US2308665A - Refrigeration - Google Patents

Description

Patented Jan. 19, 1943 2,308,665 REFRIGERATION Glenn F. Zellhoefer,

Urbana, 111., and Michael J. Copley, phia, Pa., assignors,

Corporation, Bloomington,

Normal, and Carl S. Marvel,

Philadelby direct and mesne assignments, to Williams-Oil-O-Matic Heating Ill., a corporation of Illinois No Drawing. Application May 10, 1940, Serial No. 334,346

11 Claims. (Cl. 252-69) The present invention relates to refrigeration, and more particularly to refrigeration by means of the absorption principle.

One of the objects of the present invention is to provide a new and improved working fluid or medium for an absorption refrigerating system, which is especially adapted for air conditioning purposes. Y

A further object is a working fluid of the character described which requires a minimum amount of power per unit of refrigeration to effect transfer of the solution from the low side to-the high side of the system.

Another object is to provide an absorption refrigeration machine which may be operated with a slight differential between those presv sures prevailing within the machine and atmospheric pressure, thereby permitting the fabrication of the machine from lighter construction materials.

A still further object is to provide a working fluid. such that the pressure differential between the low side and the high side of the absorption refrigerating system is relatively small, thereby minimizing the possibility of pump failures, as well as reducing the power requirements per ton of refrigeration for effecting the circulation of the solution.

Another object is to provide a novel refrigerantabsorbent combination wherein the refrigerant forms a thermally unstable, loose molecular compound with the absorbent, by intermolecular ydrogen bonding.

The foregoing and other objects may be accomplished in accordance with the present invention, one aspect of which includes a novel refrigerant-absorbent combination in which the refrigerant comprises a member selected from the group consisting of water and alcohols boiling below approximately 212 F., and the absorbent comprises a member selected from the group consisting of relatively nonvolatile aliphatic amines and relatively nonvolatile aliphatic amides.

The refrigerant component of the present invention comprises either water or a volatile a1- cohol having a boiling point below approximately 212 F. i As specific examples of the refrigerant, mention may be made of the following compounds: water, methyl alcohol, ethyl alcohol,

isopropyl alcohol, normal propyl alcohol, tertiary butyl alcohol, secondary butyl alcohol and the like. The foregoing compounds are mentioned merely by way of example and serve to indicate the type of refrigerant embraced within the scope of the present invention.

The solvent or absorbent component of the present invention comprises either a nonvolatile aliphatic amine or a nonvolatile aliphatic amide, or mixtures thereof. Preferably the absorbent should have a boiling point above approximately 364 F., inasmuch as a solvent of lower boiling point creates fractionation difficulties in separating the refrigerant from the absorbent. From a theoretical point of view, the only requirement is that the boiling points of the refrigerant and the absorbent should differ to such an extent that the materials may be separated by suitable fractionating equipment. However, from a practical point of view, the greater the difference between the boiling points of the absorbent and the refrigerant, the less difficult will be the fractionation problem, and, in general, absorbents boiling below approximately 364 F. will be found to be impractical because of the elaborate equipment required for fractionation.

The absorbents may comprise the monoamines and/or the monoamides, as before indicated. However, the polyamines and/or polyamides in general are preferred. Of. the many compounds of the class described which may be used, the following may be mentioned purely by way of example: triethylene tetramine; tetraethylene pentamine; methylated triethylene tetramine (new compound, vide infra); trimethyl triethylene tetramine, new compound, vide infra); hexamethylene diamine; decamethylene diamine; hydroxyethyl ethylene diamine; dimethyl acetamide; dimethyl vvaleramide; methyl acetamide;

' tetramethyl oxamide; triacetyl trimethyl triethylene tetramine (new compound, vide infra) and the like, either alone or in combination. The foregoing specific compounds are mentioned purely for the purpose of illustrating the nature of the absorbent contemplated by the present invention.

The physical properties of certain specific examples of the refrigerant and absorbent components preferred in accordance with the present invention are set forth in Table I. From an inspection of Table I, it will be apparent that the latent heats of vaporization of the refrigerants are relatively high and that their vapor pressures are relatively low. The low vapor pressures permit the fabrication of the machine from relatively light construction materials. The small differential in pressure between the low side and high side reduces the difliculty in pumping the solution from the low side of the system to the high side. Moreover, the low pressure used in the operation of the machine re- ;iucges the probability of loss of chemical due to ea s.

