A supercritical biodiesel production process via transesterification of vegetable oil with methanol, using CO2 as co-solvent is designed, simulated, and validated with experimental data. A preliminary study of the liquid-vapor equilibrium of the reacting mixture at different compositions was done to determine the supercritical conditions, by means of pressure-temperature diagrams. Under supercritical conditions, the presence of a single phase increases the reaction kinetics, avoiding the limitation by interphase mass transfer, and enabling to carry out the process with low residence time. The proposed process is based on two fixed-bed catalytic reactors in series, with intermediate glycerol separation. CO2 used as co-solvent decreases the critical temperature, enabling to carry out the process in milder conditions. The intermediate glycerol separation displaces the chemical equilibrium towards higher conversion of triglyceride, increasing biodiesel yield. The results of a complete experimental study are used to validate the model, through a comparison with the simulations result.
Pölling, B.; Prados, M.; Torquati, B.; Giacchè, G.; Recasens, F.; Paffarini, C.; Alfranca, O.; Lorleberg, W. Moravian Geographical Reports Vol. 25, num. 3, p. 1-15 DOI: 10.1515/mgr-2017-0015 Data de publicació: 2017-01-01 Article en revista
The "Urban Agriculture Europe" EU COST-Action (2012-2016) has shown that the complexity of urban agriculture (UA) is hardly compressible into classic business management models and has proposed new management models, such as the Business Model Canvas (BMC). Business models of UA have to be different from rural ones. In particular, factors such as differentiation and diversification, but also low cost-oriented specialisation, are characteristic and necessary business models for UA to stay profitable in the long term under challenging city conditions. This paper aims to highlight how farm enterprises have to adjust to urban conditions by stepping into appropriate business models aiming to stay competitive and profitable, and how the BMC is useful to analyse their organisation and performance, both economically and socially. The paper offers an inter-regional analysis of UA enterprises located in Spain, Italy, and Germany, which are further subdivided into: local food, leisure, educational, social, therapeutic, agri-environmental, cultural heritage and experimental farms. The analysis demonstrates that UA is differentially adjusted to specific urban conditions and that the BMC is useful for analysing urban farming. Heterogeneous local food farms and the integration of local and organic food production in social farming business models are most frequent in our case studies.
En la presente tesis doctoral se acomete el estudio del uso, gracias a sus propiedades deshidratantes, de una solución acuosa de LiCl como refrigerante secundario, en aquellas aplicaciones frigoríficas que requieren principalmente la deshumidificación del aire y donde los métodos convencionales presentan dificultades técnicas y/o elevado coste energético. Se realiza el estudio de la transferencia de masa y calor entre la solución acuosa de LiCl y el aire y se aplica a diferentes condiciones de temperatura seca y humedad relativa del aire.Se resuelve la regeneración de la solución acuosa de LiCl utilizando la potencia térmica del condensador del mismo circuito frigorífico, eliminando así la dependencia de otras fuentes de calor externas y aumentando la eficiencia energética de la instalación. El análisis de los resultados obtenidos y la comparativa energética respecto a los métodos convencionales que se utilizan hasta ahora, muestra que es una alternativa a considerar.
The present thesis is undertaken to study the use of an aqueous solution of LiCl as a secondary refrigerant, due to its dehydrating properties, in those refrigeration applications that require mainly the air dehumidification and where the conventional methods show technical difficulties and/or a high energetic cost.
The study of mass and heat transference between the aqueous solution of LiCl and the air is made, and it is applied to different conditions of dry temperature and air relative humidity.
Regeneration of the aqueous solution of LiCl is solved using the condenser thermal power from the same refrigeration circuit, removing the dependence on other external heat sources, thus increasing the installation energetic efficiency.
The analysis of the obtained results and the energetic comparative regarding to the conventional methods used so far show this is really an alternative to consider.
