FR2529651A1 - Cooling and/or heating by using electrochemical reactions. - Google Patents

Abstract

Cooling and/or heating by using an electrochemical separation of a body contained in a mixture. A gaseous mixture of two separate chemical components A and B passes into an electrochemical separator S: the component A traverses the wall P and is returned to the generator E in the gaseous state; the component B is sent to the condenser C and returned to the generator E in the liquid state.

Description

The present invention relates to a new process for producing cold and / or heat by the use of any electrochemical reactions.

The processes for producing cold and / or heat by means of thermodynamic cycles generally use the heat exchanges associated with changes of state, dissolutions or chemical equilibria. The thermal or temperature levels at which these heat exchanges take place are determined most of the time by the operating pressure and the physico-chemical composition of the and / or fluids present.

The so-called compression systems require mechanical energy which, via a compressor, varies the pressure of the working fluid in the gaseous state.

The so-called absorption and absorption systems require a solvent in which the fluid is capable in a first step of dissolving in order to be desorbed again in a second step.

The present invention uses, in an original way for 3: a production of cold and / or heat, the separation power linked to electrochemical reactions.

One of the characteristics of the invention is therefore to produce cold and / or heat from electrical energy without first converting this electrical energy into mechanical energy as is necessary when using a compressor, a circulator and / or a pump.

A second characteristic of the method according to the invention is that the absence of a rotating mechanical member is superimposed on the advantage, essential in certain applications, of eliminating the main source of noise.

Another characteristic of the process lies in its better energy efficiency in comparison with known static processes for producing cold by Peltier effect or for producing heat by Joule effect, by radiation or by electromagnetic induction.

Another characteristic of the process resides in the possibility of producing reverse thermal phenomena (production of cold instead of production of heat and vice versa) by simple reversal of the direction of the electric current and to the exclusion of any modification of valve position, as it occurs during the defrosting periods of heat pumps.

Another characteristic of the process according to the invention is the use of a substantially identical pressure in all the components of the circuit, thus avoiding the risks of mechanical deterioration liable to occur during failures of the expansion members used in conventional systems.

Another characteristic of the process according to the invention is the possibility of avoiding any material transfer member (compressor, fan, pump), by simple use of the gravity flow between enclosures at substantially the same pressure.

The method according to the invention is described in principle by FIGS. 1 and FIG. 2.

Figure 3 relates to the electrochemical separator.

FIG. 4 represents in detail the seat electrodes for el = trochemical reactions.

FIG. 5 represents an exemplary embodiment.

In principle, the invention is characterized by the following stages: a) a gaseous mixture of individuals A and B is sent in contact with the first face of an electrochemical separator permeable to the individual
A and impermeable to individual B, so as to produce, on contact with said first face, a gaseous phase (G1) relatively depleted in individual A and enriched in individual B, and on contact with the second face of the separator, a phase gas (G2) enriched in individual A, b) the gaseous phase (G1) is cooled so as to condense at least part of the individual B or to dissolve at least part of it in a liquid phase having absorption properties selective wis-said individual B and to be collected separately:
- a condensate or solution of individual B and
- a gaseous phase (G3) relatively depleted in individual B and enriched in individual A, and c) the condensate or solution, collected (e) in step (b), is brought into contact with the gaseous phases (G2 ) and (G3) obtained in steps (a) and (b) respectively and heat is supplied to the zone of this contact, so as to evaporate the individual B and to reconstitute the gaseous mixture of the individuals A and B from step (a) and the said mixture is returned to step (a).

The principle of the invention is illustrated in FIG. 1.

Via line 1 a gaseous mixture of two gaseous species A and
B enters the separator (S) essentially consisting of a chamber 6 into which this mixture arrives, a double wall P capable of electrochemically transferring the single species A and a chamber 7 collecting this product A The electrical energy W supplied to the double wall P, the operation of which is explained below, ensures or accelerates the transfer of species A.

Line 2 essentially filled with gas A allows, at a pressure preferably substantially equal to that of the gas mixture AB, for the gas phase A to reach the enclosure E.

Line 3 is essentially filled with gas B of a pressure substantially equal to the mixture pressure AB entering the enclosure S.

In the enclosure C (condenser) a cooling device not shown in FIG. 1 ensures the evacuation, at the adequate thermal level, of a quantity of heat Qc linked to the condensation of the gas phase B.

