US1896038A - Manufacture of pulp, etc. - Google Patents

Description

Patented Jan. 31, 1933 I UNITED STATES PATENT oar-"ice 1.11m BRADLEY, or uolv'rcnnn, NEW. JERSEY, AND nnwann r. mcxnizrn, or rm'r'rsmmo, NEW Yonx, assmnons r BRADLEY-McKIEFE coarona'rron, or NEW Yoax, N. Y., A ooaroaarron or NEW JERSEY umorac'runn or run, ETC.

11o Drawing. Application filed April 4,

.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 pulp-making operatlon; and it includes the new pulps and the new papers made therefrom. It also in? cludes a new and improved method of regeneration of the cooking liquor, and improvements in the process of treating the residual liquors; as well as a complete regenerative process for the regeneration of the cooking liquor and the carrying out of successive cooking operations with regenerated cook: ing liquor; the details of which are hereinafter more fully set forth.

In our prior application, Serial No. 481,147, filed June 28, 1921, we have described an im roved process of producing chemical pulp rom woods in which the woods are subjected to a cooking operation with a cooking liquor containing essentially a normal alkali sulphite, either alone or with a smal amount of caustic soda, etc.

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 a cooking liquor containing essentially a normal alkali sulphite and an alkali thiosulphate, the sulphite generally being in prepo'nderating amount. The cooking liquor may contain moderate amounts of other constituents such as sodium carbonate,

1924. Serial No. 704,176.

vanta eous one when such, other constituents are su stantially absent.

We have found that chemical pulp can be produced vfrom woods of various kinds. by cooking the wood chips with a cooking liquor containing both normal sodium sulphite and sodium thiosulphate, and that a satisfactory pulp, can be thus produced which can be commercially bleached, provided sodium sulphite is present in sufficient amount. This result is surprising in view of the fact that, for example, when aspen chips are cooked with a cooking liquor composed essentially of a solution of sodium thiosulphate the resulting pulp is of a very dark color and very difiicult to bleach, and the pulp is of an entirely different character. We do not claim in this application the cooking of wood with a cookin iquor composed essentially of a solution 0% sodium thiosulphate, as this is being included in a separate application.

The cooking liquor containing both the normal sodium sulphite and sodium thfosulphate may advantageously be produced from the residual liquor from the cooking operation, in one or another of the various meth= ods of treatment hereinafter described. The cooking liquor can, however, be produced in the first instance in any suitable manner, and

oxide with the sodium carbonate to roduce sodium sulfite, and with reaction 0 sulfur dioxide with the sodium sulfide or polysulfide to .producesome sodium thiosulfate. \Vhere elementary sulfur (especially when finely'divicled) is present in or added to the solution treated, this may also react with sodium sulfite to produce some sodium thio sulfate. x

In our investigation of the action of so? dium thiosulfate 'm a. cooking liquor we have investigated the use of sodium thiosulfate aloneas well as its use in conjunction with being readily bleachable by commercial bleaching methods. .The odor from the freshly opened digester is also quite offensive when sodium thiosulfate alone or with caustic soda is used as the cooking liquor. We

have also found that if sodiumsulfite and sodium thiosulfate are ,used together for cooking woods, it is difiicult or impossible to obtain a commercially bleachable pulp if the amount of sodium thiosulfate is too high and the amount of sodium sulfite is too small.

We have found, however, as a result of our investigations, that if the cooking liquor contains a sufiicient amount of sodlum sulfite, based on the weight of the wood, and the concentration of the liquor and the time and temperature of cooking are suitable, a satisfactory pulp can be obtained even though the cooking liquor contains quite a large amount ofsodium thiosulfate. In practice,

we have found that an amount of sodium sulfite equivalent to about 30% or more on the bone dr weight of the woods is desirable, and we aveused much more than this with excellent results; for example, we have used as much as 50% and even more of sodium sulfite. In general, the amount of sodium thiosulfate should be less than that of the sodium sulfite. For best results we consider that only a relatively small amount of sodium thiosulfate is desirable. For example, where the amount of sodium sulfite is equivalent to at least 30% of the'bone dry weight of the wood, the amount of sodium thiosulfate may vary from a few percents up to say 15% of the bone dry wood, or even more SOdllllIl thiosulfate may be present, although, as above stated we consider it more advantageous to use a smaller amount, amounting, for example, to only a few percent on the bone dry weight of the wood.

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-mak ing 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 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 forwthe production of high grade pulp. The process of the present invention is applicab e not only to the common ulp woods, such as poplar and spruce, etc.,

at 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 including not only spruces, firs, and balsam, but also hemloc s, 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 of suitable chemical pulp therefrom.

The cooking operation can be carried out in digesters of the type now used, for example, in the soda'or sulfate processes. Where the cooking liquor contains only sodium sulfite and sodium thiosulfate, or only these chemicals together with others which are neutral or alkaline to phenolphthalein, the provision of an acid resistant lining in the digester is not necessary, but ordinar steel digesters (preferably 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 also may be used with distinct advantage.

In carrying out the cooking operation, different temperatures may be employed, for example, a temperature corresponding to saturated steam at pressures up to 180 lbs. to the square inch, gauge reading. The invention presents the advantage that high tem peratures, corresponding to gauge pressures around 120 "lbs. or higher of saturated steam, can be used without unduly injuring the pulp produced. Temperatures corresponding to around 140 lbs. steam gauge pressure, or even higher, can thus be used in commercial operairon or tions. In general, we have found it advantageous to use higher temperatures with coniferous woods than with non-coniferous woods. With non-coniferous woods it is advantageous to use temperatures around C. or higher, and with coniferous woods,.temperatures around C. and higher, e. g., around to 1 0 C.

The amounts of sodium sulfite and sodium thiosulfatecan be varied. In general, the amount of sodium sulfite should be around 30% or more based on the bone dry weight of the wood treated, and more than this can ployed can be considerably in excess of that actually required in the process since the excess does not have such an 111111110118 action on the fibres that a slmilar excess of react1ve chemicals has in, for example, the soda process. The amount of sultite may be e. g. around 40 to 50% of the bone dry weight of the wood, or even higher, .e. g., or more, but such large amounts are not necessary.

In carrying out the process of the present invention, the procedure may differ 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 as disclosed in' a companion application; while with coniferous woods we find it important to heatup the digester charge gradually soas to secure thorough penetration of the wood chips with the cooking'liquor at a temperature below the active cooking temperature, before heat ing the charge to the active cooking temperature.

When the cooking operation is completed, the charge can be blown in to a blow it and the pulp washed and subjected to urther 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. 1

It is an important advantage of the present invention that the yield of pulp obtained is considerably higher than is commonly obtained by the ordinary chemical pulp-making processes. The yield of pulp may be, for example, several per cent more from poplar wood (aspen) than commonly obtained b the ordinary soda process from that woo We have also found that somewhat increased yields can be obtained from coniferous woods suchas spruces and pines, when treated according to the present invention, as compared, for example, with the ordinary acidsulfite process so-called.

It is a further advantage of the process that heavy woods, such as birches, beeches and maples, oaks, etc., or locust, certain-pines, tamarack, etc., can be used even though the weight of a digester charge of these woods is considerably greater than the weight of a similar charge of poplar or spruce, and even though a correspondingly increased amount .of chemical in the cooking liquor is required. With a di ter charged withwvood'chips, the volume o cooking liquor which can be introducedinto the digester is limited and with the soda process, for example, the strength of the caustic soda solution which can be satisfactorily used in the process is also limited. Suchdense or heavy woods cannot therefore be quite so satisfactorily (cooked by the soda process when the digester is fully charged. In the process of the present invention, however, a digester full of chips obtainedfrom such heavy woods canlbe satisfactorily cooked, inasmuchas the chemicals used in the process can be :used in a sufiiciently concentrated solution to bring about the cookin of the entire digester charge, even thong the process is carried out at a much higher temperature and pressure than is commonly practiced in the present day pulp-making operations. When such dense heavy woods used, it should be evident that :a greatly creased yield of chemical pulp will be tained per digester charge of wood.

