Refining system and refining method of polymer grade isosorbide

Abstract

The invention provides a refining system and a refining method of isosorbide. The system is coupled with a rectification system and a melt crystallization system and is used for purifying isosorbide. The purity of the obtained isosorbide is higher than 99.9%, and the isosorbide can meet the requirements of PIC melt polymerization. Compared with the traditional process, the problem of low product purity is solved, and the separation effect is improved. The whole operation uses a PLC integrated system, is simple and easy to control, does not use an organic solvent or a third component in the purification process, and is green and environment-friendly. And through automatic switching of the multiple falling film crystallizers connected in parallel, continuous operation can be achieved, and the requirement for large-scale industrial production can be met.

Description

Technical Field

[0001] The invention belongs to the technical field of separation or purification of organic matter, and in particular relates to a refining system and a refining method of isosorbide, which are used for obtaining polymerization-grade isosorbide. Background Art

[0002] Polycarbonate (PC), as one of the five major engineering plastics, is inseparable from human life. The application of PC produced by traditional bisphenol A (BPA) polymerization is limited due to the unsustainable and toxic raw material resources. The sustained release of BPA during the use of BPA-PC has estrogenic effects and chronic toxic effects, which seriously harms people's health. Many countries have banned the use of BPA-PC in industries such as medical devices and food packaging. Based on the above facts, there is an urgent need to develop a green, non-toxic, and high-performance polycarbonate. Isosorbide-based polycarbonate (PIC) is considered to be an ideal substitute for BPA-PC because of its green, non-toxic and renewable raw materials. Using bio-based isosorbide to replace BPA to produce PC has become a future development trend of the industry.

[0003] PIC is an excellent engineering plastic with the following characteristics:

[0004] -Excellent impact strength

[0005] -Excellent surface properties, good wear resistance

[0006] -Wide operating temperature range, good heat resistance

[0007] -Excellent electrical insulation

[0008] -Precise formability and dimensional stability

[0009] -Excellent light resistance, no yellowing

[0010] -High transmittance, small optical distortion

[0011] These characteristics make PIC an ideal raw material, which is widely used in optical films and lenses, electronic panels, electrical and electronic components, automotive parts, cosmetic containers, transparent building materials and other fields. Compared with traditional BPA-PC, PIC surpasses BPA-PC in transparency and other characteristics. In 2013, Teijin of Japan developed the "PLANENTD-7000" product. The Tg, surface hardness, weather resistance and chemical resistance of this new grade of product are much higher than similar bisphenol A products. It also has high impact resistance and the industry's highest level of flame retardancy. In 2013, the "DURABIOTM" product developed by Mitsubishi Chemical showed excellent optical characteristics; high heat resistance; good light resistance; high surface hardness; strong rigidity and other advantages. Mitsubishi Chemical makes full use of these characteristics and widely applies it to the most advanced optical and energy-related parts, electronic instruments, automobile boxes, interior and exterior materials and other fields. In 2016, Mitsubishi Chemical announced that French car manufacturer Renault will use Mitsubishi Chemical's new bioengineered plastic "DURABIOTM" as the instrument panel shell material for its new Koleos.

[0012] Overall, driven by market demand and technological innovation, my country urgently needs to accelerate the development and marketization of isosorbide polycarbonate. As a bio-based engineering plastic with excellent performance, PIC has broad development prospects in the future, driven by policies and other forces. However, due to the low purity and low activity of the raw material isosorbide used in PIC polymerization, the polymerization process conditions are harsh and accompanied by a large number of side reactions, making it difficult for PIC to meet the performance standards. At present, the technology for industrial synthesis of isosorbide mainly faces problems such as low yield, difficult product separation, and high purification cost, which hinders the large-scale promotion and application of isosorbide-based polymer materials.

[0013] The traditional method of producing isosorbide is to heat and melt sorbitol, add an acidic catalyst, dehydrate under reduced pressure to obtain 1,4-anhydrosorbitol, and then dehydrate to obtain isosorbide by secondary dehydration. This process has many side reactions. While dehydrating to produce isosorbide, other by-products are also produced, making the purification of isosorbide difficult. At present, the purification methods of isosorbide include distillation, ion exchange, recrystallization, chromatographic separation and other methods. Among them, vacuum distillation is more widely used, and crude isosorbide can be obtained by vacuum distillation. Purification of crude products such as secondary distillation is energy-intensive and uneconomical, and the purity of isosorbide obtained by crystallization and ion exchange cannot meet the requirements of existing industry. As a monomer for PIC copolymerization, the purity of isosorbide is required to reach more than 99.5%. In order to meet the polymerization requirements of PIC, it is necessary to find an efficient and economical method for purifying isosorbide. Summary of the invention

[0014] In view of the above problems existing in the prior art, the present invention provides a refining system for obtaining polymerization-grade isosorbide, application of the system in isosorbide purification, and a method for purifying isosorbide.

