Chemical Composition And Corrosiveness Of The Condensate .
CORROSION SCIENCE SECTIONChemical Composition and Corrosivenessof the Condensate in Top-of-the-Line CorrosionD. Hinkson,‡,* Z. Zhang,** M. Singer,*** and S. Nes̆ić***ABSTRACTThe three key aspects of the top-of-the-line corrosion processare condensation, chemical speciation, and corrosion. Thefocus of this study is on the condensate speciation through athermodynamic approach. Specifically, the goal of this studywas to determine the concentration of acetic acid in the condensate. The presence of acetic acid (CH3COOH) tends toincrease the corrosion rate and to promote localized corrosion.The results of this study show that the concentration of freeacetic acid in the condensate is determined predominantlyby the pH of the liquid phase, which is changed by the corrosion process. The concentration of total acetic acid seems todecrease as the condensation rate increases. The understanding and results gained from this study will lead to the creationof a complete predictive model for top-of-the-line corrosion.KEY WORDS: acetic acid, condensation, top-of-the-line corrosionINTRODUCTIONTop-of-the-line corrosion is mutually influenced bythree factors. First, the amount of water present onthe metal surface at the top of the line is determinedby the condensation rate. Second, the compositionand distribution of chemical species in the condensateinfluences the corrosiveness of the condensate. Third,the corrosion process, in turn, influences the conden Submitted for publication October 13, 2008; in revised form,November 12, 2009.‡Corresponding author. E-mail; dezra hinkson@oxy.com.* Occidental Petroleum Corporation, 28590 Highway 119, PO Box1001, Tupman, CA 93276-1001.** BP America Inc., 501 Westlake Park Blvd., Houston, TX 77079.*** Institute for Corrosion and Multiphase Technology, Ohio University, 342 West State St., Athens, OH 45701.045002-1sate chemistry by introducing corrosion products (ferrous ions) and altering the pH and the pH-dependentequilibria. The desire to better describe the mechanistic interaction of these three factors on top-of-the-linecorrosion has motivated the present research.In wet gas pipelines, the main corrosive speciesare carbon dioxide (CO2), hydrogen sulfide (H2S), andorganic acids. All of these species can be found inboth the gas phase and the liquid phase. From bottom-of-the-line corrosion studies, organic acids areknown to increase the risk of corrosion.1 Since organicacids are volatile, they can be a potential cause of corrosion in the condensed liquid at the top of the line.This begs several questions:—What is the concentration of organic acids atthe top of the line?—What is the distribution of organic acids between the corrosive, undissociated form andthe dissociated form that is not related to metalloss?—How can the concentration and chemical speciation at the top of the line be predicted?To answer these questions, acetic acid(CH3COOH) was chosen as being a representative ofthe low-molecular-weight organic acids encounteredin oil and gas operations, specifically C1 through C4(that is, formic acid (HCOOH), acetic acid, propionicacid (C2H5COOH) and butanoic acid (C3H7COOH)). Thecorrosive and volatile behavior of acetic acid is typicalfor the low-molecular-weight organic acids. The aciddissociation values of propionic and butanoic acidsare similar to that of acetic acid.2 The acid dissociation constant of formic acid is ten times larger (or theISSN 0010-9312 (print), 1938-159X (online)10/000047/ 5.00 0.50/0 2010, NACE InternationalCORROSION—APRIL 2010
