US1898613A - Manufacture of pulp, etc. - Google Patents

Description

patented Feb. 21,

iearaiur or iec LINN BRADLEY, OF MONTCLAIR, NEWJERSEY, AND EDWARD'P. MCKEEFE, OF PLATTS BURG', NEW YORK, ASSIGNGRS T BRADLEY-MGKEEFE CORPORATION, OF NEW YORK,

N. Y., A CORPORATION OF NEW YORK MANUFACTURE OF PULP, ETC.

No Drawing. App1ication filed May 14, 1924,

This invention relates to improvements in the production of chemical pulp from wood (both coniferous and non-coniferous) whereby a good yield of'chemical pulp can be 5 obtained.

The invention also includes "a new cooking liquor for the cooking of wood,as well as the new and improved pulp-making or cooking operation itself for the production of the pulp from the wood; and it includes the residual liquors produced by the pulpmaking operation; and also it includes the new pulps and the new papers madetherefrom. It also includes a new and improved method of regeneration of cooking liquors,

and improvements in the process of treating the residual liquors; as well as a regenerative process for the regeneration of the cooking liquor and the carrying out of a successive 0 cooking operation wit-h the regenerated cooking liquor.

According to one embodiment of the present invention wood is subjected to a cooking operation under pressure and at an elevated temperature with a cooking liquor containing an oxygen-bearing alkaline compound, e. g., caustic alkali, a trioxy-sulfur-bearing compound, e. g., an alkali thiosulfate and an alkali sulfide. The cooking liquor may also I contain other constituents such as sodium carbonate, sodium sulfite, etc.

The new pulp-making or cooking process of the present invention may be considered as a modification of the so-called sulfate proc ess. In the sulfate process, the cooking operation is carried out with 'a cooking liquor containing essentially caustic soda and' so dium sulfide. In the process of the present invention the cooking liquor contains caustic soda. sodium sulfide and sodium thiosulfate, advantageously with the amount of sodium present in the sodium hydroxide and in the sodium sulfide being larger than that at present in the sodium thiosulfate.

In the process of making chemical, pulp from wood according to the present invention. the wood may be freed from bark, chipped and then subjected-to a cooking operation under pressure and at an elevated temperature with the new cooking liquor.

Serial No. 713,257. Renewed July 13, 1932.

Woods of various kinds can be treated for the production of chemical pulp by the proc ess of the present invention, and such pulp can be produced therefrom. The cooking liquor containing the caustic soda, sodium thiosulfate and sodium sulfidemay advantageously be produced from residual liquor from a pulp-making operation, in one or another of the various methods of treatment hereinafter described. The cooking liquor can, however, be produced in any suitable manner, and additional chemicals to supplement or modify that regenerated from residual liquors can also be supplied in any suitable manner.

In producing the cooking liquor in the first instance, a solution containing caustic soda and sodium sulfide may beused, and some elementary sulfur dissolved therein to form a solution containing caustic soda together With-a regulated amount of sodium sulfide or polysulfide or both. Normal sodium sulfite can be added to this solution in regulated amounts to react with the loosely combined sulfur of any polysulfide present to form sodium thiosulfate. Instead of producing the cooking liquor in this way, sodium thiosulfate may be prepared separately and added to a solution containing caustic soda and sodium sulfide.

Sodium suliite in solution may be converted into thiosulfate by reaction with free or loosely combined sulfur, e. g. by a polysulfide or with elementary sulfur. The latter may be added in finely divided form and the solution heated to aid in the solution of the sulfur. Sulfur may be obtained also by decomposition of a sulfide or polysulfide, of sodium and some of this sulfur taken up by sodium sulfite. A mixture of sodium sulfite and sodium sulfide may be treated with sulfur dioxide or sodium bisulfite and produce sodium thiosulfate in solution. A mixture of sodium carbonate and sodium sulfide or polysulfide may be treated with sulfur dioxide or sodium bisulfite and leave some sodium thiosulfate in solution. In case the carbonate is present in 5 too great an amount for the quantity of sulfide or polysulfide the resulting sulfited solution may also contain some sodium sulfite.

' precipitation of calcium sulfate or carbonate,

leaving sodium sulfide or polysulfide or both in solution. By heating sulfur and an excess of lime with a solution containing a. sufficient amount sodium carbonate, the lime will causticfze some of the sodium carbonate and convert it into caustic soda so that the solution will then contain caustic soda in addition to sodium sulfide or polysulfide. Sodium thiosulfate, sodium sulfite, etc, may be produced therein or added thereto in such amount as may be desired.

It is particularly advantageous, however, to produce the cooking liquor of the process of the present invention by treatment of the residual liquor produced by the cooking operation of the process. The process can be carried out to a large extent, for example, in a mill such as is now used for carrying out the so-called sulfate process. The residual liquor can be concentrated, the concentrated or dried product then subjected to carbonization or charring, and the resulting material can be subjected to a further operation to give a melt or smelt containing considerable amounts of sodium carbonate and sodium sulfide. By dissolving this melt a solution is obtained containing the sodium compounds.

The solution so obtained, and containing sodium carbonate and sodium sulfide can then be subjected to treatment with a regulated amount of sulfur dioxide or sodium bi sulfite or both, and of elementary sulfur as needed or desired to convert part of the soda content into thiosulfate, and to give a solution containing sodium carbonate, sodium thiosulfate, and a sulfide of sodium. This solution can then be subjected to causticizing with lime to convert some of the sodium carbonate into caustic soda. thus giving a solution containing caustic soda, sodium thiosulfate and a sulfide of sodium.

