Monolithic reactors in catalysis: excellent control

Available online at www.sciencedirect.com

Monolithic reactors in catalysis: excellent control Jacob A Moulijn and Freek Kapteijn Structured reactors offer high precision in catalysis at all relevant length scales of the catalytic process, from the catalytic species up to the reactor. They offer unusual freedom in design with respect to diffusion length, hydrodynamic regime and reactor configuration. Monoliths are the prime example of such systems. Addresses Catalysis Engineering, ChemE, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands Corresponding author: Moulijn, Jacob A ([email protected])

Current Opinion in Chemical Engineering 2013, 2:346–353 This review comes from a themed issue on Reaction engineering and catalysis Edited by Marc-Olivier Coppens and Theodore T Tsotsis For a complete overview see the Issue and the Editorial Available online 27th June 2013 2211-3398/$ – see front matter, # 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.coche.2013.05.003

Introduction Fixed bed and slurry reactors are the workhorses in the chemical industry and they share the benefits of simplicity of construction on the upside and chaotic and hard-topredict fluid mechanics on the downside. Instead of accepting the random and chaotic behavior of classical reactors, one can design and build reactors with regular spatial structures (Figure 1). Such structures may be designed in full detail, up to the local surroundings of the catalyst species. This opportunity offers the potential of optimal performance of catalytic functions and simplification of the fluid mechanics. Such reactors are referred to as structured reactors [1,2]. In nearly all respects, they outperform random/ chaotic reactors. Because of its dominance in automotive exhaust gas treatment, the monolith is the most popular structured reactor [3]. It consists of large numbers of parallel channels. In static mixers the units are combinations of corrugated sheets. A related structure (catalyst bales) is used as a packing in catalytic distillation: the catalyst particles are placed in the pockets of a structured wire packing [4]. Foams are three-dimensional cellular materials made of interconnected pores. Catalyst bodies can also be made of knitted fibers, woven fabrics, etc. Current Opinion in Chemical Engineering 2013, 2:346–353

[3,5,6]. Microfabricated reactors belong also to the family of structured reactors [7]. In this perspective we emphasize monolith reactors, conceptually the simplest and most widespread.

Monoliths The name ‘monolith’ stems from the Greek mono and lithos, single and stone. In catalytic reaction engineering, a monolith is defined as a single block of catalyst-containing material through which reactants and products are transported by convection. It has such macroscopic dimensions that one or a few monoliths can completely fill the catalytic reactor space. In separation technology and in flow chemistry [8] reactor-filling rods with welldefined macro- and mesoporosity are used, also referred to as ‘monoliths’. These structures are not part of this review. Monoliths are characterized by channel shape, cell density, and wall thickness [3,9]. For example, the square 400 cpsi monolith, containing 400 cells per square inch with a wall thickness of typically 0.13 mm, is often used in three-way catalysts for conversion of automobile exhaust. Channel shapes are usually square, rectangular, hexagonal, or triangular [10]. The monolith is probably the most popular catalytic reactor of all. Why is it so popular? The large, open frontal area giving access to straight channels results in an extremely low pressure drop, which is essential for end-of-pipe technology for exhaust systems. In contrast to a packed bed no attrition occurs when vibration is induced by for instance the moving automobile. The straight channels prevent the accumulation of dust in demanding applications such as those in coal-fired power stations for NOx control. A monolith can be mounted at any angle: vertical, horizontal, etc. Monoliths are mainly produced by extrusion, although other methods are applied, for instance the manufacture of metal monoliths from thin corrugated sheets. The size of the channels and the wall thickness can be varied independently. An optimum can be established between the amount of solid phase, void space, and wall thickness. Because of the large scale of production these sophisticated structures are commercially available at modest cost. It should be noted that monolith structures can be used as such (the wall material is the catalyst or catalyst support) or the catalytic material is placed as a layer at the monolith walls (usually by washcoating). In the former case the wall thickness is a degree of freedom, in latter the www.sciencedirect.com

Monolith reactors Moulijn and Kapteijn 347

Figure 1

400 cpsi

1mm

Conventional

1.27 mm 2740 m2/m3 1mm

Monolith

Permeable walls

High-performance

1 mm

Foam cell Pore

2.5 mm

Static mixer

Catalyst bale

Foam

Single capillary

Fibre structure

Microfabricated reactor Current Opinion in Chemical Engineering

Structured packings/reactors.