CORROSION SCIENCE SECTIONpKa of formic acid is 1 log unit less) than that of acetic acid.3 Despite this, equivalent concentrations ofundissociated acetic acid and undissociated formicacid lead to a similar corrosive rate.4 Additionally, inmost oil and gas fields, acetic acid is the predominantspecies of organic acid present.Organic acids can affect the corrosion rate inthree ways:—By increasing the cathodic reaction rate:Organic acids, for example, acetic acid (hererepresented as HAc), can increase the cathodicreaction rate by acting as a source of protons (Equation [1]), which then can be reduced(Equation [2]):HAcHAc H Ac –(1)1H2 2(2)H e – 2HAc 2e – H2 2 AAcc–(3)—By inhibiting the anodic dissolution reaction:Crolet, et al., found that acetic acid has a slightinhibiting effect on the anodic dissolution ofiron.5 Sercombe, et al., also observed inhibitionof the corrosion rate by acetic acid at low temperatures (25 C to 40 C), possibly due to a filmforming effect.6—By changing the solubility and protectivenessof the corrosion product films: Crolet and Bonissuggest that acetic acid prevents the precipitation of protective iron carbonate by favoring thesoluble iron acetate.2 On the contrary, Nafdayand Nes̆ić argued that free acetic acid increasesthe corrosion rate by lowering the pH and notby providing a more soluble corrosion product.7More recently, Fajardo, et al., demonstratedthat organic acids increase the amount of timerequired to form a protective iron carbonatefilm, thereby lengthening the time during whichhigh corrosion rates can be sustained.4Regardless of the mechanism, it is accepted thatthe corrosion rate increases as the concentration ofacetic acid increases even at the same pH. Specific tothe top of the line, Singer, et al., observed that as littleas 18 mg/L of free acetic acid is sufficient to almostdouble the corrosion rate at the top of the line inshort-term tests.8Because of the ability of organic acids to increasethe corrosion rate, the composition and distribution oforganic acids in the condensate at the top of the linewas investigated experimentally. A thermodynamic(1)By analyzing standard solutions of acetic acid, the systematicerror of the ion chromatography method was found to be 10%.Random errors were addressed by performing each analysis onduplicate samples. The average of the duplicated readings wereused for the reported acetic acid concentrations.CORROSION—Vol. 66, No. 4modeling approach was developed to predict the concentration of acetic acid at the top of the line.EXPERIMENTAL PROCEDURESThe interaction between condensation, chemicalspeciation, and corrosion was studied in two series ofexperiments. In the first series, experiments were performed in non-corroding systems to characterize theinfluences of condensation and chemical speciationon the resulting condensate chemistry. The secondseries of experiments went a step further by includingthe corrosion aspect.Series 1: Non-Corroding SystemsThe non-corroding system studied was CO2/HAc/H2O. The objective here was to understand the vapor/liquid partitioning of these species at different condensing conditions, that is, for different condensationrates.The condensation process supplies the undissociated acetic acid to the condensate according to thevapor/liquid equilibrium.HAcHAc( g ) HAHAcc(aaqq)(4)The condensation of acidic species (organic acidsplus dissolved CO2) leads to a pH decrease.Series 1: Non-Corroding Systems, Experimental — The experimental setup for this series of testsconsisted of a modified distillation apparatus (Figure 1). Two flasks were filled with solutions containing the same concentration of acetic acid. The firstflask served as a “prebubbler.” This prebubbler wasused to saturate the gas phase with acetic acid andthereby prevent stripping of acetic acid from the second flask, labeled as the “tank.” The “tank” simulatedthe source of acetic acid to the gas phase, which in apipeline scenario would be the bottom of the line. Thecarrier gas, CO2, was bubbled through the “prebubbler,” then the “tank,” and finally was allowed to cooland partly condense in the condenser before beingvented. Either CO2 or water was used as the coolantin the condenser, depending on the desired temperature drop that needed to be achieved. After the condensate temperature had stabilized, the condensedliquid was collected by overfilling a sample vial toeliminate the vapor phase, tightly sealing it and storing it under refrigerated conditions until analysis. Theconcentration of total organic acid was analyzed byion chromatography using an ion-exclusion column.(1)Typically, 30 min to 1 h were needed to collect a sufficient amount of sample for analysis using this setup.The test parameters are given in Table 1. The temperatures (liquid, vapor, and condensate), gas flow rates(carrier gas and cooling gas), and the concentration ofacetic acid (tank liquid and condensate) were all measured and recorded.045002-2
