ASTM D7796-12

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Designation: D7796 − 12 An American National Standard
Standard Test Method for
Analysis of Ethyl tert-Butyl Ether (ETBE) by Gas
Chromatography
This standard is issued under the fixed designation D7796; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
2.1 ASTM Standards:
1.1 This test method covers the determination of the purity
D3700 Practice for Obtaining LPG Samples Using a Float-
ofethyl tert-butylether(ETBE)bygaschromatography.Italso
ing Piston Cylinder
provides a procedure to measure impurities in ETBE such as
D4057 Practice for Manual Sampling of Petroleum and
C to C olefins, methyl, isopropyl and tert-butyl alcohols,
4 12
Petroleum Products
methyl sec-butyl and methyl tert-amyl ethers, acetone, and
D4307 Practice for Preparation of Liquid Blends for Use as
methyl ethyl ketone.
Analytical Standards
1.2 This test method is not applicable to the determination
D4626 Practice for Calculation of Gas Chromatographic
of ETBE in gasoline.
Response Factors
D6304 Test Method for Determination of Water in Petro-
1.3 Water cannot be determined by this test method and
leum Products, Lubricating Oils, and Additives by Cou-
shall be measured by a procedure such as Test Method D6304
lometric Karl Fischer Titration
and the result used to normalize the chromatographic values.
D7618 Specification for Ethyl Tertiary-Butyl Ether (ETBE)
1.4 Most of the impurities in ETBE are resolved by the test
for Blending with Aviation Spark-Ignition Engine Fuel
method, however, some co-elution is encountered.
E355 Practice for Gas Chromatography Terms and Relation-
ships
1.5 This test method is inappropriate for impurities that boil
E594 Practice for Testing Flame Ionization Detectors Used
at temperatures higher than 180 °C or for impurities that cause
in Gas or Supercritical Fluid Chromatography
poor or no response in a flame ionization detector, such as
water.
3. Terminology
1.6 The values stated in SI units of measurement are
3.1 Definitions—This test method makes reference to many
preferred and used throughout the standard. Alternate units, in
common gas chromatographic procedures, terms, and relation-
commonusage,arealsoprovidedtoimproveclarityandaidthe
ships. Detailed definitions of these can be found in Practices
user of this test methods.
E355 and E594.
1.7 This standard does not purport to address all of the
3.2 Definitions of Terms Specific to This Standard:
safety concerns, if any, associated with its use. It is the
3.2.1 C to C olefins, n—common olefin impurities in
4 12
responsibility of the user of this standard to establish appro-
ETBE including unreacted feedstock and dimers or trimers of
priate safety and health practices and determine the applica-
feed such as trimethylpentene or pentamethylheptene.
bility of regulatory limitations prior to use.
1.8 This international standard was developed in accor-
4. Summary of Test Method
dance with internationally recognized principles on standard-
4.1 Arepresentative aliquot of the ETBE product sample is
ization established in the Decision on Principles for the
introduced into a gas chromatograph equipped with a methyl
Development of International Standards, Guides and Recom-
silicon bonded phase fused silica open tubular column. Helium
mendations issued by the World Trade Organization Technical
carrier gas transports the vaporized aliquot through the column
Barriers to Trade (TBT) Committee.
where the components are separated by the chromatographic
process. Components are sensed by a flame ionization detector
as they elute from the column.
This test method is under the jurisdiction of ASTM Committee D02 on
Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of
Subcommittee D02.04.0L on Gas Chromatography Methods.
Current edition approved May 15, 2012. Published November 2012. DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/D7796-12. contact ASTM Customer Service at service@astm.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7796 − 12
4.2 The detector signal is processed by an electronic data and electronics, designed for optimum response with open
acquisition system or integrating computer. Each eluting com- tubular columns, is required.
ponent is identified by comparing its retention time to those
7.2 Sample Introduction—Manual or automatic liquid sy-
established by analyzing standards under identical conditions.
ringe sample injection to the splitting injector is employed.
4.3 The concentration of each component in mass percent is Devices capable of 0.1 µL to 0.5 µL injections are suitable. It
determined by normalization of the peak areas after each peak should be noted that inadequate splitter design, or poor
area has been corrected by a detector response multiplication injection technique, or both, can result in poor resolution.
factor and the water content of the sample. The detector Overloadingofthecolumncanalsocauselossofresolutionfor
response factors are determined by analyzing prepared stan- some components and, since overloaded peaks are skewed,
dards with the concentrations similar to those encountered in variation in retention times. Watch for any skewed peaks that
the sample. indicate overloading during column evaluation. Observe the
component size and where possible, avoid conditions leading
5. Significance and Use
to this problem during the analyses.
