Important Parameters for the Manufacture of Slow-Release Matrix Pellets With an Aqueous Dispersion of Quaternary Poly(meth)acrylates in the Rotary Fluidized Bed

ABSTRACT

The manufacture of slow-release matrix pellets with an aqueous dispersion of quaternary poly(meth)acrylates was investigated in the rotary fluidized bed. By considering the moisture content of the fluidized bed to be the key process parameter, it was measured on-line throughout the whole manufacturing process. A specially designed sampling device opened new ways to apply NIR spectrometry in laboratory scale processes. It was shown that reproducibly improved pellet properties can be achieved by reproducing the moisture content of the (rotary) fluidized bed. Moisture plateaus proved to be a suitable way to optimize the sphericity of the pellets. Premoisturizing was found to be a very effective tool to achieve slow-release dissolution of the model drug theophylline.     

Research Papers: Preparation of Indobufen Pellets by Using Centrifugal Rotary Fluidized Bed Equipment Without Starting Seeds

ABSTRACT

Pellets containing Indobufen as model drug were prepared by using the centrifugal-rotary fluidized bed equipment without employing non-pareil seeds.

The influence of different amounts of spheronization enhancer (microcrystalline cellulose) and of different fillers (lactose, mannitol, calcium carbonate) on both processing and physical properties of the pellets were evaluated.

The preparation reproducibility was also investigated. The use of 30% w/w of microcrystalline cellulose was essential to produce a good quality pellets; the incorporation of filler decreased the qualitative characteristics of the pellets.

The water feeding rate proved to be an important parameter for the pellet growth.

Therefore, the results showed that this technology based on the rotary fluidized bed is a promising and alternative method in producing pellets.     

Viscosity and separation performance of a gas-solid separation fluidized beds

A theoretical model of viscosity in gas-solid separation fluidized beds is established according to the two-phase flow theory of fluidized beds. After comparing theoretical and measured values, the correlation coefficient between the two is as high as 0.99, showing that the model has good predictability for the viscosity of fluidized beds. Meanwhile, the viscosity and its influencing factors were studied using a Brookfield viscometer. The study shows that smaller medium particles (0.074–0.15?mm) can reduce the viscosity of fluidized beds, but they will aggravate the viscosity fluctuation at more than 5?wt% addition, which is unfavorable to the stability of fluidized beds. In addition, in the actual separation process, the external factors (such as moisture and coal powder content) also affect the viscosity of the fluidized beds. Increasing the moisture increases the viscosity of the fluidized bed, whereas coal dust has the opposite effect. In order to ensure the stability of the fluidized bed, the bed moisture content should be controlled below 1?wt%, while the content of coal powder should be limited below 5?wt%. Based on separation tests, reducing the viscosity will improve the separation performance of a fluidized bed at the proper fluidized gas velocity, with the lowest possible error E_p of 0.085.     

Proportional control of moisture content of granules by adjusting inlet air temperature in fluidized bed granulation using near-infrared spectroscopy

For process control of fluidized bed granulation process, we investigated proportional (P) moisture content control via adjustment of inlet air temperature in proportion to the difference between measured and target moisture content of granules. Here, we first validated P moisture content control by comparison with bed temperature control. We then confirmed that P moisture content control is effective in maintaining the moisture content, and in minimizing the variance of the particle size of granules following granulation. Furthermore, we observed that when the target temperature was higher than the measured value of inlet air temperature the P moisture content control response was accelerated. In contrast, when the target temperature was less than the measured value of inlet air temperature (<50 °C) the response was delayed. In summary, P moisture content control has good scalability and can be introduced without changing granulation conditions in the development of orally administered pharmaceutical products.     

Manufacture of slow-release matrix granules by wet granulation with an aqueous dispersion of quaternary poly(meth)acrylates in the fluidized bed

Slow-release matrix granules were manufactured in the fluidized bed using an aqueous dispersion of quaternary poly(meth)acrylates (Eudragit® RS 30 D) as binder for granulation. A factorial design was carried out to investigate the influence of the following parameters, spraying rate, applied polymer amount, and inlet air temperature, on various granule properties. Prerequisites for a slow release of the model drug theophylline are high spraying rate, high amount of polymer, and low inlet air temperature. No considerable decrease of the drug release rate can be achieved without a subsequent curing of the dry granules. A clear correlation exists between the moisture content of the fluidized bed, indicated by the terminal moisture content (TMC), and the mean dissolution time for 80% of the drug (MDT₈₀).     

