Separation system and separation process of hydrogen cyanide by-product of acrylonitrile

Abstract

The application discloses a separation system and separation process of hydrogen cyanide byproduct of acrylonitrile, which comprises a dehydrogen cyanide tower, internal gas-liquid phase heat exchange is carried out in the dehydrogen cyanide tower; a condensing outer loop is connected with the top of the dehydrogen cyanide tower, and is used for cooling the gas stream output from the top of the tower and realizing partial reflux; a polymerization inhibitor input system comprises an acid input subsystem, the acid input subsystem comprises an acid input pipeline and an acid input control device, the acid input control device controls the acid input pipeline to input an acidic polymerization inhibitor for preventing hydrogen cyanide from polymerizing into the gas phase pipeline, the liquid phase pipeline of the top reflux of the dehydrogen cyanide tower and the cooling equipment in the condensing outer loop at a preset ratio, so that a branch of the condensing outer loop outputs high-purity hydrogen cyanide product. The application can evenly distribute the polymerization inhibitor in the tower, effectively reduce the polymerization risk of the material and improve the purity of the material at the top of the tower and the bottom of the tower, and further improve the purity of the hydrogen cyanide at the top of the tower and reduce the water content in combination with the special top reflux ratio design, so that the requirements of the raw material of adiponitrile device are met.

Description

Technical Field

[0001] This invention belongs to the field of chemical production technology, and specifically refers to a separation system and process for hydrogen cyanide produced as a byproduct of acrylonitrile. Background Technology

[0002] Hydrogen cyanide has a simple structure and is chemically reactive. It is an important raw material for organic chemical synthesis and is mainly used in the production of chemical products such as acetone cyanohydrin, adiponitrile, methyl methacrylate (MMA), sodium cyanide, methionine, and chelating agents. These products have wide applications in synthetic fibers, pharmaceuticals, pesticides, fuels, additives, and metallurgy, and the market demand is huge.

[0003] With continuous technological advancements, DuPont developed a route for directly producing adiponitrile from butadiene and hydrogen cyanide, followed by the further production of caprolactam and hexamethylenediamine from adiponitrile. This process boasts advantages such as the absence of ammonium sulfate as a byproduct, simplicity, low investment, and low energy consumption, gradually becoming one of the main routes for adiponitrile production and making it an important part of the downstream hydrogen cyanide industry chain. Since the hexamethylenediamine obtained through co-production can be used to synthesize Nylon 66, one of the five major engineering plastics, and Nylon 66 possesses excellent heat resistance, oil resistance, and abrasion resistance, it is highly favored by the market, leading to rapid market growth. Consequently, the market demand for hydrogen cyanide has also increased rapidly.

[0004] The main industrial production processes for hydrogen cyanide include the Angle process, light oil cracking, methanol ammoxidation, and acrylonitrile by-product process. The Angle process, also known as the methane ammoxidation process, is one of the main methods for producing hydrogen cyanide globally and is also the primary source of hydrogen cyanide as a feedstock in adiponitrile production. In addition, the acrylonitrile by-product process is the lowest-cost and most economical method for producing hydrogen cyanide and is also the main source of hydrogen cyanide in China. However, existing acrylonitrile plants require a water content of ≤500 ppm for the by-product hydrogen cyanide, while adiponitrile feedstock requires a water content of ≤100 ppm. This means that the hydrogen cyanide produced by-products from existing acrylonitrile plants cannot meet the feedstock requirements for adiponitrile production, limiting its application. In China, hydrogen cyanide from acrylonitrile plants is mainly used to produce acetone cyanohydrin and MMA. With the continuous development of acrylonitrile technology and plant scale, more and more hydrogen cyanide needs to be further applied to downstream plants. Improving the purity of hydrogen cyanide from acrylonitrile plants is gradually becoming an important issue in promoting hydrogen cyanide consumption. If hydrocyanic acid, a byproduct of acrylonitrile, is successfully applied to the production of adiponitrile, it will not only reduce the production cost of adiponitrile but also promote the development of the acrylonitrile industry.

[0005] In an acrylonitrile plant, hydrogen cyanide and acrylonitrile are separated by a dehydrocyanate tower to obtain high-purity hydrogen cyanide and acrylonitrile. The high-purity hydrogen cyanide is directly fed into downstream units as a raw material, while the acrylonitrile is further purified to obtain the finished product. The design of the dehydrocyanate tower is a key piece of equipment for achieving efficient separation of hydrogen cyanide and acrylonitrile to obtain high-purity hydrogen cyanide. In existing acrylonitrile technologies, in addition to the problem of high water content in the hydrogen cyanide product at the top of the tower, the problem of easy clogging of the tower trays during operation is also particularly prominent. How to solve these problems is the key to improving the separation efficiency of the dehydrocyanate tower and extending the equipment's operating cycle, and it is also crucial to the successful application of hydrogen cyanide, a byproduct of the acrylonitrile plant, as a feedstock in the adiponitrile plant.

[0006] Patent CN112441944A discloses a dehydrocyanic acid tower system for acrylonitrile production, aiming to achieve high-precision separation of the dehydrocyanic acid tower through precise control of the tower and the amount of acetic acid added. By adjusting the material return flow rate of the dehydrocyanic acid tower, a cascade control system is formed with the temperature control unit and the liquid level control unit to achieve precise tower control. Simultaneously, acetic acid is added at the outlets of the first and second condensers, and flow meters are installed on the pipelines to measure the amount of acetic acid used, achieving precise addition. This method only ensures stable operation of the dehydrocyanic acid tower and guarantees that the acetic acid content in the product does not exceed the standard. It cannot obtain a low-water-content, high-purity hydrogen cyanide product using the original process, nor does it solve the problem of easy clogging of the tower plates.

