Method for preparing sodium borohydride

Abstract

The present invention relates to a method for preparing NaBH4, the method comprising: an MB(OR)4 production step for reacting a borate compound with alcohol to produce a tetraalkoxyborate salt (MB(OR)4); and an NaBH4 production step for converting the tetraalkoxyborate salt (MB(OR)4) into sodium borohydride (NaBH4) through a reduction reaction, wherein M is an alkali metal cation, and R is a C1-10 hydrocarbon group.

Description

Sodium Borohydride Manufacturing Method

[0001] The present invention relates to a method for manufacturing sodium borohydride (NaBH4).

[0002] NaBH4 is used as an essential reducing agent in various industrial fields, and is widely utilized, particularly in chemical synthesis, pharmaceuticals, water treatment, paper manufacturing, and the dye industry. Furthermore, due to its property of generating hydrogen upon reaction with water, it holds significant importance in eco-friendly energy technologies such as fuel cells and hydrogen storage applications. However, high production costs and low resource efficiency are cited as major factors limiting its commercial utilization.

[0003] The Schlesinger method (or Brown-Schlesinger process) was developed by Schlesinger and Brown in 1953 and was once established as the standard for mass production of NaBH4; however, alternative processes are currently being researched due to the complexity of the process and its environmental burden. This process is a multi-step process that synthesizes NaBH4 by reacting Na2B4O7 with H2SO4 to produce H3BO3, converting it to NaBO2 and then reacting it with an alcohol to produce B(OCH3)3, and finally using NaH as a reducing agent. However, the Schlesinger method has limitations in terms of commercial efficiency due to complex process steps, the use of expensive NaH, and environmental burden.

[0004] Recently, various alternative processes are being researched to overcome these limitations. For example, direct elemental synthesis, regeneration processes, and catalyst-based processes have been proposed, aiming to reduce NaBH4 production costs and minimize environmental burden. Ball milling and thermochemical regeneration processes are more efficient than conventional processes, and synthesis utilizing catalysts has been reported to significantly improve NaBH4 productivity.

[0005] While new processes are expected to contribute to increasing the commercial utility of NaBH4 and improving production efficiency, further research and process optimization are required for stable application on a commercial scale. Therefore, the development of innovative manufacturing methods for the economical and environmentally friendly production of NaBH4 remains an important task.

[0006] [Prior Art Literature]

[0007] [Patent Literature]

[0008] (Patent Document 1) Republic of Korea Registered Patent No. 10-1853745

[0009] The present invention aims to provide a method for producing NaBH4, comprising: a step of producing a tetraalkoxyborate salt (MB(OR)4) by reacting a borate compound with an alcohol; and a step of producing NaBH4 by converting the tetraalkoxyborate salt (MB(OR)4) into sodium borohydride (NaBH4) through a reduction reaction, wherein M is an alkali metal cation and R is a hydrocarbon group having 1 to 10 carbon atoms.

[0010] In addition, the present invention provides a method for producing NaBH4 that further includes a borate compound generation step in which borax (Na2B4O7) and sodium hydroxide (NaOH) react to produce sodium metaborate (NaBO2) prior to the MB(OR)4 generation step, thereby preventing Na from being wasted as a byproduct Na2SO4 and providing the possibility of using an inexpensive reducing agent other than NaH in the synthesis of NaBH4.

[0011] In particular, the present invention aims to reduce the cost of manufacturing NaBH4 by simplifying the process, by providing a method for manufacturing NaBH4 in which the borate compound generation step, the MB(OR)4 generation step, and the NaBH4 generation step can be performed continuously in a single reactor.

[0012] In addition, the present invention aims to reduce the cost of manufacturing NaBH4 by providing a method for manufacturing NaBH4 that further includes a process for recycling by-products, unreacted materials, and used solvent generated at each step of the above method for manufacturing NaBH4.

[0013] Furthermore, the present invention aims to provide a method for producing NaBH4 with improved purity and yield by additionally including a purification step at each step of the above-described NaBH4 manufacturing method to minimize the influence of impurities, and by adjusting optimized temperature and pressure conditions and the equivalent ratio of the reducing agent to the reactant.

[0014] However, the problems that this invention seeks to solve are not limited to those mentioned above, and other unmentioned problems will be clearly understood by a person skilled in the art from the description below.

[0015] One aspect of the present invention provides a method for producing NaBH4, comprising: a step of producing a tetraalkoxyborate salt (MB(OR)4) by reacting a borate compound with an alcohol; and a step of producing NaBH4 by converting the tetraalkoxyborate salt (MB(OR)4) into sodium borohydride (NaBH4) through a reduction reaction, wherein M is an alkali metal cation and R is a hydrocarbon group having 1 to 10 carbon atoms.

[0016] The NaBH4 manufacturing method according to the present invention can continuously perform the borate compound generation step, the MB(OR)4 generation step, and the NaBH4 generation step in a single reactor, thereby improving process efficiency and economic feasibility.

[0017] Furthermore, the method for manufacturing NaBH4 according to the present invention can reduce resource waste and minimize waste generation by recycling the solvent used in the process and the unreacted materials and by-products of the reaction, thereby alleviating the environmental burden. Through this, a sustainable manufacturing process can be realized, and eco-friendly effects can be provided.

[0018] In addition, the method for manufacturing NaBH4 according to the present invention can further improve the economic efficiency of the manufacturing process by providing the possibility to selectively use an inexpensive reducing agent in addition to NaH through the optimization of reaction conditions.

[0019] In addition, the NaBH4 manufacturing method according to the present invention provides a technical basis for improving the yield and purity of the generated NaBH4 by optimizing the purification method and reaction conditions, thereby enabling the stable production of high-quality products.

[0020] Figure 1 is a diagram illustrating the changes in intermediate materials and reactants in the present process compared to the conventional process (Brown Schlesinger process).

[0021] Figure 2 is a diagram illustrating the difference between the present process and the conventional process (Brown Schlesinger process), in that the reaction can proceed continuously in a single reactor.

[0022] Figure 3 is a schematic diagram illustrating the process of recycling by-products, unreacted materials, and used solvents in the present process.

[0023] Figures 4(a) and 4(b) respectively show the reference signals of Na2B4O7 and NaBO2. 11 This is the result of B-NMR analysis, and Fig. 4(c) is for the product of Preparation Example 1 11 This is the result of B-NMR analysis.

[0024] Figure 5 shows the results of 1H-NMR analysis of the product of Preparation Example 2. Figure 5(a) shows the analysis results to confirm the presence of CH3OH in the crystal of NaB(OCH3)4, and Figure 5(b) shows the analysis results to calculate the conversion rate of the reaction of Preparation Example 2.

[0025] Figure 6 is a graph showing the change in yield according to reaction temperature in Example 1.

[0026] Figure 7 is a graph showing the change in yield according to the equivalent amount of the reducing agent added in Example 2.

[0027] Figure 8 is a graph showing the change in yield of NaBH4 according to the difference in the NaB(OCH3)4 purification method in Example 3.

[0028] Figure 9 shows the 1H-NMR analysis results to confirm whether methylcyclopentane was recycled in Example 4. Figure 9(a) shows the result of confirming the reference signal of methylcyclopentane, and Figure 9(b) shows the analysis result of the recovered methylcyclopentane.

[0029] Figure 10 is the result of 1H-NMR analysis to confirm whether pyridine was recycled in Example 4. Figure 10(a) is the result of confirming the reference signal of pyridine, and Figure 10(b) is the result of analysis of the recovered pyridine.

[0030] Figure 11 shows the 1H-NMR analysis results to confirm whether the ether was recycled in Example 4. Figure 11(a) shows the result of confirming the reference signal of the ether, and Figure 11(b) shows the analysis result of the recovered ether.

[0031] FIG. 12 shows, in Example 5, to recover and verify whether the unreacted material from the MB(OR)4 generation step is recyclable. 11 This is the result of measuring B-NMR. Fig. 12(a) shows the result of confirming the reference signal of NaBO2, and Fig. 12(b) shows the analysis result of the recovered solid.

[0032] Figure 13 is the result of 1H-NMR analysis to confirm whether NaOCH3, a byproduct of the NaBH4 generation step in Example 6, is recyclable.

[0033] The operation and effects of the invention will be described in more detail below through specific embodiments. However, these embodiments are merely examples of the invention and do not define the scope of the invention.

[0034] Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings, but should be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor can appropriately define the concept of the terms to best describe his invention.

