Process for preparing isosorbide through heterogeneous azeotropic reaction rectification

Abstract

The invention provides a process for preparing isosorbide through heterogeneous azeotropic reaction rectification, and belongs to the technical field of chemical engineering. The method comprises the following steps: heating and melting a reaction raw material sorbitol, inputting into the middle part of a reactive distillation tower, inputting an entrainer into the upper part of the reactive distillation tower, carrying out a dehydration reaction under the action of a catalyst filled in a reactor in the reactive distillation tower, extracting azeotrope from the top of the reactive distillation tower, condensing and separating the azeotrope, and returning the entrainer to the upper part of the reactive distillation tower, extracting crude isosorbide from a tower kettle of the reactive distillation tower; wherein the reactive distillation tower internally comprises a distillation section, a reaction section and a stripping section, a plurality of tower plates are arranged above and below the distillation section and the stripping section, a plurality of reaction stages are arranged above and below the reaction section, and each reaction stage is composed of a tower plate, a downcomer located at an outlet weir of the tower plate and a reactor in the downcomer. And the reactor of any reaction stage is used as an inlet weir of the tower plate in the next reaction stage. And reaction and azeotropic separation are carried out simultaneously, so that dehydration reaction can be accelerated and entrained products during water evaporation can be reduced simultaneously.

Description

Technical Field

[0001] The invention relates to the technical field of chemical processes, and in particular to a process for preparing isosorbide by heterogeneous azeotropic reaction distillation. Background Art

[0002] Bisphenol A (BPA) has a huge global market size and is one of the most produced chemicals in the world. The production of polycarbonate and epoxy resin prepared with it as raw material accounts for about 68% and 30% of BPA production capacity respectively. However, since bisphenol A is an endocrine disruptor and estrogen chemical, it may cause various health problems, such as obesity, diabetes, carcinogenesis and a series of diseases such as neurological diseases. Therefore, it is necessary to find green and non-toxic substitutes for bisphenol A, among which isosorbide has great potential and is favored by researchers. At present, isosorbide has been used to study as a substitute for bisphenol A in the production of high-performance polycarbonate and epoxy resin. For example, the commercialized isosorbide-type polycarbonate of DURABIO and PLANEXT is an engineering plastic that has the excellent properties of both polymethyl methacrylate and bisphenol A-type polycarbonate.

[0003] Isosorbide is the only bio-based diol that has been industrialized so far. It has a unique stereochemistry and geometry. It consists of two tetrahydrofuran rings that form a rigid molecular configuration, which can provide mechanical strength for the corresponding derivatives. At the same time, isosorbide has two hydroxyl groups with different reactivity. After appropriate derivatization reactions, bifunctional polymers such as polyesters, polycarbonates, polyurethanes and polyamides can be obtained. The most common industrial production method of isosorbide is to convert glucose into sorbitol by hydrogenation, and then selectively catalytically dehydrate sorbitol to prepare isosorbide.

[0004] At present, the process flow for continuous production of isosorbide is generally a reactor plus crystallization process flow, or irrigation reaction distillation technology. The reactor plus crystallization process involves multiple steps, including reaction, crystallization, separation and purification, which increases the complexity of the process and the investment cost of the equipment is high. Although the irrigation reaction distillation technology is carried out in a distillation device, it reduces the investment cost compared to the reactor plus crystallization process, but it is necessary to pump the material in the tower bottom back into the tower, which consumes a lot of cost. In addition, the irrigation reaction distillation does not deal with the effect of product water on the reaction. The presence of water will cause the acid sites to be covered, so that the catalytic reaction is inhibited from being converted to isosorbide. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention discloses a process for preparing isosorbide by heterogeneous azeotropic reaction distillation. The process for preparing isosorbide by heterogeneous azeotropic reaction distillation of the present invention performs reaction and azeotropic separation simultaneously, and can simultaneously take into account the acceleration of the forward progress of the dehydration reaction and the reduction of isosorbide entrained during water evaporation, thereby improving the yield of isosorbide.