[0007] Patent CN114870421A discloses a process and system for recovering acrylonitrile and hydrogen cyanide from a head fractionation column pump circulation. The process involves distilling the feed stream in a head fractionation column to generate a head fractionation column overhead distillate containing hydrogen cyanide and a bottom liquid stream containing acrylonitrile. A side stream, containing water and organic matter, is removed from the side stream. At least some water and organic matter are separated from the side stream to provide an organic stream, which is then returned to the head fractionation column. By adjusting the ratio of the amount of side stream removed from the head fractionation column (dehydrocyanide column) to the amount of organic stream returned to the head fractionation column below the side stream, the hydrogen cyanide content in the bottom product is guaranteed to be ≤500 ppm, and the acrylonitrile content in the overhead distillate ≤100 ppm. While this method can achieve a low acrylonitrile content in the overhead distillate, it does not effectively reduce the water content, failing to meet the low water content quality requirements. Summary of the Invention

[0008] To address the technical problems of high water content in the top hydrogen cyanide product and easy clogging of the trays in existing dehydrocyanate dehydrocyanation tower processes, the present invention aims to provide a separation system and process for acrylonitrile by-product hydrogen cyanide. This system enables a balanced distribution of polymerization inhibitors within the tower, effectively reducing the risk of material polymerization. Simultaneously, it reduces the residue of polymerization inhibitors in the acrylonitrile solution at the bottom of the tower, which is beneficial for improving the purity of the top and bottom materials. Combined with a special top reflux ratio design, the water content is reduced, further improving the purity of the top hydrogen cyanide. Therefore, the hydrogen cyanide product obtained by this system meets the feedstock requirements of adiponitrile units.

[0009] The specific technological principle upon which this patent is based is as follows:

[0010] In the dehydrocyanic acid dehydrogenation tower, both acrylonitrile and hydrogen cyanide are polar molecules with active properties, which are prone to polymerization. The polymers can easily clog the tower plates and affect the operation of the equipment.

[0011] Acrylonitrile polymerization is greatly affected by temperature. Polymerization can occur when the temperature is above 30°C, and both increased temperature and increased concentration will accelerate the polymerization rate of acrylonitrile.

[0012] Hydrogen cyanide is highly reactive and particularly sensitive to temperature and alkaline substances. It can undergo self-polymerization at temperatures above 20°C, and under hydrated conditions, it readily hydrolyzes to produce NH3, which is alkaline and readily triggers the self-polymerization of hydrogen cyanide.

[0013] The main technical concept of this patent is as follows:

[0014] Based on the polymerization principle of acrylonitrile and hydrogen cyanide described above, and combined with the material properties in the dehydrocyanic acid tower process, polymerization inhibitors in the dehydrocyanic acid tower process can be divided into three categories: organic acids, acidic gases, and compound polymerization inhibitors.

[0015] The aforementioned organic acids are primarily used to prevent the polymerization of liquid-phase hydrogen cyanide. In the dehydrocyanate dehydrocyanide tower, the hydrogen cyanide concentration is highest at the top. The gaseous hydrogen cyanide at the top is cooled to 8°C by an external cooler, causing some of the hydrogen cyanide to condense into a liquid phase. The uncondensed gaseous phase is further cooled to -8°C by an external recooler, ensuring maximum condensation of the hydrogen cyanide in the gaseous phase into a liquid phase, yielding liquid-phase hydrogen cyanide and a small amount of non-condensable gas. The non-condensable gas is pressurized and sent to the flare for treatment. The liquid phase cooled by the two coolers is a high-purity hydrogen cyanide product, which is prone to polymerization. However, due to the low temperature of the hydrogen cyanide at these two locations, a small amount of organic acid is added at the inlet of the cooling equipment to prevent the hydrogen cyanide liquid phase generated during condensation from polymerizing and accumulating on the heat exchanger tube sheet, causing blockage. The liquid-phase hydrogen cyanide produced after cooling by the cooler and recooler is mixed and pressurized by the dehydrocyanate tower reflux pump. A portion of the liquid-phase hydrogen cyanide is returned to the dehydrocyanate dehydrocyanide tower for purification reflux, while the remainder is distilled off into the acrylonitrile unit as hydrogen cyanide product. At this time, due to the high temperature inside the tower and the high concentration of hydrogen cyanide on the top plate of the dehydrocyanide tower, in order to prevent the liquid hydrogen cyanide returning to the tower as reflux from the top of the dehydrocyanide tower from polymerizing, a certain amount of organic acid needs to be added to the reflux stream to adjust the pH inside the tower to be acidic. Therefore, there are three points for adding organic acid: the cooler inlet, the recooler inlet, and the top reflux inlet.

[0016] To maintain the pH within the tower at 4–5, the organic acid addition rate is controlled at 5–7 kg / tHCN. An organic acid addition control system is designed: organic acid inlet streams are designed at three addition points, corresponding to the cooler inlet, recooler inlet, and tower top reflux inlet. Regulating valves, flow controllers, and flow sensors are installed on the main and branch organic acid streams to adjust the addition rate at each point. A pH sensor and pH controller are installed on the acrylonitrile product outlet pipe of the dehydrocyanic acid tower bottom to monitor the pH of the bottom liquid online. The monitoring data is transmitted to the organic acid calculation module, which calculates the required organic acid dosage based on the pH. The resulting control signal is then sent to the flow controller on the main organic acid inlet pipe, further controlling the opening of the main flow regulating valve and adjusting the total organic acid addition. Simultaneously, the flow control signal is transmitted to the organic acid distribution and metering module. The input values ​​of the flow controllers for each branch are calculated according to a certain ratio. By comparing the set values ​​of each branch's flow controller with the actual flow values ​​detected by the corresponding flow sensors, an adjustment signal is obtained to control the opening of the corresponding regulating valve. This achieves cascade adjustment of the pH of the feed liquid in the tower and the proportion of organic acid added, as well as proportional adjustment of the amount of organic acid added at different addition points, thus achieving precise pH control within the tower. This ensures that the organic acid is evenly distributed in the liquid-phase hydrogen cyanide, minimizing the risk of material polymerization, reducing water content, and improving the quality of the hydrogen cyanide product.

