Characterization of Two Industrial Gas Hydrate Inhibitors using

the 3-in-1 Technique

Andres Felipe Lara Contreras

December 16, 2017

An undergraduate thesis submitted to Universidad de los Andes (Colombia), in partial fulfillment of the requirements of

the degree of Chemical Engineer at Universidad de los Andes.

Abstract

Gas hydrates are crystalline compounds, present in nature and considered dangerous if their formationtakes place inside gas or oil exploitation pipelines. The 3-in-1 technique is used to characterize twodifferent industrial hydrate inhibitors on morphology, kinetics and phase equilibria. A mass fraction of0.1% is used to evaluate the behavior of both inhibitors and the results are compared to the uninhibitedsystem and other hydrate inhibitors. The technique shows reliability comparing results from previousexperiments and consistent replicates for this work. Both gas hydrate inhibitors are classified as KineticInhibitors with a slight thermodynamic promoter effect. ”Sandwich” theory is proposed according to theresults obtained in contact angle measurement and aging tests. The selection of one of the inhibitors ismade based on the performance and advantages for field applications.

1 Introduction

Gas hydrates (also known as clathrate hydrates)are non-stoichiometric solid compounds which areformed when water and volatile molecules get incontact at low temperature and high pressure [1, 2].This water molecules form hydrogen-bonded cageswhich trap volatile (also known as guest) molecules,stabilizing the structure thanks to Van der Wallsforces [3]. The guest particles are usually gasmolecules with a diameter less than 0.9 nm ascarbon dioxide, methane, nitrogen, and propane[4]. There is no chemical reaction involved in hy-drate formation, but only a physical transformation[2]. Deposits of gas hydrates can be found in na-ture, most of them formed by light gases such asmethane, ethane or mixtures [1, 5], but also, forma-tion can be achieved in laboratories to study theircharacteristics and measure different properties tounderstand the behavior at different conditions.

According to experts’ estimates, stored energyin hydrates is equivalent to twice the energy pro-duced by other combustible fuels altogether [1].If only 1% of the estimated US in-place hydratedmethane gas were exploited, the US energy supplywould be assured for approximately 87 years at theconsumption rate of 2004 [4]. Also, hydrates could

be used for different purposes such as natural gasstorage and transportation, sea water desaliniza-tion and carbon dioxide sequestration[6, 7].

On the other hand, the safety in oil and gaspipelines is threatened by the formation of thesecrystals if the flow gets into high pressures and lowtemperatures. These conditions are in many casesoptimum for clathrate formation. Hydrates havebecome relevant because of its energy high densityand the implication of its formation in pipelines.The pipeline plugging phenomenon was discoveredin 1934, getting the attention of the scientific com-munity [1, 8]. Once the pipelines are being ob-structed by hydrates, it is required to dissociatethe plug by different methods explained below.

Thermodynamic inhibitors (THI) are additivesused in high concentration (usually greater than20%) and their function is to shift the Hydrate-Liquid-Vapor equilibrium curve (HLV) to higherpressures and lower temperatures [9, 1]. With thischange in hydrate equilibrium conditions, the hy-drate is not allowed to be formed with the pipelineoperating conditions. Examples of such kind of in-hibitors are Mono Ethylene Glycol, Methanol andNaCl [9, 10, 11].

On the other side, there is another kind of in-hibitors, denominated as Low Dosage Hydrate In-

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hibitors (LDHI). These can be used in a concen-tration range between 0.1 and 5 mass percent-age [9, 12]. LDHI’s can split into two: KineticInhibitors (KHI’s) and Antiagglomerants (AA’s).These two are being used commonly in the industrybecause the advantages including reduced volumesof material to be injected into the flow and lowercosts [12].

The main characteristic of kinetic inhibitors isthe effect they have on the induction time. It meansthat the hydrate formation is delayed, and con-sequently, the flow achieves operating conditionswhich hydrate phase is not stable [9, 13]. Anothereffect of KHI’s is the reduction on the growth rateas consequence of the adhesion of polymer parti-cles to the crystal [14]. Antiagglomerants, on theother side, allow hydrate formation and growth, butprevent the plug formation. The hydrate crystalsflow with the fluid phase until achieving the con-ditions in which the hydrate cannot be stable any-more. AA’s are in constant development to reducethe high toxicity of the components used on them[15].

