Experimental Study On The Synthesis Of Natural Gas Hydrate Suitable For Ship Transportation

Natural gas is the cleanest fossil fuel,mainly containing methane and a small amount of high hydrocarbons.It currently accounts for about 24%of global energy demand.Natural gas can be stored and transported in gas,liquid or solid state.Natural gas hydrate is stored and transported natural gas in solid way.As the main channel of energy transportation in the world,there is no precedent of using natural gas hydrate for natural gas storage and transportation.Therefore,combining with the existing research basis,it is great significance to study a fast synthesis method of natural gas hydrate suitable for ship transportation.At present,the main reason restricts the development of natural gas hydrate technology is because the synthesis process of hydrate is a very complex process of mass transfer and heat transfer which involves three-phase or even four-phase equilibrium.The existing synthesis method is too slow and there is no rule to induce nucleation,and the randomness is too high.In this paper,the research results of predecessors at home and abroad are summarized,and the formation mechanism of natural gas hydrate is studied.It is found that structure H natural gas hydrate is easy to be synthesized,with large gas storage per unit volume,and is suitable for shipping as the carrier of natural gas hydrate.Then,the author systematically analyzes the energy barrier,critical size,driving force and nucleation rate of hydrate nucleation,studies and analyzes the thermodynamic and dynamic model of structure H hydrate,designs the basic conditions of experiment according to the hydrate formation mechanism,designs and builds a set of natural gas hydrate synthesis experimental platform,and carries out a series of structure H natural gas hydrate Experimental study.In the experiment of the influence of different LGMSs(Large Guest molecule matters)on the synthesis of structure H natural gas hydrate,the following conclusions are drawn.To improve the reaction efficiency:Cycloheptane>Cycloheptanone>MTBE>Methylcyclohexane>Methylcyclopentane.Promotion effect of gas storage:Cycloheptanone>Cycloheptane>MTBE>Methylcyclohexane>Methylcyclopentane.Compared with the experimental data,the kinetic model selected in this paper can predict the reaction time trend of structure H hydrate.Therefore,if we only consider the synthesis speed in the experiment,we should give priority.to the Cycloheptane and Cycloheptanone.However,they are expensive and not suitable for large-scale development and application.In large-scale synthesis,MTBE and Mhylcylohexane with low price and good effect can be selected as LGMSs.It was found in the experiment that different surfactants influence the synthesis of SH type natural gas hydrate.Improving the reaction efficiency by shortening the induction time and accelerating the reaction speed of SH type natural gas hydrate:SDS>Rhamnolipid>Tween 80.Promotion effect of gas storage:SDS>Tween 80>Rhamnolipid.SDS is the best one among the three surfactants.As a biosurfactant,rhamnolipid is used in the synthesis of SH hydrate for the first time in this paper and it has good environmental friendliness.At the same time,the improvement of reaction efficiency is only weaker than SDS and much higher than Tween 80.Therefore,rhamnolipid can be selected preferentially in consideration of environmental protection.Combined with the above results,it can be seen that the size of the molecule itself has a great influence on the hydration reaction of SH-type hydrate,and the macromolecular substance with small molecule is more likely to have hydration reaction;its own functional group properties and solubility in water will also affect the reaction,and the functional group has high hydrophilicity,and the reaction is easy to occur.The surface tension of macroguest molecules is also an important factor to promote hydrate formation.The lower the surface tension,the easier hydrate formation.In the selection of surfactant,the influence of surfactant on the surface tension is an important standard to measure the promotion effect of surfactant.At the same time,whether the use conditions of surfactant meet the conditions of hydrate synthesis should also be considered.In this paper,methyl cyclohexane and MTBE are more suitable for the synthesis of natural gas hydrate for ship transportation.Under the conditions of 275.15k,5.0mpa temperature,pressure and 500r/min stirring driving,adding 0.25%surfactant SDS or rhamnolipid can quickly synthesize structure H natural gas hydrate.This provides practical and reliable experimental data and theoretical support for the industrial synthesis and commercial application of natural gas hydrate to solve the problems of long induction time and imperfect preparation process in the research of SH type natural gas hydrate synthesis technology.