module 3. green chemistry - northwestern...

Michigan Technological University1

Module 3. Green Chemistry

NSF Summer Institute on Nano Mechanics and Materials:A Short Course on Nanotechnology, Biotechnology, and Green

Manufacturing for Creating Sustainable Technologies

June 20-24 , 2005

David R. Shonnard

Associate Professor

Department of Chemical Engineering

Michigan Technological University


Green Chemistry principles (chapter 7)

Inherently green chemical reaction conditions

(chapter 7)

Atom economy / mass economy (chapter 7)

Pollution prevention for chemical reactions (chapter 9)

Early design evaluation of reaction pathways

(chapter 8)

Expansion of system boundaries (chapter 13)

Module 3 overview


It is better to prevent waste than to treat or clean up waste

Atom Economy: incorporate of all materials into the final product.

Less Hazardous Chemical Syntheses

Designing Safer Chemicals

Safer Solvents and Auxiliaries

Design for Energy Efficiency

Use of Renewable Feedstocks

Reduce Derivatives

Catalytic reagents (as selective as possible) are superior to

stoichiometric reagents

Design for Degradation

Real-time analysis for Pollution Prevention

Inherently Safer Chemistry for Accident Prevention

*Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice, Oxford University

Press: New York, 1998, p.30. By permission of Oxford University Press.

12 Principles of Green Chemistry


Important considerations

» Human / ecosystem health properties– Bioaccumulative?

– Persistent?

– Toxic?

– Global warming, Ozone depletion, Smog formation?

– Flammable or otherwise hazardous?

– Renewable or non renewable resource?

» Life cycle environmental burdens? - Ch 13, 14

Feedstocks and solvents


Alternative choices: raw materials

Benzene• fossil fuel source• carcinogenic

Glucose• renewable source• non-toxic


Alternative choices: Solvents

Supercritical CO2Non-toxic, non-flammable, renewable sources

Water as alternative solvent (as a co-solvent with an alcohol)

Selectivity enhancement with SC CO2

Reaction rate enhancements


Synthesis pathways

Reaction Type Waste Generation Potential

Addition Reaction Isobutylene + methanol → methyl tert-butyl ether C4H8 + CH3OH → (C4H9)-O-CH3

• completely incorporate starting material into product

Substitution Reaction Phenol + ammonia → analine + water C6H5-OH+ NH3 → C6H5-NH2 + H2O

• stoichiometric amounts of waste are generated

Elimination Reaction Ethylbenzene → styrene + hydrogen C6H5-C2H5 → C6H5-C2H3 + H2

• stoichiometric amounts of waste are generated


Software:Green Chemistry Expert System

TOPIC AREAS• Green Synthetic Reactions - search a database for alternatives• Designing Safer Chemicals - information on chemical classes• Green Solvents/Reaction Conditions - alternative solvents / uses

- solvent propertieshttp://www.epa.gov/oppt/greenengineering


Atom and Mass Efficiency:magnitude of improvements possible

Atom Efficiency- the fraction of starting material incorporated into the desired product -

C6H5-OH+ NH3 → C6H5-NH2 + H2O• Carbon - 100%• Hydrogen - 7/9 x 100 = 77.8%• Oxygen - 0/1 x 100 = 0%• Nitrogen - 100%

Mass Efficiency (Basis 1 mole of product)C6H5-OH+ NH3 → C6H5-NH2 + H2O

Mass in Product = (6 C) (12) + (7 H) x (1) + (0 O) x 16) + (1 N) x (14) = 93 grams

Mass in Reactants = (6 C) (12) + (9 H) x (1) + (1 O) x 16) + (1 N) x (14) = 111 grams

Mass Efficiency = 93/111 x 100 = 83.8%


Adipic acid synthesisTraditional vs. New

Traditional Route - from cyclohexanol/cyclohexanoneCu (.1-.5%)

C6H12O+ 2 HNO3 + 2 H2O C6H10O4 + (NO, NO2, N2O, N2)V (.02-.1%)

92-96% Yield of Adipic Acid

• Carbon - 100%• Oxygen - 4/9 x 100 = 44.4%• Hydrogen - 10/18 x 100 = 55.6%• Nitrogen - 0%

Product Mass = (6 C)(12) + (10 H)(1) + (4 O)(16) = 146 g

Reactant Mass = (6 C)(12) + (18 H)(1) + (9 O)(16) + (2 N)(14) = 262 g

Mass Efficiency = 146/262 x 100 = 55.7%

global warmingozone depletion

hazardous

Davis and Kemp, 1991, Adipic Acid, in Kirk-Othmer Encyclopedia of Chemical Technology, V. 1, 466 - 493


