US1781449A - Method for manufacturing high-grade alpha cellulose - Google Patents

Description

Patented Nov 1 1, 1930 UNITED STATES PATENT OFFICE LAUBI I. DURCHMAN, OI PETEBSBUBG,

My invention relates to a new and useful method for manufacturing high-grade alphacellulose suitable for making explosives,

rayon, lacquers, etc., from unbleached easy 5 bleaching sulphate or soda-cellulose, independent of what kind of woodhas been used in the pulping process. This method as described below can wholly or partly be used for that, same purpose to treat sulphite or any kind in chemical way pulped suitable fibrous material.

The unbleached sulphate cellulose contains a large number of incrusting substances thus as lignins, pentosans, fats, waxes and rosins which give the pulp a certain color variable from pale yellow to dark brown. The ordinary kraft pulp contains about 7 585% of alphacellulose and the rest is beta and gamma cellulose known by the collective name hemicelluloses. To make the pulp easier for bleaching it has to be digested in a'certain known way with a certain amount of alkaline solution and at a certain pressure fora certain time. Thus digested pulp contains between 80-90% alphacellulose. But

still the incrusting substances and the color are very resistant against every bleaching agent so the pulp has to be given a certain treatment prior to the bleaching to avoid an excess of bleaching solution which would increase the bleaching costs and decrease the percentage of alphacellulose.

The present invention com rehends the preliminar treatment before leaching the cellulose, e bleaching of the cellulose with an alkaline bleaching solution, the treatment of thus bleached pulp with white liquor, (sulphate or soda) containing as main part NaOH and the final treatment with oxalic acid-v As above mentioned the cellulose has after it has been washed, screened and thickened to be given a treatment prior to the bleaching to dissolve and remove organic matters a which resist against the bleaching agents.

HIGH-GRADE ALPHA onLLULosE 1929. Serial No. 381,545.

This treatment has to' be carried out in an open tank using a mixture of from 2% to 5% sodium hydroxide (NaOH) or 'with corre sponding amount of so called white liquor and from 1% to 3% sodium sulphite (Na sO based on the dry weight of the cellulose for 5 to 6 hours. are obtained if this operation is done in a digester under certain conditions of pressure and time. Satisfactory results are obtained by cooking from 4 to 6 hours at a ressure of from 20 to pounds. This'coo ing ac- 'tion dissolves a great proportion of the lig- Better results 7 neous and resmous compounds and forms 4 water-soluble organic compounds which can be thus removed.

After being thoroughly washed and thickened the cellulose is to be bleached with an alkaline bleaching solution which contains from 13% of sodiumsulphite based on the bleaching powder which is used to make up the bleaching solution. The temperature after 2-3 hours bleaching can be raised to about 40-45 degrees C. The presence of alkali prevents oxidation and too quick bleaching action and decomposes certain ligneous and resinous compounds, so that the loss is only from 24%, while by using a calcium hypochlorite solution the losses are from 48%, and sometimes hi her. Itis referable to use two stage b caching ad ingat first about of the necessary amount of bleaching solution and after the chlorine is exhausted and the pulp thoroughly washed to add the second part or last A of the solution. The principle of this kind of bleaching is to chlorinate the liquors and other incrusting matters in the first sta e and to oxidize the coloring matters in t e second stage. The pulp has then to'be washed thoroughly, thickened and centrifuged to highest ossible d ness before adding the usual coo mg or white liquor containing Na s, M34003. and as main part NaOH. The total amount of alkali in this so-called white liquor is usually 120-180 gr. per liter and as effective NaOH 100-140 gr. per liter.

' This'treatment with alkali effects-the dissolving of the less resistant substances known as beta and gamma celluloses and depends ing upon the amount of alphacellulose in the pulp after the bleaching and upon the strength of the alkaline solution usedand of the time and temperature of the treatment,-certain grades of high alphacellulose ranging from 90100% can be obtained. By adding the alkaline '(white) liquor-to the bleached pulp it becomes a yellow greenish color which mostly disappears by adding a very small amount of acetic, lactic, or oxalic acid. If the color should not disappear the cellulose has to be treated with a small amount of bleaching solution for a short time. This treatment will restore and increase the whiteness of the pulp. The'white liquor such as used in the soda and sulphate pulp mills has to be well settled or filtered so it will not contain any sludge which would increase the ash and iron in the-pulp. After the treatment is finished the cellulose has to be centrifuged to highest dryness so' that the highest possible amount of used alkaline (white) liquor can be recovered and used without any treatment for cooking of the wood chips. The strong wash-water can be used for the first cooking treatment prior to the bleaching. The total recovered amount of white liquor is from 80-90%. For the manufacture of rayon, lacquers, explosives, films, etc., "a low ash and iron content is required so the cellulose after the alkaline treatment has to be given a treatment to remove the calcium and to dissolve the iron compounds.

