Quality Control of Activated Carbon by the Nuclear Magnetic Resonance Method

The production of activated carbon by pyrogenetic decomposition is a complex high-temperature process that involves several stages. The quality of the produced activated carbon primarily depends on the moisture content of raw material and the degree of removal of impurities from the solid carbon residue, operational assessment of which is rather difficult due to the production specifics. The use of NMR relaxometry methods can significantly speed up the process of measuring these parameters in at-line, on-line and in situ conditions. The research aims at determining the absolute moisture content of the raw material, intermediate and finished products, as well as controlling their pyrolysis degree at different stages of activated carbon production via proton density. Samples of the lignocellulosic group (from wet raw material to the finished product) were the research objects. NMR experiments with the Magic Sandwich Echo (MSE) pulse sequence were carried out for measuring the moisture content and proton density of the samples. The study revealed an unambiguous correlation between the values of proton density and the pyrolysis degree of the samples. The experimental results can be used in further improvement of the proposed methods for estimating the specified parameters. It was found that the MSE experiment makes it possible to determine quite accurately the moisture content in both the initial plant raw material and the carbonization products, including activated carbon. The paper presents data on the dynamics of changes in the proton density of samples of plant raw materials during thermal decomposition. A direct correlation was found between changes in the proton density of the samples and their specific density during thermal processing. The proton density of the raw material samples has different values, while the proton density of the carbon samples varies much less. This observation shows that chemicals are being removed from the samples, causing the proton density to decrease. The research results will improve the systems of intermediate and final control in the process of obtaining activated carbon by thermal processing.