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Znd. Eng. Chem. Res. 1992,31, 2134-2140
MATERIALS AND INTERFACES Synthesis of 13X Zeolite from Calcined Kaolins and Sodium Silicate for Use in Detergents Antonio de Lucas,* M. Angeles Uguina, Ignacio Coviln, and Lourdes Rodriguez Department of Chemical Engineering, Universidad Compluteme, 28040 Madrid,Spain
The synthesis of 13X zeolite from a calcined kaolin and sodium silicate solution has been investigated. The process variables for the different synthesis steps have been optimized in order to produce 13X zeolite at a lower price for ita use as a builder in detergents. The recovery of the mother liquors required for the economical kiability as well as the scale-up to a pilot plant reactor has been verified. The detersive efficacy of a mixture of 4A zeolite and the synthesized 13X zeolite have been tested. An economical evaluation of this process has been carried out with an estimated price for the zeolite produced of 58 pesetas ($0.56)/kg.
Introduction Since the 19605,the use of phosphates as builders in laundry detergents has been increasinglycriticized, in spite of their excellent washing properties, because they contribute to the eutrophication of surface waters (rivers and lakes). Existing or planned legislative regulations or voluntary agreements require a reduction or total ban of phosphates in laundry detergents in several West European countries, Japan, and North America (Kurzendofer et al., 1987). The selection of a suitable substitute for phosphates not only has to measure up to significant ecological and toxicological criteria, it also has to satisfy practical considerations of use and performance, as well as being economically viable (Schwuger and Liphard, 1989). Builders in detergents have the ability to soften the washing liquor, reducing the Ca2+and Mg2+cation contents in the water by forming complexes with them. This effect avoids the precipitation of surfactants contained in the washing liquors as insoluble calcium and magnesium salts. These salts may be deposited on fibers and the heating elements of washing machines, shorting their lifetime. The phosphate substitutes may be classified in two groups: water-soluble and water-dispersible builders. Nitrilotriacetate, sodium carbonate, ethylenediaminetetraacetate, and other complexing agents as well as polycarboxylates belong to the first type. Zeolites are a representative example of the second group. Because of their advantageousproperties of application and ecological safety, their use as phosphate substitutes has won increasing recognition since the 1970s (Greek and Layman, 1989;Schwuger and Liphard, 1989). Natural zeolites, having a low cost, are really attractive as phosphate substitutes. However, they are colored and they have a high concentration of impurities, especially metallic ions (Fe3+).For this reason, the use of synthetic *Address correspondence to this author at Department of Chemical Engineering,Universidad de Castilla-La Mancha,13071 Ciudad Real, Spain.
zeolites as builders in detergent formulation led to an increase on their production from 146 X lo3metric tons in 1978 to 720 X lo3 metric tons in 1990. At the same time, consumption of phosphates fell from 725 X loeto 450 X lo6 metric tons. Among the synthetic zeolites, 4A zeolite is actually used in the detergent industry as a builder. In previous investigations the synthesis of 4A zeolite from natural clays with the required specifications for its use in detergents has been optimized (Ruiz, 1986;Costa et al., 1988a,b).An economical evaluation showed that it is possible to obtain 4A zeolite at a competitive price for its use as phosphate substitute. Studies on zeolite exchange have shown that the 4A zeolite is very effective to eliminate Ca2+and Mg2+ions. However, ita capacity to remove Mg2+cations, especially at low temperature, is lower (Burzio and Pasetti, 1983; Costa et al., 1987;Schwuger and Liphard, 1989). For this reason, it was thought that other zeolites, such as 13X, could constitute an important complement to or substitute for 4A zeolite (Burzio and Pasetti, 1983). 13X zeolite with Si/Al ratio close to 1 showed a capacity to remove Mg2+ clearly higher than 4A zeolite. For its use in detergent formulation, zeolite needs to fulfii the established specifications: high crystallinity (x, E loo%), calcium binding (C,E 2.8 mmol/g), whiteness (Hunter index, L > 90?%),and adequate particle size distribution (average diameter cz 4 pm; 99 wt % in the range 1-10 pm) (Derleth et al., 1977;Enders and Drave, 1978;Ettlinger and Ferch, 1978;Gresser, 1982). Moreover, it is necessary to have a competitive price with regard to phosphates and other possible sequestrants. For this reason, zeolites must be synthesized from economical raw materials such as natural clays. In a previous work the synthesis of 4A zeolite from differentSpanish clay minerals has been investigated (Costa et al., 1988a). Three Spanish kaolins were selected, based on their optimum Si02/A1203 high purity (kaolinite > 90 wt %), and molar ratio (~21, easy pretreatment by calcination. Kaolins are also the most adequate natural clay to synthesize 13X zeolite with low silica content. However, they have not a Si/Al ratio high enough and the addition of silica from another source
