Catalyst for synthesizing ortho-cresol as well as preparation method and application of catalyst

Abstract

The invention relates to a catalyst for synthesizing ortho-cresol as well as a preparation method and application of the catalyst. The molar ratio of Zn element to Al element in the metal spinel catalyst ZnAl2O4 is 1: (0.25-16), and the preparation method comprises the following steps: uniformly mixing aluminum nitrate nonahydrate and zinc nitrate hexahydrate in deionized water, stirring, adding a precipitator, and adjusting the pH value of the solution to form a precipitate dispersion liquid; and aging the precipitate dispersion liquid, carrying out suction filtration on the suspension liquid, washing, drying, and calcining to obtain the catalyst. Compared with the prior art, the catalyst disclosed by the invention is high in activity, simple to prepare, non-toxic, good in stability, long in service life, suitable for synthesizing o-cresol and 2, 6-xylenol through reaction of phenol and methanol, good in ortho-selectivity and few in by-products.

Description

Technical Field

[0001] The invention relates to the technical field of chemical production, in particular to a catalyst for synthesizing o-cresol and a preparation method and application thereof. Background Art

[0002] The traditional production method of cresol is through sulfonation and alkali fusion process, which has disadvantages such as environmental pollution and high energy consumption. To solve these shortcomings, chemists have explored a green synthesis method, that is, a method of gas phase synthesis using phenol and methanol. The main products of the ortho-alkylation reaction of phenol and methanol gas are o-cresol and 2,6-dimethylphenol, which, as key intermediates in the fine chemical industry, show extremely high market value in many important fields. Among them, o-cresol is not only widely used in the synthesis of o-cresol-formaldehyde resin and o-cresol-formaldehyde epoxy resin with excellent heat resistance and electrical properties, but also as a basic raw material for the manufacture of phenoxycarboxylic acid herbicides, and is used to produce o-hydroxybenzaldehyde, specific dyes, fragrances and high-performance antioxidants to meet the diversified needs of the food, pharmaceutical and cosmetic industries; 2,6-dimethylphenol, as a key raw material for high-performance engineering plastic polyphenylene ether resin (PPO), plays an important role in the automotive, electronics and aerospace fields, and is used to prepare 2,6-dimethylaniline and antioxidants.

[0003] The V2O5-Fe2O3 series catalyst developed by Hunan Chemical Research Institute in 1990 has a single-pass yield of 51.8% for o-cresol. This process has the disadvantages of low o-cresol selectivity, short catalyst life, and difficulty in regeneration. Chinese patent CN118164828A provides a phenol ortho-methylation catalyst and a method for producing ortho-methylated phenol using the catalyst. Phenol-methanol is loaded with La3.6g on SiO2 at a ratio of 1.2% weight metal per gram of carrier. The temperature is 280°C, the reaction pressure is 0.1MPa, and the space velocity is 0.3h -1 Under the conditions of , o-cresol and / or 2,6-dimethylphenol are produced by a reactor. The phenol of the invention has a conversion rate of 70%, but the selectivity of o-cresol is low (15%), and the product is mostly anisole (80%). Although other catalysts in the patent have higher conversion rates and higher ortho-selectivity, they require higher temperatures or higher pressures. Chinese patent CN101992118A proposes an improved phenol-methanol gas-phase alkylation process using Fe- and V-modified MCM-41 mesoporous molecular sieves as catalysts. The phenol conversion rate is as high as 49.8%, and the ortho-methyl compound selectivity is as high as 91.8%, but the stability is poor. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a catalyst for the synthesis of o-cresol and its preparation method and application. The present invention prepares a ZnAl2O4 catalyst with good stability and adopts a gas phase alkylation reaction process of phenol and methanol to synthesize o-cresol with high selectivity and high yield at a relatively low temperature.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] In one aspect, the present invention provides a method for preparing a catalyst for the synthesis of o-cresol, comprising the following steps:

[0007] S1: mixing aluminum nitrate nonahydrate and zinc nitrate hexahydrate in deionized water in a certain proportion, adding a precipitant after stirring for a certain period of time, and adjusting the pH of the solution to form a precipitate dispersion;

[0008] S2: The precipitate dispersion obtained in S1 is aged for a certain period of time, filtered, washed, dried, and then calcined to obtain a metal spinel catalyst ZnAl2O4.

