A method and device for double-tower coupled rectification capable of switching between series and parallel connection

Abstract

The present application relates to the technical field of chlorosilane separation and purification in silicon material production, and particularly to a double-tower coupled rectification method and device capable of switching between series and parallel connection, comprising: selectively feeding a chlorosilane mixture containing silicon tetrachloride into a first rectification tower and a second rectification tower or into the first rectification tower; selectively feeding tower bottom material of the first rectification tower out or into the second rectification tower; using tower top material of the second rectification tower to heat exchange the tower bottom material of the first rectification tower; and switching the material conveying path to make the first rectification tower and the second rectification tower selectively form a parallel operation state or a series operation state. The present application switches the feeding path of the chlorosilane mixture containing silicon tetrachloride and the conveying path of the tower bottom material of the first rectification tower to make the first rectification tower and the second rectification tower switch between the parallel operation state and the series operation state.

Description

Technical Field

[0001] This invention relates to the field of chlorosilane separation and purification technology in silicon material production, and in particular to a dual-tower coupled distillation method and apparatus that can be switched in series and parallel. Background Technology

[0002] Silicon tetrachloride is an important material in the chlorosilane system. In the production of silicon materials, chlorosilane mixtures containing silicon tetrachloride typically also contain light and heavy components with different boiling points, requiring distillation separation based on the differences in volatility. To balance material handling capacity, separation depth, and production energy consumption, engineering typically employs two distillation columns for separation, with the columns operating in parallel or in series depending on the separation task. Furthermore, to reduce energy consumption during distillation, a thermal coupling relationship can be established between the two distillation columns.

[0003] However, in existing dual-tower distillation processes, the feed path, the bottom material conveying path, and the connection between the two towers are usually fixed during the plant design phase. The two distillation towers can only operate in a predetermined parallel or series configuration. When the raw material composition, production load, or purity requirements of the silicon tetrachloride product change, the fixed parallel operation configuration is insufficient to achieve a high separation depth, while the fixed series operation configuration may limit the full utilization of the processing capacity of the two distillation towers. To adapt to different production tasks, it is often necessary to modify the existing pipelines, add subsequent separation equipment, or build independent production lines, resulting in low equipment utilization and increased plant investment and operation management costs.

[0004] Therefore, how to achieve flexible switching between parallel and series operation in the same dual-tower coupled distillation system, and maintain thermal coupling between the two distillation towers under different operating conditions, has become a technical problem that needs to be solved in this field. Summary of the Invention

[0005] In this section, as well as in the abstract and title of this application, some simplifications or omissions may be made to avoid obscuring the purpose of this section, the abstract, and the title of this application, and such simplifications or omissions shall not be used to limit the scope of the invention.

[0006] To address the shortcomings of existing technologies, one objective of this invention is to provide a dual-tower coupled distillation method that can be switched between series and parallel operation.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: a dual-tower coupled distillation method with series-parallel switching capability, comprising: selectively feeding a chlorosilane mixture containing silicon tetrachloride into a first distillation column and a second distillation column, or feeding it into the first distillation column; selectively sending the bottom material of the first distillation column externally, or sending it into the second distillation column; using the top material of the second distillation column to exchange heat with the bottom material of the first distillation column; and through the switching of the above material conveying paths, enabling the first distillation column and the second distillation column to selectively form a parallel operation state or a series operation state.

[0008] As a preferred embodiment of the dual-tower coupled distillation method that can be switched between series and parallel according to the present invention, wherein: in the parallel operation state, the chlorosilane mixture containing silicon tetrachloride enters the first distillation column and the second distillation column respectively, the first distillation column and the second distillation column respectively distill and separate the chlorosilane mixture, and collect silicon tetrachloride product from the bottom of the column respectively.

[0009] In a preferred embodiment of the dual-tower coupled distillation method with series-parallel switching as described in this invention, in the series operation state, the chlorosilane mixture containing silicon tetrachloride enters the first distillation column, the light component is discharged from the top of the first distillation column, the bottom material of the first distillation column enters the second distillation column for distillation separation, the silicon tetrachloride product is collected from the top of the second distillation column, and the heavy component is discharged from the bottom of the second distillation column.

[0010] As a preferred embodiment of the dual-tower coupled distillation method that can be switched between series and parallel operation according to the present invention, when the first distillation column and the second distillation column switch from parallel operation to series operation, before the top material of the second distillation column reaches the preset purity, the top material of the second distillation column is returned to the feed end of the first distillation column for further distillation and separation.

[0011] In a preferred embodiment of the dual-tower coupled distillation method with series-parallel switching capability described in this invention, when switching from the parallel operation state to the series operation state, the following steps are performed sequentially: stopping the feeding of the chlorosilane mixture into the second distillation column; switching the feed material from the bottom of the first distillation column from external delivery to the second distillation column; and switching the feed material from the top of the second distillation column from external delivery to return to the feed end of the first distillation column. When the feed material from the top of the second distillation column reaches the preset purity, the feed material from the top of the second distillation column is switched back to external delivery.

[0012] As a preferred embodiment of the dual-tower coupled distillation method that can be switched between series and parallel as described in this invention, the top material of the second distillation column enters the first reboiler heat exchanger of the first distillation column in a gaseous state and condenses and releases heat in the first reboiler heat exchanger. The top temperature of the second distillation column is 12-15°C higher than the reboiler temperature of the first distillation column.

[0013] In a preferred embodiment of the dual-tower coupled distillation method with series-parallel switching capability described in this invention, the operating parameters of the first distillation column and the second distillation column are determined as follows: the top temperature of the first distillation column is determined based on the top pressure of the first distillation column and the correspondence between the saturated vapor pressure and temperature of trichlorosilane; the bottom temperature of the first distillation column is determined based on the bottom pressure of the first distillation column and the correspondence between the saturated vapor pressure and temperature of silicon tetrachloride; the top temperature of the second distillation column is determined based on the bottom temperature of the first distillation column and the temperature difference between the top temperature of the second distillation column and the bottom temperature of the first distillation column; in the parallel operation state, the top pressure of the second distillation column is determined based on the correspondence between the saturated vapor pressure and temperature of trichlorosilane; in the series operation state, the top pressure of the second distillation column is determined based on the correspondence between the saturated vapor pressure and temperature of silicon tetrachloride.

[0014] As a preferred embodiment of the dual-tower coupled distillation method with series-parallel switching as described in this invention, the first distillation column has a top pressure of 0.11–0.12 MPaG, a top temperature of 55–56°C, and a bottom temperature of 85.5–86°C.

[0015] As a preferred embodiment of the dual-tower coupled distillation method with series-parallel switching capability described in this invention, wherein: in the parallel operation state, the top pressure of the second distillation column is 0.58–0.60 MPaG, and the reflux ratio is 0.8–0.9; in the series operation state, the top pressure of the second distillation column is 0.24–0.25 MPaG, and the reflux ratio is 1.2–1.5.

[0016] To address the shortcomings of existing technologies, another objective of this invention is to provide a dual-tower coupled distillation apparatus that can be switched between series and parallel operation.