2,sos,ee 3

The solubility characteristics of several em- In order to'show the significant improvement bodiments of the present working fluid, wherein the emciency of an absorption system proin specific amides are employed as the absorvided with the working fluid of the present inbents, are given in Table III. vention, calculations were made for various TABLE III Amides Solubility of refrigerant insolvent Solvent .Refrigerant Mol fractions Grarns/ gram Calcd. Observed Dirnethyl aeetamide Hi0 0.0627 0.177 0.232 0. 215 0. 22a 0. son 0. 242 0.200 0.314 Dimethyl valeramide 0. 124 0. 223 0. 337. Methyl aeetamide 0.184 0. 223 0.297 Triacetyl dimethyl triethylene ten-amine w compound-v1de infra) (fig g. 210 f. 50% dimethyl acetamide, 50% dimethyl ether of tetraethylenc glycol. 0.123

1 Observed solubility of refrigerant in solvent at 90 F. under pressure corresponding to vapor pressure of refrigerant at 40 F. in terms of grams refrigerant r gram solvent, except as otherwise noted.

Observed so ubility of refrigerant in solvent at 100 F. under pressure corresponding to vapor pressure of refrigerant at 40 F. in terms of grams refrigerant per gram solvent. 1

3 Calculated solubility under same conditions, in terms of mol fractions.

4 Observed solubility under same conditions in terms of mo] fractions.

working media to show the power required per ton of refrigeration to effect transfer of the solution from the low side to the high side of the 0f the numerous absorbents available which system (disregarding friction), the results bemay be used in accordance with the present ining given in Table V. Such calculations are vention, triethylene tetramine and hexamethylmade with reference to a machine designed for ene diamine constitute the preferred embodiair conditioning, operating under the following ments. Accordingly, in the following descripconditions: refrigerant temperature on the low tion, the invention will be described with parside, 40 F.; temperature of solution leaving the ticular reference thereto, it being clearly underheater, 228 to 235 F.; temperature of solution stood, however,'that these examples are merely leaving the absorber,- 95 to 105 F.; and rerepresentative of the type of solvents contemfrigerant temperature'in the receiver, 95 to 110 plated by the present invention. F. It should be understood that in the follow- The solubility characteristics of various reing discussion, the quantitative data, where givfrigerants inthe preferred solvents, at pressures en, are to be taken in a relative sense only; in other than those shown in Table I, are given in other words, the data are intended to be com- Table IV. parative, rather than absolute.

I TABLE V Power requirements to efiect circulation Solubility Vapor pressures SPPM lb./rnin./ PF Solvent Refrigerant ton of Sou-m 8230-108 A S P40 Pins A P refrig- GJg. (i G./g. lb./in. lb./in. lb./in. eration Triethylene tetrarnine HaO 0-174 0-0 0 0-164 .123 1.105 0.982 1.348 1.325 Hexamcthylene diarnine... 3. 77 .0538 323 758 5. 175 5. 417 1. 799 0. 735 .318 .0505 201 322 2. 71 2. 39 2. 752 0. 51s

Sp =Solubility of refrigerant in solvent at 00 F. under pressure corresponding to vapor pressure of refrigerant at 40 F. in terms of grains refrigerant per gram solvent. Q sm-mFsolubility of refrigerant in same solvent at 230 F under pressure corresponding to vapor pressure of refrigerant at 105 F. in terms 01 grams refrigerant per gram solvent. AS=Sno-m 1855 220-105. Prh=Vapor pressure of refrigerant at 40 F. in pounds per square inch abs. PmFg-por prg ssure of refrigerant at 105 F. in pounds per square inch abs. AP= 105 less 40.

SPPM=required rate of circulation of strong solution in pounds per minute to give one ton of refrigerant. with saturated gaseous refrigerant temperature of 40 F. in low side, saturated gaseous refrigerant temperature of 105 F. in condenser, 100% saturated solution leaving absorber at 90 F. under pressure corresponding to vapor pressure of the refrigerant at 40 F. and 100% saturated solution leaving heater at 230 F. under pressure corresponding to vapor pressure of refrigerant at 105 F.

PF=SPPM times AP.

