Catalytic membrane reactor-separator for environmental applications.

Flow-through catalytic membrane reactors offer the potential for improved conversions at reduced operating temperature due to product separation and catalyst activity. An experimental work dealing with a forced flow-through membrane reactor is the subject of this thesis. The focus is on the performance and transport characteristics of selective thin-supported silica membranes and flow-through catalytic membrane systems. The improvement of VOC-selective, H2-selective and CO2-selective membrane properties by the use of systematic dip-coating techniques and the application of the technique in a bi-layer membrane repair concept for gas separation membranes has been studied. In addition, several methods were used to characterize the membranes, including scanning electron microscopy, energy diffraction X-ray, nitrogen adsorption and gas permeation. In the first part of this work, CO2 permeance (3.39 x 10-8 mol m-2 s-1 Pa-1 at 25 0C for γ-Al2O3 membrane after exposing boehmite to the support) was mainly attributed to the Knudsen diffusion mechanism. CO2/CH4 selectivity of 24.07 was obtained from the silica membrane at 25 0C and 0.7 bar. Such a selectivity value could be useful in small-scale carbon dioxide removal units for natural gas treatment processes. In addition, H2/N2 selectivity of 1.36 and 2.72 at 1 bar were obtained from macro and meso porous membranes at 25 0C. The selectivity of propylene (C3H6) over N2 was also obtained. Higher selectivity of 1.79 at 0.05 bar was obtained. This selectivity increased by a factor of 2 compared to the ideal Knudsen selectivity (0.82). Remarkable propane conversion of 95.47% was achieved at a temperature of 378 0C on a 3.52 wt% platinum (Pt) catalyst at different total flow rates, ranging from 166 to 270ml/min. The temperature at which the catalytic combustion takes place for the VOC corroborates with (or is lower than) the one obtained from the literature for the same VOC on 5 wt% Pt/γ-Al2O3 catalysts

A study of gas diffusion characteristics on a micro porous composite silica ceramic membrane.

The purpose of this study is to investigate gas permeation behaviour of five gases (CO2, He, H2, N2 and Ar) across two silica modified ceramic membranes, Membrane Y and Membrane Z. An examination of the variations in their layer thickness and flow rate was determined. Solution-dip coating process was used for the modification process specifically for pore size reduction. This resulted in some level of modifications in the layer thickness after a successive dipping time as well as flow rate in relation to pressure drop. The effect of number of dips generally influenced the layer thickness of both membranes. Membrane Y layer thickness through five successive dipping was in the range of 89.2-36μm while Membrane Z ranges between 150.72 and 43.69μm. Gas permeability as a function of mean pressure for Membrane Z was calculated using data obtained experimentally. The permeation tests confirmed the contribution of both Knudsen and viscous flow mechanism with an estimation and prediction of the membrane pore radius

Validation of a novel approach for CO2/N2 gas separations by means of a hybrid ceramic membrane.

Global warming has been documented as one of the world's foremost ecological concerns. Although it is difficult to totally end human related global warming, there is a possibility to alleviate these effects through a wide spectrum of options. One such possibility is the reduction of atmospheric carbon dioxide emissions, a major greenhouse gas widely thought to be responsible for global warming. This paper therefore looks at an experimental validation of gas separation by means of a high selective membrane for CO2 recovery applications. Analysis of the results obtained is in good agreement with literature experimental data. Additional results show that CO2 selectivity factor is reasonable for capture of CO2 from N2 as a key constituent in a flue gas stream

Performance evaluation of an inventive CO2 gas separation inorganic ceramic membrane.

Atmospheric carbon dioxide emissions are considered as the greatest environmental challenge the world is facing today. The tasks to control the emissions include the recovery of CO2 from flue gas. This concern has been improved due to recent advances in materials process engineering resulting in the development of inorganic gas separation membranes with excellent thermal and mechanical stability required for most gas separations. This paper, therefore, evaluates the performance of a highly selective inorganic membrane for CO2 recovery applications. Analysis of results obtained is in agreement with experimental literature data. Further results show the prediction performance of the membranes for gas separation and the future direction of research. The materials selection and the membrane preparation techniques are discussed. Method of improving the interface defects in the membrane and its effect on the separation performance has also been reviewed and in addition advances to totally exploit the potential usage of this innovative membrane

Propylene oxidation using Pt-alumina impregnated catalytic membrane reactor.

Pt/{esc}gc{esc}s-Al2O3 membrane was prepared through the evaporative-crystallization deposition method for volatile organic compounds (VOCs) destruction. SEM-EDXA observation, BET measurement, permeability assessment and the catalytic oxidation of propylene was obtained. Nearly 80% propylene conversion was achieved by varying the reaction temperature using flow-through catalytic membrane reactor operating in the Knudsen flow regime

Gas permeation study using ceramic membranes.

