Abstract
Plastics are used every day for a variety of different purposes. These uses extend from packaging foods to serving as a primary material in medical devices, construction, and electronics. The widespread use of plastics in everyday life has made it a problem because they cannot easily biodegrade and have gained attention for their environmental impact. Plastic is now often found in oceans, rivers, and lakes, and the impact of microplastic consumption by humans and other animals remains under study. People need to start investing in a new type of plastic, one that can maintain the same purpose and efficiency, but also reduce any negative environmental impact. Currently, the vast majority of global plastic production relies on nonrenewable hydrocarbon sources. One possible solution to this is using a biodegradable plastic, such as polylactic acid (PLA). PLA is a biodegradable thermoplastic made from renewable plant-based resources, such as corn starch, sugarcane, or sugar beet pulp. The use of PLA creates a circular economy by using a renewable resource to create a biodegradable plastic. In the technical portion of this project, I examine the plausibility of developing an industrial-scale plant for producing PLA from sugarcane bagasse in Brazil. Sugarcane bagasse is a fibrous residue that is left over after crushing sugarcane to extract its juice. Except for occasionally being burned as low-value fuel, this waste product serves no purpose. I designed, scaled, and priced all unit operations with kinetic data, Aspen Plus Modeling, and general chemical engineering considerations. The plant is located in Brazil, the world’s largest sugar producer. The upstream system begins with steam-exploding the sugarcane bagasse to release the necessary sugars for further processing. Next, the steam-exploded sugarcane bagasse proceeds through multiple washing steps followed by enzymatic hydrolysis to break down complex molecules into more usable components. Finally, fermentation employs Bacillus Coagulans to convert usable sugars into lactic acid. Next, the downstream system uses multiple purification and concentration steps to create a concentrated stream of lactic acid. This lactic acid then reacts to create lactide, a cyclic dimer, which increases the molecular weight and quality of the final product. Ultimately, lactide reacts to form PLA pellets, which are sold to the end user. For the economic considerations of this plant, I evaluated equipment, labor, operating, raw material, and utility costs. After analyzing the total cost of the plant, associated taxes, and depreciation, I determined that this plant provides an unfavorable return on investment. The raw material and utility costs are too high for this process design to break even in most economic conditions, and so the process is not recommended for future use. I chose sugarcane bagasse as a feedstock for this process because a significant amount is available due to the mass cultivation of sugarcane in Brazil. This motivated the topic of the social portion of this thesis: how do different social groups in Brazil construct and contest the idea of sugarcane as a sustainable industry? I apply the SCOT framework to analyze how different groups define sustainability in Brazil’s sugarcane industry and how these interpretations shape policy. My analysis focuses on the roles and impacts of policymakers, consumers, farmers, and indigenous communities in Brazil’s sugarcane industry. The Brazilian sugarcane industry defines sustainability with a narrow scope. However, sustainability is not objective; it is a socially constructed concept that is shaped by power, policy, and economic initiatives. The Brazilian sugarcane industry typically benefits policymakers, large sugar corporations, and land-owning farmers through economic growth. However, members of indigenous communities, as well as the average consumer, can experience higher living costs, displacement, and heightened vulnerability. Overall, the technical and sociotechnical components of this thesis outline a potential process that promotes sustainability through producing a bioplastic from a waste product. Simultaneously, in the sociotechnical section, I evaluate whether the industry where this waste product originates is actually sustainable in the first place. My analysis can be applied to many industrial processes that claim to be sustainable based on narrow metrics, such as carbon negativity or through the creation of biodegradable resources. However, evaluating these processes further upstream, where the main input to the process is cultivated, dives deeper into the true sustainability of an industry. Holistically, it is important to evaluate not only the sustainability of an industry itself, but also the impact on the surrounding community. Sustainability is relevant both when creating the process inputs and when carrying out the process. After all of this is considered, then the sustainability of an industry can be justified.
