A method for uniform diffusion of a heterogeneous material in a reactor during the hydrogenation of dimethyl terephthalate

Abstract

The present application relates to a method for uniform diffusion of multiphase materials in a reactor during dimethyl terephthalate hydrogenation process. In the present application, DMT solution and hydrogen are respectively exchanged with DMCD, mixed after heat exchange, heated to the required reaction temperature through a preheater, and then enter the reactor from the top under certain pressure conditions. The mixed multiphase materials pass through the step-by-step distributor to the catalyst bed in the trickle bed hydrogenation reactor, uniformly react with the catalyst, and then are purified by rectification after the reaction is completed, and continue to enter the second hydrogenation reaction to generate CHDM. The method of the present application can make the high condensation point raw material mixed with hydrogen to contact with the catalyst in a continuous, stable and uniform dispersion state, avoid excessive reaction, intense heat release, increase of by-products, runaway of temperature, and influence on the yield of intermediate products. The method of the present application makes the heat release of the catalyst bed uniform during the reaction process, and the hydrogenation effect is excellent.

Description

Technical Field

[0001] This invention relates to the field of dimethyl terephthalate (DMT) hydrogenation technology, specifically to a method for uniform diffusion of multiphase materials within a reactor during the dimethyl terephthalate hydrogenation process. Background Technology

[0002] 1,4-Cyclohexanediethanol (CHDM) is mainly produced industrially using dimethyl terephthalate (DMT) and hydrogen as raw materials.

[0003] The route map is shown below:

[0004]

[0005] The advantage of this process route lies in its efficient conversion of dimethyl terephthalate (DMT) to CHDM, while the resulting byproducts are relatively easy to handle. Industrially, this two-step hydrogenation process is typically carried out under high temperature and high pressure conditions. During the reaction, careful attention must be paid to factors such as the purity of the raw materials, the control of reaction temperature and pressure, and the amount and type of catalyst. Furthermore, the generated byproducts need to be properly treated or recovered to reduce environmental impact and improve economic efficiency. Therefore, the hydrogenation of DMT to DMC requires precise control of the uniform distribution of multiphase materials in the reactor and the efficient selection of the catalyst to ensure high-purity products, thereby improving production efficiency and significantly reducing byproduct formation.

[0006] Existing technology CN208275377U discloses an overflow gas-liquid distributor and its hydrogenation reactor. The overflow gas-liquid distributor includes a central tube, an outer cylinder, a splash cone, and a connecting rod. The central tube is located at the center of the outer cylinder and serves as the central tube for the gas phase channel. A necked nozzle is installed at the lower part of the central tube to increase the gas velocity and facilitate the dispersion of liquid droplets. The top of the outer cylinder is provided with a first toothed groove to effectively avoid flow deviation caused by tray leveling issues and improve the uniformity of material distribution. The bottom of the outer cylinder is provided with a conical tube to generate a splash flow pattern, which disperses the liquid phase and provides a larger dispersion area. However, this device cannot solve the problem of uniform diffusion of multiphase materials during the DMT hydrogenation reaction, cannot achieve uniform material distribution, and cannot stably control the catalyst bed temperature to avoid temperature runaway.

[0007] Existing technology CN113842840A discloses a tubular gas-liquid distributor, including a distribution plate, a central pipe, and an overflow weir. The lower end of the central pipe passes through a mounting hole on the distribution plate and is fixed to the distribution plate. The overflow weir is fixed by an overflow weir support and blocks the opening at the upper end of the central pipe. The space between the overflow weir support below the overflow weir serves as a gas phase inlet, and a slit parallel to the axis of the central pipe is provided on the wall of the central pipe above the distribution plate as a liquid phase inlet. The overflow weir is a long rectangular trough, which is fixedly connected to multiple central pipes and is shared by multiple central pipes. However, this distributor cannot solve the problem of efficient contact between the gas and liquid phases after mixing high-pour-point raw materials with hydrogen, thus failing to solve the problem of spray uniformity.

