Evaporation Regularities of Elemental Selenium in the Vacuum Distillation Process

Abstract

Vacuum distillation technology has been identified as an efficient method for purifying selenium. In this work, the evaporation regularities of elemental selenium in the vacuum distillation process were investigated based on experimental evaporation rates reported for temperatures and pressures of 523–723 K and 2–1500 Pa. The experimental results indicated that the logarithm of the selenium evaporation rate was linearly related to the reciprocal of temperature and described by the dependent linear equation lgω=AT+B. The evaporation rate of elemental selenium at ambient pressure conformed to the logistic model ω=A1-A21+(p/p0)m+A2. Additionally, the critical pressure, maximum evaporation rate, evaporation coefficient, and kinetic parameters for selenium evaporation were determined. The actual maximum evaporation rate of elemental selenium showed a linear correlation with the reciprocal of temperature, as expressed by ωmax,actual=-3152.38T+2.5. The evaporation coefficient α varied between 0.003 and 0.1 with temperature due to the complex molecular structure of Se in the gas phase. A kinetic analysis showed that evaporation of elemental Se was controlled by diffusion through the vapor boundary layer. The present study provides basic evaporation parameters, describes the behavior of elemental selenium under vacuum, and offers theoretical guidance for vacuum distillation refining of selenium.