April 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
which it is immersed is established slowly under practical conditions and a t a rate which is greatly affected by theempirical conditions of the dielectric assembly. Data also indicate that the moisture contained in the oil-treated cellulose in practical equilibrium with the water-saturated immersion oil, whose surface is exposed to humid air, is smaller than the water content which i s established for the same insulation in direct contact with air of like humidity. The power factor of cellulose insulation is increased by unlimited water adsorption but in the case of dried, oil-treated cellulose immersed in new oil, the power factor is substantially unaffected by water adsorption up to about 0.85% of the weight of the paper. This condition is attained with new and unoxidized oil only after prolonged exposure of the oil-immersed insulation to highly humid air. It is suggested that the greater moisture adsorption characteristic of commercial experience is promoted by the greater solubility of moisture in oxidized mineral oil. The power factor test as an analytical method for the evaluation of the moisture in cellulose inmlation impregnated with new and unoxidized oil is of little value for water contents in the range up to 0.85%. For higher water contents, the power factor m e w ured a t a temperature in the range of 75 O C. is more sensitive to changes in the moisture content of the insulation than is the room temperature power factor value. Because of its ability to adsorb moisture and thereby concentrate it in areas of high voltage stress, and in view of the limited moisture adsorption which has been obtained in the exposure of dried cellulose impregnated with and immersed in new and unoxidized mineral oil, further studies are needed to evaluate the effect of oxidized oil on the moisture equilibrium established in oil-treated cellulose. Presently available data indicate that the utility of the power factor test as a gage of insulation deterioration in commercial service is closely associated with the presence or absence of ioniz-
893
able contaminants, including the products of oil oxidation, the dielectric effects of which are made more pronounced by the presence of moisture. LITERATURE CITED
Abrams, A,, &ndBrabender, G. J., Paper Trade J., 102,204-13 (1936). “A.S.T.M. Standards,” p. 411, Designation D 149-44, Philadelphia, American Society for Testing Materials, 1949. Brabender, G. J., Paper TradeJ., 110,27 (1941). Clark, F. M., Elec. Eng., 54,1088-94 (1935). Ibid., 59,433-41 (1940). Ibid., 61,742-49 (1942). Clark, F. M.,IND. ENQ.CHEM.,31, 327 (1939). Clark, F.M.,Trans. EEectrochem. Soc., 83, 143-60 (1943). Clark, F.M.,and %ab, E. L., IXD. ENG.CHEM.,34,110(1942). Davideon Chemical Corp., Philadelphia, Pa., “Silica Gel,” 1939. Evans, R. N., Davenport, J. E., and Revikas, A. J., IND. ENG. C H ~ MANAL. ., ED.,11,553-65 (1939). Hasselblatt, M., 2.anorg. u. allgem. Chem., 154,375 (1936). Hill, C. F.,Elec. J . , 35, 195 (1938). Hirshfeld, C. F.,Meyer, A. A., and Connell, L. H., minutes of the Association of Edison Illuminating CompanieB, 1929. “International Critical Tables,” 1st ed., pp. 2,322, New York, McGraw-Hill Book Co., Ino., 1926 Piper, J. D., Ekc. Eng., 65,791-97,1152-5 (1946). Rawls, J. A., Am. Inst. Elec. Engrs., paper 51-37 (1950). Rottmann, C. J., J. Frunklin Inst., 409,188 (1919). Schwaiger, A., Science Abstracts, B 18, Item 654, 334-5 (1915); Archiv.-Elektrotech., 3, 332-34 (1915). Simril, V. L., and Smith, Sherman, IND. ENG.CHEW,34,22&30 (1942). I Smith, L. W., Doble Engineering Co., Rept. 2,601 (1950). (22) Urguhart, A. R., and Williams, A. N., J. Teztile Inst., 15, 138 (1924). (23) Walker, A. C., J. Applied Phys., 8,261-8 (1937). (24)Williams, R. R.,and Murphy, E. J., Bell System Tech. J.,8 , 225 (1929). RECEIVED for review 1Meroh 16, 1551.
