Method of preparing reproducibly stable aqueous suspensions of sodium dithionite for woodpulp bleaching
AssigneeVirginia Chemicals Inc.
InventorsEdwin D. Little, Karsten R. Minzghor
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Abstract
Aqueous sodium dithionite slurries or suspensions, which are nonsettling during shipment thereof and are thereafter pumpable after storage at 32.degree.-40.degree. F. for at least fourteen days, comprise, on a weight basis, about 34% of sodium dithionite, about 0.17% of a xanthan gum, 5.5-6.5% of 50% sodium hydroxide, about 0.26% of a chelate, and about 1.96% of sodium tripolyphosphate which is added after adding the sodium dithionite. Preferably, the sodium tripolyphosphate is added last in making the slurry which is used as a woodpulp bleaching composition.
Claims9
A method for reproducibly preparing a storable and pumpable aqueous dithionite suspension which contains sodium dithionite and is useful for woodpulp bleaching, said method comprising the following steps, based on weight percentages of said suspension:
- A. preparing a dilute hydrosol containing about 0.144-0.180% of xanthan gum;
- B. sequentially adding 5.48-6.32% of 50% sodium hydroxide and 0.24-0.28% of a chelate to said dilute hydrosol;
- C. cooling said hydrosol to below 45.degree. F. to form a cold dilute hydrosol;
- D. adding 31.20-36.00% sodium dithionite, containing 88-90% Na.sub.2 S.sub.2 O.sub.4, to said cold dilute hydrosol at such a rate as to maintain its temperature below 45.degree. F. to form a suspension;
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- E. adding 1.85-2.00% of sodium tripolyphosphate to said suspension to form said storable and pumpable aqueous dithionite suspension.
A method for making a storable and pumpable aqueous dithionite suspension for woodpulp bleaching, which is physically stable at storage temperatures of 32.degree.-40.degree. F. for at least fourteen days by adding sodium dithionite to a hydrosol of water and xanthan gum and subsequently adding sodium tripolyphosphate thereto, said suspension additionally comprising sodium hydroxide and a chelate, said xanthan gum being 0.144-0.18 wt. % of said suspension and said sodium dithionite being 31.2-36.0 wt. % of said suspension.
Dependencies are inferred from the claim text.