To characterize gas hydrates, three key aspectsto study are: morphology, which consists on theshape, color, opacity, texture and grain form of thecrystal; apparent kinetics, measuring the crystalgrowth rate and other time dependant phenomena;and phase equilibria, finding the thermodynamicbehaviour of the system by measuring the equilib-rium conditions (pressure and temperature) for hy-drate, liquid water and vapor phases.

The driving force is the deviation of the exper-imental conditions from those at equilibrium state[16, 3]. This force has a direct effect on kinetics andmorphology [16, 17]. The aging process has also animportant role in the morphology of gas hydrates.It has been observed by researchers that for longerformation periods, the hydrate tends to smooth andhomogenize the surface [18].

Currently, different apparatuses and experimen-tal settings are used to measure the mentioned char-acteristics. These include flowloops, high-pressurevessels, crystallizers and more [15]. These meth-ods require lots of time and resources in order toobtain one point of data for each one of the char-acteristics of gas hydrates [15, 19]. With the 3-in-1technique, it is possible to achieve multiple datafor all three characterization aspects of hydrate in-hibitors, drastically reducing the experimentationtime, with a high reproducibility compared to othermethods [19, 20].

2 Experimental

2.1 Apparatus

The apparatus is represented in figure 1. It con-sists of a high-pressure vessel built of 316 stainlesssteel and equipped with sapphire windows (Ray-otek, CA, USA) located on the top and bottom tohave a clear birds eye’s view of the sample. Thesample was illuminated by a Schott KL2500 LCDcold light source (Optikon, ON, Canada) set on thebottom, and a PCO 5.5 sCMOS camera (Optikon,ON, Canada) is located on the top to monitor thesample and record the process. A NIKON AF-Micro Nikkor 60 mm lens was attached to the cam-era for standard magnification images. For HighMagnification, it was used an Infinity KC Micro-scope equipped with IF series objectives (Optikon,ON, Canada). The vessel had several ports forgas inlet and outlet, temperature probes, pressuretransducer connection, and wiring.

Inside the vessel, it is used a High-Pressure Bi-lateral Temperature Control Stage (HP-BTCS) tocontrol the experimental temperature. A graphicrepresentation of this can be found in figure 2.In both ends of the slide, Thermoelectric CoolerModules (TEMs) (TE Technology, MI, USA) areused. The temperature on the TEMs was con-trolled using a bi-polar PID temperature controller(TE Technology, MI, USA) with a resolution of±0.01 K. To uniformly distribute the temperaturein the TEMs, copper plates were affixed on topand bottom of each TEM. In the copper plates,a fast-response thermistor (TE Technology, MI,USA) measured the temperature with an instru-mental standard uncertainty of uTthermistor

= 0.01K. The temperature inside the reactor was mea-sured using a platinum RTD Probe (Omega Engi-neering, QC, Canada) with an instrumental stan-dard uncertainty uTRTD = ±0.32 K. The pressureinside the reactor was measured using a Rosemont3051s Pressure Transmitter (Laurentide Controls,QC, Canada) with an instrumental uncertainty ofuP = ±0.005 MPa.

The temperature inside the reactor was con-trolled using a copper coil wrapped around the ves-sel. A mixture of 50/50 (v/v)% ethylene glycol andwater was circulated into the copper coil. The mix-ture was cooled using a Thermo Scientific AC200refrigerated circulator (Fisher Scientific, Canada).

2.2 Materials

Table 1 shows the composition of the different in-hibitors used during the experimental phase of theproject. A mass fraction of 0.1% of the respectiveinhibitor was used for inhibited experiments.

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Figure 1: Graphic representation of the apparatus. (A) 316Stainless steel pressure vessel. (B) Sapphire sight windows.(C) Video camera. (D) Cold light source. (E) Coolantjacket. (F) Refrigerated circulator. (G) Bi-polar PID tem-perature controllers. Reproduced from [19].

