CN1099316C - Catalyst for acrylonitrile fluid bed - Google Patents

Abstract

The present invention relates to a fluidized bed catalyst for acrylonitrile, which contains a silica carrier and a composition with the following chemical formula in terms of atomic ratio: A _a B _b C _c Ge _d Na _e Mg _f Fe _g Bi _h Mo _i O _x formula In which A is selected from at least one of Li, K, Rb, Cs or Sm; B is selected from at least one of Sr, Ba, Pb, V, Cr, Mn or Ni; C is selected from B, P or As at least one. The catalyst of the invention is especially suitable for use under the conditions of lower reaction temperature, higher reaction pressure and high propylene load, and can maintain a high single yield of acrylonitrile, and can be used in industrial production.

Description

Acrylonitrile Fluidized Bed Catalyst

The present invention relates to an acrylonitrile fluidized bed catalyst.

Acrylonitrile is an important organic chemical raw material, which is produced by ammoxidation of propylene. In order to obtain a fluidized bed catalyst with high activity and high selectivity, people have made a series of improvements through continuous exploration. Most of these improvements involve the active part of the catalyst, focusing on the combination of the active components of the catalyst to improve the activity and selectivity of the catalyst, thereby achieving an increase in the yield of acrylonitrile per pass and an increase in production load.

After more than 30 years of development in the production of acrylonitrile by ammoxidation, the production capacity of the factory has reached a close balance with the market demand. At present, the main development trend of acrylonitrile production has shifted from the construction of new devices to the transformation of existing factories, so as to further reduce raw material consumption and increase production capacity. Through the transformation of the original factory, the replacement of high-efficiency catalysts and the elimination of bottlenecks in the production process, the production capacity of acrylonitrile may be increased by 50-80%, while the required investment is only 20-30% of that of the new equipment, and the economic benefits are very high. huge.

There will be two problems in the transformation of the factory: ①The reaction pressure of the fluidized bed reactor will rise; ②The loading of the catalyst should not be too much. For this reason, the catalyst required to be replaced should have a higher propylene load and be able to withstand a higher reaction pressure.

The reaction pressure of the fluidized bed reactor is determined by the resistance drop of a series of heat exchangers, towers and pipes between the outlet of the reactor and the top of the absorption tower. Due to the increase in production capacity, the amount of material at the outlet of the reactor increases significantly, which increases the above-mentioned resistance drop. In addition, if the heat transfer area of each heat exchanger is not enough, it is necessary to increase the heat exchange equipment to further increase the resistance drop. Due to environmental protection requirements, the reaction waste gas at the top of the absorption tower is not allowed to be directly discharged into the atmosphere, but must be sent to the furnace for burning. In this way, if the induced draft fan is not used, the pressure at the top of the absorption tower must be increased. Due to the above reasons, the current operating pressure of the reactor is 0.5 to 1.0 times higher than the design value, that is, it reaches more than 0.08MPa.

The second problem mentioned above is the loading of the catalyst, ie WWH. It is defined as how many tons of propylene can be processed per ton of catalyst per hour. Due to the increase in the feed to the reactor, if the catalyst load remains unchanged, the catalyst loading should also increase accordingly. However, the height of the cooling water pipe in the originally designed fluidized bed reactor is not enough, so the fluidization height of the catalyst in the reactor may exceed the height of the cooling water pipe. In addition, due to the increased feed to the reactor, the operating line speed is also significantly increased. The combined effect of these two changes may increase the temperature of the dilute phase in the reactor, resulting in an increase in the generation of carbon dioxide and a decrease in the selectivity of acrylonitrile. Therefore, a higher WWH of the catalyst can prevent the above-mentioned problems. In addition, if the reaction temperature can be effectively reduced, energy consumption can be reduced on the one hand, and reaction conditions can be improved on the other hand, so as to achieve the purpose of increasing the yield of acrylonitrile.