Manufacture of Slow-Release Matrix Granules by Wet Granulation with an Aqueous Dispersion of Quaternary Poly(meth)acrylates in the Fluidized Bed

ABSTRACT

Slow-release matrix granules were manufactured in the fluidized bed using an aqueous dispersion of quaternary poly(meth)acrylates (Eudragit® RS 30 D) as binder for granulation. A factorial design was carried out to investigate the influence of the following parameters, spraying rate, applied polymer amount, and inlet air temperature, on various granule properties. Prerequisites for a slow release of the model drug theophylline are high spraying rate, high amount of polymer, and low inlet air temperature. No considerable decrease of the drug release rate can be achieved without a subsequent curing of the dry granules. A clear correlation exists between the moisture content of the fluidized bed, indicated by the terminal moisture content (TMC), and the mean dissolution time for 80% of the drug (MDT₈₀).     

Heat and mass transfer in fluidized-bed furnaces in combustion of a coal-water mixture

The possibility in principle of burning highly ballasted fuel, including irrigated fuel, is considered. The permissible limits of the ash content and the moisture content are determined. The process of the thermal interaction between a drop of a coal-water mixture (CWM) and a fluidized bed is analyzed. Calculations of the distribution of volatiles and moisture in the fluidized bed in one-sided introduction of CWM are performed. The combustion of a CWM in a boiler furnace confirmed the practical possibility and expediency of recovering irrigated fuel waste of coal cleaning by this method. Ural State Technical University, Ekaterinburg, Russia. Translated from Inzhenerno-Fizicheski Zhurnal, Vol. 69, No. 6, pp. 993–999, November–December, 1996.     

Studies on the effects of physical properties of feed samples on the performance of fluidized bed dryer

The physical properties of grains are analysed at different levels of moisture contents using a fluidized bed dryer. The performance of fluidized bed dryer measured in terms of its efficiency is determined by using different grains as feed samples in the present work. The effects of various system parameters on the moisture content of the samples in turn on the dryer performance are studied. Again, effects of moisture content on different properties of sample, namely, grain volume, surface area, sphericity, bulk density, true density and porosity are studied. These properties of feed sample which determine the flow characteristics of the sample in a fluidized bed dryer are found to affect the dryer efficiency, in turn, the drying quality. An attempt is made to correlate the performance of the dryer against these physical properties of the materials. Thus, the efficiencies of the dryer calculated through the developed correlation and as per the literature are compared with each other. The comparison results show good agreement, thereby implying that the proposed correlation can be used for estimating the dryer performance over a wide range of parameters. With this study, the dryer can be designed properly in a cost-efficient manner.     

Fluctuations of the number of solid-phase particles in a fluidized bed

An analytic expression is obtained for calculating the relative fluctuation of the number of particles in a fluidized bed. The fluctuation of the number of particles in a bed consisting of glass pellets fluidized with water has been experimentally investigated. The relative fluctuations obtained in these experiments are compared with the theoretical values for a fluidized bed and an ideal gas.     

Comparison of the characteristics of bottom and fly ashes generated from various incineration processes

This study analyzed and compared the characteristics of bottom and fly ashes from three municipal solid waste incinerators (MSWIs) in Taiwan. Different incineration furnaces were investigated, including: (1) fluidized bed, (2) mass-burning, and (3) mass-burning linked rotary kiln. The particle size distribution, morphology, mineralogical and chemical composition, and leaching behavior of heavy metals of ash samples were evaluated. The results revealed that three types of incineration processes have different characteristic for ashes due to transportation and mixing system inside furnace. Particle size distribution indicated that 28.5% of MSWI-B bottom ash has lower than 180 microm and 61.2% of MSWI-A fly ash has larger than the 250 microm. The leaching concentration of Pb exceeded the regulatory level set by the Taiwan EPA in fly ashes from MSWI-B and MSWI-C, and thus must be considered hazardous wastes. Specifically, the leaching concentration of heavy metals of fly ashes from MSWI-A (fluidized bed incinerator) was lower than that of the others, and was corresponded to the regulatory levels. Therefore, a fluidized bed incineration process appears a potential of handling heavy metals for ashes. The result was also provided the valuable information for incinerator design and operation.     

