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 producing high-purity boron trifluoride Field of invention

[0001] 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. Technical background

[0002] Boron trifluoride (BF3) is a gas which 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.

[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 come from the raw materials used or from residues of some of these raw materials. Contents of the impurities mentioned 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.

[0004] Some prior art documents disclose purification techniques for partially removing some of these impurities. JP59050018 discloses a process for purifying BF3 using H2O2 and water in sulfuric acid to remove SO2 and SO3. US 3,625,651 and FR 2 003 557 also disclose 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 EP 0 922 672 is a process using treatment with H2O2 and treatment with air to purify the gaseous BF3 which is recycled in sulfuric acid by washing. of the air flow and BF3 so as to recycle the boron fluoride tri to the production of compressed BF3 gas.

[0005] Despite these purification processes applicable to technical boron trifluoride, there is still a need for a process for producing very pure boron trifluoride that makes it possible to eliminate volatile impurities such as those mentioned above, and in particular SiF4 or hydrogen fluoride. Furthermore, there is also a need to provide such a process using oleum and allowing the elimination of SO2 present in the oleum without resorting to activated carbon (activated carbon being responsible for the production of dust). There is also a need for an efficient and simple-to-implement process that makes it possible to 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. Summary of the invention

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

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

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

[0009] - of a sulfuric acid solution and of 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 gas phase G1 comprising said additional volatile compounds F1 and F2;

[0014] c) Continuous removal of the gaseous phase G1 comprising said additional volatile compounds F1 and F2, preferably by depression;

[0015] d) Continuous introduction of the liquid phase L1 into a second reactor R2 and continuous introduction into the reactor R2 of a composition DI of water or of an aqueous composition of boron trifluoride D2 or 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 gaseous phase E of boron trifluoride and a liquid phase L2.

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

[0017] 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.

[0018] In one embodiment, said composition A is a BF3 composition comprising one or more additional volatile compounds F1 selected from group consisting of H2O, N2, O2, C02, 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 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.

[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 greater than 112% by weight, preferably greater than 113% by weight, more preferably 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 oleum concentration in reactor RI is higher than that in reactor R2.

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

[0025] [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. 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) Providing a composition A comprising boron trifluoride (BF3) and optionally one or more additional volatile compounds Fl;

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

[0030] - of a sulfuric acid solution and of 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 F1 and F2;

[0035] c) Continuous removal of the gaseous phase G1 comprising said additional volatile compounds F1 and F2, preferably by depression;

[0036] d) Continuous introduction of the liquid phase L1 into a second reactor R2 and continuous introduction into the reactor R2 of a composition DI of water or of an aqueous composition of boron trifluoride D2 or a composition D3 comprising hydrated boron trifluoride, called boron trifluoride hydrates, the compositions DI and D2 not containing any additional compound F1 to produce a gaseous phase E of boron trifluoride and a liquid phase L2.

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

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

[0039] 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. Step a)

[0040] The boron trifluoride contained in composition A may have different origins. The boron trifluoride may be gaseous BF3, BF3,xH2O with x = 0 impure or technical grade. For example, the gaseous BF3 contained in composition A may be BF3 having a purity less than or equal to 99.5%, that is to say that 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 may 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 derived from 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. In a particularly preferred manner, 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 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 BF3 content in said composition A may 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 comprise, 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 comprises 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 F1.

[0045] In the case where composition A does not comprise volatile compounds F1 then this composition A could be a composition D2 or D3 as described below.

[0046] 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 can therefore comprise one, two, three, four, five, six, seven, eight or all of the additional volatile compounds F1 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 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.

[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 based on the total composition.

[0049] In particular, if it contains it, said composition A may comprise from 10 ppm to 1 mol%, preferably 100 ppm to 0.5 mol% 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 mol%, preferably from 10 ppm to 0.1% of CO2 based on the total composition.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Thus said composition A can 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 mol%, preferably from 100 ppm to 0.5 mol% of O2 based on the total composition; and / or - from 10 ppm to 0.5 mol%, preferably from 10 ppm to 0.1% of 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 mol%, preferably from 10 ppm to 0.5 mol%, of H2 based on the total composition; and / or - from 10 ppm to 2 mol%, preferably from 10 ppm to 0.5 mol% 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 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% by mole based on the total composition.

