A highly efficient and controllable fixed-bed tubular reactor and its application in the preparation of vinyl acetate

Abstract

The present invention discloses an efficient and controllable fixed-bed tubular reactor, relating to the field of petrochemical technology, comprising a housing, wherein a plurality of longitudinally arranged reaction tubes are arranged in the housing, wherein the reaction tubes are filled with a catalyst bed; the catalyst bed is provided with at least one oxygen supply port at a height of 20-30%, 50-60%, and 80-85%, respectively; a dual-channel heat-carrying fluid guide device is provided on the periphery of the reaction tubes, wherein a first guide channel is located on the periphery of the reaction tubes, and one or more of circulating water, mixed alcohol, and salt solution are introduced for absorbing reaction heat, and a second guide channel is nested inside the first guide channel and is introduced with steam for local temperature increase. The present invention significantly improves the conversion rate of ethylene and acetic acid, product selectivity, and reaction stability by optimizing the catalyst bed structure, segmented oxygen supply technology, and intelligent temperature control system.

Description

Technical Field

[0001] The present invention relates to the technical field of petrochemical industry, and in particular to a highly efficient and controllable fixed-bed tubular reactor and application thereof in the preparation of vinyl acetate. Background Art

[0002] Vinyl acetate (also known as vinyl acetate or vinyl acetate) is an organic chemical raw material with a wide range of applications. Through self-polymerization or copolymerization with other monomers, it can produce products such as polyvinyl alcohol (PVA), vinyl acetate / ethylene copolymer (VAE), and vinyl chloride / vinyl acetate copolymer (PVCA). These products have a wide range of uses, including adhesives, paper and fabric sizing agents, paints, inks, leather processing, emulsifiers, water-soluble films, and soil conditioners. As vinyl acetate serves as an intermediate, the expansion of non-fiber applications for polyvinyl alcohol has led to increasing demand for vinyl acetate.

[0003] Currently, the production of vinyl acetate (VAc) by gas-phase oxidation of ethylene is the mainstream process in industrial production, with the core equipment being a fixed-bed tubular reactor. However, the existing technology has the following technical bottlenecks:

[0004] Reaction thermal management deficiencies: Ethylene oxidation is a highly exothermic reaction (ΔH≈-180 kJ / mol). Traditional reactors rely on a single heat-carrying fluid (such as circulating water) for temperature control. This can easily lead to local overheating (fluctuations >±5°C), which can cause catalyst sintering and deactivation, and increase the amount of byproduct CO2 produced (usually ≥2%).

[0005] Uneven oxygen distribution: The existing technology uses a single-point oxygen feed mode, which leads to excessively high oxygen concentration in the front section of the bed, triggering deep oxidation of ethylene and reducing selectivity to below 97%;

[0006] Although the specific surface area of ​​traditional activated carbon carrier is high (>800m 2 / g), but the compressive strength is low (≤20N / cm), and it is easy to pulverize during long-term operation, resulting in the loss of the active component zinc acetate, and the catalyst life is less than 12 months;

[0007] Low heat recovery rate: The utilization rate of reaction waste heat is less than 70%, failing to effectively achieve energy recycling.

[0008] To address these issues, existing improvements have proposed multi-stage bed designs, but these fail to address the coupling issue between oxygen gradient control and dynamic temperature regulation, resulting in limited success in industrial applications. Therefore, the present invention provides a highly efficient and controllable fixed-bed tubular reactor and its application in the production of vinyl acetate. By optimizing the reactor structure, modifying the catalyst support, implementing a staged oxygen addition strategy, and synergizing with an intelligent temperature control system, the present invention significantly improves reaction conversion, product selectivity, and comprehensive thermal energy utilization efficiency, making it suitable for large-scale industrial continuous production. Summary of the Invention

[0009] In order to solve the above problems, the present invention provides a highly efficient and controllable fixed-bed tubular reactor and its application in the preparation of vinyl acetate.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A highly efficient and controllable fixed-bed tubular reactor comprises a shell, wherein a plurality of longitudinally arranged reaction tubes are arranged in the shell, and a catalyst bed is filled in the reaction tubes;

[0012] The catalyst bed is provided with at least one oxygen supply port at 20-30%, 50-60% and 80-85% of the height, respectively. Each supply port is connected to an oxygen storage tank through an independent pipeline and equipped with a mass flow controller (MFC) to adjust the oxygen supply amount in real time.

