System and method for mixing, freezing and dehydrating vinyl chloride before synthesis
By combining staged cooling with a parallel molecular sieve dryer, a hybrid cryogenic dehydration system was developed, which solved the problem of unstable dehydration in the vinyl chloride synthesis process, achieving a highly efficient and stable vinyl chloride synthesis process and reducing equipment corrosion risks and production costs.
Patent Information
- Application Number
- CN202511677189.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-17
- Publication Date
- 2026-02-10
AI Technical Summary
In the existing vinyl chloride synthesis process, the mixing and dehydration step suffers from problems such as difficulty in achieving dynamic equilibrium between the gas and liquid phases, equipment coking and blockage, difficulty in treating corrosive waste acid, and insufficient production continuity, which affect the stability and economy of vinyl chloride synthesis.
A hybrid cryogenic dehydration system combining staged cooling and parallel molecular sieve dryers is adopted. Hydrogen chloride and acetylene are pretreated by staged coolers and molecular sieve dryers, and acid liquid is managed by airflow circulation regeneration device and acid collection tank, so as to achieve efficient dehydration and stable process flow.
It significantly reduces the water content of the mixed gas, improves the dehydration effect, ensures catalytic performance, simplifies acid management, improves process continuity and economy, and reduces the risk of equipment corrosion.
Smart Images
Figure CN121490538A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of chemical technology, and more specifically, to a mixed cryogenic dehydration system and method for vinyl chloride synthesis. Background Technology
[0002] In the calcium carbide-based polyvinyl chloride (PVC) production process, the efficient conduct of the vinyl chloride synthesis reaction highly depends on the stability and precision of the mixing and dehydration process. Current industrial practice faces multiple technical bottlenecks in the mixing and dehydration process: traditional processes use a mixture of acetylene and hydrogen chloride followed by deep cooling with -36°C chilled water. However, due to the difficulty in achieving dynamic equilibrium between the gas and liquid phases at low temperatures, moisture cannot be fully extracted from the mixed gas, resulting in actual water content often exceeding the upper limit of process parameters during high-temperature seasons, severely interfering with the catalytic performance of subsequent catalysts. While the alternative of mixing and dehydration combined with sulfuric acid drying can partially reduce water content, concentrated sulfuric acid easily triggers carbonization side reactions during operation, causing coking and blockage inside the equipment, while also generating large amounts of corrosive waste acid, which is difficult to treat and poses high environmental risks. Although the existing acetylene molecular sieve segmented dehydration process incorporates a molecular sieve drying unit, the molecular sieve needs a regeneration process to restore its adsorption capacity after adsorbing moisture to saturation, leading to insufficient continuity of the production process. These problems collectively restrict the continuity and economy of vinyl chloride synthesis, necessitating an integrated solution to optimize dehydration effects, improve equipment reliability, and simplify acid management. Summary of the Invention
[0003] The purpose of this invention is to provide a mixed cryogenic dehydration system and method before vinyl chloride synthesis, which has the advantages of effectively controlling the moisture content of the gas, simplifying acid collection and management, and improving process continuity and economy.
