TW201605772A - Control of ammonia feed for ammoxidation reactor - Google Patents

Abstract

A process and system are provided for controlling an amount of ammonia and/or air provided to an ammoxidation reactor. The process includes maintaining a pH of a quench water bottoms and adjusting an amount of ammonia in a reactor feed to provide an ammonia to hydrocarbon ratio of about 1 to about 2 in the reactor feed. Further, the process may include adjusting an amount of air the reactor feed to provide an air to hydrocarbon ratio of about 9 to about 10 in the reactor feed.

Description

Control of ammonia feed for ammonia oxidation reactor Field of invention

A process for controlling the amount of ammonia and/or air provided to an ammoxidation reactor is provided. More specifically, the process includes maintaining the pH of the bottom of the quench water and adjusting the amount of ammonia in the reactor feed to provide an ammonia to hydrocarbon ratio of from about 1 to about 2 in the reactor feed. Additionally, the process can include adjusting the amount of air in the reactor feed to provide a ratio of air to hydrocarbon of from about 9 to about 10 in the reactor feed.

Background of the invention

In the commercial manufacture of acrylonitrile, propylene, ammonia and oxygen are reacted together according to the following reaction scheme: CH ₂ =CH-CH ₃ +NH ₃ +3/2O ₂ →CH ₂ =CH-CN+3H ₂ O

This process, commonly referred to as ammoxidation, is carried out in the gas phase at elevated temperatures (e.g., 350 ° C to 480 ° C) in the presence of a suitable fluidized bed ammoxidation catalyst.

Figure 1 shows a typical acrylonitrile reactor for carrying out the process. As shown here, reactor 10 includes a reactor housing 12, an air grill 14, a feed sprinkler 16, a cooling coil 18, and a cyclone 20. Process air is charged into reactor 10 through air inlet 22 during normal operation At the same time, a mixture of propylene and ammonia from the propylene inlet 34 and the ammonia inlet 36 is charged into the reactor 10 by means of a feed sprinkler 16. The flow rate of these feeds is high enough to fluidize the ammonia oxidation catalyst bed 24 in the interior of the reactor where catalytic ammoxidation of propylene and ammonia to acrylonitrile occurs.

The reaction gas exits the reactor 10 through the reactor effluent outlet 26. Prior to doing so, they travel through cyclone separator 20, which removes any ammonia oxidation catalyst that may be entrained by these gases for return to catalyst bed 24 through dip tube 25. Ammonia oxidation is extremely hot, and the cooling coil 18 is used to recover waste heat and thus maintain the reaction temperature at an appropriate level.

As further shown in FIG. 1, the first step of recovering acrylonitrile and other by-products from the hot reaction gases exiting the typical acrylonitrile reactor 10 is to cool them by spraying them with quench water in quench tower 30. These reactive gases contain unreacted ammonia which is removed before these gases are further processed. For this purpose, sulfuric acid is added to the quench water, which reacts with the unreacted ammonia to produce ammonium sulfate according to the following reaction: H ₂ SO ₄ + ₂ NH ₃ → (NH ₄ ) ₂ SO ₄

The ammonium sulfate is dissolved in the bottom of the quench water column, which is discharged through the quench bottom outlet line 31 for disposal. The hot reaction gas, which is generally cooler and substantially free of unreacted ammonia, exits from the upper portion of the quench tower through the quench gas outlet line 33 for further processing. Since the amount of unreacted ammonia in these overall reactant gases in the reactor effluent outlet 26 can vary over time, the pH of the water at the bottom of the quench column is monitored by pH monitor 37 and controlled by means of sulfuric acid control valve 40 and controller 42. Adjust the amount of sulfuric acid added to the quench tower to This pH is maintained at the desired level. The make-up water can be added to the quenching via line 45 as needed.

