RogerH (Petroleum):
This is a very important subject because it involves expensive catalyst savings, production time, and safety issues that necessitate the catalyst change-out in a Hydrogen environment. In some cases, it involves vessel entry by humans - a procedure that I always try to eliminate or reduce due to the hazards related to this procedure.
First, let me start by correctly identifying this Unit Operation as CO ADSORPTION, as opposed to CO ABSORPTION. The difference, while it may seem insignificant to some people, is important in that the Adsorbent's selective Sorptivity is involved. This Sorptivity is affected by the adsorbent's age, type, manufacturer, contaminants (poisons), superficial space velocity, channeling, adsorption temperature & pressure, regeneration levels, and cycle times. There are other factors, but what I want to make sure is that you appreciate that the manufacturer designs and controls the quality of the adsorbent (I presume we both agree on Molecular Sieves being the adsorbent of choice here) and, as such, should be the expert you rely on for selection and recommendations. I highly recommend that you work directly with pre-selected and qualified Mol Sieve manufacturers (notice I write "manufacturers" - and not distributors or sales offices). The manufacturer holds the key information on sorptivity design levels and expectations, once they receive your key information (ALL the key information; be honest and candid, don't hold anything back): suspected contaminants, operating procedures with temperatures & pressures, required CO removal rates and levels of concentration that must be achieved. Discuss your priorities in DEPTH with them and explain what you are prepared to trade-off and what you can't trade-off. They should be very detailed and explicit in explaining their recommended cycles, adsorbent and regeneration methods to you - complete with estimated adsorbent quantities, prices, regeneration requirements, and adsorber sizes.
Adsorbent manufacturers can also further recommend engineering and fabrication companies that will design, furnish and warrant a complete Adsorber Packaged unit that will do your specified job - on an automatic or manual operation cycle.
If your Isomerization unit stands to profit from a dehydrated feed stream that is also devoid of CO contamination, than I can save you some consulting bucks by freely advising you that you are headed in the precise and correct process direction when you propose to install a Mol Sieve Adsorption step prior to the Isomerization. I suspect that you are dealing with Big Buck $$savings when you start to economize on catalyst activity - not to mention the potential positive effect of completely dried feed stock. I have used Mol Sieves to reduce water moisture in gases down to 0.5 PPM - a level that is so hard to read and monitor that we finally didn't bother. It works, and it works well. Simultaneous (really, step-wise) adsorption of both water vapor and CO should be a snap. This is routinely done on PSA units (although more emphasis is made on CO2 + water vapor removal).
Molecular Sieves are human-engineered and designed adsorbents as compared with activated carbon, which is designed by Nature. There are Mol Sieves custom-made for CO removal - just as there are for CO2 and water.
I hope this information and experience is helpful.
Art Montemayor
