US1877219A - Production of chemical pulp - Google Patents

Description

Patented Sept. 13, 1932 umreo. om n: j

LINN BRADLEY, or mom'cnam, new JERSEY, AND EDWARD r. MCKEEEE, or

. rmr'rsnunen, nnw'ironx PRODUCTION OF CHEMICAL PULP No Drawing. Application filed September 2, 1926,-Ser1a1 No. 188,291. Benewed'0etober'2 6, 192.9.

This'invention relates to the production of chemical pulp, and to the treatment of residual liquors for the regeneration of cooking liquors. a 5 More particularly the invention relates to cyclic and interrelated operations in which two different kinds or types of sulfur-containing cooking liquors are employed, of which soda is the base, some of the same sul- L fur being present in one type of cooking liq cooking processes and sodium sulfid type ofcooking processes, in which cooking liquor for one type of cooking process is regenerated (at least in part) from residual liquor constituents from another type of cooking operation. The acid sulfite cooking processes to which the invention particularly relates are those in which a relatively high content :0 of combined sulfite is present in the cooking liquor as charged into the digester, more particularly cooking liquors in which there is a considerable amount of a sulfite of sodium but which are substantially free from ex- 5 cess sulfurous acid beyond the sodium bisulfite state (i. e. they contain NaHSO but contain no additional H SO Generally the cooking liquors employed, of the acid sulfite type, may be considered as made up princi- 0 pally of solutions of sodium bisulfite (NaHSO which contain also some sodium monosulfite (Na SO3).. The sulfid type of cooking liquorsto which the invention particularly relates are cooking liquors in which 5 the sodium present as sodium sulfid is less in amount than the sodium present as sodium hydroxide, these cooking liquors generally containing primarily sodium hydroxide and sodium sulfid and being prepared by causti J cizing with lime a solution of sodium carbonate and sodium sulfid, at least some of these sodium compounds having been obtained from residual liquor from a cooking operationof the acid sulfite type.

According to one embodiment of the invention, wood chi s are cooked with an acid sulfite type of coo 'ng liquor which contains sodium monosulfite and sodium bisulfite, the resulting residual liquor is separated from the pulp, after which it is subjected to a suitan able concentrating operation, the solid con- 'stituents are subjected to a furnacing operation whereby sodium carbonate and sodium sulfid are formed, these compounds are dissolved in a suitable amount of water and 05 such solution is c'austicized by lime to convert the greater part of the sodium carbonate into sodlum hydroxide, the cooking liquor .is separated from the lime mud and-thereafter is employed for cooking wood.

Prior to subjecting the residual liquor from the acid sulfite type of cooking operation to the concentrating step, it may advantageously have added thereto a sufficient amount of a reactive alkaline sodium compound to render the liquor neutral or even alkaline to I litmus. For example, some of the sodium carbonate and sodium sulfid solution referred to in the preceding paragraph may be employed for this purpose, or some of the residual liquor from the alkaline type of cooking. operation may be so employed. This utilization 'of some non-sulfur-containing sodium compound for such treatment facili tates the production of sodium sulfid. When the residual liquor from the acid sulfite type of cooking operation is thus treated with an alkaline sodium compound or compounds, and especially when residual liquor from the alkaline type of cooking operation is so utilized, some organic matter maybe separated out from solution. The liquor may be separated from such suspended matter, to a considerable extent at least, and y the concentration step is thus facilitated. A 9:; moderate amount of strong alkali, e. g.,sodium hydroxide, may be added to the sepa-' rated liquor in order to redissolve remaining suspended organic matter. Such treated residual liquor may be concentrated in any suitable type of apparatus, e. g. a multiple-effect evaporator.

