cre module1 with text - washington university in st. louis · pdf fileplug flow reactor 2. ......
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Chemical Reaction Engineering, the Environment, Pollution Prevention, Sustainable Development and Green Processing
Chemical Reaction Engineering Laboratory (CREL)Washington University
St. Louis, MO 63130, USA
M.P. Dudukovic
IntroductionPollution Prevention StrategiesRole (Current and Future) of CRE in Pollution Prevention and Green ProcessingConclusions
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Module 1:
Reaction Engineering for Environmentally Benign Processing
CHEMICAL REACTION ENGINEERING LABORATORY
CHEMISTRY - The science that treats of the composition of substances and of the transformation which they undergo.
REACTION - Act of chemical change.ENGINEERING - The art and sciences by which the properties of matter
and the sources of power in nature are made useful to man in structures, machines and manufactured products.
ENVIRONMENT - That which environs; The surrounding conditions, influences and forces.
- The aggregate of all external conditions and influences affecting the life and development of an organism.
POLLUTE - To make or render unclean or impure.
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(Definitions from Webster Dictionary)
SUSTAINABLEDEVELOPMENT⇒ Meeting the needs of the present without
compromising the ability of future generations to meet their needs.
Total population
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Key Factors Affecting the Environment and Sustainability
• Agricultural practices• Mining practices• Energy utilization
Lifestyle
• Recreational activities• Manufacturing practices
CHEMICAL ENGINEERING is the profession in which a knowledge of mathematics, chemistry and other natural sciences gained by study, experience and practice is applied with judgment to develop economic and environmentally acceptable ways of using materials and energy for the benefit of mankind.
Raw Materials Products
Non Renewable:• Petroleum• Coal• Ores• Minerals
Renewable:• Plants• Animals
FuelsMaterialsPlasticsPharmaceuticalsFoodFeedetc.
Chemical andPhysical
Transformations
Pollution
The domain of chemical engineering consists of chemical and physical transformation of starting
materials to products
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CHEMICAL REACTION ENGINEERING LABORATORYS5
GLOBAL VIEWPessimistic Assessment
( ) ( )( )efficiencyprocess
populationcapitapernconsumptioPollution ∝
Optimistic Assessment( ) ( ) ( )populationcapitapernconsumptio
cyinefficien processefficiencyprocess - 1Pollution
4444 34444 21∝
Popu
latio
n
Con
sum
ptio
n P
er C
apita
Pro
cess
Effi
cien
cy
Time Time Time (Investment)
GLOBALLY, Pollution prevention and reduction will ultimately depend either on population and consumption control or on introduction of environmentally benign and highly efficient sustainable technologies.
LOCALLY, or on a national level, the focus has been on waste reduction via
- Better education and operation practices at existing manufacturing facilities (more than pays for itself)
- Retrofitting of existing facilities (done only if resulting in improved profitability)
- Installation of pollution abatement equipment (done only if under regulatory or peer pressures)
- Moving and opening new manufacturing facilities off-shore (let them have our pollution while we manage money – service industry)
- Development and installation of cleaner processes (requires substantial capital expenditures and new unit operations and newconcepts needed for ultra pure systems) S6
),()( bbb TCRCL η=
∑ ηΔ−=j
bbjjRbh TCRHTLj
),()()(
( )transport;kineticsf=η00 P,C,T
P,C,T
product, QREACTOR PERFORMANCE = f ( input & operating variables ; rates ; mixing pattern )
REACTOR MOLECULAR SCALEEDDY/PARTICLEfeed, Q
CHEMICAL REACTION ENGINEERING (CRE) METHODOLOGY
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MOLECULAR SCALE (RATE FORMS)
Strictly Empirical Mechanism Based Elementary Steps
REACTOR SCALE
Axial Dispersion CFDPhenomenological Models
EDDY OR PARTICLE SCALE TRANSPORT
DNS / CFDEmpirical Micromixing Models
PROCESS SCALE
Steady State Balances Dynamic Models forControl & Optimization
10-10 m
102 m
10-16 (s)
104 (s)
PFR/CSTR
Green Chemistry and Green Processing
Raw MaterialsEnergy
Value added products
Waste or pollutants
ReactorPretreatment Separator
Raw Materials
Energy
Energy Energy
Global Scale
Plant Scale Waste or pollutants
CRE
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CHEMICAL REACTION ENGINEERING LABORATORY
Environmental Acceptability,as Measured by the E-Factor
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Industry
Oil refining
Bulk chemicals
Fine chemicals
Pharmaceuticals
Product tons
per year
106 – 108
104 – 106
102 – 104
100 - 103
Waste/product
ratio by weight
~ 0.1
< 1 – 5
5 – 50
25 - > 100
CHEMICAL REACTION ENGINEERING LABORATORYS10
HOTHOTZONEZONE
LIQUIDSULFUR
LIQUIDSULFUR
GRAPHITEELECTRODE
CS2gas product
CARBONFEED
MANHOLECOVER
EUROPEAN (GERMAN) PROCESS:
CARBON + SULFUR CARBON DISULFIDEC 2S CS2
My First Assignmentas a Process Engineer (1967)
electric arc
REACTOR: REFRACTORY LINED KILN WITH
GRAPHITE ELECTRODES
S11Reactor Clearly Environmentally Unfriendly !Reactor Clearly Environmentally Unfriendly !