thickness of the catalyst layer is an additional degree of freedom. A prominent trade-off in heterogeneous catalysis reactor design concerns the catalyst particle size. Table 1 gives typical time scales for diffusion in heterogeneous catalysis. The characteristic contact times for industrial catalytic reactions are typically in the range of minutes to seconds. These values suggest that particle diameters, in particular when the reactants and products are in the liquid phase, have to be in a micrometer rather than in the millimeter range. www.sciencedirect.com

In slurry reactors the particle size is in the micrometer range but in trickle-bed reactors this is unfeasible, because this would lead to a too large pressure drop. Possible solutions are ring-shaped catalysts, ‘egg-shell’ catalysts, and catalyst particles with porosity of a fractal design including diffusion channels, typically mesopores or macropores [11,12]. These structures make sense, but in general they lead to a sub-optimal design. An elegant alternative approach is to go away from random packed beds by turning to structured reactors. The thickness of the wall of a monolith can be chosen independently of the diameter of the channels. The wall thickness determines the molecular transport rate, and Current Opinion in Chemical Engineering 2013, 2:346–353

348 Reaction engineering and catalysis

Table 1 Characteristic time scales for diffusion distances in constrained spaces Characteristic catalyst dimension, L Phase of diffusing species Gas Liquid Liquid in typical catalyst pore ‘Liquid’ in zeolite pore

2

Deff (m /s) 10 5 10 9 10 10 <10 11

the channel size the pressure drop. In packed beds, both dimensions are coupled. The possibility offered by monoliths to choose the length scales independently introduces a degree of freedom that allows maximum catalyst performance with minimal pressure drop [13]. From first principles, the desired thickness of a catalytic coating can be estimated to be 10–100 mm. Thus, the wall of a commercial monolith (typically 100–200 mm) is too thick to be used entirely as catalyst. Synthesizing a thin coating is a logical strategy, but at the cost of a low catalyst loading per unit of reactor volume. An alternative approach could be to apply monoliths with walls that are permeable and allow convective transport. Indeed, such monoliths have been developed (Figure 2) [14–16]. For fast reactions they showed excellent performance [17]. This conclusion is in agreement with a general analysis of the optimal design of the distribution of the catalyst material in the reactor space [18,19], showing that for maximal productivity a high open porosity at the level of the catalyst is most important. One might wonder about the laminar flow profile in the small channels: would not it be unfavorable in comparison with the turbulent flow conditions prevailing in most industrial reactors? Table 1 shows that channels with dimensions in range of millimeters do not pose any problem for most gas-phase processes, because in the usual designs the channel diameter is 1–3 mm. However, there are exceptions. For instance, in SCR configurations for coal-fired plants dust concentrations are high and, as a consequence, the channel diameters are relatively high (in the order of 6 mm), associated with external mass transfer limitations [20]. In operations with liquids, Table 1 suggests that the laminar flow regime as a rule might be problematic. Remarkably, for the often encountered multiphase (gas/liquid) systems this is not the case, as follows from an evaluation of the hydrodynamics.

1 mm 50 ms 500 s 5000 s >50 ks

100 mm 500 ms 5s 50 s >500 s

10 mm 5 ms 50 ms 0.5 s >5 s

1 mm 50 ns 0.5 ms 5 ms >50 ms

flow conditions is high for two reasons [23]. First, the liquid layer between bubble and catalyst coating is thin, generating fast mass transfer. Second, the liquid in the slugs circulates internally, leveling out any radial gradients. The gas bubbles push the liquid slug forward as a piston, resulting in essentially plug-flow characteristics. Thus, Taylor flow combines good radial mixing with limited axial mixing [24], being completely opposite to single phase flow. For multiphase operation under Taylor flow conditions, the mass transfer is an order of magnitude faster than for single-phase liquid flow. The same conclusion holds for a comparison of monoliths with conventional reactors, kla for trickle bed, slurry and monolith reactors typically are 0.01–01, 0.03–0.3 and >1 s 1, respectively. These high mass transfer rates were obtained at negligible pressure drop. In sharp contrast, other high-intensity contactors, such as agitated tanks and bubble columns, generally consume significant amounts of energy to create high gas–liquid contact areas. This contrast is explained by the difference in flow regimes. In turbulent contactors bubbles are constantly broken up by the random turbulent flow fluctuations in the liquid, keeping the coalescing bubbles small, but it is inefficient. The largest part of turbulent kinetic energy is dissipated within the liquid itself. In contrast, in the small monolith channels, bubbles do not coalesce and no energy input is needed to maintain a small bubble size [24].

