ASTM D3120-96(2002)e1

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
An American National Standard
e1
Designation:D3120–96 (Reapproved 2002)
Standard Test Method for
Trace Quantities of Sulfur in Light Liquid Petroleum
Hydrocarbons by Oxidative Microcoulometry
This standard is issued under the fixed designation D3120; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
e NOTE—Warning information was moved editorially from notes to section text in September 2002.
1. Scope 2.3 Thesemicroequivalentsoftriiodide(iodine)areequalto
the number of microequivalents of titratable sample ion enter-
1.1 This test method covers the determination of sulfur in
ing the titration cell.
the range from 3.0 to 100 ppm (µg/g) in light liquid hydrocar-
bons boiling in the range from 26 to 274°C (80 to 525°F).
3. Significance and Use
1.2 This test method may be extended to liquid materials
3.1 This test method is used to determine trace quantities of
with higher sulfur concentrations by appropriate dilution.
sulfur in reformer charge stocks and similar petroleum frac-
1.3 The preferred units are micrograms per grams. Values
tions where such trace concentrations of sulfur are deleterious
stated in SI units are to be regarded as the standard. Values in
to the performance and life of the catalyst used in the process.
inch-pound units are for information only.
Higher concentrations of sulfur in products analyzed by this
1.4 This standard does not purport to address all of the
test method after appropriate dilution are often detrimental to
safety concerns, if any, associated with its use. It is the
the use of the product.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
4. Interferences
bility of regulatory limitations prior to use. For specific hazard
4.1 This test method is applicable in the presence of total
statements, see 6.3, 6.4, 6.8, and 6.10.
halideconcentrationsofupto10timesthesulfurlevelandtotal
2. Summary of Test Method nitrogen concentrations of up to 1000 times the sulfur level.
4.2 This test method is not applicable in the presence of
2.1 A liquid sample is injected into a combustion tube
total heavy metal concentrations (for example, Ni, V, Pb, etc.)
maintained at about 800°C having a flowing stream of gas
in excess of 500 µg/g (ppm).
containing about 80 % oxygen and 20 % inert gas (for
example, nitrogen, argon, etc.). Oxidative pyrolysis converts
NOTE 1—To attain the quantitative detectability that the method is
thesulfurtosulfurdioxidewhichthenflowsintoatitrationcell capable of, stringent techniques must be employed and all possible
sources of sulfur contamination must be eliminated.
whereitreactswithtriiodideionpresentintheelectrolyte.The
triiodide thus consumed, is coulometrically replaced and the
5. Apparatus
total current required to replace it is a measure of the sulfur
5.1 Pyrolysis Furnace—The sample should be pyrolyzed in
present in the sample injected.
an electric furnace having at least two separate and indepen-
2.2 The reaction occurring in the titration cell as sulfur
dently controlled temperature zones, the first being an inlet
dioxide enters is:
section that can maintain a temperature sufficient to volatilize
2 2 1
I 1 SO 1 H O→ SO 13I 12H (1)
3 2 2 3
all the organic sample. The second zone shall be a pyrolysis
The triiodide ion consumed in the above reaction is gener- section that can maintain a temperature sufficient to pyrolyze
ated coulometrically thus:
theorganicmatrixandoxidizealltheorganicallyboundsulfur.
A third outlet temperature zone is optional.
2 2 2
3I → I 12e (2)
The apparatus described in Sections 5.1 to 5.5 inclusive, is similar in
This test method is under the jurisdiction of ASTM Committee D02 on specifications to equipment available from Dohrmann Div. of Rosemount, 3240
Petroleum Products and Lubricants and is the direct responsibility of Subcommittee Scott Blvd., Santa Clara, CA95050. For further detailed discussions, in equipment,
D02.03 on Elemental Analysis. see: Preprints—Division of Petroleum Chemistry,American Chemical Society, Vol
Current edition approved April 10, 1996. Published June 1996. Originally 1, No. 3, Sept. 7–12, 1969, p. B232 “Determination of Sulfur, Nitrogen, and
published as D 3120–72T. Last previous edition D 3120–92. Chlorine in Petroleum by Microcoulometry,” by Harry V. Drushel.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
e1
D3120–96 (2002)
5.1.1 Pyrolysis furnace temperature zones for light liquid sufficiently high purity to permit its use without lessening the
petroleum hydrocarbons should be variable as follows: accuracy of the determination.
Inlet zone up to at least 700°C 6.2 Purity of Water—The water used in preparing the cell
Center pyrolysis zone 800 to 1000°C
electrolyte should be demineralized or distilled or both. Water
Outlet zone (optional) up to at least 800°C
of high purity is essential.
