Multi-stage control method for co-producing trichloroethylene and tetrachloroethylene by cracking tetrachloroethane

Abstract

The invention discloses a multi-stage control method for co-producing trichloroethylene and tetrachloroethylene by cracking tetrachloroethane. The multi-stage control method comprises the following steps: S1, preheating a tetrachloroethane raw material to 250-300 DEG C; s2, mixing the preheated tetrachloroethane and chlorine according to a molar ratio of (15-11): 1; s3, the mixed materials are introduced into a first tubular reactor, a first-stage cracking reaction is carried out under the radiation heating and convection heating composite heat supply condition, the reaction pressure is controlled to range from 0 KPa to 100 KPa, the reaction temperature is controlled to range from 380 DEG C to 450 DEG C, and an intermediate product containing trichloroethylene and tetrachloroethylene is generated. The contradiction that the conversion rate and the selectivity in a single-section reactor are difficult to collaboratively optimize is effectively overcome, and the total yield of a target product is greatly improved; by introducing a real-time online monitoring and feedback linkage regulation and control mechanism, accurate and flexible control of the generation proportion of tetrachloroethylene is realized, and the response capability of the process to the market demand is enhanced.

Description

Technical Field

[0001] This invention relates to the field of tetrachloroethylene production processes, specifically a multi-stage control method for the co-production of trichloroethylene and tetrachloroethylene by tetrachloroethane cracking. Background Technology

[0002] Tetrachloroethylene (PCE) and trichloroethylene (TCE) are important organochlorine solvents and chemical intermediates, widely used in metal cleaning, extraction, degreasing, and fluorocarbon production. Industrially, tetrachloroethane is often produced through co-production via cracking, a method typically achieved through high-temperature gas-phase cracking.

[0003] In existing technologies, the processes for producing TCE and PCE from tetrachloroethane via cracking mostly employ single-stage tubular reactors or fixed-bed reactors, adjusting product distribution by controlling reaction temperature and chlorine ratio. However, these methods have significant limitations: First, single-stage reactors struggle to simultaneously achieve high conversion rates and high selectivity, as over-chlorination or deep cracking easily occurs during the reaction, leading to increased byproducts and reduced yield of the target product. Regarding catalysts, existing technologies often use single catalyst systems, making it difficult to achieve synergistic effects between cracking and chlorination reactions, particularly in the selective formation of PCE. Furthermore, the reactor structure is relatively simple, resulting in low heat transfer efficiency and a tendency for localized overheating or uneven temperature distribution, affecting catalyst lifetime and reaction stability.

[0004] Secondly, conventional processes have relatively crude control over reaction conditions, lack real-time monitoring and feedback adjustment mechanisms for the reaction process, and have poor precision in product ratio control, making it difficult to flexibly respond to changes in market demand for TCE and PCE. In addition, traditional processes have high energy consumption, and the reaction heat cannot be effectively recovered and utilized, further increasing operating costs. Summary of the Invention

[0005] This application provides a multi-stage control method for the co-production of trichloroethylene and tetrachloroethylene from tetrachloroethane cracking, which addresses the technical problems in the prior art, such as the difficulty in achieving both tetrachloroethane conversion and target product selectivity, inaccurate product ratio control, ineffective integration and utilization of reaction heat energy, and catalyst deactivation and poor reaction stability caused by local overheating or uneven temperature distribution.

