Method for preparing methyl nitrite through reaction of NO and methanol

Abstract

The invention discloses a method for preparing methyl nitrite through a reaction of NO and methanol, belongs to the technical field of methyl nitrite, and aims to solve the technical problems that in the process of preparing methyl nitrite through a reaction of NO and methanol in the prior art, the conversion rate, the selectivity and the purity of converting NO into methyl nitrite need to be further improved. The method specifically comprises the following steps: filling a catalyst in a catalytic section of a reaction tower protected by nitrogen, raising the temperature of the catalytic section of the reaction tower to 50-60 DEG C, and raising the pressure of the reaction tower to 0.1-0.2 MPa; according to the method, reaction parameters in the process of preparing the methyl nitrite through the reaction of the NO and the methanol are optimized, so that the conversion rate and the selectivity of converting the NO into the methyl nitrite are effectively improved, the by-product process is reduced, the content of water, nitric acid and other impurities in the prepared methyl nitrite is extremely low, and the method is suitable for industrial production. The catalyst can be directly suitable for reacting with CO to prepare dimethyl carbonate.

Description

Technical Field

[0001] The present invention relates to the technical field of methyl nitrite preparation, and specifically relates to a method for preparing methyl nitrite by reacting NO and methanol. Background Art

[0002] Preparing dimethyl carbonate by reacting methyl nitrite and carbon monoxide (CO) is one of the commonly used methods in industry. Its raw materials, methyl nitrite and carbon monoxide, are inexpensive, carbon monoxide can be recycled, and compared with the phosgene method and the transesterification method, there are no highly toxic by-products, which conforms to the principles of green chemistry.

[0003] In the prior art, a patent with the publication number CN103373925A discloses a method for preparing methyl nitrite. This method uses a gas containing NO, O2, and methanol as raw materials, inputs the gas containing NO, O2, and methanol into at least one esterification tower for reaction to obtain methyl nitrite, nitric acid, and the remaining methanol. The remaining methanol is recovered in at least one methanol recovery tower, and nitric acid is recovered in at least one nitric acid recovery tower. Compared with the prior art, it can efficiently generate methyl nitrite, improve the NO conversion rate, increase the methyl nitrite yield, and reduce the heating amount at the bottom of the esterification tower. Moreover, the wastewater discharged from the system does not contain nitric acid, completely solving the problem of nitric acid wastewater generated during the process of generating methyl nitrite using NO.

[0004] Currently, during the synthesis of methyl nitrite, since the gas-phase oxidation reaction between NO and oxygen generates a nitrogen-oxygen mixture containing dinitrogen tetroxide, and the process of dinitrogen tetroxide reacting with methanol to prepare methyl nitrite is an exothermic reaction. During the reaction process, it is easy to generate runaway temperature, resulting in an increase in the reaction by-product nitric acid, a decrease in the conversion rate and selectivity of NO to methyl nitrite. Moreover, if the content of impurities such as nitric acid and water in methyl nitrite is relatively high, it will poison the catalyst when participating in the dimethyl carbonate reaction, affecting the reaction of dimethyl carbonate. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing methyl nitrite by reacting NO and methanol, aiming to solve the technical problem that the conversion rate, selectivity, and purity of converting NO to methyl nitrite during the process of preparing methyl nitrite by reacting NO and methanol in the prior art need to be further improved.

[0006] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing methyl nitrite by reacting NO and methanol, comprising the following steps:

[0007] S1. Load a catalyst in the catalytic section of a reaction tower under nitrogen protection, raise the temperature of the catalytic section of the reaction tower to 50 - 60 °C, and raise the pressure of the reaction tower to 0.1 - 0.2 MPa;

[0008] S2. Mix NO and oxygen in a gas mixer and then transport the resulting gas mixture to the lower part of the catalytic section. After being catalyzed by the catalyst in the catalytic section, it reacts with the reactant methanol to obtain a reaction gas.

