[0001] The present invention concerns a method of manufacturing sodium metal oxide by burning
from compounds containing sodium and the respective metal, said metal being aluminium,
titanium,or vanadium. The process is intended preferably for use in producing sodium
aluminium oxide, or sodium aluminate, in connection with the recovery and regeneration
of the digesting and/or bleaching chemicals for cellulose on a sodium basis. The process
is furthermore intended for use in the manufacture of pure oxides and other compounds
of said metals.
[0002] Aluminium and aluminium compounds have a very strong tendency to operate as an autocausticizing
agent by replacing the anoinic components of sodium salts as they react with sodium
salts. Based on this, aluminium and aluminium compounds may be advantageously used
when producing sodium sulfite for cellulose digestion, out of sodium compounds. A
process, based on the powerful autocausticizing tendency of aluminium compounds, for
the manufacturing of sodium sulfite for use in cellulose digestion, out of sodium
compounds and aluminium compounds, is known through U.S. Patent No. 3,061,408 (J.
LURIE). In this process, the liquor waste from the digestion of a substance containing
lignocellulose is concentrated and burned in the presence of compounds containing
silicon or aluminium in abundance; the sodium-containing reaction products are converted
into sodium sulfite with the aid of sulphur dioxide, sulfurous acid or sodium bisulfite,
said silicon and aluminium compounds containing Si0
2 or A1
20
3 respectively as reactive components. In said publication it is particularly emphasized
that a long retention time of the reacting substance is necessary for the reaction
to be completed. Such long retention time is achieved by using a kraft or a glass
furnace.
[0003] In U.S. Patent No. 3,787,283 (D.R. SHEELEY ET AL.) a procedure of the same type as
that in the above-mentioned patent to LURIE has been used, except for the fact that
in order to achieve a long retention time a rotating furnace is used, into which are
supplied granules made up by aluminium ashes gained from burning and by waste liquor
on a sodium basis. In this way about one-third of the ashes which are formed can be
recovered as sodium aluminate.
[0004] In the making of sodium aluminate essential significance attaches to the phase forms
of the compound and to their changes. When the temperature is about 390 to 720 °K
(120 to 450 °C) mainly water molecules are detached from the sodium aluminate solution.
Up to 1370 °K (1100 °C) sodium aluminate occurs as compound NaAlO
2. At temperatures between 1370 and 1470 °K (1100 and 1200 °C) the decomposition of
sodium aluminate starts. If free carbon is present, there is formed x.Na
20 y.A1
2O
3, where x/y is 1/1 or 1/11, as well as sodium and carbon monoxide. At the same time
the oxide beta-Al
2O
3 begins to form, which is decomposed at 1670 to 1770 K (1400 to 150C °C) and the oxide
alfa-Al
2O
3, or corundum, which is an extremely stable and difficultly soluble compound and one
which is difficult to handle. When sodium aluminate is being made of sodium carbonate
and aluminium oxide the formation of the compound NaAl
2 begins at 770 °K (500 °C); the reaction mainly takes place at 920 to 1370 °K (650
to 1100 °C).
[0005] Sodium aluminate, which is excellently suited for the production of sodium sulfite
with the aid of sulphur dioxide in the manner outlined above, is produced in the water
phase and in dry conditions at temperatures between 350 and 1470
0K (80 and 1200 °C) independent of the state of the starting substances. In practice,
too, sodium aluminate is being made by the wet and the dry methods.
[0006] In the wet sodium aluminate producing method, bauxite or trihydrate of aluminium
oxide is solved in a hot sodium hydroxide solution having a temperature, for instance,of
490 to 520 °K (220 to 250 °C). The viscous solution thus obtained is dried in drum
dryers at a temperature lower than 470 °K (200 °C) whereby white crystalline sodium
aluminate is obtained, having a moisture content of about 20 %. The aluminate is dried
at about 990 °K (720 °C) in order to complete the reaction. The moisture of the end
product amounts to about 0.6 %.
