316
IXDUSTRIAL AND ENGINEERING CHEMISTRY
(3) Newman, Trans. Am. I n s t . Chem. Eng., 27, 310 (1931).
Vol. 25, No. 3
(8) Sherwood, Trans. Am. Insf. Chem. Eng., 27, 190 (1931); IND.
ENG.CHEM.,24, 307 (1932).
(4) Newman, Ibid., 27, 203 (1931).
(5) Sherwood, IND. ENO.CHEM.,21, 12 (1929). (6) Sherwood, Ibid., 21, 976 (1929). (7) Sherwood, Trans. Am. Inst. Chem. Eng., 23, 28 (1929); 1x0. EXG. CHEM.,22, 132 (1930).
RECEIVEDNovember 11, 1932. Presented before the meeting of the American Institute of Chemical Engineers, Washingt,on, D. C., December 6 to 9, 1932.
4ction of Salt Solutions on Wood Cellulose
I
ERICHRICHTER,Desbiens, Quebec, Canada
T
HE action of salt soluused. However, an opportunity Floating in sea water f o r some time contions on cellulose in the to follow the results of these taminates the cellulose-lignin fiber of wood by form of wood or comphysical tests was given in other the absorption of small quantities of salt (0.020 m e r c i a l sulfite p u l p , e i t h e r west e r n mills which produced per cent hydrochloric acid was found to be a bleached or unbleached, has rebleached sulfite. One example maximum amount in the digester liquor for cently again been the subject of (averages of about two-hundred tests for each month) is given in study (4, 6). The experiments unaffected wood; it corresponds to about 0.20 Table I. Other western m i l l s were generally m a d e with per cent on wet and to about 0.50 per cent on producing bleached sulfite also concentrated s o l u t i o n s o n a dry wood substance). For contaminated wood, reported serious loss of strength laboratory s c a1e only. About the practical consequences in sulfite making for certain intervals; a t other twenty years ago Bache-Wijg are: ( 1 ) decrease in yield (observed up to 10 times the quality stood up well claimed that he was able to imfor weeks. prove commercial cooking condiper cent); (2) comparatively small decrease in The data of Figure 2 give the tions, as well as the color of the customary strength qualities on unbleached sulJite fluctuations in bursting strength sulfite pulp, by adding to the di( i f proper evaluation is used, however, the on b l e a c h e d stock, compared gester liquor a small amount of lowering of quality is of the same order as in with the age of the wood a t the sodium chloride. According to bleached p u l p ) ; and (3) serious decrease in mill site. T e s t s o n wood of reliable reports the process was different age were made continucarefully tested in mills in the general strength qualities of bleached stock. ously, and the actual changes in eastern part of this continent but Unbleached sulfite coming in contact with the age of the wood were not as was found unsuccessful. About salt-containing water suffers a n equicalent deabrupt as the wood rectangles in five years ago peculiar variations crease in physical properties. Figure 2 suggest. The ends of in yield and quality of product in I n both cases the resulting bleached stock has those periods which they reprecertain western sulfite mills again sent are really oveclapping. Yet a n inferior yellow tinge, lowered alpha-cellulose brought to the fore the problem it is certain that, with increasing of the influence of salt solutions content, high copper number, etc. age of wood in salt mater, the on sulfite making. Presentation a v e r a g e strength of the white of the results and conclusions on an investigation of this problem are the purpose of the present stock goes down. The fluctuations are still more pronounced if the stocks are evaluated with the aid of the copper paper. number (6). Figure 2 suggests either that the cellulose fiber ACTION OF SALTSOLUTIOSS ON CELLULOSE IS FORM of wood deteriorates if it lies in salt water more than 3 months, OF WOOD or that the salt absorbed weakens the fiber during the cooking For many years, the records of a mill making unbleached process. sulfite from western hemlock (Tsuga heterophylla) in the TABLE I. SEASONAL VARIATIOXS O F BURSTINQ S T R E N Q T H AND Northwest gave the variations in production shown in Figure FREENESS" 1. The results were practically the same each year. BLEACHED STOCK BROWN STOCK YIELDPER Bursting Bursting Nearly all the mills along the Pacific Coast are situated on DIQESTER strength Freeness strength Freeness MONTH deep water, and the majority of them transport the logs to Tons % 420 380 85 salt water and raft the wood to the mills through inlets. August 13.3 410 380 80 12.4 September For the case cited above, it was found that over a period of October 76 350 410 13.0 280 385 70 12.6 November several years 85 per cent of the wood came from the same December 390 276 69 12.2 slope and soil, thus