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Research Interests: Geography and Humanities
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Two ways of synthesis to produce biodiesel from waste cooking oil were compared: 1) Transesterification of fatty acids with basic catalyst (KOH) and 2) Esterification with H2SO4 followed by the transesterification evaluated previously,... more
Two ways of synthesis to produce biodiesel from waste cooking oil were compared: 1) Transesterification of fatty acids with basic catalyst (KOH) and 2) Esterification with H2SO4 followed by the transesterification evaluated previously, using factorial designs 23 with central points and the Surface Response Methodology (RSM). Raw material was characterized through its acid value and moisture content. In synthesis (1) the factorial design factors were: reaction temperature, catalyst wt%/ weight of processed oil and, methanol:oil molar ratio, and response variables were: yield of reaction, density and, kinematic viscosity, with 75 minutes as reaction time. Yields around 88% were achieved. In synthesis (2) the factorial design was applied only for esterification reaction, using two of the preceding factors and reaction time instead of temperature (fixed at 60ºC). The best conditions determined for synthesis (1) were applied and yield of reaction increased to 97%. The kinematic viscositi...
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La matriz energética mundial está basada en combustibles fósiles que emiten enormes cantidades de GEI causantes del cambio climático, con graves consecuencias sobre nuestro planeta. En las últimas dos décadas, las energías renovables han... more
La matriz energética mundial está basada en combustibles fósiles que emiten enormes cantidades de GEI causantes del cambio climático, con graves consecuencias sobre nuestro planeta. En las últimas dos décadas, las energías renovables han aumentado su participación para mitigar los efectos sobre el clima. En este trabajo, se evalúa el rol del gas natural en la transición energética, considerando políticas energéticas e innovaciones tecnológicas. Fue aplicado el método de Delphi contando con expertos en energía y ambiente. Los resultados muestran tres factores clave: gas natural como combustible fósil más amigable con el ambiente, energías renovables no podrán satisfacer 100% de la demanda y alta variabilidad del suministro eléctrico basado en energías eólica y solar. Además, se visualizan dos oportunidades relevantes: crecimiento del consumo de energía y expansión del negocio del GNL. Estos hallazgos permiten señalar que el gas natural fungirá como combustible-puente en la transición...
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... Sabrina Di Scipio Cimetta. ... Estas variables (Salager et al, 1997; Briceño et al, 2002; Salager et al, 2002; Mira et al, 2003) se pueden clasificar en varios grupos, entre de los que se encuentran: 1) variables referidas a la... more
... Sabrina Di Scipio Cimetta. ... Estas variables (Salager et al, 1997; Briceño et al, 2002; Salager et al, 2002; Mira et al, 2003) se pueden clasificar en varios grupos, entre de los que se encuentran: 1) variables referidas a la geometría del tanque (diámetro del tanque, número y ...
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ABSTRACT More than 95% of the installed LNG facilities by 2012 use a precooling cycle as the first stage of the process. In this work, a technical comparison between different precooling cycles for LNG processes is carried out through... more
ABSTRACT More than 95% of the installed LNG facilities by 2012 use a precooling cycle as the first stage of the process. In this work, a technical comparison between different precooling cycles for LNG processes is carried out through computational simulations using Aspen HYSYS®. The aim is to provide future developments with a clear idea of the technical advantages/disadvantages involved in the selection of the process for the precooling cycle. A three stage propane precooled cycle was found to be the most energetically efficient among the studied cases, even better than a two stage mixed refrigerant process (C2/C3) for both climate conditions, warm (25 °C) and cold (6 °C). However, due to the reduced power share that may be reached with a propane cycle temperature restriction, the mixed refrigerant precooling cycle is the preferred alternative under the cold climate condition.
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When the theoretical values of the interfacial tension -resulting from the homogeneous distribution of ionic surfactant molecules amongst the interface of emulsion drops- are plotted against the total surfactant concentration, they... more
When the theoretical values of the interfacial tension -resulting from the homogeneous distribution of ionic surfactant molecules amongst the interface of emulsion drops- are plotted against the total surfactant concentration, they produce a curve comparable to the Gibbs adsorption isotherm. However, the actual isotherm takes into account the solubility of the surfactant in the aqueous bulk phase. Hence, assuming that the total surfactant population is only distributed among the available oil/water interfaces, one can calculate what surface concentration is necessary to reproduce the experimental values of the interfacial tension. A similar procedure can be followed using the zeta potential of the drops as a standard for a given set of salt and surfactant concentrations. We applied these procedures to the case of hexadecane/water nanoemulsions at different salt concentrations. This information was used to compute typical interaction potentials between non-deformable nanoemulsion dro...
