DE1254587B - Low boiling coolant - Google Patents

Description

GERMAN PATENT OFFICE

German class: 12 a-7

EDITORIAL

Number: 1254587

File number: A 46204IV c / 12 a

^ 254 587 filing date: June 3, 1964

Opening day: November 23, 1967

The invention relates to constant boiling mixtures of fluorinated hydrocarbons and is another Formation of the invention described in Patent 1,201,810.

The cooling capacity of a given coolant is largely a function of its boiling point, with the lower boiling point coolants generally having the greater cooling capacity at a given evaporating temperature. This factor is essential to the design of a cooling system and affects cooling capacity, energy requirements, and the size and cost of the system. Another important factor, which is directly related to the boiling point of the refrigerant, is the lowest temperature that is reached in the evaporator during the refrigeration cycle, the lower the temperature being used, the lower the refrigerant used. For these reasons, a large number of refrigerants of different boiling points and different KAPA ao capacities necessary to make adaptable to the coolers, and the technology faces the problem of finding novel coolant when new capacity and new types of cooling systems are required.

The low molecular weight aliphatic hydrocarbons substituted with chlorine or fluorine are known coolants. Many of these chlorofluorocarbons have very desirable properties on how low cost, low specific volume, low toxicity and chemical inertness, which have led to the use of such compounds on a large scale and for many different cooling purposes be used.

Examples of such compounds are difluorochloromethane, bp. -29.8 ⁰ C, chlorodifluoromethane, bp. -40.8 ° C, fluorodichloromethane, Kp. 8.9 ° C, fluorotrichloromethane, bp. 23.8 ° C, and Tetrafiuordichloräthan, Bp. 3.5 ^° C. These chlorine-fluorine derivatives cover a range of coolants that is suitable for many purposes. However, very few of them boil at temperatures sufficiently low to have sufficient capacity when used as cryogenic refrigerants. A main reason for this is the presence of the relatively heavy chlorine as a substituent, which generally results in a boiling point which is higher than that of corresponding compounds which predominantly contain fluorine or hydrogen.

A compound of considerable cooling capacity is difluoromethane with a b.p. -51.6 ° C. This fluorocarbon owns many of the low-boiling refrigerants used for refrigeration purposes

Addendum to the patent: 1201 810

Applicant:

Allied Chemical Corporation,
New York, NY (V. St. A.)

Representative:

Dr. I. Ruch, patent attorney,
Munich 5, Reichenbachstr. 51

Named as inventor:
Robert Derry Broadley,
Morris Plains, Ν. J. (V. St. A.)

Claimed priority:

V. St. v. America October 3, 1963 (313 643)

desirable properties. However, it is flammable because of the two hydrogen atoms, which for some Cooling purposes is disadvantageous. Although fluorocarbons of this type have low boiling points, is the number of such compounds having the properties desired for cooling purposes is limited, and the boiling points of these compounds are very different so that they are not a satisfactory range result in low-boiling coolants of various capacities.

The progressive development in the field of cryogens or refrigerants and cryogenic cooling has led to a need for new cryogenic refrigerants with capacities other than those currently available.

Two-component mixtures of coolants with a minimum boiling point that have already been used,

709 689/400

had the disadvantage that only mixtures in a relatively narrow composition range the lowest temperature and that this lowest temperature is generally only 1 to 3 ° C is below the boiling point of the lower boiling component.

The relatively sudden change in the boiling point when the proportions of the components change involves considerable fractionation when the mixtures are distilled, which is extraordinary is undesirable.

According to the patent 1201810, mixtures of 13 to 18 mole percent Monochlorpentafluoräthan and the rest of difluoromethane are especially valuable as a refrigerant, because they boil at temperatures from -57 ⁰ C, ie more than 5 ° C below the boiling point of difluoromethane.

It has now been found that mixtures of monochloropentafluoroethane and difluoromethane in one a much wider range of compositions, namely those from more than 18 and up to 65 mol percent, in particular contain 30 to 33 mol percent monochloropentafluoroethane, are valuable coolants.

It is known that mixtures of difluoromethane and monochloropentafluoroethane, which are about 30 to 33 mol percent monofluoropentafluoroethane contain, form an azeotrope boiling at 57.3 ° C and that Mixtures containing 13 to 65 mole percent monochloropentafluoroethane have boiling points that are differ only slightly (by less than 0.75 ° C) from that of the azeotrope. Because of this very little There is no significant fractionation in this composition range when the boiling point is changed, when the mixtures are distilled, what happens when the mixtures are used as a coolant is extremely desirable.

As with the mixtures of the main patent, the flammability of difluoromethane is determined by admixture of monochloropentafluoroethane so largely reduced that the mixtures of the invention are practically flame retardant.

