784
Ind. Eng. Chem. Res. 1994,33, 784-789
KINETICS, CATALYSIS, AND REACTION ENGINEERING Methane Partial Oxidation to Methanol. 1. Effects of Reaction Conditions and Additives Kohji Omata,' Nobuyuki Fukuoka, and Kaoru Fujimoto Faculty of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan
Noncatalytic direct oxidation of methane was conducted in a high pressure flow type system to clarify the effect of operational factors and additives. The reaction conditions were 300-500 "C; 21-41 atm; CH4/air ratio, 3/1-1711; residence time, 3-15 s, Methanol selectivity was affected by reaction conditions, especially the methane/oxygen ratio. Additives such as carbon dioxide, hydrogen, and hydrocarbons improved methanol selectivity and reduced the initiation temperature of the methane-oxygen reaction. The observations suggest that hydrogen-donating species may be essential for selective methanol formation.
Introduction The industrial manufacture of methanol from natural gas uses a two-stage process consisting of the steam reforming of methane to syngas, followed by synthesis of methanol from the syngas. The economics of the process are limited by the low thermal efficiency and high cost of steam reforming. In contrast, the direct oxidation of methane to methanol is potentially free from such constraints. When the one-pass conversion of methane is 10% and methanol selectivity is about 80%, the cost of direct conversion may be lower than that of the conventional two-stage process, even if oxygen is used as the oxidizing agent instead of air (Edwards and Forster, 1986). Much research has been conducted on the partial oxidation of methane to methanol, but only one system which satisfies these criteria has been reported (Yarlagadda et al., 1988). This excellent system achieved a methane conversion of 8-10% and a methanol selectivity of 7080% using reaction conditions of 25-65 atm and 410-480 "C in a tubular reactor with a Pyrex glass liner. Burch et al. (19891, however, reported that the methanol selectivity was about 40 % under similar conditions. The discrepancy was discussed in a recent review (Brown and Parkyns, 1992). Direct methane oxidation has been reviewed by several authors (Gesser and Hunter, 1985; Forster, 1985; Pitchai and Klier, 1986; Brown and Parkyns, 1992). Reaction conditions, reactor materials, and additives are the controlling factors for both methane conversion and methanol selectivity. Generally,low temperature and high pressure favor methanol production (Rytz and Baiker, 1991). High pressure also lowers the initiation temperature (Burch et al., 1989). Metal surfaces such as steel or copper used for reactors lower the initiation temperature of methane conversion but at the same time reduce the methanol selectivity (Mahajan et al., 1977), although Hunter et al. reported that steel did not affect the methanol selectivity (Hunter et al., 1990). Quartz or Pyrex glass tubes are recommended as inert materials for the reactor liner (Burch et al., 19891,especially at low surface/volume ratio of a reactor (Chun and Anthony, 1993). Hydrogen abstraction from methane is the initial step and determines the total methane conversion. The initiation temperature is lowered by the presence of ethane in the methane feed because radicals formed in the ethane-oxygen reaction
actively abstract hydrogen (Burch et al., 1989). It was also reported that some additives lower the minimum temperature of complete oxygen consumption and improve the methanol selectivity (Hunter et al., 1990). Chou and Albright (1978) successfully simulated the product yield in a tubular reactor based on 22 elementary reactions. It was also pointed out that reactions between radicals and the reactor surface are important (Mahajan and Albright, 1977; Thomas et al., 1992). Much kinetic data for these elemental reactions of methane pyrolysis and combustion, (Tsang and Hampson, 1986) and methanol (Tsang, 19871, ethane (Tsang and Hampson, 19861, propane (Tsang, 19881, and butane (Tsang, 1990) combustion are available and are important for understanding the experimental phenomena. Various factors controlling direct methane oxidation have been studied in detail, but no guiding principles for selective methanol synthesis have yet been established. The present authors reported that propane added to the methane feed (Fukuoka et al., 1989) and radicals formed by the H2-02 reaction on the surface of Pt wire (Omata et al., 1992) both improve the methanol selectivity. We concluded that hydrogen-donating species are important in the reaction network for better methanol selectivity. The present study investigated the effects of operational factors and additives on the initiation or termination of the noncatalytic CH4-02 reaction in a high pressure flow type system to clarify ways to improve the methanol selectivity.
