Wood-derived olefins by steam cracking of hydrodeoxygenated tall oils

Tall oil fractions obtained from Norwegian spruce pulping were hydrodeoxygenated (HDO) at pilot scale using a commercial NiMo hydrotreating catalyst. Comprehensive two dimensional gas chromatography (GC × GC) showed that HDO of both tall oil fatty acids (TOFA) and distilled tall oil (DTO) produced highly paraffinic hydrocarbon liquids. The hydrotreated fractions also contained fatty acid methyl esters and norabietane and norabietatriene isomers. Steam cracking of HDO–TOFA in a pilot plant revealed that high light olefin yields can be obtained, with 35.4 wt.% of ethene and 18.2 wt.% of propene at a coil outlet pressure (COP) of 1.7 bara, a dilution of 0.45 kgsteam/kgHDO–TOFA and a coil outlet temperature (COT) of 820 °C. A pilot plant coking experiment indicated that cracking of HDO–TOFA at a COT of 850 °C results in limited fouling in the reactor. Co-cracking of HDO tall oil fractions with a typical fossil-based naphtha showed improved selectivity to desired light olefins, further demonstrating the potential of large scale olefin production from hydrotreated tall oil fractions in conventional crackers.

► Tall oil fatty acid and distilled tall oil hydrodeoxygenation produces paraffinic liquids. ► Steam cracking of hydrodeoxygenated tall oils at pilot plant scale. ► High light olefin yields when cracking hydrodeoxygenated tall oil fatty acids. ► Pilot plant cokes test indicates that reasonable run lengths can be expected.