04/16/2024
By Danielle Fretwell

The Francis College of Engineering, Department of Energy Engineering - Renewable, invites you to attend a Doctoral Dissertation defense by Christian Ayafor on: "Sustainable Processes for Waste Plastic Upcycling and the Use of Safer Solvents."

Candidate Name: Christian Ayafor
Degree: Doctoral
Defense Date: Tuesday, April 30, 2024
Time: 2 to 4 p.m.
Location: Perry Hall 415

Committee:

  • Advisor: Hsi-Wu Wong, Ph.D., Associate Chair for Graduate Studies, Chemical Engineering, University of Massachusetts Lowell
  • Margaret J. Sobkowicz Kline, Ph.D., Professor, Plastics Engineering, University of Massachusetts Lowell
  • Dongming Xie, Ph.D., Associate Professor, Chemical Engineering, University of Massachusetts Lowell
  • Gregory Morose, Sc.D., Research Manager, Toxics Use Reduction Institute (TURI), University of Massachusetts Lowell

Brief Abstract:
The preservation of the environment for current and future generations entails applying sustainability principles to evolving innovative processes for meeting up with the ever-growing population and its demand. Sustainable measures contribute to nurturing prosperity, enhancing community resiliency, and safeguarding the environment. In this Ph.D. dissertation, two research topics are specifically explored: (1) safer solvents for active pharmaceutical ingredient purification using column chromatography and (2) enzymatic depolymerization of poly(ethylene terephthalate) (PET) via in-situ product removal. The overarching goal of the dissertation is to obtain enabled knowledge for the development of sustainable processes that help reduce non-benign substances to the environment, such as harmful solvents and plastic waste.

The first research topic aims to identify safer solvents for use in column chromatography, a technique widely used in pharmaceutical manufacturing for the purification of active pharmaceutical ingredients (APIs). This technique mainly employs a blend of dichloromethane (DCM) and methanol (MeOH) as the solvent of choice, thereby exposing workers of this sector to the health and safety risks caused by these harmful solvents and making this sector one of the major contributors to chlorinated solvent waste. In this study, the performance of safer solvent blends in column chromatography is compared against that of DCM/MeOH in terms of purification of ibuprofen and acetaminophen as model APIs, with caffeine used as a model impurity. Overall, the safer solvent blends were found to provide a better economic potential (higher API recovery and lower silica gel required) compared to DCM/MeOH in addition to health, safety, and environmental benefits (improved safer ratings and lower E factor). This work addresses the safety concerns in pharmaceutical manufacturing by providing a probable solution to replace the DCM/MeOH blend used in the pharmaceutical industry.

The second research topic aims at developing novel strategies to recycle poly(ethylene terephthalate) (PET), a common single-use synthetic polymer and a major contributor to plastic waste. PET upcycling through enzymatic depolymerization has drawn significant interest, but the lack of robust enzymes in acidic environments remains a challenge. This study investigates in-situ product removal (ISPR) of terephthalic acid (TPA), the main product from enzymatic PET depolymerization but also the main contributor to enzyme deactivation due to its acidity, via a membrane reactor. We have focused on the ICCG variant of leaf branch compost cutinase (LCCICCG), which shows high reactivity towards PET hydrolysis. The study further investigates the non-enzymatic and enzymatic hydrolysis of the intermediate products from the enzymatic reactions, mono- and bis-(2-hydroxyl) terephthalate, with LCCICCG and MHETase enzymes. Valuable insights from the ISPR membrane reactor experiments and the non-enzymatic and enzymatic hydrolysis of the intermediate products enabled the design of a predictive model for enzymatic depolymerization of PET, capable of efficiently predicting product yields. The ISPR membrane reactor technology is further advanced through the use of a dual enzyme system to improve TPA yields. It is observed that the ISPR membrane reactor offers a great potential for higher TPA yields and accelerated depolymerization rates. The results provide valuable insights for future ISPR developments, addressing the pressing need for more sustainable solutions towards plastic recycling and environmental conservation.