US1797678A - Production of chemical pulp - Google Patents

Description

Patented Mar. 24, 1931 UNITED STATES PATENT OFFICE LINN BRADLEY, OF MONTCLAIB, NEW JERSEY. AND EDWARD P. MCKEEIE, OF PLATTS- BURG, NEW YORK, ASSIGNORS TO BBADLEY-MCKEEFE CORPORATION, OF NEW YORK,

N. Y., A CORPORATION on NEW YORK rnonuorron OF CHEMICAL PULP No Drawing.

This invention relates to the production of chemical pulp, and to the treatment of residual liquors for the regeneration of cooking liquors.

5 More particularly the invention relates to cyclic and interrelated operations in which two diiferent kinds or types of sulfur-containing liquors are employed in cooking operations, of which soda is the base, some of the same sulfur being present as sodium sulfite in one type of cooking liquor, in one instance, and being present as sodium sulfid in one of the cooking liquors, in another instance, and with successive employment of some of the same soda as sodium sulfite and, in a succeeding operation, as sodium sulfid, although the soda and the sulfur may in part be present as other compounds.

Among the particular improvements which the invention presents are interrelated operations or steps in which cooking liquor for one type of cooking operation is regenerated at least in part) from residual liquor constituents from another type of cookmg operation. The two kinds or types of cooking liquors, to which the invention more particularly relates, are those which may be described in the following general manner. )ne contains as much and usually more sodium hydroxide than sodium sulfid and is generally free from any large amount of sodium sulfite; the other generally contains as much, and usually more, of its soda content 0 in the form of sodium sulfite as is present therein in the form of sodium sulfid, and either contains a lesser amount of sodium hydroxide than of sodium sulfid or is free from sodium hydroxide. The cooking liquor 40 first described is called the caustic cookin liquor, owing to its high content of NaOl the other cooking liquor is called the sulfid cooking liquor, owing to the cooking being primarily due to its content of Na s.

According to one embodiment of theinven- A plication filed September 2, 1926. Serial No. 133,294.

tion, one lot of wood chips is cooked in a suitable amount of the caustic cooking liquor, thereby producing chemical pulp and a residual liquor, another lot of wood is cooked in a suitable amount of the sulfid cooking liquor, thereby producing chemical pulp and a residual liquor different in type as compared with the other residual liquor, the pulps are separated from the residual liquors, respectively, and residual liquor from one cooking operation is admixed with residual liquor from the other cooking operation, the admixed liquor is concentrated and the product subjected to a furnacing treatment under reducing conditions, thereby decomposing organic compounds and forming a product which contains mainly sodium carbonate and a relatively high content of sodium sulfid. The furnacing operation, which may be carried out after previously subjecting the concentrated mixture of residual liquors to treatment by gases from the furnace which contain sulfur compounds, is

advantageously so regulated that the resulting soda product contains a considerable portion of the sulfur content of the admixed rcsidual liquors in the form of sodium sulfid, care being taken to avoid driving off an excessive amount of such sulfur along with the.

gases. Any combustible sulfur compounds carried by the gases may be subjected to an oxidizing treatment, e. g. by admixing a regulated amount of air therewith, and some of such oxidized sulfur compounds may be absorbed in the residual liquor which is subject ed to the action of such gases. By employing such liquor in a disc-evaporator, some of such sulfur may be regained from the furnace gases which are caused to pass through it.

