US1880043A - Production of high grade chemical pulps - Google Patents

Description

UNITED" STATE Patented Sept. 27, I

s PATENT OFFICE GEORGE A. RICHTER, OF BERLIN, NEW HAMPSHIRE, ASSIGNOR 'IO BROWN COMPANY, OF BERLIN, NEW'HAMPSHIRE, A CORPORATION OF MAINE PRODUCTION OF HIGH GRADE CHEMICAL PULPS 1T Drawing.

This invention relates to the production of cellulose pulps or kindred raw cellulosic material, beingmore particularly concerned with the so-called chemical pulps in the production of which chemical liquors are emkaline character, e. g.,

indifferent chemical liquors do not act in the same way' upon the non-fibrous or upon the fibrous constituent of the wood. The acid liquors containing bisulphites are more selective in their action on the pentosans than are :0 the alkaline liquors, but the resulting pulp in either case has a substantial residue of pen-- tosanS,-amounting to as high as 3% to 4% in' the usual commercial sulphite pulps and to as high as 8% to 10% in the usual commercial kraft and soda pulps. It is possible to remove pentosans from wood pulps by chemical refining processes which include the step of treating the raw pulp under suitable conditions-with solutions of alkalies, but such solutions are not especialy effective or coni- "plete in their action even over considerable periods of time. 3

The production of wood pulps low in pentosan content-and other non-alpha cellulose components is highly desirable when such pulps are to be used in the preparation of cellulose derivatives suchas the nitrate, acetate, and xanthate, and in the manufacture of high grade papers, as it has been found that the" freer the wood fiber is from nonalpha cellulose components including pentosans, the better is the quality, color and stability of its derivatives, and the more near- 1y do papers made therefrom approach the qualities of new-rag papers.

I have found that if .wood chips, e. g.,.

spruce, or kindred raw cellulosic material is initially treated with a solution of a mineral acid, and more particularly one which is highly ionized in water, and is then cooked at Application filed December 18, 1929. Serial No. 415,124. r

elevated temperature and under pressure in a solution of a suitable alkali, for instance in the usual kraft or soda liquors, it is possible to produce cellulose pulps of high alpha cellulose content and of exceedingly low pentosan content. The resulting product may have an alpha cellulose content of from i 94% to 98% and a pentosan content of less than 1%, depending upon the particular conditions under which the initial treatment with acid solution and the subsequent cooking in alkaline liquor are carried out. In bleached condition, the product is eminently suitable for use in the papermaking and derivative industries. One of the major ad-' vantages of the process is that it may be controlled to produce a product of unusually low solution viscosity, as-some derivatives,

such as the lower nitrocelluloses intended for l lacquer manufacture, must have low solution viscosity. Whereas it is necessary to subjectthe usual fibers or derivatives to special chemical treatments designed to bring about a lowering of solution viscosity, the product of the present process need not requlre such treatment. I do not, however, herein claim the product, as this subject matter has been described more fully and claimed in my application Serial No. 435,962, filed March 14, 1930.

, Evidently the use of mineral acid solutions in the initial treatment causes a substantially complete hydrolysis of the pentosans into soluble sugars and other reaction products which are readily soluble in alkaline cooking liquors. The initial treatment is not in the nature of a fiber-liberating operation, sinceeven When sulphurous acid solutions are used, they should be substantially free from bisulphites, which promote fiber liberation by reacting upon and dissolving the ligneous a strongly acid liquor, it is essential that the I i be effected while the wood particularly advantageous,

acid solution ers are bound together and are associated with more reactive constituents, which evidently protect the fibers from degradation by undergoing reaction themselves. ment may also transform the alpha cellulose to a form profoundly diiierent from that present in wood pulp, such as sulphite or kraft, for not only may the final product be of surprisingly low solution viscosity when tested by the usual cuprammoniumcellulose solution standard, but other derivatives, such as the nitrocelluloses prepared therefrom, have even lower solution viscosity than similar derivatives prepared from other fibers whose cuprammonium cellulose solution viscosity has been lowered by one or more special treatments to the same value as that possessed by a cuprammonium cellulose solution prepared therefrom.

In the initial treatment ofthe wood chips with an acid solution, various acids and or acid salts and various conditions oftreatinitial treatment with strolgi ment may be used. The acids or acid salts employed,however, should be comparatively strong or highly ionized in a ueous solution and to this end mineral aci s such as sulphuric, sulphurous, nitric, and hydrochloric, or acid salts of, these acids, are suitable, since they effect the desired reaction upon the pentosan content of the wood. The use of involatile mineral acids such as sulphuric is inasmuch as there is no liberation of obnoxious gas from the solution even when the treatment is carried out at boiling temperatures in open tanks. If desired, a sufliciently strong solution of such mineral acids may be used'so that the desired reaction takes place under room temperature conditions, under which conditions the use of special apparatus and steam is avoided. For instance, when using concentrated acid solutions of from 15% to 35% acid content, the treatment may be carried out'under atmospheric pressure condi-. tions of, say, from 20 to 40 C. for a period of about one hour, but the use of dilute acid solutions of, say, an acid content of about 1% makes necessary the use of much higher temperatures, for instance, 100 C., or higher, and a periodof treatment of about two hours.

