JPH0569815B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a new method for producing oxalic acid diesters. More particularly, the present invention relates to a process for producing oxalate diesters by contacting carbon monoxide with nitrite esters under pressure in the presence of a palladium catalyst supported on alpha-alumina (support) having a low surface area. It is something. The production of oxalic acid diesters (oxalates) is of particular interest because of the variety of uses these compounds have. Not only do these diesters serve as raw materials for the production of important compounds such as oxalic acid, oxamide or ethylene glycol, but they also have extensive use as dyes, pharmaceuticals and other intermediates. Prior to the present invention, many methods have been proposed for producing oxalate diesters or oxalates in liquid phase reactions using various catalysts, cocatalysts, reaction promoters, and the like. However, these conventional processes suffer from the drawbacks associated with the production of large amounts of by-products, as can be expected from other conventional liquid phase processes. A particularly interesting process designed to produce oxalic acid diesters in the liquid phase is disclosed in US Pat. No. 4,138,587. This patent uses nitric acid or nitrogen oxide as promoters in the presence of solid palladium metal or its salts, molecular oxygen, alcohol and carbon monoxide to produce oxalic acid diesters. Unfortunately, because it is a liquid phase process, this process has important practical problems such as loss due to dissolution of the catalyst, production of large amounts of by-products, and low product yields, e.g., low efficiency of a few percent. There are various drawbacks in terms of. US Pat. No. 4,229,591 discloses a gas phase process. The patented process involves contacting an ester of nitrous acid with carbon monoxide at normal pressure and a temperature between 50°C and 200°C in the presence of a solid catalyst containing metallic palladium or a salt thereof; The esters of nitrous acid used are nitrous esters of alcohols having 1 to 8 carbon atoms. Although said process has advantages over liquid phase processes, it cannot be distinguished from the role played by the catalyst and its support used in such heterophasic gas phase processes. This can be clearly seen by looking at the examples of this patent. Various palladium catalysts are described in Examples 1 to 24,
In each case either carbon or SiO ₂ is used as support in the palladium catalyst.
This patent specification covers alumina, diatomaceous earth, pumice,
Zeolites and molecular fluorites are also described. As can be seen, however, the broad general description of these carriers is silent on the advantages of any one of them over the other. By the way, carbon and silica (SiO ₂ ) supports are acidic supports with a high surface area (10 m ² /g
above). The patent also mentions alumina as a carrier, for example, but this includes a wide variety of materials ranging from high surface area acidic alumina (gamma-alumina), fibrous alumina to alpha-alumina. It will be done. The present invention relates to a method for producing oxalic acid diesters by a gas-phase heterophase reaction, which method involves supporting solid palladium or its salts, consisting of metallic palladium deposited on α-alumina (support) having a low surface area. It consists of contacting a vaporous alkyl ester of nitrous acid with carbon monoxide under pressure and at a temperature of about 50°C to about 200°C in the presence of a catalyst. This process thus recovers dialkyl oxalate having an alkyl moiety corresponding to the alcohol used to make the nitrite. More specifically, according to the present invention, in the production of oxalate diester from nitrite and carbon monoxide in the gas phase (i.e., the oxalate process), α-alumina (e.g., less than about 10 m 2 /g) having a low surface area (e.g., about 10 m ² /g or less) is used. The use of a palladium catalyst deposited on a support provides advantages such as high conversion to the diester product, longer catalyst life, lower production of by-products and the possibility of using catalysts with low palladium content. It has been found that various advantages are obtained. (In this specification, "vapor state" or "gas phase"
These expressions have the same meaning. ) The nitrite ester used in the method of the present invention can be prepared by conventional synthetic methods, or introduced into the reaction system in the form of a nitrogen compound that produces the nitrite ester in situ by reaction with an alcohol as described below. May be provided. Examples of nitrogen compounds that can be used to make nitrite esters or to generate nitrite esters in situ include nitrogen monoxide, nitrogen dioxide, dinitrogen trioxide, and dinitrogen tetroxide. and their hydrates. When using nitric oxide, it is necessary to combine it with molecular oxygen in order to generate the required nitrogen compounds. Preferred esters of nitrous acid are esters derived from saturated monohydric aliphatic alcohols yielding alkyl nitrites, such as saturated monohydric open-chain aliphatic alcohols having from 1 to 8 carbon atoms or
Esters derived from cycloaliphatic alcohols having ~8 carbon atoms. And the most preferred nitrite ester is an ester made from methanol or ethanol. This alcohol component includes methanol, ethanol, n-propanol, isopropanol, n-butanol,
