3-Methylpiperidine dehydrogenation catalyst, and preparation method therefor and application thereof

Abstract

Disclosed is a 3-methylpiperidine dehydrogenation catalyst, which uses a metal oxide as a carrier, a noble metal as an active component, and an alkali metal and alkaline earth metal as auxiliary agent

Description

The present invention belongs to the field of fine chemical industry and relates to a 3-methylpiperidine dehydrogenation catalyst and a preparation method therefor, and use of the catalyst in the preparation of 3-methylpyridine by dehydrogenation. BACKGROUND 3-methylpyridine is an important fine chemical raw material and has wide application. It is mainly used for preparing nicotinic acid and nicotinamide, and also used as an intermediate for synthesizing spices, dyes, solvents, alcohol denaturants, rubber vulcanization accelerators and the like. Reported methods for preparing 3-methylpyridine include a coal tar extraction, an acrolein ammonia method, a 2-methyl-l,5-pentanediamine cyclization, and an aldehyde ammonia method to prepare a pyridine base with the coproduction of 3-methylpyridine. The aldehyde ammonia method to prepare a pyridine base with the coproduction of 3-methylpyridine is a main production method. The coal tar extraction is an early production method, has low efficiency and thus is abandoned for a long time. The main problems of the acrolein ammonia method and the 2-methyl-l,5-pentanediamine cyclization are that the reaction conditions are harsh and the yield of 3-methylpyridine is low. In the aldehyde ammonia method to prepare a pyridine base with the coproduction of 3-methylpyridine, 3-methylpyridine is only a by-product. The method has a significant disadvantage of low selectivity of catalysts and a problem of separation from pyridine. A preparation of 3-methylpyridine by dehydrogenating 3-methylpiperidine has high selectivity, can avoid the separation problem, and becomes an efficient method for preparing 3-methylpyridine. It has been reported that 3-methylpiperidine dehydrogenation catalysts are as follows: U.S. Patent No. 8530664 discloses a 3-methylpiperidine dehydrogenation catalyst, which takes a silicon-aluminum oxide as a carrier, a noble metal Pd as an active component with the loading capacity of 7.5%, and mixed gas of nitrogen and hydrogen as a carrier gas, the mass space velocity of 3-methylpiperidine is 3 h’1, the reaction is carried out at 300°C for 509 h, and the yield of 3-methylpyridine is stabilized at 98%. Chinese patent CN101384525 and U.S. Patent No. 8324388 disclose a 3-methylpiperidine dehydrogenation catalyst, which takes ZrO2 as a carrier, a noble metal Pd as an active component with the loading capacity of 0.9%, and mixed gas of nitrogen and hydrogen as a carrier gas, the volume space velocity of 3-methylpiperidine is 0.3 h’1, the conversion rate is 99.5%, the volume space velocity is 1.2 h’1, and the conversion rate is 78%. There is no report about a service life of the catalyst. U.S. Patent No. 4762929 discloses a catalyst for preparing 3-methylpyridine by dehydrogenating 3-methylpiperidine, which takes a noble metal Pd as an active component with the loading capacity of 1%, the conversion rate of 3-methylpiperidine is 95%, the selectivity of 3-methylpiperidine is 93%, and a service life of the catalyst is 100 days. The 3-methylpiperidine dehydrogenation catalysts all take a single noble metal palladium as an active component, have high loading capacity, require continuous introduction of mixed gas of nitrogen and hydrogen as a carrier gas in the reaction process, and are not beneficial to industrial production. SUMMARY The present invention aims to provide a 3-methylpiperidine dehydrogenation catalyst, which solves the problems that the prior art has high loading capacity of a noble metal, and nitrogen and hydrogen as a carrier gas are required to be continuously introduced in a reaction. The objectives of the present invention are achieved by the following technical solutions: a 3-methylpiperidine dehydrogenation catalyst, which takes a metal oxide as a carrier, a noble metal as an active component, and an alkali metal and an alkaline earth metal as an auxiliary agent, the loading capacity of the active component (calculated by a mass ratio of the noble metal element to the carrier) is 0.05%-0.5%, and the loading capacity of the auxiliary agent (calculated by a mass ratio of the alkali metal element and the alkaline earth metal element to the carrier) is 0.1%-1.0%. Preferably, the loading capacity of the active component is 0.05%-0.1% and the loading capacity of the auxiliary agent is 0.1%-0.5%. Preferably, a mass ratio of the alkali metal to the alkaline earth metal is 1:(1-5). Preferably, the carrier is one of AI2O3, ZrO2, and