Nitrogen ttrichloride --- revised

1. RISKS & CONTROLS
OF
NITROGEN TRI-CHLORIDE
Presented by
H S.SEHGAL, DY.GM
Gujarat Alkalies & Chemicals Ltd
Vadodara,
Gujarat (India)

2. PREFACE
•The Production of Chlorine has expanded rapidly in the recent
years and larger quantities are stored, used and transported.
•Nitrogen tri chloride is an extremely hazardous chemical which is
synthesized in small quantities in all chlorine manufacturing plants.
•Nitrogen tri chloride under certain circumstances is extremely
unstable and can produce violet explosion.
•It must be handled and disposed off with extreme cautions.

3. AREAS OF POTENTIAL CONCERNS
1.Chlorine Liquefiers
2.Chlorine Storages
3.Mobile Containers
4.Liquid Chlorine Tonners/ Cylinders
5.Vaporizers
6.Upset Conditions in Process or Preparation for Maintenance
7.Recycling of various streams
8.Modification Jobs
9.Destruction Process of Nitrogen Tri Chloride

4. OBJECTIVE OF STUDY
PURPOSE - To highlight the potential problem with
accumulation of reactive material
Nitrogen Tri Chloride in liquid Chlorine.
- To describe the constraints which need
to be observed in order to avoid the
risks associated with its presence in
routine Chlorine storage, transport and
use.
Any Chlorine user who is uncertain of the potential problem which
can arise from accumulation of NCl
3
, should consult the Chlorine
suppliers to confirm acceptable level and level of risk.

5. OCCURRENCE & FORMATION OF NCl
3
Nitrogen Tri-Chloride was first observed in 1811 from the action of
Chlorine on the solution of Ammonium Chloride.
This compound is a yellow oil with a pungent Chlorine like Odour.
It is insoluble in water and soluble in most organic solvents.
A drop of oil explodes violently when touched with a feather dipped in
turpentine.
Nitrogen Tri-Chloride is formed during the production of Chlorine when
Ammonical Nitrogen is present in the brine fed to the electrolytic cells.
Any ammonical compound in the brine or water will be converted to
NCl
3
in short time. 30 ppm of ammonia in water is converted to NCl
3
in
20 seconds.
NCl
3
is soluble to the extent of 7.3 mg/l in liquid Chlorine.

6. OCCURRENCE & FORMATION OF NCl
3
Once NCl
3
forms in the electrolytic cells, it will pass with Chlorine
gas through the coolers, scrubbers, acid seal pumps and will be
condensed with the liquid Chlorine.
NCl
3
Vapor pressure is a function of temperature. Under the usual
brine electrolysis conditions NCl
3
will be readily swept out of the
cells with chlorine .
NCl
3
concentrates itself in the layer of liquid Chlorine next to vapor
phase. As the liquid Chlorine is used up, the concentration of NCl
3
keeps increasing at vapor-liquid inter-phase.
Chemical reaction is as under---
NH
3
+ Cl
2
------NH
2
Cl+HCl
NH
2
Cl+Cl
2
------NHCl + HCl
NHCl+ Cl
2
------ NCl
3
+HCl

7. ASSOCIATED HAZARDS
Nitrogen Tri-Chloride is one of the most hazardous material in Chlor-
Alkali industry.
Fatalities have occurred and workers have been injured by NCl
3
explosions.
The explosive power of small quantity of NCl
3 can be catastrophic &
can cause
release of Chlorine &
large scale damage to personnel, plant equipment .
NCl
3 is
sensitive to light, impact and ultrasonic radiation
A spontaneous explosive compound.
Explosive potential is 30% of TNT.
The compound has +72 Kcal/mol free energy of formation and
decomposition gives 54.7 Kcal/mol.
On detonation at constant volume, a temperature of 2128
0
C and
pressure of 5361 atm is reached.
Decomposition of as little as 0.3 gm/cm
2
of exposed wall area in a
confined volume can overstress steel and can create a very hazardous
situation.

8. ASSOCIATED HAZARDS (CONTD)
 Increasing the number to 1.5 gm/cm
2
results in fracture.
 The hazard is less when Chlorine contaminated with NCl
3
is spread
in a wide pool than it collects in a nozzle or section of piping.
 NCl
3
is much less volatile (Boiling point:71
0
C) than Liquid Chlorine
(Boiling point:-34
0
C). It tends to accumulate at different points in the
process. Any NCl
3 present in the gas shall concentrate in liquid
chlorine. Vapor pressure of NCl
3 is 0.11 atm and for chlorine is 3.68
atm at 0
0
C which shows NCl
3 will remain on evaporation of liquid
chlorine.
 Yellow oil of NCl
3
explodes violently :
When heated in greater than 93
0
C
Exposed to light
Brought in contact with Ozone, Phosphorous, Arsenic, Alkali and
organic matter.
 Spill of NCl
3
is a hazardous residue. Spilled NCl
3
can detonate on
simple walking through it.

