A method for producing methylphenol by gas-phase alkylation of phenol and methanol in a fixed-bed adiabatic reactor

Abstract

The present invention discloses a method for producing methylphenol by gas-phase alkylation of phenol and methanol in a fixed-bed adiabatic reactor. Phenol and methanol are separately vaporized, mixed in a certain mass ratio, and then introduced into a fixed-bed adiabatic reactor containing a catalyst. The phenol and methanol undergo a gas-phase alkylation reaction to produce o-cresol, m-cresol, p-cresol, and some xylenols. By controlling the mass ratio of phenol and methanol, the purpose of controlling the adiabatic temperature rise is achieved. The products generated by the reaction are subjected to rectification and separation to obtain a mixture of o-cresol, m-cresol, and p-cresol, as well as products such as xylenol. Compared with the existing technology, the method for producing methylphenol by gas-phase alkylation of phenol and methanol in a fixed-bed adiabatic reactor provided by the present invention has the advantages of a simple reaction process, high catalyst loading efficiency, and no addition of inert circulating materials. It also achieves the advantages of reducing equipment investment, energy consumption, and wastewater.

Description

Technical Field

[0001] The invention relates to a method for producing methylphenol by using phenol and methanol as raw materials, and in particular to a method for producing methylphenol by gas-phase alkylation of phenol and methanol in a fixed-bed adiabatic reactor. Background Art

[0002] Methylphenol consists of three isomers: o-cresol, m-cresol, and p-cresol. Methylphenol is an important fine chemical raw material. Early methylphenol was primarily isolated from natural sources. To meet the growing demand for methylphenol and the increasing quality requirements, modern chemical industry has developed numerous methods for synthesizing methylphenol.

[0003] The toluene sulfonation alkali fusion method and toluene chlorination hydrolysis method reported in the literature have been gradually eliminated due to their serious environmental pollution and equipment corrosion problems. What has been developed next is a method for producing methylphenol by gas-solid catalytic alkylation using phenol and methanol as raw materials.

[0004] The alkylation reaction of phenol and methanol is a highly exothermic chemical reaction. In order to achieve temperature control during the reaction process, the existing methods for producing methylphenol have adopted various methods.

[0005] Chinese invention patent application No. 201110161301.9 discloses a method for producing o-cresol by vapor-phase alkylation of phenol and methanol. The patent provides a method in which the molar ratio of phenol:methanol:water is 1:(2-5):(1-3), with the water controlling the reaction temperature.

[0006] In his doctoral thesis "Study on Selective Synthesis of High-Quality o-Cresol by Alkylation of Phenol and Methanol Catalyzed by α-Fe2O3", P103-P113, Huang Hua conducted research on an industrial single-row tube reaction with a catalyst loading of 5L for the alkylation of phenol and methanol to produce o-Cresol. While using molten salt to control the reactor temperature, it is still necessary to introduce a dilution gas at the same time to achieve control of the reaction temperature.

[0007] Another issue with shell-and-tube reactors is their low catalyst loading rate, making loading difficult. Furthermore, since the reaction temperature is above 300°C, using superheated water to remove heat from the tubes of the reactor is not feasible due to the high pressure of the superheated water at this temperature. This makes the manufacture of large-scale reactors very difficult and significantly increases costs.

[0008] Chinese patent application No. 201310240660.2 reports a method for producing cresol using phenol (anisole) and methanol as raw materials, using a modified molecular sieve as a catalyst, to produce methylphenol via gas-phase catalysis. In the method provided in this patent, the reaction materials are mixed with water vapor before entering the reactor, thereby achieving control over the reaction temperature. The addition of water to the reaction materials artificially increases wastewater generation, thereby increasing wastewater treatment costs.

[0009] Whether using a tubular reactor, a molten salt heat transfer method, or a method of adding water vapor to the reaction mass, the process difficulty of producing methylphenol by vapor-phase alkylation of phenol and methanol to produce methylphenol is increased. To date, there is no method that can achieve the production of methylphenol by vapor-phase alkylation of phenol and methanol without adding a diluent (inert circulating material) to the reaction mass or using an external heat transfer medium circulation condition.

[0010] The present invention provides a method for producing methylphenol by vapor-phase alkylation of phenol with methanol in a fixed-bed adiabatic reactor. The method is characterized in that the alkylation reaction of phenol and methanol is carried out in the fixed-bed adiabatic reactor, and an inert circulating material is added to the middle of the material entering the reactor to dilute the reaction mass. Furthermore, the method does not require any means for removing the reaction heat outside the reactor.

