CN1640860A - Method for preparing hydrofluoride hydrocarbon - Google Patents

Abstract

The liquid phase fluorination process of preparing fluorohydrocarbon with hydrogen-containing halogenated hydrocarbon and anhydrous hydrogen fluoride in the presence of catalyst has the fluoric reflux liquid collected from the fluorinating and separating tower heated externally to provide the reaction with required heat, and thus has reduced or even no heat transferred via the sandwiched jacket to the reactor, lowered reactor wall temperature, minimized corrosion of reaction liquid to the reactor and prolonged reactor life.

Description

Process for the preparation of hydrofluorocarbons

field of invention

The invention relates to a method for preparing hydrofluorocarbons, in particular to a method for preparing hydrofluorocarbons by liquid-phase fluorination of hydrogen-containing halogenated hydrocarbons.

Background of the invention

Since hydrofluorocarbons (HFCs) do not deplete the ozone layer, they are gradually replacing chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs) and halons that deplete the ozone layer. Some HFC varieties with good application prospects such as 1, 1, 1,3,3,3-hexafluoropropane (HFC236fa), 1,1,1,3,3-pentafluoropropane (HFC245fa), 1,1,1,4,4-pentafluorobutane (HFC365mfc), etc. , and its preparation and production process are getting more and more attention. Usually, these products are mostly prepared by liquid-phase fluorination of corresponding chlorinated alkanes and anhydrous hydrogen fluoride.

The raw materials used in the liquid-phase fluorination reaction and some of the products generated, such as hydrogen fluoride, hydrogen chloride, Lewis acid catalyst, etc., are quite corrosive to metal reactors. Especially when antimony halides are used as catalysts, highly corrosive peracids can be formed, which will seriously damage the structural integrity of the fluorination reactor and affect normal production under high temperature and high pressure.

For this reason, those skilled in the art have proposed many improvement measures, such as Chinese patent CN1261337A has proposed to adopt fluorine-containing resin lining to solve the reactor corrosion problem, well-known, fluorine-containing resin has good corrosion resistance, but its thermal conductivity is too poor, The heat provided by the reactor jacket is too small to meet the heat required for the reaction, especially when preparing products containing more carbon atoms such as HFC236fa, HFC245fa, etc., because the raw material halogenated alkanes are easy to decompose when heated, by preheating the raw material The method of delivering calories is limited. Chinese patent CN1308597 proposes a liquid-phase fluorination system and method, which includes a reactor, a pre-washing tower, a set of distillation equipment, a pretreatment system and an evaporator to solve the corrosion and promotion of the reaction system. The problem of heat exchange, but the system is too complex and cumbersome, and it is difficult to apply it in practice.

Contents of the invention

Aiming at the problems existing in the preparation of hydrofluorocarbons by liquid-phase fluorination, the inventors skillfully utilized the process of external heating of the fluorination reflux liquid to meet the heat demand of the liquid-phase fluorination reaction and better relieve the reaction liquid on the reactor. corrosion, thereby prolonging the life of the reactor and reducing production costs.

The hydrofluorocarbons described in the present invention are prepared by a liquid-phase fluorination reaction in the presence of a hydrogen-containing halogenated hydrocarbon and anhydrous hydrogen fluoride in the presence of a catalyst. The rectification separation of the tower and the fluorinated condenser, collecting part of the fluorinated reflux liquid from the body of the fluorinated separation tower, and then entering the reactor after external heating to provide the heat required for the reaction; the product hydrofluorine is obtained from the top of the fluorinated condenser hydrocarbon. Therefore, heat transfer to the reactor through the jacket is reduced or even eliminated, the wall temperature of the reactor is reduced, and the corrosion of the reactor by the reaction liquid is minimized.

