uct rare earths when the conditions are optimum as described in the procedure. Samples of yttrium, terbium, europium, samarium, and neodymium were counted for several half-lives with no apparent contamination present. Gadolinium precipitates, containing no Gd activity, were checked on the counters and found to contain no greater than O . O l ~ o contamination for Y and/or Tb. DISCUSSION
During this investigation the effects of changing mesh sizes and cross linkages of Dowex-50 were studied. Direct comparison tests showed that the cross 12 linkage resins give greater separation between elements hut that the time intervals were of the order of three to four times as long as with cross 8 linkage resins (Figure 3). By decreasing the size of the particles, we again observed increased separation of the elements at the expense of time, increased flow rate, and/or increased molarity of the eluants; conversely, increased resin particle size did not give adequate
RELATIVE ELUTION TIME
__ x-8
DOWEX 50 RESINS
Nancy Sawley and Alice Conover and for the invaluable aid given by Walter E. Nervik. LITERATURE CITED
( 1 ) Myatt, E., Nash, N., Jones, T., et al.,
NO OF TUBES
Figure 3. Comparative elution of some rare earths with Dowex-50-X 8 and -X 12 resins
separations under the conditions of the experiments. We believe that by the use of Dowex-50-X 8 100-200 mesh cation exchange resin and using the procedure described, we have achieved an optimum separation of the rare earths (Y, Tb, Gd, Eu, Sm, and Nd) with minimum time. ACKNOWLEDGMENT
The author is grateful for the assistance in -pray counting given by
McClellan Central Laboratory, USAF, 1963. private communication. (2) Nervik, W. E., J . Phys. Chem. 59, 690 (1955). (3) Quill, L. L., Rodden, C. J., “Scandium, Yttrium and the Rare Earths,” in “Analytical Chemistry of the Manhattan Project,” C. J. Rodden, ed., McGraw-Hill, New York, 1950. (4)Smith, H. L., Hoffman, D. C., J. Znorg. Nucl. Chem. 3, 243 (1956). (5) \ , Stevenson. P. C.. Nervik. W. E.. “The Radiochemistry of the Rare Earths, Scandium, Yttrium and Actinium,” NAS-NS 3020, Office of Technical Services, Washington, D. C. (1961). (6) Wolfsberg, K., “Determination of Rare Earths by Ion Exchange at Room Temperature,’] Los Alamos Scientific Laboratory, University of California, Los Alamos, N. M., 1963.
RECEIVEDfor review October 26, 1964. Accepted February 1, 1965. This work was performed under the auspices of the U. S. Atomic Energy Commission.
Gas Chromatographic Analysis of Products from Controlled Application of Heat to Paper and Levoglucosan SEYMOUR GLASSNER and A. R. PIERCE 111 Si. Regis Technical Center, Route 59A, West Nyack, N. Y . A small oven has been attached directly to a gas chromatograph SO that the volatile products from the thermal degradation of cellulose may b e analyzed without intermediate trapping. The application of heat has been controlled over a temperature range of 170” to 360’ C. for various periods of time. The close similarity of the volatile products from levoglucosan and cellulose, as found by direct analysis, adds to and confirms the data reported in the literature. The new evidence also supports the mechanism of degradation as postulated by earlier investigators that most of the thermal degradation producing the volatile compounds proceeds through levoglucosan.