[0013] A dual-channel heat-carrying fluid guide device is provided on the periphery of the reaction tubes, wherein the first guide channel is located on the periphery of the reaction tubes, and one or more of circulating water, mixed alcohol, and salt solution are introduced to absorb the reaction heat; the second guide channel is nested inside the first guide channel, and steam is introduced to increase the temperature locally.

[0014] Preferably, the catalyst used in the catalyst bed is a catalyst with carbon-coated alumina as a carrier and zinc acetate as an active component;

[0015] The carbon-coated alumina is a carbon layer uniformly coated on the surface of the alumina by chemical vapor deposition; the carbon content is 5-25% of the mass of the carrier, the thickness of the carbon layer is 10-200 nm, and the loading amount of zinc acetate is 8-12% of the mass of the carrier.

[0016] Preferably, the specific surface area of ​​the carbon-coated alumina is 280-350m 2 / g, crushing strength ≥50N / cm;

[0017] The zinc acetate is loaded by an impregnation method, the roasting temperature is 400-500° C., and the roasting time is 3-5 hours.

[0018] The present invention slightly cokes and carbonizes the surface of the catalyst, thereby enhancing the mechanical strength of the catalyst without losing many active sites and greatly reducing the probability of catalyst poisoning.

[0019] Preferably, the reaction tubes are arranged in a regular hexagonal honeycomb shape, and the tube spacing is 1.2-1.5 times the outer diameter of the reaction tubes.

[0020] Preferably, thermocouples are respectively provided in the upper, middle and lower sections of the reaction tubes to monitor temperature fluctuations and feed back to a central controller, which dynamically adjusts the electronic regulating valve through a fuzzy PID algorithm to adjust the temperature of the dual-channel heat-carrying fluid guide device so that the reaction temperature fluctuation range is ≤±1°C.

[0021] Preferably, the circulating water is selected, wherein the first diversion channel is fed with 25-35℃ circulating water with a flow rate of 10-18m 3 / h, absorbing the heat released by the main reaction zone; the second guide channel introduces 0.5MPa saturated steam with a flow rate of 1.2-2.5t / h to compensate for the temperature at the end of the bed.

[0022] The use of the fixed-bed tubular reactor in the preparation of vinyl acetate as described above is characterized in that the preparation of vinyl acetate adopts an ethylene gas phase method.

[0023] Preferably, the ethylene gas phase process comprises the following steps:

[0024] Ethylene, acetic acid vapor and initial oxygen are mixed evenly, preheated to 150-165° C. and then introduced into the above-mentioned fixed-bed tubular reactor to react and generate vinyl acetate.

[0025] Preferably, the molar ratio of the ethylene, the acetic acid vapor and the initial oxygen is 3:1:0.1-0.3.

[0026] Preferably, the reaction conditions are: pressure of 0.8-1.2 MPa, temperature of 160-180°C, an introduction rate of 800-1200 h-1, an oxygen concentration gradient in the reaction zone of 0.5-1.5% / m, and oxygen supply ports at heights of 20-30%, 50-60% and 80-85% with an oxygen supply volume ratio of 1:2:3, and the total oxygen supply amount accounts for 10-40% of the initial oxygen intake.

[0027] Preferably, the vinyl acetate further comprises two-stage condensation, an acetic acid absorption tower and a distillation tower separation treatment to obtain vinyl acetate with a purity of ≥99.9%, and the unreacted ethylene is pressurized by a compressor and recycled, with a circulation rate of ≥95%.

