FR2994659A1 - PROCESS FOR EXTRACTING AND PURIFYING SODIUM BROMIDE - Google Patents

Abstract

Extracting and purifying sodium bromide, involves (a) mixing a residue, solid or pasty material comprising sodium bromide and organic and/or inorganic impurities with methanol to obtain a solution of sodium bromide in methanol and a solid residue containing organic and/or inorganic impurities, (b) concentrating the solution of sodium bromide to obtain the solid sodium bromide, (c) washing the solid sodium bromide using solution comprising a mixture of alcohol consisting of methanol and ethanol and an acid to obtain a purified sodium bromide, and (d) recovering the purified sodium bromide. Extracting and purifying sodium bromide, comprises (a) mixing a residue, solid or pasty material comprising sodium bromide and organic and/or inorganic impurities with methanol to obtain a solution of sodium bromide in methanol and a solid residue containing organic and/or inorganic impurities, (b) concentrating the solution of sodium bromide to obtain the solid sodium bromide, where the concentration step comprises evaporating the methanol, (c) washing the obtained solid sodium bromide using a solution comprising a mixture of an alcohol consisting of methanol and ethanol and an acid to obtain a purified sodium bromide, and (d) recovering the purified sodium bromide. An independent claim is included for use of the method in recycling of industrial effluents comprising water, sodium bromide and optionally one or more organic solvent(s).

Description

The present invention relates to a process for extracting and purifying sodium bromide contained in a residue comprising sodium bromide and organic and / or mineral impurities, and the use of said process in the recycling of industrial effluents.

The treatment of industrial effluents is a major issue from an ecological point of view and these effluents can represent an important source of raw materials. In particular, effluents from the untreated chemical and pharmaceutical industries can be a source of pollution. In addition, they may contain chemical substances such as organic and / or inorganic products, solvents which, once extracted and / or purified, represent an important source of raw materials that can be used in other industrial synthesis processes. Organobromine compounds, especially alkyl bromides, bromoacids and bromoesters, are synthetic intermediates commonly used in the chemical and pharmaceutical industry for the manufacture of organic molecules by grafting the organic part of the organobromine compound onto another molecule. In these reactions, bromine is in fact only a transfer agent. At the end of the reaction, it is generally found in the form of alkali bromides in the effluents. In addition to bromides (alkaline bromides, ammonium bromides, HBr), these brominated effluents contain polluting organic compounds.

Users of organobromine compounds are thus faced with a problem of effluent discharge, linked both to the very nature of said effluents, which are generally aqueous brominated solutions containing alkaline bromides, ammonium bromides, or even HBr, and also to polluting organic compounds. These organic compounds can be acids, amines, alcohols, solvents or ammonium salts. The organic compound content of the effluents is expressed as total organic carbon or TOC. An excessively high TOC content is unacceptable for recovery of the bromides contained in these effluents in the form of elemental bromine (Br2) by conventional methods such as, for example, the Kubierschky process. The method comprises contacting a brominated aqueous solution with chlorine gas and steam in a packed tower (bromine tower) to oxidize the bromide. At the top of the tower, a mixture of elemental bromine (Br2), chlorine and steam is cooled and cooled to condense the bromine.

However, the presence of organic compounds in the brominated aqueous starting solution constitutes a risk of pollution of the released bromine. In addition, the presence of oxidizable organic materials and / or nitrogenous organic materials may lead to explosive risks (formation including NBr3, explosive). It must also be remembered that a too high content of organic materials in the starting solution may lead to the formation of solid products which may lead to blockages in the installation. It is therefore imperative to reduce as much as possible the organic compounds and nitrogen compound content of the brominated effluents to be upgraded.

