JP6718825B2 - Method for stabilizing crude acrylonitrile and its storage tank - Google Patents

Description

The present disclosure relates to improvements in methods of making acrylonitrile and methacrylonitrile. Specifically, the present disclosure relates to operation of a crude acrylonitrile tank.

Acrylonitrile is an important commodity chemical used primarily as a monomer for the manufacture of various polymeric materials, such as polymers for acrylic fibers used in textiles and resins such as ABS and SAN resins. Acrylonitrile is produced in an amount of over 4 million tons per year worldwide. The most commonly used method for the production of olefinically unsaturated nitriles such as acrylonitrile or methacrylonitrile is the production of acrylonitrile using air or another source of molecular oxygen as an oxidant in an ammoxidation reactor. Suitable hydrocarbons such as propylene or propane for production, or isobutylene for the production of methacrylonitrile are reacted in the presence of ammonia. Such an oxidation reaction, also commonly referred to as an ammoxidation reaction, uses a solid, particulate, heterogeneous catalyst in a fluidized catalyst bed to provide the desired conversion and yield of the desired acrylonitrile or methacrylonitrile. Catalyzes ammoxidation reactions. In addition to the formation of olefinically unsaturated nitriles, such ammoxidation reactions also generally produce other products such as acetonitrile, hydrogen cyanide (HCN) and other by-products. Catalytic oxidation processes from hydrocarbons to acrylonitrile are disclosed, for example, in U.S. Pat. Nos. 4,503,001, 4,767,878, 4,863,891 and 5,093,299. , All of these patents are incorporated herein by reference.

It is important that the acrylonitrile product meets specifications including a maximum amount of certain chemical impurities, and predetermined amounts of water and polymerization inhibitors. Controlling the water and polymer content of the acrylonitrile product is important to the stability of the acrylonitrile product. Generally, the amount of water in the acrylonitrile product and the amount of monomethyl ether hydroquinone or hydroquinone methyl ether (hereinafter "MEHQ") polymerization inhibitor must be maintained within specified levels or ranges. The MEHQ polymerization inhibitor requires a certain amount of water to function and to suppress the unwanted polymerization of the acrylonitrile product. Due to the high reactivity of acrylonitrile products that do not contain a certain amount of water and inhibitors, specifications such as shipping specifications between the United States and the United States generally require shipping acrylonitrile products to contain a minimum amount of water and inhibitors. Need to be. The maximum content of water and inhibitor is also usually stated, since excess water and inhibitor make the desired subsequent reaction of the acrylonitrile slow and difficult. Acrylonitrile product specifications usually specify maximum amounts for certain impurities such as hydrogen cyanide, acetonitrile and acetone.

At times, it may be necessary to introduce unrefined or substandard products into the holding tank. In such cases, it may be necessary to use the crude acrylonitrile tank as a crude or substandard product holding tank.

U.S. Pat. No. 4,503,001 U.S. Pat. No. 4,767,878 U.S. Pat. No. 4,863,891 US Pat. No. 5,093,299

Although the production of acrylonitrile/methacrylonitrile has been carried out commercially for many years, there are still areas where improvements can provide significant advantages. Crude acrylonitrile from the recovery column usually contains acrylonitrile, cyanide and water and is therefore not particularly stable. Thus, crude acrylonitrile can be prone to polymerization reactions and loss of acrylonitrile product. It would be useful to reduce or eliminate polymerization reactions and loss of acrylonitrile product by having a method and apparatus that result in more efficient operation of the crude acrylonitrile tank than conventional methods and apparatus.

The above and other aspects, features and advantages of the present disclosure will become apparent from the following detailed description of the exemplary embodiments, read in conjunction with the accompanying drawings.

Accordingly, aspects of the present disclosure provide a safe, effective, and cost-effective method and device that overcomes or reduces the disadvantages of conventional methods and devices.

A method of maintaining storage of crude acrylonitrile in a crude tank is provided. This method comprises the steps of transporting crude acrylonitrile to a crude tank, adding to the crude acrylonitrile in the crude tank an amount of acid effective to maintain the pH below the target pH, and removing the crude acrylonitrile in the crude tank. Maintaining the temperature below the target temperature.