[0008] The challenge of the DMT single-stage hydrogenation process lies in its highly exothermic reaction and the susceptibility of the catalyst to temperature runaway. To ensure the reaction proceeds normally, the liquid reactants must be uniformly distributed in the hydrogen atmosphere and in contact with the solid catalyst. If the liquid reactants accumulate locally in the catalyst bed, it will cause violent exothermic reactions. This can lead to over-reaction, increased byproducts, and reduced yield of DMC intermediates; in severe cases, it can cause temperature runaway. Therefore, reactor design and achieving uniform material distribution are crucial for controlling exothermic reactions and reducing byproducts. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies, this invention provides a method for the uniform diffusion of multiphase materials within a reactor during the hydrogenation of dimethyl terephthalate (DMT). Through improvements to the apparatus and method, in the first stage of the DMT hydrogenation reaction, the high-pour-point feedstock, after being mixed with hydrogen, reacts with the catalyst in a continuous, stable, and uniformly dispersed state. This avoids problems such as violent exothermic reactions, over-reaction, increased byproducts, temperature runaway, and negative impacts on the yield of DMT intermediate products.

[0010] The present invention adopts the following technical solution: DMT solution and hydrogen are heat exchanged with DMCD at a temperature of 120-185℃. After heat exchange, they are mixed and heated to the required reaction temperature of 135-170℃ by a preheater. Under a pressure of 8-12MPa, the mixture enters the reactor from the top and reacts. The mixed multiphase material reaches the catalyst bed through a step-by-step distributor in the trickle bed hydrogenation reactor, reacts uniformly with the catalyst, and is then deheated. After the reaction is completed, the mixture is purified by distillation and then enters the second-stage hydrogenation reaction to generate CHDM.

[0011] The liquid feedstock of the DMT first-stage hydrogenation reaction product includes 15-30% DMT and 70-85% DMCD, more preferably 25-30% DMT and 70-75% DMCD.

[0012] The preferred reaction temperature is 135-140℃ and the pressure is 10-11MPa.

[0013] The molar ratio of hydrogen to DMT is (50-150):1.

[0014] The distributor is installed on the upper part of each catalyst bed section in the reactor. The height of the upper and lower spaces of the distributor has a certain impact on the gas-liquid distribution effect. In this invention, the distance between the distribution plate of the distributor and the lower catalyst bed is 300-310mm, and the distance between the gas-liquid distributor plate and the upper space is 250-260mm.

[0015] Furthermore, the reactor comprises at least two catalyst beds.

[0016] Furthermore, the number of distributors is related to the number of catalyst bed segments. That is, two layers of distributors are set for two beds, three layers of distributors are set for three beds, and the number of distributors in each layer is based on the corresponding installation of the distribution plate, and so on. As a preferred embodiment of the present invention, the number of beds with strong exothermic hydrogenation reaction in one stage of the present invention is greater than 3. The exothermic reaction of the upper bed is absorbed in time by injecting room temperature hydrogen gas between the beds, thereby controlling the temperature of the material entering the lower bed.

[0017] The distributor can be selected as a gas-liquid distributor with suction and overflow flow. Preferably, the gas-liquid distributor described in the applicant's published patent (202022011879.3) is used.

[0018] Single-stage hydrogenation reactions typically require the use of a catalyst and need to control reaction conditions to obtain the desired product yield and quality. In actual production, factors such as equipment investment, operating costs, and energy consumption must also be considered. In single-stage hydrogenation reactions, selecting a suitable catalyst is crucial for the smooth progress of the reaction. This invention selects copper-based catalysts, nickel-based catalysts, etc. Among them, copper-based catalysts have high activity and selectivity and are widely used in the single-stage hydrogenation reaction of DMT.

[0019] Besides the choice of catalyst, reaction conditions are also crucial factors affecting the hydrogenation reaction. Reaction temperature, pressure, and hydrogen flow rate all influence the yield and quality of the product. Therefore, in actual production, it is necessary to optimize and control the reaction conditions according to different conditions to obtain the best reaction results. In this invention, the reactor temperature is controlled at 135-170℃.

[0020] The trickle-bed hydrogenation reactor used in this invention is a gas-liquid-solid three-phase catalytic reactor, in which gas and liquid flow downwards through a solid catalyst bed.

[0021] In applying the trickle bed hydrogenation reactor, this invention first selects appropriate catalysts and reaction conditions based on the specific reaction system and process requirements. Secondly, for different reaction systems, a reasonable trickle bed structure is designed to ensure uniform fluid distribution and mixing. A jet-ring type inlet gas-liquid diffuser is installed at the feed inlet to enable the reactor to achieve efficient and stable operation.