[0017] The aforementioned acidic gas is primarily used to neutralize ammonia in the gaseous hydrogen cyanide and prevent its polymerization. Therefore, it is added at the top gas phase pipeline of the dehydrocyanic acid tower and the inlet gas phase pipeline of the dehydrocyanic acid tower recooler. The acidic gas is added through both the top gas phase acid supply pipeline and the cooler outlet gas phase acid supply pipeline, and the amount added is constantly monitored using a gas flow monitoring system to prevent excessive addition that could affect the quality of the hydrogen cyanide product.

[0018] The aforementioned compound polymerization inhibitor is used to simultaneously prevent the polymerization of acrylonitrile and hydrogen cyanide in the feed solution. The reflux bottom liquid from the acrylonitrile unit is the feed to the dehydrocyanate tower (60-65 trays in total) between trays 40 and 43. The feed is rich in acrylonitrile and hydrogen cyanide, and the feed temperature is 40°C. During the distillation process in the dehydrocyanate tower, the temperature gradually increases from the top to the bottom, with the highest hydrogen cyanide concentration at the top and the highest acrylonitrile concentration at the bottom. Furthermore, the tray with the highest total organic matter concentration of both is located there. Therefore, a compound polymerization inhibitor is needed to effectively inhibit the polymerization of acrylonitrile and hydrogen cyanide simultaneously. The injection point of the compound polymerization inhibitor should be selected at a location with high temperature, high organic matter concentration, and high acrylonitrile concentration.

[0019] In this patent, all liquid is drawn from the central collection tank of the dehydrocyanic acid tower. This stream exchanges heat with the oil phase of the dehydrocyanic acid tower separator through a side-stream heat exchanger 3-2. After being cooled, it is further cooled to 38°C by a side-stream cooler 3-3 and then sent into the dehydrocyanic acid tower separator for oil-water phase separation. The aqueous phase from separator 3-4 is sent to the recovery tower via a recovery water pump. The oil phase from separator 3-4 is returned to one of the 20th to 24th trays in the lower section of the dehydrocyanic acid tower after heat exchange with the side-stream drawn stream via a side-stream reflux pump. Metered compound polymerization inhibitors are added to the feed stream, the tray with the highest organic concentration in the dehydrocyanic acid tower (between trays 50 and 55), and the oil phase stream from the separator at the outlet of the recovery water pump, respectively, to prevent the polymerization of acrylonitrile and hydrogen cyanide. Therefore, three addition points are set in the system: the feed stream, the tray with the highest organic concentration in the reactor, and the side-stream organic return pipeline. At the same time, the amount of compounded polymerization inhibitor added is monitored in real time by the flow monitoring component to prevent excessive addition from affecting the quality of hydrogen cyanide and acrylonitrile products.

[0020] Some technical solutions improve the tray structure by designing a high-efficiency guided solid valve. This solid valve features a convex valve plate, constructed by connecting a U-shaped plate and a vertical plate via an arc transition. Both the U-shaped and vertical plates are wider at the top and narrower at the bottom. The valve holes on both sides of the valve plate are oriented in the same direction as the liquid flow. This structure effectively improves gas-phase guidance, prolongs gas-liquid contact time, enhances gas-liquid separation efficiency, and avoids the risk of clogging.

[0021] The present invention, by employing the above technical solution, has at least the following beneficial effects:

[0022] 1. The present invention provides a separation system and process for hydrogen cyanide by-product of acrylonitrile. By controlling the input of an acidic polymerization inhibitor to prevent the polymerization of hydrogen cyanide in the cooling equipment of the top gas phase pipeline, the top liquid phase pipeline, and the condensation outer loop at a preset ratio, the risk of material polymerization in the tower and the risk of tray blockage are significantly reduced.

[0023] 2. The present invention provides a separation system and process for hydrogen cyanide by-product of acrylonitrile, which adopts a special design for the addition point and amount of organic acid, and combines a cascade control system for adjusting the flow rate ratio of different organic acid addition points and the pH of the bottom of the column, to accurately control the pH of the bottom of the column and the amount of organic acid added, reduce the risk of material polymerization, effectively prevent the clogging of the column tray, and reduce the residue of polymerization inhibitor in the acrylonitrile solution in the bottom of the column, thereby improving the quality of the solution at the top and bottom of the column.

[0024] 3. The present invention provides a separation system and process for acrylonitrile by-product hydrogen cyanide, which precisely adds organic acid, acidic gas and compounded polymerization inhibitor according to different organic forms and the concentration and temperature of organic matter at different locations, so that the polymerization inhibitor in the dehydrocyanide tower is evenly distributed, reducing the risk of material polymerization in the tower while avoiding the entrainment of impurities in the hydrogen cyanide product and improving the purity of the hydrogen cyanide product.

[0025] 4. The present invention patent provides a separation system and process for acrylonitrile by-product hydrogen cyanide, which, with the selection and ratio of different polymerization inhibitors, can better inhibit the polymerization of acrylonitrile or hydrogen cyanide.

[0026] 5. The present invention provides a separation system for acrylonitrile by-product hydrogen cyanide, which adopts a high-efficiency solid valve tray with a special structure that has a self-cleaning function, thereby improving the separation efficiency of unit mass transfer, reducing the risk of tray blockage, and extending the equipment operating cycle;

[0027] 6. The present invention provides a separation process for hydrogen cyanide by-product of acrylonitrile, which adopts a special top reflux ratio design to improve the separation efficiency of the tower, improve the purity of the top hydrogen cyanide, and reduce the water content;

[0028] 7. The present invention provides a separation system and process for acrylonitrile by-product hydrogen cyanide, wherein the hydrogen cyanide concentration at the top of the dehydrocyanate dehydrocyanate tower is ≥99.9%, the water content is ≤100ppm, the acrylonitrile content is ≤30ppm, the acid gas content is ≤200ppm, and the organic acid content is ≤20ppm; the acrylonitrile content in the bottom feed is ≥99.9%, the hydrogen cyanide content is ≤100ppm, the water content is ≤200ppm, and the compounded polymerization inhibitor content is ≤80ppm. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings and their markings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the acrylonitrile by-product hydrogen cyanide separation system according to an embodiment of the present invention;

[0031] Figure 2 This is a schematic diagram of the structure of the solid valve described in an embodiment of the present invention;

[0032] Figure 3 This is a cross-sectional schematic diagram of the solid valve described in an embodiment of the present invention;

[0033] Figure 4 This is a top view of the solid valve described in an embodiment of the present invention.

