KR20180000427A - Sequential Operating System of Mineralization Process and Microalgal Cultivation for Mass Reduction of Carbon Dioxide and Production of High-value Products - Google Patents

Abstract

The present invention relates to a method for converting carbon dioxide through a mineralization and light cultivation process, and according to the present invention, high-concentration carbon dioxide generated in a power plant or carbon dioxide in combusted exhaust gas is rapidly converted into a carbonate form in large quantities through mineralization, and carbon dioxide, generated through a mineralization reaction of carbon dioxide remaining in a solution and an inorganic carbon source, is continuously utilized in the light cultivation process to show a carbon dioxide reduction effect of 80-90% with additional carbon dioxide reduction through photosynthesis, thereby producing high-value materials such as biofuels, biopolymers, medicines and the like due to the biological conversion of carbon dioxide.

Description

[TECHNICAL FIELD] The present invention relates to a process for producing a high-value-added carbon dioxide and a method for producing the same,

The present invention relates to a method for converting carbon dioxide through a mineralization and light cultivation process, and more particularly, to a method for converting carbon dioxide into carbon dioxide by liquefying carbon dioxide into carbon dioxide; (b) converting calcium ions into carbonates by adding calcium ions or magnesium ions to the solution containing carbonate ions converted in step (a), thereby mineralizing the carbonate ions; And (c) adding residual carbonate ions and carbon dioxide to the culture medium after mineralization in step (b), followed by photo-culturing the microalgae to obtain a biomass. In the mineralization and light- To a method of switching.

As the global warming phenomenon accelerates due to the increase of carbon dioxide, the development of carbon capture and sequestration (CCS) has been actively carried out worldwide to reduce carbon dioxide. CCS technology captures large amounts of carbon dioxide emitted from various carbon sources, including thermal power plants, at high concentrations and then injects them into the ground or seabed to isolate them from the atmosphere. This CCS technology has the effect of reducing a large amount of carbon dioxide in a short period of time, but stable storage problem, location selection, and high installation cost are obstacles to realization of practical CCS in Korea. Therefore, unlike CCS technology, CCU (Carbon Capture & Utilization), which directly uses carbon dioxide for industrial purposes rather than storage, or converts it into a substance with high added value, is in the spotlight. In Korea, development of a process for converting carbon dioxide into various high- . Mineralization, which stores carbon dioxide in the form of minerals, and biological conversion processes using microalgae, complement each other's shortcomings and disadvantages, thereby enhancing the effect of reducing carbon dioxide. At the same time, It is possible to produce high value-added materials such as plastics and medicines, thus enabling economical process development that can generate high profit.

Mineralization is the conversion of carbon dioxide into solid inorganic carbonates through chemical reactions. (MgCO ₃ ) or calcium carbonate (CaCO ₃ ) carbonate using calcium oxide (CaO), magnesium oxide (MgO) or the like contained in natural silicate cancer and the like. Mineralized carbon dioxide can be maintained in a stable state for a long time and can be utilized for cement, building materials, coal mine landfill, etc. without concern about potential carbon dioxide leaks. have. Mineralization can be largely divided into direct and indirect methods, and the direct method is carbonated by a single process such as high-calcium or magnesium-rich serpentine.

Such a process is simple but requires low purity of the product and must be reacted directly with the solid. Therefore, it is required to react at high temperature / high pressure and high-purity carbon dioxide is required, which makes it difficult to construct an economical process. In contrast, an indirect method requires liquefaction of carbon dioxide to generate carbonate by adding calcium ions (Ca ²⁺ ) or magnesium ions (Mg ²⁺ ) in the solution, which requires an additional process as compared with the direct method. However, , The purity of the product is high. Therefore, it is the most widely used method. It is important to maintain the pH of the reaction between pH 7 and pH 9 in order to increase the economical efficiency of the process. It is supplied through electrolysis of salt water using caustic soda (NaOH). Mineralization of carbon dioxide has the advantage that it can treat large amounts of carbon dioxide quickly and easily, and can be stored for a long time in the form of a thermodynamically stabilized carbonate. However, since it is difficult to produce high-value-added materials through mineralization, it is difficult to match the economical efficiency of the process used for electrolysis. In order to overcome these disadvantages, it is required to be integrated with biological conversion process using microalgae.

