Ind. Eng. Chem. Prod. Res. Dev. IQ04, 23, 467-470
467
Development of Germanium Oxide Media for the Production of Concentrated Hydrogen by the Steam-Iron Process Aklra Mlyamoto; Morlmlchl Mlura, Kenjl Sakamoto, Shlnjl Kamltomal, Yuklo Kosakl, and Yulchl Murakaml Department of Synthetic Chemistty, Faculty of Engineering, Nagoya Unlversi~,Chikusa-ku, Nagoya 464, Japan
Some germanium oxide media were found to convert dilute H, to concentrated H, more effectively than the iron oxide medium used for the present steam-iron process. Although the yield of concentrated H2 for unsupported GeO, medii was lower than that for the iron oxide medium, G&2/A,O3 media exhibited h myields of concentrated H,. The addition of third components such as Ni and Cu to Ge02/A1203 further increased the yield and enhanced the stability of the medium. I t was also found that dilute CO gas was converted to concentrated H, by using germanium oxide media. Although the Ge02/Al,03 medium did not exhibit a high yield of concentrated H, from the dilute CO gas, the addition of third components (e.g., Ni and Cu) markedly enhanced the yield. The yield of concentrated H2 for the germanium oxide media was not decreased by the addition of H2S to the dilute H2 gas, while that for the iron oxMe was lowered slightly. From the results of X-ray diffraction of the media, a role of the third component was also discussed.
Introduction Hydrogen is a clean fuel. It can also convert "dirty" fuels such as coal and residues to "clean" gaseous or liquid fuels. Moreover, hydrogen is an important raw material in chemical processes and syntheses, especially, in the syntheses of methanol and ammonia. The steam-iron process is one of the most promising methods for the production of concentrated hydrogen (Tarman, 1973,1976,1979;Tarman et al., 1974; Murakami et al., 1982; Igarashi et al., 1982; Kat0 et al., 1979a, b; Otsuka et al., 1981; Otsuka et al., 1982a, b). As shown in the principle of this process (Figure l),the production of concentrated hydrogen is made by alternate introduction of dilute lean reducing gas and steam to iron oxide (M,O,; M = Fe) which is referred to in this paper as a medium. The medium is reduced by the dilute lean reducing gas to form the reduced iron oxide (MnO,,,-l) which then reacts with steam to form concentrated H2 and an oxidized medium (M,O,). This process has been extensively investigated in the Institute of Gas Technology in the USA mainly from the industrial point of view (Tarman, 1973, 1976, 1979; Tarman et al., 1974). The reducing components in the reducing gas are converted to concentrated H2 by the steam-iron process. Therefore, one of the most important factors in this process is the yield of concentrated H2, that is, the percentage of the amount of the reducing components in the dilute gas which can be converted to concentrated HP For this purpose, the iron oxide medium is not always an effective medium (Murakami et al., 1982). (1)The iron oxide is not an effective medium at low temperatures such as 300 and 500 "C. Neither its reduction with dilute H2 nor ita oxidation with H 2 0 proceeds rapidly. (2) It is easy to obtain 5040% yield of concentrated H2from dilute H2at 700 "C. It is, however, very difficult to obtain higher yields of concentrated H2 (e.g., 90%) by using the iron oxide medium a t 700 "C because the yield is limited by the thermodynamics but not by the kinetics. These disadvantages of the iron oxide medium stimulate us to develop new kinds of media providing higher yield of concentrated HP.The purposes of this study were then to make thermodynamic calculations for selecting possible metal oxides as media for the steam-iron process and to develop new media which provide the yield of concentrated
H2 higher than that for the iron oxide medium.
