Formaldehyde from methane

Formaldehyde production from natural gas is one of the most promising directions in modem chemical industry. However, the industrial realization of producing formaldehyde from methane is hampered by severe disadvantages, among which the most important are the low yields of the target product and multiple side reaction products. Therefore, the task in hand is the development of direct selective oxidation of methane to formaldehyde without formation of admixtures, which require additional thorough purification. 

The activation of methane [1] is also included as one of the most desired yet not technically viable reactions. Abundant amounts of methane occur with crude oil and as gas in remote locations it is also produced in large quantities during hydrocarbon processing. A large fraction of this methane is flared, because economical use or transportation is not possible. This gas and the abundant resources of methane gas hydrates would make a very suitable feedstock for higher hydrocarbons, if its activation to produce molecules other than synthesis gas were feasible. Despite enormous fundamental and practical efforts [1-5], no applicable method has yet been found for creation of ethylene, methanol, or formaldehyde from methane. 

Methanol oxidation experiments were carried out in order to determine if methanol was an intermediate in the production of formaldehyde from methane. To this end a methanol saturator was placed upstream of the reactor. The saturator was submerged in an ice/acetone bath (at -16 to - 20 °C) keeping the saturated methanol partial pressure at 5 kPa. This was approximately equivalent to the total carbon containing products generated during standard reaction conditions. The gas feed stream to the saturator consisted of 81 kPa helium and 20 kPa air. The flow rate was varied from 6.25 - 100 ml min. ... 

The partial oxidation of natural gas, consisting chiefly of methane, currently holds tremendous industrial potential. Possible routes for the direct synthesis of formaldehyde from methane, either via chlorine-based catalysts or with the use of chlorine-containing compounds in the gas feed (both using chlorine-modified supported palladium catalysts and at temperatures of 450-650°C) gave formaldehyde yields less than 7.7% under optimum conditions... 

Oxidation of methane to formaldehyde. One of the first studies in this area was reportedly an experimental factory production of formalin in the United States from natural gas (Empire Refining Co., 1930) with a capacity of 70 million gallons (265 million litres) of a mixture of formaldehyde, methanol, and acetaldehyde. The description of the installation and the method, as well as the yields, has not been published. However, in contrast to the oxidation of propane and butane (associated gas), the processes of direct oxidation of methane have not received widespread in the United States. Two industrial processes for production of formaldehyde from methane were developed in Germany. To produce formaldehyde, methane was oxidized with molecular oxygen in the presence of 1—2% of nitrogen oxides or a heterogeneous catalyst (94% Cu, and 6% Sn). The oxidation of methane in the presence of platinum or palladium yielded mainly formic acid. In this case, the reaction proceeds at a very high rate, so it is impossible to isolate oxidation intermediates, formaldehyde, and methanol [174]. 

Production of Formaldehyde from Methane and Other Hydrocarbon Gases... 

Research on the production of formaldehyde from methane, propane, and the hydrocarbon mixtures encountered in natural gas have been described by Bibb. Studies involving ethane, propane, and higher paraffins are also reported by Wiezevich and Frolich, who used iron, nickel, aluminum, and other metals as catalysts and employed pressures up to 135 atmospheres. 

The term "acetal resins" commonly denotes the family of homopolymers and copolymers whose main chains are completely or essentially composed of repeating oxymethylene units (—CH2—O—). The polymers are derived chiefly from formaldehyde or methanal [50-00-00] either directly or through its cychc trimer, trioxane or 1,3,5-trioxacyclohexane [110-88-3]. 

Historically, formaldehyde has been and continues to be manufactured from methanol. EoUowing World War II, however, as much as 20% of the formaldehyde produced in the United States was made by the vapor-phase, noncatalytic oxidation of propane and butanes (72). This nonselective oxidation process produces a broad spectmm of coproducts (73) which requites a complex cosdy separation system (74). Hence, the methanol process is preferred. The methanol raw material is normally produced from synthesis gas that is produced from methane. 

One possible route is to make formaldehyde direcdy from methane by partial oxidation. This process has been extensively studied (106—108). The incentive for such a process is reduction of raw material costs by avoiding the capital and expense of producing the methanol from methane. 