The pulps produced by the process of the resent inventionare different :in character that inasmuch as different woods differ in their fibre structures from each other, the pulps producedtherefrom 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 characterist1c in the ulp which it gives.

Owing to t e valuable properties which the pulps produced by the present invention possess, they can be advantageously used for purposes for which other pulps from the same kinds of wood could not be used so satisfactorily. Y The present invention as hereinbefore stated is also applicable for the production of a high quality of chemical pulp from various species of woods which heretofore have not been generally considered as pul woods, or

have been considered of little i any valuefor the manufacture of high grade chemical pulp. In particular, we have found that resinous woods. such as -pines of various kinds, can be advantageously treated by our improved process without serious diflicult arising from the resinous constituents whic 50 sodium sulfite and sodium thiosnlfate canthese woods contain, particularly if the cooking operation is carried out with gradual heating of the digester charge together with adequate liquor circulation over a 'consi er- 5 able period of time before it is finally brou t to the active cooking temperature and pressure. In the case of various heavy woods, the process of the present invention gives high grade pulps with high yields.

The residual liquors produced by the proces 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 wlth the chemicals contained in the cooking liquor, and that the nature of the reaction and of the reaction products produced varies with the cooking hquor employed. When both sodium sulfite and sodium thiosulfate are present in the cooking liquor, both of these chemical substances appear to have a char- [acteristic and dist. nctive action upon the wood treated and the residual liquor contains the soluble reaction products so produced. The residual liquors, moreover, may be substantially free from products of degradation of cellulose, such as usually are present in relatively large amountsin the black liquor from the soda process. The constituents of the residual liquor, however, will differ somewhat according to the character of wood' treated.

We have found that these residual liquors can advantageously be treated for the regen eration'of further amounts of cooking liquor therefrom, for further use in the carrying out of the cooking operation. A part of the residual liquor may be used directly without treatment, for admixture with regenerated liquor; or the residual liquor as a whole may in some cases be used over again, with additions of sodium sulfite or sodium thiosulfate or both thereto before each successive cook if necessary.

Instead of using the residual liquor over again without treatment, we have found that this liquor can be treated in such a way that a fresh amount of cooking liquor containing readily be produced therefrom. When the residualliquor from the pulp making operation is evaporated to dryness, and carbonized 'to destroy organic matter, and the resulting sodium compounds are dissolved in water. the resulting solution may contain some sodium thiosulfate. some sodium sulfite, and some sodium sulfide, some sodium sulfides such as are known as polysulfides, some sodium carbonate and it may even also contain some sodium sulfate, particularly if subjected to oxidation during or after the carbonization. The nature and amounts of the different chemical compounds present will vary somewhat with the conditions underiwhich the carbonization is carried out, but particularly at high temperatures, complex reaction seems to take place between the complex organic substances in the product undergoing carbonization with the result that various sodium compounds containing sulfur are found in the solution obtained therefrom, among them frequently orcommonly being sodium sulfide or sulfides and sodium thiosulfate. While the carbonization can be carried out at relatively low temperatures with avoidance or minimizing of sulfides and thiosu-lfates in the resulting solution, and while the solution produced by dissolving the sodium compounds from the carbonized product can be treated so as to obtain a reduction in the amount of thiosulfate present therein after sulfiting, we have found that such treatment is unnecessary and that some sodium thicsulfate may advantageously be present in the regenerated cooking liquor, when it contains sufficient sodium sulfite, and may advantageously be increased by converting sodium sulfide or polysulfides into additional thiosulfrte by treatment with sulfur dioxide or sodium bisulfite or both, when the amount of thiosulfate is too small.

'hen the carbonized product from the carbonizing operation is in addition'subjectcd to a smelting operation and the resulting smelted or molten material is dissolved in water or in aqueous solution to produce a solution of sodium compounds, varying amounts of sodium sulfides or polysulfides, and sodium thiosulfate, sodium sulfite, sodium sulfate, sodium carbonate, etc., may be present in the solution. If the amount of sodium sulfide or polysulfide is not too large, the solution may be treated directly with sulfur dioxide or sodium bisulfite or both for the conversion of such sulfides into sulfite, thiosulfate or both. Where a large amount of sodium sulfide or polysulfide is present in the solution of the dissolved sodium compounds, sodium sulfide may advantageously be converted into sodium sulfite, for example, by treating the solution first with carbon dioxide to drive 0H hydrogen sulfide and convert sodium sultide into sodiumcarbonate or bicarbonate, and then by treating the carbonated solution or resulting solids or both with sulfur dioxide or sodium bisulfite or both to convert sodium carbonate or bicarbonate or both into sodium sulfite and to convert the remaining sodium sulfide if any into sodium sulfite'or thiosulfate or both.

Accordingly the solution of the recovered sodium compounds recovered either from the carbonized product from the carbonizing operation, or from the melt from the smelter, after clarification 'if'desired or necessary. can be treated with sulfur dioxide or with sodium bisulfite or both, and where these solutions contain proper amounts of sodium sulfide or of polysulfide the treatment will'result in the presence therein of additional sodium thiosulfate, in addition to whatever sodium thiosulfate may be present in the solution before such treatment. This treatment with sulfur dioxide or sodium bisulfite will also serve to convert sodium carbonate into sodium sulfite although some of the sulfite may be converted sulfur than does the sodium monosulfite.

The method of carrying out the treatment of the residual liquors for the production of a further amount of cooking liquor therefrom, will be illustrated by the following more detailed description. It is one advantage of the invention that the process can advantageous- 1y be carried out in the equipment such as is now found in pulp mills constructed and operated for carrying out the soda process or the sulfate process with the addition of the necessary auxiliary equipment.

In eneral, the residual liquor may be evaporated in multiple effect evaporators until the concentrated liquor tests about to B.

' at 160 to 190 F.; then the hot concentrated liquor may be fed in re ulated amounts into the back end of a rotary urnace such as is customarily employed in the soda process pulp mills, this rotary furnace being-about 16 to 20 feet long and about 8 to 9 ,feet indiametei, and being lined with a good grade red brick. The rotary furnace may be provided with a suitable burner at the front end, for example an oil burner, so arranged that a long flame is pro'ected into the rotary furnace, and so that t e intensity of the flame can be con.- trolled byadjusting the feed of fuel and air. The rotary furnace may be rotated at about 2 revolutions per minute. As the water 5 is evaporated, the material is carried forward in the rotary furnace and the temperature becomes high enough to carbonize the organic matter and some volatile and combustible matter is given off from the material and may be ignited, thus helping to carry on the rotary furnace operation. Reducing the speed, for

example, to one revolution per minute changes the operation to some extent, since volatile gases have a different opportunity to l become ignited, as the material does not roll over so frequently as at the higher speed. By

' controlling the liquor feed and the flame at opposite ends of the rotary furnace, the-ash can be delivered either in molten condition or as a well-burned ash, or as an underdone or green ash. The ash may be melted quite easiy in the furnace, and when molten gives off combustible gas. When the rotary furnace is running at good rate, producing a wellburned but granular ash, with'little or no melting of ash in the rotary furnace, we have observed that a greenish yellow flame arose from the material within the furnace,- especially along the upper surface and between the middle of the rotary furnace and the discharge or front end of the furnace. When the large amount of material in the lower part of the furnace rolled over, it sometimes extinguished this peculiar flame. This flame is apparently due to the liberation of elementary sulfur from the complex organic matter or sulafo-organic matter or perhaps from some thio-compound existing in the material undergoing decomposition, and to the burning of the elementary sulfur to sulfur dioxide. Sometimes the ash will continue to burn or to give off volatile and combustible gas even after it is discharged from the rotary furnace, this burning or combustion, sometimes continuing for amappreciable period of time.

