INDUSTRIAL AND ENGINEERING CHEMIXTRY
March, 1927
371
Chemistry of Pulping Flax Straw' Hydrolysis with Sodium Sulfite By Mark W. Bray and Clifford E. Peterson U. S. FOREST PRODUCTS LABOR.ATORY, MADISON, 'Xis.
K THE course of the pulp-
The action of sodium sulfite solution upon flax Straw grown for seed purposes at two concentrations of chemical and at two ratios of chemical to oven-dry material under cooking conditions otherwise constant has been studied. The data indicate that a change of concentration of the sodium Sulfite solution from 40 grams to 80 grams per liter has but little effect on time of cooking or upon the relation of chemical Properties of the fibrous residue to yield; but that a change in the ratio of chemical to Straw from 20 per Cent to 40 per
lation of the heater both autoclave and bath were made to come to the desired temperature-namely, 155O C. -it this point the thermoregulator was adjusted and the ten1perature of bath and autoc l a v e jvas maintained colis t a n t \ v i t h i n 10.15" thereafter. cent by weight greatly accelerates the rate of cooking. The time required for the The progress and results of the reaction are outlined. whole manipulation of bringing the autoclave from room Material temperature to t,he final temperature of 155' C. was approxiThe flax straTv used in the experilnellt,s was gron.n for seed inately 20 minutes in every case. For comparative purpurposes. cpo1l che1nical analysis it shelved the folloming poses the cooking time "" counted from the monlellt that the autoclave was first immersed in the bath. characteristics: Per ceiil A t the end of the predetermined cooking period the autoSolubility in hot w a t e r , . . . . . . . . . . . . . . . . . . . . . . . . . 12.05 clave was removed from the bath, cooled to approximately Solubility in 1 per cent NaOH . . . . . . . . . . . . . . . . . . . . 33 .73 3.33 45' C. by immersion in cold water, and the contents were Solubility in alcohol-benzene mixture.. . . . . . . . . . . . . . . Lignin., . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23.28 removed for analysis. The pulp was separated from the Total cellulose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53.80 Pentosan-free cellulose. . . . . . . . . . . . . . . . . . . . . . . 46,:; liquor by filtration through a filter paper in a Buchner funnel. Total pentosans,. . . . . . . . . . . . . . . . . . . . . . 17.10 After filtration a sample of the liquor was taken for analysis Pentosans in cellulose (based on weight of cellulose) . . . 1 3 , l O Pentosans in cellulose (based on weight of original straw) . 7 .U3 and the amount of sodium sulfite remaining was estimated by Ash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 . 6 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulfur., 0.02 a direct titration with i ~ d i n e . ~ The filter paper had been Coppernumber . . . . . . . . . . . . . . . . . . . . . . . . . . . . .97 previously dried a t 105" C., cooled, and weighed in an aluI n order to obtain uniform samples for comparison and to minum dish provided wit,h a tight-fitting cover. The fibrous facilitate penetration of the chemical solutions into the flax residue or pulp was washed by filtration with approximately straw and thus obtain uniform cooking, a suppl). of straw one liter of boiling water, acidified with 10 per cent acetic adequate for all the tests was ground to pass a 40-mesh stand- acid, and washed again with about 1.5 liters of hot disard sieve and thoroughly mixed. The advantages of a tilled water: It was then transferred, together with the filfinely ground material were in some cases partly offset, how- ter paper, to a large watch glass and air-dried for 16 hours. ever, by difficulty in filtering the finely divided and a t t'imes Pulp and filter paper were next placed in the aluminum dish somewhat gelatinized residue. and oven-dried for 8 hours a t 105" C., covered, cooled in the Apparatus desiccator, weighed, and the pulp yield calculated. The fibrous residue was finally removed from the filter paper and For the pulping reactions a Steel autoclave was used, passed through a small grinder in order to afford a uniforln which was similar to the one reported in a previous paperJ2 sample for chemical analysis. A~~~~~~~~OF F~~~~~~ REsIDuE-The pulp samples were although modified in some details of construction and provided with a thermometer well. severally analyzed for the following: cellulose, lignin, total thermostatic Oil bath, for heating the auto- pentosans, pentosans in the cellulose, solubility in 1 per cent clave, while essentially similar in principle to the one pre- sodium hydroxide solution, and copper number. ~ i was ~ viously described, was modified to afford an even higher determined by a modification of the method of Ost and accuracy of control. Wilkening4 and copper number by a slight modification of the Staud and Gray methods5 All the other determinations Experimental Procedure were made according to methods reported by Schorger. DIGEST1oN-The Oil bath was first heated "Ider hand B sample of untreated flax was subjected to the same analyses control. The autoclave, charged with approximately 25 as the pulp samples. grams of flax straw and chemical solution, was immersed in the bath when the latter had reached a temperature of Description of Tests 175" C. The bath temperature was then held approximately constant until the temperature of the contents of the autoThree series of tests were made, in which the conditions clave reached 150" C. At this point the autoclave was tem- were controlled according to the schedule in Table I. porarily removed and the bath temperature was lowered to Throughout each series the conditions of treatment-namely, about 159" C., which required approximately 5 minutes, temperature, concentration of chemical, volume of liquor, The autoclave was again immersed in the bath and by manipu8 Rawling and Staidl, Papev Ind., 7, 901 (1925).
I
ing studies of flax straw now in progress at this laboratory it recently became desirable to d e t e r m i n e i n detail the chemical action of sodium sulfite on the straw. This paper deals wit,h the effectof a change in concentration of the chemical and of a change in the ratio of weights of chenlical and straw.
e.
I
l Presented before the Division of Cellulose Chemistry ;it the 72nd Meeting of t h e American Chemical Society, Philadelphia, P a . , September 5 t o 11. 1926. Miller and Swanson, THISJOURNAL, 17, 843 (1925).