The acid liquor associated with the wood after the treatmentis of dark brown color as a result of the solution of organic matter and the hydrolysis of pentosans present in the wood to soluble sugars. When a strong sulphuric} or other acid solution is initially employed, separated from the wood and employed wholly or in part for the treatment of other raw wood, but if too dilute or contaminated for reuse, its'sulphur content, in the case of sulphurousor sul huric acid solutions, may

recovered by m xing it with the spent alka- The initial acid treat-v it may be drained or otherwiseline liquor recovered from the second cooking step before the latter is subjected to the well-known recovery treatment practised in the kraft process? solutions or of niter cake solutions in the acid treatment of the wood is not only advantageous for those reasons already glven, but

The use of sulphuric acid because these chemicals are comparatively inexpensive and furnish a high concentration of hydrogen ion, which evidently favors the desired hydrolyzing action on the pentosans. These chemicals are further advantageous,

in that the sulphur content of the spent acid may be of high sulphidity, may be advanmy process, as it is preferable to use one containing sodium sulphide, because the resulting pulp has better physical characteristics and is more easily bleachable.

The acid-treated wood is of much darker' color than the raw wood, usually being of a reddish hue. While it may be readily crushed at this stage into fragments, nevertheless it is so high in ligneous matter that it does not lend itself'to ready disintegration into a pulp suitable for conversion into paper or derivatives. The wood is preferably washed free of residual spent acid liquor before it is subjected to cooking in an alkaline liquor which, as previously stated, preferably consists of a solution of sodium hydroxide and sodium sulphide and may beef a concentra- I tion and composition similar to that used in the kraft process. The chips may, for example, be cooked in a liquor containing about 1.5 1pgunds of alkali per cubic foot, both inthe fo' of caustic soda and sodium sulphite, thealkali compound being calculated as active Na O. The sulphidity of the liquor may amount to about'40%,which corresponds to the sulphidity of a typical kraft liquor.

The smelted compounds, which I tageously employed in-the production of the I alkaline cooking liquor for the second step of The cooking-operation mayfbe carried out in the usual alkaline digester and the digester contents may be heated to a maximum tempe'rature of from 300 to 335 F. in two.

hours, after which the digester. contents may be maintained at this temperature with a- .of about 100 I corresponding steam pressure pounds for about two hours. At the end of this cooking operation, the wood has been converted into a pulp, so that the digester may be blown as usual and the pulp washed free of spent 1i uor. The pulp may be'con- 'verted to a pro uct of high whiteness by the use of hyp ochlorite bleach liquor, but to bleaching operation, it is -in asolution containing 1% .at a suitable stock consistency wlth about 1% chlorine, based on the weight of dry pulp, whereupon it may then be washed, digested caustic soda, based on the weight of dry pulp, and a ain washed. Thereupon it may be blcache to a high degree of whiteness with only about 2% hypochlorite bleach, based on the weight of dry pulp. In order to preserve the hi h alpha cellulose content of the pulp during t e bleaching in a hypochlorite liquor containing a slight amount of free alkali, such as caustic soda, and to maintain such liquor at a temperature of between and 120 F. In lieu of hypochlorite bleach, other bleaches, such as permanganates, peroxides, perborates, or the like, may be employed.

In the initial treatment of the raw cellulosic material with a mineral acid solution, it may be desirable to add a small amount of suitable oxidizing or reducing agent to the solution when the acid itself does not act as such, as the presence of such agents often accelerates the desired-modification in the raw material and, in the case of reducing agents, sometimes improves the papermaking characteristics of the finished product. For instance, whena solution ofsulphuric acid is employed, an oxidizing agent such as permanganate may be added thereto, but no such addition need be made to a solution of nitric acid, which itself is an oxidizing agent.

One ofthe major advantages residing in a process such as described is that it is possible to produce a product having the desirable characteristics mentioned, by the use of comparatively inexpensive chemicals and by rapid treatment in inexpensive apparatus. In producing refined pulps from wood or kindred raw cellulosic materials, it has here tofore been the practice to repare acraw wood pulp such as sulphite or raft, and then to dissolve non-alpha cellulose components from such pulp by the use of alkaline liquors. Aside from the fact that such a process does not result in a product of minimum pentosan content or of exceedingly low solution viscosity, strong alkalies, such as caustic. soda, are much more expensive than acids such as sulphuric, and it is generally necessary to consume, as much, if not more, of such alkali to produce a given weight of finished pulp.

I claim:

1. A process which comprises treating chipped rawwood with a solution. of sulphuric acid to effect reaction more particularly upon the pentosan content of the wood, and then cooking the wood at elevated temperature and under pressure in an alkaline liquor to effect fiber liberation into a pulp of high preferable to effect alpha cellulose content viscosity.

and low 'solut ion 2. A process which comprises treating chipped raw wood with a hot, dilute solution of sulphuric acid to efiect reaction more particularly upon the pentosan content of the wood, and then cooking the wood in'an alkaline liquor under pressure to efiec't fiber liberation into a pulp of high alpha cellulose content. and low solution viscosity.

3. A process which comprises treating chipped raw wood witha solution ofsulphuric acid to effect reaction more particular- 1 ly upon the pentosan content of the wood, washing the wood, and then cooking the washed wood in an alkaline liquor under pressureto efiect fiber liberation into a pulp of high alpha cellulose viscosity.

4. A process which comprises treating chip ed wood with solution of niter cake to e ect reaction more particularly upon the pentosan content of the wood, and then cooking the wood in an fiber liberation.

5. A process which comprises treating chipped wood with a solution of sulphuric acid to efi'ect reactio:;. more particularly upon the pentosan content of the wood, and then cooking the Wood to eifect fiber liberation in 3.11: (elkaline liquor containing sodium sul' p l e. I

6. process which comprises chipped raw Wood with a solution phuric acid to effect reaction more particularly upon the entosan content of the wood, and then coo ing the wood at elevated tem-' perature and under pressure in an alkaline liquor containing sodium sulphide to effect fiber liberation into a high grade paper-making pulp of high alpha cellulose content and low solution viscosity.

In testimony whereof I have affixed my signature.

' GEORGE A. RICHTER.

treating of sulcontent and low solution alkaline liquor to effect Ill