Note: Descriptions are shown in the official language in which they were submitted.
V39
This invention relates to a method for the
reduction of ferric chloride.
More particularly this invention relates to
a method for the partial dec~lorination of ferric
5 chloride to ferrous chloride in the presence of one
or more suitable reducing agents.
According to a particu]ar aspect of this
invention the partial dechlorination of ferric chloride
is a step in a method for the recovery of the chlorine
10 values from iron chloride obtained as a by-product, for
example, from the chlorination of a titaniferrous material
containing more than 5% by~eight iron oxide such as
ilmenite, or obtained as a by-product from the chlorination
of an aluminous material, such as bauxite.
United States Patent No, 41407ll6 describes a
process ior the recovery of the chlorine values Lrom
iron ch]oride obtained as a by-product from the chlor-
ination of a titaniferrous material cont~ining more than
5% by weight iron oxide which comprises the steps of:
(a) subjecting ferric chloride to partial
dechlorination in the presence of one or more suitable
reducing a~ents to produce ferrous chloride and a chloride
compound;
(~) subjecting ferrous chloride to an oxidation
"~ reaction in the presence of oxygen or a molecular ox~en-
11~0039
containin~ ~as at a temperature between 300C and
1200C to produce ferric chloride and ferric oxide; and
(c) recycling the resulting ferric chloride to
the ~artial dechlorination step (a).
Similar methods for recovering the chlorine
values from iron chloride are disclosed in Canad~an
application No. 327,367 relatin~ to iron chloride by-
produe~d in thc chlorination o~ an aluminolls material
e.g. bauxite.
In those processes, a suitable reducin~
agent for ~age (a) is defined as one which meets t~le
two following conditions: ~irst that it is effective in
dec}llorinating ferric chloride to ferrous chloride;
second, that in reaction wit~ ferric chloride, it produces
15 a chlolide compound which, directly or after further
processin~, is either suitable for recycle to the
chlorination process (if appropriate) or has other
industrial utility.
One such suitable reducin~ agent described
20 in the United States Patent No. 4140746 and
Canadian Application No. 327,367 is sulphur, and the
method o~ usin~ it was summarised in the followin~
equation (1):-
Fe2C16(s) + 2S(l)--~FeC12(s) + S2C12(~)....(1)
5 (where (s) represents solid, (1) represents liquid andtg) r~presents gas).
~0039
--4--
Thus in equation (1) liquid sulphur is
reacted with solid ferric chloride to produce solid
ferroujchloride and gaseous sulphur monochloride.
The method of using sulphur as the reducing
5 agent for ferric chloride, which is summarised in
equation (1), has been established experimentally as
an effective and successful procedure. Howe~er, it
has two major drawbacks. First, it requires that the
ferric chloride produced in the oxi~ation stage (b)
is condensed from the ~as stream, which is a costly
an~ elaborate procedure. Second, the equipment required
for contacting and mixing liquid sulphur with solid
ferric chloride is, again, costly and elaborate.
It has now surprisingly been found that the
15 reaction represented by equation (1) can be carried out
much more conveniently and advantageously using gaseous
sulphur or a gaseous sulphur chloride in which the atomic
ratio of the sulphur to chlorine is more than 1:1.
The fact that this reaction can be successfully
~0 carried out is surprising because the literature sug~ests
that sulphur monochloride is increasingly decomposed
into sulphur and chlorine as its temperature nses, until
at the boiling point of sulphur (444C) it is iully
decomposed. Thus the use of gaseous su]phur or ~aseous
sulphur chloride in which the atomic ratio of sulphur to
ll~Q039
chlorine is more than 1:1 to produce sulphur monochloride
and ferrous chloride by reaction with l'erric chloride
did not appear promising.
Nevertheless, it has been found that sulphur
5 or gaseous sulphur chloride in which the atomic ratio
of sulphur to chlorine is more than 1:1 is an effective
reducin~ agent for ~aseous ferric chloride, particularly
when used in a gas fluidised bed of solid ferrous chlorde.