In order for the acrylonitrile reactor 10 to operate at maximum efficiency, the amount of ammonia fed to the reactor at any given time should be slightly greater in molar excess than the conversion of all of the propylene fed to the reactor at the same time to acrylonitrile. The amount required. Since the propylene flow rate into a number of reasons may vary over time, it is common practice to continuously monitor the flow rate F _1, and by means of the ammonia control valve 32 and the controller 38 in response to the measured flow rate of the propylene continuously adjust The flow rate of ammonia entering.

To further ensure that a slight excess of ammonia is fed to the acrylonitrile reactor, it is also desirable that a small but suitable amount of unreacted ammonia be present in the overall reaction product gas in the reactor effluent outlet 26. For this purpose, the ammonia concentration in these gases is measured periodically and the target or set point ammonia/propylene ratio in the controller 38 is adjusted in response to the measured unreacted ammonia concentration (ie, NH ₃ /C ₃ ⁼ ratio). So, for example, if the measured concentration of unreacted ammonia is too low, NH ₃ /C ₃ ⁼ programmed to controller 38 is slightly increased from the set point to provide a slight amount of ammonia relative to the continuously fed propylene. Feed to the reactor.

The periodic determination of the concentration of unreacted ammonia in the reactor effluent outlet 26 is generally done regularly, for example, several times per week. Thus, fine adjustment of the controller 38 is inherently limited by the target ammonia concentration NH ₃ / C ₃ ⁼ ratio in response to the effluent outlet 26 of the reactor unreacted, because the information can not be obtained on this concentration more often .

The lack of this information is not too cumbersome when using a balanced catalyst (i.e., an ammoxidation catalyst that has been used multiple times and thus has achieved an equilibrium concentration of both oxygen and molybdenum). However, when changes are made (such as C ₃ ⁼ change in flow rate) of the operating conditions of the reactor, the reactor effluent information about the unreacted ammonia is unknown until analysis Analysis of the reactor effluent. Furthermore, this lack of precision can lead to significant problems when using fresh catalysts, as it is known that fresh catalysts exhibit significant ammonia burning, ie, ammonia is directly oxidized to nitrogen oxides and water, both It's superfluous and can change quickly over time.

Summary of invention

A process for controlling the amount of ammonia provided to an ammoxidation reaction includes providing a reactor feed to a reactor, the reactor feed comprising ammonia, oxygen, and a choice from from propane, propylene, isobutane, and isobutylene, and combinations thereof The resulting pool of hydrocarbons; the reactor feed is reacted in the presence of a catalyst to provide a reactor effluent stream; the reactor effluent stream is provided to a quench vessel; the quench liquid is supplied to the quench vessel; the gaseous stream is quenched Liquid contact; monitoring the pH of the bottom of the quench water; and adjusting the amount of ammonia in the reactor feed to provide an ammonia to hydrocarbon ratio of from about 1 to about 2 in the reactor feed.

A process for controlling the amount of air provided to an ammoxidation reaction includes providing a reactor feed to a reactor, the reactor feed comprising ammonia, oxygen, and a choice from propane, propylene, isobutane, and isobutylene, and combinations thereof The resulting pool of hydrocarbons; reacting the reactor feed in the presence of a catalyst to provide a reactor effluent stream; monitoring the amount of oxygen in the reactor effluent; and adjusting the amount of air in the reactor feed to A ratio of air to hydrocarbon of from about 9 to about 10 is provided in the reactor feed.

An ammoxidation process includes providing a reactor feed to a reactor, the reactor feed comprising ammonia, oxygen, and a selected hydrocarbon selected from the group consisting of propane, propylene, isobutane, and isobutylene, and combinations thereof; in the presence of a catalyst The reactor feed reaction is provided to provide a reactor effluent stream; the quench liquid is supplied to the quench vessel; the gaseous stream is contacted with the quench liquid; the pH of the quench water bottom is monitored, and the amount of oxygen in the reactor effluent stream is monitored; Adjusting the amount of ammonia in the reactor feed to provide an ammonia to hydrocarbon ratio of from about 1 to about 2 in the reactor feed; and adjusting the amount of air in the reactor feed to provide approximately in the reactor feed A ratio of air to hydrocarbon of from 9 to about 10.

