Recovery of bromine from organic bromides
United States Patent 1 Davis Apr. 1, 1975 1 1 RECOVERY OF BROMINE FROM ORGANIC BROMIDES [75] Inventor: Ralph A. Davis, Midland, Mich.  
 [73] Assignee: The Dow Chemical Co.,- Midland,  
 Mich.  
 [221 Filed: Dec. 7, 1970 [21] Appl. No.1 95,883  
 [52] US. Cl 423/481, 260/654 1),,260/656 R [51] Int. Cl COlb 7/12 [58] Field of Search .1 23/154, 216; 260/656 R,  
 [56] References Cited UNITED STATES PATENTS 12/1935 Arnold et a1 260/668 R 4/1950 Bordncr 260/656 R X 2.803.669 8/1957 Brainerd, Jr. et a1. 23/154 X 2,886,605 5/1959 McClure et al. 260/656 R X 3.125.608 3/1964 McDonald 3,310.380 3/1967 Lester 3,705.010 12/1972 Davis et a1. 423/502 Primary E.\-aminerEdward Stern Attorney, Agent, or Firm-Robert W. Selby [5 7] ABSTRACT 34 Claims, N0 Drawings RECOVERY OF BROMINE FROM ORGANIC BROMIDES BACKGROUND OF THE INVENTION Certain parts of the world, in which there is a shortage of bromine, find it necessary to import this useful halogen either in the elemental form or as HBr. A major use for bromine is in the preparation of methyl bromide. A convenient method of preparing methyl bromide is by the high temperature reaction of methyl alcohol and HBr in the presence of acontact catalyst. In order to carry out such a process, a ready supply of HBr is desirable. Bromine poor areas import HBr, or bromine for conversion to HBr; but such importation is complicated by the fact that bromineand HBr are corrosive thereby requiring special vessels during shipment.  
  Organic bromides, such as ethylene dibromide, are non-corrosive, and can be transported as any other liquid such as by pipeline or in the hold of a tanker. In order for the transportation of organic bromides as bromine sources to be economical, a convenient method for recovering the bromine values in a useful form is necessary. Regardless of the problems encountered in transporting bromine and HBr, an improved method of recovering bromine values from excess organic bromides would be desirable.  
  Ethylene dibromide can be thermally cracked to provide vinyl bromide and HBr; however, even at 100% conversions, only one molecule of HBr is produced per molecule EDB cracked. In order to recover the maximum amount of bromine as HBr, a catalyzed reduction with H: is necessary. It has been reported that chlorobenzenes have been reduced with a nickel at temperatures of 270 C and above. In this process there is a constant loss of nickel due to the vapor pressure of nickel halides as these higher temperatures and the catalyst is rapidly depleted.  
  It is an object of the present invention to provide a novel method for the recovery of the bromine values of organic bromides. An additional object is to provide such a method in which the bromine values are recov ered as HBr.  
  It is an additional object to provide such a method which results in a larger percentage of bromine being recovered than does the uncatalyzed thermal cracking of organic bromides.  
  A further object is to provide such a method which employs as a catalyst a composition which does not form halides which are highly volatile under the conditions of the reaction.  
 SUMMARY OF THE INVENTION The present invention involves a method for the recovery of bromine values from organic bromides. The process involves reacting the organic bromide with hydrogen at a temperature within the range of from 300 to 600 C in the presence of a suitable catalyst. Examples of suitable catalysts are the oxides of chromium, vanadium, tungsten, cerium, molybdenum or aluminum.  
 DESCRIPTION OF PREFERRED EMBODIMENTS Preferred organic bromides for use as bromine sources are those aliphatic bromides containing up to six carbon atoms. Aromatic bromides, having bromine attached to either the ring, or side chain in the case of alkaryl bromides, are operable. Those alkaryl bromides containing up to 9 carbon atoms are preferred. Selection of organic bromides containing more than the preferred number of carbon atoms, while providing an operable process, results in rapid accumulation of tars in the reaction zone. Organic bromides having only one or two carbon atoms, e.g., ethylene dibromide and methylene bromide are especially useful bromine sources. Examples of other aliphatic bromides which may be employed in the process as bromine source materials are monoor poly-brominated hexanes, pentenes pentynes, cyclobutanes, propanes, and propenes. Aromatic bromides useful in the process are, for example, the monoor poly-brominated benzenes, toluenes, ethylbenzenes, dipropyl benzenes, diphenyls, and napththalenes.  
  In one mode of practicing the invention, the catalyst bed is heated to the desired reaction temperature and the gaseous organic bromide/hydrogen mixture is contacted with the catalyst, as by flowing the mixture through the catalyst bed. The catalyzed reaction results in the bromine values of the organic bromide being converted to readily usable HBr. For substantially complete conversion to I-IBr, the reaction should be carried out at a temperature of from 400 to 600 C, with an excess of hydrogen of at least about 0.55 mole hydrogen per mole of&#39;bromine contained in the organic bromide, e.g., a mole ratio of H /organic bromide of at least about l.l/l should be used when ethylene dibromide (EDB) is the bromine source and substantially complete conversions are desired. Residence times of 5 to 60 seconds are preferred under the reaction conditions set out above. If some intermediate bromides are desired as byproducts, e.g., CH CI-IBr from CH BrCI-I Br or CH -,Br from CHZBIQ, lower mole ratios of hydrogen to organic bromide and lower temperatures are used. Temperatures above 550 C increase the amount of carbon formation on the catalyst making relatively frequent regenerations necessary. Accordingly a reaction temperature of from 400 to 550 C is preferred for maximum conversion to HBr with maximum catalyst life.  
