Method for preparing vinyl chloride from calcium carbide acetylene

Abstract

The invention belongs to the technical field of vinyl chloride, and discloses a method for preparing vinyl chloride from calcium carbide acetylene. The method comprises the following steps: mixing dry acetylene and hydrogen chloride gas, preheating, feeding into a vinyl chloride conversion process, and reacting the mixed gas under the action of a two-stage converter and a mercury-free gold-based catalyst to generate vinyl chloride gas and a small amount of by-products such as acetaldehyde. The acetylene conversion rate of the foreground converter is about 70%, the mixed gas at the outlet of the foreground converter contains 20-30% of unconverted acetylene gas, the mixed gas enters the background converter along with the crude vinyl chloride for continuous reaction, the unconverted acetylene gas in the gas at the outlet of the background converter is controlled to be below 3% after the reaction is finished, the reaction temperature does not need to be increased, and after passing through the background converter, the acetylene gas in the outlet of the background converter can be recovered. And the total conversion rate of acetylene reaches 99%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chloroethylene, in particular to a method for preparing chloroethylene by calcium carbide acetylene. BACKGROUND

[0002] Polyvinyl chloride (PVC) resin is a polymer polymerized from vinyl chloride monomer (VCM). Due to its characteristics such as flame retardant, wear-resistant, biodegradation-resistant, chemical corrosion-resistant, excellent insulation and thermal insulation performance, etc., it is widely used in important fields such as industry, agriculture, national defense, building materials, etc., and becomes the second largest general-purpose resin in the world, and its consumption is still increasing year by year.

[0003] Currently, there are two main VCM production processes, namely the ethylene process based on the petroleum route and the calcium carbide acetylene process based on the coal route. In the calcium carbide process, industrial mercury chloride catalyst (HgCl2 / AC) is used to prepare vinyl chloride monomer. HgCl2 is a highly toxic compound, which has great potential risks and safety hazards in transportation, storage and use. Due to high temperature and other factors in the reaction process, Hg element volatilizes, part of Hg enters the product with the raw material gas, and another part enters the environment through "three wastes", which has great harm to the environment and workers' health. Although low-mercury catalyst has replaced high-mercury catalyst, the content of HgCl2 is less than 6.5 wt%, but the low-mercury catalyst still has many problems such as poor stability, high mercury loss rate, poor system stability, etc. in the use process, which can only play a transitional role. According to the calculation that 1.2 kg of low-mercury catalyst is consumed for producing 1 ton of polyvinyl chloride, the PVC output of calcium carbide acetylene method reaches 28 million tons in 2025, and the Hg resources consumed reach about 1350 tons, of which about 408 tons can be recycled, and 942 tons of Hg enters the environment, causing great pollution to the environment.

[0004] According to statistics, the mercury consumption of acetylene process accounts for more than 60% of the total mercury consumption. Moreover, with the decline of mercury ore grade and the depletion of mercury ore resources, the price of mercury resources is gradually increasing. And with the increasing calls for "limiting mercury and banning mercury" at home and abroad, the environmental protection pressure is increasing. These challenges and pressures on the acetylene process are unprecedented. In order to reduce the consumption and dependence on mercury resources and alleviate the increasing environmental pressure, in the case of not changing the current PVC industry structure, using mercury-free catalyst to replace the current industrial HgCl2 / AC catalyst to realize green and clean production of acetylene process is undoubtedly the best solution.

[0005] Since last century, domestic and foreign experts and scholars have carried out a large number of researches on the mercury pollution problem of the PVC industry prepared by calcium carbide acetylene method, and started to develop mercury-free catalysts for acetylene hydrochlorination that can replace the existing mercuric chloride. According to the active components, the mercury-free catalysts are roughly divided into two categories of noble metals and non-noble metals, supplemented by other metal compounds as additives. The base metal catalytic system is one kind of catalytic system taking Cu, Bi, Sn, Ca, Cd, Zn and other metals as catalytic active components, and the other kind of catalytic system taking group IIIB elements as main active components supplemented by rare earth metal compounds such as cerium oxide and lanthanum oxide. At present, relevant scientific researchers have basically screened the activity and life of most non-noble metal compounds, and compared with mercuric chloride catalyst, the non-noble metal mercury-free catalyst generally has the shortcomings of low activity or short life. From the current achievements, the research of non-noble metals is largely at the laboratory stage, and it is difficult to achieve long life and high activity, and few can obtain industrial application breakthrough.

