DE2829530A1 - Electrodialytic element - for desalination or power generation using dissociable metal salt solns. - Google Patents

Abstract

A system of electrodialysis for use in the desalination of seawater, the generation of electrical power from brine of different concn., or the storage of electrical energy uses in the electrode chambers solns. of substances which can dissociate into ions and can be reduced or oxidised as the ions change their charge, without passing into the gaseous phase. The pref. dissociable substances metallic salts or metallic complexes. This eliminates the release of chlorine and hydrogen gas and the shortening of the life of the electrodes and membranes by the attack from aggressive gases. The complicated means for the disposal of the gases are saved.

Description

Electrodialysis process

The invention relates to improvements in electrodialysis processes as well as novel applications for storing electrical energy for generation electrical energy from heat and devices for carrying out these processes.

In Figure 1 is an electrodialytic element corresponding to the current state of the art shown schematically. This element can e.g. B. to Desalination of sea water or to generate electrical energy from salty Serve water with different concentration. The element shown consists from the two outer electrode chambers with the anode and the cathode. Between These two chambers I and II are attached, which alternate through anion-selective (A) and cation-selective (K) membranes are separated from one another. In the chambers there are NaCl solutions of concentration or activity c and c2. When passing through of a direct current from the anode (+) to the cathode (-) the Na + and Cl ions migrate from chambers I into chambers II and the solution in chamber I is desalinated.

Conversely, if there are different initial concentrations c1 and c2, an electric current can be drawn from the electrodes. On the electrodes Discharge processes take place, which in this example lead to the formation of chlorine gas at the anode and hydrogen gas at the cathode. These discharge processes represent a major disadvantage of the process.

Since the discharge voltages are relatively high (compared to the Mambranpoter.tialen), they sssn consume a high proportion of the energy. Further Environmentally hostile aggressive gases are produced, which also extend the service life of the electrodes and shorten the membranes, and the removal of the gases requires complicated construction Activities.

These disadvantages can be according to the invention by the in Prevent claims 1 to 3 described measures. As reducible and oxidizable Substances are many substances known to the average person skilled in the art. Substances in which the charge of the cations changes with the degree of oxidation, are in particular compounds metals, which are in different valency levels occur, especially their salts and complex compounds. The latter have the Advantage of one in general good solubility regardless of pH; value and degree of oxidation and a greatly reduced rate of diffusion the membranes. Among the numerous substances in question are only a few a few examples mentioned: salts of Fe +++, Cu + / Cu ++, Co ++ / 'o +++, Cr ++ / Cr +++, Mn ++ / Mn +++ and hemoglobin. Examples of substances in which the charge state of the anions changes are polysulfides and mercaptans. These can also be built into larger Molecules the diffusion speed can be reduced arbitrarily.

Figure 2 shows the processes using the example of a Me + / Me ++ salt.

k # rnm # rn Will the anode and cathodes: with the same metal connection loaded, the two redo potentials balance each other out and it falls apart of any concentration potentials if the solution circulation is too slow, no electrode potential on. When using substances with different redox potential, these can different containers are taken and fed and then as Entgiespeicker to serve.

The proposed method also brings about an improvement, if the electrical energy is not supplied via electrodes, but as in In the example shown in Figure 3, the osmotic potential of two solutions different concentration is taken. In this example there are in chambers I and I 'more concentrated brine, in chambers II and II' sea water and desalinated water in chambers III and III '.

The concentration potential between brine and sea water is provided here the electrical energy for the desalination, so that no electricity is supplied via electrodes is required. In this case, however, there is already a slight charge transport leads to a very high polarization voltage in the two chambers I and I '', must @@ the solutions in these chambers very quickly and with corresponding Energy expenditure are mutually exchanged and pumped around. By bringing in a Reducible / oxidizable substance in the two outer chambers is building a Polarization voltage prevented. The emergence of much less potential for concentration can be stopped by slowly exchanging the two chamber contents.

To a migration of the metal ions by the cation-selective membrane To prevent from the chamber 1 ″, a further chamber V is expediently attached, which is separated from chamber 1 '' by an anion-selective membrane. In the sense of the terminology used here, chambers I and V are electrode chambers to be considered even though these do not contain electrodes.

The examples shown here are to simplify the illustrations only one or two electrodialysis elements are shown in each case, while the In practicing these procedures, a variety of such elements are generally used are attached in a battery-like arrangement between the electrodes »R-chambers.

for storing electrical energy. The application according to the invention the electrodialysisMis described in claims 5 to 13. The easiest for this required device is shown in the middle part of Fig. 4.

