Reactive chemical hazards - PowerPoint Presentation

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Reactive chemical hazards

This module provides a systematic and simplified way to to understand and identify reactive chemical hazards (RCH in short).

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About the module

This module is developed for undergraduate Chemical Engineering students prior to plant design project.The goal of this

module

is to:Raise awareness of RCH studyMotivate students to study RCH by showcase the consequences from RCHHelp students to understand the nature of RCHProvide tools for students to identify RCHProvide examples for students to estimate the extent of RCHControl and Prevention of RCH will not be discussed in details in this module as it involves substantial technical and theoretical learning.

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What

can happen?3Slide4

Table of Contents

IntroductionDefinition of Hazard and RiskDefinition of Reactive Chemical Hazards (RCH)Desired and Undesired ReactionsType of

RCH

Process of RCH StudiesUnderstandingQualify RCHQuantify RCHControl and PreventionReferences4Slide5

Hazard and Risk Definition

“•“ An intrinsic chemical, physical, societal, economic or political condition that has the potential for causing damage to a risk receptor (people, property or the environment)”•“A measure of the human injury, environmental damage or economic loss in terms of both the frequency and the magnitude of the loss of injury”

•

-- Definition from the Centre for Chemical Process Safety

5IntroductionType of RCHProcess of RCH StudiesReferencesSlide6

R

eactive Chemical Hazard (RCH) DefinitionReactivity: Tendency

of

substances to undergo chemical changeA reactive chemical hazard (RCH) is a situation with the potential for an UNCONTROLLED chemical reaction – with significant increases in Temperature, Pressure, and/or gas evolution – that can result directly or indirectly in serious harm to people, property or the environment6IntroductionType of RCHProcess of RCH StudiesReferencesSlide7

Nature of RCH…

Chemical reactions involve energy changesMost reactions liberate energy as

heat

– exothermicSome energy is absorbed into products – endothermicRCH involves high rates of energy releaseToo high to be absorbed by the immediate environment of the reacting systemResult in damagesSafeguarding information is provided later in this presentation7IntroductionType of RCH

Process of RCH Studies

ReferencesSlide8

Desired and Undesired Reactions

Desired reactions can be controlledProcess Hazards Analysis – assess effect of deviations on process conditionsE.g. temperature, feed rate, pressure, etc… Undesired reactions must be preventedTypes of undesired reactions: Side

reactions

Mixing of incompatible chemicals

Formation of self-reacting chemicalsUnintended decomposition8IntroductionType of RCHProcess of RCH StudiesReferencesSlide9

Significant Disasters in History

9

Involving

Desired ReactionsInvolving Undesired ReactionsSeveso, Italy 1976 (alkaline hydrolysis runaway reaction)Negaunee, Michigan 1878Nitro-Glycerine Tragedy (self-reacting impact sensitive)Jacksonville, Florida 2007(T2 laboratory explosion due to runaway reactions)Bhopal, India 1984 (mixing of incompatible chemicals: MIC+water)IntroductionType of RCHProcess of RCH StudiesReferencesSlide10

Recap

After reading the case studies, which of the following is NOT a cause from chemical reactivity disasters?Untrained laboursFalse alarmUncontrolled reactionLack of responsibility

None of the above

ALL contributes to a potential disaster!!!

10IntroductionType of RCHProcess of RCH StudiesReferencesSlide11

Types of RCH?

Self-Reacting impact-sensitive or thermally sensitive materialsRunaway reactions

Chemical incompatibility

11

IntroductionType of RCHProcess of RCH StudiesReferencesSlide12

Self

-Reacting impact-sensitive or thermally sensitive materialsWhen subjected to heat or impact, these chemicals may rapidly decompose, resulting in a potentially explosive release of energy.

These

are undesired or unintentional reactionsExamples: organic peroxidescopper acetylide 12IntroductionType of RCHProcess of RCH StudiesReferencesSlide13

Chemical

Incompatibility13

Between two or more substances

These hazards occur when a chemical is suddenly mixed or comes into contact with another chemical, resulting in a violent reaction.

