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 Michigan Technological University

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Module 3 overview z

Green Chemistry principles (chapter 7)

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Inherently green chemical reaction conditions (chapter 7)

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Atom economy / mass economy (chapter 7)

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Pollution prevention for chemical reactions (chapter 9)

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Early design evaluation of reaction pathways (chapter 8)

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Expansion of system boundaries (chapter 13)

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12 Principles of Green Chemistry z z z z z z z z z

z z z

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. Michigan Technological University

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Feedstocks and solvents z

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 Michigan Technological University

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Alternative choices: raw materials Benzene • fossil fuel source • carcinogenic Glucose • renewable source • non-toxic

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Alternative choices: Solvents Supercritical CO2 Non-toxic, non-flammable, renewable sources Selectivity enhancement with SC CO2

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

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Synthesis pathways Reaction Type

Waste Generation Potential

Addition Reaction

• completely incorporate starting material into product

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

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

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

• stoichiometric amounts of waste are generated

• stoichiometric amounts of waste are generated

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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 properties http://www.epa.gov/oppt/greenengineering Michigan Technological University

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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%

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Adipic acid synthesis Traditional vs. New Traditional Route - from cyclohexanol/cyclohexanone Cu (.1-.5%) C6H12O+ 2 HNO3 + 2 H2O

C6H10O4 + (NO, NO2, N2O, N2) V (.02-.1%)

92-96% Yield of Adipic Acid

hazardous

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

global warming ozone depletion

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%

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

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Adipic Acid Synthesis Traditional vs. New New Route - from cyclohexene Na2WO4•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% Sato, et al. 1998, A “green” route to adipic acid:…, Science, V. 281, 11 Sept. 1646 - 1647

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Maleic anhydride synthesis: Benzene vs n-butane - mass efficiency Benzene Route (Hedley et al. 1975, reference in ch. 8) V2O5 2 C6H6 + 9 O2 (air)

2 C4H2O3 + H2O + 4 CO2 MoO3

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

Mass Efficiency =

2(4)(12) + 3(2)(16) + 2(2)(1) (100) = 44.4% 2(6)(12) + 9(2)(16) + 2(6)(1)

Butane Route (VO)2P2O5 C4H10 + 3.5 O2 (air)

C4H2O0 + 4 H2O

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

Mass Efficiency =

(4)(12) + (3)(16) + (2)(1) (100) = 57.6% (4)(12) + 3.5(2)(16) + (10)(1)

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

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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

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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

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Pollution prevention for chemical reactions CH4 + H2O ↔ CO + 3H2 CO + H2O ↔ CO2 + H2

Reversible Series Reactions Steam reforming of CH4 R = CH4 P = CO W = CO2

Separate and recycle waste to extinction 15

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Pollution prevention mixing effects

CSTR

Bo Ao

k1 A + B ⎯⎯ →P

Irreversible 2nd order competitive-consecutive reactions 1

k2 →W P + B ⎯⎯

0.95 0.9 0.85

Y/Yexp

0.8

Yexp

⎡ A ⎛ A ⎞ k 2 / k1 ⎤ P R 1 ⎥ ⎢ = = −⎜ ⎟ Ao (k2 / k1 − 1) ⎢⎣ Ao ⎝ Ao ⎠ ⎦⎥

0.75 0.7

Y = yield = P/Ao Yexp = expected yield τ = mixing time scale Increased mixing will increase observed yield

0.65

1.E-05

1.E-04

1.E-03

(k1 Bo τ)(Ao/Bo)

1.E-02

0.6 1.E-01

Increased mixing

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Pollution prevention mixing effects 3/ 4 10 −5 0.882ν Lf = 7/ 4 Ao k1 (u' ) 3/ 4

τ=

5.29

u’ = 0.45 π D N

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CSTR

Bo

2-minute discussion

Ao

Irreversible 2nd order competitive-consecutive reactions

k1 A + B ⎯⎯ →P k2 →W P + B ⎯⎯

1 0.95 0.9 0.85

Y/Yexp

0.8 0.75 0.7 0.65

1.E-05

1.E-04

1.E-03

1.E-02

(k1 Bo τ)(Ao/Bo)

0.6 1.E-01

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. .

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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 Michigan Technological University

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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

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Batch Reactive Distillation (BRD) Distillation Column

Damkohler No., Da Batch Reactor

Ratio of process time to reaction time

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

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Separative reactors with adsorption Simulated Countercurrent Moving-bed Chromatographic Reactor

CH4 + O4 in stoichiometric amts

Desired Reactions 2CH 4 + 1/2O2 → C2H6 + H2O 2CH4 + O2 → C2H4 + 2H2O Reactors (1,000 ºK) Chromatographic Columns (cool)

Waste Reaction CH4 + 2O2 → CO2 + 2H2O

Yields of product from CH4 increase from 50% Allen, D.T. and Shonnard, D.R., “Green Engineering: Environmentally Conscious Design of Chemical Processes, Prentice-Hall, Upper Saddle River, NJ, 2002

