Method for continuously preparing 2,6-dimethylnaphthalene

Abstract

The present invention provides a method for continuously preparing 2,6-dimethylnaphthalene. The method comprises: alternately introducing a gas-phase carrier and a liquid-phase carrier into a fixed-bed reactor, mixing the gas-phase carrier and the liquid-phase carrier with liquid reaction starting material continuously fed into the fixed-bed reactor, and bringing the reaction starting material into contact with a solid acid catalyst bed in the fixed-bed reactor to perform isomerization, thereby obtaining 2,6-dimethylnaphthalene. The preparation method involves a simple process and has low energy consumption.

Description

Method for continuous preparation of 2,6-dimethylnaphthalene

[0001] Cross-reference information

[0002] This application claims priority to Chinese Patent Application No. 202411441019.X, filed on October 15, 2024, entitled “Method for Continuous Preparation of 2,6-Dimethylnaphthalene”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a method for the continuous preparation of 2,6-dimethylnaphthalene, belonging to the field of aromatic hydrocarbon production technology. Background Technology

[0004] 2,6-Dimethylnaphthalene (2,6-DMN) is a high-value-added bicyclic aromatic molecule. Its oxidation product, 2,6-naphthalenedicarboxylic acid (2,6-NDA), reacts with ethylene glycol to obtain high-performance polyester material polyethylene 2,6-naphthalenedicarboxylic acid (PEN).

[0005] EP0589490B1 and US4783569 disclose a dimethylnaphthalene isomerization catalyst and its application method, which uses a Y-type molecular sieve (FAU structure molecular sieve) to prepare the catalyst and conducts an isomerization reaction under low pressure. US3888938, US4041089, and US5495060 disclose isomerization catalysts with hydrogen-form mordenite (MOR structure molecular sieve) as the active component, applied to the dimethylnaphthalene isomerization reaction. US4556751 discloses an isomerization catalyst with a ten-membered ring channel ZSM-5 molecular sieve (MFI structure molecular sieve) as the active component. CN1762932A discloses a method for preparing 2,6-dimethylnaphthalene by alkyl transfer reaction, wherein the catalyst is a metal-modified ZSM-5 molecular sieve, a Y-type, a mordenite, or a β-type molecular sieve. CN101092320A discloses a method for preparing 2,6-dimethylnaphthalene by isomerization reaction under normal pressure using hydrogen-form β-zeolite as a catalyst.

[0006] Currently, large-scale production of 2,6-DMN mainly adopts the traditional process route using o-xylene and butadiene as raw materials, but the preparation process is relatively complex and energy-intensive. Therefore, it is necessary to provide a new method for preparing 2,6-dimethylnaphthalene to improve the above-mentioned problems. Summary of the Invention

[0007] To address the aforementioned technical problems, the present invention aims to provide a method for the continuous preparation of 2,6-dimethylnaphthalene, which has a simple process and low energy consumption.

[0008] To achieve the above objectives, the present invention provides a method for the continuous preparation of 2,6-dimethylnaphthalene, comprising: alternately introducing a gas-phase carrier and a liquid-phase carrier into a fixed-bed reactor, mixing them with a liquid reactant continuously introduced into the fixed-bed reactor, and driving the reactant into contact with a solid acid catalyst bed in the fixed-bed reactor to undergo an isomerization reaction, thereby obtaining 2,6-dimethylnaphthalene. Each sequential alternation of the gas-phase carrier and liquid-phase carrier is defined as one alternation cycle, and the method for the continuous preparation of 2,6-dimethylnaphthalene includes at least one alternation cycle; the gas-phase carrier is selected from nitrogen and / or hydrogen; the liquid-phase carrier is selected from one or more combinations of benzene, naphthalene, and toluene.

[0009] This invention employs an alternating gas-phase and liquid-phase carrier approach, enabling continuous isomerization of 2,6-dimethylnaphthalene while simultaneously regenerating the catalyst. This process is simple and energy-efficient. The alternating gas-phase and liquid-phase carrier approach allows the gas-phase carrier to not only facilitate contact between the reactants and catalyst for isomerization but also reduce the prolonged residence of reactants and products within the catalyst pores and surface, thereby minimizing side reactions, extending the catalyst's single-pass life, and slowing its deactivation. The liquid-phase carrier not only facilitates contact between the reactants and catalyst for isomerization but also washes away deactivated catalyst during the isomerization process, achieving catalyst regeneration. This regeneration can be performed without interrupting the isomerization reaction, further simplifying the process and reducing energy consumption.

