Falling film crystallization facility

Abstract

The utility model relates to a falling film crystallization facility for purifying a crude composition through crystallization, which comprises a falling film crystallizer, the falling film crystallizer comprises a feed inlet line for a crude composition, a melt outlet line and a melt inlet line connected to each other via a recirculation line, a plurality of hollow tubes, an inlet line for a heat transfer medium, and an outlet line for a heat transfer medium, wherein the falling film crystallization plant further comprises at least two parallel heat exchangers via which the inlet line for the heat transfer medium and the outlet line for the heat transfer medium are connected to each other, the falling film crystallization facility further comprises a vacuum unit connected with the falling film crystallizer.

Description

Technical Field

[0001] The utility model relates to a falling film crystallization facility for purifying a crude composition through crystallization. Background Art

[0002] Usually, the crude product obtained from chemical synthesis process is a mixture of target compound and impurity, and impurity is an undesirable by-product component. And, usually, the content of impurity is higher than the content desired in the crude product. Therefore, the crude product from chemical reactor (it has been synthesized in a conventional manner, or the final product manufactured in the past is recovered to reclaim the crude product) needs to be purified by removing the impurity of appropriate amount from the crude product by suitable separation technology, so as to obtain the target compound of desired final purity. For example, using oxygen-containing gas to catalytically oxidize propylene in gas phase produces a crude composition comprising acrylic acid as the target compound and impurity (such as acetic acid, propionic acid, maleic acid, maleic anhydride, acrolein, furfural, benzaldehyde, phenothiazine and protoanemonin). Known multiple separations (that is, purification process) are used to purify this type of crude composition, such as distillation, crystallization, extraction, absorption, adsorption, ion exchange chromatography, etc. Usually, several techniques in the above-mentioned purification process are combined after cost optimization.

[0003] A common purification technique is distillation, which allows the separation of organic compounds based on their different boiling points. During distillation, the mixture to be separated is heated, which causes the compounds with the lower boiling point to mainly evaporate and rise, highly concentrated in the vapor stream, to the top of the distillation column, where they are taken off as an overhead stream, condensed and then further processed as required. In contrast, the compounds with the higher boiling point remain mainly in liquid form and are highly concentrated in the liquid stream, flowing down to the bottom of the distillation column, where they are removed as a bottom stream and then further processed as required. However, distillation is not suitable for separating different compounds with similar boiling points.

[0004] Crystallization is another important industrial process for separating and purifying compounds from a mixture, wherein the target compound to be purified is contained in a high concentration, a medium concentration, or even as low as about 70% by weight. Generally, the separation efficiency of crystallization increases significantly with the increase in the purity of the crystallized product. For this reason, crystallization is generally used to purify compositions with high concentrations of target compounds (such as close to 100% by weight, for example 99.99% by weight). Crystallization is mainly based on the different melting points of organic compounds to separate organic compounds. More specifically, the target compound is highly concentrated in solid crystals, while impurities are concentrated in the residual melt, and impurities are then separated from the crystals after the crystallization stage ends. Generally, the crystallization process is subdivided into layer crystallization and suspension crystallization. In suspension melt crystallization, a melt comprising the target compound and at least one different compound is cooled in a vessel so that crystals are formed in a suspension of crystallized particles, the target compound is rich in these crystals, and these crystals are dispersed in the melt exhausted of the target compound. After crystallization is completed, the crystal is separated from the melt, for example, by a filter, a centrifuge or other equipment for solid / liquid separation, and if necessary, such as in a second crystallization stage or by means of another suitable purification method, it is further purified. In contrast, in layered melt crystallization, the crystal grows on the cooled wall surface in the form of a crystal layer, wherein the crystallization heat generated is transferred to the cooling medium flowing on the other side of the cooled wall by the crystal layer. Therefore, the crystal layer is in a layered melt crystallization lower than the melt temperature. More precisely, the temperature at the surface of the crystal layer in contact with the melt is almost equal to the melt temperature, but the relative surface of the crystal layer attached to the cooled wall is close to the cooling medium temperature lower than the melt temperature. The temperature gradient generated from the melt across the crystal layer to the cooling medium is the driving force for the solidification heat to flow from the crystallization front to the cooling medium. On the contrary, the temperature of the crystal in the suspension is substantially equal to the melt temperature. The layered crystallization process is particularly important in industry. At present, two common types of layered crystallization are known, i.e., static crystallization and dynamic crystallization.

[0005] A prominent dynamic crystallization technique is falling film crystallization, which is implemented in a falling film crystallizer, which is a crystallization tower, which includes a hollow tube bundle arranged at least substantially vertically and extending from the upper part of the falling film crystallizer to the bottom area of ​​the falling film crystallizer in a shell. In this bottom area, a storage tank is placed in the crystallizer tower, directly below the lower end of the tube bundle. Before the crystallization process begins, a liquid feed crude composition including a certain concentration of the target compound and one or more other (undesirable) compounds is filled into the storage tank area of ​​the falling film crystallizer. During the crystallization process, a portion of this liquid composition is continuously pumped from the storage tank area of ​​the falling film crystallizer to the upper part of the falling film crystallizer by means of one or more pumps, and is introduced into the upper end of the hollow tube and is allowed to fall back to the storage tank of the falling film crystallizer in the form of a falling film on the inner surface of the hollow tube. At the same time, the outer wall of the hollow tube is cooled to a temperature below the freezing temperature of the liquid composition by allowing a cold heat transfer medium to fall on the outer surface of the hollow tube in the form of a falling film, so that a crystal layer rich in the target compound is deposited on the cooled inner wall surface of the hollow tube. Since the crystal layer of the target compound is deposited on the cooled inner wall surface of the hollow tube, thereby causing the exhaustion of this compound in the liquid crude composition, a mother liquor is formed by the liquid feed crude composition, which is a residual melt. Therefore, the concentration of the target compound in the mother liquor is lower than that in the liquid feed crude composition, but it is concentrated with respect to the impurity compound. Whenever necessary, the mother liquor is circulated to crystallize the desired amount of the target compound from the mother liquor and deposit it on the inner wall surface of the hollow tube as a crystal layer. After the crystallization is completed, the mother liquor is completely removed from the falling film crystallizer, the crystal layer deposited on the inner wall surface of the hollow tube is melted, and then it is removed from the falling film crystallizer to obtain the separated and purified target compound. Optionally, in order to increase the purity of the target compound, the crystal layer can be sweated by gently heating the crystal layer to a temperature close to the melting point of the purified compound, so that the remaining mother liquor is discharged from the pores of the crystal layer, and then the purified crystals are completely melted. If the purity of the obtained product composition is not high enough, the product composition can be subjected to one or more subsequent falling film crystallization stages in order to increase the degree of purity. In general, layer crystallization, and in particular falling film crystallization, is a batch process comprising a filling and precooling stage, a subsequent crystallization stage, optionally one or more subsequent sweating stages and a melting stage, and then the purified product is taken out from the falling film crystallizer in the product removal stage. Most commercially operated crystallization processes require more than one stage to obtain a target compound of a specified purity. In this multi-stage operation mode, the molten crystals of one stage are recrystallized in subsequent stages until the desired degree of purity has been reached in a certain stage of this stage sequence (the last stage of the sequence).The more stages required in the sequence of stages of a commercially operated crystallization process, the larger the crystallizers that must be employed to achieve a given production capacity and the higher the energy consumption per ton of purified target compound produced.

