Comparison of FT-IR with Wet Chemical Reference Methods

1. Comparison of FT-IR with Wet Chemical Reference Methods Dr. Marc Coleman National Physical Laboratory

2. 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

3. 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

4. Detected Emission Species

5. Experimental Design

6. 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

7. FT-IR vs. USEPA for HCl

8. 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

9. FT-IR vs. Contractors In-House Method for HCl

10. 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

11. 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

12. Species Model

13. Region for HCl Analysis

14. Fitting HCl+H2O Model to Measured Spectrum

15. 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

16. Advantages of FT-IR

17. 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.