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The advent of shale gas and the increasing spread between the supply and demand curves for propylene present an opportunity for adopting alternative pathways to produce propylene. This study aims to investigate a sustainable process design approach to on-purpose propylene production. A hierarchical approach to sustainable process design is proposed and implemented in a case study with propane dehydrogenation as the process under consideration. A base case design was developed, and process integration and intensification techniques were applied to reduce dependence on external utilities and to lower the overall capital investment. Waste heat recovery and offgas recycle were additional options used to intensify the overall energy consumption of the process. Emissions from the process were calculated from the Environmental Protection Agency's guidelines. Economic and environmental metrics were then used to study the impact of integration and intensification techniques. Up to 70% reductions in CO 2 emissions were achieved as a result of this approach to sustainable design. The Sustainability Weighted Return on Investment metric was evaluated for all cases. Multiobjective decision making for the optimum design was facilitated by the sustainability metrics augmented with the traditional economic criteria.

Dry reforming of methane (DRM) is an important technology that utilizes CO 2 to convert methane to a mixture of H 2 and CO (syngas). Commercial applicability of DRM has been challenged by the high energy requirement, susceptibility to coke formation, and low-quality syngas (syngas ratio, H 2 /CO ∼ 1). On the other hand, DRM provides an attractive pathway to the cost-effective sequestration of CO 2 via transformation to value-added chemicals and fuels. DRM may be used in conjunction with other reforming technologies to produce the needed quality of syngas and to exploit synergism in energy release and demand. In this work, an optimization-based approach is used to compare the carbon footprint of conventional reforming technologies with other processes involving DRM to produce syngas of different H 2 /CO ratios. Technical, economic, and environmental metrics are used to assess the various options. Additionally, the model accounts for the carbon footprint associated with the reforming process, catalyst regeneration, and other energy requirements. The results of the optimization formulation show that the CO 2 fixation using DRM is highly dependent on the desired syngas ratio. Net CO 2 fixation occurs only at low syngas ratios of 1 and below. The results also indicate that producing syngas through a parallel reforming network involving existing technologies (steam methane reforming and partial oxidation) with DRM does not result in overall CO 2 emissions reduction. Finally, two novel process concepts have been studiedCO removal from DRM syngas (DRM + COSORB) and H 2 addition from an external source. Both these cases, while producing high H 2 /CO ratio syngas, have potential in terms of CO 2 emissions reduction and competitive operating costs but will have certain limitations. The DRM + COSORB (captured CO sold as feedstock) process was found to be the best among all options studied in terms of overall reduction of CO 2 emissions and operating costs.