A device and process for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid

Abstract

The present invention discloses an apparatus for continuously producing hydroxyacetonitrile using liquid-phase hydrocyanic acid. The apparatus comprises multiple reactors connected in series, wherein a first-stage reactor is connected to a formaldehyde feed pipe, a hydrocyanic acid feed pipe, and a catalyst feed pipe for continuous feeding; adjacent reactors are connected in series via discharge pipes; each first-stage reactor is provided with a mixing mechanism; a neutralization tank and a storage tank are sequentially connected to the final-stage reactor; the neutralization tank is used to receive the reaction liquid flowing out of the final-stage reactor; the storage tank is used to receive the finished hydroxyacetonitrile discharged from the neutralization tank; and each first-stage reactor and the storage tank are connected to a heat exchange mechanism. The present invention also provides a process for continuously producing hydroxyacetonitrile using liquid-phase hydrocyanic acid. The apparatus has a simple structure and process, operates smoothly, is suitable for industrial production, and can ensure the stability of product quality and yield.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical production and relates to a device and process for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid. Background Art

[0002] Hydroxyacetonitrile (2-Hydroxyacetonitrile) is soluble in water, unstable to heat and alkali, and readily polymerizes. It readily decomposes into formaldehyde and hydrocyanic acid, initiating the polymerization of hydrocyanic acid. After polymerization, the color darkens and heat is released, further promoting polymerization. Hydroxyacetonitrile can be hydrolyzed to glycolic acid under acidic conditions. When mixed with ammonia, it spontaneously generates aminoacetonitrile, which can be condensed to produce serine, and then hydrolyzed with alkaline or hydrolysis to produce glycine. Hydroxyacetonitrile reacts with ammonia at high temperatures to produce iminodiacetonitrile. It reacts with aniline to produce anilinoacetonitrile, which is used in the production of indigo. Through esterification, it is used to synthesize various compounds, such as herbicides like chloromethyl. Hydroxyacetonitrile is also the main raw material for many chelating agents and is a good flotation agent.

[0003] The main methods for preparing hydroxyacetonitrile include acetonitrile oxidation and hydrocyanic acid hydroxymethylation. In industrial production, the hydrocyanic acid hydroxymethylation method is the main method. The principle of the hydrocyanic acid hydroxymethylation method is that formaldehyde and hydrocyanic acid react under appropriate acid and base conditions to produce hydroxyacetonitrile at normal pressure. The reaction releases a large amount of heat. The reaction equation is as follows:

[0004] HCN+HCHO→HOCH2CN-Q

[0005] Although the reaction principle is simple, due to the highly active chemical properties of hydrocyanic acid and hydroxyacetonitrile, they readily polymerize under alkaline conditions, at room temperature, or with extended residence times. Furthermore, because hydrocyanic acid is highly toxic, it is typically reacted with an excess of industrial formaldehyde solution, resulting in a high level of residual formaldehyde in the hydroxyacetonitrile product. However, there is no effective method for removing this residual formaldehyde, which in turn affects the downstream production of hydroxyacetonitrile products (such as aminoacetonitrile and glycine), resulting in side reactions and the formation of impurities. Formaldehyde can also generate colored impurities, darkening the color of downstream products and affecting product quality.

[0006] The hydrocyanic acid hydroxymethylation method can be divided into a gas phase method and a liquid phase method based on the phase of the raw hydrocyanic acid. The hydrocyanic acid in the gas phase method is gaseous, while the hydrocyanic acid in the liquid phase method is liquid. Domestically, hydroxyacetonitrile is mostly produced by reacting low-concentration gaseous hydrocyanic acid with formaldehyde. Gas-phase hydrocyanic acid is mostly produced by ammoxidation of natural gas or cracking of light oil. The hydrocyanic acid concentration is relatively low, and the hydroxyacetonitrile product is absorbed by formaldehyde solution. For example, Chinese patent document CN201410460442.4 discloses a method for the industrial continuous production of hydroxyacetonitrile by gas-phase hydrocyanic acid, and Chinese patent document CN201610000966.4 discloses a method for producing hydroxyacetonitrile by gas-phase hydrocyanic acid containing cyanide tail gas. Due to the low concentration of gaseous hydrocyanic acid, although the reaction is easy to control, it consumes a lot of energy and the product contains a high impurity content.

[0007] The method for synthesizing hydroxyacetonitrile with liquid phase hydrocyanic acid is mainly a batch process, and there is no report on the industrial continuous production of hydroxyacetonitrile with liquid phase hydrocyanic acid.

[0008] Chinese patent document CN201710313478.3 discloses an industrial preparation method for hydroxyacetonitrile. The method uses liquid hydrocyanic acid and formaldehyde to produce hydroxyacetonitrile. After the formaldehyde temperature is cooled to 20°C, hydrocyanic acid is added dropwise. The pH is controlled at 6.5-7.5 by a dropper. After the addition is complete, the temperature is controlled and stirred for about 30 minutes. After sampling and analysis, acid is added to terminate the reaction and the product is transferred to a storage tank. The formaldehyde content of the finished hydroxyacetonitrile solution does not exceed 0.2%, and the free hydrocyanic acid content does not exceed 0.25%. This method is batch production and is not suitable for large-scale industrial continuous production. The formaldehyde content in the finished product is high, which limits the application of hydroxyacetonitrile products.

[0009] Chinese patent document CN200610048135.0 discloses a method for producing hydroxyacetonitrile using liquid hydrocyanic acid, a byproduct of acrylonitrile. This method involves first adding a formaldehyde solution to a reactor, then adding a catalyst, cooling the solution to 0-20°C, and then dropwise adding hydrocyanic acid at a ratio of 1:1-1.5. An addition reaction then occurs at 0-40°C to produce hydroxyacetonitrile. After the reaction, the pH is adjusted to 2-5 with an inorganic acid to obtain the finished product. This method is still a batch process, far from large-scale continuous industrial production. Furthermore, the pH value for the addition reaction is not specified, posing a risk of polymerization in industrial production.

