Carson Ph., Mumford C. Hazardous Chemicals Handbook (Справочник по опасным химическим веществам)

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Table 7.18 Characteristics of some different types of reaction

Oxidation Feedstocks generally hydrocarbons

Hazard of fire/explosion arises from contact of flammable material with oxygen

Reactions highly exothermic: equilibrium favours complete reaction

Polymerization Exothermic reaction which, unless carefully controlled, can run-away and create a thermal

explosion or vessel overpressurization

Refer to Table 7.20 for common monomers

Certain processes require polymerization of feedstock at high pressure, with associated

hazards

Many vinyl monomers (e.g. vinyl chloride, acrylonitrile) pose a chronic toxicity hazard

Refer to Table 7.19 for basic precautions

Halogenation The commercially important halogens are chlorine, bromine, fluorine, iodine. Refer to Table

5.19 for properties

All are highly toxic

Reactions are highly exothermic and chain reactions can occur, which may result in detonation

Hydroprocesses Hydrogen is chemically stable and relatively unreactive at ordinary temperatures; most

processes utilizing it require a catalyst. Above 500°C it reacts readily with oxygen and

confined flammable mixtures explode violently if ignited

Main hazards: fire, explosion, metallurgical problems arising from hydrogen attack

Nitration Hazards arise from the strong oxidizing nature of the nitrating agents used (e.g. mixture of

nitric and sulphuric acids) and from the explosive characteristics of some end products

Reactions and side reactions involving oxidation are highly exothermic and may occur

rapidly

Sensitive temperature control is essential to avoid run-away

Alkylation Hazards arise from the alkylating agents, e.g. dimethyl sulphate (suspected human carcinogen),

hydrogen fluoride (highly toxic irritant gas)

Thermal alkylation processes require higher temperatures and pressures, with associated

problems

High pressure reactions High inventories of stored pressure (e.g. in pressurized reactors or associated plant) can

result in catastrophic failure of the pressure shell

Table 7.19 Basic precautions in monomer storage

Indoors

Cool, well-ventilated area

Non-combustible construction

Segregated from other flammables/reactants

Outdoors

Well-spaced tanks, possibly with water cooling, refrigeration, buried

Some monomers (e.g. acrylic acid) may require provisions to avoid freezing

Provision for inhibitor/stabilizer addition

Provision for atmosphere inerting may be required

• Venting to a knock-out vessel, to remove non-gaseous substances. (This may be followed by a

scrubbing unit for gases or a flare-stack.)

The kinetics and thermodynamics of the reaction, and of possible side reactions, need to be

understood. The explosive potential of chemicals liable to exothermic reaction should be carefully

appraised.

A thorough assessment should be made before undertaking:

HAZARDS ARISING IN CHEMICALS PROCESSING 249

250 REACTIVE CHEMICALS

Table 7.20 Properties of common monomers

Flash Ignition Flammable Specific Vapour Boiling Properties

point temp. limits gravity density point

(°C) (°C) (% by vol. (Water (Air = 1.0) (°C)

in air) = 1.0)

