= = = =
cathode exit stream concentration, mole fraction argon anode exit stream concentration, mole fraction argon inlet gas stream concentration, mole fraction argon distance along discharge, c m .
investigated the effect of‘ changing the discharge length in a static d i x h a r g e , and found that the separation in terms of the conccritration ditrerence between the t\vo electrodes was increased.
xc xa
Nomenclature
literature Cited
discharge tube cross section? sq. cm. diftusion coefficient? s q cm.;sec. I, = rciuivalent discharge length between inlet point and anode (or cathode), cm. Py = sbsteni p r r w i r e , mm. Ilg Q = inlrt gas fiow rate. (rnm. Hg)(cc.,!sec.) Q,, = diffusion flo\\,: (mm. Hg)(cc. Xr/’sec.)! a t room temperature 7‘, Q , z ’ = diffusion floiv a t system temperature T A 0, = equivalent ion current a t room temperature, (mm. Hg) (cc. .4r ‘ w c . ) Q 2 ’=- cq\iivalent ion currcnt a t system temperature R = neiitral rare gas atom K * = excited rare gas atom R.’ = atomic rare gas ion R, = molecular rare gas ion 7’, = room temperature. O K . 7.. = s)btt‘m temperature, O E;.
(1) Baly, E. C. C , London, Edinburgh Dublin Phil. .Wag. 35, Ser. 5, 200 (1893). (2) Dahler, J. S., Franklin, J. I>.,Munson, M. S. B., Field, F. H., J . Chem. Phys. 36(12), 3332 (1962). (3) Flinn, J. E., doctoral dissertation, University of Cincinnati, 1965 ; in press, University of Michigan microfilm. (4) Francis, G., “Handbuch der Physik,” Vol. XXI, pp. 53-203 (in English), Springer-Verlag, Berlin, 1956. (5) Frish, S. E., Matveeva, N. A,, Soviet Phys. 3(5): 971 (1958). (6) Grew: K. E., Ibbs, T. L., “Thermal Diffusion in Gases.”
A
= =
D
X,
2
Cambridge University Press, Loridon, 1952. (7) Lo&, L. B.: “Basic Processes of Gaseous Electronics,” p. 107, UniLersity of California Press, Berkeley and Los Angeles, 1961. (8) Matveeva, N. 4.,Bull. Acad. Sa., USSR, Phys. Ser. 23, 1009 (1 959). (9) Skaupy, F., Verh. deut. Physik. Ges. 18, 230-2 (1916). (10) Skaupy, F., Bobek, F., 2. Tech. Phys. 6,284 (1925).
+
RECEIVED for review February 23, 1965 ACCEPTED July 19, 1965
HYDROLYSIS OF CELLULOSE ESTERS C A R L J . M A L M , R . E. G L E G G , J A N E T T. S A L Z E R , D. F. INGERICK, AND LEO J. T A N G H E Cellulose Technology Division, Eustman Kodak Go., Rochester, N . Y .
