Process for the production of high-purity boron trifluoride

Abstract

The invention relates to a process for the continuous production of gaseous boron trifluoride comprising the steps of: a) Supplying a composition A comprising boron trifluoride (BF3) and optionally one or more additional volatile compounds F1; b) In a first reactor R1, continuous introduction of: - a sulfuric acid solution and a solution B comprising oleum and additional volatile compounds F2 to form a solution C; - composition A; to form: - a liquid phase L1 comprising oleum, sulfuric acid and BF3 and - a gaseous phase G1 comprising said additional volatile compounds F1 and F2; c) Continuous removal of the gaseous phase G1 comprising said additional volatile compounds F1 and F2, preferably by vacuum;d) Continuous introduction of the liquid phase L1 into a second reactor R2 and continuous introduction into reactor R2 of a composition D1 of water or an aqueous composition of boron trifluoride D2 or a composition D3 comprising hydrated boron trifluoride, referred to as boron trifluoride hydrates, compositions D1 and D2 not containing any additional compound F1 to produce a gaseous phase E of boron trifluoride and a liquid phase L2. No figure for the abstract.

Description

Title of the invention: Process for the production of high-purity boron trifluoride Scope of the invention

[0001] The present invention relates to a process for the production of boron trifluoride. In particular, the present invention relates to a continuous process for the production of high-purity boron trifluoride. Technical background

[0002] Boron trifluoride (BF3) is a gas primarily used in industry as a catalyst in a wide range of reactions: polymerization, esterification, alkylation, isomerization, or for use in electronic transistors as a raw material in the manufacture of boranes BH3, B2H6, etc. Gaseous and anhydrous boron trifluoride is generally obtained by reacting liquid anhydrous hydrofluoric acid with boric acid dissolved in sulfuric acid and by the addition of oleum. Gaseous boron trifluoride is also obtained by treating a concentrated aqueous solution of BF3 hydrate with sulfuric acid or sulfuric acid mixed with oleum. However, the presence of impurities in gaseous and anhydrous boron trifluoride poses problems for certain applications requiring a high-purity grade.

[0003] Reents, Anal. Chem. 1986, 58, 2797-2800 describes the impurities that are generally present in boron trifluoride. These include BF2OH, HCl, HF, N2, O2, F2, CO2, and SiF4. Some of these impurities are generated during the BF3 manufacturing process or originate from the raw materials used or from residues of some of these raw materials. The levels of the impurities mentioned can range from a few hundred ppm to 1.5%. Such levels are unacceptable in the field of electronics. Indeed, boron trifluoride is also used in the manufacturing processes of electronic microprocessors.

[0004] Some prior art documents describe purification techniques for partially removing some of these impurities. A purification process for BF3 using H2O2 and water in sulfuric acid to remove SO2 and SO3 is known from JP59050018. A process for removing sulfur dioxide from BF3 using activated carbon at very low temperature is also known from US 3,625,651 and FR 2,003,557; however, this process tends to contaminate the gaseous BF3 with nitrogen used to desorb the SO2-saturated activated carbon column. A process using treatment with H2O2 and air treatment to purify gaseous BF3, which is then recycled back into sulfuric acid by washing, is also known from EP 0 922 672. of the airflow and BF3 so as to recycle the boron fluoride sorting to the production of compressed BF3 gas.

[0005] Despite these purification processes applicable to technical grade boron trifluoride, there remains a need for a process to produce highly pure boron trifluoride that removes volatile impurities such as those mentioned above, particularly SiF4 or hydrogen fluoride. Furthermore, there is also a need for such a process using oleum that removes SO2 from the oleum without the use of activated carbon (activated carbon being responsible for dust production). There is also a need for an efficient and easy-to-implement process for obtaining high-purity boron trifluoride. Finally, there is a need for such a process that can be easily integrated into existing technical grade BF3 production lines. Summary of the invention

[0006] The invention relates primarily to a continuous production process for gaseous boron trifluoride comprising the steps of:

[0007] a) Supply of a composition A comprising boron trifluoride (BF3) and optionally one or more additional volatile compounds Fl;

[0008] b) In a first RI reactor, continuous introduction:

[0009] - of a sulfuric acid solution and a solution B comprising oleum and additional volatile compounds F2 to form a solution C;

[0010] - of composition A;

[0011] to form:

[0012] - a liquid phase L1 comprising oleum, sulfuric acid and BF3 and

[0013] - a gaseous phase G1 comprising said additional volatile compounds Fl and F2;

[0014] c) Continuous removal of the gaseous phase G1 comprising said additional volatile compounds Fl and F2, preferably by depression;

[0015] d) Continuous introduction of the liquid phase L1 into a second reactor R2 and continuous introduction into reactor R2 of a composition DI of water or an aqueous composition of boron trifluoride D2 or a composition D3 comprising hydrated boron trifluoride, referred to as boron trifluoride hydrates, the compositions D1, D2 and D3 not containing any additional compound Fl to produce a gaseous phase E of boron trifluoride and a liquid phase L2.

[0016] In one embodiment, said gas stream E is recovered in a container.

[0017] Preferably, the content of boron trifluoride in said gas stream E is greater than 99.9% by volume on the basis of the total volume of the gas stream E.

[0018] In one embodiment, said composition A is a composition of BF3 comprising one or more additional volatile compounds Fl selected from the group consisting of H2O, N2, O2, CO2, SiF4, H2 and HCl.

[0019] In one embodiment, the boron trifluoride of composition A is gaseous BF3 BF3,xH2O with x = 0 optionally mixed with BF2OH, or a boron trifluoride hydrate BF3,xH2O with x varying between 0.5 and 4 or an aqueous solution of boron trifluoride BF3,xH2O with x greater than 4 or is obtained from the reaction between a boron compound selected from B(OH)3, B2O3 or HBO2 and a fluorinated compound selected by HF or HSO3F.

[0020] Preferably, said solution D1, D2 and D3 is free of N2, O2, CO2, SiF4, H2 and HCl.

[0021] Preferably, solution C has a sulfuric acid content greater than 100% by weight, advantageously greater than 101% by weight, preferably greater than 102% by weight, more preferably greater than 103% by weight, in particular greater than 104% by weight, more particularly greater than 105% by weight, more preferably greater than 106% by weight, preferably greater than 107% by weight, more preferably greater than 108% by weight, in particular greater than 109% by weight, more particularly greater than 110% by weight, preferably greater than 111% by weight, advantageously preferred greater than 112% by weight, preferably preferred greater than 113% by weight, more preferably preferred greater than 114% by weight.

[0022] In one embodiment, step b) is generally carried out at a temperature of 30°C to 120°C, preferably 45 to 120°C, preferably 70 to 120°C and even more preferably 80 to 110°C.

[0023] Preferably, the concentration of oleum in reactor RI is greater than that of reactor R2.

[0024] In one embodiment, the composition L2 from R2 is partly reintroduced into RI as a sulfuric acid solution. Description of the figures

[0025] [Fig. 1] schematically represents an installation for implementing the continuous boron trifluoride production process according to a particular embodiment of the present invention. Detailed description

[0026] The invention is now described in more detail and in a non-limiting manner in the following description.