Experimental Section Apparatus. All experiments were carried out in a high pressure flow type reactor (Figure 1). The outer tube was made of stainless steel, surrounding an internal quartz tube of 10.5 mm i.d. or glass tube of 6.5 mm i.d. A Viton O-ring was placed between the top ends of the outer and inner tubes to prevent gas contact with the steel surface. The thermocouple was centered in reaction zone, inside a stainless steel tube of 3.0 mm 0.d. with a dead end. The open end of the stainless steel tube covering the thermocouple was sealed with Swagelock,and the tube was placed in a quartz tube of 6.4 mm 0.d. with a dead end. This assembly was necessary to position the sensor in the reaction zone and prevent contact of the reactants with
08~8-5885/9~/2633-0784~~4.5~l0 0 1994 American Chemical Society
Ind. Eng. Chem. Res., Vol. 33, No. 4,1994 785 Table 1. Analytical Conditions on Gas Chromatograph compound
detector TCD TCD FID FID FID
CHI. 09. N9 CHsOH, HCHO, C2HaOH. CHsCHO hydrocarbons a
carrier H2 Ar N2 N2 N2
packed column molecular sieve 5A molecular sieve 13X Porapak Ro APs201a Porapak R
column temp (OC) 60 room temp room temp 100 room temp100
With methanizer.
I gas ?I
, O-ring
SUS tube
QD
quartz tube
gas outlet
thermocouple Figure 1. Reactor.
the stainless steel surface. Residence time was controlled by placing a quartz tube of 7.8 mm i.d. and 9.8 mm 0.d. in the reaction zone. The reactor was placed vertically in an electric furnace with a flat temperature zone of 20 cm. The heated volume was calculated by multiplying this length by the cross section. Reaction. The reaction conditions were in the ranges: 300-500"C; 21-41 atm; CHdair ratio, 3/1-17/1;residence time, 3-15 s. Methane was purified by passage through columns of 5A molecular sieves and potassium hydroxide to remove water and carbon dioxide, respectively. Air was also purified using a molecular sieve column. Methane and air flows were first mixed and then supplied to the reactor. The flow rate of each gas was controlled by a thermal mass flow controller (Ueschima-Brooks) and the pressure controlled by a back-pressure regulator (GO) which was maintained at 150 "C. Analysis. The product mixture was sampled by a sixway valve and a hot gas-tight injector. Products that contain carbon were separated by a packed column followed by conversion to methane with a methanizer (Ru/ A1203, 480 "C). The conditions (detector, carrier gas, column, temperature) used for gas chromatography are summarized in Table 1. Product yield (Yip %) was defined as
CiNi yi = Fout Fin
where Fout (mmol/h) = flow rate of outlet gas, Fi,(mmol/ g) = flow rate of methane feed, Ci (%) = concentration of product i in outlet gas, Ni = carbon number of product i. Unconverted methane can be estimated in a similar manner. Methane conversion was calculated as a sum-
0
2
1
3
4
5
Residence time (s) Figure 2. Product selectivity as a function of residence time at 400 "C, 41 atm, C)4/0a/N2 = 30/1/4.
mation of yields of all products which contain carbon. The total of unconverted methane and methane conversion was accurate to 100 f 5%. The product selectivity (Si, % ) was defined as
s: =
Yi
C
x 100 Yi
pr ucta
Rssults Effect of Operational Factor. The products were methanol (MeOH), formaldehyde, oxygenates (acetaldehyde and ethanol ai oxy), carbon oxides (COX),and C2 hydrocarbons (C2). The effect of residence time is shown in Figure 2. Oxygen conversion increased sharply after 3 s, suggesting the presence of autocatalytic reactions. Methanol selectivity was stable at about 30% from the initiation of reaction until the termination of the reaction when oxygen conversion is 100%. Methanol is stable in the presence of oxygen (Burch et al., 19881,and Figure 2 shows that methanol is stable even in the presence of the radicals formed during oxidation reactions. Formaldehyde, another initial product, decomposes into carbon monoxide and then is converted to carbon dioxide as the reaction proceeds. Figure 3 shows the effect of reaction temperature. No product was observed below 400 "C. Between 460 and 500 "C, oxygen conversion was 100%. The range from 460 to 480 "C achieves the optimum selectivity and yield of methanol,because above 500 "C the methanol selectivity decreases while the C2 selectivity increases. Since it is clarified in Figure 2 that methanol is stable under reaction conditions, the ratio of methanol to COX indicates the ratio of methanol/formaldehyde a t the initial stage of reaction. This ratio is smaller at lower temperatures, suggesting that methanol selectivity is not improved even
786 Ind. Eng. Chem. Res., Vol. 33, No.4, 1994
o* mnverSlOn (%) n
n
Irn
35-
Haon YlSXl IS,
25-
0 50
o_ 0 m
2-
jr 3 ' 5 -
I
xa
001
11
1-
05-
Figure 3. Effect of reaction temperature at 41 atm. residence time = 1 8 , CHJOdNz = 30/1/4.
