U.S. patent application number 10/203750 was filed with the patent office on 2003-07-31 for method for producing shaped inorganic cyanide bodies and products obtained according to said method.
Invention is credited to Dickmann, Annette, Franke, Stefan, Gail, Ernst, Jafeld, Markus, Rubo, Andreas, Sauer, Manfred, Schflein, Stephan, Steier, Norbert.
Application Number | 20030143147 10/203750 |
Document ID | / |
Family ID | 7631069 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030143147 |
Kind Code |
A1 |
Jafeld, Markus ; et
al. |
July 31, 2003 |
Method for producing shaped inorganic cyanide bodies and products
obtained according to said method
Abstract
The invention relates to a method for producing shaped inorganic
cyanide bodies, especially made of alkaline metal cyanides and
alkaline earth metal cyanides, by pressing particulate inorganic
cyanide obtained by means of a crystallization method. According to
the invention, a cyanide crystallate separated from a mother liquor
by means of a solid-liquid separation device and containing 2-15
wt. % water is fed to a forming device without the addition of an
auxiliary forming agent and placed under pressure and compressed to
form shaped bodies containing 0.1-12 wt. % water. The amount of
water contained by the shaped bodies is always less than that
contained in the crystallates used for the production thereof.
Preferably, the crystallite is pressed out of a rotary filter or a
centrifuge at a temperature of more than 40.degree. C. to form
shaped bodies containing 0.2-6 wt. % residual water. The inventive
method can be carried out in a more economical manner than
previously known methods using dried cyanide. The invention also
relates to shaped inorganic cyanide bodies obtained according to
said method.
Inventors: |
Jafeld, Markus; (Frechen,
DE) ; Schflein, Stephan; (Haltern, DE) ;
Steier, Norbert; (Euskirchen, DE) ; Dickmann,
Annette; (Rodenbach, DE) ; Franke, Stefan;
(Bad Vilbel, DE) ; Rubo, Andreas; (Leihgestern,
DE) ; Sauer, Manfred; (Rodenbach, DE) ; Gail,
Ernst; (Egelsbach, DE) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL, LLP
1850 M STREET, N.W., SUITE 800
WASHINGTON
DC
20036
US
|
Family ID: |
7631069 |
Appl. No.: |
10/203750 |
Filed: |
November 18, 2002 |
PCT Filed: |
January 24, 2001 |
PCT NO: |
PCT/EP01/00757 |
Current U.S.
Class: |
423/371 ;
264/109; 264/141 |
Current CPC
Class: |
C01C 3/10 20130101; C01C
3/08 20130101 |
Class at
Publication: |
423/371 ;
264/109; 264/141 |
International
Class: |
C01C 003/08; B29B
009/02; B29B 009/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2000 |
DE |
100 06 862.6 |
Claims
1. A process for producing shaped articles of inorganic cyanides,
in particular alkali metal cyanides and alkaline earth metal
cyanides, comprising shaping of particle-form inorganic cyanide,
obtained by a crystallisation process, by means of a device for
shaping the particle-form cyanide by press moulding, characterised
in that a cyanide crystallisate with a total water content of from
2 to 15 wt. %, separated off from a mother liquor during the
crystallisation process by means of a solid/liquid separating
device, is fed to a shaping device without the addition of a
shaping auxiliary and press moulded under pressure into shaped
articles with a water content in the range of from 0.1 to 12 wt. %,
wherein the water content of the shaped articles is always lower
than that of the crystallisate used in the production thereof.
2. A process according to claim 1, characterised in that press
moulding in the shaping device proceeds at a temperature in the
range of from 40 to 70.degree. C.
3. A process according to claim 1 or claim 2, characterised in that
shaping is performed in a briquetting, tabletting or extrusion
device.
4. A device according to one of claims 1 to 3, characterised in
that cyanide crystallisate from a rotary filter with a water
content of from 4 to 13 wt. % or from a centrifuge with a water
content of from 2 to 10 wt. % is fed to the shaping device.
5. A process according to one of claims 1 to 4, characterised in
that sodium cyanide or potassium cyanide crystallisate from a
rotary filter or a centrifuge is converted into shaped articles,
wherein the crystallisate is press moulded at a temperature above
the transition temperature of sodium cyanide dihydrate
(T.sub.u=35.7.degree. C.) and at least partially dewatered at the
same time.