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Una de las tecnologias mas usadas a nivel mundial para licuar el gas natural, por su simplicidad y facilidad de manejo, es la de ciclo simple denominada PRICO®. En este trabajo se realizo la simulacion de un ciclo de licuefaccion similar... more
Una de las tecnologias mas usadas a nivel mundial para licuar el gas natural, por su simplicidad y facilidad de manejo, es la de ciclo simple denominada PRICO®. En este trabajo se realizo la simulacion de un ciclo de licuefaccion similar al de esta tecnologia, utilizando el programa comercial PRO/II® version 9.1. Se simulo un caso base y se llevo a cabo un analisis de varianza (ANOVA) de presiones y flujos usando el programa Statgraphics Centurion XVI ® . Ademas, se realizo un procedimiento de optimizacion de presiones y composicion de refrigerantes. Se determino que el coeficiente de rendimiento (COP) se ve afectado de forma directamente proporcional por las presiones de alta y de baja del ciclo, y que la modificacion de la presion intermedia entre los dos compresores no fue significativa. La variacion en el contenido de pentano en la mezcla de refrigerante presento el mayor efecto positivo sobre el COP seguido por el propano; sin embargo, se debe tener presente que el pentano pued...
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In the Food Industry, oil in water (O/W) emulsions are commonly used or prepared. Egg yolk and monostearates are the most frequently employed surfactants. In this work was evaluated the influence of disperse phase content, and surfactant... more
In the Food Industry, oil in water (O/W) emulsions are commonly used or prepared. Egg yolk and monostearates are the most frequently employed surfactants. In this work was evaluated the influence of disperse phase content, and surfactant concentrations on the rheological behavior and mean drop diameter (d43) of concentrated corn oil in water emulsions, which constitute the base for some salad dressings. The samples were prepared using surfactant blends at laboratory scale. The experimental method was based on factorial design 2 3 with central points. The concentration of commercial ethoxylated non-ionic surfactant, Tween 60, was established at 2000, 3000, and 4000 ppm, while the active egg yolk concentration varied in 1000, 2500, and 4000 ppm. The dispersed phase (corn oil) concentration was varied in 60, 70, and 80 weight percent. As expected, the increase in the blend surfactant concentration produced a reduction in the emulsion’s mean drop diameter. However, this d43 reduction no...
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The analysis of physico-chemical aspects (formulation-composition) associated with the characterization of a water in oil emulsion (O/W), manufactured by the Food Industry, is of a great importance due to its contribution into the knowhow... more
The analysis of physico-chemical aspects (formulation-composition) associated with the characterization of a water in oil emulsion (O/W), manufactured by the Food Industry, is of a great importance due to its contribution into the knowhow of its elaboration process. This type of system must have good stability to endure long storage times, often under thermal stress. Edible corn oil in water emulsions, stabilized with a non ionic surfactant (HLB=15), were elaborated by direct emulsification, varying the water oil ratio (φ) and surfactant concentration. It was used a mixing system setting the geometrical dimensions of stator, impeller and the nominal potency of the engine. The studied properties were: conductivity, stability as percent of clarified and coalesced volume, viscosity, rheological behaviour and, drop size distribution. The information gathered was plotted as 3D plots. Conductivity was notably dependent on Internal Phase Ratio (IPR) and surfactant concentration. The higher...
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In the present experimental study it was obtained soap as subproduct of the transesterification reaction with basic catalysis of waste cooking oils, in order to evaluate the feasibility to produce biodiesel from this waste through acid... more
In the present experimental study it was obtained soap as subproduct of the transesterification reaction with basic catalysis of waste cooking oils, in order to evaluate the feasibility to produce biodiesel from this waste through acid catalysis. A factorial design 2 2 with 5 central points was used, and the selected variables for the study were: reaction time (6-10 hours) and acid concentration (5-15 %w/w of H 2 SO 4 ) with respect to the sub-product quantity employed as raw material. The yield of reaction, density, acid number and calorific power were measured. The acid concentration was a determinant factor in the reaction yield while the influence of time was negligible. The best values obtained for density and calorific power of the produced biodiesel were 881 kg/m 3 and 39.17 MJ/kg, respectively, which are according to the norms UNEEN 14214 and EN-590. Even though the feasibility of the process was verified, the yields obtained were low (20.8-43.7 %) thus affecting its profitability.
