Two stage membrane process

Trzcinski, A. P., Stuckey, D. C. (2009). Continuous treatment of the organic fraction of municipal sohd waste in an anaerobic two-stage membrane process with liquid recycle. Water Research, 43, 2449—2462. 

As detailed in the simulation section above, this level of selectivity requires a two-stage membrane process for the CO2 capture ratio and purity to be attained. For a higher selectivity to be attainable, chemically reactive materials are necessary. Numerous studies have addressed this issue and the different performances which can be obtained by the various types of membrane materials are summarized in Table 2.6. 

Figure 7.2 Simplified flow sheet of a two-stage membrane process with and without retentate recycling.

Figure 7.3 Specific energy demand of a two-stage membrane process without retentate recycling as a function of the overall CO2 recovery for different flue gas pressures (curly brackets) and different feed pressures of the second stage (dotted line 3 bar, dashed line 4 bar, solid line 5 bar) 0.2 bar permeate pressure in both stages.

Figures 7.7 to 7.10 present the technical and economic KPIs as function of the overall CO2 recovery for a two stage membrane process with retentate recycling.

The techno-economic analysis of two stage membrane processes for post-combusion CO2 capture revealed that CO2 capture by membranes appears to be feasible. Nevertheless, the CO2 product stream contains at least 1 vol.% O2, thus violating strict purity requirements, e.g. for enhanced oil recovery. Membrane costs substantially affect the optimal operation mode of the capture process. Residual recycling is particularly attractive to enhance overall CO2 recovery. Since the application of residual recycling leads to a flat minimum of the avoidance costs, capture levels between 80% and 95% seem to be most attractive. 

A two-stage ED process was also proposed to recover succinic acid [HOOC (CH2)2COOH] from sugar- and triptophane-based fermentation media (Glassner and Datta, 1992). The broth was previously concentrated via ED using monopolar membranes and then separated into sodium hydroxide-and free succinic acid-rich streams using bipolar membranes. Further removal of sodium cations and sulfate anions was achieved using weakly acid and -basic IER. 

Figure 8.31 Flow scheme of one-stage and two-stage membrane separation plants to remove carbon dioxide from natural gas. Because the one-stage design has no moving parts, it is very competitive with other technologies especially if there is a use for the low-pressure permeate gas. Two-stage processes are more expensive because a large compressor is required to compress the permeate gas. However, the loss of methane with the fuel gas is much reduced...

Figure 8.9 Block diagram of a two-stage membrane system to process 100 million scfd of natural gas. Reproduced with permission from Ind. Eng. Chem. Res. 2008, 47(7), 2109—2121.

Figure P3-10 shows a two-stage membrane cascade with recycling for producing ethylene product with a polymer-grade composition of 0.999 mol percent. The fresh feed pressure of2605 kPa and temperature of 28°C are identical to the conditions shown for stream 4 in the series configuration hybrid system presented in Fig. P3-8. The process conditions for this cascade contiguration are shown in the accompanying table.

Thin zeolite membranes can also be prepared through a spin-coating process of a nanoparticle suspension. Yan and coworkers synthesized silicalite-1 and silicalite-2 in a nanoparticle suspension using a two-stage hydrothermal process.[138,139] First, the precursor... 

Figure 4.8 Process flow diagram of two-stage membrane separation for CO2 removal from natural gas stream data correspond to the optimal solution ( / in Figure 4.9.

Fig. 7.10 Oxygen/air separation process designs (a) one-stage membrane-separation process, (b) two-stage separation process.

Figure 3.3.68 Process scheme for natural gas treatment by two-stage membrane separation of CO,. Adapted from Drioli and Ciorno (2009).

Membrane gas separation processes can be improved by using multistage separation as depicted in Figure 3.3.68 for natural gas treatment with a two-stage membrane for the separation of CO2. Traditionally, amine absorption is used to separate CO2 from natural gas. Membrane plants require less operator attention and smaller units may even operate unattended. Hence, membrane separations are favored in remote locations like offshore platforms. 

Heating the feed stream is not beneficial since the membrane is cheap and saving in the membrane area does not have economic impact. For a feed of 8 bar and 5 mol% hydrogen the specific cost of two stage PI process is similar to the CMSM as shown in Fig. 10.7 where the comparison of two stage PI and CMSM are made. This is because CMSM membrane area is large and the membrane is expensive while the PI process requires extra compression for the second stage. 

The most economically attractive process is a hybrid system that combines cryogenic, PSA, and membrane units to produce 99.99% helium from dilute natural gas. The process is shown in F iire 15-22. The feed is natural gas containing 2.1% helium. The feed is first cooled to -60°F to condense the heavier hydrocarbons. Then the gas is cooled to -240°F to condense most of the methane and some nitrogen. At this point the gas contains 30-35% helium. The crude helium is then fed to a two-stage membrane unit that produces a 95% helium stream. PSA is used to upgrade this stream to Grade A purity. 

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