US1730383A - of berlin - Google Patents

Description

Patented Oct. 8, 1929 UNITED STATES FATE FFEE GEORGE A. RICHTER, OF BERLIN, NEW HAMPSHIRE, ASSIGNOR TO BROWN COMPAHY, OF BERLIN, NEVI HAMPSHIRE, A CORPORATION OF MAINE GYGLIC PROCESS OF FIBER LIBERATION No Drawing. Application filed May 19,

This invention relates to a cyclic process of liberating fiber from raw cellulosic materials, such as wood, and has for its object the production of a high grade, easily bleachable pulp, suitable for use, for example, in the manufacture of bond, ledger, and writing papers and as a raw material for the production of a refined fiber of high alpha cellu' lose content.

There are at present being commercially practised various chemical processes of fiber liberation from raw cel'lulosic materials such as wood, these processes involving the use of cooking liquors of either an acid or alkaline character and the digestion of the Wood in a chipped condition in the liquor under pressure and at elevated temperature until a liberation of the fibers from the encrusting material of the wood has been effected. One of the widely usedprocesses fortheproductionof an easily bleachable pulp used in the manufacture of high grade white papers is the so-called acid sulphite process, the cooking liquor usually being a sulphurous acid solution of calcium bisulphite. When such a cooking liquor is employed, it is the custom to discharge the spent liquor resulting from digestion into nearby waterways, owing to the difficulty of regenerating the spent liquor economically. Not only does this cause a pollution of the waters into which such spent liquors are discharged and the destruction of piscatorial lite therein, but also a loss of the valuable components of the spent liquor.

I have discovered that it is possible to pr0- duce a high grade pulp by employing a cooking liquor comprising a sulphurous acid solution of sodium-boron salts, such as borax, the temperature, pressure and time necessary for liberating the pulp from Wood being substantially similar to the I conditions maintained when producing the usual commercial sulphite pulp. One of the major advantages of the process of the present invention is that it makes possible an economical cyclic process, as the spent liquor resulting from digestion may be concentrated and its organic content then burned and its inorganic content smelted to produce a smelt which when dissolved in aqueous solution and acidified with 1328. Serial No. 279,205.

sulphur dioxide is suitable for reuse in the pulping of other raw cellulosic material.

l Vhen sodium-boron salts, such as borax, are dissolved in a sulphurous acid solution in producing the cooking liquor of the present invention, a metathesis probably takes place to produce sodium sulphite and free boric acid according to the following equations:

zia s ow H3305 ee oaia so 415 120 Doubtless the sodium sulphite is the chemical which under the acid conditions prevailing in the liquor... reacts with and dissolves the encrusting material of the wood, thereby liberating its fibers. As the sodium sulphite is consumed by reaction, more sodium sulphite is generated according to the reac .tion hereinbefore given, so that the borax is progressively converted into sodium sulphite and free boric acid. Boric acid, being a comparatively weak or lowly ionized acid, does no injury to the pulp, but apparently aids the sulphurous acid in hydrolyzing the encrusting material. Furthermore, being comparatively involatile, it does not escape from the liquor when sulphur dioxide is released thereu from during the latter stages of cooking and so remains in the cooking liquor. Consequently, when the spent liquor resulting from digestion is subsequently neutralized, for instance with sodium carbonate, borax or other sodium-boron salts are again produced, and remain as such during the subsequent smelting operation, the resulting smelt consisting of a mixture of sodium-boron salts such as sodium borate sodium carbonate, and so- S0 content is about 5%. The borax used as a raw material may be used in crude condition, that is, as found in nature, the liquor preferably being filtered before being used. Chipped wood, e. g., spruce chips of 7 size, may be digested in a cooking liquor of the composition described, under practically the same conditions as are ordinarily maintained during acid sulphite digestion. To this end, a charge of liquor and chips may be introduccd into the usual digesters of the acid type and then gradually heated to a temperaure of about 255 to 285 F., and brought up to a pressure of about 45 to 75 pounds. After digesting under these conditions for about eight to twelve hours, it will be found that a comparatively high yield of a light colored pulp quite similar in appearance to the ordinary sulphite pulp has been produced. l i hen the pulp is tested, it will be found that it is characterized by a tear resistance higher than that of the ordinary sulphite pulp, this of course being advantageous in the manufacture of high grade papers. The pulp is readily bleachable to whiteness and serves well as a raw material for refining to a white fiber of high alpha cellulose content. The desirable characteristics, including high s rength and tear resistance, of a raw pulp produced according to the present invention remain associated with such pulp through subsequent chemical refining treatments, so that such pulp offers advantages over the usual sulphite pulp for use as a raw material in the production of a white wood fiber refined to high alpha cellulose content and intended foruse as a new rag fiber substitute in the manufac ture of high grade papers. 7

