better amine system operations through chemical analysis - lrgcc 2013 finalrev2[1].pdf

MPR Services, Inc. 2/25/2013

Better Alkanolamine System Operations ThroughChemical Analysis

Arthur L. CummingsGlen D. Smith

MPR Services Inc., Dickinson Texas© MPR Services, Inc. 2013

ABSTRACT

Chemical analysis opens the door to understanding, responding to, and preventingalkanolamine (amine) system operational difficulties. Unfortunately, the link between theanalysis report and the amine system operation is often unclear. The uncertainty resultsfrom several factors that can lead to misunderstandings, misinterpretations, frustrations,and mistrust of the lab. This paper attempts to provide clear definitions of analyticalterms, link them to their operational importance, translates terminology from differentsources to a uniform set of terms, and exposes analytical methods that can mislead you.This paper also provides questions you can ask your chemist, lab analyst, or aminevendor to avoid operational pitfalls and get the information you need from the analysisreports.

INTRODUCTION

An alkanolamine acid gas scrubbing system is a simple concept: a solution of water andalkanolamine absorbs acid gases from petroleum gas or liquid, and is pumped to a heatedregenerator that releases the acid gases, and then the amine is cooled as it returns to theabsorber. The amine solution can continuously circulate. The simple acid-base chemistryof the process can be monitored by a few analytical titrations (Table 1) and operatorsneed only to monitor temperatures, pressures, and flow rates to balance the amineabsorbing capacity with the acid gas removal requirement of the incoming petroleum gasor liquid. (The acid gas content of the sweetened product is, of course, the ultimatecontrol measure, but is beyond the scope of this paper.) This simplified view of aminesystems and operational conditions is the basis for which the most common analyticalmethods were developed.

Scott W. Waite


Table 1Fundamental Analytical Parameters of Amine Solutions

Parameter Analyte DescriptionAmine Strength Free Amine (FA) Amine available for acid gas

absorptionAcid Gas Loading(AGL)

Rich Loading (RL)

Lean Loading (LL)

Acid gas (H2S & CO2) in the solutionexiting the AbsorberAcid gas (H2S & CO2) in the solutionexiting the Regenerator

Water Water The remainder of the solution (if nocontaminants)

If no contaminants accumulated in the amine system, this could be the extent of theanalytical information required to operate. Unfortunately, contaminants do accumulate inamine systems and affect the equipment longevity and the success of the operation of theamine system. More unfortunate is the fact that the contaminants can affect the results ofthe fundamental analytical methods, misleading the operator, and yet the operatorcontinues to rely on these few simple tests for day-to-day operations.

Increased awareness of the effects of contaminants on operations has led to increasedunderstanding of the variety and identity of contaminants that exist in amine systems.Common analytical methods have been adapted, modified, and sometimes misapplied tocontaminant analysis. Contaminant-specific analytical methods have multiplied. Theamine system operator can now be confronted with a maze of analytical parameters, ablur of analytical results, and a host of analyte names and acronyms which can beambiguous, confusing and even misleading.

BETTER ANALYTICAL METHODS ARE NEEDED

A prime example of misleading results is illustrated in Figure 1 and Table 2. When weakacids (such as formic acid, acetic acid, etc.) have accumulated in the amine solution,forming Heat Stable Salts (HSS), the titration to determine free amine can also respond tothe weak acid anions. The choice of pH for the endpoint of the titration determineswhether the free amine titration is accurate or over-estimates the amine strength. A pH orcolor indicator that provides accurate amine strength in a clean amine solution cangrossly over-estimate the amine strength of a solution which contains weak acid anions(HSS or LL). Note, for example, in Figure 1, that Methyl Purple and Bromthymol Blueare both acceptable indicators for titration of clean amine solutions, but fail miserably ifthe solution contains significant weak acid HSS. The same is true for a pH “dead-stop”titration. The most common amine strength titration methods were developed for aminesolutions with no contaminants. Thus, contaminants may cause errors.


Figure 1

TABLE 2ERROR OF FIXED pH ENDPOINT TITRATION

45 wt% MDEA

ACETATEwt%

FORMATEwt%

SODIUM

wt%

ACTUALFREE

AMINEwt%

FOUND FREE AMINE,wt%

at Endpoint pH4.5 3.5 3.2

0 0 0 45.0 45.0 45.1 45.2

1 1 0 40.3 42.0 44.0 44.5

1 0 0 43.0 44.3 45.0 45.1

1 1 .5 42.9 44.6 46.6 47.1

1 0 .5 45.0 46.9 47.6 47.7


ENGINEERS AND CHEMISTS NEED AN UNDERSTANDING OF ANALYSES

With knowledge of the preceding information, the engineer responsible for the aminesystem can now ask the analytical chemist, or operator, “What endpoint indicator do youuse for the amine strength titration?” If the chemist responds “bromphenol blue” or “pH4.5” the engineer knows that amine strength results are probably higher than their actuallevel, unless there are no weak acids in the amine solution.

The better titration methods require tracking pH or conductivity during the titration anddetermining the endpoints by inflexion points in the first or second derivative,respectively. Both pH and conductivity can provide accurate free amine results, butconductivity is preferred because it also provides clear endpoints for the weak acids (SeeAppendix A).

This and other difficulties with amine strength determination, and their effects onoperations, are discussed at length in Amine Best Practices Group presentations at the2004 and 2005 Brimstone Sulfur Symposia.1,2

Before we seek to understand analytical methods, let’s clarify our understanding of theamine solvent itself.

THE AMINE SYSTEM IS SUPPOSED TO MAKE SALTS

The chemistry of alkanolamine solutions is quite simple, but is often described in termswhich lead to an incorrect view of amine interactions with acid gases and contaminants.Consequently, the understanding of analytical results becomes more difficult.

Alkanolamines are bases. Bases react with acids to make salts. Acid gases are absorbedand held in amine solutions because the amine forms a salt with the acid gas: The acidgas becomes an anion (negatively charged ion) and is associated with an amine cation(positively charged ion). The acid gas ion is no longer in a gaseous state and it cannotleave the amine solution as long as it remains as an anion.

The regenerable salts in Table 3 and the heat stable salts in Table 4 are written toemphasis the separateness of the ions. A cation is a positively charged molecule that isphysically disconnected from its neighboring anion, which is an independent moleculewith a negative charge. Anions and cations must be in equal numbers and uniformlydistributed throughout the solution, but are continually changing partners. This view ofions is critical to the understanding of amine acid gas absorption and regeneration.

For example, H2S absorbed in an amine solution is not bound to the amine. Rather, theamine has taken a hydrogen ion (H+) from the H2S, creating an AmH+ cation and an HS-

anion which cannot escape from the solution. The amine is bound to the H+, and does notreadily release it. The only way for the HS- to escape the solution is to take an H+ from


an AmH+, thereby recreating H2S, which has low solubility and high volatility and willexit the solution, unless another amine molecule reacts with it and removes one of its H+

to form another salt.

Acid gases are readily released from the thin films of liquid amine solution in an aminesystem regenerator, not because temperature “breaks the salts”, but because at highertemperatures and lower temperatures AmH+ more readily releases its H+, and the anionsof the acid gases readily take the H+ creating the gases that are less soluble and morevolatile at the elevated temperature and decreased pressure of the regenerator.

Heat stable salts, such as those in Table 4, do not leave the amine solution in the aminesystem regenerator. The acids of these salts are generally stronger acids than the acidgases (thus not as readily accept the H+ offered by the AmH+), and are more soluble andless volatile than the acid gases (thus do not leave the solution). The HSS anions can beclassed as weak acid anions (WAA) and strong acid anions (SAA). The functionaldistinction between WAA and SAA is seen in titration with acid in water: WAA- + H+

HWAA; SAA- + H+ SAA- + H+ . In words: WAA consumes H+ (making an acidmolecule), SAA do not.

