Preparation method and application of a p-toluenesulfonic acid-based low-halogen deep eutectic solvent

Abstract

The application discloses a preparation method of a p-toluenesulfonic acid-based low-halogen deep eutectic solvent, and comprises the following steps: under constant temperature conditions, mixing a hydrogen bond donor and a hydrogen bond acceptor, and removing halogen by vacuumizing and nitrogen blowing, so as to obtain the p-toluenesulfonic acid-based low-halogen deep eutectic solvent. The application provides a simple, efficient, low-cost and acid-controllable preparation method of the p-toluenesulfonic acid-based low-halogen deep eutectic solvent, which is used in alkenyl alkoxy carbonylation reaction, realizes automatic separation of a catalyst after an alkenyl alkoxy carbonylation system reaction, retains high activity of a homogeneous reaction in the homogeneous reaction, is easy to separate the catalyst, reduces the cost of catalyst separation, and improves the activity of the catalyst.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of olefin alkoxy carbonylation catalysts, and particularly relates to a preparation method and application of a p-toluenesulfonic acid-based low-halogen deep eutectic solvent. BACKGROUND

[0002] Ester compounds are widely used in the industries of perfumes, fragrances and organic synthesis due to their unique fragrance, solubility and as synthetic intermediates. Among them, methyl propionate (Methyl propionate, abbreviated as MP) is of great concern because it can be used as a precursor for the two-step synthesis of methyl methacrylate (Methyl methacrylate, abbreviated as MMA) in the lucite alpha process. Methyl methacrylate can be used to synthesize adhesives and acrylic fibers, and is particularly concerned as a precursor for the synthesis of polymethyl methacrylate (polymethyl methacrylate, abbreviated as PMMA), commonly known as organic glass or acrylic. The commonly used method for synthesizing methyl methacrylate is the acetone cyanhydrin method, which has been industrialized since 1937, accounting for about two-thirds of the installed capacity of methyl methacrylate production. However, the acetone cyanhydrin method requires the use of highly toxic hydrogen cyanide and concentrated sulfuric acid, which poses a great threat to equipment and the environment, and the production of 1.2 tons of ammonium bisulfate byproduct is required for every ton of methyl methacrylate produced. For many years, scientists have made a lot of research to avoid the treatment of byproducts and the use of highly toxic hydrogen cyanide, aiming to develop new and cost-effective process technologies. Now these research efforts have borne fruit, and many alternative routes have been commercialized, and several methods are close to commercialization. These new routes include the use of new raw materials such as isobutylene, ethylene, and even propyne, as well as the development of technologies to recover hydrogen cyanide or ammonium bisulfate. The lucite alpha process is of great concern because it only requires two steps to synthesize the product methyl methacrylate. The lucite alpha process can utilize low-cost coal chemical products such as ethylene, methanol, carbon monoxide and formaldehyde to synthesize methyl methacrylate. In the first step, ethylene reacts with carbon monoxide and methanol under mild conditions in the presence of methanesulfonic acid or p-toluenesulfonic acid and a palladium-1,2-bis(di-tert-butylphosphinomethyl) benzene (1,2-Bis(di-tert-butylphosphinomethyl)benzene, abbreviated as 1,2-DTBPMB) complex to produce methyl propionate with very high conversion and selectivity; in the second step, methyl propionate undergoes aldol condensation in the presence of Cs / SiO2 to produce the product methyl methacrylate. This route has the advantages of low cost and easy availability of raw materials, and the first step is atomically economic, and the only byproduct of the second step is water, which has cost and environmental advantages. Compared with processes that use acetone or isobutylene as raw materials, the lucite alpha process has better raw material adaptability, less corrosion to equipment, fewer byproducts and lower geographical restrictions.

[0003] Currently, catalysts commonly used in the synthesis of methyl propionate via the methoxycarbonylation of ethylene include complexes formed from palladium acetate and 1,2-bis(di-tert-butylphosphine)benzene or triphenylphosphine, as well as strong acids with weak coordination abilities such as p-toluenesulfonic acid or methanesulfonic acid. The ligands stabilize the catalytically active sites to prevent the formation of inactive palladium black precipitate and enhance catalyst activity by regulating steric hindrance and charge density. The strong acids primarily generate the important intermediate Pd-H species for this reaction. Because the noble metal palladium is required, along with complex organic ligands, traditional distillation separation of the products can lead to rapid ligand decomposition due to thermal stress, resulting in catalyst deactivation and the formation of inactive palladium black precipitate. Therefore, the cost of ligands is often even higher than that of the noble metal, making catalyst recovery a critical problem to be solved for this homogeneous reaction. Common methods for catalyst recovery include supporting catalysts with resins, silica, porous organic ligand polymers, and ionic liquids. However, these methods often face challenges such as high catalyst leaching rates, the ability to recover only precious metals, and the retention of some catalyst residues in the product due to acidity or ligands. Furthermore, the synthesis of porous organic ligand polymers requires customized monomers and involves complex steps, while ionic liquid synthesis is also complex and costly. Compared to traditional recovery methods, eutectic solvents involve fewer synthesis steps, use low-cost chemicals as raw materials with low toxicity, and allow for flexible acidity control, offering significant advantages over traditional catalyst recovery methods.

[0004] Patent application WO0110551A1 discloses the deactivation of catalysts over time and uses polyacrylic acid as a polymer dispersant in the alkoxycarbonylation of ethylene to stabilize the catalyst. Although this method does not generate palladium black precipitate, it suffers from polymer impurities in the product. Patent WO2007020379A1 finds that an excess of ligands over metals is beneficial to the system because the ligands can act as a base to buffer acid levels and prevent substrate degradation, and proposes a method to improve reaction activity. Patent US4622423A explores Rh-catalyzed alkoxycarbonylation. Compared to Pd-catalyzed alkoxycarbonylation, Rh-catalyzed alkoxycarbonylation requires more stringent conditions and has poorer selectivity. Patent application CN104011007A describes a method for synthesizing methyl propionate by methoxycarbonylation of ethylene with carbon monoxide and methanol using a supported ionic liquid, achieving continuous fixed-bed production of ethylene methoxycarbonylation. Patent WO2011026860A1 describes a palladium-catalyzed ethylene methoxycarbonylation system comprising zwitterionic and / or acid-functionalized ionic liquids, and explores the effects of a series of ions on the reaction.