En la presente tesis doctoral se acomete el estudio del uso, gracias a sus propiedades deshidratantes, de una solución acuosa de LiCl como refrigerante secundario, en aquellas aplicaciones frigoríficas que requieren principalmente la deshumidificación del aire y donde los métodos convencionales presentan dificultades técnicas y/o elevado coste energético. Se realiza el estudio de la transferencia de masa y calor entre la solución acuosa de LiCl y el aire y se aplica a diferentes condiciones de temperatura seca y humedad relativa del aire. Se resuelve la regeneración de la solución acuosa de LiCl utilizando la potencia térmica del condensador del mismo circuito frigorífico, eliminando así la dependencia de otras fuentes de calor externas y aumentando la eficiencia energética de la instalación. El análisis de los resultados obtenidos y la comparativa energética respecto a los métodos convencionales que se utilizan hasta ahora, muestra que es una alternativa a considerar.
Hydrogenation of vegetable oils is an important process in the food industry
because of its widespread application to produce margarines, shortenings, and other
food components. Supercritical technology has proven to be a reliable alternative to
conventional hydrogenation process because not only the trans isomer levels can be
reduced, but also offers a clean, economic and environmental friendly process.
Computational Fluid Dynamics (CFD) modeling applied to the supercritical hydrogenation reaction can be useful in visualizing and understanding the mass transfer phenomena involved. CFD is applied to the study of the catalytic hydrogenation of sunflower oil in the presence of a supercritical solvent. A mix of sunflower oil, hydrogen and supercritical propane (used as a solvent) is the flowing fluid. Their transport properties at high pressure are incorporated within a CFD commercial code in order to estimate them online within the simulation process. A 2D CFD model of a single Pd-based catalyst pellet is presented. Intra-particle and surface concentration profiles and surface mass fluxes for all species present in the mixture (oil triglycerides and hydrogen) are obtained and compared against experimental results. Different temperatures, flow velocities and particle sizes are studied and external and internal
mass transfer phenomena are analyzed. External mass transfer coefficients for hydrogen and oil triglycerides are obtained and a correlation for estimating them is presented.
Costa, A.; Santana, A.; Quadri, M.; Machado, R.; Recasens, F.; Larrayoz, M. The Journal of supercritical fluids Vol. 58, num. 2, p. 226-232 DOI: 10.1016/j.supflu.2011.06.012 Data de publicació: 2011-09 Article en revista
In this study, glycerol desorption from Purolite® PD206 resin was investigated using conventional and supercritical fluids (SCF) techniques. Untreated biodiesel was purified by dry washing using the resin and, after purification, the glycerol desorption was carried out using absolute ethanol under atmospheric conditions at different mass flows (10–30 g/min) or using ethanol-modified supercritical CO2 (1:3 molar
ratio of ethanol:CO2), under a pressure of 140 bar, within a temperature range of 106–134ºC and with mass flow rates of 6–34 g/min. The results showed that ethanol is an efficient solvent for this process and that the supercritical desorption is much faster than conventional desorption process. Employing the Response Surface Methodology (RSM) it was found that temperature has the greatest effect on the resin regeneration time using supercritical fluids. Optimum conditions obtained were 106.1ºC and 21.9 g/min, in which the resin was regenerated in only 4.17 min.
A simulation study of a SCF process is carried out using Aspen™ with previously available catalytic kinetics for the simulation of the reactor. Two supported catalysts were considered: a standard Pd/carbon, and an egg-shell Pd/alumina, in a vapour-phase process that uses propane as solvent. Best reactor–catalyst combination was selected using optimization. Optimal reactor–catalyst conditions were: Pd (0.5 wt%) on alumina catalyst in tubes, shell cooling, inlet temperature 170 °C, space-time 100 s, 4 mol% of H2 in the feed, oil feed 1 mol%, propane 95 mol%, with pressure up to 20 MPa. Three SC solvents, were considered in the simulation. These were (i) SC propane, (ii) a cosolvent case with hexane-modified CO2, and (iii) a case with pure liquid hexane. In plant simulation, three recycle streams (H2, CO2 and cosolvent) complicate the separations. In order to assess the safety differences between these options, a study was done using the Dow Fire and Explosion Index to roughly figure out process safety. It is shown that plant complexity increases with cosolvent use, but the hazard index is sensibly reduced, from F&EI = 150 (pure propane) to a low value (F&EI = 60) for a plant with CO2 with 40 mol% of hexane as cosolvent.
