CN116003262B - Synthesis method of N, N-dimethylaniline - Google Patents
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Abstract
The invention discloses a synthesis method of N, N-dimethylanilineComprising the following steps: snO using metal solid acid catalyst 2 ‑γ‑Al 2 O 3 /Hβ (m) The method comprises the steps of (1) taking a mixed solution of methanol and aniline as a reaction raw material, carrying out alkylation reaction, and finishing the reaction; metallic solid acid catalyst SnO 2 ‑γ‑Al 2 O 3 /Hβ (m) In multistage pore H beta (m) Molecular sieve is carried gamma-Al by carrier 2 O 3 And SnO 2 Multistage pore H beta (m) The molecular sieve is prepared by calcining, alkali treatment and ion exchange of H beta molecular sieve. The invention adopts an isovolumetric impregnation method to prepare SnO 2 ‑γ‑Al 2 O 3 /Hβ (m) The catalyst not only has higher stability, but also has stronger coking resistance and longer service life; meanwhile, the catalyst has the characteristics of high conversion rate, high selectivity, high yield and the like for the synthesis reaction of N, N-dimethylaniline.
Description
Technical Field
The invention relates to the field of materials and chemical industry, in particular to a synthetic method of N, N-dimethylaniline.
Background
N, N-Dimethylaniline (DMA) is an important chemical raw material and has wide application in the aspects of dyes, fragrances, medicines, pesticides and the like. In the dye industry, DMA is mainly used for producing trityl methane dyes, and also used for producing basic dye intermediates tetramethyl ketone, etc.; in the fragrance industry, DMA is mainly used for the production of vanillin; in the pharmaceutical industry, DMA is used for the manufacture of cephalosporin V, sulfa-b-methoxypyrimidine, fluoropyrimidine, etc.; in the pesticide industry, DMA is useful as a synthetic cortisone.
The method for producing N, N-dimethylaniline reported in the literature at home and abroad mainly comprises the following steps: aniline methanol process, halohydrocarbon process, dimethyl carbonate process and CO 2 /H 2 N-methylation methods, and the like.
The industrial production method of N, N-dimethylaniline mainly comprises a liquid phase method and a gas phase method. Most of liquid phase methods adopt inorganic acid as a catalyst, and have a large amount of byproducts and high energy consumption. The gas phase method mainly adopts solid acid as a catalyst, can react under normal pressure and can be continuously produced, and the solid acid catalyst generally comprises inorganic salt, molecular sieve, composite oxide, alumina and the like.
At present, the process method for producing N, N-dimethylaniline has the problems of high reaction temperature, low raw material conversion rate, short service life and the like, wherein the gamma-alumina is used as a catalyst, the higher reaction temperature is needed, and the yield of a target product is lower; the H beta molecular sieve is used as the catalyst, so that the reaction temperature can be reduced, the energy consumption is reduced, but the byproduct growth rate is faster, and the service life of the catalyst is influenced. Therefore, the development of the catalyst with high conversion rate, strong coking resistance and long service life has potential industrial application value.
Disclosure of Invention
The invention aims to: in order to solve the technical problems existing in the prior art, the invention aims to provide a synthesis method of N, N-dimethylaniline and SnO 2 -γ-Al 2 O 3 /Hβ (m) A preparation method and application of the catalyst.
The technical scheme is as follows: the synthesis method of the N, N-dimethylaniline comprises the following steps: snO using metal solid acid catalyst 2 -γ-Al 2 O 3 /Hβ (m) And (3) taking a mixed solution of methanol and aniline as a reaction raw material, and carrying out alkylation reaction to obtain the N, N-dimethylaniline after the reaction is finished.