[0009] S3. After the reaction stabilizes, adjust the oxygen inlet amount so that the concentration of NO in the reaction gas is 5 - 7 vol%. The reaction gas enters the absorption section and contacts the adsorbent methanol flowing from top to bottom for purification to obtain a crude methyl nitrite product.

[0010] S4. After the crude methyl nitrite product is discharged through the top exhaust pipe, it is absorbed by a solution to obtain a methyl nitrite solution.

[0011] The reactions involved in the synthesis process of methyl nitrite include:

[0012] ;

[0013] .

[0014] The elemental reactions include:

[0015] ;

[0016] ;

[0017] ;

[0018] ;

[0019] ;

[0020] ;

[0021] Further, in step S1, the catalyst is a CuO-ZnO / Al2O3 catalyst.

[0022] Further, the preparation method of the CuO-ZnO / Al2O3 catalyst is as follows: Mix copper nitrate, zinc nitrate, aluminum nitrate and deionized water, stir until the system dissolves, raise the temperature of the reaction system to 55 - 65 °C, add polyvinyl alcohol to the reaction system, stir for 30 - 50 min, add absolute ethanol to the reaction system, stir for 60 - 80 min, lower the temperature of the reaction system to room temperature, add sodium hydroxide solution to the reaction system, adjust the pH of the system to 10, stir for 10 - 15 min, and perform post-treatment to obtain the CuO-ZnO / Al2O3 catalyst.

[0023] Furthermore, the dosage ratio of copper nitrate, zinc nitrate, aluminum nitrate, deionized water, polyvinyl alcohol and absolute ethanol is 2 - 3 g: 1 - 1.3 g: 5 - 7 g: 30 mL: 1.6 - 1.9 g: 60 mL. The post-treatment includes: after the reaction is completed, suction filtration is carried out. The filter cake is washed 3 times with 50 wt% ethanol aqueous solution and then dried. The solid is transferred to a muffle furnace at a temperature of 400 - 500 °C, kept for roasting for 4 - 6 h, cooled and discharged to obtain the CuO-ZnO / Al2O3 catalyst.

[0024] Furthermore, in step S2, the volume ratio of NO to oxygen in the mixed gas is 6:1, and the volume ratio of the mixed gas to the reactant methanol is 1:6 - 8.

[0025] Furthermore, a sprayer is provided above the top of the catalytic section. One side of the reaction tower is externally provided with a feed pipe and a liquid delivery pump connected to the sprayer for spraying methanol in the form of atomized spray on the top of the catalytic section. A drain pipe is provided at the bottom of the reaction tower for discharging the methanol waste liquid collected at the bottom of the reaction tower to the outside of the reaction tower.

[0026] Furthermore, in step S3, the temperature of methanol in the absorption section is 50 - 60 °C, and the volume ratio of methanol to NO is 6 - 10:1.

[0027] Furthermore, the absorption section includes a plurality of flow guiding plates, arc-shaped plates, liquid inlet pipes and liquid outlet pipes. The plurality of flow guiding plates are arranged in a staggered manner, and the top of the flow guiding plate has an inclined surface inclined downward along the fluid flow direction. The arc-shaped plate is located below the flow guiding plate for receiving the methanol solution flowing out from the bottommost flow guiding plate. The liquid inlet pipe extends into the interior of the reaction tower and is located at the top of the topmost flow guiding plate for evenly distributing and flowing the methanol solution along the surface of the flow guiding plate. The liquid outlet pipe extends to the top of the arc-shaped plate for leading out the methanol solution in the arc-shaped plate to the outside of the reaction tower.

[0028] Furthermore, the preparation method of the methyl nitrite solution is as follows: after the crude methyl nitrite is cooled to room temperature, it is transported through a pipeline into methanol at a temperature of 5 - 10 °C and absorbed until saturated to obtain the methyl nitrite solution.

