Extraction of Hemicelluloses
from Plant Materials QUANTITATIVE STUDY E. YANOVSICY Bureau of Chemistry and Soils, U. S. Department of Agriculture, Washington, D. C.
The course of extraction of hemicelluloses from beet pulp, rice hulls, and peanut shells was studied. Ex-~ traction by both acid and alkaline solutions was investigated. Normal extraction curves were obtained for rice hulls and peanut shells, but certain peculiarities (breaks in the curve) in the behavior of beet pulp were noted on extraction with both acid and alkali. That this phenomenon is due to the presence of pectin in beet pulp is advanced as a probable explanation.
T
about a 20 per cent solution of sodium hydroxide, then with about 20 per cent hydrochloric acid, and thoroughly washed with water. The precipitate in the crucible was washed several times with hot water (150-200 cc.). The filtrate is a solution of a number of substances. Hawley and Wise (4) enumerate eight different reactions which take place while wood is being treated with dilute acid under pressure. In the present work the filtrate was discarded. The crucibles with the residue from extraction were dried at about 105" C. overnight. From the weight of the residue the amount and percentage of extracted fraction were calculated. Part of the residue was used for furfural determination. The figure for pentosans thus obtained was com uted t o original weight of the sample, and this permitted the ca?culation of the percentage of pentosans extracted. Actual determination of pentosans was made by the Krober method (1).
HE term "hemicellulose" was introduced into chemistry in 1891 by Schulze (7) who believed that the compounds extracted by him from various plant materials were either pentosans or hexosans, or combinations of both. Later the presence of uronic acids was demonstrated in the hemicellulose complex. That our knowledge of hemicelluloses is still in its infancy can be judged from the definition given by Norman (6)in 1937, who considered hemicelluloses as "those cell-wall polysaccharides which may be extracted from plant tissues by treatment with dilute alkalies, either cold or hot, but not with water, and which may be hydrolyzed to constituent sugar and sugar-acid units by boiling with hot dilute mineral acids." Until recently the hemicelluloses and the pentose sugars xylose and arabinose have been of purely theoretical interest. For the last decade or so, however, the question of industrial utilization of farm wastes, which is primarily cellulosic and hemicellulosic material, has engaged the attention of industrial research chemists. The problem of commercial extraction of hemicelluloses from plant material has assumed greater importance; in later works-e. g., Hall, Slater, and Acree (3) and Bryner, Christensen, and Fulmer (%h)-t'e optimum conditions for extraction had been sought before the extracted hemicelluloses were studied. This paper gives results of the extraction of three typical farm and factory waste materials with various concentrations of acid and alkali a t several different temperatures.
Preliminary Experiments with Beet Pulp The range of concentrations of acid and alkali used in the following experiments extended both above and below the concentrations ordinarily used for hydrolysis or extraction of hemicelluloses. It is well known that, with increasing concentrations of acid or alkali, the cellulose fraction of the plant will be attacked by the reagent. It would therefore be of interest to know whether a simple extraction curve would be continuous or would break a t a point where the acid or alkali begins to act upon the cellulose of the plant. Table I and Figure 1show the results of extraction of beet pulp with various concentrations of hydrochloric and sulfuric