The last four entries in Table 4 exemplify non-amine heat stable salts: salts whose cationis a Strong Cation such as sodium or potassium. These are often called Inorganic HeatStable Salts (IHSS) and are formed in amine solutions from addition of caustics (sodiumor potassium hydroxide or carbonate). The last two entries illustrate that excessiveconcentration of Strong Cations makes heat stable salts of the anions of acid gases,causing the lean loading of the regenerated amine to rise. Strong Cations must never beallowed to rise to the level that any acid gas becomes heat stable. This starts to occurwhen the molar ratio of strong cations to HSS anions reaches approximately 0.66.

Acid gas regeneration is aided by a low concentration of Amine heat stable salts, becausethey increase the population of AmH+ by decreasing the pH. The anions of acid gasesthen have a higher probability of obtaining H+ to convert back to the gaseous state andescape the solution of amine.

Acid gas regeneration can be hampered by Strong Cations, because they have no H+ togive. Anions of acid gases are attracted to the strong cations because of their positivecharge, and then must remain in the amine solution, because they cannot obtain an H+

from the strong cation.

Heat Stable Salts reduce amine strength, increase corrosivity, increase viscosity, increasedensity and displace water from the amine solution3,4. All these have deleterious effectson amine system operations. It is thus very important to know what and how much ofthese salts are accumulating in one’s amine system.


Table 3Regenerable Salts from Acids Gases in Amine Solutions

Acid + Base Cation + Anion

Acid Base Salt . Salt NameH2S Free Amine (“Am”) AmH+ + HS- Aminium bisulfideCO2 + H2O H2CO3

Am AmH+ + HCO3- Aminium bicarbonate

HCO3- Am 2AmH+ + CO3

= Aminium carbonateCO2 Am + Am AmH+ + AmCO2

- Aminium amine carbamate

Table 4Heat Stable Salts from Acids in Amine Solutions

Acid + Base Cation + Anion

Acid Base Salt . Salt NameFormic Am AmH+ + formate- Aminium formateAcetic Am AmH+ + acetate- Aminium acetatePropionic Am AmH+ + propionate- Aminium propionateThiocyanic Am AmH+ + SCN- Aminium thiocyanateThiosulfuric Am + Am AmH+ + S2O3

= + AmH+ Aminium thiosulfateHydrochloric(HCl)

Am AmH+ + Cl- Aminium chloride

Sulfuric Am + Am AmH+ + SO4= + AmH+ Aminium sulfate

Formic NaOH Na+ + formate- Sodium formateAcetate NaOH Na+ + acetate- Sodium acetateAcid gases are heat stable with caustics, for example:H2S NaOH Na+ + HS- + H2O Sodium bisulfideHCO3

- KOH K+ + CO3= + H2O Potassium carbonate

WHAT ANALYSES ARE NEEDED?

The first tier parameters affecting amine system performance are free amine and watercontent. The free amine represents the carrying capacity of the solution and the watercontent affects the acid gas absorption and desorption rates. The amine solvent supplier,amine system designer or the amine technical support person typically provides operatorswith recommended ranges of free amine and water for the particular application. If thereare no contaminants in the amine system, the Table 1 analyses would be sufficient –water could even be determined by difference. However, contaminants are common in


amines systems and a more detailed analysis is required. Table 5 shows severalparameters requiring analysis for proper operation of clean amine systems.

Table 5Solvent Parameters of Amine Solutions

Parameter Analyte Description and roleAmine Strength Free Amine (FA);

Regenerable FreeBase (RFB)

Amine available for acid gasabsorption

Reacted Amine Bound Amine (BA) Amine that has reacted with an acidand now carries an hydrogen ion:AmH+.

Total Amine Total Amine (TA)= FA + BA;Actual Total Base(ATB)

All the amine in the solution

Activators Proprietary additives that enhance theamine solution’s absorption rate orselectivity. Generally are included inFA, BA, and TA results

Water Water Water is essential for acid gasabsorption.

Physical Properties DensityViscosityConductivitySurface TensionAppearance

Physical properties of the solutionprovide monitors of compositionalchanges in the amine solution thataffect absorption, regeneration, heatdemand, corrosivity, and equipmentlongevity.

The trends in the amine system should be monitored on a regular basis. When BA rises orTA+Water departs significantly from near 100% the amine system could be becomingcontaminated and more information is needed. The second tier analyses – for dissolvedsubstances – are listed in Table 6.


Table 6Dissolved Substances in Amine Solutions (other than Solvent Amine)

Type Analytes Description and RoleAcid Gas (AG) Rich Loading (RL)

Lean Loading (LL)

H2S, CO2,Acid Gas Loading(AGL)

Acid gas (H2S & CO2) in the solutionexiting the AbsorberAcid gas (H2S & CO2) in the solutionexiting the RegeneratorThe acid gases measured separately; Inamine solution are ionic: HS-, HCO3

-,CO3

2-, and carbamate ions.Acids – organicand inorganic, alsocalled Heat StableSalts (HSS)

Heat Stable Salts(HSS); Total HSS;BA; HSAS; IHSS;individual anions*;ATB-RFB;Conductivity;

Acids which accumulate in the aminesolution by absorption and chemicalreactions within the amine solution.They reduce amine capacity, contributeto corrosion, increase density andviscosity and conductivity. Twogeneral types: Weak Acid Anion(WAA) and Strong Acid Anions(SAA) (see Appendix A)

Acids – amino(AA)

Bicine; Total AminoAcids; BA

Amino acid derivatives of amines byreactions within the amine solution;may be included among HSS; Aminoacids titrate as BA and as TA. Aminoacids strongly enhance corrosion.

Cations, Inorganic,also called StrongCations (SC)

Strong Cations (SC),e.g. K+, Na+;Corrosion metal ions(Fe, Cr, Ni, etc)Inorganic HSS (IHSS)

Alkali cations which accumulate in theamine solutions from cooling waterleaks or deliberate caustic addition;Corrosion metals result fromaggressive acid gases, erosion,enhanced by HSS and amino acids

BasicDegradationProducts (BDP)

Total Base (TB); TotalAmine Base (TAB);Actual Total Base(ATB); Total Nitrogen(TN); TB-ATB;dimers (THEED,HEED, HEP, etc),ureas.

Amines and amine dimers that resultfrom chemical degradation of thesolvent amine; have some acid gasabsorbing capacity. Amine dimersenhance corrosion


NeutralDegradationProducts (NDP)

Amides,formylamines,Oxazolidones;Hydrolysables; TotalNitrogen (TN);TN-TB;

Non-ion results of chemicaldegradation of the solvent amine;Amides are in active reversibleequilibrium with their correspondingorganic acid HSS anion.

*HSS anions most commonly determined individually include formate, acetate,propionate, glycolate, oxalate, chloride, thiocyanate, thiosulfate, sulfate, and sulfite

The numerous analytes listed in Table 6 can be daunting. The several analytes shownwithin individual boxes of Table 6 may each show a different result, or overlap, or evendisagree with one another, requiring informed interpretation of the respective results.

Many of the dissolved substance cause corrosion or enhance corrosion by attacking theprotective iron sulfide layer. Iron carbonate can form protective layers, but most oftencreates suspended solids. Corrosion products create solids in the amine solution, andalong with other insoluble or semi-soluble substances create the third tier of analyticalproblems listed in Table 7.

