Method for producing high-purity boron trifluoride

Abstract

The invention relates to a method for the continuous production of gaseous boron trifluoride, the method comprising the steps of: a) providing a composition A comprising boron trifluoride (BF3) and optionally one or more additional volatile compounds F1; b) continuously adding, to a first reactor R1: - a sulphuric acid solution and a solution B comprising oleum and volatile additional compounds F2 to form a solution C; - composition A; to form: - a liquid phase L1 comprising oleum, sulphuric acid and BF3 and - a gaseous phase G1 comprising the volatile additional compounds F1 and F2; c) continuously removing the gas phase G1 comprising the additional volatile compounds F1 and F2, preferably by means of negative pressure; d) continuously adding the liquid phase L1 to a second reactor R2 and continuously adding, to the reactor R2, 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, wherein the compositions D1 and D2 do not contain any additional compound F1 to produce a gaseous phase E of boron trifluoride and a liquid phase L2.

Description

[0001] Process for the production of high purity boron trifluoride

[0002] Field of invention

[0003] The present invention relates to a process for producing boron trifluoride. In particular, the present invention relates to a continuous process for producing high purity boron trifluoride.

[0004] Technical background

[0005] Boron trifluoride (BF3) is a gas that is mainly used in industry as a catalyst in a large number of reactions: polymerization, esterification, alkylation, isomerization or for the implementation of transistors in the electronics industry as a raw material for 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 additional addition of oleum. Gaseous boron trifluoride is also obtained by treatment with sulfuric acid or sulfuric acid in a mixture with oleum of a concentrated aqueous solution of BF3 hydrate. However, the presence of impurities in gaseous and anhydrous boron trifluoride poses problems for certain applications requiring a high purity grade.

[0006] 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 come from the raw materials used or from residues of some of these raw materials. Contents of the impurities cited can range from a few hundred ppm to 1.5%. Such contents are not acceptable in the field of electronics. Indeed, boron trifluoride is also used in electronic microprocessor manufacturing processes. Some prior art documents disclose purification techniques to partially eliminate some of these impurities. A process for purifying BFs using H2O2 and water in sulfuric acid to remove SO2 and SO3 is known from JP59050018.Also known from US 3,625,651 and FR 2 003 557 is a process for removing sulfur dioxide from BF3 using activated carbon at very low temperature; but this process tends to pollute the gaseous BF3 with nitrogen used to desorb the column of activated carbon saturated with SO2. Also known from document EP 0 922 672 is a process using treatment with H2O2 and air treatment to purify the gaseous BF3 which is recycled in sulfuric acid by washing the air and BF3 flow so as to recycle the boron fluoride trifluoride to the production of compressed BF3 gas.

[0007] Despite these purification processes applicable to technical boron trifluoride, there is still a need for a process for producing very pure boron trifluoride that can eliminate volatile impurities such as those mentioned above, including SiF4 or hydrogen fluoride. Furthermore, there is also a need to provide such a process using oleum and allowing the removal of SO2 present in oleum without resorting to activated carbon (activated carbon being responsible for dust production). There is also a need for an efficient and simple-to-implement process that can obtain high-purity boron trifluoride. There is also a need to provide such a process that can be easily adapted to existing technical BF3 production lines.

[0008] Summary of the invention

[0009] The invention relates firstly to a process for the continuous production of gaseous boron trifluoride comprising the steps of: a) Providing a composition A comprising boron trifluoride (BF3) and optionally one or more additional volatile compounds F1; b) In a first reactor R1 continuous introduction:

[0010] - a sulfuric acid solution and a solution B comprising oleum and additional volatile compounds F2 to form a solution C;

[0011] - of composition A; to form: - a liquid phase L1 comprising oleum, sulfuric acid and B Fs and

[0012] - a gas phase G1 comprising said additional volatile compounds F1 and F2; c) Continuous removal of the gas 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 the reactor R2 of a composition D1 of water or of an aqueous composition of boron trifluoride D2 or of a composition D3 comprising hydrated boron trifluoride, called boron trifluoride hydrates, the compositions D1, D2 and D3 not containing any additional compound F1 to produce a gas phase E of boron trifluoride and a liquid phase L2.

[0013] In one embodiment, said gas stream E is recovered in a container.

[0014] Preferably, the boron trifluoride content in said gas stream E is greater than 99.9% by volume based on the total volume of the gas stream E.

[0015] In one embodiment, said composition A is a BF3 composition comprising one or more additional volatile compounds F1 selected from the group consisting of H2O, N2, O2, CO2, SiF4, H2 and HCl.

[0016] 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 derived from the reaction between a boron compound selected from B(OH)3, B2O3 or HBO2 and a fluorinated compound selected by HF or HSO3F.

[0017] Preferably, said solution D1, D2 and D3 is free of N2, O2, CO2, Si F4, H2 and HCl. 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 greater than 112% by weight, preferably greater than 113% by weight, more preferably greater than 114% by weight.

[0018] 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.

[0019] Preferably, the oleum concentration in reactor R1 is higher than that in reactor R2.

[0020] In one embodiment, composition L2 from R2 is partially reintroduced into R1 as a sulfuric acid solution.

[0021] Description of figures

[0022] [Fig.1] schematically represents an installation for implementing the process for the continuous production of boron trifluoride according to a particular embodiment of the present invention.

[0023] Detailed description

[0024] The invention is now described in more detail and in a non-limiting manner in the following description.

