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Article pubs.acs.org/IECR

Research on Compatibility between Ethyl Fluoride with/without Lubricant Oils, and Plastics and Elastomers Xiaohong Han, Xiaorong Yuan, Zhezhen Xu, Xuehui Wang, Guangming Chen, and Xiangguo Xu* Institute of Refrigeration and Cryogenics, State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, People’s Republic of China ABSTRACT: According to the method of alternative materials compatibility study accepted by an international institute, an experimental device to study the compatibility between refrigerant and materials was designed and constructed. The compatibility between ethyl fluoride (HFC-161, C2H5F, CAS No. 353-36-6) with/without the presence of lubricant oils (polyolester (POE) and polyalkylene glycol (PAG)) and five types of plastics (acrylonitrile butadiene styrene (ABS) plastic, polytetrafluoroethylene (PTFE), polypropylene (PP), polyvinyl chloride (PVC), and nylon) and three types of elastomers (natural rubber, silicone rubber, and neoprene) was evaluated in the high-pressure glass tank at 60 °C, respectively. The experimental results indicated that PTFE, PP, PVC, and nylon, as well as silicone rubber and natural rubber, could be used in the refrigeration systems of HFC-161, while ABS and neoprene were not recommended. The absorption of POE oil by the three types of elastomers was stronger than that of PAG oil. Furthermore, results showed that the presence of the lubricant oils could reduce the corrosive effect of HFC-161 to ABS to some extent.

1. INTRODUCTION In recent years, with the more profound understanding of ozone depletion and the greenhouse effect, the search for the environmentally friendly alternative refrigerants is becoming one of the research focuses in the refrigeration and airconditioning industry. One particular hydrofluorocarbon (HFC)ethyl fluoride (HFC-161, C2H5F, CAS No. 353-366)has been paid wide attention, because of its good environmental performance, no ozone depletion potential (ODP= 0), and low global-warming potential (GWP = 12).1 To promote its actual application process in the airconditioning and refrigeration field, much research on the characteristics of HFC-161 and its mixture has been conducted, such as PVT, density, vapor−liquid equilibrium (VLE), and the boiling heat transfer characteristics.2−6 However, it is wellknown that the understanding on compatibility between refrigerant HFC-161 and materials is still one of key technologies to be achieved. This is because the materials, such as plastics, elastomers, and others, would be closely touched with the refrigerant and lubricant oils when they were used in the actual refrigeration systems; thus, the compatibility between refrigerant and materials will have an essential effect on the long-term reliability of the air-conditioning and refrigeration systems using HFC-161. The compatibility research between refrigerant and material is usually based on the two standards: the American ASHRAE Standard ANSI/ASHRAE 97-1999 (RA2003)7 and the Underwriters Laboratories (UL) Standard UL-984.8 According to these two standards, Shi et al. established a new experimental device named the high-pressure sealed-tube method.9 This method utilized glass tubes to isolate the materials in the autoclave. The experimental process remained the same as that decribed earlier by Underwriters Laboratories (UL) Standard UL-984. The compatibility measurement method used by the Shanghai Hitachi Group was similar to the American ASHRAE Standard ANSI/ASHRAE 97-1999 (RA2003).10 They applied © 2014 American Chemical Society

industrial alcohol and dry ice instead of liquid nitrogen to provide the cooling bath in the perfusion apparatus. In addition, the compatibility between refrigerant with/without the presence of lubricant oils and plastics (ABS (acrylonitrile butadiene styrene plastic), PTFE (polytetrafluoroethylene), PP (polypropylene), PVC (polyvinyl chloride), nylon) and elastomers (natural rubber, silicone rubber and neoprene) were widely studied by the A-GAS, Dupont and some other scientific research institutions.11,12 However, the compatibility between refrigerant HFC-161 with or without the presence of lubricant oils and the materials mentioned above has not been openly published. Therefore, the goal of this work is to develop an experimental device to evaluate the compatibility between HFC-161 with or without the presence of the two lubricant oils (Polyolester (POE) and Polyalkylene Glycol (PAG)) and these five types of plastics (ABS, PTFE, PP, PVC, nylon)/three types of elastomers (natural rubber, silicone rubber and neoprene). Experimental results of current research are expected to benefit the design of refrigeration and air conditioning systems using HFC-161 and propel the actual application process of HFC161.

