Khashayar Saleh

Fluidized bed coating and granulation: influence of process-related variables and physicochemical properties on the growth kinetics

Abstract This study, which deals with the coating and granulation of solid particles by aqueous solutions of polymers or inorganic salts, aims to understand the effect of: – process-related variables such as the excess gas velocity, atomizer location, liquid flow rate and concentration, and atomizing air flow rate, – physicochemical-related variables such as the viscosity of solutions, wettability of the granulating liquid on solid particle surfaces, initial particle mean size, and porosity of the particles on the agglomeration kinetics of solid particles in a fluidized bed. The results showed that for a given particle size, the fluidizing air velocity was the most important factor affecting the growth kinetics and the stability of the operation. An increase of the relative humidity, depending on the liquid flow rate as well as the air flow rate, favor agglomeration mechanism especially for values greater than 0.4. An increase in the particle initial size leads to an enhancement of the layering mechanism, especially for values greater than 300 μm. The effect of the interfacial tension is investigated by adding different concentrations of a non-ionic surfactant to the binding solution. The effect of the contact angle is then studied using non-hydrophobic, partly hydrophobic, or totally hydrophobic particles. The growth of agglomerates appears to be favoured when the interfacial tension increases and the contact angle decreases. The viscosity of the solution has less effect than the interfacial parameters. The results show that the dominant forces in the granulation process are the capillary forces.

EXPERIMENTAL STUDY AND MODELING OF FLUIDIZED BED COATING AND AGGLOMERATION

This work deals with the fluidized bed coating and agglomeration of solid particles. The effect of particle size on coating criteria was investigated using sand particles as the coating support and aqueous solutions containing NaCl as coating liquid. The results showed that both growth rate and efficiency increase with decreasing the particle size. The growth was mainly governed by layering for particles larger than 200 μm, whereas for finer particles it occurred by agglomeration. As the particle size became less than 90 μm, the coating operation led to uncontrolled growth and bed quenching. However, the coating of the same particles was successfully achieved by adding some coarser particles. In addition, a mathematical model based on the population balance concept, taking into account the simultaneous growth by layering and agglomeration, was established to predict the time evolution of the particle size distribution. The comparison between experimental and calculated data permitted the establishment of a law for the size dependency of the agglomeration kernel.

Influence of the physicochemical properties on the growth of solid particles by granulation in fluidized bed

This work aims at investigating the effects of the physicochemical properties, such as the viscosity and the wettability of a granulating liquid on solid particles surfaces, on the agglomeration kinetics of solid particles in a fluidized bed. A series of batch experiments are carried out in a fluidized bed granulator at 50°C with 2 kg of solid particles. The use of solutions of Sodium CarboxyMethylCellulose (CMC) as binder with different concentrations leads to the study of the viscosity of the solution. The effect of the surface tension is investigated by adding different concentrations of a nonionic surfactant to the binding solution. The effect of the contact angle is then studied by using nonhydrophobic or partly or totally hydrophobic particles. The growth of agglomerates appears to be favored when the interfacial tension increases and the contact angle decreases. The viscosity of the solution has less effect than the interfacial parameters. The results point out that the dominant forces in the granulation process are the capillary forces. When an aqueous solution is pulverized into a fluidized bed containing hydrophobic particles, most of the binder is elutriated and collected in the cyclone. This shows that the main mechanism is in this case spray drying. As this process occurs at low temperature, it is useful for drying thermosensitive solutions.

