CN1094073C - Fluidized bed catalyst for production of acrylonitrile - Google Patents

Abstract

The invention relates to a fluidized bed catalyst for the production of acrylonitrile, which consists of a silica carrier and a composition with the following chemical formula in terms of atomic ratio: Mo ₁₂ Bi _a Fe _b W _c Pr _d Na _e X _f Y _g Z _h O In _{the i} formula, X is selected from at least one of P, As, B, Ge, Ga, Al, Sn, Pb, Cr, V, Nb or Tb; Y is selected from Co, Ni, Mn, Mg, Ca, Sr, Zn Or at least one of Cd; Z is selected from at least one of K, Rb, Cs, In, Tl, Sm or Te. The catalyst of the invention is particularly suitable for use under relatively high reaction pressure and high propylene loading conditions, and can maintain a high single yield of acrylonitrile, and can be used in industrial production.

Description

Fluidized bed catalyst for the production of acrylonitrile

The invention relates to a fluidized bed catalyst for producing acrylonitrile.

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.

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.

Document US4746753 introduces a process for preparing acrylonitrile by ammoxidation of propylene using a catalyst of alkali metal, molybdenum, bismuth, cerium and tungsten. It can be seen from its examples that its catalytic system is sodium-free, and although the metal element praseodymium (Pr) is mentioned in the optional elements, it is only used as an optional element. The embodiment does not disclose the combination of praseodymium and tungsten elements, and does not mention the specific reaction pressure and operating load data in the experimental operation.

Introduced a kind of manufacture method of acrylonitrile in the document flat 8-27089. It adopts catalysts of molybdenum, bismuth, iron, magnesium and tungsten to carry out the ammoxidation reaction of propylene. The investigation condition in the examples of this document is normal pressure, and there is no mention of the situation data under the condition of high pressure and high operating load.

The purpose of the present invention is to overcome the problems that the catalysts in the above documents cannot adapt to higher reaction pressure and operating load, and provide a new fluidized bed catalyst for producing acrylonitrile. The catalyst can be adapted to operate under higher reaction pressure and higher load conditions, and maintain a high single-pass yield of acrylonitrile.

The purpose of the present invention is achieved by the following technical solutions: a fluidized bed catalyst for the production of acrylonitrile is made up of a silicon dioxide carrier and a composition with the following chemical formula in atomic ratio:

Mo ₁₂ Bi _a Fe _b W _c Pr _d Na _e X _f Y _g Z _h O _i

In the formula, X is selected from at least one of P, As, B, Ge, Ga, Al, Sn, Pb, Cr, V, Nb or Tb;

Y is selected from at least one of Co, Ni, Mn, Mg, Ca, Sr, Zn or Cd;

Z is selected from at least one of K, Rb, Cs, In, Tl, Sm or Te.

The value range of a is 0.01~3.0;

The value range of b is 0.1~5.0;

The value range of c is 0.01~2.0;

The value range of d is 0.01～2.0;

The value range of e is 0.05~0.7;

The value range of f is 0.01～3.0;

The value range of g is 0.10～12.0;

The value range of h is 0.01～1.5;

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

Wherein the amount of carrier silicon dioxide in the catalyst is 30-70% by weight.

In the above technical solution, the preferred range of d is 0.01-1.0, the preferred range of c is 0.05-1.5, the preferred range of e is 0.1-0.5, the preferred range of f is 0.01-2.0, g The preferred range of values is 0.1-10.0, and the preferred range of h is 0.05-1.0. The amount of silicon dioxide in the catalyst 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; tungsten can use ammonium tungstate or tungsten oxide; germanium can use its oxide; vanadium can use ammonium metavanadate; 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 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 430-450°C. The catalyst of the present invention is a catalyst suitable for 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.

Since tungsten in the components is beneficial to increase the load, praseodymium can improve the performance of the catalyst at high reaction pressure, so remove some components that have a negative impact on the high pressure and high load reaction performance, increase the use of tungsten, and tungsten and praseodymium at the same time Using, the catalyst has the operating ability under the conditions of higher reaction pressure (0.14MPa) and higher load (WWH is 0.090 hours ^-1 ), and the single-pass yield of acrylonitrile reaches the highest level of 82%, which has achieved relatively good results. Good 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 catalyst loading is 550g, the reaction temperature is 440°C, the reaction pressure is 0.14MPa, the raw material ratio (mole) is propylene:ammonia:air=1:1.2:9.8, and the propylene loading (WWH) of the catalyst is 0.090h ^-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】

0.72 gram of cesium nitrate, 4.8 gram of sodium nitrate and 2.43 gram of potassium nitrate are mixed, add 30 grams of water, dissolve after heating, obtain material (A); Dissolve 18.67 gram of chromium trioxide in 8.4 gram of water, obtain material (B); Dissolve 19.4 grams of ammonium tungstate in 100 milliliters of 5% ammonia by weight, dissolve 395.2 grams of ammonium molybdate in 325 grams of hot water at 50-90°C, and mix the two solutions to obtain material (C); 90.4 grams of nitric acid Mix bismuth, 4.91 grams of niobium oxide, 2.45 grams of praseodymium nitrate, 434 grams of nickel nitrate and 150.8 grams of ferric nitrate, add 70 grams of water, dissolve after heating, and obtain material (D).

