Process for increasing the yield of hcn production by the andrusso method

Abstract

This application discloses a process for improving the yield of HCN prepared by the Andruse process, belonging to the field of HCN preparation technology. This application utilizes the tail gas after HCN removal and dehydration reactions, using residual methane in the tail gas to increase methane conversion, using CO in the tail gas to inhibit methane decomposition and improve methane selectivity, and using H2 in the tail gas, with H2 combustion providing heat instead of the heat provided by methane decomposition. This improves the conversion rate of methane to HCN, increases the overall reaction yield, and eliminates ammonia residue in the post-reaction gas, saving the ammonia removal step. Simultaneously, it reduces air consumption and increases the ratio of ammonia to methane to oxygen, allowing the reaction to proceed far from the explosion zone, thus improving process safety.

Description

Technical Field

[0001] This application belongs to the field of HCN preparation technology, and in particular relates to a process for improving the yield of HCN prepared by the Andruse method. Background Technology

[0002] Hydrogen cyanide (HCN) is an important basic chemical raw material, widely used in the synthesis of acrylonitrile, adiponitrile, cyanides, chelating agents, and pharmaceutical and pesticide intermediates. The mainstream industrial method for producing hydrogen cyanide is the Andruse process. Its basic principle involves mixing ammonia, methane, and an oxygen-containing gas (air or pure oxygen) in a specific ratio, and reacting them at high temperatures under the action of a platinum or platinum alloy catalyst to produce hydrogen cyanide. The main reaction in this system is the reaction of methane and ammonia to produce hydrogen cyanide and hydrogen gas. This reaction is strongly endothermic, with a heat of reaction as high as 63041 kcal / kmol. Theoretically, the reaction temperature needs to be maintained at 800-2500 °C to drive the forward reaction.

[0003] To maintain such high reaction temperatures, industrial practice typically uses the heat released from the combustion of some methane with oxygen to provide heat for the endothermic main reaction. However, this method inevitably leads to methane waste: a significant portion of the high-value methane feedstock is directly consumed through combustion, reducing overall feedstock utilization. Furthermore, the choice of oxygen source presents a dilemma: if air is used, the large amount of inert nitrogen (approximately 79%) not only does not participate in the reaction but also absorbs a significant amount of reaction heat at high temperatures and is discharged with the exhaust gas, resulting in decreased system thermal efficiency. If pure oxygen is used, while reducing heat loss from inert gases and increasing the reaction temperature, the flammability limits of the reaction system significantly widen in a pure oxygen environment, drastically increasing the explosion risk and imposing stringent requirements on the safety interlocks and operational control of the equipment. Therefore, in the existing Andruse process, manufacturers often make trade-offs in reaction conditions (raw material ratio, reaction temperature, type of oxygen source), but it is always difficult to simultaneously achieve high raw material utilization, high energy efficiency and intrinsic safety.

[0004] In existing technologies, the separation of hydrogen cyanide products typically employs water absorption or acid absorption processes. After the reaction, the gas is cooled and then enters an absorption tower, where the hydrogen cyanide is absorbed by the absorbent. The exhaust gas from the absorption tower mainly contains unreacted methane, hydrogen, nitrogen (if air is used), carbon monoxide, carbon dioxide, and a small amount of water vapor. For a long time, this exhaust gas has usually been directly sent to a downstream incineration system for treatment, or simply vented after heat recovery. Although those skilled in the art know that the exhaust gas contains a certain amount of combustible components (such as unreacted methane and hydrogen), due to the moisture content and large fluctuations in the concentration of each component, direct reuse in the reaction system would severely affect catalyst activity and reaction stability. Therefore, there is no industrial practice of directly reusing the exhaust gas from the absorption stage for the reaction stage. Some patent literature mentions separating and purifying the hydrogen in the exhaust gas for use as fuel, but the separation and purification equipment requires high investment and is complex to operate, and it does not solve the problem of reusing other combustible gases such as methane.

