Preparation method and application of catalyst for preparing vinyl chloride by cracking 1,2-dichloroethane

Abstract

The application discloses a preparation method and application of a catalyst for cracking 1,2-dichloroethane to produce vinyl chloride, and comprises the following steps: 1) a neodymium ore is leached with hydrochloric acid, and after filtering a leaching solution, potassium chloride is added to form a doped precursor K2[NdCl3]; 2) an active metal oxide is dissolved in hydrochloric acid, and then added into the doped precursor K2[NdCl3] solution, and co-precipitation is carried out by adding alkali to obtain an emulsion of a doped active component; the active metal oxide is at least one of oxides of vanadium, manganese, titanium and scandium; 3) the emulsion of the doped active component is mixed with a liquid carrier to obtain the catalyst; the liquid carrier is one or more of chloroform, carbon tetrachloride, 1,1,2-trichloroethane and chlorobenzene.

Description

Technical Field

[0001] This invention relates to a catalyst for the catalytic cracking of vinyl chloride, and more particularly to a method for preparing and applying a catalyst for the cracking of 1,2-dichloroethane to vinyl chloride, which belongs to the petrochemical industry chain. Background Technology

[0002] Vinyl chloride (VCM) is a very important chemical raw material, mainly used in the synthesis of polyvinyl chloride resin (PVC), vinylidene chloride, and refrigerants. Currently, the main production processes for vinyl chloride include the calcium carbide acetylene method, the balanced oxychlorination method, and newer processes such as direct chlorination / hydrogen chlorination of ethylene and direct oxychlorination of ethane. The balanced oxychlorination method accounts for over 90% of total VCM production, making it the most widely used VCM production method.

[0003] The balanced oxychlorination process generally consists of three parts: direct ethylene chlorination, ethylene oxychlorination, and 1,2-dichloroethane (EDC) cracking. The plant mainly comprises process units such as direct chlorination, oxychlorination, EDC cracking, EDC refining, and VCM refining. The EDC cracking process currently employs thermal cracking at a temperature of 450–550°C, converting 1,2-dichloroethane into vinyl chloride, hydrogen chloride, and other byproducts. This reaction requires large quantities of natural gas or other fuels, and significant coking occurs during the process, necessitating periodic shutdowns for decoking, which greatly impacts normal production. The causes of coking are significantly influenced by temperature and feedstock composition. Lowering the temperature or adjusting the coking-promoting components can effectively reduce coking. Therefore, using suitable catalytic components and lowering the cracking reaction temperature is beneficial to the cracking process, yielding significant benefits in terms of fuel savings and extended operating time.

[0004] US Patent 5008225A discloses a catalyst for the catalytic cracking of 1,2-dichloroethane to vinyl chloride, which involves supporting rare earth elements on HFZ-20, HFZ-30, and HFZ-55 molecular sieves to catalytically crack 1,2-dichloroethane to obtain vinyl chloride. When the conversion rate of 1,2-dichloroethane is 35.8%, the selectivity of the catalytic cracking process (VCM) is at most 90.1%, which is not very high. CN105268457B discloses a catalyst for the cracking of 1,2-dichloroethane, which involves supporting a metal chloride. This catalyst allows for cracking under milder operating conditions, further improving the conversion rate and selectivity. However, this catalyst must be loaded into a fixed bed or fluidized bed, which is incompatible with the operating conditions of industrial cracking furnaces. CN102247884B discloses a catalyst for the production of vinyl chloride from 1,2-dichloroethane, which is composed of 10.0–80.0 wt% zeolite and 20.0–90.0 wt% inorganic oxide matrix. It is also used in a fluidized bed system, which is inconsistent with the operating conditions of industrial cracking furnaces.