New Route - from cyclohexeneNa2WO4•2H2O (1%)

C6H10 + 4 H2O2 C6H10O4 + 4 H2O[CH3(n-C8H17) 3N]HSO4 (1%)

90% Yield of Adipic Acid

• Carbon - 100%• Oxygen - 4/8 x 100 = 50%• Hydrogen - 10/18 x 100 = 55.6%

Product Mass = (6 C)(12) + (10 H)(1) + (4 O)(16) = 146 g

Reactant Mass = (6 C)(12) + (18 H)(1) + (8 O)(16) = 218 g

Mass Efficiency = 146/218 x 100 = 67%

Adipic Acid SynthesisTraditional vs. New

Sato, et al. 1998, A “green” route to adipic acid:…, Science, V. 281, 11 Sept. 1646 - 1647


Maleic anhydride synthesis:Benzene vs n-butane - mass efficiency

Benzene Route (Hedley et al. 1975, reference in ch. 8)V2O5

2 C6H6 + 9 O2 2 C4H2O3 + H2O + 4 CO2

(air) MoO3

70% Yield of Maleic Anhydride from Benzene in Fixed Bed Reactor

Butane Route(VO)2P2O5

C4H10 + 3.5 O2 C4H2O0 + 4 H2O(air)

60% Yield of Maleic Anhydride from Butane in Fixed Bed Reactor

Mass Efficiency = 2(4)(12) + 3(2)(16) + 2(2)(1)

2(6)(12) + 9(2)(16) + 2(6)(1) (100) = 44.4%

Mass Efficiency = (4)(12) + (3)(16) + (2)(1)

(4)(12) + 3.5(2)(16) + (10)(1) (100) = 57.6%

Felthouse et al., 1991, “Maleic Anhydride, ..”, in Kirk-Othmer Encyclopedia of Chemical Technology, V. 15, 893 - 928


Pollution prevention through material selection - reactor applications

1. Catalysts:

• that allow the use of more environmentally benign raw materials - e.g. less hazardous raw materials

• that convert wastes to usable products and feedstocks

• products more environmentally friendly - e.g. RFG / low S diesel fuel

2. Oxidants: in partial oxidation reactions

• replace air with pure O2 or enriched air to reduce NOx emissions

3. Solvents and diluents :

• replace toxic solvents with benign alternatives for polymer synthesis

• replace air with CO2 as heat sinks in exothermic gas phase reactions


Pollution prevention for chemical reactors

1. Reaction type:

• series versus parallel pathways

• irreversible versus reversible

• competitive-consecutive reaction pathway

2. Reactor type:

• issues of residence time, mixing, heat transfer

3. Reaction conditions:

• effects of temperature on product selectivity

• effect of mixing on yield and selectivity


Reversible Series Reactions CH4 + H2O ↔ CO + 3H2

Steam reforming of CH4 CO + H2O ↔ CO2 + H2

R = CH4

P = CO

W = CO2

Separate and recycle waste to extinction

Pollution prevention for chemical reactions


Pollution prevention -mixing effects

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.E-05 1.E-04 1.E-03 1.E-02 1.E-01

(k1 Bo τ)(Ao/Bo)

Y/Yexp

Irreversible 2nd order competitive-consecutive reactions A + Bk1⎯ → ⎯ P

P + Bk2⎯ → ⎯ W

Y = yield= P/Ao

Yexp = expectedyield

τ = mixing timescale

Increasedmixing will increase observed yield

Ao

BoCSTR

Yexp =R

Ao

=1

(k2 / k1 −1)

A

Ao

−A

Ao

⎛ ⎝ ⎜

⎞ ⎠ ⎟

k 2 / k1⎡

⎣ ⎢ ⎢

⎤

⎦ ⎥ ⎥

Increased mixing

P


Pollution prevention -mixing effects

τ =10−5

Ao k1

=0.882ν 3/ 4 Lf

3/ 4

(u' ) 7/ 4

u’ = 0.45 π D N

5.29


2-minute discussion

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

1.E-05 1.E-04 1.E-03 1.E-02 1.E-01

(k1 Bo τ)(Ao/Bo)

Y/Yexp

Irreversible 2nd order competitive-consecutive reactions A + Bk1⎯ → ⎯ P

P + Bk2⎯ → ⎯ W

Suggest alternative ways to increase yield of P and decrease the generation of W besides increasing the agitation rate in the CSTR. Discuss with your neighbor for a minute:1.2.3..

