Preparation Of SAPO-34 Crystals And Membranes And Their Applications For CO₂/CH₄ Separation

As one of the three major fossil fuels,the main ingredient of natural gas is methane.Among the natural gas,CO₂ is the main impurity,which can not only lower the caloric value,but also affect the transportation process.So it makes great sense to separate the CO₂ from methane.In this paper,we will focus on the synthesis of SAPO-34 crystals,the PEBA2533/SAPO-34 mixed matrix membranes and the SAPO-34 membranes,and their application for the CO₂/CH₄ separation.In this work,the SAPO-34 crystals were synthesized by microwave heating.The effects of heating methods,crystallization time and the template content were explored in this work.It was found that the SAPO-34 crystals synthesized by conventional heating were cubic,while the SAPO-34 crystals synthesized by microwave heating were flaky,and the diameter was smaller.The crystallization time also had a great effect on the synthesis of SAPO-34 crystals.When the crystallization time was 4 h,the SAPO-34 crystals with higher crystallinity and phase purity were formed.The template content also affect the crystallinity,the phase purity and particle size of SAPO-34 crystals.With the template content increased,the average particle size increased,the crystallinity and phase purity were higher when the mole ratio of each component was 1.0Al₂O₃:1.0P₂O₅:0.3SiO₂:1.2TEAOH:0.5DPA:52H₂O.The PEBA2533/SAPO-34 mixed matrix membranes were prepared by physical blending and they were used for gas separation.The effects of SAPO-34 content,the diameter of SAPO-34 crystals and pressure drop were explored on the separation performance.It was found that the CO₂ permeance increased with the increasing SAPO-34 content,the selectivity began to decrease after increasing to a certain degree;the mixed matrix membranes with smaller diameter of SAPO-34 crystals showed better gas separation performance;the CO₂ permeance and selectivity decreased with the pressure drop increased.The SAPO-34 crystals synthesized by microwave heating were used as the seeds to prepare the SAPO-34 membranes.The SAPO-34 membranes after template removal were used to separate the CO₂ from CH₄.The effects of heating methods,heating time,pressure drop and the composition of the gas mixture were explored during the gas separation process.It was found that compared with the conventional heating,the membranes synthesized by microwave heating were thinner and denser,and showed higher selectivity for gas separation;compared with membranes synthesized by microwave heating for 2 h,membranes synthesized by microwave heating for 4 h were denser and showed higher separation selectivity;the gas separation increased with the pressure drop decreased;the selectivity and the CO₂permeance increased with the ratio of CO₂ increased.