US1846672A - Production of pulp - Google Patents

Description

1 Patented Feb. 23, 1932 UNITED STATES.

PATENT'JOFFICE LINN BRADLEY, OF MONTCLAIR, NEW JERSEY, AN P. MCKEEFE, OF PLATTS- BURG, NEW YORK, ASSIGNORS TO BRAD'LEY-MCKEEFE CORPORATION, OF NEW. YORK,

N. Y., A CORPORATION OF NEW YORK PRODUCTION OF PULP No Drawing.

This invention relates to improvements in the production of chemical pulp from Wood, both coniferous and non-coniferous, whereby good yields of chemical pulp can be obtained.

The present invention includes a new meth d of cooking or digesting wood chips in which the cooking liquor is an alkaline liquor containing both a sulfite and a thiosulfate of an alkali. This method is distinguished by the fact that caustic soda is present in suificient amounts to give an alkalinecooking liquor of appropriate strength, while both sodium sulfite and sodium thiosulfate are also present in substantial amount. The composite cooking liquor, containing caustic soda, together with sodium sulfite and sodium thiosulfate, can vary somewhat in its composition and in the proportion of caustic soda and of sodium thiosulfate and sodium sulfite. Ordinarily a preponderating proportion of caustic soda will be used, for example, so that from to 90% of the total sodium of the cooking liquor will be present as caustic soda and the remainder mainly as sodium sulfite and sodium thiosulfate. A cooking liquor may thus be used containing at least 40 gr. of sodium per liter, of which at least 40% is present as sodium hydroxide and at least 5% as sodium sulfite and sodik um thiosulfate, with the particular amounts of caustic soda and sodium thiosulfate and sodium sulfite, varying somewhat above these percentages. The amount of cooking liquor may be about 700 to 1100 gallons for a cord of wood (measured before chipping), the liquor containing the higher percentages of caustic soda being used in smaller amount, and those containing the smaller percentages of caustic soda being used in larger amount. By the use of such an alkaline cooking liquor containing thiosulfate and sulfite, it is possible to produce satisfactory pulp or cellulose material from forest products and other cellulose-bearing materials which, due to their inherent composition and properties, have been unsuited to the production of high grade cellulose material by the processes heretofore commonly practiced. Materials such as woods and other forest material of inferior Application filed February 10, 1926. 'Serial No. 87,456.

value (fortreatment according to common methods) as well as materials such as bagasse, reeds, grasses, bamboo, cornstalks, straws, etc., can advantageously be subjected to digestion with such alkaline sulfite and thiosulfate cooking liquor and high grade pulp or cellulose material produced therefrom. This method, therefore, increases the available supply of raw materials for the productiotg of high grade pulp or cellulose products.

In carrying out the digestion with such an alkaline sulfite and thiosulfate liquor, the amount and proportion of chemicals and the time of treatment, temperature, pressure, e tc., can-be varied depending upon the particular Wood or other material undergoing digestion; but the process can be carried out 'under similar conditions of temperature and pressure to those commonly used in the soda process, by heating the digester by direct steam at a pressure which may vary from about 90 to 140 lbs., and with circulation of the liquor within the digester by the steam'during the digestion. The digestion will, however, be modified by the action of the composite cooking liquor so that less injury to the cellulose material will take place and so that a superior pulp or cellulose material will be produced. I

The cooking liquor containing the caustic alkali, alkali thiosulfate, and alkali sulfite, may be advantageously produced from the residual liquor of the process, in one or another of the various methods of treatment hereinafter described. The cooki'ng'liquor can, however, be produced in the first instance in any suitable manner and additional amounts required to'supplement or modify that regenerated from the residual liquor can lated amount of sodium sulfite. vOr normal sodium sulfite can be added to the solution in regulated amount to react with the excess sulfur of the polysulfide to form sodium' thiosulfate and this action can be supplemented by the action of sulfur dioxide or sodium acid sulfite to convert some of the sulfide of the solution to thiosulfate'. with the production of sodium sulfite and thiosulfatein regulated amounts in the solution.

