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Comparison of FT-IR with Wet Chemical Reference Methods. Dr. Marc Coleman National Physical Laboratory. Contents. Description of measurements performed at a fibreglass manufacturing plant Comparison of HCl readings made by FT-IR and wet reference methods

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comparison of ft ir with wet chemical reference methods

Comparison of FT-IR with Wet Chemical Reference Methods

Dr. Marc Coleman

National Physical Laboratory

contents
Contents
  • Description of measurements performed at a fibreglass manufacturing plant
  • Comparison of HCl readings made by FT-IR and wet reference methods
  • Validation of HCl FT-IR reading via. modelling
  • Benefits of on-line FT-IR monitoring to fibreglass manufacturers and related industries
fibreglass case study aims
Fibreglass Case Study Aims
  • VAM 1.6 funded by NMS
    • To promote and validate the use of spectrometric techniques for multi-component on-line analysis
  • Currently, a contractor performs measurements of HCl and HF
    • Total fluorides and chlorides by a method based on USEPA 26a
  • Two-fold aim of case study
    • Compare FT-IR to a recognised reference method
    • Validate FT-IR reading via. modelling
experimental theory
Experimental Theory
  • Contractors “in-house” monitoring method
    • 5 impingers of H2O2 with silica gel in last impinger
    • Will dissolve total chlorides and fluorides
    • FT-IR cannot measure Cl2 due to spectroscopic selection rule
  • USEPA method 26
    • 1 empty impinger followed by 2 impingers of H2SO4 , 2 of NaOH and one of silica gel
    • Can discriminate between HCl and Cl2
    • Enabling direct comparison to FT-IR HCl readings
  • Four 1h runs performed of each method
  • Contractor sent all samples to a UKAS accredited lab for analysis
  • Samples from last run of each technique sent to a 2nd UKAS accredited lab for comparison
cl 2 determined from chloride found in naoh impingers

Run

Dry Cl2 concentration / ppm

EPA2

0.5

EPA3

0.7

EPA4

0.7

EPA5

0.6

0.7 (2nd UKAS lab)

Cl2 Determined from Chloride Found in NaOH Impingers
remarks
Remarks
  • FT-IR and USEPA values agree well
  • Difference between FT-IR and contractors in-house method greater
  • USEPA method indicates small quantities of Cl2 present
  • May rationalise difference in FT-IR and contractors in-house method readings
  • HCl and Cl2 can be inferred as the only Cl based species present. Otherwise wet methods would report higher chloride readings than the FT-IR HCl reading
    • Only holds for chlorides soluble in either H2SO4 or NaOH
modelling
Modelling
  • Raw IR spectra analysed and concentrations reported in real time by commercial software
  • How valid is analysis of commercial software?
  • Can answer by fitting a model calculated from an internationally accepted database
    • HITRAN
  • Modelling methodology – complex issue but briefly
    • Remove any interferents
    • Fit model by matching ILS
    • Compare HCl concentration obtained from modelling to that reported by commercial software to determine degree of validity
hcl fitted concentration
HCl Fitted Concentration
  • Fitted model yields an HCl concentration of 6.4 ppm
  • Analysing same spectrum commercial software determines a concentration of 5.8 ppm
  • Within error limits of commercial software the fit matches
  • Conclusions drawn in regard of comparison to wet chemical reference methods valid
benefits to fibreglass industry
Benefits to Fibreglass Industry
  • Economic
    • £35k on contractor monitoring
    • £6.5k on internal monitoring
    • Installing an FT-IR (~£50k) operated in-house could save ~£27k per annum. 2 year payback!
  • Technique applicable to many other industries. In particular, HF monitoring important to aluminium smelting and brick work industries.