Page 261 - Biosystems Engineering

Biomass Pyr olysis and Bio-Oil Refineries 239

reducing coke formation and catalyst deactivation, more attrition-
resistant catalysts should be developed (Davidian et al. 2007).
Hydrolysis, Neutralization, Detoxification, and
Fermentation of Pyrolytic Sugars
The most abundant anhydrosugars resulting from cellulose depoly-
merization reactions are levoglucosan (1,6-anhydro-β−D-glucopyranose)
and cellobiosan (β-D-glucopyranosyl-(1-4)-1, 6-anhydro-D-glucopy-
ranose). These sugars can easily be separated from most lignin-
derived compounds by adding water to the oils. The sugars recovered
in the resulting aqueous phase can be hydrolyzed to form glucose at
°
temperatures between 90 and 110 C and concentrations of sulfuric
acid around 500 mM. The carboxylic acids and phenols that also solu-
bilize in the aqueous phase are known to be toxic to the yeasts. Muya-
fuji et al. (2005) proved that increasing the pH to values over 5.5 and
removing the phenols over activated carbon can result in a detoxified
solution. The sugars can then be readily fermented to ethanol using
yeasts (Saccharomyces cerevisiae).
Aqueous Phase Catalytic Processes
The University of Wisconsin has patented a technology for the reform-
ing or hydrogenation of aqueous solutions containing biomass-
derived oxygenated organic compounds (Cortright and Dumesic
2005). This process could be potentially employed to convert bio-oil
water soluble fractions into hydrogen and alkanes ranging from C to
1
C . Alkanes with molecular weight ranging from C to C can be pro-
15 1 6
duced by aqueous phase dehydration/hydrogenation (APD/H). This
APD/H process involves a bifunctional pathway in which the sugars
are repeatedly dehydrated by a solid acid (SiO –Al O ) or a mineral
2 2 3
acid (HCl) catalyst and then hydrogenated on a metal catalyst
(Pt or Pd) (Huber and Dumesic 2006). Liquid alkanes ranging from C
7
to C (naphtha) can be produced from carbohydrates by combining
15
the dehydration/hydrogenation process with an upstream aldol con-
densation step to form C–C bonds (Huber and Dumesic 2006).
Hydroprocessing
Extensive studies for the hydroprocessing of fast pyrolysis oils have
been conducted for more than 25 years (Churin et al. 1987; Elliott and
Baker 1987; Gagnon and Kaliaguine 1988; Piskorz et al. 1989a, 1989b;
Baldauf et al. 1994; Centeno et al. 1995; Elliot 2007).
Piskorz et al. (1989a, 1989b) studied the hydrotreatment of the so-
called pyrolytic lignin (decanted oil) with positive results. After
hydrotreatment, the decanted oils are converted to light hydrocar-
bons (60 to 65 mass%), water (20 mass%), and gases (8 to 10 mass%).
The heavy residue that formed was only 1 to 2 mass%. The light com-
pounds have an H/C ratio of 1.5 with 0.46 mass% of oxygen. As much
as 50 percent of the pyrolytic lignin was converted to compounds in