High-Quality Bio-Oil Production from Co-Pyrolysis of Acetic Acid Pretreated Nypa Fronds and High-density Polyethylene with Ni–Cu Modified Fly Ash Catalyst

Abstract

Co-pyrolysis has emerged as a promising thermochemical approach to enhance both the yield and quality of bio-oil compared to conventional pyrolysis. In this study, Nypa fruticans frond (NFF) was initially pyrolyzed following pretreatment with acetic acid diluted in peat water (AAPW) at concentrations of 2.5, 5, 7.5, and 10 w/w% to identify the optimal pretreatment condition for bio-oil production. Subsequently, co-pyrolysis was conducted using NFF pretreated at the selected AAPW concentration (2.5 w/w%) with high-density polyethylene (HDPE) at feed ratios of 30:70, 50:50, and 70:30 (NFF/HDPE, w/w). Finally, catalytic co-pyrolysis was performed at the optimal feed ratio (70:30) by adding Ni–Cu/FA catalyst loadings of 5%, 10%, and 15% (w/w). All experiments were conducted at 500 °C for 60 min. Results showed that increasing AAPW concentration enhanced the bio-oil yield, while the incorporation of HDPE significantly improved both yield and quality. Catalytic co-pyrolysis provided the greatest upgrading effect, with 15% Ni–Cu/FA catalyst achieving the highest bio-oil yield (71.87 ± 2.21%), heating value (45.55 MJ/kg), energy yield (89.61%), and superior physicochemical properties, including near-neutral pH (6.82), high density (0.78 g/cm3), and 98.43% hydrocarbon content. Overall, the combination of AAPW pretreatment, plastic co-feeding, and catalytic upgrading proved effective in producing high-quality bio-oil characterized by elevated hydrocarbon content and near-neutral acidity.