KR900008170B1 - Process for preparing methyl-pyrazine - Google Patents

Abstract

Methylpyrazine of formula (III) are prepared by the catalytic reaction of propylene glycol of formula (I) and ethylene diamine of formula (II) in the stream of hydrogen and/or nitrogen. The used catatyst is pref. copper-chromite and/or zinc-chromite catalyst. The reaction temp. in the Zn-chromite catalyst is pref. 320-450 deg.C and the reaction temp. in the Cu-chromite catalyst is pref. 300-400 deg.C.

Description

Method for preparing methylpyrazine

The present invention relates to an industrial process for producing methylpyrazine (III) from propylene glycol (I) and ethylenediamine (II) through high temperature gas phase catalysis.

More specifically, a device packed with a double catalyst layer in a single reactor using a copper-chromite catalyst and a zinc-chromite catalyst that has been reduced at high temperature, or a reactor and a copper-chromite packed with a zinc-chromite catalyst It relates to a method for producing methylpyrazine from a mixture of propylene glycol and ethylenediamine 1: 1 (molar ratio) under a stream of hydrogen and nitrogen, or hydrogen alone in a two-stage reactor connected in series with a catalyst-charged reactor in series. .

Looking at the existing methods for the preparation of methylpyrazine, first, to prepare methylpyrazine from propylene glycol and ethylenediamine. The fixed-bed multi-tube high-temperature reactor filled with a catalyst coated with zinc oxide on the surface of the soft brick debris or pottery debris was injected at 490-500 ° C. for 16 hours to obtain 61.4 kg of methylpyrazine with 90% purity. This method not only has a relatively high reaction temperature, but also a relatively low yield of 60%.

(2) Using ZnO / Zn-chromite catalyst and Pd as cocatalyst, 60% 2-methylpyrazine is obtained at 90% conversion from ethylenediamine and propylene glycol at 367-427 ° C. This also has the drawback of low selectivity (Appd, Catal, 29 (1987) 161,).

Meanwhile, looking at a method of preparing methylpyrazine using various starting materials, (3) Method of Korean Patent Publication No. 82-719: 5 g of N- (2-alkylhydroxy ethylenediamine), which is a reactant, is directly added dropwise to the upper portion of the catalyst layer. The reaction product was extracted with ether, dried over anhydrous magnesium sulfate and evaporated to give 3.2 g of alkylpyrazine, which was activated by passing 4 L of air at 350 ° C. for 2 hours and 1 L of hydrogen for 1 hour. As such, the space velocity, that is, the injection rate of the reactant per hour with respect to the unit weight of the catalyst has a disadvantage of giving a low yield of 80% at a low processing capacity of about 0.17 by weight.

(4) Method of Japanese Patent Application Laid-Open No. 55-122,769: Cr203-CuO is 1.26 to 1 in weight ratio and 5% of carbon in powder form is molded using water, followed by nitrogen at 170-200 ° C. at a relatively low temperature. Activate for 18 hours with hydrogen mixed with water. Although the catalyst treatment temperature is low, there is a disadvantage in that hydrotreating takes too long. In addition, although the reaction is low as 365-300 ℃, there is a disadvantage that gives a low conversion rate and yield with a conversion rate of 82% and about 78%.

(5) Method of German Patent No. 2,722,307: Yield is low by reacting diamine with alkylene glycol to obtain 55-78% of pyrazines.

(6) Method of Japanese Patent Publication No. 49-25,947: 0.069 moles of pyrazine, 0.01 moles of 1 mole of NH2-NH2 and 1 mole of HO-CH2-CH2-OH at a reaction temperature of 400 ° C on an alumina catalyst. By obtaining methylpyrazine, 0.121 mol of ethylpyrazine, etc., it is greatly inferior in selectivity and activity.

(7) Method of Japanese Unexamined Patent Publication No. 49-30,383: A method of obtaining pyrazine by dehydrogenation from piperazine, showing a low activity of only 79% at a reaction temperature of 350-370 ° C.

