Membrane, nitrogen recovery

Figure 8.25 Nitrogen recovery as a function of product nitrogen concentration for membranes with selectivities between 2 and 20...

Operating cost is primarily the cost of power to operate the air compressor. This is easily calculated for a system once nitrogen recovery is specified by the membrane vendor. 

Figure 1.5 Applications of membrane systems. (Source Prism Gas Separation Systems, Monsanto Chemical Co., St. Louis, MO Air Products and Chemicals, Inc., Allentown, PA.) Gaseous components and systems include argon, helium, hydrogen, carbon monoxide/syngas, nitrogen, oxygen, CO,-removal, H,S-removal, dehydration. Capacity for nitrogen recovery is up to 35,000 SCF/hr for 97% purity, and about one-tenth of this for 99+% purity.

Nitrogen Recovery with Membranes 2.2.3.1 Physical Principle... 

Figure 7.2.2. (a) Oxygen mole fraction in permeate vs. stage cut for a membrane having oo -nj = 6.0. (b) Two permeators in series operation with recycle of permeate from the second permeator to die f. (c) Fractional nitrogen recovery vs. residual oxygen mole fraction in NBA for different membrane selectivities. (part(c) after Baker (2004).)... 

The membrane selectively rejects oxygen and nitrogen. The field test showed a selectivity for chlorine over nitrogen of about ten. That this is so much lower than that obtained in the laboratory is attributed to concentration polarisation. Increasing the rate of flow through the module can alleviate this. At the same time, chlorine recovery can be maintained by adding modules in series. This is precisely what would be done in a commercial unit, and so one can reasonably expect better results in full-scale operation. 

Applying this information to a typical diaphragm-cell tail gas, Fig. 7.4 shows the logarithm of the amount of unrecovered chlorine versus the relative membrane area required. Recovery of chlorine is not far from a first-order process. As chlorine selectively passes through the membrane, the partial pressures of the impurities increase in the remaining gas. This causes their rates of permeation to increase. The membrane area required for permeation of, say, 30% of the nitrogen is less than twice that required for 15%. 

Reszka et al. [168] used ultrahltration to separate free mitoxantrone from PBCA nanoparticles. The particle suspension was passed through a cellulose nitrate membrane with a pore size of 20 nm with magnetic stirring and pressurized nitrogen. The filtrate obtained was analyzed for free drug content. Recovery of the particles is not possible with... 

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