[0029] The present invention has the following beneficial effects:

[0030] 1. The present invention uses a CuO-ZnO / Al2O3 catalyst as the reaction catalyst to catalyze the reaction of NO and oxygen to generate dinitrogen trioxide, which then reacts with methanol to prepare methyl nitrate. During the preparation process, by optimizing the reaction temperature and pressure, the collision frequency between reactant molecules is increased, and the reaction rate is improved. During the reaction process, while using methanol as the reaction raw material, it is used as a heat exchange medium to timely remove the heat generated by the reaction. By controlling its temperature, the temperature of the catalytic section can be accurately controlled, avoiding runaway temperature in the catalytic section and reducing the occurrence of side reactions. Moreover, the nitric acid and water produced by side reactions can dissolve in methanol, and the by-products generated can be discharged in a timely manner along with the circulating methanol, reducing its impact on the catalyst bed and avoiding the large accumulation of by-product water, which affects the catalytic performance of the catalyst bed. Nitric acid dissolves in methanol, and the by-products can be recovered through simple distillation.

[0031] 2. In the process of preparing methyl nitrite in the present invention, if the content of NO in the reaction system is 0, it will cause residual oxygen, resulting in the mixing of methyl nitrite produced by the reaction with oxygen, expanding the flammable range of the reaction gas and posing a greater risk of combustion and explosion. Moreover, if the content of NO is low during the reaction process, it will increase the conversion rate of N2O4, resulting in an increase in the amount of nitric acid produced by side reactions and a decrease in the conversion rate of methyl nitrite. By exploring the content of NO in the reaction, while suppressing the occurrence of side reactions during the catalytic process, the conversion rate of methyl nitrite is improved.

[0032] 3. The present invention uses methanol as the adsorption solution, raises the temperature of the methanol solution, and high temperature destroys the hydrogen bond interaction between methanol molecules, reducing its solubility in methyl nitrite. High temperature also increases the kinetic energy of methyl nitrite molecules, making them more likely to escape from the solution. Moreover, the Henry coefficient of methyl nitrite in methanol increases with the increase in temperature, indicating that the solubility decreases with the increase in temperature. By controlling the temperature of methanol, impurities that are easily soluble in methanol in the reaction gas water vapor, etc. can be effectively separated from methyl nitrite, reducing its impurity content and improving the purity of methyl nitrite. And the produced methyl nitrite is adsorbed by low-temperature methanol, which is convenient for it to directly participate in the preparation of dimethyl carbonate, avoiding the introduction of other impurities including ethanol. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0034] Figure 1 It is a schematic structural diagram of the reaction tower in the present invention;

[0035] Figure 2 This is a schematic diagram of the internal structure of the absorption section of the reaction tower in the present invention.

[0036] In the figure: 101, catalytic section; 102, absorption section; 1021, deflector plate; 1022, arc plate; 1023, liquid inlet pipe; 1024, liquid outlet pipe; 103, exhaust pipe. Specific embodiments

[0037] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0038] Embodiment 1

[0039] Please refer to Figure 1-2 , this embodiment provides a reaction tower for preparing methyl nitrite by the reaction of NO and methanol, including a tower body, a catalytic section 101 and an absorption section 102 located inside the reaction tower;

[0040] The catalytic section 101 includes a bottom plate, a first packing layer, a catalyst bed layer, a second packing layer and a top plate arranged in sequence from bottom to top. Both the bottom plate and the top plate are porous plates with filter cloth layers. Both the first packing layer and the second packing layer are formed by laying pineapple porcelain balls with a diameter of 3-10 mm;

[0041] A sprayer is provided above the top of the catalytic section. A feed pipe 105 and a liquid delivery pump are provided outside one side of the reaction tower and are connected to the sprayer, for spraying methanol in the form of atomized spray on the top of the catalytic section. A liquid discharge pipe 104 is provided at the bottom of the reaction tower for discharging the methanol waste liquid collected at the bottom of the reaction tower to the outside of the reaction tower.

