Method for high-selectivity R142b cracking preparation of vinylidene fluoride

Abstract

The invention discloses a method for high-selectivity R142b cracking preparation of vinylidene fluoride. The method comprises 1, heating a cracking furnace to a temperature of 650-750 DEG C and keeping the uniform and stable cracking furnace temperature, 2, controlling raw material buffer tank pressure in a range of 0.22-0.28MPa by control of a raw material buffer tank inlet steam regulating valve, and 3, controlling a raw material buffer tank discharge regulating valve so that the raw material flows into a cracking furnace at a flowing rate of 15-20m<3> / h (in contact time of 17s) and undergoes a cracking reaction. The method greatly improves reaction selectivity by control of a reaction temperature and raw material staying time, does not reduce a conversion rate, reduces impurities at the source, reduces follow-up process difficulty, reduces impurity generation and has a high yield.

Description

technical field [0001] The invention relates to a method for preparing vinylidene fluoride by cracking R142b with high selectivity. Background technique [0002] At present, as far as the world is concerned, the output of polyvinylidene fluoride (PVDF) is a fluoroplastic second only to polyvinylidene fluoride. body. In fluoroelastomers, almost all contain VDF components. [0003] According to relevant literature, there are currently five main methods for preparing VDF: the first is the CH2CCl2 (VDC) fluorination method. Patent US 4827055 mentions a method for preparing VDF by catalytic fluorination of VDC. Although the yield of VDF is relatively high, However, it is difficult to realize industrialization because of its short catalyst life and easy deactivation; the second is 1,1,1-trifluoroethane (HCFC-143a) de-HF method, which has an obvious shortcoming that HCFC-143a Selectivity and conversion cannot be balanced, so industrialization is more difficult; the third is 1,1-...

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Problems solved by technology

However, the cracked gas obtained by HCFC-142b cracking method has more impurities: CH 3 F, CH 3 CHF 2 、C 2 h 3 F, C 2 h 2 ClF etc.

It is difficult to remove these impurities by rectification. When these impurities accumulate to a certain extent, it will increase the difficulty of temperature control in the rectification tower and increase energy consumption.

In the DE1068695 patent, although HCFC-142b was invented at 850°C through silver or platinum heat pipes, the conversion rate of HCFC-142b was 97%, but the selectivity of VDF was only 60%.

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