Drying of thermally-weak organic powder in a centrifugal fluidized bed

The drying characteristics of thermally-weak organic powders of [2,2-Azobisisobutyrinitrile(AIBN) and HN] were studied in a centrifugal fluidized bed, since any kind of heating and hot gas cannot be employed for the drying of thermally-weak organic powders to prevent from sensitive reaction or decomposition during being dried. It could be a solution to use highly amount of gas in the centrifugal field for the drying of thermally-weak organic powders, which could overcome the limitation of gas velocity for the more efficient drying. The effects of gas velocity, rotational speed of the bed, initial moisture content of the powder, and amount of powder loading on the drying characteristics were determined. The pressure drop in the bed displayed an almost constant value that had a plateau, with increasing gas velocity. The moisture content of the organic powder decreased with an increase in the gas velocity or rotational speed of the bed, however, its variation trend did not change considerably with a variation of feed loading or an initial moisture content within this experimental conditions. The variation of the drying rates with respect to the moisture content was almost linear in the falling rate period.     

Numerical analysis of drying characteristics of frozen material immersed in fluidized bed at low temperature under reduced pressure

A spherical frozen material was dried in a fluidized bed of inert particles at a low temperature (lower than the melting point of water) under reduced pressure. To evaluate the drying characteristics of the frozen material, the heat and mass transfers in the material during the drying process were calculated using one-dimensional differential equations. The fitting parameters (accommodation coefficient of internal sublimation and heat transfer coefficient at the surface of the material) were determined to fit the calculation results and the experimental data. Drying characteristics, such as the distributions of moisture content and temperature in the material during drying, were calculated. Operational conditions, such as bed temperature, humidity, and heat transfer coefficient (gas velocity) at the surface of the material were varied in the calculation, and the effects on the end time of drying were estimated. Sublimation in the interior of the material governs the drying characteristics. The dry region in the material became resistant to heat transfer. The calculation results are reasonable for expressing the drying characteristics of freeze-drying, that is, our calculation method can be used to estimate the drying characteristics of frozen material in a fluidized bed.     

Moisture distribution in granular material during drying in a fluidized bed

This paper gives the results of a determination of the moisture content gradient and an investigation of the moisture distribution in a granular material during drying in a fluidized bed.     

Monitoring and control of coating and granulation processes in fluidized beds – A review

This review presents a compilation of works of the main techniques for monitoring and control fluidization regimes, particle size and moisture content during coating and granulation processes in the fluidized bed. The development of monitoring and control systems for coating and granulation of particles is highly desirable, not only to allow the operation in a stable bubbling fluidization regime, which intensifies heat and mass transfer, but also to ensure strict quality specifications for products, such as, uniform particle size distribution, low moisture content and good flowability. This paper focuses on the discussion of methods used and results obtained in studies on monitoring and control of granulation and coating process in the fluidized bed reported in the literature in the last decades. Pressure fluctuation signal analysis is widely discussed as a tool of regime monitoring. To monitor particle size, techniques such as, Near Infrared spectroscopy (NIR), Focused Beam Reflectance Measurements (FBRMs), among others are presented in detail. As for moisture content tracking, the methods are reviewed like acoustic signals, capacitance, microwave resonance and spectroscopy. It is evident that although these processes are highly complex, the techniques presented here have evolved mainly due to the efforts of several research groups, showing great potential for applications in industry, emphasizing the importance of this research field.     

A protein powder agglomeration process using açaí pulp as the binder: An analysis of the process parameters

This work investigated the fluidized bed agglomeration of a plant protein powder blend using an açaí pulp binder in order to improve the physical and handling properties. The blend was prepared mixing isolated pea protein powder and concentrated rice protein powder. The influence of air temperature and binder flow rate on the moisture content, particle size and process yield was evaluated using a factorial design. The anthocyanins content, wettability and flowability of the powder was also evaluated. The agglomeration produced large granules with better physical properties, indicating that açaí pulp can be used as a binder. Statistical analysis showed that binder flow rate had the greatest influence on moisture content and process yield; air temperature had a greater effect on particle size. The optimum condition (T = 75 °C, Q = 2.0 mL/min) resulted in granules that were twice as large as the initial particles. Anthocyanins were incorporated (2.34 mg/100 g) with an acceptable moisture content (≤10%) and a high yield (>75%). Flowability was greater in the agglomerated powder than in the raw material with a wetting time reduction of about 77.0%. The resulting protein powder combines the properties of an instant powder with health and nutritional benefits.     

