Real-time monitoring of a high pressure reactor using a gas density sensor

We investigate a gas density sensor based on quartz crystal resonators for high pressure (2.5 × 106 Pa) and high temperature (340 K) application. The suitability of tuning fork resonators for density measurement in pure gases has been demonstrated. Furthermore, thickness shear-mode resonators are commonly used for viscosity and density measurement in liquids. In our contribution, these devices are compared with respect to their sensitivity to gas density for the target application in a polymerization reactor, involving high ambient pressures. It was confirmed, that tuning fork resonators are mainly sensitive to density, whereas shear-mode resonators are more suitable for viscosity measurement. Moreover, a density sensor for density measurements in unknown gases and gas mixtures, based on two tuning forks, is presented. At high pressures, an additional pressure-dependent frequency shift has to be considered.