[0010] In some alternative embodiments, pumps can be used to inject gaseous and liquid carriers into a fixed-bed reactor to mix with the continuously entering reactants. As the carriers and reactants continuously enter the reactor, a small pressure difference is formed, which pushes the reactants and the solid acid catalyst bed into contact. This is something that can be achieved by those skilled in the art, and will not be elaborated on here.

[0011] Further, the feed volume ratio of the gaseous support to the reactants is 50–1000:1, for example, it can be 50:1, 100:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, or 1000:1. Preferably, the feed volume ratio of the gaseous support to the reactants is 100–500:1.

[0012] Further, the feed volume ratio of the liquid carrier to the reactants is 0.2 to 30:1, for example, it can be 0.2:1, 1:1, 2:1, 5:1, 6:1, 8:1, 10:1, 12:1, 20:1 or 30:1. Preferably, the feed volume ratio of the liquid carrier to the reactants is 1 to 20:1.

[0013] Furthermore, within each alternation cycle, the ratio of the entry time of the gas phase carrier to the entry time of the liquid phase carrier is 0.1 to 100:1, for example, it can be 0.1:1, 1:1, 2:1, 3:1, 10:1, 30:1, 50:1, 70:1 or 100:1.

[0014] Furthermore, the volume hourly space velocity (VHSV) during the isomerization reaction is 0.2–3.0 h⁻¹. -1 For example, it can be 0.2h -1 0.25h -1 0.5h -1 1.0h -1 2.0h -1 2.5h -1 or 3.0h -1 Preferably, the volumetric hourly space velocity is 0.25–2.0 h⁻¹. -1 Volumetric hourly space velocity (VHSV) refers to the volume of liquid feedstock per unit time entering a fixed-bed reactor. Specifically, when a gaseous carrier enters, VHSV is calculated based on the volume of reactants; when a liquid carrier enters, VHSV is calculated as the sum of the volumes of reactants and liquid carrier. In other words, when a gaseous carrier enters, VHSV = volume of reactants per unit time / catalyst volume; when a liquid carrier enters, VHSV = (volume of reactants per unit time + volume of liquid carrier per unit time) / catalyst volume.

[0015] It should also be noted that the volume hourly space velocity (VHSV) when the gaseous carrier enters and when the liquid carrier enters are not necessarily the same, but it is preferable that they are the same. This is because the liquid flow rate is related to the processing capacity of the subsequent devices. In the entire continuous reaction process, a consistent liquid flow rate is beneficial to the stable operation of the subsequent devices.

[0016] Furthermore, the catalyst packing material of the solid acid catalyst bed includes a molecular sieve; the molecular sieve is selected from one or more combinations of BEA molecular sieves, MWW molecular sieves, FAU molecular sieves, MOR molecular sieves, and MTW molecular sieves. Preferably, the molecular sieve is selected from BEA molecular sieves and / or MWW molecular sieves. In some optional embodiments, the molecular sieve can be used alone as a catalyst, or it can be used in combination with oxides, metals, and inorganic substances commonly used in this art as a catalyst. This can be achieved by those skilled in the art based on existing known technologies, and will not be elaborated here.

[0017] Furthermore, the reactants include 1,5-dimethylnaphthalene and / or 1,6-dimethylnaphthalene. In some alternative embodiments, the reactants can be heated to melt them into a liquid phase for feeding. Liquid-phase feeding is more stable than gas-phase feeding and also reduces side reactions.

[0018] Furthermore, the reaction temperature of the isomerization reaction is 220–300°C; the pressure of the isomerization reaction is 2–6 MPa. Preferably, the reaction temperature of the isomerization reaction is 240–280°C; the pressure of the isomerization reaction is 2.5–5 MPa. Attached Figure Description

[0019] Figure 1 is a schematic diagram of a fixed-bed reactor according to one embodiment of the present invention. Detailed Implementation

[0020] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0021] Sources of catalyst packing material in solid acid catalyst beds:

[0022] Catalyst 1: by weight percentage, it comprises 100 wt% MWW structured molecular sieve.

[0023] Catalyst 2: by weight percentage, it comprises 50 wt% MWW structured molecular sieve and 50 wt% BEA structured molecular sieve.

