Research On The Preparation And Actelyene Separation Properties Of Stable Metal-Organic Framework

Ethylene（C₂H₄）and acetylene（C₂H₂）are important petrochemical raw materials,which are widely used to produce polyethylene,vinyl chloride,acetic acid and other chemical products.High purity of raw materials is usually required in practical application.The production of polyethylene requires more than 99.95%of high-purity ethylene and the purity of acetylene should be more than 99.7%.A small amount of C₂H₂ impurities will be produced in the production of C₂H₄ by traditional cracking process.The production of C₂H₂ by partial combustion of methane and oxygen is often accompanied by CO₂ by-products.Therefore,how to remove trace amounts of acetylene from ethylene or separate high-purity acetylene from carbon dioxide are the crucial to realize efficient utilization.However,it faces daunting challenge to efficiently separate C₂H₂ from C₂H₄ and CO₂ because of their similar physicochemical properties.Although catalytic hydrogenation and cryogenic rectification to separate such light hydrocarbons are currently very mature process operations in the petrochemical industry,they require huge initial investment and separation energy consumption.Pressure swing adsorption（PSA）technology has been gradually attracted the attention of a large number of scientists due of its advantages of low energy consumption,simple process and low investment,which is expected to create more efficient gas separation and purification technology.The key of this technology is the choice of high-efficiency adsorbent.Metal-organic frameworks（MOF）have been regarded as a new type of hybrid crystalline porous adsorbent with excellent performance due to its diverse composition,adjustable pore structure and functional pore surface.In recent years,many MOF materials have been reported for the separation of C₂H₂/CO₂ and C₂H₂/C₂H₄,but it is difficult to achieve the efficient separation of two-component mixtures using the same material.In the actual production process,the feed gas is usually accompanied by multiple gas components,so it is a huge challenge to recover C₂H₂ from refinery gas with multiple mixed components.In addition,in order to be used as an alternative material for simultaneous separation of C₂H₂/C₂H₄ and C₂H₂/CO₂ in practical industry,it is required to have the characteristics of simple and rapid prepared with high structural stability and easy regeneration.Therefore,this research aims to prepare a MOF material that is easy to scale synthesis and has high stability,and good separation performance of C₂H₂/C₂H₄,C₂H₂/CO₂ and multicomponent mixture based on the structural design.In this paper,a series of research about two kinds of metal organic frameworks were carried out from three aspects of material preparation,performance control and applicability.The main research contents and conclusions are as follows:（1）Ni₂（btec）（bipy）₃（btec:1,2,4,5-Benzenetetracarboxy L;bipy:4,4-Bipyridine）was prepared at room temperature through the improvement of the synthesis method,which improved the synthesis rate and yield.The separation performance of Ni₂（btec）（bipy）₃ for two mixtures were studied.It was confirmed that Ni₂（btec）（bipy）₃ could efficiently adsorb and separate C₂H₂ from C₂H₂/C₂H₄ or C₂H₂/CO₂ mixture by breakthrough experiment.At the same time,high purity C₂H₄（>99.999%）and CO₂（>99.99%）can be obtained in one separation cycle.The cycle breakthrough experiment proved that Ni₂（btec）（bipy）₃ has good regeneration.The specific recognition sites and adsorption mechanism of acetylene were determined by Grand Canonical Monte Carlo simulation calculation（GCMC）.In addition,the X-ray powder diffraction（XRD）characterization confirmed the good air stability and solvent stability of the material,indicating that it has potential application value in practical industry.（2）For the two-dimensional MOF material Zn₂（btec）（bipy）with interlayer cavities,we explored its synthesis conditions,adsorption and separation performance for C₂H₂/C₂H₄,C₂H₂/CO₂ and multi-component mixtures,and the stability of this material was investigated.Through the optimization of the reaction conditions,Zn₂（btec）（bipy）can be directly synthesized on a large scale with water as solvent at room temperature,and the product of more than hundred grams can be obtained in one reaction.Secondly,Zn₂（btec）（bipy）has ideal pore size and hydrogen bonding sites,which can achieve C₂H₂ molecular sieving and has high selectivity for C₂H₂/C₂H₄ and C₂H₂/CO₂.Through the breakthrough separation experiment,it is proved that C₂H₄（99.999%）of polymerization grade can be directly obtained,and high-purity C₂H₂（>98%）can be recovered（>92%recovery rate）in the regeneration process.In addition,Zn₂（btec）（bipy）has an efficient C₂H₂ separation ability in the simulated steam cracking mixture C₂H₂ capture experiment,and high purity C₂H₂（>98%）can be obtained during the regeneration process.Most importantly,the characterization results of XRD,thermogravimetric analysis（TGA）and gas isotherm adsorption tests showed that Zn₂（btec）（bipy）has good water stability,chemical stability,thermal stability and cycle stability,and can be obtained high-purity C₂H₂ and C₂H₄by breakthrough separation experiment,highlighting the prospect of this material for industrial C₂H₂ separation.