Liquid nitrogen assisted erythritol crystallization method

Abstract

The invention belongs to the technical field of erythritol production, and particularly relates to a liquid nitrogen assisted erythritol crystallization method. The method comprises the following steps: under the conditions of liquid nitrogen assisted cooling and first stirring, mixing an erythritol concentrated solution and an erythritol seed crystal, and carrying out first-stage cooling crystallization to obtain a first-stage crystallized material; performing second-stage crystallization on the first-stage crystallization material under a second stirring condition to obtain a second-stage crystallization material; the second-stage crystallization material is subjected to standing, solid-liquid separation and drying in sequence, and erythritol crystals are obtained. According to the method provided by the invention, the erythritol crystal with uniform granularity can be obtained, and the quality and the stability of the erythritol crystal product are improved; the crystallization time is short, and the production efficiency is high.

Description

Technical Field

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

[0002] Erythritol, as an important low-calorie sweetener, is widely used in food, medicine and other fields.

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

[0004] The object of the present invention is to provide a method for liquid nitrogen-assisted erythritol crystallization. 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 the crystallization time is short and the production efficiency is high.

[0005] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for liquid nitrogen-assisted erythritol crystallization, comprising the following steps: Under the conditions of liquid nitrogen-assisted cooling and first stirring, the erythritol concentrate and the erythritol seed crystals are mixed to perform first stage cooling crystallization to obtain a first stage crystallization material; Under the second stirring condition, subjecting the first-stage crystallization material to a 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.

[0006] Preferably, the mass concentration of erythritol in the erythritol concentrate is 500-700 g / L.

[0007] Preferably, the mesh size of the erythritol seed crystals is 30-60 mesh; The ratio of the mass of the erythritol seed crystals to the volume of the erythritol concentrated solution is (10-30) g:1L.

[0008] Preferably, the temperature at which the erythritol concentrate and the erythritol seed crystals are mixed is 60-70°C.

[0009] Preferably, the liquid nitrogen is introduced from the bottom of the erythritol concentrated solution, and the volume flow rate of the liquid nitrogen is 0.8-2 L / min.

[0010] Preferably, the first stirring speed is 100-150 rpm; The timing starts when the erythritol concentrate and the erythritol seed crystals are mixed, and the time for the first stage of cooling and crystallization is 1 to 3 hours.

[0011] Preferably, the second stirring speed is 100-150 rpm; the temperature of the second stage crystallization is ≤35° C., and the time is 0.5-1 h.

[0012] Preferably, the standing temperature is ≤35°C and the standing time is 0.5-1h.

[0013] Preferably, the average particle size of the erythritol crystals is 40-55 μm.

[0014] Preferably, the erythritol concentrate is obtained by distilling an erythritol solution under reduced pressure; the pressure of the reduced pressure distillation is -0.09Mpa to -0.095Mpa, and the temperature is 80 to 85°C.

[0015] The present invention provides a method for crystallizing erythritol assisted by liquid nitrogen, comprising the following steps: under the conditions of liquid nitrogen assisted cooling and first stirring, mixing erythritol concentrate and erythritol seed crystals for first stage cooling crystallization to obtain first stage crystallization material; under the conditions of second stirring, the first stage crystallization material is subjected to second stage crystallization to obtain 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 adopts a segmented crystallization method, and in the first stage cooling crystallization process, a liquid nitrogen assisted stirring crystallization method is adopted. The low temperature characteristics of liquid nitrogen can quickly reduce the temperature of the material to be crystallized, create a larger supersaturation, thereby accelerating the crystallization speed, shortening the crystallization time, and improving production efficiency. At the same time, the present invention stirs while passing liquid nitrogen, so that a uniformly distributed temperature field is formed in the material to be crystallized by liquid nitrogen, so that erythritol crystals can be grown in a uniform temperature and concentration, and crystals with uniform particle size are obtained, thereby improving the quality and stability of erythritol crystal products. Finally, the present invention further improves the particle size uniformity and product stability of the erythritol crystal product by performing crystal growth through the second stage crystallization and standing.

