US1833313A - Treatment of residual liquors - Google Patents

Description

L, BRADLEY ET AL TREATMENT OF RESIDUAL LI QUORS.

Nov. 24, 1931.

Filed Jan. 14, 1924 \powwwaEou 3 INVENTORS BY PMM W ATTORNEY-.

Patented Nw 24, I 1931 I UNITED STATES PATENT orrlca LINN BRADLEY, or non'rcraxn, NEW innsEY, AND EDWARD-.1. ucxnnrn, or NEW YORK, n. Y., ASSIGNOBS 'ro BRADLEY mcxnnrn CORPORATION, A conropa'non or NEW Yoax rnmmn'n'r or nnsnmn. mavens a i neauon mm January 14, 1924. Serial No. esa a'z.

This invention relates to improvements in the manufacture of pulp from wood with a cooking liquor containing essentially sodium sulfite, either alone or admixed with caustic n improvedtmethod of pulp manufacture in which the pulp making operation is carried out with a cooking liquor containing essen- [tially normal sodium sulfite, either with or without the addition of small amounts of 5 caustic soda. In ourprior application Serial No. ,535,034,' filed February 28, 1922, we have described another method of pulp manufacture in which the cookin liquor employed is made upessentially o caustic soda and 0 sodium sulfite, with the caustic soda in predominating amount.- In our prior apphcation Serial No; 665,224 filed September 27, 1923 we have described still another method of pulp manufacture in which the cooking l5 liquor is made up essentially of sodium sulfite with excess sulfur dioxide, in excess of that required for the normal sodiumsulfite.

The present invention relates to improve- 1 ments in the processes of said prior applications, andparticularly inthe treatment of residual liquors from the, igestion or cooking operations of said processes, for \the regeneration of further amounts of cooking liquor for use in such processes. According to the'present invention, the cpoking or digestion operation and the regeneration or recovery operations may advantageously be. carried out in apparatus constructed and'intended for carrying. out the sulfate process so-called. p I In the-sulfate process so-called the-cooking liquor consists essentially ofcaustic soda and sodium sulfide; Varying amounts of, so-

diurmcarbohate, sodium sulfate, and other sodiumcompounds may also be present, but they are/generally considered to be, inert-in the process. Sodium sulfate or'nitre cake is I employed as the source of the sodium sulfide, so and a considerable part of it is reducedto tion.

or which mayhereafter be pro ,SOdllllIl sulfide during the smeltingopera- The sulfate process is recognized as having-certain objections and limitations. The

residual liquor is diflicult to handle during the concentrating, calcining and smelting operations. Furthermore, the sulfate process is so objectionable in the malodors given ofi that sulfate pulp mills. should .be located away from centers of lar 'e population. Where located in' well popu ated territory, the resulting nuisance has been such that court action has been successfully, invoked to prevent operation of the process.

The process of the present invention may utilize the lant and equipment of existing sulfate mill 's, liquor as char line to litmus, ut it avoids the nuisance produced bythe objectionable odors of the sulfate process,'0r so greatly reduces the odors formed that it is accordingly well adapted for use in-existing sulfate mills which are located near centers of population where operation of the sulfate process is rohibited, hibited; by court order; I

j the practice of the present invention, we may employ the digester of the sulfate- 'mill for carrying out the cooking operation,

provided it possesses sufiicient strength. We prefer-toemploy digesters cadpable of operating'at as high as 160 poun s pressure per' square in h, and where the cooking li nor is aid to -litmus tohave the digester lined to protect the shell. We employ. as cooking liquor a solution containingsessentially norespecially-when the cooking e into the digesters is alka-j mal sodimn sulfite' (Na SOs) or sodium sul- 'fite=and caustic soda, or sodium sulfite and excess sulfur dioxide. By the term excess sulfur dioxide? we mean the sulfur dioxide content over and above the amount required to form the normal The cook- I mg hquor may contain sodium sulfide and it may contain some thiosulfa'te;

or other sodium'sulfur compounds as well as other sodium compounds. But we-have found that where thiosulfa'te, or other sodium compounds which contain looselyhcombined sulfur, arelpresent in the cooking liquor,

objectionable odors are much less when the cooking liquor contains a preponderating amount of sodium sulfite than when such reagent is absent. Especially when sodium thiosulfate is present in appreciable amount, sodium sulfite in amount sufficient to cook the wood overcomes the objectionable features which the thiosulfate would produce if used alone. Therefore in this invention the cooking of wood to produce pulp does not result in the formation of. the malodorous compounds'characteristic of the sulfate process, or at least such compounds are formed in a less objectionable degree.

The residual liquors from the cooking 0peration, with neutralization of free acid content if any, may be treated, according to the present invention, in the evaporators, ro-.

.in'g out the improved process of the present invention with small expense for added equipment.

i The process of the present invention varies somewhat with the composition of the cooking liquor employed. These distinctions,

from the standpoint of the cooking operation, 7

are referred to in our prior applications in which these. respective processes are described. The cooking operations can be carried out with cooking liquors of varying compositions, and upon different kinds of woods, as pointed out in-said prior applications. 1

Insofar asthe pulp making operation itself is concerned, the process of the present invention presents the same advantages as the processes of our said prior applications,

and is of more or less general application to woods ofvarious-kindsflncluding woods which'are not commonly regarded as pulp woods at all. The present invention is thus appllicable not only to the usual pulp woods sue to short-fiber hard woods such for example as I .birches, beeches ;maples, etc. and also to other long fibered conifers, such as jack-pine, tamai'ack, loblollypine. hemlock. etc.

.-At the-end of the cooking or digestion operation, the residual liquor will be ofa different composition and character from the residual liquor of the sulfate process. Some of the residual liquor may be usedover' again in making up the cooking liquor for a successive cook. Where dense hard woods are employed',-the composition of the residual liquors will be somewhat different than when as spruce and poplar, but is applicable coniferous woods such as for example jack pine, are used. It is one advantage of the process that the residual liquor may already e concentrated to a considerable degree in the sense that it mayicontain relatively much more organic matter and much more sodiumcompounds per unit volume than the residual liquor from the sulfate process when the latter isoperated exclusively with fresh liquor.

The residual liquor, according to the present invention, is subjected to evaporation, calcination and smelting, using evaporators, calcining furnaces and smelters which may be. those of a sulfate mill. The process does not present the difficulties of concentration which the black liquor from a sulfate mill presents,-

and the liquor can be concentrated to a high degree in multiple effect evaporators .b'efore introduction into the calcining furnaces; althoughthe residual liquor may in some cases be produced directly of such a concentration that it can be fed directly to the calcining furnaces.

From the calciners, the black ash may be charged into the smelter, together with additional carbonaceous material if necessary,

- and there subjected to a smelting operation,

This smelting operation is distinguished in important respects from the smelting operation of the sulfate process. The black ash is easier to smelt- The melt or smelt ob tained from the-smelter can be dissolvedin water and treated for the production of further amounts of cooking liquor therefrom without the use of lime.

The operations thus far described may be carried out in the existing equipment of-a sulfate mill, although the operations differ in important respectsfrom the correspond-fing operations of the sulfate process. In particulaL-the digestion, concentration, calcination and smelting operations are carried out with materials of a different character and with less objectionable odors than-the sul- I fate process gives.

' In the sulfate process. smelter contains relativelylarge amounts of sodium sulfide, and this sulfide is employed in the further carrying-out of the cooking process. In the process of the present invention. however, the melt from the smelter will usually contain onlv a relatively small amount of sodium sulfide. This amount may be so small that it canbe utilized in the cookprocess, in which case the cooking liquor will the melt from the inc," liquor in the further carrving out of the contain a small amount of sodium sulfide as I well as a prepon'deratinsz amount-of sodium sulfite, or of sodium 'sulfite and caustic soda. It may also contain some sodium thiosulfate.