  The metal oxide catalyst is normally a combination of two or more of the oxides of chromium, vanadium, tungsten, cerium, molybdenum or aluminum. As is the case with the use of metal oxides as cracking catalysts, the major component supports the minor component upon which it has been placed by impregnation. Commercially available metal oxide cracking catalysts may be used in the practice of the invention. A chromia/alumina catalyst with chromia comprising from 5 to 50 weight.percent of the combination is preferred. The catalyst may contain substantial amounts of inactive ingredients in addition to the metal oxides. Other useful metal oxide combinations are V 0 supported by AI O CeO supported by A1 0 and Cr O V 0 supported by A1 0 As is the case with most gas phase catalyzed reactions, a catalyst having a high sur face area is desirable. Those metal oxide catalysts having a BET surface area of from 25 to m lgm. are preferred.  
  The oxidation state of metal oxide is not critical. All of the known oxides of aluminum, chromium, vanadium, molybdenum or tungsten may be used as catalyst. Examples of such oxides are A1 0 Cr- O V 0 V205, M003, M0303, M0205, M002, ceog, W02, W203,  
 and W Under the reaction conditions, the metals will be reduced to their lowest oxidation state.  
  The invention is further illustrated by the following examples.  
 were reacted at 500C. The mole ratio (H- CH- Brwas 1.05 and the reactor temperature was 500C. The flow rate was adjusted to provide a residence time of seconds. The HBr recovered from the water scrubber Exam es 1 5 5 was 0.966 M or 84.5% of the bromine fed. Eight grams p of methyl bromide containing a trace of CH Br were A 4 Inch by 30 In Vycor tube as p k Wlth recovered from the dry ice trap. This calculates to 5/32 inch diameter pellets ofa chromia-alumina crack- 0084 M&#39; 74% f h b i f d i i a total b ing catalyst. The catalyst consisted of 19 weight peri recovery f 91 99 7 TABLE I Moles /1 Conversion to Example Furnace Moles Fed H2/EDB Residence Moles C .H -,Br+ C H -,Br+ /1 Bromine No. Temp 0C H2 EDB Mole Ratio Time See HBr C H Br HBr C. -H;,Br Recovery (pure z a l The analysis of this material was X1; \&#39;in \l bromide and 19&#39;&#39;) ethyl bromide. In addition to this cold trap material 16 gr.. 0.085 M. of ED]! representing 0.17 M of HBr were reemered from the air cooled trap and scrubber unreacted. Furnace packed with vyeor rings no catalyst. Actual total comersion o1 EDI! to HBr \\&#39;as 389.  
 cent Cr O supported by A1 0 which accounted for the balance. The catalyst had a density of 60 lb/ft and a BET surface area of 60 m /gm. The tube was heated over 24 inches of its length with an electric resistance furnace.  
  Ethylene dibromide was introduced into the top of the reactor from a dropping funnel and hydrogen was metered through the reactor just above the furnace. The exit gases passed through an air cooled trap, a water scrubber, a calcium chloride drier and a dry ice cooled trap.  
  With the furnace controlled at 520 C, ethylene dibromide (l 18 gm., 0.627M) and H (0.90M) was passedthrough the reactor in 2 hours and 20 minutes. This gave a mole ratio (H /EDB) of 1.43 and a residence time of 14 seconds.  
  Analysis of the scrubber solution showed that 1.19 moles of HBr had been formed. Chromatographic analysis of the 3.5 gm. ofliquid found in the dry ice trap indicated that it was mainly ethyl bromide (80%) and vinyl bromide (20% The bromine recovery was as follows:  
 HBr 1.19 M 94.97! C -H -,Br .032 M 2.6%  
  (as HBr) C. .H ,Br .008 M .57!  
  (as HBr) Total Br recovery 98.0%  
  The gases passing through the cold trap were analyzed by mass spectroscopy and found to be CH =CH with a small amount of ethane and CH =CHBr and CH CH Br as minor components. Table I summarizes the results of five runs made in the above-described manner.  
 Example 6 Methylene bromide, CH BR- was also reacted with hydrogen using the equipment and catalyst described in Example 1. The procedure was as follows:  
 Methylene bromide, 0.57 mole, and H 0.6 mole,  
 What is claimed is:  
  l. A process which comprises reacting an organic bromide with hydrogen at a temperature within the range from about 300 to about 600C. in the presence of a catalyst, said catalyst being selected from two or more of the oxides of chromium, vanadium, tungsten, cerium, molybdenum or aluminum; and separating HBr from the reaction product.  