Material (A) is mixed with 1250 grams of silica sol with a weight concentration of 40%, and materials (B) and (C) and (D) are added under stirring, fully stirred to obtain a slurry, and the prepared slurry is prepared according to the usual method It is formed into microspheres in a spray dryer, and finally the inner diameter is 89 mm, and the length is 1700 mm (φ89 × 1700 mm) in a rotary roaster. Roasting at 630 ° C for 1 hour, the catalyst composition is: 50% Mo ₁₂ Bi _1.0 Fe _2.0 W _0.45 Pr _0.05 Na _0.3 Ni _8.0 Cr _1.0 Nb _0.2 K _0.13 Cs _0.02 O ₁ +50% SiO ₂ . [Examples 2-9 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:

    φ38 mm fluidized bed reactor

Reaction temperature 440℃

  Reaction pressure 0.14MPa

    Catalyst loading capacity 550g

Catalyst propylene loading (WWH) 0.090 hours ^-1

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

Table 1 Example Catalyst Composition Acrylonitrile yield% Example 1 Mo ₁₂ Bi _1.0 Fe _2.0 W _0.45 Pr _0.05 Na _0.3 Ni _8.0 Cr _1.0 Nb _0.2 K _0.13 Cs _0.02 O _i 80.3 Example 2 Mo ₁₂ Bi _1.0 Fe _2.0 W _0.45 Pr _0.1 Na _0.3 Ni _8.0 Cr _0.5 Ga _0.5 K _0.05 Cs _0.05 Tl _0.05 O _i 81.4 Example 3 Mo ₁₂ Bi _1.0 Fe _2.0 W _0.75 Pr _0.2 Na _0.3 Ni _8.0 Ge _0.05 Al _0.5 Cs _0.15 Tl _0.05 O _i 80.0 Example 4 Mo ₁₂ Bi _1.0 Fe _2.0 W _0.75 Pr _0.25 Na _0.3 Ni _6.0 Mn _2.0 Ge _0.1 Nb _0.1 Cr _1.0 K _0.08 Cs _0.12 O _i 79.9 Example 5 Mo ₁₂ Bi _1.0 Fe _2.0 W _1.0 Pr _0.75 Na _0.3 Ni _6.0 Mn _2.0 Ga _0.1 Cr _0.75 Ge _0.5 K _0.1 Cs _0.05 Tl _0.15 O _i 81.9 Example 6 Mo ₁₂ Bi _1.0 Fe _2.0 W _0.75 Pr _0.15 Na _0.3 Ni _8.0 Cr _0.5 Ge _0.08 K _0.15 Rb _0.08 Tl _0.12 O _i 80.7 Example 7 Mo ₁₂ Bi _1.0 Fe _2.0 W _0.45 Pr _0.2 Na _0.3 Ni _8.0 Nb _0.1 Cr _0.8 Ge _0.2 Rb _0.05 Cs _0.15 Tl _0.05 O _i 79.5 Example 8 Mo ₁₂ Bi _1.0 Fe _2.0 W _0.45 Pr _0.5 Na _0.3 Ni _6.0 Ca _2.0 Cr _0.5 Ge _0.5 K _0.08 Cs _0.05 Tl _0.15 O _i 82.0 Example 9 Mo ₁₂ Bi _1.0 Fe _2.0 W _0.1 Pr _0.1 Na _0.3 Ni _6.0 Ca _2.0 Cr _0.8 Ga _0.1 K _0.1 Rb _0.05 Cs _0.03 O _i 80.5 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 O _i 76.8 Comparative example 2 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 Oi} 76.2 Comparative example 3 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 O _i 77.1 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 O _i 77.4

Claims (8)

1, a kind of fluid catalyst of producing vinyl cyanide, form by silica supports with the following composition of atomic ratio measuring chemical formula:

Mo ₁₂Bi _aFe _bW _cPr _dNa _eX _fY _gZ _hO _i

X is selected among P, As, B, Ge, Ga, Al, Sn, Pb, Cr, V, Nb or the Tb at least a in the formula;

Y is selected among Co, Ni, Mn, Mg, Ca, Sr, Zn or the Cd at least a;

Z is selected among K, Rb, Cs, In, Tl, Sm or the Te at least a.

The span of a is 0.01～3.0;

The span of b is 0.1～5.0;

The span of c is 0.01～2.0;

The span of d is 0.01～2.0;

The span of e is 0.05～0.7;

The span of f is 0.01～3.0;

The span of g is 0.10～12.0;

The span of h is 0.01～1.5;

I satisfies the required Sauerstoffatom sum of each element valence in the catalyzer;

Wherein the amount of carrier silicon-dioxide is 30～70% by weight percentage in the catalyzer.

2, according to the fluid catalyst of the described production vinyl cyanide of claim 1, the span that it is characterized in that d is 0.01～1.0.

3, according to the fluid catalyst of the described production vinyl cyanide of claim 1, the span that it is characterized in that c is 0.05～1.5.

4, according to the fluid catalyst of the described production vinyl cyanide of claim 1, the span that it is characterized in that e is 0.1～0.5.

5, according to the fluid catalyst of the described production vinyl cyanide of claim 1, the span that it is characterized in that f is 0.01～2.0.

6, according to the fluid catalyst of the described production vinyl cyanide of claim 1, the span that it is characterized in that g is 0.1～10.

7, according to the fluid catalyst of the described production vinyl cyanide of claim 1, the span that it is characterized in that h is 0.05～1.0.

8, according to the fluid catalyst of the described production vinyl cyanide of claim 1, the amount that it is characterized in that silicon-dioxide in the catalyzer is 40～60% by weight percentage.