A system and control method for controlling the concentration of hydrogen gas in a reaction gas in a polymerization reaction

Abstract

The application discloses a system for controlling the concentration of hydrogen in a reaction gas in a polymerization reaction, comprising a polymerization unit, a membrane separation assembly, a first heat exchanger, a second heat exchanger, a first separation tank and a second separation tank. The application also discloses a control method, wherein a high-pressure circulating gas is extracted from the reaction unit, permeated through the membrane separation assembly to obtain hydrogen-rich gas, the hydrogen-rich gas is first subjected to heat exchange through the first and second heat exchangers, then subjected to gas-liquid separation through the first separation tank, the separated gas phase is first subjected to refrigeration through a refrigerator, then input into the second heat exchanger to cool the hydrogen-rich gas in the second heat exchanger, and finally discharged; the separated liquid phase is first input into the first heat exchanger to cool the hydrogen-rich gas in the first heat exchanger, then input into the second separation tank to be subjected to gas-liquid separation, and finally the separated streams are returned to the polymerization unit. Compared with the prior art, the application can accurately control the concentration of hydrogen in the reaction gas, maximally recover effective components in the discharged gas, improve the utilization rate of raw materials, and has higher economic efficiency.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high polymer materials, and particularly relates to a system and a control method for controlling the concentration of reaction gas hydrogen in a polymerization reaction. BACKGROUND

[0002] In the production of polymer industry, common polymerization processes include gas phase method, solution method and slurry method.

[0003] Regardless of the polymerization process, hydrogen is commonly used as a relative molecular weight regulator of resin in industry, which plays a role of chain transfer in the polymerization process. With the increase of hydrogen concentration in monomer material, the relative molecular weight of polymer decreases, and the melt flow rate (hereinafter referred to as MFR) increases, so as to control the MFR of polymer. This process is called hydrogen regulation.

[0004] When the hydrogen regulation method is used to prepare polymer materials, the prepared polymer material product has a wide molecular weight distribution, stable quality, colorless and transparent appearance, and no odor. However, the high hydrogen concentration in the reaction gas easily leads to unstable production, and the monomer feed amount needs to be increased. However, when the hydrogen amount is increased to a certain extent, the degree of increase of melt index is reduced, and the catalytic activity is decreased, which affects the catalytic efficiency. Therefore, the addition amount of hydrogen is limited by the polymerization process.

[0005] In industrial devices, excess hydrogen is often added to the hydrogen feed. In order to maintain the stability of each component of the reactor and prevent the accumulation of non-condensable gas, a certain amount of effective gas is often extracted from the top of the reactor and directly discharged, which causes serious waste. Some processes extract a certain amount of gas from the circulating gas to hydrogen membrane components, separate hydrogen from the reaction gas, and thus control the hydrogen concentration in the reaction gas.

[0006] Membrane separation technology is a new type of separation technology for separating, purifying and concentrating mixtures under the action of external force by using specially manufactured membranes with selective permeability. The core part is the separation membrane module, which is composed of tens of thousands of hollow fiber filaments. The principle is that the raw gas enters the membrane separator and flows along the outer surface of the fiber bundle. The gas is driven by the pressure difference between the inside and outside of the membrane, and is separated by relying on the selectivity of the membrane to various gases through the steps of dissolution, diffusion and analysis.

[0007] The commonly used hydrogen separation membrane module materials in industry include polyimide, polyethylene trimethylsilane, polyphenylene ether and polyamide.

[0008] Although the membrane with high hydrogen permeation rate is used, due to the low hydrogen concentration in the reaction gas itself, the effective gas content on the membrane side is still very high, which is a waste and poor in economy. For example, the hydrogen in the reaction gas is usually in the order of 0.1%, even if the membrane separation assembly can increase the hydrogen concentration by 10 times, the hydrogen concentration is only 1%, and the remaining 99% of the gas needs to be discharged. Therefore, controlling the hydrogen concentration in the reaction gas, recovering the effective components in the discharged gas, improving the utilization rate of raw materials, and reducing the VOC pollutant emissions have always been the goal of polymer production process.

[0009] For polymerization processes with high reaction temperature, simple circulating water condensation is usually used. This circulating water condensation method can usually better recover solvents such as hexane, and the recovery rate can reach about 20-50%. However, for some light component monomers such as ethylene and propylene, it is difficult to be condensed. SUMMARY

[0010] The first technical problem to be solved by the present application is to provide a system for accurately controlling the hydrogen concentration in the reaction gas in the polymerization reaction in view of the current situation of the prior art, so as to recover the effective components in the discharged gas and reduce the VOC pollutant emissions.

[0011] The second technical problem to be solved by the present application is to provide a method for controlling the hydrogen concentration in the reaction gas by using the above-mentioned system.

[0012] The technical scheme adopted by the present application to solve the above-mentioned first technical problem is as follows: a system for controlling the hydrogen concentration in the reaction gas in the polymerization reaction, comprising:

[0013] a polymerization unit having a polymerization inlet for feeding raw materials and a polymerization outlet for discharging unreacted effective gas;

[0014] characterized in that it further comprises:

[0015] a membrane separation assembly, the inlet of the membrane separation assembly being connected to the polymerization outlet of the polymerization unit, and the high-pressure side outlet of the membrane of the membrane separation assembly being connected to the polymerization inlet of the polymerization unit;

[0016] a first heat exchanger having a first hot medium channel and a first cold medium channel, the inlet of the first hot medium channel being connected to the low-pressure side outlet of the membrane of the membrane separation assembly;

[0017] a second heat exchanger having a second hot medium channel and a second cold medium channel, the inlet of the second hot medium channel being connected to the outlet of the first hot medium channel of the first heat exchanger;

[0018] a first separation tank for gas-liquid separation, having a first separation inlet, a first gas phase outlet, and a first liquid phase outlet, the first separation inlet being connected to the outlet of the second heat medium channel of the second heat exchanger, the first liquid phase outlet being connected to the inlet of the first cold medium channel of the first heat exchanger, and the first gas phase outlet being connected to the inlet of the second cold medium channel of the second heat exchanger through a pipeline with a refrigerating machine;

[0019] a second separation tank for gas-liquid separation, having a second separation inlet, a second gas phase outlet, and a second liquid phase outlet, the second separation inlet being connected to the outlet of the first cold medium channel of the first heat exchanger, and the second gas phase outlet and the second liquid phase outlet being connected to the polymerization inlet of the polymerization unit.