[0024] Catalyst 3: by weight percentage, it includes 50 wt% MWW structured molecular sieve, 30 wt% BEA structured molecular sieve, and 20 wt% FAU structured molecular sieve.

[0025] Catalyst 4: by weight percentage, it comprises 50 wt% MWW structured molecular sieve, 30 wt% BEA structured molecular sieve, and 20 wt% alumina binder.

[0026] Catalyst 5: by weight percentage, it comprises 40 wt% BEA structured molecular sieve, 20 wt% MOR structured molecular sieve, 20 wt% MTW structured molecular sieve, and 20 wt% alumina binder.

[0027] Example 1

[0028] This embodiment provides a method for the continuous preparation of 2,6-dimethylnaphthalene, including:

[0029] 1,5-Dimethylnaphthalene was heated and melted into a liquid state, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, nitrogen gas was first introduced to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed (using catalyst 1) in the fixed-bed reactor to initiate an isomerization reaction. After 500 hours of reaction, benzene gas was introduced to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed in the fixed-bed reactor to initiate an isomerization reaction. This process was accompanied by catalyst regeneration. After 200 hours of reaction, one alternating cycle was completed. In one alternating cycle, the feed volume ratio of the gas-phase carrier to the reactants was 100:1, and the feed volume ratio of the liquid-phase carrier to the reactants was 1:1. The cycle was continuously operated for 5 cycles, and instantaneous product samples were collected every 10 hours for analysis. The analysis results are detailed in Table 1. The isomerization reaction conditions were: reaction temperature 250℃, reaction pressure 4MPa, and volume hourly space velocity 1h. -1 .

[0030] Example 2

[0031] This embodiment provides a method for the continuous preparation of 2,6-dimethylnaphthalene, including:

[0032] 1,5-Dimethylnaphthalene was heated and melted into a liquid phase, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, hydrogen gas was first introduced to mix with the reactants and drive them into contact with the solid acid catalyst bed (Catalyst 1) in the fixed-bed reactor to initiate an isomerization reaction. After 1000 hours of reaction, benzene gas was introduced as a liquid carrier to mix with the reactants and drive them into contact with the solid acid catalyst bed in the fixed-bed reactor to initiate an isomerization reaction. This process was accompanied by catalyst regeneration. After 150 hours of reaction, one alternating cycle was completed. In one alternating cycle, the feed volume ratio of the gas carrier to the reactants was 200:1, and the feed volume ratio of the liquid carrier to the reactants was 6:1. The cycle was continuously operated for 5 cycles, with instantaneous product samples collected every 10 hours for analysis. The analysis results are detailed in Table 1. The isomerization reaction conditions were: reaction temperature 280℃, reaction pressure 5MPa, and volume hourly space velocity 2h⁻¹. -1 .

[0033] Example 3

[0034] This embodiment provides a method for the continuous preparation of 2,6-dimethylnaphthalene, including:

[0035] 1,6-Dimethylnaphthalene was heated and melted into a liquid phase, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, nitrogen gas was first introduced as a gaseous carrier to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed (catalyst 2) in the fixed-bed reactor, initiating an isomerization reaction. After 1200 h of reaction, toluene gas was introduced as a liquid carrier to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed in the fixed-bed reactor, initiating another isomerization reaction. This process was accompanied by catalyst regeneration. After 120 h of reaction, one alternating cycle was completed. Within one alternating cycle, the feed volume ratio of the gaseous carrier to the reactants was 300:1, and the feed volume ratio of the liquid carrier to the reactants was 10:1. The cycle was continuously operated for 5 cycles, with instantaneous product samples collected every 10 h for analysis. The analysis results are detailed in Table 1. The isomerization reaction conditions were: reaction temperature 260℃, reaction pressure 2 MPa, and volume hourly space velocity 2.5 h⁻¹. -1 .

