PROCESS OF RECOVERING ALKALI METAL SULFATE

Abstract

The present invention relates to a process of recovering an alkali metal sulfate, comprising: forming an organic acid fermentation liquid containing an alkali metal salt of organic acid; and adding sulfuric acid to the organic acid fermentation liquid to form and recover an alkali metal sulfate, wherein the alkali metal sulfate has a radioactivity concentration index of 1 or less, and to an alkali metal sulfate crystal comprising a predetermined peak in an X-ray diffraction spectrum (XRD) and having a radioactivity concentration index of 1 or less.

Claims

1. A process of recovering an alkali metal sulfate, comprising: forming an organic acid fermentation liquid containing an alkali metal salt of an organic acid; and adding sulfuric acid to the organic acid fermentation liquid to form and recover an alkali metal sulfate, wherein the alkali metal sulfate has a radioactivity concentration index of 0.5 or less.

2. The process of recovering an alkali metal sulfate according to claim 1, wherein: the radioactivity concentration index is obtained from radioactivity concentrations which are measured with respect to potassium-40 for 10,000 seconds, measured with respect to radium-226 for 10,000 seconds, measured with respect to uranium-238 for 10,000 seconds, and measured with respect to thorium-232 for 10,000 seconds, using a high-purity germanium gamma-ray nuclide detector.

3. The process of recovering an alkali metal sulfate according to claim 1, wherein: the alkali metal sulfate includes calcium sulfate or calcium sulfate hydrate.

4. The process of recovering an alkali metal sulfate according to claim 1, wherein: the alkali metal sulfate contains 70 wt. % or more of gypsum dihydrate based on 100 wt. % of the alkali metal sulfate, and the alkali metal sulfate contains 25 wt. % or less of gypsum hemihydrate based on 100 wt. % of the alkali metal sulfate.

5. The process of recovering an alkali metal sulfate according to claim 1, wherein: the alkali metal sulfate is recovered as an alkali metal sulfate crystal having an X-ray diffraction spectrum (XRD) having 5 to 10 peaks at a diffraction angle (20.2) of 12 to 32.

6. The process of recovering an alkali metal sulfate according to claim 1, wherein: the alkali metal sulfate is recovered as a crystal of the alkali metal sulfate having a particle size of 0.5 m to 100 m.

7. The process of recovering an alkali metal sulfate according to claim 1, wherein: the adding sulfuric acid to the organic acid fermentation liquid to form and recover an alkali metal sulfate further comprises, forming and separating an alkali metal salt crystal of the organic acid in the organic acid fermentation liquid in the presence of the alkali metal salt; preparing a solution containing the alkali metal salt crystal of the organic acid; and adding the sulfuric acid to the solution containing the alkali metal salt crystal of the organic acid to form and recover the alkali metal sulfate.

8. The process of recovering an alkali metal sulfate according to claim 1, wherein: the organic acid fermentation liquid or the solution containing the alkali metal salt crystal of the organic acid contains 10 g/L to 600 g/L of the an alkali metal salt of the organic acid or the organic acid.

9. The process of recovering an alkali metal sulfate according to claim 1, wherein: in the adding of sulfuric acid to the organic acid fermentation liquid, the equivalent of the sulfuric acid added is 0.5 to 2.0 times the total equivalent of the alkali metal salt of the organic acid or the organic acid contained in the organic acid fermentation liquid.

10. The process of recovering an alkali metal sulfate according to claim 1, further comprising: recovering an organic acid formed when adding the sulfuric acid to the organic acid fermentation liquid containing the alkali metal salt of organic acid.

11. The process of recovering an alkali metal sulfate according to claim 1, wherein: the forming of an organic acid fermentation liquid containing an alkali metal salt of an organic acid comprises, adding an alkali metal or the alkali metal salt while fermenting a bacterium strain having an organic acid-producing ability in the presence of a carbon source.

12. An alkali metal sulfate crystal having an X-ray diffraction spectrum (XRD) having 5 to 10 peaks at a diffraction angle (20.2) of 12 to 32, wherein the alkali metal sulfate has a radioactivity concentration index of 0.5 or less.

