Glycerol-rich Phase Research Articles

Phase transition at subcritical and supercritical conditions of triglycerides methanolysis

The analysis of phase equilibrium between methanol and glycerides during methyl esters of fatty acids (FAME or biodiesel) synthesis at high pressure and temperature is very important for describing the kinetic and process design. It was studied at pressure between 1.1 and 28.0 MPa and temperature from 150 to 270 °C. The transition of phases and composition of identified phases was calculated using RK-Aspen EOS and obtained values were also compared to experimentally determined data at subcritical condition (1.1–4.5 MPa and 150–210 °C). Results of experimental investigation, as well as performed simulation of some specified composition of reaction mixture, showed that system of triglycerides and methanol, at the beginning of reaction (at all analysed conditions except for supercritical state of mixture) is in equilibrium between two liquid phases. During the methanolysis of triglycerides, the phase's distribution was changed accordingly and it highly depends on actual composition of reaction mixture, temperature and pressure. Calculated and measured values indicated that distribution of methanol between the oil phase, the methyl esters, and the glycerol rich phase exists and depends of working condition. As a consequence of fact, that the methanolysis of triglycerides (oil) is mainly realized in the oil-rich phase, at the end of reaction, after all triglycerides are converted into FAME and glycerol, the oil phase disappears. Furthermore, according to the results of phase composition calculation, it was shown that from the beginning to the end of reaction one phase only exists, for methanolysis performed at 270 °C and 20.0 MPa.

Low-temperature heat capacity of a two-dimensionally ordered structure of ice crystallized from glycerol aqueous solutions

A two-dimensionally ordered structure of ice crystallized from a glycerol 55% (w/w) aqueous matrix has been studied by adiabatic calorimetry. Its heat capacity was measured between T = 5 K and T = 15 K and found to be consistently larger than that of hexagonal ice (ice Ih) by an average of 1.3%. The composition and the heat capacity of the maximally freeze-concentrated solution, i.e. the non-crystallizing glycerol-rich phase that remains after water's partial crystallization, were also investigated.

Interface/morphology relationships in polymer blends with thermoplastic starch

In this paper, the interface/morphology relationship in polyethylene/TPS blends prepared by a one-step extrusion process is examined in detail. Emulsification curves tracking the change in phase size with added quantity of PE-g-MA copolymer are used to identify the critical concentration required for saturation of the interface as well as to estimate the areal density of grafted copolymer chains at the interface. The level of glycerol content in the TPS is shown to lead to different emulsification behaviors. Dynamic mechanical analysis clearly shows a partial miscibility between glycerol and starch in the TPS with glycerol-rich and starch-rich peaks being clearly identified. This phase separation is more evident in the case of high glycerol levels in the TPS (>24% glycerol). Furthermore, the glycerol-rich peak decreases in intensity with added PE-g-MA graft copolymer. At high glycerol contents (>24% glycerol) in the TPS, a 20% thermoplastic starch-based binary blend with polyethylene can reach an elongation at break value as high as 200%. When also modified at the appropriate level with a PE-g-MA copolymer, this elongation at break further increases to 600%. However, at lower glycerol contents, the elongation at break is comparatively low at 20–50% even after the addition of PE-g-MA copolymer. We explain these results through a proposed double mechanism of interfacial modification between the HDPE matrix and the TPS dispersed phase. Under dynamic melt-mixing conditions, it is suggested that a small portion of the low molecular weight glycerol-rich phase tends to migrate to the HDPE-TPS interface as predicted by Harkins spreading theory. Once at the interface, this glycerol-rich outer layer is readily deformed by an applied stress and this stress is then transferred to the starch-rich phase due to their mutual partial miscibility. Added PE-g-MA copolymer initially reacts with the glycerol-rich outer layer but if the level of copolymer is high enough, it then reacts with the starch-rich phase via a classic interfacial modification protocol. Also, both the elongation at break and impact properties dramatically increase at a copolymer level associated with interfacial saturation. The above mechanism effectively explains all the emulsification and mechanical property observations.