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

[0058] The BF3 in composition A containing Fl may be BF3 trihydrate or its aqueous solutions originating from by-products of BF3 catalyst gas used in alkylation units with a catalyst for the manufacture of synthetic oil for applications for lubricating thermal engines. Step b)

[0059] Step b) of the present process consists of continuously introducing, into the 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, 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 added SO3 or as a percentage of equivalent H2SO4 if the necessary amount of water were added (amount of water required to transform 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 = 114.6, i.e. a sulfuric acid with a strength of 114.6.

[0063] The sulfuric acid composition introduced in step b) may 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 more preferably greater than 112% by weight, preferably more preferably more than 113% by weight, more preferably more preferably more than 114% by weight.

[0065] Sulfuric acid with a strength greater than 100% by weight corresponds to anhydrous sulfuric acid (free of water) comprising SO3. Indeed, the SO3 present in the 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 se 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 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.

[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 based on 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 based on 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 based on 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 based on 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 can 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 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 SO2 based on the total solution; - from 10 ppm to 0.10 mol%, preferably from 10 ppm to 0.25 mol%, of free SO3 based on the total solution.

[0073] 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.

[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 based on 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 mol% of CO2 based on 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 mol% of SO2 based on 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 based on 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 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 mol%, preferably from 100 ppm to 0.5 mol% of O2 on a base of the total solution; and / or

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

[0083] - from 10 ppm to 1 mol%, preferably from 10 ppm to 0.5 mol% of SO2 based on of the total solution;

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

[0085] The reactor RI 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 the 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 said additional compounds F1 and F2. The reaction between composition A and composition C forms in particular a complex compound between BF3 and SO3 allowing advantageously to keep the BF3 solubilized in the oleum unlike the volatile compounds Fl and F2 (including SO2) which are found 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 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 120°C. Step b) can be carried out at atmospheric pressure.

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

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

[0090] Solution C will make it possible to complex the BF3 contained in composition A with the SO3. It is therefore necessary for composition C to include a sufficient quantity of SO3 to complex all the BF3 present in composition A.

[0091] 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 l*((BF3)y.xH2O, with x>0 and y generally 1), preferably the quantity of SO3 increases proportionally to the quantity of water in the hydrated BF3, preferably according to the equation:

[0092] Thus in step b) the overall 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 an overall quantity of SO3 of = 3*1+1*3=6.

[0093] Preferably, the total molar amount of oleum, for the boron trifluoride trihydrate, is twice the amount of oleum required to complex the BF3 contained in the 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 flows in composition A, B and sulfuric acid are such that the saturation threshold of the oleum by BF3 is approached.

[0095] The quantity of boron trifluoride capable of dissolving in the liquid phase L1 resulting from the mixture between composition A and mixture C can be calculated prior to implementing the method. It is sufficient, for example, to mix composition A with said mixture C in the same proportions and under the same conditions operational until the detection of gaseous boron trifluoride then leaving with the gases Fl or F2. This gas 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 measurement with a flow meter of a sudden increase in flow rate in the reactor due to the release of gaseous boron trifluoride.

[0096] In the case where the total molar quantity of SO3 added in step b) would not be sufficient to complex all the BF3 contained in composition A, 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 column of sulphuric acid at 98 or 100% by weight 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 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.

[0098] 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.

[0099] For example, in step b) with (BF3)2,H2O, a total quantity of SO3 = 3y+l*x in which y=2 and x=l, we would have a total quantity of SO3 of = 3*(2)+l*(l)=7, i.e. 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.

[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 quantity of oleum at 86 mol% 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).

[0101] According to another embodiment, when the boron trifluoride of composition A is BF3,H2O, 25 mol% excess oleum is introduced to the additional quantity of 75 mol% oleum already used to complex BF3 already 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 BF3,1,5H2O, 33 mol% of excess oleum is introduced to the complete quantity 67 mol% oleum supplement already used to complex BF3 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 BF3.2H2O, 40 mol% excess oleum is introduced to the additional quantity 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 additional quantity 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 quantity of oleum at 33 mol% 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 additional quantity of oleum at 25 mol% 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) 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 BF3 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 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 BF3 in the liquid phase L1 as long as step d) is not implemented.

