Treatment of Cellulose Prior to
Acetvlation
J C. J. MALM, K. T. BARKEY, D. C. iMAY, AND E. B. LEFFERTS Cellulose Acetate Development Diuision, Eastman Kodak Co., Rochester, N . Y .
I
h' T H E manufacture of cellulose acetate, cellulose is usually
and the temperature was recorded. The temperature was then read a t 5-minute intervals with 30 seconds of stirring before each reading. The time-temperature curve and time to give an esterification reaction mixture of good clarity were used to evaluate reactivity.
reacted with acetic anhydride using sulfuric acid as a catalyst and acetic acid as a solvent. The cellulose acetate must be of considerably shorter chain length than native cellulose t o be soluble in organic solvents and to give solutions of the viscosity desired for commercial applications ( 7 ) . This chain length reduction is sometimes done prior to the esterification and may follow a previous reaction in which the cellulose is activated with various liquids. The esterification is then carried out under relatively mild conditions. This paper summarizes an investigation of the factors controlling the activation and catalyst treatment steps in the acetylation of cellulose. Commercial acetylation-grade cotton linters were used throughout this investigation.
PRELlRlIlVARY STUDY
ACTIVATING EFFECT OF LIQUIDS. Aqueous solutions of acetic acid (4)or sodium hydroxide ( 6 ) ,water (4), and fatty acids, such as formic ( 3 ) and acetic ( 8 ) , have been used to activate cellulose for acetylation. A comparison of certain activating liquids is made in Table I. Cotton linters containing 3.8% moisture were activated 1 hour with 10 parts of various liquids a t 25' C. No agitation was included in these preliminary experiments. The excess liquid was removed, and the linters were rapidly washed with acetic acid several times before acetylation.
DEFINITION O F TERMS
Certain terms concerned with these reactions are defined to clarify their usage. Activation is the treatment of the cellulose with liquids containing no esterification catalyst. Catalyst treatment refers to the reduction of the cellulose chain length by the action of sulfuric acid in acetic acid. Viscosity of a 2.5% solution of the recovered cellulose sample in cuprammonium solution following the ACS procedure is used to indicate average chain length ( 2 ) . The sample weight of the vacuum-dried sample is corrected for small amounts of acetyl groups and moisture. Catalyst concentration is the moles sulfuric acid per 100 grams of cellulose. Dehydration refers to the removal of water from the cellulose by repeated changes of acetic acid, The freezing point of the acetic acid is used to determine when equilibrium is attained. Sorption of sulfuric acid is a term describing the selective retention of sulfuric acid by the cellulose, determined by difference between the amount of sulfuric acid in the acetic acid before and after the catalyst treatment. This includes the sulfuric acid chemically combined plus that physically or mechanically retained. The sulfuric acid solution is titrated with guanidine acetate, using crystal violet indicator (6). Per cent moisture in the cellulose is the percentage of volatile material removed a t 110' C. in 2 hours. Esterification time is the time in minutes to acetylate adiabatically 1 part of cellulose with 10 parts of acetic anhydride in 20 parts of acetic acid, starting a t 20' C., and using 0.072 mole of sulfuric acid catalyst per 100 grams of cellulose. Samples of the linters were acetylated in a calorimeter. This consisted of a vacuum flask placed in a stainless steel can and packed in glass wool for added insulation and mechanical protection. The quantities of reagents for each reaction were adjusted to allow for any acetic acid and sulfuric acid adhering to the linters. The total amount present in each esterification was the same, consisting of 26.7 grams of cellulose, 533 grams of acetic acid, 267 grams of acetic anhydride, and 1.96 grams of 95% sulfuric acid. The freshly prepared esterification mixture was adjusted to 20" & 0.2' C. in the calorimeter which was equipped with a thermometer and ring-type stirrer. After the cellulose was added t o the calorimeter, the reaction mixture was stirred for 1 minute