13. The alkali metal sulfate crystal according to claim 12, wherein: the alkali metal sulfate includes calcium sulfate or calcium sulfate hydrate.

14. The alkali metal sulfate crystal according to claim 12, wherein: the alkali metal sulfate contains 70 wt. % or more of gypsum dihydrate based on 100 wt. % of the alkali metal sulfate crystal, and the alkali metal sulfate contains 25 wt. % or less of gypsum hemihydrate based on 100 wt. % of the alkali metal sulfate crystal.

15. The alkali metal sulfate crystal according to claim 12, wherein: the alkali metal sulfate crystal has a particle size of 0.5 m to 100 m.

16. The alkali metal sulfate crystal according to claim 12, wherein: the alkali metal sulfate crystal has a particle size distribution D.sub.50 of 0.5 m to 50 m.

17. The process of recovering an alkali metal sulfate according to claim 5, wherein: the alkali metal sulfate is recovered as a crystal of the alkali metal sulfate having a particle size of 0.5 m to 100 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0169] FIG. 1 shows the results of X-ray diffraction analysis of alkali metal sulfate crystals recovered in Example 1.

[0170] FIG. 2 shows a scanning electron microscope (SEM) cross-sectional photograph of alkali metal sulfate crystals recovered in Example 1.

[0171] Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are for illustrative purposes only, and are not intended to limit the scope of the present invention.

Preparation Example 1: Preparation of Bacterium Strain for Producing 3-Hydroxypropionic Acid

[0172] Recombinant vectors into which genes encoding glycerol dehydratase and aldehyde dehydrogenase, which are known to produce 3-hydroxypropionic acid (3HP) using glycerol as a substrate, were introduced were manufactured. The prepared recombinant vector was introduced into E.coli W3110 strain to prepare a 3-hydroxypropionic acid-producing strain.

[0173] More specifically, a BtuR gene encoding adenosyltransferase was cloned into plasmid pCDF containing a gene (dhaB) encoding glycerol dehydratase, a gene (aldH) encoding aldehyde dehydrogenase and a gene (gdrAB) encoding glycerol dehydratase reactivase. The resulting pCDF_J23101_dhaB_gdrAB_J23100_aldH_btuR vector was introduced into strain W3110 (KCCM 40219) by an electroporation method using an electroporation device (Bio-Rad, Gene Pulser Xcell) to prepare 3-hydroxypropionic acid-producing strain. The process of preparing the 3-hydroxypropionic acid-producing strain of Preparation Example 1 and the vectors, primers, and enzymes used were carried out with reference to Example 1 of Korean Unexamined Patent Publication No. 10-2020-0051375, which is incorporated herein by reference.

Preparation Example 2: Preparation of Ca(3HP).SUB.2 .Fermentation Liquid

[0174] The 3-hydroxypropionic acid-producing strain prepared in Preparation Example 1 was fermented and cultured at 35 C. in a 5 L fermenter using unpurified glycerol as a carbon source to produce 3-hydroxypropionic acid. In order to prevent the lowering of pH due to the production of 3-hydroxypropionic acid, calcium hydroxide (Ca(OH).sub.2), which is an alkali metal salt, was added thereto to maintain the pH to be neutral during the fermentation.

[0175] After fermentation culture, cells were removed by centrifugation (4000 rpm, 10 minutes, 4 C.), and primary fermentation liquid purification (primary purification) was performed using activated carbon. Specifically, activated carbon was added to the fermentation liquid from which bacterial cells were removed by centrifugation, the mixture was well mixed, and then centrifuged again to separate the activated carbon. Then, the fermentation liquid from which the activated carbon was separated was filtered with a vacuum pump through a 0.7 m filter paper to purify the 3-hydroxypropionic acid fermentation liquid. The concentration of 3-hydroxypropionic acid in the fermentation liquid after completion of the primary purification was a level of 75 g/L.

Preparation Example 3: Preparation of Ca(3HP).SUB.2 .Crystal

[0176] The 3-hydroxypropionic acid-producing strain prepared in Preparation Example 1 was fermented and cultured at 35 C. in a 5L fermenter using unpurified glycerol as a carbon source to produce 3-hydroxypropionic acid. In order to prevent the lowering of pH due to the production of 3-hydroxypropionic acid, calcium hydroxide (Ca(OH).sub.2), which is an alkali metal salt, was added thereto to maintain the pH to be neutral during the fermentation.

