A method for crystallizing erythritol assisted by liquid nitrogen

Abstract

The present invention belongs to the technical field of erythritol production, and particularly relates to a method for cryogenic nitrogen-assisted crystallization of erythritol. Under the conditions of cryogenic nitrogen-assisted cooling and first stirring, an erythritol concentrate and erythritol crystal seeds are mixed to carry out first-stage cooling crystallization to obtain a first-stage crystallization material; under the condition of second stirring, the first-stage crystallization material is subjected to second-stage crystallization to obtain a second-stage crystallization material; the second-stage crystallization material is sequentially subjected to standing, solid-liquid separation and drying to obtain erythritol crystals. The method provided by the present invention can obtain erythritol crystals with uniform particle size, improve the quality and stability of erythritol crystal products; moreover, the crystallization time is short and the production efficiency is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of erythritol production, and particularly relates to a method for assisting erythritol crystallization with liquid nitrogen. Background Art

[0002] As an important low-calorie sweetener, erythritol has been widely used in the fields of food, medicine, etc.

[0003] At present, erythritol is generally prepared by crystallization. However, the crystallization process of erythritol has problems such as slow crystallization speed and low production efficiency, and the particle size distribution of the obtained crystal products is uneven, and the quality of the erythritol crystal products needs to be further improved. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for assisting erythritol crystallization with liquid nitrogen. The method provided by the present invention can obtain erythritol crystals with uniform particle size, improve the quality and stability of erythritol crystal products; and has a short crystallization time and high production efficiency.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a method for assisting erythritol crystallization with liquid nitrogen, comprising the following steps:

[0007] Under the conditions of liquid nitrogen-assisted cooling and first stirring, mix the erythritol concentrate and erythritol crystal seeds for first-stage cooling crystallization to obtain first-stage crystallization materials;

[0008] Perform second-stage crystallization on the first-stage crystallization materials under the condition of second stirring to obtain second-stage crystallization materials;

[0009] Let the second-stage crystallization materials stand, perform solid-liquid separation and drying in sequence to obtain erythritol crystals.

[0010] Preferably, the mass concentration of erythritol in the erythritol concentrate is 500-700 g / L.

[0011] Preferably, the mesh number of the erythritol crystal seeds is 30-60 mesh;

[0012] The mass ratio of the erythritol crystal seeds to the volume of the erythritol concentrate is (10-30) g:1 L.

[0013] Preferably, the mixing temperature of the erythritol concentrate and erythritol crystal seeds is 60-70 °C.

[0014] Preferably, the liquid nitrogen is introduced from the bottom of the erythritol concentrate, and the volume flow rate of the liquid nitrogen is 0.8-2 L / min.

[0015] Preferably, the rotation speed of the first stirring is 100 - 150 rpm;

[0016] Start timing when the erythritol concentrate and erythritol seed crystals are mixed, and the time for the first-stage cooling crystallization is 1 - 3 h.

[0017] Preferably, the rotation speed of the second stirring is 100 - 150 rpm; the temperature of the second-stage crystallization is ≤ 35°C, and the time is 0.5 - 1 h.

[0018] Preferably, the temperature for standing is ≤ 35°C, and the time is 0.5 - 1 h.

[0019] Preferably, the average particle size of the erythritol crystals is 40 - 55 μm.

[0020] Preferably, the erythritol concentrate is obtained by vacuum distillation of an erythritol solution; the pressure of the vacuum distillation is -0.09 Mpa - -0.095 Mpa, and the temperature is 80 - 85°C.