Where, however. the sodium sulfide is'not desired in thelcookine liquor or where the amount of sodium-sulfide in the melt is larger than is desired in the cooking liquor, the solu-v tion of the melt may be treated for the conversion of the sodium sulfide into other compounds. The invention includes different methods of treatment of the solution for this purpose.

The addition of further amounts of sodium compounds to make up for losses in the process may take place at different stages of the process. Salt cake or niter cake for example can be added to the desired extent to the little added equipment to that of a sulfate residual liquor before or after concentration and advantageously before calcination, or

after calcination and before smelting, and in.

such case, the added sodium sulfate .may be converted largely into sodium sulfide by the smelting operatiomso that the solution of the melt will contain a correspondingly increased amount of sodium sulfide, which may be utilized in the cooking operation or which may be advantageously converted into sodium sulfite or other compounds by suitable treatment. .5

Instead ofadding sodium sulfate or niter cake or salt cake to supply added amounts of sodium, sodium carbonate may be employed and may be added for example to the solution of the melt before it is subjected to fur ther treatment. A One way of treating the solution of the recovered sodium compounds, after calcination and smelting, to convert sodium sulfide into other sodium compounds of the kind described, is to subject the solution to treatment with carbon dioxide in such mannerthat a carbonate of sodium is formed. Hydrogen sulfide which is given off may be burned to produce sulfur dioxide and this sulfur dioxide utilized to'convert sodium carbonate into sodium sulfite. This hydrogen sulfide can be regenerated containing essentially sodium sulfite or containing sodium sulfite and caustic soda. The regenerated solution can also, where desired, be admixed with residual liquor from the digesters in making up the proper volume and concentration of active chemicals to the desired point for use in the further carrying out of the cooking operation.

The process thus far described requires but mill. A small sulfur burner, a simple absorption tower, and conversion tanks for converting the sodium sulfide into other sodium compounds constitute most of the added equipment necessary. The added reagents to make up for those lost in the process may be supplied by lime, sodium carbonate and the burning of sulfur, or in part by niter cake or salt cake.

Where sodium bisulfarte is added to the residual liquor, this sodium bisulfate will react with reactive sodium compounds to form normal sodium-sulfate. The solution containing sodium sulfate and other sodium compounds and organic matter may be evaporated and calcined in other apparatus than the vacuum evaporators and rotary kilns. For example, the liquor may be. subjected to spray'evaporation with hot gases or-otherwise, and the resulting dried product then subjected to the smelting operation. Where the liquor itself does not contain sufficient reducing materials (e. g. carbon from decomposition), further amounts of carbonaceous materials may be added so that the sodium sulfate will be largely reduced to sodiumsulfide, and so that the melt may contain sodium carbonate and sodium sulfide y be burned n the combustion c together with some sodium sl11fite,'sodium of a sulfur burner and thus mixed with sulfur dioxide gas resulting -from the combustion of sulfur, and this sulfur dioxide can be used for treating the solution containing the I sodium carbonate to convert the carbonate to the desired extent into sodium sulfite..

The liquor maybe treated to free it from sodium sulfide, where such treatment is desired, and thentreated with lime to convert the greater portion of the contained sodium carbonate into caustic soda, care being taken that the sodium sulfite that may be contained in the-liquor is not converted to any large extent into caustic soda. The causticized liquor will then contain caustic soda together 1 with more or less'sodiumsulfit'e', and it may also contain varying amounts of sodium-carbonate, sodiumsulfate, sodium thiosulfate, etc. The composition of the liquor can be regulated for example by add ng sodium carbonate before causticizing where the. amount of caustic'soda is to be increased, or by adding further amounts of sodium sulfite, or" by formin further amounts ofsodium sulfite in the sulfate and other compounds.

The incineration or calcination of the dried residual liquor results in the destructive dIS- tillation of the material and the formation of valuable products which may be passed through a condenser to condense'combustile liquids such as alcohols, acetone, etc. Such',-

liquor can be utilized by blending with other 2 ingredients such as gasoline,-3;lcohol, benzene, acetylene, etc. for making mdtor fuel or other fuel compositions; The non-condensible lid gases from the incineration or destructive distillation. can be utilized as fuel, :for ex-- ample, in drying'or evaporating the residual iquor.

considerable amount of sodiumsulfide or When the solution of the melt contains a the treatment of this solution directly with sulfur dioxide gas will set free carbondioxide and cause more or less of the sodium sulfide and polysulfides to be converted into sodium thiosulfate '(ua smn. If-= the solu'-" tion contains a fairlyahighj percentage of.

quor. In this way a cooking liquor? sulfidef or polys ulfides, this'fiirect treatment of the solution with sulfur dioxide will result in a solution containing a high proportion of thiosulfate. Ac ording to the process of another invention of ours we take advantage of l this formation of thiosulfate in producing a cooking liquor for cooking broad leaved or deciduous Woods to produce a special kind of pulp therefrom. We have found that the use of such a cooking liquor, consisting primarily ofthiosulfate, is of advantage as applied to broad-leaved or deciduous woods for producing certain kinds of special pulp, and that the residual liquor from such pulp making operations can. be treated for the recovery of the thiosulfate for further use in the cooking operation. This thiosulfate process, however, forms the subject of a separate application and we do not claim the same herein. Where it is desired to obtain wood pulp suitable for bleaching, we have 'found that I it'is desirable to avoidthe presence of a proportionally large amount of thiosulfate in the cooking liquor, and that it is desirable to treat the residual liquors so that the cook-' ing liquor obtained therefrom will contain a proportionally large amount of sodium sulfite. By using suflicient sodium sulfite in the cooking liquor, and only a relatively small amount of thiosulfate, or no thiosulfate at all, the formation of dark pulp diflicult to bleach is prevented. 'If the amount of sodium sulfite in the cooking .liquor is equal toaround 30 to of the bone dry weight of the wood, a considerable amount of thiosulfate may'be contained in the cooking liquoranda readily bleach'able pulp nevertheless obtained. i

Wherefthe residual liquor from such a cooking operation, in which some sodium thiosulfate is used, is evaporated,- calcined in the presence of air, and subsequently smelteduthe thiosulfate undergoes decomposition and some sulfur is eliminated froni the cycle, so that the recoveredchemicals can be treated for the production of cooking liquor of suitable composition without. objectionable upbuilding' of thiosulfate in the cooking liquor.

By suitable. treatment of the solution of the melt, the formation of sodium thiosulfate from the sodium'sulfide of the solution can be substantially prevented. -For this purpose, the solution can advantageously be treated first withcarbon dioxide to convert the sodium sulfide into. carbonate or bicar-- bonate-and liberate hydrogen sulfide. Carbon dioxide gas, preferably in highly-concentrated condition, may thus be passed into an absorption tower or tank containing the solution of the melt. .By decomposing the sulfides in this way and removing the hydrogen sulfide liberated, the formation of thiosulfate upon subsequent treatment of the solution with sulfur dioxide, is substantially avoided. By using relatively pure and conccntrated carbon dioxide and a suitable tower or tank, a nearly pure and concentrated hydrogen sulfide gas is driven off from the top of the tower or tank. This hydrogen sulfide gas, accompanied by any unabsorbed carbondioxide, can then be burned, for example, by introducing it into the combustion chamber of a sulfur burner, thereby burning the hydrogen sulfide to-sulfur d1- oxide and Water. formed will admix with that from the sulfur burner and can be employed in the manufacture of sodium sulfite.