The preferred process flow for the preparation of hydrofluorocarbons according to the present invention is shown in the accompanying drawings: the hydrogen-containing halogenated hydrocarbon raw material and the anhydrous hydrogen fluoride preheated by the heat exchanger [1] are added to the reactor [2] with a catalyst reaction, the resulting product flow is separated by rectification of the fluorination separation tower [4] and the fluorination condenser [5], and part of the reflux is collected from the body of the fluorination separation tower [4] through the fluorination reflux liquid collection device [3] liquid to the transition tank [8], the reflux liquid is input into the heat exchanger [6] with the pump [7], and after heating, it is input into the liquid-phase reaction liquid of the reactor [2] to provide the heat required for the reaction; from the top of the fluorinated condenser A reaction gas mainly containing hydrofluorocarbons, HCl, a small amount of hydrogen fluoride and by-products is obtained, and the reaction gas is washed with water and alkali to obtain the required hydrofluorocarbons.

The hydrofluorocarbons in the present invention refer to aliphatic hydrocarbons containing at least one hydrogen atom in the molecule and the rest are fluorine atoms, and its structural formula is C _x H _y F _z , where x is 1 to 5, y≥1, y=2x +2-z, z≥1, preferably x=3～4, more preferably, when x=3, its chemical formula is CF ₃ CH ₂ CHF ₂ (HFC245fa) and CF ₃ CH ₂ CF ₃ (HFC236fa), When x=4, its chemical formula is CF ₃ CH ₂ CF ₂ CH ₃ (HFC365mfc).

The raw material of hydrogen-containing halogenated hydrocarbons in the present invention refers to the synthesis of halogenated alkanes corresponding to the above-mentioned hydrofluorocarbons, which requires hydrogen and at least one halogen atom that can be substituted by fluorine in its molecule, especially halogenated hydrocarbons containing 1 Hydrochlorocarbons with ~5 carbon atoms, preferably 1,1,1,3,3,3-hexachloropropane (HCC230), 1,1,1,3,3-pentachloropropane (HCC240), 1 , 1,1,4,4-pentachlorobutane (HCC450) and so on.

Catalysts described in the present invention mainly refer to metal halides and mixtures of two or more thereof for fluorination, preferred catalysts are chlorides, fluorides, fluoride chlorides or mixtures thereof of antimony and tin, more preferably The most preferred is SbCl ₅ because of its high activity and low price. Since the catalyst is prone to deactivation after a period of time, it is advantageous to periodically or continuously feed a small amount of chlorine gas for regeneration during the reaction, and the appropriate amount of chlorine gas feeding per hour is 0.02-1.0% of the weight of the catalyst.

The concentration of the catalyst of the present invention is controlled at 5% to 30% (weight ratio). If the concentration is too low, the reaction speed will be slow; if the concentration is too high, side reactions will easily occur, preferably 10% to 20%.

The heat required for the reaction of the present invention is preferably provided by the preheating of the raw material HF and the external heating of the fluorination reflux liquid. The HF preheating temperature is controlled at 70-150°C, preferably 90-120°C; the heat collected from the fluorination separation tower body The fluorinated reflux liquid mainly contains hydrogen fluoride, hydrofluorocarbons and their incompletely fluorinated intermediates. The catalyst content is extremely low, and there is little corrosion to subsequent equipment. The heating temperature of the fluorinated reflux liquid is controlled at 70-150°C, preferably 90-120°C. The reactor jacket can be assisted or unheated. The fluorination reaction temperature is mainly controlled by adjusting the collection speed and heating temperature of the fluorination reflux liquid, generally at 50-110°C, preferably 60-90°C.

The reaction pressure can be changed, and the convenient operating pressure is controlled at 0.5-1.5Mpa, preferably 0.8-1.3Mpa.

In order to ensure the conversion rate of raw material halogenated hydrocarbons, the molar ratio of anhydrous hydrogen fluoride and raw material halogenated hydrocarbons should be higher than the theoretical amount, and the molar ratio is generally controlled at 1-2, preferably 1.05-1.3.

The liquid-phase fluorination reaction of the present invention is carried out under pressure, and the reactor used is generally made of metal materials, such as carbon steel, stainless steel, Inconel, Monel and the like. The reaction kettle can also be lined with corrosion-resistant fluoropolymer, and the fluoropolymer can be polytetrafluoroethylene, tetrafluoroethylene and hexafluoropropylene copolymer.

