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Water for Energy and Fuel Production
13/6 as indicated by the above reaction [15,60–63,66,67,87–89]. Very little CO will
be produced due to very favorable conditions for forward water–gas shift reaction.
While the original APR process identified various strategies for upgrading
monofunctional groups to different types of liquid fuels (Figure 6.5), bioforming process further developed these strategies to build a continuous process
(Figure 6.6). The process tested various system operating conditions to produce
different intermediate compounds appropriate for use in the downstream condensation reactions that generate different types of fuels or chemicals. The research
showed that monofunctional groups can be converted to aromatics and isoalkanes
via direct catalytic condensation over acid catalysts, such as solid acids and zeolites [32,48,58,59,64,65,67–86,90–98]. Zeolite ZSM-5 carries out a series of reactions that include the following [15,78,60–64,66,67,87–98]: (1) dehydration of
oxygenates to alkenes, (2) oligomerization of the alkenes, (3) cracking, (4) cyclization and dehydrogenation of larger alkenes to form aromatics, (5) alkane isomerization, and (6) hydrogen transfer to form alkanes [95,96]. All of these reactions
are important to produce liquid fuels of varying properties such as gasoline, diesel, and jet fuel. The heavier components are generally separated by distillation
and blended into jet fuel [15].
Based on further research and development of BioForming process, Blommel and
Cortright at Virent [15,60–63,66,67,87–89] proposed a unified continuous process
for the conversion of sucrose and xylose into gasoline-range hydrocarbons using proprietary APR catalyst and ZSM-5 (Figure 6.6). The new integrated process, which
uses four different types of catalyst beds with no intermediate separation, is schematically described in Figure 6.7 [15]. In this process, each catalyst bed carries out
different set of reactions and hydrogen is added with sucrose/xylose mixture in the
first reactor. The first reactor (with two stages) operates with aqueous mixtures. The
APR process is carried out at 523  K that generates hydrogen, light alkanes, and
monofunctional groups. The product from the first reactor is heated to 648 K and
passed over two different catalyst beds, both containing different types of acid catalysts. The final carbon number distribution coming out of the second reactor includes
+ , which is necessary for the liquid fuel productions. About 60% of hydrogen used
C 6
in the first reactor is recovered by the APR process [15].
Blommel and Cortright [15,60–63,66,67,87–89] pointed out that this transformation requires numerous types of condensation reactions such as (1) aldol condensation to form beta-hydroxy ketone and aldehydes; (2) dehydration of these
products to form enone; (3) hydrogenation of conjugated enone to ketone, aldehyde,
or alcohol; and finally (4) dehydration/hydrogenation or hydrogenolysis to form
alkanes. This multifunctional process allows the formation of longer chain and
branched hydrocarbons needed to produce gasoline, diesel, and jet fuels with subsequent distillation [15,60–64,66,67,78,87–89,98]. Many oxygenates such as alcohols, carbonyls, and acids can form C–C bonds through aldol and decarboxylative
condensation reactions [15,64,78,98]. Further analysis and details on various types
of condensation reactions and the role of different catalysts are given by Blommel
and Cortright [15] along with some other published reports [60–63,66,67,87–89].
Currently, Virent Inc. is building a pilot plant to demonstrate the viability of the
BioForming process at a larger scale with the aim of making a commercial process.