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Synthesis of AlPO4-5 in a microwave-heated, continuous-flow, high-pressure tube reactor
Microporous and Mesoporous Materials 23 (1998) 79–81
Synthesis of AlPO -5 in a microwave-heated, continuous-flow, 4 high-pressure tube reactor I. Braun a, G. Schulz-Ekloff a,*, D. Wo¨hrle b, W. Lautenschla¨ger c a Institut fu¨r Angewandte und Physikalische Chemie, Universita¨t Bremen, 28334 Bremen, Germany b Institut fu¨r Organische und Makromolekulare Chemie, Universita¨t Bremen, 28334 Bremen, Germany c MLS-Mikrowellen-Laborsysteme GmbH, Auenweg 37, 88299 Leutkirch, Germany Received 13 May 1998; received in revised form 28 May 1998; accepted 29 May 1998
Abstract Synthesis of AlPO -5 in a microwave-heated, continuous-flow, high-pressure tube reactor is described, based on (i) 4 a commercially available equipment and (ii) recipes optimized for microwave-heated batch reactors. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Synthesis; AlPO -5; Microwave-heated flow reactor 4
Microwave heating has been applied successfully for the rapid synthesis of molecular sieves [1–3] and the protecting encapsulation of dyes in AlPO -5 [4,5]. The short penetration depth of the 4 microwave radiation into the hydrothermal synthesis mixture limits the dimensions of reactors and autoclaves. Therefore, the application of continuous-flow tube reactors is a prerequisite in all cases where larger charges or higher space–time yields are needed, e.g., for the production of zeolite-based inclusion pigments on a larger scale. The synthesis of molecular sieves in a resistanceheated continuous-flow tube reactor has already been achieved [6 ]. The application of a microwaveheated flow reactor for the hydrothermal crystallization of AlPO -5 is described for the first time in 4 this communication. * Corresponding author. Fax: +49-421-218-4918; E-mail: [email protected] 1387-1811/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII: S1 3 8 7 -1 8 1 1 ( 9 8 ) 0 0 18 0 - 2
The microwave-heated flow tube reactor used (MLS ETHOS contFLOW ) consists of a microwave-transparent, chemically inert (polytetrafluoroethylene, Teflon) and tubular coil (120 cm3 internal volume) fitted in a microwave cavity ( Fig. 1). The aqueous suspension (390 cm3) of the gel reaction mixture in the storage vessel is pumped through the reactor under high pressure. The synthesis temperature of >160°C, which has to be reached within 1 min in order to obtain a pure AlPO -5 phase, is obtained rapidly by using 900 W 4 for the initial microwave heating. Subsequently, the desired temperature is controlled with an accuracy of ±3°C. The average applied pressure in the reactor of 2.5 MPa is generated by a high-pressure membrane pump, controlled by a gauge at the inlet of the reactor pipe and held by a valve at the reactor exit. A cooling jacket around the outlet tube of the flow reactor enables rapid cooling of the reaction slurry; i.e., the achievement of the
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I. Braun et al. / Microporous and Mesoporous Materials 23 (1998) 79–81
precise high-temperature residence time or crystallization time. The gel suspension from the outlet, containing a fraction of crystalline material, is added to the storage vessel under stirring and thus recirculated through the reactor. Optimum process parameters turned out to be: (1) a flow rate of 900 cm3/h (residence time: 8 min) and (2) a temperature range of 180 to 190°C. The composition of the synthesis gel, based on standard recipes [7], is found to be optimal for 1.0 Al O :1.0 P O :1.5 Pr N:150 H O, using 2 3 2 5 3 2 123.2 mmol of Al O (16.88 g Pural SB, Condea 2 3 Chemie) as aluminum source, 123.2 mmol of P O (28.4 g phosphoric acid, 85 wt% p.a., Merck) 2 5 as phosphorus source and 184.8 mmol of tri-npropylamine as template. The phosphoric acid, dissolved in 15% of the water, is given to the Al O suspended in 85% of the water, under strong 2 3 stirring. After 5 min the uniform gel is obtained. The template is added slowly under stirring, and the agitated gel is aged for 12 h at room temperature. The synthesis gel is fully crystallized (crystal sizes: 1–10 mm) after 160 min (Fig. 2), yielding 0.1 g of AlPO -5 crystals from 2 g of gel, the 4 quality of which is checked by X-ray diffraction and scanning electron microscopy, as usually [4]. Hence, the synthesis mixture passed through the reactor about six times and the residence time under reaction conditions sums up to 48 min. The results demonstrate the superiority of the continuous preparation technique, since discontinuous
Fig. 1. Microwave-heated, continuous-flow, high-pressure tube reactor comprising reaction mixture inlet (1), pressure jacket (2), isolation jacket (3), reactor tube coil in the microwaveheated cavity (4), thermocouple (5), cooling jacket (6) and reaction mixture outlet (7).
