Ind. Eng. Chem. Prod. Res. Dev. 1983, 22, 699-709
699
Production of Oxalic Acid via the Nitric Acid Oxidation of Hardwood (Red Oak) Sawdust Jack M. Sulllvan," Joseph W. Wllllard, David L. Whlte, and Yong K. Klm Division of Chemical Development, National Fertilizer Development Center, Tennessee Valley Authority, Muscle Shoals. Alabama 35660
Kinetic and statistically designed experiments were used to determine the optimum reaction conditions for the nitric acid oxidation of red oak sawdust to produce oxalic acid in mixed HN03/H2S0,/V205 reaction media. The data suggest that the optimum conditions for the batchwise production of oxalic acid are reaction temperature, 75 OC; reaction time, 2 h; H2S04 concentration, 50 wt %; ratio HNO,:sawdust, 8:l;V2O5 catalyst, 0.003%; and oxygen flow rate, 21.1 mL/g of sawdust/min. Under these conditions the sawdust to oxalic acid conversion is 80.2 wt %, with a nitric acid recovery ratio (i.e., g of H2C2O4 produced/g of HNO, unrecovered) of 3.59. Losses of nitric acid occur by its reduction to N, and N20, while losses of carbon result from the formation of COP and CO. An estimate of raw material requirements for production of oxalic acid is given.
Introduction The potential production of oxalic acid by the nitric acid oxidation of waste cellulosic materials has long been recognized (Kirk-Other, 1967; 1981). Numerous patents and papers concerning this process have appeared in the chemical literature (Simpson, 1936; Brooks, 1943; Agrawal and Rao, 1979; Deshpande and Vyas, 1979). Most of these processes involve the prior hydrolysis of the cellulosic material to produce a glucose solution, which in turn is oxidized in a nitric acid or a nitric acid/sulfuric acid medium according to the idealized reaction C6HI2O6+ 6HN03 3H2C204+ 6 N 0 + 2H20 (1)
-
However, nitric acid is capable of effecting the simultaneous hydrolysis and oxidation of solid cellulosic materials according to the following idealized equation (Webber, 1934; Bailey, 1954; Chaudhuri and Rao, 1963; Kothalkar et al., 1975). (C6H,,,O5),H@ + ( x - 1)H20+ 6xHN03 3xH2C204 + 6xNO 6xH20 (2)
-+
In order to make the process economically viable it is necessary to recover the oxides of nitrogen produced during the reaction. We have investigated the nitric acid and mixed nitric acid/sulfuric acid oxidation of various cellulosic materials (waste paper, wheat straw, ground oats, and sawdust) as a possible route to oxalic acid for further use in the processing of phosphate rock and as an intermediate in the production of oxamide, a potentially valuable slow-release nitrogen fertilizer (Sullivan et al., 1981). In this report we describe the results of a kinetic and a statistically designed study to determine the optimum conditions for the production of oxalic acid from hardwood (red oak) sawdust in a mixed nitric acid/sulfuric acid reaction medium. Previous batch experiments have indicated that near optimum yields of oxalic acid may be achieved in a mixed HN03/H2S04solution containing 50 wt % H2S04prepared by mixing 97 wt % H2S04and 57 wt % HN03 The optimum nitric acid (as 100% HNOJ to sawdust weight ratio was 8:1, with V205catalyst added to the extent of 0.003%, with respect to nitric acid. Yields were considerably reduced in the absence of V205. Results had further suggested that the addition of small quantitites of TiOz (ruti1e:sawdust 0.0075) might improve the yield of oxalic acid.
-
Experimental Section Rate Study. The oxalic acid formation experiments were conducted with "run-of-the-mill" red oak sawdust (43.6% C, 5.56% H, 0.98% N, and 14.6% moisture), which varied in texture from a fine powder to thin, curled shavings. Reagent grade oxalic acid dihydrate (Baker reagent) was used without further purification. Sawdust (1.09 g) or H2C2O4-2H20 (1.14 g) was charged to a series of 250-mL volumetric flasks. The flasks were submerged in a stirred ethylene glycol bath controlled at 70,75, or 80 f 0.5 "C. Twenty milliliters (31.872 g) of aqueous solution containing 8.72 g of HN03, 15.94 g of H2S04,and 0.000262 g of V2O5 was pipetted into the flask. At the conclusion of the desired reaction period, the flasks were removed from the bath and quickly submerged in chilled water to quench the reaction. The contents of the flasks then were transferred to 100-mL volumetric flasks, diluted to the mark with distilled water, and analyzed for oxalic acid, nitric acid, and sulfate. Only negligible quantities of residue remained undissolved. No attempt was made to recover the oxides of nitrogen which were liberated during the reactions. A second set of identical experiments was conducted in which 0.0082 g of Ti02 (rutile) was added to each flask prior to the addition of reaction solution. Statistically Designed Study. The experimental apparatus is shown in Figure 1. The reactor was a 40 cm X 64 mm Pyrex glass tube equipped with a thermocouple well, an oxygen sparger, and a 4-mm Teflon stopcock at the bottom. The gases exciting the reactor flowed through 9-mm glass tubing to the bottom of the nitrogen oxide absorption column, where they were sparged into distilled water. The 40 cm X 64 mm absorption column was packed with 5-mm glass beads. A water reservoir equipped with a stopcock was mounted above the column to allow the dripping of water countercurrent to the exiting off-gases. The reactions were initiated by charging the weighed quantity of sawdust to the bottom of the reactor, adding the desired quantity of acid, and connecting the oxygen flowline to the oxygen sparger (0, flow rate was preset). The addition of acid generally resulted in considerable self-heating, which brought the reactor close to the desired reaction temperature. The acid-sawdust mixture rapidly became syrupy and some foaming occurred during the initial stages of the reaction. However, the foaming was much less pronounced with hardwood sawdust than was previously encountered during similar oxidations of
This article not subject to US. Copyright. Published 1983 by the American Chemical Society
700
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983 4- iVATER
40 CM x 6 4 M M GLASS ABSORPTION COLUMN
~
+--
OXYGEN
4 0 C M x 6 4 M M GLASS REACTOR 5 M M GLASS BEADS
THERMOCOUPLE WELL WATER
--+
5
HNO3 REACTION
MEDIUM 02 SPARGER
4 M M TEFLON STOPCOCK
Figure 1. Apparatus for the catalytic oxidation of carbohydrates.