CORROSION SCIENCE SECTIONFIGURE 1. Depiction of setup used for Series 1: non-corroding system experiments.TABLE 1Test Parameters for Series 1: Non-Corroding ExperimentsParameter Value(s)Temperature, Tgas,inTemperature difference condensation ratePressure[HAc, total]tank68 C (Ttank,liq set at 70 C)5, 10, 20, 30, 40 C1 atm1,000 mg/LSeries 1: Non-Corroding Systems, Results — Thevariation of concentration of total acetic acid in thecondensate vs. the temperature drop over whichcondensation occurred is shown in Figure 2. It wasobserved that the concentration of total acetic acid inthe condensate decreased as the temperature drop forcondensation increased, that is, as the condensationrate increased. Since these results are for freshly condensing liquid in the absence of corrosion, the condensate pH was low ( 3.5) and there was minimaldissociation of acetic acid to acetate.FIGURE 2. Decrease in concentration of total acetic acid withincreasing temperature drop for condensation for the non-corrodingsystem.Series 2: Corroding SystemsThe chemical composition of the condensate isalso influenced by the corrosion process (Figure 3).The corrosion process tends to lead to an increase ofpH as H ions are consumed by the cathodic reaction(Equation [2]).In a related study, the change in concentrationof free acetic acid in the condensate was found to beinfluenced predominantly by the liquid equilibrium.9The liquid equilibrium refers to the acid dissociation equilibria in the liquid. The liquid equilibrium isachieved 8 to 10 orders of magnitude faster than thevapor/liquid equilibrium.Series 2: Corroding Systems, Experimental — Theexperimental setup shown in Figure 1 was modifiedfor testing the distribution of organic acids in a corroding system (Figure 4). A carbon steel tube wasinserted into the condenser such that condensation045002-3FIGURE 3. Schematic of the key processes influencing the chemicalspeciation in a droplet.occurred directly on the inside surface of the steeltube. Thus, the condensation and corrosion processeswere studied together.As in Series 1, the condensation rate was controlled by adjusting the flow rate of the coolant (here,water) and measuring the temperature drop overwhich condensation occurred. The test matrix is givenin Table 2. The condensate was analyzed for the concentrations of total acetic acid (by ion chromatography), dissolved iron (by spectrophotometry), andhydrogen ions (by pH measurement).CORROSION—APRIL 2010
CORROSION SCIENCE SECTIONFIGURE 4. Depiction of setup used for Series 2: corroding system experiments.TABLE 2Test Parameters for Series 2: Corroding ExperimentsParameter Value(s)Temperature, Tgas,inTemperature difference condensation ratePressure[HAc, total]tank68 ºC (Ttank,liq set at 70 C)4 C to 16 C1 atm1,200 mg/LSeries 2: Corroding Systems, Results — As withthe non-corroding system (Figure 2), it was observedthat the concentration of total acetic acid in the corroding system decreased as the temperature drop forcondensation increased (Figure 5). The explanation forthis behavior is presented in the following section onthermodynamic modeling.The dissolved iron concentration showed aslightly increasing trend, although there was somescatter in the data (Figure 6). Each of these testslasted for 2 h but the actual time of contact betweenthe condensing liquid and the corroding steel wasmuch shorter than this. Thus, the vapor/liquid equilibrium was not maintained accurately in these tests.FIGURE 6. Increase of dissolved iron in the condensate as thetemperature drop for condensation increased.CORROSION—Vol. 66, No. 4FIGURE 5. Slight decrease in concentration of total acetic acid asthe temperature drop for condensation increased.Consequently, the increase of pH due to the releaseof ferrous ions by corrosion resulted in dissociationof acetic acid in the condensate. Because the concentration of dissolved iron (and the pH) increased withthe temperature drop, the concentration of free acetic acid decreased (Figure 7). It is postulated that inthe pipeline scenario, the relatively short droplet res-FIGURE 7. Decrease in concentration of free acetic acid in thecondensate as the temperature drop for condensation increased.045002-4
