Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
r~
BACKGROUND OF THE INVENTION :~
Heretofore, a process for producing needle-like crystal-
line fiber of ~-type calcium sulfate hem.ihydrate by heating a
slurry of calcium sulfate dihydrate at a temperature of from 100
to 150C have been known [Japanese patent application No. 30626/lg74:
to Kôkai Tokkyo Kônô published March.l9, 1974]. Furkher, an im-
provement of said process employing vari~us kinds o~ crystallizer ~ :
or a process for obtaining long fibrous product by retarding the
production of crystal nucleus by controlling particularly heating
conditions have been proposed [Japanese patent application No~
156198/1977 to Kôkai Tokkyo K~h~ publi.shed December 26, 1977.
On the other hand, a process for producing ~-type
calcium sul~ate hemihydrate comprising o~ the addition of said
needle-like crystalline fiber of a-type calcium sulfate hemi-
hydrate obtained by the above processes as a seed ~Japanese
patent appl~cation Nos. 156199/1977 and 2526/1978]to K~kai
Tokkyo Kôhô published December 26, 19~7 ~nd January 11, 1978,
respectively, is also known. Further, fibrous or spherical ~:
calcium sulfate product can be obtained by the use of various :
type of aqueous medium [Japanese patent application No~ 109295/
1976, to.Kôkai Tokkyo Kah8 published September 28, 1976].
However, conventional processes have a disadvantage
that a control of the formation of crystal nucleus is very dif-
ficult.
SUMMARY OF THE INVENTION
The present invention relates to a process for
producing ~-type calcium sulfate hemihydrate from calcium sulfate ;: :
dihy~rate, ~-type calcium sulfate hemihydrate, soluble calcium -:~
30 sulfate anhydrite or mixture thereof by making a slurry .
. . .
` ~: .
C ~,
1 of said starting material with an aqueous medium and mixing or
stirring said slurry at a temperature of from 100 to 180C ~o
perform a hydrothermal reaction until fibrous calcium sulfate
and/or spherical calcium sulfate formed of said fibrous calcium
sulfate is formed, wherein the improvement which comprises adding
a powdery inorganic substance to said slurry. Further, according
to the present invention, calcium sulfate anhydrite is produced
by subjecting said ~-type calcium sulfate hemlhydrate to calcination,
and calcium sulfate dihydrate is produced by contacting said ~-type
calcium sulfate hemihydrate with water.
In one aspect the present invention provides a process
for producing fibrous and/or spherical ~-type calcium sulfate
hemihydrate comprising
1) ~orming a slurry of st~rting calcium sulfate at least
one selected frvm the group consistiny of calcium sulfate dihydrate,
~-type calcium sulfate hemihydrate and soluble calcium sulfate
anhydrite in an aqueous medium at least one selected ~rom the group
of consisting of water and aqueous solut~on containing acid
selected from the group consisting of formic acid, acetic acid,
maleic acidl tartaric acid, hydrochloric acid, sulfuric acid,
nitric acid, and boric acid, wherein the amount of the starting
calcium sulfate is from 1 to 35 parts b~ weigh:t per 100 parts
by weight of the aqueous medium,
2) adding a powdery inorganic substance selected fro~
the group consisting of talc, silicic anh~drite, silicic acid,
calcium carbonate, calcium sulfate hemihydrater soluble calcium
sulfate anhydrlte and a mixture thereof to the slurry, and
3) agitating the slurry to perfoxm a hydrothermal re--
action until at least one of fibrous ~-type calcium sulfate hemi-
hydrate and spherical ~-type calcium sulfate hemihydrate formed
by intertwining of the fibrous a-type calcium sulfate hemihydrate
is formed.
--2--
,
DE:TArLED DE5CRIPTION OF THE INVENTION
The present invention is to provide a process for pro-
ducing fibrous and/or spherical calcium sulfate efficiently. ;~
As to the starting material of the present invention,~-type calcium sulfate hemihydrate, calcium sulfate dihydrate,
soluble calcium sulfate anhydrite and a mixture thereo~ can be
used.
As the starting material of the present invention, cal- ::
cium sulfate of every origin ean be employed, so any of natural
calcium sulfate, chemical calcium sulfate~ and calcium sulfate
obtained as a by-product of a desulfurization process of flue
gas can be used optionally, The ~mo~nt of starting ealeium - `
sul~ate is from 0.5 to 50 parts by weight, preferably from 1 to
35 parts by weight per 100 parts by weightr of an aqueous
medium described after.