The condensate is transferred via line 5 into enclosure E (evaporator) where the simultaneous introduction of the gaseous phase A, via line 2, causes the compound B to evaporate. Evaporation is made possible by adding heat QE not shown in Figure 1, lower thermal level than the thermal level prevailing in the condenser C.

Line 4 connects enclosure C with enclosure S and ensures the return to the separator of the portion of gas phase which has not condensed.

In fact, if the gas phase present in line 3 is composed of a mixture rich in B, there is however a non-zero quantity of compound A which has not been transferred electrochemically from the other side of the wall. In the condenser C it is essentially the compound B which condenses and the line 4 therefore ensures the transfer of the species A accompanied by a small quantity of vapor B.

A preferred arrangement for circulating the gases in the separator S consists in circulating the gases against the current, on either side of the wall.

A modification of the direction of flow of the electric current reverses the direction of transport of the product A. As a result, the conduit 2 transfers a gas rich in B which will condense in the enclosure E of FIG. 1.

Line 1 allows the evacuation of a vapor phase poor in A, which, enriched with this latter body, gst evacuated by 3. The liquid condensed in E pours into C or it is again evaporated by the gaseous supply coming from by 3. this gas enriched in B is evacuated by 4 towards S. It will therefore inversion of the functions taking place in E and C compared to what occurs when the direction of the current is not reversed.

The system therefore behaves like a conventional refrigeration and / or heat production device having a condenser and an evaporator. The method according to the invention is distinguished, however, by the absence of expansion device and by the use of a substantially isobaric electrochemical separator in place of the conventional compressor.

By analogy with conventional systems for producing cold and / or heat, the separator S can be compared to a "compressor" of species B. The increase in pressure of species B is a con.

direct sequence of the separation, at constant total pressure, of the mixture AB into a gas phase rich in A and a second gas phase rich in B.

FIG. 2 represents another embodiment of the method according to the invention, in which the compound B is absorbed in the ABS enclosure by a solvent. A pump P ensures the circulation of this solvent in the pipes 5 and 5 ', the exchanger EC, the ABS enclosure and return to the DES enclosure.

In this enclosure, the passage of the gas coming from the enclosure S through the pipe 2, desorbs part of the compound B dissolved in the solvent.

 Such an embodiment which does not essentially modify the pro cd according to the invention makes it possible to use as product B non-condensable compounds, under the chosen operating conditions (super critical state), or leading to excessively high pressures.

Figure 3 relates to the enclosure defined as the separator S.

There is, as already described, the pipe 1 which allows the gaseous mixture AB to enter the enclosure. The mixture AB travels the volume of the chamber 6 and is in contact with a wall 10 having the main characteristics of a porous gas electrode. Such a type of electrode, described in more detail below, essentially ensures that the gas mixture AB is in contact with an electrolyte 9 contained between the two electrodes G and 10. The physical structure of the electrode allows the gas phase to '' be in contact with the electrolyte, solid or liquid, without it being able to flow towards the volume occupied by the gas. This is commonly provided by a wettable porous structure filled with electrolyte adjacent to a non-wettable porous structure.

It is therefore possible to obtain, inside the electrode, an electrolyte interface, gaseous mixture AB. By having a catalyst at this interface during the production of such a type of electrode and by ensuring continuity of electronic conduction, it is possible to carry out electrochemical reactions between the gas phase and the electrolyte. According to the rules of thermodynamics, there is a transformation of compound A from its gaseous form in the mixture
AB into a new ionic species present in the electrolyte. The method according to the invention uses two electrodes which can be structurally opposite. Within .. within electrode 10, the compound
A is transferred electrochemically, that is to say in the presence of an electric field and of a continuous type electric current in the electrolyte.

The ionic form obtained migrates by bizou diffusion effect by mobility of the electrolyte, towards the second electrode 8. Within this second electrode the ionic species becomes again the species A by electrochemical reaction opposite to that which takes place in 10. However, if the final state in chamber 7 is different from that defined in chamber 6 (pressure, temperature, composition), it is necessary that the energy balance of the transfer is not zero. On the other hand, a certain number of thermodynamic irreversibilities arise during this transfer. it is therefore normal to note that it is necessary to provide a certain electrical energy to ensure the separation of A from AB and its almost pure transfer into a second chamber.

