The catalytic characteristics of 2-methylnaphthalene acylation with AlCl3 immobilized on Hβ as Lewis acid catalyst

Jingjing Sun; Haibo Jin; Xuefeng Mao; Guangxiang He; Junfang Li; Zihao Yan; Fating Hu; Lei Ma; Xiaoyan Guo; Suohe Yang

doi:10.1515/gps-2023-0003

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The catalytic characteristics of 2-methylnaphthalene acylation with AlCl₃ immobilized on Hβ as Lewis acid catalyst

Jingjing Sun , Haibo Jin , Xuefeng Mao , Guangxiang He , Junfang Li , Zihao Yan , Fating Hu , Lei Ma , Xiaoyan Guo und Suohe Yang

Veröffentlicht/Copyright: 9. Januar 2023

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Aus der Zeitschrift Green Processing and Synthesis Band 12 Heft 1

Abstract

The heterogeneous supported Lewis acid catalyst prepared by immobilization technology has high reaction activity. It is an environment-friendly catalyst. Using Lewis acid immobilized as the catalyst, 2-methyl-6-propionyl naphthalene is synthesized by Friedel–Crafts reaction with 2-methylnaphthalene and propionic anhydride, which has a good development prospect. A variety of AlCl₃ catalysts supported by H-zeolite molecular sieves are prepared using the solvent reflux method in the paper. It is found that AlCl₃/Hβ has better catalytic performance. The results showed that AlCl₃/Hβ catalyst is mainly composed of L acid. The acid content of B acid and the specific surface area increase, and the pore volume and pore size decreases. With the increase in AlCl₃ concentration, the acid content of strong acid, medium strong acid, and weak acid increases, but the solubility of AlCl₃ in CHCl₃ is limited. When the concentration of AlCl₃ is too high, too much AlCl₃ is deposited on the surface of the molecular sieve, which is useless to its binding with Si–OH. AlCl₃/Hβ’s activity is higher when the concentration of AlCl₃ is 3 g·L⁻¹, and the solvent is refluxed for 8 h and calcined at 550°C for 3 h. Under these conditions, the conversion of 2-methylnaphthalene is 85.86%, and the yield of β,β-methyl propyl naphthalene is increased to 81.19%.

Keywords: 2-methylnaphthalene; β,β-methyl propyl naphthalene; acylation; immobilized AlCl3 ; zeolite molecular sieve

1 Introduction

β,β-Methyl propyl naphthalene is an important organic chemical raw material. The 2-methyl-6-propionyl naphthalene (2,6-MPN) is oxidized with ethylene glycol to obtain polyethylene 2,6-naphthalene dicarboxylate (PEN). It is a high-end polyester with excellent physical and chemical properties [1,2,3,4,5,6]. The synthesis method of 2,6-MPN mainly uses Lewis acid anhydrous AlCl₃ as the catalyst to catalyze the Friedel–Crafts acylation reaction between 2-methylnaphthalene (2-MN) and propyl chloride [7,8,9]. Li et al. [10] used an anhydrous AlCl₃ catalyst to carry out the 2-MN acylation reaction in a stainless-steel microchannel reactor, which had a high heat transfer rate. The yield of 2,6-MPN is 85.8%, and the selectivity is 87.5%. Although anhydrous AlCl₃ has good catalytic activity, it also has many shortcomings, such as large consumption, severe pollution, equipment corrosion, non-regeneration, and poor safety [11,12,13]. Therefore, it is urgent to develop a new acylation catalyst and green synthesis process of 2,6-MPN. The immobilized AlCl₃ catalyst can maintain the high catalytic activity of AlCl₃ and overcome the shortcomings of AlCl₃ decomposition in water, which is an ideal heterogeneous catalyst [14,15,16,17,18,19,20,21,22]. There are two methods to prepare an immobilized AlCl₃ catalyst: the physical adsorption method and the chemical bonding method [23,24,25,26]. Chemical bonding refers to the bonding between AlCl₃ and the hydroxyl group on the surface and the removal of the HCl molecule to obtain a heterogeneous catalyst containing AlCl₃.

There are two main methods to immobilize AlCl₃ by chemical bond: the gas phase method [27] and the liquid phase method [22,28,29,30]. AlCl₃ is easy to sublimate, and N₂ is used to react with zeolite molecular sieve and other carriers to form the immobilized AlCl₃. The experimental operation is simple, but the equipment is too high to realize. The liquid phase method dissolves AlCl₃ in halogenated alkane solvent and reacts with the carrier for a period to generate the embedded AlCl₃. The solvent used in the liquid phase reaction is toxic, but the operation is simple. Both methods of immobilized AlCl₃ have been presented, and the prepared immobilized AlCl₃ catalyst has good catalytic activity in many organic reactions, especially Friedel–Crafts reactions. In this article, a series of catalysts were prepared using H-zeolite molecular sieves as carriers and using the solvent reflux method to immobilize AlCl₃ under different conditions. The preparation conditions and the catalytic performance of the 2-MN acylation reaction were studied. This is a new green catalytic process, which can accelerate the research and production process of PEN and improve people’s quality of life.

