JPS6035172B2 - Hydrogen fluoride removal from gas mixtures by absorption on alkaline earth metal fluorides - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides hydrogen fluoride (HF) containing up to about 20% by weight of the gas mixture and other gases that are inert to alkali metal fluorides. It concerns the removal of HF from gas mixtures in the absence of water.

The gas mixture is passed in contact with the granular anhydrous alkaline earth metal chloride in the absence of water. Preferably, the anhydrous alkaline earth metal chloride is purified by contacting the anhydrous alkaline earth metal chloride with a dry gas mixture that is inert to the chloride except for a small proportion of HF. Be stripped down. Alternatively, the granular anhydrous alkali metal fluoride used in the process of the invention can be obtained by using a dry gas or dry fluorine gas containing at least a large amount of HF. After the HF gas has been absorbed in an amount up to the absorption capacity of the specified anhydrous alkali metal hydrogen fluoride, the flow of the gas mixture is stopped or diverted.

The absorbed HF is removed from the alkali metal fluoride, preferably by thermal desorption. The regenerated alkaline earth metal fluoride is then used again in the HF removal process. Liquids other than aqueous liquids may be tolerated in the gas mixture as long as they do not collect in the process vessel in sufficient quantities to cover a significant amount of the surface area of the absorbent material. When the term "absorption" is used herein, it encompasses not only absorption but also adsorption and chemisorption.

The alkali metal compounds used in the present invention are chlorides and fluorides of calcium, barium or strontium, and are in anhydrous form.

Calcium is the preferred alkali metal and will therefore be used primarily below to further illustrate the invention. The anhydrous form of the alkali metal chloride is prepared by drying its water of hydration at a temperature that leads to removal of the water of hydration. The gas mixtures encompassed by the present invention contain up to about 20% by weight of the mixture of star HF and other gases that are inert to alkali metal fluorides, but such Gas mixtures include, for example, mixtures of HF, hydrogen chloride (in HC) and volatile organic gases obtained from various production processes: HF and HC mixtures thereof substantially free of other gases; Gas mixtures of HF and fluorine with or without active gases; dry air containing traces of HF; waste gases containing anhydrous HF from petroleum alkylation processes; Examples include the contained waste gas. The method of the present invention is particularly useful for treating HF-contaminated hydrogen chloride gases encountered as a by-product in the synthesis of fluorinated hydrocarbons.

To be more specific, CC 4, CHC 3, CH
Fluorinated hydrocarbons include HF fluorination of chlorinated hydrocarbons such as 3CCSO3 and CCSO2 = CCSO2 (this includes CCSO3F, CCSO2F2, CC〆F
3.CHC〆2F,CHC〆F2,CHF3,CH3C
Cso F2, CH3CC evening 2F, CH3CF3, CC〆2
Industrial methods of manufacturing FCC〆F2, CC〆F2, CC〆F2, CC〆F2, etc., and these products are useful as refrigerants, blowing agents, and aerosol propellants) contain hydrogen fluoride in varying amounts but in significant proportions. Large amounts of hydrogen chloride are obtained as a by-product. And this hydrogen chloride creation creature is
It cannot be disposed of for obvious economic and ecological reasons. However, this contaminated hydrogen chloride can be used in industrial applications that do not tolerate the presence of HF, such as oxychlorination, food processing, steel pickling, and brine treatments used in electrolytic chlorine production. Must be refined. F. R. U.S. Patent No. 3140916 for Rhodermilk
No. 1, 2003, suggests one method for removing HF contaminants.

There, a gaseous mixture of hydrogen chloride and hydrogen fluoride is passed through an aqueous solution of calcium chloride, thereby causing the hydrogen fluoride to react with the calcium chloride in solution form and converting the calcium fluoride into a solid precipitate that can be recovered by furnace. is forming. This multi-step aqueous technology includes HC〆, CaCso2 and Ca
There are several significant drawbacks resulting from treatment problems of aqueous systems containing F2. This mixture is highly corrosive, and the CaF2 precipitated in the water (ie, the CaF2-water mixture) constitutes an abrasive slurry. Both such corrosive and abrasive properties are therefore highly detrimental to plant equipment. Rodermilk also describes that aluminum oxide has been used as an absorbent to remove HF from HC. One of the inventors, D. R.
Merchant, in U.S. Application No. 354,715, filed April 26, 1973, discloses a simple and economical method for removing HF impurities from hydrogen chloride gas mixtures.

