Preparation Of PEBA2533/NaY Hybrid Membranes And The Study Of Their Seperation Performance Of Ethylene/propylene Mixture

Ethylene and propylene are important raw materials for the chemical industry, traditional olefin production process uses naphtha as the raw material. In our country, the reserve of oil resource is low, while the coal resource is rich, so it’s very important to use coal as the olefin feedstock instead of oil and adopt coal-to-olefins technology to produce light olefins in order to get rid of oil dependence and achieve sustainable economic development. Currently, the products of coal-to-olefins are separated by using conventional cryogenic technology in which the energy consumption accounts for 2/3 of the overall process. Applying membrane technology to the separation of propylene/ethylene mixture could significantly reduce energy consumption and achieve energy conservation.In this paper, rubbery polymer PEBA2533 is used as the base membrane and NaY molecular sieve is used as the inorganic additive. The two materials are mixed together to prepare PEBA2533/Na Y organic-inorganic hybrid memnranes and the membranes arecharacterized by Transmission Electron Microscope（TEM）, Scanning Electron Microscopy（SEM） and X-Ray Diffraction, etc. The hybrid membranes are applied to separate the ethylene/propylene mixture. The effect of operation conditions, thickness of the hybrid film, the amount of zeolite added, the ethylene/propylene ratio on the microstructure and separation performance is investigated. The results are as follws:1.When the operation conditions is changed for gas separation, that is the temperature varies from 35 degrees below zero to 20 degrees, the pressure varies from 0.2MPa to 0.5MPa and the volume ratio of ethylene/propylene is 1:1, for the hybrid film with 5wt% NaY zeolites, it is found that the higher of the temperature, the greater the separation factor of propylene/ethylene and the smaller the permeability coefficient of light olefins. While the greater the pressure, the smaller the separation factor of propylene/ethylene and the greater the permeability coefficient of light olefins. The separation factor of propylene/ethylene mixture can reach the max of 7.43 with the permeability coefficient of propylene of233 Barrer when the operation temperature is 35 degrees below zero and the pressure is 0.2MPa.2.The particle size of NaY molecular sieve is between 500 nm and600 nm. Inorganic particles are evenly dispersed in the organic medium and the compatibility of the two phases is well when the amount of zeolite is less than 6wt%, while the inorganic particle agglomerationoccurs and the two-phase interface appears obvious cavity when the zeolite content is higher than 6wt%. With the increasing of the content of the zeolites, the separation factor of propylene/ethylene increases at first and then decreases while the permeability coefficien of ethylene and propylene increase. When the amount of Na Y zeolite added is exactly6wt%, the separation factor can reach the maximum value of 8.84 with a permeability coefficien of propylene of 317 Barrer.3.When the thickness of the membranes changes from 30μm to130μm, the effect of the membrane thickness is not significant on its separation performance at low temperatures（-35⁰℃）, while the flux of the membrane varies widely. For the hybrid membrane with 6wt% Na Y zeolites, the separation factor of propylene/ethylene is 8.46 with a permeate flux of 1.07×10^-5cm³（STP）/（cm²scmHg） when the thickness of the membrane is 30μm,under the temperature of 35 degrees below zero and the pressure of 0.2MPa. When the thickness is 130μm, the separation factor of propylene/ethylene increases to 9, but the total flux of the membrane decreases to 7×10^-7cm³（STP）/（cm²scmHg）. At 20 degrees,increasing the thickness of the membrane, the separation factor increases greatly from 2.86 to 3.83, and the flux decreases from 4.4×10^-5cm³（STP）/（cm²scmHg） to 7×10^-7cm³（STP）/（cm²scmHg）.4.When the volume fraction of propylene in ethylene/propylene mixture decreases gradually from 70Vol%, 50Vol% and 30Vol% finally to10Vol%, the separation factor of propylene/ethylene reduces gradually from 11, 8.84, 3.11 to 1.22 at last. With the decreasing of the volume fraction of propylene, the permeability coefficient of ethylene increases from 23 Barrer to 176 Barrer and the permeability coefficient of propylene decreases from 430 Barrer to 126 Barrer.5.During the temperature rising from 35 degrees below zero to 25 degrees below zero at 0.2 MPa, there is a non-steady state of the mixture.In this state, the separation factor of propylene/ethylene surged. For the hybrid membrane with 6 wt% NaY zeolites, its separation factor increases from 9 to 21 with the permeability coefficient of propylene increasing from 2000 Barrer to 4000 Barrer, while the permeability coefficient of ethylene has no significant changes. This phenomenon can’t be found in pure PEBA2533 membrane.