[0004] This invention provides a mixed cryogenic dehydration system before vinyl chloride synthesis, the technical solution of which is as follows: It includes a hydrogen chloride primary cooler, a hydrogen chloride secondary cooler, a first molecular sieve dryer, a second molecular sieve dryer, an airflow regeneration device, an acid collection tank, a mixer, a hydrogen chloride delivery pipeline, and an acetylene delivery pipeline. The hydrogen chloride delivery pipeline is connected to the inlet of the hydrogen chloride primary cooler. The outlet of the hydrogen chloride primary cooler is connected to the inlet of the hydrogen chloride secondary cooler via a pipeline. The outlet of the hydrogen chloride secondary cooler is connected to the first inlet of the mixer. The acid discharge ports of the hydrogen chloride primary cooler and the hydrogen chloride secondary cooler are connected to the acid collection tank via pipelines. The acetylene delivery pipeline is connected to the raw material gas inlets of the first and second molecular sieve dryers via pipelines. The raw material gas inlets of the first and second molecular sieve dryers are each connected to a regeneration vent pipe. The dry gas outlets of the first and second molecular sieve dryers are each connected to the second inlet of the mixer. The dry gas outlets of the first and second molecular sieve dryers are each connected to the airflow circulation regeneration device via pipelines. Valves are installed on the regeneration vent pipe, the pipeline between the raw material gas inlet and the acetylene delivery pipeline, the pipeline between the dry gas outlet and the mixer, and the pipeline between the dry gas outlet and the airflow circulation regeneration device. The acid discharge port of the mixer is connected to the acid collection tank via pipelines. Furthermore, the present invention also proposes that the airflow circulation regeneration device includes a nitrogen delivery pipeline, a nitrogen heating pipeline, and a cold nitrogen pipeline. The nitrogen delivery pipeline is connected to the inlet of the nitrogen heating pipeline and the cold nitrogen pipeline, respectively. The outlet of the nitrogen heating pipeline and the cold nitrogen pipeline are connected to the dry gas outlet through pipelines, respectively. A coalescer and a nitrogen heater are provided on the nitrogen heating pipeline. Valves are provided on the nitrogen heating pipeline and the cold nitrogen pipeline. Furthermore, the present invention also proposes that it further includes a PLC controller, a dew point moisture probe, and a solenoid valve. The dew point moisture probe is installed on the pipeline at the outlet of the drying gas, and the PLC controller is electrically connected to the dew point moisture probe, the nitrogen heater, and the valve respectively. Furthermore, the present invention also proposes a mixed cryogenic dehydration method before vinyl chloride synthesis, comprising the following steps: Step 1: After washing, cooling and demisting the acetylene with water, it is transported into the molecular sieve dryer through the acetylene delivery pipeline for drying. The dried acetylene is then transported into the mixer. Step 2: Hydrogen chloride flows sequentially through a primary hydrogen chloride cooler and a secondary hydrogen chloride cooler for staged cooling. The cooled hydrogen chloride is then transported into a mixer. The acid produced by the primary and secondary hydrogen chloride coolers is transported to an acid collection tank for collection. Step 3: The dried acetylene and the cooled hydrogen chloride form a mixed gas in the mixer. The acid produced during the mixing process is transported to the acid collection tank for collection, and the mixed gas is transported to the vinyl chloride conversion station. Furthermore, the present invention also proposes that, in step one, the acetylene is cooled to 2-3°C. Furthermore, the present invention also proposes that in step two, hydrogen chloride is cooled to 15°C by a primary hydrogen chloride cooler and then cooled to 5°C by a secondary hydrogen chloride cooler.
[0005] The present invention has the following beneficial effects: 1. High-efficiency dehydration: By combining staged cooling with parallel molecular sieve deep drying, the water volume fraction of the mixed gas is stably controlled within 0.003%, which significantly improves the dehydration effect and ensures the efficiency of subsequent catalyst activity and vinyl chloride synthesis reaction. The parallel molecular sieve dryer can automatically switch according to the saturation to ensure the continuity of the process.
[0006] 2. Cost control: Reduce catalyst consumption (taking a 400,000 t / a unit as an example, it is estimated that 200 t of catalyst will be saved annually), reduce the amount of high-boiling by-products and acid production; the acid collection tank collects acid liquid in a unified manner, which is convenient for centralized treatment or recycling, and further reduces costs.
[0007] 3. Process optimization: A complete raw material gas pretreatment, molecular sieve dehydration and regeneration system, combined with an acid collection and treatment scheme, achieves full-process optimization of the mixed dehydration process. Attached Figure Description
[0008] Figure 1 This is a schematic diagram of the structure of the present invention.