TABLE I. ACTIVATIONOF COTTON LIXTERSWITH VARIOUS LIQUIDS Activation L i p i d Removed with Acetic Acid 10% KaOH s o h . followed bv water Water 75% acetic acid solution Formic acid, 99% Aceti+ acid, 99.8% Propionic acid Butyric acid Isobutyric acid
Time, min. 50
80
70
85 105 > 150
>I50 >150
Esterification Rate, O C. per mi; 0.40
0.30 0.28 0.21
0.13
0.10 0.093 0.088
When compared to acetic acid as a standard, sodium hydroxide solution, water, 75% acetic acid solution, and formic acid increase the reaction rate, whereas propionic, butyric, and isobutyric acids give Ion-er rates. I n Figure 1 additional data are shown for experiments in which the linters were soaked in either acetic or butyric acid for 1 hour followed by a rapid washing with either of the two acids. The reactivity obtained from soaking linters for 1 hour a t 25" C. in acetic acid is not lost when the acetic acid is replaced with butyric acid. On the other hand, activation with butyric acid for 1 hour is not nearly so effective as acetic acid followed by the butyric acid. Furthermore, when the linters are activated for 1 hour in butyric acid and the latter is rapidly replaced with acetic acid, increased reaction rate is observed, approaching that obtained when linters are treated with acetic acid alone. This is due to the activating effect of the acetic acid wash, as will be shown later. It is, therefore, concluded that the activation rate varies for different liquids. The rates in Table I for acetic acid and the better activating agents give a measure of the relative activating efficiencies of these liquids, the poorer activating agents being influenced by the acetic acid wash. Of the lower aliphatic acids acetic acid is the best practical activating liquid. Formic acid gives greater activity but introduces undesirable formyl groups which have to be replaced later (3). Aqueous solutions of sodium hydroxide and of acetic acid, as well as water alone, activate the cellulose more rapidly. These
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December 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
2905
taining 0.07 mole of sulfuric acid per 100 grams of cellulose for various lengths of time. Table I11 illustrates the rapid diffusion of 38 sulfuric acid and rapid acetylation time. These results suggest uniformity of fiber swelling and sorbed sulfuric acid. The effect of differences in cellulose chain length on sorption and reactivity of linters is summarized in Table IV. The degraded cellulose was prepared by treating linters with a 0.33% water solution of phosphoric acid for 20 hours a t 90' C. The data of Table IV show that the reactivity of highly activated linters is essentially independent of chain length. One hour a t 25%. Rapidly washed with The effect of ratio of sulfuric acid to celluI Acetic acid Acetic acid lose on rate a t which the cellulose chain 0 Acetic acid Butyric acid 2 o Butvric acid Acetic acid length is reduced is shown in Figures 2 and Butyric acid / 3 o BuGric acid 3. Figure 2 shows that the rate increases with increase in the amount of sulfuric acid present during the catalyst treatment, whereas Figure 3 indicates that breakdown rate ac20 I I I I I I I I I, I I tually correlates with the quantity of sulfuric 0 20 40 60 80 100 120 140 160 180 200 220 acid sorbed on the cellulose. Acetylation t i m e in m i n u t e s EFFECT OF LIQUID-SOLID RATIOO N BREAKFigure 1. Acetylation Time-Temperature Curves of Linters Activated DOWN RATEOF CELLULOSE.If the quantity with Acetic and Butyric Acids of sorbed sulfuric acid is uniformly distributed