Page 148 - Advances in bioenergy (2016)

bio-oils, even from clean wood at 50 ppm or less, may still be sufficient to deactivate the
catalyst in the long term.

The primary issue interfering with long-term operation has been the fouling of the catalyst bed
by carbonaceous deposits. These deposits appear to be condensation reaction products forming
at elevated temperature from the most reactive components in the bio-oil. Low-temperature
hydroprocessing of the bio-oil prior to conventional hydroprocessing appears to ameliorate
this problem. Another option under development is the use of an ebullated bed reactor, see Box
6.1. Refinement of the processing conditions to allow long-term operation remains at the
forefront of the process R&D.

Product Properties

Dependent on the processing severity, a range of deoxygenated products can be produced from
bio-oil catalytic hydroprocessing. Nearly deoxygenated hydrocarbons (<0.5 wt% oxygen) have
been of most interest. These product mixtures are different from petroleum crudes in that they
are high in cyclic hydrocarbon structures, both saturated (naphthenes) and aromatic. These
cyclic structures are clearly derived from the cyclic structures in the bio-oil itself. With less
severe processing, higher space velocity or lower temperature, more oxygen is left in the
product mix. The most stable oxygenates, and the last to be eliminated, have been reported to
be the phenolics. 22