It is diflicult to determine the exact nature of the chemical reactions which take place is allowed to oxidize, there may be a considerable amount of sodium sulfate in it; although by suitably reducing the material the amount of sulfate can be kept low. If a sulfate of sodium is added to the residual li uor before evaporation, or to the evaporate or dried products before carbonization, or to the smelter charge before smelting, an increased amount of sodium sulfide may be present in thesmelted product, especially if a smelter is used. v

We have examined someof the molten material from the rotary furnace, when the carbonizing operation was carried out so as to melt the charge, and our examination, after cooling, seems to show the presence of ap- "preciable amounts of elementary sulfur, i. e.,

Apparently free and uncombined sulfur. the complexsulfo-organic compoun s of the residual liquor decompose, in part at least, into sodium carbonate and liberate some sulfar in an uncombined state, this reaction perhaps being' analogous to the. decomposition of sodium thiosulfate under heat treatment.

The reactions which take place are, however, apparently quite complex and we do not wish to limit ourselves by any theoretical explanation of what the reactions may be.

In the treatment of the residual liquors for the regenerationof further amounts of cook- 'ing liquors therefrom, we find it desirable to prevent the building up of the sodium thiosulfate to an objectionable or excessive degree. The amount of-sodium thiosulfate can be regulated in part by suitable regulation of the carbonizing operation in the r0 tary furnace, and in part by proper treat ment of the leach liquor obtained from the ash discharged from such furnace. Some of the leach liquors obtained from theash from such rotary furnace we have found to contain considerable percentages of sodium thiosulfate, even before the leached liquor was sulfited. By controlling the rotary furnace operation, however, this amount can be regulated to a greater or lesser degree, apparent! 1y by elimination of sulfur therefrom which may be burned to sulfur dioxide Some of the sulfur may be eliminated during the smelting operation in a smelter if the ash from the rotary furnace is to be subjected to smelting. The sodium which would otherwise be present as sodium thiosulfate may be present in the leached liquor in part as sodium sulfite or sodium sulfide or even as sodium carbonate.

The stack gases coming from the rotary furnace during the carbonizing operatlon contain quitean amount of sulfur dioxide; and some of the sulfur dioxide may become further oxidized to sulfur trioxid We have collected considerable amounts 0 solids from the flue between the rotary furnace and the stack and found that under certain conditions these solids consisted largely of sodium sulfate. By scrubbing the stack gases with a solution containing sodium carbonate, a considerable portion of the sulfur compounds escaping in the stack gases may be collected either as sodium sulfite, sodium thiosulfate, or sodium sulfate.

The ash discharged from the rotary furnace may be directly subjected to a leaching operation, for example, by conveying it to a dissolving tank or leaching tank where thesodium compounds are leached away from the insoluble carbon. We have found that a good granular ash leached somewhat better eration is advantageously regulated and controlled to avoid any large percentage of molten material and to produce a suitable prodsodium compounds can readily be leached,

leaving the carbon behind.

The residual liquors from a pulp making operation in which the cooking liquor contains essentially normal sodium sulfite, without any appreciable amount of sodium thiosulfate, cansimilarly be treated according to the 'rocess of the present invention for the pro notion of a cooking liquor containing both sodium sulfite and sodium thiosulfate. When such a residual liquor is evaporated to dryness and the dried residue carbonized in a rotary furnace, more or less of the sulfurcontaining compounds ofthe product will be decomposed and some sulfur separated therefrom. Varying amounts of the sodium contents of the carbonized product may be present as sodium carbonate, some of the sulfur originally combined with the sodium apparently having been driven off or converted into some other compound, Some of the sulfurcontaining compounds, varying with the conditions under which the carbonization is carried out, will usually be converted into sodium sulfide or polysulfide, and appreciable amounts of sodium sulfide and polysulfide may be present in the carbonized product, particularly where the carbonization is carried out at higher temperatures and with melting or fusion of the product.

In the carrying out of such a process, we have obtained a composite leach liquor in which sodium compounds were present in approximately the following ratio, namely, about 5 parts of sodium carbonate. about 4 parts of sodium sulfite, and about 1 part of sodium sulfide. In another case where the rotary furnace operation was carried out with a long flame and using hot strong liquor directly from the evaporators, a well-burned granular ash was obtained, which showed approximately the following ratio, namely, about 75 parts of sodium carbonate, about 20 parts of sodium sulfite, and about 5 parts of sodium sulfide.

Solutions of suchcompounds in the ratio above stated, after leaching away from carbon, and clarification in whole or in part when necessar can be treated with sulfur dioxide gas, or example, by running the solution'over an absorption tower, through which or into which sulfur dioxide'is intropresent in the solution sulfited, and dependmg also upon the amount of sodium thiosulfate, if any, present in the solution before it is sulfited.

In examining the product, we have examined the melted material which was dug out of the rotary furnace after cooling and found that it varied from black through grey and some of it was even pinkish in color in the interior of some of the lumps. In places there were apprecable amounts of yellow material, appearing to be elementary sulfur.

While the material was being treated in the rotary furnace, there was a thin flame which resembled burning sulfur. This flame occurred, however, only in the hot portion of the furnace and it is our opinion that some of the sulfur, originally present as sulfurcompouuds in the residual liquor, is set free as elementary sulfur, or is converted into some other compound and volatilized during the rotary furnace operation. The fact that some sulfur is eliminated and some sodium carbonate is formed, indicates that carbon dioxide in some way replaces or displaces sulfur or a sulfur-containing radical to which the sodium is united. It may even be that some carbon directly displaces some sulfur, and may to some extent react with sulfur to form carbon bisulfide, although we do not limit ourselves by any such explanation of the actual reactions which go on.

Ingener'al it is advantageous to carry out the rotary furnace operation under regulated conditions which will retain as much as possible of the sulfur so that it can be recovered as sodium sulfite in the regenerated cooking liquor, without forming too much sodium sulfide and sodium sulfate. We have found it desirable to carbonize the dried material under regulated temperature and air conditions so as to avoid the production of excessive amounts of sodium sulfide and sodium sulfate and also. to avoid the preseiice of an excessive amount of sodium thiosulfate in the regenerated cooking liquor. By using along oil flame fed in at the same end as the hot strong liquor, and carrying the flame and material in the same direction, excessive temperatures can be more readilyavoided, and

y regulating the temperature of such anoperation and the amount of air, a large amount of sulfite can be directly recovered and.made available in the regenerated cook ing' liquor.

Vhere the ash from the rotary furnace is not directly leached, but is subjected to smelting, the resulting melt from the smelter contains such a small amount of carbon that the solution of the sodium compounds of the melt may be separated from undissolved residue by decantation, and maybe thereafter clarified when considered desirable.

As a step in the treatment of the solution produced by dissolving the melt'or by leaching the ash from the carbonizing operation, we have found it advantageous to orough- 1y .mix a small amount of caustic soda with the liquor-or solution. and then thoroughly mix in a small amount of magnesium sulfite. The resulting decomposition which occurs aids 1n the coagulatlonof suspended carbon andfacilitates the separation of a clarified liquor from the insoluble carbon and other insoluble materials.

