Synthesis of Brominated Alkanes via Heterogeneous Catalytic Distillation over Al₂O₃/SO₄²⁻/ZrO₂

Abstract

Concentrated sulfuric acid is generally used as a catalyst for producing brominated alkanes in traditional methods, but is highly corrosive and difficult to separate. This work reports the preparation of bromopropane from n-propanol based on a reactive distillation strategy combined with alumina-modified sulfated zirconia (Al₂O₃/SO₄²⁻/ZrO₂) as a heterogenous catalyst. As expected, under the optimum reaction conditions (110 °C), the yield of bromopropane was 96.18% without side reactions due to the reactive distillation strategy. Meanwhile, the microscopic morphology and performance of Al₂O₃/SO₄²⁻/ZrO₂ were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunner–Emmet–Teller (BET), Fourier transform infrared spectroscopy (FT–IR), and other characterization methods. The results confirmed that the morphology of zirconia sulfate is effectively regulated by the modification method of alumina, and more edges and angles provide more catalytic acid sites for the reaction. Furthermore, Al₂O₃/SO₄²⁻/ZrO₂ exhibited high stability and remarkable reusability due to the strong chemical bond Zr–Al–Zr. This work provides a practical method for the preparation of bromopropane and can be further extended to the preparation of other bromoalkanes.

1. Introduction

The development of green synthesis technology and improvement of atomic economic efficiency have become hotspots of current research with the trend toward increasing industrialization and urbanization. Brominated alkanes are critical industrial solvents and raw chemical materials, used as intermediates for various products such as medicines, pesticides, perfumes, dyes, surfactants, and photosensitive materials. However, the traditional method uses sulfuric acid as a catalyst in brominated alkane production, resulting in several tough issues including equipment corrosion, by-product separation, and environmental pollution. Taking the factors mentioned above into account, developing a low-cost, pragmatic, and efficient method for producing brominated alkanes remains a challenge.

As early as the middle of the 19th century, scientists began to research solid acid catalysts. Currently, several solid acid catalysts are used in various catalytic reactions and industry. Compared to liquid acid catalysts, solid catalysts have multiple advantages including a simple preparation process, high reactivity, and low corrosivity. Furthermore, the use of solid acid catalysts also alleviates various problems caused by homogeneous reactions, such as the separation and recovery of products and catalysts. Sulfated zirconium oxide (SZ) is one of the metal oxide solid acid catalysts widely studied this year due to its high reactivity and environmental friendliness. It has a wide range of applications in alkylation, isomerization, and other reactions [1,2,3]. In 1979, Hino et al. [4]. synthesized a sulfated oxide super acid catalyst, SO₄²⁻/ZrO₂, and several studies since have thoroughly researched its preparation process and other aspects. However, SZ does have some issues including fast deactivation, poor channel structure, and insufficient acid sites. In early research, scientists modified sulfated zirconium oxide with expensive metals such as platinum and palladium to improve its catalytic activity [5].

As one of the most used additives and catalytic aids, alumina can improve the catalyst structure and properties in several ways, including mechanical strength and catalyst formation, catalyst-specific surface properties, acidic properties, reactivity, etc. [6]. At the same time, it is also low-cost, easily accessed, conveniently stored, and environment-friendly. In the field of sulfurized zirconia, several studies have indicated that adding a small amount of alumina component to the catalyst sample can be advantageous in producing a crystalline structure, aperture structure, surface sulfate load, catalyst acidity, and structural stability [7]. In a light alkane isomerization reaction, alumina added to super acid typically produces a significantly greater reaction conversion rate and higher stability [8,9]. A large body of literature has reported on the modification effect of Al₂O₃ on superacid catalysts. Kim et al. [10] found that alumina-modified super acid increased the reaction conversion rate by about 30% in butane isomerization reactions. At the same time, the addition of aluminum would also change the composition and properties of the original acidic catalyst center. Zhou et al. [3] used a variety of laboratory and industrial catalyst preparation methods to prepare alumina-modified solid composite catalysts. The results showed that the addition of active aluminum significantly impacts the structural and acidic properties of the catalyst. Cao [11,12] used aluminum sulfate and gallium sulfate as vulcanizing agents when introducing sulfur-containing species into the catalyst preparation process. Compared with the traditional SO₄²⁻/ZrO₂ catalyst, this approach improved the structural performance of the catalytic material while increasing activity, and delayed the growth of ZrO₂ crystal grains.

