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Abstract A mathematical model was developed based on data obtained on Fischer-Tropsch (FT) laboratory scale unit operated in steady state, belonging to BIOENERGY 2020+ GmbH, Austria to demonstrate alpha-parameter dependence on carbon number. The lab-scale unit processed the synthesis gas, obtained by the gasification of biomass (woodchips), to produce liquid fuels for transportation applications. The FT reaction took place in a slurry reactor filled with dispersed cobalt-based catalyst. The products were then separated by partial condensation depending on their boiling points. The final output of the FT laboratory scale unit comprised three product streams – wax, diesel and naphtha. The reaction and separation of products were simulated in Aspen Plus software. The mathematical model used kinetic description based on power-law rate equations. The modeled product selectivity was controlled using an alpha-parameter of the Anderson-Schulz-Flory distribution. Because of the significant deviation of products spectrum from typical Anderson-Schulz-Flory distribution, a modified description of reaction selectivity was developed. The description introduces variable alpha-parameter, dependent on number of carbon atoms in the reacting molecule. The mathematical model developed using MATLAB software considered the production of aliphatic paraffins having a number of carbon atoms from C1 to C60. The mathematical model of simulated lab-scale unit comprised an ideally mixed reactor RCSTR and three FLASH2 separators for the separation of desired products. The results from mathematical model were validated by a comparison with experimental results from FT lab-scale unit. The modified polynomial dependency of alpha-parameter on carbon number showed significantly better description of composition and amounts of FT products, especially for wax stream where the description using constant alpha led to enormous deviations. Such better prediction of composition and amounts of acquired products is important for evaluating efficiency of further upgrading the FT products to liquid fuel. [ABSTRACT FROM AUTHOR]

Many newly developed active pharmaceutical ingredients (APIs) have very low solubility in aqueous media. The preparation of solid dispersions (SDs) is one way of avoiding this problem. However, compound wettability and thus solubility are influenced by surface energy. In this study, we used inverse gas chromatography (IGC) to evaluate the surface energies of prepared SDs, and compared them with those obtained for physical mixtures (PMs). SDs containing different weight ratios of crystalline acetaminophen and one of three polymers (Kollidon ® 12 PF, Kollidon ® VA 64 or Soluplus ® ) were prepared by the melt-quenching of corresponding PMs. In all cases, as the polymer content increased, the surface energy decreased significantly. For the SDs and PMs containing Soluplus ® , this decrease in surface energy showed the same non-linear trend. In the cases of Kollidon ® 12 PF and Kollidon ® VA 64, the trend was linear, with the SDs showing a steeper decrease in surface energy than the corresponding PMs. Typically, such decreases are ascribed to the dissolution of the crystalline structure of an API. Our results suggest that in the case of the Kollidons, the steeper decrease is caused by another mechanism, namely, strong API-Kollidon interaction leading to the less wettable surface of SDs. [ABSTRACT FROM AUTHOR]