practically excluding variations in the The bursting strength is the maximum reached in an experimental fresh wood supply. Manufacturing conditions deviated beater. Freeness is measured with the Schopper-Riegler apparatus at the maximum burstlng strength. somewhat during the interval, but these changes prevailed irregularly during periods of high and low yield, and careful I n commercial operation the average amount of salt which checks proved beyond a doubt that the output per digester penetrates into the wood can best be determined as chlorine remained entirely independent of reasonable variations in ion with silver nitrate in the sulfite cooking liquor. Tests cooking acid, temperature, pressure, etc. The only factor made on a number of cooks gave the results shown in Table 11. in fairly good relation to the variations in yield was the age O F C H L O R I N E I O N DURING C O O K I N G of the wood. The logging operations started early in the TABLE11. DISTRIBUTION OPERATION spring and lasted until the end of October so that, from COOKIXQ COOKINQ COOKINQ HC1 November to March, wood was used which had been immersed PERIOD PERIOD HC1 PERIOD HC1 Hours % Hours % Hours % in salt water from 3 to 5 months. An attempt was made to 1 0.030 4 0,028 8 0.018 follow the strength tests of the fibers over long periods, but Trace 2 0.032 6 0.028 Waste liquor 3 0.033 owing to the lack of certain data the results could not be 0
March, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
Previous to 2 hours of cooking the equilibrium between sulfite liquor and salt content of the wood was found to be incomplete. Between 2 and 4 hours the acid showed H maximum percentage of chlorine ion. This meant that at that time interval a complete diffusion had taken place between the salt in the wood and the surrounding acid. During the later periods of the cooking process the precipitate with silver nitrate decreased until it almost disappeared with the waste liquor. This indicated that the chlorine ion Eiad entered into the anion with organic compounds and consequently did not react further with silver nitrate.
317
artificially. Macroscopically the wood fiber contained much salt, but the cellulose fiber was still unaffected. The meaning of the results becomes clear if the time required for the salt to penetrate into the wood fiber is considered. In one case the salt solution had sufficient time and opportunity to react with the cellulose in the wood, in the other case it had not. Figures 2 and 3 show that about 3 months of salt water action on logs is the critical time. Rood lying in sea water for more than 3 months will invariably result in lower physical qualities in its sulfite fiber and a reduced yield per digester. When the old and new wood are well mixed in the production of sulfite pulp, the detrimental influences on strength, or the decrease in yield may easily he overlooked. ACTIONOF SALTSOLTJTIOS-s os CELLULOSE I N FORM OF
I n different mills more than fifteen hundred chlorine-ion determinations of the digester liquor (between 2 and 4 hours of cooking) were compared with strength tests, an extract of which is given in Figure 3 . The white stock strength, especially, drops considerably if the hydrochloric acid or chlorine-ion content is higher than the equivalent of 0.02 per cent hydrochloric acid. As about 15 per cent of all results deviated from this rule, the following commercial experiments were made: In one mill, fresh wood was used, giving normally bleached pulp of a certain strength and value. Salt water was then turned into the acid plant, resulting in a test of 0.169 per cent hydrochloric acid in the digester liquor. During the interval following, no noticeable drop in strength or value of white stock was observed, which proved that the fibers were not weakened by the presence of salt during cooking. I n another mill, commercial salt was added to the digester equivalent to 0.059 per cent hydrochloric acid. Again no deviation was shown in the stock qualities. Since the wood was fresh in both cases, strong sulfite was obtained. On the other hand, extracting the salt from the old wood by storing the logs in a fresh water pond, or washing the chips in the digester with water previous to cooking, gave the same low grade pulp that would have been obtained if the salted wood had been directly chipped and cooked. As shown above, the chlorine ion disappeared during cooking if wood was used which had been contaminated with salt through storage in sea water. I n these cases it was also found that the sulfuric acid in waste liquor was unduly increased from a maximum in normal cooks of 0.06 to 0.10 per cent ( 2 ) . Salt freshly added to acid or