WO1993006039A1

WO1993006039A1 - Process for producing bromine from bromide salts

Info

Publication number: WO1993006039A1
Application number: PCT/US1992/007831
Authority: WO
Inventors: Paul F. Schubert; Arnold R. Smith; Henry Taube; David W. Schubert
Original assignee: Catalytica, Inc.
Priority date: 1991-09-16
Filing date: 1992-09-16
Publication date: 1993-04-01
Also published as: AU2674892A; IL103186A0

Abstract

This invention is a combination process for producing elemental bromine using bromide salt feedstocks. The process involves acidifying an inorganic bromide salt with a strong and concentrated acid, preferably sulfuric acid, to produce a gaseous HBr stream. The HBr stream is then mixed with an O2-containing gas and passed to an oxidation reactor where it is catalytically oxidized to produce a stream of Br2 and H2O. The hot reactor effluent is quenched and the product Br2 is separated from the H2O. In the figure, HBr stream is introduced into an evaporator (204) and to superheater (206). The O2 feedstream (208) is warmed. A reactor feedstream (214) is introduced into (216). The reaction product stream (218) is cooled in stages (220) and (222) and condensed. The condensate is then separated into a Br2 stream (224) added to water stream giving stream (226) and (228). The device (230) is a separator and (232) is a refrigeration unit. The resulting stream (234) is mixed with Br2 stream (224) giving noncondensed oxygen vapor stream (236) which is scrubbed in a gas treater (238). Distillation column (242) produces two streams (252) and (244). The overhead vapor stream (244) is condensed in overhead condenser (246) and collected in drum (248). The stream (250) is mixed with other streams. Device (256) is an absorption tower and (258) is the Br2 product stream.

Description

PROCESS FOR PRODUCING BROMINE FROM BROMIDE SALTS

Field of the Invention

This invention is a combination process for producing elemental bromine using bromide salt feedstocks. The process involves acidifying an inorganic bromide salt with a strong and concentrated acid, preferably sulfuric acid, to produce a gaseous HBr stream. The HBr stream is then mixed with an 0₂- containing gas and passed to a oxidation reactor where it is catalytically oxidized to produce a stream of Br₂ and H₂0. The hot reactor effluent is quenched and the product Br₂ is separated from the H₂0.

Background of the Invention This invention is a process for producing elemental bromine from bromide salts in which an intermediate catalytic step comprises oxidizing hydrogen bromide with 0₂ to form that elemental bromine.

Bromine is a chemical feedstock often used for the production of bromoalkanes or olefins from alkanes. Bromine is present in nature only in dilute sources such as in seawater or in brines of the Dead Sea or the United States. This invention is a process for recycling bromide salt streams such as those produced as byproducts of other processes. The process includes an acidification step in which the bromide salt solution is mixed with a strong, concentrated acid to spring HBr free from the solution; a catalytic process step in which the HBr stream (potentially containing H₂0) is oxidized to produce a wet Br₂ stream, and separation steps for the isolation of Br₂ from the water.

We know of no process in which elemental bromine is produced from bromide salts and which uses a catalyst to produce the desired Br₂.

There are a number of processes described in the open literature which produce bromine according to the equation:

4 HBr + 0₂ > 2 Br₂ + 2 H₂0. one such process (British Patent 930,341) involves the conversion of hydrobromic acid solutions using dissolved metal ion catalysts. The soluble metal may be gold, cerium, chromium, nickel, platinum, thorium, titanium, or vanadium; but preferably is iron or copper. A gas containing oxygen is passed through the acidic solution containing HBr and the dissolved metal, all at a temperature below the boiling point of the liquid. The gaseous effluent is then separated via condensation and distillation into product bromine, water, and HBr for recycle to the oxidation step.

Similarly, U.S.Pat.No. 3,179,498, to Harding et al, disclose a process in which a nitrite catalyst is employed in the acidic, aqueous solution of HBr to effect the oxidation of the HBr to Br₂. The temperature of the liquid is maintained between 0° and 100°C. Although any inorganic or organic nitrite is said to be suitable, preferred catalysts are alkali or alkaline earth metal nitrites.

There are a number of processes which use heterogeneous catalysts to effect that conversion.

U.S. Pat. No. 2,536,457, to Mugdan, teaches such a process. The conversion is carried out at a temperature between 800° and 1200°C (preferably between 800° and 1000°C) with an excess of oxygen. The catalyst is preferably cerium oxide and may be supported on pumice granules or other refractory materials. If excessive water is included in the reactor, a combustible gas such as hydrogen is included to maintain the reaction temperature. Clearly the reaction temperature for this process is quite high.