I
PAST 20 years considerable effort has been expended to determine the mechanism of the thermal degradation of cellulose, of cellulose derivatives, and of cellulose treated with flame retardant compounds. However, more than 100 years ago, GayN THE
Lussac (2) postulated a theory to support the flame retardancy of watersoluble salts-namely, that the flame retardant is decomposed by heat to form a glass-like coating on the individual fibers. The coating in turn serves as a barrier against the flame and oxygen from the air, and the highly flammable tars of decomposition become entrapped in this solid foam and are inhibited from further combustion reac t,ions. I n 1955 Esteve and coworkers (6) advanced the theory of the degradation of cellulose through a n intermediate, levoglucosan, a n anhydromonosaccharide, which subsequently undergoes two competing reactions: further degradation to flammable, volatile lower molecular weight compounds and tar, and repolymerization and aromatization to form char. It had previously been shown that flammability was related to the amount of tar and volatile materials produced (1, 7 , 8,12). Schwenker and Pacsu (IO)working on the tarry fraction from cellulose pyrolysis found water and levoglucosan to be
the major components; levoglucosan content was about 12%. They proposed that the cellulose might be chemically modified so as to inhibit the formation of the levoglucosan (6). Schwenker and Beck (9) studied the volatile products from the pyrolysis of cellulose by gas chromatography in order to further elucidate the mechanism involved. They found some 37 volatile products. I n conjunction with an investigation into the thermal stability of paperboard, it was thought worthwhile to study the volatiles of levoglucosan in comparison with cellulose to further clarify the degradation mechanism. The purpose of this work was to determine the extent of degradation in terms of various heating conditions in order to develop paper and paperboard with It was improved thermal stability. desirable therefore, to correlate the volatile products from the thermal degradation of paper with the parameters of temperature and time. A valuable tool might be developed for the analysis of additives that cannot be VOL. 37, NO. 4, APRIL 1965
525
CARTRIDGE HEATER wl W 2
8 v)
W
K
a w
z!
0
P
r '"I
HOLDER TEMP ( ' C ) TIME (MIN)
70.
EXPERIMENTAL
Apparatus and Operating Conditions. T h e apparatus used was a n F &, i\3. Model 720, dual-column, linear programmed, high temperature gas chromatograph with thermal conductivity detectors. This unit can be operated isothermally or by temperature programming at various heating rates, a t column temperatures up to 500" C . Two columns were used. Both columns were made of l/*-inch 0.d. copper tubing. The primary analytical column was 12 feet long and packed with 5% Carbowax 20?v.I, a polyethylene glycol, coated on 30-60 mesh Haloport F. The second column which was used to check retention data was 6 feet long, packed with 5y0 diethylene glycol succinate coated on 30-60 mesh Haloport F. The column was temperature programmed from 50" to 245" C. a t a rate of 5" per minute. The flow rate of helium carrier gas was 30 cc. per minute. The detector temperature was 380" C. The injection port temperature was 280" C. The detertor current was set a t 150 ma. -4heating chamber was designed that is quite different from that reported in the literature. This oven type chamber was necessary because it was desired t o experiment eventually with 526
ANALYTICAL CHEMISTRY
H
150'
20
170'
210
190.
230
250.
30
R
ISOTmAL
I 0
Figure 1 . Heating chamber showing top view, cross-section, and sample holder
extracted or analyzed by conventional methods. Our data substantiate the conclusions of previous reports (3, 6, 7 , 10, 11), that levoglucosan is the intermediate through which cellulose is degraded, and that cellulose degrades at temperatures as low as 170' C.
130.
10
I nK
ll
110.
90'
0
TIME (MINUTES)
20
40
Figure 2. Comparison of volatiles produced in heating chamber and by more conventional flash pyrolysis
paper samples as large as 1.0 gram. An oven also serves the purpose better than a hot wire filament pyrolyzer because the conditions of temperature and time can be more precisely controlled, The results were comparable to those obtained by more conventional pyrolysis apparatus. Figure 1 is a detailed drawing of the oven. The chamber and cap are made of stainless steel to withstand high temperatures; the cap has a gasket made of D u Pont Vycor. The oven is heated with four 60-watt cartridge heaters inserted in brass tubes welded to the sides of the chamber. The heating elements are connected in parallel to a variable voltage transformer. The outer surface of the oven is covered b y a '/'2-inch layer of Thermon, a heat conducting material which hardens from a paste into a solid mass providing even distribution of heat around the oven. The oven temperature can be regulated up to 400' C., above which temperature the gasket will deteriorate rapidly. h drop in temperature takes place when the sample holder is inserted; however, all reported temperatures have been corrected and indicate the actual temperature at the time of injection into the gas chromatograph. The oven is connected in parallel with the carrier gas and is located as close as the plumbing will allow to the injection port. Condensation in the tubing is kept to a minimum by the heat conducted from the injection port and the oven. Procedure. A sample is weighed into the brass sample holder which is then placed into the preheated oven.
