The authors thank American Chemical Society - Petroleum Research Fund (ACS - PFR), grant number: PRF # 57216-UNI9, for financial support.

1. Hydrate formation on water droplet in cyclopentane
NOTE: The experimental procedure described below is for the study of hydrate formation on a water droplet in cyclopentane using the IMPd and hydrate visualization cell described in the introduction.
<ol>
	<li>Attach a 19 G needle to the 1 mL glass syringe (Figure 2b, C).</li>
	<li>Rinse the 1 mL glass syringe and 19 G needle 3x with DI water.</li>
	<li>Fill the syringe with DI water.</li>
	<l...

<ol>
	<li>Graham, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Deep water: The Gulf Oil disaster and the future of offshore drilling. Report to the President. , (2011).</li><li>Hammerschmidt, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Formation+of+gas+hydrates+in+natural+gas+transmission+lines.">Formation of gas hydrates in natural gas transmission lines.</a> Industrial &amp; Engineering Chemistry. 26, 851-855 (1934).</li><li>Sloan, E. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+changing+hydrate+paradigm-from+apprehension+to+avoidance+to+risk+management.">A changing hydrate paradigm-from apprehension to avoidance to risk management.</a> Fluid Phase Equilibria. 228-229, 67-74 (2005).</li><li>Xiaokai, L., Latifa, N., Abbas, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anti-agglomeration+in+cyclopentane+hydrates+from+bio-+and+co-surfactants.">Anti-agglomeration in cyclopentane hydrates from bio- and co-surfactants.</a> Energy &amp; Fuels. 24, 4937-4943 (2010).</li><li>Sloan, E. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fundamental+principles+and+applications+of+natural+gas+hydrates.">Fundamental principles and applications of natural gas hydrates.</a> Nature. 426, 353-363 (2003).</li><li>Sloan, E. D., Koh, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Clathrate Hydrates of Natural Gases. , (2007).</li><li>Lee, J. D., Englezos, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unusual+kinetic+inhibitor+effects+on+gas+hydrate+formation.">Unusual kinetic inhibitor effects on gas hydrate formation.</a> Chemical Engineering Science. 61, 1368-1376 (2006).</li><li>Daimaru, T., Yamasaki, A., Yanagisawa, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+surfactant+carbon+chain+length+on+hydrate+formation+kinetics.">Effect of surfactant carbon chain length on hydrate formation kinetics.</a> Journal of Petroleum Science and Engineering. 56, 89-96 (2007).</li><li>Karanjkar, P. U., Lee, J. W., Morris, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surfactant+effects+on+hydrate+crystallization+at+the+water-oil+interface:+hollow-conical+crystals.">Surfactant effects on hydrate crystallization at the water-oil interface: hollow-conical crystals.</a> Crystal Growth &amp; Design. 12, 3817-3824 (2012).</li><li>Leopercio, B. C., de Souza Mendes, P. R., Fuller, G. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Growth+kinetics+and+mechanics+of+hydrate+films+by+interfacial+rheology.">Growth kinetics and mechanics of hydrate films by interfacial rheology.</a> Langmuir. 32, 4203-4209 (2016).</li><li>Karanjkar, P. U., Lee, J. W., Morris, J. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Calorimetric+investigation+of+cyclopentane+hydrate+formation+in+an+emulsion.">Calorimetric investigation of cyclopentane hydrate formation in an emulsion.</a> Chemical Engineering Science. 68, 481-491 (2012).</li><li>Mori, Y. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Harkins-brown+correction+factor+for+drop+formation.">Harkins-brown correction factor for drop formation.</a> AIChE Journal. 36, 1272-1274 (1990).</li><li>Dann, K., Rosenfeld, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surfactant+effect+on+hydrate+crystallization+at+oil-water+interface.">Surfactant effect on hydrate crystallization at oil-water interface.</a> Langmuir. 34 (21), 6085-6094 (2018).</li><li>Ibach, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Physics of Surfaces and Interfaces. , (2006).</li></ol>

In this article we describe an experimental technique to study hydrate crystallization at the oil-water interface in the presence of nonionic surfactants. The apparatus is comprised of a temperature control system and a visualization cell that includes a brass chamber with windows, CMOS camera, and pressure transducer. The temperature control system is comprised of a microcontroller, powerful Peltier plate, 120 mm CPU cooler as the heatsink, and a waterproof digital temperature sensor. A hydrate visualization brass cell ...