[0006] In various cases, the crude composition feed contains low boiling point components, which have not been removed to a sufficient extent from the crude composition feed by previous distillation. In this case, pretreatment of the crude composition feed by evaporation equipment (such as falling film evaporation) will help to reduce the crystallization work and thus reduce the size of the crystallization equipment. However, the additional cost of the evaporator equipment will far exceed the cost savings of the crystallization equipment. In addition, due to the size of commercially available falling film evaporators, several such equipment will be required considering the typical production capacity of a crystallization facility. Utility Model Content

[0007] In view of this, the object of the present invention is to provide a falling film crystallization facility and a falling film crystallization process for purifying a crude composition by crystallization, which are more efficient in particular in removing low-boiling components and are characterized by having a lower total cost than the known falling film crystallization facilities and processes, respectively.

[0008] According to the utility model, this object is met by providing a falling film crystallization facility for purifying a crude composition by crystallization, wherein the falling film crystallization facility comprises a falling film crystallizer, the falling film crystallizer comprises a feed inlet pipeline for the crude composition, a melt outlet pipeline and a melt inlet pipeline interconnected via a recycling pipeline, a plurality of hollow tubes, an inlet pipeline for a heat transfer medium and an outlet pipeline for the heat transfer medium, wherein the falling film crystallization facility further comprises at least two parallel heat exchangers, wherein the inlet pipeline for the heat transfer medium and the outlet pipeline for the heat transfer medium are interconnected via the at least two parallel heat exchangers, and wherein the falling film crystallization facility further comprises a vacuum unit connected to the falling film crystallizer.

[0009] As a result, the operating cost of falling film crystallization is significantly reduced. In a common falling film crystallization process, the falling film crystallizer is operated under a slight overpressure using a protective gas (such as nitrogen), and the protective gas is supplied to the falling film crystallizer from an exhaust unit, so that there is no oxygen in the falling film crystallizer, and no oxygen can enter the falling film crystallizer in the event of a leak, etc., thereby reliably avoiding any oxidation reaction or corrosion in the falling film crystallizer. In contrast, the falling film crystallizer of the falling film crystallization facility according to the utility model includes a vacuum unit connected to the falling film crystallizer, which allows the implementation of a complete crystallization process or one or more single stages of the crystallization process under vacuum. For example, if a vacuum is applied to the falling film crystallizer during the sweating stage and / or the melting stage, impurities with a relatively low boiling point present in the pores of the crystal evaporate and are taken out of the falling film crystallizer via the vacuum unit. If a vacuum is applied during the crystallization stage, the same situation occurs, even if the degree is lower. If, as suggested for the present invention, a vacuum is applied during the filling and optional but preferred preheating phase (with delayed precooling), impurities with a relatively low boiling point evaporate directly from the crude composition present in the sump of the falling film crystallizer and are taken out of the falling film crystallizer via the vacuum unit in the form of a falling film on the inner wall of the crystallization tube. Since the crystallization is carried out in the form of melt crystallization according to the present invention, the crude composition filled into the sump of the falling film crystallizer during the filling and optional but preferred preheating phase is usually a melt of the crude composition. By removing the corresponding impurities by means of evaporation, fewer impurities must be removed by crystallization and / or sweating, so that the crystallization time and / or the number of sweating phases and / or the number of subsequent falling film crystallization phases are reduced, which leads to a reduction in operating costs based on a given amount of target compound with a predetermined degree of purity. Therefore, in principle, the falling film crystallization facility according to the present invention combines falling film evaporation and falling film crystallization in one facility and one process, respectively. Unlike a common falling film crystallizer, the falling film crystallizer of the falling film crystallization facility according to the present invention includes a vacuum unit, and unlike a common falling film evaporator, the falling film crystallizer of the falling film crystallization facility according to the present invention includes two parallel heat exchangers, one for cooling the melt during the crystallization stage, and one for heating the falling film crystallizer during the sweating and melting stages. Even though the falling film crystallizer of the falling film crystallization facility according to the present invention is a combination of a falling film crystallizer and a falling film evaporator, for ease of description, it will be referred to as a falling film crystallizer hereinafter.

[0010] The term crude composition as used herein refers to a mixture of generally organic components, generally directly from a chemical reactor, or in most cases, as a crude product after pre-purification by other processes (such as distillation). However, the crude composition may also be, for example, a fraction of coal tar distillation, such as a crude naphthalene or crude anthracene fraction. High purity naphthalene and anthracene are particularly useful for the manufacture of specialty plastics, dyes and pigments, specific drugs, and the like. Moreover, falling film crystallization may be used to purify specific inorganic compounds, such as, for example, hydrazine, which is purified to obtain an ultra-high purity of more than 99.99% by weight for use in spacecraft auxiliary engines.

[0011] According to the utility model, the falling film crystallization facility comprises a vacuum unit connected to the falling film crystallizer, thereby allowing a pressure lower than atmospheric pressure to be generated in the falling film crystallizer during its operation. Preferably, the vacuum unit (which comprises a vacuum source, such as a vacuum pump) is connected to the falling film crystallizer via a pipeline or a vacuum pipeline, respectively.

[0012] Furthermore, the falling film crystallizer comprises a melt outlet line and a melt inlet line connected to each other via a recirculation line. At the start of the process, i.e., before the start of the crystallization stage, the melt transported from the melt outlet to the melt inlet via the recirculation line is the melt of the crude composition, and the melt transported via the recirculation line after the start of crystallization is the mother liquor formed by the crystals of the target compound being deposited on the cooled inner wall surface of the hollow tube, thereby causing the compound to be depleted in the melt of the crude composition. In order to transport the melt via the recirculation line, preferably, a pump is arranged in the recirculation line.

[0013] In addition, the falling film crystallizer comprises a plurality of hollow tubes. The number of hollow tubes depends on the size of the falling film crystallizer and the desired production capacity and purification work, ie, the number of repeated crystallization stages before reaching the desired purity.

[0014] Preferably, the falling film crystallizer and the plurality of hollow tubes within the falling film crystallizer are at least substantially vertically arranged, wherein at least substantially vertically arranged means that the angle between the length axis of the falling film crystallizer and the length axis of the plurality of hollow tubes and the vertical direction is at most 10°, preferably at most 5°, more preferably at most 1.5°, and most preferably 0°.

[0015] Good results are particularly obtained when each of the plurality of hollow tubes extends from an upper portion to a lower portion of the falling film crystallizer. Preferably, each of the plurality of hollow tubes extends from a point located at 0 to 30%, and preferably 0 to 10%, of the distance from the top to the bottom of the falling film crystallizer to a point located at 60 to 80%, and preferably 70 to 80% of the distance from the top to the bottom of the falling film crystallizer, as seen from the top to the bottom of the falling film crystallizer, so that a sump portion in which no hollow tube is arranged is located below the lower ends of the plurality of hollow tubes.

[0016] According to an alternative embodiment of the present invention, seeing from the top to the bottom of the falling film crystallizer, each of the plurality of hollow tubes extends from a point located at 0 to 10%, and preferably 0 to 5%, of the distance from the top to the bottom of the falling film crystallizer to the bottom of the falling film crystallizer, wherein a separate vessel is placed directly below the falling film crystallizer and is connected to the falling film crystallizer via a product discharge line extending from the bottom of the falling film crystallizer to the top of the separate vessel.

[0017] Furthermore, preferably, the melt inlet pipeline is connected to the top of the falling film crystallizer, and the melt outlet pipeline is connected to the bottom of the falling film crystallizer.

[0018] Each of the hollow tubes comprises an inner cavity which is delimited by the inner wall of the corresponding hollow tube at its peripheral region, and is open at its top and at its bottom. Even though the cross-sectional form of the hollow tube may be square, rectangular, polygonal or elliptical, preferably, the cross-sectional form of the hollow tube is circular, i.e., the hollow tube has the form of a hollow cylinder in three dimensions. When the heat transfer medium flows around the outer wall of the hollow tube during operation of the falling film crystallizer, the melt flows through the inner cavity of the hollow tube, and more specifically, flows downward in the form of a thin film on the surface of the inner wall of the hollow tube, thereby allowing, during the crystallization phase, crystals to be formed on the surface of the cooled inner wall of the hollow tube. Therefore, one open end of each hollow tube, and preferably the upper open end of each hollow tube, is the inlet of the melt of the hollow tube, and the opposite, and preferably the lower open end of each hollow tube is the outlet of the melt of the hollow tube.

