October 1949
2197
INDUSTRIAL A N D ENGINEERING CHEMISTRY
perature. There reactions occur t o at' least some extent over the entire catalyst bed. T h e data in Figures 10 to 16 were extrapolated t o zero bed length, as shown by the broken extensions of the curves. Alt,hough the validity of this extrapolation is rather uncertain, the extended curve.< indichte that a t least part of the met,hane, saturate,d mid unsaturared hydrocarhons, and csi,hon iliosidr are Formed by primary proceasr3. Craxford (8) rt9yvrted data on the formation of inethane and aarbmi dioxide which are similar to those reported in this paper, and attriluted the formation of these components to secondary hydrocracliirig of hydrocnrbons and the water-gas reaction, respectirely. Hon-ever, Craxford (8) postulated that the nwniai synrh& occurs on parts of the surface converted t o cobalt carbide whereas the secondary reactions occur on parts of the surface covered by cobalt atoms that are not actively engagrd in t h e of hydrocarbons. The authors' data indicate thnt thest reactions occurred throughout moat of the catalyst bed, Jvhere the $ y n r h r Gof hydrocarbons was proceeding in a normal m:innrr: I n thrir experiments carbon dioxide was formed in greater amount+ 6-ith 1Hz to 1CO gas than with 2H2 t o 1CO gas. The gas with rhe highw carbon monoxide concentration should favor forrnatiorc of carbide on the surface and, according t o Craxiord's poptulates, should produce less rather than more carbon dioxide. I t has never bccn established that a surface carbide is the active catalyst in the synthesis, and it has been shown that cobalt cstnlysts rather completely converted to carbide were inactive in the aynthesis is! ?I ). Thus, the postulates of Craxford are not a simple nsplaiiii tjon of methane and carbon dioxide formation. The authors' data indicate that these products are formed coiicurrently n ith the normal synthesis by secondary and to wme 9st>eiitby primary reactions, and that their FormRtiorr i q a fiirrntinn ' i f t h e gar? composition a n d trmpw:i,tiire
\(:KYOW- LF;D(:MEhT
I t 16 a ple,ibure tu :ickriowledpe t8heassistance of several perJons in this Kork: H. H. Storch for helpful criticisms of the final manuscript j J. Lecky, A , Dudash, and the crew of operators for assistance in obtaining and computing the data; and A. Sharkey. R. Borgnian. and the niws apect,rnmeter group for the gas nnnlv?is rht;j. LITERATURE CITED
Allrnqui,t and Hlark, J . Am. Chem. Soc., 48, 2814 (1926,. Anderson, Hall, Hewlett, and Beligman, Ibid..69, 3114 (1947) Anderson, Hall, and I-Iofer, Ibid., 70, 2465 (1948). Anderson, Hall, Krieg, and Beligman, Ibid., 71, 183 (1949). \nderaon, Krieg, Seligman, and O'Neill, Im. E m . C H E M . .39 1848 (1947). C raxford, Fuel, 26, 119 (1947); J . SOC. Chem Jnd. 66. $117 (1847). Crexford, Trans. Faraday Soc., 35, 946 (1939). Ibid.. 42, 576 (1946). Emnwtt and Brunauer, J . Am. Chenz. Soe., 52, 2682 (1930, Fischer and Pichler, Brennstof-Chem., 12, 365 (1931). I b i d . , 14, 306 (1933). I b i d . , 20, 41 (1939). Hall and Smith, J . SOC.Chem. I d . , 65, 128 (1946). Hougen and Watson, IND.ENG.C n a x , 35, 529 (19433.
Jerosejev, Runtso, and Volkova, Acta Phusicochim. U.R.S.S.. 13 111 (1940).
