JPH0478337B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL FIELD OF THE INVENTION The present invention relates to aqueous slurries, particularly non-settling flowable aqueous slurries of sodium dithionite that remain in pumpable form without significant swelling, settling or gelling. BACKGROUND OF THE INVENTION Sodium dithionite (commonly called sodium bisulfite and less precisely sodium hydrosulfite) has been used for some time for bleaching, especially for the bleaching of wood pulps such as textiles and groundwood pulps and semi-chemical pulps. It is a strong reducing agent. Sodium dithionite was usually produced by significantly different methods based on zinc dust, sodium formate, sodium borohydride or sodium bisulfite (electrolytic). Such methods are described, for example, in U.S. Pat. No. 2,938,771;
No. 3259457; No. 3411875; No. 3718732; No. 3718732;
No. 3872221; No. 3887695; No. 3897544; No. 3897544;
No. 3927190; and No. 4127642. The products of these processes are referred to herein as zinc-derived, formate-derived, borohydride-derived and electrolytically-derived sodium dithionite, respectively. Since zinc dithionite produced by the zinc process is no longer ecologically acceptable, zinc dithionite is converted to sodium dithionite by adding sodium hydroxide or sodium carbonate, thereby converting zinc hydroxide or zinc carbonate into Precipitate and remove by filtration. When anhydrous sodium dithionite crystals are dissolved under aerobic or anaerobic conditions to produce large quantities of aqueous solutions, the resulting solutions cannot be stored for long-term use. Since the sodium dithionite solution hydrolyzes at neutral PH, decomposition proceeds rapidly from that point through a self-chain reaction as the decomposition products create acidic conditions that promote decomposition. However, aqueous solutions of dithionite salts are commercially acceptable in US Pat.
When stabilized by additives such as those described in this patent, they decompose at an industrially acceptable rate. These additives include chelating agents, sodium carbonate, sodium tripolyphosphate, sodium hydroxide and amines. Although such stabilized solutions can be protected from decomposition for long enough periods for shipping and routine industrial use under suitable conditions, anhydrous dithionite crystals cannot be stored in sealed containers. Storage under dry inert gas during storage was the more common practice. Even though the crystals are thereby chemically stable for long periods of time, they begin to decompose as soon as they are exposed to air and moisture when the container is opened for use. Furthermore, containers of sodium dithionite available on the market indicate that when this is combined with suitable additives,
They are expensive to transport as they have a concentration of 12-13% and also generally require refrigeration during shipping and storage. In this way, about 7 times as much water as the product is transported.
There is a tendency to make product sales dependent on distance. As a result, the slurry is of interest to avoid or at least minimize the storage costs and difficulties associated with sodium dithionite in solution form, without diminishing the convenience that the purchaser derives from solution. It seemed to provide a means. However, the economical production, stabilization, handling, and shipping of such slurries is not straightforward. It is also not easy to produce suitable suspensions without stirring, so that they can be transported by ship and then pumped from tank cars. Indeed, the complexity of the idea is readily appreciated when one considers the variety of methods available for producing sodium dithionite, including unique by-products, crystal structures, etc. Additionally, slurries have not been extensively studied or commercially utilized like other forms of sodium dithionite. U.S. Patent No. 3,536,445 discloses that sodium-
A method is described for producing sodium dithionite from a zinc alloy by first making zinc dithionite and then converting it to sodium dithionite by adding caustic soda. After removing the zinc hydroxide by filtration, the dihydrate of sodium dithionite is salted out from the mother liquor using sodium chloride and alcohol to form a slurry. U.S. Patent No. 3,804,944 discloses caustic soda 1
~30% containing ~8% (relative to dithionite)
Slurry (formate-derived sodium dithionite)
18.5% and zinc-derived sodium dithionite (11.5%). Tests have shown that these slurries require frequent agitation to prevent condensation and processing difficulties. U.S. Pat. No. 3,839,217 discloses reducing the particle size of sodium dithionite crystals and/or introducing suspending or thickening agents into the liquid containing the crystals, such as an alcoholic salt solution. We show that it is possible to create a fluid, homogeneous, pourable dispersion of solid dithionite particles that is chemically and physically stable for long periods of time, but with the exception of dissolving the dithionite. Suppressing brine and/or