[0177] After fermentation culture, cells were removed by centrifugation (4000 rpm, 10 minutes, 4 C.), and primary fermentation liquid purification (primary purification) was performed using activated carbon. Specifically, activated carbon was added to the fermentation liquid from which bacterial cells were removed by centrifugation, the mixture was well mixed, and then centrifuged again to separate the activated carbon. Then, the fermentation liquid from which the activated carbon was separated was filtered with a vacuum pump through a 0.7 m filter paper to purify the 3-hydroxypropionic acid fermentation liquid.

[0178] The concentration of 3-hydroxypropionic acid in the fermentation liquid after completion of the primary purification was a level of 50 to 100 g/L, and the fermentation liquid was concentrated to a concentration of 600 g/L using a rotary evaporator (50 C., 50 mbar) to prepare a concentrate, and ethanol was added in an amount of two times the volume of the concentrate, and stirred (300 rpm) at room temperature to produce Ca(3HP).sub.2 crystals. At this time, the concentration of the alkali metal salt in the concentrate was 493.3 g/L (based on Ca(OH).sub.2). The resulting crystals were washed three times with ethanol (EtOH) and dried in an oven at 50 C. to finally recover the crystals.

Example 1

[0179] 3.5 L of the fermentation liquid obtained in Preparation Example 2 was prepared (contains about 75 g/L of 3-hydroxypropionic acid, and about 91 g/L of 3-hydroxypropionic acid calcium salt), and heated up to a temperature of 60 C. Then, 294 mL of 5M sulfuric acid solution was added to the heated fermentation liquid at a uniform rate for 5 minutes, and further stirred for 30 minutes to form a slurry containing CaSO.sub.4 precipitate and 3-hydroxypropionic acid.

[0180] Filtration was performed using a filtration flask and a vacuum pump in order to separate the CaSO.sub.4 precipitate. The CaSO.sub.4 precipitate was dried in an oven at a temperature of 40 C. for 20 hours. Finally, the dried CaSO.sub.4 precipitate was obtained, and a filtrate containing 3-hydroxypropionic acid was obtained.

Example 2

[0181] 0.5 L of the fermentation liquid obtained in Preparation Example 2 was prepared (containing about 79 g/L of 3-hydroxypropionic acid, and about 96.8 g/L of 3-hydroxypropionic acid calcium salt), and heated up to a temperature of 60 C. Then, 46 mL of 5M sulfuric acid solution was added to the fermentation liquid at a uniform rate for 5 minutes, and further stirred for 30 minutes to form a slurry containing CaSO.sub.4 precipitate and 3-hydroxypropionic acid.

[0182] Filtration was performed using a filtration flask and a vacuum pump in order to separate the CaSO.sub.4 precipitate. The CaSO.sub.4 precipitate was dried in an oven at a temperature of 40 C. for 20 hours. Finally, the dried CaSO.sub.4 precipitate was obtained, and a filtrate containing 3-hydroxypropionic acid was obtained.

Example 3

[0183] An aqueous solution containing 600 g/L of Ca(3HP).sub.2 crystal recovered in Preparation Example 3 was prepared, and stirred at a temperature of 25 C. and 350 rpm for 10 minutes. 37 ml of 5M sulfuric acid solution was added to 77 ml of the aqueous solution at a uniform rate for 5 minutes, and further stirred for 30 minutes to form a slurry containing CaSO.sub.4 precipitate and 3-hydroxypropionic acid.

[0184] Filtration was performed using a filtration flask and a vacuum pump in order to separate the CaSO.sub.4 precipitate. Then, a filtrate (A) before washing was obtained in a filtering flask, and the filtered CaSO.sub.4 precipitate was washed with 30 ml of distilled water, and then filtered to obtain a filtrate (B) after washing. Then, the CaSO.sub.4 precipitate was dried in an oven at a temperature of 60 C. for 20 hours to finally obtain the dried CaSO.sub.4 precipitate. In addition, filtrates (A) and (B) containing 3-hydroxypropionic acid were obtained.

