Device for preparing mono-dicyandiamide through thermal cracking

Abstract

The utility model belongs to the technical field of cyanamide production, and particularly relates to a device for preparing mono-dicyandiamide through thermal cracking. The device comprises a heater (1), a catalyst tank (2), a melamine tank (3), a downer reactor (4) and a gas-solid separator (5), a heat source inlet (1-1) and a heat source outlet (1-2) are respectively arranged on the heater (1), and a nitrogen inlet (1-3) is arranged close to the heat source outlet (1-2). A catalyst tank (2) is arranged between the nitrogen inlet (1-3) and the heat source outlet (1-2); the heater (1) is connected with the downer reactor (4), and the melamine charging bucket (3) and the like are arranged between the heater (1) and the downer reactor (4). According to the utility model, melamine is taken as a raw material and passes through the downer reactor, rapid cracking is realized at high temperature, back mixing is reduced, the product purity is improved, re-purification and purification of the product are not needed, the working procedure is shortened, and the production efficiency is improved.

Description

Technical Field

[0001] The utility model belongs to the technical field of cyanamide production, in particular to a device for preparing monocyanamide and dicyandiamide through thermal cracking. Background Art

[0002] Both cyanamide and dicyandiamide are important chemical raw materials, widely used in pharmaceutical synthesis, new materials and other fields. Therefore, the production of cyanamide and dicyandiamide has become a technology of great concern in the chemical industry.

[0003] The mainstream process for the existing production of cyanamide and dicyandiamide uses the lime nitrogen process, in which lime nitrogen is hydrolyzed into calcium cyanamide, which is then decalcified to obtain cyanamide, and cyanamide is dimerized to obtain dicyandiamide. The production of lime nitrogen involves the calcium carbide industry, which has the problems of high energy consumption, serious pollution, and great pressure to save energy and reduce emissions.

[0004] Prior art also reports on processes using urea as a raw material and dehydration over molecular sieve catalysts, as well as technologies for producing cyanamide and dicyandiamide through the thermal decomposition of melamine. However, these technologies generally employ fixed-bed or fixed-fluidized-bed processes. Cyanamide is a highly reactive chemical substance that is difficult to maintain stable over extended periods at room temperature. Under the high temperatures required by these processes, it readily reacts with catalysts, generating complex reactants and making product purification and quality control difficult. Therefore, further research and development of production equipment for cyanamide and dicyandiamide is needed to overcome these technical challenges. Utility Model Content

[0005] The purpose of the utility model is to provide a device for preparing monocyanamide and dicyandiamide by thermal cracking in response to the problems existing in the current prior art; in the device, a down-flow bed thermal cracking device is adopted, melamine is used as a raw material and passes through a down-flow bed reactor, where it is rapidly cracked at a high temperature, back mixing is reduced, and the purity of the product is improved, and there is no need for further purification and purification of the product, thereby shortening the process and improving production efficiency.

[0006] In order to achieve the above utility model purpose, the technical solution of the utility model is as follows:

[0007] A device for preparing monocyandiamide by thermal cracking comprises a heater, a catalyst tank, a melamine feed tank, a downer reactor and a gas-solid separator. The heater is provided with a heat source inlet and a heat source outlet, and a nitrogen inlet is provided near the heat source outlet. The catalyst tank is provided between the nitrogen inlet and the heat source outlet. The heater is connected to the downer reactor, and the melamine feed tank is provided between the heater and the downer reactor. The downer reactor is connected to the gas-solid separator.

[0008] Furthermore, a nitrogen inlet is also provided on the pipeline between the melamine feed tank, the heater and the downer reactor.

[0009] Furthermore, a filter is provided inside the gas-solid separator, the top of the gas-solid separator is a gas phase outlet, and the gas-solid separator is connected to an ice water cooling tank through a pipeline through the gas phase outlet, so that the product can be quickly dissolved and absorbed by ice water.

[0010] Furthermore, the ice water cooling tank can also be replaced by a device filled with a low-temperature alkaline aqueous solution.