[0006] In order to achieve the above technical objectives, the present invention proposes a process for preparing isosorbide by heterogeneous azeotropic reaction distillation, wherein the reaction raw material sorbitol is heated and melted and then input into the middle of a reaction distillation tower, an entrainer is input into the upper part of the reaction distillation tower, a dehydration reaction is carried out under the action of a catalyst loaded in a reactor in the reaction distillation tower, an azeotrope is extracted from the top of the reaction distillation tower, the azeotrope is condensed and separated, and the entrainer is returned to the upper part of the reaction distillation tower, and crude isosorbide is extracted from the reactor of the reaction distillation tower;

[0007] The interior of the reaction distillation tower includes a distillation section, a reaction section and a stripping section. The distillation section and the stripping section are provided with a plurality of tower plates above and below. The reaction section is provided with a plurality of reaction stages above and below. The reaction stage is composed of a tower plate, a downcomer located at the tower plate outlet weir, and a reactor in the downcomer. The reactor of any reaction stage serves as the inlet weir of the tower plate in the next reaction stage.

[0008] In the process of preparing Isosorbide by traditional sorbitol dehydration, due to the restriction of reaction conditions, a large amount of by products are often produced, such as isomers, polymeric products of Isosorbide, etc., and the generation of these by products not only reduces the productive rate of Isosorbide, but also increases the difficulty of subsequent separation and purification. And in the technique of the present invention, by adding entrainer as dewatering agent, the moisture in the reaction system can be effectively removed, thereby suppressing the side reaction caused by the presence of moisture, reducing the generation of by product. Meanwhile, the selective dehydration of entrainer also makes the reaction more inclined to generate Isosorbide, improves the selectivity of reaction.

[0009] In the reactive distillation process, due to the gas-liquid contact and mass transfer on the tower plate, part of Isosorbide may be entrained in the azeotrope at the tower top, causing the loss of Isosorbide and the reduction of the productive rate. And in the process of the present invention, the entrainer added can form an azeotropic mixture with water, which can absorb a large amount of heat in this process, thereby reducing the temperature of the tower plate. The reduction of temperature helps to reduce the evaporation and entrainment of Isosorbide on the tower plate, so that it flows more to the tower reactor of the reactive distillation tower, thereby improving the productive rate of Isosorbide.

[0010] The azeotropes of the entrainer and water extracted from the top of the reaction distillation tower of the present invention are condensed into liquids, and then the liquids are subjected to liquid-liquid separation. After separation, the entrainer is returned to the reaction distillation tower, and the water is collected or further processed. Such a process design helps to improve the efficiency of the heterogeneous azeotropic reaction and the recovery rate of the entrainer.

[0011] The reaction distillation tower of the process for preparing isosorbide by heterogeneous azeotropic reaction distillation of the present invention is a comprehensive reaction distillation tower having a rectification section, a reaction section and a stripping section, and a plurality of reaction stages are arranged above and below the reaction section, each reaction stage undertakes certain chemical reaction and material separation tasks, and together completes the entire reaction distillation process. Each reaction stage is composed of a tower plate, a downcomer located at the tower plate outlet weir, and a reactor in the downcomer, the tower plate plays a role in promoting material exchange and heat transfer, the downcomer located at the tower plate outlet weir plays a role in liquid transmission and distribution, and the reactor in the downcomer is the place where the chemical reaction is actually carried out; and the outlet weir of the tower plate in any reaction stage is connected to the reactor, and the reactor, as the inlet weir of the tower plate in the next reaction stage, realizes the continuous flow and reaction separation of materials in the entire tower, ensuring the continuity of the material flow in the entire tower and the smooth progress of the entire reaction distillation process. The high-viscosity fluid flows horizontally across the tower plate and fully exchanges gas and liquid with the upward steam. After the liquid level is higher than the weir edge of the downcomer, it flows into the reactor through the downcomer. The catalyst fully contacts the inflowing fluid in the reactor and catalytically reacts. After the fluid flows over the edge of the tower plate where the reactor is located, it flows horizontally across the tower plate again and fully exchanges gas and liquid with the upward steam, thereby achieving the purpose of sufficient dehydration.