9. ASSOCIATED HAZARDS (CONTD)
The use of containers are cause of concern. When liquid chlorine is
exhausted in containers and gas is withdrawn to storage, vaporization
or other process use then decomposition of NCl
3
starts. Once
decomposition begins, the exothermic heat of reaction causes to
propagates very rapidly and move on to detonation.

10. INCIDENT LOCATION DATE
Storage Tank (3) Explosions China April, 2004
Detonation in copper tubing Australia July, 1998
Explosion of an empty railcar which had been Belgium February, 1995
unloaded via the gas phase
Chlorine suction chiller explosion; Major Louisiana (USA) March, 1994
equipment damage
Compressor suciton chiller drain piping
explosion killing two people and severing Colombia November, 1993
one person's leg above the knee
Purification column pot exploded killing one West Virginia (USA) March, 1983
Cooling tower (believed to be compressor Michigan (USA) November, 1978
suction chlorine cooler) exploded killing one
Two explosions in chlorine vaporizers have Brazil Not known
been rerported, no details available
One-ton container exploded Not known Febryuary, 1949
One-ton container exploded Not known November, 1948
Tank car cover blew off killing two Norway January, 1940
Three interconnected storage tanks (45 tons
total capacity) at a pulp mill exploded Romania December, 1939
releasing 21 tons of chlorine
Two one-ton containers exploded Not known July, 1928
An evaporator explosion was reported India 1965
Several evaportators explosions investigated South America 1981
(NCl3 concn. 50 to 300 mg/ltr.)
SUSPECTED NITROGEN TRICHLORIDE INCIDENTS

11. SOURCES OF NITROGENOUS IMPURITY
Nitrogen compounds may be present in salt and other chemicals
added during processing.
Nitrogenous explosives used to break the beds in the mines.
Anti-caking agent present in ppm concentration.
Salt delivery vehicle is a potential source of contamination.
Dissolving water is the source of nitrogenous matter in solution
mining.
Calcium Chloride used in some brine systems – a by-product of
Solvay Process of Soda Ash is a source of Ammonical impurity.

12. SOURCES OF NITROGENOUS IMPURITY
KCl salt recovered by the use of Amines as separator can add
Nitrogenous impurity.
H
2
SO
4
used in Chlorine drying is also source of Ammonia
compounds sometimes.
Plant utilities are likely sources like
use of impure water to prepare treatment chemicals,
flushing water on rotating equipments seals,
water recycle from waste minimization systems,
direct contact cooling water.
Steam and its condensate are also potential sources. The culprits
are usually the amines used as corrosion inhibitors in steam system.

13. SOURCES OF NITROGENOUS IMPURITY
Higher risk of Nitrogen Tri-Chloride formation or accumulation during
 periods of start up,
shut downs,
process modifications,
maintenance,
process upsets or process fluctuations
Not all compounds are converted to Nitrogen Tri-Chloride. Water
contaminated with nitrogenous material like Caprolactum does not
contribute rise in NCl
3
(used in mine brine).
Nitrogen gas introduced into Chlorine is not converted to NCl
3
.
Fully oxidized form of Nitrate salts (Potassium Nitrate or Sodium
Nitrate) do not form NCl
3
with interaction with Chlorine.

14. Awareness to the suppliers
Suppliers to be made aware about the importance of preventing
contamination of the materials and the hazards involved in chlor-alkali
industry.
1 ppm of Ammonia in the feed brine can produce >50 ppm of NCl
3
in dry
Chlorine and 1 ppm of Ammonia in salt can produce about 12 ppm of NCl
3
in the Chlorine.
Salt to be mined with the help of an explosive which is free from
Nitrogenous matter.
Salt to be stored without anti-caking agent.
Safer type of water for the manufacture of salt.
Rigid analytical programme for the analysis of the salt.
Dedicated vehicles for the transportation of salt to avoid any nitrogen
compound contamination.

