Latest Technological Advances in Fluorinated Alkanes and Fluoropolymers      

The fluorine chemical industry begins from fluorite resources and uses hydrofluoric acid as the basic raw material. It derivates four major types of products: fluorinated alkanes, fluoropolymers, fluorine-containing fine chemicals and fluoride salts. Among them, the former three types are defined as organic fluorine chemicals. There are several hundred types of fluorine-containing fine chemicals. They all have a small production and are highly technologically secretive.

1. Fluorinated alkanes

Fluorinated alkanes are mainly used as the raw materials of fluoropolymers and industrial additives such as refrigerants and foaming agents. Because traditional HCFCs refrigerants can damage the ozone layer, the international community has decided to phase out them as soon as possible. They will be gradually replaced by hydrofluorocarbons (HFCs) and their mixed refrigerants.
   In November 2008, China started to phase out HCFCs. By 2013, China's total consumption of HCFCs will be fixed at the average level between 2009 and 2010. It will be reduced by 10% by 2015, 35% by 2020 and 67.5% by 2025. By 2030, China will completely cease the production and consumption of HCFCs. Among HCFCs, the most important product is difluoro-chloromethane (HCFC-22). Although it can still be used as a refrigerant within the disabled period of time, it will be mainly used as raw material of fluoropolymers in the future.

1.1  HCFC-22
The production of HCFC-22 uses trichloromethane (chloroform) and anhydrous hydrofluoric acid as raw materials. Its production processes can be divided into the indirect method and the direct method. The indirect method is to add chloroform and hydrofluoric acid into the reaction vessel and use antimony pentachloride as the catalyst and fluorinate chloroform into crude HCFC-22 gas at 50 grade centigrade. The direct method is to synthesize HCFC-22 directly from methane, chlorine and anhydrous hydrogen fluoride in a fluidized bed reactor. After the reaction is finished, hydrogen chloride is separated from the product mixture. After being dried, purified and distilled to remove other chlorofluoromethanes and impurities, the product can be obtained.
   Although the direct method does not need the chloroform synthesis process and can reduce production costs, it can produce many side products which are difficult to separate. So the indirect method is now widely used in China and other countries.

1.2  HFC-134a
In the world, there are two routes to produce HFC-134a, that is, the perchloroethylene (PCE) route and the trichloroethylene (TCE) route. In the TCE route, the current industrial production of HFC-134a basically uses the double-step fluorination process that produces 1, 1, 1 - trifluoro-chloroethane (HCFC-133a) as an intermediate product.
   The fluorination process can be divided into the gas-phase method and the liquid-phase method. The gas-phase method uses hydrogen fluoride as the fluorinating agent. Under the action of the catalyst, trichloroethylene is first turned into HCFC-133a as an intermediate and is finally turned into HFC-134a. The gas-phase method has less corrosion to equipment and less pollutant emissions. It has been adopted by Sinochem Taicang Chemical Industry Park, Juhua Group Corp, Dongyue Group and Bailian Group in China.

1.3  HFC-125
According to different raw materials, the industrial synthesis routes of HFC-125 can be divided into the PCE route, the TCE route and the tetrafluoroethylene route. The PCE route has a convenient source of raw materials and can share a set of production facilities with HFC-134a, but it has a relatively high production cost.
   The TCE route usually contains the HCFC-133a chlorination or disproportionation step which has a relatively low yield rate. So it is generally used only for the co-production of HFC-134a and HFC-125.
   The tetrafluoroethylene route uses tetrafluoroethylene and hydrogen fluoride as raw materials. After the addition reaction, the raw materials can be synthesized into pentafluoroethane at one step. However, because tetrafluoroethylene is produced from HCFC-22, the price of HCFC-22 can affect the production cost of this synthesis route. The tetrafluoroethylene route that uses tetrafluoroethylene and hydrogen fluoride as the raw materials to produce HFC-125 is divided into the gas-phase method and the liquid-phase method. The liquid-phase method can be easily industrialized and can cause little environmental pollution. In the tetrafluoroethylene route, the liquid-phase method has become the mainstream production process of HFC-125 and got the support of the Chinese Ministry of Environmental Protection.

1.4  HFC-32
With the existing of catalyst and at a certain temperature and pressure, crude HFC-32 can be synthesized from industrial anhydrous hydrogen fluoride and dichloromethane. Tsinghua University, Dongyue Group and Changshu 3F Fluorochemical Industry Co Ltd have mastered the production technology of HFC-32.

1.5  Cogeneration technology
Recently, many research and development efforts have been done to produce a variety of fluorohydrocarbons, such as HFC-125, HFC-32, HFC-134a and HFC-143a, in a single equipment.
   Zhejiang Quhua Fluor-Chemistry Co Ltd used trichloroethylene, vinylidene chloride and hydrogen fluoride as raw materials to study the gas-phase catalytic fluorination reaction and obtained HFC-143a and HFC-134a at the same time.
   Zhejiang Fluorescence Chemical Co Ltd has developed a method to co-generate HFC-125 and HFC-134a using trichloroethylene as the raw material alone. This method needs three steps of reaction, and its reaction process needs to consume chlorine. Its reaction and separation operations need to be further optimized.

1.6  Refrigerants mixture
Because refrigerants mixture has relatively good safety and small greenhouse effect, they have rapidly developed in recent years. Refrigerants mixture R407C and R410A are now used in Europe, Japan, the United States and Canada. Honeywell is the original patent holder of R410A. According to the U.S. patent law, this original patent was valid until December 18th, 2007. DuPont is the sole holder of the R410A patent in China. The patent will be valid in China until December 11th, 2011. In 1991, DuPont applied for the patent of B407C from the Chinese State Intellectual Property Office. The patent will be valid in China until December 11th, 2011. Honeywell, DuPont and Arkema each have their own products and trademarks of R410A and R407C. Tsinghua University walks in the forefront of the research and development of green refrigerants in China. After more than a decade of efforts, it has developed THR01, THR02, THR03 and THR04 in which the university owns intellectual property rights.

2. Fluoropolymers and
supporting monomers

2.1  Tetrafluoroethylene (TFE)
The production processes of TFE include the HCFC-22 empty tube cracking, the HCFC-22 steam-diluted cracking, the chloroform cracking and the 1, 2-dichlorotetrafluoroethane dechlorination. However, the industrial production of TFE mostly uses the HCFC-22 empty tube cracking process and the HCFC-22 steam-diluted cracking process. Since China developed the first industrial TFE installation in the 1960s, both the empty tube cracking and steam-diluted cracking processes have been used in China. But the automation level of China's TFE units is generally relatively low.

2.2  Vinylidene fluoride (VDF)
The production of VDF mainly has the following four raw material routes: (1) calcium carbide and hydrogen fluoride; (2) vinylidene chloride and hydrogen