A process for the production of vinyl chloride using a mercury-free catalyst

Abstract

The present application provides a process for producing vinyl chloride using a mercury-free catalyst, belonging to the technical field of synthesis of vinyl chloride by acetylene method. The process controls the parallel or counter-current heat exchange of the first and second stage converters, and uses different heat exchange media in the first and second stage converters, so as to match the temperature requirements of the catalysts at different periods and different positions, ensure that the catalysts are always in the active temperature range throughout the life cycle, prevent the catalyst from flying temperature, and prolong the service life of the catalyst. The number of catalyst turnover can also be reduced, and the loss of catalyst pulverization can also be reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of synthesis method of chloroethylene by acetylene method, and particularly relates to a process for producing chloroethylene by using mercury-free catalyst. BACKGROUND

[0002] Polyvinyl chloride (PVC) is one of the most important synthetic plastics in the world, which has become the most commonly used product in daily life. The chloroethylene monomer is the main raw material for the synthesis of PVC. At present, there are three main methods for producing chloroethylene in the world, namely, ethylene oxychlorination method, ethane method and calcium carbide method. Due to the rich coal resources in China and the rising cost of petroleum, the acetylene method is one of the most popular and important processes for industrial production in China.

[0003] At present, 80% of the PVC production capacity in China is by the calcium carbide method, and the mercury consumption of the calcium carbide method PVC accounts for more than 80% of the domestic mercury consumption, which is the largest user of mercury in China. As a signatory country of the Minamata Convention on Mercury, China has promised to reduce the domestic mercury consumption. The Minamata Convention has officially come into effect globally on August 16, 2017, prohibiting the construction of new mercury process projects by the calcium carbide method, and stipulating that the mercury consumption per unit of product should be reduced by 50% in 2020 compared with that in 2010. At the same time, the Minamata Convention strongly supports the research and development of mercury-free catalysts and processes, and does not allow the use of mercury by the signatory countries after 5 years based on the existing process mercury-free catalyst technology and economic feasibility. China's PVC industry is facing the challenge of green mercury-free development, and is also expected to usher in a historical opportunity for strategic upgrading of the whole industry to break through the bottleneck. Therefore, the preparation of chloroethylene by low-cost mercury-free catalyst is the top priority for the sustainable development of the PVC industry.

[0004] In recent years, mercury-free catalysts with copper, gold and ruthenium as active metals have made great achievements and progress. Various types of mercury-free catalysts have entered industrial experiments, and gold-based and copper-based catalysts have shown excellent catalytic performance in industrial applications. However, due to the large difference in active temperature between gold and copper catalysts and mercury catalysts, it is urgent to optimize and reform the existing reaction equipment and process to better match the industrial application of mercury-free catalysts.

[0005] Several reports have been published on this topic. Chinese patent CN 202010935651 discloses an apparatus and method for the hydrochlorination of acetylene to vinyl chloride using a copper-based catalyst. This method employs co-current heat exchange between the feed gas and the heat exchange medium to prevent excessively high reaction temperatures and protect the catalyst. Chinese patent CN 201922219754 discloses a heat removal system for the conversion of vinyl chloride to heptane using a mercury-free catalyst. Based on existing converters, it increases the temperature of the heat removal medium to ensure the mercury-free catalyst operates within its activity range of 160–220°C. Chinese patent CN2019219112740 discloses a multi-mode mercury-free catalytic synthesis process apparatus for vinyl chloride, including a feed mixer and a hot water pump. The feed mixer is connected to a mixed gas preheater, which is connected to the material inlets of both the front-end and back-end converters. The material outlets of the front-end and back-end converters are interconnected and connected to an adsorption device. This utility model patent provides a multi-mode mercury-free catalytic synthesis process apparatus for vinyl chloride, where the front and back-end converters can be adjusted according to the process requirements.

[0006] The process requires the implementation of three modes: series, parallel, or a combination of series and parallel. When the activity of the mercury-free catalyst is high in the early stage, the parallel operation mode is adopted; when the activity is low in the later stage, the series or series-parallel operation mode is adopted. Adjusting these three modes can fully utilize the catalytic capacity of the mercury-free catalyst in the front-end converter and extend the service life of the mercury-free catalyst.

