Towards intensified separation processes in gas/vapour-liquid systems Prof. Dr.-Ing. Eugeny Kenig
Why intensification? - Requests through global changes Fast population growth Rising life expectations Rising life standards More energy! Change in the way and intensity of communication ( open World ) Scarcer resources, price escalation Rising environmental awareness of the society Efficient energy, clean energy! Change in energy policy Impact of Process Industries! -2-
Why Intensification? Possibilities available New materials New manufacturing technologies New investigation tools, both experimental and theoretical New communication culture Progress in the computer technology -3-
Why Intensification? Possibilities available New materials New manufacturing technologies New investigation tools, both experimental and theoretical New communication culture Progress in the computer technology -4-
Progress in the computer technology Revolutionary improvements in power, memory capacity, data transfer, operability, comfort Advances in numerical data processing, new experimental methods (e.g., optics, tomography, nuclear magnetic resonance spectroscopy) Powerful numerical methods und software tools Facilitated/automated simulation steps User friendly pre-processing and post-processing Significant progress in numerical simulation of several processes This is the factor that makes fast progress of process engineering possible! -5-
What is PI? A simple definition: PI = any chemical engineering development that leads to a substantially smaller, cleaner, and more energy efficient technology Stankiewicz & Moulijn, Chem. Eng. Progress, 96 (2000) Idea: To get the maximum out of any apparatus, tool or process -6-
PI from industrial point of view Anticipated advantages/aims Barriers + Simplified process arrangement + Smaller equipment/smaller units + Increased safety + Decreased energy consumption + Decreased operational costs + Shorter Time to market + Decreased waste/side products + Better company image - Reliability of conventional technology - Risk due to lack of precedent - Expensive new pilot plant facilities - Concerns about safety and control - Knowledge about how and where to intensify - Lack of validated PI units - Missing criteria to evaluate PI - Often more complex modelling Stankiewicz & Moulijn, Re-engineering the chemical processing plant, Marcel Dekker, 2004; Lutze et al., Chem. Eng. Process. 49, 2010-7-
Ways towards PI and their feasibility Integration Miniaturisation and modularisation Application of innovative driving forces (e.g. microwaves) Rising complexity Deep understanding of the basic phenomena and their interactions is necessary Possible, largely thanks to the significant progress in the computer technology -8-
Ways towards PI and their feasibility Integration Miniaturisation and modularisation Application of innovative driving forces (e.g. microwaves) Rising complexity Deep understanding of the basic phenomena and their interactions is necessary Possible, largely thanks to the significant progress in the computer technology -9-
PI via integration What can be combined: Single process steps Separation units Column internals Heat streams Further elements/components/functions -10-
PI via integration What can be combined: Single process steps Separation units Column internals Heat streams Further elements/components/functions -11-
Integration of single process steps - reaction and separation Reactive separations reactive distillation reactive absorption reactive extraction reactive stripping Classical separations distillation absorption extraction stripping -12-
Reactive distillation -13-
Reactive distillation: what for? Problem: reaction (equilibrium limited) A + B C+ D products C and D required in pure form in addition: distillative separation possible and desired Solution possibilities: 1. conventional process: reactor + distillation column 2. reactive distillation -14-
Reactive distillation as an alternative Reaction Traditional separation Reactive distillation Separation Improved conversion Increased selectivity Direct heat integration Separation of azeotropic and close boiling mixtures Suppression of undesired side reactions Reduced capital investment and operating cost! -15-
Synthesis of methyl acetate: Conventional scheme acetic acid + methanol 118 C 65 C K x 5 methyl acetate + water 57 C 100 C Binary azeotropes x MeAc [-] T B [ C] MeAc - H2O 0,93 56,8 MeAc - MeOH 0,68 53,9 After Siirola, AIChE Symp. Ser., 1995-16-
Synthesis of methyl acetate: Reactive distillation Development of a RD-process with the goal to solve a) conversion problems (chem. equilibrium) RD-column with 4 zones: a) Reactive zone (MeAc-building) b) Extractive distillation (MeOH-MeAc - azeotrope is broken with the aid of HAc) c) Rectifying section (HAc-separation) d) Stripping section (MeOH-separation) Acetic acid Sulphuric acid (catalyst) Methanol Methyl acetate Methyl acetate accumulation (c) Water extraction (b) Reaction zone (a) Methanol stripping (d) Water (+ sulphuric acid) Agreda et al., Chem. Eng. Progress, 1990 b) separation problems (MeOH-MeAcazeotrope) -17-