digester liquor retained its power to react with silver nitrate to the end of the cook, without any increase in sulfuric acid in the waste liquor. These facts suggested the following conclusions: In 85 per cent of all cases, the wood naturally became contaminated with salt and, when cooked with sulfite liquor, gave inferior fiber qualities-lower strength, lower freeness, higher copper number, and increase in sulfuric acid in the waste liquor. The chlorine disappeared during cooking. This action obviously was not due to any salt or hydrochloric acid influence during heating, because salt added immediately before cooking had no detrimental influence whatever. Excess of salt removed before digesting the wood did not restore the desired physical qualities t o the fibers. Apparently the remaining 15 per cent of those cases that deviated from the general rule behaved similarly to those cooks which had been salted
UXBLEACHED SULFITE
Does the experience gained so far give us any reason to expect further improvements in the art of sulfite making? The answer is decidedly in the affirmative. Wood may be considered as a mixture of cellulose and lignin, and unbleached stock may be regarded as the same kind of substance but with different percentages of the components. The free sulfite fiber therefore should present almost ideal conditions for the penetration of salt solution into the finest cellulose particles. Figure 4 represents laboratory experiments along this line. One large sample of brown sulfite from the pit was divided in half. One part was washed and screened with fresh water, the other with water containing an equivalent of 0.020 per cent hydrochloric acid in the form of calcium chloride. Half of each brown stock sample was again tested for strength; the other two quarters were bleached in separate jars, but simultaneously and under exactly the same temperature conditions, etc. Stock 2, treated with salt-containing water, is slightly lower in strength when unbleached, but gives a material drop in physical quality in the bleached form.
FIGURE2 The rise in bursting strength a t the end of curve 2 denotes figures obtained with stock already in the parchmentized state, with low freeness and general unsuitability for practical paper making. Hundreds of similar experiments gave varying but substantially the same decrease in physical properties as represented above. Some tests were also made with other salts present in an effort to determine whether the cation or anion produced the actual effect. Some were made with the intention of determining the minimum percentages of salt below which no influence was recorded. The former showed an increase in effect using a cation with higher molecular weight. Sulfates were a t least as detrimental as chlorides. Exact evaluations of unbleached and bleached sulfite, and routine mill tests, made similar to those given below, proved the pulp to be still affected if more than 0.001 per cent sodium chloride could be found in the mill water with which the unbleached material was processed. The mill experiments were checked with the so-called standard Valley Iron Works beater. Four periods of about 10 days each mere
I N D U S T R I A L A N D E N G I N E E R I N G. C H E M I S T R Y
318
TABLEIV. COMPARISONS BETWEEN COPPERNUMBERAND ALPHA-CELLULOSE CONTENT COPPER U-CEL- COPPERU-CIL- COPPERU-CEL- COPPERa-CIL-
used and the averages taken (approximately seventy cooks for each period; commercial bleaching conditions were kept uniform).
NO.
TABLE111. IMPROVEMENT OF PULPQUALITIES WITH DECREASE OF CHLORINE IONIN PROCESS WATER MAX. B U R S T I N G FREE- COPPIOR PERIOD STRENQTHNESS No. 1 2 3 4
.
5.%
73 79 i8 81
AQE O F WOOD
C1 I N WHITE WATERUSED O N BROWN STOCK T" I-
320 390 441 496
2151 2.12 1.97
Old Fairly fresh and constant
0.020 and more 0.010-0.020
Vol. 25, No. 3
2.60 2.30
LULOSE
%
83.20 86.90
NO.
2.21 2.12
LCLOBE
NO.
85.40
85.80
LULOBE
NO. LULOBE
%
%
2.03 1.90
86.70 87.10
1.82 1.70
% 87.80
88.20
These figures were compiled in one mill, but similar conditions were obtained with sulfites of different origins. Probably because of commercially uncontrolled variations in pH during
0.0012-0.0015 0,0010 and below
These results on bleached sulfite show without a doubt a considerable detrimental influence of salt on the fiber. With decreasing chlorine-ion content in the white water, the bursting strength increases 10 per cent. Simultaneously the freeness rises materially, denoting more beating resistance of the pulp. This would ultimately lead to much higher strength factors with other experimental or commercial beating equipment. The health of the fiber, expressed by the copper number, is also greatly improved.