[0015] The present invention provides an isosorbide refining system, comprising a distillation system and a melt crystallization system arranged downstream of the distillation system;

[0016] The distillation system comprises a distillation tower, and the melt crystallization system comprises a falling film crystallizer.

[0017] According to an embodiment of the present invention, the distillation system further comprises a reboiler arranged in the bottom of the distillation tower, and a condenser arranged at the top of the distillation tower. The isosorbide gas phase coming out of the top of the distillation tower enters the condenser to obtain liquid isosorbide.

[0018] Furthermore, the distillation system also includes a first container connected to the condenser for storing liquid isosorbide; preferably, the first container is a condensation tank.

[0019] According to an embodiment of the present invention, the distillation tower may be a packed tower, a sieve plate tower or a bubble tower, etc.

[0020] According to an embodiment of the present invention, the first container is provided with at least one liquid outlet end connected to the liquid inlet of the falling film crystallizer. In another embodiment, the first container may also be provided with a second liquid outlet end connected to the upper end of the distillation tower, that is, the upper end of the distillation tower, the condenser and the first container form a loop.

[0021] According to an embodiment of the present invention, the melt crystallization system further comprises a product processing unit connected to the liquid outlet of the falling film crystallizer.

[0022] According to an embodiment of the present invention, the product processing unit includes a second container, a third container, and a fourth container, the second container is used to recover uncrystallized isosorbide mother liquor, the third container is used to recover the sweat liquid of isosorbide crude crystals, and the fourth container is used to collect isosorbide purified by sweating.

[0023] The present invention has no particular limitation on the order of the positions of the second container, the third container, and the fourth container, and those skilled in the art may adjust them as needed, for example, arranging the second container first, the third container in the middle, and the fourth container last.

[0024] Valves are also provided on the connecting pipelines of the second container, the third container, the fourth container and the liquid outlet of the falling film crystallizer, and the valves are switched according to the processes occurring in the falling film crystallizer. Specifically, when the isosorbide mother liquor crystallization process is in progress, the valve connected to the second container is opened, and the isosorbide mother liquor that has not been crystallized after the crystallization is completed is recycled to the second container; when the sweating process is in progress, the valve connected to the third container is opened, and the sweating liquid is recycled to the third container; when the crystallization melting process is in progress, the valve connected to the fourth container is opened, and the melted isosorbide is collected in the fourth container.

[0025] According to an embodiment of the present invention, the number of falling film crystallizers N≥1, preferably N≥2, for example, 2 to 5, and can be listed as 2, 3, 4 or 5, among which N=2 is the best. When N≥2, the falling film crystallizers are arranged in parallel. During operation, it is ensured that at least one of the entire melt crystallization system is in a crystallization state and one is in a sweating / melting state in the same time period. The falling film crystallizer has low heat diffusion resistance, good temperature uniformity, and compact structure, which can improve crystallization efficiency and product quality.

[0026] According to an embodiment of the present invention, the falling film crystallizer is a vertical shell-and-tube structure, comprising a cylinder, a crystallization tube bundle (a tube bundle is formed by a plurality of crystallization tubes) arranged in the cylinder, and a film distribution structure.

[0027] According to the implementation scheme of the present invention, each crystallization tube is manufactured as a whole without splicing, and the crystallization tube is connected to the upper and lower tube plates by expansion welding, so that the liquid flows into each crystallization tube more evenly, greatly improving the film-making and crystallization effects.

[0028] According to a selected embodiment of the present invention, the main body material of the falling film crystallizer is stainless steel.

[0029] According to an embodiment of the present invention, the material of the crystallization tube bundle is stainless steel.

[0030] According to an embodiment of the present invention, each crystallization tube is a single-pass tube bundle, and the aspect ratio of each crystallization tube is 100-800, preferably 200-300.

[0031] According to an embodiment of the present invention, the crystallized tube bundle has a fin structure or a microgroove structure.

[0032] According to an embodiment of the present invention, the microgroove structure is disposed on the side of the tube bundle that contacts the isosorbide slurry (such as the inside or outside of the tube bundle);

[0033] The micro-groove structure is a tooth groove structure, a twill structure or a thread structure; further, the groove width and the groove depth are continuous from top to bottom, showing a regular or decreasing trend.

[0034] According to an embodiment of the present invention, the microgrooves are arranged in an axial, twill, radial or spiral manner, and the extension direction can also change continuously or stepwise from top to bottom.

[0035] According to an embodiment of the present invention, the falling film crystallizer further comprises an upper tube box, the film structure is arranged inside the upper tube box and is located at the top of the crystallization tube bundle, maintaining a certain concentricity with the crystallization tube, so as to promote the material to achieve film flow in the tube. The film flow has the advantages of high heat transfer efficiency and small liquid holdup, which can strengthen the heat transfer in the crystallization process, promote the migration of impurities to the liquid phase, and improve the purity of the crystal.

