Catalytic packing module and use thereof

Abstract

Disclosed is a catalytic packing module suitable for a catalytic rectification device, sequentially comprising, from inside to outside, a solid catalyst layer at the center, a first mesh layer wrapping the catalyst layer, an inert packing layer wrapping the first mesh layer, and a second mesh layer wrapping the inert packing layer. The catalytic packing module uses a special layered structure design, thereby ensuing sufficient contact between reaction materials and a catalyst, and the catalytic packing module further has the advantages of convenient loading / unloading, stable operation, minimal catalyst attrition, flexibility to adjust the use amount of the catalyst and the like.

Description

A catalytic filler module and its application Technical Field

[0001] The present application relates to the technical field of reactive distillation, and in particular to a catalytic packing module and its application. Background Art

[0002] Polylactic acid, also known as polylactide (PLA), is made from renewable biomass such as corn, cassava, and straw. It is fermented to produce lactic acid monomers, which are then polymerized through a series of reactions. It exhibits excellent mechanical properties, processability, and biodegradability. After use, its products can be composted and degraded into CO2 and water, thus achieving a natural recycling cycle. Currently, the main process for producing PLA is to use lactic acid as the raw material to first produce lactide, which is then ring-opening polymerized to produce PLA, as shown in the following formula.

[0003] As the key core of the entire polylactic acid industry chain, there are currently two main methods for synthesizing lactide. One is the "two-step method", which is the current industrial production process. Specifically, lactic acid is polymerized to generate lactic acid oligomers, and then the oligomers are depolymerized to generate lactide; the other is the "one-step method", that is, lactic acid is synthesized into lactide in one step under the action of a catalyst.

[0004] The "one-step method" for producing lactide has low energy consumption, does not require negative pressure operation, and has a relatively simple process route. However, it has the disadvantages of relatively low yield, uncontrollable process, and easy hydrolysis of the product in the aqueous reaction system, and is difficult to industrialize continuously. There are two ways to produce lactide in one step. One is a liquid-phase one-step reaction process (for example, the article "Shape-selective zeolite catalysis for bioplastics production" published by M. Dusselier's team at the University of Leuven in Belgium in 2015 in Science, Volume 349, and the article "Breaking the Si / Al limit of nanosized β-Zeolites: promoting catalytic production of lactide" published by Jilin University and the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences in 2020 in Chemistry of Materials, Volume 32, Issue 2). The reaction process temperature is relatively low, and the product yield and selectivity are high, but it is currently mostly operated in batch mode, which makes scale-up difficult. The other is a gas-phase one-step reaction process (for example, as described in DuPont's patent US5043458). The reaction process temperature is relatively high and is mostly carried out in fixed-bed, fluidized-bed and other reactors. The product yield is low and racemization is relatively serious, but it can be operated continuously.

[0005] Catalytic distillation is a process that integrates the reaction process and the separation process into the same equipment. It has the characteristics of low energy consumption and low investment. It can break the limitations of chemical equilibrium, improve reaction selectivity, and theoretically play a positive role in promoting the forward reaction of direct cyclization of lactic acid to produce lactide and timely separation of reaction water. The key to catalytic distillation technology lies in the construction of the catalytic distillation components in the catalytic distillation tower, among which the configuration of the packing and the filling method of the catalyst and packing, that is, the catalytic packing module or assembly, is one of the key influencing factors. The existing technology has carried out some work on catalytic distillation modules or components. In combination with the gas-liquid-solid three-phase reaction system, some devices for enhancing catalytic reaction distillation have also appeared.

[0006] U.S. Patent No. 4,443,559 discloses a catalytic distillation structure for use in a catalytic distillation reaction section. The structure places the catalyst into a small mesh bag to form a catalyst bundle, which is then rolled up and connected with an elastic member to form a cylindrical catalytic distillation member having the dual functions of catalytic reaction and distillation separation. The member is then loaded into a catalytic distillation tower. However, this loading method suffers from uneven gas-liquid distribution within the tower, which affects the coupling of the distillation and separation effects.

[0007] Both US Patent No. 52621012 and Chinese Patent No. CN1042664A disclose a method of loading the catalyst in bulk into the catalytic distillation reaction section. The obvious disadvantage of this loading method is that the gas and liquid in the tower are unevenly distributed, which easily causes catalyst wear and affects the conversion rate.

[0008] The current technology for producing lactide through the one-step liquid-phase cyclization of lactic acid is characterized by continuous reaction, high selectivity, and high yield. The inventors of this application have discovered that continuous reaction can be achieved through program control by combining the characteristics of catalytic distillation equipment. However, improving reaction selectivity and reducing the probability of lactide hydrolysis remain key issues. Therefore, a new catalytic packing module suitable for catalytic distillation equipment is needed.

[0009] Summary of the Invention

[0010] In response to the above-mentioned technical problems and the shortcomings of the prior art, the purpose of this application is to provide a new type of catalytic packing module and its application. The catalytic packing module adopts a special layered structure design to ensure sufficient contact between the reaction materials and the catalyst. At the same time, it also has the advantages of easy loading and unloading, stable operation, small catalyst wear, and timely adjustment of catalyst dosage.

[0011] In order to achieve the above-mentioned objectives, on the one hand, the present application provides a catalytic packing module suitable for a catalytic distillation device, which includes, from the inside to the outside, a solid catalyst layer located in the center, a first mesh layer wrapped around the outside of the catalyst layer, an inert packing layer wrapped around the outside of the first mesh layer, and a second mesh layer wrapped around the outside of the inert packing layer.

[0012] Preferably, the first mesh layer and the second mesh layer are made of corrosion-resistant materials having different hydrophilic and / or oleophilic properties.

[0013] More preferably, the first mesh layer is made of a hydrophobic and corrosion-resistant material, and the second mesh layer is made of a hydrophilic and corrosion-resistant material having high permeability.

[0014] On the other hand, the present application provides a structured catalytic packing, comprising catalytic packing modules and packing modules alternately arranged in a horizontal direction, wherein the catalytic packing modules are the catalytic packing modules of the present application.

[0015] On the other hand, the present application provides a catalytic distillation device, comprising an upper distillation section and a lower reaction section, a raw material inlet is provided between the upper distillation section and the lower reaction section, wherein the lower reaction section is filled with at least one layer of structured catalytic filler of the present application.

[0016] Preferably, the lower reaction section of the catalytic distillation device is filled with multiple layers of the structured catalytic packing of the present application, and the catalytic packing modules and packing modules of two adjacent layers of the structured catalytic packing in the multiple layers are staggered in the vertical direction.

[0017] On the other hand, the present invention provides an application of the catalytic packing module, structured catalytic packing, or catalytic distillation device in the solid-phase catalytic reaction of liquid raw materials, particularly in the reaction process of preparing lactide from lactic acid via a liquid-phase one-step method.

[0018] On the other hand, the present application provides a catalytic distillation reaction method, comprising the steps of allowing a liquid feedstock to contact and react with a solid catalyst arranged in the catalytic packing module in a reaction section of the catalytic distillation device of the present application, and the steps of separating the resulting reaction products in the distillation section.