[0010] As mentioned above, the liquid phase hydrocyanic acid batch process produces hydroxyacetonitrile, and the hydrocyanic acid feed is mainly added dropwise, which has a good mixing effect between hydrocyanic acid and the material, low heat release, uniform and controllable reaction, and a relatively high reaction pH value, generally reaching 6.5 to 9. At present, the industrial production of hydroxyacetonitrile by liquid phase hydrocyanic acid generally adopts a batch process, which has the following main characteristics: the above batch process has many disadvantages: 1) the dropwise feed amount is small, the industrial production scale is small, and the labor intensity is high; 2) batch production, the quality is unstable; 3) the feed is generally made with excessive formaldehyde, and the residual formaldehyde content of the hydroxyacetonitrile product is high. There is no effective method to remove the residual formaldehyde, which in turn affects the downstream production of hydroxyacetonitrile (such as aminoacetonitrile and glycine), causes side reactions and the formation of impurities. Formaldehyde will generate some colored impurities, causing the color of downstream products to become darker, affecting product quality, thereby limiting the application range of hydroxyacetonitrile.

[0011] In the continuous production of hydroxyacetonitrile from liquid-phase hydrocyanic acid, continuous feeding makes the reaction faster, more likely to produce by-products, and increases the risk. As a result, there are many difficulties in the continuous production of hydroxyacetonitrile by the liquid-phase method. This is also the reason why there is currently no suitable industrial continuous production process for hydroxyacetonitrile by the liquid-phase method.

[0012] Based on this, it is extremely necessary for those skilled in the art to provide a device and process for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid that has a simple structure and process, is suitable for industrial production, and ensures product quality and yield. Summary of the Invention

[0013] The present invention aims to address the deficiencies in the above-mentioned prior art and to provide a device and process for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid, which has a simple structure and process, stable operation, is suitable for industrial production, and ensures product quality and yield stability.

[0014] The technical solutions provided by the present invention are as follows:

[0015] A device for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid comprises a plurality of reactors connected in series, wherein a first-stage reactor is connected to a formaldehyde feed pipe, a hydrocyanic acid feed pipe, and a catalyst feed pipe for continuous feeding; adjacent reactors are connected in series via discharge pipes; and a mixing mechanism is provided in each first-stage reactor.

[0016] It also includes a neutralization tank and a storage tank connected in sequence to the final reactor; the neutralization tank is used to receive the reaction liquid flowing out of the final reactor; the storage tank is used to receive the hydroxyacetonitrile product discharged from the neutralization tank;

[0017] Wherein, each stage reactor and storage tank are connected with a heat exchange mechanism.

[0018] Preferably, the heat exchange mechanism includes an external circulation cooling loop with a circulation pump and a circulation cooler connected to the primary reactor, and the material at the outlet of the circulation cooler is returned to the primary reactor through the external circulation cooling loop;

[0019] The heat exchange mechanism includes heat exchange coils arranged in the remaining reactors connected in series with the primary reactor and in the neutralization tank, and the heat exchange coils are used for circulating cooling medium.

[0020] Furthermore, the heat exchange mechanism also includes a heat exchange jacket connected to any one-stage reactor, and the heat exchange jacket is used to circulate a cooling medium.

[0021] Furthermore, the device also includes a volatile gas condenser, and the volatile gases from the circulating cooler, reactor, neutralization tank and storage tank are collected in the volatile gas condenser. The outlet of the volatile gas condenser is connected to the primary reactor, so that the volatile gas is condensed and returned to the primary reactor for recycling.

[0022] Furthermore, each stage reactor is provided with a thermometer for monitoring the reaction temperature, and the outlet of the circulation cooler is provided with a thermometer for monitoring the temperature of the reaction material returning to each reactor; wherein: the outlet temperature of the circulation cooler is controlled to be -5 to 10°C, the circulation ratio of the material flow rate returning to the first stage reactor from the outlet of the circulation cooler to the material flow rate overflowing to the next stage reactor is controlled to be 5 to 20, and the temperature in the reactor is controlled to be 10 to 25°C.

[0023] Furthermore, the primary reactor is provided with a pH meter for monitoring the pH value of the reaction; the catalyst feed pipe is provided with a catalyst feed valve, and the outlet of the catalyst feed pipe is connected to the primary reactor, and the pH in the reactor is controlled to be 3-5.5 by adjusting the catalyst feed valve.

[0024] Furthermore, the device also includes a control system, and the thermometer, pH meter, and catalyst feed valve are all electrically connected to the control system.

[0025] Preferably, the mixing mechanism comprises an agitator provided in each stage of the reactor, and the agitator is provided with at least two layers of stirring paddles.

[0026] Preferably, the neutralization tank is arranged in parallel with at least two stages downstream of the final reactor, and any neutralization tank is connected with an online hydrocyanic acid analyzer, a formaldehyde analyzer, an inorganic acid feeding pipe, a thermometer, and a pH meter.

[0027] Preferably, a first hydrocyanic acid distributor and a second hydrocyanic acid distributor are respectively provided in the primary reactor; the first hydrocyanic acid distributor and the second hydrocyanic acid distributor are relatively arranged on the upper side and the lower side of the mixing mechanism.

[0028] Furthermore, the first hydrocyanic acid distributor includes a first annular tube, and the bottom of the first annular tube is an open area along its radial cross section with a fan-shaped angle θ1;

[0029] The second hydrocyanic acid distributor includes a second annular tube, and the outer side of the second annular tube is an opening area with an angle range of a fan-shaped angle θ2 along its radial cross section.