[0028] Preferably, the acetic acid absorption tower adopts two-stage countercurrent absorption, the first-stage absorption liquid is a mixture of acetic acid and water (volume ratio 7:3), the second-stage is pure acetic acid, and the absorption temperature is controlled at 40-60°C.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The highly efficient and controllable fixed-bed tubular reactor of the present invention improves the reaction efficiency, and the space-time yield is increased from 2.5t / m 3 d increased to 3.2t / m 3 d, vinyl acetate selectivity ≥99.3%;

[0031] (2) The catalyst preparation method of the present invention prolongs the catalyst life, the composite carrier crushing strength is ≥55N / cm, and the activity retention rate is ≥90% after 18 months of operation;

[0032] (3) After adopting the technical solution of the present invention, energy consumption is reduced, 0.5MPa steam is produced as a by-product (output 0.8t / h), and the overall energy consumption is reduced by 22%; and the environmental protection benefits are significant, CO2 emissions are ≤0.6%, and the unreacted ethylene recovery rate is ≥95%. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. The drawings in this description are merely embodiments of the present invention.

[0034] Figure 1 This is a structural diagram of a highly efficient and controllable fixed-bed tubular reactor according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The following describes embodiments of the present invention, examples of which are shown in the accompanying drawings. The embodiments described with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but are not to be construed as limiting the present invention.

[0036] Example 1

[0037] like Figure 1 The present invention provides a highly efficient and controllable fixed-bed tubular reactor, comprising a shell 5, wherein a plurality of groups of vertically arranged reaction tubes 2 are arranged in the shell 5, and a catalyst bed 1 is filled in the reaction tubes 2;

[0038] Shell 5 is made of Inconel 625 nickel-based alloy with a wall thickness of 30 mm, a design pressure of 2.0 MPa, and a temperature resistance range of -50-3400°C;

[0039] The reaction tubes 2 are arranged in a regular hexagon, with a tube diameter of Φ32mm and a tube spacing of 42mm (1.3 times the tube diameter). The total number of tubes is 1,200, and the effective heat transfer area is increased by 18%;

[0040] An oxygen supply port 4 is provided at the height of 20-30%, 50-60% and 80-85% of the catalyst bed 1. Each supply port is connected to an oxygen storage tank through an independent pipeline and is equipped with a mass flow controller (MFC) to adjust the oxygen supply amount in real time;

[0041] A dual-channel heat transfer fluid guide device is provided around the reaction tubes 2. The first guide channel 3a is located outside the reaction tubes 2 and is fed with circulating water to absorb the reaction heat. The second guide channel 3b is nested inside the first guide channel 3a and is fed with steam for local heating.

[0042] The catalyst used in the catalyst bed 1 is a carbon-coated alumina catalyst as a carrier and zinc acetate as an active component; the preparation process is as follows:

[0043] Carrier modification: γ-Al2O3 spherical carrier (diameter 4mm, specific surface area 280m 2 / g) was placed in a fluidized bed reactor, and a C2H2 / N2 mixed gas (volume ratio 1:4) was introduced, and chemical vapor deposition (CVD) was performed at 650℃ for 30min to form a uniform carbon layer with a thickness of 50-80nm and a carbon content of 15%;

[0044] Active component loading: The modified support was immersed in a zinc acetate-ethanol solution (concentration 20%), ultrasonically assisted for 40 min, vacuum dried at 120 ° C for 6 h, and calcined in a muffle furnace at 480 ° C for 4 h. The final zinc acetate loading was 10.2%, and the specific surface area of ​​the carbon-coated alumina was 320 m 2 / g, crushing strength ≥50N / cm;

[0045] Thermocouples 6 are installed in the upper, middle, and lower sections of the reaction tubes 2 to monitor temperature fluctuations and provide feedback to the central controller. The central controller dynamically adjusts the electronic control valve 7 through a fuzzy PID algorithm to adjust the temperature of the dual-channel heat transfer fluid guide device to control the reaction temperature fluctuation range ≤±1°C. The reaction temperature is dynamically controlled by the heat transfer fluid. When the local temperature of the bed exceeds the set value by 1°C, the circulating water flow rate is increased and the steam input is reduced. Otherwise, the circulating water is reduced and the steam ratio is increased.