Reactors and reactor configurations Monoliths are flexible to operate. They are well suited to semi-batch, batch, continuous, and transient processing. Catalytic conversion can be combined with in situ separation, catalytic reactions can be combined, and heat integration is possible Scale-up

For multiphase systems in monoliths the two important flow patterns are film flow and Taylor flow (Figure 2). Film flow occurs at relatively high gas flow rates. The smooth channels allow liquid to run down with minimal hydrodynamic interaction with the gas phase. In a tricklebed reactor such a regime can only be achieved at low gas flow rates [21,22]. Taylor flow is the commonly encountered flow regime. The rate of mass transfer under Taylor Current Opinion in Chemical Engineering 2013, 2:346–353

Scale-up of monolithic reactors seems straightforward. Usually to a first-order approximation the channels are regarded as identical. However, it has been shown that the channels of a monolith slightly, but significantly vary in dimension (typically with a variance of 5–10% [25]). Besides this internal maldistribution, external maldistribution is important, for instance as the result of the inlet design. In contrast to a packed bed, a monolithic reactor www.sciencedirect.com

Monolith reactors Moulijn and Kapteijn 349

Figure 2

Cocurrent Countercurrent

Film flow

Solids flow

Taylor flow

Structured packed and moving beds Batch reactor Purge

Connuous reactor Liquid feed

Monolithic srrer Gas/liquid separator Product Pump

Inial gas mixture (A + B) Gas outlet (regeneraon products)

Gas recirculaon

Monolith Coolant

Heat exchanger

Monolith

Gas recirculaon

Gas feed

Heat exchanger

Gas feed Pump

Clean gas (B)

Uptake secon Purge secon Regeneraon secon

Regeneraon gas

Rotang monolith Current Opinion in Chemical Engineering

Flow regimes and reactor configurations.

has no flow in the radial direction. When the initial distribution of liquid in the radial direction is non-homogeneous, this distribution will propagate down the reactor unchanged. Even for gas phase applications a careful inlet design is needed in order to prevent preferential flow through part of the reactor (usually the center part). Designs of inlets and outlets of monolith reactors have been investigated extensively. In the Taylor flow regime www.sciencedirect.com

gas injection is achieved by entrainment by the flowing liquid. All the channels should be identical, and the liquid droplets should irrigate the channels uniformly. A stack of monolith slices with decreasing cell densities toward the liquid inlet has been shown to be satisfactory. For countercurrent operation, flooding has to be prevented, which can be done by applying a similar stack of thin monolith slices with decreasing cell density toward the outlet Current Opinion in Chemical Engineering 2013, 2:346–353

350 Reaction engineering and catalysis

(where flooding most often originates), facilitating efficient drainage of the liquid [22]. Similar stacks can be used as spacers between monolith blocks [22,26,27]. Catalyst synthesis

In new technologies often novel preparation methods are drivers to innovation [28]. Fascinating results were obtained by the synthesis of carbon nanofibers (CNF layers) with an open, network-like structure, allowing an excellent accessibility [29–32]. Metal organic frameworks are a new class of crystalline porous materials with a high potential in adsorption, storage, separation, and catalysis [33–35]. In slurry operation the crystals suffer from attrition, and coating of these materials is an obvious avenue for improving their applicability [36]. Excellent results were found for MIL-101(Cr) grown on the channels of a monolith [37]. Coated monoliths should have the advantage of a tunable, well-defined catalyst layer thickness. However, as a consequence of the (usual) square channel geometry in commercially available monoliths in the corners the layer thickness is significantly greater than in the flat parts of the walls. On top of this, the macroporous structure of extruded monolith can accommodate active sites. By first dipcoating the bare monolith with small (nonporous) particles a nearly ideal support is obtained, a ‘Highperformance’ monolith (Figure 2). The optimized monolith showed significantly improved selectivity [38]. Reactor configurations

