US1842712A - Manufacture of wood pulp, etc. - Google Patents

Description

Patented den. 26, 1932 UNITED STATES PATENT (OFFICE.

lLINN BRADLEY, F MDNTCLAIR, NEW JERSEY, AND EDWARD P. MOKEEFE, OF NEW YORK, N. Y.

MANUFACTURE OI WOOD PULP, ETC.

N0 llrawing. Application filed June 28,

This invention relates to improvements in the production of pulp from Wood and similar cellulose-bearing materials.

The common methods of producing wood pulp chemically, are the so-called soda, sulfate and sulfite'processes. In the so-called soda process, the main cooking operation is dependent upon caustic soda. In the socalled sulfate process the main cooking operw ation is dependent upon caustic soda assisted more or less by sodium sulfide, although some sodium carbonate and sodium sulfate may be present. in the so-called sulfite process the main cooking operation depends upon bisul- M tites in the presence of sulfurous acid. In the soda and sulfate processes, accordingly, the cooking liquor is strongly alkaline, while in the sulfite process the cooking liquor is strongly acid; and it has been considered immy practical to cook wood successfully, for the production of chemical pulp, unless the cooking liquor was either strongly acid or strongly alkaline.

in all three of the processes mentioned, the as cooking liquors employed act not only upon the encrusting and so-called non-cellulose constituents or'so-called lignin or lignified tissues of thewood, but also to a greater or less extent upon the cellulose or pulp mak 3o ing fibres, and usually destroy or injure a considerable portion of the valuable fibres or' cellulose, or convert an appreciable portion thereof into constituents which are removed from the pulp. Sometimes the residual liquors from the process are also of such a character that they leave in the pulp constituents which make the pulp difficult to bleach "with the usual bleaching materials and operations, so that the fibres maybe still further 40 injured by the severe bleaching treatment which it is necessary to employ.

The rapidly decreasing supply of woods suitable and availablefor pulp making purposes and the high cost of equipment and R operation of chemical pulp mills makes it of 1921. Serial No. 481,146.

great national and economic importance to materially increase the yield of pulp from woods which are commonly used for the purtained by chemical methodsof disintegrating wood, even those now employed, is far superior in quality, including strength, to that obtained by the ground Wood process, and a much wider range of woods canbe used.

As the result of our investigations, we have been impressed with the fact that a considerable portion of the pulp content of the wood treated was not being recovered in the form of pulp, and We have therefore studied the cooking processes with the View of determining whether an increased yield of pulp could be obtained-from the same amount of wood by other methods than those heretofore employed.

We have found that if, instead of a strongly acid or strongly alkaline cooking liquor, the cooking liquor is neutral in character or is only weakly alkaline, an increased yield of a superior pulp can be, obtained. We have studied the effect of various cooking liquors and various treatments upon different kinds of wood and have determined that the ingredients associated with the Wood fibres may generally be considered as consisting of two kinds, namely, constituents readily re1novable from the fibres by a mild reagent in the presence of water at a suitable temperature and pressure, and other constituents which are less readilyremovable by mild reagents but which are readily removable with strong 7 tion upon the fibres.

ably near the end of the cook. Tn any event, however, the amount of caustic soda required will be small, and will be insufficient in amount to have objectionable action upon the fibres so that the pulp produced will contain" substantially all of the fibres originally pres ent in the wood, freed from non-fibrous con- I soluble in the amount of liquor used should be suitably circulated so as to keep the undissolved reagent in suspension and fairly uniformly distributed. This avoids the production of acidic liquors in localized zones.

The cooking operation may also be carried out with less of the reagents than will completely cook the wood, and a partially cooked or under-cooked woodpulp produced. For eirample. sodium sulfite alone can be used under conditions such that the wood is partially cooked, and the cooking operation can then be followed by a mechanical treatment or another chemical treatment to further prepare the wood pulp for subsequent treatment or use.