[0007] The aforementioned technologies all ensure, to some extent, that the mercury-free catalyst operates within its active temperature range. However, as the catalyst's operating time increases, the catalyst in the first stage of the converter deactivates first, and the hot spot shifts away from the feed gas inlet. At this point, the catalyst must be flipped between the front and rear stages to continue matching the exothermic and heat exchange of the catalytic reaction. However, the flipping process easily causes catalyst pulverization and loss, and the start-up and shutdown of the converter also affects the stability of production operations, potentially posing safety risks. Furthermore, domestic acetylene processes often employ a series process. Heptane, as a heat exchange medium, can effectively ensure that the mercury-free catalyst in the first-stage converter operates within its active range. However, the acetylene content at the inlet of the second-stage converter is low, making it difficult to guarantee that the reaction temperature remains within the active range even when using heptane. Summary of the Invention

[0008] This invention addresses the problems existing in the prior art by providing a process for synthesizing vinyl chloride using a mercury-free catalyst. Based on the existing vinyl chloride process and heat exchange system, certain adjustments are made. By controlling the co-current or counter-current heat exchange in the first and second stage converters and using different heat exchange media in the first and second stage converters, the temperature requirements of the catalyst at different times and locations are matched. This ensures that the catalyst remains within its active temperature range throughout its entire life cycle, prevents catalyst overheating, extends catalyst lifespan, and reduces the number of times the catalyst is turned over, thus reducing catalyst pulverization and loss.

[0009] To achieve the above object, the device comprises: a raw material gas pipeline 1, a first and second stage converter communication pipeline 2, a product crude vinyl chloride pipeline 3, a first stage converter 4, a second stage converter 5, valves 6, 7, 8, 9, wherein the raw material gas pipeline 1 is connected to the upper end of the first stage converter 4 through the valve 6 and connected to the lower end of the first stage converter 4 through the valve 7, the first and second stage converter communication pipeline 2 is connected to the upper end of the first stage converter 4 through the valve 6 and connected to the lower end of the first stage converter 4 through the valve 7, the first and second stage converter communication pipeline 2 is connected to the upper end of the second stage converter 5 through the valve 8 and connected to the lower end of the second stage converter 5 through the valve 9, the product crude vinyl chloride pipeline 3 is connected to the upper end of the second stage converter 5 through the valve 8 and connected to the lower end of the second stage converter 5 through the valve 9; wherein the first stage converter and the second stage converter are tubular fixed bed reactors, and the tubular fixed bed reactors are filled with mercury-free catalysts.

[0010] Preferably, the mixed acetylene and HCl enter the tubular fixed bed reactor of the first stage converter 4 through the raw material gas pipeline 1, then enter the second stage converter 5 for further reaction, and the product crude vinyl chloride is sent to the subsequent section through the pipeline 3. The heat exchange medium enters the shell side of the lower end of the converter, absorbs the heat released in the reactor, and then flows out from the upper end of the converter. The raw material gas enters the upper end of the first stage converter from the lower end or enters the lower end from the upper end through the valves 6 and 7, and the outlet of the first stage converter 4 enters the lower end of the second stage converter 5 from the upper end or enters the upper end from the lower end through the valves 8 and 9.

[0011] Preferably, at the initial stage of catalyst loading, the raw material gas enters the converter from the lower end for co-current heat exchange with the heat exchange medium, and at the end of catalyst use, the raw material gas enters the converter from the upper end for counter-current heat exchange with the heat exchange medium.

[0012] Preferably, the mercury-free catalyst filled in the converter is a gold-based mercury-free catalyst.

[0013] Preferably, the heat exchange medium used in the first and second stage converters is one or more of hot water, heptane, and octane.

[0014] Preferably, the heat exchange medium used in the first stage converter is a heat exchange medium with a larger saturated vapor pressure, and the heat exchange medium used in the second stage converter is a heat exchange medium with a smaller saturated vapor pressure.

