INFLUENCE OF SURFACTANTS ON THE FORMATION AND DISSOCIATION OF GAS HYDRATES IN FIXED BED MEDIA

Abstract

Rapid growth in energy demand with depleting energy resources, along with anthropological discharge of CO2 in environment has lead to search for unconventional energy resources like Natural Gas Hydrates (NGH), of which Methane Hydrates are the most commonly encountered Hydrates [Demirbas, 2010] found Naturally in abundance. The worldwide organic carbon in the Gas Hydrates is estimated to be roughly about 10000 X 1015 grams which is almost double the carbon content in total fossil fuel reserves of the world [Satoh et al, 1996, Collett, 2002]. Methane Gas Hydrates is source of Methane Gas found as crystalline ice like structure in permafrost regions and under the sea in outer continental margins. Gas Hydrates belong to a class of inclusion compounds that are commonly known as clathrates. Gas Hydrates are solid nonstoichiometric crystalline compound having cage like structure comprising of water as host and Gas as a guest molecule formed at high pressure and low temperature [Sloan, 1998]. Gas Hydrates have tremendous application potential in the fields of energy and the environment [Koh et al, 2011] like Methane and Natural Gas storage as well as transportation in the form of synthetic Gas Hydrate [Gudmundsson et al, 2006, Kim et al, 2010], Hydrate based carbon dioxide capture, Hydrate based Gas separation [Babu et al, 2014]. Successful commercialization of NGH would require efficient and safe technology for their generation, Dissociation, storage and transportation; extensive research programmes are being conducted to find less energy intensive, economic, clean and green technology for the promotion of Gas Hydrates Formation. Although synthetic surfactant promote Hydrate Formation but at the same time their limited biodegradability and toxicity hinders them from adopting their use as Hydrates promoters. The microbes like Bacillus subtilis and Members of gammaproteobacteria are identified in Gulf of Mexico Gas Hydrate mounds [Lanoil et al, 2001] and are found to produce Surfactin and Rhamnolipids biosurfactants respectively which influence the induction time and rate of Formation of Gas Hydrates (GH). It is anticipated that secondary metabolites from ii gammaproteobacteria like Pseudomonas aeruginosa may have beneficial effect on Gas Hydrate Formation. Despite plethora of efforts to develop Hydrate-based technology, none has been established effectively for practical application. Hydrate based CO2 capture and separation process can be commercialized by increasing the Hydrate Formation rate and reducing the operating pressure conditions. Hydrate Formation in quiescent condition is very slow; a thin film of Hydrate is formed on the water surface which stops effective migration of Gas further into the system resulting in slower kinetics of Hydrate Formation. In this context, higher solubility of Gas in water and larger contact area between host molecule i.e. water and guest molecules i.e. Gases are very vital so as to enhance the Hydrate Formation rate [Linga et al, 2012, Kumar et al, 2013, Kang et al, 2010]. Synthetic surfactants as a chemical additive has been useful in enhancing Hydrate Formation rate by increasing Gas solubility, supporting micelle Formation and providing the nucleation sites for Hydrate Formation [Saw et al, 2014]. Use of synthetic surfactant such as sodium dodeccyl sulphate (SDS), sodium tetradecyl sulphate (STS), sodium hexadecyl sulphate (SHS) has shown good results and enhance the Hydrate growth considerably. However its use in Natural environment for enhancing NGH generation may be detrimental for the living organisms [Michael et al, 1991, Banat et al, 2014]. Desire to have environmentally compatible surfactants has propelled search for a substitutes from biological origin which are considered better than their synthetic counterparts for their lower toxicity, environment-friendly nature and stability under extreme conditions like high temperature, pH, and high salinity [Banat et al, 2014]. Very few studies pertaining to influence of biosurfactants on NGH Formation has restricted our knowledge and thus, limiting the potential application of biosurfactants in Gas Hydrate generation, storage and transportation [Rogers et al, 2003, Rogers et al, 2003, Woods, 2004]. Moreover, the studies have largely