FIELD OF THE INVENTION:
This invention relates to a method for the estimation of sulpur in coke
samples.
BACKGROUND OF THE INVENTION:
Coke is used as fuel in blast furnace. Coke contains sulfur which is
transferred to hot metal during blast furnace operation. Sulpur is
present as impurity in hot metal and is not a desirable element in steel
also. Sulfur has a detrimental influence on the properties of steel. For
high sulfur additional fuel is required in the blast furnace and at steel
melting shop extra DS compound is required to lower the level of sulfur.
Hence it is very important to ascertain the sulfur content in coke, for
blast furnace operation.
According to existing methods, the coke sample is ground to pass a 72
mesh sieve, and is heated with eschka mixture which is a 2:1 mixture of
magnesium oxide and anhydrous sodium carbonate. The reaction is
conducted in an oxidizing atmosphere at 800°C to convert all sulpur into
sulphate, which is extracted and determined gravimetrically. In this
method, an accurately weighed quantity of sample is transferred to a
porcelain crucible and mixed with eschka mixture. It is levelled and
covered with a further quantity of reagent, and the crucible is kept for
four hours in a muffle furnace at 800°C.
The cake formed in crucible is extracted, acidified and boiled to expel
carbon dioxide and filtered through a paid which is washed with water.
The acidity of the solution is maintained at (3-4%). The solution is boiled
and precipitated out as barium sulphate by adding barium chloride. The
precipitate is filtered washed with water, ignited in a pre weighed silica
crucible, at 800°C for 1 hours, cooled and weighed.
A blank is run simultaneously, to allow for any atmospheric
contamination, and sulphur is calculated from the corrected weight of
barium Sulphate.
This is a process involving a number of steps of heating, extraction,
filtration, acedification etc. rendering the process time consuming and
cumbersome. Therefore, the need exists in the industry to develop a
process which is easy to run, quick and cost-effective.
OBEJCTS OF THE INVENTION:
It is therefore an object of this invention to propose a process for
estimation of sulphur in coke samples which is quick and simple.
It is a further object of this invention to propose a process for estimation
of sulphur in coke samples which uses simple, easily available reagents
and is cost-effective.
These and other object of the invention will be apparent from the ensuing
description.
At the outset of the description, which follows, it is to be understood that
the ensuing description only illustrates a particular form of this
invention. However, such a particular form is only an exemplary
embodiment and the teachings of the invention is not intended to be
taken restrictively.
BREIF DESCRIPTION OF THE INVENTION:
Thus according to this invention is provided a method for the estimation
of sulphur in coke samples.
In accordance with this invention the coke sample is ignited in a stream
of oxygen, whereby the sulphur in the sample of coke is converted into
sulphur dioxide which is bubbled into a solution of iodine liberated from
the reaction of potassium iodate and potassium iodide in acidic medium.
The excess of iodine is back titrated with std. sodium thio-sulphate
solution.
A solution of concentrated hydrochloric acid, potassium iodide and
standard potassium iodate solution are taken in an absorption vessel
alongwith a few drops of starch solution, as indicator. A quantity of the
dried sample is placed in a combustion boat. A small piece of tin-foil is
placed below the sample. The boat is carefully inserted into the hot zone
(Temperature 1150-1200°C) of the combustion tube of furnace. The same
is preheated for one minute and then oxygen (free from SO2) is passed at
high speed of 1.5 to 2.0 L/minute.
Gas is bubbled through the iodine solution. The colour of solution
gradually disappears and tends to become colourless. At this time some
more standard potassium iodate solution is added so that the colour of
the solution persists.
The flow of oxygen is further continued for 30 seconds to ensure that
there is no further change in the colour.
If the std. potassium iodate solution is added in excess, then the excess
of iodine is back titrated with std. Na-thio-sulphate solution.
A reference sample is also analysed, and appropriate correction is
applied to get the actual value of the sample.
Sulphur is calculated from the formula =X(0.1) x Std. correction
Where X= Volume of std. KIO3 solution.
The invention will now be explained in greater detail with the help of the
following non-limiting example.
Example:
Reagents: Conc. HC1, Potassium iodide (2.5%), (N/32) Std. Potassium
iodate solution, (N/32) Std. Na-thio-sulphate and (1%) Starch solution.
A furnace unit is fitted with a combustion tube and the coke sample is
ignited in a stream of oxygen at 1200°C.
10 ml. Conc. HC1, 8 ml . (2.5%) KI solution 3-4 ml. std. KI03 solution are
taken in the absorption vessel. The volume is made 100 ml. with chilled
distilled water. A few drops of freshly prepared starch solution is also
added as indicator.
0.5 gm of the dried sample is place in a combustion boat and a small
piece of tin-foil is placed below the sample. The boat is carefully inserted
into a hot zone of the combustion tube of furnace. The sample is
preheated for one minute and then oxygen (free from SO2) is passed at a
speed of 2L/min and the sample is ignited at 1200°C.
Gas is bubbled through the iodine solution. As the colour of solution
gradually disappears more standard potassium iodate solution is added
from the burette so that the colour of the solution persists.
The flow of oxygen is further continued for 30 seconds to ensure that
there is no more change in the colour. The excess is back titrated using
std. sodium thiosulphate solution.
In order to validate the method samples has been analysed by both the
methods and the results are given below.

However, the method according to the present invention is far more
efficient, quick and cost effective compared to the methods existing in the
prior art.
WE CLAIM;
1. A method for the estimation of sulphur in a coke sample,
comprising the steps of igniting the coke sample in a stream of
oxygen to convert the sulphur in the sample to sulphur dioxide,
passing the sulphur dioxide into a solution of iodine, followed
by estimation of the excess iodine, and calculating the quantity
of sulpur from the formula
X(0.1) x standard correction
where X= volume of Potassium iodate solution.
2. The method as claimed in claim 1, wherein the coke sample is
ignited at a temperature in the range of 1150 to 1200°C.
3. The method as claimed in claim 1 wherein the iodine solution is
prepared using concentrate hydrochloric acid, potassium iodide
(KI) and standard potassium iodate (KI03) solution in
predetermined quantities.
4. The method as claimed in claim 1, wherein the iodine solution
includes an indicator such as starch.
5. The method as claimed in claim 1, wherein a small tin-foil is
kept below the coke sample during ignition.
6. The method as claimed in claim 1, wherein the stream of oxygen
is passed into the sample at a speed of 1.5 to 2 litres /minute.
7. The method as claimed in claim 1, wherein excess of potassium
iodate is added to the KI-KIO3 solution while sulphur dioxide is
passed into it, so that the colour of iodine persists.
8. The method as claimed in the preceding claims, wherein the
flow of oxygen containing sulphur dioxide, is continued upto a
time where no more change in iodine colour is observed.
9. The method as claimed in claim 1, wherein the excess iodine is
estimated by back-titrating with a standard sodium
thiosulphate solution.
10. The method as claimed in claim 1, wherein the standard
correction is introduced by analyzing a reference sample.

1. A method for the estimation of sulphur in a coke sample,
comprising the steps of igniting the coke sample in a stream of
oxygen to convert the sulphur in the sample to sulphur dioxide,
passing the sulphur dioxide into a solution of iodine, followed
by estimation of the excess iodine, and calculating the quantity
of sulpur from the formula
X(0.1) x standard correction
where X= volume of Potassium iodate solution.