Advanced Chemical Engineering

 

 

 

Reforming of liquid fuels to hydrogen is being considered to enable hydrogen-powered fuel cells
to be used to generate remote power. For example, the military is interested in using hydrogen
fuel cells to replace conventional batteries, which have a low power density and a short lifetime.
Reforming, then, could be used to transform military fuels to hydrogen to power fuel cells.
Autothermal reforming is one means for converting liquid fuels to hydrogen. In this process, the
liquid fuel is reacted with oxygen and water to produce hydrogen. The overall reaction involves
multiple reactions. Assuming that isooctane (2,2,4 trimethyl pentane) is the fuel, the overall
reaction scheme can be written:
C8H18 + 12.5 O2  8 CO2 + 9 H2O
C8H18 + 8 H2O  8 CO + 17 H2
C8H18 + 8 CO2  16 CO + 9 H2
C8H18 + 16 H2O  8 CO2 + 25 H2
CO + H2O  CO2 + H2
Your assignment is to model the reforming of isooctane in a packed-bed reactor.
Reaction Kinetics
Pacheco, et. al. (Pacheco, 2003) fit experimental data for a proprietary Pt/CeO2 catalyst to obtain
reaction kinetics for each of these reactions. The reaction rate laws they used are shown in
Table 1, where the reaction order corresponds to that shown above, and the rate law constants
are given in Table 2.
2
Table 1. Reaction rate laws for all reactions involved in isooctane reforming
r1 = k1Pic8PO2
( )








++++

=
2
22 88 222
2
3
28 2
5.2
2
2
2
1 /
/
COCO HH i Ci C HOHOH
i C HOH CO
H PPKPKPKPK
KPPPP
P
k
r








= −
283
2
2
2
2833 1
iC CO
CO H
iC CO PPK
PP
PPkr
( )








++++

=
2
22 88 222
42
4
2
2
28
5.3
2
4
1 /
4 /
COCO HH i Ci C HOHOH
i C HOH CO
H PPKPKPKPK
KPPPP
P
k
r
( )








++++

=
2
22 88 222
2 522
2
5
5
1 /
/
COCO HH i Ci C HOHOH
CO HOH CO
H PPKPKPKPK
KPPPP
P
k
r
Table 2. Kinetic parameters for all reactions involved in isooctane reforming
Parameter Pre-exponential factor
or KTR
Activation energy and heat of
adsorption (kJ/mol)
k1 (mol/gcat/s/bar2
) 2.58E+08 166
k2 (mol bar0.5/gcat/s) 2.61E+09 240.1
k3 (mol/gcat/s/bar2
) 2.78E-05 23.7
k4 (mol bar0.5/gcat/s) 1.52E+07 243.9
k5 (mol/gcat/s/bar) 1.55E+01 67.1
KH2O (dimensionless) 1.57E+04 HH2O= 88.7
KH2 (dimensionless) 0.0296 (TR=648 K) HH2= -82.9
KCO (dimensionless) 40.91 (TR=648 K) HCO= -70.65
KiC8 (dimensionless) 0.1791 (TR=823 K) HiC8= -38.28
Note: For H2, CO, and iC8, K is found from:















−
=
R
R
T
TTR
H
KK
R
11
exp
For H2O, K is found from:
TRHKK )//exp(
o −= R
Note that the equilibrium constants are calculated assuming reaction stoichiometry for methane,
not iso-octane. For example, K2 is the equilibrium constant for the following reaction:
C8H18 + H2O  CO + 3 H2

 

 

 

Sample Solution

peace and security. This is supported by Vittola, who implies proportionality again to justify action: ‘care must be taken where evil doesn’t outweigh the possible benefits (Begby et al (2006b), Page 325).’ This is further supported by Frowe who explains it is lawful to unintentionally kill, whenever the combatant has full knowledge of his actions and seeks to complete his aim, but it would come at a cost. However, this does not hide the fact the unintended still killed innocent people, showing immorality in their actions. Thus, it depends again on proportionality as Thomson argues (Frowe (2011), Page 141).
This leads to question of what qualifies to be a combatant, and whether it is lawful to kill each other as combatants. Combatants are people who are involved directly or indirectly with the war and it is lawful to kill ‘to shelter the innocent from harm…punish evildoers (Begby et al (2006b), Page 290).However, as mentioned above civilian cannot be harmed, showing combatants as the only legitimate targets, another condition of jus in bello, as ‘we may not use the sword against those who have not harmed us (Begby et al (2006b), Page 314).’ In addition, Frowe suggested combatants must be identified as combatants, to avoid the presence of guerrilla warfare which can end up in a higher death count, for example, the Vietnam War. Moreover, he argued they must be part of the army, bear arms and apply to the rules of jus in bello. (Frowe (2011), Page 101-3). This suggests Frowe seeks a fair, just war between two participants avoiding non-combatant deaths, but wouldn’t this lead to higher death rate for combatants, as both sides have relatively equal chance to win since both use similar tactics? Nevertheless, arguably Frowe will argue that combatant can lawfully kill each other, showing this is just, which is also supported by Vittola, who states: ‘it is lawful to draw the sword and use it against malefactors (Begby et al (2006b), Page 309).’
In addition, Vittola expresses the extent of military tactics used, but never reaches a conclusion whether it’s lawful or not to proceed these actions, as he constantly found a middle ground, where it can be lawful to do such things but never always (Begby et al (2006b), Page 326-31). This is supported by Frowe, who measures the legitimate tactics according to proportionality and military necessity. It depends on the magnitude of how much damage done to one another, in order to judge the actions after a war. For example, one cannot simply nuke the terrorist groups throughout the middle-east, because it is not only proportional, it will damage the whole population, an unintended consequence. More importantly, the soldiers must have the right intention in what they are going to achieve, sacrificing the costs to their actions. For example: if soldiers want to execute all prisoners of war, they must do it for the right intention and for a just cause, proportional to the harm done to them. This is supported by Vittola: ‘not always lawful to execute all combatants…we must take account… scale of the injury inflicted by the enemy.’ This is further supported by Frowe approach, which is a lot more moral than Vittola’s view but implies the same agendas: ‘can’t be punished simply for fighting.’ This means one cannot simply punish another because they have been a combatant. They must be treated as humanely as possible. However, the situation is escalated if killing them can lead to peace and security, within the interests of all parties.
Overall, jus in bello suggests in wars, harm can only be used against combatants, never against the innocent. But in the end, the aim is to establish peace and security within the commonwealth. As Vittola’s conclusion: ‘the pursuit of justice for which he fights and the defence of his homeland’ is what nations should be fighting for in wars (Begby et al (2006b), Page 332). Thus, although today’s world has developed, we can see not much different from the modernist accounts on warfare and the traditionists, giving another section of the theory of the just war. Nevertheless, we can still conclude

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