- Email: [email protected]
International VPO Workshop: Preface
Applied Catalysis A: General 376 (2010) 1–3
Contents lists available at ScienceDirect
Applied Catalysis A: General journal homepage: www.elsevier.com/locate/apcata
International VPO Workshop: Preface
This special issue of Applied Catalysis highlights a research collaboration devoted to vanadium phosphorus oxide (VPO) catalysts from a very broad perspective including catalyst synthesis and characterization, reactor engineering and new applications beyond n-butane partial oxidation to maleic anhydride (MA). The collaboration has its origin in a donation from E.I. du Pont de Nemours & Co. of 3000 kg of VPO: 1000 kg precursor, 1000 kg calcined (activated) catalyst and 1000 kg of ‘‘equilibrated’’ catalyst that had been run in their Circulating Fluidized Bed reactor (CFB), located in Asturias, Spain, for over 2 years. Catalyst samples have been distributed to over 20 universities and research centers throughout the world for experiments. An International Workshop was set-up and launched during the first CONCORDE European network conference in Louvain-la-Neuve (Belgium) in 2005 [1]. Besides using DuPont’s catalyst as a standard to compare experimental methods, the objectives of the International VPO Workshop included gaining insight into structural properties and reactor engineering, developing improved formulations, and identifying new applications. Before summarizing the contributions of this special issue, we shall briefly describe DuPont’s THF process development that began in the early 1980s. The motivation was to expand THF capacity for the manufacture of Lycra1 fibers with a zero emission process to replace Reppe technology. The commercial plant came on line in 1996 and operated for close to a decade. In the first step, butane was oxidized to maleic anhydride over VPO catalyst in a (CFB). In the second step, maleic acid was hydrogenated to THF. Purification was the third step of the process. The development of both catalytic processes began with a lengthy laboratory discovery phase followed by catalyst manufacture optimization and extensive pilot plant studies.
0926-860X/$ – see front matter ß 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2010.02.010
Preface / Applied Catalysis A: General 376 (2010) 1–3
2
The originality of the first step, butane oxidation to MA, was to use a CFB to run a partial oxidation reaction. It was inspired by Fluid Catalytic Cracking (FCC) of petroleum in which the catalyst cracks heavy petroleum, becomes coked and is regenerated by air in a fluidized bed reactor. The great scientific inspiration put forward by Contractor was to apply the concept to a two-step redox reaction [2]. Indeed, the process itself mimics the redox mechanism in which the individual steps of oxidation and reduction are decoupled in two reactors: catalyst reduction by hydrocarbon in one vessel followed by re-oxidation with air in a separate vessel. Often the requirements of each reaction are not the same and separating the two allows one to independently optimize the operating conditions [3]. The minimum essential physicochemical properties for a successful CFB process include attrition resistance and catalyst performance – selectivity, activity and oxygen carrying capacity. The possibility to run under pure redox mode drove the catalyst development towards a P/V ratio close to 1.00, compared to most processes that require slightly higher values to avoid the formation of oxidized phases. The way to protect the VPO from mechanical stress, inherent in fluidized bed systems, was to form a resistant outer silica shell, an innovation due to Bergna [4]. The piloting and technology demonstration period lasted 18 months and many of the major uncertainties regarding the concept were clarified: precursor synthesis at the commercial scale plus micronization, spray drying and calcination and activation were demonstrated; cycling catalyst between reducing and oxidizing atmospheres worked; catalyst lattice oxygen was sufficient; recycling butane and operating with high butane partial pressures was feasible; VPO mechanical strength was adequate; and, the risk of explosion was manageable [5]. A large parameter space was tested to delimit the conditions that maximized maleic yield: temperature, butane concentration, oxygen concentration, solids circulation rate and regenerator residence time were the major performance criteria. Several sparger designs were implemented and stripping conditions (residence time, inventory, and gas composition) were established. Originally, heat transfer and attrition resistance were suspected to be critical parameters to achieve the financial metrics set out for the process. However, DuPont researchers were able to increase attrition resistance of the catalyst by an order of magnitude versus the experimental scale and sufficient design allowances were made for heat transfer to operate the plant at over 30% design capacity. During the commercial start-up phase, operational difficulties arose due to catalyst agglomeration and cohesiveness. The combination of high water vapour concentrations and oxygen resulted in the formation of detrimental oxidized b-VOPO4 as well as agglomerates of VOPO42H2O dihydrate that could become as large as footballs. Some of the operational challenges experienced in DuPont’s CFB process apply to both current fixed bed and fluidized bed technologies. However, most of the industrial research is devoted to producing catalyst with higher activity and selectivity. Catalyst cost (related to raw material and manufacturing processes) and stability are additional opportunities that continue to inspire research efforts in VPO catalysis. The overall objective of the International Workshop is to advance the level of understanding of catalysis by VPO material.1 DuPont’s samples are intended to serve as a standard to calibrate experimental techniques including reaction kinetics and physicochemical characterization – surface area, pore size distribution and the like, but also crystalline phases, reactivity, etc. They may also be used as a standard to compare the effect of promoters and new formulations, and they provide an opportunity to characterize the 1
Samples remain available to any group (http://www.polymtl.ca/vpoworkshop/).