[0036] According to an embodiment of the present invention, the membrane structure may be a grid type or a sieve plate type.

[0037] In one embodiment, the sieve plate type membrane structure includes a baffle plate with a vertical tube arranged from top to bottom, a weir, and a sieve plate or a distribution plate, wherein the sieve plate or the distribution plate has a hole structure; for example, the hole diameter is 5 to 50 mm, for example, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm or 45 mm.

[0038] According to an embodiment of the present invention, the anti-collision plate includes but is not limited to a primary hole structure (all holes have the same diameter) or a secondary or higher hole structure (having holes with two different diameters).

[0039] In one embodiment, the grid-type membrane structure includes a feed nozzle, a wire mesh and a grid arranged from top to bottom; preferably, the spacing between adjacent grids is 5 to 50 mm, for example, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm or 45 mm.

[0040] According to an embodiment of the present invention, the cone angle of the spray range of the feed nozzle is 90° to 150°, preferably 100° to 120°. By providing the feed nozzle, the automatic cleaning and uniform feeding functions of the membrane structure are realized.

[0041] According to an embodiment of the present invention, the falling film crystallizer may further include a discharge branch, which is arranged below the crystallization tube bundle and connected to the first container.

[0042] According to an embodiment of the present invention, the falling film crystallizer further comprises a heat exchange medium inlet and an outlet, which are respectively arranged at the upper end and the lower end of the crystallization tube bundle, so that the heat exchange medium fills the crystallization tube bundle area.

[0043] According to an embodiment of the present invention, the melt crystallization system also includes a heat exchange medium supply end and a fifth container for storing the heat exchange medium; preferably, the heat exchange medium supply end is connected to the heat exchange medium inlet, the heat exchange medium outlet is connected to one end of the fifth container, and the other end of the fifth container is connected to the heat exchange medium supply end to form a heat exchange medium circulation unit.

[0044] According to an embodiment of the present invention, the heat exchange medium supply end is used to supply a cooling medium and / or a heating medium.

[0045] In an exemplary embodiment, the refining system comprises:

[0046] A distillation system and a melt crystallization system disposed downstream of the distillation system;

[0047] The distillation system includes a distillation tower, a condenser and a first container, and the melt crystallization system includes a falling film crystallizer, a product processing unit and a heat exchange medium circulation unit;

[0048] The condenser is arranged at the top of the distillation tower; one end of the first container is connected to the condenser, and the other end is connected to the feed liquid inlet of the falling film crystallizer;

[0049] The number of falling film crystallizers N≥1, preferably N≥2, when N≥2, the falling film crystallizers are arranged in parallel;

[0050] The falling film crystallizer is a vertical shell-and-tube structure, comprising a cylinder, a crystallization tube bundle (a tube bundle formed by a plurality of crystallization tubes) arranged in the cylinder, a film structure, a heat exchange medium inlet and a heat exchange medium outlet; the film structure is a grid-type or sieve-plate-type film structure; the crystallization tube bundle has a fin or micro-groove structure;

[0051] The product processing unit comprises a second container, a third container and a fourth container, wherein the second container, the third container and the fourth container are all connected to the liquid outlet of the falling film crystallizer, and valves are arranged on each connecting pipeline, and the valves are switched according to the process occurring in the falling film crystallizer;

[0052] The heat exchange medium circulation unit includes a heat exchange medium supply end and a fifth container for storing heat exchange medium; the heat exchange medium supply end is connected to the heat exchange medium inlet, the heat exchange medium outlet is connected to one end of the fifth container, and the other end of the fifth container is connected to the heat exchange medium supply end.

[0053] According to the embodiment of the present invention, the refining system also includes a control system, such as a PLC programmable controller, which adopts a group operation process mode to ensure continuous operation of the system, thereby improving the reliability and simplicity of operation. The falling film crystallizer completes each step of operation under the main control of the PLC system, and achieves full automatic control by setting the operation time, which can realize the step-by-step operation of crystallization, sweating, and melting, and can be sent to the DCS system for centralized control as needed. Each falling film crystallizer operates in a cycle, and the control part adopts a PLC programmable controller, and adopts a group operation process mode to ensure continuous operation of the system, thereby improving the reliability and simplicity of operation.

[0054] Those skilled in the art can, as required, install a pump on the connecting pipeline for feeding or circulation; the connection between the various devices is, for example, flange and bolt connection.