Pichler, Brennslof-Chem., 2 4 , 3 9 (1943). Storch et al., Bur. Mines, Tech. P a p e r 709 (1948). Tsuneoka and Fujimura. J . S n c , Chem. I n d . J a p a n . 37 binding, p . 363 (1934). [bid.,p. 704. Weller, J . A m . Chem. &IC., 69, 2432 (1947),
wL)r)l
KPllrr, IIofer iinrl \ i i c l ~ ~ : n n ,T b f d , , 70, 799 jl9.&8, R h c h I ' m J u l i 30, 1 B l b . F r o m a. thesis presented by A b r a h a m Krieg t u thr Gniversity of P i t t i h u r g h i n partial fulfillment of t h e requirements for t h e iegree of master of science, 1948. Previous articles of this series have appeared in ISD. Eso. CHEM.,40, 2347 (1918); 39, 1548 (1947): and J. A rn phpm. P n r 71. 188 '1949): '70. 2408 (1948): 69, 3114 (1947)
Viscose Processing of Cellulose CHANGES IN BASIC VROP~RTTZES R. L. MITCHELL Kayonirr f n t * o r p o m t e d ,Shdtori. W a s h . Changeb in degree of polymerization, a-cellulose, carboxyl, and pentosan content which occur during the steeping, aging, xanthation, and spinning stages of viscose processing are shown for several pulps of different initial degrees of purity. Special consideration is &\en to depolymerization reactions since the permanent drop in degree of polymerization has perhaps the greatest effect on the rither hasir ana1)tiral propertie9 o f the relliilnse.
I
3ome elfects of time, temperature, and oxygen concentration on the extent and type of alkaline degradation are shown. The presence or absence of oxygen may be the factor determining which of two types of alkaline degradation will occur. A special recovery technique i+ described for retaining low degree of poll mrrization gamma r a n s t i t u e n t s a - the water-in~nluhle n i t t a t i . rlerivatites.
K THE rnanufarture of rayon or cellophane by the viscose
process, certain operations command positions of prima,ry importance---namely : ( 1) steeping, which under suitable conditions serves the double funrtioii of purifying 2nd mercerizing the cellulose starting mat,erial; ( 2 ) aging, which serves in large rneasurc to effect the desired degree of depolyrnerizatioii: (3, santhntion, which t ' o n V w t , * the ot:llulose to the aoluhlv forin: ttnd (4j spinning, which regenerates the cellulose iu :i ilesired physical form more usable than the original. I n t'hese steps, not only is the native cellulose changed to hydrate cellulose of a different physical structure, but many of t,lw hasic analytical properties of the cellulose are modified as well.
Thebe alteratioua in analytical properties result mainly
ri u i r l
.!ravage of the w l h i l n v chain due to alkaline oxidation which m u r - at certain .tLtges of proresbiug, notably in alkali cellu1o.r iging m d i n uitrtrhation. A typical wood pulp- -for example,,
having an initirtl dtgree nf po1yrneriL:ttrun of 1150-is converted by preeeni i;omnieicial prarticr into J, rayon having a degree of pol~merisatioriof 360. hnalj tiral properties of the celldoze itre dfiected LLIV by the iernu\,tl i n the hteeping operdtion of varying amounts of hemicellulose and of noncellulosic impurities. Cei Gain of the properties are further affected by the physical form and molecular order of the structure laid down in the spinning I
)perntioii
2198
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 41. No. 10
s
x25 \
$w e 0 d
I
I
g 15 IW
z 0
'
IO
I
I
I
F i g u r e 1. Effect of b-iscose Processing on a-Cellulose C o n t e n t Pulp A = rajon grade wood pulp from wehtern hemloch; B = tire cord grade wood pulp from southern pine. C = specially purified experimental wood pulp from sodthern pine; D = viscose t t p e cotton linters pulp. (Complete analttical data are shown i n Table I ; this same pulp identification is used i n each of the additional figures)
EXPERIMENTAL
Four pulps of different initial a-cellulose content (91 t o (39%) were converted into rayon by a procedure closely paralleling commercial practice; the various operations were carried out in pilot scale equipment under representative conditions of processing. The pulps were steeped as G5O-gram books of 10-inch square sheets in 18.5% hemi-free sodium hydroxide for GO minutes at 25' C.; pressed t o 2.60 press ratio; shredded for GO minutes at 30" C.; aged a t 30" C. to give a viscose viscosity suitable for spinning; xanthated for about 120 minute;. a t 30" C. using 34% carbon disulfide based on the cellulose in the alkali cellulose; mised to give a viscose containing 7.5% cellulose and 6.5% sodium hydroxide; ripened a t 20" C. to a salt index of 4.5; anti spun into a spin bat,h comprising 11% sulfuric acid, 19% sodium sulfate, 1% zinc sulfate, and 4% glucose to give 150 denier, GO filament yarn. The yarn was washed acid-free, desulfured for 25 minutes a t 60" C. in a bath containing 0.870 sodium sulfide and 0.025% sodium hydroxide, then bleached a t 25' C. in a bat'h containing 0.10 