morphological changes through the manufacturing process to commercial operation. Because of the enormous amount of catalyst donated, sufficient quantities are available to conduct large scale studies and detailed calcination/activation trials. For example, the group of Werther et al. received 50 kg to test attrition properties in pilot scale facilities. The papers in this special issue include contributions dealing with several fundamental aspects of synthesis, characterization, catalysis and reactor engineering, including reactions other than nbutane to MA. Most papers use DuPont samples, the properties of which were in some cases compared to samples prepared in-house. The three VPO samples – precursor, calcined and equilibrated catalysts – were used by A. Martin et al. in the ammoxidation of 3picoline to nicotinonitrile. They also carried out solid state characterization tests that showed phase alteration used in ammoxidation, including an NH4+ ion containing precursor. The versatility of VPO is demonstrated in two other challenging reactions. The selective oxidation of cyclohexane to cyclohexanol was studied by Borah and Datta using an original preparation of VPO (VOPO42H2O dihydrate dispersed on Al2O3), which led to special crystalline properties. The valorization of glycerol through its oxidative dehydration to acrolein was studied by Fang et al. They prepared a series of vanadium pyrophosphate catalysts by thermal treatment of precursor at various temperatures and showed that molecular oxygen greatly enhanced the selectivity to C3 useful products, including acrolein. The contribution by Delimitis dealt with a structural study of VPO precursor by a combination of electron diffraction experiments and diffraction pattern simulation. He demonstrated that up to 8% vanadium is lacking in the VOHPO40.5H2O precursor. This finding throws light on the way dopants can be accommodated into the lattice and how they can bring about enhanced activity and selectivity. Kourtakis et al. synthesized new VPO catalysts in an original way by grafting reactive metal alkoxides onto pre-formed precursor and thus creating doped-VPO catalysts. Promoted VPO catalysts containing molybdenum combined with other promoters showed enhanced activity to butane conversion and MA selectivity. Dummer et al. focused on the micro-structural and surface compositional changes of the DuPont samples with a novel X-ray ultramicroscopy technique. Thon and Werther studied the attrition resistance of the VPO catalyst in two apparatus – in a cyclone and in a bubblingfluidized bed. They found that it compares favourably to ‘‘standard’’ FCC catalyst. Several studies examined the reaction kinetics. Based on steady-state and transient kinetic measurements during in situ oxidizing or hydrolyzing treatments, Cavani’s team concluded that very small changes in the P/V ratio significantly affect the catalytic activity. Ferna´ndez et al. used the calcined VPO DuPont catalyst in a fluidized bed reactor, operated both conventionally and by forced concentration cycling of oxidizing and reducing feeds in order to simulate the CFB operation. The experimental results showed higher MA productivity for a wide range of operating conditions. Experimental data from DuPont’s laboratory facilities, pilot plant and commercial reactor are presented in the contribution of Patience and Bockrath. Shekari et al. described the relationship between maleic anhydride selectivity and the local oxidizing environment and demonstrated that more oxygen is better. One of the major technology advances of the CFB technology was the ability to introduce pure oxygen through spargers to a vessel operating with elevated n-butane concentrations at high temperature. Hutcheson et al. described experimental work and proposed an elementary step kinetic model to study the local reaction behaviour and to evaluate the effect of operating conditions on the onset of combustion in the homogeneous gas phase regions of the reactor.