Table 7Insoluble, Partially Soluble or Dispersed Substances in Amine Solutions

Type Analytes Description and roleSolids Total Suspended

Solids (TSS)From corrosion products, chemicaland physical; TSS contribute to furthercorrosion, flow restrictions, andplugging. TSS stabilize foam

Hydrocarbons Total PetroleumHydrocarbons(TPH)

TPH carryover from contact withpetroleum gas or liquid. TPH maycontribute to or inhibit foam.

Surfactants Foaming Tendency,Break time,Foaming Potential;Surface Tension;

Polar/non-polar molecules that causefoaming. Typically in very lowconcentrations but have large physicaleffects inhibiting acid gas absorptionand stripping. Surfactants causesystem upsets and solvent losses

Antifoam Si (confirmpresence of siliconeantifoams only); nodirect analyses

Antifoam is deliberately added toreduce foaming; Note: excessantifoam can cause foam.

All of the contaminants in Tables 6 and 7 have their effects on the amine solventperformance and/or the amine system hardware. Contaminants can change the physicalproperties (density, viscosity, surface tension, thermal conductivity, electrical


conductivity, foaming tendency) and the water content, which can influence filmabsorption and desorption rates. Longer term affects include corrosion, plugging, flowrestriction, foaming, and inhibited processing rates. Given the importance of short andlong term characteristic effects of these contaminants it is very important have regularanalytical reports. But how does one make sense of them?

RECONCILING VARIOUS ANALYTICAL METHODS

When one compares reports from two different labs there may appear to be inexplicabledifferences in apparently the same analyte. Some of the confusion results fromdifferences in terminology and some from differences in lab procedural definition ofanalytes of the same name. For example, the question “What is the Heat Stable Saltscontent of this sample” could have the following CORRECT answers:

Heat Stable Salt Anions 14609 ppm(m)Total Heat Stable Salts 3.13% as DEAHSAS 1.49% as DEAIHSS 1.63% as DEATotal HSS/Total Amine 11.14% of DEA

0.1114 mol/mol

From 1.5 to 11 %! No wonder we are confused! Notice the importance of theprepositions “as” and “of” which are sometimes not included in conversation or reports.We prefer the first two in the above list, because they are direct expressions of the twoparts of the Total Heat Stable Salts: the anions and the amine equivalent cations. Theothers have good utility, however, and need to be understood.

Table 8 can be used to help understand the differences between different analysis reportsand to show to translate various reports to a common basis. The “Really is” column usesterms defined in bold face items in Tables5, 6, and 7. The “Method Description” columnprovides information you can use to help your chemist tell you which analyte really is onthe analysis report. Similar analytes are grouped together in the table and are translatedto a common basis. Table 8 is a compilation of parameters reported by various aminesuppliers and third party labs. It may be a good idea to contact these labs for furtherclarification of the specifics of their tests.


Table 8RECONCILIATION OF ANALYTICAL METHODS AND THEIR REPORTS

Reported as Really is Method Description CommentsFree Amine(FA) orRegenerableFree Base(RFB)

Free Amine(includingBasicDegradationProducts(BDP))

Titration of sample as receivedwith HCl, tracked by pH orConductivity to calculate correctendpoint

Reliable FA ifcorrect endpoint.Must subtract freeOH- in rare casesthat it is significant

Free Amine(FA) orRegenerableFree Base(RFB)

Free Amine +WAA

Titration of sample as receivedwith HCl with colorimetric ordead-stop pH endpoint

Overestimate FAUNLESS no WAApresent. Mustsubtract free OH- inrare cases that it issignificant

Total Amine(TA)

Total Amines(includingBDP)

TA titration: Over-acidifysample, (nitrogen) purge acid gas,titrate with NaOH to excess,tracking pH or Conductivity tocalculate correct endpoints foramine

Reliable TA, ifendpoints arecorrectly chosen.BDP can have 2xcontributions ifsubtle endpoint isnot considered.

Total Amine(TA)

BA + FA Add results of FA and BAtitrations

Not as accurate asthe TA titration(see BA and BAobserved)

Alkalinity FA (see Free Amine) (see Free Amine)Amine by GC Total solvent

amineGas Chromatography peak(s)specific to the intended amines inthe solvent.

Excludes BDP, socomparison to TAcan reveal BDP.For formulatedamines only theamine supplier candetermine this.

Amine by IC Total solventamine

Ion Chromatography peak(s)specific to the intended amines inthe solvent.

(see GC amine)

AmineBalance

BDP estimate Titrated TA minus IC- or GC-identified solvent amine

If >0, BDP may bepresent; if <0,faulty analysis

Nitrogen TotalNitrogen(TN)

Elemental analysis of nitrogen inthe sample. Using Aminemolecular weight, calculate TNas amine.



Reported as Really is Method Description CommentsNitrogenBalance

NeutralDegradationProducts(NDP)estimate

TN - TA If >0, NDP arepresent. If <0,amines of highermolecular weightthan assumed arepresent or TA iswrong.

DegradationProducts,itemized(HEED, HEI,THEED,HEP,formylaminesOxazolidones,etc)

BDP andNDP species

HPLC and GC analysis calibratedfor specific degradation products

The best way todetermine what andhow much BDP orNDP are present.GC requiresderivatization toavoid errors fromon columndegradation.

nFDEA,FDEA,DEAF,FDIPADIPAF,FMEA, etc

Amides,formylamines(part of NDP)

HPLC or GC (withderivatization)

(see BDP andNDP)Only in primaryand secondaryamines (MDEA andTEA cannot formamides); activeequilibrium withformate salts

Hydrolyzables Amides +idones (TotalNDP)

Hydrolysis in excess base andheat and measure the acidsproduced by the hydrolysis.Calculate amides from WAAHSS produced and Oxazolidonesfrom CO2 produced

A good check onrecovery of HPLCand GC speciesanalyses. Heavieramides are detected

Acid GasLoading(AGL)

AGL by BAchange

BA before – BA after boiling Detects H2S andCO2, butapproximatebecause boilingdoes not expel allAG from all amines


AGL bychargebalance

BA observed + Strong Cations –Total HSS

OK if no aminoacids are presentand HCO3

-/AGLare small.



Reported as Really is Method Description CommentsH2Sor Acid GasLoading(AGL)

H2S Titration of Sulfide by AgNO3;direct titration of amine samplediluted in water.

Most reliable H2Smethod; can detectmercaptansseparately; Doesn’tdetect CO2 so maynot be total AGL.

H2Sor AGL

H2S + S2O3=

+ SO3=

Titration of excess Iodine withsodium thiosulfate after additionof amine sample to acidic Iodine

False high H2Sresults if thiosulfateHSS are present


H2S + CO2 Sum of direct measure of H2Sand CO2 individually. Best ifH2S by AgNO3 titration and CO2

by TIC

Most reliable AGL.When translated tomol AGL/molAmine can givefalse lowimpression ofamount amineinvolved if CO3

= ispresent.


AGL/FA (H2S + CO2)/FA, mol/mol Most commonexpression of LLand RL


AGL/TA (H2S + CO2)/TA, mol/mol Similar, but notidentical toAGL/FA. Differsby the factorFA/TA

CO2 CO2 (approx.) Add BaCl2 (hot), titrate BaCO3

precipitate with HClPoor accuracy andrepeatability inamine solutions

CO2 CO2 Total Inorganic Carbon (TIC):Instrument that automates theacidification of the sample,trapping the released CO2 gas andthe coulometric titration or by IRspectroscopy; removes H2Sbefore titration for the titrationmethod.