• Mixing/co-milling with chitosan increased dissolution rate of meloxicam greatly. • The observed effect was facilitated by meloxicam-chitosan interactive mixtures. • Specific surface area and total amount of the mixture were controlling parameters. • Work of adhesion/cohesion ratio of 0.9 indicated stability of interactive mixtures. • No marked drug amorphization or other crystalline structure changes were detected. To enhance dissolution rate of meloxicam (MX), a poorly soluble model drug, a natural polysaccharide excipient chitosan (CH) is employed in this work as a carrier to prepare binary interactive mixtures by either mixing or co-milling techniques. The MX-CH mixtures of three different drug loads were characterized for morphological, granulometric, and thermal properties as well as drug crystallinity. The relative dissolution rate of MX was determined in phosphate buffer of pH 6.8 using the USP-4 apparatus; a significant increase in MX dissolution rate was observed for both mixed and co-milled mixtures comparing to the raw drug. Higher dissolution rate of MX was evidently connected to surface activation by mixing or milling, which was pronounced by the higher specific surface energy as detected by inverse gas chromatography. In addition to the particle size reduction, the carrier effect of the CH was confirmed for co-milling by linear regression between the MX maximum relative dissolution rate and the total surface area of the mixture (R2 = 0.863). No MX amorphization or crystalline structure change were detected. The work of adhesion/cohesion ratio of 0.9 supports the existence of preferential adherence of MX to the coarse particles of CH to form stable interactive mixtures. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract Surface energy is extensively adopted to predict the surface properties of materials nowadays. Our study was aimed at utilizing the surface free energy measured by inverse gas chromatography to determine inter-particle interactions and to describe the overall behaviour of mixtures. The model drugs of different solubility (tadalafil, levocetirizine dihydrochloride, vardenafil hydrochloride, and amlodipine besylate) and two grades of polyvinylpyrrolidone (Kollidon® 12 PF, Kollidon® VA 64) were mixed in various ratios. Investigated components were characterized using inverse gas chromatography, particle size distribution and specific surface area. We also determined the work of adhesion and cohesion between the components in the binary mixtures. Due to the formation of levocetirizine agglomerates, the effect of mixing time on both components of the surface free energy was also studied for the binary mixture with Kollidon® VA 64. The results based on the energy analysis, especially positive or negative excess surface energies in theoretical and real binary mixtures, indicate that we can predict whether the components can form the desired ordered (interactive) mixture. For this reason, we have proposed, to the best of our knowledge, different approach to predict the interactions between components and their behaviour in the binary mixtures using inverse gas chromatography in terms of the energy balance based only on the surface parameters (surface free energy, dispersive and specific surface energy). Therefore, the approach of energy balance is an innovative and comparatively simple tool for analysis and identification of interactions between components in particulate systems, which can also predict the quality of the mixing. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract The mechanism of colloidal silica action to improve flow properties of pharmaceutical powders is known to be based on inter-particle force disruption by silica particles adhered to the particle surface. In the present article, the kinetic aspects of this action are investigated, focusing on non-spherical particles of different size. Blends comprising microcrystalline cellulose or calcium hydrogen phosphate dihydrate and colloidal silica were examined using powder rheometer. The blends were formulated to represent effects of particle size, surface texture, colloidal silica loading, and mixing time. Pre-conditioning, shear testing, compressibility, and flow energy measurements were used to monitor flow properties. Components and blends were analyzed using particle size analysis and scanning electron microscopy (SEM), using energy dispersive spectroscopy (EDS) and back-scattered electron (BSE) detection to determine surface particle arrangement. All studied parameters were found to have substantial effects on flow properties of powder blends. Those effects were explained by identifying key steps of colloidal silica action, which were found to proceed at substantially different rates, causing the flow properties change over time being dependent on the blend formulation and the component properties. [ABSTRACT FROM AUTHOR]

In pharmaceutical industry, the use of lubricants is mostly based on historical experiences or trial and error methods even these days. It may be demanding in terms of the material consumption and may result in sub-optimal drug composition. Powder rheology enables more accurate monitoring of the flow properties and because the measurements need only a small sample it is perfectly suitable for the rare or expensive substances. In this work, rheological properties of four common excipients (pregelatinized maize starch, microcrystalline cellulose, croscarmellose sodium and magnesium stearate) were studied by the FT4 Powder Rheometer, which was used for measuring the compressibility index by a piston and flow properties of the powders by a rotational shear cell. After an initial set of measurements, two excipients (pregelatinized maize starch and microcrystalline cellulose) were chosen and mixed, in varying amounts, with anhydrous colloidal silicon dioxide (Aerosil 200) used as a glidant. The bulk (conditioned and compressed densities, compressibility index), dynamic (basic flowability energy) and shear (friction coefficient, flow factor) properties were determined to find an optimum ratio of the glidant. Simultaneously, the particle size data were obtained using a low-angle laser light scattering (LALLS) system and scanning electron microscopy was performed in order to examine the relationship between the rheological properties and the inner structure of the materials. The optimum of flowability for the mixture composition was found, to correspond to empirical findings known from general literature. In addition the mechanism of colloidal silicone dioxide action to improve flowability was suggested and the hypothesis was confirmed by independent test. New findings represent a progress towards future application of determining the optimum concentration of glidant from the basic characteristics of the powder in the pharmaceutical research and development. [ABSTRACT FROM AUTHOR]

