US1685800A

US1685800A - Treatment of sulphite-wood-pulp liquor

Info

Publication number: US1685800A
Application number: US539285A
Authority: US
Inventors: Baker Webster E Byron
Original assignee: Individual
Current assignee: Individual
Priority date: 1922-02-25
Filing date: 1922-02-25
Publication date: 1928-10-02
Anticipated expiration: 1945-10-02

Description

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The process includes a number of which are enumerated and explained below. The first step consists of the collection of the sulphite waste liquors from the blow pits it into whichthe sulphite pulp is discharged from the digesters. The liquor is drained from the pulp through a perforated bottom in the blow pits. llf necessary or justified under the particular conditions most of the tilt liquor which may still cling to the fibrous pulp after draina e by virtue of capillarity may be displaced by the gradual addition of water, which is evenly distributed over the surface of the pulp mass.

Tn the second step these liquors while still hot are subjected to filtration through a filter capable of retaining any and allfibers and solids in suspension. These fibers are returned to the blow pit, and the clear liquor an while still hot may or may not be sprayed through a nozzle pr nozzles into the atmosphere, according .to the process which the liquors are subjected to for the recovery of organic constituents. at The third step in the process consists in the collection of these (sprayed or unsprayed) liquors, and subsequent treatment at a temperature of substantially not less than 80 to fi5 ce ntigrade, with the oxide or hydroxide to of an alkaline earth metal in a tank provided with an elficient agitator, until the loosely combined sulphur dioxide contained in the liquoris changed to the sulphite of the alkaa line earth metal, and until the hydrogen ion as concentration of the liquor is substantially suchas is designated by the symbol or expression plil fi. The first half or two-thirds (not more) ofthe required treatment may be done in' soine respectsadvantageously with to the equivalent amount'of a carbonate of an alkalineeai'th metal, if this is desirable or cheaper, but the rate-of reaction is afiected unfavorably, the carbonate of an alkaline steps,

earth metal being considered an equivalent at and as such'included in the claims. When \using the oxide, it is always slaked, forming a hydroxide solution or suspension. The hydroxideis always furnished to the liquor in dissolved or suspended form. an The selection of the alkaline earth metal oxide, hydroxide, or carbonate is governed by cost to a large. extent,-but disregarding this factor, or weighing it against the effectiveness of the result, the chemicalconsiderations entering into the proposition are the solubilities of the treating compounds, and

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the solubilities of the products resulting therefrom. Tn this process it is most favortlti ing order, viz., barium, strontium, calcium,

and magnesium. The comparatively low cost of lime, and the relative insolubility of its sulphate and sulphite make it quite satis factory for the manufacture of a suitable product at the present time. Tn step three one object is to accomplish. principally three things, (1) the removal by conversion into insoluble form of some of the sulphur present, whether it be in the form of sulphites, sulphates, sulphurous acid gas, or loosely combined and reversible sulphurous acid, (2) the change of the reaction of the liquor from acidic to basic, (3) the conversion into insoluble form of any such compounds which would take place at much slower rate at lower temperature. lit may be noted that the reagent used-should contain only minimum amounts of iron.

The fourth step in the process consists in filtering the insoluble matter produced in the third step from the resulting liquor. Gomplete separation is desirable, and the separated liquor should preferably be crystal clear. if or this reason it is advisable to subject the liquor to sedimentation in any of the known forms of sedimentation or thickening apparatus, or simply 111 a tank, for a sufficient time to settle the major portion of the larger particles. The supernatant liquor is drawn ofi and passed through a-filter capable of holding the finest precipitates. While ll do not limit this procedure to any particular a form of filtration apparatus, it will be found preferable in most cases touse a high speed centrifugal of the unperforated basket or bowl. type, which discharges the clear liquid from the basket or bowl through the cake, which is precipitated in a compact mass on the side of the' bowlor basket, while the filtrate flows over the top of the basket or bowl, or out of the bottom. Tn step four some of the purposes are the minimizing of the decomposition of the liquor in its subsequent treatment for organic products recovery, the minimizing of corrosion of and deposition of scale on the surfaces of ltd without passing it llltl any concentration apparatus in which the liquor is subsequently treated, and the production of a purer resulting concentrated product than if filtration were not resorted to, but one of the principal reasons for filtration is the recovery of these mineral solids, which it is the purpose of the invention to utilize in the preparation of the sulphite cooking liquor used in the beginning of the sulphite pulp manufacturing process, because of the alkaline earth metals and the sulphur these solids contain.

The fifth step covers the proper utilization of the above separated solids by adding them to sulphite cooking liquor in the course of its preparation. The chemical considerations involved are as follows: Regardless of the alkaline earth compound selected for the treatment in the th1rd step, the residue, or

at least the major portion of it, is soluble in sulphite liquor containing excess sulphurous acid, that is, in the cooking liquor or acid used in sulphite pulp manufacture. The sediment will contain more sulphite and less hydroxide if the alkaline earth metal compounds are chosen in the order named, i. e., progressing from barium to magnesium. Both the sulphite and the hydrate are valuable in the making of the cooking liquor, as by adding the sulphite tothe liquor in the course of manufacture the soluble bisulphites are formed, and the equivalent amount of sulphur and alkaline earth metal base is saved over that used in the original preparation of the liquor. The hydroxide part of the sediment is valuable because these compounds unite with the sulphur dioxide gas used in the preparation of the cooking acid, forming the corresponding bisulphite compounds, effecting an equivalent saving in the alkaline earth base, usually limestone or lime, used in the cooking liquor preparation. These 'reactions may be expressed symbolically as follows In the above equation m and n are arbitrary numbers and R-is the metal.