Under normal circumstances, metal oxides and SO₄²⁻ have three coordination forms: single coordination, chelating double coordination, and bridge double coordination [13]. In the SO₄²⁻/M_xO_y type solid super acid, the latter two coordination effects between SO₄²⁻ and metal oxide dominate [14]. The acidic center of the catalyst super acid is due to the strong induction effect between the metal oxide and SO₄²⁻. During the calcination process, the ionic S=O bond is transformed into a covalent S=O bond, and the S=O group is a strong electron withdrawing group. Due to the electron-withdrawing induction effect of the covalent bond, the electron cloud density on the M–O bond is reduced, resulting in a strong L acid center, which then exhibits super acidity, and water molecules or –OH adsorb and dissociate at the L acid center. The B acid center is also produced. The synergistic effect of B and L acid centers makes the acidity of the catalyst higher than that of 100% sulfuric acid. The reaction mechanism is shown in Figure S1.

Inspired by the above works, alumina modified sulfated zirconia (Al₂O₃/SO₄²⁻/ZrO₂) through co-precipitation was used as a heterogeneous catalyst to replace the traditional liquid acid catalyst for bromination reaction. The optimal preparation conditions for Al₂O₃/SO₄²⁻/ZrO₂ were obtained by screening the catalyst preparation and reaction conditions. Meanwhile, the reactive distillation strategy was proposed for the first time in this reaction, in which both separation and rectification are carried out simultaneously for rapid product transfer. Rapid removal of the product not only overcomes the limit of equilibrium conversion of reversible reaction, but also reduces energy consumption. Therefore, the research content of this article has important significance and reference value for a green brominated alkane production process and the application of Al₂O₃ modified SO₄²⁻/ZrO₂ solid acid catalysts. Furthermore, a catalytic distillation reaction was used to separate and prepare bromopropane to reduce energy consumption during product purification, contributing to the development prospects of current green chemistry.

2. Results

2.1. Characterization of the Catalysts

Figure 1A displays the XRD spectra of Al₂O₃/SO₄²⁻/ZrO₂ catalysts at different calcination temperatures. It can be seen from Figure 1A that when the calcination temperature was lower than 600 °C, there was no obvious characteristic peak. The reason for this was deemed to be that the calcination temperature was too low, and no crystals were formed in the catalyst, thus 600 °C was selected as the calcination temperature of the catalyst.

Figure 1B displays the XRD spectra of Al₂O₃/SO₄²⁻/ZrO₂ catalysts with different Al₂O₃ loadings, at a calcination temperature of 600 °C. It can be seen from Figure 1B that the diffraction peaks 2θ = 30.5, 35.4, 50.9, and 60.8° were found in almost all samples. After comparison with relevant literature [10,15], the results were verified to be the diffraction peaks of ZrO₂ crystal, indicating that the catalyst support of SO₄²⁻/ZrO₂ had been successfully prepared. The literature detailed a catalyst modified by Al₂O₃, and which predominantly consisted of tetragonal phase type ZrO₂ and a small amount of monoclinic phase type ZrO₂ [16]. The sample XRD spectra of a small amount of Al₂O₃ added via co-precipitation shown that it completely changed to tetragonal phase, as the monoclinic phase type ZrO₂ disappeared. Zalewski et al. [17] believe that in sulfurized zirconia catalysts, the modest amount of small Al₂O₃ grains added via co-precipitation was mainly concentrated in the ZrO₂lattice gaps, causing the ZrO₂ crystal grain size to be less than the pure sulfurized zirconia after calcination. At the same time, the small ZrO₂ crystal grains made it easier to form a metastable tetragonal phase type ZrO₂ during the calcination process [18]. Relevant literature shows that additional tetragonal crystal ZrO₂ is beneficial in ensuring the excellent catalytic activity of sulfated zirconia catalysts [19]. There is a corresponding relationship between catalytic activity and the proportion of tetragonal crystal [20]. There was no Al₂O₃ diffraction peak in the spectrum, which means that Al₂O₃ was uniformly dispersed in the sample and the crystal size was very small.