To understand t h e factors that influence t h e breakdown of cellulose a c e t a t e , propionate, a n d b u t y r a t e during hydrolysis, studies w e r e m a d e with triesters in solution in aliphatic acid-water solutions with sulfuric acid catalyst. An increase in w a t e r Concentration caused a d e c r e a s e in t h e r a t e s of hydrolysis of t h e cellulose b u t y r a t e a n d p r o p i o n a t e but not the a c e t a t e ; it also c a u s e d a d e c r e a s e in t h e r a t e of viscosity reduction, the amount of viscosity reduction for a given d e g r e e of hydrolysis, a n d the acidity a s measured b y t h e acidity function, H,. T h e effect of t h e acyl g r o u p in t h e ester a n d in t h e solvent w a s investigated independently und together. With different esters in acetic acid-water solutions the r a t e of hydrolysis and of viscosity reduction d e c r e a s e d in the order: acetyl, propionyl, n-butyryl; with the s a m e ester a n d different acyl groups in t h e solvent, t h e o r d e r is reversed, even when t h e results are corrected for re-esterification. T h e s a m e effect w a s previously found for the viscosity reduction of triesters in aliphatic acid-anhydride mixtures. The relative r a t e s of hydrolysis a n d viscosity reduction of cellulose a c e t a t e in acetic acid-water, cellulose p r o p i o n a t e in propionic acid-water, a n d cellulose b u t y r a t e in butyric acid-water d e p e n d on the concentration of the w a t e r in the solution. (3: 4>6) described the various factors that P influence . bvork the viscosity reduction of cellulose esters during KEVIOL‘S
the process of esterification. T h e present experiments extend this work to include factors influencing viscosity reduction during the hydrolysis of cellulose esters. I n the dope process for cellulose esterification the first product is a triester which sometimes is hydrolyzed to improve its solubility ; commercial cellulose esters are hydrolyzed to less than one hydroxyl group per dnhydroglucose unit, most to less than 0.5. ‘The viscosity reduction during hydrolysis rriust be minimized because the major viscosity rediiction has already occurred during esterification. Cellulose triesters were studied in aliphatic acid-water solutions containing sulfuric acid calalyst. Measurements were made of the increase in hydroxyl groups a n d the decrease in viscosity \vith time, under the influence of such variables as trrnperature, water concentration, a n d acyl group in the solvent
and ester. T h e results help to define the conditions best suited to the hydrolysis of cellulose acetate in acetic acid-water, cellulose propionate in propionic acid-water, and cellulose butyrate in butyric acid-water. Acidity function, H,, was measured in the various solvents a t different levels of water concentration in a n attempt to find correlatioris Lyith rates of hydiolysis a n d viscosity reduction. Materials a n d Methods Cellulose Esters. ‘I’he experiments were done with a n acetate, propionate, and butyrate that were essentially triesters (Table I) made from cotton linters. Hydrolysis. T h e hydrolysis was studied in acid-water solutions containing 2 to 207, water. T h e esters were dried a t 110’ C. for 2 hours before dissolving in the solvent. LVhen the ester was completely dissolved (by warming), the temperature was adjusted, the catalyst added with vigorous stirring, and the sample placed in a constant temperature b a t h . VOL. 5
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81
Table I.
)/
Analyses of Esters Acetatea Propionate 0.19 0.02 0.022 0,004 37.5 *.. 8.1 51.8
Butyrate 0.05 0,025 0.3 yGPropionyl 1.2 yo Butyryl ... ... 53.4 In1 in FeTNab 2.61 2.97 3.45 I V in MeCIZ-MeOHc 1.62 1.69 1.79 a T h i s ester with a small amount ofpropionyl &'as used because a triacetate will not dissoloe in acetic acid-water; referred to hereafter a s a n acetate. Intrinsic viscosity of regenerated cellulose in iron-sodium tartrate. Inherent viscosity of ester (cellulose basis) in methylene chloridemethanol ( 9 0 :70).
.......A
% Hydroxyl % Sulfur % Acetyl
...... ..................3
I
'
38°C.
0.08
I
O
65OC.
.........A ................. A .................p
t -
0 12
16
% Water
Figure 1 . Effect of temperature and water concentration on solubility of sulfuric acid in butyric acid-water mixtures H2S04 added to butyric acid-water 0.01 hi
0 0.05M, A 0.02M,
0.05M H2 SO, , 38°C.
Acetate in Acetic Acid-Water
+ -
5
?',
Propionate in Propionic Acid-Water
io
06
/
15% 10%
5% 3% + 0
0
1
2
3
0
1
2
3
Reoction time (days)
0.02M H, SO,, Propionate in Propionic Acid-Water
65°C.