[0017] This invention adopts the following technical solution: a dual-tower coupled distillation device capable of series-parallel switching, comprising a first distillation column, a second distillation column, a feed main, and a first column reboiler heat exchanger; the feed main is connected to the feed inlet of the first distillation column and the feed inlet of the second distillation column respectively through a first feed branch and a second feed branch, and feed switching components are provided on the first feed branch and the second feed branch; the reboiler outlet of the first distillation column is connected to the product delivery pipeline and the feed inlet of the second distillation column respectively through a first column reboiler outlet branch and an inter-tower conveying branch, and the first column... The reboiler outlet branch and the inter-tower conveying branch are equipped with a reboiler switching assembly; the material channel of the first reboiler heat exchanger is connected to the reboiler of the first distillation column, and the heating medium channel of the first reboiler heat exchanger is connected to the top vapor outlet of the second distillation column, so that the top vapor material of the second distillation column serves as the heat source for the reboiler of the first distillation column; the feed switching assembly and the reboiler switching assembly change the conveying path of the feed main and the reboiler material of the first distillation column, so that the first distillation column and the second distillation column form a parallel material flow path or a series material flow path.

[0018] As a preferred embodiment of the dual-tower coupled distillation apparatus that can be switched in series and parallel according to the present invention, wherein: the top material conveying pipeline of the second distillation tower is provided with a return branch and a top external delivery branch, the return branch is connected to the feed end of the first distillation tower, and the return branch and the top external delivery branch are respectively provided with a return switching component and an external delivery switching component.

[0019] In a preferred embodiment of the dual-tower coupled distillation apparatus capable of series-parallel switching described in this invention, the following configuration is provided: the top vapor outlet of the first distillation column is sequentially connected to a first top condenser and a first reflux pump; the outlet of the first reflux pump is connected to the reflux inlet of the first distillation column and a light component delivery pipeline, respectively; the heating medium channel of the first reboiler heat exchanger is connected to a heating medium input pipeline and a condensate output pipeline, respectively; the heating medium input pipeline is connected to the top vapor outlet of the second distillation column; the condensate output pipeline is connected to the second top condenser; the outlet of the second top condenser is connected to a second reflux pump; the outlet of the second reflux pump is connected to the reflux inlet of the second distillation column and the top material delivery pipeline of the second distillation column, respectively.

[0020] As a preferred embodiment of the dual-tower coupled distillation apparatus that can be switched in series and parallel according to the present invention, wherein: the bottom of the second distillation column is provided with a second bottom heat exchanger, the material channel of the second bottom heat exchanger is connected to the bottom of the second distillation column, and the heating medium channel of the second bottom heat exchanger is connected to the steam input pipeline and the condensate output pipeline respectively.

[0021] As a preferred embodiment of the dual-tower coupled distillation apparatus capable of series-parallel switching according to the present invention, wherein: the feed switching assembly includes a first feed valve disposed on the first feed branch and a second feed valve disposed on the second feed branch; the reboiler switching assembly includes a first switching valve disposed on the first reboiler discharge branch and a second switching valve disposed on the inter-tower conveying branch; the return feed switching assembly includes a third switching valve disposed on the return feed branch; and the external feed switching assembly includes a fourth switching valve disposed on the top external feed branch; the reboiler discharge port of the first distillation column is connected to the inlet of the first reboiler pump, and the outlet of the first reboiler pump is connected to both the first reboiler discharge branch and the inter-tower conveying branch; the reboiler discharge port of the second distillation column is connected to the inlet of the second reboiler pump, and the outlet of the second reboiler pump is connected to the product external feed pipeline.

[0022] The beneficial effects of this invention are as follows: By selectively switching the inlet path of the chlorosilane mixture containing silicon tetrachloride and the conveying path of the bottom material of the first distillation column, this invention enables the first and second distillation columns to switch between parallel and series operation. In parallel operation, the two distillation columns can receive the chlorosilane mixture separately and share the distillation load, which is beneficial to improving the material handling capacity of the unit. In series operation, the bottom material of the first distillation column can enter the second distillation column for further separation, which is beneficial to improving the separation depth and meeting the production requirements of higher purity silicon tetrachloride products. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This diagram illustrates the material flow direction and inter-tower thermal coupling relationship of the dual-tower coupled distillation method of the present invention, which can be switched between series and parallel operation, in parallel and series operation states.

[0025] Figure 2 This is a schematic diagram of the material conveying path switching when the operation state of the present invention is switched from parallel operation state to series operation state. It shows the return state of the material at the top of the second distillation column before reaching the preset purity and the external delivery state after reaching the preset purity.

[0026] Figure 3 This is a schematic diagram of the overall structure, main material flow path, and inter-tower thermal coupling relationship of the dual-tower coupled distillation device that can be switched between series and parallel according to the present invention.

[0027] Figure 4 This is a detailed diagram showing the piping connections and the locations of each switching component in the dual-tower coupled distillation apparatus of the present invention, which can be switched in series and in parallel.

[0028] In the diagram: 100, First distillation column; 110, First column top condenser; 120, First reflux pump; 130, First column reboiler heat exchanger; 131, Heating medium input line; 132, Condensate output line; 140, First column reboiler pump; 141, First column reboiler discharge branch; 141a, First switching valve; 142, Inter-column conveying branch; 142a, Second switching valve; 200, Second distillation column; 210, Second column top condenser; 220, Second reflux pump; 230, Second... 231. Steam input pipeline; 232. Condensate output pipeline; 240. Second reboiler pump; 300. Main feed pipe; 310. First feed branch; 311. First feed valve; 320. Second feed branch; 321. Second feed valve; 400. Product delivery pipeline; 500. Top material conveying pipeline; 510. Return material branch; 511. Third switching valve; 520. Top material delivery branch; 521. Fourth switching valve; 600. Light component delivery pipeline. Detailed Implementation

[0029] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0030] The terminology used in this invention is that which is currently widely used in the art in consideration of the function of the invention; however, these terms may vary according to the intent of those skilled in the art, precedent, or new technology in the art. Furthermore, specific terms may be chosen by the applicant, and in such cases, their detailed meanings will be described in the detailed description of the invention. Therefore, the terms used in this specification should not be construed as simple names, but rather based on their meanings and the overall description of the invention.

[0031] In this embodiment, the chlorosilane mixture containing silicon tetrachloride may include relatively low-boiling-point components such as trichlorosilane, dichlorosilane, and methylchlorosilane, or relatively high-boiling-point components such as hexachlorodisilane, siloxanes, polymers, and metallic impurities. "Light components" refer to components that are more easily enriched at the top of the column compared to silicon tetrachloride, while "heavy components" refer to components that are more easily enriched in the bottom of the column compared to silicon tetrachloride. "Selective delivery" refers to selecting the material between two or more preset paths according to the operating mode using valves, three-way switches, or equivalent control elements capable of changing the flow path, rather than requiring all paths to be open simultaneously at all times. Unless otherwise specified, all pressures are gauge pressures.

