A method for preparing hydrocyanic acid by dehydrating formamide

Abstract

The present invention relates to a method for preparing hydrocyanic acid by dehydrating formamide, which includes the step of dehydrating formamide and air to produce hydrocyanic acid under the action of a catalyst. The catalyst mainly consists of a carrier and a metal active component, and its preparation method is divided into two steps: the first step is to prepare a porous carrier, and the second step is to impregnate a certain amount of active component on the basis of the above carrier. The catalyst of the present invention has a relatively high specific surface area, strength, and high dispersion, without by-products, and has good catalytic performance when applied to the dehydration of formamide to produce hydrocyanic acid. The conversion rate of formamide is greater than 98%, the yield of ammonia is less than 0.05%, and the yield of hydrocyanic acid is greater than 99%.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic technology, and particularly relates to a method for producing hydrocyanic acid by dehydrating formamide. Background Art

[0002] Hydrocyanic acid is an important chemical raw material, mainly used in the production of adiponitrile, MMA, methionine and other chemical products, with wide applications. However, due to its highly toxic nature, hydrocyanic acid cannot be transported. Therefore, all demands for hydrocyanic acid need to be self-sufficient. Currently, the sources of hydrocyanic acid in society mainly include several categories, including by-products of acrylonitrile, methane method, and methanol method. With the continuous development of acrylonitrile catalysts, the yield of hydrocyanic acid by-produced from acrylonitrile is getting lower and lower. In addition, the methane method requires the use of expensive noble metal catalysts, the reaction temperature exceeds 1000 °C, and the yield is relatively low. Therefore, the methane method has poor economic efficiency. The methanol method brings great challenges to the safety of the ammonium sulfate process due to the inevitable formation of formaldehyde.

[0003] Another technology for producing hydrocyanic acid is the formamide dehydration process, and the reaction equation is as follows:

[0004] HCONH 2 →HCN + H 2 O

[0005] Its main principle is that under the action of high temperature and catalyst, formamide is dehydrated to produce hydrocyanic acid. However, there is also a side reaction that restricts the yield of hydrocyanic acid in this reaction, that is, formamide decomposes to produce ammonia and carbon monoxide, and the equation is as follows:

[0006] HCONH 2 →CO + NH 3

[0007] The existence of this side reaction seriously restricts the economic efficiency of producing hydrocyanic acid from formamide.

[0008] Therefore, how to improve the selectivity and conversion rate of the formamide dehydration to hydrocyanic acid reaction remains the main challenge. Summary of the Invention

[0009] In view of the above-mentioned problems, the present invention provides a method for producing hydrocyanic acid by dehydrating formamide. The catalyst of this method avoids the limitation of special reactor materials. In a tubular reactor made of ordinary 304L material, the conversion rate of formamide is greater than 98%, the yield of hydrocyanic acid is greater than 99%, and the yield of ammonia is less than 0.05%.

[0010] To achieve the above object, the technical solution of the present invention is as follows:

[0011] A method for preparing hydrocyanic acid by dehydrating formamide comprises the steps of preparing hydrocyanic acid by dehydrating formamide and air under the action of a catalyst, wherein the catalyst is prepared by the following steps:

[0012] (1) grinding kaolin, pseudo-boehmite, zirconium silicate and sesbania powder by wet ball milling, and then spray drying to obtain fine powder, preferably, the fine powder has a particle size of 1-10 μm;

[0013] (2) mixing the fine powder, binder and water uniformly, extruding, pelletizing and calcining to obtain a porous carrier;

[0014] (3) preparing a salt solution containing metal active components, impregnating the porous carrier into the salt solution by an impregnation method, and then drying and calcining to obtain the catalyst.

[0015] In a specific embodiment, the ratio of the raw materials in step (1) is calculated by mass percentage, wherein kaolin is 65-75wt%, pseudo-boehmite is 10-20wt%, zirconium silicate is 4-14wt%, and field blue powder is 1-11wt%.

[0016] In a specific embodiment, the binder in step (2) is selected from any one or more of polyvinyl pyrrolidone, hydroxypropyl methylcellulose, soluble starch, and sodium lignin sulfonate.

[0017] In a specific embodiment, the mass ratio of fine powder, binder and water in step (2) is 1:(0.2-0.5):(0.1-0.5).