In aliphatic alcohols such as isobutanol, secondary butanol, tertiary butanol, n-amyl alcohol, isoamyl alcohol, hexanol, octanol and others and alicyclic alcohols such as cyclohexanol, methylcyclohexanol, etc. be. These alcohols may contain substituents, such as alkoxy groups, which do not inhibit this reaction. The method of preparing these nitrite esters need not be narrowly limited as long as the nitrite esters do not contain harmful components such as nitric acid that adversely affect the palladium catalyst. The nitrite ester is used in the reaction of the process of the invention with carbon monoxide obtained from any conventional source. It may be pure, contain small amounts of hydrogen, and/or diluted with inert gaseous diluents such as nitrogen, carbon dioxide, and others. The concentration of carbon monoxide in the reaction zone is not limited to a narrow range and can range over a wide range from about 1% by volume to about 99% by volume. Typically this concentration of carbon monoxide is from about 10% by volume to about 95% by volume, where the actual concentration of carbon monoxide in the reaction mixture depends on the alkyl nitrite used, its concentration, and the method. depending on the catalyst used, the concentration of inert gaseous diluent and the process conditions selected. The oxalate process is preferably carried out in the presence of an inert gaseous diluent in order to moderate the reaction and prevent the formation of explosive mixtures and to prevent excessive production of undesired by-products. An inert gaseous diluent for this purpose, if it is not used during the production of the nitrite ester,
It may be added together with this nitrite. Preference is given to using nitrogen, carbon dioxide or other inert gaseous compounds as the inert diluent. The use of carbon dioxide is preferred as it has a higher heat capacity compared to nitrogen. The inert gaseous diluent is used in an amount sufficient to provide the purposes mentioned above. An inert gaseous diluent may be used in this method such that from about 0 to about 99% by volume consists of the inert gaseous diluent. Typically, the concentration of this inert gaseous diluent will be from about 1% by volume to about 90% by volume, although the actual concentration used will be selected as described above for the concentration of carbon monoxide. This oxalate method generally operates at about 50°C and about 200°C.
℃ and preferably between about 75℃ and about
Perform between 150℃ and 150℃. The reaction pressure is generally above atmospheric, such as at atmospheric pressure (14.7 psia) or between about 1 atm (14.7 psia) and about 7 atm, and most preferably at a pressure between about 1 and 4 atm. Adopt the pressure of However, a reduced pressure state may be employed if desired. This vapor state reaction to form the diester of oxalic acid is preferably carried out by providing an oxalate forming reaction zone which is preferably free of harmful amounts of water. Although some amounts of water may be tolerated, the amount of water generated within the nitrite-forming reaction zone is detrimental, so a sufficient amount of that water is removed prior to its introduction into the oxalate-forming reaction zone. Good. This means that after the alkyl nitrite is formed, a water condenser (such as a vapor-liquid separator)
This can be achieved by the use of water or other water removal methods. The amount of water detrimental to the vapor state reaction for the production of oxalate diesters can be determined in part by the choice of nitrite, temperature, pressure, etc. In general, a hazardous amount of water will result in a
The amount of water is such that it produces an appreciable change in the rate of oxalate production. The amount of water in the oxalate-forming reaction zone is then preferably about 5.0% by volume or less, more preferably about 2.0% by volume or less, and most preferably about 1.0% by volume or less based on the total reaction volume. . The process of the invention may be carried out in a tubular reactor with a fixed catalyst bed or a dynamic catalyst bed, such as a floating catalyst bed. The particulate catalyst may be diluted with particles of an inert carrier or other inert material to facilitate control of the reaction temperature. The contact or residence time for this reaction process to occur is generally less than about 30 seconds, preferably about
Between 0.05 seconds and about 10 seconds. However, longer or shorter times may also be used. Catalyst Generally speaking, the specific catalyst used in this process is a granular alpha-alumina (support) with a low surface area.
metal palladium or its salts deposited on top. The catalyst support is essentially inert to the reaction components and products under the reaction conditions and is commonly referred to as macroporous, with no more than about 10 m ² per gram of support, and preferably It is composed of a porous material with a low surface area of about 5 m ² or less. This surface area is Pournoel S,
Emmett P. and Teller E., Journal of the American Chemical Society, Vol. 60, pp. 309-316 (1938)
Measured by BET method. Here, "low surface area" means a surface area of not more than about 10 ^m2 per gram, preferably about 100 m2 per gram.