[0012] Furthermore, the entrainer is cyclohexane, which has a relatively high boiling point. As an entrainer, it can form an azeotropic mixture with water or other low-boiling point substances in the reaction system, thereby distilling these substances from the reaction system at a lower temperature. This helps to reduce the temperature of the entire reaction process, reduce energy consumption, and may improve the selectivity and yield of the reaction; cyclohexane is relatively stable, not easy to decompose to produce harmful substances, and has less impact on the environment; at the same time, the cost of cyclohexane is relatively low, and its use can reduce production costs and improve economic benefits.

[0013] Furthermore, the total number of plates of the reactive distillation tower is 28 to 35. The total number of plates is the total number of plates of the rectification section, reaction section and stripping section in the reactive distillation tower.

[0014] Furthermore, the number of reaction stages of the reactive distillation tower is 15 to 28, preferably 15 to 25. Each reaction stage of the present invention is composed of a tower plate, a downcomer located at the tower plate outlet weir, and a reactor in the downcomer. Therefore, the number of tower plates, downcomers, and reactors in the reactive distillation tower is 15 to 28; the number of reaction stages is preferably 15 to 25. The embodiment of the present invention shows the specific parameters of the relevant reaction stages in the reactive distillation tower.

[0015] Furthermore, the tower plate is a bubble cap tower plate or a valve tower plate.

[0016] Furthermore, the reactor is filled with the catalyst, which is a solid acid catalyst, preferably H-β or Amberlyst.

[0017] The present invention adopts a solid acid catalyst, which is fixed in a reaction distillation tower, so that the mixed liquid after the reaction of each stage of the reactor can be immediately distilled and separated. On the one hand, the isosorbide product can be separated, and on the other hand, the reaction concentration in the mixed liquid after distillation and separation is increased, which can improve the reaction rate.

[0018] Furthermore, the top temperature of the reactive distillation tower is 100-120°C, and the bottom temperature is 250-300°C.

[0019] Furthermore, the feed rate of the reaction raw material sorbitol is 0.8-5 kg / h, the loading height of the catalyst is 0.3-0.6 m, and the feed rate of the entrainer is 0.08-0.5 kg / h.

[0020] The contact time between the reactants and the catalyst of the present invention is controllable. The overall contact time between the materials and the catalyst is controlled by controlling the feed rate, catalyst filling height and circulation volume of the reaction distillation tower. The total contact time is controlled to be 3 to 5 hours.

[0021] Further, the entrainer is input into the distillation section of the reaction distillation tower, and the reaction raw material sorbitol is input into the reaction section of the reaction distillation tower. Preferably, the entrainer is input into the first plate of the distillation section of the reaction distillation tower, and the reaction raw material sorbitol is input into the first plate of the reaction section of the reaction distillation tower.

[0022] Furthermore, the reactor is a porous reaction box, and the porous reaction box is made of an acid-corrosion-resistant mesh with a pore size smaller than the diameter of the catalyst.

[0023] The process of preparing isosorbide by heterogeneous azeotropic reaction distillation of the present invention is as follows: after sorbitol is heated and melted in a preheater, it enters the distillation tower from the middle of the distillation tower, under the action of gravity, liquid sorbitol gradually overflows through the inlet weir through the tower plate and enters a reactor equipped with a catalyst, the liquid sorbitol fully contacts and reacts with the solid catalyst in the reactor, the liquid level of the reacted material overflows after being higher than the outlet weir, enters the tower plate to carry out gas-liquid phase equilibrium, and then flows downward to the next reactor bed layer under the action of gravity to carry out the next stage of reaction-distillation process, finally, the high boiling point product and isosorbide are extracted at the bottom of the tower, the entrainer is added from the top of the tower, flows downward, and forms an azeotrope with the water generated by the reaction in the distillation section and the reaction section, and is more easily extracted from the top of the tower, and after the entrainer is separated from water after condensation, the entrainer will flow back into the reaction distillation tower again, during which part of the entrainer will be lost, and the lost entrainer will be replenished again from the inlet of the top of the tower.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) In the process for preparing isosorbide by heterogeneous azeotropic reactive distillation of the present invention, the reaction and separation are completed in the same equipment unit, which can not only reduce the equipment cost, but also enable the steam in the reactor of the reactive distillation tower to heat the reaction section in the reactive distillation tower, thereby intensively utilizing the heat energy and reducing the energy consumption; and the liquid can automatically flow out of the catalyst bed under the action of gravity, without the need for further filtering and separation of the catalyst and the reaction liquid, thereby simplifying the difficulty of subsequent process treatment.