A scanning electron microscope was used to further observe and analyze the ZrO₂ catalyst morphology pre- and post- modification with Al₂O₃, as shown in Figure 2A,B. The results showed that the sulfated zirconia catalyst particles were not modified by aluminum and were large and irregularly arranged with a relatively rough surface, which provides more acidic sites for catalytic reactions. The surface morphology of the composite catalyst modified by co-precipitation had undergone significant changes. It can be seen from Figure 2B that the surface of the catalyst particles became smoother, the particles became smaller, and their surfaces became denser. The surface morphology of the catalyst changed because ZrO₂ and alumina are relatively tightly bonded during the preparation process, and are likely to affect each other during the high-temperature calcination process. Furthermore, alumina, as a relatively rigid oxide, easily forms a specific structure and surface morphology at high temperature, which will impact the specific surface properties of the catalyst.

BET technology was used to study the effect of alumina addition on the catalyst specific surface area, and the results are shown in

Table 1. Comparison of surface area and pore size for prepared SO₄²⁻/ZrO₂ and Al₂O₃/ SO₄²⁻/ZrO_2.

Catalysts	SBET a (m2/g)	Dmean b (nm)
ZrO2	43.5	50.27
2(Zr/Al)	69.6	33.65
3(Zr/Al)	57.8	37.60
4(Zr/Al)	105.9	26.80
5(Zr/Al)	98.1	22.23
6(Zr/Al)	87.9	8.98

^a BET surface area was determined from N₂ adsorption isotherm. ^b Average pore size was determined from the desorption average pore diameter (4 V/A by BET).

. It can be seen that with the addition of alumina, the catalyst overall specific surface area showed an increasing trend, and pore diameter decreased. This is because a microporous alumina system was introduced into a mesoporous ZrO₂ system. It is generally believed that the larger the catalyst-specific surface area, the more active sites are exposed, which enhances the reaction progress.

Additionally, the Al₂O₃ modified ZrO₂ catalyst was subjected to energy–dispersive X-ray spectroscopy (EDS) element distribution measurement, and a catalyst sample with a Zr/Al ratio of 4:1 was selected for measurement and analysis, as shown in Figure 3. EDS element analysis showed that the element composition was slightly different from the original, by about 4.1. The deviation analysis considered element loss during synthesis, and a spectrum analysis was obtained after three repetitions. It can be seen from the figure that Al was uniformly distributed in the material, and the S content was 3.37%.

2.2. Catalytic Activity of Al₂O₃/SO₄²⁻/ZrO₂

To determine the influence of alumina content on the binding state of sulfate radicals on the catalyst, FT-IR characterization was performed on catalysts with different alumina contents. The structure is shown in Figure 4. According to the relevant literature [21,22], the bands at 1120 and 1240 cm⁻¹ were attributable to the asymmetric O=S=O stretching vibration [23,24], and the band at 1640 cm⁻¹ was attributable to the deformation vibration of adsorbed water. The figure shows that as the alumina content increased, the O=S=O stretching vibration band gradually shifted, and the state of the surface catalyst sulfate species was affected by the catalyst content.

To further determine the valence state of the elements in the Al₂O₃/SO₄²⁻/ZrO₂ catalyst, the catalyst was characterized by XPS, as shown in Figure 5. The spectrum indicated the presence of Zr, Al, C, and S. According to Figure 5 and related literature, the S 2p region of the Al₂O₃/SO₄²⁻/ZrO₂ catalyst had only one peak at 169 eV [25,26], which belongs to a positive hexavalent sulfate species, indicating that only the highest valence sulfate was present in the catalyst.

We now know that the Al₂O₃ component in superacid catalysts affects the crystal structure, specific surface properties, and surface sulfur species, and that these properties will inevitably cause changes in the acidic properties and catalytic activity of the catalyst. Therefore, in-situ pyridine infrared technology was used to characterize the influence of alumina addition and calcination on catalyst acid content and type. The infrared spectrum and corresponding acid data are shown in Figure 6 and

Table 2. Acidity of prepared SO₄²⁻/ZrO₂ and Al₂O₃/ SO₄²⁻/ZrO₂ catalysts.

