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

Summary

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.

Abstract

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.

Introduction

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's effort to prevent hydrate plug agglomeration and the subsequ....

Protocol

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.

1. Attach a 19 G needle to the 1 mL glass syringe (Figure 2b, C).
2. Rinse the 1 mL glass syringe and 19 G needle 3x with DI water.
3. Fill the syringe with DI water.
4. Fill the hydrate visualization cell (Figure 2b, E) with 25 mL of cyclopentane.
5. Using the sy....

Results

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.......

Discussion

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 .......

Materials

List of materials used in this article

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