[0015] Preferably, the heat exchange medium used in the first stage converter is heptane or water, and the heat exchange medium used in the second stage converter is octane.

[0016] According to the catalyst deactivation, the heat exchange mode of the parallel flow or the counter flow is flexibly adjusted, the raw material gas is adjusted to enter from the lower end of the converter to exchange heat with the heat exchange medium in the parallel flow at the initial stage of catalyst loading, and the raw material gas is adjusted to enter from the upper end of the converter to exchange heat with the heat exchange medium in the counter flow at the end stage of catalyst use, so that the heat exchange demand of the mercury-free catalyst in different periods can be effectively matched, and the catalyst is prevented from being overheated and deactivated. Meanwhile, the catalyst overturning frequency is reduced, and the catalyst pulverization and loss are reduced.

[0017] In addition, the heat exchange medium of the primary converter 4 adopts a heat exchange medium with a large saturated steam pressure (for example, heptane or water), so that the temperature of the heat exchange medium of the primary converter can be controlled at a relatively low level as much as possible within a limited pressure range (the design pressure of the existing shell side of the acetylene hydrochlorination converter is generally 0.3 MPa), and the primary converter is prevented from being overheated; and the heat exchange medium of the secondary converter adopts a heat exchange medium with a small saturated steam pressure (for example, octane), so that the temperature of the heat exchange medium of the secondary converter can be controlled to be higher within a limited pressure range (the design pressure of the existing shell side of the acetylene hydrochlorination converter is generally 0.3 MPa), and the reaction temperature of the latter stage converter is increased.

[0018] The beneficial effects of the present application are as follows:

[0019] The present application provides a process for synthesizing vinyl chloride by using mercury-free catalyst, and the feed form of the converter and the heat exchange medium of the primary and secondary converters are slightly changed and matched under the existing device conditions, so that the following beneficial effects are achieved:

[0020] 1) The catalyst is controlled to be in a reasonable temperature range in the whole life cycle by switching the parallel flow / counter flow heat exchange mode, and the service life of the catalyst is prolonged;

[0021] 2) The catalyst pulverization and loss caused by the up-down overturning are reduced;

[0022] 3) Different heat exchange media are used in the primary and secondary converters, the heat exchange medium with a low saturated steam pressure is used in the primary converter to prevent overheating, and the heat exchange medium with a high saturated steam pressure is used in the secondary converter, so that the catalyst can still maintain a high activity at the end of the life, which is beneficial to improving the catalyst activity and prolonging the service life of the catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a device structure schematic diagram used in the process for synthesizing vinyl chloride by using mercury-free catalyst.

[0024] In the figure, 1 is a raw material gas pipeline, 2 is a primary and secondary converter communication pipeline, 3 is a product crude vinyl chloride pipeline, 4 is a primary converter, 5 is a secondary converter, and 6-9 are valves. DETAILED DESCRIPTION

[0025] The technical solutions of the present application are described below through specific examples. It should be understood that the one or more method steps mentioned in the present application do not exclude other method steps before and after the combination steps or other method steps inserted between the explicitly mentioned steps; it should also be understood that the examples are only used to illustrate the present application and not to limit the scope of the present application. Moreover, unless otherwise specified, the numbering of the method steps is only a convenient tool to identify the method steps and is not a limitation on the arrangement order of the method steps or a limitation on the scope of the present application that can be implemented, and the change or adjustment of the relative relationship without substantial change of the technical content is also regarded as the scope of the present application that can be implemented.