[0005] Due to mass transfer limitations, supported catalysts experience a significant loss of catalytic activity compared to homogeneous catalytic systems. While ionic liquids can achieve automated catalyst separation while retaining the high activity of homogeneous catalysis, their application is limited by complex and costly synthesis methods. Eutectic solvents, on the other hand, have become a promising alternative to ionic liquids due to their simple synthesis methods and controllable acidity. Currently used strongly acidic eutectic solvents all contain halogens, and high concentrations of halogens can corrode equipment and poison palladium catalysts used in alkoxycarbonylation reactions, leading to rapid catalyst deactivation. To achieve simple catalyst separation while retaining the high activity of homogeneous catalysis, it is necessary to develop a highly stable, low-halogen-content eutectic solvent to facilitate the separation of homogeneous and heterogeneous catalysis in the catalytic system, thereby aiding in catalyst recovery. Summary of the Invention

[0006] The first objective of this invention is to provide a method for preparing a p-toluenesulfonic acid-based low-halogen deep eutectic solvent.

[0007] A second objective of this invention is to provide an application of the p-toluenesulfonic acid-based low-halogen deep eutectic solvent prepared by the method described above in the alkoxycarbonylation reaction of olefins.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] The first aspect of the present invention provides a method for preparing a p-toluenesulfonic acid-based low-halogen deep eutectic solvent, comprising the following steps: mixing a hydrogen bond donor and a hydrogen bond acceptor under constant temperature conditions, removing halogens by vacuuming and nitrogen purging, and obtaining the p-toluenesulfonic acid-based low-halogen deep eutectic solvent.

[0010] The p-toluenesulfonic acid-based low-halogen deep eutectic solvent, when used in the alkoxycarbonylation reaction of olefins, can achieve automatic catalyst separation and improve catalyst activity.

[0011] The preparation method of the p-toluenesulfonic acid-based low-halogen deep eutectic solvent includes the following steps:

[0012] Under constant temperature conditions of 40–100°C, hydrogen bond donors and hydrogen bond acceptors with a molar ratio of (0.5–5):1 were mixed, and a vacuum was drawn, maintaining the vacuum level between 0 and -101.3 kPa. After 1 hour of vacuuming, nitrogen gas was purged simultaneously with the vacuuming process, maintaining the gauge pressure between -100 and 101.3 kPa. The above vacuuming and nitrogen purging were repeated, with nitrogen purging once every 1 hour of vacuuming. The total vacuuming time was 1–24 hours, and nitrogen purging was performed one to twenty-four times. After the reaction was completed, the p-toluenesulfonic acid-based low-halogen deep eutectic solvent was obtained.

[0013] The nitrogen purging time is 5 to 15 minutes.

[0014] The hydrogen bond donors are selected from p-toluenesulfonic acid and p-toluenesulfonic acid monohydrate.

[0015] The hydrogen bond acceptor is selected from choline chloride, acetic choline, benzyltriphenylphosphine chloride, 1-butyl-3-methylimidazolium chloride, tetrabutylammonium chloride, tetramethylammonium chloride, methyltriphenylphosphine chloride, and allyltriphenylphosphine chloride.

[0016] A third aspect of the present invention provides the application of the p-toluenesulfonic acid-based low-halogen deep eutectic solvent prepared by the method described above in the alkoxycarbonylation reaction of olefins.

[0017] The application includes the following steps:

[0018] In a high-pressure reactor, a p-toluenesulfonic acid-based low-halogen deep eutectic solvent and methanol were mixed in a mass ratio of (0.1–0.6):1. Palladium acetate and 1,2-bis(di-tert-butylphosphine)benzene were added. The molar ratio of palladium acetate to ethylene was (0.8–0.99):1, and the molar ratio of 1,2-bis(di-tert-butylphosphine)styrene was (1–10):1. The high-pressure reactor was sealed, and nitrogen gas was introduced to a pressure of 0.5–4.0 MPa. After mixing for 5–30 minutes, the gas was released. This process was repeated twice to purge air from the high-pressure reactor. The temperature was then increased to 60–100 °C, and a mixture of ethylene and a... A carbon monoxide mixture was introduced into the autoclave at a pressure of 0.5–4.0 MPa, and timing began. Timing ended when the mixture was completely reacted in the autoclave, i.e., when the ethylene conversion rate was 100%, which was recorded as cycle 1. After cycle 1, a mixture of ethylene and carbon monoxide at a molar ratio of (0.1–10):1 at 0.5–4.0 MPa was introduced into the autoclave, and timing began simultaneously. Timing ended when the mixture in the autoclave was completely consumed, which was recorded as cycle 2. The same steps were repeated until the reaction was completed. The heating was turned off and the reaction was quenched by rapid cooling. After the autoclave temperature was cooled to room temperature, the remaining gas in the autoclave was discharged. The autoclave body was opened to collect the product and analyzed by gas chromatography.

[0019] By adopting the above technical solution, the present invention has the following advantages and beneficial effects:

[0020] This invention provides a simple, low-cost, and acid-controllable method for preparing a low-halogen deep eutectic solvent for p-toluenesulfonic acid groups, which is used in the alkoxycarbonylation reaction of olefins. This method enables the automatic separation of the catalyst after the olefin alkoxycarbonylation system reaction, retains the high activity of the homogeneous reaction in the homogeneous reaction, facilitates catalyst separation, reduces the cost of catalyst separation, and improves the activity of the catalyst.