[0019] Therefore, preferably, each upper end of the inner cavity of the plurality of hollow tubes is directly or indirectly connected to the melt inlet pipeline of the falling film crystallizer, and each lower end of the inner cavity of the plurality of hollow tubes is directly or indirectly connected to the melt outlet pipeline of the falling film crystallizer, so that the melt can flow from the melt inlet pipeline through the inner cavity of each hollow tube to the melt outlet pipeline of the falling film crystallizer, and then recirculate through the recirculation pipeline during the crystallization stage. More preferably, the lower end of each of the hollow tubes is indirectly connected to the melt outlet pipeline of the falling film crystallizer, that is, the lower end of each of the hollow tubes is connected to the sump part of the falling film crystallizer, which in turn is connected to the melt outlet pipeline of the falling film crystallizer at its opposite end. Furthermore, a distributor can be arranged between the melt inlet pipeline of the falling film crystallizer and the upper ends of the inner cavities of the plurality of hollow tubes so as to evenly distribute the melt to the individual cavities of the plurality of hollow tubes. Preferably, the distributor for the melt is designed so that individual thermal expansion of the individual tubes is possible. Examples of such designs are described, for example, in CH478392 and CH478393.

[0020] In a further development of the concept of the invention, it is proposed that the feed inlet line for the crude composition is connected to the sump section of the falling film crystallizer.

[0021] In order to avoid contamination of the recycled melt by the heat transfer medium, it is important that the portion of the falling film crystallizer through which the heat transfer medium flows is liquid-tightly separated from the portion of the falling film crystallizer through which the melt flows. For this purpose, preferably, a separation device is arranged in the falling film crystallizer, and the separation device separates the hollow space formed between the outer peripheral walls of the plurality of hollow tubes from the inner cavity of each hollow tube in a liquid-tight manner, so that no heat transfer medium can flow from the hollow space formed between the outer peripheral walls of the plurality of hollow tubes into any of the cavities of the plurality of hollow tubes, no melt can flow from any of the inner cavities of the plurality of hollow tubes into the hollow space formed between the outer peripheral walls of the plurality of hollow tubes, and no melt can flow from the outside through the separation device into the hollow space formed between the outer peripheral walls of the plurality of hollow tubes.

[0022] Preferably, the falling film crystallizer and the plurality of hollow tubes are arranged at least substantially vertically, wherein an upper perforated plate and a lower perforated plate are arranged in the falling film crystallizer as a separation device, wherein each perforation of the upper perforated plate surrounds the hollow tube liquid-tightly, and each perforation of the lower perforated plate surrounds the hollow tube liquid-tightly, so that a hollow space is formed between the outer peripheral walls of the plurality of hollow tubes and between the upper perforated plate and the lower perforated plate, wherein the hollow space is bounded by the non-perforated portions of the upper perforated plate and the lower perforated plate and the peripheral inner wall of the falling film crystallizer. Therefore, preferably, each hollow tube is surrounded by the upper perforated plate at its upper end and by the lower perforated plate at its lower end. When the hollow tube comprises a lower portion having a first diameter and an upper portion having a second reduced diameter, each perforation of the upper perforated plate surrounds the upper portion of the hollow tube liquid-tightly, and each perforation of the lower perforated plate surrounds the lower portion of the hollow tube liquid-tightly. If the pipes are connected as in the above-mentioned CH478392 and / or CH478393, the liquid tightness is provided by the distributor and does not need to be provided by the upper plate perforations.

[0023] To allow the heat transfer medium to enter and leave the hollow space forming the heat transfer medium compartment of the falling film crystallizer, an inlet line for the heat transfer medium and an outlet line for the heat transfer medium are preferably connected to the hollow space formed between the outer peripheral walls of the plurality of hollow tubes and delimited by upper and lower perforated plates.

[0024] According to the utility model, the inlet pipeline for the heat transfer medium and the outlet pipeline for the heat transfer medium are connected to each other via at least two parallel heat exchangers of the falling film crystallization facility. According to a particularly preferred embodiment of the utility model, the outlet pipeline for the heat transfer medium is divided into a first branch pipeline and a second branch pipeline. The first branch pipeline is connected to the first valve, connected to the first heat exchanger of the at least two parallel heat exchangers downstream of the first valve, and connected to the inlet pipeline for the heat transfer medium downstream of the first heat exchanger; the second branch pipeline is connected to the second valve, connected to the second heat exchanger of the at least two parallel heat exchangers downstream of the second valve, and connected to the inlet pipeline for the heat transfer medium downstream of the second heat exchanger. In addition, preferably, the inlet pipeline for the heat transfer medium and / or the outlet pipeline for the heat transfer medium are connected to a pump, thereby allowing the heat transfer medium to be pumped through the corresponding pipelines. This arrangement allows the heat transfer medium to be selectively transported through the first heat exchanger by opening the first valve and closing the second valve, and the heat transfer medium to be selectively transported through the second heat exchanger by closing the first valve and opening the second valve. For example, the first heat exchanger is operated with a coolant and the second heat exchanger is operated with a heating agent, wherein during the crystallization stage, the first valve is opened and the second valve is closed, so that the heat transfer medium is selectively transported through the first heat exchanger and cooled therein, thereby cooling the wall of the hollow tube; and during the optional preheating stage and the sweating and melting stage, the first valve is closed and the second valve is opened, so that the heat transfer medium is selectively transported through the second heat exchanger and heated therein, thereby heating the wall of the hollow tube.

[0025] Good results are particularly obtained when at least one of the at least two parallel heat exchangers, and preferably each of the at least two parallel heat exchangers, is a shell and tube heat exchanger or a plate and frame heat exchanger. For example, one of the shell or tube sides of the first heat exchanger is connected to a first branch line, and the other of the shell or tube sides of the first heat exchanger is connected to an inlet line and an outlet line for a coolant; while one of the shell or tube sides of the second exchanger is connected to a second branch line, and the other of the shell or tube sides of the second heat exchanger is connected to an inlet line and an outlet line for a heating agent (such as steam, tempering water, hot thermal crude oil or the like).

[0026] In a further development of the concept of the utility model, it is proposed to arrange a process energy buffer device between at least one of the at least two heat exchangers and the falling film crystallizer, wherein the energy buffer device is connected to an inlet line for the heat transfer medium to the falling film crystallizer and an outlet line for the heat transfer medium leading from the falling film crystallizer, and wherein the buffer device is connected to separate inlet and outlet lines to and from the corresponding heat exchanger. The process energy buffer device allows to keep the heat load of the heat exchanger almost constant, while the cooling and heating loads requested during different phases of the crystallization stage can vary strongly.

[0027] According to the present invention, the falling film crystallization facility comprises a vacuum unit, which is connected to the falling film crystallizer. In the simplest embodiment, the vacuum unit consists of a vacuum source (such as preferably a vacuum pump), which is connected to the falling film crystallizer via a vacuum line. However, preferably, the vacuum unit comprises other elements in addition to the vacuum source.

[0028] More specifically, preferably, a valve is arranged in the vacuum line between the falling film crystallizer and the vacuum source so that the vacuum line can be opened and closed, thereby allowing a vacuum to be applied during a single stage of operation of the falling film crystallization facility, while a vacuum is not applied in other stages. For example, during the sweating and melting stages, the valve of the vacuum line is opened, and a vacuum is thus applied to the falling film crystallizer; but during the filling and precooling stages, during the crystallization stage, and during the product removal stage, the valve of the vacuum line is closed. Alternatively, during all stages of the filling and precooling stages, the crystallization stage, the sweating stage, and the melting stage, but not during the product removal stage, the valve of the vacuum line is opened, and a vacuum is thus applied to the falling film crystallizer. Alternatively again, during the filling and precooling stages and during the crystallization stage, but not during the sweating stage, the melting stage, and the product removal stage, the valve of the vacuum line is opened, and a vacuum is thus applied to the falling film crystallizer.