[0009] Furthermore, in S1, the molar ratio of the aluminum nitrate nonahydrate to the zinc nitrate hexahydrate is (0.25-16):1.

[0010] Furthermore, in S1, the stirring time is 10 to 30 minutes.

[0011] Furthermore, in S1, the precipitant is ammonia water, and the pH value of the solution is 8-10.

[0012] More preferably, the concentration of the ammonia water is 25%.

[0013] Furthermore, in S2, the aging time is 12 to 36 hours.

[0014] Furthermore, in S2, the drying temperature is 80-110°C.

[0015] Furthermore, in S2, the calcination step comprises: raising the temperature to 800°C at a rate of 5°C / min under an inert gas purge of 50 mL / min, and calcining at 600-800°C for 8 hours.

[0016] On the other hand, the present invention provides a catalyst prepared by the method as described above, wherein the catalyst is a metal spinel catalyst ZnAl2O4, wherein the molar ratio of Zn element to Al element is 1:(0.25-16), and the specific surface area of ​​the metal spinel catalyst ZnAl2O4 is 40-200m 2 / g. Zn is added as an active metal to Al2O3 during the modification process of the spinel.

[0017] On the other hand, the present invention also provides an application of the above-mentioned catalyst for synthesizing o-cresol, comprising the following steps: placing a metal spinel catalyst ZnAl2O4 in a fixed bed reactor, and adding phenol and methanol as reaction raw materials, and controlling a certain temperature and weight space velocity to react under normal pressure.

[0018] Furthermore, the molar ratio of phenol to methanol is 1:(0.2-0.5), the reaction temperature is 200-300°C, and the weight space velocity is WHSV 1-5h -1 .

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) The catalyst preparation method provided by the present invention has simple steps, a safe preparation process, and mild reaction conditions. The prepared metal spinel ZnAl2O4 catalyst has high stability, long life, high reaction efficiency, and excellent acid-base controllability. The acid-base properties of the catalyst can be adjusted according to needs. The presence of suitable L acid sites and B acid sites is the reason for its excellent catalytic performance. At the same time, by regulating the molar ratio of zinc and aluminum elements during the catalyst preparation process, the number and properties of active sites in the catalyst can be accurately controlled, thereby optimizing its catalytic performance.

[0021] (2) The catalyst prepared by the present invention can be used for the synthesis of o-cresol. The metal spinel catalyst ZnAl2O4 can react with phenol and methanol to synthesize o-cresol at a relatively low temperature with high efficiency and high yield. The reaction has few side reactions, low loss rates of phenol and methanol, and has significant economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a SEM image of the metal spinel catalyst ZnAl2O4 in Example 1 of the present invention;

[0023] Figure 2 This is a stability test chart of the metal spinel catalyst ZnAl2O4 in Example 5 of the present invention within 720 hours. DETAILED DESCRIPTION

[0024] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. Any features such as preparation means, materials, structures or composition ratios not clearly described in this technical solution are regarded as common technical features disclosed in the prior art.

[0025] A method for preparing a catalyst for synthesizing o-cresol comprises the following steps:

[0026] S1: mixing aluminum nitrate nonahydrate and zinc nitrate hexahydrate in deionized water, adding ammonia water after stirring, and adjusting the pH of the solution to 8-10 to form a precipitate dispersion;

[0027] S2: The precipitate dispersion obtained in S1 is aged, filtered, washed, dried, and subsequently calcined. Under an inert gas purge of 50 mL / min, the temperature is raised to 800°C at a rate of 5°C / min, and calcined at 600-800°C for 8 h to obtain a metal spinel catalyst ZnAl2O4.

