CN1634655A - Catalyst for producing methylal by selective oxidation of methanol and preparation method and use thereof - Google Patents

Abstract

A catalyst for the selective oxidation of methanol to produce methylal, which is loaded with vanadium on acidic and sulfur-containing modified titanium dioxide, wherein the sulfur content of the modified titanium dioxide is 1.0-4.5% based on the mass of sulfate radicals. The loading amount of vanadium on the titanium dioxide is 5-20% based on the mass of vanadium pentoxide. The preparation method of the catalyst for methanol selective oxidation to produce methylal is simple and low in cost, and the catalyst can directly produce methylal by one-step reaction of methanol, greatly reducing the production cost and investment cost of producing methylal. The conversion rate of methylal methanol produced by using the catalyst for the selective oxidation of methanol to produce methylal of the present invention can reach 17.6-62.8%, and the selectivity of methylal can reach 67.8-97.9%, which is obviously better than that of unmodified titanium dioxide loaded with vanadium catalyst.

Description

Catalyst for producing methylal by selective oxidation of methanol, its preparation method and application

1. Technical field

The invention relates to a catalyst for directly producing methylal by oxidation of methanol under mild conditions, a preparation method thereof and a method for preparing methylal with the catalyst.

2. Background technology

Methylal, also known as dimethoxymethane, can be used as a solvent for the production of fragrances and synthetic drugs because of its very low toxicity, and can also be used as an intermediate for the production of polyoxymethylene, which is an important engineering plastic. It has a wide range of applications in the automobile industry. In addition, due to the potential application of methylal in the field of diesel additives, methylal has attracted more and more attention.

At present, methylal is mainly produced by the dehydration of methanol and formaldehyde on an acidic catalyst. Commonly used acidic catalysts include inorganic acids, acidic molecular sieves, and macroporous cationic acidic resins. For example, Chinese patent CN 1301688 once disclosed a -5 molecular sieves are used as a catalyst to produce methylal from methanol and formaldehyde in the liquid phase; US Patent No. 4,967,014 uses macroporous cationic resins to fill in reactors to produce methylal. The raw materials for the production of methylal by these two methods are methanol and formaldehyde, and formaldehyde is also produced by partial oxidation of methanol. A typical formaldehyde production process is to oxidize methanol with oxygen or air in the presence of a silver catalyst or an iron-molybdenum catalyst to produce formaldehyde. Therefore, in order to obtain methylal, methanol must first be oxidized to formaldehyde, and then formaldehyde reacts with methanol to produce methylal. Like this from methyl alcohol to methylal through two-step reaction, the technological route is longer. Obviously, the process of producing methylal by direct oxidation of methanol will reduce the investment and production cost compared with the current methanol two-step process for producing methylal. Therefore, some inventors have applied for a patent for the direct synthesis of methylal by oxidation of methanol. One of the more effective methods is to oxidize methanol with oxygen-containing gas under the catalysis of SbRe ₂ O ₆ to obtain impressive Satisfactory methanol conversion and methylal selectivity (US Pat. No. 6,403,841). For example, according to the specification, at a reaction temperature of 300-400°C, the conversion rate of methanol can reach 50%, and the selectivity of methylal is close to 90%. However, the high price of Re limits the use of this method. In addition, high-valent oxides of Re are volatile at high temperatures, which may be difficult in actual use. At the same time, the higher reaction temperature has higher requirements for production equipment.

An important aspect of methanol oxidation research in the literature is to study the oxidation reaction of methanol on supported or non-supported vanadium pentoxide, mainly for the purpose of obtaining oxygen-containing organic compounds, such as formaldehyde, methyl formate, etc., U.S. Patent Disclosed in US 6,281,378 patent. When studying these reactions, methylal is considered as a by-product of the partial oxidation of methanol, especially when the temperature is low, the selectivity of methylal is high, up to 50%, but the corresponding methanol conversion rate is less than 30% (Tronconi E, Ind. Eng. Chem. Res., Vol. 26, 1987, p. 1369). As the temperature rises, the conversion rate of methanol increases, but the selectivity of methylal drops sharply, while the selectivity of formaldehyde and methyl formate increases and becomes the main product; the temperature rises further, and the selectivity of carbon monoxide and carbon dioxide in the product gradually increases. The deep oxidation of methanol occurs, so the biggest difficulty in preparing methylal by these methods is that when the conversion rate of methanol is high, the selectivity of methylal is low, so it has no practical value.