The present invention relates to a process in which HC gas containing HF is passed in contact with substantially anhydrous granular solid calcium chloride. However, when this method was carried out, it was noted that the calcium fluoride obtained in situ by the conversion of CaC〆2 had the ability to absorb f' up to slightly more than 50% of its weight. . Moreover, the calcium fluoride retains the size, shape, appearance, free-flowing properties, and other handling properties of the precursor calcium chloride. W.
L. Colvin is AEC Report K
II17 discloses the use of calcium fluoride produced by direct fluorination of calcium sulfate as an absorbent for hydrogen fluoride.

However, he only observed a very low payload at the HF breakthrough point. According to the invention, an average HF loading of about 20% on CaF2 is obtained under standard operating conditions. Similarly, Corvin reports a surface area of 129 g/g for his absorbent. When this calcium fluoride is used in the present invention, it has a surface area of about 12-17/g. Thus, the method of the present invention has the unobvious but unexpected result of removing more IJF per unit weight of absorbent than the prior art with a significantly lower surface area. Laboratory tests have shown that naturally occurring calcium fluoride does not have the ability to absorb significant amounts of HF.

Naturally occurring calcium fluoride has a breakthrough point of F of approximately 5
Calcium fluoride produced from the reaction of calcium chloride with HF could only absorb ~2% by weight of HF before breakthrough under the same flow, temperature and pressure conditions. can be absorbed. The term “breakthrough point (
When "breakthrough" is used herein, it is explained as follows.

That is, when HF is being absorbed by passing the HF-containing gas through an absorption medium, the HF concentration in the outlet gas is generally fairly uniform or increasing at low flow rates.

The "breakthrough point" has already been reached when the HF concentration in the outlet gas begins to increase at a high flow rate (compared to the previous flow rate).
In the absence of water anhydrous calcium chloride (CaC) layer
Regarding the surface area of calcium fluoride (CaF2) prepared by passing anhydrous HF through it until the CaC2 is converted to CaF2 (this is determined by solids content analysis) and the HF absorption on the calcium fluoride. Measurements were taken.

The results are summarized in Table 1 below. In addition, the absorbed HF
was desorbed by heating and air purge. Table 1 * American Chemical Society BET method [Brunauer (Brhada auer), Emmett (Em
Met) and Teller].

These results indicate that the compound CaC2 underwent a significant change in physical structure when it was reacted with HF to form CaF2.

Natural fluorite CaF2 is shown as sample m, and its surface area is approximately the same as that of CcC2. It is only 1 under the same conditions as sample 1 and sample LO.
Only 0% HF was absorbed. It can be manufactured as described above.
The HF absorbed by the synthetic calcium fluoride can be desorbed by suitable heating means, and the CaF2 thus regenerated serves again as a medium for absorbing further HF present in the gas mixture.

HF Must Be Removed The HF-containing gas mixture treated in accordance with the present invention may contain from 0.3 to about 20% by weight HF, based on the total weight of the mixture. However, the regeneration-recirculation system embodied in the present invention is suitable for use with moderately large amounts of e.g.
~about 6. It is particularly suitable for mixtures containing % by weight of HF. In a further useful application of the method, one or more volatile halogenated hydrocarbons, ie chlorofluorohydrocarbons, chlorohydrocarbons and fluorohydrocarbons, such as CC4, CC3F, CC2F2, CC etc. F3,
CHC So2F, CHC SoF2, CHF3, CHC So3
, CH3CC SoF2, CH3CC So2F, CC So2FC
C and F2, CC so F2 CC Ku F2, CC〆2CC so2
and the like may be present in admixture with the HF-containing hydrogen chloride gas mixture up to about 70% by weight, preferably up to about 6% by weight, based on the total amount of the gas mixture. Such volatile halogenated hydrocarbons do not interfere with HF absorption, and CaF2
No appreciable change occurs upon contact with. Separation of the HC product from such organic components can be accomplished by distillation to obtain anhydrous HC gas or by absorption in water to obtain an aqueous solution of HC. Small amounts of organic substances absorbed in the can be easily removed by blowing air or other gases or by absorption over activated carbon or molecular sieves.The absorption columns used in carrying out the process of the invention include First, a layer of suitable granular CaF2 made from substantially anhydrous calcium chloride as previously described may be charged, but in a preferred embodiment an anhydrous CaC layer is charged.

In this case, the loaded CaC2 is usually converted to CaF2 when a feed stream of HF-containing HC gas is passed in contact with it. This granular calcium fluoride is
It can be from the size of a powder to the size of granules or stamens. That is, the calcium fluoride
They can have average particle sizes over a wide range (37 skins).
However, in preferred embodiments, the calcium fluoride is
It is pellet-shaped with a particle size of 5 to 0.937 mm).
The temperature at which the hydrogen chloride gas mixture and particulate CaF2 contact is between about 600F (15.500F) and about 1300F (54.5F).
qo) Preferably about 700F (2ro) to 1150F (
4500).