In another aspect, a method of preparing a crude tank for receiving crude acrylonitrile comprises the steps of adding to the crude tank an amount of water effective to absorb organisms under the floating roof of the crude tank; Maintaining the temperature of about 25° C. or less and acidifying the water to a pH of 4 or less.

In another aspect, a crude acrylonitrile storage tank is configured to remove crude acrylonitrile from the crude acrylonitrile storage tank and a plurality of temperature sensors configured to detect temperatures at different heights within the crude acrylonitrile storage tank. And a plurality of removal points. This tank comprises a pH sensor configured to detect the pH of crude acrylonitrile in the crude acrylonitrile storage tank and a cooler configured to cool the recirculation stream drawn from the removal location of the crude acrylonitrile storage tank. And a return line configured to return at least a portion of the recycle stream to the crude acrylonitrile storage tank.

The above and other aspects, features and advantages of the present disclosure will become apparent from the following detailed description of the exemplary embodiments, read in conjunction with the accompanying drawings.

A complete understanding of the exemplary embodiments of the present disclosure and its advantages can be obtained by reference to the following description in light of the accompanying drawings, in which like features are designated by like reference numerals.

FIG. 3 is a schematic flow diagram of an embodiment as applied to the manufacture of an acrylonitrile product according to aspects of the disclosure. 6 is a flow diagram of a method in accordance with aspects of the disclosure.

It is important to monitor and control both temperature and pH for storage of crude acrylonitrile. In this aspect, the method includes detecting a plurality of liquid temperatures at different heights of the crude tank. The method comprises the steps of circulating a recirculation flow drawn from the outflow height of the crude tank, cooling the recirculation flow, and at least a portion of the recirculation flow when the detected temperature is outside a predetermined temperature range. Back to the tank.

The methods described herein require less time and steps to release the acrylonitrile product to the final product store than conventional systems and methods. Laboratories and factories can be reduced in analyzing samples and adjusting operating parameters to produce acrylonitrile products within specifications. Another advantage is that the number and/or capacity of rundown tanks can be reduced relative to the number and/or capacity of rundown tanks required in conventional systems and methods. Another advantage is that the faster detection of substandard acrylonitrile products for chemical impurities allows corrective action to be taken and the amount of acrylonitrile product that re-passes through the part (s) of the system This is a reduction to the amount required in the system and method.

In the following, referring to the figures, further reference will be made to the method and the apparatus for carrying it out.

As shown in FIG. 1, the device 10 includes a tank 12. Tank 12 may be configured to receive crude acrylonitrile product stream 14 via line 16. Crude acrylonitrile product stream 14 can be conveyed to tank 12 from a recovery tower or other vessel (not shown). The crude acrylonitrile product stream 14 can be conveyed via line 16 into tank 12 at location 18. The temperature sensors 20, 22, 24, 26 and 28 may be configured to measure the temperature of the liquid in the tank 12 at corresponding vertical heights 30, 32, 34, 36 and 38 of the liquid in the tank 12. it can. The crude acrylonitrile product in tank 12 can be carried out of tank 12 via line 40. The overhead vapor 110 can be conveyed from the tank 12 via a line 112 to a scrubber (not shown).

The crude acrylonitrile product may be conveyed from tank 12 via lines 82, 84, 86 and/or 88. Valves 92, 94, 96 and 98 can correspond to conduits 82, 84, 86 and 88, respectively. Nozzles 102, 104, 106 and 108 can correspond to conduits 82, 84, 86 and 88, respectively. The nozzles 102, 104, 106 and 108 may have vertical heights in the tank 12 that correspond to vertical heights 32, 34, 36 and 38 of liquid in the tank 12, respectively. The distance between nozzles in a series of nozzles can be the same. Therefore, the distance between the nozzle 102 and the nozzle 104 is the same as the distance between the nozzle 104 and the nozzle 106, and the others can be the same. In one aspect, the distance between successive nozzles can be about 2 to about 12 feet, in another aspect about 5 to about 12 feet, and in another aspect about 8 to about 12 feet. It may be 12 feet, and in another embodiment about 10 feet. Although the vertical height of the nozzle 100 is shown in FIG. 1 as being lower than the vertical height 30, the nozzle 100 can also have the same or approximately the same vertical height as the vertical height 30.