Butyrate in Butyric Acid -Water IO% H20
Portions of the solution were precipitated a t predetermined times, and the precipitates were washed several times with distilled water, once with a weak solution of sodium carbonate, then again with water. T h e esters were dried a t 50' C. overnight. The experiments were carried out with 5% ester in solution, because viscosity reduction and rate of hydrolysis were not affected when the ester concentration was varied from 0.5 to 10yc. Precipitants. The acetate and propionate were precipitared in water from both acetic acid-water and propionic acidwater mixtures. T h e butyrate was precipitated in water containing just enough sodium carbonate to neutralize all the available acids; frothing during neutralization did not present a serious problem as long as the precipitation was carried out slowly. Viscosity Determination. The cellulose was regenerated from the esters using 0.5M sodium methylate in methanol; then the intrinsic viscosity of the regenerated sample was determined in 0.3M FeTNa (iron-sodium tartrate) ( 3 ) . Inherent viscosities of some of the esters were measured in methylene chlorideemethanol and the results recalculated to a cellulose basis (7) ,).fter determining hydroxyl ( 7 ) and acyl groups (5). Solubility of Sulfuric Acid in Butyric Acid-Water. When 0.05M sulfuric acid was added to butyric acid-water systems containing 2 to 10% water a t 25' C., the mixtures became turbid. This problem was not encountered with acetic acidwater or propionic acid-water. Further investigation showed that the turbidity in the butyric acid-water was caused by droplets containing a large portion of the sulfuric acid. Q u a n titative solubility studies were made a t water concentrations of 2, 5 , 1 0 , and 15% a t 25', 38', and 65' C. A stock solution of 2.5M sulfuric acid in butyric acid was prepared for this study. Aliquots of this solution were added to 250 grams of butyric acid-water containing 2 to 15Yo water by weight, so that the final sulfuric acid concentrations would be 0.01.44, 0.02M, and 0.05:M if all the sulfuric acid dissolved. T h e butyric acid-water was warmed to the desired temperature, sulfuric acid was added, and the mixture was stirred rapidly for 15 minutes with a Lightnin mixer. I n some cases turbidity developed, but after standing for 6 days droplets settled and the top layer was no longer turbid; the bottom layer never exceeded about 3 ml. T h e completion of settling was determined from quantitative measurements of the amount of light transmitted by the top portion. A sample was taken from the clear top portion for determination of sulfate ion by the gravimetric method with barium chloride. Acidity Function. The acidity function, H,, is given by the expression ( 2 )
Ho
Reoction time ( d o y s )
Figure 2. Effect of water concentration o n hydrolysis of cellulose esters in corresponding acid-water mixtures 82
I&EC PROCESS DESIGN AND DEVELOPMENT
= PKa
f log(cB/cBE+)
where pK, is the indicator constant, and cB and CBH+ are the concentrations of indicator in the basic (colored) and protonated (colorless) forms, respectively. I n practice the ratio of basic to protonated forms of the indicator is determined from absorbance measurements of the test solution, and of two other solutions containing identical amounts of indicator, all in the basic and protonated forms, respectively :
cg CBR+
=
Absorbance of - absorbance in test solution protonated form __ absorbance in - absorbance of basic form test solution ~~
~
~~
0.05M HzS04, 38°C Acetate in Acetic Acid-Water
~~~
T h e indicators used in this work were ,1;:V-dimethyl-2,4dinitroaniline, pK, -0.68 (390 mp), and S,,V-dimethyl-4nitroaniline, pK, +1.08 (372 mp). Stock solutions approximately 0.0005M were prepared in acetic, propionic, and nbutyric acids, respectively. Test solutions \yere prepared in the absence of cellulose ester and in the presence of cellulose tripropionate (0.027, O H ) and of hydrolyzed cellulose propionate (5.39% OH). T h e cellulose estrr (2.5 grams) was placed in a 125-ml. glassstoppered Erlenmeyer flask, and 5 ml. of stock indicator solution was added. Most of the solvent acid was then added, followed by water to give the desired water content. T h e mixture was then tumbled overnight, and heated on the steam bath if necessary to bring the ester into solution. Sulfuric acid f j ml. of 0.5M stock solution in the solvent acid) was added, followed by sufficient solvent acid to bring the total weight to SO grams. T h e mixture was then gently swirled to obtain a uniform solution without suspended air bubbles. Along with each test solution similar solutions were prepared \vith the indicator in the basic and protonated forms by substituting for the stock solution of sulfuric acid 1 drop of pyridine and 1 drop of perchloric acid. respectively. Absorbance measurements were made in 1-cm. Corex cells, using a Beckman DU spectrophotometer, with solvent of the same composition in the reference cell. M'hen the same acidity function \vas found in the absence and presence of cellulose esters, further measurements were made with solvent only, and the solutions were made up in volumetric flasks. Most measurements were made a t room temperature (ca. 25' C , ) . At 38' and 65' C. the absorbance of the test and reference solutions was lower, but the acidity function was practically unchanged.