2 Experimental

2.1 Preparation of AlCl₃ supported catalyst

The zeolite molecular sieve was pretreated in a muffle furnace at 600°C for 3 h. Anhydrous AlCl₃ was weighed and placed in a 250 mL three-way flask. Then, 100 mL CHCl₃ solution was added. After nitrogen was pumped in and the air was emptied, the metal bath controller was turned on to stir. After AlCl₃ was fully dissolved, 10 g of pretreated zeolite molecular sieve (sieve agent ratio 1:10) was added and stirred at a high temperature to reflux the solvent. After a while, the heating was stopped. The three-end flask was cooled to room temperature, filtered, and washed with CHCl₃. The solid was placed in a vacuum oven at 50°C overnight. After grinding, it was roasted at 550°C for 3 h in a muffle furnace and cooled to room temperature. Finally, the immobilized AlCl₃ catalyst was obtained.

2.2 Characterization of the supported catalyst

Acidity was determined using an automatic temperature-programmed chemisorption (NH₃-TPD) unit developed by Micromeritics (AutoChem II 2920) with a thermal conductivity detector (TCD). The 0.2 g catalyst sample was first flushed with helium (30 mL·min⁻¹) at 700°C for 3 h, cooled to 150°C, saturated with NH₃ until equilibrated, and then flushed again with helium until the baseline of the integrator was stable. The NH₃-TPD treatment quickly starts from 150°C to 700°C, and the heating rate was 15°C·min⁻¹. Surface morphology was observed using the TESCAN MIRA4 ultra-high resolution field emission scanning electron microscope (SEM) manufactured in the Czech Republic. The electron gun was a Schottky field emission gun, the magnification was 2–50 k, and the test voltage was 30 kV.

Specific surface area and pore volume aperture (BET) were measured using Micromeritics ASAP 2460 3.01. About 0.12 g of the sample was weighed into a sample tube, vacuum-dried, and then de-vacuumed (300°C degassing for 3 h), and then N₂ was adsorbed in liquid nitrogen −196°C. After the test was completed, the specific surface area of the catalyst was calculated by the BET method. The BJH model calculated the pore size distribution.

A PANalytical Axios X-ray fluorescence spectrometer (XRF) produced by Philips was used to determine the contents of each component in the catalyst. The instrument type was multi-channel, and the power of the X-ray was 4 kW. Pyridine absorption infrared spectroscopy (Py-IR) used a Thermo Fisher Nicolet iS50 infrared spectrometer to measure the concentration of Brönsted and Lewis acids in the samples. The transmission method was used for testing, the number of infrared scanning was 32 times, the scanning wavelength was 400–4,000 cm⁻¹, and the resolution was 4 cm⁻¹.

2.3 Catalyst evaluation

A certain amount of 2-MN and propionic anhydride (PA) were added to a three-necked round-bottomed flask equipped with a condenser tube, a thermometer, a drying tube, and a metal bath. Then, an appropriate amount of solvent was added. After stirring evenly, the catalyst was added, and the temperature was raised and stirred continuously for a while. Then, the catalyst was separated by filtration, and the reaction solution was analyzed using a gas chromatograph.

GC-2014C (SHIMADZU, Japan) was equipped with an FID detector. The temperature program mode (215°C for 30 min) was used to analyze the extracted reaction solution. The chromatographic column was HP-5 50 m × 0.20 mm. N₂ was used as carrier gas at the nitrogen pressure of 0.5 MPa. The detector temperature was 300°C, and the injection port temperature was 300°C. The injection quantity was 0.2 μL.

3 Results and discussion

3.1 Effect of different molecular sieve carriers on 2-MN acylation catalyzed by AlCl₃

Five H-zeolite molecular sieves USY (SiO₂/Al₂O₃ = 6), HY (SiO₂/Al₂O₃ = 6), meridians (MOR: SiO₂/Al₂O₃ = 10), HZSM-5 (SiO₂/Al₂O₃ = 25), and Hβ (SiO₂/Al₂O₃ = 25) were used as carriers to prepare the immobilized AlCl₃ catalyst under the same conditions, which was used to catalyze the acylation reaction of 2-MN with PA. Tetramethylene sulfone (TS) was used as the solvent. The results are shown in Table 1.