[0029] According to another preferred embodiment of the utility model, the vacuum unit of the falling film crystallization facility comprises a condenser. Thus, at least a part of the impurities with a low boiling point taken out from the falling film crystallizer during the period of applying vacuum to the falling film crystallizer is condensed and can be taken out from the crystallization unit; while only a small amount of impurities is taken out from the falling film crystallization facility as waste gas. Good results are particularly obtained when the condenser is a shell and tube condenser, wherein one of the shell side or the tube side of the shell and tube condenser is connected to the vacuum line, and the other is connected to the inlet line and the outlet line for the coolant.

[0030] Preferably, the condenser is arranged in the vacuum line between the valve and the vacuum source.

[0031] In a further development of the concept of the utility model, it is proposed that the falling film crystallization facility further comprises an exhaust unit, which is connected to the falling film crystallizer via an exhaust line, in which a valve is arranged. The presence of the exhaust unit allows the falling film crystallization facility and in particular the falling film crystallizer to be exhausted with a blanketing gas or a protective gas (such as nitrogen) under a slight overpressure during the period when no vacuum is applied to the falling film crystallization facility and in particular to the falling film crystallizer. In other words, the valve of the exhaust unit is opened only when the valve of the vacuum unit is closed; and the valve of the vacuum unit is opened only when the valve of the exhaust unit is closed. For example, during the sweating and melting phases, the valve of the vacuum unit is open, and thus a vacuum is applied to the falling film crystallizer, but the valve of the exhaust unit is closed; while during the filling and optional but preferred preheating phases, during the crystallization phase and during the product removal phase, the valve of the vacuum unit is closed, and the valve of the exhaust unit is opened, and thus the falling film crystallizer is exhausted. Alternatively, during all of the filling and optional but preferred preheating phases, the crystallization phase, the sweating phase and the melting phase, the valve of the vacuum unit is closed and a vacuum is thus applied to the falling film crystallizer, but the valve of the exhaust unit is closed, whereas during the product removal phase, the valve of the vacuum unit is closed and the valve of the exhaust unit is opened and the falling film crystallizer is thus exhausted. Alternatively again, during the filling and optional but preferred preheating phases and during the crystallization phase, the valve of the vacuum unit is opened and a vacuum is thus applied to the falling film crystallizer, but the valve of the exhaust unit is closed, whereas during the sweating phase, the melting phase and the product removal phase, the valve of the vacuum unit is closed and the valve of the exhaust unit is opened and the falling film crystallizer is thus exhausted.

[0032] According to another preferred embodiment of the present invention, the falling film crystallizer comprises a connecting pipeline, and the connecting pipeline is divided into the vacuum pipeline and the exhaust pipeline.

[0033] In a further development of the inventive concept, it is proposed that the exhaust gas line is connected downstream of the exhaust gas line valve to a pressure equalization line, downstream thereof to a cover gas supply line via a further valve, and downstream thereof to a cover exhaust gas line via a further valve.

[0034] According to another particularly preferred embodiment of the utility model, the falling film crystallizer further comprises a stripping agent inlet line, which is preferably connected to the recirculation line or the storage tank part of the falling film crystallizer. This allows the addition of a stripping agent (such as water) to the melt recycled through the recirculation line, which allows the evaporation selectivity of impurities with a low boiling point to be improved during the period of applying a vacuum to the falling film crystallization facility and in particular to the falling film crystallizer.

[0035] Furthermore, the falling film crystallization facility preferably further comprises a discharge line for discharging the purified product from the falling film crystallization facility during the product withdrawal phase. Good results are particularly obtained when the discharge line, which is equipped with a valve, is connected to the melt outlet line, preferably upstream of a pump located in the recirculation line, such that the valve allows opening the discharge line during the product withdrawal phase and closing the discharge line during all other phases.

[0036] In a further development of the concept of the utility model, it is proposed that the facility further comprises a bypass line, which branches from the outlet line for the heat transfer medium and is connected to the inlet line for the heat transfer medium at a position downstream of the at least two parallel heat exchangers, thereby allowing the heat transfer medium to bypass the at least two parallel heat exchangers during operation of the facility. Preferably, the valve is arranged in the bypass line, just upstream of the position where the bypass line is connected to the inlet line for the heat transfer medium. Similarly, preferably, the valve is arranged in the inlet line for the heat transfer medium, just upstream of the position where the first and second branch lines are connected to the inlet line. In addition, preferably, the facility comprises a temperature measuring instrument arranged downstream of the position where the bypass line is connected to the inlet line for the heat transfer medium. The temperature instrument and the two valves are components of a temperature control loop, in which the positions of the two valves are controlled according to the difference between the desired temperature and the measured temperature. The two valves move in opposite directions, that is, if one valve increases its opening, the other valve reduces its opening, and vice versa. Furthermore, the two control valves are preferably operated in such a way that the common heat carrier medium flow rate remains constant at all positions of the valves. With this arrangement, the temperature of the heat transfer medium flowing to the falling film crystallizer via the inlet line for the heat transfer medium can be adjusted by adjusting the split ratio between the flow through the at least two parallel heat exchangers and the flow through the bypass line. Thus, the temperature control loop achieves a more accurate control of the process temperature, i.e., the temperature of the heat transfer medium flowing to the head of the falling film crystallizer via the inlet line for the heat transfer medium.

[0037] According to an alternative particularly preferred embodiment of the utility model, the falling film crystallization facility does not include an exhaust unit. In this embodiment, preferably, the recirculation line equipped with a pump further includes a valve downstream of the pump, and the discharge line is connected to the recirculation line at a position downstream of the pump but upstream of the valve of the recirculation line. During the product removal stage, the target compound melt can be completely discharged from the falling film crystallization facility by opening the valve of the discharge line, running the pump and closing the valve of the recirculation line until the storage tank of the falling film crystallizer becomes partially empty. Then, stop the pump, close the valve of the discharge line, and open the valve of the recirculation line. This embodiment without an exhaust unit has the following advantages: the vacuum in the falling film crystallizer is permanently maintained, which means that the size of the covering gas consumption and the vacuum unit can be significantly reduced.

[0038] In an alternative variant of an embodiment of the utility model in which the falling film crystallization facility does not include an exhaust unit, preferably, a discharge line equipped with a valve is connected to the melt outlet line of the falling film crystallizer, and is preferably arranged upstream of a pump located in the recirculation line, wherein the facility further comprises a measuring vessel, the measuring vessel is connected to the discharge line, and is equipped with at least one instrument for measuring the product melt mass discharged into the measuring vessel. In addition, the measuring vessel is preferably connected to a product outlet line equipped with a pump and a valve, and the measuring vessel is further connected to a vacuum line of a vacuum unit via a connecting line. This variant allows the melt of the target compound to be completely discharged from the falling film crystallization facility during the product removal phase by running the pump, opening the valve of the discharge line, and opening the valve of the product outlet line until the storage tank of the falling film crystallizer is partially empty. Moreover, this variant of the embodiment without an exhaust unit has the advantage that the vacuum in the falling film crystallizer is permanently maintained, which means that the size of the covering gas consumption and the vacuum unit can be significantly reduced. In another advantage, this variant allows a more accurate separation between the different liquid product fractions discharged from the falling film crystallizer. This is all the more important the higher the desired final purity of the final target compound.