6. A process according to one of claims 1 to 5, characterised in
that shaping is performed above 40.degree. C. under a pressure
which allows dewatering to a shaped article residual water content
(adherent moisture and hydrates) equal to or less than 6 wt. %, in
particular 0.2 to 5 wt. %.
7. Shaped articles of inorganic cyanides, especially alkali metal
and alkaline earth metal cyanides, in particular sodium cyanide
shaped articles, obtainable by the process according to one of
claims 1 to 6.
8. Shaped articles according to claim 7, characterised in that they
contain from 0.1 to 1 wt. %, in particular 0.2 to 0.7 wt. % of the
metal hydroxide on which the cyanide is based.
Description
[0001] The invention relates to a process for producing shaped
articles, such as in particular briquets, of inorganic cyanides, in
particular shaped articles of alkali cyanides and alkaline earth
cyanides, such as sodium, potassium and calcium cyanide. The
process comprises the conversion of particle-form cyanide obtained
by a crystallisation process into substantially dust-free shaped
articles by press moulding. The invention further relates to
products obtainable using the process according to the
invention.
[0002] Conventional commercial forms of inorganic cyanides used in
the mining industry, chemical industry, electroplating companies
and hardening shops comprise virtually dust-free pellets with a
grain size in the range of from 0.1 to 5 mm, pulvinate briquets of
approx. 15-40 g and cylindrical tablets of approx. 20-40 g and
20-40 mm diameter,
[0003] Inorganic cyanides, such as alkali and alkaline earth
cyanides, are currently produced by a neutralisation process
entailing reacting a solution of metal hydroxide/ with liquid or
gaseous hydrogen cyanide. The reaction is generally performed at an
elevated temperature; the neutralisation temperature is used for
subsequent evaporation of water. Despite the simplicity of the
reaction, careful process control is necessary, to prevent
polymerisation of HCN, cyanide hydrolysis, formate formation and
carbonate formation. Concentration and precipitation of the cyanide
are appropriately performed in the presence of a small alkali
hydroxide content under reduced pressure at below 100.degree. C.,
preferably in a vacuum crystalliser. The crystals are separated off
in a solid/liquid separating device, generally a filter or a
centrifuge, from the mother liquor, which is recycled. The moist
cyanide (=filter cake), the total water content of which (adherent
moisture and water of hydration) is in the range of from 2 to 15
wt. %, but usually in the range of from 4 to 13 wt. %, depending on
the solid/liquid separation conditions, is then dried by means of
various processes to residual moisture contents of below 1 wt. %,
generally below 0.1 wt. %, and converted into conventional
commercial forms.
[0004] In the process according to U.S. Pat. No. 3,615,176, the
cyanide is separated off from the mother liquor in a rotary filter,
wherein air heated to 250 to 450.degree. C. is fed to the filter
hood, whereby predrying is performed and the moisture content is
reduced to below 5 wt. %. The predried product is then dried
adiabatically with hot air in a downstream drier to a residual
moisture content of less than 0.05 wt. %. The dry powder is then
compacted between compacting rolls under high pressure and the
semi-plastic strip obtained is broken up and the pellets
screen-fractionated. This multi-stage drying and shaping process is
very energy-intensive and requires corresponding investment and
maintenance-intensive plant. In addition, a considerable amount of
dust arises, which has to be reliably separated off and
recycled.
[0005] In the process according to EP-A 0 197 216, the two-stage
drying of the previously described process is followed by
briquetting of the dry cyanide, any dust fractions adhering to the
surface being removed by means of a device for post-treating the
briquet. This process is also technically very complex and has
similar energy requirements to the process in U.S. Pat. No.
3,615,176.
[0006] Another, again very complex process for producing sodium
cyanide pellets is disclosed in CN 1172071 A: after the
neutralisation reaction, sodium cyanide dihydrate is crystallised
out at low temperature (-6 to -12.degree. C.); the crystals are
melted, mixed with previously dried pellets and then pelletised;
the pellets are dried by means of microwave drying to a residual
moisture level of less than 0.5 wt. %. The process requires a large
amount of energy, because approx. 0.7 t of water have to be
evaporated per t of dried NaCN pellets and refrigerating brine is
additionally required.
