Mechanism of Palm Oil Waste Pyrolysis in a Packed Bed

Abstract

To better understand the process mechanism, pyrolysis of palm oil wastes was investigated at different temperatures in a packed bed, with focus on the changing of chemical structure and physical characteristics of solid residues and gas-releasing properties. First, three palm oil wastes were pyrolyzed with temperature increasing from the ambient to 1000 °C, and the main products from it were solid charcoal, liquid oil, and hydrogen-rich gas. The gas component mainly consisted of H2, CO2, CO, and CH4 together with trace C2H4 and C2H6. CO and CO2 evolved out at lower temperature (<450 °C), while H2 released at higher temperature (600−700 °C). Second, the decomposition property of biomass shell was analyzed at variable temperatures (300, 400, ..., 1000 °C). The pyrolysis products were thoroughly identified using various approaches (including micro-GC, FTIR, GC-MS, ASAP2010, SEM, and CNHS/O analyzer) to understand the influence of temperature on product properties and, thus, reaction mechanism involved. Starting from low temperature at 300 °C, CO and CO2 evolved out easily because of the breaking of carbonyl and carboxyl functional groups, and the releasing of CH4 increased at the price of CH alkyl breaking and diminishing. Following that, at temperature > 400 °C, aromatic rings broke gradually with a lot of H2 evolving out. Meanwhile, a large amount of pores in the biomass sample were opened in the course of pyrolysis, and the Brunauer−Emmett−Teller (BET) surface area increased greatly. The maximum yield of oil was achieved at 500 °C, and it is a mixture of acid, ether, phenol, etc. High temperature (>700 °C) was favorable for the evolving of hydrogen-rich gases, while medium temperature (500−600 °C) was recommendable for a higher generation of liquid oil and charcoal with a large BET surface area and fine pore size.