KR20000022505A - Separation of hydrogen fluoride from a fluorocarbon/hydrogen fluoride azeotropic mixture by sulfuric acid - Google Patents

Abstract

PURPOSE: A process for the separation of azeotropic mixtures of fluorocarbons from hydrogen fluoride is provided by using sulfuric acid as an extracting agent. CONSTITUTION: Mixtures of fluorocarbons and hydrogen fluoride are such as azeotropic mixtures, and the most preferred fluorocarbon is 1,1,1,3,3-pentafluoropropane, which is also known as HFC-245fa. The separation is conducted by adding sulfuric acid to a mixture comprising a fluorocarbon and hydrogen fluoride to form a first phase rich in the fluorocarbon and a second phase rich in the hydrogen fluoride and sulfuric acid; wherein the weight ratio of sulfuric acid to hydrogen fluoride ranges from about 1: 1 to about 10: 1.

Description

Separation method of hydrogen fluoride from fluorocarbon / hydrogen fluoride azeotrope with sulfuric acid

It is well known to produce fluorocarbons (HFCs) by reacting hydrogen fluoride with various hydrochlorocarbon compounds. Such fluorocarbons are useful among many applications, especially as solvents, refrigerants, blowing agents and aerosol spraying agents. Fluorocarbons are considered to be much more environmentally beneficial than hydrochlorocarbons because they do not reduce ozone and are nonflammable and nontoxic compared to chlorine-containing chlorocarbons. In the preparation of fluorocarbons, typical product streams contain not only the desired HFC but also unreacted hydrogen fluoride, other starting reagents and by-products. Various conventional separation methods, such as distillation and water washing, can separate certain by-products and starting materials from the product stream, but may experience particular difficulties in removing fluorocarbons from hydrogen fluoride. This is especially true for fluorocarbons having a boiling point close to that of HF. One of these fluorocarbons is 1,1,1,3,3-pentafluoropropane, also known as HFC-245fa. HFC-245fa has a boiling point of about 14 ° C. at standard atmospheric pressure and is therefore particularly useful as a blowing agent or aerosol spray agent. HFC-245fa is well known per se in the art as described in US Pat. No. 2,942,036, Canada 684,687, EP 381 986A and JP 02,272,086. Its preparation is described in WO 95/04022. All of these patents are incorporated herein by reference. In a typical method of preparing HFC-245fa, the precursor reagent is fluorinated with hydrogen fluoride. It is desirable to produce substantially pure HFC-245fa, but this proves difficult because HFC-245fa and hydrogen fluoride form an azeotrope that is substantially inseparable by distillation.

As a prior art, various methods for separating an azeotrope of fluorocarbons have been proposed. In this regard, European patent application EP 0 472 391 proposes, among others, to separate HFC-134a from mixtures with chlorine-containing hydrochlorofluorocarbons using extractants such as trichloroethylene or perchloroethylene. . European patent application EP 0 467 531 is a method for separating HFC-134a from a mixture of HFC-134a and HF, which is passed through a distillation column to separate the mixture from the pure HFC-134a residue and then collecting the residue. Teaching the way. U.S. Patent 5,211,817 attempts to separate the fluorocarbons from the azeotrope with HF by column distillation, recover the steam sidestreams, and then introduce the sidestreams into the rectifier tower equipped with a condenser and operated at high reflux ratio. . These cannot be said to be satisfactory solutions to this problem.

According to the present invention there is provided a method for separating fluorocarbon and hydrogen fluoride from a mixture of fluorocarbon and hydrogen fluoride using sulfuric acid as extractant. So far sulfuric acid has been used to separate gaseous mixtures of HF from chlorine containing chlorofluorocarbons, ie FC-22, as described in US Pat. No. 3,873,629. However, sulfuric acid is not known as an extractant for separating HF from fluorocarbons and hydrofluorocarbons which do not contain chlorine.

Summary of the Invention

The present invention is a method for separating fluorocarbon and hydrogen fluoride from a mixture containing fluorocarbon and hydrogen fluoride, wherein sulfuric acid is added to the mixture containing fluorocarbon and hydrogen fluoride to give a fluorocarbon-rich first phase and fluorine. A method comprising forming a second phase rich in hydrogen and sulfuric acid, wherein the weight ratio of sulfuric acid to hydrogen fluoride is in the range of about 1: 1 to about 10: 1.

The invention also provides a process for separating fluorocarbon and hydrogen fluoride from a gas mixture containing fluorocarbon and hydrogen fluoride, wherein the flow of gas mixture of fluorocarbon and hydrogen fluoride is flowed through a conduit and then the mixture is Provided is a method comprising contacting sulfuric acid, wherein the weight ratio of sulfuric acid to hydrogen fluoride is in the range of about 1: 1 to about 10: 1.

