Junhang Dong

Template-removal-associated microstructural development of porous-ceramic-supported MFI zeolite membranes

Defect-free thin MFI zeolite films were synthesized on porous α-alumina and yttria-doped zirconia (YZ) substrates by an in situ crystallization method using tetrapropylammonium hydroxide (TPAOH) as a template. The microstructure evolution of the supported zeolite films during calcination for template removal was studied by high-temperature X-ray diffraction and in situ gas permeance. Removal of the template from the zeolite films occurs at 350–500°C and is accompanied by a substantial shrinkage in the zeolite framework. After the template is removed from the zeolite at high temperatures, the zeolite crystals expand on cooling while the support shrinks. A compressive stress develops in the zeolite film during the cooling process when the zeolite crystallites are bound to the support after template removal. Without annealing prior to template removal, this stress induces cracks in the YZ-supported MFI films. High-quality MFI membranes were obtained on both α-alumina and YZ supports by using a suitable calcination temperature program. Removal of the template can either create or enlarge intercrystalline gaps as the zeolite crystallites decrease in size and draw away from adjacent crystallites. These gaps constitute the microporous non-zeolitic pores affecting the permselectivity of single-gas permeation for H2 and SF6. Both alumina- and YZ-supported MFI membranes show very good separation properties for hydrogen and n-butane mixtures, although the YZ-supported MFI films appear to have larger non-zeolitic pores than the alumina-supported membranes.

Microporous inorganic membranes for high temperature hydrogen purification

The general mechanisms of gas separation in microporous inorganic membranes are reviewed in this article. Emphasis has been placed on discussing the requirements of membrane pore structure and material properties for high temperature hydrogen separation from other small gases involved in processes of hydrogen production from fossil fuels. The recent research progresses in developing the crystalline zeolite membranes, and amorphous silica-based membranes for high temperature hydrogen separation are critically reviewed. The fundamental issues associated with the zeolite and silica membranes relevant to the practical applications are analyzed based on the relationships between the separation performance and membrane structural and chemical properties.

Internal surface modification of MFI-type zeolite membranes for high selectivity and high flux for hydrogen.

MFI-type zeolite membranes were modified by depositing molecular silica at a small number of active sites in the internal surface by in situ catalytic cracking of silane precursor. The limited silica deposition reduced the effective size of the zeolitic channels that dramatically enhanced the H(2) selectivity without causing a large increase in H(2) transport resistance. The modified zeolite membrane achieved an extraordinary H(2)/CO(2) permselectivity of 141 with a high H(2) permeance of 3.96 x 10(-7) mol/m(2) x s x Pa at 723 K. The effect of pore modification on the gas transport behavior was studied on the basis of single gas permeation data.

Zeolite thin film-coated long period fiber grating sensor for measuring trace chemical.

This paper reports the development of a new zeolite thin film-coated long period fiber grating (LPFG) sensor for direct measurement of trace organic vapors. The sensor was fabricated by growing pure silica MFI-type zeolite thin film on the optical fiber grating by in situ hydrothermal crystallization. The sensor measures chemical vapor concentration by monitoring the molecular adsorption-induced shift of LPFG resonant wavelength (lambda(R)) in near infrared (IR) region. Upon loading analyte molecules, the zeolites refractive index changes in the close vicinity of the fiber index where the LPFG has a large response to achieve high sensitivity.

High pressure vapor liquid equilibria at 293 K for systems containing nitrogen, methane and carbon dioxide

Abstract Xu, N., Dong, J., Wang, Y. and Shi, J. High pressure vapor liquid equilibria at 293 K for systems containing nitrogen,methane,and carbon dioxide. Vapor liquid equilibria were measured for N2-CO2 and CH4 - CO 2 two binary systems at 288 K and 293 K. Vapor liquid equilibria measurements were made for the N2-CH4-CO2 ternary system at 293 K and 6.04, 6.25, 7.15 and 8. 26 MPa. The data obtained in this work and available literature data on this systems were correlated and predicted by the original Peng-Robinson equation of state and its modified form.