wr 0
vel Mehl
9 3
on,
Hcm
MeOH Yield(%)
m2
4Irn
0 61
21am
0.50
'0, "
?
a
0
2:
dj
m
1991
smm1991
qumlul
material [Slv] (cm-') Figure 6. Effecta of reactor material and S/V at 440 'C. 41 atm. residence time = 5 8, CH,/OdNz = 30/1/4.
100
w1
Selectivity (%) Figure 4. Effect of reaction pressure at 440 'C. residence time = 5 8. CHJOdNz = 15/1/4. MeOH Yleldl%~ 1511
0.61
3011
0.77
8511
0.36
N
% I 0
Reaction temperature CC) 0
20
4c
50
, Bc1
~~~
~~
>
Figure 7. Effect of COz addition at 41 atm. residenm time = 1 8, CHJOdNz = 301114, COZ= 10 mol 9% in CH,.
1W
(3
0.6 I
Selectivity (%) Figure 6. Effect of CHJOz ratio at 440 OC, 41 atm, residence time =5a.
if reaction is initiated at lower temperatures by an initiator or prolonged reaction time. The effect of reaction pressure is illustrated in Figure 4. Oxygen conversion was 100% at all pressures. As the reaction pressure was raised the selectivity and yield of methanol increased. The effect of pressure, however, was more pronounced for C2 compounds such as ethane and ethylene. The CHd02 ratio in the feed had a significant effect on the product selectivity (Figure 5). Oxygen conversion was always 100%. Selectivitiesfor methanoland formaldehyde increased with increasing CHJ02 ratio while C2 and CO selectivities decreased. A high CHJO2 ratio favors methanol formation, suggesting that the partial pressure of 02 significantly influences methanol formation. The reactor material influences the yield of methanol (Chouand Albright, 1978). Figure6shows thecomparison of Pyrex glass and quartz that is inert. The inner surface area of the solid surface in the reaction zone (S) and the volume of the reaction zone (VI were controlled independently by charging chips of Pyrex or quartz. The results show that Pyrex glass is as inert as quartz in this temperature range. A low S/V ratio resulted in a high methanol yield and low CO2 yield, suggesting that the reactor surface hinders methanol formation. Therefore, a low S / V is essential to attain high methanol selectivity (Thomas et al., 1992; Chun and Anthony, 1993). Effect of Additive. Figure 7 shows the yields of
.al
m 1.5 ",
- 0.3 0
0.2
I 0.5
0.1
n
.~
400
420
440
460
480
506
Reaction temperature ("C) Figure 8. Effect of hydrogen addition at 41 atm, residence time = 1 8, CHJOdNz = 30/1/4, HP = 4 mol 9% in methane.
methanol and CO as a function of temperature in the presence and absence of 10% CO2 in the methane feed. The methanol yield wasclearly increased by CO2 addition, but the methanol selectivity would not be determined because the rate of COz formation cannot be distinguished from the supplied COz. The role of CO2 will be discussed later. The effect of hydrogen is shown in Figure 8. The temperature at which reaction was initiated was not affected by hydrogenaddition, showingthat hydrogendoes not act asan initiator. However, hydrogen additioncaused an increase in methanol yield a t low temperature (42C460 "C) and suppressed COz formation. Since natural gas often contains a small amount of
Ind. Eng. Chem. Res., Vol. 33, No. 4,1994 787 CH4
1
HA
CH3
Reaction temperature ("C) Figure 9. Effect of hydrocarbon addition on methane conversion at 41 atm, residence time = 1 a, CH4/02/N2 = 30/1/4,hydrocarbon = 3 mol % in CHI.