It is a term used to characterize supports having a surface area in the range of 0.001 m ² to about 10 m ² and most preferably from about 0.01 m ² to about 5 m ² per gram. The α-alumina that can be used in the process according to the invention is preferably an agglomerate of α-alumina particles, such as silica or heavy earth (barium oxide).
May be fused or cemented together with (baryta). In many cases, this preferred carrier is, for example, U.S. Pat.
The α-alumina described in patent documents such as No. 3,423,328 and No. 3,563,914 is the best example. The α-alumina support used so far is:
Its chemical composition and crystal structure are conventional. These physical characteristics are within the parameters mentioned above. In particular, the porosity of this support is between about 0.1 and about 0.8 cc per gram, preferably between 0.2 and about 0.6 cc, and the surface area is between about ^0.3 and about 10 m ^{2 per} gram. preferably between about 0.6 m ² and 8 m ² per gram, and the average pore size of the support is between about 0.05 micron and about 8 m 2 per gram.
200 microns, and the main proportion of these pores is approximately
The preferred average pore size is from about 0.1 micron to about 60 microns or more. The metal palladium or its salt deposited on the support is typically in the form of small particles. The size of the particles of deposited metallic palladium or its salts and the relative proportions of these particles are generally important for the completion of the catalyst. Generally speaking, the greater the degree of dispersion, the higher the production rate of large seed objects. The actual dispersion of these particles onto a carrier is believed to be related to the surface properties of the carrier. Deposition of palladium or its salts onto the surface of the support can be accomplished by a variety of techniques, but there are two methods that are frequently employed.
One method involves impregnating the support with a palladium solution and then heat-treating the impregnated support to effect the deposition of palladium on the support. The palladium particles are deposited onto the carrier by first forming a slurry, which deposits the palladium particles onto the carrier, and then heating the carrier to remove any liquid previously present and allowing it to settle on the surface of the carrier. This gives rise to a coating of These various treatment methods are described in U.S. Patent No. 2773844, U.S. Pat.
No. 3,664,970 (or British Patent No. 754,593) and British Patent No. 3,172,893. The surface area provided by the support is of great interest in the development of various catalysts. A description of the surface area of this class of catalyst supports is found in U.S. Pat. No. 2,766,261 (which ranges from 0.002 to 10
A surface area of m ² is stated to be suitable. ), U.S. Pat. No. 3,172,893 (which mentions a porosity of 35-65% and a pore diameter of 80-200 microns), U.S. Pat. Surface areas of up to ² and average pore diameters of 10 to 15 microns are stated), U.S. Pat.
No. 3,664,970 (which uses a support having at least 90% pores with a pore diameter in the range of 1 to 30 microns and a minimum porosity of about 30%), and US Pat. Patent No. 3563914 (in which a catalyst support with a surface area of less than 1 m ² per gram, a volume of 0.23 ml/g and particles with a size between 0.074 mm and 0.30 mm is used), etc. It is in. US Pat. No. 4,038,175 discloses a hydrogenation process using palladium metal dispersed on the surface of a palladium or alpha-alumina support. And starting from the 42nd line of the 3rd column, the 4th column
The description up to line 24 and the description in column 5, line 2 to column 8, line 22 are descriptions regarding α-alumina and the method for producing the catalyst disclosed therein, but these are also adopted in the practice of the present invention. Since it is possible, it is included here as a reference. Regarding the choice of carrier, narrow control over the chemical composition of the carrier is unnecessary. And α−
Alumina-based supports are highly preferred. The most preferred α-alumina support is at least 80
% alpha-alumina, the balance being silicon dioxide, various alkali oxides, alkaline earth metal oxides, iron oxides and mixtures of other metal oxides and non-metal oxides. It is of purity. Alpha-alumina supports having a purity of at least about 98% by weight, the remainder of which consists of silica, oxides of alkali metals (e.g., sodium oxide), and trace amounts of other metal and nonmetallic impurities, are used in the present invention. It is very suitable for implementation. A wide variety of such carriers are available on the market. These carriers are preferably granulated and in the form of extruded pellets, spheres, rings, cylindrical rings, and other forms. The size of this carrier is about 0.16 cm to 1.27 cm.
