Patent Publication Number: US-5829259-A

Title: Aqueous absorption fluids

Description:
This application is a continuation-in-part of application Ser. No. 08/443,707 filed May 18, 1995, now U.S. Pat. No. 5,577,388 which is a continuation-in-part of application Ser. No. 08/180,712 filed Jan. 13, 1994 now U.S. Pat. No. 5,419,145. 
    
    
     BACKGROUND OF THE INVENTION 
     In the aforesaid co-pending applications, there is disclosed the use of amines as additives for improving and increasing the rate of water vapor absorption in absorption cycle cooling and/or heating systems. In the aforesaid applications, the working fluid is an aqueous alkali metal hydroxide solution. The present invention includes the use of amines as effective additives in aqueous absorption working fluids where other metal salts are used in the absorption solution. 
     SUMMARY OF THE INVENTION 
     According to the present invention primary, secondary and tertiary aliphatic, cycloaliphatic, heterocyclic and aromatic amines are highly effective heat and mass transfer additives in aqueous metal salt and alkali metal hydroxide solutions used in water vapor absorption cycle systems. The presence of such amines increases the rate of water vapor absorption by the aqueous metal salt absorption fluids thereby achieving important advantages and improvements in system performance. The improvements include absorber power load increases and improvements in the change of absorber fluid concentrations. Further improvements include increase in overall heat transfer coefficients and sorption fluid side film heat transfer coefficients. The advantage of such improved absorption fluid performance allows for reduction of sorber heat exchange surface areas needed to satisfy a given load resulting in reduction of absorber size and costs. These and other improvements and advantages will be evident from the following detailed description. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The specific improved aqueous absorption solutions used in the systems of the present invention are aqueous solutions of metal salt or alkali metal hydroxide solutions in which water is substantially the only solvent. By this description, it is intended to exclude those solutions containing additional solvents such as glycols, polyglycols, alcohols, glycol ethers, glycerol and the like in solvent amounts. The preferred metal salts are alkali metal halides, particularly lithium bromide, lithium chloride and lithium iodide and mixtures of two or more of them. The most preferred working fluid is an aqueous solution of lithium bromide as the only absorbent present in the aqueous solution. However, in addition to the preferred lithium bromide, one or more of the following salts may also be present: ZnCl 2 , ZnBr 2 , MnCl 2 , MnBr 2 , MgCl 2 , MgBr 2 , SrCl 2 , SrBr 2 , CaCl 2 , CaBr 2 , FeCl 2 , FeBr 2 , LiCl, LiI, LiNO 2 , LiNO 3 , LiSCN and LiClO 3 . The amount of salt present, whether lithium bromide alone or a mixture of two or more of the aforesaid salts is preferably between about 40% and about 85%, by weight and if zinc is used, between about 40% and about 90%, by weight. However, the presence of calcium or zinc in the absorption fluid may cause precipitation of some amines which may make such systems unattractive. The aforesaid LiBr aqueous absorption solutions are well known to those skilled in the art as disclosed, for example, in U.S. Pat. No. 3,478,530. 
     The alkali metal hydroxide absorption fluids are aqueous solutions of sodium hydroxide, potassium hydroxide or mixtures thereof. Preferred hydroxide compositions are those utilizing a mixture of the two hydroxides, and preferably those in which the total hydroxide concentration is between about 30% and about 80%, by weight. It has been found that optimum energy storage potentials are realized when sodium hydroxide is present between about 35% and about 75%, by weight, of the combined sodium hydroxide and potassium hydroxide weight. The amount of sodium hydroxide present in the salt mixture for systems at crystallization temperatures above 30° C. is 50% or above, whereas for temperatures below 30° C., the preferred amount of sodium hydroxide is at or below 50% of the salt mixture. The most preferred amount of sodium hydroxide is between 40% and 55% of the combined weight of sodium hydroxide and potassium hydroxide for crystallization temperatures below 30° C. In addition to the aforesaid sodium and/or potassium hydroxide solutions, relatively small amounts of other alkali metal hydroxides may be added as well. Thus, the hydroxide solutions may contain up to about 10-15% cesium, rubidium, and/or lithium hydroxide, based on the weight of sodium and/or potassium hydroxides. 
