(57e) Lumped Product Kinetic Model of Plastics – Biomass Mixtures during Hydrothermal Liquefaction

Hydrothermal liquefaction (HTL) can be used to valorize waste plastics and biomass. Previous work indicates synergistic interactions between plastics and biomass and among plastics that increase the oil yields and influence product distributions. These interactions have the potential to reduce the process temperatures and improve the sustainability metrics for the process. Hence, understanding and modeling these interactions is pivotal to co-processing mixed (plastic – biomass) waste streams using HTL.

Herein to study these interactions, we take cellulose, polypropylene (PP), and polycarbonate (PC) as the model lignocellulose, polyolefin, and condensation polymer, respectively. We perform HTL experiments on each component alone (i.e., cellulose alone), each equi-mass binary combination (i.e., PP – cellulose (1:1 mixture)) and one equi-mass ternary combination (PP – PC – cellulose (1:1:1 mixture)) at 350 °C and six different batch holding times (1 – 60 min). We also vary the relative amount of each component in binary mixtures to analyze the ratio effects for each of the interactions through additional experimentation. A lumped product kinetic model is developed using these experimental results based on the pathway shown in the above figure.

The initial experimental analysis indicates synergistic interactions between PP – cellulose, and PC – cellulose that increase the oil yield. This means that mixing PP and cellulose and processing them together gives a higher oil yield than processing PP and cellulose separately. On the other hand, interactions among PP and PC are antagonistic and decrease oil yield. The increases in oil yield are accompanied by decreases in solid yield, while increases in solid yields accompany the decreases in oil yield. The degree of change caused by these interactions is further influenced by reaction times. Hence, kinetic models are ideal for understanding the interplay between reaction time and interactions and further understanding the reactions promoted/curbed by these interactions.