[0019] On the other hand, the present application provides a one-step continuous preparation method for lactide, comprising the step of contacting lactic acid with a catalyst to react in the catalytic distillation device of the present application to obtain lactide, wherein a raw material containing lactic acid enters through the raw material inlet of the catalytic distillation device and contacts and reacts with the catalyst in the catalytic packing module in the reaction section, and an inert reaction gas enters through the gas inlet at the bottom of the reaction section, ascends through the reaction section, and strips part of the water and part of the unreacted lactic acid in the reaction material to the distillation section, and a crude lactide product is produced from the product outlet at the bottom of the reaction section.

[0020] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0021] (1) The catalytic packing module of the present application adopts a special layered structure design, in which the catalyst and inert filler are wrapped in layers, allowing the use of fine catalyst particles, providing sufficient gas-liquid contact area for the reaction, and ensuring sufficient contact between the reactants and the catalyst. In addition, it has the advantages of easy loading and unloading, stable operation, low catalyst wear, and timely adjustment of catalyst dosage.

[0022] (2) The first and second mesh layers of the catalytic filler module of the present application are allowed to be made of materials with different properties, so that the reaction target product and by-product components with different polarity or hydrophilicity can be separated in time, reducing the probability of reverse reaction between the two.

[0023] (3) In the structured catalytic packing of the present application, the catalytic packing modules and the packing modules are arranged alternately in the horizontal direction, which can not only achieve uniform distribution of the catalyst on the cross section of the reaction section of the catalytic distillation device, but also increase the liquid holdup and achieve sufficient contact between the reaction raw materials and the catalyst. At the same time, when multiple layers of structured catalytic packing are used in combination, and the catalytic packing modules and the packing modules of two adjacent layers of structured catalytic packing in the vertical direction are arranged in an upper and lower staggered manner, it can further achieve uniform distribution of the catalyst in the horizontal and vertical directions throughout the entire reaction section of the catalytic distillation device, and reduce the pressure drop of the bed layer, so that the generated light by-products can be removed from the reaction system in a timely manner.

[0024] (4) The present application applies a catalytic packing module with a special layered structure to a catalytic distillation device and to the process of continuous preparation of lactide from lactic acid by a one-step liquid phase method. This can improve heat and mass transfer, reduce tower pressure drop, and steadily and orderly remove free water and intermolecular bound water produced during the reaction, thereby ensuring the steady cyclization reaction of lactic acid dimers and trimers on the catalyst, avoiding the rapid rehydrolysis of lactide when it encounters water at high temperature, improving the reaction efficiency, and achieving continuous and stable operation during the reaction process, thereby realizing continuous production of lactide.

[0025] (5) The catalytic distillation device of the present application is applied to the process of producing lactide by liquid-phase cyclization of lactic acid, and can also effectively avoid the process of re-separation and activation of the catalyst and the reaction system in the traditional kettle reactor, effectively prolonging the service life of the catalyst and improving the catalyst utilization rate. The single-pass yield of lactide can reach more than 80%, the chemical purity of the crude lactide can reach more than 78%, and can reach up to 88%. The m-lactide content can be controlled within 2.0%.

[0026] Other features and advantages of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the following detailed description, they are used to explain the present application but do not constitute a limitation of the present application. In the accompanying drawings:

[0028] FIG1 shows a cross-sectional view of a preferred embodiment of the catalytic packing module of the present application;

[0029] FIG2 shows a cross-sectional view of a preferred embodiment of the structured catalytic packing of the present application, and a cross-sectional view of adjacent structured catalytic packings when multiple layers of structured catalytic packings are arranged in a longitudinally staggered manner;

[0030] FIG3 shows a cross-sectional view of another preferred embodiment of the structured catalytic packing of the present application, and a cross-sectional view of adjacent structured catalytic packings when multiple layers of structured catalytic packings are arranged in a longitudinally staggered manner;

[0031] FIG4 shows a schematic diagram of a preferred embodiment of the catalytic distillation device of the present application;

[0032] FIG5 shows a schematic diagram of a preferred embodiment of the first and second mesh layers of the catalytic packing module of the present application; and

[0033] FIG6 shows a schematic diagram of another preferred embodiment of the first and second mesh layers of the catalytic packing module of the present application.

[0034] Explanation of reference numerals 101 second mesh layer, 102 inert filler layer, 103 first mesh layer, 104 catalyst particle layer, 201 catalytic filler module, 202 filler module, 203 inner wall of catalytic distillation device, 401 catalytic distillation device, 411 distillation section, 412 reaction section, 413 top condenser. DETAILED DESCRIPTION

[0035] The following describes the specific embodiments of the present application in detail with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present application and are not intended to limit the present application.

[0036] Any specific numerical value disclosed herein (including the endpoints of a numerical range) is not limited to the exact value of the numerical value, but should be understood to also include values ​​close to the exact value, such as all possible values ​​within ±5% of the exact value. Moreover, for a disclosed numerical range, any combination of the endpoints of the range, between the endpoints and the specific points in the range, and between the specific points can be used to generate one or more new numerical ranges, and these new numerical ranges should also be considered to be specifically disclosed herein.

[0037] Unless otherwise specified, the terms used herein have the same meaning as commonly understood by those skilled in the art. If a term is defined herein and its definition is different from the commonly understood meaning in the art, the definition herein shall prevail.

[0038] In this application, except for the contents explicitly stated, any matters or issues not mentioned are directly applicable to aspects known in the art without any changes. Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solutions or technical ideas formed thereby are deemed to be part of the original disclosure or original record of this application, and should not be regarded as new content not disclosed or anticipated herein, unless a person skilled in the art considers that the combination is obviously unreasonable.

[0039] All patent and non-patent literature, including but not limited to textbooks and journal articles, mentioned herein are incorporated by reference in their entirety.

[0040] As described above, in the first aspect, the present application provides a catalytic packing module suitable for a catalytic distillation device, which includes, from the inside to the outside, a solid catalyst layer located in the center, a first mesh layer wrapped around the outside of the catalyst layer, an inert packing layer wrapped around the outside of the first mesh layer, and a second mesh layer wrapped around the outside of the inert packing layer.

[0041] The catalytic filler module of the present application adopts a special layered structure design, in which the solid catalyst and the inert filler are wrapped in layers, so that fine particle catalysts can be used, providing sufficient gas-liquid contact area for the reaction and ensuring sufficient contact between the reaction materials and the catalyst.

[0042] In a preferred embodiment, the first mesh layer and the second mesh layer are made of corrosion-resistant materials having different hydrophilic and / or oleophilic properties. Further preferably, the first mesh layer (also referred to as the mesh inner layer) wrapped around the outside of the catalyst layer and in contact therewith is made of a hydrophobic and corrosion-resistant material, for example, made of polyester, fluoropolymer or hydrophobic metal-based composite material, the material including but not limited to polycarbonate, polyvinylidene fluoride, fluorinated amphiphilic polymer, hydrophobic titanium-based composite material, etc.; and the second mesh layer (also referred to as the outer layer) wrapped around the outside of the inert filler layer and in contact therewith is made of a corrosion-resistant material with high permeability and hydrophilicity, for example, made of a hydrophilic fiber agglomerate material with high permeability, the material including but not limited to glass fiber fabric, surface coated, modified or grafted PVDF material, TiO2 material treated with surface chemical modification means such as SiO2 composite or ion doping.

