Structural transformations in polyacrylonitrile during modification and fabrication of fibres and films with catalytic properties

Abstract

It was found that creation of structured cells for metal particles can be regulated by varying the modification parameters and optimum functioning of catalytic systems can be ensured with them. Mechanisms of formation and the possible structure of variable-ligand Fe 3+ -containing complexes localized on the surface of the fibre support were investigated.A number of problems arise in creating fibrous catalysts with high activity, and the quality and area of the catalyst are dependent on solving these problems. They primarily concern the catalytic activity of the metal and the strength of its attachment to the fibre, the mechanical strength of the fibre itself, and the stability of the catalyst formed.All of these problems are related to selection of the conditions of modification of the initial polymer used as the fibrous support and the technology of attaching the metal to it. Copolymeric polyacrylonitrile (PAN) fibre is the almost irreplaceable initial material for fibrous catalysts [1][2][3][4][5]. This polymer, due to the presence of reactive nitrile groups, allows deliberate structural modification in the course of polymer-analog transformations [3] and thus makes it possible to obtain a polydentate ligand which can be used to coordinate the metal atom during subsequent transformations.Iron-containing fibrous catalysts are relatively universal [1,5,6]. The main process questions in formation of active sites of trivalent iron ions on PAN fibre have been solved. However, more detailed studies are required on formation of functional group complexing agents, realized by treating the initial fibre with an aqueous solution of a mixture of hydroxylamine hydrochloride and hydrazine hydrochloride followed by treatment in aqueous solutions of NaOH and FeCl 3 ⋅6H 2 O.The purpose of our studies was to search for parameters for creating a Fe 3+ -containing catalyst which would ensure the optimum (from a practical point of view) activity and stability of the catalyst while preserving acceptable strength of the PAN fibre.We conducted the studies of the structural transformations of polyacrylonitrile during modification on industrially manufactured PAN complex fibre made with the thiocyanate method from the ternary copolymer of acrylonitrile (92.3%), methyl acrylate (6.2%), and itaconic acid (1.5%) and modeled on PAN films.The ratio of the concentrations of hydrazine and hydroxylamine hydrochlorides (0.5-1), modifying solution pH (2-10), holding time (0.25-2 h), and treatment temperature (100-150°C) were varied in preliminary studies. The treatment temperature in the aqueous solution of NaOH was 95-100°C and the duration was 30-120 sec.We note that by varying the conditions of modification, these groups -ligands -can be contained in the constructed polymer support with different statistical weight. The strength of attachment of Fe 3+ and the stability of the catalyst are essentially a function of their ratio [5]. The optimum parameters for modification of PAN fibre that most completely satisfy the above requirements were sel...

Investigation on the Low-Temperature Transformations of Poly(furfuryl alcohol) Deposited on MCM-41

“…This aldehyde can be easily transformed into furfuryl alcohol (FA), this being a monomer for the synthesis of poly(furfuryl alcohol) (PFA). PFA was found to be a useful polymer for the fabrication of high quality, reproducible, and stable carbon-based, microporous adsorbents by pyrolysis and optionally subsequent modification. − Polyacrylonitrile (PAN), a high-melting and spinnable duroplast, is another extensively studied raw material for the production of carbon fibers, filaments, and films. ,,− …”

A study of the kinetics of phenol oxidation on a fibrous catalyst

“…First, the material was treated with an aqueous solution of hydrazine and hydroxylamine salts. As a result, nitrogen-and oxygen-containing groups of acid and basic nature, capable of fi rmly binding iron ions, were introduced into PAN [2]. Due to chemical cross-links by hydrazine, the fi ber becomes highly chemically stable.…”