acids a t 50" and 80" C . These data reveal a peculiarity common to all four curves. At a certain concentration of the acid there is a distinct break, a minimum is reached, and the curve slowly rises again. With increase in temperature the breaking point of the curve shifts towards lower acidity. The breakingpoints are: sulfuric acid, about 4.6 N a t 50" and about 0.7 N a t 80" C.; hydrochloric acid, about 2.3 N a t 50" and about 0.3 N a t 80" C. As will be shown later (Figure 4 ) , a t 100" C. the break in the curve for the sulfuric acid extraction curve is still perceptible (at 0.45N acid), but it has entirely disappeared in the hydrochloric acid curve. The fact that the peculiarity in the shape of the extraction curve was found in four distinct experiments greatly militates against the possibility of experimental error. However, to verify it still further, the same phenomenon has been found in a somewhat different manner, If we choose an acid concentration somewhere near the breaking point of the curve and vary the time of extraction, starting with shorter periods than those (3 hours) used in the above experiments and gradu-
Materials and Procedure The plant materials used for this work had not been subjected to any preliminary purification. Beet pulp was obtained from a beet sugar factory. It contained 9.3 per cent moisture, 3.4 ash, 2.3 nonreducing sugar, and 9.6 crude protein (N X 6.25). The rice hulls contained 8.25 per cent moisture, 21.3 ash, a trace of sugar, and 2.1 per cent crude protein. Peanut shells contained 11.8 per cent moisture, 3.0 ash, 0.9 reducing sugars, 0.7 nonreducing sugars, and 5.8 crude protein. All materials were ground, and the same supply of ground material was used throughout the experiments. A weighed amount of plant material (usually 2 grams) was mjxed with measured amounts (usually 100 cc.) of acid or alkali of known concentration in a 500-CC.flask. The flask was connected with a condenser (ground-glass joints) and kept immersed in a constant-temperature bath containing either water or glycerol. An electrical or gas (6) thermoregulator was used to control the temperature to *0.5' C. At the end of the experiment the mixture was filtered while still hot through a weighed Gooch crucible. The asbestos for the crucibles had been digested with 95
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z
TABLE I. EXTRACTION OF BEETPULP WITH ACIDS
E
6
(2 grams pulp equivalent t o 1.814 grams dry material: 100 cc. acid; 3 hours) Loss on Extraction Normality ~ - 5 0 ~ C-. --so0 c.-
5 Eis
%
OL
Gram
Gram
zm5
%
VI
0 0.07 0.15 0.30 0.61 1.0 1.5 2.3 3.1 4.1 4.6 6.4 8.7
Hydrochloric Acid Extraction 0.222 12.2 0.264 0.434 23.9 0.877 0.539 29.7 0.985 0.641 35.3 1.069 0.745 41.1 1,040 0.813 44.8 0.991 0.886 48.8 0,989 0.961 53.0 1.037 0.806 44.4 1.098 0.843 46.5 1.166 0.880 48.5 1.208 0.981 54.1 1.266 1,181 65.1 ...
14.6 48.3 54.3 58.9 57.3 54.6 54.5 57.2 60.5 64.3 66.6 69.8
TABLE 11. INFLUENCE OF TIMEON EXTRACTION OF BEETPULP
0 0.06 0.12 0.28 0.45 0.70 1.2 1.8 2.8 2.9 3.7 4.6 5.8 8.7
Sulfuric Acid Extraction 0.222 12.2 0.378 20.8 0.434 23.9 0.512 28.2 0.602 33.2 0.668 36.8 0.742 40.9 0.795 43.8 0.863 47.6 0.867 47.8 0.901 49.7 0.918 50.6 0.794 43.8 0.826 45.5
14.6 42.6 47.9 54.8 56.9 69.3 56.4 54.2 51.4 51.8 52.5 53.1 54.6 60.9
(1 gram pulp equivalent t o 0.907 gram dry material; 50 cc. acid; 50’ C.) 7 Loss on Extraction Time -2.4 N BC1-4.2 N HC1Hours Cram % Uram % 1 0.421 46.4 0.496 54.7 1.5 0.504 55.6 2 0:465 5i:3 0.462 50.9 2.5 0.430 47.4 5318 0.431 47.5 3 0:489 4 0.496 54.7 0.429 47.3 4.5 0.441 48.6 46.2 0: 4i9 5 0.419 47:3 45.2 5.5 0.410 6 0.406 44.8 0:432 4?:6 7 0.423 46.6 0.446 49.2
0.264 0.773 0.868 0.994 1.032 1.076 1.023 0.984 0.933 0.940 0.952 0.963 0.991 1.104
3
TIME IN HOURS
FIGURE 2.