CORROSION SCIENCE SECTIONTABLE nInlet gas temperature of the pipeline sectionOutlet gas temperature of the pipeline sectionPartial pressure of water at the specified gas temperature, Tgas, as calculated byAntoine’s equationTotal volume of water that condensed out (assuming condensation rate is given by thedominant species, water only)Concentration of undissociated acetic acid in the tankConcentration of undissociated acetic acid in the condensateHenry’s law constant for acetic acid calculated at the specified gas temperature, TgasHenry’s law constant for CO2 calculated at the specified gas temperature, TgasPartial pressure of acetic acid at the specified gas temperature, TgasPartial pressure of CO2 at the specified gas temperature, TgasConcentration of dissolved CO2Number of moles of acetic acid (or CO2) present in the gas entering the pipe section,calculated using ideal gas assumption at the inlet gas temperature, Tgas,inNumber of moles of acetic acid (or CO2) present in the gas leaving the pipe section,calculated using ideal gas assumption at the exit gas temperature, Tgas,outNumber of moles of acetic acid (or CO2) that condenses out into the liquid phaseDissociation constant of acetic acid; this is only a function of temperature—Define gas temperature: Tgas,in and Tgas,out—pH2O(Tgas,in) – pH2O(Tgas,out) volume condensed,Vliq—Input conditions: [HAc,free]in pHAc; pCO2 Henry’s Law:pH ( TgapHAcgass,out ) [HAHAcc, ffree ]HHA(HAcc Tggasas,outout )pCOO2 ( Tgagass,out ) [CO2 ( l )]HCO ( Tgagass,out )2FIGURE 8. Comparison of experimental and theoretical results forSeries 1: non-corroding system.idence time means that a similar situation to thisseries of tests develops: that the vapor/liquid equilibrium is not sustained and the concentration of freeorganic acid in the condensate is determined by thepH change due to corrosion.THERMODYNAMIC MODELINGThe system was modeled using a thermodynamicapproach wherein steady-state or equilibrium conditions were assumed. First, the modeling of non-corroding systems is presented. The vapor/liquid equilibrium can be described by Henry’s law for acetic acidand Antoine’s equation for water. In the liquid, theequilibria among aqueous species were described bythe acid dissociation expressions. To solve for the concentration of species, the set of equations was completed by applying the conservation of mass (speciesmass balances) and the conservation of charge (electroneutrality condition). The calculation scheme isgiven below, and nomenclature is defined in Table 3.045002-5 Mole balance:ngas,in ngas,out nliq,cond(Solved for both HAc and CO2 species.) Dissociation in the droplet:[ Ac – ] K HA,]HAcc,dissoc [HAc,free[H ](Similarly, CO2(l) dissociates into H2CO3,HCO3–, and CO32–.)The results of the thermodynamic calculationsshowed that as the temperature drop for condensationincreased, the concentration of acetic acid in the condensate decreased. The agreement between these theoretical predictions and the results of the experimentsdone in a non-corroding system (Series 1) validatesthe model (Figure 8). Translating the model predictionfor a non-corroding system to a pipeline scenario givesthe profile for freshly condensing liquid before theonset of corrosion (Figure 9).In Figure 9 a simulation was done where it wasassumed that the concentration at the bottom of theline is constant. Each “droplet” at the top of the lineis in equilibrium with the bottom of the line, considering a temperature drop from 70 C to 69 C, 70 C toCORROSION—APRIL 2010