TABLE IV 5 From the data given in Table V, it will be apparent that the pressure differential between mummy with when at the high side and the low side of the system,

100 F. G./g. vapor pressure corresponding to: in an absorption machine provided with the Solvent Refrigerant present working fluid, is relatively small (see 35F. F. F. F. AP, column 8,. Table V). As a result, he

amount of power required to effect circulation 'lricthylenetetramine H10 .009 .127 .164 .200 of the solution in the system (as indicated by the gg ggfii: egg 33*; it: fi value of "PF," last column, Table v) is signifi- Hexamethylencdiarn- #0 11101 .244 .367 .456 -552 cantly 10W.

are. g In the evaluation of refrigerant-solvent com- (about twenty-four hours).

binations, it is convenient to express numerically the relative amount of work required to efl'ect circulation of one refrigerant-solvent combina-' tion as compared to another. For this purpose the "relative efllciency" with respect to the work required to circulate the fluid of one combination in comparison to that of a standard or reference combination, may be defined by the equation:

RE=PFrlPFe where PF: is the PF value (SPPM times AP) of a standard or .reference working fluid, and PF. is the PF value of the fluid being evaluated. Ta ble VI gives the RE values for the preferred embodiments of the present invention, using (a) methylene chloride-dimethyl ether of tetraethylene glycol (col. 3) and (b) methylamine-ethylene glycol (col. 4), as reference media of the prior art.

TAsLr: VI

R d com are to H01: RE

com d Solvent Refrigerant "2x523" to cfigl fi +ethylene ethylene 1W0! glycol 'Iriethylenetetramine Hz0...-.. 51.5 103.7 Hexamethylena diaminem. 01130111--.. 7.15 14.13 CzHiO 10.38 20.92

Dimethyl ether of tetra- CH2Oh-.." 1.000 2.015

eth lene lycol(reierence) Ethy eneg you] (reference). CH;NH,.. 0. 495 1.000

From an inspection of Table VI, it will be apparent that the preferred embodiments of the present invention are vastly superior in respect to power requirements to the two standards selected. Thus, for example, the RE of triethylene tetramine plus water is 51.5, compared t methylene chloride plus dimethyl ether of tetraethylene glycol. In other words, the power requirement for the reference combination (in this bath. The residue of amine hydrochloride was refluxed with concentrated sodium hydroxide solution (1 kg./1.) and the amine layer separated.

- One kilogram of solid sodium hydroxide 'was added, the mixture refluxed for five hours and the liquid layers decanted from the sodium chloride which was precipitated from solution. The amine layer was separated and treatment with solid sodium hydroxide repeated several times as above until all the water was removed as indicated by presence of one liquid layer over hot alkali. The amine was then dried by heating over sodium chips for ten hours and then purified by vacuum distfllation to give 500 g. of a clear, non-viscous liquid, B. P. 99-103 C. at 2 mm.

Anal. Calcd. for CloHflcNi (tetramethyl): N, 27.7. Calcd. for C11H2aN4 (Dentamethyl): N, 25.9. Found: N, 26.3. Hence the amine has an average of about 4.7 methyl groups per molecule.

Trimethul triethylene tetramine 600 g. of dimethyl sulfate (4.8 moles) was added dropwise while the cold (IS-18 C.) solution was stirred vigorously with a mechanical stirrer. This case methylene chloride plusdhncthyl ether of tetraethylene glycol) is nearly 52 times as g'reat as that of the combination of triethylene tetramine plus water. The unexpected improvement in eiflciency accomplished by means of the present invention will be clearly evident from the data given in Table VI.

Preparation of new absorbents Methylation of triethylene tetramine The amine was methylated using the method of Clarke, Gillespie and Weishaus. Clarke, Gillespie and Weishaus, J. Am. Chem. 800., 55, 457 (1933). One and one-half kilograms of 90 per cent formic acid (30 moles) was added slowly to 500 g. of triethylene tetramine (3.4 moles). Considerable heat was evolved. To this red solution 800 cc. of 40 per cent formaldehyde (12 moles) was added, the mixture refluxed on a steam bath until the evolution of carbon dioxide ceased I One liter of concentrated hydrochloric acid was added and the mixture evaporated to dryness in vacuo on a steamaddition required six hours. After all the dimethyl sulfate had been added the mixture was allowed to warm to room temperature (28 C.) and remain thus with stirring overnight. The tan reaction mixture was poured into a solution of 500 g. of sodium hydroxide dissolved in 1 l. of

, water and refluxed for ten hours on a. steam bath to decompose the addition complex. The liquid layers were decanted from the sodium sulfate which had precipitated and the amine layer separated from the sodium hydroxide layer. The

amine was refluxed with solid sodium hydroxide to remove water. This process was repeated until no separation into liquid'layers occurred on refluxing the amine with solid sodium hydroxide. The amine was dried by heating overnight with sodium chips, and then purified by vacuum distillation to give 400 g. of slightly yellow, non-viscous liquid, B. P. 97-107 C. at 2-3 mm.

