CA1109855A

CA1109855A - Production of cyclohexanone

Info

Publication number: CA1109855A
Application number: CA286,935A
Authority: CA
Inventors: Jan F. Van Peppen; William B. Fisher
Original assignee: Honeywell International Inc
Current assignee: Honeywell International Inc
Priority date: 1976-11-24
Filing date: 1977-09-16
Publication date: 1981-09-29
Also published as: FR2372136B1; FR2372136A1; NL7712893A; IT1143838B; GB1563044A; DE2752291A1

Abstract

ABSTRACT OF THE DISCLOSURE

A method for promoting the selective hydrogenation of phenol to cyclohexanone in the presence of an improved palladium-on-carbon catalyst which comprises effecting the hydrogenation reaction in the presence of an in situ promoter preferably from the group consisting of sodium hydroxide, sodium carbonate, and sodium phenate. The characteristic properties of the palladium-on-carbon catalyst used in this process are significantly different from commercially available catalyst, and the present invention involves apparent interaction of the in situ promoter with the present unique catalyst. Respecting safety of operation, it is important that the present process and catalyst permit hydrogenation of phenol in the liquid phase utilizing at least 2, preferably 3 to 8, reactors in series with each reactor maintained at or below the atmospheric boiling point of the reaction mixture in the reactor.

Description

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BACKGROUND OF THE INVENTION
This invention relates to the hydrogenation of phenol and, more particularly, to the promotion of the hydrogenation of phenol to cyclohexanone in the presence of a promoted palladium catalyst.
In the hydrogenation of phenol employing a palladium catalyst, the activity of the catalyst, and hence the rate of hydrogenation, decreases with continued use of the catalyst due to impurities present in the hydrogenation reaction mixture which poison the catalyst.
While processes, such as those disclosed in U.S. Patents 3,692,845 and 3,187,050, have been developed to purify organic compounds such as phenol to be hydrogenated, the poisoning of metallic catalysts has not been en-tirely eliminated in large scale commercial processes due to long-term accumulation of impurities, such as those impurities which are introduced with the phenol and the hydrogen gas, and those impurities which are produced during the processing.
To avoid the economically prohibitive alter-natives of discarding poisoned catalyst or continuing to use the poisoned catalyst at a reduced rate of hydrogenation, it is desirable to promote the rate of hydrogenation, thereby overcoming the disadvantages of continued use of such poisoned palladium catalysts.
The hydrogenation of phenol to cyclohexanone has been promoted by the use of "promoted palladium-on-carbon catalysts", i.e., catalysts which have been treated prior to their addition to the hydrogenation reaction mixture, to incorporate on the catalysts a material which ,'X ~k ~9.~i enhances their activity. Thus, in U.S. Patent 3,076,810, cyclohexanone is produced by hydrogenating phenol using a sodium-promoted catalyst, i.e., a palladium catalyst which has been modified prior to its introduction to the reaction mixture, to incorporate sodium thereon. Alkaline reacting agents in limited amounts are also disclosed as being added to assist in promotion when the sodium-promoted catalysts of that reference are employed. However, such catalyst systems have not been entirely satisfactory, and research has continued to develop an improved process and/or catalyst.
Surprisingly, the present invention provides significantly improved catalyst selectivity and activity in the hydrogenation of phenol to cyclohexanone;
moreover, it is applicable to present commercial plants.
Further, the present invention provides an improved process that will produce less by-products and can be operated at a lower temperature than present commercial plants without sacrificing production rate. Obviously, reaction at relatively low temperature is highly desirable as a factor increasing safety of the overall operation.
SUMMARY OF THE INVENTION

