22-02-2013, 02:32 PM
ULTIMATE ANALYSIS OF COAL SAMPLE
Theory :
% Nitrogen is determined by Kjehdal’s method, which consists
of following steps
1. Acid digestion - the coal sample is first digested in strong
sulfuric acid in the presence of a catalyst, which helps in the
conversion of the amine nitrogen to ammonium ions,
N + H2SO4→ (NH4) 2SO4 + CO2 + H2O
ammonium ions are then converted into ammonia gas. Digestion
is completed when digesting liquor clarifies with release of
fumes.
2. Distillation - The ammonia gas is led into a trapping solution
where it dissolves and becomes an ammonium ion once again.
After ammonia distillation is complete and the residue in the
boiling (Kjeldahl) flask is cooled down.
3. Titration - finally the amount of the ammonia that has been
trapped is determined by titration with a standard alkali solution.
Procedure :
1. Weigh approximately 1 gm of the coal sample, making a note
of the weight, and placing the sample into a digestion flask, along
with 12-15 ml of concentrated sulfuric acid (H2SO4). Add seven
grams of potassium sulfate and a catalyst.
2. Bring the digestion tube/flask and mixture to a "rolling boil"
(about 370oC to 400oC) using a heating a block. Heating the
mixture in the tube/flask until white fumes can be seen, and then
continuing the heating for about 60-90 mins.
3. Raise the pH of the mixture by adding sodium hydroxide (45%
NaOH solution). This has the effect of changing the ammonium
(NH4
+) ions (which are dissolved in the liquid) to ammonia (NH3),
which is a gas.
4. separating the nitrogen away from the digestion mixture by
distilling the ammonia (converting it to a volatile gas, by raising
the temperature to boiling point) and then trapping the distilled
vapors in a special trapping solution of about 15 ml 0.01 N HCl
(hydrochloric acid).
5. Remove the trapping flask and rinse the condenser with water
so as to make sure that all the ammonia has been dissolved.
As the ammonia dissolves in the acid trapping solution, it
neutralizes some of the HCl.
Result : % N = _________ %.
Theory :
% Nitrogen is determined by Kjehdal’s method, which consists
of following steps
1. Acid digestion - the coal sample is first digested in strong
sulfuric acid in the presence of a catalyst, which helps in the
conversion of the amine nitrogen to ammonium ions,
N + H2SO4→ (NH4) 2SO4 + CO2 + H2O
ammonium ions are then converted into ammonia gas. Digestion
is completed when digesting liquor clarifies with release of
fumes.
2. Distillation - The ammonia gas is led into a trapping solution
where it dissolves and becomes an ammonium ion once again.
After ammonia distillation is complete and the residue in the
boiling (Kjeldahl) flask is cooled down.
3. Titration - finally the amount of the ammonia that has been
trapped is determined by titration with a standard alkali solution.
Procedure :
1. Weigh approximately 1 gm of the coal sample, making a note
of the weight, and placing the sample into a digestion flask, along
with 12-15 ml of concentrated sulfuric acid (H2SO4). Add seven
grams of potassium sulfate and a catalyst.
2. Bring the digestion tube/flask and mixture to a "rolling boil"
(about 370oC to 400oC) using a heating a block. Heating the
mixture in the tube/flask until white fumes can be seen, and then
continuing the heating for about 60-90 mins.
3. Raise the pH of the mixture by adding sodium hydroxide (45%
NaOH solution). This has the effect of changing the ammonium
(NH4
+) ions (which are dissolved in the liquid) to ammonia (NH3),
which is a gas.
4. separating the nitrogen away from the digestion mixture by
distilling the ammonia (converting it to a volatile gas, by raising
the temperature to boiling point) and then trapping the distilled
vapors in a special trapping solution of about 15 ml 0.01 N HCl
(hydrochloric acid).
5. Remove the trapping flask and rinse the condenser with water
so as to make sure that all the ammonia has been dissolved.
As the ammonia dissolves in the acid trapping solution, it
neutralizes some of the HCl.
Result : % N = _________ %.