ACCEPTED December 15, 1551.
Basic Degree of Polymerization
of Cellulose Acetate L. A. COX AND 0. A. BATTISTA American Viscose Corp., Marcus Hook, Pa.
K
NOWN solvents for cellulose, for example cuprammonium
.
hydroxide or cupriethylenediamine, are sufficiently alkaline t o de-esterify completely certain cellulose esters. When a cellulose ester such as cellulose acetate, therefore, is dissolved in cuprammonium hydroxide, the resulting specific viscosity of the sample is due to homologous chains of regenerated cellulose. I n other words, a solvent such as cuprammonium hydroxide is suitable for the measurement of the viscosity or weight-average molecular weight of both cellulose and cellulose acetate. Various investigators (3, 6-10,14) already have considered deesterifying cellulose esters for the purpose of measuring the molecular weights of the resulting regenerated cellulose in a cellulose solvent such as cuprammonium hydroxide. For example, Staudinger and Daumiller (14) showed that cellulose acetates may be dissolved directly in cuprammonium hydroxide without degradation when the proper precautions are taken. Heuser and coworkers (6, r) as well as Howlett and his associates (8-10) have considered both the direct solution of cellulose acetates in cuprammonium hydroxide as well as a predgacetylation by ammonium hydroxide followed by the solution of the regenerated cellulose in c u p
rammonium hydroxide. Harrison (5) used cuprammonium hydroxide as a solvent for measuring the degrees of polymerization of cellulose acetates and other esters, such as cellitaose butyrates, which he found were insoluble in organic solvents because all of them had been incompletely esterified by heterogeneous methods. In a classical piece of work, Howlett et al. (IO),determined a series of K,,, values for a number of soluble cellulose acetates having a wide range of acetyl values in various organic solvents. The reason Howlett did this was that if the viscosities of cellulose acetates in organic solvents are t o be used for calculating molecular weights, different K , values are necessary for each acetyl composition in each solvent system. Such a situation is not desirable or practical for most studies. The use of a single solvent, such as cuprammonium hydroxide, is the best way of eliminating the need ’ for a series of different K , values. As has already been pointed out, however, Howlett and coworkers (8-10) did use cuprammonium viscosities in lieu of organic solvent viscosities in some of their work. More recently Malm and his associates (12) found that in the case of a series of aliphatic acid esters of cellulose, the intrinsic viscosities of these esters varied with the acyl group and the solvent
894
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
used, However, after these esters IT-ere completely de-est,erilied, the degrees of polymerization of the regenerated celluloses were found to be substantially the same. The present paper is devoted to the presentation of a procedure for measui,ing: the hasic degrees of polymerization of cellulo~e acet,ates in ouprannnonium hydroxide by means of single viscosity measurements a t 0.50% concent,ration,and to t.he practical application of t,his method in the study of cellulose acetates having a \Tide range of acet'yl contents and varying compatibilities in organic solvents. In addition, for convenience in routine work involving commercial cellulose acetates (acetyls between 38 to 41%) a conversion curve has been constructed whereby a single viscosity measurement, using acetone (96%)-a,ater (4%) as the solvent, may be converted to a basic degree of polymerization value based on the use of cuprammonium hydroxide solvent. EXPERIMENTAL PROCEDURES ~ ~ E A S U R Z B I E X OF T BASIC DEGREE OF POLYMERIZATIOK OF CELLULOSE ACETATES I N C ~ P R A M M O X I C ~IfI Y D R O X I D E SOLVENT.
The method used for measuring the viscosities of cellulose acetates in cupranimoniuni hydroxide solvent and for calculating the basic degrees of polymerization from single viscosity measurements is essentially that described by Battista (a). Modified Ostwald viscometers of the C:tnnon-Fenske type were used for the measurement of the solution viscosities at 20" C. Capillary diameters of the viscometers n-ere chosen so as to reduce kinetic energy corrections to a minimum for each basic degree of polymerization range.