The concentrated liquor may-:be given a further concentrating treatment, e. g. in a 5 disc-evaporator, and then charged into a suitable heating furnace. The concentrated liquor may be charged directly into the heating furnace without passing through a discevaporator, if desired, but by employing. a, disc-evaporator, or other scrubbing device, some sulfur or sulfur compounds may be recovered from the furnace gases and thus be available for the production of sodium sulfid. Combustible sulfur compounds, which..-may.

the sulfur oxide or oxides absorbed in alkaline liquor or solution and the resulting sodium compounds utilized in the cycle of the invention. The introduction of a regulated amount of air to react with the gases at a the soda contentof the residual liquor or thetreated residual liquor, as the case may be, is obtained in a furnace product largely as sodium carbonate and as sodium sulfid, the sodium sulfid being formed by a reduction of sodium-oxy-sulfur compounds. Ordinarily a considerable amount of sodium sulfid will be present in such product. Sodium sulfate, for example in amount'suflicient to replace soda which may be lost in the operations of the cycle, may be added to the product which is to be given the furnace treatment, so that some sodium sulfid may be formed therefrom. The furnacing operation should be so regulated that a considerable amount of the sulfur content of the residual liquor from the acid sulfite type of cooking operation, is present in the furnace product as sodium sulfid. The treatment of the residual liquor with some ,non-sulfur-containing sodium compound, e. g. sodium-organic compounds or sodium .carbonate .or various mixtures thereof, in the manner heretofore described, isof advantage .in that it aids in retaining surfur along with the soda and that it thus aids in the production of sodium sulfid.

The ratio of sodium carbonate to sodium sulfid in the furnace product is capable of variation so that a solution of these compounds yields, upon suitable causticization by means of lime, a cooking liquor which carries the desired ratio of sodium hydroxide to sodium sulfid, for example from 50 to 80 parts of NaOH to every 50 to 20 parts of be present in the gases from the-heating furnace, are advantageously oxidized 'to .;su1-

, cooking liquor. fur dioxide or sulfur trioxide or both and' Na s. By increasing the amount of soda as compared to sulfur in the product being charged into the reducing furnace, the amount of Na CO in the furnace product may be relatively increased and the sodium sulfid (Na s) relatively decreased.

The alkaline type of cooking liquor, for example containing about parts of NaOH and about 30 parts of Na S, by weight, for every 400 and 500 pounds of wood (oven-dry basis) is then employed for cooking wood, the amount of active chemicals being adjusted to suit the kind and amount of wood treated and the quality of pulp desired. This type of cooking operation can be carried out in the usual manner of cooking with this type of [The-residual liquor resulting from such cooking operationis separated from the pulp I and, where a further lot of cooking liquor of the acid sulfite type is desired to be obtained from recovered soda, such residual liquor may be, in whole or in part, as may be required, treated so as to form a recovered soda product which is suited for sulfiting by S0 gas. In case a portion of such alkaline type of residual liquor has been employed for admixing with residual liquor of the acid sulfite type, the remaining portion may be concentrated in any suitable manner and solid constituents thereof subjected to a heating treatment in any suitable type of furnace, e. g. the usual type of rotary incinerator such as is employed in mills operating the well-known soda process. Such treatment serves to drive off a considerable portion of the sulfur content of the alkaline type of residual liquor, especially when the Na S of the cooking liquor has been caused to react to a very large extent with organic constituents of wood. I Some of the residue of sulfur, remaining associated with the soda of the resulting fu r nace product, may be present as Na S, but it is advantageous to so conduct the furnacing operation as to drive off most of the sulfur and to have the sulfur which does remain in the furnace product largely in the form of an oxidized compound, e. g. sulfite or sulfate. Thus a considerable excess of air may be passed through therotary furnace, or other type of furnace when such is employed for the furnacing treatment, to facilitate in removing sulfur and in oxidizing the sulfur residue to sulfite or sulfate or both. 'However, it is difiicult to avoid the presence of Na s in the furnace roduct, when the furnacing operation is o ,a'simple type, such as above: It is satisfactory for the purposes of thecycle of the present invention, to have the furnace product composed mainly of sodium carbonate, since some Na s can be satisfacto r- 'ily utilized if present therein. Such sodium sodium compounds through the tower, and

thus absorbing sulfur dioxide in the liquor. The sulfiting may be discontinued when the liquor contains the desired ratio of combined to uncombined SO i. e. containing the de sired content of sodium sulfitcand of sodium I bisulfite. Some sodium thi'osulfate is generi of residual'liquorsof their respective'types,"

ally formed, due to interaction between Na S and H 80 but in the cycle of the present invention such Na S O may remain in the cooking liquor which is charged into the digester. The amount of combined sulfite in the cooking liquor is sufficiently high to nulli-' fy the otherwise detrimental character of Na s O e. g. such as when cooking liquors of the usual acid-sulfite type are employed. In the cooking liquors employed in the acidsulfite type of cooking operation of the present invention, the amount of sodium monosulfite is so regulated that it is suflicient to prevent objectionable reactions due to the Na S O In-general the amount of Na SO should exceed that of the Na Si O and usually a considerably larger amount should be employed for safety.

