Adsorption-based Separation Of Butene Isomers With Mg-CUK-1

Butene isomers,including 1,3-butadiene(1,3-C4H6),n-butene(n-C4Hs),and iso-butene(iso-C4H8)etc.,are basic organic raw materials for the production of a variety of chemicals,such as synthetic rubbers,methyl tert-butyl ether(MTBE),sec-butanol,and methyl ethyl ketone.The separation of the butene isomers is also of great interest for the petrochemical industry.However,these butene isomers have very similar physical properties and molecular structures.Similar boiling points of the butene isomers make their separation with a high selectivity very difficult.Currently,the industrial separation of the butene isomers is carried out by extractive distillation with organic solvent,which is an energy-consuming and environmentally unfriendly process and thus a new separation technology should be developed.Adsorption-based separation using porous materials is a promising energy-saving technology for the butene isomers.Mg-CUK-1 is a new Mg?-based porous coordination polymer with one-dimensional pore structure possessing a pore size of about 1.38 nm.Mg-CUK-1 has a good hydrolytic stability under humidity.This thesis focuses on the investigation of the adsorption and separation of the butene isomers using Mg-CUK-1,and the main results are summarized as follows:1.Via a hydrothermal method,Mg-CUK-1 was prepared in an oven at 473 K for 15 h using Mg(NO3)2·6H2O as raw material,2,4-pyridinedicarboxylic acid(C7H5NO4)as organic ligand,and KOH solution as solvent.After the synthesized sample was treated with momentary ultrasonic circulation for several times and then washed with ethanol,the BET surface area,framework density,and pore volume of Mg-CUK-1 were 570 m2.g-1,1,142 kg.m-3,and 0.626 cm3.g-1,respectively,with an average crystal size of 30-40 ?m.2.A volumetric method was used to measure the single-component gas isotherms of the butene isomers on Mg-CUK-1 at 298,310,and 323 K.At 298 K and a total pressure of 100 kPa,the adsorbed amount of the butene isomers has a order of cis-2-butene>1,3-butadiene>n-butene>trans-2-butene>iso-butene,indicating that Mg-CUK-1 has different adsorption affinities to the butene isomers and thus would have a selective separation for butene isomer mixtures.Then,a Dual-site Langmuir model was employed to fit the measured adsorption isotherms,and the results show that the model can approciately describe the single-component isotherms of the butene isomers.Furthermore,the IAST was employed to predict the adsorption.selectivities of n-C4Hs/iso-C4H8 and cis-2-C4H8/trans-2-C4H8 mixtures,and the corresponding discussion was conducted.3.A combination of a quantum chemical method and classical molecular simulations was employed to study the differences in adsorption between the butane isomers on Mg-CUK-1.The dispersion corrected density functinoal theory method,DFT-D2,was used to calculate the binding energy of each butene isomer adsorbed in the pores of Mg-CUK-1.Furthermore,GCMC simulations were performed to simulate the adsorption isotherms of each component at 298,310,and 323 K.The results show that there is a strong van der Waals force between adsorbent and adsorbate,and the adsorbate-adsorbate interactions with different degrees for different butene isomers also enhance the adsorption strength of the adsorbate molecule in Mg-CUK-1.These lead to the differences in adsorption between the butene isomers,providing a theoretic base for the adsorption-based separation of the butene isomers.