Table 1

Effect of different zeolite carriers on 2-MN propionyl catalyzed by AlCl₃

Catalysts	Conversion (%)	Selective (%)
Catalysts	Conversion (%)	2,6-MPN	2,7-MPN	Others
AlCl₃/USY	49.6	41.8	25.7	32.5
AlCl₃/HY	55.0	34.3	12.5	53.2
AlCl₃/MOR	48.1	21.7	9.8	68.5
AlCl₃/HZSM-5	49.7	23.4	23.5	53.1
AlCl₃/Hβ	76.2	48.0	46.4	5.6

Reaction conditions: 2-MN 0.0125 mol, PA 0.025 mol, TS 10 g, catalyst (calcination at 600°C for 3 h) 3 g, 190°C, 10 h.

Hβ zeolite molecular sieve as a carrier of AlCl₃ had significantly more vigorous catalytic activity than other zeolite molecular sieves, with a higher conversion of 2-MN and a selectivity of β,β-MPN up to 94.4%. There were two possible reasons: on the one hand, Hβ had open three-dimensional channels, the pore size was much larger than HZSM-5, PA could freely access Hβ channels, AlCl₃/Hβ surface-active center was completely contacted, and chemical adsorption could form a large number of acyl carbocation, conducive to the reaction; on the other hand, Hβ itself had a large number of medium and strong acids that promoted Friedel–Crafts acylation reaction between 2-MN and PA, and its acidity was much more than HY, USY, MOR, and HZSM-5, which was the main reason why AlCl₃/Hβ had more vital catalytic activity than other zeolite molecular sieves immobilized AlCl₃. However, other zeolite molecular sieves had less strong acid and limited AlCl₃ load, so the active intermediates generated on the active center were inadequate to attack the inert aromatic ring, resulting in low catalytic activity. Therefore, the Hβ zeolite molecular sieve (Si/Al ratio of 25) was used as the carrier to prepare AlCl₃/Hβ catalyst.

3.2 Characterization analysis of AlCl₃/Hβ catalyst

3.2.1 XRD characterization of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

The AlCl₃/Hβ catalysts prepared by the solvent reflux method with different concentrations of AlCl₃ were characterized by XRD. According to the results in Figure 1, the XRD diffraction peaks of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃ showed the standard diffraction peaks of Hβ (PDF # 48-0074). Moreover, the peak pattern was sharp, indicating that the crystal phase of Hβ was undamaged in the modification process, and the crystal phase was intact. There was no diffraction peak of AlCl₃ in the figure, and the skeleton structure of the catalyst was still Hβ, indicating that AlCl₃ existed in an amorphous form in the AlCl₃/Hβ catalyst and AlCl₃ was well dispersed in Hβ. Compared with Hβ, the diffraction peak intensity of the catalyst with AlCl₃ immobilized was more vigorous overall. The diffraction peak intensity of the catalyst immobilized with 1 g·L⁻¹ AlCl₃ had a non-significant difference from the unmodified Hβ. The diffraction peak of AlCl₃/Hβ catalyst with an AlCl₃ concentration of 1 g·L⁻¹ was inconspicuous from that of unmodified Hβ.

Figure 1

XRD patterns of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃.

3.2.2 SEM characterization of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

SEM characterized the AlCl₃/Hβ catalysts obtained with different concentrations of AlCl₃, and the results are shown in Figure 2.

Figure 2

SEM of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃: (a) AlCl₃ (1 g·L⁻¹)/Hβ, (b) AlCl₃ (3 g·L⁻¹)/Hβ, and (c) AlCl₃ (5 g·L⁻¹)/Hβ.

The AlCl₃/Hβ catalyst particles were small cubes, but the size distribution of surface particles was uneven, and there was an agglomeration phenomenon. With the increase in AlCl₃ concentration, the tiny particles immobilized on the surface of the 3 g·L⁻¹ AlCl₃-modified Hβ became more extensive. The distribution was relatively uniform compared with that of 1 g·L⁻¹ void became smaller. As the concentration of AlCl₃ increased, the surface particles increased, the voids continued to decrease, and some pores were blocked, which was adverse to catalyzing the 2-MN acylation reaction.

3.2.3 BET characterization of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

The effect of different concentrations of AlCl₃ loading on the specific surface area, pore volume, and pore size distribution of Hβ was studied, and the BET characterization was carried out. The results are shown in Table 2.

