CA1115025A

CA1115025A - Process for producing calcium sulfate

Info

Publication number: CA1115025A
Application number: CA318,237A
Authority: CA
Inventors: Shinho Shiho; Shiro Kozakura; Masahiko Shiraishi
Original assignee: Idemitsu Kosan Co Ltd
Current assignee: Idemitsu Kosan Co Ltd
Priority date: 1977-12-29
Filing date: 1978-12-19
Publication date: 1981-12-29
Also published as: DE2854722A1; IT7852460A0; GB2053874A; GB2053874B; FR2413339B1; DE2854722C2; IT1158192B; GB2011363B; GB2011363A; FR2413339A1

Abstract

ABSTRACT OF THE DISCLOSURE
A process for producing .alpha.-type calcium sulfate hemi-hydrate or calcium sulfate anhydrite or calcium sulfate dihydrate by a hydrothermal reaction of a starting material of calcium sul-fate in an aqueous medium. The calcium sulfate produced is in either fibrous and/or spherical form. The .alpha.-type calcium sulfate is produced efficiently by adding a powdery inorganic substance to a slurry of the starting material. The addition of the powdery inorganic substance advantageously eliminates difficulties in-volved in the control of the hydrothermal reaction experienced with conventional processes. The addition of the powdery inorganic substances also enables production of spherical calcium sulfate under conditions unsuitable therefore under conventional processes.

Description

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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 .
. . .
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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.

, 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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.,~ " ' ~' ~5~Z5 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 . .-. . - - .

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 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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,~ _ 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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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for producing fibrous and/or spherical .alpha.-type calcium sulfate hemihydrate comprising 1) forming a slurry of starting calcium sulfate at least one selected from the group consisting of calcium sulfate dihydrate, .beta.-type calcium sulfate hemihydrate and soluble calcium sulfate anhydrite in an aqueous medium at least one selected from the group consisting of water and aqueous solution con-taining acid selected from the group consisting of formic acid, acetic acid, maleic acid, tartaric acid, hydrochloric acid, sul-furic acid, nitric acid, and boric acid, wherein the amount of the starting calcium sulfate is from 1 to 35 parts by weight per 100 parts by weight of the aqueous medium, 2) adding a powdery inorganic substance selected from the group consisting of talc, silicic anhydrite, silicic acid, calcium carbonate, calcium sulfate hemihydrate, soluble calcium sulfate anhydrite and a mixture thereof to the slurry, and 3) agitating the slurry to perform a hydrothermal re-action until at least one of fibrous .alpha.-type calcium sulfate hemi-hydrate and spherical .alpha.-type calcium sulfate hemihydrate formed by intertwining of the fibrous .alpha.-type calcium sulfate hemihydrate is formed.

2. A process according to claim 1, wherein .alpha.-type cal-cium sulfate hemihydrate formed is then subjected to calcination in order to convert the same to calcium sulfate anhydrite.

3. A process according to claim 2, wherein said calcination is carried out at a temperature of about 200°C to form soluble calcium sulfate anhydrite.

4. A process according to claim 2, wherein said calcination is carried out at a temperature of from 500 to 1000°C to form insoluble calcium sulfate anhydrite.

5. A process according to claim 1, wherein .alpha.-type calcium sulfate hemihydrate formed is then contacted with water to form calcium sulfate dihydrate.