The only reliablyaccurate methodsfor CO2 in allamine solutions



Reported as Really is Method Description CommentsHSS,Total HSS, orHSS bytitration

Total HSS After removing amine, strongcations and amino acids by cationexchange, titrating with base(NaOH or KOH) and determiningendpoints by inflexion points inpH or conductivity

Detects all HSSanions. Excludesamino acids. Highthiosulfate is under-reported. Candetermine WeakAcids and StrongAcids as separategroups if useconductivity (seeAttachment A).Estimate amidesfrom WAA.

HSS HSAS Boil sample to remove LL, titratewith base (NaOH)

LL incompletelyremoved frommany amines, somay give highestimate of HSAS

HSS Total HSS(unless SCpresent)

Over-acidify sample, purge acidgas, then titrate with NaOH toexcess, tracking pH orConductivity to find correctendpoints. Calc HSS bydifference of much largernumbers.

Poor accuracyexcept for large (>5wt%) HSS and zeroSC. Purging of AGby boiling couldlose Formate HSS:use N2 or air.WAA endpoint isweak if by pH.

HSS HSS species Sum of HSS anions determinedindividually by IonChromatography

Reliable for anionsreported. Not allpossible anions areknown, so HSSspecies is typicallyless than TotalHSS. Some labsinclude bicine,others don’t.

Strong AcidAnions

HSS species Sum of all HSS anionsdetermined individually by IonChromatography

(See “HSSspecies”). “Strongacid” here means“stronger acid thanthe Acid Gases”.Thus it means SAA+ WAA.



Reported as Really is Method Description CommentsStrong AcidAnions (SAA)

HSS species,Anions ofStrong Acidsonly (SAA)

Sum of the Strong or“polarizable” anions determinedindividually by IonChromatography

Include chloride,thiocyanate, sulfate,thiosulfate, nitrate,oxalate, sulfite,bromide,phosphate, arsenate(anions of strongeracids than formicacid)

Strong AcidAnions (SAA)

Anions ofStrong Acids(SAA)

From the Total HSS titration, theStrong Acid section. Clearlydiscernable with conductivity;difficult to discern with pH (seeAppendix A). Sample prep bycation exchange trades thecounter cation (AmH+ or Na+ orK+) for H+ which is then titratedwith base (NaOH)

SAA do notconsume H+ whentitrated with acid.Accurately detectedas a group by thisprocedure

Weak AcidAnions(WAA)

Anions ofWeak Acids(WAA)

From the Total HSS titration, theWeak Acid section. Clearlydiscernable with conductivity;difficult to discern with pH (seeAppendix A) Sample prep bycation exchange trades thecounter cation (AmH+ or Na+ orK+) for H+ which bonds withWAA, then is titrated away againwith base (NaOH)

WAA consume H+(making an acidmolecule).Accurately detectedas a group by thisprocedure.

Weak AcidAnions

HSS species,Anions ofWeak Acidsonly (WAA)

Sum of the Weak Acid anionsdetermined individually by IonChromatography

Include formate,acetate, propionate,butyrates, glycolate

HSAS or BA BA observed Titrate sample as received withbase (NaOH)

Includes aminoacids (more thanbicine) and LL plusHCO3

- again.Reliable when CO2

is small relative toBA.



Reported as Really is Method Description CommentsHSAS or BA BA BA corrected = BA observed

minus extra HCO3- contribution,

calculated by charge balance:LL+HSS-Strong Cations.

Actual AmH+ insolution asreceived. Can beused in massbalance whereamino acids areitemized separately.Estimate HCO3

-

correction fromTIC, pH, and Ka2

HSAS HSAS Total HSS – IHSS orTotal HSS – Strong Cations

Generally reliable;Accuracy dependson Total HSSaccuracy

HSAS HSAS HSS Species – IHSS orHSS Species – Strong Cations

May underestimate(see HSS Species)

HSSneutralized

SC/TotalHSS Calculation: fraction of TotalHSSthat are IHSS: expressed asfraction or %.

Helps avoidexcessive caustic.Best close to zero;can cause LL rise ifexceeds 0.6 (60%)

S2O3= HSS S2O3

= + SO3=

+ H2STitration of excess Iodine withsodium thiosulfate after additionof amine sample to acidic Iodine

False highthiosulfate if H2S ispresent

Chloride (Cl-)HSS

Chloride (Cl-)(one HSSspecies)

Titration of Cl- by AgNO3 afteracidification of amine sample inwater, (nitrogen) purging of acid,and iodine oxidation of anyS2O3

=.

Very reliablechloridemeasurement, evento < 20 ppm withlarge sample.

Thiocyanate(SCN-) HSS

Thiocyanate(SCN-)(one HSSspecies)

Titration of SCN- by AgNO3 bysame procedure as titration of Cl-.

Very reliable SCN-

measurement, butwill include anyBromide if present.(e.g., sea or groundwatercontamination)



Reported as Really is Method Description CommentsStrongCations

StrongCations

“Strong Cations Titration”:Anions (AGL and HSS) in theamine sample are replaced byOH- by anion exchange. AnyAmH+ is neutralized to FA andH2O, leaving all Strong Cationswith an OH- companion anion.The OH- is then titrated withacid, equaling the Strong Cations.

Excellent accuratedetermination ofthe Strong Cationcharacteristic inamine solutions,

Na+, K+, Ca2+,Mg2+

StrongCations

ICP or IC measurement ICP accurate; ICmay haveinterference fromamines for K+

Strong Bases StrongCations

Determined by ICP, IC,calculated to wt% as amine

Another name forStrong Cations orIHSS

Ash StrongCations

After burning the sample in afurnace, weigh the amount of ashremaining, report as wt% ash inthe sample. Three varietiespossible: sulfated ash, carbonateash, oxide ash

Typicallyinterpreted as Naash, but includes allmetal cationspresent. Na ≈sulfated ash/3.1,carbonate ash/2.3,Na2O/1.4

IHSS(InorganicHeat StableSalts)

StrongCations

Sodium and Potassium by ICP,IC, or Strong Cations Titration,then calculate the equivalentamount of amine; report as wt%as amine

Assumes all strongcations have HSSanion companion.Reported as aminewt% for directcomparability withHSAS and TotalHSS

Bicine Bicine Amino Acids analysis by IonChromatography

Accurate ifcarefully calibratedand run with checkstandards.

Amino Acids,total

Total AminoAcids by IC

Amino Acids analysis by IonChromatography, amino acidstandardization applied to peakswith retention similar to theknown amino acid standards –this is an estimate of amino acidlevel.

Goodapproximation;check against TotalAmino Acids bycharge balance



Reported as Really is Method Description CommentsAmino Acids,total

Total AminoAcids bychargebalance

Amino Acids = BA observed –Total HSS – AGL - HCO3- +Strong Cations

Fair approximation,better if HCO3- isinsignificant.Assure moles andequivalents arecorrectly applied

PetroleumHydrocarbonsor TPH

TPH (IR) Infrared measurement: Acidifiedsample is extracted intetrachloroethylene, then Infraredabsorbance is measured

Acidification is aMUST. Samplingprocedures arecritical. In the labmust assureuniform dispersionof hydrocarbonsbefore and duringsampling.

PetroleumHydrocarbonsor TPH

TPH (GC) GC measurement: Acidifiedsample is extracted intetrachloroethylene or toluene,then injected in GasChromatograph. Integratespecified range of retentiontimes.

Acidification to pH<3 is a MUST(major errors haveoccurred by notexcluding amine).Sampling (see TPH(IR))

TSS TSS Large sample (50 to 100 g) isfiltered through 1 micron filter.Mass of solids on filter isdetermined. Calculate mg solidsper L solution.