Theoretically, increasing the WWH of the catalyst should increase the adsorption capacity of the catalyst for propylene, but there is no theory that a certain element in the catalyst can improve the adsorption capacity for propylene. Propose the catalyst of following composition in document CN1021638C:

A _a B _b C _c Ni _d Co _e Na _f Fe _g Bi _h M _i Mo _j O _x

Among them, A is potassium, rubidium, cesium, samarium, thallium; B is manganese, magnesium, strontium, calcium, barium, lanthanum, rare earth elements; C is phosphorus, arsenic, boron, antimony, chromium; M is tungsten, vanadium.

The above-mentioned catalyst can obtain higher single yield of acrylonitrile, but the propylene load of the catalyst is lower, and the single yield of acrylonitrile decreases greatly under higher reaction pressure. Further studies have shown that components B and M in the above catalyst are related to the loading of the catalyst and the performance under high pressure. Although some elements in component B have an effect on improving the single absorption of acrylonitrile, they have a negative impact on the improvement of the catalyst load and the performance of high reaction pressure, which is not conducive to the catalyst's ability to adapt to higher pressure and operate under higher load conditions. In addition, in CN1021638C, it was stipulated that in the above-mentioned catalyst composition, the sum of i and j is 12, which is a constant. In the present invention, this regulation is canceled, because the molybdenum component will decrease when the M component is increased according to this regulation, which will affect the single collection of acrylonitrile.

Documents US5688739 and US5770757 introduce a germanium-containing ammoxidation catalyst to obtain a high yield of acrylonitrile. Adopt molybdenum, bismuth, germanium system in this document, contain alkali metal in the optional element, but do not disclose the example containing sodium in the embodiment, only disclosed in this document in addition that reaction pressure is the reaction condition of normal pressure, does not have under high pressure, Specific investigation data under high load conditions. A catalyst for the production of acrylonitrile or methacrylonitrile is described in document US5212137. This document adopts the catalyst technical scheme containing Mo-Bi-Fe-Ni-Mg-K-Cs, discloses the fixed bed reaction performance data at 430°C, and does not disclose the fluidized bed performance under high pressure and high load conditions data.

The purpose of the present invention is to overcome the problem that the catalyzer that exists in the above-mentioned literature does not relate to the problem of adapting to higher reaction pressure, high operating load and reaction performance under low reaction temperature conditions, to provide a kind of new ammoxidation of propylene to produce acrylonitrile fluidized bed catalyst. The catalyst can be adapted to operate under the conditions of higher reaction pressure, higher load, lower reaction temperature and lower air/propylene ratio, and maintain a high single-pass yield of acrylonitrile.

The object of the present invention is achieved by the following technical scheme: a kind of acrylonitrile fluidized bed catalyst is made up of the following compositions in terms of atomic ratio chemical formula:

A _a B _b C _c Ge _d Na _e Mg _f Fe _g Bi _h Mo _i O _x

In the formula, A is selected from at least one of Li, K, Rb, Cs or Sm;

B is selected from at least one of Sr, Ba, Pb, V, Cr, Mn or Ni;

C is selected from at least one of B, P or As;

The trustworthiness range of a is 0.01~1.5;

The value range of b is 0.1~8.0;

The value range of c is 0.1~0.6;

The value range of d is 0.01～1.0;

The value range of e is 0.01~0.7;

The value range of f is 0.8～7.5;

The value range of g is 0.1～8.0;

The value range of h is 0.5～1.0;

The value range of i is 12.0~14.5;

x is the total number of oxygen atoms required to satisfy the valence of each element in the catalyst;

Wherein the catalyst carrier is selected from silicon dioxide, aluminum oxide or a mixture thereof, and the amount thereof is 30-70% by weight.

In the above technical solution, the preferred range of a is 0.01 to 0.7, the preferred range of d is 0.10 to 0.15, the preferred range of e is 0.05 to 0.5, the preferred range of f is 1.0 to 7.0, and the preferred range of g is The preferred range of value is 1.0-3.0. The catalyst carrier is preferably silicon dioxide, and its amount is 40-60% by weight.

The preparation method of the catalyst of the present invention has no special requirements, and can be carried out by conventional methods. First, each component of the catalyst is made into a solution, and then mixed with a carrier to make a slurry, which is spray-dried and formed into a microsphere, and finally calcined to make a catalyst. The preparation of slurry is preferably carried out according to CN1005248C method.

