CO2/CH4 permeance ratio

Fig. 8.7. Pure CO2/CH4 permeance ratio of asymmetric poly(phenylene oxide) membranes as a function of surface tension of chloroform/alcohol mixtures. Nonsolvent additives include 2-ethyl-1-hexanol (1m), 1-octanol (2m), 2-propanol (3d), 2-decanol (4m), 3,5,5-trimethyl-1-hexanol (5m), 2,4-dimethyl-3-pentanol (6d), 2,4,4-trimethyl-1-pentanol (7d), and 2-methyl-3-hexanol (lOd). Merged is indicated by m discrete is indicated by d. Reprinted from [22], with kind permission from J. Tan...

Table 8.7 shows the 02/N2and CO2/CH4 permeance ratio for the as-cast P3AcET membrane and the base- or acid-treated membrane. As the table shows, the base or acid treatment resulted in a dramatic increase in the O2/N2 permeance ratio, while... 

Pure gas permeation data of membranes prepared using these additives were obtained from a constant pressure permeation system for CO2, CH4, O2 and N2. In order to know the effect of the structure of the nonsolvents, nonlinear regression analysis was attempted. Each additive was split into structural components groups. Several linear polynomial first and second order equations as well as nonlinear polynomial equations were attempted to derive an empirical correlation between the number of structural components and gas permeation data. A second order polynomial equation was derived to predict the pure CO2/CH4 permeance ratio from the structural components of the nonsolvents. From the structural studies the authors concluded that nonsolvent additives that possess a long straight hydrocarbon chain such as 2-ethyl-l-hexanol, 1-octanol and 2-decanol showed the highest pure gas permeance ratio. 

Module Cone. Of SPPO, wt.% Solvent mixture composition, wt./wt.% Methanol Ethanol Nos. of coating layers Permeance, GPU CO2 CH4 Permeance ratio, CO2/CH4... 

Memb. Type Solvent Solution concentration wt/wt % Permeance, GPU CO2 O2 Permeance ratio CO2/CH4 O2/N2 Ref. 

The data shown in Table 22 describes the effect of concentration of SPPOBr solutions and the numbers of layers of coating on CO2/CH4 permeances and permeance ratios. Use of more dilute solutions and more... 

Figure 43 shows the correlation between CO2/CH4 permeance rate ratio and the intrinsic viscosity measured for eight additives. It can be seen that as the intrinsic viscosity increases, the permeance rate ratio increases with an exception of 3,5,5-trimethyl-l-hexanol (shown as 5). The increase in intrinsic viscosity means that the polymer tends to spread in the solution rather than be coiled, due to a stronger polymer/solvent interaction. Therefore the chance of... 

From both these figures, it can be seen that long chain alcohols of nonsolvent additives tend to result in solvent-nonsolvent additive solutions with higher surface tension and membranes with merged nodules. This results in higher pure O2/N2 and CO2/CH4 permeance rate ratios. Lower pure O2/N2 and CO2/CH4 permeance rate ratios are expected when shorter and highly branched chain alcohols were used. They produced membranes with discrete nodules due to lower surface tensions in their solvent-nonsolvent additive solutions. 

It levelled off after the membrane was etched from 120 to 190 seconds. In Figure 52, pure CO2/CH4 permeance rate ratios reached a maximum for coupons CIO and Cll after the coupons were etched for 20 seconds. After coupon C9 was etched for 190 seconds, Oco2/ch4 decreased by 81% of its original value from 17.8 to 3.33. 

It should be however kept in mind that the membrane preparation procedure could influence its structure and gas transport properties. Thus, casting of the integrally skinned asymmetric membranes from p-DMePO solution using different nonsolvent additives produced the nodule structures in the surface skin layer of the membranes, which affected the permeance ratios for O2/N2 and CO2/CH4 [72]. In the homogeneous films of polyphenylene oxides considered in this chapter such structures apparently do not exist. 

Morphology studies done by tapping mode atomic force microscope revealed that membranes prepared from a PPO solution with 2-ethyl-1-hexanol as the additive had the lowest mean diameter of nodules. Interestingly these were the membranes that exhibited the highest permeance ratio of 5.5 for O2/N2 24.5 for CO2/CH4 (second highest after 1-octanol). Pure gas... 

SPPO was first prepared by sulfonating PPO of intrinsic viscosity of 1.58 dL/g in chloroform at 2S C. Solutions of SPPOH in different solvents like ethoxyether and butoxyether were coated onto the surface of commercial polyethersulfone ultrafiltration membranes. All coated membranes were dried at 60° C for overnight. TFC membranes prepared from a solution of SPPO in ethoxyethanol demonstrated higher permeances and permeance ratios for CO2/CH4 gas pair. These membranes were immersed in solutions of alkali metal hydroxide or alkaline earth metal hydroxide of 0.1 to IN concentrations, depending on the solubility of the respective hydroxide in water. When the solubility was low, the solution saturated with hydroxide was used. The TFC membranes were kept immersed for 48 hours at room temperature to complete the exchange of the proton with metal cations. Solutions of magnesium nitrate and aluminium chloride were used to replace the proton with Mg and AF respectively. 

The effect of the metal cations on the performance of the cation-exchanged SPPO-PES TFC membranes is shown in Table 19. The permeance ratio of CO2/CH4 gas pair for TFC membranes in the divalent cation form is higher than that for the monovalent cation form when ions of similar sizes are... 

The membranes tested here showed very high permeance ratio for O2/N2 gas pair. The permeance for O2 was on an average of 10.5 GPU. The permeance ratio for CO2/CH4 gas pair in these cases was also high and close to the intrinsic permeability ratio of 59 in most of the membranes tested. 

Single gas experiments CO2 permeance, GPU Permeance ratio, CO2/CH4 Mbced gas experiments CO2 mole fraction in ... 

Surface tension data was collected for a number of solvent-nonsolvent additive systems related to PPO gas separation asymmetric membranes. These membranes were made from different types of nonsolvent additives and were characterised from gas permeation experiments. The results of pure gas permeance ratios for O2/N2 and CO2/CH4 are shown in Figures 44 and 45. 

The effect of the surface tension of chloroform-nonsolvent additive systems on the formation of nodules are reflected in the correlation between surface tension and pure O2/N2 (Figure 44) and CO2/CH4 (Figure 45) permeance rate ratios. Both figures show that as the surface tension increased, the pure gas permeance rate ratios increased. Also, most of the membranes with merged nodules are found in the range of surface tensions greater than... 

The permeance ratios for both O2/N2 and CO2/CH4 gas pairs show maxima as the etching time increases. 

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