Solutions containing sodium carbonate and sodium sulfide can be subjected to a sulfiting treatment with the sulfurous acid radical, for example, using sulfur dioxide-or acid sodium sulfite or both, and some of the sulfide converted into thiosulfate, while by continuing the sulfiting treatment sodium carbonate can be converted into sodium sulfite to the desired degree. If an excess of sodium carbonate is present, the solution can then be causticized with lime to convert the sodium carbonate into caustic soda with formation and precipitation of calcium carbonate.

Byregulating the sulfiting treatment of a solution containing sodium carbonate and sodium sulfide and by subsequently causticizing the resulting solution, a solution containing caustic soda, sodium thiosulfate and s0- dium'sulfite can be obtained and the proportions of these respective compounds in the solution can be regulated by regulating the sulfiting and causticizing operations.

Instead of producing the cooking liquor in one or another of these ways, it can advantageously be produced from the residual liquors of the process.

The treatment of the residual liquor for the production of further amounts of cooking liquor can advantageously be carried out in apparatus such as is, now used in the so-called sulfate process. The residual liquor can thus be evaporated or concentrated, the concentrated or dried product then subjected to carbonization or calcining, and the resulting product subjected to a smelting operation to give a melt or a smelt containing considerable amounts of sodium carbonate and sodium sul- By .dissolving this melt a solution is obtained containing these and other sodium salts. Some sodium thiosulfate may thus be directly obtained without further treatment, but this amount may be supplementel by the further treatment to which the solution is subjected. 1

The solution of the melt. according to one method of treatment is subjected to a sulfit- "ing treatment with the sulfurous acid radical, for examle,'using sulfur dioxide or so- By continuing the sulfiting treatment of the solution, beyond the point where all of the sulfide is decomposed, a regulated amount of sodium sulfite can also be produced in the solution, for example, by reaction with sulfur dioxide, or sodium acid sulfite on a part of the sodium carbonate. By then subjecting the solution to causticizing with lime to convert the greater part of the remaining sodium carbonate into caustic soda, a liquor is obtained containing caustic soda, sodium thiosulfate, and sodium sulfite. The relative amounts of these respective compounds can be regulated or controlled, and additional amounts of sodium carbonate can be added to the solution if desired to increase the sodium content thereof. The sodium content thereof can also be increased by adding sodium acid sulfite for the sulfiting operation.

The sulfiting operation can also be carried out instages, using normal sodium sulfite first to react with the excess sulfur of the polysulfide, and bythen continuing the sulfiting operation with sulfur dioxide or sodium acid-sulfite or both. So also, calcium sulfite can be used for treating the solution, the calcium sulfite reacting with sodium carbonate to form calcium carbonate as a precipitate, and sodium sulfite in solution. The calcium carbonate can be separated and can then be treated with sulfur dioxide to form further amounts of calcium sulfite for use in the process.

The amounts and proportions of caustic soda, sodum thiosulfate, and sodium sulfite in the cooking liquor used in the process can be varied. The sodium thiosulfate may be present in larger amount than the sodium sulfite but in general we consider it more advantageous to have a larger amount of sodium sulfite than of sodium thiosulfate.

The regenerative pulp making process of the lnvention can be advantageously carried out in mills constructed or designed for carrymg out the present day so-called sulfate process. In the sulfate process so-called the cooking liquor is made up mainly of caustic soda and sodium sulfide; and the residual liquor from the process is subjected to evaporation to dryness, carbonization, usually in a rotary calcining furnace, and smelting, and the solution of the melt is causticized with lime to give a solution containing mainly caustic soda and sodium sulfide.

This sulfate process so-called is recognized as havlng certain objections and limitations. Furthermore, the process gives off obj ectionable odors which make the process a nuisance so that the process has been the occasion of litigation and even of injunction to restrain the further operation of the process.

The process of the present invention is free from or presents comparatively little objection as compared with the sulfate process;

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but the process of the present invention can nevertheless advantageously be carried out in the apparatus of the sulfate process mill. In fact, it is one advantage of the present invention that it maybe so carried out in the plant and equipment of existing sulfate mills requiring a minimum of change both in the mill construction and in the general method of operation. The cooking, concentrating or evaporating, carbonizing, and/or smelting operations may be carried out in the apparatus now used in the so-called sulfate process, although these operations will be changed or modified by the different character of the cooking liquor employed and the different nature of the residual liquor and pulp prodnot, and in the different treatmentof theresidual liquor for the production of a further amount of cooking liquor therefrom.

