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

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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

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•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

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(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

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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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