5.2 Pyrolysis Tube, fabricated from quartz and constructed
NOTE 3—Distilledwaterobtainedfromanallborosilicateglassstill,fed
in such a way that a sample, which is vaporized completely in
from a demineralizer, has proven very satisfactory.
theinletsection,issweptintothepyrolysiszonebyaninertgas
6.3 Acetic Acid (rel dens 1.05)—Glacial acetic acid
where it mixes with oxygen and is burned.The inlet end of the
(CH COOH). (Warning—Poison. Corrosive. Combustible.
tube shall hold a septum for syringe entry of the sample and
May be fatal if swallowed. Causes severe burns. Harmful if
side arms for the introduction of oxygen and inert gases. The
inhaled.)
center or pyrolysis section should be of sufficient volume to
ensure complete pyrolysis of the sample. 6.4 Argon, Helium, or Nitrogen, high purity grade (HP),
used as carrier gas. (Warning—Compressed gas under high
5.3 Titration Cell, containing a sensor-reference pair of
electrodes to detect changes in triiodide ion concentration and pressure. Gas reduces oxygen available for breathing.)
a generator anode-cathode pair of electrodes to maintain 6.5 Cell Electrolyte Solution—Dissolve 0.5 g of potassium
constant triiodide ion concentration and an inlet for a gaseous iodide(KI)and0.6gofsodiumazide(NaN )inapproximately
500 mL of high-purity water, add 5 mL of acetic acid (CH
sample from the pyrolysis tube. The sensor electrode shall be
platinum foil and reference electrode platinum wire in satu- 3COOH) and dilute to 1000 mL.
rated triiodide half-cell. The generator anode and cathode
NOTE 4—Bulk quantities of the electrolyte should be stored in a dark
half-cell shall also be platinum. The titration cell shall require
bottle or in a dark place and be prepared fresh at least every 3 months.
mixing, which can be accomplished through the use of a
6.6 Gas Regulators—Two-stage gas regulators must be
magnetic stirring bar, stream of inert gas, or other suitable
used on the reactant and carrier gas.
means. (Warning—Excessive speed will decouple the stirring
6.7 Iodine (I), 20 mesh or less, for saturated reference
bar,causingittoriseinthecellanddamagetheelectrodes.The
electrode.
creation of a slight vortex is adequate.)
6.8 Iso octane (2,2,4-trimethylpentane). (Warning—
5.4 Microcoulometer,havingvariableattenuation,gaincon-
Extremely flammable. Harmful if inhaled. Vapors may cause
trol, and capable of measuring the potential of the sensing-
flash fire.)
reference electrode pair, and comparing this potential with a
biaspotential,amplifyingthepotentialdifference,andapplying
NOTE 5—The most reliable solvent is a sulfur-free form of the sample
theamplifieddifferencetotheworking-auxiliaryelectrodepair
type to be analyzed.Alternatively, use a high-purity form of cyclohexane
so as to generate a titrant. Also the microcoulometer output
[boiling point 80°C (176°F)], isooctane (2,2,4-trimethyl pentane) [boiling
point, 99.3°C (211°F)], or hexadecane [boiling point, 287.5°C (549.5°F)].
voltage signal shall be proportional to the generating current.
5.5 Recorder,havingasensitivityofatleast0.1mV/in.with
6.9 n-Butyl Sulfide (CH CH CH CH ) S.
3 2 2 2 2
chart speeds of ⁄2 to 1 in./min. Use of a suitable electronic or
6.10 Oxygen, high purity grade (HP), used as the reactant
mechanical integrator is recommended but optional.
gas. (Warning—Oxygen vigorously accelerates combustion.)
5.6 Sampling Syringe—A microlitre syringe of 10-µL ca-
6.11 Potassium Iodide (KI), fine granular.
pacity capable of accurately delivering 1 to 10 µL of sample
6.12 Sodium Azide (NaN ), fine granular. (Warning—
into the pyrolysis tube. 3-in. by 24-gage needles are recom-
Toxic, causes eye and skin irritation; explosive.)
mended to reach the inlet zone of the pyrolysis furnace.
6.13 Sulfur, Standard Solution (approximately 30 µg/g
NOTE 2—Since care must be taken not to overload the pyrolyzing
(ppm))—Pipet 10 mL of sulfur stock solution (reagent 6.14)
capacity of the tube by too fast a sample injection rate, means should be
into a 100-mL volumetric flask and dilute to volume with
provided for controlling the sample addition rate (0.1 to 0.2 µL/s).
isooctane.