[0005] In summary, most catalysts for the cracking of 1,2-dichloroethane are molecular sieve-supported types, which are applied to fixed-bed or fluidized-bed systems after molding, resulting in high consumption and generally poor performance. In reality, during industrial cracking, 1,2-dichloroethane is vaporized in a vaporizer and enters the cracking furnace in the gas phase, where it undergoes high-speed cracking within the furnace tubes. Therefore, how to achieve catalysis in this process is a problem that needs to be solved. Summary of the Invention

[0006] To address the above technical problems, this invention proposes a method for preparing a catalyst for the cracking of 1,2-dichloroethane to produce vinyl chloride and its application.

[0007] Through continuous research, the inventors have discovered that the cracking of 1,2-dichloroethane to produce vinyl chloride is essentially a dehalogenation process, in which the dehalogenation reaction is the controlling step, determined by the Brønsted acid sites at the catalyst's active sites. However, in actual catalytic reactions, on the one hand, carbon deposition at the active sites obscures them, preventing reactant molecules from approaching the Brønsted acid sites, leading to Brønsted acid site dysfunction (i.e., alkali poisoning), which is one cause of catalyst deactivation. On the other hand, the reaction of generated Cl with active components (such as Cl-Mn and Cl-V combinations) reduces the amount of active components (i.e., chlorine poisoning), which is another reason for catalyst deactivation. Regarding the support, inappropriate support selection, failing to provide a large active surface area or Brønsted acid sites, is another reason for poor catalytic performance. Furthermore, once a suitable active component or support is selected, how it is injected into the gas-phase process deserves consideration. Existing molecular sieve catalysts are generally used in fixed-bed systems because they cannot be applied in gas-phase cracking.

[0008] This invention addresses the aforementioned pyrolysis process by designing a gasifiable catalyst component based on catalyst principles and morphology. This component ensures catalytic performance while being more convenient to add to the gas-phase process, offering significant advantages.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing a catalyst for the cracking of 1,2-dichloroethane to vinyl chloride includes the following steps:

[0011] 1) Neodymium ore was heap leached with hydrochloric acid, and after filtering the leaching solution, potassium chloride was added to complex and generate the doped precursor K2[NdCl3];

[0012] 2) The active metal oxide is dissolved in hydrochloric acid and then added to the above-mentioned doping precursor K2[NdCl3] solution. Alkali is added for co-precipitation to obtain an emulsion of the doped active component; the active metal oxide is an oxide of at least one of vanadium, manganese, titanium, and scandium.

[0013] 3) The emulsion containing the active component is mixed with a liquid carrier to obtain the catalyst; when the catalyst is applied to the reaction of 1,2-dichloroethane cracking to produce vinyl chloride, it is fully mixed with 1,2-dichloroethane and preheated to vaporize the feed to catalyze the reaction and improve the reaction efficiency.

[0014] The liquid carrier is one or more of chloroform, carbon tetrachloride, 1,1,2-trichloroethane, and chlorobenzene.

[0015] In some examples of the present invention, the neodymium content in the neodymium ore is 19-23 wt%. For example, the neodymium ore that can be selected is the Bayan Obo West tailings neodymium ore (Nd content 23 wt%), the Xiangshan neodymium ore in Jiangxi (Nd content 21 wt%), the Zhenjiang rare earth neodymium ore (Nd content 19 wt%), etc.

[0016] In some examples of the present invention, in step 1), the mass of potassium chloride added is 1-3 times the mass of metallic neodymium in the neodymium ore.

[0017] In some examples of the present invention, the complexation reaction conditions may be stirring at room temperature for 30-60 minutes.

[0018] In some examples of the present invention, the amount of raw materials used in step 2) is (6-10):1, based on the mass ratio of active metal oxide to neodymium.

[0019] In some examples of the present invention, the amount of alkali added in step 2) is such that the pH of the solution is adjusted to 8-11;

[0020] In some examples of the present invention, the alkali is one or more of sodium hydroxide and potassium hydroxide.

[0021] In some examples of the present invention, in step 2), the coprecipitation reaction time is, for example, 20-60 min.

[0022] In some examples of the present invention, in step 3), the volume ratio of the emulsion doped with the active component to the liquid carrier is (1-5):1000, and preferably the mixing time is 20-60 min.