Further, the molar ratio of methanol to aniline is 2-5:1, preferably 4:1, and the alkylation reaction conditions are: normal pressure, reaction temperature of 200-240 ℃ and mass space velocity of the reaction raw materials of 0.2-0.6 h -1 。
The catalyst for synthesizing N, N-dimethylaniline is a metal solid acid catalyst SnO 2 -γ-Al 2 O 3 /Hβ (m) In multistage pore H beta (m) Molecular sieve as carrier and gamma-Al supported 2 O 3 And SnO 2 。
Further, the hierarchical pore hβ (m) The molecular sieve is prepared by calcining H beta molecular sieve, alkali treatment and ion exchange, and gamma-Al 2 O 3 And a hierarchical pore H beta (m) The mass ratio of the molecular sieve is 0.25-1:1, snO 2 Accounting for 1-10 percent wt percent of the total mass of the catalyst,preferably 5 wt%.
The preparation method of the catalyst for synthesizing N, N-dimethylaniline comprises the following steps:
(1) The H beta molecular sieve is calcined, alkali treated and ion exchanged to prepare the hierarchical pore H beta (m) A molecular sieve;
（2）γ-Al 2 O 3 after calcination treatment, with a hierarchical pore H beta (m) Mixing molecular sieve, extrusion aid and peptizer to obtain gamma-Al 2 O 3 / Hβ (m) A composite carrier;
(3) gamma-Al 2 O 3 /Hβ (m) Placing the composite carrier in ethanol solution of stannic chloride, carrying out isovolumetric impregnation, taking out, drying, grinding and calcining to obtain the metal solid acid catalyst SnO 2 -γ-Al 2 O 3 / Hβ (m) 。
Further, in the step (1), the silicon-aluminum ratio of the H beta molecular sieve is 25-100, preferably 25; the alkali treatment process specifically comprises the following steps: mixing H beta molecular sieve with NaOH solution with concentration of 0.1-0.5 mol/L according to solid-liquid ratio (g/ml) of 1:10-30, stirring, immersing and refluxing, treating 0.4-0.6 and H at 60-80 ℃, cooling to room temperature, washing with water, suction filtering until filtrate PH=7, putting the obtained filter cake into a 100-120 ℃ oven, drying for 8-10H, and grinding the dried solid into powder; the ion exchange process comprises the following steps: the powder obtained by alkali treatment and NH with the concentration of 0.4-0.6 mol/L are mixed according to the solid-to-liquid ratio (g/ml) of 1:10-30 4 Mixing Cl solution, performing ion exchange at 60-80deg.C for 1-1.5. 1.5 h, filtering, repeating for 3-5 times, washing with water, and filtering until the solution contains no Cl - And (3) putting the obtained filter cake into a baking oven at 100-120 ℃ to dry 8-10 h, grinding the dried filter cake into powder, and then calcining.
Further, in the step (2), the extrusion assisting agent is sesbania powder, and the dosage is gamma-Al 2 O 3 And a hierarchical pore H beta (m) 3-5% of the total mass of the molecular sieve, the peptizing agent is dilute nitric acid solution with the concentration of 2-4%, and the dosage of the peptizing agent and gamma-Al are equal 2 O 3 Multistage pore H beta (m) The ratio of the total mass of the molecular sieve to the extrusion aid is 1-1.2 ml:1g, preferably 1 ml:1 g.
Further, in the step (3), the volume ratio of the stannic chloride to the ethanol is 0.036-0.394:10, preferably 0.187:10, and the time of the isovolumetric impregnation is 8-20 h, preferably 12 h.
Further, in the steps (1) to (3), the conditions of the calcination treatment are as follows: 500-600 deg.c and 3-5 h.
The principle of the invention: in the preparation method adopted by the invention, the H beta molecular sieve is desilicated by a proper amount of NaOH solution, a mesoporous structure is introduced under the condition of keeping the microporous structure undamaged, the specific surface area of the catalyst is increased, and the loading of the active component metal oxide is facilitated. gamma-Al 2 O 3 The function of the catalyst is to increase the acid amount of the catalyst and improve the conversion rate of the reaction; snO (SnO) 2 The catalyst has the functions of increasing Lewis acid sites of the catalyst, improving the reaction selectivity and inhibiting the generation of macromolecular byproducts. N-alkylation reaction of methanol and aniline occurs on Lewis acid sites on the surface of a molecular sieve and in a pore canal, and an active component SnO is adopted at the same time 2 In the reaction with water formation there is also no Bronsted acid site, gamma-Al 2 O 3 With SnO 2 The synergistic effect between the two components greatly improves the catalytic activity of the catalyst and effectively prolongs the service life of the catalyst.