in thecellulose and remains relatively constant a t different liquid-solid ratios, the rate a t which the cellulose chain also are practical activating agents if followed by acetic acid length is reduced would be expected to be independent of the dehydration. liquid-solid ratio. I n Table V a comparison of cuprammonium SORPTION OF SULFURIC ACID. I n all subsequent experiments viscosities is presented for 100 grams of linters reacted a t 25" C. a 10-gallon Werner-Pfleiderer type of mixer was used for the with 0.07 mole of sulfuric acid in acetic acid. The liquid-solid activation and catalyst treatment steps. ratio was varied from 0.8 to 1 t o 5 to 1. These are practical During the catalyst treatment sulfuric acid is sorbed by the limits; above a 5 to 1 ratio sorption values decrease to such an linters. Table I1 shows sulfuric acid sorption-time series of extent that constancy cannot be assumed. Between 2 to 1 and cotton linters humidified to 3.9% moisture and of linters which 5 t o 1 ratios the variations are of the same order of precision as had been water activated and acetic acid dehydrated. A liquidthe viscosity measurement. This makes i t impossible to dissolid ratio of 4 to 1 and a temperature of 25" C. were used. tinguish any differences from changes that would result in sulfuric acid sorption varying with liquid-solid ratios. The higher initial values a t 0.8 to 1 liquid-solid ratio can be explained by poorer TABLE 11. SULFURICACIDSORPTION-TIME SERIES Sulfuric Acid Sorption in Mol- per uniformity. 100 Grams Linters EFFECT OF MOISTURE ON CELLULOSE ACTIVITYAND CATALYST Untreated linters, Activated linters, Time, Min. A B TREATMENT. Adding water to the catalyst treatment solution 10 0.006 0.044 decreases the rate a t which the cellulose chain length is reduced. 45 0.023 0.045 Table VI illustrates the effects obtained from the presence of 0 60 0.028 0.044 120 0.039 0.043 to 8% water when activated linters are reacted for 1 hour a t 180 0.042 0.042
1
275 360 Total available sulfuric acid
0,043 0.041
0.042 0.041
0.072
0.072
When no preliminary treatment is included, considerable time is required to reach maximum sorption. Activated linters sorb sulfuric acid faster and to a slightly greater extent than unactivated linters. The sorption rate is indicative of uniformity of sulfuric acid diffusion and cellulose swelling. Where maximum sorption occurs rapidly as shown in column B, Table 11, uniform dispersion is considered to have been achieved. Water-treated linters dehydrated with acetic acid are, therefore, considered to be uniformly and highly activated. Hence, a study made with these activated linters would be expected to show minimum adverse effects from diffusion and uniformity variations during the catalyst treatment.
TABLE111. EXPERIMENTS TO SHOWRAPID SULFURICACID SORPTION RATEAND RESULTINGCELLULOSE ACTIVITY Catalyst Treatment Time, Min. 5 16
Moles &SO4 per 100 G. Linters Available Sorbed 0.039 0.073 0.073 0.039
Esterification Time, Min.
16 16
TABLEIV. EFFECT OF CELLULOSE CHAIN LENQTHON SULFURIC ACIDSORPTION AND ACTIVATION Linters5
Moles HzSO? per 100 Grams Linters Available Sorbed
Adiabatic Esterification Time, Min.
STUDY OF ACTIVATED LINTERS
SULFURIC ACIDSORPTION AND CELLULOSE REACTIVITY. Wateractivated linters were treated a t 25" C. with acetic acid con-
5 A = degraded linters, cuprammonium viscosity 26 cp.; B = linters, cuprammonium viscosity 4725 cp.
INDUSTRIAL AND ENGINEERING CHEMISTRY
2906
Ol 0 Figure 2.
I
I I I I I 40 60 80 100 120 Catalyst treatment time in minutes
20
Effect of Available Sulfuric Acid on Chain Length Reduction Rate at 25" C.
25" C. This can be explained by the decrease in superacidity
of the sulfuric acid in aqueous acetic acid solution ( 3 ) . The data on activated linters indicat,e t h a t the breakdown rate during the catalyst treatment depends on the mqisture content of the system and the quantity of sulfuric acid sorbed.
