1210
INDUSTRIAL A N D ENGINEERING CHEMISTRY
pressures a t high temperatures. The reaction may then be represented as occurring in two stages-equations (1) and (2)-and in a series of qualitative experiments it was found that reduction of pure phosphorus pentoxide by carbon begins a t about 800” C., which indicates that a t 1200” C. reduction would probably be complete and practically instantaneous. At 1200” C., for instance, the dissociation pressure of tricalcium phosphate may be so small as to be practically unmeasurable, but in the presence of carbon the phosphorus pentoxide liberated would be immediately reduced to elemental phosphorus and dissociation of the tricalcium phosphate would consequently be accelerated to a considerable extent. Furthermore, extremely fine grinding and intimate mixing would not be necessary in order to obtain practically complete reduction of the phosphate because of the presence of a vapor phase in the form of phosphorus pentoxide. Tricalcium phosphate undoubtedly has definite dissociation pressures a t high temperatures, and experimental evidence on this point would be valuable in explaining the mechanism of the reaction with carbon in the solid state. Bibliography 1-Berthier, Ann. chim. phys., [2], 83, 178 (1826). 2-Blome, Metallurgie, 7, 659, 698 (1910).
Vol. 20, N o . 11
3-Bryan, Mehring, and Ross, IND. END. CHEM.,16, 821 (1924). 4-Carothers, Ibid.. 10, 35 (1918). 5-Dieckmann and Houdremont, 2. anorg. allgem. Chem., 120, 129 (1921). 6--Flacke, Z.Elektrochem., 21, 37 (1915). 7-Foote, Fairchild, and Harrison, Bur. Standards, Tech. Paper 170, 117 (1921). &Greenwood, J . Chem. SOL.(Londgn), 98, 1483 (1908). 9-Hedvall and Heuberger, Z.anorg. allgem. Chem., 130, 49 (1924). 10-Hempel, 2. angew. Chem., 18, 132 (1905). 11-Lassieur, Orig. Communications, 8th Intern. Cong. A p p l i e d Chem., 2 , 171 (1912). 12-Lerch and Bogue, IND.ENG.CHEM.,18, 739 (1926). Mitt. Kaiser-Wilhelm Inst. Eisenforsch. Diisseldorf, 9, 2 i 3 13-Meyer, (1927). 14-Moser and Brukl, Z.anovg. allgem. Chem., 121, 73 (1921). E-Nernst, “Theoretical Chemistry,” p. 758, Macmillan & Co., London, ’ 1916. 16--h’ielsen, Ferrum, 10, 97 (1912). 17-Preuner and Brockmoller, 2. physik. Chem., 81, 129 (1912-13). lS-Ross, Carothers, and Merz, J. IND. ENC. CHEM.,9, 26 (1917). 19--Ross, Mehring, and Jones, Ibid., 16, 563 (1924). 2O-Schloesing, Comet. rend., 69, 384 (1864). 21-Swann, J. IND.ENC.CHEM.,14, 630 (1922). 22-Thorpe, “Outlines of Industrial Chemistry.” p. 256, Macmillan Co., New York, 1916. 23-Waggaman, Easterwood, and Turley, U. S. Dept. Agr., Bull. 1179 (1923). 24-Zeller and O’Harra, School Mines Met., Univ. Missouri, Tech. Bull. 6, 3 (1925).
Chemistry of the Cellulose Determination’ Clifford E. Peterson and Mark W. Bray U. S. FOREST PRODUCTS LABORATORY, MADISON,WIS.
