Method for improving mannitol yield through alcohol precipitation

Abstract

The invention relates to a method for improving the yield of mannitol through alcohol precipitation, which comprises the following steps: concentrating to obtain a mannitol concentrated solution, cooling to a process temperature, adding methanol in a fed-batch manner, continuously cooling after adding methanol, then separating a crystallization solution, and improving the yield of mannitol through alcohol precipitation. According to the present invention, the solubility of mannitol in methanol is low, and the methanol is added to the mannitol solution to crystallize, such that the yield of the obtained mannitol is 15% or more higher than the yield of the mannitol crystallization in the aqueous solution; the method is simple and easy to implement, low in production cost and high in feasibility.

Description

Technical Field

[0001] This invention relates to a method for reducing the concentration of mannitol and increasing the yield of mannitol through alcohol precipitation, belonging to the field of biological solid-liquid separation technology. Background Technology

[0002] Mannitol, also known as mannitol, is a natural hexose sugar alcohol widely used in the food, medical, and chemical industries. Currently, mannitol is produced through extraction, chemical synthesis, enzymatic conversion, and microbial fermentation. Chemical synthesis was the primary method for mannitol production for a long time. Its principle involves mixing fructose and glucose, placing them in a high-temperature, high-pressure environment, and using Raney nickel as a catalyst to hydrogenate the mixture to obtain mannitol. However, due to the poor selectivity of the Raney nickel catalyst, this method produces a significant amount of sorbitol as a byproduct, resulting in low efficiency and difficulty in controlling production costs. Enzymatic conversion of mannitol mainly involves glucose isomerization, fructose conversion to mannitol, purification, and crystallization. Purification and crystallization aim to obtain high-purity mannitol.

[0003] Purification involves removing impurities and pigments from the obtained mannitol, while crystallization precipitates mannitol from the solution in crystalline form for easier separation and collection. Mannitol fermentation broth has a complex composition, mainly including mycelial proteins, sodium gluconate, divalent metals, and pigments.

[0004] The traditional method involves feeding the mannitol clarified solution obtained from decolorization and filtration into a vacuum crystallizer. Once a certain liquid level is reached, evaporation is carried out under specific process conditions at 60-75℃. When the mannitol reaches a certain concentration, an appropriate amount of seed crystals is added (crystallization vacuum degree 0.065-0.090 MPa). Evaporation continues, allowing the mannitol to slowly crystallize out (boiling vacuum degree 0.060-0.095 MPa). The temperature is then lowered to 50-70℃, and the resulting liquid is fed into a crystallizer for further crystallization to obtain mannitol. However, this method yields a low amount of mannitol and urgently needs improvement. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for improving mannitol yield through alcohol precipitation.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for improving mannitol yield through alcohol precipitation includes the following steps:

[0008] (1) Using mannitol concentrate as raw material, measure a certain volume of mannitol concentrate;

[0009] (2) Heat the mannitol concentrate to 55°C to completely dissolve the mannitol, then slowly cool it down to 35-36°C. Then, meter the methanol in the concentrate with 1-4 times the volume of mannitol using a peristaltic pump. The addition time should be controlled within 2.5 hours. When the solution reaches supersaturation, add seed crystals. During the addition process, maintain the temperature of the solution at 35°C-36°C and keep it warm for 30 minutes.

[0010] (3) After adding methanol, the temperature is lowered for crystallization at a rate of 3-6℃ / h. The resulting crystallized liquid is separated by vacuum filtration at 20℃ to obtain mannitol.

[0011] Preferably, in step (2), methanol with a volume of 3 times that of mannitol is added to the concentrate, and the seed crystal is pulverized mannitol powder.

[0012] This invention involves concentrating mannitol to obtain a concentrated solution, cooling it to the process temperature, adding methanol, and then continuing to cool the solution after the methanol addition. The crystallization liquid is then separated, and alcohol precipitation is used to improve the mannitol yield. Methanol is used to dissolve pigments and reduce the impurity carryover in mannitol. This invention utilizes the low solubility of mannitol in methanol, and crystallization is achieved by adding methanol to the mannitol solution.

[0013] The beneficial effects of this invention are:

[0014] (1) This invention utilizes the difference in solubility of mannitol in methanol and water, and by adding different proportions of methanol to the mannitol solution, comparing the crystallization of normal mannitol aqueous solution, to perform solid-liquid separation, and separating mannitol according to the change in crystallization yield, which can improve the primary crystallization yield of mannitol, and provides a better method for improving the crystallization yield of mannitol.

[0015] (2) In this invention, mannitol concentrate is obtained by concentration, and methanol is added after the temperature is lowered to the process temperature. After the methanol is added, the temperature is further lowered, and then the crystallization liquid is separated. The yield of mannitol is improved by alcohol precipitation. By controlling the cooling rate, mannitol with different particle sizes and crystal forms can be obtained according to the requirements.

