2012 Corporate Capabilities - Spectroscopy

22 Spectroscopy 26(12) December 2011 www.spectroscopyonline.com
Figure 1: Temporary setup of FT-IR analyzer
for analysis of the ethylene stream in case
study 1 for use with attended operation only.
Figure 2: Temporary setup of FT-IR analyzer
in case study 2 for continuous 24/7 data
collection.
referred to as “traceable” because
analysts can refer to primary and
secondary standards corresponding
to the spectral information from
the process sample. Analysts may
also examine the raw spectral data
for interferences that have not been
present previously or do not match
the anticipated stream composition.
A variety of chemometric modeling
techniques (1) are available to obtain
quantitative information, trending
information, or simple qualitative
stream composition analysis from
the raw spectra depending on the
purpose and requirements of the
particular application.
The insights and data obtained
from continuous online FT-IR can be
applied to optimize process control
models, validate the consistency of
production quality, or inform development
of robust and reliable permanent
process analyzer applications.
The following case studies focus on
process control optimization and
product quality.
Experimental
Before discussing case studies it will
be useful to highlight a few basic
considerations for installing a FT-IR
system in a process environment. Of
course, spectrometer setup, operation,
and data processing must be
appropriately specified for a given
application, but unless the sample is
reliably and safely delivered to the
spectrometer the analysis details are
mute. Process analyzer installation
and methods can be complex (2), but
two major design considerations for
temporary analysis are safety and
sample system design. The first to
consider is safety. Although some
safety concerns associated with handling
samples for laboratory analysis
are mitigated by using a process
analyzer and eliminating routine
grab sampling, a distinct set of other
safety related hazards must be addressed.
Of primary concern is assuring
area classifications are met to
mitigate explosion or exposure risks.
In the first case study, the stream was
comprised mostly of ethylene and the
area classification issue was of critical
importance. Because the FT-IR
system that was used was not classified
for a Class 1 Division 2 area,
operating procedures were developed
designating attended operation with
appropriate area lower explosion
limit (LEL) monitoring and emergency
shutdown plans should the
LEL monitor indicate the presence
of a flammable atmosphere. A picture
of the field setup of the analyzer
is shown in Figure 1. On days when
there was a threat of rain, a canopy
was placed over the whole system.
The preferred option would have
been to package the spectrometer in
a z-purged analyzer enclosure. Cost
and timing constraints prevented the
preferred path of C1D2 packaging for
the analyzer in the ethylene analysis
case study. Figure 2 shows the analyzer
packaged for the product quality
case study where the analyzer was
installed in the field and operating
under nonattended operation 24/7.
In the product quality case study, the
location was a nonclassified area, but
the stream composition was highly
toxic and corrosive. The analyzer
enclosure was exposed to the elements
and vortex coolers were used
to control the temperature inside
the enclosure.
The second set of design considerations
revolve around sample systems
and sample handling panels.
Having a continuous online analysis
is not useful if the analyzer is not
provided with a consistent and representative
process sample for analysis.
Sample systems are an integral
part of the success or failure of a process
analytical system (3). FT-IR and
spectroscopic techniques in general
demand much simpler sample systems
than required by typical process
gas chromatography systems,
but fundamentals such as flow and
pressure as well as avoiding condensation,
particulates, and plugging
are still essential. Key methods for
liquid- and gas-phase sample systems
for FT-IR implementation are different.
Here, the focus is on gas-phase
FT-IR as this technique has repeatedly
been demonstrated to meet the
temporary online stream characterization
requirements in a variety of
Dow processes. When it comes to liquid-phase
analysis, attenuated total
reflectance (ATR) FT-IR techniques
are occasionally used, but probe
fouling and lack of ability to monitor
trace levels can be limiting and
the use of a near-infrared or Raman
system may be preferable. For gasphase
process streams, long-pathlength
FT-IR analysis is a workhorse
for stream characterization. The
two systems that were used in the
case studies discussed below are the
MKS 2032 MultiGas FT-IR system
(MKS Instruments, Andover, Massachusetts)
and the Gasmet DX4000