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