U.S. Pat. No. 3,273,964, to De Rosset, shows a process in which the effluent from a dehydrobromination reaction is contacted with a catalyst-adsorbent composite. The effluent contains olefinic hydrocarbons and is produced by a series of steps in which an alkane is brominated to forma a bromoalkane; the bromoalkane is then dehydrobrominated to form the effluent of olefinic hydrocarbons and HBr. The catalyst-adsorbent composite adsorbs the HBr in a first step and, during regeneration, catalyzes the oxidation of HBr to form the desired Br₂. The composite contains an adsorbent of a basic metal oxide such as magnesium, calcium, or zinc oxide, and a catalyst of a Group IV-B metal oxide such as titania, magnesia, or zirconia. The preferred composite contains magnesia and zirconia in a ratio from about 0.5:1 to about 5:1.

U.S. Pat. No. 3,260,568, to Bloch et al. teaches a process in which a stream containing substantially dry HBr contacts a solid adsorbent containing a metal "subchloride" and which is the reaction product of a refractory metal oxide and a metal chloride. The contact takes place at conditions where the HBr replaces at least a portion of the chloride in the adsorbent. When the adsorbent has reached about six percent by weight, the adsorbent is regenerated by contacting it with a dry hydrogen chloride gas. The patent does not appear to suggest the conversion of the adsorbed HBr to Br₂ even though the adsorbent is suggested to be selected from metal chlorides such as aluminum, antimony, beryllium, iron, gallium, tin, titanium, and zinc chlorides.

U.S. Pat. No. 3,310,380, to Lester, discloses a process for the adsorption of combined bromine (e.g., HBr and alkyl bromides) on a catalytic-adsorbent composite, recovering unsaturated hydrocarbons, and when the adsorbent is filled, contacting the composite with an oxygen-containing gas at a temperature between 50° and 450°C to produce a Br₂ stream also containing water and ^' unreacted HBr. This stream (also in admixture with an oxygen-containing gas) is then contacted with a second stage reactor also containing the composite but at a temperature between 200° and 600°C. The composite in the first stage comprises, preferably, 0.5 to 10% by weight of copper or cerium oxide composited on magnesium oxide: the second stage composite comprises, preferably, 2.0 to about 50% by weight of copper or cerium oxide composited on an alumina or zirconia support.

Similarly, U.S. Pat. No. 3,346,340, to Louvar et al. suggests a process for the oxidation of HBr to Br₂ using a catalyst-inert support composite. The composite comprises a copper or cerium oxide on an inert support having a surface area between 5 and 100 square meters per gram and containing less than about 50 micromoles of hydroxyl per gram. The supports may be alpha- or theta- alumina or zirconia. The preferred temperature is between 300° and 600°C.

U.S. Pat. No. 3,353,916, to Lester, discloses a two stage process for oxidizing HBr to form Br₂ by the steps of mixing the HBr-containing gas with an oxygen- containing gas and passing the mixture at a temperature of at least 225°C over a catalyst selected from the oxides and salts of cerium, manganese, chromium, iron, nickel, and cobalt and converting a major portion of the HBr to Br₂. The partially converted gas, still containing excess oxygen, is then passed through a second stage catalyst comprising a copper oxide or salt at a temperature of at least about 225°C but not exceeding a "catalyst peak temperature" of 350°C to convert the remaining HBr. The preferred support appears to be zirconia.

This two-stage arrangement is carried out to prevent loss of copper catalyst. Because the preferred copper oxide is converted to copper bromide during the course of the reaction, at reaction conditions, and copper bromide volatilizes at "temperatures in excess of about 350°C", the "copper bromide migrates through the catalyst mass in the direction of flow with eventual loss of copper bromide and premature deactivation." Use of a first catalyst stage which is tolerant of high temperatures, even though the first stage catalyst is apparently not as active a catalyst as is copper, allows a cooler second catalyst stage containing copper to complete "quantitative conversion of bromine from hydrogen bromide."

U.S. Pat. No. 3,379,506, to Massonne et al. a process for the selective oxidation of hydrogen bromide to bromine in the presence of fluorocarbons by passing the mixture of gases over a Deacon catalyst at a temperature of 250 to 500°C, preferably between 300 and 400°C. The Deacon catalyst is said to be a "mostly porous carrier such as pumice, alumina, silica gel, clay, or bentonite, impregnated with a solution of bromides or chlorides of metals such as copper, iron, titanium, vanadium, chromium, manganese, cobalt, molybdenum, tungsten, or mixtures thereof." The preferred catalyst is said to be a chloride of copper. The patent notes that "[a] very efficient and stable catalyst is an oxidation catalyst which is prepared by impregnating active alumina with chlorides of copper, rare earths and\or alkali metals, drying at about 120°C and subsequent activation at a temperature of 300° to 450^oC." One example shows the production and use of a catalyst of alumina, potassium, copper, and an amount of "rare earths of the cerite group as chlorides".

Another patent which notes the problem with the volatilization of copper bromide in the oxidation of hydrogen bromide to bromine is U.S. Pat. No. 3,437,445, to Hay et al. The solution is to eliminate the copper in favor of a noble metal, such as platinum and palladium. The reaction is carried out at a temperature of about 175° and about 700°C with a contact time of at least about 0.1 sec, "but for best operation a contact time of about five and 25 seconds is preferred." The yield of bromine is only between 28 and 78 molar percentage. U.S. Pat. No. 4,131,626, to Sharma et al. suggests a process in which bromide salts are heated in the presence of an oxygen-containing gas, silicon dioxide, and an oxidation catalyst at a temperature of about 500° to 1000°C. The bromine is produced in conjunction with sodium silicate.