[0026] (2) In the process for preparing isosorbide by heterogeneous azeotropic reactive distillation of the present invention, an entrainer is added as a dehydrating agent to extract water, thereby achieving the purpose of reducing the generation of by-products and selectively generating isosorbide; at the same time, the addition of the entrainer can form an azeotrope with water, absorb a large amount of heat, thereby reducing the temperature of the tower plate, so that the entrained isosorbide is liquefied and flows to the reactor of the reactive distillation tower for extraction, thereby improving the yield of isosorbide. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0028] Figure 1 A schematic diagram of a heterogeneous azeotropic reaction distillation device of the present invention is shown.

[0029] The above drawings include the following reference numerals:

[0030] 1. preheater, 2. reaction distillation tower, 3. first feed inlet, 4. second feed inlet, 5. tower plate, 6. downcomer, 7. porous reaction box, 8. tower bottom discharge port, 9. condenser, 10. liquid-liquid two-phase separator. DETAILED DESCRIPTION

[0031] The following is an explanation of the embodiments of the present invention by specific embodiments. Those skilled in the art can easily understand the advantages of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied by other different embodiments, and the details in this specification can also be given different modifications and changes based on different viewpoints and applications without deviating from the spirit disclosed by the present invention. In addition, all ranges and values ​​herein are inclusive and combinable. Any numerical value or point falling within the range described herein, such as any integer, can be used as a minimum value or maximum value to derive a lower range, etc.

[0032] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively below, and preferred embodiments of the present invention are given. However, it should be understood that these embodiments are only used for more detailed description, and should not be understood as limiting the present invention in any form, that is, not limiting the scope of protection of the present invention. Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs.

[0033] Example 1

[0034] A process for preparing isosorbide by heterogeneous azeotropic reaction distillation, such as Figure 1 As shown, the reaction raw material sorbitol is heated and melted and then input into the middle of the reaction distillation tower 2, and the entrainer is input into the upper part of the reaction distillation tower 2. A dehydration reaction is carried out under the action of the catalyst loaded in the reactor of the reaction distillation tower 2, and an azeotrope is extracted from the top of the reaction distillation tower 2. After the azeotrope is condensed and separated, the entrainer is returned to the upper part of the reaction distillation tower, and crude isosorbide is extracted from the reactor of the reaction distillation tower;

[0035] The interior of the reaction distillation tower 2 includes a distillation section, a reaction section and a stripping section. The distillation section and the stripping section are provided with a plurality of tower plates 5 above and below. The reaction section is provided with a plurality of reaction stages above and below. The reaction stage is composed of a tower plate 5 and a downcomer 6 located at the tower plate outlet weir and a reactor in the downcomer. The reactor of any reaction stage serves as the inlet weir of the tower plate in the next reaction stage.

[0036] Sorbitol means that the reaction stream is mainly composed of sorbitol and contains a small amount of impurities, wherein the sorbitol can be prepared by any known method, such as the conversion of glucose into sorbitol by hydrogenation, etc.; and the impurities are by-products derived from the above-mentioned known methods, such as mannitol, glycerol and other components produced as by-products in the conversion of glucose into sorbitol by hydrogenation.

[0037] The entrainer should be able to form a stable azeotrope with water, and the azeotropic temperature should be lower than the boiling point of sorbitol and isosorbide to avoid loss of raw materials or products during the dehydration process. Exemplary entrainers are organic solvents such as cyclohexane, toluene, and xylene, and preferably, the entrainer is cyclohexane.

[0038] The entrainer in the azeotrope is input into the reaction distillation tower for circulation. In this case, a small amount of entrainer needs to be additionally introduced during recovery because there will be a certain amount of loss in actual industry. The ratio of the amount of recovered entrainer to the amount of additional entrainer is generally 5:1.