' The sulfur dioxide from the sulfur burner, together with'the added sulfur dioxide from the combustion of the hydrogen sulfide, may

be absorbed in an absorption tower or tank ina solution of sodium sulfite which gradual- .ly increases in freeacid content. The temperature and'the percentage of free and combined sulfur dioxide can be controlled at Wlll.

By regulating the concentration and rate of The sulfur dioxide thus admixture thereof, with thorough agitation,

and with the resulting setting free of carbon dioxide and the: formation of a correspond ing amount ofsodium sulfite. This nearly pure carbon dioxide gas, or as much of it as necessary, can be used intreating the solu tion of the melt for converting the sodium sulfide into sodium carbonate and driving off hydrogen sulfide. The resulting solution, which may be substantially free-from sodium sulfide, and containing a corresponding in-I creased content .of, carbon dioxide, may be the solution to which the acid sulfite solution is added as above described. WVhen the process is thus carried out, carbon dioxide may be used repeatedly and successively in reacting with the sodium sulfide to form diumcarbonate which is later decomposed wit fite.

The carbonated solution from. the carbonating tower or tank, after the conversion of sodium sulfide into sodium carbonate is divided in suchproportion as needed, part going to the sulfur dioxide absorption tower.

or tank and part going to make up the cookingliquor for the cooking "operation. Where the cooking liquor is to contain essentially sodium sulfite (Naso with only small the acid sulfitesolution to drive off the carbon, dipxide again and formsodium sulamounts of other sodium salts or of caustic soda, the carbonated solution from the car bonating tower or tank may be neutralized with the acid sodium sulfite solution from the sulfur dioxide absorption tower or tank tion employed in making up the cooking hquor.

and a su-flicient amount of the resulting solu- 1 Where the cooking liquor is to contain both sodium sulfite and caustic soda, at part of the sodium carbonate may be treated with lime and subjected toaregulated causticizing operation, and the proportions of caustic soda and sodium sulfite may be varied as desired.

It will be evident that where a cooking liquor which is acid in character is desired,

for examplega'booking liquor containing an;

amount of sulfur dioxide greater than that corresponding to sodium sulfite and less than that cprresponding to sodium, bisulfite, the residual liquor can be subjected to a similar concentration, drying, calcining and smelting operation, and the solution'of the melt can be treated in the manner above described, and the solutions so produced can be so combined that a cooking liquor containin the desired amounts ,of sulfur dioxide both res and combined can be obtained. Where for examplean acid sodium sulfite cooking liquor is dean acid-proof lining maybe required in the digester during the cooking operation, particularly where a large excess. of sulfur dioxide is present. If the amount-of excess sulfur dioxide is sufiiciently small, an' acidproof lining maybe unnecessary. The di-' gester, when operated at higher pressures "than those commonly employed in the sulfate process, should of course .be of a stronger or; reinforced construction which will use of the high pressures desired.

The residual liquors from such an acid sul fite process in which an excess'of sulfur dioxide is used over and above that required for the normal sodium sulfite can be treated In a 811111131 manner to that above described,

' tus;

making use of the existing equipment of asulfate m1ll ,.or using other suitable appara- A flow sheet illustrating the recovery process above described is shown conventionally in the accompanying drawin The residual liquor from the digester is su bjected to evaporation in evaporators and then to incineration in incinerators, and to smelting, and the smelted product is then dissolved in dissolving tanks. "the apparatus "used in these operations mayb'e those'of the sulfate process,

as above described.

containing sodium carbonate and varying amounts of sodium sulfide, depending upon the composition of the residual liquor treated and the method of'incineration, passes to one or the other'of thetwo stora e tanks indicated on the flowsheet as 2 circulating tanks. Fi'om one or the other of these tanks the solution is circulated through the carbo- 'GO tower. In this tower the solution is subjected to the action of carbon dioxide which acts upon the sodium sulfide to form ,a carbonate of sodium and to set free hydrogen sulfide. The hydro en sulfide togetherwith any unabsorbed carbon'dioxide may be conveyed to the. combustion chamber of the sulfur burner where the hydrogen sulfide is burned to form sulfur dioxideand water vaporsufliciently carbonated it is pumped to one or the other of the two adjusting tanks where it is subjected to treatment with a solution of sodium bisulfite, or a solution of sodium sulfite containing a greater or smaller amount of SO than corresponds to sodium bisulfite, preferably with introduction of the bisulfite solution at the bottom,.and'with gentle agitation. The action of this sodium bisulfite solution upon the sodium carbonate solution is to set free carbon dioxide in a relatively pure and concentrated state. The carbon dinating tower referred to on the-blue print as,

When one of the tanks of liquor has been From the dissolving tanks, the liquor oxide may be collected in a gasometer from Which a sufficient amount is supplied to the carbonating tower or tank' while the surplus carbondioxid'e can be passed to a compressor or otherwise utilized. q

When one of the adjusting tanks has'been neutralized and the carbonate decomposed the resulting solution of normal sodium 'sulfite can be in part conveyed to the digesters for use asamake-up liquor for further cookingoperations, or its composition canbe modi fied .to give a cooking liquor of either acid or alkaline'character'. The remainder of th 'sodium sulfite solution from the adjusting ank may be conveyedto one or the other of the sulfur dioxide circulating tanks from which it"is' circulated through the sulfur dioxide aabsorption towerortan-k to absorb a sulfur dioxide from the sulfur burner. By passing the hot gases from the sulfur burner-through the absorption tower down which the sodium sulfite solution passes, the solution gradually increases in temperature, and in excess sulfur dioxide conteiit. By regulating the concen-' tration and rate of flowof liquor and gas, the

'- amount of sulfur dioxide absorbed can be regulated and controlled until a solution corresponding to sodium. bisulfite, or with greater'or less sulfur dioxide contant" is obtained. The percentage of sulfur dioxide,

tion.

absorbed can be controlled at will. This sodium bisulfite liquor can then be returned to one of the adjusting-tanks or it can be in part employed in further cooking opera- 1 The sulfur dioxide from the sulfur burner together with the sulfur dioxide formed from the hydrogen sulfide is absorbed in the S0 tower or tank while the .inert gases (nitro-' genand carbon dioxide) escape to the atmosphere. The process of the flow sheet as described and illustrated is a self contained process in I which the only addedreagent is sulfur for v p v the sulfur burner to supply additional sulfur dioxide; while the regenerative process gives a solution of either normal sodium sulfite or of sodium-bisulfite or liquors of intermediate composition which can be used as such or further modified in the carrying out of the proc ess. Carbon dioxide may be obtained as'a by-product. Additional sodium to make up for losses in the process can be supplied in various ways. Sodaash or sodium carbonate can be added at any point prior to the treatment of the solution of odium carbonate with theacid sodium sulfite solution. Sodium sulfate or niter cake, if used, should be added before the incineration so that it will be in 3 part reduced to sodium sulfide during the smelting operation. "The. sodium sulfide so produced may be utilized for the formation of sodium carbonate, and the hydrogen sulfide given ofi may be recovered and can be' 35 recombined after oxidation to SO with the sodium carbonate solution to'giv sodium sulfite and set free carbon dioxide.

The recovery process above described is itself a new recovery process for the treatment of residual li uors of the character tion of the calcined or incinerated product hereinbefore referre to for the production therefrom of further amounts ofcookingliqs uors. It is of special value and application where sodium sulfide is resent in the-soluand where sodium sulfide" is not desired,'or

" where a considrable reduction of the amount of sodium sulfide is desired, in a cooking li uo'r.