Ao

BoCSTR


Pollution prevention -other reactor modifications

1. Improve Reactant Addition:

• premix reactants and catalysts prior to reactor addition

• add low density materials at reactor bottom to ensure effective mixing

2. Catalysts:

• use a heterogeneous catalyst to avoid heavy metal waste streams

• select catalysts with higher selectivity and physical characteristics

(size, porosity, shape, etc.)

3. Distribute flow in fixed-bed reactors

4. Heating/Cooling:

• use co-current coolant flow for better temperature control

• use inert diluents (CO2) to control temperature in gas phase reactions

5. Improve reactor monitoring and control


Pollution prevention - reactor types

1. CSTR:

• not always the best choice if residence time is critical

2. Plug flow reactor:

• better control over residence time

• temperature control may be a problem for highly exothermic reactions

3. Fluidized bed reactor :

• if selectivity is affected by temperature, tighter control is possible

4. Separative reactors:

• remove product before byproduct formation can occur: series reactions


Batch Reactive Distillation (BRD)

Malone, M.F., Huss, R.S., and Doherty, M.f., “Green Chemical Engineering: Aspects of Reactive Distillation, 2003, ES&T, 37(23), 5325-5329.

Damkohler No., Da

Ratio of process time to reaction time

DistillationColumn

BatchReactor


Separative reactors -with adsorption

2CH4 + 1/2O2 → C2H6 + H2O

2CH4 + O2 → C2H4 + 2H2O

CH4 + 2O2 → CO2 + 2H2O

Desired Reactions

Waste Reaction

Yields of product from CH4 increase from <20% to > 50%

Simulated Countercurrent Moving-bed Chromatographic Reactor

Reactors (1,000 ºK)

Chromatographic Columns (cool)

Allen, D.T. and Shonnard, D.R., “Green Engineering: Environmentally Conscious Design of Chemical Processes, Prentice-Hall, Upper Saddle River, NJ, 2002

CH4 + O4 in stoichiometric amts


Separative reactors -with membranes

Yields of product increase 15% and selectivity increases 2-5%

reactants

byproduct

product

membrane

reactant 1

reactant 2

product

A B

Product/byproduct removal mode

Reactant addition mode of operation

CH3CH2 – C6H6 → CH2CH – C6H6 + H2

Dehydrogenation of ethylbenzene to styrene reaction


Maleic ayhydride production: conversions and yields

n-Butane ProcessBenzene Process

OHCOOHCOHC 22324266 44292 ++→+

OHCOOOHC 22324 4 +→+

OHCOOHC 2266 61292 +→+

OHCOOOHC 222324 43 +→+

OHCOOHC 22266 612152 +→+

OHOHCOHC 23242104 8272 +→+

OHCOOOHC 22324 4 +→+OHCOOOHC 222324 43 +→+

OHCOOHC 22104 10892 +→+

OHCOOHC 222104 108132 +→+

V2O5-MoO3 VPO

n-butane conversion, 85%MA Yield, 60% Air/n-butane, ~ 62 (moles)Temperature, 400°CPressure, 150 kPa

Benzene conversion, 95%MA Yield, 70% Air/Benzene, ~ 66 (moles)Temperature, 375°CPressure, 150 kPa

Early Design Evaluation of Reaction Pathways


Maleic anhydride synthesisbenzene vs butane - summary table

Chapter 8Material

Stoichiometry 1 $/lb 2 TLV 3 TW 4 Persistence 5

Air Water (d) (d)

logBCF 5

Benzene Process

Benzene [71-43-2]

Maleic Anhydride

-1.19

1.00

0.184

0.530

10

0.25

100

----

10

1.7

10

7x10-4

1.0

----

Butane Process

Butane [106-97-8]

Maleic Anhydride

-1.22

1.00

0.141

0.530

800

0.25

----

----

7.25

1.7

----

7x10-4

----

----

1 Rudd et al. 1981, “Petroleum Technology Assessment”, Wiley Interscience, New York2 Chemical Marketing Reporter (Benzene and MA 6/12/00); Texas Liquid (Butane 6/22/00)3 Threshold Limit Value, ACGIH - Amer. Conf. of Gov. Indust. Hyg., Inc. , www.acgih.org4 Toxicity Weight, www.epa.gov/opptintr/env_ind/index.html and www.epa.gov/ngispgm3/iris/subst/index.html5 ChemFate Database - www.esc.syrres.com, EFDB menu item