[0016] In addition, the method provided by the present invention is simple, safe and easy to control. Liquid nitrogen is gaseous at room temperature and pressure, and does not react chemically with water and erythritol, does not pollute the environment, and has high safety as long as it is operated in accordance with the operating procedures during use. At the same time, compared with traditional cooling water cooling, the method provided by the present invention saves water resources and energy, and saves production costs.

[0017] Furthermore, in the present invention, the volume flow rate of the liquid nitrogen is 0.8-2 L / min; the speed of the first stirring is 100-150 rpm. The present invention can form a more uniform crystallization temperature field by controlling the liquid nitrogen introduction speed and the speed of the first stirring in the first stage of cooling crystallization, thereby obtaining an erythritol crystal product with a more uniform particle size distribution, and the stability between batches of crystal products is higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a microscope photograph of the erythritol crystals prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0019] The present invention provides a method for liquid nitrogen-assisted erythritol crystallization, comprising the following steps: Under the conditions of liquid nitrogen-assisted cooling and first stirring, the erythritol concentrate and the erythritol seed crystals are mixed to perform first stage cooling crystallization to obtain a first stage crystallization material; Under the second stirring condition, subjecting the first-stage crystallization material to a 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.

[0020] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0021] The present invention mixes erythritol concentrated liquid and erythritol seed crystals under the conditions of liquid nitrogen-assisted cooling and first stirring to perform first-stage cooling crystallization to obtain first-stage crystallization material.

[0022] In the present invention, the mass concentration of erythritol in the erythritol concentrate is preferably 500-700 g / L.

[0023] 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 -0.09Mpa~-0.095Mpa, and the temperature is preferably 80~85°C. The present invention preferably adopts a vacuum distillation method, and the pressure and temperature of the vacuum distillation are controlled at the same time, which can effectively concentrate the erythritol solution while reducing the decomposition and deterioration of erythritol under excessively high temperature conditions. In the present invention, the initial temperature of the erythritol concentrate obtained by the vacuum distillation is preferably 80~85°C.

[0024] The present invention preferably cools the erythritol concentrate from the initial temperature to the temperature at which the erythritol concentrate and the erythritol seed crystals are mixed, and then mixes with the erythritol seed crystals. The temperature at which the erythritol concentrate and the erythritol seed crystals are mixed is preferably 60-70°C. The temperature (60-70°C) at which the erythritol concentrate and the erythritol seed crystals are mixed is the temperature at which the erythritol concentrate begins to crystallize. The erythritol concentrate is preferably cooled from the initial temperature (i.e., 80-85°C) to the temperature (60-70°C) at the time of mixing, preferably under the conditions of passing 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 0.8-2L / min, which can be 0.8L / min, 1L / min, 1.2L / min, 1.5L / min, 1.8L / min or 2L / min in the embodiment. The stirring speed of the cooling is preferably 100-150 rpm, and in the embodiment, it can be 100 rpm, 125 rpm or 150 rpm.

[0025] In the present invention, the mesh number of the erythritol seed crystals is 30-60 mesh, that is, the erythritol seed crystals are preferably 30 mesh undersize and 60 mesh oversize. In the present invention, the erythritol seed crystals are preferably erythritol. The ratio of the mass of the erythritol seed crystals to the volume of the erythritol concentrate is preferably (10-30) g:1L, and in the embodiments, it can be 10g:1L, 15g:1L, 20g:1L, 25g:1L or 30:1L.

[0026] In the present invention, the temperature when the erythritol concentrate and the erythritol seed crystals are mixed is preferably 60-70°C. The mixing is preferably adding the erythritol seed crystals to the erythritol concentrated solution. During the mixing, liquid nitrogen is continuously introduced into the erythritol concentrated solution, and the volume flow rate of the liquid nitrogen is maintained at the same volume flow rate when the erythritol concentrated solution is cooled. The present invention adds erythritol seed crystals to the erythritol concentrated solution, and the addition of erythritol seed crystals and the reasonable control of the added quality of the seed crystals help to induce the growth of erythritol crystals, improve the efficiency of crystallization and the uniformity of the particle size of the erythritol crystal product.

