A process for synthesizing vinyl chloride without mercury catalysis

Abstract

The present invention provides a process for synthesizing vinyl chloride without mercury catalysis, which relates to the technical field of vinyl chloride synthesis methods by the acetylene method. In this process, a part of the crude vinyl chloride at the outlet of the converter is mixed with the inlet raw materials to dilute the inlet raw material gas, or an inert gas is used to dilute the raw material gas, so as to reduce the concentration of reactants in the raw material gas; and a certain proportion of activated carbon is incorporated into the inlet part of the converter, or a catalyst with a relatively low activity of active components is used in the inlet section of the converter, thereby reducing the activity of the catalyst in the inlet section of the converter. This method can effectively shorten the induction period at the initial stage of using the mercury-free catalyst, reduce the inactivation caused by catalyst runaway temperature, and extend the service life of the catalyst.

Description

Technical Field

[0001] The present invention relates to the technical field of vinyl chloride synthesis methods by the acetylene method, and specifically relates to a process for synthesizing vinyl chloride by mercury-free catalysis. Background Art

[0002] Polyvinyl chloride (PVC) is the second largest general-purpose synthetic resin. The synthesis methods of the PVC polymerization monomer vinyl chloride are mainly the ethylene method and the acetylene method. Among them, the acetylene method is the main production method. However, the existing acetylene method processes all use mercury catalysts, which will cause a large amount of pollution and mercury consumption. In view of such problems, there is an urgent need for new catalysts to reduce mercury consumption and pollution.

[0003] Mercury-free catalysts such as gold and ruthenium for acetylene hydrochlorination have become the focus of research in the past few years due to their high activity, selectivity and stability in the acetylene hydrochlorination reaction. Many enterprises and research institutions have developed acetylene hydrochlorination catalysts with excellent performance. For example, a gold catalyst loaded with ionic liquid disclosed in Chinese Patent CN 201910940508 shows extremely high activity and stability. Chinese Patent CN 202111422143 discloses a ruthenium-based catalyst for acetylene hydrochlorination, which has better HCl adsorption capacity, making the catalyst have higher stability. At the same time, as mercury-free catalysts gradually mature, some enterprise units have carried out industrial-scale tests and applications, and proposed many processes and technologies supporting mercury-free catalysts. For example, Chinese Patent CN201911082316 discloses a process for synthesizing vinyl chloride by mercury-free catalysis. By setting up a multi-stage mixing preheater and realizing series, parallel or series-parallel combination of front and back stage converters, different operation modes are flexibly adopted to effectively extend the service life of the mercury-free catalyst. Chinese Patent CN 202021847169 discloses a vinyl chloride synthesis process device suitable for mercury-free catalysts. The process method uses a copper-based catalyst in the front stage and a gold catalyst in the back stage to solve the problems that the heat release is concentrated in the initial stage of the gold catalyst, the hot spot is difficult to control, and it is easy to cause the catalyst to deactivate at high temperature.

[0004] However, regardless of whether it is a series or parallel process, highly active catalysts such as gold and ruthenium are very likely to cause runaway temperature due to their high activity and violent reactions during the induction period. Generally, the operating temperature of acetylene hydrochlorination catalysts is below 200°C. However, in the actual production process, due to the high concentration of reactants in the raw material gas at the inlet section of the reactor and poor heat exchange, runaway temperature often occurs. Factories generally control the reaction temperature by gradually increasing the feed flow rate. However, this method often takes up to a month to raise the load to the normal level, which greatly affects production efficiency, and this method cannot avoid the situation of local overheating of the catalyst. In addition, in the acetylene hydrochlorination series process, the background catalyst that has been used for a period of time is often refilled into the front-end converter for continued use, which can give full play to the role of the catalyst and extend the service life of the catalyst. In the above-mentioned patented technology, although using a copper-based catalyst with a lower operating temperature at the front end and a gold catalyst at the back end makes it easier to control the front-end temperature, the situation of local runaway temperature is still difficult to avoid, which is likely to cause loss of the copper-based catalyst. At the same time, since this patented technology does not perform the operation of replacing the background catalyst with the front-end catalyst, the catalyst is not fully utilized, but instead increases the operating cost of the catalyst.

