Stabilization of sodium dithionite by means of various additives

Abstract

The present invention relates to a method for reducing or preventing the decomposition of a composition Z comprising Z1 a salt of dithionous acid in an amount ranging from 50 to 100 wt % and optionally Z2 an additive selected from the group consisting of alkali metal carbonate, alkaline earth metal carbonate, alkali metal or alkaline earth metal tripolyphosphate (Na.sub.5P.sub.3O.sub.10), alkali metal or alkaline earth metal sulfite, disulfite or sulfate, dextrose and complexing agents in a combined amount ranging from 0.0001 to 40 wt %, which comprises contacting the components Z1 and optionally Z2 in the solid and/or dry or solvent-dissolved or -suspended state with at least one of the following compounds V in the solid and/or dry or solvent-dissolved or -suspended state, wherein the compounds V are selected from the group consisting of: (a) oxides of the alkali metals lithium, sodium, potassium, rubidium, cesium, or of magnesium, (b) sodium tetrahydroborate (NaBH.sub.4), (c) anhydrous copper(II) sulfate (Cu(SO.sub.4)), phosphorus pentoxide and (d) basic amino acids arginine, lysine, histidine, wherein the solvent for Z1, optionally Z2 and V is practically water-free.

Claims

1. A method for reducing or preventing the decomposition of a composition Z comprising Z1 a salt of dithionous acid in an amount ranging from 50 to 100 wt % and optionally Z2 an additive selected from the group consisting of alkali metal carbonate, alkaline earth metal carbonate, alkali metal or alkaline earth metal tripolyphosphate (Na.sub.5P.sub.3O.sub.10), alkali metal or alkaline earth metal sulfite, disulfite or sulfate, dextrose and complexing agents in a combined amount when present ranging from 0.0001 to 40 wt %, which comprises contacting the components Z1 and optionally Z2 in the solid and/or dry or solvent-dissolved or -suspended state with at least one of the following compounds V in the solid and/or dry or solvent-dissolved or -suspended state, wherein the compounds V are selected from the group consisting of: (a) oxides of the alkali metals lithium, sodium, potassium, rubidium, cesium, or of magnesium, (b) sodium tetrahydroborate (NaBH.sub.4), (c) anhydrous copper(II) sulfate (Cu(SO.sub.4)), phosphorus pentoxide and (d) basic amino acids arginine, lysine, histidine, wherein the solvent for Z1, optionally Z2 and V is practically water-free and the solvent comprises less than 1000 wt-ppm of water.

2. The method as defined in claim 1, wherein the salt of dithionous acid Z1 is sodium dithionite.

3. The method according to claim 1, wherein the compound V is used in a total amount ranging from 0.01 to 0.9 wt %, based on the composition Z, except for sodium tetrahydroborate (NaBH.sub.4), which may also be present in a total amount ranging from 0.01 to 5 wt %.

4. The method according to claim 2, wherein the compound V is used in a total amount ranging from 0.01 to 0.9 wt %, based on the composition Z, except for sodium tetrahydroborate (NaBH.sub.4), which may also be present in a total amount ranging from 0.01 to 5 wt %.

5. The process according to claim 4, wherein Z2 is present.

6. The process according to claim 1, wherein Z1 is present from 70 to 95 wt. %, all based on the composition of Z.

7. The process according to claim 5, wherein Z1 is present from 70 to 95 wt. %, all based on the composition of Z.

8. The process according to claim 1, wherein Z2 is present from 0.0001 to 10 wt. %, all based on the composition of Z.

9. The process according to claim 7, wherein Z2 is present from 0.0001 to 10 wt. %, all based on the composition of Z.

10. The process according to claim 1, wherein Z2 is present from 1 to 5 wt. %, all based on the composition of Z.

11. The process according to claim 9, wherein Z2 is present from 1 to 5 wt. %, all based on the composition of Z.

12. The method according to claim 1, wherein the solvent comprises less than 100 wt-ppm of water.

13. The method according to claim 11, wherein the solvent comprises less than 100 wt-ppm of water.

Description

EXAMPLES

(1) The quantification of the sodium dithionite content was in each case done iodometrically.

Example 1a

(2) 45 g of sodium dithionite (Hydrosulfit F from BASF SE) comprising from 2 to 4 wt % of sodium carbonate (anhydrous) were mixed, at room temperature and low relative humidity, with a component V, as a dry solid, as reported below in Table 1 and conditioned at 65 C. for 7 days in an ampule vial sealed with an overpressureproof septum. Thereafter, the sodium dithionite content of the conditioned mixture was determined and the flowability thereof evaluated by pouring the conditioned mixture out of the particular ampule vial. Flowability was rated from 0 (utterly caked) to 100 (instantly flowable). The wt % ages reported in Table 1 a are based on the mixture as a whole.

(3) TABLE-US-00001 TABLE 1a [Wt %] Sodium dithionite Component V component V [wt %] Flowability 60-72 20-40 Magnesium oxide 1 76 80 MgO Sodium oxide Na.sub.2O 0.5 82 100 Lithium oxide Li.sub.2O 1 78 90 Lithium oxide Li.sub.2O 0.5 77 90 Sodium borohydrite 1 91 90 NaBH.sub.4 Phosphorus pentox- 1 82 90 ide Copper(II) sulfate 2 83 100 (CuSO.sub.4) anhydrous Arginine 1 84 95 Lysine 1 82 90

Example 1b

(4) Example 1a was repeated except that the sodium dithionite product contained less than 1 wt % of sodium carbonate (anhydrous). The results are shown in Table 1b. The wt % ages reported in Table 1b are based on the mixture as a whole.

(5) TABLE-US-00002 TABLE 1b [Wt %] Sodium dithionite Component V component V [wt %] Flowability Phosphorus pentox- 1 80 90 ide

Example 2

(6) 50 g of sodium dithionite (Hydrosulfit F from BASF SE) comprising 0.8 wt % of sodium carbonate (anhydrous) were mixed, at room temperature, with a component V, dry as solids, as reported below in Table 4, and filled into 100 ml sealable Schott glass bottles. A plastics sponge drenched with 0.5 ml of water was inserted into each bottle neck and then the Schott glass bottle was sealed tight with the screw lid and stored for 7 days at 30 C. (drying cabinet). Thereafter, the sodium dithionite content of the conditioned mixture was determined and the flowability thereof evaluated by pouring the conditioned mixture out of the particular Schott glass bottle. Flowability was rated from 0 (utterly caked) to 100 (instantly flowable). The wt % ages reported in Table 1 b are based on the mixture as a whole.

(7) TABLE-US-00003 TABLE 2 [Wt %] Sodium dithionite component V Component V [wt %] Flowability 1 Phosphorus pentox- 78 50 ide 1 L-Arginine 86 80