[0039] Example 2

[0040] Based on the process for preparing isosorbide by heterogeneous azeotropic reaction distillation shown in Example 1, this embodiment is a preferred embodiment. The reaction raw material sorbitol is heated and melted by the preheater 1. After the material is heated and melted by the preheater 1, the temperature is increased, which helps the material to reach the required reaction temperature or operating temperature more quickly during the subsequent treatment of the reaction distillation tower. At the same time, the preheater 1 can also reduce the energy consumption required by the reaction distillation tower; the preheater 1 can use any known equipment with a preheating function. For example, the fixed preheater can be selected from coil type, plate type, tube bundle type, spiral type, etc.; the flow preheater can be selected from stable bed type, fluidized bed type, spray type, cyclone bed type, etc.

[0041] The condensing device used for condensing the azeotrope is a condenser 9. The top of the reaction distillation tower is connected to the condenser 9 to receive the top stream of the reaction distillation tower and cool its steam to its dew point temperature or lower than its dew point temperature, thereby forming a liquid. The condenser 9 can also be any known device with a condensing function. For example, a partition-type condenser can be a shell-and-tube type or a cross-flow type; a contact-type condenser can be a direct contact type or a jet type.

[0042] The separation device is a liquid-liquid two-phase separator 10, which is used to separate the mixed liquid after the entrainer and water extracted from the top of the reaction distillation tower are condensed by the condenser. The liquid-liquid two-phase separator 10 can also adopt any known equipment with liquid-liquid separation function, for example, a centrifugal liquid-liquid separator, an extractive liquid-liquid separator, a membrane liquid-liquid separator, etc.

[0043] Example 3

[0044] Based on the process for preparing isosorbide by heterogeneous azeotropic reaction distillation shown in Example 1, this embodiment is a preferred embodiment, the first tower plate of the distillation section is set at the azeotropic agent input port, the first tower plate of the reaction section is set at the sorbitol feed port after heating and melting, and at the same time, the outlet weir of the first tower plate 5 is set with the first downcomer 6, the first reactor is set in the first downcomer 6, the inlet weir of the second tower plate 5 is connected to the first reactor, and so on, different operating conditions may require different numbers of reaction stages to achieve the best operating effect. Therefore, when actually designing and operating a reaction distillation tower, it is necessary to determine the number of reaction stages according to the specific situation.

[0045] The total number of plates of the reaction distillation tower is 28 to 35. The total number of plates is the total number of plates in the distillation section, reaction section and stripping section in the reaction distillation tower.

[0046] The reactive distillation tower has 15 to 28 reaction stages, preferably 15 to 25. Each reaction stage of the present invention is composed of a tower plate, a downcomer located at the tower plate outlet weir, and a reactor in the downcomer. Therefore, the number of tower plates, downcomers, and reactors in the reactive distillation tower is 15 to 28; the number of reaction stages is preferably 15 to 25.

[0047] The tower plate 5 is a bubble cap tower plate or a floating valve tower plate. Among them, the bubble cap tower plate is not prone to leakage, has good operating stability and operating flexibility, and is easy to control. When the gas and liquid loads fluctuate greatly, it can maintain an almost stable plate efficiency and has strong adaptability to various materials; the production capacity per unit area of ​​the floating valve tower plate is 20% to 30% higher than that of the bubble cap tower plate, which can meet the needs of large-scale production. The plate efficiency of the floating valve tower plate is about 10% higher than that of the bubble cap tower plate, which is conducive to improving the mass transfer and heat transfer efficiency. The bubble cap tower plate and the floating valve tower plate each have unique advantages and applicable occasions. When selecting the type of tower plate, it is necessary to comprehensively consider factors such as specific process requirements, operating conditions and economy.

[0048] Example 4

[0049] Based on the process for preparing isosorbide by heterogeneous azeotropic reaction distillation shown in Example 1, this embodiment is a preferred embodiment, and the catalyst loaded in the reactor is a solid acid catalyst, preferably H-β or Amberlyst. Solid acid catalysts are a class of solid substances with acidic properties, which can provide an acidic environment in a chemical reaction, thereby accelerating or promoting the reaction. H-β is a zeolite catalyst with a specific crystal structure and acidic properties, and Amberlyst is an ion exchange resin catalyst, which also has strong acidity.

