The Cooking Process 111. Cooking Wood with Sodium Sulfate S. 1. ARONOVSKY AND Ross AIKEN GORTNER, Minnesota Agricultural Experiment Station, St. Paul, Minn.
I
N THE first of this series of investigations it was shown sulfate is neutral, and its effect on the maiu constituents of that water as the sole cooking agent ( 1 ) had a profound the wood should be different from those produced by sodium effect on the various constituents of the wood. Thr carbonate. pentosans were almost coniplet.ely hydrolyzed or destroyed. The lyotropic effectsof different anions upon c o h i d sj&xns Comparatively large portions of the Cross and Bevan cellulose are well known. 111order to determine whether the ions have and alpha-cellulose coiltents of the wood a w e partially similar effects in the cooking processes, one cook was made hydrolyzed to sugars and partially broken down to gaseons with sodium bromide as the pulping agent, since, in their products. Some of the lignin was removed hy the water, effects on protein systems the sulfate and bromide ions are at whereas a portion of the remainder left in the wood had he- the opposite ends of the lyotropic series (3'). come soluble in ethyl alcohol, acetone, or glacial acetic acid, EXlTXUQfEXTAL hoCEDUllE denoting a probable depolymerization of the lignin brought about by cooking the wood with water. A series of cooks was run a t 170' and 186'" C. [lo0 and 150 Sodium carbonate as a cooking agent ( 2 ) did not have as pounds per square incli (7 and 9.1 kg. per sq. em.) stea.m drastic effects on the pentosans pressure, r e s p e c t i v e l y ] for a durationof 2 and 12 hours. The as did water alone; portions of Aspen sawdust was cooked with sodium sulfale concentrations of sodium sulfate it remained in the wood, under the conditions used in this series used were 6.7, 13.4, 26.8, and at 170' and 186' C. for 2 and 12 hours, using 6.7, of investigations, in a more or Y3.6 per cent of the o v e n - d r y 13.4, 26.6, and 53.6 per cent qf the salt (based less stable association with the weight of the wood charge (91.0 on the oven-dry wood), equivalmt, on the sodium grams for the 6.7 and 13.4 per Cross and B e v a n cellulose. basis, to 5 , 10, 20, and 40 per cent sodium carMore lignin was found in the cent sodium s u l f a t e , and 90.3 bonate, respectively. More organic matter and r e s i d u a l black liquors of the g r a m s for t h e o t l i e r cooks). sodium carbonate cooks than in T h e s e concenl ations of s a l t volatile organic acids, as acetic acid, and less are equivalent, on the sodium t h o s e of t h e w a t e r c o o k s . reducing sugars were found in the residual b a s i s , t o 5 , 10, 20, a n d 40 Sodium carbonate also caused a in those liquors of the sodium sulfate cooks than greater conversion of the original per cent sodium c a r b o n a t e , of the corresponding water cooks; the amounts alpha-cellulose into the alkalirespectirely. (The cooks with if lignin (72 per cent sulfuric acid method) and soluble v a r i e t i e s , beta- and the lower salt concentrations-6.7 and 13.4 p e r cent--were gamma-celluloses. No reducing pentosans were approximately the same in the sugars or furfural were found run after t h e o t h e r c o o k s , residual liquors of both of these series of c0ok.s. which showed rather d r a s t i c in the residual liquors of the The residual woods were darker than those of the sodium carbonate cooks. effects upon some of the wood water cooks, but the total yields and the lignin, Sodium sulfate, the salt used constituents, especially a l p h a pentosan, and Cross and Bevan cellulose conin the series of cooks reported in cellulose, were c o m p l e t e d . ) this paper, is present in all the One cook was run a t 186" C. tents were ahout the same .for bofh the sodium commercia I sulfur-containing for 12 hours with 57.5 per cent sulfate and water cooks. The conversion of alalkaline cooking liquors used in sodium bromide, e q u i v a l e n t , pha-cellulose was greater with the use of sodium on the sodium basis, to 29.6 the manufacture of pulp, mainly sulfate as the cooking agent. Sodium bromide the Kraft and Keebra liquors. per cent sodium c a r b o n a t e . acled in lhe same manner as sodium sulfate. The wood used was aspen sawThe aqueous solution of sodiiim 30.5