Or suppose there is a substance like salt in alcohol. The majority of particles should be approximately 0.6-0.8 microns in size. methylcellulose,
Hydroxyethyl cellulose, polyvinyl alcohol, guar gum and other conventional thickening, dispersing or suspending agents can be used. Thickened dispersions typically have a Bruckfield viscosity of 9000 c.ps and contain up to 34% Na ₂ S ₂ O ₄ . U.S. Pat. No. 3,839,218 maintains a dispersion of crystalline zinc dithionite or alkali metal by continuous or periodic mechanical stirring so that the crystals can be stored for long periods of time without dispersion. To achieve this, a method is provided in which the dispersion medium is aqueous or non-aqueous and contains a substance that inhibits dissolution of dithionite solids. The pH of the liquid is at least
6.5, the viscosity of the dispersion must be below about 50,000 centipoise, and the inhibitor may be a water-soluble organic compound or a saturated salt solution or a mixture thereof. Thickening and suspending agents may be used. Suitable thickening and suspending agents include polysaccharides,
Includes water-soluble polymers, and moderate molecular weight proteins. Representative agents include guar gum, tragacanth, gelatin and starch. U.S. Pat. No. 4,283,303 discloses that a sodium dithionite solution is mixed with a heating medium at a temperature of 220 to 250% (approximately 104.4 about
Maintain solutions and slurries under a vacuum of at least 25 inches (635 mm) Hg (110-155 °C).
A method is described in which the slurry is maintained at a temperature of about 43.3° C. to about 68.3° C. for evaporation, and the resulting slurry is rapidly cooled while stirring. The vacuum is preferably 26.5 to 27.5 inches (673.1 to 698.5 mm). A preferred sodium dithionite solution is a zinc-derived sodination solution to which 4-5% by weight of sodium dithionite, NaOH and a chelating agent are added as stabilizers. Although these evaporated slurries have very good stability, they have experienced settling problems over a period of 2 to 5 days, especially under the vibrations created by tank truck transport. Such settling and subsequent hardening resulted in a cargo that could not be unloaded by pumping as is customary. Slurries are commonly used in foods, coatings, paints,
Used as dyes, explosives, oil well fluids, etc., often containing natural or synthetic rubbers, forming liquid colloidal systems in which solid particles are dispersed. Such rubber-containing liquid systems, without solid particles, are considered to be sols, and more precisely, when based on water, are called hydrosols. Rubbers typically provide viscosity to the sols in which they are formulated, thereby providing a thickening agent function. When a shear force is generated by stirring the sol and no change in viscosity occurs, the behavior of the thickener is said to be so-called uniton flow. When the viscosity of the sol at rest is greater than when a shear force is applied by stirring, when the viscosity decreases when the applied shear force increases, and when the viscosity decreases when the magnitude of the shear force decreases. If it recovers quickly, the behavior of the thickener is said to be plastic. A sol is described as pseudoplastic if the flow rate increases more rapidly than is normal with respect to the applied shear stress. Generally, when the sol is stationary, the plastic thickener molecules arrange themselves in a more or less stable manner. Application of shear forces is necessary to disrupt this stable molecular arrangement and generate a sol. The shear force required to generate and flow the sol is called the yield point or gel strength. Once the gel strength of the plastic sol is overcome, the viscosity of the sol decreases proportionately when large shear forces are applied. A large number of natural and synthetic rubbers are widely used for the production of hydrosols. An advantageous gum for many hydrosols is the guar tree (Cyamopsis
It is a galactomanna gum like guar gum derived from the endosperm of A. tetragonolobus. Another water-soluble gum that is increasingly used is Xanthomonas hydrophilic colloid (commonly called xanthan gum), which is a
It can be produced by the action of various species of the genus. Carbohydrate Bacterium Xanthomonas campestris
The fermentation products of the reaction of B. campestris (preferred species) are produced by Kelco Corporation (Kelco
It is commercially available as "Kelzan" manufactured by San Diego, California.