CORROSION SCIENCE SECTIONFIGURE 9. Schematic of acetic acid concentration in freshly condensed liquid along a pipeline.68 C, and so on. Thus, the third “droplet” shows theconcentration of total acetic acid expected at the topof the line if the gas was to be condensed from 70 C to67 C.Simple reasoning based on the fact that the boiling point of acetic acid is slightly above that of watermay lead one to conclude that the concentration ofacetic acid should increase as the difference in temperature (or the condensation rate) is increased. However, the observed behavior was contrary to this. Thisis best explained by considering that the amount ofacetic acid in the condensate is related to the changein partial pressure of acetic acid in the gas. As shownin Table 4 and Figure 10, the ratio of the change inpartial pressure of acetic acid to the change in partial pressure of water (an indication of the concentration of acetic acid in the condensed liquid) decreasedfor the larger temperature drop. That is to say, for alarger temperature drop, the condensed liquid is lessconcentrated in acetic acid due to the relationshipbetween partial pressure and temperature. This dataTABLE 4Variation of Partial Pressures of Waterand Acetic Acid with Temperature Drop10 CTemperature Drop(90 C 80 C)20 CTemperature Drop(90 C 70 C)DpHAc /bar6.92 10–51.13 10–4DpH2O /bar2.33 10–13.98 10–1Ratio ofDpHAc:DpH2O2.98 10–42.85 10–4was calculated using Antoine’s equation for water andHenry’s law for acetic acid, considering a free aceticacid concentration of 1,000 mg/L in the initial liquidphase. It may seem that the ratios of change in partial pressure of acetic acid to that of water were quitesmall. This is because the data is given in bar/barand the partial pressure of acetic acid is also quitesmall. However, it sufficiently illustrates that as theFIGURE 10. Variation of partial pressures of water and acetic acid with temperature.CORROSION—Vol. 66, No. 4045002-6
CORROSION SCIENCE SECTIONevaluated based on modifying the charge balance toinclude ferrous ions (Equation [5]).[H ] 2[Fe 2 ] [OH – ] [ Ac – ] [HCO3– ] 2[CO23 – ]FIGURE 11. Schematic of the model parameters for a pipelinescenario.temperature drop is increased, the ratio of change inpartial pressure of acetic acid to that of water (indicative of the concentration of acetic acid in the condensed liquid) decreases.This relationship between the change in partialpressure of acetic acid vs. that of water around 70 Cis confirmed further by the behavior of the vapor/liquid equilibrium at the boundary conditions. If there isonly a minor temperature drop, then the concentration of acetic acid of the condensate at the top of theline more closely compares with the concentration inthe source liquid at the bottom of the line. As shownin Figure 9, a bottom-of-the-line free acetic acid concentration of 970 mg/L corresponds with a top-ofthe-line acetic acid concentration of 965 mg/L for atemperature drop of 1 C (from 70 C to 69 C). At theother extreme, if the gas is condensed completely,then the concentration of acetic acid in the condensate is comparable with the concentration of aceticacid in the gas phase. A bottom-of-the-line free aceticacid concentration of 970 mg/L is in equilibrium with 670 mg/L of acetic acid in the vapor phase (at 70 C).If all this vapor was condensed completely, the concentration of acetic acid in the condensate would be equalto the concentration in the gas phase, 670 mg/L.Between these two extremes, there is a decrease inconcentration of acetic acid in the condensate withincreasing temperature drop, which is approximatelylinear (see theoretical results in Figure 8.)The experimental work and calculations describedabove have led to two important conclusions, whichcan be used as the starting point to determine the distribution of chemical species in a corroding system.First, the above experiments prove that the thermodynamic approach can be used successfully to predict the concentration of species in freshly condensedliquid. Second, the distribution of species in the condensate is influenced predominantly by the liquidequilibrium and more specifically, the pH. These findings will be used as the assumptions when considering the corroding system.For the corroding system, the calculation schemegiven earlier in this section was used to obtain theconcentration of total organic acid in the condensate.The acid dissociation in the condensate was then045002-7(5)A concentration of ferrous ions was introducedinto the model and the concentration of all specieswas recalculated to restore equilibrium. The concentration of ferrous iron was then increased incrementally to simulate what would happen as the steelcorroded. Reiterations were done until the condensatewas supersaturated with iron