[0011] Furthermore, a heat source inlet of the downer reactor is provided at the lower part, and a heat source outlet of the downer reactor is provided at the upper part; thermometers are provided at the upper, middle and lower parts of the downer reactor, and valves are provided at both ends.

[0012] Furthermore, a distributor is provided on the upper part of the downer reactor to facilitate uniform distribution.

[0013] Another solution:

[0014] A device for preparing monocyanamide and dicyandiamide by thermal cracking comprises a preheater, a melamine material tank, a nitrogen inlet, a downer reactor, a gas-solid separator, a dehydration and drying system, a riser, a circulation pump and an ice-water cooling tank; the melamine material tank is connected to the nitrogen inlet pipeline and then connected to the downer reactor; the downer reactor is connected to the gas-solid separator; the ice-water cooling tank is respectively connected to the circulation pump and the dehydration and drying system through pipelines; the dehydration and drying system is connected to the preheater; the dehydration and drying system is connected to the preheater; and the preheater is connected to the riser.

[0015] Similarly, in the device for preparing monocyandiamide by thermal cracking, a heat source inlet of the downer reactor is provided at the lower part of the downer reactor, and a heat source outlet of the downer reactor is provided at the upper part; thermometers are provided at the upper, middle and lower parts of the downer reactor, and valves are provided at both ends of the inlet and outlet.

[0016] Similarly, in the device for preparing monocyandiamide by thermal cracking, a filter is provided inside the gas-solid separator, the top of the gas-solid separator is a gas phase outlet, and the gas-solid separator is connected to an ice-water cooling tank through a gas phase outlet and a pipeline; a gas-liquid separation device is provided in the ice-water cooling tank; the top of the ice-water cooling tank is circulatedly connected to a circulation pump through a pipeline; and the circulation pump is connected to the bottom of the ice-water cooling tank.

[0017] Furthermore, in the device for preparing monocyanamide by thermal cracking, it is characterized in that: a heat source inlet and a heat source outlet are provided on the preheater, the feed end is the heat source outlet, and the discharge end is the heat source inlet; the preheater is connected to the riser through a pipeline, and a nitrogen inlet is provided in the middle of the connected pipeline.

[0018] Furthermore, in the device for preparing monocyandiamide by thermal cracking, a riser heat source inlet and a riser heat source outlet are also provided at the upper and lower ends of the riser, the feed end side is the riser heat source inlet, and the discharge end side is the riser heat source outlet; the riser is adapted to be equipped with a riser heater.

[0019] Furthermore, a gas-liquid separation device is provided in the ice-water cooling tank; a gas phase outlet is provided on the gas-liquid separation device, and the gas phase outlet is connected to the water removal and drying system through a pipeline.

[0020] Furthermore, the top of the ice water cooling tank is connected to a circulation pump through a pipeline, and the circulation pump is communicated with the bottom of the ice water cooling tank.

[0021] Furthermore, after the liquid in the ice water cooling tank is discharged, it is sequentially connected to the reverse osmosis concentration device and the vacuum evaporation concentration crystallization integrated device to facilitate subsequent operations.

[0022] A method for preparing dicyandiamide by thermal cracking using the above device comprises the following steps:

[0023] Preheat the melamine raw material to 300-350℃. If the temperature is too low, the melamine will not be fully vaporized. If the temperature is too high, some deamination reactions will occur to generate melamine and meleamine. The more preferred temperature range is 320-340℃.

[0024] The carrier gas carrying the catalyst is preheated to 600-700°C, preferably 630-650°C.

[0025] The preheated vaporized melamine is rapidly mixed with the carrier gas and the catalyst flow on the upper part of the descender, and the temperature is rapidly raised to 500-550°C (more preferably 520-530°C). The raw materials, catalyst and carrier gas flow descend along the descender, exchange heat and react with the reactor in the descender, and after exiting the reactor, enter the gas-solid separator to separate the catalyst. The carrier gas flow carries the product cyanamide into the rapid cooler, where it comes into contact with a large amount of circulating refrigerated water and is rapidly cooled and absorbed.