[0022] The reaction feed device of this invention employs a jet-ring pipe type inlet gas-liquid diffuser, which features significant atomization and diffusion effects of the gas phase flow on the liquid phase flow, resulting in high spray uniformity. Its structure includes a cap body, an inverted cone, and a support plate. The support plate connects the cap body and the inverted cone as a first-stage annular nozzle. Below the inverted cone, an upper arc-shaped strip and a horizontal circular plate form a second-stage annular nozzle. Below the horizontal circular plate, an annular nozzle atomizing sprayer is located. The downcomer contains solid spiral blades and a third annular nozzle. The higher the degree of atomization of the gas phase flow on the liquid phase flow after passing through the diffuser, the greater the diffusion and the better the droplet buoyancy, which is beneficial for improving the spray uniformity in the top head space of the reactor. This structure can achieve efficient gas-liquid contact and uniform spraying. After being sprayed through a three-stage annular nozzle, the gas-phase flow achieves a diffusion rate (atomization rate) of over 85% in the liquid phase. The fine droplets facilitate the dissolution of new hydrogen into the liquid droplets and improve droplet buoyancy, ensuring thorough and uniform mixing of the gas and liquid to promote the chemical reaction. Its unique structural design allows for sufficient contact between the gas and liquid, thereby improving the efficiency of the chemical reaction and the quality of the products. Furthermore, the high uniformity of spraying reduces localized overheating during the reaction process, preventing catalyst deactivation and equipment damage.

[0023] Furthermore, the preheater controls the temperature by adjusting the flow rate of the heat transfer medium, i.e., it uses heat transfer oil for heating. Heat transfer oil heating is a method of transferring heat through heat transfer oil. It is commonly used in systems that require maintaining a constant temperature. Heat transfer oil is a liquid with excellent thermal conductivity, and high-temperature synthetic oils or silicone oils are typically used. This method allows for precise temperature control and has high heat transfer efficiency and stability.

[0024] Beneficial effects:

[0025] This invention provides a method for the uniform diffusion of multiphase materials within a reactor during the hydrogenation of dimethyl terephthalate (DMT). Through improvements to the apparatus and method, in the first stage of the DMT hydrogenation reaction, the high-pour-point feedstock is mixed with hydrogen and reacts with the catalyst in a continuous, stable, and uniformly dispersed state. This avoids problems such as over-reaction, violent exothermic reactions, increased byproducts, temperature runaway, and negative impacts on the yield of DMCD intermediates. Using the method of this invention, the catalyst bed exhibits uniform exothermic reaction during the DMT hydrogenation process, resulting in excellent hydrogenation performance. Attached Figure Description

[0026] Figure 1 Schematic diagram of the distributor installation of this invention;

[0027] Figure 2 A schematic diagram of the jet-ring tube type inlet gas-liquid diffuser structure of the present invention.

[0028] Figure 3 Figure 2 Sectional view along the AA direction;

[0029] Figure 4 A schematic diagram of the diffuser of the present invention installed inside the reactor.

[0030] Among them, 1. Positioning ring plate, 2. Cylinder body, 3. Upper flange ring plate, 4. Lower flange ring plate, 5. Single-head welded stud, 6. Nut, 7. Inverted cone body, 8. Umbrella cap body, 9. Support plate I, 10. Support plate II, 11. Circular plate, 12. Nut, 13. Bolt, 14. Clamping plate, 15. Clamping plate, 16. Base plate, 17. Annular nozzle atomizing sprayer, 18. Inlet diffuser, 19. Top distribution plate. Detailed Implementation

[0031] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0032] To facilitate understanding of the invention, certain technical and scientific terms are specifically defined below. Unless otherwise expressly defined elsewhere in this document, all other technical and scientific terms used herein have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains.

[0033] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0034] In the following embodiments, the reactor temperature of the present invention is limited to 135-170°C. In a single-stage hydrogenation reaction, DMT reacts with hydrogen under high temperature and high pressure conditions. Typically, a single-stage hydrogenation reaction requires control of temperature and pressure to obtain the desired product yield and quality. The inventors have experimentally verified that a reactor temperature of 135-170°C is optimal.

