ASHRAE Journal - August 2009 - 23

Their refrigerant numbering scheme is summarized. The flammability and toxicity of these isomers is briefly addressed. Estimated fundamental parameters and thermodynamic properties for eight of these isomers is presented. And, the ideal cycle performances of these eight isomers are estimated for three typical applications. Fluorinated Propene Isomers Refrigerant Numbering First Appended Letter: Refers to the Substitution on the Central Carbon Group Substitution −Cl −F −H Letter x y z Second Appended Letter: Refers to the Substitution on the Terminal Methylene Carbon Group Substitution =CCl2 =CClF =CF2 =CHCl =CHF =CH2 Letter a b c d e f Two recently proposed ANSI/ASHRAE Table 1: Proposed suffix scheme for propene Standard 34, Designation and Safety Classification of Refrigerants, addenda adopt nomenclature also referred to as “trans” isomers and the zusammen isomers rules consistent with those already in use in industry and aca- are also referred to as “cis” isomers. Figure 16 shows the demia for ethene (ethylene, R-1150, CH2=CH2) and propene two stereoisomers for R-1234ye. (propylene, R-1270, CH3CH=CH2,) based refrigerants. In particular, Addendum w5 adds R-1234yf to Tables 1 and D1 Possible Isomers of ANSI/ASHRAE Standard 34, and Addendum z6 addresses The fluorinated propene isomers with bases 1252 and 1261, isomer and stereoisomer (defined in the next subsection) desig- i.e., isomers containing 4 H/2 F and 5 H/1 F, respectively, are nation suffixes as well as composition-designating prefixes. Al- most likely highly flammable and will not be considered further though the proposed Addendum z addresses ethane and propene in this article. Table 2 lists all of the remaining nineteen posbased refrigerants, this article focuses only on propene isomers. sible fluorinated propene isomers with the bases 1225, 1234, Propene isomers contain an unsaturated (carbon-carbon and 1243, i.e., isomers containing 1 H/5 F, 2 H/4 F, and 3 H/3 F, double) bond and can also be referred to as olefins or alkenes. respectively. In addition to these isomers carrying the designation R, the fluorinated isomers also can be identified with the prefixes HFO Toxicity and Flammability (hydrofluoro-olefin), HFA (hydrofluoroalkene), or HFC (hydroAlthough it is difficult to predict without testing the exact fluorocarbon). For example, R-1234yf could also be referred to flammability characteristics of the fluorinated propene isomers, as HFO-1234yf, HFA-1234yf, or HFC-1234yf. one can reasonably conjecture that as the number of hydrogen Table 1 summarizes the numbering scheme for the two ap- atoms in the molecule relative to the total number of hydrogen pended lowercase letters that distinguish the propene isomers, and fluorine atoms increases, the flammability of the molecule where the groups containing chlorine (nonzero ODP) are high- will increase, which would indicate increasing flammability lighted in red, and the groups containing hydrogen and fluorine from the R-1225 isomers to the R-1243 isomers. are highlighted in green. For a propene isomer to possess zero Although testing has shown that R-1234yf is flammable,5 ODP, the first appended letter must be either a ‘y’ or ‘z,’ and the (the proposed ASHRAE Addendum z suggests categorizing second appended letter must be either ‘c,’ ‘e,’ or ‘f.’ it as a Class 2 refrigerant), a significantly larger amount of energy is required to ignite the refrigerant than for other comStereoisomers mon Class 2 refrigerants.7 In recognition of this, the SSPC When a carbon-carbon double bond exists, stereoisomers 34 Flammability Subcommittee recently began studying a (a.k.a. enantiomers), isomers with the same bonding but continuous maintenance proposal to add a 2L Subclass to differing in their geometrical arrangements, may exist. In ANSI/ASHRAE Standard 34-2007, which has already been particular, stereoisomers around carbon-carbon double bonds incorporated into a Committee Draft version of ISO 817.8 specify the arrangements of the substituted atoms or groups The Committee Draft version of ISO 817 assigns refrigerants at either end of the carbon-carbon double bond. Therefore, to Subclass 2L that meet the conditions for Class 2 refrigerfor fluorinated propene isomers, stereoisomers exist if the ants and, in addition, have a burning velocity ≤0.328 ft/s second appended letter is ‘e’ (i.e., =CHF). For example, (≤0.10 m/s) when tested at 73.4°F (23.0°C) and 14.9 psia CHF2CF=CHF (R-1234ye) has two stereoisomers since the (101.3 kPa). hydrogen and fluorine atoms attached to the terminal methyToxicity is much more difficult to estimate via a rule-oflene carbon can be arranged either across the carbon-carbon thumb; however, several of the R-1225 isomers are no longer double bond from each other (designated with an appended being developed because of toxicity concerns.9,10 Toxicity “(E)” for entgegen “opposite”) or on the same side of the testing for the fluorinated propene isomers has been (and is) carbon-carbon double bond (designated with an appended playing an important role in the development efforts being “(Z)” for zusammen “together”). The entgegen isomers are expended on these isomers. isomers.6 August 2009 ASHRAE Journal 23
ASHRAE Journal - August 2009

Table of Contents for the Digital Edition of ASHRAE Journal - August 2009
