Alcohol ammoxidation

Alcohol ammoxidation provides an option to augment the production of HCN and/or acetonitrile in a propylene ammoxidation process for producing acrylonitrile (103). This is accomplished by co-feeding alcohol or alcohol mixtures with propylene over conventional molybdate or antimonate ammoxidation catalysts under typical process conditions for propylene ammoxidation. 

The handling of toxic materials and disposal of ammonium bisulfate have led to the development of alternative methods to produce this acid and the methyl ester. There are two technologies for production from isobutylene now available ammoxidation to methyl methacrylate (the Sohio process), which is then solvolyzed, similar to acetone cyanohydrin, to methyl methacrylate and direct oxidation of isobutylene in two stages via methacrolein [78-85-3] to methacryhc acid, which is then esterified (125). Since direct oxidation avoids the need for HCN and NH, and thus toxic wastes, all new plants have elected to use this technology. Two plants, Oxirane and Rohm and Haas (126), came on-stream in the early 1980s. The Oxirane plant uses the coproduct tert-huty alcohol direcdy rather than dehydrating it first to isobutylene (see Methacrylic acid). 

The surface transformations of propylene, allyl alcohol and acrylic acid in the presence or absence of NHs over V-antimonate catalysts were studied by IR spectroscopy. The results show the existence of various possible pathways of surface transformation in the mechanism of propane ammoxidation, depending on the reaction condition and the surface coverage with chemisorbed NH3. A surface reaction network is proposed and used to explain the catalytic behavior observed in flow reactor conditions. 

The cost of producing acrylonitrile dropped when the ammoxidation process was introduced in the 1960s. Then it became economical at that time to produce methyl and ethyl esters of acrylic acid by hydrolyzing acrylonitrile in the presence of alcohol. The hydrolysis and esterification take place at the same time, in the presence of sulfuric acid at about 225°F. Yields are about 98%. 

Pyridine can also be prepared from cyclopentadiene by ammoxidation, or from 2-pentenenitrile by cyclization and dehydrogenation. Furfuryl alcohol or furfural reacts with ammonia in the gas phase to give pyridine (Scriven et al., 1996). 

Propene is used as a starting material for numerous other compounds. Chief among these are isopropyl alcohol, acrylonitrile, and propylene oxide. Isopropyl alcohol results from the hydration of propylene during cracking and is the primary chemical derived from propylene. Isopropyl alcohol is used as a solvent, antifreeze, and as rubbing alcohol, but its major use is for the production of acetone. Acrylonitrile is used primarily as a monomer in the production of acrylic fibers. Polymerized acrylonitrile fibers are produced under the trade names such as Orion (DuPont) and Acrilan (Monsanto). Acrylonitrile is also a reactant in the synthesis of dyes, pharmaceuticals, synthetic rubber, and resins. Acrylonitrile production occurs primarily through ammoxidation of propylene CH3- CH = CH2 + NH3 + 1.5 02—> CH2 = CH - C = N + 3 H20. 

Oxidation of the allylic carbon of alkenes may lead to allylic alcohols and derivatives or a, 3-unsaturated carbonyl compounds. Selenium dioxide is the reagent of choice to carry out the former transformation. In the latter process, which is more difficult to accomplish, Cr(VI) compounds are usually applied. In certain cases, mixture of products of both types of oxidation, as well as isomeric compounds resulting from allylic rearrangement, may be formed. Oxidation of 2-alkenes to the corresponding cc,p-unsaturated carboxylic acids, particularly the oxidation of propylene to acrolein and acrylic acid, as well as ammoxidation to acrylonitrile, has commercial importance (see Sections 9.5.2 and 9.5.3). 

Potential applications of superconducting cuprates in electronics and other technologies are commonly known. These cuprates also exhibit significant catalytic activity. Thus, YBa2Cu307 3 and related cuprates act as catalysts in oxidation or dehydrogenation reactions (Hansen et al. 1988 Halasz 1989 Mizuno et al. 1988). Carbon monoxide and alcohol are readily oxidized over the cuprates. NH3 is oxidized to N2 and H20 on these surfaces. Ammoxidation of toluene to benzonitrile has been found to occur on YBa2Cu307 (Hansen et al. 1990). 

Ammoxidation of allyl alcohol on MOO3 initially requires about 6 molecules of NH3 per allyl alcohol in the vapor phase for maximum acrylonitrile yield (Fig. 15). However, after all surface Mo=O undergo ammonolysis to form Mo=NH, only a stoichiometric (or slightly higher) amount of ammonia is required to sustain maximum AN yield under catalytic conditions. These results suggest that N incorporation results from an O to N-allylic rearrangement (Scheme 10) (27). 

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)... 

The yields and selectivities for the ammoxidation of substrate molecules to the corresponding nitriles generally increase as a function of the reactant type in the following order alkane < alkene < alcohol < aldehyde (see table below). 

The low pifa values for alcohols ( 16 for methanol), compared to about 30 and 44 for alkenes and alkanes, respectively, along with the acid-base character of metal oxides, allows this step to be easily facilitated by a number of (amm)oxidation catalysts. These characteristics of the reaction allow selective ammoxidation of alcohols to be conducted under milder reaction conditions than ammoxidation of alkenes and alkanes, generally at temperatures below 400°C. This promotes selectivity for the ammoxidation of the alcohol to the corresponding nitrile product by lessening the oxidation activity of the catalyst for complete oxidation to COg. 

Catalytic ammoxidation of alcohols was a direct outgrowth of groundbreaking propylene ammoxidation technology developed for acrylonitrile manufacture. Early disclosures by Distillers Co. Ltd. employed the same Sn-Sb-O-based catalysts found effective for the propylene ammoxidation reactions (93,94). Yields of HCN from methanol of up to 88% were obtained. Realization that the same families of metal oxide catalysts effective for the propylene aimnoxidation reaction could be used for methanol ammoxidation quickly led to a proliferation of patents that included Bi-Mo-0 (95-97) and Fe-Sb-0 (98). Researchers at Nitto Chemical Industry Co. Ltd. refined the Fe-Sb-0 propylene ammoxidation family of catalysts to optimize yields of HCN from methanol. They developed catalyst preparation methods to obtain an attrition-resistant version of the modified catalyst so that it could be operated in a fluid-bed reactor with all the concomitant economic and operating advantages that entails (99). The resulting Fe-Sb-O-based catalyst modified, with phosphorus in addition to the other promoter elements used... 

Ammoxidation of Other Alcohols. Isopropanol and n-propanol are am-moxidized to nitrile products, primarily acrylonitrile, with co-products including acetonitrile, HCN, and propionitrile. 

The two reaction steps can occur over a single ammoxidation catalyst tailored for propylene ammoxidation, or the two steps can be separated in two reactors. In the case of the latter, the first reactor uses an acidic alcohol dehydration catalyst with the resulting propylene containing product sent to a second reactor containing a conventional propylene ammoxidation catalyst (104). 

Ishida T, Watanabe H, Take T, Hamasaki A, Tokunaga M, Haruta M (2012) Metal oxide-catalyzed ammoxidation of alcohols to nitriles and promotion effect of gold nanoparticles for one-pot amide synthesis. Appl Catal A Gen 425 26 85-90... 

Scheme 4.7 The general pathway for the ammoxidation of alcohols to nitriles...

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