     The heat and mass transfer additives of the invention are primary, secondary or tertiary aliphatic, cycloaliphatic, heterocyclic or aromatic amines. Preferred amines are those that are normally liquid at system operating conditions, for example, between about 30° C. and up to 100° C. or more. Additives of the present invention may be used in systems with absorber temperatures of about 20° C. or less if they are selected from those amines with a melting point less than the absorber temperature. The additives may be liquid over a wider temperature range, both higher and lower, without adversely affecting the operation of the invention. Thus, for example, aniline is a satisfactory additive, with a freezing point of -6° C. and a normal boiling point of 184° C. The amines may contain one amine functional group, or may have multiple amine groups including two, three or more functional groups in the same molecule. Preferred amine additives, according to the invention, are aliphatic and aromatic amines, preferably having between four and twenty and more preferably between six and twelve carbon atoms. For the alkali metal halides, and particularly the lithium bromide solutions, the most preferred amines are ethylhexylamine, N,N-dimethyloctylamine, aniline and benzylamine. Other examples of useful aliphatic amines include tert-octylamine, n-octylamine, di-sec-butylamine, pentylamine, butylmethylamine, dipropylamine, butylethylamine, triethylamine, pentylethylamine, hexylamine, cyclohexylamine, trans-1,2-diaminocyclohexane, N,N-diethylcyclohexylamine, 1,5-dimethylhexylamine, N,N-dimethylhexylamine, N-methyldibutylamine, nonylamine, N,N,diisopropylethylamine and 2-methyl-1,5-diaminopentane and others disclosed in the aforesaid application and incorporated herein by reference. A most preferred amine additive for the lithium bromide absorption solutions of the invention is 2-ethylhexylamine. Other preferred primary amines include cycloaliphatic or alicyclic amines such as cyclohexylamine and diaminocyclohexane and its different isomers. Other particularly useful and effective amines include secondary aliphatic and saturated cyclic or heterocyclic amines of 4-12 carbon atoms such as dialkylamines, piperidine and substituted piperidines, and pyrrolidine and substituted pyrrolidines. Preferred derivatives are alkyl or halogen substituted. Another preferred group of amines include tertiary aliphatic and saturated heterocyclic amines such as N,N-dimethyloctylamine, N,N-diethyloctylamine, N,N-diisopropylethylamine, and N-methylpiperidine. Another useful group are the aromatic amines such as aniline, and substituted anilines such as 3,5-bis-trifluoromethylaniline, 2,3,4,5,6-pentafluoroaniline, and the different isomers of toluidine and anisidine. The aromatic amines may be polycyclic such as α-naphthylamine and β-naphthylamine, and alkyl substituted napthylamines. Unsaturated heterocyclic and aromatic nitrogen compounds such as quinoline, isoquinoline, pyrrole, pyrroline, and pyridine, and alkyl and halogen-substituted heterocyclic aromatics, particularly methyl and fluorine substituted derivatives, are also useful and preferred additives of the invention. Other active nitrogen compounds included aliphatic and aromatic nitriles such as benzonitrile, tolunitrile, and octylnitrile. By the term heterocyclic amines as used herein, it is intended to include heterocyclic amines in which nitrogen is the only hetero atom. Thus, heterocyclic compounds containing oxygen and/or sulfur are specifically excluded. 
