Co-gasification of biomass and plastic waste has a bright outlook and, in this regard, air and steam co-gasification of eucalyptus and polypropylene was investigated in this study. Various composition ratios of eucalyptus and polypropylene were considered and air and steam co-gasification performances have been analyzed with respect to polypropylene content, moisture content of feedstock, and gasification temperature. Air- and steam-based system performances have been tri-objective optimized using central composite design to attain a clean and efficient gasification performance. The results confirmed that hydrogen production was improved by increasing polypropylene content based on water–gas reaction. The polypropylene concentration significantly affected the efficiencies of steam co-gasification. Increasing polypropylene concentration from 0 to 100 wt% improved energy efficiency of steam co-gasification from 56 to 83%. Moisture content of 26 wt%, temperature of 955 °C, and polypropylene concentration of 54 wt% were optimum conditions of air co-gasification. Steam co-gasification was optimized at moisture content of 30 wt%, temperature of 1000 °C, and polypropylene concentration of 100 wt%. At the optimum conditions, air co-gasification resulted in higher energy efficiency (81% compared with 77%) while steam co-gasification led to higher hydrogen efficiency (50% compared with 42%) and lower CO2 emission (2.2 g/s compared with 9.4 g/s).