[0011] The method for preparing methylphenol by gas-phase alkylation of phenol and methanol in a fixed-bed adiabatic reactor provided by the present invention has the advantages of high catalyst loading efficiency in the reactor, a convenient and simple loading process, a simple and easy-to-control operation method, low energy consumption in the production process, low investment in the reaction device, and ease of large-scale production. Summary of the Invention

[0012] The present invention mainly solves the technical problems existing in the above-mentioned prior art. Therefore, this patent provides a method for producing methylphenol by gas-phase alkylation of phenol and methanol in a fixed-bed adiabatic reactor to solve the heat transfer problem caused by the strong exothermic reaction, thereby providing a method for producing methylphenol by gas-phase alkylation of phenol and methanol with low equipment investment, high catalyst loading rate, simple loading method and easy operation.

[0013] In order to achieve the above object, the present invention adopts the following technical scheme: a method for producing methylphenol by gas-phase alkylation of phenol and methanol in a fixed-bed adiabatic reactor;

[0014] (1) The raw materials phenol and methanol are delivered by a metering pump in a certain proportion, heat exchanged, gasified, and after the start-up heater is adjusted to an appropriate temperature, they are mixed and entered into a reactor equipped with a catalyst. At a certain temperature and pressure and under the action of the catalyst, phenol and methanol undergo an alkylation reaction to produce methylphenol, and some xylenol is produced as a by-product;

[0015] (2) After the reaction product leaves the reactor, it enters the product buffer tank after heat exchange and water cooling. The gaseous product at the top of the tank is sent out, and the product at the bottom of the tank enters the distillation system;

[0016] ⑶ In the flash tower, the water and other low-boiling products generated by the reaction are flash-distilled and separated, the bottom product enters the phenol tower, and the phenol obtained at the top of the benzene tower is used as a raw material to continue to participate in the reaction;

[0017] (4) The bottom product of the phenol tower enters the o-cresol tower for further separation, and the o-cresol product is obtained at the top of the tower. The bottom product enters the m-cresol tower, and the mixture of m-cresol and p-cresol is separated at the top of the tower, and the mixed xylenol product is obtained at the bottom of the tower.

[0018] Preferably, the reactor in step (1) is a fixed bed adiabatic reactor, and no heat exchange equipment is required outside the reactor, and there is no structural member for heat exchange inside the reactor.

[0019] Preferably, the molar ratio of phenol to methanol in step (1) is 1:(0.3-0.66), and the mass ratio of phenol to methanol is 1:(0.1-0.25).

[0020] Preferably, the total mass space velocity of the raw materials (phenol + methanol) described in step (1) relative to the catalyst is 0.3-3.0h -1 ; In the reactor inlet materials, except phenol and methanol, no additional diluents are needed to be added as inert circulating materials to achieve intervention in the reaction temperature.

[0021] Preferably, the temperature of the fixed bed adiabatic reactor in step (1) is 280° C.-450° C., and the pressure is between 0.1-1.5 MPa (gauge pressure);

[0022] In methods for producing methylphenol by vapor-phase alkylation of phenol and methanol using different catalysts, the initial temperature of the materials at the reactor inlet may vary. The phenol alkylation reaction that occurs after the reaction materials enter the reactor is a highly exothermic reaction, which will cause the temperatures of the reaction materials and the catalyst bed to rise, i.e., produce a certain adiabatic temperature rise. According to the method for producing methylphenol by vapor-phase alkylation of phenol and methanol using a fixed-bed adiabatic reactor provided by the present invention, the adiabatic temperature rise within the fixed-bed adiabatic reactor is 30-120°C. Therefore, the temperature distribution within the reactor gradually increases along the axial direction of the reactor material flow, and after reaching the maximum adiabatic temperature rise, the temperature reaches a constant state.

[0023] Preferably, the catalyst in step (1) can be H(M)ZSM-5 molecular sieve, wherein M is a metal element used for modification. M can be any one of Mg, Zn, Fe, and Zr, or any combination thereof. The catalyst in step (1) can also be an Fe / Mg / M composite oxide, wherein M is a third metal element, which can be one or more metal elements selected from the group consisting of La, Ce, Zn, Mn, and Cu.

[0024] Beneficial effects

[0025] 1. Compared with the prior art, the method for preparing methylphenol by vapor-phase alkylation of phenol and methanol in a fixed-bed adiabatic reactor provided by the present invention has the advantages of high catalyst loading rate and simple loading method in the fixed-bed adiabatic reactor;

[0026] 2. The method for preparing methylphenol by vapor-phase alkylation of phenol and methanol in a fixed-bed adiabatic reactor provided by the present invention has the advantages that, since no external medium circulation heat transfer is required, the manufacture of a large-scale reactor is simpler and the reactor manufacturing cost is significantly reduced;