concentrated on kinetics and related parameters [Rogers et al, 2003, Carvajal et al, 2013, Woods, 2004]. Influence of microbial surfactant like Rhamnolipids and surfactin on thermodynamics of Gas Hydrates Formation has not been reported in literature. Thus, limiting the potential application of biosurfactants in Gas Hydrates generation, storage and transportation. As discussed above, Hydrate promoters has proven application in Gas Hydrate based technological processes. Similarly, design and application of Gas Hydrate inhibitors is also very iii important. Unlike Hydrate promoters, inhibitors are required to reduce the possibility of Hydrate nucleation and growth. Gas Hydrate Formation has been considered as a nuisance in oil and Gas industries because of plugging problem of Gas pipelines and these industries are very concerned about this problem as Hydrates can destroy the whole pipeline and can be a danger for human life. Formation of gas hydrates leads to the blocking of pipe lines actually hydrate propagation gradually forms a plug which separates the pipe into two pressure zones: a pressure zone between the well and the plug and the second section at low pressure between the plug and recovery division. In the upstream section a pipe blast can take place due to pressure rise. The plug behaves like a projectile which destroys the pipe when the pressure difference between the upstream and downstream section increases. Both these events can destroy the whole pipeline. Traditionally this problem has been sorted out by using thermodynamic Hydrate inhibitors (methanol, glycol etc.) which change the phase equilibria of Hydrate Formation, however, they are not considered environment friendly. To address this problem few polymeric compounds like Polyvinylpyrrolidone (PVP), Polyvinylcaprolactam (PVCAP), Polyethylene oxide (PEO) etc. have been explored as kinetic Hydrate inhibitors (KHI) [Kelland, 2006, Freer et al, 2000]. These chemicals do not prevent Hydrate Formation but they delay Hydrate Formation in pipelines as they pass through the Hydrate sensitive zone. Although these compounds are successful at very low concentrations but because of their limited biodegradability they are not certified for use in all regions (for example the North Sea).Recently Anti Freeze Proteins (AFP) has been utilized to inhibit Gas Hydrates Formation in laboratory scale experimentation. However, extracting AFP in large scale is commercially not viable and thus there is a strong motivation for inventing economic green biodegradable inhibitor. During the course of this thesis we have tried lignin an abundant biomass as inhibitor which is economic and has never been reported as a Gas Hydrate inhibitor. Lignocelluloses are attractive materials due to their renewability and availability i.e. 1.8 trillion tons of annual production [McKendry, 2002]. The energy intensive mechanical agitation processes used for Gas Hydrate Formation needs to be replaced by less energy intensive process using fixed bed media. So the current study explores the use of its bed media FDM for the hydrate based CO2 Capture which can lead to replace the energy intensive processes like agitation used for the hydrate formation. In this thesis, the performance of SDS for carbon dioxide GH Formation in two different fixed bed media: Silica iv sand and zeolites (5A and 13X) was evaluated as a base line case. The concentration of SDS was always fixed at 0.5 wt% of water used in the experiment Experiments were carried out in batch mode with the initial pressure fixed at 3.0 MPa, and the temperature was kept constant at 274.65 K. The experiments were conducted at 3.0 MPa at 274.65 K because this pressure leads to the formation of carbon dioxide gas hydrate at this temperature as this much pressure is sufficient to give the required driving force. It was found that the effect of SDS is media dependant. In the case of Silica sand, SDS greatly impacted the Hydrate Formation kinetics whereas it did not have such a marked effect in the case of zeolites. Presence of SDS in the system was found to lower the induction time. Again to understand the base case kinetics, various porous media were evaluated in a fixed bed reactor (FBR) and also compared to stirred tank reactor (STR). Carbon dioxide Hydrate Formation experiments were carried out at a pressure 3.0 MPa and constant temperature of 274.5K. Silica