Some of the solution of sodium carbonate and sodium sulfid obtained by dissolving the recovered soda compounds produced by the furnacing treatment of residual liquor from the alkaline type of cooking operation, may be used for mixing with residual liquor from the acid sulfite type of cooking operation, if desired. Also, some of such solution may be causticized, either separatelyor after mixing with other sodium carbonate and sodium sulfid, e. g. that obtained from the reducing treatment of the constituents in the acid sulfite type of residual liquor, and be again employed in an alkaline cooking operation.

In an alternative arrangement, the residual liquors from the alkaline type of cooking operation maybe admixed with the residual liquors from the acid sulfite type of cooking operation, and the admixed liquors treated by concentrating and furnacing steps to form a recovered soda product which contains sodium carbonate and sodium sulfid." These compounds may be dissolved-to form a solution and a portion thereof may be caustici zedto form an alkaline type of cookingliquor and another portion thereof may be sulfited to form an acid sulfite type of cooking liquor,

these respective-cooking liquors be1ng"employed to cook wood and-yield further lots; I

and the simple cycle repeated.

Where sodium carbonate is employed'for replacing lost soda, it is advantageously add; ed to the sodium carbonate liquor which is to be sulfited to form the acid sulfite type of cooking liquor.

Some of the sulfur content of thefurnace gases can be recovered for reuse. For example, the gases may be subjected to electrical precipitation at a suitable temperature, preferably above the dew point so as to secure solids in a more or less dry form. Such solids are usually high in sodium sulfate, especially when the combustible furnace gases have been oxidized by the introduction of suflicient air at high temperature to effect such oxidation. These solids-are advantageously addedto the product which is to undergo a reducing furnace treatment. The more or less cleaned gases may then be subjected to a scrubbing action with a liquor which contains principally sodium carbonate when freshly supplied, to absorb S0 thereby and form a sulfite of sodium in the liquor. This sulfite of sodium is then available for employment in a cooking liquor, e. g. the acid sulfite type of cooking liquor referred to herein. It may be further sulfited if desired or necessary to provide cooking liquor of the proper composition, and further amounts of sodium carbonate may be added thereto to increase'the soda content thereof.

, The kind of acid sulfite cooking liquors,

featured herein, release little or no SO When thedigester is relieved to promote liquor circulation therein, or even at the completion covery' apparatus, such as provided and utirequired and hence is not provided.

In a companion appllcatlon, Serial No.

133,289, filed September 2, 1926, we have given examples of several cooking liquors of the acid sulfite type, which are suitable for. the

cycle of the invention herein described and featured. In such companion application, we have also described cooking liquors which contain both sodium sulfid and sodium hydroxide, but in such application claims are 'NaOH than of N a S. The a1 aline type of I e a cooking liquors of the present invention may contain a moderate amount ofsodium sulfite in addition to sodium hydroxide and sodium.

sulfid, but the'sodium hydroxide in such cases is greater than the amount of Na S.

Sulfur required forthe sulfiting operation may be supplied in any suitable manner, e. g. by burning sulfurin air, or bytheroasting of sulfide ores, or b thebumin of sulfur and roasting of sulfide ores in one operation.

'To the extent that sulfur may be recovered .of the cooking operation, hence in the cycle ,of'the present invention, elaborate S0 re- 10 lized in the usual acid sulfi-teprocess, is not hereinafter-mentioned from the furnace gases, the amount of fresh- 1y supplied sulfur may be somewhat less than where no such sulfur recovery is carried out.

