Continuous Production of Quinacridone Nanocrystals and Control of Crystal Form by High-Temperature Water Crystallization Method

Abstract

A high-temperature water (HTW) crystallization method was applied to produce size- and form-controlled organic nanocrystals without the use of any organic solvents. HTW and room-temperature water (RTW) were used as the extraction and cooling solvents, respectively. Nanocrystals are precipitated by mixing a high-temperature quinacridone aqueous solution in a newly developed micromixing unit with RTW from another line. Quinacridone nanocrystals having an average diameter of ca. 9 nm as determined from transmission electron microscopy observations and ca. 83 nm from dynamic light scattering measurements were produced at 250.6°C and 24 MPa with a flow rate of 10 g/min for HTW and 20 g/min for RTW. In addition, it was found that nanocrystals having different crystal sizes and forms could be obtained by changing the temperature and flow rate of RTW. This new method promises an environmentally sustainable process for the continuous production of organic nanocrystals.

Size-controlled production of quinacridone nanocrystals using hot compressed water recrystallization method

“…An increase in dispersant concentration lowered crystal size, as shown in Table 1. In previous work [10], the form of the crystals obtained changed from the α-form to the β-from as the cooling water flow rate decreased. Generally, the transition from the metastable to the stable phases proceeds at high temperatures.…”

“…In previous work in the absence of dispersant [10], large crystals of average size 1691 nm were obtained due to strong aggregation; in contrast, the preesnt work has shown that the 9 addition of dispersants reduced aggregation of the precipitated nanocrystals and allowed the formation of small crystals with an average size of 85 -241 nm. An increase in dispersant concentration lowered crystal size, as shown in Table 1.…”

“…Thus, it seems possible that in the case of POE, β-crystals are produced by a slow cooling rate and phase transition occurs during the prolonged duration ate high temperature. In constrast, the α-form is secured using SDS as a result of rapid quenching rates most likely 10 because of the greater quantity of water that would be attracted to the surfactant / particle precipitants.…”

“…Although studies have been made of the HCW recrystallization method [5][6][7]10], the 4 precipitation mechanism is unclear. To translate the method to an industrial scale, it would be useful to understand the relationship between particle size and the experimental factors associated with nucleation, crystal growth and solubility.…”

Synthesis of polyacenequinones via crossed aldol condensation in pressurized hot water in the absence of added catalysts

“…Orange-brown powdery solids were obtained from the reactions carried out at or higher than 370 • C, whereas yellow fine needles were obtained mostly from lower temperature experiments (<300 • C). Sue et al found that high-temperature crystallization from water was a recommended method for production of nanocrystals of stable organic compounds 20 such as quinacridone that happens to be a nitrogen-containing pentacyclic analog of the pentacenequinone.…”