Continuous process for the production of a crystalline monosaccharide

Abstract

A continuous process for obtaining a crystalline monosaccharide, comprising: - a continuous crystallization of the monosaccharide in a main crystallizer (10), - wherein in the main crystallizer (10) an evaporation and / or cooling crystallization is continuously carried out on a crystal suspension in order to allow crystals of the monosaccharide to grow in the crystal suspension, - separating crystals of the monosaccharide from the crystal suspension to obtain crystalline monosaccharide; - the continuous formation of a mass of crystallization magma for the main crystallizer (10) in a cascade, - wherein the cascade comprises at least a first (13) and a last stage (15) connected in series, and each stage comprises at least one pre-crystallizer (13A, 15A), - wherein in the at least one pre-crystallizer (13A) of the first stage (13), solution containing monosaccharide is seeded by monosaccharide seed crystals to obtain a pre-crystallization magma, and a mass of crystallization magma for the downstream stage (14, 15) is formed from the pre-crystallization magma by means of cooling crystallization and / or evaporation crystallization, and - wherein a solution containing monosaccharide and a mass of crystallization magma from the preceding stage are fed into the at least one pre-crystallizer (15A, 15B, 15C) of the last stage (15) in order to obtain a pre-crystallization magma, and a mass of crystallization magma for the main crystallizer (10) is formed from the pre-crystallization magma in the at least one pre-crystallizer (15A, 15B, 15C) of the last stage (15) by means of cooling crystallization and / or evaporation crystallization; - continuously feeding a solution containing the monosaccharide and a mass of crystallization magma from the at least one pre-crystallizer (15A, 15B, 15C) of the last stage (15) of the cascade into the main crystallizer (10) to provide the crystal suspension, the method being characterized in that the mass of crystallization magma formed in a pre-crystallizer (14A, 14B, 15A, 15B, 15C) of a stage (14, 15) exceeds the mass of crystallization magma formed in a pre-crystallizer (13A, 13B, 14A, 14B, 15A, 15B, 15C) of the preceding stage (13, 14) by a factor of 2 to 12.

Description

[0001] The invention relates to a continuous process for obtaining a crystalline monosaccharide and to an apparatus for obtaining a crystalline monosaccharide, in particular for carrying out the continuous process according to the invention.

[0002] Evaporation crystallizers and cooling crystallizers are used to crystallize saccharides, the design and operation of which are familiar to those skilled in the art. To prevent spontaneous crystal formation, seed crystals or a crystallization magma containing seed crystals is added to a crystal-free concentrated solution containing the sugar to initiate the crystallization process, allowing crystal growth to occur under controlled conditions in a crystallizer.

[0003] US Patent No. 3,981,739 A discloses a process for the continuous crystallization of sugar. The system consists of several evaporative crystallizers in which the solution concentration and temperature are controlled. The mass of the crystallization magma decreases from crystallizer to crystallizer.

[0004] Patent WO 2018 / 081557 A2 describes a process for producing allulose crystals by controlled cooling and stirring of an allulose syrup containing seed crystals, resulting in a massecuite of crystals and mother liquor. This massecuite can optionally be divided, mixed with fresh syrup, and subjected to further crystallization. Crystallization is achieved exclusively by temperature control and stirring.

[0005] Allulose (D-psicose) is a monosaccharide from the group of ketohexoses, which has become producible in larger quantities through the development of new processes (Takeshita et al., Journal of Bioscience and Bioengineering Vol. 90, No. 4, pp. 453 to 455, 2000; Korean Patent Application No. 10-2009-0118465, CJ Cheiljedang Corp. Korea).

[0006] The crystallization of allulose on an industrial scale is described in the literature by a patent application and a patent grant (PCT / KR2015 / 009449 and EP 3210478 A1, both CJ Cheiljedang Corp., Korea). The publication describes that, after purification and concentration, D-psicose is converted from the liquid phase to the crystalline state by applying cooling crystallization. After concentration, the solution is cooled to 30 to 40 °C using a heat exchanger and seed crystals are added. The preparation of the seed crystals to initiate allulose crystallization is not described. When the crystal growth rate decreases (upon reaching equilibrium), a defined amount of the concentrated allulose solution cooled to 30 to 40 °C is added to the crystal suspension 1 to 2 times per hour. This procedure is repeated until the crystallizer reaches its maximum working volume.

[0007] Due to the discontinuous manufacturing process, industrial production of crystalline allulose is complex and uneconomical. For other monosaccharides, there is also a need to enable continuous production of the crystalline form or to improve existing processes and equipment. A particular challenge in the industrial production of crystalline sugar is controlling crystal growth. On the one hand, the highest possible yield is desired. On the other hand, conditions that enable a high yield do not necessarily lead to a process suitable for large-scale, especially continuous, production. Crystal growth can be influenced by numerous factors, such as the crystallization temperature and method, the mixing of the crystal suspension, and the type of sugar.These factors can therefore influence the yield, shape, and size of the sugar crystals. In turn, the shape and size of the crystals, as well as their concentration in the crystal suspension, can affect the flow behavior of the crystal suspension in a plant. If crystal growth cannot be precisely controlled, a large-scale, and especially a continuous, process is not conceivable due to the poor processability of the crystal suspensions. A narrow particle size distribution is also generally desired with a view to further process steps. A further difficulty in a continuous production process is the continuous production of a sufficiently large mass of crystallization magma to inoculate a crystallization solution. This is because, during a crystallization step, the technically achievable desugaring of the solution is limited by the crystal content in a crystal suspension.A limitation of the available mass of crystallization magma arises from the fact that the production processes for crystallization magma are usually carried out discontinuously.

[0008] Therefore, it is an object of the present invention to provide a continuous process for obtaining a crystalline monosaccharide and an apparatus for obtaining a crystalline monosaccharide, in particular for carrying out the continuous process according to the invention.

[0009] The process or device should also enable the continuous provision of a sufficiently large amount of crystallization magma for inoculating the crystallization solution so that the entire process can be carried out continuously.

[0010] Furthermore, the crystal growth in the process or device must be controlled by the given conditions and lead to manageable, e.g. stirrable and homogenizable, mixtures.

[0011] A further task is to enable the process or device to be used for a continuous process with high efficiency and yield in large quantities.

[0012] According to the invention, this object is achieved by a method according to claim 1. With regard to the device, this object is achieved by the subject matter of claim 15.

[0013] Preferably, at least one of these objects is achieved by the continuous process according to the invention for obtaining a crystalline monosaccharide, wherein the continuous process preferably comprises a continuous crystallization of the monosaccharide in a main crystallizer, a separation of crystals of the monosaccharide from a crystal suspension (a crystallization mixture) to obtain crystalline monosaccharide, the continuous formation of a mass of crystallization magma for the main crystallizer in a cascade (from pre-crystallizers) and the continuous feeding of a solution containing the monosaccharide and a mass of a crystallization magma from the at least one pre-crystallizer of the last stage of the cascade into the main crystallizer to provide the crystal suspension,During the continuous crystallization of the monosaccharide in a main crystallizer, evaporation and / or cooling crystallization is continuously carried out on a crystal suspension in the main crystallizer in order to allow crystals of the monosaccharide to grow in the crystal suspension. The continuous formation of a mass of crystallization magma for the main crystallizer takes place in a cascade, wherein the cascade comprises at least a first and a last stage connected in series, and each stage comprises at least one pre-crystallizer. In the at least one pre-crystallizer of the first stage, a solution containing monosaccharide is seeded with monosaccharide seed crystals to obtain a (so-called) pre-crystallization magma, and a mass of crystallization magma for the downstream stage is formed from the pre-crystallization magma by means of cooling crystallization and / or evaporation crystallization.and wherein a solution containing monosaccharide and a mass of crystallization magma from the preceding stage are fed into the at least one pre-crystallizer of the final stage to obtain a pre-crystallization magma, and a mass of crystallization magma for the main crystallizer is formed from the pre-crystallization magma in the at least one pre-crystallizer of the final stage by means of cooling crystallization and / or evaporation crystallization. The process is characterized in that the mass of crystallization magma formed in a pre-crystallizer of a stage exceeds the mass of crystallization magma formed in a pre-crystallizer of the preceding stage by a factor of 2 to 12.

