Method and system for generating hydrocyanic acid by cracking formamide

Abstract

The invention discloses a method for generating hydrocyanic acid by cracking formamide, which comprises the following steps: by taking formamide as a raw material, carrying out cracking reaction on the formamide under a negative pressure condition, absorbing the cracked synthesis gas by using a phosphoric acid solution to remove ammonia gas in the synthesis gas, and then cooling the hydrocyanic acid gas into liquid through a cryogenic process to obtain liquid hydrocyanic acid, the tail gas is discharged after being treated by the tail gas absorption tower. The invention also provides a system for generating hydrocyanic acid by cracking formamide, which is used in the method. The method and the system for generating hydrocyanic acid by cracking formamide solve the problems of low conversion rate and low selectivity of the existing process for producing hydrocyanic acid by using formamide.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical hydrocyanic acid production methods, and particularly relates to a method for generating hydrocyanic acid by cracking formamide, and also relates to a system for generating hydrocyanic acid by cracking formamide. Background Art

[0002] Hydrocyanic acid is a colorless, transparent, highly toxic, and easily polymerized chemical raw material commonly used in pharmaceuticals, pesticides, polymer materials, metallurgy, chemical synthesis, and fine chemicals. Hydrocyanic acid is primarily produced through the formamide cracking method, the methanol ammoxidation method, and the acrylonitrile by-product method. Ammonia, a by-product of the hydrocyanic acid production process, is a major factor affecting its quality and causing safety accidents caused by hydrocyanic acid polymerization. In the industrial production of hydrocyanic acid using the formamide cracking method, improper formamide cracking catalyst selection and irrational formamide cracker design result in low conversion and selectivity of formamide to hydrocyanic acid, resulting in large amounts of by-product ammonia and the generation of large amounts of tar-containing cyanide wastewater. This results in a low overall utilization rate of formamide, significantly limiting the industrial application of hydrocyanic acid.

[0003] Therefore, it is necessary to find a method and system for producing hydrocyanic acid by cracking formamide to achieve the preparation of high-quality hydrocyanic acid. Summary of the Invention

[0004] The first object of the present invention is to provide a method for generating hydrocyanic acid by cracking formamide, which solves the problems of low conversion rate and selectivity in the existing process for producing hydrocyanic acid from formamide.

[0005] A second object of the present invention is to provide a system for generating hydrocyanic acid by cleavage of formamide.

[0006] The first technical solution adopted by the present invention is: a method for generating hydrocyanic acid by cracking formamide, using formamide as a raw material, causing the formamide to undergo a cracking reaction under negative pressure conditions, removing ammonia from the cracked synthesis gas by absorbing it with a phosphoric acid solution, and then cooling the hydrocyanic acid gas into a liquid through a deep cooling process to obtain liquid hydrocyanic acid, and the tail gas is discharged after being treated in a tail gas absorption tower.

[0007] The first technical solution adopted by the present invention is also characterized in that: Furthermore, the method for generating hydrocyanic acid by cleavage of formamide is specifically prepared according to the following steps: Step 1, formamide cracking process: formamide is cracked under negative pressure conditions. Liquid formamide is first vaporized at high temperature in a formamide evaporator by heating with molten salt, and then reacted in a formamide cracking reactor under high temperature catalyst conditions to produce hydrocyanic acid and water, accompanied by the production of small amounts of ammonia and carbon monoxide as by-products; Step 2, synthesis gas deamination process: the hydrocyanic acid synthesis gas is absorbed by 15% to 20% phosphoric acid solution to remove ammonia in the synthesis gas; Step 3, cryogenic process: cool the hydrocyanic acid gas to -1°C~-5°C. After cooling, the hydrocyanic acid gas becomes liquid to obtain liquid hydrocyanic acid. The remaining tail gas is discharged to the tail gas absorption tower for treatment and then discharged.

[0008] Furthermore, in step 1, air is introduced into the reactor inlet of the formamide cracking process to suppress the formation of coke. The added air causes the carbon monoxide produced by the cracking of formamide to form carbon dioxide, which promotes the combustion of black tar substances and avoids clogging of the pipeline.

[0009] Furthermore, in the hydrocyanic acid synthesis gas produced by the cracking of formamide in step 1, hydrocyanic acid accounts for 65% to 87.04%, ammonia accounts for 0.1% to 2%, water accounts for 2% to 30%, and carbon monoxide accounts for 0.1-0.5.

[0010] Furthermore, in step 1, the catalyst is a 4-6 mm cylindrical stainless steel tube, and its material is composed of 65%-75% Fe, 8%-12% Ni, 12%-19% Cr, and 1%-3% Al.

[0011] Furthermore, the phosphoric acid used in the synthesis gas deamination process in step 2 is a 15% to 20% phosphoric acid aqueous solution, and the temperature of phosphoric acid absorption is 40°C to 60°C; after the formamide cracking hydrocyanic acid synthesis gas is treated with phosphoric acid to absorb ammonia, the hydrocyanic acid content of the synthesis gas is 90% to 97.04%.

[0012] Furthermore, the liquid hydrocyanic acid obtained in step 3 has a purity of 90% to 95%, and the liquefaction rate of hydrocyanic acid gas in the hydrocyanic acid synthesis gas is 50% to 90%.