[0005] In view of the problems in the prior art such as the large pollution of mercury catalysts, the long induction period of mercury-free catalysts, the high activity during the induction period, and the easy runaway temperature and deactivation, it is very necessary to find a process method for mercury-free catalytic synthesis of vinyl chloride. Summary of the Invention

[0006] In view of the problems existing in the prior art, the present invention provides a process method for mercury-free catalytic synthesis of vinyl chloride, which solves the problems of long induction period of mercury-free catalysts, high activity during the induction period, and easy runaway temperature and deactivation.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] The present invention provides a process method for synthesizing vinyl chloride. The device for synthesizing vinyl chloride includes a mixer 1, a converter 2, and a converter 3, and the converter 2 and the converter 3 are in parallel;

[0009] The inlet raw material gas and the inert gas enter the mixer 1 for mixing, and then enter the converter 2 and the converter 3. The reaction gas at the outlet of the converter 2 includes gas B and gas D; the reaction gas at the outlet of the converter 3 includes gas C and gas E. Among them, both gas C and gas B enter the subsequent process section, and gas D and gas E are mixed into gas F and then recycled to the mixer 1 to be mixed with the raw material gas and the inert gas.

[0010] Further, the volume ratio of gas D to gas B is 0-10:1, and the volume ratio of gas E to gas C is 0-10:1.

[0011] Further, the imported raw material gas, inert gas, and recycle gas F are mixed to obtain gas A; in terms of the molar ratio, the proportion of the recycle gas F in gas A ranges from 0 to 100%, and the proportion of the inert gas in gas A ranges from 0 to 100%.

[0012] In some specific embodiments, when the converters 2 and 3 are connected in parallel, the reaction gas at the outlets of the converters 2 and 3 is divided into two streams. Among them, gases D and E are used as recycle gas and mixed with the raw materials, and gases C and B enter the subsequent process sections; in the general parallel process, the concentration of vinyl chloride at the converter outlet is about 90%-100%. The vinyl chloride at the outlet of the recycle converter can dilute the concentration of the imported raw material gas under the condition of parallel operation.

[0013] When a new plant starts up, all the converters are new converters, and there is no vinyl chloride at the converter outlet for recycling and dilution at this time. At this time, an inert gas can be introduced into the mixer 1 and mixed with the raw material gas, which can also achieve the effect of weakening the reaction heat at the inlet of the converter, shortening the induction period, and reducing the deactivation of the catalyst due to temperature runaway during the initial startup stage. When the system tends to be stable, the inert gas is then switched to the recycle gas. This can reduce the excess inert gas in the system and lower the operating cost.

[0014] Further, the inert gas includes argon and / or nitrogen, and the imported raw material gas includes acetylene and HCl.

[0015] Further, both the converters 2 and 3 include a tube side 1 and a shell side 2. The tube side 1 includes a section A and a section B. The section A is filled with activated carbon and / or mercury-free catalyst in a mixed manner, and the section B is filled with mercury-free catalyst.

[0016] Preferably, the section A is filled with activated carbon and ordinary mercury-free catalyst in a mixed manner, or filled with a low-activity mercury-free catalyst (i.e., a catalyst with a lower content of active components, such as gold, copper, ruthenium catalysts, where the active components of the gold, copper, ruthenium catalysts are ionic states or compounds of substances such as gold, copper, ruthenium, etc.), and the section B is filled with ordinary mercury-free catalyst.

[0017] It should be noted that the low-activity mercury-free catalyst refers to that the mass content of the active component of this catalyst is 10-70% of that of the ordinary mercury-free catalyst; for example, the low-activity mercury-free catalyst corresponding to the 1‰ gold catalyst is a 0.1-0.7‰ gold catalyst.

[0018] Further, the length of the section A is 10-40 cm, and the mass content of activated carbon in the section A ranges from 0 to 100%.

[0019] Further, the shell side 2 uses a heat exchange medium, and the heat exchange medium includes one or more of hot water, heptane, and octane; the catalyst includes one or more of gold, ruthenium, and copper catalysts.

[0020] Further, in the converter, the feed gas, the inert gas and / or the recycle gas flow through the tube side 1, and the heat exchange medium flows through the shell side 2.

[0021] Since the heat exchange medium and the reaction feedstock are in countercurrent heat exchange in industry, the higher the proportion of gas phase in the heat exchange medium and the worse the heat removal effect are as it gets closer to the inlet section of the converter. By mixing and loading activated carbon and catalyst in section A, or loading a catalyst with a lower content of active components, the overall activity of the catalyst at the inlet can be reduced, thereby reducing the intensity of the reaction at the inlet. At the same time, the position where the reaction is most intense is moved to a part far from the inlet of the converter, improving the heat removal capacity at this position.