[0027] In the present invention, the liquid nitrogen assisted cooling is preferably cooling 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 0.8~2L / min, and can be 0.8L / min, 1L / min, 1.2L / min, 1.5L / min, 1.8L / min or 2L / min in the embodiment. The speed of the first stirring is preferably 100~150rpm, and can be 100rpm, 125rpm or 150rpm in the embodiment. The timing starts when the erythritol concentrate and the erythritol seed crystal are mixed. The time of the first stage cooling crystallization is preferably 1~3h, and can be 1h, 1.5h, 2h, 2.5h or 3h in the embodiment. After the first stage cooling crystallization is completed, the liquid nitrogen is stopped. The present invention can ensure the uniformity of the temperature in the solution in space by performing the first stirring while passing the liquid nitrogen, and controlling the volume flow rate of the liquid nitrogen and the speed of the first stirring, thereby promoting the uniform growth of the crystal.

[0028] In an embodiment of the present invention, the first stage cooling crystallization process preferably includes: passing liquid nitrogen into the erythritol concentrated solution with a temperature preferably of 82-85°C, adding erythritol seed crystals when the temperature is cooled to 60-70°C under the first stirring condition, and then continuing to perform the first stage cooling crystallization under the conditions of passing liquid nitrogen and the first stirring condition to obtain the first stage crystallization material.

[0029] In the present invention, the temperature of the first-stage crystallization material obtained by the first-stage temperature reduction crystallization is preferably ≤35°C, more preferably 20-30°C, and further preferably 25-30°C.

[0030] After obtaining the first stage crystallization material, the present invention performs a second stage crystallization on the first stage crystallization material under the condition of a second stirring to obtain a 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 speed of the second stirring is preferably 100~150rpm, and in the embodiment, it can be 100rpm, 125rpm or 150rpm, and the time of the second stage crystallization is preferably 0.5~1h. The present invention can ensure that the crystallization process of the erythritol crystals is fully carried out by continuing the second stage crystallization after the first stage cooling crystallization is carried out by introducing liquid nitrogen.

[0031] After obtaining the second stage crystallization material, the present invention sequentially performs standing, solid-liquid separation and drying on the second stage crystallization material to obtain erythritol crystals. In the present invention, the standing temperature is preferably ≤35°C, more preferably 20-30°C, and further preferably 25-30°C. The standing time is preferably 0.5-1h. The present invention can further grow and improve erythritol crystals through the standing. The solid-liquid separation method is preferably centrifugation or filtration. The centrifugal speed is preferably 3000-5000rpm. The drying temperature is preferably 100-105°C.

[0032] In the present invention, the average particle size of the erythritol crystals is preferably 40-55 μm.

[0033] The liquid nitrogen assisted erythritol crystallization method provided by the present invention can effectively shorten the cooling crystallization time and improve the crystallization production efficiency. At the same time, the present invention can obtain erythritol crystals with uniform particle size by controlling the liquid nitrogen introduction speed and stirring speed, thereby 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 traditional cooling methods, and saves production costs.

[0034] The present invention provides a device used in the method for liquid nitrogen-assisted erythritol crystallization described in the above technical solution, comprising a crystallization tank, wherein the crystallization tank is provided with a feed inlet, a discharge port, a liquid nitrogen inlet and a stirring device interface; A liquid nitrogen storage tank is connected to the liquid nitrogen inlet of the crystallization tank through a liquid nitrogen delivery pipeline.

[0035] In the present invention, the feed port is arranged at the top of the crystallization tank. The discharge port 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.

[0036] In the present invention, the device preferably further comprises 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.

[0037] In the present invention, the crystallization tank preferably has a double-layer jacket structure, with the inner layer being made of stainless steel and the outer layer being made of insulation material.

[0038] In the present invention, the liquid nitrogen delivery pipeline is preferably provided with a flow meter and a valve for controlling the flow rate of the liquid nitrogen. A nozzle is provided at the end of the liquid nitrogen delivery pipeline, and the nozzle is located at the bottom of the crystallization tank. The nozzle is used to spray the liquid nitrogen into the crystallization tank. The nozzle can evenly distribute the liquid nitrogen in the material to be crystallized, thereby improving the cooling effect of the liquid nitrogen.

