Note: Descriptions are shown in the official language in which they were submitted.
~L752~3
BACKGROUND OF THE INVE;NTIt:)N
.
The present invention providss continuous process
for the production of light-weight calcium sulfate. More
particularly, it provides a process for continuously producing
light-weight and high quality calcium sulfate.
Various methods to produce light-weight ibrous calcium
sulfate by subjecting raw calcium sulfate comprising mainly
calcium sulfate dihydrate to a hydrothermal reaction are known.
Japanese Patent Laid-Open Gazette (Kokai) No. 152692/1979
discloses a continuous process for the production of needle
crystalline calcium sulfate which comprises injecting steam into
an aqueous slurry of raw calcium sulfate to heat the aqueous
slurry to a temperature of 115C. or more and then injecting
- said aqueous slurry into an autoclave. In accordance with
this process, the aqueous slurry is heated to above 115C. ~ith
the steam in a high performance gas-liquid mixing apparatus
and, thereafter, the resulting slurry is introduced into the
autoclave. Namely, it is important to adjust the temperature
- of`the aqueous slurry to above 115C. before introducing it to
the autoclave. Furthermore, in this disclosurel it is pointed
out that a stream of the aqueous slurry should be allowed to
come near a piskon flow. Accordingly, control of the feed
amount of tha aqueous slurry is an important factor as well as
thè control of the reaction temperature. It is also disclosed
to set the feed amount of the aqueous slurr~ preferably to above
11.7 centimetexs per minute, more preferably to 14 centimeters
per minute.
The foregoing process, however, is not always advan-
tageous from an economic standpoint with respect to installation
cost and productivity because the dispersion of the aqueous
-- 1 ~
'~7~9
1 slurry in the autoclaYe requires a stirring device and .the
amount of the feea is limited
SUMM~RY OF THE: INVENTION
It is an object o~ the presen-t invention to provide a
continuous process for the production of light-weight calcium
sulfate with excellent productivity
It has been f~und that the object can be attained by
employing a tubular reactor and introducing.steam directly into
a slurry of the raw calcium sulfate in the tu~ular reactor,
tO The present invention, therefore~ provides a continuous
process for the production of light-weight a-type calcium
sulfate hemihydrate which comprises contlnuously introducing an
aqueous slurry of raw calci.um sulfate into a tubular reactor
and, at the same time, introducing steam directly into the
aqueous slurry in the tubular reactor to ~bject the raw calcium
sulfate to a hydrothermal reaction,
In one of its aspects the present invention provides
a continuous process for the production o~ an a-type calcium
sulfate hemihydrate in a -fibrous form and/or in a spherical
. 20 form in which the fibers o~ the fibrous form are intertwined,
the a-type calcium sulfate hemihydrate having a bulk density of
from 0.08 to 0~16 gJcc, the process comprising hydrothermally
treating an aqueous slurry which.has a solids concentration
o from 1 to 30% by weight of a calcium sulfate starting
material by.preheating said slurry to a temperature of from
about 60C to 100C then passing the slur.ry through a tu~ular
reactor equipped with a static mixer,.the linear velocity of
the slurry through the reactor being from 90 to 450 centimeters
per minute, the heat for the hydrothermal treatment bein~
provided by the introduction of steam into the aqueous slurLy
in the tu~ular reactor
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~ , ~ . . ..... . ...... .. . ...
~5~(D9
BRIEF DESC~IPTION OF THE DRAWING
The Figure is a schematic diagram of the process of
the present i.nvention~
' DETAILED' DES'CRI'PTI'ON OF' TEIE INVENTI'ON
The raw calcium sulfate as used herein is usually
calcium sulfate`dihydrate, In additi:on, calcium.sulfate hemi-
hydrate, soluble calcium sulfate anhydride, and a mixture thereof
can be used. Any of a-type and ~-type calcium sulfate hemi-
hydrate can be used. As such raw calcium sul~ate, any natural
calcium sulfate, chemically produced calcium sulfate, by-
product calcium sulfate produced in a crude oil desulfurization
process, etc., can be usea,
Water is usually used as a solvent in preparing the
~0
-2a-
,
:.
75i2~
1 aqueous slurry of a raw calci~n sulEate in accordance with the
present invention. In addition, an acidic aqueous solution and
a water-soluble org~nlc compoun~-cont~ining aqueous solution
can be used.
Organic and inorganic acids can be used as the acid
component for the acidic aqueous solution. Examples of such
organic acids include acetic acid, tartaric acid, formic acid,
malic acid, etc., and examples of such inorganic acids
include sulfuric acid, nitric acid, boric acid, etc. Although
the concentration of the acid component in the acidic aqueous
solution is subject to no particular limitations, it is usually
from about 0.1 to 20~ by weight.
Water-soluble organic compounds which are used in
preparin~ the water-soluble organic compound-containing aqueous
solution include such polyhydroxy compounds as ethylene
glycol, diethylene glycol, glycerol, etc. The content of the
water-soluble organic compound is usually from about 0.1 to 20
parts by weight per 100 parts by weight of water, although it
varies depending on various conditions. Addition of such an
acid component or water-soluble organic compound to water makes
- calcium sulfate precipitation easier in subsequent s~ep.s.