0888-5885/92/ 2631-2134$03.00/0 0 1992 American Chemical Society
Ind. Eng. Chem. Res., Vol. 31, No. 9,1992 2136 Table I. Chemical and Mineralogical Cornposition and Particle Size of Kaolin P (Caonil, S.A.) Chemical Composition, wt % SiOz 49.00 37.00 A1203 0.46 Fez03 TiO2 0.25 0.12 MgO 0.17 CaO 0.48 K2O 0.06 NazO calcination loss 12.80 Si02/A1203 2.25
Mineralogical Composition, w t % kaolinite 93.0 mica 2.0 quartz 5.0 Particle Size, wt %
d, > 10 pm d, < 2 pm
13.0 53.0
(sodium silicate, active silica or another clay with higher silica content as bentonite, sepiolite) is necessary. This silica addition allows the formation of pure 13X zeolite (Breck, 1974). In this paper, the experience acquired in our department in the synthesis of 4A zeolite (Costa et al., 1988a,b) has been used to obtain 13X zeolite. Process variables are optimized to obtain a zeolite from a Spanish kaolin (kaolin P) with the established specifications for its use in detergent formulation. Sodium silicate solution has been used as an additional silica source.
Experimental Section The experiments were carried out in two different experimental sets previously used in another work (Costa et al., 19%). They are basically constituted by two spherical, stirred reactors that are geometrically similar: a laboratory reactor of 1-L capacity and a pilot plant reactor of 50-L capacity. Both of them are hermetically sealed and equipped with a heating system with temperature measure and control. The reactanta used were kaolin P (Caosil, S.A.) as a source of Si02and A 1 2 0 3 and sodium silicate solution (27% Si02-8%Na20, FORET) as an additional source of Si02. Syntheses were carried out following seven sequential steps: previous kaolin pretreatment, gel formation, aging time, crystallization, filtration, washing, and drying. Table I shows the chemical and mineralogical compositions and the particle size of the kaolin used. The kaolin was pretreated in the conditions established in a previous investigation (Costa et al., 1988b): crushed and screened to particle diameters lower than 40 pm and calcined at 900 "C for 30 min. The gel was prepared by dissolving the pretreated kaolin (55% Si02-42.26% A1203) in a NaOH solution and adding the sodium silicate solution. After an aging time, the gel was crystallized under desired conditions. The crystallization product was fast filtered under vacuum, washed with distilled water (1mL of water/g of zeolite), and dried at 120 "C for more than 12 h. All the experiments were carried out using a constant volume of water in the initial gel: laboratory experiments, V = 0.5 L;pilot plant experiments, V = 30 L. The following variables were modified. Gel formation: time, tD;temperature, T,;and stirring speed, ND. Aging time: time, tE; and temperature, TE. Crystallization: temperature, TR;time, tR;stirring speed, NR;gel composition: Si02/A1203,H20/Na20,NazO/Si02,
and K20/(K20 + Na20) molar ratios; seeding, I. Periodic samples and the final product were analyzed to determine the following properties (Covih, 1991): crystallinity, Si/Al ratio, exchange capacity, particle size distribution curve (PSD), and whiteness. Using X-ray diffraction (Siemens Kristalloflex D500 computerized powder diffradometer, with Cu Ka radiation and Ni filter), the crystalline zeolite phase, x,, and the Si/M ratio were determined (Hermans and Weidinger, 1963,Dempsey, 1969; Gutierrez, 1977). The morphological characteristics for the different species obtained were determined by warming electron microscopy (SEW. The calcium and magnesium binding were determined by ion exchange with aqueous solutions of CaC12and MgC12,respectively (Ruiz,1986; Costa et al., 1987). The particle size distribution curve (PSD) was established with a cilas 715 laser diffraction particle size distribution analyzer with X = 632.8 nm, using zeolite samples dispersed in water. The whiteness was measured in a spectra scan PR-713 spectrum radiometer, in the spectral radiation range 390-1170 nm, referred in percentage to Ba2S04as the standard (Hunter index, L).