[0006] The noble metal catalytic system is a catalytic system taking Au, Pt, Pd and other noble metals as catalytic active components. The researchers found that in the research of metal catalysts in acetylene hydrochlorination reaction, with the increase of the standard electrode potential of the metal, the activity of the catalyst will increase accordingly, which indicates that gold with high standard electrode potential will be a very effective catalyst for acetylene hydrochlorination reaction. The experiment has proved this point. Further experimental research proves that Au / AC catalyst is the most potential catalyst to replace industrial HgCl2 / AC catalyst. Compared with industrial HgCl2 / AC catalyst, it has obvious advantages in catalytic activity, vinyl chloride selectivity and environmental protection. Moreover, Au component will not be lost obviously in the process of catalytic reaction, and the recovery process of Au in the scrapped Au catalyst is relatively mature and perfect, so Au can be recycled and reused as much as possible from the scrapped catalyst. Although the one-time investment cost of Au catalyst is relatively high, due to the recyclability, the long-term investment cost is not very high, and it has good industrialization prospect.

[0007] However, in the current Au / AC catalytic acetylene process, only part of the front conversion uses gold-based catalyst, and there is no gold-based catalyst in the back conversion, and the acetylene conversion rate is low; at the same time, after the converter leaks, AuCl3 is dissolved in hydrochloric acid to precipitate, and the catalyst loses activity. SUMMARY

[0008] The purpose of the present application is to provide a method for preparing vinyl chloride by calcium carbide acetylene method, which solves the above problems existing in the Au / AC catalytic acetylene method process of the prior art.

[0009] In order to achieve the above-mentioned purpose of the application, the present application provides the following technical solutions: The present application provides a method for preparing vinyl chloride by calcium carbide acetylene method, comprising the following steps: The acetylene gas and the hydrogen chloride gas are mixed in a mixer, and then preheated by a preheater to obtain a mixed gas; the mixed gas is sent into a front-stage converter filled with a mercury-free gold-based catalyst to perform a first reaction, so as to obtain crude vinyl chloride; the crude vinyl chloride is sent into a back-stage converter filled with a mercury-free gold-based catalyst to perform a second reaction, so as to obtain the vinyl chloride; The acetylene gas and the hydrogen chloride gas are mixed in a mixer, and then preheated by a preheater to obtain a mixed gas; the mixed gas is sent into a front-stage converter filled with a mercury-free gold-based catalyst to perform a first reaction, so as to obtain crude vinyl chloride; the crude vinyl chloride is sent into a back-stage converter filled with a mercury-free gold-based catalyst to perform a second reaction, so as to obtain the vinyl chloride;

[0010] Preferably, in the method for preparing the vinyl chloride by using the acetylene prepared from the calcium carbide, the volume ratio of the acetylene gas to the hydrogen chloride gas is 1:1.05-1.1.

[0011] Preferably, in the method for preparing the vinyl chloride by using the acetylene prepared from the calcium carbide, the preheating temperature is 90°C; and the temperature of the first reaction and the second reaction is independently 130-180°C.

[0012] Preferably, in the method for preparing the vinyl chloride by using the acetylene prepared from the calcium carbide, each of the front-stage converter and the back-stage converter filled with the mercury-free gold-based catalyst is a fixed-bed tube reactor, and the mercury-free gold-based catalyst fills the fixed-bed tube.

[0013] Preferably, in the method for preparing the vinyl chloride by using the acetylene prepared from the calcium carbide, the mercury-free gold-based catalyst comprises a carrier and a gold-based active component; the carrier is activated carbon; and the mass content of the gold-based active component in the mercury-free gold-based catalyst is 0.095-0.105%.

[0014] Preferably, in the method for preparing the vinyl chloride by using the acetylene prepared from the calcium carbide, the front-stage converter and the back-stage converter adopt heptane for heat removal.