Large relative errorpossible because ofsmall mass ofsolids. Samplingtechnique is critical(see TPH)

TSS byabsorbance

turbidity Transmittance of 810 micronwavelength light compared toclean solvent. Reduction intransmittance due to scattering oflight by particles.

Quick easy test,good for trackinggross trends orfilter effectiveness.Can roughlycalibrate againstTSS for short rangeof concentrationsand uniformparticle sizedistribution.


As can be seen in the table, there are a large number of parameters that are measured by avariety of techniques and a thorough understanding of the terminology is required tocorrectly interpret Amine analysis reports and to take action based on the analysis.

A complete list of the terms and abbreviations used in amine analysis reports is providedin alphabetical order in Appendix B.

SOME QUESTIONS TO ASK THE ANALYST/CHEMIST TO ASSURE THEMEASUREMENTS ARE CLEAR AND UNDERSTOOD

Proper sampling is essential to achieving good analysis results and understanding how thesample was taken is essential in helping you interpret the results. The following questionsshould be suitably answered before the analyst or operator takes a sample.

1. Was the dead leg flushed before taking the sampling?2. Were the operating conditions of the unit recorded when the samples were taken?

Is there a plant upset or unique operating conditions?3. Was the reason for sample collection recorded (routine or non-routine trouble

shooting)?4. Where was the sample taken? Up-stream or down-stream of the filters and carbon

beds?

You should make sure that the measurements for Free Amine (FA) or amine strengthmeasurement is correct so you know how much amine is available for acid gasadsorption. The following questions are helpful to interpret the results..

1. Is it a titration with acid? If yes, good.2. Is the endpoint of the titration determined by inflection points in a conductivity or

pH curve? If yes, good.3. Is the endpoint determined by color indicator? If yes, worry about accuracy.4. Is the endpoint determined by “dead-stop” at a specified pH? If yes, worry about

accuracy.5. Spiking with Acetic Acid before titration can help get more accurate endpoint for

FA.

An important parameter for operational control is the total concentration of the amine inthe unit. The questions below should be asked so you can understand how the total levelof amine was determined.

1. How total amine test is done (GC, IC, HPLC, titration, other)?2. If GC, IC, or HPLC, ask what amines are quantified and are there noteworthy not

quantified / unidentified peaks.3. If titration, ask if other basic species like amino acids or piperazine are subtracted

from the reported total amine number. If the number is reported as titrated, thetotal amine number is actually a total base number.


One of the most important analysis in amine systems is the measurement of Heat StableSalts. A number of methods can be used for this analysis and it is recommended thatmore than one method be used and the results compared to make sure that accurateresults are obtained. These questions are useful in obtaining a good understanding of theresults.

1. How HSS measurement is made (IC or titration)?2. If by IC, the individual analysis of species should be available. See if the common

anions are analyzed for; i.e. formate, acetate, propionate, glycolate, oxalate,chloride, thiocyanate, thiosulfate, sulfate, and nitrate.

3. If by titration:a. Is a direct titration of the amine sample with base? If so, the result is BA.b. How is Lean Loading (AGL) removed? If boiling of direct sample, worry

about false high results.c. How are strong cations removed before analysis or how is their affect

accounted for in the final HSS result? Caution: some acidification and back-titration methods detect WAA HSS (not SAA HSS) and detect only the strongcations which exceed the equivalent of the Total HSS. Such methods estimateHSAS, not Total HSS.

Strong cations can enter amine systems unintentionally through heat exchanger leaks,from the treated product, or intentionally by addition of caustic to ‘neutralize’ heat stablesalts. Proper analysis is important to make sure they do not contribute to high leanloading and stripping difficulties or contribute to viscosity and corrosion problems. Thereare several methods of analysis for strong cations and the following questions should beasked.

1. How are Strong Cations (Sodium, Potassium, Calcium, etc.) determined?2. If by IC or ICP,

a. Was the signal within the calibration range?b. Are there any false highs due to interferences (such as amine with K+ in

IC)3. If by titration:

a. Was sufficient strong base anion exchange resin used to absorb all the LLand HSS anions (at least 2 times the equivalent)?

b. Has the titration been checked against ICP or IC for this amine system? (Itis a good check on endpoint determination technique. Rarely, but it hashappened, the titration method will grossly exceed the actual strongcations concentration for unknown reasons)

c. Only strong alkali and alkaline earth metals are detected by titration

It is important to measure metals in order to have an early detection system for possibleoperational difficulties due to corrosion products or to loss of metal integrity in the unit.Metals are measured by ICP and AA and there are several relevant questions that youshould ask and items you should consider.


1. Was the sample filtered or digested? (dissolved or total metals)? Highdissolved metals in lean amine samples indicates presence of HSS, aminoacids, and/or polymeric amines (BDP)

2. Sample preparation of ICP samples, especially for solutions that containsolids, will affect the results. If the sample is just filtered before the digestionof the liquid sample, then the measurement is of only the dissolved metals.

3. If the samples are not filtered until after acid digestion then the metals in thesolids (total metals) are included metals report.

4. Generally it is more instructive to determine the metals in the filtered solidsseparately from the liquid so solids and dissolved solids profiles can bedetermined.

Performing a mass balance or “Residue calculation can be instructive. It requires that anaccurate water analysis by Karl Fisher titration, accurate total amine measurement, anaccurate knowledge of the amine molecular weight (maybe difficult if it is a blended orformulated amine), accurate analysis of strong cations, heat stable salts, amino acids,AGL, BDP, NDP, and amides. A mass balance of less than 100% can indicate that thereare contaminants present that have not been analyzed. A mass balance of greater or lessthan 100% can also indicate errors in the analysis methods, especially for total amine andwater.

If your lab does not have the capability of running all the tests, don’t hesitate to use anoutside lab to compliment your in-house testing. It is also a good idea to have a completeanalysis by an outside lab once per year as a check your in-house analysis results. Ifcontaminants are growing or changing, it may be advised to have outside analysis on amore frequent basis. Remember that HSS, amino acids, and BDP contribute to corrosionand can cause severe damage to the amine treating unit.

WHAT OPERATIONS-SIGNIFICANT INFORMATION IS REVEALED BYANALYSIS OF CONTAMINANTS?

By closely monitoring trends in the analytical data, one can detect possible operationalproblems before they become a big problem for the unit. Table 9 provides someexamples.


Table 9Analytical Symptoms of some Amine System problems

Symptom Possible InterpretationsFA decreasing - Amine losses (carryover, entrainment,

valve error, etc)- Water purge out of balance (total

solution volume increasing)- HSS ingress- NDP forming: amides, if primary or

secondary amine; oxazolidones if in highpressure CO2 service

Total HSS increasing - HSS ingress- Water content decreasing- Corrosivity increasing- Need HSS removed

FA increasing while BAincreasing

- FA analysis error: FA report includesWeak Acid HSS

LL rise with no change inoperating conditions

- Greater AG load in absorbers- Strong Cations ingress into solvent.

