Upgrading of Municipal Solid Waste Fast-Pyrolysis Oil via Esterification and Hydrotreating

An Aspen Plus model was developed to evaluate the upgrading of municipal solid waste (MSW) fast-pyrolysis oil into transportation-compatible biofuels. MSW-derived bio-oil is compositionally complex, containing oxygenated and nitrogen-containing compounds together with substantial water, resulting in low stability and poor fuel quality. This study compared a one-stage high-temperature hydrotreating (HTH) process with a two-stage configuration incorporating low-temperature esterification (LTE) pretreatment. The assessment focused on upgraded bio-oil yield, fuel quality and hydrogen demand. In both configurations, hydrogen was generated internally by autothermal reforming of a fraction of the bio-oil or esterified oil. The higher heating value increased from approximately 28 MJ/kg for the untreated bio-oil to 40 MJ/kg and 46 MJ/kg for the one and two-stage processes, respectively. The molar H/C ratio increased from 1.11 to 1.26 and 1.88, placing the two-stage product within the range of conventional transportation fuels. A reforming fraction of 0.25 of the esterified bio-oil was sufficient for hydrogen self-sufficiency in the two-stage process, whereas the one-stage process required a fraction of above 0.30. The one-stage process achieved higher carbon retention, upgraded bio-oil yield, and overall fuel efficiency than the two-stage process, with values of 31%, 16%, and 33%, compared to 24%, 13%, and 29%, respectively. However, the two-stage process increased hydrogen retention from 26% to 30%, while its decoupled DMSW carbon retention was 26.41%. Esterification therefore enhanced hydrogen retention and fuel quality at the expense of carbon retention, liquid yield, and overall fuel efficiency, highlighting the quality–efficiency trade-off of the two-stage configuration.