[0021] The present invention provides a method for cryogenic nitrogen-assisted crystallization of erythritol, comprising the following steps: Under the conditions of cryogenic nitrogen-assisted cooling and first stirring, mix the erythritol concentrate and erythritol seed crystals for the first-stage cooling crystallization to obtain the first-stage crystallization material; under the condition of second stirring, carry out the second-stage crystallization on the first-stage crystallization material to obtain the second-stage crystallization material; sequentially carry out standing, solid-liquid separation and drying on the second-stage crystallization material to obtain erythritol crystals. The method provided by the present invention adopts a segmented crystallization method. In the process of the first-stage cooling crystallization, a cryogenic nitrogen-assisted stirring crystallization method is adopted. The low-temperature characteristics of cryogenic nitrogen can rapidly reduce the temperature of the material to be crystallized, create a large supersaturation, thereby accelerating the crystallization speed, shortening the crystallization time, and improving the production efficiency. At the same time, the present invention stirs while introducing cryogenic nitrogen, so as to form a uniformly distributed temperature field in the material to be crystallized by cryogenic nitrogen, so that the erythritol crystals can grow in a uniform temperature and concentration, and obtain crystals with uniform particle size, improving the quality and stability of the erythritol crystal product. Finally, the present invention carries out crystal cultivation through the second-stage crystallization and standing, further improving the particle size uniformity and product stability of the erythritol crystal product.

[0022] In addition, the method provided by the present invention is simple and safe to operate and easy to control. Cryogenic nitrogen is in a gaseous state under normal temperature and pressure, and does not chemically react with water and erythritol, will not cause environmental pollution, and has high safety as long as it is operated according to the operating procedures during use. At the same time, compared with the traditional cooling water cooling, the method provided by the present invention saves water resources and energy and reduces the production cost.

[0023] Furthermore, in the present invention, the volume flow rate of the liquid nitrogen is 0.8 - 2 L / min; the rotation speed of the first stirring is 100 - 150 rpm. By controlling the feeding speed of the liquid nitrogen and the rotation speed of the first stirring during the first-stage cooling crystallization process, the present invention can form a more uniform crystallization temperature field, thereby obtaining an erythritol crystal product with a more uniform particle size distribution and higher stability between batches of the crystal product. Description of the Drawings

[0024] Figure 1 It is a microscope photograph of the erythritol crystals prepared in Example 1 of the present invention. Detailed Embodiments

[0025] The present invention provides a method for liquid nitrogen-assisted erythritol crystallization, comprising the following steps:

[0026] Under the conditions of liquid nitrogen-assisted cooling and first stirring, an erythritol concentrate and erythritol crystal seeds are mixed for first-stage cooling crystallization to obtain a first-stage crystallization material;

[0027] Under the condition of second stirring, the first-stage crystallization material is subjected to second-stage crystallization to obtain a second-stage crystallization material;

[0028] The second-stage crystallization material is sequentially subjected to standing, solid-liquid separation and drying to obtain erythritol crystals.

[0029] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well-known to those skilled in the art.

[0030] In the present invention, under the conditions of liquid nitrogen-assisted cooling and first stirring, an erythritol concentrate and erythritol crystal seeds are mixed for first-stage cooling crystallization to obtain a first-stage crystallization material.

[0031] In the present invention, the mass concentration of erythritol in the erythritol concentrate is preferably 500 - 700 g / L.

[0032] In the present invention, the erythritol concentrate is preferably obtained by vacuum distillation of an erythritol solution. The erythritol solution is preferably obtained by fermentation and purification. The pressure of the vacuum distillation is preferably -0.09 Mpa to -0.095 Mpa, and the temperature is preferably 80 - 85°C. The present invention preferably adopts the method of vacuum distillation and controls the pressure and temperature of the vacuum distillation at the same time, which can effectively concentrate the erythritol solution while reducing the decomposition and deterioration of erythritol under high temperature conditions. In the present invention, the initial temperature of the erythritol concentrate obtained by vacuum distillation is preferably 80 - 85°C.

[0033] Preferably, in the present invention, the erythritol concentrate is cooled from the initial temperature to the temperature at which the erythritol concentrate is mixed with the erythritol seed crystals, and then mixed with the erythritol seed crystals. The temperature at which the erythritol concentrate is mixed with the erythritol seed crystals is preferably 60-70°C. The temperature (60-70°C) at which the erythritol concentrate is mixed with the erythritol seed crystals is the temperature at which the erythritol concentrate begins to crystallize. During the process of cooling the erythritol concentrate from the initial temperature (i.e., 80-85°C) to the mixing temperature (60-70°C), it is preferably carried out under the conditions of introducing liquid nitrogen and stirring. The liquid nitrogen is preferably introduced from the bottom of the erythritol concentrate, and the volume flow rate of the liquid nitrogen is preferably 0.8-2 L / min, and can be 0.8 L / min, 1 L / min, 1.2 L / min, 1.5 L / min, 1.8 L / min or 2 L / min in the examples. The stirring speed for cooling is preferably 100-150 rpm, and can be 100 rpm, 125 rpm or 150 rpm in the examples.