[0036] Example 4

[0037] This embodiment provides a method for the continuous preparation of 2,6-dimethylnaphthalene, including:

[0038] 1,6-Dimethylnaphthalene was heated and melted into a liquid phase, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, hydrogen gas was first introduced as a carrier to mix with the reactants and drive them into contact with the solid acid catalyst bed (catalyst 3) in the fixed-bed reactor to initiate an isomerization reaction. After 1500 h of reaction, toluene gas was introduced as a carrier to mix with the reactants and drive them into contact with the solid acid catalyst bed in the fixed-bed reactor to initiate an isomerization reaction. This process was accompanied by catalyst regeneration. After 100 h of reaction, one alternating cycle was completed. In one alternating cycle, the feed volume ratio of the gas carrier to the reactants was 400:1, and the feed volume ratio of the liquid carrier to the reactants was 15:1. The cycle was continuously operated for 5 cycles, and instantaneous product samples were collected every 10 h for analysis. The analysis results are detailed in Table 1. The isomerization reaction conditions were: reaction temperature 240℃, reaction pressure 2.5 MPa, and volume hourly space velocity (VHSV) 0.2 h⁻¹. -1 .

[0039] Example 5

[0040] This embodiment provides a method for the continuous preparation of 2,6-dimethylnaphthalene, including:

[0041] 1,6-Dimethylnaphthalene was heated and melted into a liquid state, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, nitrogen gas was first introduced to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed in the fixed-bed reactor, initiating an isomerization reaction. After 2000 hours of reaction, benzene gas was introduced as a liquid carrier to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed (catalyst 4) in the fixed-bed reactor, initiating an isomerization reaction. This process was accompanied by catalyst regeneration. After 80 hours of reaction, one alternating cycle was completed. Within one alternating cycle, the feed volume ratio of the gas carrier to the reactants was 500:1, and the feed volume ratio of the liquid carrier to the reactants was 20:1. The cycle was continuously operated for 5 cycles, with instantaneous product samples collected every 10 hours for analysis. The analysis results are detailed in Table 1. The isomerization reaction conditions were: reaction temperature 270℃, reaction pressure 4.5MPa, and volume hourly space velocity (VHSV) 0.5h⁻¹. -1 .

[0042] Example 6

[0043] This embodiment provides a method for the continuous preparation of 2,6-dimethylnaphthalene, including:

[0044] 1,6-Dimethylnaphthalene was heated and melted into a liquid state, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, nitrogen gas was first introduced to mix with the reactants and drive them into contact with the solid acid catalyst bed in the fixed-bed reactor to initiate an isomerization reaction. After 2000 hours of reaction, benzene gas was introduced as a liquid carrier to mix with the reactants and drive them into contact with the solid acid catalyst bed (catalyst 4) in the fixed-bed reactor to initiate an isomerization reaction. This process was accompanied by catalyst regeneration. After 80 hours of reaction, one alternating cycle was completed. In one alternating cycle, the feed volume ratio of the gas carrier to the reactants was 50:1, and the feed volume ratio of the liquid carrier to the reactants was 20:1. The cycle was continuously operated for 5 cycles, with instantaneous product samples collected every 10 hours for analysis. The analysis results are detailed in Table 1. The isomerization reaction conditions were: reaction temperature 270℃, reaction pressure 4.5MPa, and volume hourly space velocity (VHSV) 0.5h⁻¹. -1 .

[0045] Example 7

[0046] This embodiment provides a method for the continuous preparation of 2,6-dimethylnaphthalene, including:

[0047] 1,6-Dimethylnaphthalene was heated and melted into a liquid state, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, nitrogen gas was first introduced to mix with the reactants and drive them into contact with the solid acid catalyst bed in the fixed-bed reactor to initiate an isomerization reaction. After 2000 hours of reaction, benzene gas was introduced as a liquid carrier to mix with the reactants and drive them into contact with the solid acid catalyst bed (catalyst 4) in the fixed-bed reactor to initiate an isomerization reaction. This process was accompanied by catalyst regeneration. After 80 hours of reaction, one alternating cycle was completed. Within one alternating cycle, the feed volume ratio of the gas carrier to the reactants was 1000:1, and the feed volume ratio of the liquid carrier to the reactants was 20:1. The cycle was continuously operated for 5 cycles, with instantaneous product samples collected every 10 hours for analysis. The analysis results are detailed in Table 1. The isomerization reaction conditions were: reaction temperature 270℃, reaction pressure 4.5MPa, and volume hourly space velocity (VHSV) 0.5h⁻¹. -1 .