Figure 2: Graphic representation of the High-Pressure Bi-Lateral Temperature Control Stage (HP-BTCS) found insidethe high-pressure vessel. Reproduced from [19].

Table 1: Approximate composition of the commercial hy-drates inhibitors reported by the provider.

Inh. Component 102. Mass fraction

B1

Amine Compound 30 to 40Toluene 30 to 40

Isopropanol 20 to 30Amine Compound 1 to 5Amine Compound 1 to 5

Tetradecanol 0.1 to 1

B2Toluene 50 to 60

Amine Compound 30 to 40Alkyl Ether 1 to 5

Table 2: Materials used during the experimental procedurelisting purity and provider. Purity is shown in mole fraction.

Chemical name Source PurityDeionized water In-house -

Methane Air Liquide 99.99%Nitrogen Air Liquide 99.99%

2.3 Methods

The sapphire slide was washed three times with de-tergent and rinsed with cold water. Subsequently,the slide was dried with compressed air and sub-merged during five minutes in acetone in a son-ication bath. Then, the slide was submerged inisopropanol for a period of five minutes also in asonication bath and finally, dried using dust-freecompressed air. A droplet of deionized water of20 µL is placed between the two ends of the sap-phire slide. Then, the vessel was sealed and purgedthree times with nitrogen. Later, the same purgingprocedure was performed using methane. Table 2shows th purity and source of materials.

Figure 3: Sample pretreatment cycle. (a) Initial tempera-ture and pressure inside the vessel. (b) Frozen droplet, onlyice and vapor phase are present. (c) Pressurization of thevessel, hydrate formation from ice. (d) Hydrate phase in thedroplet. (e) First dissociation process, droplet with liquidand vapor phases present.

Sample Pretreatment: The sample was pre-treated as shown in the figure 3. The initial condi-tions are environmental temperature and pressureof 0.1 MPa. The vessel is cooled until a tempera-ture around 278.15 K is achieved. Then, the stageis cooled to 258.15 K until ice is formed. After that,the vessel is pressurized up to 5.1 MPa which is theexperimental pressure and hydrate starts formingwhen the temperature is raised to 278.15 K. Then,the hydrate is dissociated by increasing the tem-perature to 281.15 K. Before forming the hydrateagain, the sample was kept for 2 minutes at 281.15K . For inhibited systems using inhibitor B2, thewaiting time before hydrate formation was 3.5 min-utes. The temperature inside the vessel remainedconstant at 279.15 K.

Hydrate formation: Two different settings wereused to form hydrate on the stage. Figure 4 rep-resents the hydrate formation at uniform temper-ature. For uniform surface temperature experi-ments, both TEM’s had the same temperature set-point (T ), below THLV to allow the hydrate forma-tion. For the constant temperature gradient, eachTEM had a specific set-point. The difference be-

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tween the TEM’s temperature (Tgap) was set as 6 Kto include a bigger range of temperatures comparedto other works. A graphic representation of theconstant temperature gradient formation is shownin figure 5.

Figure 4: Uniform hydrate formation setting. Both sides ofthe stage are at the same temperature.

Figure 5: Constant gradient formation setting. Each side ofthe stage has a different temperature. Th > Tc.

Hydrate dissociation: For hydrate dissociation,also two different methods were used. Figure 4represents the hydrate dissociation at uniform tem-perature. For uniform surface temperature exper-iments, both TEM’s were held at the same exper-imental temperature (T ) starting below the equi-librium temperature at the experimental pressure(THLV = 279.5 K at P = 5.1 MPa). The temper-ature was increased 0.2 K every 30 minutes untilinitial hydrate dissociation is observed. After that,the increase rate is reduced to 0.1 K with a waitingtime of 30 minutes. For the constant temperaturegradient, each TEM had a specific set-point, bothof them starting below the equilibrium temperature(THLV). The difference between the TEM’s tem-perature (Tgap) was defined as 6 K again. The set-point of the TEM’s is increased each 30 minutes,

keeping the same temperature difference betweenthem. The process is repeated until completed dis-sociation is achieved.