The soda compounds produced as a result of such treatment, are dissolved in water to form a suitable solution. A regulated portion of such solution is (-austicizcd with sufsulfited to form the required amount of sodium sulfite for the sulfid cooking liquor. Such sulfiting step may be carried out in any suitable manner. For example, one portion may be subjected to a direct sulfiting treatment, provided the solution contains a suitable ratio of sodium carbonate to sodium sulfid, and for this purpose some sodium carbonate maybe dissolved in such portion of the solution which is to be so sulfited. Such sodium carbonate may be that which is added for replenishing the soda required for the cycle. The sodium sulfite solution thus prepared may be admixed with the required amount of untreated solution, so as to form a cooking liquor which contains the required amount of sodium sulfid and of sodium sulfite. he cooking liquor thus prepared will usually contain sodium thiosulfate. Another method of sulfiting the sodium carbonate in a portion of the solution of sodium carbonate and sodium sulfid, comprises adding thereto the required amount of calcium monosulfite, preferably freshly prepared, agitating the mixture long enough to form the desired amount of sodium sulfite in the liquor with a corresponding amount of calcium carbonate, after which the solution may be separated from the solids in any suitable manner. Such cooking liquor may contain little if any sodium thiosulfate, being composed primarily of sodium sulfid and sodium sulfite and accompanied by such an amount of sodium carbonate as remains unchanged. The caustic cooking liquor, and the sulfid cooking liquor, which have been regenerated in the manner described, are employed in their respective type of cooking operation.

\Vhere sodium sulfate is added to the cycle for replenishing the soda, it is preferably added to the product which is to he sub ected to the reducing furnace treatment, thereby augmenting or supplementing the sodiumsulfur constituents and thus facilitating the production of a soda product which contarns a sutiiciently high content of sodium slll iltl. Sodium sulfid may be added for replenishing soda and may be added to cooking liquor of either t pe and advantage taken of such addition to orm cooking liquor which contains the desired content of sodium sultid as compared with the other constituents thereot'. Sodium hydroxide, if employed for replenishing soda, is usually added to the caustic cooking liquor after it is separated from the lime mud resulting from the causticizing treatment.

The following examples will serve to illustrate the two types of cooking liquors. the amount of reagents being expressed in.pounds and being based on a charge of 000 pounds of wood (oven-dry basis) such as pir hir. For woods which require mori= chvniiral than does poplar, the amounts may be varied to suit the conditions.

Caustic cooking liquors Nmsoi NaOH NazS NBzCOa Sulfid cooking liquors N328 Nalsol N82CO3 NaOH Some sodium sulfate, or/and some sodium thiosulfate may be present in such cooking liquors or any of them, but these are usually present in only moderate amount, if at all.

The cooking operations of the present invention may be carried out either in a single stage or in a multiple stage. For example enough cooking liquor, containing the required amount of active chemicals, may be charged into a digester containing the freshly charged chips and the contents subjected to a suitable elevated temperature until the cooking operation has reached a point whereby good chemical pulp may be produced by blowing the contents of the digester into a blow-pit in the usual way. Alternatively, the freshly charged chips may be given a prehmmary treating operation to remove some of the more readily removable constituents thereof, and the final pulping treatment he carried out thereafter by introducing sufficlent cooking liquor of suitable composition into the digester which contains the partially treated chips and thereafter concluding the pulp-producing operation. The residual liquor separated from the pulp after completion of the pulping operation. may be employed to effect the prelin'iinary treatment of the freshly charged chips. and such residual liquor may be employed without modifying it or it may have active reagents added thereto to fortify it and thus to increase its act-ivity. such as NaOH. or/and Na s. Thus the composition of the liquor employed in the stages may differ considerably. In the concluding stage, the cooking liquor either contains both sodium hydroxide and sodium sulfid in regulated amounts. or sodium sulfid and sodiunrsultite. thus securing the combined advantages of such reagents in the final stage of the cooking operation. \Vhen the two-stage method of cooking is employed, it appears to be possible to produce good quality pulp from wood by employing a smaller amount of active chemicals than where the entire pulping operation carried ing a furnace product containing its sodium ing its sodium compounds mainly in the form 1 material.