[0042] The liquid supply of the feed pipe 105 and the liquid discharge of the liquid discharge pipe 104 form a liquid supply-discharge cycle. The reactant methanol enters the upper and lower parts of the catalytic section through the feed pipe 105 and flows downwards from the top of the catalyst. By controlling the temperature of the methanol entering the reaction tower, the reactant methanol is composed of low-temperature methanol (10-20 °C) and high-temperature methanol (50-60 °C). By monitoring the temperature inside the reaction tower, the mixing ratio of low-temperature methanol and high-temperature methanol is adjusted. Using the raw material methanol as a heat exchange medium, the temperature of the catalytic section is effectively controlled. The methanol solution discharged through the liquid discharge pipe 104 contains impurity components. Through distillation-condensation recovery, the methanol content reaches 99.8% and the water content is lower than 0.05%. It can enter the reaction tower through the feed pipe 105 as recycled methanol for recycling, reducing the loss of methanol.

[0043] The absorption section 102 includes a plurality of flow guiding plates 1021, arc-shaped plates 1022, a liquid inlet pipe 1023 and a liquid outlet pipe 1024. The plurality of flow guiding plates 1021 are arranged staggeredly, and the top of the flow guiding plate 1021 has an inclined surface that is inclined downward along the fluid flow direction. The arc-shaped plate 1022 is located below the flow guiding plate 1021 and is used to catch the methanol solution flowing out from the bottommost flow guiding plate 1021. The liquid inlet pipe 1023 extends into the interior of the reaction tower and is located at the top of the topmost flow guiding plate 1021, and is used to evenly distribute and flow the methanol solution along the surface of the flow guiding plate 1021. The liquid outlet pipe 1024 extends to the top of the arc-shaped plate 1022 and is used to lead the methanol solution in the arc-shaped plate 1022 out of the reaction tower.

[0044] The end of the liquid inlet pipe 1023 extending into the tower body is of a long arc structure and is used to evenly distribute the fluid entering the tower body on the top of the flow guiding plate 1021. A plurality of flow guiding grooves are arranged on the top surface of the flow guiding plate 1021 along the direction of its inclined surface, and the plurality of flow guiding grooves are densely arranged adjacent to each other. A gap for air flow to enter is provided between the end of the arc-shaped plate 1022 close to the bottom of the flow guiding plate 1021 and the bottom of the flow guiding plate 1021. The end of the liquid outlet pipe 1024 extending into the tower body is flush with the bottom of the arc-shaped plate 1022. A flow control valve is provided on the liquid outlet pipe 1024, so that the end of the liquid outlet pipe 1024 located inside the tower body is always submerged by the fluid, forming a water seal to prevent the gas in the tower from overflowing from the liquid outlet pipe 1024. After the methanol liquid output from the liquid outlet pipe 1024 is distilled and condensed, the methanol content reaches more than 99.5% and can be recycled.

[0045] Example 2

[0046] This example provides a method for preparing methyl nitrite by reacting NO with methanol, which includes the following steps:

[0047] Step 1, preparing a catalyst

[0048] Weigh: 200 g of copper nitrate, 100 g of zinc nitrate, 500 g of aluminum nitrate and 3000 mL of deionized water and add them to a reaction flask and stir until the system dissolves. The temperature of the reaction flask is raised to 55 °C. Add 160 g of polyvinyl alcohol to the reaction flask and stir for 30 min. Add 6000 mL of absolute ethanol to the reaction flask and stir for 60 min. The temperature of the reaction flask is lowered to room temperature. Add 2 mol / L sodium hydroxide solution to the reaction flask to adjust the pH of the system to 10 and stir for 10 min. Filter by suction. The filter cake is washed 3 times with 50 wt% ethanol aqueous solution and then dried. The solid is transferred to a muffle furnace at 400 °C, kept for roasting for 4 h, cooled and discharged to obtain the CuO-ZnO / Al2O3 catalyst.

