Process for the preparation of hydrocyanic acid by methanol ammoxidation

Abstract

The present application relates to a kind of methods for preparing hydrogen cyanide by methanol ammoxidation, the method is that methanol is mixed with ammonia, air is preheated and then enters the reactor containing catalyst to carry out ammoxidation reaction, and generates the reaction gas containing hydrogen cyanide, the reaction gas is sequentially subjected to cooling, ammonia neutralization, hydrogen cyanide absorption and rectification process to obtain high-purity hydrogen cyanide, wherein, the absolute humidity in the mixed gas of gaseous methanol, ammonia and air is controlled to be 0.5-5.0g / m 3 The present application effectively reduces the generation of by-products such as formaldehyde and hydroxyacetonitrile during the reaction, improves the yield and purity of hydrogen cyanide, and reduces the problem of pipeline blockage caused by by-products.

Description

Technical Field

[0001] This invention belongs to the technical field of hydrogen cyanide preparation, specifically relating to a method for preparing hydrogen cyanide by methanol ammoxidation with low by-products. Background Technology

[0002] Hydrogen cyanide is an important chemical raw material, mainly used to produce sodium cyanide, adiponitrile, MMA, methionine, and other chemical products, with a wide range of applications. However, because hydrogen cyanide is a highly toxic chemical, it cannot be transported. Therefore, the demand for hydrogen cyanide must be met domestically. Currently, there are several main sources of hydrogen cyanide, including acrylonitrile byproducts, the methane process, and the methanol process. With the continuous development of acrylonitrile catalysts, the yield of hydrogen cyanide is decreasing. The methane process requires expensive precious metal catalysts, reaction temperatures exceeding 1000℃, and has a low yield, making it uneconomical. The methanol process is an economical method for producing hydrogen cyanide. It uses methanol, ammonia, and air as raw materials, producing hydrogen cyanide under the action of a catalyst. Its production conditions are mild, the yield of hydrogen cyanide is high, and it has a significant cost advantage.

[0003] The mainstream catalyst for producing hydrogen cyanide from methanol is an iron-molybdenum bimetallic oxide catalyst. Excess ammonia in the feedstock necessitates an ammonium sulfate system to recover the excess ammonia. However, this process has a drawback: the presence of iron and molybdenum inevitably generates formaldehyde during the reaction. Formaldehyde reacts with hydrogen cyanide to form hydroxyacetonitrile and other substances. These large molecules easily polymerize and clog pipes and filters. Since the formation of hydroxyacetonitrile is a reversible reaction, cleaning the filters releases a large amount of hydrogen cyanide, posing a significant safety hazard. Furthermore, frequent clogging presents a major challenge to the stable operation of the plant. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies and, based on the current mainstream Fe-Mo oxide as a methanol ammonia oxidation catalyst, provide a new technical solution to reduce byproducts such as formaldehyde and hydroxyacetonitrile, improve the yield of hydrogen cyanide, and reduce safety hazards caused by the cleaning system process.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] Our research found that controlling the absolute humidity in a mixture of gaseous methanol, ammonia, and air within the range of 0.5-5.0 g / m³ is effective. 3 In this way, the activity and selectivity of the catalyst can be adjusted to the optimal range, which reduces the problem of low conversion rate or deep oxidation to carbon dioxide of methanol due to unsuitable catalyst activity, and also reduces the problem of increased formaldehyde by-products due to low reaction selectivity of methanol.

[0007] Specific methods for preparing hydrogen cyanide from methanol by ammoxidation include:

[0008] 1) Methanol, ammonia and air are preheated and mixed, and then introduced into the reactor;

[0009] 2) Under the action of a catalyst, a reaction occurs to produce a reaction gas containing hydrogen cyanide;

[0010] 3) After cooling the reaction gas, high-purity hydrogen cyanide is obtained through ammonia neutralization, hydrogen cyanide absorption and distillation purification processes.

