Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B15/00—Operating or servicing cells
  • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/14—Alkali metal compounds
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
  • C25C3/02—Electrolytic production, recovery or refining of metals by electrolysis of melts of alkali or alkaline earth metals
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C7/00—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells
  • C25C7/005—Constructional parts, or assemblies thereof, of cells; Servicing or operating of cells of cells for the electrolysis of melts

Definitions

• the invention relates to a process for the preparation of an alkali metal from a solvent-soluble salt of the alkali metal.
• Alkali metals used as important basic inorganic chemicals are especially lithium, potassium and sodium.
• lithium is used for the preparation of organolithium compounds, as an alloying additive for aluminum or magnesium, and for lithium batteries.
• lithium is produced by fused-salt electrolysis of a eutectic mixture of lithium chloride and potassium chloride at 400 to 460 ° C.
• this process has a high energy consumption.
• the process has the serious disadvantage that only anhydrous lithium chloride can be used.
• the lithium chloride present primarily as an aqueous solution must therefore be worked up in an energy-consuming process to give the anhydrous solid. Since lithium chloride is hygroscopic, drying and handling require special effort.
• sodium is used to make sodium amide, sodium alcoholates and sodium borohydride.
• sodium is recovered by electrolysis of molten common salt after the Downs process. This process has a high energy consumption of more than 10 kWh / kg of sodium. Furthermore, the method has the serious disadvantage that the electrolysis cells are destroyed by the solidification of the molten salt during shutdown. Furthermore, the sodium metal obtained by the Downs process has the disadvantage that it is contaminated with calcium due to the process, the residual content of which is only reduced by subsequent purification steps, but can never be completely eliminated.
• Potassium is used, for example, for the production of potassium alcoholates, potassium amides and potassium alloys.
• potassium is mainly obtained by reduction of potassium chloride with sodium.
• the sodium-potassium alloy NaK is produced, which is then fractionally distilled.
• a good yield is achieved by constantly removing potassium vapor from the reaction zone. which shifts the equilibrium of the reaction to the potassium side.
• this process works at high temperatures of about 870 ° C.
• the resulting potassium contains about 1% sodium as an impurity and must therefore be purified by another rectification.
• the biggest disadvantage, however, is that the sodium used is expensive, since this must be obtained technically after the Downs process by electrolysis of molten salt.
• an aqueous solution of an alkali metal salt is fed to an electrolysis cell which has a cathode compartment and an anode compartment, which are separated from one another by a solid electrolyte.
• the solid electrolyte has at least one further ion-conducting layer.
• the cathode compartment has a solid cathode core and is filled with a molten alkali metal or a liquid electrolyte. At the cathode, the alkali metal forms and rises in the liquid electrolyte and can then be removed.
• liquid electrolyte molten salts of the alkali metal to be recovered are preferably used.
• the disadvantage of the method lies in the increased electrical resistance and in the unsatisfactory stability of the combination of solid electrolyte and the further ion-conducting layer.
• the object of the present invention is to provide a process for the production of an alkali metal which, on the one hand, does not have the disadvantages known from the prior art, in particular with less energy consumption and is less expensive to operate in apparatus.
• the object is achieved by a process for producing an alkali metal from a solvent-soluble salt of the alkali metal, which comprises the following steps:
• Melting temperature of the alkali metal in a second electrolytic cell comprising an anode compartment and a cathode compartment, wherein the anode compartment and the cathode compartment of the second electrolytic cell are separated by an alkali metal cation conductive solid electrolyte and the alkali metal (poly) sulfide melt from step (b) is supplied to the anode compartment and sulfur and unreacted alkali metal (poly) sulfide melt are removed from the anode space and liquid alkali metal is withdrawn from the cathode space.
• the process according to the invention is suitable for the preparation of an essentially pure alkali metal, in particular for the preparation of sodium, potassium and lithium, very particularly preferably for the preparation of sodium.
• Substantially pure in the context of the present invention means that the proportion of impurities by foreign metals in the alkali metal is at most 30 ppm.