[0026] The nitrogen exiting the rapid cooler enters a molecular sieve dehydration unit, where water is removed to a dew point below -40°C. The nitrogen exiting the dryer enters a nitrogen circulation preheater. This preheated nitrogen, along with make-up nitrogen, carries the catalyst separated from the gas-solid separation tank into a carrier gas catalytic heater, where it is heated to 600-700°C, preferably 630-650°C, achieving a continuous process cycle.

[0027] The cyanamide solution in the rapid cooler is continuously withdrawn, concentrated and adjusted in concentration, and stabilizers are added to obtain cyanamide solution products of different specifications.

[0028] The cyanamide solution is polymerized into dicyandiamide according to the current mature dimerization process, and further crystallized, separated and dried to obtain the dicyandiamide product.

[0029] Furthermore, in the descending bed, the reaction time is controlled to be less than 5s; more preferably, the reaction time is less than 2s.

[0030] Furthermore, in this method step, nitrogen is used as a carrier gas; preferably, the purity of the nitrogen is greater than 99.9%. If the nitrogen purity is further improved, the cost will increase. If the purity is too low, the oxygen content will increase, causing melamine to undergo an oxidation reaction with oxygen at high temperature, increasing the consumption of raw materials.

[0031] The utility model adopts a down-going bed, which has high production efficiency. Its principle advantage is that the reaction is as close to plug flow as possible, and there is almost no back mixing. For a cascade reaction process with multiple possible side reactions, it is extremely beneficial to control the generation of by-products. The down-going bed has good advantages in the process of thermal decomposition of melamine to produce monocyanamide and dicyandiamide.

[0032] Compared with the existing technology, the beneficial effects of the utility model are:

[0033] (1) The device has a fast and efficient response;

[0034] (2) With this device, the reaction residence time is extremely short, there are almost no by-products, and the product quality is high.

[0035] (3) The use of this device shortens the process, produces fewer by-products and reduces the purification process compared to existing processes; it has high production efficiency and saves investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic structural diagram of a device for preparing dicyandiamide by thermal decomposition in Example 1 of the present utility model;

[0037] Among them, 1 is heater, 1-1 is heat source inlet, 1-2 is heat source outlet, 1-3 is nitrogen inlet, 2 is catalyst tank, 3 is melamine material tank, 4 is downer reactor, 4-1 is heat source inlet of downer reactor, 4-2 is heat source outlet of downer reactor, 5 is gas-solid separator, 5-1 is gas phase outlet, and 6 is ice water cooling tank.

[0038] Figure 2 HPLC profile of the product prepared in Example 1;

[0039] Figure 3 This is a schematic structural diagram of a device for preparing dicyandiamide by thermal decomposition in Example 2 of the present utility model;

[0040] Among them, 1 is a preheater, 1-1 is a heat source inlet, 1-2 is a heat source outlet, 1-3 is a nitrogen inlet, 3 is a melamine material tank, 4 is a down-flow reactor, 4-1 is a heat source inlet of the down-flow reactor, 4-2 is a heat source outlet of the down-flow reactor, 5 is a gas-solid separator, 5-1 is a gas phase outlet, 6 is an ice water cooling tank, 7 is a circulation pump, 8 is a water removal and drying system, 10 is a riser, 10-1 is a riser heater, 10-2 is a heat source inlet of the riser, and 10-2 is a heat source outlet of the riser.

[0041] Figure 4 HPLC profile of the product prepared in Example 2;

[0042] Figure 5 The HPLC pattern of the product prepared in the comparative example is shown. DETAILED DESCRIPTION

[0043] All features disclosed in this specification, or all steps in the disclosed methods or processes, except mutually exclusive features and / or steps, can be combined in any manner.

