The growth behavior and growth rates of naphthalene single crystals in supercritical carbon dioxide were observed and measured at temperatures 307.7, 312.7, and 317.7 K and pressures 15, 17.5, and 20 MPa to highlight the behavior of crystal growth in the supercritical phase. The morphology of naphthalene crystals did not change during the steady growth in the supercritical phase. The crystal growth rates from the supercritical phase were almost independent of pressure and higher with increasing temperature or supersaturation and were approximately between 4 × 10-9 and 2.5 × 10-8 m s-1 as supersaturation varied from 0.018 to 0.073, values which were found to be intermediate between those from a liquid or vapor phase at the same supersaturation. The activation energy for crystal growth from the supercritical phase was determined as 70.9 kJ mol-1, which showed that the crystal growth mechanism in the supercritical phase is almost similar to that in the liquid or vapor phase and that the growth rates were governed by the surface integration step.

This paper describes a liquid-liquid biphasic flow reaction system that is simple to control. In a liquid-liquid biphasic flow reaction, the slug-flow in the tube reactors generally improves the reaction rate. However, we show that larger tube diameters decreased the reaction rate and the formation of the slug-flow was influenced by the tube diameter, the size of the mixer, and the pump mechanism. These results indicated that technical difficulties with the slug-flow could be an obstacle to scale-up. To resolve this problem, we suggest the use of a Taylor vortex flow reactor to achieve a higher reaction rate than with batch and slugflow systems.

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Colorimetric analysis with diphenylcarbazide has been used as a simple method to determine hexavalent chromium (Cr(VI)). However, the low sensitivity of this technique makes it difficult to determine concentrations close to the environmental standard value (0.05 mg/L). We found that the phase separation phenomenon produced a small amount of the extraction phase when a mixture of 2-propanol and a small amount of dimethyl phthalate were added to a water sample, and that the Cr(VI)-diphenylcarbazide complex was extracted into this phase with high efficiency. Based on these findings, we report a simple method for colorimetric analysis for determining Cr(VI) with high sensitivity via homogeneous liquid-liquid extraction using water, 2-propanol, and dimethyl phthalate. As a result, the extraction percentage for Cr(VI) was 88% and the concentration factor improved up to 121-fold (27.4 mL → 226 µL). Using the proposed extraction method, determination limit (10σ) and detection limit (3σ) were 0.11 ppb and 0.03 ppb, respectively. This method can be employed for the determination of hexavalent chromium in groundwater systems by the use of EDTA as masking agent.

The rapid determination of sub-ppm heavy metals in the solution state was examined via portable X-ray fluorescence spectrometry (XRF) based on homogeneous liquid-liquid extraction (HoLLE) in the water-ethanol-dimethyl phthalate ternary component system. The percentage of cadmium extracted into the sedimented liquid phase was 91.3%. After phase separation, the volume ratio (Va/Vs) of the aqueous phase (Va) and the sedimented liquid phase (Vs) was 121 (29.0 → 0.240 mL). Based on an analysis of the sedimented liquid phase in the solution state via the portable XRF, the presence of cadmium was determined over a concentration range of 0.100-4.00 mg L-1 .

This work established the integration of a continuous flow reaction and continuous crystallization using Taylor vortex flow reactors. We previously developed liquid–liquid biphasic flow alkylation using a Taylor vortex flow reactor, which is a scalable flow reactor with high mixing efficiency. To maximize the efficiency of this methodology, we evaluated process parameters and instrumental parameters, such as the rotating speed and tilt of the reactor, and optimized the reaction conditions. As a result, the throughput increased more than 20-fold compared to our previous work, and a long-run experiment verified its robustness. Liquid–liquid biphasic flow alkylation, quenching, phase separation, continuous crystallization, and filtration were integrated by using Taylor vortex flow reactors for both the flow reaction and continuous crystallization. The integrated system using two Taylor vortex flow reactors provided the alkylated product continuously from the solution of the starting material.

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