The incentive to understand the mechanism of hydrate crystallization and inhibition comes from the fact that hydrates occur naturally in oil pipelines and can result in difficulties in flow assurance. For example, the 2010 Gulf of Mexico oil spill1 was a result of hydrate accumulation in an underwater oil piping system, causing contamination to the environment. Hence, understanding hydrate formation and inhibition is crucial in order to prevent future environmental disasters. Much of the driving force for the study of hydrate crystallization in the past years is the oil industry&#39;s effort to prevent hydrate plug agglomeration and the subsequent blockage of flow. The first study to determine that hydrates were responsible for plugged flowlines was done by Hammerschmidt in 19342. To this day, oil producers find it highly important to understand and inhibit hydrate formation for flow assurance3.
One way to prevent hydrate formation is to insulate deep water pipelines so that ice does not form. However, it is expensive to adequately insulate the pipelines, and the additional costs can be in the order of $1 million/km3. Thermodynamic inhibitors, such as methanol, can be injected into wellheads to prevent the formation of hydrates. However, large volumetric ratios of water to alcohol, as great as 1:1, are needed in order to adequately prevent the formation of hydrates4. Recently, the global cost to use methanol for hydrate prevention has been reported as $220 million/year. This is not a sustainable amount of alcohol usage5. In addition, the use of methanol is problematic because it is environmentally hazardous, and cannot be used for large-scale transport5. Alternatively, kinetic inhibitors, such as surfactants, can suppress hydrate growth at small quantities and temperatures of up to 20 &#176;C6. Hence, surfactant presence can reduce the large amount of alcohols needed for hydrate prevention.
Surfactants are considered good inhibitors for hydrate crystallization due to two main reasons:
1) They can inhibit hydrate formation through surface property changes; and 2) They initially help the formation of hydrate cells but prevent further growth and agglomeration of the crystal down the pipeline7. Although surfactants have proved to be efficient inhibitors, there is still a large amount of information missing regarding the crystallization process in the presence of surfactants. While some studies have shown that the use of surfactants can extend the initial hydrate crystallization time at certain subcoolings, other studies have found exceptions at low surfactant concentrations. At low surfactant concentrations, the water droplets tend to coalesce and accelerate the process of hydrate formation8. The inhibition process has been explained by surfactant molecules interrupting planar hydrate growth, forcing the hydrate into hollow-conical crystal formation. The conical crystals form a mechanical barrier for crystal growth9, and thus inhibit the growth.
In this study we designed and implemented a low-cost, integrated modular Peltier device (IMPd) along with a hydrate visualization cell and used them to study cyclopentane hydrate formation in the presence of nonionic surfactants. The reason for using cyclopentane instead of low molecular weight gases (e.g., CH4 and CO2) that usually form hydrates in deep sea reservoirs, is that these gases require higher pressures and lower temperatures to form stable hydrates. Because cyclopentane forms hydrates at ambient pressure and temperatures up to ~7.5 &#176;C, it is often used as a model material for hydrate formation10.
The integrated modular Peltier device (IMPd) consists of an open-source microcontroller, Peltier plate, CPU cooler (heat sink), and waterproof digital temperature sensor. The device can deliver a maximum temperature differential of 68 &#176;C. The minimum temperature resolution is 1/16 &#176;C. The entire system, including the electrical circuitry and hardware, can be constructed for less than $200. The temperature sensor reports to the microcontroller, which sends output signals to the transistor. The transistor then passes current from the DC power source through the Peltier element. The heat sink helps cool the Peltier element by convecting the heat coming from the hot side of the Peltier to the ambient air. The assembled hardware components of the IMPd system are shown in Figure 1a,b. Figure 1c shows the wiring schematic with all the components of the control loop (proportional-integral-derivative [PID] controller) and the pin-outs. The output current of the microcontroller was limited with the gate resistor R1 to a maximum current of 23 mA (I = 5 V/220 W). The pull-down resistor R2 in Figure 1c allows the gate charge to dissipate and to turn the system off. To tune the PID controller, Ziegler-Nichols based methods combined with an iterative process are used11. Microcontroller integrated development environment (IDE) software is used to monitor and send commands to the microcontroller for temperature regulation.