[0015] Preferably, in the method for preparing the vinyl chloride by using the acetylene prepared from the calcium carbide, the crude vinyl chloride further contains acetylene gas; and the volume fraction of the acetylene gas in the crude vinyl chloride is 20-30%.

[0016] Preferably, in the method for preparing the vinyl chloride by using the acetylene prepared from the calcium carbide, the method further comprises: when the volume fraction of the acetylene gas in the outlet gas of the back-stage converter is greater than 3%, the back-stage converter is used as the front-stage converter; and when the conversion rate of the acetylene gas in the front-stage converter is less than 30%, the mercury-free gold-based catalyst filled therein is extracted and recycled by a catalyst recycling system.

[0017] According to the technical solution, compared with the prior art, the present application has the following beneficial effects: The present application mixes dry acetylene and hydrogen chloride gas, preheats them, and then sends them into a vinyl chloride conversion process. The mixed gas is reacted in two-stage converters and mercury-free gold-based catalysts to produce vinyl chloride gas and a small amount of byproducts such as acetaldehyde. The acetylene conversion rate of the front-stage converter is about 70%, and the mixed gas at the outlet of the front-stage converter contains 20-30% of unconverted acetylene gas, which is sent into the back-stage converter to continue the reaction with the crude vinyl chloride. After the reaction, the unconverted acetylene gas at the outlet of the back-stage converter is controlled to be less than 3%, and the reaction temperature does not need to be increased. After the back-stage converter, the total conversion rate of acetylene reaches 99%. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description.

[0019] Figure 1 A flowchart of a process for preparing vinyl chloride from calcium carbide acetylene according to the present application. DETAILED DESCRIPTION

[0020] The present application provides a method for preparing vinyl chloride from calcium carbide acetylene, and a flowchart is shown as follows: Figure 1 The method comprises the following steps: The acetylene gas and hydrogen chloride gas are mixed in a mixer, and then preheated in a preheater to obtain a mixed gas. The mixed gas is sent into a front-stage converter filled with mercury-free gold-based catalysts to perform a first reaction, and then crude vinyl chloride is obtained. The crude vinyl chloride is sent into a back-stage converter filled with mercury-free gold-based catalysts to perform a second reaction, and then vinyl chloride is obtained.

[0021] In the present application, the chemical reaction formula of the reaction is as follows: Main reaction: C2H2+HCl→C2H3Cl Byproduct reaction: C2H2+H2O→C2H4O C2H2+2HCl→C2H4Cl2 In the present application, the acetylene gas is calcium carbide acetylene gas.

[0022] In the present application, the acetylene gas and hydrogen chloride gas are further subjected to dehydration before mixing in the mixer; the dehydration method of the acetylene gas is pressure swing adsorption method; the dehydration method of the hydrogen chloride gas is sulfuric acid drying; the water content of the acetylene gas after dehydration is < 30 ppm; the water content of the hydrogen chloride gas after dehydration is < 50 ppm. The present application dehydrates the reaction gas in advance and controls the water content, so as to meet the requirement that the water content of the mixed gas is < 100 ppm, ensure that the mercury-free gold-based catalyst operates in a high activity state, and make the operating time of the mercury-free gold-based catalyst reach more than 8000 h; if the water content of the mixed gas is > 100 ppm, the requirement of the gold-based catalyst cannot be met (the gold-based catalyst is easily inactivated when water is encountered, and it cannot be recycled and regenerated).

[0023] In the present application, the volume ratio of the acetylene gas to the hydrogen chloride gas is preferably 1:1.05-1.1, further preferably 1:1.08-1.1, and more preferably 1:1.1.

[0024] In the present application, the preheating temperature is preferably 90°C; the temperature of the first reaction and the second reaction is independently preferably 130-180°C, further preferably 130-170°C, and more preferably 130°C. The first reaction and the second reaction of the present application are isothermal catalytic reactions, the reaction process is easy to control, and the side reactions are less.