Referring to Figure 3, the mixture AB is introduced through line t. On contact with electrode 10, a
+ - electrochemical reaction symbolized by A + A + e
The ionic species A + migrates into the electrolyte medium 9.

The electric generator 12 ensures - by the conductors 11 and 13 the transfer of electrons from one electrode to the other so that at the level of electrode 8 takes place the reaction A + e + A.

If in the chamber 6 the mixing of the gas phase is not significant, it is noted that between the pipe 1 and the pipe 3 there is a progressive enrichment of the gas phase in this case B.

Similarly, there is enrichment of the compound A in the space 7 supplied by the piping 4 in a gaseous phase containing a mixture of A and B. Through the conduit 2 is discharged a gas rich in A.

Any type of electrode involving a gas phase with an electrolyte can be envisaged in the context of the present invention. By way of example, illustrated in FIG. 4, the electrodes 8 and 10 can be made of an electrically conductive material 15 allowing the electrolyte to pass through its thickness, as happens with a screen, a perforated sheet, an open porosity sinter or any other known method. It is often recommended to accelerate the kinetics of electrochemical exchange to dispcser a catalyst 16 specific for the envisaged reaction. Such a catalyst can be a solid chemical compound in the finely divided state or supported by a second solid such as a carbon large mass area or any other known catalysis support. it is preferable, however, to ensure continuity of electrical transfer to the catalyst and therefore to choose a support which is rather electrically conductive. In this catalytic layer 16 and in the hypothesis of the use of a liquid electrolyte, a chemical compound having water-repellent properties vis-à-vis the liquid electrolyte may be available in adequate concentration.

Polytetrafluoroethylene (PTFE) can be used for this purpose vis-à-vis basic or acidic aqueous solutions and also has the advantage of serving as a binder to the catalytic powder. This ensures total non-filling of the catalyst with the liquid phase and thereby The gaseous mixture AB has easier access to the catalytic site. For the same purpose, there is finally a porous layer of gas 17 but strictly impermeable to liquid.

The use of pure porous PTFE is excellent for this use; it allows a passage of the gaseous mixture AB and prevents the compartment reserved for the gas from being drowned by the electrolyte.

Such electrodes are used in particular for fuel cells in which the fuel is hydrogen and the oxidizer is pure oxygen or diluted in nitrogen as it is in the air.

Such electrodes are also used for the electrolytic decomposition of a chemical such as water into its hydrogen and oxygen constituents.

there are also many other electrodes involving a gas phase at the reaction level.

An example may be the combination of two electrodes composed of a porous nickel support, on which is deposited in first layer a catalyst such as carbon with Raney nickel, and in the second layer a porous wall permeable to hydrogen gas and impermeable to the electrolyte. The latter is, for example, an aqueous solution of potassium hydroxide (for example at a concentration of 30% by weight in water), at a temperature of, for example, 60 C. The reaction on contact with electrode where current is introduced is 1/2 H2 + OH- # H2O + e- the opposite reaction taking place at the other electrode.

Another example may be the combination of two electrodes on the same type of support as previously described, the catalyst being for one nickel-based electrode and for the other electrode of the divided silver.

With the same electrolyte (potassium hydroxide) the reactions involved are
02 + 4th + 2H20 + 40H silver catalyst and 40H- # O2 + 4th + 2H2O nickel catalyst
Another example may be the use of an acid electrolyte such as an aqueous solution of phosphoric acid between two electrodes composed of a porous carbon support and a catalyst based on platinum and / or palladium. reactions are then
H2 # 2H + + 2e2H + + 2e + H2
With the same type of electrode and the same electrolyte oxygen can also be used according to: 02 + 4H + + 4th- # 2H2O 2H2O # O2 + 4H + + 4th
Ion membranes can be used as acid electrolyte as shown by P. Blondeau and J. Lemaignen in the collective work published under the patronage of the General Delegation for Research
Scientific and Technical in 1965 under the title "Les Piles à Combustibles" published by Technip.

Another example may be the use of an electrolyte formed from an aqueous solution of sodium chloride and porous electrodes with a platinum catalyst.

