The Cooking Process VI, Cooking Wood with Sodium Sulfide S. I. ARONOVSKE. AND Ross AIKEN GORTNER,Minnesota Agricultural Experiment Station, St. Paul, Minn. with sodium sulfite (S), by multiplying the total organic carbon contents of these liquors by the factor 2.0. The quantities of total organic matter thus found in the residual liquors are shown in Table I and Figure 1. The addition of 14.7 per cent sodium sulfide to the water r e s u l t e d in large increases in the quantities of organic matter found in the l i q u o r s . D o u b l i n g the quantity of the salt increased the amounts of organic matter in the liquors, but the increases in organic matter between zero and 14.7 p e r c e n t s o d i u m sulfide were g r e a t e r t h a n those betveen 14.7 and 29.4 per cent of this salt. Raising the cooking t e m p e r a t u r e f r o m 170" t o 186" C. increased the quantities of organic m a t t e r i n the liquors to considerable extent, fate, kTas uked in these c o o k s . The sodium sulfide was used in quantities equal to 14.7 and these increases being greater for the 12-hour than for the 2-hour 29.4 per cent of the weight of oren-dry wood, equivalent, cooks. The longer cooking periods resulted in larger quantion the sodium basis, to 20 and 40 per cent sodium carbonate, ties of total organic matter in the residual liquors. The 1281) respectively. The wood used in these cooks (100.0 grams air- hour, 186" C., 29.4 per cent sodium sulfide cook (KO. dry equals 90.0 grains oven-dry) mas aspen sandust from the yielded a quantity of organic matter in the liquor equal to 50 same batch described in the report on cooking with mater per cent of the original dry wood. This yield was larger than only. The analytical results given are the means of two or that obtained from the corresponding sodium sulfite cook ( 5 ) . more determinations. DISTRIBUTIONOF SALTS. The residual liquors were analyzed for the sulfide, sulfite, thiosulfate, and sulfate radiRESIDUAL LIQCORS cals. The results are given in Table 11. The amounts of The residual liquors from the sodium sulfide cooks were sodium sulfide, as such, found in the residual liquors of the orange-red to dark red cooks in which 13.23 and clear when hot, grams of this salt had and brown-black and been a d d e d , were t u r b i d w h e n cold. negligible. The conThey had the typical v e r s i o n o r decoms u l f a t e liquor odor position of the sodium and were alkaline to sulfide i n c o o k i n g litmus paper. Small with26.5gramsof this quantities of grayish salt was almost combrown solid m a t t e r plete e x c e p t in the separated out upon c a s e of c o o k 85 (2 standing and could be hours, 170" C.). An quickly dispersed in increase in the time the liquor with shakand temperature of ing. T h e l i q u o r s cooking tended to infoamed readily and crease the decomposip r o f u s e l y , but the tion of this salt. foam d i s a p p e a r e d Relatively s m a l l quickly. quantities of sodium T O T A LORQANIC sulfite a n d s o d i u m MATTER. The total sulfate were formed o r g a n i c m a t t e r in in this series of cooks. these liquors was deRather large quantiCourtesy, Northwest Paper Company termined, as given in tiesof thiosulfate were the report on cooking A MODERN SAWMILL DEVOTED ALMOST EXCLUSIVELY TO SAWING WHITEPINE formed, the maximum
HE use of water ( 1 ) and
T
Aspen sawdust was cooked with 14.7 and 29.4 per cent sodium suljide (based o n ihe oven-dry wood), equivalent, o n the sodium basis, to 20 and 40 per cent sodium carbonate, respectively, f o r 2 and 12 hours at 170" and 186" C. The total organic matter, volatile organic acids (as acetic acid), pentosans and lignin (72 per cent sulfuric acid method) were found in greater amounts in these liquors than in the residual liquors of the water cooks. The residual woods were brownish gray 20 dark brown in color, and partially to completely pulped. These pulps contained less EXPERIMENTAL PROCEDURE lignin and more pentosans and Cross and Bevan cellulose than did the residual woods of the cor-4series of e i g h t c o o k s was responding water cooks. Sodium suljde inmade a t 170" and 186" C. for cooking d u r a t i o n s of 2 or 12 hibited the destructice effects of water on the hours. A solution of c. P. sodium alpha-cellulose at the higher temperatures and sulfide, analyzing 140.6 grams longer cooking periods. Sodium sulJide is a p e r l i t e r s o d i u m sulfide and strong pulping agent. 0.33 n a m Der liter sodium sul-
aqueous solutions of the carbonate ( g ) , s u l f a t e and bromide (S), t h i o s u l f a t e (4),and sulfite (5) of sodium, as cooking agents, ha,s been discussed in Parts I to V. The salt used in the series of cooks to be reported here was sodium sulfide. It is one of the two main ingredients of the cooking liquor used to produce sulfate or Kraft pulp.
