Post on 04-May-2018
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
Michigan Technological University2
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
Michigan Technological University3
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
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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
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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 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
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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
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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 propertieshttp://www.epa.gov/oppt/greenengineering
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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 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
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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
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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 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
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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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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
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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
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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
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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
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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
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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)
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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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%)
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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
10% hemicellulose5% lignin
Black liquor
Evaporation of Water
WaterCombustion
of Solids
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Bleaching process 1
Bleaching using elemental chlorine, Cl2
ChlorinationUnbeached pulp85% cellulose
10% hemicellulose5% lignin
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
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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)
Beached pulp100% cellulose
Unbeached pulp85% cellulose
10% hemicellulose5% lignin
9:1 water:pulp(1 kg pulp / L solution)
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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)
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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)
Beached pulp100% cellulose
Unbeached pulp85% cellulose
10% hemicellulose5% lignin
9:1 water:pulp(1 kg pulp / L solution)
ClO2
TAML™
TAML™
TAML™
50 g / ton pulp
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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???
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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
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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.
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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
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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
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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