Fatty acid methyl esters (biodiesel) were produced by the transesterification of triglycerides with compressed
methanol (critical point at 240 C and 81 bar) in the presence of solid acids as heterogeneous catalyst
(SAC-13). Addition of a co-solvent, supercritical carbon dioxide (critical point at 31 C and 73 bar),
increased the rate of the supercritical alcohols transesterification, making it possible to obtain high biodiesel
yields at mild temperature conditions. Experiments were carried out in a fixed bed reactor, and
reactions were studied at 150–205 C, mass flow rate 6–24 ml/min at a pressure of 250 bar. The molar
ratio of methanol to oil, and catalyst amount were kept constant (9 g). The reaction temperature and
space time were investigated to determine the best way for producing biodiesel. The results obtained
show that the observed reaction rate is 20 time faster than conventional biodiesel production processes.
The temperature of 200 C with a reaction time of 2 min were found to be optimal for the maximum
(88%) conversion to methyl ester and the free glycerol content was found below the specification limits.
Hydrogenation of vegetable fats is an important biomolecule modification process, traditionally carried out in a slurry reactor at low pressure (2–6 bar). Here, the hydrogenation of sunflower oil in supercritical propane and dimethyl ether catalysed by Pd (supported on activated carbon or alumina) is studied. One-dimensional simulation models for plug flow and mixed flow reactors, as well as two-dimensional dispersed plug flow reactor models, were developed for the case of isothermal and adiabatic operation. The hydrogenation of sunflower oil is considered as a reaction network based on linoleate, oleate (cis C18:1), elaidate (trans C18:1) and stearate triesters. Since trans fatty C18:1 ester and stearate formation is not desired, the question arises as to which reactor type is best to achieve a low elaidate content. Depending on the final allowed stearate content, different mixed and plug flow reactor models can be applied. However, for a fixed stearate formation rate, the mixed reactor gives a lower trans content than the plug flow reactor in most cases. Also, low temperature operation results in better oleate/stearate selectivity. Two-dimensional tubular reactor dispersed simulation does not give further insight into the problem. The use of Multiphysics (finite element method) for solving the dispersed plug flow model provides a way to simulate CSTR reactor behaviour. In our case, both heat and mass Péclet numbers of 10−4 or less are sufficient to describe well-mixed reactor behaviour using the 2D mass and heat transfer pseudo-homogeneous model with radial and axial effects, with parameter values available for SCF. The models can be used for planning reaction operations in SCF as solvents intended for low trans fatty acid.
Guardo, A.; Casanovas, M.; Ramirez, E.; Recasens, F.; Magaña, I.; Martínez, D.; Larrayoz, M. Chemical engineering science Vol. 62, num. 18-20, p. 5054-5061 Data de publicació: 2007-09 Article en revista
Guardo, A.; Casanovas, M.; Ramirez, E.; Larrayoz, M.; Recasens, F. 5th International Symposium on High Pressure Processes Technology and Chemical Engineering p. 58 Data de presentació: 2007-06-26 Presentació treball a congrés
Santana, A.; Fernandez-Francos, X.; Ramirez, E.; Larrayoz, M.; Recasens, F. 5th International Symposium on High Pressure Processes Technology and Chemical Engineering p. 157 Presentació treball a congrés
Proceso de hidrogenación parcial de triglicéridos insaturados en fase vapor a alta presión y reactor para la realización de dicho proceso.
Se describe un proceso de hidrogenación de aceites vegetales sobre paladio, en fase vapor homogénea, que emplea una mezcla de triglicéridos, hidrógeno y un solvente gaseoso a alta presión.
El proceso se realiza en un reactor de flujo mezclado consistente en un lecho fijo de partículas de catalizadores con flujo radial o bien en un reactor monolito, ambos con pequeño tamaño de partícula y baja pérdida de carga. El efecto de mezcla perfecta en ambos se consigue por recirculación de la mezcla reactante.
Empleando alta turbulencia en el reactor y pequeño tamaño de partícula del catalizador, se consiguen contenidos del isómero C18:1 trans inferiores al 3,5% en peso.