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A sensitivity analysis of a Natural Gas (NG) Liquefaction Cycle with mixed refrigerant was done varying the operational conditions. It was used PROII/8.1® to simulate the process and in each case study the variation of the coefficient of... more
A sensitivity analysis of a Natural Gas (NG) Liquefaction Cycle with mixed refrigerant was done varying the operational conditions. It was used PROII/8.1® to simulate the process and in each case study the variation of the coefficient of performance (COP) and the refrigerant flow rate required for the total gas liquefaction was analyzed. The use of different pressure levels and the best intermediate pressure for the cycle were evaluated. The composition of the mixed refrigerant was varied in order to reduce the flow required for the liquefaction. The refrigerant flow rate was proportional to the inlet NG temperature. The most favorable intermediate pressure for the cycle was obtained from the geometric mean of the low and high pressure. The increment of propane in the studied mixed refrigerant improved the cycle performance coefficient. The feasibility to apply this technology of liquefaction in Venezuelan fields with different gas compositions was determined.
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El analisis de los aspectos fisico-quimicos (formulacion-composicion) asociados con la caracterizacion de una emulsionde aceite en agua (O/W), manufacturada por la industria alimentaria, es de gran importancia porque aporta una base... more
El analisis de los aspectos fisico-quimicos (formulacion-composicion) asociados con la caracterizacion de una emulsionde aceite en agua (O/W), manufacturada por la industria alimentaria, es de gran importancia porque aporta una base deconocimiento para su elaboracion. Este tipo de sistemas debe poseer gran estabilidad porque se somete a altos tiemposde almacenamiento, muchas veces bajo estres termico. Se elaboraron emulsiones de aceite de maiz en agua con unsurfactante no ionico (HLB=15), mediante emulsificacion directa variando la relacion aceite en agua (φ) y concentracionde surfactante. Se utilizo un sistema de mezclado ajustando la configuracion geometrica del estator, del impulsor y lapotencia nominal del motor. Las propiedades estudiadas fueron: conductividad, estabilidad como porcentaje de volumencoalescido y clarificado, comportamiento reologico y distribuciones de diametro de gota. La informacion recolectada seuso para la generacion de mapas 3D. La conductividad dependio no...
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In the Food Industry, highly-concentrated disperse phase emulsions (> 75%) are frequently produced, considering physicochemical and compositional parameters, and the mixing conditions. Most of the research related to the mixing of... more
In the Food Industry, highly-concentrated disperse phase emulsions (> 75%) are frequently produced, considering physicochemical and compositional parameters, and the mixing conditions. Most of the research related to the mixing of disperse systems has studied diluted systems without surfactants. The present work deals with the preparation of highly-concentrated corn oil in water emulsions with ethoxylated non ionic surfactant. The experimental method was based on factorial design 2 3 with central and axial points, where impeller rotational speed, time agitation and, oil: water ratio were varied. The influence of those variables on volume and surface area mean drop diameter of emulsions, d 43 and d 32 , respectively, was evaluated. Through the analysis of variance of experimental space, eliminating the non-significant effects, it was determined that d 43 can be predicted almost by 99% by a quadratic model, but this model, by itself, can not explain the d 32 whole extension respons...
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To liquefy the Natural Gas the second most employed technology in the world is the Phillips Optimized Cascade®. In this work the simulation of a natural gas liquefaction cascade process with pure refrigerants (propane, ethylene, and... more
To liquefy the Natural Gas the second most employed technology in the world is the Phillips Optimized Cascade®. In this work the simulation of a natural gas liquefaction cascade process with pure refrigerants (propane, ethylene, and methane) was done. The commercial processes simulator PRO/II® was used for comparing the thermodynamics models of Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK). Initially, the base case was simulated and a global coefficient of performance (COP global ) for the cycle equal to 0.52 was obtained. Later, the feasibility of using CO 2 as a refrigerant in the process was studied considering three scenarios: 1) as a substitute for propane, in that case a COP global of 0.41 was obtained; 2) as pre-cooling of the cascade cycle, reaching a COP global of 0.49; and 3) as a condenser of the whole cycle with the three cascades. In the last scenario, the COP global was 0.46, including the CO 2 compressor duty, and was 0.63 when it was not considered.