TiO2, preferably AI2O3. Preferably, the carrier is a globular carrier with the diameter of 1-5 mm. Preferably, the noble metal is one of Ru, Pt, Pd, and Rh, preferably Pd. Preferably, the alkali metal is at least one of alkali metals Na or K and combined with at least one of alkaline earth metals Mg and Ca; and further preferably, the auxiliary agent is a combination of K and Mg. The 3-methylpiperidine dehydrogenation catalyst of the present invention is prepared by using an isovolumetric soaking method. Another objective of the present invention is to provide a method for preparing the 3-methylpiperidine dehydrogenation catalyst, comprising: taking a solvent with the same volume as the saturated absorption capacity of the carrier to be soaked, dissolving an active component precursor and an auxiliary agent precursor in the solvent to prepare a homogeneous solution, dispersing the carrier in the solution, fully turning over and stirring the carrier to fully soak the carrier with the solution, and naturally drying, drying and roasting same to prepare the 3-methylpiperidine dehydrogenation catalyst. The active component precursor is one of a chloride salt, a nitrate or an acetate corresponding to the noble metal such as Ru, Pt, Pd, and Rh, preferably a chloride salt. The auxiliary agent precursor is one of a chloride salt, a nitrate or an acetate of the alkali metal to the alkaline earth metal, preferably a chloride salt. The solvent is one or a mixture of two of water, hydrochloric acid, ethanol, and ammonium hydroxide, preferably water or hydrochloric acid. The hydrochloric acid is 5% hydrochloric acid. The drying temperature is 120-140°C and the drying time is 6-12 h. The roasting temperature is 500-600°C and the roasting time is 4-6 h. Another objective of the present invention is to provide use of the 3-methylpiperidine dehydrogenation catalyst in the preparation of 3-methylpyridine by dehydrogenating 3-methylpiperidine. A method for preparing 3-methylpyridine, wherein 3-methylpiperidine is used as a raw material, and heated and vaporized, and passes through a fixed bed reactor packed with the 3-methylpiperidine dehydrogenation catalyst, the mass space velocity of the 3-methylpiperidine is 1-5 h’1, preferably 2-4 h’1, and the process conditions are as follows: normal pressure and reaction temperature of 180-300°C, preferably 200-260°C. Compared with the prior art, the present invention has the following beneficial effects: the 3-methylpiperidine dehydrogenation catalyst of the present invention can greatly reduce the loading capacity of a noble metal to be <0.1% by adding cheap and easily obtained alkali metals and alkaline earth metals as auxiliary agents. No carrier gas is required during the reaction process, 3-methylpiperidine is vaporized and reacted by a fixed bed to prepare 3-methylpyridine, the activity of the catalyst is not attenuated after a long time running, a service life is 3,000 h or more, the conversion rate can be maintained to be >99%, and the yield of the 3-methylpyridine is >98%. The 3-methylpiperidine dehydrogenation catalyst has an obvious cost advantage and industrial application prospect. DETAILED DESCRIPTION The technical solutions of the present invention are described in detail below in conjunction with the examples, but the protection scope of the present invention is not limited thereto. Example 1 100 g of dried AI2O3 globules having the diameter of 3 mm were taken, water was used as a solvent, and the saturated water absorption capacity was determined to be 98 g. 0.168 g of anhydrous palladium chloride, 0.382 g of potassium chloride, and 0.794 g of magnesium chloride were weighed and added into 98 g of water, and stirred and dissolved to obtain a uniform transparent solution, the solution was dropwise added onto 100 g of the dried AI2O3 globules, and the carrier globules were turned over and stirred continuously during the dropwise addition process to ensure that the carrier was uniformly soaked in the solution. After the dropwise addition, the carrier was placed in a fuming cupboard for natural air-drying for 12 h, then placed in an oven for drying at 120°C for 12 h, and placed in a muffle furnace for roasting at 550°C for 4 h, and the obtained catalyst comprised 0.1%Pd+0.2%K+0.2%Mg / A1203 and was marked as catalyst 1. Example 2 The carrier of example 1 was replaced by dried ZrO2 globules having the diameter of 3 mm. 100 g of dried ZrO2 globules having the diameter of 3 mm were taken, water was used as a solvent, and the saturated water absorption capacity was determined to be 87 g. 0.168 g of anhydrous palladium chloride, 0.382 g of potassium chloride, and 0.794 g of magnesium chloride were weighed and added into 87 g of water, and stirred and dissolved to obtain a