Glowing Red Hot Coal !!!Glowing Red Hot Coal !!!
Poisonous Gases !!!Poisonous Gases !!!
THAR’ IT BLOWSTHAR’ IT BLOWS !!!!!!
VOLCANIC ERUPTIONS ONCE A WEEK (on the average) !!!
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• Runaway caused by thermal instability and ‘hot spots’ in the reactor – not controllable
• Recommendation of young engineers to the boss:“Prevolatize the sulfur and suspend smaller coke particles in sulphur vapor – run the process in a fluidized bed”
fixedbed
s(ℓ)
kiln
CS2(g)
MORALEIf pollution was part of the cost, risk would have been taken to go for new technology. Without it no new process.
EPILOGUEFour years after our recommendation a Japanese company proved fluidized bed concept viable.
CS2(g)
C(s)S(g)
Fluidized bed
• Boss’s Response“No way! You know nothing about fluidization technology! Go improve on the German kilns!”
• ConclusionThe “improved design of the “German” kilns (positioning more bottom electrodes to expand the hot zone) led to “our” kilns erupting once every two to three weeks (a big improvement according to our boss)
The Twelve Principles of Green Chemistry
1. Waste prevention
2. Atom Economy
3. Less Hazardous Chemical Syntheses
4. Designing Safer Chemicals
5. Safer Solvents and Auxiliaries
6. Design for Energy Efficiency.
7. Use of Renewable Feedstocks
8. Reduce Derivatives
9. Catalysis
10. Design for Degradation
11. Real-time analysis for Pollution Prevention
12. Inherently Safer Chemistry for Accident Prevention
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Green Chemistry and Green Processing
Better HousekeepingRaw material selectionEquipment maintenanceTemperature controlPressure controlVent and relief system tuning
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Green Chemistry and Green ProcessingGuidelines for Improved Reactors
Use non-hazardous raw materials.Use renewable resources.Reduce by-products and generate less wasteProduce products easy to separate.Recycle un-reacted materials.Reduce use of solvents.Use benign solvents.Improve atom efficiency.Improve energy efficiency.Use heat integration.Replace liquid phase routes by solid catalyzed routes.Do not over-design.
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Successes in Process ChangesExample
Catalyst3ll CA
Ethylbenzene synthesis from Benzene and Ethylene (390,000 t/y):OLD:
1. Liquid Phase Process ( )3,900 tons to be handled3ll CA
2. Vapor Phase Process (BF3/Al2O3 Catalyst)500 t/y solid waste800 t/y liquid (benzene saturated) waste
NEW:
3. New Process (H-ZSM-5)35 t/y solid waste265 t/y liquid waste
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OLD APPROACH:
Scale-up In Size
NEW APPROACH:Apply fundamentals on:
Molecular
Reactor Scale
Eddy / Particle
Green Chemistry and Green Processing
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Green Chemistry and Green Processing
Past & Present… … Future
REACTION ENGINEERING…Art Science
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REACTION ENGINEERING ENCOMPASSES A MULTITUDE
OF SCALES
Molecular scale (micro)Small eddies and particle scale (meso)Reactor scale (macro)
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All of these scales can affect reactor performance and hence the overall process performance and its environmental impact.