[0028] The metal spinel catalyst ZnAl2O4 has a molar ratio of Zn to Al of 1:(0.25-16), and can be used as a catalyst for gas-phase alkylation of phenol and methanol. The method for using the catalyst for gas-phase alkylation of phenol and methanol is to introduce methanol and phenol into a reactor containing the catalyst for reaction at normal pressure, a reaction temperature of 280°C, and a weight space velocity of WHSV1-3h -1 , the molar ratio of methanol to phenol is 1:(0.2-0.5). The reactor can be a fixed bed reactor, the reaction products are separated by a distillation tower, and methanol and phenol are used as raw materials to continue the reaction.

[0029] Example 1

[0030] 0.08 mol aluminum nitrate nine hydrate and 0.01 mol zinc nitrate hexahydrate were mixed evenly in 200 mL of deionized water, stirred for 30 min, and then 44 mL of 25% ammonia water was added to adjust the pH of the solution to 8-9 to form a precipitate dispersion; the precipitate dispersion was aged for 36 h, then filtered, washed, and dried at 100 ° C. After drying, the temperature was raised to 800 ° C at a rate of 5 ° C / min under an inert gas purge of 50 mL / min, and calcined at 800 ° C for 8 h to obtain a metal spinel catalyst ZnAl2O4 (Zn / Al molar ratio is 1:8). The specific surface area of ​​the catalyst prepared in this embodiment is 182.86 m 2 / g.

[0031] 293.75g phenol and 50g methanol were fed into the preheater as reaction materials through a mass metering pump. The temperature of the preheater was set at 250°C. After sufficient preheating, they were passed into the fixed bed reactor. The fixed bed reactor was pre-filled with 2g ZnAl2O4 (Zn / Al molar ratio was 1:8). The pressure was 0.1MPa, the temperature was 280°C, and the weight space velocity was WHSV 1h -1The reaction was carried out under the conditions of 8h, and the composition of the reaction product was analyzed by gas chromatograph GC9720 to obtain o-cresol, 2,6-dimethylphenol and anisole, and the ortho selectivity was 94%. After the alkylation reaction, the reaction product was separated from the gas and liquid and condensed, and the reaction product was separated by multiple distillation towers, and the unreacted phenol and methanol were recycled into the alkylation reaction system as reaction raw materials for further alkylation reaction. The reaction results are listed in Table 1.

[0032] Example 2

[0033] 0.08 mol aluminum nitrate nonahydrate and 0.08 mol zinc nitrate hexahydrate were mixed evenly in 200 mL of deionized water, stirred for 30 min, and then 44 mL of ammonia water was added to adjust the pH of the solution to 8-9 to form a precipitate dispersion; the precipitate dispersion was aged for 36 h, then filtered, washed, and dried at 100 ° C. After drying, the temperature was raised to 800 ° C at a rate of 5 ° C / min under an inert gas purge of 50 mL / min, and calcined at 800 ° C for 8 h to obtain a metal spinel catalyst ZnAl2O4 (Zn / Al molar ratio is 1:1). The specific surface area of ​​the catalyst prepared in this embodiment is 48.726 m 2 / g.

[0034] 367g phenol and 50g methanol were fed into the preheater as reaction materials through a mass metering pump. The temperature of the preheater was set at 250℃. After sufficient preheating, they were passed into the fixed bed reactor. The fixed bed reactor was pre-filled with 2g ZnAl2O4 (Zn / Al molar ratio was 1:1). The pressure was 0.1MPa, the temperature was 280℃, and the weight space velocity was WHSV 2h -1 The reaction was carried out under the conditions of 8h, and the composition of the reaction product was analyzed by gas chromatograph GC9720 to obtain o-cresol, 2,6-dimethylphenol and anisole, and the ortho selectivity was 90%. After the alkylation reaction, the reaction product was separated by gas-liquid separation and condensed, and the reaction product was separated by passing through multiple distillation towers, and the unreacted phenol and methanol were recycled into the alkylation reaction system as reaction raw materials for further alkylation reaction. The reaction results are listed in Table 1.

