WO2021133304A1

WO2021133304A1 - Boric acid production through pressurized carbon dioxide from colemanite mineral

Info

Publication number: WO2021133304A1
Application number: PCT/TR2020/051167
Authority: WO
Inventors: Mehmet GONEN
Original assignee: Gonen Mehmet
Priority date: 2019-12-26
Filing date: 2020-11-25
Publication date: 2021-07-01

Abstract

The present invention relates to the production of boric acid from colemanite mineral by using pressurized carbon dioxide (CO2) gas in aqueous phase, it describes the boric acid production method comprising the following process steps; feeding water and colemanite mineral as a mixture into the pressurized reactor (3), pressurizing the CO2 gas with the compressor (2) and feeding the CO2 gas into the pressurized reactor (3), obtaining boric acid and forming carbonate as a consequence of the reaction, separating the unreacted solids (dolomite, clay) and the precipitated calcium carbonate by filtering in the filtration unit (4), concentrating boric acid-containing main solution under vacuum at a temperature of 60-80°C, subjecting the solution concentrated in the previous step to crystallization in the crystallization unit (5), separating the solid product in pulp form after crystallization with the decanter (6) and recycling the boric acid-containing solution into the reactor, subjecting the product (boric acid containing 8-11% H2O) to the drying process in the drying unit (7).

Description

BORIC ACID PRODUCTION THROUGH PRESSURIZED CARBON DIOXIDE FROM

COLEMANITE MINERAL Technical Field of the Invention

The present invention relates to a process for producing boric acid from boron mineral, more specifically from colemanite. The present invention describes a boric acid production method by using pressurized carbon dioxide (CO₂₎ gas in an aqueous environment from colemanite mineral with supercritical fluid extraction. An important characteristic of the inventive method is the use of pressurized CO₂ gas in an aqueous environment instead of conventional acids (H₂SO₄, HCI, etc.).

State of the Art

Colemanite mineral is reacted with concentrated sulfuric acid in an aqueous environment in the conventional boric acid production. This conventional continuous process consists of a reactor operating at atmospheric pressure, a filter and a washing system, a crystallization unit, a decantation unit, a second washing, and filtration system, and a product drying unit. In this process, sulfuric acid (H₂SO₄₎ is preferred since it is the cheapest acid and it is comparatively easier to separate the formed by-products from boric acid (H₃BO₃₎ .

However, the sulfuric acid production process has many environmental problems. On the other hand, critical amounts of CO₂ are released into the atmosphere depending on fossil fuel consumption in the industry. Its level in the atmosphere has reached to the limits of approximately 400 ppm today. The use of CO₂ which is one of the important factors of global climate change, as a raw material in chemical processes is necessary for a sustainable life and development. The heterogeneous reaction between colemanite mineral and concentrated sulfuric acid occurs between 90-98°C in the reactor that operates at atmospheric pressure. The released heat keeps the reactor at the required temperature since the reaction is exothermic. Furthermore, dolomite (CaMg(CO₃)₂) being as impurities in the colemanite mineral reacts with sulfuric acid and forms a highly soluble magnesium sulfate in water.

Moreover, this by-product is carried with the boric acid solution throughout the process, it forms impurities in the product, or requires extra washing steps so as to obtain pure boric acid.

In the inventive production method, since CO₂ dissolves in water and forms carbonic acid (H₂CO₃₎ , it provides the required proton (H⁺) for the dissolution of colemanite mineral so as to eliminate these problems different from the state of the art.

Increasing the partial pressure of CO₂ in the reactor also increases the amount of CO₂ dissolved in water, thus increases the proton concentration in the aqueous medium. Furthermore, limestone (CaCO3) is formed as a by-product in CO₂ use in the process and the solubility of this substance is lower than the solubility of the by-product, gypsum (CaSO4.2H20) in the traditional method. Thus, it becomes easy to separate boric acid from the by-products that are formed. Furthermore, the CO₂ resulting from the fuel burned in the energy unit is used directly in this process, thus it provides an advantage in reducing CO₂ released into the atmosphere.

