The Studies On Efficient Separation Methods Of Linear/branched Hydrocarbons

Separation of linear/branched compounds is a key technology in the manufacture of basic chemicals and separation and purification of biologically active substances.However,the similarities in molecular structures,size and physical properties for linear/branched hydrocarbons compounds exert great separation challenges.At present,traditional extractive distillation suffers from high energy consumption,high equipment investments and complex process,thus processes with low cost and high efficiency are urgently required for the separation of linear/branched hydrocarbons.Herein,the work focuses on two important separation systems:1)separation and purification of C5 olefins;2)separation of linear/branched hydrocarbons in Fischer-Tropsch synthetic naphtha.Adsorption and complexation methods were respectively employed in the above two separations.The separation mechanism were explored in order to provide better understanding of the separation process of linear/branched hydrocarbons.Firstly,according to the molecular structural differences of C5 olefin isomers(1-pentene,trans-2-pentene and isoprene),series of interpenetrating anionic pillared materials with different inorganic anions and metal ions were choose and synthesized as adsorbents,due to the high density of anions in pore channels and finely tunable pore sizes of anionic pillared materials,including ZU-62(NbOFFIVE-2-Cu-i)and TIFSIX-2-Cu-i.Equilibrium adsorption capacity and separation performance of 1-pentene,trans-2-pentene and isoprene on these two adsorbents were systematically studied and the dynamic breakthrough experiments data proved that TIFSIX-2-Cu-i and ZU-62 could efficiently separate the three C5 olefins.The adsorption isotherm,adsorption capacity and the dynamic breakthrough experiment results proved that TIFSIX-2-Cu-i and ZU-62 can separate there C5 olefins efficiently.The ideal adsorbed solution theory(IAST)selectivities on TIFSIX-2-Cu-i for trans-2-pentene/isoprene,1-pentene/isoprene were 51-115 and 11-26,respectively.And the IAST selectivity on ZU-26 for equimolar 1-pentene/isoprene at low pressure(0?6 kPa)was up to 300,which is significantly higher than the reported value on material[Cu3(BTC)2].In addition,TIFSIX-2-Cu-i also exhibited a high adsorption capacity for linear C5 olefins.The adsorption capacity of trans-2-pentene at 298 K and 45 kPa was as high as 3.1 mmol g-1,which was 1.5 times of 5A molecular sieve.Based on a collaborative strategy of molecular recognition and molecule sieving,an efficient separation of linear/branched C5 olefins was achieved and the adsorbents were found to perform much better than 5A molecular sieve.The interactions between the adsorbates(1-pentene,trans-2-pentene,and isoprene)with TIFSIX-2-Cu-i were revealed by using density functional theory(DFT-D).Besides,dynamic breakthrough experiment indicated unexpectedly that TIFSIX-2-Cu-i and ZU-62 could identify ? olefins and ?olefins,and the materials could be regenerated easily by purging with inert gas at normal temperature.Secondly,complexation method was carried out to explore the separation of normal hydrocarbons from refined Fischer-Tropsch synthetic naphtha(C4-C12)and cutting Fischer-Tropsch synthetic naphtha(C8-C12),respectively.These complex mixtures have wide carbon number distributions(C4-C12)and majorities of the composition were normal hydrocarbons.Urea and thiourea can form hexagonal spiral crystal channel structures with different sizes and include hydrocarbons.With urea and thiourea as complexing agents and ethanol as activator,complexation separations were optimized through orthogonal experiments by using model oils and the influencing factors and optimal complexing conditions were explored.The results showed that n-paraffin content of model oil increased from the original 80%to 95.6%by using the optimized urea inclusion conditioner.Under this condition,the n-paraffin content of refined Fischer-Tropsch synthetic naphtha increase from 94%to 99.3%and the n-paraffin content of cutting Fischer-Tropsch synthetic naphtha increased from 87%to 96%(excluding the effects of oxygenated compounds).By using thiourea inclusion,the n-paraffin content of model oil increased from 80%to 93.7%under optimized condition.The study showed that physical inclusion methods can efficiently separate normal/branched hydrocarbons in coal-based Fischer-Tropsch synthetic naphtha.