[0044] Any feature disclosed in this specification (including claims and abstract), unless otherwise stated, may be replaced by other equivalent or similar features. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0045] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0046] Example 1:

[0047] A device for preparing monocyandiamide by thermal cracking comprises a heater 1, a catalyst tank 2, a melamine feed tank 3, a downer reactor 4 and a gas-solid separator 5. A heat source inlet 1-1 and a heat source outlet 1-2 are respectively provided on the heater 1, and a nitrogen inlet 1-3 is provided near the heat source outlet 1-2; the catalyst tank 2 is provided between the nitrogen inlet 1-3 and the heat source outlet 1-2; the heater 1 is connected to the downer reactor 4, and the melamine feed tank 3 is provided between the heater 1 and the downer reactor 4; and the downer reactor 4 is connected to the gas-solid separator 5.

[0048] Furthermore, a filter is provided inside the gas-solid separator 5 , and the top of the gas-solid separator 5 is a gas phase outlet 5 - 1 , and the gas-solid separator 5 is connected to the ice water cooling tank 6 through a pipeline via the gas phase outlet 5 - 1 .

[0049] Furthermore, a heat source inlet 4-1 of the downer reactor is provided at the lower part of the downer reactor 4, and a heat source outlet 4-2 of the downer reactor is provided at the upper part; thermometers are provided at the upper, middle and lower parts of the downer reactor 4, and valves are provided at both ends of the inlet and outlet.

[0050] Furthermore, a distributor is provided on the upper portion of the downer reactor 4 .

[0051] Furthermore, a gas-liquid separation device is provided in the ice-water cooling tank 6 ; a gas phase outlet is provided on the gas-liquid separation device, and is connected to the ice-water cooling tank 6 through the gas phase outlet.

[0052] The melamine raw material was preheated to 333°C in a preheater and added at a rate of 2g / min into a hot carrier gas flow at a flow rate of 40L / min and a catalyst of 40g / min at 300-350°C. The carrier gas carrying the catalyst was preheated to 635°C before mixing.

[0053] The preheated vaporized melamine, carrier gas, and catalyst flow are rapidly mixed on the upper portion of the descending bed. The mixture falls along the DN20 descending tubular reactor, where the temperature is controlled at 530°C. The melamine gas fully contacts and reacts with the carrier gas and catalyst, cracking under the action of heat. It exits the reactor after 0.9 seconds. The mixed gas and catalyst are then passed into a constant temperature ice water tank at 0°C. The product is rapidly dissolved and absorbed by the ice water. At the end of the experiment, a water sample is taken to test the cyanamide concentration of 2%. The HPLC spectrum is shown below. Figure 1 As shown in the figure, no other components were observed. Figure 2 shown.

[0054] Example 2:

[0055] A device for preparing dicyandiamide by thermal cracking, the structural diagram of which is shown in FIG. Figure 2 shown.

[0056] The device includes a melamine material tank 3, a nitrogen inlet, a downer reactor 4, a gas-solid separator 5, a preheater 1, a water removal and drying system 8, a riser 10, a circulation pump 7 and an ice water cooling tank 6.

[0057] The melamine material tank 3 is connected to the nitrogen inlet pipe and then connected to the downer reactor 4. The downer reactor 4 is connected to the gas-solid separator 5.

[0058] Furthermore, a heat source inlet 4-1 of the downer reactor is provided at the lower part of the downer reactor 4, and a heat source outlet 4-2 of the downer reactor is provided at the upper part; thermometers are provided at the upper, middle and lower parts of the downer reactor 4, and valves are provided at both ends of the inlet and outlet.

[0059] Furthermore, a filter is provided inside the gas-solid separator 5, and the top of the gas-solid separator 5 is a gas phase outlet 5-1, which is connected to the ice water cooling tank 6 through a pipeline. The gas-solid separator 5 is also used as a catalyst tank.

[0060] Furthermore, the ice water cooling tank 6 has a gas phase cooling function and is provided with a gas-liquid separation device; the ice water cooling tank 6 is circulatedly connected to the circulation pump 7 through a pipeline, and the ice water cooling tank can be filled with a low-temperature alkaline aqueous solution.

[0061] Furthermore, the ice water cooling tank 6 is connected to the dehydration and drying system 8 through a pipeline. The dehydration and drying system 8 is connected to the preheater 1.

