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Trends and Developments in Process GC in the
Petrochemical Industry Tom Lynch BP Chemicals,
Hull, England
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Future Strategy for Process Plant Analysis

• Petrochemical plants are large high volume assets
  often producing several hundred thousand tonnes
  per year (Hull has 6 plants making gt2m TPA)
• GoalProvide faster real-time control of
  processes and product release through application
  of new analyser technology.
• Consequencereduce routine lab testing and move
  to on-line and at-line analysis.
• Laboratory becomes a function focussed on the
  development of on-line and at-line process
  analysis and specialist problem solving.

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Conventional Process GC
Or back to the time when Dinosaurs still walked
on the earth!

• Safety requirements Certification (limits
  performance).
• Generally single application, may use sample
  stream switching.
• Generally Packed columns
• Air bath isothermal ovens
• Simple detectors, generally max of 2 per
  instrument
• Short cycle time can be very important
• Simple but inflexible data processing
• Relied heavily on column switching and
  multidimensional techniques with valves to
  achieve separations
• Operator interaction via a screen on the
  instrument

So Whats Changed?
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The Siemens Advance Maxum 2 Process GC

• Complete Plug and Play Components
• Dual Air Bath or Dual Airless Ovens
• 8 Channels of EPC
• Flexible 10 port valves (gt12)
• New Detectors
• TCD 6 measurement and 2 reference cells per unit
• FID with integral independant heater
• up to 3 detector units per GC ( eg 24 TCD cells)
• Capillary columns
• Live Switching Technology
• Parallel Chromatography
• EZChrom software for control and data
  processing
• Open system Network Communications

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Siemens- Live Switching

• Live Switching is used exclusively by Siemens in
  their On-Line GCs and has many advantages over
  conventional valve switching including
• Suitable for use with packed and capillary
  columns, very low dead volume.
• Completely pneumatic - no mechanical valves (more
  reliable).
• Inert system, important for highly active
  compounds such as organic acids.
• One live T piece can replace 2 conventional
  valves!!

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Simplifying Multidimensional Chromatography
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Methyl Acetate Process Stream

• Crucial for process control result determines
  whether stream is diverted to off spec.
• Currently carried out using 2 analysers
• One for methanol (10) and water (1)
• The other for ppm butyl acetate (normally lt5ppm)
• Main aim is to carry out both analysis on one
  instrument
• Secondary aim is to include other components of
  interest such as methyl acetate (85) and the
  other impurities, namely acetone (0.1) and ethyl
  methyl ketone (EMK) (250ppm), could be useful.

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Methyl Acetate Process StreamThe live-T
solution

• 2 x 30m 0.32id DB 624 columns joined by live T
• Cut from column 1 outlet to FID for ppm levels
• Straight to column 2 for further separation and
  detection by TCD for water and other level
  components

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Methyl Acetate Stream Chromatograms

• The sample is injected onto Column 1 and the
  early eluting components namely water, methanol,
  acetone, and methyl acetate are allowed to
  continue through to Column 2 for further
  separation and then detection by the TCD.

• After the methyl acetate has passed into column
  2 the live T is activated and the later eluting
  components, namely EMK and butyl acetate are
  directed out the cut vent for detection at the
  FID.

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Methyl Acetate Stream Butyl Acetate
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Methyl Acetate Stream Summary

• A single analyser application has replaced two
  analysers
• The new method uses a single inject valve with a
  single capillary column cut at its mid point and
  re-joined with a live T. The old methods needed 2
  inject valves 3 stream switch valves and 5
  columns.
• In addition to hardware there will be significant
  utilities savings and lower maintenance.
• More components can be determined for free!!!

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Multidimensional Process GC Trace Propionic Acid
in Pure Acetic Acid

• Crucial for both process control and product
  specification.
• The acids are highly polar and active which
  gives severe problems due to adsorption on
  surfaces in current process GCs with valve
  switching.
• None of the existing analysers give satisfactory
  performance with the heart cut method and would
  not be acceptable for direct product rundown..
• Could Live switching provide the necessary
  performance?