[0034] In the present invention, the mesh number of the erythritol seed crystals is 30-60 mesh, that is, the erythritol seed crystals are preferably the material passing through a 30-mesh sieve and retained on a 60-mesh sieve. In the present invention, the erythritol seed crystals are preferably erythritol. The mass ratio of the erythritol seed crystals to the volume of the erythritol concentrate is preferably (10-30) g:1 L, and can be 10 g:1 L, 15 g:1 L, 20 g:1 L, 25 g:1 L or 30:1 L in the examples.

[0035] In the present invention, the temperature at which the erythritol concentrate is mixed with the erythritol seed crystals is preferably 60-70°C. The mixing is preferably adding the erythritol seed crystals to the erythritol concentrate. During the mixing, liquid nitrogen is continuously introduced into the erythritol concentrate, and the volume flow rate of the liquid nitrogen remains unchanged at the volume flow rate when the erythritol concentrate is cooled. By adding erythritol seed crystals to the erythritol concentrate in the present invention, the addition of the erythritol seed crystals, and reasonably controlling the added mass of the seed crystals contribute to inducing the growth of erythritol crystals, improving the crystallization efficiency and the particle size uniformity of the erythritol crystal product.

[0036] In the present invention, the liquid nitrogen-assisted cooling is preferably carried out by passing the liquid nitrogen through the erythritol concentrate, and the liquid nitrogen is preferably introduced from the bottom of the erythritol concentrate. The volume flow rate of the liquid nitrogen is preferably 0.8 - 2 L / min, and in the examples, it can be 0.8 L / min, 1 L / min, 1.2 L / min, 1.5 L / min, 1.8 L / min or 2 L / min. The rotation speed of the first stirring is preferably 100 - 150 rpm, and in the examples, it can be 100 rpm, 125 rpm or 150 rpm. When the erythritol concentrate and the erythritol crystal seeds are mixed, timing starts, and the time for the first-stage cooling crystallization is preferably 1 - 3 h, and in the examples, it can be 1 h, 1.5 h, 2 h, 2.5 h or 3 h. After the first-stage cooling crystallization ends, the liquid nitrogen supply is stopped. By carrying out the first stirring while passing the liquid nitrogen and controlling the volume flow rate of the liquid nitrogen introduced and the rotation speed of the first stirring, the present invention can ensure the uniformity of the temperature in the solution in space, thereby promoting the uniform growth of crystals.

[0037] In the examples of the present invention, the process of the first-stage cooling crystallization preferably includes: passing liquid nitrogen through the erythritol concentrate with a temperature preferably of 82 - 85 °C, adding erythritol crystal seeds when the temperature is cooled to 60 - 70 °C under the condition of the first stirring, and then continuing the first-stage cooling crystallization under the conditions of passing liquid nitrogen and the first stirring to obtain the first-stage crystallization material.

[0038] In the present invention, the temperature of the first-stage crystallization material obtained by the first-stage cooling crystallization is preferably ≤ 35 °C, more preferably 20 - 30 °C, and further preferably 25 - 30 °C.

[0039] After obtaining the first-stage crystallization material, the present invention carries out the second-stage crystallization on the first-stage crystallization material under the condition of the second stirring to obtain the second-stage crystallization material. In the present invention, the temperature of the second-stage crystallization is preferably ≤ 35 °C, more preferably 20 - 30 °C, and further preferably 25 - 30 °C. The rotation speed of the second stirring is preferably 100 - 150 rpm, and in the examples, it can be 100 rpm, 125 rpm or 150 rpm. The time for the second-stage crystallization is preferably 0.5 - 1 h. By continuing the second-stage crystallization after carrying out the first-stage cooling crystallization by passing liquid nitrogen, the present invention can ensure that the crystallization process of the erythritol crystals is fully carried out.

