Hydrolysis and Catalytic Oxidation
“Devil Duster” f o r Agitating Raw Cotton to Shake O u t t h e Dust and Loose Foreign Matter (above); Sect i o n of Continuous Conveyor Type of Dryer Used to Dry the Cotton Following I t s Puri5cation f o r the Manufacture of Finishes ( r i g h t ) Courtesy, du Pout Company
Procedures which seem to yield semiquantitative estimates of crystalline and noncrystalline composition of various celluloses are suggested and applied. The data employed for the purpose are obtained by a quantitative acid-hydrolysis method. The same data also appear to yield a measure of the crystallite reactivity. The moisture affinities of intact celluloses and hydrolysis products derived from them
offer considerable support for the methods advanced. In addition, the moisture regain evidence confirms a structural heterogeneity. Simultaneous utilization of quantitative hydrolysis and moisture regain data suggests that crystallite permeability is high in viscose rayon and mercerized cotton, low or absent in natural celluloses. Some implications of the work are discussed.
of Cellulosic Materials BROUGHT out in previous papers in this series, the digestion of cellulosic materials in hydrochloric acidferric chloride reagent (6)yields time-cellulose hydrolyzed curves that appear to reflect the amorphous-crystalline character of these materials (4, 6). The amounts of crystalline and amorphous components in a given cellulose may have considerable theoretical and practical importance, and it seemed worth while to investigate the possibilities of the hydrolysis method for quantitative differentiation. Six widely different cellulosic materials were examined experimentally; the results, together with derived estimates of amorphous and crystalline contents, are presented in this paper. Moisture regain data obtained on some of the hydrolytic products appear to have considerable significance. Ferric chloride-hydrochloric acid reagent a t its boiling point evolves carbon dioxide from glucose and cellulosic materials. In the case of glucose, the evolution is rapid; and the rate, fairly constant for 6 hours, depends directly upon the amount of glucose present. Cellulosic materials, however, yield carbon dioxide a t lower but ever-increasing rates. On the assumption that hydrolysis of the cellulose produces glucose which, in turn, yields carbon dioxide, the apparent amounts of glucose in solution a t any time can be calculated from the rates of carbon dioxide evolution, or the corresponding amounts of cellulose hydrolyzed to glucose can be obtained. Percentage hydrolyzed-time curves found in this way for different cellulosic materials differ in degree but are similar in shape. There is a rapid initial rise in amount hydrolyzed that merges gradually into a slower and more or less constant rate of hydrolysis. In accordance with present concepts of
.. .
cellulose structure, the surge at the outset is attributed to the rapid cleavage of the reactive (S), amorphous, or expanded chain network (2); the final slower rate is attributed to the dense, less-reactive crystalline aggregates or crystallites. The smooth transition from fast to slow rates, which may involve mesomorphous cellulose of intermediate properties, makes difficult a sharp differentiation of crystalline and noncrystalline components. The variation of moisture affinity of a cellulose with amount of hydrolysis seems to offer useful possibilities. That the hygroscopic properties of cellulose are associated directly with free hydroxyls and indirectly with condensation in structural capillaries is well established. If cellulose contains crystallized and amorphous or expanded regions, a differential moisture affinity might be expected. That is, crystallization may represent an interaction of hydroxyls such that the external surfaces of crystallites possess highly active groups while unsequestered portions of chains in amorphous or well expanded regions may approach the condition of having three free hydroxyls per glucose unit. Regions of the latter type would have relatively high moisture affinity and, by virtue of their exposed character, would be highly susceptible to hydrolytic attack. I n fact, it has been observed that moisture affinity and rate of hydrolysis are roughly parallel ( 4 ) s Ost (8) noted that hydrocellulose is less hygroscopic than unhydrolyzed cellulose. Birtwell, Clibbens, and Geake (1) found that cotton attacked by sulfuric acid of increasing concentration suffers first a loss in affinity for basic dyes and then acquires an enhanced affinity. The initial loss of affinity was said to be a normal effect of acid attack. Urquhart and Williams (IO) observed that a basic dye lowered the regain df cotton by a greater amount than would be expected from a simple loading effect. Presumably, basic dyes lower moisture affinity by blocking free acidic hydroxyls, and thus there may be a direct relationship between moisture and basic dye affinities. Moreover, it is entirely possible that acid attack occurs first in regions which possess high dye- and moisture-absorbing capacities. The present experiments indicate a sharp decrease and subsequent rise in regain with progressive hydrolysis.