(8) Method of Japanese Laid-Open Patent Publication No. 54-27,577: Synthesis on a silica-alumina catalyst from ammonia and ethyl oxide at 355 ° C. yields morpholine and piperazine at the same time and has a greater selectivity to morpholine. have.

By analyzing and evaluating the above known methods, overall yield is low, and byproducts such as piperazine and pyrazine substituted with several (two or more) alkyl groups are prepared together, and thus the content of such piperazine is high. Difficulties in land type put a heavy load on the separation process.

In order to solve the above problems, a catalyst on a high-temperature group from N- (2-propylhydroxy) ethylenediamine using a copper-chromite-based catalyst reduced at high temperature in Korean Patent Publication No. 87-15,841, which was selected by the present applicant. Through the reaction, a method of preparing methylpyrazine having a yield of 90% or more at a conversion rate of 97% or more is proposed. However, the starting material N- (2-propylhydroxy) ethylenediamine is obtained from the reaction of ethylenediamine and propylene oxide, so one more manufacturing process is required. Methylpyrazine may be prepared directly from propylene glycol and ethylenediamine instead of N- (2-propylhydroxy) ethylenediamine.

The reaction formula for preparing methylpyrazine from propylene glycol and ethylenediamine is as follows.

Looking at the reaction equation, it can be seen that when the methylpyrazine is synthesized from propylene glycol and ethylenediamine, cyclization by dehydration and dehydrogenation occur simultaneously. Thus, there is a need for a catalyst that is highly active in both dehydration and dehydrogenation reactions. Korean Patent Publication No. 87-15,841, which has already been filed, has shown that the copper-chromite catalyst has good activity in dehydrogenation. However, this reaction required the development of a catalyst having good activity even in the dehydration reaction because two molecules of water is missing. In the present invention, in order to solve this problem, a double catalyst bed reactor using a copper-chromite catalyst and a zinc-chromite catalyst having better activity in dehydration, or a zinc-chromite catalyst reactor and a copper-chromium. A method for producing methylpyrazine from propylene glycol and ethylenediamine while maintaining the catalytic activity for a long time under hydrogen or hydrogenated nitrogen stream using a reactor connected in series with a mite catalyst reactor was developed.

The copper-chromite catalyst is prepared by precipitation method of Atkins, etc. so that the weight ratio of CuO and Cr203 is 4: 1, molded with some carbon and calcined to give a phase of CuO and CuCr204, and then hydrogen Reduction to maximize the activity of the catalyst surface. The zinc-chromite catalyst was prepared by coprecipitation of zinc-nitrate and chromium-nitrate in NaHCO 3 such that the weight ratio of ZnO and Cr203 was 4: 1, and calcined at 360 ° C., followed by reduction with hydrogen. The reduction treatment of the copper and zinc-chromite catalysts is not directly at high temperatures, but gradually increases from low temperatures, while the concentration of hydrogen gradually increases the ratio of hydrogen to nitrogen gas at low concentrations to pure water. It was done. Accordingly, the reduction temperature of the catalyst was 300-450 ° C. for the copper-chromite catalyst and 350-550 ° C. for the zinc-chromite catalyst. Reduction of the copper and zinc-chromite catalysts was found to have a close relationship with the reaction activity and selectivity to methylpyrazine. On the other hand, zinc-chromite catalysts are known to have good activity in both dehydration and dehydrogenation reactions with ZnO alone. However, when ZnO alone is used, zinc-chromite catalysts having a spinel structure are used because ZnO alone reduces the catalytic activity. Use was required.