For example, NaCl serves as the salt. Wander while charging Na + ions from chamber II into chamber III, C1 - ions from chamber r II into chamber, also from the membrane pair between chamber III and I H + ions in chamber I and OH -Ions in chamber III. In chamber II NaCl is consumed, while in chamber I HCl and NaOH are formed in chamber III. To get the highest possible capacity, it is advisable to add a salt solution to chamber II during the charging process and withdraw a more dilute saline solution or water therefrom. Likewise, the Chambers I and III water supplied and acid or alkali removed from it and up saved for the unloading process. The diluted water can also be used as the water to be supplied Salt solutions, acids or alkalis are used, which accumulate as drainage from other chambers. This saves the storage tank for this water. Where a sufficient amount Water from the environment, e.g. B. also sea water, is available, hii one this use, but then have to expect losses of salt or brine, which are but can also be replaced from seawater.

In a materially closed system, this is stored per Energy required storage volume urso smaller, the more concentrated the salt solution and which are acid and alkali. For practical reasons, especially because of not one hundred percent Selectivity of the membranes can be in the central Element generally not to concentrate salt solutions with any concentration Acids and alkalis are implemented. It can therefore be useful to go through the system one device each for electrodialytic dilution or concentration of the salt solution to supplement the acid and alkali. These electrodialysis elements, which in principle like the work shown in Figure 1 are expediently operated in countercurrent, in order to obtain a constant membrane potential over the whole concentration range. In Figure 4 is this expanded electrodialytic device for storing electrical Energy shown during the charging process. During the unloading process, they all run away Material flows and electrical flows in the opposite direction.

Since the direction of the electric current in the dilution device for the saline solution runs the other way around as in the other elements, e.g. during the charging process Energy is given off, it is advisable to do without this device, if the volume of the required saline solution does not matter, e.g. B. from Sea water can be assumed. In this case the storage capacity increases, as the dilution energy is also stored in addition to the neutralization energy can be. The theoretical storage capacity is around flfxkg 16 kWh / Mkg depending on the salt or acid / alkali system used, in the same order of magnitude as with a lead-sulfuric acid accumulator or even higher.

Since the water required for the formation of the H + and OH ions is without Difficulty can diffuse through both membranes and thus from neighboring ones eae8nrn is a special Wa ## i # sift # s # chamber between the Chambers III and I not required. Nevertheless, it can be useful to have one Chamber IV to be provided in order to pass through the membranes which are not ~ one hundred percent selective Rinse out diffusing cations and anions with water. Otherwise you would these compete with the H + and OH - ions and reduce the performance of the element. An additional increase in selectivity is opposed by the attachment selective membranes on the inside of chamber IV possible. Da deionized Rinsing water has only a very low conductivity, the conductivity can according to Claim 4 reducible by adding; / oxidizable substances are increased, for what in particular, non-diffusing complexes come into question. Such a chamber IV is shown in the right half of the middle part of Figure 4. the Rinsed ions can be removed from the rinsing water by means of ion exchangers or through electrodialytic desalination can be removed again.

The inventive method for generating electrical energy from heat is described in claim 14 and in claims 17 to 21. The expression aqueous solvent means water or a solvent in which a dissociable substance is dissociated into anions and cations. The essentials this method consists in that the from the environment by means of a temperature difference the thermal energy extracted from the temperatures T1 and T2 by utilizing the temperature dependency the solubility of a substance initially in the osmotic energy of solutions of different Concentration of a dissociable substance is converted. The osmotic energy is then converted into electrical energy in an electrodialysis element.

The process has compared to the known energy conversion processes in heat engines that work according to the evaporation / condensation principle, the advantage of Adass because of the low / ######## ### ####### energy / the efficiency is much higher and therefore also low temperature differences, e.g. B. Day and night cycles or differences in sea water temperature can be used to generate energy. There no pressure differences occur, the heat exchangers can be thin-walled and thus be constructed more economically.

z dependency The temperature that can be used for the genutxts procedure ######### The solubility can affect both the solubility of the dissociable substance in an aqueous ####################### solvent or an extractant as well as the solubility of the aqueous solvent in an extractant relate. In the latter case there is swelling of a solid ######## material in water as physico-chemical equivalent Process of solubility equate.

Figure 5 shows the process using the example of a salt solution shown. The salt solution with the concentration c2 is brought to the temperature T2 brought, at which the solubility is less than c2. The separating Salt is heated to temperature T1 together with solvent, whereby it is in Solution goes and forms a solution with concentration c4. The mother liquor is on the other hand decreased to the concentration c1. In the electrodialytic cell or Battery, which in order to achieve a constant voltage, advantageously in countercurrent is operated, the osmotic energy of the concentration c1 and c4 becomes electrical Energy converted. The cell results in a constant over the entire countercurrent area Voltage if the ratio of the activities corresponding to the concentrations c a2 / a1 = a4 / aD, where C3 means the concentration at the upper outflow of the cell. It can therefore be useful not to limit the discharge with the concentration cD at the inflow of c4, but only further down into the middle cell. The same effect can be achieved by dividing the cells equally into two cells will.