[0013] The second technical solution adopted by the present invention is: the system for generating hydrocyanic acid by cracking formamide used in the above method comprises a formamide evaporator, the inlet of the formamide evaporator is connected to a formamide metering tank, the outlet of the formamide evaporator is connected to the air inlet of a formamide cracking reactor, the outlet of the formamide cracking reaction is connected to the inlet of a synthesis gas cooler, the outlet of the synthesis gas cooler is connected to the inlet of a condensate buffer tank, the outlet of the condensate buffer tank is connected to the inlet of an ammonia absorption tower, the gas phase at the outlet of the ammonia absorption tower is connected to the air inlet of a vacuum phosphoric acid solution buffer tank via a deammoniation gas cooler, the gas phase hydrocyanic acid after deammoniation is extracted from the outlet of the vacuum phosphoric acid solution buffer tank by a vacuum pump, and then condensed in a hydrocyanic acid condenser and enters a hydrocyanic acid receiving tank, the bottom liquid of the ammonia absorption tower is transported to the phosphoric acid solution to the inlet of an ammonia removal tower via an ammonia absorption tower circulation pump, and the gas phase outlet of the ammonia removal tower is connected to an ammonia buffer tank via an ammonia gas cooler.

[0014] The second technical solution adopted by the present invention is also characterized in that: Furthermore, the inlet and outlet of the ammonia absorption tower are circulated through an ammonia absorption circulating cooler and an ammonia absorption tower circulating pump, the liquid phase outlet of the ammonia absorption tower is also connected to the inlet of the decyanation flash tank, the gas phase outlet of the decyanation flash tank is also connected to the inlet of the ammonia absorption tower, and the liquid phase outlet of the decyanation flash tank is connected to the inlet of the ammonia removal tower; The outlets of the formamide evaporator and the formamide cracking reactor are respectively connected to the inlet of the gas-liquid separation tank, the outlet of the gas-liquid separation tank is connected to the formamide metering tank, and the inlet of the formamide metering tank is connected to the outlet of the condensate buffer tank; The inlet and outlet of the ammonia removal tower are connected in a circulation manner through the ammonia removal tower reboiler and the ammonia removal tower circulation pump in sequence through a circulation pipeline.

[0015] Furthermore, a formamide metering pump is provided on the connecting pipeline between the formamide evaporator and the formamide metering tank; A condensate pump is provided on the outlet pipeline of the condensate buffer tank; A phosphoric acid solution pump is provided on the pipeline connecting the decyanide flash tank and the ammonia removal tower; The formamide evaporator outlet position is provided with a formamide evaporator outlet pressure gauge and a formamide evaporator outlet temperature gauge; The outlet of the formamide cracking reactor is provided with a formamide reactor outlet temperature gauge and a formamide reactor outlet pressure gauge, and the inlet position is provided with a formamide reactor inlet temperature gauge; The top of the ammonia absorption tower is equipped with an ammonia absorption tower top temperature gauge and an ammonia absorption tower top pressure gauge, and the middle section is equipped with an ammonia absorption tower kettle temperature gauge; A synthesis gas cooler outlet temperature gauge is provided at the synthesis gas cooler outlet; The top of the hydrocyanic acid receiving tank is equipped with a hydrocyanic acid receiving tank pressure gauge and a hydrocyanic acid receiving tank temperature gauge; The top of the ammonia decomposition tower is equipped with an ammonia decomposition tower top temperature gauge and an ammonia decomposition tower top pressure gauge, and the middle section is equipped with an ammonia decomposition tower kettle temperature gauge; A decyanide flash tank top temperature gauge is provided on the top of the decyanide flash tank; An air flow meter is provided on the pipeline connecting the formamide evaporator and the gas-liquid separation tank.

[0016] The beneficial effects of the present invention are: 1. The present invention adopts a method for performing formamide cracking under negative pressure. The entire operation process is in a negative pressure state, which avoids the leakage and polymerization of hydrocyanic acid and greatly reduces the investment in equipment and the safety risk during operation.

[0017] 2. Highly selective catalytic activity. The catalyst of this invention utilizes a high-temperature heat-treated catalyst and a surface passivation treatment that inhibits side reaction pathways, increasing the selectivity of hydrocyanic acid to >98%. Compared to traditional alumina-silica composite catalysts (selectivity of 95-96%), the production of byproducts such as ammonia and CO is effectively reduced.

[0018] 3. Optimized anti-coking performance: The catalyst of this invention incorporates a small amount of other metals, such as molybdenum, manganese, aluminum, and titanium, as additives at a ratio of 0% to 5%. This maintains catalytic activity while inhibiting tar deposition during the pyrolysis of formamide and reducing the generation of cyanide-containing wastewater by over 60%. Combined with negative pressure operation, the catalyst life is extended by three times.

[0019] 4. Dynamic negative pressure control. The system operates under negative pressure, suppressing residual ammonia through micro-injection of oxygen (0.5-3 mol%). The byproduct ammonia concentration is reduced to <0.1%, eliminating the need for an additional sulfuric acid scrubbing unit. Compared to the atmospheric pressure process, the utilization rate of the raw material formamide is increased to 98.5%.