In order to regenerate a cooking liquor from the leached liquor or from the solution of the molten material, such liquor or solution maybe subjected, either directly or after further treatment, to a sulfiting operation or treatment. This treatment may be with sulfur dioxide or with an'acid solution of sodium sulfite containing varyin amounts of excess sulfur dioxide over an above that corresponding to the normal sodium sulfite. The sulfur dioxide, either introduced as such, or in an acid sulfite SOllltiOIlfWill react with sodium carbonate, or bicarbonate, setting free carbon dioxide, and forming sodium sulfite. Sodium thiosulfate already present in the liquor or solution apparently remains substantially unchanged by' this sulfitingoperation. Sodium sulfide or polysulfides may react with sulfur dioxide or acid sulfite to produce additional ilmounts of sodium thiosulfate; and some thiosulfate may be formed by the reaction of sodiumsulfite with sulfur present in'the liquor as such or as polysulfidesulfur in the solution. Ordinarily, the proportion of sodiumcarbonate' in the solution or leach liquor will be such that a prepondering amount of sodium sulfite will be directly produced, and the amount of sodium thiosulphate will be relatively low, especially when the carbonizing operation is properly conducted.

Where, however, the liquor prior to the sulfiting operation contains a large amount of sodium, sulfidesit may advantageously be subjected to a preliminary treatment before sulfiting in order to reduce the amount of sulfides which it contains. For this purpose it may be treated with carbon dioxide in suflie cient amount to convert some of the sodium sulfide into a carbonate of sodium and liberate hydrogen sulfide gas. This gas may be burned to produce sulfur dioxide and the latter used inthe production of the regenerated cooking liquor. By. carbonation of the solution of the recovered sodium compounds in this way, prior to sulfiting, some of the sulfur is eliminated as hydrogen sulfide, thus reducing the amount of'sodium sulfide in the liquor and correspondingly reducing the ambunt of thiosulfate which will 'be present in the liquor after the sulfiting sodium compounds, or an actual sulfiting of a sample 'of'the solution, followed by analysis, willshow whether it is desirable to car bonate the solution prior to the sulfitin operation for the production of a regenerate cooking liquor.

The carbonating treatment, where this is desirable, may be carried out in different ways. One advantageous method which we have used successfull consists in introducing into the bottom 0 a tall tank containing the solution of the recovered sodium compounds, a strong solution of acid sodium sulte, and causing this to react so that carbon dioxide displaces h drogen sulfide from some of the sodium sul de contained in the solutiori. to react with sodium carbonate to form bicarbonate andthen react to set free carbon dioxide which will then displace hydrogen sulfide from some of the sodium sulfide of the solution. The thiosulfate already present in the solution may be increased in amount when desired, by additional thiosulfate produced from uncarbonated sulfides or produced from polysulfide sulfur or in any other suitable manner.

By regulating the carbonating operation,

the amount of additional thiosulfate subse-" quently formed by the sulfiting operation can be regulated. If the carbonating treatment is omitted entirely, the maximum increased amount of thiosulfate ma be formed; while if all or as muchas possi le of the sulfide is carbonated and converted into a carbonate of sodium, a lesser amount of additional thiosulfate may be formed; and any intermediate amount may be formed by regulating the carbonating operation prior to sulfiting.

In analyzing or testing the regenerated cooking liquor, we have found that good results can be obtained by titration with standard sulfuric acid solution using methylorange as an indicator for the purpose of determining the amount of active sodium sulfite, due allowance being made for any small amounts of other reactive sodium compounds, if any, which may be present. The other reactive sulfur compounds may be determined by the use of standard iodine solution, making allowance for the sodium sulfite determined as above. If the standard iodine solution were alone relied upon and the entire result computed as sodium sulfite (NB SO without allowing for the thiosulfate contents, there would be danger of the operator employing too little actual sodium sulfite and in some cases too-much sodium thiosulfate in the cooking operation and this would result in the production of an unsatisfactory pulp, but

- by properly analyzing or testing the leach liquor or the solution of the melt when using a smelter, its composition can be determined and its treatment then regulated and con-' trolled to give a regenerated cooking liquor That is, the acid sulfite will first tend After extended investigation we have i found it important in using such a regenerated cooking liquor for cooking additional charges of wood chips to employ enough actual sodium sulfite (Na sO to avoid the ob'ectionablefeatures of an excess of sodium thiosulfate (Na S O when used with too small an amount of sodium sulfite; since, if not enough sodium sulfite is employed, it is difiirult or impossible to obtain a good quality and good color of pulp which can be satisfactorily and economically bleached by commercial bleaching methods.

Insofar as we are aware, it is broadly new to cook wood with such a cooking liquor containing a sufficiently large amount of sodium sulfite, the cooking liquor also containing some sodium thiosulfate. Satisfactory cooking of the wood chips can be effected with the sodium thiosulfate as an ingredient of the cooking liquor, and without the objection resultin from the use of an insuflicient amount of sodium sulfite, accompanied by a large amountTof sodium thiosulfate in the cooking liquor. We believe that we are the first to discover how to cook woods successfully with a solution containing essentially both sodium sulfite and sodium thiosulfate, either with or without a small amount of caustic soda, etc., so as to get pulp of a good quality which is economically bleachable by commercial bleaching methods. We also believe we are the first to treata residual liquor from such a cooking operation for the production therefrom of further amounts of cooking liquor containing sodium sulfite accompanied, by sodium thiosulfate. WVe believe we are also the first to show how the residual liquor can be treated so as to recover the sodium content and to regenerate a cooking liquor therefrom which contains a regulated amount of sodium thiosulfate together with a suflicient and preponderating amount of sodium sulfite.

In order to make up for losses of chemicals in the process, or to rectify or to further regulate and control the composition of the cooking liquor, additional amounts of suitable reagents may be added thereto. For example, additional sodium carbonate can be added to the solution which is to be sulfited, and sodium sulfite-produced therefrom. So also, by using sodium bisulfite, or an acid sodium sulfite solution, for the sulfiting operation, the additional sodium sulfite thus added will increase the amount which the regenerated cooking liquor will contain. When the ash h therefrom. This sodium sulfide may be sulfited to the desired extent or the solution can first be subjected to carbonation to convert some of the sodium sulfide into a carbonate of sodium and drive oil hydrogen sulfide, and the sodium compounds may then be subjected to the sulfiting operation.

.By properly regulating the treatment of the constituents of the residual liquor during carbonization, or during carbonization and smelting, and by proper treatment of the resulting solution obtained from the carbonized product or from the melt obtained therefrom, regenerated cooking liquor can be produced of suitable composition for the further carrying out of the pulp making operation.

This pulp making operation, as previously explained, is carried out with a cooking liquor (which may be regenerated from the residual liquor) containing a large amount of sodium sulfite, for example, amounting to 30% or more by weight of the bone dry weight of the wood, together with sodium thiosulfate. Insofar as we are aware, it is broadly new in the pulp making art to subject wood to a cooking operation with a liquor containing both sodium sulfite and a regulated but smaller amount of sodium thiosulfate without caustic soda; and accordingly we claim the use of such a'cooking liquor broadly as well as the cooking of wood for the production of chemical pulp with such a composite cooking liquor. The cooking liquor need not, as hereinbefore explained, contain only sodium thiosulfate and sodium sulfite as it may contain small and regulated amounts of sodium carbonate. I

Where certain pines, such as those which contain a large amount of resinous'constituents (especially the yellow pines of the southern portion of the United States of America which are the main source of naval stores), are to be cooked with a cooking liquor which contains a large amount of sodium sulfite in conjunction with sodium thiosulfate, etc. for the production of chemical pulp, they may advantageously be given a regulated preliminary treatment for the purpose of removing a portion or all of the non-fibrous constituents which are readily soluble in a suitable volatile solvent. Vhere desirable, the solution of the non-fibrous constituents in the volatile solventmay be subsequently treated so as to separate and reclaim the volatile solvent and permit the recovery of the non-fibrous constituents.