[0023] Application of a catalyst prepared according to the method described above in the reaction of 1,2-dichloroethane cracking to produce vinyl chloride.

[0024] In some examples of this invention, the specific application method is as follows:

[0025] The catalyst and liquid 1,2-dichloroethane are mixed, preheated to vaporization, and then fed into a cracking furnace for cracking reaction. The inlet temperature is maintained at 225-235℃, and the reaction residence time is 10-15s. After the reaction, the mixture is rapidly cooled and separated. The bottom stream of the product vinyl chloride is obtained, and the top stream of hydrogen chloride is collected for further recovery and treatment. The bottom stream also contains a certain amount of unreacted 1,2-dichloroethane, which can be further purified into vinyl chloride through conventional purification separation.

[0026] In some examples of the present invention, the amount of catalyst used is 0.5-1 wt% of the mass of 1,2-dichloroethane.

[0027] The positive effects of this invention are as follows:

[0028] (1) A previously unconsidered metallic neodymium was introduced to prepare a doped active catalyst, and it was unexpectedly found that it could effectively prevent the loss of active components and carbon deposition at active sites, thereby improving the catalyst's resistance to poisoning.

[0029] (2) Chlorine-containing organic solvents are selected as catalyst carriers. They can be vaporized and enter the cracking furnace to meet the working conditions of gas phase cracking. The presence of chlorine-containing components has a certain catalytic effect and anti-coking effect on cracking.

[0030] (3) The catalyst of the present invention has a significant effect on the catalytic cracking of EDC, which can increase the EDC conversion rate to more than 88% and the VCM selectivity to more than 98%. Detailed Implementation

[0031] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0032] Unless otherwise specified, all raw materials and reagents used in the following embodiments of the present invention are of analytical grade (AR). These include neodymium tailings ore from Bayan Obo West (Nd content 23 wt%), neodymium ore from Xiangshan, Jiangxi (Nd content 21 wt%), and rare earth neodymium ore from Zhenjiang (Nd content 19 wt%).

[0033] The testing or calculation methods used in the following embodiments of the present invention are as follows:

[0034]

[0035]

[0036] Example 1

[0037] (1) Take 100g of Bayan Obo West neodymium tailings (Nd content 23wt%), add 500mL of 28wt% hydrochloric acid for heap leaching and dissolution, filter after reaction to obtain filtrate, add 173g of 40wt% potassium chloride solution to filtrate, react at room temperature for 60min to obtain doped precursor K2[NdCl3] solution.

[0038] (2) Dissolve 230g of MnO in 500mL of 28wt% hydrochloric acid, then add it to the above-mentioned doped precursor K2[NdCl3] solution, then add NaOH to adjust the pH to 8, stir at room temperature for 30min to obtain an emulsion of doped active components.

[0039] (3) The emulsion containing the active component and the liquid carrier are mixed at a volume ratio of 5:1000 and stirred for 60 min to obtain the catalyst. The liquid carrier is a mixture of chloroform, carbon tetrachloride and 1,1,2-trichloroethane at a volume ratio of 1:1:1.

[0040] Example 2

[0041] (1) Take 100g of Zhenjiang rare earth neodymium ore (Nd content 19wt%), add 500mL of 28wt% hydrochloric acid for heap leaching and dissolution, filter after reaction to obtain filtrate, add 53g of 40wt% potassium chloride solution to filtrate, react at room temperature for 30min to obtain doped precursor K2[NdCl3] solution.

[0042] (2) Dissolve 130g of V2O5 in 500mL of 28wt% hydrochloric acid, then add it to the above-mentioned doped precursor K2[NdCl3] solution, then add NaOH to adjust the pH to 8, stir at room temperature for 40min to obtain an emulsion of doped active components.

[0043] (3) The emulsion containing the active component and the liquid carrier are mixed at a volume ratio of 1:1000 and stirred for 20 min to obtain the catalyst. The liquid carrier is a mixture of chloroform and chlorobenzene at a volume ratio of 1:1.