[0049] Step 2, preparing the reaction tower

[0050] Place the CuO-ZnO / Al2O3 catalyst prepared in Step 1 inside the reaction tower. Introduce nitrogen into the reaction tower to displace the air in the reaction tower. When the pressure of the reaction tower rises to 0.1 MPa, the reactant methanol is transported into the interior of the reaction tower through the feed pipe 105. After being sprayed by the sprayer, it enters the catalytic section 101 and flows downward along the catalytic section 101, collecting at the bottom of the reaction tower and then being discharged outside the reaction tower through the drain pipe 104. Using the reactant methanol as the heat exchange medium, by controlling the temperature of the reactant methanol, the temperature of the catalytic section 101 is increased, and the temperature of the catalytic section 101 is controlled to rise to 50 °C.

[0051] Step 3: Prepare crude methyl nitrite

[0052] Add NO and oxygen to the gas mixer in a volume ratio of 6:1 to form a mixed gas;

[0053] According to the volume ratio of the mixed gas to the reactant methanol being 1:6, transport the mixed gas to the lower part of the catalytic section 101. After being catalyzed by the catalyst in the catalytic section 101, it reacts with the reactant methanol. After the reaction stabilizes, adjust the oxygen inlet amount so that the concentration of NO in the gas discharged from the catalytic section 101 is 5 vol% to obtain a reaction gas;

[0054] When the temperature of the adsorbed methanol rises to 50 °C, transport it to the absorption section 102 according to the volume ratio of the adsorbed methanol to the mixed gas being 6:1, and make the adsorbed methanol flow downwards to contact the reaction gas flowing upwards, and conduct contact purification on the reaction gas to obtain crude methyl nitrite.

[0055] Step 4: Prepare methyl nitrite solution

[0056] Load methanol with a water content of 0.005% into the absorption tank, and lower the temperature of the methanol to 5 °C. The crude methyl nitrite is transported into the absorption tank from the bottom of the absorption tank through a pipeline to contact the methanol. After absorption saturation, a methyl nitrite solution is obtained.

[0057] Example 3

[0058] This example provides a method for preparing methyl nitrite by reacting NO and methanol, including the following steps:

[0059] Step 1: Prepare the catalyst

[0060] Weigh: 250 g of copper nitrate, 115 g of zinc nitrate, 600 g of aluminum nitrate and 3000 mL of deionized water are added to a reaction flask and stirred until the system dissolves. The temperature of the reaction flask rises to 60 °C. 175 g of polyvinyl alcohol is added to the reaction flask and stirred for 40 min. 6000 mL of absolute ethanol is added to the reaction flask and stirred for 70 min. The temperature of the reaction flask is lowered to room temperature. 2 mol / L sodium hydroxide solution is added to the reaction flask to adjust the pH of the system to 10 and stirred for 13 min. Then, filtration is carried out. The filter cake is washed 3 times with 50 wt% ethanol aqueous solution and then dried. The solid is transferred to a muffle furnace at 450 °C and calcined for 5 h while maintaining the temperature. After cooling, the product is discharged to obtain the CuO-ZnO / Al2O3 catalyst.

[0061] Step 2: Preparation of the reaction tower

[0062] The CuO-ZnO / Al2O3 catalyst prepared in Step 1 is filled into the interior of the reaction tower. Nitrogen is introduced into the reaction tower to displace the air in the reaction tower. The pressure of the reaction tower rises to 0.15 MPa. The temperature of the reactant methanol rises to 55 °C and is transported into the interior of the reaction tower through the feed pipe 105. After being sprayed by the sprayer, it enters the catalytic section 101 and flows downward along the catalytic section 101, converges at the bottom of the reaction tower, and then is discharged outside the reaction tower through the drain pipe 104. Using the reactant methanol as the heat exchange medium, by controlling the temperature of the reactant methanol, the temperature of the catalytic section 101 is increased, and the temperature of the catalytic section 101 is controlled to rise to 55 °C.