[0007] In the dry method, the aluminium-containing substance is admixed to a sodium compound,
such as carbonate for instance, and the mixture is heated in a rotating furnace at
1170 to 1370 °K (900 to 1100 °C) until the reaction has come to an end. Crystallisation
of the sodium aluminate implies a comparatively high alkali content. When the temperature
exceeds about 1370 °K (1100 °C) the oxides beta-A1
20
3 and alfa-A1
20
3 begin to form. Sodium aluminate is also obtained at temperatures lower than those
mentioned, by reacting sodium hydroxide and natural aluminium oxide with each other.
[0008] Other processes for the production of NaA10
2 have been described, for instance, in German Patents No. 93 and 1 650 of 1877, in
German Patents No. 7256, 31 675, 80 063 and 112 173, and in U.S. Patents No. 877,376
and 2,734,796.
[0009] The main drawback of the above-described processes to LURIE and SHEELEY is the long
retention time which the reaction of the sodium and aluminium compounds requires to
allow the reaction to proceed to its end, whereby a large kraft furnace, glass furnace,
or rotating furnace becomes necessary. The capacity - and the price - of the furnace
will thus be high, and the operating expenses of the process are likewise high.
[0010] When producing sodium aluminate by the wet method, allowing sodium and aluminium
solutions to react with each other, one has to handle large quantities of solutions.
This naturally implies large size tanks and liquid handling equipment. Furthermore
the aluminate obtained has to be dried at an elevated temperature. When producing
sodium aluminate by the dry method it is likewise necessary to use big reactors. This
is because the raw material mix (aluminium compound plus sodium compound) is handled
in granular form, the compounds reacting with each other in granular form.
[0011] In the production of sodium aluminate additional difficulties are caused by the formation
of an insoluble oxide, i. e. of corundum. To wit, at temperatures beyond 1370
oK (1100 °C) the formation of corundum starts, particularly if no excess alkali is
present.
[0012] It is an object of the present invention to eliminate the drawbacks mentioned. It
is a further object of the invention to develop a new process for the production of
sodium aluminate in which the formation reaction of the sodium aluminate proceeds
in such a rapid manner that the retention time in the reactor is short. It is still
an other object of the invention to develop a new method for the production of sodium
aluminate in which no corundum is produced. It is yet a further object of the invention
to develop a new process for the production of sodium aluminate in which it is possible
to use inexpensive sodium compounds and inexpensive aluminium compounds as raw materials.
It is still another object of the invention to develop a new process for producing
sodium aluminate which is particularly appropriate for the making of sodium sulfite
intended for use in sulfite cellulose digestion and in which waste liquors from sodium-based
cellulose digestion and aluminium hydroxide are used as raw materials.
[0013] The characteristic features of the invention are outlined in the attached claims.
[0014] The invention will now be described in greater detail and with reference to preferred
embodiments to the accompanying drawings, in which
Fig. 1 shows, by way of a block diagram, the production of sodium aluminate by the
process according to the invention, and
Fig. 2 shows, by way of a block diagram, a cellulose digesting process employing the
process of the invention, and the sodium aluminate produced thereby in the production
of sodium sulfite.
[0015] Fig. 1 shows a burning process according to the invention, for making sodium-metal
oxide from compounds containing sodium 1 and the respective metal 2, by burning, said
metal being aluminium, titanium or vanadium. In the embodiment presented, the compounds
1 and 2 containing sodium and the particular respective metal, for instance a sodium
salt and a metal hydroxide, are conducted into a mixer 3 and further, in the form
of an aqueous suspension 4 mixed in the mixer, into a nozzle 5, by which the suspension
is sprayed into a burning chamber 6 in the form of droplets and is burned at a temperature
between 970 and 1870 °K (700 and 1600 °C) to become sodium-metal oxide. From the burning
chamber 6, the sodium-metal oxide 8, such as sodium aluminate or NaAl0
2 ash for instance, is separated by the aid of separating means 9 and removed for further
treatment or conversion as indicated by numeral 10. The flue gases 7 from the burning
chamber 6 are removed and carried to a unit for recovering heat and chemicals. In
addition to the metal compound, combustion air 12 is also conducted into the burning
chamber 6.