The amounts and proportions of sodium hydroxide, sodium thiosulfate and sodium sullide used in the cooking liquor may be varied considerably. The amount of caustic soda may be the same as that ordinarily used in the sulfate process, but it may advantageously be considerably less than so used, while in certain cases it may be even somewhat greater than the amount ordinarily used in the sulfate process. The sulfide content of the cook: ing liquor, particularly with decreased caustic soda content in the liquor, may be as great as or even greater than that ordinarily used in the sulfate process; although when the amount of caustic soda is larger than that ordinarily used in the sulfate process the amount of sulfide will generally be less and may be considerably less, because of the thiosulfate content of the liquor. Sodium thiosulfate will also be present in the various cooking liquors in considerable amount, and this amount may vary. Particularly when dense hard woods are used which require a relatively large amount of chemical in the cooking liquor, the amount of caustic soda based upon the total weight of the Wood can advantageously be regulated to a point where the wood will not be overcooked or injured to an objectionable degree, and the presence of the sulfide and thiosulfate in suflicient amounts will nevertheless enable the cooking operation to be carried to completion. Sodium thiosulfate appears to react in a somewhat different manner than sodium sulfide, and the combined actions of the thiosulfate and sulfide together with caustic soda is such that the action of the caustic soda is advantageously supplemented by the sulfide and the thiosulfate. The amount of the thiosulfate may be equal-to or greater than the amount of the sulfide, although in some cases the amount of thiosulfate may be less than the amount of sulfide.

It is one advantage of the present inven tion that it may be carried out in the plant and with the equipment of existing sulfate mills,requiring but moderate change both in the mill construction and in the general method of operation. The cooking, concentrating or evaporating, carboni'zing or calcining, and smelting operations may be carried out in the apparatus now used in the socalled 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 produced, and in the treatment of the residual liquor for the production of a further amount of cooking liquor therefrom.

One of the important characteristics which the present invention possesses is that it is applicable to the treatment of various kinds of wood, both coniferous and non-coniferous, including various woods that are commonly considered as inferior for the production of satisfactory chemical pulp therefrom. The rapidly decreasing supply of wood suitable and available for pulp-making purposes, 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 chemical pulp from woods which are commonly 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 ap plicable not only to the common pulp woods, such as poplar and spruce, but also to various other woods, both coniferous and, lion-cniferous, 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 white pine, ack pine, longleaf pine, shortleaf pine, lodgepole pine, slash pine, and other similar pines can thus be treated according to the present invention for the production of suitable chemical pulp therefrom.

The cooking operation of the present invention can be carried out indigesters 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, but ordinary iron or steel digesters, preferably forge or hammer welded, can be used. The digesters may 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 through a suitable distributor can be employed, and with suitable heating of the cooking liquor which is being circulated. Rotary digesters may be used with distinct advantage.

In carrying out the cooking operation, different temperatures may be employed, for example, a temperature corresponding to a saturated steam pressure of 100 to 125 lbs. saturated steam. gauge pressure, a temperature around 338 to 353 F.; or the temperature may be higher or lower than this.

The cooking liquor may contain, for example, for poplar wood, from l0 to 60 grams per liter of caustic soda, from to grams per liter of sodium thiosulfate and from 15 to -14) grams per liter of sodium sulfide, although these amounts a'nd relative proportions can be varied. For coniferous or resinous woods such as spruce, jack pine, slash pine. etc, the cooking liquor may contain, for example. from $0 to grams per liter of caustic soda. from 10 to 25 grams per liter of sodium thiosulfate. and from 20 to 45 grams per liter of sodium sulfide. In general. the total sodium content of-the cooking liquor should be at least 1271.: on the bone dry weight of the wood cooked. it may range from 12 to 20ft.

In carrying out the process of the present invention, the procedure may differ some- Ordinarily all? what with non-coniferous woods, and particularly dense hard woods such as blrches,

beeches, and maples, etc.,and with less dense woods such as poplars, etc, or with coniferous woods such as spruces, some pines, etc. With non-coniferous woods, for example, the digester charge may be heated in a relatively rapid manner to the cooking temperature while with coniferous woods it is advantageous to heat up the digester charge more gradually so as to secure fairly thorough penetration of the wood chips with the cooking liquor at a moderate temperature before heating the charge to the higher cooking temperature.

lVith the dense heavy hard woods which have a much greater weight of wood per cubic foot, the digester charge, if the digester is filled with the hard wood chips, will be far greater in weight and in wood content than with the soft and less dense coniferous woods or woods such as poplar. T he increased weight of these dense hard woods will require a greatly increased amount of chemical per digester charge for satisfactory cooking. If the amount of caustic soda in the cooking liquor is too great, the wood chips will be injured; but the present invention presents the advantage that the amount of caustic soda can be kept below the point which will injure the chips and the pulp to an objectionable degree, and the action of the caustic soda will be so supplemented by the sodium sulfide and sodium thiosulfate that a satisfactory cooking operation can nevertheless be obtained, the amount of sulfide and thiosulfate being sufficient to supplement the action of the caustic to give the desired cooking action upon the wood chips.

