MXPA99011371A - A fluidized bed reactor for the ammoxidation of hydrocarbons - Google Patents

Abstract

Se provee un procedimiento para eliminar amoniaco sin reaccionar a partir de un efluente de un lecho de catalizador utilizado en una reacción de amoxidación de hidrocarburos;el procedimiento incluye el paso de proveer un reactor de lecho fluidizado;el reactor incluye el lecho de catalizador para hacer reaccionar el amoniaco y los hidrocarburos en el mismo;el reactor también incluye una fase de dilución del lecho de catalizador dispuesta sobre el lecho de catalizador;el reactor además incluye un conjunto de elementos internos colocados al menos de manera parcial en el lecho de catalizador;a[ menos de manera parcial, la fase de dilución del lecho de catalizador estácolocada en el conjunto de elementos internos;el reactor además incluye una entrada de un separador de ciclones de primera etapa dispuesta sobre el conjunto de elementos internos;el procedimiento también incluye un paso de eliminación de amoniaco sin reaccionar a partir del efluente del lecho de catalizador mediante el paso del efluente a través del conjunto de elementos internos;el amoniaco e hidrocarburos presentes en el efluente hacen contacto con la fase de dilución del lecho de catalizador y reaccionan en el mismo.

Description

FLUIDIZED BED REACTOR FOR AMOXIDATION OF HYDROCARBONS This invention relates to a fluidized bed reactor for the ammoxidation of hydrocarbons and, more particularly, to a fluidized bed reactor with internal elements installed near the upper region of the catalyst bed with the ability to improve efficiency of contact between the gas and the solid phase. It is an important issue in the petrochemical industry the production of unsaturated nitriles by ammoxidation procedure from hydrocarbons, including the ammoxidation of propylene and isobutene has been marketed much for the manufacture of acrylonitrile and methylacrylonitrile, respectively; and the ammoxidation of paraffinic hydrocarbons has also been under development. A common problem related to these reactions is due to the fact that unsaturated nitriles are usually unstable and unlikely to polymerize under basic conditions; therefore, for any ammoxidation, it is necessary to remove unreacted ammonia to from the product gases. To remove the unreacted ammonia, the prior art has employed a method by extinguishing sulfuric acid. This method will produce large amounts of waste water with ammonium sulfate containing nitrile, which is difficult to discard. The written legislation "^ '** ^' ^ 1 * '^ imposed for emissions in most ^ ^ ISES translated waste byproduct ammonium sulfate as a serious matter. Taking the ammoxidation of propylene to acrylonitrile as an example, the propylene, passing through a fluidized bed reactor along with ammonia and air, is oxidized ammonia to form a superior product acrylonitrile and some products including acetonitrile, hydrogen cyanide, acrolein, acrylic acid, carbon monoxide and dioxide carbon and small amounts of ammonia and unreacted propylene. After leaving the reactor, the gaseous effluent is cooled and then enters a column neutralization, where the unreacted ammonia is absorbed by aqueous sulfuric acid to produce ammonium sulfate. At the same time, the water vapor parts also condense, which causes the formation of waste water with ammonium sulfate. unreacted ammonia, the gas is introduced into an absorber, where all the organic compounds are absorbed from the gas by means of water at low temperature; then, the absorption liquid is sent to an acrylonitrile recovery and refining unit for the higher purity separation of acrylonitrile, hydrogen cyanide and acetonitrile. In the above described method of acrylonitrile production, is very important to remove unreacted ammonia with sulfuric acid from the effluent gas column neutralization as acrylonitrile and hydrogen cyanide are substances Hables to polymerization, especially in neutral and slightly alkaline conditions. This will not only cause a loss of acrylonitrile and hydrogen cyanide product, but will contaminate the equipment and produce waste water with ammonium sulfate. The composition of waste water with ammonium sulfate is complex, and approximately comprises the following groups: 1.- Polymers: Since the pH value of the circulating liquid in the neutralization column is controlled within the range of 2-7 , certain amount of products, such as acrylonitrile, hydrogen cyanide, acrolein, can be polymerized to form higher polymers. The losses caused by polymerization, calculated based on the total amount of its formation are: acrylonitrile 2-5%, hydrogen cyanide 3-8%, and acrolein up to 40-80%; therefore, the polymer content in the waste water with ammonium sulfate is very high. A wider molecular weight distribution is another characteristic of polymers present, ie, some low molecular weight polymers are soluble in the waste water with ammonium sulfate, but other polymers with higher molecular weight will form a black solid insoluble in water, which will cause the difficulty in the recovery of the sulphate of ammonium. 2.- High boiling point components: Since the operating temperature inside the neutralization column is around 80 ° C, the acrylic acid will be condensed from the effluent gas and will be present in the waste water with ammonium sulfate . Another component of »^^^^ = ^ * - High boiling point is cyanidrine, which is formed by condensation between carbonyl compounds and hydrogen cyanide. 3.