[0007] Finally, according to ES-Patent 538,296, shaped articles of
inorganic cyanides may be produced by mixing crystallisate with a
water content of from 2 to 8 wt. % with a cross-linking or swelling
binder and a stabiliser and the mixture is pelletised at
approximately 35.degree. C. and then press moulded into cylindrical
tablets. Instead of the combination of pelletisation and press
moulding, it is also possible, according to ES-Patent 446,317, to
convert an NaCN crystallisate containing binder into strands by
means of an extruder; the strands are dried to a residual water
content of approximately 0.2 wt. %. The advantages of these
processes are lower investment costs and a lower energy
requirement. A disadvantage, however, is the use of 0.1 to 10 wt. %
of a foreign binder, such as mono-, di- or polysaccharide,
agar-agar or gelatine, whereby product purity is reduced.
[0008] The object of the invention is consequently to provide a
further, economically improved process for converting particle-form
inorganic cyanide with a residual water content (sum of water of
hydration and adherent water) in the range of from 2 to 15 wt. %,
obtained using a crystallisation process, into stable,
substantially dust-free shaped articles. The process should be
performable without using shaping auxiliaries, product quality thus
not being reduced by the presence of auxiliaries. According to a
further object, the process should preferably not require a
separate drying stage and should thus have only a small energy
requirement. According to a further object, the shaped articles
obtainable by the process according to the invention should be
distinguished by a hardness level sufficient for practical purposes
and quick solubility in water together with good storage
stability.
[0009] These objects are achieved by a process for producing shaped
articles of inorganic cyanides, in particular alkali metal cyanides
and alkaline earth metal cyanides, comprising shaping of
particle-form inorganic cyanide, obtained by a crystallisation
process, by means of a device for shaping the particle-form cyanide
by press moulding, which process is characterised in that a cyanide
crystallisate with a total water content of from 2 to 15 wt. %,
separated off from a mother liquor during the crystallisation
process by means of a solid/liquid separating device, is fed to a
shaping device without the addition of a shaping auxiliary and
press moulded under pressure into shaped articles with a water
content in the range of from 0.1 to 12 wt. %, wherein the water
content of the shaped articles is always lower than that of the
crystallisate used in the production thereof. The subclaims relate
to preferred embodiments.
[0010] The process relates to the production of shaped articles of
inorganic metal cyanides, but not cyano complexes. It relates
especially to alkali metal and alkaline earth metal cyanides
(hereinafter alkali and alkaline earth cyanides), such as in
particular sodium, potassium and calcium cyanide, wherein sodium
cyanide is particularly preferred as the industrially most
important product from this series.
[0011] The process proper according to the invention is preceded by
conventional cyanide production involving neutralisation of the
metal hydroxide with hydrogen cyanide and crystallisation of the
cyanide. The crystallised cyanide is separated off from the mother
liquor by means of a conventional solid/liquid separating device,
in particular a filter apparatus, such as a rotary filter, or a
centrifuge. Separation of the crystallisate and partial dewatering
preferably proceed continuously. In general, phase separation
proceeds at a temperature in the range of from 20 to 80.degree. C.,
but in particular from 40 to 70.degree. C. Too high a total water
content in the separated-off NaCN crystallisate is prevented by
using a temperature above the transition temperature of sodium
cyanide dihydrate (34.7.degree. C.). Depending on the
crystallisation conditions, the separating device used and the
operating conditions therefor, the water content of the
crystallisate is in the range of from 2 to 15 wt. %. Using a
conventional rotary filter, a crystallisate may generally be
obtained which has a water content in the range of from 4 to 15 wt.
%, in particular 8 to 13 wt. %, while a centrifuge produces a
crystallisate with a water content of from 2 to 10 wt. %.
[0012] The crystallisate thus obtained, which, as a result of the
production process and for stabilisation purposes, preferably
contains a small amount (0.1 to 1 wt. %, in particular 0.2 to 0.74
wt. %) of the metal hydroxide on which the cyanide is based, is fed
to the shaping device without further drying and without the
addition of a binder and press moulded therein. If desired, an
additional stabiliser may also be added to the crystallisate.
However, as a rule no stabiliser or other auxiliary is added, in
order to achieve as pure as possible a product.