Vol. 44, No. 12
with the cellulose or t o the activating or catalyst solution. The effect of moisture within the cellulose is not equaled by adding the equivalent amount to the activating or catalyst solution. Table VI11 illustrates this point. Higher cuprammonium viscosity values and longer esterification times are observed for the initially drier material. These analyses indicate the greater nonuniformity of reaction of the cellulose containing less moisture. The uniformity of dispersion of the sulfuric acid in the cellulose is indicated by the rate a t which the sulfuric acid is sorbed, Moikture content of the cellulose and concentration of sulfuric acid affect the sorption rate, as shorn-n in Table I X . A lower moisture content decreases the sulfuric acid sorption rate and increased sulfuric acid concentration increases the time required to reach maximum sorption. I n addition, higher maximum sorption is obtained with greater cellulose moisture content. Linters of different moisture contents were treated with acetic acid in one case and compared to linters treated with catalyst solution to observe differences in esterification times. The results are shown in Table X. For each group of data decreased esterification time is obtained with increased cotton moisture. Acetic acid alone is a more effective activating agent than acetic acid containing sulfuric acid. Shorter esterifications and smaller differences between the 30- and BO-minute sample8 were obtained when acetic acid alone was used. Activated linters (1%-ater-soakedand acetic acid-dehydrated) have increased activity \Then treated with sulfuric acid prior t o adiabatic acetylation. This is opposite to the results obtained with linters not previously activated. In the former case sulfuric acid diffusion is rapid, t o give uniformly reactive material. Xaximum amount of sorbed bulfuric acid, uniformly distributed, accounts for the increase in activity. On the other hand, increased moisture and acetic acid activation of previously unactivated linters aid the uniform diffusion of sulfuric acid during esterification. Thus, in both cases uniformity is used t o explain the data. ACTIVATIOS DURIXG THE C.4TALYST TREATMENT. In Table X acetic acid was shown t o be a more effective activating agent than
STUDY OF UNACTIVATED LINTERS
Commercial grades of cellulose used for acetylation usually contain less than 8% moisture. For many production procedures the cellulose is dried to lower moisture content, sometimes below 2.0%, before being activated with acetic acid for esterification. I t s reactivity is considerably less than n-ater-soaked and acetic acid-dehydrated cellulose. Diffusion and uniformity variables complicate the system. UNIFORMITY OF BREAKDOWK.Cuprammonium viscosity represents a n average value, without indicating uniformity. The effect of uniformity must be considered in interpreting cuprammonium viscosity data. I n Table VI1 the lower magnitude of viscosities for activated material is compared to those obtained from similarly treated, unactivated linters containing 3.9% moisture. Viscosity values greater than those obtained with the wateractivated linters can be interpreted as a measure of nonuniformity of the cellulose breakdown. EFFECT OF MOISTURE CONTENT O N CHAINLEXGTH REDUCTION RATE. The decreased breakdown rate that is obtained when activated linters are reacted with sulfuric acid in the presence of water may not be obtained with unactivated linters. As will be shown later, if linters are activated with acetic acid longer than a predetermined minimum time before the catalyst treatment, the chain length reduction proceeds a t the same rate as obtained with water-activated linters. It is only when the activation time is shorter t h a t the moisture content of the system affectsthe uniformity of diffusion into the unactivated cellulose. Increased water content may, therefore, aid diffusion and result in raising the apparent breakdown rate. Moisture may be added either
TABLE V. EFFECT OF LIQUID-SOLID RATIOON AVERAGE BREAKDOWN RATEO F ACTIVaTED LINTERS 2.5% Cuprammonium Viscosity Values Cp
Lisuid-Solid Ratio 0.8-1 2-1 3-1 4- 1 6-1
for Various Catalyst Treatment Times,' 5 10 20 30 46 732 317 146 98 60 227 124 90 68 66 265 124 77 60 51 214 146 90 64 56 223 120 86 64 56
60 56 51
43 47 dl
TABLE VI. EFFECTOF ADDEDWATERON
THE CHAINLENGTH REDUCTION OF ACTIVATED LINTERS
%rater Added, Cellulose Basis, 0
4 8
2.5% Cuprammonium Viscosity, Cp., at 25O C. No H&Oa 0.036 mole €Mi01 0.072 mole H2SO 68 34 94 49 128 84
TABLEVII. 2.5% CCiPRAM.IAIONIUM VISCOSITIES O F LIKTERS TREATED WITH SULFURIC A C I D I N ACETIC A C I D (Concentration of HzS04, 0.07 mole per io0 grams of linters; liquid-solid ratio, 4-1; temperature. 2.5' C.) Time, 2.5% Cuprammonium Viscosity, Cp.. fox Min. Unactivated linters Activated linters 10
30
60 120
180 360
...
810 500 180 85 22
96 40 35 27
23
December 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLEVIII. AND
COMPARISONBETWEEN HUMIDIFIED LINTERS LINTERSTO WHICH THE EQUIVALENT WATERWAS ADDED
2901
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Moisture, %, Based on Cellulose 2.5% Cuprammonium During Esterification During catalyst Viscosity, Time, Originally activation treatment CP. min. 1.6 4.80 23 1 95 4.8 4.8a 48 55 48 35 3.8 1.5 3:kb 18 37 3.8 3.86 3.8 a 0.018 mole of HzSOa catalyst treatment for 60 minutes. b Activation, 20 minutes a t 25O C., followed by 0.072 mole of H&Ot catalyst treatment for 20 minutes.
