MICROWAVE REGENERABLE AIR PURIFICATION DEVICE · MICROWAVE REGENERABLE AIR PURIFICATION DEVICE James E. Atwater John T. Holtsnider Richard R. Wheeler, Jr. August 1996 FINAL REPORT

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MICROWAVE REGENERABLE AIR PURIFICATION DEVICE

James E. Atwater

John T. Holtsnider

Richard R. Wheeler, Jr.

August 1996

FINAL REPORT

CONTRACT NAS2-14374

Prepared for:

NASA AMES RESEARCH CENTER

MOFFETT FIELD, CALIFORNIA

UMPQUA RESEARCH COMPANY

P.O. Box 609 - 125 Volunteer Way

Myrtle Creek, OR 97457

Telephone: (541) 863-7770

FAX: (541) 863-7775

E-Mail: [email protected]

Home Page: http://www.quake.net/~umpqua

URC R0647

https://ntrs.nasa.gov/search.jsp?R=19960045813 2020-01-02T20:36:36+00:00Z

MICROWAVE REGENERABLE AIR PURIFICATION DEVICE

James E. Atwater

John T. Holtsnider

Richard R. Wheeler, Jr.

August 1996

FINAL REPORT

CONTRACT NAS2-14374

Prepared for:

NASA AMES RESEARCH CENTER

MOFFETT FIELD, CALIFORNIA

UMPQUA RESEARCH COMPANY

P.O. Box 609 - 125 Volunteer Way

Myrtle Creek, OR 97457

Telephone: (541) 863-7770

FAX: (541) 863-7775

E-Mail: [email protected]

Home Page: http://www.quake.net/~umpqua

URC 80647

TABLE OF CONTENTS

PROJECT SUMMARY .................................................................................................................. 1

I. INTRODUCTION ..................................................................................................................... 2

II EXPERIMENTAL SECTION ................................................................................................... 4

Experimental Approach .......................................................................................................... 4

Sorption-Desorption Studies ............................................................................................... 4

Microwave Spectral Studies ................................................................................................ 4

Materials and Apparatus ......................................................................................................... 5

Microwave Powered Thermal Desporption Apparatus ...................................................... 5

Multifrequency Microwave Transmission and Reflection Apparatus ................................. 9

Sorbernts ........................................................................................................................... 11

Contaminants .................................................................................................................... 11

Analytical Instruments ...................................................................................................... 11

III. RESULTS AND DISCUSSION ............................................................................................ 12

Microwave Powered Thermal Regeneration of Sorbents ..................................................... 12

Sorption and Thermal Desorption of Acetone .................................................................. 13

Sorption and Thermal Desorption of Carbon Dioxide ..................................................... 16

Sorption and Thermal Desorption of Trichloroethylene (TCE) ........................................ 27

Sorption and Thermal Desorption of Water Vapor .......................................................... 32

Sorption and Regeneration of Layered Media for COz, Water Vapor

and Trace Organics .......................................................................................................... 38

Microwave Reflection and Transmission Spectra ................................................................. 44

IV. CONCLUSIONS .................................................................................................................... 61

V. REFERENCES ........................................................................................................................ 63

URC 80647 i

LIST OF FIGURES

1. Microwave Powered Thermal Regeneration Experimental Apparatus ...................................... 6

2. Microwave Power versus Variable Transformer Setting ........................................................... 7

3. Device for Mounting Sorbent Beds in the Rectangular Waveguide .......................................... 7

4. Sparging Apparatus for Humidifying the Contaminated Gas Stream ........................................ 8

5. Multifrequency Microwave Transmission Test Apparatus ...................................................... 10

6. Sorption of Acetone on Activated Carbon ............................................................................... 14

7. Thermal Regeneration of Acetone Loaded Activated Carbon ................................................. 15

8. Sorption of Acetone on Carbosieve S-III ................................................................................. 17