sand, Silica Gel (100 nm and 5 nm pore size) and a blend of Silica Gel (5nm) with zeolite 5A were used as a porous media in FBR. The results have shown that the kinetics of Hydrate Formation and conversion of water to Hydrate in a FBR system is significantly greater than that in a STR system. Among all the different porous media studied, 100 nm pore size Silica Gel was found to be a good candidate to enhance Hydrate Formation kinetics. There was a significant increase in the rate of Hydrate Formation in the case of FBR whereas STR was found to be not a suitable approach for scaling up the Hydrate based Gas capture and separation processes because the power required for mechanical agitation is very significant and it is also plagued by other limitations such as the low Gas uptake and low water to Hydrate conversions. Further with Silica Gel and zeolite as packing media effect of porosity on CO2 Gas Hydrate Formation kinetics was studied. Silica Gel of mesh size 230-400 and certain percentage of zeolite as a solid additive have been used as a medium of Hydrate Formation from distributed water in its pores. Zeolite 3A (beads) and zeolite 5A (beads) were used with different water saturation amount. Above study revealed that zeolite certainly performs well as Silica Gel and enhances the Hydrate Formation rate and conversion. Biosurfactant synthesized from strain A11 was found to be Rhamnolipids after characterizing with techniques such as Thin layer chromatography (TLC), Fourier transform infrared spectroscopy (FTIR), Nuclear magnetic resonance (NMR), Liquid Chromatography-Mass v Spectrometry (LC-MS), Matrix-assisted laser desorption/ionization (MALDI). Purified Rhamnolipids produced by strain A11 can reduce the surface tension of water from 72 mN/m to 36 mN/m with critical micelles concentration CMC of 70 mg/L. Rhamnolipids produced by strain A11 has dirhamnolipids (RhaRhaC10C10) as most dominant congener. Apart from RhaRhaC10C10 olefinic Rhamnolipids RhaC22, RhlRhaC10C10/ RhlRhaC10C12, RhaRhaC10C10 / RhaRhaC10C12 were also produced by strain A11. Biosurfactant synthesized from strain A21 was found to be Surfactin after characterizing with techniques such as TLC, FTIR, High Performance Liquid Chromatography (HPLC), MALDI, NMR, Amino Acids Sequence (AAS) . Purified Surfactin produced by strain A21 can reduce the surface tension of water from72 mN/m to 29 mN/m with CMC of 33 mg/L. The purpose of this set of experiments was to explore the feasibility of using glycolipids (Rhamnolipids) type biosurfactant as Methane Hydrate generation promoter. Rhamnolipids (glycolipids) type biosurfactant was produced by rhizobacteria, Pseudomonas aeruginosa strain A11. Study compares Methane Hydrate Formation in the quiescent water and fixed bed system of water saturated C type Silica Gel in the presence of different concentration of biosurfactants. The thermodynamics and kinetics of Gas Hydrate Formation were studied to gain a better understanding of the process. Using Rhamnolipids solution in C type Silica Gel increased the rate of Methane Hydrate Formation as compared to other systems, increased in the number of moles of Methane consumed in Hydrate Formation and reduction in induction time. Presence of Rhamnolipids also shifted Methane Hydrate Formation temperature to higher values relative to the system without biosurfactant. The Dissociation behaviour of Methane Hydrate using thermal stimulation technique was also studied. The enthalpies of Dissociation were also calculated. Results from thermodynamic and kinetic studies suggest that Rhamnolipids can be applied as environment-friendly Methane Hydrate promoter. The goal of this set of experiments was to understand the thermodynamics and kinetics of Methane Hydrate Formation in quiescent water system and fixed bed system of porous media i.e C type Silica Gel amended with different concentration of cyclic biosurfactant i.e Surfactin (lipopeptide). Biosurfactants was produced by rhizospheric bacteria Bacillus Subtilis strain A21. Saturating Silica Gel surfactin solution increased the rate of Methane Hydrate Formation when compared to other systems. Addition of surfactin solution also increased the number of moles of Methane consumed in Hydrate Formation, Methane Hydrate Formation rate, increased vi percentage conversion and reduced the induction time significantly. Surfactin also shifted Methane