Thus, the present invention provides a method
10 of reducing ferric chloride to ferrous chloride wherein
ferric chloridc in ~e gaseous or solid statc is partially
dechlorinated in the presence of gaseous sulphur or a
gaseous sulphur chloride in which the atomic ratio of
sulphur to chlorine is more than 1:1 to form ferrous
15 chloride in the solid state in accordance with the following
reaction equations:
Fe2cl6(g/s) + S2(g)--~ 2~eC12(s) ~ S2C12(g) --(2)
2-z~e2C16(g/S) + S5C12(g)--~ 5FeC12(s) + 2-1-S2C12(g)..(3)
In these equations, the second term in equation
2~ (3) represents an example of a sulphur chloride on which
the atomic ratio ~ sulphur to chlorine is more than 1:1.
In practice a ~aseous mixture of S2Cl" and S may be employed
as the sulphur chloride.
The method according to the present invention is
particularly suited to be the partial dechlorination step
(a) of' a method for the recovery of -tlle chlorine values
1110~39
~,
from iron chloride,
Thus the ferric chloride input to the method summarised
in equations (2) ~md (3) preferably deri~es from the
processes disclosed in United States Patent No. 4140746
and Canadian Application No. 327,367. However, the present
invention is not limited to ~erric chloride derive~
from any ~articular source,
The reaction between ~seous sulphur/gaseous
sulphur chloride and ferric chloride is preferably
carrie~ out in a fluidised bed of (product) ferrous
chlori~e, The be~ temperature should be at least
suf~icient to maintain the sulphur or sull)hur chloride
in the gas phase, The actual minimum temperature for
this purpose will vary with the composition of the
source of sulphur values and with thc 4uantity of any
inert ~ases present in thc n~ctor, Thus the overall
temperature limits for the reaction are ~)etween 120C
and 650C, preferably between ~()0C aJId ~50C and more
particularly between 300C and 450C,
Alternatively, a stirred hed ~actor or a rotary
kiln coul(l be used. The reaction is prcferably carried
out continuously,
The sulphur ~alues, either as elemental
sulphur or as a sulphur chloride in which the atomic
ratio of sulphur to chlorine is more than 1:1, are
1~10039
preferably introduced to the reactor as a gas, but
may a1so be introduced as a liqui~l in which case
the liquid is immediately gasified by contact with
the hot reaction bed prior to reaction of the sulphur
chloride with the ferric chloride.
The ferric chloride is preferably introduced
to the reactor as a gas, but may also be introduced
as a solid.
The off-gas from the reactor is preferably
condensed to a liquid and centrifu~ed to remove solid
lO particles (ferric and ferrous chlonde). The resulting
sulphur chloride, which is predominantly S2Cl2, may then
be treated by various methods depending on the industrial
circumstances to the plant. If the ferric chloride feed
to t~le process accordin~ to the invention has been
15 obtained by a sulpho-chlorination process, for example
a bauxitc sulpho-ch10rination process, it is preferred
to recycle the S~C12 to the sulpho-cl-l~rination process.
However, if the ferric chloride feed has been
obtained by a carbo-chlorination process, for example
20 an ilmenite carbo-chlorination, it is preferred to
pass the S2Cl2 to a fractional distillation p~oce~s.
By fractional distillation, chlorine is recovered as the
overhea~ product an(l a sulphur chloride with between
60~/o and 80~o atomic percent sulphur i~ obtained as the
1~10C)39
bottom produet whieh ean then be reeyeled to the
re~uetion proeess aeeording to the invention.
Alternatively, the S2Cl2 obtained from the off-gas
may be reae~ed with earbon disulphide to produee earbon
tetraehloride whieh ean be used either for reeyele to
the earbo-elllorination reaetion or for sale to other
industrial l)rocesses, with the by-product sulphur being
rccyclcd to the re(llletion reaction: or the S2Cl2 product
may be reactc(l with carbon monoxide to produee phosgene
whieh may be recyeled to the earbo-ehlorination reaetion
or ~)assc(l f`or sale to other industrual proeGsses, with
the by-l)roduet sulptlur or sulphur ehloride being
recycle(l to -the reduetion reaction.