[0018] In a specific embodiment, in step (2), a twin-screw extruder is used for extrusion, and a clover-shaped mold with a diameter of 2-5 mm is selected as the mold. After extrusion, the extruded particles are broken into particles with a length of 1-5 mm by pelletizing.

[0019] In a specific embodiment, the particles obtained by dicing in step (2) are dried and then calcined in an air atmosphere at 400-800° C. for 2-10 hours to obtain a porous carrier.

[0020] In a specific embodiment, the metal active component in step (3) is selected from one or more of Sc, V, W, Fe, Cu, and Ag.

[0021] In a specific embodiment, the concentration of the salt solution during impregnation in step (3) is 0.5-1.5 mol / L, its mass is 2-10 times the mass of the porous carrier, and the impregnation time is 2-5 h; preferably, after the impregnation is completed, the excess salt solution is poured out, and the mixture is dried at 100-150° C. for 5-10 h and calcined at 400-600° C. for 3-8 h.

[0022] In a specific embodiment, the specific surface area of ​​the catalyst is 50-400 m 2 / g, preferably 200-400m 2 / g, and the mesopore volume is 1-10cm 3 / g, preferably 5-8cm 3 / g, and the compressive strength is 200-500N / cm, preferably 300-450N / cm.

[0023] In a specific embodiment, the molar ratio of formamide to air is 1:80-100, the feed temperature is 300-600°C, and the air velocity is 1000-5000h -1 .

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The method of the invention adopts a special catalyst and avoids the limitation of special reactor materials. In a shell-and-tube reactor made of ordinary 304L material, the conversion rate of formamide is greater than 98%, the yield of hydrocyanic acid is greater than 99%, and the yield of ammonia is less than 0.05%. DETAILED DESCRIPTION

[0026] In order to better understand the technical solution of the present invention, the following examples will further illustrate the method provided by the present invention, but the present invention is not limited to the listed examples, and should also include any other known changes within the scope of the claims of the present invention.

[0027] A method for preparing hydrocyanic acid by dehydrating formamide comprises the following steps:

[0028] (1) A certain proportion of kaolin, pseudo-boehmite, zirconium silicate and sesbania powder is ground by wet ball milling, and then spray dried to obtain fine powder.

[0029] Wherein, a mixture of kaolin, pseudo-boehmite, zirconium silicate and Tianqing powder is ground into a slurry by a ball mill, and then spray-dried to obtain a fine powder with a particle size of about 1-10 μm. Preferably, the subdivided particle size distribution D90=8-10 μm. The mixture of the four raw materials is calculated by mass fraction, and kaolin accounts for 65-75wt%, pseudo-boehmite accounts for 10-20wt%, zirconium silicate accounts for 4-14wt%, and Tianqing powder accounts for 1-11wt%. For example, the mass ratio of the four raw materials is 70wt% kaolin, 15wt% pseudo-boehmite, 9wt% zirconium silicate, and 6wt% Tianqing powder. Wherein, the particle size of the four raw materials is not particularly limited, for example, 1-50μm, and finally wet ball milled to 28μm, and then spray-dried into a fine powder of the target particle size.

[0030] (2) The above-mentioned fine powder, binder and water are mixed evenly in a certain proportion, extruded, granulated and calcined to obtain a porous carrier.

[0031] Among them, the fine powder and the binder are first mixed evenly, and then water is added in small amounts and multiple times, and stirred continuously to obtain a "dough"-like substance with moderate hardness, and then extruded. The selected binder is one or more of polyvinyl pyrrolidone, hydroxypropyl methylcellulose, soluble starch, and sodium lignin sulfonate. In terms of mass ratio, the ratio of fine powder, binder and water is 1:0.2-0.5:0.1-0.5, preferably 1:0.2-0.4:0.3-0.5. When multiple binders are selected, the mass ratio of various binders is, for example, 1:z:j, where the z value is 0-5, the j value is 0-5, and z and j are different and are 0.

[0032] When extruding, a clover-shaped die is selected, and the average diameter of the die hole is 2-5 mm, preferably 2.5-4.5 mm. After extrusion, the strips are pelletized into particles with a length of 1-5 mm, preferably 3.5-5 mm. The obtained particles are dried and roasted, wherein the roasting temperature is 400-800° C., preferably 500-750° C., and the roasting time is 2-10 hours, preferably 3-8 hours, to obtain a porous carrier.