Catalysis	Brønsted Acid Sites (µmol/g)	Lewis Acid Sites (µmol/g)	Total Acids (µmol/g)	Ratio of Brønsted to Lewis
ZrO2	21.77	39.90	61.67	0.55
(4)Zr/Al Uncalcined	12.69	22.27	24.96	0.57
(4)Zr/Al	8.69	5.62	14.31	1.54

. It is evident that the addition of alumina to the catalyst will have a particular impact on the acid content and type. According to related literature, the L acid in the sulfated zirconia catalyst comes from the electron withdrawing effect of the high valence state S⁶⁺ on the catalyst surface on Zr⁴⁺ [27]. As a result, the Zr–O electron cloud shifts and exhibits a specific electron-acquiring ability on the metal Zr. At the same time, the electron-acquiring ability of Zr shifts the hydroxyl group (–OH) of the crystal water on the catalyst, so the crystal water H⁺ displays B acid acidity. The acidity of the pure ZrO₂ catalyst sample is dominated by L acid, the amount of which is approximately twice that of total B acid. Fottinger et al. [28] believed that L acid occupied a dominant position in low-sulfur sulfated zirconia catalysts, which corresponds with the research results. However, this acidic distribution is not conducive to the reaction of brominated alkanes. Several studies have shown that adding an appropriate amount of alumina to superacid catalysts can significantly change the distribution of both L acid and B acid [23,29,30]. Analysis of the composition of the L and B acids in an uncalcined catalyst found it to be similar to pure ZrO₂ with added alumina. It is considered that the alumina and ZrO₂ in the uncalcined catalyst were not tightly combined, and no Zr–O–Al chemical bond was formed. It can be seen from the pyridine adsorption Fourier-transform infrared (Py–IR) that with the addition of alumina, more B acid centers formed, and the B acid content was about 1.5 times the L acid content. It may be that the introduction of alumina led to the sulfate content increase on the catalyst surface, and since sulfate is a prerequisite for super acidic acid formation, the Zr–O–Al bond enhanced the B acid center.

2.3. Optimization of Reaction Parameters

2.3.1. The Effect of Catalyst Preparation Conditions on the Bromopropane Yield

During the catalyst preparation, it was evident that the preparation conditions had an influence on catalytic effect, and consequently the catalyst preparation conditions were optimized. The calcination temperature, amount of Al added, and acid concentration of the prepared catalyst were carefully considered. Firstly, when the calcination temperature was 450–650 °C, the Zr/Al ratio was 2–6, and the acidification concentration was 0.25–2 mol/L. The catalytic performance of the prepared Al₂O₃/SO₄²⁻/ZrO₂ catalyst on the reaction was then assessed. The amount of catalyst was 2.5 wt% of the reaction liquid. As shown in Figure 7, when the reaction conditions were an acid-to-alcohol ratio of 3:1, the reaction temperature and time were 110 °C and 3 h. The higher the calcination temperature, the higher the conversion rate of n-propanol. When the calcination temperature was higher than 600 °C, crystals were formed in the catalyst, and the catalytic performance was highest. When the amount of Zr/Al was increased, the catalyst catalytic performance improved. However, too high an Al content reduced the number of acidic sites in the catalyst, and its performance declined. An increase in acidification concentration obviously increases the catalyst acidity, but an excessively high acidification concentration did not significantly improve the catalyst’s performance. Therefore, after comprehensive screening, a calcination temperature of 600 °C, Zr/Al 4:1 ratio, and acidification concentration of 1 mol/L were determined as appropriate. The catalyst preparation conditions were the most ideal possible in order to optimize the reaction.

2.3.2. The Effect of Reaction Temperature and Reaction Time on Bromopropane Yield

After determining the optimal conditions for preparation of the Al₂O₃/SO₄²⁻/ZrO₂ catalyst, the effects of reaction temperature and time on the production of bromopropane via an n-propanol reaction were discussed. With a catalyst dosage of 2.5 wt% of the reaction liquid, a temperature range of 105–125 °C, a controlled reaction time of 3 h, a ratio of 3:1 HBr to n-propanol, the reaction yield was analyzed. As shown in Figure 8, the preparation of bromopropane is essentially a reversible reaction for preparing halogenated alkanes from primary alcohols. It is a bimolecular affinity substitution reaction, so the reaction temperature must not be too high. When the temperature increased, the reaction yield increased slightly. If the temperature was too high, it would not significantly impact the reaction. From the perspective of saving energy, 110 °C was the optimal temperature for the reaction. Additionally, the influence of reaction time on bromopropane yield was analyzed. At 110 °C, with a ratio of HBr to n-propanol of 3:1, the reaction yield was investigated with reaction times between 1–6 h. As shown in the figure, with a 3 h reaction time, the bromopropane yield reached 96.18%. With longer reaction times, the yield did not increase significantly, but after 6 h the conversion rate decreased slightly. This may be due to the increased time allowing a reverse reaction, which in turn affected the yield. Therefore, from the perspectives of cost and energy economy, 110 °C and 3 h were selected as the best reaction and test conditions for the remaining parameter evaluation process.