hen the cooking operation is completed, the charge. can be blown into a blow pit, the residual liquor recovered and the pulp washed and subjected to further treatment in a 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 somewhat different in character from the pulps commonly produced by the usual methods, and we accordingly regard the pulps as new and improved pulps. Various pine woods, such as, for example, slash pine, jack pine, etc. as well as spruces, tamarack, hemlock and other coniferous woods, may be treated according to the process of the present invention to yield pulps of excellent strength. It will be evident, however, that inasmuch as different woods differ from each, other in their fibre structures, the pulps produced therefrom will differ somewhat from each other. The process of the present 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 reactions which take 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 reactions and of the reaction products produced varies with the cooking liquor employed. Sodium thiosulfate,-when present in appreciable amounts in the cooking liquor, reacts in a characteristic way with the reactive constituents or groups of the wood substance, and when both sodium thiosulfate and sodium sulfide, together with caustic soda, are present in the cooking liquor, the combined reactions of these various chemical substances upon the reactive substances results in the production of a residual liquor containing the reaction products of these various chemicals with the reactive substances. 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 solution can then be treated for the production of further amounts of cooking liquor therefrom; Vhen the residual liquor from the pnlpmaking operation is evaporated to dryness, and carbonized to destroy organic'matter. and the resulting carbonized product is subjected to a smelting operation, the solution of the resulting melt or smelt generally contains considerable amounts of sodium carbonate, and of sodium sulfide, and it may contain other sodium compounds 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 a sulfate of sodium can be added to the residual liquor before carbonizing or to the carbonized product before smelting, and the amount of the sodium sulfide. or of sodium sulfide and polysulfide, can thereby be increased in the resulting melt. The carbonized or charred p"oduct from the carbonizing or charring furnace may also have additional carbonareaders ceous material added thereto if necessary or desirable for the smelting operation.

The melt or smelt produced in the present process, somewhat like the melt or smelt from the snielte: of the sulfate-process, contains relatively large amounts of sodium sulfide or of sodium sulfide and polysulfide or polysulfides. In the sulfate process, all of this sulfide usually is employedv again in the cooking operation, after causticizing the solution to convert some of the sodium carbonate into caustic soda. In the process of the present invention, however, apart of the sodium sulfide may be convertedinto sodium thiosulfate, or the solution of the melt may be treated to convert loosely combined sulfur of the polysulfide, when present, int-o sodium thiosulfate.

The solution of the melt or a portion thereof, may, for example, be treated directly with sulfur dioxide in regulated amount. Some sulfur dioxide mayreact with sodium polysulfide, when present, or with sodium sulfide, or loth, with the production of sodium thio sulfate. The solution can in this way be substantially freed from polysulfide, and the amount of sodium sulfide also can be reduced and part of it converted into sodium thiosulfate, and this conversion can be regulated by regulating the sulfur dioxide treatment.

In tead of treating the solution of the melt or a portion thereof with sulfur dioxide it can be treated with sodium bisu'lfite or acid sodium sulfite, or with sodium sulfite and sulfur dioxide. and the amount of such reagents and the treatment can be regulated and cont-rolled to give a solution containing a regulated amount of sodium thiosulfate. Elementary sulfur may be added, if needed, to convert sulfite into thiosulfate.

Instead of treating the solution of the melt with sulfur dioxide or acid sodium sulfite, it may be treated with normal sodium sulfite, which will react with loosely combined sulfur of the polysulfide if any present to form sodium thiosulfate, and this'treatment may be supplemented by a further treatment of a portion of the solution, if desired, with sulfur dioxide or sodium bisulfite to produce a further amount of thiosulfate. Added sodium compounds and sulfur can be introduced for further use in the carrying'out of the cooking operation, for example, to make up for their losses in the operations. Additional sodium can also be introduced, for example. in the form of a sulfate of sodium at some point prior to the smelting operation. This sodium sulfate will be reduced to a greater or less extent to sodium sulfide, and this sulfide. for example, by reaction with sulfur dioxide in solution, can be converted at least in part into sodium thiosulfate.

In subjecting the solution ofthe melt to a sulfiting operation, as above described, this sulfiting operation is regulated and limited.

iii)

eeaoie if an excess of sulfur dioxide or sodium acid. sulfite were employed, all of the sodium sulfide would be converted into sodium thiosulfate or other compounds and little or no sodium sulfide would be left, and the resulting solution on causticizing might then contain largely caustic soda, sodium sulfite and sodium thiosulfate. In the process of treating the residual liquors according to the present invention, the solution of the melt is not sulfited to such an extent as to react with all of the sulfide, but part of the sulfide is left in the solution and a part is converted into thiosulfate. and the relative amount of sulfide and thiosulfate can be regulated and controlled by regulating and controlling the operations, especially When one portion is sulfited, the other portion causticized and the two portions thereafter mixed.

After the sulfiting operation, the solution of the melt or the unsulfited portion thereof may be subjected to causticizing With lime, in a manner similar to that practiced in the presentday sulfate-process for treating the solution of the melt to regenerate a cooking liquor containing caustic soda and sodium sulfide. 'l he causticized liquor according to the present invention, however, will contain both sodium sulfide and sodium thiosulfate, in addition to caustic soda especially when the two portions are separately treated and then mixed together.