[0016] When the burning process is initiated, the temperature inside the burning chamber
6 (of Fig. 1), in which the burning of sodium-metal oxide as taught by the invention
takes place may be adjusted to its desired quantity by means of an additional burner
11 using additional fuel and by which the burning chamber is heated to a burning temperature
of 970 to 1870
oK (700 to 1600 °C) preferably 1170 to 1570 K (9oo to 1300 °C). When substances with
a high thermal value , such as for instance sodium lignosulfonates, alkali lignins
obtained from cellulose digestion and aluminium hydroxide, are used as compounds containing
sodium and the respective metal no additional heat is usually required in the burning
chamber, i.e., the heat derived from the process will maintain the desired temperature.
[0017] When sodium aluminate is being produced by the procedure according to the invention,
the principal part of the compound used is preferably an aluminium compound, for instance
aluminium hydroxide, bauxite, pure aluminium, aluminium oxide, or another equivalent
aluminium compound.
[0018] The sodium containing compound utilized may consist, for instance, of sodium compounds
obtained from waste liquor of sodium-based cellulose digestion such as sodium lignosulfonates
or alkali lignins, sodium sulfide, sodium hydroxide, sodium oxide, sodium bicarbonate,
sodium sulfate, sodium sulfite, sodium bisulfite, or other equivalent sodium compounds.
[0019] When compounds containing sodium and aluminium are being burned, the sodium in said
compounds and the respective metal are preferably in an essentially stoichiometric
proportion when the burning takes place. In that case the material that is being burned,
i. e. the blended compounds containing sodium and aluminium, in the aqueous phase
and in dropshape, contains sodium and aluminium in a substantially stoichiometric
proportion, the ratio Na:Al being 0.5 to 1.5 (preferably 0.9 to 1.1) advantageously
about 1. The ratio of sodium and aluminium, which is expressed as a molar ratio, is
important in view of expedient use of raw materials, from the viewpoint of the melting
point of the burning product achieved and in order to prevent the formation of disadvantageous,
difficultly soluble corundum. If the material that is to be burned contains an excess
of sodium, i. e. if the proportion of sodium ahd aluminium is 1.5 or at least higher
than about 1.1, sodium carbonate is produced lowering the melting point, about 1870
0K (1600 °C),of the sodium aluminate, or evaporating as ions. If there is substantially
less sodium than aluminium in the material that is being burned, i. e. if the proportion
of sodium an aluminium is below 0.5, preferably less than 0.9 or 1, there is aluminium
in excess, causing the formation of inert harmful corundum, or causing unnecessary
circulation when the sodium aluminate is used for the purpose of preparing the sulfite
digesting for cellulose as presented below.
[0020] In burning sodium and the compounds containing the respective metal, e. g. aluminium
in an aqueous phase in suspension, the dry matter content of the suspension to be
burned is usually between 45 and 75 % by weight. The concentration of the suspension,
that is the amount of water, has no great significance in itself. It is important
that the suspension be easily fluid in view of its handling. Furthermore the solution
of the sodium is important. Maximizing the concentration of the suspension is advantageous
with respect to energy economy, that is in the sense of minimizing the water quantity
evaporated in the burning process. The compounds containing sodium and the respective
metal may be mixed in a separate mixing container, the proportion of the quantities
of sodium and the metals being adjustable as desired. It is further possible to mix
the compounds containing sodium and the respective metal, in a mixer built in conjunction
with the burning chamber, or also in the nozzle by the aid of which the drops to be
burned are produced.
[0021] The process of the invention for making sodium-metal oxide is based on the burning
of compounds containing sodium and the respective metal, in the shape of droplets
in suspension and/or as a solution. When the compounds are burned in the form of spray
or aerosol type droplets, the burning is rapid, i. e. instantaneous. The compounds
to be burned being mixed together, the droplets contain sodium and the respective
metal in correct proportion, whereby the use of sodium and of metal in excess is avoided;
furthermore the sodium and the respective metal react in controlled and desired mixing
proportion.
[0022] It has been found in studies that have been made, that when compounds containing
sodium and the respective metal in question, such as aluminium, in droplets in an
aqueous phase are being burned, no difficultly soluble oxides such as corundum will
be formed. This is apparently due to the presence of sodium ions and of water. The
respective metal is also partly dissociated in water, whereby the substances are highly
reactive and no harmful byproducts can be formed.