[0021] The advantages of the p-toluenesulfonic acid-based low-halogen deep eutectic solvent prepared by this invention in the alkoxycarbonylation reaction of olefins are as follows: 1. The p-toluenesulfonic acid-based low-halogen deep eutectic solvent is simple to prepare and has excellent results, requiring only simple constant-temperature water bath vacuum distillation and intermittent nitrogen purging. Table 2 lists the chloride ion content in the untreated and treated deep eutectic solvents as measured by high-performance ion chromatography. The molar ratio of hydrogen bond donors to hydrogen bond acceptors in the deep eutectic solvents prepared in Comparative Example 2 and Example 3 is 1.25. Example 3 underwent the above treatment, while Comparative Example 2 was only stirred and mixed under constant-temperature water bath conditions. The chloride ion concentration in Comparative Example 2 is 67976 μg / g, while the chloride ion concentration in Example 3 is 356 μg / g, representing a 191-fold decrease in chloride ion concentration after treatment. The molar ratio of hydrogen bond donor to hydrogen bond acceptor in the deep eutectic solvents prepared in Comparative Example 3 and Example 7 was 2.00. Example 7 underwent the above treatment, while Comparative Example 3 was only stirred and mixed under constant temperature water bath conditions. The chloride ion concentration in Comparative Example 3 was 56789 μg / g, while the chloride ion concentration in Example 7 was 9 μg / g, a decrease of 6310 times after treatment. This indicates that the above treatment can effectively remove chloride ions from the deep eutectic solvent. 2. Acidity is controllable. By changing the molar ratio between the hydrogen bond donor p-toluenesulfonic acid and the hydrogen bond acceptor, the acidity of the p-toluenesulfonic acid-based low-halogen deep eutectic solvent can be controlled. 3. Improved catalytic activity and reduced time required to complete catalysis. Compared with Comparative Example 2, the time required to complete the first catalytic cycle in Example 3 after halogen removal was reduced from 364 min in Comparative Example 2 to 3 min, improving the catalytic activity. 4. The deep eutectic solvent has excellent stability. Figure 2 The low-halogen eutectic solvent after halogen removal shown in Example 8 can be used for 23 cycles (recovered every 7 cycles) without significant activity reduction, and Figure 3 The thermogravimetric analysis (TGA) spectrum of the p-toluenesulfonic acid-based low-halogen eutectic solvent synthesized in Example 3 shows that its decomposition temperature is above 250°C, indicating its high stability. 5. Automatic separation of catalysts. Figure 1The table shows the state of the catalytic system of Example 8 before the reaction and after 7 catalytic cycles. After the reaction, the system changed from a single phase before the reaction to a nearly colorless upper methyl propionate product phase and a darker lower eutectic solvent phase containing ligands and palladium acetate catalyst. Table 3 shows the palladium and phosphorus content in the upper methyl propionate phase and the lower eutectic solvent phase formed after 7 catalytic cycles in Example 8, as measured by ICP-OES. The palladium concentration in the upper methyl propionate phase was 16 ppm, and the phosphorus concentration was 46 ppm. The palladium concentration in the lower eutectic solvent phase was 490 ppm, and the phosphorus concentration was 1100 ppm. This indicates that palladium is mainly enriched in the lower eutectic solvent phase, demonstrating that the addition of the eutectic solvent can effectively achieve catalyst separation. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the reaction system in Example 8 before the reaction (left) and after 7 cycles (right).

[0023] Figure 2 This is a schematic diagram of the catalyst recovery experiment in Example 8, where the catalyst is recovered once every 7 cycles.

[0024] Figure 3 This is a schematic diagram of the thermogravimetric analysis of the p-toluenesulfonic acid-based low-halogen deep eutectic solvent synthesized in Example 3. Detailed Implementation

[0025] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0026] Example 1

[0027] A method for preparing a p-toluenesulfonic acid-based low-halogen deep eutectic solvent includes the following steps:

[0028] Choline chloride (0.0358 mol, 5 g) and p-toluenesulfonic acid monohydrate (0.0358 mol, 6.81 g) in a 1:1 molar ratio were mixed in a three-necked flask. The mixture was then evacuated under vacuum at a constant temperature of -100 kPa in a 90°C water bath. After evacuation for 1 hour, nitrogen gas was purged for 8 minutes while evacuating, with the gauge pressure maintained at -50 kPa. This evacuation and nitrogen purging process was repeated, with nitrogen purging for 8 minutes after each 1 hour of evacuation. The total evacuation time was 9 hours, and nitrogen purging was performed nine times. After the reaction was completed, a white solid, p-toluenesulfonic acid-based low-halogen deep eutectic solvent (No. 1) was obtained.

[0029] The application of p-toluenesulfonic acid-based low-halogen eutectic solvent No. 1 in the methoxycarbonylation of ethylene with carbon monoxide and methanol to synthesize methyl propionate includes the following steps:

[0030] Methanol (4.75 g), palladium acetate (0.0143 mmol, 3.2 mg), 1,2-bis(di-tert-butylphosphine)benzene (0.0855 mmol, 33.7 mg), and p-toluenesulfonic acid-based low-halogen deep eutectic solvent (35 wt%) (1.66 g) were added to a 50 ml Hastelloy autoclave. The autoclave was sealed and nitrogen gas was introduced to 0.5 MPa. After mixing for 15 min under stirring, the gas was released. This process was repeated twice to remove air from the autoclave. The autoclave was heated to 80 °C according to its set temperature program. Ethylene (0.0146 mol, 0.409 g) and carbon monoxide were introduced in a 1:1 molar ratio. After the mixed gas (0.0146 mol, 0.409 g) was heated to 2.0 MPa, timing began and ended when the mixed gas in the autoclave reacted completely, i.e., the ethylene conversion rate reached 100%, which is recorded as cycle 1. After cycle 1, a 2.0 MPa mixed gas of ethylene and carbon monoxide with a molar ratio of 1:1 was introduced into the autoclave, and timing began again. Timing ended when the mixed gas in the autoclave was consumed, which is recorded as cycle 2. The same steps were repeated until cycle 4. The heating was turned off and the autoclave was placed in ice water for rapid cooling to quench the reaction. After the autoclave temperature was cooled to room temperature, the remaining gas in the autoclave was discharged, the autoclave body was opened, the product was collected, and quantitative analysis was performed by gas chromatography. The results are listed in Table 1. The time for cycle 1 was 172 min, and the selectivity for methyl propionate was greater than 99%.

[0031] Example 2

[0032] A method for preparing a p-toluenesulfonic acid-based low-halogen deep eutectic solvent includes the following steps:

[0033] Choline chloride (0.0358 mol, 5 g) and p-toluenesulfonic acid monohydrate (0.0412 mol, 7.83 g) in a molar ratio of 1:1.15 were mixed in a three-necked flask. The mixture was then evacuated under vacuum at a constant temperature of -100 kPa in a 90°C water bath. After evacuation for 1 hour, nitrogen gas was purged for 5 minutes while evacuating, with the gauge pressure maintained at -50 kPa. This evacuation and nitrogen purging process was repeated, with nitrogen purging for 5 minutes after each 1 hour of evacuation. The total evacuation time was 9 hours, and nitrogen purging was performed nine times. After the reaction was completed, a transparent liquid deep eutectic solvent was obtained. After being left at room temperature for a period of time, it turned into a white opaque solid. This solid was p-toluenesulfonic acid-based low-halogen deep eutectic solvent No. 2.