The monolithic reactor can be used as a stirred reactor type by application of a high recirculation flow rate — achievable without a large energy input, because of the low pressure drop [3,39]. Thus, a monolithic reactor, although usually made from ceramics (poor heat conducting), is a feasible alternative for highly exothermic reactions often carried out in slurry reactors [39–42]. Monoliths are not by definition adiabatic reactors. Metal monoliths can be made from corrugated sheets but even by extrusion of metal powders [43]. Without recycle streams depending on the conditions such a monolith can operate close to isothermal for exothermic reactions. A monolith reactor that might be particularly useful, at least in small-scale operations, is based on a monolithic stirrer [44,45,46,47] (Figure 2). The monolith impellers have a strikingly large geometric catalyst surface area. The long entrance region for mass transfer results in excellent transport, even in single liquid phase. Rotating contactors are applied for cyclic processes like adsorption/desorption in exhaust gas treatment [48]. This design combines a simple process lay-out and a product flow with constant composition. Monoliths are suited for this technology. Separation of n-butane and i-butane was Current Opinion in Chemical Engineering 2013, 2:346–353

successfully carried out in a rotating monolith/zeolite system (Figure 2) [49]. Monoliths are parallel channel reactors. In R&D scaling down can be done by decreasing the number of channels, ultimately to one channel. However, there is more value in a single channel system: it is well suited for continuous chemicals production in fine chemistry [50]. This reactor design is extremely flexible with respect to the residence time. The straight channels of a monolith are ideal for movingbed applications, but they are also favorable for hosting particles in a fixed bed, Figure 2. The monolith allows the combination of an optimized catalyst particles inventory and an optimal liquid hold-up, while still having the relatively low flow resistance [51]. Blocks of monoliths filled with particles may find applications in catalytic distillation or three levels of porosity reactors [3,52].

Conclusions Monolithic reactors offer high precision combined with a high efficiency. Compared to most other structured reactors they are cost-effective and they can be obtained in a large variety of materials (ceramics, metals, polymers [53], carbon [54]). Table 2 lists major commercial and potentially attractive applications. Monoliths are the state-of-the-art reactors in many practical applications in environmental catalysis, because of the low pressure drops at high flow rates, the dust tolerance and the easiness of positioning. Commercial applications include the use as post-reactor because of the easiness of retrofitting and superior performance. Similarly, they are applied to replace slurry reactors because of their combination of a high selectivity and convenience of operation. They are a valuable tool for process intensification. Monoliths allow the efficient use of small catalyst particles, such as zeolites. Time-consuming research in extrusion can be avoided by starting from commercially available monolith supports. When higher loadings are needed, extrusion of the catalytic material is possible, and the catalyst loading may be as much as 80–90%. Monoliths can be used as structured internals for moving bed applications, as catalysts filled with a second catalyst, and as catalyst bales in catalytic distillation. The fundamental aspects of reactor design are rather well understood. The flow in monoliths is laminar, associated with high efficiency and minimum chaotic characteristics. In a wide range of conditions in multiphase systems, Taylor flow (segmented flow) prevails, allowing high rates of mass transport notwithstanding low energy consumption. The Taylor flow regime is per definition cocurrent, www.sciencedirect.com

Monolith reactors Moulijn and Kapteijn 351

Table 2 Realized and promising applications Reactions Oxidation CO, HC; reduction NOx Reduction of NOx with NH3 or urea O3 decomposition

Phases

Sector (supplier)

Category

Scale

Effect

Ref. 

Gas

Otto engines

End-of-pipe

>10 000 000

Robust efficient

[9 ,56,57]

Gas

Power plants

End-of-pipe

Widely applied

Robust low Dp

[20]

Gas

Air planes

Intake air

Low Dp

[58]

Selective oxidation of xylene Total oxidation VOC Adsorption

Gas

Bulk chemicals

High yields

[59]

Gas Gas

Consumers Personal protection

Postreactor, packed bed replacement Toilet, kitchen, chimney Gas mask

Standard in air planes >2 plants

Low Dp

[60] [61,62,63]

Selective oxidation of ammonia Acylation butanol

Gas

Fertilizer industry

Replacement Pt-gauze

Less Pt loss

[64]

Liquid

Biocatalysis

Lipase support

[47]

Hydrogenation step in AO process Total oxidation VOC

Gas/liquid

Chemicals production Bulk chemicals

Catalyst separation

[65]

Gas/liquid

Water purification

Hydrogenation polymers Hydrogenation of nitroaromatics Selective oxidation of cyclohexane

Gas/liquid

Materials

Replacement conventional reactor Polymers with C C or CN

Gas/liquid

Bulk chemicals

Replacement slurry reactor

Gas/liquid

Photocatalysis

Novel reactor with guided light

Commercial Successfully demonstrated >10 plants

Replacement slurry reactor

but the film flow regime can be realized either in co- or countercurrent mode, making the monolith a good structure for novel technologies such as catalytic distillation, extraction, absorption, aeration in gas–liquid (bio-) contactors, and liquid–liquid interphase or phase-transfer catalysis. Loop reactor configurations including heat exchange are suitable for strongly exo- and endothermic reactions. For applications in fine chemistry and in the laboratory, two new reactor types are presented, a convenient monolithic stirrer reactor and a single capillary reactor with a catalyst wall coating. Monoliths have inspired a tremendous amount of research. Many concepts developed are now being applied in micro reactor technology [55].