The patent application EP 1 004 354 thus proposes a process for lowering the content of organic materials and nitrogen products contained in a brominated effluent in the form of a brominated aqueous solution or of a brominated solid, in particular in order to recovering the bromides contained in said effluent in elemental bromine. According to the examples of this patent application, this method consists of subjecting a brominated effluent, previously acidified or added with a base, to one or more steam trainings to remove ammonia and light organic compounds and / or or subjecting a solid residue of NaBr or KBr to a wash with isopropanol or acetone (in the case of NaBr only). On an industrial scale, this process would require the handling of large amounts of acid and base. This is not only an environmental disadvantage, but is also incompatible with some solvents that may be present in the brominated effluent. There is therefore still a need for a new process which would constitute an alternative to the process proposed in EP 1 408 006. An object of the invention is therefore to provide a process for extracting and purifying bromide of high purity effluents. and bromine residues in the chemical and pharmaceutical industry. Another object of the invention is to provide a process for extraction and purification of bromide which can be easily implemented on an industrial scale and at a lower cost, by using readily accessible solvents and / or chemicals, cheap.

It is therefore the merit of the Applicant to have developed, after intensive research, a process for extracting and purifying sodium bromide that meets all these requirements. An object of the present invention is to provide a method for extracting and purifying sodium bromide comprising the steps of: (1) a step of mixing a solid or pasty residue comprising sodium bromide and organic impurities and / or mineral, with methanol, so as to obtain a solution of sodium bromide in methanol and a solid residue containing organic and / or mineral impurities, (2) concentration of the sodium bromide solution so as to obtaining solid sodium bromide, this concentration step comprising a step of evaporation of the methanol, (3) at least one washing of the sodium bromide obtained in the preceding step with a washing solution comprising a mixture of a chosen alcohol from methanol and ethanol, and an acid to obtain purified sodium bromide and used wash solution, (4) recovery of purified sodium bromide. The term "sodium bromide" refers to the compound of formula NaBr and the solvates thereof. Non-limiting examples of solvated molecules are water, methanol and ethanol. The organic or inorganic impurities of the residue used in stage 1 include in particular organic salts of sulfur compounds and / or nitrogen compounds. The process according to the invention makes it possible to largely eliminate organic compounds, ammonium compounds and heavy metals. According to the inventors, the good performance of the process of the invention is in particular due to the good solubility of sodium bromide in methanol and to the fact that many impurities such as organic salts, in particular alkaline salts and more particularly sodium salts, sulphonates and sulfur compounds are only slightly soluble in methanol.

Thus, the purified sodium bromide obtained has a purity greater than or equal to 85% by weight, preferably greater than or equal to 87% by weight, more preferably greater than or equal to 90% by weight. More particularly, it has a total organic carbon (TOC) content of less than or equal to 0.1%, preferably less than or equal to 0.07%, more preferably less than or equal to 0.05% by weight relative to the total weight. purified sodium bromide. Advantageously, the purified sodium bromide also has one, two or all of the following characteristics: an ammonium content less than or equal to 250 mg / kg, preferably less than or equal to 150 mg / kg, more preferably less than or equal to 100 mg / kg, a phosphorus content less than or equal to 500 mg / kg, preferably less than or equal to 400 mg / kg, more preferably less than or equal to 300 mg / kg and / or a total heavy metal content of less than or equal to 150 mg / kg, preferably less than or equal to 100 mg / kg, more preferably less than or equal to 50 mg / kg. The process according to the invention thus makes it possible to obtain sodium bromide having a purity sufficient for use in the industrial synthesis of dibroma.

An advantage of the process according to the invention is that it can be used on residues more or less rich in sodium bromide. Thus, it makes it possible to recover the sodium bromide, in good quantity and quality, from residue having a not very high level of sodium bromide, such as for example 60% by weight or less. Step 1 is advantageously carried out at a temperature between 10 and 50 ° C, preferably between 10 and 30 ° C, more preferably at room temperature, that is to say approximately between 20 and 25 ° C. The solution of sodium bromide in the alcohol and the solid residue containing organic and / or mineral impurities obtained at the end of step 1 can be separated by any suitable means known to those skilled in the art before proceeding to Step 2. This separation can in particular be carried out by filtration.

