Tantalum pentafluoride, catalyst

Fluorides. Tantalum pentafluoride [7783-71-3] TaF, (mp = 96.8° C, bp = 229.5° C) is used in petrochemistry as an isomerization and alkalation catalyst. In addition, the fluoride can be utilized as a fluorination catalyst for the production of fluorinated hydrocarbons. The pentafluoride is produced by the direct fluorination of tantalum metal or by reacting anhydrous hydrogen fluoride with the corresponding pentoxide or oxychloride in the presence of a suitable dehydrating agent (71). The ability of TaF to act as a fluoride ion acceptor in anhydrous HF has been used in the preparation of salts of the AsH, H S, and PH ions (72). The oxyfluorides TaOF [20263-47-2] and Ta02F [13597-27-8] do not find any industrial appHcation. 

Niobium and tantalum pentafluorides are also effective catalysts for iodofluorination of TFE, while A1C13 and ZnCl2 show no activity. 

HF TaFs is a catalyst for various hydrocarbon conversions of practical importance. In contrast to antimony pentafluoride, tantalum pentafluoride is stable in a reducing environment. The HF TaF5 superacid system has attracted attention mainly through the studies concerning alkane alkylation and aromatic protonation. Generally, heterogeneous mixtures such as 10 1 and 30 1 HF TaFs have been used because of the low solubility of TaFs in HF (0.9% at 19°C and 0.6% at 0°C). For this reason, acidity measurements have been limited to very dilute solutions, and an Ho value of —18.85 has been found for the 0.6% solution. Both electrochemical studies and aromatic protona-... 

HFC-143a can also be synthesized in liquid phase medium starting from vinylidene chloride [62-64], vinylidene fluoride [65, 66], and 1,1-dichloro-1-fluoroethane [67] using catalysts like antimony pentachloride, titanium tetrachloride, tantalum pentachloride, tantalum pentafluoride, chloro/fluoro-sulfonic acid. The reaction temperatures are in the range of 30-120°C and reaction pressures are in the range of 1-20 bar. The feedstock and catalyst options for HFC-143a liquid phase synthesis are highlighted in Fig. 11.7. 

With increase in the acidity of the catalyst, methyl alcohol or dimethyl ether undergo condensation to saturated hydrocarbons or aromatics, with no olefin by-products. With tantalum or niobium pentafluoride based catalyst the studies at 300 °C resulted in conversion to gasoline range branched hydrocarbons and some aromatics (30% of the product) This composition is similar to that reported with H-ZSM-5 zeolite catalyst. 

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