[0020] 5. Intrinsic safety is improved. The negative pressure operation of the entire system of the present invention is combined with online hydrocyanic acid alarm device monitoring to avoid the risk of hydrocyanic acid leakage.

[0021] 6. Flexible production compatibility: the system of the present invention can operate stably in the range of 580-600°C and supports intermittent on-demand production mode. It is particularly suitable for small and medium-sized customized hydrocyanic acid demand scenarios (such as pharmaceutical intermediate synthesis) BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 Schematic diagram of the system structure of the present invention.

[0022] In the figure, 1, formamide evaporator, 2, formamide cracking reactor, 3, ammonia absorption tower, 4, ammonia desorption tower, 5, condensate buffer tank, 6, vacuum phosphoric acid solution buffer tank, 7, hydrocyanic acid receiving tank, 8, decyanation flash tank, 9, gas-liquid separation tank, 10, formamide metering tank, 11, synthesis gas cooler, 12, ammonia absorption circulation cooler, 13, deammoniation gas cooler, 14, hydrocyanic acid condenser, 15, vacuum pump, 16, ammonia cooler, 17, ammonia buffer tank, 18, ammonia desorption tower reboiler, 19, formamide metering pump, 20, condensate pump, 21, ammonia absorption tower circulation pump, 22, phosphoric acid solution pump, 23, ammonia desorption Tower circulation pump, 24. Formamide evaporator outlet pressure gauge, 25. Formamide evaporator outlet temperature gauge, 26. Formamide reactor outlet temperature gauge, 27. Formamide reactor outlet pressure gauge, 28. Formamide reactor inlet temperature gauge, 29. Ammonia absorption tower top temperature gauge, 30. Ammonia absorption tower top pressure gauge, 31. Synthesis gas cooler outlet temperature gauge, 32. Ammonia absorption tower kettle temperature gauge, 33. Hydrocyanic acid receiving tank pressure gauge, 34. Hydrocyanic acid receiving tank temperature gauge, 35. Ammonia desorption tower top temperature gauge, 36. Ammonia desorption tower top pressure gauge, 37. Ammonia desorption tower kettle temperature gauge, 38. Decyanide flash tank top temperature gauge, 39. Air flow meter. DETAILED DESCRIPTION

[0023] The present invention will be further described below with reference to the accompanying drawings and examples.

[0024] The present invention provides a method for generating hydrocyanic acid by cracking formamide, which can significantly improve the purity of hydrocyanic acid and the utilization efficiency of hydrocyanic acid. At the same time, high-purity hydrocyanic acid can be directly produced through the cracking and deamination process of formamide without the need for distillation of hydrocyanic acid.

[0025] Specifically, formamide is subjected to a cleavage reaction under negative pressure, which is carried out according to equation (1):

[0026] The reaction is accompanied by the decomposition of formamide according to equation (2), forming ammonia and carbon monoxide:

[0027] The ammonia formed will catalyze the polymerization reaction of the desired hydrocyanic acid and thus lead to a decrease in the quality of the hydrocyanic acid and a decrease in the yield of the desired hydrocyanic acid. Therefore, the present invention designs a synthesis gas deamination step in the production process.

[0028] The present invention uses formamide as a raw material and obtains liquid hydrocyanic acid through a formamide cracking process, a synthesis gas deamination process, and a cryogenic process. The formamide cracking process is to first gasify the liquid formamide at high temperature in a formamide evaporator by heating with molten salt, and then react in a formamide cracking reactor under high temperature catalyst conditions to generate hydrocyanic acid and water, accompanied by the generation of a small amount of ammonia and carbon monoxide as by-products. In the formamide cracking process, air is introduced into the reactor inlet to suppress the generation of coking. The added air causes the carbon monoxide generated according to equation (2) to form carbon dioxide, promotes the combustion of black tar substances, and avoids clogging of pipelines.

[0029] The synthesis gas deamination process is to absorb the hydrocyanic acid synthesis gas with 15% to 20% phosphoric acid solution to remove ammonia in the synthesis gas; the deep cooling process is to cool the hydrocyanic acid gas to -1°C to -5°C. After cooling, most of the hydrocyanic acid gas becomes liquid to obtain liquid hydrocyanic acid. In addition, a small amount of carbon monoxide and carbon dioxide gas is discharged to the tail gas absorption tower for treatment and then discharged.

[0030] The raw material formamide cracking hydrocyanic acid synthesis gas contains 65% to 97.04% hydrocyanic acid, 0.1% to 2% ammonia, and 2% to 30% water.

[0031] The phosphoric acid used in the synthesis gas deamination process is a 15% to 20% phosphoric acid aqueous solution, and the temperature of phosphoric acid absorption is 40°C to 60°C; after the formamide cracking hydrocyanic acid synthesis gas is treated with phosphoric acid to absorb ammonia, the hydrocyanic acid content of the synthesis gas is 65% to 97.04%.

[0032] The catalyst is a 4-6 mm cylindrical stainless steel tube, which is composed of 65%-75% Fe, 8%-12% Ni, 12%-19% Cr, and 1%-3% Al.