The sequestration of CO₂ in the atmosphere by mineral carbonation has played an important role in the formation process of the earth. In this process, CO₂ in the atmosphere reacted with the rocks in the crust of the earth and sequestrated as carbonate. Alkali and alkaline earth metals or minerals containing thereof can be used in CO₂ sequestration. Alkaline earth metals are preferred because carbonates obtained from alkali metals are highly soluble in water. Among the alkaline earth metals, magnesium (Mg) metal is preferred since it is found in purer minerals rather than calcium (Ca) that reacts more easily. The most important advantage of this method is that; the obtained carbonates are significantly thermodynamically stable and do not create any risk to the environment. Some of the minerals used in sequestration of CO₂ can be listed as follows; CaSiO3 (Wollastonite), Mg₂SiO₄ (Forsterite), (Mg₃Si₂O5(OH)4) (Serpentine) (Zevenhoven, 2011).

On the other hand, many studies have been performed for sequestration of CO₂ in the world. In some of these studies, CO₂ mineralization is studied, and some natural minerals are investigated. However, the results showed that these processes are not applicable since the economic added value of the obtained products is low. The development of processes that use CO₂ by both separating boric acid from boron minerals and storing CO₂ in a stable state will be both economical and sustainable .

To summarize the problems mentioned above in the state of the art, the most important one is; in case the sulfuric acid is used as seen in the conventional methods, it causes environmental problems and CO₂ is released into the atmosphere in large amounts. The secondary most important problem is that; separation processes are difficult and require additional washing steps since impurities in the mineral are also dissolved in the reaction. Further equipment, process cost, time, and labor also cause indirect problems.

Furthermore, since the sulfuric acid preferred in the art is a very strong acid, corrosion problem is also seen in the reactor during the reaction of mineral and sulfuric acid in boric acid production. Another disadvantage is that; when sulfuric acid is used, calcium sulfate is formed as a by product as a consequence of the reaction. However, when the inventive production method is used, calcium carbonate is formed as a by-product using CO₂. When the solubility of these two substances is compared, since calcium carbonate is less soluble, the separation process is easier and more cost- efficient .

In the state of the art, the solutions applied to the technique for removing impurities are given in the relevant patent applications.

In said invention, which is seen in the state of the art, with the title of "Development of the boric acid production process" numbered TR201008667, which is the subject of the Turkish patent registration of the ETI Mine Works General Directorate, a method is described comprising the following process steps; after the boric acid production process, after crystallization, respectively concentrating, product washing, SO4 reduction and pre-dewatering, homogeneous, moist and thick product feeding, product mixing, microwave drying, and crystal comminution, sizing. In said invention, crystallization processes after boric acid production are described.

The invention subject to the American patent registration numbered US3953580(A) and titled "Boric acid process" describes a development made in the continuous boric acid production process comprising the following process steps; reacting borate-containing ore with sulfuric acid in an aqueous medium, crystallizing the boric acid obtained from the main liquor and separating the main liquor as a solvent in the process for borate ore amounts in the following steps. This development comprises the following; passing the recycle main liquor through a porous permeable cellulose acetate membrane that has been annealed at low temperatures and has a low boron rejection level and thus removing the impurities from the liquor and recycling the permeate into said process.

As it can be seen in this description, a boric acid production method that involves treating the borate mineral/ore (sodium borate or colemanite) with sulfuric acid is disclosed. Moreover, the improvement performed so as to remove impurities found in the prior art is described. The technical solution found here is to remove impurities by passing the same through a porous cellulose membrane.

The invention subject to US patent registration with the title of "Process for the obtainment of boric acid from colemanite and/ or Howlite minerals" numbered US4756894 (A), describes a method for obtaining boric acid from the colemanite mineral Howlite mineral or a mixture thereof, comprising the following process steps; treating the mineral with sulfuric acid to dissolve boron compounds, separating the solution formed in this way from the insoluble solids in the suspension, reacting said solution with hydrogen sulfide so as to precipitate arsenic and iron impurities, separating the precipitated impurities from the remaining solution, cooling the remaining solution so as to precipitate boric acid and separating boric acid from the remaining solution. As it is described in the present invention, the process of obtaining boric acid by treatment with sulfuric acid was carried out. A solution was found by performing the reaction process step with hydrogen sulfide so as to precipitate the impurities (arsenic and iron).