...
OF MOISTUREAND CATALYST TABLE I X . EFFECT CONCENTRATION ON SORPTION RATE
Series
A
B
C
Cotton Moisture, % 0.1 1.0 4.0 7.8 0.1 1.8 3.9 7.5 0.1 0.9 3.6 5.4
Moles HzS04 per 100 G. Cellulose Sorbed Total 30 min. 60 min. 0.0164 0.0037 0.0050 0.0164 0.0053 0.0071 0.0166 0.0133 0.0144 0.0166 0.0138 0.0141 0.0337 0.0044 0.0069 0.0338 0.0069 0.0098 0.0333 0.0177 0.0217 0.0331 0.0245 0.0244 0.0670 0.0058 0.0062 0.0671 0.0081 0.0131 0.0663 0.0217 0.0299 0.0671 0.0314 0.0393
acetic acid containing sulfuric acid. An additional comparison of the two is shown in Table XI. For the acetic acid-activated linters (experiments A through C), greater sulfuric acid concentration during the last 10 minutes increases the chain length reduction rate and reactivity. As the initial sulfuric acid concentration is increased for linters with no acetic acid activation (experiments D through H), the reaction is less uniform and masks the effects so apparent with the activated linters. This effect is emphasized by comparing reactions C and H. I n 10 minutes sulfuric acid reduced the average chain length of activated linters t o a value lower than obtained in 60 minutes with unactivated linters. The results of Table X I and Table IV indicate that 50 minutes were sufficient to activate these linters when they contained 3.9% moisture to a reactivity comparable t o water-soaked and acetic acid-dehydrated linters, Sulfuric acid sorption and acetylation times agree very well. Also, Table XI shows that the acetic acid-sulfuric acid mixtures failed to activate the linters uniformly in 60 minutes. Recognition of the difference in activating rate of acetic acid and acetic acid containing sulfuric acid is important. Reaction time is an important variable. MINIMUMACTIVATION TIME. It is of importance to establish the interrelationship of the activation and catalyst treatment steps. Table X I 1 (series A) shows the effect of varying the activation liquid-solid ratio, activation time, and catalyst treatment time a t constant temperature. A constant 5 t o 1 catalyst treatment liquid-solid ratio was used. Standard statistical analysis ( I ) of the data shows that activation time is the major variable affecting the acetylation reactivity. Twenty minutes are insufficient to activate the linters uniformly under the conditions specified. The activation liquid-solid ratio has a minor effect on this particular series of experiments, although the trend is toward greater reactivity from lower liquid-solid ratios. The catalyst treatment time affects reactivity even less. Sulfuric acid sorption is comparable for the series; cuprammonium viscosity is primarily a function of catalyst treatment time. A 2 t o 1 activation liquid-solid ratio is practical. Between 20 and 40 minutes of activation are required to obtain rapid acetylation. I n Table XI1 (series B) activation time, liquid-solid ratio, and time of catalyst treatment are varied. Standard statistical analysis shows that a 10-minute activation is insuffi-
40' .015
A2
,A25
Moles H$O,
.d3 .d35 .d4 .d45 sorbed per 1OOg. linters
(
5
Figure 3. Effect of Sorbed Sulfuric Acid on Chain Length Reduction Rate at 25' C. cient and that 25 minutes is adequate for activating these linters. Variations in catalyst treatment time and liquid-solid ratio affect the active linters to a negligible degree. This is also true of wateractivated cellulose. When activation is less than the minimum time, i.e., 10 minutes in Table X I 1 (B), the catalyst treatment affects the reactivity.
TABLE X. ESTERIFICATION TIMESOF LINTERSTREATED WITH ACETICACIDALONEOR ACETICACIDCONTAINING SULFURIC ACID
L
> 150 0.1 0.9 4.1 5.4 5.9
0.0620 0.0686 0.0738 0.0671 0.0674
0 0058 0.0081 0.0293 0.0314 I
....