T h e cap is screwed on tightly and the sample is heated for the desired length of time. T h e atmosphere in the oven can be made inert by purging the chamber with helium carrier gas during sample insertion. The oven is designed so that the gas will enter a t the bottom and exit a t the top, thus allowing an efficient sweep. Introduction into the gas chromatograph is accomplished by manipulating valves which divert the carrier gas through the oven and into the injection port. An injection time of 30 seconds was sufficient to effect a complete sweeping out of the volatiles. iifter 30 seconds the valves are returned to their normal positions and the carrier gas bypasses the oven. The pulp used in these experiments was an alpha cellulose pulp. The pulpboard was cut into strips 1'/* inches in length by inch wide, and 300 mg. of the pulp was placed in the sample holder and dried a t 110" C. for 40 minutes prior to insertion into the oven. For the pure alpha cellulose and levoglucosan, the sample holder was fitted with a small aluminum dish into which 100 mg. of cellulose or 25 mg. of the levoglucosan was weighed. RESULTS AND DISCUSSION
Figure 2 shows two chromatograms: the upper one of a run of pulp pyrolyzed a t 365' C. for 6 minutes, and the lower one produced by the more conventional hot wire-flash pyrolysis of cellulose and wnalyzed on a Carbowax 20M column. The resolution needed to draw conclusions from the data has been attained as evidenced by the
C
C 170' 20MIN.
255' I5 MIN.
L
L 170' 2 0 MIN.
255' 15 MIN.
C 190' 20MIN.
2 85' 6 MIN.
C
I I.,. I I.,.
Table I. Identification of Volatiles from Thermal Degradation of Cellulose '
n
,.
..
L
L 190' 2 0 MIN.
285' 6 MIN.
C
C 215' 2 0 MIN.
322'
L 215. 20MIN
L 322' 6MIN
6 MIN.
C
242. 15 MIN. PULtBOARD 322
L
242' 15 MIN.
I .., ;&,N.
lo
*O
RETENTION TIME
4o
Wo WWIN
IO
20
30
40
50
RETENTION TIME
Figure 3. Volatile products of cellulose (C) and levoglucosan ( I )at varying temperatures and heating times. Position of bars indicates elution time and size of bars indicates relative quantities of separated compounds
similarity of the chromatograms. The results rule out the following criticisms of oven type pyrolysis: the possible catalytic action of the metal of the oven on the sample and pyrolyzates; and the possible interractions of the volatiles while in the chamber. A minimum of 34 different volatile products are indicated in these chromatograms and the air peak contains three or four more unresolved fixed gases. The identification of as many compounds as possible is important in the interpretation of time-temperature data. Compounds which were positively identified are shown in Table I and are in agreement with those previously reported (9). They are primarily aldehydes, ketones, and acids. Work is presently being conducted on the identity of the unknown peaks which may be due to glycolic acid, lactic acid, and dilactic acid. The peaks were identified by comparison of the retention times with those of known compounds. This technique was complemented by performing functional group tests on the individual effluents. As a cross check, the retention times of the unknown and known peaks were determined on the diethylene glycol succinate column. The table indicates how each material was identified. The mechanism for the thermal degradation of cellulose and the relationship of levoglucosan to the mechanism has been investigated and discussed by several workers (S, 6, 7 , 10, 11). Levo-
