When traditional process-design methodologies are applied to the conceptual design of biorefineries, the main drivers for their development are poorly considered. Biorefinery plants are facilities integrating biomass-conversion processes and equipment to produce fuels, energy, chemical intermediates, and end-use products. Appropriate design tools must consider their sustainability in terms of: a) potential displacement of fossil fuels and materials, b) mitigation of environmental impacts, c) renewability, d) economic feasibility, e) biodiversity preservation, and f) social responsibility. Performance on addressing these drivers should be assessed from appropriate environmental, social and economic perspectives. This paper illustrates the application of a methodology that incorporates these principles in the conceptual design of a switchgrass-based biorefinery. The results show that the proposed design complies with the definition of sustainability in 10 out of 11 indicators. The indicator Baseline-emissions reduction fell in the unsustainable range mainly due to the high SO 2-eq and PO 4-eq emissions over the life cycle of the proposed system, derived from fertilizers and pesticides application. The techno-economic analysis showed economic feasibility of the biorefinery when the minimum acceptable rate of return is below 12%. The proposed methodology shows great potential as a valuable complement to classic process-design methodologies, by quantifying their sustainability during the conceptual-design stage, and requiring little extra effort beyond performing the technoeconomic analysis and a Life Cycle Assessment.
-Chlorella vulgaris and Scenedesmus obliquus were grown in artificial-wastewater using a new nitrogen-limitation strategy aimed at increasing lipid productivity. This strategy consisted in a multi-stage process with sequential reduction of N-NH 4 concentration (from 90 to 60, 40, and 20 mg.L -1 ) to promote a balance between cell growth and lipid accumulation. Lipid productivity was compared against a reference process consisting of nitrogen reduction in two stages, where the nitrogen concentration was suddenly reduced from 90 mg.L -1 to three different concentrations (10, 20, and 30 mg.L -1 ). In the multi-stage mode, only C. vulgaris exhibited a net lipid-productivity increase. Lipid content of S. obliquus did not present a significant increase, thus decreasing lipid productivity. The highest lipid productivities were observed in the two-stage mode for both S. obliquus and C. vulgaris (194.9 and 133.5 mg.L -1 .d -1 , respectively), and these values are among the highest reported in the literature to date.
-In this paper, three quality or performance indices (Luyben's capacity factor, total annual costs, and annual profit) were applied for the design of a batch distillation column working at variable reflux. This work used the Fenske-Underwood-Gilliland short-cut method to solve a problem of four components (benzene, toluene, ethyl-benzene, and ortho-xylene) that needed to be separated and purified to a mole fraction of 0.97 or better. The performance of the system was evaluated using distillation columns with 10, 20, 30, 40 and 50 theoretical stages with a boil-up vapor flow set at 100 kmol/h. It was found that the annual profit was the best quality index, while the best case for variable reflux was the column with 50 stages. It was confirmed that the best case always required a reflux ratio close to the minimum.
<p class="p1">Se describen la modelación, la construcción y el uso de un reactor continuo de tanque agitado para la obtención de datos experimentales de rapidez de reacción heterogénea. En primer lugar, mediante análisis de balances de materia se enfatiza cómo la capacidad de este tipo de reactor de operar en estado estacionario es ventajosa para el estudio de sistemas catalíticos heterogéneos. Consecuentemente, se propone una práctica experimental para determinar ecuaciones de rapidez globales a partir de ecuaciones intrínsecas obtenidas por el método de la etapa limitante. Se emplea un reactor continuo de tanque agitado cuya fabricación y operación son sencillos y se describen a detalle. La hidrólisis de sacarosa se implementa como reacción modelo a 60 °C y 1 atm, siendo de fácil monitoreo. La reacción se cataliza con una resina ácida (Amberlite 120 H, capacidad total de intercambio ≥ 1.80 eq/L). El experimento ilustra una aplicación del método de la etapa limitante para la obtención de ecuaciones de rapidez de reacción global y es una herramienta didáctica para reforzar el aprendizaje práctico en cursos de ingeniería de reacciones heterogéneas.</p>
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