The increased toxicity potential associated with waste solvents can hardly be overstated. The use of conventional waste disposal techniques such as incineration, onsite and offsite disposal have been explored; however, these traditional waste disposal approaches tend to increase the overall carbon and ecological footprints. Solvent recovery methods present a better alternative to these conventional approaches to improve industrial processes’ circularity. Emergy is one way to quantify the sustainability of an industrial process. It is defined as the amount of available energy (exergy) of one kind that is directly and indirectly used up in transformations to make a product. Different energy flow type into a process needs to be converted into a solar energy equivalent, termed as solar emjoules (sej). This emjoules sets the basis for all emergy calculations. Another metric that presents a good basis for sustainability analysis is the sustainable process index (SPI), which estimates the total area needed by a process to produce a unit of product. The choice of area as the basis for calculation is based on the idea that solar energy is the real long-term input with its utilization bound to the planet’s limited surface area. Thus, SPI represents the area needed by the process to provide one unit of product, while emergy helps to account for all the work done by nature and the human-economy in the production process. Due to the common denominator of solar energy and the use of several interrelated indices in the estimation of SPI and emergy, only one metric is insufficient to present a comprehensive sustainability analysis for a process. Therefore, to offer a holistic view of sustainability for a process, it is essential to integrate both SPI and emergy. In this work, a superstructure-based solvent recovery framework has been developed that considers multiple separation technologies simultaneously to recover waste solvents. We integrated mathematical models that consider the SPI, Emergy, and Economics of the recovery pathway. We then formulated a multi-objective problem that seeks to minimize all three metrics simultaneously. Our results indicate that solvent recovery presents a good alternative to conventional waste solvent disposal techniques such as incineration. Additionally, the integrated SPI-emergy analysis offers an approach to quantify the environment’s role in absorbing and processing pollution.

Sustainability assessment of solvent recovery pathways via the SPI and emergy metrics

ACS Spring Meeting 2021

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