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Separative reactors with membranes membrane byproduct

reactant 2 product

reactant 1

reactants

product

A

B

Product/byproduct removal mode

Reactant addition mode of operation

CH3CH2 – C6H6 → CH2CH – C6H6 + H2 Dehydrogenation of ethylbenzene to styrene reaction

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

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Maleic ayhydride production: conversions and yields Early Design Evaluation of Reaction Pathways Benzene Process

n-Butane Process

V2O5-MoO3

2C6 H 6 + 9O2 → 2C 4 H 2 O3 + 4CO2 + 4 H 2 O

VPO

2C 6 H 6 + 9O 2 → 12CO + 6 H 2 O

2C 4 H 10 + 7O2 → 2C 4 H 2 O3 + 8H 2 O 2C 4 H 10 + 9O2 → 8CO + 10 H 2 O

2C 6 H 6 + 15O 2 → 12CO 2 + 6 H 2 O C 4 H 2 O3 + O 2 → 4CO + H 2 O C4 H 2O3 + 3O2 → 4CO2 + H 2O

2C 4 H 10 + 13O2 → 8CO2 + 10 H 2 O C 4 H 2 O3 + 3O2 → 4CO2 + H 2 O C 4 H 2 O3 + O2 → 4CO + H 2 O

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

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

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Maleic anhydride synthesis benzene vs butane - summary table Stoichiometry 1

Chapter 8 Material

$/lb 2

TLV 3

TW 4

Persistence 5 Air (d)

Water (d)

log BCF 5

Benzene Process Benzene [71-43-2]

-1.19

0.184

10

100

10

10

1.0

Maleic Anhydride

1.00

0.530

0.25

----

1.7

7x10-4

----

Butane [106-97-8]

-1.22

0.141

800

----

7.25

----

----

Maleic Anhydride

1.00

0.530

0.25

----

1.7

7x10-4

----

Butane Process

1 Rudd et al. 1981, “Petroleum Technology Assessment”, Wiley Interscience, New York 2 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.org 4 Toxicity Weight, www.epa.gov/opptintr/env_ind/index.html and www.epa.gov/ngispgm3/iris/subst/index.html 5 ChemFate Database - www.esc.syrres.com, EFDB menu item

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Maleic anhydride synthesis benzene vs butane - Tier 1 assessment (TLV Index) Environmental Index (non - carcinogenic) =

∑|ν

i

| × (TLVi )−1

i

Benzene Route

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

Butane Route

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

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Maleic anhydride synthesis benzene vs butane - Tier 1 assessment EPA Index Environmental Index (carcinogenic) =

∑| ν | × (Maximum toxicity weight) i

i

i

Benzene Route

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

Butane Route

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

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MA production: IO assumptions Input / Output Information CO2 H2O, air traces of CO, MA benzene, n-butane

Benzene or n-butane

Unreacted Benzene or n-butane

Reactor Air

MA, CO, CO2 , H2O air

Pollution Control 99% control CO, CO2 , H2O, air, MA

Product Recovery 99% MA recovery

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Basis: 1 mole MA 28

Maleic anhydride synthesis benzene vs butane - Emissions Benzene Exiting Reactor : (1 mole/0.70 mole) × (1 - 0.95) = 0.0714 mole benzene/mo le of MA Benzene Emission from Pollution Control : (0.01) × (0.0714 mole/mole of MA) = 7.14x10 - 4 mole benzene/mo le of MA n - Butane Exiting Reactor : (1 mole/0.60 mole) × (1 - 0.85) = 0.25 mole benzene/mo le of MA n - Butane Emission from Pollution Control : (0.01) × (0.25 mole/mole of MA) = 2.5x10 -3 mole benzene/mo le of MA 29

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Maleic anhydride synthesis benzene vs butane – CO emissions Benzene Process : CO Exiting Reactor : (1 mole/0.70 mole) × (0.95 - 0.7) ×

6 mole CO = 1.071 2 mole MA

Benzene Process : CO Emission from Pollution Control : (0.01) × (1.071 mole/mole of MA) = 1.07x10 -2

mole CO mole MA

n - Butane Process : CO Exiting Reactor : (1 mole/0.60 mole) × (0.85 - 0.6) ×

4 mole CO = 0.833 2 mole MA

n - Butane Process : CO Emission from Pollution Control : (0.01) × (0.833 mole/mole of MA) = 8.33x10 -3 Michigan Technological University

mole CO mole MA

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Maleic anhydride synthesis benzene vs butane – CO2 emissions Benzene Process : CO2 Exiting Reactor : (1 mole MA)(

2 mole CO2 6 mole CO2 ) + (1 mole/0.70 mole) × (0.95 - 0.7) × = 3.071 mole MA 2 mole MA