A system for ammonia control in an ammoxidation reactor includes an ammoxidation reactor configured to supply a reactor effluent to a quench tower, and a pH sensor for monitoring the pH of the quench water bottom from the quench tower And a controller electronically coupled to the pH sensor and the ammonia control valve. An ammonia control valve configured to control the flow of ammonia to the ammonia oxidation reactor and controller is configured to increase or decrease the flow of ammonia through the ammonia control valve.

10‧‧‧Reactor

12‧‧‧Reactor housing

14‧‧‧Air grille

16‧‧‧Sprinkler

18‧‧‧Cooling coil

20‧‧‧Cyclone separator

22‧‧‧Air inlet

24‧‧‧ Catalyst bed

25‧‧‧ dip tube

26‧‧‧Reactor effluent outlet; reactor effluent line

30‧‧‧Quench Tower

31‧‧‧Quickly cooled bottom outlet line

32‧‧‧Ammonia control valve

33‧‧‧Quick gas outlet line

34‧‧‧propylene inlet

36‧‧‧Ammonia inlet

37‧‧‧pH monitor; sensor

38‧‧‧ Controller

40‧‧‧Control valve

42‧‧‧ Controller

45‧‧‧ pipeline

F ₁ ‧‧‧ flow rate

The above and other aspects, features and advantages of several aspects of the process will become apparent from the following drawings.

1 is a schematic diagram showing the precise control of the amount of ammonia fed to a commercial acrylonitrile reactor; and FIG. 2 is a schematic diagram showing another aspect of the precise control of the amount of ammonia fed to a commercial acrylonitrile reactor.

Corresponding reference numerals indicate corresponding components throughout the several views of the drawings. The skilled person will recognize that the elements in the figure are for simplicity and It is clear and not necessarily to scale. For example, the size of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of the various aspects. In addition, common but well-known elements that are available or required in commercially feasible aspects are generally not shown in order to facilitate less obscuring the observation of these various aspects.

Detailed description of the preferred embodiment

The following description is not to be taken in a limiting sense, but only for the purpose of describing the general principles of the exemplary embodiments. Aspects of the invention should be determined with reference to the scope of the claims.

Ammonia control

Acrylonitrile supplied commercially for precise control of the amount of ammonia reactor according to the present invention 38 NH ₃ / C ₃ ⁼ ratio setpoint is achieved by adjusting the controller for response to the quench water 30 in the bottom of the quenching tower The pH is measured to control the operation of the ammonia control valve 32. As shown in FIG. 2, pH sensor 37 continuously monitors the pH of the bottom of the quench water column in quench column 30. The sensor 37 is electronically coupled to the controller 38. In addition, controller 38 is programmed to modify its predetermined NH ₃ /C ₃ ⁼ ratio set point (which is used to control ammonia control valve 32 in response to the measured flow rate F _{1 of} incoming propylene) in response to quench tower 30 The measured pH at the bottom of the quench water is adjusted to the predetermined set point.

As indicated above, the measured pH at the bottom of these quench water towers provides an accurate indication of the concentration of unreacted ammonia in the hot reaction gases in reactor effluent line 26. Accordingly, the present invention changes the controller 38 NH ₃ / C ₃ ⁼ ratio set point by utilizing this phenomenon in response to the measured pH. Thus, for example, if the measured pH becomes too low, indicating that more sulfuric acid is required to be delivered to the quench column 30, this in turn indicates that the amount of unreacted ammonia in the reactor effluent line 26 has been reduced. Small, NH ₃ /C ₃ ^{= of} controller 38 automatically increases by a corresponding amount than the set point. This set point reduction causes a reduction in the relative amount of propylene fed to the reactor, and thus a corresponding increase in the relative amount of ammonia fed to the reactor, which in turn results in a reactor effluent line 26 The amount of unreacted ammonia in the hot reaction gas increases back to its desired value.

