Mixtures membrane areas

Belanich et al.63 reported the removal of endotoxins from protein mixtures. Endotoxins in a bacterial extract containing a protein photolyase was passed through a stack of 10 disk membranes (Q-type, Sartorius). LAL assay was used to monitor the endotoxin levels after each pass. There was over 5 log reduction in endotoxin content after three passes through the membranes. The protein content was reduced during this process, however, the enzyme s specific activity was increased 35-fold. This study also determined that the binding capacity of the membrane was greater than 2.25 million EU/cm2 of membrane area. 

Recently [43] Gao et al. applied a zeolite-fiOlled polyvinyl alcohol (PVA) membrane in esterification and acetalization reactions. Zeolites NaA, KA and CaA as well as NaX were loaded into PVA up to 27 wt% and the composites tested in selective water removal during reaction. A pervaporation cell with a membrane area of 22.9 cm was coimected to a collection system kept at a vacuum of 0.1 mm Hg. A sulfonated resin was used as Bronsted acid catalyst in the esterification mixture (120 ml). Figure 28 shows the progress of the esterification of salicylic acid and methanol at 60°C. The reaction is accelerated considerably as a result of the water removal. 

Pilot plant smdied have also been performed by Larsen et al. [37], who obtained stable operation and more than 95% SO2 removal from flue gas streams with a gas-side pressure drop of less than 1000 Pa. The importance of the membrane structure on the SO2 removal has been studied by Iversen et al. [6], who calculated the influence of the membrane resistance on the estimated membrane area required for 95% SO2 removal from a coal-fired power plant. Authors performed experiments on different hydrophobic membranes with sodium sulfite as absorbent to measure the SO2 flux and the overall mass-transfer coefficient. The gas mixture contained 1000 ppm of SO2 in N2. For the same thickness, porosity, and pore size, membranes with a structure similar to random spheres (typical of stretched membranes) showed a better performance than those with a closely packed spheres stmcture. 

For a binary mixture of components A and B, the flux can be expressed for the entire permeate (J, total flux) or each component and u, the flux of component A and B, respectively), having dimensions of mass/(area x time). The flux can be calculated provided the mass of the permeating component, the membrane area and the time of measurement are known. To this end, the following expression can be used ... 

Figure 10.17 shows an example of the separation efficiency of the SSF membrane for SMROG-PS A waste gas.64 It plots the rejection ( ) of the more selectively adsorbed components of the gas mixture (i = C02, CH4/CO) as a function of H2 recovery (aH2). The rejection of component i is defined by the ratio of the molar flow rate of that component in the low-pressure permeate stream to that in the feed stream. The recovery of H2 is defined by the ratio of the molar flow rate of H2 in the high-pressure effluent stream to that in the feed stream. The plot also shows the ratio of the membrane area (A) needed to process a given flow rate (F) of the feed gas. These data are sufficient to design the membrane for a given feed gas composition and flow rate.69... 

Detailed steps for a typical sample are as follows (i) mix 18 wt% PSF and 9 wt% PVP (molecular weight, 40,000) (h) add 43 wt% of dimethyl acetamide (DMAc), 29 wt% of dimethyl sulfoxide (DMSO) and 1 wt% of water (in) stir the mixture for 15 h to dissolve the components, maintaining it at 85°C (iv) spin the hollow fiber [Kobayashi and Tanaka, 1992] (v) replace the solution in the fiber with a solution of glycerin (70 wt%) (vi) prepare a fiber module with a membrane area of 0.7 m (vii) wash the module with warm water (35°C) and charge it with water ... 

Gas permeation is used to separate gas mixtures, for example, hydrogen fixjm methane. High pressures on the order of 500 psia are used to force the molecules through a dense polymer membrane, which is packaged in pressure-vessel modules, each containing up to 4,000 ft of membrane surface area. Membrane modules cost approximately 35/ft of membrane surface area. Multiple modules are arranged in parallel to achieve the desired total membrane area. 

The aforementioned tendency does not hold here. On the contrary, many very selective polymers also have a very high permeability Numerous polymers are available v ith water vapor selectivities of 5000 and more. For the following calculation a two-component water vapor/methane mixture has been assumed with 0.2% water vapor. The membrane unit shall reduce this water content by one order of magnitude i.e. the retentate water concentration has been set to 0.02%. The simple equation (10) cannot be applied, the equations first derived by Weller and Steiner [322] have been used for the calculation of methane loss and the equation of Saltonstall [323] for calculation of membrane area. The methane loss is simply defined by methane permeate stream divided by methane feed stream times 100. In Fig. 7.14 the methane loss is plotted versus membrane selectivity for two different pressure ratios. 