[0027] The present invention relates to a process for the continuous production of gaseous boron trifluoride comprising the steps of:

[0028] a) Supply of a composition A comprising boron trifluoride (BF3) and optionally one or more additional volatile compounds Fl;

[0029] b) In a first RI reactor, continuous introduction:

[0030] - of a sulfuric acid solution and a solution B comprising oleum and additional volatile compounds F2 to form a solution C;

[0031] - of composition A;

[0032] to form:

[0033] - a liquid phase L1 comprising oleum, sulfuric acid and BF3 and

[0034] - a gaseous phase G1 comprising said additional volatile compounds Fl and F2;

[0035] c) Continuous removal of the gaseous phase G1 comprising said additional volatile compounds Fl and F2, preferably by depression;

[0036] d) Continuous introduction of the liquid phase L1 into a second reactor R2 and continuous introduction into reactor R2 of a composition DI of water or an aqueous composition of boron trifluoride D2 or a composition D3 comprising hydrated boron trifluoride, referred to as boron trifluoride hydrates, the compositions DI and D2 not containing any additional compound Fl to produce a gaseous phase E of boron trifluoride and a liquid phase L2.

[0037] The gas stream E of boron trifluoride obtained at the outlet of reactor R2 is thus of high purity.

[0038] According to a preferred embodiment, said gas stream E is recovered in a container.

[0039] According to a preferred embodiment, the content of boron trifluoride in said gas stream E is greater than 99.9% by volume on the basis of the total volume of the gas stream E. Step a)

[0040] The boron trifluoride contained in composition A can have different origins. The boron trifluoride can be gaseous BF3, BF3·xH2O with x = 0, impure or of technical grade. For example, the gaseous BF3 contained in composition A can be BF3 having a purity less than or equal to 99.5%, that is to say, the BF3 composition used to form composition A comprises at most 99.5% by weight of BF3 based on the total weight of said composition. The BF3 can optionally be mixed with BF2OH. The boron trifluoride contained in composition A may be a boron trifluoride hydrate, such as BF3,xH2O with x varying between 0.05 and 4, preferably between 0.5 and 4. The boron trifluoride contained in composition A may be produced by the reaction between a boron compound selected from B(OH)3, B2O3 or HBO2 and a fluorinated compound selected from HF or HSO3F.The boron trifluoride contained in composition A may be an aqueous solution of boron trifluoride BF3,xH2O with x greater than 4. Particularly preferred, the boron trifluoride of composition A is a boron fluoride trihydrate (BF3.3H2 O).

[0041] Boron trifluoride (BF3)2,H2O, BF3,H2O, BF3,1,5H2O, BF3,2H2O, BF3,3H2O is a liquid hydrate. Boron trifluoride, BF3,4H2O + 2H2O and BF3,4H2O + 5H2O is a liquid hydrate in aqueous solution.

[0042] Thus, the BF3 content in said composition A can be a few percent or more, preferably it is between 30% and 99.5% by weight based on the total weight of composition A. Preferably, the BF3 content in said composition A can be from 45% to 99.5% by weight based on the total weight of composition A.

[0043] As mentioned above, said composition A may or may not include, in addition to boron trifluoride, one or more additional volatile compound(s) Fl. Said one or more additional volatile compound(s) Fl is / are preferably selected from the group consisting of H2O, N2, O2, CO2, SiF4, H2, and HCl. It is not excluded that composition A may include gaseous compounds having a boiling point below 0°C other than those mentioned above. In such a case, these compounds (such as argon or helium) would be found in the gaseous phase Gl.

[0044] Preferably, composition A comprises volatile compounds Fl.

[0045] In the case where composition A does not include volatile compounds Fl then This composition A could be a composition D2 or D3 as described below.

[0046] Preferably, the total molar content of additional volatile compounds Fl if present in A is greater than 0.1%, more preferably greater than 0.2%, in particular greater than 0.3% on the basis of the total composition A. Said composition A may therefore comprise one, two, three, four, five, six, seven, eight or all of the additional volatile compounds Fl as mentioned above.

[0047] In particular, if it contains it, said composition A may comprise from 10 ppm to 70% by weight, preferably from 100 ppm to 55% by weight of H2O based on the total weight of the total composition A. The water content in said composition A varies widely within the range mentioned herein depending on the BF3 used to form said composition A. Thus, if boron trifluoride hydrate is used to form composition A, the water content therein will more particularly be between 34% and 65% based on the total weight of composition A. If a purer grade is used to form composition A, for example boron trifluoride having a purity between 98% and 99.5%, then the water content therein will more particularly be between 10 ppm and 1%, preferably between 10 ppm and 1000 ppm based on the total weight of composition A.

[0048] In particular, if it contains it, said composition A may comprise from 10 ppm to 5%, preferably from 100 ppm to 1% by mole of N2 on the basis of the total composition.

[0049] In particular, if it contains it, said composition A may comprise from 10 ppm to 1% by mole, preferably from 100 ppm to 0.5% by mole of O2 based on the total composition.

[0050] In particular, if it contains it, said composition A may comprise from 10 ppm to 0.5% by mole, preferably from 10 ppm to 0.1% of CO2 on the basis of the total composition.

[0051] In particular, if it contains it, said composition A may comprise from 10 ppm to 0.5% by mole, preferably from 10 ppm to 0.1% by mole of SiF4 on the basis of the total composition.

[0052] In particular, if it contains it, said composition A may comprise from 10 ppm to 1% by mole, preferably from 10 ppm to 0.5% by mole, of H2 on the basis of the total composition.

[0053] In particular, if it contains it, said composition A may comprise from 10 ppm to 2% by mole, preferably from 10 ppm to 0.5% by mole of HCl on the basis of the total composition.

[0054] Thus, said composition A may therefore comprise: - 30% to 99.5% by weight of BF3, preferably 45% to 99.5% by weight on based on the total weight of composition A; and - from 10 ppm to 70% by weight, preferably from 100 ppm to 55% by weight of H2O based on the total weight of the total composition A; and / or - from 10 ppm to 5%, preferably from 100 ppm to 1% by mole of N2 based on the total composition; and / or - from 10 ppm to 1% by mole, preferably from 100 ppm to 0.5% by mole of O2 based on the total composition; and / or - from 10 ppm to 0.5% by mol, preferably from 10 ppm to 0.1% CO2 based on the total composition; and / or - from 10 ppm to 0.5 mol%, preferably from 10 ppm to 0.1 mol% of SiF4 based on the total composition; and / or - from 10 ppm to 1% by mol, preferably from 10 ppm to 0.5% by mol, of H2 based on the total composition; and / or - from 10 ppm to 2% by mole, preferably from 10 ppm to 0.5% by mole of HCl based on the total composition.

[0055] The total molar content of additional volatile compounds Fl being in particular greater than 0.3%.

[0056] In addition to the compounds mentioned above, said composition A may also include compounds such as HF and BF2OH. If it contains them, said composition A may include from 10 ppm to 2% of BF2OH, preferably from 1000 ppm to 1% by mol based on the total composition.

[0057] The BF3 in composition A is preferably BF3 trihydrate.

[0058] The BF3 in composition A containing Fl can be BF3 trihydrate or its aqueous solutions from BF3 by-products. Catalyst gas used in alkylation units with a catalyst for the manufacture of synthetic oil for applications to lubricate internal combustion engines. Step b)

[0059] Step b) of the present process consists of continuously introducing into reactor RI:

[0060] - a sulfuric acid solution and a solution B comprising oleum and additional volatile compounds F2 to form a composition C;

[0061] - composition A.

