JPS5843377B2 - Method for purifying malic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying malic acid by crystallization from an aqueous malic acid solution containing maleic acid and fumaric acid.

More specifically, the present invention aims to industrially obtain malic acid crystals of high purity and large grains.

Generally, malic acid is synthesized by subjecting maleic acid and/or fumaric acid to a water conservation reaction under high temperature and pressure.

This reaction is in equilibrium, with 45-60% malic acid (
All numbers and parts in the specification are by weight), 40-5
A tripartite equilibrium mixture of 0% fumaric acid and 2-3% maleic acid is obtained as a crude malic acid aqueous solution.

When using this synthetic malic acid as a food additive, it is necessary to minimize the amount of maleic acid that is harmful to the human body.

Further, although fumaric acid is not harmful to the human body, its solubility in water is extremely low, so if even a small amount is contained, it causes cloudiness in the malic acid aqueous solution, significantly impairing its commercial value.

As mentioned above, high purity malic acid is required for use as a food additive.

In order to obtain malic acid crystals from the crude malic acid aqueous solution, as described in Japanese Patent Publication No. 50-26526, fumaric acid is first crystallized and removed by filtration. A commonly used method is to crystallize and separate and extract the crystals by filtration, washing, dehydration, etc.

It is relatively easy to remove most of fumaric acid from a crude malic acid aqueous solution by crystallization using the difference in solubility of malic acid and fumaric acid in water.

On the other hand, both malic acid and maleic acid have high solubility in water, but if malic acid is present in large excess compared to maleic acid, it is not difficult to crystallize only malic acid from this mixed solution. .

However, when malic acid is crystallized from an aqueous solution, it is difficult to obtain large crystals because secondary nuclei (naturally occurring crystal seeds) are particularly easy to form compared to other substances.

If the crystals of malic acid produced at this time are fine, the purity of the filtrate will not be high when the crystals are filtered, and the filtrate will be difficult to clean, and the replacement efficiency will also be poor when washing out the attached filtrate.

In addition, since thin crystals easily dissolve during washing, the yield also decreases.

Conventionally, in order to obtain high-purity malic acid, complicated processes such as repeated recrystallization or the combined use of an ion exchange resin method and a long time were required, resulting in many industrial inconveniences.

In addition, fine crystals of dried malic acid tend to scatter during use, irritating the eyes, nose, skin, etc. of workers and making the work environment worse. There was no way.

As a result of intensive study on conditions suitable for the crystallization of malic acid, the present inventors have determined that the generation of secondary nuclei can be prevented by a combination of solution concentration, crystallization initiation temperature, amount of seed crystals added, and cooling rate. We found a method to obtain large malic acid crystals by growing only the seed crystals, and by one crystallization followed by a separation step, fumaric acid is less than 0.5% and maleic acid is less than 0.5%.
We have completed a new method for obtaining large malic acid crystals with a high purity of 0.5% or less.

The present invention provides an apple yeast solution obtained by removing most of fumaric acid by crystallization from a crude malic acid aqueous solution obtained by a hydration reaction of maleic acid and/or fumaric acid.
2) After concentrating and preparing a saturated aqueous solution containing 70 to 80% malic acid at 55 to 75 °C, 2) adding malic acid crystals corresponding to 0.5% or more of the amount of malic acid contained in the aqueous solution. , 3) This aqueous solution is cooled at a rate of 6°C or less per hour with gentle stirring to grow malic acid crystals, and 4) Malic acid crystals are then separated by filtration, washing, drying, and sieving. We are careful from the series of steps 1) to 4).

The case where the present invention is carried out industrially will be explained in detail below.

Malic acid is synthesized by heating a 30-60% maleic acid and/or fumaric acid aqueous solution at 150-200'C for several hours to carry out a water utilization reaction.

Next, the reaction solution is cooled in a reactor while evaporating water using its own heat, and further concentrated under reduced pressure to form an aqueous solution with a ratio of malic acid to water of 60 to 62 to 38 to 40 at 30°C.