• (poly) sulfide anions are understood as meaning anions of the general formula S x 2_ , where x is any integer from 1 to 6.
• alkali metal (poly) sulfide is understood as meaning all compounds of the general formula Me 2 S x , where Me is the alkali metal, for example sodium, potassium or lithium, and x is any integer between 1 and 6.
• Substantially solvent-free alkali metal (poly) sulfide melt means in the context of the present invention that the alkali metal (poly) sulfide melt contains at most 5% by weight of solvent, preferably at most 3% by weight of solvent and in particular not more than 1.5% by weight of solvent.
• a first electrolysis is carried out in a first electrolytic cell comprising an anode space and a cathode space.
• the anode compartment of the electrolysis cell is supplied with the salt of the alkali metal dissolved in the solvent.
• salt which is supplied to the anode compartment of the first electrolytic cell, are particularly suitable alkali metal halides.
• the solvent is, for example, water or an organic solvent, for example an alcohol.
• the solvent is water. If the process for the production of sodium is used, in particular an aqueous sodium chloride solution is fed to the anode chamber of the first electrolysis cell.
• an aqueous alkali metal salt solution for example an aqueous sodium chloride solution or an aqueous potassium chloride solution
• a solution is preferably used, as is also customary in the chlor-alkali electrolysis.
• the alkali metal chloride solution Before being added to the anode compartment of the first electrolytic cell, the alkali metal chloride solution is usually purified to remove non-alkali metal ions.
• sodium chloride solution is supplied as the solution supplied to the anode compartment, it preferably contains at most 500 ppm of potassium based on the total amount of sodium and potassium contained in the solution.
• an aqueous potassium chloride solution which has also been purified as known from chlor-alkali electrolysis and free of alkali-earth metal ions.
• the solution preferably contains at most 0.1% by weight of sodium, based on the total amount of potassium and sodium in the solution.
• the solution of the alkali metal salt fed to the anode chamber of the first electrolysis cell is preferably almost saturated and contains, for example, sodium chloride, preferably from 5 to 27% by weight, in particular from 15 to 25% by weight, for example 23% by weight, sodium chloride.
• the cathode compartment of the electrolysis cell, a second solvent and sulfur powder are fed as a suspension.
• Spatially added solution in addition conductive salts for example, alkali metal hydroxide or more preferably alkali metal (poly) sulfides, to increase the conductivity of the solution.
• the alkali metal of the alkali metal hydroxide or alkali metal (poly) sulfides is preferably the same as the alkali metal to be recovered.
• the solution supplied to the cathode compartment contains from 50 to 95% by weight of solvent and from 2 to 25% by weight of elemental sulfur.
• alkali metal hydroxide and 0 to 48 wt .-% of ionic alkali metal sulfur compounds are included. It is particularly preferred if the solution is circulated in continuous operation in the cathode compartment.
• the circulating solution is continuously fed to second solvent and sulfur powder so that the recirculated solution contains a concentration of 25 to 50% by weight of ionic sulfur compounds. This is achieved by adding to the circulating solution a suspension of 50 to 82% by weight of water and 18 to 50% by weight of sulfur powder.
• the second solvent may be an organic solvent, for example an alcohol or water.
• the second solvent is water.
• Alkali metal cation permeable membranes are all cation selective membranes which are permeable to alkali metal cations.
• Suitable cation permeable membranes are, for example, Nafion® membranes, which are commercially available.
• Such a membrane usually has a skeleton of polytetrafluoroethylene with immobilized anions, usually sulfonic acid groups and / or carboxylate groups on.
• the anode for example, an anode is used, as it is known from the chlor-alkali electrolysis.
• the electrode design it is generally possible to use perforated materials which are designed, for example, in the form of nets, lamellae, oval profile webs, V webs or round profile webs.
• the anode is a dimensionally stable anode, which is generally constructed of coated titanium, wherein the coating metal mixed oxides of titanium, tantalum and / or platinum metals such as iridium, ruthenium, platinum and rhodium are used.