newspaper, wheatstraw, and pine sawdust. The reaction during this early stage is quite vigorous, with the copious evolution of nitrogen oxides and a precipitous drop in the off-gas flow rate (due to oxygen consumption). Some oxides of nitrogen escaped the reaction column during this vigorous stage, as was evident from the evolution of yellow fumes. This was true even when two absorption columns in tandem were employed and suggests a temporary oxygen deficit. However, the reaction quickly moderates (15-20 min), the solution becomes progressively less viscous, and electrical heating by means of a heating tape is required to maintain the desired reaction temperature. The off-gas flow rate was periodically measured using a soap bubble flowmeter. It should be noted that although oxygen flow rates during these experiments supplied an approximately&fold excess of oxygen during the reaction, similar results were obtained when a 4-fold excess of oxygen was employed. However, attempts to use air rather than oxygen resulted in unacceptably low recoveries of nitric acid (oxalic acid yields were not affected). At the conclusion of each experiment the acid media from the reactor and the absorption column were drained into separate 1-L flasks. The reactor and the absorption column were thoroughly washed down with distilled water and the washings were collected in the 1-L flasks. These flasks were analyzed for total oxalic acid, nitric acid, and sulfuric acid. The nitric acid unrecovered was determined from a "control" in which exactly the same volume of reaction solution as used in the experiment was added to a 1-L flask and submitted for analysis. In addition to the experiments discussed above, gas chromatography was used to measure the quantities of N2, N20, CO, and C02produced during the oxidation process at the zero level of the experimental design. The analysis was conducted with a Hewlett-Packard Model 5730A gas chromatograph equipped with a gas sampling valve. Carbon monoxide and nitrogen were separated with a 4 f t X 1/8 in. molecular sieve 5A column, while separation of carbon dioxide and nitrous oxide required a 6 f t X ' I 8 in. Porapak-QS column. The procedure consisted of sampling the off-gas stream at about 6-min intervals during the entire course of the reaction. Measurement of the off-gas flow rate and prior calibration of the chromatograph allowed the quantities of the individual gaseous components to be determined as a function of reaction time. The variables tested were reaction temperatures (xl) of 65, 70, 75, 80, and 85 "C, digestion time ( x q ) of 2, 3, 4, 5,
and 6 h, and wt % H2S04in solution (x3) of 40,45, 50,55, and 60%. The reaction conditions held constant were ratio of HNOB(as 100% HNOJ to sawdust (8:1), red oak sawdust (14.2 g), V205catalyst (0.003% with respect to HNO,), and O2 flow rate (300 mL/min). The sulfuric acid was added as a 97 wt % solution, while the nitric acid concentration was 57.87 wt %. No Ti02 was added in these experiments since the kinetic results indicated that it had no influence upon oxalic acid yield. The HN03/H2S04/ Vz06reaction solution was premixed prior to addition to the sawdust. Results Kinetic Studies. Table I shows the quantities (grams) of oxalic acid, nitric acid, and sulfate present in the reaction solution as a function of time (min) for both sawdust oxidation and oxalic acid decomposition. It may be noted that sulfate remains unconsumed during the oxidation processes. The kinetic analysis of the results is complicated by the fact that the stoichiometry of the reactions changes continuously during the course of the oxidation processes and by the fact that a considerable weight of nitric oxides (NO,) and carbon dioxide is liberated from the solutions. These effects preclude the use of integrated rate expressions for analysis of the kinetic data. However, the data can be interpreted by differential procedures. The red oak sawdust had the composition: 43.60% C, 5.56% H, 0.98% N, and 49.86% 0 (by difference), corresponding to the empirical formula C1H1.516N0,01g30~.85&Hence, the oxidation may be visualized as proceeding by the following equations. 2.877HN03
-
+ CH1.516N0.019300.858 0.5H2C204 + 1.697H2O + 2.896NO2 (3)
0*946HN03
+ CH1.516N0.019300.85t3
0*705HN03
+ CH1.516N0.019300.858
0.5HzC204 + 0.731H2O + 0.965NO (4)
0.5 H2C204
0.560HN03
-
+ 0.611H20 + 0.362N20 (5)
+ CH1.516N0.019300.858
0.5H2C204 + 0.538H2O + 0.288N2 (6)
No N2 or N20 is liberated during the oxidation of H2C204. Thus, the corresponding equations for the oxidative decomposition of oxalic acid are 2HN03 + H2C2O4
-
2C02 + 2H20 + 2N02
0.67HN03 + H2C204 ---* 2C02
+ 1.33H2O + 0.67NO
(7) (8)
The ratio of the weight of nitric acid consumed per weight of sawdust oxidized generally ranged from about 8 during the initial stages of the reaction down to about 4 as the reaction proceeded. Equations 3-6 predict HNOSsawdust consumptions ratios of 6.58, 2.16, 1.61, and 1.28, respectively; while eq 7-8 would yield ratios of 2.29 and 0.76, respectively. These results suggest that sawdust oxidation proceeds primarily by eq 3 during the early stages, but tends toward eq 4 as the oxidation progresses. However, eq 5-6 also have been shown to occur (see Statistically Designed Study section). Evaluation of the rate data was conducted by plotting the quantities (grams) of oxalic acid and nitric acid as functions of reaction time (Table I), as shown in Figure 2 for the oxidation of sawdust and oxalic acid at 75 "C in the absence of Ti02. Smooth curves were fitted to the data for oxalic acid formation and nitric acid consumption. The smoothed values for nitric acid and oxalic acid converted to a basis of 100 g of initial solution are shown for a typical experiment at 75" C in columns 6 and 7 of Table 11.
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983 701 T.
'C
9
70
C H 2 C 2 0 4 , SAWWST OXIDATION
08
8
07
7
i
- 5.0 06 m
- H 2 C 2 0 4 , OXALIC ACID OXIDNION
44
H N03, SAWDUST OXIDATION 4
02
ii
0.1
Figure 2. Oxidation of 1.09 g of red oak sawdust or 0.81 g of oxalic acid in 8 1 HN03:sawdust mixtures containing 50% HzSOl and 0.003% Vz05at 75 O C .