A comparison between the physico-chemical properties of tuber and cereal starches

Biofilms based on waxy maize and cassava starches (cereal and tuber starch, respectively), plasticized with glycerol were characterized through their crystallinity, dynamic-mechanical behavior (DMA), thermal degradation (TGA), moisture content and water vapor permeability (WVP). X-ray diffraction experiments show that both materials were mainly amorphous, with the waxy starch presenting a discreetly A-type X-ray pattern. Microscopic investigation of the cryo-fractured surfaces supported this observation. The glass transition of the glycerol-rich phase (measured by DMA) occurs at higher temperatures for cassava than for waxy maize starch, suggesting that the dispersion level of glycerol is higher in the former. TGA showed that maize starch has a slightly higher thermal stability than cassava starch, while glycerol interacts more strongly with the last one. The WVP was 18% higher in the case of the cassava starch film.

Starch-vegetable fibre composites to protect food products

The influence of wheat bran content in biodegradable composites based on cassava starch and containing glycerol and potassium sorbate were studied. Films were produced by casting and three different fractions of wheat bran fibre were used: 1.5 mg, 13.5 mg and 27.1 mg/g of matrix. It was observed that the addition of wheat bran, which contains 40 g of water insoluble fibre per 100 g of bran, shifted the glycerol-rich phase glass transition temperature toward higher temperatures, broadening and diminishing in intensity the peak associated with this relaxation. This effect suggests that the presence of fibre led to an enhancement in the glycerol dispersion. At room temperature, an increase in fibre content did not affect density of the matrix but caused the increase of the storage modulus and the decrease of loss tangent, moisture content and water vapor permeability. Besides, the addition of fibres led to the increase of the yellow index. The improvement in water vapor barrier properties jointly with the enhancement of mechanical properties when fibre was present, lead to the idea that the composite developed can be used to protect food and extend its shelf life.

Physical characterization of cassava starch biofilms with special reference to dynamic mechanical properties at low temperatures

Biofilms based on cassava starch and containing glycerol as a plasticizer were characterized with respect to the effect of potassium sorbate concentration and pH on color, crystallinity and mechanical performance al low temperature. It could be observed that a lower pH resulted in lower values of yellow index and tan δ and higher crystallinities. Crystallinity decreased with sorbate addition, which also resulted, in general, an increase in yellow index and moisture content and a decrease of storage modulus for temperatures higher than the glycerol glass transition. Increase in sorbate content displaced the glass transition temperature of a glycerol-rich phase toward lower temperatures and increased the difference between the value that E′ took in the glassy region and the value that it took in the rubbery region. It is concluded that the physical properties of edible films can be affected by the antimicrobial agent, sorbate potentially compromising biofilm performance.

Starch films reinforced with mineral clay

A mineral clay was used as filler in order to improve the mechanical properties of glycerol-plasticized Cará starch films. These were characterized by mechanical and dynamic mechanical analysis, X-ray diffraction (XRD), thermogravimetry, infrared spectroscopy, and scanning electron microscopy. Dynamic mechanical analyses showed that the composite films give rise to three relaxation processes, attributable to a transition of the glassy state of the glycerol-rich phase, to water loss including the interlayer water from the clay structure, and to the starch-rich phase. A film obtained with 30% in w/w of clay showed an increase of more than 70% in the Young modulus compared to non-reinforced plasticized starch. Both XRD and infrared spectroscopy showed that glycerol can be intercalated into the clay galleries and that there is a possible conformational change of starch in the plasticized starch/clay composite films. Clay exfoliation occurred in unplasticized starch/clay mixtures.