[0032] The first reboiler heat exchanger 130 has isolated material channels and heating medium channels, where the two media only exchange heat between the walls without mixing. In this embodiment, the heating medium inlet line 131 transports the vaporous chlorosilane process steam from the top of the second distillation column 200, which serves as the heating medium. The condensate outlet line 132 transports the condensed or gas-liquid mixed chlorosilane material formed after heat exchange with the process steam; it is not necessarily utility steam or water. The steam inlet line 231 and the condensate outlet line 232 can respectively transport utility heating steam and its condensate. Through the above definitions, the inter-column thermal coupling loop of the first reboiler heat exchanger 130 can be clearly distinguished from the external steam heating loop of the second reboiler heat exchanger 230.

[0033] Example 1

[0034] Reference Figure 1 , Figure 3 and Figure 4 This embodiment provides a dual-tower coupled distillation method with series-parallel switching capability. A chlorosilane mixture containing silicon tetrachloride is fed into the device through a feed manifold 300. The feed manifold 300 is connected to the feed inlets of the first distillation column 100 and the second distillation column 200 via a first feed branch 310 and a second feed branch 320. The first feed branch 310 and the second feed branch 320 each have independent flow path control capabilities, allowing the feed material to enter both distillation columns simultaneously or only the first distillation column 100. The bottom outlet of the first distillation column 100 also has two selectable destinations: the first destination is via the first bottom outlet branch 141 into the product delivery pipeline 400, and the second destination is via the inter-column conveying branch 142 into the feed outlet of the second distillation column 200.

[0035] When parallel operation is selected, both the first feed branch 310 and the second feed branch 320 are open, and the chlorosilane mixture is distributed to the first distillation column 100 and the second distillation column 200. The bottom material of the first distillation column 100 is sent out through the first bottom discharge branch 141, and the inter-column conveying branch 142 is closed or remains un-conveyed. In this case, the two distillation columns each bear the distillation load, which is suitable for situations where the raw material throughput is large or the target product has relatively low requirements for deep deweighting. The feed rates of the two columns can be the same, or they can be distributed according to a preset ratio based on the column diameter, tray efficiency, pressure drop inside the column, and actual load.

[0036] When the series operation mode is selected, the second feed branch 320 stops conveying the fresh chlorosilane mixture, and the fresh feedstock enters the first distillation column 100 through the first feed branch 310. The first distillation column 100 is used to preferentially remove light components, and the material rich in silicon tetrachloride in its bottom is no longer directly sent out, but enters the second distillation column 200 through the inter-column conveying branch 142. The second distillation column 200 further distills the material, enriching the heavy components in the bottom and the silicon tetrachloride in the top. Through this stepwise separation, the first distillation column 100 completes the pre-stage separation mainly for removing light components, and the second distillation column 200 completes the post-stage separation mainly for removing heavy components and product purification, thus forming a deeper separation path without adding a third distillation column.

[0037] Regardless of whether the two distillation columns are operating in parallel or in series, the vaporous material at the top of the second distillation column 200 is introduced into the heating medium channel of the first distillation column's reboiler heat exchanger 130, while the liquid at the bottom of the first distillation column 100 enters the material channel of the first reboiler heat exchanger 130. The vaporous material at the top of the second distillation column 200 cools and at least partially condenses in the heating medium channel, releasing heat to raise the temperature of the liquid at the bottom of the first distillation column 100 and at least partially vaporize it. The reboiler material from the first distillation column, after heat exchange, returns to the first distillation column 100, while the material at the top of the second distillation column, after heat exchange, continues to enter the second top condenser 210 for supplemental condensation. Therefore, the second distillation column 200 serves as both a material separation unit and a heat source generation unit for the first distillation column 100.

[0038] Conventional fixed parallel systems struggle to establish progressively separating light and heavy materials, while conventional fixed series systems cannot fully utilize the parallel capabilities of the two towers when increased throughput is required. This embodiment switches separation tasks by changing the first two types of material paths, while maintaining the third type of thermal coupling path. Switching between two product tasks does not require disassembling and reassembling the towers or rebuilding the heat source system, and the heat utilization relationship between towers remains uninterrupted due to changes in material topology, thereby simultaneously improving the system's operational flexibility, equipment utilization, and energy efficiency.

[0039] Example 2

[0040] Reference Figure 1 As shown on the left, in parallel operation, this embodiment simultaneously feeds a mixture of chlorosilanes containing silicon tetrachloride into the first distillation column 100 and the second distillation column 200. Both the first feed valve 311 and the second feed valve 321 are in the open state, the first switching valve 141a is open, and the second switching valve 142a is closed, allowing the bottom material of the first distillation column 100 to enter the product delivery pipeline 400 via the first bottom outlet branch 141. The bottom material of the second distillation column 200 enters the product delivery pipeline 400 via the second bottom pump 240. The two distillation columns respectively perform light component separation and collect silicon tetrachloride product from their bottoms.

[0041] During operation, relatively volatile components such as trichlorosilane and dichlorosilane in the first distillation column 100 and the second distillation column 200 are enriched at the top of the column, while silicon tetrachloride is enriched at the bottom. The light components at the top of the first distillation column 100 are condensed by the first top condenser 110, with a portion returned to the column via the first reflux pump 120, and the remainder discharged via the light component delivery pipeline 600. The vaporous material at the top of the second distillation column 200 first enters the first bottom heat exchanger 130 to heat the first distillation column 100, then is condensed by the second top condenser 210, and a portion is sent back to the second distillation column 200 by the second reflux pump 220 to form reflux, while the remainder is discharged via the top material delivery pipeline 500.

[0042] Example 3

[0043] Reference Figure 1 As shown on the right in the series operation configuration, in this embodiment, the fresh chlorosilane mixture enters the first distillation column 100 only through the first feed branch 310, while the second feed branch 320 stops supplying fresh raw materials. The top of the first distillation column 100 is used to discharge relatively volatile light components, and its bottom yields an intermediate material mainly composed of silicon tetrachloride. The first switching valve 141a is closed, and the second switching valve 142a is opened. The first bottom pump 140 then sends this intermediate material to the inlet of the second distillation column 200 via the inter-column conveying branch 142.

[0044] The second distillation column 200 further distills the intermediate materials. Hexachlorodisilane, siloxanes, polymers, and non-volatile impurities such as boron, phosphorus, iron, aluminum, and calcium are enriched in the bottom of the second distillation column 200 and discharged by the second bottom pump 240; silicon tetrachloride is enriched at the top of the second distillation column 200. The silicon tetrachloride vapor at the top of the column first enters the first bottom heat exchanger 130 for condensation and heat release, and then is condensed by the second top condenser 210. Part of the condensate is returned to the second distillation column 200 by the second reflux pump 220 for continuous washing of entrained heavy components in the top section, and the other part is sent out as silicon tetrachloride product via the top delivery branch 520.