Anal. calcd. for cumin. (trimethyl): C. 57.5; H, 12.8; N, 29.8. Found: C, 57.9; H, 12.6; N, 29.6.

Acetulation of trimethill triethulene'tetramine To 57 g. of trimethyl triethylene tetra-mine in an all-glass refluxing flask and condenser an excess (200 cc.) of acetic anhydride was added slowly. A vigorous reaction occurred immediately with the formation of a dark-brown solution and evolution of much heat. The mixture was refluxed overnight. The acetic anhydride was distilled from the reaction mixture leaving a dark brown tar. The tar was distilled in vacuo with slight decomposition to. give g. of an extremely viscous brown liquid with a green fluorescence, B. P. 200-225 C. at 2-4 mm. This amide is water soluble and alcohol soluble. Treatment of the water solution with Norite did not result in decolorizing the amide.

Anal. calcd. for C15HsoOaN4 (trimethyl triacetyl): N, 17.8. Fond: N, 17.6.

In the foregoing detailed description of the presentinvention, certain aspects thereof have been illustrated with reference to an absorption refrigerating system of the two-fluid type. It should be understood, however, that this was done merely by way of example, and that the invention may be used, if desired, in the Platen- Munters system by supplementing the disclosed two-fluid combination with a third fluid such as hydrogen, helium or the like. It will also be apparent that the invention is not to be restricted to the specific embodiments hereinbefore more particularly described, since these embodiments were mentioned merely for the purpose of illustrating the basic principles of the invention. The foregoing description will be suflicient to enable those skilled in the art, after a mastery of the fundamentals of the present invention, to select or provide a very large number of refrigerantabsorbent combinations which may be substituted for those hereinbefore specifically cited. Many other variations will be readily apparent to those skilled in the art. The present invention is therefore to be restricted only in accordance with the following patent claims.

We claim: I

1. A working fluid for an absorption'refrigerating' system, which comprises a refrigerant selected from the group consisting of water andal-' cohols boiling below approximately 212 F. and a normally liquid absorbent having a boiling point above approximately 364 F. which is selected from the group consisting of aliphatic' polyamines, N- substituted aliphatic polyamides, and N- substituted aliphatic amides.

2. A working fluid for an absorption refrigerating system, which comprises a refrigerant selected from the group consisting of water and alcohols boiling below approximately 212 F. and an absorbent having a boiling point above approximately 364 F. and comprising a compound having the formula NI-MCI-IzCHzNI-DflCI-IzCHzNHz, where n is a small whole number.

3. The working fluid of claim 2 wherein said absorbent comprises triethylene tetramine.

4. A working fluid for an absorption refrigerating system, which comprises a refrigerant selected from the group consisting of water and alcohols boiling below approximately 212 F. and an absorbent having a boiling point above approximately 364 F. and comprising a poly- .methylene diamine.

.cludes absorbing said refrigerant in polymethylene diamine comprises hexamethyl ene diamine.

6. The working fluid of claim 2 wherein said refrigerant comprises methyl alcohol.

7. The working fluid of claim 2 whereln said refrigerant comprises ethyl alcohol.

8. In an absorption refrigerating process wherein a refrigerant selected from the group consisting of water and alcohols boiling below approximately 212 F. is alternately absorbed in and expelled from an absorbent, includes absorbing said refrigerant in a normally liquid absorbent having a boiling point above approximately 364 F. which is selected from the group consisting of aliphatic polyamines, N- substituted aliphatic polyamides, and N- substituted aliphatic amides.

9. In an absorption refrigerating process wherein a refrigerant selected from the group consisting of water and alcohols boiling below approximately 212 F. is alternately absorbed and expelled from an absorbent, the step which inan absorbent having a boiling point above approximately 364 F. and having the formula Nfiawl-laCflzNl-l) nCH2CH2NH-2,

where n is a small whole number.

10. In an absorption refrigerating processwherein a refrigerant selected from the group consisting of water and alcohols havingja' boiling point below approximately 212 F. is alternately absorbed in and expelled, from an absorb- 5. The working fluid of claim 4 wherein said ent. the step which includes absorbing said refrigerant in an absorbent comprising a polymethylene diamine having a boiling point above approximately 364 F.

11. A working fluid for an absorption refrigcrating system which comprises a refrigerant selected from the group consisting of water and a1- cohols boiling below approximately 212 F. and an absorbent comprising a relatively nonvolatile N- substituted aliphatic amide having a boilin point above approximately 364 F. GLENN F. ZEILHOEFER. CARL S. MARVEL. MICHAEL J. COPLEY.- I

the step which