[0014] This continuous process makes the efficient extraction of a crystalline monosaccharide possible and economical.

[0015] In particular, the continuous provision of crystallization magma in sufficient quantities is achieved so that the entire process can be carried out continuously.

[0016] Furthermore, crystal growth is controllable under the given conditions and leads to coordinated crystal suspensions, allowing the process to be carried out continuously in a large-scale facility, thus minimizing equipment requirements. The multi-stage crystallization magma generation allows for targeted influence on the particle size distribution. In the subsequent continuous crystallization in the main crystallizer, crystal growth can be precisely adjusted to the target crystal size. Furthermore, the continuous process exhibits high efficiency and yield, as explained below.

[0017] The continuous crystallization of the monosaccharide in the main crystallizer is carried out by cooling or alternatively by evaporation or by a combination of the two processes.

[0018] Evaporative crystallization can be carried out under atmospheric pressure or preferably below.

[0019] The structure and operation of evaporative crystallizers and cooling crystallizers are known to those skilled in the art. The implementation of evaporative crystallization and / or cooling crystallization, either continuously or discontinuously, is also known to those skilled in the art. Continuous crystallization of the monosaccharide in a main crystallizer can be carried out, for example, with a BMA OVC (oscillating vertical cooling crystallizer) when cooling crystallization is used. Continuous crystallization of the monosaccharide in a main crystallizer can be carried out with a BMA VKT (evaporative crystallization tower) when evaporative crystallization is used.The advantages of continuous crystallization include better space-time yields, reduced setup times for cleaning, filling, and emptying, and higher throughput rates with less space required. Overall, productivity is significantly increased, whereas batch production is significantly more labor-intensive.

[0020] In the present patent application, the solutions, crystal suspension, pre-crystallization magma, crystallization magma, seed suspension, etc., preferably contain water as the solvent. However, other solvents are also conceivable, particularly alcohols and mixtures thereof with water.

[0021] A "solution containing the monosaccharide" describes a solution containing the monosaccharide and fed to the main crystallizer. A "solution with monosaccharide" describes a solution containing the monosaccharide and fed to a pre-crystallizer.

[0022] In preferred embodiments, the "solution containing the monosaccharide" is not different from the "solution with monosaccharide." In other words, in preferred embodiments, the "solution with monosaccharide" is the "solution containing the monosaccharide."

[0023] The solution with monosaccharide and the solution containing the monosaccharide may have the same components and properties, i.e. be identical, or have different components and properties, i.e. be different.

[0024] The monosaccharide solution and the mass of crystallization magma from the upstream stage can be combined in the at least one pre-crystallizer of each stage or beforehand. The solution containing the monosaccharide and the mass of crystallization magma can be combined in the main crystallizer or beforehand. The inoculation of the monosaccharide solution with monosaccharide seed crystals can take place in the at least one pre-crystallizer of the first stage and / or in an upstream inoculation device. In other words, the at least one pre-crystallizer of the first stage can comprise an inoculation device.

[0025] Cooling or evaporation crystallization in a stage of the cascade can be terminated at any time upon reaching certain quality characteristics of the crystallization magma (e.g., shape, size, size distribution, viscosity) depending on the monosaccharide. Since the yield (formed crystal mass relative to the initial mass of the crystal-forming substance in the solution(s) or degradation of the dry substance in the liquid phase) is determined in the continuous crystallization step in the main crystallizer, the yields within the cascade are irrelevant for the overall process. To prevent spontaneous crystal formation, to initiate the crystallization process and to generate a defined crystal size, the solution containing monosaccharide is seeded with monosaccharide seed crystals, which are suspended in the solution, in at least one pre-crystallizer of the first stage.The monosaccharide seed crystals can be added in dry form or by adding them in the form of a seed suspension, a so-called slurry, in which the monosaccharide seed crystals are suspended in a suspending agent. The seed suspension is prepared from high-purity (> 99%) crystalline monosaccharide by comminution, preferably by grinding crystalline monosaccharide with isopropanol or by grinding a supersaturated aqueous monosaccharide solution, so that the suspended particles preferably have a size of 10 to 20 µm.

[0026] To produce pre-crystallization magma or a mass of crystallization magma in at least one pre-crystallizer of the first stage, the necessary crystal concentration (number of crystals in the amount to be inoculated) can be calculated according to known calculation equations (e.g. V.Gnielinski, A.Mersmann, F.Thurner: “Verdampfung, Kristallization, Trocknung”, Springer Fachmedien Wiesbaden GmbH 1993) depending on the crystal size of the seed suspension, the desired final size of the crystals, the crystal content to be achieved and the crystal shape.

[0027] The pre-crystallization magma and the crystallization magma contain crystals of the monosaccharide.

[0028] Preferably, the pre-crystallization magma is a suspension containing crystals of the monosaccharide and is formed from a solution containing monosaccharide and a mass of crystallization magma or monosaccharide seed crystals.

[0029] Preferably, a crystallization magma is formed from the pre-crystallization magma by crystallization in a pre-crystallizer. The crystallization magma is preferably used to inoculate a solution containing the monosaccharide in a pre-crystallizer and / or to inoculate a solution containing the monosaccharide in the main crystallizer.

[0030] The pre-crystallization magma and the crystallization magma contain crystals of the monosaccharide.

[0031] The term “crystallizer” preferably describes a device, in particular for carrying out a crystallization process.

[0032] Preferably, a pre-crystallizer is a crystallizer, in particular for producing crystallization magma.

[0033] Preferably, the term “main crystallizer” describes a device in which a major part of the crystalline monosaccharide is formed.

[0034] The term “residence time” describes the hydraulic residence time, which results from the volume of a crystallizer divided by the volume flow.

[0035] Preferred embodiments are specified in the subclaims.

[0036] Different embodiments of the invention may be combined with one another unless the context indicates otherwise.

[0037] In a preferred embodiment, each stage comprises a single pre-crystallizer and in the pre-crystallizer of each stage, a mass of crystallization magma is continuously formed from the pre-crystallization magma by means of evaporative crystallization.

[0038] This embodiment allows for a simpler process design. Evaporative crystallization can be carried out continuously, allowing a continuous mass of crystallization magma to be formed. The cascade of pre-crystallizers allows a large mass of crystallization magma to be formed.

[0039] In a further preferred embodiment, each stage comprises two to three pre-crystallizers, and in the pre-crystallizers of each stage, a mass of crystallization magma is formed from the pre-crystallization magma discontinuously by means of cooling crystallization and / or continuously by means of evaporative crystallization, wherein the mass of crystallization magma which is continuously fed to the main crystallizer is alternately fed from the pre-crystallizers of the last stage in the case of discontinuous formation by means of cooling crystallization.

[0040] If the crystallization magma is formed discontinuously by means of cooling crystallization in only one pre-crystallizer per stage, a continuous supply, even in a sufficient quantity, to the main crystallizer for a continuous crystallization process is not possible. This problem can be overcome by the previously described embodiment. Since each stage has several pre-crystallizers, crystallization magma can be continuously fed into the main crystallizer from several pre-crystallizers, even when using discontinuous cooling crystallization in the last stage. In other words, the pre-crystallizers of the stages are interconnected in such a way that a continuous supply of the crystallization magma from the last stage of the cascade to the continuously operating main crystallizer is ensured.