• platinum metals and the metal content are designed to achieve the lowest possible deposition overpotential for chlorine and the highest possible overvoltage for oxygen.
• the chlorine overvoltage is from 0.1 to 0.4 volts and the oxygen overvoltage from 0.6 to 0.9 volts.
• graphite is also suitable as the material for the anode, but generally they are not dimensionally stable under the operating conditions, so that the anodes produced therefrom must be readjusted during operation in the cell and regularly replaced, while For titanium passivated with mixed oxides, only the coating must be replaced after 2 to 4 years of continuous operation.
• a cathode can be used, as it is known from the chlor-alkali electrolysis.
• a stainless steel cathode or a nickel electrode for example, a stainless steel cathode or a nickel electrode.
• a graphite felt is introduced into the electrode gap between the stainless steel cathode and the membrane.
• the first electrolysis is preferably carried out continuously, wherein the anode space is continuously supplied with the salt of the alkali metal dissolved in a solvent and the cathode space is continuously fed with the sulfur suspension or the (poly) sulfide sulfur mixture and second solvent recycled from the second electrolysis.
• alkali metal cations migrate through the cation-selective membrane from the anode side to the cathode side.
• chlorine forms, which is removed from the anode compartment.
• the alkali metal salt-containing solution is removed from the anode compartment.
• the removed solution of the alkali metal salt is dechlorinated in one embodiment, concentrated to feed concentration, purified and returned to the anode compartment. For concentration, it is possible, for example, to introduce alkali metal salt directly into the solution of the alkali metal salt.
• a mixture of alkali metal (poly) sulfides and ionic sulfur compounds is formed, for example, sulfites, thiosulfates, to give a solution containing alkali metal cations and ionic sulfur compounds.
• the solution initially contains further unreacted, undissolved elemental sulfur.
• the solution is removed from the cathode compartment and preferably recirculated to concentrate the product, namely the alkali metal cations and the ionic sulfur compounds.
• a partial stream is withdrawn from the second solvent, alkali metal cations, (poly) sulfide anions and ionic sulfur compounds leaving the cathode compartment and concentrated in step (b).
• the electrolysis in step (a) is preferably carried out at a temperature in the range from 25 to 120 ° C., preferably in the range from 50 to 90 ° C. and in particular in the range from 75 to 85 ° C.
• Suitable current densities are in the range of 400 to 4000 A / m 2 and suitable voltages in the range of 2.5 to 6 volts.
• the mixture leaving the cathode compartment, containing second solvent, alkali metal cations and (poly) sulfide anions and other ionic sulfur compounds mixture is concentrated in step (b) by removal of the second solvent.
• concentration of the second solvent, alkali metal cations and (poly) sulfide anions and further ionic sulfur compounds taken from the cathode space be carried out in an evaporator.
• the evaporator can be operated continuously or discontinuously.
• any known to the expert evaporator for performing the concentration in step (b) is suitable.
• continuous evaporation are, for example, circulation evaporator with natural circulation, circulation evaporator with forced circulation, falling film evaporator or thin film evaporator.
• a discontinuous concentration by evaporation is particularly suitable for a stirred tank.
• a condenser with condenser is used.
• the alkali metal cations, (poly) sulfide anions and other ionic sulfur compounds and second solvent containing mixture fed to the evaporator may be preheated before being added to the evaporator.
• any device for heating a liquid material flow can be used.
• a heat exchanger is used.
• the heating can be carried out with a heat transfer medium or electrically. Suitable heat transfer media are, for example, thermal oils, steam or any other heat transfer medium known to the person skilled in the art.
• the concentration of the alkali metal cations and (poly) sulfide anions by evaporation is preferably at a temperature in the range of 80 to 400 ° C, in particular at a temperature in the range of 120 to 350 ° C and most preferably at a temperature in the range of 150 to 300 ° C performed.
• the broth pressure of the evaporation is preferably in the range of 0.1 to 2 bar absolute, more preferably in the range of 0.2 to 1 bar absolute, in particular in the range of 0.5 to 1 bar absolute.