The fluorination separation tower of the present invention is vertically installed above the reactor, and the separation tower is filled with fillers. Compared with the common fluorination separation tower, it is special in that a fluorination reflux liquid collection device is installed on the tower body. The device is similar to the liquid phase receiving equipment in the traditional rectification system, and is used to collect the fluorinated reflux liquid with low catalyst content.

The invention adopts the external heating process of the fluorination reflux liquid to carry out the liquid phase fluorination to prepare the hydrofluorocarbon, changes the input mode of the heat required for the reaction, slows down the corrosion of the reactor, and prolongs the service life of the equipment.

specific embodiment

Example 1 Preparation of 1,1,1,3,3,3-hexafluoropropane (HFC236fa)

Add 200kg of catalyst SbCl ₅ into a 2m ³ carbon steel reactor, then add 300kg of HF preheated to 100-110°C to activate the catalyst, then continuously put in HCC230 and HF 140kg/hr and 74kg/hr, the heating temperature of fluorinated reflux liquid is 100～110℃, the speed is 150～250kg/hr, the jacket is not heated, the reaction temperature is controlled between 60～75℃, and the reaction pressure is 1.0～ 1.2Mpa, pass a small amount of liquid chlorine during the reaction to keep the catalyst activity, the speed is 1kg/hr.

The reaction gas was collected after washing with water and alkali, and the selectivity of HFC236fa was 98.3% and the yield was 90.2% through chromatographic analysis. After the reaction stopped, the reactor was checked and no obvious corrosion was found.

Example 2 Preparation of 1,1,1,3,3,3-hexafluoropropane (HFC236fa)

By the method for embodiment 1, adopt ^2m The carbon steel reactor of liner polytetrafluoroethylene, reactor jacket auxiliary heating, the control jacket temperature is the same as reaction temperature, the feeding speed of HCC230 and HF is respectively 180kg/hr and 96kg/hr, all the other conditions are with embodiment 1. According to chromatographic analysis, the selectivity of HFC236fa is 99.1%, and the yield is 90.4%. The reactor is lined with PTFE to prevent corrosion.

Claims (7)

1. A method for preparing hydrofluorocarbons by reaction of hydrogen-containing halogenated hydrocarbons and anhydrous hydrogen fluoride in the presence of a catalyst, characterized in that the product generated by the reaction flows through the rectification separation of the fluorination separation tower and the fluorination condenser, from Part of the fluorinated reflux liquid is collected from the body of the fluorinated separation tower, and then input to the reactor after external heating to provide the heat required for the reaction; the product hydrofluorocarbons are obtained from the top of the fluorinated condenser. 2. The method according to claim 1, wherein the hydrofluorocarbon refers to an aliphatic hydrocarbon containing at least one hydrogen atom in its molecule and the rest being fluorine atoms, and its structural formula is C _x H _y F _z , where x =1～5, y≥1, z≥1, y=2x+2-z. 3. The method according to claim 1, characterized in that said hydrofluorocarbon refers to CF ₃ CH ₂ CF ₃ (HFC236fa), CF ₃ CH ₂ CHF ₂ (HFC245fa), CF ₃ CH ₂ CF ₂ CH ₃ (HFC365mfc). 4. The method according to claim 1, characterized in that the HF preheating temperature is controlled at 70-150°C; the heating temperature of the fluorinated reflux liquid is controlled at 70-150°C. The reactor jacket can be assisted or unheated. The reaction temperature is controlled at 50-110°C. 5. The method according to claim 4, characterized in that the HF preheating temperature is controlled at 90-120°C; the heating temperature of the fluorinated reflux liquid is controlled at 90-120°C. The reaction temperature is controlled at 60-90°C. 6. The method according to claim 1, characterized in that the catalyst used is antimony and tin chlorides, fluorides, fluorochlorides or mixtures thereof. 7. Process according to claim 6, characterized in that the catalyst used is _SbCl5 .

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