Annotation of the results obtained in 2023
In accordance with the project plan for 2023, the influence of the type of functional groups of the ion-exchange material and the nature of its matrix on organic fouling by aromatic amino acids with different structure of the side radical - tyrosine, phenylalanine, tryptophan has been revealed. The list of ion exchange materials have been studied: heterogeneous medium-basic and highly basic anion-exchange membranes, homogeneous highly basic anion-exchange membranes. A comparison was made of the effect of aromatic amino acids on heterogeneous as well as homogeneous cation exchange membranes with functional sulfo groups. Alterations in the characteristics of the bipolar membrane upon contact with the studied amino acids were considered. The influence of the type of functional groups and the shape of the ion-exchange material on its ability to extract aromatic compounds from aqueous solutions has been shown by comparing the capacity characteristics of sorbents in different forms (granules, fibers) and with different basicity (high and low basic) relative to a number of hydroxybenzaldehydes and hydroxybenzenes. The equilibrium parameters of sorption of hydroxybenzaldehydes and hydroxybenzenes with different positions of substituents (4-hydroxybenzaldehyde, 4-hydroxy-3-methoxybenzaldehyde (vanillin), 4-hydroxy-3-ethoxybenzaldehyde (ethylvanillin), 4-hydroxy-3,5-dimethoxybenzaldehyde (syringaldehyde), hydroxybenzene (phenol), 1,3-dihydroxybenzene, 1,3,5-trihydroxybenzene) by fibrous and granular ion-exchange materials were determined based on the formal analysis of sorption isotherms. The values of distribution coefficients were estimated. Data were obtained on the influence of competing inorganic anions on the capacity of high- and low-basic anion exchangers for substituted aromatic aldehydes under static conditions when studying the systems anion exchanger - hydroxybenzaldehyde - mineral salt and anion exchanger - hydroxybenzene - mineral salt. In the process of aromatic amino acids separation from mineral salts and carbohydrates using electrodialysis and in the process of amino acid solution electrodeionization, the evolution of transport and current-voltage characteristics of monopolar heterogeneous and homogeneous membranes, a heterogeneous bipolar membrane with different functional groups and/or structure of the polymer matrix was studied. Alterations in the state of the surface of ion exchange membranes with various functional groups and different polymer matrix have been found, expressed in an increase in the roughness and hydrophobicity of the surface of the materials with the development of organic fouling by aromatic amino acids with different structures of the side radical. High-frequency spectra of the electrochemical impedance of ion-exchange membranes were recorded, a comparative analysis of the electrical conductivity of studied ion-exchange membranes was carried out for the samples after uptake of mineral salt ions, amino acids (Tyr, Phe, Trp), for the samples after their long-term contact with a solution of aromatic amino acids with different side radicals, as well as for the form obtained after sorption of the amino acid and mineral salt ions from their mixed solution. Using the isopiesting method, a change in the hydration of the anion-exchange material before and after sorption of vanillin, ethylvanillin and isovanillin was found. A decrease of weakly bound water content in sorbent phase was confirmed. The mechanisms of organic fouling of ion-exchange materials in solutions of the studied aromatic compounds have been elucidated. An assessment was made of the possible interactions of the functional groups of anion-exchangers with the functional groups of sorbates, the sorbent matrix with aromatic fragments of the compounds under study, as well as the catalytic oxidation reactions involving tyrosine and tryptophan with the identification of their products by spectral methods. Chemical and electrochemical procedures have been developed and tested to reduce fouling and regenerate ion-exchange materials with various functional groups and polymer matrix, allowing to maintain or restore their structural, capacitive and transport characteristics.