[0033] The proportion of iron in the catalyst is ≥50%, preferably ≥60%, particularly preferably ≥70%, the balance is usually nickel and chromium, and a small amount of other metals such as molybdenum, manganese, aluminum, titanium, etc. is added in a proportion of 0% to 5%.

[0034] In the present invention, the hydrocyanic acid synthesis gas after the removal of ammonia and water is cryogenically cooled to obtain liquid hydrocyanic acid with a purity of 90% to 95%. The liquefaction rate of hydrocyanic acid gas in the hydrocyanic acid synthesis gas is 50% to 90%.

[0035] The formamide cracking and synthesis gas deamination of the present invention are both carried out under negative pressure.

[0036] The present invention also provides a system for generating liquid hydrocyanic acid through a formamide cracking reaction, comprising a formamide evaporator 1, wherein the inlet of the formamide evaporator 1 is connected to a formamide metering tank 10, the outlet of the formamide evaporator 1 is connected to the air inlet of a formamide cracking reactor 2, the outlet of the formamide cracking reactor 2 is connected to the inlet of a synthesis gas cooler 11, the outlet of the synthesis gas cooler 11 is connected to the inlet of a condensate buffer tank 5, the outlet of the condensate buffer tank 5 is connected to the inlet of an ammonia absorption tower 3, the outlet gas phase of the ammonia absorption tower 3 is connected to the air inlet of a vacuum phosphoric acid solution buffer tank 6 via a deammoniation gas cooler 13, the outlet of the vacuum phosphoric acid solution buffer tank 6 extracts the deaminated gas phase hydrocyanic acid through a vacuum pump 15, and then condenses the deaminated gas phase hydrocyanic acid through a hydrocyanic acid condenser 14 and enters a hydrocyanic acid receiving tank 7, the bottom liquid of the ammonia absorption tower is transported to the inlet of an ammonia removal tower 4 via an ammonia absorption tower circulating pump 21, and the gas phase outlet of the ammonia removal tower 4 is connected to an ammonia water buffer tank 17 via an ammonia gas cooler 16.

[0037] The formamide evaporator 1 controls the feed amount through the formamide metering pump 19. The outlet of the formamide evaporator 1 is connected to the air inlet of the formamide cracking reactor 2. The outlet of the formamide cracking reactor 2 is connected to the inlet of the synthesis gas cooler 11. The outlet of the synthesis gas cooler 11 is connected to the inlet of the condensate buffer tank 5. The outlet of the condensate buffer tank 5 is connected to the inlet of the ammonia absorption tower 3. The gas phase at the outlet of the ammonia absorption tower 3 is extracted by the vacuum pump 15 to extract the deaminated gaseous hydrogen cyanide, which is condensed by the hydrogen cyanide condenser 14 and then enters the hydrogen cyanide receiving tank 7. Then, it is directly pumped into the next process for direct use.

[0038] The gas phase from the condensate buffer tank 5 enters the ammonia absorption tower 3, where it absorbs ammonia through phosphoric acid. After absorbing ammonia, the phosphoric acid in the ammonia absorption tower turns into a mixture of monoammonium phosphate and diammonium phosphate. To maintain the pH of the bottom liquid in the ammonia absorption tower below 6.0, the bottom liquid is removed by the ammonia absorption tower circulation pump 21 for deammoniation treatment. New monoammonium phosphate solution is promptly replenished from the ammonia removal tower. The mixed gas after these two absorptions is pumped out by a vacuum pump, dehydrated in a vacuum phosphoric acid solution buffer tank, and then fed to the next process.

[0039] The bottom liquid of ammonia absorption tower 3 contains a small amount of hydrocyanic acid, requiring decyanation. The bottom liquid is pumped by phosphoric acid pump 22 and passed through decyanation flash tank 8 under negative pressure to remove hydrocyanic acid. The flashed gas phase from decyanation flash tank 8 contains hydrocyanic acid and a small amount of ammonia, which is returned to ammonia absorption tower 3 for recycling. The liquid phase in decyanation flash tank 8, primarily diammonium phosphate solution, is pumped by phosphoric acid pump 22 into the ammonia removal tower for ammonia desorption.

[0040] The diammonium phosphate solution from the decyanation flash tank 8 enters the ammonia removal tower 4 and is heated by the ammonia removal tower reboiler 18 to remove ammonia. After deamination, the bottom of the ammonia removal tower mainly contains monoammonium phosphate solution, which is extracted by the ammonia removal tower circulation pump 23 and returned to the ammonia absorption tower. The ammonia and water vapor at the top of the tower are cooled by the tower top ammonia cooler 16 and then enter the ammonia buffer tank 17. Finally, they are treated together, and the non-condensable gas is connected to the tail gas absorption tower.

[0041] Based on the above system, a method for generating liquid hydrocyanic acid by cleavage reaction of formamide is provided. In order to make the purpose, technical solution and advantages of the present invention clearer, a detailed description will be given in conjunction with preferred examples of the present invention.