[0034] The application of p-toluenesulfonic acid-based low-halogen deep eutectic solvent No. 2 in the methoxycarbonylation of ethylene with carbon monoxide and methanol to synthesize methyl propionate includes the following steps:

[0035] Methanol (4.75 g), palladium acetate (0.0143 mmol, 3.2 mg), 1,2-bis(di-tert-butylphosphine)benzene (0.0855 mmol, 33.7 mg), and p-toluenesulfonic acid-based low-halogen deep eutectic solvent (35 wt%) (1.66 g) were added to a 50 ml Hastelloy autoclave. The autoclave was sealed and nitrogen gas was introduced to 0.5 MPa. After mixing for 15 min under stirring, the gas was released. This process was repeated twice to remove air from the autoclave. The autoclave was heated to 80 °C according to its set temperature program. Ethylene (0.0146 mol, 0.409 g) and carbon monoxide were introduced in a 1:1 molar ratio. After the mixed gas (0.0146 mol, 0.409 g) was heated to 2.0 MPa, timing began and ended when the mixed gas in the autoclave reacted completely, i.e., the ethylene conversion rate reached 100%, which is recorded as cycle 1. After cycle 1, a 2.0 MPa mixed gas of ethylene and carbon monoxide with a molar ratio of 1:1 was introduced into the autoclave, and timing began again. Timing ended when the mixed gas in the autoclave was consumed, which is recorded as cycle 2. The same steps were repeated until cycle 4. The heating was turned off and the autoclave was placed in ice water for rapid cooling to quench the reaction. After the autoclave temperature was cooled to room temperature, the remaining gas in the autoclave was discharged, the autoclave body was opened, the product was collected, and quantitative analysis was performed by gas chromatography. The results are listed in Table 1. It was found that cycle 1 took 32 min and the selectivity of methyl propionate was greater than 99%.

[0036] Example 3

[0037] A method for preparing a p-toluenesulfonic acid-based low-halogen deep eutectic solvent includes the following steps:

[0038] Choline chloride (0.0358 mol, 5 g) and p-toluenesulfonic acid monohydrate (0.0448 mol, 8.51 g) in a molar ratio of 1:1.25 were mixed in a three-necked flask. The mixture was then subjected to vacuum in a 90°C water bath, maintaining a vacuum of -100 kPa. After 1 hour of vacuuming, nitrogen gas was purged for 5 minutes simultaneously, with the gauge pressure maintained at -50 kPa. This vacuuming and nitrogen purging process was repeated, with nitrogen purging for 5 minutes after each 1 hour of vacuuming, for a total of 9 hours and nine nitrogen purging cycles. After the reaction, a transparent liquid eutectic solvent was obtained, which turned into a white opaque solid after being left at room temperature for a period of time. This solid was identified as p-toluenesulfonic acid-based low-halogen eutectic solvent No. 3. Thermogravimetric data for this sample are shown below. Figure 3 , Figure 3This is a schematic thermogravimetric analysis (TGA) image of the p-toluenesulfonic acid-based low-halogen deep eutectic solvent synthesized in Example 3. The TGA image shows that the decomposition temperature of this sample is greater than 250℃, indicating that the sample has good thermal stability. The chloride ion content of the sample is shown in Table 2. Compared with the chloride ion concentration of 67976 μg / g in Comparative Example 2, the chloride ion concentration after auxiliary vacuuming and intermittent nitrogen purging was 356 μg / g, a decrease of 191 times, indicating that the above method can effectively remove chloride ions from the deep eutectic solvent.

[0039] The application of p-toluenesulfonic acid-based low-halogen deep eutectic solvent No. 3 in the methoxycarbonylation of ethylene with carbon monoxide and methanol to synthesize methyl propionate includes the following steps:

[0040] Methanol (4.75 g), palladium acetate (0.0143 mmol, 3.2 mg), 1,2-bis(di-tert-butylphosphine)benzene (0.0855 mmol, 33.7 mg), and p-toluenesulfonic acid-based low-halogen deep eutectic solvent (35 wt%) (1.66 g) were added to a 50 ml Hastelloy autoclave. The autoclave was sealed and nitrogen gas was introduced to 0.5 MPa. After mixing for 15 min under stirring, the gas was released. This process was repeated twice to purge air from the autoclave. The autoclave was heated to 80 °C according to its set temperature program. Ethylene (0.0146 mol, 0.409 g) and monoxide were then introduced in a 1:1 molar ratio. A carbon-containing mixed gas (0.0146 mol, 0.409 g) was introduced to 2.0 MPa, and timing was started. Timing ended when the mixed gas in the autoclave reacted completely, i.e., the ethylene conversion rate reached 100%, and this was recorded as cycle 1. After cycle 1, a 2.0 MPa mixture of ethylene and carbon monoxide with a molar ratio of 1:1 was introduced into the autoclave, and timing was started simultaneously. Timing ended when the mixed gas in the autoclave was consumed, and this was recorded as cycle 2. The same steps were repeated until cycle 4. Heating was turned off, and the autoclave was rapidly cooled in ice water to quench the reaction. After the autoclave temperature cooled to room temperature, the remaining gas in the autoclave was discharged. The autoclave was opened, the product was collected, and quantitative analysis was performed by gas chromatography. The results are listed in Table 1. Cycle 1 took 3 min, and the selectivity for methyl propionate was greater than 99%. Compared with Comparative Example 2, which took 364 min to complete cycle 1, Example 3 completed the reaction in less time under the same reaction conditions, indicating that the catalyst activity was significantly improved after removing chloride ions.

[0041] Example 4

[0042] A method for preparing a p-toluenesulfonic acid-based low-halogen deep eutectic solvent includes the following steps:

[0043] Choline chloride (0.0358 mol, 5 g) and p-toluenesulfonic acid monohydrate (0.0448 mol, 8.51 g) in a molar ratio of 1:1.25 were mixed in a three-necked flask. The mixture was then evacuated under vacuum at a constant temperature of -100 kPa in a 60°C water bath. After evacuation for 1 hour, nitrogen gas was purged for 5 minutes while evacuating, with the gauge pressure maintained at -50 kPa. This evacuation and nitrogen purging process was repeated, with nitrogen purging for 5 minutes after each 1 hour of evacuation. The total evacuation time was 9 hours, and nitrogen purging was performed nine times. After the reaction was completed, a transparent liquid deep eutectic solvent was obtained. After being left at room temperature for a period of time, it turned into a white opaque solid. This solid was p-toluenesulfonic acid-based low-halogen deep eutectic solvent No. 4.