[0033] (3) preparing a salt solution of a certain concentration, immersing the carrier into the salt solution by an immersion method, and then drying and calcining to obtain the catalyst.

[0034] Wherein, the salt solution is a salt solution of metal active components, and the concentration of the salt solution is 0.5-1.5 mol / L. The metal active component is selected from one or more of Sc, V, W, Fe, Cu, and Ag. It is usually selected that when impregnating, it is best to heat the impregnated salt solution to a temperature of, for example, 60-80°C. Specifically, an excessive impregnation method is adopted, the mass of the impregnation liquid is 2-10 times the mass of the carrier, preferably 5-8 times, and the impregnation time is 2-5h, preferably 3-4.5h. After the impregnation is completed, the excess liquid is poured out and dried. The drying temperature is 100-150°C, preferably 120-130°C. After completion, the catalyst is calcined at 400-600°C for 3-8h, preferably 450-550°C for 4-6h.

[0035] The specific surface area of ​​the catalyst prepared by the above steps is 50-400m 2 / g, preferably 200-400m 2 / g, and the mesopore volume is 1-10cm 3 / g, preferably 5-8cm 3 / g, and the compressive strength is 200-500N / cm, preferably 300-450N / cm.

[0036] (4) In a tubular reactor, formamide and air are mixed in a certain proportion, preheated, and then enter the reaction tube for reaction. Formamide and air are dehydrated to produce hydrocyanic acid under the action of a catalyst, and the outlet is analyzed by online gas chromatography.

[0037] Wherein, the molar ratio of formamide to air is 1:80-100, such as 1:80, 1:85, 1:90, 1:95, 1:100, etc., the feed temperature is 300-600°C, such as 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, etc., and the air velocity is 1000-5000h -1 For example, 1000h -1 、1500h -1 , 2000h -1 、2500h -1 、3000h -1 、3500h -1 , 4000h -1 、4500h -1 , 5000h -1 The reaction pressure of the present invention is not particularly limited and is usually carried out under normal pressure. It will be appreciated by those skilled in the art that it can also be achieved under slightly positive pressure.

[0038] The present invention is further explained below by more specific examples, but does not constitute any limitation.

[0039] The main raw material sources used in the embodiments are as follows:

[0040] Kaolin, pseudoboehmite, and Tianqing powder were purchased from Jinan Qicai Chemical Co., Ltd.;

[0041] Zirconium silicate, tungsten phosphate, and copper nitrate were purchased from Aladdin Reagent Co., Ltd.

[0042] The gas chromatography analysis conditions used in the examples are: Agilent HP-INNOWAX column, inlet temperature: 280°C; detector temperature: 240°C; H2 flow rate: 35 ml / min; air flow rate: 350 ml / min.

[0043] Example 1

[0044] Take 65g kaolin, 18g pseudo-boehmite, 6g zirconium silicate, and 11g Tianqing powder, mix them evenly, grind them into slurry with a ball mill, spray dry them, and obtain fine powder with D50=8.5μm. Then take 100g fine powder, 20g soluble starch, and 40g water and mix them evenly. Select clover mold extrusion strips with an average diameter of 2.5mm, break them into particles with a length of 3.5mm, and roast them at 500℃ for 4h to obtain a carrier. Prepare 500g of a mixed solution of tungsten phosphate and copper nitrate, in which the molar concentration of tungsten phosphate is 0.5mol / L and the molar concentration of copper nitrate is 0.8mol / L. After sufficient dissolution, add 100g of the carrier and soak for 3h. Then pour out the excess impregnation solution, dry it at 120℃, and then roast it at 450℃ for 4h to obtain catalyst A.

[0045] The catalyst was evaluated in a fixed bed reactor. Formamide and air were fed in a molar ratio of 1:20, the feed temperature was 300 °C, and the space velocity was 1000 h -1 The reaction tail gas was analyzed by online chromatography.