Contact Angle Assessment of Hydrophobic Silica Nanoparticles Related to the Mechanisms of Dry Water Formation

Dry water is a very convenient way of encapsulating a high amount of aqueous solutions in a powder form made of hydrophobic silica nanoparticles. It was demonstrated in previous studies that both solid and liquid interfacial properties influence the quality of the final product resulting occasionally in mousse formation. To explain this behavior, contact angles of silica nanoparticles have been measured for water and water/ethanol solution by means of liquid intrusion experiments. It was found that the quality of the final product correlates with the contact angle, i.e., contact angle close to 105 degrees leads to mousse formation whereas a slightly higher value of approximately 118 degrees allows dry water formation. The proposed explanation was based on the energy of immersion and adhesion defined as the energy needed for a spherical particle to respectively penetrate into the liquid or attach at the liquid/air interface. Significantly lower energy of immersion calculated for lower contact angle might account for particle penetration into the liquid phase during processing, leading to continuous network aggregation, air entrapment, and finally mousse formation.

Chapter 7 Coating and encapsulation processes in powder technology

Publisher Summary Coating of particulate materials is a fundamental operation widely practiced in a variety of chemical industries including pharmaceuticals, food, fertilizer, cosmetics, biomedical, and nuclear. The coating process involves the covering of particulate materials including seeds, agglomerates, pellets, and powders with a surrounding layer of a coating agent (or coating material). The coating process can be applied to a variety of substrates ranging from submicron particles to very large objects. The coating thickness might vary from a few nanometers (chemical deposition) to several micrometers (film coating) or even several millimeters (e.g. sugar coating). There are several methods to introduce the coating agent into the system: dispersed or dissolved in an easily evaporable solvent, molten, or applied in the form of a very fine dry powder. In majority of cases, the final deposited layer (or coating layer) is a solid-phase material called a “shell.” In a few singular applications the coating layer can also be a liquid film. Furthermore, the introduction of a liquid into a particulate system leads most often to formation of liquid bridges among wetted particles. This behavior results in agglomeration phenomenon, which consists of adhesion of several elementary particles to form bigger entities called “agglomerates.” Another term subject to controversy in the technical and scientific literature is “encapsulation,” which is generally admitted to be a special kind of coating. In this chapter, the term encapsulation is used to distinguish one of the two following special cases: (1) the coating process is performed by immersion in a liquid phase, and (2) the product core constitutes of a liquid-phase formulation.

Chapter 5 Roll pressing

Publisher Summary Roll compaction is a continuous dry granulation process which is widely employed in the pharmaceutical, chemical, minerals, and food industries in order to manufacture free-flowing agglomerates. Roll compaction is conceptually very simple: the feed powder is passed through two counter-rotating rolls with the flow being induced by the friction acting upon the surfaces of the rolls. The powder is subjected to high pressure in the narrow gap among the rolls, leading to the formation of a compact in the form of a continuous strip or discrete briquettes. Roll compaction is designed to improve the flow properties, increase the bulk density, and ensure the uniformity of particulate formulations, in order to prevent the segregation of pharmaceutical drugs, for example. It offers advantages compared with wet granulation for processing physically or chemically moisture-sensitive materials because a liquid binder is not required. A further advantage is that it does not require a drying stage and is therefore suitable for use with compounds that either have a low melting point or degrade rapidly upon heating. The key factor in roll compaction is that the binding of particles results from the compression forces alone. The choice of powder to be compacted is therefore critical. Some active ingredients can be compressed directly. Others may be processed in combination with another material, which is selected for its favorable compaction properties. Consequently, the bulk of the material to be compacted often consists of an excipient or mixture of excipients, which are the materials that are mixed in with a drug in order to control drug delivery, to enhance patient acceptability and to aid in the tabletting process.

Stability of W/O Emulsions Encapsulating Polysaccharides

In the frame of formulation of W/O emulsions entrapping polysaccharides devoted to agricultural applications, the aim of this work was to study the stability over time of these emulsions, stabilized with either soybean lecithin or polyglycerol polyricinoleate (PGPR) as emulsifiers. Emulsifiers were dissolved in oil phase, and polysaccharides (carboxymethycellulose (CMC), guar, xanthan) in ultrapure water. Emulsions stability was studied through natural aging tests and accelerated aging tests, using bottle tests, microscopy and calorimetry. Experiments showed that PGPR was more efficient than lecithin to stabilize emulsions containing the polysaccharides studied, and that emulsions prepared with CMC showed the best stability.