[0026] A device used in a process for synthesizing vinyl chloride using a mercury-free catalyst is shown in FIG. 1. Figure 1 The device includes a raw material gas pipeline 1, a first and second stage converter communication pipeline 2, a product crude vinyl chloride pipeline 3, a first stage converter 4, a second stage converter 5, valves 6, 7, 8, and 9, wherein the raw material gas pipeline 1 is connected to the upper end of the first stage converter 4 through the valve 6 and connected to the lower end of the first stage converter 4 through the valve 7, the first and second stage converter communication pipeline 2 is connected to the upper end of the first stage converter 4 through the valve 6 and connected to the lower end of the first stage converter 4 through the valve 7, the first and second stage converter communication pipeline 2 is connected to the upper end of the second stage converter 5 through the valve 8 and connected to the lower end of the second stage converter 5 through the valve 9, and the product crude vinyl chloride pipeline 3 is connected to the upper end of the second stage converter 5 through the valve 8 and connected to the lower end of the second stage converter 5 through the valve 9; wherein the first stage converter and the second stage converter are shell-and-tube fixed bed reactors, and the tubes are filled with mercury-free catalysts.

[0027] The mixed acetylene and HCl enter the tubes of the first stage converter 4 from the raw material gas pipeline 1 to react, and then enter the second stage converter 5 to continue to react, and the product crude vinyl chloride is sent to the subsequent section from the pipeline 3. The heat exchange medium enters the shell side of the lower end of the converter, absorbs the heat released in the reactor, and then flows out from the upper end of the converter, is cooled and reused, the raw material gas is adjusted to enter from the lower end to the upper end or from the upper end to the lower end of the first stage converter through the valves 6 and 7, and the outlet of the first stage converter 4 is adjusted to enter from the upper end to the lower end or from the lower end to the upper end of the second stage converter 5 through the valves 8 and 9. At the initial stage of catalyst loading, the raw material gas is adjusted to enter from the lower end of the converter to exchange heat with the heat exchange medium in parallel flow, and at the end of catalyst use, the raw material gas is adjusted to enter from the upper end of the converter to exchange heat with the heat exchange medium in counterflow.

[0028] Example 1

[0029] The present embodiment relates to a process for producing vinyl chloride using mercury-free catalysts, which is carried out in the following manner: both the first and second converters are filled with fresh gold-based catalyst, and valves 6 and 7 and valves 8 and 9 are adjusted so that the raw material gas from raw material gas pipeline 1 enters the reactor tubes from the upper end of the first converter 4 and exchanges heat countercurrently with the heptane heat exchange medium in the shell side, the reacted gas flows out from the lower end of the first converter 4 and enters the upper end of the second converter 5 and exchanges heat countercurrently with the heptane heat exchange medium, and the generated product crude vinyl chloride is sent to the subsequent section by pipeline 3. The upper limit of the control pressure of the heat exchange medium is 0.3 MPa (gauge pressure).

[0030] Example 2

[0031] The same as example 1, except that the raw material gas enters from the lower end of the first converter 4, the outlet gas enters from the upper end of the first converter into the upper end of the second converter, and the crude vinyl chloride flows out from the lower end of the second converter 5 and is sent to the subsequent section by pipeline 3.

[0032] Example 3

[0033] The same as example 1, except that the raw material gas enters from the lower end of the first converter 4, the outlet gas enters from the upper end of the first converter into the lower end of the second converter, and the crude vinyl chloride flows out from the upper end of the second converter 5 and is sent to the subsequent section by pipeline 3.

[0034] Example 4

[0035] The same as example 1, except that the raw material gas enters from the upper end of the first converter 4, the outlet gas enters from the lower end of the first converter into the lower end of the second converter, and the crude vinyl chloride flows out from the upper end of the second converter 5 and is sent to the subsequent section by pipeline 3.

[0036] Example 5

[0037] Both the first and second converters are filled with fresh gold-based catalyst, and valves 6 and 7 and valves 8 and 9 are adjusted so that the raw material gas from raw material gas pipeline 1 enters the reactor tubes from the upper end of the first converter 4 and exchanges heat countercurrently with the heptane heat exchange medium in the shell side, the reacted gas flows out from the lower end of the first converter 4 and enters the upper end of the second converter 5 and exchanges heat countercurrently with the heptane heat exchange medium, and the generated product crude vinyl chloride is sent to the subsequent section by pipeline 3. The upper limit of the control pressure of the heat exchange medium is 0.3 MPa (gauge pressure).