[0009] Figure 2 This is a schematic diagram of the system control of the present invention. Detailed Implementation
[0010] like Figure 1 The mixed cryogenic dehydration system shown includes a hydrogen chloride primary cooler 1, a hydrogen chloride secondary cooler 2, a first molecular sieve dryer 3, a second molecular sieve dryer 4, an airflow circulation regeneration device, an acid collection tank 5, a mixer 6, a hydrogen chloride delivery pipeline 7, and an acetylene delivery pipeline 8. The hydrogen chloride delivery pipeline 7 is connected to the inlet of the hydrogen chloride primary cooler 1. The outlet of the hydrogen chloride primary cooler 1 is connected to the inlet of the hydrogen chloride secondary cooler 2 through a pipeline. The outlet of the hydrogen chloride secondary cooler 2 is connected to the first inlet of the mixer 6. The acid discharge ports of the hydrogen chloride primary cooler 1 and the hydrogen chloride secondary cooler 2 are connected to the acid collection tank 5 through pipelines. The acetylene delivery pipeline 8 is connected to the raw material gas inlets 10 of the first molecular sieve dryer 3 and the second molecular sieve dryer 4 via pipelines. The raw material gas inlets 10 of the first molecular sieve dryer 3 and the second molecular sieve dryer 4 are each connected to a regeneration vent pipe 9. The dry gas outlets 11 of the first molecular sieve dryer 3 and the second molecular sieve dryer 4 are each connected to the second inlet of the mixer 6 via pipelines. The dry gas outlets 11 of the first molecular sieve dryer 3 and the second molecular sieve dryer 4 are each connected to the airflow circulation regeneration device via pipelines. Valves 12 are respectively installed on the regeneration vent pipe 9, the pipeline between the raw material gas inlet 10 and the acetylene delivery pipeline 8, the pipeline between the dry gas outlet 11 and the mixer 6, and the pipeline between the dry gas outlet 11 and the airflow circulation regeneration device. The acid discharge port of the mixer 6 is connected to the acid collection tank 5 via pipelines.
[0011] In this mixed cryogenic dehydration system, hydrogen chloride and acetylene are pretreated separately to achieve efficient dehydration. Hydrogen chloride is introduced into the primary hydrogen chloride cooler 1 via hydrogen chloride delivery pipe 7 for initial cooling. The cooled gas then enters the secondary hydrogen chloride cooler 2 for further cooling. The finally cooled hydrogen chloride is delivered to the first inlet of the mixer 6. Simultaneously, the acid generated during the cooling process in the primary and secondary hydrogen chloride coolers 1 and 2 is collected in the acid collection tank 5 via the acid drain port. Acetylene is distributed to the first molecular sieve dryer 3 or the second molecular sieve dryer 4 via acetylene delivery pipe 8 for drying. The dried acetylene is guided to the second inlet of the mixer 6 through the drying gas outlet 11. The acid generated during the mixing and drying of acetylene and the cooling of hydrogen chloride in the mixer 6 is also delivered to the acid collection tank 5 via the acid drain port. Furthermore, the first molecular sieve dryer 3 and the second molecular sieve dryer 4 undergo alternating regeneration operations via an airflow circulation regeneration device. The regeneration process is precisely controlled by valves 12 located in the pipelines between the regeneration vent pipe 9, the raw material gas inlet 10 and the acetylene delivery pipeline 8, the drying gas outlet 11 and the mixer 6, and the pipeline between the drying gas outlet 11 and the airflow circulation regeneration device. This ensures that the molecular sieves can restore their adsorption capacity while maintaining continuous operation. As a preferred embodiment, the first molecular sieve dryer 3 can specifically be a cylindrical drying tower filled with type 3A molecular sieves, with an inner diameter of 500 mm and a height of 2000 mm to provide sufficient drying surface area. Therefore, by separating the acetylene drying and hydrogen chloride cooling processes, the system avoids the problem of excessive water content caused by the imbalance of the gas and liquid phases after mixing; the staged cooling mechanism of hydrogen chloride reduces thermal stress impact and acid mist formation, thereby reducing the risk of equipment corrosion; the centralized collection method of acid collection tank 5 simplifies the acid treatment process and avoids the management complexity caused by decentralized discharge; the precise switching control of valve 12 enables the alternating drying and regeneration operations of the first molecular sieve dryer 3 and the second molecular sieve dryer 4, improving the continuity and stability of the overall process.
