Effects of System Materials toward the Breakdown of Lubricants and Low-GWP Refrigerants

摘要

Process chemicals, including cleaners, degreasers, coolants, sealants, metalworking fluids, brazing fluxes, rust inhibitors, and bearing slushing compounds, may be added directly to air-conditioning or refrigeration systems or may be left as residue after an attempt has been made to remove them from a system component. Some of these chemicals have been shown to cause degradation of refrigerants and/or compressor lubricants, and their compatibility with the refrigerant/lubricant systems needs to be determined to ensure the long-term reliability of air-conditioning and refrigeration equipment. As the heating, ventilation, air-conditioning, and refrigeration (HVAC&R) industry transitions to lower global warming potential (GWP) refrigerants, many research and development programs have been focused on hydrofluorolefins (HFOs), which have been evaluated as alternative refrigerants to hydrochlorofluorocarbons (HCFC) and hydrofluorocarbons (HFC). Previous research on the compatibility of process chemicals with HFC refrigerants and polyolester (POE) lubricants provides a sound knowledge base for the evaluation of HFO/POE systems. This research project was conducted to determine the chemical reactivity of process chemicals in HFO/POE systems and their impact on the performance and reliability of HVAC&R systems, with the following objectives: 1. Determine the effects of the selected process chemicals on the chemical stability of HFO/POE. 2. Compare the chemical reactivity of process chemicals in HFO/POE to that of the same chemicals in R-134a/POE. 3. Identify the process chemicals that would require careful consideration for use in HFO/POE systems due to their high reactivity. The process chemicals selected for testing included: poly-oxyethylene nonyl phenol ether, propylene glycol, benzotri-azole, sodium gluconate, boric acid, ethylene diamine tetraacetic acid (EDTA), iron (III)phosphate dihydrate, potassium hydroxide, sodium molybdate, sodium paratoluene sulfonate, triethanolamine, zinc chloride, potassium fluoride, potassium hydrogen fluoride, trisodium phosphate dodecahy-drate, neutral calcium alkylaryl sulfonate, sodium nitrite, ethanolamine, sulfamic acid, sodium carbonate, neodecanoic acid, chloroparaffin, ferric chloride, hydroxyethyl cellulose, and sodium palmitate. These chemicals are currently in use or being considered for use with the HFO refrigerant systems. They were screened using sealed tube tests according to ANSI/ ASHRAE Standard 97, Sealed Glass Tube Method to Test the Chemical Stability of Materials for Use within Refrigerant System (ASHRAE 2007). The test matrix included 1 low-GWP refrigerant blend of R-32/R-1234yf/R-l234ze at 33.3 weight-percent each, I non-additized ISO 22 POE lubricant, 25 chemical species,2 concentrations for each chemical (0.1 and 1.0 weight-percent based on lubricant weight), one aging temperature [175℃ (347℉)] and 1 aging time (14 days). The results from this study showed that many of the chemicals found in process fluids would react with theR-134a/POE and (HFO Blend)/POE systems. Chemical reactions resulted in changes in a number of properties, such as darker lubricant color, cloudiness, deposit, film formation, darker metal color, dullness, corrosion, increased total acid number (TAN), increased total organic acid (TOA), presence of metals in solution, presence of reaction products (such as fluoride ions in the [HFO blend]/POE system). This study showed that the extent of reaction depends on the chemical and its concentration, while previous studies with R-134a/POE showed that it also depends on the aging temperature and the aging time. However, the decision of whether a chemical is compatible for use in a refrigeration system is highly subjective and depends on the user, the application, and the equipment.