[0040] After obtaining the second-stage crystallization material, the present invention sequentially subjects the second-stage crystallization material to standing, solid-liquid separation, and drying to obtain erythritol crystals. In the present invention, the temperature for standing is preferably ≤35°C, more preferably 20 - 30°C, and further preferably 25 - 30°C. The time for standing is preferably 0.5 - 1 h. Through the standing, the erythritol crystals can further grow and perfect in the present invention. The method for solid-liquid separation is preferably centrifugation or filtration. The rotation speed for centrifugation is preferably 3000 - 5000 rpm. The temperature for drying is preferably 100 - 105°C.

[0041] In the present invention, the average particle size of the erythritol crystals is preferably 40 - 55 μm.

[0042] The method for liquid nitrogen-assisted erythritol crystallization provided by the present invention can effectively shorten the cooling crystallization time and improve the crystallization production efficiency. At the same time, by controlling the feeding speed of liquid nitrogen and the stirring speed, the present invention can obtain erythritol crystals with uniform particle size, improving the quality and stability of the product. Moreover, the crystallization method provided by the present invention is relatively simple, easy to operate and control, reduces water consumption compared with the traditional cooling method, and saves production costs.

[0043] The present invention provides a device for using the method for liquid nitrogen-assisted erythritol crystallization according to the above technical solution, including a crystallization tank, and the crystallization tank is provided with a feed inlet, a discharge outlet, a liquid nitrogen inlet, and a stirring device interface;

[0044] A liquid nitrogen storage tank, and the liquid nitrogen storage tank is communicated with the liquid nitrogen inlet of the crystallization tank through a liquid nitrogen delivery pipeline.

[0045] In the present invention, the feed inlet is arranged at the top of the crystallization tank. The discharge outlet is arranged at the bottom of the crystallization tank. The liquid nitrogen inlet is arranged at the bottom of the crystallization tank. The stirring device interface is arranged at the top of the crystallization tank.

[0046] In the present invention, the device preferably further includes a stirring paddle, and the stirring paddle is preferably placed in the crystallization tank through the stirring device interface. The shape and size of the stirring paddle are designed according to the size of the crystallization tank and the properties of the solution to achieve the best stirring effect.

[0047] In the present invention, the crystallization tank preferably has a double-layer jacket structure, with the inner layer made of stainless steel and the outer layer made of heat-insulating material.

[0048] In the present invention, a flow meter and a valve are preferably provided on the liquid nitrogen delivery pipeline to control the flow rate of liquid nitrogen. The end of the liquid nitrogen delivery pipeline is provided with a spray head, and the spray head is located at the bottom inside the crystallization tank. The spray head is used to spray the liquid nitrogen into the crystallization tank. The spray head can evenly distribute the liquid nitrogen in the material to be crystallized, improving the cooling effect of the liquid nitrogen.

[0049] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0050] Example 1

[0051] This example provides a method for liquid nitrogen-assisted crystallization of erythritol, including the following steps:

[0052] The erythritol solution obtained through fermentation and purification is subjected to vacuum distillation to obtain an erythritol concentrate. The vacuum distillation is carried out in an evaporator, and the vacuum degree of the evaporator is controlled to be -0.090 MPa to -0.095 MPa, and the evaporation temperature is 80 to 85 °C. The mass concentration of the obtained erythritol concentrate is 600 g / L.

[0053] Take 100 L of erythritol concentrate with a mass concentration of 600 g / L (80 - 85 °C) and place it in the crystallization tank. Slowly open the liquid nitrogen inlet valve, and introduce liquid nitrogen from the bottom of the crystallization tank at a speed of 0.8 L / min. Start the stirring device, and set the stirring speed to 100 rpm. Under the conditions of introducing liquid nitrogen and stirring, cool the erythritol concentrate to 60 °C.