0.1 이어야 하며 가장 적절하게는 수소/불활성가스

0.3 이어야 한다. 여기서 불활성가스라 함은 반응에 영향을 미치지 않는 가스로 질소, 아르곤, 헬륨등을 지칭한다. 유통가스는 반응물 1g망 100ml-1000ml의 부피로 흘려주는 것이 좋은데 200ml-400ml로 흘려주는 것이 가장 적절하다. 다음에 몇가지 실시예 및 비교예를 들어 본 발명의 취지를 보다 구체적으로 설명하고자 한다. 다음에 기술하는 실시예는 본발명의 일부분을 예시하는 것으로 본 발명을 제한하는 것은 아니다.The reaction temperature of the reactants on the catalyst is preferably maintained in the range of 270 ° C.-500 ° C., most preferably in the range 320 ° C.-450 ° C. in the Zn-chromite layer. In the Cu-chromite catalyst layer, the reaction is preferably performed in the temperature range of 250 ° C-450 ° C, most preferably in the temperature range of 300 ° C-400 ° C. The rate at which the reactants pass through the catalyst bed can vary, but it is appropriate to have a space velocity (per catalyst unit weight) of 0.05-3.0 / hour. The flow gas mixed with the reactants and passing through the catalyst bed uses a mixed gas of hydrogen and inert gas. The molar concentration of hydrogen is hydrogen / inert gas.

Should be 0.1 and most suitably hydrogen / inert gas

Should be 0.3. Inert gas is a gas that does not affect the reaction refers to nitrogen, argon, helium and the like. The distribution gas is preferably flowed in a volume of 100ml-1000ml of 1g of the reactant network, and 200ml-400ml is most appropriate. Next, some examples and comparative examples will be described in more detail with the gist of the present invention. The following examples illustrate some parts of the invention and do not limit the invention.

Example 1

The copper-chromite catalyst 100gr was prepared by the precipitation method so that the ratio of CuO and Cr203 was 4: 1 by weight ratio, and the zinc-chromite catalyst 100gr was prepared by the precipitation method so that ZnO and Cr203 were also 4: 1 by weight ratio, respectively. It baked at 350 degreeC. It was charged in a 1 "diameter SUS tubular reactor with the copper-chromite catalyst downwards and the zinc-chromite catalyst upwards. The reactor was charged with nitrogen gas gradually increasing hydrogen gas from 2% to 50% per minute. Flowing at a rate of 300 ml, the temperature of the reactor was increased from room temperature to 400 ° C. and the lower copper-chromite layer from room temperature to 350 ° C. to 2 ° C. to reduce the catalyst in the reactor. The temperature of the copper-chromite layer was fixed at 350 ° C and the temperature of the zinc-chromite layer was changed from 270 ° C to 500 ° C while flowing a flow gas containing 50% hydrogen gas in nitrogen gas on the reduced catalyst. And quantitatively varying the injection amount (weight: gr.) Of the reaction mixture of propylene glycol and ethylenediamine in a molar ratio of 1: 1 to the weight of the catalyst unit. Using a loop was injected through a pre-heater, each of the zinc-and the results are shown according to the change in the injection amount of the reaction temperature and the reaction product of chromite layer are shown in Table 1.

Analysis of the reaction was performed by gas chromatography using an OV-17 (10%) column.

TABLE 1

Example 2

A catalyst was prepared in the same manner as in Example 1, and the catalyst was charged and reduced in the same manner, and then the reaction temperature of zinc and chromite was charged at 380 ° C and the copper-chromite layer at 340 ° C. The reaction was carried out by injecting 100 gr of propylene glycol and ethylenediamine 1: 1 mixed reactant while changing the amount of flow gas with respect to the amount (weight: gr) of the reaction mixture while changing the result, and the results are shown in Table 2.

TABLE 2

Example 3

Zinc-chromite 200gr was prepared by the method of Example 1 and charged in the same reactor as in Example 1, and then the catalyst was reduced to 400 ° C under the same conditions, followed by reaction by injecting the reaction mixture 100gr per hour at the reaction temperature of 380 ° C. As a result, the reaction conversion of propylene glycol and ethylenediamine was about 90%, respectively, and the selectivity to methylpyrazine was 30% and the yield was low as 27%. At this time, the most produced side reaction was methyl piperazine, and the yield was 55%.

Example 4

The copper-chromite catalyst 200gr was prepared in the same manner as in Example 1, charged in the same reactor as in Example 1, and the catalyst was reduced to 350 ° C. under the same conditions. . As a result, the reaction conversion rate of propylene glycol and ethylenediamine was 75%, the selectivity to methylpyrazine was 70%, the yield was low as 65%, and pyrazine was produced as a side reaction 30%.