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In accordance with the present invention, we provide a process for producing cyclohexanone comprising hydrogenating phenol by passing hydrogen in contact with phenol in the presence of a palladium catalyst, preferably promoted by sodium in an amount of at least 1000 ppm, based on the weight of the catalyst, at a 30 temperature of 135C. to 185C., preferably 145C. to 185C., sald catalyst being further characterized in that it is composed of palladium coated carbon particles, said carbon particles having diameters of 3 to 300 mierons and a surface area of 100 to 2000 m /gram, said phenol containing a small amount of an ln situ promoter selected from the group consisting of alkali metal hydroxides, carbonates, phenates, bicarbonates and nitrates, said amount being 10 to 300 ppm, preferably 11 to 150 ppm, in terms of alkali metal of said promoter.
Although in U.S. Patent 3,076,810, it was said that higher concentrations, i.e., more than 10 ppm, of an alkaline reacting compound in the phenol favored the formation of eyclohexanol, we have found that in the presenee of our improved palladium-on-earbon eatalyst, not only is the reaction rate enhaneed but also the produetion of cyclohexanol is redueed by operating within the range of 10 to 300 ppm of alkali metal in the phenol. The reason for this surprising discovery is not known with certainty, but it is believed that the unexpected element of the present invention involves the apparent interaction of the in situ promoter with the present unique eatalyst, together with eareful eontrol of the reaetion temperature as specified hereinabove.
The palladium catalysts useful in the present invention contain palladium, in either its elemental or combined form, as a catalytically active metal.
Preferably, 30 to 75 percent of the total palladium is present as elemental palladium, i.e., as palladium zero.
The palladium is desirably absorbed or coated on the 98~

surface of a support consisting of carbon particles, said carbon particles having diameters of 3 to 300 microns and a surface area o~ 100 to 2000 m2/gram.
It is preferred that the catalyst have about 95 to 98 weight percent of the particles between 4 and 150 microns in diameter. While the amount of palladium incorporated on the selected support may vary widely, the catalyst preferably contains from about 0.1 to 50 weight percent palladium, and most preferably from about 0.2 to 10 weight percent. A satisfactory and readily prepared catalyst contains 1 to 5 weight percent palladium on charcoal. In addition, the palladium catalysts useful in the present invention may contain catalytically active metals in addition to palladium.
Such additional catalytically active metals which may be employed are those selected from the group consisting of elements of the platinum series. Exemplary of platinum series elements which may be employed are ruthenium, rhodium, osmium, iridium, platinum and mixtures thereof.
The preferred promoters of the present invention are members selected from the group consisting of sodium hydroxide, sodium carbonate, sodium phenate, and mixtures thereof. Particularly preferred as promoters in the present invention are sodium hydroxide and sodium phenate, with sodium phenate being especially preferred.
The selected promoter may be added to the hydrogenation reaction mixture as a phenol slurry containing up to about 25 weight percent, and preferably from about 1 to 10 weight percent, of the selected promoter.

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~ 8~j Alternatively, the promoter may be added to the hydrogenation reaction mixture as an aqueous solution.
The phenol which may be employed in the present invention may be obtained from conventional sources, such as by the oxidation of cumene to form cumene hydroperoxide and the decomposition of the resulting hydroperoxide. However, the phenol treated in accordance with the process of the present invention will generally contain no more than about 100 ppm sulfur impurities, and preferably not greater than about 10 ppm sulfur impurities containing divalent sulfur, not greater than about 20 ppm sulfur impurities containing tetra-valent sulfur and not greater than about 80 ppm, and most preferably not greater than about 40 ppm, sulfur impurities containing hexavalent sulfur.
The phenol also preferably contains not greater than 2 ppm, and most preferably not greater than 1 ppm, iron values (calculated as elemental iron); and preferably not greater than 100 ppm, and most preferably not greater than 50 ppm, acetol (i.e., hydroxy-2-propanone).
The phenol hydrogenated in accordance with the process of the present invention may also contain a wide variety of other impurities. These impurities include, for example, halogen compounds and deleterious nitrogen compounds, i.e., nitrogen-containing compounds which inhibit the hydrogenation of phenol to cyclo-hexanone employing palladium catalysts. Typical deleterious nitrogen compounds include aromatic amines, ammonium salts, polyamines, and tertiary and primary amines. Preferably, the phenol contains less than 10 ppm halogen and less than 50 ppm of nitrogen as deleterious nitrogen compounds. Continuous or batch techniques can be used in this improved process for S hydrogenating phenol to cyclohexanone, the equipment used being that which is usual in such processes.
The selected promoter may be introduced to the hydrogenation reaction mixture either prior to hydrogenation or during hydrogenation. Thus, the conditions of temperature under which the promoter may be added to the hydrogenation mixture are not critical and may vary widely. For example, the temperature at which the promoter is added to the hydrogenation reaction mixture may vary from about 25C. to about 185C. and the pressure may vary from about atmospheric to 300 psig. While an improved rate of hydrogenation is generally observed immediately upon addition to the hydrogenation reaction mixture of a promoter of the present invention, even more improved resul~s may be obtained where the hydro-genation reaction mixture is maintalned at a temperature within the range of about 135C. to 185C. and a pressure of 80-200 psig. for a period of 15 to 30 minutes after addition thereto of the selected promoter.
The selected in situ promoter may be added to the hydrogenation reaction mixture and the reaction product may be withdrawn from the hydrogenation vessel either continuously or batchwise. Upon withdrawal of the hydrogenation product from the reaction vessel, the palladium catalyst may be recovered from the product X