I have discovered that oxalic acid is a very suitable agent to use-because it dissolves the iron and precipitates the'calciumcompounds which are in or around the fiber cells, not completely, but to a certain extent. An absolutely complete precipitation of the calcium'compounds is not possible without using a great excess of oxalic acid and. thereby decreasing the alphacellulose' percentage through oxidation by the strong organic acid solution because the organic matters in the fibers prevent the influence ofthe acid to react completely with the calcium compounds. The. amount of oxalic acid necessary to precipitate the calcium compound is dependent upon the amount of ash the pulp contains after the strong alkaline treatment, but 6 8% oxalic acid based on the dry-weight of the pulp gives an excess of joxalic'acid Which is necessary to reach the desirable precipitation of calcium compounds m at cium oxalates. Abou.t8090% of the used 1 Fourdrinier or fSargent drying machine:

illustrated Eapy Teaching pulp (sulphate 9094% alphacelluose . Washed, screened and thickened.

I, Digesting in open tan k With Na0H(2-5%) Na S0 (13%) based on air dry weight of the pulp.

centrifpging Strong liquor to the wash pans.

washmg Weak liquor to the sewer.

Bleaching, washing and centrifuging.

.Strong liquor to chip In Treatment with white (11 stlon liquor containing} ng igie H t .1 t

' quor o s from10 14% NaOH treatment.

Centrifuging and washing.

1 Treatment with 6-8% weight of the pulp.

IV oxalic acid based on air dry 1 centrifuging and washing. Oxalic acid for reuse.

l V Drying of the 97-99% alphacellulose.

Having thus fully described my said invention, what I claim as new and desire to secure by Letters Patent, is:.

1. The process of treating chemical wood pulp to convert incrusting substances into water-soluble compounds comprising treating the pulp for a period of four to six hours at 20 to 60 pounds pressure with a solution containing 2% to 5% NaOH and 1% to 3% a a- I 2. The process of treating cellulose material to remove incrusting substances therefrom which comprises treating such cellulose material for a period of four tosix hours with a mixture of from 2% to 5% sodium hydroxide and 1% to 3% sodium sulphite at a pressure of from 20 to 60 pounds.

3. The process of treating chemical wood pulp to convert incrusting substances into water-soluble compounds comprising treating the pulp for a period of four to six hours at 20 to 60 pounds pressure with a solution containing 2% to 5% NaOH and 1% to 3% Na SO bleaching, and thereafter treating the bleached pulp at room temperature for three to five hours with white liquor to effect removal of incrusting substances for obtaining a high grade alphacellulose.

4. The process of treating chemical wood pulp to convert incrusting substances into water-soluble compounds comprising treating the pulp for a period of four to" six hours at 20 to 60 pounds pressure with a solution containing 2% to 5% NaOH and 1% to 3% Na' SO bleaching, thereafter treating the bleachedpulp at room temperature for three to five hours with white liquor to effect removal of incrusting substances for obtaining a high grade alphacellulose, washing, and

treating the pulp with an organic acid to neutraliz'e residual alkali and to extract other residual and coloring impurities thereby re- 111% pu p with:

storing the whiteness of pulp discolored by treatment with white liquor. I

. '5. The pulp to convert incrusting substances into water-soluble compounds comprising treating the pulp for a period of four to six ours at to 60 pounds-pressure with a so ution containin 2% to 5% NaOH and 1% to 3% Na SO leaching,

rature for three to five hours with white hquor to effect remoVal of incrusting substances for obtaina high grade alphacellulose, treating the oxalic acid to precipitate the cal- 5 mm compounds and to dissolve the iron the iron and calcium com oun compounds, and washing the gsulp remoye In testimony whereof "aifixm si ature. v LAURI I. LrDUR HfiiLN.

process of treating chemical wood I thereafter treating the bleached pulp at room tem