An in-situ conductometric apparatus for physicochemical characterization of solutions and in-line monitoring of separation processes at elevated temperatures and pressures

Abstract

Specific conductance and frequency-dependent resistance (impedance) data are widely utilized for understanding the physicochemical characteristics of aqueous and non-aqueous fluids and for evaluating the performance of chemical processes. However, the implementation of such an in-situ probe in high-temperature and high-pressure environments is not trivial. This work provides a description of both the hardware and software associated with implementing a parallel-type in-situ electrochemical sensor. The sensor can be used for in-line monitoring of thermal desalination processes and for impedance measurements in fluids at high temperature and pressure. A comparison between the experimental measurements on the specific conductance in aqueous sodium chloride solutions and the conductance model demonstrate that the methodology yields reasonable agreement with both the model and literature data. A combination of hardware components, a softwarebased correction for experimental artifacts, and computational fluid dynamics (CFD) calculations used in this work provide a sound basis for implementing such in-situ electrochemical sensors to measure frequency-dependent resistance spectra.

Electrical Conductivities and Association Constants in Dilute Aqueous NdCl3Solutions from 298 to 523 K along an Isobar of 25 MPa

“…The cell constant was calculated as 2.985 ± 0.050 m –1 at room temperature using the specific conductivity data provided by Spedding and did not show a noticeable degradation. This cell constant value agrees well with the result obtained in our earlier work . In the earlier work, we used NaCl­(aq) as a calibration liquid, and the cell constant was obtained as 2.959 ± 0.050 m –1 .…”

“…Figure shows the schematic of the continuous flow unit. The instrument details can be found elsewhere . Here, only a brief description of the measurement protocol is given.…”

“…We followed the specific conductivity estimation protocol suggested in our earlier work for sodium chloride solutions . Before every measurement, the cell was flushed with distilled water at elevated temperatures and pressure.…”

“…According to the algorithm, the averaged impedance spectrum is given as where Z O , Z S , and Z MUT are Open , Short , and MUT impedances. By fitting an equivalent circuit model, the bulk resistance in a solution ( R MUT ) was estimated (see Figure d and our earlier work for the detailed description). The bulk solution resistance was converted to the specific conductivity (κ) as where l / A is the cell constant.…”

“…A continuous flow cell equipped with an in situ conductometric sensor was utilized to obtain their equivalent conductivities at 25 MPa. The conductivity data were analyzed based on the Metropolis-Hastings algorithm together with the mean spherical approximation (MSA) and chemical speciation analyses proposed in our earlier works. − …”