Synthesis of methyl acetate: Reactive distillation Conventional scheme: 9 columns + 1 reactor RD: 1 RD-column up to 99% product purity significant equipment reduction Agreda et al., Chem. Eng. Progress, 1990-18-
Possible applications Esterifications and transesterifications (e.g. MeAc, fatty acid esters,...) Etherifications (e.g. MTBE, TAME, ETBE,...) Alcylations (e.g. cumene from benzene and propylene) Aldol condensation (e.g. DAA from acetone) Hydrolysis of epoxides (e.g. ethylene glycol from EO)... Separation of closely boiling mixtures (e.g. m- and p-xylol) -19-
Reactive distillation: Reaction types Homogeneously catalysed (e.g., strong inorganic acids) Heterogeneously catalysed (e.g., ion exchangers) Low costs Simpler simulation Corrosion problems Product contamination Sometimes necessity of catalyst separation Indefinite reaction zone High product purity No special materials No corrosion problems Determined reaction zone Catalyst poisoning Temperature limit (130 C) Difficult catalyst exchange -20-
Reactive distillation columns Structured packings (metal, plastic, gauze wire) MONTZ-PAK Type BSH-400 Sulzer KATAPAK-SP Catalytic packings ( sandwich - form KATAPAK-SP by Sulzer Chemtech) -21-
Catalytic internals Requirements: sufficient residence time plug-flow when consecutive reactions sufficient separation efficiency low pressure drop temperature resistance -22-
Catalytic internals Sulzer Katapak-SP 11 Sulzer Katapak-SP 12 Behrens, Dissertation, Delft, 2006-23-
Reactive absorption -24-
Reactive absorption: What for? Numerous applications in food, paper, cement industries, naphtha and fuel sectors, emission treatment, etc. Some examples: Gas purification (e. g. separation of CO 2 and H 2 S from industrial waste gases) Manufacturing of chemicals (e.g. nitric acid, sulphuric acid) Drying (e. g. air drying) Removal of foul gases -25-
Reactive absorption: Important features Contrary to physical absorption, there is no need in high partial pressures significant physical solubility of gaseous species Instead, a high solubility of the conversed species (product of the reaction with the absorbed component) is advantageous The effect of chemical reactions is favorable at low gas-phase concentrations Compared to RD: independent fluxes often fast reactions mass transfer is a crucial issue! electrolyte systems, ion components hardly any catalyst application -26-
Reactive absorption: A typical example SO 2 -absorption plant in a maleic anhydride production factory Multiplied reactions Simplified flowsheet of a (reactive) closed-loop absorption/desorption (wash) unit -27-
Reactive stripping -28-
Reactive stripping: what for? A supplementary operation to reactive absorption (homogeneous) An alternative to reactive distillation (catalytic, heterogeneous) a stripping (inert) gas is involved temperature can be below boiling point can be carried out both in co-current and counter-current mode efficient removal of inhibiting components out of reaction zone -29-
Reactive stripping Esterification of 1-octanol with hexanoic acid (with cumene as solvent) towards octyl hexanoate and water Stripping in the counter-current mode and concentration profiles A finned monolith: A photo and a simplified cross-section representation Beers et al., Catalysis Today, 66 (2001) -30-
Hybrid separations -31-
PI by coupling of unit operations An example of hybrid separations Distillation & Membranes Production of ethanol: First step: Separation of a fermentation liquor in a combination of distillation & stripping Distillate: a binary mixture ethanol/water Subsequently: azeotrope breaking via a combination of distillation & vapour permeation Keller et al., Chem. Ing. Techn. 83, 2011-32-
PI by coupling of unit operations An example of hybrid separations Distillation & Membranes Distillation & Stripping Distillation & Vapour permeation Fermentation liquor Ethanol Water (azeotrope) Ethanol Ethanol Water Recycle Water Keller et al., Chem. Ing. Techn. 83, 2011-33-
PI by coupling unit operations An example of hybrid separations Distillation & Membranes + Lower energy consumption + Possibly enhanced product quality + Avoiding entrainers + Applicable to separation of close boiling and azeotropic mixtures - Insufficient long-term stability of membranes - Missing design methods for this complex process conjunction -34-
PI via integration What can be combined: Single process steps Separation units Column internals Heat streams Further elements/components/functions -35-