Experimental Section Materials. Iron oxide (Nissan-GirdlerG-64) and Ge02-I (Mitsuwa Pure Chemicals) were commercially available. Ge02-IIwas prepared by hydrolysis of GeCl,, followed by drying and subsequent calcining in a stream of O2at 500 OC for 3 h. Ge02/A1203was prepared by impregnation of 7-A1203with an ethanolic solution of GeC14 followed by its hydrolysis with H 2 0 and subsequent calcination in a stream of O2 at 500 "C for 3 h. Ni/A1203, Cu/A1203, Mn/A1203,C0/A1203, Fe/A1203, and Mo/A1203were prepared by impregnation of 7-A1203 with aqueous solutions of Ni(NOJ2, CU(NOB)~, Mn(N0d2, C O ( N O ~ )Fe(N03)3, ~, and (NH4)6M07024,respectively. Ni-Ge02/A1203, CuGe02/A1203, Mn-Ge02/A1203, Co-Ge02/A1203, FeGe02/A1203,Mo-Ge02/A1203, and Pt-Ge02/A1203 were prepared from the Ni/A1203, Cu/A1203,Mn/A1203, Co/ A1203,Fe/A1203, Mo/A1203,and Pt/A1203(Nippon Engelhard Ltd.;0.5 wt % of Pt loading), respectively, in a manner similar to that for the GeO2/Al2O3, The BET surface areas of the iron oxide, Ge02-I, Ge02-II, Ge02/ Al2O3, Ni-Ge02/A1203,and Cu-Ge02/A1203were 8.7,1.0, 2.3, 59.1, 60.0, and 48.2 m2/g, respectively. H2, Ar, CO, and H2S were obtained commercially. Apparatus and Procedure. Figure 2 shows a periodic pulse reaction apparatus used in this study which is composed of the following three parts (Murakami et al., 1982): In part I, dilute reducing gas (a mixture of H2, CO, and Ar) and steam were prepared and these were alternately introduced into the reactor (10) by periodically turning and returning the four-way solenoid valve (9). Although dilute reducing gas and steam were alternately introduced into the reactor, an Ar pulse (1min) was introduced between two pulses to remove the effect of remaining reducing gas (or H20) by electronically turning the three-way solenoid valve (8A). When the effect of H2S was examined, 1cm3 (STP) of H2Swas pulsed from the injection port (23) into flowing reducing gas. Part I1 was composed of a quartzglass reactor (10) heated in a fluidized bed (11). In part 111, the volume of concentrated H2 produced by the reaction of H 2 0 with the reduced medium was measured. Since the unreacted H 2 0 in the product was removed by an ice-cooled trap (12) and CaClz column (13), one could
0~96-432~/a4/~~23-0487$01.50/0 0 1984 American Chemical Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 3, 1984
408
Concentrated H20
H, L
\
x
4
R
/ i
3
-
-2
Spent
gas
0
Lean reducing gas (H2, CO, HC, etc)
300
Figure 1. Principle of the steam-iron process: M,O,, oxidized medium; MnOm+reduced medium; M = Fe for the present steamiron process.
400 500 600 iemperature ( ' C )
700
Figure 3. Dependence of VH2and YHzon reaction temperature: (0) Ge02-I;(0) GeO,-II; ( 0 )GeOz (30w t %)/AlzOs; (A)Fe301. Experiments were done under standard conditions with dilute HP.
ward and backward reactions of eq 1 for various metal oxides (M,O,)
I
!L
I
II
I
I
L _I Figure 2. Periodic pulse reaction apparatus for the production of concentrated Hz: (1) stop valve; (2) pressure regulator; (3) flow regulator; (4) Pd/asbestos column; (6) silica gel column; (7) flowmeter; (8) solenoid three-way valve; (9) solenoid four-way valve; (10) quartz glass reactor; (11) fluidized bed; (12) ice-cooled trap; (13) CaClz column; (14) gas buret; (15) reduced Cu column; (16) electric heater; (17) solenoid three-way valve; (la) microfeeder of HzO; (19) heater; (20) high-speed gas chromatograph; (21) thermocouple; (22) soap-film flowmeter; (23) inlet of H 2 S . ' _J
,
