iGC Symposium Online 2021

Speaker: Alina Dumitru, Imperial College London Abstract: Achieving optimal powder flow in pharmaceutical powder processing is often a challenge due to handling fine, cohesive excipients and APIs (Valverde, et al. 2000). Generally, poor flow behaviour is encountered with small particles due to the strong interparticle interactions associated with such systems (Zhou, et al. 2011). Although particle size contributes greatly to explaining powder flow patterns, it is thought that surface chemistry can play a significant role in underpinning powder flow behaviour for many formulations in the pharmaceutical sector. This study was designed to systematically focus on the effects of surface chemistry, and in turn surface energy, on the powder flow performance of four model systems prepared through controlled surface functionalisation of D-mannitol powders. IGC was used as a physical characterisation method to assess the surface energy and thus chemical alterations undertaken on D-mannitol, as well as the surface area. Powder flow performance was assessed using the FT4 Powder Rheometer, where dynamic, bulk and shear properties have been analysed. It was found that the surface chemistry can be responsible for altering the flow properties of these powders, whilst other key material attributes such as particle size distribution or particle morphology remain unchanged. Increasing the hydrophobic character of the samples, a positive correlation was observed in the total flowability energy, where less energy was required to instigate powder flow for lower surface energy functionalisations, such as phenylated-mannitol and methylated-mannitol. A key finding which can surely present broader implications for many pharmaceutical powders was seen with the fluorinated powders developed, where the electrostatic charge associated with this superhydrophobic sample, overwhelmed the low surface energy character of the fluorinated sample. This work emphasises the importance of investigating a broader range of powder surface chemistries as well as developing a deeper understanding of the electrostatic behaviour of powders which have fluorinated surface groups.

Speaker: Dr. Maria Holuszko, University of British Columbia Flotation is the main concentration process for recovery of valuable minerals, and it has been successfully applied for more than hundred years in mining industry. In simple terms, in froth flotation mineral particles are made hydrophobic by adsorption of chemical reagents referred to as collectors then the hydrophobic minerals are attached to the air bubble and carried over to the top of the flotation cell to be collected as a concentrate. In flotation, many interfacial interactions occur between gas/liquid/solid (mineral) surface molecules. The interfacial behavior of minerals is controlled by the surface energy of the mineral (solid). The wetting process occurs when the adhesion force between a solid-mineral and liquid is greater than the cohesion force between the liquid’s molecules while non-wetting (hydrophobicity) condition is required for flotation (Leja, 1983). Many methods have been developed to study the wetting characteristics of minerals relevant to flotation. Some of these methods include contact angle, film flotation, displacement pressure, and penetration rate, heat of immersion, immersion/sink time, imbibition time, and induction time measurements of fine powders (Buckton, 1990; Good and Li, 1976; Arkhipov et.al.2011). However, there are many limitations to each of the methods, and in all of these methods physical properties of particles like size, shape affect the final results, while surface energy of solids can provide good means for evaluation of degree of hydrophobicity for particulate solids. In addition, IGC system was shown to be successfully used to map the surface energy of mineral particles and provide parameters to evaluate their wettability independently of minerals’ physical characteristics. It has been shown that the surface energy distribution i.e.  the distribution of dispersive and acid/base surface energy components can be used for correlation with the addition of reagents and response of minerals in flotation (Ali et al. 2013; Mohammedi-Jam et al., (2014). In addition, the hydrophilicity index can be derived to assess the surface properties of heterogeneous minerals systems such as coal (Niu et al., 2018). Froth flotation has also been used to recover various types of plastic from their mixtures (Wang et al., 2013; Wang et al., 2015. Plastic flotation is usually used for selective separation for the purpose of reuse or to obtain a pure quality product (Fraunholcz, 2004; Shent et al., 1999). In mineral flotation, the challenge is typically in making the minerals’ surfaces selectively hydrophobic. While in plastic flotation the opposite is true, since most of the plastic polymers are highly hydrophobic, plastic surfaces need to be made selectively wettable-hydrophilic if an efficient separation of different plastics is required. In plastic flotation, a variety of depressants are usually studied to facilitate selective bubble-particle attachment while exploiting differences between surface energy of various plastic polymers for achieving selectivity (Buchan, R., & Yarar, B. (1995). The attempts are also made to investigate the mechanisms of their adsorption on different plastics and the IGC can be used to facilitate development of such understanding. The presentation will review practical application of IGC in flotation as applicable to mineral processing as well as in flotation of plastic and non-metal fractions from e-waste recycling streams.

Speaker: Dr. Kristian Waters, McGill University

... Heat of Sorption Derived Solubility Parameter Speaker: Dr. Anett Kondor, Surface Measurement Systems Inverse gas chromatography (IGC) is a rapid technique to determine thermodynamic parameters of gas–solid interactions and to characterize physicochemical properties of solid substrates. IGC offers its applicability where it is difficult and even impossible to characterize the surface of some forms of solids (powders and grains) by means of other popular techniques as wetting method or FTIR. Actually, the solids and liquids in every form can be easily studied by means of IGC [1]. High Temperture Measurements Adsorption isotherm data of some alkyl aromatic hydrocarbons (benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene) measured in the temperature range of 423–523 K on a partially dealuminated faujasite type DAY F20 zeolite by inverse gas chromatography. The temperature dependent form of Tóth’s equation has been fitted to the multiple temperature adsorption isotherms. The gas–solid equilibria and modelling were interpreted on the basis of the interfacial properties of the zeolite, by dispersive, specific and total surface energy heterogeneity profiles and distributions of the adsorbent measured by surface energy analysis. Solibility Parameter Analysis Determination of solubility parameter for solid materials by means of inverse gas chromatography is based on the model of adsorption described by Snyder and Karger and requires the knowledge of value of adsorption energy (EA) or Heat of Sorption determined from temperature dependence of specific retention volume [1]. References [1] A. Voelkel et al., Inverse gas chromatography as a source of physiochemical data, Journal of Chromatography A., 1216 (2009)