gram per liter of chlorine as sodium hypochlorite. Samples of cellulose were recovered after each of the processing stages of steeping, shredding, aging, and xanthation b>stirring a sample containing the equivalent of 100 grams of cellulose (dry basis) into a dilute sulfuric acid solution (100 ml. of sulfuric in 2000 ml. of water), filtered, washed on a 200-mesh screen, and dried in circulated air a t 50' C. The yield was checked by weighing the recovered dried residue and by determining the hemicellulose in the acid filtrate. Recovered xanthate samples were desulfured in 0.2% sodium hydroxide a t 90' C. prior to washing and drying. I n special aging and xanthation studies, alkali cellulose samples prepared as described above were aged or xanthated as indicated for various lengths of time and a t different temperatures under atmospheres of nitrogen, air, or oxygen, then recovered as described for normally processed samples. Cellulose which was of such l o x degree of polynierizat'ion that the fiber structure had been destroyed was washed with water by decantation, then washed successively with methanol and benzene prior t o drying in circulated moisture-free air a t 50" C.; thereby formation of a hard horny structure was prevented. A special recovery technique was used in retaining the extremely loa. degree of polymerization fractions shown in Figure 8. The usual loss of water-soluble gamma was avoided by recovering the aged allali cellulose samples direct,ly in a large excess of a nitrating acid mixture; in this way the \\ater-soluble low degree
$ 0
ORIGIWL
F i g u r e 2.
AFTER STEEP
AFTER SHRED
AFTER AGE
RAYON
Effect of \ i s c o s e Processing on Carhoml Content
of polymerization portions were converted into the waterinsoluble nitrate derivatives. I n this procedure a 30-gram sample of aged alkali cellulose j s introduced bit by bit with stirring into 900 nil. of a nitrating acid mixture consisting of G4% nitric acid, 26% phosphoric acid, 10% phosphorus pentoxide (?), coolpd t o a temperature of 10" C. Sfter a nitration period of 1 hour at 20' C., the mixture is poured slowly, with stirring, into 4 liters of distilled water at 20" C. The nitrate is washed with distilled ivater repeatedly by decant,ation, transferred to a 200meah \\.irehaslcet and dried in circulated air a t 50" C. The a i i s l ~ ~ons t,he recovered cellulose and rayon sitmples n-ere made by generally accepted methods which have been modified in t,kiis l a h r a t o r y to more adequately fit particular needs. Tlic a-cellulose content (al)was determined by a conventiond method similar to the T-iPPI Standard ( I O ) ; nondilution alpha (a:)hy a method giving true solubility in 18% sodium hvdroside ( 1 2 ) ; pentosan by hydrogen broniide disMlation and barbituric acid precipitat,ion (6): carhoxyl content by the calciuni acetate method (13), and an estimate of aldehyde by a rerun of carbosyl after a chlorous acid oxidat'ion; potassium hydroside soluhility h y a method similar t o T.1PPI Standard ( 1 2 ) except for the use of 10% potassium hydroxide instead of 1% sodium hydroxide; degree of polymerization by the viscometric nitration method ( 7 , 9 ) ; and chain 1engt.h distribution by Iraction:il ~ o l u r i o rof~ the nitrate ( 7 , 9 ) . DISCUSSIOh
From the tiara i n Table I and Figures 1-5, the effect of the various viscose processing operations on some basic analytical properties of cellulose may be visualized. The changes in values are primarily a result of: removal of short chain length material in the steeping operation, reduction in degree of polymerization due to alkaline oxidation occurring in steeping, shredding, aging, and uanthation; and, as far as conventional alpha values are concerned, changes in orirntation, crystallinity, and superniulecular structure of the rayon filament as compared with the original natural fiber. The changes in structure due to solution and regeneration seem to affect only the alpha values, notably the conventional alpha for rayons. Actually this is due to the alpha method itself which fails to provide for adequate extraction and washing of the highly swollen rayon structure. Increased swelling and solubility arise, largely in the dilution step, from decreases in crystallinity and in orientation which have occurred in the replacement of the degraded native fiber structure by the regenerated rayon structure. This effect of structure on alpha is evident by comparison a t the same degree of polymerization level of alpha values for aged alkali cellulose fibers and rayon filaments. To an extent depending on the original pulp analysis, purification in steeping is effective in raising alkali cellulose content
z
E
PULP B ORIGINAL
1600
I-
Y
2199
INDUSTRIAL AND ENGINEERING CHEMISTRY
October 1949
1.5
I
I-
EI- 1.0
8 f
E
0.5
z w a 0 ORIGINAL AFTER STEEP
Figure 3.