15. To Control the formation of NCl
3
in liquid chlorine, it is essential to
limit the entry of Nitrogen compound in Salt and Brine solution in
process continuously.
Analysis on line :-
An on line analysis has been developed by a French organization
website :- www.seres-france.com.
It works in on principle of sequential analysis
It can measure Ammoniac salt(NH4) Concentration in Brine &
Ncl3 Concentration in Cl2 gas at the exit of Cl2 Compressor.
Magnetic fields & photo sensibility of Ncl3 influence the analyzer.
Therefore the analyzer must be installed:-
At a sufficient distance from the Cells House.
In a close Cabinet with air conditioning & with no external light.
All Transparent piping (Teflon etc) has to be covered.

DETECTION

16. DETECTION
ANALYSIS OF NCL3 IN LIQUID CL2 :-
Instrument technique & chemical determinations based on
conversion to ammonium ions are available.
Instrument technique is based on absorption of ultra violet or
infrared radiation, Gas chromatography or liquid chromatography.
The Instrument technique can not analyze Ncl3 that has
decomposed to Ammonium chloride & also not applicable for
whole concentration range.
Chemical determinations of Ncl3 are based on the determinations
of ammonium ions that are formed When the equilibrium is moved
to the right. Chemical principle method is preferred as compared
to the other methods.
The Chemical method is suitable for 0.2-20000mg/kgs Ncl3 in Cl2.

17. DETECTION
In this process Liquid Cl2 sample is taken in a refrigerated special
steel trap (-60 C) . Max. sample capacity is 500ml.
Liquid Cl2 is evaporated in the presence of Hydrochloric acid & the
gas is scrubbed by hydrochloric acid to form Ammonium chloride.
After removal of the dissolved Chlorine ,the hydrochloric acid
solution is carefully neutralized & the Ammonium ion is
determined either by Spectrophotometry of the Indophenols
Complex or by an Ammonia gas sensing Electrode for level up to
200mg/kg Ncl3 Or by Distillation & titration for higher levels.
For lowest level of Ncl3 5mg/kg of Cl2, the Spectrophotometry
method is preferred.
Results achieved by these methods are claimed to be reliable.

18. DETECTION
NCl
3
is assayed by the old Kjedahl Nitrogen test. It is
Time consuming (6.5 hours)
Not very sensitive at low concentration.
Is off-line process
Can be used for grab samples only.
This method of analysis is a three distinct process –
digestion,
distillation
titration
moreover, it over-reports Nitrogen.
Chromatographic method
Is rapid and precise.
Time required for analysis is 20 minutes.
Detector uses ultra-violet light.
Has been certified by ASTM (E2036-99) and has been further modified to
take low concentration of sample for better results. This process is suitable
for carbon tetrachloride system and require dilution 100:1 for safety
reasons.
Depends on partial evaporation of Chlorine from chilled sample of liquid
followed by addition of chromatographic elluent (methanol + dilute acetate
buffer at PH-4) and injection into column.

19. METHODS OF CONTROLL
When Ammonia compounds are in brine despite preventive
measures, destruction can be done by
controlled Chlorination at pH > 8.5 to form very volatile
monochloroamine
allowing Nitrogen content to be removed by venting or surging with
air.
NCL3 IN CL2 GAS IS CONTROLED BY ;
Irradiating the Chlorine gas exiting in the cells with ultra-violet light
in the spectrum of 3600-4400 before the Chlorine enters the
scrubbers ,
UV system is used to remove the small quantities of NCl
3
formed.

20. METHODS OF CONTROLL
Due to thermal instability of NCl
3,
decomposition becomes useful at
70
o
C.Temperature in excess of this are found in Chlorine compressors.
(Reciprocating and centrifugal)
Iron and its compounds can also cause decomposition.
Destruction of NCl
3
by scrubbing with cold HCl and contact with reducing
agents can be done. But this practice is not followed widely.
Because of the possibility of combustion of Chlorine with Iron as well as higher
activity of copper alloys, the grease free Monel shaving would be preferred.
Treatment of filtered dry gas
with activated carbon—this process is not in use. It was used in some
plants, few years ago.
Silica and Alumina are other candidates.
These may be impregnated to increase their reactivity.
This process is not in commercial use as it requires careful management due to
possible exothermic reaction