, ,
Besides water, as an aqueous medium, aqueous solution
eontaining acid and/or water soluble organic substances can be ~ -
employed~ Examples of said acid are organic aeids such. as
formic acid, acetic aeid, maleic acid, tartarie acid, e-tc, and ` :~
inorganic acids such as hydrochloric acid, sulfurie aeid, i::
`: ``'' '
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1 nitric acid, boric acid, e-tc. As the water soluble organic
substances, ethylene glycol, diethyleneglycol, glycerine, etc.
are listed. The concentration of these substances in aqueous
solution is : as to organic acids, 0.05-80 weight percent, ~;
preferably 0.2-~0 weight percent; as to inorganic acids, 0.01-
S0 weight percent, preferably 0.05-20 weight percent; and as to
water soluble organic substances, 0.02-~0 weigh-t percent,
preferably 0.1-20 weight percent.
The starting calcium sulfate is mixed with an aqueous
medium to make a slurry. According to the present invention
powdery inorganic substance is added further when preparing
the slurry or to the slurry prepared. The powdery inorganic
substance is pre~erably a substance, of which particle size is
10 ~ or less. ~xamples of said powdery substances are talc,
silicic anhydride, silicic acid, calcium carbonate, ~-type cal-
cium sulfate hemihydrate and soluble calcium sulfate anhydrite.
These substances can be used either singly or in combination
thereof and are added preferably in the amount of from 0.001 to
50 weight percent based on the weight of the starting calcium
Sulfate.
Mixing o~ starting calcium sulfate, aqueous medium and
powder~ inorganic substance can be carried out in an~ manner,
and no limitation to the order o~ addition is required.
Heating for hydrothermal reaction can be performed
after the above components are mixed at room temperature, or it
is also possible to heat aqueous medium previously, and then the
other components are added to the medium. Heating is effected
at a temperature of from 100 to 180C, preferably from 105 to
140C, and usually performed under pressure. Agitation of the
slurry becomes to be difficult when the amount of the st~rtlng
.
'
1 calcium sulfate in the slurry is beyond the range described
above. Hydrothermal reaction is carried out with mixing or
stirring the slurry for a period o~ from 1 to 90 minutes,
preferably from 3 to 60 minutes. Procedure of stirring can be
chosen optionally, so can be determined in view of the factors
such as form and size of the reaction vessel, and the kind o~
impeller.
By hydrothermal reaction fibrous ~-type calcium
sulfate hemihydrate and/or spherical salcium sulfate ~ormed of
said fibrou~ one is produced. The length o~ fibrous calcium
sulfate is from 100 to 400 ~,and the spherical calcium sulfate ~
formed by intertwining of said fibrous calcium sulfate each -`
other is from 0.01 to 10 millimeters in diameter and from 0.02
to 0.8 grams per cubic centimeter in bulk density.
After the reaction is finished, solid-liquid separation
is effected, and then the resulting calcium sulfate is utilized ;i
for various purpose. Usually the reaction mixture under~oes
solid-liquid separation at heating, and the liquid is re-used
as reaction solvent.
Alpha-type calcium sulfate hemihydrate obtained by
solid-liquid separation can be used not only as it is, but also
in other states. l1hat is, as soluble calclum sulfate anhydrite
after dried and treated with a heat of about 200C, or as
insoluble calcium sulfake anhydrite after calcining said calcium
sulfate anhydrite at a temperature of from 500 to 1000C.
Moreover, it is also possible to utilize ~-type calcium sulfate
hemihydrate after converting to calcium sulfate dihydrate by
contactiny it with water. -
The present invention, where hydrothermal reaction is
performed with addition of powdery inorganic substance, does not
--4--
. .-. . - - .
1 require any severe controllin~ o~ hea-ting and other reaction
conditions in contrast to the conventional process. Since the
time and amoun-t of the addition of the powdery inorganic
substance can be set up optionally, operations for reaction are
very convenient, and that reaction period can be shortened. A
remarkable feature of the present invention is that addition of
powdery inorganic substances enables to obtain spherical calcium
sulfate, even under the conditions that only fibrous calcium
sulfate is expected to form if said powdery substances are not
added. The resulting spherical calcium sulfate is homogeneous
in particle size, and small in bulk density, and the fibrous
calcium sul~ate produced there has rather small diameter.
The calcium sulfate obtained by the process o~ the
present invention has above mentioned features, and is utilized
as construction materials such as panels, heat insulating material
and core material, filler for various plastics, absorbent, filter
aid, catalyst, etc. in chemical industry, and furthermore, the
use in agriculture field is expected.