Results and Discussion The process variables of the different synthesis steps have been optimized in order to produce 13X zeolite at a lower price with the established specifications for use in detergent formulation. The ranges of the variables investigated in each step are as follows: Gel formation: temperature (TD)= 50-80 "C;time ( t ~ ) = 0.5-3 h; stirring speed (ND)= 125-750 rpm. = 20-40 "C; time ( t ~ = ) Aging time: temperature (TE) 0-48 h. Crystallization: temperature (TR)= 50-90 "C; stirring speed (NR)= 125-750 rpm; gel composition: molar ratios SiO2/Al2O,= 2.5-4.5; H20/(Na20+ K20) = 28-70; (Na20 + K20)/Si02= 0.9-2.0, and KzO/(K20+ Na20) = 04.2; seeding (weight ratio zeolite 13X/kaolinite) = 0-10%. Gel Formation. Preliminary work (Covih, 1991) confirmed that the best method for gel formation was the kaolin addition to the sodium hydroxide solution under constant stirring until complete dissolution of the kaolin. Then sodium silicate solution was added and the reaction medium was stirred for 10 min. In previous investigations carried out in our department (Ruiz, 1986; Costa et al., 1988b) using pure reactants, it has been established that an increase of H20/Na20molar ratio produces a decrease of gel nucleation. Therefore, in order to establish the adquate conditions for the gel formation, a constant value of 30 (lower range value) was used for the Hz0/Na20molar ratio. Kinetic curves varying temperature, stirring speed, and time of gel formation in the range specified above were obtained. From the results achieved, the selected conditions for the gel formation were ND = 500 rpm, TD = 70 "C, and tD = 1h, which led to an adequate speed of kaolin destruction and to 13X zeolite with high stability and crystallinity. Aging Time. In a previous work (Uguina, 1979), it has been shown that the aging causes an increase in the nucleation of amorphous gel which enhances its reactivity practically without influence on the maximum crystallinity of the zeolite obtained. This effect is lower as the aging time increases (Uguina, 1979; Costa et al., 1988a). Taking that into account, experiments varying time and temperature of aging were carried out. From the results obtained, it was concluded that the best aging conditions
2136 Ind. Eng. Chem. Rea., Vol. 31, No. 9.1992
b
Figure 1. SEM micrograph of
B
mixture of 4A and 13X zeolites.
c Figura 2. SEM miemgraph
Pczeolite over particles of 13X zeolite.
were t E = 12 h and TE= 20 "c. Crystallization. To investigate the influence of different variahles on the crystallization process, a factorial design of Z5 has heen used. The ranges of the five variahles considered were TR= 70-90 O C ; NR = 125-750 rpm; gel composition: molar ratios SiO2/A1,O3 = 2.9-4.5; H20/ (NazO+ KzO) = 30-50, and (NazO+ K,O)/SiO, = 1-1.8. From the results achieved (Covih, 1991), the following conclusions are reached. 1. Low temperatures and low stirring speeds favored the synthesis of 13X zeolite with low B/Al ratio. 2. Si02/Al,03 molar ratios as low as possible led to 13X zeolites with high crystallinity and low Si/Al ratio. 3. To obtain 13X zeolites with the established specifications, there are only two possible combinations of Na20/Si02and H20/Na20molar ratics Na20/Si0, = 1.8, H20/Na,0 = 50; and NazO/SiOz = 1.0, HzO/Na20= 30. 4. When low SiOz/Alz03molar ratios, high temperatures, and very reactive and concentrated gels were wed, mixtures of 4A and 13X zeolites were obtained. This fact has heen evidenced in the SEM micrographs obtained for the synthesized zeolites. Figure 1 shows one of the SEM micrographs of pure 13X zeolite. 5. When high Si02/A1203molar ratios, high temperatures, high stirring speeds and few reactive and concentrated gels were used, P, zeolite appears with 13X zeolite during crystallization. Figure 2 showa one of the SEM micrographs that noticed the presence of the P,zeolite over the 13X particles. Taking into amount t h e conclusions, two different gels have been selected for their optimization: a gel with low reactivity (NazO/SiOz) 5 1.2) and high concentration (H,O/Na,O 5 36). gel 1; and a gel with high reactivity
tR(h) Figure 5. Optimhtion of rrystauition conditions for gel 1. Influence of Na,O/SiO, molar ratio. Gel formation: To= 70 O C ; tD = 1 h; No = 500 rpm; SiOz/A120s = 2.9; HzO/Nn,O = 30; K,O/ (Na20 + K,O) = 0. Aging time: T . = 20 'C; t . = 12 h. CrystaUilation: TR= 80 O C ; NR = 250 rpm; I = 0%. ( 0 )Na,O/SiO, = 0.9; ( 0 )Na2O/SiO2= 1.0: (A) Na20/SiOz = 1.1; ( 0 ) Na,O/SiO, = 1.2.
