The quantitative aspects of the photoacoustic(PA) technique for powder system of HZSM-5 zeolite, which presents difficulties in conventional spectroscopic techniques, was investigated.
HZSM-5 zeolite was impregnated with Cr(III), and it was diluted with HZSM-5 zeolite and Magnesium oxide as diluent. For three kinds of samples, PA signals were measured. It was found that the PA signals were strongly dependent on diluent itself. In case of HZSM-5 zeolite, the PA signals showed a deviation from linearity in low range of Cr(III) content. In case of MgO, however, a linear relationship was found between Cr(III) content and PA signal through a full range which PA signals were measured.
Determination of the coke content deposited over HZSM-5 zeolite from MTG processes was performed using conventional thermogravimetric method and PA method, wherein standard for calibration was activated carbon. Comparison of the results from two methods showed a good agreement. This was explained by the coke deposition mechanism corresponding to the characteristic pore structure of ZSM-5 zeolite. It was also pointed out that the characteristics of PA cell could be useful to relieve the signal saturation. In our PA cell, a resonance which could be explained by Helmoltz model occurred at the chopping frequency of approx. 750Hz.