Figure 6: Uniform dissociation setting. Both sides of thestage are at the same temperature below THLV.

Figure 7: Constant gradient dissociation setting. The high-est temperature (Th) is above the equilibrium temperature(THLV). The lowest temperature (Tc) is below THLV.

3 Results and discussion

3.1 Morphology

The hydrate formation of the system CH4 +H2O isshown in figure 8. A driving force of ∆Tsub = 5.9K was used to form the hydrate in a uniform tem-perature stage. A single growth point is observedin each replicate, with the presence of bubbles inthe middle of the droplet. A radial growth mech-anism is observed until a certain point, in whichthe radial marks disappear showing a clear bound-ary in the growth. Beyond this point, the surfacebecomes smooth until covering the whole droplet.This smooth texture is considered as an effect ofthe high subcooling conditions in which the hydratewas formed [21].

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Figure 8: Three replicates of uninhibited methane + water system.

Figure 9: Methane hydrate formations obtained from quiescent droplets at different driving forces in uniform temperaturesettings and mantained at a constant subcooling. [20, 22]

The differences in morphology are caused by thedifference of the subcooling conditions used for ex-periments in each work using the same apparatus[20, 22]. DuQuesnay and Kumar observed a granu-lar formation at lower driving forces (2 and 4 K) asobserved in figure 9. The subcooling in this work is6 K with a difference in pressure of 1 MPa comparedto the experiments made by DuQuesnay and Ku-mar. This change in pressure increases the drivingforce but has a little effect compared to the subcool-ing [23]. It is noticeable the effect of the subcoolingin the morphology of each grain, even at similarsubcooling temperatures. The three grains on theleft (a-c) show different textures and crystal sizesand shapes. Specificaly in (b), it shows a roughersurface compared to the others, with irregular for-mation [20], even with a hydrate formed at similar

conditions (a).

For hydrate formation of the system CH4 +H2O + B1, the observed morphology on the grainconfirm the results found by Ovalle [24] as shownin figure 10. The evidence of the reproducibility ofthe results using the same system and similar con-ditions gives confidence about the reliability of thetechnique for characterization purposes. The grainshows a smooth surface, with differentiated grainboundaries. This is the result of the misorientationof the crystal structures [25, 26].

The same kind of misalignment is seen in theformation of hydrate in the inhibited system CH4+H2O+B2 for high driving forces. In figure 11 thereare compared side to side two formations of the sys-tem at different driving forces but the same pres-sure. The driving forces are ∆Tsub = 5.4K and

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∆Tsub = 3.4K. The morphology of the hydrateshows a smoother surface at higher driving forcesOn the low driving force uniform formation, the hy-drate is formed from a single growth point, with adendritic morphology and a rougher surface com-pared to the morphology observed in the high driv-ing force formation. The low subcooling formationshows a particular transparence that is not per-ceived in the high driving force (shiny faces of thecrystal). Taking into account that the light sourceis located at the bottom of the vessel, and environ-mental light is restricted on the top by the cameraposition, the shiny faces are product of light goingthrough the crystal. This is similar to the resultsfound by Ovalle at low driving forces for the inhib-ited system with 0.1% of B1 [24]. It is also possibleto see some extensions of the hydrate structure inthe low driving force formation in figure 11. Thisindicate the presence of small droplets in the sap-phire surface, which become hydrate by propaga-tion. This propagation phenomenon was previouslydescribed by Beltran and Servio[16].

Constant temperature gradient formation ex-periments were done in presence of B1 with resultsshown in figure 12. The influence of subcooling oncrystallization of polycrystalline spherulites [21] isclearly observed in all three formations though thegradient. The three formations show a smoothersurface at the bottom of the pictures where thedriving force is higher, and through the gradient,the texture becomes rougher as the driving force islower. The subcooling at the hot side of the slide(Th = 278 K) is ∆Tsub = 1 K and close tempera-tures (up to ∆Tsub = 3.5 K) has a morphology withvery similar characteristics to the high driving forceobserved in figure 11 (b). The same case, on thecoldest side, with a driving force of ∆Tsub = 4.5,the morphology is similar to the morphology foundin figure 11 (a).