Acetaldehyde –38 185 4.0–55.0 0.8 1.5 21 Colourless fuming liquid

(Acetic aldehyde, Pungent odour

ethanal) Irritant

CHO Water soluble

Can polymerize

exothermically, form

explosive peroxides, or

react violently with other

chemicals

Acrolein –26 278 2.8–31.0 0.8 1.9 53 Colourless/yellow liquid

(Allyl aldehyde, Pungent unpleasant odour

propenal) Water soluble

:CHCHO Irritant

Can polymerize

exothermically with

strong alkalis, heat or light

Can form peroxides

Acrylic acid 54 – – 1.1 2.5 140 Colourless, water soluble

(Propenoic acid, liquid

propene acid) Freezing point 14°C

:CHCOOH Polymerizes readily with

oxygen

Must be inhibited

Acrylonitrile 0 481 3.0–17.0 0.8 1.8 77 Colourless, partially water

(Vinyl cyanide, soluble liquid

propenenitrile) Experimental carcinogen

:CHCN Polymerizes violently with

organic peroxides or

concentrated caustic

alkalis

Highly toxic

Usually inhibited

1,3-Butadiene –76 450 2.0–11.5 0.6 1.9 –4 Colourless, odourless

(Butadiene, liquefiable gas

vinylethylene) Polymerizes readily,

:CHCH:CH

particularly if O

traces of catalyst present

Can form explosive peroxides

Normally contains inhibitor

(liquid phase) and

antioxidant

Epichlorhydrin 32 – – 1.2 3.3 115 Colourless, partly water

(Chloropropylene soluble liquid

oxide) Highly toxic

:OCHCH

Cl Polymerizes exothermically

with acids, bases, certain

salts and catalysts

Can react with water

Ethyl acrylate 15 – 1.8–– 1.2 – 100 Colourless liquid

:CHCOOC

Acrid odour

Polymerizes readily,

accelerated by heat, light,

organic peroxides

Irritant

Ethylene oxide <–18 429 3.0–100 0.9 1.5 11 Colourless gas at room

:CH

temperature

Irritant to eyes and

O respiratory tract, and an

experimental carcinogen

Polymerizes uncontrollably

with immense explosive

force on contact with

certain chemicals (e.g.

ammonia)

Formaldehyde gas 430 7.0–73.0 – 1.1 –21 Colourless

(Oxymethylene) Water soluble gas producing

HCHO formalin solutions

Suffocating odour

Polymerizes readily

Highly toxic

Respiratory sensitizer

Methacrylic acid 77 – – – – 158 Colourless, water soluble

:C(CH

)COOH liquid

Polymerizes readily unless

inhibited or stored <15°C

Irritant

Methyl acrylate –3 – 2.8–25.0 1.0 3.0 80 Colourless liquid

:CHCOOCH

Acrid odour

Extremely irritating to

respiratory system, skin

and mucous membranes

Methyl methacrylate 29 – 2.1–12.5 0.9 3.4 101 Colourless liquid

:C(CH

)COOCH

Acrid odour

Styrene 32 490 1.1–6.1 0.9 3.6 145 Colourless/oily yellow liquid

(Vinyl benzene) Penetrating odour

CH:CH

Polymerizes slowly in air or

light, accelerated by heat

or catalysts

Ignition/explosion possible

Usually inhibited

Store <21°C

Vinyl acetate –8 427 2.6–13.4 1.1 3.0 72 Colourless, partially water

COOCH:CH

soluble liquid

Faint odour

Polymerizes with heat or

organic peroxides

Vinyl chloride –78 472 4.0–22.0 1.0 2.1 –14 Colourless, sweet smelling

(Chloroethene) liquefiable gas

:CHCl Polymerizes with light, heat,

air or catalysts

Normally inhibited

Human carcinogen

Vinylidene chloride –10 458 5.6–11.4 1.3 3.3 37 Colourless volatile liquid

(Dichloroethylene-1,1) Polymerizes unless inhibited

:CCl

Decomposes at 457°C

HAZARDS ARISING IN CHEMICALS PROCESSING 251

Table 7.20 Cont’d

Flash Ignition Flammable Specific Vapour Boiling Properties

point temp. limits gravity density point

(°C) (°C) (% by vol. (Water (Air = 1.0) (°C)

in air) = 1.0)

252 REACTIVE CHEMICALS

(a) (b) (c)

(d) (e) (f)

Temperature Temperature Temperature

Reaction rate Reaction rate

Incorrect kinetic

assumptions

Incorrect initiation

Insufficient mixing

Temperature too low

Impurities (inhibitors)

Feed rate too fast

Accumulation of

reactants or

intermediates

Insufficient

cooling

Emergency loss of

cooling, stirring

Impurities (catalysts)

that accelerate rate

Incorrect assumptions

on heat balance

Temperature of heat

transfer fluid too high

Storage temperature too high

Triggering of

undesired reaction

ANDAND

Heat accumulation,

uncontrollable

temperature rise

Thermal runaway

Figure 7.4

Common causes of thermal runaway in reactors or storage tanks

Figure 7.5

Types of reaction rate/temperature curve

a Rapid increase with temperature – normal characteristic

b Slow increase in rate with temperature – characteristic of some heterogeneous reactions

c Very rapid increase at one point – the ignition point in an explosion

d Decrease in rate at higher temperature – characteristic of catalytic reactions

e Decrease in rate at intermediate temperatures, followed by an increase

f Slow decrease in rate with temperature

Table 7.21 Safety features in chemical engineering operations

Inventory Reduce inventory of chemicals:

Continuous operation may be preferable to batch

Low residence time contacting equipment may be better than cheaper alternatives

etc.