9. Thermal Regeneration of Acetone Loaded Carbosieve S-Ill ................................................... 18

10. Sorption of Acetone on Zeolite ZSM-5 .................................................................................. 19

11. Thermal Regeneration of Acetone Loaded ZSM-5 ................................................................. 20

12. Chemisorption of CO 2 by LiOH ............................................................................................. 22

13. Sorption of CO 2 by Molecular Sieve 5A. ............................................................................... 23

14. Microwave Powered Thermal Decomposition of Silver Carbonate ....................................... 26

15. Sorption of CO 2 on Composite MS/5A. ................................................................................. 28

16. Thermal Regeneration of CO 2 Loaded MS 5A Composite Bed ............................................ 29

17. Sorption of TCE on Activated Carbon .................................................................................... 30

18. Regeneration of TCE Loaded Activated Carbon .................................................................... 31

19. Sorption of TCE on Carbosieve S-Ill ...................................................................................... 33

20. Regeneration of TCE Loaded Carbosieve S-Ill ...................................................................... 34

21. Thermal Regeneration of TCE Loaded ZSM-5 ....................................................................... 35

22. Initial Sorption of Water Vapor on Silica Gel ........................................................................ 36

23. Sorption of Water Vapor on Silica Gel Following Regeneration ........................................... 37

24. Initial Sorption of Water Vapor on Molecular Sieve 13X ...................................................... 39

25. Sorption of Water Vapor on Molecular Sieve 13X Following Regeneration ......................... 40

26. Initial Sorption of Water Vapor on Molecular Sieve 5A ........................................................ 41

27. Thermal Regeneration of Water Loaded Molecular Sieve 5A ................................................ 42

28. Sorption of Water Vapor on Molecular Sieve 5A Following Regeneration ........................... 43

29. Composite Bed: Initial Sorption of CO2, Water Vapor, Acetone and TCE ............................ 45

30. Composite Bed: Repeat Sorption after Microwave Powered Regeneration ........................... 46

31. Relative Transmitted and Reflected Power for Empty Sample Chamber ............................... 47

32. Relative Transmitted and Reflected Power: CECA-8301MC Activated Carbon ................... 48

33. Relative Transmitted and Reflected Power: Alltech 5769 Activated Carbon ......................... 49

34. Relative Transmitted and Reflected Power: Lithium Hydroxide ........................................... 5035. Relative

36. Relative

37. Relative

38. Relative

39. Relative

Transmitted and

Transmitted and

Transmitted and

Transmitted and

Transmitted and

Reflected Power: Molecular Sieve 5A. ......................................... 51

Reflected Power: Molecular Sieve 13X. ....................................... 52

Reflected Power: Silica Gel .......................................................... 53

Reflected Power: Silica Gel with Adsorbed Water ...................... 54

Reflected Power: Silver Carbonate ............................................... 55

URC 80647 ii

LIST OF FIGURES (Continued)

40. Transmitted Power Phase Shift:Top-Empty Cell, Bottom-CECA-830IMC ........................... 56

41. Transmitted Power Phase Shift:Top-5769 Activated Carbon, Bottom: LiOH ....................... 57

42. Transmitted Power Phase Shift: Top-MS 5A, Bottom-MS 13X ............................................ 58

43. Transmitted Power Phase Shift: Top-Dry Silica Gel, Bottom-Wet Silica Gel ....................... 59

44. Transmitted Power Phase Shift: Silver Carbonate .................................................................. 60

LIST OF TABLES

I. Summary of Individual Sorption/Regeneration Experiments ................................................... 12

II. Waveguide Microwave Heating Tests Results at 2.45 GHz .................................................... 60

URC 80647 "ffi

PROJECT SUMMARY

Feasibility of the use of microwave heating for the fast and efficient thermal

regeneration of sorbents for the removal of carbon dioxide, water vapor, and trace organics

from contaminated air streams has been conclusively demonstrated. The use of microwave

power offers several advantages, including: improved heat transfer, lower thermal losses,

improved power utilization, and enhanced operational capabilities.