The solution of sodium carbonate, which may carry a small amount of sodium sulfid,

which is to be sulfited, should contain very little if any iron compound. To facilitate removal of iron therefrom, if required, a moderate amount of lime may be thoroughly agitated with the solution and a clarified liquor separated from the solids, and this clarified and treated liquor may then be sulfited, preferably with iron-free S0 gas.

We claim:

1. The process'of treating residual liquor resulting from cooking wood with a cooking liquor which contains sodium bisulfite, which comprises adding thereto some alkaline liquor formed by dissolving the sodium carbonate and sodium sulfid produced by the reducing furnace treatment, thereby rendering the mixture of liquors non-acid and forming some sodium thiosulfate therein, subjecting the treated liquor to concentration and solid constituents thereof to a reducing furnace treatment whereby a melt is formed which contains sodium carbonate and sodium sulfid, dissolving such sodium carbonate and sodium sulfid, thereby forming an'alkaline liquor, and using a portion of the thus formed alkaline liquor to treat the residual liquor first mentioned.

2. The process for producing pulp from wood which comprises cooking wood with a liquor which contains sodium bisulfite, add" ing to the -resulting residual liquor some alkaline liquor formed by. dissolving the sodium carbonate and sodium sulfid produced by a hereinafter-mentioned reducing furnace treatment, subjecting the treated liquor to a concentration, and solid constituents thereof to a reducing furnace treatment whereby a melt is formed which contains sodium carbonate and sodium sulfid, dissolving such sodium carbonate and sodium sulfid, thereby forming an alkalinev liquor, causticizing a portion of this alkaline liquor with. sufiicient lime so as to yield a liquor which contains more sodium hydroxide than sodium sulfide, cooking wood with a liquor which comprises sodium hydrogride and sodium sulfide so formed, concentrating residual liquor from this alkaline cooking operation, and subjecting constitutents thereof to a reducing furnace treatment whereby a product is formed which contains sodium sulfid and a relatively high proportion of the soda in the form of sodium carbonate.

3. The cyclic process of producing pulp from wood which comprises cooking wood with a liquor which contains sodium sulfite and sodium bisulfite, adding to the resulting residual liquor some alkaline liquor formed by dissolving the sodium carbonate and sodium sulfid produced by a hereinafter-mentioned reducing furnace treatment, thereby which contains sodium carbonate and sodium sulfide, dissolving such sodium carbonate and sodium sulfid, thereby forming an alkaline liquor, causticizing a portion of this alkaline liquors so as to yield an alkaline cooking liquor which contains more sodium hydroxide than sodium sulfide, cooking wood in such alkaline cooking liquor, subjecting residual liquor from such alkaline cook to a concentrating treatment and solids thereof to a reducing furnace treatment to form a product which contains sodium carbonate and a lesser amount of sodium sulfid, dissolving the thus formed sodium carbonate and sodium sulfid inwater, thereby forming an alkaline liquor, subjecting sodium carbonate of said alkaline liquor to a sulfiting treatment to produce a cooking liquor containing sodium sulfite and sodium bisulfite and repeating the cycleQ';

4. The process of treating residual liquor resulting from cooking wood with a cooking liquor which contains sodium bisulfite, which comprises rendering the residual liquor alkalineby adding thereto hereinafter-mentioned alkaline liquor that contains sodium carbonate and sodium sulfid dissolved from the hereinafter-mentioned melt, subjecting the treated residual liquor to concentration and solid constituents thereof to a reduclng furnacing treatment whereby a melt is formed which contains sodium carbonate and sodium sulfid, treating the melt with water thereby forming an unclarified alkaline liquor that contains in solution the thus formed sodium after-mentioned furnace product with water to obtain in solution the sodium carbonate and sodium sulfid present in such furnace product, subjecting the treated residual liquor to concentration, and solid constituents thereof to a reducing furnace treatment whereby a furnace product is formed which contains sodium carbonate and sodium sul-. fide. treating the said furnace product with water to form an alkaline liquor containing in solution the thus formed sodium carbonate and sodium sulfid, 'causticizingsuch alkaline valkaline liquor by dissolving sodium compounds from' the furnace roduct, sulfitingliquor with lime and forming a cooking liquor which contains more sodium hydroxide than sodiumsulfide, cooking wood with such cooking liquor, con'centr'atmg residual liquor from this alkaline cooking operation, subjecting constituents'thereof to a furnacing treatment whereby a furnace product is formed which contains sodium carbonate and a lesser amount of sodium sulfid, treating this furnace product with water and forming'an the solution so as to pro uce therefrom a cooking liquor which contains sodium bisulfite but is free from excess sulfurous acid beyond the bisulfite stage, and cooking wood therewith.