[0044] The application of p-toluenesulfonic acid-based low-halogen deep eutectic solvent No. 4 in the methoxycarbonylation of ethylene with carbon monoxide and methanol to synthesize methyl propionate includes the following steps:

[0045] Methanol (4.75 g), palladium acetate (0.0143 mmol, 3.2 mg), 1,2-bis(di-tert-butylphosphine)benzene (0.0855 mmol, 33.7 mg), and p-toluenesulfonic acid-based low-halogen deep eutectic solvent (35 wt%) (1.66 g) were added to a 50 ml Hastelloy autoclave. The autoclave was sealed and nitrogen gas was introduced to 0.5 MPa. After mixing for 15 min under stirring, the gas was released. This process was repeated twice to remove air from the autoclave. The autoclave was heated to 80 °C according to its set temperature program. Ethylene (0.0146 mol, 0.409 g) and monoxide were then introduced in a 1:1 molar ratio. A carbon-containing gas mixture (0.0146 mol, 0.409 g) was introduced to 2.0 MPa, and timing was started. Timing ended when the gas mixture in the autoclave reacted completely, i.e., when the ethylene conversion reached 100%, marking this as cycle 1. After cycle 1, a 2.0 MPa mixture of ethylene and carbon monoxide with a molar ratio of 1:1 was introduced into the autoclave, and timing was started simultaneously. Timing ended when the gas mixture in the autoclave was completely consumed, marking this as cycle 2. This process was repeated until cycle 4. Heating was then turned off, and the autoclave was rapidly cooled in ice water to quench the reaction. After the autoclave temperature cooled to room temperature, the remaining gas in the autoclave was discharged. The autoclave was opened, the product was collected, and quantitative analysis was performed by gas chromatography. The results are shown in Table 1. Cycle 1 took 10 min, and the selectivity for methyl propionate was greater than 99%.

[0046] Example 5

[0047] A method for preparing a p-toluenesulfonic acid-based low-halogen deep eutectic solvent includes the following steps:

[0048] Methyltriphenylphosphine chloride (0.0320 mol, 10 g) and p-toluenesulfonic acid monohydrate (0.040 mol, 7.61 g) in a molar ratio of 1:1.25 were mixed in a three-necked flask. The mixture was then evacuated under vacuum at a constant temperature of -100 kPa in a 90°C water bath. After evacuation for 1 hour, nitrogen gas was purged for 5 minutes while evacuating, with the gauge pressure maintained at -50 kPa. This evacuation and nitrogen purging process was repeated, with nitrogen purging for 5 minutes after each 1 hour of evacuation. The total evacuation time was 9 hours, and nitrogen purging was performed nine times. After the reaction was completed, a viscous liquid deep eutectic solvent was obtained. The viscosity increased after being left at room temperature for a period of time. This liquid was identified as a p-toluenesulfonic acid-based low-halogen deep eutectic solvent.

[0049] The application of p-toluenesulfonic acid-based low-halogen deep eutectic solvent No. 5 in the methoxycarbonylation of ethylene with carbon monoxide and methanol to synthesize methyl propionate includes the following steps:

[0050] Methanol (4.75 g), palladium acetate (0.0143 mmol, 3.2 mg), 1,2-bis(di-tert-butylphosphine)benzene (0.0855 mmol, 33.7 mg), and p-toluenesulfonic acid-based low-halogen deep eutectic solvent (1.66 g) were added to a 50 ml Hastelloy autoclave. The autoclave was sealed and nitrogen gas was introduced to 0.5 MPa. After mixing for 15 min under stirring, the gas was released. This process was repeated twice to purge air from the autoclave. The autoclave was heated to 80 °C according to its set temperature program, and a mixture of ethylene (0.0146 mol, 0.409 g) and carbon monoxide in a 1:1 molar ratio was introduced. The mixture (0.0146 mol, 0.409 g) was heated to 2.0 MPa, and timing was started. Timing ended when the mixed gas in the autoclave reacted completely, i.e., the ethylene conversion rate reached 100%, which was recorded as cycle 1. After cycle 1, a 1:1 molar ratio of ethylene to carbon monoxide mixed gas at 2.0 MPa was introduced into the autoclave, and timing was started simultaneously. Timing ended when the mixed gas in the autoclave was consumed, which was recorded as cycle 2. The same steps were repeated until cycle 4. Heating was turned off, and the autoclave was rapidly cooled in ice water to quench the reaction. After the autoclave temperature cooled to room temperature, the remaining gas in the autoclave was discharged. The product was collected by gas chromatography and quantitative analysis was performed. The results are listed in Table 1. Cycle 1 took 8 min, and the selectivity for methyl propionate was greater than 99%.

[0051] Example 6

[0052] A method for preparing a p-toluenesulfonic acid-based low-halogen deep eutectic solvent includes the following steps:

[0053] Choline chloride (0.0358 mol, 5 g) and p-toluenesulfonic acid monohydrate (0.0537 mol, 10.22 g) in a molar ratio of 1:1.50 were mixed in a three-necked flask. The mixture was then evacuated under vacuum at a constant temperature of -100 kPa in a 90°C water bath. After evacuation for 1 hour, nitrogen gas was purged for 5 minutes while evacuating, with the gauge pressure maintained at -50 kPa. This evacuation and nitrogen purging process was repeated, with nitrogen purging for 5 minutes after each 1 hour of evacuation. The total evacuation time was 9 hours, and nitrogen purging was performed nine times. After the reaction was completed, a transparent liquid deep eutectic solvent was obtained. This liquid remained transparent after being left at room temperature for a period of time. This liquid was identified as a p-toluenesulfonic acid-based low-halogen deep eutectic solvent.