from the digestion of cellulosic material in in a cooking liquor containing caustic soda an alkaline cooking liquor containing caustic and sodium sulfid as its main constituents, sm In as its main constituent, thereby producthereby producing a furnace product containcompounds mainly in the form of sodium of sodium carbonate and sodium sulfid, and

carbonate and sodium sulfid, and treating treating the resulting sodium compounds to such sodium compounds to produce an alkaproduce cooking liquors of th e types emline cooking liquor for the alkaline cooking ployed in the respective digestion treatments. liquor for the alkaline digestion of cellulosic 7. The process which comprises subject- 4. The process which comprises subjectconditions the inorganic content and admixed ing to a furnacing treatment under reducing organic matter of a concentrated mixture of conditions the inorganic content with adresidual liquors resulting from the digestion mixed organic matter of a concentrated mixof cellulosic material, one of said residual ture of the waste residual liquor resulting liquors resulting from the digestion of celfrom the digestion of cellulosic material in lulosic material in an alkaline solution of a solution of sodium-sulfur salts containing sodium sulfite containing the greater part most of the sodium in the form of a sulfite of of its sodium in the form of sodium sulfite, sodium and the residual liquor resulting from and the other of said residual liquors resulttbe digestion of cellulosic material in an aling from the digestion of cellulosic material kaline solution containing sodium com in an alkaline cooking liquor containing pounds, the major portion of which are sulcaustic soda as itsmain constituent, thereby fur-free sodium compounds, thereby producproducing a furnace product containing its ing a furnace product containing the sodium sodium compounds mainly in the form of compounds mainly as sodium carbonate and sodium carbonate and sodium sulfid, and sodium sulfid, and treating the resulting sotreating the resulting sodium compounds to dium compounds to produce an alkaline cookproduce cooking liquors of the types emiug liquor for the digestion of cellulosicmaployed in the respective digestion treatments. terial, the gaseous products from the reducing 8. The process which comprises subjecting furnacing treatment being passed into conto a furnacing treatment under reducing contact with residual liquor for the recovery of ditions the inorganic content and admixed orinorganic constituents therefrom in the liquor ganic matter of residual liquor resulting from before the inorganic constituents of such the digestion of cellulosic material in a cookliquor are subjected to the reducing furnacing solution of sodium-sulfur salts and coning treatment. taining a sulfite of sodium as the main sodium The process which comprises subjectsalt, and thereby producing a furnace proding to a furnacing treatment under reducing uct containing its sodium compounds mainly ,conditions the inorganic content with adin the form of sodium carbonate and sodium mixed organic matter of a concentrated mixsulfid, and treating the resulting furnace ture of the waste residual liquor resulting product to form a cooking liquor containing from the digestion of cellulosic material in a, the sodium sulfid of such furnace product as solution of sodium-sulfur salts containing one of its main constituents and digestion celinost of the sodium in the form of .a sulfite of lulosic material-therewith. sodium and the residual liquor resulting from In testimony whereof we aflix our signailie digestion of cellulosic material in an altures. lt'aline solution containing sodium com- LINN BRADLEY. pounds, the major portion of which are sul- EDlVARD P. MoKEEFE. fur-free sodium compounds, thereby producing a furnace product containing the sodium compounds mainly as sodium carbonate. and sodium sulfid, and treating the resulting sodium compounds to produce cooking liquors of the types employed in the respective digestion treatments.

6. The process which comprises subjecting to a furnacing treatment under reducing conditions the inorganic content and admixed organic matter of a concentrated mixture of two different kinds of residual liquors resulting from the digestion of cellulosic material, one of said residual liquors resulting from digestion of cellulosic material in cooking liquor containing a sulfite of sodium as its main constituent, and the other residual liquor resulting from digestion of cellulosic material ing to a furnacing treatment under reducing i it) a fortified or an unfortified residual liquor,