3. Contents of the invention

Through in-depth research on the selective oxidation reaction of methanol on a supported vanadium pentoxide catalyst, the present invention finds that the selectivity of forming methylal is closely related to the oxidation and acidity of the catalyst. The reaction of direct oxidation of methanol to formaldehyde can be regarded as the coupling of methanol oxidation to formaldehyde (reaction 1) and condensation of formaldehyde with methanol (reaction 2). In the reaction of oxidation of methanol to formaldehyde, a suitable catalyst is required. Oxidation, and in the condensation reaction of formaldehyde and methanol, the catalyst needs to have appropriate acidity.

(2)

The so-called appropriate oxidation means that the oxidation product of methanol on the catalyst at a certain temperature is mainly formaldehyde, rather than further oxidation into formic acid or carbon oxides (COx); appropriate acidity means that the dehydration on the catalyst at a certain temperature The condensation reaction is mainly the reaction between methanol and formaldehyde to form methylal, rather than the dehydration between methanol molecules to form dimethyl ether. The oxidation ability and dehydration ability of the catalyst are closely related to the reaction temperature. For oxidation reactions, increasing the temperature tends to increase the selectivity of deeply oxidized products; for dehydration reactions, increasing the temperature is conducive to the generation of dehydration reaction products with higher activation energy, and the activation energy of methanol dehydration to dimethyl ether is higher than that of the reaction. (2) has a much higher activation energy. According to the above analysis, if the oxidizing ability and acidity of the catalyst can be properly matched, methanol can be oxidized to methylal under mild conditions, and have a high methanol conversion rate and methylal selectivity.

One of the purposes of the present invention is to provide a kind of high-efficiency bifunctional catalyst and its preparation method directly producing methylal by the oxidation of methanol, another purpose of the present invention is to provide the method for producing methylal with the catalyst prepared by the method of the present invention .

Technical scheme of the present invention is as follows:

A catalyst for the selective oxidation of methanol to produce methylal. It supports vanadium on acidic and sulfur-containing modified titanium dioxide, wherein the sulfur content of the modified titanium dioxide is 1.0-4.5% based on the mass of sulfate radicals. The modified titanium dioxide The loading amount of vanadium is 5-20% based on the mass of vanadium pentoxide, and the preferred loading amount of vanadium is 10-15% based on the mass of vanadium pentoxide.

Acidic, sulfur-containing modified titanium dioxide can be prepared as follows: dissolve titanium sulfate in water, then add titanium dioxide powder, stir, dry, and roast to obtain acidic, sulfur-containing modified titanium dioxide (see: Acta Catalysis , 1999, Vol. 20, p. 321; J. Catal., 1997, vol. 168, p. 482). The modified titanium dioxide obtained in this way has certain acidity, but it is not strongly acidic. Its notable feature is that the conversion rate of the modified titanium dioxide catalyzing methanol dehydration to dimethyl ether below 200 ° C is less than 5%, and below 150 ° C. Methanol dehydration produces The conversion of dimethyl ether was negligible.

A method for preparing a catalyst for the selective oxidation of methanol to produce methylal of the present invention, which is to mix ammonium metavanadate and oxalic acid in a mass ratio of 1:2, add water and dissolve to obtain a dark green solution, and in the above dark green solution Add metered acidic, sulfur-containing modified titanium dioxide powder, stir to form a paste, dry, and roast to obtain the modified titanium dioxide loaded with 5-20% vanadium based on the mass of vanadium pentoxide. Catalyst for the oxidative production of methylal.

In the method for preparing the catalyst for the selective oxidation of methanol above to produce methylal, the quality of the added water is 3.75-17 times that of ammonium metavanadate.

In the above method for preparing a catalyst for selective oxidation of methanol to produce methylal, the drying is at 100-120°C.

In the above method for preparing a catalyst for the selective oxidation of methanol to produce methylal, the calcination is carried out at 390-460°C for 5-10 hours.

A method for producing methylal with the catalyst for the selective oxidation of methanol to produce methylal of the present invention, it is that the catalyst for the production of methylal by the selective oxidation of methanol of the present invention is packed in a reactor, heated, and the temperature of the reactor is controlled at 130-160°C, feed a mixture of methanol vapor and oxygen-containing gas preheated to 130-160°C, the ratio of the amount of methanol vapor to oxygen is 5:1-5:10, the total flow rate of the gas 1.1×10 ⁴ ml/hour per gram of catalyst to obtain methylal.

The oxygen-containing gas described in the above production method is pure O ₂ , air, or nitrogen or helium containing molecular O ₂ .