[0011] The absolute humidity in the mixture of methanol, ammonia, and air is controlled to be 0.5-5.0 g / m³. 3 .

[0012] In this invention, the raw materials methanol, ammonia, and air in step 1) need to be preheated separately before entering the reactor. The preheating temperature is 100-250℃, preferably 150-200℃, and then they are mixed. After being mixed evenly, they are introduced into the reactor. The methanol, ammonia, and air are mixed in a certain proportion, with a molar feed ratio of 1:x:y, where x is 1.01-2, preferably 1.05-1.3, and y is 20-30, preferably 22-26. The air used comes from the natural environment, and the moisture content of the air is controlled by pre-treatment with a condenser. Preferably, the condenser treatment temperature is -30-0℃.

[0013] In this invention, step 1) requires controlling the absolute humidity of the mixture of methanol, ammonia, and air to be 0.5-5.0 g / m³. 3 The absolute humidity refers to the mass of water per unit volume, determined by the water content of the raw materials. The industrial-grade methanol used contains 0.01%-0.15% water by mass, and the high-purity ammonia used contains ≤0.001% water by mass. The air comes from the natural environment, and the water content needs to be treated by a condenser to control the air humidity at 0.4-4.7 g / m³. 3 The preferred concentration is 1.0-3.0 g / m³. 3 The condenser's condensing temperature is -30 to 0℃. The calculated relationship between the absolute humidity of the mixed gas and the moisture content of each component is as follows:

[0014]

[0015] In equation (1), dq represents the absolute humidity of the mixed gas, with units of g / m³. 3 ;

[0016] m1 is the mass of water in the methanol introduced per unit time, in grams;

[0017] m2 is the mass of water in the ammonia gas introduced per unit time, expressed in grams.

[0018] m3 is the mass of moisture in the air introduced per unit time, expressed in grams.

[0019] V1 is the partial volume of methanol in the gas mixture formed per unit time, in cubic meters per second (m³). 3 ;

[0020] V2 is the partial volume of ammonia in the gas mixture formed per unit time, in cubic meters (m³). 3 ;

[0021] V3 is the partial volume of air in the gas mixture formed per unit time, with units of m³. 3 .

[0022] In this invention, the catalyst used in step 2) is Fe-Mo oxide supported on silica or alumina spheres, with the Fe-Mo oxide content accounting for approximately 10% of the total catalyst mass, such as the iron-molybdenum catalyst from Zibo Tianchengtai. The reactor is a single-tube fixed-bed reactor with an effective packing height of 50 cm, a tube diameter of 2 cm, a catalyst loading of 50 g, and a total volumetric space velocity of 1500-3000 h⁻¹. -1 Preferred 2000-2500h -1 .

[0023] In this invention, heating is achieved through molten salt in the reactor jacket. The molten salt temperature is 300-400℃, preferably 320-380℃, and the hot spot temperature is 400-500℃, pre-selected as 450-480℃. The hot spot is located 10-20cm from the top of the catalyst. The reaction pressure is 10-100 kPa gauge pressure, preferably 30-60 kPa.

[0024] In this invention, the hydrogen cyanide reaction gas obtained in step 2) needs to be rapidly cooled to 200-300°C. At this temperature, the hydrogen cyanide reaction gas is relatively stable. When the temperature is below 200°C, hydrogen cyanide is prone to polymerization. When hydrogen cyanide is oligomerized, it is a black viscous oily substance, and when it is polymerized, it is a black solid substance, causing equipment and pipeline blockage.

[0025] In this invention, the cooled hydrogen cyanide reaction gas from step 3) enters a neutralization tower, where excess ammonia is captured and neutralized by an acidic aqueous solution. To ensure complete neutralization of the ammonia and prevent excess ammonia from entering the gas phase pipeline with the hydrogen cyanide and causing hydrogen cyanide polymerization, the acidity of the captured solution needs to be monitored in real time, with a pH of 2.0-6.0, preferably 4.0-5.0. To reduce the amount of hydrogen cyanide dissolved in the liquid phase, the temperature of the captured acidic aqueous solution is adjusted to control the temperature of the captured solution at 50-80°C. The captured acidic aqueous solution is selected from one or more of sulfuric acid aqueous solution or phosphoric acid aqueous solution.

