Process for the catalytic oxidation of hydrocarbons

Details Process for the catalytic oxidation of hydrocarbons Process for the catalytic oxidation of hydrocarbons

2000-06-08

2002-04-30

Barts, Samuel (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C568S910000

Reexamination Certificate

active

06380444

ABSTRACT:

This application is the national phase under 35 U.S.C. §371 of PCT International Application No. PCT/DK98/00488 which has an International filling date of Nov. 11, 1988, which designated the United State of America.
FIELD OF THE INVENTION
The present invention relates to the catalytic oxidation of hydrocarbons to give useful oxidation products thereof. In particular, an important aspect of the invention relates to a process for the production of alkanols, e.g. lower alkanols, such as C
1
-C
3
alkanols (e.g. methanol or ethanol), from the corresponding alkanes (i.e. methane and ethane, respectively, in the case of methanol and ethanol), wherein an alkanol is produced via the formation, and subsequent hydrolysis, of an intermediate (e.g. methyl bisulfate in the case of methane as starting hydrocarbon) formed by catalytic oxidation of the hydrocarbon in a liquid, essentially anhydrous sulfuric acid (H
2
SO
4
) medium containing a catalyst and preferably containing a significant proportion of dissolved sulfur trioxide (SO
3
).
BACKGROUND OF THE INVENTION
Methane is a raw material of great synthetic importance and an abundant natural resource as the main constituent of natural gas. Nevertheless, it is primarily used only as fuel because two factors limit its use as a raw chemical. The first is that transporting methane gas or even liquefied natural gas is not economical. Therefore, it is highly desirable to transform methane into transportable raw materials or products. The second factor is that methane is a very stable molecule and its direct conversion to useful chemicals is very difficult. Today, over 90% of the produced methane is consumed as heating fuel. Because transportation of natural gas from remote sites is costly, it has often been suggested that natural gas, namely methane, should be converted to more easily transported liquid fuel.
As a raw material for chemical industries, the two leading uses of methane are in the production of methanol and ammonia. Methane must be first transformed into synthesis gas before usage in either ammonia or methanol synthesis. Clearly, this process makes conversion into synthesis gas the dominant process of methane upgrading. The term synthesis gas is generally used for a mixture of carbon monoxide and hydrogen, preferably at a 1:2 or 1:3 ratio. Today the dominant route to the production of synthesis gas is the methane steam reforming process. The reaction can be stoichiometrically expressed as
CH
4
+H
2
O→CO+3H
2
A considerable disadvantage of the steam reforming process is that it is an endothermic reaction. The endothermicity results from addition of steam in which a significant amount of energy is required to decompose water into its elements.
In addition to synthesis gas formation, several documents disclose a variety of methods for activating methane to produce other higher molecular weight materials. Mobil Oil Corporation is the assignee in several U.S. patents using sulfur or certain sulfur-containing compounds as the reactants in non-catalytic reactions with methane to produce methyl intermediates which can then be converted to higher molecular weight hydrocarbons.
In U.S. Pat. No. 4,543,434, Chang teaches a process using the following steps:
CH
4
+4S→CS
2
+2H
2
S
CS
2
+3H
2
(Co or Ni)→CH
3
SH+H
2
S
CH
3
SH (HZSM-5)→[CH
2
]+H
2
S
4H
2
S→4H
2
+4S
where “[CH
2
]” is a hydrocarbon having at least two carbon atoms.
Another Mobil disclosure (U.S. Pat. No. 4,864,073 to Han et al.) suggests a carbonyl sulfide-based process in which methane and carbonyl sulfide are contacted in the presence of ultraviolet light under conditions sufficient to produce CH
3
SH. No other reaction initiators are said to be present. The reaction scheme is shown to be:
 CH
4
+COS→CH
3
SH+CO
CH
3
SH (HZSM-5)→[CH
2
]H
2
S
(H
2
S→S), a regeneration step
