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1 Membrane Reactors Membrane Separations. 2 Outline Introduction: overview, advantages and bottlenecks. MR’s Classifications, types and functions. Transport.

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Presentation on theme: "1 Membrane Reactors Membrane Separations. 2 Outline Introduction: overview, advantages and bottlenecks. MR’s Classifications, types and functions. Transport."— Presentation transcript:

1 1 Membrane Reactors Membrane Separations

2 2 Outline Introduction: overview, advantages and bottlenecks. MR’s Classifications, types and functions. Transport mechanisms Applications

3 3 conversion effect (catalyst) separation effect (membrane) A B Catalytic membrane reactor Reaction unit and membrane unit are separated A B AB Introduction

4 4 Classical Advantages The possibility of separating molecules in a customized but cheap manner Minimization of thermal damage The possibility for recycling and lower exhausts The moderate energy consumption General Advantages... New items Increased reaction rates Reduced by-product formation

5 5...And Bottlenecks Lack of robustness - high risk Lack of unit operations approach Fouling Process considered to be expensive

6 6 Field of Application of MR Bioprocess engineering Used in biological degradation of waste products. Most membrane bioreactors use polymeric membranes Temperatures under 60ºC Catalytic reaction engineering Frontier between Catalysis, Membrane Science and Ch.Eng Inorganic membrane materials Elevated temperatures (up to 1000ºC)

7 7 TypesProperties Physical Configuration Inorganic Membranes high resistance to temperature (1000ºC) high resistance to chemically harsh environments good mechanical stability Dense o porous Made from metals, carbon, glass or ceramics Porous structure: homogeneous or asymmetric; uniform in composition or composite Supported on: porous glass, sintered metal, granular carbon or ceramics such alumina Shapes: flat discs, tubes, hollow fiber Polymeric Membranes low resistance to temperature (100ºC) low resistance to chemically harsh environments Porous Shapes: flat plates, tubes, multi-hole elements, hollow fiber

8 8 IM: Selectivity & Permeability Type of membraneMaterialSelectivityPermeability DenseMetallic Solid electrolytes High (H2, O2)Low to moderate Porous (oxides, carbon, glass, metal, zeolites) Macroporous Mesoporous Microporous Non-selective Low to moderate Can be very selective High Moderate to high Moderate CompositeGlass±metal Ceramic±metal Metal±metal Can be very selectiveModerate PM: higher permeability gas transport mechanisms DM: permselective to H2 or O2 solution-diffusion or ionic conductivity mechanisms

9 9 Distributor: Addition of reactant Active contactor: Catalyst retention Extractor: Removal of product MR functions

10 10 Ref.: J. Coronas, Santamaría J., Catalysis Today 51 (1999) MR functions

11 11 Ref.: J. Coronas, Santamaría J., Catalysis Today 51 (1999) MR functions

12 12 Membrane has only separative effects Membrane has both catalytic and separative effects 1) Catalyst physically separated from an inert membrane 2) Catalyst dispersed in an inert porous membrane 3) Inherently catalytic membranes Catalysis arrangements

13 13 Transport Mechanisms J=K l A  C g /m-C l  Gas transport through a porous membrane (MBR for waste gas treatment) J... flux through the membrane (mol/s) K l...overall mass transfer coefficient (m/s), A... membrane surface area (m 2 ), C g, C l... concentrations in the gas and liquid phases (mol/m 3 ), m.. air/water partition coefficient (-), (conc. in gas/ conc. in water) Flux of a volatile component

14 14 Hydrophobic polymer matrix Pore diameters: n m  P=(2  cos  )/R ... interfacial tension between gas and liquid (N/m), ...  contact angle with polymer surface (°), R... pore radius (m). Critical Pressure:

15 15 Hydrophobic polymer matrix Overall mass transfer resistance: D... diffusion coefficient (m 2 /s) ... porosity of the membrane ... tortuosity of the membrane ... membrane thickness (m) k g... mass transfer coefficient in gas phase (m/s) k m... mass transfer coefficient in membrane (m/s) k l... mass transfer coefficient in water phase (m/s) Mass transfer resistance inside the membrane:

16 16 P... Permeability of dense membrane (m 2 /s) D m... Diffusion coefficient in the membrane (m 2 /s) S m... Solubility Dense membranes Overall mass transfer resistance: Mass transfer resistance inside the membrane:

17 17 Membrane Bioreactors Membrane Bioreactors (MBR’s) can be broadly defined as systems integrating biological degradation of waste products with membrane filtration. Advantages: -better control of biological activity -effluent that is free of bacteria and pathogens -smaller plant size -and higher organic loading rates Disadvantages: high capital costs and high energy costs, Concentration polarization and other membrane fouling Current applications: -water recycling in buildings -municipal wastewater treatment for small communities -industrial wastewater treatment -landfill leachate treatment

18 18 Applications Bioreactors: Wastewater treatment Excellent effluent quality capable of meeting stringent discharge requirements and opening the door to direct water reuse The possibility of retaining all bacteria and viruses, eliminating extensive disinfections and the corresponding hazards related to disinfections by products Optimum control of the microbial population and flexibility in operation. More compact systems than conventional processes

19 19 Conventional Wastewater Treatment Membrane Bioreactors Conventional treatment including tertiary membrane filtration

20 20 Integrated MBR System Recirculated (external) MBR Systems

21 21 MR: H 2 production

22 22 MR: H 2 production

23 23 Another Applications Steam methane reforming Immobilized enzyme arrays Multiphase hydrogenation reactions: water remediation by catalytic hydrogenation H 2 O 2 synthesis The removal of poorly water-soluble pollutants from air can be considered to be the most promising application for MBR

24 24 Commercial Development MR complexity Separation effect Combined with the catalyst Inherently catalytic membranes Cost ($) and Risk

25 25 New Concepts in MRs The Chemical Valve Concept Ref.: A. Julbe et al. Journal of Membrane Science 181 (2001) 3-20

26 26 Improving porous membranes Porous infiltrated composite membranes good thermo-chemical resistance low sensitivity to the presence of defects a sufficiently low permeability and are more easy reproducible

27 27 Conclusions The interest on catalytic membrane reactors (CMR) is continuously increasing due to the broad range of possible applications from refinery to environment protection. Compact, efficient and operating at single Temperature and Pressure Uses well-known chemistry Operate at low and high temperatures High construction costs

28 28 References A. Julbe et al. Journal of Membrane Science 181 (2001) 3-20 C. Chen Catalytic Inorganic Membrane Reactors (Presentation, 2002) J. Coronas, Santamaría J., Catalysis Today 51 (1999) Reij M.W., Keurentjes J.T.F., Hartmans S., Journal of Biotechnology 59 (1998) 155–167 Production of Hydrogen from Nuclear Power Using Membrane Reactors (Presentation, San Diego 2002) S. Guttau et al. Journal of Desalination 144 (2002) S. Tennison, MAST International Ltd.


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