61
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Vol. 26, No. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
62
being about 52 per cent by weight of the sodium sulfide added to the autoclave. The thiosulfate was formed in larger quantities when 26.5 grams of sodium sulfide were used in cooking. Increasing the time and temperature of cooking generally caused slight decreases in the amounts of thiosulfate formed except in the case of cook 80 (2 hours, 186" C., 29.4 per cent sodium sulfide). The formation of the sodium thiosulfate was probably brought about by the addition of sulfur to the sodium sulfite formed. The following equations show some of the reactions which undoubtedly took place in the cooking process: 2NazS soz --ic 2Na2SOs NazS 2Hz0 2NaOH HzS 2HzS 0 2 + 2Hz0 25 HzS03 NaZSO3 2Hz0 e 2NaOH
IJIGSIY. More lignin was found in these liquors than in the residual liquors obtained by using water as the cooking agent. These data are given in Table I11 and Figure 1. The amounts of lignin increased with increasing concentration of sodium sulfide in the cooking liquors, but an increase in time and temperature of cooking had but little effect on this substance. Nearly twice as much lignin was obtained with 29.4 per cent sodium sulfide as with 14.7 per cent, indicating that the solution or peptization of lignin by sodium sulfide is approximately proportional to the concentration of the salt within the range which was used. Appreciable quantities of sulfur were found to be held in chemical combination by the lignin. The thimbles containing the lignin and sulfur were extracted with carbon disulfide to remove the elemental sulfur present. The conHz0 SOz tents of the thimbles were then dissolved in concentrated 2HR Na2S03--f 2NaR H20 SO2 nitric acid and the solutions analyzed for sulfur according to 2HzS SO2 + 2H20 35 the Benedict-Denis method ( 7 ) . The results are given in NaZS03 S + Na2SzOa Table 111. The amounts of sulfur chemically combined with The quantities of sodium combined with the organic matter the lignin increased with the increase in sodium sulfide used in the residual liquors were generally higher than the values in cooking. The time and temperature of cooking had very found for the sodium sulfite cooks ( 5 ) . The increases in little effect upon the sulfur content of the lignin, except in the time and temperature of cooking, and in the amount of case of cook 83 where the results are out of proportion with sodium sulfide used, resulted in larger quantities of sodium the other cooks in this series. It appears from the above combined with the organic matter of the residual liquors. data that the percentages of lignin-sulfur compounds formed were dependent, not on the amounts of lignin present, but TIBLE I. YIELDSOF RESIDUAL WOODSAXD TOTAL ORGANIC on the quantities of sodium sulfide used in the cooking liquors. MATTER IN RESIDUAL LIQUORS. The lignin values given in Table I11 represent the net lignin TOTAL MATERIAL and not the lignin-sulfur compounds. ORQANIC UNMATTERIN ACCOUNTED PENTOSES AND PENTOSANS. The quantities of pentoses R ~ S I D U A L FOR BY and pentosans (calculated together as