[0055] According to an embodiment of the present invention, the melt crystallization system further comprises a product extraction pipeline, the product extraction pipeline further comprises a built-in density measuring instrument and a control valve matched therewith, and a defective isosorbide reflux pipeline is connected between the product extraction pipeline and the pump. The present invention also provides a method for purifying isosorbide, comprising:

[0056] The raw material is subjected to vacuum distillation to obtain an isosorbide gas phase, which is condensed and then enters a falling film evaporator as a mother liquid; the isosorbide product with a purity of not less than 99.0wt% (preferably not less than 99.5wt%) is obtained by cooling, crystallizing, sweating, removing impurities, and heating and melting;

[0057] Preferably, the falling film evaporator has the definitions as shown above;

[0058] Preferably, the vacuum distillation is carried out in a distillation tower, and also preferably, the distillation tower has the definitions as shown above.

[0059] According to an embodiment of the present invention, the tower top temperature of the vacuum distillation process is controlled at 150-250°C, preferably 165-185°C; and / or the tower top pressure is 0.5-5kPa, preferably 0.5-2.5kPa.

[0060] According to an embodiment of the present invention, the temperature of the mother liquor (i.e. the condensed isosorbide) is 60-90°C, preferably 65-75°C, reaching the temperature required for entering the falling film crystallizer.

[0061] According to an embodiment of the present invention, the cooling crystallization comprises: adjusting the temperature of the falling film crystallizer to 45-50°C, then introducing the mother liquor, staying for 0.5-1.0h to allow the crystal layer to grow, and then cooling at a rate of 0.02-0.1°C / min to allow the crystal layer to continue to grow for 1-2h, and discharging the mother liquor without crystallization after crystallization. In this process, when the mother liquor contacts the cold crystallization wall, a crystal nucleus is generated, and grows into a crystal at a certain rate. A layer of isosorbide crystals is formed on the inner surface of the cooled crystallization tube.

[0062] According to an embodiment of the present invention, the sweating impurity removal includes: after the cooling crystallization is completed, the temperature of the falling film crystallizer is increased at a rate of 0.02-0.1°C / min, and the sweating end temperature is 45-65°C; at this time, the impurities contained in the crystal layer are melted and discharged, and the crystal layer is purified.

[0063] According to an embodiment of the present invention, the heating and melting comprises: after the sweating and impurity removal is completed, the falling film crystallizer is heated to above 82° C., the crystal layer is completely melted, and the isosorbide product is collected.

[0064] The thickness of the crystal film formed should be moderate, generally between 5-30mm. The cooling rate during the crystallization process is 0.02-0.1℃ / min, and the cooling time is 1-2h. As the crystallization process proceeds, the isosorbide content in the mother liquor decreases, the crystallization rate slows down, and the effect of cooling on crystallization becomes smaller. Therefore, when the temperature drops to a certain level, the temperature can be kept constant to allow the crystals to continue to grow to a certain thickness. The thickness of the crystal layer growth is determined by the size of the falling film crystallizer and the efficiency of the sweating operation. The heating rate during the sweating process is 0.02-0.1℃ / min, and the sweating endpoint temperature is 45-65℃ (for example, 50℃, 53℃, 55℃, 58℃ or 60℃).

[0065] According to a preferred embodiment of the present invention, two falling film evaporators are connected in parallel. In the same time period, the A / B falling film crystallizers are dynamically switched, one of which is in a cooling and crystallizing state, and the other is in a sweating, impurity removal, heating and melting state. This is beneficial to improving the purification efficiency. In conjunction with the continuous feeding of the distillation tower, the A / B falling film crystallizers are dynamically switched to achieve continuous operation of the refining system.

[0066] According to an embodiment of the present invention, the purification method is carried out in the above-mentioned refining system.

[0067] According to an exemplary embodiment of the present invention, the purification method comprises the following steps:

[0068] (1) The raw material enters a distillation tower, undergoes vacuum distillation in the distillation tower, and the isosorbide gas phase flowing out from the top of the tower enters a condenser;

[0069] (2) the isosorbide gas phase is condensed into a liquid state and enters a first container (such as a condensation tank), a portion of which is refluxed to the distillation tower, and a portion of which is directly entered into a falling film crystallizer as a mother liquid;

[0070] (3) Cooling crystallization: Use a refrigerant to adjust the temperature of the falling film crystallizer to 45-50°C, introduce the mother liquor, and allow it to stay for 0.5-1.0 h to allow the crystal layer to grow, then cool it down at a rate of 0.02-0.1°C / min to allow the crystal layer to continue to grow for 1-2 h, and the uncrystallized mother liquor enters the second container;

[0071] (4) Sweating and removing impurities: After step (3) is completed, the heat medium is switched, and the temperature of the falling film crystallizer is increased at a rate of 0.02-0.1°C / min, and the sweating end point temperature is 45-65°C; the sweating liquid is recovered into a third container;

[0072] (5) Heating and melting: After step (4) is completed, the falling film crystallizer is heated to above 82° C., the crystal layer is completely melted, and the obtained isosorbide product with a purity of not less than 99.5 wt % is collected in a fourth container.