ROSS and Bevan2 in 1880 reported that the cellulose content of plant materials may be estimated by subjecting the moistened material to the action of chlorine gas and then removing the reaction products of the lignin and other bodies with a hot dilute solution of sodium sulfite. H a ~ gin , ~his experiments with wheat straw, found that the lignin could not be entirely removed by the use of sodium sulfite solution after chlorination. When, however, he substituted for the sulfite a 1per cent solution of sodium hydroxide a t 70” C. for 10 minutes, he obtained practically the same yield of cellulose as by the original method and was unable to detect lignin in the residue with zinc iodide stain. To obtain from wood by the Cross and Bevan method a uniformly white residue of cellulose that develops no pink coloration on treatment with sodium sulfite solution, four to five chlorinations are generally r e q ~ i r e d . ~Commercial pulps produced by either the sulfite or the alkaline processes are found always to contain appreciable amounts of lignin, even after bleaching with calcium hyp~chlorite.~This lignin seems to be more resistant to chemical action than the major part of the lignin present in wood; three chlorinations are usually required to complete its removal. Miller, Swanson, and Soderquist6have shown that a hydrolysis of wood with dilute acid renders lignin largely insoluble by the ordinary sulfite cooking process. The lignin is still removable, however, by chlorination. Similarly, Michel-Jaffard’ reports that he was unable to pulp Bordeaux pine by the sulfite process after a preliminary extraction with sodium hydroxide solution. I n addition,
C
Received May 16, 1928. J . Chem. SOC.(London). 88, 666A (1880); Chem. News, 42, 77 (1880). “Uber die Natur der Cellulose aus Getreidestroh,” Berlin (1916). 4 Schorger, J. IND.ENC.CHEM., 9, 556 (1917). 6 Bray and Andrews, Paper Trade J . , 76, No. 3, 49; No. l 9 , 4 9 (1923). 6 Ibid., 81,No. 9, 58 (1926). 7 Papier, 27, 213 (1924): Paper I n d . , 6, 869 (1924); Paper Trade J., 79, No. 18, 159TS (1924). 1 2
Schafer and Peterson8have observed that the rate of delignification of flax straw with sodium sulfite is retarded by a previous digestion with caustic soda. Klasong has shown by chemical means that two forms of lignin exist in plant substances. He estimates that in spruce wood 63 per cent of the total lignin is alpha- or acrolein-lignin, and that 37 per cent is beta- or carboxyl-lignin. Ritter,Io working on red alder and western white pine, has made a mechanical separation of two forms of lignin, which he has characterized physically. One form occurs in the middle lamella or partition wall between cells, is light brown in color, shows structural form, and has a comparatively high methoxy1 content (13.6 and 10.8 per cent in red alder and western white pine, respectively); the other form, found in the cell wall proper, is darker, is amorphous, and has a low methoxyl content (4.8 and 4.3 per cent, respectively, in the two species). From the foregoing considerations it is conceivable that one or more of the chemicals used in the cellulose determination exert a hydrolytic effect, which renders a part of the lignin soluble with difficulty, or that one of the types of lignin just described is more resistant to chemical action than the other. -4third and more likely view is that the lignin in the middle lamella is removed readily because of the separation of the fibers that occurs during chemical treatment, while the cellwall lignin is afforded a mechanical protection that retards its reduction by the chemical reagents. Wood contains also pentosans, or furfural-yielding substances, part of which are removed during the pulping processes and also during the cellulose determination and part of which remain in the cellulosic residue. I n view of the various points of uncertainty attaching to the Cross and Bevan chlorination process, it was thought that a study of the changes in chemical composition of spruce wood 8 9 10
Pafier Trade J . , 8 6 , No. 3, 51 (1928). Paper I n d . , 4, 262 (1922). IND.ENG.CHBM.,17, 1194 (1925).
1211
I S D CSTRIAL A S D E-VGINEERIiVG CHEMISTRY
Sovember, 1928
Table I-Results
of Analysis of Partially Chlorinated Spruce Wood
(All results are expressed on t h e basis of the weight of oven-dry wood unless otherwise designated)
CONSTITCEXTS O F CHLORINATED RESIDUE
N O . OF
10-MIK. YIELD OF CHLORINA- RESIDUE
Lignin
TIOXS ~
.. N-one 1 1
3 4 5 6
I 00.0
84.9 62.8 59.0
% 31 ..ZO 15.18 Colloidal Colloidal
%
%
57:4
13.45 10.95
56.0 54.9
54.6 54.6 53.4
1.38 1.19 1.10
54.4 53.1 53.4 52.6
85.90 86.2 65.4 66.4
19.15
57.8
Colloidal
55.9
SERIES 2
348
1
349
(I
Total pentosans
Pentosans in C & B cellulose
Pentosans not in C & B cellulose
Pentosanfree cellulose
CHIO basis, sample analyzed
~~
SERIES 1
341 342 343 344 345 346 347
Cellulose
330
3
3.51
4
5s,4 3.0 55,7
7.22 6.59 5.10
5.10 4.77
%
5.97'
%
7.4s
%
51.43
4.64 4.90
5.50 2.09 1.48 0.46 0.20
0.70
50.55 49. SO 49.20 48.45 48.60 48.50
6.19
5,?6
51.65
5.70
2,45
50.22
573
0.91
50.40
5.45 5.13
5.11
4.07
1.08
56.1
11.45 8.1.5 6.64
0.61
54.6
5.64
4.8;
0 ii
49. i o
0.81
54.0
6.54
5,02
0.32
49.00
%
5.02
2.04 0.40 0.32 0: i 5 0.06
Chlorination was carried out in duplicate runs, the yields of which were mixed for analysis.