[0026] In this invention, the hydrogen cyanide gas and other non-condensable gases that were not captured in step 3) are further subjected to a water absorption process. The absorption temperature is -10 to 10°C, preferably 0 to 5°C. After absorption, the hydrogen cyanide content is 0.5 to 10% of the total weight of the aqueous solution, and the volume fraction of hydrogen cyanide in the gas that was not absorbed in the water absorption process is 0.01 to 0.1%.

[0027] In this invention, the aqueous solution of hydrogen cyanide obtained in step 3) needs to be further purified by distillation. The gauge pressure at the top of the distillation column is 0-5 kPa, the number of trays is 15-20, the temperature at the bottom of the column is 100-110°C, and the hydrogen cyanide fraction at 25-28°C is collected at the top of the column. The purity of the obtained hydrogen cyanide is ≥99.0%, and the overall yield of hydrogen cyanide is ≥85%.

[0028] In this invention, the specific purification process of the hydrocyanic acid aqueous solution and the ammonium sulfate or ammonium phosphate aqueous solution at the bottom of the neutralization tower is well known in the art and will not be described in detail here.

[0029] In this invention, the monitoring site for byproduct formaldehyde derivatives is the bottom of the ammonia neutralization tower. The specific monitored substances include free formaldehyde, hydroxyacetonitrile, and other formaldehyde derivatives. The formaldehyde content is tested by titration, and the hydroxyacetonitrile content is tested by gas chromatography.

[0030] The technical solution provided by this invention has the following beneficial effects:

[0031] In the method for preparing hydrogen cyanide by methanol ammoxidation, the absolute humidity in the raw material mixed gas is controlled at 0.5-5.0 g / m³. 3 Within a certain range, the catalyst's reactivity and selectivity were effectively controlled, improving the yield of hydrogen cyanide to greater than or equal to 85%, while avoiding the formation of formaldehyde-derived byproducts such as formaldehyde and hydroxyacetonitrile, with a content of less than or equal to 0.05%. Furthermore, no pipe or equipment blockage problems caused by the polymerization of formaldehyde derivatives occurred during long-term operation. When the absolute humidity in the raw material mixture gas is <0.5 g / m³, the reaction is successful. 3 Within a certain range, the catalyst's upstream reaction activity is too high, causing the hot spot to shift upwards, leading to deep oxidation of hydrogen cyanide or methanol to produce carbon dioxide, thus reducing the hydrogen cyanide reaction yield; when the absolute humidity in the feed gas mixture is >5 g / m³, 3 Within the specified range, the hot spot shifts downward, the reactivity decreases, the yield of byproducts such as formaldehyde and hydroxyacetonitrile increases significantly, and the operating cycle is significantly shortened. Detailed Implementation

[0032] The present invention will be further described below with reference to the embodiments, but the present invention is not limited to the listed embodiments, and should also include any other known modifications within the scope of the claims of the present invention.

[0033] Raw material source:

[0034] Methanol, Tianjin Damao Reagent Factory;

[0035] Ammonia, Yantai Huasheng Gas, 99.999%, moisture content 0.001%.

[0036] Iron-molybdenum catalyst, Zibo Tianchengtai Chemical Co., Ltd.

[0037] The gas chromatographic analysis conditions for testing hydroxyacetonitrile in the embodiments and comparative examples of this invention are as follows: Agilent, column: HP-INNOWAX, FID detector, injector temperature 280℃, detector temperature 260℃, carrier gas: nitrogen (10 mL / min), split ratio 10:1, injection volume: 10 μL. The column oven initial temperature is 100℃, held for 0.5 minutes, then increased to 160℃ at 15℃ / min, held for 1.5 minutes, and then increased to 260℃ at 20℃ / min, held for 9 minutes.