[0034] The meanings of the symbols marked in the figure are as follows:

[0035] 1-1: Dehydrocyanic acid tower; 1-2: Tray; 2-1: Cooler; 2-2: Recooler; 3-2: Side-stream heat exchanger; 3-3: Side-stream cooler; 3-4: Separator.

[0036] 1-21: U-shaped plate; 1-22: flow guide; 1-23: valve hole; 1-24: vertical plate;

[0037] 20—Organic acid main pipe, 21—Cooler acid supply line, 22—Recooler acid supply line, 23—Top reflux acid supply line;

[0038] 201—First branch regulating valve, 202—First branch flow controller, 203—First branch flow sensor, 204—Second branch regulating valve, 205—Second branch flow controller, 206—Second branch flow sensor, 207—Third branch regulating valve, 208—Third branch flow controller, 209—Third branch flow sensor, 210—Organic acid metering module, 211—pH controller, 212—pH sensor, 213—Main line regulating valve, 214—Main line flow sensor, 215—Main line flow controller, 216—Organic acid distribution metering module;

[0039] 41—Top gas phase acid supply line, 401—First branch gas flow sensor, 42—Cooler output gas phase acid supply line, 402—Second branch gas flow sensor;

[0040] 51—Feed supply line, 501—First branch reagent flow sensor, 52—Supply line to the tray with the highest organic concentration in the reactor, 502—Second branch reagent flow sensor, 53—Side line organic matter return supply line, 503—Third branch reagent flow sensor. Detailed Implementation

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific implementation methods of the present invention will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0042] To keep the drawings concise, each figure only schematically shows the parts relevant to the invention, and these do not represent the actual structure of the product. Furthermore, to facilitate understanding, in some figures, only one of components with the same structure or function is schematically depicted, or only one is labeled. In this document, "one" not only means "only one," but can also mean "more than one."

[0043] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0044] In this document, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0045] Furthermore, in the description of this application, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0046] In one embodiment, please refer to Figure 1This paper illustrates a separation system for hydrogen cyanide, a byproduct of acrylonitrile, comprising a dehydrocyanate tower 1-1, a condenser outer loop, and a polymerization inhibitor input system. The dehydrocyanate tower 1-1 undergoes gas-liquid two-phase mass and heat exchange. The condenser outer loop is connected to the top of the dehydrocyanate tower 1-1 and is equipped with a cooler 2-1 and a recooler 2-2 connected in sequence to continuously cool the gas stream output from the top of the tower and achieve partial reflux. The polymerization inhibitor input system includes an acid inlet subsystem, which comprises an acid inlet pipeline and an acid inlet control device. The acid inlet control device controls the acid inlet pipeline to input an acidic polymerization inhibitor, preventing the self-polymerization of hydrogen cyanide, into the gas phase output pipeline at the top of the dehydrocyanate tower 1-1, the liquid phase reflux pipeline at the top of the tower, and the cooling equipment on the condenser outer loop at a preset ratio, so that one branch of the condenser outer loop outputs high-purity hydrogen cyanide product.

[0047] In this embodiment, by selecting the acidic polymerization inhibitor addition points at various points on the outer loop of the condenser at the top of the tower and strictly controlling the addition ratio, the polymerization risk of hydrogen cyanide can be effectively reduced, while reducing the residual polymerization inhibitor in the hydrogen cyanide product at the top of the tower and improving the quality of the hydrogen cyanide product.

[0048] In the above embodiments, the acid inlet pipeline includes an organic acid inlet pipe, which is provided in three ways: the cooler acid supply pipeline 21, the recooler acid supply pipeline 22, and the tower top reflux acid supply pipeline 23.

[0049] The acid inlet control device includes an organic acid distribution and metering module and flow control components respectively installed on three organic acid inlet pipes. The flow control components include a first branch flow sensor 203, a first branch flow controller 202 and a first branch regulating valve 201 installed on the cooler acid supply pipe 21; a second branch flow sensor 206, a second branch flow controller 205 and a second branch regulating valve 204 installed on the recooler acid supply pipe 22; and a third branch flow sensor 209, a third branch flow controller 208 and a third branch regulating valve 207 installed on the tower top reflux acid supply pipe 23. The first branch flow sensor 203 is connected to the input terminal of the first branch flow controller 202, and the output terminal of the first branch flow controller 202 is connected to the first branch regulating valve 201. The second branch flow sensor 206 is connected to the input terminal of the second branch flow controller 205, and the output terminal of the second branch flow controller 205 is connected to the second branch regulating valve 204. The third branch flow sensor 209 is connected to the input terminal of the third branch flow controller 208, and the output terminal of the third branch flow controller 208 is connected to the third branch regulating valve 207. The first branch flow controller 202, the second branch flow controller 205, and the third branch flow controller 208 are all connected to the output terminal of the organic acid distribution metering module 216.

[0050] Furthermore, the acid inlet control device also includes an organic acid metering module 210, which is electrically connected to the main flow controller 215 installed on the organic acid main pipe 20. The input end of the main flow controller 215 is connected to the main flow sensor 214, and its first output end is connected to the main regulating valve 213, and its second output end is connected to the organic acid distribution metering module 216.

[0051] Furthermore, the bottom of the dehydrocyanic acid tower 1-1 is connected to an acrylonitrile product outlet pipe, and an acid-base monitoring component is installed on the acrylonitrile product outlet pipe. The acid-base monitoring component includes a pH sensor 212 and a pH controller 211. The pH sensor 212 is electrically connected to the pH controller 211, and the pH controller 211 is electrically connected to the organic acid metering module 210.

