Experimental studies of dehumidification of air by an improved ceramic membrane.

Abstract

The authors previously proposed a method of making a thin porous ceramic membranesupported on a coarse porous solid for gas separation. The membrane was applied to dehumidification of air in the previous work,1} in which leakage of air was found to be fairly large at relatively high temperatures and at low relative humidity.In the present work, the performance of an improved ceramic membraneused as a dehumidifier was studied experimentally and the separation mechanism was considered. ExperimentalThin porous membranes of silica-alumina were formed at the outer surfaces of coarse porous ceramic cylinders by the methods proposed in the previous works.1~3) Some relatively large pin-holes in the preliminary step of the membrane-making procedures were found to have a large effect on performance of the final membrane. These large holes were shown in the previous work3) to be filled to some extent by pressuring alumina sol into the porous cylindrical membrane module while it was dried. A membrane module (module A) used in this work was prepared by the method described in the previous work.3) Another module (module B) was made in the same way as module A except for being kept in a dilute aqueous solution of sodium silicate at 100°C for about 10 min just before its washing in boiling water.The experimental apparatus and procedures are quite similar to those described in the previous work.1* Only two small improvements were added to the apparatus to control and to measure the inside pressure of the membranemodule during dehumidification measurements. Permeabilities of pure gases in membrane moduleAwere also measured. 2. Results and Discussion In Fig. 1 are shown some observed results of apparent permeabilities of gases with membrane module A and its substrate. The observed permeability of Received July 18, 1985. Correspondence concerning this article should be addressed to M. Asaeda. 238helium is reduced to nearly half that reported in the previous work,2) where some relatively large pinholes remained in the membrane.If the flow mechanism is considered to diverge from Knudsen flow at around 200kPa, the pore diameter must be about 10 nanometers, which would not have given the large separation factors (larger than 60) for alcohol/water gaseous mixtures in the previous work3) and the quite small air leakage in the dehumidification of air mentioned below. The reason for this divergence of flow mechanism from Knudsen's near atmospheric pressure is probably due to the pore structure of constriction.The dotted lines in this figure show the estimated Knudsen permeabilities assuming that helium is nonadsorptive and that the flow mechanismis Knudsen's for each gas. The observed permeabilities for nitrogen, argon, propane and propylene are larger than

Advanced Membrane Separation Technologies For Energy Recovery From Industrial Process Streams

“…Porous membranes typically depend on some combination of molecular sieving, diffusivity, and surface effects to manage the segregation of gaseous species [6]. Porous membranes, depending on pore size can achieve higher transport fluxes than nonporous membranes but the separation ratio is usually much lower [4,7,8].…”

Moisture Transport Through a Porous Plate with Micro Pores

“…From the point of view of saving space, it is desirable to recover and reuse the humidity in the exhaust gas using the supply air. In the present study, a method involving a thin porous plate for air dehumidification (Asaeda et al, 1984(Asaeda et al, , 1986,in which direct recovery of the moisture of the exhaust gas to the supply air through a thin porous plate or membrane, is considered. In this case, the following phenomena may occur: 1) mass and heat transport and an accompanying phase change inside the porous plate, 2) water evaporation from the surface of the porous plate and moisture diffusion around the surface of the plate on the supply air side, and 3) condensation of moisture on the porous plate surface on the exhaust gas side.…”

A basic study on humidity recovery using micro‐porous media: General characteristics and effect of material properties on transport performance

“…In addition, from the viewpoint of saving space, it is desirable to recover and reuse the humidity in the exhaust gas using the supply air. In the present study, a method involving a thin porous plate for air dehumidification [4,5], in which direct recovery of the moisture from the exhaust gas to the supply air through a thin porous plate or membrane, is considered. In this case, phenomena such as the transport of water, steam, and air inside the porous plate are examined.…”