(728a) Bioprocess Synthesis, Design and Analysis through a Group-Contribution Approach

Modelling and simulation of a process flowsheet usually involves identifying the structure of the flowsheet (defined by operations involved and their sequence), deriving model equations to represent each operation, and solving the resulting total model equations according to various simulation strategies. The flowsheet synthesis problem determines the type of operations and their sequence while the flowsheet design problem determines the optimal values for the conditions of operation and other operation/equipment related variables. The main idea here is to apply the group-contribution approach (from property estimation) to the synthesis, design and analysis of chemical and biochemical processes with groups representing process unit operations (reactor, distillation, flash, crystallization, etc.), bonds representing streams and/or recycles, rules for molecule feasibility representing process flowsheet feasibility and sum of group contributions representing the performance of the flowsheet.

The proposed paper will present the process groups based approach to model, design and analyze the bioethanol production process. The production route for the bioethanol process has been selected, due to the current interest in the use of renewable sources to produce important chemicals (the biorefiney concept). Also biofuels have become a priority to reduce the dependence on fossil fuels. The production of bioethanol has increased all over the world in the last few years through expansion of existing plants and construction of new facilities, but the economic competitiveness of bioethanol as a liquid fuel strongly depends on the energy resources used during its production. This implies the need for generation of sustainable alternatives to determine the optimal values for the conditions of operation and other operation/equipment related variables for the synthesized process flowsheet, which will be highlighted through the process group approach.

The sustainability of bioethanol production from alternative renewable sources will be analyzed together with a breakdown of the operational and equipment costs in different parts of the bioethanol process. Each part of the process (pretreatment, fermentation, ethanol recovery/purification) has been analyzed in detail. From this analysis, it has been identified that the economic feasibility of the bioethanol process can be improved through higher product yields and/or more efficient product recovery. Since the fermentor effluents are dilute aqueous solutions of the product, recovery is not straightforward. Furthermore, separation by distillation is both difficult and expensive because of the ethanol-water azeotrope. The option of increased product yield in the reaction is beyond the scope of this presentation as it involves the design/selection/testing of new catalysts or enzymes. In this presentation different schemes for ethanol recovery/purification will be presented using the process-groups approach. The optimal sustainable process for bioethanol production will be presented together with a lifecycle assessment. Finally, extension of the proposed approach to other chemicals within the biorefinery concept will be discussed.