CHE 380: Sustainability in Chemical Engineering
Estimated study time: 9 minutes
Table of contents
Sources and References
Primary texts — Allen, D.T. and Shonnard, D.R., Sustainable Engineering: Concepts, Design, and Case Studies, Prentice Hall, 2012; Crowl, D.A. and Louvar, J.F., Chemical Process Safety: Fundamentals with Applications, 4th ed., Prentice Hall, 2019.
Supplementary texts — Turton, R. et al., Analysis, Synthesis, and Design of Chemical Processes, 5th ed., Prentice Hall, 2018; Peters, M.S., Timmerhaus, K.D., and West, R.E., Plant Design and Economics for Chemical Engineers, 5th ed., McGraw-Hill, 2003.
Online resources — MIT OCW 10.27 “Energy Engineering Projects Laboratory”; EPA Risk Management Program public documents; OSHA Process Safety Management standard 29 CFR 1910.119; CCPS AIChE open hazard identification resources; ISO 14040/14044 (public summaries) on life-cycle assessment; IPCC Assessment Reports.
Chapter 1: The Three Pillars of Sustainability
1.1 Framing
Sustainability in engineering rests on three interdependent pillars: environmental (emissions, resource depletion, ecosystems), economic (cost, value, feasibility), and social (safety, health, equity). Decisions that optimize one pillar at the expense of the others rarely endure. The Brundtland definition—meeting present needs without compromising future generations’ ability to meet theirs—guides professional responsibility.
1.2 Process Design Implications
Sustainability shapes every phase of design. At concept selection: which feedstock, which chemistry, which solvents? At flowsheet synthesis: heat integration, solvent recovery, byproduct valorization. At equipment sizing: overdesign wastes capital, underdesign costs throughput and safety. At operation: energy efficiency, waste minimization, plant safety culture. Retrofit of existing plants often offers more leverage than greenfield construction.
1.3 Green Chemistry Principles
Anastas and Warner’s twelve principles (prevention of waste, atom economy, less hazardous synthesis, designing safer chemicals, safer solvents and auxiliaries, energy efficiency, renewable feedstocks, reduced derivatives, catalysis, design for degradation, real-time analysis for pollution prevention, inherently safer chemistry for accident prevention) frame chemistry-level decisions. Atom economy,
\[ \text{AE} = \frac{\text{MW of desired product}}{\sum \text{MW of all reactants}}, \]differs from yield by including waste as stoichiometric byproducts.
Chapter 2: Health, Safety, and Environment (HSE)
2.1 Hazards and Risk
Hazard is the inherent potential to cause harm; risk multiplies hazard by exposure and likelihood. Engineers control risk by eliminating hazards (inherent safety) and, failing that, by engineered (active, passive) and administrative controls.
2.2 Toxicity and Exposure
Dose-response curves relate exposure to adverse effect. Threshold concepts: LD\(_{50}\) (acute), NOAEL, LOAEL, reference dose. Occupational exposure limits (TLV, PEL) cap workplace concentrations. For environmental releases, USEPA and equivalent agencies set ambient standards based on epidemiology and animal studies.
2.3 Flammability and Explosions
Flammable mixtures ignite between lower and upper flammability limits (LFL, UFL). Flash point marks the lowest temperature at which a liquid’s vapor will ignite; autoignition temperature marks spontaneous combustion without ignition source. Explosions partition into deflagrations (subsonic) and detonations (supersonic). Dust explosions, often underappreciated, require five elements: fuel, oxygen, ignition, dispersion, confinement.
2.4 Source Models
Release rates from holes, pipes, and vessels:
- Liquid through a hole: \( \dot m = C_d A \sqrt{2\rho(P - P_{atm})} \).
- Gas through a hole (choked flow): \( \dot m = C_d A P_0 \sqrt{\gamma M/(RT_0)}[2/(\gamma+1)]^{(\gamma+1)/(2(\gamma-1))} \).
- Two-phase flashing release: Homogeneous Equilibrium Model.
Dispersion models (Gaussian plume, Pasquill-Gifford stability classes) estimate downwind concentrations.
Chapter 3: Risk Assessment and Management
3.1 Hazard Identification Techniques
HAZOP (Hazard and Operability Study): a team systematically walks through each node of a process, applying guide words (NO, MORE, LESS, REVERSE, AS WELL AS, PART OF, OTHER THAN) to parameters (flow, temperature, pressure, composition). What-If analysis, checklists, FMEA (Failure Mode and Effects Analysis), and LOPA (Layer of Protection Analysis) complement HAZOP at different stages of design.