Tn the treatment of certain woods by the use of a strong reagent such as caustic alkali in addition to the mild reagent, to produce a well-cooked wood pulp, the cooking operation may advantageously be divided into two steps or stages. The first part of the operation can thus he carried out with a mild. reagent or reagents either alone or with a small amount of a strong reagent, and the second part of the cooking operation can be carried out with a strong reagent, either alone or with amild reagent. For example, by using sodium sulfite alone for the preliminary part of the cook and by then adding a small amount of caustic soda and completing the operation, the caustic soda will not have op portunity to act upon the wood until it has been disintegrated to a considerable extent by the sodium sulfite. A better opportunity is thus afforded for the action of the sodium sulfite upon the wood, and this action is supplemented by the subsequent portion of the cook carried out with added caustic soda. This enables a lesser amount of caustic soda to be used, as it is not present during the entire cooking operation. So also, it acts upon the wood chips for a shorter period of time, thus lessening the possibility of injurious ac- A particularly advantageous method of carrying out the two-stage cook above described is to introduce, for example, suitable sodium sulfite cooking liquor, into the sodium sulfite cooking llquor, to introduce a suiiicient amount of lime to causticize a part of the sodium snlfite. That is, by introducing a small and regulated amount of lime into the digester, the lime'will react with the sodium sulfite to form caustic sodaand calcium sulfite, so that. the cooking liquor will thereafter contain both sodium sulfite and caustic soda together with calcium sulfite. The lime is preferably introduced in the form of screened milk of lime and the reaction is brought about by the circulation which takes place within the digester. The caustic soda is thus produced within the digester as needed.

Instead of carrying out the process as a two stage cook, by adding the milk'of lime ing operation 50 that a mixture of sodium sulfite and caustic soda will be formed in this way at the outsetof the process; or the lime may be added in stages as the cooking operation proceeds thusprogressively producing sodium hydroxide in the cooking liquor.

If the calcium sulfite or other calcium compounds are objectionable in the pulp, they can be removed therefrom, for example, by. washing the pulp with a dilute acid such as sulfurous acid inwater after the pulp has been removed from the digester. Where the presence of calcium compounds is unobjectionable in the pulp, for example, the presence of calcium sulfate or gypsum, the pulp can be treated with dilute sulfuric acid or a solution of sodium bisulfate to form calcium sulfate and set free any organic acids, etc., with which the calcium is combined. The calcium sulfate may be left in the pulp as a filler, and where the organic compounds are suitable, they may also be left inthe pulp as sizing or binding materials.

By using neutral or weakly alkaline reacting liquors, the process can be carried out in iron vessels, so,that linings such as are now.

used in the so-"called sulfite process can be dispensed with, with resulting increased capacity of the digester. The digester can also be charged with hot liquors, and the digester can be l filled as'full as practicable with the wood \khips. The cooking liquors are sufiiciently ii -gt in their action upon the valuable fibres st that chips can be cooked for different peifods of time in the same charge without 0' ject-ionable injury due to overcooking of part of the charge. As a result, a partof the charge can be introduced and the cooking operation commenced so that the charge can be compacted in the digester and a further amount of chips introduced so that the char e as a Whole can be materially increased. For example, the

When a multi-stage cook is used and one liquor is removed before introducing another, the digester may be opened at a suit-- able time, such as between the successive stages, and advantage taken of the fact that the wood chips already partially cooked, have packed considerably, thus leaving a considerable amount of available space which can be filled with additional wood chips which will be subjected to the successive portions of the cooking operation. An additional amount of wood chips can be treated in this way in the same apparatus. Where diiferent cooking liquors are employed in successive stages [of the cook, the residual liquors obtained will vary in character from each other.

When the two stage cook is carried out with a sodium sulfite cooking liquor, the liquors may smilarly be withdrawn at the end of the successive stages. For example, resinous pine woods may be cooked at a temperature corresponding to about 120 pounds saturated steam pressure for about four or five hours with a solution containing an ex-.

cess of sodium sulfite, and the residual liquor can then be removed from the fiber-bearing material and the fiber-bearing material then cooked for a further period'of, for example,

four hours at the same temperature and steam pressure and with a solution containing a suitable amount of caustic soda, insuflicient to injure the fibres to any objectionable extent, but suflicient to remove resinous and tained in this way in relatively large amount similar non-fibrous constituents not. removed by the sodium sulfite. The final liquor will be relatively more saponaceous due to the presence of resin soap. This soap' can be ohand made available for use as a soap ingre- 9 client or for sizing or other purposes. When normal sodium sulfite alone is used in excess during the early portion of the cook, its action accordingly is more or less selective in that only a part of the resinous constituents are attacked and removed, so' that such con-y stituents as reinain can be later removed by the dilute caustic soda treatment, but without the necessity for'using more than a small amount of caustic soda which is insulficient toserlously injure the fibres. a