The beneficial effects are that: compared with the prior art, the invention has the following remarkable advantages:
(1) The invention adopts the SnO prepared by an isovolumetric impregnation method 2 -γ-Al 2 O 3 /Hβ (m) The catalyst not only has higher stability, but also has stronger coking resistance and longer service life;
(2) The preparation method of the catalyst used in the invention is simple and easy to operate;
(3) SnO prepared by the invention 2 -γ-Al 2 O 3 /Hβ (m) The catalyst has the characteristics of high conversion rate, high selectivity, high yield and the like for the synthesis of N, N-dimethylaniline.
Drawings
FIG. 1 is a graph showing the performance of the catalysts prepared in example 1 and comparative examples 1 to 4 according to the present invention;
FIG. 2 shows the SnO catalysts prepared in example 1 and comparative examples 3-4 of the present invention 2 -γ-Al 2 O 3 /Hβ (m)、 γ-Al 2 O 3 Hbeta and gamma-Al 2 O 3 /Hβ (m) XRD contrast pattern of (b);
FIG. 3 shows the SnO catalysts prepared in example 1 and comparative example 1, comparative examples 3-4 of the present invention 2 -γ-Al 2 O 3 /Hβ (m)、 γ-Al 2 O 3 、γ-Al 2 O 3 Hbeta and gamma-Al 2 O 3 /Hβ (m) N of (2) 2 Adsorption-desorption drawing;
FIG. 4 shows the SnO catalysts obtained in example 1 and comparative example 1, comparative examples 3-4 according to the present invention 2 -γ-Al 2 O 3 /Hβ (m)、 γ-Al 2 O 3 、γ-Al 2 O 3 Hbeta and gamma-Al 2 O 3 /Hβ (m) Is a pore size distribution map of (1);
FIG. 5 shows the SnO catalyst prepared in example 1 and comparative example 4 of the present invention 2 -γ-Al 2 O 3 /Hβ (m) gamma-Al 2 O 3 /Hβ (m) NH of (C) 3 Adsorption-desorption drawing;
FIG. 6 is a catalyst SnO of example 7 of the present invention 2 -γ-Al 2 O 3 /Hβ (m) And (3) a life span investigation experiment result trend graph.
Detailed Description
The invention will be further described with reference to specific examples and figures.
Example 1: the metal solid acid catalyst SnO of the invention 2 -γ-Al 2 O 3 /Hβ (m) The preparation method of the (C) comprises the following steps:
(1) Roasting H beta molecular sieve raw powder at 550 ℃ to 5H; the calcined H.beta.molecular sieve was then mixed with 0.3 mol/L NaOH solution at a solids to liquid ratio (g/mL) of 1:20 and stirred in a 65℃round bottom flask at 0.5H, then the round bottom flask was cooled to room temperature in water, washed with water and suction filtered to pH=7 and dried at 110℃for 10.h, grinding the obtained solid into powder; the powder was added to 0.5 mol/LNH at a solids to liquid ratio (g/mL) of 1:20 4 Performing ion exchange on Cl solution at 60 ℃ for 1H and suction filtration, repeating the above operation four times, washing with deionized water until the filtrate contains no chloride ions, drying in a 110 ℃ oven for 10H, grinding into powder, placing in a muffle furnace, and roasting at 550 ℃ for 5H to obtain micro-mesoporous H beta molecular sieve, which is marked as multi-stage pore H beta (m) A molecular sieve;
(2) Taking gamma-Al 2 O 3 Roasting 5H at 550 deg.C, mixing it with hierarchical pore H beta (m) Mechanically mixing molecular sieves according to the mass ratio of 0.5:1, and adding gamma-Al 2 O 3 With H beta (m) After the sesbania powder accounting for 3 percent of the total mass is fully and uniformly mixed, the carrier is wetted by 3 percent of dilute nitric acid, and the dosage of a peptizing agent and gamma-Al are adopted 2 O 3 Multistage pore H beta (m) The total mass ratio of the molecular sieve to the extrusion aid is 1 ml to 1 g, and the mixture is put into a 100 ℃ oven for drying 5 h, and then is fully ground into powder, thus obtaining the gamma-Al 2 O 3 /Hβ (m) A composite carrier;
(3) gamma-Al 2 O 3 /Hβ (m) Ethanol solution of composite carrier and tin tetrachloride (volume ratio of tin tetrachloride to ethanol is 0.187:10) is added into a round bottom flask for medium volume impregnation of 12 h (SnO) 2 5-wt% of the total mass of the catalyst), drying at 110deg.C in an oven for 10-h to obtain solid, grinding into powder, placing in a muffle furnace, and calcining at 550deg.C to 5-h in air atmosphere to obtain metal solid acid catalyst SnO 2 -γ-Al 2 O 3 /Hβ (m) 。
Comparative example 1: by gamma-Al 2 O 3 As a catalyst.