2.3.3. The Effect of Substrate Concentration and Catalyst Dosage on Bromopropane Yield

It was theorized that a higher bromopropane yield would be obtained under the conditions of a low acid-to-alcohol ratio and low catalyst dosage. Therefore, the influence of the hydrobromic acid and n-propanol ratio, and of the catalyst dosage on reaction yield, was studied. As shown in Figure 9, as the molar ratio of acid to alcohol continued to increase, the bromopropane yield gradually increased. When the molar ratio of hydrobromic acid to n-propanol was 3:1, the bromopropane yield reached its maximum, but as the molar ratio continued to increase, the yield began to decrease. This may be due to the substantial molar ratio causing a decrease in the concentration of n-propanol in the reaction stage, thereby reducing the bromopropane yield. When the amount of Al₂O₃/SO₄²⁻/ZrO₂ catalyst was 2.5 wt%, the bromopropane yield reached its peak, and when the amount of catalyst was increased further, the yield decreased. This could be due to the excessive catalyst increasing the number of acidic sites in the solution, and n-propanol dehydrating into ether, which would cause side reactions. Therefore, under optimized conditions, when the ratio of hydrobromic acid to n-propanol was 3:1 and the catalyst amount was 2.5 wt%, the bromopropane yield was greatest.

2.4. Catalytic Stability of Al₂O₃/SO₄²⁻/ZrO₂

Reusability is one of the critical characteristics of solid acid catalysts, so the reusability of Al₂O₃/SO₄²⁻/ZrO₂ catalysts was explored. The used catalyst was filtered from the reaction solution, washed with deionized water to remove impurities, dried at 110 °C for 24 h, and then calcined for 3 h at 600 °C. As shown in Figure 10, the bromopropane yield could still reach more than 80% after four cycles. FT-IR characterization of the recycled catalyst was carried out, and the results compared with fresh catalyst, as shown in Figure 4B. It was found that the bands at 1240 and 1120 cm⁻¹, which were attributed to the asymmetric O=S=O of the used catalyst, were weakened, so it was considered that the loss of sulfate radicals leads to a reduction in catalytic performance. The addition of Al₂O₃ dramatically increases the number of acidic sites in the catalyst, so that more acidic sites can be used continuously and simultaneously. This suppresses the decomposition and loss of sulfur-containing species during the reaction process, thereby prolonging the service life of the catalyst. Compared with other types of catalysts and homogeneous catalysts, as shown in Table S1, when Al₂O₃/SO₄²⁻/ZrO₂ is used as the catalyst, the TOF at this time is larger and the reaction yield is better. The catalyst was applied to other reactions for preparing brominated alkanes, as shown in Table S2. It was found that the selected catalyst has a good catalytic effect on the bromination of other short-chain alcohols to prepare brominated alkanes. Experiments have found that the catalyst has the same catalytic effect on hindered alcohols. In the experiment of preparing isobromopropane from isopropanol, the use of a catalyst can make the yield of the reaction reach more than 95%.

3. Materials and Methods

3.1. Materials

Zirconium oxychloride (ZrClO₂·8H₂O) was obtained from Aladdin (Shanghai, China). NH₃·H₂O, aluminum nitrate (Al(NO₃)₃·9H₂O), N-propanol, and concentrated sulfuric acid were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Hydrobromic acid (40%) was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Deionized water was self-made by the laboratory. All purchased chemicals were without further purification.

3.2. Catalyst Preparation

In this paper, the co-precipitation method [31,32,33] was used to prepare the catalyst. A certain proportion of ZrClO₂·8H₂O and Al(NO₃)₃·9H₂O were dissolved in deionized water, and stirring was continued to ensure complete dissolution. Ammonia water was selected as a precipitant and added dropwise to the solution to keep the pH of the slurry at about 8–10; the solution was then left to stand for 24 h. The obtained solid was washed with deionized water until there was no Cl⁻ (AgNO₃ aqueous solution detection), and dried in an oven at 110 °C for 24 h. The solid was impregnated with a certain concentration of H₂SO₄ solution for 6 h and then dried in an oven at 110 °C for 24 h. It was then calcined in a muffle furnace for 3 h to obtain the desired catalyst.