Successfully demonstrated 200 ktpy Successfully demonstrated Successfully demonstrated Retrofitting in fine chemistry

[66] Tuning materials properties Catalyst separation

[67,68]

Activity issue

[70]

[69]

Overview of the status of monolith catalysis from fundamentals to applications should be read in combination with this opinion paper. Kapteijn F, Heiszwolf JJ, Nijhuis TA, Moulijn JA: Monoliths in multiphase catalytic processes — aspects and prospects. CATTECH 1999, 3:24-41. The first popular manuscript on monoliths. Launched creative ideas for monolith applications that have not been realized to date.

3. 

4.

Behrens M, Olujic Z, Jansens PJ: Liquid flow behavior in catalyst-containing pockets of modular catalytic structured packing katapak SP. Ind Eng Chem Res 2006, 46:3884-3890.

5.

Mikkola JP, Aumo J, Murzin DY, Salmi T: Structured but not overstructured: woven active carbon fibre matt catalyst. Catal Today 2005, 105:325-330.

Pangarkar KV, Schildhauer TJ, Ommen JRv, Nijenhuis J, Kapteijn F, Moulijn JA: Structured packings for multiphase catalytic reactors. Ind Eng Chem Res 2008, 47:3720-3751. Review focused on heat transport in structured reactors.

6. 

7.

Hessel V, Hardt S, Lo¨we H: Chemical Micro Process Engineering. Wiley-VCH Verlag GmbH & Co. KGaA; 2004.

Monoliths are ready for use, it is time for more industrial applications!

8.

Ley SV, Baxendale IR: New tools and concepts for modern organic synthesis. Nat Rev Drug Discov 2002, 1:573-586.

References and recommended reading

9. 

Papers of particular interest, published within the period of review, have been highlighted as:  of special interest  of outstanding interest 1. Cybulski A, Moulijn JA (Eds): Boca Raton: Structured Catalysts  and Reactors. CRC Taylor & Francis; 2006. Timely review by experts in the field. 2. 

Moulijn JA, Kreutzer MT, Nijhuis TA, Kapteijn F: Monolithic catalysts and reactors: high precision with low energy consumption. In Advances in Catalysis, vol. 54. Edited by Gates BC, Kno¨zinger H, Jentoft F. Elsevier; 2011:249-328.

www.sciencedirect.com

Gulati ST: Ceramic catalyst supports for gasoline fuel. In Structured Catalysts and Reactors, edn 2. Edited by Cybulski A, Moulijn JA.Boca Raton, USA: CRC Taylor & Francis; 2006:21-70. Thorough description of practical aspects of design of ceramic monoliths. 10. Gulati ST, Makkee M, Setiabudi A: Ceramic catalysts, supports, and filters for diesel exhaust after-treatment. In Structured Catalysts and Reactors, edn 2. Edited by Cybulski A, Moulijn JA.Boca Raton, USA: CRC Taylor & Francis; 2006:663-700.

11. Wang G, Johannessen E, Kleijn CR, de Leeuwa SW, Coppens MO: Optimizing transport in nanostructured catalysts: a computational study. Chem Eng Sci 2007, 62:5110-5116. 12. Johannessen E, Wang G, Coppens MO: Optimal distributor networks in porous catalyst pellets, I. Molecular diffusion. Ind Eng Chem Res 2007, 46:4245-4256. Current Opinion in Chemical Engineering 2013, 2:346–353