Comparative example 2: the H beta molecular sieve raw powder is used as a catalyst.
Comparative example 3: by gamma-Al 2 O 3 The preparation method of the catalyst comprises the following steps of: respectively weighing gamma-Al 2 O 3 Roasting 5H with H beta molecular sieve at 550 deg.c, mixing mechanically in the mass ratio of 0.5 to 1, and adding gamma-Al 2 O 3 With H beta (m) Fully and uniformly mixing sesbania powder accounting for 3% of the total mass, wetting a carrier by 3% of dilute nitric acid, putting the carrier into a 100 ℃ oven for drying 5 h, and fully grinding the carrier into powder to obtain gamma-Al 2 O 3 H.beta.catalyst.
Comparative example 4: by gamma-Al 2 O 3 /Hβ (m) As a catalyst, the preparation method comprises the following steps: taking gamma-Al 2 O 3 Roasting 5H at 550 deg.C, mixing it with hierarchical pore H beta (m) Mechanically mixing molecular sieves according to the mass ratio of 0.5:1, and adding gamma-Al 2 O 3 With H beta (m) Fully and uniformly mixing sesbania powder accounting for 3% of the total mass, wetting a carrier by 3% of dilute nitric acid, putting the carrier into a 100 ℃ oven for drying 5 h, and fully grinding the carrier into powder to obtain gamma-Al 2 O 3 /Hβ (m) A catalyst.
Example 2: the synthesis of N, N-dimethylaniline was carried out using the catalysts prepared in example 1 and comparative examples 1 to 4 above, by the steps of: 5 g catalyst is added into a reaction tube, and the mixed solution of methanol and aniline is used as a reaction raw material to carry out alkylation reaction under the following reaction conditions: normal pressure, preheating temperature of 223 ℃, reaction temperature of 220 ℃ and mass space velocity of 0.3 h -1 The molar ratio of methanol to aniline is 4:1, the raw materials are cooled after reaction, and the alkylated product is collected and detected by GC-7890 Plus gas chromatography.
At the same time, for gamma-Al 2 O 3 、Hβ、γ-Al 2 O 3 /Hβ、γ-Al 2 O 3 /Hβ (m) SnO (zinc oxide) 2 -γ-Al 2 O 3 /Hβ (m) The results of the comparison of the alkylation performance of (2) are shown in FIG. 1, from which it is clear that SnO 2 -γ-Al 2 O 3 /Hβ (m) Compared with gamma-Al 2 O 3 And H beta, the catalytic activity of the catalyst is obviously improved, and the yield of N, N-dimethylaniline is respectively improved by 7.18 percent and 1.64 percent; snO (SnO) 2 -γ-Al 2 O 3 /Hβ (m) Compared with gamma-Al 2 O 3 Hbeta and gamma-Al 2 O 3 /Hβ (m) The yields of N, N-dimethylaniline are respectively improved by 1.49 percent and 1.01 percent.