The cooking operation of the present invention can be carried out in digesters of the type now used for example in the soda or sulfate processes. The digesters of present day sulfate mills can advantageously be used. The provision of an acid resisting lining in the digester is not necessary and ordinary iron or steel digesters, preferably welded, can be used. The digesters can be heated and the cooking liquor circulated therein in any suitable manner. Outside circulation of the cooking liquor from the bottom of the digester with reintroduction at the top througha suitable distributor can be employed, or with suitable heating of the cooking liquor which is being circulated. Rotary digesters can-also be used with distinct advantage.

One of the important advantages which the present invention presents is that it is applicable to the treatment of various kinds of woods, both coniferous and non-coniferous, including various woods that are not commonly considered available for the production of satisfactory chemical pulp therefrom. The rapidly decreasing supply of wood suitable and available for pulp-makingpurposes,

according to the usual present day processes, and the high cost of equipment and operation of chemical pulp mills, makes it of industrial and economic importance to increase the yield of pulp from woods which are common 1y used for pulp-making purposes and to make available for pulp-making purposes woods ordinarily considered of little or no value for the production of high grade pulp.

The process of the present invention is applicable not only to the common pulp woods, such as poplar and spruce, vetc., but also to other Woods, both coniferous and non-coniferous, which are not commonly included among. the pulp woods. Non-coniferous woods, including the heavy dense hard woods,

such as birches, beeches and maples, the different kinds of oak, hickory, eucalyptus, elm, ash, etc., may be used as well as poplars, aspens, bass wood, cotton wood, chestnut,

gums, etc. So also coniferous woods may be used, including not only spruces, firs, and balsam, but also hemlocks, cedars, cypress, larches, tamarack and the various pines. Pines of a resinous character, such as yellow pines, white pine, jack pine, longleaf pine, shortleaf pine, lodgepole .pine, and other similar pines can thus be treated according to the present invention for the production ofv suitable chemical pulp therefrom.

In carrying out the process of the present invention, the procedure may vary somewhat with non-coniferous woods, and particularly dense hard woods such as birches, beeches, and maples and with less dense woods such as poplars or with coniferous woods such as spruces and pines. With non-coniferous woods, for example, the digester charge can be heated in a'relatively rapid manner to the cooking temperature; while with coniferous woods we find it important to heat up the digestercharge gradually so as to secure thorough penetration of the wood chips with the cooking liquor at a temperature below the active cooking temperature, before heating the charge to the active cooking temperature.

When the cooking operation is completed, the charge can be blown intoa blow pit, the

residual liquor separated and the pulp Washed and subjected to further treatment in the manner customary in the subsequent treatment of chemical pulp either for the manufacture of merchantable pulp or for the manufacture of paper or other products therefrom.

The pulps produced by the process of the present'invention are different in character from the pulps commonly produced by the usual methods, and we accordingly regard the pulps new and improved pulps. They contain characteristic fibres of distinctive feel and possessing great strength. Various pine woods, such as, for example, jack pine as well as spruce, hemlock and other coniferous woods, when treated according to the process of the present invention, yield pulps of excellent strength. It will be evident, however, that inasmuch as dilferent woods differ in their fibre structures from each other, the pulps produced therefrom will differ somewhat from each other. The process of thepresent invention accordingly will give different kinds of pulp from different kinds of wood, each wood being more or less characteristic in the pulp which it gives.

The residual liquors produced by the process of the present invention are of characteristic composition and properties. Our investigation of the chemical reaction which takes place during the cooking of woods leads us to believe that the wood substance is a complex reactive chemical substance which reacts with the chemicals contained in the cooking liquor, and that the nature of the reaction and of the reaction products produced varies with the cooking liquor employed. VVhenboth sodium thiosulfate and sodium sulfite, together with caustic soda, are pres ent in the cooking liquor, the combined reactions of these various chemical substances upon the reactive portion of the Wood cooked results in the production. of a. residual liquor containing thereaction products of these various chemicals with the reactive portions of the wood substance. The residual liquors contain the soluble reaction products of these chemical reactions.

