Fuel ethanol production: process design trends and integration opportunities

Current fuel ethanol research and development deals with process engineering trends for improving biotechnological production of ethanol. In this work, the key role that process design plays during the development of cost-effective technologies is recognized through the analysis of major trends in process synthesis, modeling, simulation and optimization related to ethanol production. Main directions in techno-economical evaluation of fuel ethanol processes are described as well as some prospecting configurations. The most promising alternatives for compensating ethanol production costs by the generation of valuable co-products are analyzed. Opportunities for integration of fuel ethanol production processes and their implications are underlined. Main ways of process intensification through reaction-reaction, reaction-separation and separation-separation processes are analyzed in the case of bioethanol production. Some examples of energy integration during ethanol production are also highlighted. Finally, some concluding considerations on current and future research tendencies in fuel ethanol production regarding process design and integration are presented.

Effect of temperature on the microaerophilic metabolism of Pachysolen tannophilus

Xylitol production by Pachysolen tannophilus from detoxified hemicellulose hydrolysate was investigated under microaerophilic conditions at temperature ranging from 20 to 40 degrees C. A carbon balance previously proposed to study the influence of pH was used in this work to evaluate the amounts of carbon source (xylose) utilised in competitive metabolic ways: reductive production of xylitol, ethanol fermentation and respiration. At pH = 5.5 more than 83% of xylose was reduced to xylitol at 25 < T < 30 degrees C, whereas respiration became the main process at low temperature (71.1% at 20 degrees C). At high temperature, on the other hand, all three processes took place at comparable rate, consuming at 40 degrees C nearly the same percentage of carbon source (33-35%). Finally, the maximum values of volumetric productivity calculated at variable temperature were used to estimate the main thermodynamic parameters of both xylitol production (Deltah* = 105.4 kJ mol(-1); Deltas* = -13.2 J mol(-1) K(-1)) and thermal deactivation (Deltah*(D) = 210.5 kJ mol(-1); Deltas*(D) = 3.63 J mol(-1) K(-1)).