Since the molar reaction heat of the reaction is relatively large, a certain proportion of inert gas, such as nitrogen or helium, is added to the reaction mixture gas, which is beneficial to the control of the reaction temperature. The general reaction should avoid operating within the explosion limit of methanol.

The reactor used in the method for producing methylal by using the catalyst for the selective oxidation of methanol to produce methylal of the present invention can be a fixed-bed gas-solid phase reactor or a fluidized-bed gas-solid phase reactor.

The preparation method of the catalyst for producing methylal by selective oxidation of methanol is simple and low in cost, and the catalyst can directly produce methylal by one-step reaction of methanol, greatly reducing the production cost and investment cost of producing methylal. The catalyst for the selective oxidation of methanol to produce methylal of the present invention can produce methylal with a conversion rate of 17.6-62.8% and a selectivity of methylal of 67.8-97.9%, which is obviously better than that of unmodified titanium dioxide supported vanadium catalyst.

4. Specific implementation

The present invention will be further described with following examples:

Example 1:

Mix 71.0g of ammonium metavanadate and 142.0g of oxalic acid, add 600.0ml of water, stir and dissolve to obtain a dark green solution, add 500.0g of powdered titanium dioxide to the above dark green solution and stir to form a light green paste, and place it for 2 hours Dry at 110°C for 12 hours, and then bake in air at 400°C for 6 hours to obtain a yellow powdery vanadium-titanium catalyst A containing V ₂ O ₅ . A part of the prepared powdery vanadium-titanium catalyst A is pressed into a sheet, and then the sheet-shaped vanadium-titanium catalyst is smashed, sieved, and a particle size of 20-40 meshes is used for activity detection. The composition of the catalyst was analyzed, and the V ₂ O ₅ content was 9.8%. This sample was designated as Catalyst #1 for comparison.

Example 2:

Mix 77.2g of ammonium metavanadate and 154.4g of oxalic acid, add 290.0ml of water, stir and dissolve to obtain a dark green solution, add 240.0g of powdered titanium dioxide to the above dark green solution and stir to form a light green paste, and leave it for 2 hours Dry at 110° C. for 12 hours, and then bake at 400° C. in air for 6 hours to obtain vanadium-titanium catalyst B in yellow powder form. A part of the prepared powdery vanadium-titanium catalyst B is pressed into a sheet, and then the sheet-shaped vanadium-titanium catalyst is smashed, sieved, and a particle size of 20-40 meshes is used for activity detection. The composition of the catalyst was analyzed, and the V ₂ O ₅ content was 20.1%. This sample was designated #2 catalyst for comparison.

Example 3:

Put 6.2g of crystalline titanium sulfate into a 200ml crucible, add 150.0ml of distilled water and stir to dissolve it, weigh another 135.0g of titanium dioxide powder and add it to the above solution, stir for 10 minutes, let it stand for 5 hours and then dry it overnight at 110°C, then Calcined at 400°C for 5 hours to produce modified titanium dioxide.

Example 4:

Put 2.14g of crystalline titanium sulfate into a 200ml crucible, add 150.0ml of distilled water and stir to dissolve it, weigh another 135.0g of titanium dioxide powder and add it to the above solution, stir for 10 minutes, let it stand for 5 hours and then dry it overnight at 110°C. Calcined at 400°C for 5 hours to produce modified titanium dioxide.

Example 5:

Put 6.64g of crystalline titanium sulfate in a 200ml crucible, add 150.0ml of distilled water and stir to dissolve it, weigh another 135.0g of titanium dioxide powder and add it to the above solution, stir for 10 minutes, let it stand for 5 hours and then dry it overnight at 110°C. Calcined at 400°C for 5 hours to produce modified titanium dioxide.

Embodiment 6:

Mix 35.1 g of ammonium metavanadate and 70.2 g of oxalic acid, add 600.0 ml of water, stir and dissolve to obtain a dark green solution, add 500.0 g of the modified titanium dioxide powder prepared in Example 3 into the above dark green solution and stir to form a light green paste After standing for 2 hours, it was dried at 110°C for 12 hours, and then calcined in air at 400°C for 6 hours to obtain a yellow powdered vanadium-titanium catalyst supported by modified titanium dioxide. A part of the prepared powdery vanadium-titanium catalyst is pressed into a sheet, and then the sheet-shaped vanadium-titanium catalyst is smashed, sieved, and a particle size of 20-40 meshes is used for activity detection. The composition of the catalyst was analyzed, and the V ₂ O ₅ content was 5.0%. This sample was designated #3 Catalyst.