Se realizó un análisis de sensibilidad de un ciclo de licuefacción de Gas Natural (GN) con mezcla de refrigerantes variando las condiciones de operación. Se utilizó PRO II/8.1® para la simulación del proceso y en cada caso de estudio se... more
Se realizó un análisis de sensibilidad de un ciclo de licuefacción de Gas Natural (GN) con mezcla de refrigerantes variando las condiciones de operación. Se utilizó PRO II/8.1® para la simulación del proceso y en cada caso de estudio se analizó la variación en el coeficiente de rendimiento del ciclo (COP) y el flujo de refrigerante requerido para la total licuefacción del gas. Se evaluó el uso de diferentes niveles de presión y la presión intermedia más adecuada para el ciclo. Se varió la composición de la mezcla de refrigerantes, con el objetivo de reducir la cantidad de flujo necesario para la licuefacción. El flujo de refrigerante resultó proporcional a la temperatura de entrada de GN. La presión intermedia más favorable para el ciclo se obtuvo calculando el promedio geométrico de las presiones de baja y de alta. El incremento de propano en la mezcla de refrigerante estudiada mejoró el coeficiente de rendimiento del ciclo. Se determinó la factibilidad de la aplicación de esta tecnología de licuefacción en campos venezolanos con diferentes composiciones de gas.
In the present experimental study it was obtained soap as subproduct of the transesterification reaction with basic catalysis of waste cooking oils, in order to evaluate the feasibility to produce biodiesel from this waste through acid... more
In the present experimental study it was obtained soap as subproduct of the transesterification reaction with basic catalysis of waste cooking oils, in order to evaluate the feasibility to produce biodiesel from this waste through acid catalysis. A factorial design 2 2 with 5 central points was used, and the selected variables for the study were: reaction time (6-10 hours) and acid concentration (5-15 %w/w of H 2 SO 4 ) with respect to the sub-product quantity employed as raw material. The yield of reaction, density, acid number and calorific power were measured. The acid concentration was a determinant factor in the reaction yield while the influence of time was negligible. The best values obtained for density and calorific power of the produced biodiesel were 881 kg/m 3 and 39.17 MJ/kg, respectively, which are according to the norms UNEEN 14214 and EN-590. Even though the feasibility of the process was verified, the yields obtained were low (20.8-43.7 %) thus affecting its profita...
Research Interests:
In the present experimental study it was obtained soap as subproduct of the transesterification reaction with basic catalysis of waste cooking oils, in order to evaluate the feasibility to produce biodiesel from this waste through acid... more
In the present experimental study it was obtained soap as subproduct of the transesterification reaction with basic catalysis of waste cooking oils, in order to evaluate the feasibility to produce biodiesel from this waste through acid catalysis. A factorial design 22 with 5 central points was used, and the selected variables for the study were: reaction time (6-10 hours) and acid concentration (5-15 %w/w of H2SO4) with respect to the sub-product quantity employed as raw material. The yield of reaction, density, acid number and calorific power were measured. The acid concentration was a determinant factor in the reaction yield while the influence of time was negligible. The best values obtained for density and calorific power of the produced biodiesel were 881 kg/m3 and 39.17 MJ/kg, respectively, which are according to the norms UNEEN 14214 and EN-590. Even though the feasibility of the process was verified, the yields obtained were low (20.8-43.7 %) thus affecting its profitability.
Research Interests:
In the Food Industry, highly-concentrated disperse phase emulsions (> 75%) are frequently produced, considering physicochemical and compositional parameters, and the mixing conditions. Most of the research related to the mixing of... more
In the Food Industry, highly-concentrated disperse phase emulsions (> 75%) are frequently produced, considering physicochemical and compositional parameters, and the mixing conditions. Most of the research related to the mixing of disperse systems has studied diluted systems without surfactants. The present work deals with the preparation of highly-concentrated corn oil in water emulsions with ethoxylated non ionic surfactant. The experimental method was based on factorial design 23 with central and axial points, where impeller rotational speed, time agitation and, oil: water ratio were varied. The influence of those variables on volume and surface area mean drop diameter of emulsions, d43 and d32, respectively, was evaluated. Through the analysis of variance of experimental space, eliminating the non-significant effects, it was determined that d43 can be predicted almost by 99% by a quadratic model, but this model, by itself, can not explain the d32 whole extension response surf...
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When the theoretical values of the interfacial tension -resulting from the homogeneous distribution of ionic surfactant molecules amongst the interface of emulsion drops- are plotted against the total surfactant concentration, they... more
When the theoretical values of the interfacial tension -resulting from the homogeneous distribution of ionic surfactant molecules amongst the interface of emulsion drops- are plotted against the total surfactant concentration, they produce a curve comparable to the Gibbs adsorption isotherm. However, the actual
isotherm takes into account the solubility of the surfactant in the aqueous bulk phase. Hence, assuming that the total surfactant population is only distributed among the available oil/water interfaces, one can calculate what surface concentration is necessary to reproduce the experimental values of the interfacial tension. A similar procedure can be followed using the zeta potential of the drops as a standard for a given set of salt and surfactant concentrations. We applied these procedures to the case of hexadecane/water nanoemulsions at different salt concentrations. This information was used to compute typical interaction potentials between non-deformable nanoemulsion drops. The results indicate that there are significant differences between the surfactant population expected from macroscopic adsorption isotherms, and the actual surfactant population
adsorbed to the surface of nanoemulsion drops.