Monitoring Monitor temperature, pressure flow, composition, freedom from contamination and other

appropriate properties of all streams where relevant. Consider automatic control

Isolation Provide for isolation from upstream and downstream operations. Consider provision of

automatic and/or remotely operated isolation. Consider isolation for cleaning needs

Contaminants Provide measures to remove unacceptable contaminants from feed materials, process

streams and services, e.g. entrained liquid, tramp metal, unwanted particulate solids

Pressure/temperature Operate at moderate temperature and pressure where possible. Avoid superheated

liquids, which will flash-off, if practicable

Allow for effects of over-/under-temperature, over-/under-pressure. Following assessment

(e.g. by HAZOP)

Continuous flow With continuous flow operations consider (e.g. using a HAZOP procedure) the effects of:

No flow

Reduced flow

Reverse flow

Increased flow

Contaminated flow

Flow of a substituted material, etc.

Start-up/shutdown Provide for safe start-up, including purging if necessary

Provide for safe shutdown:

Normal

By a trip

On standby

In various emergency situations, etc.

Instrumentation Provide safety instrumentation in addition to process instrumentation

Consider high–high and low–low alarms. Consider automatic activation of emergency

responses, e.g. venting, emergency cooling, recycling, discharge of liquid streams,

shutdown

High/low temperature

pressure

flow

level

etc.

linked to trips for automatic operation where appropriate

Protective features Provide protective as well as control features, e.g. pressure and vacuum relief, explosion

suppression relief, advance inerting, containment

Waste streams Cater for routine and emergency, safe discharge of all waste streams, e.g. atmospheric

venting, possibly after treatment, discharge of liquid effluents including out-of-specification

streams, discharges of particulate or bulk solids

Common-mode failure Avoid common-mode failure possibilities with services, control systems, safety systems

etc.

• Scale-up (since it may result in a decrease in heat transfer capacity per unit mass of reactant).

• Modifications in reactor geometry, agitation and control (e.g. instrumentation, cooling, venting).

• Changes in reaction materials, (e.g. source, purity, concentration), diluents, catalysts charging

procedures.

• Changes in operating conditions.

The characteristics of some potentially hazardous reactions are summarized in Tables 7.18 and

7.22.

Many processes require equipment designed to rigid specifications together with automatic

control and safety devices. Consideration should be given to the control, and limitation of the

effects, of equipment malfunction or maloperation including:

HAZARDS ARISING IN CHEMICALS PROCESSING 253

254 REACTIVE CHEMICALS

Table 7.22 Hazard rating of chemical reactions

Reaction Degree of Reaction Degree of

hazard hazard

Reduction

Clemmensen D

Sodium-amalgam D

Zinc–acetic acid E

Zinc–hydrochloric acid E

Zinc–sodium hydroxide E

Ferrous ammonium sulphate E

Lead tetraacetate E

Meerwein–Pondorff D

Lithium aluminium hydride B

Dialkyl aluminium hydride B

Rosenmund A

Catalytic high pressure A

Catalytic low pressure B

Oxidation

Hydrogen peroxide – dilute aqueous E

Air or I

(mercaptan to

disulphide) D

Oppenauer D

Selenium dioxide D

Aqueous solution nitric acid,

permanganate, manganic

dioxide, chromic acid,

dichromate E

Electrolytic B

Chromyl chloride C

Ozonolysis A

Nitrous acids A

Peracids – low molecular

weight or two or more

positive groups A

Peracids – high molecular

weight B

-Butyl hypochlorite C

Chlorine C

Alkylation

Carbon–carbon

Alkali metal C

Alkali metal alcoholate D

Alkali metal amides and hydrides C

Reformatsky E

Michael E

Grignard B

Organometallics, such as

dialkyl zinc or cadmium–

alkyl or aryl lithium B

Alkali acetylides A

Diels–Alder D

Arndt–Eistert A

Diazoalkane and aldehyde A

Aldehydes or ketones and

hydrogen cyanide C

Carbon–oxygen

Williamson D

Formaldehyde – hydrochloric

acid E

Ethylene oxide C

Dialkyl sulphate D

Diazoalkane A

Carbon–nitrogen

Cyanomethylation C

Chloromethylation D

Ethylenimine C

Ethylene oxide C

Quaternization D

Condensation

Erlenmeyer D

Perkin D

Acetoacetic ester D

Aldol D

Claisen D

Knoevenagel D

Condensations using catalysts

such as phosphoric acid;

AlCl

; KHSO

; SnCl

;

; ZnCl

NaHSO

;