The amount of cellulose acetate required was calculated on the basis of combined acetyl content, to give a 0.50% solution of regenerated cellulose in cuprarnnionium hydroxide after complete deacetylation. The viscosities were converted to basic degree of polymerization (1, 2 ) \There the basic degree of polymerization = 2160 log [(llr+ 1) - 0.267'1 for samples having a basic degree of polymerization greater than 300. In the case of 0.50% cupraminonium solutions of cellulose haring basic degrees of polymerization less than 300, it has been shown ( 1 ) that qsl,/c is essentially equivalent to [VI, where [ q ] is the intrinsic viscosit'y. For very 1 0 v basic degree of polymerization cclluloses, therefore, the Kraemer ( 1 1 ) constant may be applied directly and the basic degree of polynierization = 260 X qsl,/c, whcre c is the concentration in grams per 100 ml. of the solution, and is 0.50% or less. MEASUREMENT O F ISTRIKSIC vlSCOSITIES O F CELLULOSE ACETATES IN ACETOXE-WATER SOLVENT.Inasmuch as many commercial acetates have combined acetj~lcontents between 38 and 41% the use of a single organic solvent within this range of acet'yls has practical value for measuring solution viscosities in routine work. Of several solvents tried, an acetone (96% by weight)water (4% by weight) solvent at 25' C. was found t o be most satisfactory. Intrinsic viscosity data reported for cellulose acetates in organic solvents were obtaintd by extrapolating curves of the semilogarithmic plot of qsp, L'S. cusing a minimum of three values of c (from 0.10 to 0.50%). MEASUREMEXT OF ACETYL C,ONTENT. The combined acetyl content of the cellulose acetate samples was determined by the Eberstadt method as modified by Genung and Mallatt (4).
Conversion of viscosity tiat2 t o basic degree of polymerization values is donc iri order to establish a convenient yardstick whereby rclative changes in the average degree of polymerization of cellulose and cellulose acetates may be followed. JTithin this organization, the term basic degree of polymerization is used in lieu of measured units such as the viscosity in centipoises or the fluidity in rhm, because it serves m a more effective way of discussing cellulose degradation data among management, production, and research, VALIDITYOF THE D~FLECT SOLT-TION PROCEDURE. The experiments described in Table I justify dissolving cellulose acetates directly in cuprammonium hydroxide solvent. These data confirm the conclusions of Sta,udinger and Daumiller (14) who found that cellulose acetate could be deacetylated by ammonium hydroxide without degradation. Table I1 gives the rate of deacetylation of a commercial secondary cellulose acetate yarn in various concentrations of ammonium hydroxide. In the present work, deacetylation to 1% acetyl or less was obtained by immersing the cellulose acet,ates in 20% aqueous amnionium solution for I6 hours at room temperature.
TABLE I. COIVIPARISOK OF D I R E C T AND ISDIRECT ~V~ETHODS OF MEASURING BASICDEGREE OF POLYMERIZATION OF CELLCLO~L ACETATESUSISG CUPRAMMOSIUM HYDROXIDE SOLVENT Sample
Direct 12Iethoda
Indtiect Metliodb
A
302 328 390
298 324
€3
C 386 T.iscose rayon yarn (control) 408 414 Sample dissolved directly in ciiprammonium hydroxide. Sample weiglit adjusted t o give 0.80% soliition of cellulose, assuming complete deaoetylation in solvent. b Sample deacetylated completely in 20% ammonium hydroxide (16 hours a t room temperature), parified. a n d dried. Weight of sample ealciilated t o give 0.507, solution. (1
TABLE 11. RETEROGENEOT-s DEACETYLATION OF SECONDARY CELLULOSE ACETATE Y A R X B Y L4hlSfONIChf HYDROXIDE AT 18" (>.
Concd. Ammonia
C:ontrol 5 910% 1 A cy-
50%
25% 28%
After 2 hr.