Along with the IMPd, we applied a novel approach using visualization techniques and internal pressure measurements. The hydrate visualization cell, which is placed on top of the IMPd, is comprised of a brass cell equipped with two double-paned observation windows. The windows allow video recording of the hydrate formation process on the water droplet in cyclopentane. The complementary metal-oxide semiconductor (CMOS) camera is placed outside the window and the pressure transducer is connected to the water injection line in order to get the internal pressure measurements of the drop. A digital transducer application is used to get the readings from the pressure transducer. A camera viewer is used to capture the videos and images from the CMOS camera. The software controls the exposure and snapshot frequency. Image processing software programs are used to track the growth of the hydrate. Figure 2a shows a schematic description of the hydrate visualization cell and Figure 2b shows an overview of the entire experimental system. The seed hydrate (Figure 2a) is required for consistent nucleation and tracking of the hydrate growth rate. The seed hydrate is a small volume (e.g., 50&#8211;100 &#181;L) of pure water deposited on the floor of the hydrate cell. As the temperature decreases, the drop forms ice, which then turns to hydrate as the temperature increases. The small piece of the seed hydrate then contacts the water droplet. This process controls the initiation of the hydrate in the submerged water droplet. Silica desiccant is inserted into the gap between the two glass slides (Figure 2c), which serve as viewing windows. The silica desiccant helps reduce the amount of frosting and fogging on the windows. Anti-fog is also applied to the outer window to reduce fogging. Images are captured with a CMOS camera and a 28&#8211;90 mm lens. A 150 W fiber optic goose-neck lamp is used for illumination. An acrylic cover is placed on top of the brass cell in order to limit evaporation of cyclopentane. Plumbing consists of a combination of flexible polytetrafluoroethylene (PTFE) tubing and rigid brass tubing. A syringe pump with a 1 mL glass syringe and a 19 G needle control the flow of water and surfactant solution. A pressure transducer monitors the pressure changes inside the water surfactant solution droplet. 19 G PTFE tubing connects the syringe to the T-fitting and 1/16 in. (1.588 mm) brass tubing connects the transducer and brass hook to the T-fitting (Figure 2d). A brass hook, approximately 5 cm in length with a 180&#176; bend, generates the water/surfactant solution droplet. The bend ensures that the droplet generated by the syringe sits on top of the tube throughout the experiment. A 1/16 in. stainless steel T-fitting in conjunction with PTFE crush ferrules and PTFE thread tape seal the fittings.
Using this apparatus, we examined four different nonionic surfactants with different hydrophilic-lipophilic balances (HLB) that are commonly used in the oil industry: sorbitane monolaurate, sorbitane monooleate, PEG-PPG-PEG, and polyoxyethylenesorbitan tristearate.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>1/16 in. Swagelok 316 stainless steel T-fitting</td>
			<td>Swagelok</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>19 gauge PTFE tubing</td>
			<td>Scientific Commodities, Inc.</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>19-gauge needle (model: 1001 LTSN SYR)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1-Wire DS18B20 - waterproof digital temperature sensor</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Anti fog</td>
			<td>RainX</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Arduino Leonardo open-source microcontroller</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Brass tubing 1/16 in.</td>
			<td>K&#38;S Precision Metals</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Chemyx Fusion 100 Infusion Pump</td>
			<td>Chemyx</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>cMOS camera acA640-750um</td>
			<td>Basler</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cyclopentane 98% extra pure</td>
			<td>ACROS organics</td>
			<td>AC111481000</td>
			<td></td>
		</tr>
		<tr>
			<td>Fiber optic goose-neck lamp 150W</td>
			<td>AmScope</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fotodiox macro extension tubes, 35 mm</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Hamilton glass syringe 1 mL</td>
			<td>Hamilton</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ImageJ software</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Kipon EOS to C-mount adapter</td>
			<td>Kipon</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Lens 28-90 mm</td>
			<td>Canon</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Mathematica software</td>
			<td>Mathematica</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>OMEGA PX409-10WGUSBH pressure transducer</td>
			<td>OMEGA</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Peltier plate TEC1-12715</td>
			<td>Amazon</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Pluronic L31 (PEG-PPG-PEG)</td>
			<td>Sigma Aldrich</td>
			<td>9003-11-6</td>
			<td></td>
		</tr>
		<tr>
			<td>Pylon Viewer v5.0.0.6150</td>
			<td>Basler</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Span 20 (Sorbitan laurate, Sorbitan monolaurate)</td>
			<td>Sigma Aldrich</td>
			<td>1338-39-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Span 80 (Sorbitan Monooteate)</td>
			<td>Sigma Aldrich</td>
			<td>1338-43-8</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermaltake NiC C4 120mm CPU cooler</td>
			<td>Thermaltake</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Tween 65 (Polyoxyethylenesorbitan Tristearate)</td>
			<td>Sigma Aldrich</td>
			<td>9005-71-4</td>
			<td></td>
		</tr>
		<tr>
			<td>variable Tooluxe DC power supply</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