[0045] Example 4

[0046] Reference Figure 2 In the initial stage of switching from parallel operation to series operation, the original liquid holding and reflux system of the second distillation column 200 still contains a relatively large amount of light components. If the top material of the second distillation column 200 is immediately sent out as high-purity silicon tetrachloride product, it is easy for the transitional material to enter the qualified product pipeline network. Therefore, in this embodiment, a return branch 510 is set on the top material conveying pipeline 500 of the second distillation column 200, and the return branch 510 is connected to the feed end of the first distillation column 100.

[0047] After the switchover begins, the overhead material from the second distillation column 200 is condensed by the first reboiler heat exchanger 130 and the second overhead condenser 210, and then transported by the second reflux pump 220 to the overhead material delivery pipeline 500. At this time, the overhead delivery branch 520 is closed and the return branch 510 is opened, allowing the overhead material that has not yet reached the preset purity to merge with the feed entering the first distillation column 100. The first distillation column 100 again separates the light components in the return material, and the silicon tetrachloride in the return material re-enters the reboiler and returns to the second distillation column 200 via the inter-column delivery branch 142. This closed-loop cycle allows the transition material to remain inside the dual-column system for further separation, rather than being discharged into the product system or as waste.

[0048] The preset purity can be set according to product standards, such as setting the silicon tetrachloride mass fraction to be no less than 99.9% or 99.95%, or simultaneously limiting the content of individual impurities such as trichlorosilane, methylchlorosilane, and heavy metals. Purity determination can be performed continuously by an online analyzer at the top of the column, or offline by sampling at the sampling port set before the external feed branch 520 at the top of the column.

[0049] Example 5

[0050] This embodiment provides a complete operation process for switching from parallel operation to series operation. Before switching, the first feed valve 311, the second feed valve 321, the first switching valve 141a, and the fourth switching valve 521 are open, while the second switching valve 142a and the third switching valve 511 are closed. The chlorosilane mixture enters the two columns respectively, the bottom products of the two columns are sent out, and the top material of the second distillation column 200 is discharged through the top delivery branch 520.

[0051] The first step is to stop feeding the fresh chlorosilane mixture into the second distillation column 200 through the second feed branch 320. This can be done by closing the second feed valve 321, or by gradually reducing the flow rate of the second feed branch 320 before closing the second feed valve 321, to minimize level and pressure fluctuations in the second distillation column 200. The first feed valve 311 remains open, allowing all fresh feedstock to enter the first distillation column 100.

[0052] The second step is to switch the material in the bottom of the first distillation column 100 from external delivery to inter-column conveying. Specifically, the first switching valve 141a is closed and the second switching valve 142a is opened, so that the outlet of the first bottom pump 140 is switched from the first bottom discharge branch 141 to the inter-column conveying branch 142. During the switching, it is preferable to adjust the flow rate of the first bottom pump 140 through a level controller to avoid a sudden rise or fall in the liquid level of the bottom of the first distillation column 100; the inlet of the inter-column conveying branch 142 is set at a suitable feed height in the second distillation column 200, so that the intermediate material in the bottom of the first column enters the separation section of the second distillation column 200.

[0053] The third step involves switching the top material of the second distillation column 200 from an external feed state to a return state. The fourth switching valve 521 is closed and the third switching valve 511 is opened, allowing the top material to return to the feed end of the first distillation column 100 via the return branch 510. During valve switching, interlocking can be used to ensure that the outlet of the second reflux pump 220 always has at least one unobstructed path, or the pump outlet flow rate can be reduced before switching to avoid prolonged pump outlet closure. Subsequently, the top pressure and reflux ratio of the second distillation column 200 are gradually adjusted to transition it from parallel operation to series operation.

[0054] The fourth step involves continuously operating and monitoring the top material of the second distillation column 200 under reflux conditions. Once the top temperature, pressure, and reflux ratio are within the permissible range for series operation, and the purity of the top material has been confirmed to reach the preset value through one or multiple consecutive tests, the third switching valve 511 is closed and the fourth switching valve 521 is opened, allowing the qualified top material to be sent to the product system via the top delivery branch 520. The switching process for a specific unit can last approximately 5–6 hours, with the actual time depending on the liquid holdup of the second distillation column 200, the initial light component content, the reflux rate, and the return material flow rate.

[0055] The above sequence allows the destinations of fresh raw materials, the first column bottom material, and the second column top product to be switched step-by-step according to separation logic. This avoids premature introduction of the first column bottom material while the second distillation column 200 is still receiving parallel raw materials, and also prevents substandard top material from entering the product pipeline. Ordinary single-valve switching only changes the on / off state of one pipeline and cannot handle the transition issues of existing material and product quality within the column. This embodiment achieves state reconstruction through the coordination of three sets of paths and quality feedback, thereby supporting the switching of the two columns under actual continuous production conditions.

[0056] Example 6

[0057] This embodiment specifically describes the thermal coupling relationship between the second distillation column 200 and the first reboiler heat exchanger 130. The vapor outlet at the top of the second distillation column 200 is connected to the heating medium inlet of the first reboiler heat exchanger 130 via a heating medium inlet pipeline 131. The heating medium outlet of the first reboiler heat exchanger 130 is connected to the second top condenser 210 via a condensate outlet pipeline 132. The liquid material in the reboiler of the first distillation column 100 enters its material channel through the material inlet of the first reboiler heat exchanger 130, and returns to the reboiler of the first distillation column 100 after being heated, via the material outlet. The two channels are separated by a heat exchange wall to prevent direct mixing of materials from different columns.

[0058] The overhead material of the second distillation column 200 enters the heating medium channel in a high-temperature gaseous state, condenses on one side of the heat exchange wall, and releases sensible heat and latent heat of phase change. The bottom material of the first distillation column 100 absorbs heat on the other side of the heat exchange wall, undergoes heating and partial vaporization, and the resulting gas-liquid mixture returns to the first distillation column 100, driving the vapor-liquid mass transfer within the column. Compared with ordinary heat exchange methods that only utilize the sensible heat of the high-temperature liquid, utilizing the latent heat of condensation of the overhead gas phase can provide a more stable heat flow under smaller temperature changes, thus being more suitable for maintaining continuous boiling in the bottom of the first distillation column 100.

[0059] To generate an effective heat transfer driving force, the top temperature of the second distillation column 200 is 12–15°C higher than the bottom temperature of the first distillation column 100, preferably close to 15°C. This temperature difference is not arbitrarily increased: if the temperature difference is too small, the heat transfer area of ​​the first column bottom heat exchanger 130 will be insufficient to provide the required heat load, resulting in insufficient vaporization in the first distillation column 100; if the temperature difference is too large, the operating temperature or pressure of the second distillation column 200 needs to be increased, increasing the equipment load and potentially affecting component separation. Therefore, 12–15°C is a matching range established between ensuring the driving force of phase change heat transfer, pressure feasibility, and device stability.