measure the volume of concentrated H2 (VHJ with a gas buret (14). The concentration of H2 in the concentrated H2 was determined with a Yanaco HSG-1 high-speed gas chromatograph (20). Unless otherwise specified, the reaction was carried out under the following standard conditions: weight of medium, 5 g; concentration of reducing components (H2and CO), 13%; total flow rate of the reducing gas, 195 cm3 (STP)/min; feed rate of the 100% steam, 132 cm3 (STP)/min; width of the reducing gas or steam pulse, 4 min; reaction temperature, 3W700 OC; total pressure, 1 atm. In most experiments, the reducing gas was Hz diluted with Ar, while the effects of CO and H2S were also examined. An X-ray diffraction diagram of the medium was measured with a Rigaku GF-2035 diffractometer. Results and Discussion Thermodynamic Criterion as Medium of the Steam-Iron Process. When dilute Hz is used as the reducing gas, the steam-iron process is described by for-
where Kp(H2)is the equilibrium constant. When Kp(H2) for a metal oxide is much larger than 1, the reduction of the metal oxide may occur easily, while the reoxidation of the reduced metal oxide with H20 hardly takes place. Therefore, such a metal oxide cannot be used as a medium of the reduction-oxidation cycles. Similarly, a metal oxide having too small a value of Kp(H2)is not suitable for the medium. When Kp(H2)for a metal oxide is close to 1, it is considered that both the reduction of the metal oxide with dilute Hzand oxidation of the reduced metal oxide with HzO may proceed for the metal oxide. This criterion, i.e., Kp(H2) = 1, leads to following classification of the metal oxides on the basis of the value of Kp(H2): Class A, llog Kp(H2)I < 1; Class B, 1 I [log Kp(Hz)I < 5; and Class C, 5 5 llog Kp(H2)I< 10. Here, the values-l,5, and 10-have no special meaning but are tentatively used to classify the metal oxides. Judging from the value of Kp(H2)?Class A metal oxides are considered to be most promising as media of the steam-iron process. Kp(H2)was calculated from the reported thermochemical data for various metal oxides at various temperatures (Weast, 1970). From the calculated results of Kp(H,), we get classification of the metal oxides as shown in Table I. As shown, Class A includes oxides of K, Rb, Cs, Ge, Sn, Mo, W, Fe, Co, Cd, and In. It should be noted that the iron oxide employed in the present "steam-iron process" belongs to Class A. Since the equilibrium constant of the reduction of a metal oxide changes with the kind of reducing gas, e.g., CO and hydrocarbons, metal oxides belonging to Classes B and C may be used as media depending on the kind of the reducing gas and reaction condition. Oxides of In (Class A), Sn (Class A), W (Class A), Ce (Class B), and V (Class B) have also been shown to carry out reduction-oxidation cycles to produce hydrogen (Kato et al., 1979a, b; Igarashi et al., 1982; Otsuka et al., 1981; Otsuka et al., 1982a, b). According to our preliminary experimenta, concentrated H2 was produced from dilute H2 by using oxides of Ge (Class A), Mo (Class A), Cr (Class C), and GeOz exhibited best performance at 700 "C. Further investigations were therefore made for GeOz medium. Ge.Oz-I and GeOz-II. Figure 3 shows the amount of concentrated H2 (VHJ and its yield (YHJ at various temperatures for Ge02-I,GeO2-II,and FesOl media; the concentration of H2 in the concentrated hydrogen was found to be 100% by using the high-speed gas chromatograph. Here, YH2is defined as VH,divided by the amount of the
