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Nucleation kinetics of high linoleic and high oleic polyunsaturated fatty acid (PUFA) mixtures were investigated during melt crystallization by means of an Focused beam reflectance measurement (FBRM) sensor. Samples were analyzed thermally and chemically in the Differential Scanning Calorimeter (DSC) and Gas Chromatograph (GC) respectively. Investigations showed that a high oleic content in the PUFA mixtures lead to higher induction times, τi. Unlike previous investigations, a clear relation between τi and cooling rates was established. τi increases with increasing cooling rates and decreasing supercooling. Activation energies of nucleation, ∆Gc' were determined by means of the Fisher Turnbull equation wherein ∆Gc' decreases exponentially with increasing supercooling. Investigations and further evaluations conclude that while the plot establishes the effect of supercooling on ∆Gc' , it does not incorporate the effects of molecular diffusion or the cooling rate. Hence, 3D modeling was performed to visualize the combined effects of cooling rate and supercooling on induction time.
Characterisation and materials flow management for WEEE plastics from German dismantling centres
(2015)
Enriched plant based unsaturated fatty acid mixtures are increasingly finding applications in various fields like those of production of bio-fuels and polymerization of epoxy resins. In the case of production of epoxy resins, they are highly advantageous due to the presence of multiple double bonds in the fatty acids which provide opportunities for cross linking by substitution. On the other hand, bio-fuels need raw materials with very low crystallization temperatures. This special property can also be attributed to these enriched unsaturated fractions due to their weak inter-molecular interactions owing to the kink in their structures.
Melt crystallization has long been established as an optimal method for purification and enrichment of fractions from mixtures [1,2]. Previous studies have shown promising results with regard to enrichment of unsaturated fractions by melt crystallization processes [1]. Melt crystallization kinetics of two plant based poly-unsaturated fatty acid mixtures have been investigated in this study [3]. A high oleic and a high linoleic fatty acid mixture were chosen for comparison purposes. A V-form reactor was developed for optimal in-situ analysis with the help of the focused beam reflectance measurement (FBRM®, Mettler Toledo Ltd., Switzerland) instrument [3]. Enhanced heat transfer especially to deal with the heat given out during crystallization was enabled through minimal volume of sample, optimized mixing and the special shape of the reactor. Important parameters like induction time, mixing speed, etc have been determined and compared as functions of degree of supercooling and composition of PUFA mixtures. In accordance to theory, the induction times in both the cases decreased with increasing supercooling and mixer speed. On the other hand, the high linoleic fatty acid mixture required much higher supercooling (4.4K to 5.4K) than the high oleic mixture (2.2K to 3.2K) for favorable induction times.
References
[1] S. Dasgupta, N. Dreiack, P. Ay, presented at the 5th Workshop on Fats and Oils as Renewable Feedstock for the Chemical Industry (Eds: J.O. Metzger, M.A.R. Meier), Karlsruhe 2012
[2] G.F. Arkenbout, Melt Crystallization Technology, Technomic Publishing Company Inc., Pennsylvania 1995
[3] S. Xu, Master thesis, Chair of Mineral Processing, Processing of Biogenous Resources, Brandenburg University of Technology, Cottbus 2010
Enriched plant based unsaturated fatty acid mixtures are increasingly finding applications in various fields like those of production of bio-fuels and polymerization of epoxy resins. In the case of production of epoxy resins, they are highly advantageous due to the presence of multiple double bonds in the fatty acids which provide opportunities for cross linking by substitution. On the other hand, bio-fuels need raw materials with very low crystallization temperatures. This special property can also be attributed to these enriched unsaturated fractions due to their weak inter-molecular interactions owing to the kink in their structures.
Melt crystallization has long been established as an optimal method for purification and enrichment of fractions from mixtures [1,2]. Previous studies have shown promising results with regard to enrichment of unsaturated fractions by melt crystallization processes [1]. Melt crystallization kinetics of two plant based poly-unsaturated fatty acid mixtures have been investigated in this study [3]. A high oleic and a high linoleic fatty acid mixture were chosen for comparison purposes. A V-form reactor was developed for optimal in-situ analysis with the help of the focused beam reflectance measurement (FBRM®, Mettler Toledo Ltd., Switzerland) instrument [3]. Enhanced heat transfer especially to deal with the heat given out during crystallization was enabled through minimal volume of sample, optimized mixing and the special shape of the reactor. Important parameters like induction time, mixing speed, etc have been determined and compared as functions of degree of supercooling and composition of PUFA mixtures. In accordance to theory, the induction times in both the cases decreased with increasing supercooling and mixer speed. On the other hand, the high linoleic fatty acid mixture required much higher supercooling (4.4K to 5.4K) than the high oleic mixture (2.2K to 3.2K) for favorable induction times.