pentosans) in the RESIDUAL WOOD LIQUORb , ANALTBIS On On On residual liquors of the sodium sulfide cooks were larger than basjs basis those found by cooking with water only, except in the 2-hour, ba$s origiorigiorigiNa?S nal nal nal 170" C. cooks. The yields of pentosans in this series of liquors ADDED ovenovenovenTO dry dry dry were similar to those obtained by cooking with sodium sulfite. COOKTIMETEMP. DIGESTER Weight wood Weight wood Weight wood Doubling the sulfide concentration of the cooking liquors reHrs. C. Gram8 Grams % Grams % Grams % sulted in slight increases in the amounts of pentoses and pento13 2 170 Hz0 onlye 6 3 . 7 7 0 . 9 4 1 9 . 2 1 f 2 1 . 3 9 6 . 9 7 . 8 7 2 84 170 13.25d 58.5 65.00 26.60 29.56 4.9 5.44 sans obtained, but the increases in time and temperature of 2 85 170 8.2 9.06 2 6 . 50e 51.8 57.56 30.04 33.38 16 12 cooking had very little effect on these constituents of the 170 Hz0 onlye 6 1 . 8 6 8 . 8 2 1 4 . 9 8 1 6 . 6 8 1 3 . 0 1 4 . 5 0 82 12 13.25 7.7 8.54 170 5 4 . 4 60.44 27.92 31.02 residual liquors. 12 9 . 1 10.09 83 26.50 170 47.1 52.33 33.82 37.58 17 2 186 H20onlyC 6 1 . 6 6 8 . 6 0 1 6 . 3 1 1 8 . 1 6 1 1 . 9 1 3 . 2 4 REDUCING SUGARS.Only traces of reducing sugars were 4.9 5.40 79 2 186 5 4 . 5 60.56 30.64 34.04 13.25 found in the residual liquors of the sodium sulfide cooks. 80 4.7 5.20 2 186 26.50 47.1 52.33 38.22 42.47 21 12 186 HzOonlyC 5 4 . 5 6 0 . 6 9 1 5 . 9 0 1 7 . 7 1 1 9 . 4 2 1 . 6 0 This was due to the alkalinity of the cooking liquors. 78 186 50.8 56.22 33.08 36.76 6.1 7.02 12 13.25 VOLATILEORQ.~NICACIDS. The volatile organic acids 3.38 3.0 81 12 186 26.50 42.2 46.89 44.76 49.73 (calculated as acetic acid) found in these residual liquors 9 0 . 0 grams oven-dry wood ( 1 0 0 . 0 grams air-dry were used ineachqook. 6 Total organic matter in the sulfide cooks was determined by multiplywere considerably larger than those obtained by cooking with ing the total organic carbon content of the liquors by 2. 0 8 9 . 8 grams oven-dry wood (100.0 grams air-dry) were used in cooking water only. These acid yields were similar to those obtained with water only. with sodium carbonate ( 2 ) and greater than those found in d 14.72% of weight of oven-dry wood used, and equivalent on sodium basis t o 20% NarCOa (Hz0 3350 grams). the residual liquors of the sodium sulfite cooks ( 5 ) . The e 29.44% of weigdt of oven-dry wood used, and equivalent on sodium basis to 40% NaKOs (HeO, 3350 grams). increases in the amounts of volatile acids were rather small i Total organic matter in water cooks includes furfural in digester oonwhen the sodium sulfide was increased from 14.7 to 20.4 per densate. cent of the wood. The increases in time and temperature of cooking also resulted in slightly larger acid yields. These IRON REMOVED FROM DIGESTERWALLS. Relatively small quantities of iron were found in these liquors, increasing data point to the fact that the volatile acids were obtained somewhat with the concentration of chemical and the time of mainly by saponification of the acetyl groups present in the wood. The maximum yield of volatile acids, 12.3 per cent cooking, as shown in Table 11.