The morphology of the gradient on the top andbottom of the pictures in figure 12 looks very simi-lar to the morphology observed in figure 11 for bothdifferent subcooling conditions. It shows evidenceof the power of the technique as the analytic scopeis extensive to different systems while other tech-niques could not. This technique allows seeing theeffect of different driving forces at the same timewith an accurate approximation to the specific re-sults. Details are obtained using the uniform tem-perature experiments.

Figure 13 shows two formations sequences of in-hibited system (CH4 + H2O + B1). In the first one,(a-e) it is observed the growth of hydrate startingat one single point. The interface is curved indicat-ing a dendritic mechanism radially oriented. Thiskind of mechanism is described by Granasy in 2014

for experimental systems [25]. Small crystals areformed and then join the main structure, show-ing the smooth surface with an observable granulartexture [27]. For the sequence (f-j), many growthpoints are formed all over the droplet. Afterwards,each one keeps growing with the same mechanismas sequence (a-e) until the boundaries meet and re-sulting in the grain boundaries formation. All theformations show a circular alteration of the surfacein the growth point, present in spherulites whichgrows radially [27]. The initial growth point is lo-cated close to the boundary of the droplet for singleand multiple growth point formations, contrary tothe uninhibited system in which the growth pointis located in the center of the droplet as shown infigure 8. Surface in both cases keeps the same mor-phology as the subcooling is the driving force in thehydrate formation

Figure 10: Uniform temperature hydrate formation found inthe present work and results previously obtained by Ovalle(2017) [24] using the same equipment at slightly differentsubcooling conditions.

Figure 11: Characteristic morphology obtained in a dropletafter hydrate formation under two different driving forces forthe system CH4 + H2O + B2

With the inhibited system using B2, two dif-ferent growth mechanisms are shown in figure 14.

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Figure 12: Three replicates of constant temperature gradient hydrate formations.

Figure 13: Uniform temperature hydrate formation sequences. (a-e) Hydrate formation from single initial growth point.(f-j) Hydrate formation from multiple initial growth points.

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Figure 14: Uniform temperature hydrate formation sequences at two different driving forces.

Figure 15: Constant gradient dissociation sequences for all the studied systems.

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The sequence of the top (a-d) shows the formationof hydrate at low driving force in uniform temper-ature T = 276.1K and the bottom (e-h) shows theformation in high driving force at a temperatureT = 274.1K. In the low driving force hydrate for-mation, the interphase is irregular, with a dendriticgrowth, single growth point located at the bound-ary of the droplet. It is noticeable that the growthdirection changes slightly, following a ’dizzy’ den-dritic growth more than a radially directed growthseen in the inhibited system with B1.

For the high driving force hydrate formationobserved in figure 14 (e-h), contrary to the lowdriving force formation, the initial growth pointsquantity has noticeably increased. All the initialgrowth points are distributed around the periph-ery of the droplet, same as the formation with in-hibitor B1. There is presence of clearly differenti-ated grains due to the boundaries formed by themisorientation of the crystal structures from eachcrystal. The interface is curved, regular and fol-lows a radially-directed growth pattern. Comparedto the initial growth point morphology observed inhydrate formations with presence of B1, InhibitorB2 shows a protuberance instead of a depression.This could be the result of interaction between theliquid phase containing water and inhibitor, andthe hydrate crystal. Possible surface tension dif-ference due to the composition of the liquid phasemay affect the contact angle between both hydrateand liquid phases [28]. Interfacial interaction willbe discussed latter in the document.

3.2 Phase Equilibria

The equilibrium temperature can be obtained us-ing either uniform temperature or constant gradienttemperature profiles through the droplet. With theconstant gradient temperature, the THLV is mea-sured according to the interface posicion of the hy-drate layer in the droplet with respect to the coldside of the stage. Detailed calculations were sta-blished bu DuQuesnay, Diaz and Beltran in 2015(See [19]). The gradient was determined to beg = 0.41 K∗mm−1 with an uncertainty of ug = 0.03K ∗ mm−1 .