2. MATERIAL AND METHODS 2.1. Sample Preparation. All plastics and elastomers were processed into cubes with different dimensions (shown in Figure 1; these are also described later in this paper in Tables 5, 8, and 11). HFC-161 used in the tests had a mass fraction purity larger than 99.97% and was used without any further purification. The types of POE oil and PAG oil were SUNICE T-68 and Cognis Breox RFL100-x, respectively. The typical properties of lubricant oils are shown in Table 1. Received: October 25, 2013 Accepted: September 1, 2014 Published: September 1, 2014 14650

dx.doi.org/10.1021/ie502264w | Ind. Eng. Chem. Res. 2014, 53, 14650−14658

Industrial & Engineering Chemistry Research

Article

The temperature was measured and maintained by the thermostatic chamber (HASUC, Model DHG-9030A). The pressures were measured by the pressure sensor (GE Druck, Model PTX7517), and the pressure data were logged using a data collection instrument (Agilent, Model 34970A). All of the standard pressure uncertainties were within 13 kPa. The dimensions of the materials were measured by a vernier caliper (Hautine, Model MT1056A). The mass of the materials was weighed by the electronic balance (Mettler-Toledo, Model AL104). The mass of the refrigerant and lubricant oil were weighed by the electronic balance (Setra, Model BL-5000S). The liquid phase and gas phase of refrigerant were carefully sampled with a micro injector and analyzed using a gas chromatograph (KEXIAO, Model GC 1690) with Ø 4 mm × 6000 mm column (Model GDX-104), respectively. The temperature of thermal conductivity detector (TCD) was kept at 383.15 K. The temperatures of the column and the injection port of the gas chromatograph were all maintained at 358.15 K. The bridge current of the TCD device was 100 mA. The precolumn pressure of carrier gas hydrogen was maintained at 0.3 MPa. The accuracy and necessary information on the measuring instruments are shown in Table 3. 2.3. Experimental Procedure. The experimental procedures were as follows: (a) the tested materials (plastic or elastomer) were processed into suitable dimensions, their mass and dimensions were measured; (b) the testing tubes were purged with the acetone and deionized water repeatedly, and then the testing tubes were placed in the thermostatic chamber at 125 °C for 24 h to remove the moisture; (c) the plastics, the elastomers, or the desired amount of lubricant oils were first placed in the testing tubes, respectively; and then the testing tubes were sealed and placed on the casing bracket, which was placed into the thermostatic chamber; (d) the testing system then was evacuated to ensure that there were no impurities in the system; (e) the desired amount of refrigerant was then charged into the testing tubes (shown in Figure 6), and then the temperature of the thermostatic chamber was set to 60 °C; (f) the exposure experiment was conducted for 14 days, and the color changes of the liquid refrigerant and mixture (refrigerant + lubricant oil) and the variations of the material characteristics were observed regularly during the experiment; (g) 14 days later, a gas chromatographic analysis was carried out to analyze whether the components of refrigerant had changed; (h) the stainless steel casing was opened and the materials were removed with a tweezer; (i) the mass and dimensions of the materials were measured, and the changes in appearance and brittleness (or elasticity) of the materials were observed at atmospheric pressure (the oil attached on the surface of the material was removed by the absorbent paper gently before measuring the materials’ mass and dimensions).

Figure 1. Tested materials.

2.2. Experimental Apparatus. The schematic layout of the experimental system is shown in Figure 2, and a photograph of the experimental device is given in Figure 3. The experimental apparatus mainly consists of the stainless steel casing (in which the testing tube was inserted; the inner volume of the testing tube is 15 mL), a pressure sensor, a thermostatic chamber, a casing rack, pipes, and valves. During the experiment, the tested samples (HFC-161 and materials, HFC-161 + lubricant oil and materials) were put in the testing tube (the detailed procedures are given later, in section 2.3). The stainless steel casing holding the testing tube was placed in the thermostatic chamber to keep its temperature constant. To ensure both the ability of bearing a high pressure and the visualization of the testing tube, the stainless steel casing had an opening of 8 mm × 200 mm, through which the color change of the liquid refrigerant or mixture (refrigerant + lubricant oil) and the tested material surface in the testing tube can be observed. The testing tube was carefully designed and manufactured. Dimensions of the testing tube provided by the manufacturer are given in Table 2. Details of the stainless steel casing, the testing tube, and their combination method are given in Figures 4 and 5. The testing tube was made of quartz glass with a flange on the top. The flange is placed at the top of the casing for the convenience of sealing. The stainless steel casing was applied to seal the testing tube. The top of the stainless steel casing acted as a nut (internal thread). The stud is external thread with a through-hole (diameter of d = 3.5 mm) in the middle, which is welded to a stainless steel pipe (d = 3 mm). The other pipes were connected to the stainless steel pipe. The testing tube was sealed in the stainless steel casing through the screwed connection of the stud and the nut. Table 1. Typical Properties of the Lubricant Oil POE/PAG property density kinematic viscosity (@ 313.15 K) kinematic viscosity (@ 373.15 K) pour point flash point total acid number

test method ASTM ASTM ASTM ASTM ASTM ASTM

D1250 D445 D445 D97 D92 D974

POE (SUNICE T-68)

PAG (RFL100-X)

0.960 g cm−3 (@288.15 K) 66.6 mm2 s−1 8.22 mm2 s−1 233.15 K 527.15 K 0.01 mg KOH g−1

0.999 g cm−3 (@293.15 K) 107.3 mm2 s−1 20 mm2 s−1 230.15 K >473.15 K (