[0041] It should be noted that not every stage needs to have the same number of pre-crystallizers. Furthermore, the pre-crystallizers in each stage can be interconnected in a variety of ways.

[0042] Evaporative crystallization is particularly useful when the conditions for evaporative crystallization of the monosaccharide are met. These depend on the temperature sensitivity of the solution and the solubility of the product. If the solubility increases only moderately or very little with increasing temperature, evaporative crystallization is preferred, often under vacuum. If the solubility increases significantly with increasing temperature, cooling crystallization is the preferred crystallization method.

[0043] In certain embodiments, it is preferred that the first stage comprises one to two, preferably two, pre-crystallizers, the last stage comprises two to four, preferably three, pre-crystallizers and a further stage comprises two to four, preferably two, pre-crystallizers, wherein in the pre-crystallizers of each stage a mass of crystallization magma is formed discontinuously from the pre-crystallization magma by means of cooling crystallization and wherein the mass of crystallization magma which is continuously fed to the main crystallizer is fed alternately from the pre-crystallizers of the last stage.

[0044] In a particular embodiment in which at least one stage comprises more than one pre-crystallizer, the pre-crystallizers of the same stage each form the same mass of crystallization magma.

[0045] This allows a large mass of crystallization magma to be continuously fed into the main crystallizer from several pre-crystallizers.

[0046] In a preferred embodiment, the mass of crystallization magma formed in a pre-crystallizer of one stage exceeds the mass of crystallization magma formed in a pre-crystallizer of the upstream stage by a factor of 4 to 7.

[0047] Thus, with each stage, the mass of crystallization magma can be increased considerably, ensuring sufficient crystallization magma for the continuous feeding of a mass of crystallization magma into the main crystallizer and thus continuous crystallization of the monosaccharide in the main crystallizer. This factor cannot be increased arbitrarily, since a certain concentration of supplied crystallization magma must be present in the pre-crystallization magma in the pre-crystallizers to achieve efficient and predictable crystal growth.

[0048] In a preferred embodiment, the cascade comprises one to eight, preferably one to three, most preferably one, further stage or stages connected in series between the first and the last stage, wherein the further stage or further stages each have at least one pre-crystallizer into which solution with monosaccharide and a mass of crystallization magma from the upstream stage is fed in order to obtain pre-crystallization magma, and wherein in the at least one pre-crystallizer of each further stage a mass of crystallization magma for the downstream stage is formed from the pre-crystallization magma discontinuously by means of cooling crystallization and / or continuously by means of evaporation crystallization.

[0049] By adding further stages, the mass of crystallization magma that is fed from the last stage of the cascade into the main crystallizer can be further increased.

[0050] Thus, with each additional stage, the mass of crystallization magma can be significantly increased, ensuring sufficient crystallization magma for a continuous supply of a mass of crystallization magma to the main crystallizer and thus continuous crystallization of the monosaccharide in the main crystallizer. The preferred number of stages enables predictable crystal growth, which is adapted to the chemical-physical properties of the monosaccharide and the desired production quantity.

[0051] In certain embodiments, the stages or the at least one pre-crystallizer of each stage are connected to one another in such a way that it is possible to omit individual further stages.

[0052] This is particularly advantageous for continuous maintenance and cleaning of the system. Furthermore, it is advantageous for producing smaller amounts of crystallization magma if less crystallization magma is required for the main crystallization.

[0053] In a preferred embodiment, the monosaccharide seed crystals have an average diameter of 5 to 50 µm, preferably 10 to 20 µm.

[0054] It has been found that a continuous process for obtaining a crystalline monosaccharide is particularly feasible when the monosaccharide seed crystals have this diameter. By producing the crystallization magma in the cascade, the average particle size increases from stage to stage. With an initial size as mentioned above, crystal growth in the cascade and main crystallizer occurs in such a way that crystals of the desired size are obtained in the main crystallizer with a good yield.

[0055] In a certain preferred embodiment, a temperature gradient of the crystal suspension over the length of the main crystallizer is set from 70 to 15 °C and preferably from 45 to 25 °C.

[0056] In certain embodiments, a cooling crystallization is continuously carried out on a crystal suspension in the main crystallizer, wherein the crystal suspension is cooled in the main crystallizer from preferably 70 - 30 °C, preferably to 35 - 15 °C.

[0057] In certain similar embodiments, a cooling crystallization is continuously carried out on a crystal suspension in the main crystallizer, wherein the crystal suspension is cooled in the main crystallizer from preferably 70 - 33 °C, preferably to 32 - 15 °C.

[0058] In certain embodiments, the cooling crystallization in the continuously operating main crystallizer operates with a temperature gradient (temperature profile) from top to bottom, depending on the monosaccharide. In these embodiments, the temperature of the crystal suspension in the area of ​​the feed of the solution containing the monosaccharide and the crystallization magma (top) is preferably between 70 and 30 °C, and at the discharge area of ​​the crystal suspension (bottom) is preferably between 35 and 15 °C.

[0059] At these temperature profiles, crystals form in the desired size and yield. At the same time, the crystal suspension does not become too viscous, which would complicate further processing.

[0060] In a particularly preferred embodiment, a cooling crystallization is continuously carried out on a crystal suspension in the main crystallizer, wherein the crystal suspension is cooled in the main crystallizer from preferably 45-35 °C, preferably to 30-20 °C. This embodiment is particularly preferred when it is a continuous process for obtaining crystalline allulose.

[0061] At this temperature profile, allulose crystals form in the desired size and yield. At the same time, the allulose crystal suspension does not become too viscous, which would complicate further processing.

[0062] In a preferred embodiment, the residence time of the crystal suspension in the main crystallizer is 30 to 70 hours.

[0063] It was found that at this residence time, crystal formation of the desired size and yield occurs.

[0064] In a preferred embodiment, the contents of each pre-crystallizer, preferably one or more solutions, suspensions, pre-crystallization magma and / or crystallization magma, are stirred by a stirrer with a specific power input of 0.1 to 4 kW / m 3 , preferably 0.5 to 2.0 kW / m 3 The stirring process evenly distributes the crystalline phase or crystallization magma in the liquid phase or monosaccharide solution, thereby promoting mass transfer and increasing the increase in crystal mass per unit time. Furthermore, the crystals in the pre-crystallizers become homogenized.

[0065] The stirrer type, shape, and specific energy input via the stirrer must be tailored to the specific viscosities in the individual stages of the cascade. For low viscosities (< 0.5 Pas), a pitched-blade, paddle, or propeller stirrer is preferred for suspending the crystals in the liquid phase. In the medium viscosity range (0.5 to 5.0 Pas), an Intermig, cross-beam, or blade stirrer is preferred. In the high viscosity range (> 5.0 Pas), anchor and helical stirrers are preferred.

[0066] Surprisingly, it was found that during the crystallization of allulose, by increasing the specific energy input of the stirrer, focused crystal growth in the longitudinal direction could be suppressed, thereby reducing the diameter-to-length ratio from, for example, 1:10 to half. For crystals that tend to grow longitudinally (rods, needles), the specific energy input via the stirrer can influence the morphology of the crystals. If the specific power input of the stirrer is increased from, for example, 0.5 kW / m 3 to e.g. 2.0 kW / m 3It was observed that this could influence the growth behavior of the crystals (elongation) and thus reduce the elongation. In contrast to sucrose, allulose exhibits much stronger elongation. In this respect, the stirrers offer advantages not found in conventional sucrose systems. The specific energy input of such stirrers allows for a targeted influence on crystal growth.