Finally, U.S. Pat. No. 2,705,670, to Chao, teaches a process for acidifying a bromide salt with sulfuric acid to produce HBr. There is no suggestion to produce Br₂ and, indeed, there is a suggestion that Br₂ is not desirable.

None of these documents suggest a combination process in which Br₂ is produced from bromide salts via a catalytic HBr oxidation step.

Summary of the Invention

This invention is a process for producing Br₂ from bromide salts in which an intermediate catalytic step comprises oxidizing hydrogen bromide with 0₂ to form that elemental bromine.

The process involves acidifying an inorganic bromide salt (such as NaBr or KBr and their mixtures) with a strong and concentrated acid, preferably sulfuric acid, to produce a gaseous HBr stream. The HBr stream is stripped of any S0₂, mixed with an 0₂-containing gas, and passed to a oxidation reactor where it is catalytically oxidized to produce a stream of Br₂ and H₂0. The oxidation reactor is operated at a temperature between about 125°C and about 500°C. The Br₂ is then separated from the feed and co-produced water by quenching the reactor stream, absorbing the Br₂ in a bromide salt solution, and desorbing pure Br. The Br₂ may be further dried, if so desired.

Brief Description of the Drawings

Figure 1 is a diagram of a process "front end" suitable for producing HBr useful in the inventive oxidation stages depicted in Figures 2 and 3.

Figures 2 and 3 are diagrams of two variations of the inventive oxidation stages.

Figure 4 is a graph of the performance of a preferred HBr oxidation catalyst over a range of operating temperatures.

Figure 5 is a graph of the performance of a preferred HBr oxidation catalyst over a period of time.

Description of the Invention As noted above, this invention is a process for producing bromine from bromide salts. The desirability of the process centers largely around the intermediate catalytic step of oxidizing hydrogen bromide with an oxygen-containing gas to form elemental bromine according -r- to the equation:

4 HBr + 0₂ > 2 Br₂ + 2 H₂0.

This permits exclusion of a major portion of the chlorine typically used in such processes. Process

This invention is a process for producing Br₂ from inorganic bromide salts using an intermediate catalytic step which comprises oxidizing hydrogen bromide to form that elemental Br₂. Figure 1 shows a series of steps suitable for producing HBr from the bromide salts. Figures show steps suitable for producing Br₂ from the HBr produced in the Figure 1 steps.

As is shown in Figure 1, in this process a metal bromide (MBr) , typically an alkali metal bromide in which "M" is K or Na or a mixture of both, is introduced via feed line (102) to a mixing vessel (104) where it is mixed with a strong, concentrated acid from line (106) such as H₂S0₄. Strong H₂S0₄ is an acid stream containing more than about 70% by weight of H₂S0₄. This mixing produces the following reaction:

MBr + H₂S0₄ —> HBr + MHS0₄ where "M" is an alkali metal particularly K or Na or their mixtures. The MHS0₄ is generally insoluble at the concentrations utilized in the process and consequently should be removed via line (108) . The MHS0₄ may be filtered from any water suspending those crystals; the ^"water may be returned to mixing vessel (104) .

Although it is desirable to maintain the acid concentration and water concentration at a level such that the weight ratio of H₂0 to Br present in the solution is between 1:1 and 1:15, it is not absolutely necessary. This range of ratios is said to produce an HBr/H₂0 azeotrope stream which is considered to be suitable for conversion to Br₂. If the H₂0 content is outside that range, the HBr/H₂0 azeotrope stream (110) _? _ contains S0₂ which potentially causes problems both with the oxidation catalyst and with downstream processing equipment and product streams. If the HBr/H₂0 stream (110) contains S0₂, then the stream should be condensed in condenser (112) and the S0₂ converted to H₂S0₄ by reaction with Br₂ injected into line (110) through line (113) . HBr is then stripped from the resulting liquid stream in stripper column (114) using a reboiler (115) . The bottoms H₂S0₄ solution (116) may be recycled back to mixing vessel (104) . If the mixing vessel (104) is operated so that S0₂ is not produced, then condenser (112) , stripper (114) , and reboiler (115) are not necessary and the HBr/H₂0 azeotrope stream (110) may be sent directly to the oxidation reactor (124) via line (117) . Alternatively, S0₂ may be removed from the stream using a suitable absorbent.

The oxidation step involves the simple expedient of mixing the gaseous or vaporous HBr from the feed preparation step with a suitable amount of an oxygen-containing gas, such as air, oxygen-enhanced air, or oxygen and passing the mixture to the catalyst. The 0₂ is desirably added in an amount producing an HBr:0₂ molar ratio of between about 3.00 and 4.25. The 0₂ may be present in excess not only to assist in the HBr oxidation but also to oxidize any hydrocarbonaceous materials present in the feedstream. Nevertheless an HBr:0₂ molar ratio of between above 3.9 and up to 4.1 is preferred.