FIGURE 1. EXTRACTION OF BEET PULPWITH HYDROCHLORIC AND SULFURICACIDS
Correlation between the Break i n the Curve and Hemicellulose Extraction The break in the extraction curves seems to occur a t comparatively low concentrations of acid and a t comparatively low
INFLUENCE OF TIMEON EXTRACTION OF BEET PULP
..
ally increasing the extraction time to periods beyond the usual 3 hours, we should obtain a smooth curve a t first, come t o a break a t about 3 hours, reach a minimum, and then observe a gradual rise of the curve. In other words, we should obtain a curve of approximately the same shape as those described above. If, however, we choose an acid concentration somewhere near the minimum after the break in the curve and vary the time of extraction, the break should be observed a t the earlier stage of the extraction (below 3 hours). This reasoning was verified by actual experiments, as shown in Table I1 and Figure 2. For 2.4 N hydrochloric acid the break in the curve occurred between 3 and 4 hours, as was expected. The break for 4.2 N acid curve is a t about 1.5 hours.
4
temperatures to justify assumptionof a considerable chemical action of acids on the cellulose of the plant material. A possible explanation of this phenomenon is given later. How does this break in extraction curves affect the extraction of hemicelluloses with acids? The answer is given in Table I11and Figure 3. When figures representing per cent total loss are plotted with those for per cent total pentosans extracted, approximately parallel curves are obtained. Therefore the break in the curve is apparently due to a break in the values of hemicelluloses extracted. Attention is called to the last column of Table I11and following tables. The calculated values for per cent pentosans in the extracted material give an idea as to the “purity” of extract with respect to pentosans. These figures, however, have a direct meaning only in alkaline extraction when the hemicelluloses are presumed to be extracted as such. In acid extraction the figures represent (for lower concentrations of acid) the per cent of sugars and uronic acids in the solid material of the extract. At higher concentrations of acid, decomposition of both sugars and uronic acids takes place.
TABLE111. RELATION BETWEEN TOTAL AND PENTOSAN EXTRACTION (2 grams pulp equivalent t o 1.814 grama dry material; 100 cc. hydrochloric acid; 3 hours: pentosans in original material, 26.5 per cent on dry basis) -Pentosans in- -PentosansResidue Extd. Calcd. % of to %.of total Pentosans orir;inal original pento- in Extd. Detd. weight material sans Material Normality Loss on Extn. Crams
1.0 2.5 3.1 5.05
0.826 0.968 0.848 0.908
0 0.08 0.15 0.32 1.0 1.5 2.5 3.1
0.257 0.899 0.983 1.072 0.984 0.967 1.037 1.075
%
%
%
Extraction a t 50’ C. 45.5 12.7 6.9 19.6 53.4 10.3 4.8 21.7 46.8 12.3 6.5 20.0 6.4 50.1 12.9 20.1 Extraction a t 80’ C. 25.6 22.0 14.2 4.5 49.6 11.5 5.8 20.7 54.2 21.9 10.0 4.6 59.1 7.9 3.2 23.3 54.2 10.5 4.8 21.7 21.2 53.3 11.3 5.3 57.2 21.8 10.9 4.7 9.4 3.8 22.7 59.3
% 74.0 81.9 75.5 75.8
43.1 40.6 42.7 40.1
17.0 78.1 82.6 87.9 81.9 80.0 82.3 85.7
31.7 41.7 40.4 39.4 40.0 39.8 38.1 38.3
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Extraction of Beet Pulp