'e process makes possible the elimination of the sulfide byconverting it into sodium carbonateand hydrogen sulfide,

while, the hydrogen-sulfide may. be burned to sulfur dioxide for further use in the process. In this way the objections incident to the presence of sulfide in -the cooking operation are overcome; -while the process neverthel'ms makes posible theuse ofw sulfatelor nifer. cake as a source of additional sodium compounds in the bon dioxide'toform of sodium "iFi'a 'm the process may eonthe umv'ersionbf sulfide, the decom ofthe'aodium sulfide with car:-

further carbonatin operations, p

7 Other methods 0 decomposing the sodium sulfide or 'polysulfides and removing them from a solution of the melt can also be emformation of sodium carformed by treating the sodium carbonate s o-' lution with sodium bisulfite will be'in excess of that required for converting sodium sul 1 fide into sodium carbonate. Apart of this excess carbon dioxide may be used to convert sodium carbonate into sodium bicarbonate which may be precipitated in the carbonating tower or tank and recovered therefrom. v The introduction of carbon dioxide into the solution' of sodium carbonate and sodium sulfide may take placein an absorption tower with baflles 'or other filling material or obstructions to insure adequate absorption and reaction, orv carbon dioxide can be introduced through a porous bottom, e. g., filtros bottom,

into a tank of suificient de th to insure adequate absorption of the car 11 dioxide in the li uor. I

nstead of using difierent a 'paratus for the carbonating' operation an the sulfur dioxide absorption operation, these opera tions can advantageously be combined by'using'a deep tank of small cross section and in through a porous medium suchas filtros plates. By introducing sulfur dioxide in this manner into a solution containing sodium carbonate and sodium sulfide, sodium troducing thesulfur dioxide at the bottom 1 sulfide will be deeomposed and hydrogen sul fide driven ofi, while the sulfur dioxide will react upon the 'sodium'carbonatein the lower part of the tank, setting free carbon dioxide which in its upwardpassage will react with the sodium sulfide to set. free. hydrogen sulfide. When operating in this way main portion of carbon dioxide will be subsequently removed. The hydro en sulfide can beutilized as above describe while the carbon dioxide can similarly be employed for ployed, although we considerfthe cycli'c process above escribed' as particularly advantageousf Where only small amounts of "sulfide are present, they may be removed for example by adding iron sulfate, with resultthe hy- F V 'drogen sulfide will-be driven off first with a limited amount of carbon dioxide and the.

precipitation of iron sulfide. Where ium carbonate, is present, calcium sulfate.

can be added to remove the carbon dioxide as calcium carbonate, leaving sodium sulfate in dium sulfite with excess sulfur dioxide.

We have further found that when residual liquors of the character referred to are subjected to calcination without smelting, the solution or extract obtained from the calcined Further amounts of cooking liquors therefrom, or a part of the residual liquor can be returnedwithout treatment for use in making up the charge for further cooking operations, in which case the cooking liquor will be a mixtureof residual liquor and fresh sodium sulfite liquor which 'may be that obtained by the regenerat ve process. I The residual liquor from thle; cooking process in which sodium sulfite and causticsoda are employed, or1from the process in which sodium sulfite'and excess sulfur dioxide are employed, can similarly be treated product may contain small amounts of so-j directly forthe recovery of fresh cooking dium sulfide or polysulfides, particularly where the calcination is carried out under reducing conditions; and that the solutions so obtained can advantageously be treated in .the same manner as solutions of smelted products for the removal of sulfides therefrom. Thus, in case the residual liquor is evaporated and calcined or carbonized under reducing conditions, and then leached to extract the soluble salts therefrom, and a solution obtained which contains sodium sulfide,

this solution can be treated first to convert the sodium sulfide into other compounds, in much the same manner that solutions of the smelted product are treated for the conversion of the sodium sulfide into other products.

The invention will be further illustrated by the following specific examples.

Woods of varying kinds, such as spruce,.x

and insuring a thorough penetrationof the chips with the 'cookingliquor duringthe preliminary portion of the heating operation,

(preferably below 110 C.) the digester can,

subsequently be heated to a higher temperature and pressure without. objectionable action upon the chips, and with substantially complete cooking of the chips even when long fibered resinous woods are employed. The

cooking operation carrbe carried out as a single stage operation, on n successive stages,

a and, where two stages are employed, a different cooking liquor canb'e used in the second stage. When a normal sodiumsulfite 'cgoking liquor is used. in the first stage, sodium sulfide. may be present in the second stage with less objections than are incident to. it use in t Sulfatepro'cess. \l l The residual liquor from the normal sodium sulfite cooks above meat-erred to can be directly treated forthe recovery of fresh liquors therefrom or a part of the residual liquor can be returned without'treatment for use in making up the charge of further cool;- ing operations, in which case the cooking liquor will be of a composite character, being made up in part of residual liquor and in part of fresh cooking liquor obtained by the regenerative process of the present invention By returning part ofthe residual liquor and reusing it, the content of the residual liquor in organic material and inorganic constituents can be built up so thata more concentrated liquor is available for further treatment in the. regeneration process and we claim such operations as part 0 our invention.

The residual liquor may be evaporated in amultiple effect evaporator such as a triple effect Yaryan evaporator to about 36 to 38 B.. and then run through a rotary furnace and converted into a product which may be referred to as reen ash. This green ash may then be fed m-to the. preheated smelter and burned and s'melted to form a free run- 'nin melt which is conveyed to the dissolving tan The green ash was found to contain a s'uflicient amount of organic matter to burn readily without additional fuel, and the burning and melting operations appear more advantageous than those of'the sulfate rocess. The calcination ofthe concentrate liquor in rotary furnacesaalso appeared to take place with less flame appears in the sulate process, so; that"a;*g'reater percentage of total .heat units isretamd in the green ash when dischar the rotary "to be charged into t 'e ainelter.; The ease of burning of'the ash and th ow melting point of the smelted product as foimd to enable the smelting operation placein a particularly advantageousfifiannerf When the liquorin thetank,

into which the hotjrnelt. was received had reached a density: of about 26"" B6, hot the liquor was found on analysisto contain considerable' carbonate, some sulfides "and a conslderable amount of sulfite. When this liquor was treated: with hydrochloric acid. considerable' sulfur was thrown" out of solution. When treated with sodium bisulfite Solution httle sulfur was thrown out of solution, al-

though the liquor was made acid to phenolphthalein. r

I Instead of using fresh water or wash water to dissolve the melt, or to leach the calcined unsmelted product, the residual liquor fromthe process'can be used for this purpose, thus building up the strength of the liquor and I saving in evaporation. Where the residual liquor contains considerable unconsumed sodium sulfite, thisexcess ofreagent will-be made availablein further cooking operations. By dissolving the melt-in the fresh residual liquor, and by then removing the somewhat di hydrogen sulfide and so treating the result: ing solution with sulfur dioxide. as to convert the carbonate into sulfite, and by clarifying if necessary to remove precipitated material, etc., a suitably concentrated cooking liquor can be obtained well adapted for reuse in the cooking step of.the process.

Instead of treating residual liquors from the normal sodium sulfite cooking process, the residual liquor from the process in which caustic soda and sodium sulfite are employed can betreated in a similar way. In this case,

however, the residual liquor will be of a rent composition, and, in order to regene te a similar cooking liquor,

- causticizing of some of the sodium carbonate with lime can replace the conversion of acorresponding amount of sodium carbonate to sodium sulfites may be used, and the residual liquor by evaporation, calcination, smelting and dissolving, can be carried out in a similar manner to that above described with the normal sodium sulfite residual liquors. To the extent that the resulting solution of the melt is r uired to be converted into sodium sulfite, snnilar methods tdthose above described can be used, supplemented by causticizing of part of the-liquor with lime to convert sodium carbonate into caustic soda.