[0025] The present invention relates to a process for the continuous production of gaseous boron trifluoride comprising the steps of: a) Providing a composition A comprising boron trifluoride (BFs) and optionally one or more additional volatile compounds F1; b) In a first reactor R1 continuously introducing: - a sulfuric acid solution and a solution B comprising oleum and additional volatile compounds F2 to form a solution C;

[0026] - of composition A; to form:

[0027] - a liquid phase L1 comprising oleum, sulfuric acid and B Fs and

[0028] - a gas phase G1 comprising said additional volatile compounds F1 and F2; c) Continuous removal of the gas 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 the reactor R2 of a composition D1 of water or of an aqueous composition of boron trifluoride D2 or of a composition D3 comprising hydrated boron trifluoride, called boron trifluoride hydrates, the compositions D1 and D2 not containing any additional compound F1 to produce a gas phase E of boron trifluoride and a liquid phase L2.

[0029] The gaseous stream E of boron trifluoride obtained at the outlet of reactor R2 is thus of high purity.

[0030] According to a preferred embodiment, said gaseous stream E is recovered in a container.

[0031] According to a preferred embodiment, the boron trifluoride content in said gas stream E is greater than 99.9% by volume based on the total volume of the gas stream E.

[0032] Step a)

[0033] The boron trifluoride contained in composition A may have different origins. The boron trifluoride may be gaseous BFs, BFS, XH2O with x = 0 impure or technical grade. For example, the gaseous BFs contained in composition A may be BFs having a purity less than or equal to 99.5%, that is to say that the BFs composition used to form composition A comprises at most 99.5% by weight of BFs based on the total weight of said composition. The BFs may optionally be mixed with BF2OH. The boron trifluoride contained in composition A may be a boron trifluoride hydrate, such as BFs,xH2O with x varying between 0.05 and 4, preferably between 0.5 and 4. The boron trifluoride contained in composition A may be derived from the reaction between a boron compound selected from B(OH)s, 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 BFs,xH2O with x greater than 4. Particularly preferably, the boron trifluoride of composition A is a boron fluoride trihydrate (BF3.3H2O).

[0034] Boron trifluoride (BFs^FLO, BFs,H2O, BFs,1,5H2O, BFs,2H2O, BFS,3H2O is a liquid hydrate. Boron trifluoride, BFs,4H2O + 2H2O and BFS,4H2O + 5H2O is a liquid hydrate in aqueous solution.

[0035] Thus, the BF3 content in said composition A may be a few% or more, preferably it is between 30% and 99.5% by weight based on the total weight of composition A. Preferably, the BFs content in said composition A may be from 45% to 99.5% by weight based on the total weight of composition A.

[0036] As mentioned above, said composition A may or may not comprise, in addition to boron trifluoride, one or more additional volatile compound(s) F1. Said one or more additional volatile compound(s) F1 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 comprise 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 gas phase G1.

[0037] Preferably, composition A comprises volatile compounds F1.

[0038] In the case where composition A does not include volatile compounds F1 then this composition A could be a composition D2 or D3 as described below.

[0039] Preferably, the total molar content of additional volatile compounds F1 if present in A is greater than 0.1%, more preferably greater than 0.2%, in particular greater than 0.3% based on 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 F1 as mentioned above.

[0040] 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 mass content of water therein will be more particularly 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 mass content of water therein will be more particularly between 10 ppm and 1%, preferably between 10 ppm and 1000 ppm based on the total weight of composition A.

[0041] 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 based on the total composition.

[0042] In particular, if it contains it, said composition A may comprise from 10 ppm to 1 mol%, preferably from 100 ppm to 0.5 mol% of O2 based on the total composition.

[0043] In particular, if it contains it, said composition A may comprise from 10 ppm to 0.5 mol%, preferably from 10 ppm to 0.1% of CO2 based on the total composition.

[0044] In particular, if it contains it, said composition A may comprise from 10 ppm to 0.5 mol%, preferably from 10 ppm to 0.1 mol% of SiF4 based on the total composition.

[0045] In particular, if it contains it, said composition A may comprise from 10 ppm to 1 mol%, preferably from 10 ppm to 0.5 mol%, of H2 based on the total composition.

[0046] In particular, if it contains it, said composition A may comprise from 10 ppm to 2 mol%, preferably from 10 ppm to 0.5 mol% of HCl based on the total composition. Thus, said composition A may therefore comprise:

[0047] - 30% to 99.5% by weight of BFs, preferably from 45% to 99.5% by weight 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

[0048] - from 10 ppm to 5%, preferably from 100 ppm to 1% by mole of N2 based on the total composition; and / or

[0049] - from 10 ppm to 1 mol%, preferably from 100 ppm to 0.5 mol% of O2 based on the total composition; and / or

[0050] - from 10 ppm to 0.5 mol%, preferably from 10 ppm to 0.1% of CO2 based on the total composition; and / or

[0051] - from 10 ppm to 0.5 mol%, preferably from 10 ppm to 0.1 mol% of SiF4 based on the total composition; and / or

[0052] - from 10 ppm to 1 mol%, preferably from 10 ppm to 0.5 mol%, of H2 based on the total composition; and / or

[0053] - from 10 ppm to 2 mol%, preferably from 10 ppm to 0.5 mol% of HCl based on the total composition.

[0054] The total molar content of additional volatile compounds F1 being in particular greater than 0.3%.

[0055] In addition to the above-mentioned compounds, said composition A may also comprise compounds such as HF and BF2OH. If it contains them, said composition A may comprise from 10 ppm to 2% of BF2OH, preferably from 1000 ppm to 1 mol% based on the total composition.

[0056] The BF3 in composition A is preferably BF3 trihydrate.

[0057] The BF3 in composition A containing F1 may be BF3 trihydrate or its aqueous solutions from by-products of BF3 catalyst gas used in alkylation units with a catalyst for the manufacture of synthetic oil for applications to lubricate thermal engines.

[0058] Step b)

[0059] Step b) of the present process consists of continuously introducing, into the reactor R1: - a sulfuric acid solution and a solution B comprising oleum and additional volatile compounds F2 to form a composition C;

[0060] - composition A.