[0062] Preferably, solution B is oleum at a concentration of 1% to 65% by weight, more preferably 10% to 65% by weight, and in particular 40% to 65% by weight. Oleum is a mixture of H₂SO₄ and SO₃ in the form H₂S₂O₇ (balanced reaction). The SO₃ content in the oleum is expressed as a percentage of added SO₃ or as a percentage of equivalent H₂SO₄ if the necessary amount of water were added (the amount of water required to convert all the SO₃ to H₂SO₄): typical concentrations are 40% oleum by weight (corresponding to 109% H₂SO₄ by weight) and 65% oleum by weight (corresponding to 114.6% H₂SO₄ by weight); pure H₂S₂O₇ is a melting solid at 35 °C. For example, 65% oleum corresponds to 65 g of SO3 per 100 g and to neutralize the SO3 you would need to add 14.6 g of water, i.e. 100 + 14.6 = 114.6, i.e. a sulfuric acid with a strength of 114.6.

[0063] The composition of sulfuric acid introduced in step b) can be the composition L2 obtained at the outlet of reactor R2.

[0064] Preferably, the solution C formed in step b) has a sulfuric acid content greater than 100% by weight, advantageously greater than 101% by weight, preferably greater than 102% by weight, more preferably greater than 103% by weight, in particular greater than 104% by weight, more particularly greater than 105% by weight. Advantageously, the solution C thus formed has a sulfuric acid content greater than 106% by weight, preferably greater than 107% by weight, more preferably greater than 108% by weight, in particular greater than 109% by weight, more particularly greater than 110%, preferably greater than 111% by weight, advantageously greater than 112% by weight, preferably greater than 113% by weight, more preferably greater than 114% by weight.

[0065] Sulfuric acid with a concentration greater than 100% by weight corresponds to anhydrous sulfuric acid (devoid of water) containing SO3. Indeed, the SO3 present in sulfuric acid will be hydrolyzed into H2SO4 in the presence of water and will allow the sulfuric acid to remain anhydrous as long as SO3 is present in it.

[0066] Said solution B may also contain one or more volatile compounds F2 selected from the group consisting of SO2, free SO3, CO2, N2, and O2. The term free SO3 corresponds to SO3 present in the oleum but which is in equilibrium with H2S2O7 at a very low concentration compared to that of H2S2O7. In particular, if it contains it, said solution B may comprise from 10 ppm to 5%, preferably from 100 ppm to 1% by mole of N2 on a basis of the total solution.

[0067] In particular, if it contains it, said solution B may comprise from 10 ppm to 1%, preferably from 100 ppm to 0.5% by mole of O2 on the basis of the total solution.

[0068] In particular, if it contains it, said solution B may comprise from 10 ppm to 0.5%, preferably from 10 ppm to 0.1% by mole of CO2 on the basis of the total solution.

[0069] In particular, if it contains it, said solution B may comprise from 10 ppm to 1%, preferably from 10 ppm to 0.5% by mole of SO2 on the basis of the total solution.

[0070] In particular, if it contains it, said solution B may comprise from 10 ppm to 0.1%, preferably from 10 ppm to 0.25% by mole of free SO3 on the basis of the total solution.

[0071] Said solution B may contain at least one, two, three, four or all of said one or more additional volatile compounds F2. Preferably, said solution B comprises at least free SO3 and SO2. In particular, said solution B comprises all of the additional volatile compounds F2.

[0072] Thus, preferably, said solution B may therefore comprise: - from 10 ppm to 5%, preferably from 100 ppm to 1% by mole of N2 based on the total solution; and / or - from 10 ppm to 1% by mole, preferably from 100 ppm to 0.5% by mole of O2 based on the total solution; and / or - from 10 ppm to 0.5% by mol, preferably from 10 ppm to 0.1% CO2 based on the total solution; and / or - from 10 ppm to 1% by mole, preferably from 10 ppm to 0.5% by mole of SO2 on the basis of the total solution; - from 10 ppm to 0.10% by mole, preferably from 10 ppm to 0.25% by mole, of free SO3 on the basis of the total solution.

[0073] After mixing solution B and sulfuric acid, the aforementioned volatile additional compounds F2 are contained in said mixture C. Said mixture C may also contain one or more volatile compounds F2 selected from the group consisting of SO2, free SO3, CO2, N2, and O2. In particular, if it contains them, said mixture C may comprise from 10 ppm to 5%, preferably from 100 ppm to 1% by mol of N2 on a basis of the total solution.

[0074] In particular, if it contains it, said mixture C may comprise from 10 ppm to 1%, preferably from 100 ppm to 0.5% by mole of O2 on the basis of the total solution.

[0075] In particular, if it contains it, said mixture C may comprise from 10 ppm to 0.5 %, preferably from 10 ppm to 0.1% by mole of CO2 on a basis of the total solution.

[0076] In particular, if it contains it, said mixture C may comprise from 10 ppm to 1%, preferably from 10 ppm to 0.5% by mole of SO2 on a basis of the total solution.

[0077] In particular, if it contains it, said mixture C may comprise from 10 ppm to 0.1%, preferably from 10 ppm to 0.25% by mole of free SO3 on the basis of the total solution.

[0078] Said mixture C may contain at least one, two, three, four or all of said one or more additional volatile compounds F2. Preferably, said mixture C comprises at least free SO3 and SO2. In particular, said mixture C comprises all of the additional volatile compounds F2.

[0079] Thus, said mixture C has a sulfuric acid content greater than 100% by weight, advantageously greater than 101% by weight, preferably greater than 102% by weight, more preferably greater than 103% by weight, in particular greater than 104% by weight, more particularly greater than 105% by weight. Advantageously, the solution C thus formed has a sulfuric acid content greater than 106% by weight, preferably greater than 107% by weight, more preferably greater than 108% by weight, in particular greater than 109% by weight, more particularly greater than 110% by weight, preferably greater than 111% by weight, advantageously and preferably greater than 112% by weight, preferably greater than 113% by weight, more preferably greater than 114% by weight, and comprises:

[0080] - from 10 ppm to 5%, preferably from 100 ppm to 1% by mole of N2 based on the total solution; and / or

[0081] - from 10 ppm to 1% by mole, preferably from 100 ppm to 0.5% by mole of O2 on a base of the total solution; and / or

[0082] - from 10 ppm to 0.5% by mole, preferably from 10 ppm to 0.1% CO2 based on the total solution; and / or

[0083] - from 10 ppm to 1% by mole, preferably from 10 ppm to 0.5% by mole of SO2 on a base of the total solution;

[0084] - from 10 ppm to 0.25% by mol, preferably from 10 ppm to 0.10% by mol, of SO3 free based on the total solution.

[0085] The RI reactor may contain air before the introduction of the various reagents. Alternatively, the reactor may be evacuated before the introduction of the reagents to remove any oxygen or nitrogen present.

[0086] The reaction between composition A and composition C forms a liquid phase L1 comprising oleum, sulfuric acid, and BF3, and a gaseous phase G1 comprising the aforementioned additional compounds Fl and F2. The reaction between composition A and composition C notably forms a complex compound between BF3 and SO3, enabling advantageously retains the solubilized BF3 in the oleum, unlike the volatile compounds Fl and F2 (including SO2) which end up in the gas phase and can be eliminated.