[0006] In view of the above problems, this application provides a multi-stage control method for the co-production of trichloroethylene and tetrachloroethylene by cracking tetrachloroethane, comprising the following steps: S1. Preheat the tetrachloroethane feedstock to 250-300℃; S2. Mix the preheated tetrachloroethane with chlorine gas at a molar ratio of 15-11:1; S3. The mixed material is fed into the first tubular reactor and the first stage of pyrolysis reaction is carried out under the combined heating conditions of radiation heating and convection heating. The reaction pressure is controlled at 0-100KPa and the reaction temperature is controlled at 380-450℃ to generate intermediate products containing trichloroethylene and tetrachloroethylene. S4. The conversion rate of tetrachloroethane in the intermediate product is monitored in real time by an online analyzer installed at the outlet of the first tubular reactor. S5. The intermediate product obtained in step S3 is subjected to rapid cooling to reduce its temperature to 100-150℃. S6. The intermediate product after rapid cooling is introduced into the second fixed-bed reactor, which is filled with a high-nickel structured packing catalyst throughout the straight section. S7. Supplementary chlorine gas is introduced into the second fixed-bed reactor, and the feed rate is adjusted within the range of 30-600 kg; S8. The reaction temperatures of the upper and lower sections of the second fixed-bed reactor are independently controlled by a segmented temperature control system. The upper section temperature is controlled at 280-320℃, and the lower section temperature is controlled at 220-260℃ to carry out the second stage reaction. S9. The ratio of trichloroethylene to tetrachloroethylene in the reaction product is monitored in real time by using an online product sampling and chromatographic analysis system located at the outlet of the second fixed-bed reactor. S10. Based on the tetrachloroethane conversion rate monitored in step S4 and the product ratio monitored in step S9, the feed amount of chlorine supplementation in step S7 and the reaction temperature settings of the upper and lower sections in step S8 are adjusted in a coordinated manner to achieve precise control of the selective production ratio of tetrachloroethylene.

[0007] Furthermore, in step S3, the first tubular reactor adopts a multi-pass structure with a total feed pipe diameter of DN500 and 120 high-temperature resistant stainless steel branch pipes with a diameter of DN25 and a length of 10 meters. The outer wall of the branch pipes is coated with a silicon carbide high-radiation material coating. The composite heating is a combination of natural gas radiation heating and reaction effluent convection heating.

[0008] Furthermore, the convective heating of the reaction effluent is achieved by an intermediate heat exchanger located downstream of the first tubular reactor, using the thermal energy of the high-temperature intermediate product before the rapid cooling treatment in step S5 to preheat the mixture in step S2.

[0009] Furthermore, the segmented temperature control system described in step S8 is achieved by independent external circulating heat medium coils respectively set in the upper and lower sections of the second fixed bed reactor. The upper section uses heat transfer oil circulation to control the temperature, and the lower section uses warm water circulation to control the temperature.

[0010] Furthermore, the linkage adjustment in step S10 is achieved through a DCS system. The DCS system automatically and dynamically optimizes and outputs control commands to the chlorine feed regulating valve and the temperature control actuator based on the received online data and a preset target product distribution model.

[0011] The coordinated adjustment is achieved through a distributed control system (DCS). First, the real-time collected conversion rate and product ratio are compared with preset target values. Then, the internal model is invoked to perform calculations and dynamically generate optimized control commands. Finally, the commands are output to the regulating valve on the chlorine feed pipeline and the temperature control actuator (such as the three-way valve of the heat transfer oil system) of the segmented temperature control system, automatically adjusting the chlorine feed rate within the range of 30-600 kg and independently fine-tuning the set values ​​of the upper and lower reaction temperatures (adjustment accuracy ±1°C), thus forming a real-time feedback, closed-loop control intelligent loop to ensure the stability and accuracy of the PCE production ratio.

[0012] Furthermore, the rapid cooling process in step S5 adopts a two-stage rapid cooling method. The first stage cools the gaseous intermediate product to below the dew point, realizing the condensation and liquefaction of most of the condensable components. The second stage uses tetrachloroethane raw material for direct spray rapid cooling, specifically to absorb and remove residual chlorine.

[0013] One or more technical solutions provided in this application have at least the following technical effects or advantages: This application effectively overcomes the contradiction of difficulty in synergistically optimizing conversion rate and selectivity in single-stage reactors by adopting a process that combines multi-stage reaction with intelligent control, significantly improving the overall yield of the target product. By introducing a real-time online monitoring and feedback linkage control mechanism, precise and flexible control of the tetrachloroethylene production ratio is achieved, enhancing the process's responsiveness to market demands. Through composite heating and energy cascade integrated utilization, system energy consumption is significantly reduced. At the same time, the design of segmented temperature control in the reactor and the combined loading of dedicated catalysts effectively improves the temperature distribution within the reactor, suppresses local overheating, extends catalyst lifespan, and improves the stability and overall economy of the reaction process.