glucosan is a primary component of the tar portion of the pyrolysis products of cellulose. It is also thought to be the intermediate through which cellulose is thermally degraded to lower molecular weight materials. Scission of the 1, 4glycosidic linkages followed by intramolecular rearrangements of the monomer is thought to produce levoglucosan. Figure 3 shows the relative chromatographic peaks from volatile products of levoglucosan and cellulose produced a t varying thermal conditions. Each bar indicates the height of the peak. No distinction is made for the size of full scale peaks. The degradation conditions are indicated to the left. Graphs of cellulose are indicated by (C), and the levoglucosan graphs by ( L ) . Sample weights were 100 mg. for the cellulose and 25 mg. for the levoglucosan. A qualitative evaluation of Figure 3 reveals that for temperatures 242' C. and above, the degradation products are essentially the same for levoglucosan and cellulose. Murphy (4) has pointed out that thermal decomposition of cellulose proceeds a t a finite rate a t temperatures as low as 100' C. At 170" C. acetaldehyde and acetone are present in relatively small amounts. As the severity of heating conditions is increased, the volatile products increase in number and concentration. The data for 190" and 215' C., for some undetermined reason, do not correlate as well as the other temperature ranges. With the exception of this intermediate
Column, 12-ft. 5y0 Carbowax 20M on Haloport F Flow rate, 30 ml./min. Temperature program, 50°, 250' C. a t 5"/min. Method of Peak identifiKO. Compound cation' 1 Unknown Rt 2 Formaldehyde 3 Acetaldehyde Rt, CT 4 Propionaldehyde Rt, CT 5 Acetone Rt, CT 6 Acrolein Rt, CT 7 n-Butyraldehyde/ R , CT methanol 8 Methyl ethyl ketone R t 10 Carbonyl-containing CT 11 Water Rt 15 Glyoxal Rt, CT 18 Acetic acid Rt, 0 20 Furfural Rt, C T , 0 a Rt = retention time; 0 = odor; CT = chemical test. range, the data therefore substantiate the mechanism proposed by Esteve and his coworkers (6) that levoglucosan is an intermediate in the thermal degradation of cellulose. ACKNOWLEDGMENT
Conrad Schuerch of the College of Forestry, Syracuse, N. Y., provided the levoglucosan. LITERATURE CITED
(1) Church, J., Dept. of
the Army, Office of the Quartermaster General, Textile Series Report No. 38, (1952). (2) Gay-Lussac, J. L., Ann. Chem. Phys. 18, 211 (1821). ( 3 ) Madorsky, S. L., Hart, T'. E., Straus S., J . Res. il'atl. Bur. Std., A 56, 343 (1956). (4) Murphy, E. J., J. Polymer Sci. 58, 649 (1962). (5) Pacsu, E., Schwenker, R., Testile Res. J . 27, 173-5 (1957). (6) Parks, W. G., Esteve, R., Lollis, M., Guercia, R., Petrarca, A., Abstracts, 127th Meeting, ACS, Cincinnati, Ohio, April 5 , 1955. ( 7 ) Pictet, A,, Sarasin, J., Helv. Chim. Acta. 1 , 87 (1918). (8) Schuyten, H. A., Weaver, J. N. Read, J. D., Advan. Chem. Ser. 19, 7-2U (June 1954). (9) Schwenker, R., Beck, L., J . Polymer SCZ.C, 331-40 (1963). (10) Schwenker, R., Pacsu, E., Ind. Eng. Chem. 2 , 83-8 (1957). (11) Tamaru, K., Bull. Chem. SOC.Japan 24, 164 (1951). (12) Venn, H. J. P., J . Textile Inst. 15, 414 (1924). RECEIVEDfor review October 16, 1964. Accepted February 5, 1965. Division of Cellulose, Wood and Fiber Chemistry, 148th Meeting, ACS, Chicago, Ill., September 1964.
VOL. 37, NO. 4, APRIL 1965
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