INDUSTRIAL ASD ENGINEERIKG CHEMISTRY
306
Vol. 23, NO. 3
vacuum distillation or to violent mixing, and the foam produced by the latter means was stable for more than 24 hours. The residual 20 liquor of the sodium bromide cook was similar P in all of the above respects to the sodium /5 sulfate residual liquors. HYDROGEN-ION C o N C E N T R A T I o N . The 5 /o liquors were strongly acid to litmus paper, J and therefore pH determinations were made 5 on these solutions before and after concentration and also on the distillates obtained by 0 53.6 these means. A hydrogen electrode could not be used for the residual liquors because of a 25 constant drift of the e. m. f. toward lower I I / I values, and consequent inability to procure check results. This drift may be explained by the removal of hydrogen from the platinum sponge of the electrode by some substance or substances in the solutions, probably lignin or furfural residues with their double bonds The use of the quinhydrone electrode resulted in check values for the pH of the residual liquors, which are given in Table I. 0 53.6 The original volumes of the residual liquors, CmhiT 7%- - 2 h Cooi(mgLmp.-l86%. Cwhmyiimmr -/Z.%s. Corr(vgZmp. -I&? 6.0 to 6.5 liters, were reduced to 1.5 to 1.8 FIGURE1. YIELDS OF TOTALORGANICMATTER,REDUCINGSUGARS, liters by vacuum distillation. The p H values, VOLATILE ORGANIC ACIDS, LIGNIN,AND PENTOSES AND PENTOS.4NS IN given in Table I, show that the hydrogen-ion RESIDUAL LIQUORS concentrations of the c o n c e n t r a t e d liquors (Zero per cent sodium sulfate represents cooking with water only) were greater than before distillation. The d i s t i l l a t e s tasted s l i g h t l y sour, and this dust from the same batch described in the earlier papers (1,Z). acidity was probably due to the volatile orgahic acids The ratios of weights of wood to volumes of liquors (3 to loo), (formic and acetic) remaining in the liquors after the greater the cooking procedures, methods of preparing the products portions of these acids were removed from the digester in for analysis, and methods of analysis were the same as out- reducing the pressure in the latter upon completion of cooking. These distillates, 4.5 to 5.0 liters each, had a p H of lined in the previous reports. The data are tabulated in Tables I to VI and shown graphi- 3.4 to 3.9. They were discarded since they contained very cally in Figures 1 to 3. The results given are the means of little acid (0.001 N acetic acid has a pH equal to 3.87). TOTAL ORGANICMATTER. The total organic matter in two or more analyses. the residual liquors was obtained by determining the total solids and then subtracting from the latter the residue obRESIDUAL LIQCORS tained by ashing the dried sample, a little sulfuric acid being The residual liquors from the sodium sulfate cooks were added to prevent the reduction of sulfates to sulfides The orange-red to dark red when hot, and dark brown t o black quantities thus obtained are shown in Tables I and I1 and when cold. Small quantities of solid matter separated out Figure 1. The lower salt concentrations resulted, generally, upon standing, but there was little or no variation in the in slightly lower yields of total organic matter than were quantities of these substances observed in the different obtained by cooking with water only; 26.8 and 53.6 per cent cooks. The liquors foamed profusely when submitted to sodium sulfate yielded somewhat larger quantities of organic
s P
OF RESIDUAL LIQUORSAND VOLATILE ACIDSI N RESIDEAL LIQEORS AND DIGESTER CONDENSATES TABLE I. PH AND IRONCONTENT
NazSO4
COOK 35 l3 36 16 37 38 l7 57 56 39 40 21 58 59 42 43 60
0
b c
TIME Hours 2 2 2
12 12 12 2 2 2
2
2 12 12 12 12 12 12
TEMP.
