CN100384531C - A Fluidized Bed Catalyst for Preparation of Acrylonitrile by Ammoxidation - Google Patents

Abstract

The invention relates to a fluidized bed catalyst for producing acrylonitrile by ammoxidation of propylene, which mainly solves the problems in the prior art that the catalyst does not involve relatively high propylene load and high pressure. The present invention adopts a composition containing a silica carrier and having the following chemical formula in terms of atomic ratio: A _a B _b C _c D _{d We} Fe Fe _{f Big} Mo ₁₂ O _x ; in the formula, A is selected from Li, Na, K At least one of , Rb or Cs; B is selected from at least one of V, Cr, Ni or Co; C is selected from at least one of B, Tl or P; D is selected from the technical scheme of Ce and Sm Solved the problem well. The catalyst of the invention is especially suitable for use under relatively high reaction pressure and high propylene load conditions, can obtain relatively high acrylonitrile yield, and can be used in the industrial production of acrylonitrile.

Description

A Fluidized Bed Catalyst for Preparation of Acrylonitrile by Ammoxidation

technical field

The invention relates to a fluidized bed catalyst for preparing acrylonitrile by ammoxidation, in particular to a fluidized bed catalyst for preparing acrylonitrile by ammoxidation of propylene.

Background technique

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 composition 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 single-pass yield of acrylonitrile and an increase in production load.

After more than 40 years of development in the production of acrylonitrile by ammoxidation, the production capacity of the factory and the market demand are close to balance. At present, the main development trend of acrylonitrile production has shifted from focusing on the construction of new devices to the technical transformation of existing factories in order 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%, and the required investment is only 20-30% of that of the new plant, which is very economical. 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 higher propylene load and be able to withstand higher reaction pressure, and maintain a higher yield of acrylonitrile.

Theoretically, increasing the WWH of the catalyst should increase the adsorption and activation ability of the catalyst for propylene, but there is no report that a certain element in the catalyst can improve the adsorption and activation ability 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.

Above-mentioned catalyst can obtain higher yield of acrylonitrile, but the propylene loading of catalyst is lower, and the yield of acrylonitrile drops greatly under higher reaction pressure. 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 increases according to this regulation, which will affect the acrylonitrile single collection.

Documents US5093299 and US5212137 introduce a catalyst for the ammoxidation of propylene to acrylonitrile using a catalyst system of molybdenum, bismuth, iron, nickel, magnesium, potassium and cesium. According to the patent, its catalyst can be operated at generally slightly lower reaction temperature, and it has higher catalytic activity and excellent oxidation-reduction stability, so it is suitable for operation at a lower air/propylene ratio. However, it should be noted that the inspection conditions of the above-mentioned patent examples are fixed bed, 430°C reaction temperature, and there is no mention of the specific reaction pressure and operating load data in the experimental operation. The fixed bed investigation conditions are difficult to reflect the situation of fluidized bed operation.

Document Hei 8-27089 introduces a method for producing acrylonitrile, which uses catalysts of molybdenum, bismuth, iron, magnesium and tungsten to carry out the ammoxidation reaction of propylene. The investigation conditions in the examples of this document are normal pressure.

In terms of the yield of acrylonitrile at the initial stage of the reaction, the catalysts disclosed in the above patent documents have been greatly improved. However, none of the above-mentioned patents involves the data on the yield of acrylonitrile of the catalyst under higher propylene loading and higher reaction pressure.

Documents JP9401312 and CN1121321A disclose a catalyst for preparing acrylonitrile by ammoxidation of propylene containing at least one of molybdenum, bismuth, cerium, iron, nickel, magnesium or zinc, and at least one of potassium, cesium or rubidium. Introduced in this patent, its catalyst can effectively prevent the yield of acrylonitrile from decreasing when the reaction time is prolonged, but its catalyst evaluation is carried out under conditions of relatively low reaction pressure and low operating load.

Contents of the invention

The technical problem to be solved by the present invention is to provide a new fluidized bed catalyst for preparing acrylonitrile by ammoxidation, which is the problem of higher propylene load and higher reaction pressure that the catalyst does not involve in the prior art. The catalyst has a higher yield of acrylonitrile under higher propylene loading and higher reaction pressure.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is as follows: a fluidized bed catalyst for preparing acrylonitrile by ammoxidation, containing a silica carrier and a composition with the following chemical formula in terms of atomic ratio:

A _a B _b C _c D _d W _e Fe _{f Big} Mo ₁₂ O _x

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

B is selected from at least one of V, Cr, Ni or Co;

C is selected from at least one of B, T1 or P;

D is selected from Ce and Sm;

The value range of a is 0.01~1.5;

The value range of b is 0.1~12.0;

The value range of c is 0.01~3.0;

The value range of d is 0.01～3.5;

The value range of e is 0.01~3.0;

The value range of f is 0.1~7.0;

The value range of g is 0.01～3.0;

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 0.01-0.7, the preferred range of b is 3.0-8.5, the preferred range of c is 0.01-1.2, the preferred range of d is 0.01-2.0, and the preferred range of e is 0.01-2.0. The preferred range of values is 0.01-1.0, the preferred range of f is 0.5-3.0, and the preferred range of g is 0.1-1.5. The catalyst carrier is preferably silicon dioxide, and the preferred range of its usage 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.