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stream and returned to the vessel for hydrogenation of additional phenol. The recovery of the catalyst from the product stream may be effected by any standard solids separation pxocedure, e.g., centrifugation, vacuum filtering, and the like.
Vessels which may be employed during the hydrogenation are conventional, and include the typical hydrogenation apparatus such as, for example, the apparatus described in U.S. Patent 3,076,810.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention is further illustrated by reference to the following examples wherein parts and percentages are by weight unless otherwise indicated.
The improved catalyst and the improved rates of hydrogenation achieved by the process of the present invention are especially significant in view of the large tonnages of palladium catalysts used annually by industry in the hydrogenation of phenol to cyclohexanone.
Furthermore, the in situ promoters of the present invention have been unexpectedly found to promote the hydrogenation of phenol to cyclohexanone while appreciably decreasing the amount of cyclohexanol produced by the further hydrogenation of the desired cyclohexanone hydrogenation product. Thus, recovery of cyclohexanone from the hydrogenation product stream, as by distillation, is not further complicated by the formation of substantial amounts of undesired products, i.e., cyclohexanol.

1~9~5 PART A: About 1000 parts of phenol containing less than 1 ppm of soluble iron, less than 2 ppm of sulfur, less than 5 ppm of halogen, less than 40 ppm of nitrogen as deleterious nitrogen compounds and 0.23 part of sodium carbonate is mixed with 10 parts of sodium-promoted, palladium-on-carbon catalyst having a sodium content of 0.32 percent, said catalyst being further characterized in that it is composed of about 0.93 percent palladium coated on carbon particles having diameters of about 4 to 150 microns and a surface area of 500 to 1500 m2/gram. The mixture is heated in a reaction vessel under nitrogen to 160C., then agitated at that temperature while hydrogen is admitted through a diffuser located near the bottom of the vessel and at a rate sufficient to maintain a pressure of 80 psig.
Periodically, the reaction mixture is sampled and analyzed. Results are tabulated in Table 1.

Hydrogenation Cyclohexanol, Cyclohexanone, Phenol, Time, M _ tes Percent Percent Percent 62 0 38.5 61.5 0 53.8 ~6.2 120 0.5 65.6 33.8 25150 0.6 74.9 24.4 180 0.8 82.3 16.9 210 1.1 87.5 11.4 Less than 0.1 percent of cyclohexyl-cylcohexanone is found in the reaction mixture. At the end of the experiment, the catalyst is recovered and is found U'f 8~

to contain 0.93 percent palladium (60 percent to 75 percent of total as elemental palladium) and 0.76 percent sodium.
PART B: The procedure of Part A is repeated with the exception that no sodium carbonate is added to the phenol. The results are tabulated in Table 2.
TAB~E 2 Hydrogenation Cyclohexanol, Cyclohexanone, Phenol, Time, Minu es _ Percent Percent Percent 0.3 28.1 71.6 120 0.6 48.4 50.9 210 1.4 65.9 32.5 300 2.2 77.4 20.1 390 3.2 84.3 12.1 450 3.9 88.6 7.0 In addition, about 0.47 percent of cyclohexyl-cyclohexanone is found in the reaction mixture at the end of the experiment.
By comparison of Part A and Part B, it is clear that while in the prior art the in situ addition of an alkali metal promoter above a level of 10 ppm based on phenol caused loss of selectivity, the catalyst of the present invention continued to improve in selectivity with addition of sodium carbonate to the phenol at 230 ppm, which corresponds to 100 ppm of sodium. The unexpected element of the present invention lies in the apparent interaction of the promoter with the present unique catalyst in combination with the relatively low reaction temperature.

3~8!~S

The procedure of Example 1, Part A, is repeated with the exception that 100 ppm of sodium in the form of sodium hydroxide is added to the reaction mixture in place of the sodium carbonate. Results obtained are similar to those obtained in Example 1, Part A.