[0013] The shaping device may be of various designs, but in all
cases the material introduced is compacted under pressure. Suitable
devices are known to the person skilled in the art--by way of
example, reference is made to the following documents: Ullmann's
encyclopedia of industrial chemistry, 5.sup.th ed. (1988), Vol. B2,
7-28 to 7-32; Lehrbuch fur Mechanische Verfahrenstechnik, Springer
(1994), Press Agglomeration chapter, pages 210-224. Suitable
devices are screw and roll compressors, extruders, briquetting
machines, stamping presses and tabletting machines. Continuously
operating briquetting machines are particularly preferred, wherein
the compacting rolls have a structure corresponding to the shape of
the shaped articles to be produced. The compacting pressure to be
applied depends on the desired degree of compaction and hardness of
the shaped articles. The force applied in a conventional
briquetting machine is generally in the range of from 10 to 140
N/cm with a roll diameter of 1000 mm.
[0014] In the case of compaction and in particular briquetting,
where a crystallisate is used with the claimed water content a
sludge-type liquid (=suspension of metal cyanide in water) is
discharged at the nip, which is drained away and recycled in the
crystalliser. Thus, compacting results in dewatering of the shaped
article to be formed, such that hot gas or microwave drying is not
necessary. As is clear from the Examples, a crystallisate with a
water content of from 8 to 13 wt. % may be dewatered in a
briquetting machines to yield briquets with a water content of from
0.5 to 6 wt. %. In the case of a lower feedstock water content,
i.e. approximately 2 to 10%, in particularly 3 to 8%, as may be
obtained by centrifuging the crystallisate, briquets may be
obtained with a water content in the range of from 0.1 to 5 wt.
%.
[0015] In the process according to the invention, in particular in
the production of shaped articles of uniform size, such as briquets
and tablets or extrudates, dust contamination is prevented. No
drying stage is necessary either before or after shaping. The
temperature of the material to be compacted, the water content
thereof and the compaction pressure are parameters which affect the
properties of the shaped articles.
[0016] The invention also provides the shaped articles of inorganic
cyanides, especially sodium cyanide shaped articles, exhibiting an
exceptional combination of properties which may be obtained by the
process according to the invention.
[0017] Surprisingly, compaction of the crystallisate containing
from 2 to 15 wt. % water results in shaped articles whose water
content is usually reduced by compaction, in general to values
equal to or less than 6 wt. %, preferably equal to/less than 5 wt.
%, and which post-harden within a few minutes of compaction. This
post-hardening effect is particularly pronounced with sodium
cyanide; this may be a consequence of dihydrate formation with the
residual water.
[0018] The shaped articles produced according to the invention
surprisingly exhibit hardness sufficient for a saleable and thus
dust-free product despite the considerably lower pressure used
during press moulding in comparison with press moulding of a
conventionally dried product. Moreover, it has been noted that the
shaped articles according to the invention dissolve at least as
quickly and sometimes more quickly in water than shaped articles
made from dried cyanide.
[0019] The shaped articles according to the invention are
distinguished by high product purity, because no auxiliaries are
added as binders for shaping. The sole binder appears to be the
residual water remaining in the shaped articles. Despite a certain
residual water content of equal to/less than 6 wt. % to
approximately 0.2 wt. % in the shaped articles according to the
invention, the latter surprisingly do not exhibit formate and
carbonate contents any greater than those of shaped articles
produced by previously known processes, whose water content was
reduced to values of below 0.1 wt. % by drying before, during or
after shaping. Despite said certain residual water content and a
low metal hydroxide content of from 0.1 to 1 wt. %, especially of
around/below 0.5 wt. %, substantially no formate or ammonia
formation and no undesired HCN polymerisation and thus no
discoloration occur under conventional storage conditions over
three months of storage. Another non-foreseeable property was the
reduced lump forming tendency of metal cyanide shaped articles, in
particular sodium cyanide shaped articles, according to the
invention as compared with shaped articles made of particle-form
cyanide previously subjected to intensive drying. The following
Examples illustrate the process according to the invention together
with the products obtainable thereby.