Instead of subjectingthe solution of the melt to sulfiting and then to subsequent causticizing with lime, the solution may first be subjected to causticizing with lime, and then subjected to a regulated sulfiting operation. The causticizing with lime is usually incomplete, some sodium carbonate being left behind in the solution. During the sulfiting operation some of the sodium carbonate may be converted into sodium sulfite, which may in turn react with loosely combined sulfur of the polysulfide, if any is present, to form sodium thiosulfate. When the causticized solution is sulfited with sulfur dioxide, the sulfur dioxide may react first with the caustic soda to form sodium sulfite, and some of this may then react with loosely combined sulfur of the polysullideif any to form sodium thiosulfate. Sulfur may be added to convert l ?a SO into Na t a O if necessary or desired. instead of subjecting the residual liquor to evaporation to dryness, carbonizing, and subsequent smelting. the smelting operation may be omitted, and the dried residue from the drying of the residual liquor can be sub jected to a regulated carbonizing or calcining operation, for example, in a rotary furnace such as is used in the soda process mills, and the carbonizing operation can be carried out so as to give a furnace productfrom which a solution can be obtained containing sodium carbonate and some sodium sulfide,

together with varying amounts of sodium thiosulfate, sodium sulfate, etc, and the resulting solution can then be subjected to a subsequent causticizing operation of the character above described. These liquors may also be given a regulated sulfur treatment if desired or necessary.

The regulated sulfiting operation can be carried out, for example, by running the solution of the recovered soda compounds or a portion thereof through a suitable tower into which a regulated amount of "sulfur dioxide is introduced. The resulting solution or the other portion thereof can then be run to the causticizing tank for treatment with lime to causticize sodium carbonate to produce caustic soda. The added reagents required to make up for those lost in the process may be supplied by lime, e. g. for the causticizing, sodium carbonate, e. g. by adding to the solution of the melt before causticizing, or sodium sulfate or bisulfate e. g. for adding to the residual liquor or dried. product before smelting, and sulfur or sulfur dioxide or all of these materials;

@ther suitable compounds may be used in the production of a regenerated cooking liquor for the process herein. Sodium car bonate may be used and subjected to causticizing, or sulflting, etc. to furnish additional sodium hydroxide or sodium sulfite or sodium thiosulfate. Calcium carbonate may be burned to form the oxide and this used for converting sodium carbonate in solution into caustic soda. Elementary sulfur or sulfur dioxide may be used for introducing sulfur when the other sulfur-bearing compounds are not adequate for furnishing the desired sulfur content in the cooking liquor.

When the cooking liquor contains a smaller amount of caustic soda than in the ordinary sulfate process cooking operation, and correspondingly larger amounts of sodium-sulfur compound or compounds,the cooking operation may advantageously be carried out at a somewhat higher. temperature than usual, especially when the amount-of thiosulfate or sulfite is quite high as compared with the sulfide. Y

Coniferous Woods and non-coniferous Woods'behave somewhat differently, but in general the non-coniferous woods are more easily pulped than the coniferous, and since they also contain relatively shorter or smaller fibres, greater care should be taken in the cooking operation to avoid excessive injury. By carefully cooking, non-coniferous Wood pulp can be obtained Which is quite strong and useful in making relatively strong papers.'

Another modification of the process of this invention Where long fibred Woods are cooked with a liquor Which contains caustic soda, sodium thiosulfate and sodium sulfide, is to concentrate the residual liquor from the cooking operation to some extent, for example to about 20 to 25 B. at about 135 F., and then subject the concentrated residual liquor to a regulated sulfiting treatment, e. g. with sulfur dioxide or with sodium bisultite or both, to convert a considerable portion of the contained soda compounds into sodium sulfite together with some sodium thiosulfate. The residual liquor usually contains a fair amount of sodium thiosulfate, and may also contain some sodium sulfide. The latter, upon sulfiting may be converted to a considerable extent into sodium thiosulfate. By rendering the partially concentrated liquor slightly acid to litmus, considerable organic matter is precipitated from the solution. When the liquor is warm enough this or ganic matter coagulates, some of it settles and in some cases some of the precipitated organic matter floats to the top of the liquor. The liquor may be withdrawn so as to obtain it substantially free from the precipitated organic matter, although it is not necessary that the separated liquor be entirely free from such precipitate. It is advisable to promptly separate the liquor from the precipitated organic matter after sulfiting to avoid re-solution of the precipitated organic matter which takes place to some extent upon prolonged standing in the presence of the acid. The separated liquor may be used as a cooking liquor, using a digester which is so constructed as to withstand the action of the acid liquor; or the acid liquor may be neutralized in any suitable manner, e. g. by adding the required amount of sodium carbonate so that the neutralized liquor is alkaline to litmus and only slightly alkaline to phenolphthalin.

The neutralized liquor contains as essential cooking ingredients, sodium sulfite and sodium thiosulfate. The method of using such a cooking liquor for the production of chemical pulp from wood is more fully set forth in our patent application, Serial Number 7 04,176 filed April 4, 1924. For such a cook, the liquor may be tested by titrating it with standard iodine solution to determine the reactive sulfur compounds, then another portion of the liquor may be treated with an excess of barium chloride solution, allowed to settle, and an aliquot portion of the clarified liquor removed and titrated with standard iodine solution. The difference in the amount of standard iodine required can be taken as a measure of the amount of sodium sulfite in the cooking liquor. The cooking liquor may be adjusted in strength so that it contains the requisite amount of sodium sulfite, as set forth in the said application.