The HBr-0₂ mixture is then passed through one or more beds of the catalysts described above. As noted elsewhere, this reaction is highly exothermic. The temperature in the reactor may be controlled in a variety of ways. For instance, if an adiabatic reactor is desired, the feed HBr likely will need be diluted with steam, nitrogen, air, product stream recycle, or the like /06039

- /o- to prevent excessive temperature rise in the reactor. Specifically, the HBr feedstream may have an HBr content of between 25% and 99.5% (wt) but desirably has an HBr content between 35% and 55% (wt) but most preferably between 45% and 55% (wt) . Use of anhydrous (or highly concentrated) HBr and pure 0₂ as the oxidant is difficult in that the temperature rise in an adiabatic reactor is nearly 2000°C; even the use of air and anhydrous HBr results in an adiabatic temperature rise of 1000°C — a possible but unlikely candidate for ease of operation. Consequently, the use of air and an HBr feed of between 45% and 55% (wt) is very desirable and readily operable.

In other reactor configurations, some provision may be made for removing or controlling the heat of reaction, e.g., by inclusion of the bed or beds in an appropriately cooled heat exchanger (such as by tubes of catalyst in a steam generator) , by adding the oxygen- containing gas in a series of steps with cooling steps amongst sequential catalyst beds, etc. The catalyst bed or beds may be fluidized or ebullated if so desired. Fluidization allows superior control of the bed temperature and prevents the occurrence of "hot-spots" in the catalyst.

The materials of construction for the reactor should be selected using normal materials criteria but bearing in mind that the system is fairly corrosive. For instance, if the reactor is operated at the lower end of the reaction range noted above and the reactor is a nickel alloy, the reactor should be maintained above the temperature of condensation lest liquid phase corrosion occur. Similarly, the upper range of temperature should be controlled to prevent vapor phase corrosion. If a ceramic system is chosen, similar criteria are applicable to prevent dissolution of the ceramic or to prevent creep of the polymeric seals used at joints and flanges. The product separations stage may include the generic steps of quenching the reactor product, recovering and concentrating the Br₂, and recovering materials such as HBr for recycle. Figures 2 and 3 show desirable integrated processes for the oxidation of HBr to Br₂. Figure 2 shows a process using reasonably pure 0₂ as the process feed; Figure 3 shows a process in which air is the process feed.

Oxygen Process

In this embodiment of the inventive process, shown in Figure 2, an HBr stream (118) is introduced to an evaporator (204) and to a superheater (206) . The resulting HBr vapor should be at a temperature of about 230°-250°C. The oxygen feedstream (208) is similarly warmed to about 230°-250°C with superheater (210) . The heat for superheaters (206) and (210) may, for instance, be supplied by a circulating hot oil system including hot oil heater (212) .

The heated HBr feedstream and the heated oxygen feedstream are then mixed to form a reactor feedstream (214) which is then introduced into reactor (216) . The reactor (216) is desirably of a multi-tube design containing the catalyst described above or may be of a multi-bed design. Since the reaction is quite exothermic, reactor designs which are capable of removing the heat of reaction from the catalyst mass are obviously very desirable. The reactor design shown is also used as a steam generator.

The reaction product stream (218) may then be cooled in two stages. The first stage of cooling (220) shown is a desuperheater and merely lowers the temperature of the stream down to the neighborhood of the stream's dew point, e.g., about 150°C. This stream is then condensed and cooled to a temperature of about 40°C in condenser (222) .

The condensate is then separated into a liquid Br₂ stream (224) saturated with water, a water stream (226) saturated with Br₂, and a vaporous vent stream

(228) containing unreacted oxygen, bromine, water, and a small amount of inerts. The device used for that separation (230) may be a simple phase separation device - such as a decanter. Other density separation devices are just as suitable.

The vapor stream (228) is then chilled in refrigeration unit (232) to a temperature sufficient to remove most of the Br₂ found in the vent stream. The condensed Br₂ stream is separated in drum (232) and the resulting Br₂ stream (234) is mixed with Br₂ stream (224) for further processing. The resulting non-condensed oxygen vapor stream (236) is scrubbed in a gas treater (238) using, for instance, sodium hydroxide remove any remaining Br₂ before the treated oxygen is vented (240) into the atmosphere. The vent gas treatment step may be omitted and recycled into the reactor (216) if the oxygen is of sufficient purity.

The aqueous stream (226) coming from the separator (232) is then stripped of its Br₂ content in a distillation column (242) . Distillation column (242) produces two streams. The overhead vapor stream (244) is condensed in overhead condenser (246) and collected in reflux drum (248) . The reflux drum (248) is a decanter design. The lighter phase is largely water and is recycled to the distillation tower (242) as reflux. The heavier phase is Br₂ and the stream (250) is mixed with other Br₂ streams, (224) and (234), for further treatment such as by drying with strong H₂S0₄ in a countercurrent absorption tower (256) . The tower produces a weaker H₂S0₄ stream and the desired Br₂ product stream (258). The bottom stream (252) from distillation tower (242) is partially reboiled in reboiled in reboiler (254) . The remainder of the stream is mostly water containing unconverted HBr feed and the water of reaction formed in the reactor (216) . All or a portion of this stream may be treated by neutralization with, e.g., caustic soda, to produce a waste water stream (262) . If the inventive process is used as an integrated portion of a process which is capable of using a dilute HBr, the dilute HBr stream may be so recycled.