+++ + + ++
__
+ ++ ++
+
+
O F SALTS I N ORIGINAL AND RESIDUAL LIQUORS 11. DISTRIBUTION
TABLE
YalO C O M B I N E D
--CHEXI(
ALS
C o o s TIME Hours 84 85 82 83 79 80 78 81
2 2 12 12 2 2 12 12
TEMP, C. 170 170 170 170
a
NazS Grams 13.25 26.50 13.25 26.50 13.25 26.50 13.25 26.50
WITH
TOTAL ADDED--
NazSO4 Gram 0.03 0.06 0.03 0.06 0.03 0.06 0.03 0.06
Total
Naf6 (1) Grams 10.54 21.08 10.54 21.08 10.54 21.08 10.54 21.08
-SALTS,
Na2S Grams 0.28 7.04 None 2.23 0.06 1.69 None 0.76
FOUNDIN RESIDUAL LIQUOR NazSOa NazSzOa NazSOd Gram Grams Grams A0 SUCH,
0.26 0.64 0.13 0.90 0.18 0.80 0.31 0.62
3.38 9.02 2.26 10.15 2.93 13.70 1.55 10.83
0.54 0.72 0.84 1.13 0.59 1.04 0.69 1.38
SALTS AS
NarO (2) Grams 1.89 9.76 1.22 6.68 1.55 7.56 1.06 5.76
ORGANIC
MATTER M I N U S (2) On basis original Weight NazO (1)
FerOa FOUND IN
Grams
%
RESIDUAL LIQUOR Gram
8.65 11.32 9.32 14.40 8.99 13.52 9.48 15.32
82.1 53.7 88.4 68.3 85.3 64.1 89.9 72,7
0.14 0.30 0.15 0.33 0.32 0.38 0.26 0.64
January, 1934
INDUSTRIAL AND ENGINEERING
.,
of the oven-dry wood, was obtained by cooking the aspen sawdust for 12 hours a t 186" C. with 29.4 per cent sodium sulfide.
0 40
DIGESTER CONDENSATES The condensate liquors were neutral to litmus paper. They varied from milky white to dark blue-gray in color and contained large quantities of sulfur in suspension. All of these liquors smelled strongly of mercaptans and hydrogen sulfide. Tests run for furfural gave negative results
CHEMISTRY
r d u i OT-9.",c
/%f/er
- V d o / r ( e Acjds
63
rJ
- L p n
0
-Pzn/osonr
30
zz5
~ ~ E S I D U A WOODS L
The residual woods from the sodium sulfide cooks were much darker than those obtained from the sodium 5 sulfite cooks and lighter than the residues from the sodium thiosulfate and water cooks. The residues from cooks 84 and 85 (2 hours, 170" C.) were not pulped, while those from cooks 79 and 82 could be pulped by 9o rubbing the moist residues between the fingers. The residues from the remaining cooks (78, 80, 81, and 83) 3J were in pulp form. The yields of residual woods from the sodiuni sulfide 3o cooks are given in Tables I and I V and Figure 2. The increases in all three factors, salt concentration, time, 25 and temperature of cooking, resulted in decreased yields of residual woods or pulps. These yields were considerz ably lower than those obtained from the water cooks. The increase in sodium sulfide from 14.7 to 29.4 per cent 2 '5 of the dry wood had a greater effect in decreasing the pulp yields than was found in cooking with sodium lo sulfite under similar conditions. Cooking with sodium sulfide generally resulted in lower pulp yields than those obtained by cooking with sodium sulfite (5), - except -in 5 30 Z JO* 151 cooks 78 and 81 (12 hours, 186" C.). 