These residual liquors can advantageously be treated for the regeneration of further amounts of cooking liquor therefrom for further use in the carrying out of the cook ing operation. The residual liquor can be treated for example in the evaporators, ro-

tary furnaces and smelters of the sulfate process mill'to give a meltwhich can be dissolved, and the resulting solution can then be treated for the production of further amounts of cooking liquor therefrom. When the residual liquor from the pulp making operation is evaporated to dryness, and carbonized to destroy organic matter, and theresulting carbonized product is subjected to a smelting operation, the solution of the re= sulting melt will contain considerable amounts of sodium carbonate, considerable sodium sulfide, and it may contain \other sodium salts, such as sodium sulfate, sodium thiosulfate, sodium sulfite,-etc. Part of the sodium sulfide may be present as polysulfide or as polysulfides.

The concentrating, carbonizing and smelting operations can, as above pointed out, be carried out in a sulfate mill, with little if any alteration in the equipment of such a sulfate mill. Furthermore, additional amounts of sodium sulfate or of sodium acid sulfate or nitre cake can be added to the concentrated residual liquor before carbonizing or to the carbonized product before smelting,

siderable amounts of sodium sulfide. It may also contain some sodium thiosulfate. In the sulfate process so-called, all of the-sulfide is employed again in the cooking operation, after causticizing the solution with lime to convert sodium carbonate into caustic soda. In the process of the present invention, however, the sulfide is caused to react so that it is converted partly or entirely into thiosulfate, so that a reduced amount of sulfide is present in the resulting soluoxide will react with the polysulfide or with the sodium sulfide or both with the roduction of some sodium thiosulfate. T is particular solution can in this way be practically freed from sulfide and polysulfide where desired and a solution containing a considerable amount of thiosulfate and of sodium carbonate obtained. Another portion may be causticized and thetwo portions mixed.

Instead of treating the solution of the melt with sulfur dioxide it can be treated with odium bisulfite or sodium acid sulfite or Witn sodium sulfite and sulfur dioxide and the amount of such reagents can be regulated and controlled. By continuing the sulfiting treatment, for example, with sulfur dioxide or sodium acid sulfite or both, a regulated amount of sodium sulfite can be formed in the solution so that the solution will then contain mainly sodium carbonate, sodium sulfite, and sodium thiosulfate, together with varying amounts of other salts such as sodium sulfate, etc. Added sodium can be introduced into the solution in the form of sodium carbonate, or by adding sodium sulsulfate, the solution of the melt or a portion v thereof can be subjected to a carbonating treatment with carbon dioxide or sodium bicarbonate to decompose a part of the sulfide into sodium carbonate and to drive off hydrogen sulfide. This hydrogen sulfide can be burned to form sulfur dioxide which may be used in the sulfiting step of the process or for absorption in a sodium carbonate solution to form sodium sulfite or acid sulfite.

By regulating the carbonating treatment, the

amount of sulfide converted into carbonate can be regulated, leaving the proper amount of sulfide in solution for reaction with the sulfurous acid radical during the sulfiting step. By continuing the sulfiting step the desired amount of sodium sulfite can also be formed in the solution and this amount can be regulated.

After the regulated sulfiting treatment, the solution containing sodium carbonate can then be subjected to a causticizing operation, by treatment with lime and the greater part of the sodium carbonate can be converted into caustic soda.

Instead of subjecting the residual liquor to evaporation to dryness, carbonizing, and subsequent smelting, the smelting operation Win 20%, to as much as 40 or such as. those of may be omitted, and the dried residue from the drying of the residual liquor can be subjected to a regulated carbonizing or calcining operation, for example, "in a rotary furnace such as is used in the sulfate and soda process mills, and the carbonizing operation can be carried out so as to give a furnace product from which a solution can be leached contain ing sodium carbonate and sodium sulfide, together with varying amounts of sodium thiosulfate, sodium sulfite, etc., and the resulting solution can then be subjected to sulfiting and causticizing operations of the character above described.