[0020] Preferably, a cooler is further included in the connecting pipeline between the low-pressure side outlet of the membrane of the membrane separation assembly and the inlet of the first heat medium channel of the first heat exchanger.

[0021] Preferably, the first heat exchanger and the second heat exchanger are combined into a multi-pass heat exchanger with one tube pass and two shell passes, the first heat medium channel and the second heat medium channel are connected in sequence and serve as the tube pass of the multi-pass heat exchanger, and the inlet of the first heat medium channel serves as the inlet of the tube pass and the outlet of the second heat medium channel serves as the outlet of the tube pass.

[0022] The two shell passes of the multi-pass heat exchanger are referred to as a first shell pass and a second shell pass, respectively, and the first shell pass and the second shell pass are arranged in sequence along the direction from the inlet of the tube pass to the outlet of the tube pass, and the first cold medium channel of the first heat exchanger serves as the first shell pass and the second cold medium channel of the second heat exchanger serves as the second shell pass.

[0023] Further, the outlet of the second cold medium channel of the second heat exchanger is connected to an exhaust pipeline for discharging exhaust gas, and an exhaust valve for controlling the flow of the exhaust gas is arranged in the exhaust pipeline.

[0024] The technical solution adopted by the present application to solve the second technical problem is a method for controlling the concentration of hydrogen gas in a reaction gas by using the system as described above, characterized in that the steps are as follows:

[0025] I. The unreacted active gas output from the polymerization outlet of the polymerization unit is divided into two parts, a first stream and a second stream, with a flow ratio of (10-100):1. The first stream is returned to the polymerization unit, and the second stream is transported to the membrane separation assembly for separation. The high-pressure hydrogen-poor gas after separation is recorded as a third stream, which is output from the high-pressure side of the membrane of the membrane separation assembly and returned to the polymerization unit. The medium-pressure hydrogen-rich gas after separation is recorded as a fourth stream, which is output from the low-pressure side of the membrane of the membrane separation assembly. The pressure of the second stream is 2.5-4.0 MPaG, and the temperature is 80-150℃. The pressure of the fourth stream is 1.0-3.2 MPaG, and the temperature is 80-150℃.

[0026] II. The fourth stream output from the membrane separation assembly passes through the first heat medium channel of the first heat exchanger and the second heat medium channel of the second heat exchanger in sequence, is output from the second heat medium channel, and then enters the first separation tank for gas-liquid separation. The pressure of the fourth stream output from the first heat medium channel is 1.0-3.2 MPaG, and the temperature is -20-20℃. The pressure of the fourth stream output from the second heat medium channel is 1.0-3.2 MPaG, and the temperature is -60-0℃. The pressure in the first separation tank is 1.0-3.2 MPaG, and the temperature is -90-0℃.

[0027] III. The liquid phase separated from the first separation tank is output from the first liquid phase outlet of the first separation tank, then enters the first cold medium channel of the first heat exchanger, exchanges heat with the fourth stream in the first heat medium channel, the liquid phase after heat exchange is output from the outlet of the first cold medium channel, and enters the second separation tank for gas-liquid separation, and then returns to the polymerization unit. The pressure in the second separation tank is 0-0.2 MPaG, and the temperature is -30-30℃.

[0028] IV. The gas phase separated from the first separation tank is output from the first gas phase outlet of the first separation tank, cooled to -135--60℃ by a refrigeration machine, and then enters the second cold medium channel of the second heat exchanger, exchanges heat with the fourth stream in the second heat medium channel, and the gas phase after heat exchange is discharged from the outlet of the second cold medium channel.

[0029] Preferably, the unreacted active gas in step I includes at least one of ethylene, propylene, n-hexane, cyclohexane, 1-butene, 1-hexene, and 1-octene.

[0030] Preferably, the material of the membrane of the membrane separation assembly is at least one of polyimide, polysulfone, polyvinyltrimethylsilane, polyphenylene ether, and polyamide.

[0031] Further, the membrane separation assembly is at least one of a hollow fiber type membrane separation assembly, a winding type membrane separation assembly, and a plate and frame type membrane separation assembly.

[0032] Further, the refrigeration principle of the refrigerating machine is at least one of isentropic expansion and throttling expansion.

[0033] The polymerization process in the polymerization unit is preferably solution method or slurry method, and more preferably solution method.

[0034] Compared with the prior art, the application has the advantages that: the application extracts a high-pressure circulating gas from the reaction unit, obtains hydrogen-rich gas after permeation through a membrane separation assembly, and then cools the hydrogen-rich gas through the first and second heat exchangers, and then separates the gas and liquid through the first separation tank; the separated gas phase is first cooled by the refrigerating machine, and then input into the second heat exchanger to cool the hydrogen-rich gas in the second heat exchanger, and finally discharged; the separated liquid phase is first input into the first heat exchanger to cool the hydrogen-rich gas in the first heat exchanger, and then input into the second separation tank to separate the gas and liquid, and the separated streams are returned to the polymerization unit. In this way, the application can accurately control the concentration of hydrogen in the reaction gas, maximize the recovery of effective components in the exhaust gas, reduce VOC emissions, improve raw material utilization, and has high economic efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 Fig. 1 is a structural schematic diagram of embodiment 1 of the application;

[0036] Figure 2 Fig. 2 is a structural schematic diagram of a multi-stream heat exchanger in embodiment 1 of the application;

[0037] Figure 3 Fig. 3 is a structural schematic diagram of embodiment 2 of the application;

[0038] Figure 4 Fig. 4 is a structural schematic diagram of a comparative example. DETAILED DESCRIPTION

[0039] The application will be further described in detail below with reference to the embodiments of the drawings.

