DEVELOPMENT OF MEMBRANE-BASED PROCESS FOR CO2 CAPTURE

• Main Author: Rahmah, Widda
• Format: Theses
• Language: Indonesia
• Subjects: Teknik kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/49964
• Institution: Institut Teknologi Bandung

Silicoaluminophosphate-34 (SAPO-34) based membrane is an interesting candidate for CO2 separation processes. SAPO-34 has a CHA framework with small pore size (0.38 nm) which can be used to separate CO2 from CH4 molecules based on diffusion rate differences. SAPO- 34 membranes can be prepared by the secondary growth method using SAPO-34 seeds. To date, membrane defects due to grain boundaries formation in between the SAPO-34 seeds are the biggest issue affecting separation performances and consequently stalling the commercialization of the SAPO-34 membranes. The grain boundaries population can be reduced by fabricating SAPO-34 membranes using SAPO-34 seeds of higher aspect-ratio (? = 0.5 x width / thickness). In this study, the SAPO-34 material was morphologically modified by adding polyethylene glycol-6000 and polyethylene glycol-20000 (PEG-6000 and PEG-20000) into the synthesis solutions before hydrothermal treatment at 180oC for 48 hours. Morpholine was chosen as an organic structure-directing agent (OSDA) to support the formation of CHA framework. Both PEG and morpholine molecules were removed from the products over calcination at 550oC for 6 hours. The calcined products were then characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). XRD patterns of the synthesis products indicated a very high resemblance of the products’ structure to the CHA structure. The synthesized seeds’ morphology as observed on the SEM images revealed cubic shape which is the characteristic shape of chabazite materials. Lastly, EDS analysis confirmed the existence of aluminum, silicon, and phosphorous atoms in the seeds. Through the series of analyses, it was accepted that crystalline SAPO-34 seeds have been successfully synthesized. The effect of PEG administration was studied by comparing the SAPO-34 seeds relative-crystallinity and aspect-ratio which were inferred from the XRD pattern and SEM image of the seeds, respectively. The results signified that PEG interference caused most of the synthesized seeds to experience mild to severe crystal damage and decreased crystallinity, while the other seeds underwent changes in morphology and crystallinity. Two-dimensional particles with a high aspect-ratio (?average of 5.26) were produced due to PEG-20000 and ethanol addition. However, the crystallinity of the twodimensional particle collapsed greatly. Some of the seeds synthesized with tetraethyl orthosilicate as the silicon source and PEG-20000 as the additive showed particles with unique morphologies of higher aspect-ratio (? of 3.87 and 6.84). However, the seeds’ particle shape and size uniformity are very poor. PEG-6000 and ethanol adduction into a synthesis solution produced SAPO-34 seeds with relatively high ?average (1.59), preserved crystallinity (70.9%), and sufficiently uniform size distribution suitable for SAPO-34 membrane fabrication. In overall, the addition of PEG-6000 and PEG-20000 into a synthetic solution of a certain molar composition with the help of ethanol could elevate the resultant SAPO-34 seeds’ ?average, so that the seeds can be fabricated into a better performing membrane for CO2 capture processes.