γ-Al 2 O 3 、γ-Al 2 O 3 /Hβ、γ-Al 2 O 3 /Hβ (m) SnO (zinc oxide) 2 -γ-Al 2 O 3 /Hβ (m) The relevant characterization of the catalyst is shown in figures 2-5.
FIG. 2 is gamma-Al 2 O 3 /Hβ、γ-Al 2 O 3 /Hβ (m) And SnO 2 -γ-Al 2 O 3 /Hβ (m) XRD characterization of the catalyst. As can be seen from the graph, three samples all show characteristic diffraction peaks of H beta at 2 theta of 7.8 DEG and 22.4 DEG, wherein gamma-Al 2 O 3 /Hβ (m) And SnO 2 -γ-Al 2 O 3 /Hβ (m) The diffraction peak intensity of the H beta molecular sieve is obviously reduced, which indicates that the BEA framework structure of the H beta molecular sieve is basically unchanged after being treated by NaOH alkaline solution, but the crystallinity of the Si-Al structure of the H beta molecular sieve is reduced. At the same time, three samples also showed Al at 31.94 °, 37.6 °, 45.86 °, 67.03 ° in 2θ 2 O 3 The characteristic diffraction peaks of (220), (311), (400), (440) crystal planes of (C) indicate gamma-Al in the composite catalyst carrier 2 O 3 The addition of (2) has no effect on the crystallinity of the H.beta.molecular sieve. Furthermore, snO 2 Is characterized by SnO at 26.48 DEG, 33.89 DEG and 51.77 DEG in terms of 2 theta 2 -γ-Al 2 O 3 /Hβ (m) No diffraction peak is observed due to SnO 2 The catalyst is in a highly dispersed state on the surface of the carrier, and the metal loading is low.
FIGS. 3 and 4 are gamma-Al 2 O 3 、γ-Al 2 O 3 /Hβ、γ-Al 2 O 3 /Hβ (m) SnO (zinc oxide) 2 -γ-Al 2 O 3 /Hβ (m) N of four catalysts 2 Adsorption-desorption curves and pore size distribution curves. As can be seen from FIG. 3, gamma-Al 2 O 3 Is of the typical IV type with a distinct hysteresis loop of H1 type, the adsorption-desorption hysteresis loop being concentrated in the range of 0.5-0.8, indicating gamma-Al 2 O 3 The porous membrane is provided with mesoporous channels with uniform pore size distribution; gamma-Al 2 O 3 Adsorption isotherms of H.beta.are typicalForm I, indicating gamma-Al 2 O 3 Hβ has a microporous structure; gamma-Al 2 O 3 /Hβ (m) Adsorption isotherms at low P/P 0 The adsorption-desorption curves of the zones are overlapped, then the adsorption-desorption curves are suddenly increased, and an H4 type hysteresis loop gradually appears, which indicates gamma-Al 2 O 3 /Hβ (m) A microporous structure and a mesoporous structure exist in the silicon-containing material, wherein the generation of the mesoporous structure is caused by the removal of skeleton silicon; snO (SnO) 2 -γ-Al 2 O 3 /Hβ (m) Adsorption isotherms of (2) and gamma-Al 2 O 3 /Hβ (m) Is substantially consistent with the characterization result of (c). As can also be seen from the pore size distribution diagram of FIG. 4, gamma-Al 2 O 3 Pore distribution peaks appear in the range of 5-10 nm, while gamma-Al 2 O 3 Hbeta and gamma-Al 2 O 3 /Hβ (m) Pore distribution peaks appeared in the range of 5-16 nm, indicating gamma-Al 2 O 3 The doping of the H beta molecular sieve has a certain influence on the aperture and the pore volume of the H beta molecular sieve, and the treatment of the NaOH solution enables the H beta molecular sieve catalyst to generate more mesoporous structures; furthermore, snO 2 -γ-Al 2 O 3 /Hβ (m) Pore distribution peaks appear in the range of 5-16 nm, which indicates that the porous material has cylindrical pore channels and narrower pore size distribution, and SnO 2 The doping of (a) does not alter the overall pore structure of the support.