[0062] Furthermore, a heat source inlet 1-1 and a heat source outlet 1-2 are provided on the preheater 1, the feed end is the heat source outlet 1-2, and the discharge end is the heat source inlet 1-1.

[0063] The preheater 1 is connected to the riser 10 through a pipeline, and a nitrogen inlet 1-3 is provided in the middle of the connected pipeline.

[0064] Furthermore, the riser 10 is also provided with a riser heat source inlet 10-2 and a riser heat source outlet 10-3 at the upper and lower ends, with the feed end being the riser heat source inlet 10-2 and the discharge end being the riser heat source outlet 10-3. Furthermore, the riser 10 is adapted to be equipped with a riser heater 10-1; the dehydration and drying system 8 is connected to the preheater 9, which is in turn connected to the riser.

[0065] Furthermore, the liquid in the ice water cooling tank 6 is discharged and sequentially connected to a reverse osmosis concentration device and a vacuum evaporation concentration crystallization integrated device.

[0066] The specific process using the above device is as follows: melamine raw material is added to the raw material transport nitrogen flow to form a raw material dense phase airflow transport mixture, which is preheated to 345°C in a preheater. The nitrogen purity of the hot circulating nitrogen carrier gas is controlled at 99.9%, and the mass ratio of nitrogen to catalyst is 1:1.3. The circulating carrier gas carrying the catalyst is heated to 648°C.

[0067] The preheated vaporized melamine and the hot carrier fluid containing the catalyst are rapidly mixed on the upper part of the descending bed and evenly distributed by the distributor. The mixture falls along the DN300 descending tubular reactor. The bed temperature in the reactor is controlled at 521°C. The melamine gas fully contacts and reacts with the carrier gas and the catalyst, and is cracked under the action of heat. It exits the reactor after 1.6 seconds. The mixed gas after exiting the reactor enters the gas-solid separator to separate the catalyst from the gas. The gas carries the reaction products and is rapidly absorbed by the circulating low-temperature alkaline aqueous solution. The nitrogen after exiting the absorber is dried and preheated, and then mixed with the catalyst from the separation tank. It is preheated again in the riser and then enters the heater to realize the circulation of the carrier gas flow. The alkaline absorption water containing cyanamide is further concentrated by reverse osmosis and vacuum evaporation, concentration and crystallization integrated equipment. Under weak alkaline conditions, cyanamide is concentrated and crystallized to obtain dicyandiamide product according to the current mature process. The purity of dicyandiamide is detected to be 99.2%. HPLC spectrum is as follows Figure 4 shown.

[0068] Comparative Example 1:

[0069] Melamine is preheated to 300°C and fed into a bubbling bed fluidized bed reactor with N2 as the carrier gas. The reaction temperature is controlled at 530°C. The catalyst is separated by a cyclone, and the catalyst dust is further filtered by a bag filter. The gas stream containing the reaction product is rapidly cooled and absorbed. The obtained monocyanamide content is detected to be 1.3%. The absorption liquid is slightly yellowish, and the color of the absorption liquid will become darker with cumulative circulation. To obtain high-quality products, it is necessary to purify and separate impurities through adsorption purification or membrane separation processes. HPLC spectrum is shown as follows: Figure 5 shown.

[0070] The above-described embodiments merely represent specific implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of protection of the present application. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the technical concept of the present application, and all such variations and improvements fall within the scope of protection of the present application.

[0071] This background technology section is provided to generally present the context of the present invention, and the work of the presently named inventors, the work to the extent described in this background technology section, and aspects of the description in this section that did not constitute prior art at the time of application are neither explicitly nor implicitly admitted to be prior art to the present invention.