• the heating of the evaporator used can be done, for example, up to 200 ° C with steam.
• heating is both with piping routed through the apparatus as well as with double jacket possible.
• any other heat transfer medium such as a thermal oil or a molten salt can be used.
• the evaporation can be carried out in one or more stages. In a multi-stage evaporation, it is also advantageous if a Brüdensch arrangement is provided with or without vapor recompression in countercurrent.
• the multi-stage evaporation is preferably carried out in cascade. In the case of a cascaded evaporation, identical or different types of evaporator can be used in the individual stages of the evaporator cascade.
• step (b) produces a top stream containing second solvent and optionally hydrogen sulfide.
• the bottom stream obtained in the evaporation contains sulfur, alkali metal (poly) sulfide and other ionic sulfur compounds, as well as traces of second solvent and optionally also sodium thiosulfate and sodium hydroxide.
• the evaporation residue in the sodium preparation preferably contains from 65 to 75% by weight of sulfur, from 20 to 25% by weight of sodium and from 4 to 10% by weight of oxygen, for example a proportion of 69% by weight. % Sulfur, 23 wt% sodium and 8 wt% oxygen.
• the evaporation residue for elemental analysis contains, for example, from 60 to 70% by weight of sulfur, from 25 to 37% by weight of potassium and from 4 to 10% by weight of oxygen.
• the obtained, concentrated mixture obtained in the evaporation as a bottom stream in a preferred embodiment before performing the second electrolysis in step (c) with respect to the ionic sulfur oxygen compounds contained therein.
• a gaseous stream containing hydrogen sulfide containing hydrogen sulfide.
• the hydrogen sulfide used for the purification is preferably technically pure hydrogen sulfide.
• the supplied gas stream may also contain inert gases for the process.
• inert gas Those which may be contained are, for example, nitrogen, hydrogen or noble gases, in particular nitrogen.
• alkali metal hydroxide still contained in the bottom stream reacts with the hydrogen sulphide to form alkali metal (poly) sulphide and water.
• the concentrated mixture of (b) and the gaseous hydrogen sulfide-containing stream are preferably passed in countercurrent.
• the column used is preferably a column with internals.
• internals are, for example, soils, packing or structured packings.
• the apparatus in which the purification is carried out for example the column, is preferably dimensioned such that a residence time of the concentrated mixture from step (b) of at least 10 s to 30 min, preferably of at least 2 min is achieved.
• the column in which the purification is carried out additionally heated below the side feed for the gaseous, hydrogen sulfide-containing stream.
• the heating can be effected, for example, by a double jacket or a tube introduced into the column through which a heat transfer medium flows.
• Suitable heat transfer agents are, for example, steam, thermal oils or salt melts.
• hydrogen sulfides formed in the mixture are split into hydrogen sulfide and alkali metal (poly) sulfide.
• a temperature in the range of 320 to 400 ° C, preferably in the range of 340 to 350 ° C is set with the additional heating in the column.
• a mixture which contains essentially alkali metal (poly) sulfides.
• more can Contain contamination of at most 0.5 wt .-%, preferably of at most 0.1 wt .-%.
• impurities include, in particular, alkali metal hydroxide.
• a gas stream containing second solvent and hydrogen sulfide is obtained.
• the second solvent and hydrogen sulfide-containing, gaseous stream which is removed from the apparatus for purification, in particular the column, at the top, is passed into a condenser.
• the second solvent is condensed and removed from the second solvent and hydrogen sulfide-containing stream.
• the condensed second solvent is generally contaminated with hydrogen sulfide and is preferably fed into the cathode compartment of the first electrolysis.
• the gaseous, substantially solvent-free hydrogen sulfide is returned to the column.
• step (b) it is possible to carry out the additional purification in one of the evaporation stages, preferably in the last evaporation stage, when the second solvent is almost completely removed.
• the obtained, containing alkali metal (poly) sulfide stream of a second electrolysis is fed.