This preliminary treatment of the wood,

ing liquor such as referred to above, with the production of a suitable grade of chemical pulp. In particular, it is important to avoid heating the chips to a temperature so high that the non-fibrous constituents are so changed chemically that they may not be readily made soluble in aqueous solution by cooking at elevated temperature and pressure with a cooking liquor such as referred to above. In general the treatment, prior to thorough impregnation of the wood chips with cooking liquor, should not be allowed to exceed about The treating of wood chips with water alone at temperatures much above 100 C. so changes the chips that they can not readily be pulped with asolution containing essentially sodium sulfite and sodium thiosulfate without further treatment, for example, with caustic soda solution, and a similar action apparently takes place where the chips are heated above 100 C. before thorough impregnation. In certain cases, as where the digester charge of pine chips is heated rapidly to the cooking temperature, it may be desirable to cook the pine wood chips with a cooking liquor such as is referred to above, and thereafter to treat the resulting wood chips or the pulp obtained therefrom, with a liquor which contains a small amount of caustic soda or other suitable reagent such, for 1nstance, as sodium sulficl which is capable of -readily removing certain non-fibrous constituents which are not readily removable by cooking with a cooking liquor which contains essentially sodium sulfite and sodium thiosulfate. The caustic soda etc. can be added, for example, near the end of the cook, or after a partial cook, or a cooking liquor containing the caustic soda etc. can be used after the first liquor is drawn off.

leached liquor Grams per litre NaOI-I Na S A--- 3.8 Na- SO 15.75 Nagsgog 99.935 Na cO 120.97

leached liquor Grams per litre Na CO 53.66 NaOI-I None Na s 8.77 Nagsgog Na12SO3- Regenerated liquor f Grams per litre Na SO 169.9 Na s O 21.33 5.74

NilgCOg The followingis a suitable method of analysis for analyzing liquors of the character above indicated.

Total alkalinity. A 10 cc. sample of liquoris titrated with normal sulfuric acid using methyl orange as an indicator. This total alkalinity represents caustic soda, sodium carbonate, sodium sulfide and one-half the sodium sulfite.

3 Another 10 cc. sample is treated with excess barium chloride in a 250 cc. flask, made up aliquot part is titrated with tenth normal acetate paper as outside indicator.

ammoniacal zincchloride solution using lead gives the sodium sulfide.

The precipitate formed as above described by treating the 10 cc. sample with excess barium chloride is filtered off and the precipitate washed with hot water. This precipitate of barium carbonate and barium sulfite is transferred to a beaker, distilled water added, then tenth normal iodine solution added in excess of the possible sulfite content, the precipitate then dissolved in diluted bydrochloric acid, starch solution added, and the solution titrated with tenth normal sodium thiosulfate. The difference between the tenth normal thiosulfate reading and the tenth normal iodine reading represents the sodium sulfite (M280 The amount of sodium carbonate is determined by subtracting the amount of caustic soda, sodium sulfide, and half the sodium sulfite from the total alkalinity.

The following description of operations on various woods with a cooking liquor such as referred to herein will serve to show how the process may be operated in practice with good results. An unlined Welded digester, of the stationary, vertical type, the capacity of which was about 1,900 cubic feet, was filled with jack pine chips. These chips were ob tained by barking sticks of two foot length jack pine (Pinus divaricata or Banksiana), then chipping and screening so as to get fairly uniform chips of about to inch in length along the grain. The chips contained about 10 to 20% moisture. About 7,500 gallons of regenerated cooking liquor was used in a digester charge. About 9,000 pounds of sodium sulphite was contained in about 6,000 gallons of fresh regenerated cooking liquor, which we call white liquor, and there was This also added about 1,500 gallons of residual liquor from the process which we call red liquor, the amount of unused sodiumsulphite and sodium thiosulphate in the red liquor being undetermined. The white liquor contained about 1,000 pounds of sodium thiosulphate in some instances, while in other instances the amount was sometimes less and sometimes more than this.

The digester was sealed up and then steam introduced into the digester slowly and gradually, at the same time causing the cooking liquor to circulate throughout the body of chips so as to give them substantially uniform treatment. About three to five hours was taken in heating the digester charge from about 20 deg. cent. up to about 180 to 190 deg. centigrade- The contents of the digester were maintained at this high range of temperature for about seven to fifteen hours. Sometimes the digesters were held for a longer time than fifteen hours and sometimes for a shorter time than seven hours.

lVe have found that by providing a false bottom in the digesters, and suitable piping and pumps so that the cooking liquor can be withdrawn from beneath the false bottom and circulated in copious amount 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, and the liquor is progressively heated during its passage from the bottom to the top of the digester, splendid results may be readily obtained.

As an aid in determining when the cooking operation has progressed to the desired degree, a sampling device may be installed at one or more places in the side of the digester, through which samples of stock may be drawn from time to time. So also thermometers may be installed at various points.

Other digesters of the same size and kind, provided with the same type of circulation equipment, were filled in some instances with wood chips obtained from barked aspen (northern poplar) and in other instances from barked white birch. The same volume of cooking liquor and substantially the same composition as was,used on the jack pine chips, was used satisfactorily in cooking the non-coniferous woods. In these various instances, splendid chemical pulp of very light color in the unbleached condition, was obtained. We found, however, that the time taken for heating the digester contents when aspen or birch were being cooked, as well as the time during which the contents were held at the higher range of temperature, could be materially reduced from that which was found necessary or desirable with the jack pine.

While the cooking liquor charges referred to above contained about 9,000 pounds of sodium sulfite, we have found by actual operations that the amount of chemicals can be centration of the chemicals, and especially of sodium sulfite, in the cooking liquor, the more active the cooking operation, also within reasonable limits. The higher the temperature, the more active the cooking liquor ecomes, but we have found that it is not advisable to cook coniferous woods at a temperature much below 180 C. and we prefer that the temperature be even higher than this, for example up to 190 C. At temperatures much higher than this, the digester and boiler strength required entails considerable additional expense, while if the cooking temperature be too low, the time required is needlessly long.

Non-coniferous woods, in general, are more easily pulped by this process than are the coniferous woods, as a general class.

The chemical pulps obtained from woods by this process are capable of being made into very strong papers, possessing light color, even when unbleached.

The pulps obtained by this process from various woods, for example aspen and birch, may be made into unbleached papers which are lighter in color than papers made with chemical pulp from the same woods when cooked by either the soda process or the sulphate process, when the same kind of treatment in the paper making operation is given to them. And with the same kind of treatment, the papers are stronger than those obtained by the other processes referred to, if the same lightness in color is obtained. in the unbleached and uncolored papers. That is to say, that with this new process new kinds of papers may be produced from the unbleached and uncolored pulps which are characterized by relatively greater strength. For instance, paper made from a fibre furnish of 100% aspen pulp, obtained by this process, being' unbleached but having a small amount of blue color added to the stock in the beater,

was made in weights ranging from 30 pounds to 60 pounds, for example, per ream of 480 sheets each 24 x 36", which showed a bursting strength when tested by the Mullen tester of from three-fourths to over a point a pound. Similar papers were made from 100% white birch pulp from this process'which tested relatively higher than the similar paper made from the aspen pulp. Similar papers made from 100% fibre furnish of jack pine pulp obtained by this process showed bursting strength of from one to as high as one and a half points per pound. Some have tested considerably higher than this, depending upon the cooking conditions and also upon the subsequent treatment which the stock received.

