10/31/2022
By Erin Caples

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a master’s thesis defense by Kalsoom Jan on “Hydrothermal liquefaction of polyethylene with different molecular weights in supercritical water.”

Candidate Name: Kalsoom Jan
Defense Date: Thursday, Nov. 10, 2022
Time): Noon to 2 p.m.
Location: Perry Hall 415. Those interested in attending remotely should contact Grace_Chen@uml.edu to request access to the Zoom link.,

Committee: Advisor: Prof. Wan-Ting (Grace) Chen, Plastics Engineering, University of Massachusetts Lowell

Committee Members:

  • Prof. Margaret Sobkowicz, Plastics Engineering, University of Massachusetts Lowell
  • Prof. Hsi-Wu Wong, Chemical Engineering, University of Massachusetts Lowell

Brief Abstract:
Plastic waste is accumulated at an increasing rate day by day, causing a severe threat to human beings and the ecosystem. Polyethylene (PE) is used widely for many different applications (e.g., packaging, consumer goods, textile) and accounts for 33% produced each year. Thus, upcycling PE is an important challenge to address. Hydrothermal liquefaction (HTL), which uses sub- and super-critical water as reaction media, has been proven to be a robust and energy-efficient method for valorizing plastic waste. However, HTL of PE still requires high temperatures (450-475°C). We hypothesize that when the molecular weight of PE is lower, the required HTL temperature to produce oil from PE would also be lower. We envision that the results obtained from this study could improve the energy efficiency of upcycling PE waste by integrating mechanical and chemical recycling.

To examine this hypothesis, in this study, PE with different molecular weight ranges (1,200-187200 g/mol) was converted into oil products via HTL at 400-475°C with a reaction time of 1-2 h. The oil products are characterized by Fourier-Transform Infrared Spectroscopy (FTIR), Gel Permeation Chromatography (GPC) and Gas Chromatography Mass Spectrometry (GC-MS), which showed that major components of oil include aromatics, cyclics, olefins and paraffins with the carbon number ranging from 6 to 20. The higher oil yield was obtained at 450°C with a 2-h reaction time (i.e., a full conversion condition). At this full conversion condition, no significant difference in the oil yield was observed with PE of different molecular weights under HTL, but more aromatics were obtained from PE of lower molecular weight (1200 g/mol). To better observe the effect of the molecular weight of PE on HTL, a milder reaction condition (425°C, 2 h) was used to convert linear low-density PE (LLDPE) into oil. The product yields from LLDPE validated our hypothesis—the lower molecular weight of PE, the lower temperature needed to depolymerize LLDPE under HTL. More specifically, when the molecular weight is within the range of 7200-13600 (g/mol), a comparable oil yield was obtained. However, when the molecular weight increased from 50000 to 128900 (g/mol), a lower oil yield was gained, except for the oil yield converted from a post-consumer PE waste (PCR-PE). This exception could be because PCR-PE may contain impurities that unexpectedly catalyze depolymerization of PE under HTL. More research is needed to elucidate the effect of impurities on the HTL of PE.

All interested students and faculty members are invited to attend.