Kinetic Investigation Of Tetra-n-butylammonium Bromide Hydrate Formation In Confined Space

Tetra-n-butylammonium bromide(TBAB)is a semiclathrate which combined with water molecules.Much emphasis has been put on the applications of TBAB hydrate.Most of studies of nucleation and growth of TBAB hydrate are conducted in bulk system.However,in many cases,a large portion of accumulation processes of hydrate occur within pores,in which the space for hydrate growth is confined.The mechanism of hydrate growth in confined space is unclear.Thus,a confined space is used to investigate growth kinetic of TBAB hydrate and its influencing factors in this paper.A self-made transparent perfluoroalkoxy ethylene(PFA)tube was employed as confined space,where TBAB hydrate nucleate and grow.A microscopic imaging system was utilized to study the influencing facors affact morphology and face growth rate of TBAB hydrate on a micro level,which including solution concentration,temperature,additive content and growth space.TBAB hydrate was tested and identified by Raman spectroscopic.Growth mechanism was studied based on the experiments and a kinetic model was proposed to describe formation process and its influencing factors.The results show that heat and mass transfer process on growth rate of TBAB hydrate is vanished in PFA tube,making it more convenient to study growth kinetic.Solution concentration and temperature affect morphology of TBAB hydrate.In the range of experimental concentration of solution,type B hydrate was formed when TBAB hydrate generated at lower concentration solution(5~15wt%).Small crystal,long nucleation time and slower face growth rate are obtained.Morphologies of TBAB hydrate are conductive to mass and heat transfer.Type A hydrate was formed when TBAB hydrate generated at higher concentration solution(30~40wt%).It is showed that compact crystal,short nucleation time and faster face growth rate.Morphology varied within different content of sodium dodecyl sulfate(SDS).Hydrate mainly concentrated at the interface,and the hydrate growth rate slowed down when the content of SDS increased.Results show that the growth rate in large dimensional space is less than that of in small dimensional tube.Growth mechanism of TBAB hydrate was explored in this paper,a growth kinetic model of TBAB hydrate was established,negative activation energy(Ea=-58.26kJ/mol)of TBAB hydrate is obtained.It is assumed that there are incomplete cages of hydrate in metastable state,which is stable than TBAB solution.Order of reaction of TBAB hydrate in confined space is also obtained.