The present invention relates to a method for separating fluorocarbon and hydrogen fluoride from a mixture of fluorocarbon and hydrogen fluoride. More specifically, the present invention relates to a method for separating an azeotrope of fluorocarbons from hydrogen fluoride. Most preferred fluorocarbons in the present invention are 1,1,1,3,3-pentafluoropropane, also known as HFC-245fa.

As used herein, the term fluorocarbon means a compound containing only atoms selected from carbon, hydrogen and fluorine. It does not contain other halogen atoms.

The process of the invention starts with a mixture of fluorocarbons and hydrogen fluoride. This mixture may be an azeotrope but this condition is not essential. The fluorocarbons can be pentafluoropropane, for example 1,1,1,3,3-pentafluoropropane. It is also possible to start with a liquid mixture of fluorocarbons and hydrogen fluoride and then add sulfuric acid to the mixture. The amount of HF in the azeotrope of 1,1,1,3,3-pentafluoropropane and hydrogen fluoride changes with temperature. This azeotrope contains 25 ± 5 wt% HF at 20 ° C. and 26 psia and 17 ± 5 wt% HF at 75 ° C. and 142 psia.

The amount of sulfuric acid required for the separation depends on the amount of HF present in the system. From the solubility of HF in 100% sulfuric acid as a function of the temperature curve, the minimum amount of sulfuric acid actually required can be determined. For example, at 30 ° C., about 34 g of HF is dissolved in 100 g of 100% sulfuric acid. However, at 100 ° C, only about 10 g of HF is dissolved in 100% sulfuric acid. Sulfuric acid used in the present invention preferably has a purity of about 98% to about 100%.

In a preferred embodiment, the weight ratio of sulfuric acid to hydrogen fluoride is in the range of about 1: 1 to about 10: 1. More preferably, the weight ratio is in the range of about 1: 1 to about 8: 1, most preferably in the range of about 2: 1 to about 4: 1. The reaction is preferably carried out at a temperature of about 0 ° C. to about 100 ° C., more preferably about 0 ° C. to about 40 ° C., and most preferably about 20 ° C. to about 40 ° C. The reaction is usually carried out at normal atmospheric pressure, but higher or lower pressure conditions can be used by those skilled in the art. When sulfuric acid is added to a mixture of fluorocarbons and HF, two phases form rapidly. That is, a top phase rich in fluorocarbons and a bottom phase rich in HF / sulfuric acid are formed. The term "rich" means that the phase contains more than 50%, preferably more than 80%, of the indicator components thereon. The extraction efficiency of fluorocarbons may range from about 90% to about 99%.

After phase separation, the fluorocarbon rich top phase is removed from the hydrogen fluoride and sulfuric acid bottom phase. This can be done by decantation, siphoning, distillation or other methods well known in the art. The fluorocarbon extraction may optionally be repeated by further adding sulfuric acid on the removed bottoms. If the weight ratio of sulfuric acid to hydrogen fluoride is about 2.25: 1, an extraction efficiency of about 92% can be obtained in one step. Preferably, the hydrogen fluoride and sulfuric acid are then separated. The low solubility of HF in sulfuric acid at high temperatures can be used to recover HF from sulfuric acid. For example, at 140 ° C, only 4 g of HF is dissolved in 100% sulfuric acid. HF can be recovered by heating the HF / sulfuric acid solution to 250 ° C. HF and sulfuric acid can then be recycled. That is, HF can be recycled to the initiation reaction for fluorocarbon formation and sulfuric acid can be recycled for use in the extraction step.

In another embodiment of the present invention, a mixture of fluorocarbon and hydrogen fluoride can be treated in the gas phase by a continuous introduction of sulfuric acid into the flow of fluorocarbon and hydrogen fluoride. The mixture of fluorocarbons and hydrogen fluoride can also be treated by flowing a stream of sulfuric acid countercurrent to the flow of fluorocarbons and hydrogen fluoride in a standard washing tower.

The invention is illustrated by the following non-limiting examples.

Example 1

75 g of 1,1,1,3,3-pentafluoropropane (HFC-245fa) was dissolved in 25 g of HF to produce a homogeneous azeotrope. 56 g of sulfuric acid was then added to the mixture, which immediately formed two phases. The upper organic rich phase consisted of 99.6 wt% pentafluoropropane and 0.4 wt% HF / sulfuric acid. The bottom phase consisted of 5.5 wt% pentafluoropropane and 94.5 wt% HF / sulfuric acid. The extraction efficiency from the material balance is calculated to be 92%. This experiment was performed at room temperature (25 degreeC). HF and sulfuric acid concentrations were determined by IC (ion chromatography), fluoride electrode and total acid titration.

Example 2

58.7 g of 1,1,1,3,3-pentafluoropropane (HFC-245fa) are dissolved in 20.1 g of HF to produce a homogeneous azeotrope. Then, 45.3 g of sulfuric acid is added to this mixture, and two phases are formed immediately. The upper organic rich phase consists of 99.6 weight percent pentafluoropropane and 0.4 weight percent HF / sulfuric acid. The lower phase consists of 5.5% by weight pentafluoropropane and 94.5% by weight HF / sulfuric acid. The extraction efficiency from the mass balance is calculated to be 92%. This experiment is performed at room temperature (25 degreeC).

