US1790170A - Process for the production of high alpha-cellulose fiber - Google Patents

Description

A G1. A. RICHTER PHOcEss FOR THE PRODUCTION OF HIGH ALPHA OELLULOSE FIBER Jan. 27, 1931.

Original Filed May 6 w15 ai w w 1 n W u Patented .Isa 27, 1931 l UNITED STATES PATENT oFFlcE GEORGE A. RICHTER, F BERLIN, NEW HAMPSHIRE, ASSIGNOR TO BROWN COMPANY 0F BERLIN, NEW HAMPSHIRE, A CORPORATION OF MAINE PROCESS FORLTHE PRODUCTION OF HIGH ALPHA-CEIBLULOSE FIBER Application led Hay 6, 1925, Serial No. 28,339. Renewed July 23, 1927.

This invention relates to the utilization of the heat and the recovery of spent sodium digesting constituent fromv the spent liquor of an alpha-cellulose liber plant operated simultaneously or in connect-ion with a kraftor sodium sulphate plant.

High alpha-cellulosefiber may be produced by an alkaline digestion of, for instance, unp bleached sulphite pulp,--a caustic soda, soda 4 very white color /after bleaching. The alka-v line digestion may take place in digesters at any suitable temperatures and pressures, although I have found it in many cases to be more economical and expedient to digest the sulphite pulp at atmospheric pressure inopen tanks under heat. In order4 to render the process more economical, the spent sodium constituent should be recovered and the available heat contentof the spent liquor should be utilized.

In my (fo-pending application Serial No. 26,361, filed April 28, 1925, a process for the recovery of the sodium constitue-nt and the utilization ofthe available heat content of the spent digesting liquor has been outlined. ASuch a process, however, requires a special 35 recovery plant, where it is practiced in a plant wherein sulphite pulp only is produced. The objectof this invention is to provide a. method for practicing the economies set forth in the co-pending application, while combining the recovery of sodium constituent from the spent liquor in au alphascellulose plant with the recovery of sodium constituent from. the spent black liquor o" a kraft plant, thereby eliminating the necessity for special recovery apparatus in the alpha-cellulose plant. This invention may best be understood from the following description thereofwhen taken in connection with the accompanying drawing, which represents what may be termed a flow sheet. ff-

viously a continuous cyclic process is preferable.

Before proceeding to the features of invention involved herein, the operation Aof the alphaplant, which has been fully described in the co-pending application, will be brieliy n reviewed.

Sulphite pulp is produced, as usual, by the digestion of Wood chips (e. g., spruce) in a digester, in a suitable sulphite liquor, as, for example, calcium bisulphite digesting liquor. After the necessary period of digestion, the digester contents are blown, and the sulphite pulp is successively Washed, screened, and thickened to, say, a consistency of about 50%, as by press rolls. The thickened, -unbleached sulphite stock thus obtained is continuously fed into a digesting tank A, and is diluted to a consistency of about 10% with water and the amount of caustic soda or soda ash solution required for the purification of the sulphite pulp. The diluted sulphite pulp is continuously delivered yinto the bottom portion of a second digesting tank B, from the tank A, at the same rate as it is being madev up in the tank A, by a slow-moving worm conveyor, and overliows from the second tank B. TheA stock is digested and slowly agitated yduring its passage through the tanks A'and B at 180 F; to 212 F., by blowing steam at suitable points .into the suspension,-the lessresistant celluloses and the ligneous and other coloringv matters contained in the sulphiteA pulp reacting with and being dissolved by the alkaline solution so that the product which leaves the top portion of the second tank B is high in alpha or resistant cellulose. The agitation rovided for during the digestion and the eed of the stock by the Worm from one tank to the other gives intimate contact between the stock and the liquor, and thereby promotes a thorough reaction between the sulphite pulp and the alkalineliquor, resulting in a uniform high alphacellulose pulp product. Of course, the digestion may be carried out as a batch process, but ob- The stock, together with the spent digesting liquor associated therewith, leaving the top portion of tank B, and now containing a high percentage of alpha-cellulose, is passed 10o 'through a counter-current washer, wherein the stock is thoroughly washed free from substantially all the digesting liquor, and the washed stock is then passed to the bleachery. The Wash Water used in the washing apparatus assumes practically the same tem erature as the hot spent digesting liquor an the hot pulp as they are passed in the washing apparatus. The hot wash water (which for convenience of designation I term the alpha spent liquor") contains substantially all the sodium constituent in any form, spent or otherwise, associated with the alpha stock as it was passed into the washer. The alpha spent liquor is re-circulated to the digesting tank A, and comprises in volumelapproximately the volume of water associated with the pulp after digestion, plus the total volume of wash water used in the Washer, minus that portion absorbed by the washed alpha pulp as it passes to the bleachery; During this stage of the process, the volume of this` wash water employed in washing the digested sulphite pulp is so regulated that the volume of spent alpha liquor obtained from the washer and re-circulated into the tank A is substantially equal to the volume of Water and digesting solution employed in making up the initial 10% stock suspension in the tank A. To this re-circulated wash water is continuously added a sufficient quantity of sulphite pulp and the amount of concentrated caustic soda or soda ash solution necessary to remove the less-resistant celluloses and the ligneous matter contained in the sulphite pulp to produce a stock suspension of about 10%. The new 10% stock suspension formed with the re-circulated wash water is digested, and the cycle of operations as hereinbefore described in connection with the initial 10% stock suspension is repeated. The hot spent liquor obtained from the washer at this point in the process contains a higher per cent of dissolved material. This spent liquoris recirculated as before and the process as describedis continued or repeated until a hot, syrupy spent-liquor of about 10 to 15 Baum results.` Such a concentrated spent liquor may profitably be evaporated and the combustible content thereof burned to recover-the valuable sodium constituent.