The size of the support is selected depending on the type of reactor employed. Generally, for the use of fixed bed reactors, particles having a size in the range of 0.32 cm to 0.95 cm for typical tubular reactors used in industrial operations are preferred. A monolithic carrier has been found to be advantageous due to its thermal conductive properties. Various methods can be employed to prepare the palladium catalyst used in the present invention. Representative of these methods are disclosed in US Pat. No. 4,038,175. Next, we will discuss the two most common methods. (1) impregnating a porous catalyst carrier with a solution consisting of a sufficient amount of palladium salt and a solvent or solubilizer to deposit a desired weight of palladium on the carrier; (2) applying a coating of palladium onto the support from a palladium-containing suspension or slurry; Then the support is subjected to heat treatment as described above. Impregnating the carrier is generally the preferred technique for depositing palladium because it utilizes the palladium more efficiently than coating methods. It should be noted that it is generally not possible to effectively deposit palladium on the internal surface of the carrier using the coating method.
Moreover, in catalysts coated by this method, palladium is likely to be lost due to mechanical abrasion. The palladium solution used to impregnate the carrier generally consists of a palladium salt or complex compound, among other solvents or complexing/solubilizing agents. There are no particular restrictions on the specific palladium salt or complex compound used for this purpose. This includes, for example, palladium nitrates, sulphates, halides, phosphates, various carboxylates such as palladium acetates, benzoates, oxalates, citrates, phthalates, lactates, propionates. , butyrate and higher fatty acid salts or palladium acetylacetonate and other analogs. Although any palladium salt may be used to prepare the palladium catalyst used in the process of the present invention, the catalyst must be prepared so that the resulting catalyst is substantially free of halogens, particularly chlorine and sulfur. is desirable. The presence of halogen or sulfur atoms inhibits the production of oxalic acid diester, which is the object of the present invention. In addition, the presence of halogen or sulfur atoms increases the formation of harmful by-products such as carboxylates, formates, and others, resulting in reduced yields of oxalate diesters. Therefore, the concentration of halogen atoms or ionic atoms is preferably about 10 ppm by weight or less based on the palladium deposited on the carrier. There is no need for narrow limits on the amount of palladium deposited on the support, which ranges from about 0.001 to about 10% by weight, calculated as metallic palladium, preferably about
0.01 to about 5% by weight, and most preferably about 0.1
~0.2% by weight. After impregnation of the catalyst support with palladium or its salts, the thus impregnated support particles are separated from the unabsorbed solution or slurry. This can be conveniently accomplished by sucking off the excess impregnating medium or by separation techniques such as filtration or centrifugation.
The impregnated support is then generally subjected to heat treatment (eg, roasting) to decompose or reduce the palladium salt to metallic palladium, if desired.
Such heat treatment may conveniently be carried out in an atmosphere of air, nitrogen, hydrogen, carbon dioxide, or a combination thereof. For such heat treatment, an apparatus that can effectively perform reduction in a static or fluid atmosphere of these gases can be used. A typical α-alumina support that can be used in the practice of the present invention has the following chemical composition and physical properties, and is herein referred to as Support A. Chemical composition of carrier A Weight% α-alumina 98.5 Silicon dioxide 0.74 Calcium oxide 0.22 Sodium oxide 0.16 Iron oxide 0.14 Potassium oxide 0.04 Magnesium oxide 0.03 Physical properties of carrier A Surface area (1) ~0.3 ^{m 2} /g Pore volume (2) (or water absorption) ~0.50cc/g Packing density (3) 0.70g/ml Median pore diameter (4) 21 microns Pore size distribution, percent (%) of total pore volume Size (microns) Total pore volume (%) 0.1-1.0 1.5 1.0-10.0 38.5 10.0-30.0 20.0 30-100 32.0 >100 8.0 Values (1) to (4) in the above table are as follows. (1) According to the measurement method described in "Absorption, Surface Area and Porosity" by SJ Gretzg and KSW Singh, Academic Press (1967), pages 316-321. (2) Based on the measurement method described in ASTMC20-46. (3) A value calculated from conventional measurements of the weight of the carrier in a container of known volume. (4) Based on the measurement method described in "Applications of Mercury Penetration to Materials Analysis" by Mr. C. Orr Giunia, Powder Technology Vol. 3, pages 117-123 (1970) . The solution used to impregnate the support is prepared at such a concentration that the complete catalyst contains the desired amount of palladium. The required concentration of palladium in solution for a given carrier is calculated from the known or easily measured packing density (g/cc) and pore volume of the carrier. Assuming that all of the palladium in the impregnation solution is deposited on the support,
The amount of palladium needed in that solution is about 0.001-10
% of palladium is provided on the carrier. The particle size of the metal palladium or its salt deposited on the support and the distribution of the palladium depend on the catalyst preparation method employed. The particular choice of solvent and/or complexing agent, palladium salt, heat treatment conditions, catalyst support, etc. thus influences to a considerable extent the size of the resulting palladium particles. For catalysts of general interest for the production of oxalic acid diesters, a distribution of palladium particle sizes of less than about 10,000 angstroms is preferred. However, the role of palladium particle size and distribution on the effectiveness of catalysts in producing oxalic acid diesters is still not clearly understood. Due to the fact that palladium particles can migrate on the surface of a catalyst when the catalyst is used in a catalytic reaction, causing significant changes in the size and shape of the particles.
