Патент USA US2404800код для вставки
Patented July 30, 1946 2,404,800 UNITED‘ STATES PATENT OFFICE ] PROCESS FOR THE PRODUCTION OF ALKYL ‘ BROMIDES Wilhelm .Hirschkind, Berkeley, =Oalif.,. assignor to The Dow Chemical Company, Midland, Mich, a corporation of Michigan Application January 31, 1944, Serial No. 520,487 4 Claims. 1 This invention relates to the manufacture of alkyl bromides, such as methyl bromide and ethyl bromide. ‘The’ usual process for making alkyl bromides is by the reaction of hydrobromic acid and the corresponding monohydric alcohol in the ‘presence of a dehydrating agent, such as sulphuric acid. An improvement on the conven tional process is described in U. S. Patent No. 2,l73,l33,'in- which ‘the hydrobromic acid to be (Cl. 260-657) The mixture is then added-to the alcohol, e. g. methyl alcohol, whereby HBr reacts with the al cohol according to the equation <2) ‘ ' HBr+oH3oHzcH3Br+H2o vformingymethyl bromide and water. The water so formed reacts in ‘turn with the sulphur and excess bromine which is present according to‘the equation ' 3 reacted with the alcohol is formed in situ by re action ‘of S02 and bromine. The latter‘process is successfullyused commercially, but is subject and this additional \H'Br also reacts, with thee! to a practical limitation in requiring the use of cohol according to Equation ‘2. forming methyl bromide. A summation of the foregoing reac S02‘ of a high ‘degree of concentration, which is not readily available at many ‘locations. It is 16 tions is expressed by the following equation; , desirable to enable volatile alkyl bromides to be made by a process having the advantages of the process of Patent No. 2,173,133, but without re quiring a plant for making concentrated S02 at the same vlocation. 'It is,itherefore, an object of the present in vention to provide a process for making alkyl bromides from the corresponding alcohols and In carrying out the process the reagents are preferably employed in approximately the pro portions shown by Equation 4. ‘It is seen that only one mo] ofHzS is requiredfor formation of 8 mols of CHaBr. Water and H2SO4 ‘produced hydrobromic acid, wherein the latter is formed in situ during the process, which process is free in the reaction are in proportions'such as‘to form from limitation as to an available source of con centration. The simultaneous formation of sul phuric acid. is advantageous, in that the acid acts as a dehydrating agent for the esteri?ca centrated S02. ' A further object is to obviate the necessity for employing ‘$02 in such process. Another object is to enable volatile alkyl bro .mides to be produced by a continuous process with minimum consumption of raw‘ materials. a solution of H2SO4 of abouts’? per cent con ‘ tion-of the alcohol, which is required to secure an equilibrium condition favorable to a high per centage yield of alkyl bromide. The acid solu tion thereby formed is not of sufficient strength to cause any. substantial ‘dehydration of the al Still another object is to provide a continuous cohol to form the corresponding ether as an un process for making methyl bromide or ethyl bro desired by-product. ‘For the reaction anhydrous ‘ mide of a high degree of purity. alcohol is preferred, although it may contain up In a co-pending application of David J. Pye, to about 5 per cent of water without material Serial No. 520,486, ?led Jan. 31, 1944, a process disadvantage, so long as the strength ‘of the re of the present general character is ‘disclosed, in sulting acid solution is not reduced below about which sulphur and bromine are reacted in the presence of an aliphatic alcohol whereby hydro- 4‘ 50 per cent. The process can be carried on as a batch ‘ope bromic acid is formed in situ and in turn reacts eration. It is well adapted to continuous opera with the alcohol to form the alkyl bromide. The tion, in which the reaction mixture of HzS and present invention is a modi?cation of the process Brz is introduced into a rectifying column and described in the said co-pending application, in which hydrogen sulphide is employed instead of " there intermixed with ‘an in?owing stream of alcohol. The volatile alkyl bromide'is continu sulphur to obtain certain additional advantages, as will hereinafter appear, ‘ ously removed as vapor overhead, while the acid According to my invention hydrogen sulphide solution is withdrawn