[0040] In an industrial device, a certain gas phase space is left in the polymerization reactor to facilitate the extraction of excess reaction gas for heat removal. Since the circulating amount of the reactor circulating gas is large, the inlet hydrogen gas has a smaller feed amount than the circulating amount, and adjusting the inlet hydrogen gas flow has a lag, so an industrial device often extracts a reaction gas in the heat removal line to adjust the concentration of hydrogen.

[0041] Deep cooling separation method, simply speaking, is to separate gas by different temperatures. Reaction gas deep cooling separation is to use the different relative volatility of various hydrocarbons in the gas to condense all the hydrocarbons except hydrogen at low temperature. Generally, the higher the pressure of reaction gas, the higher the deep cooling temperature. For example, ethylene needs -104℃ at normal pressure of 0.1 MPaG, and it only needs -20℃ to recover ethylene at medium pressure of 2.53 MPaG, but it only needs 0℃ to recover ethylene at high pressure of 4.097 MPaG. The boiling points of ethylene and propylene at different pressures are shown in Table 1.

[0042] Table 1 Boiling points of ethylene and propylene at different pressures

[0043]

[0044]

[0045] Membrane separation method has the characteristics of no chemical reaction, no use of any chemical additives, low cost, low energy consumption, strong adaptability, low requirement for the size of device level configuration, high safety factor, high reliability, etc. Deep cooling separation method has the characteristic of relatively high purity of separated gas.

[0046] The gas separation device using membrane separation and deep cooling separation method first uses membrane separation method for rough separation, and completes the separation under the conditions of low cost and energy consumption, thereby reducing the load of subsequent deep cooling separation; the deep cooling separation method is used for separation at medium pressure, so as to reduce the circulation amount of deep cooling and save energy, thereby obtaining effective gas with relatively high gas precision.

[0047] A circulating gas stream is extracted from the reaction gas of the reaction kettle, which can come from the top of the reaction kettle or the outlet of the circulating gas compressor. The former reaction gas can contain polymer solids, and a filter needs to be added. The latter is cleaner than the former. In order to make the membrane assembly and the deep cooling separation operate in a reasonable range and achieve high separation effect, the flow rate and pressure of this stream are very important. The pressure ratio is actually a process of mutual coordination of the hydrogen membrane separation capacity and the deep cooling separation capacity; the flow rate plays a key role in the separation capacity of the membrane assembly and the energy consumption of the subsequent process, and is generally controlled at 5-30% of the circulating amount of the circulating gas; after the flow rate range and the pressure ratio are determined, the expansion amount required when the deep cooling separation temperature is controlled at -80℃, and the pressure ratio is generally controlled at 1.25-3.

[0048] At the same time, the heat removal line extracted from the reaction kettle is generally a high-temperature stream. A certain high temperature is beneficial to membrane separation. After membrane separation, cooling water needs to be set to cool down before deep cooling separation, so as to reduce the amount of expanded gas and save energy.

[0049] When a gas has a certain pressure and temperature, it possesses potential energy, manifested by pressure, and kinetic energy, manifested by temperature; these two types of energy are collectively called internal energy. In industrial refrigeration, the refrigeration principles commonly used can be isentropic expansion and throttling expansion. When a gas undergoes adiabatic expansion in an expander, doing work on its surroundings, this is an isentropic process because there is no heat exchange with the environment; this is called isentropic expansion. When a fluid (gas or liquid) at a higher pressure undergoes adiabatic expansion through a porous plug (or throttling valve) towards a lower pressure, this is called throttling expansion. Throttling expansion is an irreversible process; after reaching equilibrium, the system is in a non-equilibrium state.

[0050] As the gas expands and does work, the gas pressure decreases after the work is done. The effective gas cannot be directly returned to the original system and needs to be added to the raw material gas compressor before entering the system.

[0051] Example 1:

[0052] like Figure 1 , 2 As shown, this is a preferred embodiment 1 of a system and control method for controlling the concentration of hydrogen gas in a polymerization reaction according to the present invention. The system includes a polymerization unit 1, a membrane separation component 2, a multi-stream heat exchanger 300, a first separation tank 5, a second separation tank 7, and a cooler 8.

[0053] The polymerization unit 1 has a polymerization inlet for inputting raw materials and a polymerization outlet for outputting unreacted usable gas. In this embodiment, polymerization unit 1 is described below. Figure 1 The part circled by the dashed box includes a mixing tank 11 and a reaction vessel 12. The side wall of the mixing tank 11 has a monomer inlet 111 for monomer input, a solvent inlet 112 for solvent and catalyst input, and a raw material gas inlet 113 for raw material gas input. The raw material gas pipeline for conveying raw material gas is connected to the raw material gas inlet 113 of the mixing tank 11 through the raw material gas compressor 13. The top of the mixing tank 11 has a gas inlet 114 for circulating gas input and output and a gas outlet 115. The bottom of the mixing tank 11 has a mixing outlet 116. The lower part of the reactor 12 has a mixing inlet 121, which is connected to the mixing outlet 116 of the mixing tank 11 via a mixing pipeline, and a feed pump 14 is connected to the mixing pipeline. The top of the reactor 12 has a circulating gas outlet 122 for outputting circulating gas and a circulating gas inlet 123 for entering circulating gas. The circulating gas outlet 122 is connected to the gas inlet 114 of the mixing tank 11 via a first circulating gas pipeline, and a reactor top cooler 15 is provided on the first circulating gas pipeline. The circulating gas inlet 123 is connected to the gas outlet 115 of the mixing tank 11 via a second circulating gas pipeline, and a circulating gas compressor 16 is connected to the second circulating gas pipeline. In this embodiment, the outlet of the circulating gas compressor 16 is the polymerization outlet of the polymerization unit 1 for outputting unreacted effective gas. The polymerization unit 1 has multiple polymerization inlets for inputting raw materials, which will be detailed below.