[0035] Therefore, it should be understood that the configuration of the embodiments described in this specification is merely one of the most preferred embodiments of the present invention and does not represent all of the technical ideas of the present invention, and that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0036] In this specification, singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising,” “comprising,” or “having” are intended to specify the existence of the implemented features, numbers, steps, components, or combinations thereof, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0037] In the present specification, "a to b" and "a~b" indicating numerical ranges, "to" and "~" are defined as ≥a and ≤b.

[0038] A method for producing NaBH4 according to one aspect of the present invention comprises: an MB(OR)4 production step of reacting a borate compound with an alcohol to produce a tetraalkoxyborate salt (MB(OR)4); and a NaBH4 production step of converting the tetraalkoxyborate salt (MB(OR)4) into sodium borohydride (NaBH4) through a reduction reaction; wherein M is an alkali metal cation and R may be a hydrocarbon group having 1 or more carbon atoms and 10 or fewer carbon atoms.

[0039] In one embodiment of the present invention, the alkali metal may be lithium (Li), sodium (Na), potassium (K), or a combination thereof.

[0040] For example, the alkali metal mentioned above may be sodium (Na).

[0041] In one embodiment of the present invention, R is a straight-chain, branched, or cyclic hydrocarbon group, optionally comprising one or more substituents, and may be saturated or unsaturated.

[0042] For example, the above R is a methyl group (-CH3), ethyl group (-CH2CH3), propyl group (-CH2CH2CH3), n-butyl group (-CH2CH2CH2CH3), cyclohexyl group (-C6H 11 ), phenyl group (-C6H5), cyclohexylmethyl group (-CH2C6H 11 It may be an isopropyl group (-CH(CH3)2), a methoxymethyl group (-CH2OCH3), a 2-methylpropyl group (-CH(CH3)2CH3), or a combination thereof.

[0043] Meanwhile, the above R is a methyl group (-CH3), an ethyl group (-CH2CH3), or a cyclohexyl group (-C6H 11 It may be a phenyl group (-C6H5), a propyl group (-CH2CH2CH3), or a combination thereof.

[0044] Preferably, the R may be a methyl group (-CH3).

[0045] In one embodiment of the present invention, the alcohol is methanol (CH3OH), ethanol (C2H5OH), n-propanol (C3H7OH), n-butanol (C4H9OH), cyclohexanol (C6H 12 OH), benzyl alcohol (C6H5CH2OH), cyclohexylmethanol (C6H 11 It may be CH2OH), isopropanol (C3H7OH), methoxymethanol (CH3OCH2OH), 2-methyl-1-propanol (C4H9OH) or a combination thereof.

[0046] For example, the above alcohols are methanol (CH3OH), ethanol (C2H5OH), and cyclohexanol (C6H 12 It may be OH), benzyl alcohol (C6H5CH2OH), n-propanol (C3H7OH), or a combination thereof.

[0047] Meanwhile, the above alcohol may be methanol (CH3OH).

[0048] In one embodiment of the present invention, the tetraalkoxyborate salt may be sodium tetramethoxyborate (NaB(OCH3)4), sodium tetraethoxyborate (NaB(OC2H5)4), sodium tetra-n-propoxyborate (NaB(OC3H7)4), lithium tetramethoxyborate (LiB(OCH3)4), lithium tetraethoxyborate (LiB(OC2H5)4), potassium tetramethoxyborate (KB(OCH3)4), potassium tetraethoxyborate (KB(OC2H5)4), sodium tetraisopropoxyborate (NaB(OCH(CH3)2)4), or a combination thereof.

[0049] For example, the tetraalkoxyborate salt may be sodium tetramethoxyborate (NaB(OCH3)4), sodium tetraethoxyborate (NaB(OC2H5)4), sodium tetra-n-propoxyborate (NaB(OC3H7)4), or a combination thereof.

[0050] Meanwhile, the above tetraalkoxyborate salt may be sodium tetramethoxyborate (NaB(OCH3)4).

[0051] In one embodiment of the present invention, the borate compound is a compound comprising a bond (BO bond) between boron and oxygen, and may be sodium metaborate (NaBO2), potassium metaborate (KBO2), lithium metaborate (LiBO2), or a combination thereof.

[0052] For example, the borate compound may be sodium metaborate (NaBO2).

[0053] In one embodiment of the present invention, prior to the MB(OR)4 generation step, a borate compound generation step may be further included in which borax (Na2B4O7) and sodium hydroxide (NaOH) react to produce sodium metaborate (NaBO2).

[0054] Looking at the schematic diagram in Fig. 1, one can see the difference between the existing process (Brown-Schlesinger process) and the new process of the present invention. In the existing process, borax (Na2B4O7) was used with sulfuric acid to produce a borate compound, and thus sodium sulfate (Na2SO4) was produced as a byproduct. The process of the present invention can prevent the formation of such byproducts, and thus prevents the waste of sodium due to byproducts, thereby enabling cost reduction.

[0055] In one embodiment of the present invention, the borate compound generation step; the MB(OR)4 generation step; and the NaBH4 generation step may be performed sequentially in a single reactor.

[0056] Looking at the schematic diagram in Fig. 2, one can see the structure of the present process, in which a continuous reaction can occur in a single reactor, unlike the conventional process (Brown-Schlesinger process). That is, in the case of the conventional process, sodium sulfate (Na2SO4) is generated as a byproduct during the borate compound formation stage, requiring an additional process to separate and remove it. On the other hand, in the present process, water is generated as a byproduct, so it can be considered easy to separate and remove.

[0057] In addition, the product of the second step reaction of the conventional process, which corresponds to the MB(OR)4 generation step of the present process, is B(OCH3)3. This molecule has a boiling point similar to that of alcohol, which is both a solvent and a reactant, making separation and purification difficult. On the other hand, in the present process, a tetraalkoxyborate salt is generated during the MB(OR)4 generation step, which can exist as a solid within the reaction temperature range, making separation from alcohol easy. Therefore, due to this, the reaction can be carried out continuously in a single reactor.

[0058] Therefore, in the present invention, if the borate compound generation step, the MB(OR)4 generation step, and the NaBH4 generation step are performed continuously in a single reactor, process efficiency and economic feasibility can be significantly improved. Since the appropriate reaction conditions for each step can be continuously adjusted and carried out within a single reactor, there is no need to separate or transfer intermediates outside the reactor. This minimizes intermediate loss and saves energy and resources required for additional purification and separation processes.

[0059] Furthermore, since the intermediate can proceed directly to the next step without purification, the process can be simplified, processing time shortened, and operating costs reduced. Through a continuous process, the reaction can be controlled in real-time to suppress side reactions and reduce the generation of byproducts, ultimately increasing the yield and purity of NaBH4. These improvements enable process simplification and increased productivity, thereby strengthening the economic efficiency and competitiveness of the manufacturing process.

[0060] In one embodiment of the present invention, in the step of producing the borate compound, the reaction temperature is 50°C or higher and 150°C or lower, the reaction time is 1 hour or higher and 3 hours or lower, and the molar ratio of the borax and the sodium hydroxide (moles of borax:moles of sodium hydroxide) may be 1:1.5 to 1:4.

[0061] For example, in the step of producing the borate compound, the reaction temperature may be 50°C or higher and 90°C or lower, 90°C or higher and 150°C or lower, 60°C or higher and 110°C or lower, 70°C or higher and 100°C or lower, or 80°C or higher and 95°C or lower.

[0062] If the above reaction temperature falls below the range of the present invention, the reaction rate decreases and the borate compound is not sufficiently formed, which may result in a decrease in the yield and quality of the product.

[0063] On the other hand, if the scope of the present invention is exceeded, side reactions increase, by-products are formed due to the evaporation of water, the reaction environment becomes unstable, and process costs may increase.

[0064] For example, in the borate compound generation step, the reaction time may be 1 hour or more and 2 hours 30 minutes or less, 2 hours 30 minutes or more and 3 hours or less, 1 hour 45 minutes or more and 2 hours 45 minutes or less, 2 hours or more and 2 hours 40 minutes or less, or 2 hours 15 minutes or more and 2 hours 35 minutes or less.

[0065] If the above reaction time falls below the range of the present invention, the borax and sodium hydroxide may not react sufficiently, and the product may be formed incompletely.

[0066] On the other hand, if the scope of the present invention is exceeded, by-products accumulate due to side reactions, and the purification process becomes complex, which may lead to reduced process efficiency and increased costs.

[0067] For example, in the step of producing the borate compound, the molar ratio of the borax and the sodium hydroxide (moles of borax:moles of sodium hydroxide) may be 1:1.5 to 1:2, 1:2 to 1:4, 1:1.6 to 1:2.4, 1:1.7 to 1:2.2, or 1:1.8 to 1:2.1.