Embodiment 7:

Mix 71.0 g of ammonium metavanadate and 142.0 g of oxalic acid, add 600.0 ml of water, stir and dissolve to obtain a dark green solution, add 500.0 g of the modified titanium dioxide powder prepared in Example 4 into the above dark green solution and stir to form a light green paste After standing for 2 hours, it was dried at 110°C for 12 hours, and then calcined in air at 400°C for 6 hours to obtain a yellow powdered vanadium-titanium catalyst supported by modified titanium dioxide. A part of the prepared powdery vanadium-titanium catalyst is pressed into a sheet, and then the sheet-shaped vanadium-titanium catalyst is smashed, sieved, and a particle size of 20-40 meshes is used for activity detection. The composition of the catalyst was analyzed, and the V ₂ O ₅ content was 9.9%. This sample was designated #4 Catalyst.

Embodiment 8:

Mix 77.2g of ammonium metavanadate and 154.4g of oxalic acid, add 290.0ml of water, stir and dissolve to obtain a dark green solution, add 240.0g of the modified titanium dioxide powder obtained in Example 5 into the above dark green solution and stir to form a light green paste After standing for 2 hours, it was dried at 110°C for 12 hours, and then calcined in air at 400°C for 6 hours to obtain a yellow powdered vanadium-titanium catalyst supported by modified titanium dioxide. Taking a part of the prepared powdery vanadium-titanium catalyst and pressing it into a sheet, crushing the sheet-shaped vanadium-titanium catalyst, sieving, and taking a particle size of 20-40 mesh for activity detection. Analyzing the catalyst composition, the V ₂ O ₅ content was 19.9%. This sample was designated #5 Catalyst.

Embodiment 9:

Weigh 0.5g of #1 catalyst sample, put it into a glass reaction tube with an inner diameter of 8mm, preheat to 150°C, and preheat the raw material gas with volume composition of methanol 5%, O ₂ 6%, N ₂ 89% to 150°C ℃ through the reaction tube. The reaction system is under normal pressure. The gas space velocity was 1.1×10 ⁴ ml/h per gram of catalyst. The composition of reaction raw material gas and reaction tail gas was analyzed online by gas chromatography. Methanol conversion and product selectivity were calculated as follows.

Embodiment 10-13: Measure the activity of #2-#5 catalyst sample according to the method of embodiment 9 respectively, and the measurement results are listed in Table 1.

Example 14:

Weigh 0.5g of #5 catalyst sample, put it into a glass reaction tube with an inner diameter of 8mm, preheat to 130°C, and preheat the raw material gas with a volume composition of methanol 5%, O ₂ 6%, and N ₂ 89% to 130°C ℃ through the reaction tube. The reaction system is under normal pressure. The gas space velocity was 1.1×10 ⁴ ml/h per gram of catalyst. The composition of reaction raw material gas and reaction tail gas was analyzed online by gas chromatography. The methanol conversion and product selectivity were calculated using the method in Example 9.

Example 15:

Weigh 0.5g of #5 catalyst sample, put it into a glass reaction tube with an inner diameter of 8mm, preheat to 160°C, and preheat the raw material gas with a volume composition of methanol 5%, O ₂ 6%, N ₂ 89% to 160°C ℃ through the reaction tube. The reaction system is under normal pressure. The gas space velocity was 1.1×10 ⁴ ml/h per gram of catalyst. The composition of reaction raw material gas and reaction tail gas was analyzed online by gas chromatography. The methanol conversion and product selectivity were calculated using the method in Example 9.

Embodiment 14,15 measurement result is listed in Table 2, lists the measurement result of embodiment 13 simultaneously, for comparison.

Example 16:

Weigh 0.5g of #4 catalyst sample, put it into a glass reaction tube with an inner diameter of 8mm, preheat to 150°C, and preheat the raw material gas with a volume composition of 5% methanol, O ₂ 10%, and N ₂ 85% to 150°C °C through the reaction tube. The reaction system is under normal pressure. The gas space velocity was 1.1×10 ⁴ ml/h per gram of catalyst. The composition of reaction raw material gas and reaction tail gas was analyzed online by gas chromatography. Calculate methanol conversion and product selectivity with the method of embodiment 9

Example 17:

Weigh 0.5g of #4 catalyst sample, put it into a glass reaction tube with an inner diameter of 8mm, preheat to 150°C, and preheat the feed gas with a volume composition of methanol 5%, O ₂ 1%, and N ₂ 94% to 150°C ℃ through the reaction tube. The reaction system is under normal pressure. The gas space velocity was 1.1×10 ⁴ ml/h per gram of catalyst. The composition of reaction raw material gas and reaction tail gas was analyzed online by gas chromatography. Calculate methanol conversion and product selectivity with the method of embodiment 9

Embodiment 16,17 measurement result is listed in Table 3, lists the measurement result of embodiment 12 simultaneously, for comparison.

