Minimizing costs in near critical bioethanol extraction and dehydration processes,

CECILIA I. PAULO; MARIA SOLEDAD DIAZ; ESTEBAN A. BRIGNOLE

Napoli

Congreso; 9th Conference on Supercriticalfluids and Their Applications; 2010

Universita degli Studi di Salerno

There has been increasing interest on biomass derived ethanol due to the rapid increase in the price of crude oil and the perceived strength of the global demand of petroleum. Downstream from fermentation processes there is usually a dilute aqueous solution, the so-called beer, containing about 5-12wt% ethanol. Separation of ethanol from beer is an energy-intensive process, which usually takes up a large fraction of the total energy requirement for the whole biorefinery. The potential of near critical fluid extraction and high pressure distillation for separating alcohols from water has been discussed by several authors (Brignole et al., 1987, Zabaloy et al., 1992; Horizoe et al., 1993). The inclusion of different process schemes has been formulated as a mixed integer nonlinear programming (MINLP) problem, whose solution has provided improved energy consumption options (Gros et al., 1998, Diaz et al., 2000).  Compared to the basic scheme, vapor recompression, could be highly energy efficient. Special attention has been devoted to a new scheme that integrates vapor recompression scheme to the  beer column, which provides additional reduction in total energy consumption (Paulo et al., 2009). In the present work, we propose a rigorous model for an 80,000.00 ton/year bioethanol dehydration process with supercritical propane to minimize costs. We further consider alternative integration schemes between process streams within different nonlinear programming (NLP) problems for capital and operating costs minimization. In particular, we analyze integration between a heat pump option for the distillation column top vapor with the beer column, which can provide reduction in total energy consumption, as well as lower operating costs. Thermodynamic predictions are performed with an upgraded Group Contribution with Association Equation of State. We demonstrate that bioethanol dehydration can be a sustainable alternative that is energetically, as well as economically, competitive with molecular sieves in the production of this biofuel.