[0043] In the preferred embodiment described above, the first and second mesh layers of the catalytic packing module are constructed of materials with different properties, enabling the timely separation of target reaction products and byproduct components with varying polarity or hydrophilicity, thereby reducing the likelihood of reverse reactions between the two. For example, when used in a one-step liquid-phase process for preparing lactide from lactic acid, the catalytic packing module ensures that lactic acid dimers and trimers rapidly enter the catalyst pores to react, while also ensuring that the generated small water molecules promptly exit the reaction system and aggregate into small droplets on the outer surface of the second mesh layer for rapid removal. This reduces the likelihood of reverse reactions between water and lactide, thereby improving the efficiency of the one-step liquid-phase process.

[0044] According to the present application, the first mesh layer and the second mesh layer can be various conventional mesh structures and can be selected according to the needs of the actual application. The present application does not have strict restrictions on this, as long as they can allow liquid to pass freely while preventing solid catalyst and inert filler from passing. In a preferred embodiment, the first mesh layer and the second mesh layer are each independently selected from a mesh material such as a corrugated mesh or a wire mesh. In addition, the first mesh layer and the second mesh layer themselves can be a single layer or multiple layers, and can be selected according to the needs of the actual application. The present application does not have strict restrictions on this.

[0045] According to the present application, the mesh shapes of the first mesh layer and the second mesh layer can be various conventional shapes, including but not limited to square, circle, diamond, triangle, hexagon, oblong, and plum blossom, etc., and can be selected according to actual application needs. This application does not strictly limit this. In a preferred embodiment, the mesh shapes of the first mesh layer and the second mesh layer are each independently selected from the group consisting of circle and oblong.

[0046] According to the present application, the porosity and mesh size of the first and second mesh layers can be selected according to the needs of the actual application, and this application does not strictly limit this. In a preferred embodiment, the porosity of the first and second mesh layers is independently 50.0-70.0%, and the mesh size is independently 7-30 mesh, preferably 10-25 mesh.

[0047] In the catalytic packing module of the present application, the inert filler can separate the first and second mesh layers, in particular the first and second mesh layers made of different materials, and help to achieve the enrichment of different reaction products (such as water and lactide) at the first and second mesh layers, respectively, to reduce the probability of contact between the two reaction products, reduce the probability of reverse reaction, and play a role in product separation. According to the present application, the inert filler can be an inert filler commonly used in various catalytic distillation devices, and can be selected according to actual application needs, and the present application has no strict restrictions on this. In a preferred embodiment, the inert filler is selected from glass balls, ceramic rings, ceramic balls, ceramic skeletons, quartz sand, silica sand, bentonite, or a combination thereof. Further preferably, the particle size of the filler is 1.0-2.0 mm.

[0048] According to the present application, the solid catalyst contained in the catalytic filler module can be selected according to the specific catalytic reaction applied, and the present application has no strict restrictions on this. For example, when used in the reaction of preparing lactide by a one-step liquid phase method of lactic acid, the catalyst contained in the catalytic filler module can be various conventionally used solid catalysts capable of catalyzing the liquid phase reaction of lactic acid to generate lactide, preferably a catalyst based on a molecular sieve loaded with Sn and / or Ti, more preferably a catalyst based on a Beta molecular sieve loaded with Sn and / or Ti, and particularly preferably a catalyst based on a Beta molecular sieve loaded with Sn and Ti. The catalyst can be prepared by various known catalyst preparation methods, such as conventional impregnation loading methods, and the present application has no strict restrictions on this.

[0049] According to the present application, the catalyst can be a catalyst shape and structure commonly used in various catalytic distillation devices, and can be selected according to actual application needs, and the present application has no strict restrictions on this. In a preferred embodiment, the catalyst is a spherical or porous spherical shape with a diameter of 1-5mm, a cylindrical or porous cylindrical shape with a diameter of 0.5-3mm and a length of 1-5mm, or a clover-shaped or polyhedral shape with an equivalent diameter of 1-5mm. The catalyst can be made into the desired shape and structure by various known catalyst molding methods, such as powder extrusion molding technology.

[0050] Figure 1 shows a schematic diagram of a preferred embodiment of the catalytic packing module of the present application, wherein the module includes, from the inside to the outside, a catalyst particle layer 104 located in the center, a first mesh layer 103 wrapped around the outside of the catalyst layer, an inert packing layer 102 wrapped around the outside of the first mesh layer, and a second mesh layer 101 wrapped around the outside of the inert packing layer.

[0051] Figure 5 shows a schematic diagram of a preferred embodiment of the first and second mesh layers of the catalytic packing module of the present application. As shown in the figure, in this preferred embodiment, the first mesh layer and / or the second mesh layer is in the form of a circular hole corrugated mesh.

[0052] Figure 6 shows a schematic diagram of another preferred embodiment of the first and second mesh layers of the catalytic packing module of the present application. As shown in the figure, in this preferred embodiment, the first mesh layer and / or the second mesh layer are in the form of a circular mesh.

[0053] In a second aspect, the present application provides a structured catalytic packing, comprising catalytic packing modules and packing modules alternately arranged in a horizontal direction, wherein the catalytic packing modules are the catalytic packing modules of the present application.

[0054] According to the present application, the packing modules may be of the structure and form commonly used in various catalytic distillation devices and may be selected based on the needs of the actual application. This application does not impose strict restrictions on this. In a preferred embodiment, the packing modules are composed of stainless steel wire mesh corrugated packing, which can provide support for adjacent catalytic packing modules.

[0055] According to the present application, in the structured catalytic packing, the catalytic packing modules and the packing modules are arranged alternately in the horizontal direction, for example, they are arranged alternately in the form of "catalytic packing module||packing module||catalytic packing module||packing module". The specific arrangement method can be selected according to actual application needs. The present application does not have strict restrictions on this, as long as any two catalytic packing modules are not adjacent in the horizontal direction and any two packing modules are not adjacent.

[0056] FIG2 shows a schematic diagram of a preferred embodiment of the structured catalytic packing of the present application, wherein the catalytic packing modules 201 and the packing modules 202 are alternately arranged in a horizontal direction.

[0057] FIG3 shows a schematic diagram of another preferred embodiment of the structured catalytic packing of the present application, wherein the catalytic packing modules and the packing modules are alternately arranged in both horizontal directions.

[0058] In the structured catalytic packing of the present application, the alternating arrangement of the catalytic packing modules and the packing modules in the horizontal direction can not only achieve uniform distribution of the catalyst on the cross-section of the reaction section of the catalytic distillation device, but also increase the liquid holdup and achieve sufficient contact between the reaction raw materials and the catalyst. At the same time, when multiple layers of structured catalytic packing are used in combination, and the catalytic packing modules and the packing modules of two adjacent layers of structured catalytic packing in the vertical direction are staggered up and down, the catalyst can be further uniformly distributed in the entire reaction section of the catalytic distillation device in the horizontal and vertical directions, and the pressure drop of the bed can be reduced, so that the generated light by-products can be removed from the reaction system in a timely manner.