The boiling points of difluoromethane-monochloropentafluoroethane mixtures were determined using difluoromethane and monochloropentafluoroethane with purities of more than 99.8%. All materials were dried _{over P 2} O _{5 prior to use.} The static method was used to measure the boiling points of the mixtures. Weighed amounts of the components were distilled into a bomb and kept at a constant temperature throughout by means of a thermostat. To avoid errors due to segregation, the system was always kept 50 to 80% filled with liquid. The vapor pressure was determined directly with a Wallace & Tierman FA-135 mercury manometer to an accuracy of greater than 1 part in 1000 and all readings were ^{corrected to 760 mm Hg at 0} ° C and standard density. The bath temperature was held constant within less than ± 0.05 ° C and was measured by an L&N platinum resistance thermometer calibrated using an NBS platinum resistance thermometer calibrated by the National Bureau of Standards of America. The accuracy of the temperature measurements was ± 0.02 ° C. The bath temperature was adjusted until the vapor pressure of the mixture was equal to one atmosphere. The normal boiling points were as follows:

Normal boiling points of CH ₂ F ₂ -C ₂ F ₅ Cl mixtures

Mole percent C ₂ F ₅ Cl
in the solution Normal boiling point
⁰ C 0.0 -51.75 6.8 -55.60 11.4 -56.60 16.8 -57.05 21.7 -57.16 31.3 -57.26 60.9 -56.85 81.7 -54.72 100.0 -38.7

Independently of these measurements, the composition of the azeotropic mixture was checked by distillation. Approximately equimolar amounts of CH ₂ F ₂ and C ₂ F ₅ Cl were placed in a 20-interfloor cryogenic still from which samples of the distilling mixture and the top fraction could be taken. About one third of the initial charge was distilled off at -57 ° C. This product was returned to the still and refluxed until equilibrium was reached. Samples were taken from the top fraction and the distillation residue and analyzed by vapor chromatography. The analyzes agreed within the experimental error limits and, by calibrating the chromatograph, resulted in a composition for the azeotrope of 32 ± 1.0%. The boiling point of this sample was determined to be -57.26 ° C. in the static system described above.

These boiling point values are shown graphically in the drawing. The boiling point of the mixture at 760 mm Hg in ° C. is indicated on the vertical axis and the amount of monochloropentafluoroethane in the mixture is indicated on the horizontal axis. From the curve it can be seen that there is a mixture of difluoromethane and monochloropentachloroethane which boils at a very low temperature and contains about 30 to 33 mol percent C ₂ F ₅ Cl. The curve is relatively flat in the area of the minimum, ie there is a composition range within which the boiling points deviate only slightly from the minimum temperature of -57.3 ° C of the mixture containing _{30 to 33% C 2} F _{5 Cl.} The curve shows that this range comprises mixtures containing about 13 to 65% C ₂ F ₅ Cl.

Even if slight deviations in the compositions of vapor and liquid are to be avoided, it is of course most advantageous to use practically azeotropic mixtures with 30 to 33% C ₂ F ₆ Cl as the coolant. Since the deviations of the boiling points from that of the azeotrope in mixtures with a C ₂ F ₅ Cl content in the range from 25 to 35% are not considerable, all such mixtures are excellent coolants. If lower requirements are made, mixtures with are preferred C ₂ F ₅ Cl levels in the range of 15 to 55 ° C, all boiling at about or below -57 ° C, and are found to be excellent because they all boil within about 0.25 ° C.

Apart from the use of the specified amounts of difluoromethane and monochloropentafluoro-

Claims (1)

1 254 587 Ethane does not require any special methods for the preparation of the mixtures of this area for use in refrigeration. Plants difluoro, in which the cooling of methane by condensation and Monochlorpentafluoräthan are possible and subsequent evaporation of the coolant be liehst pure in, that is, their purity should preferably be close to the effected body to be cooled, are, at least about 99, be 0% , and they shall 5 These mixtures may also include in the known no substances which an undesirable situation where the use of difluoromethane influence on the boiling points of the mixtures or on a coolant or with equivalent capacity have their utility as a refrigerant. The coolants of the invention can of course also be used in cooling systems for other purposes, for example systems of relatively small size when referenced as heat transfer media, gaseous vapor evaporation temperatures from about -15 ° C. to electrics, low-temperature solvents and hydrauunter to for example -70 to 80 ° C used Hsche media, can be used,
will. The mixtures of the present invention ent- patent claim: wrap the desired cooling effect at low 15 Cost, low specific volume, non-toxicity, low boiling point, serving as a coolant, chemical and chemical inertness. They have both the fluorine methane and Monochlorpentafluoräthan entwertvollen cooling properties of the Chlorfluorkohlen- retaining mixture in modification of the mixture hydrogens German Patent 1201 810, d a-difluoromethane and how this low Siedetempe- in and the high cooling capacity of according to 20 by that the proportion temperatures . The practically constant boiling points of monochloropentafluoroethane of more than 18 mixtures containing 13 to 65% C ₂ F ₅ Cl, and up to 65 mol percent, in particular 30 to things that mixtures with compositions in 33 mol percent. 1 sheet of drawings 709 689/400 11.67 @ Bundesdruckerei Berlin