Example 5

A zinc-chromite catalyst and a copper-chromite catalyst were prepared in the same manner as in Example 1, and two 1 "SUS tubular reactors were filled with 100 gr each, and the reactor filled with zinc-chromite catalyst was connected to a preheater and copper The reactor packed with the chromite catalyst was connected in series with the reactor packed with the zinc-chromite catalyst and then reduced in the same manner as in Example 1. The temperature of the zinc-chromite catalyst layer on the reduced catalyst was reduced to 380. Maintaining the temperature and the temperature of the copper-chromite layer at 350 ° C while injecting 100 gr of the reaction mixture per hour, the synthesis of methylpyrazine resulted in the conversion of propylene glycol and ethylene thiamine to about 100%, and the selectivity to methylpyrazine was 89.3. The yield was above 89%.

When Examples 1 and 5 were compared to Examples 3 and 4, when the zinc-chromite catalyst and the copper-chromite catalyst were used in the double catalyst bed or the two-stage reactor as in Examples 1 and 5, each catalyst was used alone. It can be seen that the yield of methylpyrazine increases when used as. This is because, as shown in Example 3, the zinc-chromite catalyst has a high reaction conversion rate, but the dehydrogenation activity is relatively low so that the reaction is stopped in methylpiperazine. In Example 4, the copper-chromite catalyst is high in the dehydrogenation reaction. This is because it has activity but is easily deactivated by water generated during the reaction, and the overall reaction conversion rate is lowered.

In the present invention, by using a double catalyst layer reactor and a two-stage reactor of zinc-chromite and copper-chromite, the conversion rate from the reactants to intermediates such as methylpiperazine in the zinc-chromite catalyst layer is controlled to the maximum, and copper-chromium is used. In the mite catalyst layer, not only the conversion of an intermediate such as methylpiperazine to methylpyrazine is increased, but also the unreacted reactant in the zinc-chromite catalyst can be converted back to methylpyrazine to maximize the reaction yield. On the other hand, when hydrogen was used as the gas, the conversion rate of the reactants and the selectivity for methylpyrazine increased not only when nitrogen gas was used alone, but also the activity of the catalyst was maintained according to the reaction time.

Claims (4)

Mixing the mixture of propylene glycol and ethylenediamine (molar ratio 1: 1) in a gaseous state in a gaseous mixture of hydrogen and an inert gas containing nitrogen and passing through a heated solid catalyst to separate the resulting methylpyrazine In the method of preparing methylpyrazine to be recovered, the hydrogen concentration in the flow gas is 0.1 or more in a molar ratio, and 100 ml-1000 ml of the flow gas is mixed per 1 g of the reaction mixture, and the solid catalyst phase is heated from low temperature to 350 ° C.-550 ° C. while the inert gas and the hydrogen are heated. The two types of catalysts, the reduced zinc-chromite and the reduced copper-chromite in the mixed gas stream of inert gas and hydrogen, are layered separately in a mixed gas stream of The reaction mixture first passes the zinc-chromite catalyst layer heated to 270 ° C.-550 ° C. at a space velocity of 0.05-3.0 per hour and then continuously 250 ° C.-450 ° C. The copper-chromite catalyst layer heated to < RTI ID = 0.0 > A method for producing methylpyrazine, characterized by passing at a space velocity of 05-3.0. The method of claim 1, wherein the zinc-chromite catalyst and the copper-chromite catalyst are sequentially charged to form a double layer in a single reactor. The method of claim 1, wherein the zinc-chromite catalyst and the copper-chromite catalyst are separately charged in different reactors, and a two-stage reactor in which these two reactors are connected in series is used. The zinc-chromite catalyst layer according to claim 1, 2 and 3, wherein the molar concentration of hydrogen in the flow gas is 0.3 or more and 200 ml-400 ml of the flow gas per 1 g of the reaction mixture is mixed. Method for producing methylpyrazine, characterized in that the temperature of the copper-chromite catalyst layer is 300 ℃ -400 ℃.