The size of the palladium particles may or may not be a significant factor in its effect on catalytic performance. A high distribution of palladium is considered favorable. The method of the present invention will be explained in more detail with reference to the following examples. However, these Examples are merely for illustrating the present invention, and are not intended to limit the present invention in any way. EXPERIMENTAL METHODS The following examples were carried out in a tubular reactor constructed of 4 foot long, 1 inch inside diameter stainless steel tubing and operated under downward flow conditions. The top (inlet) of the reactor was filled with glass bulbs to serve as a preheating zone for the alkyl nitrite (inert gaseous diluent) and carbon monoxide mixture prior to its introduction into the catalyst bed. The catalyst bed was prepared by placing 10 c.c. of supported palladium co-catalyst in place with a light padding of porous glass wool as shown in each example. The tubular reactor was held in a liquid-containing jacket surrounded by electrical resistors and heaters to ensure uniform heating. The temperature of the catalyst bed was measured by a thermocouple placed therein. Alkyl nitrite is its liquid alkyl nitrite (saturator)
was introduced by passing a CO/N ₂ mixture through the solution, thereby forming a vaporous gas stream consisting of CO, N ₂ and alkyl nitrite. Examples 1-6 The following catalyst manufacturing method was carried out to prepare the catalysts used in Examples 1-6. The catalysts used in Examples 1-6 were prepared using Norton LA4102 α-alumina (US standard 8-20 mesh) as the support having the following chemical composition and physical properties. Chemical composition weight (%) α-Alumina 99.6 Silicon dioxide 0.01 Calcium oxide 0.07 Sodium oxide 0.21 Iron oxide 0.05 Potassium oxide 0.03 Magnesium oxide 0.01 Physical properties Surface area ~1.0m ² /g Apparent porosity (1%) ~50~ 56 Apparent density (g/cc) 1.7-2.0 Packing density (bond/cubic feet) 67-73 Note that a pound is approximately 453g, and a foot is approximately
Approximately converted to 30cm. To prepare the catalyst, 800 g of crushed Norton LA4102 support was placed in a round bottom flask using a mortar and pestle and heated to about 60° C. under vacuum using a heating lamp.
Separately palladium acetylacetonate (11.45g)
was dissolved in 280 c.c. of toluene at 70° C. and the hot solution was added to the hot alumina particles through a syringe while shaking the flask. The resulting mixture 30
After standing for a minute, it was transferred to an open dish. This catalyst was incubated at 110 °C for 1 h at 85 °C in an oven with _N2 flow.
for 2 hours and finally at 150° C. for 2 hours and then cooled to room temperature. The catalyst was then placed in a quartz tube and placed in a 50:50 volume mixture of nitrogen and air for 45 minutes.
Heated to 500°C for minutes. Its flow rate is generally about 200
cc/min. Next, this catalyst was heated in 100% air for 3 hours.
time, then heated to 500 °C for 15 min in 100% _N2 . This was further heated to 500° C. under 100% H ₂ for 3 hours, then cooled to 80° C. under 100% N ₂ and further cooled to room temperature. Parameters and results of the steps in Examples 1 to 6 will be listed later. Comparative Examples 7 to 12 These Comparative Examples 7 to 12 are the above-mentioned invention examples 1 to 12.