6. The cyclic process of producing pulp from cellulosic fibrous material which comprises treating such material with a cooking liquor containing sodium bisulfite free from excess sulfurous acid, subjecting the residual liquor to a treatment including a reducing furnacing step adapted to yield a furnace product containing sodium carbonate and sodiumsulfide, dissolving such sodium carbonate and sodium sulfid, causticizing. such dissolved sodium carbonate and forming a cooking liquor containing sodium hydroxide and a lesser amount of sodium sulfide, treating cellulosic fibrous material withcooking liquor so formed, subjecting resulting residual liquor to a treatment including a furnacing step adapted to yield'afurnace product containing sodium carbonate, dissolving sodium compounds 'containedin the result-" ing furnace product to'produce" an alkaline liquor, agitating lime with the alkaline" liquor, separating a clarified alkaline liquor from the solids, thereafter sulfiting this clarified and treated liquor to produce a cooking liquor containing sodium bisulfite, and repeating the cycle. a

7. The cyclic process of producing pulp from wood, which comprises cooking one lot. of wood with a cooking liquor containing alarger amount of sodium monosulfite than of sodium thiosulfate and also containing sodium bisulfite, thereby forming an acid "residual liquor, cooking another lot of wood with a cooking liquor containing sodium hydroxide and sodium sulfid, thereb forming an alkaline residual liquor, ren 'ering the acid residual liquor alkaline by adding there to some of the alkaline liquo'r formed by treating a hereinafter-mentioned furnace product with water-to dissolve its contained 1 sodium carbonate and sodiumsulfid, furnac ing solids of the resulting mixture of-liquors under reducing conditions to formafurnace product which contains sodium carbonate and a lesser amount of sodium sulfid, dis

solving these sodium compounds to form an alkaline liquor, causticizing a portion of the alkaline liquor with lime to form-a cooking portion .of the alkaline liquor to form a cook- :in'g liquor containing sodiumfmonosulfite,

sodium thiosulfate and sodium bisulfite, cooking. wood with each of these" cooking liquors, thereby forming more residual liquor of each type, and repeating the process.

8. The process for producing pulp from wood, which comprises cookingwood with a cooking liquor which contains a larger amount of sodium monosulfite than of sodium thiosulfate and also contains sodium bisulfite, rendering the resulting acid residual liquor alkaline by'adding thereto alkaline liquor formed by treating a hereinafter-mentioned furnace product with water to dissolve its contained sodium carbonate and sodium sulfid, subjecting the resulting mixture of liquors to a concentration and solid constituents thereof to a furnacing treatment under reducing conditions whereby a furnace product is formed which contains sodium carbonate and sodium sulfid, treating this furnace product with water .to form an alkaline liquor by dissolving its contained sodium carbonate and sodium sulfid,-treating at least a portion liquorwhich comprises sodium hydroxide and sodium sulfid so formed, concentrating,

residual liquor from this alkaline cooking operation, subjecting solid constituents thereof to a furnacing-treatment-under reducing con 7 ditions whereby a furnace product is formed that contains a relatively high proportion of its soda in the form ofsodium carbonate and a lesser proportion in the form of sodium sulfid, treating this furnace product with waterto dissolve such constituents and produce an alkaline liquor containing these recovered sodium compounds, sulfiting at least a portion of such liquor while hot, thereby producing a. cooking liquor that contains sodium sulfite,

sodium bisulfite and sodium thiosulfate, the.

sulfiting treatment being regulated so that this acid cooking liquor contains more sodium sulfite than sodium thiosulfate.