Benzene Process : CO2 Emission from Pollution Control : (3.071) + (0.99)(1.071) + (0.99)(0.0714)(6) + (0.01)(0.99)(4) = 4.595

mole CO2 mole MA

n - Butane Process : CO2 Exiting Reactor : (1 mole/0.60 mole) × (0.85 - 0.6) ×

4 mole CO2 = 0.833 2 mole MA

n - Butane Process : CO2 Emission from Pollution Control : (0.833) + (0.99)(0.833) + (0.99)(0.25)(4) + (0.01)(0.99)(4) = 2.69 Michigan Technological University

mole CO2 mole MA 31

Maleic anhydride (MA) production: Raw material costs “Tier 1” Economic analysis (raw materials costs only) Benzene Process (1 mole/0.70 mole) × (78 g/mole) × (0.00028 $/g) = 0.0312 $/mole of MA

MA Yield

Bz MW

Benzene cost

N-butane process has lower cost

n-Butane Process (1mole/0.60 mole) × (58 g/mole) × (0.00021 $/g) = 0.0203 $/mole of MA

MA Yield

nC4 MW

nC4 cost

Assumption: raw material costs dominate total cost of the process Michigan Technological University

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Green Chemistry analysis: Pulp and paper bleaching

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Pulp is the raw material used to manufacture products like paper, paperboard, and fiberboard

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Wood is the main source of 99% of the pulp fiber produced in the United States

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Bleaching of pulp is the final step in the manufacture of high brightness paper

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Wood is composed of, on a dry basis; cellulose (4050%), hemicellulose (15-25%), and lignin (25-30%) 33

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Turning wood into unbleached pulp

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Kraft Process – dissolve lignin and hemicellulose Alkaline Digestion

Wood chips 50% cellulose 20% hemicellulose 30% lignin

Water

170ºC 18% Alkalinity 3:1 NaOH:Na2S 9:1 water:wood

Unbeached pulp 85% cellulose 10% hemicellulose 5% lignin

Black liquor Water

Evaporation of Water

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Combustion of Solids 34

Bleaching process 1

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Bleaching using elemental chlorine, Cl2 Unbeached pulp

85% cellulose 10% hemicellulose 5% lignin 9:1 water:pulp (1 kg pulp / L solution)

Chlorination

Cl2 Chlorinated organics

NaOH Wash Brightening

ClO2

NaOH Wash Brightening

9 kg / ton pulp (Persistent Bioaccumulative & Toxic)

ClO2

Beached pulp 35

100% cellulose

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Bleaching process 2

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Elemental chlorine free (ECF) Unbeached pulp

85% cellulose 10% hemicellulose 5% lignin 9:1 water:pulp (1 kg pulp / L solution)

Chlorination, 70ºC

ClO2

NaOH Wash , 50ºC

Chlorinated organics

Brightening , 70ºC

0.5 kg / ton pulp (less Persistent Bioaccumulative & Toxic)

ClO2

NaOH Wash , 50ºC Brightening , 70ºC

ClO2

Beached pulp 100% cellulose

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TAML™ activators

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“tetraamido-macrocyclic ligand” activators TAML™ (mimics natural enzymes)

H2O2

2 •OH

Hydroxyl radical (a natural oxidant that removes lignin)

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

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Bleaching process 3

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Total chlorine free – almost! (TCF) 50 g / ton pulp

Unbeached pulp 85% cellulose 10% hemicellulose 5% lignin 9:1 water:pulp (1 kg pulp / L solution)

ClO2

Peroxidation, 50ºC

TAML™

Peroxidation, 50ºC

TAML™

Peroxidation, 50ºC

TAML™

Brightening, 70ºC Beached pulp 100% cellulose Michigan Technological University

Chlorinated organics 0.0 kg / ton pulp (less Persistent Bioaccumulative & Toxic) 38

In-process energy analysis of pulp bleaching z

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???

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Pulp and paper industry energy consumption z

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

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Energy savings z

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. 41

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Energy analysis: Expansion of system boundaries ClO2 bleaching

Mining of NaCl

NaCl

electrolysis 6 kWh/kg NaClO3

electrolysis

electrolysis Cl2

Material flow chain energy impacts

TAML bleaching

Extraction of Natural Gas

Mining of NaCl

Natural Gas

NaClO3

2 HCl

electrolysis NaCl

steam reforming

H2

Air

Material flow chain energy impacts Michigan Technological University

ClO2 0.2 ton/ ton pulp

NaOH 0.07 ton/ ton pulp

H2O2 1.2 ton/ ton pulp

TAMLTM 50 g / ton pulp

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Module 3 review z

Green Chemistry principles

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Inherently green chemical reaction conditions

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Atom economy / mass economy

z

Pollution prevention for chemical reactions

z

Early design evaluation of reaction pathways

z

Expansion of system boundaries

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Module 4: preview Evaluating process performance z

Review of risk assessment concepts

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Introduction to environmental multimedia models

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Tier III environmental impact assessment for chemical process flowsheets

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Early design application of Tier III environmental impact assessment

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