[0052] In a preferred embodiment, the acid inlet line also includes an acid gas inlet line, which has two branches: the tower top gas phase acid supply line 41 and the cooler output gas phase acid supply line 42.

[0053] The acid inlet control device also includes a gas flow monitoring component, which includes a first branch gas flow sensor 401 installed on the gas phase acid supply line 41 at the top of the tower and a second branch gas flow sensor 402 installed on the gas phase acid supply line 42 at the cooler output.

[0054] This application employs a special design for the addition point and amount of polymerization inhibitor, combined with a cascade control system for adjusting the flow rate ratio at different organic acid addition points and the pH of the column bottom. This precisely controls the pH of the column bottom and the amount of organic acid added, reducing the risk of material polymerization, effectively preventing tray blockage, and reducing the residue of polymerization inhibitor in the acrylonitrile solution in the column bottom, thereby improving the quality of the column bottom solution.

[0055] In the above embodiments, the polymerization inhibitor input system further includes a compound input subsystem, which includes a compound polymerization inhibitor input pipeline and a compound input control device.

[0056] The compounded polymerization inhibitor input pipeline is set up with three lines: feed supply pipeline 51, supply pipeline 52 at the tray with the highest organic concentration in the reactor, and side line organic matter return supply pipeline 53.

[0057] The compounding input control device includes a reagent flow monitoring component, which includes a first branch reagent flow sensor 501 located on the feed supply line 51, a second branch reagent flow sensor 502 located on the supply line 52 at the highest organic concentration tray in the reactor, and a third branch reagent flow sensor 503 located on the side line organic matter return supply line 53.

[0058] This application comprehensively considers the polymerization conditions of acrylonitrile and hydrogen cyanide, and combines the properties of the materials in the dehydrocyanic acid tower process. It specifically selects the type and addition point of the polymerization inhibitor in the tower, and precisely controls the addition ratio to ensure that the polymerization inhibitor is evenly distributed in the reactor, thereby minimizing the polymerization risk of the materials, avoiding the risk of tower plate blockage, and maintaining the long-term stable operation of the system.

[0059] In another embodiment, the interior of the dehydrocyanic acid tower 1-1 is provided with several trays 1-2 spaced vertically. Multiple solid valves with guiding functions are evenly distributed on the trays 1-2 in the mass transfer zone. (See attached diagram) Figure 2-4 The valve has an upwardly convex valve plate, which is designed in two parts: a U-shaped plate 1-21 and a vertical plate 1-24. The bottom edges of both the U-shaped plate 1-21 and the vertical plate 1-24 are connected to the tray 1-2. The tops of the two valve plates are connected in an arc shape and have a smooth surface, which can buffer the airflow and prevent polymer accumulation and blockage.

[0060] Specifically, the U-shaped plate 1-21 is connected to the tray 1-2 at an angle of α, which is preferably 8 to 17°. The vertical plate 1-24 is connected to the tray 1-2 perpendicularly. The valve body height of the high-efficiency guided solid valve is preferably 8 to 40 mm.

[0061] In a preferred embodiment, both the U-shaped plate 1-21 and the vertical plate 1-24 are wider at the top and narrower at the bottom, with the two short sides having the same length and the ratio of the length of the long side to the short side being 1.2 to 1.8. This structure can effectively improve the gas phase guiding effect. At the same time, the U-shaped plate 1-21 and the vertical plate 1-24 surround the tray to form two valve holes 1-23 on the left and right sides. The length of the valve holes 1-23 is generally 20 to 150 mm, and the opening direction of the valve holes 1-23 is parallel to the liquid flow direction. The gas phase material from below the tray flows in a parallel direction with the liquid phase on the tray 1-2 through the two valve holes, which can effectively promote the liquid phase flow and increase the gas-liquid contact area and contact time, thereby greatly improving the gas-liquid mass transfer efficiency. At the same time, the design of the valve hole size can control the gas phase material to pass through the solid valve at a higher gas velocity, flushing out the polymer that may accumulate in the solid valve and further improving the anti-clogging performance of the solid valve.

[0062] In another preferred embodiment, guide ports 1-22 are provided at the top and bottom of the U-shaped plates 1-21. The upper guide port reduces eddies and improves the airflow direction; a small amount of gas phase flows out from the lower guide port and comes into vertical contact with the liquid phase in the mass transfer zone, increasing gas-liquid disturbance, enhancing gas-liquid contact effect, and improving the separation efficiency of the tray.

[0063] In another embodiment, this application further provides a separation process for hydrogen cyanide, a byproduct of acrylonitrile, comprising the following steps:

[0064] The feed stream rich in acrylonitrile and hydrogen cyanide is provided to the dehydrocyanate tower 1-1 for mass and heat exchange between the gas and liquid phases. The gaseous hydrogen cyanide at the top of the dehydrocyanate tower 1-1 is partially refluxed after being continuously cooled by the condenser outer ring passage.

[0065] An acidic polymerization inhibitor to prevent the self-polymerization of hydrogen cyanide is introduced at a preset ratio into the gas phase output pipeline at the top of the dehydrocyanide tower, the liquid phase return pipeline at the top of the tower, and the cooling equipment in the outer condensation loop, so that a branch of the outer condensation loop outputs high-purity hydrogen cyanide product.

[0066] In the above embodiments, the acidic polymerization inhibitor includes an organic acid, which is selected from one or more of the following: formic acid, acetic acid, propionic acid, sulfuric acid, and phosphoric acid, in an acidic aqueous solution. The addition of organic acid is controlled by the output signal of the organic acid distribution and metering module to add metered organic acid to the cooler acid supply line, the recooler acid supply line, and the top reflux acid supply line of the tower. The organic acid distribution and metering module performs distribution and metering according to the output signal of the organic acid metering module, and the organic acid metering module measures the total amount of organic acid based on the pH value of the acrylonitrile solution in the bottom of the dehydrocyanate tower.