lYhen this concentration of spent liquor is ariived at, the flow of -`fresh water to. the

washer is increased. As stated previously, up

- stituent is taken into account; but there is now an excess of spent liquor. This eiessjs continuously withdrawn from the spent liq- A uor obtained from the washer, and mixed with the black liquor -resulting from a kraft or sulphate pulp digestion as it is passed to the evaporators. The rest of the spent alpha liquor is re-circulated into the alpha. digesting tank A. The increase in quantity of wash water,that is, the excess passed along with the black liquor to the evaporators, is so adj usted as to maintain an equilibrium within the system at this particular concentra-l tion: that is, the excess spent liquor mixed with the spent kraft liquor contains substantially the amount of spent sodium constituent which was formed in the preceding digestion (the term sodium or sodium constituent as used in thisl specification and the appended claims will, of course, be understood to mean sodium in combined form, that is, in the form of a sodium compound).

As indicated on the drawing, it may be stated that the black spent liquor hereinbefore referred to results from the digestion of wood chips in a digester in the usual kraft or sulphate digesting liquor, which contains essentially caustic soda. sodium sulphide, together with a small quantity of sodium carbonate. After digestion, the digester contents are blown and the kraft pulp is passed through a counter-current washer similar to the one in which the alpha-cellulose pulp is washed. The washwater from the washer contains substantially all the di esting constituent associated with the kra t pulp as it is passed into the washer, is black and of about a 14 Baum,and is known as spent kraft liquor. In some cases, it may be desirable to re-circulate one portion (usually about one-half the total of such spent liquor to the kraft digester) for use together with newly made digesting liquor in a subsequent kraft digestion. The other portion of black kraft spent liquor is passed into a storage. tank,

from which it is continually withdrawn to the evaporators. To this black liquor, as has been previously stated. is added the excess spent liquor of from 10 to 15 Baum, obtained from the alpha spent liquor, so that a mixture of alpha and kraft liquors of about the same degree Baume is pamd in to the evaporators for concentration. The resulting concentrate is burned, preferably in a' combined boiler and smelting furnace, in a reducing atmosphere. Additional sulphur may be added as described in Letters Patent No. 1,469,960, dated October 9, 1923,-to the mixed concentrated liquor,-the amount of sulphur added thereto being regulated and controlled so as to form a smelt of approximately the samev composition asV the usual kraft smelt. The ciuent smelt from the furnace is caught in a relativelysmall quantity of water in a dissolving tank, and a concentrated solution is formed which contains essentally sodium carbonate, sodium sulphide, and relatively small quantities of unreduced sodium sulphate .and sodium hydroxide.

This solutionis then causticized with lime,

' resultant white4 sulphide liquor, which contains sodium hydroxide, sodium sulphide, and smaller quantities of unreduced sulphate and unconverted sodiumcarbonate, is passed to a storage tank.

This strong white liquor may furnish a portion of the alkaline digesting, agent re-v quired in the alpha plant tanks. This portion is preferably such that, together with thel unspent alkali present in the re-circulated portion of spent alpha liquor, it contains the total alkali necessary for the alpha digestion, minus the losses suffered in both the alpha and kraft pulp cycles.. From the foregoing statement it is obvious that if the alpha pulp and kraft pulp. production happen to be in a certain proportion; that is, when the fore- 1 going difference is zero or a minus quantity,

no white -liquor will be supplied to the alpha pulp digesters, in whichcase the alkali-necessary for the alpha digestion is supplied directly to the digesting tank A, as shown. To

understand this Vmore clearly, the following example will suiice.