Algae is a group of photosynthetic organisms that can grow through photosynthesis by utilizing carbon dioxide and sunlight, except for land plants. It is composed of 5 μm sized micro-algae such as Chlamydomonas and Chlorella microalgae, and seaweed, macroalgae, such as waterweed. In particular, microalgae can be converted into high-value-added materials such as biofuels, biopolymers, and pharmaceuticals through photosynthesis, and is attracting attention as a next-generation biomass that can replace petroleum for transportation. In addition, micro-algae-based biodiesel has similar cetane number, calorific value, viscosity and phase change characteristics compared with light oil, so it can be easily supplied without mixing with light oil. In addition, production of 1 tonne of biodiesel through microalgae produces 2.2-2.8 tons of carbon dioxide, resulting in a clean energy source in line with the world's and domestic new and renewable energy standards (RFS, Renewable Fuel Standard) system. It is possible. Microalgae have a higher growth rate than plants and have 20-100 times higher biomass productivity per unit area than first-generation biofuels such as soybean, corn and rape seeds, and can be cultivated in large quantities through marine or wasteland , Sewage, and seawater wastewater. Particularly, since the combustion exhaust gas from a carbon source such as a thermal power plant can be directly used for cell culture, a process for reducing carbon dioxide is being developed all over the world.

The cultivation method of microalgae can be divided into open pond (open pond) and photobioreactor (photobioreactor). The open pond culture system is the most widely used method because it has low initial investment cost and operating cost. For effective light transmission, the depth of the reactor is about 0.3m and it is made of concrete or plastic material. Using the aberration, To prevent sedimentation. However, since it is exposed to the outside, pollution, temperature control, low productivity, and the like are caused, and most of the supplied carbon dioxide is lost to the atmosphere. The photobioreactor is a closed type reactor. It has high microalgae biomass productivity, stable management and high initial investment and operation cost compared to open pond system. The photobioreactor is made of various materials such as plastic, vinyl, etc. for economical process development.

In the case of microalgae bioprocessing, it is possible to convert carbon dioxide into a variety of high value-added substances such as biodiesel, biopolymers, pharmaceuticals, health foods and natural pigments. . However, in photosynthetic organisms capable of photosynthesis efficiency and carbon conversion efficiency and take advantage of culture in general, the CO ₂ of 5% due to the lower limitation, up to 10-20% of the amount of biomass supplied only angry with CO ₂ There is a drawback that the reduction effect is low. Therefore, it is necessary to develop a fusion process capable of realizing commercialization by maximizing carbon dioxide conversion efficiency through connection with the above-mentioned carbon dioxide mineralization process, and securing economical efficiency through production of high value-added materials.

Therefore, the present inventors have made intensive efforts to develop a method for more efficiently converting carbon dioxide. As a result, they have found that carbon dioxide captured at a high concentration is liquefied with carbonic acid ions using NaOH, then converted into carbonates to perform mineralization, It has been confirmed that carbon dioxide can be converted more efficiently when the ions are converted into biomass through optical culture using microalgae, and the present invention has been completed.

An object of the present invention is to provide a method capable of increasing the conversion efficiency of carbon dioxide and simultaneously producing a high-value-added material from carbon dioxide.

In order to accomplish the above object, the present invention provides a method for producing carbon dioxide, comprising the steps of: (a) liquefying carbon dioxide into carbonate ion; (b) converting calcium ions into carbonates by adding calcium ions or magnesium ions to the solution containing carbonate ions converted in step (a), thereby mineralizing the carbonate ions; And (c) adding residual carbonate ions and carbon dioxide to the culture medium after mineralization in step (b), followed by photo-culturing the microalgae to obtain a biomass. In the mineralization and light- To provide a method of switching.

According to the present invention, a high concentration of carbon dioxide generated in a power plant or carbon dioxide in a combustion exhaust gas is rapidly converted into a carbonate form in a large amount through mineralization, and the carbon dioxide and inorganic carbon source remaining in the solution and the carbon dioxide By continuous use in algae light cultivation process, additional carbon dioxide reduction through photosynthesis can produce more than 80-90% carbon dioxide reduction effect, and it can produce high value-added materials such as biofuels, biopolymers and pharmaceuticals due to bioconversion of carbon dioxide.

