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6 Flexible Manufacturing and the Circular Economy
Pages 151-175

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From page 151...
... Given their critical role in manufacturing, chemical engineers have many opportunities to increase its environmental sustainability. This chapter provides an overview of the intersection of manufacturing and chemical engineering, followed by a discussion of feedstock flexibility, distributed manufacturing and process intensification, and the importance of transitioning from a linear to a circular economy.
From page 152...
... . More recently, consideration of environmental and social justice has become increasingly important for chemical engineers in these analyses.
From page 153...
... Use of Renewable Feedstocks -- a raw material or feedstock should be renewable rather than depleting whenever technically and economically practicable. Reduce Derivatives -- unnecessary derivatization (use of blocking groups, protection/deprotec tion, temporary modification of physical/chemical processes)
From page 154...
... Some of these concepts are likely to play major roles in the deployment of manufacturing to low- and middle-income countries and to economically depressed regions of higher-income countries, as well as in various efforts at reshoring of manufacturing through new technologies. Indeed, industrial manufacturing has the potential in this century to at least partially transform physically from the scale of the petrochemical complexes studied by today's undergraduate chemical engineers to more heterogeneous intensified and distributed manufacturing sites, including those with electrically driven power sources.
From page 155...
... Transitioning manufacturing from a linear to a circular economy is a key opportunity for chemical engineers. FEEDSTOCK FLEXIBILITY FOR MANUFACTURING OF EXISTING AND ADVANTAGED PRODUCTS The chemical engineering profession emerged in large part to confront the urgent challenges faced more than a century ago in the then-burgeoning petroleum refining industry.
From page 156...
... For example, the availability of stranded natural gas resources, along with the potential harm of leakage of GHGs from those resources, makes conversion of these streams via chemical, biological, electrochemical, or other means a key opportunity for chemical engineers. The use of nonthermal approaches requiring minimal utility infrastructure may be critical for the ultimate feasibility of small-scale and distributed harnessing of such feedstocks as stranded natural gas; industrial waste gases; and industrial, commercial, or municipal wastewater (Khalilpour and Karimi, 2012; Tuck et al., 2012)
From page 157...
... The manufacturing of direct-replacement chemicals offers substantial opportunities for chemical engineers to develop scaled-out, distributed manufacturing systems and innovative, large-scale processes that can compete with the conversion of fossil resources. Conversely, performance-advantaged bioproducts could also serve as economic incentives to invest in new capital infrastructure at scale to displace the fossil carbon-based feed streams that dominate chemicals and materials production at scale today.
From page 158...
... New separation technologies will be critical to realizing these transformations, as will catalysts that can enable the necessary reductive chemistry while remaining stable in aqueous environments. Beyond innovative process and chemistry developments, there are fundamental research problems for chemical engineers to solve in the feedstock flexibility arena.
From page 159...
... In an intensified process, ammonia and hydrofluoric acid are added directly to a modified fluorine electrochemical cell to produce nitrogen trifluoride without a solid waste stream (Coronell et al., 1997; Hart et al., 2015; Krouse et al., 2016)
From page 160...
... , hybrid processes (e.g., extractive crystallization, heat-integrated distillation, reactive distillation, selective/catalytic membrane reactors) , energy transfer processes (e.g., rotating packed beds, sonochemical reactors, microwave-enhanced operations)
From page 161...
... Because much work in additive manufacturing is taking place in the mechanical engineering and materials science communities, chemical engineers have numerous opportunities to combine expertise from these adjacent fields with application-specific needs in chemical processing.
From page 162...
... Opportunities for chemical engineers in AM broadly include supporting advances for faster printing with higher resolution, as well as use of multiple or more advanced and sustainable materials with attention to end of life. These efforts are best undertaken in partnership with mechanical and software engineers, collaboratively improving the technologies that scale these processes for widespread use.
From page 163...
... . The world's linear economy annually generated about 110 million metric tons of MSW in 1900, more than 1 billion metric tons in 2000 (including about 80 percent of consumer products, excluding packaging, disposed of after a single use)
From page 164...
... that are consistent with the principles of green chemistry and engineering:  Strategy 1: Design to avoid pollution and waste -- Reduce or eliminate GHG emissions and hazardous substances and the resulting pollution of air, land, and water. Also limit, if not eliminate, waste of materials during the manu facturing of products and packaging, as well as during the discarding of prod ucts and packages at their end of life.
From page 165...
... Chemical engineers are uniquely positioned to solve problems associated with the three strategies of the circular economy. Their contributions could include redesigning processes and products to reduce or eliminate pollution, developing new ways to reduce and utilize waste, designing products to be used longer, and designing processes and products using sustainable feedstocks.
From page 166...
...  Dispose of the plastic in the product and/or package in a managed landfill. FIGURE 6-4 Global production, use, and fate of polymer resins, synthetic fibers, and additives, 1950–2019, in millions of metric tons.
From page 167...
... Chemical engineers also have an important role to play in increasing and improving the recycling of plastics. Opportunities exist in all recycling technologies, such as mechanical recycling; dissolution recycling; and advanced recycling methods, such as depolymerization, pyrolysis, and gasification (Figure 6-5)
From page 168...
... . The main unit operations that chemical engineers can further develop, optimize, scale up, and commercialize are polymer dissolution, extraction, processing, layer separation, filtration, contaminant migration, and solvent diffusion and recycling (Pappa et al., 2001; Walker et al., 2020; Zhao et al., 2018)
From page 169...
... Other potential solutions to the plastics disposal problem beyond the recycling technologies discussed above include the following:  Use of biodegradable plastics and various enzymes and biodegrading organ isms for plastics -- LCAs are necessary to determine whether in some envi ronments, the negative effects of the uncontrolled release of the biodegrada tion products into the atmosphere outweigh the benefits of using biodegradable plastics.  Closed-loop recycling of polymers synthesized with in-chain functional groups that act as break points -- For example, Häuβler and colleagues (2021)
From page 170...
... and the development of monomaterial solutions that achieve the same performance as multimaterial solutions are two key areas in which chemical engineers will continue to contribute. Regeneration of Natural Systems A biobased economy includes both biobased materials and biobased fuels (fuel uses are discussed in Chapter 3)
From page 171...
...  Pyrolysis oil -- Biomass pyrolysis produces pyrolysis oil, which can then be upgraded to different chemicals. Biobased plastics are also part of the circular economy of plastics.
From page 172...
... , biobased plastics can potentially have a lower carbon footprint and additional end-of-life options, such as composting. The global production of biobased plastics was 2.1 million metric tons in 2020, representing less than 1 percent of total plastics production.
From page 173...
... More specifically, challenges and opportunities for chemical engineers in this domain include  scalable and economical processes for producing biobased plastics (e.g., PEF and PBS) and biobased monomers (e.g., biobased terephthalic acid; Collias et al., 2014)
From page 174...
... The continued drive toward more efficient, environmentally friendly, and cost-effective manufacturing processes will benefit from a much wider range of available feedstocks for use as building blocks to produce chemicals and materials. The challenge of feedstock flexibility offers chemical engineers an opportunity to develop advances in reductive chemistry and processes that will allow the use of oxygenated feedstocks, such as lignocellulosic biomass.
From page 175...
... Flexible Manufacturing and the Circular Economy 175 cused on pilot- and demonstration-scale projects in advanced manufacturing, including scaled-down and scaled-out processes; process intensification; and the transition from fossil-based organic feedstocks and virgin-extracted inorganic feedstocks to new, more sustainable feedstocks for chemical and materials manufacturing.


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