[0039] The falling film crystallization facility according to the present invention can be used to operate a process for purifying a crude composition by crystallization, and preferably melt crystallization, wherein the process is carried out in the above-mentioned falling film crystallization facility.

[0040] The process may include, as in the prior art processes, not only the stages of cooling and crystallizing the crude composition, sweating and subsequent melting of the crystals and taking out the resulting melt from the crystallizer in each crystallization stage, but also, at least at the beginning of the first crystallization stage, and more preferably at the beginning of each crystallization stage, a preheating stage, preferably carried out under vacuum. The preheating stage allows the removal of low-boiling impurities from the composition to be crystallized and thus increases the purification efficiency.

[0041] Therefore, preferably, the process sequentially includes: a filling and preheating stage of feeding the crude composition into the falling film crystallizer and preheating it; a subsequent crystallization stage of guiding the melt in the form of a film on the surface of the inner wall of a plurality of hollow tubes to form crystals of the target compound; one or more subsequent sweating stages of heating the crystals to a temperature close to the melting point of the target compound; a subsequent melting stage of melting the crystals to obtain a melt of the target compound; and a final product removal stage of removing the target compound melt from the falling film crystallization facility.

[0042] The falling film crystallization facility, and in particular the falling film crystallizer, can be subjected to vacuum during all process phases or only during one or some process phases. Good results are particularly obtained when a vacuum is applied to the falling film crystallization facility during the following periods:

[0043] i) during said melting phase,

[0044] ii) during said one or more sweating phases and during said melting phase,

[0045] iii) during the crystallization phase,

[0046] iv) during the filling and preheating phase and during the melting phase, or

[0047] v) during the filling and preheating phases, during the crystallization phase, during the one or more sweating phases and during the melting phase.

[0048] In addition, a stripping agent (such as water or any other suitable compound) can be added to the melt before or during the crystallization stage so that the melt has a stripping agent content of 1 to 100,000 ppm based on 100% by weight of the melt. Preferably, the stripping agent is added to the melt before the crystallization stage or at the latest at the beginning of the crystallization stage. Even if the mother liquor includes up to 100,000 ppm or 10% by weight of the stripping agent (which can be a solvent) in this embodiment, the corresponding crystallization is still considered as melt crystallization. According to the utility model, solvent crystallization means the crystallization of a liquid composition comprising at least 50% by weight of a solvent.

[0049] Furthermore, during the crystallization phase, the heat transfer medium may be directed through one of the at least two parallel heat exchangers operated with a coolant, and during the one or more sweating phases and during the melting phase, the heat transfer medium is directed through another of the at least two parallel heat exchangers operated with a heating agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The invention is then described with the aid of illustrative, non-limiting figures, in which:

[0051] Figure 1 is a schematic diagram of a falling film crystallization facility for purifying a crude composition by crystallization according to one embodiment of the present invention.

[0052] Figure 2 is a schematic diagram of a falling film crystallization facility for purifying a crude composition by crystallization according to another embodiment of the present invention.

[0053] Figure 3 is a schematic diagram of a falling film crystallization facility for purifying a crude composition by crystallization according to yet another embodiment of the present invention.

[0054] Figure 4 is a schematic diagram of a falling film crystallization facility for purifying a crude composition by crystallization according to yet another embodiment of the present invention.

[0055] Figure 5 is a schematic diagram of a falling film crystallization facility for purifying a crude composition by crystallization according to yet another embodiment of the present invention. DETAILED DESCRIPTION

[0056] Figure 1 The falling film crystallization facility 10 for purifying a crude composition by crystallization shown in FIG. 1 comprises a falling film crystallizer 12, two parallel heat exchangers 14, 16, a vacuum unit 18 and an exhaust unit 20. The falling film crystallizer 12 comprises a plurality of hollow tubes 22, Figure 1 In addition, the falling film crystallizer 12 comprises: a feed inlet line 24 for the crude composition, which comprises a feed valve 25, wherein the feed inlet line 24 opens into the falling film crystallizer 12 at a position below the plurality of hollow tubes 22; a connecting line 26; a melt outlet line 28 at the bottom; a melt inlet line 30 at the top; an inlet line 32 for a heat transfer medium in the upper part; and an outlet line 34 for a heat transfer medium in the lower part.

[0057] The falling film crystallizer 12 and the plurality of hollow tubes 22 are arranged at least vertically, wherein the falling film crystallizer 12 further comprises an upper perforated plate 36 and a lower perforated plate 38. Both the upper perforated plate 36 and the lower perforated plate 38 act as separation devices. More specifically, the upper perforated plate 36 and the lower perforated plate 38 are arranged in the falling film crystallizer 12 so that each perforation or opening of the upper perforated plate 36 respectively surrounds the hollow tube 22 in a liquid-tight manner, and each perforation or opening of the lower perforated plate 38 respectively surrounds the hollow tube 22 in a liquid-tight manner, so that each hollow tube 22 is surrounded by the upper perforated plate 36 on its upper end and by the lower perforated plate 38 on its lower end. Thus, a hollow space 40 is formed between the outer peripheral walls 42 of the plurality of hollow tubes 22 and between the upper perforated plate 36 and the lower perforated plate 38, wherein the hollow space 40 is bounded by the unperforated portion of the upper plate 36 and the unperforated portion of the lower perforated plate 38 and the peripheral inner wall 44 of the falling film crystallizer 12. Therefore, the hollow space 40 is liquid-tightly separated from the inner cavity 46 of each hollow tube 22. Although the inlet line 32 for heat transfer medium and the outlet line 34 for heat transfer medium are connected to the hollow space 40 formed between the outer peripheral inner walls 44 of the plurality of hollow tubes 22, the melt inlet line 30 connected to the top of the falling film crystallizer 12 is connected to each upper end of the inner cavity 46 of the plurality of hollow tubes 22, and each lower end of the inner cavity of the plurality of hollow tubes is connected to the lower portion of the falling film crystallizer 12. Therefore, the hollow space 40 formed between the outer peripheral walls 42 of the plurality of hollow tubes 22 and between the upper perforated plate 36 and the lower perforated plate 38 serves as a heat transfer compartment in which the heat transfer medium flows in the form of a film on the surface of the outer wall of the hollow tube. In contrast, the inner cavity 46 of the hollow tube 22, which is liquid-tightly separated from the hollow space 40, serves as a crystallization compartment, thereby allowing the melt to flow from the melt inlet line 30 on the surface of the inner wall 47 through the inner cavity 46 of each hollow tube 22 to the lower portion of the falling film crystallizer 12, and from there to the melt outlet line 28, thereby allowing crystals to be formed on the surface of the inner wall 47 of the plurality of hollow tubes 22.

[0058] A feed inlet line 24 for the crude composition is connected to the sump section 48 of the falling film crystallizer 12 .

[0059] Furthermore, the outlet pipeline 34 for heat transfer medium is divided into a first branch pipeline 50 and a second branch pipeline 52. The first branch pipeline 50 is connected to a first valve 54, connected to the first heat exchanger 14 downstream of the first valve 54, and connected to the inlet pipeline 32 for heat transfer medium downstream of the first heat exchanger 14; the second branch pipeline 52 is connected to a second valve 56, connected to the second heat exchanger 16 downstream of the second valve 56, and connected to the inlet pipeline 32 for heat transfer medium downstream of the second heat exchanger 16. In order to transport the heat transfer medium through these pipelines, a pump 58 is provided in the outlet pipeline 34 for heat transfer medium. Therefore, if the first valve 54 is closed and the second valve 56 is open, the heat transfer medium flows into the hollow space 40 of the falling film crystallizer via the outlet line 34 for the heat transfer medium, via the second branch line 52, via the second heat exchanger 16, and via the inlet line 32 for the heat transfer medium; and if the first valve 54 is open and the second valve 56 is closed, the heat transfer medium flows into the hollow space 40 of the falling film crystallizer via the outlet line 34 for the heat transfer medium, via the first branch line 50, via the first heat exchanger 14, and via the inlet line 32 for the heat transfer medium. Thus, when the first heat exchanger 14 and the second heat exchanger 16 are operated with different media (such as, in the crystallization stage, the first heat exchanger 14 is operated with a cooling medium; and in the sweating and melting stages, the second heat exchanger 16 is operated with a heating medium), the temperature of the heat transfer medium can be changed efficiently and quickly.