[0042] Example 1 The system for generating hydrocyanic acid by cracking formamide comprises a formamide evaporator 1, wherein the inlet of the formamide evaporator 1 is connected to a formamide metering tank 10, the outlet of the formamide evaporator 1 is connected to the air inlet of a formamide cracking reactor 2, the outlet of the formamide cracking reactor 2 is connected to the inlet of a synthesis gas cooler 11, the outlet of the synthesis gas cooler 11 is connected to the inlet of a condensate buffer tank 5, the outlet of the condensate buffer tank 5 is connected to the inlet of an ammonia absorption tower 3, the gas phase at the outlet of the ammonia absorption tower 3 is connected to the air inlet of a vacuum phosphoric acid solution buffer tank 6 via a deammoniation gas cooler 13, the deaminated gaseous hydrocyanic acid at the outlet of the vacuum phosphoric acid solution buffer tank 6 is extracted by a vacuum pump 15, condensed by a hydrocyanic acid condenser 14, and then enters a hydrocyanic acid receiving tank 7, the bottom liquid of the ammonia absorption tower is transported to the phosphoric acid solution via an ammonia absorption tower circulating pump 21 to the inlet of an ammonia removal tower 4, and the gas phase outlet of the ammonia removal tower 4 is connected to an ammonia water buffer tank 17 via an ammonia gas cooler 16.

[0043] The inlet and outlet of the ammonia absorption tower 3 are circulated through the ammonia absorption circulation cooler 12 and the ammonia absorption tower circulation pump 21. The liquid phase outlet of the ammonia absorption tower 3 is also connected to the inlet of the decyanation flash tank 8. The gas phase outlet of the decyanation flash tank 8 is also connected to the inlet of the ammonia absorption tower 3. The liquid phase outlet of the decyanation flash tank 8 is connected to the inlet of the ammonia removal tower 4. The outlets of the formamide evaporator 1 and the formamide cracking reactor 2 are respectively connected to the inlet of the gas-liquid separation tank 9, the outlet of the gas-liquid separation tank 9 is connected to the formamide metering tank 10, and the inlet of the formamide metering tank 10 is connected to the outlet of the condensate buffer tank 5; The inlet and outlet of the ammonia removal tower 4 are connected in a circulation manner through the ammonia removal tower reboiler 18 and the ammonia removal tower circulation pump 23 in sequence through a circulation pipeline.

[0044] Example 2 On the basis of Example 1, a formamide metering pump 19 is provided on the connecting pipeline between the formamide evaporator 1 and the formamide metering tank 10; A condensate pump 20 is provided on the outlet pipeline of the condensate buffer tank 5; A phosphoric acid solution pump 22 is provided on the pipeline connecting the decyanide flash tank 8 and the ammonia removal tower 4; The outlet of the formamide evaporator 1 is provided with a formamide evaporator outlet pressure gauge 24 and a formamide evaporator outlet temperature gauge 25; The outlet of the formamide cracking reactor 2 is provided with a formamide reactor outlet temperature gauge 26 and a formamide reactor outlet pressure gauge 27, and the inlet is provided with a formamide reactor inlet temperature gauge 28; The top of the ammonia absorption tower 3 is provided with an ammonia absorption tower top temperature gauge 29 and an ammonia absorption tower top pressure gauge 30, and the middle section is provided with an ammonia absorption tower kettle temperature gauge 32; A synthesis gas cooler outlet temperature gauge 31 is provided at the outlet of the synthesis gas cooler 11; A hydrocyanic acid receiving tank pressure gauge 33 and a hydrocyanic acid receiving tank temperature gauge 34 are provided on the top of the hydrocyanic acid receiving tank 7; The top of the ammonia decomposition tower 4 is provided with an ammonia decomposition tower top temperature gauge 35 and an ammonia decomposition tower top pressure gauge 36, and the middle section is provided with an ammonia decomposition tower kettle temperature gauge 37; A decyanide flash tank top temperature gauge 38 is provided on the top of the decyanide flash tank 8; An air flow meter 39 is provided on the pipeline connecting the formamide evaporator 1 and the gas-liquid separation tank 9 .

[0045] Example 3 A method for generating hydrocyanic acid by cracking formamide uses the system of Example 2, takes formamide as a raw material, and performs a cracking reaction on the formamide under negative pressure conditions. The ammonia in the cracked synthesis gas is absorbed by a phosphoric acid solution to remove the ammonia in the synthesis gas. The hydrocyanic acid gas is then cooled to a liquid through a deep cooling process to obtain liquid hydrocyanic acid. The tail gas is treated in a tail gas absorption tower and then discharged.

[0046] Example 4 The method for generating hydrocyanic acid by cleavage of formamide is prepared using the system of Example 2 in accordance with the following steps: Step 1, formamide cracking process: formamide is cracked under negative pressure conditions. Liquid formamide is first vaporized at high temperature in a formamide evaporator by heating with molten salt, and then reacted in a formamide cracking reactor under high temperature catalyst conditions to produce hydrocyanic acid and water, accompanied by the production of small amounts of ammonia and carbon monoxide as by-products; Step 2, synthesis gas deamination process: the hydrocyanic acid synthesis gas is absorbed by 15% to 20% phosphoric acid solution to remove ammonia in the synthesis gas; Step 3, cryogenic process: cool the hydrocyanic acid gas to -1°C~-5°C. After cooling, the hydrocyanic acid gas becomes liquid to obtain liquid hydrocyanic acid. The remaining tail gas is discharged to the tail gas absorption tower for treatment and then discharged.