During this time, by stirring and adding seed crystals of fumaric acid if necessary, most of the fumaric acid with low solubility is analyzed and the reaction liquid becomes a slurry.

When this slurry is centrifuged to remove fumaric acid crystals, a filtrate is obtained as an apple yeast liquid containing fumaric acid in a ratio of about 1 to malic acid and a large number of maleic acids.

The apple yeast liquid from which most of the fumaric acid has been removed in advance as described above undergoes the following steps 1) to 4).
Residual fumaric acid and maleic acid are removed and purified.

Step 1): The apple yeast liquid is concentrated under reduced pressure at 55-75°C to form a saturated aqueous solution containing 70-80% malic acid.

The temperature of this aqueous solution is 55-75°C, preferably 60-75°C.
It is important to adjust the temperature to 75°C.

If crystallization is performed outside this temperature or concentration range, step 3
), the generation of secondary nuclei increases, so the malic acid crystals obtained tend to have many fine particles and the purity decreases.

Furthermore, when malic acid and fumaric acid are dissolved in water, the proportion of fumaric acid increases as the temperature increases, so the aqueous solution is kept at a relatively high temperature of 55 to 75°C to prevent crystallization of malic acid. By starting, the proportion of fumaric acid in the crystal can be reduced.

Step 2): Malic acid crystals corresponding to 0.5% or more of the amount of malic acid contained in the aqueous solution are added as seed crystals to the aqueous solution prepared in Step 1).

The size of the seed crystals to be added is preferably 48 to 200 mesh (US standard sieve mesh size).The effect of the seed crystals is proportional to the total surface area, so the smaller the seed crystal grains, the smaller the amount. Usually, the larger the grains, the more you have to add.

If the amount added is below the above range, the generation of secondary nuclei will be significant in step 3), resulting in many fine malic acid crystals and a decrease in purity.

Step 3) While gently stirring the above malic acid aqueous solution, heat the solution at a rate of 6°C or less per hour, preferably 1 to 4°C.
It is cooled to ~30°C, and only the seed crystals added in step 2) are allowed to grow, and the malic acid contained in the aqueous solution is
60% is crystallized.

If the cooling rate is faster than the above range, the generation of secondary nuclei will become more intense, resulting in more fine malic acid crystals and lower purity.

During this time, fumaric acid also precipitates in a very small amount, but since no seed crystals are added, only thin crystals are formed.

The equipment used here keeps the supersaturation level of the solution stable and
In order to prevent new secondary nuclei of malic acid from being generated, a horizontal device is suitable that has a stirring blade that rotates slowly close to the entire wall of the container, or that has a cylindrical container itself that rotates slowly.

Step 4): The large malic acid crystals grown in step 3) are
Filtration, washing, dehydration, drying, and sieving are performed to separate from the aqueous solution to obtain highly pure malic acid crystals.

Filtration and dehydration are preferably carried out using a centrifuge.

The large malic acid crystals grown in step 3) do not form a cake during filtration and dehydration using a centrifugal separator, so they can be separated from the filtration very well, and the amount of liquid attached is less than 5%.

At this point, malic acid crystals contain less than 0.7% fumaric acid,
Contains less than 0.3% maleic acid.

Further, if necessary, the crystals are washed with 10 to 40% of the crystals in water at 30 DEG C. or lower or a high-purity malic acid aqueous solution.

As a result, mainly maleic acid is washed out, and malic acid crystals containing 0.7% or less of fumaric acid and 0.05% or less of maleic acid are obtained.

When the malic acid crystals are air-dried and sieved through a sieve with a mesh size of 48, malic acid crystals larger than 48 mesh can be obtained at a yield of 90 or more.

Malic acid crystals are grown from added seed crystals and are large in size, but fumaric acid crystals are small in size and can be removed by sieving.

The crystals obtained here with a size of 48 mesh or more are malic acid 99
, 5%, fumaric acid 0.5% or less, maleic acid 0.05%
It is a high purity malic acid crystal with the following composition.

Although the above describes the batch-type purification method of the present invention, the present invention can also be operated in a continuous mode, which will be briefly explained below.

