Znd. Eng. Chem. Res. 1991,30, 267-270 Sioda, R. E. Normal Cylinder-in-flow-tube Mass Transfer Problem with Inclusion of Parabolic Flow Velocity Distribution. Chem. Eng. Sci. 1989, 44, 1263. Von Stackelberg, M.; Pilgram, M.; Toone, V. Bestimmung von Diffusionskoeffizienten einiger Ionen in Gegenwart von Fremdelektrolyten. 2.Electrochem. 1953, 57, 342.
267
Weast, R. C., Ed. CRC Handbook of Chemistry and Physics, 63rd ed.; CRC Press Inc.: Boca Raton, FL, 1982; p D253.
Received for reuiew May 1, 1990 Reuised manuscript received July 23, 1990 Accepted August 1, 1990
Oxidation of Hydrolyzed Olive Pits and Almond Shells with Nitric Acid in the Production of Humic-Based Fertilizers Francisco A. Riera, Ricardo Alvarez, and Josd Coca* Department of Chemical Engineering, University of Ouiedo, 33071 Oviedo, Spain
Hydrolyzed olive pits and almond shells, waste products in the production of furfural, were oxidized with nitric acid as the first step to obtain humic-based fertilizers. The acidity of the product and the loss of weight of the solid material were studied in the following range of reaction parameters: temperature, 20-80 "C;reaction time, 30-240 min; nitric acid concentration, 5-45 wt %; and solid/liquid ratio, 0.143-0.400 by weight. Statistical analysis of the experimental data makes it possible to obtain polynomial equations that describe the process and allow its optimization. High acid concentrations and low temperatures proved to be the most suitable conditions for obtaining a high level of acidity in the product and a reasonably small loss in weight.
Introduction Natural organic materials such as manures, garbage, and forestry and agricultural byproducts were, at the dawn of the agriculture age, the most common fertilizers. Because of their low nitrogen content and often slow release of nitrogen, they were replaced by synthetic compounds such as ammonium nitrate, urea, nitrogen-phosphorus-potassium (NPK) complexes, and, recently, slow-release fertilizers (Kerr, 1986; Lahalih et al., 1987). However, it is estimated that only 45-5070 of the applied synthetic fertilizer nitrogen is used by crops. The other half is partially converted to soil organic nitrogen (25%) and lost by leaching and denitrification reactions (25%), sometimes causing pollution problems (Coca et al., 1988). Extensive use of inorganic fertilizers with a scarce supply of organic material leads to a decrease in soil fertility, particularly in arid land.s,and has an important effect on chemical and biochemical equilibria in the soil (Knonova, 1982). The availability of large amounts of agricultural, industrial, and municipal wastes makes them an important source of humic material, which could improve the physical and chemical structure of soil. Those wastes may have to be oxidized, digested, ammoniated, etc., in order to increase their nitrogen content and value as fertilizers (Mukherjee et al., 1963; Chakrabartty and Berkowitz, 1969; Kim et al., 1981; Fuertes, 1983; Coca et al., 1984, 1985). Furfural is usually produced by acid-catalyzed dehydration of pentose contained in forestry wastes and agrowastes such as bagasse, corncobs, rice hull, etc. In some areas, almond shells and olive pits are also a raw material for producing furfural. A considerable amount of solid residues is produced in the furfural process. Part of this is used as fuel to generate the steam needed in the process. The remainder may pose a disposal problem. A potential alternative for this residue is to use it as a source of humic material. The aim of this work is to investigate the oxidation of hydrolyzed almond shells and olive pits with nitric acid, as the first step to the ammoniation reaction for producing a nitrogenous humic-based fertilizer. Carboxyl and hydroxyl groups are formed as a result of the oxidation re0888.5885191 12630-0261$02.50/0
Table I. Ultimate Analysis and Composition of Hydrolyzed Olive Pits and Almond Shells (Weight Percent Dry Basis) olive pits almond shells C 54.2 55.4 H 5.9 5.6 N 1.3 0.3 S 0.3 0.3 0 (by diff) 38.4 38.2 catechols-tanninsa 21.9 9.5 resins-waxes-fatsb 10.9 8.9 ligninc 30.6 37.5 extractivesd 12.9 4.4
*
Ethanol extraction (4 h). Ethanol-benzene extraction (7 h). 'Solids left after digestion with H2SOo(76%) (2 h). dBoiling water extraction (3 h).
action. By further treatment with ammonia, those groups fix the nitrogen in the form of amides, ammonium salts, or cyclic compounds.