[0023] Furthermore, in the burning of compounds containing sodium and the respective metal,
in aqueous phase and as droplets, the proportion of sodium and of the respective metal
is easily controlled because the mixing of the substances may be carried out in the
water phase. If the substances were burned and mixed in dry condition, then the achievement
of a satisfactory and sufficient result of mixing would require accurate grinding,
weighing, and mixing operations, the handling of the dry compounds
still being cumbersome and necessitating additional handling steps, such as drying
for instance.
[0024] The burning reactor, or burner, required due to the burning in droplet form, which
is instantaneous, may be constructed to be comparatively small and simple in construction,
for instance such as has been disclosed in U.S. Patent No. 2,985,506. Then the retention
time in the reactor will be short, and the space requirements of the reactor are extremely
small, for instance compared with the drum furnaces conventionally used in the manufacturing
of sodium aluminate (see U.S. Patents No. 3,061,408 and 3,787,283).
[0025] Fig. 2 shows another embodiment of the invention, wherein the process has been utilized
in a sulfite cellulose manufacturing process on an industrial scale. In the process,
the waste liquor 1 containing sodium lignosulfonates is separated in a separator 34
from the pulp 320 obtained from the digester 32, and for burning it is conducted together
with aluminium hydroxide 2 to a mixer-evaporator 3 and further to a burning reactor
6. The burning of the compounds 1,2 containing sodium and aluminium takes place in
a similar manner as in the embodiment of Fig. 1, by spraying the compounds mixed with
each other into the burning chamber, as an aqueous suspension with 45 to 75 % by weight
dry matter content in dropletshape, the burning taking place at a temperature between
970 and 1870 °K (700 to 1600 °C). The sodium aluminate ashes produced in the burning
process 8, is separated by means of an elec- trofilter 9 and conducted - as indicated
by 10 - into a tank 12 to be suspended in water and, further in suspended condition
130, to a storage tank 13. The flue gases 7 arising from the burning of the compounds
1 and 2 in the burning chamber 6, mainly consisting of carbon dioxide and sulphur
dioxide, are carried to sulphur dioxide recovery venturis 21,22,23,24.
[0026] The sodium aluminate emerging from the process is used together with the sulphur
dioxide that is obtained, to prepare the digesting liquor or solution. From the storage
tank 13, the sodium aluminate suspension 140 is conducted through a separator 14 separating
solids 2' and through a container 15 via pipe conduits 151 and 150 to the bottom of
a countercurrent washing venturi 24. Simultaneously the flue gases 7 are washed with
water in the washing venturi 21, and the washing water 250 is carried, together with
the sulphur dioxide dissolved therein, from the bottom of the venturi to the bottom
of venturi 24. The flue gases 222 not solved in water in venturi 21 are conducted
to the next venture 22 for washing, further-indicated by 232 - to the next venture
23, and finally - indicated by 242 - to venturi 24 and then to a flue gas outlet 260.
From the venture 24, the aqueous solution and suspension 243,formed there by flue
gases and by sodium aluminate is conducted to the preceding venturi 23, and further
- as indicated by 233 - to the venturi 22 and finally - as indicated by 223 - to the
mixing tank 16. The venturis 21 to 24 additionally have an internal circulation, and
solution is continuously circulated from the bottom of the venturis through the upper
part of the venturi.
[0027] During the washing of flue gases 7 in the venturis 21 to 24, the sodium aluminate
and the sulphur dioxide react as follows:

[0028] Thus, the reaction products containing sodium which are formed in the dissolving
of sodium aluminate are converted into sodium bisulfite with the aid of sulphur dioxide.
[0029] From a mixing tank 16, the suspension containing sodium bisulfite and aluminium hydroxide
that has been formed is conducted to an aluminium hydroxide separator 18, where the
aluminium hydroxide 170 is separated and conducted to a mixing tank 17, and through
a second separator 19 for sodium bisulfite 201 to the mixer-evaporator 3 for burning.
The sodium bisulfite solution 200,201 obtained from the separators 18 and 19 is conducted
to an acid concentration reactor 20, and the concentrated acid 310 to an acid tank
31 and further to a digesting acid preparing tank 33 and to a digester 32. There is
a continuous circulation between the tanks 31 and 33, and the digesting chemicals
are added in the tank 33. The digesting liquor for the digester 32 is taken from the
circulation pipe system 330.