- Low boiling components: Mainly acrylonitrile, acetonitrile and hydrogen cyanide, etc., dissolved in the waste water with ammonium sulfate, whose content is normally in the range of 500-5000 ppm, depending on the Spray liquid temperature. 4.- Fine catalyst particles: During the production of acrylonitrile in a fluidized bed reactor, the main part of fine particles of catalyst coming from the catalyst bed by the product gas is recovered by cyclones and recirculated to the bed. . However, a small amount of fine particles of catalyst will be expelled with air from the reactor by the effluent gas and then swept down in the neutralization column. The amount expelled from the catalyst is around 0.2-0.7 kg per tonne of acrylonitrile produced. Therefore, it is very difficult to recover the crystalline ammonium sulfate from the waste water with ammonium sulfate. Simply, the combustion of the effluents without prior recovery of the ammonium sulfate 20 from them will cause secondary pollution due to the formation of sulfur dioxide, which is forbidden to discharge directly into the atmosphere in most countries. Another problem related to the disposal of waste water with ammonium sulphate by the method of The combustion is a combustion temperature of 850 - 1100 ° C, required to burn the cyanides from the waste water, thus causing large amounts of fuel consumption. Since the sulfur dioxide contained in the flue gas is corrosive to steel, the use of waste heaters to recover heat energy is limited; In addition, the direct opening of the high temperature duct gas will cause thermal pollution in the atmospheric environment. In summary, the formation of ammonium sulfate in the production of acrylonitrile leads to a serious problem that has severely limited further development in the acrylonitrile manufacturing industry; therefore, the development of a clean process for the production of acrylonitrile that does not produce ammonium sulfate has become the point of interest in the world-wide technique. The key point of this clean procedure is to optimize the conversion of ammonia during production in order to eliminate the unreacted ammonia. The removal of unreacted ammonia can be achieved by two ways: one initiates with the catalyst to increase the ammonia conversion of the catalyst; the other starts with the ammoxidation reaction to allow the ammoxidation of propylene and the removal of unreacted ammonia to proceed separately. In addition, the increase in ammonia conversion of the propylene ammoxidation catalyst may be difficult to achieve. Just to take into account the ammoxidation, it is necessary that the catalyst has the f ^ s ^ t ^ ^ ^^ s ^ m &,. lower ability to decompose the ammonia, that is, to produce a higher yield of acrylonitrile while using a lower feed ratio of propylene with ammonia. If the catalyst has a greater decomposition ability for ammonia, the increase in ammonia consumption will make it more expensive; therefore, these two needs are contradictory. Since the ammonia conversion of the present catalyst is too low to increase the ammonia conversion of the catalyst to a certain level without increasing the ammonia consumption it still deserves attention. Since a certain amount of acrylic acid is also formed during the ammoxidation of propylene, it is not necessary to increase the ammonia conversion of the catalyst to 100%. For a conversion up to 97-98%, in essence, the addition of sulfuric acid for neutralization may be unnecessary. For example, Chinese patent 96116456.5 is an example in an effort to increase the ammonia conversion of the catalyst. From the point of view of the extended stable operation of the plant, the inventor believes that there must be other measures to achieve the complete elimination of the unreacted ammonia. This is due to the fact that the ability of a catalyst to decompose the ammonia is related to the time it has been used, and is also influenced by the operating conditions of the reactor that can not be maintained unchanged for long periods. The removal of unreacted ammonia by virtue of the propylene side reaction is a useful method and has been described in patents. U.S. Patent Nos. 5,457,223 and 5,466,857, Japanese Patent No. 96-27087 and WO 9625391 describe that methanol, acetonitrile and other oxidizable organic compounds, introduced into the dilution portion in the upper region of a fluidized bed reactor where propylene is ammoxidized with a mplibdeno-bismuth-iron system catalyst to synthesize acrylonitrile, can react with ammonia therein to form hydrogen cyanide and remove ammonia. Under optimum conditions the ammonia can be reacted completely; however, this method has the problem of oxygen decrease in the dilution phase of the reactor where oxygen is necessary to react the ammonia organic compounds, and therefore, the catalyst will be reduced in excess. As a result, the performance of a single step of acrylonitrile will decrease and the stability of the catalyst may also be affected. WO 9623766 describes another method by adjusting the molar ratio of the feed to the reactor to preserve the molar ratio of the organic acids formed, such as, for example, acrylic acid, etc., to the unreacted ammonia in the 0.8-3.0 scale . In this case, the unreacted ammonia will subsequently be combined with the organic acids to form the corresponding ammonium salts, whereby the need for sulfuric acid will be eliminated. The disadvantage of this method is the formation of unsaturated carbonyl compounds in large quantities together with the formation of organic acids. This will cause the difficulty for the recovery and refinement of acrylonitrile, as well as a decrease in the performance of a single step.