A 6000 nm ceramic membrane was repaired with boehmite solution (ALOOH) through the repeat dip-coating technique. The permeance of hydrogen (H2) and carbon dioxide (CO2) were obtained through the membrane in relation to average pressure at room temperature for the support membrane and as cracked membrane. A repair process was carried out on the cracked membrane by same dip coating process and results obtained after first and second dips. The permeance of the support membrane obtained ranged between 1.50 to 3.04 {D7} 10-7 mol m-2 s-1 Pa-1. However, as a result of a crack that occurred during the removal of the membrane from the reactor, the permeance increased from 2.96 to 5.82 10-7 mol m-2 s-1 Pa-1. Further application of boehmite solution on the membrane lead to an improvement on the surface of the membrane with some degree and surface cracks were reduced. This also decreased the permeance to 1.26 - 3.39 {D7} 10-8 mol m-2 s-1 Pa-1 after the second dip. Consequently, another silica based modified membrane was used for carbon dioxide and nitrogen (N2) permeation. The plots show that carbon dioxide permeated faster than the other gases, indicating dominance of a more selective adsorptive transport mechanism. Accordingly, results obtained show an appreciable high carbon dioxide permeance of 3.42 {D7} 10-6 mol m-2 s-1 Pa-1 at a relatively low pressure when compared to nitrogenconfirming that the membrane has so far exhibited a high permeability, selectivity and high CO2 gas recovery. The permselectivities of CO2 over H2 at room temperature was also obtained which were higher than the Knudsen selectivity

Preparation and characterization of inorganic membranes for hydrogen separation.

A tubular commercially available alumina support was coated using the dip coating technique. The objective is to prepare silica and Pt impregnated membranes. Scanning electron microscopy (SEM), energy diffraction X-ray analysis (EDXA), nitrogen adsorption-desorption at 77{A0}K and gas permeation measurements were employed for membrane characterization. The permeation of H2, He and N2 revealed that the membranes are crack-free. H2/N2 selectivity for the silica membrane obtained the highest value of 2.93 at 0.9 barg and 25{A0}{deg}C. On the other hand, H2/He selectivity of 1.96 at 1.6 barg and 300{A0}{deg}C for the Pt membrane was obtained and found to be higher than the theoretical Knudsen selectivity. While the silica membrane realised on the thin film coating to enhance the selectivity to hydrogen, the Pt impregnated membrane on the other hand enhance hydrogen transport through an activated surface diffusion in addition to Knudsen flow

Hydrogen separation using inorganic membranes.

Gas permeation of hydrogen (H2) and nitrogen (N2) were obtained from 30 and 6000 nm pore diameter tubular commercial alumina ceramic membranes at 0.05 to 1.00 bar and 298 K. Flow rates of up to 3.279 and 2.296 l/min were obtained for H2 and N2 respectively. The ratio of H2/N2 flow rates were used to calculate H2/N2 selectivity. The experimental H2/N2 selectivities obtained were 1.85 and 1.43 for the 30 and 6000 nm respectively

High molecular permeance dual-layer ceramic membrane for capturing CO2 from flue gas stream.

With the objective to create technologically advanced materials to be scientifically applicable, dual-layer silica alumina membranes were molecularly fabricated by continuous surface coating silica layers containing hybrid material onto a ceramic porous substrate for flue gas separation applications. The dual-layer silica alumina membrane was prepared by dip coating technique before further drying in an oven at elevated temperature. The effects of substrate physical appearance, coating quantity, cross-linking agent, number of coatings and testing conditions on gas separation performance of the membrane have been investigated. Scanning electron microscope was used to investigate the development of coating thickness. The membrane shows impressive perm selectivity especially for CO2 and N2 binary mixture representing a stimulated flue gas stream

Hydrogen separation using silica-based composite membranes.

Silica sol-gel membranes have been developed for moderate temperature (300°C) separation of hydrogen (H2) from nitrogen (N2), methane (CH4) and argon (Ar) gas molecules. Tubular ceramic support with 15 nm nominal pore diameter and 45% porosity was modified by dip-coating method. Gas permeation characteristics were evaluated. Defect free silica layer over the substrate for hydrogen gas separation was obtained. Hydrogen gas permeate flux of 4.82x10-1 mol/sec m2 at 1.0 barg feed pressure was obtained. Selectivities of H2 over N2, CH4 and Ar of 3.07, 2.23 and 3.75 at 300°C, 200°C and 300°C and 0.9 barg were obtained with the silica membranes. The gas permeation and the selectivity performance of the membrane were evaluated