     From the aforesaid specific examples, it will be noted that the amino compounds may have one or more amine functional groups in the same molecule. However, not all polyfunctional amine additives will be active with all fluids. Particularly for lithium containing solutions, it is important to avoid additives that form a chelation complex with the cations of the absorbent thereby reducing or preventing heat and mass transfer activity. For example, 1,2-diaminocyclohexane can form a five-membered ring in LiBr-H 2  O, consisting of the lithium atom, the two amine nitrogen atoms, and carbon atoms number 1 and 2 on the cyclohexane ring. Thus, five, six and seven-membered rings are to be avoided with lithium. The tendency toward chelate formation with additives is more prevalent with LiBr solutions than with metal hydroxide solutions such as NaOH-H 2  O. For example, while 1,2-diaminocyclohexane is an active additive for NaOH and KOH solutions, and mixtures thereof as shown in application Ser. No. 08/180,712, it is not active with LiBr-H 2  O solutions. The capability of a polyfunctional additive to form such rings will be obvious to those practitioners skilled in the chemical art. The amine molecule may also include one or more other functional groups such as alcohols, halogens, thiols, ethers, and ketones, provided such functional groups do not cause the amine to form a precipitate or otherwise induce chemical instability in the presence of the metal halide or hydroxide solutions. Thus, where the metal salts include zinc or calcium salts, specifically zinc chloride and/or zinc bromide, only fluoro substituted amines, as previously disclosed, may be used. It has been found that amines substituted with aforesaid functional groups, other than fluorine, will form a precipitate in the presence of the zinc or calcium salts. It is also to be understood that the specific amines disclosed are given by way of example only, and any of the aforesaid amines or combinations thereof within the disclosed groups of amines may be used. 
     The effective additive amounts of amine additive added to the aqueous salt solutions for the purpose of improving heat and mass transfer is from at least about two parts per million and preferably up to about 20,000 ppm, by weight. Preferred concentrations are between about 2 ppm and 10,000 ppm and more preferably between about 5 ppm and about 5,000 ppm, although amounts in excess of this range up to 20,000 ppm or more will not adversely affect the system operation. Mixtures of the aforesaid amine additives may also be used. In addition to mixtures of the amines other known heat and mass transfer additives, particularly alcohols having 6-10 carbon atoms such as 2-ethylhexanol or n-octanol as disclosed in U.S. Pat. No. 5,419,145 may also be added where a mixture of additives is desired or where such other additive is already present in the absorption fluid. 
     According to the invention, it has been found that the presence of an amine in the aqueous absorption fluid containing a lithium halide or the sodium or potassium hydroxides, or mixtures of the hydroxides results in substantially improved heat and mass transfer performance of the absorption working fluid composition. Specifically, the performance of the system improves in the following manner: water cooling temperature change in the absorber, for a constant water flow rate, rises significantly; the absorber power load increases proportional to the change in water cooling temperature; the steady state vapor pressure drops, and if brought back to its initial value to achieve a constant evaporator temperature, the change in concentration of the absorber fluid increases significantly; the absorber solution subcooling, i.e., the difference between the maximum temperature at equilibrium (saturation) and the actual solution temperature, is decreased by several degrees; the absorber solution-heat exchanger tube interface comprises a highly agitated turbulent film as compared to a generally laminar flow pattern without presence of the additive; and overall heat transfer coefficients and sorption fluid film heat transfer coefficients are increased. 