[0046] Example 2

[0047] Take 73g kaolin, 12g pseudo-boehmite, 5g zirconium silicate, 10g Tianqing powder and mix them evenly, grind them into slurry with a ball mill, spray dry them, and obtain fine powder with D50=9.5μm. Then take 100g fine powder, 30g sodium lignin sulfonate, and 50g water and mix them evenly. Select clover mold extrusion strips with an average diameter of 3.5mm, break them into particles with a length of 5mm, and roast them at 750℃ for 8h to obtain a carrier. Prepare a mixed solution of 500g ferric sulfate and vanadium pentoxide, in which the molar concentration of iron is 0.8mol / L and the molar concentration of vanadium is 0.25mol / L. After sufficient dissolution, add 62.5g of the carrier and soak for 4.5h. Then pour out the excess impregnation solution, dry at 130℃, and then roast at 550℃ for 4h to obtain catalyst B.

[0048] The catalyst was evaluated in a fixed bed reactor, with formamide and air fed at a molar ratio of 1:20, a feed temperature of 370 °C, and a space velocity of 3100 h -1 The reaction tail gas was analyzed by online chromatography.

[0049] Example 3

[0050] Take 68g kaolin, 17g pseudo-boehmite, 10g zirconium silicate, 5g Tianqing powder and mix them evenly, grind them into slurry with a ball mill, spray dry them, and obtain fine powder with D50=10μm. Then take 100g fine powder, 40g polyvinyl pyrrolidone, and 30g water and mix them evenly. Select clover mold extrusion strips with an average diameter of 3mm, break them into particles with a length of 4mm, and roast them at 600℃ for 6h to obtain a carrier. Prepare a mixed solution of 500g silver nitrate and copper acetate, in which the molar concentration of Ag is 0.65mol / L and the molar concentration of copper is 0.23mol / L. After sufficient dissolution, add 71.43g of the carrier and soak for 5h. Then pour out the excess impregnation solution, dry at 130℃, and then roast at 550℃ for 6h to obtain catalyst C.

[0051] The catalyst was evaluated in a fixed bed reactor with formamide and air fed at a molar ratio of 1:50, a feed temperature of 450 °C, and a space velocity of 2400 h -1 The reaction tail gas was analyzed by online chromatography.

[0052] Example 4

[0053] Take 68g kaolin, 17g pseudo-boehmite, 10g zirconium silicate, 5g Tianqing powder and mix them evenly, grind them into slurry with a ball mill, spray dry them, and obtain fine powder with D50=10μm. Then take 100g fine powder, 40g polyvinyl pyrrolidone, and 30g water and mix them evenly. Select clover mold extrusion strips with an average diameter of 3mm, break them into particles with a length of 4mm, and roast them at 600℃ for 6h to obtain a carrier. Prepare a mixed solution of 500g silver nitrate and copper acetate, in which the molar concentration of Ag is 0.65mol / L and the molar concentration of copper is 0.23mol / L. After sufficient dissolution, add 71.43g of the carrier and soak for 5h. Then pour out the excess impregnation solution, dry at 130℃, and then roast at 550℃ for 6h to obtain catalyst D.

[0054] The catalyst was evaluated in a fixed bed reactor, with formamide and air fed at a molar ratio of 1:80, a feed temperature of 430 °C, and a space velocity of 2400 h -1 The reaction tail gas was analyzed by online chromatography.

[0055] Comparative Example 1

[0056] The steps for preparing the catalyst are the same as those in Example 1, except that catalyst E is obtained without adding tungsten phosphate and copper nitrate.

[0057] The evaluation was carried out using the method of Example 1.

[0058] Comparative Example 2

[0059] The conventional alumina catalyst F purchased from Pingxiang Dongtao Ceramics was used for evaluation. The method of Example 1 was used for evaluation.

[0060] Comparative Example 3

[0061] Take 50g kaolin, 31g pseudo-boehmite, 15g zirconium silicate, and 4g Tianqing powder, mix them evenly, grind them into slurry with a ball mill, spray dry them, and obtain fine powder with D50=10μm. Then take 100g fine powder, 40g polyvinyl pyrrolidone, and 30g water and mix them evenly. Select clover mold extrusion strips with an average diameter of 3mm, break them into particles with a length of 4mm, and roast them at 600℃ for 6h to obtain a carrier. Prepare a mixed solution of 500g silver nitrate and copper acetate, in which the molar concentration of Ag is 0.65mol / L and the molar concentration of copper is 0.23mol / L. After sufficient dissolution, add 71.43g of the carrier and soak for 5h. Then pour out the excess impregnation solution, dry at 130℃, and then roast at 550℃ for 6h to obtain catalyst G.