[0030] In addition to the digesting acid, the lignocellulose- containing raw materials,
such as wood chips 340 are fed into the digester 32. Upon digestion, after defi- bration
has taken place, fibrous matter 40 is separated from the pulp obtained, in the separator
34, and the waste liquor 1 containing sodium lignosulfonates is conducted to the mixer-evaporator
3 to be evaporated and further for burning.
Example 1
[0031] To waste or spent liquor containing sodium lignosulfonate, obtained from the sulfite
digestion of cellulose, there was added aluminium hydroxide, and the suspension thus
obtained was burned, using an experimental set-up as shown in Fig. 1, in a horizontal
cylindrical burning chamber. The temperature in the burning chamber was raised to
a starting temperature above 1470
0K (1200 °C) by burning hydrocarbons by an ancillary burner. The ashes thus formed
consisted, of sodium aluminate as found out by way of an x-ray diffraction analysis;
on dissolving the ashes in water, 80 % sodium aluminate were solved, calculated on
the dry matter content of the burnt suspension. When burning said suspension air was
conducted into the burning chamber; an analysis revealed the following composition
of the flue gases: 2,7 % hydrogen, 0.9 % argon and oxygen, 77.2 % nitrogen, 2,4 %
carbon monoxide, 16.1 % carbon dioxide, 0.3 % hydrogen sulfide, 0.02 % sulphur compounds
of carbon, 0.05 % sulphur dioxide, and 0.2 % methane.
[0032] The experiment was repeated, using spent or waste liquor obtained from sulfate digestion
of cellulose (alkalilig- nins) as sodium compound instead of waste liquor from sulfite
digestion.
Example 2
[0033] Aluminium hydroxide was admixed to waste liquor derived from sodium bisulfite digestion
of cellulose, and the suspension was burned by spraying it through a Urquhart nozzle
into a burning chamber as shown in Fig. 1. The temperature in the burning chamber
was regulated with the aid of an ancillary burner using hydrocarbons. The chamber
consisted of a vertical cylinder, the supplying of the suspension and of additional
fuel as well as of combustion air thereinto being performed through the inner end
of the cylinder. The lower end of the burning chamber opened into the fire chamber
of a steam boiler, with a capacity of 24 t/h. The ashes which formed in the burning
chamber were dissolved in water, and the solution was analysed. Table 1 shows the
results:

[0034] The examples of the embodiments are only meant to illustrate the invention, without
restricting it in any way whatsoever.
1. Method of producing sodium-metal oxide by burning from compounds containing sodium
and the respective metal, said metal being aluminium, titanium, or vanadium, characterized
in that compounds containing sodium and the respective metal are mixed together, sprayed
into a burning chamber in the aqueous phase and in droplet shape, and burned at a
temperature between 970 and 1870 oK (700 and 1600 °C) to become sodium-metal oxide.
2. Method according to claim 1, characterized in that the sodium compound and the
metal compound used are burned at a temperature between 1170 and1570 oK (900 and 1300 °C), preferably between 1270 and 1520 oK (1000 and 1250 °C).
3. Method according to claim 1 or 2, characterized in that the sodium and the respective
metal contained in the sodium and metal compounds are substantially in stoichiometric
proportion in the drops or droplets to be burned.
4. Method according to any of claims1 to 3, characterized in that the main part of
the metal compound used is an aluminium compound.
5. Method according to claim 4, characterized in that the main part of the metal compound
used is aluminium hydroxide.
6. Method according to any of claims 1 to 5, characterized in that the main part of
the compound containing sodium is composed of lignosulfonates.
7. Method according to any of claims 1 to 5, characterized in that the main part of
the compound containing sodium is composed of alkali lignins.
8. Method according to any of claims 1 to 7, characterized in that the material to
be burned contains sodium and aluminium in aproportion Na:Al totalling 0.5 to 1.1,
preferably 0.9 to 1.1, advantageously about 1.
9. Method according to any of claims 1 to 8, characterized in that the compounds containing
in their main parts sodium lignosulfonates and aluminium hydroxide are mixed with
each other and sprayed into a burning chamber as an aqueous suspension in the form
of droplets and are burned to become NaAI02 at a temperature between 1170 and 1570 °K (900 and 1300 °C), the proportion of the
quantities of sodium and aluminium in the droplets being between 0.9 and 1.1.