The methanol evaporated in step 2 can be recovered and advantageously reused in steps 1 and / or 3 of the process according to the invention. The alcohol used in step 3 may be identical to or different from that used in step 1. Thus, methanol can be used for the two steps or methanol for step 1 and ethanol for Step 3. The use of ethanol in washing step 3 has the advantage of a lower solubility of sodium bromide than in methanol. In an advantageous embodiment, use of methanol in step 1 and ethanol in step 3 so as to have a solubility of sodium bromide best suited to each of these steps.

In another advantageous embodiment, methanol will be used for the two steps, so as to limit the number of solvents involved in the process according to the invention. The washing solution employed in step 3 preferably has a pH of 2 to 4, preferably 2.5 to 3.5 and even more preferably about 2.8. Advantageously, the acid used in the washing step 3 is chosen from the group consisting of hydrochloric acid, sulfuric acid and phosphoric acid, preferably hydrochloric acid and sulfuric acid, more preferably the hydrochloric acid. The washing step 3 can be performed one or more times. Preferably, only one wash with the acid wash solution is carried out so as to limit the loss of NaBr due to its dissolution in the wash solution.

In one embodiment, the method according to the invention further comprises an additional drying step carried out after step 4. The used washing solution obtained in step 3 which consists essentially of organic impurities and / or mineral, alcohol, acid, water but also sodium bromide can be advantageously reprocessed.

Thus, in one embodiment, the method according to the invention also comprises the following steps: (6) recovery of the used washing solution obtained at the end of step 3, (7) neutralization of the solution of washing by addition of a basic aqueous solution, (8) concentration by distillation or evaporation, preferably by distillation, so as to separate the alcohol and an aqueous solution consisting essentially of organic and / or mineral impurities, water and sodium bromide, (9) recovery of the alcohol obtained in step 7 on the one hand, and the aqueous solution consisting essentially of organic and / or mineral impurities, water and sodium bromide, somewhere else. Advantageously, the basic aqueous solution used in step 7 is an aqueous solution of sodium hydroxide or potassium hydroxide, preferably sodium hydroxide.

The alcohol recovered in step 9 may advantageously be reused in steps 1 and 3 of the process according to the invention when it is methanol or in step 3 in the case of ethanol. The aqueous solution recovered in step 9 can be concentrated, in particular by evaporation. There is thus obtained a residue comprising sodium bromide which can be introduced in step 1 of the process for extracting and purifying sodium bromide according to the invention. In addition to making it possible to obtain sodium bromide having a purity sufficient for use in the industrial synthesis of dibroma, the process according to the invention is carried out with solvents (methanol, ethanol) and acids (for example: hydrochloric acid, sulfuric acid, phosphoric acid) and optionally bases (eg sodium and potassium hydroxides) readily available and inexpensive. Moreover, these solvents, acids and bases do not present, in the quantities in which they are used, any major risks for the environment. From an ecological and economic point of view, the method according to the invention is also advantageous in that it allows the recovery and reuse of alcohol solvents according to the needs of the user.

The process according to the invention is therefore very versatile and can be used in the recycling of industrial effluents comprising sodium bromide, in particular industrial effluents comprising water, sodium bromide and optionally one or more solvents ( s) organic (s).