uniform transparent solution, other operation methods were the same as those in example 1, and the obtained catalyst comprised 0.1%Pd+0.2%K+0.2%Mg / Zr02 and was marked as catalyst 2. Example 3 The carrier of example 1 was replaced by dried TiO2 globules having the diameter of 3 mm. 100 g of dried TiO2 globules having the diameter of 3 mm were taken, water was used as a solvent, and the saturated water absorption capacity was determined to be 82 g. 0.168 g of anhydrous palladium chloride, 0.382 g of potassium chloride, and 0.794 g of magnesium chloride were weighed and added into 82 g of water, and stirred and dissolved to obtain a uniform transparent solution, other operation methods were the same as those in example 1, and the obtained catalyst comprised 0.1%Pd+0.2%K+0.2%Mg / Ti02 and was marked as catalyst 3. Example 4 The active component precursor palladium chloride of example 1 was replaced by chloroplatinic acid hexahydrate to prepare a platinum-loaded catalyst. 0.266 g of chloroplatinic acid hexahydrate, 0.382 g of potassium chloride, and 0.794 g of magnesium chloride were weighed and added into 98 g of water, and stirred and dissolved to obtain a uniform transparent solution, other operation methods were the same as those in example 1, and the obtained catalyst comprised 0.1%Pt+0.2%K+0.2%Mg / A1203 and was marked as catalyst 4. Example 5 The active component precursor palladium chloride of example 1 was replaced by anhydrous ruthenium trichloride to prepare a ruthenium-loaded catalyst. 0.205 g of anhydrous ruthenium trichloride, 0.382 g of potassium chloride, and 0.794 g of magnesium chloride were weighed and added into 98 g of water, and stirred and dissolved to obtain a uniform transparent solution, other operation methods were the same as those in example 1, and the obtained catalyst comprised 0.1%Ru+0.2%K+0.2%Mg / A1203 and was marked as catalyst 5. Example 6 The solvent of example 1 was replaced by 5% hydrochloric acid. 100 g of dried AI2O3 globules having the diameter of 3 mm were taken, and the saturated water absorption capacity was determined to be 102 g. 0.168 g of anhydrous palladium chloride, 0.382 g of potassium chloride, and 0.794 g of magnesium chloride were weighed and added into 102 g of 5% hydrochloric acid, and stirred and dissolved to obtain a uniform transparent solution, other operation methods were the same as those in example 1, and the obtained catalyst comprised 0.1%Pd+0.2%K+0.2%Mg / A1203 and was marked as catalyst 6. Comparative example 1 In the present example, only a noble metal Pd was loaded, alkali metal and alkaline earth metal auxiliary agents were not added, pure palladium chloride had very low solubility in water, but good solubility in a dilute hydrochloric acid solution, and thus 5% hydrochloric acid was used as a solvent. 0.168 g of anhydrous palladium chloride was weighed and added into 102 g of 5% hydrochloric acid to ensure that 100 g of dried AI2O3 globules having the diameter of 3 mm were uniformly soaked in the solution, other operation methods were the same as those in example 1, and the obtained catalyst comprised 0.1%Pd / A12O3 and was marked as catalyst 7. Comparative example 2 In the present example, a noble metal Pd was not loaded, and a carrier was only soaked with alkali metal and alkaline earth metal auxiliary agents. 100 g of dried AI2O3 globules having the diameter of 3 mm were taken, water is used as a solvent, and the saturated water absorption capacity was determined to be 98 g. 0.382 g of potassium chloride and 0.794 g of magnesium chloride were weighed and added into 98 g of water, and stirred and dissolved to obtain a uniform transparent solution, the solution was dropwise added onto 100 g of the dried AI2O3 globules, and the carrier globules were turned over and stirred continuously during the dropwise addition process to ensure that the carrier was uniformly soaked in the solution. After the dropwise addition, the carrier was placed in a fuming cupboard for natural air-drying for 12 h, then placed in an oven for drying at 120°C for 12 h, and placed in a muffle furnace for roasting at 550°C for 4 h, and the obtained catalyst comprised 0.2%K+0.2%Mg / A1203 and was marked as catalyst 8. Initial activity evaluation of catalysts 10 g of the catalysts prepared in examples 1-6 and comparative examples 1-2 were respectively taken and packed into a fixed bed tubular reactor having the inner diameter of 2 cm, 3-methylpiperidine was fed by a metering pump with the feeding amount of 20 g / h, and preheated and vaporized, and entered the fixed bed reactor, the temperature of a catalyst bed was controlled at 250°C, the reaction was carried out for 10 h, a reaction product was collected at an outlet of the reactor, and the cumulative product was taken