The procedure of Example 1, Part A, is repeated with the exception that 100 ppm of sodium in the form of sodium phenate is added to the reaction mixture in place of the sodium carbonate. Results obtained are similar to those obtained in Example 1, Part A.

This example demonstrates one effective method of preparing the catalyst of the present invention.
However, the method of this example is relatively expensive as compared with the procedure of Example 5.
About 150 parts of a commercially available 5 percent palladium-on-carbon catalyst is used as starting material. A slurry of the commercially available palladium catalyst in an aqueous solution of sodium hydroxide is prepared and the slurry is then evaporated to dryness in accordance with the procedure of U.S. Patent 3,076,810. The resulting catalyst preferably contains 2,500 - 10,000 ppm of sodium. About 150 parts of the sodium-promoted, palladium-on-carbon catalyst is thoroughly mixed with 1850 parts of cyclohexanone and this mixture is passed at the rate of 2000 parts per hour through a continuous centrifuge which operates at 3800 revolutions per minute. In ' . ' 38~;~

accordance with this procedure, part of the catalyst consisting of the finer particles passes out of the centrifuge with the cyclohexanone. The catalyst collected in the centrifuge has a size distribution of 98 to 99 percent greater than 4 microns, with substantially all particles in the range 4 to 150 microns; the palladium content is 0.6 to 1.2 percent, and the sodium content is 0.25 to 0.40 percent. This catalyst is suitable for use in the process of this invention. The finer catalyst particles may be recovered from the cyclohexanone by conventional procedures; the finer catalyst particles are unsuitable for use in the process of this invention.

About 150 parts of commercially available charcoal catalyst support having particle size distribution of 30 percent less than 10 microns, 67 percent in the range 10 to 100 microns, and 3 percent greater than 100 microns is thoroughly mixed with 1850 parts of cyclohexanone, and this mixture is passed through a continuous centrifuge which operates at 3800 revolutions per minute. By this procedure, part of the charcoal particles consisting of the finer particles, passes out of the centrifuge with the cyclohexanone. The - 25 charcoal particles collected in the centrifuge, after drying, consist of about 100 parts of particles having diameters of 10 to 100 microns and a surface area of about 1000 m2/gram. To 100 parts of the resulting charcoal is added 1000 parts of aqueous palladium chloride solution containing 5 parts palladium and ~r ~1098~5 3 parts hydrochloric acid. The solution is gradually neutralized with a sodium carbonate solution up to pH = 1.5. The mixture is stirred and then filtered.
The solids are dried at 100C. for 8 hours following which they are impregnated with 80 parts of a solution containing 5 parts of sodium carbonate. After drying at 100-120C. the solids are placed into a cylindrical reactor which is flushed with hydrogen at 140C. This catalyst is suitable for use in the present invention.

This example demonstrates the feasibility of continuously operating the hydrogenation process of the present invention. The phenol used was similar to that used in Example 1.
The first of a series of five a~itated hydro-genation vessels is charged with 45,694 parts per hour of phenol, 1.3 to 2.0 parts of sodium carbonate, and 1,200 parts per hour of a sodium-promoted, palladium-on-carbon catalyst ha~ing a sodium content of 0.25 - 0.40 percent, said catalyst containing about 0.93 percent palladium on carbon particles having diameters of about 5 to 150 microns and a surface area of about 1000 m /gram.
About 67 percent of the palladium on the catalyst is present as elemental palladium. Each hydrogenation vessel is connected in series so that the reaction mixture flows throu~h the five vessels in about 3.1 hours, the hydrogen being charged to the first vessel. The pressure is between 80 and 200 psig. The temperature in each vessel is as follows: 179C. in the first vessel; 168C. in the second vessel; 166~C. in the third vessel; 164C. in the 9~3~5 fourth vessel, and 162C. in the fifth vessel. It is noteworthy for reasons of safety that the temperature in each vessel is less than 10C. above the atmospheric boiling point of the reaction mixture present in the vessel. About 24,570 parts per hour of distillate, primarily cyclohexanone, is separated from the last three vessels; this distillate is rectified to provide substantially pure cyclohexanone. The reaction mass flowing from the fifth reaction vessel is fed to a continuous centrifuge, wherein the catalyst is separated from the crude cyclohexanone; the catalyst is recycled in the process. The crude cyclohexanone is rectified to recover substantially pure cyclohexanone which may be combined with the cyclohexanone recovered as described above.
In this continuous operation carried out for several days, cyclohexanone recovery is 42,856 parts per hour. Also recovered is 684 parts per hour of cyclohexanol~ 1481 parts per hour of phenol, and 211 parts per hour of higher boiling by-products. Only 3 parts per hour of make-up catalyst is required in the process. Similar results are obtained when an equivalent amount of sodium as sodium hydroxide or sodium phenate is substituted for the sodium carbonate added to the process in the phenol.
EX~MPLE 7 The procedure of Example 6 is followed except that the reaction temperature in each of the reaction vessels is further reduced for reasons of increased safety, i.e., the reaction temperature is reduced to 173C. in the first vessel, 166C. in the second vessel, X