Maleic anhydride synthesisbenzene vs butane - Tier 1 assessment

Benzene Route

Butane Route

(TLV Index)

Environmental Index (non - carcinogenic) = | ν i | × (TLVi )−1

i∑

TLV Index = (1.19)(1 / 10) + (1.0)(1 / .25) = 4.12

TLV Index = (1.22)(1 / 800) + (1.0)(1/ .25) = 4.00


EPA Index

Environmental Index (carcinogenic) = | ν i | × (Maximum toxicity weight)i i

∑

Benzene Route

Butane Route

EPA Index = (1.19)(100) + (1.0)(0) = 119

EPA Index = (1.22)(0) + (1.0)(0) = 0

Maleic anhydride synthesisbenzene vs butane - Tier 1 assessment


MA production: IO assumptions

Input / Output Information

Reactor ProductRecovery

PollutionControl

Benzeneorn-butane

Air MA, CO,CO2 , H2Oair

CO, CO2 , H2O, air, MA

Basis: 1 mole MA

UnreactedBenzeneorn-butane

CO2 H2O, airtraces of CO, MA benzene, n-butane

99% control

99% MA recovery


Maleic anhydride synthesisbenzene vs butane - Emissions

MA of lebenzene/mo mole 2.5x10 MA) of mole/mole (0.25 (0.01)

:Control Pollution from Emission Butane-n

MA of lebenzene/mo mole 0.25 0.85) - (1 mole) mole/0.60 (1

:Reactor Exiting Butane-n

MA of lebenzene/mo mole 7.14x10 MA) of mole/mole (0.0714 (0.01)

:Control Pollution from Emission Benzene

MA of lebenzene/mo mole 0.0714 0.95) - (1 mole) mole/0.70 (1

:Reactor Exiting Benzene

3-

4-

=×

=×

=×

=×

Michigan Technological University30MA mole

CO mole 8.33x10 MA) of mole/mole (0.833 (0.01)

:Control Pollution from Emission CO :Process Butane-n

MA mole

CO mole 0.833

2

4 0.6)-(0.85 mole) mole/0.60 (1

:Reactor Exiting CO :Process Butane-n

MA mole

CO mole 1.07x10 MA) of mole/mole (1.071 (0.01)

:Control Pollution from Emission CO :Process Benzene

MA mole

CO mole 1.071

2

6 0.7)-(0.95 mole) mole/0.70 (1

:Reactor Exiting CO :Process Benzene

3-

2-

=×

=××

=×

=××

Maleic anhydride synthesisbenzene vs butane – CO emissions

Michigan Technological University31MA mole

CO mole 2.69 9)(4)(0.01)(0.9 5)(4)(0.99)(0.2 33)(0.99)(0.8 (0.833)

:Control Pollution from Emission CO :Process Butane-n

MA mole

CO mole 0.833

2

4 0.6)-(0.85 mole) mole/0.60 (1

:Reactor Exiting CO :Process Butane-n

MA mole

CO mole 4.595 9)(4)(0.01)(0.9 714)(6)(0.99)(0.0 71)(0.99)(1.0 (3.071)

:Control Pollution from Emission CO :Process Benzene

MA mole

CO mole 3.071

2

6 0.7)-(0.95 mole) mole/0.70 (1 )

MA mole

CO mole 2MA)( mole (1

:Reactor Exiting CO :Process Benzene

2

2

2

2

2

2

22

2

=+++

=××

=+++

=××+

Maleic anhydride synthesisbenzene vs butane – CO2 emissions


Maleic anhydride (MA) production: Raw material costs

n-Butane Process

Benzene Process

“Tier 1” Economic analysis (raw materials costs only)

(1 mole/0.70 mole) × (78 g/mole) × (0.00028 $/g) = 0.0312 $/mole of MA

(1mole/0.60 mole) × (58 g/mole) × (0.00021 $/g) = 0.0203 $/mole of MA

MA Yield Bz MW Benzene cost

MA Yield nC4 MW nC4 cost

Assumption: raw material costs dominate total cost of the process

N-butane process has lower cost


Green Chemistry analysis:Pulp and paper bleaching

Pulp is the raw material used to manufacture products

like paper, paperboard, and fiberboard

Wood is the main source of 99% of the pulp fiber

produced in the United States

Bleaching of pulp is the final step in the manufacture

of high brightness paper

Wood is composed of, on a dry basis; cellulose (40-

50%), hemicellulose (15-25%), and lignin (25-30%)