Hydrate Formation temperature to higher values relative to the system without biosurfactant. The Dissociation behaviour of Methane Hydrate using thermal stimulation technique was also studied. Results from thermodynamic and kinetic studies suggest that surfactin can act as environment-friendly additive for Methane Hydrate promoter. In this study, we have investigated experimentally a bio-surfactant i.e. Calcium lignosulphonate (CaLS) generated from waste of pulp and paper for inhibiting the nucleation or growth of Methane and Natural Gas Hydrate Formation. Calcium lignosulphonate was characterized by FTIR, Ultraviolet – Visible Spectrometry (UV-VIS), Carbon Hydrogen Nitrogen Sulphur Analysis (CHNS), Gel Permeation Chromatography (GPC), Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-ray Spectroscopy (EDS), FE-SEM Mixing, Inductively Coupled Plasma Mass Spectroscopy (ICPMS), Thermo gravimetric analysis (TGA) and Solid NMR and was found to be the same. All techniques have given signatures of various elements present in calcium lignosulphonate and the molecular weight determined from Gel permeation chromatography has confirmed its polymeric nature. Different dosage (0.1, 1 and 5 wt %) of bio-surfactant is used in Hydrate Formation in presence of Methane and Natural Gas Hydrate decomposition behaviour of Methane Hydrates was also investigated in the presence of inhibitor. The induction time was delayed to 11.2 hours in presence of 1 wt% CaLS from 44 minutes when it is not present .Hence, there is a major shift in the induction time of Gas Hydrates. The outcome of the thesis is that an economic and less energy intensive fixed bed media of Silica Gel (100 nm) was found to be more efficient amongst fixed bed of Silica sand, Silica Gel (5 nm), blend of Silica Gel (5nm) and zeolites and stirred tank rectors for Hydrate based carbon dioxide capture. Fixed bed media are capable of replacing the expensive and energy intensive method of mechanical agitation used for Gas Hydrate. Rhamnolipids and surfactin were found to be dual promoters i.e kinetic as well as thermodynamic promoter for Methane Hydrate Formation. These Biosurfactants are capable of replacing their counter parts i.e synthetic surfactants which are toxic, non-environment-friendly and non-biodegradable. Hence these biosurfactants can help in designing a green, clean, biodegradable and environment-friendly technology for promoting the Formation of Natural Gas Hydrates. Methane Gas Hydrates are vii fuels of the future generation provided an economical viable technology is developed. Thermal stimulation technique is found to be very effective for Dissociation of Methane Hydrates. The small dosage of Rhamnolipids produced by Pseudomonas aeruginosa Strain A11 and Surfactin produced by Bacillus subtilis Strain A21 must clear the role of these biosurfactants as promoter in Natural Gas Hydrate sites (as in Gulf of Mexico). Calcium LignoSulphonate (CaLS) is found to be an economic, low dose, green and biodegradable kinetic inhibitor for Methane as well as Natural Gas Hydrates which can replace their very expansive low dose antifreeze proteins (AFP) used currently by industry for inhibition of Natural Gas Hydrates. Overall, this study has shown the significance of Biosurfactants i.e. Rhamnolipids and Surfactin on Methane Hydrate Formation. In addition, the production and characterization protocol of biosurfactants were discussed. The role of microbes at Natural Gas Hydrate sites, the insight of using Biosurfactants as Hydrate promotes so that Hydrate based technologies can use biodegradable and environment-friendly promoters and an economic green biosurfactant inhibitor were also discussed. As the future lies in Hydrate based CO2 Capture, Hydrate based Natural Gas transportation and storage and designing an economical viable technology like CO2 sequestration to exploit this vast source of energy. So in the current study the fixed bed media (FBM) approach was found to be more effective, economic and efficient for Hydrate based CO2 capture. The present study reports the significance of microorganisms and their metabolites. Biosurfactant are produced in the ocean floor which catalyze the Gas Hydrates Formation, so, the above thesis has lighten the Formation of Gas Hydrates in marine conditions and given the better understanding of the Formation of Natural Gas Hydrates in ocean floor.