[0060] The material from the second column top after heat exchange can be completely condensed in the first column bottom heat exchanger 130, or only partially condensed. When only partially condensed, the gas-liquid mixture continues to enter the second column top condenser 210, where the remaining condensation and temperature regulation are completed by an external cooling medium to ensure that the inlet of the second reflux pump 220 is a stably deliverable liquid phase. Thus, the first column bottom heat exchanger 130 undertakes the functions of heat recovery and main condensation, while the second column top condenser 210 undertakes the functions of terminal condensation and precise temperature control; the two stages of heat exchange equipment work together in a coordinated manner. The second column bottom heat exchanger 230 provides external heat to the second distillation column 200, which is further transferred to the first distillation column 100 after passing through the second column top gas phase and the first column bottom heat exchanger 130, realizing the cascade utilization of one unit of external heat in the two columns.

[0061] Example 7

[0062] In this embodiment, the saturated vapor pressure-temperature relationship of trichlorosilane shown in Table 1 and the saturated vapor pressure-temperature relationship of silicon tetrachloride shown in Table 2 are used to determine the parameters of the two distillation columns. The core of parameter determination is to first establish a stable temperature reference for the first distillation column 100, then determine the top temperature of the second distillation column 200 based on the temperature difference required for heat exchange between the columns, and finally deduce the corresponding pressure based on the physical properties of the dominant component at the top of the second distillation column under different operating conditions.

[0063] Table 1: Saturated vapor pressure of trichlorosilane at different temperatures

[0064] Table 2: Saturated vapor pressure of silicon tetrachloride at different temperatures

[0065] First, determine the top pressure of the first distillation column 100. The first distillation column 100, in both parallel and series configurations, is responsible for removing light components from a chlorosilane mixture containing silicon tetrachloride. The top vapor phase mainly consists of light components such as trichlorosilane. Therefore, a top pressure of approximately 0.11–0.12 MPaG can be selected for the first distillation column 100, and the corresponding temperature can be determined using the trichlorosilane property table. In Table 1, 55.46℃ corresponds to 114.12 kPaG, and 56.47℃ corresponds to 120.59 kPaG. Therefore, when the top pressure is controlled within the above range, the top temperature of the first distillation column 100 can be stabilized at approximately 55–56℃. When the setpoint lies between adjacent table data, linear interpolation can be used, or the table data can be written into the control system to form a lookup function.

[0066] Secondly, the reboiler pressure was obtained based on the pressure drop inside the first distillation column 100, and the reboiler temperature was determined using the silicon tetrachloride property table. The reboiler material of the first distillation column 100 is mainly silicon tetrachloride, and under a specific operating condition, the reboiler pressure is approximately 0.13 MPaG. In Table 2, 85.31℃ corresponds to 130.54 kPaG, and 86.12℃ corresponds to 135.57 kPaG. Therefore, when the reboiler pressure of the first distillation column 100 is approximately 0.131–0.136 MPaG, the reboiler temperature is approximately 85.5–86℃. This temperature reflects both the phase equilibrium state of the silicon tetrachloride in the reboiler and serves as the design benchmark for the top temperature of the second distillation column 200.

[0067] Secondly, a heat transfer temperature difference of 12–15°C is added to the reboiler temperature of the first distillation column 100. Preferably, a design temperature difference of approximately 15°C is used, so that the target top temperature of the second distillation column 200 is approximately 100.5–101°C, and can reach approximately 101.8°C within the allowable fluctuation range. This temperature allows the vapor phase at the top of the second column to condense in the reboiler heat exchanger 130 of the first column, while simultaneously maintaining the vaporization of the material in the reboiler of the first column. The control system can calculate the setpoint for the top temperature of the second column based on the real-time temperature of the first column reboiler, keeping the temperature difference between the two within a preset range, rather than using separate, unrelated fixed temperatures.

[0068] Finally, the pressure of the second distillation column 200 was determined based on the dominant components at the top of the column under different modes. In parallel operation, the second distillation column 200, like the first distillation column 100, receives a mixture of chlorosilanes containing silicon tetrachloride. The proportion of light components such as trichlorosilane in the top vapor phase is relatively high, so Table 1 is used. In Table 1, 100.52℃ corresponds to 580.00 kPaG, 101.37℃ corresponds to 592.94 kPaG, and 101.79℃ corresponds to 599.41 kPaG. Therefore, the top pressure of the second distillation column 200 in parallel operation can be determined to be approximately 0.58–0.60 MPaG. In series operation, the second distillation column 200 receives the silicon tetrachloride-rich material from the bottom of the first distillation column 100, and its top is used to collect the silicon tetrachloride product; therefore, Table 2 is used. In Table 2, 100.60℃ corresponds to 241.28 kPaG, 101.20℃ corresponds to 246.31 kPaG, and 101.80℃ corresponds to 251.34 kPaG. Therefore, the pressure at the top of the tower in series can be determined to be approximately 0.24 to 0.25 MPaG.

[0069] Therefore, both modes require maintaining similar second column top temperatures to satisfy the inter-column heat exchange temperature difference. However, due to the different dominant components at the column top, the corresponding saturated vapor pressures differ significantly. In the parallel configuration, the higher pressure is determined using the properties of trichlorosilane, while in the series configuration, the lower pressure is determined using the properties of silicon tetrachloride. This parameter determination method establishes a complete causal chain between the separation objective, column top composition, phase equilibrium pressure, and thermally coupled temperature difference, avoiding insufficient inter-column heat exchange or intra-column separation instability caused by relying solely on empirically applied pressures.

[0070] Example 8

[0071] In this embodiment, the first distillation column 100 is used as the stable reference column for the dual-column switching system. The top pressure of the first distillation column 100 is controlled at 0.11–0.12 MPaG, the top temperature at 55–56°C, and the bottom temperature at 85.5–86°C. The top pressure can be stabilized by adjusting the cooling load of the first top condenser 110, the light component output rate, and the reflux flow rate of the first reflux pump 120; the bottom temperature is adjusted by the heat load of the first bottom heat exchanger 130 and the bottom liquid level. There is a pressure difference between the top and bottom of the first distillation column 100 corresponding to the resistance of the trays or packing. The bottom pressure is formed by the combined pressure of the top pressure and the pressure drop within the column.

[0072] In parallel operation, the first distillation column 100 receives a portion of the fresh feed and collects silicon tetrachloride from the bottom. In series operation, the first distillation column 100 receives all the fresh feed and feeds the bottom material into the second distillation column 200. Although the destination of the materials changes, the primary task of the first distillation column 100 in both operations is to remove light components, and the dominant components at the top and bottom remain relatively consistent. Therefore, maintaining essentially the same pressure and temperature in the first distillation column 100 reduces thermal inertia disturbances during mode switching and provides a stable reference for calculating the top temperature of the second distillation column 200.

[0073] The improvement of this setup lies in the fact that it does not require both columns to drastically change all parameters simultaneously when switching modes. Instead, it keeps the separation baseline of the first distillation column 100 fixed, and only makes major adjustments to the pressure, reflux ratio, and material path of the second distillation column 200. This reduces the coupling between control variables, shortens the time for the control system to find a new steady state, and keeps the cold-side temperature boundary of the first column reboiler heat exchanger 130 predictable.