6. Reagents and Materials NOTE 6—Theanalystmaychooseothersulfurcompoundsforstandards
appropriate to sample boiling range and sulfur type which cover the
6.1 Purity of Reagents—Reagent grade chemicals shall be
concentration range of sulfur expected.
used in all tests. Unless otherwise indicated, it is intended that
all reagents shall conform to the specifications of the Commit- 6.14 Sulfur, Standard Stock Solution(approximately 300µg/
tee onAnalytical Reagents of theAmerican Chemical Society, g (ppm))—Weigh accurately 0.5000 g of n-butyl sulfide into a
where such specifications are available. Other grades may be tared 500-mL volumetric flask. Dilute to the mark with
used, provided it is first ascertained that the reagent is of isooctane and reweigh.
gof n2butylsulfide 30.2187 310
S,ppm ~µg/g!5 (3)
gof ~n2butylsulfide 1solvent!
Reagent Chemicals, American Chemical Society Specifications, American
Chemical Society, Washington, DC. For Suggestions on the testing of reagents not
listed by the American Chemical Society, see Annual Standards for Laboratory
Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia High-purity grade gas has a minimum purity of 99.995%.
and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, Pesticide test grade such as Mallinckrodt “Nano-grade” isooctane has been
MD. found satisfactory.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
e1
D3120–96 (2002)
7. Preparation of Apparatus with an automatic injection adapter, the injection rate (volume/
pulse) should be calibrated to deliver 0.1 to 0.2 µL/s.
7.1 Carefully insert the quartz pyrolysis tube in the pyroly-
8.5 Repeat the measurement of each calibration standard at
sis furnace and connect the reactant and carrier gas lines.
least three times.
7.2 Addtheelectrolytesolutiontothetitrationcellandflush
1 1
several times. Maintain an electrolyte level of ⁄8 to ⁄4in. (3.2
NOTE 8—Not all of the sulfur in the sample comes through the furnace
astitratableSO .Inthestronglyoxidativeconditionsofthepyrolysistube
to 6.4 mm) above the platinum electrodes.
some of the sulfur is also converted to SO which does not react with the
7.3 Place the heating tape on the inlet of the titration cell. 3
titrant. Accordingly, sulfur standards of n-butyl sulfide in isooctane or
7.4 Position the platinum foil electrodes (mounted on the
sulfur standards appropriate to sample boiling range and sulfur type and
moveable cell head) so that the gas inlet flow is parallel to the
sulfur concentration should be prepared to guarantee adequate standard-
electrodes with the generator anode adjacent to the generator
ization. Recoveries less than 75 % are to be considered suspect. Low
cathode. Assemble and connect the coulometer and recorder
recoveries are an indication to the operator that he should check his
(integrator optional) as designed or in accordance with the parameters, his operating techniques, and his coulometric system. If the
instrumentisbeingoperatedproperly,recoveriesbetween75and90%are
manufacturer’s instructions. Fig. X1.2 illustrates the typical
to be expected. Satisfactory standard materials are given in Table 2.
assembly and gas flow through a coulometric apparatus.
7.4.1 Turn the heating tape on.
8.6 IfthefractionofsulfurconvertedtoSO dropsbelow75
7.5 Adjust the flow of the gases, the pyrolysis furnace
% of the standard solutions, fresh standards should be pre-
temperature, titration cell, and the coulometer to the desired
pared. If a low conversion factor persists, procedural details
operating conditions. Typical operational conditions are given
should be reviewed.
in Table 1.
9. Procedure
8. Calibration and Standardization
9.1 Flushthe10-µLsyringeseveraltimeswiththeunknown
8.1 Prepare a series of calibration standards covering the
sample. Determine the sulfur concentration in accordance with
range of sulfur concentration expected. Follow instructions in
8.2 to 8.6.
6.13, 6.14, or dilute to appropriate level with isooctane.
9.2 Sulfur concentration may require adjustment of sensi-
8.2 Adjust the operational parameters (7.5).
tivity settings or sample volume or both.
NOTE 7—See Fig. 1 for the variance of percent recoveries with gas
10. Calculation
ratios and temperature.
10.1 Calculate the sulfur content of the sample in parts per
8.3 Thesamplesizecanbedeterminedeithervolumetrically
million, ppm µg/g, by mass as follows:
or by mass. The sample size should be 80 % or less of the
syringe capacity.
Sulfur,ppmµg/g 5 ~A 31.99!/~R 3 M 3 F! (4)
8.3.1 Volumetricmeasurementcanbeobtainedbyfillingthe
Sulfur,ppm 5 A 31.99 310 / R 3 V 3 D 3 F (5)
~ ! ~ !
syringe with about 8 µL or less of sample, being careful to
eliminate bubbles, retracting the plunger so that the lower where:
liquid meniscus falls on the 1-µL mark, and recording the A = area under curve, in. ,
1.99 = derivation will be found in X1.3,
volume of liquid in the syringe. After the sample has been
R = coulometer range switch setting, V,
injected, again retract the plunger so that the lower liquid
M = mass of sam
...