Residual liquors from the pulp making 1 process in which acid sodium sulfite, or sodium sufite with excess sulfur dioxide (as hereinbefore defined), are used, can also be treated in-a somewhat similar way for the regeneration of cooking. liquor therefrom In ,this case, however, the residual liquor will beef :1 somewhat difierentcomposition and the treatment may be modified.v The acid character of the residual liquor, and the increased'content of sulfur dioxide in proportion to the sodium content tends'to cause an increased amount of the sulfurdioxide to be given off duringthe concentrating, calcining and smelting operations. .Ihis sulfur di-- oxide can be recovered, however, e. g., by absor tion and returnedgto the process. .The

' residual liquor can also be advantageously treated to neutralize it before it subjected to the concentrating, carbonizing and smelt-' ing operation.- For this purpose the solution of the; melt, or the partially caustici'zed 05 solution of the melt, may be used.'- By adds ing the desired amount of the melt directly.

to such a residual liquor, the liquor will serve to dissolve the melt and will be preheated and neutralized to a greater or less extent at the same time. The neutralized residual liquor, neutralized in this or someother suitable manner, may then be subjected to evaporation,

process itself, in the manner hereinbefore refrredto.

It will thus tion provides improved methods of-regen-' crating the residual liquors from processes in which normal sodium sulfite, or sodium sulfite and caustic soda, or sodium sulfite and sodium 'bisulfite, or sodium sulfite and sul be seen that the present invenfurous acid, etc. are employedffor the production of further amountsof cooking liquor therefrom; and that theoperations can in thiswaybe. improved and regulated and controlled in a particularly advantageous manner. Among the various features of advantage which the invention presents, as hereinbefore described, are included the reutilization of re"idual liquor itself in further cooking operations either with or without admixthe recovery of the chemicals contained in the residual liquor by various methods of procedure whereby they are-made available.

ture of fresh amounts of reagents thereto;

for furthericooking operations; the evaporation of'the residual liquors, carbonization and smelting, and dissolving of the melt with subsequent treatment of the resulting solution for the regeneration of cooking liquor therefrom; the carbonizationof the concentrated residual liquor without excessive reduction and resulting recovery from the;carbonize d product of soda for further use in the process the utilization of existing equipment of sulfate mills with a moderate amount of'ehange fun and expense, and'with advantages hereinbefore described, and with avoidance of certain objections incident to the sulfateprocess itself; the'utilization of sodium sulfate or 'niter cake in supplyingadditional chemicals f to the. pr0cess, with elimination of sulfide. radical if desired and utilizatiouof the sulfur content thereof in the further carrying on -'of the process; 'the treatment of solutions colitainingvsodium sulfide to'remove sulfur therefrom and convert the sodium. intoso 'dium sulfite, with utilization of the hydrogen sulfide givenoiflfor producing sulfur dioxide by combustion; and various'other features of improvement hereinbefore described.

The improvements of the present invention supplement the improvements of our prior applications and are of value in connection with manufacture of pulp and paper from woods of various kinds, including not only woods commonly considered as pulp woods such as spruce and poplar, but also woods which are not commonly considered as pulpwoods at all, or woods which are considered of. little value for pulp making purposes, such as the heavy hard woods (birches, beeches, maples, oaks, gums, etc.) and resinous coniferous or long fibered woods such as ack-pine, loblolly pine, tamarack, etc.

While the invention has been described more particularly in connection with the use of sulfites of sodium, yet it will be understood that sulfite's of potassium or mixtures of sulfites ofsodium and potassium can be similarly used; and that sulfites of magnesium can to some extent likewise be used, although we consider the use of sodium sulfites as particularly advantageous. Sulfites' of potassium will ordinarily be too expensive for commercial use,although they-may be used where cheap deposits containing suitable potassium compounds are available. Similarly, mixtures of .magnesium and sodium sulfites maybe used, and the residual liquors from their use treated for the regeneration of further amounts of-cooking liquor therefrom.v V Magnesium sulfate, either alone or accompanied'by'sodium sulfate, may be added to a solution of'the melt to convert the sodium carbonate into sodium sulfate and the magnesium sulfate into magnesium carbonate. 40 ,The sodium sulfide may-be eliminated by precipitation or by volatilization of the sulfide radicle. For example, iron sulfate can be used for precipitation of iron sulfide, or sulfuric acid, nitre cake, or CO may be used to drive off l-LS. The sodium sulfate solution can then be treated with GaSO and H 80 to form Ca'SO 2H O and leave an acid solution containing sodium sulfite.' Other solu ble metallic salts may be used to precipitate insoluble metallic sulfides, e. g. copper sulfate.. a We claim: 1. In the treatment of residual liquors from pulp-making operations in which an alkali metal sulfite is employed in the cooking liquor, the improvement which comprises evaporatin such liquors, subjecting the residue to calcination, smelting the calcined product, dissolving the result'fiig melt and .60 treating the solution to decompose sulfide contained therein.

21- In the treatment ofresidual liquors from,.pulp-making operations in which an alkali 'metal sulfite is employedin the cooking liquor, the improvement which comprises evaporating such liquor, subjecting the residue to calcination, smelting the calcined product, dissolving the resulting melt and treating the solution to decompose sulfide contained therein, said treatment including the treatment of the solution with carbon dioxide to convert sulfide into a carbonate and to drive off hydrogen sulfide.

3. In the treatment of residual liquors.

from pulp-making operations in which an alkali metal sulfite is employed in the cooking liquor, the improvement which comprises subjecting such residual liquors to evaporation, subjecting the residue to calcination, and subjecting the calcined product to a smelting operation.

4. In the treatment of residual liquors' I the resulting solution treated for the production of further amounts of cooking liquor therefrom.

' 7. The further improvement in the process of claim 4in which the melt is dissolved in a portion of the residual liquor and the resulting solution treated for the production of further amounts ofcooking liquor therefrom. I

8. The improvement in the process of claim 4 in which the melt is dissolved to form a solution, the solution treated with carbonic acid radical to decompose sodium sulfide and drive off hydrogen sulfide, the hydrogen sulfideburned to sulfur dioxideand sulfur di-.'

oxide absorbed in the solution from which the hydrogen sulfide has beendriven off.

9. The improvement in the process of claim 4 whieh 'c'omprises dissolving the melt to form a solution thereof, treating the solution with carbon dioxide to decompose sodium 'sulfide and drive off hydrogen sulfide, burning'the hydrogen sulfide and some sulfur for the production of sulfur dioxide, and treating the solution of the melt from which the hydrogen sulfide has been driven off with sulfurous-- acid radical to convert the carbonate into a sulfite. a y 10. The improvement in the treatment of residual liquors from pulp-making operations in which .a sulfite of sodium is employed in the cooking liquor, which comprises evaporating the. residual liquor, calcining and smelting the residual material, dissolving the melt to form a solutionthereof, treating solution containing sodium carbonate and so-.

the solution with carbon dioxide to decomse sodium sulfide and drive ofi hydrogen sulfide, treating the resulting solution with an acid sulfite solution containing suificient sulfur dioxide to convert the carbonate to sulfite, burning sulfur and the hydrogen sulfide to-form sulfur dioxide, absorbing sulfur dioxide to form a further amount ofacid sulfite solution, and employing such acid sulfite solution for treating the solution of the melt in the earlier step of the process.