Example 4

[0185] 1.0 L of the fermentation liquid obtained in Preparation Example 2 was prepared (containing about 84 g/L of 3-hydroxypropionic acid, and about 103 g/L of 3-hydroxypropionic acid calcium salt), and heated up to a temperature of 60 C. Then, 185 mL of 5M sulfuric acid solution was added to the fermentation liquid at a uniform rate for 5 minutes, and further stirred for 30 minutes to form a slurry containing CaSO.sub.4 precipitate and 3-hydroxypropionic acid.

[0186] Filtration was performed using a filtration flask and a vacuum pump in order to separate the CaSO.sub.4 precipitate. The CaSO.sub.4 precipitate was dried in an oven at a temperature of 40 C. for 20 hours. Finally, the dried CaSO.sub.4 precipitate was obtained, and a filtrate containing 3-hydroxypropionic acid was obtained.

Example 5

[0187] 1.0 L of the fermentation liquid obtained in Preparation Example 2 was prepared (containing about 122 g/L of 3-hydroxypropionic acid, and about 149.5 g/L of 3-hydroxypropionic acid calcium salt), and heated up to a temperature of 60 C. Then, 500 mL of 5M sulfuric acid solution was added to the fermentation liquid at a uniform rate for 5 minutes, and further stirred for 30 minutes to form a slurry containing CaSO.sub.4 precipitate and 3-hydroxypropionic acid.

[0188] Filtration was performed using a filtration flask and a vacuum pump in order to separate the CaSO.sub.4 precipitate. The CaSO.sub.4 precipitate was dried in an oven at a temperature of 40 C. for 20 hours. Finally, the dried CaSO.sub.4 precipitate was obtained, and a filtrate containing 3-hydroxypropionic acid was obtained.

TEST EXAMPLE

1. Analysis of Precipitate Components

[0189] The precipitate containing CaSO.sub.4 was dried, and specific component analysis of the finally obtained product was performed using an X-ray fluorescence spectrometer (XRF).

[0190] Specifically, primary element chemical analysis was performed on a ThermoARL Advant'X Sequential XRF with Uniquant standardless software and loss on ignition (LOI) normalization (moisture content included in the normalization), the loss on ignition (LOI) value was measured in an electric furnace maintained at 975 C., and the crystal moisture was determined by the LOI difference in a drying oven at 250 C.

TABLE-US-00001 TABLE 1 Component Crystal (wt. %) SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 CaO MgO SO.sub.3 LOI moisture Example 1 0.51 0.35 33.93 51.38 12.93 12.4 Example 3 0.53 0.68 0.42 31.19 52.83 13.44 12.38

[0191] Then, the type and crystal form of the material were measured for the finally obtained product using an X-ray diffraction analyzer (Bruker AXS D4-Endeavor XRD). Specifically, measurement was performed under the following conditions; the applied voltage was 40 kV, the applied current was 40 mA, Cu-K radiation (wavelength =1.54184 ) was irradiated, the range of 2theta measured was 10 to 90, and it was scanned at intervals of 0.05.

TABLE-US-00002 TABLE 2 Gypsums Gypsum Gypsum Gypsum Minerals wt. % dihydrate hemihydrate anhydrite Subtotal Quartz dolomite Magnesite illite chlorite microcline Pyrite Exam- 48.29 46.50 2.48 97.24 0.29 0.39 0.21 1.26 0.13 0.44 ple 1 Exam- 1.56 42.57 51.69 95.82 0.16 0.78 0.41 0.27 2.56 4.18 ple 3 Exam- 95.77 0.19 0 95.96 2.07 ple 4 Exam- 72.04 23.65 2.12 97.81 0.07 0.22 1.04 0.83 0.03 ple 5

[0192] On the other hand, FIG. 1 shows the results of X-ray diffraction analysis of alkali metal sulfate crystals recovered in Example 1, and the main peak values and intensities at the diffraction angle (20.2) shown in the XRD analysis results are shown in Table 3 below.