[0027] 3. The method for producing methylphenol by vapor-phase alkylation of phenol and methanol in a fixed-bed adiabatic reactor provided by the present invention does not require the addition of water to the reactants, nor does it require other inert circulating materials to control the reaction temperature. Therefore, a third advantage of this method is reduced wastewater production and lower wastewater treatment costs. The elimination of inert circulating materials further reduces energy consumption during the production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0029] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0030] Example 1 discloses a method for preparing methylphenol by gas-phase alkylation of phenol and methanol in a fixed-bed adiabatic reactor:

[0031] 800 kg of HZSM-5 molecular sieve raw powder with a silicon-aluminum molar ratio of 75, a crystallinity greater than 96%, and a grain size of 90 nm was added to 280 kg of pseudo-boehmite and water. The mixture was kneaded in a kneader and extruded into strips using a twin-screw extruder. The strips were placed in a mesh belt kiln and dried at 120°C for 4 hours. The strips were then calcined in the mesh belt kiln at 550°C for 4 hours to obtain 1000 kg of HZSM-5 molecular sieve catalyst.

[0032] 46.4 kg of zinc nitrate (molecular formula: Zn(NO₃)₂.6H₂O) was added to 500 kg of deionized water to prepare a zinc nitrate aqueous solution for later use. Using an equal volume impregnation method, the prepared zinc nitrate aqueous solution was added to the HZSM-5 molecular sieve prepared above for impregnation. After aging for one hour, the sieve was removed from the sieve and dried in a mesh belt kiln at 120°C for four hours. It was then calcined in the mesh belt kiln at 550°C for four hours. This yielded a zinc-modified H(Zn)ZSM-5 molecular sieve catalyst with a zinc content of 1.00% by weight.

[0033] Example 2, in a volume of 10m 3 In a stainless steel stirring kettle, add 4.5 ml of 95% ethanol 3 , introduce nitrogen from the bottom entrance of the kettle, start stirring, add 5.556 tons of iron nitrate (Fe(NO3)3·9H2O), wait for it to be completely dissolved, then add 0.959 tons of magnesium nitrate (Mg(NO3)2·6H2O), stir, wait for it to be completely dissolved, then add 28kg of cerium nitrate (Ce(NO3)3·6H2O), stir, heat to 40°C, and keep constant temperature. Under stirring, gradually add 4.3 tons of concentrated ammonia water with a content of 25%, continue to use 25% ammonia water to adjust the pH value of the solution to 9.5, and the precipitation is completed. The above precipitate continues to age for 4 hours under stirring, filtered, and washed with deionized water until neutral. Take out the filter cake, divide it into plates and put it into a mesh belt kiln, dry it at 120°C for 4 hours, then move it into a mesh belt kiln, and roast it at 500°C for 6 hours. The above-mentioned raw powder that has been roasted is put into a ball mill and ground for 4 hours, and then formed into tablets using a tablet press. So far, Fe1Mg 0.17 / Ce 0.005 The preparation of the composite oxide catalyst is completed.

[0034] Example 3: A phenol-methanol vapor-phase alkylation reaction apparatus for producing methylphenol was installed according to the process flow diagram in the accompanying drawings. The fixed-bed adiabatic reactor was constructed of stainless steel, with an inner diameter of 800 mm and a straight pipe section capable of loading the catalyst of 3000 mm in height. Other equipment, piping, and valves were also constructed and installed using stainless steel.

[0035] The reactor was filled with the H(Zn)ZSM-5 molecular sieve catalyst prepared in Example 1. The catalyst filling height was 2450 mm and the filling volume was 1.23 m 3 The catalyst mass is 0.78 tons and the packing density is 0.63t / m 3 The catalyst packing height-to-diameter ratio is 3.1.

[0036] Nitrogen displacement system. The system pressure is maintained at 0.5 MPa, and the system temperature is raised using nitrogen circulation. When the catalyst bed temperature reaches 330°C, the phenol metering pump is activated, pumping phenol into the phenol vaporizer at a rate of 0.341 t / h. The methanol metering pump is activated, pumping methanol into the methanol vaporizer at a rate of 0.048 t / h. The molar ratio of phenol to methanol is 1:0.353, and the mass ratio of phenol to methanol is 1:0.120. The phenol and methanol vapors mix and enter a heat exchanger, where they exchange heat with the hot material from the hard gas outlet to raise the temperature. The mixture then enters an electric heater to further heat it to 330°C before entering a fixed-bed adiabatic reactor containing the catalyst. Over the action of the H(Zn)ZSM-5 molecular sieve catalyst, phenol and methanol undergo an alkylation reaction, producing phenolic products such as o-cresol, m-cresol, p-cresol, and xylenol, as well as process water. The heat released by the reaction causes the material in the reactor to produce an adiabatic temperature rise of 65°C. The highest temperature point in the bed reaches 395°C, and this temperature is maintained as the material leaves the catalyst bed and flows out from the reactor outlet.

