A novel multiple cell photo-sensor instrument: principles and application to the study of THF hydrate formation

A new multiple cell photo-sensor instrument has been constructed to study the kinetic process of crystallization from solution. Tetrahydrofuran (THF) hydrate formation from water/THF solutions was chosen as an example application. The instrument simultaneously monitors the entire hydrate formation process in a group of 12 water/THF samples, by measuring four physical parameters: transmitted light intensity (Pi), the change in the polarizing state of emerging light (B), the half depth diameter of the vortex (D-v) and magnetic bar spinning rate (V-str). The appearance and location of the new THF hydrate phase were identified by analysing the following parameters plotted as a function of time: transmission, vortex and change in the polarizing state of the emerging light. The macroscopic completion of hydrate crystal growth was determined as the time taken for the magnetic bar inside the sample tube to cease movement. These studies show that hydrate crystallization from 27:1 mole ratio solutions of water/THF commence at the vapour-liquid interface and near the internal wall of the glass sample tube. This was in contrast to stoichiometric mole ratio solutions of water/THF in which THF hydrate formation commenced in the bulk liquid phase.