WITH ACIDSAT 100" C. I n the usual laboratory practice the pentosans are extracted with dilute boiling acids. To approach the practical conditions of extraction, the experiments were repeated a t 100' C. The results (Table IV, Figure 4) show that the break in the curve is still noticeable in the sulfuric acid curve for both total and pentosan extraction, but for all practical purposes there is no break in the hydrochloric acid curve. The results also show that 90 per cent of the pentosans can be extracted by 0.15 N sulfuric acid or by 0.08 N hydrochloric acid, and that a considerable increase in acidity is required to extract further quantities of pentosans. After the percentage of pentosans in the extracted material decreases somewhat (with figure for zero normality omitted), it remains reasonably constant with further increase in acidity of the extract. WITHALKALI. Alkaline extraction of plant material is resorted to when it is desirable to obtain the hemicelluloses rather than their decomposition products. Extraction with sodium hydroxide a t 50' C. (Table V, Figure 5 ) shows that there is a distinct break a t about 1.8 N alkali. All the figures of Table V are averages for two well-agreeing experiments. When the temperature was raised to 80" C. (Table VI, Figure 5 ) , the break in the curve for both total and pentosan extraction shifted to about 0.5 N alkali. Ninety per cent of the pentosans are extracted with 1.1N alkali, and considerable in-
NORMALITY OF ACID
FIGURE 3. RELATION BETWEEN TOTAL AND PENTOSAN EXTRACTION
TABLE V. EXTRACTION OF BEETPULP WITH SODIUM HYDROXID~ AT 50' C. (1 gram pulp equivalent t o 0.907 gram dry material; 50 cc. alkali; 3 hours) Normality loss on Extn.Normality -Loss on Extn.-
Gram 0 0.09 0.18 0.36 0.75 1.1 1.8 2.8
%
Gram 3.6 4.5 5.9 7.5
9.5 10.9 14.9 18.0
0.615 0.626 0.650 0.651
OF BEETPULP WITH ACIDSAT 100' C. FIGURE 4. EXTRACTION
TABLE IV. EXTRACTION OF BEETPULPWITH ACIDSAT 100' C. (2 grams pulp equivalent to 1.814 grams dry material: 100 cc. acid; 3 hours: pentosans in original material, 26.5 per cent on dry basis) -Pentosans in-PentosansResidue Extd. Calcd. to pf Et:; Pentosans original original pento- in Extd. Material Normality Loss on Extn. Detd. weight material sans
Grams 0 0,012 0.025 0.059 0.12 0.26 0.45 0.87 1.2 2.2 2.9 3.3 4.3 4.6 5.8 9.4
0.427 0.710 0.916 1.069 1.124 1.174 1.185 1.167 1.161 1.195 1.216 1.208 1.236 1.240 1.258 1.260
0 0.018 0.032 0.080 0.17 0.32 0.66 0.99 1.6 2.4 3.2
0.432 0,889 1.080 1.172 1.200 1.200 1.222 1.248 1.267 1.290 1.300
%
%
%
Sulfuric Acid Extraction 6.4 23.5 26.3 20.1 16.1 10.4 39.1 17.1 20.5 6.0 50.5 12.2 22.8 3.7 9.0 58.4 2.9 23.6 7.6 62.0 2.2 24.3 6.2 64.7 1.5 25.0 4.2 65.3 2.2 24.3 6.2 64.3 24.1 2.4 6.6 64.0 1.9 24.6 5.6 65.9 25.2 4.0 1.3 67.0 1.7 24.8 5,1 66.5 25.1 1.4 4.5 68.1 25.2 1.3 4.2 68.4 0.9 26.6 3.1 69.4 .. .. .. 69.5 Hydrochloric Acid Extraction 19.8 6.7 23.8 26.0 19.8 49.0 13.1 6.7 3.9 22.6 59.5 9.6 23.9 2.6 64.6 7.5 2.0 24.5 6.0 66.2 1 . 5 25.0 4 . 3 66.2 25.3 1.2 3.8 67.4 25,5 1.0 3.3 68.8 0.7 25.8 2.3 69.9 0.5 26.0 71.1 1.8 0.5 26.0 71.7 1.6
% 24.2 60.8 77.4 86.1 89.1 91.7 94.3 91.7 90.9 92.8 95.1 93.6 94.7 95.1 96.6
27.2 41.2 40.6 39.0 38.1 37.6 38.3 37.8 37.7 37.3 37.6 37.3 36.9 36.8 36.9
25.3 74.7 85.3 90.2 92.5 94.3 95.5 96.2 97.4 98.1 98.1
28.1 40.4 38.0 37.0 37.0 37.8 37.5 37.1 36.9 36.6 36.3
..
'
..