[0039] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0040] Example 1 This embodiment provides a method for liquid nitrogen-assisted erythritol crystallization, comprising the following steps: The erythritol solution obtained after fermentation and purification is subjected to reduced pressure distillation to obtain an erythritol concentrate. 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℃, and the mass concentration of the obtained erythritol concentrate is 600g / L.

[0041] Take 100L of erythritol concentrate (80-85℃) with a mass concentration of 600g / L and place it in a crystallizer. Slowly open the liquid nitrogen inlet valve, and introduce liquid nitrogen from the bottom of the crystallizer (at a rate of 0.8L / min). Turn on the stirring device and set the stirring speed to 100rpm. Cool the erythritol concentrate to 60℃ under the conditions of liquid nitrogen and stirring.

[0042] Then, under the conditions of continuous liquid nitrogen (0.8L / min) and stirring (100rpm), 2kg of erythritol seed crystals (30-60 mesh) were added to the erythritol concentrate at 60°C. The timing started when the erythritol seed crystals were added, and the liquid nitrogen introduction time was 3h. During the process of introducing liquid nitrogen, the temperature and state of the solution were closely observed to ensure that the crystallization process proceeded normally.

[0043] After the liquid nitrogen was introduced, the temperature of the feed liquid was 30°C, and the solution was stirred for 0.5 h with the stirring speed set to 100 rpm. Then the stirring was stopped and the solution was allowed to stand at 30°C for 0.5 h.

[0044] Finally, the erythritol crystals were separated from the mother liquor using a centrifuge at a speed of 3000 rpm and dried at 105°C to obtain the erythritol crystal product. 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. Figure 1 This is a microscope photo of erythritol crystals prepared in Example 1 of the present invention. Figure 1 It can be seen that the particle size distribution of the erythritol crystals prepared in this example is uniform.

[0045] Example 2 This embodiment provides a method for liquid nitrogen-assisted erythritol crystallization, comprising the following steps: The erythritol solution obtained after fermentation and purification is subjected to reduced pressure distillation to obtain an erythritol concentrate. 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 650g / L.

[0046] Take 150L of erythritol concentrate (80-85℃) with a mass concentration of 650g / L and put it into the crystallizer. Slowly open the liquid nitrogen inlet valve, and introduce liquid nitrogen from the bottom of the crystallizer (at a rate of 2L / min). Turn on the stirring device and set the stirring speed to 130rpm. Cool the erythritol concentrate to 60℃ under the conditions of liquid nitrogen and stirring.

[0047] Then, under the conditions of continuous liquid nitrogen (2L / min) and stirring (130rpm), 3kg of erythritol seed crystals (30-60 mesh) were added to the erythritol concentrate at 60°C. The timing started when the erythritol seed crystals were added, and the liquid nitrogen introduction time was 1.5h. During the process of introducing liquid nitrogen, the temperature and state of the solution were closely observed to ensure that the crystallization process proceeded normally.

[0048] After the liquid nitrogen was introduced, the liquid temperature was 30°C, and stirring was continued for 0.8 h. The stirring speed was adjusted to 130 rpm, and then stirring was stopped, and the solution was allowed to stand at 30°C for 0.8 h.

[0049] Finally, the erythritol crystals were separated from the mother liquor using a centrifuge at a speed of 3000 rpm and dried at 105°C to obtain the erythritol crystal product. After testing, the purity of the obtained erythritol crystals reached 99.3%, the yield was 98.4%, the average particle size was 45 μm, and the crystal quality was good.

[0050] Comparative Example 1 The method is basically the same as that in Example 1, except that the step of adding "2 kg of erythritol seed crystals" in the example is omitted.

[0051] In this comparative example, due to the lack of the step of adding seed crystals, the lack of seed crystals to assist crystallization leads to a reduction in the crystal growth time of erythritol crystals, showing that the finished erythritol crystals are smaller in size, about 25-30 μm.

[0052] Comparative Example 2 The method is basically the same as that in 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.

[0053] Comparative Example 3 The method is basically the same as that 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 size is small due to the excessively fast cooling speed, and the production cost and energy consumption are increased.