9. The process for producing pulp-from wood, which comprises cooking wood with av I cooking liquor which contains sodium sulfite,

ents thereof to a furnacing treatment under reducing conditions whereby a product is sodium bisulfite and sodium thiosulphate, the

. amount of sodium monosulfite exceeding that formed which contains sodium carbonate and F sodium sulfid, causticizinga solution containmg these recovered sodium compounds with sufficient lime so as to yield a liquor which contains sodium hydroxide and a lesser amount of sodium sulfid, cooking wood with cooking liquor which comprises sodium hydroxide and sodium sulfid so formed, concentrating residual liquor from this alkaline cooking operation, subjecting solid constituents thereof to a furnacing treatment under reducing conditions wherebya furnace product is formed that contains a relatively high proportion of its soda in the form of sodium carbonate and a lesser proportion in the form of sodium sulfid, dissolving such constituents to produce an alkaline liquor containing these recovered sodium compounds, admixing lime with the alkaline liquor, separating the undissolved solids from the liquor to obtain a clarified alkaline liquor, sulfiting the thus clarified liquor while hot, thereby producing a cooking liquor that contains sodium sulfite, sodium bisulfite and sodium thiosulfate, the sulfiting treatment being regulated so that this acid cooking liquor contains more sodium sulfite than sodium thiosulfate.

10. The interrelated process of producing pulp and treating residual liquors, which comprises the following steps: (a) digesting wood with an acid cooking liquor that .con-

tains sodium bisulfite, sodium sulfite and sodium thiosulfate and in Which the amount of sodium sulfite is larger than the amount of sodium thiosulfate; (b) digesting wood with an alkaline cooking hquor that contains soditer compound including sulfur derived from the said sodium compounds utilized in step (a) (f) dissolving the sodium carbonate and sodium sulfid produced in ste (e) to form an alkaline liquor; (g),caustic1zing by means of limealkaline liquor produced in ste (f) thereby producing an alkaline cooking 'quor that contains sodium hydroxide and a lesser amount of sodium sulfid; (h), employing in step (b) alkaline cooking liquor produced in step (g) (i), removing water from residualliquor produced in step (b) (j), furnacing solid constituents, derived from the liquor treated in step (i) under reducing conditions,

thereby obtaining a furnace product that contains the major portion ofitssoda as sodium carbonate and a lesser portion as sodium sulfid; (is), dissolving the sodium carbonate and sodium sulfid, produced in step (j), to produce an alkaline liquor; (Z), admlxing lime with this alkaline liquor and thereafter separating a clarified alkaline li nor from the undissolved solids; (m), sul fiting this clarified liquor so as to produce an acid cooking liquor of the kind described in step (a) and ('n), employing this acid cooking liquor in step (a) of the process.

11. In a process for produclng pulp in which raw cellulosic-fibre-bearing material is digested with an acid cooking liquor con-' decompose organic matter thereof and form a furnace product that contains sodium carbonate and sodium sulfid, treating this furnace product with water to dissolve these sodium compounds and forms the alkaline liquor, and using this alkaline liquor for the treatment of the acid residual liquor without an intervening digesting treatment of raw cellulosic-fibre-bearing material therewith.

12. In a process for producing pulp in which raw cellulosic fibre-bearing material is digested with cooking} liquor containing a sulfite of sodium, theiimprovement which comprises evaporating water of the resulting residualliquor, furnacing resulting solids under reducing conditions to decompose organic matter thereof and form a, furnace product that contains sodium carbonate and sodium sulfid, treating this product with water to'dissolve these'sodium compounds and form an alkaline liquor, admixing lime with this liquor, thereafter separating a clarified alkaline liquor from the resulting undissolved matter, and subsequently sulfiting sodium compounds thereof to form a cooking liquor thatcontains a sulfite of sodium and is substantially free from dissolved iron compounds.

In testimony whereof we aflix our signatures. v

LINN BRADLEY. EDWARD P. MCKEEFE.

CERTIFICATE OF CORRECTION. 7

Patent No. 1,877,219. September 13, 1932.

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 2, line 74, for "and" read to; page 4, line 69, claim 3, after "liquor" insert the word to; and in line 76, same claim, for "liquors" read liquor; and that the said Letters Patent should be read with'these corrections therein that the same may conform to the record of the ease in the Patent Office.

Signed and sealed this 22nd day of November, A. D. 1932.

M. J. Moore, 7

(Seal) Acting Commissioner of Patents.