Electric and thermal energy from bioethanol : process intensification by using diluted feeds

Bioethanol attracted growing interest as raw material for the production of hydrogen. The latter can be successfully used to feed fuel cells with the aim of combined heat and power (CHP) cogeneration. A demonstrative project has been carried out c/o our Dept. [1] by running an integrated CHP unit with residential size, i.e. 5 kWel + 5 kWth. It was constituted by 6 integrated reactors, connected in series, fed with bioethanol and water, to produce reformate gas (prereformer and steam reformer) and to accomplish gas purification from CO (high- and low-temperature water gas shift reactors and two methanators). The purified reformate is suitable to feed a PEM fuel cell with the above mentioned power output. The aim of this work was to focus on process intensification, to achieve an economically sustainable solution. This was done at first by identifying the effect of bioethanol concentration on process output and proposing suitable means to achieve bioethanol purification. This is particularly straightforward because second generation bioethanol is nowadays proposed as fuel or as blending agent for gasoline, thus requiring deep dehydration. However, if used as feed for steam reforming, much lower concentration is needed, allowing to limit distillation/dehydration cost, which account for 50-80% of bioethanol production expenses [2,3]. Process layout has been revised by comparing different possible schemes, compared as for heat and power duty (input) and output. Different solutions to account for energy input to the reformer have been also compared. Accordingly, different options for the purification of raw bioethanol beer have been compared, in order to meet the required specifications and to limit the cost of the reformer feed. The effect of the purity of the resulting bioethanol stream on reformer performance has been also experimentally addressed. As well, the effect of reactor temperature was considered, and this was set at the minimum level to guarantee optimal product yield, suitable catalyst durability and minimum heat input to the reactor. Process simulation has been carried out by using the Aspen Plus software and economic assessment of the solutions proposed has been carried out by using the Aspen ONE cost evaluation tool. References [1] Rossetti, I.; Biffi, C.; Tantardini, G.F.; Raimondi, M.; Vitto, E.; Alberti, D. Int. J. Hydrogen Energy, 2012, 37, 8499. [2] Rossetti, I.; Compagnoni, M.; Torli, M. Chem Eng. J., 2015, 281, 1024. [3] Rossetti, I.; Compagnoni, M.; Torli, M. Chem Eng. J., 2015, 281, 1036