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162C. in the third vessel, 159C. in the fourth vessel, and 156C. in the fifth vessel. Regarding safety in operation, it is important that the temperature in each reactor is maintained at or below the atmospheric boiling point of the reaction mixture present in the reactor.
The phenol is fed to the first vessel at a rate of 45,550 parts per hour~ together with 2 parts per hour of sodium carbonate and 1,200 parts per hour of a sodium-promoted palladium-on-carbon catalyst having a sodium content of about 0.35 percent, said catalyst containing about 0.9 percent palladium on carbon particles having diameters of about 3 to 32 microns and a surface area of about lO00 m2/gram. A commercially available sodium-promoted palladium-on-carbon catalyst containing about l percent sodium and about 5 percent palladium is added to the recycled catalyst as make-up catalyst at the rate of about 2.5 parts per hour. The make-up catalyst contains about 16.5 volume percent of particles finer than 3 microns in diameter, but most of these finer particles are removed from the process in the crude cyclohexanone recovered in the centrifuge. A sample of the make-up catalyst has the following size analysis.

~' l~L,r398;~5 Size Range, Percent of Microns Total Volume 1.26 to 1.59 l.S
1.59 to 2.00 2.0

2.00 to 2.52 4.0 2.52 to 3.17 9.0

3.17 to 4.00 11.5

4.00 to 5.04 13.5

5.04 to 6.35 12.5

6.35 to 8.00 14.0 8.00 to 10.08 13.0 10.08 to 12.7 10.0 12.7 to 16.0 5.0 16.0 to 10.2 2.5 20.2 to 25.4 1.0 25.4 to 32.0 0.5 In this example/ average yield of cyclohexanone over a one month test period is 98 percent of theory based on phenol fed to the process. Cyclohexanol is produced at a very low rate of about 610 parts per hour.
At the end of the test period, the recycling catalyst contains about 0.45 percent sodium and about 0.9 percent palladium. A sample of the recycling catalyst has the following size analysis.

~r J9~355 Size Range, Percent of Microns Total Volume . .
1.26 to 1.59 0.5 1.59 to 2.00 0.5 2.0C to 2.52 0.5 2.52 to 3.17 0.5 3.17 to 4.00 1.5 4.00 to 5.04 11.0 5.04 to 6.35 24.0 6.35 to 8.00 23.5 8.00 to 10.08 16.5 10.08 to 12.7 10.0 12.7 to 16.0 6.0 16.0 to 10.2 3.5 20.2 to 25.4 1.5 25.4 to 32.0 0.5 It will be noted that the make-up catalyst shows a fairly normal distribution in size range while the recycling catalyst shows a shift toward larger particles and a skewed distribution. We postulate that said shift toward larger catalyst particles in combination with the in situ promoter tend to promote rapid and selective hydrogenation of the phenol to cyclohexanone, i.e., produces high yields of cyclohexanone and low yields of cyclohexanol and other by-products.
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Claims

WE CLAIM:

1. A process for producing cyclohexanone comprising hydrogenating phenol by passing hydrogen in contact with phenol in the presence of a palladium catalyst at a temperature of 135°C. to 185°C., said catalyst being further characterized in that it is composed of palladium coated carbon particles, said carbon particles having diameters of 3 to 300 microns and a surface area of 100 to 2000 m2/gram, said phenol containing a small amount of an in situ promoter selected from the group consisting of alkali metal hydroxides, carbonates, phenates, bicarbonates and nitrates, said amount being 10 to 300 ppm in terms of alkali metal of said in situ promoter.