[0108] Furthermore, during the implementation of step b), the formation of HSO 3F 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 im- dissolution 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 of between 13 and 36% by weight relative to the total weight of the liquid phase L1.

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

[0111] 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.

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

[0113] 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 because of 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).

[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 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 RI can be surmounted by a condenser cooler connected to a vacuum pump for evacuating the gaseous flow G1 from RI. Preferably, the pressure PI to be applied for implementing step c) is lower than atmospheric pressure. Preferably the pressure PI 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 PI 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 PI for carrying out step c) is between the vapor pressure of the sulfuric acid at the temperature for carrying out step b). implementation 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] It may be useful, in this embodiment, to compensate for any losses of SO3 in gaseous form by a higher flow rate of oleum. A person 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 RI 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 RI 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.

[0116] 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 bottom of the reactor to the reactor cover. Thus, the liquid phase L1 is transported from the bottom of the reactor 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 PI defined above. As indicated above, the pressure is very low.

[0117] In another embodiment, step c) is distinct from step b). In this case, a vacuum enclosure is introduced between the reactor RI 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 RI. 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 PI 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 BF2 OH. Thus, the pressure PI for implementing 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 implementing step b).Preferably, the pressure PI 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. Step d)

[0118] 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 RI or, where appropriate, from the vacuum chamber itself supplied by RI, and of a solution of a composition DI of water or of an aqueous composition of boron trifluoride D2 or 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.

[0119] 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 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 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.

[0121] The addition of solution D1 to the liquid phase L1 advantageously makes it possible to release the boron trifluoride dissolved therein, in the form of BF3 gas while maintaining the HF and BF2OH compounds in said liquid phase L2.

[0122] 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.

[0123] 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 devoid of HF and BF2OH.

[0124] Said gas stream E is withdrawn from the overhead 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 is of 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 during step d) is lower than that of 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 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 longer any HSO4- bands at 1043cm-1. The sulfuric acid content is in particular 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 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 completed by measuring peaks at 913 cm1 and 1162 cm 1 whose intensity 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 HSO4 located at 1043 cm1.

[0128] Preferably, the 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 the 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 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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] The liquid phase L2 can be treated to remove the HF then present in the form of high-boiling 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 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 the RI reactor as a sulfuric acid stream or be 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% sulfuric acid by weight, two commercial grades in high demand (see for example patent EP0115719).

[0134] [Fig.l] 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 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 such as non-silicon tetrafluoride. desired in boron trifluoride for the electronic silicon doping industries. Facility

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

[0137] - a first reactor (RI) 1 and a second reactor (R2) 2 and a pump system peristaltic or gravitational by barometric leg used to transport the liquid phase between RI and R2 while ensuring a liquid phase non-return valve function with respect to R2 towards RI to prevent the liquid phase from rising 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 with:

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

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

[0141] - a continuous feed device 5 allowing the acid feed sulfuric or a feed device 6 allowing the feed of reactor 1 with composition L2 leaving reactor 2;

[0142] - a sealed cover provided 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] - an overflow allowing reactor 2 to be supplied with the outgoing composition L1 from reactor 1 via feed device 9;

[0144] - the second reactor 2 is equipped with:

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

[0146] - a device 10 for continuously supplying the composition D1, D2 or D3;

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

[0148] - an overflow outlet 12 in the middle of the reactor allowing the recovery of the com position L2 of oleum rich in sulfuric acid which can, via a valve 13, be partly reintegrated or not reintegrated at all into the reactor RI via the feed device 6 and feed a stripping device 14 making it possible to treat the hot sulfuric acid in air to eliminate the boron and fluorine which are harmful 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 liter, 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 sulfuric acid, including 0.2% by weight of water, were introduced at the bottom of the tank.

[0152] The reactor is equipped with a sealed cover 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 of 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 the 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.

[0153] 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 released regularly and proportionally about 90 g of BF3 gas in 80 minutes by simultaneous adjustments 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 S03 / 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 gaseous BF3 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 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. Example 2 (according to the present invention)

[0156] Description of the installation:

[0157] The installation comprises 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) passing through the Imhoff cone, while (R2) will feed (RI) with part of the liquid phase L2 leaving (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 (RI) 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 (RI) and (R2) and between the Imhoff cone and (RI) 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 (RD to ensure the desired flow of oleum rich in sulfuric acid that it must provide it.Piston pumps have the same effects as peristaltic pumps in terms of flow control functions or check valve effects.