[0038] The methods for testing free formaldehyde in the embodiments and comparative examples of this invention refer to GB / T30796-2014.

[0039] Neutralization tower: 5 trays, reactant gas enters from the bottom of the packing, and acidic aqueous solution enters from the top of the packing.

[0040] Absorption tower: 5 trays. Hydrogen cyanide and non-condensable gases enter from the bottom of the packing, while water enters from the top of the packing.

[0041] Absolute humidity meter: Rozhnik GmbH, Switzerland, model SMG530-TB.

[0042] Example 1

[0043] 50g of iron-molybdenum catalyst was added to a single-tube fixed-bed reactor, with a catalyst packing height of 50cm. Methanol, liquid ammonia, and air with a moisture content of 0.15% were preheated to 150℃ and then mixed. The air was first treated by passing it through a 0℃ condenser before preheating. The absolute humidity of the treated air was measured to be 4.9g / m³. 3 After mixing, the absolute humidity of the mixed gas was measured to be 4.6 g / m³. 3 Methanol, ammonia, and air were introduced into the reactor at a molar ratio of 1:1.01:20, with a space velocity of 1500 h⁻¹. -1 The molten salt temperature was set to 300℃. After the reaction stabilized, the gauge pressure inside the reactor was 10 kPa. The hot spot temperature was observed at 15 cm above the catalyst, and the hot spot temperature was 400℃.

[0044] The hydrogen cyanide reaction gas from the reaction tube outlet is first cooled to 200°C via a heat exchanger, then enters a neutralization tower where it is captured using a 5°C sulfuric acid aqueous solution. After capture, the pH of the ammonium sulfate aqueous solution at the bottom of the tower is 2.0, and the temperature is 50°C. The gaseous component from the neutralization tower enters a water absorption tower at a temperature of -10°C. The concentration of hydrogen cyanide in the aqueous solution is 10%. Unabsorbed hydrogen cyanide is detected, accounting for 0.1% of the total gas phase fraction. The hydrogen cyanide aqueous solution is further subjected to distillation. The gauge pressure at the top of the distillation column is 2 kPa, the number of trays is 15, the bottom temperature is 105°C, and the top exit temperature is 26.0°C, yielding hydrogen cyanide with a purity ≥99.0%. The overall yield of hydrogen cyanide is calculated to be 85.4%.

[0045] The bottom liquid of the neutralization tower was sampled and analyzed to test the content of dissolved free formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile, and the yield of formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile was calculated to be 0.0456%.

[0046] Example 2

[0047] 50g of iron-molybdenum catalyst was added to a single-tube fixed-bed reactor, with a catalyst packing height of 50cm. Methanol, liquid ammonia, and air with a moisture content of 0.10% were preheated to 200℃ and then mixed. The air was first treated by passing it through a -30℃ condenser before preheating. The absolute humidity of the treated air was measured to be 0.5g / m³. 3 After mixing, the absolute humidity in the mixed gas was measured to be 0.51 g / m³. 3 Methanol, ammonia, and air were introduced into the reactor at a molar ratio of 1:1.05:30, with a space velocity of 3000 h⁻¹. -1 The molten salt temperature was set to 320℃. After the reaction stabilized, the gauge pressure inside the reactor was 30KPa. The hot spot temperature was observed at 20cm above the catalyst and was 450℃.

[0048] The hydrogen cyanide reaction gas from the reaction tube outlet is first cooled to 220°C via a heat exchanger, then enters a neutralization tower where it is captured using a 20°C sulfuric acid aqueous solution. After capture, the pH of the ammonium sulfate aqueous solution at the bottom of the tower is 2.5, and the temperature is 80°C. The gaseous component from the neutralization tower enters a water absorption tower at 5°C. The concentration of hydrogen cyanide in the aqueous solution is 1%. Unabsorbed hydrogen cyanide was detected, accounting for 0.06% of the total gas phase fraction. The hydrogen cyanide aqueous solution is further subjected to distillation. The top gauge pressure of the distillation column is 0 kPa, the number of trays is 15, the bottom temperature is 102°C, and the top exit temperature is 25.6°C, yielding hydrogen cyanide with a purity ≥99.0%. The overall yield of hydrogen cyanide is calculated to be 85.3%.