[0087] Temperature and pressure are not critical parameters for the implementation of step b). However, step b) is generally implemented at a temperature of 30°C to 120°C, preferably 45°C to 120°C, preferably 70°C to 120°C, and even more preferably 80°C to 120°C. Step b) can be implemented at atmospheric pressure.

[0088] The liquid phase L1 is preferably agitated to promote mixing between A and C.

[0089] When said composition A includes HF and BF2OH, these two compounds are present in said liquid phase L1 during the implementation of step b), including the transformation of HF into HSO3F.

[0090] Solution C will allow the BF3 contained in composition A to complex with SO3. It is therefore necessary that composition C contain a sufficient quantity of SO3 to complex all the BF3 present in composition A.

[0091] Preferably, the flow rates of solution B, sulfuric acid, and composition A are such that oleum is in large excess relative to BF3. Preferably, the amount of SO3 introduced is at least 3 times greater than the amount of gaseous BF3. Thus, if composition A is an anhydrous or nearly anhydrous BF3 composition (less than 1000 ppm water to less than 1% by mass of water relative to the mass of BF3), the amount of SO3 is at least 3 times the amount of BF3. The amount of SO3 increases if the BF3 in composition A is a hydrated BF3 of l*((BF3)y.xH2O, with x>0 and y generally 1). Preferably, the amount of SO3 increases proportionally to the amount of water in the hydrated BF3, preferably according to the equation:

[0092] Thus in step b) the total quantity of SO3 is preferably equal to 3y+l*x, for example for y=l and for x=3 of the hydrate BF3,3H2O, we have a total quantity of SO3 of = 3*1+1*3=6.

[0093] Preferably, the total molar amount of oleum, for boron trifluoride trihydrate is twice the amount of oleum required to complex the BF3 contained in boron trifluoride trihydrate.

[0094] It is therefore preferable to introduce SO3 in sufficient quantity to complex all the BF3 contained in composition A and remove all the water contained in composition A. Preferably, the fluxes in composition A, B and sulfuric acid are such that we approach the saturation threshold of the oleum by the BF3.

[0095] The amount of boron trifluoride likely to dissolve in the liquid phase L1 resulting from the mixture of composition A and mixture C can be calculated prior to the implementation of the process. For example, it is sufficient to mix composition A with mixture C in the same proportions and under the same conditions. operational until the detection of gaseous boron trifluoride, which then leaves with the Fl or F2 gases. This gaseous detection can be implemented by high-resolution infrared for SO2, SO3, CO2, CO, HCl, BF3 according to the usual techniques in the technical field or by measuring with a flow meter a sudden rise in flow in the reactor due to the release of gaseous boron trifluoride.

[0096] In the event that the total molar quantity of SO3 added in step b) is not sufficient to complex all the BF3 contained in composition A, some BF3 gas could be found in the gas phase Gl. Preferably, this BF3 gas contained in the gas phase Gl could be recovered, for example, in a 98 or 100% by weight sulfuric acid column and could be recycled in the process, in particular in step a) and / or in step d), preferably in step d).

[0097] According to a preferred embodiment, when the boron trifluoride of composition A is gaseous BF3 possibly mixed with BF2OH, 100% by weight of the amount of BF3 contained in composition A capable of dissolving in the mixture C under the conditions of implementation of step b) is introduced.

[0098] This is particularly relevant when the boron trifluoride contained in composition A is not gaseous boron trifluoride, more specifically when the boron trifluoride is a hydrate (a liquid, possibly in aqueous solution). Indeed, some of the oleum will react with the water from the boron trifluoride.

[0099] For example, in step b) with (BF3)2,H2O, a total amount of SO3 = 3y + l*x where y = 2 and x = l, we would have a total amount of SO3 of = 3*(2) + l*(l) = 7, representing an additional introduction of oleum to the complexation of BF3, to neutralize the new water input from the hydrate, which is 1 / 7 = 0.14 = 14% by mole. Since the 86% molar oleum has already been added to complex the BF3, this additional excess of 14% molar allows us to reach the maximum and optimal amount of oleum to be introduced.

[0100] According to another embodiment, when the boron trifluoride of composition A is (BF3)2,H2O, 14 mol% excess oleum is introduced to the additional amount of 86 mol% oleum already used to complex the BF3 already contained in composition A capable of dissolving in the mixture C under the conditions of implementation of step b).

[0101] According to another embodiment, when the boron trifluoride of composition A is BF3,H2O, 25 mol% excess oleum is introduced to the complementary amount of 75 mol% oleum already used to complex BF3 already contained in composition A capable of dissolving in the mixture C under the conditions of implementation of step b).

[0102] According to another embodiment, when the boron trifluoride of composition A is BF3,1,5H2O, 33 mol% excess oleum is introduced to the completed amount 67% molar oleum already used to complex BF3 contained in composition A likely to dissolve in mixture C under the conditions of implementation of step b).

[0103] According to another embodiment, when the boron trifluoride of composition A is BF3,2H2O, 40 mol% excess oleum is introduced to the complementary amount of 60 mol% oleum already used to complex BF3 contained in composition A capable of dissolving in mixture C under the conditions of implementation of step b).

[0104] According to another embodiment, when the boron trifluoride of composition A is BF3,3H2O, 50 mol% excess oleum is introduced to the complementary amount of 50 mol% oleum already used to complex BF3 contained in composition A capable of dissolving in mixture C under the conditions of implementation of step b).

[0105] According to another embodiment, when the boron trifluoride of composition A is BF3,4H2O + 2H2O, 67 mol% excess oleum is introduced to the additional 33 mol% oleum already used to complex BF3 contained in composition A capable of dissolving in mixture C under the conditions of implementation of step b).

[0106] According to another embodiment, when the boron trifluoride of composition A is BF3,4H2O + 5H2O, 75 mol% excess oleum is introduced to the complementary amount of 25 mol% oleum already used to complex BF3 contained in composition A capable of dissolving in mixture C under the conditions of implementation of step b).

[0107] Step b) allows a significant amount of boron trifluoride to be solubilized in the liquid phase L1. It has been demonstrated by the present invention that adding composition A to mixture C allows more BF3 to be solubilized in the liquid phase L1 than in sulfuric acid alone. For example, at a temperature between 70°C and 120°C, the solubility of BF3 in sulfuric acid is between 0.9% and 1.7% by weight relative to the weight of the solution. By implementing the present process, and particularly by implementing step b), the solubility of boron trifluoride in the liquid phase L1 is greater than 4% by weight relative to the weight of the solution, preferably greater than 4.5% by weight relative to the weight of the solution. This represents a substantial increase demonstrating the effectiveness of the present process for storing BF3 in the liquid phase Ll until step d) is implemented.

[0108] Furthermore, during the implementation of step b), the formation of HSO3F in the liquid phase L1 was observed by Raman infrared spectroscopy. The formation of free SO3 from a traditional oleum is thus significantly reduced by this dissolution im- BF3 carrier in Ll.

[0109] The liquid phase L1 obtained in step b) preferably has a sulfuric acid content greater than 100% by weight and less than that of composition C. Preferably, the sulfuric acid content of L1 is between 103% and 108% by weight, preferably expressed as SO3 content between 13 and 36% by weight relative to the total weight of the liquid phase L1.