Propionate in Propionic Acid-Water
\'
60
I
3%H20
\'
3% H20
401 3 -
3 -
Reaction time ( d a y s ) 0.02 M H SO,
65°C.
Propionate in Propionic Acid-Water
Butyrate in Butyric Acid-Water
20% H20
60
40
I
O
1
i
2
3
4
0
1
2
3
~
Reaction time (days 1
Figure 3. Effect of water concentration on viscosity reduction of cellulose esters in corresponding acid-water mixtures
Results and Discussion 0.05M Y,SO,,
Solubility of Sulfuric Acid in Butyric Acid-Water Solutions. Figure 1 shows plots of the weight per cent of water in
36°C
Acetate in Acetic Acid-Water
Propionate in Propionic Acid-Water
the butyric acid against the molar concentration of sulfuric acid dissolved in the upper portion of the settled mixture. These data show: An increase in solubility with increasing temperature. An increase in solubility \vith increasing amounts of water in excess of 57,. Butyric acid will dissolve a t least 2.5.M sulfuric acid, but a 0.05.M solution a t 25' C. will become turbid when a small amount of water (less than 0.5%) is added. At a given temperature the same solubility curve is obtained when different amounts of sulfuric acid are added. This figure may be further simplified by considering the area above the solid line as representing t\vo phases; all points below the solid line represent complete solubility. Figure 1 sho1z.s that 0.02M sulfuric acid is soluble a t 65' C. a t all the water concentrations; these conditions were therefore selected for the experiments with butyric acid. Effect of Water Concentration on Hydrolysis and Viscosity Reduction. A cellulose acetate and propionate were hydrolyzed a t 38' C. bvith 0.05MH2S04 and a propionate and butyrate a t 65' C. with 0.02M H2SOa. I n each case the ester was dissolved in the corresponding aliphatic acid-water solution. An increase in water concentration causes a definite decrease in the rate of hydrolysis (Figure 2) and the rate of viscosity reduction (Figure 3), and less viscosity reduction for a given degree of hydrolysis (Figure 4 ) , except in the case of the acetate, ivhere an increase in water produces a slight increase in the rate of hydrolysis (Figure 2). Effect of Acyl Group on Hydrolysis and Viscosity Reduction. SAME ACYLGROUPI N ESTERAND SOLVEST. T h e
401
0
a'
04
08
t 0
04
Total hydroxyl/glucose
unit
12
12
08
0.02M H z S 0 4 , 65°C Propionate in Propionic Acid-Water
Butyrate in Butyric Acid-Water
0 C 0
f
6
-
k
04
Toto1 hydroxyl/glucose
unit
0
\O
OS
/E
1'6
Figure 4. Effect of water concentration on viscosity reduction for a given degree of hydrolysis of cellulose esters in corresponding acid-water mixtures VOL. 5
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JANUARY
1966
83
r
0.02M H,SO,,
65" C.
0.05M HzSOa, 38' C. 1.01
P
I
P
Acetate
I
Propionate 1
1.0
0.4 02
15% H20
10% H2O
0 0
I
2
3
2
0
3
Reaction time (days)
Reaction t i m e ( d a y s )
Figure 7. Hydrolysis of cellulose propionate and butyrate in corresponding acid-water mixtures
Figure 5. Hydrolysis of cellulose acetate and propionate in corresponding acid-water mixtures
0 . 0 2 M HzS04, 65' C.
