A COMPARISON OF TWO NaCl TEST SYSTEMS USED FOR MEASURING FILTER EFFICIENCY

ABSTRACT

The filter efficiency of materials to be used in respiratory protective devices is commonly measured by using a solid NaCl particle challenge and a flame ionization detector. The Moore's BS 4400 Bench Rig is an example of such equipment.

Recently, TSI, Inc. introduced their Model 8110. This system also produces a NaCl particle challenge. It uses a laser diode detector.

The filter efficiencies of two different filter materials were determined in a comparative study utilizing several Moore's and TSI systems. The results indicate that the two test systems are relatable and that the between-machine consistency of the Model 8110 is better than the Moore's system.     

QUICK AND RELIABLE FILTER TESTS WITH A MODULAR FILTER TEST RIG

A technique is described which reduces the duration of the measurement period in filter testing by approximately a factor of 3 in comparison to existing techniques.

Information concerning filter performance must be obtained reliably, reproducibly and quickly, without incurring large costs and without the need for specialized staff.

The components used (generators for powders, fluids or NaCI, discharge gap, filter holder, dilution systems and particle counter) meet the requirements of various standards (for example, Eurovent, CEN EN 143, DIN 24183, DIN 24185, draft of DIN 71460 and draft of VDI 3926))M     

Solid Dispersion Controlled Release: Effect of Particle Size, Compression Force and Temperature

Solid dispersions are dynamic systems, a careful control of processing variables is required to produce desired physicochemical properties of these systems.

The influence of drug particle size, dispersion temperature and compression force on the release rate of theophylline from solid dispersed system tablets was studied. Theophylline base (micronized and granulate) were embedded into a polymeric mixture of PEG and acrylic/methacrylic esters at controlled temperature and shock cooled. Tablets were made at two compressional forces and drug release was measured spectrophotometrically over a period of fifteen hours.

The release rate of drug dispersed in these insoluble matrices was independent of particle size but not of hardness.

However, variations in ratios of polymeric mixture and dispersion temperature controls the drug release rate from inert matrix more effectively than such factors as drug particle size and lower range of tablet hardness. The fast cooling produced excellent reproducibility of drug content throughout the entire entrapment product. X-ray diffraction study demonstrated no changes in crystalline form of theophylline.     

DESIGN AND CALIBRATION OF A STACK SAMPLER FOR OIL FLY ASH

A particle sampling system was developed for the collection of Fly ash the stacks of ail-fired electrical generation plants. The apparatus has a cyclone separator which is designed to provide a cutpoint of approximately 2.5 µ followed by a pulse jet fabric filter. Flow rate is a nominal 226 L/min (8 cfm).

The system was tested in the laboratory with monodisperse aerosols to determine the fractionation characteristics of the cyclone and the inlet probe. Efficiencies of three candidate filters were examined with clean media, with a dust cake and with the dust cake removed. Tests were conducted using monodisperse polystyrene aerosols of 0.50, 0.76 and 1.09 µ

The pulse Jet apparatus was checked by operating the system at a flow rate of 200 L/min, loading the filter with AC fine test dust, and determining the stable filter pressure drop as a function of pulse jet air pressure.     

Disintegrants in Solid Dosage Forms

The dynamic approach to tablet disintegration, which is based on the measurement of the force that develops inside the compact upon water entrance, is basically taken up.

The combined measurements of force development and water uptake, simultaneously effected on the same compact, provide a novel parameter that is proposed to quantify and compare the efficiency of disintegrants.

The new parameter, which is based on the “force-equivalent” concept, expresses the capability of a disintegrant of transforming water uptaken into swelling (or disintegrating) force. A few examples, that illustrate the usefulness of this parameter for disintegrant characterization, are given.

In parallel to the quantification of swelling (or disintegrating) efficiency inside compacts, attention is also being paid to the characterization of swelling disintegrants as pure materials.

In particular the case of the so-called limited swelling materials, for which the quantification of intrinsic swelling (particle volume increase in swelling media) is critical, is considered.

The applicability of an instrumental method, which is based on the employment of a Coulter Counter, is discussed alternatively to microscopic methods.

Disintegrant characterization may also be considered in view of new possible exploitations of the swelling properties of polymers in controlling drug release.     