Total HSS > BA - Caustic ingress or addition- Cooling water leak into amine solution

BA > Total HSS - Amino Acids present (not included inTotal HSS)

- BA includes high LLThiosulfate HSS - Oxygen ingress

- SO2 break-through (Claus Tail Gas)Bicine (and other amino acids) - Oxygen ingress (gas plants)

- O2, SO2 and/or S2O3= attack (refinery)

Strong Cations - Caustic addition- “amine slops” added to amine and

included some caustic- Cooling water leak into amine- “hidden” HSS- foaming tendency increasing (soaps)

Formate HSS - Caused Cyanide or Carbon Monoxideingress

- If primary or secondary amine, Amidesincrease as Formate increases so TotalAmine and Free Amine reduced =>apparent amine loss, but it can berecovered (don’t throw it away)

Acetate HSS - Acetonitrile ingress- Oxygen ingress


Table 9Analytical Symptoms of some Amine System problems

Symptom Possible InterpretationsThiocyanate (SCN-) HSS - Cyanide reacting with H2SChloride HSS - Cooling water leak

- HCl ingressSolids (TSS) rising - Corrosion

- filters inadequate or spentTPH - Hydrocarbon carry-over into amine:

inadequate knock-out drum“Residue” increasing, but BA not - Caustic ingress or addition

- Cooling water leak into amine solution- Amine chemical degradation

SUMMARY

We have shown both the simplicity of the amine system and the complicated array ofcontaminants that pollute amine solutions and cause problems for amine system functionand longevity. The even larger array of analytical methods employed to determinecontaminant concentrations in amine solutions can lead to confusion if the analyticalreports are not properly understood and interpreted. While there is some duplicationamong the tables, each provides a different perspective and thus can possibly provide aidto different people in the variety of situations amine systems present to focus on theanalytical methods and data that are most instructive for the need at hand.

The fundamental focus for amine analysis must be on the following, which can betracked with a relatively few well selected analytical methods: Free Amine (FA), TotalAmine (TA), Bound Amine (BA), H2S, and CO2,Total Heat Stable Salts (HSS) includingWAA and SAA estimates from conductivity titrations, Strong Cations (SC), Chloride,Thiocyanate, Amino Acids, Amides, and Water. With the exception of CO2, these can allbe done with an autotitrator.

A mass balance or residue calculation using the analysis in the previous paragraph yieldsan estimate of Basic Degradation Products (BDP) and Neutral Degradation Products(NDP).

Instrumental methods can be added to measure Total Nitrogen (TN), Amine species byGC or IC, and HSS speciation by IC. Then by “amine balance” and “nitrogen balance”BDP and NDP estimates might be segregated. These can be supported by HPLC and GCidentification of specific BDP and NDP species.


Other important measurements that can provide information on the ‘health’ of the amineinclude Total Suspended Solids (TSS), Total Petroleum Hydrocarbons (TPH), FoamingTendency, Foam break time, Density, pH, Conductivity, Viscosity, and Surface Tension.

Tracking and graphing various data over long periods of time makes it easier to spottrends, to gain a sense for normal analytical/sampling variability, to recognize possibleerrors, to key in on unexpected results, and to track cause and effect on unit operations.

A plant needs to have locally only an automatic titrator, conductivity meter and probe, pHmeter and probe, sulfide ion selective electrode and reference electrode, CO2 analyzer,and Karl Fischer titrator in order to provide the most important analyses (free amine, totalamine, bound amine, H2S, CO2, total heat stable salts, strong cations, chloride,thiocyanate, and water). The other analytes can be done monthly, quarterly, or as neededby your company’s central analytical lab, amine vendor, or reclaimer.

TRADEMARKS FOOTNOTES

DGA® is a registered trademark of Huntsman corporation

REFERENCES

1. D. Tunnell, J. Asquith, F. Bela, F. Buzuik, R, Eguren, G. Cosma, N. Hatcher, A.Keller, B. Kennedy, R. Schendel, C. Smith, L. Stern, B. Welch, M. Zacher,“Evaluation of Amine Analytical Methods Part One: Amine Strength,”Proceedings of the Brimstone Sulfur Symposia, Vail, Colorado, 2004.

2. D. Tunnell, J. Asquith, F. Bela, F. Buzuik, R, Eguren, G. Cosma, N. Hatcher, A.Keller, B. Kennedy, R. Schendel, C. Smith, L. Stern, B. Welch, M. Zacher,“Choices for Determining Amine Strength: Effects on Operations andOptimization,” Proceedings of the Brimstone Sulfur Symposia, Vail, Colorado,2005.

3. P. Rooney, T. Bacon, M. Dupart, “Effect of Heat Stable Salts on MDEA SolutionCorrosivity: Part 1,” Hydrocarbon Processing, March 1996, 95-103.

4. P. Rooney, T. Bacon, M. Dupart, “Effect of Heat Stable Salts on MDEA SolutionCorrosivity: Part 2,” Hydrocarbon Processing, April 1997, 65-71.


Appendix AConductivity Titrations Provide More Information than pH Titrations


APPENDIX BGLOSSARY OF AMINE ANALYTICAL TERMS

(Alphabetical by Term)Table B. Analytical Definitions and Measurement comments

Term DefinitionAcetate Acetate ion, one of the HSS anions; a WAA; determined by IC.AG Acid Gases H2S and CO2. HCN is also an acid gas, but is rarely

determined, because it typically reacts in amine solutions to becomeformate or thiocyanate HSS.

AGL Acid Gas Loading, the AG concentration in an amine solutionAlkalinity (see FA [Free Amine])AmineBalance

Amine balance is Total Amine (TA) by titration minus the identifiedamine by Gas Chromatography or Ion Chromatography. If positive, BDPare present; if negative, faulty analysis.

Amine byGC

Amine measured by GC (Gas Chromatography) The difficulty with theGC method it will only measure the specific amine(s) you are looking forand other basic species in the amine may not be detected or reported.

Amine,primary

[see Primary Amine]

Amine,secondary

[see Secondary Amine]

Amine,tertiary

[see Tertiary Amine]

Amino Acid(AA)

A molecule with an amine nitrogen attached to a carboxylic acid group.A common degradation product in alkanolamine solutions, detectable by aspecific IC amino acids method. Bicine and HES have been specificallymeasured in amine solutions. Total amino acids can be approximatedfrom Bicine, HES, and other unidentified peaks in the chromatogram, orfrom Bound Amine titration.

Appearance The appearance of the solution can give clues to difficulties present in theamine system. Particles are indication of corrosion/erosion in the system.Color indicates dissolved or suspended contaminants. An emeraldgreenish color can be due to extremely small (colloidal) iron sulfideparticles in solution. Hydrocarbons can be visually observed.

ATB Actual Total Base = Free amine or RFB + base bound to other acids.Depending on measurement may be the same as TB or Total Amine Bases(TAB).

BA Bound Amine – Amine that cannot participate in acid gas adsorptionbecause it has already reacted with an acid and is bound to a HydrogenIon (H+); also designated by AmH+. It rises as HSS and/or AGL rise.

BDP Basic Degradation Products: amines and amine dimers that result fromchemical degradation of the solvent amine; have some acid gas absorbingcapacity. Amine dimers enhance corrosion.


Table B. Analytical Definitions and Measurement commentsTerm DefinitionBicine An Amino Acid found in amine solutions (primarily MDEA and DEA)

now routinely determined by IC amino acids method. In some reports,included in HSS species; in other reports, treated separately from HSS.pKa very close to that of MDEA, so is indistinguishable from amines inacid/base titrations.

butyrate Butyrate ion, one of the HSS anions; a WAA; determined by IC, butrarely found; strong positive interference by CO2.

Cl- Chloride ion, one of the HSS anions, a SAA; determined by AgNO3titration or by IC.

CO2 Carbon dioxide, an acid gas (AG), absorbed in amine solution with aid ofacid/base reaction or CO2 addition to a primary or secondary amine,resulting in HCO3

- (bicarbonate), CO3= (carbonate), and/or AmCOO-

(carbamate) ions.Conductivity Electrical conductance of the solutions. As ionic contaminants (including

AGL) increase in the solution, the conductivity increases. Thusconductivity is useful for showing contaminant trends within a system, butnot for determination of actual contaminant concentration. This is aconductivity meter measurement and normally reported as milliSiemens.