There are other ways of eliminating the water produced in the reactor. For instance, by operating separator (232) at different conditions, e.g., at a temperature above 40°C, the overhead stream (236) will contain the water of reaction.

Air Process

The process is preferably operated using a less concentrated oxygen feedstream, e.g., air or oxygen- enriched air. This variation is shown in Figure 3.

In a general sense, the process scheme is similar to that used in the oxygen process described above. The reactor and condensation sections are identical. As above, an HBr feedstream (118) is sent to an evaporator (304) and to a superheater (306) . The air feedstream (308) is compressed in compressor (309) and heated in superheater (310) . The heat for superheaters (306) and (310) may, for instance, be supplied by a circulating hot oil system including hot oil heater (312) .

The heated HBr feedstream and the heated oxygen feedstream are then mixed to form a reactor feedstream (314) which is then introduced into reactor (316) . The reactor (316) is desirably of a design similar to that -l< - described above although because of the additional diluent in the feedstream is a little less sensitive to reactor design, but those which are capable of removing the heat of reaction from the catalyst mass are obviously very desirable.

The reaction product stream (318) may then be cooled in two stages. The first stage of cooling (320) shown is a desuperheater and lowers the temperature of the stream down to the neighborhood of the stream's dew point, e.g., about 150°C. This stream is then condensed and cooled to a temperature of about 40°C in condenser (322) . The condensed reactor product stream (324) is fed to a phase separator (326) where it is separated into an aqueous stream (328) saturated in Br₂ and containing any unconverted HBr and an overhead vapor stream (330) containing all of the Br₂.

The aqueous stream (328) may be treated in a manner similar to that discussed above. The aqueous stream (328) coming from the separator (326) is stripped of its Br₂ content in a distillation column (330) .

Distillation column (330) produces an overhead vapor stream (332) which is condensed in overhead condenser (334) and collected in reflux drum (336) . Water from the drum is recycled to the distillation tower (330) as reflux. The Br₂ stream (338) is mixed with other Br₂ streams for further treatment such as drying.

The bottom stream (340) from distillation tower (330) is reboiled. The stream is mostly water and contains unconverted HBr feed and the water of reaction formed in the reactor (316) . All or a portion of this stream (342) may be neutralized to produce a waste water stream (346) or may be recycled via line (348) .

Returning to the phase separator (326) , the overhead vapor stream (N₂, Br₂, and H₂0) may be introduced into the bottom of an absorption column (350) where cold - \ -

(-15°C) lean NaBr brine (352) is fed to the top to act as absorption media for Br₂. The overhead stream (354) is substantially free of Br₂.

The bottom stream (356) is heated (preferably in feed-effluent heat exchanger (358) with the heat from the bottom of stripper column (360)) and introduced into stripper column (360) . In that column, Br₂ is stripped from the NaBr brine into an overhead stream (362) . That steam is condensed in exchanger (364) and collected in reflux vessel (366) . The water stream is decanted in reflux vessel (366) and is both used as reflux in stripper tower (360) and in the feed to distillation tower (330) .

The vapor line (368) from the reflux drum (366) may be mixed with the overhead vapor stream (354) from absorber (350) and treated by neutralization in absorber (370) to remove any remaining HBr before disposing of the N₂ via vent (372) .

The decanted Br₂ (374) from reflux vessel (366) may be mixed with the Br₂ stream (338) from reflux vessel (336) and treated with concentrated H₂S0₄ in absorber (376) to remove water and produce the dry product Br₂.

This process is a desirable embodiment of the overall concept of the invention. There are others which are suitable for synthesizing the desired Br₂ product from a bromine-containing feed.

The Catalyst Catalysts suitable for this process include a wide variety of supported or homogeneous materials. For instance, the active catalyst may be selected from the metals; and the oxides, halides (particularly chlorides and bromides) , and oxyhalides of the following metals: Group IB (particularly Cu) , Group IVB (particularly Ti and Zr) , Group VB (particularly V) , Group VIB (particularly Cr,Mo, and W) , Group VIIB (particularly Mn and Re) , Group VIII (particularly Fe, Co, Ni, Pt, And Pd) , and the rare earth lanthanides series (particularly Ce) . The active catalyst may be promoted with one or more Group IIA (particularly Ca) metals or lanthanides, if so desired. The active catalyst and the promoter,if any, may be supported .on known catalyst supports such as MgO, A1₂0₃ (particularly in eta- or delta-form) , Zr0₂, Hf0₂, Si0₂ (particularly in silica gel form) , clays such as bentonite or attapulgite, and natural materials such as pumice.