As we learned in Chapters 3 and 4, many inorganic compounds, not just ammonia, are derived from synthesis gas, made from methane by steam-reforming. In the top 50 this would include carbon dioxide, ammonia, nitric acid, ammonium nitrate, and urea. No further mention need be made of these important processes. We discussed MTBE in Chapter 7, Section 4, and Chapter 10, Section 9, since it is an important gasoline additive and C4 derivative. In Chapter 10, Section 6, we presented -butyraldehyde, made by the 0x0 process with propylene and synthesis gas, which is made from methane. In Chapter 11, Section 8, we discussed dimethyl terephthalate. Review these pertinent sections. That leaves only two chemicals, methanol and formaldehyde, as derivatives of methane that have not been discussed. We will take up the carbonylation of methanol to acetic acid, now the most important process for making this acid. Vinyl acetate is made from acetic... 

Figure 11-10 Flowsheet of an integrated process to produce PMMA and phenol-formaldehyde polymers simultaneously starting from methane, propane, and cyclohexane through a cumene intermediate.

Methane is an important starting material for numerous other chemicals. The most important of these are ammonia, methanol, acetylene, synthesis gas, formaldehyde, chlorinated methanes, and chlorofluorocarbons. Methane is used in the petrochemical industry to produce synthesis gas or syn gas, which is then used as a feedstock in other reactions. Synthesis gas is a mixture of hydrogen and carbon monoxide. It is produced through steam-methane reforming by reacting methane with steam at approximately 900°C in the presence of a metal catalyst CH4 + H20 —> CO + 3H2. Alternately, methane is partially oxidized and the energy from its partial combustion is used to produce syn gas ... 

An ozone-sensitized oxidative conversion of methane to methanol has been reported.54 A double-layered Sr on La203 then M0O3 on a silica catalyst bed exhibited significantly higher yields of formaldehyde from a methane-air mixture than did M0O3 on silica alone.55... 

Minute traces of formaldehyde are formed spontaneously from methane and oxygen. Cham carriers are formed by reaction of formaldehyde and oxygen. Formaldehyde is formed by reaction between chain carriers and methane. Formaldehyde is destroyed by reaction with chain carriers. 

Atmospheric oxidation of methane, 81 dimethyl peroxide from, 81 formaldehyde from, 81 formic acid from, 81... 

Reaction of organometallic compounds with carbonyl compounds a. primary alcohols from methanal (formaldehyde)... 

Ozone decomposition in airplanes Selective catalytic reduction of NOx Arrays of corrugated plates Arrays of fibers Gauzes Ag Methanol -> formaldehyde Pt/Rh NO production from ammonia HCN production from methane Foams Catalytic membranes reactors... 

While it is difficult, if not impossible, to duplicate experimentally the conditions of burning in air and to collect intermediate reaction products, it has been possible to change the conditions in such a way as to retard the process to the point where some intermediate products may be isolated (3, 20). Studies on the composition (13) of the products from the destructive distillation of cellulose have shown that the gaseous and liquid portions formed in the first stage of burning are comprised of such low molecular weight volatile compounds as acetic acid, methyl ethyl ketone, formaldehyde, and methane, and that the tars give rise to aliphatic, aromatic, and heterocyclic compounds. 

The simplest alcohol, methanol, is commonly known as wood alcohol, because it was once obtained by heating wood in the absence of air, a process that also produced charcoal. Now methanol is synthesized from methane in natural gas. Methanol itself has a relatively low toxicity. However, methanol is oxidized (metabolized) in the liver to formaldehyde and then to formic acid, both of which are much more toxic. 

Let us note once again that comparison of the results on methanol oxidation with hydrogen peroxide with methane oxidation data under atmospheric pressure (refer to Table 4.3, Figures 4.10 and 4.11) indicates significant differences in these processes. Methane is oxidized to formaldehyde at a higher rate and higher selectivity than at methanol oxidation. Low methanol yields at methane oxidation compared with formaldehyde confirm parallel proceeding of formaldehyde and methanol synthesis from methane. 