It is one advantage of the present invention that indirect heating of the digester'can be employed in a particularly advantageous manner, inasmuch as the cooking liquor is either neutral or mildly alkaline, so that it has no objectionable corroding action such as results from the use of acid liquors. The residual liquors produced, as well as the cooking liquors during the cooking operation, have less organic matter in solution than the liquors of the usual pulp processes, if the same amount of liquor is employed, and the organic matter partakes of a somewhat different character and is less liable to deposit on the tubes or coils of a heater or heat exchanger. So, also, pumps can more readily be operated to circulate the liquor against the high pressures and at the high temperatures employed, where the liquor is neutral or weakly alkaline than where the liquor is either strongly acid or strongly alkaline.

We have also found that it is not necessary to keep the chips submerged during the cooking operations, provided the chips are properly subjected to the action of the cooking liquor by employing suitable circulation for example, by spreading the cooking liquor at the tops of the digester and allowing it to penetrate down around or through the chips to be again returned to the top and recirculated. This method of procedure permits the employment of a lesser quantity of cooking liquor, with saving in the amount of liquor to be pumped and in the heat required for heating the body of liquor, as well as in evaporation and other recovery steps owing to the lesser amount of residual liquor to hanliquor to be circulated can be varied by introducing additional liquor of a different character, so that it will be introduced into the digester along with the other li uor that is being circulated. When the co g operation has reached a desired point, for example, the liquor can be changed so that the subsequent portion of the cook will have a modified cooking liquor. The liquor used in one cooking operation or in a preliminary portion of the cook may even be drawn off and circulated through another digester, thus further carrying out the selective treatment of different charges of chips in different digesters, or utilizing the same liquor for treating successive charges in different digesters.

It will accordingly be seen that the present invention provides a process of producing wood pulp from wood in which both strong acid and strong alkali cooking liquors are avoided, and in which a neutral or weakly al-' agents for effecting-the major portion of the cooking operation, either alone or together with a strong reagent in small and regulated It will also be seen that the present process utilizes a mild reagent or reamount, either with the mild reagent or alone, and either in a single or multi-stage cooking operation, so as to insure the separation of the fibres from the associated ingredients to such an extent as to form a suitable pulp. By using the mild and strong reagents in this way, it is possible to reduce the amount of the strong reagent to a minimum such that it has no seriously objectionable action upon the fibres of the wood treated.

Tn the claims the term acid in the phrase to prevent the cooking liquor from becoming acid refers to the use of litm-us as the indicator.

l. The method of treating wood so as to produce wood pulp, which comprises subjecting the wood to a cooking operation under pressure and at an elevated temperature with a cooking liquor utilizing a mild cooking reagent and thereafter changing the composition of the cooking liquor by the addition of an alkali and completing the cook with said changed liquor.

2. The method of treating wood so as to produce wood pulp, which comprises subjecting the wood to a cooking operation under pressure and at an elevated temperature with a cooking liquor utilizing a mild cooking reagent and thereafter changing the composition of the cooking liquor by the addition of a reagent or reagents without complete reduction of the pressure within the cooking apparatus.

8. The method of treating wood so as to produce wood pulp, which comprises subjecting the wood to a cooking operation under pressure and at an elevated temperature with a cooking liquor utilizing a mild cooking reagent and thereafter changing the composition of the cooking liquor by the addition of a reagent or reagents without greatly reducing the temperature and pressure within the cooking apparatus, and thereafter completing the cooking operation.

at. The method of treating wood chips which comprises subjecting the chips to a partial cooking operation with one cooking liquor and completing the cooking operation with a cooking liquor of modified composi-,

'tion, the cooking liquor being circulated and controlled so that the chips are cooked by percolation without the chips being completely submerged, the cooking liquor being maintained neutral or alkaline and being prevented from becoming acid during the cooking operation.