352 Reaction engineering and catalysis

13. Kreutzer MT, Kapteijn F, Moulijn JA: Should’nt catalysts shape up? Structured reactors in general and gas–liquid monolith reactors in particular. Catal Today 2006, 111:111-118. 14. Bakker JJW, Kreutzer MT, Lathouder KMd, Kapteijn F, Moulijn JA, Wallin S: Hydrodynamic properties of a novel ‘open wall’ monolith reactor. Catal Today 2005, 105:385-390. 15. Moyer JR, Hughes NN: A catalytic process for mullite whiskers. J Am Ceram Soc 1994, 77:1083-1086. 16. Lathouder KMd, Bakker JJW, Kreutzer MT, Kapteijn F, Moulijn JA, Wallin S: Structured reactors for enzyme immobilization: advantages of tuning the wall morphology. Chem Eng Sci 2004, 59:5027-5033. 17. Bakker JJW, Groendijk WJ, Lathouder KMd, Kapteijn F, Moulijn JA, Kreutzer MT, Wallin S: Enhancement of catalyst performance using pressure pulses on macroporous structured catalysts. Ind Eng Chem Res 2007, 46:8574-8583. 18. Desmet G, De Greef J, Verelst H, Baron GV: Performance limits of isothermal packed bed and perforated monolithic bed reactors operated under laminar flow conditions, I. General optimization analysis. Chem Eng Sci 2003, 58:3187-3202. 19. Desmet G, De Greef J, Verelst H, Baron GV: Performance limits of isothermal packed bed and perforated monolithic bed reactors operated under laminar flow conditions, Part II: Performance comparison and design considerations. Chem Eng Sci 2003, 58:3203-3214. 20. Nova I, Beretta A, Groppi G, Lietti L, Tronconi E, Forzatti P: Monolithic catalysts for NOx removal from stationary sources. In Structured Catalysts and Reactors, edn 2. Edited by Cybulski A, Moulijn JA.Boca Raton, USA: CRC Taylor & Francis; 2006:171214. 21. Lebens PJM, Meijden Rvd, Edvinsson RK, Kapteijn F, Sie ST, Moulijn JA: Hydrodynamics of gas–liquid countercurrent flow in internally finned monolithic structures. Chem Eng Sci 1997, 52:3893-3899. 22. Heibel AK, Jamison JA, Woehl P, Kapteijn F, Moulijn JA: Improving flooding performance for countercurrent monolith  reactors. Ind Eng Chem Res 2004, 43:4848-4855. The article shows the design of monolith configurations allowing countercurrent operation at industrial conditions.

32. Garcia-Bordeje E, Kvande I, Chen D, Ronning M: Synthesis of composite materials of carbon nanofibres and ceramic monoliths with uniform and tuneable nanofibre layer thickness. Carbon 2007, 45:1828-1838. 33. Kitagawa S, Kitaura R, Noro SI: Functional porous coordination polymers. Angew Chem Int Ed 2004, 43:2334-2375. 34. Mueller U, Schubert M, Teich F, Puetter H, Schierle-Arndt K, Pastre J: Metal-organic frameworks — prospective industrial applications. J Mater Chem 2006, 16:626-636. 35. Rowsell JLC, Yaghi OM: Metal-organic frameworks: a new class of porous materials. Microporous Mesoporous Mater 2004, 73:3-14. 36. Gascon J, Aguado S, Kapteijn F: Manufacture of dense coatings of Cu3(BTC)3 (HKUST-1) on a-alumina. Microporous Mesoporous Mater 2008, 113:132-138. 37. Ramos-Ferna´ndez EV, Garcia-Domingos M, Juan Alcan˜iz J,  Gascon J, Kapteijn F: MOFs meet monoliths: hierarchical structuring metal organic framework catalysts. Appl Catal A: Gen 2011, 391:261-267. The first application of the monolithic stirrer reactor with MOFs prevents attrition and eases separation from the reaction medium. 38. Pe´rez-Cadenas AF, Zieverink MMP, Kapteijn F, Moulijn JA: High performance monolithic catalysts for hydrogenation reactions. Catal Today 2005, 105:623-628. 39. Heiszwolf JJ, Engelvaart LB, Eijnden MGvd, Kreutzer MT, Kapteijn F, Moulijn JA: Hydrodynamic aspects of the monolithic loop reactor. Chem Eng Sci 2001, 56:805-812. 40. Machado RM, Parillo DJ, Boehme RP, Broekhuis RR: Use of a monolith catalyst for the hydrogenation of dinitrotoluene to toluendiamine. Air Products and Chemicals, US6,005,143, 1999. 41. Deugd RMd, Chougule RB, Kreutzer MT, Meeuse FM, Grievink J, Kapteijn F, Moulijn JA: Is a monolithic loop reactor a viable option for Fischer–Tropsch synthesis? Chem Eng Sci 2003, 58:583-591. 42. Boger T, Roy S, Heibel AK, Borchers O: A monolith loop reactor as an attractive alternative to slurry reactors. Catal Today 2003, 79:441-451.