isotherm takes into account the solubility of the surfactant in the aqueous bulk phase. Hence, assuming that the total surfactant population is only distributed among the available oil/water interfaces, one can calculate what surface concentration is necessary to reproduce the experimental values of the interfacial tension. A similar procedure can be followed using the zeta potential of the drops as a standard for a given set of salt and surfactant concentrations. We applied these procedures to the case of hexadecane/water nanoemulsions at different salt concentrations. This information was used to compute typical interaction potentials between non-deformable nanoemulsion drops. The results indicate that there are significant differences between the surfactant population expected from macroscopic adsorption isotherms, and the actual surfactant population
adsorbed to the surface of nanoemulsion drops.
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When the theoretical values of the interfacial tension -resulting from the homogeneous distribution of ionic surfactant molecules amongst the interface of emulsion drops- are plotted against the total surfactant concentration, they... more
When the theoretical values of the interfacial tension -resulting from the homogeneous distribution of ionic surfactant molecules amongst the interface of emulsion drops- are plotted against the total surfactant concentration, they produce a curve comparable to the Gibbs adsorption isotherm. However, the actual isotherm takes into account the solubility of the surfactant in the aqueous bulk phase. Hence, assuming that the total surfactant population is only distributed among the available oil/water interfaces, one can calculate what surface concentration is necessary to reproduce the experimental values of the interfacial tension. A similar procedure can be followed using the zeta potential of the drops as a standard for a given set of salt and surfactant concentrations. We applied these procedures to the case of hexadecane/water nanoemulsions at different salt concentrations. This information was used to compute typical interaction potentials between non-deformable nanoemulsion drops. The results indicate that there are significant differences between the surfactant population expected from macroscopic adsorption isotherms, and the actual surfactant popula- tion adsorbed to the surface of nanoemulsion drops.
A sensitivity analysis of a Natural Gas (NG) Liquefaction Cycle with mixed refrigerant was done varying the operational conditions. It was used PROII/8.1® to simulate the process and in each case study the variation of the coefficient of... more
A sensitivity analysis of a Natural Gas (NG) Liquefaction Cycle with mixed refrigerant was done varying the operational conditions. It was used PROII/8.1® to simulate the process and in each case study the variation of the coefficient of performance (COP) and the refrigerant flow rate required for the total gas liquefaction was analyzed. The use of different pressure levels and the best intermediate pressure for the cycle were evaluated. The composition of the mixed refrigerant was varied in order to reduce the flow required for the liquefaction. The refrigerant flow rate was proportional to the inlet NG temperature. The most favorable intermediate pressure for the cycle was obtained from the geometric mean of the low and high pressure. The increment of propane in the studied mixed refrigerant improved the cycle performance coefficient. The feasibility to apply this technology of liquefaction in Venezuelan fields with different gas compositions was determined.
At distances greater than 4000 km from the source of production, the most profitable way to transport the natural gas (NG) is as liquefied natural gas (LNG). Between years 2000-2010 the natural gas consumption increased 31.4% and LNG... more
At distances greater than 4000 km from the source of production, the most profitable way to transport the natural gas (NG) is as liquefied natural gas (LNG). Between years 2000-2010 the natural gas consumption increased 31.4% and LNG represents 30.5% of the global NG trade in 2010 [1]. Venezuela has important proven reserves of NG, therefore the construction of a LNG plant is being considered. The Linde-Statoil Mixed Fluid Cascade process (MFC ®) was selected; it consists in three cascades that use different refrigerant blends in each cycle. In the present work a process similar to the MFC, considering cold and tropical temperature for the inlet gas (12 and 30°C) was simulated. The commercial software ProII was used to study the influence on the coefficient of performance (COP) and flow rates of refrigerants of three main operational variables: low and high pressure of the compressors, and outlet temperatures of the main heat exchangers. The following assumptions were made for the s...
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In the Food Industry, oil in water (O/W) emulsions are commonly used or prepared. Egg yolk and monostearates are the most frequently employed surfactants. In this work was evaluated the influence of disperse phase content, and surfactant... more
In the Food Industry, oil in water (O/W) emulsions are commonly used or prepared. Egg yolk and monostearates are the most frequently employed surfactants. In this work was evaluated the influence of disperse phase content, and surfactant concentrations on the rheological ...