[0048] Example 8

[0049] This embodiment provides a method for the continuous preparation of 2,6-dimethylnaphthalene, including:

[0050] 1,6-Dimethylnaphthalene was heated and melted into a liquid state, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, nitrogen gas was first introduced as a carrier to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed in the fixed-bed reactor, initiating an isomerization reaction. After 2000 hours of reaction, benzene gas was introduced as a carrier to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed (catalyst 4) in the fixed-bed reactor, initiating an isomerization reaction. This process was accompanied by catalyst regeneration. After 80 hours of reaction, one alternating cycle was completed. Within one alternating cycle, the feed volume ratio of the gas carrier to the reactants was 500:1, and the feed volume ratio of the liquid carrier to the reactants was 0.2:1. The cycle was continuously operated for 5 cycles, with instantaneous product samples collected every 10 hours for analysis. The analysis results are detailed in Table 1. The isomerization reaction conditions were: reaction temperature 270℃, reaction pressure 4.5MPa, and volume hourly space velocity (VHSV) 0.5h⁻¹. -1 .

[0051] Example 9

[0052] This embodiment provides a method for the continuous preparation of 2,6-dimethylnaphthalene, including:

[0053] 1,6-Dimethylnaphthalene was heated and melted into a liquid state, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, nitrogen gas was first introduced as a carrier gas to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed (catalyst 4) in the fixed-bed reactor, initiating an isomerization reaction. After 2000 hours of reaction, benzene gas was introduced as a carrier gas to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed in the fixed-bed reactor, initiating an isomerization reaction. This process was accompanied by catalyst regeneration. After 1000 hours of reaction, one alternating cycle was completed. Within one alternating cycle, the feed volume ratio of the carrier gas to the reactants was 500:1, and the feed volume ratio of the carrier gas to the reactants was 0.2:1. The cycle was continuously operated for 5 cycles, with instantaneous product samples collected every 10 hours for analysis. The analysis results are detailed in Table 1. The isomerization reaction conditions were: reaction temperature 270℃, reaction pressure 4.5MPa, and volume hourly space velocity (VHSV) 0.5h⁻¹. -1 .

[0054] Example 10

[0055] This embodiment provides a method for the continuous preparation of 2,6-dimethylnaphthalene, including:

[0056] 1,6-Dimethylnaphthalene was heated and melted into a liquid state, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, nitrogen gas was first introduced as a carrier gas to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed (catalyst 4) in the fixed-bed reactor, initiating an isomerization reaction. After 2000 h of reaction, benzene gas was introduced as a carrier gas to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed in the fixed-bed reactor, initiating an isomerization reaction. This process was accompanied by catalyst regeneration. After 80 h of reaction, one alternating cycle was completed. Within one alternating cycle, the feed volume ratio of the gas carrier to the reactants was 500:1, and the feed volume ratio of the liquid carrier to the reactants was 1:1. The cycle was continuously operated for 5 cycles, with instantaneous product samples collected every 10 h for analysis. The analysis results are detailed in Table 1. The isomerization reaction conditions were: reaction temperature 270℃, reaction pressure 4.5 MPa, and volume hourly space velocity (VHSV) 0.5 h⁻¹. -1 .

[0057] Example 11

[0058] This embodiment provides a method for the continuous preparation of 2,6-dimethylnaphthalene, including:

[0059] 1,5-Dimethylnaphthalene was heated and melted into a liquid state, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, nitrogen gas was first introduced to mix with the reactants and drive them to contact the solid acid catalyst bed (catalyst 1) in the fixed-bed reactor to initiate an isomerization reaction. After 500 hours of reaction, benzene gas was introduced to mix with the reactants and drive them to contact the solid acid catalyst bed in the fixed-bed reactor to initiate an isomerization reaction. This process was accompanied by catalyst regeneration. After 5000 hours of reaction, one alternating cycle was completed. In one alternating cycle, the feed volume ratio of the gas-phase carrier to the reactants was 100:1, and the feed volume ratio of the liquid-phase carrier to the reactants was 30:1. The cycle was continuously operated for 5 cycles, and instantaneous product samples were collected every 10 hours for analysis. The analysis results are detailed in Table 1. The isomerization reaction conditions were: reaction temperature 250℃, reaction pressure 4MPa, and volume hourly space velocity 1h. -1 .