• the second electrolysis is preferably carried out in a second electrolysis cell, which is composed of an anode space and a cathode space, which are separated by an alkali metal cation-conducting solid electrolyte.
• electrolysis cell for the second electrolysis are particularly suitable electrolysis cells whose structure corresponds to the structure of electrolysis cells, which can be used in sodium-sulfur batteries set.
• the solid electrolyte is preferably an alkali metal cation-conducting ceramic, in particular ⁇ -alumina, ⁇ "-alumina or ⁇ / ⁇ " -alumina.
• Each of the ceramics contains alkali metal cations of the alkali metal to be produced.
• alkali metal ⁇ -aluminum oxide alkali metal ⁇ "-alumina or alkali metal ⁇ / ⁇ " -aluminum oxide, corresponding alkali metal analogs of NASICON® ceramics are also suitable.
• the alkali metal used is in each case the alkali metal which is to be obtained by the process according to the invention.
• the alkali metal to be produced is lithium, LISICONs, and more preferably, garnet-structured Li ion conductors such as Li 5 La 3 Ta20 2 or Li 7 La 3 Zr 2 O 2 are also suitable.
• the alkali metal (poly) sulfide melt obtained in the concentration in step (b), or the alkali metal (poly) sulfide from the additional purification is electrochemically separated into alkali metal and sulfur.
• the electrolysis is carried out at a temperature at which the alkali metal to be produced is molten.
• the electrolysis is carried out at a temperature in the range from 290 to 330 ° C, in particular at 310 to 320 ° C under atmospheric pressure.
• an electrode made of a molybdenum-stabilized stainless steel is preferably used, for example stainless steel with the material number 1.4571, which may be chrome-plated, or an electrode made of a chromium steel, for example steel of the material number 1 .7218.
• the cathode is preferably an alkali metal electrode. In this case, the recovered alkali metal serves as an electrode.
• the alkali metal (poly) sulfide is fed to the anode compartment in liquid form.
• the alkali metal (poly) sulfide is cleaved into alkali metal cations and (poly) sulfide anions.
• the alkali metal cations are passed through the solid electrolyte and thus get into the cathode compartment.
• the alkali metal cations absorb electrons, forming the molten alkali metal.
• the (poly) sulfide anions release electrons to the anode, producing initially reduced (poly) sulfides and finally sulfur.
• the sulfur Due to the temperature of the electrolysis of the sulfur is liquid and can be removed from the anode compartment. Usually, the sulfur is taken from the upper part of the anode compartment, since the sulfur has a lower density than the alkali metal (poly) sulfide. The sulfur thus rises.
• the sulfur obtained in the second electrolysis and unconverted ionic sulfur compounds are returned in a particularly preferred embodiment to the first electrolysis.
• the sulfur is preferably sprayed together with the unreacted ionic sulfur compounds in the form of a melt in the guided in the cathode compartment of the first electrolysis suspension.
• the melt solidifies and finely distributed sulfur particles are formed in the second solvent.
• FIG. 1 shows a process flow diagram of the first electrolysis
• FIG. 2 shows a process flow diagram of the concentration
• FIG. 3 shows a process flow diagram of the additional purification
• FIG. 4 shows a process flow diagram of the second electrolysis
• FIG. 5 shows a process flow diagram of the overall process
• FIG. 6 shows a laboratory electrolysis cell for carrying out the second electrolysis.
• FIG. 1 shows the first electrolysis in the form of a process flow diagram.
• a first electrolysis cell 1 comprises an anode chamber 3 and a cathode chamber 5, which are separated from one another by a membrane 7.
• an anode chamber 3 is an anode 9, which is preferably made of coated titanium, wherein the coating of metal mixed oxides of titanium, tantalum and / or platinum metals such as iridium, ruthenium, platinum and rhodium is constructed.
• a cathode 1 1 is added, which is preferably made of stainless steel.
• the anode chamber 3 is supplied via a first inlet 13 from a first feed tank 15, an alkali metal salt solution.
