I n d . Eng. Chem. Res. 1992,31, 1780-1784
1780
Davim, G. G. Unit Operations in Hydrometallurgy, Chem. Znd. 1981, 420-427. Handley, T. H.; Dean, J. A. Trialkyl Thiophosphates. Selective Extractants for Silver and Mercury. Anal. Chem. 1960, 32, 18761883. Hagfeldt, E. Stability Constants of Metal-Zon complexes, Part A: Inorganic Ligands; IUPAC Chemical Data Series 21; Pergamon Press: Oxford, 1982. Kolthoff, I. M.; Elving, P. J. Treatbe on Analytical Chemistry; Interscience, New York, 1966; Vol. 13, p 331. Nedjate, H. Etude CinBtique des RBactions d'Extraction des Ions Zn2+et Ni2+par les Acides Dialkyl- et Diaryldithiophoriques. C. R. Acad. Sci. Paris, Ser. C 1977,284,885-887. Nedjate, H.; Sabot, J. L. Extraction du Nickel(I1) par les Acides Dialkyldithiophosphoriques: Etude des Conditions de Wxtraction. C. R. Acad. Sci. Paris, Ser. C 1977a, 285,141-144. Nedjate, H.; Sabot, J. L. Selectivite de la SCparation Nickel(I1)Zinc(I1) au Cours de leur Extraction par l'Acide Di6thyl-2hexyldithiophosphorique. Bull. SOC.Chim. Fr. 1977b, No. 11-12, 1089-1092. Nedjate, H.; Sabot, J. L.; Bauer, D. Extraction du Nickel par lea Acides Dialkyldithiophosphoriques: RBle de la Nature du Groupement Alkyle. Hydrometallurgy 1978,3, 283-295. Perrin, D. D. Zonisation Constants of Inorganic Acids and Bases in Aqueous Solution, 2nd ed.; IUPAC Chemical Data Series 29; Pergamon Press: Oxford, 1982. Pesavento, M.; Profumo, A.; Biesuz, R. Exchange of Protons Between Some Poly(amido-amine) Resins and Aqueous Solutions: a Thermodynamic Interpretation. React. Polym. 1989,11,37-45. Piotrowicz, J.; Bogacki, M. B.; Wasylkiewicz, S.; Szymanowski, J. Chemical Model for Copper Extraction from Acidic Sulfate Solutions by Hydroxy Oximes. Znd. Eng. Chem. Res. 1989, 28, 284-288. Rod, V. Unconventional Extraction-Stripping Flow Sheets for the
Separation of Metal by Liquid-Liquid Extraction, Chem. Eng. J. 1984,29, 77-83. Rodina, T. F.; Varentsova, V. I.; Kolyshev, A. N.; Levin, I. S. Determination of the Association, Distribution and Acid Diasociation Constants of Bis(2-ethylhexy1)hydrogen Phosphorodithioate in Some Diluenta. Zzv. Sib. Otd. Akad. Nauk SSSR, Ser. Khim. Nauk 1973,6,14-18. Sabot, J. L. Extraction Liquide-Liquide du Nickel en Solution Acide par les Acides Dialkyldithiophosphoriques. These de Doctorat d'tEtat, Paris VI, 1978. Sabot, J. L.; Bauer, D. Liquid-Liquid Extraction of Nickel(I1) by DialkylphosphorodithioicAcids. J . Znorg. Nucl. Chem. 1978,40, 1129-1134. Sabot, J. L.; Bauer, D. Liquid-Liquid Extraction of Nickel(I1) by Dialkylphosphorodithioic Acids. Proceedings ZSEC'77; CIM Special Volume 21; Canadian Institute of Mining and Metallurgy: Montreal, 1979; Vol. 2, 509-516. Sillen, L. G.; Martell, A. E. Stability Constants of Metal-Zon Complexes, Section I: Inorganic Ligands; Special Publication 17; The Chemical Society: Burlington House, London, 1964. Sillen, L. G.; Martell, A. E. Stability Constants of Metal-Zon Complexes, Supplement No. l., Part I: Inorganic Ligands; The Chemical Society: Burlington House, London, 1971. Szymanowski, J.; Jeszka, P. Modeling of Simple Multistage and Counter Current multistage Copper Extraction by Hydroxyoximes. Ind. Eng. Chem. Process Des. Dev. 1985, 24, 244-250. Zucal, R. H.; Dean, J. A.; Handley, T. H. Behaviour of Dialkyl Phosphorodithioic Acids in Liquid Extraction Systems. Anal. Chem. 1963,35,988-991.