Thesodium sulphate losses in a very efficient 'kraft plant amount to about 220 pounds of salt cake (sodium sulphate) per ton of pulp produced. .The salt cake required to 'make up these losses is equivalent to about 125 pounds of caustic soda,"and would repreduction of high alpha pulp. Assuming, then,

that the alpha plant and the kraft plant are producing the same quantities of pulp, the

f spent liquor recovered' from the alpha-cellusay, the total' recovered sodiumin the mixed spent liquors would'contain just the correct l amount of sodiumconstituent for the next digestion in the kraft plant, and under such `conditions no white liquor would be delivered `to the alpha digesting tanks. In other Words,

Y the recovered sodium constituent from a ton i of alpha pulp would serv@l as a make-up niaducing a tonvof kraft terial for the sodium losses suffered in propulp, andin J4"such a case itwouild be necessary to add. to the alpha tanks the total sodium losses suffered in both Y' cycles, which would be equal to the amount of sodium constituent required for digesting the unbleached sulphite ulp.-

In actual practice, owever, it is quitelikely that'such a balance could not be' n'1ain'4 tained, since the quantity of alphapulplpro ducedV mightA be slightlyin excess of. the

the next kraft digestion, and this excess4 70 would be returned to the alpha digesting tanks. In addition to this returned White liquor, in order to maintain the system at equilibrium, an amount of alkali equal to the kraft and alpha cyclelosses is added to the. alpha digesting tanks, and the entirecycle may be repeated. 0r, if the quantity of kraft .pul produced is slightly in excess of the alp a pulp production, no White liquor would be delivered to the alpha digesters. In'this 80 case, the amount of alkali Which it would be necessary to introduce into the alpha digesters if the production of both the alpha and kraft plants were equal is then ladded to the alpha digesters. The kraft cycle losses not made i of sufficient sodium constituent in the form of sodium-sulphate, or in the form of sodium carbonate, caustic soda, and sulphur, to the mixed.. spent liquor so as to give the usual kraft smelt.

Under conditions when no alkaline liquor is available from the kraft mill, then the unbleached sulphite pulp is digested entirely in caustic soda digesting liquor. If the alpha fiber plant uses available liquorfrom the i kraft mill, there are present in the -liquor a certain amount of sodium'sulphide and a relativel small amount/of other constituents, v10e so that t e sulphite pulp is digested in a mixture of caustic soda and sodium sulphide. Such a liquor produces as satisfactory an alpha pulp as isproduced with caustic soda solution alone. liquor may be a solution of sodium carbonate or of a` mixture of sodium carbonate and caustic soda, or of a mixture of sodium car bonate, sodium hydroxide, and sodium sulphide, or any other combination of these con-v'. 110 stituents.

Aside from the advantages outlined in the l co-pending application, this invention provides for the recovery of sodium constituent and available. heat content from the spent-1 115 liquor in the alpha fiber plant, without the installation' of special recovery apparatus.-

I do not herein claim any features eneric lto application, Serial No. 72,522, filed ecember 1, 1925, by Milton O. Schur and myself;l .12e nor'do I herein cla-imany. features generic to my applications Serial Nos. 26,361 and 26,362, both filed April 28, 1925.

What .I'claim is: l -1. A. 'process which lcomprises digesting- 125 predigested pulp inl an alkaline liquor containing sodium digesting'v constituent re ciigred from the spentliquor resulting from theidigestion of cellulose material in the pro",- kraft pulp production, so that theA White duction of sulphateor kraft pulp,j ,togethei f 130 Of course, the digesting.

with the spent liquor resulting from previous digestion of like predigested pulp with alkaline liquor.

2. A process which comprises digesting predigested pulp in a. fresh alkaline liquor containing sodium compounds, mixing sufcient spent liquor from such digestion with spent kraft liquor to make up sodium losses suffered in the kraft digesting cycle, and recovering the sodium constituent from the spent mixed liquors.

3. An inter-related process of producing high alpha-cellulose pulp and kraft pulp, which comprises digesting predigested pulp in an alkaline liquor containing sodium compounds, re-employing one portion of the spent liquor of the first-mentioned digestion in another digestion of like predigested pulp, and mixing the .other portion with the spent black liquor from kraft digestion, recovering the sodium constituent of the mixture, and using recovered sodium constituent ina subsequent kraftdigestion and any excess thereof in another digestion of predigested pulp.

4. An inter-related process' of producing high alpha-cellulose pulp and kraft pulp, which comprises digesting predigested pulp in an alkaline liquor containing sodium compounds, re-employing one portion of the spent liquor of the first-mentioned digestion in another digestion of predigested pulp,

mixing the other portion containing substantially the amount of, spent digesting agent formed in a preceding digestion with the black liquor resulting from kraft digestion, vrecovering the sodium constituent of the mixture,using the recovered sodium constituent necessary for the kraft digestion in. such digestion. and using any excess recovered sodium constituent in another digestion of predigested pulp, together with the reemployed portion of said first-mentioned spent li'quor.