[0030] According to the device provided above, a process for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid can also be provided, comprising the following steps:

[0031] S1, formaldehyde solution, hydrocyanic acid and catalyst solution are continuously added to the primary reactor respectively, wherein hydrocyanic acid is fed in multiple layers, rapidly mixed and reacted in the primary reactor, while releasing reaction heat, the reaction liquid of the primary reactor overflows to the next reactor through the overflow port at the top to continue the reaction, and the reaction liquid after the reaction in the final reactor overflows to the neutralization tank through the overflow port at the top; wherein the reaction liquid in each reactor is controlled to have a reaction temperature within the range of 10 to 25° C. through the heat exchange system; during the reaction process, the catalyst solution is added through the catalyst feed pipe to adjust the pH value in the primary reactor to 3 to 5.5;

[0032] S2. In the neutralization tank, the overflow reaction liquid of the final reactor is analyzed for residual amounts of hydrocyanic acid and formaldehyde. If the residual amounts are qualified, inorganic acid is added and the pH value is controlled to 1-2.5 by a pH meter. The qualified hydroxyacetonitrile product after acidification is sent to a storage tank. If the residual value does not meet the requirements, an appropriate amount of formaldehyde or hydrocyanic acid is added to continue the reaction to meet the requirements, and then inorganic acid is added and the product is transferred to a storage tank.

[0033] Preferably, in step S1: the reaction temperature in each stage of the reactor is controlled to be 17-23°C.

[0034] Preferably, in step S1: the pH in the primary reactor is adjusted to 4-5.2.

[0035] Preferably, in step S1: the molar ratio of hydrocyanic acid to formaldehyde in the reaction material is controlled to be 1 to 1.15:1.

[0036] Compared with the gas-phase hydrocyanic acid method for synthesizing hydroxyacetonitrile, the liquid-phase hydrocyanic acid method uses liquid hydrocyanic acid (purity 99.5%) and formaldehyde solution (10-50% wt) as raw materials. The hydrocyanic acid raw material of the present invention is of high purity, the reaction heat removal is difficult, and the reaction control requires high precision. However, it can achieve liquid-phase continuous production and obtain the beneficial effect of high product purity. More details are as follows:

[0037] 1) The present invention adopts a multi-stage reactor to form a fully mixed reaction system with series overflow, realizes the continuous process of liquid-phase hydrocyanic acid hydroxymethylation to produce hydroxyacetonitrile, greatly improves the production scale, and can ensure stable product quality. By making formaldehyde solution, hydrocyanic acid and catalyst solution separately and continuously added into the first-stage reactor, the first-stage reactor is rapidly mixed and completes the main reaction under the action of the mixing mechanism, and enters the next-stage reactor through the discharge pipe, so that the unreacted hydrocyanic acid and formaldehyde further contact and react to generate hydroxyacetonitrile; and, the large amount of heat released during the reaction can be fully transferred by the heat exchange mechanism, which can further enhance the mass transfer and heat transfer of the reaction system, and the polymerization risk is low, thereby reliably realizing the industrial continuous production of hydroxyacetonitrile, greatly improving the production scale, and ensuring stable product quality.

[0038] 2) In the primary reactor of the present invention, the agitator adopts multi-layer stirring paddles, and the hydrocyanic acid feed pipe is designed with multi-layer heterogeneous feeding, so that the hydrocyanic acid feed can be quickly taken away by the agitator and mixed and diluted with the materials in the reactor. In addition, by setting an external circulation loop with a large circulation ratio of 15 to 30, the mixing is enhanced, the mixing effect is improved, the unevenness in the kettle is reduced, local over-concentration and overheating are avoided, side reactions are reduced, and the yield is improved. At the same time, combined with the setting of a heat exchange jacket, the probability of temperature runaway is reduced.

[0039] 3) The present invention can realize closed and clean production by uniformly collecting the gas phases at the top of the reactor, neutralization tank and storage tank, and recycling them after condensation.

[0040] 4) The present invention controls the reaction conditions to avoid polymerization accidents caused by overheating and excessively high pH, ​​and ensures stable industrial production and product quality.

[0041] In summary, through the combination of the device and process conditions of the present invention, it is possible to ensure that the hydroxyacetonitrile product produced in liquid phase is of stable quality and low impurity content; and the process is highly safe and suitable for industrial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The present invention is a schematic structural diagram of a device for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid.

[0043] Figure 2 The present invention is a schematic structural diagram of the first hydrocyanic acid distributor used in the device for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid.

[0044] Figure 3 for Figure 2 Cross-sectional view of section aa.

[0045] Figure 4 The present invention is a schematic structural diagram of the second hydrocyanic acid distributor used in the device for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid.

[0046] Figure 5 for Figure 4 Cross-sectional view of section aa.

[0047] The meanings of the symbols in the figure are as follows:

[0048] 1-reactor, 10-primary reactor, 100-formaldehyde feed pipe; 101-hydrocyanic acid feed pipe; 102-catalyst feed pipe, 1020-catalyst feed valve, 103-first hydrocyanic acid distributor, 104-second hydrocyanic acid distributor, S1 / S2-opening area, 1040-drain hole; 11-secondary reactor, 12-tertiary reactor; 2-mixing mechanism, 20-agitator; 3-neutralization tank, 30-inorganic acid feed pipe, 31- Online hydrocyanic acid analyzer, 32-online formaldehyde analyzer, 33-neutralization circulation cooling loop, 330-neutralization circulation pump, 331-neutralization circulation cooler; 4-storage tank, 40-cooling coil; 5-heat exchange mechanism, 50-external circulation cooling loop, 51-circulating pump, 52-circulating cooler, 53-heat exchange coil, 54-heat exchange jacket; 60 / 61 / 62-thermometer; 70 / 71-pH meter; 8-volatile gas condenser; 9-control system. DETAILED DESCRIPTION

[0049] The following examples are only used to illustrate the technical solution of the present invention more clearly, and are not intended to limit the scope of protection of the present invention.