22. METHODS OF CONTROLL
NCl
3 in liquid cl2 is Removed by passing through carbon tetrachloride
solvent or equivalent as under :-
Cl2 gas containing Ncl3 is passed through purifying tower containing
liquid cl2.
Ncl3 impurity in gas is washed out by liquid cl2
This liquid cl2 + Ncl3 is passed through purge drain tank containing
carbon tetrachloride maintained at 50 c-60 c.
Ncl3 impurity accumulates carbon tetrachloride & cl2 gas recycled
through dryer system.
Contaminated carbon tetrachloride is reacted with Naoh or suitable
reducing agents.
Waste Solvent is incinerated & caustic is neutralized appropriately.
The Solvent carbon tetrachloride has to be replaced at scheduled
interval & conc. Of C4 vapors to be minimized & recorded.
Flow sheet of the process is attached for reference.
NCl
3 in liquid Cl
2 can be controlled/destroyed by,
Purging
Purging NCl
3
+ liquid Chlorine from the vaporizer is a method of reducing concentration of NCl
3
. In
this process NCl
3
enriched liquid chlorine is bottled in Tonners / Cylinders in a scheduled way.
Toleration in Cl
2
tonners is higher(20ppm) than storage tanks(2ppm). Moreover the tonners
becomes empty frequently at the customer end which eliminate the possibility of NCl
3
accumulation
in the system.
Purging and destruction process.
Collection of NCl
3
+ liquid chlorine from the bottoms of chiller/evaporator gives another opportunity
for thermal decomposition. Part of the Material is collected in a separate pot and decomposed by
heating with steam upto 80
0
C.
Spill of NCl
3

is a hazardous residue.
Spilled NCl
3
can detonate on simple walking through it.
A spray of approximately 5% solution of reducing agents and washing with water
will remove all traces of NCl
3.

23. FLOW SHEET
PROCESS FLOW DIAGRAM FOR THE CHLORINE HANDLING SYSTEM
H2SO
4

DIRECT CONTACT COOLER
WET CL
2
CELL GAS 90 - 95
0
C
WET GAS DEMISTER
DRAWING TOWER
PURIFICATION
LIQUID CHLORINE TOWER
FREON LIQUIFIER
90-95
0
C
CL2 to H2SO4 Towers
NAOH
DRY GAS DEMISTER
WASTE
INCINERATION
PURGE DRUM
LIQUID CL
2
COMPRESSOR
DISPOSAL
15 TO 17
0
C
25 TO 30
0
C
CCL4

24. METHODS OF CONTROLL
NCl
3
in liquid Cl
2
can be controlled/destroyed by,
Purging
Purging NCl
3
+ liquid Chlorine from the vaporizer is a method of
reducing concentration of NCl
3. In this process NCl
3 enriched liquid
chlorine is bottled in Tonners / Cylinders in a scheduled way.
Toleration in Cl
2 tonners is higher(20ppm) than storage tanks(2ppm).
Moreover the tonners becomes empty frequently at the customer end
which eliminate the possibility of NCl
3 accumulation in the system.
Purging and destruction process.
Collection of NCl
3
+ liquid chlorine from the bottoms of
chiller/evaporator gives another opportunity for thermal
decomposition. Part of the Material is collected in a separate pot and
decomposed by heating with steam upto 80
0
C.
Spill of NCl
3

is a hazardous residue.
Spilled NCl
3
can detonate on simple walking through it.
A spray of approximately 5% solution of reducing agents and washing
with water will remove all traces of NCl
3
.

25. DECOMPOSITION OF NCl
3
THERMAL
2NCl
3 N
2 + 3Cl
2 (CHAIN REACTION)
NCl
3
NCl
2
+ Cl, Cl + NCl
3
NCl
2
+ Cl
2
NCl
2
+ NCl
3
N
2
+ 2Cl
2
+ Cl
VAPOUR PHASE - MAY LEAD TO EXPLOSION
LIQUID PHASE - HIGHLY UNSTABLE
SOLID PHASE - MAY DETONATE ON THAWING
SOLUTION NCL3 - STABLE 1.5 WT % < 30

O
C
BEYOND INITIATION TEMPERATURE
SELF ACCELERATING – EXPLOSION
AT ~ 100
O
C. CATALYZED BY HEAT,
LIGHT, TRANSITION METAL OXIDES.

26. DECOMPOSITION OF NCl
3
REDUCTION - BY A NUMBER OF COMPOUNDS
NCl
3
+ 4 HCl NH
4
Cl + 3Cl
2
3Na
2
SO
3
+ NCL
3
+ 3H
2
O NH
4
Cl + 3Na
2
SO
4
+ 2HCl
RADIATION
2NCl
3
N
2
+ 3Cl
2
HEAT
U.V.

27. NCl
3
SAFE OPERATION LIMITS
VESSEL CAPACITY
MAXIMUM CONCENTRATION OF NCL
3
PPM W/W
CALCULATED RECOMMENDED
50 KG 200-300 20
1000 KG 50- 60 20
20 T 15 5
50 T 8 2
• 20 ppm w/w NCl
3
is generally accepted maximum level
for liquid Chlorine.