[0067] It is also conceivable that several stirrers are used in each pre-crystallizer to achieve the same technical effect.

[0068] Preferably, the solution containing the monosaccharide and a mass of crystallization magma are fed to the main crystallizer in a mass ratio of 1:5 to 1:20, preferably 1:7 to 1:11.

[0069] Thus, crystalline monosaccharide can be efficiently formed in large quantities in a relatively short time with high yield in the main crystallizer.

[0070] Preferably, the monosaccharide solution for the pre-crystallizers has a supersaturation of 0 to 60%. In other words, the crystallization magma from an upstream stage is supplied to the downstream stage and mixed with fresh, particularly crystal-free, monosaccharide solution with a supersaturation of 0 to 60% within the metastable range.

[0071] This creates a constantly high driving force for crystal growth at each stage of the cascade.

[0072] Preferably, the residence times in the respective stages are determined by the prevailing supersaturation (equilibrium state). The process is controlled by determining the dry matter content of the liquid phase or the crystallization magma, for example, by determining the refractive index, by radiometric density measurement, or by microwave measurement. Alternatively, optical methods can be used to detect unwanted new crystal formation and thus for process optimization.

[0073] The process according to the invention produces, at the end of the cascade, a crystallization magma with a defined number of crystals of the desired grain size and grain size distribution, which can be used as crystallization magma for controlled crystal growth in the continuously operating main crystallizer.

[0074] Preferably, the solution containing the monosaccharide is supersaturated when fed into the main crystallizer.

[0075] Thus, crystalline monosaccharide can be efficiently formed in large quantities in a short time with high yield in the main crystallizer.

[0076] Preferably, the mass of crystallization magma when fed into the main crystallizer has a crystal content of 1 to 5% (wt.%) and / or an average particle diameter of 50 to 150 µm.

[0077] Thus, crystalline monosaccharide can be efficiently formed in the main crystallizer in large quantities in a short time with high yield. At the same time, the crystals in the main crystallizer grow to a size suitable for further processing.

[0078] To obtain crystalline monosaccharide, crystals of the monosaccharide with an average diameter of 200 to 400 µm and / or a purity of > 99% are preferably separated.

[0079] The separated crystalline monosaccharide is well suited for further processing due to its size and purity. The size and purity of the separated crystalline monosaccharide are determined by the process according to the invention.

[0080] In certain embodiments, the pre-crystallization magma in the pre-crystallizers and / or the crystal suspension in the main crystallizer is cooled by 0.1 to 5.0 K / h.

[0081] The crystal growth rate can be influenced by varying the cooling rate. At a cooling rate of 0.1 to 5.0 K / h, crystallization occurs in the metastable range, and the formation of fine grains due to uncontrolled primary or secondary nucleation is largely avoided. Thus, homogeneous crystal growth and a narrow particle size distribution can be achieved.

[0082] In certain embodiments, the separation of crystals of the monosaccharide from the crystal suspension comprises centrifugation of the crystal suspension, wherein the separation can also be carried out continuously if the centrifugation is carried out alternately in different centrifuges.

[0083] In preferred embodiments, the process comprises a step in which the solution containing monosaccharide, preferably with a supersaturation of 0 to 60%, and / or the solution containing the monosaccharide and which is preferably supersaturated, is formed from a monosaccharide-containing solution by evaporation.

[0084] In addition, the process may comprise a drying step, for example in a fluidized bed or drum dryer, which is preferably followed by product cooling, if necessary with conditioned air.

[0085] Part of the present invention is also a crystalline monosaccharide with an average diameter of 200 to 400 µm and / or a purity of >99%.

[0086] Part of the present invention is also a crystalline monosaccharide obtained by a process according to the invention or using a device according to the invention.

[0087] For advantages, explanations and preferred embodiments of the crystalline monosaccharide, reference is also made to the explanations of the method and device according to the invention, unless the description indicates otherwise.

[0088] The invention is also based on the object of providing a device for obtaining a crystalline monosaccharide. The device according to the invention comprises a main crystallizer with means for continuously carrying out evaporation and / or cooling crystallization on a crystal suspension to generate crystal growth of crystalline monosaccharide in the crystal suspension, means for separating crystals of the monosaccharide from the crystal suspension. The device according to the invention further comprises a cascade for continuously forming a mass of crystallization magma for the main crystallizer. The cascade comprises, connected in series, at least a first and a last stage, each with at least one pre-crystallizer, means for seeding a monosaccharide solution with monosaccharide seed crystals in at least one pre-crystallizer of the first stage to obtain a pre-crystallization magma,and means for carrying out cooling crystallization and / or evaporative crystallization on the pre-crystallization magma in the at least one pre-crystallizer of the first stage to form a mass of crystallization magma for the downstream stage, and means for feeding a solution containing monosaccharide and a mass of crystallization magma from the upstream stage into the at least one pre-crystallizer of the last stage to obtain a pre-crystallization magma, and means for carrying out cooling crystallization and / or evaporative crystallization on the pre-crystallization magma in the at least one pre-crystallizer of the last stage to form a mass of crystallization magma for the main crystallizer. The device according to the invention further comprises means for continuously feeding a solution containing the monosaccharide,and a mass of a crystallization magma from the at least one pre-crystallizer of the last stage of the cascade into the main crystallizer to form the crystal suspension, wherein the device is characterized in that the pre-crystallizers are designed such that the mass of crystallization magma formed in the pre-crystallizers increases by a factor of 2 to 12 with each stage, starting from the first stage.

[0089] For advantages, explanations, and preferred embodiments, reference is also made to the statements regarding the method according to the invention, which also apply to the device unless otherwise stated in the description. Furthermore, certain preferred embodiments are specified in the subclaims: In a preferred embodiment, each stage comprises a single pre-crystallizer and the cascade comprises means for continuously forming a mass of crystallization magma from the pre-crystallization magma in the pre-crystallizers by means of evaporative crystallization.

[0090] In a further preferred embodiment, each stage comprises two to three pre-crystallizers, and the cascade comprises means for discontinuously forming a mass of crystallization magma by means of cooling crystallization and / or for continuously forming a mass of crystallization magma by means of evaporative crystallization in the pre-crystallizers of each stage from the pre-crystallization magma. Furthermore, in the case of discontinuous formation of a mass of crystallization magma by means of cooling crystallization, the cascade comprises means for continuously feeding a mass of crystallization magma, alternating from the pre-crystallizers of the last stage, into the main crystallizer.

[0091] In certain embodiments, at least one stage of the cascade comprises more than one pre-crystallizer, and the pre-crystallizers of the same stage each have means for forming preferably equal masses of crystallization magma.

[0092] It should be noted that not every stage of the cascade needs to have the same number of pre-crystallizers. The pre-crystallizers can be interconnected in a variety of ways within each stage.

[0093] In certain embodiments, it is preferred that the first stage comprises one to two, preferably two, pre-crystallizers, the last stage comprises two to four, preferably three, pre-crystallizers and a further stage comprises two to four, preferably two, pre-crystallizers and the cascade comprises means for discontinuously forming a mass of crystallization magma from the pre-crystallization magma in the pre-crystallizers of each stage by means of cooling crystallization and the cascade comprises means for continuously and alternately supplying the mass of crystallization magma to the main crystallizer from the pre-crystallizers of the last stage.

[0094] In certain embodiments, the stages or the at least one pre-crystallizer of each stage are connected to one another in such a way that it is possible to omit individual further stages.

[0095] This is particularly advantageous for continuous maintenance and cleaning of the system. Furthermore, it is advantageous for producing smaller amounts of crystallization magma if less crystallization magma is required for the main crystallization.