[0061] Preferably, solution B is oleum at a concentration of 1% to 65% by weight, more preferably 10% to 65% by weight, 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 oleum is expressed as a percentage of SO3 added or as a percentage of equivalent H2SO4 if the necessary amount of water were added (amount of water required to convert all the SO3 into H2SO4): the usual concentrations are oleum at 40% by weight (corresponding to 109% by weight H2SO4) and oleum at 65% by weight (corresponding to 114.6% by weight H2SO4); pure H2S2O7 is a solid melting at 35°C. For example, 65% oleum corresponds to 65 g of SO3 per 100 g and to neutralize the SO3 it would be necessary to add 14.6 g of water, i.e. 100 + 14.6 = 1 14.6, i.e. a sulfuric acid with a strength of 114.6.

[0062] The sulfuric acid composition introduced in step b) can be the composition L2 obtained at the outlet of reactor R2.

[0063] 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 more preferably greater than 112% by weight, preferably more preferably more than 113% by weight, more preferably more preferably more than 114% by weight.

[0064] Sulfuric acid with a strength greater than 100% by weight corresponds to anhydrous sulfuric acid (free 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.

[0065] 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 H2S2O? in 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 based on the total solution.

[0066] 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 based on the total solution.

[0067] 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 based on the total solution.

[0068] 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 based on the total solution.

[0069] 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 based on the total solution.

[0070] 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.

[0071] Thus, preferably, said solution B can therefore comprise:

[0072] - from 10 ppm to 5%, preferably from 100 ppm to 1% by mole of N2 based on the total solution; and / or

[0073] - from 10 ppm to 1 mol%, preferably from 100 ppm to 0.5 mol% of O2 based on the total solution; and / or

[0074] - from 10 ppm to 0.5 mol%, preferably from 10 ppm to 0.1% of CO2 based on the total solution; and / or - from 10 ppm to 1 mol%, preferably from 10 ppm to 0.5 mol% of SO2 based on the total solution;

[0075] - from 10 ppm to 0.10 mol%, preferably from 10 ppm to 0.25 mol%, of free SO3 based on the total solution.

[0076] After mixing solution B and sulfuric acid, said additional volatile 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 mole of N2 based on the total solution.

[0077] 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 based on the total solution.

[0078] 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 based on the total solution.

[0079] 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 based on the total solution.

[0080] 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 based on the total solution.

[0081] 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.

[0082] 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 more preferably greater than 112% by weight, preferably more preferably greater than 113% by weight, more preferably more preferably greater than 114% by weight and comprises: 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 mol%, preferably from 100 ppm to 0.5 mol% of O2 based on the total solution; and / or from 10 ppm to 0.5 mol%, preferably from 10 ppm to 0.1% of CO2 based on the total solution; and / or from 10 ppm to 1 mol%, preferably from 10 ppm to 0.5 mol% of SC based on the total solution; from 10 ppm to 0.25 mol%, preferably from 10 ppm to 0.10 mol%, of free SO3 based on the total solution.;

[0083] Reactor R1 may contain air before the introduction of the various reactants. Alternatively, said reactor may be placed under vacuum before the introduction of the reactants to eliminate any oxygen or nitrogen present.

[0084] 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 said additional compounds F1 and F2. The reaction between composition A and composition C forms in particular a complex compound between BF3 and SO3 advantageously making it possible to keep the BF3 solubilized in the oleum unlike the volatile compounds F1 and F2 (including SO2) which are found in the gaseous phase and can be eliminated.

[0085] Temperature and pressure are not critical parameters for the implementation of step b). However, step b) is generally carried out at a temperature of 30°C to 120°C, preferably 45 to 120°C, more preferably 70 to 120°C and even more preferably 80 to 120°C. Step b) can be carried out at atmospheric pressure.

[0086] The liquid phase L1 is preferably stirred to promote mixing between A and C.

[0087] When said composition A comprises HF and BF2OH, these two compounds are present in said liquid phase L1 during the implementation of step b), in particular with the transformation of HF into HSO3F.

[0088] Solution C will allow the BF3 contained in composition A to be complexed with SO3. It is therefore necessary that composition C includes a sufficient quantity of SO3 to complex all the BF3 present in composition A.

[0089] Preferably, the flow rates of the solution B, sulfuric acid and composition A streams are such that the oleum is in large excess relative to the BF3. Preferably the quantity of SO3 introduced is at least 3 times greater than the quantity of BF3 gas. Thus, if composition A is an anhydrous or quasi-anhydrous BF3 composition (less than 1000 ppm of water at less than 1% by mass of water relative to the mass of BF3), the quantity of SO3 is at least 3 times the quantity of BF3. The quantity of SO3 increases if the BF3 of composition A is a hydrated BF3 of 1 * ((BFs)y.xH2O, with x>0 and y generally of 1), preferably the quantity of SO3 increases proportionally to the quantity of water in the hydrated BF3, preferably according to the equation:

[0090] Thus in step b) the overall quantity of SO3 is preferably equal to 3y+1 *x, for example for y=1 and for x=3 of the hydrate BFs,3H2O, we have an overall quantity of SO3 of = 3*1 +1 *3=6.

[0091] Preferably, the total molar amount of oleum, for boron trifluoride trihydrate is twice the amount of oleum required to complex the BF3 contained in the boron trifluoride trihydrate.

[0092] 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 flows in composition A, B and sulfuric acid are such that the saturation threshold of oleum by BF3 is approached.

