FR2575175A1 - Compositions based on chlorofluoro oils for absorption machines - Google Patents

Abstract

Compositions of solvents and of heat-generating fluids for absorption heating or cooling equipment. The compositions according to the invention contain a chlorofluorohydrocarbon with a boiling point of between -40 and +50 DEG C and a chlorofluoro oil consisting of one or more compounds of formula: where n can take any value ranging from 2 to 4.n

Description

COMPOSITIONS BASED ON CHLOROFLUORINATED OILS
FOR ABSORPTION MACHINES ~ o ~ o ~ o ~ o ~ o ~
The present invention relates to solvent and heat generating fluid compositions for use in absorption heating or cooling apparatus.

 These machines, the operating principle of which is based on the extraction by absorption of low-level heat energy, borrowed for example from the outside air paur a heat pump or from a refrigeration enclosure for a refrigerant unit, and on the restitution of this energy in the room to be heated or in the surrounding space in the second case, uses an easily vaporizable compound (calogen) and a low volatility compound which is preferably a good solvent for the first.

 In a heat pump, the solution enriched in heat-generating fluid after absorption returns to the boiler where the two fluids are again separated by heating. The calogen is vaporized and sent into the pump circuit where it first undergoes condensation at high temperature, then expansion followed by evaporation before returning to the absorber.

The couples of calogen and solvent chosen must meet a certain number of criteria related to the very functioning of this type of machine.
a) The boiling points under normal pressure must have a difference of at least 150 to 200 "C in order to avoid the use of a device for retrograding the solvent.

 b) The boiling point of the heat-generating fluid must be neither too low to avoid the use of high operating pressures, nor too high to comply with the previous condition.

 c) Both compounds must be. completely miscible in the proportions of use over a wide range of temperatures.

 d) The solvent must remain liquid at low temperature and have a solidification point as low as possible in order to maintain an acceptable viscosity at temperatures of the order of -20 to 0 C.

 e) The mixture must have excellent thermal and chemical stability in the temperature range iiplicated by the thermodynamic cycle, that is to say in a temperature zone ranging, in the particular case of heat pumps, from -10 ° C. for the cold source (absorber) at 150-180 "C for the boiler.

 f) Finally, the products chosen must not present any character of toxicity.

 For safety reasons and also to take account of their good thermal and chemical stability, most heat-generating fluids are chosen from fluorinated hydrocarbons and, more especially, from chlorofluorinated hydrocarbons with one or two carbon atoms which correspond best to volatility and solubility criteria defined above. The most used compounds are fiuorotrichloromethane (R 11), dichlorodifluoromethane (R 12), dichlorofluoromethane (R 21), chlorodifluoromethane (R 22), chlorofluoromethane (R 31) , 1,2-dichloro tetrafluoro-1,2,2,2 ethane (R 114), dichloro-1,1 tetrafluoro-1,2,2,2 ethane (R 114a), chlorcpentafluoroethane (R 115), dichloro-l, l trifluoro-2,2,2 ethane (R 123), dichloro-1,2 trifluoro-1,2,2 ethane (R 123a), dichloro-l, l trifluoro-1,2, 2 ethane (R 123 b), chloro-1 tetrafluoro-1,2,2,2 ethane (R 124), chloro-1 tetrafluoro-1,1,2,2 ethane (R 124a), chloro-l 1,2,2-trifluoroethane (R 133), the chloro-1 trifluoro-2,2,2 ethane (R 133a), chloro-1 trifluoro-1,1,2 ethane (R 133b) and chloro-1 difluoro-l, ethane (R 142b).

 The best solvents, when the fluorinated hydrocarbon contains one or more hydrogen atoms, are those capable of forming intermolecular associations by hydrogen bonding and are recruited from the classes of carbonyl derivatives (esters, ketones, amides, lactams), alcohols or polyethylene glycol ethers.

Among the most widely used solvents, mention may be made of dimethyl ethers of tri- or tetra-ethyleneglycol (patent SU 150113 and applications JP 79-152257 and DE 3202377), N-methyl-pyrrolidone (patent SU 643524 and applications JP 79- 145774 and JP 82-132545), N, N-dimethylformamide (application JP 82-121759) and dibutyl phthalate (patent SU 346326). Also recommended as solvents, imidazolines and phosphoramides (applications JP 82-132544 and DE 2944189) as well as derivatives of tetrahydrofurfuryl alcohol (U.S. patent 4,251,382).