5.1 The presence of impurities in ETBE product can have a
7.3 Open Tubular Column —This test method utilizes a
deleterious effect upon the value of ETBE as a fuel additive.
fused silica open tubular column with non-polar methyl sili-
Oxygenateandolefincontentsareofprimaryconcern.Thistest
cone bonded (cross-linked) phase internal coating such as one
method provides a knowledge of the composition of ETBE
of the following:
product. This is useful in the evaluation of process operations
Column length 50 m 100 m 150 m
control, in the valuation of the product, and for regulatory
Film thickness 0.5 µm 0.5 µm 1.0 µm
Internal diameter 0.20 mm 0.25 mm 0.25 mm
purposes.
Other columns with equal or greater resolving power may be
6. Interferences
used. A minimum resolution between trans-2-pentene and
tert-butanol, and between cis-2-pentene and tert-butanol of 1.3
6.1 Cyclopentane and 2,3-dimethylbutane have been ob-
is required. The 150 m column is expected to decrease the
served to co-elute with MTBE. However, these are not com-
likelihood of co-elution of impurities.
monly found impurities in MTBE, and MTBE is typically
present at very low concentrations in ETBE.
7.4 Electronic Data Acquisition System—Any data acquisi-
tion and integration device used for quantification of these
7. Apparatus
analyses shall meet or exceed these minimum requirements:
7.4.1 Capacity for at least 50 peaks per analysis,
7.1 Gas Chromatograph—Instrumentation capable of oper-
7.4.2 Normalized area percent calculations with response
ating at the conditions listed in Table 1. A heated flash
factors,
vaporizing injector designed to provide a linear sample split
7.4.3 Identification of individual components based on re-
injection (that is, 200:1) is required for proper sample intro-
tention time,
duction. Carrier gas controls shall be of adequate precision to
7.4.4 Noise and spike rejection capability,
provide reproducible column flows and split ratios in order to
7.4.5 Sampling rate for fast (<1 s) peaks,
maintain analytical integrity. Pressure control devices and
7.4.6 Positive and negative sloping baseline correction,
gages shall be designed to attain the linear velocity required in
7.4.7 Peak detection sensitivity compensation for narrow
the column used (for example, if a 150 m column is used, a
and broad peaks, and
pressure of approximately 550 kPa (80 psig) is required). A
7.4.8 Non-resolved peaks separated by perpendicular drop
hydrogenflameionizationdetectorwithassociatedgascontrols
or tangential skimming as needed.
8. Reagents and Materials
TABLE 1 Typical Operating Conditions
Column Temperature Program
8.1 Carrier Gas, helium, 99.99 % pure. (Warning—
Column length 50 m 100 m 150 m
Compressed gas under high pressure.)
Initial temperature 40 °C 50 °C 60 °C
Initial hold time 13 min 13 min 13 min
8.2 Fuel Gas, hydrogen, 99.99 % pure. (Warning—
Program rate 10 °C ⁄min 10 °C ⁄min 10 °C ⁄min
Extremely flammable gas under pressure.)
Final temperature 180 °C 180 °C 180 °C
Final hold time 3 min 7 min 20 min
8.3 Ethyl tert-Butyl Ether, 99.99 % pure. (Warning—
Injector
Flammable liquid. Harmful if inhaled.)
Temperature 200 °C
Split ratio 200:1
8.4 Oxidant, air, oil free. (Warning—Compressed gas un-
Sample size 0.1 µL to 0.5 µL
der high pressure.)
Detector
Type flame ionization
8.5 Make-Up Gas, nitrogen, 99.99 % pure. (Warning—
Temperature 250 °C
Fuel gas hydrogen ('30 mL ⁄min) Compressed gas under high pressure.)
Oxidizing gas air ('300 mL ⁄min)
Make-up gas nitrogen ('30 mL/min)
Carrier Gas
Petrocol DH series columns from Supelco, Inc., Bellefonte, PA were used to
Type helium
Average linear velocity 20 cm ⁄s – 24 cm/s obtain the retention data and example chromatogram shown in this standard. Other
suitable columns are available commercially.
D7796 − 12
8.6 Reference Standards: specimen for analysis directly from the sealed septum vial, for
8.6.1 tert-Amyl methyl ether.(Warning—Flammableliquid. either manual or automatic syringe injection.
Harmful if inhaled.)
10. Preparation of Apparatus
8.6.2 Butane. (Warning—Flammable liquid. Harmful if
inhaled.)
10.1 Install and condition column in accordance with manu-
8.6.3 tert-Butanol. (Warning—Flammable liquid. Harmful
facturer’s or supplier’s instructions. After conditioning, attach
if inhaled.)
column outlet to flame ionization detector inlet and check for
8.6.4 sec-Butyl methyl ether. (Warning—Flammable liquid.
leaks throughout the system. When leaks are found, tighten or
Harmful if inhaled.)
replace fittings before proceeding.