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23, No. 3, 1984 46s
Table I. Classification of Metal Oxides on the Basis of K p (Ha)" C B OS* RS' temp: K OS6 RSc
KzOz
KZO
KO2 Rb203
K2°3
>BOO >500
Rb
>500
cs
csZ03 Sb204
>600
SbZ03 BiO Bi Po
Biz03 BiO Po02
>550 >550 >400 >I00 >550 >550
uo2
U308
Ti306 TiOz
Ti0 Ti203 V
vo
>600 >BOO
NazO GazO GaZ03 T120 PbO SbZ03 CeOz Am02
Na Ga GazO T1 Pb Sb
vZ04
vZo3
Mn304 TcOZ Reo3 NiO ZnO
MnO Tc Re Ni Zn
NbZ04 NbZOS TazOs CrZ03 Moo3 MnO
temp: K
OSb
CeZ03
>400 >400 >300 >700
RbZO capo GeO GeO, SnO Sn02 MoOZ WO2
>600
w4011
>500
wo3
>600
FeO Fe304 Fe304 coo CdO
>400 >BOO
temp: K >900 >I50
RSc
K
KZO
>goo >600 >BOO >BOO >500
VO >700 Nb >I00 NbZ04 >800 Ta >BOO >600 Cr MoOp >400 Mn304 >BOO Mn >650 >BOO RuO~ Ru COB04 coo >I00 RhzO Rh >750 RhZ03 Rho >750 cuzo cu >I00 ZnO Zn >450 " A 0 I llog Kp(H2)J< 1;B: 1 I (log Kp(Hz)l < 5; C: 5 I llog Kp(H,)I the thermodynamic criterion is satisfied. vZo3
A
Rb cs Ge GeO Sn SnO Mo W WOZ
>600 >300 >600 >600
>600 >600
>600 >500 >400 >600
w4011
Fe Fe FeO co Cd In
>600 >BOO
>I00 >400 >goo
< 10. Oxidized state. "educed state. dTemperature at which
100
1
100 I
1
700'C 700 ' C
-t! N
r >
50
m
n
v
"
n
"
fl
400Y
0 none N i Cu Mn Co
Fe No P t
Third c o m m e n t
Figure 5. Yield of concentrated Hz (YHJfor GeOz/A1203containing various third components at 700 "C. Content of GeOz, 30 wt 7%; content of third component, 15 wt % except for Pt (0.5 wt %). Experiments were done under standard conditions with dilute Hz 40 500 'C
N
I
>
20
10
0
none N I cu Mn co Fe NO
Pt
Third Component
Figure 6. Yield of concentrated Hz (YHJfor GeOz/A1203containing various third components at 500 OC. Content of Ge02, 30 wt %; content of third component, 15 wt % except for Pt (0.5 wt %). Experiments were done under standard conditions with dilute Hz
Promoted Ge02/A1203.Figures 5 and 6 show effects of third components on the yield of concentrated Ha. As for the reaction a t 700 "C (Figure 5), Ni and Cu were effective to increase YHpwhile Mn, Co, Fe, Mo, or Pt did not exhibit significant promoting effects. The yield of concentrated H2for Ni-Ge02/A1203and Cu-Ge02/A1203 attained as high as 80% at 700 "C, which was much higher
470
Ind. Eng. Chem. Prod. Res. Dev., Vol. 23,No. 3, 1984 d 1%)
Medlum
1.5
2.0
1 Oxldlzed Ge02-I
2 5
3.0
TTTQT
t tPtt
3.5
T I
P
T
Reduced Ge02-I
P
?~T?tttt??? Reduced Ge02- I AL
L
errroi
f
l
i
"
5
I I
r
(El
OxldlZed Ni -Ge02/ A1203
-
T (C
tlh2
r
Figure 7. Yield of concentrated H, (YH) from dilute CO and H2 mixture with various concentrations of C 6 at 700 "C. Experiments were done under standard conditions.
500 * I I -
I
I
c q
G
e
'B)
P
? L
40
Reduced NI-GeO2/ ;Ai203
c ~
t
1
P
,?
I IGI
1
I
f I Figure 9. X-ray diffraction diagrams for germanium oxide media after reduction or oxidation cycle of the steam-iron process. (A), (D), and (F): medium after the oxidation cycle with steam [132 cm3 (STP)/min for 4 min] at 700 "C; (B),(E), and (G):medium after the reduction cycle with dilute Hz[195 cm3 (STP)/min (H, concentration 13%)for 4 min] at 700 O C ; (C) Ge0,-I medium reduced with 100% Hz [25 cm3(STP)/min] for 3 h at 700 O C ; ( 0 )GeO, phase; (0) GeO phase; ( 0 ) Ge phase; (A) 7-Al,03 phase; (0)Ni phase; (m) GeI2Ni,, phase.
t1 1
2
3
4
5
6
hbwber a i remx i y i l e s
Figure 8. Influence of HzS addition to the dilute Hzgas on the yield of concentrated Hz (YHJ for Ni-GeOz/Al2O3and Fe304 medium. Open symbols, YH2in the absence of H2S;closed symbols, YH2in the presence of H,S (1 cm3 (STP)/cycle).