or a freshly charged liquor containing little or no organic matter, so that about one half of the non-cellulose material is removed from the digester, e. g. in solution or/and in suspension therein, about two thirds of the amount of active chemical ordinarily employed in a single stage cook, may be sufficient when employed in the cooking liquor for completing the pulping operation. The liquor employed in the preliminary treatment may even be a solution of sodium carbonate and sodium sulfid which has not been causticized or sulfited, such liquor being able to remove quite a large amount of non-cellulose material from the wood and leaving the chips in better condition for the final pulping treatment than if they had not been so treated. Thus a part only of the sodium carbonate-sodium sulfid solution may be sulfited, e. g. by (32130,, to form a cooking liquor for the second stage treatment which contains primarily sodium sulfite and sodium sulfid and such liquor being employed in the final pulping stage, the chips having been previously treated by residual liquor or by sodium carbonate sodium sulfid liquor so as to remove a considerable amount of non-cellulose material therefrom, e. g. so that about one fourth to one half of the non-cellulose is thus removed in the preliminary treatment. The residual liquor from the caustic cooking treatment of wood may be advantageously employed for such preliminary treatment of the lot of chips which is to be further treated by Na s, etc. Such utilization of the residual liquor from a caustic cooking operation is advanta eously carried out prior to admixing sucfi residual liquor with that which results from the utilization of sodium sulfid be subjected to a separate furnace treatment to produce a recovered soda product. Such furnace treatment may be carried out in any suitable manner and the soda utilized or disposed of as desired.

The steps of the cycle described in this specification facilitate the recovered soda product whic 1 contains a considerable amount of sodium sulfid, and, esperoduction of a cially when the soda losses are kept down to a low point, the sulfur utilization disclosed is taken advantage of for the production, on the one hand, of caustic cooking liquors which contain a desirable ratio of NaOH to Na s; and the operation may be regulated to this end. Various woods may be pulped by the cooking liquors described, and various pulps thereby produced.

This application is in part a continuation of our applications Serial Nos. 456,187, filed March 28, 1921; 481,146 and 481,147, filed June 28, 1921; 686,137, filed Jan. 14, 1924; and 757,766, filed Dec. 23, 1924.

We claim:

1. The process which comprises subjecting to a furnacing treatment under reducing conditions the inorganic content with admixed organic matter of a concentrated mixture of the Waste residual liquor resulting from the digestion of cellulosic material in a solution of sodium-sulfur salts containing most of the sodium in the form of a sulfite of sodium and the residual liquor resulting from the digestion of cellulosic material in an alkaline solution containing sodium compounds the major portion of which are sulfur-free sodium compounds, thereby producing a furnace product containing the sodium compounds mainly as sodium carbonate and sodium sulfid, and treating the resulting sodium compounds to produce an alkaline cooking liquor for the digestion of cellulosic material.

2. The process which comprises subjecting to a furnacing treatment under reducing conditions the inorganic content and admixed organic matter of a concentrated mixture of two different kinds of residual liquors resulting from the digestion of cellulosic material, one of said residual liquors resulting from digestion of cellulosic material in cooking liquor containing a sulfite of sodium as its main constituent, and the other residual liquor resulting from digestion of cellulosic material in a cooking liquor containing caustic soda and sodium sulfid as its main constituent, thereby producing a furnace product containing its solution compounds mainly in the form of sodium carbonate and sodium sulfid, and treating such sodium compounds to lproduce an alkaline cooking liquor for the al aline digestion of cellulosic material.-

3. The process which comprises subjecting to a furnacing treatment under reducing conditions the inorganic content and admixed organic matter of a concentrated mixture of residual liquors resulting from the digestion of cellulosic material, one of said residual liquors resulting from the digestion of cellulosic material in an alkaline solution of sodium sulfite containing the greater art of its sodium in the form of sodium sul te, and the other of said residual liquors resulting CERTIFICATE OF CORRECTION.

Patent No. 1,797,678. Granted March 24, 1931, to

LINN BRADLEY ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, line 113, claim 2, for the word "constituent" read constituents, and line 114, for "solution"' read sodium; page 4, lines 8 and 9, claim 3, beginning with the word "cooking" second occurrence, strike out the words "cooking liquor for the alkaline"; same page, line 107, claim 8, for "digestion" read digesting; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in' the Patent Office.

Signed and sealed this 28th day of April, A. D. 1931.

M. J. Moore. (Seal) Acting Commissioner of Patents.