='i
0
0
0 Butyrate
u
Propionate
o Propionate
c
e
r
U
-
40
-
10% H,O
c
t
'5v0Hzo
3 -
Reaction time (days)
Reaction time (days)
Figure 6. Viscosity reduction of cellulose acetate and propionate in corresponding acid-water mixtures
Figure 8. Viscosity reduction of cellulose propionate and butyrate in corresponding acid-water mixtures
acetate hydrolyzes faster than the propionate a t 5, 10, and 15Y0 water, while the propionate hydrolyzes faster a t 370 H20 (Figure 5). T h e propionate undergoes slightly less viscosity reduction than the acetate a t all four water concentrations (Figure 6). I n the comparison of the propionate and butyrate a t 65' C., the propionate hydrolyzes faster than the butyrate a t 5, 10, and 20% H 2 0 , while the butyrate hydrolyzes faster a t 2% H20 (Figure 7). T h e viscosity reduction for both is the same a t 2 and 576 H20; however, a t 10 and 20% H20 the butyrate has less viscosity reduction than the propionate (Figure 8). T h e acetate has more viscosity reduction for a given degree of hydrolysis than the propionate at 3 and 5y0 H20, while a t 10 and 207, they have the same amount of viscosity reduction for a given degree of hydrolysis (Figure 9). O n the other hand, the difference between the propionate and butyrate occurs
only a t 20% water, where the butyrate undergoes more viscosity reduction for a given degree of hydrolysis (Figure 10). These results are summarized in Table 11. DIFFERENT ACYL GROUPSIN ESTER(SAMESOLVENT).A cellulose acetate, propionate, and butyrate were hydrolyzed in a solution containing 3% water and 9770 acetic acid. This comparison was restricted to acetic acid because the triacetate is not soluble in propionic or butyric acid. T h e rates of hydrolysis and of viscosity reduction were fastest for the acetate: intermediate for the propionate, and slowest for the butyrate (Figure 11). DIFFERENT ACYLGROUPS IN SOLVENT (SAMEESTER). For this study the cellulose tripropionate was hydrolyzed under the same conditions of temperature and catalyst concentration in solutions containing 3 and 15% water in acetic, propionic, or butyric acid. At both water concentrations hydrolysis and
84
l&EC PROCESS DESIGN A N D DEVELOPMENT
0 . 0 5 ~H ~ S O3~a,a
+ ._ C
c.
97% A c e t i c A c i d -3% H20 0.05M H2S04, 38°C.
3
W ln
0
u
a -
ACETATE PROPIONATE
u
BUTYRATE
0
c
2 0
U al
+ 0
3 8
c
10% HZO
4oc
[0
,
025
,
05
,
075
1.0
15% HO ,
L 05
,
0
0.75
025
Total hydroxyl/glucose
IO
8
unit
V
60
I
1
I
Figure 9. Viscosity reduction for a given degree of hydrolysis of cellulose acetate and propionate in corresponding acid-water mixtures 0.02M H,so4, 65'
--
C.
97% Acid - 3% HZO 0.01M H2S04, 38°C.
3 C
W
BUTYRIC ACID U
2
10
0
c
Propionate o Butyrate 0
100
60
0
0.6
I2
1.8
0
0.6
Total hydroxyl/glucose
I2
40
1.8
unit
Figure 10. Viscosity reduction for a given degree of hydrolysis of cellulose propionate and butyrate in corresponding acid-water mixtures
viscosity reduction were fastest in butyric acid-water and slowest in acetic acid-water (Figure 12). This effect of the acyl group in the solvent is the opposite of that for the acyl group in the ester. Re-esterification during Hydrolysis. Some of the hydroxyl groups liberated during the hydrolysis of a cellulose ester are subsequently re-esterified by the aliphatic acid present in the solution (8). T h e process of re-esterification was studied by further analyses of products described in the previous section. When the tripropionate is hydrolyzed in acetic acid-water and butyric acid-water, the re-esterification is represented by the amount of acetyl or butyryl introduced into the ester, and this was determined by the procedure for analyzing mixed esters (5). The total hydrolysis is then obtained by adding the acetyl or butyryl per glucose unit introduced by re-esterification to the measured hydroxyl per glucose unit (Table I11 and Figure 13).
0
2
6
IO
14
18
22
Reaction time ( d a y s )
Figure 12. Effect of acyl group in solvent on hydrolysis and viscosity reduction of cellulose tripropionate
Table 11." Effect of Acyl Group at Different Water Concentrations on Hydrolysis and Viscosity Reduction (Same acyl group in solvent and ester) Acyl Water Group 3 5-20 3-20 3-5 10-20 2-10 20 ~
VlS-
Rate of -___ Hydrolysis
E
Bu a
cosity Reduction
1 I 1 1
Viscosity Reduction for Given Degree of Hydrolysis ,same
]same
1
Rates increase in direction of arrow.