This cooking liquor derived from the black liquor may advantageously be employed for the production of chemical pulp from short fibred woods. e. g. non-coniferous woods The residual liquor or red liquor resulting from such pulping operations may be used, in part, for making up the cooking liquor which contains caustic soda, sodium thiosulfate and sodium sulfide. The red liquor may also contain some sodium sulfite which may be so added to the cooking liquor.

The other portion of the red liquor may be concentrated, the dried matter carbonized in a rotary furnace, e. g. such as is usually used in soda process mills, or it may be charred and then smelted in much the same way is usually followed in sulfate process mills. The recovered soda compounds generally contain a substantial amount of sodium carbonate and sodium sulfide, which when treated with lime yield cooking liquors which contain caustic soda and sodium sulfide, and which by the process of this invention, may be changed to contain the desired amount of sodium thiosulfate. The organic matter precipitated following sulfiting contains considerable soda compounds. This material may be added to the other material undergoing treatment in the rotary furnace and thus the organic matter destroyed and the soda compounds recovered along with those from the untreated residual liquor.

The relatively strong short fibred pulp and the long fibred pulp obtained by the combined cooking operations above described may be mixed and the mixture of pulps used for the production of strong and well formed papers. Or the pulps may be bleached and used in any manner customary in the art. The combined method of operation is particularly advantageous where the long fibred woods are resinous coniferous woods which grow in the southern portion of the United States of America, and the short fibred Woods are the gums and other similar trees which grow abundantly in the same region.

In the combined operation the soda and the sulfur are used to especial advantage, the amount of water to be removed by evaporation is'considerably reduced and the use of recovery apparatus is modified in an advantageous manner, with the result that the expense is reduced and the loss of soda and sulfur is decreased. By using some of the digesters'in amill for cooking coniferous 1 woods with the strongly alkaline cooking liquor, and using the black liquor therefrom for the production of a cooking liquor which 7 contains sodium sulfite, and using some of the red liquor for the production of the strongly alkaline cooking liquorand some of the red liquor for mixture with a strongly alkaline cooking liquor, a number of advantages are obtained.

The paper made fromthe mixture of unbleached long fibred and short fibred pulp derived in the combined cooking operation has certain advantages which distinguish it froln paper made exclusively from pulps from coniferous trees.

The following specific description will further illustrate the process of the invention, using the new cookingliquor for the production of chemical pulp from wood A vertical, stationary type welded steel digester, about seven feet diameter by 25 feet high overall. is charged with about three and a half to four cords of wood, e. g. jack pine in the form of chips about 7 to inch long along the grain, then about 3,000 to 3,500 gallons of cooking liquor is run into the digester. The cooking liquor may contain about 1.500 pounds of caustic soda, about 700 pounds of sodium sulfide and about 700 pounds of sodium t-hiosulfate. The wood chips in the charge may amount to about 10,000 pounds of bone dry Wood.

The digester is provided with a perforated false bottom and with suitable piping, valves. pump, etc., so that the cooking liquor may be withdrawn from the lower portion of the digester and circulated in copious amount through the charge in the digester, by rein-- troduction of the cooking liquor in the upper portion of the digester, with means within the upper portion to spread the liquor out above the chips. Steam may be with advantage introduced into the liquor during its passage through the circulating pipe line.

The digester may he gradually heated for anhour or so. or until such time as the chips are penetrated with cooking liquor to the desired extent, and thereafter the charge may be further heated until a temperature within the digester of about 170 to 175 centigrade or higher is obtained. Thermometers at va rious points in the digester will indicate whether or not the temperature throughout the charge is substantially uniform. The heating at the temperature shown above may be continued until samples of pulp withdrawn through sampling devices indicate that the cook has been completed. This may require about two to five hours. depending somewhat upon the cha 'acter of stock desired and upon the other conditions of the cooking operation.

Non-coniferous wood. such as aspen (northern poplar) or dense hard woods. such as birches. maples. beeches. oaks. et c.. can be cooked in a similar way. but with these woods the digester charge may with advantage be heated more rapidlv to the main cooking temperature. it-h all woods, however. it is advantageous to provide thorough circulation of the cooking liquonand to secure uniform treatment and cooking of the entire digester charge.

The pulps produced by the process of the present invention are of somewhat different character from the pulps prodrced bv the usual so-called sulfate process. The replact ment of a part of the caustic or the sodium sulfide or both with sodium thiosulfate results in a modified reaction of the cooking liquor upon the reactive constituents which is somewhat different from the reaction with the ordinary cooking liquor of the sulfateprocess, and this is reflected in both the residual liquor and in the pulp produced.

The pulp produced may be used for the manufacture of paper, and especially when produced from coniferous woods paper of great strength may be obtained. Satisfactory pulp can also be produced from nonconiferous woods, including not cnly the common pulp woods, such as poplar, but including also the dense heavy hardwoods, such as birches, maples, beeches, oaks, etc. Mixed pulps can also be produced. and especially unbleached mixed pulps, having advantages in the production of certain grades of paper.