23. Kreutzer MT, Du P, Heiszwolf JJ, Kapteijn F, Moulijn JA: Mass transfer characteristics of three-phase monolith reactors. Chem Eng Sci 2001, 56:6015-6023.

43. Groppi G, Tronconi E, Cortelli C, Leanza R: Conductive monolithic catalysts: development and industrial pilot tests for  the oxidation of o-xylene to phthalic anhydride. Ind Eng Chem Res 2012, 51:7590-7596. Excellent radial heat transport of Al honeycombs is demonstrated.

24. Kreutzer MT, Kapteijn F, Moulijn JA, Heiszwolf JJ: Multiphase  monolith reactors: chemical reaction engineering of segmented flow in microchannels. Chem Eng Sci 2005, 60:5895-5916. Review of fluid dynamics of segmented (Taylor) flow based on simple physically principles; also relevant for microreactors.

44. Edvinsson-Albers RK, Houterman MJJ, Vergunst Th, Grolman E,  Moulijn JA: Novel monolithic stirred reactor. AIChE J 1998, 44:2459-2464. The monolithic stirrer reactor is described for the first time in the open literature.

25. Gulijk Cv, Linders MJG, Valde´s-Solı´s T, Kapteijn F: Intrinsic channel maldistribution in monolithic catalyst support structures. Chem Eng J 2005, 109:89-96. 26. Schildhauer TJ, Kapteijn F, Moulijn JA: Stacking of film-flow monoliths for improved performance in reactive stripping. Ind Eng Chem Res 2005, 44:9556-9560. 27. Boger T, Heibel AK, Sorensen CM: Monolithic catalysts for the chemical industry. Ind Eng Chem Res 2004, 43:4602-4611. 28. Nijhuis TA, Beers AEW, Vergunst Th, Hoek I, Kapteijn F, Moulijn JA: Preparation of monolithic catalysts. Catal. Rev. Sci. Eng. 2001, 43:345-380. 29. Jarrah N, van Ommen JG, Lefferts L: Development of monolith with a carbon-nanofiber-washcoat as a structured catalyst support in liquid phase. Catal Today 2003, 79:29-33. 30. Lathouder KMd, Marques Flo´ T, Kapteijn F, Moulijn JA: A novel structured bioreactor: development of a monolithic stirrer reactor with immobilized lipase. Catal Today 2005, 105:443-447. 31. Kovalenko GA, Kuznetsova EV, Mogilnykh YI, Andreeva IS, Kuvshinov DG, Rudina NA: Catalytic filamentous carbons for immobilization of biologically active substances and nongrowing bacterial cells. Carbon 2001, 39:1033-1043. Current Opinion in Chemical Engineering 2013, 2:346–353

45. Edvinsson RK, Moulijn JA: Monolith reactor. DSM NV, WO9830323-A, 1998. 46. Hoek I, Nijhuis TA, Stankiewicz A, Moulijn JA: Performance of the monolithic stirrer reactor: applicability in multiphase processes. Chem Eng Sci 2004, 59:4975-4981. 47. Lathouder KMd, Bakker JJW, Kreutzer MT, Wallin S, Kapteijn F, Moulijn JA: Structured reactors for enzyme immobilization: application in a monolithic stirrer reactor. Chem Eng Res Des 2006, 84:390-398. 48. Yamauchi H, Kodama A, Hirose T, Okano H, Yamada Ki: Performance of VOC abatement by thermal swing honeycomb rotor adsorbers. Ind Eng Chem Res 2007, 46:4316-4322. 49. Babich IV, Langeveld ADv, Zhu W, Bakker WJW, Moulijn JA: A rotating adsorber for multistage cyclic processes: principle and experimental demonstration in the separation of paraffins. Ind Eng Chem Res 2001, 40:357-363. 50. Bakker JJW, Zieverink MMP, Reintjens RWEG, Kapteijn F,  Moulijn JA, Kreutzer MT: Heterogeneously catalyzed continuous-flow hydrogenation using segmented flow in capillary columns. ChemCatchem 2011, 3:1155-1157. Simple and cheap milli-reactor for fine chemical synthesis and kinetic studies, an alternative to microreactors. www.sciencedirect.com