Table 2

BET characterization results of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

Catalysts	Surface area (m²·g⁻¹)	Micropore area (m²·g⁻¹)	External surface area (m²·g⁻¹)	Pore volume (cm³·g⁻¹)	Micropore volume (cm³·g⁻¹)	Mesoporous volume (cm³·g⁻¹)	Pore size (nm)
Hβ	530	358	172	0.45	0.17	0.29	4.63
AlCl₃(1)/Hβ	534	362	172	0.44	0.17	0.27	4.63
AlCl₃(3)/Hβ	559	376	183	0.45	0.16	0.25	4.50
AlCl₃(5)/Hβ	543	371	172	0.33	0.15	0.18	4.26

Compared with the unmodified Hβ, the Hβ-specific surface area of AlCl₃ supported by solvent reflux increased significantly with AlCl₃ concentration. The reason can be explained that the load increases with the concentration increasing of AlCl₃. Combined with SEM results, it was shown that the number of small particles on the surface increased, resulting in an increase in specific surface area and a decrease in pore volume and pore size. It may be due to the reaction between AlCl₃ and Si–OH on the surface of zeolite, resulting in the reduction of pore size. When the concentration of AlCl₃ continued to increase, the particles on the surface gradually increased. The bonding between the bonds leads to a decrease in the specific surface area, pore volume, and aperture. In addition, due to the high concentration of AlCl₃ load, AlCl₃/Hβ catalyst appeared to sinter after calcination, which was also one reason for reducing the specific surface area. At the same time, the results characterized by BET also showed that the specific surface area was the largest, and the void space of the catalyst was rich and uniform when the AlCl₃ concentration was 3 g·L⁻¹.

3.2.4 NH₃-TPD characterization of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

NH₃-TPD spectra of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃ are shown in Figure 3.

Figure 3

NH₃-TPD spectra of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃.

Compared with the unmodified Hβ zeolite molecular sieve, with the increase in AlCl₃ concentration, the strong acid strength and acid content of AlCl₃/Hβ only changed slightly. In general, there was still an increase in acid content. It may be due to the increase in the number of L-acid sites, which happened to be caused by strong acid sites, thus increasing acid strength and acid content. However, as the concentration of AlCl₃ continued to increase, the strength of strong acid was unchanged, but the acid content increased slightly. The strength of medium–strong acid increased compared with Hβ, but it was still slightly decreased compared with the Hβ molecular sieve loaded with 3 g·L⁻¹ AlCl₃. The reason may be that the concentration of AlCl₃ was too high. The undissolved AlCl₃ was deposited on the surface of Hβ in a free state. Part of the AlCl₃ was sintered during calcining, destroying the part of the acid center.

3.2.5 Py-IR characterization of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

Pyridine adsorption infrared data of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃ at different temperatures are shown in Figure 4.

Figure 4

Py-IR spectra of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃: (a) 150°C, (b) 300°C, and (c) 450°C.

To more intuitively compare the acidity of Hβ molecular sieves loaded with AlCl₃, the data of the pyridine infrared spectrum were summarized, as shown in Table 3.

Table 3

Py-IR data of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

Catalysts	Strong acid (μmol·g⁻¹)			Mediate strong acid (μmol·g⁻¹)			Weak acid (μmol·g⁻¹)
Catalysts	Bronsted acid	Lewis acid	Total acid	Bronsted acid	Lewis acid	Total acid	Bronsted acid	Lewis acid	Total acid
AlCl₃(1)/Hβ	1.74	14.20	15.93	2.68	71.03	73.71	3.48	262.03	265.31
AlCl₃(3)/Hβ	2.06	65.69	67.75	6.45	176.15	182.60	9.49	401.30	410.79
AlCl₃(5)/Hβ	2.76	147.30	150.06	6.48	174.21	180.69	18.00	413.42	431.42

Figure 4a–c corresponds to the changes in acid content and acid strength of AlCl₃/Hβ catalysts prepared at different concentrations of AlCl₃ at 150°C, 300°C, and 450°C, respectively. With the increase in AlCl₃ concentration, compared with strong acid and medium–strong acid, the increasing trend of weak acid was the largest, and the increasing trend of strong acid was also more extensive. The increasing trend of Lewis acid was more prominent than that of Bronsted acid. The main reason was that strong acid sites increased Lewis acid quantity, and AlCl₃ itself was a Lewis acid. With the further increase of AlCl₃ concentration, the medium and strong acid contents decreased, while the change in the Bronsted acid content was minor. As the concentration of AlCl₃ continued to increase, part of AlCl₃ attached to the surface of Hβ did not form chemical bonds with the surface elements. It is also reflected in the preparation process of increasing bonds mainly for Hβ molecular sieve increased the Bronsted acid center. The ratio of Bronsted acid and Lewis acid determines the increase of medium strong acid.

3.2.6 XRF characterization of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

For the supported zeolite catalyst, the Si/Al ratio and other components of the supported zeolite have a significant influence on the activity of the catalyst. Table 4 compares the percentage content and ratio of each component in AlCl₃/Hβ catalysts supported by different concentrations of AlCl₃.