Materials and Methods The six different cellulosic materials subjected to hydrolytic analysis included:
Courtesy, Hercules Powder C o m p a n y
Bale of Pure Chemical Cotton Pulp Ready f o r Shipment to Be Made i n t o Nitrocellulose
1481
1. Unmercerized cotton in the form of clean, bleached, filler-free cloth from American fiber. 2. Mercerized cotton (as the above cloth) immersed without tension for 30 minutes in cool 25 per cent aqueous sodium hydroxide, washed thoroughly in cool water, soured for 30 minutes in cool 1 per cent acetic acid, rinsed several times, and air-dried. 3. Industrial cotton linters in the form of high-viscosity, acetate-grade, bleached fiber prepared by Hercules Powder Company and used without further treatment. 4. Hydrocellulose as a se arate portion of the above linters, which was [oiled for 4 hours in hydrochloric acid-ferric chloride reagent, washed free of acid and iron salt, and air-dried.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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5. Wood pulp in the form of spruce sheets used by the viscose industry. 6. Viscose rayon from cotton linters as tire cord, which was washed thoroughly in warm soapy water, rinsed, and air-dried.
log plot. After about 1.5 hours, the fit is satisfactory, and consequently the following equation can be employed: where A , B a t
I .o 0.9 J
0.8 0.7 0.6
Vol. 34, No. 12
=
= =
COZ = A ( t constants induction period elapsed time
a)B
(1)
Constants A and B for pure dextrose and for the celluloses investigated are given in Table I, together with the range over which the log-log plot is essentially linear.
0.5
~
TABLE I. COSSTANTS FOR THE EVOLUTION OF CARBOX DIOXIDE FROM DIFFERENT MATERIALS AND RANGE OF APPLICABILITYOF THE LOG-LOG FUNCTION Material Dextrose Unmercerised ootton Mercerized ootton High-grade linters Hydrocellulose from linters Wood pulp Viscose from linters
.06 v)
.05
Y
$ .04
Constant A 0.910 0.060 0.125 0.065 0.032 0.120 0.220
Constant B 1 .OO 1.46 1.41
1.47 1.64 1.33 1.44
Region of Fit Up to 6 hr. From 1.4 hr. on From 1 hr. on From 1.4 hr. on From 3 hr. on From 1.4 hr. on From 1 hr. on
-I
.03
z
The calculation of percentages of cellulose hydrolyzed has already been discussed in part (5, 6) and can be made in this instance with the equation,
.02
0.3
0.4 O S a6 0.8 ID H O U R S OF D I G E S T I O N I N
2.0
HCI-
3.0 4.0 5.0 6.0
TIMn
=
(100 A B )
FeCI,REAGENT
FIGURE1, LOG-LOGPLOT OXIDE-CORRECTED
% hydrolyzed
OF CARBON DIDATA FOR COTTON
LINTERS
Carbon dioxide evolution data were obtained by the method and with the apparatus previously described (4, 6). I n each case a known weight of vacuum-dried sample was digested for a total of 7 hours in boiling, 2.4 N hydrochloric acid-0.6 M ferric chloride, and the accumulated carbon dioxide vias determined a t frequent intervals. Solid residues of hydrocellulose present as dispersions in the digestion liquid a t the end of the runs were recovered as follows: The contents of the flask, except the Carborundum chips used to prevent superheating, were filtered on a coarse alundum crucible; the crucible and contents were washed first with dilute hydrochloric acid and then with hot water, and finally dried to constant weight a t 105-110" C.; the weight lost in subsequent ashing was taken as hydrocellulose recovered. Moisture regain measurements were made after the samples had been in vacuo over phosphoric anhydride for 24 hours. The materials were exposed in a circulated atmosphere a t 21' C. and 65 per cent relative humidity for 24 hours, weighed, and dried to constant weight over phosphoric anhydride. Hydrocellulose preparations for moisture regain experiments were made by refluxing the material in boiling 2.4 iV hydrochloric acid. Portions of the boiling suspension were siphoned out a t various intervals, filtered on alundum crucibles, washed thoroughly with water, and then allowed to digest for a total of 30 minutes in warm 5 per cent aqueous ammonia. Finally, the products were boiled in 1per cent sodium carbonate for a few minutes, acidified with acetic acid, filtered, washed, and air-dried. Specific viscosities in cuprammonia were obtained from 0.5 per cent solutions in British standard reagent a t 25' C. A typical set of time-carbon dioxide data, corrected for a constant induction period (e), is shown in Figure 1 as a log-
100 AB ( t
- a)B-l
(2)
which contains the first derivative (slope) of Equation 1, and glucose and cellulose conversion factors. The percentages so obtained are valid only over the linear region of the log-log plot. The initial parts of the carbon dioxide-time curves are fitted separately by any convenient means, such as by plot-
0
I
2
3
4
H O U R S O F D I G E S T I O N IN HCI-FeCI,
5 REAGENT
6
7
FIGCRE 2. TIME-PERCENTAGE CELLULOSEHYDROLYZED CURVE^^ FOR VARIOUS MATERIALS UNDER CONDITIONS OF PRESENT HYDROLYSIS
December, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY
ting carbon dioxide values against (t - a ) l J . The product of the slope of the carbon dioxide-time relation a t any time and the factor lOO/(l.ll) (0.910) gives the corresponding percentage. Hydrolysis curves calculated by this combination of methods are shown in Figure 2 for the various celluloses. The amounts of solid hydrocellulose residue recovered at the end of the 7-hour runs are given in Table 11,together with the calculated amounts hydrolyzed during the period. Within a small error, the calculations are substantiated by the recoveries. Additional complete determinations on the wood pulp did not alter the figures given.
