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The separation of atomic and molecular gases from helium by cataphoresis

Citation

Remer, Donald Sherwood (1970) The separation of atomic and molecular gases from helium by cataphoresis. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/e8fd-be69. https://resolver.caltech.edu/CaltechTHESIS:09032015-135156772

Abstract

The cataphoretic purification of helium was investigated for binary mixtures of He with Ar, Ne, N2, O2, CO, and CO2 in DC glow discharge. An experimental technique was developed to continuously measure the composition in the anode end-bulb without sample withdrawal. Discharge currents ranged from 10 ma to 100 ma. Total gas pressure ranged from 2 torr to 9 torr. Initial compositions of the minority component in He ranged from 1.2 mole percent to 7.5 mole percent.

The cataphoretic separation of Ar and Ne from He was found to be in agreement with previous investigators. The cataphoretic separation of N2, O2, and CO from He was found to be similar to noble gas systems in that the steady-state separation improved with (1) increasing discharge current, (2) increasing gas pressure, and (3) decreasing initial composition of the minority component. In the He-CO2 mixture, the CO2 dissociated to CO plus O2. The fraction of CO2 dissociated was directly proportional to the current and pressure and independent of initial composition.

The experimental results for the separation of Ar, Ne, N2, O2, and CO from He were interpreted in the framework of a recently proposed theoretical model involving an electrostatic Peclet number. In the model the electric field was assumed to be constant. This assumption was checked experimentally and the maximum variation in electric field was 35% in time and 30% in position. Consequently, the assumption of constant electric field introduced no more than 55% variation in the electrostatic Peclet number during a separation.

To aid in the design of new cataphoretic systems, the following design criteria were developed and tested in detail: (1) electric field independent of discharge current, (2) electric field directly proportional to total pressure, (3) ion fraction of impurity directly proportional to discharge current, and (4) ion fraction of impurity independent of total pressure. Although these assumptions are approximate, they enabled the steady-state concentration profile to be predicted to within 25% for 75% of the data. The theoretical model was also tested with respect to the characteristic time associated with transient cataphoresis. Over 80% of the data was within a factor of two of the calculated characteristic times.

The electrostatic Peclet number ranged in value from 0.13 to 4.33. Back-calculated ion fractions of the impurity component ranged in value from 4.8x10-6 to 178x10-6.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Chemistry
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Shair, Fredrick H.
Thesis Committee:
  • Unknown, Unknown
Defense Date:12 May 1970
Funders:
Funding AgencyGrant Number
Atlantic-Richfield FellowshipUNSPECIFIED
NSFUNSPECIFIED
Atomic Energy CommissionUNSPECIFIED
Record Number:CaltechTHESIS:09032015-135156772
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:09032015-135156772
DOI:10.7907/e8fd-be69
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9136
Collection:CaltechTHESIS
Deposited By:INVALID USER
Deposited On:03 Sep 2015 22:27
Last Modified:16 Apr 2021 22:15

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