[0059] In a third aspect, the present application provides a catalytic distillation device, comprising an upper distillation section and a lower reaction section, a raw material inlet being provided between the upper distillation section and the lower reaction section, wherein the lower reaction section is filled with at least one layer of the structured catalytic filler of the present application.

[0060] In a preferred embodiment, the lower reaction section of the catalytic distillation device is filled with multiple layers, generally 4-16 layers, of the structured catalytic packing of the present application, and in the vertical direction, the catalytic packing modules and the packing modules of two adjacent layers of structured catalytic packing in the multiple layers of structured catalytic packing are staggered up and down.

[0061] In such a preferred embodiment, in the catalytic distillation device, in the vertical direction, the catalytic packing modules and the packing modules of the adjacent two layers of structured catalytic packing are arranged in an up-down staggered manner, so that in the vertical direction, the catalytic packing modules and the packing modules of the multiple layers of structured catalytic packing are arranged alternately, that is, the catalytic packing modules of the lower layer of structured catalytic packing are above the packing modules of the adjacent upper layer of structured catalytic packing, and the packing modules of the lower layer of structured catalytic packing are above the catalytic packing modules of the adjacent upper layer of structured catalytic packing, and so on. This can not only make the catalyst uniformly distributed in the entire reaction section of the catalytic distillation device in the horizontal and vertical directions, but also increase the liquid holdup, achieve full contact between the reaction raw materials and the catalyst, and at the same time reduce the pressure drop of the entire reaction section, so that the generated light by-products can be removed from the reaction system in a timely manner. For example, when used in the process of continuously preparing lactide from lactic acid in a one-step liquid phase process, the catalytic distillation device can not only increase the liquid holdup, achieve full contact between lactic acid polymers and the catalyst, but also reduce the pressure drop of the entire reaction section, promote the timely escape of water in a relatively viscous system, and improve the reaction efficiency.

[0062] Figures 2 and 3 show a preferred embodiment of the arrangement of multiple layers of structured catalytic packing in the catalytic distillation device of the present application, wherein the structured catalytic packing on the left and the structured catalytic packing on the right are arranged adjacent to each other up and down, so that the catalytic packing modules and packing modules of the lower layer of structured catalytic packing and the catalytic packing modules and packing modules of the upper layer of structured catalytic packing are staggered up and down.

[0063] According to the present application, the upper rectifying section of the catalytic distillation apparatus may be equipped with various internal components and / or packing commonly used in the rectifying sections of catalytic distillation apparatuses, and these components may be selected based on actual application needs, and the present application does not impose strict restrictions thereon. For example, in certain preferred embodiments, the upper rectifying section of the catalytic distillation apparatus of the present application is packed with structured packing selected from titanium wire mesh corrugated packing, perforated plate corrugated packing, or a combination thereof, to separate light components from entrained relatively heavy components.

[0064] In a preferred embodiment, the catalytic distillation device further includes a condenser disposed at the top, which can achieve cooling and separation of the vapor phase at the top of the device. For example, in the process of preparing lactide from lactic acid by a one-step liquid phase method, rapid separation of water and non-condensable steam (reaction inert gas) can be achieved. The separated non-condensable steam can be directly recycled after dehydration and heating.

[0065] In a preferred embodiment, the catalytic distillation device further comprises a gas inlet and a product outlet arranged at the bottom of the reaction section.

[0066] Optionally, as needed, a raw material distributor may be provided at the raw material inlet of the catalytic distillation device, and / or a gas distributor may be provided at the gas inlet, so as to evenly distribute the raw material and / or gas over the cross section of the reaction section.

[0067] Optionally, a reboiler may be provided at the bottom of the catalytic distillation device as required.

[0068] FIG4 shows a schematic diagram of a preferred embodiment of the catalytic distillation apparatus of the present application, wherein the catalytic distillation apparatus 401 is in the form of a catalytic distillation tower, comprising an upper distillation section 411 and a lower reaction section 412. The reaction section 412 is filled with multiple layers of the structured catalytic packing of the present application, and a feed inlet is provided between the upper distillation section 411 and the lower reaction section 412. The catalytic distillation apparatus also includes a condenser 413 disposed at the top, and a gas inlet and product outlet disposed at the bottom of the reaction section. Optionally, a gas distributor may also be provided at the gas inlet.

[0069] In a fourth aspect, the present invention provides an application of the catalytic packing module, structured catalytic packing or catalytic distillation device in the solid-phase catalytic reaction of liquid raw materials, particularly in the reaction process of preparing lactide from lactic acid via a liquid-phase one-step method.

[0070] The catalytic packing module, structured catalytic packing or catalytic distillation device of the present application is suitable for various solid-phase catalytic reactions of liquid raw materials suitable for catalytic distillation, such as the synthesis reaction of lactate, the synthesis reaction of isosorbide, the synthesis reaction of furandicarboxylic acid, etc.

[0071] In a preferred embodiment, the first mesh layer and the second mesh layer of the catalytic filler module are made of corrosion-resistant materials having different hydrophilic and / or oleophilic properties.

[0072] In a further preferred embodiment, the first mesh layer of the catalytic packing module is made of a hydrophobic and corrosion-resistant material, such as polyester, fluoropolymer or metal composite material, in particular made of polyvinylidene fluoride; and the second mesh layer of the catalytic packing module is made of a highly permeable and hydrophilic corrosion-resistant material, such as a highly permeable hydrophilic fiber agglomerate material, in particular made of glass fiber fabric.

[0073] In a fifth aspect, a catalytic distillation reaction method is provided, comprising the steps of allowing a liquid raw material to contact and react with a solid catalyst arranged in the catalytic packing module in the reaction section of the catalytic distillation device of the present application, and the steps of separating the obtained reaction products in the distillation section.

[0074] In a preferred embodiment, the first mesh layer and the second mesh layer of the catalytic filler module are made of corrosion-resistant materials having different hydrophilic and / or oleophilic properties.

[0075] In a sixth aspect, a one-step continuous preparation method for lactide is provided, comprising the step of contacting lactic acid with a catalyst to react in the catalytic distillation apparatus of the present application to obtain lactide, wherein a raw material containing lactic acid enters through the raw material inlet of the catalytic distillation apparatus and contacts and reacts with the catalyst in the catalytic packing module in the reaction section, and a reaction inert gas enters through the gas inlet at the bottom of the reaction section, ascends through the reaction section, and strips part of the water and part of the unreacted lactic acid in the reaction material therein to the distillation section, and a crude lactide product is produced from the product outlet at the bottom of the reaction section.

[0076] In a preferred embodiment, the first mesh layer of the catalytic packing module is made of a hydrophobic and corrosion-resistant material, such as polyester, fluoropolymer or metal composite material, in particular polyvinylidene fluoride; and the second mesh layer of the catalytic packing module is made of a highly permeable and hydrophilic corrosion-resistant material, such as a highly permeable hydrophilic fiber agglomerate material, in particular glass fiber fabric.