HD: CH4, CH20 :Hydrogendonor HA: 0 2 , OH, Hop, H :Hydrogen acceptor
Table 2. Effect of Hydrocarbon Addition on Product Distribution of Methane Oxidation Products. hydro- temp CHI selectivity (C mol %) carbon ("C) conv(%) CH30H HCHO CO COz oxy 460 2.2 23.0 0.8 42.6 32.5 0 C2Hs 440 3.0 26.5 2.2 54.0 9.7 1.1 CsHs 400 2.9 29.4 5.0 41.8 9.5 7.1 ~ - C ~ H ~400 IJ 2.9 31.0 2.8 50.4 11.6 3.4
Figure 11. Reaction scheme. C2 1.1 6.6 7.1 0.8
a Pressure, 41 atm; CHd/air ratio, 6/1;hydrocarbon, 3 mol % in CH4; residence time, 1 a.
1.2
1
C
CO 0.4
320
1
HD CH30H
340
Reaction temperature (OC) Figure 10. Effect of hydrocarbon addition on methanol yield at 41 atm, residence time = 1a, CH4/02/N2= 30/1/4, hydrocarbon = 3 mol % in CH4.
ethane, the effect of ethane on methane conversion should be clarified. Ethane reduces the initiation temperature of methane oxidation (Hunter et al., 1986; Burch et al., 1989). The initiator function is important because radicals such as C2H5, CH3, and H are generated at a lower temperature (Kastanas et al., 1988)than those from CH4. We tried to clarify the effects of hydrocarbons with primary $,He), secondary (C3H8),and tertiary (1'-C4H10)hydrogen atoms. Methane conversion is shown in Figure 9 as a function of temperature. Hydrocarbon (3 mol %) was added to the methane. The initiation temperature of the methane conversionwas reduced by hydrocarbon addition. The extent of temperature reduction was in the order: 1'44H10 > C3Ha > C2H6, and the differences were 60,50, and 30 "C, respectively. Table 2 summarizes the product distribution at the minimum temperature for 100% oxygen conversion. Hydrocarbon addition caused an increase of MeOH selectivity and a decrease of C02 selectivity. All hydrocarbons improved the methanol yield (Figure 10). Discussion Reaction Mechanism. The partial oxidation of methane involves many elementary reactions. The product pattern has been simulated based on these reactions. (Chuan and Albright, 1978) We classified these reactions
based on the following categories of molecules and radical species: those containing a methyl group, hydrogen donor (HD),and hydrogen acceptor (HA). HDs are for example methane, higher hydrocarbons, and formaldehyde. HAS are oxygen and radicals such as H, OH, and HOz. The reaction path is illustrated in Figure 11. The combustion of methanol was not considered because the reaction hardly proceeds in the presence of oxygen. The methoxy radical is an important intermediate in this pathway. Elimination of hydrogen from the methoxy radical in a reaction such as oxidative dehydrogenation gives formaldehyde, which is easily converted to CO and C02. Hydrogenation of the radical yields methanol. Stabilization of the methoxy radical by hydrogenation is a key step to achieve a high methanol yield. (Gesser et al., 1985) Effect of Reaction Conditions. The methanol eelectivity observed in the present study was 10% without additives. Higher selectivity has been reported (Burch et al., 1989; Yarlagadda et al., 1988) under similar reaction conditions. For catalytic methane oxidation, the distance between the catalyst bed and the cooling bed had a large influence on formaldehyde yield (Pitchai and Klier, 1986). Rapid quenching of radicals apparently reduces selectivity to COXformation. Furthermore, we found that the S/V (surfacearealvolume ratio), which is determined by reactor design and dimension, also influences the methanol selectivity. These considerations suggest that apparatus design is an important factor in addition to apparent reaction conditions. Differencesin results between studies can be attributed to such factors. The considerable effect of the CH$02 ratio on methanol selectivity can be explained on the basis of the reaction pathway. Methanol selectivity is determined by the competition between hydrogenation of the methoxy radical by HD, especially CH4 (eq l ) , and hydrogen abstraction CH,O
+ CH4
-
CH30H + CH,
(1)
from the methoxy radical (eq 2). These reactions are HA (especially 02)
CH,O
CH,O
(2)
parallel ones. For any pressure, the partial pressure of methane (HD) increases with increasing CHd02 ratio, while the partial pressure of oxygen (HA) decreases, resulting in acceleration of reaction 1and suppression of reaction 2, with reduced successive COX formation.