 

Publications

---

Annotation of the results obtained in 2022
The organic fouling phenomenon and its influence on physical-chemical properties of ion-exchange materials were studied in accordance with the project plan. The alterations of essential properties for ion-exchange membranes, fiber and granular ion-exchange sorbents being in contact with solutions of aromatic amino acids, hydroxybenzaldehydes and phenols have been revealed. Based on the equilibrium and kinetics characteristics studies as well as on the breakthrough curves for the considered compounds uptake it is shown that the ion-exchange technologies are effective in the extraction of them from the liquid media despite they can be not in ionized state in the treated solutions. In the course of studied substances sorption along with the mechanism based on their ionization in the alkaline medium of hydroxyl form of an anion-exchanger phase with subsequent uptake according to the ion-exchange mechanism one can find some other sorption mechanisms: physical adsorption, stacking-effect, chemisorption (for weak basic anion-exchange resins with primary and secondary amino groups) which can lead to the evolution of organic fouling phenomenon. It was established by the IR-spectroscopy that the chemical transformations of studied sorbates are possible in prolonged contact of solutions with anion-exchangers which lead to some side products formation. Fiber materials of various basicity are considered as perspective sorbents of hydroxybenzaldehydes. It is shown that the high basic fiber A-1has maximal capacity to hydroxybenzaldehydes. Besides, it is elucidated that the highest rate of uptake is observed for the fiber materials. However it is found that the organic fouling appears for the fibers with quaternary ammonium functional groups after the performance in vanillin solution. The low basic fiber anion-exchange resin can be regenerated up to 100% after the uptake of hydroxybenzaldehydes despite the mechanism of uptake in this case is chemisorption (imines formation). In the course of the project realization it is shown that the organic fouling of ion-exchange materials depends on the nature and size of the side radicals of aromatic amino acids, from the nature and size of the substitutes in the benzene ring of hydroxybenzaldehydes. The higher values of total capacity for high-basic anion-exchangers (Marathon MSA, A-1) are observed for vanillin in comparison with phenol that is due to the higher ability of vanillin to ionization (the difference in pKa values for two sorbates is 2.5). Consequently, the studied physical-chemical properties of the anion-exchange resins after hydroxybenzaldehydes sorption are changed more dramatically. It is necessary to underline the role of sorbate associates formation in the solid phase. The vanillin dimers formation is confirmed by IR-spectroscopy method. It is established that ion-exchange fibers, granules and membranes can be applied in the processes of tryptophane (aromatic amino acid) extraction from liquid media but the significant changes of solid phase properties are found, the surface and volume organic fouling is observed. The alterations of anion-exchange fiber A-1 surface are studied after the sorption of tryptophan by the method of AFM. The IR-spectra confirm the structural changes for the high-basic, as well as for the weak-basic fiber sorbents after tryptophan uptake. The features of aromatic amino acids sorption and mass transfer in electrodialysis are considered to reveal the physical-chemical essence of the ion-exchange membranes organic fouling phenomenon. The alterations in current-voltage characteristics (CVC) of membranes as well as in their structure and surface state are revealed in the prolonged performance for the electrodialysis of solutions containing tyrosine, tryptophane and phenylalanine. The studied systems have been chosen in accordance with the current practical tasks such as desalination of amino acids solutions, separation of amino acids and sugars in the processes of their microbiological synthesis. The quantitative characteristics of separation for the model solutions are calculated. They demonstrate the possibilities and advantages of electrodialysis in solving the mentioned tasks. The possibilities of fouling mitigation is also shown The obtained results indicate the alterations in transport and current-voltage characteristics of ion-exchange membranes in prolonged electrodialysis tests. The experimental results confirm the phenomenon of organic fouling. However for the most part of the considered systems the changes of the membrane properties are reversible. The suggested approach is electrochemical regeneration in the overlimiting range of current density. The components of the treated solution, the products of the organic fouling can be “washed out” the membrane phase by the hydroxyl and hydrogen ions from water splitting reaction. This is some kind of cleaning in place decision. The influence of amino acid side radicals on the electrochemical characteristics of the ion-exchange membranes alterations in electrodialysis is shown.

 

Publications

---