[0096] In certain embodiments, the device comprises at least one centrifuge for separating crystals of the monosaccharide from the crystal suspension. In certain embodiments, the device for continuous separation comprises several centrifuges, wherein the centrifugation in the several centrifuges preferably takes place in batches.

[0097] In certain embodiments, the device comprises a drying unit, in particular a fluidized bed or drum dryer, which is preferably followed by product cooling, if necessary with conditioned air.

[0098] In preferred embodiments, the device comprises an evaporation station in which the solution containing monosaccharide, preferably with a supersaturation of 0 to 60%, and / or the solution containing the monosaccharide and which is preferably supersaturated, is formed from a monosaccharide-containing solution by evaporation and preferably setting a suitable evaporation rate.

[0099] Preferably, the pre-crystallizers are designed such that the mass of crystallization magma formed in the pre-crystallizers increases by a factor of 4 to 7 with each stage, starting from the first stage.

[0100] Preferably, the cascade comprises one to eight, preferably one to three, most preferably one, further stage(s) connected in series between the first and the last stage, wherein the further stage(s) each have at least one pre-crystallizer. Furthermore, the cascade preferably has means for feeding solution containing monosaccharide and a mass of crystallization magma from the upstream stage into the at least one pre-crystallizer of each further stage in order to obtain pre-crystallization magma, and means for forming a mass of crystallization magma in the at least one pre-crystallizer of each further stage for the downstream stage from the pre-crystallization magma discontinuously by means of cooling crystallization and / or continuously by means of evaporative crystallization.

[0101] Preferably, the device comprises means for providing monosaccharide seed crystals having an average diameter of 5 to 30 µm, preferably 10 to 20 µm.

[0102] In a preferred embodiment, the main crystallizer has means for setting a temperature gradient of the crystal suspension over the length of the main crystallizer of 70 to 15 °C and preferably of 45 to 25 °C.

[0103] In certain embodiments, the main crystallizer comprises means for continuously carrying out a cooling crystallization on a crystal suspension in the main crystallizer and for cooling the crystal suspension in the main crystallizer from preferably 70-30 °C, preferably down to 35-15 °C.

[0104] In certain embodiments, the main crystallizer comprises means for continuously carrying out a cooling crystallization on a crystal suspension in the main crystallizer and for cooling the crystal suspension in the main crystallizer from preferably 70 - 33 °C, preferably down to 32 - 15 °C.

[0105] In a preferred embodiment, the device is a device for obtaining crystalline allulose and the main crystallizer has means for continuously carrying out a cooling crystallization on a crystal suspension in the main crystallizer and for cooling the crystal suspension in the main crystallizer from preferably 45 - 35 °C, preferably down to 30 - 20 °C.

[0106] Preferably, the pre-crystallizers each have a stirrer with a specific power input of 0.1 to 4 kW / m 3 , preferably from 0.5 to 2.0 kW / m 3 , on.

[0107] It is also conceivable that each pre-crystallizer has several stirrers in order to achieve the same technical effect described above.

[0108] In preferred embodiments, the means for continuously feeding a solution containing the monosaccharide and for continuously feeding a mass of crystallization magma into the main crystallizer are designed such that the solution containing the monosaccharide and a mass of crystallization magma are fed to the main crystallizer in a mass ratio of 1:5 to 1:20, preferably 1:7 to 1:11.

[0109] In certain embodiments, the apparatus comprises means for cooling the pre-crystallization magma in the pre-crystallizers and / or the crystal suspension in the main crystallizer by 0.1 to 5.0 K / h.

[0110] The monosaccharide of the method according to the invention or the device according to the invention or the monosaccharide according to the invention is in particular a monosaccharide with a melting point of 90 to 165°C. In particular, it is a monosaccharide of the D configuration. It is particularly preferably a hexulose, a hexose, a pentose, or a tetrose with a melting point of 90 to 165°C. Most preferably, the monosaccharide is a hexulose, in particular psicose (allulose), in particular D-psicose.

[0111] With reference to the figures, the invention is explained using an embodiment.

[0112] Show Fig. 1 shows a main crystallizer according to an apparatus of the present invention and in a method of the present invention; Fig. 2 Main crystallizer and pre-crystallizers in a cascade with three stages, each with a pre-crystallizer according to an apparatus of the present invention and in a process of the present invention; Fig. 3 Main crystallizer and pre-crystallizers in a cascade with three stages, each with several pre-crystallizers according to an apparatus of the present invention and in a process of the present invention.

[0113] Fig. Figure 1 shows a main crystallizer 10 in an apparatus according to the invention for carrying out the process according to the invention. In this example, the solution containing the monosaccharide and the solution with monosaccharide are identical, i.e., they contain the same components in equal amounts. The solution is thickened in an evaporation station.

[0114] The main crystallizer 10 has injection points 2 for a solution containing the monosaccharide. The injection points 2 are distributed along the height of the main crystallizer 10 and around the circumference of the main crystallizer 10. In this example, four injection points at one height form an injection ring. Eight such injection rings are distributed along the height of the main crystallizer 10. The valves are timed so that all injection points of an injection ring are open or closed.

[0115] A mass of crystallization magma is introduced from a line 3 from the last stage of the cascade together with solution containing the monosaccharide from a line 4 at the top into the main crystallizer 10.

[0116] In this example, the main crystallizer 10 has eight separate heat exchangers 5 inside for setting a temperature profile. The heat exchangers 5 are distributed throughout the height of the main crystallizer 10 and are each supplied with a water circuit for heating / cooling the crystal suspension. The flow and temperature of the circulating water are regulated, allowing the product temperature / temperature profile to be influenced in a controlled manner.

[0117] From the main crystallizer 10, a line 6 leads to a centrifuge station in which crystals of the monosaccharide are separated from the crystal suspension.

[0118] Fig. Figure 2 shows an embodiment of the invention. In a main crystallizer 10, cooling crystallization is continuously carried out on a crystal suspension in order to grow crystalline monosaccharide in the crystal suspension. The main crystallizer 10 is a vertical cooling crystallizer with oscillating cooling tube bundles. Crystal suspension is continuously discharged from the main crystallizer 10, and in a centrifuge station 11, grown crystals of the monosaccharide are separated from the crystal suspension to obtain crystalline monosaccharide. A solution containing the monosaccharide and a mass of crystallization magma are continuously fed to the main crystallizer 10 to provide the crystal suspension. The crystallization magma originates from a cascade for the continuous formation of a mass of crystallization magma.

[0119] In this example, the solution containing the monosaccharide and the solution with monosaccharide are identical, i.e., they contain the same components in equal amounts. In this example, a solution containing the monosaccharide and the solution with monosaccharide, respectively, are prepared in an evaporation station 12 with a dry matter concentration of 82% and a temperature of 40°C. This solution, which contains the monosaccharide, is thus fed to the pre-crystallizers 13A, 14A, 15A and the main crystallizer 10.

[0120] The cascade comprises three series-connected stages 13, 14, and 15, each with a pre-crystallizer 13A, 14A, and 15A. Evaporative crystallization is continuously carried out in each pre-crystallizer 13A, 14A, and 15A. A solution containing monosaccharide and a mass of crystallization magma from the preceding stage 14 are fed into the pre-crystallizer 15A of the final stage 15 to obtain a pre-crystallization magma. In the pre-crystallizer 15A of the final stage 15, a mass of crystallization magma for the main crystallizer 10 is then formed from the pre-crystallization magma by means of evaporative crystallization.