Example 3

The flow of HFC-245fa gas from the reactor is brought into contact with the flow of sulfuric acid liquid in a countercurrent flow in a conventional scrubber which is maintained at a temperature above the boiling point of the HFC-245fa / HF mixture to keep the flow gaseous. Gas flow is introduced at the bottom of the tower and liquid sulfuric acid is introduced at the top of the tower. The composition of the gas is close to that of the azeotrope of HFC-245fa / HF (25 weight percent HF). The weight ratio of sulfuric acid to HF in HFC-245fa / HF is about 3: 1 to ensure complete removal of HF from the HFC-245fa / HF stream. The amount of sulfuric acid required depends on the solubility of HF in sulfuric acid at the operating temperature. HFC-245fa, which remains at the top of the column, does not contain HF, while a mixture of HF and sulfuric acid is collected in the bottom stream for recycle. HF is separated from sulfuric acid by distillation.

Claims (25)

A method for separating fluorocarbon and hydrogen fluoride from a mixture containing fluorocarbon and hydrogen fluoride, wherein sulfuric acid is added to a mixture containing fluorocarbon and hydrogen fluoride to give a fluorocarbon-rich first phase and hydrogen fluoride and sulfuric acid. Forming a rich second phase, wherein the weight ratio of sulfuric acid to hydrogen fluoride is in the range of about 1: 1 to about 10: 1. The method of claim 1, further comprising the subsequent step of removing the fluorocarbon rich first phase from the hydrogen fluoride and sulfuric acid rich second phase. The method of claim 2, further comprising the subsequent step of adding sulfuric acid to the removed second phase. The method of claim 2 further comprising the subsequent step of separating hydrogen fluoride and sulfuric acid. The method of claim 1 wherein the separation is performed at a temperature of about 0 ° C. to about 100 ° C. 7. The method of claim 1 wherein the fluorocarbon is pentafluoropropane. The method of claim 1 wherein the fluorocarbon is 1,1,1,3,3-pentafluoropropane. The method of claim 1 wherein the mixture of fluorocarbon and hydrogen fluoride is an azeotrope. The method of claim 1 wherein the mixture of fluorocarbon and hydrogen fluoride is in a liquid state. The method of claim 1 wherein the weight ratio of sulfuric acid to hydrogen fluoride is in the range of about 1: 1 to about 8: 1. The method of claim 1 wherein the weight ratio of sulfuric acid to hydrogen fluoride is in the range of about 2: 1 to about 4: 1. A method for separating fluorocarbon and hydrogen fluoride from a gas mixture containing fluorocarbon and hydrogen fluoride, wherein a flow of gas mixture of fluorocarbon and hydrogen fluoride is flowed through a conduit and then the mixture is contacted with sulfuric acid. Wherein the weight ratio of sulfuric acid to hydrogen fluoride is in the range of about 1: 1 to about 10: 1. 13. A process according to claim 12, wherein the contacting is carried out by backflow of sulfuric acid. 13. A method according to claim 12, wherein the contacting is carried out by backflow of liquid sulfuric acid. 13. The process according to claim 12, wherein the contact forms a first phase rich in fluorocarbons and a second phase rich in hydrogen fluoride and sulfuric acid. 16. The method of claim 15, further comprising the subsequent step of removing the fluorocarbon rich first phase from the hydrogen fluoride and sulfuric acid rich second phase. 17. The method of claim 16, further comprising the subsequent step of separating hydrogen fluoride and sulfuric acid. 13. The method of claim 12, further comprising contacting at a temperature above the boiling point of the mixture of fluorocarbons and hydrogen fluoride. 13. The method of claim 12, wherein the contacting is carried out at a temperature of about 25 ° C to about 100 ° C. 13. The method of claim 12 wherein the fluorocarbon is pentafluoropropane. 13. The process of claim 12 wherein the fluorocarbon is 1,1,1,3,3-pentafluoropropane. 13. The process of claim 12 wherein the mixture of fluorocarbons and hydrogen fluoride is an azeotrope. 13. The method of claim 12, wherein the weight ratio of sulfuric acid to hydrogen fluoride is in the range of about 1: 1 to about 8: 1. 13. The process of claim 12 wherein the weight ratio of sulfuric acid to hydrogen fluoride is in the range of about 2: 1 to about 4: 1. 13. The process of claim 12, wherein the contacting is carried out in a washing tower, a stream of gaseous mixture of fluorocarbon and hydrogen fluoride is introduced at the bottom of the column, a countercurrent of liquid sulfuric acid is introduced at the top of the column, and then the separated fluorocarbon Is left at the top of the column and a mixture of separated hydrogen fluoride and sulfuric acid is left at the bottom of the column.