Table 4

Comparison of percentage content and ratio of AlCl₃/Hβ catalysts supported by different concentrations of AlCl₃

Catalysts	Al₂O₃ (wt%)	SiO₂ (wt%)	Cl (wt%)	SiO₂/Al₂O₃	Si (wt%)	Al (wt%)	Si/Al
Hβ	6.665	92.802	0	23.628	43.379	3.528	11.814
AlCl₃(1)/Hβ	9.709	89.562	0.094	15.654	88.600	10.219	8.328
AlCl₃(3)/Hβ	10.652	88.129	0.113	14.040	86.898	11.108	7.514
AlCl₃(5)/Hβ	11.716	87.592	0.111	12.687	86.702	12.178	6.838

The Si/Al ratio of Hβ immobilized with AlCl₃ decreased, the SiO₂/Al₂O₃ ratio of the modified zeolite decreased from 23.628 to 12.687, and the content of Cl remained unchanged. The percentage content of Cl increased gradually with the increase in AlCl₃ concentration. It indicated that the immobilized AlCl₃ was combined with the Si–OH on the surface of the Hβ molecular sieve. Qi et al. [26] used the ²⁷Al MAS NMR method to study the possible binding forms of AlCl₃ and Si–OH after immobilization in the molecular sieve, as shown in Figure 5.

Figure 5

Possible binding form of AlCl₃ and Si–OH after loading on molecular sieve.

Different concentrations of AlCl₃ may predominate AlCl₃/Hβ in one or more forms shown in Figure 5a–d. However, either form increased Cl in terms of acidity and acid strength, thus modulating the acidity of the catalyst, catalytic activity, and selectivity to the target product β,β-MPN.

3.3 Effect of preparation conditions on propionyl of 2-MN catalyzed by AlCl₃/Hβ catalyst

3.3.1 Effect of AlCl₃ concentration on the catalytic performance of AlCl₃/Hβ

The effect of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃ on the acylation reaction of 2-MN and PA is shown in Figure 6.

Figure 6

Effect of AlCl₃ concentration on the catalytic performance of AlCl₃/Hβ. Reaction conditions: n _(2-MN):n _(PA) = 1:1.8, TS 10 g, AlCl₃/Hβ (reflux for 8 h and calcination at 550°C for 3 h) 3 g, 190°C, 10 h.

As shown in Figure 6, with the increase of AlCl₃ concentration, the conversion of 2-MN gradually increased and reached the highest point at 3 g·L⁻¹, which may be the maximum AlCl₃ loading capacity of the catalyst prepared at this concentration. However, when AlCl₃ was immobilized with Hβ, two B-acid sites were converted into one L-acid site. The total acid content showed an increasing trend, so the catalytic activity increased. In addition, the reaction between AlCl₃ and part of Si–OH in Hβ channels increased the pore size and the shape selectivity of AlCl₃/Hβ, which was conducive to the formation of 2,6-MPN. To further increase the concentration of AlCl₃, due to the high concentration part of AlCl₃ exhalation, deposition on the surface of Hβ, after calcining sintered parts, affects the catalytic activity of catalysts. It can be seen from the SEM in the figure that a high concentration of AlCl₃ Hβ surface structure of the load was affected, selectivity of the catalyst declined. Therefore, the appropriate concentration of AlCl₃ was 3 g·L⁻¹.

3.3.2 Effect of reflux time on the catalytic performance of AlCl₃/Hβ

The effect of AlCl₃/Hβ catalysts prepared at different load times on the 2-MN acylation reaction is shown in Figure 7. When Hβ zeolites were reflux reacted in CHCl₃ solution of AlCl₃ for 9 h, the conversion was the highest, 82.2%, but the selectivity of the target product 2,6-MPN was slightly reduced. When the load time was 8 h, the selectivity for 2,6-MPN was up to 49.7%, although the catalytic activity decreased. It may be because when the load time was 9 h, AlCl₃ had completely reacted with Si–OH on the pore surface, and part of AlCl₃ was attached to the surface. Although a large amount of AlCl₃ can catalyze the acylation of 2-MN, the decrease of pore size resulted in some β,β-MPN with larger molecular diameters trapped in the pore, and an increase of other by-products. Therefore, the appropriate load time was 9 h.

Figure 7

Influence of reflux time on catalytic performance of AlCl₃/Hβ. Reaction conditions: n _(2-MN):n _(PA) = 1:1.8, TS 10 g, AlCl₃/Hβ (AlCl₃ 3 g·L⁻¹ and calcination at 550°C for 3 h) 3 g, 190°C, 10 h.