The process thus far described requires but little added equipment to that of a sulfate mill. A simple sulfur burner, a suitable absorption tower, or conversion tank for absorbing the sulfur dioxide during the sulfiting peration, constitute mostof the added equipment necessary, although it may be desirable to supply added tanks. The regulated sulfiting operation can be carried out, for example, by running a portion of the solution of the melt through a tower in which a regulated amount of sulfur dioxide is introduced, and the resulting solution can then be mixed with the other portion of the solution in the causticizing tank for treatment with lime to effect the causticizing of the sodium carbonate to produce caustic soda. The added reagents required to make up for those lost in the process may be supplied by lime for the causticizing, either using sodium carbonate for adding to the solution of the melt before causticizing, or using sodium sulfate for adding to the residual liquor or dried product before smelting, and sulfur for the sulfur burner. Where absorption towers the acid sulfite process socalled are available, the sulfur dioxide from the sulfurbunnercan be absorbed in the absorption towers to form a solution of calcium bisulfite which may then be used either for a regulated sulfiting of the solution of the melt, or for reaction with sodium, sulfate to produce a solution containing sodium sulfite which may then be used for the sulfiting operation.

In carrying out the cooking operation, for example, for jack pine (Pinus dz'oam'aata or banlcsz'ana), the wood is first barked and then chipped and screened so as to give fairly uniform chips of about to inch in length along the grain. The chips may varyin their moisture content, for example, from 10 to inthe case of wood which is keptwet inthe wood pile. In cooking jack pine, after the .digester is charged with the wood chips and with the cooking liquor, the digester charge is advantageously heated by introducing steam grad-' ually, atthe same time causing the cooking 1 liquor to circulate'throu'ghout the body of ChlPS so as to give them substantially uniliquor before the main cooking form treatment, and so as to. secure thorough penetration of the chips with the cooking temperature and pressure are reached. By providing a false bottom in the digesters, and suitable piping and pumps, the cooking liquor can be withdrawn from beneath the false bottom and circulated in copious amounts and discharged into the upper portion of the digester above the wood chips, so that the cooking liquor is quite uniformly spread out above the entire body of chips and caused to percolate in a substantially uniform manner downward through the body of chips.' The liquor can be progressively heated during its passage from the bottom to the top of the digester, and the digester charge can be heated gradually in this way to the cooking temperature. As an aid in determining when the cooking operation has progressed to the desired degree, a sampling device may be installed at digester, through which samples of stock may be drawn from time to time. So also thermometers may be installed at various points.

Deciduous woods, such as aspen (northern poplar) or dense hard woods, such as birches, maples, beech, oak, etc., can be cooked in a similar way, but-with these woods the digester charge can be advantageously heated more rapidly to the cooking temperature. With these woods, however, it is likewise advantageous to secure thorough circulation of the cooking liquor and substantially uniform treatment and cooking of the entire digester charge.

The following is a specific example of the Y cooking of poplar wood, in accordance with the invention, with a cooking liquor which comprises a preponderating amount of sod1-' one or more places in the side of the um hydroxide, and substantial amounts of sodium sulfite and sodium thiosulfate. In this example, the amounts are given as Na O equivalent, i. e., the amounts of actual Na O contained in or equivalent to the sodium compounds mentioned. I

A vertical, stationary type ofwelded steel digester, of the usual shape, having a. capacity of about 1,900 to 2,000 cubic feet, and which is provided with the usual cover, valves, pipe lines, blow-line, etc., and may be provided with special means for circulating the liquor throughout the b'ody of chips, is charged with about eight cords of wood (sea-. soned poplar), in the form of chips of the usual kind, thus representing about 16,000 to 17,000 lbs. of actual wood substance (bonedry basis) and carrying about 3,500 to 4,000 lbs. of water. Some of the cooking liquor is addedwhile some of the chips are being introduced so as the digester, and the added liquor is circu ated so as to facilitate the charging of the chips and liquor. About 1,000 cubic feet of 1 7 a charge of wood chips. A suitable charge may consist of 3,000 lbs. to 3,500 lbs. sodium hydroxide; 400 lbs. to 800 lbs. sodium sulfite;

