Method for continuously producing trans-dichloroethylene by using two-phase solvent system

Abstract

The invention discloses a method for continuously producing trans-dichloroethylene by using a two-phase solvent system, which comprises the following steps: contacting perfluoro-n-octane dissolved with chlorine with acetonitrile dissolved with acetylene, controlling the reaction temperature at 60-90 DEG C, and irradiating by using ultraviolet light with the wavelength of 200-400nm to initiate free radical addition reaction, so that the chlorine reacts with acetylene to generate trans-1, 3-dichloroethylene. 2, 2-dichloroethylene; the method has the advantages of simple process, mild reaction conditions, recyclable reaction solvent, high product selectivity and reaction controllability, and safe and efficient experimental operation process; the selectivity of a target product is effectively improved.

Description

Technical Field

[0001] The invention belongs to the fields of organic synthetic chemistry and fine chemical industry, and in particular relates to a method for continuously producing trans-dichloroethylene by utilizing a two-phase solvent system. Background Art

[0002] Trans-1,2-dichloroethylene (trans-1,2-dichloroethylene) is a chlorine-containing organic compound with a symmetrical structure, moderate volatility, and excellent solubility and thermal stability. It is widely used in electronic component cleaning, metal surface treatment, and polymer synthesis. Compared to its cis-isomer, the trans-isomer offers greater thermodynamic and chemical stability, making it more suitable as an industrial solvent.

[0003] In recent years, with the continued advancement of green chemistry and increasing demands for clean production, the research and application of trans-dichloroethylene as a low-toxic solvent alternative has attracted considerable attention. According to public market data, the global trans-dichloroethylene market was estimated to be worth approximately US$2.15 billion in 2024 and is projected to grow to US$3.1 billion by 2033, achieving a compound annual growth rate (CAGR) of 4.5%. Existing methods for producing trans-dichloroethylene primarily include direct acetylene synthesis and the vinyl chloride byproduct method.

[0004] Direct acetylene synthesis is currently one of the mainstream processes for producing high-purity trans-dichloroethylene. This method typically involves reacting acetylene (C2H2) with chlorine or hydrogen chloride (HCl) in the presence of a catalyst. Specifically, the reaction is typically carried out in the presence of cuprous chloride (CuCl2), which acts as both a catalyst and participates in the formation of intermediates. Furthermore, the process requires a certain temperature and moderate pressure, along with the addition of a co-catalyst such as calcium chloride (CaCl2) to regulate the ionic strength of the solution, in order to achieve high conversion and selectivity.

[0005] The direct synthesis of acetylene has certain limitations:

[0006] (a) The copper salts and mercuric chloride additives (such as HgCl2) in the catalysts required for the reaction have high environmental toxicity and biopersistence, requiring strict control of waste liquid treatment and catalyst recovery to avoid secondary pollution;

[0007] (b) Although acetylene as a raw material is highly reactive, its flammable and explosive properties place higher demands on reaction equipment and operational safety;

[0008] (c) The process is sensitive to parameters such as temperature, pH and reaction gas ratio. Slight fluctuations may lead to reduced isomer selectivity or increased by-products, thereby affecting product purity and yield.

[0009] The vinyl chloride byproduct method is another major process for producing trans-dichloroethylene. It primarily uses byproducts generated during the vinyl chloride (VCM) production process as raw materials and recovers trans-1,2-dichloroethylene through physical separation. Vinyl chloride is typically produced through the reaction of ethylene with chlorine. During this process, 1,2-dichloroethylene is produced as an intermediate. Furthermore, due to variations in raw materials, catalysts, and reaction conditions, 1,2-dichloroethylene can produce both cis- and trans-isomers. Due to the significant difference in boiling points between the two, this method typically uses atmospheric distillation or extractive distillation to separate and purify the trans-isomer.