during the process, siniilar to chemical studies of pulpiiig that hare been conducted a t the Forest Products Laboratory, would afford information of considerable interest on the effect of the repeated action of chlorine and of sodium sulfite on each of the important constituents of the wood. Such a study mas accordingly undertaken. Experimental Procedure
The wood used was sound spruce (Picea canadensis). This was finely ground and only the portion passing a 60-mesh and retained on an 80-mesh standard sieve was used for analysis. The whole was first extracted with a 2:l mixture of benzene and alcohol. In the first series of chlorinations and sulfite treatments 20gram samples were used in order to afford enough of the chlorinated residue for the subsequent analyses. I n a second series duplicate 10-gram samples were used in order to check the effect of size of sample in comparison with the first series and also to determine how closely the yields in duplicate runs would check. Each chlorination lasted 10 minutes, during which time the beakers containing the samples were cooled by running water and the samples were stirred twice. After each chlorination, sulfur dioxide water was added to remove the free chlorine, and the residue was filtered, washed, and heated in a boiling water bath for 1 hour with 200 cc. of a 2 per cent solution of sodium sulfite. Then the samples were again filtered and thoroughly vashed with hot and with cold water. At this point one sample was removed from the cycle for analysis. It was washed with alcohol and ether and was dried at 105" C. to constant weight. Tared aluminum dishe, with tight covers were used in drying and weighing. CLOTHFILTER--k satisfactory filter medium was prepared from tracing cloth by boiling it with successive portions of dilute hydrochloric acid until the iodine test showed that all starch had been removed. It was then washed, cut to size, chlorinated for 30 minutes, boiled with sodium sulfite solution. washed. dried. and weighed. A separate cloth thus prepared was used for the filtration of each sample. Axu,YsEs-The following constituents were determined on the chlorinated residues by various standard methods in use at the Forest Products Laboratory: cellulose (by continuing the chlorination of a 2-gram sample), total pentosans. and pentosans in the cellulose-all by the methods reported by Schorger;4 methoxyl content by the method of Beise1;ll and 11
Monatsh , 6, 989 (1885).