(Na,O/SiO,) Z 1.7) and low concentration (H,O/Na,O 2 46). gel 2. (i) Optimization of Crystallization Conditions for Gel 1. Kinetic cwven and PSD curves varying temperature and stirring speed in the ranges specified above were o b tained. The resulta ohtained show that when temperature rises, the nucleation time and the growth time decrease and that a temperature of 85 "C leads to a mixture of 4A and 13X zeolites. On the other hand, it can he observed that stirring speeds higher than 500 rpm lead to a decrease of the crystallinity. That may he explained taking into account that an exeeaeive stirring can dissolve the zeolite synthesized. The PSD curves obtained shift to the right when temperature increases. These curves show a high percentage of particles with d , < 1 pm. Consequently, a temperature of 80 "C and a stirring speed of 250 rpm were selected. Regarding the Si02/A1203molar ratio, it has heen o b served that values of this parameter lower than 2.9 lead to mixtures of 4A and 13X zeolites without an important influence over the properties of the zeolite obtained. Therefore, a value of 2.9 was fixed. Figure 3 shows the kinetic curves obtained using different Na20/Si02molar ratios. It can he observed that when values of this parameter higher than 1.0 were used, mixtures of 4A and 13X zeolites were obtained. Values lower than 1.0 decrease the crystallinity of the zeolite obtained. On the other hand, this parameter has no practical influence on the Si/Al ratio and on the properties of the zeolite synthesized. Consequently, the value 1.0 wa8 selected for this variable. Then the average size of the zeolite particlen obtained has to he adjusted through the HzO/N@Omolar ratio that measures the saturation of the crystallization medium. Figure 4 shows the kinetic curves and the PSD curves achieved by modifying the H20/Na20molar ratio to obtain zeolite with the adequate PSD. In all cases, the crystallinity, binding capacity, and whiteness of the zeolites ohtained are practically the same. However, the zeolite ohtained using HzO/NazO = 32 is the only one that fulfills the percentage of particles with d , < 1 pm (0.7% < 1 % )
Ind. Eng. Chem. Res., Vol. 31, No. 9,1992 2137 100
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9.
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Figure 4. Optimization of crystallization conditions for gel 1. Influence of HzO/NazOmolar ratio. Gel formation: TD = 70 "C; t~ = 1 h; ND = 500 rpm; Si02/&0, = 2.9; NazO/SiOz = 1;KzO/(Na20 KzO) = 0. Aging time: TE= 20 "C; t E = 12 h. Crystallization: TR = 80 "C; NR = 250 rpm; I = 0%. (0)HzO/NazO = 30; (0) HzO/NazO = 32; (A) H20/Naz0 = 34; ( 0 ) HzO/NazO = 36.
50
5
10
Figure 5. Optimization of crystallization conditions for gel 1. Influence of K20/(Naz0+ KzO) molar ratio. Gel formation: TD= 70 "C; t~ = 1 h; ND = 500 rpm; Si02/Alz03= 2.9; HzO/(NazO+ Kz0) = 32; (NazO + KzO)/SiOz = 1. Aging time: TE= 20 OC; t E = 12 h. Crystallization: TR= 80 "C;NR = 250 rpm; Z = 0%. (0)KzO/(NazO + KzO) = 0.15; (0)KzO/(NazO + KzO) = 0.10; (A) KzO/(NazO + KzO) = 0.08; ( 0 ) KzO/(NazO + K20) = 0.05.
with the lowest percentage of particles with d, > 10 pm (10%) that may be easily removed. Finally, to reduce the Si/Al ratio increasing the binding capacity of the zeolite 13X for its use in detergents, Wolf (1985)suggested the partial substitution of Na20 by K 2 0 during the gel formation. Accordingly, experiments varying the K20/(K20+ Na20) molar ratio were carried out. The results achieved are shown in Figure 5. It can be observed that values of this variable higher than 0.1 increase the production of P, zeolite, this zeolite being the only crystalline phase formed when valuea higher than 0.2 were used. At the same time, the Si/Al ratio slightly decreases when the percentage of K+ increases. For this
Figure 6. Optimization of crystallization Conditions for gel 2. Influence of NaZO/SiOzmolar ratio. Gel formation: TD = 70 "C; t~ = 1 h; ND = 500 rpm; SiOz/Alz03= 2.9; HzO/NazO = 50; KzO! (NazO + KzO) = 0. Aging time: TE= 20 "C; t~ = 12 h. CrystalliNaZO/SiO2= 1.7; zation: TR = 70 "C;NR = 250 rpm; I = 0%. (0) (0) NazO/SiOz = 1.8; (A) Na20/SiOz = 1.9; ( 0 ) NazO/SiOz = 2.0.