C. 170 170 170 170 170 170 186 186 186 186 186 186 186 186 186 186 186
A D D E D TO DIQEBTER
Grams
Hz0 on;y 24.2 48.4d HnO only 24.2C 48.4d RzO only 6.1° 12.2; 24.2 48.4d Hz0 only 6.112.2b 24.2e 48.4d 70.7”
ORQANIC MATTER IN REBIDUAL
LIQUOR Grama 17.88 10.58 14.03 12.53 13.91 15.49 12.80 11.31 10.63 12.28 13.10 13.89 15.32 13.80 17.37 15.56 14.57
P H OF:-RESIDUAL LIQUOR DISTILLATE OBTAINED Before After evapoeVap0- ON EVAPORATION ration ratlon
4:66 4.92
4141 4.62
3:+8 3.75
4:81 4.92
4:31 4.48
3:67 3.85
4:33 4.10 4.39 4.52
4:03 4.05 4.17 4.24
3:4S 3.41 3.53 3.52
4:i4 4.17 4.74 4.76 4.15
4:io 4.11 4.33 4.30 4.07
3:43 3.43 3.55 3.59 3.55
VOLATILE A C I D 6 (AS ACETIC) I N RESIDUAL LIQUOR AND D I Q E S T E R
Weight Grama 1.77 3.40 4.40 1.58 5.30 6.28 1.34 3.89 3.81 4.78 5.33 1.60 4.74 4.92 5.73 6.45 3.77
IRON(Fe) I N CONDENSATE RESIDUAL LIQUOR On basis On basis
On basis residual liquor
original wood
0. d.
%
%
9.90 32.14 31.36 12.61 38.10 40.54 10.47 34.39 36.18 38.93 40.69 11.52 30.94 35.65 32.99 41.45 25.87
1.97 3.77 4.87 1.76 5.87 6.95 1.49 4.28 4.19 5.29 5.90 1.78 5.21 5.41 6.35 7.14 4.14
Weight Grama
%
2.13
19:09 15.18
2:99 3.41
2i:io 22.01
1:51 1.59 2.15 2.31
13.’35 15.10 17.51 17.63
2:94 3.21 3.15 3.83 2.87
ii:ig 23.26 18.13 24.61 19.70
2:02
(NaBr.2HzO) 6 7’7 of weight of oven-dry wood (91.0grams) added to digester, and equivalent on sodium basis to 5% NazC03 (Hz0 3350 grams). 13.4% of weight of oven-dry wood (91.0grams) added to digester, and equivalent on sodium baais to 10% NazCOa ( H n 0 3350 grams) 26.89 of weight of oven-dry wood (90.3grams) added to digester, and equivalent on sodium basis to 20’7 NazCOa ( H n 0 3350 grams): #E$; of weight of oven-dry wood (90.3grams) added to digester, and equivalent on sodium basis to 4 0 d NazCOa (HzO 3350 grams). of weight of oven-dry wood (91.0grams) added to digester, and equivalent on sodium basis to 29.6% NazC03 (Hz0 3350 grams).