Fig. 2. SEM image of AlPO -5 crystals ranging from 1 to 15 mm. 4
I. Braun et al. / Microporous and Mesoporous Materials 23 (1998) 79–81
production in a standard (MLS 1200) microwaveheated batch reactor (ca. 25 cm3) requires at least 1.5 h for one cycle of charging (10 min), synthesis (20 min), cooling (20 min), discharging (20 min) and cleaning (20 min). In summary, microwave equipment for continuous-flow, high-pressure tube reactors, being comparable in their dimensions to conventional batch-reactor equipment, enable an increase of the space–time yields by a factor ranging from 10 to 100.
Acknowledgement Financial support by the Deutsche Forschungsgemeinschaft (SCHU 426/10-2) is gratefully acknowledged.
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References [1] A. Arafat, J.C. Jansen, A.R. Ebaid, H. van Bekkum, Zeolites 13 (1993) 162. [2] I. Girnus, M.-M. Pohl, J. Richter-Mendau, M. Schneider, M. Noack, D. Venzke, J. Caro, Advanced Materials 8 (1995) 711. [3] M. Park, S. Komarneni, Microporous and Mesoporous Materials 20 (1998) 39. [4] I. Braun, G. Schulz-Ekloff, M. Bockstette, D. Wo¨hrle, Zeolites 19 (1997) 128. [5] M. Bockstette, D. Wo¨hrle, I. Braun, G. Schulz-Ekloff, Microporous and Mesoporous Materials 23 (1998) 83. [6 ] R. Thome´, A. Tissler, Method for the preparation of crystalline and zeolitic aluminosilicate, EP 0402801 B1, 1994. [7] S.T. Wilson, in: H. van Bekkum, E.M. Flanigen, J.C. Jansen (Eds.), Introduction to Zeolite Science and Practice (Stud. Surf. Sci. Catal., vol. 58), Elsevier, Amsterdam, 1991, p. 137.
Synthesis of AlPO -5 in a microwave-heated, continuous-flow, 4 high-pressure tube reactor I. Braun a, G. Schulz-Ekloff a,*, D. Wo¨hrle b, W. Lautenschla¨ger c a Institut fu¨r Angewandte und Physikalische Chemie, Universita¨t Bremen, 28334 Bremen, Germany b Institut fu¨r Organische und Makromolekulare Chemie, Universita¨t Bremen, 28334 Bremen, Germany c MLS-Mikrowellen-Laborsysteme GmbH, Auenweg 37, 88299 Leutkirch, Germany Received 13 May 1998; received in revised form 28 May 1998; accepted 29 May 1998
Abstract Synthesis of AlPO -5 in a microwave-heated, continuous-flow, high-pressure tube reactor is described, based on (i) 4 a commercially available equipment and (ii) recipes optimized for microwave-heated batch reactors. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Synthesis; AlPO -5; Microwave-heated flow reactor 4
Microwave heating has been applied successfully for the rapid synthesis of molecular sieves [1–3] and the protecting encapsulation of dyes in AlPO -5 [4,5]. The short penetration depth of the 4 microwave radiation into the hydrothermal synthesis mixture limits the dimensions of reactors and autoclaves. Therefore, the application of continuous-flow tube reactors is a prerequisite in all cases where larger charges or higher space–time yields are needed, e.g., for the production of zeolite-based inclusion pigments on a larger scale. The synthesis of molecular sieves in a resistanceheated continuous-flow tube reactor has already been achieved [6 ]. The application of a microwaveheated flow reactor for the hydrothermal crystallization of AlPO -5 is described for the first time in 4 this communication. * Corresponding author. Fax: +49-421-218-4918; E-mail: [email protected] 1387-1811/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII: S1 3 8 7 -1 8 1 1 ( 9 8 ) 0 0 18 0 - 2