CO+S→COS
The selectivity of the first reaction is said to be high, i.e., around 81%, however, the conversion appears to be quite low.
A disclosure similar to that of Chang is found in Mobil's U.S. Pat. No. 4,864,074 to Han et al. As in Chang, the methane is contacted with sulfur. The process conditions are changed, however, so that either CS
2
or CH
3
SH is formed. These sulfur compounds may then be converted in the presence of the preferred HZSM-5 zeolite catalyst to produce hydrocarbons having two or more carbon atoms. Also, as was the case with “Chang”, the step of contacting the methane to produce a methyl-sulfur compound is performed in the absence of a catalyst.
Other methods are known for producing substituted methanes which are suitable for further reaction to heavier hydrocarbons. A thermal methane chlorination process is shown in U.S. Pat. No. 4,804,797 to Minet et al. A similar process is disclosed in U.S. Pat. No. 3,979,470 to Fimhaber et al. (Although a preference for C
3
hydrocarbon feeds is expressed in the patent).
One method shown in U.S. Pat. No.4,523,040 to Olah utilizes either a solid strongly acidic catalyst or a supported Group VIII metal (particularly platinum and palladium) in the gas phase halogenation of methane to produce methyl halides. The patent indicates that monohalides are produced with 85% to 99% selectivity. Olah suggests that subsequent or concurrent catalytic hydrolysis produces methyl alcohol and/or dimethyl ether. Production of methyl oxo-esters is not shown.
The reaction of methane with palladium (II) acetate in trifluoroacetic acid to effect the trifluoroacetoxolation of methane is shown in Sen et al., “Palladium (II) Mediated Oxidative Functionalization of Alkanes and Arenes”,
New Journal of Chemistry
(1 989), Vol. 13, No. 10-11, pp. 756-760. A yield of 60% based on palladium was reported when the reaction was practiced using methane as the reactant. Consequently, the reaction with methane utilized palladium as a reactant and not as a catalyst. The extent of methane conversion, selectivity, and reaction rates were not stated.
The Sen et al. article has been criticized in Vargaftik et al., “High Selective Partial Oxidation of Methane to Methyl Trifluoroacetate”,
Journal of the Chemical Society, Chemical Communications
(1990), pp. 1049-1050, to the extent that the results were not found to be reproducible. Vargaftik et al. discloses the catalytic oxo-esterification of methane to methyl trifluoroacetate with cobalt in trifluoroacetic acid but shows that palladium is not even suitable for stoichiometric methane oxidation in the process. With Pd, less than 0.1% yield of methyl trifluoroacetate based on palladium (II) trifluoroacetate was obtained.
The Vargaftik et al. article discloses that although palladium is ineffective for the conversion of methane to methyl trifluoroacetate, Co(III) can be used for this reaction. The Co(III) is said to be catalytic in the presence of oxygen. The rate of the reaction was very low, 2.5×10
−11
mol/cc sec, (or four to five orders of magnitude away from typical commercial rates of about 10
−6
mol/cc.sec). Only four turnovers of the Co ion were disclosed. The extent of methane conversion was not stated. In addition to Co, other metals were suggested which were said to allow stoichiometric oxidation of methane to methyl trifluoroacetate in varying yields (based on amount of metal charged): Mn(30%), Cu(0.1%), and Pb(10%).
A later publication by Sen et al (“Homogeneous Palladium (II) Mediated Oxidation of Methane”,
Platinum Metals Review
, (1991), Vol 35, No. 3, pp. 126-132) discloses a catalytic system using palladium as the catalyst, peroxytrifluoroacetic acid as the oxidant, and a mixture of trifluoroacetic acid and trifluoroacetic anhydride as the solvent. The reaction rate was low (4.2×10
−9
mol/cc.sec) and only 5.3 turnovers of Pd were observed. The extent of methane conversion and selectivity were not stated.
There are several lesser routes to upgrade methane such as ammoxidation to HCN, chlorination to chloromethanes, carbon disulfide production and acetylene sy

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