FOCUS ON SULPHUR ANALYSIS


Figure 2: GSV injection of Sulphur components. 500 ppb level; PFPD.


The analysis of impurities like Sulphur components, Arsine and Phosphine at low ppb level is highly important when critical catalytic processes are involved like several refi ning stages or feedstock characterisation for fuel cell development. Gas


chromatography coupled with sensitive and selective detectors like FPD, PFPD, SCD and Mass Spectrometer is the proven technique for analysing individual species at ppb level in several matrices.


Applications


Gaseous samples like Natural Gas and Ethylene are injected using GSV (Gas Sampling Valve), according to ASTM D6228, D5303, D5504, UOP791 and ISO 19739. Liquid samples like fi nished fuels are injected using SSL (Split injector) or PTV (Programmable Temperature Vaporiser), according to ASTM D5623.


LPG samples are analysed by GSV after vaporising or by LSV (Liquid Sampling Valve). The Sample Securitiser is used for guaranteed quantitative liquid injection of LPG (see fi gure 1), handling all involved laboratory safety issues.


Figure 3: low level ppb Sulphur analysis using GCMS, SIM mode. GCMS


The Mass Spectrometer is usually not considered for low level Sulphur species analysis; (P)FPD and SCD have traditionally dominated this application. However GC-quadrupole MS is a very interesting alternative, providing in fact better sensitivity and selectivity and positive component identifi cation as added value. Figure 3 shows the mass chromatograms of H2S and COS at low ppb level while fi gure 4 demonstrates good linearity.


Figure 4: GCMS analysis of COS, linearity: R2 = 0.994 from 2 to 10 ppb. Arsine and Phosphine


Catalysts are not only extremely prone to poisoning by feedstock impurities such as Sulphur components, but also by contaminants like Arsine (AsH3) ad Phosphine (PH3). GCMS provides low level single digit ppb analysis of these components, see fi gure 5. Beside better sensitivity, GCMS offers positive component identifi cation for a variety of components groups, for instance oxygenates.


Figure 1: Sample Securitiser for guaranteed quantitative and safe injection of LPG samples


FPD or PFPD?


FPD (Flame Photometric Detector) and PFPD (Pulsed-FPD) both provide robust and reliable analysis. With PFPD the highest sensitivity is achieved: 15-35 ppb (depending on component), while LODs for FPD are in the 100-200 ppb range (based on signal to noise factor 3). Good selectivity is offered as well; hydrocarbon components show no positive response. However co-elution with very high amounts of hydrocarbons (bulk) decreases sensitivity and therefore chromatographic separation is optimised for each standardised method. Since selectivity and dynamic range of FPD and PFPD are comparable for both detectors, the choice is often determined by the needed sensitivity. PFPD offers 5 times better LODs, but its price is more than double. Figure 2 shows low level Sulphur analysis using GSV.


Figure 5: GCMS analysis of Arsine and Phosphine. Limit of detection is below 10 ppb.


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116