In practicing this step the sediment is con-- veyed by suspension in water, or any other method of conveyance to a tank, where it may be mixed with sulphite cookin liquor containing a considerable excess of ree sulphurous acid, or may be treated along with the cooking liquor withthe highly concentrated relief gas coming from the digesters. The tank maybe so constructed and arranged that the whole massis subjected to a mild stirring action. The tank may also be arranged that a mild pressure may be carried, to facilitate the reaction. The sulphurous acid present dissolves nearly all of the sediment, the insoluble matter remaining'being of little or no value to the process.

The tank is also provided with a means of filtration or sedimentation, preferably the latter, so that these undesirable insoluble solids will not be carried along through the subsequent steps of the sulphite cooking liquor making process, The liquor, after sedimentation, is discharged from the tank ready for further use in the sulphite cooking process.

It is also to be noted that when barium or strontium is used, though only in amounts equivalent to a relatively small proportion of the total treating agent, an additional advantage is realized in that the sulphuric acid present in the cooking acid is precipitated as the very sparingly soluble sulphate, resulting in the removal of this acid from the sphere of action in the sulphite pulp cooking process. This sulphuric acid, while ordinarily conceived to be present in the combined form with lime (calcium sulphate) in the cooking liquors, acts as if in the free state, and in fact may partially exist in the free state, because of the effect of the far greater relative mass of free sulphurous acid present. In other words, in the cooking the sulphuric acid can at least in part come into play according to the following formula:

This sulphuric acid, at the high temperature at which it exists, exerts a hydrolytic action on the pulp in the sulphite (ligcstel,

tending to weaken and soften it, and decrease the yield of the fiber. It has been the experience in thepast that a better pul was always obtained when sulphuric aci was present only in the smallest amounts possible.

The above procedure therefore clearly effects a considerable economy in the operation, and also offers some advantage in the improvement of the method of preparing the sulphite cooking liquors.

It is understood that the sulphite waste liquor which remained after the filtration in the fourth step, is to be further concentrated. or otherwise treated, and thereby converted into useful products, such as binders, adhesives, tanning extracts, etc., by any of the known processes, and it is furthermore understood that it is particularly adapted to the manufacture of a tanning extract by the rocreaaoo containing principally sulphites insoluble in water by neutralizing the waste liquor with alkaline earth metal base suflicient to produce the degree of alkalinity expressed as pH=9 or greater alkalinity and su'llicient to decompose the reversibly combined sulphurous acid present in combinationwith the substances dissolved from the wood to increase the recovery of the sulphur as monosulphite, and in the preparation of cooking liquor, treating the solids with cooking acid which contains free sulphurous acid for the conversion of the solids into soluble bisulphites.

' 2. ln the treatment of wood pulp liquor the process which consists in recovering from the sulphite waste liquor solids containing principally sulphites insoluble in water y neutralizing the waste liquor with alkaline earth metal base sufficient .to producethe degree of alkalinity expressed as pl-l[=9 or greater alkalinity and suflicient to decompose the reversibly combined sulphurous acid present in combination with the substances dissolved from the wood to increase the re covery of the sulphur as monosulphite.

3; In the treatment of wood pulp liquor the process which consists in recovering from the sulphite waste liquor solids useful in the preparation of sulphite cooking liquor and including sulph-ites insoluble in water by neutralizing the waste liquor at substantially the process which consists in recovering from.

the sulphite waste liquor solids lncludmg sulnot less than 80 to 85 C. with alkaline earth metal base until the hydrogen ion concentration of the liquor is pH=9, or greater alkalinity and in the manufacture of cooking liquor treating the solids with sulphurous acid present in the cooking liquor for the conversion of the solids into soluble bisu'lphite.-

4:. ln the treatment of wood pulp liquor phites insoluble in water by neutralizing the waste liquor at substantially not less than 80 to 85 Q. with alkaline earth metal base until the hydrogenion concentration of the liquor is pH=9 or greater alkalinity.

5.111 the treatment of wood pulp liquor the process which consists in recovering from the sulphite waste liquor solids useful in the preparation of sulphite cooking liquor and including insoluble sulphites by neutralizing the Waste liquor until the hydrogen ion concentration of the liquor is pH=9 or greater alkalinity and decomposing the reversible sulphurous acid present in combination with the substances dissolved from the wood to increase the recovery of the sulphur as monosulphite at substantially not less than 80 to 85 C.'with alkaline earth metal compounds including some barium or strontium having basic deportment toward acid solutions and in the manufacture of the cooking liquor treating the solids with sulphurous acid present in the cooking liquor for the conversion of the solids into soluble bisulphites.

6. In the treatment ofwood pulp liquor the process which consists in recovering from the sulphite waste liquor solids including insoluble sulphites by neutralizing the waste liquor until the hydrogen ion concentration of the liquor is pH==9 or greater alkalinity and decomposing the reversible sulphurous acid present in combination with the substances dissolved from the wood to increase the re covery substantially not less-than to C. with alkaline earth metal compounds having basic deportment toward acid solutions.

7. In the treatment of sulphite wood pulp liquor the process which consists in recov- .ering from the waste liquor solids useful in present in the cooking liquor to convert them into soluble bisulphites which reacting with the free sulphuric acid in the cooking liquor eliminate such acid therefrom.

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of the sulphur as monosulphite at