Experimental Section Olive pits and almond shell residues produced after hydrolysis to yield furfural were supplied by Furfural Espafiol S.A. (Murcia). The hydrolysis reaction conditions were 140 "C, 8 wt 5% H2S04(acid-water basis), and 4 h of reaction time. The ultimate analysis of the material and its composition as determined by Soxhlet extraction is shown in Table I. The hydrolyzed residues were first dried at 60 "C and then ground and sieved. Fractions in the range 0.1-1.0 mm were collected. The oxidation reactions were carried out in a 0.4-L round-bottom flask. Samples of 50 g of material were slurried in the flask with the desired amount of nitric acid with constant stirring at 350-450 rpm. The temperature was measured with a Fe/constantan thermocouple, and the acid solution was preheated if necessary. At high temperatures (>40 "C) and nitric acid concentrations (>25 wt %), the reaction is not easily controlled due to foam formation and nitrogen oxide generation. In these experiments, cold nitric acid was added slowly to the reaction mixture in order to keep the temperature constant. After a certain time, the reaction mixture was cooled and filtered through a medium porosity fritted porcelain funnel 0 1991 American Chemical Society
268 Ind. Eng. Chem. Res., Vol. 30,No. 1, 1991
,
?
I
/
90,
I 10
I
I 20
,
I 30
I
I
LO
t lmin I
Figure 1. Titration plot for an almond shell oxidized sample (oxidation conditions: T = 50 O C , HNOB= 25 wt %, t = 36 min, S/L = 0.27). Table 11. Range of Independent Variables for the Oxidation of Hydrolyzed Olive Pits and Almond Shells coded var T, O C C, wt % t, min S/L, wt % 0.143 -1 20 5 30 0.273 25 135 0 50 0.400 +1 80 45 240
and washed with distilled water. The cake of oxidized material was titrated with NaOH (0.1 N) to determine the total acidity. It was observed that after 20 min the titration was completed, as shown in Figure l for an experimental run. Acidity is expressed as milliliters of NaOH (0.1 N) per gram of oxidized product. The experiments were designed by chosing as the extent of the system performance the base-exchange capacity of the sample (or acidity, Y,) and the loss in weight of the solid material after the oxidation step (Y& As dependent variables, the following were selected: (1)reaction temperature, (2) nitric acid concentration, (3) reaction time, and (4) weight ratio of solid raw material to nitric acid. The range of independent variables is summarized in Table 11.
Results and Discussion The results obtained from experiments for acidity and weight loss using olive pits and almond shells show a similar trend in both cases, and hence, only a few graphical representations of the experimental data will be shown. Loss in weight, Y,, has been studied at five nitric acid concentrations (5, 10, 25, 35, and 45 w t %), three temperatures (20,60, and 80 "C), and seven solid-liquid (S/L) ratios (in the range 0.182-2 wt 9%). Experimental results for olive pits oxidized at 60 "C are shown in Figure 2. The highest point of solubilization for lignin takes place in the first 2 h, and as might be expected, the extent of solubilization is the highest for the highest concentration of acid. The degradation of lignin yields oxalic, acetic, and formic acids in solution. The S/L ratio has a negligible effect on weight loss. For a certain acid concentration, changes are never higher than 10%. The acidity of oxidized samples, Y., expressed as milliliters of NaOH (0.1 N)/gram of oxidized product, was also determined, and experimental results for olive pits oxidized at 60 "C are shown in Figure 3. When biomass residues are treated with nitric acid, carboxyl and hydroxyl groups are generated in the solid
-1
60
30
120
2LO
t (mml
Figure 2. Weight losses of hydrolyzed olive pits after oxidation with nitric acid a t 60 O C .
IO '1. 25 'i. 35 ' i . L5 '1.
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B
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l
l
80
~
120
l
160
l
200
1
l 1
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t (mini Figure 3. Acidity of hydrolyzed olive pits after oxidation with nitric acid at 60 "C.
