Accuracy and Uncertainties of Mercury Fractionation in Hydrocarbons using CV-AFS Dr Bin Chen Dr Warren Corns P S Analytical. Orpington, United Kingdom www.psanalytical.com

Mercury in Crude Oil, Gas Condensates and Refined Products? Important feedstock for many industrial applications. Detrimental effect on refining operations such as poisoning of catalysts & corrosion of aluminium alloys and cryogenic cold boxes due to Hg induced embrittlement Product quality defines price! Less than 1ppbw required for high spec Naphtha. Measurement and sampling is therefore critical. Optimisation, design and monitoring efficiency of Hg removal strategies. Hg Speciation/fractionation important to understand the fate and transport of Hg across the process

Hg Species? Mercury Classification Forms of Mercury Elemental Hg Hgo(gas), Hgo (dissolved) , Hgo (solids) Particulate Hg HgS, Hg (solid associated), Hg (insoluble) Inorganic Hg Hg2+, Hg22+ Organometallic Hg R-Hg+ ,R-Hg-R, Hg thiolates - Unknowns?? Complexity of sample matrix and number of potential species of Hg inhibits the use of a single approach for determining all Hg species Fractionation Methods are therefore used

The Fractionation Method Hg Total CV-AFS Particulate Hg HgS Aqua Regia Other Particulate Hg Nitric Acid Volatile Hg Purge & Trap Dissolved Hg KCl extraction Ionic Hg Aqueous Phase Unknown Hg Organic Phase Organic Hg GC-AFS

Total, Dissolved & Particulate Hg Sample (1-3 g) Aqua Regia reflux (10 ml, 3 hrs) CV-AFS T-Hg Filtered Sample (0.45µm, 1-3 g) Aqua Regia reflux (10 ml, 3 hrs) CV-AFS Total Dissolved Hg T-Hg – D-Hg = P-Hg

Volatile Hg Hgo and R2Hg species Sample (5-50 g) Bubbler Argon 250 ml/min for 30 min Gold trap AFS Bubbler is washed with diluted HCl/NH2OHHCl between samples

KCl Extraction 40% KCl, 0.5% HCl, 0.1 g/L NH2OHHCl Filtered Sample (0.45µm, 10 g) Shake with KCl (10 ml, 0.5 hrs) Bromination of the aqueous phase KCl extractable ionic Hg Organic phase, AR or direct Non extractable Hg (organic?)

Organometallic Hg R-Hg-R, R-Hg+ , Hgo Filtered Sample (0.45 µm) Direct Injection GC-AFS Pyrolyser 8000C Detection as Hg0 Samples analysed with and without gold trap inline of AFS detector to confirm that signal is Hg

MDL and LODs Hg, ng/g MDL LOD Volatile Hg 0.001 0.0001 Total Hg 0.05 Dissolved Hg Ionic Hg Organic Hg by GCAFS 1

Hg Fractionation in Condensates Example data Sample A Sample B Sample C Sample D Sample E Sample F Sample G Sample H Sample I Total Hg 1.00 1.24 780.80 8.17 420.74 73.73 168.30 1034.00 925.30 Dissolved Hg 0.73 0.66 552.70 0.00 19.82 0.44 0.50 14.00 2.30 Ionic Hg, KCl 0.57 0.36 13.60 3.95 18.59 0.18 0.23 0.25 Unknown Hg, non - KCl NA NA (0.23) 539.10 Organic Hg Particulate Hg 0.27 0.58 226.20 4.06 400.92 73.29 167.80 1020.00 923.00 Volatile Hg 0.10 0.07 1.90 0.01 0.06 0.84 0.05 0.24 0.35 Fraction Sum 0.94 (94%) 1.01 (81%) (100%) 8.02 (98%) 419.57 74.31 (101%) 168.03 1020.47 (99%) 923.60 NA = Not Analysed - Only analysed if summation of fractions is poor ND = Not detected, MDL= 1ng/g All results in ng/g (ppbw) Fraction Sum = summation of columns in yellow Results have higher confidence if total Hg and Fraction Sum are in good agreement

Hg Fractionation in Crude Oil Example Data B1 B2 B3 B4 B5 B6 B7 B8 Total Hg 538.24 98.79 60.80 37.04 62.56 46.79 42.38 84.83 96.00 Dissolved Hg 43.44 7.72 9.12 4.25 11.82 7.79 6.69 13.13 4.99 Ionic Hg, KCl 19.06 4.73 7.59 3.43 6.08 4.46 3.82 6.60 0.74 Unknown Hg non-KCl NA Organic Hg ND Particulate Hg 494.80 91.07 51.68 32.79 50.74 39.00 35.69 71.70 91.01 Volatile Hg 24.25 0.20 0.10 0.08 0.12 0.33 0.25 0.37 Fraction Sum 538.11 (100%) (97%) 59.37 (98%) 36.30 57.02 (91%) 39.12 (84%) 39.84 (94%) 78.55 (93%) 92.12 (96%) NA = Not Analysed - Only analysed if summation of fractions is poor ND = Not detected. MDL = 1ng/g All results in ng/g (ppbw) Fraction Sum = summation of columns in yellow Results have higher confidence if total Hg and Fraction Sum are in good agreement Sample B – Same plant sampled at different periods

Hg Fractionation in Naphtha Example Data Sample A Sample B Sample C Sample D Sample E Sample F Total Hg 6.05 14.45 4.40 161.3 18.91 14.93 Dissolved Hg 4.33 13.15 2.30 161.2 1.36 0.49 Ionic Hg 1.61 1.86 1.90 160.6 2.35 0.09 Unknown Hg, non-KCl NA (2.70) NA (10.94) NA Organic Hg ND Particulate Hg 1.72 1.30 2.20 17.54 14.4 Volatile Hg 0.03 0.05 0.01 6.3 Fraction Sum 3.36 (56%) 3.21 (23%) 4.11 (93%) 166.9 (103%) 19.9 (105%) 14.52 (97%) NA = Not Analysed – ( Calculated shortfall in summation) ND = Not Detected, MDL = 1ng/g All results in ng/g (ppbw) Fraction Sum = summation of columns in yellow Results have higher confidence if total Hg and Fraction Sum are in good agreement.

Sampling Uncertainties for Liquid Hydrocarbons Depressurization and stabilization might release volatile Hg compounds such as elemental mercury vapour. Potential Loss of Mercury on sampling components. Materials and speed loop should be carefully considered. Losses of Mercury from association with particulates and aqueous phase. Sample filtration devices and sample point selection should be carefully considered. Losses and species conversion of Mercury during storage and shipping of samples. Sample containers and storage conditions are critical. Sample homogenization is required prior to measurement. Shipping regulations often require metal containers!

Measurement Uncertainty Questions? How does Homogenization and Filtration of sample affect accuracy. Solids and free water issues. Is the particulate Hg measurement influenced by Hg scavenging solids collected on the filter? What Hg species do we extract with each fractionation step? More research is needed to identify the ionic and organic species present. KCl extracted aqueous phase requires a full digestion inorganic divalent Hg is unlikely species. In most cases summation data compared to total Hg is very good. On some samples however summations can be lower? Our results indicate that missing portion is present in organic phase after KCl extraction. Analysis of this fraction will know be included for all samples. Do mercury removal sorbents trap all Hg species? Lack of CRM’s for this application and Inter-lab proficiency schemes

Questions? Thank you for your attention