[0037] The material at the reactor outlet is cooled by heat exchange with a mixture of raw phenol and methanol vapor. It is further cooled to 45°C in a water cooler before entering the product buffer tank. A small amount of gaseous product is discharged from the top of the tank. The bottom product enters the flash column of the separation system, where process water and a small amount of low-boiling products are distilled off at the top. The bottom of the flash column enters the phenol column, where phenol is recovered at the top and returned for further use as raw material. The bottom of the column enters the o-cresol column, where o-cresol is obtained as the product at the top of the o-cresol column. The bottom product enters the m-p-phenol column. A mixture of m-p-cresol and xylenol is obtained at the top of the m-p-cresol column, while the bottom product is mixed xylenes.

[0038] The flow rate of the product was measured, and the product was analyzed by gas chromatography. The reaction results such as phenol conversion rate and product distribution were calculated and shown in Table 1.

[0039]

[0040] Table 1. Reaction results of Example 3

[0041] Examples 4-8 employed the catalyst of Example 1, the reaction apparatus, and the start-up method of Example 3. The phenol feed mass flow rate was maintained at 0.341 t / cm2, but the methanol feed rate was varied to alter the molar ratio of phenol to methanol. The reaction temperature and pressure were adjusted to obtain the reaction results shown in Table 2.

[0042]

[0043] Table 2. Reaction results of Examples 4-8

[0044] Examples 9-12 employed the catalyst of Example 1 and the reaction apparatus and operating method of Example 3. The reaction pressure was controlled at 0.6 MPa, and the inlet temperature of the reaction mass was controlled at 330° C. The molar ratio of methanol to phenol was maintained at 0.413 (methanol to phenol mass ratio 0.141). By varying the feed rates of phenol and methanol, and thereby varying the mass space velocity of the reaction mass, the reaction results of Examples 9-12 were obtained, as shown in Table 3.

[0045]

[0046] Table 3. Reaction results of Examples 9-12

[0047] In Examples 13-16, the reaction apparatus of Example 3 was used, and the Fe1Mg prepared in Example 2 was loaded into the reactor. 0.17 / Ce 0.005 Composite oxide catalyst. The catalyst loading height is 1030mm and the loading volume is 0.52m 3 The catalyst mass is 0.78 tons and the packing density is 1.5t / m 3 The catalyst packing height-to-diameter ratio is 1.3.

[0048] Following the start-up method of Example 3, the phenol feed rate was maintained at 0.341 t / h, and the methanol feed rate was varied to obtain different phenol-methanol feed molar ratios. The reaction temperature and pressure were adjusted to obtain the reaction results of Examples 13-16, as shown in Table 4.

[0049]

[0050] Table 4. Reaction results of Examples 13-16.

Claims

1. A method for producing methylphenol by vapor-phase alkylation of phenol and methanol in a fixed-bed adiabatic reactor, characterized by comprising the following steps: (1) Raw materials phenol and methanol are delivered through a metering pump in a certain proportion, heat exchanged, gasified, and after the start-up heater is adjusted to an appropriate temperature, mixed and entered into a reactor equipped with a catalyst. At a certain temperature and pressure and under the action of the catalyst, phenol and methanol undergo an alkylation reaction to generate methylphenol and produce some xylenol as a by-product. The reactor is a fixed-bed adiabatic reactor, the molar ratio of phenol to methanol is 1:(0.3-0.413), and the total mass space velocity of the raw materials (phenol + methanol) relative to the catalyst is 0.3-3.0h -1 The temperature of the fixed-bed adiabatic reactor is 280°C-450°C, the pressure is between 0.1-1.5 MPa (gauge pressure), and the adiabatic temperature rise range of the fixed-bed adiabatic reactor containing the catalyst is 75-120°C; (2) After the reaction product leaves the reactor, it enters the product buffer tank after heat exchange and water cooling. The gaseous product at the top of the tank is sent out, and the product at the bottom of the tank enters the distillation system; ⑶ In the flash tower, the water and other low-boiling products generated by the reaction are flash-distilled and separated, the bottom product enters the phenol tower, and the phenol obtained at the top of the benzene tower is used as a raw material to continue to participate in the reaction; (4) The bottom product of the phenol tower enters the o-cresol tower for further separation, and the o-cresol product is obtained at the top of the tower. The bottom product enters the m-cresol tower, and the mixture of m-cresol and p-cresol is separated at the top of the tower, and the mixed xylenol product is obtained at the bottom of the tower.

2. The method for producing methylphenol by gas-phase alkylation of phenol and methanol in a fixed-bed adiabatic reactor according to claim 1, characterized in that: The catalyst is H(M)ZSM-5 molecular sieve, wherein M is a metal element used for modification, which is any one of Mg, Zn, Fe, and Zr, or a combination of any of them; or the catalyst is Fe / Mg / M composite oxide, wherein M is one or more metal elements of La, Ce, Zn, Mn, and Cu.

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