reason, a value of K20/(K20+ Na20) = 0.1 was selected. (ii) Optimization of Crystallization Conditions for Gel 2. Experimentscarried out at different temperatures and stirring speed showed that when temperature rises, mixtures of 4A and 13X zeolite at 75 "C and mixtures of 4A, P,, and 13X zeolites at 80 O C are obtained. On the other hand, stirring speeds higher than 250 rpm lead to mixtures of P, and 13X zeolite. This indicates that gel 2 is more sensible to stirring speed than gel 1,due probably to the higher dilution of this gel which favored the formation of P zeolite. Taking this into account, the selected conditions were TR = 70 "C and NR = 250 rpm. To study the influence of the Si02/A1203molar ratio over the Si/Al ratio and over the binding capacity, experiments varying this parameter were carried out. The results obtained showed that a decrease of this variable increased the percentage of 4A zeolite synthesized, with the Si/Al ratio in the 13X zeolite produced remaining constant. Thus, a value of 2.9has been selected for this parameter. Figure 6 shows the kinetics curves obtained by using different Na20/Si02molar ratios. It can be observed that the kinetic curves and the properties of the zeolites obtained were practically the same. Only the experiment carried out by using Na20/Si02= 2.0showed a decrease in the crystallinity due to the presence of 4A zeolite. Therefore, as the &/A1 ratio is inversely proportional to the Na20/Si02ratio, the maximum value possible for this ratio (1.9)was selected as the optimum one. Ultimately, in order to adjust the size of the zeolite obtained, different H20/Na20molar ratios were assayed. As observed in Figure 7, nucleation time increases as this variable increases. When the H20/Na20molar ratio decreases, the percentage of particles with d, > 10 pm also decreases and 4A zeolite appears as an impurity at H20/Na20= 46. From this result, a value of 48 was selected for this molar ratio. The 13X zeolites synthesized by using gel 2 in the selected conditions fulfill all the specifications required for their use in detergent formulations; however, the average particle size (12 pm) is too big and the percentage of
2138 Ind. Eng. Chem. Res., Vol. 31,No. 9,1992 100
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Figure 7. Optimizationof crystallization conditions for gel 2. Influence of Hz0/Na20 molar ratio. Gel formation: TD = 70 O C ; t~ = 1 h; ND = 500 rpm; SiOz/Alz03= 2.9; NazO/SiOZ= 1.9; K20/ (Na20+ KzO) = 0. Aging time: TE= 20 O C ; t~ = 12 h. Crystallization: TR= 70 "C; NR = 250 rpm; Z = 0%. (0)HzO/NazO= 52; (0) H20/Naz0 = 50; (A) Hz0/Na20 = 48; ( 0 ) H20/Na20= 46.
particles with d, > 10 pm is 18%. The long time required to synthesize the zeolite and the low yield obtained in each experiment makes the syntheais using gel 2 less interesting than that using gel 1. Synthesis at Low Temperatures Using Gel 2 (Gel 2 LT). To decrease the Si/Al ratio, increasing the binding capacity, comparative experiments were carried out by using gels similar to gel 2 and decreasing reactivity and crystallization temperature. That allows decreasing the Si/Al ratio of 13X zeolite without the formation of 4A zeolite. Under these conditions, it can be interesting to increase the nucleation rate, in order to study the effect of the seeding. When seeding was used, it was observed that the nucleation of 13X zeolite increased. All the experiments carried out by using different percentages of seeding (5% and 10%) can be fitted to a single kinetic curve. The zeolites obtained had a lower Si/Al ratio and, 80, a higher binding capacity. Hence, a seeding of 5 % was selected. Due to the long reaction time required, higher crystallization temperatures were assayed. The results obtained showed that temperatures higher than 60 "C lead to mixtures of zeolites. Thus, the highest temperature that may be used is 60 "C. However, by using this value, 48 h is necessary to obtain zeolite 13X. Taking that into account, experiments modifyingthe temperature from 60 to 80 "C during the crystallization time were carried out. Figure 8 shows the results achieved. It is observed that when the gel was maintained for 12 h at 60 "C, 5 h at 80 "C is enough to obtain a 13X zeolite with the maximum crystallinity,a Si/Al ratio equal to 1.06, a binding capacity of 2.5 mmol of Ca2+/gof dry zeolite, and a whiteness of 95%. To optimize gel composition, experiments varying Si02/A1203,NazO/Si02,and H20/N&0 molar ratios were carried out. Figure 9 shows that mixtures of 4A and 13X zeolites were obtained when SiOZ/Al2O3 and HzO/NazO molar ratios decreased and when NazO/SiOzmolar ratio increased. When a value of HzO/NkO = 65 was used,only 4 h at 80 "C after 12 h at 60 "C was necessary. The average size of the particles obtained was 8.8 Fm. Recovery of Mother Liquors. The mother liquors are concentrated NaOH solutions whose recovery is required
4
6
tdh) Figure 8. Optimization of crystallizationconditionsfor gel 2 at low temperature. Influence of the use of two different temperatures d & g crystalliition. Crystallization: NR = 250 rpm;Z = 5%; Si02/Alz03= 2.7; HzO/NazO = 70; NazO/SiOz= 1.5. ( 0 ) TR= 60 "C (15 h)/80 "C; (*)TR 60 O C (12 h)/80 "C; (+) TR 60 "C (10 h)/80 "C. 100
,
_ - - - 13
X Zeolite Phases mixture
I/ I!
