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

Abstract

The invention discloses a preparation method and application of a catalyst for preparing vinyl chloride by cracking 1, 2-dichloroethane, and the method comprises the following steps: 1) carrying out dump leaching on neodymium ore with hydrochloric acid, filtering the impregnation liquid, adding potassium chloride, and complexing to generate a doped precursor K2 [NdCl3]; 2) dissolving an active metal oxide with hydrochloric acid, adding the active metal oxide into the doped precursor K2 [NdCl3] solution, and adding alkali for coprecipitation to obtain an active component doped emulsion; the active metal oxide is an oxide of at least one of metal vanadium, manganese, titanium and scandium; and 3) mixing the emulsion doped with the active component 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.

Description

Technical Field

[0001] The present invention relates to a catalyst for producing vinyl chloride by catalytic cracking, and in particular to a method for preparing a catalyst for producing vinyl chloride by cracking 1,2-dichloroethane and its application, and belongs to the petrochemical industry chain. Background Art

[0002] Vinyl chloride (VCM for short) is a very important chemical raw material, mainly used for the synthesis of polyvinyl chloride resin (PVC) and vinylidene chloride, refrigerants, etc. At present, the main production processes of vinyl chloride include calcium carbide acetylene method, balanced oxychlorination method, and new processes such as direct chlorination of ethylene / hydrogen chloride oxidation and direct oxychlorination of ethane. The production of VCM using the balanced oxychlorination method accounts for more than 90% of the total production of VCM, and is the most widely used VCM production method.

[0003] The reaction process of the balanced oxychlorination method is generally divided into three parts: direct chlorination of ethylene, oxychlorination of ethylene, and cracking of 1,2-dichloroethane (EDC for short). Its device is mainly composed of process units such as direct chlorination unit, oxychlorination unit, EDC cracking unit, EDC refining unit and VCM refining unit. The EDC cracking process currently adopts a thermal cracking method. The reaction is carried out at a cracking temperature of 450-550°C, and 1,2-dichloroethane is converted into vinyl chloride and hydrogen chloride and other by-products. This reaction requires a large amount of natural gas or other fuels during the production process, and a large amount of coking occurs during the reaction process. It is necessary to stop and clean the coke regularly, which has a great impact on the normal operation of production. The cause of coking is greatly affected by temperature and raw material composition. When the temperature is lowered or the coking-promoting components are adjusted, the occurrence of coking can be effectively reduced. Therefore, the use of suitable catalytic components to reduce the reaction temperature of cracking is beneficial to the cracking process, and greater benefits will be obtained in terms of saving fuel and extending the operating time.

[0004] U.S. Patent US5008225A discloses a catalyst for catalytic cracking of 1,2-dichloroethane to produce vinyl chloride, which is prepared by loading rare earth elements on HFZ-20, HFZ-30, and HFZ-55 molecular sieves to catalytically crack 1,2-dichloroethane to produce vinyl chloride. When the conversion rate of 1,2-dichloroethane is 35.8%, the maximum selectivity of VCM is 90.1%, which is not very high. CN105268457B discloses a catalyst for cracking 1,2-dichloroethane, which is loaded with a metal chloride. The catalyst can be used to carry out cracking reactions under milder operating conditions, further improving the conversion rate and high selectivity, but the catalyst must be loaded in a fixed bed or a fluidized bed, which is inconsistent with the operating conditions of an industrial cracking furnace. CN102247884B discloses a catalyst for preparing vinyl chloride from 1,2-dichloroethane, which is composed of 10.0-80.0wt% of zeolite and 20.0-90.0wt% of an inorganic oxide matrix and is also applied in a fluidized bed system, which is inconsistent with the operating conditions of an industrial cracking furnace.

[0005] In summary, most of the catalysts for catalytic cracking of 1,2-dichloroethane are molecular sieve-loaded, which are used in fixed beds or fluidized beds after molding, with large consumption and average effect. In fact, in the industrial cracking process, 1,2-dichloroethane is vaporized by the vaporizer and enters the cracking furnace in the gas phase, and is cracked at high speed in the furnace tube. Therefore, how to achieve catalysis in this process is a problem that needs to be solved. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for preparing a catalyst for preparing vinyl chloride by cracking 1,2-dichloroethane and its application.

[0007] The inventors have continued to study and found that the reaction of 1,2-dichloroethane cracking to generate vinyl chloride is actually a dehalogenation reaction process, in which the dehalogenation reaction is the controlling step, which is determined by the B acid position of the catalyst active center. In the actual catalytic reaction process, on the one hand, due to the carbon deposition of the active center, the active center is covered, and the reactant molecules cannot approach the B acid position, resulting in the loss of B acid position function (i.e., alkali poisoning), which is one of the reasons for the deactivation of the catalyst. On the other hand, the generated Cl reacts with the active component (such as the combination of Cl-Mn and Cl-V forms), resulting in the reduction of active components (i.e., chlorine poisoning), which is another reason for the deactivation of the catalyst. In terms of the carrier, due to improper selection of the carrier, it is another reason for the poor catalytic effect that a larger active surface or B acid position cannot be provided. In addition, when a suitable active component or carrier is selected, how to be injected into the gas phase process is worth considering. The existing molecular sieve catalyst cannot be used in gas phase cracking, so it is generally used in a fixed bed system.