A sustainable approach to the recycling of rice straw through pelletization and controlled burning

A technique for controlled burning of rice straw is presented. It relies on well-designed rice straw pellets to be burned in fluidized bed. The developed pellets have high burning rate, no fly ashes emissions and minimum bed fouling. The pellets are manufactured from ground rice straw in a disc pelletizer with the aid of bonding and suitable additive materials. The pellets are tested under controlled conditions in a test rig, which represents a single pellet fluidized bed. It is equipped with a nitrogen gun to eject the pellet and freeze the reaction at any predetermined time during combustion. The ejected pellets are weighed as well as elementary analyzed for both carbon and hydrogen, to calculate the burning rate as well as the combustion efficiency, respectively. The effect of several parameters has been evaluated including straw particle size, pellet size, type and concentration of bonding material as well as anti-sintering additives. Also, the pellets’ mechanical characteristics have been evaluated. It has been found that char combustion phase represents the controlling phase of the pellet combustion. The burning rate is higher as the void fraction of the pellet is higher. Starch showed better combustion and mechanical characteristics out of the five tested bonding materials. Adding kaolin to the pellets results in improving the sintering characteristics of the pellets. The experimental results were compared with two combustion models: the oxygen diffusion controlled and the kinetic-diffusion models. It has been found that oxygen diffusion controlled model more accurately simulates the combustion of the pellet during its char combustion phase. The model has been used to evaluate the effect of some operational parameters on the pellet combustion characteristics such as bed temperature, gas flow and oxygen concentration.     

Devolatilization of oil sludge in a lab-scale bubbling fluidized bed

Devolatilization of oil sludge pellets was investigated in nitrogen and air atmosphere in a lab-scale bubbling fluidized bed (BFB). Devolatilization times were measured by the degree of completion of the evolution of the volatiles for individual oil sludge pellets in the 5-15 mm diameter range. The influences of pellet size, bed temperature and superficial fluidization velocity on devolatilization time were evaluated. The variation of devolatilization time with particle diameter was expressed by the correlation, τ(d) = Ad(p)(N). The devolatilization time to pellet diameter curve shows nearly a linear increase in nitrogen, whereas an exponential increase in air. No noticeable effect of superficial fluidization velocity on devolatilization time in air atmosphere was observed. The behavior of the sludge pellets in the BFB was also focused during combustion experiments, primary fragmentation (a micro-explosive combustion phenomenon) was observed for bigger pellets (>10mm) at high bed temperatures (>700 °C), which occurred towards the end of combustion and remarkably reduce the devolatilization time of the oil sludge pellet. The size analysis of bed materials and fly ash showed that entire ash particle was entrained or elutriated out of the BFB furnace due to the fragile structure of oil sludge ash particles.     

Relationship between moisture content and temperature of dispersed material in drying in a fluidized bed

Solution of the differential calorimetric equation of the heat balance of a fluidized bed leads to a relationship between the moisture content and the temperature of the dispersed material during the constant and falling drying rate periods.     

The miniwid-coater: I. design and evaluation of a temperature-controlled miniature fluid-bed pan coater

A novel miniature laboratory-scale pan coater has been developed. Small batches of 50 to 100 g of pellets, granules, large crystalls and small tablets allow the formulation development with minimal quantities of valuable drugs and new active ingredients. Although originally it is a pan coater, the core bed will be slightly fluidized by the inlet air flow due to the small dimensions of the coating pan. This allows a rapid drying and the loss of coating materials will be negligible.

A computer was used to control the core bed temperature during the coating process by varying the spraying rate of an analytical dosing pump. Additionally, the drying air temperature can be adopted. It was possible to change the parameters during the process to optimize the operation conditions within one run. The computer program described in this article provides a constant bed temperature with a precision of ± 0.3 °C.

In the MiniWiD-Coater, neutral pellets have been loaded with bisacodyl and then enteric-coated with aqueous dispersions of Eudragit L 30 D. Batch homogeneity and reproducibility were excellent. Friability of the cores and abrasion of the coat remained low. The loss of coating material during operation was always below 5 %.     

Experimental study on fluidization characteristics of vinegar residue in a vibrated fluidized bed

As a by-product in the vinegar brewing process, vinegar residue always has a high moisture content, which is detrimental to the storage and recycle process. The vibrated fluidized bed can be used to dry the vinegar residue. In present work, inert particles were added to a vibrated fluidized bed to improve the fluidization of vinegar residue. Experimental studies were carried out to investigate the fluidization behaviors of the binary mixtures. Flow pattern maps indicated that there was an upper limit to the vinegar residue mass concentration c_w at which stable fluidization could be achieved. The minimum fluidization velocity u_mf of the binary mixture increased as the vinegar residue mass concentration c_w increased and decreased with the increase of the vibration intensity Λ. As increasing vibration intensity Λ or decreasing vinegar residue mass concentration c_w, the drying rate of vinegar residue increased.