[0060] The melt outlet line 28 is divided into a discharge line 60, which can be opened or closed via a valve 62, and a recirculation line 64, which connects the melt outlet line 28 with the melt inlet line 30. This allows the mother liquor to be circulated via the recirculation line 64 between the melt outlet line 28 and the melt inlet line 30 during the crystallization phase, or the melt to be discharged during the sweating and melting phase, or the product composition to be discharged during the product removal phase, by appropriately controlling (i.e., opening or closing) the valve 62. In order to transport the fluid through the corresponding pipeline, a pump 66 is arranged in the recirculation line 64.

[0061] Furthermore, the connecting line 26 is divided into a vacuum line 68 leading to the vacuum unit 18 and an exhaust line 70 leading to the exhaust unit 20. Both the vacuum line 68 and the exhaust line 70 are provided with valves 72, 74, which allow selective opening of the respective lines 68, 70. Thus, if the falling film crystallization facility 10 is to be exhausted, the valve 72 of the vacuum unit 18 is closed and the valve 74 of the exhaust unit 20 is opened; whereas if the falling film crystallizer facility 12 is to be set at a pressure below atmospheric pressure or at a vacuum, respectively, the valve 72 of the vacuum unit 18 is opened and the valve 74 of the exhaust unit 20 is closed.

[0062] More specifically, the vacuum unit 18 comprises, downstream of the valve 72, a condenser 76 comprising a discharge line 78 for the condensed liquid and an exhaust line 80 leading to a vacuum source 82, which is a vacuum pump. In turn, the exhaust unit 20 comprises, downstream of the valve 74, a pressure equalization line 84, which is connected downstream thereof via a further valve 86 to a cover gas supply line 88 and downstream thereof via a further valve 90 to a cover exhaust line 92.

[0063] During the batch operation of the falling film crystallization facility 10 according to an exemplary embodiment, the following stages are sequentially implemented: namely, a filling and preheating stage, followed by a crystallization stage, followed by a sweating stage, followed by a melting stage, and finally a product removal stage. More specifically, at the start of the operation of the falling film crystallization facility 10, a melt of a crude composition 94 is fed into the sump portion 48 of the falling film crystallizer 12 via the feed inlet line 24. During the feeding of the melt of the crude composition 94 into the sump portion 48 of the falling film crystallizer 12, the feed valve 25 is opened; and during all other stages of the crystallization stage, the feed valve 25 is closed. When a certain level of the crude composition 94 is reached in the sump portion 48 of the falling film crystallizer 12, the pump 66 is started, and thereby the crude composition 94 is recycled into the inner cavity 46 of the hollow tube 22 via the recirculation line 64. The valve 72 of the vacuum unit 18 is opened, and the valve 74 of the exhaust unit 20 is closed, so that a pressure below atmospheric pressure generated by the vacuum pump 82 is applied to the falling film crystallization facility 10, and in particular to the falling film crystallizer 12. Due to the applied vacuum, the optional preheating stage and the circulation via the pump 58, a portion of the impurities with a low boiling point contained in the crude composition 94 is evaporated and removed from the falling film crystallization facility 10 via the connecting line 26 and the vacuum line 68.

[0064] Furthermore, to start the crystallization stage, the pump 58 is started, the first valve 54 is opened, but the second valve 56 is closed, and the first heat exchanger 14 is operated with a coolant, so that thereby the heat transfer medium is cooled in the first heat exchanger 14 and is recycled into the hollow space 40 of the falling film crystallizer 12 via the inlet 32 ​​in order to cool the outer peripheral wall 42 of the hollow tube 22. During the crystallization stage, crystals of the target compound to be purified with trace impurities are deposited on the surface of the inner wall 47 of the hollow tube 22, wherein a part of the impurities with a low boiling point contained in the crystals and in particular in the pores of the crystals evaporates due to the applied vacuum and is taken out of the falling film crystallization facility 10 via the connecting line 26 and the vacuum line 68. As the crystals of the target compound are deposited on the surface of the cooled inner wall 47 of the hollow tube 22, thereby leading to the depletion of this compound in the crude composition 94, a mother liquor 94 is formed from the crude composition 94, the mother liquor 94 having a lower target compound concentration than the crude composition 94. The mother liquor 94 is recycled via the recycling line 64 during the entire crystallization stage.

[0065] When a predetermined amount of crystals is obtained, the pump 66 is stopped in order to terminate the recycling of the mother liquor 94. Furthermore, the valve 72 of the vacuum unit 18 is closed, and the valves 74, 86 and 90 of the exhaust unit 20 are opened in order to exhaust the falling film crystallization facility 10 and in particular the falling film crystallizer 12. Thereafter, the valve 62 is opened, and the mother liquor is removed via the exhaust line 60. After the removal of the mother liquor 94 is completed, the valve 62 is closed, the valves 74, 86 and 90 of the exhaust unit 20 are closed, and the valve 72 of the vacuum unit 18 is opened in order to apply a vacuum to the falling film crystallization facility 10 and in particular the falling film crystallizer 12 again. In addition, to start the sweating phase, the first valve 54 is closed, the second valve 56 is opened, and the second heat exchanger 16 is operated with a heating agent, so that the heat transfer medium is heated in the second heat exchanger 16 and introduced into the hollow space 40 of the falling film crystallizer 12 via the inlet line 32 so as to heat the outer peripheral wall 42 of the hollow tube 22, thereby heating the crystals deposited on the inner wall 47 of the hollow tube 22 to a temperature close to the melting point of the target compound so as to partially melt the crystals. Due to the applied vacuum, a part of the impurities with a low boiling point contained in the crystals and in particular in the pores of the crystals evaporates and is taken out of the falling film crystallization facility 10 via the connecting line 26 and the vacuum line 68. When a certain amount of melt is obtained, the valve 72 of the vacuum unit 18 is closed, and the valves 74, 86 and 90 of the exhaust unit 20 are opened so as to exhaust the falling film crystallization facility 10 and in particular the falling film crystallizer 12, and then the valve 62 is opened and the obtained melt 94 is taken out via the discharge line 60. After removal of the obtained melt 94 is complete, valve 62 is closed, valves 74 , 86 and 90 of exhaust unit 20 are closed, and valve 72 of vacuum unit 18 is opened in order to apply a vacuum to falling film crystallization installation 10 and in particular falling film crystallizer 12 again.

[0066] Thereafter, the temperature of the heating agent guided through the second heat exchanger 16 is increased so as to increase the temperature of the crystals deposited on the inner wall 47 of the hollow tube 22, so as to completely melt the crystals. During this melting phase, a portion of the impurities with a low boiling point contained in the crystals and in particular in the pores of the crystals evaporates due to the applied vacuum and is removed from the falling film crystallization facility 10 via the connecting line 26 and the vacuum line 68. After the melting phase is completed, the pump 58 is stopped, the valve 72 of the vacuum unit 18 is closed, the valves 74, 86 and 90 of the exhaust unit 20 are opened, so as to start the product removal phase and provide a slight overpressure to the falling film crystallization facility 10 and in particular to the falling film crystallizer 12. Then, the valve 62 is opened and the purified target compound or product is removed from the falling film crystallization facility 10 via the discharge line 60, respectively.