The raw material of making catalyst of the present invention is:

The molybdenum component in the catalyst is molybdenum oxide or ammonium molybdate.

Phosphorus, arsenic and boron in the catalyst are preferably corresponding acids or their ammonium salts; vanadium can be ammonium metavanadate; germanium is its oxide; chromium is preferably chromium trioxide, chromium nitrate or a mixture of the two; The nitrates, oxides, or salts that can be decomposed into oxides can be used as part of the solution, but water-soluble nitrates are preferred.

As the raw material of carrier silica, silica sol, silica gel or a mixture of the two can be used. If silica sol is used, its quality will meet the requirements of CN1005248C.

The prepared slurry is heated and concentrated to a solid content of 47-55%, and then spray-dried. The spray dryer can be of pressure type, two-flow type or centrifugal rotary disc type, but the centrifugal type is better, which can ensure that the prepared catalyst has a good particle size distribution.

The calcination of the catalyst can be divided into two stages: the decomposition of the salts of each element in the catalyst and high-temperature calcination. The temperature of the decomposition stage is preferably 200-300° C., and the time is 0.5-2 hours. The firing temperature is 500-800°C, preferably 550-700°C; the firing time is 20 minutes to 2 hours. The above-mentioned decomposition and roasting are carried out separately in two roasting furnaces, or one furnace can be divided into two areas, and decomposition and roasting can be completed simultaneously in a continuous rotary roasting furnace. During the catalyst decomposition and roasting process, an appropriate amount of air should be introduced to prevent the catalyst from being excessively reduced.

The specifications of propylene, ammonia and molecular oxygen required to produce acrylonitrile by adopting the catalyst of the present invention are the same as using other ammoxidation catalysts. Although the content of low-molecular saturated hydrocarbons in the raw material propylene has no influence on the reaction, the propylene concentration is preferably greater than 85 mol% from an economic point of view. Ammonia can be used as fertilizer grade liquid ammonia. The molecular oxygen required for the reaction can be pure oxygen, enriched oxygen and air from a technical point of view, but it is best to use air from economic and safety considerations.

The molar ratio of ammonia and propylene entering the fluidized bed reactor is between 0.8-1.5, preferably 1.0-1.3. The molar ratio of air to propylene is 8-10.5, preferably 9.0-9.8. If a higher air ratio is required for some operational reasons, it can be increased to 11 without significant impact on the reaction. However, in consideration of safety, the excess oxygen in the reaction gas cannot be greater than 7% (volume), preferably not greater than 4%.

When the catalyst of the present invention is used in a fluidized bed reactor, the reaction temperature is 420-470°C, preferably 425-450°C. The catalyst of the present invention is a catalyst suitable for low temperature, high pressure and high load, so the reaction pressure in the production device can be above 0.08 MPa, for example, 0.08-0.15 MPa. If the reaction pressure is lower than 0.08MPa, there will be no adverse effect, and the single yield of acrylonitrile can be further improved.

The propylene loading (WWH) of the catalyst of the present invention is 0.06 to 0.15 hours ^-1 , preferably 0.07 to 0.10 hours ^-1 . Too low a load not only wastes the catalyst, but also increases the amount of carbon dioxide produced and reduces the selectivity, which is unfavorable. Too high a load has no practical significance, because the addition of too little catalyst will make the heat transfer area of the cooling water pipe in the catalyst layer smaller than the area required to remove the heat of reaction, resulting in uncontrollable reaction temperature.

The product recovery and refining process for producing acrylonitrile with the catalyst of the present invention can use the existing production process without any modification. That is, the effluent gas from the fluidized bed reactor passes through the neutralization tower to remove unreacted ammonia, and then absorbs all the organic products with low-temperature water. The absorption liquid is extracted and distilled, dehydrocyanic acid and dehydrated to obtain high-purity acrylonitrile products.

In the present invention, by adding component germanium to the catalytic system of molybdenum, bismuth, iron and sodium, it is found that the catalytic system has the operating ability under the conditions of higher reaction pressure (0.14MPa) and higher load (WWH is 0.085 hours ^-1 ) , and then adding component magnesium to the catalyst system, it was found that the catalyst system still had high catalytic activity and selectivity at a reaction temperature of 430°C; ℃, a higher pressure of 0.14MPa, a higher load of 0.085 hours ^-1 and a lower air/propylene ratio of 9.5:1 (mole), the highest single-pass yield of acrylonitrile can reach 80.2%, which has achieved good results. Effect.