[0005] In conclusion, how to effectively utilize unreacted raw materials and combustible components in the tail gas of the absorption section, reduce methane waste, and improve overall reaction efficiency without increasing safety risks and significantly modifying existing equipment remains a pressing technical challenge in the Androsseau process for hydrogen cyanide production. Summary of the Invention

[0006] The purpose of this application is to provide a process for improving the yield of HCN in the Andruse process, which effectively recovers and utilizes the tail gas emitted from the hydrogen cyanide absorption section, thereby reducing the waste of methane feedstock, reducing heat loss brought in by inert gas (nitrogen) or avoiding the risk of explosion under pure oxygen conditions, and ultimately improving the overall reaction efficiency of hydrogen cyanide preparation.

[0007] To achieve the above objectives, the technical solution adopted in this application is: to provide a process for improving the yield of HCN prepared by the Andruse method, specifically including the following steps: Ammonia, methane, and air are mixed and the reaction temperature is controlled by a platinum catalyst. The reaction gas is cooled, and the generated HCN is absorbed by water. After the tail gas is dehydrated, it is mixed with fresh air and recycled back into the reactor to participate in the next round of reaction. The recycling process increases the ratio of tail gas to fresh air and reduces the amount of ammonia.

[0008] In one embodiment, The molar ratio of exhaust gas to fresh air is 1:2-4.

[0009] In one embodiment, The exhaust gas, by volume fraction, includes 65-70% nitrogen, 0.2-0.4% oxygen, 4-5% carbon monoxide, and 16-18% hydrogen.

[0010] In one embodiment, The temperature at which the reaction gas is cooled is less than 120 °C.

[0011] In one embodiment, The molar ratio of methane to ammonia is 1:1-1.2.

[0012] In one embodiment, The molar ratio of methane to air is 1:5-6.2.

[0013] In one embodiment, The total gas volume to the mass ratio of the platinum catalyst is 1:0.0005-0.001.

[0014] In one embodiment, The reaction temperature is 800-1200 ℃.

[0015] This application provides a process for improving the yield of HCN preparation in the Andruse process. The tail gas discharged from the hydrogen cyanide absorption section is sequentially treated to remove HCN and then to dehydrate. A portion of the purified tail gas is then reused in the reaction system, mixed with fresh feed gas, and fed into the reactor. This tail gas reuse step not only achieves the reuse of unreacted feedstock but, more importantly, utilizes specific active components in the tail gas to synergistically improve the thermodynamics and kinetics of the reaction, thereby significantly improving the selective conversion efficiency of methane to hydrogen cyanide and enhancing the process safety margin. This application's research found that these components have the following beneficial effects after reuse: 1. Utilizing residual methane in the tail gas to improve the total methane conversion rate. The main reaction in the Androsseau process is an endothermic reaction, and the single-pass conversion rate is limited by thermodynamic equilibrium. In traditional processes, unreacted methane is directly burned with the tail gas, resulting in waste. This application reintroduces the unconverted methane in the tail gas into the reaction zone, which is equivalent to extending the residence time of methane in the reactor. This improves the overall conversion rate and reduces the raw material consumption without increasing the fresh methane feed. 2. Utilizing CO in the tail gas to suppress side reactions of methane thermal cracking and improve methane selectivity. At high temperatures, methane is prone to non-catalytic cracking, and the generated free carbon adheres to the surface of the platinum catalyst, leading to catalyst deactivation. At the same time, carbon particles can also clog the bed. The CO recycled in the tail gas can undergo the Boudouard reverse reaction (C + CO2 → 2CO) with the active carbon atoms generated by methane cracking, or directly compete for active sites, thereby inhibiting carbon deposition. In addition, the presence of CO can also regulate the chemical potential of the catalyst surface, promote the pathway of direct reaction between methane and ammonia to generate HCN, reduce the ineffective decomposition of methane into carbon and hydrogen, and significantly improve the selectivity of methane for HCN. At the same time, it improves the yield of HCN for ammonia and the selectivity of ammonia for HCN. There is no ammonia residue in the mixer after the reaction, eliminating the need for the deammoniation step in the treatment process. 3. This invention utilizes the H2 combustion in the exhaust gas to provide heat, replacing part of the methane combustion for energy, and releasing more methane for the main reaction. Traditional processes maintain a reaction temperature of 800-2500 °C by burning part of the methane. In this application, hydrogen is recycled from the exhaust gas, and the hydrogen preferentially reacts with oxygen in a combustion reaction that is exothermic and extremely fast. Since hydrogen combustion replaces the heating task originally undertaken by methane combustion, the consumption of fresh methane combustion can be reduced accordingly, allowing more methane to be used in the main reaction to generate HCN, thereby improving the conversion rate of methane to HCN. Calculations show that for every 1 kmol of hydrogen recycled, approximately 0.5 kmol of methane combustion demand can be saved. 4. By reusing tail gas, the amount of air used is reduced, and the raw material ratio is optimized, keeping the reaction away from the explosion range. In traditional processes, if air is used for oxygen supply, an excess of air is often required to maintain the high temperature, leading to nitrogen accumulation in the system and a relatively high oxygen concentration, with the mixed gas approaching the explosion limit. In this application, since hydrogen, CO, and methane in the tail gas all participate in the reaction and release heat, the amount of air (or pure oxygen) added can be reduced. Under the premise of keeping the reaction temperature constant, the absolute concentration of oxygen is reduced, thereby causing the composition of the reaction mixture to deviate from the explosion limit range, significantly improving process safety. In addition, HCN removal and dehydration treatment avoid the poisoning effect of impurities on the catalyst and ensure the cleanliness of the reused tail gas. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a process flow diagram. Detailed Implementation