[0077] In a preferred embodiment, the number of theoretical plates of the distillation section of the catalytic distillation device in the method is 4-8, thereby being able to fully separate the lactic acid entrained in the gas phase and improve the reaction conversion rate.

[0078] In a preferred embodiment, the number of theoretical plates in the reaction section of the catalytic distillation device in the method is 2-8, which can fully promote the esterification reaction between lactic acid molecules to produce lactic acid polymers, and ensure that lactic acid dimers and trimers are fully cyclized to produce lactide, thereby improving the product yield.

[0079] In a preferred embodiment, the reflux ratio of the distillation section of the catalytic distillation device in the method is 2:1 to 1:5, for example 1:2 to 1:5, to ensure smooth operation of the purification process in the distillation section of the catalytic reaction device. Further preferably, the operating conditions in the distillation section of the catalytic distillation device further include: a tower top temperature of 95-140°C and a tower top pressure of 0.02-0.1 MPa absolute pressure.

[0080] In a preferred embodiment, the catalyst in the catalytic packing module is a catalyst based on a molecular sieve loaded with Sn and / or Ti, more preferably a catalyst based on a Beta molecular sieve loaded with Sn and / or Ti, and particularly preferably a catalyst based on a Beta molecular sieve loaded with Sn and Ti.

[0081] In a preferred embodiment, the catalyst loading in the catalytic packing module in the reaction section of the catalytic distillation device in the method is 0.1-0.6 cm 3 , preferably 0.2-0.6cm 3 , more preferably 0.3-0.6cm 3 Catalyst volume / cm 3 Reaction zone volume.

[0082] In a preferred embodiment, the inert filler loading in the catalytic filler module in the reaction section of the catalytic distillation device in the method is 0.05-0.3 cm 3 , preferably 0.1-0.3cm 3 , more preferably 0.1-0.25cm 3 Inert filler / cm 3 Reaction zone volume.

[0083] In a preferred embodiment, the pressure in the reaction zone of the catalytic distillation device in the method is 0.05-0.15 MPa absolute pressure, preferably 0.08-0.12 MPa.

[0084] In a preferred embodiment, the reaction temperature in the reaction zone of the catalytic distillation device in the method is 100-160° C., preferably 120-140° C., and the residence time of the raw material containing lactic acid in the reaction zone is 20-60 min.

[0085] In a preferred embodiment, the raw material containing lactic acid in the method is a 30-60 wt% lactic acid aqueous solution, and the feed temperature is 80-100°C.

[0086] In the method of the present application, the reaction inert gas refers to a gas that does not affect the reaction process, such as nitrogen. The inert gas is introduced from the bottom of the reaction zone to strip the free water or bound water in the reaction zone. This method can avoid the use of organic solvents. The pressure of the inert gas is slightly greater than the reaction pressure to ensure smooth upward flow. In a preferred embodiment, the temperature of the inert gas in the method is 110-160°C and the introduction pressure is 0.08-0.2 MPa absolute pressure.

[0087] As shown in Figure 4, in a preferred embodiment of the method of the present application, lactic acid feedstock 100 is fed between the distillation section 411 and the reaction section 412 through the feedstock inlet, then enters the reaction section 412, where lactide is generated under the action of the catalyst. Reaction inert gas 200 is introduced into the bottom of the reaction section 412 through the gas inlet, ascends through the reaction section 412, and strips some water and some unreacted lactic acid in the reaction system to the distillation section 411. Lactic acid is separated in the distillation section 411, and a mixture of water vapor and inert gas 400 enters the condenser 413 from the top of the device to achieve separation. After condensation, the liquid phase component 500, which is mainly water, is partially refluxed and partially discharged from the system. The recovered inert gas 600 is dried, heated, and returned to the bottom of the catalytic distillation device. A crude lactide product 300 is withdrawn from the bottom of the reaction section 412.

[0088] The method of this application produces a crude lactide product extracted from the bottom of the reaction section with a weight composition of 76.0-86.0% L-lactide, ≤2.0% m-lactide, 1.0-4.0% L-lactic acid, 1.0-4.0% lactic acid dimer, 1.0-6.0% trimer, and 1.0-8.0% lactic acid polymer. The single-pass lactide yield during the synthesis process can exceed 80%.

[0089] In a preferred embodiment, the method of the present application further comprises the steps of pre-treating, refining and purifying the crude lactide product to obtain a lactide product. The pre-treatment and refining and purification of the crude lactide product can be performed by methods well known to those skilled in the art.

[0090] In certain further preferred embodiments, the pretreatment is to wash the crude lactide with a mixture of water and ethanol to remove unreacted lactic acid and polymers therein, and the washing temperature is 0-10°C to reduce the hydrolysis rate of water on lactide and the solubility of ethanol in lactide, thereby improving the product yield.

[0091] In some further preferred embodiments, the pretreatment is in the form of rinsing the crude lactide with a dilute alkaline solution and then rinsing with cold water to remove unreacted lactic acid and lactic acid polymers, and the rinsing temperature is 0-10°C.

[0092] In the above two further preferred embodiments, the crude lactide is washed, filtered, centrifuged, and then sent to a cyclone dryer or a rotary drum vacuum dryer for drying.

[0093] In a preferred embodiment, after pretreatment of crude lactide, the lactide yield can reach above 92.0%, wherein the purity of L-lactide can reach above 92%, meeting the requirements for subsequent refining and purification.

[0094] In a preferred embodiment, the refining and purification is to further treat the pretreated lactide through a melt crystallization or distillation process to obtain a lactide product to meet polymerization requirements.

[0095] Example

[0096] The present application is further described in detail below with reference to examples, but the present application is not limited to these examples.

[0097] The experiments in the following examples were conducted in the catalytic distillation apparatus shown in Figure 4. The catalytic distillation column was 1.8 m tall and 80 mm in diameter. Its lower reaction section was filled with multiple layers of structured catalytic packing assembled from catalytic packing modules and packing modules. The first mesh layer in the catalytic packing module used polyvinylidene fluoride wire mesh with a circular mesh shape, an open porosity of 60.0%, and a mesh size of 14 mesh. The second mesh layer used a glass fiber mesh with a circular mesh shape, an open porosity of 65.0%, and a mesh size of 18 mesh. The inert filler used ceramic rings with a particle size of 1.6 mm. The packing module consisted of stainless steel wire mesh corrugated packing. The catalytic packing modules and packing modules were arranged alternately horizontally as shown in Figures 2 or 3 to form the structured catalytic packing. Multiple layers were then installed vertically as shown in Figures 2 or 3 to fill the entire reaction section of the catalytic distillation apparatus. The upper distillation section of the catalytic distillation apparatus was filled with structured packing assembled from titanium wire mesh corrugated packing.

[0098] The experimental methods used in the following examples and comparative examples, unless otherwise specified, are conventional methods in the art; the experimental materials used, unless otherwise specified, can be purchased from biochemical reagent stores.