0.0062 0.0131 0.0377 0.0393 0.0394
125 65 47 > 160 >150 125 103 95
>150 105 60 47 >150 > 150 100 70 70
TABLE XI. EFFECT OF VARYING INITIAL AND FINAL CATALYST ON CUPRAMMONIUM VISCOSITYAND ESTERIFICONCENTRATION CATION TIME Expt. A
B C D E F G
H
Moles HzSOt per 100 G. Linters 50 to Sorption a t Start to 50 min. 60 min. end of 60 min. 0 0.018 0.015 0.037 0 0.029 0.071 0 0.049 0.008 0.008 0.008 0.008 0.071 0.050 0.034 0.034 0.024 0.034 0.069 0.033 0.069 0.069 0.031
2.5% cupr.Esterification Viscosity, Time CP. Min.' 454 30 257 25 184 19 184 55 124 45 428 115 492 too 53 1 115
Vol. 44, No. 12
INDUSTRIAL AND ENGINEERING CHEMISTRY
2908 TABLE XII.
ACTIVATION AND CATALYST TREATMENT STEPS ON REACTIVITY OF LINTERS
INTERRELATIONSHIP O F
Activation Series A
?LT
&$%o
20 40 60 90 20 40 60 90
1.5 2
zn
3
40 10 20 40 10 20 30
5 5 90
5
30 20 10 30 20 10 30 20 10
10 10 10 25 25 25 40 40 40
2
TABLEXIII.
Moles HzSOa per 100 G. Linters Available Sorbed 0.071 0,072 0.071 0.071 0.071 0,072 0.071 0.071 0,073 0.072 0.072 0.072 0.074 0.073 0,073 0.074
0.044 0.044 0.043 0.044 0.044 0.042 0.042 0.044 0.046 0.043 0.045 0.045 0.048 0.047 0.046 0.046
0.069 0.066 0.070
0,049 0.043 0.046 0.043 0.046 0.043 0.042 0.046 0.047
0.069
0.069 0.070 0.070 0.070 0.071
EFFECTS O F ACTIVATION AND CATALYST
2.5%
cupr.
Viscosity CP. 107 64 34 56 77 43 39 120 56 43 120 77 56 116 77 47
Acetylation Time, Min. 43 15 15 18 40 15 16 16 45 21 19 18 55 35 18 16
68 86 137 60 73 150 56 77
68 58 55 15 18 17 15 16
98
16
..
TRE.4TMENT TEUPERATURES ON
REACTIVITY OF LINTERS
Activation Time, iMin., at 2-1 LiquidSolid Ratio
Activation and Catalyst Treatment TemD.. a C.
5 5 5 5 5 5 5 5 5 5 5 5
5
4
B
Catalyst Treatment LiquidTime, solid ratio min.
0.07 Mole HzSO4
Catalvst Treatment, Min., 5-1 Liquid-Solid Ratio
Moles HzSOd Sorbed Der 100 4.
2.5%
Linters (from 0.07 Mole)
Cuprammonium Viscosity, CP.
Acetylation Time, Min.
18
10 20 30 60
10 20 30 60
0.045 0.047 0.048 0.047
253 308 133 77
60 60 45 20
29
20 30 60 10
10 20 30 60
0.044 0.043 0,042 0.041
116 56 43 39
18 18 16 57
38
30 60 10 20
10 20 30 60
0.038 0.036 0.036 0.032
34 16 22 10
15
46
60
10 20 30 60
0.035 0.032 0.030 0.025
18 15 15 13
13 15 11 12
10 20 30
;,EFFECT
OF
TEMPERATURE ON >~IKIMUAI
!LCTIVATION
14 16 15
The lower sorptions obtained a t higher catalyst treatment t e m p e r a t u r e s w e r e not obtained when the temperature was adjusted to 25" c. after higher activation temDeratures. With nearly comparable sorption figures, the constant 14-minute acetylation time figures indicate high activity for all four experiments. However, the higher cuprammonium viscosity values for the lower activation temperature experiments suggest that the cellulose breakdown was nonuniform during the first part of the catalyst treatment. Hence, a criterion for measuring the minimum activation time of a cellulose may be the activation time necessary to ensure optimum sorption, minimum cuprammonium viscosity, and lowest esterification time after the catalyst treatment. T o test this concept further, a time series mas made on linters with low moisture content. Table XV shows the results. Constant sorption, acetylation time, and cuprammonium viscosity figures after a 60-minUte activation are found in Table XV. This value may be considered the minimum activation time a t 25 o C. under the specified conditions for the particular linters used. Previously it was found (Table X I I ) that a 25-minute activation was necessary for linters containing4%
TIME.
