.1 73.4 72.1 68.0 *2 mmol/g-Pd-h According to the process of the present invention, in which a conjugated diene is reacted with a carboxylic acid and molecular oxygen in the presence of a solid catalyst to produce the corresponding unsaturated glycol carboxylic diester, high catalytic activity can be attained in producing the target diester by using a solid catalyst cont~; n ing palladium and tellurium supported as active ingredients on an inorganic porous support, and having specific distributions as disclosed herein. Therefore, the process and the catalyst of the present invention have great industrial value.
While the invention has been described in detail and with reference to specific embodiments thereof, it will be -apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

Claims (10)

1. A solid catalyst comprising an inorganic porous material as a support and palladium and tellurium as active ingredients supported on said support, wherein said solid catalyst, when analyzed with an X-ray microanalyzer (EPMA), has active-ingredient distributions in which:
(a) at least about 80% of all palladium supported on the catalyst and at least about 75% of all tellurium supported on the catalyst are present in a surface layer of the support, said surface layer extending from an outer surface of the support to a depth corresponding to about 30% of the radius of the support; and (b) at least about 50% of the palladium present in said surface layer of said support coexists with tellurium in a tellurium/palladium atomic ratio of from about 0.15 to about 0.35.

2. The solid catalyst as claimed in claim 1, wherein the inorganic porous material is silica.

3. The solid catalyst as claimed in claim 1, wherein the inorganic porous material has a particle diameter of from about 1 mm to about 8 mm.

4. The solid catalyst as claimed in claim 1, wherein the inorganic porous material has an average pore diameter of from about 10 nm to about 50 nm.

5. A process for producing an unsaturated glycol diester which comprises reacting a conjugated diene with a carboxylic acid and molecular oxygen in the presence of a solid catalyst comprising an inorganic porous material and palladium and tellurium as active ingredients supported on said support to thereby produce the corresponding unsaturated glycol diester, wherein said solid catalyst, when analyzed with an X-ray microanalyzer (EPMA), has active-ingredient distributions in which:
(a) at least about 80% of all palladium supported on the catalyst and at least about 75% of all tellurium supported on the catalyst are present in a surface layer of the support, said surface layer extending from an outer surface of the support to a depth corresponding to about 30% of the radius of the support, and (b) at least about 50% of the palladium present in said surface layer of said support coexists with tellurium in a tellurium/palladium atomic ratio of from about 0.15 to about 0.35.

6. The process for producing an unsaturated glycol diester as claimed in claim 5, wherein the inorganic porous material is silica.

7. The process for producing an unsaturated glycol diester as claimed in claim 5, wherein the inorganic porous material has a particle diameter of from about 1 mm to about

8 mm and an average pore diameter of from about 10 nm to about 50 nm.
8. The process for producing an unsaturated glycol diester as claimed in claim 5, wherein the conjugated diene is selected from the group comprising butadiene, isoprene, and alkyl-substituted butadienes.

9. The process as claimed in claim 5, wherein the carboxylic acid is acetic acid.

10. The process as claimed in claim 5, wherein the unsaturated glycol diester is 1,4-diacetoxy-2-butene.