US3055794A - Method of deresinifying cellulose derived from wood rich in resin - Google Patents

Description

3,055,794 METHOD OF DERESINIFYENG CELLULOSE DE- RIVED FROM W001) RICH IN RESIN Olof Bertil Lundn, Harnas, Karl Esbiiirn Eftring, Falun, and Bertil Fredrik Bjelke, Skutskar, Sweden, assignors to Stora Kopparbergs Bergslags Aktieholag, Faluu, Sweden, a corporation of Sweden No Drawing. Filed Nov. 30, 1956, Ser. No. 625,233 Claims priority, application Sweden Dec. 1, 1955 6 Claims. (Cl. 162-86) In the manufacture of cellulose from wood rich in resin, such as pine, it is necessary to remove most of the resin before straining the wood pulp, so that the pulp will be capable of being strained and guided on in the paper mill without resin trouble arising. The amount of resin permissible in the finished pulp so that no resin trouble will arise depends on a large number of factors which manifest themselves to a different degree in different paper mills. It has been found in practice that the content of extractable resin in the pulp should be less than 1%, if a tolerably good guarantee against resin troubles is to be obtained.

When digesting hearty pine wood i.e., pine wood having a high content of heart wood, using, e.g., the sodium bisulphite method, the cooked pulp, after removal of the spent sulphite liquor in the ordinary way, contains 2 to 5% of resin. It has been suggested before now to treat such pulp with sodium hydroxide lye to as to remove the resin. Thus Norwegian Patent No. 56,432 describes a method in which the pulp is treated, at least pulp concentration, with NaOH under vigorous pounding for the purpose of defibrating the fibres to such extent that the resin can be squeezed out and made accessible to the dissolving influence of the sodium hydroxide lye.

Renewed, detailed experiments have now shown that it is possible to reduce the resin content in sulphite pine pulp rich in resin appreciably below one percent in a simpler way and one less detrimental to the fibres, viz. without appreciable mechanical action on the fibre mass, if the pulp is produced according to the bisulphite method using a base forming soluble soaps with resinous and fatty acids.

In one series of experiments a pulp produced by cooking with sodium bisulphite in two stages and released from sulphite lye in a diffuser was treated at 3% pulp concentration and 20 C. under gentle stirring with varying amounts of sodium hydroxide lye for diiferent periods. The pulp Was then exposed to a weak vacuum on a vacuum filter bed and washed with water.

The resin content of the mass (in percent resin calculated per 90% pulp) was found as- Untreated pulp: 3.6% resin Alkali-treated pulp:

It is thus possible, with a few minutes simple stirring at low pulp concentration, to get down to resin contents below 1%, by using between 1 and 3% NaOH, calcu lated on the basis of the dry pulp. Repeated tests have shown that in certain cases less than 1% is sufiicient for obtaining resin contents of about 1%.

Good results have also been obtained with, e.g., soda and other alkaline salt solutions, pH-values between 9.0 and 12 having been found to be particularly suitable. Acidification may be carried out immediately after resin extraction, but a somewhat lower resin content is often 3,fi55,794 Patented Sept. 25, 1962 ice obtained, if the pulp is previously concentrated and/or pressed out.

It is seen that the resin can in this way, by gentle treatment at low pulp concentration and low temperature, be extracted from the fibres without extraction being preceded by mechanical action according to Norwegian Patent No. 56,432. It can be shown by microscopic investigation that the resin is, to a large extent, dissolved out of the meristem fibres also, and that it is therefore not necessary, in order to reduce the resin content, to remove these by the so-called Schibby process wherein short fibres containing resinous materials are screened out, or the like. It has thus proved possible to deresinify the pulp without any stirring at all, eg in a diffuser, in connection with the removal of lye and washing of the pulp. The same good results are also obtained with continuous counter-current washing, 'e.g. on rotating filters or plane filters. By mixing the washing liquid, at a convenient stage of the washing cycle, with a quantity of sodium hydroxide lye corresponding, e.g., to 1 to 3% of the quantity of pulp, it is possible immediately to obtain a pulp containing less than 0.5% of resin. This can be done without appreciably lengthening the duration of the washing cycle. It is thus a distinctive feature of the invention that the pulp, if desired, can be deresinified without stirring by treatment with alkaline solutions of, e.g., sulphite lye and/or water.