The rising applications of enriched unsaturated fatty acid fractions are significantly increasing the need for a cheap method of manufacturing such fractions. Melt crystallization is an established method for purification and enrichment of desired fractions from mixtures [1, 2, 3]. Enrichment of such natural unsaturated fractions by melt crystallization processes has already been proved effective in prior investigations [1, 2]. Since then many analytical and investigative methods have been applied on various natural plant oil based poly-unsaturated fatty acid (PUFA) mixtures to generate the much needed fundamental melt crystallization data [1]. One such method is the use of in-situ polarized light microscopy [1, 4, 5]. Some of the important parameters affecting the melt crystallization of PUFA mixtures are nucleation and crystal growth rate. To be able to observe and visualize these micro-scale phenomena, circular polarized transmitted light microscopy was applied. A tempered chamber (Linkam LS 120) containing the sample between two object slides was placed right within the microscope camera setup (Leica DM RME and Leica DFC 500) with a viewing window. With respect to the transmitted light, the sample was placed between two circular polarized filters such that the system is calibrated for optimal visualization. Unlike linear polarization, in this method every crystal independent of its alignment in the sample, delivers an interference color different from its background. This way, the entire crystal structure could be clearly separated from the melt. Nucleation and crystal growth rate of a high oleic sunflower oil based PUFA was measured using this method at 5K supercooling and 10K/min cooling rate. Growth curves for total crystal area and number of crystals were analyzed and illustrated graphically. A typical S- curve is observed for both the cases starting with a lag phase followed by an exponential growth phase and ending in a saturation phase.
Enrichment of natural unsaturated fractions by melt crystallization processes has already been proved to be effective in prior investigations [1]–[3]. Palmitic, stearic, oleic, linoleic and linolenic acid are the five main fatty acids present in most of these plant based natural oils. There is quite a bit of information about the liquid solid phase behavior of binary mixtures such as palmitic-oleic, stearic-oleic and palmitic-stearic acid mixtures in literature [4]–[6]. Recent investigations have shown phase diagrams of real natural oil based fatty acid systems containing up to 19% saturated content (11% stearic acid and 8% palmitic acid) [7]. Yet, there is hardly any information regarding ternary systems as those of palmitic-stearic-oleic and palmitic-stearic-linoleic acids.
In this work, synthetic mixtures have been used in order to obtain a complete overview of the liquid solid phase diagrams of these ternary mixtures. To imitate naturally occurring mixtures, a mixture with 1:1 ratio of palmitic stearic acid was prepared. Varying amounts of either oleic or linoleic acids were added to this mixture in order to obtain the entire range required for the phase diagrams. These mixtures were then subjected to a specific profile with a wide temperature range in a Differential Scanning Calorimeter (DSC) so as to record every phase transition.
This study successfully concludes that these complex mixtures could be treated as binary mixtures of their saturated and unsaturated contents. This is because there were essentially two main peaks noted in the DSC thermograms. It is to be noted that there was a third peak, assumed to represent the solid transition, in mixtures containing oleic acid. This has already been shown in detail and discussed in prior investigations [6], [7]. Another major discovery was that the solidus line depends on the type of the unsaturated content, that is, the degree of unsaturation, in the mixture.
Important parameters like supercooling and cooling rates affecting the melt crys- tallization of a polyunsaturated fatty acid (PUFA) mixture obtained from sun- flower oil were investigated and compared via high-resolution polarized-light mi- croscopy. PUFA was thermally characterized in a differential scanning calorimeter and the significant liquid-solid-phase transition temperatures determined were then implemented in the development of specific temperature profiles. Analyzed between two glass slides, induction times were found to decrease with low crystal- lization temperatures and the number of nuclei per unit area increased with high- er supercooling and cooling rates. A comparison between the linear crystal growth rates of pure standards of each of the main fatty acids present in the PUFA mixture and the PUFA mixture itself indicated that the latter is much slower than that of each of its pure components.
Multistage melt crystallization of a variety of plant-based polyunsaturated fatty acid (PUFA) mixtures was conducted to obtain an overview on their liquid-solid equilibrium behavior. Crystal fraction and mother liquor samples were analyzed at every stage. Phase behavior diagrams at low saturated fatty acid concentrations were investigated in detail as they are of significant technical relevance with respect to efficient depletion of the saturated content from the samples. A high oleic acid content in the PUFA mixtures led to difficulties in depleting the mother liquor from the saturated content by melt crystallization. Thermograms from the differential scanning calorimetry were supplemented with illustrations which allow a novel interpretation of results and verification of conclusions.
Waste electrical and electronic equipment is a complex waste stream and treatment options that work for one waste category or product may not be appropriate for others. A comprehensive case study has been performed for plastic-rich fractions that are treated in German dismantling centres. Plastics from TVs, monitors and printers and small household appliances have been characterised extensively. Based on the characterisation results, state-of-the-art treatment technologies have been combined to design an optimised recycling and upgrade process for each input fraction. High-impact polystyrene from TV casings that complies with the European directive on the restriction of hazardous substances (RoHS) was produced by applying continuous density separation with yields of about 60%. Valuable acrylonitrile butadiene styrene/ polycarbonate can be extracted from monitor and printer casings by near-
infrared-based sorting. Polyolefins and/or a halogen-free fraction of mixed styrenics can be sorted out by density separation from monitors and printers and small household appliances. Emerging separation technologies are discussed to improve recycling results.
Removal of dyes from effluents by chemical coagulation: Surface charge and particle size aspects
(2003)