[0067] Specifically, the pH value of the acrylonitrile solution in the bottom of the dehydrocyanic acid tower 1-1 is 4-5, the total amount of organic acid is controlled at 5-7 kg / tHCN, and the organic acid distribution metering module controls the mass flow rate ratio of organic acid added to the acid supply pipeline of the cooler, the acid supply pipeline of the recooler, and the acid supply pipeline of the top of the tower to be (1.2-1.8):1:(20-24).

[0068] In the above embodiments, the acidic polymerization inhibitor also includes an acidic gas. The acidic gas is selected from one or more of sulfur dioxide, phosphorus dioxide and sulfur trioxide. The acidic gas is added by metering the acidic gas into the gas phase supply pipeline at the top of the tower and the gas phase supply pipeline at the output of the cooler under the real-time monitoring of the gas flow monitoring component.

[0069] Specifically, the amount of acidic gas added is 20-40 L / tHCN, and the mass flow rate ratio of acidic gas added to the gas phase supply pipeline at the top of the tower and the gas phase supply pipeline at the output of the cooler is (1-2):1.

[0070] The above separation process also includes the following steps:

[0071] Under real-time monitoring by the reagent flow monitoring component, the compound polymerization inhibitor to prevent the polymerization of acrylonitrile and hydrogen cyanide is metered and input into the feed supply pipeline, the supply pipeline at the tray with the highest organic concentration in the reactor, and the side-stream organic matter return supply pipeline.

[0072] Specifically, the compound polymerization inhibitor is prepared by compounding one or more organic compounds selected from hydroquinone, p-hydroxyanisole, ethylene glycol, diethylene glycol monomethyl ether, hydroquinone, and alkylamine. The amount of compound polymerization inhibitor added is 0.1-0.2 kg / t of feed. The mass flow rate ratio of the compound polymerization inhibitor added to the feed supply pipeline, the supply pipeline at the tray with the highest organic concentration in the reactor, and the side-stream organic matter return supply pipeline is (2.5-3.2):1:(3-3.6).

[0073] In some specific implementations, the operating pressure of the dehydrocyanic acid tower 1-1 is 70-75 kPa, resulting in a tower top temperature of 17-18°C, less than 20°C, which effectively prevents the polymerization of high-purity hydrogen cyanide at the tower top; the cooler outlet temperature of the dehydrocyanic acid tower 1-1 is 8°C, and the recooler outlet temperature is -8°C; the flow rate ratio of the reflux liquid at the top of the dehydrocyanic acid tower to the high-purity hydrogen cyanide product liquid is 5.7-6.8, which ensures that the water content in the high-purity hydrogen cyanide is ≤100 ppm and the acrylonitrile content is ≤30 ppm; the bottom pressure of the dehydrocyanic acid tower is 95-102 kPa, and the bottom temperature is 73-75°C; the temperature of the separator 3-4 is 38°C; and the pH of the aqueous phase in the separator 3-4 is periodically monitored to ensure it is between 3 and 5.

[0074] The technical solution and its effects of the present invention are further illustrated below with reference to specific embodiments:

[0075] Example 1

[0076] A certain acrylonitrile unit has a dehydrocyanic acid tower with 62 trays. The mass transfer zone of the trays uses the high-efficiency guided solid valve of this application. The specific structural parameters of the solid valve are: α = 15°, valve body height 16mm, the ratio of the length of the wide side to the narrow side is 1.5, and the valve orifice length is 60mm.

[0077] The rich liquor from the upstream acrylonitrile recovery tower, containing 86.9 wt% acrylonitrile, 7.9 wt% hydrogen cyanide, and 5.2 wt% water, enters the 42nd tray of the dehydrocyanic acid dehydrogenation tower 1-1. Operating under vacuum with a top pressure of 73 kPa, the tower top temperature is maintained at 17.4℃, below 20℃, effectively preventing the polymerization of high-purity hydrogen cyanide at the top. The outlet temperature of the dehydrocyanic acid dehydrogenation tower cooler is 8℃, and the outlet temperature of the dehydrocyanic acid dehydrogenation tower recooler is -8℃. The flow ratio of the top reflux liquid to the high-purity hydrogen cyanide product liquid is 5.7. The bottom pressure of dehydrocyanic acid dehydrogenation tower 1-1 is 100 kPa, and the bottom temperature is 74.8℃. The temperature of the separator 3-4 is 38℃.

[0078] 90wt% acetic acid was selected as the organic acid polymerization inhibitor. By controlling the pH of the acrylonitrile solution in the bottom liquid of the dehydrocyanate tower, the total amount of acetic acid was made to be approximately 5.5 kg / tHCN. Organic acid was added to the acid supply lines to the cooler, recooler, and top reflux acid supply lines at a mass flow rate ratio of 1.2:1:20. At this time, the pH of the acrylonitrile solution in the bottom liquid of the dehydrocyanate tower was 4.5. At the same time, the pH of the aqueous phase in the separator was measured at 4.2 at regular intervals, which met the pH control requirements of the tower.

[0079] Sulfur dioxide was selected as the acidic gas polymerization inhibitor. Based on 35L / tHCN, the total amount of sulfur dioxide added was calculated, and the volumetric flow rate ratio of the gas phase acid supply line at the top of the tower to the gas phase acid supply line at the output of the cooler was controlled to be 1:1.

[0080] p-hydroxyanisole was selected as the compound polymerization inhibitor. The total amount of compound polymerization inhibitor added was calculated based on a feed rate of 0.15 kg / t. The mass flow rate ratio of the feed supply pipeline, the supply pipeline at the tray with the highest organic concentration in the reactor, and the side-stream organic matter return supply pipeline was controlled to be 2.5:1:3. The addition point of the side-stream organic matter return supply pipeline was the 52nd tray of the tower.