[0022] The present invention also provides a process for synthesizing vinyl chloride. The device for synthesizing vinyl chloride includes a mixer 1, a converter 2, and a converter 3, and the converter 2 and the converter 3 are connected in series.

[0023] The inlet feed gas and the inert gas enter the mixer 1 for mixing and then enter the converter 2. The reaction gas at the outlet of the converter 2 includes gas b and gas d. Among them, gas b enters the converter 3 for further reaction. The reaction gas at the outlet of the converter 3 includes gas c and gas e. Among them, gas c enters the subsequent process section, and gas d and gas e are mixed into gas f and then recycled to the mixer 1 to be mixed with the feed gas and the inert gas.

[0024] Further, the volume ratio of gas d to gas b is 0 - 10:1, and the volume ratio of gas e to gas c is 0 - 10:1.

[0025] Further, the inlet feed gas, the inert gas and the recycle gas f are mixed to obtain gas a. By mole ratio, the proportion of the recycle gas f in gas a ranges from 0 - 100%, and the proportion of the inert gas in gas a ranges from 0 - 100%.

[0026] In some specific embodiments, when the converter 2 and the converter 3 are connected in series, the reaction gas at the outlet of the converter 2 is divided into two streams, b and d. Among them, the gas b enters the converter 3 to continue the reaction, and the gas d is recycled to the mixer 1, where it is mixed with the raw material gas and then enters the converter 2 again. The reactor at the outlet of the converter 3 is divided into two streams, c and e. Among them, the gas e is recycled to the mixer 1, where it is mixed with the raw material gas and then enters the converter 2 again, and the gas c enters the subsequent process section. In industrial production, the raw material gas at the inlet of the converter is generally acetylene and HCL (concentration ratio 1:1.1), and the main component at the outlet of the converter is vinyl chloride. In general, in the series process, the vinyl chloride concentration at the outlet of the front-stage converter is about 50-70%, and the vinyl chloride concentration at the outlet of the rear-stage converter is about 90%-100%. Therefore, by recycling the outlet of the converter and mixing it with the raw material gas, it can play a role in diluting the concentration of the inlet raw material gas. At the same time, the unreacted raw material gas at the outlet of the converter is further reacted to ensure that the conversion rate at the outlet of the reactor meets the system requirements. This can effectively weaken the heat release of the reaction at the inlet of the converter, shorten the induction period, and reduce the inactivation caused by catalyst runaway temperature.

[0027] The technical effects achieved by the present invention are as follows:

[0028] 1. By diluting the catalyst in section A at the inlet of the converter, the intensity of the reaction at the inlet is effectively reduced. At the same time, the position where the reaction is most intense is moved to a part far from the inlet of the converter, improving the heat removal ability of the hot spot position, effectively increasing the service life of the catalyst, and reducing the operating cost.

[0029] 2. By diluting the inlet raw material gas with an inert gas, the reaction heat at the inlet of the converter can be effectively weakened, the induction period can be effectively shortened, the inactivation caused by catalyst runaway temperature can be reduced, and the service life of the catalyst can be extended.

[0030] 3. By partially recycling the outlet gas of the converter to the inlet and mixing it with the raw material gas, the acetylene concentration in the raw material gas can be effectively diluted, and the intensity of the reaction at the inlet can be reduced. At the same time, the unreacted acetylene in the recycled raw material gas is further reacted, which can also improve the acetylene recovery rate.

[0031] 4. Using a single catalyst can effectively improve the problem that the catalyst is prone to runaway temperature inactivation during the induction period, reduce the process operation difficulty, and increase the service life of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the series process flow diagram in the present invention. In the figure, 1 - mixer; 2 - converter; 3 - converter; a, b, c, d, e are all gases; f is the recycle gas;

[0033] Figure 2 This is the parallel process flow diagram in the present invention. In the figure, 1 - mixer; 2 - converter; 3 - converter; A, B, C, D, E are all gases; F is the recycle gas;

[0034] Figure 3 This is a schematic structural diagram of the converter in the present invention. In the figure, 1 is the tube side; 2 is the shell side; A and B are the A section and the B section respectively. Specific embodiments

[0035] The following specific examples illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0036] Before further describing the specific embodiments of the present invention, it should be understood that the protection scope of the present invention is not limited to the specific embodiments described below; it should also be understood that the terms used in the embodiments of the present invention are for the purpose of describing specific embodiments, rather than limiting the protection scope of the present invention.

