US1769811A - Process of pulping fibrous material - Google Patents

Description

My E, E3. s. D. WELLS PROCESS OF' PULPING FIBROUS MATERIALV 'Filed Nov. 7'. 192e XRN n.. RKNB Patented July ll, i930 are SIDNEY D. WELLS, 0F QUINCY, ILLINOIS, ASSIGNOR, BY BHESNE ASSIGNMENTS, TO THE MINE & SMELTER SUPPLY COMPANY, OF DENVER, COLORADO, A CORPORATION or comonline PROCESS OF IULPING- lFIBROUS MATERIAL Application led November This invention relates to a process of pulping fibrous vegetable material and pertains particularly to the treatment of straw and other fibrous vegetable material with caustic alkali solutions at low temperatures.

An object of this invention is to effect lignin removal with as little loss as possible of cellulose and pentosans.

In all cooking processes for separating vthe libers of straw and other fibrous vegetable material, the pulping agents should act upon the lignin to the greatest extent to bring about the most effective softening or solution of the incrusting constituents. The processes commonly used do so only with the dissolution and loss of considerable cellulose and pentosans.

Attempts have been made to diminish this loss bythe use of reducing substances such as sulphides, sulphites, and so forth, in conjunction with the cooking lyes.

In accordance with the present invention, it has been found that excellent results are obtained by soaking the fibrous material, such as straw or esparto, in solutions of caustic soda or potash at temperatures below 100 C. before disintegration of the material. By the term cold herein is meant temperatures below 100 C. in contrast Withthe higher or cooking temperatures in ordinary use.

The following table indicates the relative efficiency of typical cooking processes and the present caustic alkali process at room temasm ' perature, namely, about 25 C.

Loss of Pgg cellu- Lignm and ce1 Llgnins lose and re- Iulose pentomoved Composition of straw before Per cent Per cent .Per cem Per cent treatment 7 24. 1

Composition of ber after treati In the above table, itis noted that the cellulose and pentosans lost, are considerably 7, 1928. Serial No. 317,704.

and 2 are diagrammatic representations of the apparatus which may be used to carry out the process of this invention.

For carrying out the process of the present invention, it is preferable to employ a countercurrent method of soaking the fibrous material treated. For instance, as shown diagrammatically in the accompanying drawing, Figurev 1, there may be five sets of tanks numbered I, II, III, IV, and V connected in any suitable fashion by pipe lines as indicated.

-At a given time, one set of tanks is being filled, another set has had the fibrous material in soak vfor y three days and is being emptied, and the other three sets have had the straw in soak approximately one, two and three days respectively.

For example: Set I is being filled with straw and the straw in set V is finished and is removed to the mill for beating, washing, and manufacturing into paper. The straw in set II is completing its first day of soaking with liquor taken from set III and what is squeezed from the straw removed from set V. -The straw in set III has completed its first day of soaking in set II` and is completing its second day of soaking in liquor Vtaken from set IV. The straw in set IV has completed its first and second days of soaking in sets'II and III respectively and is completing its third day of soaking in fresh liquor.

Starting with fresh liquor containing about 15 grams ofcaustic soda per liter, after the first day of soaking in set IV, the concentration of the liquor is reduced to about 10 grams of act-ive caustic soda per liter. At the end of the soaking in set III the concentration of the liquor is about 6 grams per liter, and at thek earlier in the soaking process. For instance, l

about five tons of liquor are required to immerse one ton of straw. When the vstraw is removed from the liquor in 'a given tank, about two tons of liquor are held in each ton of the straw. Starting with dry stra'w in tank II it will be seen that only three-fifths of the required quantity of liquor is available from tank III. The other two-fifths are therefore obtained for tank II by squeezin out of the wringing Wet straw from tank V y means of squeeze rolls as shown in the diagram. The straw may be then washed out and the strongest of the wash waters used earlier in the soaking process.

Alternatively, the straw from tankV may be passed through a rod mill and the liquor removed by a dewatering or washing device after the straw has been properly pulped.

The rod mill or other beating device is operated between room temperature and 100. C. at atmospheric pressure. No pressure is permitted to develop in the rod mill and it is preferable to blow in as much steam as will condense without developing pressure. A tem* perature oi about 90 C. is thus obtained. As much as possible of the unconsumed alkali present in the straw is utilized by employing y eat in the rod mill during the pulping operation.

The pulped material from the rod mill is washed and the strongest of the wash liquors used in the first step of the soaking process. A suitable rod mill for performing this operation is shown in my Patent, No. 1,654,624,

issued January 3, 1928.

Instead of the series of tanks represented by Fig. 1, an apparatus such as that diagram matically'shown in Fig. 2 may be used, 1n the form of a long trough with straw fed in at one end and liquor at the other. The straw is carried slowl through the trough by means of some suita le conveying or raking device.

It issometimes desirable to subject the material to a digestion treatment after the soaking treatment. In this case, the soaking treatment would be carried on for the urpose of deligniying to the extent that 1t is Iplrofitable to go in the cold. Further delignication would be accomplished by digestion of the material in the liquor which it encountered after removal from the soaking treatment and at elevated temperatures up to 100 C. The second delignification results in a greater loss of pentosans and cellulose than was encountered in the soaking treatment, but the total loss in both treatments is much less thanin digestion at' elevated temperatures as commonly practiced.

Bfy the process of this invention, a more uni orm roduct is obtained than is obtained in the or inary processes in common use and cause the fibers separate into intact unit-s without rupture on account of the complete soaking it has had before the distintegration operatlon.

What I claim is 1. A process of separating the fibers of fibrous vegetable material, which process comprises soaking the fibrous material in a cold caustic alkali solution, and subjecting theusoaked material to treatment in a rod ml 2. A process of separating the fibers of fibrous vegetable material, which process comprises soaking the fibrous material in a cold caustic alkali solution, and treating the soaked material to steam in a rod mill.

3. A process of separating the fibers of fibrous vegetable material, 'which process comprises soaking the fibrous material in a cold caustic alkali solution, and treating the soaked material with steam in a rod mill at atmospheric pressure.

4. A process of separating the fibers of fibrous vegetable material, which process comprises soaking-'the fibrous material in a cold caustic alkali solution, and treating the soaked material with steam in a rod mill at atmos heric pressure below 100 C. to utilize the al ali left in the'straw from the soaking step.

5. A process of separating the fibers of fibrous vegetableI material, which process comprises soaking the fibrous material in a caustic alkali solution at a temperature below 100 C., and subjecting the soaked material to treatment in' a rod mill.

In testimony whereof I ailix my si ASIDNEY D.

ature. LLS.

Images