3.3. Catalyst Characterization

The XRD spectrum of the sample was measured with an X-ray diffractometer (XRD, Rigaku Ultima IV, Rigaku, Japan), using Cu-Kα radiation (k = 0.154 nm, 40 kV, 40 mA); the scanning rate was 10°/min, and the scanning range was 5–80°.

The XPS spectrum of the sample was measured by Thermo Flyer 250 XI (ThermoFisher K-Alpha, Thermo Fisher Scientific, Shanghai, China) with an energy range of 100–4000 eV. The vacuum degree was 8 × 10⁻⁸, and the incident angle was 90°.

The 3H-2000PS1 static volume (Beishide Instrument Technology (Beijing) Co., Ltd., Beijing, China) method was used to analyze the specific surface area and pore size. All samples were degassed in a vacuum at 120 °C for 10 h. The specific surface area was measured by the multipoint Brunauer–Emmett–Teller (BET) method, and the pore size was calculated by the Barrett–Joyner–Halenda (BJH) method.

The FT-IR spectrum of the sample was analyzed on a Nicolet 5700 spectrometer (Thermo Fisher, NYC, Waltham, MA, USA), and the spectral range was from 4000 cm⁻¹ to 400 cm⁻¹. The materials needed to be pretreated with potassium bromide and uniformly ground and compressed.

Pyridine in-situ infrared (Py-IR) was used to detect the Lewis and Brønsted acid sites of the catalyst. The catalyst was pretreated at a pressure of 10⁻⁵ Pa and 380 °C for 90 min, then reduced to 80 °C for pyridine adsorption for 30 min, and finally scanned with an infrared spectrometer at 200 °C [34].

In order to observe the microscopic morphology and element distribution of the catalytic material, a field emission scanning electron microscope (SEM, Inspect F50, FEI, Hillsboro, OR, USA) was used.

3.4. Catalytic Performance Research

A certain proportion of hydrobromic acid (HBr, 40%) and n-propanol were added to a round bottom flask. To this, 2 wt% of Al₂O₃/SO₄²⁻/ZrO₂ catalyst was added, and the solution was heated and stirred in an oil bath with adjustments to the temperature of the oil bath. A thorn-type rectification column was connected to the flask, and the condensate was collected above the rectification column. After stopping heating at a predefined time, the reaction liquid and condensate were collected for further analysis.

3.5. Product Analysis

The quantitative analysis of bromopropane produced by the reaction of hydrobromic acid and n-propanol was determined by high-performance gas chromatography (GC9160, Shanghai Ouhua) and nuclear magnetism. DMSO is used as a solvent for nuclear magnetic determination. The conversion rate and selectivity of n-propanol are calculated by the following formula:

$$\begin{gathered} Conversion=\frac{initial molar amount of n-propanol-final molar amount of n-propanol}{initial molar amount of n-propanol}\times 100\% \\ Selectivity=\frac{final molar amount of bromopropane}{initial molar amount of n-propanol}\times 100\% \end{gathered}$$

(1)

4. Conclusions

In conclusion, the Al₂O₃/SO₄²⁻/ZrO₂ catalyst was successfully prepared by the co-precipitation method. When the calcination temperature was 600 °C, the ratio of Zr/Al was 4:1, and the acidified sulfuric acid concentration was 1 mol/L, the catalyst at this time had the best catalytic performance for the bromination of n-propanol to bromopropane. Under optimal conditions, the ratio of the amount of hydrobromic acid and alcohol was 3:1, and the bromopropane output could reach 96.18% after reacting at 110 °C for 3 h. In a homogeneous reaction, when an ionic liquid and concentrated sulfuric acid are used as catalysts, the reaction temperature is relatively high. At the same time, analysis shows that no by-products are formed, which greatly improves the yield of bromopropane. Catalytic distillation was used to prepare bromopropane, and the product was separated and purified during the reaction, which reduced energy consumption. In addition, the sulfated zirconia catalyst with Al₂O₃ added could still achieve a yield of more than 80% bromopropane after being recycled 4 times; thus, adding Al₂O₃ reduced the deactivation rate of pure sulfated zirconia to a certain extent and improved its repetitive use. It was proved that it is feasible to modify sulfated zirconia with Al₂O₃.