[0074] Example 9

[0075] This embodiment sets the top pressure and reflux ratio according to the different separation tasks undertaken by the second distillation column 200 in parallel and series operation. In parallel operation, the top pressure of the second distillation column 200 is 0.58–0.60 MPaG, and the reflux ratio is 0.8–0.9. The second distillation column 200 directly receives a mixture of chlorosilanes containing silicon tetrachloride and collects silicon tetrachloride from the bottom. The top of the column mainly serves to discharge light components. The higher pressure causes the top vapor phase to condense in the range of approximately 100.5–101.8°C, providing a sufficient temperature difference for the first column bottom heat exchanger 130; the reflux ratio of 0.8–0.9 can reduce the circulating load inside the column while satisfying the separation of light components, enabling the two columns to have a higher processing capacity when connected in parallel.

[0076] In series operation, the top pressure of the second distillation column 200 is 0.24–0.25 MPaG, and the reflux ratio is 1.2–1.5. At this point, the second distillation column 200 receives the silicon tetrachloride-rich material from the first column's reboiler. The top column is responsible for collecting the silicon tetrachloride product, while the reboiler is responsible for discharging heavy components. Increasing the reflux ratio increases the amount of liquid phase flowing downwards from the top, resulting in more thorough washing of high-boiling-point components entrained in the rising vapor phase, thus helping to stabilize the purity of the silicon tetrachloride at the top. The lower top pressure matches the saturated vapor pressure of silicon tetrachloride at approximately 100.5–101.8 °C, while still maintaining the temperature difference for heating the first column's reboiler.

[0077] During mode switching, the pressure of the second distillation column 200 can be gradually changed according to a preset slope, and the reflux ratio synchronously transitions from the parallel setting range to the series setting range, avoiding a large amount of flash evaporation or liquid level fluctuation caused by instantaneous pressure drop. The pressure is adjusted by the column top pressure controller according to the condensing load of the second column top condenser 210, the column top output, or the corresponding regulating valve, and the reflux ratio is jointly determined by the reflux flow rate and the external flow rate at the outlet of the second reflux pump 220.

[0078] Example 10

[0079] Reference Figure 3 and Figure 4 This embodiment provides a dual-tower coupled distillation apparatus for implementing the above-described method. The apparatus includes a first distillation column 100, a second distillation column 200, a main feed pipe 300, a first feed branch 310, a second feed branch 320, a first column reboiler heat exchanger 130, a first column reboiler outlet branch 141, an inter-tower conveying branch 142, and a product delivery pipeline 400. The main feed pipe 300 splits into a first feed branch 310 and a second feed branch 320 at a distribution node. The first feed branch 310 connects to the inlet of the first distillation column 100, and the second feed branch 320 connects to the inlet of the second distillation column 200. Each branch can be equipped with a shut-off valve and a flow regulating element, allowing the second feed branch 320 to supply feed simultaneously with the first feed branch 310 or to stop feeding feed independently.

[0080] The bottom outlet of the first distillation column 100 is connected to the inlet of the first bottom pump 140. The outlet of the first bottom pump 140 is divided into a first bottom outlet branch 141 and an inter-column conveying branch 142 at the distribution node. The first bottom outlet branch 141 is connected to the product delivery pipeline 400, and the inter-column conveying branch 142 is connected to the feed inlet of the second distillation column 200.

[0081] The feed switching component changes whether fresh feedstock enters the second distillation column 200, and the reboiler switching component changes whether the material from the first reboiler is directly discharged or enters the second distillation column 200. In parallel operation, both feed branches are open, the first reboiler discharge branch 141 is open, and the inter-column conveying branch 142 is closed. In series operation, only the first feed branch 310 delivers fresh feedstock, the first reboiler discharge branch 141 is closed, and the inter-column conveying branch 142 is open. The device completes flow path reconfiguration through the fixed connection of the above pipelines and the state combination of the control elements, without the need for temporary disconnection of pipelines during switching.

[0082] Example 11

[0083] In this embodiment, a return branch 510 and a top delivery branch 520 are provided on the overhead material conveying pipeline 500 of the second distillation column 200. The vapor phase at the top of the second distillation column 200 passes sequentially through the first reboiler heat exchanger 130 and the second overhead condenser 210 to form a liquid phase, which is then pressurized and conveyed by the second reflux pump 220. One outlet of the second reflux pump 220 returns to the second distillation column 200 to form overhead reflux, while the other outlet enters the overhead material conveying pipeline 500. The overhead material conveying pipeline 500 is further divided into the return branch 510 and the top delivery branch 520. The return branch 510 is connected to the feed end of the first distillation column 100, and the top delivery branch 520 is connected to the product or subsequent processing system.

[0084] The connection point between the return feed branch 510 and the first distillation column 100 can be located at the confluence of the feed main 300 and the first feed branch 310, or it can be located directly upstream of the feed inlet of the first distillation column 100, as long as the return feed is sufficiently mixed with the material entering the first distillation column 100 and passes through the separation section of the first distillation column again. Preferably, a third switching valve 511, a check valve, and a flow detection element are installed on the return feed branch 510 to prevent the material in the first feed branch 310 from flowing back into the second column top system. A fourth switching valve 521 is installed on the column top outgoing branch 520, and a sampling port or online analyzer can be installed upstream of the fourth switching valve 521.

[0085] Under steady-state conditions after parallel or series production has reached the required standards, the third switching valve 511 closes and the fourth switching valve 521 opens, allowing the material from the second column top to be output via the column top delivery branch 520. During the transition from parallel to series production when the column top purity has not yet met the standards, the third switching valve 511 opens and the fourth switching valve 521 closes, returning the material from the second column top to the first distillation column 100 via the return branch 510. Through these two fixed, selectable paths, the unit eliminates the need for a transition waste tank and long-term downgrading of the transition material. The light components in the return material are discharged again from the top of the first column, and silicon tetrachloride re-enters the series separation path, thus simultaneously achieving quality isolation, material recovery, and accelerated switching.

[0086] Example 12

[0087] This embodiment provides a complete description of the connection relationship between the top systems of the two distillation columns and the first reboiler heat exchanger 130. The vapor outlet at the top of the first distillation column 100 is connected to the inlet of the first top condenser 110 via a pipeline, and the outlet of the first top condenser 110 is connected to the inlet of the first reflux pump 120. The outlet of the first reflux pump 120 has two directions: reflux and light component delivery. The reflux direction is connected to the reflux inlet of the first distillation column 100, and the delivery direction is connected to the light component delivery pipeline 600. The first top condenser 110 is used to condense the vapor phase of the light components at the top of the first column, and the first reflux pump 120 provides the pressure head required for reflux and delivery. Adjusting the reflux flow rate can stabilize the temperature at the top of the first column and the degree of separation of the light components.

[0088] The vapor outlet at the top of the second distillation column 200 is connected to the heating medium inlet of the first column reboiler heat exchanger 130 via a heating medium inlet line 131. The heating medium outlet of the first column reboiler heat exchanger 130 is connected to the inlet of the second column top condenser 210 via a condensate outlet line 132. The "vapor" in the heating medium inlet line 131 is the chlorosilane process vapor from the second column top, and the material in the condensate outlet line 132 is the condensate or gas-liquid mixture of this process vapor after heat exchange. The second column top condenser 210 performs supplementary condensation and subcooling to bring the material to the inlet condition permitted by the second reflux pump 220.