O F BEETPULP WITH FIGURE 5 . EXTRACTION SODIUM HYDROXIDE
%
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Extraction of Rice Hulls
u W
WITHHYDROCHLORIC ACID. Beet pulp discussed so far represents a factory by-product. It has gone through the diffusion batteries of the beet sugar plant and has been dried a t an elevated temperature. Both operations might have caused some physical or chemical changes in the cellulose or hemicellulose of the material. The other two plant materials studied here (rice hulls and peanut shells) are farm waste products without any previous chemical treatment. Results of extraction of rice hulls with acid are given in Table VI1 and Figure 7. The results show that rice hulls give smooth ex-
U
K 9 W c1
z sa ti
v)
2 1
$& 6 c
gs d
0.
TABLEVII. EXTRACTION OF RICEHULLS WITH HYDROCHLORIC ACID
E 4
zU
U
(2 grams hulls equivalent t o 1.835 grams dry material. 100 cc. acid: 3 hours; pentosans in original material, 20.9 per cent bn dry basis) -Pentosans in-PentosansR esid u e Extd. Calcd. % of Pento%,of total sans in to original original pentoExtd. Normality Loss on Extn. Detd. weight material sans Material
5 3 0 z
4 2 OF BEETPULP WITH FIQURE 6. EXTRACTION SODIUM HYDROXIDE AT 100' C.
0 0.09 0.18 0.36 0.75 1.1 1.8 2.8 3.6 4.5 5.6 7.5 9.5 10.1 14.9 18.0 0 0.014 0.033 0.082 0.18 0.34 0.70 1.1 1.8 2.9 3.4 5.5 7.1 10.5 10.6 17.3 20.6
0.259 0.912 1.105 1.127 1.119 1.228 1.266
%
%
%
Extraction a t 80' C. 14.3 50.3 60.9 62.1 61.7 67.7 69.8
Average, 1.350. Average, 74.3. C Average, 3.5. Extraction a t 100' C. 26.3 19.9 23.5 23.3 14.8 36.6 20.5 11.3 44.8 4.7 12.6 63.0 2.9 9.0 64.5 2.7 7.8 65.9 2.0 6.4 68.9 5.5 1.6 70.2 4.1 1.2 71.2 Trace 73.3 Trace 73.8 Trace 74.4 Trace 75.3 Trace 75.9 Trace 76.1 Trace 76.4 Trace 76.9 a
b
d e
Extraction at 22.3 6.7 10.3 19.6 16.0 15.6 21.5 11.4 9.3 23.5 6.7 26.4 5.3 28.0 3.2 30.0 2.1 31.0 Trace 31.8 Trace 32.3 Trace 32.2
Average, 0.9. Average, 25.6.
24.9 44.1 57.3 82.3 89.1 89.8 92.5 94.0 95.6
%
0 0.03 0.08 0.17 0.32 0.66 1.00 1.6 2.4 3.2 4.0 4.5
1.4 10.0 12.4 29.7 52.2 58.9 65.1 75.1 80.1 87.6 93.6 96.2
0.6 31.3 30.6 44.9 57.1 58.0 61.0 63.1 64.0 66.1 67.0 67.3
0.5 15.8 37.3 57.4 66.0 76.6 81.8 89.0 93.3
1.5 32.0 48.8 55.8 58.7 60.6 61.1 62.3 62.9
100' C. 20.8 17.6 13.1 8.9 7.1 s4.9 3.8 2.2 1..4
0.1 3.3 7.8 12.0 13.8 16.0 17.1 18.7 19.6
OF RICE HULLSWITH SODIUM TABLEVIII. EXTRACTION HYDROXIDE
g .4verage, 96.5.