These are undesired and unintentional reactionsExamples: Strong acids and strong basesWater reactive materials (sodium metal and water)Pyrophoric materials (iron sulfide and oxygen)

Introduction

Type of RCH

Process of RCH Studies

ReferencesSlide14

Runaway Reactions

14

Predominantly

involves desired/intentional reactionsSelf-reactive chemicals or mixturesIn an out-of-control reaction involving a chemical or chemical mixture, the rate at which heat is generated exceeds the rate at which it is removed through cooling media and surroundings. For example:Polystyrene batch reaction and loss of jacketed cooling controlAcetylene hydrogenation reaction and inadequate heat removal per gas flow through

reactor

U

sually

occur

during

scale

-up

as

t

he

system

becomes

more

adiabatic

as

it

increases

in

size

Introduction

Type of RCH

Process of RCH Studies

ReferencesSlide15

Recap

“In order to prevent RCH for undesired chemical reactions, we need to establish sufficient control via safety mechanisms” True or False?Answer: False“In order to prevent Reactive Chemical Hazards for undesired chemical reactions, the easiest

way

is to PREVENT incompatible materials from contacting”15IntroductionType of RCHProcess of RCH StudiesReferencesSlide16

Break time

Bhopal disaster made into a movie (watch the trailer here)16

Introduction

Type of RCH

Process of RCH StudiesReferencesSlide17

P

rocess for RCH Studies17

Step 1: What reactivity hazard question is being studied?

Desired

Concern for runawayUndesiredSingle chemical: instabilityMore than one chemical: incompatibilityStep 2: Conduct Literature Research (qualitative review)Step 3: Is information researched sufficient to make a definitive decision on reactivity hazard for specific situation under consideration?

Conclude investigation, document findings and necessary recommendations

Use qualified labs to conduct controlled/safe lab testing. Quantification can involve

calorimetry

test for heat release and kinetics

Introduction

Type of RCH

Process of RCH Studies

References

NO

YESSlide18

Step 1: Understanding

After defining the system boundary, ask this question

:

Which of the two scenario is involved? Chemical reacting by design/Desired reactione.g. desired productionChemical reacting by accident/Undesired reactione.g. inadvertent mixing of chemicals18IntroductionType of RCHProcess of RCH StudiesReferencesSlide19

Step 2: Qualify RCH – a screening tool

19Sources to

Identify

RCHReactive Functional Groups MSDS (Material Safety Data Sheet) International Chemical Safety Data CardNOAA reactivity worksheetS2S RCH online assessment Oxygen BalanceIntroductionType of RCHProcess of RCH StudiesReferencesSlide20

Reactive Functional Groups

The presence of certain functional groups is considered an indicator of reactivity. Some examples of chemicals containing functional groups can be considered potentially reactive:-NO2 organic nitro compoundsN=N=N organic/inorganic azides, a linear anion -O-O-, -O-OH organic/inorganic peroxide and hydroperoxide compounds-C≡C- triple bonded carbon atoms as in acetylene and acetylenic

compounds

20

IntroductionType of RCHProcess of RCH StudiesReferencesSlide21

Reactive

Functional GroupsSimplest reactivity screening method possible and serves as a guideline for further analysis.Cornell University’s EHS website List of Functional Groups

Properties

and Hazards, including Reactivity Hazards21IntroductionType of RCHProcess of RCH StudiesReferencesSlide22

Recap

Which of the following functional group reacts vigorously with concentrated mineral acids? (Hint: available in Cornell’s EHS website)A. aldehydesB. aliphatic aminesC. alicyclic hydrocarbons

D. alcohols

Answer

: B. aliphatic amines22IntroductionType of RCHProcess of RCH StudiesReferencesSlide23

Reactive Functional Groups

Useful source: EPA’s Chemical Compatibility ChartTo determining the compatibility of chemicals and the result

of

mixing23IntroductionType of RCHProcess of RCH StudiesReferencesSlide24

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EPA Chemical Compatibility Chart Available Here:

Introduction

Type of RCH

Process of RCH StudiesReferencesSlide25

Recap

Q: Using the EPA compatibility chart, what will happen by mixing amides and oxidizing mineral acids?25

Introduction

Type of RCH

Process of RCH StudiesReferencesSlide26

Recap

Solution26

Answer:

Toxic

gas formation and HeatIntroductionType of RCHProcess of RCH StudiesReferencesSlide27

MSDS (Material Safety Data Sheet)

Contact your supplier for MSDS firstUnder Section ‘Stability and Reactivity’Limited details

27

Introduction

Type of RCHProcess of RCH StudiesReferencesSlide28

International

Chemical Safety CardIf MSDS is not available, this is the secondary sourceAvailable on ILO (International

Labour

Organization) WebsiteOR Google international chemical safety data card CDC (Centers for Disease Control and Prevention) websiteStart search:28IntroductionType of RCHProcess of RCH StudiesReferencesSlide29