I
WITHOUT TsG
A
WITH
TiOp
In the case of oxalic acid decomposition, induction periods of 60,20, and 10 min occurred at 70,75, and 80 OC, respectively. These induction periods probably were related to the time required for the dissolution of solid H2C204*2H20. Following the induction period, oxalic acid decomposed at a linear rate with respect to time (Figure 2). The linear rate of decomposition of oxalic acid is characteristic of a zero-order reaction.
Figure 3. Plots of In k w. l/Tfor oxalic acid and sawdust oxidation.
d(0-W --dt - ko
ox kot (CHO) = (CHO)' - -- 1.635 1.635
kO,TiOz
loe exp(-19 144/RT) g/100
0.00280
g of soln min (10)
--
1.749 X 1O1O exp (-19928/RT) g/100 g of soln min (11)
As seen from Table 111and eq 10 and 11, the rates of oxalic acid oxidation are practically identical in the presence or absence of Ti02. In order to evaluate the kinetics of sawdust oxidation, it is first necessary to determine the quantities of dissolved sawdust remaining in solution as a function of reaction time. These quantities may be calculatedby assuming that sawdust oxidation proceeds in a stepwise fashion, as shown by eq 12.
The justification for this assumption is supported by the subsequent fit of the model to the kinetic data. From eq 12, it may be calculated that the consumption of 1g of sawdust (CHO) is equivalent to the production of 1.635 g of oxalic acid (OX), while the decomposition of 1.635 g of oxalic acid is equivalent to the consumption of
0.00290
1IT
an additional 1 g of sawdust. Hence, the quantity of sawdust remaining in solution at reaction time, t, is given by the equation
(9)
The zero-order rate constants as determined from the slopes of the decomposition lines (Figure 2) and corrected to a basis of 100 g of initial solution are given in the upper portion of Table 111. Plots of log ko vs. 1/57 resulted in the Arrhenius expressions (Figure 3)
ko = 5.231 X
-"."
(13)
where (CHO), is the initial quantity of sawdust (g/lOO g sol); OX is the quantity of oxalic acid present in the solution at reaction time, t; and ko is the zero-order rate constant for the decomposition of oxalic acid. This equation does not take into account the reduction in the value of ko due to the loss in weight of the solution as NO, and C02 are evolved. The error is not large, however, since ko decreases by only about 15% in the worst case (80 "C, 240 min). The calculated values for the quantities of sawdust remaining in solution as a function of reaction time are given in column 5 of Table 11. Differential procedures may now be employed to determine the order of the reaction with respect to sawdust and nitric acid. The general rate equation for the nitric acid oxidation of sawdust is
or
where (dOX/dt),,, is the corrected value for the rate of oxalic acid formation, Le., the observed rate, (dOX/dt)obd plus the rate of oxalic acid decomposition, k,; (CHO) and (HN03) are the quantities of sawdust and nitric acid, respectively, in solution; and k,, is the rate constant-the value of which is dependent upon the order of reaction (p
702
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983
Table I. Oxidation of 1.09 g of Hardwood Sawdust or 0.81 g of Oxalic Acid in 8 : l HN0,:Sawdust Mixtures Containing 50% H,SO, and 0.003%V,O, sawdust oxidn, g
oxalic acid oxidn, g
temp, "C
time, min
TiOz
HNO
H,SO,
H:C,O,
HNO,
H2C,0,
70
0 10 20 30 40 50 60 75 90 105 120 150 180 210 240 0 10 20 30 40 50 60 75 90 105 120 150 180 210 240 0 10 20 30 40 50 60 75 90 105 120 150 180 210 240 0
none none none none none none none none none none none none none none none 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 none none none none none none none none none none none none none none none 0.0083 0.0083 0.0083 0.0083 0.0083 0.0083 0.0083 0.0083 0.0083 0.0083 0.0083 0.0083 0.0083 0.0083 0.0083 none none none none none none none none none none none none none none
8.56 7.93 7.44 6.88 6.58 6.17 6.17 5.45 5.31 5.28 4.97 4.60 4.28 4.13 3.98 8.72 8.00 7.55 7.11 6.53 6.29 5.89 5.69 5.49 5.49 4.61 4.52 4.09 3.88 3.82 8.76 7.78 6.95 6.45 6.52 5.69 5.41
16.0 15.9 16.2 16.2 16.1 16.2 16.1 16.3 16.1 16.1 16.1 16.1 16.0 16.1 15.9 15.8 16.1 16.3 16.2 16.2 16.3 16.4 16.2 16.0 15.9 16.3 16.1 16.1 16.0 16.0 15.9 16.1 16.2 16.2 15.9 16.3 16.1
0 0.13 0.21 0.31 0.36 0.40 0.47 0.55 0.59 0.64 0.70 0.71 0.83 0.86 0.88 0 0.13 0.21 0.29 0.34 0.40 0.45 0.52 0.59 0.64 0.68 0.71 0.84 0.86 0.90 0 0.13 0.26 0.35 0.41 0.48 0.54