[0018] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, this application will be further described in detail. It should be understood that the specific embodiments described herein are only for explaining this application and are not intended to limit this application.

[0019] Example 1 2000 mol / h of fresh air, 340 mol / h of natural gas (methane content: 97-99%), and 306 mol / h of ammonia were mixed and reacted in a tubular reactor packed with 58 g of platinum catalyst. The catalyst bed temperature was raised to 1100 °C for the reaction. The reaction gas was then cooled to 120 °C using a heat exchanger, and the HCN generated was absorbed by 10 °C cold water. The HCN was then sent as a product to downstream processes. After dehydration of the tail gas, a portion of the tail gas was mixed with fresh air as feed gas for the next round of reaction. During the process, the ratio of tail gas to fresh air was slowly increased while the ammonia flow was slowly decreased to maintain the reaction temperature until the tail gas flow reached 600 mol / h and the fresh air flow reached 1400 mol / h, with a tail gas to fresh air molar ratio of 1:2.4. At this point, the ammonia flow decreased to 300 mol / h, a 2% reduction, while the reaction temperature was monitored and controlled at 1100 °C. The temperature was around ℃; the total amount of hydrogen cyanide obtained from the hydrogen cyanide absorption section was converted to HCN, resulting in a methane yield of 79.00% and an ammonia yield of 69.00%.

[0020] Example 2 The difference between this embodiment and Example 1 is that the initial flow rate of ammonia was 340 mol / h, which was reduced to 330 mol / h after stabilization. The molar ratio of tail gas to fresh air was 1:3, and the rest of the operation was the same to obtain HCN. The total amount of hydrogen cyanide obtained from the hydrogen cyanide absorption section was converted to HCN, and the yield of methane was 79.50%, and the yield of ammonia was 67.00%.

[0021] Example 3 The difference between this embodiment and Example 1 is that the air flow rate is 1700 mol / h, the temperature of the catalyst bed is raised to 1050 ℃, and the rest of the operation is the same, and HCN is produced; the total amount of hydrogen cyanide obtained from the hydrogen cyanide absorption section is converted to HCN yield of 78.30% for methane and 67.50% for ammonia.

[0022] Example 4 The difference between this embodiment and Example 1 is that the molar ratio of tail gas to fresh air is 1:2, the temperature of the catalyst bed is raised to 1050 °C, and the rest of the operation is the same to obtain HCN. The total amount of hydrogen cyanide obtained from the hydrogen cyanide absorption section was converted to HCN yield of 77.60% for methane and 67.30% for ammonia.

[0023] Example 5 The difference between this embodiment and Embodiment 1 is that the molar ratio of exhaust gas to fresh air is 1:3.5, while the rest of the operations are the same, to obtain HCN; the total amount of hydrogen cyanide obtained from the hydrogen cyanide absorption section was converted to HCN yield of 78.20% for methane and 67.80% for ammonia.

