The crude bio-oil produced from the glycerol-assisted liquefaction of swine manure which had large
amount of long chain esters, was upgraded by thermal cracking over a modified zeolite catalyst. The
effects of thermal cracking temperature (350–425 C), reaction time (15–60 min) and catalyst loading
(0–10 wt%) on the yield and quality of the upgraded oil were analyzed. The yield of upgraded bio-oil
decreased with the increase of reaction temperature, reaction time and catalyst loading, but the viscosity,
heating value and composition of the upgraded bio-oil became more desirable. Taking into the consideration
both the yield and quality of the upgraded bio-oil, the optimal thermal cracking could be achieved
over 5 wt% catalyst at 400 C for 30 min. Under this condition, the yield of upgraded bio-oil was
46.14 wt% of the crude bio-oil, and 62.5% of the energy stored in the crude bio-oil was recovered. The oxygen
content of the upgraded bio-oil was 15.04%, which was less than half of the original value of 33.98%.
The viscosity of the upgraded bio-oil was 3.6 cP, compared with 188.9 cP for the crude bio-oil. The heating
value of the upgraded bio-oil was 41.4 MJ/kg, compared with 30.54 MJ/kg for the crude bio-oil. Both
the viscosity and heating value of the upgraded bio-oil were comparable to those of commercial diesel.
The GC–MS analysis showed that the catalytic upgrading resulted in the increased cracking of long-chain
acid methyl esters (such as hexadecanoic acid methyl ester), forming various alkanes, alkenes and their
isomers, and short-chain acid methyl esters (such as heptanoic acid methyl ester). Elevated temperature
and high catalyst loading enhanced the selectivity of thermal cracking towards alkanes and alkenes in the
upgraded bio-oil.