4.54
16.1
0.69
3.97 3.54 3.28 3.08 2.85 8.69 7.78 6.74 5.75 5.74 5.22 5.02 4.86 4.62 4.42 4.10 3.69 3.61 3.20 2.98 8.64 7.20 6.12 5.52 5.15 4.72 4.47 4.17 3.95 3.53 3.42 3.34 2.93 2.79 2.66
16.0 16.2 16.2 16.2 16.2 15.9 16.1 16.3 16.3 16.2 16.3 16.2 16.2 16.1 16.0 16.1 16.0 16.1 15.9 16.0 15.9 16.0 16.1 16.3 16.1 16.1 16.1 16.0 16.1 16.1 16.0 16.1 15.9 15.9 16.0
0.78 0.83 0.84 0.88 0.92 0 0.11 0.26 0.35 0.42 0.49 0.56 0.63 0.70 0.71 0.77 0.83 0.85 0.89 0.88 0 0.21 0.31 0.41 0.49 0.58 0.61 0.70 0.77 0.79 0.84 0.86 0.90 0.89 0.90
8.66 8.54 8.66 8.59 8.66 8.50 8.61 8.59 8.65 8.72 8.74 8.61 8.58 8.66 8.48 8.66 8.65 8.65 8.60 8.60 8.60 8.60 8.60 8.66 8.66 8.65 8.72 8.67 8.53 8.58 8.80 8.58 8.75 8.70 8.82 8.62 8.67 8.62 8.74 8.70 8.60 8.60 8.70 8.50 8.50 8.62 8.67 8.56 8.57 8.54 8.62 8.57 8.56 8.54 8.65 8.56 8.67 8.56 8.64 8.56 8.62 8.72 8.63 8.70 8.59 8.62 8.59 8.62 8.65 8.56 8.47 8.41 8.30 8.36 8.19
0.82 0.81 0.80 0.80 0.77 0.75 0.74 0.74 0.76 0.74 0.74 0.69 0.66 0.61 0.59 0.83 0.80 0.81 0.80 0.80 0.79 0.79 0.77 0.76 0.74 0.73 0.67 0.66 0.62 0.59 0.80 0.80 0.80 0.78 0.77 0.75 0.75 0.74 0.65 0.65 0.64 0.56 0.47 0.46 0.41 0.81 0.81 0.79 0.79 0.77 0.76 0.75 0.68 0.62 0.65 0.62 0.58 0.53 0.45 0.41 0.81 0.80 0.80 0.77 0.63 0.66 0.61 0.63 0.59 0.53 0.50 0.41 0.34 0.29 0.23
75
80
10 20 30 40 50 60 75 90 105 120 150 180 210 240 0 10 20 30 40 50 60 75 90 105 120 150 180 210 240
none
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983 703
Table I (Continued)
oxalic acid oxidn, g
sawdust oxidn, g temp, "C Rn --
time, min n 10 20 30 40 50 60 75 90 105 120 150 180 210 240
TiO,
HNO,
H,SO,
H2C204
HNO,
0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082 0.0082
8.62 7.16 6.28 5.62 5.12 4.84 4.42 4.06 3.82 3.64 3.42 2.99 2.99 2.93 2.67
16.0 16.1 16.2 16.2 16.2 16.3 16.2 16.2 16.1 16.1 16.1 16.0 16.0 16.0 15.9
0 0.17 0.29 0.39 0.49 0.56 0.61 0.66 0.75 0.80 0.79 0.86 0.90 0.89 0.89
8.65 8.68 8.57 8.72 8.65 8.57 8.65 8.65 8.65 8.56 8.47 8.39 8.39 8.21 8.09
with respect to sawdust and q with respect to nitric acid). Equation 15 may be closely approximated by the equation
AOX
(Flor (-dabs +
where AOXoM is the change in the quantity of oxalic acid produced over the short time interval, AT = T2- T,, and are the average values for sawdust (CHO), and (HN03)aV and nitric acid, respectively, over the same time interval. The values of these quantities are given at intermediate times (5, 15 min, etc.) in columns 5,6,8,9, and 10 of table 11. The order of the reaction was determined by testing various integers for the exponents p and q in eq 16 to determine which values resulted in a constant value for the rate constant, kpq. The most consistent results were obtained with p = 1 and q = 1, corresponding to a second-order reaction (first order in sawdust and first order in nitric acid). The apparent second-order rate constants at 75 "C as determined from eq 16 are given in the last column of Table 11. The rate constants given in Table I1 are based on the quantities, in grams, of oxalic acid produced from 100 g of solution which initially contained 3.307 g of sawdust and 26.58 g of nitric acid. In general, rate constants are written in terms of concentration rather than weight units. For the experiment reported in Table 11, the concentrations of reactants and products changed due not only to the chemical reaction, but also due to the significant loss of NO, and C02 from the system as the reaction progressed. Knowledge of the weight loss of the solution as a function of reaction time allows the correction of the rate constants to concentration units (g/lOO g of soln). Consider the three processes by which the weight of the system changes. First, nitric acid is consumed by the reaction HN03
-
(0)+ 0.5HzO + NO,(NZO, Nz)t
(17)
In each case, the 0.5 mol of water is assumed to remain in solution. Hence, the apparent weight loss due to nitric acid consumption is 0.857(HNO: - HNO,,), where HNO,O is the initial weight of nitric acid and HNO,, is its weight at time, t. Next, sawdust is oxidized to produce oxalic acid.
(0)
C1H1.516N0.019300.858
0*5HZCZ04
(18)
The apparent weight gain due to this oxidation process is 1.635(CH0°- CHO,), where CHOO is the initial weight of
0.81 0.81 0.79 0.76 0.75 0.71 0.68 0.61 0.60 0.55 0.50 0.42 0.36 0.26 0.21
sawdust and CHO, is its weight at time, t. Finally, COz is liberated from the solution by the oxidation of oxalic acid.
