Graduation Year
2021
Document Type
Thesis
Degree
M.S.C.H.
Degree Name
MS in Chemical Engineering (M.S.C.H.)
Degree Granting Department
Chemical Engineering
Major Professor
Ramon Gonzalez, Ph.D.
Committee Member
John Kuhn, Ph.D.
Committee Member
Aydin Sunol, Ph.D.
Keywords
Polyethylene Terephthalate (PET), Plastic Bioconversion, Enzymatic Hydrolysis, Terephthalic Acid (TPA), Ethylene Glycol (EG), Fermentation, Techno-Economic Analysis
Abstract
Plastics have been used in almost every household appliance and various industrial applications for more than one hundred years. Plastic is among the most used materials in manufacturing worldwide. Plastic is cheap, light, durable, flexible, non-toxic, etc., and these properties make it suitable to use in manufacturing many types of appliances and materials. There has been an excessive reliance on plastic, leading to mass production. Despite being overly produced, there has been very little effort to recycle plastic, leading to massive accumulation of this environment. Plastic wastes are found in large patches in the world's oceans, waterways, and land. In the air, plastic exists in the form of microplastics.
Recently there has been focused attention on solving plastic waste pollution. Traditionally, there has been some recycling, but most of the plastics accumulate in landfills. Chemical recycling has been used but only to a small extent. Many organizations and companies have embarked on research to find sustainable ways of dealing with plastic waste, especially due to its environmental impact.
Traditional chemical recycling has not worked well, and the focus is now on alternative methods. One of the key methods that have been of discussion of late is biodegradation, which involves the use of microorganism to breakdown plastic polymer into simpler substances that are less harmful to the environment.
Unlike traditional chemical recycling methods, biological methods are less energy-intensive, less environmentally harmful, and may prove to be cheaper and more sustainable. Bio-upcycling involves using biological methods to breakdown plastic long-chain polymers into smaller monomeric units that can be further transformed into high-value products. This work proposes using engineered microorganisms to biodegrade Polyethylene Terephthalate (PET) plastic into Terephthalic Acid (TPA) and Ethylene Glycol (EG).
These monomers are then fermented to produce volatile organic compounds of high value. The volatile organic compounds were chosen to simplify separation, which leads to a reduction of energy consumption and makes the process energy efficient. Techno-economic analysis of such a process is done to understand the profitability of such a venture.
The study focuses on designing a plant with a capacity of 50 metric tons of PET per day. The process begins with the material collection, sorting, and then pretreatment. In pretreatment, PET undergoes shredding for size reduction of 5-10 millimeters particles. The pretreated PET then goes through enzymatic hydrolysis producing TPA and EG, which are then co-fermented to produce acetone as the volatile organic product. The acetone produced is then separated through air stripping or vacuum extraction from the fermentation broth. Economic analysis is performed to determine if the proposed design is feasible. In terms of feedstock, the primary cost driver is the price of PET, which is 10 cents per pound. Sensitivity analysis shows that costs lower than 10 cents per pound would significantly improve the process's profitability.
At a plant capacity of 50 metric tons per day, considering simultaneous hydrolysis and fermentation, the minimum selling price or acetone breakeven price is 0.69 $ per pound. This result is obtained considering the market price of acetone to be 0.3450 $ per pound, and a discounted cash flow analysis was done at an internal rate of return of 10%. These results indicate that the venture would not be profitable at this current capacity. However, when carbon yield is increased from 46% to 91%, the venture becomes profitable. However, the maximum theoretical yield attainable using acetone is 75%. Based on this result, it would be recommended to find another product that can achieve a 91% or higher carbon yield.
Additionally, when the plant capacity is increased from 50 to 500 metric tonne per day, all other parameters are kept constant; the venture would profit. At the proposed capacity of 50 metric tons per day, the plant can produce 2.2 million gallons of acetone per year. The total capital investment is 15.7 million dollars, and operating expenses cost 9 million dollars per year. Sensitivity analysis shows that the carbon yield, fermentation productivity, and PET cost significantly influence the profitability of the process
Scholar Commons Citation
Nyawanga, Benard, "Techno-Economic Analysis of Polyethylene Terephthalate Bio-upcycling" (2021). USF Tampa Graduate Theses and Dissertations.
https://digitalcommons.usf.edu/etd/9603