• the alkali metal salt solution contained in the first receiver tank 15 is preferably an aqueous alkali metal halide solution, for example, an aqueous alkali metal chloride solution.
• the alkali metal halide is sodium chloride.
• the alkali metal salt is preferably dissolved in water as a solvent. However, it is also possible to dissolve the alkali metal salt in a suitable organic solvent, for example an alcohol.
• a circuit closes and it forms at the anode 9 chlorine, which is taken together with recirculated alkali metal salt solution from the anode chamber 3.
• the chlorine is removed from the stream taken from the anode compartment and the remaining stream is returned to the first storage tank 15.
• the chlorine is removed from the process via a chlorine discharge line 23.
• alkali metal cations pass through the cation-selective membrane 17 into the cathode space 5.
• an elemental sulfur and second solvent for example, an organic solvent or water, preferably water-containing suspension.
• elemental sulfur is passed through a sulfur feed line 27 and a solvent feed line 29 second solvent into a second feed tank 31 and mixed there. From the second feed tank 31, the second solvent and sulfur-containing mixture is passed via the second inlet 25 into the cathode space 5 of the first electrolytic cell.
• a small amount of alkali metal hydroxide may be added to the second solvent and sulfur-containing mixture in the second receiver tank 31 to increase the conductivity of the mixture.
• any other mixing apparatus known to those skilled in the art it is also possible to inject the sulfur as a melt into the second solvent and then to supply it to the cathode space 5.
• a second solvent, alkali metal cations and (poly) sulfide anion-containing mixture are removed via a cathode outlet 33.
• the mixture removed via the cathode outlet 33 may also contain alkali metal hydroxide.
• the alkali metal cations and (poly) sulfide anions contained in the mixture usually form an alkali metal (poly) sulfide.
• the mixture removed via the cathode outlet 33 is circulated and enriched with sulfur and second solvent. For this purpose, it is possible, for example, initially to recycle the mixture removed via the cathode outlet 33 into the second feed container 31.
• FIG. 2 shows by way of example a concentration by evaporation in the form of a flow chart.
• the material removed as a cathode effluent 33, second solvent, alkali metal cations and (poly) sulfide anions containing stream is fed to an evaporator 41.
• the evaporator 41 is, for example, as shown in Figure 2, a circulation evaporator with natural circulation. Alternatively, it is also possible to use a circulation evaporator with forced circulation, a falling-film evaporator or a thin-film evaporator. Any other known to the expert evaporator can be used. If the evaporation is to take place discontinuously, it is also possible, for example, to use a stirred tank instead of the circulation evaporator with natural circulation shown here.
• the evaporator 41 is preferably equipped with a liquid separator 43.
• the evaporator unit 47 may be designed, for example in the form of a Rohrbündel Anlagenübertragers.
• the tubes of the tube bundle are flowed through by a heat carrier, for example steam, thermal oil or a salt melt.
• the evaporator unit 47 may have a double jacket for heating.
• a top stream is taken containing gaseous second solvent, liquid second solvent, alkali metal cations and (poly) sulfide anions and fed to the liquid separator 43.
• the gaseous second solvent is separated and removed via a solvent extraction line 49 the process.
• the second solvent, alkali metal cations and (poly) sulfide anion-containing mixture is circulated until the desired concentration of residual solvent is obtained.
• moderately second solvent, alkali metal cations and (poly) sulfide anion-containing mixture fed via the opening into the circulation line 45 cathode effluent 33 and before the supply of the mixture from the circulation line via a withdrawal line 51 the concentrated, second solvent and alkali metal (poly) taken from sulfide-containing mixture.
• the mixture removed via the withdrawal line 51 is further purified.
• the purification is shown schematically in FIG. 3 on the basis of a flow chart.
• the concentrated alkali metal (poly) sulfide melt is optionally fed to a preheater 53 and heated therein.
• the preheating can be done, for example, electrically, with a heat transfer medium, for example steam, a thermal oil or a molten salt.