than YH for the iron oxide medium. As for the reaction at 500 '6 (Figure 6), Ni, Cu, Fe, and Mo were effective to increase the yield of concentrated H2, and YH2for these media attained twice as large as YH2for the iron oxide medium. Furthermore, the addition of Ni and Cu to Ge02/A1203markedly increased the stability of the medium. Effects of the Addition of CO and H2S to Dilute H2 Gas. Figure 7 shows the yield of concentrated H2 ( Y H J at various CO concentrations in dilute CO and H2 gas. As shown, dilute CO gas (i.e., 100% CO) was also converted to concentrated H2 by using germanium oxide media and YH2was increased markedly by the addition of Ni or Cu to Ge02/A1203medium. Especially, YH2for Ni-Ge02/ A1203medium decreased only slightly with the concentration of CO in dilute gas; YHzfor dilute CO gas (i.e., 100% CO) attained as high as 73%. Figure 8 shows the effect of the H2S addition to dilute H2 gas on the yield of concentrated H2 for Ni-Ge02/A1203 medium. As shown, YHz for the Ni-Ge02/A1203 medium was not affected by the H2S addition, while YH for the Fe304medium was de~ Ge02/Al203 creased slightly. It was dso found that Y Hfor or Cu-Ge02/A120, was not decreased by the addition of H2S to dilute H2 gas. Role of Ni in Ni-Ge02/A1203. Figure 9 shows the results of X-ray diffraction diagrams of various germanium oxide media after reduction or oxidation cycle of the steam-iron process. As shown in Figures 9A and B, the oxidized Ge02-Imedium is mainly composed of the Ge02 phase and the reduction of the Ge02 medium with dilute H2 leads to only slight reduction of the medium. Since a complete reduction of the Ge02-Iwith H2at 700 "C results in the formation of Ge metal (Figure 9C), the results indicate that the reduction-oxidation for the Ge02-Iis lim-
ited to only a very small part of the medium. This is in accordance with the low yield of concentrated H2 for unsupported Ge02media (Figure 3). Intensities of diffraction peaks for the oxidized and reduced GeO2/AlZO3media (Figures 9D and E) are weak and only the Ge02 and yA1203 phases are clearly observed, suggesting that germanium oxide spreads on the A1203 support. This explains the increase in the yield of concentrated H2 by supporting Ge02 on A1203(Figures 3 and 4). As shown in Figures 9F and G, the Ni phase is observed in the X-ray diagram of the oxidized Ni-GeOz/Al2O3medium in addition to the Ge02 and y-A1203phases, while an alloy of Ni and Ge(Ge12Ni19) is formed in the reduced medium. This means that Ni interacts strongly with germanium oxide in the course of reduction of germanium oxide with dilute Hz. Such an interaction of Ni with Ge may be responsible for the high yield of the concentrated H2 and high stability for the Ni-Ge02/A1203 medium. Registry No. Hz, 1333-74-0; CO, 630-08-0; Alz03,1344-28-1; Cu, 7440-50-8; Ni, 7440-02-0; GeOz, 1310-53-8.
Literature Cited Igarashl, A.; Asano, H.; Kikuchi, Y.; Dgino, Y. Chem. Lett. 1982, 1693. Kato, Y.; Igarashi, A.; Ogino, Y. Nippon Kagaku Kalshl 1979a, 842. Kato, Y.; Igarashi, A.; Oglno, Y. Nippon Kapku Kalshl 1979b, 1472. Murakaml, Y.; Miyamoto. A.; Kamitomai, S.: Kurahashi, K.; Kosaki, Y. J . Jpn. Pet. Inst. 1982, 25, 380.
Otsuka, K.; Yasui. T.; Morikawa, A. J . Catal. 1981, 72,392. Otsuka. K.; Yasui, T.; Morikawa, A. 8011. Chem. Soc. Jpn. 1982a, 55, 1768. Otsuka, K.; Yasui, T.; Morlkawa, A. J . Chem. Soc., Faraday Trans. 1 1982b, 78,3281.
Tarman, P. 8. "Status of the Steam-Iron Process", 5th Synthetic Pipeline Symposium, 1973;p 1. Tarman, P. B.; Punwani, 0.; Bush, M.; Taiwalker, A. "Development of the Steam-Iron System for Production of Hydrogen for the Hygass Process", OCR RBD Report No. 95,Interim Report. 1974. Tarman, P. B. R o c . Synth. plpellne Qas Symp. 1978, 8 , 129. Tarman, P. B.; Bijentina, R. CoelRocess Technol. 1979, 5 , 114. Weast, R. C., Ed. "Handbook of Chemistry and Physics"; The Chemical Rubber Co.. Cleveland, 1970 p D45. Received for review October 24, 1983 Accepted March 15, 1984