[0121] In the pre-crystallizer 13A of the first stage 13, a monosaccharide solution is seeded with a seed suspension (the slurry) 16 containing monosaccharide seed crystals with an average crystal diameter of 13 µm to obtain a pre-crystallization magma. The seed suspension (the slurry) containing monosaccharide seed crystals has a crystal content of 20 wt.% and a temperature of 20 °C and is fed at a rate of 0.30 L / h or 0.43 kg / h. A monosaccharide solution is fed to the pre-crystallizer 13A at a rate of 2.7 L / h. The mixture results in a pre-crystallization magma with a crystal content of 2.1 wt.%. Evaporative crystallization is used to form a mass of crystallization magma from the pre-crystallization magma for the pre-crystallizer 14A of the downstream, middle stage 14. The net volume of the pre-crystallizer 13A of the first stage 13 is 0.15 m 3Vapors 17 are discharged at a temperature of 63 °C at a rate of 0.2 kg / h. The residence time in the pre-crystallizer 13A is 43.3 h. A mass of crystallization magma is fed to the pre-crystallizer 14A of the middle stage 14 at a rate of 2.7 L / h, a temperature of 63 °C, an average crystal diameter of 30 µm, and a crystal content of 27 wt.%. A solution containing monosaccharide is also fed to this pre-crystallizer 14A at a rate of 21.4 L / h.

[0122] The mixture produces a pre-crystallization magma with a crystal content of 3.2 wt.% and a temperature of 42.7 °C. Evaporative crystallization is used to form a mass of crystallization magma from the pre-crystallization magma for the pre-crystallizer 15A of the downstream, final stage 15. The net volume of the pre-crystallizer 14A of the middle stage 14 is 1.0 m 3Vapors 17 are discharged at a temperature of 65 °C at a rate of 1.8 kg / h. The residence time is 40.0 h, and a mass of crystallization magma of 21.8 L / h with a temperature of 65 °C, an average crystal diameter of 60 µm, and a crystal content of 27 wt.% is fed to the pre-crystallizer 15A of the final stage 15. Monosaccharide solution is also fed to the pre-crystallizer 15A at a rate of 208 L / h.

[0123] The mixture produces a pre-crystallization magma with a crystal content of 2.7 wt.% and a temperature of 42.5 °C. Evaporative crystallization is used to form a mass of crystallization magma from the pre-crystallization magma for the main crystallizer 10. The net volume of the pre-crystallizer 15A of the final stage 15 is 6.0 m 3Vapors 17 are discharged at a temperature of 70 °C at a rate of 14 kg / h. The residence time is 26.7 h, and a mass of crystallization magma of 209 L / h with a temperature of 70 °C, an average crystal diameter of 120 µm, and a crystal content of 22.5 wt.% is fed to the main crystallizer 10. A solution containing monosaccharide, which here is identical to the solution containing the monosaccharide, is also fed to the main crystallizer 10 at a rate of 1990 L / h.

[0124] The mixture produces a crystal suspension with a crystal content of 2.2 wt. % and a temperature of 43.0 °C. Crystalline monosaccharide is formed in the crystal suspension by cooling crystallization, but primarily crystals of crystalline monosaccharide grow. The net volume of the main crystallizer 10 is 157.0 m 3The residence time is 73.0 h. During this time, the crystal suspension is cooled at 0.3 K / h. The crystal suspension containing the formed crystalline monosaccharide is fed to a centrifuge station 11 at a rate of 2100 L / h, at a temperature of 19 °C, with an average crystal diameter of 300 µm and a crystal content of 35.3 wt.%. There, crystals of the monosaccharide are separated by centrifugation, thus obtaining crystalline monosaccharide.

[0125] Fig.3 shows a further embodiment of the invention. In a main crystallizer 10, a cooling crystallization is continuously carried out on a crystal suspension in order to grow monosaccharide crystals in the crystal suspension. The main crystallizer 10 is a vertical cooling crystallizer with oscillating cooling tube bundles. Crystal suspension is continuously discharged from the main crystallizer 10, and in a centrifuge station 11, (grown) crystals of the monosaccharide are separated from the crystal suspension to obtain crystalline monosaccharide. A solution containing the monosaccharide and a mass of crystallization magma are continuously fed to the main crystallizer 10 to provide the crystal suspension. The crystallization magma originates from a cascade for the continuous formation of a mass of crystallization magma.

[0126] In this example, the solution containing the monosaccharide and the solution with monosaccharide are identical, i.e., they contain the same components in equal amounts. In this example, a solution containing the monosaccharide and the solution with monosaccharide, respectively, are provided in an evaporation station 12 with a dry matter concentration of 82% and a temperature of 41°C. This solution, which includes the monosaccharide, is thus fed to the pre-crystallizers 13A, 13B, 14A, 14B, 15A, 15B, and 15C and to the main crystallizer 10.

[0127] The cascade comprises three stages 13, 14, and 15 connected in series. The first stage 13 has two pre-crystallizers 13A, 13B, the middle stage 14 has two pre-crystallizers 14A, 14B, and the final stage 15 has three pre-crystallizers 15A, 15B, and 15C. Cooling crystallization is carried out discontinuously in each pre-crystallizer 13A, 13B, 14A, 14B, 15A, 15B, and 15C. A solution containing monosaccharide and a mass of crystallization magma from the preceding stage 14 are fed into the pre-crystallization magma 15A, 15B, and 15C of the final stage 15. In the pre-crystallizers 15A, 15B, and 15C of the final stage 15, a mass of crystallization magma for the main crystallizer 10 is then formed from the pre-crystallization magma by means of cooling crystallization. The cooling crystallization in the three pre-crystallizers 15A, 15B, and 15C of the final stage 15 proceeds discontinuously.However, the cooling crystallization in the three pre-crystallizers 15A, 15B, and 15C is configured so that crystallization magma can always be fed from one pre-crystallizer into the main crystallizer 10, ensuring a continuous supply of crystallization magma to the main crystallizer 10. At the same time, the other pre-crystallizers can be cleaned or filled.

[0128] In the two pre-crystallizers 13A, 13B of the first stage 13, a monosaccharide solution is seeded with a seed suspension (a slurry) 16 containing monosaccharide seed crystals with an average crystal diameter of 13 µm to obtain a pre-crystallization magma. The seed suspension (the slurry) 16 containing monosaccharide seed crystals has a crystal content of 20 wt.% and a temperature of 20 °C and is fed to the pre-crystallizers 13A, 13B at a total rate of 0.30 L / h and 0.43 kg / h, respectively. The monosaccharide solution is fed to the pre-crystallizers 13A, 13B at a total rate of 2.6 L / h. The mixture produces a pre-crystallization magma with a crystal content of 2.2 wt.%. From the pre-crystallization magma, a mass of crystallization magma is formed by means of cooling crystallization for the two pre-crystallizers 14A, 14B of the downstream, middle stage 14.The net volume of the pre-crystallizers 13A, 13B of the first stage 13 is 0.070 m each. 3 The residence time in pre-crystallizers 13A, 13B is 43.3 h, and the cooling rate is 0.3 K / h. A mass of crystallization magma is fed to pre-crystallizers 14A, 14B of the middle stage 14 at a total rate of 2.7 L / h, with a temperature of 27 °C, an average crystal diameter of 30 µm, and a crystal content of 27 wt.%. These pre-crystallizers 14A, 14B are also fed with a solution containing monosaccharide at a total rate of 20.1 L / h.