[0025] In the present application, each of the front-stage converter loaded with the mercury-free gold-based catalyst and the back-stage converter loaded with the mercury-free gold-based catalyst is a fixed-bed tube reactor, the mercury-free gold-based catalyst fills the fixed-bed tube, and the size of the fixed-bed tube reactor is preferably 3200x5980 mm, and the loading amount of the mercury-free gold-based catalyst is preferably 5.2 tons.

[0026] In the present application, the mercury-free gold-based catalyst comprises a carrier and a gold-based active component; the carrier is preferably activated carbon; the mass content of the gold-based active component in the mercury-free gold-based catalyst is preferably 0.095-0.105%, the bulk density is preferably 430-530 g / L, and the moisture content is less than 0.6%; and the specification of the mercury-free gold-based catalyst is preferably 3x6 mm. The gold-based active component of the mercury-free gold-based catalyst used in the examples of the present application is gold, and the mercury-free gold-based catalyst is the catalyst of model FDGC617 of Liaoning Fangda Engineering Design Co., Ltd.

[0027] In the present application, heptane is used for heat removal of the front-stage converter and the back-stage converter. In the present application, the vaporization pressure of heptane is controlled by the flow of cooling hot water of the converter condenser, so as to indirectly control the temperature of the reaction. The use of heptane for heat removal in the present application can avoid the risk of external corrosion and leakage of the reactor when water is usually used as the heat removal medium.

[0028] ​​In the present application, the front-stage converter adopts 14 converters in parallel; the back-stage converter adopts 14 converters in parallel.

[0029] In the present application, the crude chloroethylene also contains acetylene gas; the volume fraction of acetylene gas in the crude chloroethylene is 20-30%. The mixed gas is sent into the front-stage converter filled with mercury-free gold-based catalyst, and the reaction is carried out until the volume fraction of acetylene gas in the crude chloroethylene is 20-30%.

[0030] In the present application, the method for preparing chloroethylene from calcium carbide acetylene also comprises: when the volume fraction of acetylene gas in the outlet gas of the back-stage converter is greater than 3%, the back-stage converter is used as the front-stage converter; when the conversion rate of acetylene gas in the front-stage converter is less than 30%, the loaded mercury-free gold-based catalyst is extracted, recycled through a catalyst recycling system, and a new mercury-free gold-based catalyst is loaded. The front-stage converter and the back-stage converter are arranged in a 1:1 manner, and the front-stage converter and the back-stage converter are switched through valve switching to achieve the switching of the front-stage catalyst and the back-stage catalyst. Since the gold-based catalyst is relatively valuable, the original traditional way of turning over the gold-based catalyst will cause the loss of gold. Through online valve switching, the back-stage converter becomes the front-stage converter, and the operation is carried out without turning over the catalyst, thereby saving manpower, time and the loss of gold-based catalyst, and protecting the ecological environment and reducing labor costs.

[0031] In the present application, the crude chloroethylene is sent into the back-stage converter filled with mercury-free gold-based catalyst, and the reaction is carried out. After the reaction is completed, the outlet gas of the back-stage converter is also sent into the purifier for post-treatment.

[0032] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0033] Embodiment 1

[0034] The present embodiment provides a method for preparing chloroethylene from calcium carbide acetylene, comprising the following steps: After the acetylene gas and the hydrogen chloride gas are dried by sulfuric acid respectively, the two are mixed in a mixer at a volume ratio of 1:1.1, and then preheated to 90°C through a preheater to obtain mixed gas; the mixed gas is sent into the front-stage converter filled with mercury-free gold-based catalyst, and the mercury-free gold-based catalyst (the mass content of gold is 0.1%, and the specification is 3×6 mm) is in a size of 3×6 mm. 3×6mm) in a size of 3×6 mm. The packing amount of the 3200x5980mm fixed bed column is 5.2 tons, the reaction temperature is controlled by heptane heat removal at 130℃, the reaction is carried out until the volume fraction of acetylene gas in the crude vinyl chloride is 30%, and the crude vinyl chloride is obtained; the crude vinyl chloride is sent into the post-conversion device packed with mercury-free gold-based catalyst, the mercury-free gold-based catalyst (the mass content of gold is 0.1%, the specification is 3x6mm) is in the size 3x6mm) in the size The packing amount of the 3200x5980mm fixed bed column is 5.2 tons, the reaction temperature is controlled by heptane heat removal at 130℃, the reaction is carried out until the volume fraction of acetylene gas in the crude vinyl chloride is 30%, and the crude vinyl chloride is obtained; the crude vinyl chloride is sent into the post-conversion device packed with mercury-free gold-based catalyst, the mercury-free gold-based catalyst (the mass content of gold is 0.1%, the specification is 3x6mm) is in the size