[0035] Example 3

[0036] 0.08 mol aluminum nitrate nonahydrate and 0.005 mol zinc nitrate hexahydrate were mixed evenly in 200 mL of deionized water, stirred for 30 min, and then 44 mL of ammonia water was added to adjust the pH of the solution to 8-9 to form a precipitate dispersion; the precipitate dispersion was aged for 36 h, then filtered, washed, and dried at 100 ° C. After drying, the temperature was raised to 800 ° C at a rate of 5 ° C / min under an inert gas purge of 50 mL / min, and calcined at 800 ° C for 8 h to obtain a metal spinel catalyst ZnAl2O4 (Zn / Al molar ratio is 1:16). The specific surface area of ​​the catalyst prepared in this embodiment is 127.65 m 2 / g.

[0037] 489.5g phenol and 50g methanol were fed into the preheater as reaction materials through a mass metering pump. The temperature of the preheater was set at 250℃. After sufficient preheating, they were passed into the fixed bed reactor. The fixed bed reactor was pre-filled with 2g ZnAl2O4 (Zn / Al molar ratio was 1:16). The pressure was 0.1MPa, the temperature was 280℃, and the weight space velocity was WHSV 3h -1 The reaction was carried out for 8 hours under the conditions of , and the composition of the reaction product was analyzed by gas chromatograph GC9720 to obtain o-cresol, 2,6-dimethylphenol and anisole, and the ortho selectivity was 86%. After the alkylation reaction, the reaction product was separated from the gas and liquid and condensed, and the reaction product was separated by passing through multiple distillation towers, and the unreacted phenol and methanol were recycled into the alkylation reaction system as reaction raw materials, and further alkylation reaction was carried out. The reaction results are listed in Table 1.

[0038] Example 4

[0039] 0.08 mol aluminum nitrate nine hydrate and 0.32 mol zinc nitrate hexahydrate were mixed evenly in 200 mL of deionized water, stirred for 30 min, and then 44 mL of ammonia water was added to adjust the pH of the solution to 8-9 to form a precipitate dispersion; the precipitate dispersion was aged for 24 h, then filtered, washed, and dried at 100 ° C. After drying, the temperature was raised to 800 ° C at a rate of 5 ° C / min under an inert gas purge of 50 mL / min, and calcined at 800 ° C for 8 h to obtain a metal spinel catalyst ZnAl2O4 (Zn / Al molar ratio is 1:0.25). The specific surface area of ​​the catalyst prepared in this embodiment is 140.69 m 2 / g.

[0040] 734.38g phenol and 50g methanol were fed into the preheater as reaction materials through a mass metering pump. The temperature of the preheater was set at 250℃. After sufficient preheating, they were passed into the fixed bed reactor. The fixed bed reactor was pre-filled with 2g ZnAl2O4 (Zn / Al molar ratio was 1:0.25). The pressure was 0.1MPa, the temperature was 280℃, and the weight space velocity was WHSV 1h -1 The reaction was carried out under the conditions of 8h, and the composition of the reaction product was analyzed by gas chromatograph GC9720 to obtain o-cresol, 2,6-dimethylphenol and anisole, and the ortho selectivity was 88%. After the alkylation reaction, the reaction product was separated by gas-liquid separation and condensed, and the reaction product was separated by passing through multiple distillation towers, and the unreacted phenol and methanol were recycled into the alkylation reaction system as reaction raw materials for further alkylation reaction. The reaction results are listed in Table 1.

[0041] Table 1 Phenol methanol alkylation reaction results

[0042]

[0043] It can be seen from the data in Table 1 that the metal spinel catalyst ZnAl2O4 prepared in Examples 1-4 provided by the present invention effectively promotes the alkylation reaction of phenol and methanol, the conversion rate of phenol is 40-45%, the selectivity of o-cresol is 63-72%, the selectivity of 2,6-dimethylphenol is 19-24%, the ortho-selectivity is 86-94%, and the side reactions are relatively few, among which the selectivity of anisole is 2-3%.