;
residual liquor
1 N D U S?' It I A 1. A N D E N G I N E E It I X C; L ti E M 1 S 1'11 Y
.UarL.li, 1933
matter. The addition of salt to tlre water generally produced slightly higlrer yields of organic matter in the residual liquors in the cooks run for the longer cooking periods a t the higher temperatures. Tlre effect of sodium bromide on the total organic matter produced was about tlie same as that of sodium sulfate. Inorr REMOVED x m o ~DIGESTERWALLS. Considerable quantities of iron were diasolvcd from the digester walls by the sodium sulfate cooking liquors. It was found in the ash obtained from the total organic matter determinations. The increases in the times and temperatures of cooking and in the concentrations of the salt increased the amounts of iron in tlre residual liquors. The quantities found in cooking with sodium sulfate were considerably larger tlian the amounts of iron found in the residual liquors of the water cooks. The corrosive effects of sodium sulfate and sodium bromide were nliout the same. These data are given in Talde I. IJGXIN. Smaller quantities of lignin were fonnd in the residual liquors of the sodium sulfate cooks tlian in those obtained by cooking with water only, as show11 in Table I11 and Figure 1. The increases in the concentration of the sodium sulfate decreased the amounts of lignin (72 per cent sulfuric acid method) found in the Iiq\mrs, but tlie changes in time or temperature of cooking liad but little effect in this respect. Apparently, thereforc, the salt hindered the solution or peptiaation of the lignin. The sodium bromide acted in the same way as tile sulfate. PENTO~ES AND PEXTOSAN~. The quantities of pentoses and pentosans (furfural-yielding substances) found in the residual liquors of the sodium sulfate and sodium bromide cooks are given in Table I11 and Figure 1. It is apparent from tlirse data that the addition of salt to water as the cooking agent l i d w r y littlc effect on the furfmal-yielding substances found in the rrsidoal liquors. I3ecanse of the acidity of these liquors it may be assumed that these furfural-yielding substances wcrc mainly pentoses. Lesser quantities of reducing sugars dual liquors of the sodium sulfate cooks than in those of tlie corresponding water cooks, when the concentrations of tlie cooking salt were 26.8 and 53.6 per cent of the weight of oven-dry wood (Table TI1 and Figure 1). A t the lower salt, concetitrations, slightly larger quantities of reducing sugars were found. The increase in sodiinn sulfate from 6.7 to 13.4 per cent of tlie wood had practically no effect on the reducing sugars produced. At the higher salt conoentrations, however, 53.6 pcr cent sodium sulfate yielded somewhat smaller quantities of sugars than were obtained with 26.8 per cent of this salt. It is apparent from the above data that the greatcst change in the yields of reducing sugars
CALENDER
J07
STACKS OF 2041NCH PAPER
&fACHrNE,
NorrTnwEsT PAPER COMPANY, C ~ Q U E TMINN. ,
occurred when the concentration of sodium sulfate was hetweeu 13.4 and 26.8 per cent of the weight of o\.en-dry wood used. Sodinin bromide acted similarly to sodium sulfate in respect to the reducing sugar yields. VOLATILEO i m . 4 ~ 1 ACIDS. ~ The volatile organic acids (calculated as acetic) formed in the cooking process were determined on a mixture of aliqnots of both the residual black liquors and digester condensates, and are shown in Table I and Figure 1. The quantities of volatile acids formed in the sodium sulfate cooks were much larger than those obtained
v"ni."anL ,a DiYEJTI" CoaDrnJATs
l~a*L"onL W""0
On basis
13
35 36
16
37
38
WiEi"&l wood
Tewu.
News 2
" c.
nroms
GrWM
%
170 170 170 170 170 170
HrO only
83.7 66.6
70.94 75.75
62.5
68.82 68.88 89.21
2 2 12 12
12
\+'eight
24.2
48.4 HrO only 24 2 48 4
66.9 61.8 62.2
Weisht
0.d.
T,MI
74.09
Gram" 17.88
10.58
14.01 12.55 1a.91
15.49
% 19.91 ll.?2 15.54 11.95 15.40
17.15
1.83 1.11 0.x4 2.45 0.99 0.88
On baria ori*inal
,>. d. wood .. 1.42 1.23 0.98 2.73 1.10 0.95
.. 6.9 12.0
7.67 13.29
8.5
9.41
13.0 13.2
14.50
11.4
12.Bl
14.62
INDUSTR IA L Ai Y D E N G I NE E R I N G C H E M I S T R Y
308 0
Wood
c - L 'yo'"
a -o( - c c u u i o , G
0 CCIl"~0,~
as sodium sulfate in regard to the furfural content of the residual liquor.
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4
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.
80
80
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.
2 60
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$40
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