AOX
"' - (CHO)PaV(HNO3)qaV - (CHO)PaV(HNO3)qaV(16)
H2C204
HzCz04
(0) _+
2C02 + HzO
(19)
The apparent weight loss is 0.978h0t, where k, is the zero-order rate constant for the oxidation of oxalic acid and t is the reaction time. Hence, the weight of solution (starting with 100 g) as a function of reaction time is given by the equation
+
solution w t = 100 - 0.857(HN030 - HN03;) 1.635(CH0° - CHO,) - 0.978kot (20) The weights of the reaction solutions as functions of reaction time are shown in column 4 of Table 11. The weights of the solutions may be used to correct the second-order rate constants to concentration units (g/ 100 g of soln). From eq 16
/ AOX 1
kllspp(
wt of soln 100
)
(22)
where the ratio 100/wt of soln corrects the rate of reaction and the quantities of CHO and HNO, to concentration units. Typical examples of the corrected second-order rate constants for the nitric acid oxidation of red oak sawdust at 75 "C are given in column 7 of Table IV. These rate constants were further adjusted slightly to give a better fit to the kinetic data. The adjusted values at each temperature are given in the lower portion of Table 111. Plots of log k,, vs. 1/T result in the following Arrhenius expressions for the rates of sawdust oxidation in the absence and presence of TiOz. kll = 1.591 X
lo7 exp(-16568/RT), kll,TiOa 4.534 X lo7 exp(-l7286/RT),
100 g of soln/g min (23) 100 g of soln/g min (24)
The Arrhenius plots for both sawdust oxidation and oxalic
704
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983
Table 11. Typical Smoothed Data and Apparent Second-Order Rate Constants for the Oxidation of Hardwood Sawdust in Terms of g/Initial 100 g of Solution
none
75
0
LOO
0
10 15 20 25 30 35 40 45 50 55 60 67.5 75 82.5 90 97.5 105 112.5 120 135 150 165 180 195 210 225 240
97.864 96.308 95.155 94.293 93.605 92.946 92.024 91.257 90.568 89.992 89.143 88.396 87.922 87.446
3.307 3.158 3.006 2.879 2.749 2.649 2.545 2.460 2.372 2.297 2.221 2.151 2.081 1.981 1.881 1.790 1.696 1.629 1.559 1.500 1.435 1.329 1.220 1.160 1.101 1.013 0.959 0.898 0.834
26.58 25.09 23.57 22.45 21.33 20.48 19.66 19.02 18.38 15.87 17.35 16.87 16.38 15.68 15.02 14.44 13.86 13.38 12.89 12.50 12.07 11.47 10.86 10.41 9.95 9.62 9.31 9.01 8 71
0
temp, "C
70 75 80
0.0006128
0.03610
0.00546
0.04156
0.0006428
0.02761
0.00546
0.03307
0.0006098
0.02215
0.00546
0.02761
0.0005900
0.01881
0.00546
0.02427
0.0005913
0.01699
0.00546
0.02245
0.0006187
0.01556
0.00546
0.02102
0.0006767
0.01417
0.00546
0.01963
0.0007591
0.00910
0.00546
0.01456
0.0006678
0.00749
0.00546
0.1295
0.0006915
0.00576
0.00546
0.01123
0.0007364
0.00364
0.00546
0.00910
0.0007548
0.00212
0.00546
0.00758
0.0007782
0.001517
0.00546
0.00698
0.0008623
1.289 1.457 1.647 1.881 2.093 2.230 2.342 2.515 2.624 2.691 2.533
It is now of interest to determine how well the derived rate expressions reproduce the experimental data given in Table I (corrected to 100 g of solution). The calculated grams of oxalic acid produced from 100 g of initial reaction solution as a function of reaction time are given by the equation
ox =
0.00346 0.00558 0 00795
[ k l : ~0( c C H O ) a v ( c H N o 3 j a v ( t n + l - tn) -
Sawdust ____ - - . kii,acij, 100 g o f kii,a&.TiO , 100 g ofsoln/i min soln/g min __
0.000443 0.000630 0.000885
0.04854
1.068
Oxalic Acid
0.00340 0.00546 0.00755
0.00546
0.792
Table 111. Rate Constants for Oxidation of Oxalic Acid and Sawdust in 26.4%HNO,, 50% H?SO,, and 0.003% V,Os Reaction Solution
70 75 80
0.04308 0.431
kotn+lI(
wt of soln
(25) --_.
0.000442 0.000630 0 000910
acid decomposition are shown in Figure 3. Within the limits of experimental error, there is no effect of Ti02 addition upon either the rate of sawdust oxidation or oxalic acid decomposition.
where (CCH& and , )C ( are the average concentrations of sawdust and nitric acid, respectively, present in the solution during the reaction period, tn+l- t,; and kll and k o are the rate constants for oxalic acid formation and decomposition, respectively. The calculated and observed grams of oxalic acid produced are given for the typical example at 75 "C in the last two columns of Table V and in Figure 4. Data beyond 240 min were obtained by linearly extrapolating the concentration of sawdust, the
Table IV. Corrected Second-Order Rate Constants for Oxidation of Hardwood Sawdust (at 7 5 "C)" 100 g of soln/g min
temp, "C
TiO:, g
time, min
75
none
15 25 35 45 55 67.5 82.5 97.5 112.5 135 165
% reaction wt of soln, g
____
12.9 19.9 25.6 30.5 35.0 40.1 45.9 50.7 54.6 59.8 64.9
97.086 95.732 94.724 93.949 93.276 92.485 91.641 90.913 90.280 89.567 88.769
-
k
1
.am
___k
0.0006428 0.0006098 0.0005900 0.0005913 0.0006187 0.0006767 0.0007591 0.0006678 0.0006915 0.0007364 0.0007548
av =
" Other temperatures available in table continuation
)
(Supplementary Material).
ii
,cor
0.0006241 0.0005838 0.0005589 0.0005555 0.000577 1 0.0006258 0.0006756 0.0006071 0.0006243 0.0006596 0.0006700 0.0006165
11
,ad]
0.000630
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22,
No. 4, 1983 705
Table V. Calculated and Observed Concentrations of Reactants and Products for HNO,/H,SO, Oxidation of Red Oak Sawdust (at 75 "C)" temp, time, "C min 75
0 10 20 30 40 50 60 756 90 105 120 150 180 210 24OC 27 0 300 350 400 450 500 550 600
giinit. 100 g of soln
g/100 g of soln
TiO,,g
wt of soln,g
CCHO
CHNO,
COX
CHO
HNO,
none none none none none none none none none none none none none none none none none none none none none none none
100.000 97.864 96.308 95.155 94.293 93.605 92.946 92.024 91.257 90.568 89.992 89.142 88.396 87.922 87.446 86.973 86.497 85.702 84.910 84.115 83.323 82.528 81.737
3.307 3.073 2.855 2.676 2.515 2.372 2.239 2.045 1.860 1.723 1.596 1.386 1.247 1.089 0.956 0.824 0.691 0.470 0.248 0.026 0 0 0
26.58 24.09 22.15 20.66 19.51 18.54 17.63 16.29 15.20 14.23 13.41 12.20 11.26 10.59 9.96 9.32 8.68 7.61 6.55 5.48 4.42 3.35 2.29
0 0.455 0.831 1.150 1.424 1.662 1.870 2.132 2.340 2.507 2.642 2.837 2.963 3.041 3.071 3.066 3.031 2.907 2.714 2.467 2.196 1.923 1.650
3.307 3.006 2.749 2.545 2.372 2.221 2.081 1.881 1.696 1.559 1.435 1.220 1.101 0.959 0.834 0.717 0.598 0.402 0.211 0.022 0 0 0
26.58 23.57 21.33 19.66 18.38 17.35 16.38 15.02 13.86 12.89 12.07 10.86 9.95 9.31 8.71 8.11 7.51 6.52 5.56 4.61 3.68 2.76 1.87
NO, 0 2.083 3.585 4.685 5.493 6.128 6.734 7.576 8.263 8.872 9.367 10.057 10.643 10.957 11.273 11.586 11.902 12.430 12.955 13.483 14.008 14.536 15.060
OX,.*d
CO, 0 0.052 0.107 0.160 0.214 0.267 0.320 0.400 0.480 0.560 0.641 0.801 0.961 1.121 1.281 1.441 1.601 1.868 2.135 2.402 2.669 2.936 3.203
OX,,bd 0 0.394 0.789 1.062 1.244 1.456 1.638
0 0.445 0.801 1.094 1.343 1.556 1.738 1.962 2.136 2.271 2.378 2.529 2.619 2.673 2.686 2.667 2.622 2.492 2.305 2.075 1.830 1.587 1.349
2.093 2.366 2.518 2.548 2.670 2.791
a Other temperatures available in table continuation (Supplementary Material). Reaction time at which sum of oxalic acid concentration plus sawdust concentration reaches maximum value. Values a t which maximum concentration of oxalic acid occurs.