For small concentration changes between feed and retentate and for a first estimation of the membrane area necessary for a specified separation a simple but useful relation can be derived. It is assumed that the change in the concentration of a component removed from a certain amount of feed mixture is proportional to the applied membrane area, to the concentration of that component, and to the so-called pure component flux, and inverse proportional to the amount of the mixture... 

In Fig. 3.23 the conversion ratio of the wanted product (ester) and the water present in the reaction mixture are plotted over the reaction time for a given membrane area and two ratios of the educts. Without removal of water from the mixture by means of a membrane the wanted product C and water are produced at the same rate, and both concentrations in the reaction mixture increase until equilibrium is reached. When water is continuously removed through the membrane at a certain time the water content passes through a maximum, when the water is removed as fast as it is formed. The time to reach this point depends on the membrane area installed. The water content then goes down and eventually reaches a value close to zero, when the water is removed much faster than formed. 

With the knowledge of the kinetic parameters for a given reaction, which are relative easily accessible by a test or even found in the relevant literature, and the membrane performance the optimum ratio Q/m of membrane area to mass of the reaction mixture can be determined for that reaction, with the initial ratio of the educts as an adaptable parameter. 

For a rapid conversion of lab-scale results into an economically viable reaction-pervaporation system, an optimum value can be determined for each parameter. Based on experimental results as well as a model describing the kinetics of the system, it has been found that the temperature has the strongest influence on the performance of the system as it affects both the kinetics of esterification and of pervaporation. The rate of reaction increases with temperature according to an Arrhenius law, whereas the pervaporation is accelerated by an increased temperature also. Consequently, the water content fluctuates much faster at a higher temperature. The second important parameter is the initial molar ratio. It has to be noted, however, that a deviation in the initial molar ratio from the stoichiometric value requires a rather expensive separation step to recover the unreacted component afterwards. The third factor is the ratio of membrane area to reaction volume, at least in the case of a batch reactor. For continuous operation, the flow rate should be considered as the determining factor for the contact time of the mixture with the membrane and subsequently the permeation... 

Another improvement in the MR configuration that leads to a further reduction of the VI was proposed by Barbieri et al When the feed mixture enters the WGS stage it has a high CO content, such as in the case of the streams coming out from coal gasification, the traditional MR configuration does not allow the best exploitation of the whole membrane area because of the low H2 partial pressure at the inlet of the MR. For this reason the authors proposed the membrane only in the second part of the catalytic bed (Figure 12.12). 

A perfectly mixed gas permeation unit is separating a mixture that is 20 mol% carbon dioxide, 5 mol% oxygen and 75 mol% nitrogen using a poly(dimethylsiloxane) membrane at 25°C. Feed flow rate is 20,000 cm (STP)/s. The membrane thickness is 1 mil (0.00254 cm). Pressure on the feed side is 3.0 atm and on the permeate side is 0.40 atm We desire a cut fraction = 0.225. Find the membrane area needed, and the outlet mole fracs of permeate and retentate. 

Both organophilic and hydrophilic membranes are utilized. The effects of the temperature, of the excess of alcohol in the initial mixture and of the ratio of the membrane area to reactor volume are studied.The results obtainable with organophilic and hydrophilic membranes are compared. 

The performances of the membrane are evaluated experimentally and theoretically. The integrated process is simulated by a mathematical model, which shows that the results are strongly affected by the ratio of the membrane area to the mass of the mixture. 

Effects of various parameters temperature. Initial molar ratio of acetic acid to n-butanol, ratio of membrane area to the reacting mixture volume, catalyst content. A relatively simple mathematical model is introduced. Comparison of experimental and calculated values. 

For the esterification with n-butanol, Liu, Zhang, and Chen (2001) used a cross-linked PVA-ceramic composite membrane (in the temperature range of 60—90 °C). This paper is a rare case of use of the Zr(S04)2 -4H20 catalyst. On the basis of a simple Fickian model, the influence of several esterification process variables, such as process temperature, initial mole ratio of acetic acid to n-butanol, the ratio of the effective membrane area to the volume of reacting mixture, and catalyst content, were discussed. A more rigorous model was defined by Liu and Chen (using a kinetic approach) comparing model outcomes with experimental outcomes (Inoue et al., 2007). 

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