Preface / Applied Catalysis A: General 376 (2010) 1–3
Recently, Ballarini et al. [6] asked the question whether nbutane partial oxidation to maleic anhydride was a goal achieved or still an open challenge. Based on much of the exciting work presented in this special edition, we propose that it is very much an open challenge! References [1] Concerted Action ‘‘CONCORDE’’, European Union framework program FP6VNMP2-CT-2004-505834, in: V. Cortes Corberan, J.C. Conesa, V. Rives, P. Ruiz (Eds.), Catal. Today 128 (2006). [2] R.M. Contractor, U.S. Patent 4,668,802 assigned to E.I. DuPont de Nemours and Company, Inc., 1987. [3] E. Bordes, R.M. Contractor, Top. Catal. 3 (1996) 365. [4] H.E. Bergna, U.S. Patent 4,667,084 assigned to E.I. DuPont de Nemours and Company, Inc., 1987. [5] Contractor, 1999 R.M. Contractor, Chem. Eng. Sci. 54 (1999) 5627; R.M. Contractor, D.I. Garnett, H.S. Horowitz, H.E. Bergna, G.S. Patience, J.T. Schwartz, G.M. Sisler, in: V.C. Corberan, S.V. Bellon (Eds.), New Developments in Selective Oxidation, Elsevier, Amsterdam, 1994, p. 233.
3
[6] N. Ballarini, F. Cavani, C. Cortelli, S. Ligi, F. Pierelli, F. Trifiro, C. Fumagalli, G. Mazzoni, T. Monti, Top. Catal. 38 (2006) 147.
Gregory S. Patience Guest Editor* Department of Chemical Engineering, E´cole Polytechnique de Montre´al, C.P. 6079, Succ. ‘‘CV’’, Montre´al, QC, Canada H3C 3A7 Elisabeth Bordes-Richard Unite´ de Catalyse et de Chimie du Solide, UMR-CNRS 8181, Universite´ des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq, France *Corresponding
author. Tel.: +1 514 340 4711x3439; fax: +1 514 340 4159 E-mail address: [email protected] (G.S. Patience) Available online 11 February 2010
Contents lists available at ScienceDirect
Applied Catalysis A: General journal homepage: www.elsevier.com/locate/apcata
International VPO Workshop: Preface
This special issue of Applied Catalysis highlights a research collaboration devoted to vanadium phosphorus oxide (VPO) catalysts from a very broad perspective including catalyst synthesis and characterization, reactor engineering and new applications beyond n-butane partial oxidation to maleic anhydride (MA). The collaboration has its origin in a donation from E.I. du Pont de Nemours & Co. of 3000 kg of VPO: 1000 kg precursor, 1000 kg calcined (activated) catalyst and 1000 kg of ‘‘equilibrated’’ catalyst that had been run in their Circulating Fluidized Bed reactor (CFB), located in Asturias, Spain, for over 2 years. Catalyst samples have been distributed to over 20 universities and research centers throughout the world for experiments. An International Workshop was set-up and launched during the first CONCORDE European network conference in Louvain-la-Neuve (Belgium) in 2005 [1]. Besides using DuPont’s catalyst as a standard to compare experimental methods, the objectives of the International VPO Workshop included gaining insight into structural properties and reactor engineering, developing improved formulations, and identifying new applications. Before summarizing the contributions of this special issue, we shall briefly describe DuPont’s THF process development that began in the early 1980s. The motivation was to expand THF capacity for the manufacture of Lycra1 fibers with a zero emission process to replace Reppe technology. The commercial plant came on line in 1996 and operated for close to a decade. In the first step, butane was oxidized to maleic anhydride over VPO catalyst in a (CFB). In the second step, maleic acid was hydrogenated to THF. Purification was the third step of the process. The development of both catalytic processes began with a lengthy laboratory discovery phase followed by catalyst manufacture optimization and extensive pilot plant studies.