[0008] Aiming at the above cracking process, the present invention designs a gasifiable catalyst component from the perspective of catalyst principle and morphology, which ensures the catalytic effect while being more convenient to add in the gas phase process, and has significant advantages.

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

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

[0011] 1) Heap leaching of neodymium ore with hydrochloric acid, filtering the leaching solution and adding potassium chloride for complexation to generate doping precursor K2[NdCl3];

[0012] 2) dissolving the active metal oxide with hydrochloric acid, adding it to the above-mentioned doping precursor K2[NdCl3] solution, adding alkali for co-precipitation, and obtaining an emulsion doped with active components; the active metal oxide is an oxide of at least one of metal vanadium, manganese, titanium, and scandium;

[0013] 3) The emulsion doped with the active component is mixed with a liquid carrier to obtain the catalyst; when the catalyst is used in the reaction of cracking 1,2-dichloroethane to prepare vinyl chloride, it is fully mixed with 1,2-dichloroethane and then 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 content of metal neodymium in the neodymium ore is 19-23wt%. For example, the neodymium ore that can be selected is the West Tailing Neodymium Ore in Bayan Obo (Nd content 23wt%), the Xiangshan Neodymium Ore in Jiangxi (Nd content 21wt%), the Zhenjiang Rare Earth Neodymium Ore (Nd content 19wt%), 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, calculated as the mass ratio of active metal oxide to metal neodymium.

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

[0020] In some examples of the present invention, the base 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 the mixing time of the two is preferably 20-60 min.

[0023] The invention discloses an application of a catalyst prepared according to the method described above in the reaction of cracking 1,2-dichloroethane to prepare vinyl chloride.

[0024] In some examples of the present invention, the specific application method is:

[0025] The catalyst and liquid 1,2-dichloroethane are mixed, preheated to vaporization, and then sent to a cracking furnace for cracking reaction, maintaining the reaction inlet temperature at 225-235°C, the reaction residence time at 10-15s, and quenching and separation after the reaction. The product vinyl chloride stream is obtained at the bottom of the tower, and hydrogen chloride is collected at the top of the tower for further recycling. The bottom stream also contains a certain amount of unreacted 1,2-dichloroethane, and the product vinyl chloride can be deeply purified by conventional refining separation.

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

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

[0028] (1) The introduction of a metal called neodymium, which has never been considered before, to prepare a doped active catalyst unexpectedly found that it can effectively prevent the loss of active components and carbon deposition at active sites, thereby improving the catalyst's ability to resist poisoning.

[0029] (2) Chlorine-containing organic solvents are selected as carriers of the catalyst, which can be vaporized and then enter the cracking furnace to meet the gas phase cracking process conditions. 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 DESCRIPTION

[0031] The present invention is further described below by means of specific examples. The examples described in the present invention are only used to illustrate the present invention and do not limit the scope of the present invention.

[0032] The raw materials and reagents used in the following examples of the present invention are all analytically pure (AR) unless otherwise specified, including Bayan Obo West Tailing Nd ore (Nd content 23wt%), Jiangxi Xiangshan Nd ore (Nd content 21wt%), and Zhenjiang rare earth Nd ore (Nd content 19wt%).

[0033] The test or calculation method used in the following embodiments of the present invention is as follows:

[0034]

[0035]

[0036] Example 1

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

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

[0039] (3) The emulsion doped with the active component is mixed with a liquid carrier at a volume ratio of 5:1000, and stirred for 60 minutes 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 to obtain a filtrate after the reaction, add 53g of 40wt% potassium chloride solution to the filtrate, react at room temperature for 30min, and obtain a doping precursor K2[NdCl3] solution.

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

[0043] (3) The emulsion doped with the active component is mixed with a liquid carrier at a volume ratio of 1:1000, and stirred for 20 minutes 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 to obtain a filtrate after the reaction, add 143g of 40wt% potassium chloride solution to the filtrate, react at room temperature for 45min, and obtain a doping precursor K2[NdCl3] solution.

[0046] (2) 152 g of V2O5 was dissolved in 500 mL of 28% hydrochloric acid, and then added to the above-mentioned doping precursor K2[NdCl3] solution, and then NaOH was added to adjust the pH to 8. The mixture was stirred at room temperature for 45 min to obtain an emulsion doped with active components.

[0047] (3) The emulsion doped with the active component is mixed with a liquid carrier at a volume ratio of 3:1000, and stirred for 20 minutes 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 substantially the same manner as in Example 1, except that MnO in step (2) was replaced by TiO2 and the liquid carrier was replaced by carbon tetrachloride.