[0054] The inlet 21 of the membrane separation assembly 2 is connected to the polymerization outlet of the polymerization unit 1, and the high-pressure side outlet 22 of the membrane of the membrane separation assembly 2 is connected to the gas inlet 114 (as one of the polymerization inlets of the polymerization unit 1) of the mixing tank 11 of the polymerization unit 1. In this embodiment, the membrane separation assembly 2 is at least one of a hollow fiber type membrane separation assembly, a winding type membrane separation assembly, and a plate and frame type membrane separation assembly, and the material of the membrane is at least one of polyimide, polysulfone, polyvinyltrimethylsilane, polyphenylene ether, and polyamide, and the membrane pressure ratio is 2.58:1.

[0055] The input end of the cooler 8 is connected to the low-pressure side outlet 23 of the membrane of the membrane separation assembly 2.

[0056] The multi-stream heat exchanger 300 has a tube pass 310 and two shell passes, the tube pass inlet 311 is connected to the output end of the cooler 8, and the two shell passes of the multi-stream heat exchanger are respectively referred to as a first shell pass 321 and a second shell pass 322, which are arranged in sequence along the direction from the tube pass inlet 311 to the tube pass outlet 312.

[0057] The first separation tank 5 is a low-temperature separation tank for gas-liquid separation, and has a first separation inlet 51, a first gas phase outlet 52, and a first liquid phase outlet 53. The first separation inlet 51 is connected to the tube pass outlet 312 of the multi-stream heat exchanger 300, the first liquid phase outlet 53 is connected to the inlet of the first shell pass 321 of the multi-stream heat exchanger 300, and the first gas phase outlet 52 is connected to the inlet of the second shell pass 322 of the multi-stream heat exchanger 300 through a pipeline with the refrigerator 6. The outlet of the second shell pass 322 is connected to a gas discharge pipeline 43 for discharging waste gas, and the gas discharge pipeline 43 is provided with a gas discharge valve 44 for controlling the flow rate of the gas. In this embodiment, the refrigerator 6 is a prior art, and its refrigeration principle is at least one of isentropic expansion and throttling expansion.

[0058] The second separation tank 7 is a normal-pressure separation tank for gas-liquid separation, and has a second separation inlet 71, a second gas phase outlet 72, and a second liquid phase outlet 73. The second separation inlet 71 is connected to the outlet of the first shell pass 321 of the multi-stream heat exchanger 300, the second gas phase outlet 72 is connected to the raw gas pipeline of the polymerization unit 1, and the second liquid phase outlet 73 is connected to the mixing pipeline through a recovery pump. The raw gas inlet of the mixing tank 11 connected to the raw gas pipeline and the mixing inlet of the reaction kettle 12 connected to the mixing pipeline are the other two polymerization inlets of the polymerization unit 1.

[0059] The control method for controlling the concentration of the reaction gas hydrogen by using the above-mentioned system of this embodiment is as follows:

[0060] I. The unreacted active gas output from the polymerization outlet of the polymerization unit 1 (the polymerization process in the polymerization unit 1 is solution or slurry method, the temperature of the unreacted active gas is 100℃, and the pressure is 3.1 MPaG) is divided into two parts, which are the first stream and the second stream, the flow rate of the second stream is 200 Kg / Hr, the temperature is 100℃, the pressure is 3.1 MPaG, and the second stream has 0.003wt% of H2, 0.21wt% of N2, 0.54wt% of C2H4, 0.027wt% of C6H 14 , 0.22wt% of 1-butene. The flow rate ratio of the first stream to the second stream is 25:1, the first stream returns to the reaction kettle 12 from the circulating gas inlet 123, and the second stream is transported to the membrane separation assembly 2 for separation, the separated high-pressure hydrogen-lean gas is recorded as the third stream, which is output from the high-pressure side outlet 22 of the membrane of the membrane separation assembly 2 and returns to the polymerization unit 1, and the separated medium-pressure hydrogen-rich gas is recorded as the fourth stream, which is output from the low-pressure side outlet 23 of the membrane of the membrane separation assembly 2, wherein the pressure of the fourth stream is 1.2 MPaG, the flow rate is 45.88 Kg / Hr, the temperature is 100℃, and the fourth stream has 0.006wt% of H2, 0.232wt% of N2, 0.564wt% of C2H4, 0.016wt% of C6H 14 , 0.181wt% of 1-butene.

