Effect of used cooking oil sludge loading on diesel-range fraction yield and fuel properties from ternary waste pyrolysis oil: Toward practical blendstock assessment

Abstract

Tri-pyrolysis oil (TPO) produced from oil palm fresh fruit bunches (PFFB), medical waste polypropylene bottles (MWPB), and used cooking oil sludge (UCOS) was separated by atmospheric fractional distillation into pyro-gasoline (PG), pyro-diesel (PD), and heavy fractions at UCOS loadings of 1:1:0.5, 1:1:1, and 1:1:2 (TPO-0.5, TPO-1, TPO-2). Increasing UCOS loading progressively redistributed the liquid product toward the diesel-range fraction, raising PD yield from 48.33 to 61.73 vol% while PG yield fell from 38.83 to 25.80 vol%, with the heavy fraction remaining nearly constant. ASTM D86 distillation showed that PD fractions had T90 values of 344–354 °C, below the 357 °C diesel specification limit, at all loadings, whereas PG fractions exhibited insufficient front-end volatility (T10 95–97 °C). FTIR and GC-MS analyses confirmed that PD became increasingly paraffinic and aromatic-free with increasing UCOS loading, with C 13+ hydrocarbons rising from 32.4% to 56.3%. Elemental analysis showed that PD approached petroleum-diesel-like H/C and O/C ratios and exhibited higher heating values (44.09–44.95 MJ/kg) than PG (35.54–36.78 MJ/kg). However, both fractions carried total acid numbers far exceeding diesel-quality limits, and blending PD with commercial diesel at B10-B30 satisfied viscosity but not acidity specifications without prior deacidification. Overall, increasing UCOS loading in this ternary waste pyrolysis system is an effective strategy for enhancing diesel-range yield and fuel-like properties. However, acid mitigation remains necessary before practical diesel blendstock application. To our knowledge, this is the first study to characterize pyro-gasoline and pyro-diesel as separate, boiling-range-resolved fractions from a PFFB-MWPB-UCOS ternary waste system, rather than relying on whole-oil analysis.