Line 46 may convey the crude acrylonitrile product to a heat exchanger or cooler 54, for example on the tube side of inlet 56 of cooler 54. The cooler 54 can be configured to cool the crude acrylonitrile product through heat transfer using a cooling fluid 58, such as cooling water, introduced to the shell side of the inlet 60 of the cooler 54. The cooling fluid 58 can be discharged from the outlet 62 of the cooler 54.

The crude acrylonitrile product can be discharged in outlet 64 after being cooled in cooler 54 and conveyed from cooler 54 via line 66 as cooled acrylonitrile product stream 78. For example, acid 68, such as glycolic acid or acetic acid and combinations thereof, can be conveyed via line 70 and added to the crude acrylonitrile product in line 66 at junction 74. Acid 68 may be pumped from acid source 76 by pump 72 through line 70. In one aspect, the acid 68 can be added to the cooled acrylonitrile product stream 78 to maintain the pH of the liquid in the tank 12 within a predetermined pH range. The cooled acrylonitrile product can be returned to tank 12 through line 80 and nozzle 100.

In one aspect, the controller 11 is responsive to the temperature of the liquid as measured by the temperature sensors 20, 22, 24, 26 and/or 28 and measurement parameters such as vertical heights 30, 32, 34, 36 and/or 38. Can be configured to process one or more signals that The controller 11 can be configured to determine whether the measured parameter is above or below a predetermined parameter range. One of ordinary skill in the art, according to the present disclosure, will know that this measurement parameter is any suitable parameter useful in the operation of tank 12 such as, for example, the temperature measured by a temperature sensor at a given vertical height. You will recognize it as good. The controller 11 adjusts the operation of one or more devices via a communication line or wireless communication (not shown in FIG. 1) when the measured parameter is below or above a predetermined parameter range. Can be configured to. For example, the controller 11 controls the operation of the cooler 54 and the operation of valves such as 92, 94, 96 and/or 98 to provide one or more nozzles 100, 102, 104, 106 and/or It can be configured to adjust the amount of crude acrylonitrile product conveyed through 108.

In one aspect, the liquid in tank 12 and/or the liquid in tank 12 is locally recirculated by recirculating the cooled acrylonitrile product, cooling the liquid in tank 12, and mixing with the liquid in tank 12. The temperature of the area can be maintained within a predetermined temperature range. In one aspect, the controller 11 is returned to the tank 12 via line 66, the amount of liquid drawn from the tank 12 via line 40, the amount of crude acrylonitrile product cooled in the cooler 54, and line 66. It can be configured to control the amount of crude acrylonitrile product (after cooling). In this aspect, recirculation to bring the temperature in the crude tank to about 25° C. or less is effective. In a related aspect, the temperature is measured at 1 to about 5 locations, and in another aspect, at 2 to about 4 locations. In one aspect, the method is effective to provide a turnover rate of about 50 to about 150 hours, and in another aspect is effective to provide a turnover rate of about 75 to about 125 hours. In an aspect, it is effective to provide a turnover rate of about 75 to about 80 hours, and in another aspect is effective to provide a turnover rate of about 100 to about 105 hours.

In one aspect, the controller 11 is configured to process one or more signals corresponding to the pH of the liquid in the tank 12 and/or the pH of the liquid drawn from the tank 12 via line 40. can do. In this aspect, pH meter 116 may be configured to measure the pH of the crude acrylonitrile product in tank 12 at location 120 and communicate a signal corresponding to the measured pH to controller 11 or flow controller 118. .. The controller 11 or the flow controller 118 can be configured to process information from the pH meter to control the flow of acid 68 to the junction 74. In one aspect, controller 11 or flow controller 118 is adapted to adjust at least one operating parameter for the flow of acid 68 to junction 74 when the pH measured at location 120 deviates from the predetermined pH. Can be configured. In one aspect, controller 11 can be configured to control the operation of flow controller 118. In one aspect, the controller 11 can include a flow controller 118. Controller 11 and/or flow controller 118 can include a processor. The processor of controller 11 and/or flow controller 118 may include a memory configured to receive and store certain conditions or parameters. The predetermined condition or parameter can be a desired pH value or pH range for the liquid at location 120.