6.6 11.7 16.2 21.8 23.6 23.8 24.5 24.9 25.3
%
0 0.08 0.15 0.32 0.61 1.00 1.5 2.5 3.2 3.9 5.1 6.4
(2 grams pulp equivalent t o 1.814 grams dry material; 100 cc. alkali; 3 hours; pentosans in original material, 26.5 per cent on dry basis) .--Pentosans in-PentosansResidue Extd. PentpCalcd. % of to % Ff total sans In Extd. original original pentoLoss on Extn. Detd. weight material sans Material Normalitg
%
%
Extraction a t 80' C. 5.0 21.7 20.6 0.3 20.1 18.8 2.1 6.7 20.0 18.3 8.5 2.6 17.1 14.7 13.8 6.2 19.1 12.4 10.0 10.9 8.6 10.9 21.2 12.3 9.5 7.3 22.8 13.6 6.9 5.2 24.9 15.7 5.4 4.0 26.4 16.9 3.6 2.6 27.7 18.3 2.0 1.4 29.1 19.5 1.1 0.8 29.9 20.1
OF BEETPULPWITH SODIUM TABLEVI. EXTRACTION HYDROXIDE AT 80" and 100' C.
Grams
%
Gram
28.1 32.0 33.9 34.6 36.6 36.1 35.5 35.6 35.5
crease in alkalinity is required t o extract further quantities of pentosans, The "purity" of the extract (last column of Table VI) remains approximately constant throughout the process of extraction. The break in the curve is still noticeable a t 100' with 0.25 N sodium hydroxide (Table VI, Figure 6). At 100' C., 90 per cent of pentosans are extracted by 0.34 N sodium hydroxide, as compared with 0.15 N sulfuric acid and 0.08 N hydrochloric acid (Table IV, Figure 4) a t the same temperature. The purity of the extract again remains constant. The tables show that about 16.0 per cent pentosans were extracted by water a t 80°, and about 25 per cent a t 100' C.
(2 grams hulls equivalent t o 1.835 grams dry material; 100 cc. alkt+; 3 hours; pentosans in the original material, 20.9 per cent on dry basis) -Pentosans in-PentosansResidue Extd. Calcd. % of Pentoto yo,of total sansin original original pentoExtd. Normality Loss on Extn. Detd. weight material sans Material Grams % % % %
Extraction a t 4.8 21.8 29.2 26.9 38.3 28.1 27.4 40.3 23.8 44.6 20.0 47.3
0 0.082 0.18 0.34 0.70 1.1 1.8 2.9 3.4 6.5 7.1 10.5 17.3 0 0.014 0,033 0.082 0.18 0.34 0.70 1.1 1.8 5,5 a
0.119 0,234 0,334 0.602 0,773 0.816 0.880
0.934 0.998 1.024 1.005
Average, 52.2.
80' C.
20.8 19 0 17.3 16.4 13.2 10.5
i :9 3.6 4.5 7.7 10.4
9:1 17.2 21.5 36.8 49.8
6:5 9.4 11.2 17.3 22.0
13.3
63.6
25.5
Extraction at 100' C. 6.5 22.6 21.1 12.8 23.4 20.4 i):5 1.8 18.2 24.3 19.1 32.8 27.0 18.1 2.8 42.1 28.6 16.6 4.3 44.5 27.7 15.4 5.5 48.0 25.3 13.2 7.7 50.9 21.3 10.5 10.4 54.4 16.3 7.4 13.5 i z : z ] d 5.9 15.0
2:4 8.6 13.4 20.6 26.3 36.8 49.8 64.6 71.8
319 9.9 8.5 10.2 12.4 16.0 20.4 24.8 26.6
..
..
..
5645::)~
b
Average, 15.9.
C
Average, 55.3.
d
..
Average, 13.4.
JANUARY, 1939
INDUSTRIAL AND ENGINEERIKG CHEMISTRY
99
tract increased with alkalinity of extracting solution. There is practically no extraction of pentosans with water a t either 80" or 100" C.