[0110] Preferably, the concentration of sulfuric acid L1 in RI is always greater than the concentration of sulfuric acid L2 contained in R2 Step c)

[0111] In the present process, step c) removes one or more of the volatile additional compounds Fl and F2, as defined above and contained in the gaseous phase Gl. Thus, the boron trifluoride contained in the liquid phase L1 is separated from the volatile additional compounds Fl and F2. The compounds HF and BF2OH also remain in the liquid phase L1 during this step c) but will be separated from the gaseous boron trifluoride in the following step e), as explained below.

[0112] Step c) is implemented so as to continuously draw off the gaseous phase Gl.

[0113] In particular, and in a highly targeted manner, this step c) makes it possible to remove sulfur dioxide (SO2) without using activated carbon, which has the disadvantage of degrading by attrition and the disadvantage of adding nitrogen to the BF3 gas due to its regeneration in the presence of nitrogen. Surprisingly, all of the SO2 initially present in composition A is removed by implementing step c).

[0114] In one embodiment, step c) can be carried out in combination with step b), i.e., the reactor RI is under vacuum, allowing continuous removal of the gaseous phase Gl. This can be done by any method known to those skilled in the art for withdrawing the gaseous phase Gl and introducing the phase L1 into the reactor R2. For example, the reactor RI can be fitted with a condenser connected to a vacuum pump for removing the gaseous flow Gl from RI. Preferably, the pressure PI to be applied for carrying out step c) is lower than atmospheric pressure. Preferably, the pressure PI is chosen so as to allow the removal of the gaseous phase Gl while preventing the evaporation of the liquid phase L1, which contains, in particular, the boron trifluoride complex, sulfuric acid, HF, and BF2OH.Thus, the PI pressure for the implementation of step c) is preferably between the vapor pressure of sulfuric acid at the implementation temperature of step b) and the implementation pressure of step b). Preferably, the PI pressure for the implementation of step c) is between the vapor pressure of sulfuric acid at the implementation temperature. work of step b) and atmospheric pressure. The vapor pressure of sulfuric acid is determined beforehand as a function of the temperature at which step b) is carried out.

[0115] In this embodiment, it may be useful to compensate for any losses of SO3 in gaseous form by a higher oleum flow rate. Those skilled in the art will be able to modify the flow rates to compensate for any losses of SO3 in gaseous form. Preferably, excesses of oleum much greater than those defined above in RI are avoided to prevent SO3 yield losses. SO3 would be lost in the gaseous phase G1 and would be lost to perform its function of complexing BF3 and destroying the water transformed into sulfuric acid in RI, and would be lost when L1 arrives in R2 to neutralize the water arriving in R2 with the addition of D1, D2, and D3. However, a slight excess is possible to avoid BF3 loss; preferably, this slight excess is such that the sulfuric acid concentration remains above 100% by weight.

[0116] According to a preferred embodiment, and in order to optimize the removal of the additional volatile compounds Fl and F2, the liquid phase L1 can undergo recirculation from the reactor base to the reactor lid. Thus, the liquid phase L1 is transported from the reactor base to the lid via a recirculation loop so as to complete the removal of the additional volatile compounds Fl and F2 by spraying the liquid phase L1 into the reactor head, subjected to the pressure PI defined above. As indicated above, the pressure is very low.

[0117] In another embodiment, step c) is separate from step b). In this case, a vacuum chamber is introduced between reactor RI and reactor R2. This vacuum chamber allows the continuous separation of the gas stream G1 and the liquid phase L1 from reactor RI. In this embodiment, the vacuum chamber is at a temperature between 60°C and 110°C, preferably between 70°C and 90°C. The pressure PI in the vacuum chamber is chosen so as to allow the removal of the gas phase G1 while preventing the evaporation of the liquid phase L1, which contains, in particular, boron trifluoride, sulfuric acid, oleum, HF, and BF2OH. Thus, the PI pressure for implementing step c) in a vacuum chamber is preferably between the vapor pressure of sulfuric acid at the temperature of the vacuum chamber and the implementation pressure of step b).Preferably, the pressure PI for carrying out step c) in a vacuum chamber is between the vapor pressure of sulfuric acid at the temperature at which step b) is carried out and atmospheric pressure. The vapor pressure of sulfuric acid is determined beforehand as a function of the temperature at which step b) is carried out. Step d)

[0118] According to the present process, step d) consists of continuously adding to reactor R2 the liquid phase L1 from reactor RI or, where applicable, from the vacuum chamber itself fed by RI, and a solution of a composition DI of water or an aqueous composition of boron trifluoride D2 or a composition D3 comprising hydrated boron trifluoride, referred to as boron trifluoride hydrates, to produce a gas stream E of boron trifluoride and a liquid phase L2. This step allows hydrolysis of the excess oleum contained in the liquid phase L1 by the solution D1, D2 or D3.

[0119] Preferably, the solution implemented in step d) is solution D2 or D3, preferably D3, since these solutions, by virtue of the BF3 they contain, will further increase the BF3 yield of the process of the invention. Advantageously, solutions D2 and D3 are degassed before use to avoid introducing impurities into reactor R2. In a preferred embodiment, said solution D2 or D3 is degassed under vacuum at a moderate temperature of 40 to 70°C in an independent upstream process prior to the implementation of step d). In a preferred embodiment, said solution D2 or D3 is a boron trifluoride hydrate BF3·xH2O with x from 0.5 to 4, more particularly obtained according to the process described in patent application WO 2013 / 050690.

[0120] Thus, and advantageously, said solution D2 or D3 contains a mass concentration of less than 5 ppm of each of the following additional volatile compounds: N2, O2, CO2, SiF4, HCl, H2. Preferably, said solution D is free of the additional volatile compounds N2, O2, CO2, SiF4, HCl, H2. This prevents contamination of the high-purity boron trifluoride gas stream E.

[0121] Adding the solution Dl to the liquid phase L1 advantageously allows the boron trifluoride dissolved therein to be released, in the form of BF3 gas while maintaining the compounds HF and BF2OH in said liquid phase L2.

[0122] Adding solution D2 or D3 to liquid phase L1 advantageously releases the boron trifluoride dissolved in D2 and D3 in addition to that dissolved in L1, in the form of BF3 gas while maintaining the HF and BF2OH compounds in said liquid phase L2.

[0123] The present process therefore makes it possible, by implementing steps c) and d), to eliminate many impurities initially present in composition A and in the oleum composition. The present process has the advantage of being easily implemented. Analysis of gas stream E shows the absence of HF and BF2OH in said stream. Thus, step d) makes it possible to produce a high-purity boron trifluoride. According to a preferred embodiment, the content of boron trifluoride in said gas stream E is greater than 99.9% by volume, in particular greater than 99.99% by volume based on the total volume of gas stream E. Preferably, said stream E is devoid of HF and BF2OH.

[0124] Said gas stream E is drawn from the ceiling of reactor R2 to be recovered for example in a container.

[0125] According to a preferred embodiment, said solution D2 or D3 is a boron trifluoride hydrate BF3,xH2O with x from 0.5 to 4 or a boron trifluoride solution with x greater than 4 or water, preferably the boron trifluoride hydrate has the formula BF3,xH2O with x from 2.5 to 3.1 preferably between 2.9 and 3.1, preferably between 3 and 3.1.