In one aspect, controller 11 and/or flow controller 118 receives a signal corresponding to the pH measured by pH meter 116 at a predetermined frequency, such as about every 6 hours, and the measurement signal is within a predetermined pH range. It can be configured to determine whether or not. In one aspect, the predetermined pH range can be about 2.5 to 4.5, and in another embodiment about 3 to about 4. In one aspect, the controller 11 and/or the flow controller 118 causes the valve 119 corresponding to the flow controller 118 to open the valve at the junction if the measured pH is at or near about 4.5. More acid 68 may be added at 74, and thus adjusted to add more acid to tank 12. When the pH measured at position 120 is at or near about 2.5, controller 11 and/or flow controller 118 causes opening of valve 119 corresponding to flow controller 118 to cause acid 68 to be added at junction 74. Can be adjusted to reduce the amount of acid 68 and thus the amount of acid 68 added to tank 12.

As shown in FIG. 1, the effluent 41 in line 40 can be withdrawn from the bottom of tank 12 at position 43. Position 43 can have a vertical height of zero or near zero with respect to the overall height of tank 12. In one aspect, the crude acrylonitrile storage tank has a length to diameter ratio of about 0.5 to about 1.5, in another aspect about 0.75 to about 1.25, and in another aspect. It is about 0.9 to about 1.1.

FIG. 2 shows a flow diagram of a method 300 according to aspects of the disclosure. The method 300 can be performed using the apparatus 10 shown in FIG. Step 301 can include detecting a first liquid temperature at a first height of the crude tank. Step 302 can include detecting a second liquid temperature at a second height of the crude tank. Step 303 may include circulating a recycle stream drawn from the outlet height of the crude tank. Step 304 can include cooling the recycle stream. Step 305 can include returning at least a first portion of the recycle stream to a first return height when the detected first temperature is outside a predetermined temperature range. The method 300 can include returning at least a second portion of the recycle stream to a second return height when the detected second temperature is outside the predetermined temperature range. In one aspect, at least the first return height or the second return height is higher than the outflow height of the crude tank.

In one aspect, a method of providing an empty crude tank for receiving a crude acrylonitrile product stream, such as crude acrylonitrile product stream 14, is provided. In one aspect, the method comprises the step of adding to the crude tank an amount of water effective to absorb organisms under the floating roof of the crude tank. Absorption of organisms is effective in preventing loss of organisms from the crude tank.

In another aspect, the start-up method comprises about 6% by weight or more in an empty crude tank, in another aspect about 6 to about 15%, and in another aspect about 6% to float the floating roof of the tank. To about 10%, in another embodiment about 6 to about 8% water. This method involves circulating water in a cooler, such as cooler 54, to bring the target temperature of the liquid in the tank to, for example, 25° C. or less, in another embodiment about 20° C. or less, In an aspect about 18° C. or less, in another aspect about 15° C. or less, in another aspect about 10° C. or less, in another aspect about 1 to about 10° C., in another aspect It can include a step of about 5 to about 10°C. The method can include the step of adding an acid to the circulating water to bring the pH of the liquid in the tank to about 4 or less, in another aspect about 3 to about 4. In this embodiment, the acid is added to the water after the water temperature reaches 25°C or below. In another aspect, crude acrylonitrile is added to the crude tank when the crude tank is at or below 25° C. and the pH is about 4 or below.

In the embodiment where the crude acrylonitrile is present in the tank, the method may include periodically sampling the pH of the liquid, such as every 6 hours, and adding additional acid if the pH exceeds about 4.5. .. The method can include circulating the crude acrylonitrile product through a cooler, such as cooler 54, to maintain a temperature below 18 degrees Celsius.

In one aspect, a method can be provided that addresses the need to introduce unrefined or substandard products into a holding tank. In such cases, it may be necessary to use the crude acrylonitrile tank as a crude or substandard product holding tank. In one aspect, tank temperature and pH are monitored to avoid or reduce chemical reactions within the tank.