[0050] In addition, in the description of the present application, “multi-level, multi-layer” means at least two levels / layers, such as two levels / layers, three levels / layers, etc., unless otherwise clearly and specifically defined.

[0051] According to an embodiment provided by the present invention, Figure 1 As shown, a device for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid comprises a multi-stage reactor 1 connected in series. The first-stage reactor 10 is connected to a formaldehyde feed pipe 100, a hydrocyanic acid feed pipe 101, and a catalyst feed pipe 102 for continuous feeding. Adjacent two-stage reactors 1 are connected in series via discharge pipes. A mixing mechanism 2 is provided in each first-stage reactor 1.

[0052] It also includes a neutralization tank 3 and a storage tank 4 connected in sequence with the final reactor; the neutralization tank 3 is used to receive the reaction liquid flowing out of the final reactor; the storage tank 4 is used to receive the hydroxyacetonitrile product discharged from the neutralization tank 3;

[0053] Wherein, any primary reactor 1 , the neutralization tank 3 and the storage tank 4 are all connected with a heat exchange mechanism 5 .

[0054] According to the device structure of this embodiment, the present invention adopts a multi-stage series fully mixed reaction structure to realize a multi-stage series overflow reaction. Specifically, the formaldehyde solution, hydrocyanic acid and catalyst solution are separately and continuously added into the first-stage reactor 10, and are rapidly mixed and reacted under the action of the mixing mechanism 2, releasing a large amount of heat. After sufficient heat is removed by the heat exchange mechanism 5, they enter the next-stage reactor through the discharge pipe, so that the unreacted hydrocyanic acid and formaldehyde further contact and react to generate hydroxyacetonitrile, and finally realize the liquid-phase hydrocyanic acid hydroxymethylation continuous method for industrial production of hydroxyacetonitrile, greatly improving the production scale and maintaining stable product quality.

[0055] As a preferred embodiment, the heat exchange mechanism 5 includes an external circulation cooling loop 50 connected to the primary reactor 10 with a circulation pump 51 and a circulation cooler 52. The material at the outlet of the circulation cooler 52 is returned to the primary reactor 10 through the external circulation cooling loop 50. In actual use, chilled brine can be used as the cooling medium in the external circulation cooling loop 50. The function of the external circulation cooling loop 50 is to enhance mixing and remove reaction heat.

[0056] The heat exchange mechanism 5 further includes heat exchange coils 53 arranged in the remaining reactors of each stage connected in series with the primary reactor 10, as well as in the neutralization tank 3 and the storage tank 4. The heat exchange coils 53 are used to circulate cooling medium.

[0057] To further enhance the heat transfer effect and improve the balance of the reaction inside the reactor, the heat exchange mechanism 5 further includes a heat exchange jacket 54 connected to any one of the reactor stages 1. A cooling medium is circulated in the heat exchange jacket 54. In actual use, the cooling medium is chilled brine.

[0058] In the above embodiment, the mixing mechanism 2 includes a stirrer 20 disposed within each reactor stage. The stirrer 20 is provided with at least two layers of stirring paddles, preferably propeller-type or paddle-type. More preferably, the stirrers 20 are spaced apart within each reactor stage 1 at intervals of 0.8 to 1.2 D (D is the reactor diameter).

[0059] The first hydrocyanic acid distributor 103 and the second hydrocyanic acid distributor 104 are respectively provided inside the primary reactor 10. Figure 1 (not shown), a first hydrocyanic acid distributor 103 and a second hydrocyanic acid distributor 104 are respectively provided in the primary reactor; the first hydrocyanic acid distributor 103 and the second hydrocyanic acid distributor 104 are arranged on the upper and lower sides of the mixing mechanism 2 relative to each other. It should be noted that when the agitator 20 of the mixing mechanism 2 is provided with at least two layers of stirring paddles, the upper side of the mixing mechanism 2 refers to the upper side of the stirring paddles other than the stirring paddles on the bottom layer; the lower side of the mixing mechanism 2 refers to the side below the stirring paddles on the bottom layer.

[0060] More specifically, the first hydrocyanic acid distributor 103 includes a first annular tube, the diameter of the first annular tube is about 1.2 to 1.5D (diameter of the stirring paddle), and the first annular tube is arranged about 0.1 to 0.5D (diameter of the stirring paddle) above the stirring paddle (except the bottom layer). The bottom of the first annular tube is an opening area S1 with a fan-shaped angle θ along its radial cross section. Figure 2 、 Figure 3 As shown, the holes in the opening area S1 are arranged in an equilateral triangle. Based on this, the hydrocyanic acid passing through the first hydrocyanic acid distributor 103 is sprayed downward and quickly brought into the agitator and mixed. In actual application, in order to obtain a more excellent uniform reaction effect, the angle θ1 is set to 90-150° and the opening aperture is set to 100°. The hole spacing is 1 to 5 times of the hole diameter, and the holes are evenly distributed in an area within the range of the fan-shaped angle θ1 along the radial cross section at the bottom of the first annular tube.