A typical method for clarifying a Xanthomonas fermentation liquor and/or recovering the Xanthomonas hydrocolloid components involves diluting the fermentation liquor with water to reduce its viscosity and optionally centrifuging or filtering the diluted fermentation liquor. to remove suspended insoluble solids. A salt such as potassium chloride and a non-solvent such as methanol or isopropanol are added to the fermentation liquid to flocculate the potassium form of the gum;
This rubber is then recovered by centrifugation or solid/liquid separation techniques. Further dissolution, reprecipitation and washing steps are commonly used. The heteropolysaccharides thus produced by bacteria of the genus Xanthomonas for carbohydrates are usually obtained as a thick viscous solution of dull yellow color. Xanthan gum is a common and widely used suspension and viscosity forming agent. Some of the then different uses are in oil well fluids, paints, sprays and cleaning fluids. However, xanthan gum has slight drawbacks. Hydration can occur since it is extremely difficult to disperse and wet in water or fermentation liquor. A high degree of shear is usually required to wet each rubber particle. Once dispersion and wetting is achieved, hydration of the rubber is extremely rapid, as evidenced by an increase in viscosity.
Xanthan gum and guar exhibit very different rheological properties (have different molecular configurations)
and come from completely different sources. Vibrations during tank car or tank truck transport, for example to textile mills or pulp mills,
Easily storable and then easily pumped for dilution to the desired solids content and for short-term storage until required, such as for bleaching textiles or wood pulp, when pumped into a storage tank There is clearly a need for stable dithionite hydrosol compositions with pseudoplastic properties that are transportable. However, attempts in accordance with the present invention to use both guar gum and xanthan gum as suspending agents for sodium dithionite crystals have shown that even during static storage, these gums surprisingly produce slurries that can gel or settle together. proved to have an unpredictable tendency to form. SUMMARY OF THE INVENTION Accordingly, the subject of the present invention is a method in which dithionite crystals can be suspended during long-term storage and transport and, if necessary, can be easily pumped.
An object of the present invention is to provide a method for producing a stable dithionite slurry containing a hydrosol. It is also an object to provide a storable and pumpable dithionite slurry as a novel composition using xanthan gum as its suspending component. The fermentation of carbohydrates to produce biosynthetic water-soluble xanthan gum through the action of Xanthomos bacteria is well known. The first research in this area was conducted by the U.S. Department of Agriculture,
Described in US Pat. No. 3,000,790.
Particularly well known is the action of Xanthomonas Campestris NRLLB-1459 on glucose substrates. Xanthomonas hydrocolloids (i.e., xanthan gum) are prepared by transferring Xanthomonas campestris bacteria to a suitable medium and conditioning it for growth in two steps before growing it in a final medium containing 3% glucose. Manufactured. After 96 hours at 30° C. with proper aeration and stirring, a Xanthomonas hydrocolloid is produced at a concentration of approximately 1%. Xanthomonas campestris is the bacterium selected for the purpose of producing biosynthetic Xanthomonas hydrocolloids, while X. begoniae, X. malvacearum, X. carotenase, X. incanae , X. phaseoli, X. vesicatoria, X. papaveriocola, X. translucens, X. vasculorum,
Other Xanthomonas species can also be used, such as X. hedrae and X. hedrae. U.S. Patent No. 3391060; U.S. Patent No. 3391061; U.S. Patent No.