When the processes for removing the impurities in the state of the art are considered, it is seen that the solution is insufficient. Moreover, a solution cannot be found for the problem of shortening the life of the reactor and the assembly thereon as a consequence of the corrosion problem arising from the use of sulfuric acid. Furthermore, water consumption increases in separating by-products from boric acid, and some solution is also separated from the process, and in some cases, further process is required. At this point, it is seen that the solutions in the state of the art are not sufficient. In addition to this, since this solution contains boric acid, it is harmful to the environment and is not discarded. Besides, the insufficient solutions developed in the patent applications given above and the problems in the art encourage the inventor to develop a novel boric acid production method.

Description of the Invention

The object of the invention is to develop a novel boric acid production method by eliminating the problems encountered in the above-mentioned prior art such as not removing the impurities, corrosion of the reactor, environmental problems due to CO2 gas emission, the formation of calcium sulfate as a by-product, etc.

The invention is essentially related to the use of pressurized CO2 gas in an aqueous phase instead of traditional acids (H2SO4, HC1, etc.) used in the production of boric acid from colemanite minerals. This method is a sustainable process wherein CO2 causing climate change is used as raw material and is stored in the form of calcite as a stable compound.

In this process, wherein boric acid is dissolved using CO2 gas from the colemanite mineral in an aqueous medium, first of all, the water and colemanite mineral are fed to the reactor together. Then, CO2 gas is fed to the pressurized reactor by means of a compressor. This process can be designed as batch or continuous with the sequential use of two reactors. The reaction temperature is between 35-70°C and the system CO2 gas pressure is kept at (60-90 atm) with respect to the reaction time of 60-180 minutes. At the end of the reaction, firstly the unreacted CO2 gas is recycled to the CO2 tank for reuse.

In cases in which natural gas (CH4) is used for energy production in the plant, CO2 production can also be achieved by cooling and compressing flue gases. As a consequence of the methane combustion, CO2 and water vapor are produced. Conventionally, CO2 is released into the atmosphere without being separated from the stack gases in energy generation plants and thus leads to an increase in the CO2 concentration in the atmosphere.

Carbon dioxide dissolves in the aqueous phase according to the reaction given in Equation 1 and it makes the aqueous solution acidic. In the balanced reaction, when the partial pressure of the carbon dioxide in the aqueous phase is increased, the reaction will shift to the direction of products and the acidity of the medium will increase. H⁺ proton in the medium attacks the colemanite structure and decomposes the structure. Diboron trioxide (B2O3) released from colemanite structure is converted into boric acid with the water in the medium (Equation 2) and calcium cations are converted into calcium carbonate by carbonate anion (Equation 3). The total reaction between colemanite mineral and CO2 in the presence of water is given in Equation 4. In this reaction, when the reaction conditions are kept above the supercritical CO2 conditions, this will have a positive effect on the conversion efficiency in the reaction.

Equations

In the reaction, so as to obtain boric acid, the reaction occurs at a temperature between 35-70°C for 60-180 minutes. After depressurizing the reactor, the solid-liquid mixture is subjected to the process of filtration at 50-80°C and washing. In filtration process, the non-reactive solid phase and the formed solid products (CaCO3) are separated from the water. Moreover, the process of washing with water in the same temperature range is carried out so as to take the remaining solid phase boric acid into the solution. The boric acid solution is saturated at temperature (60-80°C) and vacuum

(0.01-0.2 atm) before the crystallization step. The saturated solution is cooled to 30-40°C and is subjected to crystallization. After the water in the formed pulp is separated by means of a horizontal decanter, boric acid containing 8-11% H2O is subjected to the drying process with hot air at 100-120°C. A Boric acid solution separated from the decanter is recycled to the reactor.

Description of the Figures

FIGURE 1 illustrates the flow chart of the process used in the production method of the invention

Description of the References Part Number/Name of the Part

1 C0₂ Tank

2 Compressor

3 Pressurized Reactor

4 Filtration Unit

5 Crystallization Unit

6 Decanter

7 Drying Unit Detailed Description of the Invention

The present invention is a production method for producing boric acid from colemanite, comprising the following process steps:

- Feeding water and colemanite mineral as a solid-liquid suspension into the pressurized reactor (3),

- Pressurizing the CO2 gas with the compressor (2) and feeding the CO2gas into the pressurized reactor (3),

- Producing boric acid and by-product calcium carbonate in the reaction,

- Separating the precipitated calcium carbonate and unreacted solids (dolomite, clay) from aqueous phase by filtering in the filtration unit (4),

- Concentrating boric acid-containing main solution under vacuum (0.01-0.2 atm) at 60-80°C,

- Subjecting the solution concentrated in the previous step to crystallization at 30-40°C in the crystallization unit (5),

- Separating the solid product after crystallization from the aqueous phase with the decanter (6) and recycling the boric acid-containing solution into the reactor,

- Subjecting the product (boric acid containing 8-11% H2O) to the drying process with air at 100-120°C in the drying unit (7).