Following Examples are iilustrative of the present
invention.
Examples 1-15
_
Into a 300 milliliters content of glass made autoclave,
250 milliliters of solvent was se-t, heated with stirring at
200 r.p.m. up to 125C, then at that temperature predetermined
amounts of starting calcium sulfate and powdery inorganic sub-
stance were added and allowed to react at a prescribed temperature
and for a prescribed period of time ~only in Example 8, stirring ;
was made at 300 r.p.m.).
The reactant was filtered at heating, washed with
methanol to yield the product. The product was dried at 60C for
_5_-
1 3 hours to produce ~-type fibrous calcium sulfate hemihydrate
and/or spherical calcium sulfate formed by said fibrous calcium --
sulfate. The result is shown in Table I.
Examples 16 and 17
In a 300 milliliters content of glass made autoclave,
250 milliliters of solvent, prescribed ~amounts of starting
calcium sulfate and of talc as powdery inorganic substance were
placed to be in reaction at a predetermined temperature for a
prescribed period of time by heating with stirring at 200 r.p.m.
at a rate of approximately 6C per minute.
Then the reactant was filtered at heating, washed with
.. . - .
methanol to yield reaction product. Said product was performed
with drying treatment at 60C for 3 hours to form a mixture of
a-type ~ibrous calcium sulfate hemihydrate and spherical calcium
sulfate formed of said fibrous calcium sulfate. The result is
shown in Table I.
Comparative Examples 1 and 2
~ similar procedure to Examples 1-15 was carried out ;~
except that powdery inorganic substance was not added. The ~
2~ result is shown in Table I. `;
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1 Note: *l; calcium sulfa-te from waste acid
*2; calcium sulfate reagent
*3; weight par-t/100 weight parts of starting material
talc....average particle size of 4.2
silicic anhydride....average partiele size of 8m~
calcium earbonate....average partiele size of 40m~
elay....average particle size of 2
*4; ~ spherical, excellent
O spherical, average
= fibrous only
O = mixture oE iibrous and spherical
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1 Examples 18-37
In a 300 milliliters content of glass made autoclave, ;~
210 milliliters of a prescribed solvent and a predetermined
amount oE starting calcium sulfate (by-product at desulfurization
process of flue gas of thermal power plant) were placed and
heated with stirring at 200 r.p.m. at a rate of about 6C per
minute up to 90C, where powdery inorganic substance was added.
After reaching to 120C, hydrothermal reaction was carried out
for 10 minutes, then the reaction product was filtered at heating,
washed with methanol, to obtain product. The result is shown
in Table II.
Comparative Examples 3-6
... ... _ _ . . . .
A similar procedure to the above-described Examples
18-37 was carried out except that calcium sulfate dihydra*e was
employed for starting material and powdery inorganic substance
was not used. The result is shown in Table II.
Compàrative Exam~es 7 and 8
. ~
A similar procedure to the above-described Examples
18-37 was carried out except that calcium sulfate consisting of
10 weight % of ~-type calcium sulfate hemihydrate and 90 weight
% of calcium sulfate dihydrate were employed for starting
material, hydrated fully for one hour at 25C, and that powdery
inorganic su~stance was not used. The result i5 shown in ~able }I.
~ ;:
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--13a- ~
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1 Note:
*1. amount of starting material
starting material - x 100 (wt%)
solvent + starting material ~ ~ -
*2. amount of powdery inorganic substance
inorganic substance 100 t%) -
- x ( w ,
starting material
*3. ~orm of product
6 > 4 ; 9 ~> 1 rough rate
(photographs by optical microscope,
mag. 50 ~
A: fiber, B: bur, C: starting material, D: sphere.
*4. average fiber length -;
photographs by universal projector
(mag. 50 : 1) 100 pieces
*5. average fiber diameter
photographs by electron microscope
(mag. 3000 : 1) SO pieces `
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-14-
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1 Examples 3~ - ~6 ~-
Tower-type reaction vessel (length of 5.5 meters,
inner diameter of 32 millimeters) was used and the hydrothermal
reaction was carried out under the conditiQns described in
Table III. ~ ;
After the reaction, the reactant was filtered at
heating, washed with methanol to obtain reaction product. Said
product was dried at 60C for 3 hours to ~ive ~-type fibrous
calcium sulfate hemihydrate, spherical calcium sulfate formed
f said fibrous calclum sulfate and a mixture thereof. The
result is shown in Table III.
. ,:
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