[0047] Example 5 The system of Example 2 was used.

[0048] (1) Formamide cracking: The formamide raw material is added to the formamide metering tank for storage and transported to the formamide evaporator for vaporization using a formamide feed pump. The outlet temperature of the formamide evaporator is controlled to be >350°C. After being vaporized by the formamide evaporator, the formamide enters the formamide reactor (molten salt heating) from the bottom. Under the action of the catalyst, a dehydration reaction occurs to produce HCN and H2O, and a small amount of NH3 and CO are produced by side reactions. The gas phase temperature at the reactor outlet is controlled to be >450°C and the pressure is -0.080MPa. The formamide feed rate is controlled by the formamide feed pump to be 10-15L / h, and the formamide conversion rate can reach 75% to 80%.

[0049] (2) Synthesis gas ammonia absorption: The synthesis gas from the formamide reactor is cooled by the condenser and then enters the ammonia absorption tower. The temperature of the ammonia absorption tower is controlled at 40-50℃. After phosphoric acid solution is added to the ammonia absorption tower to absorb the ammonia in the synthesis gas, it becomes a mixed liquid of monoammonium phosphate and diammonium phosphate, and the pH value of the tower bottom will increase. In order to maintain the pH of the bottom liquid of the ammonia absorption tower <6.0, the bottom liquid of the ammonia absorption tower needs to be deammonified. Because the bottom liquid of the ammonia absorption tower contains a small amount of hydrocyanic acid, it needs to be decyanated. The bottom liquid is pumped out to the decyanation flash tank, and the hydrocyanic acid is removed under negative pressure. The gas phase flashed out of the decyanation flash tank contains hydrocyanic acid and a small amount of ammonia and is returned to the ammonia absorption tower for recycling. The liquid phase enters the ammonia removal tower for deammoniation treatment and then returns to the ammonia absorption tower for recycling. The mixed gas after two absorptions is pumped out by a vacuum pump, dehydrated in the vacuum phosphoric acid solution buffer tank, and then sent to the next process for use.

[0050] (3) Deamination of synthesis gas: The diammonium phosphate solution from the decyanation flash tank enters the ammonia desorption tower kettle and is pressurized to 1.1MPa-1.3MPa, and heated to 175℃~180℃ by a heat exchanger. After deamination in the ammonia desorption tower, the tower kettle is mainly monoammonium phosphate solution, which is extracted by the tower kettle circulation pump and returned to the ammonia absorption tower after cooling by the heat exchanger. The ammonia and water vapor at the top of the tower are cooled by the first-level ammonia cooler at the top of the tower and then enter the first-level condensation receiving tank at the top of the tower. The uncondensed gas phase is condensed by the second-level ammonia condenser and enters the second-level tower top receiving tank. The dilute ammonia water (5%) in the tank is discharged to the recovery tank, and the non-condensable gas is connected to the tail gas absorption tower.

[0051] (4) Deep cooling: By establishing a chilled water circulation system and setting the temperature at -5°C, the hydrogen cyanide mixed gas from the top of the ammonia absorption tower is extracted by a vacuum pump, cooled by a condenser, and then dehydrated. Most of the hydrogen cyanide gas is converted into liquid and stored in the hydrogen cyanide receiving tank. The tail gas containing a small amount of hydrogen cyanide gas enters the tail gas absorption tower for treatment and is discharged to the incineration system. The purity of the hydrogen cyanide liquid obtained after deep cooling is between 90% and 95%.

[0052] (5) Tail gas absorption: Add 10% sodium hydroxide solution to the tail gas absorption tower, and pass a small amount of hydrocyanic acid gas coming out from the top of the hydrocyanic acid receiving tank into the tail gas absorption tower. The tail gas containing hydrocyanic acid is absorbed by the sodium hydroxide solution and then discharged to the incineration system through the Roots blower. The tail gas absorption liquid after absorption is analyzed. If CN-<5g / L, the tail gas absorption liquid is collected and stored, and finally processed by outsourcing.

[0053] Example 6 Using the system of Example 2, this embodiment differs from Example 5 in that: By replacing the molten salt heating rod with a higher temperature resistance grade, the molten salt temperature was increased to 580℃-600℃, the formamide conversion rate was greatly improved, and the product concentration was relatively stable during operation.

[0054] (1) Formamide cracking: The formamide raw material is added to the formamide metering tank for storage and transported to the formamide evaporator for vaporization using a formamide feed pump. The outlet temperature of the formamide evaporator is controlled to be >350°C. After being vaporized by the formamide evaporator, the formamide enters the formamide reactor (molten salt heating) from the bottom. Under the action of the catalyst, a dehydration reaction occurs to produce HCN and H2O, and a small amount of NH3 and CO are produced by side reactions. The gas phase temperature at the reactor outlet is controlled to be >450°C and the pressure is -0.080MPa. The formamide feed rate is controlled by the formamide feed pump to be 10-15L / h, and the formamide conversion rate can reach 85% to 95%.