[0068] If the above molar ratio falls below the range of the present invention, sodium hydroxide is insufficient, resulting in a lower reaction conversion rate and inhibiting the formation of the product.

[0069] On the other hand, if the scope of the present invention is exceeded, side reactions increase and by-products are formed, which lowers the purity of the product and may complicate the purification process.

[0070] In one embodiment of the present invention, between the borate compound generation step and the MB(OR)4 generation step, a drying step at 300°C or higher and 0.1 atm or lower may be additionally included.

[0071] For example, the temperature of the drying step above may be 300°C or higher and 600°C or lower, 300°C or higher and 330°C or lower, 330°C or higher and 360°C or lower, 360°C or higher and 390°C or lower, 390°C or higher and 420°C or lower, 420°C or higher and 450°C or lower, 450°C or higher and 480°C or lower, 480°C or higher and 510°C or lower, 510°C or higher and 540°C or lower, 540°C or higher and 570°C or lower, or 570°C or higher and 600°C or lower.

[0072] If the above temperature falls below the range of the present invention, water evaporation is not sufficiently carried out, and the residual moisture of NaBO2·xH2O, (x= 0~4) may increase. This may cause side reactions due to moisture in subsequent steps, which may reduce the formation efficiency of MB(OR)4 and the final yield of NaBH4.

[0073] On the other hand, exceeding the scope of the present invention may cause NaBO2 to become thermally unstable, decompose, or have its crystal structure damaged. Additionally, excessive temperatures may increase energy consumption, thereby reducing the economic viability and efficiency of the process.

[0074] For example, the pressure in the drying step above may be 0.01 atm or more and 0.1 atm or less, 0.01 atm or more and 0.02 atm or less, 0.02 atm or more and 0.04 atm or less, 0.03 atm or more and 0.06 atm or less, 0.05 atm or more and 0.08 atm or less, or 0.07 atm or more and 0.1 atm or less.

[0075] If the above pressure falls below the range of the present invention, process costs may increase significantly because advanced vacuum equipment and energy are required to maintain an Ultra High Vacuum (UHV) environment.

[0076] On the other hand, if the range of the present invention is exceeded, the evaporation of moisture slows down, which may increase residual moisture and cause side reactions that can lower the purity and yield of the product. At high atmospheric pressure, the drying time is prolonged, which may reduce process efficiency.

[0077] In one embodiment of the present invention, in the MB(OR)4 generation step, the reaction temperature may be 100°C or higher and 300°C or lower, and the reaction time may be 2 hours or higher and 6 hours or lower.

[0078] For example, the reaction temperature of the above MB(OR)4 generation step may be 100°C or higher and 300°C or lower, 100°C or higher and 150°C or lower, 150°C or higher and 300°C or lower, 100°C or higher and 250°C or lower, 105°C or higher and 240°C or lower, 110°C or higher and 230°C or lower, 120°C or higher and 220°C or lower, 130°C or higher and 210°C or lower, 140°C or higher and 200°C or lower, 145°C or higher and 190°C or lower, 147°C or higher and 180°C or lower, 148°C or higher and 170°C or lower, or 149°C or higher and 165°C or lower.

[0079] If the above reaction temperature falls below the range of the present invention, the activation energy of the reaction may not be sufficiently satisfied, which could lead to a decrease in the reaction rate. This inhibits the formation of MB(OR)4, which in turn reduces the yield and purity of the product and may cause a decrease in process efficiency. Furthermore, as the reaction with alcohol proceeds incompletely, unreacted borate compounds may remain, or side reactions may increase.

[0080] Conversely, if the scope of the present invention is exceeded, the reaction between the borate compound and the alcohol proceeds excessively in a high-temperature environment, potentially leading to the formation of unexpected byproducts. Such side reactions can reduce the purity and yield of MB(OR)4. Furthermore, at high temperatures, the evaporation rate of the alcohol increases, potentially leading to an imbalance in the molar ratio and the possibility of thermal decomposition of the generated MB(OR)4; these factors can degrade reaction efficiency and process stability. Additionally, maintaining high temperatures requires excessive energy, which may reduce the economic viability of the process.

[0081] For example, the reaction time of the above MB(OR)4 generation step may be 2 hours or more and 6 hours or less, 2 hours or more and 4 hours or less, 4 hours or more and 6 hours or less, 3 hours or more and 5 hours or less, 3 hours 15 minutes or more and 4 hours 45 minutes or less, 3 hours 30 minutes or more and 4 hours 30 minutes or less, or 3 hours 45 minutes or more and 4 hours 15 minutes or less.

[0082] If the above reaction time falls below the range specified in the present invention, the reaction between the borate compound and the alcohol may not proceed sufficiently, thereby inhibiting the formation of MB(OR)4. Insufficient reaction time results in the reaction mixture not being formed uniformly, and there is a high likelihood of reduced yield and purity of the product. In particular, the increased likelihood of unreacted borate compounds remaining can lead to side reactions in subsequent processes or complicate the purification process. If the reaction proceeds incompletely, it may result in a degradation of the quality of the final product, NaBH4.

[0083] On the other hand, if the reaction time exceeds the scope of the present invention, the reaction time becomes excessively long, increasing the likelihood of continuous side reactions. This can lead to the accumulation of by-products, which may lower the purity and yield of MB(OR)4. Additionally, prolonged reactions can increase energy consumption and reduce the economic efficiency of the process. Furthermore, if the reaction mixture overheats or an excessive amount of solid products are produced, there is a possibility that difficulties in processing may arise in subsequent processes.

[0084] In one embodiment of the present invention, the tetraalkoxyborate salt may exist in a solid state at the reaction temperature and atmospheric pressure of the MB(OR)4 generation step.

[0085] If the tetraalkoxyborate salt (MB(OR)4) is not in a solid state, purification and separation may become complicated, and unreacted materials or by-products may be mixed in, which may reduce the purity of the final product. Additionally, the efficiency of subsequent reactions may decrease, and the likelihood of side reactions may increase. Furthermore, additional energy and work are required for the process, which may reduce the economic viability and stability of the overall process.

[0086] In one embodiment of the present invention, a moisture absorbent may be additionally used in the MB(OR)4 generation step.

[0087] For example, the above moisture absorbent may include a molecular sieve and may also include a separation membrane capable of separating alcohol and moisture.

[0088] For example, the molecular sieve may be Zeolite 3A, Zeolite 4A, Zeolite 5A, Zeolite 13X, Silica Gel, Activated Alumina, Mesoporous Silica MCM-41, Mesoporous Silica SBA-15, Activated Carbon, Hydrotalcite, Metal-Organic Framework MIL-101, or Metal-Organic Framework UiO-66.

[0089] Meanwhile, the molecular sieve may be Zeolite 3A, Silica Gel, or Activated Alumina.

[0090] For example, the separation membrane may be a NaA zeolite membrane, a polyvinyl alcohol (PVA-based) membrane, a silica-titania mixed ceramic membrane, a polydimethylsiloxane (PDMS-based) pervaporation membrane, or a MIL-53-based metal-organic framework membrane.

[0091] Meanwhile, the above separation membrane may be a NaA zeolite membrane, a polyvinyl alcohol (PVA)-based membrane, or a silica-titania mixed ceramic membrane.

[0092] If the above-mentioned moisture absorbent is not used, the generated water may remain in the reaction mixture and cause a reverse reaction. This may inhibit the formation of MB(OR)4 and potentially reduce the product yield. Furthermore, the retention of water in the reaction mixture may increase side reactions and lower the purity of the product. This situation complicates the purification process, potentially requiring additional energy and costs, and may reduce the economic viability of the overall process.

[0093] In one embodiment of the present invention, between the MB(OR)4 generation step and the NaBH4 generation step, a purification step of the tetraalkoxyborate salt may be additionally included.

[0094] In one embodiment of the present invention, the purification step may include a step of drying the tetraalkoxyborate salt at a temperature of 0°C or higher and 200°C or lower under a vacuum environment.

[0095] For example, the temperature of the drying step above may be 0°C or higher and 200°C or lower, 0°C or higher and 25°C or lower, 25°C or higher and 100°C or lower, 100°C or higher and 150°C or lower, 150°C or higher and 200°C or lower, 10°C or higher and 30°C or lower, 80°C or higher and 120°C or lower, or 140°C or higher and 160°C or lower.