[0054] The application of p-toluenesulfonic acid-based low-halogen deep eutectic solvent No. 6 in the methoxycarbonylation of ethylene with carbon monoxide and methanol to synthesize methyl propionate includes the following steps:

[0055] Methanol (4.75 g), palladium acetate (0.0143 mmol, 3.2 mg), 1,2-bis(di-tert-butylphosphine)benzene (0.0855 mmol, 33.7 mg), and p-toluenesulfonic acid-based low-halogen deep eutectic solvent (35 wt%) (1.66 g) were added to a 50 ml Hastelloy autoclave. The autoclave was sealed and nitrogen gas was introduced to 0.5 MPa. After mixing for 15 min under stirring, the gas was released. This process was repeated twice to purge air from the autoclave. The autoclave was heated to 80 °C according to its set temperature program. Ethylene (0.0146 mol, 0.409 g) and monoxide were then introduced in a 1:1 molar ratio. A carbon-containing mixed gas (0.0146 mol, 0.409 g) was introduced to 2.0 MPa, and timing was started. Timing ended when the mixed gas in the autoclave reacted completely, i.e., the ethylene conversion rate reached 100%, which was recorded as cycle 1. After cycle 1, a 2.0 MPa mixture of ethylene and carbon monoxide with a molar ratio of 1:1 was introduced into the autoclave, and timing was started simultaneously. Timing ended when the mixed gas in the autoclave was consumed, which was recorded as cycle 2. The same steps were repeated until cycle 4. Heating was turned off, and the autoclave was rapidly cooled in ice water to quench the reaction. After the autoclave temperature cooled to room temperature, the remaining gas in the autoclave was discharged. The autoclave body was opened, the product was collected, and quantitative analysis was performed by gas chromatography. The results are listed in Table 1. Cycle 1 took 6 min, and the selectivity for methyl propionate was greater than 99%.

[0056] Example 7

[0057] A method for preparing a p-toluenesulfonic acid-based low-halogen deep eutectic solvent includes the following steps:

[0058] Choline chloride (0.0358 mol, 5 g) and p-toluenesulfonic acid monohydrate (0.0716 mol, 13.62 g) in a molar ratio of 1:2 were mixed in a three-necked flask. The mixture was then evacuated under vacuum at a constant temperature of -100 kPa in a 90°C water bath. After evacuation for 1 hour, nitrogen gas was purged for 5 minutes while evacuating, with the gauge pressure maintained at -50 kPa. This evacuation and nitrogen purging process was repeated, with nitrogen purging for 5 minutes after each 1 hour of evacuation. The total evacuation time was 9 hours, and nitrogen purging was performed nine times. After the reaction was completed, a transparent liquid deep eutectic solvent was obtained. This liquid remained transparent after being left at room temperature for a period of time. This liquid was identified as a p-toluenesulfonic acid-based low-halogen deep eutectic solvent. The chloride ion content of the samples is shown in Table 2. Compared with the chloride ion concentration of 56789 μg / g in Comparative Example 3, the chloride ion concentration in this example, after auxiliary vacuuming and intermittent nitrogen purging, was 9 μg / g, which is a decrease of 6310 times. This indicates that the above method can effectively remove chloride ions from the deep eutectic solvent.

[0059] The application of p-toluenesulfonic acid-based low-halogen deep eutectic solvent No. 7 in the methoxycarbonylation of ethylene with carbon monoxide and methanol to synthesize methyl propionate includes the following steps:

[0060] Methanol (4.75 g), palladium acetate (0.0143 mmol, 3.2 mg), 1,2-bis(di-tert-butylphosphine)benzene (0.0855 mmol, 33.7 mg), and p-toluenesulfonic acid-based low-halogen deep eutectic solvent (35 wt%) (1.66 g) were added to a 50 ml Hastelloy autoclave. The autoclave was sealed and nitrogen gas was introduced to 0.5 MPa. After mixing for 15 min under stirring, the gas was released. This process was repeated twice to purge air from the autoclave. The autoclave was heated to 80 °C according to its set temperature program. Ethylene (0.0146 mol, 0.409 g) and monoxide were then introduced in a 1:1 molar ratio. A carbon-containing mixed gas (0.0146 mol, 0.409 g) was introduced to 2.0 MPa, and timing was started. Timing ended when the mixed gas in the autoclave reacted completely, i.e., the ethylene conversion rate reached 100%, which was recorded as cycle 1. After cycle 1, a 2.0 MPa mixture of ethylene and carbon monoxide with a molar ratio of 1:1 was introduced into the autoclave, and timing was started simultaneously. Timing ended when the mixed gas in the autoclave was consumed, which was recorded as cycle 2. The same steps were repeated until cycle 4. Heating was turned off, and the autoclave was rapidly cooled in ice water to quench the reaction. After the autoclave temperature cooled to room temperature, the remaining gas in the autoclave was discharged. The autoclave body was opened, the product was collected, and quantitative analysis was performed by gas chromatography. The results are listed in Table 1. Cycle 1 took 4 min, and the selectivity for methyl propionate was greater than 99%.

[0061] Example 8

[0062] A method for preparing a p-toluenesulfonic acid-based low-halogen deep eutectic solvent includes the following steps:

[0063] Choline chloride (0.0358 mol, 5 g) and p-toluenesulfonic acid monohydrate (0.0448 mol, 8.51 g) in a molar ratio of 1:1.25 were mixed in a three-necked flask. The mixture was then evacuated under vacuum at a constant temperature of -100 kPa in a 90°C water bath. After evacuation for 1 hour, nitrogen gas was purged for 5 minutes while evacuating, with the gauge pressure maintained at -50 kPa. This evacuation and nitrogen purging process was repeated, with nitrogen purging for 5 minutes after each 1 hour of evacuation. The total evacuation time was 9 hours, and nitrogen purging was performed nine times. After the reaction was completed, a transparent liquid deep eutectic solvent was obtained. After being left at room temperature for a period of time, it turned into a white opaque solid. This solid was p-toluenesulfonic acid-based low-halogen deep eutectic solvent No. 8.

