Features of the kinetics of lower aliphatic aldehydes sorption by a polyfunctional weakly basic anion exchanger

Abstract

Carbonyl compounds are organic pollutants that negatively affect the environment and human health. The extraction of such compounds from liquid media is an urgent and practically important problem, which can be solved by the sorption method using weakly basic anion exchangers as sorbents. Ion exchange materials with primary, secondary, and tertiary amino groups are capable of absorbing carbonyl compounds due to chemisorption interaction.
The aim of the study was establishment of the features of the sorption of a number of aliphatic aldehydes (methanal, ethanal, propanal) by the weakly basic anion exchanger Purolite A 830 from model aqueous solu-tions under static conditions. Based on obtained data, it was noted that, with a high selectivity of the applied sorbent to the studied sorbtives, the time of achieving equilibrium for methanal was several times lower than for ethanal and propanal (24, 195, and 125 hours, respectively). This phenomenon becomes understandable based on the result of a detailed examination of the chemistry of the studied process. Unlike methanal, etha-nal and propanal are capable of intermolecular interactions in a solution, i.e. aldol condensation. In this case the products of such interactions can be also absorbed by the anion exchanger. It is possible that the occur-rence of side reactions has a significant effect on the rate of the sorption process, increasing the sorbent ca-pacity to aldehyde.
For the interpretation obtained kinetic dependences, a formal approach, consisting in choosing the sorption equations describing the experimental data as accurately as possible was used in this study. The models used for the description of the adsorption processes were selected as models for the kinetics of sorp-tion: the pseudo-first order equation, the pseudo-second order equation, the Weber-Morris equation and the Elovich equation. The linearisation of the experimental data in the coordinates of these equations and com-parison of the reliability coefficients values (R2) allowed choosing a model of the sorption kinetics most closely describing the sorption of the lower aldehydes by Purolite A 830 in time. It was noted that the use of the Elovich equation, which was developed to describe the kinetics of adsorption in heterogeneous systems, is applicable for the description of the change in the concentration of a sorbtive in a solution upon contact with a weakly basic anion exchanger.