DEAF DEA formamide = FDEA, an NDP [see Formyl Amines]Density Density is mass per unit volume of solution, reported as g/mL. The

density of the amine solution rises with increasing salt contamination inthe solution. A correlation can be made between density and HSSconcentration if all other components are nearly constant, but water,amine, degradation products, and HSS concentration affects density.

DIPA-F DIPA formamide = FDIPA, an NDP [see Formyl Amines];DistillationResidue

The remains of a vacuum distillation procedure. Intended to be a measureof Residue2, but may include bound amine and some acid gas, thus maybe an overestimate of all contaminants.

FA Free Amine is amine in its free base state. Can be also called RegenerableFree Base (RFB) or usable amine. It can be measured by titration withacid. Reported as wt% using the molecular weight of amine. It can also becalculated from FA = TA – BA. The colorimetric titrations or dead stopendpoint titrations may report higher than the actual FA if WAA arepresent.

FDEA formylDEA, an amide of DEA, an NDP [see Formyl Amines]; in activereversible equilibrium with DEAH+ and formate-

FDIPA formylDIPA, an amide of DEA, an NDP [see Formyl Amines]; in activereversible equilibrium with DIPAH+ and formate

ferrocyanate Ferrocyanate ion, a cyanide complex of iron, one of the HSS anions; aWAA; determined by combination of AgNO3 titration and IC data. It isbelieved that CO complexes of iron exhibit the same analytical behavior.

Foam BreakTime

The time (in seconds) for the foam to break. Normally break times longerthan 10 seconds can lead to problems in a amine system due to residencetime on trays


Table B. Analytical Definitions and Measurement commentsTerm DefinitionFoamHeight/FoamTendency

It given as mL on the graduated cylinder or height above the liquid level.Interpreting results is different for different methods. Difficult to comparebetween testing methods. The tests are generally more qualitative thanquantitative. Normally less foam height is better for amine systems.

Foam Tests Can be a simple qualitative shake test or a gas purged through the aminesolution in a graduated cylinder for quantitative evaluation. Matching thefoam test results to the foaming behavior in an absorber or regeneratortower is extremely difficult, because temperature, pressure, and gasbubble size rarely match. Foaming causing compounds, surfactants, atvery low (under 100 ppm) cause foam that can severely hamper absorberand stripper tower operation. Obtaining a representative sample ofsurfactant in amine is difficult both at the plant and at the lab. Samplinggreatly affects the results of the test and how meaningful it is to thesystem operation.

FoamingPotentialRating

Break time and foam height are combined in the von Phul equation to givean indication of how likely a system is to have foaming problems, using ascale of 1 (no problem) to 10 (need intervention).

formate Formate ion, one of the HSS anions; a WAA; determined by IC.FormylAmines andotherAmides

Primary and secondary amines undergo a water elimination equilibriumreaction with a formic acid (or any organic acid) to form an amide, anNDP. The amide reduces available amine for acid gas adsorption andhides the acid, which would otherwise appear as an HSS. They have beencalled dormant HSS burden because they will revert back to amine andacid when HSS anions are removed by ion exchange. To offset thereduced amine solution capacity caused by amide formation, more amineis added or water content is reduced. Formylamines (from formic acid andamine) are normally measured by liquid chromatography (HPLC) or gaschromatography (GC). Total amides are measured by hydrolysis.

GC Gas Chromatography, an instrumental analysis method for determiningamine species, and some BDP and NDP

glycolate Glycolate ion, one of the HSS anions; a WAA; determined by IC.H2S Hydrogen sulfide, an acid gas (AG). Absorbed in amine solution with aid

of acid/base reaction resulting in HS- (bisulfide) ion.HEED hydroxethylethylenediamine, a BDP of MEAHEOD Hydroxyethyloxazolidone: the oxazolidone of DEA, an NDP of DEAHEP 1,4-bis(hydroxethyl)piperazine, a BDP of DEAHES Hydroxyethylsarcosine, an Amino Acid found in amine solutions now

routinely determined by IC amino acids method.HPLC High Performance Liquid Chromatography, an instrumental analysis

method for determining BDP, NDP, and some amine speciesHPOZD Hydroxyisopropyloxazolidone: the oxazolidone of DIPA, an NDP of

DIPA


Table B. Analytical Definitions and Measurement commentsTerm DefinitionHSAS(or AHSS)

Heat Stable Amine Salt – A heat stable salt that is made up of an aminemolecule and anion. The number is best calculated by HSAS = Total HSS– IHSS and not measured directly. It is expressed as wt% as amine usingthe amine molecular weight. It may also be calculated as BA - AGL.

HSS (total) Heat Stable Salts (total) - A salt in the alkanolamine (amine) solution thatis not affected by heat. The heat stable salt does not regenerate in theregenerator and remains in the circulating amine system. HSS (total) canbe accurately measured by a titration procedure which prepares thesample with cation exchange resin. HSS are over- or under-reported bytitration procedures that detect Bound Amine or involve over-acidification(without ion exchange) of the amine sample before titration.

Individual HSS anions can be measured by Ion Chromatography (IC).The thus identified HSS anions are summed to provide a total HSS. Ingeneral, Total HSS by titration should be the same or larger than TotalHSS by IC (HSS species). One exception is if significant thiosulfate ispresent, the titration method gives a false low HSS concentration and ICmust be relied upon.

HSS reports can be confusing, first, because the various measurementmethods provide different answers, and, second, because of units ofmeasure employed in the reports. Most often HSS will be reported as thewt% of the equivalent amount of amine. This means, for example, if HSSconcentration were 1 mole/kg of solution, it would be 10.5 wt% as DEA,11.9 wt% as MDEA, 6.1 wt% as MEA, 13.3 wt% as DIPA, etc., etc..

HSSB Heat Stable Salt Burden- Total HSS plus amides (e.g. fomylamines).HSSB recognizes that amides are in active equilibrium with theircorresponding HSS anion and amine, and are “hidden” HSS. Whenseeking HSS incursion rates, must base on it HSSB.

IC Ion Chromatography, an instrumental analysis method for determiningHSS anions, Strong Cations, amino acids, and amine species

IHSS Inorganic Heat Stable Salt – A heat stable salt that is made up of a metalcation and an anion, however it typically reported in units of wt% asamine. It is assumed all of the cationic metals present form IHSS. This iscalculated from the measured molar concentration of metal cations presentin the sample.

LeanLoading(LL)

Lean loading is the amount of acid gases (CO2 +H2S) in the lean amine.This indicates the quality of the amine stripping. CO2 is measured bycoulometric titration or by IR spectroscopy. H2S is measured bypotentiometric titration. Reported as ppm or wt% as CO2 andH2S,respectively, or as mol/mol amine. The low molar loading is oftenimportant to meeting the specification on the gas.

LL Rich Loading, the AGL in an amine solution exiting the regenerator(stripper)


Table B. Analytical Definitions and Measurement commentsTerm DefinitionMassBalance

Total percentage of measure solution components and contaminants. It ishelpful in spotting unaccounted for contaminants. The calculations can besensitive to the molecular weight used and care is necessary not to countsome species twice. It may not be possible to measure, identify andquantify all solvent components and contaminants.Total Amine+water+AGL +HSS anions +Cations+amino acids +BDP+NDP = Mass Balance

Metals Cation species can be identified by IC and ICP or AA. Include StrongCations and corrosion products. Expressed as ppm of each metal ion. Thishas the advantage of identifying the species present.

