process analytical chemistry a different world
TRANSCRIPT
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Process Analytical ChemistryA Different World
Lynn A. Melton
University of Texas at Dallas
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Process Analytical Chemistry
• PAC is the art and science of makingmeasurements for the purpose of control oflarge scale chemical processes.
• In large companies, the number of “labchemists” is decreasing and the number of“process analyzers” is increasing.
• Industry needs people with knowledge ofprocess analytical chemistry.
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Lab v. On-line Analysis
$$$$$
grabsampleanalysis
variability
processanalyzervariability
processdisasters
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Process Analytical Chemistry
• Your task is to construct an analyticallaboratory in which– data is available > 98% of the time for 15 years;
– each instrument gets one hour of service/month;
– updated analyses are available every 5 minutes;
– the samples may be high pressure, hightemperature, wet, and/or dirty;
– the lab is in a corrosive environment.
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Process Analytical ChemistryMaking Money!
• Allow better process control
• Must calculate LTCO (“long term cost ofownership”)– an analyzer which requires a lot of maintenance
can cost you money (and the engineers will stopusing the data)
– reliability is the key!
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Process Analytical Chemistry
• Simplicity is the key to reliable instrumentoperation.
• The goal is– “no moving parts”
– automated self calibration
– failure of instrument is unambiguous.
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Process Analytical ChemistryGas Chromatography
• Widely used in industry
• Advantages– multi-component analyses
– can determine isomers
• Disadvantages– speed of analysis
– the multiport valve is a “moving part”
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Online GC ApplicationsBackflush - Uses
• Used to trap “heavy” components forflushing to vent or detector– protects analytical column(s)
• more robust applications
• 6 mos - 1 year without maintenance
– reduces analysis time
– most online applications include a backflushoperation
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Online GC ApplicationsBackflush - Timing Diagram
BF AC1 TCD
carrier gas back flush gas
0 - 25 sec
BF AC1 TCD
25 - 100 sec
analyte
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Online SpectroscopyNon-Dispersive IR Analyzers
• Filter Photometers
• Luft detection
• Gas Correlation
• Maintenance Aspects
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Method for Single-beam, Single-λ
Source
Filter
Measuring Cell
Detector
Gas in
Gas out
Source
Filter
Measuring Cell
Detector
Gas in
Gas out
N2
Sample X
λ
Sig
nal
λS
igna
l
Reference
Measurement
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Method for Single-Beam, Dual-λ
Measuring CellGas in
Source
Filters
DetectorGas out
Source
Filters
Measuring Cell
Detector
Gas in
Gas out
Reference
Measurement
λS
igna
l
λ
Sig
nal
Sample X
Sample X
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Process Analytical ChemistrySampling
• Expect that the sampling system will cost40-50% of the total project
• If the sampling system does not work right,the measurements are meaningless.
• Must transport and condition the sample sothat the (one atmosphere, roomtemperature) instrument can make accurate,long term reliable measurements.
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General Characteristics ofSample Systems
• Typically cost about as much as theanalyzer
• Typically the highest maintenance part ofthe system
• The part of an analyzer system that is mostlikely to result in the failure of an analyzerproject
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In-Situ vs. Extractive Samples• In-situ analyzer sensor/probe is mounted
directly in the process vessel– fiber optic spectrometer interface
– zirconium oxide O2 analyzer
– conductivity probe
• Extractive sample is removed from theprocess pipe and delivered to the analyzer– gas chromatographs
– mass spectrometers
– paramagnetic O2 analyzers
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Sample Conditioning Systems• Extract sample from process
• Transfer sample to analyzer
• Convert or maintain the sample state to one thatis compatible with the analyzer
• Return the sample to an appropriate waste stream
• Provide additional infrastructure to support theanalyzer such as calibration, lab sample facilities,etc.
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Components of a SampleConditioning System
ProcessStream
SampleConditioning
ReturnSample
Analyzer
Lab Sample
Sample Extraction
Calibration Standard
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Sample System Design Issues (1)
• Does the sample represent the portion of theprocess you want to analyze?
• Does the sample system provide the sampleto the analyzer in a timely manner?
• Is the sample presented to the analyzer in astate that is compatible with the analyzer?
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Sample System Design Issues (2)
• Is the sample system cost effective?
• Is the sample system reliable?
• Is the sample system maintainable?
• Is the sample system safe during all processconditions and during hardware failureincidents (fail-safe)?
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Practical Aspects of ProcessAnalytical Chemistry
• In 1999, when Melton was at DowChemical Company in Freeport, Texas, heand Dow organized a one week intensiveshort course, Practical Aspects of ProcessAnalytical Chemistry.
• The course materials are now available tocollege instructors.
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Practical Aspects of ProcessAnalytical Chemistry
• In January 2001, UT-Dallas and DowChemical Company co-sponsored a oneweek workshop to help twelve collegefaculty members learn Practical Aspects ofProcess Analytical Chemistry.
• They will begin to incorporate the PAPACmaterials into their chemistry and chemicalengineering courses.