No. 3427226; No. 3455786; No. 3565763; No. 3966618; No. 4094739; No. 3773752;
Same No. 4051317; Same No. 4135979; Same No. 4296203
No. 3919189; No. 3119812; No. 3119812;
No. 3316241; No. 4282321; No. 4299825, “Encyclopedia of Chemicals”
Technology” (Encyclopedia of Chemical
Technology), 3rd edition, (1980, John Wiley &
There are a number of patents and publications describing the production of xanthan gum, including Sons, pages 62-64), the contents of which are cited herein. Xanthan gums of various companies with slightly different molecular structures and rheological properties, produced from X. camperitris or its variants, are
“Kelzan” or “Keltrol” trademark of Kelco Company
(Keltrol); “Flocon”, a trademark of Pfizer Chemical Division
(Flocon); Rhone Poulenk (Rhone−
Poulenc trademark “Rhodopol”
23”; Meer Corporation
Corporation) trademark “Merezon”
8" and "Meretec 30" as well as other manufacturers. For example, it is produced by culture fermentation with the microorganism A widely used polysaccharide sold under the trademark Kelzan as industrial xanthan gum by Kelco, has a moisture content of 12%, an ash content of 10%, a specific gravity of 1.6, and a density of 52.4 l ^b /ft ³ ( Approximately 0.84
g/ ^cm3 ), nitrogen content of 1.2% and 40
It is a dry, cream-colored powder with a mesh size of . As a 1% solution in distilled water, its PH is
7.0, its surface tension is 75dynes/cm,
Its viscosity is 850 cP as measured with a Burdskfield LVE viscometer at 60 rpm, and its freezing point is 0.0 °C
It is. Another solid xanthan rubber manufactured by Kelco under the trade name K9C57 has rheological properties of high viscosity at low concentrations, pseudoplastic flow over a wide shear rate range, and a significant yield point. Such characteristics indicate that xanthan rubber molecules have a strong molecular structure. Very low shear rate (1.
sec ^-1 ), this modified xanthan rubber exhibits more Newtonian flow than Kelsan rubber. As a 1% solution in distilled water, its PH range is 6-8 and its viscosity is 630-1000 cP. A whole xanthan fermentation solution with a viscosity in the range of 3500-4500 cP, easily pumped or injected, and with a significant yield point at biopolymer concentrations above 0.1% has a biopolymer concentration of 13.8% or 3.7%. At molecular concentration, Flocon Biopolymer from Pfizer Chemical Company
Available as 4800. This material is covered by U.S. Patent No.
No. 4119546, the contents of which are cited herein. The aqueous fermentation liquor is believed to be produced by variant strains of Xanthomonas campestris. It is protected with formaldehyde and does not exceed a 1.5% concentration of unreacted sugars. It is a gelatinous liquid with a yellow-brown appearance. It has a higher apparent content of active purified carbohydrates than commercially available solid xanthan. Because the solution of Flocon 4800 is highly pseudoplastic in nature, the viscosity that decreases when exposed to high shear is fully recovered when the solution is returned to a low shear condition.
The solution viscosity of this biopolymer is within the range of 5 to 12
Not affected by PH. It is clear that any and all forms of xanthan gum can be used in the present invention to provide a slurry that does not contain alkali tripolyphosphates, such as sodium tripolyphosphate. Only if the tripolyphosphate salt is present will certain changes have to be made, as described below. Typically, a suspendable, injectable, pumpable, tripolyphosphate-free, dithionite slurry (0.25% xanthan content) will contain 0.25 pounds of xanthan gum per 100 pounds of slurry. ) can be produced using as small a quantity as possible. This amount is equivalent to 1 pound of xanthan (approx.
0.45Kg) is equivalent to approximately 146 pounds of commercially available hydrosulfite (65.7Kg). The slurry is non-settling and within the practical range imposed by the slurry viscosity,
Fully pourable at any desired solids content. Such slurries, for example, are easily flowable and easily poured and pumped with viscosities up to 8000 cP. However, by allowing slight settling, a soft and dispersible settled slurry containing as little as 0.20% xanthan gum is obtained. Such partially suspended but dispersible slurries are useful for many purposes, such as for relatively short distance transportation. This amount is approximately hydrosulfite per pound of xanthan gum (approximately 0.54Kg).