[0061] II. The fourth stream output from the membrane separation assembly 2 successively passes through the tube side 310 of the multi-stream heat exchanger 300, and then enters the first separation tank 5 for gas-liquid separation, wherein the pressure of the fourth stream output from the tube side 310 of the multi-stream heat exchanger 300 is 1.2 MPaG, the temperature is -19℃, the pressure in the first separation tank is 1.2 MPaG, and the temperature is -90℃;

[0062] III. The liquid phase separated from the first separation tank 5 is output from the first liquid phase outlet 53 of the first separation tank 5, and then enters the first shell side 321 of the multi-stream heat exchanger 300 to exchange heat with the fourth stream in the tube side 310, the heat-exchanged liquid phase is output from the outlet of the first shell side 321 of the multi-stream heat exchanger 300, and then enters the second separation tank 7 for gas-liquid separation, and then returns to the polymerization unit 1, wherein the pressure in the second separation tank 7 is 0-0.2 MPaG, and the temperature is -30-30℃;

[0063] IV. The gas phase separated from the first separator 5 is output from the first gas phase outlet 52 of the first separator 5. After being cooled to -133.4℃ by the refrigeration unit 6, it enters the second shell side 322 of the multi-stream heat exchanger 300 and exchanges heat with the fourth stream in the tube side 310. The gas phase after heat exchange is discharged as waste gas through the exhaust pipeline 43. The discharged waste gas is referred to as the fifth stream. The pressure of the fifth stream is 0.11 MPaG, the flow rate is 13.4 Kg / Hr, the temperature is 17℃, and the fifth stream contains 0.022 wt% H2, 0.751 wt% N2, 0.225 wt% C2H4, and 0.0005 wt% 1-butene.

[0064] Example 2:

[0065] like Figure 3 As shown, this is a preferred embodiment 2 of a system and control method for controlling the concentration of hydrogen gas in a polymerization reaction according to the present invention. The system includes a polymerization unit 1, a membrane separation component 2, a first heat exchanger 3, a second heat exchanger 4, a first separation tank 5, a second separation tank 7, and a cooler 8.

[0066] The structure and connection method of the polymerization unit 1, the membrane separation component 2 and the cooler 8 are the same as those in Embodiment 1, and will not be described again here.

[0067] The first heat exchanger 3 has a first hot medium channel 31 and a first cold medium channel 32, and the inlet of the first hot medium channel 31 is connected to the output end of the cooler 8.

[0068] The second heat exchanger 4 has a second hot medium channel 41 and a second cold medium channel 42. The inlet of the second hot medium channel 41 is connected to the outlet of the first hot medium channel 31 of the first heat exchanger 3.

[0069] The first separator 5 is used for gas-liquid separation and has a first separation inlet 51, a first gas phase outlet 52, and a first liquid phase outlet 53. The first separation inlet 51 is connected to the outlet of the second hot medium channel 41 of the second heat exchanger 4, and the first liquid phase outlet 53 is connected to the inlet of the first cold medium channel 32 of the first heat exchanger 3. The first gas phase outlet 52 is connected to the inlet of the second cold medium channel 42 of the second heat exchanger 4 through a pipeline with a refrigeration unit 6. The outlet of the second cold medium channel 42 of the second heat exchanger 4 is connected to an exhaust pipeline 43 for discharging waste gas, and the exhaust pipeline 43 is equipped with an exhaust valve 44 for controlling the airflow.

[0070] The second separation tank 7 is used for gas-liquid separation and has a second separation inlet 71, a second gas phase outlet 72 and a second liquid phase outlet 73. The second separation inlet 71 is connected with the outlet of the first cold medium channel 32 of the first heat exchanger 3, and the second gas phase outlet 72 and the second liquid phase outlet 73 are connected with the polymerization inlet of the polymerization unit 1. The details are the same as those of the first embodiment, and thus are not described herein.

[0071] The control method for controlling the concentration of the reaction gas hydrogen by using the above system of the embodiment is as follows:

[0072] I. The unreacted effective gas output from the polymerization outlet of the polymerization unit 1 (the polymerization process in the polymerization unit 1 is solution method or slurry method, the temperature of the unreacted effective gas is 100℃, and the pressure is 3.1MPaG) is divided into two parts, i.e., a first stream and a second stream. The flow rate of the second stream is 200Kg / Hr, the temperature is 100℃, the pressure is 3.1MPaG, and the second stream contains 0.003wt% of H2, 0.21wt% of N2, 0.54wt% of C2H4, 0.027wt% of C6H 14 , and 0.22wt% of 1-butene. The flow rate ratio of the first stream to the second stream is 25:1. The first stream returns to the reaction kettle 12 from the circulating gas inlet 123, and the second stream is transported to the membrane separation assembly 2 for separation. The high-pressure hydrogen-lean gas after separation is recorded as a third stream, which is output from the high-pressure side outlet 22 of the membrane of the membrane separation assembly 2 and returns to the polymerization unit 1. The medium-pressure hydrogen-rich gas after separation is recorded as a fourth stream, which is output from the low-pressure side outlet 23 of the membrane of the membrane separation assembly 2. The pressure of the fourth stream is 1.2MPaG, the flow rate is 45.88Kg / Hr, the temperature is 100℃, and the fourth stream contains 0.006wt% of H2, 0.232wt% of N2, 0.564wt% of C2H4, 0.016wt% of C6H 14 , and 0.181wt% of 1-butene.

[0073] II. The fourth stream output from the membrane separation assembly 2 is sequentially subjected to the first heat medium channel 31 of the first heat exchanger 3 and the second heat medium channel 41 of the second heat exchanger 4, and then enters the first separation tank 5 for gas-liquid separation. The pressure of the fourth stream output from the first heat medium channel 31 is 1.2MPaG, and the temperature is -19.2℃. The pressure of the fourth stream output from the second heat medium channel 41 is 1.2MPaG, and the temperature is -47.2℃. The pressure in the first separation tank is 1.0-3.2MPaG, and the temperature is -90-0℃.

[0074] III. The liquid phase separated from the first separation tank 5 is output from the first liquid phase outlet 53 of the first separation tank 5, and then enters the first cold medium passage 32 of the first heat exchanger 3 to exchange heat with the fourth stream in the first hot medium passage 31. The liquid phase after heat exchange is output from the outlet of the first cold medium passage 32, and enters the second separation tank 7 for gas-liquid separation, and then returns to the polymerization unit 1. The pressure in the second separation tank 7 is 0-0.2 MPaG, and the temperature is -30-30°C.