In one embodiment, the quench liquid is provided through line 45 to the quench vessel. The quench liquid may include an acid to maintain a pH of the quench liquid of from about 3 to about 6, and in another aspect, from about 4.5 to about 6. The acid used may be sulfuric acid.

Thus, it can be seen that by adjusting the NH ₃ /C ₃ ⁼ ratio of the controller 38 in this manner, the amount of unreacted ammonia in the reactor effluent line 26 is automatically controlled in a continuous manner to ensure There is always a slight excess of ammonia in the reactor, even though the relative ratio of propylene and ammonia consumed varies with time relative to each other. In this aspect, the process includes adjusting the amount of ammonia in the reactor feed to provide a molar ratio of ammonia to hydrocarbon of from about 1 to about 2, and in another aspect, from about 1.25 to about 1.75, on the other hand. Medium, from about 1.4 to about 1.6, and in another aspect, from about 1.25 to about 1.3. Thus, a significant advantage is that relying on the NH ₃ /C ₃ ⁼ ratio of the controller 38 to set points to ensure that the amount of ammonia that is always maintained in the acrylonitrile reactor is automatically and continuously occurring, and therefore no longer depends on discontinuity A manual analysis test that occurred. In one aspect, the system is configured such that a pH change caused by increasing or decreasing ammonia flow through the ammonia control valve is detected by the pH sensor within one hour or less of the delay time. In another aspect, the delay time can be from about 10 seconds to about 60 minutes, in another aspect, from about 30 seconds to about 45 minutes, and in another aspect, from about 1 minute to about 30 minutes, on the other hand. Medium, about 1 minute to about 10 minutes, in another aspect, about 1 minute to about 5 minutes, and in another aspect, about 2 minutes to about 4 minutes.

Air control

In another aspect, a process for controlling the amount of air provided to an ammoxidation reaction includes monitoring the amount of oxygen in the reactor effluent and adjusting the amount of air in the reactor feed to provide in the reactor feed. A ratio of air to hydrocarbon of from about 9 to about 12, in another aspect, a ratio of from about 9 to about 11, in another aspect, a ratio of from about 9 to about 10, and in another aspect, from about 10.5 to about The ratio of 11, in another aspect, is a ratio of from about 9.25 to about 9.75, and in another aspect, a ratio of from about 9.4 to about 9.6. In related aspects, the reactor effluent stream comprises from about 0.5 to about 1% by weight oxygen. The process can also include continuously measuring the amount of oxygen in the reactor effluent and continuously adjusting the molar ratio of air to hydrocarbon in response. Oxygen can be measured at any location downstream of the reactor, such as, for example, between the reactor and the quench tower or downstream of the quench tower. In an aspect, the oxygen monitor is electronically coupled to controller 38. Controller 38 can be configured to increase or decrease the flow of air to the reactor. The system is configured such that an oxygen monitor causes an increase in oxygen caused by an increased or decreased oxygen flow over a one hour or less delay time. In another aspect, the delay time can be from about 10 seconds to about 60 minutes, in another aspect, from about 30 seconds to about 45 minutes, and in another aspect, from about 1 minute to about 30 minutes, on the other hand. Medium, about 1 minute to about 10 minutes, in another In one aspect, from about 1 minute to about 5 minutes, and in another aspect, from about 2 minutes to about 4 minutes.

Ammonia control and air control can be used independently, or both can be included in the ammoxidation process. In addition, it will also be appreciated that the techniques of the present invention do not require the addition of new equipment or structures to existing acrylonitrile plants because they can only use equipment already in the factory, particularly controller 38, ammonia control valve 32. And a pH sensor 37 for sensing the pH of the bottom of the quench tower water is implemented. The practice of the invention only requires electronically connecting the pH sensor 37 to the controller 38 and reprogramming the controller in response to signals generated by the sensor adjusting its NH ₃ / according to the teachings of the present invention. C ₃ ⁼ ratio is easier and cheaper to do.

