Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SP13C IFICAT IOU
TITLE OF TI~E INVENTION
Process for producing potasslum sulfate
BACKGROUND OF TIIE INVENTION
Field of the Invention: .
This invention relates to a process for producing
potassium sulfate from potassium chloride and sulfuric acid
in two steps.
Description of the Prior Art:
A process of reacting 2 mols of potasqium chloride with
one mol of sulfuric acid to obtain potassium sulfate via
potassium hydrogen sulfate and also recover hydrogen chloride
evolved, has been commercially operated, When this reaction
is carried out in dry manner, it is separated into the
following two steps:
The first step reaction proceeds even at a relatively
low temperature such as room temperature to 100C, but
a considerably high temperature such a~ 300C to 500C is
necessary for advancing the second step reaction to~a su~stantial
extent. Thus, although the reactions of the first and second
steps can be carried out in the same reactor ~only the reactor
: of the second step will be hereinafter referred to as reaction
furnace), it i~ regarded as preferable and efficient particu-
larly for the continuous production process to separate the
two step~ into a first step carried out in a reactor and
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a second step carried out in a reaction furnace to thereby
substantially alleviate the load of the reaction furnace
for the second step.
First step: ~C~ + i~2SO~ c KIISO4 ~ HCQ ~ 3RCaQ (1)
Second step: K~ISO4 + KCQ ~ K2S04 + HCR - 17KCaQ (2) "
Now, Japanese patent publication No. 756/1957 disclose~
a process of carrying out the reaction in two steps wherein
separate reactors are employed in the respective steps.
The gist of the process is as follows: a process for produc-
ing alkali metal sulfates and hydrogen chloride gas from
alkali metal chlorides and sulfuric acid which consists of
a first step of feeding into a reactor, an alkali metal
chloride and sulfuric acid in such amounts that an acid salt
containlng 35% or less of a normal salt i8 prepared, and
maintaining the reaction temperature at a temperature at
which the resulting material is molten, and a second step
of feeding a deficient amount of the alkali metal chloride
necessary for preparing the normal salt, to the molten
material to somplete the formation reaction of the normal
salt.
According to the process, however, problems with respect
of operation and corrosion have been raised. Namely, in the
first step, a temperature of 200 to 250C is required for
forming 35~ or less of the normal salt, while, in case where
the acid salt 1~ potaYsium yd gen sulfate, it melts at
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about 210C; hence agitation is difflcult as compared with
the case where they are mixed together both in the form of
powder. Further, in order to withstand hydrogen chloride
evolved at such a temperature, lt is nece~sary to employ
e.g. acid resistant brick as the material for the reactor,
and also in order to maintain the reaction temperature,
external heating is nece~sary. In addition, since a solid
phase reaction i8 carried out at 400C or higher in the
second step, heat conduction is so poor that a high temper-
ature and long time treatment is compelled.
The above-mentioned problems of the Japanese patent
publication No. 756/1957 have been partly solved by a process
disclosed in Japanese patent publication No. 2,666/1957..
Namely, accordlng to the proce~s, an acid salt containing
45~ or less of a normal ~alt i~ formed.in the reactor of
the first step, and it is once cooled, to solidify it,
followed by fine pulverization. Thereafter, a deficient
amount of the chloride necessary for preparing the normal
salt is added thereto, and they are uniformly mixed together
and then fed to the reactor of the second step, whereby the
time required at 300 to 500C is shortened for example,
from 6 hours to 3 hours. However, even when the process of
Japanese patent publication No. 2666/1957 i~ employed, the
problem that such a high temperature as 250C is required
in the reactor of the first step cannot be overcome, and
I 1 6!~fi3~
al~o the process of Japanese p~tent publication No. 2666/1977
has a disaclvantage that steps of cooling and mill-m$xing
the reaction product of the first step are newly added.
The present inventors have made studies through practical
operations for many years on the technical problems with regard
to the produc~ion ~rocess of potassium sulfate, and as a result,
the ~ollowing process ha~ been founa:
One mol of sulfuric acid and 2.0 to 2.2 mol~ of pota~sium
chloride are first subjected to the above-mentioned reaction
of the first step i.e. formation of potassium hydrogen ~ulfate,
at a temperature of room temperature to 100C in the form of
powder as it i8, and thereafter a mixture of potassium
hydrogen sulfate as the re~ulting product with unreacted
potasslum chloride is reacted together at a temperature of
300 to 400C in a reaction furnace of the ~econd ~tep.
