Tadafumi_edit.qxp 1/7/09 2:48 pm Page 37
Role of Water in Reactions Under Supercritical Conditions – Hydrocarbons
Figure 5: Time Profile of Hydrogenation of Dibenzothiophene (DBT) Figure 6: Yields of Asphaltene and Coke in Bitumen Conversion in Ar,
in the SCW–O
2
-Hexylbenzene Mixtures SCW and the SCW–HCOOH Mixture
Asphaltene Coke
100
20 20
SCW + 0
2
+ Hexylbenzene Hexylbenzene / DBT = 10
Pyrolysis
673K
ρ =0.42 g/cc
80
w
15
SCW
15
Pyrolysis
S
SCW
10 10
60
DBT
e yield (wt%)
Cok
Y
ield (mol%)
Asphaltene yield (wt%)
5 5
40 SCW-HCOOH SCW-HCOOH
0 0
20 30 40 50 60 70 80 90 100 20 30 40 50 60 70 80 90 100
20
BP
Reaction time (min) Reaction time (min)
723K 723K
Heavy oil 0.1g Heavy oil 0.1g
0
0204060
Water 0 and 1.0g Water 0 and 1.0g
CHB
(density: 0 and 100kg/m
3
) (density: 0 and 100kg/m
3
)
Reaction time (min)
Source: Adschiri et al., Ind Eng Chem Res, 1998;37(7):2634.
confirmed similar effects of the water–gas shift reaction induced by
partial oxidation
14
and by the HCOOH–SCW mixture on the
asphaltene decreased because almost the entire fraction of the lighter hydrogenation of heavy oil. As shown in Figure 6, on addition of
hydrocarbons was extracted by the SCW; this prevented the asphaltene HCOOH asphaltene consumption increased and coke formation was
reacting with the light hydrocarbons. This probably explains the plateau inhibited. Hydrogenated hydrocarbons (such as saturated
observed in the coke yield when the reaction was carried out in SCW. hydrocarbons) were categorised as maltene,
15
and hydrogenation was
known to be an effective method for inhibiting coke formation via
Hydrogenation via Water–Gas Shift Reaction radical capping. Therefore, the results shown in Figure 6 indicate that
We observed another interesting phenomenon during the hydrogenation via HCOOH (or CO + H
2
O) in SCW is an effective
hydrogenative desulphurisation in SCW.
6,7
In SCW, this reaction occurs method for carrying out bitumen upgrading.
effectively, since a homogeneous phase of H
2
gas, hydrocarbons and
water is formed. Such a homogenous phase was confirmed in the Concluding Remarks
desulphurisation of dibenzo-thiophene in H
2
and water. Interestingly, Hydrocarbon reactions carried out in SCW show some unique features
when CO gas was used in this reaction instead of H
2
, the reaction rate that are not observed in gas- or liquid-phase reactions; thus, by using
was observed to be higher, as shown in Figure 4. This increase in SCW in hydrocarbon reactions the limitations of conventional
rate was attributed to the occurrence of a water–gas shift reaction; the hydrocarbon processes can be overcome. To design hydrocarbon
intermediate material formed in this reaction probably had higher reactions that can be carried out in SCW, the effect of water on
reactivity than the H
2
molecule. Next, we used the gas mixture of H
2
the reaction should be elucidated; that is, the effect of water on phase
and CO
2
, and observed a very high reaction rate. More interestingly, on equilibrium and solubility, the role of water as an acid or base catalyst
the addition of O
2
gas to this mixture, we observed a high and the solvent effect of SCW.
hydrogenative desulphurisation rate, as shown in Figure 5. This high
rate is due to the partial oxidation of hydrocarbons in SCW, which In 2007, the Japanese government commissioned a research group
results in the formation of CO. We confirmed the selective production to initiate a new national project on heavy oil reforming in SCW. As
of CO in SCW via the partial oxidation of hydrocarbons (lignin, part of this project, 10 researchers from the field of hydrocarbon
hexadecane and PE), especially, at high water-density values.
8–11
A research and supercritical science and technology have come
similar effect of partial oxidative hydrogenation was also observed in together to conduct collaborative research. We believe this joint
the case of HCOOH–SCW mixture.
6,7,12
A possible reason why HCOOH research will help us elucidate the role of water in hydrocarbon
brought about a similar effect on hydrogenation is that HCOOH is an reactions and thus offer new prospects for developing novel
intermediate in the water–gas shift reaction.
13
Very recently, we also processes for hydrocarbon reactions. ■
1. Okuda K, Umetsu M, Takami S, Adschiri T, Disassembly of formation, Ind Eng Chem Res, 1993;32:2447–54. decomposition via pyrolysis and partial oxidation in
lignin and chemical recovery-rapid depolymerization of 6. Adschiri T, Shibata R, Sato T, et al., Catalytic supercritical water, Kobunshi Ronbunshu, 2001;58:631–41.
lignin without char formation in water-phenol mixtures, hydrodesulfurization of dibenzothiophene through partial 11. Watanabe M, Inomata H, Osadab M, et al., Catalytic
Fuel Process Technol, 2004;85:803–13. oxidation and a water–gas shift reaction in supercritical effects of NaOH and ZrO
2
for partial oxidative gasification
2. Okuda K, Ohara S, Umetsu M, et al., Disassembly of lignin water, Ind Eng Chem Res, 1998;37:2634–8. of n-hexadecane and lignin in supercritical water, Fuel,
and chemical recovery in supercritical water and p-cresol 7. Arai K, Adschiri T, Watanabe M, Hydrogenation of 2003;82:545–52.
mixture studies on lignin model compounds, Bioresource hydrocarbons through partial oxidation in supercritical 12. Adschiri T, Sato T, Shibuichi H, et al., Extraction of Taiheiyo
Technol, 2008;99:1846–52. water, Ind Eng Chem Res, 2000;39:4697–4701. coal with supercritical water–HCOOH mixture, Fuel,
3. Watanabe M, Hirakoso H, Sawamoto S, et al., Polyethylene 8. Watanabe M, Sawamoto S, Adschiri T, Arai K, Polyethylene 2000;79:243–8.
conversion in supercritical water, J Supercrit Fluids, 1998;13: conversion by partial oxidation in supercritical water, 13. Melius CF, Bergan NE, 23rd Symp (Int) Combust, 1990;217.
247–52. J Mater Cycles Waste Manag, 2001;3:99–102. 14. Sato T, Adschiri T, Arai K, et al., Upgrading of asphalt with
4. Arai K, Adschiri T, Importance of phase equilibria for 9. Watanabe M, Mochiduki M, Sawamoto S, et al., Partial and without partial oxidation in supercritical water, Fuel,
understanding supercritical fluid environments, Fluid Phase oxidation of n-hexadecane and polyethylene in supercritical 2003;82:1231–9.
Equilibria, 1999;158–160:673–84. water, J Supercrit Fluids, 2001;20:257–66. 15. Wiehe I, A solvent–resid phase diagram for tracking resid
5. Wiehe IA, A phase-separation kinetic model for coke 10. Watanabe M, Adschiri T, Arai K, Polyethylene conversion, Ind Eng Chem Res, 1992;31:530–36.
HYDROCARBON WORLD VOLUME 4 ISSUE 1
37
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