Scale up of a Spinning Disk Reactor for Preparing Fine Powder in a Continuous Mode
Date Issued
2011
Date
2011
Author(s)
Wang, Yao-Hsuan
Abstract
Nano/micro particles, which have excellent physical and chemical properties, can widely applied to various industries, such as biological, electrical, and chemical, due to their small size and imperfect surface structure, which are different from that of bulk materials. The common methods for preparing particles include milling and precipitation. For the traditional milling method, the products are usually contaminated or the crystal lattice of products is disrupted. The precipitation method is most popular in industry for its simplicity, low cost, and ease of manipulation. But the reactive precipitation method using a batch stirred vessel is hard to improve the product quality and production capacity. The particle size and shape are difficult to control because of the poor mixing efficiency. To overcome these problems, an efficient method of rotation packed bed, which is one of the high-gravity equipment, has been applied by Chen et al. (2000) to synthesize CaCO3 nanoparticles in a recycle mode. The reaction time in a rotating packed bed is around 5- 15 min for 1 L reactant aqueous solution. At the same operating conditions, the reaction time in a conventional stirred reactor is eight times as large as that in a rotating packed bed. It is apparent that recycle operation in a high-gravity reactor has shortened the reaction time. If the recycle operation is replaced by the continuous operation, the production rate will be enhanced.
There are two types of high-gravity equipment, i.e. rotation packed bed and spinning disk. The latter is better for preparing particles due to less chance of particle collision to form agglomerates. In our laboratory, several compounds have been successfully synthesized using the SDR in a continuous mode, such as CaCO3, Mg(OH)2, Ag , AgI, and SMZ (drug). In the silver particle preparation, AgNO3 and PVP (protecting agent) were dissolved in an aqueous solution, and then the solution was mixed with an aqueous solution of glucose and NaOH to produce Ag particles through a reducing reaction. In the drug precipitation reaction, the drug and protecting agent were first dissolved in an alkaline solution, and an acidic solution was added and mixed to change the solubility of solution, and then drug particles were recrystallized. However, the scale up of the SDR for preparing organic and inorganic particles in a continuous mode has not been discussed and compared. In this study, the disk diameter was scaled up to 50cm to increase the retention time and to improve the yield of silver product. In the drug particle preparation, drugs were recrystallized with the larger SDR fitted with circular tube liquid distributors to obtain smaller particles. Drugs of p-aminosalicylic acid (PAS) and glilbenclamide (GBM) were chosen in this study of continuous operation. The main theme of this research was to discuss various operation conditions on particle size and yield, and to compare the performance of organic and inorganic systems. The equipment consists of a spinning disk of diameter being 12.0cm, 19.5cm, and 50.0cm, fitted with liquid distributors of straight or circular tubes.
In the process for preparing silver nanoparticles under the appropriate operating conditions, the effects of the disk size and liquid distributors were not observed on the silver particle size with the size, which was around 10nm. In addition, when the reactant flow rate varied from 0.3 to 5.0 L/min, the particle size remained quite constant. In the process for preparing drug particles, when increasing spinning disk diameter and using circular liquid distributors, the drug particles size could be reduced to micro or submicron level. On the other hand, the particle size of drug increased with increasing reactant flow rate due to the poor mixing efficiency. Therefore, the suitable reactant flow rate was between 0.25 L/min and 0.50 L/min. The size and crystalline intensity of the recrystallized drug were lower compared to that of the commercial drug, and thus the dissolution rate was enhanced. The silver particles synthetized by the chemical reaction method were smaller than 10nm and the production rate was 31kg with the yield of 40.1%. The PAS drug particles prepared by the neutralization method were reduced to submicron level and the production rate was 23kg with the yield of 54.0%. The GBM drug particles prepared by the neutralization method were around 1μm and the production rate was 1.8kg with the yield of 92.6%.
Subjects
high-gravity technique, spinning disk reactor, precipitation method, continuous operation, silver nanoparticles, low solubility drugs, and scale up.
Type
thesis
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