[0073] The present invention also provides application of the refining system in purifying or separating isosorbide.

[0074] The invention also provides application of the purification method in separating isosorbide.

[0075] Beneficial Effects

[0076] 1. The isosorbide refining system of the present invention has low cost, good system heat exchange and stable working condition.

[0077] 2. The isosorbide refining system of the present invention adopts a process of coupling distillation and melt crystallization to purify the isosorbide with a purity higher than 99.9%, which can meet the requirements of PIC melt polymerization. Compared with the traditional process, it solves the problem of low product purity and improves the separation effect.

[0078] 3. The isosorbide refining system of the present invention has a simple and easy-to-control distillation operation, and melt crystallization does not use organic solvents and does not generate organic waste, which is an environmentally friendly and economically feasible separation operation.

[0079] 4. The isosorbide refining system of the present invention can effectively reduce the unit product energy consumption and save energy by coupling rectification and melt crystallization. It can be operated continuously by switching multiple falling film crystallizers, which is conducive to large-scale continuous production and can meet the requirements of industrial production.

[0080] 5. The inventors found that the membrane structure or its further cooperation with the crystallization tube can affect the effect of product purification.

[0081] 6. The present invention also explores the purification process parameters of isosorbide and provides a method for purifying isosorbide. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 It is a structural schematic diagram of the isosorbide refining system;

[0083] Reference numerals:

[0084] 1-rectification tower, 2-falling film crystallizer, 3-reboiler, 4-condenser, 5-first container, 6-second container, 7-third container, 8-fourth container, 9-heat exchange medium supply end, 10-fifth container;

[0085] a-raw material, b-sweating liquid, c-isosorbide product, d-heat medium, e-coolant, f-kettle residue.

[0086] Figure 2 for Figure 1 Schematic diagram of the structure of the falling film crystallizer;

[0087] Figure numerals: 21 - crystallization tube, 22 - liquid inlet, 23 - liquid outlet, 24 - heat exchange medium inlet, 25 - heat exchange medium outlet, 26 - exhaust port, 27 - membrane structure, 28 - cylinder.

[0088] Figure 3 for Figure 2 A form of cloth membrane structure: Schematic diagram of sieve plate type cloth membrane structure;

[0089] Reference numerals: 31 - vertical pipe; 32 - impact plate; 33 - weir groove; 34 - distribution plate;

[0090] Figure 4 for Figure 3 Schematic diagram of the middle impact plate;

[0091] Reference numerals: 41 - first-level pore structure, 42 - second-level pore structure;

[0092] Figure 5 for Figure 2 Another form of cloth membrane structure: Schematic diagram of grid-type cloth membrane structure;

[0093] Reference numerals:

[0094] 51-nozzle; 52-wire mesh; 53-grid.

[0095] Figure 6 Schematic diagram of three types of microgroove structures. DETAILED DESCRIPTION

[0096] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0097] If the specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or the conditions recommended by the manufacturer. If the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be obtained through commercial channels.

[0098] The process of isosorbide refining of the present invention is applicable to new equipment, can be very economical to separate and purify isosorbide, and the whole purification cost is greatly reduced. The following is further described in conjunction with specific embodiment. For the convenience of description, the device among the present invention omits conventional valves on the pipeline, conventional nozzles on the storage tank, manholes, instrument interfaces, accessories such as supports, and the technical personnel of the industry can design as required. The technical personnel of the industry can make more modifications and improvements, for example, change the feed metering mode, adjust the nozzle specifications of the device, increase the number of interfaces, and all these modifications, adjustments, and improvements should be regarded as protection scope of the present invention.

[0099] like Figure 1 The refining system shown includes: a distillation system and a melt crystallization system arranged downstream of the distillation system; that is, the raw material a first enters the distillation system;

[0100] The distillation system includes a distillation tower 1, a reboiler 3, a condenser 4 and a first container 5, and the melt crystallization system includes a falling film crystallizer 2, a product processing unit and a heat exchange medium circulation unit;

[0101] The reboiler 3 is arranged in the bottom of the distillation tower, and the bottom of the distillation tower is taken out from the bottom of the distillation tower;

[0102] The condenser 4 is arranged at the top of the distillation tower; one end of the first container 5 is connected to the condenser 4, and the other end is connected to the feed liquid inlet 22 of the falling film crystallizer;

[0103] The number of falling film crystallizers 2 is N≥1, preferably N≥2. When N≥2, the falling film crystallizers are arranged in parallel;

[0104] Falling film crystallizer 2 (see Figure 2 ) is a vertical tube shell structure, including a cylinder 28, a crystallization tube bundle (a tube bundle formed by a plurality of crystallization tubes 21) arranged in the cylinder 28, a membrane structure 27, a heat exchange medium inlet 24, a heat exchange medium outlet 25, an exhaust port 26, and a liquid outlet 23; the membrane structure is a grid-type or sieve-plate-type membrane structure; the crystallization tube is a one-way tube bundle, and the aspect ratio of each crystallization tube is 100 to 800, preferably 200 to 300;