5. A process which. comprises digesting predigested pulp in an alkaline liquor containing sodium compounds,- mixing one portion of the spent digesting liquor with the black spent liquor resulting from a kraft digestion, recovering the sodium constituent thereof, making up losses in the kraft cycle with the sodium constituent recovered from said one portion, re-mploying the other por- .tion of the spent liquor in another digestionof predigested pulp, adding any available recovered sodiuln -constituent to said other portion` and making up losses in both digesting cycles by the addition of sodium digesting agent to said other portion.

' 6. A process which comprises digesting predigested'pulp in an alkaline liquor con- -taining sodium compounds, re-employing one portion of the spent liquor in another d1- 4 gestion of pre ested pulp, and mixing the other portion o the/spent liquor containing substantially the amount of spent digesting agent which was formed in a precedin digestion with the black liquor resulting rom a kraft digestion, recovering the sodium constituent thereof, and mixing a portion of said recovered constituent with the portion of reemployed spent liquor.

7. A process which comprises digesting predigested pulp in an alkaline liquor containing sodiumv compounds, re-employing substantially all the spent alkaline liquor of the `digestion in another digestion of like pulp after the addition of sufficient sodium digesting agent thereto to make up losses therein for effective digestion, continuing such re-employment until a predetermined concentration of sodium results therein, and thereafter mixing one portion of the spent sodium alkaline liquor with the black liquor resulting from a kraft digestion, recovering the sodium constituents from the mixed liquor using the recovered sodium constituent in a subsequent kraft digestion, and

rrcs-employing the other portion of spent liquor in a subsequent digestion of predigested pulp. ,Y

8. A process which comprises digest-ing predigested pulp in ari alkaline liquor containing sodium compounds, re-employing substantially all the spent alkaline liquor of the digestion inanother pulp digestion after the addition of suiicient sodium digesting agent thereto to make up losses therein for effective digestion, continuing such re-employment until a predetermined concentration of sodium results therein, and thereafter re-employing one portion of the spent' sodium alkaline liquor in another digestion of predigested pulp and mixing the other portion of the spent liquor with the black liquor resulting from a kraft digestion, rccovering the sodium constituent from the mixed liquors, and using a portion of the recovered sodium constituentfin, a subsequent digestion ofpredigested pulp.

9. A .process which' comprises digest-ing predigested pulp in a fresh alkaline sodium base liquor, mixing spent liquor from such digestion with spent liquor resulting from the digestion of cellulosic material in kraft liquor, and recovering the sodium constituentfronithe spent mixed liquors.

10. A continuous cyclic process which comprises continuously feeding and digesting predigested pulp in an alkaline liquor containing sodium compounds, washing the resulting pulp and the entrained products of the reaction, circulating a part of the wash water back for further digestion of predigested pulp, mixing the other part with the black spent liquor resulting from a kraft digestion, evaporating said mixed liquor, burning and smelting the combustible content thereof in a reducing atmosphere, recovering the molten smelt in water, causticizing the resulting alkaline liquor', re-employing said' liquor in asubsequent kraft digestion, and

employing any excess of said liquor in a subf sequent digestion with said recirculated Wash water in the digestion of predigested pulp,

and making up losses in both digesting cycles by the addition of sodium compounds to said reirculated Wash Water. y

11. Process comprising the following steps: digesting suliite pulp in an alkaline liquor containing sodium sullide to the formation of a pulp having a high alpha cellulose content and waste alkaline liquor and using this waste alkaline liquor in the preparation of a cooking liquor for a sulfate digestion of Wood.

12. The process of making chemical wood pulp having -a high'content of alpha cellulose involving the digestion of raw cellulose ma- Y terialin an acid sulite cooking liquor, separation of theresultin Waste sulite liquoil from the resulting su lite pulp, and digestion of the sulite pulp in an alkaline cooking liquor, characterized in that the said alkaline cooking liquor is a solution comprising sodium sulfide obtained by concentrating smelting and recovering the sodium compounds present in the waste liquor from a collateral sulfate process of makin pulp.

' 13. The process of vmaing chemical wood pulp having a high content of alpha cellulose involving the digestion of raw cellulosic material in an acid sulite cooking liquor, separation of Vthe resulting waste sulfte liquor from the resulting sulfite pulp, and digestion i of the sulte pulp in an alkaline cooking liquor, characterized in that the said alkaline cooking liquor is a solution obtained by concentrating and smelting, in' a reducing atmosphere, the Waste liquor from a collateral sul- 40 fate process of making pulp,-dissolving the resulting smelt in water, and treating the resulting solution with caustic lime. In testimony whereof I have affixed my signature.

i5 p GEORGE A. RICHTER.

Images