[0063] Step 3: Preparation of crude methyl nitrite

[0064] NO and oxygen are added to a gas mixer in a volume ratio of 6:1 to form a mixed gas.

[0065] According to the volume ratio of the mixed gas to the reactant methanol of 1:7, the mixed gas is transported to the lower part of the catalytic section 101 and reacts with the reactant methanol after being catalyzed by the catalyst in the catalytic section 101. After the reaction is stable, the oxygen inlet amount is adjusted so that the concentration of NO in the gas discharged from the catalytic section 101 is 6 vol% to obtain a reaction gas.

[0066] The temperature of the adsorbed methanol rises to 55 °C. According to the volume ratio of the adsorbed methanol to the mixed gas of 8:1, it is transported to the absorption section 102 so that the adsorbed methanol flows downward and contacts the reaction gas flowing upward to purify the reaction gas by contact to obtain crude methyl nitrite.

[0067] Step 4: Preparation of methyl nitrite solution

[0068] Methanol with a water content of 0.006% is loaded into the absorption tank. The temperature of the methanol is lowered to 8 °C. The crude methyl nitrite is transported to the absorption tank through a pipeline from the bottom of the absorption tank and contacts the methanol. After absorption saturation, a methyl nitrite solution is obtained.

[0069] Example 4

[0070] This example provides a method for preparing methyl nitrite by reacting NO with methanol, comprising the following steps:

[0071] Step 1: Preparation of the catalyst

[0072] Weigh: 300 g of copper nitrate, 130 g of zinc nitrate, 700 g of aluminum nitrate and 3000 mL of deionized water, add them to a reaction flask and stir until the system dissolves. Raise the temperature of the reaction flask to 65 °C, add 190 g of polyvinyl alcohol to the reaction flask, stir for 50 min, add 6000 mL of absolute ethanol to the reaction flask, stir for 80 min, lower the temperature of the reaction flask to room temperature, add 2 mol / L sodium hydroxide solution to the reaction flask, adjust the pH of the system to 10, stir for 15 min, perform suction filtration, wash the filter cake 3 times with 50 wt% ethanol aqueous solution and then dry it. Transfer the solid to a muffle furnace at 500 °C, keep it for roasting for 6 h, cool down and discharge to obtain the CuO-ZnO / Al2O3 catalyst.

[0073] Step 2: Preparation of the reaction tower

[0074] Fill the CuO-ZnO / Al2O3 catalyst prepared in Step 1 into the interior of the reaction tower, introduce nitrogen into the reaction tower to displace the air in the reaction tower. Raise the pressure of the reaction tower to 0.2 MPa, raise the temperature of the reactant methanol to 60 °C, and transport it into the interior of the reaction tower through the feed pipe 105. After being sprayed by the sprayer, it enters the catalytic section 101 and flows downward along the catalytic section 101, collects at the bottom of the reaction tower, and then is discharged outside the reaction tower through the drain pipe 104. Using the reactant methanol as the heat exchange medium, by controlling the temperature of the reactant methanol, the temperature of the catalytic section 101 is raised, and the temperature of the catalytic section 101 is controlled to rise to 60 °C.

[0075] Step 3: Preparation of crude methyl nitrite

[0076] Add NO and oxygen to the gas mixer in a volume ratio of 6:1 to form a mixed gas;

[0077] According to the volume ratio of the mixed gas to the reactant methanol of 1:8, transport the mixed gas to the lower part of the catalytic section 101, react with the reactant methanol after being catalyzed by the catalyst in the catalytic section 101. After the reaction is stable, adjust the oxygen inlet amount so that the concentration of NO in the gas discharged from the catalytic section 101 is 7 vol% to obtain the reaction gas;

[0078] The temperature of the adsorbed methanol is raised to 60°C, and it is transported to the absorption section 102 at a volume ratio of adsorbed methanol to the mixed gas of 10:1, allowing the adsorbed methanol to flow downwards to contact the reaction gas flowing upwards, and performing contact purification on the reaction gas to obtain crude methyl nitrite.