[0060] Example 12

[0061] This embodiment provides a method for the continuous preparation of 2,6-dimethylnaphthalene, including:

[0062] 1,5-Dimethylnaphthalene was heated and melted into a liquid state, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, nitrogen gas was first introduced to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed (catalyst 1) in the fixed-bed reactor, initiating an isomerization reaction. After 500 hours of reaction, benzene gas was introduced to mix with the reactants and to drive the reactants into contact with the solid acid catalyst bed in the fixed-bed reactor, initiating another isomerization reaction. This process was accompanied by catalyst regeneration. After 5 hours of reaction, one alternating cycle was completed. Within one alternating cycle, the feed volume ratio of the gas-phase carrier to the reactants was 100:1, and the feed volume ratio of the liquid-phase carrier to the reactants was 30:1. The cycle was continuously operated for 5 cycles, with instantaneous product samples collected every 10 hours for analysis. The analysis results are detailed in Table 1. The isomerization reaction conditions were: reaction temperature 250℃, reaction pressure 4MPa, and volume hourly space velocity (VHSV) 1h⁻¹. -1 .

[0063] Example 13

[0064] This embodiment provides a method for the continuous preparation of 2,6-dimethylnaphthalene, including:

[0065] 1,5-Dimethylnaphthalene and 1,6-Dimethylnaphthalene (weight ratio 2:1) were heated and melted into a liquid state, and continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, nitrogen and hydrogen (volume ratio 2:1) were first introduced as gaseous carriers to mix with the reactants and promote contact between the reactants and the solid acid catalyst bed (catalyst 1) in the fixed-bed reactor to initiate an isomerization reaction. After 3000 h of reaction, the flow was switched to benzene and naphthalene (volume ratio 1:1) as liquid carriers to mix with the reactants and promote contact between the reactants and the solid acid catalyst bed in the fixed-bed reactor to initiate an isomerization reaction. This process was accompanied by catalyst regeneration. After 120 h of reaction, one alternation cycle was completed. In one alternation cycle, the volume ratio of gaseous carrier to reactants was 200:1, and the volume ratio of liquid carrier to reactants was 10:1. The cycle was continuously operated for 5 cycles, and instantaneous product samples were collected every 10 h for analysis. The analysis results are detailed in Table 1. The isomerization reaction conditions were: reaction temperature 300℃, reaction pressure 4MPa, and volume hourly space velocity 1h. -1 .

[0066] Comparative Example 1

[0067] This comparative example provides a method for the continuous preparation of 2,6-dimethylnaphthalene, comprising:

[0068] 1,5-Dimethylnaphthalene was heated and melted into a liquid state, and continuously fed into a fixed-bed reactor (as shown in Figure 1) as a reactant to undergo an isomerization reaction with a solid acid catalyst bed (catalyst 1). The isomerization reaction conditions were: reaction temperature 250℃, reaction pressure 4MPa, and volume hourly space velocity 1h. -1 .

[0069] After 100 hours of continuous reaction operation, the feed conversion rate began to decline, and after 300 hours of continuous operation, the catalyst was completely deactivated. Instantaneous product samples were collected every 10 hours for analysis, and the results are detailed in Table 1.

[0070] Comparative Example 2

[0071] This comparative example provides a method for the continuous preparation of 2,6-dimethylnaphthalene, comprising:

[0072] 1,5-Dimethylnaphthalene was heated and melted into a liquid state, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, nitrogen gas was introduced on a gaseous carrier to mix with the reactants and to push the reactants into contact with the solid acid catalyst bed (catalyst 1) in the fixed-bed reactor, causing an isomerization reaction. The gas-phase carrier to reactant volume ratio was 100. The isomerization reaction conditions were: reaction temperature 250℃, reaction pressure 4MPa, and volume hourly space velocity (VHSV) 1h⁻¹. -1.

[0073] After 300 hours of continuous reaction operation, the feed conversion rate began to decline, and after 600 hours of continuous operation, the catalyst was completely deactivated. Instantaneous product samples were collected every 10 hours for analysis, and the results are detailed in Table 1.

[0074] Comparative Example 3

[0075] This comparative example provides a method for the continuous preparation of 2,6-dimethylnaphthalene, comprising:

[0076] 1,5-Dimethylnaphthalene was heated and melted into a liquid phase, which was then continuously fed into a fixed-bed reactor (as shown in Figure 1). During the continuous feeding process, benzene, a liquid carrier, was introduced to mix with the reactants and push them into contact with the solid acid catalyst bed (catalyst 1) in the fixed-bed reactor to initiate an isomerization reaction. The feed volume ratio of the liquid carrier to the reactants was 1. The isomerization reaction conditions were: reaction temperature 250℃, reaction pressure 4 MPa, and volume hourly space velocity (VHSV) 1 h⁻¹. -1 .