In a continuous system, the malic acid synthesis and purification steps are operated simultaneously as a series of steps.

That is, the fumaric acid that was first crystallized and removed by filtration after the water utilization reaction was returned to the reactor as a raw material, and then the filtrate in step 4) after removing malic acid crystals from the malic acid volume solution that was the filtrate was Part is returned to the reactor, but most of it is returned to step 1.
) and mix with the malic acid solution again for use.

For example, the filtrate of step 4) after removing malic acid for the first time has an acid composition of 93-95% malic acid, 0.9-1.2% fumaric acid, and 4-5% maleic acid.

In the continuous method, about 10% of this filtrate is returned to the reactor and the remaining about 90% is returned to before step 1), so when it is recycled, the concentration of maleic acid in the malic acid solution gradually increases. Finally, steady state is reached at a maleic acid concentration of about 9-10%.

As described above, the present invention is also effective in purifying a malic acid solution having a high concentration of maleic acid.

As described above, the present invention prevents the generation of secondary nuclei by combining the crystallization initiation temperature of malic acid, solution concentration, amount of seed crystals, cooling rate, etc. under limited conditions. By growing only the crystals, large crystals of malic acid are crystallized, and subsequent separation of the crystals is made extremely easy and effective.

This became possible industrially for the first time through the combination of steps 1) to 4), which are the characteristics of the present invention, and it became possible to economically and easily obtain large crystals of malic acid with surprisingly high purity.

The malic acid crystals obtained here are not only suitable as food additives, but also help improve the working environment because they do not scatter during air transport or use, causing dust.

Examples, reference examples, and comparative examples are shown below.

Reference Example 4 A 5% maleic acid aqueous solution was heated at 180°C for 5 hours to perform a water conservation reaction, then cooled in a reactor while water was evaporated by the heat of the reaction solution itself, and then 60% malic acid was added under reduced pressure. After concentrating to a concentration and adjusting the temperature to 30°C, approximately 1
The fumaric acid was crystallized by stirring vigorously for an hour.

The crystalline fumaric acid was then removed by filtration using a centrifuge to obtain a malic acid solution having the following composition per 100 parts of the filtrate.

Malic acid 60.5 parts Fumaric acid 0.54 parts Maleic acid 1.6 parts Example 1 From 800 parts of the malic acid solution obtained in Reference Example, 160 parts of water was evaporated at 70°C under reduced pressure to bring the total acid concentration to 79. %, and the temperature of this aqueous solution was adjusted to 70°C.

[Step 1)] Next, 8.5 parts of 60 to 100 mesh malic acid crystals were added as seed crystals to this aqueous solution.

[Step 2] Next, this aqueous solution is heated to a temperature of 408°C at a rate of 1.5°C per hour while being gently stirred using the above-mentioned stirring device.
It was cooled to C over about 20 hours.

[Step 3] Next, the slurry solution was taken out, and the crystals and mother liquor were separated using a centrifuge at the same temperature.

At this point, the crystal content was 95.5%, and the amount of filtrate attached was 4.5%.

The crystals were further washed and dehydrated with 80 parts of water at 25° C. in a centrifuge.

Next, this was dried with air to obtain 219 parts of crystals.

This had the following composition per 100 parts of crystal.

Malic acid 99.46 parts Fumaric acid 0.52 parts Maleic acid 0.02 parts Finally, the crystals were sieved through a 48-mesh sieve.
After removing the fine crystals, 201 parts of large-grained crystals were obtained.

[Step 4] This product had the following composition per 100 parts of crystal.

Malic acid, fumaric acid, maleic acid Example 2 In the same manner as in Example 1, 60 to 100 meshes of malic acid crystal seeds 12 were added to the malic acid aqueous solution prepared by performing step 1).
．． Add 8 parts and heat to 3°C per hour with gentle stirring.
The mixture was cooled at a speed of about 11 hours to a temperature of 35°C.

Thereafter, the crystals were separated in the same manner as in Example 1, and finally 100
217 crystals of 48 or more meshes having the following composition per part:
I got the department.