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the crystalline. Thus, the percentages hydrolzyed during an arbitrary initial period-for example, during the first half hour-may be equally valid as first approximations. Estimates of the total noncrystalline cellulose obtained by these methods are given in Table 111. The figures, however, must be regarded as tentative because the hydrolysis curves are least accurate in the initial region and because further knowledge of the breakdown reaction is necessary. Nevertheless, the values may indicate the relative orders of magnitude of noncrystalline material in the different substances.
Reactivity of Crystalline Substance From the evidence already presented, it seems likely that, after the first hour, hydrolysis curves represent the breakdown of homogeneous or crystalline substance. That is, the slopes Amount Residue of these portions of the curves may depend upon the reacHydro1 aed Recovered Material Total, % (Calcd.y, % (Obsvd.). % tivity of the crystallites. Such slopes, obtained from plots of Dextrose 0 percentage cellulose hydrolyzed against square root of time Unmercerized cotton 2Y.3 78.3 99:s Mercerized cotton 39.2 59.4 98.6 which give essentially straight lines, are also set forth in Table High-grade linters 23.9 75.5 99.4 111. Specific viscosities, included in the same table, are not Hydrocellulose from linters 18.3 81.8 100.1 30.3 66.1 96.4 Wood pulp suggestive of any relationship. Viscose rayon from linters 74.9 26.4 101.3 It is apparent that the amounts of crystalline and noncrystalline cellulose in the samples studied may vary between wide TABLE 111. NONCRYSTALLINE CONTENT,REACTIVITY OF CRYSlimits. No claim can be made as to the accuracy of the estiTALLINE COMPONENT, AND SPECIFIC VISCOSITYOF DIFFERENT mates, but at least they may indicate the right order of magCELLULOSE~ nitude. The reactivity values for the crystalline components NonReactivity of crystalline Crystalline Specific of the various celluloses suggest that the crystallites of native Cellulosec, % Componentb Viscosity Material celluloses are much alike in behavior. I n the case of linters, Unmerceriz severe prior hydrolysis does not appear to have altered the reactivity. It is noteworthy that mercerization seems to effect a substantial increase in crystallite reactivity, as also does viscose processing. This observation is not contrary to present a Tentative estimates. The crystalline material would be given b y difconcepts. Further discussion of these effects follows. ference from 100.
TABLE 11. CALCULATED HYDROLYSIS AND OBSERVEDRECOVERIES IN 7 HOURS
b Arbitrary units, see text.