[0050] The reactor is a porous reaction box 7, which is used to fix the position of the catalyst to prevent it from being entrained by the high-viscosity sorbitol fluid. The manufacturing method is to use an acid-resistant mesh with a mesh aperture slightly smaller than the catalyst diameter, and customize it according to the position and size of the downcomer. For example, taking Amberlyst-36 catalyst as an example, the diameter of the catalyst is 0.6-0.8mm, so the aperture diameter of the porous reaction box 7 is preferably 0.2mm-0.4mm to prevent it from being entrained by the high-viscosity sorbitol material.

[0051] Example 5

[0052] Based on the process for preparing isosorbide by heterogeneous azeotropic reactive distillation shown in Example 1, this embodiment is a preferred embodiment, and the top temperature of reactive distillation tower 2 is 100-120°C, and the bottom temperature is 250-300°C. Since the sorbitol dehydration reaction uses an acidic catalyst with high catalytic activity, the control of the reaction temperature is particularly important. Exemplarily, the top temperature of reactive distillation tower 2 is 120°C, and the bottom temperature is 250°C; if the reaction temperature is too high, it is easy to cause the acid radical of the acidic catalyst to detach, resulting in catalyst degradation; if the reaction temperature is too low, the reaction rate is slow, resulting in a yield deviation of the continuous reaction.

[0053] The feed rate of the reaction raw material sorbitol is 0.8-5 kg / h, the filling height of the catalyst is 0.3-0.6 m, and the feed rate of the entrainer is 0.08-0.5 kg / h. The contact time between the reactant and the catalyst is controllable, and the overall contact time between the material and the catalyst is controlled by controlling the feed rate, the catalyst filling height, and the circulation amount of the reaction distillation tower, and the total contact time is controlled to be 3-5 hours.

[0054] Example 6

[0055] This embodiment shows the process of preparing isosorbide by heterogeneous azeotropic reaction distillation under specific working conditions. It should be noted that this process flow is only a demonstration of a better process and does not limit the scope of protection of the present invention.

[0056] A process for preparing isosorbide by heterogeneous azeotropic reaction distillation, such as Figure 1As shown, solid sorbitol is used as a raw material. After being heated and melted in a preheater 1, it enters the reaction distillation tower 2 from the first feed port 3 in the middle of the reaction distillation tower 2 at a feed rate of 5 kg / h. The entrainer n-hexane enters the reaction distillation tower through the second feed port 4 provided on the top of the reaction distillation tower 2. The reaction distillation tower 2 has a diameter of ф5m and a height of 3m. There are 15 reaction stages in the reaction distillation tower 2, each of which consists of a bubble plate 5, a downcomer 6 and a porous reaction box 7. Under the action of gravity, liquid sorbitol passes through the plate and gradually flows over the outlet weir of the plate 5 to enter the porous reaction box 7 filled with H-β molecular sieve. The bed height filled in the porous reaction box 7 is 0.3m. The liquid sorbitol fully contacts and reacts with the solid catalyst in the bed layer. The liquid level of the reacted material is higher than the outlet weir of the next stage tray and then overflows, enters the tray 5 for gas-liquid phase equilibrium, and then flows downward to the next reactor bed layer under the action of gravity for the next stage of reaction; the temperature of the reactor of the reaction distillation tower 2 is 250°C, and the temperature of the top of the tower is 120°C. A discharge port 8 is set in the reactor of the reaction distillation tower 2 for extracting sorbitol materials and by-products. A extraction port is set at the top of the reaction distillation tower, and is connected to a condenser 9 for discharging azeotropes of cyclohexane and water; a liquid-liquid two-phase separator 10 is connected after the condenser 9, and the cyclohexane after separating the cyclohexane from the water in the upper layer enters the reaction distillation tower 2 again for recycling, and the water in the lower layer is discharged.

[0057] In this embodiment, the purity of isosorbide extracted from the tower bottom discharge port 8 of the reactive distillation tower 2 is 90%, and the yield is 88%.