28. EXPERIENCES WITH NCl
3
MANAGEMENT
Different types of compressor being used for
compressing chlorine in chlor - alkali industries.
Reciprocating Chlorine Compressor.
Centrifugal chlorine Compressor.
Liquid seal ring type Compressor with sulphuric acid as sealing
material.
The management of Nitrogen tri chloride is well managed in
reciprocating and centrifugal compressor due to the
achievement of decomposition temperature 90
0
C .NCl3 is not
controlled in liquid seal ring type compressors as the operating
temperature range is 40 to 50
0
C
Practices adopted to control NCl
3
Concentration in
liquid chlorine evaporator:-
Purging system – part of the quantity at the bottom of the
evaporator is filled in tonners/cylinders at regular intervals
Purging & decomposition of part quantity of NCl
3
+Liquid
Chlorine at regular intervals is collected in a separate pot and
heated with steam at 80
0
C/25 Kg/cm
2
.
The decomposed material is released to chlorine neutralization
system.

29. EXPERIENCES WITH NCl
3
MANAGEMENT
Problems with liquid seal type compressors:
Some sulphuric acid mists are carried over to liquid chlorine
evaporators & cause iron sulphate formation.
This problem becomes more serious with the break down of mist
eliminator filter candle.
Under these conditions liquid chlorine + NCl
3
drain line (used for
transferring material) to tonners / cylinders gets chocked.
To continue the NCl
3
monitoring process, liquid chlorine + NCl
3
at the
bottom of the evaporators is transferred in the main 100m
3
storage
tank through the evaporator liquid chlorine inlet line during plant
stoppage.
No suitable online analyzer available for analysis of NCl
3
or to check
grab sample of NCl
3
control.
Details of agency to carry out analysis of NCl
3
is also not available.
Withdrawal and collection of NCl
3
sample for analysis is also difficult.
By using other type of compressors, discharge temperature can go
upto 90
0
C (NCl
3
decomposition point) against 40
0
C with liquid seal
ring type compressor. NCl3 decompositions is not appreciable with
this type of compressor

30. EXPERIENCES WITH NCl
3
MANAGEMENT
In the second process
Part of the quantity of liquid chlorine +NCl
3
mixture is decomposed
at 80
0
C in a steam heated jacketted catch pot.
The passage of liquid chlorine+NCl
3 catch pot can be reason of
explosion due to local hotspot.
The operation is done in gradual and cautious way.
After decomposition chlorine is released to chlorine neutralizing
system
Unreliability factor of analyzer and non availability of analysis facility
makes the case serious.
In order to avoid a problem of NCl
3
in the system all specifications of
raw material and chemicals are analyzed in the laboratory on
schedule basis. Possibility of online analyzers for brine is being
explored to check nitrogen compounds in the brine system.
No new material is added without thorough analysis for nitrogenous
matter.

31. NEED FOR DEVELOPMENT
Need is felt for
Availability and installation of online analyzer for brine to check
nitrogen compound
 Development of foolproof system of collecting samples of NCl
3

On line analysis at various NCl
3
accumulating pockets in chlorine
handling system.
To set up authorized agency for rechecking of on line analysis
Safe carriage of sample to external areas.
Development of a speedy and reliable test, coupled with more
frequent monitoring,
A mechanism to call for repeat analysis,
More frequent checks after one analysis has exceeded the usual
range.

32. CONCLUSION AND RECOMMENDATIONS
To establish practices & policies which will ensure the
safety of the process.
IT IS RECOMMENDED THAT ALL PRODUCERS AND CONSUMERS
SHOULD REVIEW THEIR SYSTEM AND OPERATION PERIODICALLY.
The process review should inspect/analyze the various
NCl
3 pockets in this process vessels.
In this process review, knowledge of the operating
condition to:
eliminate hazardous conditions,
for example, keep the NCl
3 concentration below 1.5% and
temperature below 30
o
C in NCl
3
accumulating pockets.

33. CONCLUSION AND RECOMMENDATIONS
The most important control over the potential level of
NCl
3
is
At source in Chlorine producing process.
Use of salt without anti-caking agent and mined salt without
nitrogenous explosives.
Use of safer type of water.
Whenever any raw material is changed a check should be made
to ensure that new NCl
3 risk has not been introduced.
Frequency level of NCl
3
analysis
Should be once in 3 months when NCl
3
is in 5-20 ppm.
Once in one year for NCl
3
concentration below 5 ppm is
suggested as guideline.

34. The Chlorine industry has gone
several years with only one
serious incident associated with
Nitrogen Tri-Chloride.
We always need to work
aggressively to prevent NCl
3

from accumulating and reaching
dangerous levels.

35. THANK YOU