It is desirable to maintain the contact temperature above the fog point of the gas mixture to prevent any organics present in the mixture from condensing within the reaction column. Pressures range from approximately atmospheric to approximately 250 psig depending on other process conditions.
atmospheric pressure). Because the system is essentially anhydrous, no foreign structural materials are required, and the absorption tower and ancillary piping and appurtenances can be conventional carbon steel, so corrosion is not an unusual problem. . When the term "anhydrous" is used herein, it means that the material contains no more than 1000 parts by weight (ppm), preferably no more than 20 parts by weight (ppm) of water per million parts of the material. . Similarly, the term "in the absence of water" means that a process is carried out with a gas having a water content of 1000 ppm or less. The advantages offered by the invention are simplicity of operation and low operating costs, as well as a high overall absorption rate for HF even at relatively low throughputs.

For example, after treating an HC-organic gas mixture with an initial HF content of about 18% according to the present invention, the HF content of the product gas is typically less than 0.05% by weight, but the flow rate of this feed gas is When measured under standard conditions of 15 psja pressure and 700 F. temperature, it can vary over a range of about 1.0 to about 100 kN/ft2 (granular CaF2). Stated another way, the above results for HF absorption indicate that the contact time (also referred to as residence time) between the HC gas mixture and the granular calcium fluoride is approximately 2
This means that it can be obtained even if the time is varied within the range of 0 to about 600 seconds. Of course, the quality of the produced gas (the amount of contamination per mark) is influenced to some extent by these flow rates. Granular Ca
Continue feeding the dry gas mixture to the F2 layer until the appropriate amount of HF has been absorbed into the layer. The amount of HF absorbed can be up to about 50% of the weight of CaF2. However, it is clear that one factor in absorption efficiency is the amount of free surface remaining in the CaF2 solid. Therefore, when a relatively pure HC product is desired, the operator should
The gas supply can be stopped or the gas supply can be redirected to a new column. However, the so-called "spent" CaF2 solids, by desorption,
That is, it is regenerated by stripping off the absorbed HF from the solid. This can be accomplished using a variety of conventional methods: (2) externally heating the absorption column to approximately 225-3500F; (2) heating the column to 2000F or more and reducing the carbon content therein;
This is conveniently accomplished either by passing an inert gas such as nitrogen, air, or anhydrous HF through the aF2 solid, or by passing an inert gas heated to {3'3500 F. or higher] through the CaF2 solid. The desorbed HF can be recovered and used for hydrofluorination. After cooling, the "regenerated" CaF2 layer is used in another cycle of processing the HF-containing gas mixture and, as previously described, is
After absorption reaches the desired level, the regeneration cycle is repeated.

When certain CaF2-loaded materials are used, their actual physical decomposition through heating and cooling cycles
The number of complete cycles is limited. Therefore, the number of cycles is limited by the allowable pressure drop of the system. At that point, the absorbent CaF2 should be replaced with a similar new layer or preferably with a new layer of substantially anhydrous granular CaC2. The depleted CaF2 solids, which may have already lost their good physical properties due to the physical field, are recovered from the bottom of the column. This can be used as a raw material for producing hydrofluoric acid in a reaction kiln. The following examples further clarify and illustrate the method of the invention.

Example 1 The by-product gas mixture obtained from the chloroform hydrofluorination process has approximately 60% HC based on the weight of the HC present.
% of organic matter [halogenated hydrocarbons (mainly CHC SOF)
2) and small amounts of CHC So2F, CHC〆3 and CHF
3] and hydrogen chloride containing 10.3% hydrogen fluoride.

3. Granular calcium fluoride. The above gas mixture was charged at 15 psi into a lin steel column packed to a depth of at.
a and 900F. The surface gas velocity at this time was in the range of 0.1500.5 ft/min. This is 110
This corresponds to a residence time of about 33 top sands. CaF2 is 3/
It had a particle size of 16 inches to 1/4 inch. It was thus obtained from a process in which anhydrous CaC particles in the particle size range were contacted with a gas stream of substantially the same composition as the gas mixture described above, in the absence of water. The HF content of the HC gas mixture decreased from 10.3% to 0.38% based on the HC gas content.