[0126] Preferably, the oleum concentration at step d) is lower than that at step b).

[0127] According to a preferred embodiment, in step d), said solution D1, D2, or D3 is added, in R2, to the liquid phase L1 leading to the liquid phase L2 as long as the latter remains above a sulfuric acid concentration greater than 100% by weight. The sulfuric acid concentration can be monitored online using Raman infrared spectroscopy equipment according to conventional techniques, whereby for a concentration greater than 100%, there are no longer any HSO4- bands at 1043 cm⁻¹. The sulfuric acid concentration is notably monitored by measuring an intensity band at 835 cm⁻¹, which decreases during the implementation of step d).This band corresponds to the compound HSO3F, which was formed during step b) and consumed during step d), and is characteristic of a sulfuric acid medium with a concentration necessarily greater than 100% by weight of sulfuric acid. This is because HSO3F, a non-ionized molecule that is not electronically dissociated into cations and anions, cannot be easily produced in a sulfuric acid with a concentration less than 100% by weight. This measurement can be supplemented by measuring peaks at 913 cm1 and 1162 cm1, the intensity of which increases during the implementation of step d), while avoiding sulfuric acid media with a concentration less than 100% by weight, which is characterized by the appearance of a band typical of HSO4 located at 1043 cm1.

[0128] Preferably, solution Dl, D2 or D3 is added so as to maintain in the liquid phase L2 at least 0.5% by weight of SO3 relative to the weight of solution L2, preferably 1%, even more preferably at most 2%.

[0129] According to a particular embodiment, prior to the addition of said solution D1, D2, or D3 to the liquid phase L1, fluorosulfonic acid HSO3F may be added to the liquid phase L1 arriving in R2 or directly into reactor R2. The fluorosulfonic acid acts as a BF2OH sequestering agent. Thus, the addition of fluorosulfonic acid helps to retain BF2OH in the liquid phase L1 during step d) and improves the separation between boron trifluoride and BF2OH.

[0130] According to a preferred embodiment, step d) is carried out at a temperature between 30°C and 120°C, preferably between 45°C and 120°C, more preferably between 70°C and 120°C, in particular between 80°C and 120°C, more preferably between 80°C and 110°C. Preferably, the pressure of reactor R2 is close to atmospheric pressure, preferably slightly above atmospheric pressure, for example between 1.0 and 1.3 bar.

[0131] Preferably, the flows of L1 and of solution Dl, D2 or D3 into reactor R2 are such that the mole ratio of the total amount of SO3 added to the process by L1 to the total amount of water added to the process by A, and by Dl, or D2 or D3 is less than the H2O / SO3 molar ratio of 1, preferably between 0.95 and 0.99.

[0132] According to a preferred embodiment, the content of boron trifluoride in the gas stream E is greater than 99.9% by volume, in particular greater than 99.99% by volume, based on the total volume of the gas stream E.

[0133] The liquid phase L2 can be treated to remove the HF present then in the form of high boiling point HSO3F or BF2OH to form a composition comprising mainly sulfuric acid and little oleum, preferably with a sulfuric acid content close to 100% by weight, preferably between 100 and 102% by weight (between 0.5% and 9% by weight of SO3 dissolved relative to the weight of the liquid phase L2) even more preferably between 100.1 and 100.5% by weight (between 0.5 and 2% by weight of SO3 dissolved relative to the weight of the liquid phase L2). The resulting liquid phase can be at least partially recycled to the RI reactor as a sulfuric acid stream or used in other applications after hydrolysis with water and then stripped in air of the boron and fluorine it contains to form 98% or 94% by weight sulfuric acid, two commercial grades in high demand (see for example patent EP0115719).

[0134] Fig. 1 schematically represents an installation according to a particular embodiment of the present invention.

[0135] The present process makes it possible to separate gases such as nitrogen and oxygen from boron trifluoride much more easily than cryogenic distillation processes, and at a lower cost. It also eliminates sulfur oxides, particularly sulfur dioxide (SO2), without using activated carbon, which has the disadvantage of releasing fine carbon particles into the adsorption columns due to the attrition forces exerted on the carbon grains. These fine particles present in the production lines contaminate the storage container holding the gaseous BF3. Furthermore, the implementation of the present process avoids the presence of BF3 hydrate, BF2OH, and / or HF in the gaseous BF3 by ensuring a sulfuric acid concentration greater than 100% by weight in the second reactor.Furthermore, the process makes it possible, by design, to eliminate any possible traces of other less frequent gaseous pollutants such as carbon dioxide CO2, or frequent ones such as non-silicon tetrafluoride. desired in boron trifluoride for use in the electronic silicon doping industries. Facility

[0136] This application also relates to an installation for implementing the process of the invention. This installation comprises:

[0137] - a first reactor (RI) 1 and a second reactor (R2) 2 and a pump system peristaltic or gravity by barometric leg used to transport the liquid phase between RI and R2 ensuring a non-return valve function of the liquid phase with respect to R2 towards RI to prevent the rise of the liquid phase from R2 preferably close to atmospheric pressure or higher towards RI which is preferably placed under atmospheric depression;

[0138] - the first reactor 1 is equipped:

[0139] - of a continuous power supply device 3 allowing the supply of com Position A

[0140] - of a continuous power supply device 4 allowing the supply of com position B

[0141] - of a continuous feed device 5 allowing the supply of acid sulfuric or a feeding device 6 allowing the reactor 1 to be fed with the composition L2 exiting reactor 2;

[0142] - of a sealed cover fitted with a refrigerant / condenser 7 connected to a pump vacuum 8 allowing continuous withdrawal of the gas phase G1 comprising the volatile compounds Fl and F2;

[0143] - of an overflow allowing the reactor 2 to be supplied with the outgoing composition L1 from reactor 1 via the feeding device 9;

[0144] - the second reactor 2 is equipped:

[0145] - of a continuous feed device 9 for supplying the reactor 2 with the composition L1 coming out of the overflow of reactor 1;

[0146] - of a continuous power supply device 10 of composition D1, D2 or D3;

[0147] - of a reactor sky outlet 11 allowing the recovery of ultrapure BF3 gas in a storage container E using a compressor 15;

[0148] - of an overflow outlet 12 in the middle of the reactor allowing recovery of the com Position L2 of oleum rich in sulfuric acid, which can, via a valve 13, be partially or not at all reintegrated into the RI reactor via the feed device 6 and feed a stripping device 14 allowing the hot sulfuric acid to be treated in air to remove boron and fluorine, which are detrimental to its recovery. Examples

[0149] The following examples illustrate the invention without limiting it.

[0150] Example 1 (comparative - simultaneous addition of oleum and BF3)

[0151] In a reactor with a capacity of 1 litre, equipped with a motor-driven agitator and with the agitator shaft passing through a stuffing box and equipped with the stirring blades at the end of the shaft, 510 g of sulfuric acid at 99.8% by weight, of which 0.2% by weight was water, was introduced at the bottom of the tank.