[0054] Then, under the conditions of continuously introducing liquid nitrogen (0.8 L / min) and stirring (100 rpm), add 2 kg of erythritol crystal seeds (30 - 60 mesh) to the erythritol concentrate at 60 °C. Start timing when adding the erythritol crystal seeds, and the liquid nitrogen introduction time is 3 h. During the process of introducing liquid nitrogen, closely observe the temperature and state of the solution to ensure the normal progress of the crystallization process.

[0055] After the liquid nitrogen introduction is completed, the temperature of the liquid material is 30 °C. Continue to stir the solution for 0.5 h, set the stirring speed to 100 rpm, then stop stirring, and let the solution stand at 30 °C for 0.5 h.

[0056] Finally, use a centrifuge with a rotation speed of 3000 rpm to separate the erythritol crystals from the mother liquor, and dry them at 105 °C to obtain erythritol crystal products. After detection, the purity of the obtained erythritol crystals reaches 99.5%, the yield is 98.6%, the particle size distribution is uniform, and the average particle size is 50 μm. Figure 1 The microscope photograph of the erythritol crystals prepared in Example 1 of the present invention, by Figure 1It can be seen that the particle size distribution of the erythritol crystals prepared in this example is uniform.

[0057] Example 2

[0058] This example provides a method for liquid nitrogen-assisted erythritol crystallization, which includes the following steps:

[0059] The erythritol solution obtained through fermentation and purification is subjected to vacuum distillation to obtain an erythritol concentrate. The vacuum distillation is carried out in an evaporator, and the vacuum degree of the evaporator is controlled at -0.090 Mpa to -0.095 Mpa, and the evaporation temperature is 80 to 85 °C. The mass concentration of the obtained erythritol concentrate is 650 g / L.

[0060] Take 150 L of erythritol concentrate with a mass concentration of 650 g / L (80 to 85 °C) and put it into a crystallization tank. Slowly open the liquid nitrogen inlet valve, and introduce liquid nitrogen from the bottom of the crystallization tank at a rate of 2 L / min. Start the stirring device, and set the stirring speed to 130 rpm. Cool the erythritol concentrate to 60 °C under the conditions of introducing liquid nitrogen and stirring.

[0061] Then, under the conditions of continuously introducing liquid nitrogen (2 L / min) and stirring (130 rpm), add 3 kg of erythritol crystal seeds (30 to 60 mesh) to the erythritol concentrate at 60 °C. Start timing when adding the erythritol crystal seeds, and the liquid nitrogen introduction time is 1.5 h. During the process of introducing liquid nitrogen, closely observe the temperature and state of the solution to ensure the normal progress of the crystallization process.

[0062] After the liquid nitrogen introduction is completed, the temperature of the liquid material is 30 °C. Continue to stir for 0.8 h, adjust the stirring speed to 130 rpm, then stop stirring, and let the solution stand at 30 °C for 0.8 h.

[0063] Finally, use a centrifuge with a rotational speed of 3000 rpm to separate the erythritol crystals from the mother liquor, and dry them at 105 °C to obtain erythritol crystal products. After testing, the purity of the obtained erythritol crystals reaches 99.3%, the yield is 98.4%, the average particle size is 45 μm, and the crystal quality is good.

[0064] Comparative Example 1

[0065] It is basically the same as the method of Example 1, except that: the step of adding "2 kg of erythritol crystal seeds" in the example is omitted.

[0066] In this comparative example, due to the lack of the step of adding crystal seeds, the crystal growth time of erythritol crystals is reduced due to the lack of crystal seed-assisted crystal precipitation, and it is shown that the size of the obtained erythritol crystal products is smaller, about 25 to 30 μm.

[0067] Comparative Example 2

[0068] It is basically the same as the method of Example 1, except that: the volume flow rate of liquid nitrogen is 0.5 L / min. In this comparative example, since the volume flow rate of nitrogen is less than 0.8 L / min, the cooling crystallization efficiency is reduced, resulting in an increase in production time.