[0062] The catalyst was evaluated in a fixed bed reactor, with formamide and air fed at a molar ratio of 1:80, a feed temperature of 430 °C, and a space velocity of 2400 h -1 The reaction tail gas was analyzed by online chromatography.

[0063] The characterization and evaluation results of the catalysts prepared in the above examples and comparative examples are shown in Table 1.

[0064] Table 1 Catalyst characterization and evaluation results

[0065]

[0066] As can be seen from the table above, through Comparative Example 2, it is shown that the catalyst of the present invention has higher activity than the traditional alumina catalyst in the formamide to hydrocyanic acid route. Comparative Example 3 proves that the increase of pseudo-boehmite in the catalyst carrier will reduce the activity of the catalyst, because the increase of pseudo-boehmite will reduce the water absorption rate of the carrier, thereby affecting the impregnation effect.

[0067] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as limiting the present invention. Those skilled in the art will appreciate that, under the guidance of this specification, some modifications or adjustments may be made to the present invention. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A method for preparing hydrocyanic acid by dehydrating formamide, comprising the steps of preparing hydrocyanic acid by dehydrating formamide and air under the action of a catalyst, It is characterized in that The catalyst is prepared by the following steps: (1) grinding kaolin, pseudo-boehmite, zirconium silicate, and sesbania powder by wet ball milling, and then spray drying to obtain fine powder; (2) mixing the fine powder, binder and water uniformly, extruding, pelletizing and calcining to obtain a porous carrier; (3) preparing a salt solution containing a metal active component, impregnating the porous support into the salt solution by an impregnation method, and then drying and calcining to obtain the catalyst; The proportion of the raw materials in step (1) is calculated by mass percentage, wherein kaolin is 65-75wt%, pseudo-boehmite is 10-20wt%, zirconium silicate is 4-14wt%, and field ash powder is 1-11wt%.

2. The method according to claim 1, It is characterized in that The particle size of the fine powder in step (1) is 1-10 μm.

3. The method according to claim 1, It is characterized in that The binder described in step (2) is selected from any one or more of polyvinyl pyrrolidone, hydroxypropyl methylcellulose, soluble starch, and sodium lignin sulfonate.

4. The method according to claim 1, It is characterized in that In step (2), the mass ratio of fine powder, binder and water is 1:(0.2-0.5):(0.1-0.5).

5. The method according to claim 1, It is characterized in that In step (2), a twin-screw extruder is used to extrude the strips, and a clover-shaped mold with a diameter of 2-5 mm is selected as the mold. After extrusion, the strips are broken into particles with a length of 1-5 mm by pelletizing.

6. The method according to claim 5, It is characterized in that In step (2), the particles obtained by dicing are dried and then calcined in an air atmosphere at 400-800° C. for 2-10 hours to obtain a porous carrier.

7. The method according to claim 1, It is characterized in that The metal active component described in step (3) is selected from one or more of Sc, V, W, Fe, Cu, and Ag.

8. The method according to claim 1, It is characterized in that During the immersion in step (3), the concentration of the salt solution is 0.5-1.5 mol / L, the mass of the salt solution is 2-10 times the mass of the porous carrier, and the immersion time is 2-5 hours.

9. The method according to claim 8, It is characterized in that After the impregnation in step (3) is completed, the excess salt solution is poured out, the mixture is dried at 100-150° C. for 5-10 hours, and then calcined at 400-600° C. for 3-8 hours.

10. The method according to any one of claims 1 to 9, It is characterized in that The specific surface area of ​​the catalyst is 50-400m 2 / g, and the mesopore volume is 1-10cm 3 / g, and the compressive strength is 200-500N / cm.

11. The method according to claim 10, It is characterized in that The specific surface area of ​​the catalyst is 200-400m 2 / g, mesopore volume is 5-8cm 3 / g, and the compressive strength is 300-450N / cm.

12. The method according to claim 1, It is characterized in that The molar ratio of formamide to air is 1:80-100, the feed temperature is 300-600°C, and the air velocity is 1000-5000h -1 .

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