[0096] If the temperature of the drying step described above falls below the range of the present invention, the drying temperature may be too low, and there is a possibility that the alcohol may not be completely removed. In such cases, the residual alcohol of MB(OR)4 may increase, causing side reactions in subsequent processes or reducing the purity and yield of the final product. Additionally, the residual alcohol may reduce the stability of the product and increase the complexity of the purification process, thereby reducing process efficiency.

[0097] On the other hand, if the scope of the present invention is exceeded, there is a possibility that MB(OR)4 may undergo thermal decomposition due to excessive high temperatures. This can damage the chemical structure of the product and lead to the formation of byproducts, thereby reducing the purity and yield of the final product. Furthermore, unnecessary energy consumption increases process costs, and high-temperature environments can compromise process stability by reducing equipment durability.

[0098] In one embodiment of the present invention, the purification step may include a step of selectively dissolving the tetraalkoxyborate salt by adding tetrahydrofuran (THF) and then filtering out impurities.

[0099] In one embodiment of the present invention, the reducing agent used in the reduction reaction may be a single hydride reducing agent (Single Hydride Donor) comprising sodium hydride (NaH), lithium hydride (LiH), and potassium hydride (KH), and a multiple hydride reducing agent (Multiple Hydride Donor) comprising magnesium hydride (MgH2) and aluminum hydride (AlH3), or a combination thereof.

[0100] For example, the reducing agent used in the above reduction reaction may be sodium hydride (NaH), lithium hydride (LiH), potassium hydride (KH), or a combination thereof.

[0101] Preferably, the reducing agent used in the above reduction reaction may be sodium hydride (NaH).

[0102] Meanwhile, if the tetraalkoxyborate salt (MB(OR)4) or the reducing agent contains a metal other than sodium (Na), a metal exchange reaction may be additionally required to finally obtain NaBH4.

[0103] The above metal exchange reaction can be carried out by adding a sodium salt (e.g., NaCl, NaBr, NaI) to the solution after the above reduction reaction has been carried out.

[0104] In one embodiment of the present invention, in the NaBH4 generation step, the reaction temperature may be 200°C or higher and 400°C or lower.

[0105] For example, in the above NaBH4 generation step, the reaction temperature may be 200°C or higher and 400°C or lower, 200°C or higher and 230°C or lower, 230°C or higher and 250°C or lower, 250°C or higher and 270°C or lower, 270°C or higher and 300°C or lower, 300°C or higher and 400°C or lower, 220°C or higher and 240°C or lower, 240°C or higher and 260°C or lower, 260°C or higher and 280°C or lower, or 290°C or higher and 310°C or lower.

[0106] In the above NaBH4 generation step, if the reaction temperature falls below the range of the present invention, the reaction temperature may not be sufficiently high, and the reaction between MB(OR)4 and the reducing agent may not proceed completely. This inhibits the formation of NaBH4, potentially leading to a decrease in the yield and purity of the product. Furthermore, at low temperatures, the reaction rate slows down and the process time increases, which may reduce productivity. There is also an increased likelihood of unreacted material remaining, which may require an additional purification process in subsequent steps.

[0107] On the other hand, if the range exceeds the scope of the present invention, the reaction temperature may become excessively high, potentially leading to the thermal decomposition of NaBH4. This not only reduces the purity and yield of the product but also increases the likelihood of unexpected byproduct formation. Excessive temperatures increase energy consumption and place a heavy thermal load on the equipment, which can impair process stability.

[0108] In one embodiment of the present invention, in the NaBH4 generation step, the equivalent ratio of the tetraalkoxyborate salt to the reducing agent used in the reduction reaction (equivalent of tetraalkoxyborate salt : equivalent of reducing agent) may be 1:3 to 1:6.

[0109] For example, in the above NaBH4 generation step, the equivalent ratio of the tetraalkoxyborate salt to the reducing agent used in the reduction reaction (equivalent of tetraalkoxyborate salt : equivalent of reducing agent) may be 1:3 to 1:6, 1:3 to 1:4.4, 1:4.4 to 1:5.0, 1:5.0 to 1:6, 1:3.5 to 1:4.6, 1:4.6 to 1:5.2, or 1:5.2 to 1:5.8.

[0110]

[0111] In the above NaBH4 generation step, if the equivalent ratio of the tetraalkoxyborate salt to the reducing agent used in the reduction reaction (equivalent of tetraalkoxyborate salt : equivalent of reducing agent) falls below the range of the present invention, the supply of the reducing agent in the reaction mixture may be insufficient, and the reaction with MB(OR)4 may not proceed sufficiently. This may inhibit the formation of NaBH4 and potentially reduce the yield of the product. Additionally, unreacted MB(OR)4 may remain, causing side reactions in subsequent processes or requiring additional purification processes.

[0112] On the other hand, if the amount exceeds the scope of the present invention, an excessive amount of reducing agent may be supplied, which could dilute the reaction concentration within the reaction mixture. This may reduce the reaction rate, and the excessive reducing agent may lead to additional energy consumption and increased process costs. Furthermore, there is a possibility that the excessive reducing agent may cause side reactions or reduce the purity of the product.

[0113] In one embodiment of the present invention, the solution in which the NaBH4 generation step was performed may further include the step of treating the solution with an aqueous sodium hydroxide (NaOH) solution to remove the unreacted reducing agent, and dissolving the generated sodium borohydride (NaBH4) in the aqueous solution.

[0114] In one embodiment of the present invention, the method may further include a step of collecting the remaining amount of alcohol used in the MB(OR)4 generation step and recycling it in the MB(OR)4 generation step.

[0115] For example, methods for collecting the residual amount of the above alcohol may include using a reflux condenser, using a fractional distillation method, using a membrane, or using a vacuum evaporation method.

[0116] Recycling the captured alcohol mentioned above can increase resource utilization and reduce process costs. In addition, it can reduce the environmental burden by decreasing waste.

[0117] In one embodiment of the present invention, the method may further include the step of selectively dissolving and filtering the borate compound by adding tetrahydrofuran (THF) to the solution in which the MB(OR)4 generation step has been performed; and the step of recycling the borate compound recovered through the filtering to the MB(OR)4 generation step.

[0118] Due to the aforementioned additional steps, reaction efficiency can be increased and process costs reduced by selectively purifying and recycling borate compounds. Furthermore, the environmental burden can be reduced by minimizing waste.

[0119] In one embodiment of the present invention, the method may further include the step of adding water to the solution in which the NaBH4 generation step has been performed to convert the sodium alkoxide (NaOR) contained in the solution into sodium hydroxide and alcohol; the step of recovering the sodium hydroxide and recycling it in the borate compound generation step; and the step of recovering the alcohol and recycling it in the MB(OR)4 generation step.

[0120] Due to the aforementioned additional steps, reaction efficiency can be increased and process costs reduced by recovering and recycling sodium hydroxide and alcohol, respectively. Furthermore, the environmental burden can be reduced by minimizing waste.

[0121] In one embodiment of the present invention, the step of recovering the sodium hydroxide and recycling it in the step of generating the borate compound may further include the step of recovering the sodium hydroxide through distillation of a solvent.

[0122] For example, the distillation method of the above solvent may be simple distillation, fractional distillation, vacuum distillation, steam distillation, or azeotropic distillation.

[0123] In one embodiment of the present invention, the step of recovering the alcohol and recycling it in the MB(OR)4 generation step; may further include the step of recovering the alcohol through distillation.

[0124] For example, the distillation method of the above alcohol may be simple distillation, fractional distillation, vacuum distillation, steam distillation, or azeotropic distillation.

[0125] In one embodiment of the present invention, after the NaBH4 generation step, a purification step may be additionally included.

[0126] In one embodiment of the present invention, the solvent used in the purification step may be recovered through distillation and recycled in the purification step.

[0127] By recycling the aforementioned solvent, reaction efficiency can be increased and process costs reduced. In addition, the environmental burden can be reduced by decreasing waste.

[0128] In one embodiment of the present invention, the purification step; comprises (a) a step of lowering the viscosity of the solution in which the NaBH4 generation step has been performed by introducing a non-polar hydrocarbon solvent, filtering the solution, and then washing the filtered solid with the non-polar hydrocarbon solvent;

[0129] (b) a step of selectively dissolving the sodium borohydride (NaBH4) from the solid by introducing a polar basic solvent and proceeding with filtering; and,

[0130] It may include step (c) of introducing a polar organic solvent to precipitate the dissolved sodium borohydride (NaBH4).

[0131] In step (a) above, by utilizing a non-polar hydrocarbon solvent to lower the viscosity of the solution and wash the solid, the removal of impurities becomes easier and the efficiency of the subsequent process can be improved.

