Investigation of the Catalytic Co-Pyrolysis of Polyethylene Terephthalate and Polyolefins with Zeolite Catalysts
Restricted (Penn State Only)
- Author:
- Okonsky, Sean
- Graduate Program:
- Chemical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 28, 2024
- Committee Members:
- Robert Rioux, Professor in Charge/Director of Graduate Studies
Robert Rioux, Major Field Member
Stephen Chmely, Outside Unit & Field Member
Phillip Savage, Major Field Member
Hilal Ezgi Toraman, Chair & Dissertation Advisor - Keywords:
- Catalytic Pyrolysis
Polyolefins
Polyethylene Terephthalate
Zeolite Catalysts - Abstract:
- In this dissertation, a summary of the plastic waste disposal crisis and the available recycling solutions which can help to fix this issue are provided. Catalytic pyrolysis is identified as a valuable chemical recycling technique which has the ability to process multilayer films, containing both polyolefins and PET, into valuable chemicals for the circular economy. In Chapter 2, a detailed discussion of the analytical techniques, such as micro-pyrolysis coupled with two-dimensional chromatography, is given. In Chapter 3, the catalytic pyrolysis of low-density polyethylene (LDPE), polyethylene terephthalate (PET), and their mixture (1:1 wt./wt.) with three zeolite catalysts (HZSM-5, H-Beta, HY) was investigated using a thermogravimetric analyzer (TGA) and a Pyroprobe® micro-reactor coupled to a gas chromatograph mass spectrometer (Py-GC/MS). The TGA results demonstrated that during pyrolysis at 10 °C/min, on average, zeolite catalysts decreased the maximum decomposition temperature by 149 °C for LDPE while only decreasing by 8 °C for PET. The derivative thermogravimetric (DTG) curve evidenced interactions when the two polymers were catalytically co-pyrolyzed for all the three catalysts. A lumped nth order reaction scheme was able to accurately model both non-catalytic and catalytic pyrolysis and co-pyrolysis by using least squares fitting approach for determining the kinetic parameters. The kinetic model was able to model well the interaction effects observed during catalytic co-pyrolysis of LDPE and PET with HZSM-5, H-Beta, and HY (Fit%Wt% > 96%, Fit%DTG > 93%). Py-GC/MS experiments for the catalytic fast pyrolysis of LDPE revealed HZSM-5 resulted in the highest selectivity to aromatic hydrocarbons (31.6%) and HY resulted in the highest selectivity to gasoline range C5-C10 paraffins and olefins (40.9%). Catalytic fast pyrolysis of PET showed high selectivity to benzene for all catalysts (> 43%) and that HZSM-5 resulted in the highest selectivity to polyaromatic hydrocarbons (24.7%). The catalytic fast co-pyrolysis of LDPE and PET revealed interaction effects for all the three catalysts evidenced by a positive synergy% for alkylated benzenes (3-142%) and polyaromatics (105-187%) with a concomitant negative synergy% for benzene (24-36%) and C5-C10 paraffins and olefins (27-53%). In Chapter 4, the catalytic (co-)pyrolysis of LDPE and PET with HZSM-5 and HY zeolite catalysts was conducted in a micro-pyrolysis reactor coupled to a two-dimensional gas chromatography system. Pyrolysis operating conditions such as the pyrolysis temperature, the catalyst to feedstock (CF) ratio, and the LDPE:PET ratio were varied. It was found that for the co-pyrolysis of LDPE and PET, HZSM-5 led to higher yields of C2-C4 olefins and monoaromatic products. Lower CF ratios increased the yield of C2-C4 olefins for LDPE pyrolysis, but decreased benzene yield for PET pyrolysis, concomitant with an increased yield in benzoic acid. A lower temperature of 400°C which was sufficient for the pyrolysis of LDPE, led to incomplete conversion of PET. Surface response diagrams were used to visualize the impact of the various pyrolysis operating conditions on the yield of C2-C4 olefins and BTEX, which serve as target products for the circular economy. In Chapter 5 the catalytic pyrolysis and co-pyrolysis of PP and PET with HZSM-5 zeolite catalyst was conducted for various catalyst to feedstock (CF) ratios, PP to PET ratios, and heating rates using a thermogravimetric analyzer (TGA). The Flynn-Wall-Ozawa (FWO) isoconversional approach was used to determine apparent activation energies for the non-catalytic and catalytic pyrolysis of PP and PET. An nth-order reaction scheme was used to model the pyrolysis at various operating conditions through the optimization of the associated kinetic parameters. Additional TGA experiments were conducted with used catalysts to gain insight into catalyst deactivation, and it was found that the inclusion of PET led to more severe deactivation. Collidine temperature programmed desorption (TPD) indicated the loss of external acid sites for catalysts coked by PET pyrolysis, explaining the severe deactivation. Catalyst deactivation was incorporated into the kinetic modelling approach, so that degradation profiles could be predicted for experiments with the used catalysts. In Chapter 6 the catalytic co-pyrolysis of PP and PET with HZSM-5 at a higher Si/Al ratio of 40 was conducted with TGA and micro-pyrolysis. The HZSM-5 catalyst was subjected to a desilication treatment in order to increase the mesoporosity of the catalyst. The two HZSM-5 catalysts (parent and desilicated) were tested in both their fresh, used, and regenerated states. It was observed that the desilication treatment led to a higher yield of C2-C4 olefins as well as enhanced degradation rates at lower temperatures.