[0061] The second hydrocyanic acid distributor 104 includes a second annular tube, the diameter of the second annular tube is about 1.2 to 1.5D (diameter of the stirring paddle), and it is arranged about 0 to 0.5D (diameter of the stirring paddle) below the bottom layer. The outer side of the second annular tube is open at a fan-shaped angle θ2 along its radial cross section as an opening area S2, and holes are only opened on the outer side. At the lowest point of the second annular tube, drain holes 1040 are provided every 20° to prevent the accumulation of hydrocyanic acid. For details, see Figure 4 、 Figure 5 As shown, the holes in the opening area S2 are arranged in an equilateral triangle. Based on this, the hydrocyanic acid passing through the second hydrocyanic acid distributor 104 in the bottom layer is mainly sprayed horizontally from the side through the lateral openings of the second loop tube, and quickly mixed with the high-speed horizontal flow below the bottom stirrer. In actual application, in order to obtain a more excellent uniform reaction effect, the angle θ2 is set to 0-30° and the opening aperture is set to The hole spacing is 1 to 5 times the hole diameter, and the holes are evenly distributed in an area within the range of the fan-shaped angle θ2 along the radial cross section at the bottom of the second annular tube.

[0062] The first hydrocyanic acid distributor 103 and the second hydrocyanic acid distributor 104 can be provided with multiple layers according to requirements.

[0063] As a preferred embodiment, each primary reactor 1 is equipped with a thermometer 60 for monitoring the reaction temperature. Furthermore, a thermometer 61 is provided at the outlet of the recirculating cooler 52 for monitoring the temperature of the reaction materials returning to the primary reactor 10. The outlet temperature of the recirculating cooler 52 is controlled to be between -5°C and 10°C, and the recirculation ratio of the material flow rate returning to the primary reactor 10 from the recirculating cooler 52 outlet to the material flow rate overflowing to the next-stage reactor is controlled to be between 5 and 20. A too low recirculation ratio results in poor mixing and cooling effects, while a too high recirculation ratio wastes energy. A suitable recirculation ratio is between 5 and 20, preferably between 10 and 15. The recirculating pump 51 is a centrifugal pump, and the recirculating cooler 52 is a shell-and-tube heat exchanger. Thus, the temperature within the reactor is controlled between 10 and 25°C, more preferably between 17 and 23°C, to ensure a fully uniform reaction between the hydrocyanic acid and formaldehyde solution, thereby improving conversion and reducing the risk of runaway polymerization.

[0064] The primary reactor 10 is equipped with a pH meter 70 for monitoring the reaction pH. A catalyst feed valve 1020 is provided on the catalyst feed pipe 102, and the outlet of the catalyst feed pipe 102 is connected to the primary reactor 10. The pH in the primary reactor is controlled by adjusting the catalyst feed valve 1020 to maintain a pH between 3 and 5.5, preferably between 4 and 5.2. Acid salts such as sodium sulfite or acid hydrogen salt solutions can be used as the catalyst. By controlling the reaction pH to an appropriate level and ensuring good mixing of the added materials, the overall reaction heat release rate is reduced, and temperature control ensures reaction stability and product quality.

[0065] The device also includes a volatile gas condenser 8. The volatile gases from the circulating cooler 51, the reactor 1, the neutralization tank 3 and the storage tank 4 are collected in the volatile gas condenser 8. The outlet of the volatile gas condenser 8 is connected to the primary reactor 10, so that the volatile gases are condensed and returned to the primary reactor 10 for recycling.

[0066] The thermometers 60 / 61, pH meter 7, and catalyst feed control valve 1020 in the above embodiment are all connected to a control system 9. The control system 9 can be a PLC or DCS control system.

[0067] The neutralization tank 3 is in the final reactor (such as Figure 1The downstream of the three-stage reactor 12 is set to at least 2 stages in parallel, and any neutralization tank 3 is connected with an online hydrocyanic acid analyzer 31, an online formaldehyde analyzer 32, an inorganic acid feeding pipe 30, a thermometer 62, and a pH meter 71. The online hydrocyanic acid analyzer 31, the online formaldehyde analyzer 32, the inorganic acid feeding pipe 30, the thermometer 62, and the pH meter 71 are all commercially available instruments and are all electrically connected to the control system 8 to provide automated processing efficiency for the entire device. Among them, the neutralization tank is set to at least 2, and when the reaction liquid level of one of them reaches the set liquid level, it switches to the other neutralization tank 3 to continue receiving the overflow reaction liquid from the final reactor, thereby improving processing efficiency.

[0068] In addition, the neutralization tank 3 is also provided with a neutralization circulation cooling circuit 33 having a neutralization circulation pump 330 and a neutralization circulation cooler 331, which is used to control the temperature within the neutralization tank 3 to prevent polymerization. In actual application, one neutralization circulation cooler 331 is provided for every two neutralization tanks 3, or one neutralization circulation cooler 331 can be provided for each neutralization tank 3.

[0069] In practical applications, the storage tank 4 is a normal pressure storage tank, and 1 to 2 tanks may be provided, with a built-in cooling coil 40 to maintain the storage temperature.

[0070] In the above embodiment, the number of stages of the reactor 1 and the neutralization tank 3 can be adjusted adaptively according to actual application. Figure 1 As shown, a three-stage reactor 1 and a two-stage neutralization tank 3 can be optionally provided.