Dissociation process using the constant tem-perature gradient method is presented in differentsteps with results for all three studied systems infigure 15. The interface position of all the systemsis well differentiated, with a straight boundary inall cases but some remaining crystals can be seenin the dissociation process of B2. Also, the equi-librium temperature at each step of the inhibitedsystems follow an increasing tendency. This effectis shown in figure 17 as the equilibrium temper-

ature of the system with no inhibitor shows norelevant change while both inhibited systems do.This phenomenon is described below. The remain-ing crystals observed in B2 dissociation sequencedo not dissociate within 30 minutes as a possibleconsequence of intereaction between hydrate, wa-ter and inhibitor. As hydrate may be formed in thepipeline, the waiting time for dissociation while us-ing B2 as inhibitor should be longer. In this case,the remaining crystals could act as starting pointfor further hydrate formation and possible pipelineplugging.

Figure 16: Measured equilibrium temperature for each of thestudied systems. Other thermodynamic hydrate inhibitorsstudied by other authors are shown. A literature data fittingis represented with a 95% prediction interval.

In figure 17 is shown the equilibrium tempera-ture observed for each one of the studied systems atthe steps observed in figure 15. There is a notice-able difference between B1 and B2 equilibrium tem-perature behavior as the interface displaces. Theinhibitor B1 has a stronger effect in the THLV com-pared to B2. This change in the equilibrium tem-perature was studied by Nagashima et al., report-ing the change in the concentration of inhibitors asNaCl in the boundary of the hydrate while it dis-sociates [29]. The equilibrium temperature in thefinal steps of each constant temperature gradientdissociation approaches to the obtained tempera-ture in the uniform temperature dissociation ex-periments for all the systems. This is the resultof the dissolution of the inhibitor in the boundaryof the grain to the similar level than the obtainedwhen the dissociations takes place all over the slideat the same temperature.

The equilibrium temperature obtained with uni-form temperature across the slide for each systemis shown in figure 16. A fitting using literature datawith a 95% prediction interval is used as referencevalue. Inhibitors B1 and B2 do not show a ther-

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modynamic inhibition at the used concentration asother inhibitors clearly do. A slight promoter ef-fect is observed as the standard uncertainties ofthe points are not overlapping, but remain withinthe prediction interval. In table 3 the equilibriumtemperatures are summarized with the standarduncertainties and pressure inside the vessel. TheTHLV value obtained for the uninhibited system isthe same reported by Ovalle within the same stan-dard uncertainty. This result shows the high re-producibility of the technique and the procedureconsistence among experiments.

Table 3: Equilibrium temperature (THLV) of the studied sys-tems with the respective standard uncertainties and opera-tion pressure.

System T/K uTHLV/K P/MPa

Water 279.6 0.05 5.1B1 279.8 0.02 5.1B2 280.1 0.05 5.1

B1 (Ovalle) 279.8 0.02 5.1

In figure 16 is observed a slight promoter effectof B1 and B2 at the studied concentrations (a massfraction of 0.1% in the aqueous phase). Comparingthe green, red and blue points, the standard uncer-tainties are not overlapping each other, showing adifferent equilibrium temperature for each system.According to the uncertainties, the promoting ef-fect of B1 and B2 (stronger for B2) is not negligi-ble. Due to the small instrumental uncertainty ofthe technique, this effect could be detected when,while using other techniques this could be unper-ceived. In spite of that, in a larger scale, the pro-moting effect of the studied inhibitors is negligibleconsidering the prediction interval.

3.3 Kinetics

The apparent kinetics was measured using uniformtemperature and constant temperature gradient hy-drate formation. The growth rate is measured asthe change in the position of the interface relative toa reference value in certain time. Figure 18 showsthe results for constant temperature gradient (infilled markers) as well as uniform temperature (inempty markers with an associated uncertainty ifavailable) growth rates for uninhibited and inhib-ited systems. The inhibition effect of both studiedinhibitors can be classified as kinetic, as the growthrate is reduced in approximately 1:4 rate. The dif-ference between both inhibitors is not completelyclear as the gradient formation growth rates areoverlapped and distributed following similar pat-terns. Table 1 shows that both inhibitors containamine compounds which, as mentioned by Kelland[9], are known to act as kinetic inhibitors.

