Influence of mixing and solid concentration on sodium bicarbonate secondary nucleation rate in stirred tank

The secondary nucleation process of 2,2-azobisisobutyronitrile (AIBN) seeded crystallisation in methanol in a stirred tank reactor was studied at varying initial supersaturation levels, temperatures, crystal seed numbers, and stirrer speeds. The average secondary nucleation rate, induction time, and agglomeration ratio were measured using on-line microscopic imaging. The initial supersaturation level, temperature, and stirrer speed were found to be positively correlated with the secondary nucleation rate. A small change in the crystal seed number, i.e., 1-20, did not substantially affect the secondary nucleation rate throughout the secondary nucleation process. An increase in the initial supersaturation level and crystal seed number decreased the induction time, and an increase in the strength of agitation promoted the initiation of secondary nucleation at a stirring rate greater than 250 revolutions per minute (rpm). Temperature exerted a complex effect on the induction time. Regarding the agglomeration ratio, the initial supersaturation level positively correlated with the agglomeration ratio, while the stirrer speed negatively correlated with this parameter. Finally, based on the measured data, the average secondary nucleation rate, induction time, and final crystal suspension density were correlated. This study provides guidance for the control of supersaturation, induction time, stirring, and other factors in the crystal seed addition process in AIBN crystallisation.

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Ultrasound in Continuous Tubular Crystallizers: Parameters Affecting the Nucleation Rate

Crystals ◽

10.3390/cryst11091054 ◽

2021 ◽

Vol 11 (9) ◽

pp. 1054

Author(s):

Arne Vancleef ◽

Tom Van Gerven ◽

Leen C. J. Thomassen ◽

Leen Braeken

Keyword(s):

Residence Time ◽

Nucleation Rate ◽

Static Pressure ◽

Scale Up ◽

Ultrasonic Power ◽

Secondary Nucleation ◽

Process Understanding ◽

Ultrasonic Process ◽

Good Scale ◽

Equal Power

Ultrasound has proven to be an important tool for controlling nucleation in continuous tubular crystallizers. However, insufficient information is available about the parameters controlling the nucleation rate in a continuous ultrasonic process. Previous research has studied parameters related to the nucleation rate, but has not measured the nucleation rate directly or continuously. In this work, the nucleation rate is measured continuously and inline to solve this problem and achieve a better process understanding. The results indicate that the ultrasound-assisted nucleation process is presumably dominated by secondary nucleation. Additionally, the supersaturation, residence time and flow rate have a strong influence on the nucleation rate. On the other hand, the influence of the ultrasonic power is crucial but levels off once a certain amount of power is reached. The static pressure in the system determines the effective ultrasonic power and is therefore also important for the nucleation rate. Finally, maintaining an equal power per unit of volume and an equal residence time by increasing the tubing diameter seems to be a good scale-up method. These results will improve understanding of ultrasonic tubular crystallizers and how to control them.

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Studies on nucleation and crystal growth kinetics of plutonium(IV) oxalatex

Radiochimica Acta ◽

10.1515/ract-2021-1074 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Chuanbo Li ◽

Bo Wang ◽

Xiang Li ◽

Taihong Yan ◽

Weifang Zheng

Keyword(s):

Growth Rate ◽

Crystal Growth ◽

Nucleation Rate ◽

Crystal Growth Rate ◽

Acid Solutions ◽

Dilution Ratio ◽

Secondary Nucleation ◽

Supersaturation Ratio ◽

Crystal Growth Kinetics ◽

Kinetics Of

Abstract A new method is developed to calculate the dilution ratio N of the two reactant solutions during nucleation rate determination. When the initial apparent supersaturation ratio S N = f(N) in the dilution tank is controlled between 1.66 and 1.67, the counted nuclei is the most, both nuclei dissolving and secondary nucleation avoided satisfactorily. Based on this methoed, Plutonium(IV) oxalate is precipitated by mixing equal volumes of tetravalent plutonium nitrate and oxalic acid solutions. Experiments are carried out by varying the supersaturation ratio from 8.37 to 22.47 and temperature from 25 to 50 °C. The experimental results show that the nucleation rate of plutonium(IV) oxalate in the supersaturation range cited above can be expressed by the equation R N = A N exp(−E a /RT)exp[−B/(ln S)2], where A N = 4.8 × 1023 m−3 s−1 , and E a = 36.2 kJ mol−1, and B = 20.2. The crystal growth rate of plutonium(IV) oxalate is determined by adding seed crystals into a batch crystallizer. The crystal growth rate can be expressed by equation G(t) = k g exp(−E’ a /RT) (c − c eq) g , where k g = 7.3 × 10−7 (mol/L)−1.1(m/s), E’ a = 25.7 kJ mol−1, and g = 1.1.

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