[0038] Example 6

[0039] The same as example 5, except that the raw material gas enters from the lower end of the first converter 4, the outlet gas enters from the upper end of the first converter into the upper end of the second converter, and the crude vinyl chloride flows out from the lower end of the second converter 5 and is sent to the subsequent section by pipeline 3.

[0040] Example 7

[0041] The same as example 5, except that the feed gas enters the lower end of the primary converter 4, the outlet gas enters the lower end of the primary converter into the lower end of the secondary converter, and the crude vinyl chloride flows out of the upper end of the secondary converter 5 through the pipeline 3 to the subsequent section.

[0042] Example 8

[0043] The same as example 5, except that the feed gas enters the upper end of the primary converter 4, the outlet gas enters the lower end of the primary converter into the lower end of the secondary converter, and the crude vinyl chloride flows out of the upper end of the secondary converter 5 through the pipeline 3 to the subsequent section.

[0044] Example 9

[0045] Both the primary and secondary converters are filled with fresh gold-based catalysts with 10000h of operation, and the valves 6, 7 and the valves 8, 9 are adjusted so that the feed gas from the feed gas pipeline 1 enters the reactor tubes in the primary converter 4 countercurrently with the heptane heat exchange medium in the shell, the reacted gas flows out of the upper end of the primary converter 4 into the lower end of the secondary converter 5 countercurrently with the heptane heat exchange medium, and the generated product crude vinyl chloride is sent to the subsequent section by the pipeline 3. The upper limit of the control pressure of the heat exchange medium is 0.3 MPa (gauge pressure).

[0046] Example 10

[0047] Both the primary and secondary converters are filled with fresh gold-based catalysts with 10000h of operation, and the valves 6, 7 and the valves 8, 9 are adjusted so that the feed gas from the feed gas pipeline 1 enters the reactor tubes in the primary converter 4 countercurrently with the heptane heat exchange medium in the shell, the reacted gas flows out of the upper end of the primary converter 4 into the lower end of the secondary converter 5 countercurrently with the heptane heat exchange medium, and the generated product crude vinyl chloride is sent to the subsequent section by the pipeline 3. The upper limit of the control pressure of the heat exchange medium is 0.3 MPa (gauge pressure).

[0048] Example 11

[0049] Both the primary and secondary converters are filled with fresh gold-based catalysts with 10000h of operation, and the valves 6, 7 and the valves 8, 9 are adjusted so that the feed gas from the feed gas pipeline 1 enters the reactor tubes in the primary converter 4 countercurrently with the heptane heat exchange medium in the shell, the reacted gas flows out of the upper end of the primary converter 4 into the lower end of the secondary converter 5 countercurrently with the heptane heat exchange medium, and the generated product crude vinyl chloride is sent to the subsequent section by the pipeline 3. The upper limit of the control pressure of the heat exchange medium is 0.3 MPa (gauge pressure).

[0050] The specific temperature indicators are shown in Table 1:

[0051] Table 1 Temperature indicators

[0052]

[0053] The following conclusions can be drawn from Comparative Examples 1-11:

[0054] From Comparative Examples 1-4 or Examples 5-8, it can be concluded that the heat exchange in the downstream direction can effectively reduce the hot spot temperature of the converter, prevent the catalyst from deactivation due to temperature runaway, and prolong the service life of the catalyst.

[0055] From Comparative Examples 1-4 and Examples 5-8, it can be concluded that the heat exchange medium of the second-stage converter is replaced with octane, which has a smaller saturated vapor pressure, and the temperature of the downstream converter can be increased within a limited operating pressure (0.3 MPa), which is beneficial to improve the catalyst activity and prolong the service life of the downstream catalyst. In addition, from Comparative Examples 9 and 11, it can be concluded that the heat exchange medium of the second-stage converter can be octane, which has a smaller saturated vapor pressure, in the later stage of the catalyst life, and the catalyst operating temperature can be basically maintained within the temperature range in the early stage of the catalyst life, which is more beneficial to maintain the activity of the catalyst in the second-stage converter and prolong the use time of the catalyst in the downstream.