[0012] like Figure 1 As shown, the present invention further proposes an airflow circulation regeneration device, including a nitrogen delivery pipe 13, a nitrogen heating pipe 14, and a cold nitrogen pipe 15. The nitrogen delivery pipe 13 is connected to the inlet of the nitrogen heating pipe 14 and the cold nitrogen pipe 15, respectively. The outlets of the nitrogen heating pipe 14 and the cold nitrogen pipe 15 are connected to the dry gas outlet 11 through pipelines. A coalescer 16 and a nitrogen heater 17 are provided on the nitrogen heating pipe 14. Valves 12 are provided on the nitrogen heating pipe 14 and the cold nitrogen pipe 15.
[0013] Among them, nitrogen delivery pipeline 13 refers to the delivery structure for a stable supply of regenerated gas, which can be made of carbon steel or stainless steel to ensure the continuity and reliability of the gas source; nitrogen heating pipeline 14 refers to a dedicated path for raising the temperature of the regenerated gas, which aims to promote the desorption of moisture adsorbed by the molecular sieve through heat input; cold nitrogen pipeline 15 refers to a backup path for delivering regenerated gas at room temperature or low temperature, which aims to meet the temperature requirements of the cooling stage or transitional operating conditions; coalescer 16 refers to a purification unit that intercepts liquid moisture and particulate impurities in the gas, which can be made of porous fiber filter or centrifugal separation structure, with the aim of preventing pollutants from re-entering the molecular sieve system; nitrogen heater 17 refers to a heat exchange device for precisely controlling the gas temperature, which can be made of electric heating wire or heat medium circulation heating device.
[0014] Specifically, the present invention provides a basic gas source through a nitrogen delivery pipeline 13, which, after being selected by valve 12, is diverted to either a nitrogen heating pipeline 14 or a cold nitrogen pipeline 15 for countercurrent purging regeneration. In the initial stage of regeneration, the nitrogen delivery pipeline 13 is connected to the cold nitrogen pipeline 15 for cold purging, with a purging flow rate of 400-550 m³ / h and a purging time of 25-35 min, removing desorbed moisture and impurities while avoiding the impact of drastic temperature changes on the molecular sieve structure. Subsequently, the nitrogen delivery pipeline 13 is connected to the nitrogen heating pipeline 14 for hot purging, with a purging temperature of 175-190℃, a purging flow rate of 400-450 m³ / h, and a purging time of 60-70 min, further promoting the desorption of residual moisture and improving regeneration efficiency. Simultaneously, the coalescer 16 ensures gas purity, the nitrogen heater 17 ensures precise temperature control, and the valve 12 enables precise path switching, thus forming a complete regeneration gas control system that effectively solves the problems of insufficient temperature flexibility and impurity interference.
[0015] like Figure 1 and Figure 2 As shown, the present invention further includes a PLC controller 18, a dew point moisture probe 19, and a solenoid valve 12. The dew point moisture probe 19 is installed on the pipeline of the dry gas outlet 11. The PLC controller 18 is electrically connected to the dew point moisture probe 19, the nitrogen heater 17, and the valve 12.
[0016] Among them, the PLC controller 18 refers to a programmable logic controller, which is used to execute automated control logic. It can be implemented by an industrial-grade modular controller or an embedded control unit. The dew point moisture probe 19 is a sensing device used to detect the dew point temperature of the gas to quantify the moisture content. The dew point moisture probe 19 is set on the pipeline of the dry gas outlet 11 to ensure that the real-time moisture status of the gas before entering the mixer 6 is directly obtained. The PLC controller 18 is electrically connected to the dew point moisture probe 19, the nitrogen heater 17, and the valve 12, respectively, so that the controller can receive moisture data and output control commands.
[0017] Specifically, the first molecular sieve dryer 3 and the second molecular sieve dryer 4 of the present invention are controlled by a PLC controller 18 to perform alternating drying and regeneration operations. For example, when the dew point moisture probe 19 detects that the dew point of the outlet gas of the first molecular sieve dryer 3 is higher than a set threshold or the moisture content exceeds a set threshold, the signal is transmitted to the PLC controller 18. The PLC controller 18 then controls the valve 12 corresponding to the first molecular sieve dryer 3 to close for regeneration, and the valve 12 corresponding to the second molecular sieve dryer 4 to open for drying. During the regeneration operation, the PLC controller 18 first controls the valve 12 of the cold nitrogen pipeline 15 to open for cold purging, and the cold purging is timed by the time relay built into the PLC controller 18. After the cold purging timer ends, the PLC controller 18 controls the valve 12 of the cold nitrogen pipeline 15 to close, the valve 12 of the nitrogen heating pipeline 14 to open, and the nitrogen heater 17 to open for hot purging, and the hot purging is closed after the hot purging timer ends.