The inventor has identified, through a consistent and thorough review of the full scale of fundamental procedures in the synthesis of acrylonitrile in a fluidized bed reactor, that unreacted ammonia can be removed by resorting to the secondary reaction of propylene ammoxidation, even without the addition of any oxidizable organic compound. To overcome these and other deficiencies of the prior art, therefore, an object of the present invention is to provide a fluidized bed reactor for the ammoxidation of hydrocarbons, which contains a set of suitable internal elements, installed near the upper region of the catalyst bed, which has the ability to improve the contact efficiency between gases and solids therein, and serves to increase the ammonia conversion, thus decreasing the unreacted ammonia content in the effluent gas. The above mentioned internal elements include packages, deflectors and sieves, etc. These internal elements help to achieve a more uniform mixture between the reactive gas leaving the catalyst bed and the catalyst carried by the gas flow in the space above the catalyst bed, thus increasing the contact efficiency between the gas and the catalyst particles, which is beneficial in the subsequent reaction occurring in the zone of dilution phase and the elimination of the unreacted ammonia from the effluent gas. > ** rfUr-r-rrfüiaMga ¿^^^^^ .... y ^? M? ^? t ?? In the reactor, the internal elements are placed for baffles or sieves, with the bottom plate (sieve) below the surface of the catalyst to conserve the depth no more than 20% of the height of the fluidized bed. , while the upper side is not beyond the entrance of the first stage cyclone separator, preferably at the level of the dust hopper of the cyclone separator. For the packages, the positions of the upper and lower sides in the reactor are the same as described above. The packages used are made of screens generally limited to 10 mesh or more, with circular, cylindrical, square, rectangular, honeycomb and similar shapes, and with an empty factor (fractional free area) in the 20-80% scale, preferably on the 35-60% scale. The packages can be stored in packages inside the reactor in a random or regular manner. The special method can also be used, for example, to fix the packages by means of springs to allow them to vibrate under the action of the product gas flow to avoid depositing the catalyst on their surfaces. Baffles or sieves used include perforated grid-shaped plates, perforated plates, perforated plates with conical or pyramidal lid or grid plates, etc. The holes can have different geometric shapes, for example rectangular, triangular, circular, elliptical, etc., with an empty factor (fractional free area) in the range of 20-80%, preferably in the range of 35-65%. Baffles or sieves can also be placed on Afc ^^^ &asig horizontal position or at a certain inclination. For inclined positioning, the angle of inclination must be greater than the angle of repose of the catalyst to avoid the accumulation of the catalyst on its surface. The separation L between different layers of baffles or screens can be identical or different, depending on the internal diameter of the reactor D. UD can vary from 0.2 to 2.0. In the upper region of the catalyst bed of the fluidized bed reactor, the ammonia goes through a secondary reaction, accompanied by the formation of heat. Therefore, the ammonia conversion of the catalyst should not be too low to prevent the temperature in the upper part of the reactor rising too high. In this invention, the conversion of ammonia is required over 85%, preferably over 93%. All olefin ammoxidation catalysts, more preferably catalysts with molybdenum oxide as the main component, are applicable to this invention, such as the catalyst described in Chinese patent CN1021638C. Greater preference is given to a catalyst with higher ammonia conversion. The gas surface velocity in the fluidized bed reactor involves a ratio to the concentration of the catalyst in the dilution phase of the upper part of the reactor; It should be on a scale of 0.5-0.8 m / s, preferably on a scale of 0.6-0.75 m / s. The temperature in the upper reactor must be the same or close to the temperature of the catalyst bed. The reaction pressure depends on the activity of the catalyst used, usually in the range of 0.05-0.2 MPa.