• the preheated, alkali metal (poly) sulfide melt is then preferably fed to a column 55 at the top.
• the column 55 generally contains internals, for example trays, packing or a structured or unstructured packing.
• the hydrogen sulfide may additionally be mixed with an inert gas, for example nitrogen.
• an inert gas for example nitrogen.
• the hydrogen sulfide and the alkali metal (poly) sulfide melt are preferably passed in countercurrent and thoroughly mixed.
• the alkali metal (poly) sulfide melt optionally still contained alkali metal hydroxide in alkali metal (poly) sulfide and water is reacted.
• a stream 67 is taken, which contains substantially solvent-free alkali metal (poly) sulfide.
• the alkali metal (poly) sulfide melt obtained in the evaporation or the alkali metal (poly) sulfide obtained by carrying out the preparation according to FIG. end stream 67 is fed to a second electrolysis. This is shown by way of example in FIG.
• the second electrolysis can be carried out in several stages. For this purpose, a plurality of electrolytic cells 71 are connected in parallel.
• the electrolysis cells 71 each have an anode space 73 into which a plurality of electrode units 75 are introduced in the embodiment shown here.
• the electrode units 75 each comprise a cylindrical body made of a solid electrolyte and thus delimit a cathode space lying in the interior of the solid electrolyte from the anode space 73.
• the anode chamber 73 of the respective electrolysis cells is fed via a feed line 79, the alkali metal (poly) sulfide melt from the evaporation shown in Figure 2 or if further purification is carried out, the alkali metal (poly) sulfide from the purification shown in Figure 3.
• the alkali metal polysulfide is electrolytically cleaved into alkali metal and sulfur.
• alkali metal cations pass through the alkali metal cation-conducting solid electrolyte into the cathode space, in which alkali metal is formed.
• the alkali metal is removed from the cathode compartment and removed via a product line 77.
• sulfur is formed at the anode from the polysulfide.
• the electrolysis is operated at a temperature at which the alkali metal is liquid.
• a stainless steel electrode is preferably accommodated in the anode chamber.
• the resulting sulfur increases because it has a lower density than the alkali metal polysulfide.
• the sulfur can then be removed at the upper part of the anode space 73 via a sulfur extraction line 81.
• the sulfur removed via the sulfur removal line 81 is preferably returned to the first electrolysis shown in FIG.
• the sulfur is passed, for example, via the sulfur feed line 27 into the second feed tank 31.
• the entire process without the additional purification shown in FIG. 3 is shown by way of example in FIG.
• sodium chloride is preferably added via the alkali metal salt feed 17 and water is preferably fed via the solvent line 19, the sodium chloride is dissolved in the water and passed over the water first inlet 13 introduced into the electrolysis cell.
• the sodium chloride is separated into sodium ions and chlorine.
• the chlorine is removed together with circulating sodium chloride solution from the anode compartment of the first electrolytic cell 1.
• the chlorine is separated off and removed from the process via the chlorine removal line 23.
• the remaining sodium chloride solution is concentrated by adding additional sodium chloride and passed back into the anode compartment of the first electrolytic cell 1.
• the cathode space 5 is flowed through with a solvent, preferably water, and a mixture containing sulfur. Since sulfur is preferentially reduced compared to hydrogen, sodium (poly) sulfide forms in the cathode compartment, dissociating the sodium (poly) sulfide into sodium cations and (poly) sulfide anions.
• the sodium (poly) sulfide-containing solution is supplied from the cathode space to the evaporator 41. In the evaporator 41, the sodium (poly) sulfide is concentrated by evaporation of the water.
• the concentrated sodium (poly) sulfide is then passed to the second electrolytic cell 71 where the sodium (poly) sulfide is electrolytically cleaved into sodium and sulfur.
• the sodium ions penetrate the sodium ion-conducting solid electrolyte and enter the cathode compartment, from which the sodium formed there is removed in molten form. Sulfur is removed from the anode compartment and returned to the first electrolysis.
• the electrolysis of the aqueous saline solution was carried out in the electrolysis cell shown in FIG.