In the boiler of absorption machines, the solutions enriched in working fluid are brought to high temperatures The walls of the boiler are generally made of metallic materials based on iron, aluminum or copper which, under the effect of the temperature, can constitute an element of destabilization of the calogen-solvent couple. It is indeed well known that a chlorofluorinated hydrocarbon of the CnHn + 2-x-yFxCly type, heated in the presence of one of the abovementioned metals and of a hydrogen donor compound, undergoes a quantitative transformation with progressive substitution of the atoms of chlorine by hydrogen atoms taken in solvent. Depending on the reactivity of the donor and the structure of the fluorinated hydrocarbon, a greater or greater proportion of ethylenic derivatives is also formed, when n is equal to or greater than 2. Thus, in the case of chloro-1 trifluoro-2, 2,2 ethane (R133a), these transformations are carried out according to the following reaction scheme
CF3-CH2Cl + Fe

CF3-CH2 "+ FeCl * CF3-CH2 * + RH (solvent)

CF3CH3 + R.

CF2 = CH? + FeCIF quant au chloro-l tétrafluoro-1,2,2,2 éthane (R 124)chauffE en présence de N-mathyl-pyrrolidone et de fer, il donne du tétrafluoro-l,l,1,2 éthane (R 134a) et un mélange de difluoro-1,I éthylène et de trifluoro-éthylène
Cette réaction s 'accompagne de la formation de goudrons aux dépens du solvant et d'une corrosion importante due à l'action des halogénures métalliques formés. La dification de la nature du couple calogène/solvant, les effets de la corrosion et notamment la formation de gaz incondensables provoquent la détérioration des conditions de fonctionnement de la pompe à chaleur et pewent entrainer très rapidement sa mise hors d'usage.CF3CH2 * + FeC1

CF2 = CH? + FeCIF as for chloro-l tetrafluoro-1,2,2,2 ethane (R 124) Heated in the presence of N-methyl-pyrrolidone and iron, it gives tetrafluoro-1,1,2,1 ethane (R 134a ) and a mixture of difluoro-1, I ethylene and trifluoro-ethylene
This reaction is accompanied by the formation of tars at the expense of the solvent and by significant corrosion due to the action of the metal halides formed. The change in the nature of the heat / solvent couple, the effects of corrosion and in particular the formation of noncondensable gases provoke the deterioration of the operating conditions of the heat pump and pewent very quickly lead to its decommissioning.

 Various proposals have been made with a view to remedying this drawback and ensuring a minimum reliability of the order of 10,000 hours. The simplest consists in stabilizing the chlorogenic fluorofluoric / solvent fluid mixture by introducing an additive in a proportion which does not appreciably modify the physicochemical and therurdynamic characteristics of the calogenic-solvent couple.

Unfortunately, these additives offer only limited effectiveness over time and their action is mainly summed up by an extension of the inhibition period.

 Another method consists in replacing the chlorofluorinated hydrocarbon with a polyfluorinated alcohol such as trifluoroethanol (applications JP 80-16315, 81-88485, 82-132545 and 83-98137). However, the relatively high boiling points of these alcohols (73.5 "C for trifluoroethanol) lead to operating part of the installation (the evaporator) at a pressure significantly lower than normal pressure.

 Finally, the nature of the solvent can be modified and chosen from a family of products which do not give rise, in the presence of chlorofluorinated metals and hydrocarbons, to the reactions described above.

In this context, the structure identity has been used in patents FR 2 075 236 and U.S. 4 003 215 which use pairs of chlorofluorinated hydrocarbons as solvent and working fluid.

However, for the pairs R 12 / R-ll and R 12 / R 113 cited in the examples, the small differences in boiling points (of the order of 40 to 80 "G) require the implementation of technological processes complex to perform the solvent / heat generator separation at the outlet of the boiler.

 The present invention therefore aims to remedy the drawbacks of the prior art and to propose chlorofluorinated solvent / chlorofluorinated calogen couples, stable at high temperature in the presence of metals and usable in particular in absorption heating or refrigeration systems.

 It has now been found that chlorofluorinated oils of low secular weight obtained by thermal cracking of trifluorochlorethylene polymers form with chlorofluorinated hydrocarbons serving as working fluid (calogen) mixtures which are stable at high temperature in the presence of metallic materials, in particular ferrous , and can therefore, without addition of stabilizer, be used in heating or refrigeration by absorption without risk of decomposition. Their chemical inertness allows the use of common materials for the production of hot parts of the installation, the safety of which is increased by the absolutely non-flammable nature of said mixtures.

 The subject of the invention is therefore compositions comprising, on the one hand, a chlorofluorinated hydrocarbon with a boiling point of between -40 and + 500 ° C., preferably between -20 and + 2 ° C., and, on the other hand, of a chlorofluorinated oil of the type previously mentioned.