This invention is the main part of a global manufacturing process of acrylonitrile which can minimize the formation of ammonium sulfate or not produce ammonium sulfate. After propylene, ammonia and air pass through the fluidized bed reactor of the invention, the product gas is cooled and enters an extinguishing column to achieve greater cooling, and then cooled to a sweeper, where all the organic matter is absorbed from the gas by the water at low temperature. The absorption liquid passes to an extraction column where the water is used as a solvent to separate the acrylonitrile from the acetonitrile. The distillation head with crude acrylonitrile leaving the column contains hydrogen cyanide and a small amount of water; then it passes through a column to remove the hydrogen cyanide and through a drain column, whereby the high purity acrylonitrile product is obtained. The present invention employs the side reaction occurring within the dilution phase of the fluidized bed reactor to remove the unreacted ammonia from the product gas, but does not add organic compounds at all. The effluent gas leaving the catalyst bed contains, in addition to acrylonitrile and byproducts such as acetonitrile, hydrogen cyanide, acrolein, acrylic acid, carbon monoxide, carbon dioxide, etc., a small amount of unreacted ammonia and propylene, which makes a contract with the catalyst present in the dilution phase of the fluidized bed to achieve a subsequent reaction. He ^ ^ ^ ^^^ unreacted ammonia reacts with byproduct of acrolein and residual propylene to form acrylonitrile, thereby increasing the production of acrylonitrile and decreasing the acrolein content; therefore, it has an advantage. Since the effluent gas leaving the catalyst bed does not rise uniformly and the internal elements installed in the dilution phase of the fluidized bed are available to achieve a more uniform mixture between the gas and the catalyst and increase the contact efficiency between the same, then the conversion of ammonia is increased to allow the content of unreacted ammonia to be lowered and good results obtained. The fluidized bed reactor of this invention is applicable to the ammoxidation of propane, propylene, isobutene and xylene, not only for the retrofitting of existing facilities, but for the development of new procedures. For the ammoxidation process, this invention can enhance productivity, increase reaction efficiency, simplify the process advancement diagram, decrease pollution in the environment, and therefore produce a higher economy. The invention will be illustrated in more detail by the following examples.

COMPARATIVE EXAMPLE 1 A catalyst of the same composition as in Example 1 of CN 102163C was used. The fluidized bed reactor was 38 mm in internal diameter and about 2 m in height; 550 g of catalyst were added with a catalyst bed height of 320 mm; the reaction temperature was 435 ° C, the reaction pressure 0.08 MPa, the feed ratio was propylene: ammonia: air = 1: 1.2: 9.8, and the feed scale of the gas mixture was 4.3 L / minute. The reaction result indicated a propylene conversion of 96.2%, one-step yield of acrylonitrile of 80.1%, selectivity of acrylonitrile of 83.3%, and ammonia conversion of 93%.

EXAMPLE 1 The same condition as in Comparative Example 1 was followed, except that five perforated plates were placed on top of the reactor, and the height of the first plate from the gas distributor to 300 mm, and the heights of the other four plates at 350, 400, 450 and 500 mm, respectively. The holes were 4 mm in diameter and the fraction of the plate consisting of a free area was 40%. The reaction result showed a propylene conversion of 98.5%, one-step yield of acrylonitrile of 81.7%, selectivity of acrylonitrile of 82.9%, and conversion of ammonia 96.2%.

¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡EXAMPLE 2 The same condition as in Example 1 was used, except that three identical perforated plates were placed, with the first plate placed at the same height as in Example 1 and the heights of the second and third plates at 400 and 500 mm, respectively. The reaction result showed a propylene conversion of 97.8%, one-step yield of acrylonitrile of 81.2%, selectivity of acrylonitrile of 83.0%, and ammonia conversion of 95.5%.