[0071] According to another embodiment provided by the present invention, a process for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid comprises the following steps:

[0072] S1, formaldehyde solution, hydrocyanic acid and catalyst solution are continuously added to the primary reactor 10 respectively, wherein hydrocyanic acid is fed into the primary reactor 10 in multiple layers, rapidly mixed and reacted in the primary reactor 10, and the reaction heat is released at the same time. The reaction liquid of the primary reactor overflows to the next reactor through the overflow port at the upper part to continue the reaction. The reaction liquid after the reaction is completed in the final reactor overflows to the neutralization tank 3 through the overflow port at the upper part; wherein, the reaction temperature of the reaction liquid in each reactor 1 is controlled within the range of 10 to 25° C. by the heat exchange mechanism 5, and the external circulation cooling loop 50 can not only reduce the temperature, but also strengthen the material circulation in the reactor, and overlap with the mechanical stirring action of the mixing mechanism 2, so as to achieve a better mixing effect, further eliminating the local overtemperature and local alkalinity overconcentration in the reactor to avoid polymerization; during the reaction process, the catalyst solution is added through the catalyst feed pipe 102 to adjust the pH value in each reactor 1 to 3 to 5.5;

[0073] S2. In the neutralization tank 3, the overflow reaction liquid of the final reactor is analyzed for residual amounts of hydrocyanic acid and formaldehyde. If the residual amounts are qualified, inorganic acid is added and the pH value is controlled to 1-2.5, preferably 1.3-2, by a pH meter 71. The qualified hydroxyacetonitrile product after acidification is sent to the storage tank 4. If the residual value does not meet the requirements, an appropriate amount of formaldehyde or hydrocyanic acid is added to continue the reaction until it meets the requirements, and then sulfuric acid is added and transferred to the storage tank 4.

[0074] According to this embodiment, formaldehyde and liquid hydrocyanic acid are continuously fed into primary reactor 10. This results in a very high reaction rate. Under the reaction conditions, almost the entire reaction is completed within primary reactor 10 (with a conversion rate exceeding 90%). This results in a significant thermal effect within the reactor, requiring a large heat transfer area, making temperature control difficult and prone to temperature runaway. By distributing the hydrocyanic acid feed in multiple layers and incorporating a heat exchange mechanism to improve heat transfer efficiency, the likelihood of temperature runaway is reduced. Consequently, by controlling the hydrocyanic acid conversion rate to exceed 90% in secondary reactor 1, while the remaining 10% of the hydrocyanic acid conversion is completed in the other reactors connected in series, the reaction system design is more rational.

[0075] In step S2, at least two neutralization tanks 3 are provided. When the reaction liquid level in one tank reaches the set level, the other neutralization tank 3 is switched to continue receiving the overflow reaction liquid from the final reactor, thereby improving processing efficiency. To ensure reaction efficiency and product quality, the reaction temperature in the reactor in step S1 is controlled at 17-23°C.

[0076] In step S1, the opening of the catalyst feed valve 1020 can be adjusted by the control system 6 so that the pH in the primary reactor is adjusted to 4-5.2 to reduce the risk of polymerization.

[0077] In step S2, sulfuric acid is added into the neutralization tank 3 to make the pH in the tank less than 2, thereby terminating the reaction, and the product is frozen and cooled to obtain the finished product, which is then transferred to the storage tank 4.

[0078] In addition, the catalyst solution is a 1-30% wt aqueous solution. Specifically, the catalyst is sodium sulfite, which is diluted to a concentration of 8-10% wt.

[0079] The mass concentration of the formaldehyde solution is 10-50% wt; if the formaldehyde concentration is too high, it is easy to polymerize; if the formaldehyde concentration is too low, the concentration of the finished hydroxyacetonitrile is low and further purification is required.

[0080] Hydrocyanic acid: 90-100% wt; using a slightly excessive amount of hydrocyanic acid, the molar ratio of hydrocyanic acid to formaldehyde (percentage) is controlled to be (1-1.15):1, preferably (1-1.05):1. This avoids residual formaldehyde, which leads to a large number of reaction impurities and affects product quality.

[0081] As described above, the alkalinity, temperature, hydrocyanic acid concentration, and the ratio of reaction raw materials in the production of hydroxyacetonitrile are controlled, the product quality is improved, the impurities are greatly reduced, and it is suitable for large-scale industrial production.

[0082] The following provides a specific embodiment of industrial production:

[0083] Comparative Example 1

[0084] Raw materials: hydrocyanic acid (concentration 99.5wt%) 437kg / h, formaldehyde solution (concentration 37wt%) 1256kg / h, hydrocyanic acid:formaldehyde (mol) = 1.04; the catalyst is sodium sulfite prepared into 8%wt sodium sulfite solution.

[0085] Device: Such as Figure 1 As shown, a primary reactor 10 is provided, the size of which is approximately The size of the secondary reactor 11 is approximately The size of the third-stage reactor 13 is approximately The agitator 20 in the primary reactor 11 is equipped with two layers of stirring paddles. The hydrocyanic acid feed pipe 101 of the primary reactor 10 is connected to two layers of loop pipes as the first and second hydrocyanic acid distributors 103 / 104, respectively. The first hydrocyanic acid distributor 103 is arranged 400 mm above the upper layer of stirring paddles, and the second hydrocyanic acid distributor 104 is arranged 200 mm below the bottom layer of stirring paddles. The primary reactor 10 is equipped with: an external circulation cooling circuit 50 with a circulation pump 51 and a circulation cooler 52, and a heat exchange jacket 54. The secondary and tertiary reactors are equipped with heat exchange jackets 54 and heat exchange coils 53. The primary reactor 10 is also equipped with a catalyst feed pipe 102.

