Sustainable supply of energy has become one of the major challenges in this century. Liquid biofuels provide one of the options for fossil fuel replacement in the short to medium term because they can use the existing infrastructure of vehicles and distribution with small modifications.

The goal of this project is to develop novel and advanced process systems engineering tools for addressing the problem of optimal design of biofuel plants under multiple criteria. The PI will undertake the following research tasks: a) Investigate superstructure optimization models to synthesize new flowsheet structures of biofuel plants; b) Develop simultaneous optimization models for the minimization of energy and freshwater consumption; c) Develop stochastic programming models to account for uncertainties in the feedstock; d) Develop bi-criterion optimization models to account for economics and life cycle analysis; e) Develop targeting models to determine maximum profit, minimum energy use, minimum freshwater consumption and minimum environmental impact. In order to achieve these objectives he intends to focus on the design of lignocellulosic bioethanol plants as the major case study. Other biofuels such as biodiesel will also be considered.

Intellectual Merit:

In the design of biofuel plants a major contribution will be process synthesis models to systematically consider many design alternatives under a superstructure optimization framework. Aside from the capability of accounting for uncertainties in the feedstock, and of optimizing both profit and environmental impact using life cycle analysis under a bicriterion optimization framework, of significance will be targets for maximum profit, minimum energy use, minimum freshwater use and minimum environmental impact, which should provide useful indicators about the viability and desirability of these designs. In the area of process synthesis the simultaneous incorporation of water management (or water networks) together with heat integration in the optimization of the superstructure will also be studied as well as the development of solution methods of bi-criterion disjunctive optimization problems under uncertainty, a problem that has not been addressed before. These design capabilities will be demonstrated with a major case study, the design of lignocellulosic bioethanol plants. In terms of transformative research, perhaps the most significant aspect will be the development of modern and comprehensive synthesis and optimization tools for the design of biofuel plants, which have not had the benefit of being subjected to more systematic and thorough optimizations as have their petrochemical counterparts.

Broader Impact:

A potential impact of the research in practice is the collaborations with Amyris and Cargill, both of whom will provide realistic data and case studies beyond the lignocellulosic ethanol case study, to help calibrate these design methodologies. The work will provide useful design concepts and tools that will improve the economic and environmental performance of biofuel plants, particularly in regard to energy and water usage, as suggested by preliminary results. These design capabilities should also help policy makers consider the best process designs when making comparisons among competing technologies. At the graduate level the PI intends to incorporate the findings of this research in a core graduate course on Process Systems Engineering. At the undergraduate level the PI intends to use as a senior design project the design of cellulosic ethanol. The results will be published as a CACHE Design case study, which will have wide distribution through CAChE as has been the case of previous design case studies, three of which the PI prepared. The preparation of the design case study for CACHE will be performed by two undergraduate students at Carnegie Mellon University. Another dimension of the project will be its dissemination through outreach activities with high schools in the Pittsburgh area. These activities, which will be performed through the Steinbrenner Institute for Environmental Education at Carnegie Mellon, will involve the PI and the graduate student visiting Several high schools to explain the concepts of renewable biofuels and integrated process water networks.

Project Report

Water is becoming a scarce natural resource. It is predicted that by 2025 two thirds of the world population will experience water stress. In the industrial sector chemical, biofuel, and petroleum processes consume significant amounts of water. Therefore, there is a significant incentive to reduce the freshwater consumption to make these process systems more sustainable. The major goal of this research project has been to develop novel mathematical optimization models to predict the minimum freshwater consumption in water networks that are present in process systems. One of the specific goals has been to develop a unique simplified model for targeting minimum freshwater consumption. This model can be applied to the design of process systems in order to establish optimal trade-offs between capital investment and energy and water consumption. The model has also ben extended to include specific treatment technologies such as sedimentation, reverse osmosis, filtration, ion exchange, oxidation, and anaerobic and aerobic treatment. The major area of application of the mathematical models for water has been in the design of second generation biofuel processes that rely on the use of lignocellulosic material like switchgrass. We especially focused in the production of bioethanol in which the major technologies included gasification and fermentation. We also considered production of biodiesel from algae. In all cases we optimized the economics and energy use of these processes while accounting for minimum freshwater consumption. The results that we obtained indicated that freshwater consumption can often be reduced by at least a factor of two compared to actual plants that are currently in operation in the U.S. The project also served to train one Ph.D. student and one postdoctoral researcher, both of whom have acquired unique knowledge and expertise in the areas of industrial water management and design of biofuel plants. Finally, another important outcome of this project has been to produce two educational case studies that we made available for their use in undergraduate design courses in chemical engineering in the U.S. and overseas.

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Carnegie-Mellon University
United States
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