[0055] (2) Synthesis gas ammonia absorption: The synthesis gas from the formamide reactor is cooled by the condenser and then enters the ammonia absorption tower. The temperature of the ammonia absorption tower is controlled at 40-50℃. After phosphoric acid solution is added to the ammonia absorption tower to absorb the ammonia in the synthesis gas, it becomes a mixed liquid of monoammonium phosphate and diammonium phosphate, and the pH value of the tower bottom will increase. In order to maintain the pH of the bottom liquid of the ammonia absorption tower <6.0, the bottom liquid of the ammonia absorption tower needs to be deammonified. Because the bottom liquid of the ammonia absorption tower contains a small amount of hydrocyanic acid, it needs to be decyanated. The bottom liquid is pumped out to the decyanation flash tank, and the hydrocyanic acid is removed under negative pressure. The gas phase flashed out of the decyanation flash tank contains hydrocyanic acid and a small amount of ammonia and is returned to the ammonia absorption tower for recycling. The liquid phase enters the ammonia removal tower for deammoniation treatment and then returns to the ammonia absorption tower for recycling. The mixed gas after two absorptions is pumped out by a vacuum pump, dehydrated in the vacuum phosphoric acid solution buffer tank, and then sent to the next process for use.

[0056] (3) Deamination of synthesis gas: The diammonium phosphate solution from the decyanation flash tank enters the ammonia desorption tower kettle and is pressurized to 1.1MPa-1.3MPa, and heated to 175℃~180℃ by a heat exchanger. After deamination in the ammonia desorption tower, the tower kettle is mainly monoammonium phosphate solution, which is extracted by the tower kettle circulation pump and returned to the ammonia absorption tower after cooling by the heat exchanger. The ammonia and water vapor at the top of the tower are cooled by the first-level ammonia cooler at the top of the tower and then enter the first-level condensation receiving tank at the top of the tower. The uncondensed gas phase is condensed by the second-level ammonia condenser and enters the second-level tower top receiving tank. The dilute ammonia water (5%) in the tank is discharged to the recovery tank, and the non-condensable gas is connected to the tail gas absorption tower.

[0057] (4) Deep cooling: By establishing a chilled water circulation system and setting the temperature at -5°C, the hydrogen cyanide mixed gas from the top of the ammonia absorption tower is extracted by a vacuum pump, cooled by a condenser, and then dehydrated. Most of the hydrogen cyanide gas is converted into liquid and stored in the hydrogen cyanide receiving tank. The tail gas containing a small amount of hydrogen cyanide gas enters the tail gas absorption tower for treatment and is discharged to the incineration system. The purity of the hydrogen cyanide liquid obtained after deep cooling is between 90% and 95%.

[0058] (5) Tail gas absorption: Add 10% sodium hydroxide solution to the tail gas absorption tower, and pass a small amount of hydrocyanic acid gas coming out from the top of the hydrocyanic acid receiving tank into the tail gas absorption tower. The tail gas containing hydrocyanic acid is absorbed by the sodium hydroxide solution and then discharged to the incineration system through the Roots blower. The tail gas absorption liquid after absorption is analyzed. If CN-<5g / L, the tail gas absorption liquid is collected and stored, and finally processed by outsourcing.

Claims

1. A method for generating hydrocyanic acid by cleavage of formamide, characterized in that: Using formamide as raw material, formamide is cracked under negative pressure. The ammonia in the synthesis gas after cracking is absorbed by phosphoric acid solution, and then the hydrocyanic acid gas is cooled into liquid through a deep cooling process to obtain liquid hydrocyanic acid. The tail gas is treated in a tail gas absorption tower and then discharged.

2. The method for generating hydrocyanic acid by decomposing formamide according to claim 1, wherein: Specifically prepared according to the following steps: Step 1, formamide cracking process: formamide is cracked under negative pressure conditions. Liquid formamide is first vaporized at high temperature in a formamide evaporator by heating with molten salt, and then reacted in a formamide cracking reactor under high temperature catalyst conditions to produce hydrocyanic acid and water, accompanied by the production of small amounts of ammonia and carbon monoxide as by-products; Step 2, synthesis gas deamination process: the hydrocyanic acid synthesis gas is absorbed by 15% to 20% phosphoric acid solution to remove ammonia in the synthesis gas; Step 3, cryogenic process: cool the hydrocyanic acid gas to -1°C~-5°C. After cooling, the hydrocyanic acid gas becomes liquid to obtain liquid hydrocyanic acid. The remaining tail gas is discharged to the tail gas absorption tower for treatment and then discharged.

3. The method for generating hydrocyanic acid by cracking formamide according to claim 2, wherein: In step 1, air is introduced into the reactor inlet of the formamide cracking process to suppress the generation of coking. The added air causes the carbon monoxide generated by the cracking of formamide to form carbon dioxide, which promotes the combustion of black tar substances and avoids clogging of the pipeline.

4. The method for generating hydrocyanic acid by decomposing formamide according to claim 3, wherein: In the hydrocyanic acid synthesis gas produced by the decomposition of formamide in step 1, hydrocyanic acid accounts for 65% to 87.04%, ammonia accounts for 0.1% to 2%, water accounts for 2% to 30%, and carbon monoxide accounts for 0.1-0.5%.

5. The method for generating hydrocyanic acid by decomposing formamide according to claim 2, wherein: The catalyst in step 1 is a 4-6 mm cylindrical stainless steel tube, which is made of 65%-75% Fe, 8%-12% Ni, 12%-19% Cr, and 1%-3% Al.