[0152] The reactor is equipped with a sealed lid connected to the stirrer and two peristaltic pumps. The first pump supplies the reactor with boron trifluoride trihydrate (BF3·3H2O) containing 55.7% BF3 by mass (i.e., 44.3% water by weight). The second peristaltic pump supplies the reactor with oleum containing 65% sulfur trioxide (SO3) by mass. The reactor's gas outlet is fitted with a wash bottle mounted on a balance. This bottle is connected to a flexible fluorinated rubber hose or a flexible PFA polymer tube. The wash bottle contains potassium hydroxide, which can then be titrated to analyze its boron and fluorine content. This analysis is redundant with the mass measured by absorption of the gaseous BF3 in a basic solution. Measurements using either method yield consistent results.The methods of analysis of boron trifluoride hydrate can be carried out by chemical analysis according to the protocol described in Wassmer Journal of the American Chemical Society, 1951,73:409-416 or more simply deduced by a density curve as a function of the BF3 content of the aqueous solution are sufficient to ascertain the mass fraction of BF3 of the boron trifluoride hydrate.

[0153] The reactor was fed with 175 g of BF3 trihydrate and 530 g of oleum at 65% SO3 by mass. Over 80 minutes, approximately 90 g of BF3 gas was released regularly and proportionally over 80 minutes by simultaneously adjusting the boron trifluoride trihydrate flow rate to 175 g / 80 minutes (2.2 g BF3·3H2O / min) and the concomitant oleum flow rate to 530 g / 80 minutes (6.62 g SO3 / min). The reactor temperature was increased by heating with the reactor's double jacket from 85°C to 105°C to further remove the dissolved BF3 gas from the sulfuric acid.

[0154] The production yield is 86% by weight.

[0155] The recovered gaseous BF3 has by-product contents of 550 ppm SO2 / SO3 (determined by a total sulfur analysis method), 30 ppm CO2 (measured by an organic and mineral carbon analyzer on a Shimadzu TOC), 125 ppm SiF4 (measured by colorimetric titration with ammonium molybdate reacting with silica to give a yellow complex titrated at the UV / visible wavelength of 810 nm), and 80 ppm HF (measured by high-resolution infrared spectroscopy). The sum of the mass contents of N2, O2, CO2, and SiF4 is 0.07%. BF2OH is detected by high-resolution infrared spectroscopy, demonstrating its presence by peak doublets between 1000 and 1100 cm⁻¹. The boron trifluoride thus obtained has a maximum value of 99.5% by weight, not counting the significant presence of BF2OH which reduces the BF3 content announced above. Example 2 (according to the present invention)

[0156] Installation description:

[0157] The installation includes a first reactor (RI) followed by a vacuum flask (allowing the capture of the gas phase Gl) and a second reactor (R2).

[0158] The two reactors (RI) and (R2) are connected to each other, (RI) will overflow into (R2) by passing through the Imhoff cone, while (R2) will supply (RI) with part of the liquid phase L2 exiting (R2). To prevent the return flow of liquid L2 from (R2) operating under negative pressure in the Imhoff cone located upstream, the liquid phase circulation between (RI) and the Imhoff cone, and then between the Imhoff cone and (R2), is ensured by peristaltic pumps. These pumps transport the liquid phase L2 with controlled flow rates determined by the pump's rotational speed. They also act as check valves for unwanted liquid products between (RI) and (R2), and between the Imhoff cone and (RI) and / or (R2). This check valve function is achieved by the compression of the pipe by the rotating roller. A peristaltic pump returns the L2 phase from (R2) to (RD) to ensure the desired flow rate of sulfuric acid-rich oleum that it must supply.Piston pumps have the same effects as peristaltic pumps on flow control functions or non-return valve effects.

[0159] Procedure:

[0160] A mixture is first prepared consisting of 530 g of oleum at 65% by weight of SO3, 510 g of sulfuric acid 100% by weight and 85 g of BF3,3H2O at 55.7% by weight of BF3, then this stable reaction medium is introduced into reactor RI until it just begins to overflow from the side tube and the filling is then stopped immediately so as not to prolong its overflow into R2.

[0161] Once reactor RI is loaded, reactor R2 is then also loaded with a composition C2 comprising:

[0162] % SO3 = 0.9% by weight

[0163] % H2SO4 = 98.3% by weight

[0164] % H2O = 0.0 wt% %BF3 = 0.8 wt%

[0165] Until it too starts to overflow and then we also stop its rem pleating. This C2 composition will then be kept constant in R2 following the start of the experiment by the reagents which will feed it permanently.

[0166] The two reactors are interconnected; RI will overflow into R2 via the Imhoff cone, while R2 will supply RI with a portion of the liquid phase L2 exiting R2. To prevent the return of the liquid L2 from R2, which is close to atmospheric pressure, into the Imhoff cone located upstream under negative pressure, the liquid phase circulates between RI and the Imhoff cone, and then between the Imhoff cone and R2 is supplied by peristaltic pumps that transport the liquid phase L2 with flow control ensured by the pump's rotational speed. These pumps also act as check valves for unwanted liquids between R2 and RI, and between the Imhoff cone and RI and / or R2, thanks to the compression of the pipe by the rotating roller. A peristaltic pump returns the L2 phase from R2 to RI to ensure the desired flow rate of sulfuric acid-rich oleum. Piston pumps have the same flow control and check valve effects as peristaltic pumps. RI Reactor:

[0167] The reaction medium in RI is then heated to between 104 and 107°C and maintained at this temperature. Reactor R2 is heated to the same temperature.

[0168] The following is then introduced continuously into RI by peristaltic pumps:

[0169] - 63.7g of BF3.3H2O per hour

[0170] - 397.5 g of oleum 65% by weight per hour

[0171] - 382 g per hour of composition L2 (oleum rich in sulfuric acid) from the reactor R2.

[0172] Composition L1, loaded with oleum, sulfuric acid, and BF3 dissolved in oleum, exits through the overflow of the lateral tube of reactor RI using a peristaltic pump with an overflow rate of 845 g / h and enters a conical flask in the shape of an Imhoff cone. The bottom of the flask is equipped with a piston pump that continuously empties the product, which enters through the cone's lid from above. A tube from the first reactor and a condenser, also attached to the lid, are connected to the vacuum-sealed lid. The condenser cools the mixture to 1°C, above which a vacuum pump removes gases G1 such as N2, CO2, CO, SO2, O2, SiF4, H2, and traces of BF3 gases not retained in the oleum-rich liquid phase of L1.

[0173] The oleum-rich liquid phase (Ll) from the bottom of the Imhoff cone arrives via the peristaltic pump in a second reactor R2 of identical volume and construction to the first reactor RI.

[0174] (Ll) has a measured H2SO4 content of approximately 103.8% by weight by acidimetric titration with NaOH. Vacuum treatment in the Imhoff cone:

[0175] A vacuum is made in this Imhof cone continuously in accordance with step d) of the present process at a temperature of about 1°C for the gases exiting downstream of the condenser, constantly maintaining the vapor pressure of sulfuric acid at 80°C, the vapors of which are cooled to 1°C as a lower vacuum threshold.

[0176] Gases such as N2, CO2, CO, SO2, O2, and SiF4 are removed, leading to the purification of the BF3 dissolved in the liquid phase L1 from these volatile compounds Fl and F2. The application under A vacuum is permanently in effect to handle the low feed rate coming from the first reactor. Second reactor R2:

[0177] A second double-jacketed reactor identical to that of RI is further equipped with a flat Pyrex lens placed on an internal wall of the reactor and allowing a connection to the optical fiber of a Raman infrared analyzer allowing the SO3 content in reactor R2 to be determined by measuring the band around 720 cm-1.

