How Can Reactive Chemical Incidents Be Prevented

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How Can Reactive Chemical Incidents Be Prevented?

• Dennis C. Hendershot (speaker)
• Albert Ness
• Rohm and Haas Company
• Engineering Division
• Croydon, PA, USA
• Dhendershot_at_rohmhaas.com
• For presentation at the
• Joint EFCOG/DOE Chemical Management Workshop
• March 8-10, 2005
• Washington, DC

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Agenda

• Discuss three reactive chemistry incidents
• In all three cases, no chemical reaction was
  INTENDED.
• Review two tools for identifying reactive
  chemistry hazards
• Briefly review checklist for design of reactive
  chemistry processes

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Three incidents

• Scrubber packing failure due to reaction with
  process materials
• Decomposition during a blending operation
• Fire from mixing of solid spills

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Three incidents

• Scrubber packing failure due to reaction with
  process materials
• Decomposition during a blending operation
• Fire from mixing of solid spills

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Scrubber packing failure due to reaction with
process materials
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What happened

• Power failure shuts off recirculation pumps and
  process water SO2 blower (steam driven)
  continued to run
• Acid vapors continued to flow to absorbers
• Flow not shutoff manually per instructions
• When power was restored acid unit restarted
• high temperature observed at top of acid scrubber
  
• abnormal pH readings observed (Temp high but
  within range)

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Consequences

• SO3 reacted with scrubber packing
• Plant had to be run at reduced rates for several
  months
• Cost was high enough to appear in company annual
  report

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Why?

• Reaction between SO3 and Polypropylene unknown to
  personnel reviewing process
• Reaction known others in company, but not at this
  location
• Scenario not identified in the Process Hazard
  Analysis (PHA)
• Unit shifted to keeping blower on to get vapors
  to the stack for environmental purposes

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Three incidents

• Scrubber packing failure due to reaction with
  process materials
• Decomposition during a blending operation
• Fire from mixing of solid spills

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Process description

• Blending only, no reaction intended
• 50/50 weight mixture of Linseed Oil and
  Cyclohexanone Oxime
• Dissolve the solid oxime at elevated temperature
• Rapidly cool solution in an external heat
  exchanger to make specified particle size slurry

• Linseed Oil a mixture of glycerides of
  unsaturated C18 fatty acids
• Oleic acid (1 double bond)
• Linoleic acid (2 double bonds)
• Linolenic acid (3 double bonds)

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Old production unit
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New production unit
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Process change

• Mix vessel temperature increased from 95 C to
  130 C
• Increased heat loss in longer pipe from mix
  vessel to heat exchanger in new system
• Same heat exchanger inlet temperature
• Management of change review held
• Did not identify any hazard associated with
  increased temperature

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First batch at higher temperature

• Temperature increased steadily over several hours
  from 133 C to 138 C
• Then, rate of temperature increase began to
  accelerate, ultimately reaching gt 170 C
• Pressure increase opened reactor relief valve on
  mix vessel discharging a two phase mixture to the
  atmosphere

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Consequences

• Relief valve size was adequate to protect the
  vessel from rupture
• By good luck, NOT DESIGN
• Relief valve not designed for unknown reaction
• No injuries
• Contaminated neighboring property
• Significant government agency involvement

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Results of laboratory ARC tests

• Cyclohexanone Oxime thermal stability
• Decomposition occurs at 180 C
• Oxime/oil 50/50 mixture
• Decomposition occurs at 128 C
• Normal product, without any contamination or
  other abnormal processing

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ARC results oxime
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ARC results - mixture
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What happened?

• Increasing the batch temperature from 95 C to
  130 C exceeded the decomposition temperature for
  a normal product mixture
• Decomposition did not require contamination or
  other process upset

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Specific actions

• Review all other products manufactured in the
  plant for potential decomposition hazards
• Improve management of change procedures to better
  recognize potential decomposition hazards from
  future changes
• Review all future new products for potential
  decomposition hazards

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Three incidents

• Scrubber packing failure due to reaction with
  process materials
• Decomposition during a blending operation
• Fire from mixing of solid spills

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Fire from mixing of solid spills

• Fire in production area near reactor
• Fire occurred under panel box
• Electrical and instrument wiring severely damaged
• 2 Reactor trains down for 1 month
• Total cost 1 Million

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Consequences
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What happened
These can react, generating heat and fire
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Common theme

• There is a common theme in all three incidents
• THE PEOPLE OPERATING THE PROCESS WERE NOT AWARE
  OF THE POTENTIAL FOR A REACTIVE CHEMISTRY
  INCIDENT.