[0132] (b) In step (b), a polar basic solvent is used to selectively dissolve NaBH4, enabling precise separation and thereby improving the purity of the product.

[0133] Finally, in step (c), if NaBH4 is precipitated using a polar organic solvent, it can be stably obtained in a solid form, making it easy to handle the product and ensuring the stability of subsequent processes.

[0134] In one embodiment of the present invention, the non-polar hydrocarbon solvent may be methylcyclopentane, cyclohexane, cyclopentane, methylcyclohexane, hexane, pentane, isohexane, octane, toluene, xylene, or a combination thereof.

[0135] For example, the non-polar hydrocarbon solvent may be methylcyclopentane, cyclohexane, cyclopentane, or a combination thereof.

[0136] Meanwhile, the above-mentioned nonpolar hydrocarbon solvent may be methylcyclopentane.

[0137] In one embodiment of the present invention, the polar basic solvent may be pyridine, 4-methylpyridine, quinoline, 2,6-lutidine, triethylamine (TEA), N-methylpyrrolidone (NMP), diethylamine, dimethylformamide (DMF), dimethylacetamide (DMAc), 1-ethyl-3-methylimidazolium salt, or a combination thereof.

[0138] For example, the polar basic solvent may be pyridine, 4-methylpyridine, quinoline, or a combination thereof.

[0139] Meanwhile, the above polar basic solvent may be pyridine.

[0140] In one embodiment of the present invention, the polar organic solvent may be ether, tetrahydrofuran (THF), methyltetrahydrofuran (Methyl-THF), dioxane (1,4-Dioxane), diethyl ether, diisopropyl ether, ethylene glycol dimethyl ether (Diglyme), diethylene glycol diethyl ether (Diethylene Glycol Diethyl Ether), acetone, methyl isobutyl ketone (MIBK), or a combination thereof.

[0141] For example, the polar organic solvent may be ether, tetrahydrofuran (THF), methyltetrahydrofuran (Methyl-THF), dioxane (1,4-Dioxane), diethyl ether, or a combination thereof.

[0142] Meanwhile, the above polar organic solvent may be an ether.

[0143] Looking at the schematic diagram in Fig. 3, the borate compound generation step, MB(OR)4 generation step, and NaBH4 generation step of the present invention, along with the process of recycling unreacted materials, by-products, and solvents in the present invention, can be seen.

[0144] First, NaBO2, an unreacted product from the MB(OR)4 generation step, can be recovered and recycled to the same step. Additionally, NaOCH3, a byproduct of the NaBH4 generation step, can be hydrolyzed to convert it into NaOH and CH3OH, which can then be recycled to the borate compound generation step and the MB(OR)4 generation step, respectively. Furthermore, the (purification) solvents used to obtain NaBH4 in solid form after the NaBH4 generation step reaction can also be recycled to the same step.

[0145] In one embodiment of the present invention, in the hydrated sodium metaborate (NaBO2·xH2O) produced through the borate compound production step, x may be 0.4 or more and 1.5 or less.

[0146] For example, in the above hydrated sodium metaborate (NaBO2·xH2O), x may be 0.4 or more and 1.5 or less, 0.4 or more and 0.59 or less, 0.59 or more and 1.5 or less, 0.45 or more and 0.7 or less, 0.5 or more and 0.8 or less, 0.55 or more and 1.0 or less, 0.6 or more and 1.2 or less, or 0.65 or more and 1.4 or less.

[0147] If the above x value exceeds the range of the present invention, unnecessary by-products may be formed during the reaction process, and there is a possibility that the purity of the product NaBH4 may be reduced. Furthermore, excessive moisture content increases energy consumption and may raise process costs by requiring an additional dehydration process. This may lead to a decrease in the efficiency and economic viability of the overall process.

[0148] In one embodiment of the present invention, the conversion rate of the borate compound generation step reaction may be 95% or more and 100% or less.

[0149] For example, the conversion rate of the borate compound generation step reaction may be 95% or more and 100% or less, 96% or more and 100% or less, 97% or more and 100% or less, 98% or more and 100% or less, 99% or more and 100% or less, or 99.5% or more and 100% or less.

[0150] If the conversion rate of the reaction in the borate compound generation step falls below the range of the present invention, the reaction does not proceed sufficiently, increasing the likelihood of residual unreacted material. This can lower the purity of the final product, NaBH4, and the accumulation of unreacted material may require additional work in subsequent purification processes. Furthermore, residual unreacted material may impede process efficiency by causing side reactions or increasing by-products.

[0151] In one embodiment of the present invention, the yield of the borate compound generation step reaction, which includes the step of recycling the recovered sodium hydroxide, may be 80% or more and 95% or less.

[0152] For example, the yield of the above reaction may be 80% or more and 95% or less, 80% or more and 87.5% or less, 87.5% or more and 95% or less, 81% or more and 95% or less, 82% or more and 94% or less, 83% or more and 93% or less, 84% or more and 92% or less, 85% or more and 91% or less, or 86% or more and 90% or less.

[0153] If the yield of the above reaction falls below the range of the present invention, the conversion of the reaction intermediate becomes incomplete, resulting in the retention of unreacted materials and byproducts, and a decrease in the production volume of the product NaBH4, which may lead to a decline in process efficiency and economic feasibility. Furthermore, it may become difficult to stably produce high-purity NaBH4.

[0154] In one embodiment of the present invention, the conversion rate of the MB(OR)4 generation step reaction may be 90% or more and 98% or less.

[0155] For example, the conversion rate of the above MB(OR)4 generation step reaction may be 90% or more and 98% or less, 90% or more and 95.1% or less, 95.1% or more and 98% or less, 91% or more and 98% or less, 92% or more and 97% or less, or 93% or more and 96% or less.

[0156] If the conversion rate of the reaction in the MB(OR)4 generation step falls below the range specified in the present invention, the reaction may not proceed sufficiently, increasing the likelihood of residual unreacted material. This can lower the purity of the final product, NaBH4, and the accumulation of unreacted material may necessitate additional work in subsequent purification processes. Furthermore, residual unreacted material may impede process efficiency by causing side reactions or increasing by-products.

[0157] In one embodiment of the present invention, the yield of the reaction in the NaBH4 generation step may be 80% or more and 95% or less.

[0158] For example, the yield of the above NaBH4 generation step reaction may be 80% or more and 95% or less, 80% or more and 83.5% or less, 83.5% or more and 90.9% or less, 90.9% or more and 95% or less, 81% or more and 94% or less, 82% or more and 93% or less, 83% or more and 92% or less, 84% or more and 91% or less, or 85% or more and 90% or less.

[0159] If the yield of the above-mentioned NaBH4 generation step reaction falls below the range of the present invention, the reaction does not proceed sufficiently, resulting in a decrease in the production volume of the product and the retention of unreacted materials and by-products, which may lower the purity of the product. This necessitates additional work during the purification process, which increases process costs and can reduce the economic feasibility of the manufacturing process.

[0160] In one embodiment of the present invention, the purity of the sodium borohydride (NaBH4) produced after the NaBH4 production step reaction may be 90% or more and 98% or less.

[0161] For example, the purity of the sodium borohydride (NaBH4) may be 90% or more and 98% or less, 90% or more and 96% or less, 96% or more and 98% or less, 91% or more and 98% or less, 92% or more and 97% or less, 93% or more and 96.5% or less, 94% or more and 96% or less, or 95% or more and 96% or less.

[0162] If the purity of the above sodium borohydride (NaBH4) falls below the range of the present invention, residual impurities may be contained in the NaBH4, which may degrade the quality and performance of the product. This may cause side reactions and increase process costs due to additional purification work, thereby impairing the economic efficiency and stability of the manufacturing process.

[0163] In one embodiment of the present invention, the total yield of the reaction in which the borate compound generation step; the MB(OR)4 generation step; and the NaBH4 generation step are performed continuously in a single reactor may be 70% or more and 80% or less.

[0164] For example, the total yield of the reaction performed continuously in the single reactor may be 70% or more and 80% or less, 70% or more and 74% or less, 74% or more and 80% or less, 71% or more and 79% or less, 72% or more and 78% or less, 73% or more and 77% or less, 73.5% or more and 76.5% or less, or 73.8% or more and 75.5% or less.

[0165] If the total yield of a reaction continuously performed in the single reactor described above falls below the range of the present invention, the reaction may not proceed sufficiently, resulting in a decrease in the production volume of the product and a reduction in the purity of the product due to the presence of unreacted materials and by-products. This may necessitate additional work during the purification process, thereby increasing process costs and reducing the economic feasibility of the manufacturing process.