[0178] The same system used in RI is designed to continuously control the contents of reactors RI and R2 in a so-called oleum composition zone where no water is possible in the reaction medium. This online analyzer prevents the reaction from occurring in an aqueous sulfuric acid zone.

[0179] The R2 reactor is then continuously supplied by the overflow of RI having passed through the Imhoff cone under vacuum and also supplied by a second flow of pure boron trifluoride trihydrate, i.e. previously degassed by hot vacuum distillation.

[0180] The overall molar ratio (taking into account both reactors) between the SO3 of the oleum used and the water of the BF3,3H2O added in the 2 reactors is close to 1.

[0181] In R2, BF3 gas is released continuously at a rate of 67 g / h, and a sulfuric acid-rich oleum composition L2 exits reactor R2 at a rate of 838 g / h into a sulfuric acid storage device for purification treatment to make it usable in other applications. The purification consists of stripping this hot sulfuric acid in air to remove boron and fluorine, which are detrimental to its use, while simultaneously adding water to reduce the sulfuric acid content to approximately 94% by weight.

[0182] The analysis of total sulfur in the BF3 gas exiting R2 indicates less than 1 ppm of sulfur therefore less than 2 ppm of SO2.

[0183] The other part of this L2 oleum rich in sulfuric acid is recycled at a rate of 382 g / h to the RI reactor. Example 3:

[0184] The process is carried out in a similar manner to that of Example 2, except that a vacuum is maintained on the RI reactor continuously with a condenser on the RI lid connected to a Teflon vacuum pump, which is designed to make the small amount of distillate that would want to leave the reactor flow back to the RI reactor.

[0185] The BF3 in gaseous form produced in the second reactor was put into a 1-liter cylinder using a 12 / 220 Volt mini electric compressor capable of filling a 1-liter cylinder in 1 hour, resistant to 300 bar. The gas can be High-resolution Fourier transform infrared spectroscopy with very long optical path lengths was used to verify the absence of SIF4 at 1040 cm⁻¹. HCl and HF exhibit a series of IR bands in multiplets above 3000 cm⁻¹, which are highly characteristic in areas where BF3 gas has no infrared absorption that hinders their observation. The spectrum is completely devoid of the IR bands characteristic of HCl and HF, leading to the conclusion of the absence of HF and gaseous HCl. Helium chromatography, using a DID detector (a very high-voltage discharge detector in helium that emits very high-energy ultraviolet radiation, ionizing everything except helium), concluded that the BF3 gas exiting reactor R2 is free of H₂, CO₂, CO, N₂, and O₂.

[0186] The recovered gaseous BF3 has a purity of over 99.99%. BF3 analysis analyzed by chonnatography, DID detector, p(abs)=32 bars B [H2] » [O2+Ar] ppmy [N2j ppmv [CO] ppmv [CH4] ppniv [CO2] BRmv Example Injection |1 Comparative Sample 17 / 10 / 22 7.5 35 3500 0.1 <0.05 1 Example Injection 3 Sample 6 / 12 / 22 0.1 0.05 0.05 <0.05 <0.05 0.2 < : means less than

[0187] Purity test example 2 = 100-(0.1+0.05+0.05+0.05+0.2) / 100000=99.999% on this table.

[0188] The recovered gaseous BF3 is free of HCl, HF, SiF4, and BF2OH, verified by the absence of infrared band absorption on a high-resolution, long-path optical instrument from MIRAN Technology. No infrared bands were detected around 1040 cm⁻¹ for SiF4 and BF2OH, and no bands were detected between 1100 and 1200 cm⁻¹ for SO2. No characteristic multiplets were detected for HCl or HF in the regions above 3000 cm⁻¹ for HCl and above 4000 cm⁻¹ for HF.

[0189] The volume of inert gas measured on a water eudiometer is zero (not measurable) for the BF3 of example 2 or example 3.

Claims

Demands

1. A process for the continuous production of gaseous boron trifluoride comprising the steps of: a) Supplying a composition A comprising boron trifluoride (BF3) and optionally one or more additional volatile compounds Fl; b) In a first RI reactor, continuously introducing: - a sulfuric acid solution and a solution B comprising oleum and additional volatile compounds F2 to form a solution C; - composition A; to form: - a liquid phase L1 comprising oleum, sulfuric acid and BF3 and - a gaseous phase G1 comprising said additional volatile compounds Fl and F2; c) Continuously removing the gaseous phase G1 comprising said additional volatile compounds Fl and F2, preferably by vacuum;d) Continuous introduction of the liquid phase L1 into a second reactor R2 and continuous introduction into reactor R2 of a composition DI of water or an aqueous composition of boron trifluoride D2 or a composition D3 comprising hydrated boron trifluoride, known as boron trifluoride hydrates, the compositions D1, D2 and D3 not containing any additional compound Fl to produce a gaseous phase E of boron trifluoride and a liquid phase L2.;

2. A method according to claim 1 characterized in that said gas stream E is recovered in a container.

3. A process according to any one of the preceding claims characterized in that the content of boron trifluoride in said gas stream E is greater than 99.9% by volume on the basis of the total volume of the gas stream E.

4. A process according to any one of the preceding claims characterized in that said composition A is a composition of BF3 comprising one or more additional volatile compounds Fl selected from the group consisting of H2O, N2, O2, CO2, SiF4, H2 and HCl.

5. A method according to any one of the preceding claims ca- characterized in that the boron trifluoride of composition A is gaseous BF3 BF3,xH2O with x = 0 possibly mixed with BF2OH, or a boron trifluoride hydrate BF3,xH2O with x varying between 0.5 and 4 or an aqueous solution of boron trifluoride BF3,xH2O with x greater than 4 or is obtained from the reaction between a boron compound selected from B(OH)3, B2O3 or HBO2 and a fluorinated compound selected from HF or HSO3F.

6. A process according to any one of the preceding claims characterized in that said solution D1, D2 and D3 is devoid of N2, O2, CO2, SiF4, H2 and HCl.

7. A process according to any one of the preceding claims characterized in that the solution C has a sulfuric acid content greater than 100% by weight, advantageously greater than 101% by weight, preferably greater than 102% by weight, more preferably greater than 103% by weight, in particular greater than 104% by weight, more particularly greater than 105% by weight, more preferably greater than 106% by weight, preferably greater than 107% by weight, more preferably greater than 108% by weight, in particular greater than 109% by weight, more particularly greater than 110% by weight, preferably greater than 111% by weight, advantageously and preferably greater than 112% by weight, preferably and preferably greater than 113% by weight, more preferably and preferably greater than 114% by weight.

8. A method according to any one of the preceding claims characterized in that step b) is carried out at a temperature of 30°C to 120°C, preferably 45 to 120°C, preferably 70 to 120°C and even more preferably 80 to 110°C.

9. A process according to any one of the preceding claims characterized in that the concentration of oleum in reactor RI is greater than that in reactor R2.

10. A process according to any one of the preceding claims characterized in that the composition L2 from R2 is partly reintroduced into RI as a sulfuric acid solution.

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