AFTER SHRED
AFTER AGE
RAYON
Effect of Viscose Processing on Pentosan Content
1200
1000
800
600
CUMULATIVE PERCENl
Figure 5 . Effect of Viscose Processing on Chain Length Distribution
and average nitrate degree of polymerization and in lowering catl'boxyl content and pentosan content. 400 Alkaline oxidation does not appreciably chnngc tho peiit,osan z content but raises the carboxyl content and l o n ~ r sl h e d q r e e of polymerizat,ion and alpha. The additional degrad:tt ion of the finished product over t h a t of the aged alkali cc~lluloseoccurs i n 1 the xanthation step and is due largely to allialinc~oxi(lation. 01 1 1 I I I I Onl\- a negligible amount of degradatioii occurs citller in the ORIGINAL AFTER AFTER AFTER AFTER RAYON STEEP SHRED AGE XANTHATE viscose solution phase comprising the stages of mixing, filtering, ripening, and spinning or in propclrly co:itrolled l-arn fiiiishing Figure 4. Effect of Viscose Processing on Degree of operations. Polymerization The data in Tables I arid I1 do not, support the conclusions of Hollihan (4)or of Pacsu (8). Hollihan claims t h a t the exTABLEI. EFFECTOF 1-ISCOSE PROCESSISG OS PROPERTIES OF CELLULOSE PULPS of aging of alkali cellulose tent 107, SondiKOH has little effect on the carboxyl Conventional, Iution SOlllPenCarAldeXiAlpha, Beta, Garnnia. % content of the finished yarn, .ilplia, bility, trate, boxyl, hyde. tosan, D.P. Me./&. 11e.iKg. Yo ai bi Yl az, % % and t h a t the carboxyl content Pulp . i a of the yarn is mainly deterOriginal 91.3 3.9 4.8 93.5 16.0 1000 l5,l 12.8 1.52 After steep 96.8 2.7 0.5 98.0 8 2 1110 7.5 ... 0.60 mined by the carboxyl con.liter shred 97.8 1010 7.7 96.4 3.1 0 3 ... 0 58 6.9 tent of the pulp from which After age 9i.3 94.9 4.4 0.7 450 19.1 .., 0.52 4.0 After xanthate 86.9 ... ... , . . 350 23.2 the yarn is made. However, .liter spin rayon 96.5 ... 350 23.7 ... 0.40 Tables I and I1 show that alPulp B b though there is a relation heOriginal 2.5 2.5 93.0 96.5 13.9 1130 17.8 4.5 1.98 99.3 Aiter steep 98.2 1.3 0.5 7.9 1200 7.6 5.3 0.66 tween the carboxyl content of Aiter shred 99.1 97.8 1.9 0.3 6.9 1075 7.9 6.2 0.60 98.7 .liter age 96.3 3.3 0.4 the finished yarn and that of 4.0 450 19.9 1.7 0.55 Aiter x a n t h a t e 9 8 . 4 ... ... ... ... 350 24.1 .,. ... the original pulp, the carAiter spin rayon 97.9 ... ... ... ... 330 24.9 I.? 0.42 boxyl content may be apprePlllP cc Original 99.1 99.7 ciably decreased by the steep0.7 0.2 6.5 1100 6.5 0.45 4.8 Aiter steep 99.5 0.5 0 100.0 p.6 1080 6.4 ... 0.38 ing operation which removes .*iter shred 99.0 0.7 0.3 99.9 J.J 945 6.5 0 . 3 7 ... .ifter age 97.9 1.5 0.6 99.6 3.3 460 16.5 ... 0.37 short chains, and very .iit er xanthate 99.5 ... 355 19.6 ... ... Aiter spin rayon 99.4 markedly increased by the ... 355 0.35 19.8 ,.. aging step xhich produces new P u l p Dd Original 1.6 0 08.5 99.5 3.5 965 7.9 4.6 0 short chains. d i t e r steep 98.8 1.2 0 99.9 3.3 950 5.9 ... 0 After shred Since there is some destruc98.5 1.5 0 99,s 3.3 865 6.0 ... 0 -4fter age 97.1 2.7 0.2 99.0 3.0 480 14.9 ... 0 tive conversion of cellulose to After xanthate ... ... ... 98.9 ... 355 18.4 ... 0 Aiter *pin rayon ... ... ... 98.8 ... 355 18.4 ... 0 carbon dioxide and water in the a g i n g p r o c e s s a n d a a R a y o n grade wood pulp f r o m western hemlock. Tire cord grade wood pulp f r o m sontliern pine. further loss of soluble short Specially purified experimental wood pulp from southern pine. d Viscose t y p e cotton linters pulp. chain length material high in end group content during the W
?
