Abstract
Storage of greenhouse gases in the form of gas hydrates is attractive and is being pursued rigorously in recent times. However, slow formation rate and inefficient water to hydrate conversion are the main hindering factors. In this report, we examine the role of two amino acids (0.5 wt%), l-methionine (l-met) and l-phenylalanine (l-phe) on the formation of gas hydrates using methane (CH4), carbon dioxide (CO2) and their mixtures as guest molecules. Experiments are conducted under non-stirred and isochoric configurations. The hydrate conversion efficiency of both amino acids is identical for hydrates formed with CH4 and mixture of (CO2+CH4). However, the hydrate conversion is significantly less in CO2 hydrates in l-phe system. Addition of amino acids to the water dramatically improved the kinetics of hydrate formation and 90% of maximum gas uptake in hydrate phase occurred in less than an hour. The water to hydrate conversion is also very efficient (>85%) in the presence of amino acids. Therefore, the amino acids containing systems are suitable for storing both CH4 and CO2 gases. The gas hydrates were characterised using powder x-ray diffraction (XRD) and Raman spectroscopic measurements. These measurements indicate the formation of sI hydrates and encasing of gas molecules as guests.
Highlights
The research on gas hydrates initially started purely as a scientific curiosity, but subsequently, it was identified as one of the leading cause for blockages in petroleum/gas carrying pipeline network
The need for inhibitors originates in preventing the hydrate growth, for some well-known applications such as gas storage and transportation one should think of promoting the hydrates
We examined hydrate formation in CO2 – H2O system, under similar experimental conditions, using some amino acids such as l-methionine, l-cystine and l-valine and found that the gas storage is high, whereas, it is less for l-phenylalanine and l-theornine containing systems[23]
Summary
The research on gas hydrates initially started purely as a scientific curiosity, but subsequently, it was identified as one of the leading cause for blockages in petroleum/gas carrying pipeline network. Bavoh et al.[21] have examined the effect of valine and arginine (1 to 5 wt%) on methane hydrates They found a slightly lower hydrate dissociation temperature (0.5 K) in the presence amino acids, but with enhanced gas uptake rate. Liu et al.[24], found that the leucines, under lower concentrations (0.1 to 1 wt%), are effective promoters for methane gas in hydrated form with a high formation rate and a high capacity. These authors have reported that l-methionine, l-tryptophan, l-phenylalanine, l-arginine, l-glutamic acid and l-histidine can promote the formation process of methane hydrate, to some lesser extent. Structural stability of hydrates, in the metastable region is examined for plausible gas storage and transportation applications
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