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Multidimensional Process GC Trace Propionic Acid
in Pure Acetic Acid
FFAP
FFAP
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Multidimensional Process GC Trace Propionic Acid
in Pure Acetic Acid

• LEFT Current On-line GC where propionic acid
  is heartcut using 2 valves and 3 GC columns.
  Note peaks not resolved and poor peak shapes with
  tailing.

• RIGHT Same analysis using 1 Live-T and 2
  columns on a Siemens Advance Maxum. There is
  baseline resolution between the acetic and
  propionic acid and less peak tailing giving
  lower detection limits and better accuracy and
  precision. Also once installed the T-piece is
  maintenance free.

Live switching instead of valves means

• From this to this with-
• Less hardware
• Lower maintenance
• Improved accuracy and precision
• i.e. Better quality for less cost!

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Permanganate Time for Acetic Acid

• Permanganate Time is a wet chemical test which
  gives a measure of the amount of readily
  oxidisable impurities which will react with
  potassium permanganate in solution.
• In order to pass the pink/purple colour of the
  permanganate must not be discharged within the
  time specified for that product. For Acetic
  Acid the specified permanganate time is 2 hours.
• All standard Pharmacopoeia and ASTM methods are
  based on a visual end-point relying on the
  detection of the pink colour of residual
  permanganate in a brown background.
• Permanganate Time is a product specification for
  Acetic acid and Anhydride, Ethanol, Methanol,
  Acetone, Pyridine and Tricresyl phosphate.
• We have now identified the impurities in acetic
  acid which consume the permanganate so could we
  infer product quality for permanganate time using
  results from a process GC.

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Permanganate Time for Acetic Acid

• 2 columns with a live-T for the cut and
  backflush.
• A 15m x 530µ id JW DB-FFAP retains the acetic
  acid while allowing the non-acidics to pass on to
  Column 2 a 30m x 530µ DB-624 and then detected
  by FID.
• The acid is then backflushed from column 1.
• Quantifies mesityl oxide (MO), methyl crotonate
  (MC) and methyl 3,3-dimethylacrylate (MDMA).
• Cycle time for the method was 6 mins compared to
  3 hours.

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Permanganate Time for Acetic Acid
Typical chromatograms obtained from the GC method
for a sample (red trace) with a permanganate
time of 73 minutes overlaid with another sample
(blue trace) with a predicted permanganate time
of circa 24 hours
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Multiple Linear Regression of Residual
Permanganate in Acetic Acid from GC Data
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Permanganate Time for Acetic Acid Summary

• Product quality for acetic acid with respect to
  permanganate time can be inferred from process GC
  data by measuring ppm levels of key impurities.
• A measure of product quality can be obtained
  on-line every 6 minutes, previous best was a lab
  result after 3 hours which only gave a pass or
  fail.
• This will allow much tighter control of the
  process and allow product to be exported directly
  without intermediate storage.
• It will also allow chemists to better understand
  what causes the formation of these impurities in
  the process and look for ways to minimise their
  production.

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Multiple Detectors for Performance Monitoring
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Multiple Detectors for Performance Monitoring
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The Future?

• The role of the laboratory GC will diminish while
  the role of the on-line process GC will increase
• The new generation of hardware allows extensive
  use of multidimensional hyphenated systems and
  this will only increase.
• Process GC can provide useful inferential
  measurements for other product quality tests.
• Process GCs will change dramatically. They will
  become highly automated systems with self
  diagnostic fault finding allowing predictive
  maintenance and self validation.
• Miniaturisation will further facilitate the use
  of fast GC and cheap multiple detectors which
  will allow the development on new instruments
  which include all the features above.

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A Final Message

• You've carefully thought out all the angles.
• You've done it a thousand times.
• It comes naturally to you.
• You know what you're doing, its what you've been
  trained to do your whole life.
• You dont need to use new technology
• Nothing could possibly go wrong, right ?

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Think Again!