and analyzed. The results were shown in Table 1. Table 1 Results of initial activity evaluation of catalysts Catalyst Conversion rate of 3-methylpiperidine / % Yield of 3-methylpyridine / % 1 99.9 99.5 2 93.6 92.1 3 94.7 93.8 4 90.3 89.9 5 89.4 88.7 6 99.5 99.1 7 89.7 88.3 8 0.5 Not produced It can be seen from Table 1, examples 1-3 showed that the catalyst prepared by using AI2O3 as the carrier had higher initial activity than the catalyst prepared by using ZrCE and TiO? as the carriers with the same active component, auxiliary agent and soaking condition. Examples 1, 4, and 5 showed that the catalyst prepared by taking AI2O3 as a carrier and anhydrous palladium chloride as an active component precursor under the same cocatalyst and soaking condition had higher catalytic initial activity than the catalyst prepared by using chloroplatinic acid hexahydrate and ruthenium chloride as active component precursors, indicating that the noble metal palladium had higher catalytic activity in the dehydrogenation reaction of 3-methylpiperidine than the noble metals platinum ruthenium. The comparison of example 1 with example 6 showed that the selection of water or hydrochloric acid as a soaking solvent had little effect on the activity of the catalyst. From the comparison between example 1 and comparative examples 1-2, it can be seen that catalyst 1 prepared by loading the noble metal Pd and simultaneously adding a certain amount of a mixture of K and Mg, and using AI2O3 as a carrier had higher initial activity. Reaction service life evaluation of catalysts Each 10 g of catalysts 6 and 7 was taken and packed into a fixed bed tubular reactor having the inner diameter of 2 cm, 3-methylpiperidine was fed by a metering pump with the feeding amount of 20 g / h, and preheated and vaporized, and entered the fixed bed tubular reactor, the temperature of a catalyst bed was controlled at 250°C, the device ran for a long time, a reaction product was collected at an outlet of the reactor, and a sample was taken intermittently and analyzed. The results were shown in Table 2. Table 2 Results of reaction service life evaluation of catalysts Reaction time / h Catalyst 6 Catalyst 7 Conversion rate of 3-methylpiperidine / % Yield of 3-methylpyridine / % Conversion rate of 3-methylpiperidine / % Yield of 3-methylpyridine / % 50 99.8 99.4 87.1 86.2 100 99.6 99.1 85.2 84.5 202 99.5 99.0 83.7 82.1 509 99.3 98.7 70.4 68.9 650 99.3 98.8 32.5 29.3 1013 99.4 98.7 - - 2007 99.1 98.5 - - 3006 99.2 98.3 - - After 650 h of the reaction, the activity of catalyst 7 rapidly decreased and the reaction evaluation was stopped. It can be seen from Table 2, compared with the prior art, the noble metal loading capacity of the catalyst of the present invention was greatly reduced by adding the alkali metal and the alkaline earth metal, the performances of the catalyst were obviously improved, and no carrier gas was required to be introduced during the reaction process. The long-time operation was carried out at the reaction temperature of 250°C and the mass space velocity of 2 h’1, and can maintain the conversion rate of 3-methylpiperidine >99% and the yield of 3-methylpyridine >98%. The catalyst of the present invention can still maintain stable catalytic activity after running for 3,000 h. The inventors examined catalyst 4 and catalyst 5 by the above method. After 650 h of the reaction, the catalytic activities of the two catalysts were respectively equal to their initial activities. After 650 h of the reaction, the activity of catalyst 4 was as follows: the conversion rate of 3-methylpiperidine was maintained at 99.0% and the yield of 3-methylpyridine was maintained at 89.5% percent; and the activity of catalyst 5 was as follows: the conversion rate of 3-methylpiperidine was maintained at 89.1% and the yield of 3-methylpyridine was maintained at 88.4%. When ran for 3,000 h or more, catalyst 4 and catalyst 5 still kept stable catalytic activity which was not obviously reduced. It is indicated that the catalyst of the present invention has an obvious cost advantage and industrial application prospect. The applicant claims that the present invention describes detailed methods of the present invention through the above examples, but the present invention is not limited to the above detailed methods, that is, the above description does not mean that the present invention must rely on the above detailed methods to be implemented. Those skilled in the art should understand that any improvement to the present invention, equivalent replacement of each raw material of the product of the present invention, addition of auxiliary components, selection of specific methods and the like fall within the scope of protection and disclosure of the present invention.