FIGURE 4
bleaching, the ratio of high copper numbers t o the alpha-
ISACTIVITY OF SALTSOLUTIOXS DERIVED FROM BLEACHIXGcellulose content is irregular. Starting with a copper number OPERATIONS Any bleaching process sooner or later produces calcium chloride. Is this, before it can be washed out, also detrimental during the bleaching process or later? The answer is given in the foregoing, and is in the negative. To produce a detrimental action, it proved to be absolutely necessary to have the cellulose-lignin complex present in the same state in which it exists in wood or in unbleached sulfite. This does not exclude the possibility that the salt solution eventually will disrupt pure cellulose micelles or valences if it has time enough to do so, but, for the practical sulfite production, only the instantaneous action through the lignin bridge is of interest a t present.
of about 2.20, the alpha-cellulose increases regularly with decreasing copper number. RECIPROCAL RATIOBETWEEK COPPERKUUBERASD SALTAFFECTEDFIBER Of more theoretical and immediate practical interest was the ratio of copper number to salt-affected fiber, as given in Tables I11 and IV. I n the work dealing with wood itself, it was shown that only that fraction of the salt was detrimental which had sufficient time to enter the smallest ducts. The fact that it affected most the qualities of white stock led to the belief that those cavities penetrated are of the cellulose fiber proper. On the other hand, from detailed work with the copper number ( I , 7), it can be concluded that the copper number of a pulp depends almost exclusively on cellulose conditions, with little or no influence upon impurities. Other factors being equal, the copper number is governed by the possibility of the copper molecules or ions penetrating into the finest cellulose particles. If the bleaching operation and all testing conditions are carefully observed, the copper number of unbleached sulfite is only slightly lower than that of bleached fiber. Unaffected brown sulfite, properly bleached, yields the same strength qualities in the white stock.
8 MONWNSLT WATD.
FIGURE 3
Sumerous experiments have proved that eastern wood and pulp are also susceptible to salt action. All samples used throughout this work were subjected to close comDarisons for bleach abilitv of brown stock. It is a natural step for the sulfite operatorto attempt to boost physical qualities in bleached fibers by leaving an excessive amount of lignin in brown stock. But in all cases where the salt action was dominant, it was found that the n,hole stock did not improve in its strength with increased content of lignin in the brown fiber corresponding t o a range of 15 to 32 per cent bleach ability. This fact is of some commercial interest. Alpha-cellulose determinations (3) were carried on throughout the work. Some characteristic results (using commacially bleached pulp) are given in Table IV.
LITERATURE CITED (1) Benson, H. K., Pacific Pulp P a p e r Ind., 5, S o . 7 , 20 (1931). (~ 2 )-Carlson. 60. 889 (1929). , , S... Wochbl. Pavierfabr.. ~. (3) Committee on Viscosity of Cellulose, IND.' ESG. C'HEX, -4nal. Ed., 1, 49 (1929). (4) Jonas, K. G., and Walter, P., Wochbl. Papierfabr..,63, Sondernummer 23A, 55 (1931). (5) Kullgren, C., Svensk Kem. Tid.,42, 179 (1930). (6) Richter, E., Paper Makers' M o n t h l y J., 68, 2 5 i , 314, 404, 438, 473 (1930); Tech. Chem. Papier- Zellstof-Fabt.., 26, 1-57, 173 (1929), 27, 1, 133 (1930), and 28, 17 (1931). (7) Richter, E., Tech. Chem. Papier- Zellstofl-Pahr., 28, 49 (1931). RECEIVED.A-ugust 27, 1932.
CHEMIC.%LSAND
ALLIED
PRODUCTS
IS
CAX.%D.%. Flnal figures
for 1931 show that the production of chemicals and allied products was valued at $105,501,905 at factory prices. his total was 12 per cent below the corresponding value of $119,969,637 for 1930, and 24 per cent below the 1929 record total of $138,545,221. with 591 A total of 621 plants reported in 1931, as in 1930, with a capital of $164,510,279, as compared with $168,119,152 in 1930.