POCl

; HCl; FeCl

Acyloin C

Diketones with hydrogen sulphide C

Diketones with diamines→

quinazolines D

Diketones with NH

OH→

isoxazolines D

Diketones with NH

→

pyrazoles C

Diketones with semicarbazide

→ pyrazoles D

Diketones with ammonia→pyrazoles D

Carbon disuphide with

aminoacetamide→thiazolone A

Nitriles and ethylene diamines

→ imidazolines D

Amination

Liquid ammonia B

Aqueous ammonia E

Alkali amides C

Esterification

Inorganic E

Alkoxy magnesium halides B

Organic:

Alcohol and acids or acid

chloride or acid anhydride D

Alkyl halide and silver salts of

acids E

Alkyl sulphate and alkali

metal salt of acid D

Alkyl chlorosulphates and

alkali salts of carboxylic acid D

Ester-exchange D

Carboxylic acid and diazomethane A

Acetylene and carboxylic

acid-vinyl ester A

Hydrolysis, aqueous nitriles,

esters E

Simple metathetical replacement D

Preparation and reaction of

peroxides and peracids

Concentrated A

Dilute D

Pyrolysis

Atmospheric pressure D

Pressure B

Schmidt B

Mannich D

Halogenation

, SOX

, SX, POX

, PX

HX D

, Br

Nitration

Dilute D

Concentrated B

Named reactions

Aldol reaction is the condensation of an aldehyde to produce longer-chain hydroxy aldehydes

2CH CHO CH CHOH CH CHO

NaOH

→⋅

Arndt-Eistert reaction is used to convert an acid compound into the next higher homologue by reaction with diazomethane

RCOCl + 2CH

→ R · COCH

H + 2N

+ CH

Claisen reaction is the condensation of benzaldehyde with aliphatic aldehydes and ketones containing α-hydrogen

C H CHO + CH CHO C H CH==CH CHO + H O

65 3

NaOH

65 2

→⋅

C H CHO + CH COCH C H CH==CH CO CH + H O

65 3 3

65 3 2

→⋅⋅

Clemmensen reaction is the reduction of carbonyl compounds with amalgamated zinc and concentrated hydrochloric acid

R CO R RCH R

⋅⋅→

Diels-Alder is the preparation of cyclic olefins from dienes and a dienophile

Hazardous

A Highly flammable

Develops high pressure instantly

Highly toxic

Special

B Flammable, perhaps explosive, mixtures form

C Flammable, or generates toxic ubstances

Conventional

D Slightly flammable

Generates or uses mildly toxic

substances

E Non-flammable

Does not use or generate toxic

substances

HAZARDS ARISING IN CHEMICALS PROCESSING 255

Table 7.22 Hazard rating of chemical reactions

Reaction Degree Reaction Degree

of of

hazard hazard

C—R

256 REACTIVE CHEMICALS

Erlenmeyer reaction is the condensation of aromatic aldehydes with hippuric acid to form azlactones (important intermediates

in the preparation of amino- and keto-acids)

CHO + CH

NHCOC

CH C C O

Grignard reaction is the use of alkyl magnesium halides to form a host of products by reaction with a variety of chemicals

RMgX + H

O → RH + Mg(OH) · X

RMgX + R′OH → RH + Mg(OR′) · X

RMgX + NH

→ RH + Mg(NH

) · X

RMgX + RN=C → R—N(MgX)=CR + R—N=C(R)MgX

Knoevenagel reaction is the synthesis of α, β-unsaturated acids by reaction of aldehydes and compounds with active

methylene groups in the presence of an organic base

RCHO + CH (CO C H ) R CH==C(CO C H ) + H O

2225

base

2252 2

→⋅

↓ KOH

R CH==CH CO H R CH==C(CO H)

150–200

⋅⋅← ⋅

Mannich reaction is the condensation between formaldehyde, ammonia, or a primary or secondary amine (preferably as the

hydrochloride), and a compound containing at least one active hydrogen atom

R CH NO + HCHO + NH Cl R C

CH NH HCl + H O

22 2

⋅→⋅

Meerwein-Pondorff reduction is the synthesis of alcohols by heating carbonyl compounds with aluminium isopropoxide in

isopropanol and distilling off acetone by-product

C=O + (CH

)

CHOAl

→ R

CHO Al

+ CH

CO CH

→ R

CHOH

Michael condensation is the addition of a compound with an active methylene group to an α, β-unsaturated keto-compound

CH (CO C H ) + (CH ) C==CH CO CH (CH ) C

CH(CO C H )

CH COCH + C H O

2 2252 32 3

CHO

225

2325

–

→

Oppenauer reaction is oxidation of secondary alcohols to ketones using aluminium t-butoxide

