parr 6400 - Calorimetry Calculations; Heat of Combustion and Corrections

Calculations
54
7
ASTM Treatment for Acid and Sulfur
In the ASTM treatment, the correction for acid
formation assumes that all the acid titrated is nitric
acid. Obviously, if sulfur is present in the sample,
which in turn produces sulfuric acid, part of the
correction for the sulfuric acid formed is already
included in the ASTM nitric acid correction (e
1
).
This is adjusted by a separate computation based
upon the sulfur content of the sample. An additional
correction of 1.37 kcal must be applied for each
gram of sulfur converted to sulfuric from sulfur
dioxide. This is based upon the heat of formation
of sulfuric acid, from sulfur dioxide, under oxygen
combustion vessel conditions, which is -72.2 kcal/
mol or -36.1cal/mEq. But remember, a correction
of 14.1cal/mEq of sulfuric acid is already included
in the ASTM nitric acid correction (e
1
). Therefore
the additional correction which must be applied for
sulfur will be the difference between 36.1 and 14.1
or 22.0cal/mEq (44.0 kcal/mol). For convenience,
this is expressed, in the ASTM e
2
formula, as 13.7cal
(44.0/32.06) for each percentage point of sulfur per
gram of sample.
ISO Calculations
Both the ISO 1928 and BSI 1016: Part 5 methods
for testing the calorific value of coal and coke, deal
with acid and sulfur corrections in a manner which
is somewhat different than ASTM procedures.
Provision has been made in the 6400 Controller for
dealing with these different procedures.
The analysis of vessel washings in these methods
call for a titration, first using 0.1N barium hydrox-
ide (V
2
) followed by filtering, and a second titration
using 0.1N HCL(V
1
) after 20 mL of a 0.1N sodium
carbonate has been added to the filtrate. Table
B-1 gives the settings which allows the results of
the two titrations, V
1
and V
2
, to be entered into the
controller directly for the calculation of the total
acid correction. V
1
should be entered at the prompt
for acid and V
2
is entered at the prompt for sulfur.
The settings in the Settings for ISO & BSI Methods
table assume that the same procedure is carried
out for both standardization and determination.
The offset value is the product of -1, the Heat of
Formation of Nitric Acid, the acid multiplier, and
the 20mL of 0.1 N sodium carbonate used in the
analysis. The formula used to get the total correc-
tion in calories is as follows: =
V
1
(Acid Multiplier)(Heat of Formation of
Nitric Acid)
V
2
(Sulfur Multiplier)(Heat of Formation of
Sulfuric Acid) + offset value.
The values for fixed acid and sulfur, which are used
in preliminary reports, will reflect a sulfur correc-
tion of 0, and a nitric acid correction of 10 calories.
Settings for ISO & BSI Methods
Page Line Setting Value
Thermochemical
Corrections
Acid Correction (STD) Entered HNO
3
13
Fixed Sulfur STD Off 7
Acid Correction (DET) Entered HNO
3
13
Fixed Sulfur DET Off 7
Calculations
Factors
Acid Multiplier 0.154
Sulfur Value is Percent Off
Sulfur Multiplier 0.1
Use Offset Correction On
Offset Value -43.5