TABLE-US-00003 TABLE 3 Diffraction angle (2 0.2) 12 15 21 23.8 26 29.5 30 32 Intensity (a.u.) 82,000 5,000 25,000 11,000 3,500 23,000 5,000 4,000

[0193] Referring to Tables 1 to 3, it was confirmed that the precipitates obtained in Examples 1 and 3 contained 95.82% or more of gypsum dihydrate, gypsum hemihydrate and gypsum anhydrite based on the total content, contained almost no minerals such as calcite and dolomite, and also contained almost no impurities such as SiO.sub.2.

3. Measurement of Radioactivity Concentration

[0194] The precipitate containing the CaSO.sub.4 was dried, and 1 kg of the finally obtained product was filled in a Marinelli beaker. Using a high-purity germanium gamma ray nuclide detector (HPGe Gamma Spectroscopy, produced by Kenbera, USA, relative efficiency: 30%, applicable energy band: 1,460 KeV), the radioactivity concentration was measured with respect to potassium-40 for 10,000 seconds, measured with respect to radium-226 for 10,000 seconds, measured with respect to uranium-238 for 10,000 seconds, and measured with respect to thorium-232 for 10,000 seconds. Then, based on the measurement result, the radioactivity concentration index of the following general formula 1 was obtained.

[0195] On the other hand, in Table 4 of the academic paper, Econ, Environ, Geol., 44(1), 37-48, 2011, the radioactivity concentration of Phosphogypsum 1 sample was shown. In addition, such Phosphogypsum was obtained after producing phosphate fertilizer from phosphate stone, and the radioactive concentration index of the following general formula 1 was also obtained for 1 kg of Phosphogypsum (Comparative Example).

[00002]$\left[\mathrm{General}\mathrm{Formula}1:\mathrm{Radioactivity}\mathrm{Concentration}\mathrm{Index}\right]\mathrm{Radioactivity}\mathrm{Concentration}\mathrm{Index}$$I=\frac{C_{\mathrm{Ra}226}}{300\mathrm{Bq}/\mathrm{kg}}+\frac{C_{\mathrm{Th}232}}{200\mathrm{Bq}/\mathrm{kg}}+\frac{C_{K40}}{3000\mathrm{Bq}/\mathrm{kg}}$ [0196] CR.sub.a226, C.sub.Th232, C.sub.K40 are respectively the radioactivity concentration (Bq/kg) of solid radium-226(.sup.226Ra), thorium-232(.sup.232Th) and potassium-40(.sup.40K)

TABLE-US-00004 TABLE 4 Radionuclide Radioactivity potassium-40 radium-226 thorium-232 concentration (Bq/Kg) (Bq/Kg) (Bq/Kg) index Exam- 18.55 0.85 below minimum below minimum 0.0062 ple 1 detectable detectable concentration concentration Com- 8.6 6 591.9 13 11.3 1 2.03 parative Example

[0197] Referring to Table 4, it was confirmed that Example can efficiently provide high-purity gypsum that contained radioactive elements in an amount that did not substantially exist, or that did not substantially emit radioactivity. On the other hand, in the case of the Phosphogypsum board using a stone furnace derived from the mineral of Comparative Example, the radioactive concentration was high.

4. Measurement of Recovery Rate of 3-Hydroxypropionic Acid

[0198] The recovery rate of 3-hydroxypropionic acid obtained in Example was measured and calculated using a high-performance liquid chromatography (HPLC).

[0199] Specifically, the absolute amount(X) of 3-hydroxypropionic acid in the fermentation liquid obtained in Preparation Example 2 and the absolute amount(Y) of 3-hydroxypropionic acid in the filtrate were measured, and the recovery rate of 3-hydroxypropionic acid was calculated according to the following general formula 2.

[00003]$\begin{array}{cc}\mathrm{Recovery}\mathrm{rate}\mathrm{of}3-\mathrm{hydroxypropionic}\mathrm{acid}\left(\%\right)=\left(Y/X\right)*100& \left[\mathrm{General}\mathrm{Formula}2\right]\end{array}$

TABLE-US-00005 TABLE 5 Recovery rate of 3-hydroxypropionic acid Example 1 87

[0200] Referring to Table 5, it was confirmed that in Example, high-purity 3-hydroxypropionic acid can be efficiently produced while separating the alkali metal sulfate.