ETHOXENE process

A technology called the Ethoxene process was developed by Union Carbide for the oxidative dehydrogenation of ethane.165 Under the relatively mild conditions applied (300-400°C, 1-40 atm) cracking is minimal and the only byproduct is acetic acid. The combined efficiency to ethylene and acetic acid is about 90% with an ethylene acetic acid ratio of 10. 

Different classes of catalysts have been claimed for the oxidation of ethane to acetic acid [3], but the catalyst that gives the best performance is made of a mixed oxide of Mo/V/Nb (plus other components in minor amounts). This compound was first described in a paper by Thorsteinson et cd. 3a] - a paper that is considered nowadays a milestone in the field of the selective oxidation of alkanes, in view of the number of active phases that have been developed starting from catalysts described therein. Several patents were also issued by Union Carbide [3a-f], now Dow Chemical, regarding this system and the ETHOXENE process. The activity in ethane oxidation was attributed to the development of a crystalline phase characterized by a broad X-ray diffraction reflection at d = 4.0 A. The best composition was claimed to be Moo.73Vo.i8Nbo.o90 c, which reached 10% conversion of ethane at 286 °C with almost total selectivity to ethylene the selectivity decreased with increasing temperature, due to the formation of carbon oxides. The main peculiarity of this catalyst is its capability to activate the paraffin at low temperatures (<250 °C). 

The work was strongly inspired by Union Carbide s Ethoxene process, a route for manufacturing ethylene from ethane and oxygen by oxidative dehydrogenation. The first catalysts consisted of molybdenum, vanadium, and niobium oxides. The selectivity for ethylene was very high but, unfortunately, the conversion of ethane was low ( 10%). Therefore, scientists at the time focused on the co-production of ethylene and acetic acid. A catalyst consisting of molybdenum, vanadium, niobium, calcium, and antimony supported on a molecular sieve was developed (63% selectivity to acetic acid, 14% selectivity to ethylene, and 3% conversion of ethane). In addition, Rhone-Poulenc (catalyst vanadium oxide or vanadyl pyrophosphate) and BP (catalyst combination of rhenium and tungsten) patented processes for the production of acetic acid from ethane. Very efficient catalysts were also disclosed by Hoechst (molybdenum vanadate, promoted with Nb, Sb, Ca, and Pd, 250-280 °C, 15 bar, 86% selectivity to acetic add at 11% conversion of ethane per pass) and Sabic (phosphorus-modified molybdenum-niobium vanadate, 260 °C, 14 bar, 50% selectivity to acetic acid at 53% conversion of ethane). 

Ethoxene A catalytic process for dehydrogenating ethane to ethylene. Developed by Union Carbide. Acetic acid is a minor by product. 

Ethoxene A process for making a mixture of ethylene and acetic acid by the catalytic oxidation of a mixture of ethane and ethylene. Developed and piloted by Union Carbide in the 1980s, but not commercialized because of inflexibility in the ratio of acetic acid to ethylene produced. 

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