CONTROLLED DEALUMINATION OF ZEOLITE Y USING TETRAALKYLAMMONIUM IN AQUEOUS ACID MEDIA

• Main Author: MAGHFIRAH (NIM:20516009), AINUL
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/25228
• Institution: Institut Teknologi Bandung

Dealumination by acid leaching is one of important technique to increase the Si/Al ratio of zeolite Y, hence, increasing hydrotermal stabilityNevertheless, this method lead to lattice destruction due to low stability of zeolite Y in aqueous acid. In this work, new strategy for controlled dealumination using tetraalkylammonium (TAA) cations was introduced. The TAAs cations employed were tetramethylammonium (TMA), tetraethylammonium (TEA), tetrapropylammonium (TPA), and tetrabutylammonium (TBA) while the acid compound employed was oxalic acid. Therefore, the purposes of this study are 1) to know the influence of the presence of TAAs cations in zeolite Y framework ondealumination process in aqueous acid and 2) to know the influnce of alkyl chain length of TAAs cations on zeolite y crystallinity after dealumination in aqueous acid. <br /> <br /> Firstly, Zeolite Y was hydrothermally synthesized without the presence of organic compound. This method resulted in pure zeolite Y with Si/Al bulk ratio of 3.4. Inclusion of TBA cation was performed by direct and post synthesis method. Direct method was performed by adding the TBABr into gel of zeolite Y before hydrothermal process, while post synthesis method was performed by adding 0.2 M TBABr solution into assynthesized zeolite Y and stirred at room temperature for 24 hours. Based on XRD analysis, compared to post synthesis method, inclusion of TBA by direct method resulted in drastic depletion of diffraction intensity. In additon, TGA data revealed that post synthesis method is more effective for loading TBA into zeolite Y framework than the direct method. Therefore, the inclusion of TMA, TEA, and TPA cations were then performed by post synthesis method. <br /> <br /> Then, oxalic treatment toward zeolite Y was performed at concentration 0.1, 0.25, and 0.5 M. XRD characterization data showed that acid treatment did not disturb the structure of zeolite Y. Nevertheless, at concentration 0.5 M, structure destruction of zeolite Y was obviously observed. This data was also supported by IR spectra in which displays the disappereance of some peaks assigned to T – O symmetry stretching and Double 6 ring of zeolite Y indicating structure destruction of zeolite Y was occured at concentration 0.5 M. Based on XRF data, the Si/Al bulk ratio of the treated zeolite Y increased by increasing the oxalic acid concentration, otherwise the crystallinity decreased. <br /> <br /> The last, the acid treatment was also performed toward zeolite Y occluded with TAAs cations at concentration of oxalic acid 0.1 and 0.25 M. At the same concentration, the loss of crystallinity of dealuminated zeolite Y with the presence of TAAs cations was lower than the dealuminated zeolite Y-TAA free. Furthermore, the difference of alkyl chain length resulted in different loss of crystallinity showing the different ability of TAA in preserving crystallinity by order TBA ~ TMA > TEA > TPA. At concentration 0.1 M, the increase of Si/Al bulk ratio for all dealuminated samples is almost the same. Meanwhile, at concentration 0.25 M, the increase of Si/Al bulk ratio of dealuminated zeolite Y occluded with TAAs cations is higher than the dealuminated zeolite Y-TAA free. These results indicate that this controlled dealumination strategy is a powerfull method to preserve zeolite Y crystallinity in acid media without inhibiting the dealumination process while the ability to protect zeolite Y crystallinity during acid treatment among the TAAs is related to charge density and steric factors. For thorough understanding, 27Al MAS NMR measurement is required .