Equal to 182 lbs (approximately 81.9 Kg), such as hydrosulfite 36.4% and xanthan gum 0.20
Examples include slurries containing %. Advantageously, the slurry contains hydrosulfite at least about
20%, chelate and alkali at least about 20%
containing so that the slurry has a PH of at least about 10. A suitable alkali is sodium hydroxide. Other bases such as potassium hydroxide or soda ash can also be used. However, sodium hydroxide is particularly advantageous over soda ash since it requires small amounts (in gram equivalents) to obtain the desired PH. A method for producing a storable and pumpable slurry from commercially available hydrosulfite is, by weight, (a) producing a hydrosol as a 1% aqueous solution of xanthan gum; (b) stirring an appropriate amount of this xanthan solution into water; (c) While stirring the above solution, sequentially add an aqueous solution of the chelate and a 50% NaOH solution; ( d) cool the resulting solution in an ice bath to a temperature below 45°C; and (e) add anhydrous sodium hydrosulfite to the cooled solution and bring the temperature below 45°C. and at a rate such that Na ₂ S ₂ O ₄ (commercial grade) is maintained at
28-36% and having a pH of at least 10. When the slurry is used for textile bleaching, it advantageously contains, by weight, at least about 36% commercially available sodium dithionite, at least about 3% sodium hydroxide as alkali, at least about 0.25% mixed chelate and Kelsan grade. Consisting of at least about 0.25% xanthan gum such as. The viscosity is in the range of 6000-8000cP. It is quite obvious that smaller amounts of dithionite (for example 20% pure) can also be used, but the ranges mentioned above are advantageous. When the slurry is used for wood pulp bleaching, it additionally contains at least about 3% by weight sodium carbonate and about 2% by weight sodium tripolyphosphate (see US Pat. No. 3,985,674). The disclosure of that US patent is incorporated herein by reference. For example, the chelate is the tetrasodium salt of ethylenediaminetetraacetic acid and is at least about 0.08% by weight of the slurry. It is clear that difficulties arise when sodium tripolyphosphate is present, for reasons that are not entirely clear. As previously mentioned, all forms of xanthan gum can be used to produce tripolyphosphate-free slurries. however,
If tripolyphosphate is present, all forms of xanthan can be used in one data example and two forms of xanthan can be used in all data examples. Two widely applicable forms of xanthan are "K9C57" and "Flocon 4800", which have already been described. In fact, when using these two forms of xanthan gum, it can be present in concentrations as low as 0.13% by weight. One data example where all forms of xanthan gum can be used is commercially available sodium dithionite 28
wt% _{, Na5P3O10 0.17wt} %, _{Na2CO3 3.28} ~
3.29% by weight, 0.78% by weight of sodium hydroxide, 0.08% by weight of chelate and water. Examples Pure _Na2S2O4 with _an average _content of 88-89%,
Experiments utilizing formate-derived sodium dithionite (F/hydrosulfite) to produce a storable and then pumpable dithionite slurry. In numerous experiments, F/hydrosulfite was used as a component of two types of commercially available bleaching products: (1) textile bleaching systems and (2) wood pulp bleaching systems (both of which are registered mixtures). These slurries are stable for at least 3 weeks during storage at 32-40°C (0 to about 4.4°C). The physical properties of the slurry are:

[Table] Examples 1 to 13 Attempts to produce a dithionite slurry that does not settle, gel, and produce unpumpable shipping materials were carried out using eight materials with thickening or charge repulsion properties. It began by adding 35% F/hydrosulfite to a dithionite slurry.
All of these slurries were observed to be insufficient as listed in Table 1.

TABLE Examples 14-23 Experiments were now conducted using guar gum as a suspending agent in two types of F/hydrosulfite slurries commercially available as bleach systems. Examples 14-19 use textile bleaching types and are listed in the table. Examples 20-23 use wood pulp bleaching types and are listed in the table. In both tables, “%F/
Hydro” indicates the weight percent of formate-derived sodium hydrosulfite used in the slurry.
As noted in the two tables, none of the guar thickened slurries were satisfactory as easily confirmed by observation.

【table】
liquid separation in parts
19 56.6 0.25 6.4 3.0
36.4 146 Coagulation

[Table] Examples 24-36 A 1% solution of gelzanxanthan gum in water,
First prepared for Examples 24-26 and 29-35. The appropriate weight of this solution was added to a predetermined amount of water, followed by the addition of alkali and chelate. The alkali was in the form of 50% NaOH. The chelate is the sodium salt of ethylenediaminetetraacetic acid (EDTA) or manufactured by Organic Chemicals Division of WR Grace & Company.
Grace and Company) [Nashua,
The chelating agent was Hampen-OH, a liquid mixture of chelating agents marketed by Hampen-OH, New Hampshire. The solution was cooled to 32°C (0°C) and solid F/hydrosulfite was added at a rate such that a temperature of 40-45°C was maintained. Next, the slurry was returned to the cooling bath, and its fluidity etc. were examined for 3 days. The use of xanthan gum is tabulated at various levels in textile bleaching slurries. Parts by weight of 1% xanthan solution are stated as parts by weight of xanthan gum for each example. Although the full flow of Example 24 is advantageous, the slight settling and flow of Examples 25 and 26 may also be advantageous for some applications, especially for conveying conditions involving relatively mild vibrations or short periods of transport. Are suitable.

