Date of Award

Spring 2022

Document Type

Open Access Thesis


Chemical Engineering

First Advisor

Jochen Lauterbach


Plastic recycling has been a prevalent issue since the commercialization of plastics due to lack of adoption and insufficient technology. There are many different types of plastics used in modern day society; however, majority of recycling efforts are focused solely on polyethylene terephthalate (PET) and polyethylene plastics. Some of these overlooked plastics include polyols and polyurethanes, which can be found in a variety of applications including furniture stuffing, adhesives, and insulation foams. Recently, plastic research has turned to catalytic cracking units as a means of plastic recyclability. Catalytic cracking of hydrocarbons is a field dominated by zeolites catalysts, especially ZSM-5. Despite a heavy research focus on the catalytic cracking reactions of PET and polyethylene, there exists preliminary research efforts in the field of pyrolysis and catalytic cracking of polyols and polyurethanes. As such, a reactor and analytical system was built to investigate the catalytic cracking of polypropylene glycol (PPG) using zeolite catalysts. Based on preliminary testing, the primary seven products of interest were propionaldehyde; 1,4- dioxane, 2,5-dimethyl; 1-propanol; 1,3-dioxolane, 2-ethyl-4-methyl; acetone; 2-ethyltrans-2-butenal; and propylene glycol. Based on an economic evaluation of the process, it was decided that the maximization of the selectivity of propionaldehyde would be the overall goal of the project.

Numerous zeolite catalysts containing varying crystalline structures, silica to alumina ratios, and porosities were tested within this reactor system. ZSM-5 with a silica to alumina ratio of 50:1 was found to be the best microporous catalyst for this reaction. However, upon varying porosities within the catalyst, mesoporous structured zeolite-Y catalyst with a 30:1 silica to alumina ratio was shown to outperform all microporous catalysts. 2-D MFI zeolites and Pt-H-ZSM-5 catalysts were also synthesized and tested. Although Pt-H-ZSM-5 showed very low conversion, likely due to catalyst deactivation, the synthesized 2-D MFI zeolites showed very high levels of selectivity toward propionaldehyde, ~70%. After preliminary catalyst testing, the reaction conditions within the system were optimized. The steam percentage in the carrier gas, the reaction temperature, and the catalyst to polyol ratio for the catalytic cracking of polypropylene glycol were tested in a Box-Behnken type design of experiment (DOE). Based on the DOE results, the reaction temperature was the most important parameter for this reaction, which allowed correlations between temperature and the seven products of interest to be drawn. Characterization of fresh and spent catalysts were also investigated through numerous characterization techniques including TGA, XRD, SEM, PALS, and nitrogen physisorption. Through these characterization techniques, the existence of coke on/in the spent zeolite samples was evident.