FIG. 1 is a schematic diagram of a mineralization and microalgae light culture fusion process for mass conversion of carbon dioxide and production of high value added materials.
FIG. 2 is a graph showing the pH change in solution and the shape of a carbon source with time when liquefying high-concentration carbon dioxide into water.
3A is a photograph of calcium carbonate (CaCO ₃ ) obtained through mineralization induced by adding calcium chloride (CaCl ₂ ) to a ₁ M sodium hydrogen carbonate (NaHCO ₃ ) solution at various concentrations. 3B is a graph showing conversion rates of converted carbon dioxide by adding calcium chloride to 1M sodium hydrogen carbonate solution at different concentrations.
FIG. 4A is a photograph showing the microscopic image of the microalgae Neochloris oleoabundans and the growth of microalgae according to the concentration of bicarbonate ions in the solution. FIG. 4B is a graph showing the growth potential of microalgae according to the concentration of bicarbonate ions in the solution.
FIG. 5 is a graph showing biomass productivity of microalgae according to concentration of bicarbonate ions in the culture medium and CO ₂ conversion rate through microalgae light culture. FIG.
FIG. 6 is a graph showing changes in carbon dioxide conversion according to the addition of calcium chloride to the solution remaining after biomass separation through microalgae light culture.

The inventors of the present invention have found that, in order to reduce a large amount of carbon dioxide, a mineralization process for producing carbonates and a high density culture process for photosynthetic microalgae are successively connected to each other to increase the effect of reducing carbon dioxide and to produce carbonates and microalgae And to develop an economical fusion process system through the production of high value added materials (biopolymers, biofuels, medicines, etc.).

Accordingly, the present invention provides a method for producing carbon dioxide, comprising: (a) liquefying carbon dioxide to convert it to carbonate ion; (b) converting calcium ions into carbonates by adding calcium ions or magnesium ions to the solution containing carbonate ions converted in step (a), thereby mineralizing the carbonate ions; And (c) adding residual carbonate ions and carbon dioxide to the culture medium after mineralization in step (b), followed by photo-culturing the microalgae to obtain a biomass. In the mineralization and light- To a method of switching.

In the present invention, the liquefaction of the carbon dioxide in the step (a) may be performed by adding 0.1 to 0.3 M of NaOH or Ca (OH) ₂ , and the liquefied solution is maintained at a pH of 7 to 9 .

In the present invention, the step of separating the carbonate obtained in the step (b) may be further performed, and the light amount may be performed in a photobioreactor.

In the present invention, (d) further comprises a step of secondary mineralization by converting the residual carbonate ion into a carbonate in the solution from which the biomass has been removed.

Examples of microalgae that can be used in the optical culture of the present invention include Neochloris sp., Chlorella sp., Chlorococcum sp., Spirulina sp., Haematococcus sp. ), Neospongiococcum sp., Scenedesmus sp., Dunaliella sp., Thaustochytrids, and the like, but are not limited thereto. Generally, carbon dioxide is used as biomass Can be used without limitation.

In an embodiment of the present invention, carbon dioxide in a highly concentrated carbon dioxide or combustion exhaust gas is liquefied in the form of bicarbonate ion (HCO ₃ ^- ) or carbonate ion (CO ₃ ^2- ), basic solution containing caustic soda (NaOH) (Ca / Mg) CO ₃ ) by adding calcium ions (Ca ²⁺ ) or magnesium ions (Mg ²⁺ ) while maintaining the pH in the solution within the range of pH 7 to 9, , The carbonate produced through the mineralization is separated, the separated solution and the carbon dioxide produced in the mineralization reaction are secured, and the separated solution and the carbon dioxide in the gaseous phase are injected into the photobioreactor for microalgae culture , And a method of continuous connection of mineralization and microalgae light cultivation process was constructed.

In another embodiment of the present invention, microalgae are cultivated to produce biomass by using carbon dioxide generated and remaining after the mineralization process and inorganic carbon sources (bicarbonate ion, carbonate ion) in the solution, and high-valued secondary metabolites Antioxidants, lipids, etc.), and extracts them to convert carbon dioxide into high-value resources using microalgae.