carbonate. The modeldeveloped and tested with a benchtop apparatus wasthen extended to model the condensate chemistry in acorroding pipeline.MODELING THE CONDENSATE COMPOSITIONIN A PIPELINEFor the pipeline scenario (Figure 11), typically thegas temperature and gas flow rate are known. For thisillustration, the condensation rate is specified and thetemperature of the gas leaving the pipe section wascalculated. Depending on the data available, it is alsopossible to use the gas temperatures (inlet and outlet)as inputs and to calculate the condensation rate fromthese.To calculate the concentration of species in thetop-of-the-line condensate, it is necessary to know thepH and concentration of volatile species in the bottomof the line. The thermodynamic modeling approachdescribed in this paper was applied using the baselineconditions shown in Table 5. The model predictionsgave the evolution of the concentration of species withtime (Figure 12).Initially, at time 0 h, the acetic species existalmost completely as undissociated acid. This isbecause the initial pH is low ( 3.3). However, as thetime increases, ferrous ions are released into solution by the corroding steel and the pH increases. Thisresults in an increase in the acetate concentrationaccompanied by a proportionate decrease in free acetic acid concentration. The concentrations of total acetic acid and of dissolved CO2 are constant because ofthe assumption that the time needed to achieve andmaintain vapor/liquid equilibrium is too slow relativeto the droplet residence time. The concentration anddistribution of all chemical species are thus defined.The simulation was truncated when the iron carbonate saturation was achieved, which, in this case,occurred after 1.25 h.CONCLUSIONS The concentration of total organic acid in the condensate at the top of the line can be predicted by athermodynamic consideration of the vapor/liquidequilibrium.CORROSION—APRIL 2010
CORROSION SCIENCE SECTIONTABLE 5Input Parameters for Model Simulation of the Condensate Chemistry in a Corroding PipelineParameter Description Baseline OL[HAc total]BOLpHBOLvgasPipe IDLrtGas temperature entering the pipe sectionGas temperature leaving the pipe sectionAverage gas temperature in the pipe sectionTotal pressurePartial pressure of CO2Condensation rateCorrosion rate at the top of the lineConcentration of total acetic acid at the bottom of the linepH at the bottom of the lineGas flow ratePipe internal diameterPipe lengthDroplet radiusMaximum residence time of a droplet The distribution of organic acid in the condensatebetween dissociated and undissociated forms is influenced predominantly by the pH of the condensate asdetermined by the increase in dissolved ferrous concentration due to corrosion and less influenced by thecondensation process and vapor/liquid equilibriumonce corrosion is initiated. As the condensation rate increases, the concentration of organic acid in the condensate decreases. Thatis, a low condensation rate would present a more concentrated solution of the organic acids at the top ofthe line than a higher condensation rate would. This thermodynamic approach can be applied toother species that are known to be problematic from acorrosion point of view, such as CO2 and H2S. The above methodology for the prediction of theconcentration of corrosive species in the condensateallows the corrosion rate at the top of the line to bedetermined accurately from mechanistically soundprinciples.ACKNOWLEDGMENTSThe author is grateful for the technical supportof the staff at the Institute for Corrosion and Multiphase Technology, Ohio University, and for organicacid analysis provided by J. Thompsen, ConocoPhillips. This work was made possible through the financial support and technical guidance of the followingcompanies: ConocoPhillips, Total, ENI, and BP.FIGURE 12. Evolution of concentration profiles within a droplet.2.3.4.5.6.7.8.REFERENCES9.1. S. Nes̆ić, “Key Issues Related to Modeling of Internal Corrosion ofOil and Gas Pipelines—A Review,” 16th Int. Corros. Cong., Key-CORROSION—Vol. 66, No. 470 CCalculated based on the condensation rateCalculated based on the condensation rate3 bar2 bar0.25 mL/m2/s0.25 mm/y100 mg/L45 m/s10 