Table VI.
Range of Variables in Experimental Design range
coded variable
-2
-1
0
+1
+2
temperature,"C ( x l ) digestion time, h (x,) wt % H,SO, ( x , )
65
70 3 45
75 4 50
80 5 55
85 6 60
2 40
oxalic acid decomposition may be obtained from the respective rate expressions
Rf - ~ I I C C H O C H NO~ _ c,L___,___
' m R E 4 m O N TiME
m
I
4CO
m
_I
Figure 4. Calculated vs. observed quantites of oxalic acid produced from oxidation of sawdust at 75 O C .
concentration of nitric acid, and the weight of the reaction solution. Table V also gives the concentrations of sawdust, nitric acid, and oxalic acid remaining in the solution (columns 5-7), as well as the total quantities (g) of reactants and products for an initial 100-g batch of reaction solution (columns 8-12). Implication of the Rate Data for Continuous Operation. In commercial practice, oxalic acid production from sawdust probably would be conducted in a continuous fashion using a stirred-tank reactor operating at steadystate conditions. In this situation, sawdust and nitric acid would be fed to the tank at a constant rate, matched by an equivalent removal and recycle of reaction solution from which oxalic acid would be recovered by crystallization (solubilities of oxalic acid in HN03/H2S04are reported by Williard et al., 1982). It is evident from the kinetic data that the steady-state concentrations of sawdust and nitric acid should be maintained at the highest possible values in order to make the second-order oxalic acid formation reaction much faster than the zero-order oxalic acid decomposition process. The ratio of the rate of oxalic acid formation to the rate of
Rd
ko 1.591 X
io7 exp(-16 ~ ~ ~ / R ~ C C H O-C H N O ~ -
5.231 X lo9 exp(-19 144/RT) 3.041 x 10-3[eXp(2576/RT)]C~~~C~~~B (26) If the concentrations of sawdust and nitric acid were maintained at 3.3 and 26.0 g/ 100 g of soln, respectively, then the ratios of the rates of oxalic acid formation to oxalic acid decomposition would be 12.8, 12.1, 11.4, 10.8, and 10.3 at 60,65,70,75, and 80 OC,respectively. Hence, very high conversion efficiencies may be achieved. These efficiencies increase at lower temperatures due to the difference in activation energies for the formation and decomposition processes. This calculation demonstrates that a considerable improvement in economics may be achieved by operating the process in a continuous, rather than a batchwise, fashion. This point will be discussed further in the next section. Statistically Designed Study Preliminary experiments had considerably narrowed the range of the reaction variables required to give good yields of oxalic acid and good recoveries of nitric acid from the mixed HN03/H2S04oxidation of hardwood (red oak) sawdust in batch-type operations. The final program in this optimization process uses a full 23 factorial design, with star points at the extremes to determine the responses oxalic acid yield, nitric acid recovery, and nitric acid re-
706
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983
I -i
* +
NWBEFIS 9 N C d R j c " CCkCEZTi?4TlG\
- E 3TE
7
5
. 'E
AT
I
-L__i-__--l--_-l t i
-r
NUMBEQS ON CURVES DENOTE *?Si4 CONCENTRATION k T "%
1
73
SL
R E 4 C - a L 'EMFER4TJRE
E5
73
75
80
REACTION TEMPERATURE
e5
9*
Y.
Figure 5. Effect of temperature and H2S04concentration on oxalic acid produced
Figure 6. Effect of temperature and H2S04concentration on HNO, lost when reaction time is 2 h.
covery ratio (i.e., g of H&O4 produced/g of HNOBunrecovered) as a function of the reaction variables: temperature (xl),digestion time (xJ,and initial wt % HzS04in solution (x3). The ranges of the reaction variables are given in Table VI. The three responses were regressed in their coded form (Table VI) according to the equation
mum yield differs very little from the zero-level value of 11.382 f 0.518 g, which corresponds to an 80.2 f 3.6 wt % conversion of sawdust to oxalic acid. Nitric Acid Loss. The regression equation for nitric acid unrecovered is
+ b,x2 + b3x3 + blzxlxz + b l 3 X 1 X 3 + b23xzx3 + bllX1' + b 2 2 X q 2 + b33X32 (27)
response = bo + blxl
where bo is the mean value of the response a t the center point (zero level, x, = 0) of the design and (bl, bz, b3),(b12, bI3,bB), and (bll, bZ2,b3) are the coefficients of the primary effects, the interaction effects, and the square terms, respectively. The variance of the data was determined from four replicates at the center point of the design. The results to be presented are significant a t the 90% confidence level. The experiments of the design were conducted in the usual randomized fashion. The results are shown in Table VII. It is evident from this table that the optimum conditions for oxalic acid yield and nitric acid recovery lie near the zero level of the experimental design, i.e., at a reaction temperature of 75 "C, a reaction time of 4 h, and a sulfuric acid concentration of 50 wt %. Oxalic Acid Yield. Regression of the response, oxalic acid produced, as a function of the reaction variables in their coded form (Table VI) results in the equation oxalic acid yield, g = 11.382 - 0 . 5 5 0 ~-~0 . 5 2 5 -~ ~ 0 . 7 7 L ~ 1-~0 . 2 8 4 ~ 3-~0.350X1X3 (28) where the coefficients of the variables are significant at the 90% confidence level and the standard deviation of the predicted value from measured data is f0.518 g. Predicted values from eq 28 are presented in Figure 5 as a function of reaction temperature and H2S04concentration. As seen from the response equation, the yield of oxalic acid is independent of the reaction time ( x z ) over the time range of the design. This result is in agreement with the kinetic data, which show that oxalic acid yield increases rapidly during the early stages of reaction, but then passes through a broad maximum during the time period 2-6 h. By taking the derivative of the response equation with respect to the variables x1 and x 3 , it is found that the optimum yield of 11.644 f 0.518 g of oxalic acid occurs at the reaction temperature of 74.1 "C and H2S04concentration of 45.8% (coded values x1 = -0.17 and x 3 = -0.83). This optimum yield corresponds to an 82.0 f 3.6 wt % conversion of sawdust to oxalic acid. However, the opti-
+