[0018] This invention also discloses a mixed cryogenic dehydration method before vinyl chloride synthesis, comprising the following steps: acetylene is washed with water, cooled, and demisted, then transported by acetylene conveying pipeline 8 into a molecular sieve dryer for drying; the dried acetylene is then transported into a mixer 6; hydrogen chloride flows sequentially through a primary hydrogen chloride cooler 1 and a secondary hydrogen chloride cooler 2 for staged cooling; the cooled hydrogen chloride is then transported into the mixer 6; the acid produced by the primary hydrogen chloride cooler 1 and the secondary hydrogen chloride cooler 2 is transported to an acid collection tank 5 for collection; the dried acetylene and the cooled hydrogen chloride form a mixed gas in the mixer 6; the acid produced during the mixing process is transported to the acid collection tank 5 for collection; and the mixed gas is then transported to the vinyl chloride conversion station.
[0019] This invention combines the independent drying of acetylene with the staged cooling of hydrogen chloride via a separate pathway, thus avoiding the problem of excessive water content caused by gas-liquid phase imbalance after mixing. Furthermore, the centralized collection of acid in acid collection tank 5 solves the problems of equipment blockage and difficult waste acid treatment, achieving a highly efficient, stable, and environmentally friendly dehydration process. Specifically, acetylene, after being washed, cooled, and demisted, enters a molecular sieve dryer to effectively remove soluble impurities and mist droplets, ensuring that the water content is strictly controlled within process parameters. Hydrogen chloride is gradually cooled through a staged cooling mechanism, reducing acid mist formation and thermal stress impact on the equipment. Centralized collection of acid in acid collection tank 5 simplifies the treatment process and avoids the management complexity caused by decentralized discharge. Therefore, this method significantly improves the stability and environmental performance of the vinyl chloride synthesis reaction.
[0020] The present invention further proposes that in step one, the acetylene is cooled to 2-3°C. Specifically, the present invention precisely controls the acetylene cooling temperature within the range of 2-3°C, utilizing the saturation characteristics of water vapor within this temperature range to controllably condense and precipitate water vapor during the cooling process. When the acetylene gas is cooled to this temperature, the water vapor reaches a saturated state and condenses into liquid water, thereby effectively reducing the water vapor content in the gas. At the same time, this temperature range avoids the risk of pipeline icing caused by excessively low temperatures and the problem of insufficient water vapor removal caused by excessively high temperatures, ensuring stable humidity of the gas entering the molecular sieve dryer, optimizing the gas-liquid phase equilibrium conditions, and ensuring that the water content of the mixed gas continuously meets the process specifications.
[0021] The present invention further proposes that in step two, hydrogen chloride is cooled to 15°C by a hydrogen chloride primary cooler 1, and then cooled to 5°C by a hydrogen chloride secondary cooler 2.
[0022] The hydrogen chloride primary cooler 1 refers to the equipment used for preliminary cooling of hydrogen chloride gas. It can be implemented using a graphite cooler. Its purpose is to control the temperature at around 15°C, so that some moisture is condensed and separated, while avoiding the risk of equipment corrosion caused by excessively low temperatures. The hydrogen chloride secondary cooler 2 refers to the equipment used for deep cooling of hydrogen chloride gas. It can be implemented using a metal corrosion-resistant cooler. Its purpose is to further reduce the temperature to 5°C to deeply remove residual moisture and ensure that the water content of the mixed gas meets the process safety threshold requirements.