The reversible reaction is then 1 Cl2 + e- # Cl2
Compound B, condensable and / or absorbable in a solvent and inert with respect to compound A1 can be chosen from any chemical family. it must have physical and chemical characteristics likely to cause non-zero thermal effects during a phase change and / or dissolution in a solvent. Among the condensable bodies, an example is a hydrocarbon, a halogenated hydrocarbon, an alcohol, water vapor, ammonia.

Among the absorbable substances, an example is a hydrocarbon, a halogenated hydrocarbon, an alcohol, water vapor, ammonia, carbon dioxide or sulfur dioxide.

The absorbent or solvent compound is chosen from any chemical family. An example is water, an alcohol, an amine, an alkanolamine, a ketone, dimethylsulfoxide, N.methylpyrolidone tri-n-butylphosphate, sulfolane.

The electrochemical separator can be of the flat plate type or of the cylindrical or cellular electrode type.

The electrodes can be rectangular, square, circular or polygonal. The electrical association between several pairs of electrodes can be a series type, parallel type, series-parallel or parallel-series type assembly.

The electrolyte can be of the solid electrolyte, liquid electrolyte or liquid electrolyte immobilized by matrix or in gel form.

 The electrolyte can be a liquid or a solid immobilized in its chamber or a liquid in connection with a reservoir or else with connections and means of circulation.

The gas phase can contain two or more compounds.

The condensable body can be pure or be composed of an azeotropic and / or non-azeotropic mixture.

The soluble bodies can be pure or be composed of an azeotropic and / or non-azeotropic mixture.

The solvent can be a pure substance in the form of a mixture consisting of one or more solid and / or liquid phases.

The temperature of the desorption or evaporation stages can usefully be between -400 C and + 800 C.

The condensation or absorption temperature can usefully be between + 200C and + 1200C.

The device is generally designed to operate at a maximum pressure of less than 50 atmospheres.

EXAMPLE
FIG. 5 relates to an exemplary embodiment of the method according to the invention with a view to producing a heat pump. The trans fluid
electrochemically fable is hydrogen, the condensable fluid chosen is dichlorotetrafluorcethane (R114).

The separator 18 consists of an assembly of chambers 19 and 21 and of double wall 20 containing as electrolyte a concentrated aqueous solution (30% by weight) of potassium hydroxide.

The electrodes are each formed of a thin nickel sheet (70 ssm) perforated with holes of 0.2 mm in diameter. Such sheets are produced industrially by electroforming. On these sheets, nickel powder is sprayed and sintered. On this 0.1 mm thick porous assembly, a catalyst based on Raney nickel and polytetrafluoroethylene (PTFE) is sprayed.

Finally, by mechanical plating, a thin sheet of pure porous PTFE is added, produced beforehand by electrostatic spraying and sintering.

The assembly has a thickness close to 0.5 mm and a front surface of 1500 cm2.

Two electrodes - are thus placed face to face, the facing metal walls being maintained without contact by a porous or mesh insulating separator of small thickness (0.1 mm) and filled with electrolyte
KOH-8N.

Leaving enclosure 35 via line 38, a gaseous mixture is evacuated containing 1 mole of hydrogen per 0.265 mole of R114.

If the pressure is 4.4 barson at this level, the partial pressure of H2 is deducted, ie 3.48 bars and for R114, 0.92 bar. The mixture issuing at 2 "C is heated in the coil 39 to 33 C and is introduced via line 22 into the separator 18. At 23, the extracted gas mixture contains 0.02 mole of H2 and always 0.265 mole of
R114.

In coil 24, 0.178 mole of R114 condenses, the heat of condensation being evacuated around 38 "C in the coil
The effluent is sent via line 28 to the enclosure 29 where a liquid 30 and a gaseous phase are collected, evacuated through line 32, containing 0.02 mole of H2 and 0.0875 mole of R114. This gas phase is returned to 380 C in the enclosure 18. In the illustrated chamber 19, this mixture is again enriched in hydrogen and, via line 41, a mixture containing 1 mole of H2 and 0.0875 mole of
R114. The heating due to the irreversibility of the reactions brings the mixture to 660 C.

The coil 42 evacuates outside in the circuit 43, 44 and 45 the heat corresponding to the cooling of the gas mixture from 660 C to 380 C. Through the conduit 46, this mixture reaches the coil 47 which exchanges heat with the coils 33 and 39. In the duct 48, the gas mixture is only 11.720 C to be brought into intimate contact with the liquid phase of R114 extracted by the duct 31 at 380 C and also cooled to 11.720 C in the coil 33.