[0075] IV. The gas phase separated from the first separation tank 5 is output from the first gas phase outlet 52 of the first separation tank 5, cooled to -111.2°C by the refrigerator 6, and then enters the second cold medium passage 42 of the second heat exchanger 4 to exchange heat with the fourth stream in the second hot medium passage 41. The gas phase after heat exchange is discharged as waste gas through the exhaust pipeline 43. The discharged waste gas is the fifth stream. The pressure of the fifth stream is 0.11 MPaG, the flow rate is 26.795 Kg / Hr, the temperature is -27.3°C, and the fifth stream contains 0.009wt% of H2, 0.332wt% of N2, 0.635wt% of C2H4, 0.00004wt% of C6H 14 , and 0.023wt% of 1-butene.

[0076] Example 3

[0077] This example is basically the same as Example 1, except that the membrane pressure ratio of the membrane separation assembly 2 in this application is 1.72:1. In this example, the flow rate of the second stream is 200 Kg / Hr, the temperature is 100°C, the pressure is 3.1 MPaG, and the second stream contains 0.003wt% of H2, 0.21wt% of N2, 0.54wt% of C2H4, 0.027wt% of C6H 14 , 0.22wt% of 1-butene. The pressure of the fourth stream is 1.8 MPaG, the flow rate is 64.518 Kg / Hr, the temperature is 100°C, and the fourth stream contains 0.004wt% of H2, 0.224wt% of N2, 0.557wt% of C2H4, 0.019wt% of C6H 14 , and 0.193wt% of 1-butene. The pressure of the fifth stream is 0.11 MPaG, the flow rate is 33.975 Kg / Hr, the temperature is -22.3°C, and the fifth stream contains 0.007wt% of H2, 0.365wt% of N2, 0.606wt% of C2H4, 0.00006wt% of C6H 14 , and 0.021wt% of 1-butene.

[0078] Example 4

[0079] The present example is basically the same as example 1, the difference is that the membrane pressure ratio of the membrane separation assembly 2 in the present application is 1.29:1. And in the present example, the flow rate of the second stream is 105 Kg / Hr, the temperature is 100℃, the pressure is 3.1 MPaG, and the second stream has 0.003wt% of H2, 0.21wt% of N2, 0.54wt% of C2H4, 0.027wt% of C6H 14 , 0.22wt% of 1-butene. The pressure of the fourth stream is 0.4 MPaG, the flow rate is 36.174 Kg / Hr, the temperature is 100℃, and the fourth stream has 0.008wt% of H2, 0.237wt% of N2, 0.567wt% of C2H4, 0.015wt% of C6H 14 , 0.171wt% of 1-butene. The pressure of the fifth stream is 0.11 MPaG, the flow rate is 27.239 Kg / Hr, the temperature is -10.1℃, and the fifth stream has 0.011wt% of H2, 0.265wt% of N2, 0.627wt% of C2H4, 0.0002wt% of C6H 14 , 0.096wt% of 1-butene.

[0080] Example 5:

[0081] The present example is basically the same as example 1, the difference is that the parameters in the control method of the present example are different from those of example 1, which are as follows:

[0082] The steps of the control method of the present example are as follows:

[0083] I. The unreacted active gas output from the polymerization outlet of the polymerization unit 1 is divided into two parts, which are the first stream and the second stream, and the flow rate ratio of the two is 100:1. The first stream returns to the polymerization unit 1, and the second stream is transported to the membrane separation assembly 2 for separation. The high-pressure hydrogen-lean gas after separation is recorded as the third stream, which is output from the high-pressure side outlet 22 of the membrane of the membrane separation assembly 2 and returns to the polymerization unit 1. The medium-pressure hydrogen-rich gas after separation is recorded as the fourth stream, which is output from the low-pressure side outlet 23 of the membrane of the membrane separation assembly 2. The pressure of the second stream is 2.5 MPaG, and the temperature is 150℃. The pressure of the fourth stream is 3.2 MPaG, and the temperature is 80℃.

[0084] II. The fourth stream output from the membrane separation assembly 2 successively passes through the first heat medium channel 31 of the first heat exchanger 3 and the second heat medium channel 41 of the second heat exchanger 4, and then enters the first separation tank 5 for gas-liquid separation. The pressure of the fourth stream output from the first heat medium channel 31 is 3.2 MPaG, and the temperature is -20℃. The pressure of the fourth stream output from the second heat medium channel 41 is 3.2 MPaG, and the temperature is -60℃. The pressure in the first separation tank is 3.2 MPaG, and the temperature is -90℃.

[0085] III. The liquid phase separated from the first separation tank 5 is output from the first liquid phase outlet 53 of the first separation tank 5, and then enters the first cold medium passage 32 of the first heat exchanger 3 to exchange heat with the fourth stream in the first hot medium passage 31. The liquid phase after heat exchange is output from the outlet of the first cold medium passage 32, and enters the second separation tank 7 for gas-liquid separation, and then returns to the polymerization unit 1. The pressure in the second separation tank 7 is 0.2 MPaG, and the temperature is -30℃;

[0086] IV. The gas phase separated from the first separation tank 5 is output from the first gas phase outlet 52 of the first separation tank 5, cooled to -135℃ by the refrigerator 6, and then enters the second cold medium passage 42 of the second heat exchanger 4 to exchange heat with the fourth stream in the second hot medium passage 41. The gas phase after heat exchange is discharged from the outlet of the second cold medium passage 42.

