Modified Ebulliometer for Measurement of Infinite Dilution Activity Coefficients

An existing design of an ebulliometer was modified by the addition of a vane-type magnetic pump to improve the performance of the ebull iometer at low pressures. The modified apparatus was used to determine the activity coefficients at infinite dilution of seven binary systems at three operating pressures each by the technique known as differential ebulliometry. The experimental results can be used to determine predictive model parameters which are of significant interest because of their ease of use and general applicability in phase equilibrium calculations.Chemical Engineerin

Synthesis and Optimization of Chitosan Ceramic-Supported Membranes in Pervaporation Ethanol Dehydration

In the present work, ceramic-supported chitosan hybrid membranes were prepared for the pervaporation dehydration of ethanol. Mullite and combined mullite-alumina (50% alumina content) tubular low-cost ceramic supports were fabricated, and their influence on membrane performance was compared to a commercial α-alumina support. The membrane preparation parameters were different ceramic supports and the concentration of chitosan solution (varying from 2 wt.% to 4 wt.%). The supports and hybrid membranes were characterized by field emission scanning electron microscopy (FE-SEM) and contact angle measurements. The results show, with increasing chitosan concentration, the permeability decreases, and selectivity increases. It was also found that the separation factor decreases with increasing feed temperature and feed water content, while the permeation flux increases. The membrane that was coated on α-alumina support with a 3 wt.% chitosan concentration exhibited the best pervaporation performance, leading to a permeation flux and separation factor of 352 g·m−2·h−1 and 200 for 90 wt.% ethanol in feed at 60 °C, respectively

A mathematical analysis of hollow fiber spinning : bore and dope velocity profiles in the air gap

Hollow fiber membranes are the most applicable form of membranes in laboratory and industrial scale with their large surface to volume ratios. Hollow fiber membranes usually are fabricated by dry-wet solution spinning, where a polymer solution is co-extruded through an annular region with a bore fluid and the nascent hollow fiber passes through an air gap and then enters a liquid coagulation bath. The spinneret dimension, dope and bore fluid flow rates, air gap length, bore fluid and dope compositions and their physical properties, coagulant composition and condition, shear stress within a spinneret, the ratio of dope to bore fluid volumetric flow rate, and the take-up-to-initial velocity ratio (draw ratio) are the primary factors that determine the final hollow fiber morphology and separation properties. All of the aforementioned parameters are not independent and some of them are functions of others. The objective of this paper is to elucidate the interdependence between some of the above parameters. For this purpose, dope and bore fluid axial velocity in the air gap was assumed as a function of the axial distance from the spinneret outlet, z, and radial velocity as a function of the radial distance from the center of the hollow fiber, r, and z. Dimensionless equations of motion and continuity were then simplified and solved simultaneously based on preceding assumptions. It was found from the analysis that the dimensionless axial velocity of dope was a function of the Reynolds number, Capillary number and Stokes number indicating that the axial velocity acceleration in the air gap is determined by viscous, capillary, and gravity force gradients. It was also concluded that the optimum value of the ratio of bore liquid flow rate to dope flow rate is equal to 0.8 of the ratio of the cross-sectional area of the bore fluid to that of the dope at the spinneret outlet

Effect of raw multi-wall carbon nanotubes on morphology and separation properties of polyimide membranes

Raw multi wall carbon nanotubes (r-MWCNTs) were embedded as fillers inside the polyimide (PI) matrix and PI/r-MWCNTs mixed matrix membranes were fabricated by the phase inversion method. The TEM images and permeation results using helium as test gas showed that r-MWCNTs were generally closed ended and acted as impermeable nano particles. Gas permeation tests using CO2 and CH4 showed that the addition of r-MWCNTs into the dope solution increased the CO2/CH4 separation factor while decreasing the carbon dioxide and methane permeances. When the r-MWCNTs content was increased from 0% to 6 wt.%, permeance of CO2 in the flat sheet mixed matrix membranes decreased from 9.15 GPU to 5.49 GPU and CO2/CH4 separation factor increased from 19.05 to 45.75. Identical to flat sheet mixed matrix membranes, the addition of 2 wt.% r-MWCNTs into a spinning dope increased the CO2/CH4 separation factor from 46.61 to 72.20. The glass transition temperature of the mixed matrix flat sheet membranes increased with an increase in the r-MWCNTs content. This implies a good segmental-level attachment between the two phases that forms a rigidified polymer region at the polymer/r-MWCNTs interface. FESEM images showed well dispersed r-MWCNTs in the polymer matrix at a loading of 2 wt% r-MWCNTs

Effect of chitosan as a functionalization agent on the performance and separation properties of polyimide/multi-walled carbon nanotubes mixed matrix flat sheet membranes

The effect of chitosan as a functionalization agent on the performance and separation properties of polyimide/multi-walled carbon nanotubes mixed matrix flat sheet membranes were investigated. Polyimide (PI)/raw multi-walled carbon nanotubes (r-MWCNTs) and polyimide (PI)/chitosan-functionalized multi-walled carbon nanotubes (C-f-MWCNTs) mixed matrix membranes were fabricated by phase inversion method. Raw and functionalized multi-walled carbon nanotubes were characterized by transmission electron microscope (TEM). The membrane samples were characterized by SEM, FESEM, DSC and gas permeation tests using He, CO2 and CH4 as test gases. TEM results and gas permeation test using He as test gas showed that r-MWCNTs were generally closed ended and after functionalization, well dispersed open ended chitosan-wrapped MWCNTs were obtained. Gas permeation results showed that addition of 1wt.% (solid base) C-f-MWCNTs into casting dope can increase the CO2 and CH4 permeabilities by 20.48 and 0.71Barrer, respectively. The increase in permeabilities of CO2, CH4 and He in this study can be attributed to the presence of high diffusivity tunnels in the MWCNTs within the polyimide matrix. It is interesting that the CO2/CH4 selectivity was also increased by 51.4% (from 10.9 to 16.5) by addition of C-f-MWCNTs. DSC and FESEM results also revealed a very good dispersion and adhesion of the C-f-MWCNTs in the polyimide matrix

State-of-the-art membrane based CO2 separation using mixed matrix membranes (MMMs): an overview on current status and future directions

The main purpose of research in membrane gas separation is to develop membranes with high permeability and selectivity. Historically, the gas separation performance of polymeric membranes has been constrained to an upper performance limit. Hence, different methods have been investigated to prepare membranes that can exceed this limitation including the incorporation of inorganic materials into polymer matrices. Membranes formed by this method are called mixed matrix membranes (MMMs). The major challenge is to prepare a defect-free polymer/inorganic nanoparticles interfaces with enhanced separation performance and mechanical and thermal stability. For this purpose, various types of nanoparticles have been proposed and examined experimentally. This review is especially devoted to summarize the fundamental concepts that have to be considered to prepare various types of MMMs, including considerations for the design novel MMMs that will eventually surpass the Robeson's trade-off upper bound. In addition, it provides the pros and cons of various factors that affect the MMM preparation especially for CO2 separation processes