[0105] The product processing unit includes a second container 6, a third container 7 and a fourth container 8. The second container 6, the third container 7 and the fourth container 8 are all connected to the liquid outlet 23 of the falling film crystallizer. Valves are arranged on each connecting pipeline, and the valves are switched according to the process occurring in the falling film crystallizer; when the isosorbide mother liquor is in the cooling crystallization process, the valve connected to the second container 6 is opened, and the uncrystallized isosorbide mother liquor after the crystallization is completed is recovered to the second container 6; when the isosorbide mother liquor is in the sweating and impurity removal process, the valve connected to the third container 7 is opened, and the sweating liquid b is recovered to the third container 7; when the isosorbide mother liquor is in the heating and melting process, the valve connected to the fourth container 8 is opened, and the melted isosorbide product c is collected in the fourth container 8.

[0106] The heat exchange medium circulation unit includes a heat exchange medium supply end 9 and a fifth container 10 for storing heat exchange medium; the heat exchange medium supply end 9 is connected to the heat exchange medium inlet 24, the heat exchange medium outlet 25 is connected to one end of the fifth container 10, and the other end of the fifth container 10 is connected to the heat exchange medium supply end 9, forming a heat exchange medium circulation unit.

[0107] The heat exchange medium supply end is used to supply hot medium d and cold medium e to adjust the temperature of the falling film crystallizer to meet the requirements of each process.

[0108] The pipelines in this refining system are all made of stainless steel, and all connections are made of flanges and bolts.

[0109] Figure 3 It is a sieve plate type membrane structure, including an anti-collision plate 32 with a vertical pipe 31, a weir groove 33 and a distribution plate 34 arranged from top to bottom; the hole diameter of the distribution plate is 5 to 50 mm, for example, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm or 45 mm;

[0110] Anti-collision plate 32 (see Figure 4 ) has a first-level pore structure 41 and a second-level pore structure 42, the diameter of the first-level pore structure 41 is 5 to 20 mm, and the diameter of the second-level pore structure 42 is 70 to 120 mm.

[0111] Figure 5 It is a grid-type membrane structure, including a feed nozzle, a wire mesh and a grid arranged from top to bottom; the spacing between adjacent grids is 5 to 50 mm, for example, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm or 45 mm; the cone angle of the spray range of the feed nozzle is 90° to 150°, preferably 100° to 120°; by setting the feed nozzle, the automatic cleaning and uniform feeding functions of the membrane structure are realized.

[0112] The crystallization tube bundle has a fin structure or a microgroove structure. The microgroove structure is arranged on the side of the tube bundle that contacts the isosorbide liquid (such as the inside or outside of the tube bundle). Figure 6 As shown, the microgroove structure is a tooth groove structure (a), a twill structure (b) or a thread structure (c); further, the groove width and groove depth are continuous from top to bottom, showing a regular or decreasing trend. The arrangement of the microgrooves is axial, twill, radial or spiral, and the extension direction can also change continuously or stepwise from top to bottom.

[0113] Example 1

[0114] The falling film evaporator used in this embodiment adopts Figure 3 The sieve plate type membrane structure shown in the figure has a sieve hole diameter of 8mm in the distribution plate, a first-level hole structure diameter of 12mm in the anti-collision plate, and a second-level hole structure diameter of 90mm. The crystallization tube bundles are all single-pass, with a micro-groove structure, a tube diameter of 25mm, and a tube bundle aspect ratio of 300.

[0115] The specific method for purifying isosorbide is as follows:

[0116] (1) The mixed raw material liquid of isosorbide is pumped into a distillation tower, the pressure of the distillation tower is controlled to be 2 kPa, the temperature is heated to 185° C., and vacuum distillation is performed. The isosorbide content of the raw material liquid is 65.0 wt%.

[0117] (2) The high boiling point fraction is discharged from the bottom of the kettle, and the low boiling point fraction isosorbide flows out from the top of the tower. After flowing out, it is condensed and enters the condensation tank. The outlet temperature of the condensation tank is 65°C, and then enters the falling film crystallizer for cooling and crystallization. The isosorbide content of the condensate is 91.5wt%.

[0118] (3) Two falling film crystallizers are operated in parallel. During operation, at least one of the entire melt crystallization system is in a crystallization state and one is in a sweating / melting state at the same time period. Falling film crystallizer A / B is switched. The specific implementation method is to close the valve of falling film crystallizer B while opening the valve of falling film crystallizer A. The initial temperature of the falling film crystallizer is adjusted to 48°C using a refrigerant, and the crude isosorbide product at the outlet of the condenser flows into the falling film crystallizer A, allowing the crude isosorbide crystal layer to grow for 1 hour.