Where fraetional distillation is employed,
1~ it is preferred to perform the disti]lation in two
sta~cs. In a first sta~e S2Cl2 is fcd to a first
distillation eolumn whieh operates at atmospherie pressure
with an overhead temperature of between 2~3C an~ 60C
and a bottom temperature of between 140C and 180C
such that there are pro(iuced a swlphur-rich bottom
pro~uct an(l a ehlorine-rich overhead prolluct. The
bottom product which preferably contains between 60
and 8~3% atomie percent of sulphur is recycled for the
reductiorl oL ferric ehloride. In a second stage, the
chlorine-rich sulphur chloride overhead pro(luct
39
g
from the first distillation column is fed to a second
distillation column which is operated at a pressure of
about 10 atmospheres with an overhead temperature of
between 20C and 60C and a bottom temperature of
5 between 160C and 220C. Pure elemental chlorine is
produced as t~ overhead product and a sulphur chloride
in which the atomic ratio of sulphur to chlorine is
approximately equal is produced as the bottom product.
The chlorine overhead product can, for e~ample, be
10 recycled to the chlorination process from which the
ferric chlorisie was ob~ained and the s~lphur chloride
bottom product may be recycled to the first distillation
column.
Instead of the two-sta~e distillation process,
15 just described, a single-sta~e distillation process may
be employed although this is more energy intensive. In
~he sase of a single-sta~e distillation process~ it is
preferred to use an elevated pressure of about 10 atmos-
pheres, with an overhead temperature of bctween 20C
20 and 60C and a bottom temperature between 200C and
'40C to produce the same products as in th~ -two-stage
process.
The ferrous chloride bed overflow from the
25 reduction reactor is preferably converted to ferric
chloride and ferric oxide by reaction with a controlled
~110~!39
--10--
4uantity of oxy~en or air, as disclosed for stage (b)
of the process, described in United States Patent No.
]~l0746 and in Canadian Application No. 327,367
re~,ating to the recovery of-chlorine values from iron
5 ch]oride derived from various sources. The resultin~
iron chloride is preferably recycled to the reduction
reaction which is the subject of this invention.
The i,nvention is further illustrated by the
following Examples:
10 EXAMPLE 1:
A 100 mm diameter bed of ferrous chloride
was fluidised at 380C usin~r a ~as mixture analysing:-
4~/min ferric chloride gas
2 ~min nitrogen
4~/min sulphur chlorine mixture
(atomic ratio sulphur to chlorine:- 2:1)
The ferric chloride and sulphur/chlorine mi~ture
entered the bed t}lrough separate orifices and the off-gas
was found to have reacted completely to give a sulphur
20 monochloride off-gas with ne~ ible reidual ferric
e~llori~e. The ferrous chloride reaction product reported
to the reaction bed.
l~X~MPII~ 2:
The distillation of S2C12 produced according
to the equation (~) was carned out in a 80 mm diameter
~ . .
1110~39
B Inconel column, which was used for ~oth stages as
~et out helow. For convenience, the quantities of
feed material used in each stage were not matched
since the critical constraint was the heat load on
5 the condcnser. Samples were collected for analysis
after three hours runnin~ time, and the results are
~iven below. The theoretical heats (i.e. the heat
input at the ~ottom and the heat load on the condensers)
were up to 50,o greater in practice , at the feed rates
l0 specified.
Sta~e l Sta~e "
Pressure: Atmospheric 10 Atmospheres
Packin~: 1.06 metre~ of Knitmesh 1.G metres of Knitmesh
Multifil packin~ (equiv- Multifil packin~ (equiv-
alent to 20 theoretical ~ent to 30 theoretical
platcs) plates)
Location Centre of Column 60~o of packing below
of Feed and ~0,~ above.
Plate:
Theoretical 47 Kcal/mole/feed l4 Kcal/mole/feed
Heat Input
at Bottom:
lIeat Load on
Condenser: 34 Kcal/mole/feed ~.5 Kcal/mole/feed
Feed Analy~is:
lOO~ S Cl 9O mole' SCl~ l0 mole '~
S Cl,~
Top Product
25 Analysis: 90 mole ~0 SCl2 l lOO~,o Cl (99.7 - 3%)
2 2
1~10039
--12--
_Sta~e l Sta~e 2
Bottom Product
Analysis: 80 mole% S 20 mole % 100~/ S2C12 ( 78- 2~o)
S2C1 2
Reflux Ratio: 5 3
5 Feed Rate &
Temperature: 27 moles/hour at 20C 170 moles/ho~ 20C
Top Production
R~.te & Temp. 22 moles/hour at 50C 76 moles/hour 30C
Bottom Production
Rate & Temp. 25 moles/hour at 160C 93 moles/hour 210C