In the carrying out of a pulpanaking process with a cooking liquor containing present invention however provides other.

processes of supplying the sodium content and the sulfur content so that the proportion of the different ingredients can be regulated and controlled. For example a quantity of sodium sultite or sodium thiosulfate or a mixture of these can be added to the solution of the melt before causticizing with lime or to the cooking liquor after the causticization operation and the removal of the calcium carbonate mud. The cooking liquor may also contain other sodium compounds than sodiiuu hydroxide, sodium sulfide, and sodium thiosulfate. By adding a consiclerable amount of thiosulfate, or by adding elementary sulfur to the liquor before. during. or after the causticization. an increased content of sulfur in the liquor can be obtained in pro portion to the sodium. Also by treating the solution of the melt or the cooking liquor with the sulfate. sulfide. sulfite, or the thiosulfate radical or a mixture of any of these.

a similar increase in the sulfur content may be obtained. By treating milk of lime with elementary sulfur. boiling. separating the solution from the residue. and adding this so lution to the liquor or liquors referred to above a precipitate of calcium carbonate may be obtained. and additional sulfur comprunds left in the solution.

e have also shown various ways of controlling the ratio of active sulfur-bearing sodium compounds to other sodium-bearing compounds especially caustic soda. We have shown how additional sulfur may be introduced either in the form of elementary sulfur or of sulfur dioxide or the sulfate or sulfite radical or by using two or more of these forms of sulfur. Ve have shown how the cooking liquor may with advantage contain sodium thiosulfate in considerable amount in addition to caustic soda and sodium sulfide, either with or without sodiumsuliur compounds such as sodium sulfite, etc.

The invention accordingly provides a complete regenerative pulp-making process which is distinguished in important respects from the usual sulfate process so-called. The methods of producing the cooking liquor, the method of carrying out the cooking operation with the particular cooking liquors employed, the method of treating the residual liquors for the production of further amounts of cooking liquor therefrom, and other aspects of the invention differentiate it from the usual sulfate process; while the process of the present invention presents various advartages such as those hereinbefore pointed out.

In the process of the present invention we do not exclude the presence of varying amounts of sodium sulfite, sodium carbonate, etc.. in the cooking liquor, although sodium sulfite need not be present in any appreciable amounts.

The process which forms thesubject of the present invention, and which is more particularly claimed herein, involves the production, and also the use of a new cooking liquor containing caustic soda, sodium thiosulfate, and sodium sulfide, either with or without other chemical substances, and the treatment of the residual liquors from such cooking process, for the regeneration of further amounts of cooking liquor therefrom and for the treatment of residual liquors from other pulp-making operations to produce a regenerated cooking liquor for use in the process of this invention.

We include the use of potassium compounds either alone or in conjunction with sodium compounds. In some instances, it is advantageous to use potassium compounds, especially when the residual liquor is to be used in the production of fertilizers.

We claim:

1. The method of producing pulp from wood which comprises subjecting the same to a cooking operation under pressure and at a temperature in excess of 175 C. with a cooking liquor containing essentially caustic soda, sodium thiosulfate, and sodium sulfide, the amount of caustic soda being at least about 40 grams per litre, the amount of sodium thiosulfate being at least about 10 grams per litre, the amount of sodium sulfide being at least about 15 grams per litre, and the total sodium content of the cooking liquor being at least 12% on the bone-dry weight of the wood cooked.

2. The method of producing pulp from wood which comprises subjecting the same to a cooking operation under pressure and at an elevated temperature with a cooking liquor containing essentially caustic soda, sodium thiosulfate, and sodium sulfide, the amount of sulfide being in excess of the amount of thiosulfate, the amount of reagents being such that the residual liquor at the termination of the cooking operation is non-acid to litmus.

3. The treatment of cellulosic fibre-bearing material which includes digesting such material with a cooking liquor which contains a compound alkaline to litmus, separating an alkaline residual liquor from fibrous material and treating the residual uncarbonized liquor with the sulphite radical, using the resulting solution for the treatment of cellulose-bearing material, separating the resulting residual liquor from the resulting cellulose-bearing material and treating the latter liquor by evaporation of water, carbonization of organic matter, and recovering a material which contains a sulphide of alkali.

l. The treatment of cellulose-bearing ma terial with a cooking liquor which contains caustic alkali, separating the residual liquor and treating the residual uncarbonized liquor with the sulphite radical, using the resulting solution for the treatment of cellulose-bearing material, separating the resulting residual liquor from the resulting cellulose-bearing material and treating the latter liquor by evaporation of water, carbonization of organic matter, and recovering a material which contains a sulphide of alkali and a carbonate of alkali, treating a solution of the alkali compounds with calcium hydroxide to produce a solution which contains caustic alkali and alkali sulphide and using the regenerated cooking liquor for the treatment of further amounts of cellulose-bearing ma terial.

5. The treatment of cellulose-bearing material with a cooking liquor which contains alkali sulphide, separating the residual liquor from the fibrous material, treating the residual uncarbonized liquor so as to produce a cooking liquor containing a trioxy sulfurbearing compound of an alkali, cooklng cellulose-bearing material with such cooking liquor, separatingt-he resulting residual l1quor from the resulting cellulose-bear ng material and treating the latter liquor so as to recover a material which contains alkali sulphide and using the material for the production' of a cooking liquor which contains a sulphide of an alkali.

6. The method of obtain ng fibrous material suitable for paper making, which includes the step of digesting wood so as to render individual fibres thereof readily separable from each other by mechanical treatment, by means of a liquor the principal reagents of which include sodium combined in the form of sodium hydroxide, a lesser amount of sodium combined as sodium sulfid and a lesser amount of sodium combined as sodium thiosulfate, but the total amount of tri-oxy-sulfur-bearing compounds being less than the total amount of sodium sulfid, the amount of sodium hydroxide being sufiicient to dissolve a substantial part of the non-fibrous organic constituents of the wood and in excess of that required to break up the inorganic constituents thereof and the treatment being adapted to yield a residual liquor at the termination of the digest on treatment which is non-acid to litmus.

