An Interesting and Novel Approach to Chemical Separations of Which I was Unaware.

[NNadir]

In 2011, the late great Nobel Laureate George Olah proposed a closed carbon cycle to address the on going and accelerating tragedy of climate change: Anthropogenic Chemical Carbon Cycle for a Sustainable Future George A. Olah, G. K. Surya Prakash, and Alain Goeppert Journal of the American Chemical Society 2011 133 (33), 12881-12898

Intrinsic to this concept is access to sustainable energy, of which there is one, and only one form, nuclear energy, since the reduction of carbon dioxide requires the addition of all the energy released when it was created (The First Law of Thermodynamics) plus the energy required to overcome the entropy of mixing connected with dumping it into the environment (The Second Law of Thermodyanmics).

To paraphrase something I read somewhere, although I cannot remember the attribution, "The best time to have discussed this was at least 20 years ago, the second best time is now."

Also intrinsic to this conception, which would include sequestering carbon in products as opposed to dumps, is the chemical separation of chemical products, already an important element of our modern life, for good and for bad, a refinery for dangerous petroleum is essentially a chemical separations plant, relying heavily on the use of distillation, with increasing sophistication.

A paper I came across this morning puts a new wrinkle on distillation, of which I was unaware, although apparently it's been around for sometime adding a dimension to adsorption based technologies (governed by Langmuir and BET theory) by adding centrifugation.

The paper is this one: Radial Temperature Profile Measurements to Understand Mass Transfer in Rotating Packed Bed Distillation
Hina Qammar, Tobias Pyka, Jörg Koop, Andrzej Górak, and Gerhard Schembecker Industrial & Engineering Chemistry Research 2023 62 (38), 15588-15599

From the introductory text:

Tray or packed columns are mostly used in thermal separation processes such as distillation, absorption, or stripping. Although high product purities can be obtained in this gravity-based equipment, the capacity is limited by the diameter of the column and the upper hydrodynamic operating limit, also known as flooding. (1) Alternative equipment to enlarge the operating window is a rotating packed bed (RPB) that utilizes centrifugal force instead of gravity to intensify the contact between the two phases. Compared to static equipment, they hold the potential for an extended operating window providing an intensified mass transfer in compact equipment with added flexibility. (2−5) The rotation of a packed bed induces the centrifugal force to intensify the contact between gas and liquid, passing countercurrently through the packing. The application of high shear forces potentially creates thin films and fine droplets, consequently leading to increased mass transfer. (4,6,7) In an RPB, the packing is mounted inside a rotor that is attached to a shaft and enclosed by a casing. The vapor stream is introduced into the casing and flows radially inward, whereas the liquid is introduced at the inner side of the annular packing and is accelerated radially outward toward the casing due to the centrifugal field. Rotational speed in an RPB offers an additional degree of freedom as the operating window and separation efficiency can be changed by changing the rotational speed. (8−10)

Maldistribution in the gas and liquid phases has been a challenge in both types of equipment, i.e., columns and RPBs. Both equipment types tend to show maldistribution, especially for the liquid phase. (1,11) Since in an RPB, the cross-sectional area of the packing increases from the inner to the outer packing diameter, the liquid load decreases throughout the packing, which may result in dewetting of packing surface areas at some parts. Therefore, liquid maldistribution along the radius of the rotor is expected to account for the reduced mass transfer performance of RPBs. Groß et al. (11) showed the results of Gamma-ray tomography and concluded that rotational speed affects liquid holdup in the packing, and at higher rotational speeds, the liquid holdup reduces rapidly along the radial packing length. Not only does the liquid load become smaller, but the strength of the centrifugal field also increases linearly with the radial position in the rotor.

Furthermore, at the inner diameter of the packing, a liquid ring exists that diminishes almost linearly toward the outer diameter of the packing. (11) Guo et al. (12) conducted a theoretical study using a three-dimensional simulation in an RPB to understand the liquid flow behavior, droplet size, specific surface area, and residence time. The results show that the particular area of liquid droplets increases, whereas the residence time of the liquid in an RPB decreases rapidly with increasing rotational speed. They proposed that increasing the rotational speed or the liquid inlet velocity could help to minimize the liquid maldistribution... (12)

...In this work, the experimental setup developed by Hampel et al. (16) and Qammar et al. (17) is further used with temperature measurements along the rotor’s radius to characterize the mass transfer profile in the packing of an RPB as well as in the casing separately. This work aimed to understand the mass transfer contribution of different sections/zones in an RPB for different rotor configurations and not to achieve the maximum separation efficiency in an RPB. Figure 1 shows an overview of the sensor positions and the process flow of distillation in RPB...

The Hampel paper, which is open sourced is here: Recent Advances in Experimental Techniques for Flow and Mass Transfer Analyses in Thermal Separation Systems Chem. Ing. Tech. 2020, 92, No. 7, 926–948.

I am not a process chemist, although I am professionally required to be aware of process chemistry, but was unaware of this particular approach. The nature of this separation comes under the general rubric of "orthogonality" which is also a component of analytical chemistry, one that is increasingly important and on which I often focus my professional research.

Cool, I think, obscure but important.

[Tetrachloride]

1. I am reminded of the quote below by the "20 years"

Lyautey asked his gardener to plant a tree in a particular part of his estate. The gardener objected that the tree the marshal had chosen was particularly slow-growing and would not reach maturity for at least a century.
The marshal replied, "In that case, there is no time to lose. Plant it this afternoon." Louis Hubert Gonzalve Lyautey (1854 - 1934)

The Fine Art of Political Wit by Leon A. Harris
The Little, Brown Book of Anecdotes, p. 372
Clifton Fadiman

(probably slightly not exact punctuation as in the Fadiman book)

[NNadir]

2. That is a wonderful quote. Thank you very much. n/t.