2H-3 C w k r n g Z m p -/86'C +H rNoCH Goor( "y Tme Z s CookmpTImp -lB6'C Cookcng T m e -/ The yields obtained by cooking with 14.7 and 29.4 per cent sodium sulfide for 12 hours a t 170" C. were identical F I G ~ R1.E YIELDS OF TOTAL ORGANICMATTER, LIGNIN,PENTOS ~ N S ,A m VOLATILEORGANICACIDS (AS ACETIC)IN RESIDUAL with the yields from the corresponding %hour, 186" C. cooks. LIQUORS A11 data based on original charge of 100.0 grams air-dry (90.0 grams ovenThe percentage losses Of wood 'Idfered in the cooking dry) aspen sawdust: zero per cent sodium hydroxide represents results obprocess (Tables 1 and V, Figure 3) were much less in this tained by cooking with water only series of cooks than were found in the corresponding water cooks. These losses were smaller in the sulfite than in quantity of sodium sulfide added to the cooking liquors. the sulfide cooks run at 170 O C., but somewhat larger a t the Longer cooking time a t 170" C. caused increased losses of mahigher cooking temperature. The increase in concentration of terial, while the increased cooking periods at 186" C. had very sodium sulfide in the cooks made at 170" C. caused greater little effect on the quantities of wood destroyed. These unexlosses of the original material, while smaller quantities of ma- pected results may be explained by the fact that, while t h e terial were destroyed a t 186" C. with a similar increase in the factor 2.0 mas used in obtaining the total organic matter in
3
TABLE111. YIELDSOF TOTAL ORGANICMATTER,LIGNIN,STTLFUR .~SSOCIATED WITH LIGNIN,PENTOSANS, VOL%TILE ORGAXIC ACIDS, AND TOTAL REDUCING STG.4RS IN RESIDUAL LIQUORS LIQNIX
(SELFURFREE) IN RESIDUALLIQUOR
On
NanS ADDED COOK
TIME
TEMP.
TO
DIGESTER MATTER^
Hours 2 2 2
C.
Grams
13 84 85
170 170 170
Hz0 only
16
12
li0
82 83 17 79 80 21 78 81 b
TOTAL ORGAXIC
13.25 26.50 H20 only 13.25 26.50 HgO only 13.25 26.50 Hz0 only 13.25 26.50
12 170 12 170 2 186 2 186 2 186 12 186 12 186 12 186 Organic carbon X 2. Ca!oulated together as pentosans Calculated as glucose.
Grams 19.21 26.60 30.04 14.98 27.92 33.82 16.31 30.64 38.22 15.90 33.08 44.76
Weight Grams 5.77 7.72 13.97 4.29 7.65 13.44
PENT os E B AND PENTOSANSb I N
RESIDVAL LIQUOR
basis original ovendry wood
Weight
09 basis original ovendry wood
%
Grams
yo
6.43 8.58
VOLATILE ORGANICACIDS ( A S ACETIC) IN
~ C L F U R ~
Asso-
b S I D U A L LIQUOR
On
Weight Grams 1.77 6.77 8.04 1.58 8.00 8.28 1.34 7.66 7.97
basis original ovendry wood % .1.97 7.52 8.93 1.76
5.12 5.70 3.83 4.26 15.52 4.23 4.70 4.78 0.60 0.67 8.50 3.29 3.66 8.89 14.93 4.46 4.96 9.20 4.95 5.51 0.75 0.83 1.49 8.98 9.98 3.77 4.19 8.51 16.73 17.48 5.05 5.61 8.86 5.10 5.68 0.54 0.60 1.60 1.78 7.33 8.14 2.41 2.68 8.45 9.39 16.47 17.19 4.06 4.51 11.08 12.31 d Based on the weight of the lignin-sulfur compound found e Less than 0.2 gram.
KEDUCINQ
SUGAR^^ IN
CIATED WITE
LIGNIS IN
RESIDUALRESIDUAL LIQUOR
Grams 11.33
. . .e
LIQUOR
% 5:?6
8.39
2.35
... ...
4.47
...
...
3:99 13.24 3161 7.48
2.83
... ...
3:+2 6.87
INDUSTRIAL AND ENGINEERING CHEMISTRY
64 @ -Wood
0 -