7. The method of producing chemical pulp from wood which comprises subjecting the same to a cooking operation under pressure and at an elevated temperature with a cooking liquor containing a caustic alkali, an alkali metal sulfide and an alkali metal thiosulfate, the amount of sulfide being less than the amount of caustic alkali and theamount of thio-sulfate being less than the amount of sulfide, but the sulfide and the thio-sulfate together being greater in amount than the 4 caustic alkali.

8. The method of producing pulp from wood which comprises subjecting the wood to a digestion with a liquor including as principal reagents, an alkali metal hydroxide, an alkali metal sulfide and an alkali metal thiosulfate, the amount of alkali metal hydroxide being larger than the amount of trioxy-sulfur-bearing compounds.

9. The method of producing pulp from wood which comprises subjecting the wood to a digestion with a liquor includmg as principal reagents an alkali metal hydroxide, a sulfide of an alkali metal, and a thiosulfate of an akali metal, the amount of "alkali metal sulfide being reater than the amount of alkali metal thlosulfate.

10. The method of producing pulp from wood which comprises subjecting the wood 7 to a digestion with a liquor including as principal reagents sodium hydroxide, a lesser amount of sodium sulfide and a lesser amount of tri-oxy sulfur-bearing material including sodium thiosulfate.

11. The process of producing pulp, which comprises digesting wood by means ofa liquor which contains as its threeessential chemical ingredients sodium hydroxide, sodium sulfid and sodium thiosulfate, the

amount of sodium present in the sodium hydroxide and that present in the sodium sulfid each being larger than that present in the sodium thiosulfate, and the amounts of hydroxide and sulfid being suificient to ren-' der soluble the major portion of the nonfibrous organic constituents of the wood.

12. The process of producing pulp, which comprises digesting wood by means of liquor supplied with an alkali metal hydroxide, an al ali metal sulfid and tri-oxy sulfur-bear-' ing compounds of an alkali metal including an alkali metal thiosulfa-te, the amount of alkali metal present as hydroxide being larger than that present in tri-oxy sulfur-bearin compounds, and the amount of alkali meta sulfid being larger than the amount of trioxy sulfur-bearing compounds of an alkali metal, and the amounts of hydroxide and sulfid being sutficient to render soluble the major portion of the non-fibrous organic constituents of the wood.

13. The process of producing pulp, which comprises digesting woodby means of liquor supplied with an alkali metal hydroxide, an alkali metal sulfid and an alkali metal thiosulfate, the amount of alkali metal present as hydroxide being larger than that present as alkali metal sulfid, and the amount of alkali metal present as. sulfid being larger than that present as alkali metal thiosulfate, and the amounts of hydroxide and sulfid being suflicient to render soluble the major portion of the non-fibrous organic constituents of the wood.-

14:. The process of producing pulp, which comprises digesting wood by means of liquor supplied with sodium hydroxide, sodium sulfid and tri-oxy sulfur-bearing com ounds of sodium including sodium thiosu fate, the amount of sodium present in the sodium hydroxide being, larger than that present in the sodium sulfid, the amount of sodium present in the sodium sulfid being larger than that present in the sodium thiosulfate, the amount of sodium hydrox-vide being at least 40' grams per litre of the liquor, the amount of sodium sulfid being at least 15 grams per litre, the amount of sodium thiosulfatebeing' at least 10 grams per litre, and the total amount of these reagents being suflicient so that the total sodium content thereof is equivalent to at least 12% upon the bone-dry weight of the wood which is treated therewith.

15. The process of producing pulp, which comprises digesting wood by means of liquor supplied with sodium hydroxide, sodium sulfid and'tri-oxy sulfur-bearing compounds of sodium including sodium thiosulfate, the amount of sodium present in the sodium hydroxide being larger than that present in the sodium sulfid, the amount of sodium hydroxide in the liquor being at least 40 but not more than 60 grams per litre, the amount of sodium sulfid in the liquor being at'least 15 but not more than 45 grams per litre, the amount of sodium thiosulfate in the liquor being at least 10 but not more than 30 grams per litre, these three reagents being supplied in suliicient amounts so that the total sodium content thereof is equivalent to at least 12% but not more than upon the bone-dry weight of the wood treated. v

16. The cyclic process for producing pulp, which comprises digesting cellulosic-fibre- 5' bearing material by means of cooking liquor containing as the three essential chemical ingredients sodium hydroxide, sodium sulfid and sodium thiosulfate, the amount of sodium present in the sodium hydroxide and also that present in the sodium sulfid being larger than that present in the sodium thiosulfate; removing residual liquor from the pulp; subjecting the residual liquor to an evaporation treatment and resulting sodium compounds to a reducing furnacing treatment to produce sodium carbonate and sodium sulfid, dissolving these compounds and treating the solution with material including lime and sulfur-bearing material to produce a regenerated cooking liquor similar to the cooking liquor above described; and digesting cellulosic-fibre-bearing material with such regenerated cooking liquor.

17. The process according to claim 16, in which sodium sulfid contained in the solution of sodium carbonate and sodium sulfid 'is treated with the sulfite radical so as to partially convert it into sodium thiosulfate, and including such sodium thiosulfate in the said regenerated cooking liquor that is used in the last-mentioned digesting step.