In another aspect, the processes and systems described herein can be used with multiple sized reactors and quench towers, including reactors having larger diameters, such as, for example, from about 9 to about 12 meters, on the other hand. Medium, about 10 to about 12 meters, in another aspect, about 10 to about 11 meters, in another aspect, about 9.4 meters and larger, and on the other hand, about 9.5 meters, and on the other hand Medium, about 10.7 meters. In this aspect, the ratio of the cross-sectional area of the ammoxidation reactor to the cross-sectional area of the quench tower is from about 1 to about 3, and in another aspect, from about 1.5 to about 2.5, and in another aspect, about 1.6 to About 1.9.

Although only a few embodiments of the invention have been described above, it should be understood that many modifications may be made without departing from the spirit and scope of the invention. All such modifications are intended to be included within the scope of the invention as limited by the scope of the appended claims.

10‧‧‧Reactor

12‧‧‧Reactor housing

14‧‧‧Air grille

16‧‧‧Sprinkler

18‧‧‧Cooling coil

20‧‧‧Cyclone separator

22‧‧‧Air inlet

24‧‧‧ Catalyst bed

25‧‧‧ dip tube

26‧‧‧Reactor effluent outlet; reactor effluent line

30‧‧‧Quench Tower

31‧‧‧Quickly cooled bottom outlet line

32‧‧‧Ammonia control valve

33‧‧‧Quick gas outlet line

34‧‧‧propylene inlet

36‧‧‧Ammonia inlet

37‧‧‧pH monitor; sensor

38‧‧‧ Controller

40‧‧‧Control valve

42‧‧‧ Controller

45‧‧‧ pipeline

F ₁ ‧‧‧ flow rate

Claims (38)