0926-860X/$ – see front matter ß 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2010.02.010
Preface / Applied Catalysis A: General 376 (2010) 1–3
2
The originality of the first step, butane oxidation to MA, was to use a CFB to run a partial oxidation reaction. It was inspired by Fluid Catalytic Cracking (FCC) of petroleum in which the catalyst cracks heavy petroleum, becomes coked and is regenerated by air in a fluidized bed reactor. The great scientific inspiration put forward by Contractor was to apply the concept to a two-step redox reaction [2]. Indeed, the process itself mimics the redox mechanism in which the individual steps of oxidation and reduction are decoupled in two reactors: catalyst reduction by hydrocarbon in one vessel followed by re-oxidation with air in a separate vessel. Often the requirements of each reaction are not the same and separating the two allows one to independently optimize the operating conditions [3]. The minimum essential physicochemical properties for a successful CFB process include attrition resistance and catalyst performance – selectivity, activity and oxygen carrying capacity. The possibility to run under pure redox mode drove the catalyst development towards a P/V ratio close to 1.00, compared to most processes that require slightly higher values to avoid the formation of oxidized phases. The way to protect the VPO from mechanical stress, inherent in fluidized bed systems, was to form a resistant outer silica shell, an innovation due to Bergna [4]. The piloting and technology demonstration period lasted 18 months and many of the major uncertainties regarding the concept were clarified: precursor synthesis at the commercial scale plus micronization, spray drying and calcination and activation were demonstrated; cycling catalyst between reducing and oxidizing atmospheres worked; catalyst lattice oxygen was sufficient; recycling butane and operating with high butane partial pressures was feasible; VPO mechanical strength was adequate; and, the risk of explosion was manageable [5]. A large parameter space was tested to delimit the conditions that maximized maleic yield: temperature, butane concentration, oxygen concentration, solids circulation rate and regenerator residence time were the major performance criteria. Several sparger designs were implemented and stripping conditions (residence time, inventory, and gas composition) were established. Originally, heat transfer and attrition resistance were suspected to be critical parameters to achieve the financial metrics set out for the process. However, DuPont researchers were able to increase attrition resistance of the catalyst by an order of magnitude versus the experimental scale and sufficient design allowances were made for heat transfer to operate the plant at over 30% design capacity. During the commercial start-up phase, operational difficulties arose due to catalyst agglomeration and cohesiveness. The combination of high water vapour concentrations and oxygen resulted in the formation of detrimental oxidized b-VOPO4 as well as agglomerates of VOPO42H2O dihydrate that could become as large as footballs. Some of the operational challenges experienced in DuPont’s CFB process apply to both current fixed bed and fluidized bed technologies. However, most of the industrial research is devoted to producing catalyst with higher activity and selectivity. Catalyst cost (related to raw material and manufacturing processes) and stability are additional opportunities that continue to inspire research efforts in VPO catalysis. The overall objective of the International Workshop is to advance the level of understanding of catalysis by VPO material.1 DuPont’s samples are intended to serve as a standard to calibrate experimental techniques including reaction kinetics and physicochemical characterization – surface area, pore size distribution and the like, but also crystalline phases, reactivity, etc. They may also be used as a standard to compare the effect of promoters and new formulations, and they provide an opportunity to characterize the 1
Samples remain available to any group (http://www.polymtl.ca/vpoworkshop/).