[0058] Example 7

[0059] Based on the process of preparing isosorbide by heterogeneous azeotropic reaction distillation shown in Example 6, the different process parameters of this embodiment and Example 6 are set as follows: the feed amount of sorbitol after heating and melting in this embodiment is 0.8kg / h, the top temperature of the reaction distillation tower 2 is 120°C, the bottom temperature is 280°C, the catalyst adopts the heterogeneous catalyst Amberlyst-36, the catalyst bed height in the downcomer is 0.3m, and the tower plate 5 is a floating valve tower plate. Under the above process conditions, the purity of isosorbide extracted from the tower bottom discharge port 8 of the reaction distillation tower 2 in this embodiment is 90%, and the yield is 89%.

[0060] Comparative Example

[0061] Based on the process of preparing isosorbide by heterogeneous azeotropic reaction distillation shown in Example 7, the different process parameters of this embodiment and Example 7 are set as follows: the azeotropic distillation method is not adopted in this embodiment, that is, the entrainer n-hexane is not added. Under the above process conditions, the purity of isosorbide extracted from the tower bottom discharge port 8 of the reaction distillation tower 2 in this embodiment is 61%, and the yield is 60%. Therefore, the addition of an entrainer can increase the yield of isosorbide.

[0062] It should be noted that the above contents are further detailed descriptions of the present invention in combination with specific implementation methods, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions; the dimensional data of this embodiment does not necessarily limit the technical solution, but only shows one of the specific working conditions. For ordinary technicians in the technical field to which the present invention belongs, several simple improvements and modifications can be made without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A process for preparing isosorbide by heterogeneous azeotropic reaction distillation, characterized in that: The reaction raw material sorbitol is heated and melted and then input into the middle of the reaction distillation tower, and the entrainer is input into the upper part of the reaction distillation tower, and a dehydration reaction is carried out under the action of the catalyst loaded in the reactor in the reaction distillation tower, and the azeotrope is extracted from the top of the reaction distillation tower. After the azeotrope is condensed and separated, the entrainer is returned to the upper part of the reaction distillation tower, and crude isosorbide is extracted from the reactor of the reaction distillation tower; The interior of the reaction distillation tower includes a distillation section, a reaction section and a stripping section. The distillation section and the stripping section are provided with a plurality of tower plates above and below. The reaction section is provided with a plurality of reaction stages above and below. The reaction stage is composed of a tower plate, a downcomer located at the tower plate outlet weir, and a reactor in the downcomer. The reactor of any reaction stage serves as the inlet weir of the tower plate in the next reaction stage.

2. The process for preparing isosorbide by heterogeneous azeotropic reaction distillation according to claim 1, characterized in that: The azeotropic agent is cyclohexane.

3. The process for preparing isosorbide by heterogeneous azeotropic reaction distillation according to claim 1, characterized in that: The total number of plates of the reactive distillation tower is 28 to 35.

4. The process for preparing isosorbide by heterogeneous azeotropic reaction distillation according to claim 1, characterized in that: The reactive distillation tower has 15 to 28 reaction stages, preferably 15 to 25 reaction stages.

5. The process for preparing isosorbide by heterogeneous azeotropic reaction distillation according to claim 1, characterized in that: The tower plate is a bubble cap tower plate or a valve tower plate.

6. The process for preparing isosorbide by heterogeneous azeotropic reaction distillation according to claim 1, characterized in that: The catalyst is a solid acid catalyst, preferably H-β or Amberlyst.

7. The process for preparing isosorbide by heterogeneous azeotropic reaction distillation according to claim 1, characterized in that: The top temperature of the reactive distillation tower is 100-120°C, and the bottom temperature is 250-300°C.

8. The process for preparing isosorbide by heterogeneous azeotropic reaction distillation according to claim 1, characterized in that: The feed rate of the reaction raw material sorbitol is 0.8-5 kg / h, the filling height of the catalyst is 0.3-0.6 m, and the feed rate of the entrainer is 0.08-0.5 kg / h.

9. The process for preparing isosorbide by heterogeneous azeotropic reaction distillation according to claim 1, characterized in that: The azeotropic agent is input into the distillation section of the reaction distillation tower, and the reaction raw material sorbitol is input into the reaction section of the reaction distillation tower.

10. The process for preparing isosorbide by heterogeneous azeotropic reaction distillation according to claim 1, characterized in that: The reactor is a porous reaction box, which is made of an acid-corrosion-resistant mesh with a pore size smaller than the catalyst diameter.

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