A process for controlling the amount of ammonia provided to an ammoxidation reaction, the process comprising: providing a reactor feed to a reactor, the reactor feed comprising ammonia, oxygen, and a choice from from propane, propylene, isobutylene a pooled hydrocarbon consisting of an alkane and isobutylene and combinations thereof; reacting the reactor feed in the presence of a catalyst to provide a reactor effluent stream; providing the reactor effluent stream to a quench vessel; quenching Providing a liquid to the quench vessel; contacting the gaseous stream with the quench liquid; monitoring the pH of the quench water bottom; and adjusting the amount of ammonia in the reactor feed to provide about 1 in the reactor feed A molar ratio of ammonia to hydrocarbon of about 2. The process of claim 1 wherein the reactor effluent stream comprises acrylonitrile and ammonia. The process of claim 1 wherein the quench liquid comprises an acid. The process of claim 3 wherein an acid is added to the quench liquid to maintain a pH of the quench liquid of from about 3 to about 6. The process of claim 4 wherein an acid is added to the quench liquid to maintain a pH of the quench liquid of from about 4.5 to about 6. The process of claim 3 wherein the acid is sulfuric acid. The process of claim 1, wherein the quenching is continuously measured The pH of the bottom of the water. The process of claim 1, wherein the molar ratio of ammonia to hydrocarbon is continuously adjusted. The process of claim 1, wherein the pH change caused by the increased or decreased ammonia flow through the ammonia control valve is detected by the pH sensor within one hour or less of the delay time. The process of claim 1, wherein the ratio of the cross-sectional area of the ammoxidation reactor to the cross-sectional area of the quench tower is from about 1 to about 3. A process for controlling the amount of air provided to an ammoxidation reaction, the process comprising: providing a reactor feed to a reactor, the reactor feed comprising ammonia, oxygen, and a choice from propane, propylene, isobutylene a pooled hydrocarbon consisting of an alkane and isobutylene and combinations thereof; reacting the reactor feed in the presence of a catalyst to provide a reactor effluent stream; monitoring the amount of oxygen in the reactor effluent; The amount of air in the reactor feed provides a molar ratio of air to hydrocarbon of from about 9 to about 12 in the reactor feed. The process of claim 11 wherein the reactor effluent stream comprises acrylonitrile and oxygen. The process of claim 11 wherein the reactor effluent stream comprises from about 0.5 to about 1% by weight oxygen. The process of claim 11 wherein the amount of oxygen in the reactor effluent is continuously measured. The process of claim 11 wherein the molar ratio of air to hydrocarbon is continuously adjusted. The process of claim 11, wherein the change in oxygen caused by the increased or decreased oxygen flow is detected by the oxygen monitor within an hour or less of the delay time. An ammoxidation process comprising: providing a reactor feed to a reactor, the reactor feed comprising ammonia, oxygen, and a selected hydrocarbon selected from the group consisting of propane, propylene, isobutane, and isobutylene, and combinations thereof Reacting the reactor feed in the presence of a catalyst to provide a reactor effluent stream; providing a quench liquid to the quench vessel; contacting the gaseous stream with the quench liquid; monitoring the pH of the quench water bottom; Monitoring the amount of oxygen in the reactor effluent stream; adjusting the amount of ammonia in the reactor feed to provide an ammonia to hydrocarbon ratio of from about 1 to about 2 in the reactor feed; and adjusting the The amount of air in the reactor feed provides about a molar ratio of air to hydrocarbon in the reactor feed of from about 9 to about 12. The process of claim 17 wherein the reactor effluent stream comprises acrylonitrile, ammonia and oxygen. The process of claim 17, wherein the quench liquid comprises an acid. The process of claim 19, wherein the acid is added to the quench liquid to maintain a pH of the quench liquid of from about 3 to about 6. The process of claim 20 wherein acid is added to the quench liquid to maintain a pH of the quench liquid of from about 4.5 to about 6. The process of claim 19, wherein the acid is sulfuric acid. The process of claim 17 wherein the reactor effluent stream comprises from about 0.5 to about 1% by weight oxygen. The process of claim 17, wherein the pH of the bottom of the quench water is continuously measured. The process of claim 17, wherein the molar ratio of ammonia to hydrocarbon is continuously adjusted. The process of claim 17, wherein the amount of oxygen in the reactor effluent is continuously measured. The process of claim 17, wherein the molar ratio of air to hydrocarbon is continuously adjusted. The process of claim 17, wherein the pH change caused by the increased or decreased ammonia flow through the ammonia control valve is detected by the pH sensor within one hour or less of the delay time. The process of claim 17, wherein the change in oxygen caused by the increased or decreased oxygen flow is detected by the oxygen monitor within one hour or less of the delay time. The process of claim 17, wherein the ratio of the cross-sectional area of the ammoxidation reactor to the cross-sectional area of the quench tower is from about 1 to about 3. A system for ammonia control in an ammoxidation reactor, the system comprising: an ammoxidation reactor configured to supply reactor effluent to a quench tower; a pH sensor for monitoring the pH of the bottom of the quench water from the quench tower; and a controller electronically coupled to the pH sensor and the ammonia control valve, the ammonia control valve system An ammonia stream is controlled to control flow to the ammonia oxidation reactor; wherein the controller is configured to increase or decrease ammonia flow through the ammonia control valve. The system of claim 31, wherein the system is configured such that an increase or decrease in the ammonia control is detected by the pH sensor within an hour or less of a delay time The pH change caused by the ammonia flow of the valve. The system of claim 31, further comprising an oxygen monitor for determining an oxygen concentration in the reactor effluent, the oxygen monitor being electronically coupled to the controller. The system of claim 32, wherein the controller is configured to increase or decrease air flow to the reactor. The system of claim 31, wherein the system is configured such that an oxygen monitor causes an increase or decrease in oxygen flow caused by oxygen flow by an oxygen monitor for an hour or less of delay time. The system of claim 31, wherein the pH sensor provides continuous measurements. The system of claim 33, wherein the oxygen monitor provides continuous measurements. The system of claim 31, wherein the ratio of the cross-sectional area of the ammoxidation reactor to the cross-sectional area of the quench tower is from about 1 to about 3.