Page 352 - Pressure Swing Adsorption

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PRESSURE SWING ADSORPTION APPENDIX C 329
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claimed an 111novat1ons over and over again. For example, several patents so that the oariial pressure of sulfur dioxide was above atmosphenc but
tlrnt were issued m the 1930s, 1940s, .and 1950s described the pnncmles of below its critical pressure. The compressed gas was then cooled and admitted
PSA, yet Skarstrom frequently receives credit for mventmg PSA, appare~tly to the adsorbent bed, while purified gas was withdrawn. Uoon 1mmment
because of the thoroughness of his first patent, which was issued m 1960:' breakthrough, the column was blown down, and the energy of compress,on
This appendix covers a variety of PSA patents, emohasizmg cycles and key was recovered. They stated that "The process may, therefore, be described as
concepts and the nch diversity of ideas that Jed to success. There are substantially isothermal and utilizes the property of the actsbrotive materiai
hund;eds from which to choose, so the coverage presented here is by no whereby the amount of gases held therein 1s substantially proportional to the
means comprehensive; 1t is regrettable but unavoidable that some seminal gaseous pressure." They did not, however, include a process flowshcet, and
contributions have been overiooked. That the material discussed here is no specific performance was claimed, for example, in terms of punty, recov-
predominately drawn from U.S. patents 1s not meant to slight the deveiop- ery, or energy consumption.
ffient of PSA technology by inventors m other natlons. For those who seek
additional mformatton, Tondeur and Wankat 4 reviewed the field of PSA
technology by categonzmg patents and publications according to cycle at- C,2,2 Finlayson and Sharp
tributes (such as the number of steps and number of columns), separat10n
applications, and corporations to which patent rights had been assigned. The patent by Finlayson and Sharp was filed 111 1931 and approved 111 1932, 2
They cited well over 100 sources, many of which were patents. Similarly, and it covered more of the basic conceots of ·rsA. For exampic, thcv
Ball 5 reviewed many U.S. patents and compiled an annotated bibliography. exolamed several specific principles that are fundamental to the operat10n of
In addition, rather than restricting this review to very recent patents, the PSA cycles and gave a detailed example of a !angle. PSA system being used to
emphasis is on earlier patents because they contain most of the fundamental alter the ratm of hydrogen to carbon monoxide m water gas. Most notably,
ideas that have proved to be widely applicable to vanous adsorbents and gas they described a oressunzat1on step followed by a· production step m which
mixtures. 1n faCt, oric might obsetve that most recent oatents tend to be "the first fraction or fractions bemg ncher in the Jess easily adsorbed
permutations of the fundamental ideas illtroduced m the early patents. component or components ... and the final fract10n or fractions bemg ncher
Considering that, one cynical reaction might be that, by now, all the patentable in the more easily adsorbed comoonent or components." Furthermore, thev
ideas in the field of PSA have already been claimed .. There is a strong case noted that the "oressure of the adsorbed gas may be released for instance t~
for that opinton, but 1t 1s a complex issue that should be left to patent a lirmtect extent or substantially to atmospheric pressure or even a vacuum
may be applied." This idea was embellished later by Skarstrom and Heilman."
attorneys to argue.
Timing s criticai for patents, not only for legal reasons, but also because Even their simple idea of using subatmosohenc pressure for desorotion has
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one of the few rewards an inventor receives 1s recognition. An unfortunate been listed among the claims of several other patents,7- and recently 1t has
exPerience for some patents is that they have languished, some for more than been popular to tout this version of PSA as VSA, as discussed in Sections 3.2
five years, while being reviewed m the Patent Office. So, from that pomt of and 6.2. They did not mclude a schematic diagram of thetr process or any
view, the filing date often reveals more about the context of an mventton_ (1.e., information describing performance or t1mmg.
what other ideas were accessible m the public domam) than the date of issue.
Thus, both dates are often mentioned here. In fact, patents are introduced
roughly m chronological order, with cross references to more recent patents C,2,3 Perley
that have used some of the same approaches.
A patent by Perley 10 happened to overlap, not only with the intended
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application, but also with the dates of the patent by Finiayson and Sharp (it
was submitted m 1928, and awarded m 1933). It described a process for
C.2 Inventors and Patents adsorbing carbon monoxide and carbon dioxide from a water gas mixture, to
yield techmcally pure hydrogen. A schematic diagram 1s shown in Figure C.1.
C.2.1 Hasche and Dargan The adsbrbent was regenerated by reducing the pressure and, optionally,
ln their patent application, filed in 1927 and approved in 19311 Hasche and heatmg the adsorbent via ourge gas·. Interestmgiy, the idea of comhinmg
Dargani described a pressure swmg process for recovering sulfur dioxide pressure swmgs with temperature swings 1s still considered novel, and has
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from smelter gases usmg silica gel. In that process, the feed was compressed been covered in recent oatents. -