[0037] When the embodiments give a numerical range, it should be understood that unless otherwise specified in the present invention, both endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0038] It is worth noting that the raw materials used in the present invention are all ordinary commercially available products, so their sources are not specifically limited.

[0039] Example 1

[0040] Adopt Figure 1 The shown series process flow. The loading method of the catalyst in the converter is as Figure 3 shown. The catalyst used in the B section is 1‰ fresh gold catalyst. The length of the A section is: 0 cm, and the mass percentage of activated carbon in the A section is 0%. The molar ratio of raw material acetylene to HCl is 1:1.1, and the acetylene space velocity is 50 h -1 , the inert gas is nitrogen and its proportion in the feed a is 0%, the proportion of the recycle gas f in the converter feed a is 0%, the flow ratio of the gas d to the gas b is 0:1, and the flow ratio of the gas e to the gas c is 0:1.

[0041] Example 2

[0042] Same as Example 1, the difference is that the proportion of the recycle gas f in the converter feed a is 15%, the flow ratio of the gas d to the gas b is 0:1, and the flow ratio of the gas e to the gas c is 2:1.

[0043] Example 3

[0044] Same as Example 1, except that the inert gas is nitrogen and its proportion in Feed a is 15%.

[0045] Example 4

[0046] Adopt Figure 2 The parallel process flow shown, the loading method of the catalyst in the converter is as Figure 3 shown. The catalyst used in section B is 1‰ fresh gold catalyst, the length of section A is: 0 cm, and the mass percentage of activated carbon in section A is 0%. The molar ratio of raw material acetylene to HCl is 1:1.1, and the acetylene space velocity is 30 h -1 , the proportion of inert gas in Feed A is 0%, the proportion of recycle gas F in Feed A of the converter is 0%, the flow ratio of Gas D to Gas B is 0:1, and the flow ratio of Gas E to Gas C is 0:1.

[0047] Example 5

[0048] Same as Example 4, except that the proportion of recycle gas F in Feed A of the converter is 15%, the flow ratio of Gas D to Gas B is 2:1, and the flow ratio of Gas E to Gas C is 2:1.

[0049] Example 6

[0050] Same as Example 4, except that the inert gas is nitrogen and its proportion in Feed A is 15%.

[0051] Example 7

[0052] Same as Example 1, except that the length of section A is: 20 cm, the mass percentage of activated carbon in section A is 50%, the rest is filled with 1‰ gold catalyst, and section B is filled with 1‰ gold catalyst.

[0053] Example 8

[0054] Same as Example 1, except that the length of section A is: 40 cm, the mass percentage of activated carbon in section A is 50%, the rest is filled with 1‰ gold catalyst, and section B is filled with 1‰ gold catalyst.

[0055] Example 9

[0056] Same as Example 1, except that the length of section A is: 20 cm, the mass percentage of activated carbon in section A is 100%, and section B is filled with 1‰ gold catalyst.

[0057] Example 10

[0058] Same as Example 1, except that the length of section A is: 20 cm, section A is filled with 0.5‰ gold catalyst, and section B is filled with 1‰ gold catalyst.

[0059] Example 11

[0060] Same as Example 4, except that the length of section A is: 20 cm, the mass percentage of activated carbon in section A is 50%, the remaining part is filled with 1‰ gold catalyst, and section B is filled with 1‰ gold catalyst.

[0061] Example 12

[0062] Same as Example 4, except that the length of section A is: 40 cm, the mass percentage of activated carbon in section A is 50%, the remaining part is filled with 1‰ gold catalyst, and section B is filled with 1‰ gold catalyst.

[0063] Example 13

[0064] Same as Example 4, except that the length of section A is: 20 cm, the mass percentage of activated carbon in section A is 100%, and section B is filled with 1‰ gold catalyst.

[0065] Example 14

[0066] Same as Example 4, except that the length of section A is: 20 cm, section A is filled with 0.5‰ gold catalyst, and section B is filled with 1‰ gold catalyst.

[0067] Using the above scheme for the experiment, a thermocouple with a jacket is inserted into the tube side to measure the temperature of the converter. The results are shown in Table 1.

[0068] Table 1

[0069]

[0070]

[0071] For the series process, the above catalyst life is the running time of the catalyst when the converter is in the front stage, under the corresponding space velocity and raw gas ratio conditions, when the conversion rate drops to 65%.