studying surfactant effects on hydrate crystallization at oil-water interfaces using a low-cost integrated modular peltier device

We introduce an approach to study the formation and growth of hydrates under the influence of nonionic surfactants. The experimental system includes a temperature regulator, visualization techniques, and inner pressure measurements. The temperature control system contains a low-cost, programmable temperature regulator made with solid-state Peltier components. Along with the temperature control system, we incorporated visualization techniques and internal pressure measurements to study hydrate formation and inhibition in the presence of nonionic surfactants. We studied the hydrate-inhibiting ability of nonionic surfactants (sorbitane monolaurate, sorbitane monooleate, PEG-PPG-PEG, and polyoxyethylenesorbitan tristearate) at low (i.e., 0.1 CMC), medium (i.e., CMC), and high (i.e., 10 CMC) concentrations. Two types of crystals were formed: planar and conical. Planar crystals were formed in plain water and low surfactant concentrations. Conical crystals were formed in high surfactant concentrations. The results of the study show that conical crystals are the most effective in terms of hydrate inhibition. Because conical crystals cannot grow past a certain size, the hydrate growth rate as a conical crystal is slower than the hydrate growth rate as planar crystal. Hence, surfactants that force hydrates to form conical crystals are the most efficient. The goal of the protocol is to provide a detailed description of an experimental system that is capable of investigating the cyclopentane hydrate crystallization process on the surface of a water droplet in the presence of surfactant molecules.

Using this experimental system one can examine the hydrate formation at the oil-water interface and measure the interfacial stress associated with the crystallization process. Figure 6 shows a representative set of results that include both crystal formation and interfacial stress. In the planar shell growth (Figure 6a), the crystal grew from the two poles towards the equator. For that reason, in the planar crystal, the hydrate shell grew consta...

Watch this Scientific Journal Video about Studying Surfactant Effects on Hydrate Crystallization at Oil-Water Interfaces Using a Low-Cost Integrated Modular Peltier Device at JoVE.com

Studying Surfactant Effects on Hydrate Crystallization at Oil-Water Interfaces Using a Low-Cost Integrated Modular Peltier Device

We present a protocol to study the formation of hydrates in the presence of nonionic surfactants on the interface of a water droplet submerged in cyclopentane. The protocol consists of building a low-cost, programmable, temperature regulator. The temperature control system is combined with visualization techniques and internal pressure measurements.

We introduce an approach to study the formation and growth of hydrates under the influence of nonionic surfactants. The experimental system includes a ...