[0087] Example 6:

[0088] This example is basically the same as Example 1, except that the parameters in the control method of this example are different from those of Example 1, which are as follows:

[0089] The steps of the control method of this example are as follows:

[0090] I. The unreacted effective gas output from the polymerization outlet of the polymerization unit 1 is divided into two parts, which are the first stream and the second stream, and the flow ratio of the two is 10:1. The first stream returns to the polymerization unit 1, and the second stream is transported to the membrane separation assembly 2 for separation. The high-pressure hydrogen-poor gas after separation is recorded as the third stream, which is output from the high-pressure side outlet 22 of the membrane of the membrane separation assembly 2 and returns to the polymerization unit 1. The medium-pressure hydrogen-rich gas after separation is recorded as the fourth stream, which is output from the low-pressure side outlet 23 of the membrane of the membrane separation assembly 2. The pressure of the second stream is 4.0 MPaG, and the temperature is 80℃. The pressure of the fourth stream is 1.0 MPaG, and the temperature is 150℃.

[0091] II. The fourth stream output from the membrane separation assembly 2 successively passes through the first hot medium passage 31 of the first heat exchanger 3 and the second hot medium passage 41 of the second heat exchanger 4, and then enters the first separation tank 5 for gas-liquid separation. The pressure of the fourth stream output from the first hot medium passage 31 is 1.0 MPaG, and the temperature is 20℃. The pressure of the fourth stream output from the second hot medium passage 41 is 1.0 MPaG, and the temperature is 0℃. The pressure in the first separation tank is 1.0 MPaG, and the temperature is 0℃.

[0092] III. The liquid phase separated from the first separation tank 5 is output from the first liquid phase outlet 53 of the first separation tank 5, and then enters the first cold medium passage 32 of the first heat exchanger 3 to exchange heat with the fourth stream in the first hot medium passage 31. The liquid phase after heat exchange is output from the outlet of the first cold medium passage 32, and enters the second separation tank 7 for gas-liquid separation, and then returns to the polymerization unit 1. The pressure in the second separation tank 7 is 0 MPaG, and the temperature is 30°C.

[0093] IV. The gas phase separated from the first separation tank 5 is output from the first gas phase outlet 52 of the first separation tank 5, cooled to -60°C by the refrigerator 6, and then enters the second cold medium passage 42 of the second heat exchanger 4 to exchange heat with the fourth stream in the second hot medium passage 41. The gas phase after heat exchange is discharged from the outlet of the second cold medium passage 42.

[0094] Comparative Example 1

[0095] The system of the present comparative example comprises a polymerization unit 1', a membrane separation assembly 2', and a cooler 8'. The structure and connection mode of the polymerization unit 1', the membrane separation assembly 2', and the cooler 8' are the same as those of Example 1. The difference lies in that the membrane pressure ratio of the membrane separation assembly 2' in the present comparative example is 28.2:1, the output end of the cooler 8' is directly connected to an exhaust line 43' for discharging waste gas, and the exhaust line 43' is provided with an exhaust valve 44' for controlling the flow rate of the gas.

[0096] In the present example, the flow rate of the second stream is 100 Kg / Hr, the temperature is 100°C, the pressure is 3.1 MPaG, and the second stream contains 0.003wt% of H2, 0.21wt% of N2, 0.54wt% of C2H4, 0.027wt% of C6H 14 , and 0.22wt% of 1-butene. The pressure of the fourth stream is 0.11 MPaG, the flow rate is 32.757 Kg / Hr, the temperature is 100°C, and the fourth stream contains 0.009wt% of H2, 0.241wt% of N2, 0.569wt% of C2H4, 0.014wt% of C6H 14 , and 0.167wt% of 1-butene. The pressure of the fifth stream is 0.11 MPaG, the flow rate is 32.757 Kg / Hr, the temperature is 100°C, and the fifth stream contains 0.009wt% of H2, 0.241wt% of N2, 0.569wt% of C2H4, 0.014wt% of C6H 14 , and 0.167wt% of 1-butene.

[0097] Comparing the embodiments and comparative examples of this application, it can be seen that different results are obtained for different reactant feed rates, reaction conditions, and membrane pressure ratios of the membrane separation unit under different grades. By changing the flow rate of the extracted reactant gas and the membrane pressure ratio of the membrane separation unit, while keeping the absolute flow rate of hydrogen emission equal, and by combining different process flows, the concentration of hydrogen in the reactor can be controlled. The comparison of the above embodiments shows that using the methods described in this application... Figure 1 , 2 In Example 1 of the main process flow of the multi-stream heat exchanger, the discharge gas flow rate in the fifth stream is the lowest, effectively avoiding material waste; the discharge temperature is close to room temperature, and under medium-pressure and low-temperature conditions, it can effectively recover the cold energy in the low-temperature separator, reducing energy consumption. Simultaneously, the isentropic expansion used in the refrigeration unit generates more cold energy than throttling expansion, which helps in the condensation and recovery of effective gas; furthermore, a smaller membrane distribution coefficient is more beneficial to this invention. Therefore, the following conclusions are drawn: When the second stream is drawn from the outlet of the circulating gas compressor of polymerization unit 1, and the pressure of the second stream is controlled at 2.5 MPaG to 4.0 MPaG, and the temperature is controlled at 80 to 150°C, i.e., the pressure of the fourth stream is 1.0 MPaG to 3.2 MPaG, and the temperature is between 80 and 150°C, the discharge flow rate in the fifth stream is the lowest, which can maximize the recovery of effective components in the discharge gas, significantly reduce VOC emissions, and improve raw material utilization.