Claims

30 06 25What is claimed is:

1. A 3-methylpiperidine dehydrogenation catalyst, wherein the catalyst takes a metal oxide as a carrier, a noble metal as an active component, and an alkali metal and an alkaline earth metal as an auxiliary agent, the loading capacity of the active component is 0.05%-0.5% calculated as a mass ratio of the active component to the carrier, and the loading capacity of the auxiliary agent is 0.1%-1.0% calculated as the mass ratio of the auxiliary agent to the carrier; the active component is one of Ru, Pt, Pd, and Rh, the auxiliary agent is a combination of at least one of alkali metals Na and K and at least one of alkaline earth metals Mg and Ca, and a mass ratio of the alkali metal to the alkaline earth metal is 1 :(1-5).

2. The 3-methylpiperidine dehydrogenation catalyst according to claim 1, wherein the loading capacity of the active component is 0.05%-0.1% and the loading capacity of the auxiliary agent is 0.1%-0.5%.

3. The 3-methylpiperidine dehydrogenation catalyst according to claim 1, wherein the carrier is one of A12O3, ZrO2, and TiO2.

4. The 3-methylpiperidine dehydrogenation catalyst according to claim 1, wherein the active component is Pd.

5. The 3-methylpiperidine dehydrogenation catalyst according to claim 1, wherein the auxiliary agent is a combination of K and Mg.

6. A method for preparing the 3-methylpiperidine dehydrogenation catalyst according to claim 1, comprising: taking a solvent with the same volume as the saturated absorption capacity of the carrier to be soaked, dissolving an active component precursor and an auxiliary agent precursor in the solvent to prepare a homogeneous solution, dispersing the carrier in the solution to fully soak the carrier with the solution, and naturally drying, drying and roasting same to prepare the 3-methylpiperidine dehydrogenation catalyst.

7. The method for preparing the 3-methylpiperidine dehydrogenation catalyst according to claim 6, wherein the active component precursor is one of a chloride salt, a nitrate or an acetate corresponding to the noble metal, preferably a chloride salt;the auxiliary agent precursor is one of a chloride salt, a nitrate or an acetate corresponding to the alkali metal to the alkaline earth metal, preferably a chloride salt; andthe solvent is one or a mixture of two of water, hydrochloric acid, ethanol, and ammonium hydroxide, preferably water or hydrochloric acid.

8. Use of the 3-methylpiperidine dehydrogenation catalyst according to any one ofclaims 1-5 in the preparation of 3-methylpyridine by dehydrogenating 3-methylpiperidine.

9. A method for preparing 3-methylpyridine, wherein 3-methylpiperidine is used as a raw material, and heated and vaporized, and passes through a fixed bed reactor packed with the 3-methylpiperidine dehydrogenation catalyst according to claim 1 to prepare 3-methylpyridine, the mass space velocity of the 3-methylpiperidine is 1-5 h-1, preferably 2-4 h-1, and the process conditions are as follows: normal pressure and reaction temperature of 180-300°C, preferably 200-260°C.30 06 25