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General lessons

• In a process hazard or management of change
  review, confirm that all materials and mixtures
  are stable at the maximum credible process
  temperature
• Absence of data does not mean that there is no
  decomposition or reaction, it may mean that
  nobody has done any testing
• Understand potential chemical interactions, even
  if you do not intend for a reaction to occur

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General lessons

• Be suspicious of energetic and potentially
  reactive chemical structures
• Double bonds, multiple double bonds, triple bonds
• Reactive groups
• Nitro groups, oximes, peroxides, etc.
• Strained ring structures, ring structures
  containing nitrogen, sulfur, oxygen, anything
  other than carbon
• Get advice from a chemist with experience with
  thermal decomposition, stability

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Some examples
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Free on-line resource

• http//info.knovel.com/ccps/
• Available free courtesy of US OSHA, US EPA,
  American Chemistry Council (ACC), Synthetic
  Organic Chemical Manufacturers Association
  (SOCMA), Center for Chemical Process Safety
  (CCPS), and Knovel

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Overall process
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Two specific tools

• Interaction Matrix
• Chemistry Hazard Analysis

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Generic chemical reaction
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Partial interaction matrix
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A famous process
Double, double toil and trouble Fire burn, and
cauldron bubble. Fillet of a fenny snake, In the
cauldron boil and bake Eye of newt and toe of
frog, Wool of bat and tongue of dog, Adder's fork
and blind-worm's sting, Lizard's leg and owlet's
wing, For a charm of powerful trouble, Like a
hell-broth boil and bubble. Double, double toil
and trouble Fire burn, and cauldron bubble. -
Macbeth, Act IV, Scene 1
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Interaction matrix
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NOAA Chemical Reactivity Worksheet results for
Incident 1 (SO3/Polypropylene)
B1 - May cause fire C1 - Heat generation by
chemical reaction, may cause pressurization D4 -
Nonflammable gas generation causes pressurization
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NOAA Chemical Reactivity Worksheet
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Chemistry Hazard Analysis

• Abbreviated HAZOP of Chemistry
• Start with the chemical reaction

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Chemistry Hazard Analysis procedure

• Apply HAZOP Guidewords to the reaction
• No Reverse
• More As Well As
• Less Other
• Not necessary to identify causes
• List consequences
• Make comments or recommendations

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Some examples

• NO reactant A, NO reactant B, NO Solvent, NO
  catalyst, NO reaction.
• MORE A, MORE B, MORE catalyst, MORE concentrated,
  MORE (HIGH) Temperature, MORE Feed time.
• LESS A, LESS B, LESS temperature, LESS reaction,
  LESS feed time..
• REVERSE reaction, REVERSE order of addition
• Other material AS WELL AS intended materials,
  Impurities AS WELL AS intended materials
• OTHER completely wrong material, no mixing, no
  cooling.

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Reactive Chemistry Design Checklist
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Questions to understand reactivity hazards

• What is the heat of reaction for all intended
  reactions? How about possible, but not intended
  reactions?
• What is the maximum adiabatic reaction
  temperature?

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Questions to understand reactivity hazards

• What is the maximum temperature from all process
  heating systems (assuming failure of all
  controls)?
• What is the maximum temperature to which the
  process material can be heated from other energy
  sources?
• For example, mechanical energy from pumping,
  agitation, grinding microwave energy other
  energy sources

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Questions to understand reactivity hazards

• Are all individual components of the mixture
  stable at the maximum attainable temperature?
• Raw materials, intermediates, products,
  by-products, catalysts, solvents, etc.
• Is the mixture stable at the maximum attainable
  temperature?

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Questions to understand reactivity hazards

• What is the minimum temperature from all process
  cooling systems (assuming failure of all
  controls)?
• What happens to the mixture at this temperature
• Freezing, precipitation, loss of reaction with
  accumulation of reactants, etc.

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Questions to understand reactivity hazards

• What is the effect of larger temperature and
  concentration gradients in production scale
  equipment?
• If you intend to do a chemical reaction, what are
  the reaction kinetics (intended reaction, side
  reactions, unintended reactions)?

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More detailed discussion

• See CCPS Safety Alert A Checklist for
  Inherently Safer Chemical Reaction Process Design
  and Operation
• Can be downloaded from
• http//www.aiche.org/ccps/safetyalerts.htm

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Chemistry haiku

• Laboratory.
• Someone mixes chemicals.
• Look! A reaction.
• - Neil Dickinson

Dont be surprised by a reaction!