[0049] The bottom liquid of the neutralization tower was sampled and analyzed to test the content of dissolved free formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile, and the yield of formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile was calculated to be 0.0315%.

[0050] Example 3

[0051] 50g of iron-molybdenum catalyst was added to a single-tube fixed-bed reactor, with a catalyst packing height of 50cm. Methanol, liquid ammonia, and air with a moisture content of 0.10% were preheated to 100℃ and then mixed. The air was first treated by passing it through a -10℃ condenser before preheating. The absolute humidity of the treated air was measured to be 1.0g / m³. 3 After mixing, the absolute humidity of the mixed gas was measured to be 0.96 g / m³. 3 Methanol, ammonia, and air were introduced into the reactor at a molar ratio of 1:1.3:22, with a space velocity of 2000 h⁻¹. -1 The molten salt temperature was set to 380℃. After the reaction stabilized, the gauge pressure inside the reactor was 60KPa. The hot spot temperature was observed at 19cm above the catalyst, and the hot spot temperature was 480℃.

[0052] The hydrogen cyanide reaction gas from the reaction tube outlet is first cooled to 260°C via a heat exchanger, then enters a neutralization tower where it is captured using a 10°C sulfuric acid aqueous solution. After capture, the pH of the ammonium sulfate aqueous solution at the bottom of the tower is 4.0, and the temperature is 60°C. The gaseous component from the neutralization tower enters a water absorption tower at 0°C. The concentration of hydrogen cyanide in the aqueous solution is 2%. Unabsorbed hydrogen cyanide is detected in the gaseous component, accounting for 0.01% of the total gas phase fraction. The hydrogen cyanide aqueous solution is further subjected to distillation. The gauge pressure at the top of the distillation column is 2 kPa, the number of trays is 20, the bottom temperature is 105°C, and the top exit temperature is 26.0°C, yielding hydrogen cyanide with a purity ≥99.0%. The overall yield of hydrogen cyanide is calculated to be 86.5%.

[0053] The bottom liquid of the neutralization tower was sampled and analyzed to determine the content of dissolved free formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile. The yield of formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile was calculated to be 0.0301%.

[0054] Example 4

[0055] 50g of iron-molybdenum catalyst was added to a single-tube fixed-bed reactor, with a catalyst packing height of 50cm. Methanol, liquid ammonia, and air with a moisture content of 0.01% were preheated to 250℃ and then mixed. The air was first treated by passing it through a -20℃ condenser before preheating. The absolute humidity of the treated air was measured to be 3.2g / m³. 3 After mixing, the absolute humidity of the mixed gas was measured to be 3.0 g / m³. 3 Methanol, ammonia, and air were introduced into the reactor at a molar ratio of 1:1.1:26, with a space velocity of 2500 h⁻¹. -1 The molten salt temperature was set to 400℃. After the reaction stabilized, the gauge pressure inside the reactor was 100KPa. The hot spot temperature was observed at 19cm above the catalyst, and the hot spot temperature was 500℃.

[0056] The hydrogen cyanide reaction gas from the reaction tube outlet is first cooled to 300℃ via a heat exchanger, then enters a neutralization tower where it is captured using an 8℃ phosphoric acid aqueous solution. After capture, the pH of the ammonium phosphate aqueous solution at the bottom of the tower is 5.0, and the temperature is 55℃. The gaseous component from the neutralization tower enters a water absorption tower at a temperature of 5℃. The concentration of hydrogen cyanide in the aqueous solution is 1%. Unabsorbed hydrogen cyanide is detected, accounting for 0.02% of the total gas phase fraction. The hydrogen cyanide aqueous solution is further subjected to distillation. The gauge pressure at the top of the distillation column is 5 kPa, the number of trays is 18, the bottom temperature is 110℃, and the top exit temperature is 28.0℃, yielding hydrogen cyanide with a purity ≥99.0%. The overall yield of hydrogen cyanide is calculated to be 86.2%.