In Figure 7 a device is shown schematically at which the splitting into different concentrations by extraction with a liquid extractant is effected, which is a temperature-dependent Has solubility for water.

In the right part of the figure is the aqueous solution's concentration C2 extracted and enriched to concentration c4 by removing water. The extractant saturated with water is in the left part on the temperature T2 brought, with water or possibly a very dilute salt solution cl separating out.

The system shown in Figure 7 can also be equipped with an extractant operated for the dissociable substance.

In this case, the depleted dilute at the outflow point C4 Solution and obtained at c1 the precipitated salt. The latter can be done with solution c2 be transferred to a saturated solution.

Instead of a circulating liquid extractant an endless belt made of a swellable material can also be used has a temperature-dependent swelling in water. One such device is shown in Figure 6. The belt running over several pulleys increases T1 on water, the solution concentration increasing from c2 to c4. At T2, the water is released again with the concentration c1. It is easy to see that this process is completely analogous to that shown in Figure 7. in the In contrast to a liquid extractant, however, the bare material can do so be chosen so that it is completely insoluble in water. This salt-enrichment-and-depletion procedure can therefore also be used in an open system, where e.g.

as solution c2 seawater or brackish water is used. So it can too serve to obtain fresh water from these waters. As with this procedure no evaporation energy has to be expended, it works with much higher Efficiency than the known evaporation-condensation process.

Another possibility for splitting the concentration is to be used 21 called. A procedure of this kind can be described in a manner analogous to Figure 5 Carry out the system, with the homogeneous solvent mixture instead of the solution c2 and instead of the salt sludge, think of the separated, salt-rich phase.

Suitable materials for carrying out the procedures mentioned there are in an almost unlimited number, of which those skilled in the art cannot be inventive To do this, you can choose the most suitable.

Therefore, only individual examples should be given to ensure that the invention is limited to these. The dissociable substances can both Salts, as well as acids or bases.

An example of a salt plit with strongly temperature-dependent solubility in water is the Glauber's salt. The systems phenol or cresol / water can be used as Examples of the method according to claim 19 are used. If T1 is higher than the demixing temperature, so it corresponds to the method according to claim 21. The demixing temperature can by adding solubilizers or adjusting the pH to the respective Working conditions can be adjusted.

A water-swellable tape can be made from crosslinked methyl cellulose manufactured which is more swellable at lower temperatures.

Since there is already a small temperature difference for the operation of these heat engines is sufficient, the enthalpy of evaporation can also be used to generate this temperature difference serve the water. In this case, if the ambient temperature is constant, the lower one Temperature generated by evaporation of water.

This process can also lead to additional enrichment serve the higher concentrated saline solution.

Addition to page 6 below: It is not necessary that the solubility limit has fallen below and the salt is actually deposited. The formation of a more concentrated solution also occurs when through the Temperature change changes the partition coefficient of the salt.

L e r s e i t e

Claims (1)