Received for review October 16, 1991 Revised manuscript received March 24, 1992 Accepted April 13, 1992
GENERAL RESEARCH Separation of Liquid Mixtures of p -Xylene and o -Xylene in X Zeolites: The Role of Water Content on the Adsorbent Selectivity Luis T. Furlan,t Beatriz C. ChavesVtand Cesar C. Santana* Polymer Division, Petrobrcis Research Center, Rio de Janeiro, RJ 2oo00,Brazil, and Department of Chemical Engineering, State University of Campinas, Campinas, 560 Paulo, 13081 Brazil
The selectivity and purity enhancement related to the separation of the isomers p-xylene and o-xylene were studied on a laboratory unit using the liquid-phase adsorption in fixed beds containing zeolite type X whose cation Na+ was replaced by Ba2+ and K+. Using adsorbents with preestablished contents of water and prepared on a special laboratory setup, experiments of the type stimulusresponse using the technique of pulses were conducted, being aimed at the determination of the selectivities on the separation of p-xylene from mixtures with ethylbenzene and also on the separation of p-xylene from mixtures with o-xylene. It is shown that an optimum water content in X zeolites with a value around 3.25 w t 3' % occurs for the selectivity in separating p-xylenes and o-xylenes. Concluding the work, we verified that it is possible to obtain with a good yield p-xylene from a stream of isomers through adsorption in zeolite type X in the liquid phase and that the developed methodology gave precise and repetitive results.
Introduction An investigation of the state of the art of adsorption processes applied to liquid-phase separation shows that
* To whom correspondence should be addressed at the State University of Campinas. PetrobrL Research Center.
most of the information is concerned with patents (Cier, 1970) with only a few studies involving details about laboratory Units to study the influence of the several variables that affect the separation process, such as temperature, rate . of . flow, feed concentration, and water content in the adsorbent. Among typical works that consider experimental results to analyze the separation of xylene isomers
0888-5885/92/2631-1780$03.00/00 1992 American Chemical Society
Ind. Eng. Chem. Res., Vol. 31, No. 7,1992 1781
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Figure 1. Experimental apparatus. Table I. Characteristics of X Zeolite" chemical composn, wt % physical characteristics Ba 18 mean diameter: 0.61 mm K 2.6 specific area (BET):386 m2/g Na 0.3 bulk density: 3.115 g/mL 0.6 Fe Si/N 1.11 a Manufactured by Linde Division, Union Carbide Corp., under The zeolite is presented in the form of the designation of 13. extended pellets with a medium pore size of 0.8 nm.
are those of Santacesaria (1980) and Carrl et al. (1982). In this work an experimental setup for the adsorption tests with o-xylene and p-xylene mixtures was developed including a section for the preparation of adsorbents with a preestablished water content. The adsorbent used in the experiments is a zeolite of type X in which the Na+ ions were replaced by Ba2+and K+.