[0093] The quantity of boron trifluoride likely to dissolve in the liquid phase L1 resulting from the mixture between composition A and mixture C can be calculated prior to implementing the process. It is sufficient, for example, to mix composition A with said mixture C in the same proportions and under the same operational conditions until the detection of gaseous boron trifluoride then leaving with gases F1 or F2. 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 increase in flow rate in the reactor due to the release of gaseous boron trifluoride. In the case where the total molar quantity of SO3 added in step b) is not sufficient to complex all the BF3 contained in composition A, BF3 gas could be found in the gas phase G1.Preferably, this BF3 gas contained in the gas phase G1 could be recovered for example in a column of 98 or 100% by weight sulfuric acid and could be recycled in the process in particular in step a) and / or in step d), preferably in step d).

[0094] According to a preferred embodiment, when the boron trifluoride of composition A is gaseous BF3 optionally mixed with BF2OH, 100% by weight of the quantity of BF3 contained in composition A capable of dissolving in mixture C under the conditions of implementation of step b) is introduced.

[0095] This is particularly implemented when the boron trifluoride contained in composition A is not gaseous boron trifluoride, more particularly when the boron trifluoride is a hydrate (liquid possibly in aqueous solution). Indeed, part of the oleum will react with the water coming from the boron trifluoride.

[0096] For example, in step b) with (BFs)2,H2O, a total quantity of SO3 = 3y+1 *x in which y=2 and x=1, we would have a total quantity of SO3 of = 3*(2)+1 *(1)=7 or an introduction of additional oleum to the complexation of BF3, to destroy the new contribution of water from the hydrate which is 1 / 7=0.14=14% in moles to destroy the water. The 86% moles of oleum having already been added to complex the BF3, this additional excess of 14% moles makes it possible to arrive at the maximum and optimal quantity of oleum to be introduced.

[0097] According to another embodiment, when the boron trifluoride of composition A is (BF3)2,H2O, 14 mol% excess oleum is introduced to the additional quantity of 86 mol% oleum already used to complex the BF3 already contained in composition A capable of dissolving in mixture C under the conditions of implementation of step b).

[0098] According to another embodiment, when the boron trifluoride of composition A is BFs,H2O, 25 mol% excess oleum is introduced to the additional quantity of 75 mol% oleum already used to complex BFs already contained in composition A capable of dissolving in mixture C under the conditions of implementation of step b).

[0099] According to another embodiment, when the boron trifluoride of composition A is BFs,1,5H2O, 33 mol% excess oleum is introduced to the additional quantity of oleum at 67 mol% already used to complex BFs contained in composition A capable of dissolving in mixture C under the conditions of implementation of step b).

[0100] According to another embodiment, when the boron trifluoride of composition A is BFs,2H2O, 40 mol% excess oleum is introduced to the additional quantity of 60 mol% oleum already used to complex BFs contained in composition A capable of dissolving in mixture C under the conditions of implementation of step b).

[0101] According to another embodiment, when the boron trifluoride of composition A is BFs,3H2O, 50 mol% excess oleum is introduced to the additional quantity of 50 mol% oleum already used to complex BFs contained in composition A capable of dissolving in mixture C under the conditions of implementation of step b).

[0102] According to another embodiment, when the boron trifluoride of composition A is BFs,4H2O + 2H2O, 67 mol% excess oleum is introduced to the additional quantity of oleum at 33 mol% already used to complex BFs contained in composition A capable of dissolving in mixture C under the conditions of implementation of step b).

[0103] According to another embodiment, when the boron trifluoride of composition A is BFs,4H2O + 5H2O, 75 mol% excess oleum is introduced to the additional quantity of oleum at 25 mol% already used to complex BFs contained in composition A capable of dissolving in mixture C under the conditions of implementation of step b).

[0104] Step b) makes it possible to solubilize a significant amount of boron trifluoride in the liquid phase L1. It has been demonstrated by the present invention that the addition of composition A to mixture C makes it possible to solubilize more BFs in the liquid phase L1 than in sulfuric acid alone. For example, at a temperature between 70°C and 120°C, the solubility of BFs in sulfuric acid is between 0.9% and 1.7% by weight relative to the weight of the solution. By implementing the present method, 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 significant increase demonstrating the effectiveness of the present process for storing BFs in the liquid phase L1 as long as step d) is not carried out.

[0105] Furthermore, during the implementation of step b), the formation of HSOsF in the liquid phase L1 was observed by Raman infrared. The formation of free SO3 of a traditional oleum is thus greatly reduced by this significant dissolution of BF3 in L1.

[0106] 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 of between 13 and 36% by weight relative to the total weight of the liquid phase L1.

[0107] Preferably, the titer of sulfuric acid L1 in R1 is always higher than the titer of sulfuric acid L2 contained in R2

[0108] Step c)

[0109] In the present process, step c) makes it possible to eliminate said one or more additional volatile compounds F1 and F2 as defined above and contained in said gaseous phase G1. Thus, the boron trifluoride contained in the liquid phase L1 is separated from the additional volatile compounds F1 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 during the following step e), as explained below.

[0110] Step c) is implemented so as to continuously withdraw the gas phase G1.

[0111] In particular, in a particularly targeted manner, this step c) makes it possible to eliminate 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 their regeneration in the presence of nitrogen. Surprisingly, all of the SO2 initially present in composition A is eliminated thanks to the implementation of step c).

[0112] In one embodiment, step c) can be carried out in combination with step b), i.e. the reactor R1 is under vacuum allowing continuous removal of the gaseous phase G1. This can be done by any method known to those skilled in the art for withdrawing the gaseous phase G1 and introducing the phase L1 into the reactor R2. For example, the reactor R1 can be surmounted by a condenser cooler connected to a vacuum pump for evacuating the gaseous flow G1 from R1. Preferably, the pressure P1 to be applied for carrying out step c) is lower than atmospheric pressure. Preferably, the pressure P1 is chosen so as to allow the removal of the gaseous phase G1 while avoiding the evaporation of the liquid phase L1 containing in particular the complex compound of boron trifluoride, sulfuric acid, HF and BF2OH.Thus, the pressure P1 for carrying out step c) is preferably between the vapor pressure of the sulfuric acid at the temperature for carrying out step b) and the pressure for carrying out step b). Preferably, the pressure P1 for carrying out step c) is between the vapor pressure of the sulfuric acid at the temperature for carrying out step b) and atmospheric pressure. The vapor pressure of the sulfuric acid is determined beforehand as a function of the temperature at which step b) is carried out.