Moisture Affinity Noncrystalline-Crystalline Distribution Resolution of curves of the type shown in Figure 2 into the crystalline and noncrystalline components of which they appear to be composed is difficult because no abrupt transition is observed. Various methods were tried but none was completely satisfactory. For example, while a pseudo-unimolecular liquid-solid reaction mechanism (9) seems applicable, semilog plots of percentages remaining unhydrolyzed against time fail in some cases to yield straight lines that might be expected when the solid residue became homogeneous (crystalline). Consequently, somewhat arbitrary approximations of relative heterogeneity in the different materials are employed. I n this respect a comparison of the results on intact linters and on hydrocellulose derived from the same linters by severe treatment with boiling acid (Table I1 and Figure 2) is indicative. The effect of the prior hydrolysis is to reduce the availability of cellulose, especially in the initial stage of the determination. After about an hour the displacement is complete and the curves then appear to become parallel. The distance between the parallels may represent the approximate amount of nonhomogeneous (amorphous and mesomorphous) material in the intact linters. I n addition, unpublished experiments (7) show clearly that hydrolysis rates become steady in about an hour and thereafter behave as if the cellulosic material were more or less completely homogeneous. Thus, an extrapolation of the type shown in Figure 2 may yield rough estimates of the noncrystalline content. It is also possible that the initial rates of hydrolysis may be proportional to the amounts of noncrystalline component because the latter is probably hydrolyzed more rapidly and completely than
The variation of moisture regain capacity of samples with time of treatment in boiling hydrochloric acid is shown in Table IV. The acid corresponds in strength to that in the ferric chloride reagent. All moisture determinations were made simultaneously to ensure comparability. Since hydrolyzing conditions were similar for the timeregain series and for the quantitive breakdowns (Figure 2), it is possible to make a direct comparison. The results of such a comparison for cotton linters, shown in Figure 3, indicate a striking resemblance of the two curves. It is also possible to calculate the change in relative regain of the various unhydrolyzed residues on the basis of intact, starting material. That is, the product of percentage of resi-
I
I
I
I
I
I
I
f 5.51/ HIGH VISCOSITY LINTERS
.-n0
I
I
I
I
1
,
._
cy
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 34, No. 12
ing power depends upon their size. In this connection it is of interest to note that the viscose relation in Figure 4 would extrapolate t o zeromoisture 7.0 hr: uptake a t complete hydrolysis. The crystallites 7.05 of mercerized cotton may be permeable to mois8.42 ture also but considerably less so than those of 6.87 viscose, while the crystallites of unmodified cotton 8.51 .... are more or less completely impervious. I n other words, moisture may be adsorbed only on the outside surfaces of cotton crystallites because, after roughly a 20 per cent decrease in unit weight and size, weight of moisture adsorbed is not changed appreciably. The view that moisture sorption is primarily a crystallite surface phenomenon in native celluloses is widely held.
OF BOILING 2.4 N HYDROCHLORIC ACIDON MOISTURE TABLE IV. EFFECT REGAIN BY ADSORPTION OF VARIOUS CELLULOSIC MATERIALS
Materisl Unmercerized cotton Mercerized cotton Cotton linters S ruce wood pulp 8 s c o s e rayon
'0 hr. 6,81 9.20 6.98 8.31 13.4
Per Cent Regain after Boiling for: 4.0 hr. 6.,4 7.99 6.56
0.05 hr. 0.20 hr. 0.80 hr, 2.0 hr. 5,62 5.73 6.03 6,34 6.98 7.12 7.50 7.70 5.69 5.83 6.05 6.27 7.40 7.55 7.89 7.99 9.64 9.44 9.37 9.47
6:50
due remaining unhydrolyzed and the percentage regain of this residue (100 minus the value plotted in Figure 2 , times the corresponding value in Table IV) gives the relative amount of moisture adsorbed by this residue. Relative adsorption values obtained in this way are plotted in Figure 4 against
Discussion of Results The moisture regain evidence and the quantitative hydrolysis measurements may seem to be contradictory. The former suggests that structural homogeneity is produced by 3 minutes of hydrolysis under the conditions of the experiments, while the latter indicate that about an hour is required. It is entirely possible that the 3-minute period represents the amorphous component and the I-hour period, the mesomorphous. I n any event, the 3-minute period of hydrolysis or its equivalent appears to be very important and is now being explored further. The crystallite reactivities given in Table I11 seem to vary as the permeabilities suggested in connection with Figure 4. Thus the breakdown rates of crystallites of viscose rayon and mercerized cotton may be rapid because the hydrolytic r e agent is able to penetrate and attack more surfaces than in
:,./
t-4
Courtesy, Hercules Powder Company
s
Sheeted Chemical Cotton Pulp, Cut and Stocked for Wrapping
percentages of starting material hydrolyzed. Curves for wood pulp and linters are omitted for clarity. The former is similar in shape to those shown and has an appreciable negative slope; the latter is almost identical with that for unmercerized cotton. The data and graphs indicate clearly that, in the adsorption of moisture, the intact samples are heterogeneous. That is, in every case there appear to be two structural components, each having its own adsorbing power. One component is highly hygroscopic, is present in relatively small amount, and is quickly removed (3 minutes under the conditions) by acid hydrolysis. The other is much less hygroscopic, represents the bulk of the material, and hydrolyzes but slowly. Figure 4 illustrates these effects and also brings out further information. As hydrolysis starts, the amount of moisture adsorbed by the unhydrolyzed residue decreases much faster than weight of the residue. Thereafter, in the cases of rayon and mercerized cotton, moisture adsorbed appears to decrease proportionally with residue weights but a t different rates. For cotton and cotton linters in the range represented, the amount of moisture adsorbed appears to be constant even though residue weight decreases. A possible explanation of these effects is that the crystallites have different moisture permeabilities. The crystallites of the viscose appear to be completely permeable and their adsorb-
FIGURE4. VARIATIONOF ACTUAL MOISTCRE REGAIN OF CELLULOSIC RESIDUES AS HYDROLYSIS PROCEEDS
December, 1942
INDUSTRIAL AND ENGINEERING CHEMISTRY -
the native celluloses. Obviously, if such a penetration occurs, the reactivity index does not necessarily indicate crystallite size. The agreement between calculations and actual recoveries of severely hydrolyzed residues (Table 11) was much better than expectation. It is possible that the precipitating action of both constituents of the ferric chloride reagent on hydrocelluloses and cellodextrins is responsible. Even in the case of the viscose, intact-appearing pieces of yarn were present after 7 hours of digestion. Examination revealed, however, that such pieces had form only and were extremely mushy.