0
2
4
6
tR(6 Figure 9. Optimization of crystallization conditions for gel 2 at low temperature. Influence of gel composition. Crystallization: TR= 60 "C/80 O C ; t ~ ( 6 0 "C) = 12 h; NR= 250 rpm;Z = 5%;K20/(Na20 + KzO)= 0. ( 0 )SiOz/A1209= 2.6, NazO/Si02 = 1.5, H20/Na20 = 70; (0)Si02/A1208= 2.7, NazO/Si02 = 1.6, Hz0/Na20 = 70; (A) SiOZ/AlzO3 = 2.7, NazO/Si02= 1.5, HzO/NhO = 65;( 0 ) SiOZ/Al2Os = 2.7, NazO/SiOz= 1.5, HzO/NazO= 60.
for the economic viability of this process. Consecutive experiments of synthesis were carried out at the optimum conditione for gel 1, each time using the mother liquor obtained from the previous experiment. It was shown that in all cases the kinetic curves and the properties of the zeolites obtained remained constant. It could also be observed that the concentration of Fe3+ ions in the mother liquors remained practically conatant, which indicates that most of the Fe203of the kaolin was incorporated into the zeolites. A minimal proportion of Fe3+ ions remained in the solution, and therefore the whiteness of the zeolites obtained was not affected.
Ind. Eng. Chem. Res., Vol. 31, No. 9,1992 2139 100
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tR(h) Figure 10. Scale-up (conditione are summarized in Table 11). (0) gel 1 (Laboratory);( 0 )gel 1 (pilot plant); (A)gel 2 LT (laboratory); ( 0 ) gel 2 LT (pilot plant).
Scale-up. Syntheses were carried out in the pilot plant equipment at the selected conditions for gel 1 and gel 2 LT, keeping constant the agitation power/volume of reaction ratios used in the laboratory. Under these conditions, 4.8 kg of zeolite was produced in each batch in approximately 21 h for gel 1 and 2.4 kg in approximately 16 h for gel 2 LT. The results obtained for the two gel compositions in the pilot plant reactor are compared in Figure 10 with the corresponding laboratory experiments. It is observed that kinetics and PSD data and properties of the zeolites obtained in both installations were practically the same for both gel compoeitions assayed. These results indicate that the scale-up criterion used is valid at least in the range used. Comparative Study. Table I1 shows that zeolites crystallized at low temperatures from gels like gel 2 show similar crystallinity and whiteness (94% and 95%), the best binding capacity for Ca2+ and Mg2+ (2.5 and 1.5 mmol/g of dry mlite),and the lowest d (8.8pm). On the other hand, if the synthesis is develope2 in only one step, 16 h is enough to obtain a 13X zeolite with the maximum crystallinity. Zedtea synthesized from gel 1 have practically the same properties as the zeolites mentioned above, excepting a higher particle size. Worse zeolites are those from gel 2 that also required the higher time for the total synthesis process. Finally, the detersive efficacy was determined for three detergents with a standard formulation (30 wt % of builder) by using sodium tripolyphosphate, zeolite 4A obtained from kaolin P, and a mixture of zeolite 4A and zeolite 13X (15:15). It was observed that the detersive efficacies of both zeolite 4A and mixture of zeolites were the same and about 8% lower than that of the detergent with sodium tripolypobsphate. To end the study carried out for the use of zeolite 13X as a detergent builder, an economical evaluation of the process proposed in this investigation, similar to that carried out in a previous work for the synthesis of 4A zeolite ((=oeta et aL, 19- Ruiz,1986),has been performed for a production of 30000 metric tons/year. Taking into consideration a period of amortization of 10 years and a benefit of 15% of the total investment of