[0046] The first diversion channel 3b is fed with circulating water at 25-35°C and a flow rate of 10-18m 3 / h, absorbing the heat released by the main reaction zone; the second guide channel 3a is introduced into 0.5MPa saturated steam with a flow rate of 1.2-2.5t / h to compensate for the end temperature of the bed;

[0047] Specific application examples are as follows:

[0048] Raw material pretreatment: High-purity ethylene (≥99.97%), acetic acid vapor (≥99.8%) and initial oxygen (≥99.6%) are mixed in a molar ratio of 3:1:0.26, and heated to 165±2°C in a tubular preheater to obtain a mixed gas;

[0049] Main reaction unit: The mixed gas is heated at a space velocity of 1000 h -1 It is introduced into the reactor and passed through the catalyst bed at a pressure of 1.0 MPa and a temperature of 170±1°C with a residence time of 2.3 seconds to obtain vinyl acetate;

[0050] Dynamic oxygen addition: initial oxygen amount 0.26 mol, 0.031 mol, 0.047 mol, and 0.063 mol were added at 25%, 55%, and 85% of the bed through MFC (Alicat Scientific MC-5SLPM), with an oxygen concentration gradient of 0.9% / m (online laser oxygen analyzer, Siemens LDS6);

[0051] The obtained vinyl acetate is subjected to two-stage condensation, separation in an acetic acid absorption tower and a distillation tower to obtain purified vinyl acetate, and the unreacted ethylene is pressurized by a compressor and then recycled;

[0052] Samples were taken every hour and the composition was analyzed using an Agilent 7890B gas chromatograph (HP-INNOWAX column, FID detector). The conversion and selectivity were calculated according to ASTM D5135.

[0053] Single experiment results: ethylene conversion 86.9%, vinyl acetate selectivity 99.5%, CO2 generation 0.52%;

[0054] Repeatability test: Continuous operation for 72 hours, taking the average value every 8 hours, data fluctuation range: conversion rate 86.7-87.1%, selectivity 99.4-99.6%, CO2 0.50-0.54% (RSD≤0.8%).

[0055] Example 2

[0056] Reaction conditions: pressure 3.0 MPa, temperature 160-180°C, space velocity 1000 h -1 ;

[0057] Catalyst parameters: carbon content 16.2%, zinc acetate loading 11.0%, specific surface area 335m 2 / g;

[0058] Oxygen addition: initial oxygen amount 0.2 mol, 0.031 mol, 0.047 mol, 0.063 mol at 25%, 55%, 85% of the bed, oxygen concentration gradient 0.9% / m;

[0059] The remaining parameters are the same as those in the embodiment. The relevant product results are shown in Table 1. As can be seen from the table, at 170°C, the selectivity of vinyl acetate is high, and at 180°C, the ethylene conversion rate is the highest, but the selectivity decreases. Taking all factors into consideration, 170°C is selected as the reaction temperature;

[0060] Table 1 Product results at different temperatures

[0061]

[0062] Example 3

[0063] Reaction conditions: pressure 1.1 MPa, temperature 170°C, space velocity 1000 h -1 ;

[0064] Oxygen variable setting: adjust the initial oxygen molar ratio to 0.1, 0.2, 0.3 (total oxygen content including supplementary amount)

[0065] Supplement ratio (bed 25%:55%:85%): distributed according to 30% of the total oxygen content, that is, adding 0.03, 0.06, and 0.09 mol;

[0066] Ethylene: acetic acid: oxygen = 3:1: (0.1-0.3), preheat to 165°C, and the remaining steps are the same as in Example 1;

[0067] Based on the online oxygen analysis data, the addition amount was precisely controlled by MFC. The relevant conclusions are shown in Table 2. It can be seen from the table that the total oxygen content will promote ethylene conversion, but too high a total oxygen content will lead to excessive oxidation of vinyl acetate. Therefore, an initial oxygen content of 0.2 mol was selected as the optimal condition.