[0064] The application of p-toluenesulfonic acid-based low-halogen eutectic solvent No. 8 in the methoxycarbonylation of ethylene with carbon monoxide and methanol to synthesize methyl propionate includes the following steps:

[0065] Methanol (4.75 g), palladium acetate (0.0143 mmol, 3.2 mg), 1,2-bis(di-tert-butylphosphine)benzene (0.0855 mmol, 33.7 mg), and p-toluenesulfonic acid-based low-halogen deep eutectic solvent (35 wt%) (1.66 g) were added to a 50 ml Hastelloy autoclave. The autoclave was sealed and nitrogen gas was introduced to 0.5 MPa. After mixing for 15 min under stirring, the gas was released. This process was repeated twice to purge air from the autoclave. The autoclave was heated to 80 °C according to its set temperature program. A mixture of ethylene (0.0146 mol, 0.409 g) and carbon monoxide (0.0146 mol) in a 1:1 molar ratio was then introduced. Add 0.409 g of methanol to 2.0 MPa, start timing, and stop timing after 20 min, recording the pressure of the mixed gas to calculate the ethylene conversion rate (Formula 1), denoted as Cycle 1. After Cycle 1, introduce a 1:1 molar ratio of ethylene to carbon monoxide mixed gas at 2.0 MPa into the autoclave and start timing again, stopping timing after 20 min and recording the pressure of the mixed gas to calculate the ethylene conversion rate (Formula 1), denoted as Cycle 2. Repeat the same steps until Cycle 7 is completed. After Cycle 7 is completed, turn off the heating and place the autoclave in ice water for rapid cooling to quench the reaction. After the autoclave temperature is cooled to room temperature, remove the remaining gas from the autoclave, open the autoclave, decant to collect the upper layer product, and perform quantitative analysis using gas chromatography. Add 5 ml of methanol to the lower layer DES phase and repeat the above operation until the conversion rate is less than 50%, at which point the reaction is terminated. A comparison of the system images before the reaction and after Cycle 7 is shown in the figure. Figure 1 , Figure 1This is a schematic diagram of the reaction system in Example 8 before the reaction (left) and after 7 cycles (right).

[0066] The ICP-OES analysis results of palladium and phosphorus in the upper methyl propionate phase and the lower eutectic solvent phase obtained in cycle 7 are listed in Table 3. The catalytic cycle results are listed in... Figure 2 . Figure 2 This is a schematic diagram illustrating the catalyst recovery experiment in Example 8, where recovery was performed every 7 cycles. From Figure 1 As can be seen from the table, compared with the system before the reaction, the system after the reaction was completed consisted of a brownish-yellow lower eutectic solvent phase and a nearly colorless upper methyl propionate phase. The ICP-OES results in Table 3 show that the palladium concentration in the lower eutectic solvent phase was 490 ppm and the phosphorus concentration was 1100 ppm, while the palladium concentration in the upper methyl propionate phase was 16 ppm and the phosphorus concentration was 46 ppm. This indicates that the palladium and phosphorus-containing ligands that make up the catalyst are mainly concentrated in the lower eutectic solvent phase, which verifies that the added p-toluenesulfonic acid-based low-halogen eutectic solvent can achieve catalyst separation. Figure 2 The catalyst was shown to be usable for 23 cycles without significant activity reduction, indicating that the catalytic system with p-toluenesulfonic acid-based low-halogen eutectic solvent has good stability.

[0067] The conversion rate of ethylene is calculated using the pressure drop of the mixed gas:

[0068]

[0069] Where p 0 ρ is the initial pressure of the mixed gas at 80°C, and p is the pressure of the mixed gas at 80°C after the reaction.

[0070] Selectivity of methyl propionate MP The calculation formula is as follows:

[0071]

[0072] Where n MP n is the molar amount of methyl propionate produced. b It is the molar amount of the byproducts generated.

[0073] Comparative Example 1

[0074] Commercially purchased p-toluenesulfonic acid.

[0075] The application of commercially available p-toluenesulfonic acid in the methoxycarbonylation of ethylene with carbon monoxide and methanol to synthesize methyl propionate includes the following steps:

[0076] Methanol (4.75 g), palladium acetate (0.0143 mmol, 3.2 mg), 1,2-bis(di-tert-butylphosphine)benzene (0.0855 mmol, 33.7 mg), and p-toluenesulfonic acid (0.257 g, the same amount as in Example 1) were added to a 50 ml Hastelloy autoclave. The autoclave was sealed and nitrogen gas was introduced to 0.5 MPa. After mixing for 15 min under stirring, the gas was released. This process was repeated twice to purge air from the autoclave. The autoclave was heated to 80 °C according to its set temperature program, and then ethylene (0.0146 mol, 0.409 g) and monoxide were introduced in a 1:1 molar ratio. A carbon-containing mixed gas (0.0146 mol, 0.409 g) was introduced into the autoclave at 2.0 MPa, and timing began. Timing ended when the mixed gas in the autoclave reacted completely, i.e., the ethylene conversion rate reached 100%, and this was recorded as cycle 1. After cycle 1, a 2.0 MPa mixture of ethylene and carbon monoxide (molar ratio 1:1) was introduced into the autoclave, and timing began simultaneously. Timing ended when the mixed gas in the autoclave was completely consumed, and this was recorded as cycle 2. This process was repeated until cycle 4. Heating was then turned off, and the autoclave was rapidly cooled in ice water to quench the reaction. After the autoclave temperature cooled to room temperature, the remaining gas in the autoclave was discharged. The autoclave was opened, the product was collected, and quantitative analysis was performed by gas chromatography. The results are listed in Table 1. Cycle 1 took 4 minutes, and the selectivity for methyl propionate was greater than 99%.

[0077] Comparative Example 2

[0078] Choline chloride (0.0358 mol, 5 g) and p-toluenesulfonic acid monohydrate (0.0448 mol, 8.52 g) in a molar ratio of 1:1.25 were mixed in a three-necked flask. The mixture was magnetically stirred in a 90°C water bath for 9 h to obtain a transparent eutectic solvent (No. 9). The chloride ion content of the sample is shown in Table 2.