The active catalysts listed above should be present in an at least a catalytic amount, that is to say, an amount sufficient at least to catalyze the reaction of HBr and oxygen to produce Br₂. Active catalytic metals, depending upon the metal selected, may be present in the amount of 0.1 % to 35 % (by weight) of the overall composition is desirable; 1.0 % to 20 % (by weight) of catalytic metal is more desirable and 3.0 % to 10.0 % (by weight) of catalytic metal is most desirable.

The promoters/stabilizers may be any salt or complex of the noted metals, whether oil or water soluble, which can be impregnated onto the catalyst support or mixed with the support, e.g., as by ball milling with the support precursor. The bromide salts are especially suitable, but other halides (iodide or chloride) , oxyhalides, oxides, phosphates , sulfides, sulfates; complexes such as acetylacetonates, and the like are also suitable. The bromides, oxybromides, oxides, and mixtures are useful and conveniently available. The promoter/stabilizer metal-bearing material should be present in an amount such that the overall content (in whatever form) is desirably between 0.1 % and 20 % (by weight) of the overall composition; 1.0 % to 6.0 % (by weight) is more desirable; 1.0 % to 4.0 % (by weight) is most desirable.

If the catalyst support is zirconium- containing, it desirably contains more than about 50% (wt) of zirconia. A minor amount of other metal oxides, e.g., alumina, titania, hafnia, yttria, silica, etc., may be included as a binder or extrusion aid or to increase surface area or pore volume if so desired. Whether the support is zirconium-containing or not, it is desirable . to use a support which has significant porosity in the range between 30 and lOoA, e.g., > 0.01 cc/gm pore volume in the range of 30 and lOoA.

Preferred Catalyst The preferred catalyst comprises promoted copper bromide on a zirconia support. At the temperatures of operation contemplated in this process, the copper bromide does not substantially migrate from the catalyst composition nor among different regions of the catalyst and is very active. This high activity permits the use of comparatively lower temperatures thereby enhancing, even more, the catalyst's stability.

This preferred catalyst is produced by placing copper bromide directly onto the support, and is not made by converting another copper-bearing material into copper bromide on the support. Although we believe that the direct addition of the copper bromide to the support is critical to the stability and activity of the catalyst, we do not wish to be bound to that theory. Additionally, the addition of certain promoters to the supported copper bromide catalyst appears to add substantial stability to the catalyst. Finally, although the support most desirably comprises a zirconium-containing material such as zirconia, other supports are suitable. Specifically the preferred catalyst is a composite comprising or desirably consisting essentially of copper bromide; promoter/stabilizer selected from materials containing one or more salts, oxides, or complexes of metals selected from Ca, Y, Nd, or La or of metals having an ionic radius between about 0.9 and 1.4

A; and an oxidic zirconium-containing catalyst support.

The preferred promoters are Nd and La. Most preferred is

La. The copper bromide should be present in at least a catalytic amount, that is to say, an amount sufficient at least to catalyze the reaction of HBr and oxygen to produce Br₂. We have found that copper bromide in the amount of 0.1 % to 20 % (by weight) of the overall composition is desirable; 1.0 % to 10 % (by weight) of copper bromide is more desirable and 3.0 % to 6.0 % (by weight) of copper bromide is most desirable.

We have found that the introduction of the copper catalyst onto the zirconium-containing catalyst support in the form of copper bromide results in a catalyst composition which is both more stable and more active than compositions in which the catalyst is introduced in another form, such as by the oxide. We have additionally found that the x-ray diffraction spectrum (Cu„) of the catalyst composition does not show the presence of crystalline CuBr₂. Specifically, the x- ray diffraction spectrum of crystalline CuBr₂ contains the following lines:

The absence of the most distinctive line (2Θ = 14.485°) demonstrates the substantial absence of copper bromide . -n- crystallinity. Catalyst compositions prepared using CuO, which converts to copper bromide in the HBr oxidation process, show the presence of that distinctive line (2Θ = 14.485°) . We believe this to indicate that the copper bromide introduced to the zirconium-containing support, in contrast to copper bromide produced on the support from another material, is essentially amorphous.

We have not, however, found the source of the promoters/stabilizers to be of significant importance. Any salt or complex of the noted metals, whether oil or water soluble, which can be impregnated onto the zirconium-containing support or mixed with the zirconium support, e.g., as by ball milling with the zirconium support precursor, is suitable. The bromide salts are especially suitable, but other halides (iodide or chloride) , oxyhalides, oxides, phosphates, sulfides, sulfates; complexes such as acetylacetonates, and the like are also suitable. Lanthanum bromide, oxybromide, oxide, and mixtures are useful and conveniently available. The promoter/stabilizer metal-bearing material should be present in an amount such that the overall content (in whatever form) is desirably between 0.1 % and 10 % (by weight) of the overall composition; 1.0 % to 6.0 % (by weight) is more desirable; 1.0 % to 4.0 % (by weight) is most desirable.