[0113] It may be useful, in this embodiment, to compensate for any losses of SO3 in gaseous form by a higher flow rate of oleum. Those skilled in the art will be able to modify the flows in order to compensate for any losses of SO3 in gaseous form. Indeed, preferably, one tries to avoid excesses of oleum much higher than those defined above in R1 to avoid losses of yield in SO3 leaving in the gaseous phase G1 and lost to ensure its function of complexing BF3 and destroying the water transformed into sulfuric acid in R1 and lost when L1 arrives in R2 to neutralize the water which would arrive in R2 with the addition of D1, D2 and D3. However, a slight excess is possible, to avoid losing BF3, preferably the slight excess is such that the sulfuric acid content remains greater than 100% by weight.

[0114] According to a preferred embodiment, and in order to optimize the elimination of the additional volatile compounds F1 and F2, the liquid phase L1 can undergo recirculation from the reactor base to the reactor cover. Thus, the liquid phase L1 is transported from the reactor base to the cover by a recirculation loop so as to complete the elimination of the additional volatile compounds F1 and F2 by spraying the liquid phase L1 into the reactor headspace, subjected to the pressure P1 defined above. As indicated above, the pressure is very low.

[0115] In another embodiment, step c) is distinct from step b). In this case, a vacuum enclosure is introduced between the reactor R1 and the reactor R2. This vacuum enclosure allows the continuous separation of the gaseous flow G1 and the liquid phase L1 coming from the reactor R1. In this embodiment, the vacuum enclosure is at a temperature between 60°C and 110°C, preferably between 70°C and 90°C. The pressure P1 in the vacuum enclosure is chosen so as to allow the elimination of the gaseous phase G1 while avoiding the evaporation of the liquid phase L1 containing in particular boron trifluoride, sulfuric acid, oleum, HF and BF2OH. Thus, the pressure P1 for carrying out step c) in a vacuum enclosure is preferably between the vapor pressure of the sulfuric acid at the temperature of the vacuum enclosure and the pressure for carrying out step b).Preferably, the pressure P1 for carrying out step c) in a vacuum chamber is between the vapor pressure of the sulfuric acid at the temperature at which step b) is carried out and atmospheric pressure. The vapor pressure of the sulfuric acid is determined beforehand as a function of the temperature at which step b) is carried out.

[0116] Step d)

[0117] According to the present method, step d) consists of the continuous addition, into the reactor R2, of the liquid phase L1 coming from the reactor R1 or where appropriate from the vacuum enclosure itself supplied by R1, and of a solution of a composition D1 of water or of an aqueous composition of boron trifluoride D2 or of a composition D3 comprising hydrated boron trifluoride, called boron trifluoride hydrates to produce a gaseous stream E of boron trifluoride and a liquid phase L2. This step allows hydrolysis of the excess oleum included in the liquid phase L1 by the solution D1, D2 or D3.

[0118] Preferably, the solution used in step d) is solution D2 or D3, preferably D3, because these solutions will make it possible, through the BF3 they contain, to further increase the BF3 yield of the process of the invention. Particularly advantageously, solutions D2 and D3 are degassed before use so as not to introduce impurities into reactor R2. According to 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 and prior to the implementation of step d). According to a preferred embodiment, said solution D2 or D3 is a boron trifluoride hydrate BFs,xH2O with x from 0.5 to 4, more particularly obtained according to the process described in patent application WO 2013 / 050690.

[0119] Thus and advantageously, said solution D2 or D3 contains a mass content of less than 5 ppm in each of the following additional volatile compounds: N2, O2, CO2, SiF4, HCl, H2. Preferably, said solution D is free of additional volatile compounds N2, O2, CO2, SiF4, HCl, H2. This makes it possible not to contaminate the gas stream E with high-purity boron trifluoride.

[0120] The addition of solution D1 to the liquid phase L1 advantageously allows the boron trifluoride dissolved in it to be released in the form of BF3 gas while maintaining the HF and BF2OH compounds in said liquid phase L2.

[0121] The addition of solution D2 or D3 to the liquid phase L1 advantageously makes it possible to release 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.

[0122] The present process therefore makes it possible, by implementing steps c) and d), to eliminate numerous impurities initially present in composition A and in the oleum composition. The present process has the advantage of being easy to implement. 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 boron trifluoride content 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 free of HF and BF2OH.

[0123] The said gas stream E is drawn from the sky of reactor R2 to be recovered, for example, in a container.

[0124] According to a preferred embodiment, said solution D2 or D3 is a boron trifluoride hydrate BFs,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 is of formula BFs,xH2O with x from 2.5 to 3.1, preferably between 2.9 and 3.1, preferably between 3 and 3.1.

[0125] Preferably, the oleum concentration in step d) is lower than that in step b).

[0126] 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 content greater than 100% by weight. The sulfuric acid content can be monitored online using Raman infrared spectroscopy equipment according to the usual techniques according to which for a content greater than 100% there are no more HSO4- bands at 1043cm-1. The sulfuric acid content is in particular monitored by measuring an intensity band at 835 cm -1which decreases during the implementation of step d). This band corresponds to the compound HSOsF which was formed during step b) and which is consumed during step d) and which is characteristic of a sulfuric medium with a titer necessarily greater than 100% by weight in sulfuric acid titer because HSO3F, a non-ionized molecule, not electronically dissociated into cation and anion, cannot be easily manufactured in a sulfuric acid with a titer lower than 100% by weight. This measurement can be supplemented by the measurement of peaks at 913 cm -1 and 1162 cm -1 the intensity of which increases during the implementation of step d) by avoiding going into a sulfuric acid medium lower than 100% by weight characterized by the appearance of a band typical of HSCU' located at 1043 cm -1 .