EFFECT OF SURFACTANT ADDITION ON THE MICROSTRUCTURE OF COAL FILTER CAKES

Currently, water removal from fine coal fractions is affected by vacuum filtration of a coal slurry followed by thermal drying. Due to high operating costs and the potentially hazardous nature of the drying operation, alternate methods are sought.

This work investigated the change of filter cake microstructure resulting from one such method, namely, surfactant addition to the coal slurry. By impregnating a coal filter cake with an epoxy resin, micrographic analysis of the cake structure could be made by using an image analyzer with the aid of quantitative stereology. This analysis provided a particle and pore size distribution of the filter cake which is fundamental to the understanding of the dewatering mechanism.

Three surfactants were investigated in this work: non-ionic Triton X-114, anionic Aerosol-OT, and cationic dodecyl pyrindinium chloride. The behavior of Triton X-114 and DPC was similar; they both enhanced dewatering by reducing the amount of particle segregation while increasing the pore size of the cake. Conversely, Aerosol-OT, while exhibiting enhanced dewatering characteristics, did not significantly alter the filter cake structure. At low concentrations all three surfactants exhibited little change in particle and pore size distributions when compared to a filter cake formed at the same conditions without surfactant.

Additionally, a linear relationship was shown to exist between the volume-surface mean diameters of the particles and that of the pores. Similar relationships are also presented for the geometric mean diameter and the geometric deviation. The best correlation between particles and pores was obtained from coal cakes formed with Aerosol-OT.     

ROOM-TYPE AIR CLEANER DESIGN CRITERIA AND PROTOTYPE PERFORMANCE

Two rules-of-thumb for minimum performance of a room-type air cleaner have been developed from consideration of a first order model for room air quality. By adopting a criterion that the use of an air cleaner should cause the particle concentration to be at least cut in half, the rule-of-thumb for a room with no smokers is that the product of filter efficiency and flow rate should be ≥.8 m³/min (≥30 cfm). If the particle concentration is dominated by smokers or other sources, the product of filter efficiency and filter flow rate should be = m³ /min (= 100 cfm)

Tests were conducted to determine the efficiencies of candidate filter media. The selected media, Filtrete G-0115, has a fractional efficiency for 1 μm particles of 97 percent when clean, and an efficiency of 78 percent when fully loaded. This drop in efficiency is due to the masking of the electrets on the surfaces of the filter fibers.

A fibrous filter room-type air cleaner was designed to perform in accordance with the rules-of-thumb. When operated with a clean filter, the maximum flow rate is 3.2 m³/min and, when operated with a fully loaded filter, the maximum flow rate is 1.8 m³/min. The system has a multispeed fan which will provide lower flow rates.     

FORMATION OF FILTER CAKES WITH PARTICLE PENETRATION AT THE FILTER SEPTUM

The mass of solid particles entering the formation is an important factor in industrial cake filtration operations. Predictions of the concentration at the filter septum require the ability to predict the mass transport of solid particles under variety of conditions.

This study analyzes cake formation, including particle penetration at the filter septum. In addition to the total instantaneous mass balance equation, mass balance equations for captured and suspended particles and the fluid phase are averaged along the cake thickness taking into account conditions at the surface and the septum. Capture mechanisms, such as surface straining, and internal cake erosion and particle capture are included in the analysis.

The results are ordinary differential equations in terms of thickness, concentration of suspended particles in the filtrate, average particle concentration, average porosity, and such operational parameters, as slurry concentration, injection rate, and volumetric solid fraction.

To test tbe validity of the analysis presented here, the numerical results are compared to results for a simplified case. The conclusions from the sensitivity analysis conducted in this study agree with earlier conclusions. Results show that the concentration of suspended particles in the filtrate increases rapidly and then decreases gradually until it reaches zero after 13 hours. This yields that after 13 hours we have a clear filtrate.     

The use of optimazation techniques in pharmaceutical development

The lecture uses selected examples to illustrate the use of mathematical methods to optimize drug dosage forms:

Elucidation of compatibility between active ingredient and excipients required in the preformulation phase by factorial design.

Calculation of maximum allowable mean of particle sizes for active ingredient and the sum of auxiliary materials to achieve a sufficient content uniformity by applying the Stange-Pool equation.

Application of surface response research for identification of the working point in an “innocuous area of landscape” for scaling ups, handing over to production, of trouble shooting by using central composite desing and in the case of multiple constraints doing computerized grid search.