[0081] At this point, the concentration of high-purity hydrogen cyanide at the top of the column was 99.9%, the water content was 90 ppm, the acrylonitrile content was 25 ppm, the SO2 content was 100 ppm, and the organic acid content was 15 ppm; the acrylonitrile liquid phase at the bottom of the column contained 99.9% acrylonitrile, 80 ppm hydrogen cyanide, 130 ppm water, 60 ppm of compound polymerization inhibitor, and the pH at the bottom of the column was 4.5. Detailed results are shown in Table 1.

[0082] Example 2

[0083] The flow rate ratio of the reflux liquid at the top of the dehydrocyanic acid tower to the high-purity hydrogen cyanic acid product liquid was changed to 6.8. All other technical contents were the same as in Example 1. The results are shown in Table 1.

[0084] Comparative Example 1

[0085] The flow rate ratio of the reflux liquid at the top of the dehydrocyanic acid tower to the high-purity hydrogen cyanic acid product liquid was changed to 5.2. All other technical contents were the same as in Example 1. The results are shown in Table 1.

[0086] Example 3

[0087] The pH of the bottom liquid in the tower was controlled at 4.2, and the amount of 90wt% acetic acid added was adjusted to approximately 7 kg / tHCN. All other technical contents were the same as in Example 1. The results are shown in Table 1.

[0088] Example 4

[0089] The amount of sulfur dioxide added was changed to 20 L / tHCN, and all other technical contents were the same as in Example 1. The results are shown in Table 1.

[0090] Example 5

[0091] Acetic acid was controlled at a mass flow ratio of 1.2:1:24 for the organic acid branches 21, 22 and 23. All other technical contents were the same as in Example 1. The results are shown in Table 1.

[0092] Example 6

[0093] Acetic acid was controlled at a mass flow ratio of 1.8:1:20 for organic acid branch pipes 21, 22 and 23. All other technical contents were the same as in Example 1. The results are shown in Table 1.

[0094] Example 7

[0095] SO2 was added at a volumetric flow rate ratio of 2:1 for branches 41 and 42. All other technical details were the same as in Example 1. The results are shown in Table 1.

[0096] Example 8

[0097] The mass flow ratio of the compounded polymerization inhibitor in branch pipes 51, 52, and 53 was controlled at 3.2:1:3. All other technical contents were the same as in Example 1. The results are shown in Table 1.

[0098] Example 9

[0099] The mass flow ratio of the compounded polymerization inhibitor in branch pipes 51, 52, and 53 was controlled at 2.5:1:3.6. All other technical contents were the same as in Example 1. The results are shown in Table 1.

[0100] Example 10

[0101] The organic acid was replaced with 92% wt sulfuric acid, and all other technical contents were the same as in Example 1. The results are shown in Table 1.

[0102] Example 11

[0103] The organic acid was replaced with formic acid and 10% wt acetic acid in a 1:1 ratio. All other technical contents were the same as in Example 1. The results are shown in Table 1.

[0104] Example 12

[0105] The acidic gas was replaced with SO3, and all other technical contents were the same as in Example 1. The results are shown in Table 1.

[0106] Example 13

[0107] The compound polymerization inhibitor was replaced with a mixture of hydroquinone, ethylene glycol and alkylamine in a ratio of 4:3:1. All other technical contents were the same as in Example 1. The results are shown in Table 1.

[0108] Comparative Example 2

[0109] The dehydrocyanate tower was replaced with a traditional floating valve, and all other technical aspects were the same as in Example 1. The results are shown in Table 1.

[0110] As shown in Table 1, the separation system and process for acrylonitrile by-product hydrogen cyanide of this application result in the following: at the top of the column, the concentration of hydrogen cyanide is ≥99.9%, the water content is ≤100ppm, the acrylonitrile content is ≤30ppm, the acid gas content is ≤200ppm, and the organic acid content is ≤20ppm; in the bottom liquid phase of the column, the acrylonitrile content is ≥99.9%, the hydrogen cyanide content is ≤100ppm, the water content is ≤200ppm, and the compounded polymerization inhibitor content is ≤80ppm.

[0111] Table 1: Results of the Examples

[0112]

[0113] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A separation system for hydrogen cyanide as a by-product of acrylonitrile production, characterized by, include: The dehydrocyanate tower undergoes mass and heat exchange between the gas and liquid phases inside. The condenser outer loop is connected to the top of the dehydrocyanic acid tower and is used to cool the gas stream output from the top of the tower and achieve partial reflux. The polymerization inhibitor input system includes an acid inlet subsystem, which includes an acid inlet pipeline and an acid inlet control device. The acid inlet control device controls the acid inlet pipeline to input an acidic polymerization inhibitor to prevent hydrogen cyanide self-polymerization into the gas phase pipeline at the top of the dehydrocyanide tower, the liquid phase pipeline returning to the top of the tower, and the cooling equipment on the condensation outer loop at a preset ratio, so that a branch of the condensation outer loop outputs high-purity hydrogen cyanide product. The acid inlet pipeline includes an organic acid inlet pipeline and an acidic gas inlet pipeline. The organic acid inlet pipeline has three branches: a cooler acid supply pipeline, a recooler acid supply pipeline, and a tower top reflux acid supply pipeline, to supply organic acid to the cooling equipment on the condenser outer loop and the tower top reflux liquid phase pipeline. The acidic gas inlet pipeline has two branches: a tower top gas phase acid supply pipeline and a cooler output gas phase acid supply pipeline, to supply acidic gas to the tower top output gas phase pipeline of the dehydrocyanic acid tower. The polymerization inhibitor input system also includes a compound input subsystem, which includes a compound polymerization inhibitor input pipeline and a compound input control device. The compound polymerization inhibitor input pipeline is configured with three lines: a feed supply pipeline, a supply pipeline to the tray with the highest organic concentration in the reactor, and a side-line organic matter return supply pipeline, to input the compound polymerization inhibitor that prevents the polymerization of acrylonitrile and hydrogen cyanide.