[0099] The lactic acid used in the following examples and comparative examples is heat-resistant grade L-lactic acid, and its optical purity is not less than 99.0%.

[0100] In the following examples and comparative examples, the chemical purity of lactide was analyzed using an Agilent high-performance liquid chromatograph with a UV detector, phosphoric acid and acetonitrile as the mobile phase, and a ZORBAX SB-Aq column with a length of 250 mm, an inner diameter of 4.6 mm, and a filler particle size of 5 μm. The detection wavelength was 200 nm, the column temperature was 40°C, the flow rate was 1 mL / min, and the injection volume was 5 μL.

[0101] In the following examples and comparative examples, an Agilent gas chromatograph was used to analyze the content of different optical isomers of lactide. A CYCLOSIL-B column was used, with a vaporizer temperature of 250°C, a detector temperature of 280°C, and a flame ionization detector. The column temperature was programmed to start at 100°C, hold for 5 minutes, increase the temperature at a rate of 4°C / min to 140°C, hold for 7 minutes, and then increase the temperature at a rate of 8°C / min to 200°C, hold for 20 minutes. The carrier gas flow rates were 1.4 mL / min for N2, 30 mL / min for hydrogen, and 400 mL / min for air. The injection volume was 0.5 μL.

[0102] In the following examples and comparative examples, the yield Y of the process for preparing lactide by the one-step liquid phase cyclization of lactic acid is calculated as follows:

[0103] Among them, m0 is the lactic acid feed rate, x0 is the content of pure lactic acid in the feed, M 丙 is the molecular weight of lactide, M 乳 is the molecular weight of lactic acid, and m is the production rate of L-lactide.

[0104] Example 1

[0105] After the L-lactic acid aqueous solution with a concentration of 50 wt% was heated to 90°C, it was continuously transported to the catalytic distillation device at a flow rate of 2.0 kg / h. The number of theoretical plates in the distillation section was 6, the condensation temperature of the top condenser was 20°C, the tower top temperature was 125°C, the tower top pressure was 0.08 MPa absolute pressure, the reflux ratio was 1:3, and the reaction section was equipped with 12 layers of structured catalytic packing (corresponding to 6 theoretical plates). The packing method shown in Figure 2 was adopted. The catalytic packing module on the structured catalytic packing was a catalytic packing module filled with Sn / Ti-Beta molecular sieve catalyst. The catalyst was in the form of spherical particles with a particle size of 2 mm. Based on the volume of the entire reaction section, the catalyst loading in the catalytic packing module was 0.40 cm 3 Catalyst / cm 3 Reaction zone volume, inert filler loading in catalytic filler module is 0.15cm 3 Inert filler / cm 3 The reaction zone volume, reaction pressure, reaction temperature were 0.1 MPa, reaction time within the reaction zone was 40 minutes. N2 stripping gas was introduced into the bottom of the reaction zone at a rate of 5.0 L / h, temperature of 140°C, and pressure of 0.15 MPa. The crude lactide product was withdrawn from the bottom of the reaction zone at a rate of 0.80 kg / h.

[0106] Analysis and calculations show that the single-pass lactide yield during the catalytic distillation reaction can reach 83.1%. The crude lactide product contains 84.3% L-lactide, 1.2% m-lactide, 2.1% L-lactic acid, 2.7% lactic acid dimers, 3.6% lactic acid trimers, and 6.3% lactic acid polymers (tetramers and higher).

[0107] The crude lactide was centrifuged and washed with 0.1 mol / L sodium hydroxide. After washing with water, it was dried in a rotary vacuum dryer at 40°C for 8 hours to obtain pretreated lactide with a purity of 93.7%. The lactide was then refined by melt crystallization to obtain a lactide product that met polymerization requirements.

[0108] Example 2

[0109] After the L-lactic acid aqueous solution with a concentration of 30 wt% was heated to 90°C, it was continuously transported to the catalytic distillation device at a flow rate of 2.0 kg / h. The number of theoretical plates in the distillation section was 8, the condensation temperature of the top condenser was 10°C, the tower top temperature was 105°C, the tower top pressure was 0.05 MPa absolute pressure, the reflux ratio was 1:5, and the reaction section was equipped with 16 layers of structured catalytic packing (corresponding to 8 theoretical plates). The packing method shown in Figure 3 was adopted. The catalytic packing module on the structured catalytic packing was a catalytic packing module filled with Sn / Ti-Beta molecular sieve catalyst. The catalyst was in the form of cylindrical particles with a diameter of 2 mm and a length of 4 mm. Based on the volume of the entire reaction section, the catalyst loading in the catalytic packing module was 0.40 cm 3 Catalyst / cm 3 Reaction zone volume, inert filler loading in catalytic filler module is 0.10 cm 3 Inert filler / cm 3 The reaction zone volume, reaction pressure, reaction temperature were 0.08 MPa, and the material residence time in the reaction zone was 30 minutes. N2 was introduced as stripping gas at the bottom of the reaction zone at a flow rate of 4.0 L / h, temperature of 120°C, and pressure of 0.15 MPa. The crude lactide product was withdrawn from the bottom of the reaction zone at a flow rate of 0.49 kg / h.

[0110] Analysis and calculations show that the single-pass lactide yield during the catalytic distillation reaction can reach 83.9%. The crude lactide product contains 81.8% L-lactide, 1.0% m-lactide, 2.4% L-lactic acid, 3.5% lactic acid dimers, 5.7% lactic acid trimers, and 5.1% lactic acid polymers (tetramers and higher).

[0111] The crude lactide was centrifuged and then washed with water and ethanol, respectively, at 10°C. The solid powder was then dried in a vacuum dryer at 40°C for 6 hours to obtain pretreated lactide with a purity of 94.5%. The lactide was then refined by melt crystallization to obtain a lactide product that met polymerization requirements.

[0112] Example 3

[0113] After the L-lactic acid aqueous solution with a concentration of 60 wt% was heated to 100° C., it was continuously transported to the catalytic distillation device at a flow rate of 2.0 kg / h. The number of theoretical plates in the distillation section was 4, the condensation temperature of the top condenser was 10° C., the tower top temperature was 135° C., the tower top pressure was 0.1 MPa absolute pressure, the reflux ratio was 1:2, and the reaction section was equipped with 8 layers of structured catalytic packing (corresponding to 4 theoretical plates). The packing method shown in FIG2 was adopted. The catalytic packing module on the structured catalytic packing was a catalytic packing module loaded with Sn / Ti-Beta molecular sieve catalyst. The catalyst was in the form of spherical particles with a particle size of 2 mm. Based on the volume of the entire reaction section, the catalyst loading in the catalytic packing module was 0.48 cm 3 Catalyst / cm 3 Reaction zone volume, inert filler loading in catalytic filler module is 0.15cm 3 Inert filler / cm 3 The reaction zone volume, reaction pressure, reaction temperature were 0.15 MPa, and the material residence time in the reaction zone was 20 minutes. N2 stripping gas was introduced into the bottom of the reaction zone at a flow rate of 6.0 L / h, temperature of 160°C, and pressure of 0.15 MPa. The crude lactide product was withdrawn from the bottom of the reaction zone at a flow rate of 0.97 kg / h.