[0056] From Comparative Examples 9 and 10, it can be concluded that adjusting the heat exchange mode from downstream to upstream in the later stage of the catalyst life can effectively improve the reaction temperature.

[0057] The technical solutions of the present application are not limited to the technical solutions disclosed by the above technical means, but also include technical solutions composed of any combination of the above technical features. The above is the specific implementation of the present application, it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, can make a number of improvements and refinements, these improvements and refinements also as the protection scope of the present application.

Claims

1. A process for producing vinyl chloride using a mercury-free catalyst, characterized in that: The apparatus includes: a raw gas pipeline (1), a connecting pipeline between the first and second stage converters (2), a crude vinyl chloride product pipeline (3), a first stage converter (4), a second stage converter (5), valves I (6), II (7), III (8), and IV (9). The raw gas pipeline (1) is connected to the upper end of the first stage converter (4) via valve I (6) and to the lower end of the first stage converter (4) via valve II (7). The connecting pipeline between the first and second stage converters (2) is connected to the first stage converter (4) via valve I (6). The upper end is connected to the lower end of the first stage converter (4) through valve II (7). The connecting pipeline (2) between the first and second stage converters is connected to the upper end of the second stage converter (5) through valve III (8) and to the lower end of the second stage converter (5) through valve IV (9). The crude vinyl chloride pipeline (3) is connected to the upper end of the second stage converter (5) through valve III (8) and to the lower end of the second stage converter (5) through valve IV (9). Among them, the first stage converter and the second stage converter are tubular fixed bed reactors, and mercury-free catalysts are filled in the tubular reactors. In the initial stage of catalyst loading, the feed gas is adjusted to enter from the lower end of the converter and exchange heat with the heat exchange medium in a co-current manner. In the final stage of catalyst use, the feed gas is adjusted to enter from the upper end of the converter and exchange heat with the heat exchange medium in a counter-current manner. The heat exchange medium of the first-stage converter is heptane or water; the heat exchange medium of the second-stage converter is octane. The reaction temperature range of the first-stage converter is 130-220℃, and the temperature range of the second-stage converter is 130-180℃. The mixed acetylene and HCl enter the tubes of the first-stage converter (4) through the raw material gas pipeline (1) for reaction, and then enter the second-stage converter (5) for further reaction. The product crude vinyl chloride is sent to the subsequent process section through the product crude vinyl chloride pipeline (3), specifically: Control valve I (6) and valve II (7) to allow the raw material gas to enter from the lower end of the first stage converter (4) and exit from the upper end; control valve III (8) and valve IV (9) to allow the gas from the outlet of the first stage converter to enter from the lower end of the second stage converter (5) and exit from the upper end. Alternatively, control valve I (6) and valve II (7) to allow the raw material gas to enter from the upper end of the first-stage converter (4) and exit from the lower end; control valve III (8) and valve IV (9) to allow the gas from the outlet of the first-stage converter to enter from the lower end of the second-stage converter (5) and exit from the upper end. Alternatively, control valve I (6) and valve II (7) to allow the raw material gas to enter from the lower end of the first-stage converter (4) and exit from the upper end; control valve III (8) and valve IV (9) to allow the gas from the outlet of the first-stage converter to enter from the upper end of the second-stage converter (5) and exit from the lower end. Alternatively, control valve I (6) and valve II (7) to allow the raw material gas to enter from the upper end of the first-stage converter (4) and exit from the lower end; control valve III (8) and valve IV (9) to allow the gas from the outlet of the first-stage converter to enter from the upper end of the second-stage converter (5) and exit from the lower end.

2. The process as described in claim 1, characterized in that: The heat exchange medium enters the shell side at the bottom of the converter, vaporizes in the reactor to absorb the heat released by the reaction, and then flows out from the top of the converter, cools, and is reused.

3. The process as described in claim 1, characterized in that: The catalyst packed in the converter is a gold-based mercury-free catalyst.

Images