[0127] Preferably, solution D1, 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%.

[0128] 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 in the reactor R2. The fluorosulfonic acid acts as a sequestering agent for BF2OH. Thus, the addition of the fluorosulfonic acid makes it possible to promote the maintenance of BF2OH in the liquid phase L1 during step d) and to improve the separation between the boron trifluoride and the BF2OH.

[0129] According to a preferred embodiment, step d) is carried out at a temperature between 30°C and 120°C, preferably between 45 and 120°C, more preferably between 70°C and 120°C, in particular between 80°C and 120°C, more preferably between 80 and 110°C. Preferably, the pressure of the reactor R2 is close to atmospheric pressure, preferably slightly higher than atmospheric pressure, for example between 1.0 and 1.3 bars.

[0130] Preferably, the flows of L1 and of the solution D1, D2 or D3 in the reactor R2 are such that the ratio in moles of the total quantity of SO3 added in the process by L1 compared to the total quantity of water added to the process by A, and by D1, or D2 or D3 is less than the molar ratio H2O / SO3 of 1, preferably between 0.95 and 0.99.

[0131] According to a preferred embodiment, the boron trifluoride content 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.

[0132] The liquid phase L2 may be treated to remove the HF then present in the form of high-boiling HSOsF 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 dissolved SO3 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 dissolved SO3 relative to the weight of the liquid phase L2). The liquid phase obtained can be at least partially recycled to reactor R1 as a sulfuric acid stream or used in other applications after hydrolysis with water and then stripping in air of the boron and fluorine it contains to form sulfuric acid 98% or 94% by weight, two commercial grades in high demand (see for example patent EP01 15719).

[0133] Fig. 1 schematically represents an installation according to a particular embodiment of the present invention.

[0134] 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 and also to eliminate sulfur oxides, in particular sulfur dioxide SO2, without using activated carbon which has the disadvantage of releasing fine particles of carbon in the adsorption columns due to the attrition forces exerted on the carbon grains. The fine particles thus present in the production lines pollute the storage container containing the gaseous BF3. In addition, the implementation of the present process avoids the presence of BF3 hydrate, BF2OH and or HF in the BF3 gas by ensuring a sulfuric acid content greater than 100% by weight in the second reactor.In addition, the process allows the elimination, by its design, of possible traces of other less frequent gaseous pollutants such as carbon dioxide CO2, or frequent ones such as silicon tetrafluoride, which are not desired in boron trifluoride intended for the electronic silicon doping industries.

[0135] Facility

[0136] The present application also relates to an installation for implementing the method of the invention. This installation comprises: - a first reactor (R1) 1 and a second reactor (R2) 2 and a peristaltic or gravity pump system by barometric leg used to transport the liquid phase between R1 and R2 while ensuring a liquid phase non-return valve function with respect to R2 towards R1 to prevent the liquid phase from rising from R2, preferably close to atmospheric pressure or higher, towards R1, preferably placed under atmospheric depression;

[0137] - the first reactor 1 is equipped with: a continuous feed device 3 allowing the feed of composition A, a continuous feed device 4 allowing the feed of composition B, a continuous feed device 5 allowing the feed of sulfuric acid or a feed device 6 allowing the feed of reactor 1 with composition L2 leaving reactor 2;

[0138] - a sealed cover fitted with a refrigerant / condenser 7 connected to a vacuum pump 8 allowing continuous extraction of the gas phase G1 comprising the volatile compounds F1 and F2;

[0139] - an overflow allowing reactor 2 to be supplied with composition L1 leaving reactor 1 via supply device 9;

[0140] - the second reactor 2 is equipped with:

[0141] - a continuous feed device 9 for feeding the reactor 2 with the composition L1 coming out of the overflow of the reactor 1;

[0142] - a continuous supply device 10 of the composition D1, D2 or D3;

[0143] - an outlet 11 in the reactor sky allowing the recovery of ultrapure BF3 gas in a storage container E using a compressor 15;

[0144] - an overflow outlet 12 in the middle of the reactor allowing the recovery of the composition L2 of oleum rich in sulfuric acid which can, via a valve 13, be partly reintegrated or not reintegrated at all into the reactor R1 via the feed device 6 and feed a stripping device 14 allowing the hot sulfuric acid to be treated in air to eliminate the boron and fluorine which are harmful to its recovery.

[0145] In a reactor with a capacity of 1 litre, equipped with a motor-driven stirrer and with the stirrer shaft passing through a stuffing box and equipped with stirring blades at the end of the shaft, 510 g of 99.8% by weight sulphuric acid, including 0.2% by weight of water, were introduced at the bottom of the tank.

[0146] The reactor is equipped with a sealed lid connected to the stirrer and two peristaltic pumps, the first being intended to feed the reactor with a boron trifluoride trihydrate BF3.3 H2O containing 55.7% by mass of BF3 (therefore 44.3% by weight in water). The second peristaltic pump is intended to feed the reactor with oleum containing 65% by mass of sulfur trioxide SO3. The gas outlet of the reactor is equipped with a washing bottle placed on a balance, bottle connected to a flexible hose made of fluorinated rubber or flexible tube made of PFA polymer. The washing bottle contains potash which can then be dosed to analyze the boron and fluorine to make redundancy with the mass weighed by absorption of BF3 gas in a basic solution. Measurements by one or other of the methods lead to 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 deducible by a density curve as a function of the BF3 content of the aqueous solution are sufficient to ensure the mass content of BF3 in the boron trifluoride hydrate.

