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Aqueous-Phase Reforming and BioForming Process
in Section 6.6 indicated that monofunctional groups generated by APR technology
can be upgraded to mono-oxygenated hydrocarbons using conventional condensation and hydrotreating techniques. The discussion also indicated such upgrading of
monofunctional groups to a variety of end products will require different catalytic
strategies.
The development of bioforming process for the secondary feedstock outlined
in Table 6.1 requires fractionation and pretreatment of these feedstock to separate
hemicellulose, cellulose, and lignin. This fractionation can be carried out using various acidic and enzymatic hydrolyses, which result in the production of five- and
six-carbon ring sugars such as xylose and glucose and other oxygenated compounds
[15,60–63,66,67,87–89]. The separated lignin can be used for the process heating.
The separated polysaccharides, C 5 and C 6 sugars, furans, phenolics, and acids are
further upgraded by hydrogenation and hydrogenolysis to sugar alcohols such as
sucrose and corn sugar, as well as water-soluble oxygenated compounds such as
diols, glycerol, and sugar alcohols [15,60–63,66,67,87–89]. The required hydrogen
for these processes can be generated in situ, recycled with excess hydrogen from the
overall process, or provided by hydrogen from an external source [15].
The centerpiece of Virent’s BioForming process is still APR technology, originally developed by Virent Inc. and Dumesic et al. [1–6,16], which utilizes heterogeneous catalysts at moderate temperatures (450–575 K) and pressures (10–90 bar) in
a number of series and parallel reactions to reduce the oxygen content of the carbohydrate feedstock. As pointed out by Blommel and Cortright [15], a key feature of
this method is the use of in situ-generated hydrogen for the defunctionalization of the
highly reactive carbohydrates to a less reactive mono-oxygenated species.
While, as discussed earlier, the APR process can generate hydrogen, syngas,
alkanes, and condensable monofunctional groups, for the purpose of BioForming
process, the most important products are hydrogen and condensable monofunctional intermediates. Just like lignin, the lower alkanes can be used for the process
heating purposes. Both hydrogen and condensable products can be formed using
Pt–Re catalysts on ZrO 2 . The literature shows the range of oxygenates generated
from a sucrose solution through a consecutive deoxygenation and APR processing
[1–6,15,16,60–63,66,67,87–89]. These results were generated by first hydrogenating aqueous solution of sucrose by Ru/C catalyst into sorbitol/mannitol mixture.
This mixture was then subjected to an APR process using Pt/Re catalyst supported on ZrO 2 [15]. The process generated 0.76 mol of hydrogen per mole of
sugar monomer and 35% of feed carbon to CO 2 [1–6,15,16,60–63,66,67,87–89].
Besides C 1 –C 6 alkanes, the process generated alcohols, ketones, acids, and
cyclized components suitable for condensation to longer chain hydrocarbons
[1–6,15,16,60–63,66,67,87–89].
The total amount of hydrogen generated by the APR process is governed by the
reaction [15]:
C H 14 O + 6 2 → 13H + 6 2
6
6
H O
2
CO
(6.15)
The generated hydrogen is either recovered or used within the overall process. If
the sorbitol is converted to xylitol, one will obtain a H 2 /CO 2 ratio of 2/1 instead of