Module 3. Evaluation of Alternative Reaction Pathways
Transcript of Module 3. Evaluation of Alternative Reaction Pathways
University of Texas at Austin Michigan Technological University1
Module 3: Evaluation of Alternative Reaction
PathwaysChapters 7 and 8
David T. AllenDepartment of Chemical Engineering
University of Texas at Austin
University of Texas at Austin Michigan Technological University2
Module 3: Outline
Educational goals and topics covered in the module
Potential uses of the module in chemical engineering courses
Green chemistry concepts - atom efficiency Tier 1 environmental impact assessment Green chemistry expert system (software) Adipic acid and maleic anhydride cases
University of Texas at Austin Michigan Technological University3
Module 3: Educational goals and topics covered in the module
Students will: understand the hierarchical design-for-environment approach
for chemical processes
learn qualitative and quantitative methodologies for Green Chemistry
be able to evaluate feedstocks, solvents, and alternative reaction pathways; both economically and environmentally.
University of Texas at Austin Michigan Technological University4
Module 3: Potential uses of the module in chemical engineering courses
Design course: Green Chemistry concepts and a screening of chemical products and raw materials on the basis of economics and environmental impacts
Reactor design course: Waste and risk minimization approaches
University of Texas at Austin Michigan Technological University5
Module 3: Hierarchical design process for pollution prevention
Design Stage P2 Tools EnvironmentalEvaluation
BookChapter
1. Reaction pathways, conversions, and yields, raw materials, solvents
• Green Chemistry• atom efficiency
Tier 1 7, 8
2. Flowsheet systhesis, specific process units defined
Release estimation,optimum choice of • mass separating agents • process units • processing conditions
Tier 2 8, 9
3. Detailed design • Process integration methods• multimedia environmental fate modeling• relative risk assessment
Tier 3 10, 11
University of Texas at Austin Michigan Technological University6
Guiding principles for reactions» Simplicity» Safety» High yield and selectivity» High energy and atom efficiency» Use of renewable resources» Recyclable reagents and raw materials
Module 3: Green Chemistry - Ch 7
University of Texas at Austin Michigan Technological University7
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
Module 3: Feedstocks and solvents
University of Texas at Austin Michigan Technological University8
Module 3: Alternative choices: raw materialsBenzene• fossil fuel source• carcinogenic
Glucose• renewable source• non-toxic
University of Texas at Austin Michigan Technological University9
Module 3: 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
University of Texas at Austin Michigan Technological University10
Module 3: Synthesis pathways
Reaction Type Waste Generation Potential
Addition ReactionIsobutylene + methanol methyl tert-butyl etherC4H8 + CH3OH (C4H9)-O-CH3
• completely incorporate starting material into product
Substitution ReactionPhenol + ammonia analine + waterC6H5-OH+ NH3 C6H5-NH2 + H2O
• stoichiometric amounts of waste are generated
Elimination ReactionEthylbenzene styrene + hydrogenC6H5-C2H5 C6H5-C2H3 + H2
• stoichiometric amounts of waste are generated
University of Texas at Austin Michigan Technological University11
Module 3: 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 gramsMass in Reactants = (6 C) (12) + (9 H) x (1) + (1 O) x 16) + (1 N) x (14) = 111 gramsMass Efficiency = 93/111 x 100 = 83.8%
University of Texas at Austin Michigan Technological University12
Module 3: Software explorationGreen 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
University of Texas at Austin Michigan Technological University13
Module 3: Software demonstration Green Chemistry Expert System
search Green Synthetic Reactions for adipic acid references
University of Texas at Austin Michigan Technological University14
Module 3: Adipic Acid SynthesisTraditional 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
• 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
University of Texas at Austin Michigan Technological University15
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%
Module 3: Adipic Acid SynthesisTraditional vs. New
Sato, et al. 1998, A “green” route to adipic acid:…, Science, V. 281, 11 Sept. 1646 - 1647
University of Texas at Austin Michigan Technological University16
Module 3: Maleic Anhydride SynthesisBenzene vs 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
95% 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
University of Texas at Austin Michigan Technological University17
Module 3: 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
University of Texas at Austin Michigan Technological University18
Module 3: Maleic Anhydride SynthesisBenzene vs Butane - Tier 1 Assessment
Benzene Route
Butane Route
(TLV Index)
Environmental Index (non - carcinogenic) = | 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
University of Texas at Austin Michigan Technological University19
EPA Index
Environmental Index (carcinogenic) = | 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
Module 3: Maleic Anhydride SynthesisBenzene vs Butane - Tier 1 Assessment
University of Texas at Austin Michigan Technological University20
Educational goals and topics covered in the module
Potential uses of the module in chemical engineering courses
Green chemistry concepts Tier 1 environmental impact assessment Green chemistry expert system (software) Adipic acid and maleic anhydride cases
Module 3: Recap
University of Texas at Austin Michigan Technological University21
Module 3: Explore Green Chemistry Expert System
search Green Solvents/Reaction ConditionsDesigning Safer Chemicals