Vacuum desorption

IVery high ratio of feed to desorption pressure (>10 1) will be required. Vacuum desorption will probably be necessary. 

OXYWELL A process for separating oxygen from air by PSA, using vacuum desorption from a zeolite. Used for medical oxygen generators, hence the name. Developed by Nippon Sanso. 

Vacuum Desorption and Electrochemical Properties Figures 4a-4d shows a series of TPD spectra of Cu from Ru(0001) (16) corresponding... 

The addition of carbon nanotubes that were either reactively milled under hydrogen mixed with Mg powder [142] or simply mixed with MgH and subsequently milled [143, 144] was investigated. In vacuum, desorption at 200°C gave 3.6 wt.% within 1,800 s [142]. Another reference reports 5 wt.%Hj desorbed at 300°C within... 

Figure 3 shows the relationships between the temperatures and molecular weight distributions for 6 successive regions of the Til profile in Figure 1. Interestingly, regions a, b and c, primarily representing the low temperature components, show relatively narrow MW distributions around M values which markedly increase with temperature. This is consistent with the proposed interpretation of the low temperature hump as a vacuum desorption and distillation process rather than as a pyrolytic process. By contrast, regions d, e and f, representing the major Til maximum in Figure 1, exhibit much broader MW...

We used desorption of deactivated catalysts in vacuo at reaction temperatures into the ion source of a mass spectrometer as a method of examining desorbable intracrystalline fouling products. The method of dissolution of deactivated catalyst, followed by adsorbate analysis, that was reported by Venuto et al. (3, 4) was also used. The latter method gives composition and quantity of total adsorbate. The vacuum desorption technique provides information on the mobility—i.e., desorption dynamics, of desorbable (rather than total) adsorbed fouling products. 

Finally more nitrogen Is recovered by vacuum desorption The adsorbent used In this process Is apparently the same - zeolite molecular sieves - as that used In oxygen PSA processes ... 

Linear paraffins separation G 5 A molecular sieve Shape-selective sieving Displacement or vacuum desorption... 

BET surfaces were determined by nitrogen adsorption at 77 K, in an automated volumetric set up after a vacuum desorption at 383 K for 1 hour. Dispersion was determined by chemisorption of CO at room temperature using the pulse technique. Prior to chemisorption, the catalysts were reduced under an hydrogen flow at 500°C and flushed with helium at the same temperature for 30... 

Very high ratio of feed lo desorption pressure (greater than 10 i) will be requited. Vacuum desorption will probably be necessary. " If adsorbate concentration in the feed is very row. it may be practical to discard the losded adsorbent or reprocess off-site. vlf ii is not nacecsary to racover [he ndsorbeie. these processes are satisfactory. 

Long straight paraffins from Cio to C15 eontained in kerosene find applieations in the detergent industry. Although these paraffins are strongly adsorbed on the 5A zeolite, a temperature-switch cyclic desorption process cannot be used, beeause it would require temperatures of over 350°C. at whieh eoking inevitably oeeurs. The only possibilities, therefore, are vacuum desorption or displacement with a desorbent. The possible desorbents include hydrogen, n-pentane, or ammonia. 

A nearly equimolar mixture of ethylene and ethane is to be separated. The stream is available at about 3 atm, and high-purity (greater than 99%) ethylene is desired at greater than 95% recovery. An adsoibent with reasonable selectivity has been found which will desorb ethylene either at pressures well below atmospheric, or in the presence of a Cj hydrocaibon or heavier, or in the presence of various inert gases. Ethylene in turn cannot displace hydrocarbons with more than four carbons, however. In Table 12.6-1, the tme statements are 1,6, 7, and 9. Statement 9 is considered to be true because ciyogenic distillation would be required to separate the ethylene from the inert or purge material. In Table 12.6-2 we see that PSA is the most likely choice, using vacuum desorption. 

Steam stripping, which is widely used in the regeneration of solvent recovery systems using an activated carbon adsorbent, can be considered as a combination of thermal swing and displacement desorption. Vacuum desorption, which is used in some versions of the Union Carbide IsoSiv process for separation of medium-chain linear paraffins as well as in some air separation systems can be considered as a special case of pressure swing. 

Vacuum desorption rather than a product purge is used to remove the adsorbed oxygen during regeneration in order to avoid the slow uptake of nitrogen which would eventually saturate the sieve and reduce the efficiency of oxygen capture. The cycle commonly operates between about 4 and 0.1 atm with a half cycle time of about 1 The general scheme is shown in... 

Several different adsorption processes for the separation of linear paraffins have been developed including Ensorb (Exxon), IsoSiv (Union Carbide), T. S. F. (Texaco), the Shell process, and the Leuna Werke process. The latter has been called Parex (paraffin extraction) but the choice of name is unfortunate because of possible confusion with the UOP Parex process for separation of xylene isomers. All these processes use a 5A molecular sieve, generally in binderless form to minimize nonselective adsorption. The C,o-C,g linear paraffins are strongly adsorbed even at temperatures as high as 350°C. Thermal swing desorption is not feasible since the temperature required for desorption is so high that coking would occur. The alternatives are therefore vacuum desorption, which is used in some versions of the IsoSiv process, or displacement desorption which is used in most if not all of the other processes. 

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