Recap

Using ICSD cards, find out at least one key reactive hazard

for

lead chromate.Solution: Decomposes on heating. This produces toxic fumes including lead oxides. Reacts violently with many substances such as combustible substances, amines, bases and metals. This generates fire and explosion hazard. 29IntroductionType of RCHProcess of RCH StudiesReferencesSlide30

NOAA Reactivity Worksheet (CRW)

A software to find out hazards of: Chemicals:

a

database of reactivity information for more than 5,000 common hazardous chemicalsReactive Groups: chemicals are assigned to 64 reactive groups to generate reactivity predictionsMixtures of chemicals: rule-based algorithm allowing you to virtually “mix” chemicals to determine compatibility of two or more chemicalsAvailable online30IntroductionType of RCHProcess of RCH StudiesReferencesSlide31

NOAA: Use functional groups instead of chemicals when…

You know the chemical class of a chemical, but not its exact name or CAS (Chemical Abstracts Service) registry number. For instance, you may be able to tell that it's a powdered metal A new compound that hasn't yet been included in major chemical databases.You work with (or store) proprietary chemicals that are not included in the CRW's chemical database. In this case, you can either use a reactive group to approximate the chemical or you could create a custom chemical datasheet in the CRW.31

Introduction

Type of RCH

Process of RCH StudiesReferencesSlide32

NOAA Example

- Single chemical32

Search

Search

ResultsWhen working with mixture, see next slideIntroductionType of RCHProcess of RCH StudiesReferencesSlide33

NOAA Example Continued…

331. Create

new

mixture2. Search compounds, then add to mixture, repeat with multiple compounds3. Will show compatibility chart

Can

obtain

summary

here

Introduction

Type of RCH

Process of RCH Studies

ReferencesSlide34

Recap: T

ry this on NOAA…Mix sodium hypochlorite and hydrogen

peroxide

togetherWhat are the predicted hazards?34IntroductionType of RCHProcess of RCH StudiesReferencesSlide35

S2S

RCH Online AssessmentTo assess the hazardous properties of your substances or the hazardous properties of your process.Select “Self

assessment

Reactivity Hazards”35IntroductionType of RCHProcess of RCH StudiesReferencesSlide36

S2S

RCH Online Assessment Follow the prompt from S2S online assessment,

practice

with sodium azide: NaN3You can use facts regarding NaN3 in MSDS or ICSCResults in a summary report indicating:Deficiencies in Good PracticeAdequate fulfillment of needsInsufficient Knowledge and PracticesInstruction: Take a screenshot of your assessment and submit HERE.36IntroductionType of RCHProcess of RCH StudiesReferencesSlide37

Oxygen

Balance (OB, or OB%) 37Used to

indicate

degree to which an explosive can be oxidizedIf an explosive molecule contains just enough chemically-bonded oxygen to convert all of its carbon to carbon dioxide, all of its hydrogen to water, and all of its metal to metal oxide with NO EXCESS, the molecule is said

to

have

a

zero

oxygen

balance

Positive

OB:

molecule

contains

more

chemically-bonded oxygen

than

is

needed.

Negative

OB:

molecule

contains

less

chemically-bonded oxygen

than

is

needed.

For

OB>-200,

it

is

considered

potential

high

risk

Important clarification - Use

of

the oxygen-balance tool

implies the presence of

oxidizing

groups (functional groups)

like

nitro, nitrate, chlorate,

peroxy

in the molecule. 

*

Using

the oxygen balance without this additional information often will lead in wrong (nonsensical) results.

Introduction

Type of RCH

Process of RCH Studies

ReferencesSlide38

Oxygen

Balance (OB, or OB%) 38

Can

also be calculated on S2S websiteLothrop and Handrick (1949) defined OB and will be calculated as:For an organic compound: CxHyOz + (x+y/4 - z/2) O2 ⇒ x CO2 + y/2 H2O and M is the molecular weight.IntroductionType of RCHProcess of RCH StudiesReferencesSlide39

Break time

T2 Laboratory Runaway Watch Online: https://www.youtube.com/watch?v=C561PCq5E1g39

Introduction

Type of RCH

Process of RCH StudiesReferencesSlide40

Step 3: Quantify RCH – an

estimating tool Tools to Quantify RCHCalorimetry Adopting TCPA (Toxic Catastrophe Prevention Act)Calculated

Adiabatic

Reaction Temperature (CART)ASTM CHETAH program40IntroductionType of RCHProcess of RCH StudiesReferencesSlide41