[0014] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application, and to make the above and other objects, features and advantages of this application more obvious and understandable, specific embodiments of this application are given below. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0016] Figure 1 A flowchart illustrating the steps of a multi-stage control method for the co-production of trichloroethylene and tetrachloroethylene from tetrachloroethane cracking, as provided in this application. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] This invention provides a multi-stage control method for the co-production of trichloroethylene and tetrachloroethylene from tetrachloroethane via cracking. Its core lies in a process design that combines multi-stage reaction, intelligent control, and energy integration to achieve precise control of the reaction process and efficient energy utilization. The invention is described in detail below through specific embodiments.

[0019] Example 1 Please see Figure 1 This embodiment provides a multi-stage control method for the co-production of trichloroethylene and tetrachloroethylene from tetrachloroethane cracking, specifically including the following steps: First, tetrachloroethane is pumped to a preheater and preheated to 280 degrees Celsius. The preheated tetrachloroethane is then thoroughly mixed with chlorine gas in a static mixer at a molar ratio of 11.5:1. The temperature of the mixed material is approximately 280 degrees Celsius.

[0020] The mixture is fed into the first tubular reactor. This reactor has a multi-pass structure with a total feed pipe diameter of DN500 and branch pipes of 120 high-temperature resistant stainless steel. The branch pipes are made of 310S stainless steel, with a diameter of DN25 and a length of 10 meters. The outer wall of the branch pipes is coated with a silicon carbide high-emissivity material coating with a thickness of 0.2 mm to enhance the radiative heat absorption efficiency.

[0021] The reactor employs a combined heating system. Firstly, a natural gas burner radiates heat the furnace, and the reaction temperature in each branch pipe is controlled at 420 degrees Celsius by adjusting the natural gas intake and the opening of the outlet baffle. Secondly, an intermediate heat exchanger located downstream of the first tubular reactor preheats the mixture using the high-temperature intermediate products before rapid cooling, achieving heat recovery. The reaction pressure is controlled at 20 kPa via a back pressure valve.

[0022] Under these conditions, tetrachloroethane undergoes a cracking reaction, mainly producing trichloroethylene and a small amount of tetrachloroethylene. The conversion rate of tetrachloroethane in the intermediate product is monitored in real time by an online infrared analyzer installed at the reactor outlet. In this example, the conversion rate is stable at 90%.

[0023] The intermediate product, with an outlet temperature of approximately 400 degrees Celsius, is fed into a quenching system. The quenching process employs a two-stage method. The first stage uses an indirect quencher that exchanges heat with the mixture to reduce the material temperature to 120 degrees Celsius. The second stage uses tetrachloroethane as a raw material for direct spray quenching, ultimately yielding pure hydrogen chloride gas and a liquid intermediate product.

[0024] The intermediate product after rapid cooling is introduced into a second fixed-bed reactor. This reactor is a vertical device, packed with a high-nickel structured packing catalyst with a nickel content of 12% by weight, a specific surface area of ​​180 square meters per gram, and a bed height of 2.5 meters. The high nickel content of the active component ensures that the catalyst has high activity and good catalytic efficiency, which can effectively promote the deep cracking and chlorination reaction of tetrachloroethane.

[0025] Supplementary chlorine gas is introduced into the reactor at a feed rate of 200 kg. The temperatures of the upper and lower sections are independently controlled by a segmented temperature control system. The upper section uses a heat transfer oil circulation system with a controlled temperature of 300 degrees Celsius, while the lower section uses a warm water circulation system with a controlled temperature of 240 degrees Celsius.

[0026] The ratio of trichloroethylene to tetrachloroethylene in the product was monitored in real time by an online gas chromatography system located at the outlet of the second fixed-bed reactor. In this embodiment, the ratio was monitored to be approximately 1:1.2.