In the process of the present invention, an aqueous
slurry prepared by adding raw, i.e. feed, calcium sulfate to the
foregoing solvent is used. Although the solid concentration in
the slurry can be appropriately determined according to the
type of the solvent used, it is usually from about 1 to 30%
by weight and preferably from about 2 to 20~ by weight. The
aqueous slurry may be maintained at room temperature, and is
preferably adjusted to from about 60 to 100C. by introd~lcing
steam directly into the slurry tank or heating the slurry tank
from the outside.
~7~i2~
1 In the process of the present inve~tion, the foregoing
aqueous slurry is conti~uously introduced into a tubular reactor
and at the same time, steam is introduced directly into the
aqueous slurry in the tubular reactor ~o subject the raw calcium
sulfate to a hydrothermal reactionO The steam is generally
- introdùced into the reactor through the same side through which
the aqueous slurry is introduced, and in the same direction as
the flow of the aqueous slurry. Alternativelv, the steam may be
countercurrently introduced into th~ tubular reactor through
the side through which the reaction product is withdrawn. Other
positions of the steam introduction into the reactor may also
be used.
The tubular reactor as used herein is generally a tower-
type reactor as shown in the Figure wherein the tubular reactor
is vertically installed. So long as the form of the reactor i5
tubular, the position in which it is installed is not critical.
For example, the tubular reactor may be installed ither
horizontally or at an angle. One of the features of the present
invention is that in such reactors installed horizontally or
at àn angle, no problems arise with respect to the dispersion
of the raw calcium sulfate and the reaction product in the
aqueous slurry.
Hereinafter, the process of ~he present invention will
be explained in detail with reference to the Figure.
Raw calcium sulfate and a solvent are introduced into a
slurry tank 1 where an aqueous slurry is prepared. The thus
- prepared slurry is continuously sent to a tower-type (tubular)
- - reactor 3 by the use of a pump 2. Usually, the aqueous slurry
is introduced into the reactor from the bottom thereof, sub-
]ected to a hydrothèrmal reaction while moving upwards, and then
1 withdrawn from the top oE the reactor. When the reactor is of
the tank type, difficulties are encount~red in carrying out the
operation continuously and furthermore stirring is needed. Thus,
such tank-type reactors are not suitable for the efficient and
continuous production of light-weight calcium sulfate having a
uniform quality.
The aqueous sluxry introduced into the foregoing towex-
type reactor 3 is heated by introducing steam directly thereinto
to per~orm the hydrothermal reaction of the raw calcium sulfate.
Auxiliary heating from the outside of the reactor may also be
appl~ed to heat the reactor contents. However, if the reactor
is heated only from the outside thereof without the introduction
of steam thereinto, scales are formed and attached into the
inner walls of the reactor, making the continuous operation
mpossible because the reactor itself is heated.
The linear velocity of the aqueous slurry in the
for~going tower-type reactor 3 is usually from about 50 to
1,000 centimeters per minute (cm/min) and preferably from about
100 to 500 cm/min. In particular, at a linear velocity of from
2~ about 250 to 350 cm~min, spherical calcium sulfate formed sub~
stantially of intertwined calcium sulfate fibers can be obtained.
The amounts of the aqueous slurry and the steam introduced into
~he reactor 3 are determined depending on the length and
diameter of the reactor, reaction temperature, etc., so that
the foregoing linear velocity is obtained.
The hydrothermal reaction in the tubular tower is
carried out by heating the aqueous slurry to a temperature of
between 105C. and 1~0C., and preferably between 110C. and
160C
3~ In the tower-type reactor 3, the aqueous slurry is
~L7~
1 continuously introduced and moved, and furthermore turbulent
flow is produced by the introduc~ion of the steam so that the
aqueous slurry and steam are stirred sufficiently. If necessary
or desired, a static mixer 4 may be provided in the reactor 3.
A residence time is set at least 30 seconds. The
residence time is determined by taking into consideration of
the reaction temperature.
The reaction product, i.e., a-type calcium sulfate
hemihydrate, produced in the tower-type reactor 3 by the hydro- ¦
thermal reaction is continuously withdrawn from the reactor and
introduced into a reservoir 5. If`necessary, it is further
introduced into a solid-liquid separator (not shown) where water
is removed, and it is taken out as a wet product. The thus-
obtained wet product is dried at ~etween about S0 to 120C. to
provide dry a-type calcium sulfate hemihydrate.
The calcium sulfate product thus obtained is a fibrous
a-type calcium sulfate hemihydrate and/or a spherical a-type
calcium sulfate hemihydrate formed substantially from the
calcium sulfate fibers which became intertwined to form spherical
particles, and thus is very light-weight. The product is
usually a mixture o the product in the form of fibers and the
larger spherical particles.