Only mentioned and not described in detail will be the methods for pharmacokinetical optimization, necessary for the development of modified release formulations.

Of course not for every development it is mandatory to use surface response research to get the necessary quality. But it is worthwile to apply refgularly factorial design for compatibility studies to calculate the necessary particle sizes and to compare in vivo results with dissolution rate data.     

Crystal Engineering and Particle Design for the Powder Compaction Process

The historical background to the subject of crystal engineering of pharmaceuticals is briefly reviewed with reference to materials as diverse as insulin and direct compression tablet excipients. In the light of the limited scientific and practical information available on the topic two questions are posed -

Is it possible to prepare 'designer' materials with preferred processing, specifically compressive, properties giving optimised product characteristics?

How can such materials be efficiently manufactured?

In order to consider these questions, several important elements of data-base requirements are regarded as essential. These include knowledge of the crystalline phases of pharmaceutical solids, full understanding of the fundamental mechanical constants and moduli of particulate solids, and the relationships describing the influence of crystallographic structure on the mechanical properties of crystals and powders. At the same time the effects of preparation, pretreatment and processing effects on crystal structure, crystallinity and thermodynamic properties of powdered solids must be established.

The topics of material based compaction problems, property groupings of pharmaceutical powders with particular emphasis on crystal structure and mechanical properties are discussed. The review then considers recent and current research work examining the compaction behaviour of modified or engineered materials, prepared using alternative crystallisation conditions and the incorporation of low level additives. Specific examples include modern direct compression excipients, 'spherical' drug particle production and high purity lubricant (magnesium stearate) powders.

In conclusion, the future potential of the concepts of crystal engineering and particle design is considered in terms of predicting mechanical and processing properties from fundamental molecular and structural information.     

ULTRA-PRECISION DIAMOND MACHINING OF ADVANCED TECHNOLOGY COMPONENTS

The design, development, and application of ultra-precision CNC machines for

the single point diamond turning of non-conventional metal optical components (Al, Ge, etc. )

the diamond grinding of ferrite and, other ceramic components for magnetic disc flying heads, etc.

is described. In both cases, tolerances on workpieces in the order of ± 0·1 μm were specified and achieved, together with the overriding need to minimize degenerated surface layers, i.e. surface damage.

The effects of chip formation at low depths of cut are discussed. The factors affecting the depths of “damaged layers” formed in turning and grinding are mentioned. Typical advanced technology components for which ultra-precision diamond turning or grinding are widely used are:

Convex mirrors for high output C0₂ laser resonators

X-ray mirrors

infrared lenses in germanium for thermal imaging systems

scanners for laser printers. and drums for copiers

elliptical mirrors for YAG laser beam collectors

spherical bearing surfaces in beryllium, copper, and other materials

ceramics for magnetic read/write heads for computer memory discs

ceramics for cams, cam followers, valve seat inserts, cylinder liners, bearings, cylinder heads, turbo impell ers, etc.

Both single point and diamond grinding for ultraprecision low stress surfaces demand high precision machines that provide

high stiffness of structures and high band-width servo drives;

low rumble, high averaging bearings such as hydrostatic air or oil;

high internal damping of stuctures and drive systems;

multi closed loop control of many parameters, including temperature of coolant and temperature gradients across structures and sub-systems;

coolant delivery to the abrasive/workpiece interface is of critical importance for controlling high surface finish and minimizing surface tresses.

The paper gives examples of how these problems are satisfied in today's state of the art ultra-precision CNC machine tools.     

Elaboration and Physical Study of an Oxodipine Solid Dispersion in Order to formulate Tablets

When drugs particles are very hydrophobic, the carrying out of solid dispersion is a good process in order to obtain a faster drugh dissolution due to the particle the particle size reduction and due to the wettability improvement of the particle surfaces.

The behaviour of these products may differ according to their physical structure, more particularly the dissolution rate of the drug and the stability of the solid dispersion obtained.

The aim of this work is

— to study a product supplied by industry, that is to say a Coprecipitate obtained by evaporation of an ethanolic Oxodipin/Povydone solution. The high melting point of Oxodipin has conduct us to choose coprecipitation. The oxodipin amount in the coprecipitate (20%), is a good compromise between efficiency and technological properties.

— to demonstrate that the product obtained is a solid dispersion.