Abstract: The search for various solid forms of an active pharmaceutical ingredient (API) is an important step in drug development. Our aim was to prepare co-crystals of trospium chloride, an anticholinergic drug used for the treatment of incontinence, and to investigate if they have advantageous properties for drug formulation. Phase identification was done by powder X-ray diffraction and single-crystal X-ray diffraction. The chemical composition was verified by solution NMR and the dissolution rate of the prepared phases was studied by IDR (intrinsic dissolution rate). For further analysis of phase stability and transitions, combined thermal analysis and temperature-resolved X-ray powder diffraction were used. Urea was selected as a co-crystallization partner. Trospium chloride urea (1:1) co-crystal was prepared by a solvent evaporation. From single-crystal data, the co-crystal structure was solved in a space group P21 /c and compared to previously published structures of trospium chloride. Intrinsic dissolution rate revealed that the co-crystal dissolves 32% faster than pure API. However, its low thermal and pressure stability makes it a challenging choice for the final drug formulation. [Copyright &y& Elsevier]

Abstract: Petroleum fractions are typical complex mixtures. For the simulation of petroleum refining processes they are characterized by substitute mixtures. In this contribution the traditional approach based on pseudocomponents is compared with the newer approach utilizing a Substitute Mixtures of Real Components (SMRCs). The main advantage of SMRC approach is the direct availability of physical property data and the knowledge of the chemical character. The most important task in many applications is to characterize the C7+ fraction. It is shown, how it can be characterized by a small number of real components. The examples used for comparison comprise separation processes and also the pyrolysis modeling, where the known chemical character of a SMRC is crucial for feeding an artificial neural network model. [Copyright &y& Elsevier]

Abstract: Processing of atmospheric gas oils (AGOs) in the petroleum industry by pyrolysis is an important task. In order to improve control of production and to predict the pyrolysis product yields, it is necessary to use novel approaches. The combination of selected analytical as well as modelling methods described in this contribution seems to be very promising and usable also for other types of pyrolysis feedstocks. Employment of an artificial neural network (ANN) model as the prediction tool is the crucial point. The main problem is the treatment of complex mixtures. While analytical methods used here give the picture of global characteristics and group composition, the method used to characterise the complex mixture by a well-defined substitute mixture of real components provides the input information for the ANN model. Unfortunately, the required measured data, typically distillation and other curves, are often incomplete and it is impossible to obtain directly the ‘phase portraits’ needed to establish the substitute mixture. Possibilities of how to solve this particular problem utilising other information about the mixture, e.g. bulk properties, are shown and applied to concrete AGO feedstocks with satisfactory results. [Copyright &y& Elsevier]

[Display omitted] • Co-milling of drugs having different glass forming ability with suitable co-formers. • Characterization of dissolution properties of physical and co-milled mixtures. • Solid state characterization of prepared mixtures. • The proper choice of excipient is the key to maximizing the dissolution rates. • The glass forming ability of the drug affects the properties of composite particles. Co-milling of a drug with a co-former is an efficient technique to improve the solubility of drugs. Besides the particle size reduction, the co-milling process induces a structural disorder and the creation of amorphous regions. The extent of drug solubility enhancement is dependent on the proper choice of co-milling co-former. The aim of this work was to compare the effects of different co-formers (meglumine and polyvinylpyrrolidone) on the dissolution rates of glass forming (indomethacin) and non-glass forming (mefenamic acid) model drugs. A positive impact of the co-milling on the dissolution behavior was observed in all co-milled mixtures, even if no substantial amorphization was observed. While meglumine exhibited pronounced effects on the dissolution rate of both drugs, the slightest enhancement was observed in mixtures with polyvinylpyrrolidone. The evaluation of specific release rate revealed the surface activation of drug particle is responsible for improving the dissolution rate of both drug types, but for the glass former, this surface activation could be persistent while maintaining a high dissolution rate even until a high fraction of drug is released. Our results, therefore, indicate that adequate co-former choice and consideration of drug glass forming ability are important for a successful co-milling approach to poorly water-soluble drugs. [ABSTRACT FROM AUTHOR]