[Table] Examples 27 and 28 are xanthan rubber (Kelzan rubber)
grade) in 21% of the total amount of water and used to make the hydrosol. The NaOH solution and chelate were then added to the remaining amount of water and the mixed solution was cooled to about 35°C. Then crystalline F/hydrosulfite (88%
Na ₂ S ₂ O ₄ ) was added to the Costic solution while cooling to maintain a temperature of 45°C. A hydrosol was added to this aqueous slurry to produce a stable slurry that did not settle within 3 days. After storage for 2 days at about 35°C, the slurry of Example 27 has a viscosity of 7.120 cP; Example 28
The slurry had a viscosity of 7.980cP. Examples 29-36, along with Examples 24-28, demonstrate that all forms of xanthan gum can be used. Example 29
Kelzan-M was used for Examples 30-32, and K9C57 was used for Example 35 (all products of Kelco). Examples 33 and 35 are FLOCON (3.7%) and Examples 34 and 36 are FLOCON (13.84%) (both Pfizer)
company's product) was used. Examples 37-48 The following examples demonstrate that various concentrations of commercially available sodium hydrosulfite (i.e., 88-89% purity) can be used to make a pumpable slurry with xanthan gum, but guar cannot be used at all. represent The results are shown in the table.

[Table] Compositions Containing Tripolyphosphate As shown above, compositions containing polyphosphate show variable results with the exception of Phizer's Flocon or Kelco's K9C57, but all forms Except for one data example where Kelsan rubber can be used. The following example illustrates this. Examples 49-65 Experiments to produce a storable, pumpable slurry for use as a wood pulp bleaching system began with 1% Kelsan gum for Examples 49-63.
It consists of making an aqueous solution and then adding an appropriate amount of this solution to water. The next additions to the water are sodium carbonate, sodium tripolyphosphate, a solution of the chelate and then a 50% NaOH solution. The entire solution was then cooled to 32°C (0°C) in an ice bath. The required amount of solid (crystalline F/hydrosulfite) was added at a rate to maintain the temperature below 45°C. The slurry was then cooled again in an ice bath for 3 days and observed for separation, sedimentation, and pourability. Examples 64 and 65 are similar to Examples 27 and 28, in which xanthan gum is dissolved in 12% of the total amount of water to create a hydrosol, and then Na ₂ CO ₃ , Na ₅ P ₃ O ₁₀ ,
Prepared by adding NaOH solution and chelate. The solution was then cooled to approximately 35°C. Solid crystalline F/hydrosulfite was added with cooling to maintain a temperature of 45°C. To this aqueous slurry, xanthan hydrosol was added to produce a stable slurry that did not settle after 3 days of storage. The slurry of Example 64 had a density of 1.37 g/ml and a viscosity of 3900 cP. The slurry of Example 65 had a viscosity of 4040 cP. The following example in the table shows the critical mass of xanthan concentration, all observations were made after 3 days in an ice bath, all percentages are in weight % (uncorrected for impurities in F/hydrosulfite) ). As an average value, correcting for impurities in the F/hydrosulfite by multiplying by 0.885, the amount of pure Na ₂ S ₂ O ₄ in the example F/hydrosulfite is: F/Hydro % Pure _{Na2S2O4 ; %} 27 23.9 28 24.8 30 26.6 31 27.4 36.4 32.2 As can be seen, only Examples 49, 63 and 64 gave acceptable results.

[Table] Examples 66-70 The next two examples in the table show Phizer's Flocon bioconcentration as 13.8% Flocon fermentation liquor in Example 66 and 3.7% Flocon fermentation liquor in Example 67 with xanthan 0.19% along with wood pulp slurry. molecule 4800
, both of which were made with F/hydrosulfite. The experiments using K9C57 xanthan gum, listed as Examples 68-70 in the table, illustrate the use of this xanthan in wood pulp slurries that normally coagulate or are unstable in some way with kelsan gum. The ratio in the penultimate column is
Sodium triphosphate ( _{expressed as Na5P3O10} )
Total number of moles of + number of moles of Na ₂ CO ₃ is 100%Na ₂ S ₂ O ₄
It is obtained by dividing by the number of moles of . Ideally, this ratio should be around 4.0 for Kelzan usage.
