Modeling vapor-liquid equilibrium data for systems containing hydrogen fluoride

Hydrogen fluoride (HF) is an important chemical used as a fluorinating agent in the production of refrigerants. Process design requires accurate vapor-liquid equilibrium (VLE) data for these systems. Hydrogen fluoride vapor exhibits very nonideal behavior due to the formation of hydrogen-bonded oligomers. Correlation of VLE data is complicated by the HIF association in both the vapor and liquid phases. Models are needed that can accurately account for the nonideal behavior of BF and mixtures containing HF. Accurate calculation of HF vapor nonidealities requires that HF association be accounted for in the model representing the vapor phase.; To develop an improved vapor model for HF/Refrigerant mixtures, available HF association models have been analyzed and an improved vapor chemical association model for pure HF has been developed based on literature PVT (pressure-volume-temperature) data ranging from 20°C to 200°C. The vapor model was tested using HF/refrigerant vapor mixture PVT data measured as part of this project. These vaporphase PVT measurements consisted of a total of 62 data points for binary mixtures of HF with HCFC-22 (chlorodifluoromethane), HFC-32 (difluoromethane) and HIFC-134a (1,1,1,2-tetrafluoroethane) at temperatures ranging from 10°C to 70°C. Pressures ranged from 100 to 1400 kPa, and HF concentrations varied from about 0.2 to 0.9 mole fraction BE The vapor model reproduced the experimental compressibility factors with an average absolute deviation of 0.8 percent.; As an application of the vapor association model, PTx. (pressure-temperature liquid composition) data for several binary systems containing HF have been correlated to obtain vapor compositions. The PTx method has been a widely used method of obtaining vapor-liquid equilibrium data. This method simplifies and expedites the experimental work required to obtain VLE compositions, but also relies on vapor and liquid models for accuracy. As a test of the HF vapor association model and to evaluate several liquid activity coefficient equations, literature PTx data were reduced to y-x data with the vapor model using four different activity coefficient models. For comparison with the values calculated from the PTx. data, a few PTxy measurements were performed in the low BF/azeotropic: region for each of the PTx data sets. The vapor association model coupled with the best activity coefficient model reproduced the experimental vapor compositions with an average deviation of 0.005 mole fraction.