These pulps being very light incolor, especially when washed with hot water after removal of the residual liquor, may readily be used for light colored papers or may even be tinted or colored to almost any desired shape, even without the pulp having been bleached. The papers referred to above were made on a Fourdrinier machine, with mesh wire, operating at 300 feet or more per minute. The wire was 118 inches wide.

We have stated above that the chemical pulps obtained from woods by this pulp making process may as a general class be bleached by the usual bleaching methods. However, we have found that where a particular grade of bleached pulp is desired, the pu1p,.after washing, preferably with hot water, may be advantageously treated with chlorine in the presence of water and at ordinary temperature so as to convert a substantial portion of the non-fibrous material into bleached, oxidized or chlorinated compounds, depending upon the character of the various constituents. These treated pulps may then be washed or otherwise treated to remove water soluble compounds and the resulting pulp given a further treatment with a solution of bleaching powder. A small amount of caustic soda may be added to the bleaching powder solution, if desired, for the purpose of increasing ;the amount of available alkali l therein.

The method of bleaching chemical pulps is more fully-described in one of our earlier patentapplications. By using this method of bleaching chemical pulps which are characterized by high white and relatively great 3 strength may be obtained and thus permit the production of paper of high white and improved strength. This refers not only to pulps obtained from coniferous woods but also and particularly to pulps obtained from 1 non-coniferous woods.

We-hav'e found that this method of bleaching is useful for the bleaching of chemical pulps obtained from woods which in their natural state contain considerable quantities .of tanning materials, dyestufis or other coloring matters which might otherwise interfere with the production of high white and the retention of strength.

We have found' that by subjecting these in the production of unbleached papers of superior quality.

It will thus be seen that the invention provides a new pulp making process in which the wood is cooked with a cooking liquor containing a mixture of sodium sulfite and sodiumthiosulfate to produce a satisfactory chemical pulp; as well as an improved and distinctive residual liquor which may be advantageously treated to regenerate further amounts of cooking liquor therefrom for further use in the cooking operation. 7

The process of the present invention accordingly presents many advantages, among which may be mentioned the following; it enables a good yield of new and improved pulps to be obtained even from the usual pulp woods; it enables a relatively high yield of satisfactory chemical pulp to be obtained from various woods which are not ordinarily considered to be pulp woods; it can be carried out in existing mills utilizing some of the existing equipment, and requires but moderate change in such mill construction;

the cooking liquors can be regenerated from the residual liquors by novel and improved methods of treatment; and the pulps have new and distinctive properties and can be blelached for the production of high grade While sodium has been used as the alkali in this case, we do not wish to exclude the use of other alkali compounds where their use is economically justified.

We claim:

1. 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 free from alkali hydroxide and containing substantial amounts of a sulfite of an alkali and a thiosulfate of an alkali, the cooking liquor being supplied with an adequate amount of alkaline reactive compound to maintain the liquor alkaline to litmus until the end of the cooking operation, at least onehalf of the alkali content of the cooking liquor being supplied as sulfur-bearing compounds and the amount of alkali supplied as a sulfite being at least as large as the amount supplied as a thiosulfate.

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 li uor free from alkali hydroxide and contaming substantial amounts of sodium sulfite and sodium thiosulfate, the amount of sodium sulfite being in excess of about 29% by weight of the bone dry weight of the wood cooked, and the amount of sodium sulfite being larger than the amount of sodium thiosulfate, and sufiicient to maintain the liquor alkaline to litmus throughout the cooking operation.

readily separable from each other, the cooking liquor being supplied with an adequate amount of alkaline reactive sodium compounds to maintain the liquor alkaline to litmus until the end of the cooking operation, the amount of sodium sulfite being larger than the amount of sodium thiosulfate and at least one-half of the sodium content of the cooking liquor being supplied as sodiumsulfur compounds. I

4. 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 substantial amounts of a sulfite of an alkali and a thiosulfate of an alkali, and subjecting the resulting product to a further cooking operation with a cooking liquor containing caustic alkali.

5. 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 substantial amounts of a sulfite of an alkali and a thiosulfate of an alkali, a caustic alkali being added during the latter part of the cooking operation.

6. The method of producing pulp from resinous woods which comprises gradually heating a digester charge of the wood to the cooking temperature with a cooking liquor substantially free from caustic soda and sodium sulfid and containing substantial amounts of a sulfite of an alkali and a thio-' sulfate of an alkali to effect impregnation of the wood with the cooking liquor before the cooking liquor reaches a temperature of 125 (1., and thereafter raising the temperature and continuing the cooking operation, the cooking liquor being supplied with more alkali in the form of a sulfite of an alkali than in the form of a thiosulfate of an alkali.

7. The method of producing pulp from resinous wood which comprises subjecting the same to a thorough impregnation at a temperature below the active cooking temperature with a cooking liquor free from alkali hydroxide, alkali sulfide, and alkali carbonate and containing substantial amounts of a sulfite of an alkali and a thiosulfate of an alkali, and subsequently raising the temperature and subjecting the same to a cooking operation under pressure and at a temperature in excess of 155 (3., at least one-half of the alkali content of the cooking liquor being supplied as alkali-sulfur compounds of which more is supplied as a sulfite of an alkali than as a thiosulfate of an alkali.

8. The method of producing pulp suitable for being converted into paper from resinous wood whch comprises subjecting the wood to a preliminary impregnation with a cooking liquor, alkaline to litmus, containing substantial amounts of a sulfite of an alkali and a thiosulfate of an alkali and also containing a carbonate of an alkali but being free from alkali hydroxide, at a temperature below 155 C. and subsequently cooking the wood at a higher temperature and pressure, the liquor being supplied with suflicient alkaline reactive compounds to maintain the liquor alkaline to litmus until the wood fibers are rendered readily separable from each other, the cooking liquor being supplied with more alkali in the form of.a sulfite of an alkali than in the form of a thiosulfate and at least one-half of the alkali content of the cooking liquor being supplied as alkali-sulfur com- 9. The method of producing pulp from heavy hardwood such as birches; maples, oaks, etc., which comprises charging the digester with the wood chips and with a cooking liquor free from alkali hydroxide and containing sustantial amounts of sodium sulfite and sodium thiosulfate, the amount of sodium sulfite being in excess of about 30% by Weight of the bone dry weight of the wood charged, and heating the digester charge to the cooking temperature, and cooking the chargeuntil the fibers are rendered readily separable from each other, the cooking treatment being carried out by means of a liquor containing more sulfite than thiosulfate of sodium.

10. In the preparation of chemical pulp, the use of a cooking liquor free from alkali hydroxide and comprising-sodium sulfite and sodium thiosulfate in substantial amount, the quantity of the sulfite being adequate to prevent the fibrous material being unduly impaired for paper making, due to the presence of-the sodium thiosul'fate, and at least one-half of the sodium content of the-cooking liquor being supplied as sodium-sulfur compounds.

11. The method of producing pulp from wood'which comprises subjecting the same to a two-stage cooking operation, the cooking liquor during the first stage containing a sulfite of an alkali and a thiosulfate of an alkali and the cooking liquorduring the second stage containing a caustic alkali.

