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Water for Energy and Fuel Production
200°C–275°C. At 250°C, about 44 wt% biocrude and 3.8 mol% H 2 were observed
after 120  min of reaction time. Other gases observed in the products were CO 2 ,
CO, and CH 4 . The liquid phase (biocrude) contained sugars (7.5  wt%), hydroxymethylfurfural (HMF)/furfural (~1  wt%), oxygenated hydrocarbons (42.4  wt%),
and monocarboxylic acids (49.1 wt%) such as acetic, formic, propionic, and lactic
(2-hydroxypropionic) acids.
6.5.5 novel reACTor deSignS
The operating conditions and the nature of the catalyst not only affect the selectivity between hydrogen and alkanes, but also the level of CO production. A low
CO concentration in the product requires an ultra shift operation in which the
reaction conditions are such that the water–gas shift reaction is favored. The
lowest level of CO requires the lowest partial pressure of CO 2 and H 2 in the
gas phase so that the forward water gas reaction is thermodynamically favored.
These conditions are achieved by operating the reactor at the saturation pressure for water (at the reaction temperature) and using low feed concentration of
oxygenates [16].
Very few studies have been done on the novel reactor design to carry out the
APR process. As mentioned earlier and shown in Figure 6.4, Davda et al. [16] proposed that a way to increase hydrogen selectivity from glucose is to operate in
two stages. D’Angelo et al. [31] studied APR of biocarbohydrates in a catalytically
stable wash-coated micro reactor, in which multiphase hydrogen removal enhanced
hydrogen efficiency. A coating method to deposit a Pt-based catalyst on the microchannel walls was selected and optimized. APR reactivity tests were performed
using ethylene glycol as the model compound. Optimum results were achieved with
a static wash coating technique in which a highly uniform and well-adhered 5 μm
layer was deposited on the walls of a 320 μm internal diameter (ID) microchannel
in one single step. During APR of ethylene glycol, the catalyst layer exhibited high
stability over 10 days after limited initial deactivation. The microchannel presented
higher conversion and selectivity to hydrogen than a fixed-bed reactor. They concluded that the benefits of using a micro reactor for APR can be further enhanced
by utilizing the increased Pt loadings, higher reaction temperatures, and larger carbohydrates (e.g., glucose). The use of micro technology for APR can allow a significant reduction in the reformer size, thus rendering it promising for distributed
hydrogen production.
Subsequently, D’Angelo et al. [9] used the 1.7 m long, 320 μm ID microchannel
reactor with a 5 μm Pt-based wash-coated catalyst layer described earlier to study
APR of sorbitol. The performance of this microchannel reactor was correlated to the
mass transfer properties, reaction kinetics, hydrogen selectivity, and product distribution. While mass transfer did not affect kinetically controlled sorbitol consumption, it did affect hydrogen selectivity and the product distribution. Compared to a
fixed-bed reactor, the hydrogen selectivity in the microchannel reactor was higher by
a factor of 2. The yield of side products (mainly C 3 and heavier hydrodeoxygenated
species) was suppressed, whereas the yield of hydrogen was increased from 1.4 to
4.0 moles per mole of sorbitol fed.