Experimental Apparatus and Method Using preliminary information published by Carrl et al. (19821, the experimental setup of the present work is shown in Figure 1. The characteristics of the zeolite used in the experiments are depicted in Table I. The solid particles were packed in cylindrical coils with 1-cm i.d. and 3-m length. The temperature was controlled by the oven shown in Figure 1. The pulse test was used in all of the experiments. The pulse test is conducted with an initial flow of the desorbent toluene through the packed bed until equilibrium is reached; then at a given instant a pulse of the feed mixture containing a pardinic diluent (n-heptane) which is not adsorbed is injected. After the feed pulse, a new load of Table 11. Levels for the Variables Studied A, % Q,mL/min lower level 1 1.2 higher level 5 6.0 av level 3 3.6
toluene flows through the bed producing the elution of the aromatic compounds and the diluent, similarly to a chromatographic column. The samples leaving the adsorption unit are analyzed by gas chromatography. A fractional factorial technique was used in the planning of the experiments necessary to verify the influence of the following variables: (a) water content in the adsorbent (A); (b) feed (d) bed length rate of flow (8);(c) feed concentration (0; (L); (e) pulse time (P);(f) temperature (7'). The 16 experiments predicted by the factorial technique were carried out on a random way aiming to verify the reproductibility and confidence of the experimental unit. In Table I1 are shown the variable levels studied in the experimental program. The effect of the adsorbent water content on the adsorbent performance was analyzed by using four different weight percents of water in the X zeolite (2,3,4, and 5.5%) for the selectivity determination considering mixtures of p-xylene and o-xylene and also for mixtures of p-xylene and ethylbenzene. A special heat treatment unit shown in Figure 2 waa built for the preparation of adsorbents containing a preestablished water content and also for the determination of the water content in virgin adsorbents and those in the presence of hydrocarbons. It consists of a Pyrex glass cell with 250-mL capacity immersed in an oven heated by quartz lamps and water refrigerated. The setup operational conditions enables a flow rate of 7.0 X Nm3/s at a pressure of 121.6 kPa in the temperature range from 353 to 673 K. The water content is obtained from successive measurements of desorbed water by nitrogen flow and condensed in traps. A calibration curve for the thermal treatment unti is depicted in Figure 3. The bed length in these experiments was 2.0 m, and the flow rate used was 3 mL/min. The complete data obtained in the experimental program was reported by Furlan (1990).
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1782 Ind. Eng. Chem. Res., Vol. 31, No. 7, 1992 THERM0 COUPLES
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-
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Figure 3. Adsorbent water content as a function of temperature.
Results and Discussion The criteria used to evaluate the results are based on the sketches of the concentration curves shown in Figures 4 and 5 and are called the selectivity (8) and the recovery of p-xylene (R) defined by eqs 1 and 2. Rp - Rd p=(1) Ro - Rd area of p-xylene after t, R = total area of p-xylene (2) In eq 1,Ri is the time corresponding to a maximum in the concentration curve for the i-component (p-xylene, o-xylene, and desorbent). In Figure 4,R is defined by eq 2.
The numerical integration program used to calculate the areas below the curves C ( t ) utilized the RungeKutta method with variable increment. Table I11 is a resume for typical runs which also contains the purity enhancement (AP), defined as the ratio between the p-xylene concen-
Figure 4. Pulse diagram for product elution (6 definition).
"' I
t
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Figure 5. Illustration for the definition of recovery (R).
tration for a given recovery and the p-xylene concentration in the feed, and the production (PRO) that corresponds to the p-xylene curve area divided by the cycle time T,. From the results summarized in Table I11 is evident the
Ind. Eng. Chem. Res., Vol. 31,No. 7, 1992 1783 Table 111. Summary of Results
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Ind. Eng. Chem. Res. 1992, 31, 1784-1792
1784
AP
= purity enhancement C = feed concentration L = bed length P = pulse time Q = feed rate of flow R = p-xylene recovery defined by eq 2 R d = time for the peak maximum of diluent R, = time for the peak maximum of o-xylene R, = time for the peak maximum of p-xylene t , = cut time T,= cycle time T = temperature
41
I I
I
I 1
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WATER CONTENT OF ADSORBENT
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Figure 8. Effect of water content of adsorbent on selectivity.