The evaporation of 0.178 mole of R114 in the enclosure 35, made possible by a thermal contribution close to 20 C by the coil between the conduits 36 and 37, provides a vapor at 20C extracted by the conduit 38 and reheated to 330 C in the coil 39.

The pressure in the chambers is, close to the pressure drops which are reduced to a minimum, close to 4.4 bars.

The evaporation of 0.178 mole of R114 requires, at 20 C, the supply of 4197 joules. Part of this energy is taken from the gas and the liquid introduced into the enclosure 35. As a result, the circuit 36, 37 is only asked for 3618 joules. The work of transferring 1 mole of hydrogen, under non-isothermal conditions and varying the molar composition of the gas mixtures on either side of the double wall 20, requires 1255 joules. The electrical losses in the electrodes and the electrolyte very appreciably worsen the energy balance and the energy really necessary for the transfer is close to 2219 joules.

Assuming an identical current surface density for each of the electrodes and close to 0.5 A / cm 2, the unit surface area of the electrode for ensuring the transfer of 1 mole of X 2 per second at 11.5 mV is 38 m2.

3618 + 2219 joules are therefore recovered in the system to which only 2219 joules have been supplied in electrical form.

The coefficient of performance defined as the ratio of recoverable thermal energy to the primary energy introduced is therefore (3618 + 2219) / 2119 = 2.63.

In the above case, the transfer of one mole of hydrogen per second requires an electrical power of 2.2 KW and we recover 5.84 KW thermal.

In operation as a cold source, the efficiency of the process is defined as the ratio between the low temperature energy available, ie 3618 joules, and the electrical energy necessary for operation, ie 2219 joules.

The efficiency thus found (1.63) is of value much higher than that which can be obtained by using electrical energy by Peltier effect (efficiency: 0.1).

Claims (6)

1- Process for producing cold and / or heat, in which the working fluid comprises at least two distinct chemical individuals A and B, chemically inert to each other, individual A being a non-condensable gas under the process conditions and individual B being liquid or dissolved in a solvent under the process conditions , characterized by the following stages a) a gaseous mixture of the individuals A and B is sent in contact with the first face of an electrochemical separator permeable to the individual A and impermeable to individual B, so as to produce, on contact with said first face, a gaseous phase (G1) relatively depleted in individual A and enriched in individual B and, - in contact with the second face of the separator, a gas phase (G2) enriched in individual A, b) the gas phase (G) is cooled so as to condense at least a portion of 11 individual B or to dissolve at least a portion thereof in a liquid phase having absorption properties selective with regard to said individual B and to be collected separately  - a condensate or solution of individual B, and  - a gas phase (G3) relatively depleted in individual B  and enriched in individual A, and c) the condensate or solution, collected in step (b), is brought into contact with the gas phases (G2) and (G3) obtained in steps (a) and ( b) respectively and heat is supplied to the zone of this contact, so as to evaporate the individual B and to reconstitute the gaseous mixture of the individuals A and B of step (a) and the said mixture is returned to step (a). 2- method according to claim 1, wherein a liquid absorption phase is used in step (b) and the liquid is returned, after evaporation of the individual B in step (c), to step (b) to reconstitute the liquid absorption phase there. 3- The method of claim 1, wherein step (b) is carried out by condensation, in the absence of liquid absorption phase. 4- The method of claim 3, wherein the individual A is hydrogen and the individual B is a halogenated hydrocarbon. 5- A method according to any one of claims t to 4, wherein the electrochemical separator is constituted by two electrodes separated by a liquid or solid electrolyte, said electrodes being connected to a source of direct current and the electrochemical reaction chosen being reversible cJest - say that the individual A consumed on the first face of the separator is regenerated on the second face of the separator. 6- A method according to any one of claims 1 there, in which the gas mixture of the individuals A and B is circulated parallel to the first face of the separator and the gas phase G3 parallel to the other face of the separator against -current of the mixture of individuals A and B, the gas phase G3 thus enriching in the gas phase G2, formed on the second face of the separator, during this circulation, and the mixture resulting from the phases G2 and G3 is sent to the step (c).