Extraction of Peanut Shells WITH HYDROCHLORIC ACID. Peanut shells behave very much like rice hulls on extraction with acid (Table IX, Figure 9). The curves of Figure 9 are almost identical with those of Figure 7 for rice hulls. Pentosans to the extent of 92.9 per cent were extracted by 2.4 N acid a t 100" and by 6.4 N acid a t 80" C. The purity of the extract increases with the increase in concentration of acid a t 80" but behaves somewhat irregularly a t 100". O F PEAKUT SHELLS WITH TABLEIx. EXTRACTION HYDROCHLORIC ACID
(2 grams shells equivalent t o 1.764 grams dry material: 100 cc. acid: 3 hours: pentosans in original material, 19.8 per cent on dry basis) ,-Pentosans in-PentosansResidue Extd. Calcd. % of Pentpto "rp pf total sans In original original pentoExtd. Normality Loss on Extn. Detd. weight material sans Material GTam
0
~ O R M A L I T Y OF A C ~ D
0.08 0.15 0.32 0.61 1.00 1.5 2.5 3.1 3.9 5.1 6.4
OF RICEHULLS WITH HYDROCHLORIC ACID FIGURE 7. EXTRACTION
0 0.03 0.08 0.17 0.32 0.66 0.99 1.6 2.4 3.2 4.5 6.0
%
%
%
%
Extraction a t 80' C. 19.6 20.9 18.9 20.9 18.7 20.9 17.0 19.2 15.6 18.3 14.2 17.2 12.4 l5,7 7.8 10.6 7.0 9.7 5.1 7.3 3.2 4.8 1.4 2.1 Extraction a t 100' C. 19.6 20.9 6.4 16.2 19.6 12.1 13.7 lE 9 13.8 9.6 11.4 16.0 8.4 9.3 20.7 5.0 6.7 25.5 3.8 5.3 28.9 2.6 3.2 32.8 1.4 2.1 35.6 Trace 37.4 Trace 37.8 Trace 37.9
0.2 0.9 1.1 2.8 4.2 5.6 7.4 12.0 12.8 14.7 16.6 18.4 3.1 29.8 44.2 63.8 55.1 58.0 55.4 52.4 51.7
i l i ~ ~ l l lI /I il Iii l i I i j
0
N O R M A L I T Y OF A L K A L I
FIQURE 8.
ICXTRACTION O F
RICEHULLSWITH SODIUM HYDROXIDE
traction curves for both total and pentosan extraction. Even a t 80" C. no trace of a break in the curve was noticed. The extraction of pentosans both a t 80" and 100" C. proceeds considerably more slowly than in beet pulp a t corresponding temperatures. Pentosans to the extent of 93.6 per cent are extracted by 5.1 N acid a t 80", and 93.3 per cent by 2.4 N acid a t 100' C. It is interesting to note that the purity of the extract increases with increase in concentration of the acid. At 80" C. pentosans constitute 67.3 per cent of the material extracted with 6.4 N acid. For 2.4 N acid a t 100" C. pentosans constitute 62.9 per cent of the extracted material. WITHALKALI. The extraction of pentosans from rice hulls with sodium hydroxide (Table VIII, Figure 8) is not as complete as with acids. Maximum extraction a t 80" C. is 63.6 per cent of total pentosans a t 2.9 N alkali and remains constant with further increase in alkalinity. At 100" C. maximum pentosan extraction reaches the value of 71.8 per cent with about 2.5 N alkali and remains constant on extraction with stronger alkali. In both cases the "purity" of the ex-
NORMALITY
OF ACID
FIGURE9. EXTRACTION OF PEANUT SHELLSWITH HYDROCHLORIC ACID
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VOL. 31, NO. 1
TABLEX. EXTRACTION OF PEANUT SHELLSWITH SODIUM HYDROXIDE (2 grams shells equivalent t o 1.764 grams dry material. 100 00. alkali; 3 hours; pentosans in original material, 19.8 per c e A on dry basis)
Normality
Loss on Extn.
%
Gram
-Pentosans in- -PentosansResidue Extd. Calcd. % of Pentpto % pf total sansin original original pento- Extd. Detd. weight material sans Material
%
%
%
Extraction a t 80' C.
s-
0
0 0.09 0.18 0.36 0.75 1.1 1.8 2.8 3.6 4.5 5.9 7.5
0.103 0.273 0.305 0.339 0.384 0.405 0.450 0.491 0.512 0.521 0.505 0.486 5 Average, 16.8. * Average, 27.3.