[0166] In one embodiment of the present invention, the borate compound generation step; the MB(OR)4 generation step; and the NaBH4 generation step are performed continuously in a single reactor, and the purity of the sodium borohydride (NaBH4) produced may be 90% or more and 99.5% or less.

[0167] For example, the purity of the sodium borohydride (NaBH4) may be 90% or more and 99.5% or less, 90% or more and 98.9% or less, 98.9% or more and 99.5% or less, 91% or more and 99.5% or less, 92% or more and 99% or less, 93% or more and 98.9% or less, 94% or more and 98.9% or less, or 95% or more and 98.9% or less.

[0168] If the purity of the above sodium borohydride (NaBH4) falls below the range of the present invention, residual impurities may be contained in the NaBH4, which may degrade the quality and performance of the product. This may cause side reactions and increase process costs due to additional purification work, thereby impairing the economic efficiency and stability of the manufacturing process.

[0169] The present invention will be explained in more detail below through examples. However, the following examples are intended to explain the invention more specifically, and the scope of the invention is not limited by the following examples.

[0170]

[0171] [Preparation Example 1]

[0172] [Borate Compound Formation Stage Reaction Process]

[0173] 749 g (0.244 mol) of Na2B4O and 19.5 g (0.487 mol) of NaOH were added to 150 mL of H2O and heated to 90°C to completely dissolve the reactants. Then, the reaction was carried out at 90°C for 2 hours and 30 minutes with the stirring speed set to 500 RPM.

[0174] Additionally, this reaction can be carried out using Na2B4O7·10H2O instead of Na2B4O7. In this case, the amount of additional H2O required for the reaction must be adjusted considering the moisture contained in Na2B4O7·10H2O.

[0175] After the reaction was complete, the product was dried under a low pressure of 300 mTorr to obtain NaBO2·xH2O (x = 0–4). Subsequently, the moisture content of NaBO2 was removed by drying at 350°C for 2 hours. It was confirmed that the H2O removal rate was over 95% through the weight change before and after drying.

[0176] The reaction equation of the above reaction process is as shown in Reaction Equation 1 below.

[0177] [Reaction Equation 1] Na2B4O7 + 2NaOH → 4NaBO2 + H2O

[0178]

[0179] [Reaction result of the borate compound formation step]

[0180] After the reaction, the reaction status and conversion rate of the product were evaluated by ¹¹B-NMR analysis. The analysis was performed using D2O as the solvent, with 32 scans and an analysis temperature of 25°C. 11 The results of the B-NMR analysis are shown in Figure 4.

[0181] Figures 4(a) and 4(b) are the results of verifying the reference signals of Na2B4O7 and NaBO2, respectively.

[0182] In Figure 4(c), the analysis results of the product after the reaction can be seen, and it was confirmed that the Na2B4O7 peak (7 ppm) disappeared and the NaBO2 peak (1 ppm) was detected. Accordingly, the Na2B4O7 → NaBO2 conversion rate was estimated to be 100%.

[0183] In addition, the total weight of the generated NaBO2 is 74.65g, and considering the theoretical mass of anhydrous NaBO2 (64.09g) and the moisture content (10.56g) in the product, the x value of the hydrate was calculated and found to be x = 0.59.

[0184]

[0185] [Preparation Example 2]

[0186] [MB(OR)4 generation step reaction process]

[0187] 25g of NaBO was added to 150mL of CH3OH, and the reaction was carried out for 4 hours under reflux conditions at 150°C. Reflux was performed by using a reflux condenser to condense CH3OH vapor and return it to the reaction system, thereby maintaining the concentration of CH3OH within the reaction system and preventing heat loss. The internal temperature of the reactor was maintained constant at 150°C, and an oil bath was used outside the reactor to increase heat transfer efficiency. Cooling water was circulated inside the reflux condenser to maximize condensation efficiency.

[0188] During reflux, a 3Å molecular sieve was installed between the reactor and the cooler to remove H2O. Meanwhile, instead of a molecular sieve, a membrane capable of separating CH3OH and H2O can also be used.

[0189] After the reaction, CH3OH was removed from the product at a low pressure of 300 mTorr to obtain NaB(OCH3)4.

[0190] The reaction equation for the above reaction process is as shown in Reaction Equation 2 below.

[0191] [Reaction Equation 2] NaBO2 + 4CH3OH → NaB(OCH3)4 + 2H2O

[0192]

[0193] [MB(OR)4 generation step reaction result]

[0194] After the reaction, the progress of the reaction was confirmed through ¹H-NMR analysis. For the NMR analysis, tetrahydrofuran-d was used as the solvent, and 4-methyl biphenyl was set as the internal standard.

[0195] The results of the ¹H-NMR analysis are shown in Figure 5.

[0196] In Fig. 5(a),¹H-NMR analysis results showed a CH3OH peak, confirming the presence of a trace amount of CH3OH in the crystal.

[0197] In addition, the reaction progress (NaBO2→NaB(OCH3)4 conversion rate) calculated by comparing the peak area with the internal standard substance in Fig. 5(b) was calculated to be 95.1%.

[0198]

[0199] [Preparation Example 3]

[0200] [NaBH4 formation step reaction process]

[0201] 49.79 g of the reactant NaB(OCH3) and 12.4 g of 60% purity NaH were placed in 70 mL of mineral oil in a 500 mL round-bottom flask (RBF), and the reaction was carried out for 3 hours after raising the temperature to 230-300°C while mechanically stirring. At this time, it is also possible to use a 90% purity product of NaH. In addition, to improve the NaBH4 yield in the above reaction, it is possible to increase the equivalent amount of NaH. Furthermore, to improve the NaBH4 yield in the above reaction, it is also possible to proceed with the reaction after applying the NaB(OCH3)4 purification method beforehand.

[0202] The reaction equation of the above reaction process is as shown in Reaction Equation 3 below.

[0203] [Reaction Equation 3] NaB(OCH3)4(s) + 4NaH → NaBH4(s) + 4NaOCH3(s)

[0204]

[0205] [Preparation Example 4]

[0206] [Reaction process for obtaining NaBH4 in solid form]

[0207] In order to utilize the NaBH4 synthesized in the reaction process of Preparation Example 3 above, it is necessary to obtain NaBH4 in a solid form. Therefore, 100 ml of methylcyclopentane (MCP) was added to the reactor in which the reaction process of Preparation Example 3 was carried out and stirred to lower the viscosity of the solution. After filtering the solution, the solid remaining on top was thoroughly washed with methylcyclopentane (MCP).

[0208] Meanwhile, it is possible to separate and recycle methylcyclopentane (MCP) through distillation of the mineral oil / methylcyclopentane (MCP) mixed solution after the above filtering process.

[0209] Subsequently, 40 ml of pyridine was added to the washed solid to selectively dissolve NaBH4, and then filtering was performed. This process was repeated three times to obtain the maximum amount of NaBH4. After filtering, the pyridine solution was concentrated, and ether was added to precipitate NaBH4.

[0210] Meanwhile, pyridine used during the concentration process can be captured and recovered, allowing it to be recycled in the purification / harvesting process in subsequent batches.

[0211] Afterwards, the precipitate was filtered and then further washed with ether.

[0212] Meanwhile, it is possible to collect the above ether, purify it, and recycle it.

[0213]

[0214] [Reaction result of obtaining NaBH4 in solid form]

[0215] Subsequently, the precipitate was vacuum-dried and weighed to determine the yield, and the purity was confirmed by potentiometric titration after dissolving the precipitate in an aqueous NaOH solution.

[0216] The yield of NaBH4 can be calculated by comparing the theoretically possible amount with the actual amount produced. In an experiment using 49.79 g of the starting material NaB(OCH3)4, the theoretically possible amount of NaBH4 was measured to be approximately 2.35 g, and the actual amount of NaBH4 produced was measured to be approximately 1.94 g, and accordingly, the yield was calculated to be 82.7%.

[0217] The purity of NaBH4 can be calculated by comparing the weight of the total precipitated sample with the actual content of NaBH4. In the experiment, the weight of the total precipitated sample was measured to be approximately 2.02 g, and the actual content of NaBH4 was measured to be approximately 1.94 g; accordingly, the purity was calculated to be 96%.

[0218]

[0219] [Preparation Example 5]

[0220] [Continuous process in a single reactor]

[0221] NaBO2 synthesis was carried out in the same manner as the reaction process of the borate compound generation step of Preparation Example 1, and after the reaction, H2O removal and NaBO2 drying were carried out at a low pressure of 300 mTorr.