I-
2ook--.-
C
2200
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLE TI.
EFFECTOF ALKALINEOxm.%Tiox
c.
steep
,.
R a j o n fron: alkali crlliilose airpd t o different drgraeb P U I ~ri
i:
; 2.5 :el'
..,
rrllulose a v c d 10 difffrent degrees
! 26
"
* , CJ
13
i , c. 0 :
99.3 98.9
0.1.'
652 172
{ 15
Original puir, i l k a l i celliilose aftel steep Rayon from alkali
09.3
9G.5
86.(I 4G.b 14.5
.... 33u
81.0 44.9
:, 55
98.8 98 5
'J.;
1.0
IG.1 1 2 ;Lorma1 a!kali-celluloar aging gives a viscose viscosity of 3.5 seuui,tii
g loo+ 0
&bsorbed should bc 0.15 x 10 X lOOO/lS, or about 109 me per kg. of cellulose. I31 a?tual analysis of the initial c ~ ~ l l u lose and cellulose of degrcte oi &-ICarpolymerization of 500, CHI'iJOSY; crate, bOXVl, D.P. ;\Ie./Kg. contents averaging 7.0 and 19.0 me. per kg. w r e i o u d 2.5 il.50 17.8 0 , Z! 1200 7.G the difference, 12.0 me. per lig,, represents thc carboxyl in rrw.v, 569 1O:l found by actual anal3:ia oi tht. 47 1 20.5 420 22.3 recoverable residue. Thii is 372 25.6 equivalent to about, 10ci of 278 34.1 Ihe total oxygen absorbed. 965 7.9 Let, us calculate, hon.c:ver. 950 5.0 what carboxyl inert residue is actually UL' 495 16.5 0,2 437 21.4 t o account for thc 0.2 371 23.0 tkgradation in thij residue 0.3 292 30.3 Again on Heuser's nic*cliav :bail fall, irz spin nisin, since 16 grams of IJXygen react 1%-ith162,000 prarii? of crsllulose (initial d e p r c : ~ of polymerization = loon). c h equivalents ~ of cariJCll~lresulting from an avcrage ciegrci. t ~ i polymerization drop froin 1000 to 500willbe 16 X 1000 X 1000 '18 X 162,000, or 6.2 me. pcr kg. of cellulose. When this ir conir):Lrccl n-irh the actual carboxvl increase in the residue of 12.0 h e . per kg., it is clear that the increase is ample t o account for thc observed degrndation. The total oxygen which is taken u p during dcyadation is in great excess of that needed and probably ib co.iaumed in conversion of part of the cellulose to highlv r i ~ i dizctrl nonrecoverable fragments.
PRUPERTIES OF RAYOS
.Ilkali Ct.lluViscosity lose Of Aging", ttesultant Hours at Viscose, 300 Second8
..
Vol. 41, No. 10
..
1
r,
AGED 21 HR AT M Y
UNAGED A C-:
G E D 4 4 H R AT 3O0C;
I 1
I
lood
AGING TIME
Figure 6. Effect of Aging Time, Temperature, and Atmosphere on Degree of Polymerization of Cellulow Recovered from Aged Alkali Cellulose
i
prooail, the carboxyl valurb for the rrcoi-rred ~ ~ I ~ ~ I u I L I w residues shown in Tables I, IT, and IT1 actually r ~ p i ~ t w ni ht t miniinuin effect of aging in increasing t h e carboxyl wntrnt,. Unfortunately, as cellulose and cellulosic degradation pro!iu