[0067] Figure 2 The facility 10 shown in FIG. 1 is different from Figure 1The facility 10 is characterized in that it does not have an exhaust unit 20. In addition, the discharge line 60 with the valve 62 is not arranged upstream of the pump 66, but downstream of the pump 66. In addition, the valve 96 is arranged in the recirculation line 64, downstream of the pump 66 and downstream of the branching point of the discharge line 60. When the facility 10 is operated, during the product withdrawal phase of withdrawing the target compound melt from the falling film crystallization facility 10, the valve 96 is closed and the valve 62 is opened until the melt is completely discharged from the storage tank part 48 of the falling film crystallizer 12. Then, the pump 66 is stopped, the valve 62 is closed, and the valve 96 is opened. In this embodiment of the utility model, the exhaust unit 20 is not required. This has the following advantages: the vacuum in the falling film crystallizer 12 is permanently maintained, which means that the covering gas consumption and the size of the vacuum unit 18 can be significantly reduced.

[0068] Figure 3 The facility 10 shown in FIG. 1 is different from Figure 1 The facility 10 is characterized in that it does not have an exhaust unit 20. In addition, the facility 10 includes a measuring vessel 98, which is connected to the discharge pipeline 60 and is equipped with a suitable instrument (not shown) for measuring the product melt material discharged into the measuring vessel 98. In addition, the measuring vessel 98 is connected to the product outlet pipeline 100 equipped with a pump 102 and a valve 104. In addition, the measuring vessel 98 is connected to the vacuum line 68 of the vacuum unit 18 via a connecting line 106. When operating the facility 10, during the product withdrawal phase of withdrawing the target compound melt from the falling film crystallization facility 10, the pump is operated and the valve 104 is opened until the melt is completely discharged from the storage tank part 48 of the falling film crystallizer 12. Then, the pump 102 is stopped and the valve 104 is closed. Also, in this embodiment, the exhaust unit 20 is not required. This has the advantage that the vacuum in the falling film crystallizer 12 is permanently maintained, which means that the covering gas consumption and the size of the vacuum unit 18 can be significantly reduced. In another advantage, Figure 3 The embodiment allows a more accurate separation between the different liquid product fractions discharged from the falling film crystallizer 12. This is all the more important the higher the desired final purity of the final target compound.

[0069] Figure 4 and Figure 5 The facility 10 shown in FIG. 1 is different from Figure 1The facility is characterized in that it includes a bypass line 108 that branches from the outlet line 34 for the heat transfer medium and is connected to the inlet line 32 for the heat transfer medium at a position downstream of the heat exchangers 14 and 16, thereby allowing the heat transfer medium to bypass the heat exchangers 14 and 16. A valve 110 is arranged in the bypass line 108, just upstream of the position where the bypass line 108 is connected to the inlet line 32 for the heat transfer medium. Similarly, a valve 112 is arranged in the inlet line 32 for the heat transfer medium, just upstream of the position where the first and second branch lines 50 and 52 are connected to the inlet line 32. In addition, the facility includes a temperature measuring instrument 114 arranged downstream of the position where the bypass line 108 is connected to the inlet line 32 for the heat transfer medium. The temperature instrument 114 and the two valves 110 and 112 are components of a temperature control loop 116, in which the positions of the two valves 110 and 112 are controlled according to the difference between the desired temperature and the measured temperature. The two valves 110 and 112 move in opposite directions, i.e., if the valve 112 increases its opening, the valve 110 decreases its opening, and vice versa. In addition, the two control valves 110 and 112 operate in such a way that the common heat carrier medium flow rate remains constant at all positions of the valves 110 and 112. By this arrangement, the temperature of the heat transfer medium flowing to the falling film crystallizer 12 via the pipeline 32 can be adjusted by adjusting the split ratio between the flow through the heat exchangers 14 and 16 and the flow through the bypass line 108. Therefore, the temperature control loop 16 achieves more accurate control of the process temperature, i.e., the temperature of the heat transfer medium flowing to the head of the falling film crystallizer 12 via the pipeline 32.

[0070] Subsequently, the invention is described by means of illustrative, non-limiting and comparative examples.

[0071] Examples and Comparable Examples

[0072] The purification of a crude composition comprising bisphenol A as the target compound and phenol as an impurity using a falling film crystallizer facility according to the present invention (example) and using a falling film crystallizer facility according to the prior art (comparative example) has been calculated using data from pilot tests for crystallization and using simulations using commercially available software for evaporation.

[0073] The results obtained are summarized in the following table, which shows a comparison of the purification progress in four stages using a conventional crystallization process (Comparative Example) and a process involving evaporation (Example).

[0074] Table: Example comparison: Purification with evaporation (Example) and without evaporation (Comparative Example); the numbers show the target component (BPA) and the impurity content in percentage (%) by weight.

[0075]

[0076]

[0077] The data show that in the operation of the comparative example without evaporation, the target phenol content below 5 ppm was already achieved after four crystallization stages; whereas the same depletion effect was already achieved after stage 3 of crystallization of the example (ie if evaporation was used).

[0078] Therefore, the significantly smaller falling film crystallization facility according to the utility model achieves the same production capacity as the falling film crystallization facility of the prior art. In addition, if the falling film crystallization facility according to the utility model is adopted, the specific cooling / heating energy consumption per ton of final product of all pumps and the specific electricity consumption per ton of final product can be significantly reduced by reducing the number of necessary stages (in this example, from four to three).

[0079] Reference numerals

[0080] 10 Falling film crystallization facility

[0081] 12 Falling Film Crystallizer

[0082] 14 The first heat exchanger of two parallel heat exchangers

[0083] 16 The second heat exchanger in two parallel heat exchangers

[0084] 18 Vacuum unit

[0085] 20 Exhaust unit

[0086] 22 Hollow tube

[0087] 24 Feed inlet pipeline

[0088] 25 Feed valve

[0089] 26 Connecting pipes

[0090] 28 Melt outlet pipeline

[0091] 30 Melt inlet pipeline

[0092] 32 Inlet line for heat transfer medium

[0093] 34 Outlet pipeline for heat transfer medium

[0094] 36 Upper perforated plate

[0095] 38 Lower perforated plate

[0096] 40 Hollow Space

[0097] 42 outer peripheral wall of the hollow tube

[0098] 44 The inner wall of the falling film crystallizer

[0099] 46 Inner cavity of hollow tube

[0100] 47 Inner wall of hollow tube

[0101] 48 Storage tank of falling film crystallizer

[0102] 50 First branch pipeline

[0103] 52 Second branch pipeline

[0104] 54 First Valve

[0105] 56 Second valve

[0106] 58 Pumps

[0107] 60 Discharge line

[0108] 62 valve

[0109] 64 Recirculation line

[0110] 66 Pumps

[0111] 68 Vacuum Line

[0112] 70 Exhaust line

[0113] 72 valve

[0114] 74 valve

[0115] 76 Condenser

[0116] 78 Discharge line

[0117] 80 Exhaust pipe

[0118] 82 Vacuum source / vacuum pump

[0119] 84 Pressure balance line

[0120] 86 valve

[0121] 88 Covering gas supply lines

[0122] 90 valve

[0123] 92 Covering the exhaust line

[0124] 94 Crude composition / mother liquor / melt

[0125] 96 valve

[0126] 98 Measuring vessels

[0127] 100 Product export pipeline

[0128] 102 Pumps

[0129] 104 valve

[0130] 106 Connecting pipeline

[0131] 108 Bypass line

[0132] 110 Valve

[0133] 112 Valve

[0134] 114 Temperature measuring instruments

[0135] 116 Temperature control loop

Claims

1. A falling film crystallization plant for purifying a crude composition by crystallization, characterized in that wherein the falling film crystallization facility comprises a falling film crystallizer, the falling film crystallizer comprising a feed inlet line for a crude composition, a melt outlet line and a melt inlet line interconnected via a recirculation line, a plurality of hollow tubes, an inlet line for a heat transfer medium and an outlet line for the heat transfer medium, wherein the falling film crystallization facility further comprises at least two parallel heat exchangers, wherein the inlet line for the heat transfer medium and the outlet line for the heat transfer medium are interconnected via the at least two parallel heat exchangers, and wherein the falling film crystallization facility further comprises a vacuum unit connected to the falling film crystallizer.