[0077] After the reaction ran continuously for 2000 hours, the catalyst showed signs of slow deactivation. Instantaneous product samples were collected every 10 hours for analysis, and the results are detailed in Table 1.

[0078] Energy consumption of the test examples and comparative examples, and the energy consumption calculation method: A dynamic model of a single reaction unit was established using ASPEN software. The reaction type was an equilibrium reaction. The system parameters mainly included reaction temperature, reaction pressure, and reaction space velocity, with only a liquid carrier as the circulating material. The test results are shown in Table 1.

[0079] Table 1

[0080] Compared to Example 1, in Comparative Example 1, where the reactants were directly introduced without using a gaseous or liquid carrier, the catalyst was rapidly deactivated due to excessively high reaction density and prolonged reaction residence time.

[0081] Compared to Example 1, Comparative Example 2, which uses only a gas-phase carrier, can extend the single-pass life of the catalyst and slow down the deactivation rate of the catalyst. However, the gas-phase carrier cannot achieve the washing and regeneration of the catalyst. As the reaction continues, the catalyst will still be deactivated during the entire continuous reaction process due to the gradual accumulation of material molecules and the aggravation of side reactions, and it cannot be used for a long time.

[0082] Compared to Example 1, Comparative Example 3 only used a liquid-phase carrier. When a gas-phase carrier enters, the volume hourly space velocity (VHSV) = volume of reactant per unit time / catalyst volume; when a liquid-phase carrier enters, the VHSV = (volume of reactant per unit time + volume of liquid-phase carrier per unit time) / catalyst volume. Therefore, under a constant VHSV, the process with a gas-phase carrier is a high-VHS reaction process. The accumulation of reactant and product molecules on the surface and within the pores of the molecular sieve is reduced under the influence of the carrier gas, and side reactions such as polymerization are also reduced. The process with a liquid-phase carrier is a low-VHS reaction process, which also washes off the reactant and product molecules accumulated on the surface and within the pores of the molecular sieve to achieve catalyst regeneration. Compared to Example 1, the passage speed of the liquid-phase carrier and reactant in the catalyst bed in Comparative Example 3 is slower, exacerbating the problem of long residence time of reactant and product in the catalyst pores and surface, increasing side reactions, and causing the catalyst to slowly deactivate during the reaction cycle. Furthermore, in continuous production, the liquid-phase carrier does not participate in the reaction but is recycled in the reaction unit, resulting in significant energy consumption and poor economic efficiency. When a gaseous carrier is introduced, the feed rate remains constant, and the throughput is mainly affected by the proportion of gaseous carrier introduced. When a liquid carrier is introduced, the space velocity remains constant, and the throughput of the liquid stream (feed and carrier) remains constant. The slower throughput when a liquid carrier is introduced is relative to when a gaseous carrier is introduced. Although molecules accumulate when a gaseous carrier is introduced, this accumulation is a dynamic equilibrium process, and side reactions such as polymerization of multiple molecules are less likely to occur, leading to increased molecular size and further carbon deposition. In this case, introducing a liquid carrier can achieve molecular elution and thus catalyst regeneration. However, when only a liquid carrier is introduced, although the molecular accumulation rate is also slower, the slower throughput makes it easier for side reactions to occur, thus failing to achieve effective regeneration, resulting in slow catalyst deactivation.

[0083] Furthermore, compared to Example 5, the compositional fluctuation of the reaction products in Example 6 was increased. This was because the lower amount of gaseous carrier led to a longer reaction residence time, which exacerbated the side reactions and caused the catalyst to slowly deactivate.

[0084] Furthermore, compared to Example 5, the compositional fluctuation of the reaction products in Example 7 was increased. This is because the higher amount of gas-phase carrier causes the reactants to rapidly penetrate the catalyst bed without reacting, resulting in a lower reaction conversion rate and disturbance of the material flow within the reactor, thus causing fluctuations in product composition. The reduced yield of the target product also leads to a higher feedstock recycling rate and increased energy consumption.