For phosphorus, arsenic and boron in the catalyst, it is best to use corresponding acids or their ammonium salts; for germanium, germanium oxide is best; for tungsten and antimony, it is best to use corresponding oxides or their ammonium salts; for niobium, it is best to use nitrates and hydroxides and oxides; chromium is preferably chromium trioxide, chromium nitrate or a mixture of the two; the remaining components are preferably nitrates, hydroxides or salts that can be decomposed into oxides.

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 form a catalytically active phase and 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 8.8-9.8. 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 410-470°C, preferably 420-450°C. The catalyst of the present invention is suitable for a slightly lower reaction temperature than usual, high pressure and high load catalyst, so the reaction pressure in the production device can be above 0.08MPa, for example, 0.08-0.18MPa. If the reaction pressure is lower than 0.08MPa, there will be no adverse effect, and the yield of acrylonitrile can be further improved.

The propylene loading (WWH) of the catalyst of the present invention is 0.06-0.15 hr ^-1 , preferably 0.08-0.13 hr ^-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 too little catalyst addition 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 a high-purity acrylonitrile product.

The components of the catalyst of the present invention have a good synergistic effect, and at the same time, a composite oxidation-reduction pair is introduced in the catalyst, which accelerates the diffusion of gaseous oxygen into the bulk phase of the catalyst and oxygen in the bulk phase, so that the reacted catalyst can be rapidly oxidized , to restore the activity, which is beneficial to improve the activity and stability of the catalyst. Use catalyst among the present invention to carry out propylene ammoxidation reaction, can obtain higher acrylonitrile yield (up to 80.4%) under higher propylene loading (WWH is 0.11 hour ^-1 ) and higher reaction pressure (0.14MPa) ), and achieved good technical results.

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 440° C., the reaction pressure is 0.14 MPa, the raw material ratio (mole) is propylene:ammonia:air=1:1.2:9.8, and the propylene loading (WWH) of the catalyst is 0.11 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.

Detailed ways

【Example 1】

Mix 11.76 grams of cesium nitrate, 2.40 grams of sodium nitrate and 5.48 grams of potassium nitrate, add 30 grams of water and dissolve after heating to obtain material (A); 6.9 grams of phosphoric acid solution is weighed as material (B); 65.45 grams of ammonium tungstate and 856.5 grams of ammonium molybdate were dissolved in 700 grams of 60～90 ℃ hot water to obtain material (C); with 156.9 grams of bismuth nitrate, 534.5 grams of nickel nitrate, 376.6 grams of cobalt nitrate, 140.5 grams of cerium nitrate, 412.5 grams of ferric nitrate and 7.0 gram of samarium nitrate is mixed, and 550 grams of water is added, and after heating and dissolving, it is used as material (D).

Mix material (A) with 2475 grams of silica sol with a weight concentration of 40%, add materials (B), (C) and (D) in turn under stirring, and obtain a slurry after thorough stirring, and prepare The slurry is formed into microspheres in a spray dryer, and finally the internal diameter is 89 mm, and the length is 1700 mm (φ89 × 1700 mm) in a rotary roaster at 600 ° C for 2.0 hours. The composition is:

50% Mo ₁₂ Bi _0.8 Ce _0.8 Co _3.2 Fe _2.5 Ni _4.5 Na _0.15 K _0.2 Cs _0.15 W _0.6 Sm _0.1 P _0.15 O _x +50% SiO ₂ .

[Examples 2-7 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 440°C

Reaction pressure 0.14MPa

Catalyst loading 400 grams

Catalyst propylene loading (WWH) 0.11 hours ^-1

Raw material ratio (mole) C ₃ ⁼ /NH ₃ /air = 1/1.2/9.8

Claims (9)

1. A kind of ammoxidation prepares the fluidized bed catalyst of acrylonitrile, contains the following compositions in terms of atomic ratio chemical formula: A _a B _b C _c D _d W _e Fe _{f Big} Mo ₁₂ O _x In the formula, A is selected from at least one of Li, Na, K, Rb or Cs; B is selected from at least one of V, Cr, Ni or Co; C is selected from at least one of B, T1 or P; D is selected from Ce and Sm; The value range of a is 0.01~1.5; The value range of b is 0.1~12.0; The value range of c is 0.01~3.0; The value range of d is 0.01～3.5; The value range of e is 0.01~3.0; The value range of f is 0.1~7.0; The value range of g is 0.01～3.0; 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 fluidized bed catalyst for preparing acrylonitrile by ammoxidation according to claim 1, characterized in that the value range of a is 0.01～0.7. 3. The fluidized-bed catalyst for preparing acrylonitrile by ammoxidation according to claim 1, characterized in that the value of b ranges from 3.0 to 8.5. 4. The fluidized bed catalyst for preparing acrylonitrile by ammoxidation according to claim 1, characterized in that the value range of c is 0.01 to 1.2. 5. The fluidized bed catalyst for preparing acrylonitrile by ammoxidation according to claim 1, characterized in that the value range of d is 0.01-2.0. 6. The fluidized bed catalyst for preparing acrylonitrile by ammoxidation according to claim 1, characterized in that the value range of e is 0.01-1.0. 7. The fluidized bed catalyst for preparing acrylonitrile by ammoxidation according to claim 1, characterized in that the value of f ranges from 0.5 to 3.0. 8. The fluidized bed catalyst for preparing acrylonitrile by ammoxidation according to claim 1, characterized in that the value of g is in the range of 0.1 to 1.5. 9. The fluidized-bed catalyst for preparing acrylonitrile by ammoxidation according to claim 1, characterized in that the catalyst carrier is silicon dioxide, and its consumption is 40-60% by weight.