This corresponds to an HF removal efficiency of 96.4%. CaF2
Total 0.5% until the amount of HF absorbed in the layer is 14% by weight.
A 36 ft3 volume of feed gas was passed through the bed. Calcium fluoride was regenerated by heating the column to 3500F with electric heating tape. (i.e. absorbed H
F was removed). Thus, the regenerated CaF2 could be directly used to process the same gas mixture as it was supplied. Example The by-product gas mixture obtained from the hydrofluorination of lomethylchloroform consists of about 54% volatile halogenated hydrocarbons (mainly CH3CC〆F2 and small amounts of CH3CC〆2F and CH3CF3) based on the weight of HC. ) and HC rice containing 18% HF.

2jn that can include two layers of CaF when embodied in the present invention
The above gas mixture was passed through a steel column. CaF2 is
The above gas mixture was made by passing the above gas mixture through anhydrous CaC solution of 1/8 inch to 1/4 inch particle size flea pellets. After this CaC〆2 was completely converted to CaF2, the absorbed HF was released by an appropriate means, and the CaF2 could be reused as it was as an absorbent. Typical operating conditions were a pressure of 2 psig and a contact temperature of about 1000F. The system was subjected to four work cycles. At that time, CaF2 was regenerated in each cycle by the method of the previous example. These results are listed in the table below.
Table o At the end of the fourth cycle, CaF2 was removed from the column as a free-flowing to free-flowing solid without any noticeable change in size, shape or appearance.

Example M has 2 layers of granular CaF of 4.5 ft.
The same HC tagas mixture as in Example B was passed through.

This CaF2 was prepared by converting the gas mixture into anhydrous CaC2 using the same HC as in Example 0, so that the CaC2 was completely converted to CaF2.
CaF2 was produced by passing it through until it was converted to CaF2 and then extruding the absorbed HF by suitable means, leaving CaF2 behind. Operating conditions were 1000F and 155 psig. The gas flow was set to FM.
Therefore, the speed is about 0.8 t/min and the contact time is 4
It was 50 seconds. In this test, two cycles were performed, and CaF2 was regenerated at the end of the first cycle. This regeneration involves externally heating the column to 4000F' and
This was achieved by passing a 500F hot nitrogen purge through the CaF2 to create absorbed HF. These results are summarized in the following table: Table m Example W Using a 6JN power ram containing two layers of CaF in a 5.5 ft length, HF, HC, CH3CC, F2 and other chlorinated fluorocarbons (in small amounts) ), or #
A series of absorption experiments were conducted on mixtures of HF, HC, CHC, and other chlorinated fluorocarbons (in small quantities).

These results are shown in the table below. Table W gas and solid H
The data in this example regarding the amount of F was obtained by standard analytical methods.

Layer samples were obtained by "coring" the layer. EXAMPLE The following table shows the results of a series of absorption experiments conducted on the gases described in Example W above using a 2 ton column that can contain two layers of VCaF to a depth of 4.5 feet.

All absorption tests were performed on the same CaF2 loading. Regeneration of CaF2 used in the series of experiments in Example V of Table V was carried out as follows.

The diameter bed was heated to 3500F by heating the outside of the 1.2t diameter column.

Dry nitrogen at ISCFM rates per lft2 of bed area was heated to 4000F by a tube heater and passed through the bed. The HF on CaF2 was desorbed and it was cooled and collected in a container. CaF2 was almost completely removed, and less than 0.5% of HF remained on CaF2. This regeneration method was used in most of the experiments. Another reproduction method is as follows. 2. By heating the outside of the column, the diameter layer was heated to 3500F.
This normal diameter layer was then depressurized to 25 g. CaF
HF was desorbed from No. 2 and collected in a cooled receiver. The residual f' on CaF2 was less than 0.5% by weight. This method was used in the last two experiments of Example V. In these two cases, the desorption was carried out in the same way as the HF was originally adsorbed onto CaF2, ie in co-current with the adsorption stream. Example: Regeneration of CaF2 contained in a 6-inch column was performed as follows: The column vessel was jacketed to allow external application of 180 psig steam to a 6-inch ram.

The CaF2 layer adsorbing and containing HF is heated to about 3500F', and then air at about 1500F is added to the CaF2 layer with an area of 0.25 to 1.2% per 2 piles of CaF2 layer area. It was introduced at a speed in the eaves CFM range. This air flow was opposite to the direction of HF absorption. That is, if HF was adsorbed from the organic stream into CaF2 by passing the organic stream from the bottom of the CaF2 layer to the top of the CaF2 layer, then the desorption air was passed from the top of the CaF2 layer to the bottom. . Ca
The F2 layer was desorbed leaving 0.5% HF remaining based on the weight of CaF2. Example: Barium chloride dihydrate (Mari C 2nd day, 2nd day 20) and calcium chloride dihydrate (CaC〆2, 2nd day 20th) are combined with mother Cso2
・Mixed at a ratio of 20 parts of Nobe on 2nd day to 201 parts of CaC on 2nd day and 2nd day.