[0035] The acetylene conversion rate after the front-conversion device reaction is 70%, the acetylene conversion rate after the post-conversion device reaction is 99%, the purity of vinyl chloride is 92wt%, the byproduct content: 1,1-dichloroethane content is 0.3wt%, acetaldehyde content is 0.003wt%.

[0036] The above only describes the preferred embodiments of the present application, it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can also be made, these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A process for the production of chloroethylene from calcium carbide acetylene, characterized in that, The method comprises the following steps: The acetylene gas and the hydrogen chloride gas are mixed in a mixer, and then preheated by a preheater to obtain a mixed gas; the mixed gas is sent into a front-stage converter filled with mercury-free gold-based catalyst to perform a first reaction to obtain crude vinyl chloride; the crude vinyl chloride is sent into a back-stage converter filled with mercury-free gold-based catalyst to perform a second reaction to obtain vinyl chloride; The acetylene gas and the hydrogen chloride gas are mixed in a mixer, and then preheated by a preheater to obtain a mixed gas; the mixed gas is sent into a front-stage converter filled with mercury-free gold-based catalyst to perform a first reaction to obtain crude vinyl chloride; the crude vinyl chloride is sent into a back-stage converter filled with mercury-free gold-based catalyst to perform a second reaction to obtain vinyl chloride; The acetylene gas and the hydrogen chloride gas are mixed in a mixer, and then preheated by a preheater to obtain a mixed gas; the mixed gas is sent into a front-stage converter filled with mercury-free gold-based catalyst to perform a first reaction to obtain crude vinyl chloride; the crude vinyl chloride is sent into a back-stage converter filled with mercury-free gold-based catalyst to perform a second reaction to obtain vinyl chloride; The acetylene gas and the hydrogen chloride gas are mixed in a mixer, and then preheated by a preheater to obtain a mixed gas; the mixed gas is sent into a front-stage converter filled with mercury-free gold-based catalyst to perform a first reaction to obtain crude vinyl chloride; the crude vinyl chloride is sent into a back-stage converter filled with mercury-free gold-based catalyst to perform a second reaction to obtain vinyl chloride; 2. A method of preparing chloroethylene from calcium carbide acetylene according to claim 1, characterized in that, The crude vinyl chloride also contains acetylene gas; the volume fraction of the acetylene gas in the crude vinyl chloride is 20-30%.

3. A method of preparing chloroethylene from calcium carbide acetylene according to claim 2, characterized in that, The volume ratio of the acetylene gas to the hydrogen chloride gas is 1:1.05-1.

1.

4. The method of claim 1, wherein the calcium carbide acetylene preparation chloroethylene method is characterized by, The preheating temperature is 90 DEG C; the temperature of the first reaction and the second reaction is independently 130-180 DEG C.

5. The method of claim 1, wherein the calcium carbide acetylene preparation chloroethylene method is characterized by, The mercury-free gold-based catalyst comprises a carrier and a gold-based active component; the carrier is activated carbon; the mass content of the gold-based active component in the mercury-free gold-based catalyst is 0.095-0.105%.

6. The method of claim 1, wherein the calcium carbide acetylene preparation chloroethylene method is characterized by, The front-stage converter and the back-stage converter adopt heptane heat removal. The method for preparing vinyl chloride from calcium carbide acetylene also comprises: when the volume fraction of the acetylene gas in the outlet gas of the back-stage converter is greater than 3%, the back-stage converter is used as a front-stage converter; when the conversion rate of the acetylene gas in the front-stage converter is less than 30%, the loaded mercury-free gold-based catalyst is extracted and recycled through a catalyst recovery system.

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