[0027] All online data, including conversion rate, product ratio, temperature, pressure, and flow rate, are transmitted to the distributed control system. This system has a built-in preset target product distribution model and automatically and dynamically optimizes control commands based on real-time data to achieve stable control of the selective production ratio of tetrachloroethylene, with fluctuations within ±2%.

[0028] Example 2 The difference between this embodiment and Embodiment 1 lies in the adjustment of process parameters, as detailed below: The tetrachloroethane feedstock is preheated to 260°C. The molar ratio of tetrachloroethane to chlorine is 13.5:1. The first-stage reaction temperature is controlled at 400°C, and the reactor operating pressure is maintained at 5.0 kPa to ensure that the reactants remain in a liquid phase at the operating temperature. The final quenching temperature is controlled at 100°C. In the second-stage reactor, the temperature is controlled at 280°C.

[0029] Under these conditions, the conversion rate of tetrachloroethane reaches 85%, the selectivity of trichloroethylene is 53%, the selectivity of tetrachloroethylene is 36%, the total yield is 92%, and the energy consumption is reduced by 23%.

[0030] Example 3 This embodiment provides another implementation method, as follows: The tetrachloroethane feedstock is preheated to 300°C. The molar ratio of tetrachloroethane to chlorine is 14:1. The first-stage reaction temperature is controlled at 440°C, and the reaction pressure is -3 kPa. The final quench temperature is controlled at 150°C. In the second-stage reactor, the upper section temperature is controlled at 320°C, and the lower section temperature is controlled at 260°C. The chlorine feed rate is 600 kg.

[0031] Under these conditions, the conversion rate of tetrachloroethane reaches 93%, the selectivity of trichloroethylene is 38%, the selectivity of tetrachloroethylene is 50%, the total yield is 95%, and the energy consumption is reduced by 31%.

[0032] Comparative Example A traditional single-stage tubular reactor process was used, with a reaction temperature of 400 degrees Celsius and a chlorine to tetrachloroethane molar ratio of 15:1. The results showed a tetrachloroethane conversion rate of 75%, a trichloroethylene selectivity of 50%, a tetrachloroethylene selectivity of 35%, and an overall yield of 85%, with no reduction in energy consumption.

[0033] Table 1: Comparison of key parameters and effects between each embodiment and the comparative example

[0034] By comparing the data from the three embodiments with those from the comparative example, it can be seen that the multi-stage control method provided by the present invention has significant advantages over the traditional single-stage process: the tetrachloroethane conversion rates in Examples 1 to 3 reached 90%, 85%, and 93%, respectively, which are significantly higher than the 75% of the comparative example; the total yield of the target product remained stable at 92%-95%, which is 7-10 percentage points higher than that of the comparative example; more importantly, by adjusting the process parameters, the selectivity distribution of TCE and PCE (TCE: 38%-43%, PCE: 36%-50%) can be flexibly adjusted to achieve precise control of the product ratio. At the same time, each embodiment achieved an energy consumption reduction of more than 20%, proving that the method has outstanding effects in improving reaction efficiency, product controllability, and energy saving.

[0035] The core mechanism of this invention lies in the organic combination of segmented reaction and intelligent control to construct a highly efficient and synergistic process system. First, a high-temperature cracking reaction in the first stage achieves the efficient conversion of tetrachloroethane, followed by rapid cooling to precisely control the reaction process. Then, in the second stage reaction, the synergistic effect of the upper and lower catalysts—the upper catalyst promoting directional molecular transformation and the lower catalyst deeply regulating the reaction pathway—combined with segmented temperature control technology, creates optimal temperature environments for different reaction stages. Finally, by real-time monitoring of product composition and intelligent feedback adjustment of raw material ratios and reaction temperature, a closed-loop control is formed. This multi-stage synergistic and precisely controlled mechanism ensures reaction efficiency, achieves flexible and adjustable product composition, and significantly reduces energy consumption.