At that time, by employing a definite muffle furnace
as a reaction furnace of the second step, and also by
carrying out feed of the raw materials and withdrawal of
the reaction product in adequate manners, the problem of
melting and corrosion brought about by the high temperature
of the first step as well as the problem of the life of the
furnace brought about by the necessity of a long retention
time at high temperature in the second step, have been both
solved.
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SUMMARY OF THE INVENTIO~
As is apparent from the above description, a fir~t
object of the present invention is to provide a dry process
for producing potassium sulfate by way of a new two-step
process. A second object thereof is to provide said process
wherein mixing with stirring i3 well effected and react$on
can be completed in a shorter time. Other objects thereof
will become apparent from the following description.
The present invention re6ides in:
(l) In the proce~s for producing potassium ~ulfate or
a mixture thereof with a ~mall amount of unreacted potasslum
chloride, by reacting potassium chloride with sulfuric acid,
the improvement which comprises
~ reacting 2.0 to 2.2 mols of potassium chloride with
one mol of sulfuric acid under mixing at a temperature of
room temperature to 100C to form potassium hydrogen sulf~te,
and then
~ reacting this potassium hydrogen sulfate with
unreacted potassium chloride at a temperature of 300 to
400C to produce potas~ium sulfate.
The present invention further resides in the following
processes:
(2) A process according to that of the above item (l) wherein
the formation reaction of potassium hydrogen sulfate is con-
tinoously carr~ed out in a r-a~ or of the flrRt step and that
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1 1 B963V
of potassium sulfate is continuously carried out in a reactor
of the second step.
~3) A process according to that of the above item ~2) wherein
a muffle furnace whose upper half surface alone can be heated
is employed as the reactor of the second step.
(4) A proce~s according to that of the above item (2) wherein
the reaction product of the second step is recovered by over-
1Ow.
DETAILED DESCRIPTION OF THE INVENTION
The constitution and effectiveness of the pre~ent invention
will be described below in detail.
~a) Reaction of the first step in the reactor of the first
step:
As is seen in the above-mentioned equation of the react$on
of the first ~tep, one mol of potassium chloride and one mol
of sulfuric acid yield one mol of potassium hydrogen ~ulfate
and one mol of hydroqen chloride, but, in the present inventlon,
sulfuric acid (98~) and potassium chloride are employed in
a proportion of one mol of the former and 2.0 to 2.2 mol~ of
the latter, and potassium chloride to be reacted in the second
step is mixed in advance in the first step. The reaction
temperature i8 in the range of room temperature to 100C, and
the reactor employed may be those made of a material resistant
to sulfuric acid and dry hydrogen chloride at the reaction
temperature;
1 1 69~3 ~)
no special material such as acid resistant brick is required
aue to the low reaction temperature~ Further, it i8 prefer-
able to employ an agitator e.g. paddle or ribbon agitator
(preferably equipped with double or more shafts) suitable
for mixing pewder ~potassium chloride, etc.) with liquid
~sulfuric acid). As for the type of the reaction vessel,
either vertical typé or horizontal type may be employed.
The reaction of the first step in the process of the present
invention proceeds very smoothly and rapidly even at a temper-
ature of room temperature to 100C, due to the pre~ence ofexcessive potassium chloride, and since only a small amount
of unreacted ~ulfuric acid is present in the reaction product,
this product is of flowable powder; hence it i8 easy to
transfer the product into the reactor of the second step.
On the other hand, hydrogen chloride evolved i~ ~ent to
an apparatus for producing concentrated hydrochloric acid,
and its concentration is in the range of 40 to 60~ by volume
although it is v~ied dependlng on the operational conditions.
The retention time in the reactor of the first step may be
in the range of 30 minutes to 3 hours, preferably in the
range of 30 minutes to one hour, both in the case of batch
process and in the case of continuous process.