Should be ±0.2. Deviations above and below this ratio require the use of K9C57 or Flocon biopolymers. On a weight basis, the biopolymer fermentation liquid is approximately equivalent to solid xanthan, commercially available under the trademark K9C57, in its ability to create satisfactory storage and pumpability.

【table】

【table】

Claims (1)

[Scope of Claims] 1. At least about 20% by weight of predominantly pure sodium dithionite, at least about xanthan gum.
A storable, pumpable, tripolyphosphate-free aqueous slurry consisting of 0.20% by weight, chelate, alkali and water and having a PH of at least 10. 2. Pure sodium dithionite is at least
25% by weight of the slurry of claim 1. 3 containing at least about 20% by weight of sodium dithionite, at least about 0.13% by weight of chelate, alkali, and xanthan gum;
A storable and pumpable tripolyphosphate-containing aqueous slurry having a pH of . 4 Mainly commercially available sodium dithionite 28% by weight, xanthan gum 0.17% by weight, Na ₅ P ₃ O ₁₀ 1.92
4. A slurry as claimed in claim 3, comprising _, by weight, 3.28-3.29% _Na2CO3 , 0.78% sodium hydroxide and 0.08% chelate, and water. 5. A process for preparing a storable, pumpable, tripolyphosphate-free aqueous slurry of dithionite from crystalline dithionite, which: (A) contains at least 0.20% by weight of xanthan gum, based on the final product; Create a dilute hydrosol; (B) Subsequently add the chelate and an aqueous solution of sodium or potassium hydroxide to the dilute hydrosol;
Add the dilute hydrosol with stirring to make an alkali hydrosol; (C) Add the alkali hydrosol to about 45 〓 (7 ml) in an ice bath.
℃) to create a cold hydrosol;
and (D) adding commercially available sodium dithionite to the cold hydrosol at a rate such that its temperature is maintained below 7°C and containing at least about 25% pure sodium dithionite and having a pH of at least 10. 1. A process for making a storable, pumpable tripolyphosphate-free aqueous slurry of dithionite, characterized in that the slurry is added in an amount sufficient to obtain a dithionite slurry having: 6. The method according to claim 5, wherein a concentrated hydrosol is prepared as a 1% aqueous solution of xanthan gum, and this concentrated hydrosol is added to water while stirring to form a dilute hydrosol. 7. If the slurry is approximately
36%, at least about 3% sodium hydroxide or potassium hydroxide, at least about 0.25% chelate, and at least about 0.25% xanthan gum.
The method described in section. 8 In the process of preparing a storable, pumpable, tripolyphosphate-containing aqueous slurry of dithionite from crystalline dithionite, (A) from about 0.13 xanthan gum to the final product;
(B) Subsequently, an aqueous solution of the chelate and sodium hydroxide or potassium hydroxide is added to the dilute hydrosol while stirring the dilute hydrosol to create an alkaline hydrosol; (C) The alkali hydrosol was heated in an ice bath at 32〓(0
(C) to form a cold hydrosol; and (D) add commercially available sodium dithionite to the cold hydrosol at a rate such as to maintain its temperature below 7°C, and at least about at least about 10% pure sodium dithionite. A process for the preparation of a storable and pumpable tripolyphosphate-containing aqueous slurry, characterized in that it is added in an amount sufficient to obtain a dithionite slurry containing 25% and having a pH of at least 10. 9. The method according to claim 8, wherein a concentrated hydrosol is prepared as a 1% aqueous solution of xanthan gum, and this concentrated hydrosol is added to water while stirring to form a dilute hydrosol. 10 The slurry is a wood pulp bleaching composition,
9. A process as claimed in claim 8, in which in step B additionally a solution of sodium carbonate and sodium tripolyphosphate is added to the dilute hydrosol in sequence with stirring.