The zirconium-containing support typically should contain more than about 50% (wt) of zirconia. A minor amount of other metal oxides, e.g., alumina, titania, hafnia, yttria, silica, etc., may be included as a binder or extrusion aid or to increase surface area or pore volume if so desired. We have found that it is very desirable to use a zirconia support which has significant porosity in the range between 30 and lOoA, e.g., > 0.01 cc/gm pore volume in the range of 30 and lOoA. General

The catalyst material may be utilized in any physical form convenient to the process in which it is utilized. Such forms may include tablets, extrudates, Pall rings, or the like. The reaction is very exothermic and consequently the relative external surface area may be an important consideration in some reactor/process configurations.

The catalyst desirably is prepared by dissolving the appropriate catalyst metal and the promoter/stabilizer metal compounds or complexes independently in aqueous acid, preferably HBr, solutions and impregnating them into the catalyst supports. The catalyst supports should be dried at, e.g., 110° to 135°C in air, before impregnation so to allow accurate measurement of the metal content added to the support. The method and sequence of impregnating the support has not been found to be critical. If the various compounds are compatible, e.g., they don't react together and don't precipitate from solution, a single solution containing the metals may be used as the impregnating solution. Depending upon the impregnating procedure chosen, the solutions may be saturated or not. If an incipient wetness method is selected, the amount of solution will match the pore volume of the support requiring that the composition of the solution be adjusted to assure that the amount of metal added to the support is appropriate. If other procedures are elected, saturated solutions may be used and a particular amount of the solutions chosen. The impregnated support is dried and ready for use.

The invention has been disclosed by direct description. Below may be found a number of examples showing various aspects of the invention. The examples are only examples of the invention and are not to be used to limit the scope of the invention in any way.

EXAMPLES Example 1

This example shows a long term test of the a highly desired CuBr₂/LaBr₃/Zrθ₂ catalyst in the HBr oxidation step.

A pure zirconia support having a pore size distribution of 0.093 cc/gm of pore volume in the range of 30-lOθA and 0.098 cc/gm in the range of 600-1000 A pore diameter was used to prepare the CuBr₂/LaBr₃/Zr0₂ catalyst. The support was a powdered zirconia support which was impregnated with solutions of CuBr₂ and LaBr₃ and pressed in a die using a carved press. This pressing was then ground and sieved to give a 20-30 mesh fraction. The finished catalyst contained 0.2 mmoles/cc of CuBr₂ and 0.6 mmoles/cc of LaBr₃. The pore size distributions were determined using a Micromeritics Autopore II 9220 mercury porosimeter.

The catalyst was tested for activity using the following procedure:

A 1 cm OD by 45 cm long glass reactor tube was filled to about its length-wise center with glass beads. A glass wool plug was then inserted. About 1 cc of catalyst was placed on the glass wool. Another glass wool plug was placed over the catalyst bed. The remainder of the glass tube was packed with glass beads. The glass reactor was then placed in a tube furnace with an aluminum sleeve between the outer reactor wall and the inner wall of the furnace to aid in heat distribution. A thermocouple was included at the center of the catalyst bed. A 48% HBr solution was delivered to the reactor at a rate of 6 cc/hr using a syringe pump. During the test, the syringe pump had to be refilled about every 20 hours. During the refilling period, nitrogen was flowed through the reactor. Upon readmittance of HBr to the reactor, an -<?3 initially lower reaction rate was observed in the first 20 minutes of testing. However, the rate then returned to the rate prior to the refilling of the syringe. Oxygen was fed to the reactor using a mass flow controller at a rate of 6 cc/hr. The temperature of the reactor was maintained at 275°C.

The reaction products and unreacted feed materials were condensed in traps containing KI. In the traps, the product Br₂ formed reacts there with the KI to form I₃ ^" ion. The I₃ ^" ion was then titrated with Na₂S₂o₃. The amount of bromine formed in the reactor was calculated from the titration results. The reactor effluent was collected in the traps, measured at various intervals, and the reaction rates calculated. The measured rate at intervals over the 100 hours is shown in the Table. The data show no decrease in activity over the 100 hour run, and perhaps show some increase in activity during that period. This indicates good long term life for the CuBr₂/LaBr₃/Zr0₂ catalyst.

Example 2

This example shows the use of the preferred CuBr₂/LaBr₃/Zr0₂ catalyst in the temperature range between 5 150°C and 350°C.

The catalyst was tested as in Example 1; again, the rate of 48% HBr feed was 6 cc/hr, and the rate of 0₂ feed was 6 cc/min. The temperature was varied to produce bed temperatures ranging from 150° to about 350^βC. 10 Figure 4 shows the average reaction rates for the catalyst as a function of temperature for a 2 hour test.

Example 3

This example shows the use of an homogeneous

15 catalyst system for conversion of HBr to Br₂. A 250 ml Fisher-Porter bottle equipped with an overhead stirrer was charged with 30 g Cu₂Br₂ (as catalyst) and 110 ml of 48% HBr. The assembly was placed in an oil bath and brought to about 135°C. The stirring rate was 750 rpm.