[0119] (4) After the crystal layer in falling film crystallizer A grows for 1 hour, it is cooled and crystallized at a rate of 0.05℃ / min, and the crystals continue to grow for 2 hours. After the crystals grow, the impurity liquid that has not been crystallized is discharged, and then the temperature of the falling film crystallizer is increased to make the crystals sweat. At this time, the valve of falling film crystallizer A is closed and the valve of falling film crystallizer B is opened, so that the distilled crude isosorbide product enters falling film crystallizer B for crystallization. Similarly, after the crystal layer in falling film crystallizer B grows to a certain extent, the valve of falling film crystallizer B is closed, and the switching and circulation are carried out in this way. The heating rate of falling film crystallizer A is controlled to be 0.05℃ / min, and the sweating end temperature is 55℃. After sweating, the sweat is discharged and the temperature is increased to above 82℃ to melt the pure isosorbide crystals and collect them in the product tank.

[0120] (5) The falling film crystallizer that has completed the crystallization is ready for the next crystallization. In the above process, two falling film crystallizers are switched to be used alternately, so that the distillation and crystallization are carried out continuously. The concentration of the obtained isosorbide is 99.92wt%.

[0121] Example 2

[0122] The falling film evaporator used in this embodiment adopts Figure 5 The grid-type membrane structure shown in the figure has a spray cone angle of 120° and a grid spacing of 10 mm. The crystallization tube bundles are all single-pass, have a fin structure, a tube diameter of 40 mm, and a tube bundle aspect ratio of 200.

[0123] The specific method for purifying isosorbide is as follows:

[0124] (1) The mixed raw material liquid of isosorbide is pumped into a distillation tower, the top pressure of the distillation tower is controlled to be 0.5 kPa, the temperature is heated to 156° C., and vacuum distillation is performed. The isosorbide content of the raw material liquid is 64.2 wt %.

[0125] (2) The high boiling point fraction is discharged from the bottom of the kettle, and the low boiling point fraction isosorbide flows out from the top of the tower, enters the condensation tank after condensation, and the outlet temperature of the condensation tank is 62°C, and then enters the falling film crystallizer for cooling crystallization. The isosorbide content of the condensate is 92.8wt%.

[0126] (3) Two falling film crystallizers are operated in parallel. During operation, at least one of the entire melt crystallization system is in a crystallization state and one is in a sweating / melting state at the same time period. Falling film crystallizer A / B is switched. The specific implementation method is to close the valve of falling film crystallizer B while opening the valve of falling film crystallizer A. The initial temperature of the falling film crystallizer is adjusted to 50°C using a refrigerant, and the crude isosorbide at the outlet of the condenser flows into the falling film crystallizer A, allowing the crystal layer of the crude isosorbide to grow for 0.5h.

[0127] (4) After the crystal layer in the falling film crystallizer has grown for 0.5 hours, the temperature is reduced and crystallized at a rate of 0.05°C / min, and the crystals continue to grow for 2 hours. After the crystals have grown, the impurity liquid that has not been crystallized is discharged, and then the temperature of the falling film crystallizer is increased to make the crystals sweat. At this time, the valve of the falling film crystallizer A is closed and the valve of the falling film crystallizer B is opened, so that the distilled crude isosorbide product enters the falling film crystallizer B for crystallization. Similarly, after the crystal layer in the falling film crystallizer B has grown to a certain extent, the valve of the falling film crystallizer B is closed, and the switching and circulation are repeated. The heating rate of the falling film crystallizer A is controlled to be 0.08°C / min, and the sweating end temperature is 58°C. After sweating, the sweat is discharged and the temperature is increased to above 82°C to melt the pure isosorbide crystals and collect them in the product tank.

[0128] (5) The falling film crystallizer that has completed the crystallization is ready for the next crystallization. In the above process, the two falling film crystallizers are used alternately so that the distillation and crystallization are carried out continuously. The concentration of the obtained isosorbide is 99.95wt%.

[0129] Comparative Example 1

[0130] Different from Example 1, Comparative Example 1 does not have a cloth membrane structure.

[0131] Comparative Example 2

[0132] Different from Example 1, Comparative Example 2 does not have a microgroove structure, and uses a crystal tube bundle with a smooth structure.

[0133] The results are shown in the following table:

[0134]

[0135] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A system for refining isosorbide, characterized in that: The refining system includes a distillation system and a melt crystallization system arranged downstream of the distillation system; The distillation system comprises a distillation tower, and the melt crystallization system comprises a falling film crystallizer.

2. The refining system according to claim 1, characterized in that: The number of the falling film crystallizers N is ≥ 1, preferably N is ≥ 2; when N is ≥ 2, the falling film crystallizers are arranged in parallel.