2. A process for producing cyclohexanone comprising hydrogenating phenol by passing hydrogen in contact with phenol in the presence of a palladium catalyst promoted by sodium in an amount of at least 1000 ppm, based on the weight of the catalyst, at a temperature of 135°C. to 185°C., said catalyst being further characterized in that it is composed of palladium coated carbon particles, said carbon particles having diameters of 3 to 300 microns and a surface area of 100 to 2000 m2/gram, said phenol containing a small amount of an in situ promoter selected from the group consisting of sodium hydroxide, sodium carbonate, and sodium phenate, said amount being 10 to 300 ppm in terms of sodium of said in situ promoter.

3. The process of claim 2 wherein said in situ promoter contained in said phenol is sodium hydroxide.

4. The process of claim 2 wherein said in situ promoter contained in said phenol is sodium carbonate.

5. The process of claim 2 wherein said in situ promoter contained in said phenol is sodium phenate.

6. The process of claim 2 wherein the palladium catalyst is promoted by sodium in an amount of 2500 to 10,000 ppm based on the weight of the catalyst.

7. The process of claim 2 wherein the phenol is hydrogenated at a temperature of 145°C. to 185°C.

8. The process of claim 2 wherein the palladium is coated on carbon particles having diameters of 4 to 150 microns and a surface area of 500 to 1500 m2/gram.

9. The process of claim 2 wherein the amount of in situ promoter in said phenol is 11 to 150 ppm in terms of sodium of said in situ promoter.

10. The process of claim 2 wherein 30 to 75 percent of the total palladium is elemental palladium.

11. A process for producing cyclohexanone comprising hydrogenating phenol by passing hydrogen in contact with phenol in the presence of a palladium catalyst promoted by sodium in an amount of 2500 to 10,000 ppm, based on the weight of the catalyst, at a temperature of 145°C.

to 185°C., said catalyst being further characterized in that it is composed of palladium coated carbon particles, said carbon particles having diameters of 4 to 150 microns and a surface area of 500 to 1500 m2/gram, said phenol containing a small amount of an in situ promoter selected from the group consisting of sodium hydroxide, sodium carbonate, and sodium phenate, said amount being 11 to 150 ppm in terms of sodium of said in situ promoter.

12. The process of claim 11 wherein the phenol is hydrogenated in a continuous manner, said phenol being fed to the first of a series of reaction zones connected in series, each reaction zone being maintained at a temperature no greater than 10°C. above the atmospheric boiling point of the reaction mixture in said zone.

13. The process of claim 12 wherein the series of reaction zones consist of 5 reaction zones and at least a portion of the cyclohexanone produced in the process is distilled from at least two of said reaction zones.

14. A catalyst for selective hydrogenation of phenol to cyclohexanone which comprises 0.2 to 10 weight percent of palladium, based on the total weight of the catalyst, supported on carbon particles having diameters of 3 to 300 microns and a surface area of 100 to 2000 m2/gram, said catalyst being promoted by sodium in an amount of at least 1000 ppm, and having selectivity considerably higher than catalyst containing particles having diameters smaller than 3 microns.

15. The catalyst of claim 11 wherein said sodium-promoted palladium catalyst is additionally promoted during said hydrogenation by contacting said catalyst with phenol containing a small amount of an in situ promoter selected from the group consisting of sodium hydroxide, sodium carbonate, and sodium phenate, said amount being 10 to 300 ppm in terms of sodium of said in situ promoter.

16. The catalyst of claim 11 wherein said sodium-promoted palladium catalyst is additionally promoted during said hydrogenation by contacting said catalyst with phenol containing a small amount of an in situ promoter selected from the group consisting of sodium hydroxide, sodium carbonate, and sodium phenate, said amount being 11 to 150 ppm in terms of sodium of said in situ promoter.

17. A process for preparing a catalyst for selective hydrogenation of phenol to cyclohexanone which comprises coating carbon particles with 0.2 to 10 weight percent of palladium, based on the weight of the catalyst, said carbon particles having diameters of 3 to 300 microns and a surface area of 100 to 2000 m2/gram, and then promoting said catalyst with sodium in an amount of at least 1000 ppm, based on the total weight of said catalyst, whereby selectivity of said catalyst is considerably higher than catalyst containing particles having diameters smaller than 3 microns.

18. The process of claim 17 wherein the catalyst is promoted with sodium in an amount of 2,500 to 10,000 ppm, based on the total weight of the catalyst.

19. The process of claim 17 wherein said carbon particles are obtained by separating carbon particles having diameters of 3 to 300 microns from carbon particles having larger or smaller diameters.