[0114] Analysis and calculations show that the single-pass lactide yield during the catalytic distillation reaction can reach 81.2%. The crude lactide product contains 80.3% L-lactide, 1.9% m-lactide, 1.7% L-lactic acid, 2.8% lactic acid dimers, 4.6% lactic acid trimers, and 7.9% lactic acid polymers (tetramers and higher).

[0115] The crude lactide was centrifuged and then washed with water and ethanol, respectively, at 10°C. The solid powder was then dried in a vacuum dryer at 40°C for 6 hours to obtain pretreated lactide with a purity of 94.1%. The lactide was then refined by melt crystallization to obtain a lactide product that met polymerization requirements.

[0116] Example 4

[0117] The experiment was conducted with reference to Example 1, except that the catalytic packing module on the structured catalytic packing was a catalytic packing module loaded with Sn-Beta molecular sieve catalyst (ie, Beta molecular sieve catalyst loaded only with Sn).

[0118] The crude lactide output from the bottom of the reaction section of the catalytic distillation unit is 0.82 kg / h, with a single-pass lactide yield of 81.5%. The crude lactide product contains 79.4% L-lactide, 1.4% m-lactide, 2.6% L-lactic acid, 3.7% lactic acid dimers, 5.7% lactic acid trimers, and 7.0% lactic acid polymers (tetramers and higher).

[0119] Example 5

[0120] The experiment was conducted with reference to Example 1, except that the catalytic packing module on the structured catalytic packing was a catalytic packing module loaded with Ti-Beta molecular sieve catalyst (ie, Beta molecular sieve catalyst loaded only with Ti).

[0121] The crude lactide output from the bottom of the reaction section of the catalytic distillation unit is 0.83 kg / h, with a single-pass lactide yield of 81.0%. The crude lactide product contains 78.2% L-lactide, 1.6% m-lactide, 2.9% L-lactic acid, 3.8% lactic acid dimers, 5.7% lactic acid trimers, and 7.5% lactic acid polymers (tetramers and higher).

[0122] Comparative Example 1

[0123] A one-step liquid-phase process for producing lactide from lactic acid was conducted using a glass kettle reactor. The raw materials, catalyst, reaction temperature, and pressure used in this experiment were the same as in Example 1. A glass three-necked flask was used, and the reaction was conducted in an oil bath. 50 mL of lactic acid and 100 mL of toluene were added to the glass flask. The reaction was carried out at 125°C for 6 hours. A condenser separator was used to separate the evaporated water and toluene, and the toluene was then refluxed into the reaction system, acting as a water carrier.

[0124] After the reaction, analysis of the components at the bottom of the reactor revealed an L-lactide content of 74.5%, an m-lactide content of 1.7%, an L-lactic acid content of 2.5%, a lactic acid dimer content of 2.9%, a lactic acid trimer content of 4.6%, and a lactic acid polymer content of 14.6%. The lactide yield was 63.2%.

[0125] Comparative Example 2

[0126] The raw materials, catalyst, catalyst and inert filler loadings, and reaction process conditions were similar to those of Example 1, except that the catalytic filler modules in the structured catalytic packing in the reaction section of the catalytic distillation apparatus were composed of a mixture of catalyst and inert filler, which was then wrapped with a wire mesh. These modules were arranged alternately in the horizontal direction with the filler modules. Furthermore, the upper and lower layers of structured catalytic packing were staggered as in Example 1, and the crude lactide product was still withdrawn from the bottom of the reaction section.

[0127] Analysis of the crude lactide product revealed 75.9% L-lactide, 1.3% m-lactide, 2.3% L-lactic acid, 3.9% lactic acid dimer, 6.2% lactic acid trimer, and 10.1% lactic acid polymers (tetramers and higher). The single-pass lactide yield was only 69.4%.

[0128] Comparative Example 3

[0129] The raw materials, catalyst, catalyst loading and reaction process conditions are similar to those of Example 1, except that the catalyst and inert filler in the reaction section of the catalytic distillation device are mixed evenly and then loaded into the entire reaction section, and sieve plate support structures are respectively provided at the upper and lower ends of the catalytic reaction section to fix the catalytic reaction zone and prevent the gas from entraining the catalyst. The catalyst loading is 0.40 cm 3 Catalyst / cm 3 Reaction zone volume, inert filler loading is 0.60 cm 3 Inert filler / cm 3 The reaction section volume is reduced, and the crude lactide product is still produced from the bottom of the reaction section.

[0130] Analysis of the crude lactide product revealed 72.7% L-lactide, 1.2% m-lactide, 5.2% L-lactic acid, 4.5% lactic acid dimers, 5.9% lactic acid trimers, and 10.3% lactic acid polymers (tetramers and higher). The single-pass lactide yield was only 60.3%.

[0131] Comparative Example 4

[0132] The raw materials, catalyst, catalyst and inert filler loadings, and reaction process conditions were similar to those of Example 1, except that the reaction section of the catalytic distillation apparatus employed a layered loading of catalytic filler and structured filler. Specifically, a layer of mixed catalyst and inert filler wrapped in wire mesh and a layer of structured filler were alternately arranged. A sieve plate support structure was provided at the lower end of the catalytic reaction section, and crude lactide product was still withdrawn from the bottom of the reaction section.

[0133] Analysis of the crude lactide product revealed 75.4% L-lactide, 1.5% m-lactide, 2.2% L-lactic acid, 4.7% lactic acid dimers, 5.9% lactic acid trimers, and 10.1% lactic acid polymers (tetramers and higher). The single-pass lactide yield was only 70.9%.

[0134] By comparing the results of Examples 1-5 and Comparative Example 1, it can be clearly seen that the catalytic distillation device and process of the present application can ensure the quality of the product and improve the yield of the product while achieving continuous operation of the reaction process.

[0135] By comparing the results of Examples 1-5 with Comparative Examples 2, 3, and 4, it can be clearly seen that the use of a catalytic distillation apparatus having a reaction section filled with the structured catalytic filler of the present application can effectively improve the reaction efficiency, reduce the rehydrolysis of the lactide generated by the reaction, and significantly increase the single-pass yield of the reaction.

[0136] The preferred embodiments of the present application are described in detail above. However, the present application is not limited to the specific details of the above embodiments. Within the technical concept of the present application, various simple modifications can be made to the technical solution of the present application, and these simple modifications all fall within the scope of protection of the present application.

[0137] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner unless there is any contradiction. In order to avoid unnecessary repetition, this application will not further describe various possible combinations.

[0138] In addition, the various implementation methods of the present application may be arbitrarily combined, and as long as they do not violate the concept of the present application, they should also be regarded as the contents disclosed in the present application.

Claims

1. A catalytic packing module suitable for a catalytic distillation device, comprising, from the inside to the outside, a solid catalyst layer located in the center, a first mesh layer wrapped around the outside of the catalyst layer, an inert packing layer wrapped around the outside of the first mesh layer, and a second mesh layer wrapped around the outside of the inert packing layer.