     As previously noted, water vapor absorption systems incorporating the amine heat and mass transfer additives in the aqueous alkali metal absorption solutions of the invention include a number of different types of systems incorporating one or more absorbers in which water vapor absorption solutions are typically used. Such equipment includes absorption chillers and refrigeration systems as disclosed in U.S. Pat. Nos. 4,966,007, 5,038,574 and 5,186,009, thermal energy storage systems as disclosed in U.S. Pat. No. 4,823,864, as well as multiple effect absorption refrigeration systems, for example, double effect and dual loop systems disclosed in U.S. Pat. Nos. 3,266,266 and 4,542,628 and triple effect systems disclosed in U.S. Pat. No. 5,335,515 and 5,390,509. The description of the apparatus and systems disclosed in the aforesaid application and patents are incorporated herein by reference. Especially preferred are the single and double effect absorption chiller and refrigeration systems which includes those systems in which the single or double effect components are a portion of the system, such as a dual loop triple effect system comprising combined single stage loops as disclosed in U.S. Pat. No. 4,732,008. The aqueous working fluids of the invention may also contain a corrosion inhibitor such as chromates, nitrates, tungstates or molybdates, as disclosed for example in U.S. Pat. No. 5,186,009 and 5,335,515 or other suitable organic or inorganic corrosion inhibitors. It will also be understood to those skilled in the art that the aqueous absorption fluids containing the lithium salts will be hydroxide inhibited, with the pH balanced at between about 10-12. In the presence of zinc salts, hydroxide inhibition may also be used, but the pH will be much lower. 
     To illustrate the improvement of system performance by using the heat and mass transfer additives of the present invention, the following examples are provided. In the Table, amine additives within the scope of the present invention are shown by way of example. The results given are for a constant set of operating conditions and include: initial cooling water (&#34;Tube&#34;) temperature of 30° C., a system water vapor pressure of 10 mbar, 7° C. dew point (evaporator temperature), initial aqueous solution concentration of 60% LiBr, initial solution flow rate of 400 grams/min, and initial solution temperature of 48° C. entering the absorber, using a special bench test absorption machine. The solution flow rate used for nonylamine is 300 grams/min and for pyridine 500 grams/min. The water and solution temperatures, flow rates and vapor pressures are taken from monitor readings during operation. The concentrations are determined from fluid samples taken from the machine. 
     The results are based on heat transfer equations well known to practitioners of the art. The absorber load dQ/dt, shown as W, is calculated from the water temperature, heat capacity of water, and water flow rates, ##EQU1## For the heat transfer coefficients, the temperature change is treated as the log mean differential temperature, where ##EQU2## The outside film heat transfer coefficient h o  is calculated from ##EQU3## where ##EQU4## and where R i ,m is the thermal resistivity of the inside cooling water and copper metal tube wall. Solution subcooling is the temperature difference (ΔT) between the actual solution temperature leaving the absorber and the calculated absorber solution equilibrium temperature at the measured concentration and system vapor pressure values. Thus, lower subcooling temperature values reflect greater system efficiency as do increased outside film heat transfer coefficients, h o . The value calculated for solution subcooling is one measure of the efficiency of the system for water vapor absorption, with lower subcooling temperatures indicating an improvement. However, under certain conditions, the derived subcooling numbers may be contrary to other direct measurements of water vapor absorption. In the Table some data show higher calculated solution subcooling while also showing increased water vapor absorption rates by increases in absorber loads, and increases in heat transfer coefficients. Thus, the derived subcooling results are to be checked against other direct evidence of increased absorption rates. 
     
                       TABLE                                                       
______________________________________                                    
                  Load      ho    Subcooling                              
Additive   ppm    W         W/m2K °C.                              
______________________________________                                    
nonylamine 0      417       1099  9.4                                     
           0      512       1291  7.1                                     
           0      540       1595  6.6                                     
           15.7   563       1208  6.4                                     
           15.7   509       1092  5.4                                     
           26     678       1535  5.5                                     
           26     671       1610  5.1                                     
           36     760       1651  4.2                                     
           36     752       1588  3.6                                     
           46     787       1570  3.1                                     
           46     780       1676  5.0                                     
           56     780       1619  3.5                                     
           56     824       1872  3.9                                     
           66     849       1886  3.3                                     
           66     859       1859  2.5                                     
           80     843       1932  3.7                                     
           80     831       1927  3.9                                     
           100    870       2225  3.7                                     
           100    763       1759  5.9                                     
           100    768       1742  4.6                                     
           154    705       1704  5.3                                     
           154    756       1845  4.9                                     
           199    786       1976  4.6                                     
           199    809       2047  3.9                                     
           199    857       2308  4.5                                     
           199    870       2402  3.7                                     
(con&#39;t)    253    868       2449  3.7                                     
           253    865       2506  4.3                                     
           299    884       2360  4.5                                     
           299    911       2563  3.7                                     
nonylamine 1002   896       2548  4.1                                     
           1002   894       2644  4.1                                     
______________________________________                                    
 
    
     
         ______________________________________                                    
                     Load     ho    Subcooling                            
Additive      ppm    W        W/m2K °C.                            