[0079] Step 4: Prepare a methyl nitrite solution

[0080] Load methanol with a water content of 0.008% into the absorption tank, lower the temperature of the methanol to 10°C, and transport the crude methyl nitrite through a pipeline to the bottom of the absorption tank to contact with the methanol. After absorption saturation, a methyl nitrite solution is obtained.

[0081] Comparative Example 1

[0082] The difference between this comparative example and Example 4 is that in Step 2, the pressure in the reaction tower is normal pressure.

[0083] Comparative Example 2

[0084] The difference between this comparative example and Example 4 is that in Step 3, after the reaction is stable, the concentration of NO in the gas discharged from the catalytic section 101 is 2 vol%.

[0085] Comparative Example 3

[0086] The difference between this comparative example and Example 4 is that in Step 3, the volume ratio of the mixed gas to the reactant methanol is 1:3, and the temperature of the reactant methanol is kept constant at 60°C.

[0087] Performance test:

[0088] Formula 1: ;

[0089] Formula 2: ;

[0090] In Formula 1 and Formula 2, n 亚硝酸甲酯 is the molar amount of methyl nitrite prepared, is the molar amount of NO entering the reaction tower, is the molar amount of NO discharged from the reaction tower;

[0091] Referring to Formula 1, measure the conversion rate of nitric oxide to methyl nitrite in Examples 2 - 4 and Comparative Examples 1 - 3;

[0092] Referring to Formula 2, measure the selectivity of nitric oxide to methyl nitrite in Examples 2 - 4 and Comparative Examples 1 - 3;

[0093] The water content in the methyl nitrite solution prepared in Examples 2-4 and Comparative Examples 1-3 was determined with reference to the standard GB / T 6283-2008 Determination of Water Content in Chemical Products - Karl Fischer Method (General Method). The specific test results are shown in Table 1 below.

[0094] Table 1 - Performance Test Data Sheet of Samples

[0095]

[0096] Data Analysis:

[0097] Through comparative analysis of the data in Table 1 above, for the method for preparing methyl nitrite by reacting NO with methanol provided by the present invention, the conversion rate of nitric oxide to methyl nitrite reaches 78.7%, the selectivity of nitric oxide to methyl nitrite reaches 99.7%, and the water content is extremely low. All test data are superior to those of the comparative examples. This shows that by optimizing the reaction parameters in the process of preparing methyl nitrite by reacting NO with methanol, the present invention not only effectively improves the conversion rate and selectivity of NO to methyl nitrite, reduces the by-product process, but also the content of water, nitric acid and other impurities in the prepared methyl nitrite is extremely low, and it can be directly applied to react with CO to prepare dimethyl carbonate.

[0098] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only the specific embodiments. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principle and practical application of the present invention, so that those skilled in the art in the technical field can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

Claims

1. A method for preparing methyl nitrite by reacting NO with methanol, characterized in that, It includes the following steps: S1. Charge the catalyst into the catalytic section (101) of the reaction tower under nitrogen protection. Raise the temperature of the catalytic section (101) of the reaction tower to 50 - 60 °C and raise the pressure of the reaction tower to 0.1 - 0.2 MPa; S2. Mix NO and oxygen through a gas mixer to form a mixed gas, and transport the mixed gas to the lower part of the catalytic section (101). After being catalyzed by the catalyst in the catalytic section (101), react with the reactant methanol to obtain a reaction gas; S3. After the reaction is stable, adjust the oxygen input amount so that the concentration of NO in the reaction gas is 5 - 7 vol%. The reaction gas enters the absorption section (102) and contacts the flowing-down adsorption methanol for purification to obtain a crude methyl nitrite product; S4. After the crude methyl nitrite product is discharged through the top exhaust pipe (103) of the tower and absorbed by the solution, a methyl nitrite solution is obtained.