The present invention therefore also relates to the use of the process for extracting and purifying sodium bromide according to the invention in the recycling of industrial effluents comprising sodium bromide, in particular industrial effluents comprising water, sodium bromide and optionally one or more organic solvent (s). Among the organic solvents, non-limiting examples are N, N-dimethylformamide (DMF), N, N-dimethylacetamide, N-methylpyrrolidinone, halogenated solvents such as dichloromethane, chloroform, tetrachloride and the like. carbon, dichloroethane, sulfoxides such as dimethylsulfoxide, ketones such as acetone, butan-2-one, tetrahydrofuran, tetrahydropyran, 1,4-dioxane, ethers such as diethyl ether, alkyl acetates such as ethyl acetate, alkanes such as pentane, n-hexane, n-heptane, cycloalkanes such as cyclopentane, cyclohexane, alcohols such as methanol, ethanol n-propanol, i-propanol, t-butanol, tert-amyl alcohol, benzene, toluene. Sodium bromide is in particular a by-product obtained in chemical reactions carried out from alkyl halides or aryl halides. One of the solvents commonly used in these reactions is DMF, which is generally separated from the product of interest by washing with water which also causes sodium bromide. In one embodiment, the process according to the invention can be implemented in the recycling of an industrial effluent comprising water, sodium bromide and DMF.

The process according to the invention may especially be used in the recycling of an industrial effluent which comprises the following stages: (a) evaporation of the water and, if appropriate, of the organic solvent (s) of the industrial effluent so as to obtain a liquid phase comprising water and if appropriate the (s) organic solvent (s) on the one hand and a residue comprising sodium bromide and organic and / or mineral impurities on the other hand, (b) applying the method of extraction and purification of sodium bromide according to the invention to the residue comprising sodium bromide and organic and / or mineral impurities obtained in step a. Advantageously, step a of evaporation of the water and, if appropriate, of the organic solvent (s) is carried out at atmospheric pressure at a temperature ranging from 80 to 150 ° C., preferably from 100 to 130 ° C. C. It can also be carried out under reduced pressure. In this case the temperature will be decreased accordingly. The evaporation of the water and, if appropriate, of the organic solvent (s) causes the precipitation of the residue comprising sodium bromide and organic and / or mineral impurities. Advantageously, this residue can then be recovered by filtration. The recycling of the industrial effluent may further comprise a distillation step c of the liquid phase comprising water and the organic solvent (s) so as to separate the solvent (s) organic (s) water. In one embodiment, the distillation is performed on a reflux column.

Advantageously, the distillation step c is carried out at a temperature ranging from 40 to 120.degree. C., preferably from 70 to 100.degree. C., more preferably at about 90.degree. C., and optionally under reduced pressure of less than 200 mbar, preferably below 200.degree. at 100 mBar and more preferably still less than 50mbar. Where appropriate, the organic solvent (s) are recovered after the distillation step (c) and can be reused in other industrial synthesis processes. In one embodiment, the water is recovered after the distillation step (c) and then treated biologically to obtain industrial grade water. This water can then be reused, especially in other industrial synthesis processes. The method according to the invention, its embodiments and its uses will be better understood on reading the examples below which are in no way limiting as to the present invention and the scope of the claims. EXAMPLES Materials and Methods The TOC content was determined according to standard NF EN 1484 on an Elementar 25 High TOC apparatus.

The contents of bromide (Bi), chloride (cn, nitrates (NO3-) and sulphates (S042-) were determined according to standard NF EN 10 304 by ionic chromatography on a Methron 961 Advanced compact IC apparatus. were carried out using a Methron 744 pH meter according to standard NF T 90-008.The ammonium content was determined by a titrimetric method after steaming according to standard NF T 90-015 on a Büchi branded apparatus, referenced Unit K350 The contents of metal and alkaline earth ions were determined by ICP spectrometry according to standard NF EN 11 885 on a Varian Vista MPX spectrometer 10 Extraction and purification of sodium bromide from An industrial effluent The process according to the invention is carried out in the recycling of an industrial effluent comprising: 92 g / kg Bi, ie 118 g / kg expressed as NaBr, 42.7 g / kg Na, from 177 to 185 g. / kg of DMF (N, N-dimethylformamide), from 6 to 20 g / kg of sulfur, 70% by weight of water, and having a TOC of 105 g / kg. The effluent includes, in particular, organic salts such as alkaline salts, especially sodium salts, sulphonates, and sulfur compounds. Concentration of the industrial effluent The quantity of effluent used is 10 kg. A 500 mL oil jacketed reactor is used and fed continuously. This evaporative concentration operation is carried out under vacuum (<50 mBar) to avoid DMF degradation at elevated temperatures.