788 Ind. Eng. Chem. Res., Vol. 33, No. 4, 1994
Effect of Additive. We can expect three functions for additives in the radical reaction. When two radicals combine into a molecule it may decompose again due to excess internal energy. The excited molecule may be stabilized by collision with a third body. Additives, especially of high molecular weight, can act as the third body. The second function is to reduce the temperature where reaction occurs by radical formation at low temperature. The third is to promote target product selectivity. We call these functions “third body”, “initiator”,and “promoter”, respectively. NO and HBr have been used as the initiator for the partial oxidation of methane (McConkey and Wilkinson, 1967). The initiator, however, cannot promote methanol selectivity, because the methanol/COx ratio is almost stable at 460-480 “C and falls at lower temperatures suggesting that selectivity to methanol is not affected even if the reaction is promoted by an initiator or prolonged reaction time. COZ addition is characterized by the reduction of initiation temperature and increased methanol and CO yields. COz therefore acts as both “initiator” and “promoter”. COz reacts with hydrogen to form the hydroxyl radical (eq 3) (Tsang and Hampson, 1986). Methane reacts with hydroxyl radical (eq 4)2 orders of magnitude faster than it does with hydrogen (eq 5). The conversion of hydrogen
+ H --., CO + OH CH, + OH CH, + H,O CH, + H -. CH, + H, CO,
+ OH
-
-
-
(CH30H)*
CH,O
(4) (5)
+ 2H
+ CO,
-
CH30H + CO
-
CH,OH
+H
(8)
was not an initiator probably because the rate of reaction 9 is one-fifth that of reaction 10under reaction conditions. H, CH,
+ 0, -.H + HO, + 0,
kl0
CH,
4
+
h
0 6 0
4
r
d 3
3
h
I“2 2 L-
W
s1 \
so -c
W
-1 1.4
1.5
1.7
1.6
1000 / T (K-1)
Figure 12. Relative rate of hydrogen abstraction from hydrocarbon. as the carbon number of the additive increased. Hydrogen abstraction from the hydrocarbon is probably related to the initial step for methane conversion. When hydrocarbon is added to methane, the initiation reaction (eq 11)will proceed as well as the usual initiation reaction (eq 10). Radicals such as OH and HOz are the
main chain propagating radicals (McConkey and Wilkinson, 1967). In the present reaction the HOz radical is formed by eq 11 at low temperature and reacts with methane or hydrocarbon as a hydrogen acceptor.
(7)
Hydrogen added to the methane increased the methanol yield by stabilization of the methoxy radical, probably due to reaction 8 (Omata et al., 1992). However, hydrogen CH30 + H,
H.C. + 02 H.C.’ + HOz H.C. + HOz H.C.‘ + HzOa frequency activation frequency activation H.C. factop energyb factor energy CHI 6.7 X lO-” 238.1 3.0 X 10-13 77.74 212.8 4.9 X 10-18 62.52 CzHe 6.7 X 10-” 6.6 X 10-” 199.1 1.6 X 1 0 - T . e 58.20 C3He 184.1 6 X lO-21Tz.M 44.07 i-C4Hlo 6.6 X IO-” a In cmYmolecule/s. In kJ/mol.
