The feedstock for the process of hydroprocessed esters and fatty acids (HEFA) is being shifted to renewable waste and residues,

e.g., used cooking oil (UCO) containing (un)saturated triacylglycerides (TAG), polar substances including diacylglycerides

(DAG), monoacylglycerides (MAG) and free fatty acids (FFA), and dimeric/oligomeric products. However, the yield

of saturated hydrocarbons during hydroprocessing of refi ned UCO (r-UCO) can be lowered by the formation of oligomers via

double bonds present in unsaturated TAG and via those produced by dehydration of hydroxy groups of MAG and DAG and

β-elimination of (un)saturated TAG. Herein we attempted fi rstly to remove polar substance from the r-UCO through liquid–

liquid extraction and secondly to pre-hydrogenate unsaturated fatty acid chains before the main hydroprocessing reaction.

The fi rst attempt was eff ective for reduced oligomer formation in batch-mode experiments but not in continuous-fl ow ones.

The other attempt was to prove very successful in both modes of experiments regardless of the presence of polar substances

in r-UCO; thus, continuous-fl ow hydroprocessing of r-UCO could be sustained for 100 h without oligomer formation. Consequently,

coupling pre-hydrogenation with main hydroprocessing is very powerful in maximizing the yield of hydrocarbons

from the conversion of r-UCO because removing polar substances is meaningful but not economic.