3.2 Consequence Analysis
Events of concern include toxic release, fire (pool, jet, flash, fireball), and explosion (VCE, BLEVE). Consequence models quantify downwind contours of lethality or injury. Probit functions relate dose (concentration × time, radiant flux × time, overpressure) to fraction of population affected.
3.3 Frequency Analysis
Fault trees and event trees quantify probability per year of top events. Generic failure rate data (CCPS, OREDA, IEEE Std 500) provide frequencies for common components. Monte Carlo propagation handles uncertainty in parameter estimates.
3.4 Risk Evaluation
Individual risk (probability of fatality per year for a specific person) and societal risk (F-N curves) are benchmarked against ALARP (As Low As Reasonably Practicable) criteria. Risk decisions are rarely purely technical; acceptability reflects social values.
Chapter 4: Environmental Impact
4.1 Life-Cycle Assessment
LCA evaluates environmental impact from cradle (raw material extraction) through grave (disposal) or cradle (recycling). The four ISO 14040/14044 phases: goal and scope definition, inventory analysis, impact assessment, interpretation. Impact categories: global warming potential, ozone depletion, acidification, eutrophication, human toxicity, ecotoxicity, resource depletion.
4.2 Emissions
Air: criteria pollutants (SO\(_2\), NO\(_x\), PM, CO, O\(_3\), Pb) and hazardous air pollutants. Water: BOD, COD, suspended solids, nutrients, heavy metals. Solid waste: municipal, hazardous (RCRA), universal. Fugitive emissions from valves, flanges, and pumps require Leak Detection and Repair (LDAR) programs.
4.3 Greenhouse Gases and Climate
Global warming potential (GWP) weights emissions by radiative forcing relative to CO\(_2\) over a 100-year horizon. CH\(_4\) GWP\(_{100}\) ≈ 28–34; N\(_2\)O ≈ 265–298; some refrigerants > 10 000. Carbon capture, utilization, and storage (CCUS) and electrification of process heating are prominent mitigation levers in chemical industries.
4.4 Regulations
Canada: Canadian Environmental Protection Act (CEPA), Environmental Emergency Regulations. United States: Clean Air Act, Clean Water Act, RCRA, TSCA. EU: REACH, CLP. Engineers must be conversant with applicable law; ignorance is not a defense.
Chapter 5: Economics of Chemical Processes
5.1 Capital Cost Estimation
Equipment cost correlations (power-law scaling: \( C = C_0 (S/S_0)^n \), typical \( n \approx 0.6 \)). Factored estimates (Lang factor, module factor) extend equipment cost to total installed cost. Classes of estimates range from Class 5 (±50%, order-of-magnitude) to Class 1 (±10%, detailed).
5.2 Operating Cost Estimation
Utilities (steam, cooling water, electricity, natural gas) are frequently dominant. Raw material costs, labor, maintenance (typically 4–6% of installed capital per year), overhead, insurance, and depreciation complete the picture.
5.3 Profitability Analysis
Net present value (NPV):
\[ NPV = -C_{TCI} + \sum_{k=1}^{N}\frac{CF_k}{(1+i)^k}. \]Internal rate of return (IRR), discounted payback period, and return on investment (ROI) are common metrics. Sensitivity analysis on price, cost, and capital assumptions reveals which assumptions drive profitability.
5.4 Project Economics and Uncertainty
Decision tree analysis, real options valuation, and Monte Carlo financial simulation handle uncertain markets, policies, and technology performance. Sustainability and economics intersect: carbon pricing, investor ESG expectations, and insurance costs increasingly internalize environmental externalities.
Chapter 6: Integrated Sustainability Analysis
6.1 Pollution Prevention Hierarchy
Source reduction > recycling > treatment > disposal. Engineers minimize waste at the source by better chemistry, tighter control, and inherently safer processes. End-of-pipe treatment is last resort.
6.2 Heat and Mass Integration
Pinch analysis identifies minimum utility requirements and optimal heat exchanger networks. Mass integration extends the same framework to solvent, water, and hydrogen systems. Retrofits guided by pinch analysis typically reduce energy consumption by 20–30%.
6.3 Metrics and Benchmarking
Engineering and sustainability metrics: E-factor (kg waste / kg product, typically 5–100 for fine chemicals, 0.1 for bulk chemicals), Process Mass Intensity, energy intensity, carbon intensity, water intensity. Benchmarking against industry leaders identifies improvement opportunities.
6.4 Case Study Thinking
Bhopal, Texas City, Piper Alpha, Buncefield, Deepwater Horizon—each accident taught lessons that shaped current practice. Studying cases trains judgment: how failure mode combinations defeat layered defenses; how normalization of deviance erodes safety culture; how economic pressure and safety investment trade off over time.