37 7 36 ti
:7 A . 0 34.0 32.7 30.2
Acetyl, '7~0 After After C lir. 24 hr. 36.0 29 1
1.2
24 Hr. 330 332 323
1 0
326
i.0
1.6 1 6
323
0.9
330
I\.lIXrURES mixtures of cellulose and cellulose acetate (in yarn or fabric forms) lend themselves to relative molecular weight estimations by the direct solution method, also, as illustrated by the data in Table 111. Organic solvents capable of dissolving secondary cellulose acetates would not be suitable for studying such mixtures, but cuprammonium hydroxide is a common solvent for both components. -4PPLICATlONS O F THE DlRELT SOLUTIOL 11ETIIOD. CELLULOSE AXD CELLULOSE ACETATE. I h o w n
TABLE 111.
RIIXTCRES O F CELLULOSE AND SECOXDARY CELLU-
ACETATESIS CCPRAMMOXIUM HYDROXIDE SOLVENT
RESULTS
niethod for measuring the molecular weight of cellulose and cellulose acetate in terms of absolute degrec of polymerization unit>s. Until a universally acceptable method becomes available for doing this, it is necessary to qualify the use of a degree of polymerization expression by describing clearly how the degree of polymerization result is arrived at from measured viscosity data, The methods used in this work for measuring solution viscosities and for calculating basic degrees of polymerization therefrom have been described above.
21.0
8.0 2 3
Basic Degrees of I'olyinerization after
OF
LOSE
EXPRESSIOX O F T-ISCOSITY D.4T.4 IS TERXS01" D E G R J X O F POLYUERIZATIOX. IJnfort,unatelg, there does not exist a practical
Vol. 44, No. 4
Mixture 1 0 0 ~ cellulose o acetate rayon (38.77, acetyl), I 100% viscose rayon, I T 75% of 1 a n d 2 5 % of I1 50% of I a n d 60% of I1 2 2 % of I a n d 7670 of I1
Basic Degree of PolymerizationFound Arithmetical av.
358 414 368 376 408
I . .
...
374 386 402
DVRING A c m Y L A T I o N OF CELLCLOSE.In the commercial acetylation of cellulose using a sulfuric acid catalyst, for example, the combined acetyl content increases progressively from zero to a value fairly close to the theoretical value for a triacetate depending
INDUSTRIAL A N D ENGINEERING CHEMISTRY
April 1952
89s
use of the direct solution method in cuprammonium hydroxide. For example, as shown by the data in Table V, the intrinsic viscosities of cellulose acetates are affected by the acetyl content and type solvent used. Also, each organic solvent is only capable of dksolving cellulose acetates within a certain range of acetyls; e.g. below 33% acetyl, acetone-water (96-4) and methylene chlorideethanol (90-10) have solubility limitations. On the other hand, cuprammonium hydroxide solvent can reduce all cellulose acetates to polymer-homologous celluloses so that only a single K , (conversion factor) is necessary to convert an intrinsic viscosity value to a basic degree of polymerization value.
TABLE V.
CHANGES IN BASICDEGREE OF POLYMERIZATION OF CELLULOSE ACETATESDURING HOMOGENEOUS DEACETYLATION Intrinsic Viscosities a t 25' C. in Methylene chloride Acetone 98% formic (90%)(96%)acidU ethanol (10%) water (4%)
Acetyl, %
4
IO0 0
1I
I
05
[?I
IO
I
I
15
20
43.6 42.0 40.6 38.4 36.2 34.8 33.3 32.8 17.2
I
25
1.70 1.70 1.76 1.85 2.00 2.01 2.06 2.15
0.91 0.97
Not soluble
1.34 1.37 1.37 1.34 1.34
1 .oo
1.05 1.10 1.16 1.20
Partly soluble Partly soluble
..