MICRO-SCALE TECHNIQUES
1. Molecular Synthesis:e.g. solvent replacement group contribution approach
2. Reaction Path Synthesis:- Understanding current reactions and mechanisms
of pollutant formation- Establishing synthesis pathways for new
compounds3. Catalysis Design:
- Rational development of new catalysts that willresult in cleaner technologies
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Diffusive Transport + Reaction = Product Shape Selectivity
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( ) N33CH
( ) NH23CH
2NH3CH
CMS-PFA
2NH3CH
3NH
OH3CH+
3O2Al2SiO −
( ) NH23CH
Combined separation and catalyst (Foley, et. al., 1994)
REACTIONS IN ETHYLENE GLYCOL PRODUCTION
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CONVENTIONAL PROCESS:1. Plug flow reactor2. Large excess water in the feed3. Optimal residence time4. Downstream separation – large separation
train
PROPOSED PROCESS:1. Reactive Distillation
ADVANTAGE:Remove wanted product in situ as it is formed; Make excess water available in reaction zone
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OPTIMAL DISTRIBUTED FEED REACTIVE DISTILLATION COLUMN FOR ETHYLENE GLYCOL SYNTHESIS
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Green Chemistry and Green Processing
Atom economy is a measure of how efficiently raw materials are used.
Example: Mass economy of Maleic anhydride production via benzene & n-butane route.Benzene route:
n-Butane route:
Concept of Atom and Mass Economy
22324266 4292 352 COOHOHCOHC MoOOV ++⎯⎯⎯ →⎯+
%4.44100)1)(6(2)16)(12(9)12)(6(2)1)(2(2)16)(2(3)12)(4(2
=×++++
=EfficiencyMass
OHOHCOHC OPVO2324
)(2104 45.3 525 +⎯⎯⎯ →⎯+
%6.57100)1(10)16)(2(5.3)12(4)1)(2()16)(3()12)(4(
=×++++
=EfficiencyMass
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Butane Oxidation Over VPO
• Active catalyst is a mixture of phases, including
αΙΙ-VOPO4, δ-VOPO4, γ-VOPO4 and (VO)2P2O7
• Catalyst oxidation state is variableO2 O2
V+3 V+4 V+5
HC HC• Both heterogeneous and homogeneous reactions occur
[O]cat O2n-C4 MAN COX, H2O
O2• Intrinsic rates affected by C4, O2, H2O, surface deposits, ...
OH- OH-~C-C-C~
(VO)2P2O7n-butane
O
MAN
O O3.5 O2+ 4 H2O
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Circulating Fluid Bed (CFB) Reactor for Butane Oxidation
Maleic Anhydride
Inert Gas
Air
Off-gas (COx, H2O,..)
ButaneFeed GasReoxidized
Catalyst
ReducedCatalyst
O2 O2V+3 V+4 V+5
HC HC
RiserRiser
Regen Riser
Catalyst Catalyst RedoxRedox
O OO
O2
Main ReactionMain Reaction
SolidsFlow
Direction
V+5
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Green Chemistry and Green Processing
Traditional Routes for Alkylation
Traditional routes use liquid phase acids such as HF or H2SO4 or Lewis acid metal halides: AlCl3 and BF3
Stoichiometric quantities often needed leading to waste generation
Disposal of spent catalysts such as BF3 needed
Corrosive systems Capital cost
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HC
HF RECYCLEwith a pump !!
PRODUCTmint 40≈
OLD REACTOR: MIXER-SETTLERWITH EXTERNAL RECYCLE PUMP
HC
PRODUCT
HF INTERNAL RECYCLEno pump !!no leaky seals !!Still HF is there!!
sect 30≈
NEWER REACTOR: “LIFT”PRINCIPLE: NO RECYCLE PUMP
Alkylation: HF Catalyst (Old);
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Need reactor model to assess selectivity and productivity
Simultaneous Development of Catalyst and Reactor Technology
Deactivating Solid Supported Liquid Catalyst or Solid Acid Catalyst (New)
Radioactive Particle Tracking (CARPT) Provides Solids
Velocity and Mixing Information
Computer Tomography (CT)Provides Solids Density Distribution
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High Pressure Side(80-100 psi)
Low Pressure Side( <80 psi)
HOPPER
R
I
S
E
R
EDUCTOR
WATER TANK
PUMP
RECYCLE LINE
6′11"
6′′
PP
P
P
9′11"
Cold Flow Model
Tracer Studies Confirm Liquid In Plug Flow(N > 20)
(Devanathan, 1990; Kumar, 1994; Roy, 2000)
Trace over 38 s (1900 positions)
CARPT Results
-505
t = 60 sTime Average(25 - 100 s)
Z = 100 cm
Z = 125 cm
0
50
100
150
-7.6 -2.6 2.4 7.4
x-Position, cm
z-Po
sitio
n, c
m
-8
-3
2
7
12
17
0 1 2 3 4 5 6 7
Radial Position, cm
Axial Solids Velocity, cm/s
0
0.05
0.1
0.150.2
0.25
0.30.35
0.4
0 1 2 3 4 5 6 7
Radial Position, cm
Solids Holdup
0
10
20
30
40
50
60
70
80
0 1 2 3 4 5 6 7Radial Position, cm
Granular Temperature, cm2/s2
Comparison of CFD with Data
Ready for plant design, optimization and model based control.
