Synthesis and characterization of all-silica DDR zeolite by microwave heating

A Hybrid Zeolite Membrane-Based Breakthrough for Simultaneous CO2 Capture and CH4 Upgrading from Biogas

“…Almost ideally, deca-dodecasil 3 rhombohedral (DDR) type zeolites that have a pore size of 0.36 × 0.44 nm 2 can differentiate the molecular transport of slightly different sized molecules. − Indeed, the DDR zeolite membrane based separation of CO 2 (kinetic diameter of 0.33 nm) from the slightly larger molecules CH 4 (0.38 nm) and N 2 (0.364 nm) is suitable for biogas upgrading and postcombustion carbon capture, respectively. , In particular, biogas (a clean renewable energy source) upgrading through DDR zeolite membranes is highly desirable for recovering CH 4 (which can be used for fuels and chemicals) and segregating CO 2 (which must be stored or converted). ,, Despite this high potential of DDR zeolites, it is quite challenging to synthesize the corresponding DDR membranes. Some related issues addressed in the literature − are the wide particle size distribution of seed crystals, long synthesis duration, low reproducibility of the synthesis, and susceptibility of the synthesis to the preparation methods. Among them, the synthesis of monodispersed, small DDR seed particles (around 50–300 nm), apparently requiring alternative approaches, , is a prerequisite for reliable membrane manufacturing.…”

“…Some related issues addressed in the literature − are the wide particle size distribution of seed crystals, long synthesis duration, low reproducibility of the synthesis, and susceptibility of the synthesis to the preparation methods. Among them, the synthesis of monodispersed, small DDR seed particles (around 50–300 nm), apparently requiring alternative approaches, , is a prerequisite for reliable membrane manufacturing. Recently, a heteroepitaxial approach was demonstrated to be effective for making hybrid zeolite membranes. − Specifically, a heterogeneous hybrid film was synthesized via the structural compatibility between the DDR and chabazite (CHA) zeolites; a siliceous DDR zeolite was heteroepitaxially grown from a CHA zeolite seed layer. , Despite this effective approach, secondary growth with a synthetic precursor that contains an organic structure-directing agent (OSDA) of methyltropinium iodide (MTI) required a substantial hybrid membrane thickness (approximately 7 μm) to secure a high CO 2 permselectivity, inevitably providing a low CO 2 molar flux that should be overcome for practical uses. − …”

“…Some related issues addressed in the literature 21−27 are the wide particle size distribution of seed crystals, long synthesis duration, low reproducibility of the synthesis, and susceptibility of the synthesis to the preparation methods. Among them, the synthesis of monodispersed, small DDR seed particles (around 50−300 nm), apparently requiring alternative approaches, 24,25 is a prerequisite for reliable membrane manufacturing. Recently, a heteroepitaxial approach was demonstrated to be effective for making hybrid zeolite membranes.…”

Comparative study on different strategies for synthesizing all-silica DD3R zeolite crystals with a uniform morphology and size

“…Sen et al 46 developed a sonochemical method to synthesize pure DD3R crystals at room temperature over 5 d. A microwave-aided heating method was used to signicantly reduce the DD3R-crystal synthesis time from 25 to 3 d without seeding and to 6 h with seeding. 47 Liu et al 48 used (NH 4 ) 2 SiF 6 as a silica source to synthesize DD3R crystals over 12 h without seeding, because (NH 4 ) 2 SiF 6 is very reactive and can enhance the nucleation and crystal growth of DD3R signicantly. Bai et al 49 developed an environment-friendly synthesis method to prepare DD3R crystals, in which only the silica source, a small amount of template, and a trace amount of water were used in the synthesis, without adding a toxic solvent such as ethylenediamine or the mineralizing reagent uoride.…”

Seed-free hydrothermal synthesis of all-silica deca-dodecasil 3R with essential reagents

“…5),7),20),22),29), 30) More recently, the synthesis time has been significantly reduced by employing ultrasonic irradiation 20),21),26)28) or microwave irradiation. 29) In contrast, the acceleration of seed-free DDR synthesis simply by modifying the precursor compositions and hydrothermal conditions still remains a challenge. The hydrothermal temperatures of earlier reports were typically at or below 180°C to avoid the formation of dodecasil 1H (DOH), 36) whereas several studies have succeeded in synthesizing singlephase DDR at or above 200°C in several days.…”