On an industrial scale, methane, the main component of natural gas, can easily be converted to formaldehyde. An efficient catalytic condensation of formaldehyde to dihydroxyactone or glycolaldehyde would thus provide a route to C2- and C3-chemicals from methane. The tria-zolin-5-ylidene 94 turned out to be a powerful catalyst for the conversion of formaldehyde (95) to glycolaldehyde (96) in the formoin reaction (Teles et al. 1996). This reactivity is a useful complement to the catalytic properties of thiazolium salts which mainly afford 1,3-dihydroxy acetone as product (Scheme 23) (Castells et al. 1980 Mat-sumoto and Inoue 1983 Matsumoto et al. 1984). As triazolium ylides are much more stable than thiazolium ylids, the elimination of glycolaldehyde occurs faster than the addition of the third formaldehyde molecule. 

Fig. 1.1. Shapes of molecules represented by envelopes of constant electronic charge density. The envelope shown has the value of 0.001 au. The molecules are (a)-(f) the normal alkanes from methane to hexane (g) isobutane (h) neopentane (i) cyclopropane (j) cyclobutane (k) formaldehyde, H2OK) (/) acetone, (CH3)2C=0. The intersections of the zero-flux interatomic surfaces with the envelope are shown in some cases. They define the methyl, methylene, hydrogen, and carbonyl groups. The isobutane molecule (g), for example, exhibits three methyl groups topped...

Ammonia is by far the largest scale chemical product derived from methane. Production of ammonia and its downstream products nitric acid, urea, and ammonium nitrate, which currently rank 6th, 14th, 15th, and 17th in American volume of production, are discussed in Chapter 11. Two other petrochemicals derived from methane, methanol and formaldehyde, currently rank 21st and 24th in volume in the United States at about 4 million tonnes per year each. Details of their production will be outlined here. 

Recent theoretical calculation of hydrogen abstraction from methane by the formaldehyde triplet has shown that a = 9.2° and 3 = 108.9° in the transition state. The formaldehyde triplet is nonplanar the degree of pyramidalization is 34.8°. D. Severance, B. Pandey, and H. Morrison, J. Am. 

The methanotrophic bacteria have one known pathway for aerobic methane oxidation to CO2 31, 42,123). MMO catalyzes the first energetically difficult step in the formation of methanol from methane. The second step is catalyzed by methanol dehydrogenase (with a PQQ cofactor) and results in formation of formaldehyde, which is then converted by formaldehyde dehydrogenase (with no known cofactor) to formate. Finally, carbon dioxide is produced by formate dehydrogenase (with five different iron-sulfur clusters, a Mo-pterin cofactor, and an unusual flavin) 31, 42, 123). MMOs have a unique ability to oxidize a broad range 31,42,128,129) of hydrocarbons in addition to methane. One other system with a similar broad substrate utilization is the monoheme cytochrome P450 family, but in this case different isozymes show different specific activities (31). For soluble MMO, one single... 

Desulfurization of petroleum feedstock (FBR), catalytic cracking (MBR or FI BR), hydrodewaxing (FBR), steam reforming of methane or naphtha (FBR), water-gas shift (CO conversion) reaction (FBR-A), ammonia synthesis (FBR-A), methanol from synthesis gas (FBR), oxidation of sulfur dioxide (FBR-A), isomerization of xylenes (FBR-A), catalytic reforming of naphtha (FBR-A), reduction of nitrobenzene to aniline (FBR), butadiene from n-butanes (FBR-A), ethylbenzene by alkylation of benzene (FBR), dehydrogenation of ethylbenzene to styrene (FBR), methyl ethyl ketone from sec-butyl alcohol (by dehydrogenation) (FBR), formaldehyde from methanol (FBR), disproportionation of toluene (FBR-A), dehydration of ethanol (FBR-A), dimethylaniline from aniline and methanol (FBR), vinyl chloride from acetone (FBR), vinyl acetate from acetylene and acetic acid (FBR), phosgene from carbon monoxide (FBR), dichloroethane by oxichlorination of ethylene (FBR), oxidation of ethylene to ethylene oxide (FBR), oxidation of benzene to maleic anhydride (FBR), oxidation of toluene to benzaldehyde (FBR), phthalic anhydride from o-xylene (FBR), furane from butadiene (FBR), acrylonitrile by ammoxidation of propylene (FI BR)... 

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