(6)
it should stabilize the excited methanol by the third body effect. The increase in methanol yield is due to the relaxation of excited methanol by COZ. Another possibility is a direct reaction between COz and CHI (eq 7), but this seems improbable under present reaction conditions. CH,
Hydrocarbons
(3)
to hydroxyl radical by COZshould reduce the initiation temperature. Excited methanol is formed by a combination of methyl radical and OH and is then converted to formaldehyde and hydrogen (eq 6). COz has a high molecular weight, so CH,
Table 3. Kinetic Parameter of H Abstraction from
(9)
CH, C,H,
-
+ HO,
+ HO,
ki2
CH,
kia
C,H,
+ H,O,
+ H,O,
(12) (13)
The formation of HOz radical according to eq 11 contributes to methane conversion by reducing the initiation temperature. The initial methane conversion rate is given by eq 14 for the CH4-02 reaction and by eq 15 for the CH,-H.C.-Oz reaction (H.C. = hydrocarbon). The rate
+ HO,
Lower paraffins such as ethane and propane acted as both initiator and promoter. Hydrogen abstraction from hydrocarbons by the 0- ion is been known to proceed in the gas phase. The probability of first hydrogen abstraction increases as the carbon number increases (Bohme and Fehsenfeld, 1969). Figure 9 clearly shows that methane conversion was initiated at a lower temperature
constant for each reaction in cm3/molecule/s is listed in Table 3 (Tsang and Hampson, 1986; Tsang, 1987, 1988, 1990).
Ind. Eng. Chem. Res., Vol. 33, No. 4,1994 789
At low temperatures, where the CH4-02 reaction is negligible,the rate of formation of the HO2 radical is given by -= d[H023
dt
kllpH.C.POz
- 'l$CH,'HOZ
- 1' 3'H.c.H' o,
We can assume that the rate is zero as a steady-state approximation. Thus we obtain
Initiation temperatures where methane conversion is detectable were calculated by eqs 14, 15,and 17. The initiation temperature was 410 "C for the CH4-02 reaction as shown in Figure 1, so the ratio of r(CH4) (by eq 14)to r(CH4) a t 410 "C and the ratio of r(H.C.) (by eqs 15 and 17) to r(CH4) at 410 "C are calculated (Figure 12). The temperature where the ratio is unity is the initiation temperature for each reaction. The calculated initiation temperatures with ethane, propane, and butane were 385, 363,and 332"C, respectively,while the experimentalvalues were ca. 380,360,350"C, respectively. These values are in fair agreement confirming that the free radical formed in the H.C.42 reaction attacks CH4 a t a lower temperature to initiate methane conversion. Approximately 30% of the added propane was converted, mostly to the dehydrogenated product (propene). Hydrogen from hydrocarbons is donated to the methoxy radical to increase methanol yield during the reaction. Methanol formation by the ethane-methoxy radical (eq 18) is faster than the rate of reaction 1 (Tsang and Hampson, 1986). CH,O
+ C2H,
-
CH,OH
+ C2H,
(18)
Conclusions Methane was directly oxidized in a high pressure flow type system to clarify the effects of operational factors and additives using the followingreaction conditions: 300500 "C; 21-41 atm; CH$air ratio, 3/1-17/1;residence time, 3-15 s. The products were methanol, formaldehyde, carbon oxides,and C2 hydrocarbons. Temperatures from 460 to 480 "C achieved optimum selectivity and yield of methanol. A higher pressure is favorablefor C2formation. Selectivities for methanol and formaldehyde increased with increasing CH4/O2 ratio while those for C2 and CO decreased. A low surface areaholume ratio in the reactor achieved a high methanol yield and a low COz yield. Additives such as carbon dioxide, hydrogen, and hydrocarbons improved methanol selectivity and reduced the initiation temperature of the methane-oxygen reaction. We suggest that hydrogen-donating species are essential for selective methanol formation. Literature Cited Bohme, D. K.; Fehsenfeld, F. C. Thermal Reactions of 0- ions with Saturated Hydrocarbon Molecules. Can. J.Catal. 1969,47,27172719.
Brown, M. J.; Parkyns, N. D. Progress in the Partial Oxidation of Methane to Methanol and Formaldehyde. Catalysis Today 1991,
Chun, J.-W.; Anthony, R. G. Catalytic Oxidations of Methane to Methanol. Znd. Eng. Chem. Res. 1993,32,259-263. Edwards, J. H.; Foster, N. R. The Potential for Methanol Production from Natural Gas by Direct Catalytic Partial Oxidation. Fuel Sci. Technol. Znt. 1986,4,365-390. Foster, N. R. Direct Catalytic Oxidation of Methane to Methanol-A Review. Appl. Catal. 1985,19,1-11. Fukuoka, N.; Omata, K.; Fujimoto, K. Effect of Additives on Partial Oxidation of Methane. Preprints on Methane Activation, Conversion and Utilization, Proceedings of PACIFICCHEM 89 in Honolulu; American Chemical Society: Washington, DC, and Chemical Society of Japan: Tokyo, 1989; pp 106-107. Gesser, H. R.; Hunter, N. R.; Prakash, C. B. The Direct Conversion of Methane to Methanol by Controlled Oxidation. Chem. Reu. 1985,85,235-244.