Slow down of catalyst deactivation should be explored by CO2 addition atsupercritical conditions.
Final2-D Convection
DiffusionReactor Model for
the Riser
CFD Results
UL
Us
Dz
Dr
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Alkylation Reaction Scheme*
* deJong et. al., CES (1996), Volume 51, 2053-2060
SASOP k +⎯→⎯++ 1
YSAO k⎯→⎯++ 2
SDSOO k +⎯→⎯++ 3
XSD k⎯→⎯+ 4
P - ParaffinO - OlefinA - AlkylateD - DimerS - Active siteX - Complex blocking an acid siteY - Complex blocking an active site
Model PredictionsOlefin conversionSelectivity to alkylateCatalyst activity profileDiscerning important deactivation step
Green Chemistry and Green Processing
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System to Beat in Alkylation
Application: Combines propylene, butylene and pentylene with isobutane, in the presence of sulfuric acid catalyst, to form a high-octane, mogas component.
Products: A highly isoparaffinic, low Rvp, high-octane gasoline blend-stock is produced from the alkylation process.
Installation: 119,0000-bpd capacity at 11 locations with the sizes ranging from 2,000 to 30,000 bpd. Single reactor/settler trains with capacities up to 9,500 bpsd.
Licensor: ExxonMobil Research & Engineering Co.
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Green Chemistry and Green Processing
Solid Acid CatalystsCommon Types
Beta zeolitesIon exchange resins such as silica supported nafion.Heteropoly acids such as tungsto- phosphoric acid.
Limitations/ChallengesCatalyst DeactivationReactivation of catalyst neededComplex reactor types Pore diffusionLoss of selectivity
Developing stable solid acid acid catalyzed processes as environmentally benign alternatives to liquid acid based processes has been a major challenge for over three decades
S34
Pore DiffusionZeolites and other solid acids have macro-micro pore structureOut-diffusion rate of alkylate affects selectivity.Out-diffusion rate of dimer affects catalyst activity.Solvent tuning to alter diffusion coefficients.Model based design of catalyst structure and target goals for diffusivity.
Green Chemistry and Green Processing
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Reactor Types
Circulating fluid bedsPacked beds with periodic operationStirred tanks with or without catalyst baskets (provision for switching)Chromatographic type of reactors
Green Chemistry and Green Processing
S36
•Dynamic operation swing adsorption
•Periodic (symmetric) operation of packed beds with exothermic reactions
•Coupling of an exothermic and endothermic reaction in a periodically operated (asymmetric) packed bed
• Induced pulsing in trickle beds
•Counter current flow in gas-liquid-solid catalyzed systems
ATTRACTIVE OPTIONS FOR IMPROVED REACTOR PERFORMANCE ARE:
• Catalytic distillation
• Membrane reactors
• Flowing solids adsorbent
• Expanded solvents
IN SITU REACTOR SEPARATIONS ARE ATTRACTIVE AND CAN BE ACHIEVED VIA
S37
(CXLs) CO2-Expanded Liquids
Vapor
Liquid
CO2-Expanded
Liquid
Vapor
Add CO2
High miscibility of CO2 with most organic solvents
Pressure tunable transport and solvent properties
Mild pressures (relative to scCO2)
1 Wei, M. et al., J. Am. Chem. Soc., 124 (2002) 2513.2 Rajagopalan,B. et al., Ind. Eng. Chem. Res. 42 (2003) 6505.
CXLs successfully applied in homogeneous catalysis1,2
S38
A SYSTEMS APPROACH TO MULTIPHASE REACTOR SELECTION
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Homework Assignments1. What are the alternative chemistries for making
carbon disulfide on the large scale? Are there more benign than the carbon-sulfur route?What solvent currently has dominant use in production of rayon fibers. If it is not carbon disulfide, is it more environmentally benign and if so, why? What is the process by which the solvent is made? How is the solvent disposed of?What chemical is likely to substitute mono-ethanol glycol as antifreeze? How is it made? Is that an environmentally benign process?
Suggested Readings:
Anastas, P.T.; Warner, J.C., Green Chemistry: Theory and Practice, Oxford University Press, New York, 1998.Levenspiel, O., chemical Reaction Engineering, Third Edition, John Wiley & Sons, New York, 1999.
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