- and 200 lbs. to 400 lbs. sodium thiosulfate,

these amounts being on a Na O equivalent basis, as above described. The cooking may be carried out by the introduction of saturated steam (preferably dry or nearly dry) introduced through nozzles or a suitable steam ring at the lower end of the digester, taking about one to two hours, more or less, to heat the contents up to about 120pounds per square inch gauge pressure above atmosphere, in the upper part of the digester, care being taken to relieve either intermittently or continuously so as to thoroughly circulate the liquor throughout the chips and to uniformly heat them and avoid substantial false pressures. Any other suitable means of heating and circulating the cooking liquor may be employed. After the charge has been heated at such high temperature for about 4 to 6 hours, more or less, until samples of the stock show that the cook is done, the charge may be blown from the digester in the usual manner.

The above cooking liquor for the cooking of poplar wood chips may advantageously have a moderate amount of sodium sulfide present in the cooking liquor, especially when the cooking liquor is made up in large part from regenerated soda. In such cases the amount of sodium hydroxide can be somewhat reduced inasmuch as the moderate amo I nt of sodium sulfide can replace all or nearly all of its equivalent amount of sodium hydroxide. In any case, however, the sodium hydroxide may be present in preponderating amount. The combination of a preponderating amount of sodium hydroxide, together with lesser amounts (but in substantial quantities) of sodium sulfite, sodium sulfide and sodium thiosulfate, is of especial value in the cooking of deciduous woods to produce easybleaching pulp especially valuable in the production of book and magazine papers of high quality. The cooking liquors can be regenerated in a ready manner so as to reproduce .cooking liquors of similar composition.

In cooking coniferous woods, e. g. spruce, jack pine and other pines, the cooking liquor can be of similar composition, but the amount of active chemical should be-sufiioiently increased to yield the kind of pulp desired, although some of the coniferous woods can be cooked with some of the cooking liquor charges given above for poplar, i. e., those which have the higher chemical content.

A digester such as described above, may be charged with chips from spruce, balsam, .or pines, e. jack pine, preferably air-seasoned, and a out 1,000 to 1,200 cubic feet of cooking liquor used, containing about 2,800 to 3,400 lbs. sodium hydroxide;.400 to 600 lbs. sodium sulfide; 800 to 1,500 lbs. sodium sulfite; 300 to 500 lbs. sodium thiosulfate.- The liquor will usually contain a moderate amount of sodium carbonate and a small amount of sodium sulfate. The smaller charges are generally used where pulp is desired for strength, and where the amount of non-fibrous material to be removed is relatively small. Woods which are heavy and have a relatively large amount of non-fibrous material to be removed take the higher charges. More or less than the above can be used.

The pulps produced by the process of the present invention are characteristic, as are also the residual liquors. The pulps produced may be used for manufacture of paper, and may be produced by this process from coniferous woods such as spruce and jack pine, so as to produce a paper product of great strength. Satisfactory pulp can also be produced from deciduous woods, including not only the common pulp woods, such as poplar, but including also the dense heavy hard woods, such as birches, maples, beeches, oaks, etc.

It will thus be seen that the invention provides a new regenerative pulp making proc ess, 'as well as a new method of making a cooking liquor from the residual liquor. It will also be seen that the invention provides improvements in the treatment of the residual liquor, and in the production of the cooking liquor.

In the process of the present invention, moderate amounts of sodium sulfide may advantageously be present, and we do not exclude the presence of sodium sulfide in the cooking liquor, although the sulfiting treatment if desired, may be carried sufficiently far to practically eliminate the sulfide from the cooking liquor.

This application is in part a continuation of our co-pending application Ser. No. 686,137, filed January 14, 1924 and our Patent No. 1,747,047, issued February 11, 1930. Reference is also made to Patent No. 1,572,840, issued February 9, 1926.