EXAMPLE 1
[0020] Compaction of Sodium Cyanide Crystallisate Isolated by Means
of a Rotary Filter:
[0021] The sodium cyanide crystallisate with a residual moisture
content of from 8 to 13 wt. % obtainable using a conventional
rotary filter was used. The NaCN content was between 86 and 91%.
The minor constituents still present in the NaCN crystallisate
were: NaOH=0.2-0.7%, Na.sub.2CO.sub.3=0.1-0.4% and formate=0-0.2%.
The temperature of the crystallisate used for compaction was in the
range from 20 to 70.degree. C.
[0022] A briquetting machine of conventional construction for
producing pulvinate shaped articles with a weight of 15 g (or 7 g
in the case of an experimental briquetting machine) was loaded with
the sodium cyanide filter cake by means of a screw. Briquets were
obtained which exhibited a strength of 200-300 (force at which the
pillow breaks) after a post-hardening period of at most 30 minutes.
Moist NaCN crystallisate compacted in a temperature range of
between 50 and 70.degree. C. exhibited post-hardening of the
briquet during subsequent cooling, which is probably caused by
binding of some of the remaining water as dihydrate water of
crystallisation. The composition (wt. %) of the briquets varied in
the following range: NaCN=93-99%; NaOH=0.2-0.7%;
Na.sub.2CO.sub.3=0.1-0.4%; NaHCO.sub.2=0-0.2%. The water content
was between 0.5 and 3%.
EXAMPLE 2
[0023] Briquetting of Potassium Cyanide
[0024] Using KCN crystallisate obtained from a conventional rotary
filter (KCN=88-90%; KOH=0.3-0.6%; water=8-10%), briquets were
produced as in Example 1. The strength of the briquets obtained was
less than that of the NaCN briquets, but wholly adequate for
storage, transport and dust-free handling. The compacted material
had an average composition of 97-99% KCN, 0.2-0.6% KOH and 0.2-2%
water. The Table contains the material parameters of certain
Examples.
EXAMPLES 3.1 to 3.4
[0025] Compaction of NaCN Crystallisate Isolated by Means of a
Centrifuge
[0026] NaCN crystallisate with a residual moisture level of 2-10
wt. % H.sub.2O was obtained using a conventional centrifuge. The
NaCN content of the crystallisate was between 90 and 96%. The
concentrations of the minor constituents (NaOH, carbonate and
formate) were within the same ranges as described in Example 1. The
temperature of the crystallisate used was between 15 and 50.degree.
C. Post-hardening of the material obtained after compaction was
observed for the crystallisate from the centrifuge in the same way
as with the NaCN isolated with the rotary filter. The briquets
obtained had NaCN contents of 97-99% and water concentrations of
0.2- 5%. No increase in formate and carbonate concentrations was to
be noted in this case either.
EXAMPLE 4
[0027] Compaction of KCN crystallisate isolated by centrifuge
produced results comparable to those where rotary filter material
was used according to Example 2.
1TABLE Example Crystallisate no. feedstock Briquetting machine
Shaped articles Rotary NaCN Formate H.sub.2O Temperature Moulding
NaCN Formate H.sub.2O filter (%) (%) (%) of cryst. (.degree. C.)
pressure (%) (%) (%) Strength.sup.3) 1.1 90.7 0.1 7.0 60 170
bar.sup.1) 98.9 0.1 0.5 300 1.2 90.8 0.2 8.3 70 35 kN.sup.2) 93.7
0.2 5.5 250 KCN KCN 2.1 89.7 0.1 9.2 60 30 kN.sup.2) 97.4 0.1 2 90
Centrifuge NaCN NaCN 3.1 93.4 0.2 5.5 50 35 kN.sup.2) 94.8 0.2 4.4
200 3.2 95.0 0.1 3.0 55 40 kN.sup.2) 99.0 0.1 0.2 180 Comparative
99.5 0.1 0.1 200 170 bar.sup.1) 99.5 0.1 0.1 1000 Example
.sup.3)Stated in N, since stating values per surface area is
problematic owing to the pulvinate geometry of the briquet
.sup.1)In this test, an industrial briquetting machine (flexible
rolls, hydraulics) was used; contact pressure in bar; cannot be
applied to experimental briquetting machines # (rigid rolls,
pressure generation by precompacting screw, stated in kN)
.sup.2)Experimental briquetting machine
* * * * *