Green Chemistry and Green Chemical Engineering Part 2
Process Technology
- Prevent waste rather than treat it.
- Use and generate non-toxic substances.
- Choose substances so as to minimize the potential for chemical accidents, including releases, explosions, and fires.
- Auxiliary substances (solvents, etc.) should be made unnecessary wherever possible and innocuous when used.
- Recognized energy requirements for their environmental and economic impacts, and minimize them.
Unit Operations and Pollution Prevention
• Key principles:
– consider the environmental impact of each unit operation as the process is being designed
– don’t wait until the flowsheet is completed to perform an environmental impact assessment
Environmental Performance Evaluation Tools
Tier 2 Tools: To evaluate the process flowsheet
– Environmental release assessment (what is released)
– Quantification of release (how much is released)
– Flowsheet evaluation (overall impact)
Typical Waste Emission Sources from Chemical Processes
1. Waste streams from process units
2. Major equipment - vents on reactors, column separators, storage tanks, vacuum systems,
3. Fugitive sources - large number of small releases from pumps, valves, fittings, flanges, open pipes,
4. Loading/unloading operations
5. Vessel clean out, residuals in drums and tanks
6. Secondary sources - emissions from wastewater treatment, other waste treatment operations, on-site land applications of waste,
7. Spent catalyst residues, column residues and tars, sludge from tanks, columns, and wastewater treatment,
8. Energy consumption - criteria air pollutants, traces of hazardous air pollutants, global warming gases
Important Issues Regarding Pollution
Prevention for Unit Operations
1. Material selection: fuel type, mass separating agents (MSAs), air, water, diluents, heat transfer fluids
2. Operating conditions: temperature, pressure, mixing intensity
3. Energy consumption: high efficiency boilers, operation of units to minimize energy usage
4. Material storage and fugitive sources: storage tank choices and equipment monitoring and maintenance
5. Waste generation mechanisms: understanding this will lead to pollution prevention strategies
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