lignin, by a modification of the method of Ost and Wilkening.12 The results of the analyses are shown numerically in Table 1 for both series and graphically in Figure 1 for series 1 only. Discussion of Results
In general characteristics the curves in Figure 1 are veri. similar to those obtained by the standard pulping processes. The actual time of complete chlorination is much shorter. however, than a pulping digestion, and the final residue is more nearly pure cellulose. Moreover, the portion of cellulose frequently referred to as "easily hydrolyzable" is not lost here as in the cooking processes. The final product contains 98.5 per cent Cross and Bevan cellulose (90 per cent pentosan-free cellulose) after six chlorinations, which is very high for a pulp, although lower than would be expected with a process used for analytical determinations. BEHSVIOR OF RESIDUALLIGNIN-The present writers' experiments, agreeing with the results of Ritter and Fleck," showed that not all of the material determined as lignin is removed by chlorination. In the determination of lignin for samples Nos. 343, 344, and 349. with 72 per cent sulfuric acid, it was somewhat disconcerting to find after the customary hydrolyses with 3 per cent acid that the resulting dark residue did not settle out. Further, on filtering the suspension through an alundum crucible, the porosity of which was R. A. 98, only a small portion of this residue was retained and the material passing through could not be collected on a Goocll crucible having a thick asbestos mat. The colloidal material remained in suspension while standing one week a t room temperature, and further boiling after this period failed to coagulate it. Although former experiments had shown incidentally that the lignin from sulfite pulp does not settle so readily as the lignin from alkaline pulps, this case was far more accentuated than any previously encountered. During the examination it was thought that the residue obtained by the 7 2 per cent sulfuric acid method might be the product of charring Some of the carbohydrates rather than actual lignin, but the fact that methyl iodide is formed in the Zeisel determination indicates that true lignin is actually present, though not necessarily in the amounts found through the analytical procedure. CELLULOSE B N D PEsTosAss-Interpretation of the cellulose values in Table I is somewhat difficult because the method Cross and Bevan "Re3earches on Celluloqe," 1'01 111. p 39 (19051910), Chem -Zlg , 34, 461 (1910) l 3 I h D E N G C H E W , 16, 147 (1924)
1212
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 20, No. 11
employed for cellulose determination necessarily was the same mitting better penetration of the gas in the subsequent treatas that used to prepare the samples. These values, however, ments with chlorine. make evident the facts that hydrolysis has taken place during To test the effect of the total amount of moisture on the drying of the chlorinated residues and that about 3 per cent of rate of chlorination and the extent of delignification, the pentosan-free cellulose has been lost during the subsequent following experiment was carried out: Two-gram quantities treatments for isolating the cellulose. Since only 1 to 2 per of oven-dried wood were moistened with varying amounts of cent of the pentosans in cellulose were removed, however, water, and were allowed to stand 24 hours in stoppered bottles these pentosans seem to be more stable toward the reactions to obtain distribution of the moisture, thus securing samples of of the chlorination method than cellulose itself. Further, known moisture content. These samples were chlorinated for since the pentosan content of the cellulose does not increase 15 minutes and were then treated with 2 per cent sodium sulin the various steps of the chlorination process employed for fite solution in the usual way. This treatment was given each the isolation of cellulose in wood, the results indicate that sample except for the reduction of the second chlorination cellulose is not decom- period to 10 minutes. The results are presented numerically posed into f u r f u r a l - in Table I1 and graphically in Figure 2. The addition of yielding s u b s t a n c e s sodium sulfite solution to the chlorinated oven-dry samples during the process of failed to develop the characteristic coloration, indicating that i t s i s o l a t i o n by the no chlorination had taken place and that the loss of weight m e t h o d e m p l o y e d . shown in the yield figures is caused by the dissolving of conThe pentosans not in stituent materials in the sodium sulfite solution. This cellulose, on the other indication denotes that the moisture in the sample, up to an hand, were destroyed amount approximately equal to the weight of the oven-dry very rapidly a t first, wood, is of great importance in the chlorination of wood. even though six chlorination t r e a t m e n t s Table 11-Effect of Moisture on t h e Chlorination of Spruce Wood YIELD-BASIS, OVENfailed to remove them WATERIN WOOD DRY WOOD SAMPLE OF entirely. OVEN-DRY Y I E L D S O F P.4R-
T 1-4 L L Y CHLORIKATED
RESIDUE-AS shown in Figure 1, the yield of p a r t i a 11y chlorinated residue resulting from the f i r s t 1 0 - m i n u t e treatment appears to be somewhat high; this Figure 1 condition occurred in both series. Sodium fusions of each of these once-treated residues showed only traces of chlorine, however, proving that the unexpectedly high values were not caused by a stable chlorine addition or substitution product. Since the other values for the first treatment in each series are calculated on the basis of oven-dry weight of residue, they are correspond.ingly distorted by the high yield of chlorinated residue. After the initial treatment all such points fall on smooth curves. Haug3 found that a very thorough wetting of material before the first chlorination increased the amount of hydrochloric acid formed during the first stage of the reaction by 8 to 10 per cent, without any increase in the total amount formed during the period covered by the full determination. This fact indicates that the degree of reaction in chlorination is influenced by both the amount of water in the material and the uniformity of its distribution. The large oven-dried samples of the experiments now reported had been moistened on a Biichner filter, and it is possible that thorough and uniform penetration of moisture had not been secured in spite of stirring and the use of hot water; previous experience has repeatedly shown that water alone fails to penetrate immediately to the interior of particles of wood that has been ovendried. A moisture determination of the wetted wood, a t this point, would have shown only total content, giving no information on the essential point, that of moisture penetration and distribution; a large part of the moisture retained by the material may have been held on the surface of the wood particles. For the subsequent chlorinations, on the other hand, the samples were thoroughly impregnated with moisture by heating with a sodium sulfite solution, for one-half hour, in a water bath held a t the boiling point; such treatment tends to open up the structure of the wood fibers, thus per-
WOOD
Grams 1.9542 1,8905 1.9583 1.9662
I
Actual amount
Basis, wet wood
cc.
