Study On Adsorption Kinetics Of Organic Compounds Based On Terahertz Time Domain Spectroscopy

Adsorption,desorption and diffusion of oil-gas molecules in micro-nano scale pores play an important role in the formation of unconventional oil and gas reservoir.Therefore,adsorption behavior and mechanism of oil-gas in micro-nano scale are a necessary precondition to make sure efficient exploitation of oil and gas,and is of great significance to improve the efficiency of unconventional oil and gas exploitation.In this paper,the adsorption kinetics of organic compounds are studied based on terahertz technology.The main results are as the following:1.The dynamics of butyl acetate,ethanol,and isooctane adsorbed into active carbon pores is tracked,and a mathematical model is built in terms of the adsorbed rate parameter and the terahertz parameter.Adsorption rates increase in the order of butyl acetate < ethanol < isooctane,which indicates adsorption rates can be quantitatively characterized by terahertz spectroscopy.Hydrophobic interaction was the predominant driving force compared with hydrogen bonding in adsorption,and activated carbon had a greater affinity for hydrocarbons.On the other hand,the molecules with bigger size required more time to scatter into inner holes and be adsorbed,therefore,the adsorption rate of ethanol was higher than that of butyl acetate whose molecules were larger and it was isooctane that had the largest adsorption rate.2.In order to describe the mass transfer process of organics in the adsorption process,a terahertz double-exponential model is established to describe membrane diffusion,particle diffusion,adsorption and desorption.The terahertz double-exponential model describes the two-step mechanism controlled by diffusion.A rapid step involves external and internal diffusion,followed by a slow step controlled by intraparticle diffusion.Therefore,the organics adsorption is a diffusion controlled mechanism.3.The adsorption of four substances and their binary mixture is investigated via the terahertz time domain spectroscopy.The selected unary compound(ethanol,acetone,ethyl acetate,and n-propyl acetate)and binary mixture(solution 1 is composed of ethanol and acetone,and solution 2 is composed of ethyl acetate and n-propyl acetate)exhibit different adsorption behaviors with varied polarities.In comparison with single component,solution 1 shows shorter adsorption equilibrium time,faster adsorption rate,and stronger adsorption capacity,which conform to a synergistic adsorption mechanism,while the competitive behavior is attributed to the slower adsorption in solution 2.In addition,the pseudo-second-order equation with terahertz parameter is used to assess the rate of binary component organics.