[0036] Although embodiments of the present invention have been shown and described, these specific embodiments are merely explanations of the invention and are not intended to limit it. The specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. After reading this specification, those skilled in the art may make modifications, substitutions, and variations to the embodiments as needed without departing from the principles and spirit of the invention, but such modifications, substitutions, and variations are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A multi-stage control method for the co-production of trichloroethylene and tetrachloroethylene by cracking tetrachloroethane, characterized in that, Includes the following steps: S1. Preheat the tetrachloroethane feedstock to 250-300℃; S2. Mix the preheated tetrachloroethane with chlorine gas at a molar ratio of 15-11:1; S3. The mixed material is fed into the first tubular reactor and the first stage of pyrolysis reaction is carried out under the combined heating conditions of radiation heating and convection heating. The reaction pressure is controlled at 0-100KPa and the reaction temperature is controlled at 380-450℃ to generate intermediate products containing trichloroethylene and tetrachloroethylene. S4. The conversion rate of tetrachloroethane in the intermediate product is monitored in real time by an online analyzer installed at the outlet of the first tubular reactor. S5. The intermediate product obtained in step S3 is subjected to rapid cooling to reduce its temperature to 100-150℃. S6. The intermediate product after rapid cooling is introduced into the second fixed-bed reactor, which is filled with a high-nickel structured packing catalyst throughout the straight section. S7. Supplementary chlorine gas is introduced into the second fixed-bed reactor, and the feed rate is adjusted within the range of 30-600 kg; S8. The reaction temperatures of the upper and lower sections of the second fixed-bed reactor are independently controlled by a segmented temperature control system. The upper section temperature is controlled at 280-320℃, and the lower section temperature is controlled at 220-260℃ to carry out the second stage reaction. S9. The ratio of trichloroethylene to tetrachloroethylene in the reaction product is monitored in real time by using an online product sampling and chromatographic analysis system located at the outlet of the second fixed-bed reactor. S10. Based on the tetrachloroethane conversion rate monitored in step S4 and the product ratio monitored in step S9, the feed amount of chlorine supplementation in step S7 and the reaction temperature settings of the upper and lower sections in step S8 are adjusted in a coordinated manner to achieve precise control of the selective production ratio of tetrachloroethylene.

2. The multi-stage control method for the co-production of trichloroethylene and tetrachloroethylene by tetrachloroethane cracking according to claim 1, characterized in that, In step S3, the first tubular reactor adopts a multi-pass structure with a total feed pipe diameter of DN500 and 120 high-temperature resistant stainless steel branch pipes with a diameter of DN25 and a length of 10 meters. The outer wall of the branch pipes is coated with a silicon carbide high-radiation material coating. The composite heating is a combination of natural gas radiation heating and reaction effluent convection heating.

3. The multi-stage control method for the co-production of trichloroethylene and tetrachloroethylene by tetrachloroethane cracking according to claim 2, characterized in that, The convective heating of the reaction effluent is achieved by an intermediate heat exchanger located downstream of the first tubular reactor, which uses the thermal energy of the high-temperature intermediate product before the rapid cooling treatment in step S5 to preheat the mixture in step S2.

4. The multi-stage control method for the co-production of trichloroethylene and tetrachloroethylene by tetrachloroethane cracking according to claim 1, characterized in that, The high-nickel structured packing catalyst mentioned in step S6 is a catalyst made by using a metal as a support and a special process to load a high-nickel active component onto a structured packing monolithic channel.

5. The multi-stage control method for the co-production of trichloroethylene and tetrachloroethylene by tetrachloroethane cracking according to claim 1, characterized in that, The segmented temperature control system described in step S8 is achieved by independent external circulating heat transfer medium coils respectively set in the upper and lower sections of the second fixed bed reactor. The upper section uses heat transfer oil circulation to control the temperature, and the lower section uses warm water circulation to control the temperature.

6. The multi-stage control method for the co-production of trichloroethylene and tetrachloroethylene by tetrachloroethane cracking according to claim 1, characterized in that, The linkage adjustment in step S10 is achieved through a DCS system. The DCS system automatically and dynamically optimizes and outputs control commands to the chlorine feed regulating valve and the temperature control actuator based on the received online data and the preset target product distribution model.

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