The protocol is applicable in studying the effect of surfactant inhibitors on hydrate crystals. It provides information on both the type of the crystal and the mechanism for inhibition. Attach a 19 gauge needle to a one milliliter glass syringe.Rinse the needle and syringe three times with deionized water and then fill the syringe with deionized water. Next, fill the hydrate visualization cell with 25 milliliters of cyclopentane. Using the syringe, insert a droplet of deionized water at the bottom of the hydrate visualization cell.This water droplet is the seed hydrate. Then, place the temperature sensor inside the hydrate visualization cell close to the bottom of the cell. To prevent evaporation of the cyclopentane, put the acrylic cover on the cell and screw the cover in place.Adjust the lights and the camera to focus on the seed hydrate. Using the temperature control device, set the temperature of the Peltier plate to negative five degrees Celsius. Monitor the values reported from the temperature sensor.When the temperature reaches negative five degrees Celsius, make sure the seed hydrate at the bottom of the hydrate visualization chamber turns to ice. Set the temperature of the Peltier plate to two degrees Celsius in increments of 0.5 degrees Celsius. When the temperature reaches two degrees Celsius, fill the plumbing with water using the syringe.Then, lower the brass hook into the cyclopentane and allow it to equilibrate for five minutes. Using the software for the pressure transducer, press the Start button to start the digital transducer recordings. Connect the syringe to the syringe pump, set the syringe pump to inject a volume of two microliters and activate it.The syringe will plunge the water into the cyclopentane bath to form a submerged water droplet. Use a needle tip to remove a small piece of the seed hydrate. Bring the needle tip with the piece of seed hydrate into brief contact with the water droplet to initiate the formation of the hydrate.Press Start Recording on the camera capture software. Record images of the crystallization process at one Hertz. To find the critical micelle concentration, begin by preparing standard solutions as described in the manuscript.To measure the surface tension of each surfactant solution using the stalagmometry method, program the pump to expel one milliliter of solution at a rate of 0.5 milliliters per minute. Place the syringe pump and syringe vertically and release the drops into the air. Count the number of drops and divide one milliliter by the number of drops to find the drop volume.For each solution, calculate the surface tension as described in the manuscript and plot the surface tension as a function of surfactant concentration. The concentration where the surface tension curve flattens is the CMC, the critical micelle concentration. Repeat the procedure used to measure hydrate formation on a water droplet, but use surfactant solutions of various concentrations.Use image processing software to open the first image in the sequence of the crystallization process. Use the length tool in the software to measure the diameter of the brass tube in the image. Set the scale in the image based on the known diameter of the brass tube, one sixteenth of an inch.Select 10 equally spaced images, which capture the process from nucleation to droplet conversion. For each image, use the software to manually detect the contour of the drop and mark the contour in red. Then, manually trace the contour of the hydrate and fill the contour with black.The camera only captures the 2D projection of the spherical droplet. Use mathematical modeling software to form a 3D reconstruction of the drop and the surface area covered by the hydrate. Using this experimental system, one can examine hydrate formation at the oil water interface and measure the interfacial stress associated with the crystallization process.In pure water and low surfactant concentrations, the hydrate formed a planar shell morphology, growing at a constant rate from the two poles towards the equator. As the hydrate grew, the same number of surfactant molecules occupied a smaller area, resulting in decreased interfacial stress over time. In high surfactant concentrations, the hydrate grew as a conical crystal.When the crystal became large enough, a portion of the cone broke free from the droplet surface. This growth pattern happened over and over again in an oscillatory manner. After the conical crystal reached a critical size and detached from the droplet's surface, the sudden increase in the available surface for surfactant molecules caused an increase in the interfacial stress.A crystal then started growing again, yielding an oscillatory pattern. Most surfactant solutions inhibited hydrate growth compared to pure water. A high concentration of polyoxyethylene sorbitan tristereate was the most effective inhibitor.This system can provide information on why some surfactants inhibit hydrates better than others. The system can also be used to study the general formation of crystals at interfaces.

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6.2K vues.  San José State University. Le protocole est applicable dans l’étude de l’effet des inhibiteurs du surfactant sur les cristaux d’hydrate. Il fournit des informations à la fois sur le type de cristal et le mécanisme d’inhibition. Fixez une aiguille de calibre 19 à une seringue en verre d’un millilitre.Rincer l’aiguille et la seringue trois fois à l’eau déionisée, puis remplir la seringue d’eau déionisée. Ensuite, remplissez la cellule de visualisation des hydrates de 25 millilitres de cycl...