  2. The process of claim 1 wherein the catalysts are selected from the group consisting of Cr- O A1 0 V 0 M00 M0 0 M0 0 M00 CeO W0 W 0 3. The process of claim 1 wherein the catalysts are selected from the group consisting of A1 0 Cr O- M00 W 0 4. The process of claim 1 wherein the organic bromide is an aliphatic bromide containing up to six carbon atoms or an aromatic bromide containing up to nine carbon atoms.  
  5. The process of claim 1 wherein the organic bromide is ethylene dibromide or methylene bromide.  
  6. The process of claim 1 wherein the reaction is carried out at a temperature of from 400 to 550C.  
  7. A process which comprises reacting an organic bromide with hydrogen at a temperature within the range of from about 300 to about 600C in the presence of a catalyst, the catalyst being a mixture of the oxides of chromium and aluminum; and separating l-lBr from the reaction product.  
  8. The process of claim 7 wherein the organic bromide is ethylene dibromide or methylene bromide.  
  9. The process of claim 7 wherein the catalyst is a mixture of A1 0 and Cr O 10. The process of claim 9 wherein the organic bromide is ethylene dibromide or methylene bromide.  
  11. The process of claim 10 wherein the reaction temperature is from 400 to 550C. and the mole ratio of H /organic bromide is at least about 1.1/1.  
  12. The process of claim 11 wherein the metal oxide catalyst has a BET surface area of from 23 to m /gm.  
  13. The process of claim 1 wherein the organic bromide has a resistance time in the heated reaction zone of from 5 to 60 seconds.  
  14. The process of claim 1 wherein the catalyst has a BET surface area of from to 100 m /gm.  
  15. The process of claim 11 wherein the catalyst is a mixture of A1 0 and Cr O the organic bromide is ethylene dibromide or methylene bromide and the temperature is within the range of from 400 to 550C.  
  16. The process of claim 9 wherein the organic bromide is an aliphatic bromide containing up to six carbon atoms or an aromatic bromide containing up to nine carbon atoms.  
  17. The process of claim 9 wherein the reaction is carried out at a temperature of from 400 to 550 C.  
  18. The process of claim 9 wherein the organic bromide has a residence time in the heated reaction zone of from S to 60 seconds.  
  19. The process of claim 9 wherein the catalyst has a BET surface area of from 25 to 100 m /gm.  
  20. A process for recovering bromine as HBr from aliphatic organic bromides which comprises reacting the organic bromide with hydrogen at a temperature within a range from about 300 to about 600 C. in the presence of a mixture of alumina and a catalytic amount of chromia; and separating the HBr from the reaction product.  
  21. The process of claim 20 wherein the aliphatic organic bromide contains up to 6 carbon atoms.  
  22. The process of claim 21 wherein the organic bromide is ethylene dibromide.  
  23. The process of claim 21 wherein the organic bromide is methylene bromide.  
 24. The process of claim 20 wherein the reaction is carried out at a temperature of from 400 to 550 C.  
  25. The process of claim 24 wherein the mole ratio of H to organic bromide is at least about 1.1 l.  
  26. The process of claim 20 wherein the catalyst has a BET surface area of from 25 to m /gm.  
  27. The process of claim 20 wherein the organic bromide has a residence time in the heated reaction zone of from 5 to 60 seconds.  
  28. A process which comprises reacting an organic bromide with hydrogen at a temperature within the range from about 300 to about 600 C. in the presence of a catalytic amount of a catalyst selected from one or more of the oxides of chromium, vanadium, tungsten and molybdenum; and separating HBr from the reaction product.  
  29. The process of claim 28 wherein the catalyst is selected from one or more of the oxides of chromium, tungsten and molybdenum.  
  30. The process of claim 28 wherein the catalyst is in contact with a supporting surface.  
  31. The process of claim 28 wherein the catalyst is supported by aluminum oxide.  
  32. The process of claim 20 wherein the chromia comprises from 5 to 50 weight percent of the mixture.  
  33. The process of claim 32 wherein the chromia is (31 20 34. The process of claim 22 wherein at least 1.] moles of hydrogen is reacted with 1 mole of ethylene dibromide at a temperature within the range from 400 to 600 C. in the presence of a catalytic mixture of alumina and from 5 to 50 weight percent chromia, the catalyst having a BET surface area of from 25 to 100 m /gm.  
  UNITED STATES PATENT OFFICE CERTEHCATE OF CORRECTION PATENT NO. 3,875,293  
 DATED 1 April 1, 1975 INVENTOR(S) 1 Ralph A. Davis it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:  
 (201. 1, line 31, after &#34;molecule&#34; insert --of--;  
 C01. 1, line 37, change &#34;as&#34; to at--;  
 Cal. 3 line 39, change &#34;was&#34; to --were-;  
 Cclm 4, line 66, change &#34;23&#34; to 25---;  
 C01. 5, line 2, change &#34;resistance&#34; to --residence--.  
 Signed and sealed this 15th day of July 1975.  
  (SEAL) Attest:  
  C. MARSHALL DANN RUTH C. MASON Commissioner of Patents Attesting Officer and Trademarks