We claim:

1. The method of producing a liquor for use, in producin pulps, which comprises evaporating a resldual liquor from the treatment of wood by a process in which caustic soda and sodium-sulfur compounds are used,

calcining the residue obtained by evaporation,

smelting such residue whereby to obtain a product consisting to a large extent of sodium carbonate and sodium sulfide, treating with water to obtain a solution, and sulfiting a 7 part or all of the solution.

2. The method of producing a liquor for use in producing pulps, which comprises evaporating a resldual liquor from the treatment of wood by a process in which caustic soda and sodium sulfur compounds are used, calcining the residue obtained by evaporasome or allof the solution, a'nd causticizing .the sulfited solution.

3. The cyclic method of producing pulp,

from wood, which comprises cooking the wood with a cooking liquor containing a preponderating amount of caustic soda and lesser but substantial amounts of sodium sulfite and sodium thiosulfate, concentrating the resulting liquor, subjecting the concentrated prod- .uct to a carboni'zihg or smelting operation, dissolving the soluble salts from the resulting product, and subjecting some or all of the solution to sulfiting and to causticizing to regenerate the cooking liquor for further use in the process. 4

4. The method of producing pulp, which comprises subjecting ra-w fibrous material to a treatment with a hot liquor supplied with tri-oxy sulfur material including a sulfite of sodium and sodium thiosulfate and also supplied with another alkaline reagent, the amount of sodium present as asulfite being more than that present as thiosulfate, and the proportion of the total reactive sodium compounds supplied with tri-oxy sulfur material being larger than that present in ordinary sulphate cooking liquor.

5. The method of producing pulp, which comprises subjecting raw fibrous material to a treatment with a hot liquor supplied with tri-oxy sulfur material including a sulfite of sodium and sodium thiosulfate and also supplied with sodium hydroxide, the amount of sulfur present as a sulfite being at least as much as that present as a thiosulfate, and a larger percentage of the total available inorganic base in the liquor being supplied with tri-oxy sulfur material than in the ordinary ,sulphate cooking liquor.

6. The method of producing liquor for use in producing pulps which comprises evaporating the residual liquor from the treatment ofwood by a'process in which sodium sulfur compoundsare used, furnacing the residue obtamed by the evaporation under conditions adapted to obtain a product consisting mostly of sodium carbonate and sodium sulfide, dissolving sodinm compounds therefrom, sulfiting the resulting solution under conditions adapted to convert a substantial proportion of the sodium sulfide into sodium thiosulfate and a substantial proportion of the sodium carbonate into sodium sulfite and causticizing the solution so as to convert another and greater portion of the sodium carbonate into caustic soda.

7, The cyclic method of producing pulp.

sodium thiosulfate, concentrating the resulting residual liquor, subjecting the concentrated product to a furnacmg operation adapted to yield a product consisting mostly of sodium carbonate and sodium sulfide, dissolving soluble salts from such product, and subjecting such solution to a sulfiting treatment adaptedto convert a substantial part of the sodium sulfide into sodium thiosulfate and a substantial part of the sodium carbonate into sodium sulfite and to a causticizing treatment adapted to convert another larger part ,of the sodium carbonate into sodium hydroxide, whereby a cooking liquor is regenerated suitable for use in the, first named cooking process and repeating the process using the cooking liquor so formed.

8. The improvement in the production of pulp, which includes the step of digesting wood by means of a digesting liquor including sodium hydroxide, sodium sulfid, sodium more than that contained in ordinary sulfate liquor, and the amount of digestive material, other than tri-oxy-sulfur-bearing material, being suflicient to digest at least about two thirds of the non-fibrous organic material of the Wood.,

9. The improvement in the production of pulp, which includes the step of digesting wood by means of a digesting liquor including sodium hydroxide, sodium sulfid, sodium sulfite and sodium thiosulfate, the amount of sodium present in the original digesting liquor as hydroxide being larger than that present as either one of the other compounds, the amount of sulfite and thiosulfate being more than that contained in ordinary sulfate liquor, and the amount of digestive material, other than tri-oxy-sulfur-bearing material, being suflicient to digest at least about two-thirds of the non-fibrous organic material of the wood, but insufficient to digest all of such nonfibrous organic material.

In testimony whereof we aflix our signatures.

LINN BRADLEY. EDWARD P. MCKEEFE.