at the bottom. Such con tinuous mode of operation is more particularly is reacted with bromine. to‘form hydrobromic acid, as shown by the equation; ‘ ‘ described in connection with the annexed draw ing, in which the single ?gure is a diagrammatic representation of a suitable apparatus and also An excess of bromine is. employed which dis serves as a ?ow-sheet of materials in process. solves the sulphur formed in Equation land pre Referring to the drawing, bromine is admitted vents its precipitation in the reaction mixture. by pipe I to a supply tank 2, whence it'is for 2,404,300 3 4 traces of the alkyl ether, and occasionally HBr warded by pipe 3 to a reactor 4 packed with Raschig rings of ceramic material or the equiv alent. Hydrogen sulphide gas is admitted to re actor 4 through pipe 5. In reactor 4 the bromine or bromine, are conducted to a purifying system comprising an alkali scrubber 2G and a-drier 2|, and thence to a condenser 22. In scrubber 20 the vapors are washed with an aqueous solution of an alkali metal hydroxide or carbonate to remove acid impurities, the alkalinesolution being and hydrogen sulphide react according to Equa tion 1 supra, forming hydrogen bromide and sul phur, a suf?cient excess of bromine being used to hold the sulphur in solution. Preferably the pro pontions of bromine and hydrogen sulphide are 4 circulated by pump 23 and pipes 24 and 25. The scrubbed vapors then pass through pipe 26 to mols of the former to one mol of the latter, as“ 10 .drier 2|, which conveniently is of the adsorption type charged with silica gel or equivalent ad shown in Equation 4 supra. The reaction mix-rv sorbent, which removes water vapor and traces ture of I-IBr and S dissolved in excess bromine of ether. From the drier the vapors pass'to con flows through pipe 6 to column ‘I, entering the latter preferably at a point about one-third of? ' denser. 22, cooled by a refrigerant solution, and thefcondensate to storage tank 21. the height from the bottom. The alcohol, e. g.’ When the product of the process is methyl methanol or ethanol, is supplied through pipe 8 to a feed tank 9, from which it, is fed through ; - bromide, the above described puri?cation steps ' may be carried out at ordinary temperature with- > pipe H] to column‘! at a point preferably some out causing condensation of the methyl bromide what above the mid-section. ' Column 1 is provided’ with a packing of acid- - resistant material, such as Raschig rings ‘or the like.‘ At the bottom it communicates with a still lower part of column '1. the same in the scrubber or drier, conveniently 25 Steam connections are provided to the jacket of still I I, which isdrained through pipe l3. ' r I ' In the case of ethyl bromide suf?cient ' heat may be added to prevent condensationqof by scrubbing with an alkaline solution warmed. to a temperature above the boiling point of ethyl; H having a steam jacket or other means for heating the same. A vapor? tube Ilserves to conduct vapors from the top of still ll into the vapors. ' bromide. V .7 ' , -' j- ,a $1 The herein- described process, when carried out‘ in the continuous manner as shown,is.particu- ' larly advantageous for the reason that the con-f tinuous removal of end productsii. e; alkyl bros The mixture of bromine, sulphur and HBr in troduced into column 1 through pipe .6 is com-. 30 mide 'and'sulphuric acid solution, from the ;r,e_a,c,-, tion "zone constantly' maintains therein a, con mingled therein with the alcohol introduced dition essential for a substantially quantitative through pipe- l0 and ?owing downwardly over yield of alkyl bromide. ' l .— the packing; Reaction occurs with liberation of As a typical example showing results obtainable heat in accordance'with Equations 2 and 3 supra. Water formed by the esteri?cation reaction (2) 35 in the practice of the invention in an apparatus supplies the water requirement for reaction (3). The vaporizable components and products of the reactions whichoccur ‘simultaneously in the col umn are continuously recti?ed therein,‘th'e high est boiling'fraction being a sulphuric acid solu 40 similarto that described, bromine and hydrogen tion which‘ flows outat thebottom into the still, solved sulphur and HBr is fed into a column in sulphide are continuously added to a ?rst reactor at the rate of 421 pounds (2.63 mols) per hour and 22.4 pounds (0.65 mol) per'hour, respectively. The resulting mixture of bromine containingdis which it is intimately contacted with methanol introduced thereinto at the rate of 166.7 pounds pipe I4 at the top. By regulating the flow of (5.195 mols) per hour. The temperature within materials into'the column approximately accord; ing to the molar proportions given in Equation 4 45 the column is maintained by the heat-of reaction while a vapor fraction passes offv through vapor supra, the H2SO4 solution in still H will have a strength of about 57 per cent.’ The acid solu tion in still H is heated to boiling to expel any amounts of bromine and HBr that are dissolved plus the heat added to the still to hold the sul phuric acid solution therein at .itsboiling point of approximately 135° C. The temperature'gra dient of the column varies from 135° C.‘ at the therein, the vapors being returned to the column. 50 bottom to about 75° C. in the reaction zone at about the midpoint to 5°C. at the top ofthe col umn, where the low temperature is held by re flux of methyl bromide. The overhead vapors through outlet 13. The rate of feed of materials from the top of the column are 1100, pounds into the'column 1‘ is adjusted to establish the desired alkyl bromide production rate. The. re 55 (11.58 mols) per hour of which 616 pounds (6.49 mols) are refluxed and 484.5 pounds (5.09 mols) ?ux returned through line It is adjusted to main; are taken on as product, the yield being approxi tain a de?nite reaction zone between inlet It and mately 97 per cent of theory. ' t ‘ . a point slightly below inlet 6. Similar results are obtained in the production The volatile reaction product rises toward the’ top of the column, operation of which is ‘con 60 of ethyl bromide from ethanol, for which pur pose ordinary 95 per cent ethyl alcohol can be trolled by means of re?ux topermit the escape , As the acid ‘solution accumulates in the still it_ is V_ withdrawn, continuously or V intermittently overhead through pipe 14 of vapors consisting substantially of'pure alkyl bromide. To provide suitable reflux the overhead vapor stream is di vided, a portion being directed to a condenser l5 from which the condensate is returned to the top of column 1 as re?ux through pipe _l 6. The other portion of vapors is carried o? through pipe 11 to a puri?cation and condensation system. used with very nearly as good yield as with an- . hydrous ethanol. Iclaim: ' ‘ ' ' 1. A process for making an alkyl bromide which, comprises causing a reaction between hydrogen sulphide, bromine and 'a monohydric aliphatic alcoholv selected from the group consisting of methanol and ethanol in approximately the mo; The proportioning of the overhead vapors as re 70 lecular proportionsgiven by the equation;v ?ux and product is controlled by means of valves I 8 and I9. The product vapors in pipe H, which‘ under proper‘operation consist of the alkyl bromide to the‘ extent of more than 99 percent, but contain ‘ 2. Process according to claim 1 in which the alkyl bromide product is continuously distilled fromv the reaction mixture, and the resulting 2,404,800 0 aqueous sulphuric acid solution is continuously removed from the reaction zone, 3. A process for making an alkyl bromide which comprises reacting hydrogen sulphide with a mo 6 tions of approximately 1 mol of the former to 4 mols of the latter, ?owing the intermediate reac tion product thereby obtained into a reaction zone wherein it is intimately contacted with a stream lecular excess of bromine to form an intermediate U! of a monohydric aliphatic alcohol selected from product composed of hydrogen bromide and sul the group consisting of methanol and ethanol in phur dissolved in the excess of bromine, inter relative proportion of approximately 8 mols of mixing such intermediate product with a mono the alcohol, maintaining the reaction at a tem hydric aliphatic alcohol to form the correspond perature sufficient to vaporize the resulting alkyl ing alkyl bromide and separating such bromide 10 bromide as formed, continuously removing the from the reaction mixture. alkyl bromide vapors under re?uxing conditions, 4. A continuous process for making an alkyl and continuously withdrawing aqueous sulphuric bromide which comprises continuously reacting acid solution from the reaction zone. hydrogen sulphide with bromine in the propor WILHELM HIRSCHKIND.