Chemical Reactivity
Chapter 8: Crowl & Louvar
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Chemical Reactive Hazard
Chemical reactivity hazard: situation with potential for
an uncontrolled chemical reaction, resulting in harm to
people, equipment, or environment.
Result could be:
• Violent release of heat, toxic or flammable materials
• Build up of excessive pressure
Reaction could be:
• Self-reacting chemical (i.e., monomer)
• With other chemicals; intentional or otherwise
• Catalyzed by contamination, construction materials
• Exothermic and/or gas producing
• Due to incompatibility
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Screening for Reactive Hazards
Figure 8-1 Screening flowchart for reactive chemical hazards. An answer of “yes” at any decision point
moves more toward reactive chemisty. See Section 8.2 for more details. (Source: R.W.
Johnson, S.W. Rudy, and S. D. Unwin, Essential Practices for Managing Chemical
Reactivity Hazards (New York: AIChE Center for Chemical Process Safety, 2003.))
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Specific Chemical Reactive Hazard
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Specific Chemical Reactive Hazard
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Specific Chemical Reactive Hazard
http://response.restoration.noaa.gov/chemaids/react.html
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Specific Chemical Reactive Hazard
• Table AF-1: A few pyrophoric and spontaneously combustible
categories and chemicals (these materials combust on exposure
to air).
• Table AF-2: Some chemical structures susceptible to peroxide
formation (the peroxides formed may become unstable and
explode when disturbed).
• Table AF-3: Chemical categories susceptible to water
reactivity.
• Table AF-4: Common water-reactive chemicals.
• Table AF-5: Typical oxidizers.
• Table AF-6: Some polymerizing compounds (these chemicals
may polymerize rapidly with release of large amounts of heat).
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Reactive Functional Groups
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Sources of Information
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Understanding Reactive Systems
Cooling Water
Exothermic
Reaction
Why important: Common problem with exothermic
reactions.
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Understanding Reactive Systems
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Runaway Reactions
How?
1. Loss of coolant.
2. Increased temperature.
3. Increased energy generation.
High pressure due to: Vapor pressure of liquid.
Vapor decomposition products.
Larger vessels respond faster - less heat transfer thru
walls!!!
Some chemicals can achieve self heat rates of 100’s
deg. C/min! Styrene, Acrylic Acid
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Runaway Reactions
Some ways for runaways to occur:
• Loss of cooling.
• Overcharge reactant.
• External fire.
• Mis-charge reactant.
• Low reaction temperature in semi-batch
reactor. This is called a sleeping reactor.
• Loss of agitation.
Most reactive runaways result in 2-phase flow thru
relief and require a relief area 2 to 10 times larger
than single phase relief.
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Understanding Reactive Systems
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Application of Calorimeter Data
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Heat exchanger duty to achieve required reactor cooling
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Cooling water requirements and cooling water pump size
•
Condenser size in a reactor reflux system
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Max conc. Of reactants to prevent overpressure in the reactor
•
Reactor vessel size and pressure rating
•
Type of reactor (batch, semi-batch, tubular)
•
Reactor temperature control and sequencing
•
Semi-batch reactor reactant feed rates
•
Catalyst concentrations; max fill for batch and semi-batch reactors
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Alarm/shutdown setpoints
•
Operating and emergency procedures
•
Relief sizing and effluent treatment systems
• Solvent concentrations required to control reactor temperature
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Improving Reactive Safety
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Improving Reactive Safety
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In-Class Exercise
A company had a spray painting operation to paint automotive
parts. The spray painting was done in a paint booth to reduce
worker’s exposure and to collect any paint droplets that might be
entrained in the exhaust air. The paint droplets were collected
by fibrous filters. At the end of each day, the filters were
removed, placed in plastic bags, and stored for disposal in a
separate building.
Due to environmental concerns over volatile emissions from paint
solvents, the paint supplier reformulated the paint to use a less
volatile solvent. This change was done in consultation with the
paint company.
Several test were done to ensure the
reformulated paint worked well with the existing spray equipment
and that the quality was satisfactory.
The company switched to the reformulated paint. Several days
later the disposal building caught on fire, apparently due to a fire
started by the paint filters. Can you explain how this might have
happened. Any suggestions for prevention?
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In-Class Exercise
A university lab expansion includes installation of a distribution
system to provide gaseous oxygen from manifolded cylinders to a
biochemical engineering laboratory.
No chemical reactivity
hazards have been previously identified for the lab facilities.
Apply the screening
method of Figure 8-1
to determine if any
chemical reactivity
hazards are
expected.
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Runaway Reactions - 4
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