and nitrogen may be introduced in the form of nitro and nitroso compounds. As mentioned before, soluble acids go into solution. A high level of acidity is important for obtaining a high nitrogen content after neutralization of the acidic groups with ammonia. The acidity of the oxidized product is highly temperature dependent. Under the same condi-
~
Ind. Eng. Chem. Res., Vol. 30, No. 1, 1991 269 Table 111. Multiple Regression Fitting of Weight Losses (Y,) and Acidity of the Product (Y,)for Olive Pits and Almond Shells Oxidized with Nitric Acid Olive Pits Y, = 44.33 + 18.94T + 15.92C + 5.87t + 2.637" - 4.28t2 + 8.13TC + 4.21Tt + 3.67TC(S/L) (2) R2(adj)= 0.9688 Y. = 38.48 + 4.87T + 2.64C + 0.15t - 2.24(S/L) - 5867" 7.53TC - 1.81Tt + 0.16T(S/L) + 2.09TC(S/L) (3) R2(adj) = 0.9785
2 5 ~ S. I L = O . I
[HNOJ. t Imin)
30 60 120
240
YS
ya
0 A 0
0
A
+
X
I
S
Iv v
I
Almond Shells Y, = 48.91 + 20.557' + 23.86C + 3.76t - 0.44(S/L) - 9.55C2 + 0.33(S/L)' - 3.36TC - 1.92T(S/L) - 3.76t2 - 2.37C(S/L) 2.24T2+ 2.15Ct + 0.29t(S/L) (4) R2(adj) = 0.9580 Y, = 48.95 - 2.99t + 4.92C - 4.66t - 10.llTZ- 16.89C2+ l.OZ(S/L)' - 9.54TC - 1.63Tt - 0.86T(S/L) - 0.9Ct + 0.47C(S/L) - 5.18TtC - 2.64TC(S/L) - 0.37Ct(S/L) 1.15Tt(S/L) (5) R2(adj)= 0.9830
0
0
I
I
I
I
I
30
40
50
60
70
80
7 ("CI Figure 4. Weight losses (Y,) and acidity (Y,) of hydrolyzed almond shells after oxidation with 25 w t % nitric acid and S/L = 0.4.
tions, acidity increases as the temperature increases from 20 to 60 "C and decreases at temperatures of 80 "C. As shown in Figure 3, at 60 "C, the acidity increases during the first hour of the reaction and tends to remain constant or decrease for longer reaction times. High acid concentrations do not yield a very acidic product, while the solubility is greatly increased. Therefore, intermediate acid concentrations are more suitable for producing a high level of acidity in the product and a low level of solubility in the solid during the reaction. The behavior of almond shells is very similar to that described for olive pits, though the acidity tends to be slightly higher. A few experimental data of weight losses and acidity for almond shells are plotted in Figure 4. Statistical Analysis of the Experimental Data. A regression model has been chosen to fit the response functions, i.e., weight losses, Y,, and acidity, Y,, to the independent variables: reaction time ( t ) ,temperature (T), nitric acid concentration (C), and solid-liquid ratio (S/L). The form of the equation is as follows: A
A
1.0 .6
Figure 5. Response surface for weight losses of olive pits. Fixed variables (coded): S/L = 0, t = 1. / I
t---
---
4
i#j#k 4
a1234x1x'$3x4
+ i=l
(1)
The coefficients of eq 1have been determined by using a computer statistical program (Grethlein, 1977; Kizer et al., 1977; Cochran and Cox, 1980). For weight losses, they are based on 109 experiments for olive pits and 56 for almond shells; for acidity, they are based on 94 experiments for olive pits and 46 for almond shells. The equations for Y, and Y, along with the correlation parameters (R2(adj))are given in Table 111. Two examples of three-dimensional response plots are shown in Figures 5 and 6. These plots provide information that supplement the form of the equations for Y, and Y,. Quadratic and interaction terms in equations for Y, are responsible for the curvature of the response surface, and the influence of temperature and nitric acid concentration becomes evident. However, the curvature of the Y, response is very small for olive pits (as shown in Figure 5), and identical behavior is observed for almond shells. Equation 4 predicts negative values for the lowest values
1.0 .6
Figure 6. Response surface for acidity of oxidized olive pits. Fixed variables (coded): S/L = 0, t = 1.
of the independent variables. This can be explained as statistical deviations at extreme values, at which the number of experiments was not high enough. With regard to the acidity values, they increase as the temperature increases when the nitric acid concentration is low. Otherwise, they tend to decrease as the temperature increases. Fitting the experimental data to a model that predicts Y , and Y, well within the range of the independent variables should allow optimum experimental conditions to be obtained. Nevertheless, high acidities imply high weight losses, which are undesirable. Hence, some restrictions
Ind. Eng. Chem. Res. 1991,30, 270-275
270
Table IV. ODtimum Conditions for the Oxidation with Nitric Acid of Olive Pits and Almond Shells T,OC c, wt % t , min S/L olive pits 20 42.3 240 0.163 Y, = 34.4 wt % Y, = 42 mL of 0.1 N NaOH/g product almond shells 30 45 60 0.29 Y, = 43.6 wt % Y, = 45.1 mL of 0.1 N NaOH/g product
were introduced in the computer program, following Powell’s method (Martinez, 1985), Le., Y, (min) = 40 mL of NaOH (0.1 N)/g and Y, (max) = 50 w t 7%. Under these restrictions, the optimum operating conditions are given in Table IV. Conclusions Previously hydrolyzed olive pits and almond shells can be oxidized with nitric acid to generate acid groups, which by further treatment with ammonia yield a humic-based fertilizer. Optimization of the oxidation process, under certain restrictions, indicates that high acid concentrations and low temperatures are the most important factors for yielding a high level of acidity in the product and low weight losses. The solid-liquid ratio in the reaction mixture is not a very critical parameter. Registry No. HN03, 7697-37-2; furfural, 98-01-1; lignin, 9005-53-2.