2. The falling film crystallization facility according to claim 1, wherein: The falling film crystallizer and the plurality of hollow tubes within the falling film crystallizer are at least substantially vertically arranged, wherein at least substantially vertically arranged means that the angle between the length axis of the falling film crystallizer and the length axis of the plurality of hollow tubes and the vertical direction is at most 10°.

3. The falling film crystallization facility according to claim 2, wherein: Wherein at least substantially vertically arranged means that the angle between the length axis of the falling film crystallizer and the length axis of the plurality of hollow tubes and the vertical direction is at most 5°.

4. The falling film crystallization facility according to claim 3, wherein: Wherein at least substantially vertically arranged means that the angle between the length axis of the falling film crystallizer and the length axis of the plurality of hollow tubes and the vertical direction is at most 1.5°.

5. The falling film crystallization facility according to claim 4, wherein: The at least substantially vertical arrangement means that the angle between the length axis of the falling film crystallizer and the length axis of the plurality of hollow tubes and the vertical direction is 0°.

6. The falling film crystallization facility according to any one of claims 1 to 5, wherein: Viewed from the top to the bottom of the falling film crystallizer, each of the plurality of hollow tubes extends from a point located at 0 to 30% of the distance from the top to the bottom of the falling film crystallizer to a point located at 60 to 80% of the distance from the top to the bottom of the falling film crystallizer, so that a storage tank portion extends below lower ends of the plurality of hollow tubes, and no hollow tubes are arranged in the storage tank portion.

7. The falling film crystallization facility according to claim 6, wherein: Viewed from the top to the bottom of the falling film crystallizer, each of the plurality of hollow tubes extends from a point located at 0 to 30% of the distance from the top to the bottom of the falling film crystallizer to a point located at 70 to 80% of the distance from the top to the bottom of the falling film crystallizer, so that a storage tank portion extends below lower ends of the plurality of hollow tubes, and no hollow tubes are arranged in the storage tank portion.

8. The falling film crystallization facility according to claim 6, wherein: Viewed from the top to the bottom of the falling film crystallizer, each of the plurality of hollow tubes extends from a point located at 0 to 10% of the distance from the top to the bottom of the falling film crystallizer to a point located at 60 to 80% of the distance from the top to the bottom of the falling film crystallizer, so that a storage tank portion extends below lower ends of the plurality of hollow tubes, and no hollow tubes are arranged in the storage tank portion.

9. The falling film crystallization facility according to claim 8, wherein: Viewed from the top to the bottom of the falling film crystallizer, each of the plurality of hollow tubes extends from a point located at 0 to 10% of the distance from the top to the bottom of the falling film crystallizer to a point located at 70 to 80% of the distance from the top to the bottom of the falling film crystallizer, so that a storage tank portion extends below lower ends of the plurality of hollow tubes, and no hollow tubes are arranged in the storage tank portion.

10. The falling film crystallization facility according to any one of claims 1 to 5, wherein: The melt inlet pipeline is connected to the top of the falling film crystallizer, and the melt outlet pipeline is connected to the bottom of the falling film crystallizer, wherein each upper end of the inner cavity of the multiple hollow tubes is directly or indirectly connected to the melt inlet pipeline, and each lower end of the inner cavity of the multiple hollow tubes is directly or indirectly connected to the melt outlet pipeline, so that the melt can flow from the melt inlet pipeline through the inner cavity of each hollow tube to reach the melt outlet pipeline.

11. The falling film crystallization facility according to claim 6, wherein: A feed inlet line for the crude composition is connected to the sump portion of the falling film crystallizer.

12. The falling film crystallization facility according to any one of claims 1 to 5, wherein: A separation device is arranged in the falling film crystallizer, and the separation device liquid-tightly separates the hollow space formed between the outer peripheral walls of the multiple hollow tubes from the inner cavity of each hollow tube, so that no heat transfer medium can flow from the hollow space formed between the outer peripheral walls of the multiple hollow tubes into any of the inner cavities of the multiple hollow tubes, and no melt can flow from any of the inner cavities of the multiple hollow tubes into the hollow space formed between the outer peripheral walls of the multiple hollow tubes, wherein an upper perforated plate and a lower perforated plate are arranged in the falling film crystallizer as a separation device, wherein each perforation of the upper perforated plate liquid-tightly surrounds a hollow tube, and each perforation of the lower perforated plate liquid-tightly surrounds a hollow tube, so that a hollow space is formed between the outer peripheral walls of the multiple hollow tubes and between the upper perforated plate and the lower perforated plate, wherein the hollow space is delimited by the unperforated portions of the upper perforated plate and the lower perforated plate and the peripheral inner wall of the falling film crystallizer.

13. The falling film crystallization facility according to claim 12, wherein: An inlet line for a heat transfer medium and the outlet line for a heat transfer medium are connected to the hollow spaces formed between the outer peripheral walls of the plurality of hollow tubes.

14. The falling film crystallization facility according to any one of claims 1 to 5, wherein: an outlet pipeline for a heat transfer medium divided into a first branch pipeline and a second branch pipeline, wherein the first branch pipeline is connected to a first valve, connected to a first heat exchanger of the at least two parallel heat exchangers downstream of the first valve, and connected to an inlet pipeline for a heat transfer medium downstream of the first heat exchanger; The second branch line is connected to the second valve, connected to the second heat exchanger of the at least two parallel heat exchangers downstream of the second valve, and connected to an inlet line for heat transfer medium downstream of the second heat exchanger.

15. The falling film crystallization facility according to any one of claims 1 to 5, wherein: The vacuum unit comprises a vacuum source, and the vacuum source is connected to the falling film crystallizer via a vacuum line.

16. The falling film crystallization facility according to claim 15, wherein: The vacuum unit includes a vacuum pump.

17. The falling film crystallization facility according to claim 15, wherein: A valve is arranged in the vacuum line between the falling film crystallizer and the vacuum source.

18. The falling film crystallization facility according to claim 17, wherein: The vacuum unit includes a condenser.

19. The falling film crystallization facility according to claim 18, wherein: The condenser is arranged in the vacuum line between the valve and the vacuum source.

20. The falling film crystallization facility according to claim 18 or 19, wherein: The vacuum unit includes a shell and tube condenser.

21. The falling film crystallization facility according to claim 15, wherein: The falling film crystallization facility further comprises an exhaust unit connected to the falling film crystallizer via an exhaust line, in which a valve is arranged.

22. The falling film crystallization facility according to claim 21, wherein the falling film crystallizer comprises a connecting line which is divided into the vacuum line and the exhaust line.

23. The falling film crystallization installation according to any one of claims 1 to 5, wherein: The falling film crystallization facility does not comprise a degassing unit, but wherein: i) the recirculation line provided with a pump further comprises a valve downstream of the pump and a discharge line comprising a valve, wherein the discharge line is connected to the recirculation line at a position downstream of the pump but upstream of the valve of the recirculation line, or ii) a discharge line including a valve is connected to the melt outlet line of the falling film crystallizer, wherein the facility further comprises a measuring vessel, which is connected to the discharge line and is equipped with at least one instrument for measuring the product melt material discharged into the measuring vessel, wherein the measuring vessel is connected to the product outlet line equipped with a pump and a valve, and the measuring vessel is further connected to the vacuum line of the vacuum unit via a connecting line.

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