"
CI analytics article(P8-10)
4/6/04
9:58 AM
Page 2
8
Sulphur Analysis
article
Evaluation of Sulphur Measurement Analytical Techniques for
Sulphur in Gases and Fuel
Surinder (Sandy) Thind
author
Applications Chemist
C.I.Analytics, Chambly, QB, Canada
Tel: (1) 450 658 4965
Fax: (1) 450 658 3428
e-mail: sandythind@cianalytics.ca
www.cianalytics.com
Over the last decade, the importance of detecting sulphur in petroleum-related products has increased dramatically. This is likely related to the necessity
of complying with increasingly stringent government regulations, protecting expensive catalysts, and ensuring product quality. Reasons for detection and
control of sulphur in different process streams have existed for the last fifteen years, but detection limits have been reduced dramatically in recent times.
For example, in order to protect expensive, sulphur-intolerant catalysts, the production feed for polypropylene or polyethylene must be monitored for
sulphur content. The sulphur analyser used in this application must now have the ability to detect sulphur from 1 parts per billion to 10 parts per million.
C.I. Analytics provides the best solution for each client’s sulfur analysis requirements. We are able to
do so since, we offer any of the three best-known technologies in the field:
Country
Sulphur Levels in
Gasoline by
2002
Sulphur Levels in
Gasoline by
2005
Sulphur Levels in
Diesel by
2006
< 30 ppm
< 15 PPM
USA
< 30 PPM
< 15 PPM
Europe
< 30 PPM
< 15 PPM
Canada
< 200 ppm
(At present the levels
range from 300-600 ppm)
This paper describes and evaluates all the latest techniques available to perform these analyses with
high levels of accuracy and speed.
The most Popular Technologies available to meet Ever-Tightening Regulations and low level
detection for catalyst protection:
Sulphur measurement may prove to be difficult, particularly at low levels, but choosing the best
technological fit for the application often minimises such difficulty. This article examines the
strengths and weaknesses inherent with each sulphur measurement technology currently available
for detection of low levels of sulphur in hydrocarbon fuel samples and analysers used for blending
operations.
Best known and used Technologies offered world-wide for low-level detection of sulphur in inert
gases, hydrocarbon gases, and hydrocarbon liquids include the following:
1.
2.
3.
4.
5.
GC-Flame Photometric Detector (FPD and PFPD)
Dry Colorimetric Method (Tape-based)
Sulphur Chemiluminescence Method (SCD)
UV Fluorescence (UVF)
X-Ray Fluorescence (XRF)
1. Flame Photometric Detector (FPD) and Pulsed FPD:
These sulphur analysers, with gas chromatograph and Flame Photometric Detector, are based on
technology that has not changed over the last 40 years. The FPD, with its high selectivity for sulphur
compounds, was generally the detector of choice for on-line applications in the sixties and seventies.
Unfortunately, however, it suffers from a squared response, which limits its ability. The FPD is also
subject to quenching of the signal by hydrocarbons and carbon dioxide. This limitation requires that
the sulphur compounds be separated from the interfering matrix before detection by FPD.
To reduce the hydrocarbon quenching, and to get a linear response from this detector, the
following technique has been used. Using a high temperature pyrolyzer, a small amount of
hydrocarbon sample is burned in air to form SO2, CO2, and H2O. These three gases are then
separated on a packed column. The SO2 peak is sent to the FPD for detection while the CO2 and H20
peaks are sent to vent. At times the GC separation of H20 and SO2 is a problem.
The pulsed FPD was designed to improve upon the ‘old’ traditional FPD design but has failed to
perform well especially for on-line analysers. Even in the lab the PFPD offers many challenges and
requires special training.
PIN June/July 2004
2. Tape Based Detectors: Dry Colorimetric Detector (DCD)
Dry Colorimetric Detector Technique to detect sulphur in petroleum samples is still the most wildly used
and reliable technique.
Theory of Operation
Classical colorimetry utilises an impinger to collect gas in a liquid medium.
Chemical reagents are then added to the medium to cause it to change colour in proportion to the
concentration of gas present. The resulting colour change is measured by a laboratory spectrophometer
and compared to standards.
Sensi-Tape Detectors are also colorimetric based, but are dry reaction substrates which serve as gas
collecting and analysing media. Individually formulated for a specific gas or family of gases, each SensiTape is a nontoxic, proprietary chemical reagent system. When exposed to a target gas, the tape will
change colour in proportion to the amount of gas: the higher the concentration, the darker the stain will
appear.
The change in colour, or stain, on the Sensi-Tape is read by a photo-optical system, then compared to
a standard response curve preprogrammed into the system.
Chemical formulations deposited on the tape provide a detection medium that is fast, sensitive, and
specific.
Each of the proprietary detector tapes reacts instantly to the target gas, providing a visible colour
reaction. As a result, tape detectors provide a method of detecting and analysing toxic gases that must be
identified in process streams at PPB levels and removed.
While the Tape Detection System is extremely sensitive to its target gas, it is also very specific to that
gas. It will not react to other substances (solvents, hydrocarbons, etc.) often found in process streams.
Thus, expensive downtime due to false alarms is virtually eliminated.
"
عضویت 
ورود اعضا
راهنمای خرید