[0085] Furthermore, compared to Example 5, the product composition fluctuation in Example 8 was increased. This is because the lower amount of liquid carrier resulted in poor catalyst regeneration, making complete catalyst regeneration impossible and thus causing product composition fluctuations. Furthermore, compared to Example 8, in Example 9, extending the liquid carrier introduction stage to 1000 hours significantly reduced product fluctuations. Furthermore, compared to Example 8, in Example 10, increasing the feed volume ratio of the liquid carrier to the reactants to 1:1 resulted in smaller product fluctuations and better catalyst regeneration.

[0086] Furthermore, compared to Example 1, in Example 11, when the feed volume ratio of the liquid carrier to the reactants was increased to 30:1, the catalyst could operate continuously for a long period without deactivation. This indicates that a higher proportion of liquid carrier can not only regenerate the catalyst but also effectively dilute the reaction density, reduce the frequency of catalyst regeneration, and make the isomerization reaction more stable. However, a higher proportion of liquid carrier will reduce the yield of the target product and increase the energy consumption of the device. Furthermore, compared to Example 11, in Example 12, when the time for introducing the liquid carrier was shortened to 5 hours, the product fluctuation was smaller, indicating that a higher proportion of liquid carrier resulted in better catalyst regeneration, achieving catalyst regeneration in a shorter time and reducing energy consumption.

Claims

1. A method for the continuous preparation of 2,6-dimethylnaphthalene, wherein, include: The gas-phase carrier and liquid-phase carrier are alternately introduced into the fixed-bed reactor to mix with the liquid reactants that are continuously introduced into the fixed-bed reactor, and to promote the contact between the reactants and the solid acid catalyst bed in the fixed-bed reactor to carry out an isomerization reaction to obtain 2,6-dimethylnaphthalene; One alternation between gas-phase carrier and liquid-phase carrier is defined as one alternation cycle; the method for continuous preparation of 2,6-dimethylnaphthalene includes at least one such alternation cycle; The gaseous carrier is selected from nitrogen and / or hydrogen; the liquid carrier is selected from one or more combinations of benzene, naphthalene and toluene.

2. The method for continuous preparation of 2,6-dimethylnaphthalene according to claim 1, wherein, During one of the alternation cycles, the feed volume ratio of the gas phase carrier to the reaction raw materials is 50 to 1000:

1.

3. The method for continuous preparation of 2,6-dimethylnaphthalene according to claim 2, wherein, During one of the alternation cycles, the feed volume ratio of the liquid carrier to the reaction raw materials is 0.2 to 30:

1.

4. The method for continuous preparation of 2,6-dimethylnaphthalene according to claim 1, wherein, The volume hourly space velocity (VHSV) during the isomerization reaction is 0.2–3.0 h⁻¹. -1 .

5. The method for continuous preparation of 2,6-dimethylnaphthalene according to claim 4, wherein, Within each of the alternation cycles, the ratio of the entry time of the gas phase carrier to the entry time of the liquid phase carrier is 0.1 to 100:

1.

6. The method for continuous preparation of 2,6-dimethylnaphthalene according to claim 1, wherein, The reactants include 1,5-dimethylnaphthalene and / or 1,6-dimethylnaphthalene.

7. The method for continuous preparation of 2,6-dimethylnaphthalene according to claim 1, wherein, The isomerization reaction is carried out at a temperature of 220–300 °C.

8. The method for continuous preparation of 2,6-dimethylnaphthalene according to claim 7, wherein, The pressure of the isomerization reaction is 2–6 MPa.

9. The method for continuous preparation of 2,6-dimethylnaphthalene according to claim 1, wherein, The catalyst packing material of the solid acid catalyst bed includes molecular sieves; the molecular sieves are selected from one or more combinations of BEA molecular sieves, MWW molecular sieves, FAU molecular sieves, MOR molecular sieves and MTW molecular sieves.

10. The method for continuous preparation of 2,6-dimethylnaphthalene according to claim 1, wherein, During one alternating cycle, the feed volume ratio of the gaseous carrier to the reaction raw materials is 100 to 500:

1.

11. The method for continuous preparation of 2,6-dimethylnaphthalene according to claim 10, wherein, During one alternating cycle, the feed volume ratio of the liquid carrier to the reaction raw materials is 1 to 20:

1.

12. The method for continuous preparation of 2,6-dimethylnaphthalene according to claim 1, wherein, The isomerization reaction is carried out at a temperature of 240–280 °C.

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