[0050] Example 5

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

[0052] Comparative Example 1

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

[0054] Comparative Example 2

[0055] The catalyst was prepared in a method substantially the same as in Example 1, with the only difference being that the Bayan Obo rare earth ore in step 1 was replaced with lanthanum chloride in an amount that ensured that the masses of metallic lanthanum and metallic neodymium were the same.

[0056] Comparative Example 3

[0057] The catalyst was prepared in a method substantially the same as that in Example 1, except that the Bayan Obo rare earth ore in step 1 was replaced by a mixture of equal masses of calcium chloride and cesium chloride in an amount that ensured that the mass of metallic calcium was twice the mass of metallic neodymium.

[0058] Comparative Example 4

[0059] The catalyst was prepared in a method substantially the same as that in Example 1, except that the Bayan Obo rare earth ore in step 1 was replaced by a mixture of equal masses of calcium chloride and cesium chloride, the amount of which ensured that the mass of metallic calcium was twice the mass of metallic neodymium; at the same time, the liquid carrier used in step 3 was replaced by a 4A molecular sieve (less than 40 μm), and then the catalyst was pressed into shape.

[0060] Comparative Example 5

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

[0062] Application Examples

[0063] According to the EDC cracking experimental conditions in Table 1, the catalysts provided in each embodiment and comparative example were evaluated respectively (the solid catalysts in Comparative Examples 1 and 4 were fed by loading in the cracking furnace, and the catalysts in other embodiments and comparative examples were mixed with EDC in an amount of 0.5wt% of the mass of EDC and fed). The EDC to be evaluated came from the crude EDC produced by Wanhua, and the composition and content are detailed in Table 2 below. The relevant components were analyzed using an Agilent 7890B gas chromatograph with a four-valve six-column injection system, and the test standard was "GB / T16088-1995 Direct Injection Gas Chromatography Determination Method for Vinyl Chloride", and 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 of continuous reaction (within 6 hours)

[0069]

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

[0071]

[0072]

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

[0074] Although the solid support catalysts provided in Comparative Examples 1 and 4 can be loaded in the cracking furnace for catalytic reaction, it was found during the experiment that the catalyst was entrained and blown out during the continuous gas-phase feeding process and the pressure difference in the cracking furnace tube was large, causing the feed pipeline and the furnace tube to be blocked. The operation was forced to stop after only 6 hours, so it cannot be used for a long time in the cracking process of gas-phase feeding.

[0075] The above is only a preferred embodiment of the present invention. It should be pointed out that ordinary technicians in this field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a catalyst for cracking 1,2-dichloroethane to produce vinyl chloride, characterized in that: The following steps are involved: 1) Heap leaching of neodymium ore with hydrochloric acid, filtering the leaching solution and adding potassium chloride for complexation to generate doping precursor K2[NdCl3]; 2) dissolving the active metal oxide with hydrochloric acid, adding it to the above-mentioned doping precursor K2[NdCl3] solution, adding alkali for co-precipitation, and obtaining an emulsion doped with active components; the active metal oxide is an oxide of at least one of metal vanadium, manganese, titanium, and scandium; 3) mixing the emulsion doped with the active component 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.

2. The method for preparing a catalyst for preparing vinyl chloride by cracking 1,2-dichloroethane according to claim 1, characterized in that: The content of metallic neodymium in the neodymium ore is 19-23wt%.

3. The method for preparing a catalyst for preparing vinyl chloride by cracking 1,2-dichloroethane according to claim 2, characterized in that: In step 1), the mass of potassium chloride added is 1-3 times the mass of metallic neodymium in the neodymium ore.

4. The method for preparing a catalyst for preparing vinyl chloride by cracking 1,2-dichloroethane according to any one of claims 1 to 3, characterized in that: The amount of raw materials used in step 2) is (6-10):1 based on the mass ratio of active metal oxide to metal neodymium.

5. The method for preparing a catalyst for preparing vinyl chloride by cracking 1,2-dichloroethane according to any one of claims 1 to 3, characterized in that: In step 2), the amount of alkali added is adjusted to adjust the solution pH to 8-11.

6. The method for preparing a catalyst for preparing vinyl chloride by cracking 1,2-dichloroethane according to claim 5, characterized in that: The alkali is one or more of sodium hydroxide and potassium hydroxide.

7. The method for preparing a catalyst for preparing vinyl chloride by cracking 1,2-dichloroethane according to any one of claims 1 to 3, characterized in that: In step 3), the volume ratio of the emulsion doped with the active component to the liquid carrier is (1-5):1000, and the mixing time of the two is preferably 20-60 min.

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

9. The use according to claim 8, characterized in that: The specific application method is: The catalyst and liquid 1,2-dichloroethane are mixed, preheated to vaporization, and then sent to a cracking furnace for cracking reaction, maintaining the reaction inlet temperature at 225-235° C. and the reaction residence time at 10-15 seconds. After the reaction is completed, rapid cooling and separation are performed to obtain a product vinyl chloride flow at the bottom of the tower, and hydrogen chloride is collected at the top of the tower for further recovery and treatment.

10. The use according to claim 9, 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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