Table 11. Operational Conditions Selected and Properties of the 13X Zeolite Synthesized by the Different Crystallization Procedures Proposed gel 2 gel 1 gel 2 (low temp) selected conditions gel composition 2.9 2.9 2.7 Si02/A1209 (Na20 + K20)/SiOz 1.0 1.9 1.5 Hz0/(Na20 + KzO) 32.0 48.0 65.0 K20/(Na20+ KzO) 0.1 0.0 0.0 250 250 250 0 0 5 80 70 TR(“C) 60/80 tR (60O C ; h) 12 7.5 16 16 tR (total; h) t (total synthesis; h) 20.5 29 16 properties of 13X zeolite 93 92 94 31, (%) Si/Al 1.08 1.12 1.06 10.4 12 8.8 d (Pm) ( m o l of Ca2+/g of zeolite) 2.4 2.2 2.5 CI (mmol of Mg+/g of zeolite) 1.4 1.3 1.5 94 93 95 L (%)
6
2060 X lo6 pesetas ($20X lo6)(Ruiz, 1986),the resulting estimated price for the zeolite is 58 pesetas ($0.55)/kg. This price is comparable with other detergent builders. Acknowledgment We acknowledge ‘Industrias Quimicas del Ebro” (Fundaci6n Universidad-Empresa,FUE 1112/?0)and the “Comisi6n Internacional de Ciencia y Tecnologia” (CICYT PA 850047)for financial support. Nomenclature CI:change capacity (mmol/g) d : particle size (pm) fraction of particles with a d, size (%) I amount of seeding (%) L: Hunter index (%) N,: gel formation stirring speed (rpm) NR: crystallization stirring speed (rpm) tD: gel formation time (h) TD:gel formation temperature (“C) t ~ aging : time (h) TE:aging temperature (“C) TR:crystallization temperature (“C) tR: crystallization time (h) z,: crystalline zeolite phase (%)
4:
Literature Cited Breck, D. W. Zeolite Molecular Sieves: Structure, Chemistry and Use; Krieger: Melbar, FL, 1974;Chapter 4,pp 313-19. Bunio, F.; Pasetti, A. Induetrial intereat in the utilization of zeolites in detergents. Riv. Ztal. Sostanze Grasse 1983,60,7. Coeta, E.; Lucaa, A.; Zarca,J.; Sam,F. J. Ion-exchange Equilibrium between 4A Type Zeolite and Caz+and ions. Rev. htinoam. Zng. Quim. Quim. Apl. 1987,17,135-148. Coeta, E.; Lucae, k, Uguina, M. A.; Ruiz, J. C. Syntheaie of 4A zeolita from calcined kaolina for use in detergents. Znd. Eng.Chem. Res. 1988a,27, 1291-6. Coeta, E.;Lucae, A,; Uguina, M. A.; Ruiz,J. C. SinteSie de zeolita4A a partir de arcillae espdolas y sua minerales. An. Quim. 1988b, 84,366-73. Covih, I. Sintesis de zeolita 13X para su ueo en detergentes, Ph.D. Thesis, Universidad Complutenae de Madrid, Spain, 1991. Dempsey, E. Calculation of Madelung Potetiale for Faujaaite-Type Zeolites. I. J . Phys. Chem. 1969,73,2. Derleth, H.;Walter, L.; Bretz, K. H.; Kurs, A. Ger. Offen. Patent P2705088.0, 1977. Enders, R.; Drave, H. Ger. Often Patent P2852674.1,1978. Ettlinger, M.;Ferch, H. Synthetic Zeolites aa New Builders for Detergents. Manuf. Chem. Aerosol News 1978,49,51.
Znd. Eng. Chem. Res. 1992,31, 2140-2146
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Greek, B. F.; Layman, P. L. Higher Costa Spur New Detergent Formulations. Chem. Eng. News 1989,Jan 23,29-49. Greaser, R. Fr. Pate-nt APPL 82/10.368,1982. Gutierrez, M. L. Sintesis de zeolita A de sodio. Ph.D. Thesis, Universidad Complutense de Madrid, Spain, 1977. Hermans, P. H.; Weidinger, A. X-Ray Diffraction Determination of Crystallinity of Polycarbonate from Bisphenol A. Makromol. Chem. 1963,64,137-9. KurzendBfer, C. P.; Liphard, M.; Von Rybinski, W.;Schwuger, M. J. Sodium-Aluminum-Silicates in the washing process. Part IX: Mode of action of zeolite A additive systems. Colloid Polym. Sci. 1987,265,542-7.