6. The method for generating hydrocyanic acid by decomposing formamide according to claim 2, wherein: The phosphoric acid used in the deamination process of the synthesis gas in step 2 is a 15% to 20% phosphoric acid aqueous solution, and the temperature for phosphoric acid absorption is 40° C. to 60° C.; after the formamide cracking hydrocyanic acid synthesis gas is treated with phosphoric acid to absorb ammonia, the hydrocyanic acid content of the synthesis gas is 90% to 97.04%.

7. The method for generating hydrocyanic acid by decomposing formamide according to claim 2, wherein: The liquid hydrocyanic acid obtained in step 3 has a purity of 90% to 95%, and the liquefaction rate of hydrocyanic acid gas in the hydrocyanic acid synthesis gas is 50% to 90%.

8. The system for generating hydrocyanic acid by decomposing formamide used in the method according to any one of claims 1 to 7, characterized in that: The invention comprises a formamide evaporator (1), wherein the inlet of the formamide evaporator (1) is connected to a formamide metering tank (10), the outlet of the formamide evaporator (1) is connected to the air inlet of a formamide cracking reactor (2), the outlet of the formamide cracking reactor (2) is connected to the inlet of a synthesis gas cooler (11), the outlet of the synthesis gas cooler (11) is connected to the inlet of a condensate buffer tank (5), the outlet of the condensate buffer tank (5) is connected to the inlet of an ammonia absorption tower (3), and the ammonia absorption tower (3) is connected to the inlet of a condensate buffer tank (5). ) outlet gas phase is connected to the air inlet of the vacuum phosphoric acid solution buffer tank (6) through the deammoniation gas cooler (13); the outlet of the vacuum phosphoric acid solution buffer tank (6) extracts the deaminated gas phase hydrogen cyanide through the vacuum pump (15) and then condenses it through the hydrogen cyanide condenser (14) and enters the hydrogen cyanide receiving tank (7); the ammonia absorption tower kettle liquid is transported to the inlet of the ammonia absorption tower (4) through the ammonia absorption tower circulation pump (21); the gas phase outlet of the ammonia absorption tower (4) is connected to the ammonia buffer tank (17) through the ammonia gas cooler (16).

9. The system for generating hydrocyanic acid by decomposing formamide according to claim 8, characterized in that: The inlet and outlet of the ammonia absorption tower (3) are circulated through an ammonia absorption circulation cooler (12) and an ammonia absorption tower circulation pump (21); the liquid phase outlet of the ammonia absorption tower (3) is also connected to the inlet of the decyanation flash tank (8); the gas phase outlet of the decyanation flash tank (8) is also connected to the inlet of the ammonia absorption tower (3); and the liquid phase outlet of the decyanation flash tank (8) is connected to the inlet of the ammonia removal tower (4); The outlets of the formamide evaporator (1) and the formamide cracking reactor (2) are respectively connected to the inlet of the gas-liquid separation tank (9), the outlet of the gas-liquid separation tank (9) is connected to the formamide metering tank (10), and the inlet of the formamide metering tank (10) is connected to the outlet of the condensate buffer tank (5); The inlet and outlet of the ammonia decomposition tower (4) are connected in a circulation manner through the ammonia decomposition tower reboiler (18) and the ammonia decomposition tower circulation pump (23) in sequence.

10. The system for generating hydrocyanic acid by decomposing formamide according to claim 8, characterized in that: A formamide metering pump (19) is provided on the pipeline connecting the formamide evaporator (1) and the formamide metering tank (10); A condensate pump (20) is provided on the outlet pipeline of the condensate buffer tank (5); A phosphoric acid solution pump (22) is provided on the pipeline connecting the decyanation flash tank (8) and the ammonia removal tower (4); The formamide evaporator (1) is provided with a formamide evaporator outlet pressure gauge (24) and a formamide evaporator outlet temperature gauge (25) at the outlet position; The formamide cracking reactor (2) is provided with a formamide reactor outlet temperature gauge (26) and a formamide reactor outlet pressure gauge (27) at its outlet, and a formamide reactor inlet temperature gauge (28) at its inlet. The ammonia absorption tower (3) is provided with an ammonia absorption tower top temperature gauge (29) and an ammonia absorption tower top pressure gauge (30) at the top, and an ammonia absorption tower kettle temperature gauge (32) is provided in the middle section; A synthesis gas cooler outlet temperature gauge (31) is provided at the outlet of the synthesis gas cooler (11); The top of the hydrocyanic acid receiving tank (7) is provided with a hydrocyanic acid receiving tank pressure gauge (33) and a hydrocyanic acid receiving tank temperature gauge (34); The top of the ammonia desorption tower (4) is provided with an ammonia desorption tower top temperature gauge (35) and an ammonia desorption tower top pressure gauge (36), and the middle section is provided with an ammonia desorption tower kettle temperature gauge (37); A decyanide flash tank top temperature gauge (38) is provided on the top of the decyanide flash tank (8); An air flow meter (39) is provided on the pipeline connecting the formamide evaporator (1) and the gas-liquid separation tank (9).

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