On the other hand, it is important to show thedissociation time in order to understand the rela-tion between the water and the inhibitor. It can beobserved in figure 19 the required time to dissoci-ate hydrate from one step to another. The time re-quired by the hydrate with a mass fraction of 0.1%of inhibitor B2 is much longer than the observed forthe uninhibited and B1 systems (about 10 times lessthan B2). This demonstrates the affinity betweenthe hydrate and the inhibitor. The consequences ofthis effect on industrial applications are basicallyefficiency because of the waiting time.

Figure 17: Equilibrium temperature measured at each dis-sociation step using constant temperature gradient dissoci-ation method.

Figure 18: Growth film rates vs. Subcooling. Concentrationof inhibitor B1: 0.1%. Concentration of inhibitor B2: 0.1%.Mass percentage used as measurement unit.

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Figure 19: Single-step dissociation time for studied systemsat the same opearating conditions. Left: Initial interfaceposition is placed. Right: final position of the interface

3.4 Interface Interaction

As mentioned previously, the interfacial interactionmay have a key role in understanding the behaviorof the studied hydrates. First, the formation takesplace in a liquid phase, with the presence of a vaporphase and as result, a solid composed is obtained.The three components are interacting continuouslywith different results depending on the compositionof each phase [1, 3, 9, 20, 22]). Specifically, in thisproject, it will be considered two main interactions:Hydrate and Liquid water (H-L), and Liquid waterand substrate (L-S).

The H-L relation was breafly mentioned in sec-tion 3.2 as the inhibited system could capture thewater avoiding the phase change from hydrate toliquid water (as seen with B2 experiments presentedin figure 15). The interference of the inhibitor inthe dissociation process is strong as is delaying thephase change of the water molecules and/or therelease of methane. Particularly about dissocia-tion time, the uninhibited system and the B1 hy-drate formation have similar behavior as the differ-ence between them is about 30 seconds (dissocia-tion takes longer for B1).

Interaction between the liquid water and thesapphire slide can state a difference between thestudied systems in order to appropriately character-ize the behavior of the assessed inhibitors. The con-tact angle measurement was made to determine theinteraction between the sapphire slide and individ-ual droplets finding the results summarized in fig-ure 20. This results were obtained at atmosphericpressure and in presence of air. It is noticeable a dif-ference between the droplets with and without thepresence of inhibitor. The difference in the contactangle is about 10◦ out of the error bars (calculatedas an expanded uncertainty with a coverage factork=2). Meanwhile, the two inhibitors show the samecontact angle between the droplet and the sapphiresubstrate as the error bars are overlapping. Theseresults shows a hydrophilic relation between wa-ter with diluted inhibitor and the substrate. Thewettability of the sapphire with the water is lower,showing a lower affinity between these two com-pounds compared to the relation between sapphireand the aqueous inhibitor solutions. The measuredcontact angle for the water was θw = 49.6 ± 0.6◦

which is the same value reported in the literature[18]. The results suggest that the water with aninhibitor mass fraction of 0.1% will prefer to stickto the sapphire, more than the pure liquid water.

The L-S interaction is then evaluated by twodifferent phenomena: the aging principle of gashydrates in which, the morphology shows changesthrough the time; and the halo formation as prod-uct of the capillarity of water in the sapphire sub-strate [16]. The halo is a hydrate layer formed bythe water which spreads over the surface as the hy-drate keeps growing. This effect is limited by theavailability of water and the affinity between theliquid phase and the substrate.

Figure 20: Contact angle measurement to droplets with andwithout inhibitors at atmospheric pressure (P = 0.1 MPa)in the open air.