3. The refining system according to claim 1 or 2, characterized in that: The falling film crystallizer is a vertical shell-and-tube structure, comprising a cylinder, a crystallization tube bundle arranged in the cylinder, and a film distribution structure; Preferably, each crystallization tube is a one-way tube bundle, and the aspect ratio of each crystallization tube is 100 to 800; And / or, the crystallized tube bundle has a fin structure or a microgroove structure; And / or, the falling film crystallizer further comprises an upper tube box, the film distribution structure is arranged inside the upper tube box and located at the top of the crystallization tube bundle, maintaining concentricity with the crystallization tube; And / or, the membrane structure may be a grid type or a sieve plate type.

4. The refining system according to claim 3, characterized in that: The sieve plate type membrane structure includes an anti-collision plate with a vertical pipe, a weir groove, and a sieve plate or a distribution plate arranged from top to bottom, and the sieve plate or the distribution plate has a hole structure; for example, the hole diameter is 5 to 50 mm; Preferably, the anti-collision plate includes but is not limited to a primary hole structure or a secondary or higher hole structure.

5. The refining system according to claim 3, characterized in that: The grid-type membrane structure comprises a feed nozzle, a wire mesh and a grid arranged from top to bottom; preferably, the spacing between adjacent grids is 5 to 50 mm; Preferably, the cone angle of the spray range of the feed nozzle is 90° to 150°.

6. The refining system according to any one of claims 1 to 5, characterized in that: The distillation system further comprises a reboiler arranged in the reactor of the distillation tower, and a condenser arranged in the top of the distillation tower; Preferably, the distillation tower is a packed tower, a sieve plate tower or a bubble cap tower; And / or, the distillation system further comprises a first container connected to the condenser for storing liquid isosorbide; Preferably, the first container is provided with at least one liquid outlet end connected to the liquid inlet of the falling film crystallizer; preferably, the first container is also provided with a second liquid outlet end connected to the upper end of the distillation tower, that is, the upper end of the distillation tower, the condenser and the first container form a loop; And / or, the melt crystallization system further comprises a product processing unit connected to the liquid outlet of the falling film crystallizer; Preferably, the product processing unit comprises a second container, a third container, and a fourth container, wherein the second container is used to recover uncrystallized isosorbide mother liquor, the third container is used to recover sweating liquid of isosorbide crude crystals, and the fourth container is used to collect isosorbide purified by sweating; Preferably, the melt crystallization system further comprises a heat exchange medium supply end and a fifth container for storing the heat exchange medium; preferably, the heat exchange medium supply end is connected to the heat exchange medium inlet, the heat exchange medium outlet is connected to one end of the fifth container, and the other end of the fifth container is connected to the heat exchange medium supply end, so as to form a heat exchange medium circulation unit; Preferably, the falling film crystallizer may further include a discharge branch, which is arranged below the crystallization tube bundle and connected to the first container. Preferably, the falling film crystallizer further comprises a heat exchange medium inlet and an outlet, which are respectively arranged at the upper end and the lower end of the crystallization tube bundle; Preferably, the refining system further comprises a control system.

7. A method for purifying isosorbide, characterized in that: The purification method comprises: The raw material is subjected to vacuum distillation to obtain an isosorbide gas phase, and the isosorbide gas phase is condensed and enters a falling film crystallizer as a mother liquid; after cooling and crystallizing, sweating and removing impurities, and heating and melting, an isosorbide product with a purity of not less than 99.0wt% is obtained; Preferably, the falling film crystallizer has the definition as shown in any one of claims 1-5.

8. The purification method according to claim 7, characterized in that The tower top temperature of the vacuum distillation process is controlled at 150-250°C; and / or the tower top pressure is 0.5-5kPa; And / or, the mother liquor temperature is 60-90°C; And / or, the cooling crystallization comprises: adjusting the temperature of the falling film crystallizer to 45-50°C, then introducing the mother liquor, staying for 0.5-1.0h to allow the crystal layer to grow, and then cooling at a rate of 0.02-0.1°C / min to allow the crystal layer to continue to grow for 1-2h, and discharging the mother liquor without crystallization after crystallization; And / or, the sweating impurity removal comprises: after the cooling crystallization is completed, increasing the temperature of the falling film crystallizer at a rate of 0.02-0.1°C / min, and the sweating end point temperature is 45-65°C; And / or, the heating and melting comprises: after the sweating and impurity removal is completed, the falling film crystallizer is heated to above 82° C. to melt all the crystal layers and collect the isosorbide product; And / or, two falling film crystallizers are connected in parallel, and in the same time period, the A / B falling film crystallizers are dynamically switched, one of which is in a cooling crystallization state, and the other is in a sweating, impurity removal, heating and melting state.

9. Use of the refining system according to any one of claims 1 to 6 in purifying or separating isosorbide.

10. Use of the purification method according to any one of claims 7 to 8 in isosorbide separation.

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