______________________________________                                    
2-ethylhexylamine                                                         
              0      898      1330  7.77                                  
              0      919      1197  5.26                                  
              5      1521     2351  2.85                                  
              5      1525     2269  2.07                                  
              10     1730     2842  1.70                                  
              10     1698     2756  2.13                                  
              20     1831     3129  2.06                                  
              20     1842     3042  1.51                                  
              50     1927     3818  1.90                                  
              50     1941     3742  1.68                                  
              100    1897     4095  1.79                                  
              100    1934     4011  1.84                                  
              200    1892     3686  1.78                                  
              200    1884     3811  2.08                                  
              300    1745     4201  3.97                                  
              300    1785     4410  3.48                                  
              400    1799     3995  2.92                                  
              400    1862     3852  3.06                                  
              500    1847     3825  2.54                                  
              500    1852     3824  1.31                                  
              600    1860     3827  3.39                                  
              600    1836     3642  2.54                                  
              1000   1807     3628  3.49                                  
              1000   1806     3683  2.76                                  
______________________________________                                    
 
    
     
         ______________________________________                                    
                        Load   ho    Subcooling                           
Additive         ppm    W      W/m2K °C.                           
______________________________________                                    
N,N-diisopropylethylamine (con&#39;t)                                         
                 0      1014   1566  7.43                                 
                 0      1045   1598  6.79                                 
                 0      1041   1366  5.60                                 
                 0      1061   1414  5.89                                 
                 0      1038   1426  6.01                                 
                 0      1047   1470  6.41                                 
                 5      1149   1673  5.72                                 
                 5      1161   1704  5.67                                 
                 10     1281   1746  4.06                                 
                 10     1288   1737  4.31                                 
                 20     1364   1900  3.71                                 
                 20     1381   1932  4.23                                 
                 50     1341   1973  3.68                                 
                 50     1359   2022  4.18                                 
                 100    1423   2245  4.47                                 
                 100    1434   2285  4.37                                 
                 200    1497   2634  4.99                                 
                 200    1505   2619  5.02                                 
                 300    1450   2789  5.89                                 
                 300    1468   2878  5.66                                 
                 400    1494   2990  5.56                                 
                 400    1513   3010  5.80                                 
                 600    1487   3131  6.30                                 
                 600    1501   3127  6.42                                 
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         ______________________________________                                    
                     Load     ho    Subcooling                            
Additive      ppm    W        W/m2K °C.                            
______________________________________                                    
N,N-dimethyloctylamine                                                    
              0      967      1211  4.97                                  
              0      991      1253  5.01                                  
              0      997      1239  4.86                                  
              0      1079     1461  4.26                                  
              0      1116     1552  4.77                                  
              0      1133     1608  5.18                                  
              0      1141     1525  4.51                                  
              0      1155     1597  5.00                                  
              0      1075     1432  4.15                                  
              5      1366     2077  3.30                                  
              5      1396     2127  3.72                                  
              10     1486     2527  3.75                                  
              10     1527     2632  3.44                                  
              20     1621     2771  2.75                                  
              20     1626     2826  3.32                                  
              50     1677     3083  3.92                                  
              50     1657     3212  4.35                                  
              50     1660     3166  4.30                                  
              100    1613     3052  4.30                                  
              100    1602     3016  3.89                                  
              150    1601     3229  4.15                                  
              150    1595     3169  4.46                                  
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         ______________________________________                                    
                 Load       ho    Subcooling                              
Additive  ppm    W          W/m2K °C.                              