Hunter, N. R.; Gesser, H. D.; Morton, L. A.; Yarlagadda, P. S.; Fung, D. P. C. The Direct Conversion of Natural Gas to Alcohols. Proceedingsof the VZZZntematiomlSymposium on AlcoholFuels Technology; French Institute of Petroleum: Paris, 1986; pp 620621.
Hunter, N. R.; Gesser,H. D.; Morton, L. A.; Morton, L. A.; Y arlagadda, P. S. Methanol Formation at High Temperature by the Catalyzed Oxidation of Natural Gas and by the Sensitized Oxidation of Methane. Appl. Catal. 1990, 57, 45-54. Kastanas, G. N.; Tsigdinos, G. A.; Schwank, J. Effect of Small Amounta of Ethane on the Selective Oxidation of Methane over Chem. Silicic Acid and Quartz Glass Surfaces. J. Chem. SOC., Commun. 1988,1298-1300. McConkey, B. H.; Wilkinson, P. R. Oxidation of Methane to Formaldehyde in a Fluidized Bed Reactor. Znd. Eng. Chem. Process Des. Dev. 1967,6,436-440. Mahajan, S.; Menzies, W. R.; Albright, L. F. Partial Oxidation of Light Hydrocarbons. 1. Major Differences Noted in Various Tubular Reactors. Znd. Eng. Chem. Process Des. Dev. 1977,16, 211-274.
Mahajan, S.;Albright, L. F. Partial Oxidation of Light Hydrocarbons. 3. Mechanism Incorporating Key Surface Reactions with GasPhase Steps. Znd. Eng. Chem. Process Des. Dev. 1977,16,219281.
Omata, K.; Fukuoka, N.; Fujimoto, K. Methane Partial Oxidation to Methanol-Solid Initiated Homogeneous Methane Oxidation. Catal. Lett. 1992,12, 227-230. Pitchai, R.; Klier, K. Partial Oxidation of Methane. Catal. Rev.-Sci. Eng. 1986,28,13-88. Rytz, D. W.; Baiker, A. Partial Oxidation of Methane to Methanol in a Flow Reactor at Elevated Pressure. Znd. Eng. Chem. Res. 1991,30,2287-2292.
Thomas, D. J.; Willi, R.; Baiker, A. Partial Oxidation of Methane: The Role of Surface Reactions. Znd. Eng. Chem. Res. 1992,31, 2272-2278.
Tsang, W.; Hampson, R. F. Chemical Kinetic Data for Combustion Chemistry. Part 1. Methane and Related Compounds. J. Phys. Chem. Ref. Data 1986,15,1087-1279. Tsang, W. Chemical Kinetic Data for Combustion Chemistry. Part 2. Methanol. J. Phys. Chem. Ref. Data 1987,16,471-508. Tsang, W. Chemical Kinetic Data for Combustion Chemistry. Part 3. Propane. J. Phys. Chem. Ref. Data 1988,17,887-952. Tsang, W. Chemical Kinetic Data for Combustion Chemistry. Part 4. Isobutane. J. Phys. Chem. Ref. Data 1990,19,1-68. Yarlagadda, P. S.; Morton, L. A.; Hunter, N. R.; Gesser, H. D. Direct Conversionof Methane to Methanol in a Flow Reactor. Znd. Eng. Chem. Res. 1988,27,252-256.
8,306335.
Received for review November 11, 1993 Accepted December 3, 1993.
Burch, R.; Squire, G. D.; Tsang, S. C. Direct Conversion of Methane into Methanol. J. Chem. SOC.,Faraday Trans. 1 1989,85,35613568.
Chou, T.-C.; Albright, L. F. Partial Oxidation of Methane in Glass and Metal Tubular Reactors. Znd. Eng. Chem. Process Des. Dev. 1978,17,454-459.
@
Abstract published in Advance ACS Abstracts, February 1,
1994.
