Competitive adsorption and selectivity of water vapor/R134a on activated carbon for indoor air purification

Abstract

As an efficient tracer gas of activated carbon filter quality testing, the use of R134a is limited by relative humidity (RH) due to water vapor competitive adsorption. To analyze the competitive effect, the isosteric heats between vapor and ASZMT were calculated by C–C equation, the adsorption selectivity was predicted using the DIH method, and the binary adsorption equilibrium of water vapor and R134a on ASZMT were investigated via IAST model. Results showed that water vapor exhibited a higher isosteric heat than R134a at the same adsorption capacity, indicating a stronger interaction with ASZMT. The water vapor/R134a adsorption selectivity on ASZMT increases from 0 to 6.6, proving that the ASZMT is more selective for water vapor than R134a with water vapor pressure increasing. Besides, with water vapor pressure ratio improving, the R134a adsorption capacity on ASZMT decreases obviously, but water vapor adsorption capacity keeps increasing continuously. R134a breakthrough curves (1000 ppm) also showed that with relative humidity increasing, the R134a breakthrough times and dynamic adsorption capacities both became shorter, from 15 min to 9 min and from 6.68 mg/g to 1.49 mg/g, respectively. It proves that R134a and water vapor have obvious competitive adsorption behavior which is mainly dominated by water vapor concentration. It is necessary for ppm-level R134a to control the lower relative humidity of airflow in application.