NDP Neutral Degradation Products: non-ionic results of chemical degradationof the solvent amine; include amides and oxazolidones; amides are inactive reversible equilibrium with their corresponding organic acid HSSanion [see Formylamines and other amides]

NitrogenBalance

Total nitrogen measurement minus nitrogen calculated from TA titration.If positive, excess nitrogen could be from SCN- (a HSS anion), polymerBDP and/or NDP. If negative, faulty analysis or wrong MW for the amine

Oxalate Oxalate ion, one of the HSS anions; a SAA; determined by IC.Oxazolidone Degradation product (NPD) of primary and secondary alkanolamines with

CO2, creating an N-C-C-O-C- ring structure; formed by dehydration ofthe carbamate.

OZD 2-oxazolidone, specifically, the oxazolidone of MEApH As BA increases the pH decreases. This is a pH meter measurement. The

pH is dependant upon amine concentration and amine type. It is notsuggested to quantify contaminants by the pH measurement. In general,the primary and secondary amines are stronger bases than the tertiaryamines, run higher pH in lean and have higher lean loadings.

PrimaryAmine

An alkanolamine that has only one organic group on the Nitrogen atom,thus nitrogen has 2 Hydrogen atoms attached to it. Examples are MEAand DGA®.

propionate Propionate ion, one of the HSS anions; a WAA; determined by IC.Residue,definition 0

Residue0 (wt%) = 100% – free amine wt% – water wt%. Residue0intends to include all contaminants including acid gas and (wanted)Bound Amine associated with acid gas. Thus Residue0 can raiseunneeded concerns. It is a small number from subtraction of largenumbers, thus can have a high relative error, so is of little practical use.

Residue,definition 1

Residue1 (wt%) = 100% – Total Amine wt% – water wt%. Residue1intends to include all contaminants including acid gas. It is a smallnumber from subtraction of large numbers, thus can have a high relativeerror, so it is thus of little practical use until contaminants exceed about 5wt%.


Table B. Analytical Definitions and Measurement commentsTerm DefinitionResidue,definition 2

Residue2 (wt%) = 100% – total amine wt% – water wt% – Acid Gas wt%.Residue2 should include all contaminants other than acid gas. It is a smallnumber from subtraction of large numbers, thus can have a high relativeerror, so it is thus of little practical use until contaminants exceed about 3wt%. Then, it is a signal to analyze for HSS, ADP, and NDP.

RFB (see FA [Free Amine])RichLoading(RL)

Rich loading is the amount of acid gases (CO2 +H2S) in the rich amineexiting the Absorber. This indicates the effectiveness of the Absorber.(see also LL)

RL Rich Loading, the AGL in an amine solution exiting the absorberS2O3

= Thiosulfate ion, one of the HSS anions; a SAA; determined by IC orsometimes by total oxidizable sulfides titration (caution: positive H2Sinterference). In high concentrations only partially determined by theTotal HSS method.

SO4= Sulfate ion, one of the HSS anions; a SAA; determined by IC.

SAA Strong Acid Anions, a subset of HSS anions, which do not titrate withacid in aqueous solution. Determined by IC as polarizable ions.Determined by conductometric titration in the Total HSS method.

SAA Strong Acid Anions, intending to mean all HSS anions, from the idea thatall HSS anions are anions of acids that are stronger acids than the AG. Infact, acids as weak or weaker than AG could form HSS if they are lessvolatile and/or more soluble.

SCN- Thiocyanate ion, one of the HSS anions; a SAA; determined by AgNO3

titration or by IC.SecondaryAmine

An alkanolamine that has two organic arms on the Nitrogen atom, thusnitrogen has 1 Hydrogen atoms attached to it. Examples are DEA, DIPA,MMEA

SO3= Sulfite ion, one of the HSS anions; a SAA; determined by IC.

SolventFactor

The molecular weight of the amine divided by 10. The solvent factormultiplied by the concentration in meq/g yields the concentration in wt%.In case of blends of more than one amine, the weighted average molecularweight of the blend is defined by the amine supplier, who determines it byformulation or by analysis of the solvent components. Because blends areproprietary, generally only the amine supplier is permitted to determinethe average molecular weight by chemical analysis. The solvent factormay be discernable from a report that has Strong Cations expressed bothat cation ppm and IHSS wt% as amine.

StrongCations

Alkali cations which accumulate in the amine solutions from coolingwater leaks or deliberate caustic addition. Measured as group by acidtitration after preparation of sample through strong base anion exchange.Normally expressed as ppm Na or K whichever one is more prevalent.Also measure by Ion Chromatography (IC) or atomic emission (ICP) oratomic absorption (AA)


Table B. Analytical Definitions and Measurement commentsTerm DefinitionTA Total Amine – Total concentration of amine in the circulating system. It

can be measured by titration. It also is the sum of bound amine and freeamine. The difficulty with titration method it measures all amine basesand the basic degradation products (See total bases). It is reported in MPRCustomer Reports as the TA = total amine (obs) from titration – AminoAcids – degradation products like THEED.

TAB Total Amine Bases = In MPR reports it is the TAB = total amine titration– Amino Acids. Depending on how and who is reporting it may be thesame as the total base (TB) number or actual total bases (ATB)

TertiaryAmine

An alkanolamine that has three organic arms on the Nitrogen atom, thusnitrogen has no hydrogen atoms attached to it. Examples are MDEA andTEA. Tertiary amines cannot form amides or Oxazolidones (both NDP).

THEED tris(hydroxethyl)ethylenediamine, a BDP of DEATotal Bases(TB)

This can be total amine titration with out any adjustments. Actual totalbase (ATB) can be the same measurement = regenerable free base (RFB)+ base bound to other acids

TotalNitrogen(TN)

Often used as an indirect measure of total amines. This can be done byCHN analyzers, or Total Nitrogen = Total Kjeldahl Nitrogen + Nitrate +Nitrite. Total nitrogen does not directly measure total amine. Aminedegradation products may have nitrogen that can not absorb acid gases.

TPH Total Petroleum Hydrocarbons. Can be measured by IR, gravimetrically,or GC. These methods all have strengths and weakness depending on themethod, standards used, and the hydrocarbon species present. Normallyreported as ppm.

TSS Total Suspended Solids. Normally a gravimetric measurement(milligrams/liter) that roughly corresponds to ppm of solids in amine. Itwill not measure particles smaller than the filter pore size. Getting a goodrepresentative sample from the field is important. Particles maypreferentially form on the rich side when H2S or CO2 hits HSS or aminoacids holding dissolved iron in the lean amine solution.

Viscosity Several methods can be used. Normally reported as centiPoise. Normallyan increase in contaminants and decrease in water content will giveincreased viscosity. If the viscosity is too high the gas treating becomesmore difficult and also increased viscosity makes filtering and processingmore difficult.

WAA Weak Acid Anions, a subset of HSS anions, which do titrate with acid inaqueous solution forming an acid molecule. Determined by IC as weakacid ions. Determined by conductometric titration in the Total HSSmethod.

Water Measured by Karl Fischer water titration. Other methods lack accuracy.Water concentrations are high, so sample size is very small. Extreme careis required to accurately measure the sample amount actually introducedinto the titration. Expressed as wt%.

better amine system operations through chemical analysis - lrgcc 2013 finalrev2[1].pdf

Documents

acid gas content

acid gases

common analytical methods

acid gas removal requirement

operation of theamine

theamine system operator

maze of analytical parameters

analytical titrations