Cotton linters containing 4% moisture were activated with 2 parts of acetic acid and treated with 0.07 mole of sulfuric acid at a 5 to 1 liquid-solid ratio for various times and temperatyes before sampling for esterification. Table XI11 presents the data. These data when analyzed by standard statistical technique indicate ( 1) : 1. Sorption values decrease with increased catalyst treatment time and tem erature. 2. Esterif!cation time is rapid for experiments activated above 18' C. The 29' C. activation experiments indicate that a 10minute activation is inadequate. I n general, shorter esterification times are associated with higher activation temperatures. Part of the small time difference observed between experiments of highly activated linters is probably due to temperature differences during the adiabatic acetylation. 3. Higher activation temperature overcomes the adverse effect of short activation time.
EVALUATION OF MINIMTJ~V ACTIVATION TIME. Cotton linters were activated with 2 parts of acetic acid for 30 minutes a t 23", 29", 39", and 41' C., adjusted t o 25" C. for 10 minutes, and treated with 0.07 mole of sulfuric acid at a 5 to 1 liquid-solid ratio for 20 minutes prior t o standard adiabatic acetylation. Table XIV presents the data.
TABLE XIV. EFFECT OF ACTIVATION TEMPERATURE ON ACETYLATION TIME
Activation Temp., C. 23 29 39 41
(0.072 mole of HzSOi available for sorption) Moles H z S O I Sorbed per 100 G. Linters 2.5% Cuprammonium a t 25O C. Viscosity, Cp. 0.042 0.041 0.039 0.040
Esterification Time. Min.
86 77 56 56
TABLE XV. MINIMUM ACTIVATION TIMEAT 25' C. CONTAINNG 2.3% MOISTURE
14 14 14 14
OF
LINTERS
Activation Timen, Min.
Moles H L 3 0 4 Sorbed per 100 G. Linters
2.5% Cuprammonium
Viscosity, Cp.
Acetylation Time, Min.
1 6 10 20 30 40 50 60 90 120
0.017 0.019 0.024 0.036 0.042 0.044 0.046 0.043 0.043 0.043
1755 933 715 295 86 77 68 68 68 67
200 160 145 105 65 50 40 20 20 20
a Each was then given a 0.07 mole HzS04 treatment for 20 minutes before testing.
December 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
2909
moisture. The data of Table XI11 show that higher temperature decreases the activation time necessary to give high activity. It is reasonable to conclude that for a cellulose with a particular previous history that minimum activation time to give high activity is a function of the moisture contents of the system and cellulose and the activation temperature. Increased temperature and moisture contents decrease the minimum time required to obtain high activity. If minimum activation time is satisfied, the cuprammonium viscosity values are lower and measure the cellulose breakdown. If not, higher values are obtained, which indicate nonuniform activation.
Wiley who determined all of the cuprammonium viscosities reported in this paper.
ACKNOWLEDGMENT
RECEIVED for review M a y 12, 1952. ACCEPTBID August 14, 1962. Presented before the Division of Celluloso Chemistry a t the 122nd Meeting of the AMERICAN CHEMICAL SOCIETY, Atlantic City, N. J., 1952.
The authors gratefully acknowledge the assistance of Thomas
LITERATURE CITED
(1) Brownlee, K.A., "Industrial Experimentation," 3rd ed., Brooklyn, N. Y.,American Chemical Publishing Co., Inc., 1949. (2) Carver, E. K.,e t a l . , IND. ENQ.CHEM.,ANAL.ED.,1,49-51 (1929). (3) Chevalet, P. A., Brit. Patent 264,181 (Jan. 11, 1926). (4)Dreyfus, H., Ibid., 343,986(Feb. 16,1931). (6) Hall, N.F., and Conant, J. B., J. Am. Chem. SOC.,49,3047 (1927). (6) Hess, K.,and Ljubitsch, N., Ber., 61, 1460 (1928). (7) Staudinger, H., and Daumiller, G., Ann., 529,219 (1929). (8)Wohl, A., Brit. Patent 20,527 (July 17, 1913); French Patent 448,072 (Jan. 22, 1913).