[0010] The vinyl chloride by-product recovery method also has certain limitations:

[0011] (a) The 1,2-dichloroethylene obtained by this method is a mixture of isomers, and a high-energy separation process is required to obtain a high-purity trans product, resulting in complex operations and increased energy consumption;

[0012] (b) This method relies on the stable operation of the vinyl chloride unit and the control of raw material fluctuations. When the isomer composition of the by-product changes, it will directly affect the yield and stability of the trans product;

[0013] (c) Since the cis-isomer is more likely to form azeotropes with other impurities, the separation purity is limited, which places high demands on the precision of the equipment and the level of operating technology. Summary of the Invention

[0014] The purpose of the present invention is to provide a method for continuously producing trans-dichloroethylene using a two-phase solvent system, so as to solve the problems of high environmental toxicity, complex operation, high safety risk and insufficient selectivity in the traditional trans-dichloroethylene synthesis process.

[0015] The present invention adopts the following technical scheme: a method for continuously producing trans-dichloroethylene using a two-phase solvent system, wherein perfluorooctane containing dissolved chlorine is contacted with acetonitrile containing dissolved acetylene, the reaction temperature is controlled at 60°C to 90°C, and ultraviolet light with a wavelength of 200nm to 400nm is used to induce a free radical addition reaction, so that the chlorine and acetylene react to generate trans-1,2-dichloroethylene.

[0016] The beneficial effects of the present invention are:

[0017] The present invention has simple process, mild reaction conditions, recyclable reaction solvent, high product selectivity and reaction controllability, safe and efficient experimental operation process, and effectively improves the selectivity of the target product.

[0018] The present invention uses chlorine and acetylene as raw materials, dissolves them in perfluorooctane and acetonitrile respectively to form a two-phase solvent system, and induces a free radical addition reaction under ultraviolet light irradiation and temperature control conditions to selectively synthesize the target product trans-dichloroethylene in reactor B;

[0019] During the reaction process of the present invention, chlorine is uniformly dispersed in the chemically inert solvent perfluorooctane and enters the bottom of the reactor B, reacting with acetylene dissolved in the acetonitrile phase at the interface between the two phases. The reaction products migrate to the collection chamber based on their physical properties and the heat of acetonitrile vaporization and are collected.

[0020] The present invention utilizes the solvent effect and interphase mass transfer to effectively buffer the reaction exothermic process, reduce the reaction safety risk, and improve the reaction control accuracy and operation safety;

[0021] The present invention utilizes perfluorooctane to dissolve chlorine. Perfluorooctane has high density, low volatility and certain chlorine dissolving performance. After the reaction is completed, it can be recycled after phase separation and purification, thereby improving resource utilization and reducing operating costs.

[0022] The present invention improves reaction controllability and selectivity through ultraviolet light irradiation, does not require a metal catalyst, and is suitable for the green and controllable synthesis of trans-dichloroethylene.

[0023] The product extraction steps of the present invention are simple, the process efficiency is high, and the reaction conditions are mild; perfluorooctane and acetonitrile are used to construct a two-phase reaction medium, and ultraviolet light induction is combined to achieve precise control of the addition path of chlorine free radicals, thereby improving the generation selectivity of trans products. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 A schematic diagram of the system of the present invention;

[0025] Figure 2 is a chromatogram of the product of Example 3 of the present invention;

[0026] Figure 3 It is the mass spectrum of the product of Example 3 of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] The present invention discloses a method for continuously producing trans-dichloroethylene using a two-phase solvent system. Figure 1 As shown, perfluorooctane containing dissolved chlorine is brought into contact with acetonitrile containing dissolved acetylene, the reaction temperature is controlled at 60°C to 90°C, and ultraviolet light with a wavelength of 200nm to 400nm is used to induce a free radical addition reaction, so that chlorine and acetylene react to generate trans-1,2-dichloroethylene.

[0029] The bottoms of reactors A and B are connected, perfluorooctane is placed in reactor A, and acetonitrile is placed in reactor B. The perfluorooctane in reactor A is pressed into the bottom of reactor B by pressure, thereby forming a layered perfluorooctane / acetonitrile two-phase system in reactor B. Chlorine is introduced into reactor A, and acetylene is introduced into reactor B, so that perfluorooctane dissolved in chlorine and acetonitrile dissolved in acetylene undergo an addition reaction in reactor B.

[0030] The reactor B is also connected to a collecting chamber, in which a liquid dissolving trans-1,2-dichloroethylene is contained; the collecting chamber is used to receive steam from the reactor B and further absorb trans-1,2-dichloroethylene.