[0072] The following conclusions can be drawn by comparing Examples 1 - 14:

[0073] 1. By comparing Examples 1 - 3 and Examples 4 - 6, it can be found that whether it is a series or parallel process, after the raw gas is diluted, the hot spot temperature decreases significantly and the induction period is greatly shortened. For the gold catalyst, when the hot spot temperature is higher than 200 °C, the catalyst will accelerate deactivation, resulting in a shortened service life.

[0074] 2. Examples 7-9 or Examples 11-13 show that mixing activated carbon and mercury-free catalyst in the front section of the converter in series and parallel processes can reduce the hot spot temperature and shorten the induction period at the same time. The main reason is that the converter has countercurrent heat exchange. The closer to the inlet of the raw gas, the weaker the heat transfer capacity of the heat transfer medium. By reducing the catalyst loading in the front section of the converter to reduce the reaction heat release, the hot spot temperature can be effectively reduced. It can also be found that the longer the length of the mixed activated carbon and the larger the proportion of the mixed activated carbon, the lower the hot spot temperature and the shorter the catalyst induction period. However, the mixing length of the catalyst cannot be increased indefinitely because the more activated carbon is loaded, the fewer catalysts are in the converter, and the increase in the load per unit mass of the catalyst leads to a decrease in its service life.

[0075] 3. Examples 7 and 10 or Examples 11 and 14 show that loading low-activity mercury-free catalyst in the front section of the converter can also reduce the hot spot temperature and shorten the induction period at the same time. The principle is the same as that of mixing activated carbon.

[0076] Finally, it should be noted that the above content is only used to illustrate the technical solution of the present invention, rather than limiting the protection scope of the present invention. Any simple modification or equivalent replacement made by those of ordinary skill in the art to the technical solution of the present invention shall not depart from the essence and scope of the technical solution of the present invention.

Claims

1. A process for synthesizing vinyl chloride, characterized in that: The device for synthesizing vinyl chloride includes a mixer 1, a converter 2, and a converter 3, and the converter 2 and the converter 3 are connected in series; After the inlet raw material gas and the inert gas enter the mixer 1 and are mixed, they then enter the converter 2. The reaction gas at the outlet of the converter 2 includes gas b and gas d. Among them, gas b enters the converter 3 for further reaction; the reaction gas at the outlet of the converter 3 includes gas c and gas e. Among them, gas c enters the subsequent process section, and gas d and gas e are mixed into gas f and then recycled to the mixer 1 to be mixed with the raw material gas and the inert gas; The volume ratio of the gas d to the gas b is 0 - 10:1, and the volume ratio of the gas e to the gas c is 2 - 10:1; the inert gas includes argon and / or nitrogen, and the inlet raw material gas includes acetylene and HCl; Both the converter 2 and 3 include a tube side 1 and a shell side 2. The tube side 1 includes a section A and a section B. The section A is filled with a mixture of activated carbon and a mercury-free catalyst, and the section B is filled with a mercury-free catalyst; The mercury-free catalyst is a gold catalyst.

2. A process for synthesizing vinyl chloride, characterized in that: The device for synthesizing vinyl chloride includes a mixer 1, a converter 2, and a converter 3, and the converter 2 and the converter 3 are connected in parallel; After the inlet raw material gas and the inert gas enter the mixer 1 and are mixed, they then enter the converter 2 and the converter 3. The reaction gas at the outlet of the converter 2 includes gas B and gas D; the reaction gas at the outlet of the converter 3 includes gas C and gas E. Among them, both gas C and gas B enter the subsequent process section, and gas D and gas E are mixed into gas F and then recycled to the mixer 1 to be mixed with the raw material gas and the inert gas; The volume ratio of the gas D to the gas B is 2 - 10:1, and the volume ratio of the gas E to the gas C is 2 - 10:1; The inert gas includes argon and / or nitrogen, and the inlet raw material gas includes acetylene and HCl; Both the converter 2 and 3 include a tube side 1 and a shell side 2. The tube side 1 includes a section A and a section B. The section A is filled with a mixture of activated carbon and a mercury-free catalyst, and the section B is filled with a mercury-free catalyst; The mercury-free catalyst is a gold catalyst.

3. The process according to claim 1 or 2, characterized in that: The length of the section A is 10 - 40 cm.

4. The process according to claim 1 or 2, characterized in that: The shell side 2 passes through a heat exchange medium, and the heat exchange medium includes one or several of hot water, heptane, and octane.

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