[0069] Comparative Example 3

[0070] It is basically the same as the method of Example 1, except that: the volume flow rate of liquid nitrogen is 2.5 L / min. In this comparative example, since the volume flow rate of nitrogen is greater than 2 L / min, the crystal particle size is too small due to the too fast cooling rate, and at the same time, the production cost and energy consumption are increased.

[0071] Comparative Example 4

[0072] It is basically the same as the method of Example 2, except that: the stirring speed during the crystallization process is 60 rpm. In this comparative example, due to the too slow stirring speed, the temperature of the solution in the tank is uneven, and the size of the obtained erythritol crystal finished product is uneven.

[0073] Comparative Example 5

[0074] It is basically the same as the method of Example 2, except that: the stirring speed during the crystallization process is 180 rpm. In this comparative example, due to the too fast stirring speed, it affects crystal cultivation, and the size of the obtained erythritol crystal finished product is relatively small, about 30 - 35 μm.

[0075] As can be seen from the above examples, the method provided by the present invention adopts a segmented crystallization method. In the cooling crystallization process of the first stage, a stirring crystallization method assisted by liquid nitrogen is adopted. The low-temperature characteristic of liquid nitrogen can quickly reduce the temperature of the material to be crystallized, create a large supersaturation, thereby accelerating the crystallization speed, shortening the crystallization time, and improving the production efficiency. At the same time, the present invention stirs while introducing liquid nitrogen, so as to form a uniformly distributed temperature field in the material to be crystallized by liquid nitrogen, so that erythritol crystals can grow in a uniform temperature and concentration, and obtain crystals with uniform particle size, improving the quality and stability of the erythritol crystal product. Finally, the present invention performs crystal cultivation through the second-stage crystallization and standing, further improving the particle size uniformity and product stability of the erythritol crystal product. In addition, the method provided by the present invention is simple and safe to operate and easy to control. Liquid nitrogen is gaseous under normal temperature and pressure, and will not chemically react with water and erythritol, will not cause environmental pollution, and has high safety as long as it is operated according to the operating procedures during use. At the same time, compared with the traditional cooling water cooling, the method provided by the present invention saves water consumption and energy, and saves production costs.

[0076] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all embodiments. Other embodiments can also be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for liquid nitrogen-assisted erythritol crystallization, characterized in that: The following steps are involved: The erythritol solution obtained through fermentation and purification is subjected to reduced pressure distillation to obtain an erythritol concentrate, and the reduced pressure distillation is carried out in an evaporator, the vacuum degree of the evaporator is controlled to be -0.090MPa~-0.095MPa, the evaporation temperature is 80~85°C, and the mass concentration of the obtained erythritol concentrate is 600g / L; Take 100L of erythritol concentrate with a mass concentration of 600g / L, the temperature of the erythritol concentrate is 80-85℃, put it in a crystallization tank, slowly open the liquid nitrogen inlet valve, and introduce liquid nitrogen from the bottom of the crystallization tank at a rate of 0.8L / min. Turn on the stirring device, set the stirring speed to 100rpm, and cool the erythritol concentrate to 60℃ under the conditions of liquid nitrogen and stirring; Then, under the conditions of continuous introduction of liquid nitrogen at a rate of 0.8 L / min and a stirring speed of 100 rpm, 2 kg of erythritol seeds were added to the erythritol concentrate at 60°C. The erythritol seeds were 30-60 mesh. The timing started when the erythritol seeds were added. The introduction time of liquid nitrogen was 3 hours. During the introduction of liquid nitrogen, the temperature and state of the solution were closely observed to ensure that the crystallization process proceeded normally. After the liquid nitrogen was introduced, the temperature of the feed liquid was 30°C, and the solution was stirred for 0.5 h at a stirring speed of 100 rpm. Then the stirring was stopped and the solution was allowed to stand at 30°C for 0.5 h. Finally, the erythritol crystals were separated from the mother liquor using a centrifuge at a speed of 3000 rpm, and the erythritol crystal product was obtained by drying at 105°C. After testing, the purity of the obtained erythritol crystals reached 99.5%, the yield was 98.6%, the particle size distribution was uniform, and the average particle size was 50 μm.

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