Freezing Within Emulsions: Theoretical Aspects and Engineering Applications

Abstract

Re´sume´-Conge´lation dans les e´mulsions : aspects the´oriques et applications techniques -Cet article se concentre principalement sur le comportement a`la conge´lation des e´mulsions qui sont conside´re´es soit comme des syste`mes permettant d'obtenir des informations sur les mate´riaux en surfusion, soit comme des syste`mes disperse´s complexes implique´s dans les proce´de´s industriels. En raison du fait qu'il existe une phase disperse´e sous forme de fines gouttelettes dans les e´mulsions, des retards a`la solidification sont observe´s et les gouttelettes de liquide persistent meˆme en dessous du point de fusion du mate´riau. La corre´lation entre la tempe´rature de solidification des gouttelettes et leur taille peut eˆtre donc utilise´e pour suivre l'e´volution de la morphologie de l'e´mulsion en fonction du temps aussi bien sur terre que dans des conditions de microgravite´(projet FASES soutenu par l'ESA). Une description de ces phe´nome`nes observe´s principalement par microcalorime´trie sera donne´e pour des corps purs disperse´s ainsi que pour des solutions disperse´es. Dans certains cas, les e´mulsions peuvent eˆtre recherche´es pour leurs proprie´te´s spe´cifiques, telles que la grande taille de l'interface huile/eau, conduisant a`des transferts de masse ame´liore´s; les e´mulsions peuvent eˆtre par conse´quent utilise´es comme des membranes liquides pour l'extraction, le stockage et la libe´ration controˆle´e de matie`res actives. Dans d'autres cas, la formation d'e´mulsions a un effet ne´faste sur les proce´de´s, comme dans l'industrie pe´trolie`re ou`des e´mulsions eau-dans-pe´trole tre`s stables se forment facilement et compliquent l'ope´ration de de´shydratation du pe´trole brut.Abstract -Freezing Within Emulsions: Theoretical Aspects and Engineering Applications -This article is mainly focused on the freezing behaviour of emulsions which will be considered either as systems permitting to get information about undercooled materials or as complex dispersed systems involved in industrial processes. Due to the fact that there exists a phase dispersed as tiny droplets in emulsions, solidification delays are observed and liquid droplets are still observed under the melting points of pure materials. The correlation between the solidification temperature of the droplets and their size may be therefore used to follow the evolution of the emulsion morphology versus time on ground as in microgravity conditions (FASES project supported by ESA). A description of these phenomena mainly observed through microcalorimetry experiments will be given for dispersed pure materials as for dispersed solutions. In some cases, emulsions may be sought after for their specific properties, such as their large oil/ water interface, leading to enhanced mass transfers; emulsions may be consequently used as liquid membranes for extraction, storage and controlled release of active materials. In other cases, the formation of emulsions has a detrimental effect on the process. It is the case in the oil industry where very stable w...

Droplet Crystallization in Water-in-Crude Oil Emulsions: Influence of Salinity and Droplet Size

“…The crystallization temperature of water droplets depends strongly on droplet size. Larger water droplets exhibit higher crystallization temperatures, according to Clausse et al 24,25 , who ascertained theoretical and empirical correlations confirming that droplet size increases exponentially with peak crystallization temperature, based on an assumption of homogeneous nucleation and instantaneous freezing of a droplet upon nucleus formation. Amplification is 50X.…”

“…3 located between -40 and -46 °C is associated with the normal highest crystallization temperature of pure water 20,21,22 . As shown in series of base contributions 19,20,24,25 , the presence of bulk phase in the emulsion will give a signal at a temperature higher than the one obtained for dispersed material. Freezing point of bulk water is around -20 ºC and -35÷-45 ºC for dispersed water.…”

“…where ̇ is the scanning rate (К•s -1 ); Ais the pre exponential factor in the expression of the nucleation rate, (s -1 •m -3 ); K is the Boltzmann constant (N•m•К -1 ); γ is the interfacial tension between water and the ice nuclei (N•m -1 ); V iis the molar volume of the germ (m 3 •mole -1 ); L mis the molar melting heat (N•m•mole -1 ); and T m is a melting temperature 25 .…”

From interface towards organised network: Questioning the role of the droplets arrangements in macroscopically stable O/W emulsions composed of a conventional non-ionic surfactant, TiO2 particles, or their mixture

“…Till today, the emulsions thermal properties were studied in some specific cases, like in crude oil case (water in oil emulsion) [46] or in the food industry (oil in water emulsion) [47].…”

Characterization of Complex Crude Oil Microemulsions-DSC Contribution

“…The objective was to be able to address the case of more complex systems such as the one including real oils and formulations of surfactants, which is of prime importance to chemical EOR, especially surfactant flooding. Among the different techniques that can be applied to investigate complex dispersed systems as emulsions or microemulsions, DSC appears as a technique that can be used for physico-chemical characterization as well as for morphological studies [17,[19][20][21][22][23][24]. In this paper, we will show how DSC can be advantageously used in addition to other classical techniques to investigate complex microemulsions made of real crude oil and representative EOR formulations of surfactants.…”