Table 1. Catalyst activity and selectivity results that embodiment 9-15 measures Example number Catalyst number V ₂ O ₅ content/wt% Methanol conversion/% selectivity/% Methylal formaldehyde Methyl formate Dimethyl ether COx 9 #1 10 23.9 63.7 31.2 4.7 0.4 0 10 #2 20 30.0 64.2 23.0 12.5 0.3 0 11 #3 5 36.7 92.2 0.0 3.6 4.3 0 12 #4 10 44.4 90.6 1.0 8.2 0.2 0 13 #5 20 49.1 85.3 1.2 13.0 0.5 0

Table 2. Catalyst activity and selectivity results that embodiment 13, 14 and 15 measure Example number Catalyst number Measuring temperature/℃ Methanol conversion/% selectivity/% Methylal formaldehyde Methyl formate Dimethyl ether COx 13 #5 150 49.1 85.3 1.2 13.0 0.5 0 14 #5 130 17.6 97.9 0.0 1.4 0.7 0 15 #5 160 62.8 67.8 1.9 29.0 1.1 0.2

Table 3. Catalyst activity and selectivity results that embodiment 12, 16 and 17 measure Example number Catalyst number Raw gas O ₂ /CH ₃ OH volume ratio Methanol conversion/% selectivity/% Methylal formaldehyde Methyl formate Dimethyl ether COx 12 #4 1.2:1 44.4 90.6 1.0 8.2 0.2 0 16 #4 2:1 50.5 84.2 1.9 13.6 0.2 0 17 #4 1:5 36.1 91.4 0.6 7.8 0.2 0

Claims (9)

1. a catalyst for the selective oxidation of methanol to produce methylal, characterized in that: it is loaded with vanadium on acidic, sulfur-containing modified titanium dioxide, wherein the content of modified titanium dioxide sulfur is 1.0- 4.5%, and the loading amount of vanadium on the modified titanium dioxide is 5-20% based on the mass of vanadium pentoxide. 2. The catalyst according to claim 1, characterized in that: the loading of vanadium is 10-15% based on the mass of vanadium pentoxide. 3. a kind of preparation method of the catalyst that methyl alcohol selective oxidation is produced methylal described in claim 1 is characterized in that: it is that ammonium metavanadate and oxalic acid are mixed with the ratio of mass ratio 1: 2, add water and dissolve to get ink Green solution, adding metered acidic and sulfur-containing modified titanium dioxide powder to the above-mentioned dark green solution, stirring to form a paste, drying, and roasting, to obtain the modified titanium dioxide loaded with vanadium pentoxide. Catalyst for the selective oxidation of methanol with 5-20% vanadium to produce methylal. 4. the method for preparing the catalyst of methanol selective oxidation production methylal according to claim 3 is characterized in that: the quality of the water that adds is 3.75-17 times of ammonium metavanadate quality. 5. The method for preparing a catalyst for the selective oxidation of methanol to produce methylal according to claim 3, characterized in that: said drying is performed at 100-120°C. 6. The method for preparing a catalyst for the selective oxidation of methanol to produce methylal according to claim 3, characterized in that: said roasting is performed at 390-460° C. for 5-10 hours. 7. A method for producing methylal with the catalyst for producing methylal by the selective oxidation of methanol according to claim 1, characterized in that: it is that the catalyst for producing methylal by the selective oxidation of methanol of the present invention is loaded in the reactor During heating, control the temperature of the reactor at 130-160°C, feed the mixture of methanol vapor and oxygen-containing gas preheated to 130-160°C, the ratio of the amount of methanol vapor to oxygen is 5:1-5 : 10 to obtain methylal. 8. The production method according to claim 7, characterized in that: the oxygen-containing gas is pure O ₂ , air, or nitrogen or helium containing molecular O ₂ . 9. the method for producing methylal according to claim 7 is characterized in that: the used reactor of producing methylal can be fixed bed gas-solid phase reactor, also can be fluidized bed gas solid phase reactor.