— to test its stability during compression and during the stockage ether in ambient condition, or at 40° C, or in controled humidity conditions.

Results seem to demostrate that a solid disperision which is a solid solution is obtained. This solid dispersion presents a very good stability of its physical structure and of dissolution properties.     

EXPERIMENTAL STUDY OF DUST FILTRATION IN SURFACE-TYPE NONWOVENS

Surface type nonwovens are widely used in industrial dust control. Recently, they have been utilized in some engine air filtration applications as automotive filters, heavy-duty engine self-cleaning filters or safety filters. Because of their mechanical strength and regenerative ability they are a perfect material for applications where filter replacement is a problem. On the other hand, the random distribution of fibers and needle punching may result in pinhole formation during dust loading, especially at high aerosol velocities. As a result, the seepage mechanism is common in applications involving fine solid aerosols.

In the inertia dominated region, the collection efficiency of particles depends on the adhesion probability. When particle momentum increases, the efficiency decreases. In general, there is no agreement between filtration theory and experiment when the Stokes number is greater than one.

Filter efficiency increases with dust loading when the filter medium is a good dust cake supporter. In this case, dust reentrainment, causing seepage, may occur at high aerosol velocities and pressure drops. In contrast, reentrainment in nonwovens can take place even at lower aerosol velocities and dust loadings. It is difficult to predict conditions favorable for dust reentrainment and pinhole formation. This process depends on media geometry, dust particle size distribution, and aerosol flow parameters.

This paper discusses filter performance of surface-type nonwovens exposed to polydisperse dusts. Filter efficiency and pressure drop are discussed as functions of aerosol velocity, dust loading, and dust particle size distribution.     

The Use of Fractal Geometry in Pharmaceutical Systems

The nature of surface irregularity affects many phenomena including adsorption/desorption, catalysis, crystal growth, drug dissolution and chromatography. Many excellent models have been developed with the oversimplified assumption that all particles are smooth spheres; fractal geometry allows these models to be expanded to irregular surfaces by providing a quantitative means of assessing surface roughness.

An overview of fractal analysis is presented in the following, and the state of the art, as far as pharmaceutical systems are concerned are outlined. Erroneous approaches, as well as the directions pharmaceutical research and technology might take in the area of fractal analysis are suggested.

From a historical perspective, micromeritics (the science of particle size, shape and surface area) were first developed with the assumptions that all particles were smooth spheres.

Much excellent work has been developed with such an oversimplified model. For example, numerous workers have shown that particle flow through an orifice is a function of “particle diameter”, and experiments have most often been carried out on particles as close to spherical as possible, and as monodisperse as possible.

The science of micromeritics, the science of small particles, is the making of Dalla Valle (1943) who coined the term in a book of the same name which describes methods of particle size measurement, mostly used by soil scientists.¹     

Design and Evaluation of Four-Stage Low-Pressure Cascade Impactor Using Electrical Measurement System

The low-pressure cascade impactor has been used to collect ultrafine particles that cannot be measured by conventional cascade impactors. Low-pressure cascade impactors resemble ordinary impactors, but are operated at reduced pressures of 0.05 ∼ 0.4 atm. Many kinds of low-pressure impactors have been developed by different researchers. However, it is still difficult to accurately design and evaluate the low-pressure cascade impactor.

In this study, a four-stage low-pressure cascade impactor for measuring the size distribution of submicron aerosol particles was designed and evaluated. To evaluate particle collection efficiency of each stage, an electrical measurement system was used. The cut-point diameters of Stages 1 through 4 were 0.238, 0.173, 0.111, and 0.063 μm in aerodynamic diameter. Stage 2 showed poor steepness of the collection efficiency curve and larger cut-point Stokes number than theory, which may be attributed to high nozzle velocity. The fluorometric method for particle collection efficiency measurement was shown to be unreliable for ultrafine particles.

The solid particle collection efficiency of the designed impactor was examined with different substrate conditioning methods. Porous metal substrate and silicon-coated substrate were tested with NaCl particles. It was shown that silicon coating did not effectively reduce the particle bounce because of high nozzle velocity, whereas the porous metal substrate considerably enhanced the particle collection efficiency.     

OILWELL COMPLETION FLUID SOLIDS INTERACTION WITH AN UNCONSOLIDATED OIL RESERVOIR

This work addresses the problem of modelling, detection and evaluation of the mechanical interaction between oilwell completion fluid particles and granular reservoir rocks. These interactions contribute to a reservoir productivity reduction known as the “permeability damage” phenomenon.