[0035] In the following embodiments, a trickle bed reaction is used because the trickle bed hydrogenation reactor is a gas-liquid-solid three-phase catalytic reactor in which gas and liquid flow downwards through a solid catalyst bed. It is widely used in petroleum refining, petrochemicals, fine chemicals, and environmental engineering. This reactor has unparalleled advantages in large-scale, high-pressure heterogeneous catalytic processes. The main factors affecting the performance of the trickle bed reactor include catalyst bed characteristics, uniformity of fluid distribution, interphase heat and mass transfer, and reaction kinetics. The trickle bed hydrogenation reactor has stringent requirements for reaction conditions; therefore, the reaction conditions and internal structure need to be modified to suit the DMT hydrogenation reaction of this invention. The structure of the trickle bed hydrogenation reactor will not be described separately.

[0036] In the following embodiments, the preheater uses heat transfer oil to control the temperature. Since the device structure is the same, it will not be described in detail in the specific implementation.

[0037] Example 1

[0038] The liquid feedstock (20% DMT and 80% DMCD) from the first stage of DMT hydrogenation reaction, along with hydrogen, undergoes heat exchange with DMCD. After heat exchange, they are mixed and heated to the required reaction temperature of 135°C via a preheater. Under a pressure of 10 MPa, the mixture enters the reactor from the top of the trickle bed hydrogenation reactor. The molar ratio of hydrogen to DMT liquid feedstock is 120:1. A top-mounted jet-ring type inlet gas-liquid diffuser evenly injects the liquid feedstock and hydrogen into the reactor. The mixed multiphase materials are evenly dispersed into their respective catalyst beds via a staged distributor within the trickle bed hydrogenation reactor. After contacting and reacting with the catalyst, they enter the next stage distributor and its corresponding catalyst bed. After staged reactions, the mixture reacts and is deheated at each catalyst bed. After the reaction is complete, the second stage hydrogenation reaction begins, ultimately producing CHDM. In this invention, the reactor temperature is controlled at 135°C.

[0039] The substances involved in the DMT hydrogenation process are multiphase materials, that is, the reactants (20% DMT, 80% DMCD) are liquid, hydrogen is gaseous, and the catalyst is solid. This type of reaction has special characteristics such as high freezing point of the reactants (freezing point greater than 100℃), strong exothermic reaction, and easy overheating of the catalyst. Therefore, it is required that the liquid reactants be uniformly distributed in the hydrogen gas and react with the solid catalyst to prevent excessive exothermic reaction, control the conversion depth, and reduce the occurrence of side reactions.

[0040] The distributor is installed on the upper part of each catalyst bed section in the reactor, and the distributor is 300 mm away from the lower honeycomb catalyst bed. This embodiment has three catalyst beds.

[0041] Experiments have verified that by using a gas-liquid distributor, the raw materials and catalyst bed are in uniform contact. After passing through the trickle bed reactor, the DMT conversion rate is 99.5%, the DMCD selectivity is 96%, and the heat release is uniform with a stable temperature rise of about 25°C.

[0042] Example 2

[0043] The liquid feedstock (30% DMT and 70% DMCD) from the first stage of DMT hydrogenation reaction, along with hydrogen, undergoes heat exchange with DMCD. After heat exchange, they are mixed and heated to the required reaction temperature via a preheater. Under a pressure of 10 MPa, the mixture enters the reactor from the top of the trickle bed hydrogenation reactor. The molar ratio of hydrogen to DMT liquid feedstock is 120:1. A top-mounted jet-ring type inlet gas-liquid diffuser evenly sprays the liquid feedstock and hydrogen into the reactor. The mixed multiphase materials are evenly dispersed into their respective catalyst beds by a staged distributor within the trickle bed hydrogenation reactor. After contacting and reacting with the catalyst, they enter the next stage distributor and its corresponding catalyst bed. After staged reactions, the reaction occurs on each catalyst bed and the heat is removed. After the reaction is complete, the second stage hydrogenation reaction begins, ultimately producing CHDM. In this invention, the reactor temperature is controlled at 135°C.

[0044] The substances involved in the DMT hydrogenation process are multiphase materials, that is, the reactants (30% DMT, 70% DMCD) are liquid, hydrogen is gaseous, and the catalyst is solid. This type of reaction has the special characteristics of high freezing point (freezing point greater than 100℃) of the reactants, strong exothermic reaction, and easy overheating of the catalyst. Therefore, it is required that the liquid reactants be uniformly distributed in the hydrogen gas and react with the solid catalyst to prevent excessive exothermic reaction, control the conversion depth, and reduce the occurrence of side reactions.