Malic acid, fumaric acid, maleic acid Example 3 Add 100 to 150 mesh of malic acid crystal seeds to a malic acid aqueous solution prepared by performing step 1) in the same manner as in Example 1.
．． Add 7 parts and heat to 2°C per hour with gentle stirring.
The mixture was cooled at a speed of about 15 hours to a temperature of 35°C.

Thereafter, the crystals were separated in the same manner as in Example 1, and finally 100
212 crystals of 48 or more meshes having the following composition per part:
I got the department.

Malic acid 99.52 parts Fumaric acid 0.45 parts 99.53 parts 0.43 parts 0.04 parts 99.63 parts 0.35 parts 0.02 parts Maleic acid 0.03 parts Example 4 Obtained in Reference Example 129 parts of water was evaporated from 800 parts of malic acid solution at 59°C under reduced pressure to give a total acid concentration of 75%, and the temperature of this aqueous solution was adjusted to 59°C.

Next, 10.1 parts of malic acid crystal seeds having 48 to 100 meshes were added to this aqueous solution, and the mixture was cooled to a temperature of 30° C. over about 19 hours at a rate of 1.5° C. per hour while stirring gently.

Thereafter, the crystals were separated in the same manner as in Example 1, and finally 100
216 crystals of 48 or more meshes having the following composition per part:
I got the department.

Malic acid 99.50 parts Fumaric acid 0.47 parts Maleic acid 0.03 parts Example 5 The malic acid separation used here was for a continuous method and had the following acid composition.

Malic acid 89.9% Fumaric acid 0.9 t Maleic acid Section 9.2 The above malic acid mother liquor i, ooo part was concentrated at 70°C under reduced pressure to a total acid concentration of 80%, and this aqueous solution was heated to 70°C. After adjusting the temperature, 12.5 parts of 60-100 mesh malic acid crystal seeds were added.

Thereafter, in the same manner as in Example 1, steps 3) and 4) were performed to separate the crystals, and finally 48 having the following composition per 100 parts
278 parts of crystals larger than mesh were obtained.

Malic acid 99.56 parts Fumaric acid 0.40 parts Maleic acid 0.04 parts Comparative Example 1 Everything was the same as Example 1 except that in step 1) of Example 1, the total acid concentration was 69% and the temperature was adjusted to 50°C. The same operation was performed.

Comparative Example 2 All operations were performed in the same manner as in Example 1 except that the amount of malic acid crystal seeds added in step 2) of Example 1 was changed to 0.3%.

Comparative Example 3 The same operations as in Example 1 were performed except that the cooling rate was changed to 7°C in step 3) of Example 1.

Comparative Example 4 All steps were carried out except that step 3) of Example 1 was performed except that instead of cooling, 5.4 parts of water was evaporated per hour and concentrated and crystallized at 62° C. for about 15 hours under reduced pressure. The same operation as in Example 1 was performed.

In all of the above Comparative Examples 1 to 4, the generation of secondary nuclei was intense during crystallization, and many fine crystals were formed, resulting in cake formation during filtration using a centrifuge, and the amount of adhesion of the filtrate was 15 to 15.
It reached as much as 20%.

Therefore, the cleaning effect deteriorated and the purity decreased.

When the amount of washing liquid was increased to remove the adhering filtrate, fine crystals of malic acid were dissolved, resulting in poor yield.

Claims (1)

[Claims] 1. A method for purifying malic acid from a malic acid mother liquor after removing most of the fumaric acid by crystallization from a crude malic acid aqueous solution obtained by a hydration reaction of maleic acid and/or fumaric acid. 1) Concentrate the malic acid mother liquor to prepare a saturated malic acid aqueous solution containing 70 to 80% more malic acid by weight at a temperature of 55 to 75°C, and 2) Add 0.5 of the malic acid contained in the aqueous solution to this aqueous solution.
Add malic acid crystals equivalent to a weight of φ or more; 3) Cool the aqueous solution at a rate of 6°C or less per hour while stirring gently to precipitate the malic acid crystals; 4) Then separate the malic acid crystals. A method for purifying malic acid, comprising the steps 1) to 4) above.