nitric acid loss, g = 5.758 - 0 . 3 9 4 ~+~0 . 2 5 6 ~ ~ 0.354+ ~ ~0 ~. 4 0 4 ~ + ~0.488x1x3 ~ (29) The calculated nitric acid loss as a function of temperature and wt % HzS04for a 2-h reaction time is shown in Figure 6. The minimum loss of nitric acid, 5.057 f 0.907 g, occurs at 79.8 "C,2 h reaction time, and 47.1% HzS04(xl= 0.954, x q = -2, and x3 = -0.5761). The zero-level loss is 5.758 f 0.907 g. It should be noted that the standard errors in the coefficients of eq 29 are quite large, due to the variable modes of HNO, loss. As will be discussed later, these nitric acid losses correspond to nitric acid lost as Nz and NzO, as well as potentially recoverable oxides of nitrogen which escape the absorption column (see Experimental Section) and nitric acid which is lost in the mechanical operations involved in washing down the absorption column and recovering the reaction products. Gas chromatographic analysis at the zero level of the design showed that a loss of only about 3.2 g of nitric acid can be attributed to unrecoverable N2 and NzO. Ratio Oxalic Acid Produced:Nitric Acid Lost. Regression of the response, g of oxalic acid produced:g of nitric acid unrecovered, results in the equation oxalic acid:HN03 lost = 2.158 - 0.255X1' - 0 . 0 9 4 ~ 2-~o.185x32 - 0.173x1x3 (30) The effect of the reaction temperature and HzS04concentration on the ratio is shown in Figure 7. The maximum value for this ratio, 2.158 f 0.251, occurs at the zero level of the design. As in eq 29, this ratio is strongly influenced by mechanical losses of potentially recoverable nitric acid. Residue. Only small quantities of undissolved residue remained suspended in the acid media at the conclusion of the runs. These quantities are given by the regression equation residue, g = 0.251 - 0 . 0 8 4 ~- ~0 . 0 2 3 ~- ~0 . 0 2 8 3 ~ ~ ~(31) A t the zero level of the design the residue, 0.251 f 0.051 g, amounts to only 1.8 f 0.4% of the initial 14.2 g of sawdust charged to the reactor. Off-Gas Analysis. Figures 8 and 9 show the quantities ( g ) of CO, Nz, CO,, and N20 produced from the oxidation
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983 707
-
75
70
90
E5
80
REACTION TEMPERATURE, 'C
Figure 7. Effect of temperature and H2S04concentration on ratio of oxalic acid:HN03 lost when reaction time is 4 h.
I
I
O4I
.
, ----
/
cs
' 1
,
~
----I
/
i
30
/
/ -
I
I
I
2
3
I 4
TIME, h
Figure 8. Nitrogen and carbon monoxide evolution in experiment 01F1.
process as a function of reaction time at the zero level of the design. The totals of 0.297 g of N, and 0.643 g of NzO produced over a 4-h reaction time correspond to a nitric acid loss of 3.2 g. This value is much lower than the average value (5.3 g) determined by analysis of the reaction products and raises the nitric acid recovery ratio from 2.16 to 3.59. This finding has a considerable impact upon the economics of the process with respect to nitric acid consumption, as will be discussed later. Comparison with Kinetic Data. A number of comparisons can be made between the results of this investigation and the kinetic data. Results of the kinetic experiments gave optimum sawdust to oxalic acid conversions of about 90%, whereas the present results give values of about 80%. The kinetic data predict a total COz evolution of 5.23 g at the zero level of the design, whereas the observed value was 6.45 g. Finally, the kinetic data indicate that carbon dioxide is produced by a zero-order rate process; hence the CO, evolution curve should be linear with time rather than curved, as in Figure 9. However, the two sets of data cannot be directly compared since O2was sparged into the reaction medium of the present experiments and no oxygen was employed in the kinetic study. The sparging of oxygen into the reaction solution might initiate new chemical and physical processes which were not present in the kinetic system. The results do suggest that improved economics might be achieved by introducing the oxygen above the reaction solution rather than directly into it, as was done in the present experiments. Further research would be required to clarify this point.
I
,
J
I
2
4
TIME. h
Figure 9. Carbon dioxide and nitrous oxide evolution in experiment 01F3.
Optimum Conditions for Oxalic Acid Production and Nitric Acid Recovery. The previous analysis and the results of Table VI1 suggest that near optimum yields of oxalic acid and recoveries of nitric acid may be achieved at the zero level of the experimental design. However, the results indicate that neither oxalic acid yield nor nitric acid recovery would be significantly affected by reducing the reaction time ( x z ) from 4 to 2 h. This reduction in residence time would increase plant capacity. Also, the results of the gas chromatographic data for Nz and N20 indicate that the nitric acid recovery ratio should be increased by about 66% over that predicted by regression equations in order to take into account the mechanical losses of HNO, in the small-scale experimental equipment. Hence, the recommended operating conditions for the batchwise production of oxalic acid are reaction temperature, 75 "C; reaction time, 2 h; H2S04concentration, 50 wt %; ratio HNO,:sawdust, 8:l; V205catalyst, 0.003% (with respect to HNO,); and oxygen flow rate, 21.1 mL/g of sawdust/ min. Under these conditions the sawdust to oxalic acid conversion would be 80.2 w t %, with a nitric acid recovery ratio of 3.59. Flowsheet for Batch Process. A simplified flowsheet for the production of oxalic acid is shown in Figure 10. Makeup HNO,/H2SO4/VzO5,sawdust, and O,,along with recycled mother liquor from the oxalic acid crystallizer, C, are fed to the reactor, A, where the reaction is allowed to proceed for a period of 2 h at 75 OC. The warm reaction solution is passed to a residue removal system where any unreacted solid residue is removed by filtration or centrifugation. If desired, this residue may be recovered and used as an auxiliary feedstock along with sawdust in subsequent runs. The reaction solution then is passed to the oxalic acid crystallizer, C, where oxalic acid crystallizes as the dihydrate, HzCz04.2Hz0(Williard et al., 1982). If highly purified oxalic acid dihydrate is the desired product, then the crystals should be dissolved and recrystallized from a minimum amount of warm water. After removal of excess water (produced during the oxidation process), the mother liquor containing soluble oxalic acid, unreacted nitric acid, and sulfuric acid is recycled to the reactor, A. This excess water in the mother liquor may be removed by evaporation. An alternate procedure for water removal would involve recycle of anhydrous oxalic acid from the dehydrator, D, to the crystallizer, C, where water would be removed by recrystallization of oxalic acid dihydrate. After drying, the oxalic acid dihydrate is fed to a dehydrator, D, where most of the water of hydration is re-
708
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22, No. 4, 1983
Do
2-
Y
cr
0
x
Y Y
.d
E
1
v w
Y
0
Y
0000
mmmm s?
