Patent Application
20080011159
In accordance with this invention there is provided a process for trapping or separating at least a portion of HFC-23 from its mixture with other materials, such as fluids or gases, particularly iodocarbons so as to reduce the amount of HFC-23 in the mixture. While it is difficult to predict molecular sieve separations, the inventors have shown that iodocarbons, particularly trifluoroiodomethane are such that they can be separated from fluorocarbons such as R-23 by the use of molecular sieves whose diameters are about 5 angstroms. The process may be conducted with any suitable molecular sieve and is suitable for separating HFC-23 from its mixture with any other fluid or gas that has a molecular diameter greater than the molecular diameter of HFC-23.
The process of this invention is particularly suitable for removing HFC-23 from refrigerant compositions, especially refrigerant compositions containing iodocarbons, such as trifluoroiodomethane. The process of the invention is particularly suitable for removing HFC-23 produced in-situ by interaction between the components of a refrigerant composition containing an iodocarbon, such as trifluoroiodomethane, and optionally a lubricant. For the purpose of this invention an “iodocarbon” is any compound containing iodine and carbon atoms and optionally other atoms.
The product containing the HFC-23 as an impurity in a composition with other desirable materials, such as fluid(s) or gas(es), can be brought into contact with the molecular sieve in either the liquid or gas phase, in a process that may be either a continuous or a batch process to adsorb the HFC-23 and thereby separate and remove it from the other desirable fluid(s) or gas(es). The level to which the HFC-23 is reduced is dependent upon the capacity of the molecular sieve and the equilibrium between the HFC-23 and the mixture of gases and in the molecular sieve itself. It is preferred to use as much molecular sieve as necessary to reduce the level of HFC-23 impurity to less than about 500 ppm, preferably to level of less than about 100 ppm, and more preferably to a level of less than about 10 ppm
The process of this invention may employ any suitable molecular sieve including, but not limited to, suitable zeolite and carbon molecular sieves. The suitable molecular sieve must have an acceptable effective pore size such as to adsorb HFC-23 but not adsorb the other favorable and desired fluids or gases. It has been discovered that 4A molecular sieves (having an effective pore size of 4 Å) will not separate HFC-23 from trifluroiodomethane, however 5A series molecular sieves (with an effective pore size of 5 Å) will very effectively achieve such separation of HFC-23 from trifluroiodomethane. Thus, it is believed that HFC-23 has an effective molecular diameter of less than 5 Å and that the effective molecular diameter of trifluoroiodomethane is greater than 5 Å. Thus, given the difference in effective molecular diameters separation of HFC-23 from trifluoroiodomethane can be effected by using molecular sieves whose diameters are less than the effective molecular diameter of trifluoroiodomethane.
In a similar manner, HFC-23 can be adsorbed and separated from a composition containing HFC-23 and another fluid or gas having a greater molecular diameter than the HFC-23. For example, if the other fluid or gas is one having an effective molecular diameter of 10 Å, molecular sieves having an effective pore size of from 5 Å to 9 Å may be employed to effect the adsorption and separation of HFC-23 from the composition. Thus, for any particular separation of HFC-23 from other fluid(s) or gas(es), molecular sieves of an “effective pore size” are those molecular sieves that operate to preferentially reduce the amount of, or remove at least some of, HFC-23. Such molecular sieves having an effective pore size are generally those having an effective pore size of from 5 Å to a pore size less than the effective molecular diameter of the other fluid(s) or gas(es).
Molecular sieves useful in the process of this invention are available from a variety of sources, including but not limited to, zeolite molecular sieves from Universal oil Products, Grace and Aldrich Chemical Co., and carbon molecular sieves from Aldrich Chemical Co., Chemos GmbH of Germany and Dayung Chemical Co., Ltd. of China.
The invention is illustrated by, but limited too, the following examples.
AW500 zeolite molecular sieve (Aldrich chemical Co.) having an effective pore size of 5 Å was placed in an oven at 300° F. (149° C.) for four hours to activate the molecular sieve. This activated molecular sieve was employed in the following Examples 1, 2 and 4. The molecular sieves employed in Example 3 and Comparative Examples 1 and 2 were activated in a similar manner.
2.26 Grams of activated AW500 molecular sieve were placed into a stainless steel cylinder. 2.04 Grams of the refrigerant mixture trifluoroiodomethane/HFO-1234 (tetrafluoropropene) (25/75) were added to the cylinder. The refrigerant mixture contained 11 wt. % HFC-23. After one hour the gas in the cylinder was examined and found to contain only 3.2 wt % HFC-23 because of the adsorption of the HFC-23 by the molecular sieve.
2.26 Grams of activated AW500 molecular sieve were placed into a stainless steel cylinder. 2.04 Grams of the refrigerant mixture trifluoroiodomethane/HFO-1234yf (1,1,1,2-tetrafluoropropene) (25/75) were added to the cylinder. The refrigerant mixture contained 4.1 wt. % HFC-23. After one hour the gas in the cylinder was examined and found to contain only 0.15 wt % HFC-23 because of the adsorption of the HFC-23 by the molecular sieve.
465 Grams of 5A molecular sieve were placed into a stainless steel column. 1344 Grams of the refrigerant mixture of trifluoroiodomethane containing 0.235 wt % HFC-23 was passed through the column containing the molecular sieve. The effluent gas was examined by chromatography and HFC-23 was not detectable.
2.5 Grams of activated AW500 molecular sieve were placed into a stainless steel cylinder. 2.5 Grams of the refrigerant mixture trifluoroiodomethane/HFO-1234 (tetrafluoropropene) (25/75) were added to the cylinder. The refrigerant mixture contained 0.5 wt. % HFC-23. After one hour the gas in the cylinder was examined and found to contain only 0.003 wt % HFC-23 because of the adsorption of the HFC-23 by the molecular sieve.
2.5 Grams of activated 4A molecular sieve (having an effective pore size of 4 Å) were placed into a stainless steel cylinder. 2.5 Grams of the refrigerant mixture trifluoroiodomethane/HFO-1234 (tetrafluoropropene) (25/75) were added to the cylinder. The refrigerant mixture contained 0.5 wt. % HFC-23. After one hour the gas in the cylinder was examined and found to contain only 0.42 wt % HFC-23 showing that the amount of HFC-23 remained essentially unchanged after exposure to the 4A molecular sieve.
2.5 Grams of activated XH7 molecular sieve (having an effective pore size of 4 Å) were placed into a stainless steel cylinder. 2.5 Grams of the refrigerant mixture trifluoroiodomethane/HFO-1234 (tetrafluoropropene) (25/75) were added to the cylinder. The refrigerant mixture contained 0.5 wt. % HFC-23. After one hour the gas in the cylinder was examined and found to contain only 0.45 wt % HFC-23 showing that the amount of HFC-23 remained essentially unchanged after exposure to the 4A molecular sieve
Having described the invention in detail by reference to the preferred embodiments and specific examples thereof, it will be apparent that modifications and variations are possible without departing from the spirit and scope of the disclosure and claims.