Claims

1. A device for preparing dicyandiamide by thermal cracking, characterized in that The invention comprises a heater (1), a catalyst tank (2), a melamine material tank (3), a down-flow reactor (4) and a gas-solid separator (5); a heat source inlet (1-1) and a heat source outlet (1-2) are respectively arranged on the heater (1), and a nitrogen inlet (1-3) is arranged near the heat source outlet (1-2); a catalyst tank (2) is arranged between the nitrogen inlet (1-3) and the heat source outlet (1-2); the heater (1) is connected to the down-flow reactor (4), and the melamine material tank (3) is arranged between the heater (1) and the down-flow reactor (4); and the down-flow reactor (4) is connected to the gas-solid separator (5).

2. The device for preparing dicyandiamide by thermal decomposition according to claim 1, characterized in that: A filter is provided inside the gas-solid separator (5), the top of the gas-solid separator (5) is a gas phase outlet (5-1), and the gas-solid separator (5) is connected to an ice water cooling tank (6) through a pipeline via the gas phase outlet (5-1).

3. The device for preparing dicyandiamide by thermal decomposition according to claim 1, characterized in that: A heat source inlet (4-1) for the down-down bed reactor is provided at the lower portion of the down-down bed reactor (4), and a heat source outlet (4-2) for the down-down bed reactor is provided at the upper portion; thermometers are provided at the upper, middle and lower portions of the down-down bed reactor (4), and valves are provided at both inlet and outlet ends.

4. The device for preparing dicyandiamide by thermal decomposition according to claim 1, characterized in that: A distributor is provided at the upper portion of the downer reactor (4).

5. A device for preparing dicyandiamide by thermal cracking, characterized in that: The device comprises a preheater (1), a melamine material tank (3), a nitrogen inlet, a downer reactor (4), a gas-solid separator (5), a dehydration drying system (8), a riser (10), a circulation pump (7) and an ice-water cooling tank (6); the melamine material tank (3) is connected to the nitrogen inlet pipeline and then connected to the downer reactor (4); the downer reactor (4) is connected to the gas-solid separator (5); the ice-water cooling tank (6) is respectively connected to the circulation pump (7) and the dehydration drying system (8) through pipelines; the dehydration drying system (8) is connected to the preheater (1); and the preheater (1) is connected to the riser (10).

6. The device for preparing dicyandiamide by thermal decomposition according to claim 5, characterized in that: A heat source inlet (4-1) for the down-down bed reactor is provided at the lower portion of the down-down bed reactor (4), and a heat source outlet (4-2) for the down-down bed reactor is provided at the upper portion; thermometers are provided at the upper, middle and lower portions of the down-down bed reactor (4), and valves are provided at both inlet and outlet ends.

7. The device for preparing dicyandiamide by thermal decomposition according to claim 5, characterized in that: The gas-solid separator (5) is provided with a filter inside, the top of the gas-solid separator (5) is a gas phase outlet (5-1), and the gas-solid separator (5) is connected to the ice water cooling tank (6) through the gas phase outlet (5-1) and a pipeline; a gas-liquid separation device is provided in the ice water cooling tank (6); the top of the ice water cooling tank (6) is circulatedly connected to the circulation pump (7) through a pipeline; and the circulation pump (7) is communicated with the bottom of the ice water cooling tank (6).

8. The device for preparing dicyandiamide by thermal decomposition according to claim 5, characterized in that: A heat source inlet (1-1) and a heat source outlet (1-2) are provided on the preheater (1), the feed end is the heat source outlet (1-2), and the discharge end is the heat source inlet (1-1); the preheater (1) is connected to a riser (10) through a pipeline, and a nitrogen inlet (1-3) is provided in the middle of the connected pipeline.

9. The device for preparing dicyandiamide by thermal decomposition according to claim 5, characterized in that: A riser heat source inlet (10-2) and a riser heat source outlet (10-3) are also provided at the upper and lower ends of the riser (10), the feed end side being the riser heat source inlet (10-2), and the discharge end side being the riser heat source outlet (10-3); the riser (10) is adapted to be equipped with a riser heater (10-1).

10. The device for preparing dicyandiamide by thermal decomposition according to claim 5, characterized in that: After the liquid in the ice water cooling tank (6) is discharged, it is sequentially connected to a reverse osmosis concentration device and a vacuum evaporation concentration crystallization integrated device.

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