The purification of bioethanol fuel involves an energy-intensive separation process to concentrate the diluted streams obtained in the fermentation stage and to overcome the azeotropic behavior of the ethanol–water mixture. The conventional separation sequence employs three distillation columns that carry out several tasks, penalized by high-energy requirements: preconcentration of ethanol, extractive distillation, and solvent recovery. To solve this problem, we propose here a novel heat-pump-assisted extractive distillation process taking place in a dividing-wall column (DWC). In this configuration, the ethanol top vapor stream of the extractive DWC is recompressed from atmospheric pressure to over 3.1 bar (thus to a higher temperature) and used to drive the side reboiler of the DWC, which is responsible for the water vaporization. For a fair comparison with the previously reported studies, we consider here a mixture of 10 wt % ethanol (100 ktpy plant capacity) that is concentrated and dehydrated using ethylene glycol as mass-separating agent. Rigorous process simulations of the proposed vapor recompression (VRC) heat-pump-assisted extractive DWC were carried out in AspenTech Aspen Plus. The results show that the specific energy requirements drop from 2.07 kWh/kg (classic sequence) to only 1.24 kWh/kg ethanol (VRC-assisted extractive DWC); thus, energy savings of over 40% are possible. Considering the requirements for a compressor and use of electricity in the case of the heat-pump-assisted alternative, it is possible to reduce the total annual cost by approximately 24%, despite the 29% increase of the capital expenditures, for the novel process as compared to the optimized conventional separation process.

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Biodiesel is a biodegradable and renewable fuel, emerging as a viable alternative to petroleum diesel. Conventional biodiesel processes still suffer from problems associated with the use of homogeneous catalysts and the limitations imposed by the chemical reaction equilibrium, thus leading to severe economic and environmental penalties. This work provides a detailed review—illustrated with relevant examples—of novel reactive separation technologies used in biodiesel production: reactive distillation/absorption/extraction, and membrane reactors. Reactive separation offers new and exciting opportunities for manufacturing the fatty acid alkyl esters involved in the industrial production of biodiesel and specialty chemicals. The integration of reaction and separation into one operating unit overcomes equilibrium limitations and provides major benefits such as low capital investment and operating costs. These reactive separation processes can be further enhanced by heat‐integration and powered by heterogeneous catalysts, to eliminate all conventional catalyst related operations, using efficiently the raw materials and the reaction volume, while offering higher conversion and selectivity, as well as significant energy savings compared with conventional biodiesel processes. Remarkable, in spite of the high degree of integration, such integrated reactive‐separation processes are still very well controllable as illustrated by the included examples. Copyright © 2012 Society of Chemical Industry

Keywords 11Downstream processing, distillation, dividing-wall column, optimal design, process control 12 13 Highlights 14• Energy efficient downstream processing in the acetone-butanol-ethanol (ABE) process 15• Cost effective distillation process for butanol separation and purification 16• Optimal process design including heat-integration, still robust and controllable 17 18 Abstract 19Butanol is considered a superior biofuel, as it is more energy dense and less hygroscopic than 20 the more popular ethanol, resulting in higher possible blending ratios with gasoline. However, 21 the production cost of the acetone-butanol-ethanol (ABE) fermentation process is still high, 22 mainly due to the low butanol titer, yield and productivity in bioprocesses. The conventional 23 recovery by distillation is an energy-intensive process that has largely restricted the economic 24 production of biobutanol. Other methods based on gas stripping, liquid-liquid extraction, 25 adsorption, and membranes are also energy intensive due to the bulk removal of water. 26This work proposes a new process for the butanol recovery by enhanced distillation (e.g. 27 dividing-wall column technology) using only few operating units in an optimized sequence to 28 reduce overall costs. A plant capacity of 40 ktpy butanol is considered and purities of 99.4 29 %wt butanol, 99.4 %wt acetone and 91.4 %wt ethanol. The complete downstream processing 30 was rigorously simulated and optimized using Aspen Plus. The enhanced process is effective 31 in terms of eco-efficiency (1.24 kWh/kg butanol, significant lower costs and emissions) and 32 can be readily employed at large scale to improve the economics of biobutanol production. 33