Claims
1. A mixed cryogenic dehydration system prior to vinyl chloride synthesis, characterized in that: It includes a hydrogen chloride primary cooler (1), a hydrogen chloride secondary cooler (2), a first molecular sieve dryer (3), a second molecular sieve dryer (4), an airflow circulation regeneration device, an acid collection tank (5), a mixer (6), a hydrogen chloride delivery pipeline (7), and an acetylene delivery pipeline (8); The hydrogen chloride delivery pipeline (7) is connected to the inlet of the hydrogen chloride primary cooler (1), the outlet of the hydrogen chloride primary cooler (1) is connected to the inlet of the hydrogen chloride secondary cooler (2) through a pipeline, the outlet of the hydrogen chloride secondary cooler (2) is connected to the first inlet of the mixer (6), and the acid discharge ports of the hydrogen chloride primary cooler (1) and the hydrogen chloride secondary cooler (2) are connected to the acid collection tank (5) through pipelines. The acetylene delivery pipeline (8) is connected to the raw material gas inlet (10) of the first molecular sieve dryer (3) and the second molecular sieve dryer (4) through pipelines. The raw material gas inlet (10) of the first molecular sieve dryer (3) and the second molecular sieve dryer (4) are respectively connected to the regeneration vent pipe (9). The dry gas outlet (11) of the first molecular sieve dryer (3) and the second molecular sieve dryer (4) is connected to the second inlet of the mixer (6). The dry gas outlet (11) of the first molecular sieve dryer (3) and the second molecular sieve dryer (4) is respectively connected to the airflow circulation regeneration device through pipelines. Valves (12) are respectively installed on the pipeline between the regeneration vent pipe (9), the raw material gas inlet (10) and the acetylene delivery pipeline (8), the pipeline between the dry gas outlet (11) and the mixer (6), and the pipeline between the dry gas outlet (11) and the airflow circulation regeneration device. The acid discharge port of the mixer (6) is connected to the acid collection tank (5) through pipelines.
2. The mixing and cryogenic dehydration system before vinyl chloride synthesis as described in claim 1, characterized in that: The airflow circulation regeneration device includes a nitrogen delivery pipe (13), a nitrogen heating pipe (14), and a cold nitrogen pipe (15). The nitrogen delivery pipe (13) is connected to the inlet of the nitrogen heating pipe (14) and the cold nitrogen pipe (15), respectively. The outlet of the nitrogen heating pipe (14) and the cold nitrogen pipe (15) is connected to the dry gas outlet (11) through a pipeline. A coalescer (16) and a nitrogen heater (17) are provided on the nitrogen heating pipe (14). Valves (12) are provided on the nitrogen heating pipe (14) and the cold nitrogen pipe (15).
3. The mixing and cryogenic dehydration system before vinyl chloride synthesis as described in claim 2, characterized in that: It also includes a PLC controller (18) and a dew point moisture probe (19). The valve (12) is a solenoid valve. The dew point moisture probe (19) is installed on the pipeline of the dry gas outlet (11). The PLC controller (18) is electrically connected to the dew point moisture probe (19), the nitrogen heater (17), and the valve (12).
4. The mixed freeze-drying method for a mixed freeze-drying system prior to vinyl chloride synthesis according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: After washing, cooling and demisting the acetylene with water, it is transported into the molecular sieve dryer through the acetylene transport pipeline (8) for drying. The dried acetylene is then transported into the mixer (6). Step 2: Hydrogen chloride flows sequentially through the hydrogen chloride primary cooler (1) and the hydrogen chloride secondary cooler (2) for staged cooling. The cooled hydrogen chloride is then transported into the mixer (6). The acid produced by the hydrogen chloride primary cooler (1) and the hydrogen chloride secondary cooler (2) is transported to the acid collection tank (5) for collection. Step 3: The dried acetylene and the cooled hydrogen chloride form a mixed gas in the mixer (6). The acid produced during the mixing process is transported to the acid collection tank (5) for collection. The mixed gas is then transported to the vinyl chloride conversion station.
5. The mixed freeze-drying method as described in claim 4, characterized in that: In step one, the acetylene is cooled to 2-3°C.
6. The mixed freeze-drying method as described in claim 4, characterized in that: In step two, hydrogen chloride is cooled to 15°C by a hydrogen chloride primary cooler (1) and then cooled to 5°C by a hydrogen chloride secondary cooler (2).