[0057] The bottom liquid of the neutralization tower was sampled and analyzed to test the content of dissolved free formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile. The yield of formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile was calculated to be 0.0337%.

[0058] Example 5

[0059] 50g of iron-molybdenum catalyst was added to a single-tube fixed-bed reactor, with a catalyst packing height of 50cm. Methanol, liquid ammonia, and air with a moisture content of 0.1% were preheated to 130℃ and then mixed. The air was first treated by passing it through a -5℃ condenser before preheating. The absolute humidity of the treated air was measured to be 4.2g / m³. 3 After mixing, the absolute humidity of the mixed gas was measured to be 3.9 g / m³. 3 Methanol, ammonia, and air were introduced into the reactor at a molar ratio of 1:1.02:25, with a space velocity of 2200 h⁻¹. -1 The molten salt temperature was set to 350℃. After the reaction stabilized, the gauge pressure inside the reactor was 50 kPa. The hot spot temperature was observed at 460℃, located 16 cm above the catalyst.

[0060] The hydrogen cyanide reaction gas from the reaction tube outlet is first cooled to 230°C via a heat exchanger, then enters a neutralization tower where it is captured using a 5°C phosphoric acid aqueous solution. After capture, the pH of the ammonium phosphate aqueous solution at the bottom of the tower is 6.0, and the temperature is 50°C. The gaseous component from the neutralization tower enters a water absorption tower at a temperature of 10°C. The concentration of hydrogen cyanide in the aqueous solution is 0.5%. Unabsorbed hydrogen cyanide accounts for 0.05% of the total gas phase fraction. The hydrogen cyanide aqueous solution is further subjected to distillation. The gauge pressure at the top of the distillation column is 2 kPa, the number of trays is 16, the bottom temperature is 105°C, and the top exit temperature is 26.0°C, yielding hydrogen cyanide with a purity ≥99.0%. The overall yield of hydrogen cyanide is calculated to be 85.3%.

[0061] The bottom liquid of the neutralization tower was sampled and analyzed to test the content of dissolved free formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile, and the yield of formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile was calculated to be 0.0422%.

[0062] Comparative Example 1

[0063] 50g of iron-molybdenum catalyst was added to a single-tube fixed-bed reactor, with a catalyst packing height of 50cm. Methanol, liquid ammonia, and air with a moisture content of 0.15% were preheated to 150℃ and then mixed. The air was not condensed before preheating, and the absolute humidity of the air was measured to be 6.1g / m³. 3 After mixing, the absolute humidity of the mixed gas was measured to be 5.6 g / m³. 3 Methanol, ammonia, and air were introduced into the reactor at a molar ratio of 1:1.01:20, with a space velocity of 1500 h⁻¹. -1 The molten salt temperature was set to 300℃. After the reaction stabilized, the gauge pressure inside the reactor was 10 kPa. The hot spot temperature was observed at 21 cm above the catalyst, and the hot spot temperature was 390℃.

[0064] The hydrogen cyanide reaction gas from the reaction tube outlet is first cooled to 200°C via a heat exchanger, then enters a neutralization tower where it is captured using a 5°C sulfuric acid aqueous solution. After capture, the pH of the ammonium sulfate aqueous solution at the bottom of the tower is 2.0, and the temperature is 50°C. The gaseous component from the neutralization tower enters a water absorption tower at a temperature of -10°C. The concentration of hydrogen cyanide in the aqueous solution is 10%. Unabsorbed hydrogen cyanide is detected, accounting for 0.1% of the total gas phase fraction. The hydrogen cyanide aqueous solution is further subjected to distillation. The top gauge pressure of the distillation column is 2 kPa, the number of trays is 15, the bottom temperature is 105°C, and the top exit temperature is 26.0°C, yielding hydrogen cyanide with a purity ≥99.0%. The overall yield of hydrogen cyanide is calculated to be 84.1%.