Synthesis of MFI zeolite films on optical fibers for detection of chemical vapors

We report the development of a novel zeolite-incorporated optical fiber sensor and demonstrate its capability for in situ detection of chemical vapors. The sensor comprises a polycrystalline silicalite thin film grown upon the cleaved end face of a standard single-mode optical fiber. The sensor device operates by measuring the optical reflectivity of the zeolite crystals, which changes reversibly in response to the amount of chemical vapor adsorbed in its crystalline microporous structure. The sensor has been successfully demonstrated for measuring the concentration of isopropanol vapor in mixtures with nitrogen gas.

Fiber ring laser interrogated zeolite-coated singlemode-multimode-singlemode structure for trace chemical detection

Zeolite thin films were synthesized on the claddingless multimode portion of a singlemode-multimode-singlemode (SMS) fiber structure to construct a chemical vapor sensor. The zeolite-coated SMS structure was inserted into a fiber ring amplifier to produce a laser line. Combining the strong molecular adsorption capability of the nanoporous zeolite and the high signal-to-noise ratio of the fiber laser, the device was demonstrated for chemical vapor sensing with a low detection limit.

Measurement of CO2-laser-irradiation-induced refractive index modulation in single-mode fiber toward long-period fiber grating design and fabrication.

We report a new method to measure the CO(2)-laser-irradiation-induced refractive index modulation in the core of a single-mode optical fiber for the purpose of design and fabrication of long-period fiber gratings (LPFGs) without applying tension. Using an optical fiber Fabry-Perot interferometer, the laser-induced axial refractive index perturbation was measured. We found that the CO(2)-laser-irradiation-induced refractive index change in the fiber core had a negative value and that the magnitude was a sensitive function of the laser exposure time following almost a linear relation. Under the assumption of a Gaussian-shaped refractive index modulation profile and based on the first two terms of Fourier series approximation, the measured refractive index perturbations were used to simulate the LPFG transmission spectra. LPFGs with the same laser exposure parameters were fabricated without applying tension, and their spectra were compared with those obtained by simulations.

Perovskite-type oxide thin film integrated fiber optic sensor for high-temperature hydrogen measurement.

Small size fiber optic devices integrated with chemically sensitive photonic materials are emerging as a new class of high-performance optical chemical sensor that have the potential to meet many analytical challenges in future clean energy systems and environmental management. Here, we report the integration of a proton conducting perovskite oxide thin film with a long-period fiber grating (LPFG) device for high-temperature in situ measurement of bulk hydrogen in fossil- and biomass-derived syngas. The perovskite-type Sr(Ce(0.8)Zr(0.1))Y(0.1)O(2.95) (SCZY) nanocrystalline thin film is coated on the 125 microm diameter LPFG by a facile polymeric precursor route. This fiber optic sensor (FOS) operates by monitoring the LPFG resonant wavelength (lambda(R)), which is a function of the refractive index of the perovskite oxide overcoat. At high temperature, the types and population of the ionic and electronic defects in the SCZY structure depend on the surrounding hydrogen partial pressure. Thus, varying the H(2) concentration changes the SCZY film refractive index and light absorbing characteristics that in turn shifts the lambda(R) of the LPFG. The SCZY-coated LPFG sensor has been demonstrated for bulk hydrogen measurement at 500 degrees C for its sensitivity, stability/reversibility, and H(2)-selectivity over other relevant small gases including CO, CH(4), CO(2), H(2)O, and H(2)S, etc.

Separation of p-Xylene from multicomponent vapor mixtures using tubular MFI zeolite membranes

Abstact MFI zeolite membranes have been synthesized on tubular α-alumina substrates to investigate the separation of p-xylene (PX) from m-xylene (MX) and o-xylene (OX) in multicomponent mixtures and ranges of feed pressure and operating temperature. 1,3,5-triisopropylbenzene was added to the feed stream for online membrane modification. Separation of PX from MX and OX through the MFI membranes relies primarily on shape-selectivity when the xylene sorption level in the zeolite is sufficiently low. For an eight-component mixture containing hydrogen, hydrocarbons, PX, MX, and OX, PX/(MX+OX) selectivity of 7.71 with PX flux of 6.8×10 −6 mol/m 2 -s was obtained at 250 o C and atmospheric feed pressure.