At which stage in the treatment the alkali should be added depends on the form in which it is desired to obtain the resin. In certain cases it may be useful first to wash with dilute lye from a previous cooking step, then with alkalised dilute lye of said kind and/or water and finally to wash with water. In this way the resin solutions are obtained separate from concentrated or diluted lyes, respectively.

It has been found possible to carry out deresinification of the pulp by supplying, to a diffuser charged with pulp and spent liquor, alkalised solutions of spent sulphite liquor (possibly strongly resinous) and/or alkalised water. During passage through the acid pulp the alkali is wholly or partly absorbed, the pH of the solution sinking in the process. In case the solution supplied contains soluble resin soaps and/or fatty acid soaps, these are precipitated in finely dispersed form as acids, which will not, however, fasten on the pulp but will be carried along by the passing solution. Acids dissolved out of the alkali when the solution enters the pulp behave in the same way. It is seen that in this way free, suspended organic acids can during the washing process be transferred to the strong liquor, and their heat of combustion can be utilised while they are burnt (in a series of such tests 6075% of the resin content of the mass could be transferred to the strong liquor). Towards the end of the washing process the pH-value has risen to such an extent that the acids are kept in solution. These solutions may advantageously be used in the next washing process in the diffuser.

By taking care that suitable concentration and temperature conditions prevail in different solutions it is possible to achieve that a layer of strongly alkaline solution slowly sinks down through the diffuser, preceded by, e.g., acid strong liquor and followed by solution with relatively low but still alkaline pH-value.

It has further turned out that unsaponifiable and thus in themselves insoluble resinous materials are, during the dissolution of resinous and fatty acids, dispersed and removed from the pulp to a considerable extent. The resin content of the solution removed, eg the strong liquor, gets particularly high if base addition is in the main carried out at the start of the washing process with alkaline solution. Hence an advantage of the washing quired for deresinification can be transferred to the strong waste liquor and recovered after this has been burnt. By burning the resinous material simultaneously with the dry portion of the waste liquor their heat of combustion is therefore utilised and it is, moreover, achieved that pollution of water courses by them is prevented or substantially reduced.

Strong liquors containing up -to 1% or more of resin can be fermented to yield alcohol etc. in the usual way.

Under certain circumstances it is advantageous to alkalise the solutions with a buffer salt, e.g. soda and, besides, possibly NaOI-I. By this it is achieved that the pH-value of the supplied solution can be kept lower, which may be favourable for the colour of the pulp. It has turned out to be particularly useful to start the washing process with a high pH-value, which should, however, preferably not exceed about 12 and more preferably not exceed 11.2, and to use a lower pH-value for the following washing operation, e.g. 9-11.

Certain precautions have to be observed in carrying out such a deresinification. Thus it is true that the temperature may advantageously be above 20 C., though preferably not above 60 C. for an extended period, but it has turned out that a combination of raised temperature and raised alkali concentration can produce discolouration of the unbleached, lignin-containing pulp. This discolouration, it is true, may for the most part disappear during subsequent washing and acidification, if any, but it may unnecessarily give the finished pulp a somewhat reduced whiteness compared with what is normal.

It is useful, for instance when emptying the diffuser, when the pulp is usually diluted with water, to mix it with some acid (S or H 80 so as to prevent precipitation and staining of lime soaps. Favourable results have also been obtained by acidification of the water at the end of the washing process.

It is also useful to start adding sodium hydroxide liquor while the pulp is slightly acid and before it has been treated, at a relatively high pH-value (e.g. above 4) with larger amounts of calcium-containing water, for the Ca ions may combine with resinous and fatty acids and render their release in a subsequent alkaline treatment more diflicult.

If a very low resin content is desired, e.g. down to about 0.1 to 0.2%, it is useful to suspend the pulp deresinified as above and in suspension give it an after-treatment with small quantities of base. If desired, the mass may subsequently be acidified.

In the example below is shown a Way of carrying the invention into effect. 7

In a diffuser (blowing tank) containing pine pulp of 16 tons dry weight made soluble by means of sodium bisulphite and for the rest filled with sulphite liquor of a dry weight content of 17% (strong liquor), washing was started with medium liquor from a preceding diffuser washing operation of the same kind. This medium liquor, which had a dry weight content of 9.5%, contained resin (dissolved from the preceding cook) in the form of a suspension and as-a solution of alkaline soaps, and besides 300 kg. added sodium carbonate. This solution was fed to the diffuser at a speed of 40 m. /h. Hereupon the pulp was washed with dilute liquor of a dry weight content of 4%, also obtained from a preceding washing operation of the same kind and with a pH-value of about 9 and holding substantial amounts 4 of resin in suspension. The pulp was subsequently washed clean with water.