[0065] The bottom liquid of the neutralization tower was sampled and analyzed to test the content of dissolved free formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile, and the yield of formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile was calculated to be 0.212%.

[0066] After 15 days of operation, the pressure in the reaction tube was found to be high. Upon inspection, black coke-like material was found on the pipeline at the rear end of the heat exchanger at the reaction outlet.

[0067] Comparative Example 2

[0068] 50g of iron-molybdenum catalyst was added to a single-tube fixed-bed reactor, with a catalyst packing height of 50cm. Methanol, liquid ammonia, and air with a moisture content of 0.1% were preheated to 150℃ and then mixed. The air was first treated by passing it through a -30℃ condenser before preheating. The absolute humidity of the treated air was measured to be 0.4g / m³. 3 After mixing, the absolute humidity of the mixed gas was measured to be 0.37 g / m³.3 Methanol, ammonia, and air were introduced into the reactor at a molar ratio of 1:1.01:20, with a space velocity of 1500 h⁻¹. -1 The molten salt temperature was set to 300℃. After the reaction stabilized, the gauge pressure inside the reactor was 10 kPa. The hot spot temperature was observed at 430℃, located 14 cm above the catalyst.

[0069] The hydrogen cyanide reaction gas from the reaction tube outlet is first cooled to 200°C via a heat exchanger, then enters a neutralization tower where it is captured using a 5°C sulfuric acid aqueous solution. After capture, the pH of the ammonium sulfate aqueous solution at the bottom of the tower is 2.0, and the temperature is 50°C. The gaseous component from the neutralization tower enters a water absorption tower at a temperature of -10°C. The concentration of hydrogen cyanide in the aqueous solution is 10%. Unabsorbed hydrogen cyanide is detected, accounting for 0.1% of the total gas phase fraction. The hydrogen cyanide aqueous solution is further subjected to distillation. The top gauge pressure of the distillation column is 2 kPa, the number of trays is 15, the bottom temperature is 105°C, and the top exit temperature is 26.0°C, yielding hydrogen cyanide with a purity ≥99.0%. The overall yield of hydrogen cyanide is calculated to be 83.2%.

[0070] The bottom liquid of the neutralization tower was sampled and analyzed to determine the content of dissolved free formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile. The yield of formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile was calculated to be 0.0689%.

[0071] Example 6:

[0072] 50g of iron-molybdenum catalyst was added to a single-tube fixed-bed reactor, with a catalyst packing height of 50cm. Methanol, liquid ammonia, and air with a moisture content of 0.15% were preheated to 150℃ and then mixed. The air was first treated by passing it through a 0℃ condenser before preheating. The absolute humidity of the treated air was measured to be 4.9g / m³. 3 After mixing, the absolute humidity of the mixed gas was measured to be 4.6 g / m³. 3 Methanol, ammonia, and air were introduced into the reactor at a molar ratio of 1:1.01:20, with a space velocity of 1500 h⁻¹. -1 The molten salt temperature was set to 300℃. After the reaction stabilized, the gauge pressure inside the reactor was 10 kPa. The hot spot temperature was observed at 15 cm above the catalyst, and the hot spot temperature was 400℃.

