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Патент USA US2404800

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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.
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