VOL. 5
NO. 1 J A N U A R Y 1 9 6 6
05
:I
,
,
T r i p r o p i o n a t e in 97% Acid -
2.0
I
3% H 2 0
A
0.4
,n propionic acid-water 0 . 0 5 M H2S04, 38°C.
c
? 0.2 3
8 -
0
\ 1.2 -
10
20
30
40
24-hour
hydrolysis
o 4 8 -hour
hydrolysis
A
0
50
Butyrote
T i m e (days)
in butyric acid-water
Figure 13. Correction of measured hydroxyl for groups involved in re-esterification
0.02M
0.01 M HnSOa __ Measured
. . . .Corrected
0.4
t2.2
I
-1.21
Acetic acid ,25"C.
1i
Butyric a c i d , 65°C.
,
,
Table 111.
Re-esterification of Tripropionate Reaction HydroxyllG. L'. Soluent T i m e , Days AcyllG. U,a Measured Correctedb 97 cc acetic acid 15 0 34 0 42 0 76
97rc butyric acid
85 5 acetic acid
~ i i t v r i rarid
22 42
0 49 0 76
0 57 0 94
1 06 1 70
3 6 10 12
0 01 0 18 0 44 0 54
0 0 1 1
45 94 12 27
0 46 1 12
13 22 29 36
0 0 0 0
0 0 1 1
63 99
0 1 1 1
7
n
12 23 27 40
08 28
1 56 1 81
75 22 35 78
0 32
4 Acyl introduced by re-esteri$cation: acetyl for reactions in acetic acld, B y adding acyl/g.u. introduced by rebutyryl for those in butyric acid. estwj%ation.
~~
86
l & E C PROCESS D E S I G N A N D D E V E L O P M E N T
1 I
ti.6
I
t1.2
I tO.8
Acidity
Figure 15. drolysis
0,05M HZSO,
H2SO4, 65°C.
t/
0.2
+2.4
-
I t0.4
I 0
function (Ho)
Relationship between acidity function and hy-
With 3y0water the re-esterification was faster with butyric than acetic acid: 0 . 5 4 butyryl and 0.25 acetyl per g.u., respectively, were introduced after 1 2 days (Figure 1 3 ) . Therefore, the true difference between the rates of hydrolysis in butyric and acetic acids is even larger than would appear from a simple measurement of hydroxyl. Llrith 1j70lvater the re-esterification was slower with butyric than acetic acid: 0.11 butyryl and 0 . 2 7 acetyl per g.u., respectively, were introduced after 29 days (Table 111). The difference between the rates of hydrolysis is diminished by the correction for re-esterification. Acidity Function (H,). I n a n attempt to explain the previous observations, acidity functions of sulfuric acid were determined in the solutions used for hydrolysis. T h e acidity function was not affected by the presence of cellulose esterfor example, the acidity function of 0.05M HnSO? in 9770 acetic acid was + O . l j in the absence of ester, f 0 . 1 3 in the presence of cellulose tripropionate, and f0.14 in the presence of hydrolyzed cellulose propionate. T h e acidity function was not affected in any of the solvents by varying the temperaturefor instance, Figure 14 shows that there is no significant difference when the temperature of the propionic acid is raised from 25' to 65' C. Increasing the water concentration decreased the acidity (Figure 14). This correlates with the decrease in the rates of hydrolysis and viscosity reduction when the Gater concentration was increased (Figures 2 to 4). When the acidity function is plotted against hydroxyl a t a given time (Figure 15), a linear relationship is obtained for the propionate in propionic acidwater and the butyrate in butyric acid-water. This is not the case for the acetate in acetic acid-water. where the rate of hydrolysis was not significantly affected by changes in ivater concentration, Over the entire range of water concentration the acidity decreases as the solvent is changed from acetic to propionic to butyric acid (Figure 14). However, this is the reverse of the order for hydrolysis and viscosity reduction of cellulose tripropionate in the three acids (Figure 12).