[0147] The reactor was fed with 175 g of BF3 trihydrate with 530 g of oleum at 65% by mass of SO3 in 80 minutes, it was released regularly and proportionally about 90 g of BF3 gas in 80 minutes by simultaneous settings of a flow rate of boron trifluoride trihydrate of 175 g / 80 minutes or 2.2 g BF3.3H2O / min with a concomitant flow rate of oleum of 530 g in 80 minutes or 6.62 g SO3 / min. The temperature of the reactor was increased by heating with the double jacket of the reactor from 85 °C to 105 °C to further remove the dissolved BF3 gas from the sulfuric acid. The production yield is 86% by weight.

[0148] 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 organic and mineral carbon analyzer on Shimadzu TOC), 125 ppm SiF4 (measured by colorimetric assay with ammonium molybdate reacting with silica to give a yellow complex assayed at the UV / visible wavelength of 810 nm), 80 ppm HF (measured by high-resolution infrared). The sum of the mass contents of N2, O2, CO2, SiF4 is 0.07%. BF2OH is detected by high-resolution infrared demonstrating its presence by doublet of peaks between 1000 and 1100 cm-1. The boron trifluoride thus obtained has a content of at best 99.5% by weight, not including the significant presence of BF2OH which reduces the BF3 content announced above.

[0149] Description of the installation:

[0150] The installation comprises a first reactor (R1) followed by a vacuum flask (allowing the capture of the gas phase G1) and a second reactor (R2).

[0151] The two reactors (R1) and (R2) are connected to each other, (R1) will overflow into (R2) passing through the Imhoff cone, while (R2) will feed (R1) with part of the liquid phase L2 coming out of (R2). To ensure the non-return of the liquid L2 from (R2) operating in depression in the Imhoff cone placed upstream, the circulations of liquid phase between (R1) and the Imhoff cone then between the Imhoff cone and (R2) are ensured by peristaltic pumps which transport the liquid phase L2 with a flow control ensured by the rotation speed of the pump and having a non-return valve function for unwanted liquid products between (R1) and (R2) and between the Imhoff cone and (R1) and / or (R2), non-return valve function ensured thanks to the crushing of the pipe by the rotating roller. A peristaltic pump returns from the phase L2 of (R2) to (R1) to ensure the desired flow of oleum rich in sulfuric acid that it must provide.Piston pumps have the same effects as peristaltic pumps in terms of flow control functions or check valve effects.

[0152] Process:

[0153] A mixture is first prepared consisting of 530 g of oleum at 65% by weight of SO3, 510 g of sulfuric acid at 100% by weight and 85 g of BF3.3H2O at 55.7% by weight of BF3, then this stable reaction medium is introduced into the reactor R1 until it just begins to overflow through the side pipe and then the filling is immediately stopped so as not to prolong its overflow into R2.

[0154] Once reactor R1 is loaded, reactor R2 is then also loaded with a composition C2 comprising:

[0155] % SO3 = 0.9% by weight

[0156] % H2SO4 = 98.3% by weight

[0157] % H2O = 0.0% by weight %BF3 = 0.8% by weight

[0158] Until it too begins to overflow and then its filling is also stopped. This composition C2 will then be kept constant in R2 following the start of the experiment by the reagents which will feed it permanently.

[0159] The two reactors are connected to each other, R1 will overflow into R2 by passing through the Imhoff cone, while R2 will feed R1 with part of the liquid phase L2 leaving R2. To ensure the non-return of the liquid L2 from R2 close to atmospheric pressure in the Imhoff cone placed upstream under vacuum, the circulation of liquid phase between R1 and the Imhoff cone then between the Imhoff cone and R2 are ensured by peristaltic pumps which transport the liquid phase L2 with flow control ensured by the rotation speed of the pump and having a non-return valve function for unwanted liquid products between R2 and R1 and between the Imhoff cone and R1 and / or R2, this thanks to the crushing of the pipe by the rotating roller. A peristaltic pump returns from the phase L2 of R2 to R1 to ensure the desired flow of oleum rich in sulfuric acid which it must supply to it.Piston pumps have the same effects as peristaltic pumps in terms of flow control functions or check valve effects. Reactor 1:.

[0160] The reaction medium in R1 is then heated to between 104 and 107°C and maintained at this temperature. The reactor R2 is heated to the same temperature. The reaction medium is then continuously introduced into R1 by peristaltic pumps.

[0161] - 63.7g of BF3.3H2O per hour

[0162] - 397.5 g of oleum 65% by weight per hour

[0163] - 382 g per hour of composition L2 (oleum rich in sulfuric acid) from reactor R2.

[0164] Composition L1 loaded with oleum, sulfuric acid and BF3 dissolved in oleum leaves through the overflow of the side tube of reactor R1 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 which is equipped with a piston pump continuously emptying the product which arrives through the cone cover from above. On the vacuum-tight cover arrives a tube from the 1 er reactor and a condenser also attached to the lid and cooled to 1 °C above which a vacuum pump removes G1 gases such as N2, CO2, CO, SO2, 02, SiF4, H2 and traces of BF3 gas not retained in the liquid phase of L1 rich in oleum.

[0165] The oleum-rich liquid phase (L1) 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 R1.

[0166] (L1) has a measured H2SO4 titer of approximately 103.8% by weight by acidimetric assay using NaOH.

[0167] Vacuum treatment in the Imhoff cone:

[0168] The vacuum is created in this Imhof cone permanently in accordance with step d) of the present process at a temperature of approximately 1 °C for the gases leaving downstream of the refrigerant, while constantly maintaining the vapor pressure of the sulfuric acid at 80 °C, the vapors of which are cooled to 1 °C as a low vacuum threshold.