[0086] Process parameters: reaction pH = 4.9, temperature of the primary reactor 10 is 30°C, temperature of the secondary reactor 11 and the tertiary reactor is 20°C, normal pressure, reaction time 5.2h;

[0087] The process is as follows: all agitators 20, heat exchange jackets 54, circulating coolers 52, and the cooling medium (chilled brine) in the heat exchange coils 53 are pre-started. The reaction conditions in the primary reactor 10 are monitored using a pH meter 70 and a thermometer 60. 1256 kg / h of formaldehyde solution and 437 kg / h of hydrocyanic acid are continuously pumped into the primary reactor 10. Simultaneously, the circulating pump 51 and the catalyst feed valve 1020 are started (the amount of sodium sulfite solution added is controlled based on the pH value measured by the pH meter). The pH in the primary reactor is controlled to 4.9, and the temperature process parameters are maintained. The liquid level gradually rises and overflows into the secondary reactor 11, the tertiary reactor 12, and the neutralization tank 3 in sequence. Residual hydrocyanic acid and formaldehyde content are analyzed online. If qualified, sulfuric acid is added through the regulating valve 300 to adjust the pH to 1.8, terminate the reaction, and the product is cooled and sent to the finished product tank 40.

[0088] Results: The primary main reactor 10 experienced a temperature runaway, with the temperature rising rapidly and uncontrollably to 98°C, causing the process to stop. The material in the reactor polymerized and turned brown.

[0089] Comparative Example 2

[0090] Raw materials: same as Comparative Example 1.

[0091] Device: Same as Comparative Example 1;

[0092] Process parameters: pH = 6.7, the temperature in the first to third stage reactors is controlled at 20°C, and the rest are the same as those in Comparative Example 1;

[0093] Process: The pH in the primary reactor was controlled to be 6.7 by adjusting the catalyst feed valve 1020, and the rest was the same as in Comparative Example 1;

[0094] Result: Temperature runaway occurred in the primary reactor 10, the material in the reactor polymerized, and the material turned brown.

[0095] Example 1

[0096] Raw materials: same as Comparative Example 1.

[0097] Device: Same as Comparative Example 1;

[0098] Process parameters: The temperature in the first, second and third stage reactors was controlled at 20°C, and the other parameters were the same as those in Comparative Example 1;

[0099] Process: Same as Comparative Example 1;

[0100] Results: Hydrocyanic acid and formaldehyde solution were continuously fed for 5.2 hours to obtain 4579 kg of colorless and transparent hydroxyacetonitrile product (percentage), with a hydrocyanic acid yield of 95.9%, a hydroxyacetonitrile concentration of 51.6 wt%, residual formaldehyde of 0.042%, and residual hydrocyanic acid of 0.04%.

[0101] Example 2

[0102] Raw materials: same as in Example 1.

[0103] Device: Same as Example 1;

[0104] Process parameters: The temperature of the first, second and third stage reactors was controlled at 17°C, and the rest were the same as in Example 1.

[0105] Process: Same as Example 1;

[0106] Results: Hydrocyanic acid and formaldehyde solution were continuously fed for 5.2 hours to obtain 4541 kg of colorless and transparent hydroxyacetonitrile product (percentage), with a hydrocyanic acid yield of 95.1%, a hydroxyacetonitrile concentration of 51.2%, a formaldehyde residue of 0.047%, and a hydrocyanic acid residue of 0.043%.

[0107] Example 3

[0108] Raw materials: same as Comparative Example 1.

[0109] Device: Same as Comparative Example 1;

[0110] Process parameters: The temperature in the first, second and third stage reactors was controlled at 23°C, and the other parameters were the same as those in Comparative Example 1;

[0111] Process: Same as Comparative Example 1;

[0112] Results: Hydrocyanic acid and formaldehyde solution were continuously fed for 5.2 hours to obtain 4532 kg of colorless and transparent hydroxyacetonitrile product (percentage), with a hydrocyanic acid yield of 94.9%, a hydroxyacetonitrile concentration of 51.3%, a formaldehyde residue of 0.048%, and a hydrocyanic acid residue of 0.045%.

[0113] Example 4

[0114] Raw materials: same as in Example 1.

[0115] Device: The hydrocyanic acid feed pipe 100 is not connected to the first / second hydrocyanic acid distributor 103\104 of the loop pipe, and the rest is the same as in Example 1;

[0116] Process parameters: same as in Example 1;

[0117] Process: Same as Example 1;

[0118] Results: Hydrocyanic acid and formaldehyde solution were continuously fed for 5.2 hours to obtain 4225 kg of light yellow hydroxyacetonitrile product (percentage), with a hydrocyanic acid yield of 88.5%, a hydroxyacetonitrile concentration of 48.0%, residual formaldehyde of 0.26%, and hydrocyanic acid of 0.12%.

[0119] Example 5

[0120] Raw materials: same as in Example 1.

[0121] Device: The hydrocyanic acid feed pipe 100 is not connected to the first hydrocyanic acid distributor 103 of the loop pipe, and the rest is the same as in Example 1;

[0122] Process parameters: same as in Example 1;

[0123] Process: Same as Example 1;

[0124] Results: Hydrocyanic acid and formaldehyde solution were continuously fed for 5.2 hours to obtain 4359 kg of light yellow hydroxyacetonitrile product (percentage), with a hydrocyanic acid yield of 91.3%, a hydroxyacetonitrile concentration of 49.5%, residual formaldehyde of 0.11%, and hydrocyanic acid of 0.06%.

[0125] Example 6

[0126] Raw materials: same as in Example 1.

[0127] Device: The hydrocyanic acid feed pipe 100 is not connected to the second hydrocyanic acid distributor 104 of the loop pipe, and the rest is the same as in Example 1;

[0128] Process parameters: same as in Example 1;

[0129] Process: Same as Example 1;

[0130] Results: Hydrocyanic acid and formaldehyde solution were continuously fed for 5.2 hours to obtain 4383 kg of light yellow hydroxyacetonitrile product (percentage), with a hydrocyanic acid yield of 91.8%, a hydroxyacetonitrile concentration of 49.7%, residual formaldehyde of 0.08%, and hydrocyanic acid of 0.05%.