5.8 15.5 17.3 19.2 21.8 23.0 25.5 27.8 29.0 29.5 28.6 27.6
: NORMALITY OF ALKALI
FIGURE 10. EXTRACTION OF PEANUT SHELLSWITH SODIUM
HYDROXIDE
WITH SODIUM HYDROXIDE. The extraction of pentosans with alkali proceeds very slowly (Table X, Figure 10). Maximum extraction a t 80" C. was 39.5 per cent pentosans with 3.6N alkali and remains constant with further increase in alkalinity. The purity values increase with increase of alkalinity. At 100" C. maximum extraction of pentosans was 47.5 per cent, and this value seems to remain constant with further increase in alkalinity. The purity of the extract increased with concentration of alkali. Within experimental error water does not extract pentosans from peanut shells either a t 80" or a t 100" C.
Probable Explanation of Break in Extraction Curves Inasmuch as the break in the extraction curves was noticed for beet pulp only, it is safe to assume that this peculiarity is not due to any extent to the action of acids or alkalies on the cellulose fraction of the plant material. The cause of the abnormality, therefore, is apparently due to the composition of the beet pulp itself. It is well known that beet pulp contains a considerable amount of pectin. The presence of this substance may account for the peculiar behavior of beet pulp on extraction with acids and alkalies. It was noted during the experiments that a t the end of the extraction with lower concentration of acids and alkalies the filtration of the mixture and washing of the precipitate proceeded very easily. After reaching the concentration corresponding to the breaking point of the curve, however, the filtration and the washing of the precipitate became extremely slow apparently as a result of the swelling of the residue. The filtration improved again after the concentration corresponding to the second break in the curve had been passed. It is believed that the swelling is due to jellying (caused by the pectin) of hemicelluloses or their hydrolytic products. The formation of jelly interferes with proper washing of the residue, which accounts for the higher weight of the residue, the apparent decrease in total and pentosan extraction, and the irregular shape of the extraction curves. Spencer (8) showed the possibility of jelly formation under alkaline conditions, and therefore the above explanation
0 0.014 0.033 0.082 0.18 0.34 0.70 1.1 1.8 2.9 3.4 5.5 7.1
b
Average, 12.0.
0
Average, 7.8.
d
Average, 39.5.
Extraction at 100' C.
0.114 0.236 0.274 0.338 0.380 0.416 0.455 0.482 0.531 0.589
0.2 1.1
1.7
2.4 3.2 3.7 4.7 5.3 6.9
1.0 5.6 8.6 12.1 16.2 18.7 23.7 26.8 34.8
3.1 8.2 11.0 12.5 14.9 15.7 18.2 19.4 22.9
0.588
f Average, 0.593. o Average, 33.6. h Average, 15.7. j Average, 9.4. k Average, 47.5. 1 Average, 27.9.
i Average
10.4.
will cover both the acid and the alkaline extraction. However, some swelling and slow filtration were noticed in alkaline extraction of rice hulls and peanut shells which might have been due to gelatinizing action of alkali on cellulose. The effect, however, was not sufficient to change the character of the extraction curves. It is possible that the cellulose of the pretreated and preheated beet pulp is gelatinized, under the same conditions of treatment, to a greater extent than untreated rice hulls and peanut shells. And this gelatinization (as jellying in the case of acid) may account for the irregularity of the alkaline extraction curves.
Literature Cited (1) Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 1935. (2) Bryner, Christensen, and Fulmer, IND.ENQ.CHEM., 28, 206 (1936). (3) Hall, Slater, and Acree, Bur. Standards J. Research, 4, 329 (1930). (4) Hawley and Wise, "Chemistry of Wood," p. 220, A. C. S. Monograph Series, New York, Chemical Catalog Co., 1926. ( 5 ) Kingsbury, IND.ENQ.CHEM.,Anal. Ed., 9, 333 (1937). (6) Norman, "Biochemistry of Cellulose, etc.," London, H. Milford, Oxford Univ. Press, 1937. (7) Schulze, Bey., 24,2271 (1891). (8) Spencer, J. Phys. Chem., 33, 1987 (1929). RECEIVED July 8, 1938. Contribution 128 from the Carbohydrate Research Division, Bureau of Chemistry and S o h .
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