In another aspect of the present invention, there is provided a method of linking a culture solution to a secondary mineralization process, in order to further increase the effect of reducing carbon dioxide after a microalgae culture process; Adjusting pH in the culture medium after microalgae harvesting; Adding a calcium ion or a magnesium ion to the solution; A carbonate generating step; A carbonate separation step can be performed.

In another embodiment of the present invention, it is confirmed that carbon dioxide conversion of 80% or more can be achieved by conducting a secondary mineralization process in order to maximize the conversion rate of carbon dioxide remaining in the solution after the microalgae light cultivation process.

 Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these examples are for illustrative purposes only and that the scope of the present invention is not construed as being limited by these examples.

Example 1: Liquefaction process of carbon dioxide collected at a high concentration

In order to treat a large amount of carbon dioxide captured at a high concentration at a high speed, a process of liquefying carbon dioxide into the solution was carried out. First, when the gaseous carbon dioxide is liquefied in water, it is present in the form of carbonic acid (H ₂ CO ₃ ) in the solution and the pH in the solution is lowered. As shown in Fig. 1, 0.1M of caustic soda (NaOH) showing basicity was first added to make a high alkali of pH 13 or more for liquefaction of carbon dioxide.

Subsequently, high purity carbon dioxide was injected at a rate of 100 ml / min to measure the pH change in the solution. In addition, the form and fraction of the inorganic carbon source were analyzed through solution analysis. The pH is lowered at the same time as the liquefaction of carbon dioxide, and mainly exists in the form of carbonate ion (CO ₃ ^2- ) at pH 10-pH 14 and mainly in the form of bicarbonate ion (HCO ₃ ^- ) at pH 8- It can be confirmed that it exists mainly in the form of carbon dioxide at the following pH.

 For mineralization, carbon dioxide must be dissolved in the form of carbonate or bicarbonate ions in the solution so that it can be mineralized to carbonates through reaction with calcium ions or magnesium ions, so the pH in the solution should be maintained between pH 7-9. 0.1 M to 0.3 M NaOH was added periodically to maintain the pH in the solution.

Example 2: Primary mineralization of high concentration carbon dioxide in solution

High-density carbon dioxide was liquefied in water by the method of Example 1, and a solution containing calcium ion or magnesium was added to proceed primary mineralization. First, in order to calculate the carbon dioxide conversion rate through mineralization, bicarbonate ion, which is a liquefied carbon dioxide, was used. 1M sodium hydrogencarbonate solution was prepared, and 100 mM, 250 mM, 500 mM and 1000 mM calcium chloride solutions were prepared and mixed for mineralization, respectively. At this time, the mineralization reaction is as follows (1), and does not limit the mineralization reaction to one reaction.

(1)

(One)

As shown in Reaction Scheme (1), carbon dioxide is generated simultaneously with the formation of carbonate through the reaction. In addition, as shown in FIG. 3A, since the production of carbonates generated according to the concentration of added calcium chloride can be increased, the degree of mineralization can be controlled by adjusting the calcium chloride concentration. FIG. 3b shows the conversion rate of carbon dioxide converted through this primary mineralization. As shown in the above reaction formula (1), 1M sodium hydrogencarbonate is completely reacted with 0.5M calcium chloride, and is produced at a calcium chloride concentration of 1M or more The amount of calcium carbonate is almost the same as the amount of calcium carbonate produced as a result of mineralization using 0.5 M calcium chloride solution. It is also confirmed that up to 50% of carbon dioxide is converted through mineralization.

Example 3: Growth analysis of microalgae according to bicarbonate ion concentration

After the primary mineralization of Example 2, growth and tolerance analysis of microalgae was carried out according to the concentration of bicarbonate ions in order to carry out the microalgae light cultivation process using the solution.

The strain used for light culture is Neochloris oleoabundans (UTEX1185), which is a representative strain that is widely used industrially because of its high lipid productivity (Fig. 4A). The growth of microalgae was confirmed by the concentration of bicarbonate ions in the culture, and the growth of microalgae was confirmed by measuring the absorbance at 800 nm wavelength (FIG. 4B). The medium used for the culture was TAP-C medium, and the components thereof are shown in Table 1.