[0044] Example 5

[0045] First, 0.08 mol aluminum nitrate nine hydrate and 0.01 mol zinc nitrate hexahydrate were mixed evenly in 200 mL of deionized water, and 44 mL of 25% ammonia water was added after stirring for 30 min, and the pH of the solution was adjusted to 8-9 to form a precipitate dispersion; the precipitate dispersion was aged for 36 h, then filtered, washed, and dried at 100 ° C. After drying, the temperature was raised to 800 ° C at a rate of 5 ° C / min under an inert gas purge of 50 mL / min, and calcined at 800 ° C for 8 h to obtain a metal spinel catalyst ZnAl2O4 (Zn / Al molar ratio is 1:8). The specific surface area of ​​the catalyst prepared in this embodiment is 182.86 m 2 / g.

[0046] 293.75g phenol and 50g methanol were fed into the preheater as reaction materials through a mass metering pump. The temperature of the preheater was set at 250℃. After sufficient preheating, they were passed into the fixed bed reactor. The fixed bed reactor was pre-filled with 2g ZnAl2O4. The pressure was 0.1MPa, the temperature was 280℃, and the weight space velocity was WHSV 1h -1 The reaction was carried out under the conditions of , and o-cresol, 2,6-dimethylphenol and anisole were obtained. Samples were taken every 24 hours, and the conversion rates and selectivities of phenol, anisole, o-cresol and 2,6-dimethylphenol were calculated until the reaction lasted 720 hours. Figure 2 It can be seen that the metal spinel catalyst ZnAl2O4 prepared by the present invention has good catalytic activity and ortho-cresol selectivity. The catalyst runs for 720 hours in a single pass, the phenol conversion rate is above 40%, the ortho-cresol selectivity is above 90%, and the activity of the catalyst decays slowly with the increase of the running time.

[0047] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a catalyst for the synthesis of o-cresol, characterized in that: The following steps are involved: S1: mixing aluminum nitrate nonahydrate and zinc nitrate hexahydrate in deionized water in a certain proportion, adding a precipitant after stirring for a certain period of time, and adjusting the pH of the solution to form a precipitate dispersion; S2: The precipitate dispersion obtained in S1 is aged for a certain period of time, filtered, washed, dried, and then calcined to obtain a metal spinel catalyst ZnAl2O4.

2. The method for preparing a catalyst for o-cresol synthesis according to claim 1, characterized in that: In S1, the molar ratio of the aluminum nitrate nonahydrate to the zinc nitrate hexahydrate is (0.25-16):

1.

3. The method for preparing a catalyst for o-cresol synthesis according to claim 1, characterized in that: In S1, the stirring time is 10 to 30 minutes.

4. The method for preparing a catalyst for o-cresol synthesis according to claim 1, characterized in that: In S1, the precipitant is ammonia water, and the pH value of the solution is 8-10.

5. The method for preparing a catalyst for o-cresol synthesis according to claim 1, characterized in that: In S2, the aging time is 12 to 36 hours.

6. The method for preparing a catalyst for o-cresol synthesis according to claim 1, characterized in that: In S2, the drying temperature is 80-110°C.

7. The method for preparing a catalyst for o-cresol synthesis according to claim 1, characterized in that: In S2, the calcination step includes: raising the temperature to 800°C at a rate of 5°C / min under an inert gas purge of 50 mL / min, and calcining at 600-800°C for 8 hours.

8. A catalyst prepared by the method according to any one of claims 1 to 7, characterized in that: The catalyst is a metal spinel catalyst ZnAl2O4, wherein the molar ratio of Zn element to Al element is 1:(0.25-16), and the specific surface area of ​​the metal spinel catalyst ZnAl2O4 is 40-200m 2 / g.

9. Use of the catalyst as claimed in claim 8, characterized in that: The method is used for synthesizing o-cresol, and comprises the following steps: placing a metal spinel catalyst ZnAl2O4 in a fixed bed reactor, adding phenol and methanol as reaction raw materials, and controlling a certain temperature and weight space velocity to react under normal pressure.

10. Use of the catalyst according to claim 9, characterized in that: The molar ratio of phenol to methanol is 1:(0.2-0.5), the temperature is 200-300°C, and the weight space velocity is WHSV 1-5h -1 .

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