3.3.3 Effect of calcination temperature on the catalytic performance of AlCl₃/Hβ

The precursor of AlCl₃/Hβ catalyst prepared with AlCl₃ concentration of 3 g·L⁻¹ at 60°C for 8 h was calcined in a muffle furnace. The effect of calcination temperature was investigated, and the results are shown in Figure 8. The conversion of 2-MN was almost unchanged with calcination temperature increasing, but the yield of 2,6-MPN increased gradually. When the calcination temperature was over 550°C, the yield of 2,6-MPN decreased, while the yield of β,β-MPN was almost unchanged. The reason may be that the calcination temperature was too high, and AlCl₃/Hβ could be partially sintered, destroying the surface acid center and affecting the catalytic activity. Therefore, the appropriate roasting temperature was 550°C.

Figure 8

Influence of calcination temperature on the performance of 2-MN propionyl catalyzed by AlCl₃/Hβ. Reaction conditions: n _(2-MN):n _(PA) = 1:1.8, TS 10 g, AlCl₃/Hβ (AlCl₃ g·L⁻¹, reflux for 9 h and calcination for 3 h) 3 g, 190°C, 10 h.

3.3.4 Effect of calcination time on the catalytic performance of AlCl₃/Hβ

The results of calcination time are shown in Figure 9. It can be seen that calcination time had little effect on AlCl₃/Hβ. The conversion of 2-MN and the yield of β,β-MPN were the highest at 3 h. It showed that the structure of the carrier Hβ had been very stable. Therefore, the calcination time of 3 h was suitable.

Figure 9

Effect of calcination time on the performance of 2-MN propionyl catalyzed by AlCl₃/Hβ. Reaction conditions: n _(2-MN):n _(PA) = 1:1.8, TS 10 g, AlCl₃/Hβ (AlCl₃ 3 g·L⁻¹, reflux for 9 h and calcination at 550°C) 3 g, 190°C, 10 h.

3.4 Optimization of propionyl reaction conditions of 2-MN catalyzed by AlCl₃/Hβ catalyst

AlCl₃/Hβ catalyst was prepared with the AlCl₃ concentration of 3 g·L⁻¹ at 60°C for 8 h and calcination at 550°C for 3 h to optimize the reaction conditions of 2-MN propyl acylation.

3.4.1 Effect of catalyst dosage on 2-MN propionyl reaction

The effect of catalyst dosage on 2-MN propionyl reaction was investigated, and the results are shown in Figure 10. When the dosage of AlCl₃/Hβ was 2 g, the conversion of 2-MN was only 53.2%, and the yield of β,β-MPN was also very low. With the increase of the dosage of AlCl₃/Hβ, the conversion of 2-MN showed a trend of continuous increase because the increase of AlCl₃/Hβ accelerated the acylation reaction of 2-MN with PA. The yield of 2-MPN was the highest when the dosage was 3 g. The 2-MN conversion increased, but the by-products increased obviously. Furthermore, too much catalyst would accelerate the occurrence of side reactions and significantly increase the cost of the reaction. Overall consideration, when the dosage of AlCl₃/Hβ was 3 g, it was suitable.

Figure 10

Influence of catalyst dosage on 2-MN propionylation reaction. Reaction conditions: n _(2-MN):n _(PA) = 1:1.8, TS 10 g, AlCl₃/Hβ (AlCl₃ 3 g·L⁻¹, reflux for 9 h and calcination at 550°C for 3 h), 190°C, 10 h.

3.4.2 Effect of reaction temperature on propionyl of 2-MN

The acylation of 2-MN is an exothermic reaction. The temperature has a certain influence on the acylation reaction. Under the conditions of n _(2-MN):n _(PA) = 1:1.8, TS 10 g, AlCl₃/Hβ 3 g, and reaction time 9 h, the effects of reaction temperature on the conversion of 2-MN and the selectivity of β,β-MPN were investigated. The experimental results are shown in Figure 11.

Figure 11

Effect of reaction temperature on propionylation of 2-MN. Reaction conditions: n _(2-MN):n _(PA) = 1:1.8, TS 10 g, AlCl₃/Hβ (AlCl₃ 3 g·L⁻¹, reflux for 9 h and calcination at 550°C for 3 h) 3 g, 10 h.

With the increase in reaction temperature, the transformation of 2-MN first increased and then decreased; the highest conversion was 82.9% at 190°C. It was because when the reaction temperature was increased in the range of 170–190°C, the movement rate of molecules in the reaction was accelerated, which made the reactants 2-MN, PA, and products 2,6-MPN, 2,7-MPN molecules more easily desorbed from AlCl₃/Hβ and reduced the accumulation of macromolecules. It could improve the catalytic performance of the AlCl₃/Hβ catalyst. Therefore, the reaction temperature of 190°C was appropriate.

3.4.3 Effect of reaction time on propionyl of 2-MN

Under the conditions of n _(2-MN):n _(PA) = 1:1.8, TS 10 g, AlCl₃/Hβ 3 g, reaction temperature 190°C, the samples of different times were taken for GC detection to investigate the effect of reaction time on the conversion of 2-MN and the selectivity of β,β-MPN. The result is shown in Figure 12.