[0044] Example 3

[0045] (1) Take 100g of Jiangxi Xiangshan neodymium ore (Nd content 21wt%), add 500mL of 28wt% hydrochloric acid for heap leaching and dissolution, filter after reaction to obtain filtrate, add 143g of 40wt% potassium chloride solution to filtrate, react at room temperature for 45min to obtain doped precursor K2[NdCl3] solution.

[0046] (2) Dissolve 152g of V2O5 in 500mL of 28% hydrochloric acid, then add it to the above-mentioned doped precursor K2[NdCl3] solution, then add NaOH to adjust the pH to 8, stir at room temperature for 45min to obtain an emulsion of doped active components.

[0047] (3) The emulsion containing the active component and the liquid carrier are mixed at a volume ratio of 3:1000 and stirred for 20 min to obtain the catalyst. The liquid carrier is a mixture of chloroform, carbon tetrachloride, 1,1,2-trichloroethane and chlorobenzene at a volume ratio of 1:1:1:1.

[0048] Example 4

[0049] The catalyst was prepared in essentially the same manner as in Example 1, except that MnO in step (2) was replaced with TiO2 and the liquid support was replaced with carbon tetrachloride.

[0050] Example 5

[0051] The catalyst was prepared in essentially the same manner as in Example 1, except that MnO in step (2) was replaced with Sc2O3 and the liquid support was replaced with 1,1,2-trichloroethane.

[0052] Comparative Example 1

[0053] The catalyst was prepared using essentially the same method as in Example 1, except that the liquid support used in step 3 was replaced with a type 4A molecular sieve (below 40 μm), and then the catalyst was pressed into shape.

[0054] Comparative Example 2

[0055] The catalyst was prepared using essentially the same method as in Example 1, except that the Bayan Obo rare earth ore in step 1 was replaced with lanthanum chloride, and the amount used was such that the mass of metallic lanthanum and metallic neodymium were the same.

[0056] Comparative Example 3

[0057] The catalyst was prepared using a method essentially the same as in Example 1, except that the Bayan Obo rare earth ore in step 1 was replaced with a mixture of calcium chloride and cesium chloride in equal amounts, with the amount ensuring that the mass of metallic calcium was twice the mass of metallic neodymium.

[0058] Comparative Example 4

[0059] The catalyst was prepared using a method essentially the same as in Example 1, except that the Bayan Obo rare earth ore in step 1 was replaced with a mixture of calcium chloride and cesium chloride in equal amounts, with the amount ensuring that the mass of metallic calcium was twice the mass of metallic neodymium; at the same time, the liquid support used in step 3 was replaced with a type 4A molecular sieve (below 40 μm), and then the catalyst was pressed into shape.

[0060] Comparative Example 5

[0061] The catalyst was prepared using essentially the same method as in Example 1, except that the liquid carrier was replaced with the same volume of hexane.

[0062] Application examples

[0063] The catalysts provided in each example and comparative example were evaluated according to the EDC pyrolysis experimental conditions in Table 1 (the solid catalysts in Comparative Examples 1 and 4 were fed by loading them into the pyrolysis furnace; the catalysts in other examples and comparative examples were mixed with EDC at a dosage of 0.5 wt% of EDC). The EDC used for evaluation was crude EDC produced by Wanhua Chemical, and its composition and content are detailed in Table 2 below. The relevant component analysis was performed using an Agilent 7890B gas chromatograph with a four-valve six-column injection system. The testing standard was GB / T16088-1995 "Direct Injection Gas Chromatography Determination of Vinyl Chloride". The test results are shown in Tables 3 and 4.

[0064] Table 1. Cracking Equipment and Feed Parameters

[0065]

[0066] Table 2. Main Components of Feed EDC

[0067] Element EDC water acid chlorobenzene Carbon tetrachloride chloroform Content wt% 98.88 0.002 0.0002 0.86 0.13 0.025

[0068] Table 3. Catalyst evaluation results in the initial stage (within 6 hours) of continuous reaction.

