MODIFICATION OF CARBON FIBER WITH Cl-, Br- AND S-CONTAINING FUNCTIONAL GROUPS

UDC 676.03+621.794+544.47

Abstract

Chlorination of carbon fibre Busofit was carried out and active chlorine-containing precursors were obtained, chlorine concentration in the surface layer of the obtained samples is 2.5 mmol/g. By TPDMS method it was found that chlorine desorption occurs in the form of HCl (m/z 38 at 36) at temperatures above 200 °C. The treatment of chlorinated fibres with aqueous solutions of sodium sulfide or sodium mercaptoacetate provides replacement of surface chlorine by S-containing functional groups. Further oxidation of obtained samples by hydrogen peroxide leads to formation of strong acidic SO₃H-groups in the surface layer.  Thermo-desorption properties of the synthesized materials were studied. According to the TPDMS data desorption of sulfogroups occurs in the form of SO₂ (m/z at 64) in the temperature range 60–300 °C. It is shown that the preliminary chlorination allows obtaining samples with higher concentrations of sulfogroups in the fibres surface layer, as compared with the samples synthesized by the direct method. It was found that the concentration of sulfogroups is slightly dependents on the method of sulfonation. It is shown that the fibre samples obtained by the treatment of sodium mercaptoacetate are characterized by a little higher thermal stability as compared to the fiber obtained by treatment with sodium sulfide. Modified materials have sufficiently high thermally stability and can be used in acid-base catalysis. The catalytic activity of CFs samples containing strong acidic groups was investigated in model reaction of gas phase dehydration of isopropanol. It is shown that fibres modified with SO₃H-groups groups have significantly higher catalytic activity compared to initial ones: conversion of isopropanol to propylene is increased from 2–3% to 100%. Temperature of 100% conversion was chosen to compare catalytic activity of CFs with acidic SO₃H-groups. The highest catalytic activity of the modified CFs is observed for samples that are obtained from chlorinated precursors treated with sodium sulfide. The lowest activity is observed for samples modified with S-containing compounds without pre-chlorination. In accordance to their catalytic activity all CFs samples are arranged in sequence that fully correlates with the concentration of surface SO₃H-groups. Preliminary chlorination increases stability of the obtained catalyst when they are used repeatedly. Sulfur-containing catalysts derived from chlorinated fibers have higher stability in catalysis than their analogues derived from the brominated precursors.