In one aspect, two separate tanks 12 can be operated sequentially or simultaneously.

While the above disclosure has described the present disclosure in connection with certain preferred embodiments thereof and provided many details for purposes of illustration, one of ordinary skill in the art can appreciate that the present disclosure does not depart from the basic principles of the disclosure. It will be apparent that further embodiments of the disclosure are possible and that some of the details described herein can be modified significantly. It is to be understood that the features of the disclosure can be modified, altered, changed or substituted without departing from the spirit or scope of the disclosure and the scope of the claims. For example, the dimensions, number, size and shape of the various components can be varied to suit a particular application. Accordingly, the particular embodiments illustrated and described herein are for purposes of illustration only.

Claims (21)

A method of maintaining storage of crude acrylonitrile in a crude tank, comprising:
Conveying the crude acrylonitrile to the crude tank,
Measuring the pH of the crude acrylonitrile at one or more locations in the crude tank;
Adding to the crude acrylonitrile in the crude tank an amount of acid effective to maintain the pH below a target pH;
Maintaining the temperature of the crude acrylonitrile in the crude tank below a target temperature;
Only including,
The temperature of the crude acrylonitrile in the crude tank is maintained using a recycle stream,
An acid is added to the crude acrylonitrile in the crude tank using the recycle stream . The crude acrylonitrile comprises acrylonitrile, water and HCN,
The method of claim 1. The target pH is about 4.5 or less,
The method of claim 1. The target pH is about 2.5 to about 4.5,
The method of claim 1. Acid is added when the pH is increased by about 0.1 to about 0.5 pH units;
The method of claim 1. The acid is selected from the group consisting of organic acids, sulfuric acid and mixtures thereof,
The method of claim 1. The organic acid is selected from the group consisting of acetic acid, glycolic acid and mixtures thereof,
The method of claim 6. The temperature of the crude acrylonitrile in the crude tank is measured at one location or at two or more measurement locations,
The method of claim 1. The temperature of the crude acrylonitrile in the crude tank is measured at 1 to about 5 measurement points,
The method of claim 1. Each measurement point is at a different tank height,
The method of claim 8. The recycle stream is removed from the crude tank at one or more removal points,
The method of claim 1 . The recycle stream is removed from the crude tank at about 1 to about 5 removal points,
The method according to claim 11 . The recycle stream is cooled using a heat exchanger,
The method of claim 1 . The recirculation flow is returned to the crude tank at one location or two or more locations different from the removal location,
The method according to claim 11 . The recycle stream is effective to maintain the temperature of the crude acrylonitrile in the crude tank at about 25° C. or less.
The method of claim 1 . The recycle stream is effective to provide a turnover of about 50 to about 150 hours,
The method of claim 1 . A crude acrylonitrile storage tank,
One or more temperature sensors configured to detect temperatures at different heights within the crude acrylonitrile storage tank;
One or more removal points configured to remove crude acrylonitrile from the crude acrylonitrile storage tank;
A pH sensor configured to detect the pH of the crude acrylonitrile in the crude acrylonitrile storage tank,
A return line configured to return at least a portion of the recycle stream to the crude acrylonitrile storage tank;
An inlet for adding acid to the recycle stream,
A crude acrylonitrile storage tank comprising: Further comprising a cooler configured to cool the recycle stream withdrawn from the one or more removal points of the crude acrylonitrile storage tank.
A crude acrylonitrile storage tank according to claim 17 . Further comprising a controller configured to receive a signal from the pH sensor corresponding to the pH detected by the pH sensor and to regulate acid flow to the crude acrylonitrile storage tank.
A crude acrylonitrile storage tank according to claim 17 . The controller is configured to receive a signal from the temperature sensor corresponding to the temperature detected by the temperature sensor and is configured to regulate a flow rate of the recirculation flow.
20. The crude acrylonitrile storage tank of claim 19 . The crude acrylonitrile storage tank has a length to diameter ratio of about 0.5 to about 1.5.
A crude acrylonitrile storage tank according to claim 17 .

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