P a r t l y soluble Partly soluble Partly soluble
Basic Degree of Polymerization
340 333 334 334 326 324 322 320 197
a Any solvent such as this which is not inert to t h e solute (formylation occurs) is not recommended for intrinsic viscosity measurements.
in A c e t o n e W a t e r (96-4) a t 25' C.
Figure 1. Conversion of Intrinsic Viscosities to Average Basic Degrees of Polymerization
upon the amount of sulfuric acid used. Here is a case where organic solvents simply cannot be used to follow changes in the degradation that occur during the pretreatment and acetylation of the cellulose. However, direct solution in cuprammonium hydroside does provide a n excellent means of doing this as the data in Table IV illustrate. ,411 products listed in Table IV were isolated and purified at various steps during the pretreatment and acetylation processes in order to reduce the combined sulfur content to a minimum ( I S ) .
TABLE IV.
HETEROGENEOUS VERSUS HOMOGEXEOUS DEACETYLATION OF CELLULOSE ACETATES.The solubility of a secondary cellulose acetate in organic solvents is influenced by the method used for 40-3
3 00
CHANGES IN BASIC,DEGREE OF POLYMERIZATION OF WOODPULPDURING ACETYLATION
Step in Acetylation Process
Acetyl,
% '
0.0 Original pulp E n d of p r e t r e a t m e n t in acetic a n d sulfuric 0 4 acids E n d of acetic anhydride 22 2 addition After adding balance of 40 0 sulfuric acid catalyst 43.7 End of acetylation a Direct solution in cuprammonium hydroxide
Basic Degree of Polymerization'c
1396 640
524 483 347
10
DURINGHOMOGENEOUS DEACETYLATIOS OF
I
I
I
I
I
CELLULOSE ACETATES.In commercial practice i t usually is customary to acetylate the cellulose to the so-called primary cellulose acetate. Figure 2. Conversion of Specific Viscosities to Average Basic Degrees of Polymerization The primary acetate is substantially completely esterified and dissolves in the acetylation medium-e.g., acetic acid and anhydride' It is then TABLE VI. INTRINSIC VISCOSITY O F HOMOGENEOUS AND HETEROGENEOUS CELLULOSE ACETATES deacetylated homogeneously in IN ORGANIC SOLVENT AND CUPRAMMONIUM HYDROXIDE the aqueous solution-e&, ' Av. Homogeneous Deacetylation Heterogeneous Deacetylation aqueous acetic acid-to the Basio [ q ] i n acetone Calcd. 171 i n [? I in acetone Calcd. [?I, in (96 70 )cuprammonium cuprammonium Degree of (96%)hydroxide b water (4yo)'o)a hydroxideb secondary cellulose acetate havAoet,yl Polymerization w a t e r (4%)a ing an acetyl content between 41.4 368 1.45 1.42 1.46 1.42 1.41 366 1.46 1.42 P a r t l y soluble 40.5 38 to 41%. The measurement of 360 1 . 4 7 1 . 4 1 Partly soluble 1.39 39, Partly soluble 1.39 1.47 1.41 the basic degree of polymeriza38.8 360 Partly soluble 1.39 361 1.48 1.41 tion of these homogeneously 37*8 a A t 25O C. deacetylated secondary cellub A t 20' C. lose acetates is facilitated by the
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
896
partial deacetylation. For instance, the solubility of a homogeneously deacetylated sample (deacetylated in solution) is different from a heterogeneously deacetylated sample (deacetylated in the solid state to the same acetyl content). This fact is illustrated in Table VI where the same commercial cellulose acetate was: deacetylated homogeneously (dissolved in 95 % aqueous acetic acid) in the presence of small amounts of sulfuric acid a t low teniperatures, and deacetylated heterogeneously in 5% aqueous ammonium hydroxide (a nonsolvent). CONVERSION CURVES. I n the case of the acetone-water (964) solvent, a linear relationship was observed between the intrinsic viscosities of homogeneous cellulose acetates having acetyl contents in the range of 38 to 41% and the corresponding basic degrees of polymerization as measured by direct solution in the cupramrnonium hydroxide solvent. This is illustrated in Figure 1,and the 1 elationship is expressed by the equation basic degree of polymerization
=
228 [ s ]
+ 24
(11