When calcium sulfate hemihydrate, soluble calcium sul-
fate anhydride or a powdery inorganic substance is used as part
of the raw calcium sulfate, or a solvent containing therein an
acid is used, the major portion of the calcium sulfate obtained
is spherical.
In accordance with the process of the present invention,
as described above, a stirrer is not basically needed, the
heat efficiency is high because steam is directly introduced as a
~ 6 --
~75~
1 heat source, and the amount of the aqueous slurry fed can be
increased, and thus the productivity is very high and the plant
and operation costs can be greatly reduced. Furthermore, by
controlling the amount of the slurry or the steam fedr or by
employing a static mixer, calcium sulfate having various physical
properties can be produced. Moreover, since the hydrothermal
reaction is performed by the introduction of steam and the
reactor itself is not heated, the attachment of scales on the
walls of the reactor is prevented and the operation can be
continuously performed for long periods o time.
The fibrous calcium sulfa~e product obtained by the
process of the present invention has a small diameter and it is
very long. The spherical calcium sulfate product formed from
such fibrous calcium sulfate has a very low density. Thus,
both the fibrous calcium sulfate product and the spherical cal-
cium sulfate product are of high quality.
The light-weight calcium sulfate produced by the pro-
cess of the present invention is of high and uni-form quality
and has high strength. It can be used as a building material,
such as ceiling material, a partition material, a heat-insulating
material, a core material, a spxay material, etc., and also as
a filler for plastics in various fields.
The following Examples urther illustrate the present
invention in detail.
Examples 1 to 12
An aqueous slurry of a raw calcium sulfate (calcium
sulfate by-product of a process for desulfurization of crude
oil) was brought to 75C., and continuously introduced into a
tower-type reactor (inner diameter: 8 centimeters; length:
550 centimeters) through the bottom at a predetermined linear
~752~
1 velocity by the use of a pump. ~t the same time, steam was
introduced into the reactor through the bottom thereof and
directly injected through a gas~liquid mixer provided at the
bottom thereof to maintain the resulting mixture at a predetermined
reaction temperature. The reaction product was continuously
withdrawn from the top of the reactor and introduced into a
reservoir, and then it was subjected to a solid-liquid separation
by a centrifugal separator. The thus obtained product was dried
at 80C. for 3 hours to obtain a light-weight -type calcium
sulfate hemihydrate.
` In Examples 6 and 7, a static mixer was placed in an
upper portion of the gas-liquid mixer.
In Examples 8 to 12, three static mixers were provided
in an upper portion of the gas-liquid mixer.
: The reaction conditions employed and the physical
properties of the light-weight calcium sulfate obtained are
shown in the following Table.
- 8 -
~L'7~
#
~,_
~N
~ ~ ~ ~ ~1 In o
.~ ~ C) ~_ t` ~
a3 ~ ;~
m u~ ~
~ ~,
N U l~i Q)
*
4~ O S~
t~l rl a) c.) ~1-- o o o
~ .~ \0
3 P:; o u~
,~ ,
1 ~rl ~ N ~~) ~~D ~ Il)~1 CO ~ t~l 11
C~ ~ ~ ~ . . . . . ~ . . . . . .
~ a~ ~ o o o o o o o o o o o o
a:l ~~
-
~::
~1
a~ o ~ ~ O co c)~ Il') ,-1 ~ ~) r~J
~_
3 ~
O O~ O o O O O O O O O Q
co o ~r cn r~ co = = o ~r
~p o ~ ~ u~ ~n o
O
~1 1 a
O o o o u~
Q) a) ~o ~1 ~1 ,~ ~1 ~1
h--
al
r~ ~
:1 tq ~
O ~I X o ~n
~ ~ o-~ Z = ~ = = ~ = = = : : =
~ ~1
q~ ,1 ~
O ~ ~ ~ o ~
.~- ~.q o ~1
U~ ~ ~
U~ ~ rd a) ~ ~
~-,1 ~ ~ p~ = : = : = = : : = : ~-
O ~ 1~ ~.
- ~ u ~: a
~ C) t~
,1 ~ : ~1 - h ~
o 1~ ~P ~ ~ a~ ~P ~ ~ a
U~
o ,¢ ,¢:~: O f~
X Z ~1 ~ ~ ~ u~ ~ r~ ~ ~
- 9 -
75~9
1 *1: Per 100 paxts by weight of the solvent.
*2: 3 milliliters of light-weight calcium sulfate was placed
in a 10 milliliters content vessel a~d ~ashed with
methanol to remove the calcium sulfate fibers which are
not formed into the spherical particles of calcium
sulfate, and thus the weight ratio was de-termined.
*3: To lOO parts by weight of the light-weight calcium sulfate
obtained was added 400 to 600 parts by weight of water to
provide a slurry. The thus obtained slurry was molded by
compression and dehydration into a plate tlO x lO x 2
centimeters), which was then dried at 60C. for 8 hours to
obtain a molded pxoduct of light-weight calcium sulfate
having a density of 0.4 g/cm3. Then, the strength of
the molded product thus obtained was measured.
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