[0222] Subsequently, 150 mL of CH3OH was added to the same reactor in which the above reaction was carried out, and a reflux condenser and a 3 Å molecular sieve were connected to synthesize NaB(OCH3)4 in the same manner as the reaction process of the MB(OR)4 generation step of Preparation Example 2. After the reaction, CH3OH was removed and NaB(OCH3)4 was dried at a low pressure of 300 mTorr.

[0223] Subsequently, 70 mL of mineral oil and 60% pure NaH were added to the same reactor. Synthesis was carried out in the same manner as the reaction process for the NaBH4 generation step of Preparation Example 3, except that the reaction temperature was set to 300°C and 5 equivalents of NaH were used. After the reaction proceeded, the reaction process for obtaining the solid form of NaBH4 of Preparation Example 4 was carried out to obtain solid NaBH4.

[0224] Afterwards, the purity and yield of the reaction were measured using the NaBH4 purity and yield measurement method of Preparation Example 4.

[0225] The yield of NaBH4 can be calculated by comparing the theoretically possible amount with the actual amount produced. Based on 49.79 g of NaB(OCH3) used as the starting material, the theoretically possible amount of NaBH4 was approximately 2.35 g. However, the actual amount of NaBH4 produced was measured to be approximately 1.74 g, and based on this, the yield was calculated to be 74%.

[0226] The purity of NaBH4 can be calculated by comparing the weight of the total precipitated sample with the actual content of NaBH4. In the experiment, the weight of the total sample was measured to be approximately 1.76 g, of which the content of NaBH4 was approximately 1.74 g. Based on this, the purity was calculated to be 98.9%.

[0227]

[0228] [Example 1]

[0229] [Measurement of Yield Change by Reaction Temperature in the NaBH4 Formation Step]

[0230] In the reaction process of the NaBH4 generation step of Preparation Example 3 above, the experiment was conducted with the other conditions remaining the same, but the reaction temperature was changed to 230°C, 250°C, 270°C, and 300°C, respectively, and then the reaction process of Preparation Example 4 above was carried out, and the yield of each reaction was measured using the NaBH4 yield measurement method of Preparation Example 4 above.

[0231] Figure 6 is a graph showing the change in yield when the reaction temperature is changed to 230°C, 250°C, 270°C, and 300°C, respectively, during the NaBH4 generation step reaction process. In the graph, the horizontal axis represents the reaction temperature, and the vertical axis represents the measured yield.

[0232] Looking at the results in Figure 6, the yield was measured to be 13.9% at a reaction temperature of 230°C, 25.9% at 250°C, 44.3% at 270°C, and 70.5% at 300°C. Therefore, it was confirmed that the yield improved with increasing temperature in the range of 230°C to 300°C.

[0233] When the reaction temperature increases from 230℃ to 300℃, the reaction rate and efficiency of NaB(OCH3)4 and NaH are improved, and it is interpreted that the reactivity of NaB(OCH3)4 increases at high temperatures. Accordingly, as the activity of NaH increases, the formation of NaBH4 becomes more favorable, and it can be seen that the yield tends to increase.

[0234]

[0235] [Example 2]

[0236] [Measurement of Yield Change by Reducing Agent Equivalent in the NaBH4 Formation Step]

[0237] In the reaction process of the NaBH4 generation step of Preparation Example 3 above, the experiment was conducted by changing the equivalent ratio of NaB(OCH3)4 to the reducing agent (NaH) (equivalent of NaB(OCH3)4 : equivalent of the reducing agent (NaH)) to 1:4.4 and 1:5.0, respectively, while keeping other conditions the same, and the yield of each reaction was measured through the yield measurement method of the reaction result of the NaBH4 generation step of Preparation Example 3 above.

[0238] Figure 7 is a graph showing the change in yield when the equivalent ratio of NaB(OCH3)4 and the reducing agent (NaH) (equivalent of NaB(OCH3)4 : equivalent of the reducing agent (NaH)) is changed to 1:4.4 and 1:5.0, respectively, during the reaction process of the NaBH4 generation step.

[0239] In the graph, the horizontal axis represents the number of moles of reducing agent (NaH) per 41 moles of NaB(OCH3), and the vertical axis represents the measured yield.

[0240] Looking at the results in Figure 7, when the equivalent ratio of NaB(OCH3)4 to the reducing agent (NaH) was 1:4.4, the yield was measured to be 70.5%, and when the equivalent ratio was 1:5.0, the yield was measured to be 90.9%.

[0241] Therefore, it was confirmed that the yield improved when the equivalent amount of the reducing agent increased.

[0242] Using NaH in excess equivalents increases the likelihood of reaction with NaB(OCH3)4 and maximizes the reaction of unreacted substances, thereby improving reaction efficiency. Furthermore, the excess NaH suppresses side reactions and provides an environment that promotes the formation of NaBH4. It can also react with residual CH3OH within the NaB(OCH3)4 crystals, preventing reverse reactions caused by CH3OH. Consequently, it can be confirmed that the yield of NaBH4 increases further.

[0243]

[0244] [Example 3]

[0245] [Measurement of Yield Changes by NaB(OCH3)4 Purification Method]

[0246] A process of purifying NaB(OCH3)4 was added between the reaction process of the MB(OR)4 generation step of Preparation Example 2 and the reaction process of the NaBH4 generation step of Preparation Example 3 in the following manner.

[0247] To remove CH3OH from the crystals of the generated NaB(OCH3)4, a vacuum drying method was used by changing the temperature conditions to room temperature, 100°C, and 150°C, respectively, and a purification method was used by selectively dissolving NaB(OCH3)4 with tetrahydrofuran (THF) to remove unreacted NaBO2 and CH3OH.

[0248] Figure 8 is a graph showing the change in NaBH4 yield according to the difference in purification method when a method for purifying NaB(OCH3)4 is added between the MB(OR)4 generation step and the NaBH4 generation step. In the graph, the horizontal axis represents the purification method of NaB(OCH3)4. Starting from the left of the horizontal axis, the methods shown are drying at room temperature, drying at 100°C, drying at 150°C, and extraction using tetrahydrofuran (THF). The vertical axis of the graph represents the measured yield.

[0249] Looking at the results in Figure 8, the yield was measured to be 70.5% when vacuum dried at room temperature, 75.3% when vacuum dried at 100°C, 74.5% when vacuum dried at 150°C, and 83.5% when using the purification method with tetrahydrofuran.

[0250] The yield of room temperature vacuum drying was the lowest at about 70.5%, which appears to be because CH3OH was not sufficiently removed, causing a reverse reaction and lowering the purity of NaB(OCH3)4.

[0251] In vacuum drying at 150°C, the yield increased to about 74.5%, which may be because CH3OH was removed at higher temperatures but some CH3OH still remained.

[0252] Vacuum drying at 100°C recorded the highest yield among vacuum drying methods, with a yield of approximately 75.3%. This appears to be the result of a balance between the removal of CH3OH and the structural stability of NaB(OCH3)4.

[0253] Meanwhile, the tetrahydrofuran (THF) extraction method showed the highest yield of approximately 83.5%, which is attributed to the fact that tetrahydrofuran (THF) selectively dissolved NaB(OCH3)4 and effectively removed CH3OH and unreacted NaBO2, thereby significantly improving the purity of NaB(OCH3)4.

[0254] Consequently, among vacuum drying methods, the 100°C condition is the most effective, but to optimize the NaBH4 yield, it is considered most suitable to additionally apply the tetrahydrofuran (THF) extraction method.

[0255]

[0256] [Example 4]

[0257] [Recycling of solvents used in purification to obtain solid form of NaBH4]

[0258] An experiment was conducted to determine whether methylcyclopentane (MCP), pyridine, and ether, which were used in the reaction process to obtain the solid form of NaBH4 in Preparation Example 3 above, could be recycled.

[0259] Methylcyclopentane (MCP) was separated from the mineral oil / methylcyclopentane (MCP) mixed solution used in the filtering process through distillation.

[0260] In addition, pyridine used in the concentration process was captured and recovered.

[0261] Then, the ether used to precipitate NaBH4 was collected, purified, and recovered.

[0262] 1H-NMR analysis was performed on each of the above-mentioned recovered solvents using acetonitrile-d as the solvent.

[0263] Figure 9(a) shows the result of confirming the reference signal of methylcyclopentane (MCP), and Figure 9(b) shows the analysis result of the recovered methylcyclopentane (MCP).

[0264] Figure 10(a) shows the result of confirming the reference signal of pyridine, and Figure 10(b) shows the analysis result of the recovered pyridine.