• the electrolysis cell was divided into an anode compartment and a cathode compartment by means of a cation-exchanging membrane (Nafion® 324).
• the anode used was a titanium anode coated with Ru / Ir titanium mixed oxide in the form of an expanded metal.
• the cathode was a stainless steel expanded metal according to material number 1 .4571.
• the electrolysis was carried out batchwise with gradual increase of sodium chloride.
• the anolyte was pumped from the first storage tank 15 by means of a laboratory centrifugal pump via the anode compartment 3 of the electrolytic cell in a circle.
• 1566 g of a 23% aqueous sodium chloride solution were initially charged as anolyte.
• the catholyte was pumped from the second storage tank 31 by means of a laboratory centrifugal pump via the cathode compartment 5 of the electrolytic cell in a circle.
• 1700 g of a 2.5% aqueous solution of sodium tetrasulfide were added as catholyte.
• To this solution was added 80 g of sulfur powder.
• the electrolysis was carried out at a temperature in the range of 75 ° C to 80 ° C, a current density i of 2000A / m 2 and a cell voltage in the range of 3.5 to 5 volts.
• the electrolysis was carried out batchwise in 4 stages of 40 Ah, so that a total of 160 Ah were implemented.
• an addition of 85 g of sodium chloride to the anolyte and 80 g of sulfur to the catholyte was carried out. This was done a total of 3 times, so that a total of 320 g of sulfur and 255 g of sodium chloride were added.
• the anode side was purged with nitrogen.
• the anode-side exhaust gas passed through two consecutive scrubbers operated with 10% aqueous NaOH.
• the cathode side was also purged with nitrogen.
• the cathode-side exhaust gas was passed through a gas analyzer, which determined the hydrogen content.
• the solutions were discharged after electrolysis and analyzed for the elements.
• the Katholytaustrag was discontinuously evaporated in an electrically heated distillation flask with stirring with increasing temperature.
• the boiling temperature increased during concentration from 102 ° C to 200 ° C.
• the evaporation system was limited to 200 ° C.
• the contents in the distillation flask remained liquid over the course of the concentration. The distillation was stopped when no more distillate overflowed.
• the electrolysis of the sodium (poly) sulfide melt was carried out in the laboratory apparatus shown in FIG. 6, heated with an electric heater 101 and chambered in a steel housing 100.
• the electrolysis cell 90 was a U-tube made of borosilicate glass, both electrodes being arranged together with the ceramic membrane in an electrolysis leg 91, while the second leg 92 remained without installation.
• Membrane 93 was a beta-Al 2 O 3 ceramic carrying sodium ions, and membrane 93 was in the form of a single-ended tube, with sodium 94 inside and sodium (poly) sulfide melt 95 kept outside the tube usable surface area of the tubular membrane 93 was 14 cm 2.
• the anode 96 used was a graphite felt of the type GFD5EA (manufacturer SGL), which was electrically contacted to the plus side of the power supply unit via 4 contact plates 97 made of chromed steel with the material number 1.4404
• the cathode was molten sodium 94, which was electrically contacted to the negative side of the power supply via a stainless steel rod 98. Both electrolysis chambers were rendered inert with nitrogen.
• the electrolysis was carried out batchwise. Before the start of the electrolysis, 40 g of the sodium hydroxide obtained after concentration in the glove box were filled (poly) sulfide powder in the free leg 92 of the U-tube. Thereafter, the filling opening 99 was closed. Thereafter, the electrolyzer was heated for 10 hours from room temperature to 300 ° C. The sodium (poly) sulphide powder melted. With a slight overpressure on the free leg, this melt was transferred to the electrolysis zone.
• the electrolysis was carried out at a temperature ranging from 290 ° C to 310 ° C, a current of 1, 4A, and a cell voltage in the range of 2.5 to 3 volts over an electrolysis time of 7 hours.

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• 2013
  • 2013-07-22 JP JP2015523514A patent/JP2015529745A/ja active Pending
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