(b) Reaction of the second step in the reactor of the second
step:
As is ~een in the equation of the reaction of the second
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~tep, one mol of potassium hydrogen sulfate and one mol of
potassium chloride theoretically yield one mol of potassium
sulfate and one mol of hydrogen chloride, but, in the process
of the present invention, the amount of pota~ium chloride
fed into the reactor of the first step is in the range of
2.0 to 2.2 mols per mol of sulfuric acid. If it exceeds
2 mols, the resulting product is a mixture of pota~sium
sulfate with potassium chloride, and potassium chloride
contributes to preventing unreacted potassium hydrogen
sulfate from discharge in molten state to thereby make easy
the transfer of the reaction product after the reaction of
the ~econd step. On the other hand, even when the equimolec-
ular reaction of the present invention ~i.e. amount of RC~,
2.0 mols; amount of sulfurlc acid, one mol) $s carried out,
the presence of unreacted potassium chloride corresponding
to the presence of potassium hydrogen chloride as an inter-
mediate in the product contained in the reactor of the ~econd
step, make~ it possible to notably reduce the ~urface tackiness
of the reaction product. The reaction of the second step is
a reaction between a ~olid (KC~) and a melt ~KHSO4) and yet
is an endothermic reaction. Thus, unles~ the mutual contact
and heating ~and hence heat tran~fer) of the reactants are
~ufficient, it is impossible to improve the conver6ion and
shorten the reaction time ~retention time). Further, in
the case of continuous reaction, particularly an unreacted
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portion of the reaction mixture where reaction has not yet
advanced sufficiently should be prevented from di~charge ln
~hort-circuit manner, Now the pre~ent inventors have found
that ~ muf1e furnace capable of heating the reaction mixture
rom its upper ~urface alone is surprisingly more suitable
for attaining the above-mentioned ob~ects of the present
invention than tubular furnace capable of heating the reaction
mixture from its total periphery. Further the present
inventor~ have also found that ~ it i8 effective for prevent-
ing the above-mentioned di wharge in ~hort-circuit manner to
di~charge the reaction product of the second ~tep by overflow.
The reason fox the above item ~ iB presumed to be in that,
in the case of tubular furnace, molten potassium hydrogen
sulfate i~ more liable to adhere to the ~urface of the lower
half part of the furnace~ At any rate, heat transfer iB poor
on the surface of the lower half part of the furn~ce. Similarly
the reason for the above item ~ is presumed to be in that, in
the ca~e of overflow, a portion of the reaction mixture contain-
ing a smaller amount of melt is more liable to be smoothly
discharged. These method~ ~ and ~ , however, could not
have been entirely antlcipated from the above-mentioned
Japanese patent publication Nos. 756~1957 and 2666/1957 wherein
tubular furnace was substantially employed ~Note: The appli-
cants of these prior art inventions are substantiAlly the same
company. In addition, see Japanese patent publication
~ 1 6~630
No. 10153/1959). Further r according to these prior art
inventions, the reaction of the fir~t step is so adjusted
as to contain 35~ to 45~ of a normal salt tpotassium sulfate)
to thereby reduce the ~ubstantial load of the reactlon
furnace of the second step. In this respect, it is clear
that the techniques of these inventions are different from
the proce~s of the present invention.
As a re~ult, in the case of the Japanese patent
publication No. 2666~1957, the residual percentage of chlorine
is 2.4 to 1.6% by we$ght at 300 to 400C in one hour, wherea~
according to the proces~ of the present invention, it i8
possible to attain conversions to the same extent after
completion of the reaction of the second step, without
pa~ing through steps of cooling, solidification and fine
milling between the fir~t ~tep and the ~econd step.
~c) Quenching of the reaction product discharged from the
reactor of the second step:
The reaction product has a temperature of about 300 to
370C, and depending on the reaction condition~, it still
contains about 1.5 to 2.5~ by weight of chlorine and also
about 2.0 to 3.0~ by weight of sulfuric acid. Thus, when
the product is used as potassium sulfate for fertilizers or
indu~tries, it is necessary to neutralize the product with
lime or the like in a separate step, and also the product
must be cooled down to a suitable temperature ~uch as room
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temperature to 200C, for it~ transfer. According to
an embodiment of the present invention, it i~ possible to
partly cool the discharge by scatterlng or dropwise adding
a small amount of water thereon. The water-pourlng of this
embodiment i~ carried out by scattering or dropwise adding
water in such an extent of amount that its temperature ls
elevated by the sensible heat of the reaction product of
the second step di~charged by overflow whereby it i~
vaporized~ in a cooler or a transfer vessel ~r the product.
More concretely, for example, 40 to 60 Kg of water is
scattered on 1,000 Kg of the mixture at 300C. When the
temperature of the reaction product i~ reduced down to 100C
or lower by the water-pouring, it become~ imposslble to
vaporize the scattered water, and hence the subsequent cooling
is carried out by heat transfer or alr cooling.
~d) Summary of the effectiveness o~ the process of
the present invention:
~ he novelty and characteri~tic effectiveness of the
proce3s of the present invention have already been clarified
by the detailed descriptions in the foregoing items (a), ~b)
and (c), and they may be summarized as follows:
~ Due to the low reaction temperature in the reactor of
the first ~tep, carrying out of the reaction of the first
step, and transfer and supply of the resulting reaction
product to the reactor of the second step are very easy.