TAP-C medium components TAP-C Medium ingredient Content (in 1L water) TAP salts (in 1 L water) 25 ml NH4Cl 15.0 g
4.0 g < RTI ID = 0.0 >
2.0 g < RTI ID = 0.0 > Phosphate solution (in 100 ml water) 0.375 ml K2HPO4 28.8 g
KH 2 PO 4 14.4 g Hutner's trace elements 1.0 mL EDTA disodium salt 50 g (250 ml of water)
ZnSO4 占 H2O 22 g (100 ml water)
H3BO3 11.4 g (200 ml of water)
5.06 g (50 ml of water) of MnCl 2 .4H 2 O)
CoCl 2 揃 6H 2 O 1.61 g (50 ml water)
1.57 g of CuSO4 占 H2O (50 ml of water)
_{(NH₄) 6 Mo 7 O₂₄ ·} 4H₂O 1.10 g (50 ml water)
4.99 g of FeSO4 占 H2O (50 ml of water) Tris base 2.42 g HCl 1.0 mL

Medium containing bicarbonate ions of 0, 2, 5, 10, 15, 20, 50 and 100 mM in the TAP-C medium was inoculated and microalgae were inoculated for 3 days at a light intensity of 100 μE / m ² / And cultured at 23 ° C. As a result, Neochloris oleoabundans showed the highest growth rate in medium of 100 mM bicarbonate ion and 0.1 ~ 0.2M bicarbonate ion tolerance. In order to analyze the conversion of CO 2 through microalgae culture, cells were cultured for 7 days and centrifuged (3000 rpm, 10 minutes) to separate the cells. The dry weight of the cells was measured, and CO ₂ Were further measured via a CO ₂ analyzer.

As a result, as shown in FIG. 5, the efficiency of carbon dioxide fixed by biomass through microalgae growth is about 10%. These results can be improved through process optimization or scaling up and can be further enhanced by the photobioreactor scale or design.

Example 4: Secondary mineralization process after microscopic algae light cultivation

In the first mineralization process, about 50% of carbon dioxide was converted, followed by 10% of carbon dioxide conversion through optical culture of microalgae, but it was still contained in the form of bicarbonate ion or carbonate ion in the cell culture medium. The additional carbon dioxide reduction process can be carried out through the linkage of the mining process.

For this purpose, the microalgae cultured for 7 days were separated by centrifugation, and the mineralization was carried out by adding 100 mM, 200 mM, 300 mM and 400 mM aqueous calcium chloride solution to each reaction. In this case, the solution to be added for mineralization is not limited to an aqueous solution of calcium chloride.

As a result, as shown in FIG. 6, up to about 25% of the remaining CO ₂ could be converted into the carbonate form through the secondary mineralization reaction, which resulted in the first mineralization-microalgae light culture It is possible to demonstrate that more than 85% of carbon dioxide can be converted through a continuous fusing process of secondary mining.

Through the present example, the possibility of actual large-scale carbon dioxide conversion and high-value-added useful material production fusion process is demonstrated through the result of mineralization-microalgae light cultivation process using high-concentration carbon dioxide in laboratory scale.

While the present invention has been particularly shown and described with reference to specific embodiments thereof, those skilled in the art will appreciate that such specific embodiments are merely preferred embodiments and that the scope of the present invention is not limited thereby. something to do. It is therefore intended that the scope of the invention be defined by the claims appended hereto and their equivalents.

Claims (6)

A method of converting carbon dioxide through a mineralization and light cultivation process comprising the steps of:
(a) liquefying carbon dioxide to convert it to carbonate ion;
(b) converting calcium ions into carbonates by adding calcium ions or magnesium ions to the solution containing carbonate ions converted in step (a), thereby mineralizing the carbonate ions; And
(c) adding residual carbonate ions and carbon dioxide to the culture medium after mineralization in the step (b), and then culturing the microalgae to optically cultivate the biomass.
The method according to claim 1, wherein liquefaction of carbon dioxide in step (a) is performed by adding 0.1 to 0.3 M of NaOH or Ca (OH) ₂ .
3. The method according to claim 2, wherein the liquefied solution in step (a) maintains the pH at 7 to 9.
The method according to claim 1, further comprising the step of separating the carbonate obtained in step (b).
The method of claim 1, wherein the light magnification is performed in a photobioreactor.
The method according to claim 1, further comprising the step of (d) secondary mineralization by converting the remaining carbonate ions into a carbonate in the solution from which the biomass has been removed.

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