2. The catalytic packing module according to claim 1, wherein the first mesh layer and the second mesh layer are made of corrosion-resistant materials having different hydrophilic and / or oleophilic properties; Preferably, the first mesh layer is made of a hydrophobic and corrosion-resistant material, such as polyester, fluoropolymer or metal composite material, in particular made of polyvinylidene fluoride; and the second mesh layer is made of a highly permeable and hydrophilic corrosion-resistant material, such as a highly permeable hydrophilic fiber aggregate material, in particular made of glass fiber fabric.

3. The catalytic packing module according to claim 1 or 2, having one or more of the following features: The first mesh layer and the second mesh layer are each independently in the form of a corrugated mesh or a wire mesh; The opening rate of the first mesh layer and the second mesh layer is independently 50.0-70.0%, and the mesh size is independently 7-30 mesh, preferably 10-25 mesh; The inert filler is selected from glass balls, ceramic rings, ceramic balls, ceramic skeletons, quartz sand, silica sand, bentonite, or a combination thereof, and preferably the particle size of the filler is 1.0-2.0 mm; and The catalyst is in the form of a sphere or porous sphere with a diameter of 1-5 mm, a cylinder or porous cylinder with a diameter of 0.5-3 mm and a length of 1-5 mm, or a cloverleaf or polyhedron with an equivalent diameter of 1-5 mm.

4. The catalytic packing module according to any one of claims 1 to 3, wherein the catalyst is a catalyst based on a molecular sieve loaded with Sn and / or Ti, preferably a catalyst based on a Beta molecular sieve loaded with Sn and / or Ti, particularly preferably a catalyst based on a Beta molecular sieve loaded with Sn and Ti.

5. A structured catalytic packing, comprising catalytic packing modules and packing modules arranged alternately in a horizontal direction, wherein the catalytic packing modules are the catalytic packing modules according to any one of claims 1 to 4, Preferably, the packing module is composed of stainless steel wire mesh corrugated packing.

6. A catalytic distillation device comprising an upper distillation section and a lower reaction section, wherein a raw material inlet is provided between the upper distillation section and the lower reaction section, wherein the lower reaction section is filled with at least one layer of the structured catalytic packing according to claim 5, Preferably, the lower reaction section of the catalytic distillation device is filled with multiple layers, preferably 4-16 layers, of the structured catalytic packing according to claim 5, and in the vertical direction, the catalytic packing modules and packing modules of two adjacent layers of structured catalytic packing in the multiple layers of structured catalytic packing are staggered up and down.

7. The catalytic distillation device according to claim 6, wherein the upper distillation section of the catalytic distillation device is filled with structured packing selected from titanium wire mesh corrugated packing, perforated plate corrugated packing, or a combination thereof.

8. The catalytic distillation device according to claim 6 or 7, further comprising a condenser arranged at the top, and a gas inlet and a product outlet arranged at the bottom of the reaction section, Optionally, a raw material distributor is provided at the raw material inlet of the catalytic distillation device, and / or a gas distributor is provided at the gas inlet; and Optionally, a reboiler is further provided at the bottom of the catalytic distillation device.

9. Use of the catalytic packing module according to any one of claims 1 to 4, the structured catalytic packing according to claim 5, or the catalytic distillation device according to any one of claims 6 to 8 in a solid-phase catalytic reaction of a liquid raw material, particularly in a liquid-phase one-step process for preparing lactide from lactic acid. Preferably, the first mesh layer and the second mesh layer of the catalytic filler module are made of corrosion-resistant materials having different hydrophilic and / or oleophilic properties; Further preferably, the first mesh layer of the catalytic packing module is made of a hydrophobic and corrosion-resistant material, such as polyester, fluoropolymer or metal composite material, in particular made of polyvinylidene fluoride; and the second mesh layer of the catalytic packing module is made of a highly permeable and hydrophilic corrosion-resistant material, such as a highly permeable hydrophilic fiber agglomerate material, in particular made of glass fiber fabric.

10. A catalytic distillation reaction method, comprising the steps of contacting and reacting a liquid feedstock with a solid catalyst disposed within the catalytic packing module in a reaction section of the catalytic distillation apparatus according to any one of claims 6 to 8, and separating the resulting reaction products in a distillation section; Preferably, the first mesh layer and the second mesh layer of the catalytic filler module are made of corrosion-resistant materials having different hydrophilic and / or oleophilic properties.

11. A one-step continuous method for preparing lactide, comprising the step of contacting lactic acid with a catalyst in a catalytic distillation apparatus according to claim 8 to react to obtain lactide, wherein a feedstock containing lactic acid enters the catalytic distillation apparatus through a feedstock inlet and reacts with a catalyst in a catalytic packing module in a reaction section, an inert reaction gas enters through a gas inlet at the bottom of the reaction section, ascends through the reaction section, and strips part of the water and unreacted lactic acid in the reaction material to the distillation section, and a crude lactide product is withdrawn from a product outlet at the bottom of the reaction section. Preferably, the first mesh layer of the catalytic packing module is made of a hydrophobic and corrosion-resistant material, such as polyester, fluoropolymer or metal composite material, in particular made of polyvinylidene fluoride; and the second mesh layer of the catalytic packing module is made of a highly permeable and hydrophilic corrosion-resistant material, such as a highly permeable hydrophilic fiber agglomerate material, in particular made of glass fiber fabric.

12. The method according to claim 11, having one or more of the following features: The number of theoretical plates in the distillation section of the catalytic distillation device is 4-8; The reflux ratio of the distillation section of the catalytic distillation device is 2:1 to 1:5; and The number of theoretical plates in the reaction section of the catalytic distillation device is 2-8.

13. The method according to claim 11 or 12, having one or more of the following features: The catalyst loading in the catalytic packing module in the reaction section of the catalytic distillation device is 0.1-0.6 cm 3 , preferably 0.2-0.6cm 3 Catalyst volume / cm 3 Reaction section volume; The inert filler loading in the catalytic filler module in the reaction section of the catalytic distillation device is 0.05-0.3 cm 3 , preferably 0.1-0.3cm 3 Inert filler / cm 3 Reaction section volume; The pressure in the reaction zone of the catalytic distillation device is 0.05-0.15 MPa absolute pressure, preferably 0.08-0.12 MPa; The reaction temperature in the reaction section of the catalytic distillation device is 100-160° C., preferably 120-140° C., and the residence time of the raw material containing lactic acid in the reaction section is 20-60 min; and The operating conditions in the distillation section of the catalytic distillation device include: The temperature at the top of the tower is 95-140°C, and the pressure at the top of the tower is 0.02-0.1 MPa absolute pressure.

14. The method according to any one of claims 11 to 13, having one or more of the following features: The raw material containing lactic acid is a 30-60 wt% lactic acid aqueous solution, and the feed temperature is 80-100° C.; and The temperature of the reaction inert gas is 110-160° C., the introduction pressure is 0.08-0.2 MPa absolute pressure, and is greater than the reaction pressure in the reaction section.

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