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Thi~ i8 brought about by the fact that no melt of pota~sium
hydrogen ~ulfate i8 formed in the reactor of the first step.
~ Carrying out of the reaction of the ~econd step in
the reactor of the second step and continuous discharge of
the resulting reactlon product are very easy, and also it i8
poss~ble to complete the reactlon at a relatlvely low temper-
ature such a~ 300 to 400C, and in a reactlon time as short
as one hour. This is presumed to be brought about by the
following fact~.
0 (A) In case where the ~mount of potassium ahloride i~
in small exces~ of the equivalent to that of sulfurlc ac~d
in ~uch a manner that the molar ratio by mol of potasslum
chloride to sulfuric acid as raw materials employed is more
than 2.0 and not more than 2.2, the molar ratio of unreaoted
potass~um hydrogen sulfate to unreacted potas~lum chloride
becomes le~s with the progres~ of the reaction in the reactor
of the second step, whereby the amount of unreacted KHSO4
can be rapidly reduced down to a definite value.
(b) Further, in the case of a ratio of ~ulfuric acid/
potassium chloride of 2.0, too, the reaction mlxture of the
fir6t ~tep (pota~ium hydrogen sulfate plus potassium chlorlde)
in a very good finely mlxed state is supplied to the reactor
of the ~econd step, whereby the amount of the reaction mlxture
aischarged in ~hort-circult manner is extremely small.
~ Slnce the reaction temperature ln the reactor of the second
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step ia not necessary to be a~ high a temperature as 400-
to 500C, the 10~8 of the heat re~istant bricks on the
~urface of radlation heat muffle furnace i~ le88 tnote:
the temperature in~lde the flue of mu~fle furnaco i9 1100-
to 1200C), which make~ pos~l~le a long time operatlon as
long a~ one to three year~. Further, since the heat
trsnsfer area per unit volume may be small, it 1~ easy
to make the capaclty larger than tubular furnace.
The present invention will be further illu~trated by
way of Example, but lt should not be construed to be limited
thereby.
Example 1
Into a flrst step reactor of clo~ed and horizontal type
equipped wlth an agitatox wore contlnuously fed 163 Kg~hr o~
96~ potasslum chloride and 100 ~g/hr of 98~ sulfuric acld,
and the xeaction temperature was malntalned at 60- to 70-C
~y allowing them to cool ~KC~/H2SO4 - 2.1). In order to
prevent hydrogen chloride gas evolved, from scattering away
to the atmo~phere, the pre~ure in~ide the reactor was
maintained under a slight reduced pre~sure of -5 to -10 mm
water-gauge to obtaln 40.3 Nm3/hr of hydrogen chloride having
a concentration of S0~ by volume.
Next, the total amount o~ the reaction product of the
flrst step was continuously fed to a reactor of the second
~tep ~muffle furnace) whose upper half surface alone can be
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heated by radiatlon and which i8 equlpped wlth a double-~haft
agltator.
The reaction product of the first ~tep wa~ fed into
the muffle furnAce at a location between the central part
and the raw material-feeding port of the furnace and clo~o
to this feeaing port; the temperature of the reaction mlxture
ln the furnace wns malntalned at 350-C; and the retentlon
time was one hour. The pressure inside the reactor of the
second step was maintained under 0 to -5 mm water-gauge.
As a re~ult, 39.6 Nm3/hr of hydrogen chloride having a con-
centration of 608 by volume were obtained. Further, 183 Rg/
hr of the reaction product were overflown from the reactor
of the second step. Other re~ults are shown in Table 1.
Comparative exmaPle 1
Thl~ experlment wa~ carriod out ln the same manner a~
ln Example 1 except that potas~lum chloride and conc. ~ulfurlc
acid were fed dlrectly to the reactor of the ~econd ~tep, and
the retention time in~ide the reactor was 2 hour~. The re~ult~
are shown in Table 1. 71.7 Nm3/hr of hydrogen chloride havlng
a concentration of 60% by volume and 184 Xg/hr of a reactlon
product were obtained. Other results are al~o ~hown in
Table 1.
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Table l
Result~ of reaction
.
~eaction product Reaction product of
of first step second ~tep
C~ ~ ~12SO4 ~ C~ conver- Cl ~ H2SO4 ~ C~ conver-
~ion ~ sion
_
Example 18.6 4.342,9 2.7 1.07 93.4
Compara-
tive ex. 3 5 2.13 91.4
It is evident from Table l that ln the case of
Comparative example 1, the amount of chlorine and that of
sulfuric acld are both largerand the reaction 18 in~ufficient.
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