11. The improvement in the claim 10 in which additional sulfate of sodium is added prior to the smelting operation, thereby giving an increased amount of sodium compounds in the solution of the melt and an increased amount of sodium sulfide and of hydrogen sulfide in the process.

12. The method of producmg solutions containing sddium sulfite from a sodium sulfate which comprises reducing sodium sulfate to sodium sulfide, treating a solution containing the sodium sulfide with carbon dioxide to form a sodium carbonate and hydrogen sulfide, and absorbing sulfur dioxide in the sodium carbonate solution to form sodium sulfite. v

13. in the treatment of residual liquors from pulp-making operations in which a sulfite ofsodium is employed, andin which the residual liquor is concentrated, the residue calcined and the product leached to form a dium sulfide, the step which comprises treating such solution with carbon dioxide to conv vert thelsulfide into carbonate and set free hydrogen sulfide, and the further ste which comprises treating the solution so 0 tained with the sulfurous acid radical to convert carbonate into sulfite.

14. The cyclic process of forming solutions containing sodium sulfite from solutions containing sodium carbonate, which comprises treating such carbonate solutions with acid sodium sulfite to convert the carbonate into sulfite, absorbing sulfur dioxide in part or all of the sulfite solution so formed, and treating a fulrther amount of carbonate solution therewit 15. The cyclic process of forming solutions containing sodium sulfite from solutions containing sodium carbonate and sodium sulfide,

" which comprises subjecting such solutions to treatment-withcarbon dioxide to convert sulfide into carbonate and'set free hfydrogen suls fide, burning the hydrogen sul de together with some sulfur to form sulfur dioxide, ab:

. sorbing the sulfur dioxide in the carbnoate solution to set free carbon dioxide, and usingv the carbon dioxide in the further carrying out of the carbonatingstep of the process for -converting-sulfide"into carbonate.

16. The cyclic process of'forming solutions containing sodium sulfite from solutions contaming sodium carbonate and sodium sulfide,

taining sodium sulfide and sodium carbonate,

fite solution to convert the carbonate into sulfite, and using the carbon dioxide set free for the further carrying out of thecarbonating step of the process.

17. In the treatment of residual liquors from the cooking of cellulose-bearing material with a cooking liquor containing sodium sulfite, which residual liquors have been cons centrated and the residue calcined, and the product treated to form a solution containing sodium salts, the step which comprises treat ingsuch solution with carbon dioxide and subsequently with sulfur dioxide.

18. In the treatment of residual liquors from pulp-making operations in which a sulfite of a strong base is employed in the cooking liquor, the improvement which comprises evaporating such liquors, subjecting the residue to calcination, smelting the calcined prod: uct, dissolving the melt in a portion of the residual liquor and treating the resulting so lution for the production of further amounts of cooking liquor therefrom.

'19. The method of treating solutions containing sodium sulfide and sodium carbonate, which comprises treating such solution with carbon dioxide to decompose sulfide of sodium and form sodium carbonate in which a relatively purecarbon dioxide is used to treat the solution, thereby giving hydrogen sulfide, burning the hydrogen sulfide to form sulfur dioxide and absorbing sulfur dioxide in the solution.

20. The method'of treatingsolutions containing sodium sulfideand sodium. carbonate, which comprises treating such solution with carbon. dioxide to decompose sulfide of sodium and form sodium carbonate, burning "the. hydrogen sulfide and some sulfur to form sulfur dioxide, absorbing sulfur dioxide in a solution containing sodium sulfite, to give an acid solution of sodium sulfite, and treating the solution containing sodium carbonate with such acid sulfite solution.

21. The method of treating solutions conwhich comprises treating such solution with 123 carbon dioxide to decompose sulfide of sodium and formsodium carbonate, burning the hydrogen sulfide and some sulfur to form sulfur dioxide, absorbing sulfur dioxide in a. solution containing sodium sulfite, to give an acld solution of sodium sulfite, and treat-' ing the solution containing sodium carbonate with such acid sulfite solution in which the carbon dioxide obtained in a relatively pure and concentrated state is used tothe req ir 130 extent to treat the solution containing sodium sulfide and sodium carbonate to decompose sodium sulfide and set free hydrogen sulfide therefrom.

22. The method of treating solutions containing sodium sulfide and sodium carbonate,

which comprises treating such solution with carbon dioxide to decompose sulfide of so-.'

, and form sodium carbonate, treating the carand bonate solution, after the removal of hydrogen sulfide, with an acid-solution of sodium sulfite containing an excess of sulfur dioxide, thereby obtaining a solution. of sodium sulfite for use in further cooking operation.

24. The method of treating solutions containing sodium sulfide and sodium carbonate, which comprises treating such solution with carbon dioxide to decompose sulfide ofsodium form sodium carbonate, treating the carbonated solution, after drivingoff hydrogen sulfide, with an acid solution of sodium sulfite containing excess sulfur dioxide to convert the carbonate into a sulfite, absorbing sulfur dioxide in the resulting sodium sulfite solution or in a portion of it and thereby forming a further amount of acid sulfite solution, and'treating further amounts of carbonated solution with such acid solution.

25 A cyclic process which comprises digestmg raw cellulosic material in a sulphuro us acid solution of a soluble alkali or alkal ne earth sulphite, neutralizing the spent liquor resulting from such digestion, separating the pulp from such neutralized spent liquor, burning the combustible content and smelting the inorganic mineral content of such spent liquor in a reducing atmosphere in a manner to produce sulphide and carbonate, recoverlng the inorganic smelt in water, carbonating thesmelt solution, and acidifying the carbonated solution with sulphur dioxide 1' uor.

6. A cycl-icprocess Jvhich comprises digesting raw cellulosic material in a sulphurous acid solution of a soluble alkali or alkaline earth sulphite, neutralizing the spent liquor resulting from such digestion, separating the pulp from such neutralized and spent liquor, burning the combustible and smelting inorganic material content "of such liquor in a reducing atmosphere in a mannor to produce sulphide and carbonate, recovering-the inorganic smelt in water, car-.

bonating the smelt solution, employing a porproduce fresh acid digesting tion of such carbonate solution together with cyclic make-up compounds for such neutralization, and acidifying the remainder of the carbonated-solution with sulphur (dioxide in a manner to produce a fresh acid digesting liquor.

- 27. A process which comprises concentrating and burning the combustible content and smelting the inorganic content of spent liquor resulting from the digestion of raw eel-- lulosic material in asul hurous acid solution of soluble alkali su phite or alkaline earth sulphite, in a manner to produce substantially only sulphide and carbonate, re-- covering the smelted inorganic compounds in water, carbonating the smelt solution with substantially pure carbon dioxide and conlulosic material in a sulphurous acid solution of soluble alkali sulphite or alkaline earth sulphite, in a manner to produce substantially only sulphide and carbonate, recovering the .smelted inorganic compounds in water, carbonating the smelt solution with substantially pure carbon dioxide and controlling such carbonation to produce a substantially pure hydrogen sulphide, acidifying the carbonated solution with a substantially pure sulphur dioxide, controlling such acidification to produce a substantially pure carbon dioxide, and utilizing 'such' carbon dioxide in the carbonation of other smelt solution.

29. A- process which comprises concentrating and burning the combustible content and smelting the inorganic content of spent liquor resulting from the digestion of raw ce1-.

lulosicmaterial ina sulphurous acid solution of a soluble alkali and alkaline earth sulphite, in a reducing atmosphere in a manner to produce substantially, only, sulphide \and carbonate, recovering the smelted inorganic compounds in water, carbonating the smelt solution, oxidizing any remaining sul-.

phide, and acidifying the carbonated soluas is needed to produce a fresh acid digesting liquor.