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Figure 21: Aging process of methane hydrates formed withliquid water + 0.1% of (Top) B1 and (Bottom) B2. Theinitial point is on the left, while the same spherulite after 1hour of aging is on the right

As shown in figure 21, the formed hydrate inpresence of B2 has a stronger preference to spreadover the slide. Meanwhile, B1 spreads much slower,as, after one hour, the halo growth is almost un-perceived. Also, the hydrate surface gets smootherin hydrate with B2 presence, and the transparenceof the crystal is reduced. Conversely, the crys-tallite with B1 shows no apparent change in itsshape or texture. The granular surface seems in-tact, with a slight change in the opacity of the crys-tal. The characteristic morphology of the initialgrowth point is preserved.

The hydrate can be understood as a ”sandwich”in the way that the formation involves different lay-ers as observed in figure 22. The halo effect requiresthe spreading of water under the hydrate layer tokeep growing further than the initial boundary. De-pending on the interaction between the water andthe substrate (sapphire), the water is expected tospread more for hydrophilic interactions (dropletswith inhibitor), but surprisingly, none of the inhib-ited systems shows a big halo growth as it happenswith the pure system as can be observed in Beltranand Servio’s[16].

4 Conclusions

The 3-in-1 technique shows high reproducibilitywhen comparing the obtained results of phase equi-libria, morphology and kinetics with previous worksand also between replicates. Traditional and com-mercial inhibitors can be studied using this tech-nique and evaluate the potential industrial use.Compared to other techniques, the required sam-ple amount and resources are reduced.

Figure 22: Sandwich theory consisting in the interfacial in-teraction between the different layers of the hydrate forma-tion

The mass percentage of 0.1% shows clear ki-netic inhibition in a ratio of approximately 1:4 forboth studied inhibitors compared to the uninhib-ited system. That makes the growth rate a non-differentiator factor for the performance compari-son. A hydrate light thermodynamic promotion isobserved according to the uncertainties of the ob-tained THLV, but in a large scale, this result irrele-vant as all the temperatures and uncertainties arewithin a 95% prediction interval. Rigorous controlof temperature allows to detect phenomena thatcould be unperceived with other techniques as thepromoting effect of the studied inhibitors.

The observed morphology corresponds to den-dritic and granular morphologies for both inhib-ited systems. Morphology and kinetics are affecteddirectly by the subcooling in all studied systems.Constant temperature gradient and uniform tem-perature used in this technique are powerfull toolsto have a general view and get into details respec-tively while evaluating morphology, phase equilib-ria and kinetics. Most of the formations show reg-ular and well defined interface, but specifically gra-dient B2 at low driving force, shows an irregular’dizzy’ dendritic growth. The dissociation time re-sults very different between both inhibitors. B2shows a hydrate recalcitrance as result of the bond-ing between the inhibitor and the water. InhibitorB1 shows a step-to-step dissociation time slightlyhigher than the pure system (about 30 secondshigher). This difference in dissociation time mayhave several implications on industrial applicationof inhibitors.

The inhibitors have also an important effect onthe contact angle of the droplet in the sapphiresubstrate. Wettability of sapphire increases with

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droplets containing 0.1% of inhibitor (B1 or B2)with respect to the deionized water. The sand-wich theory shows a double interfacial interactionwhich may explain the observed behavior betweenhydrate, liquid and substrate.

The author suggests that B1 has a better per-formance for field applications than B2 taking intoaccount the wettability, dissociation time, halo for-mation over hydrophilic surfaces, the equilibriumtemperature and promoter effect.

5 Acknowledgment

I would like to extend my gratitude to Dr. JuanBeltran at Royal Military College of Canada(RMCC) for his guidance, encouragement and ad-vise throughout this project; and to Niaz Chowd-hury for his help and support. I would also like tothank the Universidad de Los Andes (Colombia) forallowing me to complete my undergraduate thesiswork in Canada at RMCC, and to the Chemistryand Chemical Engineering Department at RMCCfor welcoming me in their facilities and for cleri-cal and technical support. Financial support wasprovided by the Natural Sciences and EngineeringResearch Council of Canada, The Canadian Foun-dation for Innovation and RMCC. To my parents:Luis and Isabel, special thanks for their love, inspi-ration and financial support; to my sister, my nieceand ’Leo’ for their help and encouragement; andfinally, Jenny and Diego for their company duringmy stay in Canada.

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