Monolith reactors Moulijn and Kapteijn 353

51. Romkes SJP, Dautzenberg FM, Bleek CMvd, Calis HP: CFD modelling and experimental validation of particle-to-fluid mass and heat transfer in a packed bed at very low channel to particle diameter ratio. Chem Eng J 2003, 96:3-13. 52. Strangio VA, Dautzenberg FM, Calis HP, Gupta A: Fixed Bed Catalytic Reactor. ABB Lummus Global Inc, PCT/US99/06242, 1999. 53. Kunz U, Kirschning A, Wen HL, Solodenko W, Cecilia R, Kappe CO, Turek T: Monolithic polymer/carrier materials: versatile composites for fine chemical synthesis. Catal Today 2005, 105:318-324. 54. Vergunst Th, Linders MJG, Kapteijn F, Moulijn JA: Carbon based monolithic structures. Catal. Rev. Sci. Eng. 2001, 43:291-314. 55. Kreutzer MT, Gunther A, Jensen KF: Sample dispersion for segmented flow in microchannels with rectangular cross section. Anal Chem 2008, 80:1558-1567. 56. Twigg MV, Webster DE: Metal and Metal coated catalysts. In Structured Catalysts and Reactors, edn 2. Edited by Cybulski A, Moulijn JA.Boca Raton, USA: CRC Taylor & Francis; 2006:71-108. 57. Setten BAALv, Makkee M, Moulijn JA: Science and technology of catalytic diesel particulate filters. Catal Rev Sci Eng 2001, 43:489-564. 58. Heck RM, Farrauto RJ, Lee HC: Commercial Development and Experience with Catalytic Ozone Abatement in Jet Aircraft. Catal Today 1992, 13:43-58. 59. Boger T, Menegola M: Monolithic catalysts with high thermal conductivity for improved operation and economics in the production of phthalic anhydride. Ind Eng Chem Res 2005, 44:30-40. 60. Matsumoto T, Tabata K, Maki M: Catalytic composite for deodorizing odorous gases and a method for preparing the same. Matsushita Electric Industrial Co., US5,266,543, 1993. 61. Linders MJG, Mallens EPJ, Bokhoven JJGMv, Kapteijn F, Moulijn JA: Breakthrough of shallow activated carbon beds under constant and pulsating flow. AIHA J 2003, 64:173-180. 62. Linders MJG: Adsorption processes in gas mask filter canisters: practical aspects, new materials and modeling.

www.sciencedirect.com

Recent Advances in Adsorption Processes for Environmental Protection and Security. Springer; 2008:: 155-164. 63. Valde´s-Solı´s T, Linders MJG, Kapteijn F, Marba´n G, Fuertes AB:  Adsorption and breakthrough performance of carbon-coated ceramic monoliths at low-concentration of n-butane. Chem Eng Sci 2004, 59:2791-2800. Demonstration of the steep breakthrough profiles obtained with monoliths, providing a low pressure drop alternative for personal protection. 64. Sadykov VA, Isupova LA, Zolotarskii IA, Bobrova LN, Noskov AS, Parmon VN, Brushtein EA, Telyatnikova TV, Chernyshev VI, Lunin VV: Oxide catalysts for ammonia oxidation in nitric acid production: properties and perspectives. Appl Catal A: Gen 2000, 204:59-87. 65. Albers RE, Nystrom M, Siverstrom M, Sellin A, Dellve AC,  Andersson U, Herrmann W, Berglin T: Development of a monolith-based process for H2O2-production: from idea to large-scale implementation. Catal Today 2001, 69:247-252. The only manuscript on the classical application of monoliths in an industrial multiphase process. 66. Luck F: Wet air oxidation: past, present and future. Catal Today 1999, 53:81-91. 67. Hoffer BW, Schwab E, Henkelmann J, Szarka ZJ, Bell HP: Hydrogenation of polymers exhibiting carbon-carbon double bond or carbon-nitrogen multiple bond, useful e.g. for the preparation of cosmetics, comprises using a hydrogenation catalyst comprising mega porous substrate and metal/precursor, WO2007085581-A1. BASF AG; 2010. 68. Wigbers CW, Steiner J, Ernst M, Hoffer BW, Schwab E, Melder J: Preparing a catalyst, useful to produce primary amines e.g. hexamethylenediamine, comprises contacting a monolithic catalyst support with suspension, which contains insoluble or poorly soluble compound of the element comprising e.g. cobalt, WO2010089265-A2; WO2010089265-A3. BASF SE; 2011. 69. Air products and JM unite to market monolith catalysts. Focus Catal 2003, 2003:2. 70. Du P, Moulijn JA, Mul G: A novel photocatalytic monolith reactor for multiphase heterogeneous photocatalysis. Appl Catal A: Gen 2008, 334:119-128.

Current Opinion in Chemical Engineering 2013, 2:346–353