FIG. 5 is gamma-Al 2 O 3 /Hβ (m) SnO (zinc oxide) 2 -γ-Al 2 O 3 /Hβ (m) NH of two catalysts 3 Adsorption-desorption drawing. As can be seen, two NH's are present for two samples in the 100℃to 600℃range 3 The desorption peaks are respectively positioned between 50-250 ℃ and 250-500 ℃ and represent weak acid centers and medium strong acid centers of the sample, and the weak acid content is more than the medium strong acid content; gamma-Al 2 O 3 /Hβ (m) On to introduce SnO 2 After that, the desorption peak position is unchanged, and the peak areas corresponding to weak acid and medium strong acid are increased; thus, the acid sites of the catalyst can be considered to be related to weak mediator acid sites. Wherein SnO 2 -γ-Al 2 O 3 /Hβ (m) Is greater than gamma-Al 2 O 3 /Hβ (m) This is due to SnO 2 Is filled with H beta (m) Molecular sieve silicon cavity, and SnO 2 With Al 2 O 3 The surface mainly contains Lewis acid centers, and the synergistic effect between the two oxides increases the catalytic activity of the catalyst to a certain extent.
Example 3: research on metallic solid acid catalyst SnO 2 -γ-Al 2 O 3 /Hβ (m) Middle gamma-Al 2 O 3 And SnO 2 Load (SnO is controlled by controlling the volume ratio of stannic chloride and ethanol) 2 Load) on catalytic performance
The basic procedure is the same as in example 2, except that gamma-Al is present in the catalyst 2 O 3 And SnO 2 Different loadings of different gamma-Al 2 O 3 And SnO 2 The loading and the effect on the conversion, selectivity and yield of N, N-dimethylaniline synthesis are shown in table 1. As can be seen from Table 1, when gamma-Al 2 O 3 When the content is 50 wt%, the gamma-Al 2 O 3 /Hβ (m) The catalytic effect of the N-alkylation reaction of the para-aniline is good, so that the yield of the N, N-dimethylaniline can reach 94.11%; when SnO 2 When the content is 5 wt%, snO is used 2 -γ-Al 2 O 3 /Hβ (m) The conversion rate of aniline can reach 98.05%, the selectivity of N, N-dimethylaniline reaches 97.41%, and the yield reaches 95.51%.
TABLE 1 influence of different metal loadings on aniline conversion and N, N-dimethylaniline selectivity and yield
| γ-Al 2 O 3 Content/wt% | SnO 2 Content/wt% | Conversion/% | Selectivity/% | Yield/% |
| 25 | 0 | 96.98 | 96.79 | 93.87 |
| 50 | 0 | 97.21 | 96.82 | 94.11 |
| 75 | 0 | 97.12 | 95.48 | 92.74 |
| 100 | 0 | 97.01 | 94.4 | 91.58 |
| 50 | 1 | 96.96 | 96.45 | 93.52 |
| 50 | 3 | 97.01 | 97.02 | 94.12 |
| 50 | 5 | 98.05 | 97.41 | 95.51 |
| 50 | 10 | 97.00 | 96.48 | 93.58 |
。
Example 4: single-factor experiments of reaction temperature in the synthesis of N, N-dimethylaniline.
The basic procedure was the same as in example 2, except that the reaction temperature was different. The reaction temperatures were 200℃and 210℃and 220℃and 230℃and 240℃respectively, and the experimental results are shown in Table 2.
As can be seen from Table 2, the different reaction temperatures are specific to SnO 2 -γ-Al 2 O 3 /Hβ (m) The catalytic activity of the catalyst has a great influence. Along with itThe reaction temperature is increased, the conversion rate of aniline and the selectivity of N, N-dimethylaniline are in a trend of increasing and then decreasing, and the conversion rate of the aniline and the selectivity of the N, N-dimethylaniline are not good for the conversion of the N-methylaniline into the N, N-dimethylaniline due to the fact that the temperature is too low, so that the selectivity of the N, N-dimethylaniline is reduced; the catalyst pore is blocked by byproducts with high boiling point easily generated due to the overhigh temperature, so that the activity of the catalyst is reduced, and the yield of N, N-dimethylaniline is reduced. Therefore, in consideration of the above, the reaction temperature is preferably 220 ℃.