8.6.5 4,4-Dimethyl-2-neopentyl-1-pentene. (Warning—
10.2 Adjust the carrier gas flow rate so that an average
Flammable liquid. Harmful if inhaled.)
linear velocity at the starting temperature of the run is between
8.6.6 Isobutylene. (Warning—Flammable liquid. Harmful
21 cm⁄s and 24 cm⁄s, as determined in Eq 1. Flow rate
if inhaled.)
adjustment is made by raising or lowering the carrier gas
8.6.7 Methanol.(Warning—Toxicflammableliquid.Harm-
pressure (head pressure) to the injector. The following starting
ful if inhaled or ingested.)
point pressures can be useful to adjust the carrier gas flow:
8.6.8 2-Methyl-2-butene. (Warning—Flammable liquid.
Column length 50 m 100 m 150 m
Harmful if inhaled.)
Starting point pressure, 262 (38) 275 (40) 552 (80)
8.6.9 Methyl tert-butyl ether. 99 + % pure (Warning— kPa (psig)
Flammable liquid. Harmful if inhaled.)
10.2.1 Average Linear Gas Velocity:
8.6.10 2,2,4,6,6-Pentamethyl-3-heptene. (Warning—
µ 5 L⁄t (1)
ave m
Flammable liquid. Harmful if inhaled.)
where:
8.6.11 n-Pentane. (Warning—Flammable liquid. Harmful
if inhaled.)
L = the length of the column in cm, and
8.6.12 cis-2-Pentene.(Warning—Flammableliquid.Harm- t = the retention time in seconds of methane.
m
ful if inhaled.)
10.3 Adjust the operating conditions of the gas chromato-
8.6.13 trans-2-Pentene. (Warning—Flammable liquid.
graph to conform to the list in Table 1. Turn on the detector,
Harmful if inhaled.)
ignite the flame, and allow the system to equilibrate.
8.6.14 2,4,4-Trimethyl-1-pentene. (Warning—Flammable
10.4 When the method is first set up, ensure that the FID is
liquid. Harmful if inhaled.)
notsaturated.PlotthepeakareaversusETBEconcentrationfor
8.6.15 2,4,4-Trimethyl-2-pentene. (Warning—Flammable
prepared standards in the concentration range of interest. If the
liquid. Harmful if inhaled.)
plot is not linear, increase the split ratio, or use a less sensitive
8.6.16 Dimethyl ether. (Warning—Extremely flammable
detector range, or both.
gas. Harmful if inhaled.)
8.6.17 Diethyl ether. (Warning—Flammable liquid. Harm-
11. Column Evaluation and Optimization
ful if inhaled.)
11.1 In order to establish that the column/temperature pro-
8.6.18 2,2,4-Trimethylpentane. (Warning—Flammable liq-
gram will perform the required separation, the resolution
uid. Harmful if inhaled.)
between cis-2-pentene and tert-butanol and between trans-2-
8.6.19 Ethanol. (Warning—Flammable liquid.)
pentene and tert-butanol must be determined. The retention of
tert-butanol relative to cis- and trans-2-pentene is very tem-
9. Sampling
perature dependent. The order of elution of cis-2-pentene and
9.1 ETBE may be sampled either in a floating piston
tert-butanol reverses at subambient temperature. A column
cylinder or into an open container since vapor pressures less
which does not resolve these components after adjusting
than 70 kPa (10 psi) are expected.
operating conditions is unsuitable.
9.1.1 Cylinder Sampling—Refer to Practice D3700 for in-
11.2 Analyze a standard mixture that contains approxi-
structionsontransferringarepresentativesamplefromasource
mately 1 % each of tert-butanol, cis-2-pentene, and trans-2-
into a floating piston cylinder.Add inert gas to the ballast side
pentene in ETBE by the procedure in Section 13. Calculate
of the piston to achieve a pressure of 310 kPa (45 psi) above
resolution (R) between tert-butanol and cis-2-pentene and
the vapor pressure of the sample.
between trans-2-pentene and tert-butanol using Eq 2. Both
9.1.2 Open Container Sampling—Refer to Practice D4057
resolutions shall be at least 1.3.
for instructions on manual sampling from bulk storage into
2~t 2 t !
open containers. Stopper container immediately after drawing
B A
R 5 (2)
1.699 W 1 W
~ !
the sample.
A B
where:
9.2 Preserve the sample by cooling to approximately 4 °C
and by maintaining that temperature until immediately prior to
R = resolution,
analysis.
t = retention time Component A,
A
t = retention time Component B,
B
9.3 Transfer an aliquot of the cooled sample into a pre-
W = peak width at half height of Component A, and
A
cooled septum vial, then seal appropriately. Obtain the test
D7796 − 12
the response factors of certified blends that have been pur-
W = peak width at half height of Component B and t >t .
B B A
chased or blends prepared in accordance with Practice D4307.
12. Calibration and Standardization
13. Procedure
12.1 Identify component peaks from a sample analysis by
matchi
...