[0031] A heating device is provided on the periphery of the reactor B. An ultraviolet lamp irradiation device is provided inside the reactor B.

[0032] Reactors A and B form a series reaction system, connected at the bottom by a pipe and each equipped with an independent stirring device. An appropriate amount of pre-vacuum-degassed inert solvent, perfluorooctane, is injected into reactor A in a predetermined ratio. Using a liquid pump and gravity, the perfluorooctane is slowly introduced into the bottom of reactor B, forming a stable lower liquid phase. Simultaneously, an appropriate amount of similarly degassed acetonitrile is slowly injected into reactor B, forming an upper liquid phase. The liquid level is controlled to create a clearly stratified perfluorooctane / acetonitrile two-phase system in reactor B. Perfluorooctane, acting as a chlorine dissolving medium, resides in the lower phase, while acetonitrile, acting as an acetylene dissolving phase, resides in the upper phase.

[0033] While maintaining the reaction system sealed and stirred, the reaction gases were introduced into Reactor A and Reactor B, respectively, via a mass flow control system. Specifically, high-purity chlorine gas (purity ≥99.9%) was introduced into Reactor A at a set flow rate, where it was fully dissolved in perfluorooctane under stirring to form a saturated chlorine solution. Simultaneously, high-purity acetylene gas (purity ≥99.5%) was introduced into Reactor B and uniformly dispersed and dissolved in the acetonitrile phase, providing sufficient distribution of the gaseous reactants for subsequent reactions.

[0034] The heating device of reactor B, specifically the jacket heating system, is activated and maintained at a set temperature (preferably between 60 and 90°C). Simultaneously, the UV lamp within reactor B is activated, inducing homolytic cleavage of chlorine molecules under UV irradiation to generate chlorine free radicals (Cl·). These free radicals migrate to the acetonitrile phase and rapidly react with dissolved acetylene molecules, preferentially producing trans-1,2-dichloroethylene, accompanied by a small amount of the cis isomer and further chlorination products.

[0035] The outlet of Reactor B is connected to a collection chamber filled with fresh acetonitrile absorbent to capture any escaping reaction products. Because trans-1,2-dichloroethylene has a boiling point of 47.7°C and is prone to partial volatilization, and its solubility in acetonitrile is excellent, compared to very low solubility in perfluorooctane, it preferentially accumulates in the acetonitrile phase upon formation and migrates to the collection chamber as the acetonitrile partially vaporizes. The addition of a heating device, coupled with the heat released by the reaction, promotes the removal and transfer of reaction products.

[0036] Gas chromatography (GC) or gas chromatography-mass spectrometry (GC-MS) is used to qualitatively and quantitatively analyze trans-1,2-dichloroethylene, cis isomers, and by-products (such as tetrachloroethane) to evaluate the reaction selectivity.

[0037] The reaction equation is:

[0038]

[0039] Example 1

[0040] Start the perfluorooctane feed pump and inject 900 ml of pre-degassed inert solvent perfluorooctane from the feed port of reactor A. Inject 400 ml of pre-degassed acetonitrile from the feed port of reactor B. Control the liquid level of the system to establish a clearly stratified perfluorooctane / acetonitrile two-phase system in reactor B.

[0041] While stirring, high-purity chlorine gas (purity ≥99.9%) was continuously introduced into reactor A at a flow rate of 30 ml / min, and high-purity acetylene gas (purity ≥99.5%) was continuously introduced into reactor B at a flow rate of 100 ml / min to ensure that the chlorine gas was fully dissolved in the perfluorooctane and the acetylene was uniformly dispersed and dissolved in the acetonitrile phase.

[0042] The jacket heating system of reactor B was started to maintain the reaction system at 60° C. Simultaneously, the ultraviolet lamp irradiation device configured in reactor B was turned on and the wavelength was adjusted to 365 nm to induce the free radical addition reaction.

[0043] The reaction products escaping from the system are captured by a collection chamber containing fresh acetonitrile. The product composition is analyzed by gas chromatography, and the selectivity of trans-dichloroethylene is more than 70%, and cis-dichloroethylene and tetrachloroethane are by-products.