Per cent
None 0.70
0 27.0 50.3 75.3
II
After 15-min. After 25-min. chlorination chlorination
Per cent 93.9 81.4 75.0 74.2
Per cent 89.5 70.2 64.0 65.3
It is known that, in any capillary, the vapor phase of a substance will penetrate to points where the liquid phase alone will not go unless the capillary has been previously wetted with that particular substance. When the vapor phase enters the capillary structure of wood, displacing air, condensation of the vapor takes place upon the surface of the capillary; this allows more rapid and greater penetration by the liquid phase. With the preceding factsin mind thefollowing experiment was per- ,lo formed to test the effect of the degree of uni- 3, formity of distribution of moisture on the rate of chlorination and the e x t e n t of delignifica- ; 8 5 tion: T w o 1 0 - g r a m samples of oven-dried wood were heated in a $ 8 0 boiling water bath for ,~ 10- and 15-minute periG ods, r e s p e c t i v e l y , in order to insure uniform penetration of moisture before chlorination of 65 the sawdust. I t w a s IO I5 20 25 30 noticed that upon ad- 6 0 ~ 5 rime or Chlorinution in hfwufcs dition of water to the Figure 2 s a m p l e s of oven-dry sawdust the latter first settled to the bottom of the beaker which would lead an observer to think that the moisture had thoroughly penetrated the material. However, after heating the wood suspension to boiling the particles rose t o the surface, while further heating caused them to settle out again. The wood was separated from the hot distilled water by filtration, was washed with cold water, and was chlorinated in
E
i ’’
November, 1928
ISDL-STRIAL A.VD EAVGIiVEER1SGCHE-VISTRY
beakers for 10- and 15-minute periods, respectively. The chlorinated wood samples were given the usual sulfurous acid treatment, were extracted with 2 per cent sodium sulfite solution, and the yield of chlorinated residue was determined as previously described. Yields of 78.4 and 65.2 per cent, respectively, were obtained. These two yield points, while they are not shown in the graph because the procedure for moistening the sawdust, through which the points were obtained, is different from that usually followed in the analytical method, would fall fairly close to the yield curve in Figure 1 indicating that thorough and uniform penetration of the wood is necessary in order to secure maximum action of the chlorine gas. The results of the investigation make it clearly apparent that the amount and the uniformity of distribution of the moisture in the sample are of great importance in the chlorination of wood. The apparent discrepancies of the first chlorinations are thus explained. Incidentally, upon repeating the large-scale experiments just described. using %gram quantities in which the wood was chlorinated by forcing chlorine gas up through the moist material contained in a Jena (fritted-glass-bottom) crucible, it was found that a yield of 66.8 per cent was obtained after one 10-minute chlorination period. This fact shows that more efficient chlorination takes place when the sample is
1213
chlorinated in this manner than ensues when the sawdust is chlorinated in a beaker. Summary L4study of the chemistry of the Cross and Revan ce!.lulose determination method has shown that for spruce wood the reaction involved follows the same general course taken by the reactions occurring with the ordinary pulping reagents, but that both higher yields and greater delignification result. The experiments show that, for spruce wood, lower yields of cellulose are obtained from the oven-dried residues than froni the original wood, that lignin is not completely removed, even after a number of protracted chlorinations, and that some of the pentosans in the cellulose are removed during the first and each succeeding chlorination, while the pentosans not iii the cellulose are destroyed very rapidly during the process of cellulose isolation. The fact that the pentosans in the cellulose do not increase in the various steps of the chlorination process indicates that furfural-yielding bodies are not formed by the decomposition of cellulose during chlorination. To secure maximum reactivity, the sample of spruce to be chlorinated should contain a quantity of water at least equal to its own weight, evenly distributed through the wood. Presumably, the yield of chlorinated residue may be controlled by the amount of moisture in the sample.