RCH(OH)R + CH COCH RCOR + CH CH(OH)CH

catalyst

′

→

′

Perkin condensation is the reaction between aromatic aldehydes and aliphatic acid anhydrides (in the presence of the

sodium salt) to form β-arylacrylic acid

C H CHO + (CH CO) O C H CH==CH CO H

65 3 2

CH CO Na

65 2

→

Reformatsky reaction is the formation of β-hydroxyesters by reaction of α-bromoacid ester and a carbonyl compound,

usually in the presence of zinc

′

→

′

R CO + RCH(Br)CO C H R C(OH)CHR CO C H

2 225

225

Rosenmund reaction is the action between acid chloride and hydrogen in the presence of palladium catalyst to produce

aldehydes

RCOCl + H R CHO + HCl

→⋅

Schmidt reaction is the reaction between carbonyl compounds and hydrazoic acid in the presence of e.g. concentrated

sulphuric acid

RCHO + HN RCN + RNH CHO

→

R CO R==HN R CONHR + N

⋅⋅ →⋅

Williamson reaction is the synthesis of ethers by action of heat on a mixture of alkyl haldie and sodium or potassium alkoxide

ROK + R′X → ROR′ + KX

• Stirrer failure, mechanical or electrical.

• Attainment of abnormal reaction conditions, e.g. overpressure, over-temperature, segregation

of reactants, excessive reaction rate, initiation of side reactions.

• Power failure, affecting agitator, pumps, instruments.

• Error in valve, switch or associated equipment operation.

• Failure to actuate agitation at the proper time.

• Instrument failure, pressure, flow, temperature, level or a reaction parameter, e.g. concentration.

• Failure of instrument air or electricity.

• Loss of inert gas blanket.

• Failure of relief devices, e.g. pressure relief valves or rupture discs.

• Failure of coolant, refrigerant, or other utilities.

• Failure of high or low pressure alarms or cut-outs.

• Addition of wrong material or wrong quantities.

• Addition of materials in incorrect sequence.

• Failure to add material, e.g. short-stop or inhibitor, at correct stage.

• Spillage of material.

• Improper venting to atmosphere, i.e. other than via vents with flame arresters or scrubbers, or

via a knockout drum, or to the correct flare systems.

• Restricted or blocked vent.

• Restricted material flows in or out.

• Leakage of materials out, e.g. due to a gasket failure, or air in.

HAZARDS ARISING IN CHEMICALS PROCESSING 257

Cryogens

Cryogenics, or low-temperature technology, is the science of producing and maintaining very low

temperatures usually below 120 K, as distinct from traditional refrigeration which covers the

temperature range 120 to 273.1 K. At or below 120 K, the permanent gases including argon,

helium, hydrogen, methane, oxygen and nitrogen can be liquefied at ambient pressure as exemplified

by Table 8.1. Any object may be cooled to low temperatures by placing it in thermal contact with

a suitable liquefied gas held at constant pressure. Applications can be found in food processing,

rocket propulsion, microbiology, electronics, medicine, metal working and general laboratory

operations. Cryogenic technology has also been used to produce low-cost, high-purity gases

through fractional condensation and distillation. Cryogens are used to enhance the speed of

computers and in magnetic resonance imaging to cool high conductivity magnets for non-intrusive

body diagnostics. Low-temperature infrared detectors are used in astronomical telescopes.

Table 8.1 Properties of common cryogens

Gas Boiling point Volume of gas produced on evaporation

(°C)

of 1 litre of liquid (litres)

Helium – 269 757

Hydrogen – 253 851

Neon – 246 1438

Nitrogen – 196 696

Fluorine – 187 888

Argon – 186 847

Oxygen – 183 860

Methane – 161 578

Krypton – 151 700

Xenon – 109 573

Chlorotrifluoromethane – 81 –

Carbon dioxide – 78.5 553

Every gas has a critical temperature above which it cannot be liquefied by application of

pressure alone (Chapter 4). As a result, gases used, e.g., as an inert medium to reduce oxygen

content of atmospheres containing flammable gas or vapour (Chapter 6) are often shipped and

stored as cryogenic liquid for convenience and economy.

In the laboratory, a range of ‘slush baths’ may be used for speciality work. These are prepared

by cooling organic liquids to their melting points by the addition of liquid nitrogen. Common

examples are given in Table 8.2. Unless strict handling precautions are instituted, it is advisable

to replace the more toxic and flammable solvents by safer alternatives.