The saline phase is filtered off as it crystallizes and the filtrate is recycled to the evaporator to continue the concentration. A condensate (C1) composed of water and DMF, a crystalline phase (SNL) composed of a mixture of NaBr, organic salts of DMF and various organic impurities is obtained. It remains an ultimate non-exploitable concentrate that is destroyed. The compositions of the raw effluent and of the different phases obtained after this first concentration step are reported in Table 1. Table 1: Composition of the phases obtained after the first concentration step Phase Weight (g) Br- (g / kg) NaBr (g / kg) S (g / kg) TOC (g / kg) DMF (g / kg) Gross effluent 10,000 92 118 20 105 177 Cl 7127 0 0 0 86.25 180 SNL 1836 405.6 522 20 78 - At this point , a residue comprising sodium bromide and organic and / or inorganic impurities, corresponding to the crystallized phase SNL, is obtained and characterized in that it comprises 405.6 g / kg Bi or 52.2% by weight of NaBr, 7.8 wt% organic carbon and 5 wt% sulfur. The SNL residue comprises especially organic salts such as alkaline salts, especially sodium salts, sulfonates, and sulfur compounds. Extraction and purification of the NaBr contained in the SNL crystallized phase. 8 kg of methanol are added to 1.836 kg of SNL residue and the mixture is stirred for 30 min at room temperature. The mixture is filtered and the filtrate containing NaBr is recovered, the methanol is then evaporated to obtain 0.968 kg of a crude sodium bromide (crude NaBr). The crude NaBr (0.968 kg) is washed once with 0.630 kg of a methanol / hydrochloric acid washing solution. 1 kg of washing solution is prepared by adding 0.85 kg of methanol to 0.14 kg of an aqueous solution of 37% hydrochloric acid. The washing solution has a pH of 2.8. The washed solid is a purified sodium bromide (purified NaBr) which is then dried and obtained in an amount of 0.777 kg. The washing solution was recovered. Chemical analyzes of crude NaBr and purified NaBr are reported in Table 2.

Table 2: Chemical analyzes of crude NaBr and purified NaBr Component Unit NaBr crude NaBr purified NaBr% * 87 92 NaCl * 3.7 8 TOC% * 1 to 2 0.04 S% * 2 <0.02 P mg / kg < 1 <1 Ammonium mg / kg 60 50 Nitrate mg / kg <100 <100 Ca2 + mg / kg <1 <1 mg2 + mg / kg <1 - Sulfate mg / kg <100 <100 Al mg / kg 1 1 As mg / kg <5 <5 Cd mg / kg <0.5 <0.5 Cr mg / kg <1 <1 Cu mg / kg 1 <1 Fe mg / kg 4.2 3.5 mg / kg lig <5 <5 Mn mg / kg < 1 <1 Ni mg / kg <1 <1 Pb mg / kg <1 <1 Sn mg / kg <1 <1 V mg / kg <1 <1 Zn mg / kg 1 <1 Ba mg / kg <1 <1 Mo mg / kg <1 <1 Sb mg / kg <1 <1 Se mg / kg <1 <1 * by weight relative to the total weight of purified sodium bromide The process according to the invention makes it possible to obtain bromide sodium (purified NaBr) having a very good purity (92% by weight) and which can be used in the industrial synthesis of dibroma, especially because of its very low content of TOC, ammonium and phosphorus. In addition, its low content of heavy metals, calcium ions, magnesium and sulfate will allow the non-exploitable effluents obtained in the synthesis of bromide from purified sodium bromide according to the invention are not harmful to the environment.

