Promotion of O₂ on the co‐pyrolysis of CHF₃ and CH₄ for VDF synthesis

Abstract

Co‐pyrolysis of CHF3 and CH4 in the presence of O2 was investigated in a tubular reactor at temperatures between 700 and 860°C, atmospheric pressure, and residence time of 1.64 s. Under reaction conditions studied, introduction of O2 in the CHF3 and CH4 feed significantly improves the conversion of CH4, and while conversion of CHF3 almost stays unchanged. In the absence of O2, CH4 is activated by chain reactions which are initiated by the surface of the reactor. Following the introduction of O2, a series of additional chain reactions (reactions of CH4 with O2, O•, •HO2 and •OH radicals) generate more •CH3 radicals which are one of the key species for the formation of target product, CH2=CF2. Therefore, formation rate of CH2=CF2 is doubled under optimal reaction conditions. The suitable O2/CH4 feed ratio is suggested to be 0.06 for the formation of CH2=CF2. In addition, introduction of O2 in the feed decreases the formation of major byproduct C2F4 and C2HF3 significantly. After O2 is introduced, as more H• radicals are produced, improved formation rate of C2H3F results. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.

Catalytic coupling of CH4 with CHF3 for the synthesis of VDF over LaOF catalyst

“…Following the introduction of O 2 , a series of additional chain reactions (reaction of CH 4 with O 2 , O, HO 2 and OH radicals) generate additional CH 3 radicals, which is one of the key species for the formation of target product, CH 2 =CF 2 . As a consequence, the rate of CH 2 =CF 2 formation is tripled . This assertion is consistent with the above argument, that chain reactions play a major role in CH 4 activation rather than OCM at 750°C.…”

“…However, in contrast to the reaction at 700°C, conversion levels of CH 4 and CHF 3 and yield of VDF are almost identical to the reaction in the absence of La 2 O 3 catalyst (gas phase only); La 2 O 3 catalyst plays a very minor role in this reaction system at 750°C. As we reported previously, at high temperatures, excessive amounts of O 2 and O tend to convert CH 4 and CH 3 to CO and CO 2 . Although O 2 /CH 4 of 0.06 is optimal for the gas phase reaction (in the absence of La 2 O 3 ), the presence of La 2 O 3 catalyst provides more O or facilitates the activation of O 2 , especially at high temperatures.…”

“…Hence, the addition of initiators such as CBrF 3 and CH 3 OH facilitate chain reactions . As we reported recently, O 2 is also a potential promoter for CH 4 activation . Unfortunately, higher temperatures are necessary for these gas‐phase chain reactions, which is unfavorable for operation in industry due to the presence of highly corrosive atmosphere (HF).…”

“…At relatively low reaction temperatures such as 700°C, CH 4 is activated catalytically (blue section). At higher temperatures (above 750°C), a series of chain reactions are responsible for CH 4 conversion (red section) . CF 2 is derived from the thermal decomposition of CHF 3 in the gas phase .…”

“…Clearly, CHF 3 contains valuable C‐F bonds, and hence non‐destructive routes are being developed, which are also aimed at reducing the emission of CHF 3 into the receiving environment. Indeed, we previously reported that CHF 3 can be converted to vinylidene fluoride (VDF), a value‐added and environmentally friendly product, via its non‐oxidative reaction with CH 4 …”