[0159] Method:

[0160] A mixture 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 is first produced, then this stable reaction medium is introduced into the reactor RI 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.

[0161] Once the reactor RI is loaded, the 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% by weight %BF3 = 0.8% by weight

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

[0166] The two reactors are connected to each other, RI will overflow into R2 by passing through the Imhoff cone, while R2 will feed RI with a part of the liquid phase L2 leaving R2. To ensure that the liquid L2 from R2 close to atmospheric pressure does not return into the Imhoff cone placed upstream under vacuum, the liquid phase circulations between RI and the Imhoff cone then between the Imhoff cone and R2 are provided 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 RI and between the Imhoff cone and RI and / or R2, this thanks to the crushing of the pipe by the rotating roller. A peristaltic pump returns from the L2 phase of R2 to RI to ensure the desired flow of oleum rich in sulfuric acid that it must provide. Piston pumps have the same effects as peristaltic pumps on the functions of flow control or non-return valve effects. RI Reactor:

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

[0168] The following are then continuously introduced 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 R2 reactor.

[0172] The composition L1 loaded with oleum, sulfuric acid and BF3 dissolved in the oleum leaves through the overflow of the side tube of the 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 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 coming from the 1st reactor and a condenser also fixed to the cover and cools to 1°C above which a vacuum pump eliminates the gases G1 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.

[0173] The liquid phase (Ll) rich in oleum coming 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 titer of approximately 103.8% by weight by acidimetric assay with NaOH. Vacuum treatment in the Imhoff cone:

[0175] The vacuum is created in this Imhof cone permanently in accordance with step d) of the present method 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.

[0176] 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 Fl and F2. The placing under vacuum is permanently in effect to handle the low feed flow 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 making it possible to know the SO3 content contained in the reactor R2 thanks to the measurement of the band around 720 cm-1.

[0178] The same system equips RI to permanently control the contents of the reactors RI and R2 in a so-called oleum composition zone where there is no possible presence of water in the reaction medium. This online analyzer avoids slipping into the aqueous sulfuric acid zone.

[0179] Reactor R2 is then continuously fed by the overflow of RI having passed through the Imhoff cone drawn under vacuum and also fed 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 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.

[0181] In R2, BF3 gas is released continuously at a flow rate of 67 g / h and a composition L2 of oleum rich in sulfuric acid leaves the 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.

[0182] Analysis of the total sulfur in the BF3 gas leaving R2 indicates less than 1 ppm of sulfur and 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 the vacuum is created on the reactor RI permanently with a refrigerant on the lid of RI connected to a Teflon vacuum pump so as to cause the little distillate which would like to leave the reactor to flow back to the reactor RI.

[0185] The BF3 in gaseous form 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 cm1, HCl and HF having a series of multiplet IR bands above 3000 cm1, very characteristic where 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 helium chromatography, 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.

[0186] The recovered BF3 gas has a purity of more than 99.99%. BF3 analyses analyzed by chondratography DID detector p(abs)=32 bars B [H2] » [O2+Ar] ppmy [N2j ppmv [CO] ppmv [CH4] ppniv [CO2] BRmv Injection example |1 comparative Sample 17 / 10 / 22 7.5 35 3500 0.1 <0.05 1 Injection example 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 absorption of infrared bands on a high-resolution long-path optical device from MIRAN technology. Absence of infrared band around 1040 cm 1 for SiF4 and for BF2OH and of bands 1100 to 1200 cm-1 for SO2. No characteristic multiplets for HCl or HF in the zones above 3000 cm 1 for HCl and above 4000 cm 1 for HF.

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

Claims

Claims

1. 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 RI 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 F1 and F2; c) Continuously removing 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 the reactor R2 of a composition DI of water or of an aqueous composition of boron trifluoride D2 or 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 gaseous 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. A 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 Fl selected from the group consisting of H2O, N2, O2, CO2, SiF4, H2 and HCl.

5. A method according to any preceding claim ca- characterized in that 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 from 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. Process according to any one of the preceding claims, characterized in that 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 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 the reactor RI is greater than that of the reactor R2.

10. Method 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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