P a t e n t a n s p r ü c h e claim 1 electrodialysis process, characterized in that there are solutions of ions in the electrode chambers dissociable substances are located, which can be reduced by changing the charge of the ions or are oxidizable and do not change into the gaseous state. Claim 2 electrodialysis method according to claim 1, characterized in that that the dissociable substances are metal compounds, in particular Metal salts or complexes are. Claim 3 electrodialysis method according to claim 1 or 2, characterized marked that <during the execution of the procedure the solutions in the anode and cathode chambers against each other directly or indirectly via a Intermediate storage are performed in the circuit. Claim 4 Use of the method according to Claim 3 for transport electrical charges in and out of electrodeless chambers or within a chamber. Claim 5 method for storing electrical energy, characterized characterized in that by an arrangement of juxtaposed in groups of three Chambers ,. of which the first against the second by an anionic effect, the second against the third by a cation-selective, the third against the first of the following Group of three through an anion-selective and # '. Successive cation-selective @@@@@@ When charging an electric current in the direction of the membrane are separated first is passed to the third chamber, while in the second chamber a Saline solution and at least water in the first and third chambers -and when discharging, current is drawn in the opposite direction. Claim 6, method according to claim 5, characterized in that a saline solution and water are added to the second chamber during the charging process or a more dilute saline solution is withdrawn, as well as the enizagess in the first chamber Acid formed nix ## i and the lye formed in the third chamber withdrawn and stored and replaced by at least water than which the drain can serve from the second chamber, these flow directions during the unloading process vice versa be and an electric current in the reverse Direction is taken. Claim 7 beevorgan during the charging process, method according to Claim 6, characterized in that / the saline solution supplied to the second chamber beforehand in a countercurrent electrodialysis system in a manner known per se with recovery electrical energy is diluted, whereby for diluting the outflow from the second Chamber can serve, or the same process in reverse during the unloading process is carried out. Claim 8, method according to claim 6 or 7, characterized in that that the acid withdrawn from the first chamber and that from the third chamber withdrawn liquor in countercurrent electrodialysis systems with intake electrical energy can be brought to higher concentrations, whereby ibsr the here resulting more dilute acids or alkalis as an inflow for the first or respectively third chamber can serve, or the same process analogously during the unloading process is carried out in reverse. Claim 9, method according to claim 6, characterized in that Another chamber is located between the third and subsequent first chamber located, which from the third chamber by an anion-selective and from the first Chamber is separated by a cationic membrane, with this on the inside Membranes can also be attached to the reverse selective membranes can, and this chamber is filled with water, which increases the conductivity contain a dissociable substance that does not diffuse through the membranes can. Claim 10 device for carrying out the method according to claim 5, characterized in that there is at least one group between two electrodes of three chambers, which in the type mentioned in claim 5 against each other are separated and filled. Claim 11 Device according to Claim 10, characterized in that that they are required to carry out the procedure in accordance with the claim 6 required additions and Has drain lines. Claim 12 Device according to Claim 11, characterized in that that they are required to carry out the method according to claim 8 having additional countercurrent electrodialysis systems. Claim 13 Device according to Claim 11, characterized in that that they are required to carry out the method according to claim 9 has additional facilities. Claim 14 method for converting heat into electrical energy, characterized in that the solution utilizing a dissociable substance the temperature or uell dependence of the solubility in two different solutions Concentration is split up and the osmotic energy of these solutions in one Electrodialysis element is converted into electrical energy. Claim 15 heat engine for performing the method according to Claim 14, characterized in that it has an electrodialysis element and a Device comprises in which, taking advantage of the temperature dependence of the solubility or swelling the solution of a dissociable substance in two different solutions Concentration can be done. Claim 16 device for desalination of water, characterized in that that it has a revolving endless belt which consists of a material or contains this, which at different temperatures a different swelling in water, the rotation of the belt takes place in such a way that it is at a temperature in which the swelling is great, immersed in the salty water while it is exposed at another point in its circulation to a temperature at which the swelling decreases and the desalinated water is exuded. Claim 17 The method according to claim 14 and the device for it Implementation, characterized in that the splitting of the solution is dissociable Substance in two solutions of different concentrations by means of the device takes place according to claim 16. Claim 18 The method according to claim 14 and the device for it Implementation, characterized in that the solution is a dissociable substance at a temperature T2 at which the solubility is less than the concentration the solution is separated into mother liquor and salt sludge, then the salt sludge is brought to a temperature T1 with better solubility and the resulting more concentrated solution and the mother liquor at a temperature at which no precipitation occurs, are reacted with one another in an electrodialysis element. Claim 19 The method according to claim 14 and the device for it Implementation, characterized in that the solution is a dissociable substance in a water-like solvent IM with a second solvent ~ IM2, the has a temperature-dependent solubility for the solvent LM1, at a Temperature T1 is extracted, the resulting solution of LM1 in LM2 to a temperature T2 with lower solubility of L is brought into ~ IM2 and the deposited SM1 and the extracted solution are fed to the electrodialysis element. Claim 20 The method according to claim 14 and the device for it Implementation, characterized in that the solution is a dissociable substance in an aqueous solvent LMi with a second solvent LM2, the has a temperature-dependent solubility for the dissociable substance, at a temperature T1 is extracted, the extract obtained at a temperature T2 is brought with lower solubility and the dissociable thereby becoming more insoluble Substance is transferred into a more concentrated solution in LM1 and this as well as the more dilute extracted solution to electrodialysis Element fed will. Claim 21 The method according to claim 14 and the device for it Implementation, characterized in that the solution is a dissociable substance brought to a temperature T2 in a watery mixture of two solvents in which a separation into two phases occurs, and the two phases separately at a temperature T1 at which no segregation occurs, the electrodialysis element are fed. Claim 22, method according to claims 14 to 21 and apparatus its implementation, characterized in that the lower temperature is due to evaporation generated by water.