--
c
a -
.-
m m m m m m m m
Y
00000000
t-t-t-t-wwww 3
0
E Y
a X
0w * 0m 0m 0m 0m 0
Ind. Eng. Chem. Prod. Res. Dev., Vol. 22,
No. 4, 1983 709
H2C204 H2C204
MAKEUP HNO~/HZSO~/VO,
HN03 RESIDUE
REACTOR SAWDUST
REMOVAL RESIDUE
H2C2O4 H2S04
0 OXALIC ACID CRYSTALLIZER
@
H2Cp04'2H20
DEHYDRATOR
+
RESIDUE MOTHER
H2C204.
t
LIQUOR
1
Figure 10. Flow sheet for production of anhydrous oxalic acid from hardwood sawdust.
Table VIII. Estimate of Materials Requirement for Production of Anhydrous Oxalic Acid from Red Oak Sawdust (Basis/Short Ton Oxalic Acid) assumptions assumptions 0, flow rate: 843 ft3/min reaction temperature: 75 "C HNO,: 57% (17.502 tons) reaction time: 2 h H,SO,: 98% (18.231 tons) 95% recovery of catalyst complete 0, recycle ratio HN0,:sawdust: 8 V , 0 5 : 0.599 lb materials requirement by products material quantity material quantity sawdust 1.247 tons H2C,0, 1.000 tons CO, 0.545 ton HNO, 0.279 ton N,O 0.052 ton 0.603 ton 02 0.037 ton makeup H2S0, 0.100 ton CO makeup V,O,
0.030 lb
moved by rapid heating at 98 "C (Kirk-Othmer, 1981). The most complex aspects of the process involve nitric acid regeneration and oxygen separation for recycle, as depicted in steps E and F (Figure 10). The expense of NO, recovery and pollution control appears to mandate that the oxalic acid plant be located on the site of existing nitric acid and air fractionation facilities. Raw Materials Estimate. Table VI11 gives a materials estimate for the batchwise production of 1 short ton of anhydrous oxalic acid based upon the results of this investigation. The primary raw materials are sawdust (1.247 tons), oxygen (0.603 ton), and nitric acid (0.279 ton). The quantities of makeup sulfuric acid and vanadium pentoxide are crude estimates based upon likely losses during washing and purification of the oxalic acid cake. The process offers several avenues for improved economics. Potentially the byproduct carbon dioxide (0.545 ton) and nitrous oxide (0.052 ton) could be marketed. A major improvement would be realized if air could be substituted for oxygen for the regeneration of nitric acid. This aspect of the process needs further investigation. The results of our experiments in small-scale equipment indicated prohibitively high losses of nitric acid when air was
used. However, it is possible that these losses may have resulted from the high linear gas velocities in the reaction system resulting from the increased volume of required air. Perhaps a reaction system of enlarged dimensions would give improved nitric acid recoveries. Finally, as was pointed out in the kinetic section, a considerable saving of sawdust may be achieved by operating the process in a continuous fashion, using a stirredtank reactor. By maintaining a high steady-state concentration of sawdust and nitric acid, it should be possible to achieve an oxalic acid formation:decompositionratio of at least 7:l. This would correspond to a sawdust to oxalic acid conversion of 143 wt % and reduce the sawdust requirement to 0.699 tonlton oxalic acid. However, the problems associated with crystallizing oxalic acid from such a viscous solution would need to be investigated. Registry No. HN03, 7697-37-2; H2S04, 7664-93-9; Vz05, 1314-62-1; oxalic acid, 144-62-7.
Literature Cited Agrawai, H. P.; Rao, M. B. hdien J. Technol. 1979, 17, 11-15. Bailey, R. W. J. Appl. Chsm. 1954, 4 , 549-554. Brooks, M. J. U S . Patent 2322915, 1943. Chaudhuri, S. B.; Rao, P. R. Res. Ind. 1963, 8, 1-2. Deshpande, S. D.; Vyas, S. N. Ind. Eng. Chem. Rod. Res. D e v . 1979, 18, 69-7 1. Kirk-Othmer "Encyclopedia of Chemical Technology"; Interscience Publishers: New York, 1967; Vol. 14, pp 359-361. Kirk-0th" "Encyclopedia of Chemical Technology"; Interscience Publishers: New York, 1981; Voi. 16, pp 621-624. Kothalkar, V. D.; Badhe, A. V.; Kher, M. G. Chem. Ind. Dev. Chem. Process Eng. 1975, 21-23. Slmpson, G. S. U S . Patent 2057 119, 1936. Sullivan, J. M.; Wiiliard, J. W.; HatfieM, J. D. 182nd National Meeting of the American Chemical Society, New York, NY, Aug 1981. Webber, H. A. Iowa Engineering Experiment Station, Iowa State College, Ames, IA, 1934; Bulletin 118. Wiiiiard, J. W.; Sullivan, J. M.; Kim, Y. K. J. Chem. Eng. Data 1982, 27, 442-445.
Received f o r review February 8, 1983 Accepted July 27, 1983
Supplementary Material Available: Continuation of Tables IV and V (8 pages). Ordering information is given on any current masthead page.