The wet cake of this mixture was pressed into a billet under 300 psi hydraulic pressure. Next, this billet was made into 30
One leg was dried at 00F. The billet was then crushed and sectioned, and those finer than 1'4 inches were discarded.
Inner diameter 2n, length 24 modified so that sampling can be carried out at the outlet of 8jn length and 16;n length.
The above 1'4 il piece was charged into a steel pipe.

This 2n inner diameter x 24 inch long tube contained 655 g of the above mixture. This tube was mixed with about 3% by volume of HF and HC.
A chloroform carbon gas stream containing about 3% by volume of organic matter and about 61% by volume of organic matter was introduced. After 4 hours, the tubes were removed for analysis.

The residence time was approximately 200 seconds. Analysis after 4 hours showed that HF was on the solid at 29. It was shown that % of the mother weight was absorbed.

Analysis of the solid showed no residual chlorine in the mass. (In other words, it was a complete transformation). In the table below, 2 hours ~
4 shows the % amount of hydrogen fluoride removed from the gas stream at various times.

Table Residence time: 20$eC Sample: 655g (as BaC 2 + CaC 2) Sample: 546.3g (as BaF2 + CaF2) Absorbed HF: 161.7g Removed HF: 301.6g (
Total amount) The barium fluoride pellets prepared as described above were prepared in Example W.
Or, it could be regenerated according to any of the methods for producing example skin.

Claims (1)

[Scope of Claims] 1. Hydrogen fluoride containing up to about 20%, based on the weight of the gas mixture, and other gases that are inert to alkaline earth metal fluorides. A method for removing hydrogen hydride, the method comprising: applying said gas in contact with a granular anhydrous alkaline earth metal fluoride produced by fluorinating a granular anhydrous alkaline earth metal chloride in the absence of water. hydrogen fluoride from a gas mixture, and the method is carried out in the absence of water, thereby causing hydrogen fluoride to be absorbed onto said anhydrous alkaline earth metal fluoride. Hydrogen removal method. 2. The method according to claim 1, wherein the alkaline earth metal is calcium. 3. The method according to claim 1, wherein the alkaline earth metal is barium. 4 Fluorination of anhydrous alkaline earth metal chloride comprises hydrogen fluoride and anhydrous alkaline earth metal chloride present as one component in a gas mixture together with other gases inert to said alkaline earth metal chloride. The method according to claim 1, which is obtained by reaction with a substance. 5. The method of claim 4, wherein the gas mixture comprises hydrogen chloride. 6. The method of claim 5, wherein the gas mixture comprises a volatile halogenated hydrocarbon. 7. The method according to claim 6, wherein the alkaline earth metal is calcium. 8. An anhydrous alkaline earth metal fluoride having hydrogen fluoride adsorbed on its surface is periodically regenerated by removal of the hydrogen fluoride adsorbed on the surface, and the regenerated anhydrous alkaline earth metal fluoride 2. The method of claim 1, wherein the anhydrous alkaline earth metal fluoride is reused to absorb hydrogen fluoride from a gas mixture passed in contact with the anhydrous alkaline earth metal fluoride. 9. The method of claim 8, wherein the gas mixture comprises hydrogen chloride. 10. The method of claim 9, wherein the gas mixture comprises a volatile halogenated hydrocarbon. 11 Fluorination of granular anhydrous alkaline earth metal chloride is
11. Process according to claim 10, obtained by reaction of said chloride with hydrogen fluoride present in a gas mixture. 12. The method according to claim 8, 9, 10 or 11, wherein the alkaline earth metal is calcium. 13 The alkaline earth metal is calcium, and the average particle size in the maximum range of granular anhydrous calcium fluoride is 0.
．． 11. The method of claim 10, wherein the thickness ranges from 0.025 to 0.375 in. 14. The method of claim 13, wherein the temperature at which the gas mixture contacts the anhydrous calcium fluoride ranges from about 60<0>F to about 130<0>F. 15. The method of claim 14, wherein the ambient pressure at which the gas mixture contacts the anhydrous calcium fluoride ranges from about atmospheric pressure to about 250 psia. 16 Claim No. 1, wherein the anhydrous alkaline earth metal chloride is prepared by dehydrating an alkaline earth metal chloride hydrate, which is then fluorinated to an alkaline earth metal fluoride. The method described in Section 1.