[0016] (3) This invention utilizes the fact that mannitol has low solubility in methanol and that methanol and water are miscible. By adding methanol to the mannitol aqueous solution, the solubility of mannitol in the mixture is reduced, and crystallization is carried out. The mannitol yield is more than 15% higher than that of mannitol crystallization in aqueous solution. Considering both efficiency and production cost, three times the volume of methanol is added to the mannitol solution for crystallization.

[0017] (4) The method of the present invention is simple and easy to implement, with low production cost and strong feasibility. Attached Figure Description

[0018] Figure 1 Mannitol crystals obtained at different cooling rates. Detailed Implementation

[0019] The specific embodiments of the present invention will be further described in detail below with reference to examples.

[0020] Example 1 A method for improving mannitol yield through alcohol precipitation, comprising the following steps:

[0021] The raw material solution used is a concentrated mannitol solution obtained by rotary evaporation after removing anions and cations with anion exchange solution.

[0022] (1) Heat 300ml of mannitol concentrate from the initial temperature of 25℃ to 55℃ to completely dissolve the mannitol, and then slowly cool it down to 35℃; add 300ml of methanol to the mannitol concentrate by metering through a peristaltic pump, and control the addition time within 2.5h. When the solution reaches supersaturation, add 0.1g of 200-mesh seed crystals (crushed mannitol powder) to induce crystal formation. During the addition process, maintain the solution temperature at 35-36℃ and keep it warm for 30min.

[0023] (2) After adding methanol, the temperature is lowered to crystallize at a rate of 3-6℃ / h. The resulting crystallized liquid is then separated by vacuum filtration at 20℃ to obtain mannitol.

[0024] Table 1. Yield and yield of mannitol under different conditions

[0025]

[0026] The mannitol crystals of different sizes obtained at different cooling rates are shown in Table 1. Figure 1 Each image is magnified by 40. Figure 1 A. Large crystals, few broken crystals, easy to remove impurities, high purity; Figure 1 B. Inhomogeneous crystal grain size affects purity; Figure 1 C. Inhomogeneous crystal grain size affects purity; Figure 1 D. The crystals are relatively fine, easily trapping the mother liquor, resulting in a longer separation time. The bulk densities of the obtained mannitol crystals are A: 0.425 g / ml, B: 0.397 g / ml, C: 0.416 g / ml, and D: 0.432 g / ml, respectively.

[0027] Example 2: Comparison of mannitol yield under different methanol dosages

[0028] The mannitol concentrate, method, and steps used in the experiment were the same as in Example 1. The experiment was divided into an experimental group and a control group. The experimental group was divided into four groups, with different volumes of methanol added. Based on the volume of mannitol concentrate, 1 volume, 2 volumes, 3 volumes, and 4 volumes of methanol were added respectively according to the method in Example 1. The control group underwent normal crystallization and the temperature was reduced by 3°C per hour.

[0029] Both the experimental and control groups underwent solid-liquid separation at the same crystallization endpoint, and the mannitol yield and percentage were calculated. The results are shown in Table 2.

[0030] Table 2. Data on mannitol crystallization under different methanol dosages

[0031]

[0032] The above experiments show that, because mannitol has low solubility in methanol, adding an appropriate amount of methanol allows the method of this invention to precipitate more mannitol compared to normal crystallization, thus increasing the yield and production rate of mannitol.

[0033] When 1-4 times the volume of methanol is added to the mannitol solution, the mannitol yield is more than 15% higher than that obtained by normal crystallization of mannitol from aqueous solution. The mannitol yield increases with increasing methanol content, but stops increasing and even decreases after reaching 4 times the methanol content. Furthermore, as the methanol flow rate increases, other substances precipitate from the methanol phase, affecting product quality. Therefore, in actual production, it is preferable to add 3 times the volume of methanol to the mannitol solution for crystallization.

Claims

1. A process for improving the yield of mannitol by alcohol precipitation, characterized in that, The method comprises the following steps: (1) taking mannitol concentrate as raw material, and measuring a certain volume of mannitol concentrate; (2) heating the mannitol concentrate to 55 DEG C, so that the mannitol is completely dissolved, then slowly cooling to 35-36 DEG C, then adding 1-4 times of mannitol volume of methanol to the concentrate by a peristaltic pump, the adding time is controlled within 2.5 h, when reaching supersaturation, adding crystal seeds, maintaining the temperature of the solution at 35 DEG C-36 DEG C during the adding process, and keeping warm for 30 min; (3) after adding the methanol, cooling crystallization is carried out, the cooling speed is 3-6 DEG C / h, the obtained crystallization liquid is separated by vacuum filtration at 20 DEG C, and finally mannitol is obtained.

2. The method of claim 1, wherein, In step (2), 3 times of mannitol volume of methanol is added to the concentrate.

3. The method of claim 1, wherein, The crystal seeds are crushed mannitol powder.

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