The microwave-heated flow tube reactor used (MLS ETHOS contFLOW ) consists of a microwave-transparent, chemically inert (polytetrafluoroethylene, Teflon) and tubular coil (120 cm3 internal volume) fitted in a microwave cavity ( Fig. 1). The aqueous suspension (390 cm3) of the gel reaction mixture in the storage vessel is pumped through the reactor under high pressure. The synthesis temperature of >160°C, which has to be reached within 1 min in order to obtain a pure AlPO -5 phase, is obtained rapidly by using 900 W 4 for the initial microwave heating. Subsequently, the desired temperature is controlled with an accuracy of ±3°C. The average applied pressure in the reactor of 2.5 MPa is generated by a high-pressure membrane pump, controlled by a gauge at the inlet of the reactor pipe and held by a valve at the reactor exit. A cooling jacket around the outlet tube of the flow reactor enables rapid cooling of the reaction slurry; i.e., the achievement of the
80
I. Braun et al. / Microporous and Mesoporous Materials 23 (1998) 79–81
precise high-temperature residence time or crystallization time. The gel suspension from the outlet, containing a fraction of crystalline material, is added to the storage vessel under stirring and thus recirculated through the reactor. Optimum process parameters turned out to be: (1) a flow rate of 900 cm3/h (residence time: 8 min) and (2) a temperature range of 180 to 190°C. The composition of the synthesis gel, based on standard recipes [7], is found to be optimal for 1.0 Al O :1.0 P O :1.5 Pr N:150 H O, using 2 3 2 5 3 2 123.2 mmol of Al O (16.88 g Pural SB, Condea 2 3 Chemie) as aluminum source, 123.2 mmol of P O (28.4 g phosphoric acid, 85 wt% p.a., Merck) 2 5 as phosphorus source and 184.8 mmol of tri-npropylamine as template. The phosphoric acid, dissolved in 15% of the water, is given to the Al O suspended in 85% of the water, under strong 2 3 stirring. After 5 min the uniform gel is obtained. The template is added slowly under stirring, and the agitated gel is aged for 12 h at room temperature. The synthesis gel is fully crystallized (crystal sizes: 1–10 mm) after 160 min (Fig. 2), yielding 0.1 g of AlPO -5 crystals from 2 g of gel, the 4 quality of which is checked by X-ray diffraction and scanning electron microscopy, as usually [4]. Hence, the synthesis mixture passed through the reactor about six times and the residence time under reaction conditions sums up to 48 min. The results demonstrate the superiority of the continuous preparation technique, since discontinuous
Fig. 1. Microwave-heated, continuous-flow, high-pressure tube reactor comprising reaction mixture inlet (1), pressure jacket (2), isolation jacket (3), reactor tube coil in the microwaveheated cavity (4), thermocouple (5), cooling jacket (6) and reaction mixture outlet (7).
Fig. 2. SEM image of AlPO -5 crystals ranging from 1 to 15 mm. 4
I. Braun et al. / Microporous and Mesoporous Materials 23 (1998) 79–81
production in a standard (MLS 1200) microwaveheated batch reactor (ca. 25 cm3) requires at least 1.5 h for one cycle of charging (10 min), synthesis (20 min), cooling (20 min), discharging (20 min) and cleaning (20 min). In summary, microwave equipment for continuous-flow, high-pressure tube reactors, being comparable in their dimensions to conventional batch-reactor equipment, enable an increase of the space–time yields by a factor ranging from 10 to 100.
Acknowledgement Financial support by the Deutsche Forschungsgemeinschaft (SCHU 426/10-2) is gratefully acknowledged.
81
References [1] A. Arafat, J.C. Jansen, A.R. Ebaid, H. van Bekkum, Zeolites 13 (1993) 162. [2] I. Girnus, M.-M. Pohl, J. Richter-Mendau, M. Schneider, M. Noack, D. Venzke, J. Caro, Advanced Materials 8 (1995) 711. [3] M. Park, S. Komarneni, Microporous and Mesoporous Materials 20 (1998) 39. [4] I. Braun, G. Schulz-Ekloff, M. Bockstette, D. Wo¨hrle, Zeolites 19 (1997) 128. [5] M. Bockstette, D. Wo¨hrle, I. Braun, G. Schulz-Ekloff, Microporous and Mesoporous Materials 23 (1998) 83. [6 ] R. Thome´, A. Tissler, Method for the preparation of crystalline and zeolitic aluminosilicate, EP 0402801 B1, 1994. [7] S.T. Wilson, in: H. van Bekkum, E.M. Flanigen, J.C. Jansen (Eds.), Introduction to Zeolite Science and Practice (Stud. Surf. Sci. Catal., vol. 58), Elsevier, Amsterdam, 1991, p. 137.