Chiorofluorinated oils, used as solvent in the compositions according to the invention, correspond to the general formula
Cl- (CF2-Cvl) n-Cl (I) in which n can take any value ranging from 2 to 4. I1 is generally cuts whose yen molecular weight is around 500. The points d 'boiling of these products are between 140 and 240 C under normal pressure and therefore have, compared to chlorofluorinated hydrocarbons commonly used as heaters, a sufficient difference in volatility. On the other hand, their very low freezing points allow them to be used in liquid form over a very wide temperature range. A typical example of chlorofluorinated oil according to the invention is that sold by the applicant under the name of Voltalef Oil 1 S; its freezing point is less than -550C and its boiling point is 141 "C / 760 torr.

 Among the chlorofluorinated hydrocarbons in accordance with the present invention, it is preferred to use chloro-1 tetrafluoro-1,2,2,2 ethane (R 124), chloro-1 trifluoro-2,2,2 ethane (R 133a) and 1,2-dichloro-1,1,2,2 tetrafluoroethane (R 114).

 The compositions according to the invention have a wide range of complete miscibility. The respective proportions of chlorofluorinated hydrocarbon and chlorofluorinated oil are not critical and are only limited by mutual solubilities.

 The following tests A to C, carried out with chlorofluorinated hydrocarbon / N-methyl-pyrrolidone (EMP) pairs, are given as controls and are to be compared with examples 1 to 3 which illustrate the invention without limiting it.

TEST A
5 minutes of R 124 are introduced into a thick-walled pyrex tube containing 3 g of NMP and a metal test tube of 250 mg of ordinary steel, suitably cleaned. The tube is cooled to the temperature of liquid nitrogen, sealed under vacuum and then maintained at a temperature of 1800C for 100 hours. It is then again plunged back into liquid nitrogen, connected to a vacuum ramp and opened using an appropriate device. The volatile products are recovered by purging at low temperature and analyzed by gas chromatography. Analysis shows that 55.4 Z of the initial R 124 have been transformed, of which approximately 50% into CF3-CH2F (R 134a).

 If the ordinary steel test piece is replaced by a 620 mg aluminum test piece and heated at 1800C for 1000 hours, the decomposition rate of R 124 reaches 97.4%.

TEST B
5 mnoles of R 133a, 3 g of NMP and a plain steel test tube of 250 mg are placed in a pyrex tube and the mixture is maintained at 1800C for 100 hours. After opening the tube, it can be seen that 76.1% of the initial R 133a has been transformed, of which approximately 62.5 Z into CF3CH3 and 8.5% into CF2 = CH2.

TEST C
A mixture of 5 moles of R 124, 3 g of NMP and 45 mg of tributyl phosphate is placed, with a 250 ing test tube of plain steel, in a thick-walled pyrex tube and the whole is maintained at 180 C for 100 hours. After opening the tube, it can be seen that 28.9 X of the initial R 124 have been transformed, of which 25 X into R 134a.

= = = = = =
EXAMPLE 1
5 mmol of R 124, 3 g of Voltalef 1 S oil and a test tube of 250 ng of ordinary steel are placed in a pyrex tube and the mixture is brought to 1800C for 100 hours. After opening the tube, it is found that only 0.3% of the initial R 124 has been transformed.

EXAMPLE 2
The procedure is as in Example 1, replacing R 124 with 5 mmol of R 133a. Analysis of the residual mixture shows that the decomposition rate of R 133a does not exceed 0.6%.

EXAMPLE 3
The procedure is as in Example 1 with 5 mmol of R 114. The conversion rate of R 114 does not exceed 1%.

Claims (5)

 Cl- (CF2-CFCl) n-Cl (I) in which n can take any value ranging from 2 to 4.  -ooooo- 1. Compositions for apparatus for heating or cooling by absorption, characterized in that they contain a chlorofluorinated hydrocarbon with a boiling point of between -40 and + 50 C and a chlorofluorinated oil constituted by one or more compounds of formula 2. Compositions according to claim 1, in which the dilorofluorinated oil has an average molecular weight of approximately 500. 3. Compositions according to claim 1 or 2, in which the chlorofluorinated hydrocarbon has a boiling point of between -20 and + 20 C. 4. Compositions according to one of claims 1 to 3, in which the chlorofluorinated hydrocarbon contains one or two carbon atoms. 5. Compositions according to claim 4, in which the chlorofluorinated hydrocarbon is chloro-l tétrafluoro-1,2,2,2 ethane, chloro-l trifluoro-2,2,2 ethane or dichloro-1,2 tetrafluoro -1,1,2,2 ethane.