Ruiz, J. C. Sintesie de zeolita 4A de sodio a partir de caolines. Ph.D. Thesis, Universidad Complutense de Madrid, Spain, 1986. Schwuger, M. J.; Liphard, M. Sodium-Aluminum-Silicates in the washing process. Part X Cobuilders and optical brighteners. Colloid Polym2 Sci. 1989,267, 336-44. Uguina, M. A. Sintesis de zeolitaa X e Y de sodio. PbD. Thesis, Universidad Complutense de Madrid, Spain, 1979. Wolf, F. DDR Pat. 43221;Br. Pat. 1051621;Fr. Pat. 1387644,1985. Received for review February 14,1992 Reoised manuscript received May 11, 1992 Accepted June 1, 1992
Migration Studies of Acrylonitrile from Commercial Copolymers Michael Markelov BP America, 4440 Warrensville Center Road, Cleveland, Ohio 44128
Montgomery M. Alger General Electric Company, P.O. Box 8, Schenectady, New York 12301
Tim D.Lickly Dow Chemical, 1701 Building, Midland, Michigan 48674
Edward M, Rosen* Monsanto Company, 800 N. Lindbergh Blvd., St. Louis, Missouri 63167
Migration experiments were designed and conducted to estimate the diffusivity of acrylonitrile (AN) in four commercial copolymers in contact with water: ABS-248, ABS-LGA, SAN, and CYCOLAC. A new analytical result was used that accounts for the nonuniform concentration profile of the AN due to desorption before the start of the controlled experiment.
Introduction The migration of trace amounts of solvents, reaction by-products, additives, and monomers from polymers has received considerable study. In particular, the migration of vinyl chloride monomer (VCM) in poly(viny1chloride) has received active attention (Koros and Hopfenberg, 1979a,b; Berens and Hopfenberg, 1977). The migration of acrylonitrile (AN) from commercial copolymers is similar in that the migrant is of low concentration and the diffusivity in a given polymer would be expected to be a function of temperature alone. The models which describe the migration (Gandek,1986; Schwope et al., 1990)may require a number of parameters such as the partition coefficient as well as a mass-transfer coefficient between the polymer and the external phase. These parameters have been studied by Gandek and Hatton (1986) and Gandek et al. (1989a,b). The design of a migration experiment to evaluate the diffusivity must account for the possible effects of a nonuniform concentration profile, temperature changes, partitioning effects, and possible boundary layer resistance. With these issues in mind this study describes the experiments and analysis carried out to determine the diffusivity of the AN in the copolymers. Theory Boundary Conditions. The general model for mass transfer assumes a semi-infinite flat sheet of polymer, of half-thickness1, in which the solute migrates to the surface and then into the external phase. One of the most popular analytical models is a solution to Fick’s second law due to Boltzmann (Crank, 1975):
* Author to whom correspondence should be addressed.
Mt is the amount of solute diffusing from time 0 to t , Co is the initial concentration of AN, t is the time measured from the time the concentration is uniformly distributed, D is the diffusivity of the solute in the polymer, and r = Dt/12. Gandek (1986) calls this domain infinite-infinite since it assumes that the AN migrates from an infinite polymer into an infinite external phase or “sink”. The following boundary conditions are assumed 1. The initial concentration of AN is uniformly distributed throughout the polymer at time zero. 2. The AN concentration at the surface and in the “sink” is zero. This assumes there is no boundary layer resistance in the fluid. When more than approximately50% of the migrant has diffused, eq 1breaks down and an infinite series solution is needed (Crank, 1975): c
Since the polymer is finite the value of 1 must be known. (In eq 1 , l cancels out as the polymer is infinite.) If Mt vs time data and Coare known, the value of D can be determined by regression ( h e n and Silverman, 1990). Gandek (1986) characterized this as the finite-infinite domain since it assumes a finite polymer and an infinite external phase of zero AN concentration. When the external phase is a fluid, is of finite volume, and is perfectly mixed but the polymer is infinite, then the “infiitefmite” model should be used: M I = Cola[l - erluaerfc ( ~ ‘ / ‘ / a ) ] (3)
0888-5885/92/2631-2140$03.00/00 1992 American Chemical Society