cm1m5 mm100 minnote Address (Beijing, China: International Corrosion Council,September 2005).J.L. Crolet, M. Bonis, “Why So Low Free Acetic Acid Thresholds,in Sweet Corrosion at Low PCO2?,” CORROSION/2005, paper no.272 (Houston, TX: NACE International, 2005).M. Tomson, A. Kan, G. Fu, L. Cong, M. Al-Thubaiti, “A New Theoretically Accurate Method to Measure Alkalinity,” CORROSION/2004, paper no. 04074 (Houston, TX: NACE, 2004).V. Fajardo, C. Canto, B. Brown, S. Nes̆ić, “Effect of Organic Acidsin CO2 Corrosion,” CORROSION/2007, paper no. 07319 (Houston, TX: NACE, 2007).J.L. Crolet, N. Thevenot, A. Dugstad, “Role of Free Acetic Acid onthe CO2 Corrosion of Steels,” CORROSION/1999, paper no. 466(Houston, TX: NACE, 1999).M. Sercombe, S. Bailey, R. De Marco, B. Kinsella, “An Investigation of the Influence of Acetic Acid on Carbon Dioxide Corrosion,”Proc. Corrosion Prevention Conf., paper no. 22 (Perth, Australia:Australian Corrosion Association Inc., 2004).O.A. Nafday, S. Nes̆ić, “Iron Carbonate Film Formation and CO2Corrosion in the Presence of Acetic Acid,” CORROSION/2005,paper no. 05295 (Houston, TX: NACE, 2005).M. Singer, S. Nes̆ić, Y. Gunaltun, “Top-of-the-Line Corrosion inPresence of Acetic Acid and Carbon Dioxide,” CORROSION/2004,paper no. 04377 (Houston, TX: NACE, 2004).D. Hinkson, “A Study of the Chemical Composition and Corrosivity of the Condensate for Top-of-the-Line CO2 Corrosion” (Master’s thesis, Ohio University, 2007).045002-8
The chemical composition of the condensate is also influenced by the corrosion process (Figure 3). The corrosion process tends to lead to an increase of pH as H ions are consumed by the cathodic reaction (Equation [2]). In a related study, the change in concentration of free acetic acid in the condensate was found to be
The biodiesel corrosiveness also depends on feedstock (raw materials) due to the difference in their chemical composition, especially regarding the unsaturation degree, which leads to the degradation process and formation of products with different de-grees of corrosiveness [11,12]. On the other hand, the corrosion
A)The total surface area decreases and chemical composition changes. B)The total surface area decreases and chemical composition remains the same. C)The total surface area increases and chemical composition changes. D)The total surface area increases and chemical composition remains the same. 14.What occurs when a rock is crushed into a pile of
Chemical Formulas and Equations continued How Are Chemical Formulas Used to Write Chemical Equations? Scientists use chemical equations to describe reac-tions. A chemical equation uses chemical symbols and formulas as a short way to show what happens in a chemical reaction. A chemical equation shows that atoms are only rearranged in a chemical .
Levenspiel (2004, p. iii) has given a concise and apt description of chemical reaction engineering (CRE): Chemical reaction engineering is that engineering activity concerned with the ex-ploitation of chemical reactions on a commercial scale. Its goal is the successful design and operation of chemical reactors, and probably more than any other ac-File Size: 344KBPage Count: 56Explore further(PDF) Chemical Reaction Engineering, 3rd Edition by Octave .www.academia.edu(PDF) Elements of Chemical Reaction Engineering Fifth .www.academia.eduIntroduction to Chemical Engineering: Chemical Reaction .ethz.chFundamentals of Chemical Reactor Theory1www.seas.ucla.eduRecommended to you b
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2.2.2 Chemical composition (HR-ToF-AMS and MAAP) The chemical composition was measured using a HR-ToF-AMS (Aerodyne Research Inc., Billerica, MA) (DeCarlo et al., 2006) which has a vacuum aerodynamic cut-off diameter of 1µm. Regular calibrations were performed with ammo-nium nitrate, and the composition-dependent collection effi-ciency was .
Description Logic: A Formal Foundation for Ontology Languages and Tools Ian Horrocks Information Systems Group Oxford University Computing Laboratory Part 1: Languages . Contents Motivation Brief review of (first order) logic Description Logics as fragments of FOL Description Logic syntax and semantics Brief review of relevant complexity .