30. A process which comprises digestin raw cellulosic material in a sulphurous acid solution of a, soluble alkali sulphiteor alkaline earth sulphite, concentrating and burning the combustible content and. smelting tion with sulphur dioxide in such amount the inorganic 'conteg;

'32. A process which comprises raw cellulosic material in a sulphurous acid of spent liquor resulting from such estion in amanner .to produce, sulphide and carbonate, recovering the smelted inorganic compounds in water, 5 carbonating the smelt solutn with carbon dioxide and controlling such carbonation to produce hydrogen sulphide and to effect a conversion of substantially all the sulphide to carbonate, burning such hydrogen sulphide to produce sulphur dioxide, recovering the gaseousproducts of combustion, acidifying the carbonatedsolution with sulphur dioxide and controlling such acidification to produce a substantially pure carbon dioxide and a sulphite solution, utilizing the carbon di- 'oxide obtained in such-acidification for the carbonation of other smelt solution, and utilizing said products of-combustion in the production of a sulphite cooking liquor.

- line earth sulphite, concentrating and burning the combustible content and smelting the inorganic content of spent liquor resulting to produce -phide, and recovering the latter in an aqueous such solution with carfrom such digestion in a manner sulphide and carbonate, recovering the smelt- .ed inorganic compounds in water, carbonatdioxide, burning the hydrogen sulphide resulting from such carbonation and recovering the sulphur dioxide thereby produced,

acid iifying the carbonated solution with dibustionof'the hydrogen sulphide in the production of fresh cooking liquor.- a digesting solution of a soluble'alkali sulphite or alkaline earth sulphite, concentrating and burning the combustible content and smelting the inorganic content of spent liquor resulting from such digestion in a manner to produce sulphide and carbonate, recovering the smelt-x ed inorganiccompounds in water. earbonat,

ing the smelt solution with carbon dioxide, burning the hydrogen sulphide resulting froms'uch carbonation andrecovering the sulphur dioxide thereby produced, acidi-'- 4 fying the carbonated solution with digester relief gas, recovering and utili'zin the-carbon dioxide liberated in such acidification for the carbonation ofother smelt solution, treating said carbonated solution with sulphur burner as and the products ofconlbustion ofsai 'hdrogen sulphide,,'and finallfy adding relie gas thereto to produce a resh acid cooking liquor having a high free sg 'content. 33. A, process which comprises digesting raw oellulosie material in a sulphurousaci solution of a soluble alkali or alkaline earth 31. A process which comprises digesting ing the smelt solution with a strong carbon geste'r relief gas, recovering and utilizing aqueous solution,

. sulphur dioxide,

sulphite, recovering sulphur dioxide from the acid spent liquor resulting from such digestion, concentrating and burning the combustible content and smelting the inorganic content of such spent liquor in a manner to produce sulphide and carbonate,'recovering the smclted inorganic compounds in water, carbonating the smelt solution, burning the hydrogen sulphide resultingi'ro'm such carbonation and recovering the sulphur dioxide thereby produced, acidifying the carbonated solution with digester relief gas, utilizing the carbon dioxide liberated in such acidification for the carbonationof other smelt solution, and further treating said acidified solution with sulphur burner gas, the products of combustion of the hydrogen sulphide, and the sulphur dioxide recovered from the acid spent liquor. v

34. A cyclic process which comprises concentrating spent liquor resulting from the digestion of raw cellulosic material in a sulphurous acid solution of a soluble alkali sul-- phite or alkaline earth sulphite, smelting the lnorganic content of such liquor in a reducing atmosphere to produce carbonate and sulcarbon dioxide resulting from such acidification 'in the aforesaid carbonation of. the,

smelted and recovered, sulphide,

35. That process WhlCh comprises smeltingthe mineral content of spent liquor, result-' a ing from the digestion of raw cellulosic material in an alkaline sulphite or alkaline earth'sulphite cooking liquor, to produce mineral' sulphide and mineral carbonate, re-

covering such sulphide and carbonate in an phide, treating the resultingsolution with sulphur dioxide to produce a sulphite liquor,

recovering carbon dioxide resulting from -such acidification, and using such recovered treating such solution with carbon dioxide to carbonate the mineral sulno 36. That process which comprises smelt ing the mineral content of 5 out liquor, resulting from the digestion o raw cellulosic'.

material in analkaline sulphite or alkaline earth sulphite cooking-liquor, to produce mineral sulphide and mineral carbonate, re-' covering such sulphide and carbonate infan aqueous solution, treating'such solution with carbon dioxide to carbonate the mineral sulphide, treating the resulting solution with sulphur dioxide to produce a sulphite liquor, recovering hydrogen sulphidejfroi'n such carbonation, and burning the same to produce recovering carbon dioxide resulting from such acidification, using such last mentioned sulphur dioxide in the acidi fication of said sulphite liquor.

37. A process for recovering and utilizing the products produced in recovering the base 1; compound from spent sulphite liquors in forming a fresh sulphite cooking liquor,

which comprises treating a carbonate solution with sulphur dioxide to convert it to a'normal sulphite solution,'recovering the carbon dioxide arising from such treatment and carbonating therewith a sulphite smelt solution comprising sulphide to a carbonate solution, thereby liberating hydrogen sulphide, recovering and burning such hydrogen sulphide to sulphur dioxide, and acidifying the normal sulphite solution with the recovered sulphur dioxide.

38. A process which comprises cooking raw cellulosic material in an alkaline solution of sodium sulphite; separating the pulp from the spent cooking liquor: smelting the inorganic mineral content and burning the combustible content of such spent liquor, recovering the inorganic smelted compounds; and passing the products of combustion from such smelting operation in contact with like spent liquor, for the recovery of the soluble content of such products of combustion.

39. The cyclic process for producing pulp from wood which comprises cooking wood in an acid liquor containing a sulfite of an alkali. separating a residual liquor from the resulting fibrous material, drying the residual liquor, carbonizing organic constituents of the liquor. dissolving from the resulting product soluble compounds including alkali carbonate and alkali sulfide, subiecting the dissolved compoundsto a regulated oxidizing treatment to convert the sulfide into sulfite under'conditions to substantially prevent the formation of alkali 'thiosulfata'acidifying the resulting sulfite solution. to produce a cooking liquor substantially free from thiosulfate, and cooking more wood with said liquor.

40. The cyclic process for producing pulp from wood which comprises cooking wood in a liquor containing a sulfur compound of an alkali. separating the residual liquor from the resulting fibrous material. drying the residual liquor, burning dried carbonaceous constituents of the liquor, dissolving from the resultin ash soluble compounds including alkali sulfide and alkali carbonate, sub

jecting the alkali sulfide to a treatment to remove the sulfide-sulfur, oxidizing it to form sulfur dioxide, and recombining the sulfur dioxide so formed with the alkali compounds, forminga cooking liquor from the resulting sulfite solution, and cooking more wood with said liquor.

41. A process which comprises cooking raw cellulosic material in an alkaline solution of sodium sulfite; separating the pulp from the spent cooking liquor; smeltingthe inorganic mineral content and burning the combustible content of suchtspent liquor in a reducing atmosphere to produce sodium sulfide; and recovering the inorganic compounds for reuse in the cooking of other cellulosic material.