20 Anhydrous HBr was metered to the reactor at 350 ml per minute and 0₂ was fed at 750 ml per minute. The total pressure was maintained at 50 psig. A gas stream continuously stripped any Br₂ formed in the system, which Br₂ was trapped downstream using a KI trap. The trap

25 operated to detect the amount of Br₂ formed in the reactor by reacting with the Br₂ to form the I₃" ion. The I₃ ^~ ion was titrated with NaS₂0₃ and the amount of produced Br₂ was calculated using the result. The traps were checked about every ten minutes. Figure 5 shows the rate

³⁰ of Br₂ production as a function of time. This example shows the effectiveness of the catalyst in oxidizing HBr to Br₂.

This invention has been described using

"3 C examples to show preferred embodiments. It will be^' apparent to those skilled in the art that modifications and changes may be made which still fall within the spirit and scope of the attached claims.

Claims

WE CLAIM AS OUR INVENTION:

1. A process for producing Br₂ from bromide salts comprising the steps of: a. acidifying an alkali metal bromide stream with sulfuric acid to form a HBr reactor feedstream, b. contacting the HBr reactor feedstream and an 0₂-containing gas with a catalyst composition to convert at least a portion of the HBr to Br₂ and produce a reaction effluent stream, and c. recovering the Br₂ product.

2. The process of claim 1 where the catalyst composition comprises an active catalyst selected from the metals, and oxides, halides, and oxyhalides of the following metals: Group IB, Group IVB, Group VB, Group VIB, Group VIIB, Group VIII, and the rare earth lanthanides series.

3. The process of claim 2 where the catalyst composition additionally comprises an optional promoter and a catalyst support selected from MgO, A1₂0₃, Zr0₂, Hf0₂, Si0₂, bentonite, attapulgite, and pumice.

4. The process of claim 2 where the catalyst composition is an homogeneous liquid.

5. The process of claim 3 where the catalyst composition comprises copper bromide, a promoter, and an oxidic zirconium-containing catalyst support.

6. The process of claim 5 where the copper bromide content of the catalyst composition is within the range of about 0.1 % to 20 % by weight.

7. The process of claim 6 where the overall copper bromide content of the catalyst composition is within the range of about 1 % to 10 % by weight.

8. The process of claim 7 where the overall copper bromide content of the catalyst composition is within the range of about 0.1 % to 6 % by weight.

9. The process of claim 5 in which the promoter is selected from compounds or complexes of Ca, Y, Nd, or La.

10. The process of claim 9 in which the promoter is a lanthanum-containing compound comprises lanthanum bromide, lanthanum oxybromides, or a mixtures thereof.

11. The process of claim 5 in which the zirconium- containing catalyst support comprises zirconia.

12. The process of claim 10 in which the zirconium- containing catalyst support comprises zirconia.

13. The process of claim 11 where the catalyst's x-ray diffraction graph shows substantially no peak at 2Θ = 14.485°.

14. The process of claim 11 in which the porosity of the zirconia is greater than about 0.01 cc/gm pore volume in the range of about 30-100 A pore diameter.

15. The process of claim 5 in which the molar ratio of HBr:0₂ is between about 3.25 and 4.1.

16. The process of claim 15 in which the molar ratio of HBr:0₂ is between about 3.9 and 4.0.

- 5- 17. The process of claim 1 in which the Br₂ product recovery is effected by quenching the reaction effluent in a quench stream containing HBr and removing unreacted HBr, absorbing Br₂ from the quenched reaction effluent in a stream containing NaBr to form a Br₂ absorbate stream, desorbing Br₂ from the Br₂ absorbate stream and a water phase, decanting Br₂ from the water phase to produce a Br₂ product stream.

18. The process of claim 17 additionally comprising the step of drying the Br₂ product stream by contacting it with strong H₂S0₄.

19. A process for producing Br₂ from an alkali metal salt stream comprising the steps of: a. acidifying the alkali metal salt stream with sulfuric acid and forming a HBr reactor feedstream, b. contacting the HBr reactor feedstream with an o₂-containing gas in a molar ratio of HBr:0₂ between about 3.25 and 4.1 with a catalyst composition comprising copper bromide in an amount such that the overall copper bromide content of the composition is within the range of about 1 % to 10 % by weight, a lanthanum-containing compound selected from the group of lanthanum oxide, lanthanum bromide, lanthanum oxybromides, or mixtures thereof, and a zirconia catalyst support, under catalytic conditions sufficient to convert at least a portion of the HBr to Br₂ and produce a reaction effluent stream, c. quenching the reaction effluent in a quench stream containing HBr and removing unreacted HBr, d. absorbing Br₂ from the quenched reaction effluent in a stream containing NaBr to form a Br₂ absorbate stream, e. desorbing Br₂ from the Br₂ absorbate stream, and f. decanting Br₂ from a water phase of produce a Br₂ product stream.

20. The process of claim 19 additionally comprising the step of drying the Br₂ product stream by contacting it with strong H₂S0₄.