Separation of 1- and 2-Methyliaphthalenes by Azeotropik
Distillation JULIAN FELDMAN AND MILTON ORCHIN Synthetic Fuels Research Branch, Bureau of Mines, Bruceton, Pa., and Department of Chemistry, University of Pittsburgh, Pittsburgh, Pa.
T
HE isomeric monomethylnaphthalenes occur together in
coal tar distillates and petroleum crudes. Previous methods for separation of these isomers have been inadequate. The object of this investigation was t o study the application of the principles of azeotropic distillation t o the separation of these isomers. Physical methods, such as crystallization and careful distilla tion (IO),have been used to isolate 2-methylnaphthalene in high purity and good yield from mixtures with its isomer. However, isolation of I-methylnaphthalene of high purity has been possible only a t the expense of poor recovery. Chemical methods, such as sulfonation and desulfonation using differences in the rates of desulfonation (3) and differences in the solubilities of the sulfonic acids (il),have also been tried with similar results. Attempts t o separate the hydrocarbons by means of fractional crystallization of the picrates ( 2 )were unsuccessful. Close-boiling components of a mixture are frequently separated by azeotropic distillation, but when the components are isomers, the azeotropes with an entrainer are also close boiling and difficult to separate. At any particular pressure, the azeotrope of the more volatile isomer is richer in hydrocarbon than the corresponding azeotrope of the less volatile isomer. Since adjustment of the pressure permits alteration in the composition of an azeotrope, it is theoretically possible to select a pressure a t which very little of the more volatile isomer is contained in an azeotrope while the less volatile isomer may not form an azeotrope a t all. Under these conditions, the entrainer is selective and separation of the isomers is facilitated, since there is a greater difference between the boiling points of the azeotrope and the nonazeot'rope than between the boiling points of the two components or those of their azeotropes. I n selecting the pressure to produce the desired conditions, it is well to remember that azeotropic composition varies with pressure such that the concentration of the component having the higher heat of vaporization (usually the entrainer) increases with pressure (16).
EXPERIMENTAL
PREPARATION OF MATERIALS.2-Methylnaphthalene was isolated in high purity from commercial 1-methylnaphthalene by distillation and crystallization from alcohol. I t s freezing point was 32.23' C., indicating a purity of 99.7%. The boiling point of pure 2-methylnaphthalene is 241.1' C. a t 760 mm. 1-Methylnaphthalene was synthesized by two methods: (1) 1-Naphthyllithium formed from 1-bromonaphthalene and metallic lithium in ether solution was reacted with methyl iodide (6); and (2) methylmagnesium iodide was added to a-tetralone secured (1) by oxidation of tetralin with air (16). The carbinol was dehydrated and dehydrogenated by heating with sulfur a t 200" t o 250" C. The sample used had a freezing point of -30.947' C., indicating a purity of 99.6%. The boiling point of pure 1-methylnaphthalene is 244.8" C. a t 760 mm. The entraining agents listed in Table I were commercial materials which were purified by distillation in Heligrid columns prior to use. ANALYTICAL METHODS. Refractometric measurements were made on systems whose components had sufficiently different refractive indices. Ultraviolet absorption spectra were used for the analysis of mixtures of the isomers ( l a ) and their mixtures with quinoline-type bases. Freezing points, accurately determined by cooling and warming curves (7), were used to determine the purity of samples of the methylnaphthalenes. AZEOTROPES OF THE MONOMETHYLNAPHTHALENES. Previous studies of the azeotropes of the monomethylnaphthalenes were made only a t atmospheric pressure (9). In this investigation, entrainers were studied for azeotropic formation with 2-methylnaphthalene a t reduced pressures (Table I). Entrainers were selected on the basis of the proximity of their boiling points t o that of the hydrocarbon and of the expected deviations of the mixtures from Raoult's law. Mixtures of 50 grams of 2-methylnaphthalene and 150 ml. of entrainer were