[0089] The outlet of the second overhead condenser 210 is connected to the inlet of the second reflux pump 220. The outlet of the second reflux pump 220 is connected to the reflux inlet of the second distillation column 200 and the overhead material conveying line 500, respectively. By adjusting the flow ratio of the reflux branch and the overhead material conveying line 500, the desired reflux ratio can be achieved. The overhead material conveying line 500 is further connected to the return branch 510 and the overhead external delivery branch 520. Therefore, the same second reflux pump 220 provides pressure head for reflux within the column and also provides conveying power for transitional return or delivery of qualified products.

[0090] Example 13

[0091] In this embodiment, a second reboiler heat exchanger 230 is installed in the reboiler of the second distillation column 200. The second reboiler heat exchanger 230 has separate material channels and heating medium channels. The inlet and outlet of the material channels are connected to the reboiler of the second distillation column 200, allowing the liquid in the reboiler to enter the heat exchanger, be heated, and then return to the reboiler. The inlet of the heating medium channel is connected to the steam input pipeline 231, and the outlet is connected to the condensate output pipeline 232. Utility steam enters the heat exchanger through the steam input pipeline 231 and condenses, releasing heat. The generated condensate is discharged through the condensate output pipeline 232 and a condensate or condensate recovery device.

[0092] The second column reboiler heat exchanger 230 can be a natural circulation reboiler or a forced circulation reboiler. When using natural circulation, its material inlet is connected to the lower liquid phase zone of the column reboiler, and its material outlet is connected to the higher zone, utilizing the density difference before and after heating to establish circulation. When using forced circulation, a circulation pump can be configured in the material loop. The steam flow regulating valve adjusts its opening according to the second column reboiler temperature, column top pressure, or vaporization load within the column to ensure that the second distillation column 200 generates sufficient top vapor.

[0093] The second column reboiler heat exchanger 230 is the main external heat input terminal of the dual-column system. External steam first vaporizes the material in the second column reboiler, and the vapor phase at the top of the second column is then condensed in the first column reboiler heat exchanger 130 and supplied heat to the first column reboiler. Thus, heat is transferred sequentially through the second column reboiler heat exchanger 230, the second distillation column 200, the first column reboiler heat exchanger 130, and the first distillation column 100. Compared with having separate steam reboilers for the two columns, this cascade transfer reduces the independent steam consumption required by the first distillation column 100 and effectively utilizes the heat that would otherwise need to be discharged by the cooling system at the top of the second column.

[0094] Example 14

[0095] Reference Figure 4 In this embodiment, a first feed valve 311, a second feed valve 321, a first switching valve 141a, a second switching valve 142a, a third switching valve 511, and a fourth switching valve 521 are used to select the flow path. The first feed valve 311 is located on the first feed branch 310 and is used to control the entry of fresh feedstock into the first distillation column 100. The second feed valve 321 is located on the second feed branch 320 and is used to control the entry of fresh feedstock into the second distillation column 200. The first switching valve 141a is located on the first column bottom discharge branch 141, and the second switching valve 142a is located on the inter-column conveying branch 142. The third switching valve 511 is located on the return branch 510, and the fourth switching valve 521 is located on the column top outgoing branch 520.

[0096] In parallel operation, the first feed valve 311 and the second feed valve 321 are open, allowing both columns to receive fresh raw materials. The first switching valve 141a is open and the second switching valve 142a is closed, allowing the material from the bottom of the first column to be sent out. The third switching valve 511 is closed and the fourth switching valve 521 is open, allowing the material from the top of the second column to be sent out. In series operation with the product already meeting the standards, the first feed valve 311 is open and the second feed valve 321 is closed, allowing fresh raw materials to enter only the first distillation column 100. The first switching valve 141a is closed and the second switching valve 142a is open, allowing the material from the bottom of the first column to enter the second distillation column 200. The third switching valve 511 is closed and the fourth switching valve 521 is open, allowing the qualified product from the top of the second column to be sent out. In the transition from parallel to series operation with the product not yet meeting the standards, the first two sets of valves are combined in series, the third switching valve 511 is open and the fourth switching valve 521 is closed, allowing the material from the top of the second column to return to the first distillation column 100.

[0097] The bottom outlet of the first distillation column 100 is connected to the inlet of the first bottom pump 140, and the outlet of the first bottom pump 140 is then branched to the first bottom outlet branch 141 and the inter-column conveying branch 142. The bottom outlet of the second distillation column 200 is connected to the inlet of the second bottom pump 240, and the outlet of the second bottom pump 240 is connected to the product delivery pipeline 400.

[0098] Each valve can be a pneumatic shut-off valve, electric valve, hydraulic valve, or a three-way valve with equivalent switching function. During automatic control, the control system receives signals of at least two tower top pressures, tower top temperatures, tower bottom temperatures, tower bottom liquid levels, reflux flow rates, and product purity, and outputs valve commands according to the operating mode. The following interlocks are preferably configured: the second switching valve 142a is only allowed to open after the second feed valve 321 is confirmed to be closed; the first switching valve 141a and the second switching valve 142a should not be closed simultaneously for extended periods; the second reflux pump 220 should have a clear outlet when the third switching valve 511 and the fourth switching valve 521 are switching; the fourth switching valve 521 is only allowed to enter the product delivery position when the purity of the material at the top of the second tower reaches a preset value.

[0099] Finally, it should be noted that the methods and devices described in detail above are merely embodiments, and those skilled in the art can modify these embodiments in different ways as long as they do not depart from the scope of the present invention.

Claims

1. A dual-tower coupled distillation method with series-parallel switching capability, characterized in that: include, The chlorosilane mixture containing silicon tetrachloride is selectively fed into the first distillation column (100) and the second distillation column (200), or into the first distillation column (100). The bottom material of the first distillation column (100) may be selectively sent to an external location or sent to the second distillation column (200). The material at the top of the second distillation column (200) is used to exchange heat with the material at the bottom of the first distillation column (100); By switching the material conveying path described above, the first distillation column (100) and the second distillation column (200) can selectively operate in parallel or in series.

2. The dual-tower coupled distillation method with series-parallel switching capability as described in claim 1, characterized in that: In the parallel operation state, the chlorosilane mixture containing silicon tetrachloride enters the first distillation column (100) and the second distillation column (200) respectively. The first distillation column (100) and the second distillation column (200) respectively distill and separate the chlorosilane mixture, and collect silicon tetrachloride product from the bottom of the column respectively.

3. The dual-tower coupled distillation method with series-parallel switching capability as described in claim 2, characterized in that: In the series operation state, the chlorosilane mixture containing silicon tetrachloride enters the first distillation column (100), the light component is discharged from the top of the first distillation column (100), the bottom material of the first distillation column (100) enters the second distillation column (200) for distillation separation, the silicon tetrachloride product is collected from the top of the second distillation column (200), and the heavy component is discharged from the bottom of the second distillation column (200).

