Abstract
An in-line device for measuring the water content in ethanol was developed using a polyvinyl alcohol (PVA)-coated quartz crystal microbalance. Bio-ethanol is widely used as the replacement of gasoline, and its water content is a key component of its specifications. When the PVA-coated quartz crystal microbalance is contacted with ethanol containing a small amount of water, the water is absorbed into the PVA increasing the load on the microbalance surface to cause a frequency drop. The determination performance of the PVA-coated microbalance is examined by measuring the frequency decreases in ethanol containing 2% to 10% water while the ethanol flows through the measurement device. The measurements indicates that the higher water content is the more the frequency reduction is, though some deviation in the measurements is observed. This indicates that the frequency measurement of an unknown concentration of water in ethanol can be used to determine the water content in ethanol. The PVA coating is examined by microscopy and FTIR (Fourier transform infrared) spectroscopy.
Highlights
The prospective use of ethanol for automobile applications is expected to increase steadily, because as a fuel it is relatively clean and sustainable
In the concentration process the in-line measurement of the water content in ethanol is necessary for the process control, and a simple in-line measurement technique is preferred to help the practical operation of the concentration process
Though many instruments have been developed to measure the water content, the in-line measurement is more convenient to apply to the ethanol concentration process
Summary
The prospective use of ethanol for automobile applications is expected to increase steadily, because as a fuel it is relatively clean and sustainable. Various sensor technologies have been applied to determine water content in ethanol for in-line applications. The dielectric permittivity of the sample was measured from the variation of amplitude, which can be used to determine the ethanol and water composition These techniques utilize large instruments and require sophisticated peripheral accessories. Though many polymer film-coated sensors [20,21,22] have been applied to various applications with improved stability of the coated material and selectivity of the detected material, no application to the measurement of water content in ethanol has been reported. A measurement device for water contents in ethanol is developed by applying a PVA thin film on the electrode surface of the QCM. 2% to 10% water contents are utilized to determine the frequency drop of the polymer film-coated QCM. The characteristics of the film are investigated by microscopic observation and FTIR analysis
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