Molecular Dynamic Simulation Of Growth Mechanism Of B-axial ZSM-5 Membrane On The Surface Of Coal Gangue Derivatives

The reaction of methanol to aromatic hydrocarbon?MTA?as a non-oil route has been widely concerned since its first discovery.ZSM-5 molecular sieve is widely used in MTA reaction due to its unique b-axial pore structure.The coal gangue mainly consists of SiO₂ and Al₂O₃,which are common catalyst substrate components.In the previous research,the b-axial ZSM-5 zeolite membrane was successfully prepared on the coal gangue substrate.However,The adsorption action and behavior between ZSM-5 and the substrate and interaction among ZSM-5 crystal nucleus cannot be theoretically explained.In order to verify predecessors?work and provide theoretical guidance for the subsequent experimental work,In this paper,the crystal structure of modified coal gangue is obtained with analysis of element and crystal structure,and then the model of modified coal gangue was constructed by molecular simulation and verified by theoretical and experimental XRD.After different orientation ZSM-5/gangue models were obtained by pre-planting different orientation ZSM-5 crystal nucleus onto the surface of modified coal gangue,the optimal pre-planted crystals for b-axial ZSM-5 would be screened under molecular dynamic simulation.After the coal gangue surface suitable for b-axial ZSM-5 pre-planting was modified by inorganic?TiO₂?and organic?PVA,chitosan?modifiers,the pre-planting characteristics and optimal modifier between ZSM-5 and modified substrate surface was obtained.Finally,the b-axial ZSM-5/ZSM-5 zeolite membrane model was obtained by molecular simulation,and the growth habit of ZSM-5 on the surface of zeolite membrane was studied by molecular dynamic method.1.The structures of coal gangue at 723 K,1123 K and 1773 K represent the lattice structure of kaolinite,quartz and mullite respectively,and the primary unit and ZSM-5 nanocrystalline core are constructed and optimized by Material Studio.the XRD patterns between the experiment and simulation are of consistence.2.When pre-planting on the surface of kaolinite and mullite,ZSM-5 is great affected by the surface structure of the substrate,as a result that ZSM-5 is easier to pre-plant with c-axis;ZSM-5 pre-planting quartz substrate is great affected by interfacial friction reaction,as a result that mullite is the most suitable for c-axis pre-planting of ZSM-5,where the interaction energy is-165.41 Kcal/mol.When pre-planted on quartz?0 0 1?,the maximums of interaction energy are:-329.92 Kcal/mol?b-axial/450 K?,-257.61 Kcal/mol?a-axial/450 K?and-80.27 Kcal/mol?c-axial/450K?respectively,indicating that quartz?100?surface is the most suitable for b-axis ZSM-5 pre-planting at 450K.3.The PVA and chositan modification interacts with the substrate surface by hydrogen bond,and the organic macromolecules cross-link to form a modifier layer,belong to weak interaction;While TiO₂ modification not only interacts with substrate by hydrogen bonds and cooperation,but also interacts itself to form a dense modifier layer,so ZSM-5 is of best b-axial orientation on the TiO₂ modified substrate surface.The ZSM-5/modifier/coal gangue material was successfully prepared.Compared with PVA and chitosan,the SEM spectrum of TiO₂ modification displays that ZSM-5 distributed more evenly.4.The competitive adsorption force consists of two parts with OA growth mechanism:1.Interaction between ZSM-5 nucleus and ZSM-5 membrane;2.Interaction between ZSM-5 nucleus.The interaction between the ZSM-5 nucleus and ZSM-5 membrane can maintain pre-planting with the b-axial orientation,while the interaction between the ZSM-5 nucleus inhibits the b-axial oriented growth.The aggregation degree of ZSM-5 nucleus on the ZSM-5 membrane indicates that ZSM-5nucleus at high concentration?ZSM-5>3?will lead to ZSM-5 adsorption with c-axial orientation.However,ZSM-5 nuclei will form b-axial oriented connection mode at low concentration?ZSM-5?3?.