[0024] Example 6 The difference between this embodiment and Example 1 is that the amount of platinum catalyst added is 48 g, while the rest of the operation is the same, and HCN is prepared. The total amount of hydrogen cyanide obtained from the hydrogen cyanide absorption section was converted to HCN yield of 78.30% for methane and 67.90% for ammonia.

[0025] Example 7 The difference between this embodiment and Example 1 is that the amount of platinum catalyst added is 68 g, while the rest of the operation is the same, and HCN is prepared. The total amount of hydrogen cyanide obtained from the hydrogen cyanide absorption section is converted to HCN yield of 78.90% for methane and 69.00% for ammonia.

[0026] Example 8 The difference between this embodiment and Embodiment 1 is that the molar ratio of exhaust gas to fresh air is 1:4. The rest of the operation is the same. The total amount of hydrogen cyanide obtained from the hydrogen cyanide absorption section is converted to HCN yield of 77.50% for methane and 67.30% for ammonia.

[0027] Example 9 The difference between this embodiment and Embodiment 1 is that the exhaust gas is not used; only fresh air is used for the reaction. The rest of the operation is the same. The total amount of hydrogen cyanide obtained from the hydrogen cyanide absorption section was converted to HCN yield of 77.10% for methane and 66.90% for ammonia.

[0028] Table 1 Comparison of experimental conditions in Examples 1-9

[0029] This application provides a process for improving the yield of HCN preparation via the Andruse process, comprising the following steps: mixing ammonia, methane, and air, passing through a platinum catalyst, controlling the reaction temperature, cooling the reaction gas, absorbing unreacted ammonia with an acid solution, absorbing the generated HCN with water, and mixing the tail gas after dehydration with fresh air and recycling it into the reactor for the next round of reaction; this application improves the conversion rate of methane to HCN by partially utilizing the tail gas after HCN removal and dehydration reactions, utilizing the residual methane in the tail gas to increase the methane conversion rate, utilizing CO in the tail gas to inhibit methane decomposition and improve methane selectivity, and utilizing H2 in the tail gas, with H2 combustion providing heat instead of the heat provided by methane decomposition, thereby improving the conversion rate of methane to HCN and increasing the overall reaction yield, ensuring no ammonia residue in the gas after the reaction, and saving the ammonia removal step; at the same time, it reduces the amount of air used, increases the ratio of ammonia to methane to oxygen, and ensures that the reaction takes place far from the explosion zone, improving process safety.

[0030] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0031] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A process for improving the yield of HCN produced by the Andrussow process, characterized in that, Specifically comprising the following steps: After mixing ammonia, methane and air, the reaction gas is cooled by a platinum catalyst, the generated HCN is absorbed by water, the tail gas is mixed with fresh air after water removal, and the mixture is recycled into the reactor to participate in the next round of reaction.

2. A process for improving the yield of HCN in the Andrussow process according to claim 1, characterized in that, The recycling process increases the ratio of tail gas to fresh air and reduces the amount of ammonia.

3. A process for improving the yield of HCN in the Andrussow process according to claim 1, characterized in that, The molar ratio of the mixture of tail gas and fresh air is 1:2-4.

4. A process for improving the yield of HCN in the Andrussow process according to claim 1, characterized in that, The tail gas includes 65-70% nitrogen, 0.2-0.4% oxygen, 4-5% carbon monoxide and 16-18% hydrogen by volume fraction.

5. A process for improving the yield of HCN in Andrussow process as claimed in claim 1, wherein, The temperature of the reaction gas during cooling is less than 120°C.

6. A process for improving the yield of HCN in Andrussow process as claimed in claim 1, wherein, The molar ratio of methane to ammonia is 1:1-1.

2.

7. A process for improving the yield of HCN in Andrussow process as claimed in claim 1, wherein the process is characterized by, The molar ratio of methane to air is 1:5-6.

2.

8. A process for improving the yield of HCN in the Andrussow process according to claim 1, characterized in that, The mass ratio of total gas to platinum catalyst is 1:0.0005-0.

001.

9. A process for improving the yield of HCN in the Andrussow process according to claim 1, characterized in that, The reaction temperature is 800-1200°C.

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