[0079] The application of eutectic solvent No. 9 in the methoxycarbonylation of ethylene with carbon monoxide and methanol to synthesize methyl propionate includes the following steps:

[0080] Methanol (4.75 g), palladium acetate (0.0143 mmol, 3.2 mg), 1,2-bis(di-tert-butylphosphine)benzene (0.0855 mmol, 33.7 mg), and eutectic solvent No. 9 (35 wt%) (1.66 g) were added to a 50 ml Hastelloy autoclave. The autoclave was sealed and nitrogen gas was introduced to 0.5 MPa. After mixing for 15 min with stirring, the gas was released. This process was repeated twice to purge air from the autoclave. The temperature was then increased to 8 °C according to the autoclave's set temperature program. A mixture of ethylene (0.0146 mol, 0.409 g) and carbon monoxide (0.0146 mol, 0.409 g) in a 1:1 molar ratio was introduced at 0℃. Timing began after reaching 2.0 MPa and ended when the mixture had completely reacted in the autoclave, indicating 100% ethylene conversion; this was designated as Cycle 1. Heating was then turned off, and the autoclave was rapidly cooled in ice water to quench the reaction. After cooling to room temperature, the remaining gas in the autoclave was discharged. The product was collected and quantitatively analyzed by gas chromatography. The results are shown in Table 1. Cycle 1 took 364 min, and the selectivity for methyl propionate was greater than 99%.

[0081] Comparative Example 3

[0082] Choline chloride (0.0358 mol, 5 g) and p-toluenesulfonic acid monohydrate (0.0716 mol, 13.62 g) in a molar ratio of 1:2.0 were mixed in a three-necked flask. The mixture was magnetically stirred in a 90°C water bath for 9 h to obtain a transparent eutectic solvent (No. 10). The chloride ion content of the sample is shown in Table 2.

[0083] The application of eutectic solvent No. 10 in the methoxycarbonylation of ethylene with carbon monoxide and methanol to synthesize methyl propionate includes the following steps:

[0084] Methanol (4.75 g), palladium acetate (0.0143 mmol, 3.2 mg), 1,2-bis(di-tert-butylphosphine)benzene (0.0855 mmol, 33.7 mg), and eutectic solvent No. 9 (35 wt%) (1.66 g) were added to a 50 ml Hastelloy autoclave. The autoclave was sealed and nitrogen gas was introduced to 0.5 MPa. After mixing for 15 min under stirring, the gas was released. This process was repeated twice to purge air from the autoclave. The temperature was then increased according to the autoclave's set temperature program to [temperature missing]. After reaching 80℃, a mixture of ethylene (0.0146 mol, 0.409 g) and carbon monoxide (0.0146 mol, 0.409 g) in a 1:1 molar ratio was introduced to a pressure of 2.0 MPa. Timing was started and stopped when the mixture had completely reacted in the autoclave, i.e., when the ethylene conversion rate was 100%, which was recorded as cycle 1. Heating was turned off, and the autoclave was rapidly cooled in ice water to quench the reaction. After the autoclave temperature was cooled to room temperature, the remaining gas in the autoclave was discharged. The product was collected by gas chromatography and quantitative analysis was performed. The results are listed in Table 1. Cycle 1 took 327 min, and the selectivity for methyl propionate was greater than 99%.

[0085] Table 1

[0086]

[0087] Table 2

[0088] Cl - Ion concentration pg / g Comparative Example 2 67976 Example 3 356 Comparative Example 3 56789 Example 7 9

[0089] Table 3

[0090] Phosphorus element concentration / ppm Palladium element concentration / ppm Upper methyl propionate phase 46 16 Lower deep eutectic solvent phase 1100 490

[0091] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a p-toluenesulfonic acid-based low-halogen deep eutectic solvent, characterized in that, Includes the following steps: Under constant temperature conditions of 40–100°C, hydrogen bond donors and hydrogen bond acceptors with a molar ratio of (0.5–5):1 were mixed, and a vacuum was drawn, maintaining the vacuum level between 0 and -101.3 kPa. After 1 hour of vacuuming, nitrogen gas was purged simultaneously with the vacuuming process, and the gauge pressure was maintained between -100 and 101.3 kPa during nitrogen purging. The above vacuuming and nitrogen purging were repeated, with nitrogen purging once every 1 hour of vacuuming. The total vacuuming time was 1–24 hours, and nitrogen purging was performed one to twenty-four times. After the reaction was completed, the p-toluenesulfonic acid-based low-halogen deep eutectic solvent was obtained. The hydrogen bond donor is selected from p-toluenesulfonic acid and p-toluenesulfonic acid monohydrate; The hydrogen bond acceptor is selected from choline chloride, benzyltriphenylphosphine chloride, 1-butyl-3-methylimidazolium chloride, tetrabutylammonium chloride, tetramethylammonium chloride, methyltriphenylphosphine chloride, and allyltriphenylphosphine chloride.

2. The method for preparing the p-toluenesulfonic acid-based low-halogen deep eutectic solvent according to claim 1, characterized in that, The nitrogen purging time is 5 to 15 minutes.

3. The application of a p-toluenesulfonic acid-based low-halogen eutectic solvent prepared by the method of claim 1 or 2 in the methoxycarbonylation synthesis of methyl propionate from ethylene with carbon monoxide and methanol.

4. The application according to claim 3, characterized in that, The application includes the following steps: In a high-pressure reactor, a p-toluenesulfonic acid-based low-halogen deep eutectic solvent and methanol were mixed in a mass ratio of (0.1–0.6):

1. Palladium acetate and 1,2-bis(di-tert-butylphosphine)benzene were added, with a molar ratio of palladium acetate to ethylene of (0.8–0.99):1 and a molar ratio of 1,2-bis(di-tert-butylphosphine)benzene to ethylene of (1–10):

1. The high-pressure reactor was sealed, and nitrogen gas was introduced to a pressure of 0.5–4.0 MPa. After mixing for 5–30 minutes, the gas was released. This process was repeated twice to purge air from the reactor. The temperature was then increased to 60–100 °C, and a mixture of ethylene and methanol in a molar ratio of (0.1–10):1 was introduced. A carbon monoxide mixture is introduced into the autoclave at a pressure of 0.5–4.0 MPa. Timing begins at this point and ends when the mixture has completely reacted, i.e., when the ethylene conversion rate reaches 100%. This is recorded as Cycle 1. After Cycle 1, a mixture of ethylene and carbon monoxide at a molar ratio of (0.1–10):1 at 0.5–4.0 MPa is introduced into the autoclave, and timing begins simultaneously. Timing ends when the mixture in the autoclave is completely consumed. This is recorded as Cycle 2. The same steps are repeated until the reaction is complete. The heating is then turned off, and the reaction is quenched by rapid cooling. After the autoclave temperature is cooled to room temperature, the remaining gas in the autoclave is discharged. The autoclave body is opened to collect the product, which is then analyzed using gas chromatography.

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