Co-pyrolysis of rice straw and empty fruit bunch: effects of blending on product yields and bio-oil composition

Abstract

Co-processing of agricultural residues is a promising route for producing renewable fuels and chemicals, particularly when feedstock availability is seasonal and material properties vary significantly. In this study, co-pyrolysis of rice straw (RS) and empty fruit bunch (EFB) was investigated using three reactor systems: analytical Py-GC/MS, a single-particle reactor (SPR), and a fluidized-bed reactor (FBR). The two biomasses differ substantially in chemical composition, strongly influencing their pyrolysis behavior. Pyrolysis experiments were conducted at 500 °C for the individual samples and for three blends containing 25%, 50%, and 75% RS (dry weight basis), with the remainder consisting of EFB. RS produced lower bio-oil and higher biochar yields than EFB, primarily due to its higher ash content, particularly alkali and alkaline-earth metals. Higher apparent condensable yields were obtained in the SPR than in the FBR, since the condensable yields in the SPR were estimated by difference. Nonetheless, similar non-condensable gas yields, mainly CO and CO₂, were produced in both reactors. Py-GC/MS analyses showed that the condensable pyrolysis vapors primarily consisted of linear and cyclic oxygenates and phenolic compounds. GC-MS analyses of the bio-oils produced in the FBR revealed a similar composition. RS-derived pyrolysis vapors/bio-oils contained a higher proportion of oxygenates, while the phenolic compounds were more prominent in the EFB vapors/bio-oils. The co-pyrolysis yields closely followed the mixture rule, indicating largely independent decomposition behavior of the RS and EFB in the blend. The results of this study suggest that co-pyrolysis of biomass residues with varying availability and chemical compositions may enhance certain aspects of the fast pyrolysis process and support its overall sustainability.