2. The method for preparing methyl nitrite by reacting NO with methanol according to claim 1, wherein In step S1, the catalyst is a CuO-ZnO / Al2O3 catalyst.

3. The method for preparing methyl nitrite by reacting NO with methanol according to claim 2, characterized in that, The preparation method of the CuO-ZnO / Al2O3 catalyst is as follows: Mix copper nitrate, zinc nitrate, aluminum nitrate and deionized water, stir until the system is dissolved, raise the temperature of the reaction system to 55 - 65 °C, add polyvinyl alcohol to the reaction system, stir for 30 - 50 min, add absolute ethanol to the reaction system, stir for 60 - 80 min, lower the temperature of the reaction system to room temperature, add sodium hydroxide solution to the reaction system, adjust the pH of the system to 10, stir for 10 - 15 min, and perform post-treatment to obtain the CuO-ZnO / Al2O3 catalyst.

4. The method for preparing methyl nitrite by reacting NO with methanol according to claim 3, characterized in that, The dosage ratio of the copper nitrate, zinc nitrate, aluminum nitrate, deionized water, polyvinyl alcohol and absolute ethanol is 2 - 3 g: 1 - 1.3 g: 5 - 7 g: 30 mL: 1.6 - 1.9 g: 60 mL.

5. The method for preparing methyl nitrite by reacting NO with methanol according to claim 1, characterized in that, In step S2, the volume ratio of NO to oxygen in the mixed gas is 6:1, and the volume ratio of the mixed gas to the reactant methanol is 1:6 - 8.

6. The method for preparing methyl nitrite by reacting NO with methanol according to claim 1, characterized in that, A sprayer is provided above the top of the catalytic section. A feed pipe (105) and a liquid delivery pump connected to the sprayer are provided outside one side of the reaction tower, which are used to spray methanol in the form of atomized spray on the top of the catalytic section. A drain pipe (104) is provided at the bottom of the reaction tower, which is used to discharge the methanol waste liquid collected at the bottom of the reaction tower to the outside of the reaction tower.

7. The method for preparing methyl nitrite by reacting NO with methanol according to claim 1, characterized in that, In step S3, the temperature of the methanol in the absorption section (102) is 50 - 60 °C, and the volume ratio of methanol to NO is 6 - 10:

1.

8. The method for preparing methyl nitrite by reacting NO with methanol according to claim 1, characterized in that, The absorption section (102) includes a plurality of flow guiding plates (1021), arc-shaped plates (1022), a liquid inlet pipe (1023) and a liquid outlet pipe (1024). The plurality of flow guiding plates (1021) are arranged staggeredly, and the top of the flow guiding plate (1021) has an inclined surface that is inclined downward along the fluid flow direction. The arc-shaped plate (1022) is located below the flow guiding plate (1021) and is used to catch the methanol solution flowing out from the bottommost flow guiding plate (1021). The liquid inlet pipe (1023) extends into the interior of the reaction tower and is located at the top of the topmost flow guiding plate (1021) for uniformly distributing and flowing the methanol solution along the surface of the flow guiding plate (1021). The liquid outlet pipe (1024) extends to the top of the arc-shaped plate (1022) for leading the methanol solution in the arc-shaped plate (1022) out of the reaction tower to the outside.

9. The method for preparing methyl nitrite by reacting NO with methanol according to claim 1, characterized in that, The preparation method of the methyl nitrite solution is as follows: After the crude methyl nitrite is cooled to room temperature, it is transported through a pipeline into methanol at a temperature of 5-10°C and absorbed until saturated to obtain the methyl nitrite solution.

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