[0073] The hydrogen cyanide reaction gas from the reaction tube outlet is first cooled to 150°C via a heat exchanger, then enters a neutralization tower where it is captured using a 5°C sulfuric acid aqueous solution. After capture, the pH of the ammonium sulfate aqueous solution at the bottom of the tower is 2.0, and the temperature is 50°C. The gaseous component from the neutralization tower enters a water absorption tower at a temperature of 15°C. The concentration of hydrogen cyanide in the aqueous solution is 10%. Unabsorbed hydrogen cyanide accounts for 0.6% of the total gas phase fraction. The hydrogen cyanide aqueous solution is further subjected to distillation. The top gauge pressure of the distillation column is 2 kPa, the number of trays is 20, the bottom temperature is 105°C, and the top exit temperature is 26.0°C, yielding hydrogen cyanide with a purity ≥99.0%. The overall yield of hydrogen cyanide is calculated to be 85.0%.

[0074] The bottom liquid of the neutralization tower was sampled and analyzed to test the content of dissolved free formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile, and the yield of formaldehyde and formaldehyde derivatives such as hydroxyacetonitrile was calculated to be 0.0456%.

[0075] As can be seen from the above examples and comparative examples, the reaction process of the present invention can effectively control the generation of byproducts such as formaldehyde and hydroxyacetonitrile.

[0076] Those skilled in the art will understand that modifications or adjustments can be made to the present invention based on the teachings of this specification. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A process for the production of hydrocyanic acid by the ammoxidation of methanol, characterized in that, The method comprises: 1) mixing methanol, ammonia and air after preheating, and then feeding into a reactor; 2) under the action of a catalyst, a reaction gas containing hydrocyanic acid is generated; 3) after cooling the reaction gas, high-purity hydrocyanic acid is obtained through ammonia neutralization, hydrocyanic acid absorption and rectification purification; wherein the absolute humidity in the mixed gas of methanol, ammonia gas, and air is 0.5-5.0 g / m 3 .

2. The method of claim 1, wherein, The absolute humidity of the mixed gas in step 1) refers to the water content, and the calculation relationship between the absolute humidity of the mixed gas and the water content in each component is as follows: wherein dq in formula (1) is the absolute humidity in the mixed gas, in g / m 3 ; m1 is the mass of water in the methanol fed per unit time, in g; m2 is the mass of water in the ammonia fed per unit time, in g; m3 is the mass of water in the air fed per unit time, in g; V1 is the partial volume of methanol in the mixed gas formed per unit time, in m 3 ; V2 is the partial volume of ammonia in the mixture formed per unit of time, in m 3 ; V3 is the partial volume of air in the mixture formed per unit time, in m 3 .

3. The method of claim 1, wherein, The air used comes from the natural environment, and the water in the air is controlled by a condenser.

4. The method of claim 3, wherein, The treatment temperature of the condenser is -30-0℃.

5. The method of claim 1, wherein, The methanol, ammonia and air need to be preheated before entering the reactor, and the preheating temperature is 100-250℃.

6. The method according to any one of claims 1-5, characterized in that, The methanol, ammonia and air are mixed in a certain proportion, and the molar feeding ratio is 1:x:y, x is 1.01-2, and y is 20-30.

7. The method of claim 1, wherein, The reactor is a single-tube fixed bed reactor, the molten salt temperature is 300-400℃, and the reaction pressure is 10-100KPa.

8. The method of claim 1, wherein, In step 2) the catalyst is selected from Fe-Mo oxides, the total volume space velocity is 1500-3000 h -1 .

9. The method of claim 8, wherein, In step 2) the total volume space velocity is 2000-2500 h -1 .

10. The method according to claim 1 or 8 or 9, characterized in that, The hydrocyanic acid reaction gas obtained in step 2) is cooled to 200-300℃.

11. The method of claim 1, wherein, The cooled reaction gas in step 3) needs to be captured by an acidic aqueous solution, the temperature of the solution after capture is 50-80℃, and the pH of the solution after capture is 2-6.

12. The method of claim 11, wherein, The hydrocyanic acid gas and other non-condensable gases that are not captured in step 3) are further absorbed by water, the absorption temperature is -10-10℃, the content of hydrocyanic acid after absorption is 0.5-10% of the total weight of the aqueous solution, and the volume fraction of hydrocyanic acid in the gas that is not absorbed is 0.01-0.1%.

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