5. The method of treating wood for the production of wood pulp therefrom which comprises subjecting the wood to a partial cooking operation under pressure and at an elevated temperature with a neutral or mildly alkaline cooking liquor containing monosultite to give a partially cooked product, and subjecting the partially cooked product to a further chemical treatment to prepare wood pulp therefrom.

6. The method of treating wood for the production of wood pulp therefrom which comprises subjecting the wood to a partial ment to prepare wood pulp therefrom.

7. The method of treating wood for the production of wood pulp therefrom which comprises subjecting the wood to a partial cooking operation under pressure and at an elevated temperature with a sodium monosulfite cooking liquor, to give a partially cooked product, and subjecting the partially cooked product to a further chemical treatment to prepare wood pulp therefrom.

8. The method of treating wood for the production of wood pulp therefrom which comprises subjecting the wood to a partial cooking operation under pressure andat an elevated temperature with a sodium monosulfite cooking liquor to give (a partially cooked product, the cookin operation being will completely cook the wood, and subjecting the partially cooked product to a further chemical treatment to prepare wood pulp therefrom.

9. The method of treating wood so as to produce wood pulp which comprises subjecting the wood to a cooking operation under pressure and at an elevated temperature with a neutral or mildly alkaline cooking liquor and thereafter changing the composition of the cooking liquor containing monosulfite by the addition of an alkali. I

10. The method of treating wood chips which comprises subjecting the chips to a partial cooking operation with a neutral or mildly alkaline cooking liquorand completing carried out with less of the, reagents than the cooking operation with a cooking liquor having alkali therein, the cooking liquor being circulated and controlled so that the chips are cooked by percolation without the chips being completely submerged.

11. The method of treating wood for the production of pulp which comprises treating the wood at an elevated temperature with a cooking liquor containing undissolved reagents in suspension, the volume of which is less than would submerge the entire mass of wood and circulating the liquor so that any undissolved reagents will be kept in suspension therein and all the wood will be subjected thereto.

12. The method of treating wood chips which comprises subjecting the chips to a partial cooking operation with cooking liquors insufficient to submerge the chips, circulating the liquor in such manner thatthe liquor is distributed evenly over the top of the mass of chips and is caused to percolate down through the mass, changing the chem ical composition of the liquor by adding chemicals to the liquor during the circulation and completing the cook with the modified liquor.

13. The method of separating resins from wood with the simultaneous production of' pulp and resin soaps which comprises par tially cooking the wood in a liquor containing a mild reagent having a selective action on a part of the non-cellulose, withdrawing the liquor when substantially all the non- .cellulose materials, except the resins, have been dissolved, completing the cook with a an alkaline residual liquor containing dissolved matter derived in part from such firstmentioned organic matter; (0) subsequently washing fibres derived from the said material treated in step a.

' .17. The process according to claim 16, wherein the amount of sulfite used in step atis insuflicient to convert wood into chemical pulp.

In testimony whereof we aifix our signatures.

LINN BRADLEY.

- EDWARD P. KcKEEFE.

caustic alkali and recovering resin soap fronf lulose-containing material, by means of aliquor maintained alkaline, so as to reduce the percentage of non-cellulose therein and obtain at the termination of such latter treatment an alkaline residual liquor containing dissolved matter derived in part from such first-mentioned organic matter; (a) subsequently washing fibres derived from the sai material treated in step a.

15. The process according to claim 14 wherein the amount of digesting material used in step a is insuflicient to convert wood into chemical pulp.

16. The process of treating fibre-bearing material which comprises the following steps: (a) subjecting fibre-bearing material containing cellulose and other undissolved organic matter of wood origin to a digesting treatment so as to solubilize a substantial portion of the said organic matter by means of a sulfite; (b) subsequently supplying to fibre-bearing material, derived from the said material mentioned instep a and containing undissolved organic matter including cellulose, an a lkaline reagent which is capable oiwofibih'zing a substantialportion of such organic matter, and treating the cellulose-containing material, by means of a liquor maintained alkaline, so as to reduce the percentage of non-cellulose therein and obtain at the termination of such latter treatment iao