Figure 12

Effect of reaction time on propionylation of 2-MN. Reaction conditions: n _(2-MN):n _(PA) = 1:1.8, TS 10 g, AlCl₃/Hβ (AlCl₃ 3 g·L⁻¹, reflux for 9 h and calcination at 550°C for 3 h) 3 g, 190°C, 10 h.

With the prolongation of reaction time, the conversion of 2-MN and the yield of β,β-MPN increased gradually. When the reaction time was 10 h, the maximum yield of 2,6-MPN was 41.5%. After that, when the reaction time was 11 h, the conversion of 2-MN and the yield of other β,β-MPN continued to increase, while the yield of 2,6-MPN decreased by 0.3%. As the reaction time continued to increase, the results were predictable: The conversion of 2-MN and other β,β-MPN yields continued to increase, while the yields of 2,6-MPN gradually decreased. It may be because the propionyl reaction of 2-MN in the reaction was intermittent, and 2,6-MPN, 2,7-MPN, 2,3-MPN, and other products coexisted in the product. As the reaction time increased, the generated products would be converted into other by-products, reducing 2,6-MPN [9]. Therefore, after careful consideration, the appropriate reaction time was 10 h.

3.5 Catalytic reaction feasible mechanism

The reaction mechanism of Friedel–Crafts acylation of 2-MN catalyzed by zeolite molecular sieve is still ambiguous. Yuan et al. [9] proposed that in the catalytic process of zeolite molecular sieve catalyst, medium strong acid played a significant role. The ratio of Bronsted acid to Lewis acid could effectively catalyze the acylation reaction of the aromatic ring within an appropriate range. And the acylation reaction process of 2-MN and anhydride catalyzed by zeolite molecular sieve was proposed, as shown in Figure 13.

Figure 13

Mechanism of 2-MN propionyl catalyzed by zeolite molecular sieve.

The reaction mechanism of Hβ zeolite immobilized by AlCl₃ can be divided into two types according to the type of acid active center. One is a new acid active center formed by AlCl₃ on the surface of zeolite; The other is the existing acid active center on the surface of the zeolite molecular sieve. Although the reaction mechanism of this reaction is complicated with the previous zeolite molecular sieve catalysis, there are still many similarities in the overall reaction process. As shown in Figure 13, the anhydride first chemically adsorbed on the acid active center of the molecular sieve to form acyl carbocation, then attacked 2-MN to form active complex intermediates, and finally desorbed from the surface of the molecular sieve to form products. In addition, it can be seen from the characterization results that the acid content of the AlCl₃/Hβ catalyst increases with the increase of Cl content, indicating that the effective acid amount of the acid center formed by the bond between the molecular sieve surface and Cl is more, among which the medium and strong acids are very beneficial to the reaction.

4 Conclusion

In this article, the AlCl₃/Hβ catalysts are prepared by solvent reflux method using Hβ zeolite (Si/Al ratio of 25) as support. XRD results show that the prepared AlCl₃/Hβ catalyst has typical characteristic peaks and complete structure. SEM characterization shows that the molecular sieve loaded with AlCl₃ presents a small cube structure. With the increase in AlCl₃ concentration, more small particles are attached to the surface. BET results showed that the specific surface area of Hβ zeolite is increased, and pore volume and pore size are decreased by AlCl₃ fixation. XRF results show that immobilized AlCl₃ increases Al₂O₃ and Cl. NH₃-TPD and Py-IR showed that the AlCl₃/Hβ catalyst is mainly L-acid, and the acid content of B-acid also increases. With the increase in AlCl₃ concentration, the acid content of strong acid, medium strong acid, and weak acid all increase.

In the acylation of 2-MN with PA over AlCl₃/Hβ, the reaction activity and selectivity decrease with pore size and specific surface area and increase with Cl content and acid content. The results showed that when the concentration of AlCl₃ was 3 g·L⁻¹, the concentration of reflux solvent was 8 h, and calcination at 550°C for 3 h, the catalytic activity of AlCl₃/Hβ was better. Under atmospheric pressure, AlCl₃/Hβ catalyst has higher catalytic activity in propionyl of 2-MN with TS as the solvent and 190°C for 10 h. Under this condition, the reaction has higher activity and selectivity. The conversion of 2-MN is 85.86%, and the yield of β,β-MPN is 81.19%.

In general, AlCl₃/Hβ catalyst can catalyze the acylation of 2-methylnaphthalene effectively. Compared with the traditional AlCl₃ catalyst, the amount of AlCl₃ used is greatly reduced, and the production cost is reduced. Moreover, the immobilization catalyst can be directly filtered and separated from the solution, simplifying the post-treatment steps, and reducing the generation of a large amount of waste acid and waste gas. It is a relatively environmentally friendly green catalyst.