The activity evaluation of the catalyst of the present invention is carried out in a fluidized bed reactor with an inner diameter of 38 mm. The loading amount of the catalyst is 400 g, the reaction temperature is 430° C., the reaction pressure is 0.14 MPa, the raw material ratio (mole) is propylene: ammonia: air = 1: 1.2: 9.5, and the propylene loading (WWH) of the catalyst is 0.085 hours ⁻¹ .

In the present invention, the definition of propylene conversion rate, acrylonitrile selectivity and single-pass yield is as follows:

Below by embodiment the present invention will be further elaborated. 【Example 1】

Mix 2.02 grams of cesium nitrate, 4.21 grams of sodium nitrate, 0.96 grams of rubidium nitrate and 2.28 grams of potassium nitrate, add 30 grams of water and heat to dissolve to obtain material (A); 6.85 grams of germanium dioxide and 412.6 grams of ammonium molybdate are dissolved in 350 In 60～90 ℃ hot water, obtain material (B); Mix 66.8 grams of bismuth nitrate, 278.5 grams of nickel nitrate, 194.3 grams of magnesium nitrate, 21.8 grams of manganese nitrate, 31.4 grams of lead nitrate and 206.5 grams of iron nitrate, add 180 grams of water , as material (C) after heating and dissolving; 4.42 grams of phosphoric acid solution was weighed as material (D).

Mix the material (A) with 1285 grams of silica sol with a weight concentration of 40%, add the materials (B), (C), (D) and (E) in turn under stirring, and obtain a slurry after fully stirring. The prepared slurry is formed into microspheres in a spray dryer, and finally roasted at 575 ° C for 1.5 hours in a rotary roaster with an inner diameter of 89 mm and a length of 1700 mm (φ89 × 1700 mm) to form a composition. 55% K _0.1 Rb _0.025 Cs _0.05 P _{0.025 Ni 5.0} Mn 0.1 Pb _0.25 Ge _0.15 Na _0.20 Mg _2.0 Fe _2.5 Bi _0.50 Mo _12.5 O _x +45% SiO ₂ . [Examples 2-8 and Comparative Examples 1-4]

Catalysts with different compositions in the following table were prepared by the same method as in Example 1, and the ammoxidation of propylene to acrylonitrile was carried out with the prepared catalyst under the following reaction conditions. The results are shown in Table 1.

The reaction conditions of above-mentioned embodiment and comparative example are:

      φ38mm Fluidized Bed Reactor

  Reaction temperature 430°C

     Reaction pressure 0.14MPa

    Catalyst loading capacity 400 grams

Catalyst propylene loading (WWH) 0.085 hours ^-1

Raw material gas ratio (mole) C ₃ ⁼ /NH ₃ /air = 1/1.2/9.5

Table 1 Example Catalyst Composition Acrylonitrile yield% Acrylonitrile selectivity % Propylene conversion % Example 1 K _0.1 Rb _0.025 Cs _0.05 P _0.025 Ni _5.0 Mn _0.1 Pb _0.25 Ge _0.15 Na _0.20 Mg _2.0 Fe _2.5 Bi _0.5 Mo _{12.5 Ox} 80.2 81.6 98.3 Example 2 K _0.125 Cs _0.10 P _0.030 Ni _2.5 V _0.5 Mn _0.1 Pb _0.20 Ge _0.15 Na _0.20 Mg _2.5 Fe _3.0 Bi _0.5 Mo _{12.5 Ox} 79.8 81.4 98.0 Example 3 K _0.15 Rb _0.025 Cs _0.065 P _0.05 Ni _4.5 Mn _0.15 Cr _0.45 Ge _0.10 Na _0.20 Mg _2.5 Fe _2.5 Bi _0.75 Mo _{12.5 Ox} 79.6 81.4 97.8 Example 4 Li _0.05 K _0.125 Cs _0.05 B _0.02 As _0.015 Ni _5.0 Cr _0.35 Pb _0.15 Ge _0.15 Na _0.20 Mg _2.0 Fe _2.0 Bi _0.5 Mo _{12.5 Ox} 80.0 81.6 98.0 Example 5 K _0.15 Cs _0.075 P _0.025 Ni _2.5 V _1.5 C _r0.40 Pb _0.25 Ge _0.10 Na _0.15 Mg _2.5 Fe _2.5 Bi _0.5 Mo _{12.5 Ox} 79.6 81.6 97.6 Example 6 Li _0.05 K _0.125 Rb _0.05 B _0.02 P _0.025 Ni _3.5 V _1.0 Sm _0.1 Ge _0.15 Na _0.20 Mg _2.5 Fe _2.0 Bi _0.5 Mo _{12.5 Ox} 80.1 81.7 98.0 Example 7 K _0.1 Rb _0.05 Cs _0.025 As _0.030 Ni _5.0 Cr _0.25 Pb _0.25 Ge _0.15 Na _0.20 Mg _2.0 Fe _2.5 Bi _1.0 Mo _{12.5 Ox} 79.7 81.0 98.4 Example 8 Li _0.05 K _0.125 Rb _0.05 P _0.02 As _0.015 Ni _4.5 Sm _0.15 Mn _0.15 Ge _0.15 Na _0.20 Mg _2.5 Fe _2.5 Bi _1.0 Mo _{12.5 Ox} 79.9 82.0 97.4 Comparative example 1 Mo ₁₂ Bi _0.9 Fe _1.8 Ni _2.0 Co _5.0 Na _0.15 Mn _0.45 Cr _0.45 K _0.17 Cs _{0.05 Ox} 76.3 Comparative example 2 Mo ₁₂ Bi _0.9 Fe _1.8 Ni _2.4 Co _4.3 Na _0.15 W _0.45 Cr _0.45 K _0.15 Cs _{0.07 Ox} 76.6 Comparative example 3 Mo ₁₂ Bi _0.9 Fe _1.8 Ni _2.0 Co _5.0 Na _0.15 Mn _0.45 Cr _0.45 K _{0.21 Ox} 75.7 Comparative example 4 Mo ₁₂ Bi _0.9 Fe _1.8 Ni _5.0 Mg _2.0 Na _0.15 W _0.45 Cr _0.45 Cs _{0.09 Ox} 76.9

Claims (7)

1. An acrylonitrile fluidized bed catalyst is composed of a composition with the following chemical formula in terms of atomic ratio: A _a B _b C _c Ge _d Na _e Mg _f Fe _g Bi _h Mo _i O _x In the formula, A is selected from at least one of Li, K, Rb, Cs or Sm; B is selected from at least one of Sr, Ba, Pb, V, Cr, Mn or Ni; C is selected from at least one of B, P or As; The value range of a is 0.01~1.5; The value range of b is 0.1~8.0; The value range of c is 0.1~0.6; The value range of d is 0.01～1.0; The value range of e is 0.01~0.7; The value range of f is 0.8～7.5; The value range of g is 0.1~8.0; The value range of h is 0.5~1.0; The value range of i is 12.0~14.5; x is the total number of oxygen atoms required to satisfy the valence of each element in the catalyst; Wherein the catalyst carrier is selected from silicon dioxide, aluminum oxide or a mixture thereof, and the amount thereof is 30-70% by weight. 2. The acrylonitrile fluidized bed catalyst according to claim 1, characterized in that a ranges from 0.01 to 0.7. 3. The acrylonitrile fluidized-bed catalyst according to claim 1, characterized in that d ranges from 0.10 to 0.15. 4. The acrylonitrile fluidized-bed catalyst according to claim 1, characterized in that e ranges from 0.05 to 0.5. 5. The acrylonitrile fluidized bed catalyst according to claim 1, wherein the value of f ranges from 1.0 to 7.0. 6. The acrylonitrile fluidized bed catalyst according to claim 1, wherein the value of g ranges from 1.0 to 3.0. 7. The acrylonitrile fluidized bed catalyst according to claim 1, characterized in that the catalyst carrier is silicon dioxide, and the amount thereof is 40-60% by weight.