Literature Cited Chakrabartty, S. K.; Berkowitz, N. Chemistry of coal-ammoniaoxygen reaction. Fuel 1969, 48, 151-160. Coca, J.; Alvarez, R.; Fuertes, A. B. Production of a nitrogenous humic fertilizer by oxidation-ammoniation of lignite. Ind. Eng.
Chem. Prod. Res. Deu. 1984,23, 620-624. Coca, J.; Alvarez, R.; Fuertes, A. B.; Alonso, F. J. Oxiammoniation of pine bark particles. Can. J . Chem. Eng. 1985, 63, 835-839. Coca, J.; Alvarez, R.; Fuertes, A. B. Oxiammoniation of low rank coals for production of humic fertilizers. Adu. Coal Chem. 1988, 171-193. Cochran, W. G.; Cox, G. M. Disefios experimentales. Trillas, MBxico, 1980. Fuertes, A. B. ObtenciBn de fertilizantes htimicos nitrogenados a partir de carbones de bajo rango y residuos de madera. Ph.D. Dissertation, University of Oviedo, Spain, 1983. Grethlein, H. E. Statistical design of experiments for optimizing the casting variables for cellulose acetate membranes. In Reverse osmosis and synthetic membranes theory-technologyengineering. Sourirajan, S., Ed.; Canada, 1977. Kerr, T. J. Method for preparing a slow-release fertilizer. US. Patent 4,579,579, 1986; Chem. Abstr. 1986, 104, 185524F. Kim, Y. K.; Wendell, M. P.; Hatfield, J. D. Fertilizer from the oxidative ammoniation of sawdust. Ind. Eng. Chem. Prod. Res. 1981, 20,205-212. Kizer, 0.; Laguerie, C.; Angelino, H. Experimental study of the catalytic oxidation of benzene to maleic anhydride in a fluidized bed. Chem. Eng. J. 1977,14, 205-215. Knonova, M. M. La Materia Orgdnica del Suelo; Oikos-Tao: Barcelona, 1982. Lahalih, S. M.; Akashah, S. a.; Al-Hajjar, F. H. Development of degradable slow release multinutritional agricultural mulch film. In$. End. Chem. Res. 1987,26,2366-2372. Martinez, A. Programas BASIC para la optimizaci6n de funciones. 3. MBtodo de Powell. Ing. Quim. 1985,8, 97-101. Mukherjee, P. N.; Ramchandran, L. V.; Lahiri, A. A new method of production of nitrogenous organic manure. Chem. Ind. 1963,4, 741. Received for review November 1, 1989 Revised manuscript received May 14, 1990 Accepted June 9, 1990
RESEARCH NOTES Computer Simulation of Tee Mixers for Nonreactive and Reactive Flows Pipeline tees are frequently used for fluid mixing. Consequently, the mixing characteristics are of considerable interest, and numerous experimental studies have examined the question of optimal tee design. In this paper we discuss computer simulation of mixing downstream of a tee based on a three-dimensional flow code program utilizing the k-c model for turbulent flow. Comparison of the simulation results with available experimental data indicate reasonable agreement, and thus the model appears to be a useful tool for predicting mixing distances and assisting in tee design. Calculations are also carried out to investigate the effect of mixing on a copolymerization reaction in which a catalyst stream and a monomer stream are fed to a tubular reactor through the arms of a tee. I t is found that even when the mixing is completed in a relatively short distance downstream of the tee, steep concentration gradients near the tee inlet can have a substantial influence on copolymer composition. Introduction A significant amount of experimental effort has been devoted to studying the mixing of two streams in a 90° pipeline tee (see reviews by Forney (1986) and Gray (1986)). More recent work can be found in Cozewith and Busko (19891,Sroka and Forney (19891, Gosman and Simitovic (19861, and Tosun (1987). The development of numerical methods for computer simulation of turbulent flows raises the possibility of determining the mixing
performance of a tee by calculation rather than by experiment, In this communication, we compare the mixing efficiency predicted by turbulent flow modeling with available experimental data to determine the accuracy of model. Computations were also made by using the kinetic mechanism for a copolymerization to investigate the effect of mixing on reactor performance for fast reactions. A previous computational study of a turbulent jet emitted through a flat plate into a free stream without an
0888-5885/91/2630-0270$02.50/00 1991 American Chemical Society