TABLE 2 influence of reaction temperature on aniline conversion and N, N-dimethylaniline selectivity and yield
| Reaction temperature/. Degree.C | Mass space velocity/h -1 | Raw material proportioning | Conversion/% | Selectivity/% | Yield/% |
| 200 | 0.3 | 4:1 | 95.89 | 93.81 | 89.96 |
| 210 | 0.3 | 4:1 | 96.51 | 95.23 | 91.91 |
| 220 | 0.3 | 4:1 | 98.05 | 97.41 | 95.51 |
| 230 | 0.3 | 4:1 | 97.00 | 97.02 | 94.11 |
| 240 | 0.3 | 4:1 | 96.98 | 96.82 | 93.90 |
。
Example 5: single-factor experiments on mass space velocity in N, N-dimethylaniline synthesis.
The basic procedure is the same as in example 2, except that the mass space velocity is different. Mass space velocities of 0.2 h respectively -1 、0.3 h -1 、0.4 h -1 、0.5 h -1 、0.6 h -1 The results are shown in Table 3.
As can be seen from Table 3, the different mass space velocities versus SnO 2 -γ-Al 2 O 3 /Hβ (m) The catalytic activity of the catalyst has a great influence. This is because the larger the mass space velocity, the shorter the reaction residence time, resulting in insufficient reaction and reduced conversion; the smaller the mass space velocity, the longer the reaction residence time, resulting in an increase in the carbon deposition rate and a decrease in the yield. Thus, in combination, the reaction preferably has a mass space velocity of 0.3 h -1 。
TABLE 3 influence of mass space velocity on aniline conversion and N, N-dimethylaniline selectivity and yield
| Mass space velocity/h -1 | Reaction temperature/. Degree.C | Raw material proportioning | Conversion/% | Selectivity/% | Yield/% |
| 0.2 | 220 | 4:1 | 96.98 | 96.74 | 93.82 |
| 0.3 | 220 | 4:1 | 98.05 | 97.41 | 95.51 |
| 0.4 | 220 | 4:1 | 96.59 | 95.54 | 92.29 |
| 0.5 | 220 | 4:1 | 95.97 | 93.95 | 90.16 |
| 0.6 | 220 | 4:1 | 95.31 | 89.49 | 85.29 |
。
Example 6: single-factor experiments of raw material ratios in the synthesis of N, N-dimethylaniline.
The basic procedure was the same as in example 2, except that the raw material ratios were different. The molar ratios of methanol to aniline in the raw materials are 2:1, 3:1, 4:1, 5:1 and 6:1 respectively, and the results are shown in Table 4.
As can be seen from Table 4, the different raw material ratios are for SnO 2 -γ-Al 2 O 3 /Hβ (m) The catalytic activity of the catalyst has less influence. With the increase of the molar content of the methanol in the raw materials, the conversion rate of the aniline is gradually increased, the selectivity of the N, N-dimethylaniline is in a trend of increasing first and then decreasing later, when the molar ratio of the methanol to the aniline is more than 4, the yield of the N, N-dimethylaniline is basically kept stable, but the selectivity of byproducts is gradually increased, and the molar content of the methanol is too high, so that the resource waste is caused. Considering comprehensively, the more suitable raw material ratio of the reaction is n (methanol): n (aniline) =4:1.
TABLE 4 raw material ratio para-aniline conversion and N, N-dimethylaniline selectivity and recoveryInfluence of the Rate
| Raw material proportioning | Reaction temperature/. Degree.C | Mass space velocity/h -1 | Conversion/% | Selectivity/% | Yield/% |
| 2:1 | 220 | 0.3 | 96.12 | 94.04 | 90.39 |
| 3:1 | 220 | 0.3 | 96.91 | 96.67 | 93.69 |
| 4:1 | 220 | 0.3 | 98.05 | 97.41 | 95.51 |
| 5:1 | 220 | 0.3 | 98.59 | 96.32 | 94.96 |
。
Example 7: catalyst SnO 2 -γ-Al 2 O 3 /Hβ (m) And (5) life inspection experiments.