96/05858 Intermolecular interactions for hydrocarbons on Wyodak coal

A re-evaluation of kinetic data shows that the methoxide base-catalyzed methanolysis of soybean oil at 40°C (6:1 methanol:oil molar ratio) to form methyl esters proceeds approximately 15 times more slowly than butanolysis at 30°C. This is interpreted to be the result of a two-phase reaction in which methanolysis occurs only in the methanol phase. Low oil concentration in methanol causes the slow reaction rate; a slow dissolving rate of the oil in the methanol causes an initiation period. Intermediate mono- and diglycerides preferentially remain in the methanol, and react further, thus explaining the deviation from second-order kinetics. The same explanations apply for hydroxide ion catalyzed methanolysis.At the 6:1 methanol:oil molar ratio the addition of a cosolvent, such as 1.25 volumes of tetrahydrofuran (THF) per volume of methanol, produces an oil-dominant one-phase system in which methanolysis speeds up dramatically and occurs as fast as butanolysis. The critical separation of the glycerol-rich phase still occurs and does so faster than in the cosolvent-free system. For THF, recycle of solvent is simplified because of the similar boiling points of THF (67°C) and methanol (65°C).Possible explanations for the abnormal slowing of the methanolysis reactions are presented in terms of (1) lower rate constants for mono- and diglyceride reactions due to the formation of cyclic intermediates, (2) a fall in the polarity of the reaction mixture due to either methanol depletion or mixing of the oil, methanol and cosolvent, and (3) depletion of hydroxide ion when this is present.

Fast one-phase oil-rich processes for the preparation of vegetable oil methyl esters

A re-evaluation of kinetic data shows that the methoxide base-catalyzed methanolysis of soybean oil at 40°C (6:1 methanol:oil molar ratio) to form methyl esters proceeds approximately 15 times more slowly than butanolysis at 30°C. This is interpreted to be the result of a two-phase reaction in which methanolysis occurs only in the methanol phase. Low oil concentration in methanol causes the slow reaction rate; a slow dissolving rate of the oil in the methanol causes an initiation period. Intermediate mono- and diglycerides preferentially remain in the methanol, and react further, thus explaining the deviation from second-order kinetics. The same explanations apply for hydroxide ion catalyzed methanolysis. At the 6:1 methanol:oil molar ratio the addition of a cosolvent, such as 1.25 volumes of tetrahydrofuran (THF) per volume of methanol, produces an oil-dominant one-phase system in which methanolysis speeds up dramatically and occurs as fast as butanolysis. The critical separation of the glycerol-rich phase still occurs and does so faster than in the cosolvent-free system. For THF, recycle of solvent is simplified because of the similar boiling points of THF (67°C) and methanol (65°C). Possible explanations for the abnormal slowing of the methanolysis reactions are presented in terms of (1) lower rate constants for mono- and diglyceride reactions due to the formation of cyclic intermediates, (2) a fall in the polarity of the reaction mixture due to either methanol depletion or mixing of the oil, methanol and cosolvent, and (3) depletion of hydroxide ion when this is present.

Ternary mass transfer in liquid-liquid extraction

Isothermal interphase mass transfer measurements were carried with the partially miscible Type I system glycero (1)-water (2)-acetone (3) in a modified batch Lewis extraction cell. Three types of experiments were performed: (A) in which the acetone-rich phase was saturated and the initial glycerol-rich phase composition lay on the extension of the corresponding tie-line, (B) in which the glycerol-rich phase was saturated and the initial acetone-rich phase composition lay on the extension of the corresponding tie-line and (C) in which initially both the acetone-rich and glycerol-rich phase were unsaturated. The equilibration trajectory was monitored in both phases by sampling at suitable intervals. In experiments A and B rectilinear equilibration trajectories were obtained while in the experiment C the approach towards equilibrium was highly curvilinear in the composition space. A theoretical model, based on irreversible thermodynamics and allowing for diffusional coupling between species transfers, is developed to simulate the three types of experiments above. The matrix of equilibration rate constants, in either fluid phase, is re-constructed by determining the eigenvectors and eigenvalues from experimental observations. It is found that both matrices of rate constants in the acetone-rich and glycerol-rich phases have extremely large off-diagonal elements. It is stressed in the discussions that the experimental results cannot be explained, even qualitatively, without inclusion of these off-diagonal contributions. Some interesting mass transfer phenomena in the region of the plait point are pointed out and the need for a fundamental irreversible thermodynamics approach to interphase mass transfer is emphasised. It is concluded that rigorous mass transfer formulations, allowing for diffusional coupling, will be required to be incorporated into design of extractors involving highly non-ideal liquid mixtures.