[0045] The distributor is installed on the upper part of each catalyst bed section in the reactor, and the distributor is 300 mm away from the lower honeycomb catalyst bed. This embodiment has three catalyst beds.

[0046] Experiments have verified that by using a gas-liquid distributor, the raw materials and catalyst bed are in uniform contact. After passing through the trickle bed reactor, the DMT conversion rate is 99.9%, the DMCD selectivity is 96%, and the heat release is uniform with a stable temperature rise of about 30°C.

[0047] Comparative Example 1

[0048] The only difference between this comparative example and Example 1 is that the gas-liquid distributor of this invention was not used; only a conventional fixed-bed reactor was employed. After passing through the trickle-bed reactor, the experimental results showed that the lateral temperature measurement points of the catalyst bed indicated excessively high local temperature rises, leading to an increase in byproducts. The DMT conversion rate was 98%, the DMCD selectivity was 93%, the catalyst bed exhibited uneven heat release, and the local temperature was excessively high, with a temperature rise of approximately 34°C. This resulted in increased byproducts and poor hydrogenation performance.

[0049] Comparative Example 2

[0050] The only difference between this comparative example and Example 2 is that the gas-liquid distributor of this invention was not used; only a conventional fixed-bed reactor was employed. After passing through the trickle-bed reactor, experimental results showed that the transverse temperature measurement points of the catalyst bed exhibited excessively high local temperature rises, leading to increased byproducts. The DMT conversion rate was 95%, the DMCD selectivity was 90%, the catalyst bed exhibited uneven heat release, and the localized excessively high temperature rise was approximately 42°C, resulting in increased byproducts and poor hydrogenation performance. Therefore, conventional reactors cannot achieve the goal of uniform dispersion of multiphase materials.

[0051] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for uniform diffusion of multiphase materials within a reactor during the hydrogenation of dimethyl terephthalate, characterized in that, DMT solution and hydrogen are heat-exchanged with DMCD at 120-185℃. After heat exchange, they are mixed and heated to the required reaction temperature of 135-170℃ through a preheater. Under a pressure of 8-12MPa, they enter the reactor from the top to react. The mixed multiphase material passes through a step-by-step distributor and its catalyst bed in the trickle bed hydrogenation reactor, reacts uniformly with the catalyst, and is deheated. After the reaction is completed, it is purified by distillation and continues to enter the second stage of hydrogenation reaction to generate CHDM. The liquid feedstock of the first-stage hydrogenation reaction of DMT includes DMT at a concentration of 15-30% and DMCD at a concentration of 70-85%. The reaction feed device adopts a jet-ring pipe type inlet gas-liquid diffuser (18), the structure of which includes a cap body (8), an inverted cone body (7), a support plate I (9), and a support plate II (10). The cap body (8) is connected to the inverted cone body (7) through the support plate I (9), and the inverted cone body (7) is connected to the support plate II (10). The support plate I (9) and the support plate II (10) are connected to the cap body (8) and the inverted cone body (7) as the first-stage annular nozzle. An upper arc strip and a horizontal circular plate (11) are provided below the inverted cone body (7) to form the second-stage annular nozzle. An annular nozzle atomizing sprayer (17) is provided below the horizontal circular plate. The annular nozzle atomizing sprayer (17) includes a downcomer tube, inside which are solid spiral blades and a third annular nozzle.

2. The method according to claim 1, characterized in that, The liquid feedstock of the first-stage hydrogenation reaction of DMT includes DMT at a concentration of 25-30% and DMCD at a concentration of 70-75%.

3. The method according to claim 1, characterized in that, The reaction temperature is 135-140℃ and the pressure is 10-11MPa.

4. The method according to claim 1, characterized in that, The molar ratio of hydrogen to DMT is (50-150):

1.

5. The method according to claim 1, characterized in that, The distributor is installed on the upper part of each catalyst bed in the reactor. The distance between the distributor and the lower catalyst bed is 300-310mm, and the distance between the distributor and the upper space is 250-260mm.

6. The method according to claim 1, characterized in that, The reactor comprises at least two catalyst beds.

7. The method according to claim 1, characterized in that, The preheater controls the temperature by adjusting the flow rate of the heat transfer medium.

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