42. A process which comprises cooking raw cellulosic material in an alkaline cooking liquor containing sodium sulfite; separating the pulp from the spent cooking liquor;

burning the combustible content and smelting the inorganic mineral content of such spent liquor in a reducing atmosphere to form sodium sulfide; recovering the sodium sulfide in water; carbonating the sodium sulfide of the solution to sodium carbonate; and

acidifying the carbonate solution with sulfur dioxide. v

4;3. A process which comprises cooking raw cellulosic material in an alkaline solution of sodium sulfite; separating the pulp from the spent cooking liquor; burning the com bustible content and smelting the inorganic mineral content of such spent liquor in a reducing atmosphere in a manner to produce sodium sulfide and sodium carbonate; carbonating the sodium sulfide of the smelt solution to sodium carbonate; acidifying the whole sodium carbonate solution with sulphur dioxide to convert said sodium carbonate to sodium sulfite; and recovering and utilizing the carbon dioxide liberatedin such acidification in the carbonation of other smelt liquor. r

44. A process which comprises cooking raw cellulosic material in an alkaline'solution of sodium sulphite separating the pulp from the spent cooking liquor; burning the combustible content and smelting the inorganic mineral content of such spent liquor in a reducing atmosphere in a manner to produce sodium sulphide and sodium carbonate; carbonating the smelt solution; and recovering the sulphur to the hydrogen sulphide liberated in such carbonation in the form of a sodium salt.

45. A process which comprises cooking raw cellulosic material in an alkaline solution of sodium sulphite; separating the pulp from the spent cooking liquor; burning the combustible content and smelting theiinorganio mineral content of such spent liquor in a reducing atmosphere in a manner to produce,

' raw cellulosic material in an alkaline solution of sodium sulphite; separating the pulp from the spent cooking liquor; burning the com- 1 smelting the inorganic content of spent liquor resulting from the digestion of raw cellulosic material in an alkaline solution of sodium sulphite in a manner to produce sodium sulphide and sodium carbonate; recovering the smelted inorganic compounds in water; carbonating the smelt solution; recovering the sulphur of the hydrogen sulphide liberated in such carbonation in the form of a sodium salt; acidifying the carbonate solution with sulphurous acid; and recovering and'utilizing the carbon dioxide liberated in such acidification in the carbonation of other smelt liquor.

48. A process which comprises concentrating and burning the combustible content and smelting the inorganic mineral content of spent liquor resulting from the digestion of raw 'eellulosic material iii an alkaline solution of sodium sulphite in a manner to produce sodium sulphide and sodium carbonate; recoverlng the smelted inorganic compounds I in water; ca-rbonating the smelt solution; re-

covering the sulphur of the hydrogen sulphide liberated in such carbonation in the form of a sodium-sulphur compound; acidifying the carbonate solution with sulphur.

dioxide; and recovering and utilizing the carbon dioxide liberated in such acidification in the carbonation of other smelt liquor.

49. A process which comprises concentrating and burning the combustible content and smelting the inorganic mineral content of' spent liquor resulting from the digestion of raw cellulosic material in an alkaline solution of sodium sulphite in a manner to. produce sodium sulphide and sodium carbonate; recovering the smelted inorganic compounds in water; carbonating the smelt solution with substantially pure carbon dioxide and controlling such carbonation to produce substantially pure hydrogen sulphide: recovering and burning such hydrogen sulphide and recovering the products of combustion; acidifying the carbonate solution with asulphurous aci solution formed in part from said recovered sulphur dioxide and the products of combustion of sulphur-bearing material;

controlling such acidification to yield a sub;

stantially pure carbon dioxide; and recovering and utilizing such carbon dioxide in the carbonation of other smelt liquor.

50. A process which comprises concentrating and burning the combustible content and smeltmgthe inorganic mineral content of teasers spent liquor resulting from the digestion of raw cellulosic material in an alkaline solution of sodium sulphite in a manner to produce sodium sulphide and sodium carbonate; recovering the smelted inorganiccompounds in water; oarbonating the smelt solution with substantially pure carbon dioxide and controlling such carbonation to produce substantially pure hydrogen sulphide; recovering the sulphur of the hydrogen sulphide liberated in such carbonation in theform of a sodium salt; acidifying the carbonate solution with sulphurous acid formed from the products of combustion of sulphur-bearing material; controlling such acidification to produce a substantially pure carbon dloxide;

and recovering and utilizing such carbon dioxide in the carbonation of other smelt liquor.

51. A process which comprises concentrating and burning the combustible content and smelting the inorganic content of spent li quor resulting from the digestion of raw cellulosic material in an alkaline liquor containing sodium sulphite in a manner to produce sodium sulphide and sodium carbonate; recovering the smelted inorganic compounds in water; carbonating the smelt solution with substantially pure carbon dioxide; and controlling such carbonation to produce substantially pure ,hydrogen sulphide; recovering such hydrogen sulphide; acidifying the carbonated solution with substantially pure sulphur dioxide to convert the sodium carbonate to sodium sulphite; controlling such acidification to produce a substantially pure carbon dioxide; utilizing such carbon dioxide in the carbonation of'other smelt solution; treating a sodium compound employed for making up losses in the cycle for the production of sodium sulphide; utilizing the latter in producing a cooking liquor comprising sodium sul- 'phite and sodium sulphide; and employing such cooking liquor for the digestion of other raw cellulosic material. A.

52. A process which comprises digesting raw cellulosic material in an alkaline liquor containing sodium sulphite; concentrating and burning the combustible content and smelting the inorganic content of spentliquor resulting from such digesgion in a main ner to produce sodium sulphi e and sodium carbonate; recovering the inorganic smelted compounds in water; carbonating the smelt solution with carbon dioxide and controlling such carbonation to produce substantially pure hydrogen sulphide and to effect a conversion of substantially all the sodium sulphide to sodium, carbonate; recovering the sulphur of such hydrogen sulphide in the formof a sodium salt; acidifying. the sodium carbonate. solution with sulphur dioxide and controlling such acidification to produce a substantially pure carbon dioxide and a sodium sulphite solution, and utilizing the carbon dioxide obtained in such' acidification for the carbonation of other smelt solution.

53. A process which comprises digesting raw cellulosic material in an alkaline cook ing liquor containing sodium sulphite in solution; separating the pulp from the spent cooking liquor; smelting theinorganic mineral content and burning the combustiblecontent of such spent liquor in a manner to produce sodium sulphide and sodium carbonate; recovering the smelted inorganic compounds in Water; carbonating the smelt solution with carbon dioxide; acidifying the carbonate solution with sulphur dioxide to produce .a solution of sodium sulphite; recovering the hydrogen sulphide liberated in such treatment in the form of a sodium salt; and adding sodium constituents to one of the liquors of the cycle in the form of an alkaline sodium compound for making up losses in the cycle.

54. A process Which comprises cooking raw cellulosic material in an alkaline solution of sodium sulphite and sodium sulphide; separating the pulp from the spent cooking liquor; smelting the inorganic mineral content and burning the combustible content of such spent liquor in a reducing atmosphere to produce sodium sulphide; and recovering the inorganic smelted compounds for reuse in the cooking of other cellulosic material.

55. A process which .comprises cooking j raw cellulosic material in an alkaline cooking liquor containing sodium-sulphur compounds; separating the pulp from the spent. cooking liquor; burning the combustible content and smelting-the inorganic mineral 0011- I tent of such spent liquor in a reducing atmosphere to form sodium sulphide; recovering the sodium sulphide in water; carbonating the sodium sulphide of the solution to sodium carbonate; and acidifying the carbonate solution with sulphur dioxide.

In'testimony whereof we aflix our signatures.

LINN BRADLEY. EDWARD P.- MOKEEFE.

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