12. The method of producing pulp from coniferous woods which comprises charging the digester with the wood chips and with the cooking liquor free from alkali hydroxide and containing substantial amounts of sulfite of an alkali and a thiosulfate of an alkali, gradually heating the digester charge to the cooking temperature over a period of about three to five hours, and carrying out the cooking operation thereafter at a temperature of about 180 to 190 C. and continuing the digestion with such cooking liquor suppliedv taining substantial amounts of a sulfite of an alkali and a thiosulfate of an alkali, said cooking liquor also containing residual liquor resulting from cooking another portion of the wood with such a liquor, the cooking liquor being supplied with sufiicient alkaline reactive material to maintain the liquor alkaline to litmus until the fibers are rendered separable from each other, the amount of alkali supplied as a sulfite being more than that supplied as a thiosulfate.

14. 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 free from alkali hydroxide and containing substantial amounts of a sulfite of an alkali and a thiosulfate of an alkali, separating resulting residual liquor from fiberbearing material, supplying sodium sulfite to such residual liquor and using the resulting liquor to cook fiber-bearing material containin g organic matter including cellulose so as to solubilize organic matter thereof.

15. The method of producing pulp from wood which comprises subjecting the wood to a two-stage cooking treatment, first with a cooking liquor containing sodium sulfite and a sodium thiosulfate and then with a cooking liquor containing sodium sulfide.

16. The method of producing pulp from wood which comprises subjecting the wood to a two-stage cooking operation, the first stage including cooking the wood with a cooking liquor including sodium sulfite and sodium thiosulfate, the second stage including cooking the resulting product with a liquor including sodium sulfide and sodium carbonate, separating residual liquor from the fibrous material, subjecting the residual liquor to evaporation to dryness and to carbonizing or carbonizing and melting, dissolving the sodium salts from the resulting product, subjecting a part of the resulting solution to a sulfiting treatment and utilizing the sulfited liquor in the first stage of a similar pulp producing operation and utilizing the sodium sulfide, present in the unsulfited portlon of the materials to a suitable higher temperature, whereby the. fibers are rendered sufficiently separable from each other to be desirable for paper making, said sulfite being present in sufficient quantity to overcome the tendency of the thiosulfate to impair the fibers for paper making which occurs when an insuflicient quantity of sulfite is present in such a liquor, and the amount of alkali present as a sulfite being larger than that present as a thiosulfate.

18. The method of digesting woody material which comprises subjecting said material to heating in the presence of a liquor which includes residual liquor from a previoussimilar cooking operation and being free from alkali hydroxide and containing a thiosulfate and a sulfite of sodium in a sufficiently large quantity to substantially avoid otherwise undesirable etfect of said thiosulfate, and subsequently subjecting the resulting product to digestion at a higher temperature, whereby the fibers are rendered separable and desirable for paper making, the liquor being supplied with sutficient alkaline reactive material to maintain the liquor alkaline to litmus until the fibers are rendered separable, and the amount of sodium sulfite being larger than the amount of sodium thiosulfate. v

19. In a process of treating lignified fibrous material to render the fibers more read ily separable from each other and in which a substantial amount of loosely combined sulfur is present in a liquor utilized for treating such material and existing in a condition, such for instance as an alkali thiosulfate, capable of impairing the fibrous material for paper making, the steps which include supplying to the fibrous material in the presence of water and in the absence of an alkali hy droxide, sodium sulfite in anamount which is capable of counteracting the tendency toward impairment by, such loosely combined sulfur, and whereby there is produced, as a result of the process, fibrous material comprising fibers separable from each other and suitable for conversion into paper, the amount of alkali supplied as a sulfite being more than sulfite and sodium thiosulfate, such residual liquor being free from alkali hydroxide and including non-fibrous constituents derived from such material and including sodium sulfite in amount sulfi'cient to counteract such tendency as the thiosulfate may have had for rendering the fibrous material undesirable for paper making, while the residual liquor was in contact with the fibrous material.

21. In a process of treating lignified fibrous material to render the fibers more readily separable from each other and in which a substantial amount of loosely combined sulfur is present in a liquor utilized for treating such material and existing in a condition, such for instance as an alkali thiosulfate, capable of impairing the fibrous material for paper making, the steps which include supplying to the fibrous material in the presence of water and in the absence of alkali hydroxide, sodium sulfite in an amount which is capable of counteracting the tendency toward impairment by such loosely combined sulfur and whereby there is produced, as a result of the process, fibrous material comprising fibers separable from each other and suitable for conversion into unbleached paper, and subsequently bleaching the fibers by subjecting them to the action of an active reagent including chlorine, in the presence of water, separating resulting liquor from the resulting fibrous material, and subsequently subjecting such material to an oxidizing bleaching treatment, whereby the fibers are obtained in a bleached condition suitable for being converted into white paper.

22. The method of obtaining fibrous material suitable for paper making, which includes digesting lignified fibrous material by means of cooking liquor that is free from alkali hydroxide and is supplied with a substantial amount of a sulfite of sodium, a substantial but lesser amount of a thiosulfate of sodium and with a regulated amount of another-reactive compound capable of digesting a substantial amount of the non-fibrous constituents in such material, and terminating the digestion when the fibershave been rendered separable from each other to the desireddegree, the liquor being supplied with a sufiicient amount of a sulfite of sodium to substantially prevent loosely combined sulfur of the thiosulfate blackeningthe fibers to such a degree that they are rendered and remain unsuitable for conversion into light colored papers.

23. The method of digesting wood, which includes subjecting wood chips to a .digestion operation at elevated temperature by means of a. liquor that is free from alkali hydroxide and is supplied with a substantial amount of a sulfite of an alkali, a substantial but lesser amount of althiosulfate of an alkali, and with a sulfid of an alkali in an amount less than that of the sulfite of an alkali but adequate to effect digestion of a substantial amount of the non-fibrous constituents of the woody material and whereby, as a result of this process, fibrous material is obtained which is suitable for paper making.

24:- The regenerative process of obtaining fibrous material suitable for paper. making, which includes digesting lignified fibrous material by means of cooking liquor free from alkali hydroxide and including a substantial amount of sodium sulfite and a substantial but lesser amount of sodium thiosulfate until a suflicient amount of the non-fibrous constituents of such material have been digested so as to render the fibers separable from each other to the desired degree, thereby producing a residual liquor, at the termination of the digestion, which is alkalineto litmus and which contains sodium sulfite in amount sufficient to counteract the tendency of the thiosulfate to blacken the fibrous material, terminating the digestion without permitting the fibrous material to become impaired for paper making, separating residual liquor from the fibrous material, removing water from the other ingredients of the residual liquor, furnacing sodium organic compounds in the concentrate to produce an alkali-containing product which includes more sulfur-free alkali compound as compared to sulfur-containing alkali compound than did the residual liquor from which it was derived, subsequently forming a cooking liquor including alkali-containing material derived therefrom and employing such cooking liqnor in the digestion of lignified fibrous material.

25. The two-step process of obtaining pulp, which includes subjecting lignified fibrous material to treatment at elevated temperature by means of liquor supplied with a substantial amount of a sulfite of an alkali and a thiosulfate of an alkali, and thereafter subjecting the resulting fibrous material to treatment by means of liquor supplied with alkali hydroxide and alkali sulfide.

26. The method of producing pulp from resinous wood which comprises subjecting such wood by means ofa volatile resin solvent to a preliminary extraction to extract resinous matter at a'relatively low temperature and subsequently treating the remaining fiber-bearing material at a higher'temperature and under elevated pressure with a liquor free from alkali hydroxide and containing an alkali thiosulfate and a sulfite of an alkali until a substantial-portion of the non-fibrous organic constituents thereof have been solubilized.

