The size and fractal dimension of asphaltene aggregates were investigated for two Western Canadian bitumens diluted with n-heptane at concentrations above the onset of precipitation. Asphaltene aggregate size distributions were measured over time using focused beam reflectance and micrographic methods in a series of batch experiments at different n-heptane contents and shear rates. The fractal dimensions of the aggregates were determined from the volume of the settled aggregates. The asphaltenes formed approximately log-normal size distributions with volume mean diameters of tens to hundreds of micrometers, depending mainly upon the n-heptane content. The distributions were established in less time than the first measurement could be obtained (about 30 s) and changed relatively little afterward. The average aggregate size increased with an increasing n-heptane content but reached a plateau value at 70–80 wt % n-heptane. The fractal dimension reached a maximum at a similar n-heptane content. Micrographic images and fractal dimensions indicated that, near the onset of precipitation, compact linear and planar aggregate structures dominated. At higher n-heptane contents up to approximately 75 wt % n-heptane, the aggregates remained compact but became more three-dimensional. At higher n-heptane contents, larger, looser structures were formed that could be broken under sufficient shear but did not reaggregate. The results were consistent with simultaneous nucleation, growth, and flocculation processes, where the precipitating material was initially sticky but lost its stickiness over time. The loss in stickiness was confirmed with surface force adhesion measurements.
The settling rate of asphaltene aggregates is a key design parameter for partial deasphalting processes, and yet few data and models are available for these systems. The settling rates of asphaltene aggregates were measured in two Western Canadian bitumens diluted with n-heptane or n-pentane at 21 °C and atmospheric pressure. The density and viscosity of the mixtures, the size distributions of the aggregates, and the fractal dimensions of the aggregates were also measured. The asphaltene aggregates settled as a zone, that is, all aggregates settled at the same rate. The settling rates increased with increasing n-alkane content, reached a maximum at approximately 75 wt % n-alkane and then decreased at higher dilutions. The maximum settling rate corresponded to the maximum aggregate diameter and fractal dimension. The maximum settling rate in n-pentane diluted bitumen was 2 orders of magnitude greater than in the same bitumen diluted with n-heptane. The difference was attributed to the lower density and viscosity of the medium, larger aggregates, and higher fractal dimensions in n-pentane versus n-heptane. The settling rates were modeled with Stokes' law modified to include the fractal dimension of the aggregates. Since zone settling was observed, the settling rate was determined from a single average diameter applied to all of the aggregates. The Sauter mean diameter was found to provide the most consistent results for the diluted bitumen systems in this study. No other form of hindering was required to match the data. The model matched the measured settling rates to within 20% of the maximum settling rate. The model is sensitive to the fractal dimension of the aggregates, and therefore precise determination of the fractal dimension is critical or it must be tuned to match the settling data.
By-products valorization in bio-fuels industry is an important issue for making the global process more efficient, more profitable and closer to the concept of biorefinery. Fusel oil is a by-product of bioethanol production that can be considered as an inexpensive and renewable raw material for manufacturing value-added products. In this work, results in terms of composition and physicochemical properties of six samples of fusel oil from industrial alcohol facilities are presented. Composition of the main components was established by gas chromatography. Complementary techniques, such as headspace solid-phase microextraction and gas chromatography-mass spectrometry (GC-MS), were used for detection of minor components. Fifty-five compounds were identified. Physicochemical properties such as density, acid value, moisture content and true boiling point curves were determined. Results are useful in the conceptual design of separation strategies for recovering higher alcohols, as well as to consider new options of valorization alternatives for fusel oil.Keywords: Fuel ethanol, higher alcohols, GC-MS analysis, solid-phase microextraction, TBP. RESUMENLos subproductos para valorización en la industria de los biocombustibles es un tema importante para alcanzar un proceso global más eficiente, más rentable y más cerca del concepto de biorrefinería. El aceite de fusel es un subproducto de la producción de bioetanol que se puede considerar como una materia prima barata y renovable para la fabricación de productos de valor agregado. En este trabajo se presentan los resultados en términos de composición y de las propiedades físico-químicas de seis muestras de aceite de fusel de las instalaciones industriales de alcohol. La composición de los componentes principales se estableció mediante cromatografía de gases. Técnicas complementarias, como espacio de cabeza, microextracción en fase sólida, y cromatografía de gasesespectrometría de masas (GC-MS), fueron utilizadas para la detección de componentes menores. Se identificaron cincuenta y cinco compuestos. Se determinaron las propiedades físico-químicas, como la densidad, el índice de acidez, el contenido de humedad y las curvas de puntos verdaderos de ebullición. Los resultados son útiles en el diseño conceptual de las estrategias de separación para la recuperación de alcoholes superiores, así como para comprobar las opciones de alternativas de valorización del aceite de fusel Palabras Clave: Etanol-combustible, alcoholes pesados, análisis GC-MS, micro-extracción en fase sólida, TBP.
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