Calorimetry

To measure the heat effect of：Physical changes (melting, evaporation, dehydration)Chemical changes (acid-base reaction, dissolving, solid-state reaction, crystal phase transition)It can be used to determine:Enthalpy formation trendsPhase stabilityHeat capacity

Surface effect

According to relationship between time and heat release per

mole, we can, for intended reactions, design the safety response accordingly (e.g. cooling rate, set pressure alarm, etc.)41IntroductionType of RCHProcess of RCH StudiesReferencesSlide42

Calorimeter

An instrument determines heat effect in it by measuring temperature.Based on state of system, classified into two types:AdiabaticDirectly measures the temperature change in insulated systemNon-adiabaticMeasures heat flow of the system, with heat transfer to surroundingBased on working conditions, classified into two types:Constant pressure (e.g. coffee cup calorimeter)Constant volume (e.g. bomb calorimeter)Other types: solution

calorimetry

, scanning

calorimetry42Slide43

Schematic of a simplified calorimeter

43ReactantStirrerThermometer

Calorimeter liquid

Heater

Picture reference: Calorimetry: Fundamentals, Instrumentation and Applications, 1st ed. (Stefan M. Sarge, Gunther W. H. Hohne, and Wolfgang Hemminger.Slide44

Calorimetry Example

44When 0.7022 g of oxalic acid (C2O4H2) is burnt in the calorimeter under the same conditions as Example 6, the temperature increased by 1.602°C. The heat capacity of the calorimeter is 1.238 kJ/K. Calculate dH°combustion.Solution:The balanced equation and various quantities calculated are given in a logical order below:

C2O4H2(s) + 0.5 O2(g)



2 CO2 (g) + H2O(l)dn = 1.5 q = C dT = 1.238*1.602 = 1.984 kJn of oxalic acid = 0.7022/90 = 0.00780 moldE = -1.984 / 0.00780 = -354.4 kJ/moldH = dE + dnRT = -254.4 kJ + 1.5 mol * 0.008314 kJ/(K mol)* 298 K = -250.6 kJ/molIntroductionType of RCHProcess of RCH StudiesReferencesSimilarly, temperature increase can be calculated knowing the reaction, amount of reactants, heat capacity, and energy release. Slide45

Adopting TCPA (New Jersey)

(Toxic Catastrophe Prevention Act)TCPA’s goal: Protect the

public

from catastrophic releases of extraordinarily hazardous substances (EHS).TCPA includes two categories of reactive chemicals: Reactive Hazard Substances (RHS), list of chemicalsReactive Hazard Substance Mixtures (RHSM) determined by functional

groups

45

T

hreshold

quantity

is

calculated

as:

TQ

=

threshold

quantity

of

the

RHS,

lb

;

D

=

distance

to

property

line,

ft

;

E

=

energy

of

explosion

of

the

RHS;

2

4

=

scaled

distance

for

the

mass

of

TNT

that

results

in

a

blast

pressure

of

2.3

psi;

1024

=

energy

of

explosion

of

TNT,

cal

/g.

Introduction

Type of RCH

Process of RCH Studies

ReferencesSlide46

Threshold for Individual

RHS46

Introduction

Type of RCH

Process of RCH StudiesReferencesSlide47

Calculation

adopting from TCPAReaction threshold can be calculated with heat of reaction ΔH, and obtain using

the

table below:47IntroductionType of RCHProcess of RCH StudiesReferences

Distance

from

the

reactor

to

the

property

line

can

also

be

calculated

adopting

this

method

.

NOTE: TCPA is not our center of attention, it is the calculation that can be adopted to help with RCH evaluation.Slide48

Recap:

TCPA Example48Now, practice with the following

copolymerization

example: Styrene and acrylonitrile forms SAN (styrene-acrylonitrile)Literature value: Heat of reaction is -261 kcal/mol with 70:30 feed weight ratioFind out: For a reactor filled with 8500 lb of SAN, what would be the minimum distance for us to keep the reactor from?Solution:

Introduction

Type of RCH

Process of RCH Studies

ReferencesSlide49

Calculated

Adiabatic Reaction Temperature (CART)Also known as adiabatic

flame

temperature“For a combustion process that takes place adiabatically with no shaft work, the temperature of the products is referred to as the adiabatic flame temperature.” 49Δh1+Δh2=Δhadiabatic=0 for no work done

and

no

heat

exchanged

(over

all

enthalpy

from

initial

to

final

state

is

zero

).