Funding information: This work was financially supported by the National Natural Science Foundation of China (91634101) and The Project of Construction of Innovative Teams and Teacher Career Development for Universities and Colleges under Beijing Municipality (IDHT20180508).
Author contributions: Jingjing Sun: writing – original draft, writing – review and editing, methodology, formal analysis; Haibo Jin: writing – review and editing, resources, funding acquisition, conceptualization; Xuefeng Mao: formal analysis; Guangxiang He: writing – review and editing, methodology; Junfang Li: resources, validation; Zihao Yan: validation; Fating Hu: investigation; Lei Ma: formal analysis, investigation; Xiaoyan Guo: supervision; Suohe Yang: software.
Conflict of interest: Authors state no conflict of interest.

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Received: 2022-09-04

Revised: 2022-11-05

Accepted: 2022-12-02

Published Online: 2023-01-09

This work is licensed under the Creative Commons Attribution 4.0 International License.

Artikel in diesem Heft

https://doi.org/10.1515/gps-2023-0003

Schlagwörter für diesen Artikel

2-methylnaphthalene; β,β-methyl propyl naphthalene; acylation; immobilized AlCl3; zeolite molecular sieve

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BY 4.0

The catalytic characteristics of 2-methylnaphthalene acylation with AlCl3 immobilized on Hβ as Lewis acid catalyst

Artikel

Abstract

1 Introduction

2 Experimental

2.1 Preparation of AlCl3 supported catalyst

2.2 Characterization of the supported catalyst

2.3 Catalyst evaluation

3 Results and discussion

3.1 Effect of different molecular sieve carriers on 2-MN acylation catalyzed by AlCl3

3.2 Characterization analysis of AlCl3/Hβ catalyst

3.2.1 XRD characterization of AlCl3/Hβ catalysts prepared with different concentrations of AlCl3

3.2.2 SEM characterization of AlCl3/Hβ catalysts prepared with different concentrations of AlCl3

3.2.3 BET characterization of AlCl3/Hβ catalysts prepared with different concentrations of AlCl3

3.2.4 NH3-TPD characterization of AlCl3/Hβ catalysts prepared with different concentrations of AlCl3

3.2.5 Py-IR characterization of AlCl3/Hβ catalysts prepared with different concentrations of AlCl3

3.2.6 XRF characterization of AlCl3/Hβ catalysts prepared with different concentrations of AlCl3

3.3 Effect of preparation conditions on propionyl of 2-MN catalyzed by AlCl3/Hβ catalyst

3.3.1 Effect of AlCl3 concentration on the catalytic performance of AlCl3/Hβ

3.3.2 Effect of reflux time on the catalytic performance of AlCl3/Hβ

3.3.3 Effect of calcination temperature on the catalytic performance of AlCl3/Hβ

3.3.4 Effect of calcination time on the catalytic performance of AlCl3/Hβ

3.4 Optimization of propionyl reaction conditions of 2-MN catalyzed by AlCl3/Hβ catalyst

3.4.1 Effect of catalyst dosage on 2-MN propionyl reaction

3.4.2 Effect of reaction temperature on propionyl of 2-MN

3.4.3 Effect of reaction time on propionyl of 2-MN

3.5 Catalytic reaction feasible mechanism

4 Conclusion

References

Artikel in diesem Heft

Artikel in diesem Heft

Artikel in diesem Heft

The catalytic characteristics of 2-methylnaphthalene acylation with AlCl₃ immobilized on Hβ as Lewis acid catalyst

2.1 Preparation of AlCl₃ supported catalyst

3.1 Effect of different molecular sieve carriers on 2-MN acylation catalyzed by AlCl₃

3.2 Characterization analysis of AlCl₃/Hβ catalyst

3.2.1 XRD characterization of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

3.2.2 SEM characterization of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

3.2.3 BET characterization of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

3.2.4 NH₃-TPD characterization of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

3.2.5 Py-IR characterization of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

3.2.6 XRF characterization of AlCl₃/Hβ catalysts prepared with different concentrations of AlCl₃

3.3 Effect of preparation conditions on propionyl of 2-MN catalyzed by AlCl₃/Hβ catalyst

3.3.1 Effect of AlCl₃ concentration on the catalytic performance of AlCl₃/Hβ

3.3.2 Effect of reflux time on the catalytic performance of AlCl₃/Hβ

3.3.3 Effect of calcination temperature on the catalytic performance of AlCl₃/Hβ

3.3.4 Effect of calcination time on the catalytic performance of AlCl₃/Hβ

3.4 Optimization of propionyl reaction conditions of 2-MN catalyzed by AlCl₃/Hβ catalyst