Appendix 1

Table A.1

Summary of analytical techniques used in fouling studies

Short nameNameApplicationInformation typeSample stateAdvantagesDisadvantages/LimitationsSample sizeResolutionExperiment duration
UV–FUltraviolet–fluorescence spectroscopyDetermine aromaticity of sampleChemical structureSolidFast and easy to useQualitative information2 ml1 nm<1 min
FT–IRFourier transform–infrared spectroscopyChemical bond analysis, determining functional groupsChemical structureLiquid, solidFast and easy to useCannot analyse pure metals<0.1 ml, <10 mg±0.01 cm−1<1 min
NMRNuclear magnetic resonance spectroscopyDetermine aromaticity of sample, C/H ratio, functional groups, aromatic/aliphatic ratioChemical structureLiquid, solidHigh resolutionRequires high solubility in the solvent, longer time0.7 ml±0.01 ppm5min–1 h
GC/MSGas chromatography/Mass spectrometryDetermine molecular weight of crude oil volatile compounds with boiling point <500 °CMolecular weightLiquidMolecular weight analysis of highly complex mixtures of volatile compoundsA considerable proportion of hydrocarbons cannot be observed (400 u for aromatics, 500–550 u for aliphatic)<1 mlGC: ±1 s MS: ±0.01 mz−11–2 h
SECSize exclusion chromatographyMolecular weight distribution
Characterization of high-mass, polydisperse
Hydrocarbon mixtures		Molecular weightLiquidHigher MM ceiling respect to the GC/MSCan only detect just the soluble part of the sample<1 ml1 s1–2 h
MALDI-MSMatrix assisted laser desorption/Ionization mass spectrometryDetermine molecular weightMolecular weightSolidSoft mass analysis technique for large and sensitive materials. Higher mass ceiling.Desorbed asphaltene degradation may still a problem with MALDI-MS±0.01 mz−130 min
TGAThermogravimetric analysisAsh content, fixed carbon, % volatile lostReactivityLiquid, solidAnalysis of thermophysical properties of samples and allows probing into thermodegradation reactions at high temperature range in excess of 1000 °CLong analysis time ∼2–5 h<5 mgMass: ±0.0001 g Temp: ±0.01 °C2–5 h
Table Continued

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Short nameNameApplicationInformation typeSample stateAdvantagesDisadvantages/LimitationsSample sizeResolutionExperiment duration
STSolubility testDetermine what solvant dissolves solid samples; oil incompatibilityReactivityLiquid, solidQuick and straight forwardSubjective and imprecise; depends on physical conditions>10 ml–∼10 min
EAElemental analysisDetermine C, H, N, O, S contentElemental compositionLiquid, solidWell established; C, H, N, O difficult to determine by other meansCan be affected by other elements e.g., F>100 mg±0.01%Samples sent for analysis
XRFX-ray fluorescenceDetermine Fe, S, Si, Na, Ca, Al, metalsElemental compositionLiquid, solidFast and easy to useLarge sample size required5–10 ml, >3 g1 ppm30 min
ICPInductively coupled plasmaDetermine Fe, S, Si, Na, Ca, Al, metalsElemental compositionLiquid, solid, gasaccurate for trace metal analysisLong preparation required for samples in solution∼100 mg1 ppm1 h
OMOptical microscopyMorphology analysisMorphologySolidShows whether the foulant is isotropic or not, which suggests the main reason of coke formationLong sample preparation–1 μmN/A
SEM-EDXScanning electron microscopyTopology/Morphology analysisMorphologySolidIdentification of elements and their association with each otherLong sample preparation–1 nmN/A
XRDX-ray diffractionPhase identification, crystallinityMorphologySolidDetection of metal abundance, dispersion, and oxidation stateNo spatial information∼100 mgN/A∼30 min
XPSX-ray photoelectron spectroscopyComposition analysisMorphologySolid, liquidElemental composition of the surface–∼100 mgN/AN/A
–Spectrometer in a transmission configurationPossibility of taking chemical maps of materials and systems at the microscopic levelChemical structureLiquid and solid
Macro-ATRSpectrometer combined with macro ATR Accessories and focal plane array infrared detectorLarge fields of view for chemical imaging and characterization; studies dynamic systems in situ, studies precipitation and deposition in situ, in situ experiments at high temperatures and pressures; depth profile measurements.Chemical structureGases, liquids, and solids can be studied (including supercritical fluids)Versatility and chemical specificity–10–15 μmseconds
Table Continued

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Short nameNameApplicationInformation typeSample stateAdvantagesDisadvantages/LimitationsSample sizeResolutionExperiment duration
ATR-FTIRFTIR spectroscopic imaging system combined with microscope, for use in Micro-ATR imaging studiesChemical imaging of dynamic processesChemical structureSolid deposits, crude oilChemical specificity and high spatial resolutionGood contact with ATR crystal is required1–4 μmseconds to minutes
ATR-FTIRFTIR spectrometer combined with an infared microscope and a macro chamberChemical imaging of dynamic processesChemical structureSolid deposits, crude oilVersatility and chemical specificityGood contact with ATR crystal is required1–4 μm or 200 nmseconds to minutes
RamanRaman spectrometersChemical analysis of samples, including depth profile of microscopic samples, high spatial resolutionChemical structureSolid and liquidNoncontactThin layers studiedminutes
FT-RamanFT-Raman spectroscopic systemChemical characterization of challenging carbonaceous samples and depositsChemical structureSolidNoncontact–
TERSTip-enhanced Raman systemNanoscale imaging of samples as it combines the high spatial resolution of atomic force microscopy with the chemical information of Raman spectroscopyChemical structureSolidProvides unique nanoscale insight a very high spatial resolutionA very challenging and expensive experiment10 nmminutes to hours

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