EXAMPLE 3 The same condition as in Example 1 was used, except that eight identical perforated plates were placed, with the first plate placed at the same height as in Example 1 and a plate spacing of 30 mm. The reaction result showed a propylene conversion of 98.8%, one-step yield of acrylonitrile of 81.7%, selectivity of acrylonitrile of 82.7% and ammonia conversion of 96.5%.

EXAMPLE 4 The same condition as in Example 2 (ie, adding three perforated plates) was used, except that the catalyst amount was 750 g and the feed scale of the gas mixture was increased to 6 l / min. The reaction result showed a propylene conversion of 98.7%, one-step yield of acrylonitrile of 81.8%, selectivity of acrylonitrile of 82.9% and ammonia conversion of 97.5%. 5 EXAMPLE 5 The same condition as in Example 1 was used, except that cylindrical packing made of steel sieves was placed in the reactor. stainless 10 x 6 mm mesh. The height of the lower part of the gaskets from the gas distributor was 300 mm and the length was 200 mm. The reaction result showed a propylene conversion of 98.8, one-step yield of acrylonitrile of 81.4%, selectivity of acrylonitrile of 82.4%, and ammonia conversion of 97.2%. From the example mentioned above it can be observed: 1. For the fluidized bed reactor with internal elements comprising packages or baffles according to the invention, the conversion of ammonia is increased by 4-5%, with a yield of a only acrylonitrile step, and the selectivity of acrylonitrile remains fixed. 2.- The increase in the number of baffles (sieves) or the height of the gaskets, as well as the adequate elevation of the gas feed scale, result in a better ammonia conversion. ? a ^ &^ e ^^^^^ t sa ^ Mi ^ a ^

Claims (5)

NOVELTY OF THE INVENTION CLAIMS

1. - A process for removing unreacted ammonia from an effluent of a catalyst bed used in a hydrocarbon ammoxidation reaction, comprising the steps of: a) providing a fluidized bed reactor, said reactor comprising: 1) a catalyst bed for reacting ammonia and hydrocarbons therein, 2) a dilution phase of the catalyst bed disposed on the catalyst bed, 3) a set of internal elements arranged at least partially in the dilution phase of the bed of catalyst, 4) an inlet of a first stage cyclone separator disposed on the set of internal elements; and b) removing the unreacted ammonia from the effluent of the catalyst bed by passing the effluent through the internal elements, where the ammonia and the hydrocarbons present in the effluent make contact with the dilution phase of the catalyst bed and react in the same.

2. The method according to claim 1, further characterized in that the set of internal elements are selected from the group consisting of packages, baffles, screens and combinations thereof. Figure

3. The process according to claim 1, further characterized in that a lower side of the set of internal elements is at a depth in the catalyst bed not greater than 20% of the total height of the catalyst bed. .

4. The process according to claim 1, further characterized in that the hydrocarbons are a compound selected from the group consisting of propane, propylene, isobutene, xylene and combinations thereof.

5. A process for removing unreacted ammonia from an effluent of a catalyst bed used in a hydrocarbon ammoxidation reaction, comprising the steps of: a) providing a fluidized bed reactor, said reactor comprising: ) a catalyst bed for reacting ammonia and hydrocarbons therein, 2) a dilution phase of the catalyst bed arranged on the catalyst bed, 3) a set of internal elements arranged at least partially in the dilution phase of the catalyst bed. catalyst bed; and b) removing the unreacted ammonia from the effluent of the catalyst bed by passing the effluent through the internal elements, where the ammonia and the hydrocarbons present in the effluent make contact with the dilution phase of the catalyst bed and react in the same. A process is provided for removing unreacted ammonia from an urefine effluent of catalyst used in a hydrocarbon ammoxidation reaction; the method includes the step of providing a fluidized bed reactor; the reactor includes the catalyst bed to react the ammonia and the hydrocarbons in the same; the reactor also includes a dilution phase of the catalyst bed disposed on the catalyst bed; the reactor further includes a set of internal elements placed at least partially in the catalyst bed; at least partially, the dilution phase of the catalyst bed is placed in the set of internal elements; the reactor further includes an inlet of a first stage cyclone separator disposed on the set of internal elements; the process also includes a step of eliminating unreacted ammonia from the effluent of the catalyst bed by passing the effluent through the set of internal elements; the ammonia and hydrocarbons present in the effluent make contact with the dilution phase of the catalyst bed and react therein. IM / fpm * sff P99 / 1656F