reduction is obtained by fixing the temperature and catalyst concentration and varying the amount of water. I n the case of the acetate, an increase in the water concentration has little or no effect on the rate of hydrolysis and decreases the rate of viscosity reduction. So in practice the largest amount of water compatible with the solubility of the acetate is used, and in some cases the water concentration is continuously adjusted upwards as the solubility of the hydrolyzed ester improves. With the propionate and butyrate, increased water concentration decreases the rates of hydrolysis and viscosity reduction, and the choice of water concentration will be a compromise between the amount of viscosity reduction and time permitted (Figure 16). For example, to hydrolyze the tripropionate to 0.5 hydroxyl per g.u. would take about 33 hours in 3Y0 water, but 10% of the viscosity would be lost. If no loss in viscosity is permitted, it would be necessary to increase the water concentration to 570 and take a longer time (41 hours) to complete the hydrolysis. Ac knowledgrnent
Acidity functions were measured by Richard Brewer.
Time (hours) Figure 16. Role of water Concentration and reaction time in hydrolysis and viscosity reduction Propionate in propionic acid-water, 0.05M H z S O ~38’ ,
Literature Cited
(1) Genung, L. B., Anal. Chem. 36, 1817 (1964). (2) Hammett, L. P., “Physical Organic Chemistry,” p. 268, McGraw-Hill, New York, 1940. (3) Malm, C. J., Glegg R. E., Tanghe, L. J., Thompson, J. S., T A P P I 44, 669 (1961). (4) Malm, C. J., Glegg, R. E., Thompson, J. S., Tanghe, L. J., Ibtd.. 47. 533 11964). (5) Malm: C. J.‘, Nadeau, G. F., Genung, L. B., Ind. Eng. Chem., Anal. E d . 14, 292 (1942); ASTM Designation D 817-62T, Sections 20-27. (6) Malm, C. J., Tanghe, L. J., Glegg, R. E., Ind. Eng. Chem. 51, 1483 (1959). (7) Maim, C. J., Tanghe, L. J., Laird, B. C., Smith, G. D., Anal. Chem. 26, 188 (1954); ASTM Designation D 817-64, Sections 28-33. (8) Malm, C. J., Tanghe, L. J., Laird, B. C., Smith, G. D., J . A m . Chem. Soc. 74, 4105 (1952).
C.
I n another experiment the acidity function was adjusted to the same value (+0.60) by using different amounts of catalyst in the acetic acid system as the water concentration was changed from 3Yc to 15yc; this required 0.01M and 0.15M sulfuric acid, respectively. The time required for hydrolysis of the tripropionate at 38” C. to 0.4 hydroxyl per g.u. was 15 days with 3Tc water and 1 day with 15% water. This experiment also shows that acidity function is not the main factor influencing the reaction. Practical Significance. T h e viscosity of the final cellulose ester is usually approximated during esterification ; the goal during hydrolysis is to arrive a t the specified hydroxyl value with the least amount of viscosity reduction in a reasonable time. Usually the balance between hydroxyl and viscosity
RECEIVED for review April 19, 1965 ACCEPTED July 30, 1965 Division of Cellulose, Wood, and Fiber Chemistry, 149th Meeting, ACS, Detroit, Mich., April 1965.
REDUCTION O F AN IRON ORE CONCENTRATE W I T H HYDROGEN IN A SCREEN-PACKED FLUIDIZED BED G . L. OSBERG A ND T
.
A
.
TW EDDLE
HE direct reduction of iron ore in fluidized beds has been T s t u d i e d both in the laboratory and in the pilot plant. Ezz ( 3 ) .for example, reported on the rate of reduction with hydroqen. and on the sintering difficulties which were encountered in laboratory scale experiments with finely ground iron ores. kfrissner and Shora (10) have reported on reduction rates with C O : H 2 :N ? mixtures. and Feinman et al. (2, 4, 5 ) have ex-
,
Division of Applied Chemistry, National Research Council, Ottawa, Canada
amined the kinetics of hydrogen reduction. Pilot scale studies were reviewed by Lubker and Bruland (E),who list a t least three new processes that are applicable to large scale production. Of primary importance in any of these reduction processes is the efficient use of the reducing gas, since from thermodynamic considerations alone, it may be shown that the conVOL. 5
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JANUARY 1966
87