[0068] Table 2 Product results of different oxygen contents

[0069]

[0070] The traditional process uses single-point oxygen feeding, which easily causes excessive oxygen concentration at the front end, leading to excessive oxidation. The present invention uses segmented oxygen feeding technology combined with a mass flow controller to optimize the oxygen concentration gradient, improve selectivity and conversion rate, and reduce CO2 generation.

[0071] In addition, the traditional process does not recover enough waste heat. The process of the present invention recovers heat through a dual-channel heat carrier system and an external heat exchanger, and produces steam as a by-product, which can reduce energy consumption and improve energy utilization.

[0072] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A highly efficient and controllable fixed bed tubular reactor, characterized in that: It comprises a shell, wherein a plurality of longitudinally arranged reaction tubes are arranged in the shell, and the reaction tubes are filled with a catalyst bed; The catalyst bed is provided with at least one oxygen supply port at 20-30%, 50-60% and 80-85% of the height respectively; A dual-channel heat-carrying fluid guide device is provided on the periphery of the reaction tubes, wherein the first guide channel is located on the periphery of the reaction tubes and is passed through one or more of circulating water, mixed alcohol, and salt solution to absorb reaction heat; the second guide channel is nested inside the first guide channel and is passed through steam for local temperature increase; The catalyst used in the catalyst bed is a carbon-coated alumina as a carrier and zinc acetate as an active component; wherein the carbon-coated alumina is a carbon layer uniformly coated on the surface of the alumina by chemical vapor deposition, the carbon content is 5-25% of the mass of the carrier, the thickness of the carbon layer is 10-200nm, and the loading amount of the zinc acetate is 8-12% of the mass of the carrier.

2. The highly efficient and controllable fixed-bed tubular reactor according to claim 1, characterized in that: The specific surface area of ​​the carbon-coated alumina is 280-350m 2 / g, crushing strength ≥50N / cm; The zinc acetate is loaded by an impregnation method, the roasting temperature is 400-500° C., and the roasting time is 3-5 hours.

3. The highly efficient and controllable fixed-bed tubular reactor according to claim 1, characterized in that: The reaction tubes are arranged in a regular hexagonal honeycomb shape, and the tube spacing is 1.2-1.5 times the outer diameter of the reaction tubes.

4. The highly efficient and controllable fixed-bed tubular reactor according to claim 1, characterized in that: Thermocouples are respectively provided at the upper, middle and lower sections of the reaction tubes to monitor temperature fluctuations and feed back to a central controller, which controls the temperature of the dual-channel heat-carrying fluid guide device by adjusting an electronic regulating valve.

5. Use of the fixed-bed tubular reactor according to any one of claims 1 to 4 in the preparation of vinyl acetate, characterized in that: The preparation of vinyl acetate adopts an ethylene gas phase method.

6. The use according to claim 5, characterized in that The process of the ethylene gas phase method comprises the following steps: Ethylene, acetic acid vapor and initial oxygen are mixed evenly, preheated to 150-165° C., and then introduced into the fixed-bed tubular reactor according to any one of claims 1 to 4 to react and generate vinyl acetate.

7. The use according to claim 6, characterized in that The molar ratio of the ethylene, the acetic acid vapor and the initial oxygen is 3:1:0.1-0.

3.

8. The use according to claim 6, characterized in that The reaction conditions are: pressure of 0.8-1.2 MPa, temperature of 160-180°C, and a flow rate of 800-1200 h -1 The oxygen concentration gradient in the reaction zone is 0.5-1.5% / m, and the oxygen supply volume ratio of the oxygen supply ports set at heights of 20-30%, 50-60% and 80-85% is 1:2:3, and the total oxygen supply amount accounts for 10-40% of the initial oxygen intake.

9. The use according to claim 6, characterized in that The vinyl acetate further comprises two-stage condensation, an acetic acid absorption tower and a distillation tower for separation treatment.

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