[0265] Figure 11(a) shows the result of confirming the reference signal of the ether, and Figure 11(b) shows the result of analyzing the recovered ether.

[0266] Looking at the results in Figures 9, 10, and 11, it was confirmed that the recovered methylcyclopentane, pyridine, and ether could be recycled as no major impurities were observed when compared to the reference signal.

[0267]

[0268] [Example 5]

[0269] [Recycling of unreacted materials from the MB(OR)4 generation step]

[0270] After the reaction of the MB(OR)4 generation step of Preparation Example 2, 410g of NaB(OCH3) was selectively dissolved using tetrahydrofuran (THF) and filtered. Subsequently, the solid remaining in the filter was dried at a low pressure of 300 mTorr and recovered. The amount of recovered solid was 0.58g.

[0271] FIG. 12 shows a method for testing whether unreacted material from the MB(OR)4 generation step can be recovered and recycled by using D2O as a solvent for the solid recovered through filtering in the MB(OR)4 generation step. 11 This is the result of measuring B-NMR.

[0272] Figure 12(a) shows the result of confirming the reference signal of NaBO2, and Figure 12(b) shows the analysis result of the recovered solid.

[0273] Looking at the results in Fig. 12, it was confirmed that a peak around 1 ppm, identical to the reference signal of NaBO2, was detected in the recovered solid. Therefore, since the recovered solid is NaBO2, the unreacted material from the above step, it was confirmed that it can be recycled in the same step later.

[0274]

[0275] [Example 6]

[0276] [Recycling of by-products from the NaBH4 generation stage]

[0277] In order to recycle NaOCH3, which is a byproduct of the NaBH4 generation step of Preparation Example 3 above, a reaction as shown in Reaction Scheme 4 below can be carried out.

[0278] [Reaction Equation 4] NaOCH3 + H2O → NaOH + CH3OH

[0279] According to the above reaction scheme 4, the following experiment was conducted to determine whether NaOCH3 can be recycled in the borate compound generation step.

[0280] 7.24 g (0.019 mol) of Na2B4O7·10H2O and 2.05 g (0.038 mol) of NaOCH3 were added to an excess of H2O and the reactants were dissolved while heating to 90 °C. After the reactants were completely dissolved, the reaction was carried out at 90 °C for 2 hours and 30 minutes. The reaction scheme for the above reaction is as shown in Reaction Scheme 5 below.

[0281] [Reaction Equation 5] Na2B4O7·10H2O + 2NaOCH3 → 4NaBO2·4H2O + 2CH3OH + 5H2O

[0282] After the reaction, water and CH3OH were removed at a low pressure of 300 mTorr to obtain NaBO2·xH2O (x= 0~4).

[0283] 150 mL of CH3OH was added to the same reactor in which the above process was carried out, and a reflux condenser and a 3 Å molecular sieve were connected to synthesize NaB(OCH3)4 in the same manner as the reaction process of the MB(OR)4 generation step of Preparation Example 2. After the reaction, CH3OH was removed and NaB(OCH3)4 was dried at a low pressure of 300 mTorr.

[0284] Using the fact that the molar mass of NaOCH3 is 54.03 g / mol and the molar mass of NaB(OCH3)4 is 157.94 g / mol, the theoretically possible amount of NaB(OCH3)4 was calculated to be approximately 11.98 g. However, the actual amount of NaB(OCH3)4 was measured to be approximately 10.49 g, and accordingly, the yield was confirmed to be 87.5%.

[0285] Figure 13 shows the results of 1H-NMR analysis of the product using acetonitrile-d as a solvent, after continuously carrying out the borate compound generation step and the MB(OR)4 generation step in the same reactor by introducing NaOCH3 instead of NaOH in the borate compound generation step to determine whether NaOCH3, a byproduct of the NaBH4 generation step, is recyclable.

[0286] Looking at the results in Figure 13, although trace amounts of methanol are present in the crystal, a peak of sodium tetramethoxyborate (NaB(OCH3)4) is also observed, confirming that NaOCH3, a byproduct of the NaBH4 synthesis process, can be converted into NaOH and reused in the process.

[0287]

[0288] The scope of the present invention is defined by the claims set forth below rather than by the detailed description above, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

[0289] The NaBH4 manufacturing method according to the present invention can continuously perform the borate compound generation step, the MB(OR)4 generation step, and the NaBH4 generation step in a single reactor, thereby improving process efficiency and economic feasibility.

[0290] Furthermore, the method for manufacturing NaBH4 according to the present invention can reduce resource waste and minimize waste generation by recycling the solvent used in the process and the unreacted materials and by-products of the reaction, thereby alleviating the environmental burden. Through this, a sustainable manufacturing process can be realized, and eco-friendly effects can be provided.

[0291] In addition, the method for manufacturing NaBH4 according to the present invention can further improve the economic efficiency of the manufacturing process by providing the possibility to selectively use an inexpensive reducing agent in addition to NaH through the optimization of reaction conditions.

[0292]

[0293] In addition, the NaBH4 manufacturing method according to the present invention provides a technical basis for improving the yield and purity of the generated NaBH4 by optimizing the purification method and reaction conditions, thereby enabling the stable production of high-quality products.

Claims

1. An MB(OR)4 generation step of reacting a borate compound with an alcohol to produce a tetraalkoxyborate salt (MB(OR)4); and, A NaBH4 generation step that converts the above tetraalkoxyborate salt (MB(OR)4) into sodium borohydride (NaBH4) through a reduction reaction; Includes, The above M is an alkali metal cation, and The above R is a hydrocarbon group having 1 or more and 10 or fewer carbon atoms, Method for manufacturing NaBH4.

2. In Paragraph 1, Prior to the above MB(OR)4 generation step, A borate compound generation step in which borax (Na2B4O7) and sodium hydroxide (NaOH) react to produce sodium metaborate (NaBO2); additionally including, Method for manufacturing NaBH4.

3. In Paragraph 2, The above borate compound generation step; the above MB(OR)4 generation step; and the above NaBH4 generation step are performed continuously in a single reactor, Method for manufacturing NaBH4.

4. In Paragraph 1, The above tetraalkoxyborate salt exists in a solid state at a temperature range of 100°C to 300°C and at atmospheric pressure, Method for manufacturing NaBH4.

5. In Paragraph 1, A moisture absorbent is additionally used in the above MB(OR)4 generation step, Method for manufacturing NaBH4.

6. In Paragraph 1, Between the above MB(OR)4 generation step and the above NaBH4 generation step, A purification step of the tetraalkoxyborate salt described above; further comprising, Method for manufacturing NaBH4.

7. In Paragraph 6, The above purification step is, A drying step of the above tetraalkoxyborate salt at a temperature of 0°C or higher and 200°C or lower under a vacuum environment; comprising Method for manufacturing NaBH4.

8. In Paragraph 6, The above purification step is, A step comprising: adding tetrahydrofuran (THF) to selectively dissolve the tetraalkoxyborate salt, and then filtering out impurities; Method for manufacturing NaBH4.

9. In Paragraph 1, In the above NaBH4 generation step, The reaction temperature is between 200°C and 400°C, Method for manufacturing NaBH4.

10. In Paragraph 1, In the above NaBH4 generation step, The equivalent ratio of the tetraalkoxyborate salt to the reducing agent (equivalent of tetraalkoxyborate salt : equivalent of reducing agent) is 1:3 to 1:6, Method for manufacturing NaBH4.

11. In Paragraph 1, By collecting the remaining amount of alcohol used in the above MB(OR)4 generation step, The above MB(OR)4 generation step additionally comprising a recycling step; Method for manufacturing NaBH4.

12. In Paragraph 1, In the solution where the above MB(OR)4 generation step was performed, A step of selectively dissolving and filtering the borate compound by adding tetrahydrofuran (THF); and, A step of recycling the borate compound recovered through the above filtering into the MB(OR)4 generation step; further comprising Method for manufacturing NaBH4.

13. In Paragraph 2, A step of adding water to the solution in which the above NaBH4 generation step has been performed to convert the sodium alkoxide (NaOR) contained in the solution into sodium hydroxide and alcohol; A step of recovering the sodium hydroxide and recycling it in the borate compound generation step; and A step of recovering the above alcohol and recycling it in the above MB(OR)4 generation step; further comprising Method for manufacturing NaBH4.

14. In Paragraph 1, After the above NaBH4 generation step, a purification step; additionally comprising Method for manufacturing NaBH4.

15. In Paragraph 14, The solvent used in the above purification step is recovered through distillation, The above purification step; additionally comprising a recycling step; Method for manufacturing NaBH4.

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