[0069]

[0070] Table 4. Catalyst evaluation results after 360 hours of continuous reaction.

[0071]

[0072]

[0073] As can be seen from the test results in Tables 3 and 4, the catalyst provided in this application has excellent EDC conversion and VCM selectivity in long-term continuous catalytic EDC cracking reaction. It can solve the problems of rapid deactivation, decreased conversion and selectivity caused by carbon deposition in traditional catalysts. In particular, the introduction of neodymium metal has a significant effect on improving the catalyst's resistance to poisoning (as can be seen from the comparison between Example 1 and Comparative Examples 2 and 3).

[0074] While the solid-supported catalysts provided in Comparative Examples 1 and 4 could be loaded into the cracking furnace for catalytic reaction, it was found during the experiment that the catalyst was blown out during continuous gas-phase feeding and the pressure difference inside the cracking furnace tube was large, causing blockage of the feed line and furnace tube. The furnace was forced to shut down after only 6 hours of operation, so it could not be used for a long time in the gas-phase feeding cracking process.

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing a catalyst for the cracking of 1,2-dichloroethane to vinyl chloride, characterized by, The method comprises the following steps: 1) Neodymium ore is leached with hydrochloric acid, and after filtering the impregnation solution, potassium chloride is added to form a doping precursor K2[NdCl3]; the content of metal neodymium in the neodymium ore is 19-23 wt%; the added mass of potassium chloride is 1-3 times the mass of metal neodymium in the neodymium ore; 2) After active metal oxides are dissolved with hydrochloric acid, they are added to the doping precursor K2[NdCl3] solution, and co-precipitation is performed by adding alkali to obtain an emulsion of doped active components; the active metal oxides are oxides of at least one of metal vanadium, manganese, titanium and scandium; 3) The emulsion of doped active components is mixed with a liquid carrier to obtain the catalyst; The liquid carrier is one or more of trichloromethane, carbon tetrachloride, 1,1,2-trichloroethane and chlorobenzene.

2. The method for preparing the catalyst for the cracking of 1,2-dichloroethane to vinyl chloride according to claim 1, characterized in that, In step 2), the amount of raw material is (6-10):1 in terms of the mass ratio of active metal oxides to metal neodymium.

3. The method for preparing the catalyst for the cracking of 1,2-dichloroethane to vinyl chloride according to claim 1 or 2, characterized in that, In step 2), the amount of alkali added is adjusted to pH 8-11.

4. The method for preparing the catalyst for the cracking of 1,2-dichloroethane to vinyl chloride according to claim 3, characterized in that, The alkali is one or more of sodium hydroxide and potassium hydroxide.

5. The method for preparing the catalyst for the cracking of 1,2-dichloroethane to vinyl chloride according to claim 1 or 2, characterized in that, In step 3), the volume ratio of the emulsion of doped active components to the liquid carrier is (1-5):1000.

6. The method for preparing the catalyst for the cracking of 1,2-dichloroethane to vinyl chloride according to claim 5, characterized in that, In step 3), the mixing time of the emulsion of doped active components and the liquid carrier is 20-60 min.

7. Use of the catalyst prepared by the method of any one of claims 1-6 in a reaction of 1,2-dichloroethane cracking to produce vinyl chloride.

8. Use according to claim 7, characterized in that, The specific application method is as follows: The catalyst and liquid 1,2-dichloroethane are mixed, preheated to vaporization, and then sent to a cracking furnace for cracking reaction, the reaction inlet temperature is maintained at 225-235℃, the reaction residence time is 10-15 s, after the reaction is completed, rapid cooling and separation are performed, the product vinyl chloride stream is obtained at the bottom of the column, and hydrogen chloride is collected at the top of the column for further recovery and treatment.

9. Use according to claim 8, characterized in that, The amount of the catalyst used is 0.5-1 wt% of the mass of 1,2-dichloroethane.

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