Claims

1. A system for controlling the concentration of hydrogen gas in a polymerization reaction, comprising: The polymerization unit (1) has a polymerization inlet for inputting raw materials and a polymerization outlet for outputting unreacted effective gas; characterized in that It also includes: The membrane separation assembly (2) has an inlet (21) connected to the polymerization outlet of the polymerization unit (1) and a high-pressure side outlet (22) of the membrane of the membrane separation assembly (2) connected to the polymerization inlet of the polymerization unit (1). The first heat exchanger (3) has a first hot medium channel (31) and a first cold medium channel (32), and the inlet of the first hot medium channel (31) is connected to the low-pressure side outlet (23) of the membrane of the membrane separation assembly (2). The second heat exchanger (4) has a second hot medium channel (41) and a second cold medium channel (42), and the inlet of the second hot medium channel (41) is connected to the outlet of the first hot medium channel (31) of the first heat exchanger (3). The first separation tank (5) is used for gas-liquid separation and has a first separation inlet (51), a first gas phase outlet (52), and a first liquid phase outlet (53). The first separation inlet (51) is connected to the outlet of the second hot medium channel (41) of the second heat exchanger (4). The first liquid phase outlet (53) is connected to the inlet of the first cold medium channel (32) of the first heat exchanger (3). The first gas phase outlet (52) is connected to the inlet of the second cold medium channel (42) of the second heat exchanger (4) through a pipeline with a refrigeration unit (6). The second separation tank (7) is used for gas-liquid separation and has a second separation inlet (71), a second gas phase outlet (72), and a second liquid phase outlet (73). The second separation inlet (71) is connected to the outlet of the first cold medium channel (32) of the first heat exchanger (3). The second gas phase outlet (72) and the second liquid phase outlet (73) are connected to the polymerization inlet of the polymerization unit (1). The membrane of the membrane separation component (2) is made of at least one of polyimide, polysulfone, trimethylsilane, polyphenylene ether, and polyamide.

2. The system according to claim 1, characterized in that: It also includes a cooler (8) on the connecting line between the low-pressure side outlet (23) of the membrane of the membrane separation assembly (2) and the inlet of the first heat medium channel (31) of the first heat exchanger (3).

3. The system according to claim 1, characterized in that: The first heat exchanger (3) and the second heat exchanger (4) are combined to form a multi-flow heat exchanger (300) with one tube side (310) and two shell sides. The first heat medium channel (31) and the second heat medium channel (41) are connected in sequence and serve as the tube side (310) of the multi-flow heat exchanger (300). The inlet of the first heat medium channel (31) serves as the tube side inlet (311) and the outlet of the second heat medium channel (41) serves as the tube side outlet (312). The two shell sides of the multi-flow heat exchanger (300) are respectively referred to as the first shell side (321) and the second shell side (322). The first shell side (321) and the second shell side (322) are arranged sequentially along the direction from the tube inlet (311) to the tube outlet (312). The first cold medium channel (32) of the first heat exchanger (3) is used as the first shell side (321), and the second cold medium channel (42) of the second heat exchanger (4) is used as the second shell side (322).

4. The system according to claim 1, characterized in that: The outlet of the second cold medium passage (42) of the second heat exchanger (4) is connected to an exhaust pipe (43) for discharging waste gas, and an exhaust valve (44) for controlling the airflow is provided on the exhaust pipe (43).

5. A method for controlling the concentration of hydrogen gas in a reaction gas using the system described in any one of claims 1 to 4, characterized in that... The steps are as follows:

1. The unreacted effective gas output from the polymerization outlet of the polymerization unit (1) is divided into two parts, namely the first stream and the second stream, with a flow ratio of (10~100):

1. The first stream is returned to the polymerization unit (1), and the second stream is sent to the membrane separation module (2) for separation. The high-pressure hydrogen-poor gas after separation is recorded as the third stream, which is output from the high-pressure side outlet (22) of the membrane of the membrane separation module (2) and returned to the polymerization unit (1). The medium-pressure hydrogen-rich gas after separation is recorded as the fourth stream, which is output from the low-pressure side outlet (23) of the membrane of the membrane separation module (2). The pressure of the second stream is 2.5~4.0 MPaG and the temperature is 80~150℃. The pressure of the fourth stream is 1.0~3.2 MPaG and the temperature is 80~150℃.

2. The fourth stream output from the membrane separation unit (2) passes through the first heat medium channel (31) of the first heat exchanger (3) and the second heat medium channel (41) of the second heat exchanger (4) in sequence, and then enters the first separation tank (5) for gas-liquid separation. The pressure of the fourth stream output from the first heat medium channel (31) is 1.0~3.2MPaG and the temperature is -20~20℃. The pressure of the fourth stream output from the second heat medium channel (41) is 1.0~3.2MPaG and the temperature is -60~0℃. The pressure inside the first separation tank is 1.0~3.2MPaG and the temperature is -90~0℃.

3. The liquid phase separated from the first separator (5) is output from the first liquid phase outlet (53) of the first separator (5), and then enters the first cold medium channel (32) of the first heat exchanger (3) to exchange heat with the fourth stream in the first hot medium channel (31). The liquid phase after heat exchange is output from the outlet of the first cold medium channel (32) and enters the second separator (7) for gas-liquid separation, and then returns to the polymerization unit (1). The pressure in the second separator (7) is 0~0.2MPaG and the temperature is -30~30℃. Fourth, the gas phase separated from the first separator (5) is output from the first gas phase outlet (52) of the first separator (5), and after being cooled to -135 ~ -60℃ by the refrigeration unit (6), it enters the second cold medium channel (42) of the second heat exchanger (4) to exchange heat with the fourth stream in the second hot medium channel (41). The gas phase after heat exchange is discharged from the outlet of the second cold medium channel (42).

6. The control method according to claim 5, characterized in that: The unreacted effective gas in step one includes at least one of ethylene, propylene, n-hexane, cyclohexane, 1-butene, 1-hexene, and 1-octene.

7. The control method according to claim 5, characterized in that: The membrane separation component (2) is at least one of hollow fiber membrane separation component, wound membrane separation component, and plate and frame membrane separation component.

8. The control method according to claim 5, characterized in that: The refrigeration principle of the refrigerator (6) is at least one of isentropic expansion and throttling expansion.

9. The control method according to claim 5, characterized in that: The polymerization process in the polymerization unit (1) is either solution polymerization or slurry polymerization.

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