Development of an Experimental Setup for the Measurement of the Coefficient of Restitution under Vacuum Conditions

The Discrete Element Method is used for the simulation of particulate systems to describe and analyze them, to predict and afterwards optimize their behavior for single stages of a process or even an entire process. For the simulation with occurring particle-particle and particle-wall contacts, the value of the coefficient of restitution is required. It can be determined experimentally. The coefficient of restitution depends on several parameters like the impact velocity. Especially for fine particles the impact velocity depends on the air pressure and under atmospheric pressure high impact velocities cannot be reached. For this, a new experimental setup for free-fall tests under vacuum conditions is developed. The coefficient of restitution is determined with the impact and rebound velocity which are detected by a high-speed camera. To not hinder the view, the vacuum chamber is made of glass. Also a new release mechanism to drop one single particle under vacuum conditions is constructed. Due to that, all properties of the particle can be characterized beforehand.

W/O Emulsion Destabilization and Release of a Polysaccharide Entrapped in the Droplets

This study was conducted as part of European project VEGEPHY to develop a product for the crop protection purposes. It concerns first the destabilization of a W/O emulsion containing water droplets in which the polysaccharide carboxymethylcellulose (CMC) is trapped, the droplets being dispersed in a vegetable oil made of rapeseed methyl ester. Polyglycerolpolyricinoleate (PGPR) is used as surfactant and glycerol is added to enhance the dispersion of the CMC. The second part is dealing with the study of the release and dilution of the CMC obtained by dilution of the destabilized emulsion in water in order to obtain the required final amount of CMC for practical purposes. The destabilization of the emulsion by the demulsifier (cynthiorex PMH 1125) has been followed by differential scanning calorimetry (DSC) that permits by studying the freezing of the dispersed water to detect the presence of bulk water. The release and dilution in water of the CMC versus time was followed and quantified by measuring the conductivity of the sample. The release kinetic was modeled using a first-order empirical model. The results showed that the release process of the W/O emulsion depends on the concentration of the demulsifier, on the stirring rate, and on the temperature. The optimum amount of the non-ionic surfactant was found to be 10% and the full release of the CMC has been obtained in 600 seconds. GRAPHICAL ABSTRACT

Ultrasonic Irradiation Coupled with Microwave Treatment for Eco-friendly Process of Isolating Bacterial Cellulose Nanocrystals

The isolation of crystalline regions from fibers cellulose via the hydrolysis route generally requires corrosive chemicals, high-energy demands, and long reaction times, resulting in high economic costs and environmental impact. From this basis, this work seeks to develop environment-friendly processes for the production of Bacterial Cellulose Nanocrystals (BC-NC). To overcome the aforementioned issues, this study proposes a fast, highly-efficient and eco-friendly method for the isolation of cellulose nanocrystals from Bacterial Cellulose, BC. A two-step processes is considered: (1) partial depolymerization of Bacterial Cellulose (DP-BC) under ultrasonic conditions; (2) extraction of crystalline regions (BC-NC) by treatment with diluted HCl catalyzed by metal chlorides (MnCl2 and FeCl3.6H2O) under microwave irradiation. The effect of ultrasonic time and reactant and catalyst concentrations on the index crystallinity (CrI), chemical structure, thermal properties, and surface morphology of DP-BC and BC-NC were evaluated. The results indicated that the ultrasonic treatment induced depolymerization of BC characterized by an increase of the CrI. The microwave assisted by MnCl2-catalyzed mild acid hydrolysis enhanced the removal of the amorphous regions, yielding BC-NC. A chemical structure analysis demonstrated that the chemical structures of DP-BC and BC-NC remained unchanged after the ultrasonic treatment and MnCl2-catalyzed acid hydrolysis process.