[0169] Gases such as N2, CO2, CO, SO2, O2, SiF4 are eliminated leading to the purification of the BF3 dissolved in the liquid phase L1 from these volatile compounds F1 and F2. The vacuum is permanently effective to treat the low feed flow coming from the first reactor.

[0170] Second reactor R2:

[0171] A second double-jacketed reactor identical to that of R1 is also 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 making it possible to know the SO3 content contained in the reactor R2 thanks to the measurement of the band around 720 cm-1.

[0172] The same system equips R1 to continuously control the contents of reactors R1 and R2 in a so-called oleum composition zone where there is no possible presence of water in the reaction medium. This online analyzer prevents slippage in the aqueous sulfuric acid zone.

[0173] Reactor R2 is then continuously fed by the overflow from R1 having passed through the Imhoff cone under vacuum and also fed by a second flow of pure boron trifluoride trihydrate, i.e. previously degassed by hot vacuum distillation.

[0174] The overall molar ratio (taking into account the two reactors) between the SO3 of the oleum used and the water of the BF3,3H2O added in the two reactors is close to 1.

[0175] In R2, BF3 gas is released continuously at a rate of 67 g / h and a composition L2 of oleum rich in sulfuric acid leaves reactor R2 at a rate of 838 g / h into a sulfuric acid storage device in order to subject it to a purification treatment to make it usable in other applications. The purification consists of stripping this hot sulfuric acid in air to remove the boron and fluorine which are harmful to its recovery and at the same time adding water to lower the sulfuric acid content to around 94% by weight.

[0176] Analysis of total sulfur in the BF3 gas leaving R2 indicates less than 1 ppm sulfur and therefore less than 2 ppm SO2.

[0177] The other part of this L2 oleum rich in sulfuric acid is recycled at a rate of 382 g / h to reactor R1.

[0178] Example 3:

[0179] The process is carried out in a similar manner to that of example 2, except that the vacuum is created on reactor R1 permanently with a condenser on the cover of R1 connected to a Teflon vacuum pump so as to force back into reactor R1 the little distillate which would like to leave the reactor.

[0180] The gaseous BF3 produced in the second reactor was placed in a 1-liter bottle using a 12 / 220 Volt mini electric compressor capable of filling a 1-liter bottle in 1 hour resistant to 300 bars. The gas can be analyzed by high-resolution Fourier transform infrared and very long optical path to verify the absence of SIF4 at 1040 cm -1 , HCl and HF having a series of multiplet IR bands above 3000 cm -1, very characteristic where the BF3 gas has no disturbing infrared absorption to observe them. The spectrum is completely devoid of the characteristic IR bands of HCl and HF leading to the conclusion of the absence of HF and HCl gas. By chromatography under helium, with a DID detector which is a very high voltage discharge detector in helium which emits very high energy ultraviolet radiation, ionizing everything except helium, concluded that the BF3 gas leaving the R2 reactor is free of H2, CO2, CO, N2 and 02.

[0181] The recovered BF3 gas has a purity of more than 99.99%.

[0182] Purity test example 2 = 100-(0.1 + 0.05 + 0.05 + 0.05 + 0.2) / 100000 = 99.999% on this table. The recovered BF3 gas is free of HCl, HF, SIF4 and BF2OH verified by the absence of absorption of infrared bands on a high-resolution device with a long optical path from MIRAN technology. Absence of infrared band around 1040 cm' 1for SiF4 and for BF2OH and bands 1100 to 1200 cm-1 for SO2. No characteristic multiplets for HCl or HF in the areas above 3000 cm' 1 for HCl and above 4000 cm' 1 for HF.

[0183] The volume of inert gases measured on a water eudiometer is zero (not measurable) for BF3 of Example 2 or Example 3.

Claims

Claims 1. Process for the continuous production of gaseous boron trifluoride comprising the steps of: e) Providing a composition A comprising boron trifluoride (BF3) and optionally one or more additional volatile compounds F1; f) In a first reactor R1 continuous introduction: - a sulfuric acid solution and a solution B comprising oleum and additional volatile compounds F2 to form a solution C; - of composition A; to form: - a liquid phase L1 comprising oleum, sulfuric acid and BF3 and - a gas phase G1 comprising said additional volatile compounds F1 and F2; g) Continuous removal of the gas phase G1 comprising said additional volatile compounds F1 and F2, preferably by depression; h) Continuous introduction of the liquid phase L1 into a second reactor R2 and continuous introduction into the reactor R2 of a composition D1 of water or of an aqueous composition of boron trifluoride D2 or of a composition D3 comprising hydrated boron trifluoride, called boron trifluoride hydrates, the compositions D1, D2 and D3 not containing any additional compound F1 to produce a gas phase E of boron trifluoride and a liquid phase L2.

2. Method according to claim 1 characterized in that said gaseous stream E is recovered in a container.

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

4. Method according to any one of the preceding claims, characterized in that said composition A is a BF3 composition comprising one or more additional volatile compounds F1 selected from the group consisting of H2O, N2, O2, C02, Si F4, H2 and HCl.

5. Process according to any one of the preceding claims, characterized in that the boron trifluoride of composition A is gaseous BF3 BF3,xH2O with x = 0, optionally mixed with BF20H, 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 derived from the reaction between a boron compound selected from B(OH)3, B2O3 or HBO2 and a fluorinated compound selected by HF or HSO3F.

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

7. Method 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 greater than 112% by weight, preferably greater than 113% by weight, more preferably greater than 114% by weight.

8. Method according to any one of the preceding claims, characterized in that 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.

9. Method according to any one of the preceding claims, characterized in that the oleum concentration in reactor R1 is greater than that of reactor R2.

10. Method according to any one of the preceding claims, characterized in that the composition L2 from R2 is partly reintroduced into R1 as a sulfuric acid solution.

Images