where 171 is measured using acetone-water (96--4) as the solvent. I n routine work, it usually is advantageous and far more convenient to make a single viscosity measurement for characterizing the chain length of a sample of cellulose acetate. A conversion curve is given in Figure 2 which makes this possible. This curve permits the conversion of the specific viscosity, measured a t 0.5% concentration, of soluble cellulose acetates containing acetyl contents between 38 and 41% into basic degree of polymerization values-Le., equivalent to values obtained by direct solution in cuprammonium solvent. In lieu of the conversion curve, the following equation may be used
+
VoI. 44, No. 4
application than organic solvents. For example, cupramnioniuni solvent may be used to dissolve mixtures of cellulose and cellulose acetates, or cellulose acetates having very wide sprea&q in acetyl composition. Such mixtures are insoluble or only partially soluble in organic solvents. The use of the same solvent for cellulose and the acetate derivatives of the cellulose permits direct comparison of chain length variations, because a polymer-homologous system is always maintained. The uncertainties and inconvenience of memuring IHEM., 30, 1200-3 (1938). Malm, C. J., Mench, J. W., Iiendall, D. L., and Hiatt, G. D.,
CONCLUSIONS
(13)
Malm, C. J., Tanghe, 1,. J., and Laird, B. C., Zbid., 38, 77-82
basic degree of polymerization
=
398 log 0.5%
sap 340
68 (1944). Ibid., 43, 684-8 (1951).
A practical procedure for measuring the basic degree of polymerization of cellulose acetates, irrespective of acetyl content, by simultaneous solution and complete deacetylation in cuprammonium hydroxide is shown to have important advantag- and much wider
(1946).
(14) Staudinger, H., and Daumiller, G., Ann., 529, 219-65 (1937). RECEIVED for review June 8, 1961. ACCEPTED November 21, 1951. Presented before the Divieion of Cellulose Chemistry at the 119th Meeting of the AMERICAN CHEMICAL SOCIETY, Boston, Mass.
Propane Deasphalted Gas Oil as Catalytic Cracking Feed Stock CRACKING OVER A MIXTURE OF NATURAL AND SYNTHETIC CATALYSTS E. CLARENCE ODEN AND THOMAS S . GRANBERRY The Tutwiler Refinery, Cities Service Refining Corp., Lake Charles, La.
HEN average mixed base Gulf Coastal crudes as processed in the Tutwiler Refinery of the Cities Service Refining Corp., Lake Charles, La., are fractionated in an atmospheric tower at coil outlet temperatures ranging from 650'to 740' F., a yield of approximately 15 to 30% crude residuum is obtained, depending upon the particular crude being processed. The residuum may be suitable for lube plant feed stock, depending upon the type of crude from which it was produced, for coking operations, visbreaking, or it can be blended to heavy residual fuel oil. With the price that must be paid for crude oil a t the present time, economics more or less dictate that the residuum yield must be processed for something other than heavy residual fuel oil. If it is not utilized in one of the processes listed above, it can be reduced by installing vacuum flash equipment or propane de-
asphalting equipment to render the major part of this mntriial suitable for catalytic cracking feed stock. At this refinery a settler-type propane deasphalting unit, as previously described by Oden and Foret ( 3 ) ,is used to reduce the Conradson carbon residue content and contaminating effect of the residuum to a minimum. This is necessary since Conradson o weight to coke in the carbon residue apparently goes 1 0 0 ~ by cracking process and fluid catalytic cracking units are generally limited by coke burning capacity. The catalytic cracking of deasphalted gas oil-the valuable heavy gas oil extracted from asphaltic petroleum residues-is a relatively new commercial petroleum process. There are articles in the journals describing commercial propane deasphalting equipment of the tower type used t o prepare catalytic cracking feed stock a t other refineries