______________________________________                                    
aniline   0      911        1224  7.31                                    
          0      983        1321  7.31                                    
          0      966        1217  8.14                                    
          0      954        1088  5.35                                    
          10     954        1331  7.91                                    
          10     977        1328  7.77                                    
          10     978        1362  7.61                                    
          20     1055       1533  6.96                                    
          20     1067       1563  6.86                                    
          20     1072       1552  7.05                                    
          50     1312       2213  6.60                                    
          50     1345       2271  6.68                                    
          50     1357       2319  6.52                                    
          100    1564       3147  6.18                                    
          100    1551       3091  5.98                                    
          100    1555       3134  5.88                                    
          100    1563       3101  5.98                                    
          200    1620       3616  6.15                                    
          200    1686       3708  6.75                                    
          200    1674       3675  6.73                                    
          200    1656       3613  6.90                                    
          500    1669       3758  6.83                                    
          500    1488       3421  7.67                                    
          500    1472       3409  7.67                                    
          500    1420       3415  7.58                                    
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         ______________________________________                                    
                  Load      ho    Subcooling                              
Additive   ppm    W         W/m2K °C.                              
______________________________________                                    
benzylamine                                                               
           0      783       1031  7.06                                    
           0      771       970   6.44                                    
           0      764       973   5.80                                    
           7.9    1421      2039  2.97                                    
           7.9    1409      1942  2.38                                    
           7.9    1426      1954  2.34                                    
           15     1355      2022  3.71                                    
           15     1352      1805  2.41                                    
           15     1336      1792  2.40                                    
           25.6   1315      1885  3.51                                    
           25.6   1304      1670  2.11                                    
           25.6   1298      1676  2.34                                    
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         ______________________________________                                    
                 Load       ho    Subcooling                              
Additive  ppm    W          W/m2K °C.                              
______________________________________                                    
pyridine  0      1041       1266  5.4                                     
          0      1038       1246  4.6                                     
          0      1034       1194  4.2                                     
          0      1034       1188  4.0                                     
          5.1    1059       1233  3.7                                     
          5.1    1082       1232  3.4                                     
          5.1    1052       1199  3.5                                     
          10.3   1086       1241  3.3                                     
          10.3   1070       1215  3.3                                     
          10.3   1077       1216  3.1                                     
          20.2   1264       1536  2.8                                     
          20.2   1246       1500  2.6                                     
          20.2   1266       1506  2.3                                     
          34.8   1437       1806  2.1                                     
          34.8   1437       1796  1.9                                     
          34.8   1449       1805  1.8                                     
          49.5   1521       1942  1.7                                     
          49.5   1510       1934  1.7                                     
          49.5   1509       1926  1.4                                     
          65.5   1631       2271  2.4                                     
          65.5   1629       2252  2.2                                     
          65.5   1624       2226  2.0                                     
          80.3   1719       2367  1.1                                     
          80.3   1714       2355  1.1                                     
          80.3   1715       2362  1.1                                     
          99.8   1786       2542  1.1                                     
          99.8   1781       2532  1.1                                     
(con&#39;t)   99.8   1769       2516  1.1                                     
          124.8  1793       2677  1.3                                     
          124.8  1794       2709  1.2                                     
          124.8  1833       2712  1.3                                     
pyridine  149.8  1739       2426  1.0                                     
          149.8  1737       2352  0.6                                     
          149.8  1729       2365  0.5                                     
          174.8  1726       2353  0.5                                     
          174.8  1737       2340  0.4                                     
          174.8  1739       2358  0.4                                     
          224.7  1740       2429  1.1                                     
          224.7  1733       2393  1.0                                     
          224.7  1719       2400  1.0                                     
          278.3  1740       2456  1.0                                     
          278.3  1749       2458  0.9                                     
          278.3  1755       2450  0.7                                     