[0131] It should be noted that the above embodiments can be freely combined as needed. The above description is only a preferred embodiment of the present invention. It should be pointed out that those skilled in the art can make several improvements and modifications without departing from the principles of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A device for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid, characterized in that: The invention comprises a multi-stage reactor connected in series, wherein a formaldehyde feed pipe, a hydrocyanic acid feed pipe, and a catalyst feed pipe for continuous feeding are connected to the first-stage reactor; adjacent two-stage reactors are connected in series via discharge pipes; a mixing mechanism is provided in each first-stage reactor; wherein a first hydrocyanic acid distributor and a second hydrocyanic acid distributor are respectively provided in the first-stage reactor, the first hydrocyanic acid distributor comprising a first annular tube, the bottom of the first annular tube having an opening area S1 with an angle range of a fan-shaped included angle θ1 along its radial cross section, and holes arranged in the opening area S1 in an equilateral triangle; the second hydrocyanic acid distributor comprising a second annular tube, the outer side of the second annular tube having an opening area S2 with an angle range of a fan-shaped included angle θ2 along its radial cross section, holes only being opened on the outer side, and drain holes are provided every 20° at the lowest point of the second annular tube, and holes are arranged in the opening area S2 in an equilateral triangle; The process also includes a neutralization tank and a storage tank sequentially connected to the final reactor; the neutralization tank is used to receive the reaction liquid flowing out of the final reactor; and the storage tank is used to receive the hydroxyacetonitrile product discharged from the neutralization tank. The neutralization tanks are arranged in at least two stages in parallel downstream of the final reactor, and any one of the neutralization tanks is connected to an online hydrocyanic acid analyzer, an online formaldehyde analyzer, an inorganic acid feeding pipe, a thermometer, and a pH meter. Wherein, each primary reactor and storage tank are connected to a heat exchange mechanism, which includes an external circulation cooling loop with a circulation pump and a circulation cooler connected to the primary reactor, and the material at the outlet of the circulation cooler is returned to the primary reactor through the external circulation cooling loop; The heat exchange mechanism also includes heat exchange coils arranged in the remaining reactors and the neutralization tank, and the heat exchange coils are used to circulate cooling medium; Each stage reactor is provided with a thermometer for monitoring the reaction temperature, and the outlet of the circulation cooler is provided with a thermometer for monitoring the temperature of the reaction material returning to each reactor, wherein the outlet temperature of the circulation cooler is controlled to be -5~10°C, the circulation ratio of the material flow rate returned to the first stage reactor from the circulation cooler outlet to the material flow rate overflowing to the next stage reactor is controlled to be 5~20, and the temperature in the reactor is controlled to be 10~25°C.

2. The device for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid according to claim 1, wherein: The heat exchange mechanism further comprises a heat exchange jacket connected to any one-stage reactor, wherein the heat exchange jacket is used for circulating a cooling medium.

3. The device for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid according to claim 1, wherein: The device also includes a volatile gas condenser, and the volatile gas from the reactor, circulating cooler, neutralization tank and storage tank is collected in the volatile gas condenser. The outlet of the volatile gas condenser is connected to the primary reactor, so that the volatile gas is condensed and returned to the primary reactor for recycling.

4. The device for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid according to claim 1, wherein: The primary reactor is provided with a pH meter for monitoring the pH value of the reaction; The catalyst feed pipe is provided with a catalyst feed valve, and the outlet of the catalyst feed pipe is connected to the primary reactor. The pH in the primary reactor is controlled to be 3-5.5 by adjusting the catalyst feed valve.

5. The device for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid according to claim 4, wherein: The device also includes a control system, and the thermometer, pH meter, and catalyst feed valve are all electrically connected to the control system.

6. The device for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid according to claim 1, characterized in that: The mixing mechanism includes a stirrer arranged in each stage of the reactor, and the stirrer is provided with at least two layers of stirring paddles.

7. A process for continuously producing hydroxyacetonitrile from liquid phase hydrocyanic acid, characterized in that: The device for continuously producing hydroxyacetonitrile using the liquid-phase hydrocyanic acid according to any one of claims 1 to 6 comprises the following steps: S1, formaldehyde solution, hydrocyanic acid and catalyst solution are continuously added to the primary reactor respectively, wherein hydrocyanic acid is fed in multiple layers, rapidly mixed and reacted in the primary reactor, while releasing reaction heat, the reaction liquid of the primary reactor overflows to the next stage reactor through the overflow port at the top to continue the reaction, and the reaction liquid after the reaction in the final reactor overflows to the neutralization tank through the overflow port at the top; wherein the reaction liquid in each reactor is controlled to have a reaction temperature within the range of 10 to 25°C via a heat exchange mechanism; during the reaction process, the catalyst solution is added through the catalyst feed pipe to adjust the pH value in the primary reactor to 3 to 5.5; S2. In the neutralization tank, the overflow reaction liquid of the final reactor is analyzed for residual amounts of hydrocyanic acid and formaldehyde. If the residual amounts are qualified, inorganic acid is added and the pH value is controlled to 1-2.5 by a pH meter. The qualified hydroxyacetonitrile product after acidification is sent to a storage tank. If the residual value does not meet the requirements, an appropriate amount of formaldehyde or hydrocyanic acid is added to continue the reaction until it meets the requirements, and then inorganic acid is added and the product is transferred to a storage tank.

8. The process for continuously producing hydroxyacetonitrile from liquid-phase hydrocyanic acid according to claim 7, wherein: In step S1: Control the reaction temperature in each stage of the reactor to be 17-23°C; and / or, The pH in the primary reactor is adjusted to 4-5.2; and / or, The molar ratio of hydrocyanic acid to formaldehyde in the reaction material is controlled to be 1~1.15:1.

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