Viscosity Behavior of Foamy Oil: Experimental Study and Modeling

Abstract

Heavy oil cold production is faced with the foamy oil phenomenon: while extracted, a heavy crude oil is submitted to a depletion that can induce the formation of dispersed gas bubbles and makes it appear as a foam. This situation results in a change of the flow properties of the live oil that is still debated: correlations predict a decrease or an increase in the gas bubble-dispersed oil viscosity with the gas volume fraction. We attempted to improve the understanding of the foamy oil behavior through rheological measurements. A live oil was depleted inside the pressure cell of a controlled stress rheometer. The occurrence of bubbles was checked and visualized with x-ray scanning experiments. Viscosity was continuously measured using oscillatory and continuous tests. This particular experimental approach allowed us to successfully study the rheological behavior of a foamy oil in relationship with the two main parameters, which are the composition and the viscosity of the crude oils. A theoretical model describing the viscosity of a foamy oil has been established. It takes into account both first-order kinetics of appearance and release of bubbles in oil and a basic suspension model. Results from this model are in agreement with experimental data obtained from different heavy crude oils.     

Viscosity of Concentrated Emulsions: Relative Effect of Granulometry and Multiphase Morphology

Abstract

High viscosity and high density make heavy and extra heavy crude oils very difficult to produce. They cannot be pumped in their natural state and advanced technologies are required. Formation of oil-in-water emulsions is one of them. A typical emulsion contains 65% of dispersed phase and has a viscosity lower than 500 mPa.s. Current research is aimed at increasing the crude oil content at reduced costs with still good stability and low viscosity. Consequently, an experimental study was dedicated to the relationship between the structure and the rheological properties of heavy oil emulsions. Particular attention was paid to process parameters employed to prepare emulsions. Depending on the shear device, various emulsions have been obtained, either simple or multiple, monodisperse or bimodal. The resulting viscosity is discussed. It is particularly low when the emulsion is either coarse and unimodal or fine and simple. The highest viscosity is obtained when the emulsion is fine and multiple. The experimental results confirm that both composition variables and process parameters have to be taken into account to minimize viscosity of heavy oil emulsions.     

Biological variability in lignification of maize: Expression of the brown midrib bm3 mutation in three maize cultivars

Cell wall-linked phenolics were investigated in maize internodes located at three positions of the stem (top-middle-bottom). While the lignin content did not change drastically with position, the amount of cell wall-ester linked p-coumaric acid sharply increased from the top to the bottom internodes of the stem. Conversely, the saponified ferulic acid content remained relatively unchanged along the stem. Moreover, the highest syringyl content of the β-O-4-lignin structures was found in the basal (most mature) internode. Therefore, enhanced p-coumaric esterification of the cell wall and preferential deposition of syringyl units in the lignin polymer might indicate an extended maturity stage of the cell wall of maize internodes. The bm3 mutation in the three maize hybrids is expressed by lignin reduction and ester-bound p-coumaric decrease in the mutant lines. Furthermore, all bm3 hybrids synthesised lignin polymers which were characterised by a very low S/G molar ratio (0.16-0.43). This ratio originates from the substantial reduction of the syringyl unit content in β-O-4-lignin structures compared with the normal lignin. The occurrence in the same range of the 5-hydroxyguaiacyl unit in bm3 lignin from each type of hybrids was noteworthy, demonstrating the high heritability of the bm3 mutation at the molecular level. The alkaline solubility of lignin was greater for the three mutant lines compared to the normal cultivars. Furthermore, the alkali-labile fraction of lignin of both normal and mutant lines had a monomeric composition which was consistent with the non-condensed structures of in-situ lignin.     

Biological variability in lignification of maize: Expression of the brown midrib bm2 mutation

The cell wall phenolic components in the internodes of three maize genotypes, namely normal, bm2 and bm3 maize, were determined. The bm2 and bm3 brown midrib mutations lowered the lignin content of the bottom, middle and top internodes to a similar extent. However, unlike bm3, the bm2 trait did not induce a sharp reduction of the level of ester-bound p-coumaric acid in maize internodes. The other main alkali labile phenolic acid, ferulic acid, reached similar levels in the three genotypes. The main difference between bm2 and bm3 mutations occurred in the alkyl aryl ether linked structures of the lignin component. In contrast to bm3 lignins, which are characterised by a low syringyl content, the bm2 lignin had a lower content of guaiacyl units than lignin of normal maize internode. Consequently, the syringyl/guaiacyl molar ratio of bm2 lignin gave higher values (2.7–3.2) than those from either normal (0.9–1.5) or bm3 lignins (0.3). The alkali solubility of lignin was also compared between the three genotypes. Incorporation of the bm3 trait in maize led to a high recovery of alkali soluble lignin whereas the bm2 lignin had a similar solubility to the normal one in 2 M NaOH. The monomeric composition of the alkali soluble lignins was consistent with the non-condensed structures of the in-situ polymer. Although the bm3 and bm2 mutations had different effects on lignification, the modification of the cell wall phenolic level was also found in the bm2 maize stem as previously studied.     

Relationship of cell wall composition to in vitro cell wall digestibility of maize inbred line stems

The phenolic equipment of maize stem tissues was investigated in relation to the feeding value of the detergent fibre components. Sixteen maize inbred lines, including three brown‐midrib 3 mutants and their normal counterparts, were selected for highly divergent in vitro cell wall digestibility. These lines were grown during two years. Maize stems were analysed for detergent fibre concentration, esterified and etherified p‐hydroxycinnamic acids, lignin content and structure and in vitro digestibility. A large genotypic variation was found for neutral detergent fibre, cell wall phenolic composition and cell wall digestibility. Within the normal maize lines the in vitro neutral detergent fibre digestibility (IVNDFD) of stem fractions was negatively correlated with their Klason lignin content. A multiple regression model based on esterified p‐coumaric acid and lignin composition as two explanatory variates accounted for 58% of the IVNDFD variation. In this study, three normal maize inbred lines displaying a lignin content and a cell wall digestibility level close to those observed in the three bm3 lines could be detected, which opens up new breeding avenues. © 2000 Society of Chemical Industry     

Hydrogels Based on Pullulan Crosslinked with sodium trimetaphosphate (STMP): Rheological study

Summary Hydrogels from pullulan crosslinked with sodium trimetaphosphate (STMP) under alkaline condition have been investigated by rheological measurements. The influence of reagents concentration (pullulan, STMP, NaOH) on kinetics of reaction and rheological properties is reported. Increasing concentrations of any reagents lead to an increase of the crosslinking kinetics. Increasing the polymer concentration leads to a stronger gel whereas an increase of crosslinking reagent (STMP) evidences a critical concentration above which the rheological properties of the gel do not change anymore. This may be explained by the specificity of the system for which the polymer concentration is high and negative charges appear.