Reprocessing of the used washing solution. The pH of the wash solution was adjusted to about 7 by addition of 50% by weight aqueous sodium hydroxide solution. The methanol is evaporated, recovered, and can be reused to prepare the wash solution. The aqueous residue which still contains 206 g / kg of NaBr may be added to the industrial effluent to be recycled. Reprocessing of Cl condensate. Cl condensate which contains about 72% by weight of DMF is distilled at a temperature of 90 ° C and a vacuum of 50 mBar. Three phases are collected during the distillation: a first phase containing essentially water, a second phase containing about 30% by weight of DMF and 70% by weight of water and a third phase containing DMF with less than 0, 1% by weight of water. With a TOC of 5.3g / L, the first aqueous phase is then treated biologically to obtain industrial grade water. The second phase is fully recycled in distillation. DMF with less than 0.1% by weight of water is reused in other industrial synthesis processes.

Material balance 77% by weight of the industrial effluent could be recovered in the form of recoverable products: sodium bromide, DMF and industrial water. On 10 kg of industrial effluent containing 1.18 kg of NaBr, 1.77 kg of DMF and 7 kg of water, were recovered 0.777 kg of purified NaBr, 1.22 kg of DMF and 5.7 kg of water .

The process of extraction and purification of sodium bromide according to the invention thus allowed to recover 65% by weight of sodium bromide contained in the industrial effluent which contained only 11.8% sodium bromide. In addition, the SNL crystallized phase contained only 52.2% by weight of sodium bromide, which clearly shows that the process according to the invention is very versatile and is not limited to the residues of sodium bromide containing only few organic and / or mineral impurities. In addition, the used washing solution, after basic reprocessing and evaporation of the alcohol, provides an aqueous solution rich in sodium bromide which can be exploited in the process according to the invention after a prior concentration step.

Claims (10)

REVENDICATIONS1. A process for extracting and purifying sodium bromide comprising the following steps: (1) a step of mixing a residue, solid or pasty, comprising sodium bromide and organic and / or mineral impurities, with methanol, so as to obtain a solution of sodium bromide in methanol and a solid residue containing organic and / or mineral impurities, (2) concentration of the sodium bromide solution so as to obtain solid sodium bromide, this step of concentration comprising a step of evaporation of the methanol, (3) at least one washing of the sodium bromide obtained in the preceding step with a washing solution comprising a mixture of an alcohol chosen from methanol and ethanol, and of an acid to obtain purified sodium bromide and used wash solution, (4) recovery of purified sodium bromide. The process according to claim 1, wherein the alcohol used in step (3) is methanol. The process according to claim 1 or 2, wherein the wash solution used in step (3) has a pH of 2 to 4. A process according to any one of claims 1 to 3, wherein the acid used in step (3) is hydrochloric acid. 5. Method according to any one of claims 1 to 4, characterized in that the organic or inorganic impurities comprise organic salts of sulfur compounds and / or nitrogen compounds. 6. Process according to any one of claims 1 to 5, characterized in that the methanol evaporated in step 2 is recovered and reused in steps 1 and / or 3. 7. Use of the process according to any one of claims 1 to 6 in the recycling of an industrial effluent comprising water, sodium bromide and optionally one or more organic solvent (s). 8. Use according to claim 7, wherein the recycling of the industrial effluent comprises the following steps: (a) evaporation of the water and, if appropriate, of the organic solvent (s) so as to obtain a liquid phase comprising water and, if appropriate, the organic solvent (s) on the one hand and a residue comprising sodium bromide and organic and / or mineral impurities on the other hand (b ) Application of the method of extraction and purification of sodium bromide according to any one of claims 1 to 6 to the residue comprising sodium bromide and organic and / or inorganic impurities obtained in step (a). 9. Use according to claim 8, wherein the recycling of the industrial effluent further comprises a step (c) of distillation of the liquid phase comprising water and the organic solvent (s) of to separate the organic solvent (s) from the water. Use according to any one of claims 7 to 9, wherein the industrial effluent comprises water, sodium bromide and N, N-dimethylformamide.