Integration of separation units Conventional column sequence to separate a ternary mixture Energy-integrated column (Petlyuk configuration) A B A ABC 1 2 BC ABC 1 2 B C C Problem: High energy demand -36-
Dividing wall column concept Integration of the Petyluk configuration in one column dividing wall column + Lower equipment cost Liquid phase distribution ABC Vapour distribution Dividing wall B A Main column C + Lower energy consumption as compared to common column configurations + More compact equipment + Possibility to reach sharp separation of a ternary mixture within only one column - More complex modelling, design and control Prefractionator -37-
PI via integration What can be combined: Single process steps Separation units Column internals Heat streams Further elements/components/functions -38-
Integration of integrated units Reactive separations Classical separations Coupled separations reactive distillation distillation dividing wall column reactive dividing wall column -39-
PI via integration What can be combined: Single process steps Separation units Column internals Heat streams Further elements/components/functions -40-
Integration of internals - sandwich packing Internals as integration elements Structured packings with lower geometric surface (de-entrainment layer) Structured packings with higher geometric surface (hold-up layer) Liquid De-entrainment layer Hold-up layer Gas 41-41-
Integration of internals - sandwich packing de-entrainment layer liquid spray layer hold-up layer flooded hold-up layer downcomers gas -42-
PI via integration What can be combined: Single process steps Separation units Column internals Heat streams Further elements/components/functions -43-
Heat integration in distillation Due to high energy consumption, distillative separation covers 40-70 % of investment & operating costs of a typical chemical plant Distillation is inefficient from the energetic point of view, since the heating energy for the reboiler is supplied at high temperatures, whereas at the condenser, it is removed at low (mostly useless) temperature level Improvement potential: Application of heat pipe principle, e.g. Vapour recompression column Heat integrated distillation Bruinsma et al., Chem. Eng. Research & Design 90, 2012-44-
Heat integration in distillation An example of heat integrated distillation columns (HIDiC) Two units with different pressure level High pressure region can be used to heat the low pressure region + Reduction of total required energy - High investment costs - Complex construction - Problems with process control -45-
Heat integration in distillation Explanation of the function Integrated unit Compressor Feed Heat transfer Top product Rectifying section Stripping section Feed Throttle valve Top product Compressor Throttle valve Bottom product Bottom product -46- Keller et al., Chem. Ing. Techn. 83, 2011
PI via integration What can be combined: Single process steps Separation units Column internals Heat streams Further elements/components/functions -47-
Further integration possibilities An example of a mixer reactor Method: Mechanical mixer is replaced by a static mixer Aim: a compact and energy-efficient method to mix fluids or to bring them in contact Example: static mixer reactor of Sulzer, with heat transfer tubes used as mixing elements Application: Processes, in which mixing and intensive heat supply/ removal must be performed simultaneously, e.g. in nitration or neutralisation reactions Stankiewicz & Moulijn, Chem. Eng. Progress, 96 (2000) Fa. Sulzer, static mixer reactor -48-
PI: important questions from industry When is PI economically reasonable? Is the new variant too expensive? Which process step should be intensified? Which equipment is required? Which criteria must be involved to evaluate different PI-options? -49-
Future problems in PI New and reliable materials (e.g. catalysts or membranes) to extend feasible operational windows Development of suitable tools for automatisation of process steps, for instance in integrated separation processes Relevant modelling approaches Design methods for complex process and unit combinations. -50-
Process intensification: Concluding remarks PI is an inherent feature of today s life of process industries, mostly due to the computer technology progress Integration is one of the main ways towards PI Integrable are single process steps, units, internals, heat streams, functionalities, etc. Many integrated applications already exist Integration is on its way to maturity: some problems have to be solved in order to make it fully convincing concept for industry -51-
Process intensification: Concluding remarks Idea: To get the maximum out of any apparatus, tool or process No more of the old formula: Let s make it a foot bigger in diameter and 5 ft. higher just for good luck - Walter G. Whitman (1924) -52-
Thank you for your attention! -53-