Turning wood into unbleached pulp

Kraft Process – dissolve lignin and hemicellulose

Alkaline Digestion

170ºC18% Alkalinity3:1 NaOH:Na2S9:1 water:wood

Wood chips50% cellulose

20% hemicellulose30% lignin

Water

Unbeached pulp85% cellulose


Black liquor

Evaporation of Water

WaterCombustion

of Solids


Bleaching process 1

Bleaching using elemental chlorine, Cl2

ChlorinationUnbeached pulp85% cellulose


9:1 water:pulp(1 kg pulp / L solution)

NaOH Wash

Cl2

Brightening

NaOH Wash

ClO2

Brightening ClO2

Chlorinatedorganics

9 kg / ton pulp(Persistent

Bioaccumulative& Toxic)

Beached pulp100% cellulose


Bleaching process 2

Elemental chlorine free (ECF)

Chlorination, 70ºC

NaOH Wash , 50ºC

ClO2

Brightening , 70ºC

NaOH Wash , 50ºC

ClO2

Brightening , 70ºC ClO2

Chlorinatedorganics

0.5 kg / ton pulp(less PersistentBioaccumulative

& Toxic)






TAML™ activators

“tetraamido-macrocyclic ligand” activators

Hydroxyl radical(a natural oxidant

that removes lignin)

H2O2

T.J. Collins, 1999 Presidential Green Chemistry Challenge Award“TAML™ Oxidant Activators: General activation of hydrogen peroxide for green oxidation processes”

2 •OH

TAML™(mimics natural

enzymes)


Bleaching process 3

Total chlorine free – almost! (TCF)

Peroxidation, 50ºC

Peroxidation, 50ºC

Peroxidation, 50ºC

Brightening, 70ºC Chlorinatedorganics

0.0 kg / ton pulp(less PersistentBioaccumulative

& Toxic)





ClO2

TAML™

TAML™

TAML™

50 g / ton pulp


In-process energy analysis of pulp bleaching

In-process analysis (effect of lower temperature for

TAML™ process)

Energy Saved/ton pulp =2 stages x (20 x 9/5)ºF/stage x (2,200 Btu/ton water x 9 tons water / ton pulp)

= 1.426 x 106 Btu/ton pulp.

How large is this energy savings compared to the pulp and paper industry energy consumption???


Pulp and paper industry energy consumption

Industry energy intensity data

According to US Department of Energy statistics, in 1992 the pulp and paper industry consumed 2.6x1015 Btu

and produced 66x106 tons pulp

Energy Consumption Rate = 2.6x1015 Btu / 66x106 tons pulp

= 39.4x106 Btu/tons pulp


Energy savings

In-process analysis (TAML™ process comparison)

Energy Savings Percentage = 0.5 x 1.426/39.394 x 100

= 1.8%

Comments: The factor of 0.5 takes into account that only approximately ½ of the pulp produced in the U.S. is bleached. Considering that pulp and paper energy consumption alone is approximately 2.5% of the total United States energy consumption per year, this modest savings of 1.8% for the pulp and paper industry from a single Green Chemistry technology is quite significant on a national scale. Furthermore, it is remarkable that only a 20ºC stream temperature difference can make such a large impact on national energy consumption. But the stream flows in pulp and paper are very large, so the small temperature difference translated into a large energy savings.


Energy analysis: Expansion of system boundaries

H2O2 1.2 ton/ ton pulp

H2

Air

Natural Gas

Extraction of Natural

Gas

steam reforming

TAMLTM 50 g /

ton pulp

ClO2 0.2 ton/ ton pulp

NaClO3

2 HCl

NaCl Mining of NaCl

electrolysis 6 kWh/kg NaClO3

Cl2

electrolysis electrolysis

NaOH 0.07 ton/ ton pulp

NaCl Mining of NaCl

electrolysis Material flow chainenergy impacts

ClO2 bleaching

TAML bleaching

Material flow chainenergy impacts


Green Chemistry principles

Inherently green chemical reaction conditions

Atom economy / mass economy

Pollution prevention for chemical reactions

Early design evaluation of reaction pathways

Expansion of system boundaries

Module 3 review


Module 4: preview Evaluating process performance

Review of risk assessment concepts

Introduction to environmental multimedia models

Tier III environmental impact assessment for chemical process flowsheets

Early design application of Tier III environmental impact assessment

module 3. green chemistry - northwestern...

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