In the first step of the production method, a mixture of water and colemanite mineral with a ratio of 10:20 colemanite mineral: water by weight is used.

The pressure value range of the CO2 gas fed from the compressor (2) is between 60-90 atm and its temperature is between 35- 70°C. The mass transfer resistances are reduced with the circulation of the CO2 gas in the pressurized reactor (3) by using the compressor (2) during the reaction period. Another important advantage of the invention is that it reduces water consumption in separation processes and reduces the number of impurities in the product because the solubility of calcium carbonate (calcite) formed in the reaction between colemanite mineral and carbonic acid in the pressure reactor (3) in water is very low. The remaining solid (dolomite, clay, etc.) is washed with 50-80°C water so as to remove the boric acid therein and the diluted solution is fed back into the process. At the end of the reaction, firstly the unreacted CO2 gas is recycled to the CO2 tank for reuse.

The main solution containing boric acid is concentrated under vacuum (0.01-0.2 atm) at 60-80°C. The concentrated solution is cooled to 30-40°C and is subjected to crystallization in the crystallization unit (5).

References

• Zevenhoven, R., J. Fagerlund, and J. K. Songok

(2011). "C02 mineral sequestration: developments toward large-scale application." Greenhouse Gases: Science and Technology Volume 1(issue 1): pages 48- 57.

• Eti Maden Genel Mudurlugu, (2010), "Borik

asit üretimi prosesinin geli§tirilmesi" Turkish Patent Application, TR201008667.

• United States Borax Chem; A_lien R. P., Morgan C., A., (1974), "Boric acid process", American Patent

Application, US3953580(A)

• Materias Primas Magdalena Sa; Polendo-Loredo J.,

(1987), "Process for the obtainment of boric acid from colemanite and/or Howlite minerals", American Patent Application, US4756894(A)

Claims

1. A production method for producing boric acid from colemanite, characterized in that; it comprises the following process steps;

Feeding water and colemanite mineral as a solid- liquid suspension into the pressurized reactor (3),

Pressurizing the CO2 gas with the compressor (2) and feeding the CO2gas into the pressurized reactor (3),

Producing boric acid and by-product calcium carbonate in the reaction,

Separating the precipitated calcium carbonate and unreacted solids (dolomite, clay) from aqueous phase by filtering in the filtration unit (4),

Concentrating boric acid-containing main solution under vacuum (0.01-0.2 atm) at 60-80°C,

Subjecting the solution concentrated in the previous step to crystallization in the crystallization unit (5),

Separating the solid product after crystallization from the aqueous phase with the decanter (6) and recycling the boric acid-containing solution into the reactor,

Subjecting the product (boric acid containing 8-11% H2O) to the drying process in the drying unit (7).

2 . Production method for producing boric acid from colemanite according to Claim 1, characterized in that; it comprises the process step of feeding the mixture to the pressure reactor (3) in a manner such that the colemanite mineral: water ratio by weight is 10:20.

3. Production method for producing boric acid from colemanite according to Claim 1, characterized in that; it comprises the process step of feeding the CO2 gas between the temperature of 35-70°C with 60-90 atm pressure value range into the pressurized reactor (3).

4. Production method for producing boric acid from colemanite according to Claim 1, characterized in that; it comprises the process step of washing the solids with water at 50- 80°C so as to remove the boric acid remaining therein and recycling the diluted solution into the reactor.

5. Production method for producing boric acid from colemanite according to Claim 1, characterized in that; it comprises the process step of cooling the concentrated solution to 30-40°C and subjecting the same to crystallization in the crystallization unit (5).

6. Production method for producing boric acid from colemanite according to Claim 1, characterized in that; it comprises the process step of subjecting the product (boric acid containing 8-11% H2O) to the drying process with air at 100-120°C in the drying unit (7).