4. The dual-tower coupled distillation method with series-parallel switching capability as described in claim 3, characterized in that: When the first distillation column (100) and the second distillation column (200) switch from parallel operation to series operation, before the top material of the second distillation column (200) reaches the preset purity, the top material of the second distillation column (200) is returned to the feed end of the first distillation column (100) for further distillation and separation.

5. The dual-tower coupled distillation method with series-parallel switching capability as described in claim 4, characterized in that: When switching from the parallel operation state to the series operation state, the feeding of the chlorosilane mixture to the second distillation column (200) is stopped in sequence, the bottom material of the first distillation column (100) is switched from external feeding to feeding into the second distillation column (200), and the top material of the second distillation column (200) is switched from external feeding to returning to the feed end of the first distillation column (100); when the top material of the second distillation column (200) reaches the preset purity, the top material of the second distillation column (200) is switched to external feeding.

6. The dual-tower coupled distillation method with series-parallel switching capability as described in claim 3 or 4, characterized in that: The top material of the second distillation column (200) enters the first reboiler heat exchanger (130) of the first distillation column (100) in a gaseous state and condenses and releases heat in the first reboiler heat exchanger (130). The top temperature of the second distillation column (200) is 12-15°C higher than the reboiler temperature of the first distillation column (100).

7. The dual-tower coupled distillation method with series-parallel switching capability as described in claim 6, characterized in that: The operating parameters of the first distillation column (100) and the second distillation column (200) are determined as follows: The top temperature of the first distillation column (100) is determined based on the pressure at the top of the first distillation column (100) and the relationship between the saturated vapor pressure and temperature of trichlorosilane. The reboiler temperature of the first distillation column (100) is determined based on the reboiler pressure of the first distillation column (100) and the correspondence between the saturated vapor pressure and temperature of silicon tetrachloride. The top temperature of the second distillation column (200) is determined based on the temperature difference between the bottom temperature of the first distillation column (100) and the top temperature of the second distillation column (200) and the bottom temperature of the first distillation column (100). In the parallel operation state, the top pressure of the second distillation column (200) is determined according to the correspondence between the saturated vapor pressure and temperature of trichlorosilane; in the series operation state, the top pressure of the second distillation column (200) is determined according to the correspondence between the saturated vapor pressure and temperature of silicon tetrachloride.

8. The dual-tower coupled distillation method with series-parallel switching capability as described in claim 7, characterized in that: The first distillation column (100) has a top pressure of 0.11-0.12 MPaG, a top temperature of 55-56°C, and a bottom temperature of 85.5-86°C.

9. The dual-tower coupled distillation method with series-parallel switching capability as described in claim 8, characterized in that: In the parallel operation state, the top pressure of the second distillation column (200) is 0.58-0.60 MPaG and the reflux ratio is 0.8-0.9; in the series operation state, the top pressure of the second distillation column (200) is 0.24-0.25 MPaG and the reflux ratio is 1.2-1.

5.

10. A dual-tower coupled distillation apparatus capable of series-parallel switching, characterized in that, It includes a first distillation column (100), a second distillation column (200), a feed header (300), and a first column reboiler heat exchanger (130). The feed main (300) is connected to the feed inlet of the first distillation column (100) and the feed inlet of the second distillation column (200) through the first feed branch (310) and the second feed branch (320), respectively. Feed switching components are provided on the first feed branch (310) and the second feed branch (320). The bottom outlet of the first distillation column (100) is connected to the product delivery pipeline (400) and the inlet of the second distillation column (200) through the first bottom outlet branch (141) and the inter-column conveying branch (142), respectively. The bottom outlet branch (141) and the inter-column conveying branch (142) are equipped with bottom switching components. The material channel of the first column bottom heat exchanger (130) is connected to the bottom of the first distillation column (100), and the heating medium channel of the first column bottom heat exchanger (130) is connected to the top vapor outlet of the second distillation column (200), so that the top vapor material of the second distillation column (200) serves as the heat source for the bottom of the first distillation column (100). The feed switching assembly and the reboiler switching assembly change the conveying path of the material in the feed header (300) and the reboiler of the first distillation column (100), so that the first distillation column (100) and the second distillation column (200) form parallel material flow paths or series material flow paths.

11. The dual-tower coupled distillation apparatus with series-parallel switching capability as described in claim 10, characterized in that: The top material conveying pipeline (500) of the second distillation column (200) is provided with a return branch (510) and a top external delivery branch (520). The return branch (510) is connected to the feed end of the first distillation column (100). The return branch (510) and the top external delivery branch (520) are respectively provided with a return switching component and an external delivery switching component.

12. The dual-tower coupled distillation apparatus with series-parallel switching capability as described in claim 11, characterized in that: The top vapor outlet of the first distillation column (100) is connected in sequence to the first top condenser (110) and the first reflux pump (120), and the outlet of the first reflux pump (120) is connected to the reflux inlet of the first distillation column (100) and the light component delivery pipeline (600), respectively. The heating medium channel of the first column bottom heat exchanger (130) is connected to the heating medium input pipeline (131) and the condensate output pipeline (132) respectively. The heating medium input pipeline (131) is connected to the top gas phase outlet of the second distillation column (200), and the condensate output pipeline (132) is connected to the second column top condenser (210). The outlet of the second top condenser (210) is connected to the second reflux pump (220), and the outlet of the second reflux pump (220) is connected to the reflux inlet of the second distillation column (200) and the top material conveying pipeline (500) of the second distillation column (200).

13. The dual-tower coupled distillation apparatus capable of series-parallel switching as described in claim 11 or 12, characterized in that: The second distillation column (200) is equipped with a second reboiler heat exchanger (230). The material channel of the second reboiler heat exchanger (230) is connected to the reboiler of the second distillation column (200). The heating medium channel of the second reboiler heat exchanger (230) is connected to the steam input pipeline (231) and the condensate output pipeline (232), respectively.

14. The dual-tower coupled distillation apparatus with series-parallel switching capability as described in claim 13, characterized in that: The feed switching assembly includes a first feed valve (311) disposed on the first feed branch (310) and a second feed valve (321) disposed on the second feed branch (320). The tower reboiler switching assembly includes a first switching valve (141a) disposed on the first tower reboiler discharge branch (141) and a second switching valve (142a) disposed on the inter-tower conveying branch (142). The return material switching assembly includes a third switching valve (511) disposed on the return material branch (510), and the external delivery switching assembly includes a fourth switching valve (521) disposed on the external delivery branch (520) at the top of the tower. The bottom outlet of the first distillation column (100) is connected to the inlet of the first bottom pump (140), and the outlet of the first bottom pump (140) is connected to the first bottom outlet branch (141) and the inter-column conveying branch (142), respectively; the bottom outlet of the second distillation column (200) is connected to the inlet of the second bottom pump (240), and the outlet of the second bottom pump (240) is connected to the product delivery pipeline (400).

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