The spent liquor resulting from digestion may be neutralized with borax. sodium carbonate, or other suitable alkaline compounds. The chemical used for neutralization may be taken from the smelt while the cycle is being practised, suiiicient additional neutralizing chemical being added along with the smelt chemical to make up losses in the cycle. The neutralized spent liquor may then be concentrated as by multipleeifect evaporation to a total solids content of, say, about 50%, whereupon the concentrated liquor may then be de livered into a smelting furnace wherein its combustible content may be burned and its inorganic content smelted, preferably in an oxidizing atmosphere. The resulting smelt will consist essentially of sodium-boron salts such as sodium borate, sodium carbonate, and sodium sulphate so that when dissolved with the proper amount of water and acidulated with sulphur dioxide, a liquor suitable for cooking fresh chipped wood is produced.

lVhile the foregoing example gives a cooking liquor of one composition, it is to be un- 'derstood that the composition of the liquor may be varied. For instance, along with the borax I may employ other fiber-liberating chemicals, such as niter cake (NaHSOQ or salt cake (Na SOQ. These chemicals doubtless undergo metathesis in sulphurous acid solution during cooking to yield sodium sulphite and sulphuric acid, which, of course, is a much stronger acid than boric acid. Apparently as a result of the fact that a cooking liquor in which sodium-boron salts are employed is of weaker acidity than a liquor in which only salt cake or niter cake is employed, I am enabled to produce pulps of higher average fiber lengths and accordingly of greater tear resistance. In other words, owing to the weaker acidity or lower hydrogen ion concentrat-ion in such cooking liquors as I employ in carrying out the process of the present invention, it is quite likely that less fiber hydrolysis takes place during cooking, so that a comparatively high yield of excellent pulp is obtained. I may also add a certain amount of free boric acid to the cooking liquor, so as to increase the amount of free boric acid present during digestion and thus make possible the realization of a higher percent of sodium borate in the smelt produced from the spent liquor of digestion. Boric acid, being as already stated a comparatively weak acid, does not, if added in reasonable amount, materially affect the yield 01' quality of the resulting pulp.

Having thus described certain embodiments of this invention, it is evident that various changes and modifications may be made therein without departing from the spirit or scope of invention as described by the appended claims.

lVhat I claim is 1. A. process which comprises digesting raw cellulosic material under fiber liberating conditions in a sulphurous acid solution containing sodium-boron salt-s.

2. A process which comprises digesting raw cellulosic material under pressure and at elevated temperature in a sulphurous acid solution containing bora-X until fiber liberation has been effected.

3. A cyclic process which comprises digesting raw cellulosic material under fiber liberating conditions in a sulphurous acid solution containing boraX, separating the resulting fiber from the spent liquor of digestion, and smelting and recovering the inorganic content of the spent liquor for the prepara tion of a fresh cooking liquor.

4. A cyclic process which comprises digesting raw cellulosic material under fiber liber ating conditions in a sulphurous acid solution containing boraX, separating the resulting fiber from the spent liquor, neutralizing and concentrating the spent liquor, burning the combustible content and smelting the inorganic content of the concentrated liquor, and recovering the smelt for the preparation of a fresh cooking liquor.

5. A cyclic process which comprises digesting raw cellulosic material under fiber liberating conditions in a sulphurous acid solution containing borax, separating the resulting fiber from the spent liquor, neutralizing and concentrating the spent liquor, burning the combustible content and smelting the inorganic content of the concentrated liquor in an oxidizing atmosphere, recovering the smelt in aqueous solution, and acidulating the solution with sulphur dioxide to produce a fresh cooking liquor.

In testimony whereof I have aliixed my signature.

GEORGE A. RICHTER.