morphological changes through the manufacturing process to commercial operation. Because of the enormous amount of catalyst donated, sufficient quantities are available to conduct large scale studies and detailed calcination/activation trials. For example, the group of Werther et al. received 50 kg to test attrition properties in pilot scale facilities. The papers in this special issue include contributions dealing with several fundamental aspects of synthesis, characterization, catalysis and reactor engineering, including reactions other than nbutane to MA. Most papers use DuPont samples, the properties of which were in some cases compared to samples prepared in-house. The three VPO samples – precursor, calcined and equilibrated catalysts – were used by A. Martin et al. in the ammoxidation of 3picoline to nicotinonitrile. They also carried out solid state characterization tests that showed phase alteration used in ammoxidation, including an NH4+ ion containing precursor. The versatility of VPO is demonstrated in two other challenging reactions. The selective oxidation of cyclohexane to cyclohexanol was studied by Borah and Datta using an original preparation of VPO (VOPO42H2O dihydrate dispersed on Al2O3), which led to special crystalline properties. The valorization of glycerol through its oxidative dehydration to acrolein was studied by Fang et al. They prepared a series of vanadium pyrophosphate catalysts by thermal treatment of precursor at various temperatures and showed that molecular oxygen greatly enhanced the selectivity to C3 useful products, including acrolein. The contribution by Delimitis dealt with a structural study of VPO precursor by a combination of electron diffraction experiments and diffraction pattern simulation. He demonstrated that up to 8% vanadium is lacking in the VOHPO40.5H2O precursor. This finding throws light on the way dopants can be accommodated into the lattice and how they can bring about enhanced activity and selectivity. Kourtakis et al. synthesized new VPO catalysts in an original way by grafting reactive metal alkoxides onto pre-formed precursor and thus creating doped-VPO catalysts. Promoted VPO catalysts containing molybdenum combined with other promoters showed enhanced activity to butane conversion and MA selectivity. Dummer et al. focused on the micro-structural and surface compositional changes of the DuPont samples with a novel X-ray ultramicroscopy technique. Thon and Werther studied the attrition resistance of the VPO catalyst in two apparatus – in a cyclone and in a bubblingfluidized bed. They found that it compares favourably to ‘‘standard’’ FCC catalyst. Several studies examined the reaction kinetics. Based on steady-state and transient kinetic measurements during in situ oxidizing or hydrolyzing treatments, Cavani’s team concluded that very small changes in the P/V ratio significantly affect the catalytic activity. Ferna´ndez et al. used the calcined VPO DuPont catalyst in a fluidized bed reactor, operated both conventionally and by forced concentration cycling of oxidizing and reducing feeds in order to simulate the CFB operation. The experimental results showed higher MA productivity for a wide range of operating conditions. Experimental data from DuPont’s laboratory facilities, pilot plant and commercial reactor are presented in the contribution of Patience and Bockrath. Shekari et al. described the relationship between maleic anhydride selectivity and the local oxidizing environment and demonstrated that more oxygen is better. One of the major technology advances of the CFB technology was the ability to introduce pure oxygen through spargers to a vessel operating with elevated n-butane concentrations at high temperature. Hutcheson et al. described experimental work and proposed an elementary step kinetic model to study the local reaction behaviour and to evaluate the effect of operating conditions on the onset of combustion in the homogeneous gas phase regions of the reactor.
Preface / Applied Catalysis A: General 376 (2010) 1–3
Recently, Ballarini et al. [6] asked the question whether nbutane partial oxidation to maleic anhydride was a goal achieved or still an open challenge. Based on much of the exciting work presented in this special edition, we propose that it is very much an open challenge! References [1] Concerted Action ‘‘CONCORDE’’, European Union framework program FP6VNMP2-CT-2004-505834, in: V. Cortes Corberan, J.C. Conesa, V. Rives, P. Ruiz (Eds.), Catal. Today 128 (2006). [2] R.M. Contractor, U.S. Patent 4,668,802 assigned to E.I. DuPont de Nemours and Company, Inc., 1987. [3] E. Bordes, R.M. Contractor, Top. Catal. 3 (1996) 365. [4] H.E. Bergna, U.S. Patent 4,667,084 assigned to E.I. DuPont de Nemours and Company, Inc., 1987. [5] Contractor, 1999 R.M. Contractor, Chem. Eng. Sci. 54 (1999) 5627; R.M. Contractor, D.I. Garnett, H.S. Horowitz, H.E. Bergna, G.S. Patience, J.T. Schwartz, G.M. Sisler, in: V.C. Corberan, S.V. Bellon (Eds.), New Developments in Selective Oxidation, Elsevier, Amsterdam, 1994, p. 233.
3
[6] N. Ballarini, F. Cavani, C. Cortelli, S. Ligi, F. Pierelli, F. Trifiro, C. Fumagalli, G. Mazzoni, T. Monti, Top. Catal. 38 (2006) 147.
Gregory S. Patience Guest Editor* Department of Chemical Engineering, E´cole Polytechnique de Montre´al, C.P. 6079, Succ. ‘‘CV’’, Montre´al, QC, Canada H3C 3A7 Elisabeth Bordes-Richard Unite´ de Catalyse et de Chimie du Solide, UMR-CNRS 8181, Universite´ des Sciences et Technologies de Lille, 59655 Villeneuve d’Ascq, France *Corresponding
author. Tel.: +1 514 340 4711x3439; fax: +1 514 340 4159 E-mail address: [email protected] (G.S. Patience) Available online 11 February 2010