Conclusion An experimental program concerning the separation of p-xylene, o-xylene, and ethylbenzene isomers was carried out, enabling determination of evaluation criteria involving liquid adsorption in X zeolite. The preferential adsorption of p-xylene is mainly attributed to the physical interaction forces between pxylene and the surface. These forces were enhanced through the replacement of cation Na+ by Ba2+ and K+and through variation of the water content in the adsorbent. This water content is of paramount importance in the selectivity of p-xylene and o-xylene mixtures separation, showing an optimum value in the range of variables analyzed. Nomenclature A = water content in the adsorbent
Greek Letter
0 = Selectivity, defined by eq
1
Registry No. p-Xylene, 106-42-3; o-xylene, 9547-6; ethylbenzene, 100-41-4.
Literature Cited Carra, S.; Santacesaria, E.; Morbidelli, M.; Storti, G.; Servida, A.; Danise, P.; Mercenari, M.; Geloea, D. Separation of Xylenes on Y Zeolites. 1-3. Ind. Eng. Chem. Process Des. Dev. 1982, 21, 440-457. Cier, H. E., Xylenes and Ethylbenzene. In Kirk-Othmer Encyclopedia of Chemical Technology, 2nd ed.; Mark, H. F., Macketta, J. J., Jr., O t h e r , D. F., Eds.; John Wiley & Sons: New York, 1970; Vol. 22, pp 467-507. Furlan, L. T. M.Eng. Dissertation, State University of Campinas, 1990. Santaceearia,E. Metodi di Separazionedegli Xileni Isomeri. Chim. Znd. (Milan) 1980,62 (4), 317-322. Receiued for review September 29, 1991 Revised manuscript receiued February 11, 1992 Accepted March 11, 1992
Stable Operation Conditions for Gas-Solid Contact Regimes in Conical Spouted Beds Martin Olazar,* Maria J. S a n Jose, Andr6s T.Aguayo, Jose M. Arandes, and Javier Bilbao Departamento de Zngenieria Quimica, Universidad del Pa& Vasco, Apartado 644, 48080 Bilbao, Spain
The operation regimes of spouting and of jet spouting have been delimited in the bed expansion in conical contactors. Both contact regimes, but in particular the original regime of jet spouting, have a characteristic hydrodynamic behavior different from that of the conventional spouted bed, and they combine the characteristics of high velocity of gas and solid, typical of transport beds,with the cyclic movement typical of the spouted bed. Its interest is centered on the handling of particles of large diameter, with adherent solids and with size distribution. The ranges of the geometric factors of the contactor-particle system and of the gas velocity for stable operation in both regimes have been determined by experiments in a pilot plant using different solids. The operative ranges of both regimes in conical contactor are compared with the conventional gas-solid contact regimes. The limitations of the few correlations in the literature for design of conical spouted beds and the nonvalidity of these conventional correlations proposed for cylindricalspouted beds have been proven. Consequently, original hydrodynamic correlations for spouting and jet spouting corresponding to conical contactors have been proposed for the calculation of the minimum velocity in stable operational conditions. Introduction When using the gas-olid contact, there are situations where the regimes of fixed bed or fluidized bed are not suitable. In fast reactions, short residence times for the gas are pursued (for optimum selectivity). The innovative designs-jets (Kmiec and hchonski, 1991), cyclonic reactors (Lede et al., 1989a,b), impinging jets (Tamir, 1989), 0888-6885/92/ 2631- 1W$O3.oO/O
etc.-secure these objectives (with gas residence times between 0.03 and 1.2 a), and they even increase the demands of heat and mass transfer between phases, but they hardly combine the characteristics desired in the solid flow whose particle size or whose optimum residence time is excessively high (in cyclonic reactors for example, the residence time of the solid is between 0.07 and 1.3 e). 1992 American Chemical Society