Cross and Bevan, "Researcheg on Cellulose." Vol. 3 1910) ; Chem.-Ztg., 34, 461 (1910). 5 THIS JOURNAL, 17, 741 (1925). 6 I b i d , 9, 556 (1917).
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39 (1905-
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Vol. 19, No. 3
INDUSTRIAL A N D ENGINEERING CHEMISTRY
372
oven-dry weight of straw and therefore ratio of chemical to straw-were maintained constant. Periods of cooking were successively lengthened in the experiments of each series in order to afford a view of the reaction as it progressed. Table I-Conditions PROPORTION OF NazS08 TO
of Tests
CONCENTRATION
\'OLlJME
OF
DRYSTRAW BY WEIGHT
OF
SOLUTION
SOLUTION
Per cent
Grams/lrler
cc.
20 40 40
40 40 80
125 250 125
I I1
I11
SERIESI-The data given in Table I1 for Series I and recorded graphically in Figure 1 show that the yield of fibrous residue, or that portion of the straw remaining undissolved at the end of the pulping period, decreases very rapidly during the first hour of cooking. Beyond that point the rate of change in yield and in chemical properties with time of cooking is relatively slow. The cellulose suffers its greatest loss during the first hour of cooking. Afterward the dilute sodium sulfite solution hydrolyzes it but slowly. This loss is not indicated in the pentosans present in the Cross and Bevan cellulose, but rather in the pentosan-free cellulose, as shown in the eighth column of Table 11. The pentosans, determined in the cellulose, remain practically constant throughout 12 hours, the maximum period of cooking. During the early stages of cooking the sodium sulfite solution attacks the material determined as lignin to a much more marked degree than it does the cellulose. Beyond the first hour the lignin removal proceeds more slowly, but even after 12 hours the total amount removed exceeds that of cellulose for the same period. The pentosans not in the Cross and Bevan cellulose, like the lignin, are removed at an exceedingly rapid rate during the first hour of cooking and also, like the lignin, are more slowly removed during the remainder of the cooking period. I n the twelfth column of Table I1 i t is of interest to note that values closely approximating 100 per cent are obtained for all the cooked samples by adding together the lignin, the pentosan-free cellulose, and the total pentosans. SERIES11-Acomparison of the data for Series I and I1 shows that the rate of cooking is considerably accelerated ~ 1 sa result of increasing the ratio of chemical to straw. It Table 11-Analytical
-
NazSOa
371 388 386 384 383 382 385 I1 393 392 394 111 391 389 390
Hours 0
1 3 6"
8 10
12 1l/z
3 6 ll/pa
3" 6"
CELLULOSE
ADDED
Per 100 grams Concn. straw
I
3ASED O N OVEN-DRY WEIGHT OF RESIDUE
BASEDO N OVEN-DRY WEIGHTOF STRAW
2:;-
SERIES
is noteworthy, however, that for a given yield the chemical properties of the insoluble residue are in all cases practically identical-a fact which is observed even when the time required to reach that yield, due to doubling the ratio of chemical to straw, has been reduced by 50 per cent. SERIES111-From a comparison of the data for Series11 and I11 it is evident that a change in concentration of the sodium sulfite from 40 grams to 80 grams per liter is practically without effect upon the rate of decomposition or upon the relation of chemical properties to yield.
Data o n Flax Straw Hydrolyzed with Sodium Sulfite-Effect of Concentration, Ratio of Chemical to Straw, and Time of Cooking o n Yield and Chemical Properties
I
SAMPLE
Figure 1
Grams Grams per liter
Yield of pulp
%
Lignin
%
Total
Pentosanfree
%
70
urn of pencellulose, osan-fiee Copper
PENTOSANS
Total
%
In cellulose
%
A-ot in cellulose
70
Solub1e Consumption of chemical
ignin, and number total pentosans
70
~ A S E DO N CHEMI CAI. ADDED
Grams
Yo
33.73 10.45 7.75 10.52 8.17 8.23 8.72
None 2.86 3.07 4.31 4.17 3.96 4.13
None 56.9 61.0 84.9 82.1 78.0 82.1
70
None 40 40 40 40 40 40
100 68.36 65.59 64.36 62.97 61.95 61.37
23.28 13.75 11.70 11.10 10.45 9.45 9.80
53.80 51.15 51.15 50.15 50.80 50.40 49.50
46.75 44.30 43.60 43.35 43.40 43.00 42.50
17.10 10.32 10.23 10.11 9.50 9.57 9.45
7.06 6..84 7.58 6.78 7.40 7.44 6.97
10.05 3.48 2.65 3.33 2.10 2.13 2.48
87.13 99.98 99.84 100.21 100.50 100.05 100.54
7.97 5.17 3.64 5.10 4.36 4.62 3.99
40 40 40
40 40 40
65.26 64.19 62.01
12.10 11.81 10.16
51.00 50.00 49.15
43.60 42.83 42.38
10.02 9.58
9.87
7.43 7.12 6.73
2.44 2.90 2.85
100.40 100.75 100.20
3.00 3.35 3.68
7.29 8.13 9.81
3.00 2.85 2.71
29.85 28.40 26.90
40 40 40
80
67.74 64.79 61.94
13.16 11.50 9.95
51.80 49.60 48.85
43.95 42.75 42.15
11.00
80 80
7.85 6.87 6.73
3.15 3.58 3.17
100.51 99.80 100.02
3.31 4.94 5.38
8.56 11.29 11.75
3.04 3.60 4.43
30.1 35.5 43.7
None 20 20 20 20 20 20
Resulting pulp was filtered with difficulty.
10.45 9.90