The synthesis method of the N, N-dimethylaniline comprises the following steps: the mixed solution of methanol and aniline is taken as raw material, and 5 g catalyst SnO is added into a reaction tube 2 -γ-Al 2 O 3 /Hβ (m) The feeding speed is controlled to be 0.03 mL/min, and the mass airspeed is controlled to be 0.3 h at the normal pressure and the reaction temperature of 220 DEG C -1 The raw materials are cooled after reaction, alkylation products are collected, the service life of the catalyst is inspected, and the result is shown in figure 6. As can be seen from FIG. 6, snO is grown over time throughout the experiment 2 -γ-Al 2 O 3 /Hβ (m) The activity and selectivity of the catalyst are stable, which shows that the catalyst has higher catalytic activity and longer service life.
Claims (3)
1. The synthesis method of the N, N-dimethylaniline is characterized by comprising the following steps of: snO using metal solid acid catalyst 2 -γ-Al 2 O 3 /Hβ (m) The method comprises the steps of taking a mixed solution of methanol and aniline as a reaction raw material, carrying out an alkylation reaction, and obtaining N, N-dimethylaniline after the reaction is finished, wherein the alkylation reaction comprises the following conditions: normal pressure, reaction temperature of 200-240 ℃ and mass space velocity of the reaction raw materials of 0.2-0.6 h -1 The method comprises the steps of carrying out a first treatment on the surface of the The catalyst is metal solid acid catalyst SnO 2 -γ-Al 2 O 3 /Hβ (m) In multistage pore H beta (m) Molecular sieve as carrier and gamma-Al supported 2 O 3 And SnO 2 The method comprises the steps of carrying out a first treatment on the surface of the The gamma-Al 2 O 3 And a hierarchical pore H beta (m) The mass ratio of the molecular sieve is 0.25-1:1, snO 2 Accounting for 1-10 wt percent of the total mass of the catalyst; the preparation method of the catalyst comprises the following steps: (1) The H beta molecular sieve is calcined, alkali treated and ion exchanged to prepare the hierarchical pore H beta (m) A molecular sieve; (2) gamma-Al 2 O 3 After calcination treatment, with a hierarchical pore H beta (m) Mixing molecular sieve, extrusion aid and peptizer to obtain gamma-Al 2 O 3 /Hβ (m) A composite carrier; (3) gamma-Al 2 O 3 /Hβ (m) Placing the composite carrier in ethanol solution of stannic chloride, carrying out isovolumetric impregnation, taking out, drying, grinding and calcining to obtain the metal solid acid catalyst SnO 2 -γ-Al 2 O 3 /Hβ (m) The method comprises the steps of carrying out a first treatment on the surface of the In the step (2), the extrusion assisting agent is sesbania powder, and the dosage is gamma-Al 2 O 3 And a hierarchical pore H beta (m) 3-5% of the total mass of the molecular sieve, and peptizingThe agent is dilute nitric acid solution with concentration of 2-4%, and the dosage of peptizing agent and gamma-Al 2 O 3 Multistage pore H beta (m) The ratio of the total mass of the molecular sieve to the extrusion aid is 1-1.2 ml to 1 g; in the step (3), the volume ratio of the stannic chloride to the ethanol is 0.036-0.394:10, and the time of the isovolumetric impregnation is 8-20 h; in the steps (1) to (3), the conditions of the calcination treatment are as follows: 500-600 deg.c and 3-5 h.
2. The method for synthesizing N, N-dimethylaniline according to claim 1, wherein the molar ratio of methanol to aniline is 2 to 5:1.
3. The method for synthesizing N, N-dimethylaniline according to claim 1, wherein in the step (1), the silicon to aluminum ratio of the hβ molecular sieve is 25 to 100.
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