Fundamental concepts of cake filtration and filter medium filtration were used to formulate mathematical models of particles capturing: gradual pore blocking, screening, and straining. The models provide theoretical bases for simple diagnostic plots in which the linearity of a plot becomes an indication of a prevailing mechanism of particles' capture.

Laboratory tests were run by pumping a completion fluid through synthetic simulated cores of unconsolidated sandstone gas reservoir samples from the Adriatic Sea. By using diagnostic plots and grade passing efficiency curves, the effects of total solids concentration particle size on the type and efficiency of the capture mechanism were investigated.

The study revealed the existence of three mechanisms of particle capture and the applicability of diagnostic plots for their detection. The onset of the straining mechanisms was attributed mainly to the total solids concentration while the duration of the gradual pore blockage phase was correlated with both particle size and concentration.     

Good pharmaceutical manufacturing practices

In order to assure the quality of medicines and to encourage the implementation of the international system for the certification of the quality of pharmaceuticals, it was deemed necessary to specify the conditions under which pharmaceutical establishments should operate to provide full assurance that their products are safe for public health.

The French Government Order of 1. October. 1985 therefore provides for the establishement of new recommendations on good pharmaceutical manufacturing practices: “Bonnes Pratiques de Fabrication et de Production Pharmaceutiques: BPF 1985”.

Within the system of quality assurance, good pharmaceutical manufacturing practices represent that part which is concerned with manufacture.

Their implementation requires that the specification of the raw materials and packaging materials, the manufacturing and packaging processes and the control methods be defined and written beforehand, that the premises and equipment be adapted to the intended uses and that the staff have received appropriate training.

Good pharmaceutical manufacturing practices directly concern production departments and packing area, control laboratories, storage areas, purchasing departments, departments receiving raw materials and dispatching finished products. They also concern departments issuing instructions and written or computerised documents intended for the departments previously mentioned.

Although the collection of recommendations thus published constitutes a detailed document, the possibility of there being different methods for attaining the same objective is recognised.     

Determination of Sphericity of Pellets Prepared by Extrusion/Spheronization and the Impact of Some Process Parameters

A method for the quantitative assessment of particle shape has been evaluated and used to study the influence of some process parameters on the sphericity of particles produced by extrusion/spheronization

The measuring technique is based on the transfer of a microscopic picture of particles to a video screen. From the digitized image, the length/width ratio for a large number of particles is calculated by a computer

Processing conditions, such as added amount of liquid and spheronization speed/time, have a pronounced impact on particle sphericity

The results obtained and the convenience of the method demonstrate that the measuring technique is valuable in following changes of particle shape in relation to processing conditions     

Some Properties of an Ethoxylated Castor Oil and Ethoxylated Oleyl Alcohol

Ethoxylated derivates have been used as surfactants for some years. In this work, ethoxylated castor oil and ethoxylated oleyl alcohol alone and/or their I:I mixtures were used as surfactants in oil/water type of emulsion systems.

The physicochemical properties of ethoxylated castor oil (Simulsol OL 50) and ethoxylated oleyl alcohol (Simulsol 98) have been investigated.

Both of these materials have properties associated with non-ionic surfactants, although considerably soluble in water, the compounds have slight solubility in nonpolar solvents.

Surface tensions of aqueous solutions were measured over a temperature range of 20°C to 40°C. CMC were determined by surface tension measurements. pH, refractive index, conductivity and density of the two surfactants were also determined.     

Scheduling Policies for Automatic Warehousing Systems: Simulation Results

This paper examines and extends previous analytical work on the scheduling of stacker cranes in automatic warehousing systems. In particular, the following are examined by means of a computer simulation:

(1) The performance of the closest-open-location rule compared to random storage assignment;

(2) The dynamic behavior of the system under stochastic conditions, using various crane and rack utilization levels;

(3) The actual versus predicted reduction in crane travel time due to improved scheduling rules;

(4) The effect of imperfect information concerning the length of stay of an incoming pallet on system performance.

The results of our experiments provide evidence in support of the proposed analytical models. Most important, the experiments demonstrate the value of previously-proposed scheduling rules in a dynamic, stochastic environment operating with imperfect information.