An Impact of Sorbent-Filler on the Temperature of Thermal Degradation of Composite Sorption-Active Materials Based on Zeolite and Fluorinated Ethylene Derivatives

Abstract

The work continues the research of the physicochemical properties of composite sorption-active material (CSAM) based on polymers of fluorinated ethylene derivatives (fluoroplastics) and various adsorbents-fillers and is aimed at identifying patterns of influence of the adsorbent-filler amount in CSAM on the temperature of their thermal degradation in order to find optimal parameters of thermal regeneration. Based on studies using thermogravimetric and differential thermal analysis methods, a relationship was established between the temperature of thermal degradation of composite sorption-active materials based on polymers of fluorinated ethylene derivatives and the content of zeolite NaX therein. In the course of the experiments, it was found that at a temperature of 112.7 ± 1.5°C, the process of water vapor desorption from CSAM begins passing through a maximum at 172.8 ± 1.2°C and ending at 305.8 ± 1.9°C. The decrease in the weight of the studied CSAM samples was 26.0 ± 0.2%, which confirms almost complete desorption of water vapor from the samples under the experimental conditions. This conclusion may be proved by the gas chromatography analysis of the substances released in the temperature range of 90–310°C. Only water molecules and a small amount of acetone, which was used as a solvent at the synthesis stage, were recorded in the sample. The presence of only one endothermic effect on the DTA curves in the temperature range from 105 to 320°C indicates that during the desorption, energy is used up only on one stage—the separation of sorbate molecules from the sorbent surface. This hypothesis is validated by the fact that the DTG curves of water vapor desorption from CSAM and the NaX crystallite (acting as an adsorbent-filler) are almost identical. The fact that there is no influence of the matrix and sorbate diffusion in the secondary porous structure of the CSAM on the value of the activation energy of the desorption process, also confirms this hypothesis. It has been experimentally shown that thermal degradation of the polymer matrix begins in the temperature range of 390...450°C depending on the sample composition. An increase in the thermal stability of the fluoropolymer matrix of F-42V grade by 45–90°C with the introduction of more than 6 wt % of zeolite NaX was established. It was shown that thermal desorption at temperatures up to 390°C occurs without degradation of the material. This conclusion was validated experimentally through carrying out of 25 sorption–desorption cycles of water vapor by the studied materials and a comparison of these parameters with similar indicators of pelletized zeolite NaX-B-1G produced on a large scale, recorded under similar conditions. The geometry of sorbent samples was the same. Sorption was carried out under batch conditions at a relative humidity of ω = 44% and a temperature of (20 ± 2)°C for 120 min. Desorption of water vapor from the samples was conducted at a temperature of 340.8 ± 1.5°C for 4 h. After each sorption–desorption stage, the change in the sample weight was detected. The study of water vapor mass transfer processes in 25 successive sorption–desorption cycles confirmed the possibility of complete thermal regeneration of the obtained CSAM. The findings made it possible to recommend optimal technological parameters for the regeneration of CSAM with minimal resource costs.