The un-washed pulp contained 4.1% of resin (methylene chloride extract), i.e. 650 kg. After the mass had been washed in the way described above, it contained 0.65% of resin and, after having been strained and passed on to the dryer, 0.55%, i.e. kg. of resin. In the strong liquor were to be found 420 kg., i.e. 65% of the original resin content of the pulp, whereas it follows that only kg. of resin had run off in the washing water or the like.

The strong liquor was cooked down and burnt, after which the 300 kg. soda used for washing were found accessible in the melt from the oven and could be recovered the form of sodium bisulphite to be used in the next cook. Combustion of 420 kg. of resinous material produces about 4.5 tOns of steam, i.e. 280 kg. of steam per ton pulp mass.

What we claim is:

1. A method of producing cellulosic pulp having a low resin content from wood rich in resin comprising preparing delignified pulp by completely cooking said wood with a sulphite cooking liquor containing a base which forms a soluble soap with resinous and fatty acids, and then washing the delignified pulp containing sulphite cooking liquor with an aqueous alkaline solution having a pH between 9 and 12 at a temperature between about 20 C. and 60 C. without substantial agitation for a period of up to about one hour and prior to any other washing step to remove resins without further modification of the pulp and then further washing with water the quantity of alkali in said solution amounting to from 1 to 3% by weight of the pulp, on a dry basis.

2. The method of claim 1 wherein said pulp is washed in a diffuser with a mixture of the alkaline solution and sulphite liquor from a preceding washing operation to which additional aqueous alkaline solution has been added followed by said further washing with clean water.

3. The method of claim 1 wherein the aqueous alkaline solution comprises sodium hydroxide.

4. A method as claimed in claim 1 wherein said a1- kaline solution is buffered with soda.

5. A method as claimed in claim 1 wherein said treatment is carried out at 20 C., with sodium hydroxide in the absence of any substantial agitation of said pulp using a pulp concentration of 3% and a quantity of sodium hydroxide amounting to 1 to 3% of the quantity of dry pulp.

6. A method as claimed in claim 1 wherein said pulp is pine pulp.

References Cited in the file of this patent UNITED STATES PATENTS 1,640,853 Richter Aug. 30, 1927 1,742,219 Richter Jan. 7, 1930 1,841,551 Richter Jan. 19, 1932 1,880,044 Richter Sept. 27, 1932 1,899,637 Richter Feb. 28, 1933 2,385,955 Tomlinson Oct. 2, 1945 2,508,043 Schaefer May 16, 1950 2,528,350 Farber Oct. 31, 1950 2,542,801 Dela Roza Feb. 20, 1951 FOREIGN PATENTS 16,092/28 Australia 596,164 Great Britain Dec. 30, 1947 458,897 Canada Aug. 16, 194

Claims (1)

1. A METHOD OF PRODUCING CELLULOSIC PULP HAVING A LOW RESIN CONTENT FROM WOOD RICH IN RESIN COMPRISING PREPARING DELIGNIFIED PULP BY COMPLETELY COOKING SAID WOOD WITH A SULPHITE COOKING LIQUOR CONTAINING A BASE WHICH FORMS A SOLUBLE SOAP WITH RESINOUS AND FATTY ACIDS, AND THEN WASHING THE DELINGIFIED PULP CONTAINING SULPHITE COOKING LIQUOR WITH AN AQUEOUS ALKALINE SOLUTION HAVING A PH BETWEEN 9 AND 12 AT A TEMPERATURE BETWEEN ABOUT 20 C. AND 60*C. WITHOUT SUBSTANTIAL AGITATION FOR A PERIOD OF UP TO ABOUT ONE HOUR AND PRIOR TO ANY OTHER WASHING STEP TO REMOVE RESINS WITHOUT FURTHER MODIFICATION OF THE PULP AND THEN FURTHER WASHING WITH WATER THE QUANTITY OF ALKALI IN SAID SOLUTION AMOUNTING TO FROM 1 TO 3% BY WEIGHT OF THE PULP, ON A DRY BASI