          414    1734       2484  1.2                                     
          414    1733       2469  1.1                                     
          414    1718       2437  0.9                                     
          600    1670       2432  1.6                                     
          600    1691       2418  1.3                                     
          600    1682       2388  1.2                                     
          802    1649       2366  1.5                                     
          802    1646       2346  1.4                                     
          802    1648       2334  1.3                                     
          1002   1607       2336  1.9                                     
          1002   1599       2335  2.0                                     
(cont)    1002   1619       2291  1.6                                     
          1498   1637       2525  2.7                                     
          1498   1607       2493  2.6                                     
          1498   1613       2503  2.5                                     
          1995   1548       2436  3.4                                     
          1995   1536       2400  3.2                                     
          1995   1543       2405  3.3                                     
          2496   1379       2037  3.6                                     
pyridine  2496   1385       2016  3.3                                     
          2496   1398       2015  3.2                                     
          2990   1331       1998  4.0                                     
          2990   1325       1946  3.8                                     
          2990   1319       1933  3.8                                     
          3500   1235       1822  4.5                                     
          2500   1266       1852  4.1                                     
          2500   1259       1828  4.1                                     
          4000   1198       1774  4.8                                     
          4000   1204       1739  4.4                                     
          4000   1198       1742  4.5                                     
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         ______________________________________                                    
                  Load     ho    Subcooling                               
Additive   ppm    W        W/m2K °C.                               
______________________________________                                    
quinoline  0      936      1152  5.94                                     
           0      937      1087  4.91                                     
           0      894      1002  4.85                                     
           0      990      1288  5.94                                     
           6.6    1178     1392  3.44                                     
           6.6    1183     1535  4.41                                     
           6.6    1192     1442  3.45                                     
           12.6   1419     1777  2.65                                     
           12.6   1392     1702  2.57                                     
           12.6   1372     1681  2.43                                     
           24.9   1534     2002  2.31                                     
           24.9   1498     1978  1.75                                     
           24.9   1542     1965  2.07                                     
           49.2   1723     2801  3.91                                     
           49.2   1731     2755  3.99                                     
           49.2   1749     2795  3.97                                     
           74.3   1774     2718  2.38                                     
           74.3   1765     2714  2.58                                     
           74.3   1727     2579  2.13                                     
           100.1  1819     2680  1.34                                     
           100.1  1869     2790  1.75                                     
           100.1  1852     2758  1.80                                     
           100.1  1823     2730  1.30                                     
           100.1  1859     2733  1.31                                     
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         ______________________________________                                    
                  Load      ho    Subcooling                              
Additive   ppm    W         W/m2K °C.                              
______________________________________                                    
benzonitrile                                                              
           0      872       1199  6.79                                    
           0      883       1193  6.85                                    
           5      1187      1706  4.58                                    
           5      1197      1648  3.90                                    
           10     1277      1965  4.78                                    
           10     1267      1960  4.70                                    
           20     1354      2429  5.18                                    
           20     1380      2189  4.30                                    
           50     1440      2518  4.30                                    
           50     1459      2394  3.90                                    
           100    1435      2704  5.32                                    
           100    1438      2726  5.45                                    
           200    1284      2758  7.55                                    
           200    1325      2459  6.36                                    
           200    1362      2584  5.51                                    
           200    1418      2552  5.01                                    
           250    1386      2476  5.22                                    
           250    1390      2434  4.98                                    
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     From the test results given in the Table, utilizing representative examples of amines according to the invention, the improvements of the operating condition performance, taken from actual measurements of the laboratory bench test system as well as calculated values for fluid film heat transfer coefficients (h o ) are shown. Additionally, the absorber power load increases are shown as are the significant decreases in solution subcooling at the operating conditions. Calculated values of film heat transfer coefficients (h o ) are also increased.