27. The method. of producing pulp from wood which comprises subjecting the wood to a cooking operation at an elevated temperature with a non-acid cooking liquor free from alkali hydroxide and alkali sulfide and consisting essentially of sodium monosulfite and sodium thiosulfate, the amount of sodium monosulfite being larger than the amount of sodium thiosulfate and sufiicient to maintain the liquor alkaline to litmus throughout the cooking operation.

Q8.'The method of producing pulp from wood which comprises subjecting the wood to a cooking operation at an elevated temperature with a cooking liquor free from alkali hydroxide and consisting essentially of sodium sulfite in amountnot less than 30% of the bone dry weight of the wood and of sodium thiosulfate in amount not greater than 15% of the bone dry weight of the wood, the amount of sodium sulfite being sulficient to maintain the liquor alkaline to litmus throughout the cooking operation.

29. The method of producing pulp from wood which comprises subjecting the wood to a two-stage cooking operation, the first stage comprising a treatment with a cooking liquor comprising monosulfite of so dium, and the second stage comprising a treatment with a liquor comprising sodium sulfide.

30. The method of'treating fiber-bearing material containing cellulose and other organic matter, which comprises subjecting wood to a digesting treatment under pressure at an elevated temperature by means of a cooking liquor containing a substantial amount of a monosulfite of an alkali and a lesser but substantial amount of a thiosulfate of an alkali; subsequently supplying to fiberbearing material, derived from the wood and containing organic matter including cellulose, an alkaline compound capable of solubilizing some of such organic matter, and treating the fiber-bearing material with the resulting alkaline liquor containing the alkaline compound so as to obtain at the termination of such treatment an alkaline liquor which includesdissolved matter derived in part from such organic matter.

31. In the treatment of cellulosic fiberbea ring material, the use of a cooking liquor comprising a monosulfite of an alkali metal and a thiosulfate of an alkali metal in substantial amounts, the cooking liquor being comprises the following steps: (a) subjecting. wood to a digesting treatment under pressure and at an elevated temperature by means of cooking liquor containing a substantial amount of a monosulfite of an alkali metal so as to solubilize a substantial portion of organic matter thereof; (1)) subsequently supplying to fiber-bearing matean alkaline liquor which includes dissolved matter derived in part from such organic matter; and (c) subsequently washing fibers derived from the wood.

33. As a new product, an easily bleachable Wood pulp of light color. having separable fibers in asubst-antially unimpaired condi tion suitable for being converted into paper and having been obtained by the cooking of wood with a cooking liquor free from alkali hydroxide and containing essentially sodium sulfite and sodium thiosulfatc, which is maintained alkaline to litmus by means of'alkaline sodium compounds throughout the cooking operation, such fibers being substantially free from dark colored reaction products due to loosely combined sulfur and reactive organic matter.

34. As a new product, an easily bleachable wood pulp of light color having separable fibers in a substantially unimpaired condition suitable for being converted into paper and having been obtained by the cooking of long fibered wood with a cooking liquor that is free from alkali hydroxide and contains-carbonate of sodium, sodium sulfite and a lesser amount of sodium thiosulfate, which is maintained alkaline to litmus by means of alkaline sodium compounds throughout the cooking operation, such fibers being substantially free from dark colored reaction products-due to loosely combined sulfur and reactive organic matter.

35. As a new product, an easily bleachable wood pulp of light color having separable fibers in a substantially unimpaired condition suitable for being converted into paper and having been obtained by the cooking of short fibered wood with a cooking liquor that is free from sodium hydroxide in any substantial amount and contains carbonate of sodium, sodium sulfite and sodium thiosulfate, which is maintained alkaline to litmus throughout the cooking operation, such fibers'being substantially free from dark colored reaction products such as are produced when an insufiicient amount of sulfite is present with the thiosulfate.

36. The method of producing pulp from wood, which comprises subjecting the wood to a cooking operation with a cooking liquor that is free from alkali hydroxide and contains essentially a sulfite of an alkali, separating resulting residual liquor from resulting fiber-bearing material, treating such residual liquor to decompose organic matter thereof and to form a regenerated cooking liquor that is free from alkali hydroxide and contains essentially a sulfite of an alkali, admixing such regenerated cooking liquor with residual liquor resulting from a cooking operation such as first mentioned in this claim so as to form a cooking liquor containing more alkali in the form of a sulfite of an al kali than in the form of a thiosulfate of an alkali, and using such cooking liquor in a digesting treatment of wood.

37. The method of treating wood, which comprises the following steps: (a) subjecting the wood to a digesting treatment under pres sure and at an elevated temperature by means of cooking liquor containing a substantial amount of sodium monosulfite so as to solubilize a substantial amount of such organic matter by means of such sulfite; (b) subsequently supplying sodium sulfide to fiber-- bearing material, derived from the wood and containing organic matter including cellulose, and treating the fibre-bearing material with the resulting alkaline liquor including sodium sulfid so as to obtain at the termina tion of such treatment an alkaline liquor which includes dissolved organic matter derived from the fibre-bearing material.

38. The method of treating wood, which comprises the following steps: (a) subjecting the wood to a digesting treatment under pressure and at an elevated temperature by means of cooking liquor containing a substantial amount of sodium monosulfite so as to solubilize a substantial portion of the wood by means of such sulfite; (b) subsequently supplying alkaline material including sodium carbonate to fiber-bearing material, derived from the wood and containing organic matter including cellulose, and treating the fibrebearing material with the resulting alkaline liquor including sodium carbonate and a reducing sulfur-bearing compound of sodium so as to solubilize a portion of such organic matter.

39. The method of treating wood, which comprises subjecting the wood to a digesting treatment by means of cooking liquor that is free from alkali hydroxide and contains essentially a mono-sulfite of an alkali metal so as to solubilize organic matter thereof, subsequently adding to fiber-bearing material derived from the wood an alkaline liquor comprising sodium sulfide, and treating such fiber-bearing material therewith until some organic matter thereof has been solubilized.

40. The method of making pulp from lignified fiber-bearing 'material, which comprises digesting thematerial with a solution containing a sulfite of an alkali metal and a thiosulfate of an alkali metal, the solution being freefrom alkali hydroxide and from alkali sulfide andbeing further characterized by having substantially more alkali metal present as a sulfite than as a thiosulfate and the quantity of sulfite of alkali metal being suflicient to provide the solution, throughout further characterized'byhavirig substantially more sodium present as sodium monosulfite than as sodium thiosulfate and the quantity of sodium monosulfite being suflicient to provide the solution, throughout the digesting step, with an amount of such monosulfite that is adequate to surmount and overcome the tendency of the thiosulfate to darken the fibers.

42. The method of treating lignified fiberbearing material which comprises the fol-- lowing steps: (a) subjecting the material to a digesting treatment under pressure and at an elevated temperature by means of cooking liquor that is free from alkali hydroxide and contains essentially sulfite of sodium, thereby producing a residual liquor that contains sodium-sulfur-organic compounds; (b) evapcrating water from the residual liquor; (0) furnacing sodium-sulfur-organic compounds therefrom under reducing conditions to produce a furnace product that contains sodium carbonate and sodium sulfide; (d) treating this furnace product with water to dissolve the sodium carbonate and sodium sulfide, thereby forming an alkaline solution; and (e) treating fiber-bearing material resulting from step (a) by means of the solution mentioned in step (d) thereby dissolving some of the organic matter present in the fiber-bearing material. a

In testimony whereof We afiix our signatures.

LINN BRADLEY. EDWARD P. MoKEEFE.