Inaccuracies in Determination of Acidity of Raw Rubber by Water Extraction’ A. D. Cummings and H. E. Simmons UIVIVERSITY OF B ~ R O N AKRON, , OHIO
URIKG the course of an investigation on ultra-accelerators the basic rubber-sulfur-zinc oxide mix used for curing experiments showed a maximum tensile of 126.5 kg. per sq. cm. A mix of rubber 100, sulfur 10, with no zinc oxide, showed a tensile of less than 84.5 kg. per sq. cm. This was so low that it seemed desirable to investigate further. The first hypothesis was that the increase in tensile brought about by zinc oxide was due, not only to the reenforcing effect of the pigment, but also to the neutralization of excess acid in the smoked sheet. To determine the water-soluble acids in rubber a common method has been to extract the rubber with hot water in much the same manner as the conventional acetone extraction, This was done with the rubber in question, but failure to obtain consistent values for acid numbers led to a critical examination of the method and the conclusion that hydrolysis of esters in the rubber by the hot water can take place. The result is a very high value for water-soluble acids. To avoid all trouble, it is best to employ the procedure used by Van Rossem and Dekker* where the rubber is first extracted with acetone and the acetone extract then digested with water a t low temperature to determine water-soluble acids.
D
Experimental
Three sampies of the smoked sheet mere extracted for 8 hours with hot water and then for 8 hours with acetone. The acid numbers3 obtained are shown in Table I. 1 Presented under the title “Determination of Acidity of Raw Rubber by Water Extraction” before the Division of Rubber Chemistry a t the 75th Meeting of the American Chemical Society, St. Louis, Mo., April 16 to 19, 1928. 2 IND. ENQ.CHEH., 18, 1152 (1926). 8 Whitby and Winn, J . SOC.Chem. I n d . , 42, 336T (1923); Whitby, Trans. I n s f . Rubber I n d . , 1, 12 (1925); Whitby and Greenberg, IND. ENG. CHEW.. 18, 1168 (1926).
Table I-Acid Water extract Acetone extract
Numbers of Water and Acetone Extracts SAMPLEI SAMPLEI1 SAMPLE111 291 ( M ) 130 ( M ) 273 ( M ) 292 ( N ) 292 (1x7) 289 ( N )
These results indicated an unusually high acid content of the rubber. However, the one low value (130) caused suspicion. The three samples having been extracted a t the same time, there seemed to.be no explanation for this failure to get check results. T o test the method, a specimen of first latex crepe was selected and water extraction of samples cut from this was carried out. The acid numbers varied from 50 to 175 on six samples. From this it appeared that something more than simple extraction of water-soluble acids was taking place. In the hope of finding plausible explanation for this condition the procedure outlined by Van Rossem and Dekker was carried out. I n this process the rubber is first extracted with acetone; water-soluble acids are then determined by water extraction of this acetone extract on a water bath until further extraction shows no increase in acidity. Table 11-Acid Numbers by Van Rossem and Dekker’s Method B-Total acid number of acetone extract A-Water-soluble free fatty acids (water extraction of acetone extract a t temperature of water bath) B-Liquid and solid free fatty acids (acetone-soluble only) S S - 1 S m o k e d sheet used in mixes giving low tensile S S - 2 S m o k e d sheet known to give good tensile properties in a rubbersulfur mix ACETONE ACETONEEXTRACT EXTRACT AFTER A BOILED16 BOILEDWITH HOURS WITH WATER. WATER A + B A B 8 hours 6 hours ss-1 342 53a 289a more SS-1 (extract air - dried 1 month) 273 60 187 ss-2 248 42 ( X ) 206 64 33 Water extraction first Acetone extraction (16 hours) following ss-2 . 489 399c 238b Compare values ( M )Table I. b Compare values ( N ) Table I . c Compare value ( X ) above.
A
+