Introduction

Type of RCH

Process of RCH Studies

ReferencesSlide50

Calculated

Adiabatic Reaction Temperature (CART)CART relates to reaction mechanism and KNOWN stoichiometryEnergy release, HRXN

The

ioMosaic

Reactivity Hazard Index can then be used to compare/rank reactivity hazards“Neglible Reactivity Hazard” HRXN no more negative than – 100 cal/g, andCART  700 K“Low Reactivity Hazard” (energetic reaction but not likely to be explosive) HRXN between – 100 and – 287 cal/g, andCART  700 K“Intermediate Reactivity Hazard” (energetic reaction but not likely to be explosive) HRXN between –287 and – 717 cal/g, or700 < CART  1600 K“High Reactivity Hazard” (strong potential for being explosive reaction) HRXN more negative than – 717 cal/g, orCART 1600 K50IntroductionType of RCHProcess of RCH Studies

ReferencesSlide51

CART

Calculation ContinuedFor process 1:h2 – hi = -q1 = (hof )unit mass

where q

1

is the “heat of reaction” For process 2:we put this amount back into the products to raise their temperature to the final level.hf – h2 = -q1or, if we can approximate the specific heat as constant cp,avg (Tf – T2) = q1 Temperature change during this second process is approximately , where Tf is the adiabatic flame temperature51IntroductionType of RCHProcess of RCH StudiesReferencesSlide52

Recap: CART Practice

52Determine the constant pressure adiabatic flame temperature for the combustion of methane with a stoichiometric air at 1 atm pressure. The reactant temperature at initial condition, Ti=298 K. The reaction is CH4 + 2O2 + 7.52 N2 = CO2 + 2H2O + 7.524 N2

SUBMIT ANSWER (in K)

Introduction

Type of RCHProcess of RCH StudiesReferencesSlide53

Recap: CART Solution

53Introduction

Type of RCH

Process of RCH Studies

ReferencesSlide54

ASTM

CHETAH programA computer program for chemical thermodynamic and energy release evaluationPredict RCH associated with a pure chemical, a mixture of chemicals, or a chemical reaction.Used for:Classifying materials for their ability to decompose with violenceEstimating heats of reaction or combustionPredicting lower flammable limits Obtaining flammability parametersComplementing experimental results to help identify IF further testing is needed.

NOT used:

As a replacement for physical testing of materials

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Undesired reactions need to be prevented

Prevention examples: Segregate storage tanks/dykesUse different fittings/flanges to reduce mixupsDesired reactions need to be controlledBy controlling concentration, temperature, pressure, phase, surface area of reactants, amount of catalystKinetically, andThermodynamicallyThis section is simplified due

to

the scope and goal of this module.55Control and PreventionIntroductionType of RCHProcess of RCH StudiesReferencesSlide56

Various

methods to manage reactivity hazards:Inherente.g. Use an intended reaction pathway that uses less hazardous

chemicals

Passivee.g. Use separate storage for incompatible chemicalsActivee.g. Provide properly designed control systems to control intended reactive chemicals in the processProcedurale.g. Manage process changes that may involve reactive chemicals56Control and Prevention

For

a

complete

hierarchy

of

methods

,

please

refer

to

R

.W.

Johnson

,

S

.

W

.

Rudy

,

and

S

.D.

Unwin

,

Essential

Practices

for

Managing

Chemical

Reactivity

Hazards

(NY:

AIChE

Center

for

Chemical

Process

Safety

,

2003)

Introduction

Type of RCH

Process of RCH Studies

ReferencesSlide57

Other sources for RCH Information and Tools

SourceLocation

“Essential

Practices for Managing Chemical Reactivity Hazards”E-book on KnovelThe U.S. Coast Guard’s (USCG) Chemical Hazard Response Information System (CHRIS) databaseAvailable OnlineBrethericks Handbook of Reactive Chemical Hazards, P. Urben, ed. (2006)Google books or Elsevier PublishersSax’s Dangerous Properties of Industrial Materials, R.J. Lewis, ed. (2007)John Wiley and Sons, Inc.57Introduction

Type of RCH

Process of RCH Studies

ReferencesSlide58

Source

LocationSigma Aldrich Library of Chemical Safety Data, R.E. Lenga

, ed. (1988)

Sigma-Aldrich

Fire Protection Guide to Hazardous Materials (2010)National Fire Protection Association (NFPA)Computer Program for Chemical Thermodynamics and Energy Release Evaluation (CHETAH)American Society for Testing and Materials (ASTM)Chemical Risk Analysis, in practical working situationsGoogle book58Other sources for RCH Information and ToolsIntroductionType of RCHProcess of RCH StudiesReferences