2. The separation system for acrylonitrile-derived hydrogen cyanide according to claim 1, characterized in that, The acid inlet control device includes an organic acid distribution and metering module and flow control components respectively installed on three organic acid inlet pipes. Each flow control component includes a flow sensor, a flow controller and a regulating valve. The flow sensor and the regulating valve are electrically connected to the corresponding flow controllers of each group. The flow controllers of the three groups are all electrically connected to the organic acid distribution and metering module. The acid inlet control device also includes an organic acid metering module. The organic acid metering module is electrically connected to the main flow controller installed on the main pipeline of the organic acid inlet pipe. The input end of the main flow controller is connected to the main flow sensor, and its first output end is connected to the main regulating valve, and its second output end is connected to the organic acid distribution metering module. The bottom of the dehydrocyanic acid tower is connected to an acrylonitrile product outlet pipe, and an acid-base monitoring component is installed on the acrylonitrile product outlet pipe. The acid-base monitoring component includes a pH sensor and a pH controller. The pH sensor is electrically connected to the pH controller, and the pH controller is electrically connected to the organic acid metering module.

3. The separation system for acrylonitrile-derived hydrogen cyanide according to claim 2, characterized in that, The acid inlet control device also includes a gas flow monitoring component, which includes a first branch gas flow sensor located on the gas phase acid supply pipeline at the top of the tower and a second branch gas flow sensor located on the gas phase acid supply pipeline at the output of the cooler.

4. The separation system for acrylonitrile-derived hydrogen cyanide according to claim 1, characterized in that, The compounding input control device includes a reagent flow monitoring component, which includes a first branch reagent flow sensor on the feed supply pipeline, a second branch reagent flow sensor on the supply pipeline at the tray with the highest organic concentration in the reactor, and a third branch reagent flow sensor on the side-line organic matter return supply pipeline.

5. The separation system for acrylonitrile-derived hydrogen cyanide according to claim 1, characterized in that, The interior of the dehydrocyanic acid tower is equipped with several trays arranged vertically. On each tray, a number of solid valves with guiding function are evenly distributed in the mass transfer zone. Each solid valve has an upwardly convex valve plate, and both ends of the valve plate are connected to the tray. The valve orifice of the valve plate is opened in the same direction as the liquid flow direction.

6. The separation system for acrylonitrile-derived hydrogen cyanide according to claim 5, characterized in that, The valve plate is constructed by connecting a U-shaped plate and a vertical plate through an arc transition, and both the U-shaped plate and the vertical plate have a structure that is wider at the top and narrower at the bottom; and / or, The upper and lower parts of the U-shaped plate are respectively provided with flow guides.

7. A process for the separation of hydrogen cyanide as a by-product of acrylonitrile production, characterized in that, The separation system for acrylonitrile byproduct hydrogen cyanide according to any one of claims 1-6, the separation process comprising the following steps: The feed stream rich in acrylonitrile and hydrogen cyanide is provided to the dehydrocyanate tower for mass and heat exchange between the gas and liquid phases. The gaseous hydrogen cyanide exiting from the top of the dehydrocyanate tower is partially refluxed after continuous cooling through the outer ring condenser loop. An acidic polymerization inhibitor to prevent hydrogen cyanide self-polymerization is introduced at a preset ratio into the gas phase output pipeline at the top of the dehydrocyanic acid tower, the liquid phase return pipeline at the top of the tower, and the cooling equipment on the outer condensation loop, so that a branch of the outer condensation loop outputs high-purity hydrogen cyanide product. The acidic polymerization inhibitor includes organic acid and acidic gas. The organic acid is added to the acid supply line of the cooler, the acid supply line of the recooler, and the acid supply line of the top reflux of the tower, respectively. The acidic gas is added to the gas phase acid supply line of the top of the tower and the gas phase acid supply line of the cooler output. The separation process further includes the step of metering and inputting a compounded polymerization inhibitor to prevent the polymerization of acrylonitrile and hydrogen cyanide into the feed supply pipeline, the supply pipeline at the tray with the highest organic concentration in the reactor, and the side-stream organic matter return supply pipeline.

8. The separation process according to claim 7, characterized in that, The addition of organic acid is controlled by the output signal of the organic acid distribution and metering module to add metered organic acid to the cooler acid supply line, the recooler acid supply line and the tower top reflux acid supply line respectively. The organic acid distribution and metering module performs distribution and metering based on the output signal of the organic acid metering module, and the organic acid metering module measures the total amount of organic acid based on the pH value of the acrylonitrile solution in the bottom of the dehydrocyanate tower. The pH value of the acrylonitrile solution in the bottom of the dehydrocyanate tower is 4~5, the total amount of organic acid is controlled at 5~7 kg / tHCN, and the organic acid distribution and metering module controls the mass flow rate ratio of organic acid added to the acid supply pipeline of the cooler, the acid supply pipeline of the recooler and the acid supply pipeline of the top of the tower to be (1.2~1.8):1:(20~24).

9. The separation process according to claim 8, characterized in that, The addition of acidic gas is controlled by the gas flow monitoring component in real time, which adds metered acidic gas to the gas phase supply pipeline at the top of the tower and the gas phase supply pipeline at the output of the cooler. The amount of acidic gas added is 20~40L / tHCN, and the mass flow rate ratio of the acidic gas added to the gas phase supply pipeline at the top of the tower and the gas phase supply pipeline at the output of the cooler is (1~2):

1.

10. The separation process of claim 7, wherein, It also includes the following steps: Under real-time monitoring by the reagent flow monitoring component, a compound polymerization inhibitor to prevent the polymerization of acrylonitrile and hydrogen cyanide is metered and input into the feed supply pipeline, the supply pipeline at the highest organic concentration tray in the reactor, and the side-stream organic matter return supply pipeline, respectively; the amount of the compound polymerization inhibitor added is 0.1~0.2 kg / t feed, and the mass flow rate ratio of the compound polymerization inhibitor added to the feed supply pipeline, the supply pipeline at the highest organic concentration tray in the reactor, and the side-stream organic matter return supply pipeline is (2.5~3.2):1:(3~3.6); And / or, the reflux ratio of the dehydrocyanic acid tower is 5.7 to 6.8.

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