18-. The cyclic process of producing pulp, which comprises digesting cellulosic-fibree bearing material by means of cooking liquor;

containing as the three essential chemical in;

and sodium thiosulfate, the amount of sodium present as sodium hydroxide and as sodium sulfid belng larger than that present as so- 450 into the resulting residual liquor, thereby cellulosic-fibre-bearing material by means of 5a the regenerated cooking liquor; separating nacing solids derived therefromso as to decompose organlc matter and obtain a furnace product containing sodium carbonate and sodium sulfid; treating the furnace product with water and treating sodium carbonate thereof with calcium hydroxide to form soso dium hydroxide thereby forming another re- V fibres; removing water from the residual liqgredients, sodium hydroxide, sodium sulfid f in the form of sodium carbonate and sodium dium thlosulfate; removing residual liquorfrom the pulp; introducing sulfur dioxide' which comprises digesting wood bymeans o the resulting residual liquor from the result ing fibre-bearing material; removing water Irom the resultlng residual liquor and furobtain a melt containing sodium carbonate and sodium sulfid; treating the melt so as to produce a cooking liquor of the type described above, said treatment including converting some of the said sodium carbonate into sodium hydroxide by means of calcium hydroxide and a treatment of an aqueous liquor containing some of the said sodium carbonate and sodium sulfid with sulfur-con taining material adapted to convert a sodium compound of the liquor into sodium thiosulfate; separating the causticized liquor from undissolved solids; and digesting wood by means of the cooking liquor thus obtained, such cookin liquor containing sodium hygroxide, so ium sulfid and sodium thiosulate.

20. The cyclic process for producing pulp, which comprises digesting wood by means of cooking liquor supplied with sodium hydrox ide, sodium sulfid and sodium thiosulphate; separating resulting residual liquor from the uor; furnacing resulting solids under chemically reducing conditions so as to obtain a furnace product containing its soda. mainly sulfid; treating the furnace product with 1 water to obtain the sodium compounds insolution; treating the solution with calcium j hydroxide and with elementary sulfur to produce a cooking liquor comprising sodium ydroxide and additional sodium sulfid; sep- 1 larating the resulting cooking liquor from un- Udissolved solids; and digesting wood with Q-the resulting cooking liquor.

21. Thecyclic process for producing pulp:

cooking liquor supplied with sodium hydroxide, sodium sulfid and a trioxy sulfur compound of sodium, the amount of sodium present in the sodium hydroxide and the amount {of sodium present in the sodium sulfid being larger than that present in the trioxy sulfur compound of sodium; separating the resulting residual liquor from the fibre-bearing material; removing water from the residual liquor by an evaporating treatment; subjecting the resulting sodium compounds including an oxy-sulfurcompound derived from theresidual liquor to a smelting treatment,thereby obtaining a melt which contains sodium carbonate and sodium sulfid;

dissolving these sodium compounds in water and treating the resulting solution with elementary sulfur and with calcium hydroxide, thereby obtaining a cooking liquor which contains sodium hydroxide, sodium thiosulfate and additional sodium sulfid; separating the resulting cooking liquor from result ing lime mud; and digesting wood with the resulting cooking liquor containing the sodium thiosulfate, sodium hydroxide and sodium sulfid thereby produced.

22, The cyclic process for producing pulp, which comprises digesting 'cellulosic-fibrebearing material by means of cooking liquor supplied with sodium hydroxide, sodium sulfid and thiosulfateof sodium, the amount of sodium present in the sodium hydroxide being larger than that present in the thiosulfate of sodium; separating the resulting residual liquor from the fibre-bearing material; removing water from the resulting residual liquor by an evaporating treatment; subjecting the sodium compounds including tri-oxy' sulfur-bearing matter derived from the residual liquor to a smelting treatment, thereby obtaining a melt that contains sodium carbonate and sodium sulfid; treating these compounds with water to form a solution thereof; supplying the solution with elemen tary sulfur and with lime and: treating the solution to obtain a regenerated cooking liquor which contains sodium hydroxide, additional sodium sulfid and sodium thiosulfate; separating the regenerated cooking liquor from the lime mud; and digesting cellu losic-fibre-bearing material with the regenerated cooking liquor containing these three compounds of sodium thereby produced.

tures.

LINN BRADLEY. EDWARD P. MOKEEFE 23. The cyclic'process for: producing pulp,

which comprises digesting cellulosic-fibrebearing material by means of cooking liquor supplied with sodium hydroxide, sodium sulfid and a tri-oxy sulfur-bearing compound of sodium, the amount of sodium present in the sodium hydroxide being larger than that present in the tri-oxy sulfur-bearing compound of sodium; separating the resulting residual liquor from the fibre-bearing material removing water from the residual liquor by an evaporating treatment; subjecting resulting solids including carbonaceous matter and a trioxy sulfur compound of sodium derived from the residual liquor to a smelting treatment, thereby obtaining a melt that contains sodium carbonate and sodium sulfid; treating the melt containing these compounds with water to form a solution thereof; admixing lime with the solution and treating the solution with material including the-sulfite radical, thereby producing a regenerated cooking liquor which contains sodium hydroxide; sodium sulfid and a tri-oxy sulfur-bearing compound of sodium; separating the resulting causticized liquor from the resulting lime mud; and digesting cellu-