[0044] Example 2

[0045] This example has the same basic steps and by-products as Example 1, except that:

[0046] The jacket heating system of reactor B was started to maintain the reaction system at 70°C.

[0047] The product composition was analyzed by gas chromatography, and the selectivity of trans-dichloroethylene was above 85%.

[0048] Example 3

[0049] This example has the same basic steps and by-products as Example 1, except that:

[0050] The jacket heating system of reactor B was started to maintain the reaction system at 80°C.

[0051] The product composition was analyzed by gas chromatography, and the selectivity of trans-dichloroethylene was over 90%.

[0052] Sample analysis was performed using a Shimadzu GC-2030 gas chromatograph coupled to a Shimadzu QP-2020 mass spectrometer. A DB-624 capillary column (60 m × 0.25 mm × 1.4 μm) was used, with nitrogen as the carrier gas at a flow rate of 1.0 mL / min. The column temperature program was as follows: initial temperature at 50°C for 3 minutes, followed by a temperature increase of 10°C / min to 280°C and a hold time of 10 minutes. Mass spectrometry detection was performed in electron impact (EI) mode with an ionization energy of 70 eV, a scan range of 50–550 m / z, and an ion source temperature of 230°C. The injection volume was 1 μL, and split injection mode was used to minimize matrix effects.

[0053] Mass spectrometry results are as follows Figure 3 As shown in the figure, the molecular ion peaks of trans-dichloroethylene and cis-dichloroethylene are concentrated at m / z 95.00-100.00, while that of tetrachloroethane shows a typical chlorine isotope peak distribution at m / z 165.90-169.90.

[0054] The chromatographic results are as follows Figure 2 As shown, the products include the main product trans-1,2-dichloroethylene and the by-products cis-dichloroethylene and tetrachloroethane; the retention time of trans-1,2-dichloroethylene is 11.65 min, the retention time of cis-dichloroethylene is 13.23 min, and the retention time of tetrachloroethane is 22.44 min.

[0055] Example 4

[0056] This example has the same basic steps and by-products as Example 1, except that:

[0057] Start the jacket heating system of reactor B and maintain the reaction system at 90°C

[0058] The product composition was analyzed by gas chromatography, and the selectivity of trans-dichloroethylene was above 78%.

Claims

1. A method for continuously producing trans-dichloroethylene using a biphasic solvent system, characterized in that: Perfluorooctane containing dissolved chlorine is brought into contact with acetonitrile containing dissolved acetylene, the reaction temperature is controlled at 60°C to 90°C, and ultraviolet light with a wavelength of 200nm to 400nm is used to induce a free radical addition reaction, causing the chlorine and acetylene to react to generate trans-1,2-dichloroethylene.

2. The method for continuously producing trans-dichloroethylene using a two-phase solvent system according to claim 1, characterized in that: The bottoms of reactors A and B are connected, perfluorooctane is placed in reactor A, and acetonitrile is placed in reactor B. The perfluorooctane in reactor A is pressed into the bottom of reactor B by pressure, thereby forming a layered perfluorooctane / acetonitrile two-phase system in reactor B. Chlorine is introduced into reactor A, and acetylene is introduced into reactor B, so that perfluorooctane dissolved in chlorine and acetonitrile dissolved in acetylene undergo an addition reaction in reactor B.

3. The method for continuously producing trans-dichloroethylene using a biphasic solvent system according to claim 1, characterized in that: The reactor B is also connected to a collecting chamber, in which a liquid dissolving trans-1,2-dichloroethylene is contained; the collecting chamber is used to receive steam from the reactor B and further absorb trans-1,2-dichloroethylene.

4. The method for continuously producing trans-dichloroethylene using a biphasic solvent system according to claim 1, characterized in that: The periphery of the reactor B is provided with a heating device.

5. The method for continuously producing trans-dichloroethylene using a two-phase solvent system according to claim 1, characterized in that: The reactor B is provided with an ultraviolet lamp irradiation device.

6. The method for continuously producing trans-dichloroethylene using a biphasic solvent system according to claim 1, wherein: Irradiate with ultraviolet light at a wavelength of 365 nm.

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