[0129] The mixture produces a pre-crystallization magma with a crystal content of 3.4 wt.% and a temperature of 40.0 °C. Cooling crystallization is used to form a mass of crystallization magma from the pre-crystallization magma for the three pre-crystallizers 15A, 15B, and 15C of the downstream, final stage 15. The net volume of the pre-crystallizers 14A and 14B of the middle stage 14 is 0.50 m each. 3 The residence time in the pre-crystallizers 14A, 14B of the middle stage 14 is 40.0 h, and the cooling rate is 0.3 K / h. A total mass of crystallization magma of 21.8 L / h with a temperature of 28 °C, an average crystal diameter of 60 µm, and a crystal content of 27 wt.% is fed to the pre-crystallizers 15A, 15B, and 15C of the final stage 15. Monosaccharide solution is also fed to the pre-crystallizers 15A, 15B, and 15C of the final stage 15 at a total rate of 197 L / h.

[0130] The mixture produces a pre-crystallization magma with a crystal content of 2.8 wt.% and a temperature of 40.0 °C. Cooling crystallization is used to form a mass of crystallization magma from the pre-crystallization magma for the main crystallizer 10. The net volume of the pre-crystallizers 15A, 15B, and 15C of the final stage 15 is 2.2 m each. 3 The residence time in the final-stage pre-crystallizers 15A, 15B, and 15C is 26.7 h, and the cooling rate is 0.3 K / h. A mass of crystallization magma with a temperature of 32 °C, an average crystal diameter of 120 µm, and a crystal content of 22.5 wt.% is fed to the main crystallizer 10 at a rate of 209 L / h. A solution containing monosaccharide, which is identical to the solution containing the monosaccharide, is also fed to the main crystallizer 10 at a rate of 1990 L / h.

[0131] The mixture produces a crystal suspension with a crystal content of 2.2 wt. % and a temperature of 40.0 °C. Crystalline monosaccharide is formed in the crystal suspension by cooling crystallization. The net volume of the main crystallizer 10 is 157.0 m 3 The residence time is 73.0 h. During this time, the crystal suspension is cooled at 0.3 K / h. The crystal suspension containing the formed crystalline monosaccharide is fed to a centrifuge station 11 at a rate of 2100 L / h, a temperature of 19 °C, an average crystal diameter of 300 µm, and a crystal content of 35.0 wt.%. There, the crystalline monosaccharide is separated and recovered by centrifugation.

[0132] The purity of the crystals in the examples is > 99%. The density of the solution with monosaccharide is approximately 1.36 kg / L. The density of the crystallization magma is approximately 1.44 kg / L. Each pre-crystallizer in the examples has a stirrer with a specific power input of 0.5 to 2.0 kW / m 3 on. List of reference symbols 2 injection points 3 Conduit for a mass of crystallization magma 4 Line for a solution containing the monosaccharide 5 heat exchangers 6 Derivation to a centrifuge station 10 Main crystallizer 11 Centrifuge station 12 Evaporation station 13 first stage of the cascade 13A, 13B First stage pre-crystallizer(s) 14 second / further stage of the cascade 14A, 14B Second stage pre-crystallizer(s) 15 last stage of the cascade 15A, 15B, 15C Pre-crystallizer(s) of the final stage 16 Seed suspension (slurry) 17 brothers

Claims

[1] Continuous process for the production of a crystalline monosaccharide, comprising: - a continuous crystallization of the monosaccharide in a main crystallizer (10), - wherein in the main crystallizer (10) a continuous evaporation and / or cooling crystallization is carried out on a crystal suspension in order to allow crystals of the monosaccharide to grow in the crystal suspension, - separating crystals of the monosaccharide from the crystal suspension to obtain crystalline monosaccharide; - the continuous formation of a mass of crystallization magma for the main crystallizer (10) in a cascade, - wherein the cascade is connected in series and includes at least a first (13) and a last stage (15) and each stage includes at least one pre-crystallizer (13A, 15A), - wherein in the at least one pre-crystallizer (13A) of the first stage (13) a solution containing monosaccharide is inoculated by monosaccharide seed crystals to obtain a pre-crystallization magma, and from the pre-crystallization magma a mass of crystallization magma for the downstream stage (14, 15) is formed by means of cooling crystallization and / or evaporation crystallization, and - wherein a solution containing monosaccharide and a mass of crystallization magma from the upstream stage is supplied to at least one pre-crystallization magma (15A, 15B, 15C) of the last stage (15) to obtain a pre-crystallization magma, and in which at least one pre-crystallization magma (15A, 15B, 15C) of the last stage (15) a mass of crystallization magma for the main crystallization magma (10) is formed from the pre-crystallization magma by means of cooling crystallization and / or evaporation crystallization; - the continuous feeding of a solution containing the monosaccharide and a mass of crystallization magma from the at least one pre-crystallizer (15A, 15B, 15C) of the last stage (15) of the cascade into the main crystallizer (10) to provide the crystal suspension, the procedure characterized by is that the mass of crystallization magma formed in a pre-crystallizer (14A, 14B, 15A, 15B, 15C) of a stage (14, 15) exceeds the mass of crystallization magma formed in a pre-crystallizer (13A, 13B, 14A, 14B, 15A, 15B, 15C) of the upstream stage (13, 14) by a factor of 2 to 12. [2] Method according to claim 1, wherein each stage (13, 14, 15) of the cascade comprises a single pre-crystallizer (13A, 14A, 15A) and in the pre-crystallizer (13A, 14A, 15A) of each stage (13, 14, 15) a mass of crystallization magma is continuously formed from the pre-crystallization magma by means of evaporative crystallization. [3] The method of claim 1, wherein each stage (13, 14, 15) comprises two to three pre-crystallizers (13A, 13B, 14A, 14B, 15A, 15B, 15C) and in the pre-crystallizers (13A, 13B, 14A, 14B, 15A, 15B, 15C) of each stage (13, 14, 15) a mass of crystallization magma is formed discontinuously by cooling crystallization and / or continuously by evaporation crystallization, wherein the mass of crystallization magma that is continuously supplied to the main crystallizer (10) is supplied alternately from the pre-crystallizers (15A, 15B, 15C) of the last stage (15) in the case of discontinuous formation by cooling crystallization. [4] Method according to any of the preceding claims, in particular claim 1 or 3, wherein at least one stage (13, 14, 15) comprises more than one pre-crystallizer and the pre-crystallizers (13A, 13B, 14A, 14B, 15A, 15B, 15C) of the same stage (13, 14, 15) each preferably form the same mass of crystallization magma. [5] Method according to any of the preceding claims, wherein the mass of crystallization magma formed in a pre-crystallizer (14A, 14B, 15A, 15B, 15C) of a stage (14, 15) exceeds the mass of crystallization magma formed in a pre-crystallizer (13A, 13B, 14A, 14B, 15A, 15B, 15C) of the upstream stage (13, 14) by a factor of 4 to 7. [6] A method according to any of the preceding claims, wherein the cascade between the first (13) and the last (15) stage comprises one to eight, preferably one to three, most preferably one further stage (14) or stages connected in series, wherein the further stage (14) or further stages each comprise at least one pre-crystallizer (14A, 14B) in which a solution containing monosaccharide and a mass of crystallization magma from the upstream stage (13) is supplied to obtain pre-crystallization magma, and wherein in the at least one pre-crystallizer (14A, 14B) of each further stage (14) a mass of crystallization magma for the downstream stage (15) is formed from the pre-crystallization magma discontinuously by means of cooling crystallization and / or continuously by means of evaporation crystallization. [7] Method according to any of the preceding claims, wherein the monosaccharide seed crystals have a mean diameter of 5 to 50 µm, preferably 10 to 20 µm. [8] Method according to one of the preceding claims, wherein a temperature gradient of the crystal suspension over the length of the main crystallizer (10) is set from 70 to 15 °C and preferably from 45 to 25 °C and / or the residence time of the crystal suspension in the main crystallizer (10) is 30 to 70 hours. [9] Method according to any of the preceding claims, wherein the contents of each pre-crystallizer (13A, 13B, 14A, 14B, 15A, 15B, 15C), preferably one or more solutions, suspensions, pre-crystallization magma and / or crystallization magma, are stirred by a stirrer with a specific power input of 0.1 to 4.0 kW / m³ 3 preferably from 0.5 to 2.0 kW / m² 3 , is powered. [10] Method according to one of the preceding claims, wherein the main crystallizer (10) is supplied with the solution containing the monosaccharide and a mass of crystallization magma in a mass ratio of 1:5 to 1:20, preferably 1:7 to 1:

11. [11] Method according to any of the preceding claims, wherein the monosaccharide solution for the pre-crystallizers has a supersaturation of 0 to 60% and / or the solution containing the monosaccharide is supersaturated when fed into the main crystallizer (10). [12] Method according to any of the preceding claims, wherein the mass of crystallization magma when fed into the main crystallizer (10) has a crystal content of 1 to 5% (wt%) and / or a mean particle diameter of 50 to 150 µm. [13] Method according to any of the preceding claims, wherein crystals of the monosaccharide with a mean diameter of 200 to 400 µm and / or a purity greater than 99% are separated to obtain crystalline monosaccharide. [14] Method according to any of the preceding claims, wherein the pre-crystallization magma in the pre-crystallizers (13A, 13B, 14A, 14B, 15A, 15B, 15C) and / or the crystal suspension in the main crystallizer (10) is cooled by 0.1 to 5.0 K / h. [15] Apparatus for producing a crystalline monosaccharide, in particular for carrying out the continuous process according to any one of claims 1 to 14, comprising - a main crystallizer (10) with - Means for the continuous execution of evaporation and / or cooling crystallization on a crystal suspension to generate crystal growth of crystalline monosaccharide in the crystal suspension, - Agent for separating crystals of the monosaccharide from the crystal suspension, - a cascade for the continuous formation of a mass of crystallization magma for the main crystallizer, wherein the cascade comprises: - connected in series at least one first (13) and one last (15) stage, each with at least one pre-crystallizer (13A, 13B, 15A, 15B, 15C), - Means for inoculating a monosaccharide solution with monosaccharide seed crystals in at least one pre-crystallizer (13A, 13B) of the first stage (13) to obtain a pre-crystallization magma, and means for carrying out cooling crystallization and / or evaporative crystallization on the pre-crystallization magma in the at least one pre-crystallizer (13A, 13B) of the first stage (13) to form a mass of crystallization magma for the downstream stage, and - Means for supplying a solution containing monosaccharide and a mass of crystallization magma from the upstream stage to the at least one pre-crystallizer (15A, 15B, 15C) of the last stage (15) to obtain a pre-crystallization magma, and means for carrying out cooling crystallization and / or evaporative crystallization on the pre-crystallization magma in the at least one pre-crystallizer (15A, 15B, 15C) of the last stage to form a mass of crystallization magma for the main crystallizer (10); - Means for the continuous supply of a solution containing the monosaccharide and a mass of crystallization magma from the at least one pre-crystallizer (15A, 15B, 15C) of the last stage (15) of the cascade into the main crystallizer (10) to form the crystal suspension, wherein the device characterized by is that the pre-crystallizers (13A, 13B, 14A, 14B, 15A, 15B, 15C) are designed such that the mass of crystallization magma formed in the pre-crystallizers increases by a factor of 2 to 12 with each stage (14, 15) starting from the first stage (13). [16] Device according to claim 15, wherein each stage (13, 14, 15) comprises a single pre-crystallizer (13A, 14A, 15A) and the cascade comprises means for continuously forming a mass of crystallization magma from the pre-crystallization magma in the pre-crystallizers (13A, 14A, 15A) by means of evaporation crystallization. [17] Device according to claim 15, wherein each stage (13, 14, 15) comprises two to three pre-crystallizers (13A, 13B, 14A, 14B, 15A, 15B, 15C) and the cascade comprises means for the discontinuous formation of a mass of crystallization magma by means of cooling crystallization and / or for the continuous formation of a mass of crystallization magma by means of evaporative crystallization in the pre-crystallizers (13A, 13B, 14A, 14B, 15A, 15B, 15C) of each stage (13, 14, 15) from the pre-crystallization magma, and, in the case of discontinuous formation of a mass of crystallization magma by means of cooling crystallization, comprises means for the continuous supply of a mass of crystallization magma, alternating from the pre-crystallizers (15A, 15B, 15C) of the last stage (15), into the main crystallizer. [18] Device according to one of the preceding claims, in particular claim 15 or 17, wherein at least one stage (13, 14, 15) comprises more than one pre-crystallizer (13A, 13B, 14A, 14B, 15A, 15B, 15C) and the pre-crystallizers (13A, 13B, 14A, 14B, 15A, 15B, 15C) of the same stage each have means for forming preferably equal masses of crystallization magma. [19] Device according to one of the preceding claims, wherein the pre-crystallizers (13A, 13B, 14A, 14B, 15A, 15B, 15C) are designed such that the mass of crystallization magma formed in the pre-crystallizers increases by a factor of 4 to 7 with each stage (14, 15) starting from the first stage (13). [20] Device according to one of the preceding claims, wherein the cascade between the first (13) and the last (15) stage comprises one to eight, preferably one to three, most preferably one further stage (14) or stages connected in series, wherein the further stage (14) or further stages each have at least one pre-crystallizer (14A, 14B), and the cascade has means for introducing into the at least one pre-crystallizer (14A, 14B) of each further stage (14) a solution containing monosaccharide and a mass of crystallization magma from the upstream stage (13) to obtain pre-crystallization magma, and the cascade has means for forming a mass of crystallization magma in the at least one pre-crystallizer (14A, 14B) of each further stage for the downstream stage from the pre-crystallization magma discontinuously by means of cooling crystallization and / or continuously by means of evaporation crystallization. [21] Device according to one of the preceding claims, wherein the device comprises means for providing monosaccharide seed crystals with a mean diameter of 5 to 50 µm, preferably of 10 to 20 µm. [22] Device according to one of the preceding claims, wherein the main crystallizer (10) has means to adjust a temperature gradient of the crystal suspension over the length of the main crystallizer (10) from 70 to 15 °C and preferably from 45 to 25 °C. [23] Device according to one of the preceding claims, wherein the pre-crystallizers (13A, 13B, 14A, 14B, 15A, 15B, 15C) each have a stirrer with a specific power input of 0.1 to 4.0 kW / m 3 preferably from 0.5 to 2.0 kW / m² 3 exhibit. [24] Device according to one of the preceding claims, wherein the means for continuously supplying a solution containing the monosaccharide and for continuously supplying a mass of crystallization magma to the main crystallizer (10) are designed such that the solution containing the monosaccharide and a mass of crystallization magma are supplied to the main crystallizer (10) in a mass ratio of 1:5 to 1:20, preferably 1:7 to 1:

11. [25] Device according to any of the preceding claims, wherein the device comprises means to cool the pre-crystallization magma in the pre-crystallizers (13A, 13B, 14A, 14B, 15A, 15B, 15C) and / or the crystal suspension in the main crystallizer (10) by 0.1 to 5.0 K / h. [26] Method according to any one of claims 1 to 14 or apparatus according to any one of claims 15 to 25, wherein the monosaccharide is a monosaccharide, in particular a hexulose, a hexose, a pentose or a tetrose, having a melting point of 90 to 165 °C, wherein the monosaccharide is particularly preferably a hexulose, in particular psicose (allulose), in particular D-psicose.

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