6 to a high surface area value, i.e. 10 m ² /g
This was carried out in order to compare the results obtained by using a catalyst prepared using a carrier having the above surface area. The catalysts used in Comparative Examples 7 and 8 were prepared using Columbia (TM) carbon (manufactured by Union Carbide Corporation) having the following properties as a carrier. Properties Value Surface area (m ² /g) ~1000 Moisture ⁽³⁾ (Maximum %) 2.0 Activity ⁽¹⁾ (Minimum %) 0.05 Hardness ⁽⁵⁾ (Minimum) 90 Ash content ⁽⁴⁾ (Maximum %) 2.0 Density ^{( 2)} (maximum g/cc) 0.51 (1) is the carbon tetrachloride activity which the carrier absorbs at 35°C from dry air saturated with this vapor at 0°C. % by weight. (This value can be used as a relative indication of the adsorption capacity of the activated carbon.) Density (2) is the highest weight per unit volume that can be contained in a given container. In (3), the weight loss after heating the collected sample at 150°C for 6 hours is regarded as the water content. (4) is the total ash content, which represents the weight (%) of the residue remaining after firing at 500°C in air. The hardness (5) is the resistance value of this carbon sample to mechanical crushing. This hardness value is expressed as a percentage (%) of average diameter particles remaining after a period of mechanical agitation with a steel ball. The catalyst used in Comparative Example 7 was prepared as follows. 10 g of carbon support was placed in a round bottom flask heated with a heating lamp under vacuum, and 0.429 g of palladium acetylacetonate was added to 12 c.c. of hot toluene at 70°C.
The resulting solution was added to the carbon using a syringe while shaking the flask. The resulting material was heated in an open dish with a hood to 85°C for 1 hour and then to 115°C for 2 hours. The catalyst was then placed in a quartz tube and treated in the following order. (The gas flow in this case was generally about 200 c.c./min.) 1. 350° C. for 30 minutes under a 50:50 H ₂ /air flow, then held at 350° C. for an additional 30 minutes or more. 2 4 hours at 350° C. under 100% air flow and 3 held at 350° C. for 30 minutes under 100% nitrogen (N ₂ ) flow, then cooled to room temperature. For the preparation of the catalyst used in Comparative Example 8, 10 g of the carbon support described above was placed in a vacuum round bottom flask at room temperature. Separately, add a mixture of 6.0cc of distilled water and 6.0cc of concentrated hydrochloric acid.
0.250 g of PdCl ₂ was dissolved at 40°C. This solution was added to the carbon through a syringe while shaking the flask, then transferred to an open dish and heated to 85°C for 1 hour, 115°C for 2 hours, 150°C for 2 hours, and 200°C for an additional 2 hours. held. The catalyst was then transferred to a quartz tube and processed in the following order. (The gas flow was generally about 200 c.c./min.) 1 hour at 350° C. in a 50:50 N ₂ /H ₂ mixture flow.
It was then held at 350° C. for 1 hour, 2 hours at 350° C. in a 100% air stream, and 3 cooled to 80° C. in a 100% N ₂ stream, and further cooled to room temperature. The process variables (parameters) and results of these comparative examples 7 to 12 are listed in the table.

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Claims (1)

[Scope of Claims] 1. The vapor of ester of nitrous acid produced by reacting a saturated aliphatic monohydric alcohol with a nitrogen compound is converted into ^an α-
In the presence of a solid palladium supported catalyst consisting of metallic palladium or its salts deposited on alumina, it is contacted with carbon monoxide in the gas phase at a temperature between 50°C and 200°C; A method for producing an oxalic acid diester by a gas-phase heterophase reaction, which comprises producing a diester of oxalic acid having an ester group corresponding to the alcohol used in the preparation of the nitrite ester, and recovering the same. 2. Claim 1, wherein the α-alumina has a surface area between 0.001 m ² and 10 m ² per gram.
The method described in. 3. Process according to claim 1, wherein the α-alumina has a surface area of between 0.1 m ² and 5 m ² per gram. 4. The method of claim 1, wherein the operation is carried out at a pressure of 1 atm (14.7 psia) to above atmospheric pressure. 5. The method of claim 4, wherein the pressure is between 1 and 7 atmospheres. 6. A method according to claim 5, wherein the pressure is between 1 and 4 atmospheres. 7. The method according to claim 1, wherein the nitrite ester is methyl nitrite. 8. The method according to claim 1, wherein the nitrite is a nitrite. 9. Process according to claim 1, using a catalyst in which the amount of palladium on the palladium-supported alpha-alumina catalyst is from 0.1% to 2% by weight. 10. A method according to claim 1, wherein from 0.2% to 1.2% by weight of palladium is present. 11. The method according to claim 1, wherein the supported catalyst is substantially free of sulfur atoms. 12. The method according to claim 1, wherein the catalyst supporting palladium does not substantially contain halogen atoms. 13. The method according to claim 1, wherein the palladium particles have a size of 10,000 angstroms or less. 14. The method according to claim 1, wherein the catalyst supporting palladium has highly dispersed palladium.