[0054] Comparative Example 4 The method is basically the same as that of Example 2, except that the stirring speed during the crystallization process is 60 rpm. In this comparative example, the stirring speed is too slow, resulting in uneven temperature of the solution in the tank, and the size of the obtained erythritol crystal product is uneven.

[0055] Comparative Example 5 The method is basically the same as that of Example 2, except that the stirring speed during the crystallization process is 180 rpm. In this comparative example, due to the excessive stirring speed affecting the crystal growth, the size of the obtained erythritol crystals is relatively small, about 30-35 μm.

[0056] It can be seen from the above embodiments that the method provided by the present invention adopts a segmented crystallization method. In the first stage of the cooling crystallization process, a liquid nitrogen-assisted stirring crystallization method is adopted. The low temperature characteristics of liquid nitrogen can quickly reduce the temperature of the material to be crystallized, create a larger supersaturation, thereby accelerating the crystallization speed, shortening the crystallization time, and improving production efficiency. At the same time, the present invention is stirred while passing liquid nitrogen, so that a uniformly distributed temperature field is formed in the material to be crystallized by liquid nitrogen, so that erythritol crystals can be grown in a uniform temperature and concentration, and crystals with uniform particle size are obtained, thereby improving the quality and stability of erythritol crystal products. Finally, the present invention further improves the particle size uniformity and product stability of erythritol crystal products by crystallization and standing in the second stage. In addition, the method provided by the present invention is simple and safe to operate and easy to control. Liquid nitrogen is gaseous at normal temperature and pressure, and will not react chemically with water and erythritol, will not cause pollution to the environment, and has high safety as long as it is operated according to the operating procedures during use. At the same time, compared with traditional cooling water cooling, the method provided by the present invention saves water consumption and energy, and saves production costs.

[0057] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, 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: Under the conditions of liquid nitrogen-assisted cooling and first stirring, the erythritol concentrate and the erythritol seed crystals are mixed to perform first stage cooling crystallization to obtain a first stage crystallization material; Under the second stirring condition, subjecting the first-stage crystallization material to a 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.

2. The method for liquid nitrogen-assisted erythritol crystallization according to claim 1, characterized in that: The mass concentration of erythritol in the erythritol concentrated solution is 500-700 g / L.

3. The method for liquid nitrogen-assisted erythritol crystallization according to claim 1, characterized in that: The mesh number of the erythritol seed crystals is 30-60 mesh; The ratio of the mass of the erythritol seed crystals to the volume of the erythritol concentrated solution is (10-30) g:1L.

4. The method for liquid nitrogen-assisted erythritol crystallization according to claim 1, characterized in that: The temperature when the erythritol concentrate and the erythritol seed crystals are mixed is 60-70°C.

5. The method for liquid nitrogen-assisted erythritol crystallization according to claim 1, characterized in that: The liquid nitrogen is introduced from the bottom of the erythritol concentrated solution, and the volume flow rate of the liquid nitrogen is 0.8-2 L / min.

6. The method for liquid nitrogen-assisted erythritol crystallization according to claim 1 or 5, characterized in that: The first stirring speed is 100-150 rpm; The timing starts when the erythritol concentrate and the erythritol seed crystals are mixed, and the time for the first stage of cooling and crystallization is 1 to 3 hours.

7. The method for liquid nitrogen-assisted erythritol crystallization according to claim 1, characterized in that: The second stirring speed is 100-150 rpm; the temperature of the second stage crystallization is ≤35°C, and the time is 0.5-1h.

8. The method for liquid nitrogen-assisted erythritol crystallization according to claim 1, characterized in that: The standing temperature is ≤35°C and the standing time is 0.5-1h.

9. The method for liquid nitrogen-assisted erythritol crystallization according to claim 1, characterized in that: The average particle size of the erythritol crystals is 40-55 μm.

10. The method for liquid nitrogen-assisted erythritol crystallization according to claim 1, characterized in that: The erythritol concentrated solution is obtained by distilling the erythritol solution under reduced pressure; the pressure of the distillation under reduced pressure is -0.09Mpa to -0.095Mpa, and the temperature is 80 to 85°C.

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