Acknowledgment The author is grateful for the assistance Of J* A* Habrle, who repeated many of the experiments described here.
148s
G
Literature Cited Birtwell, C., Clibbena, D. A., and Geake, A., Shirley Inst. itfern., 5, 37 (1926). Frey-Wyssling, A., “Submikroskopische Morphologie”, Berlin, GebrOder Borntraeger, 1938. Mark, H., J . Phys. Cfiem.,44,764 (1940). Nickerson, R.F., IND. ENQ.CHEM.,33, 1022 (1941). Ibid.. 34. 85 (1942). Nickerson, R: F., IND. ENQ.CHEM.,ANAL.ED.,13,423 (1941). Nickerson. R. F., and Habrle, J . A., unpublished experiments. Ost, H., Ann., 398,313 (1913). Taylor, H. S., “Treatise on Physical Chemistry”. 2nd ed., p. 1028,New York, D.Van Nostrand Co., 1930. Urquhart, A. R., and Williams, A. M., Shirley Inst. Mem., 4, 167 (1925). PREeroNTm before t h e Division of Cellulose Chemistry a t the 102nd Meeting of t h e AMERICANCHEMICALSOCIETY,Atlantic City, N. J. Contribution from the Cotton Research Foundation Fellowship a t Mellon Institute.
Nomograph for Pressure Drop in Isothermal GEORGE W. THOMSON Flow of Compressible Fluids Ethyl Corporation, Detroit, Mich.
L
OBO, Friend, and Skaperdasl showed that the pressure drop in the isothermal flow of a compressible fluid may be readily obtained by means of the equation:
Since Equation 1 is quadratic, the solution for p z / p l gives two answers. At the tangent to the curve for a given value of Gzui/gpi,
where
This can be readily rearranged, by substitution of p,vl = pzvz, to give G2V2/gp2= 1, corresponding to critical flow conditions a t the outlet. Obviously, if (pZ/pJ2is less than GZul/gpl, critical flow conditions will be exceeded, which is impossible. Therefore the proper value of pz/pl is the one nearer pn/pl, and the other value should be disregarded. As an example of the use of the chart, take p s / p l = 0.765 and G2vl/gpl = 0.137. When these two points on the chart are connected by a line, pz/pl is found to be 0.638, in agreement with the solution given in the sample c a l c u l a t i o n of Lobo, 0*5 Friend, and Skaperdasl.
A plot of p,/pl vs. p2/pr for various values of G2Vl/gp1 was used to solve Equation 1 for pz/pl. T o avoid the difficulty of interpolation between the curves on their plot, an alignment chart is presented which gives a direct solution for p J p l .
3
t
Nomenclature
0.6 L
Any consistent set of
0.3
4
units may be used: D = diameter of pipe, ft. f a Fannin equation friction factor g = = acceleration due to gravity, 32.2 ft. G = mass velocity, lb. sec.-l f t . - 2 L = length of pipe, ft. PI = inlet pressure, Ib. f L - 2 pz = outlet pressure, lb. ft.-2
K
pn = pseudoterminal pressure, lb. ft.-e defined by Equadon 2 VI = specific volume of fluid, ft.a lb.-l
-
Lobo, W. E., Friend, Leo, IND. ENQ. a n d Skaperdas, G. T., CHEM.,34, 821 (1942).