During the Phase I research the sorption and microwave powered thermal desorption

of acetone, trichloroethylene (TCE), carbon dioxide, and water vapor was studied at 2.45 GHz

using a rectangular waveguide based test apparatus. Both activated carbon and Carbosieve S-

III were identified as excellent microwave regenerable sorbents for use in the removal of

airborne organics. Water loaded silica gel, Molecular Sieve 13X, and Molecular Sieve 5A

were also effectively regenerated under microwave irradiation at this frequency. Molecular

Sieve 5A and a earbogenie molecular sieve prepared at NASA's Jet Propulsion Laboratory

were identified as viable microwave regenerable CO 2 sorbents. A sorbent bed containing

multiple media was challenged with air containing 0.5% CO2, 300 ppm acetone, 50 ppm TCE,

and saturated with water vapor. The composite bed was shown to effectively purify the

contaminated air stream and to be completely regenerated by microwave induced heating.

Spectral studies of the reflection, transmission, and phase shifts of microwaves for a

variety of sorbents over the frequency range between 1.3 - 2.7 GHz have shown that the

dielectric loss characteristics are strong functions of frequency and material. Frequencies have

been identified with potential for more effective microwave heating of specific sorbents since

these loss characteristics are responsible for microwave heating. Based upon these results,

further development of this highly promising technology is highly recommended.

In addition to the obvious applicability to EVA and Advanced Life Support, two

specific systems with strong potential for commercial application have also been identified.

These are the acetone-Carbosieve S-I/I and TCE-ZSM-5 combinations. The first system

represents an environmentally benign method for the recovery of waste solvents in a variety of

industrial chemical processes. Using the highly selective carbon based molecular sieve, and the

extremely rapid thermal desorption capabilities inherent to microwave heating, acetone (or

similar solvents) can be recovered from waste gas streams by sorption and then concentrated

by flash thermal desorption for collection by condensation. The second commercial application

exploits the fact that ZSM-5 is not only a sorbent for removal of airborne trichloroethylene, it

is also an effective catalyst for the deep oxidation of this contaminant, particularly in the

chromium form. Thus, the TCE-ZSM-5 system forms the basis for a combined environmental

remediation process to achieve both the separation and the ultimate destruction of TCE.

URC 80647 - 1 -

L INTRODUCTION.

An investigation has been conducted to determine the feasibility of using microwave

power to promote thermal regeneration of sorbents applicable to the life support requirements

of astronauts during Extravehicular Activity (EVA). The primary advantages inherent to the

use of microwaves are the increases in energy efficiency which result from the heating of

materials by direct absorption of energy (in contrast to the indirect supply of heat by thermal

conduction from heating elements), and the extremely rapid rates of heating which are possible.

This maximizes the efficiency of energy transfer and minimizes conductive, convective, and

radiative losses as well as the need to heat additional thermal mass I. These features suggest

the possibility of a more compact and thermally efficient technology for the removal of CO2,

I_O, and trace organic contaminants from air during EVA. A second generation thermally

regenerable air purification system is envisioned in which microwave power is applied directly

to the PLSS via coaxial cable, thus providing a means for regeneration which does not require

removal of sorbent cartridges from the EMU. A third generation system could provide

capability for sorbent regeneration during EVA. While the current investigation has been

directed specifically toward EVA, the operational efficiencies which can be gained by the use

of microwave power may apply equally to other life support requirements such as Air

Revitalization within the cabin of spacecraft or within other enclosed space habitats.

Susceptibility to microwave heating is a function of the dielectric properties of the

material. Microwaves encompass the upper end of the radio frequency (RF) electromagnetic

spectrum. Due to their relatively long wavelengths, the behavior of microwaves is different in

many respects from that of more energetic (and for most researchers more familiar) regions of

the spectrum such as IR, visible, and UV light. If a high frequency RF signal is applied to a

conductor, a current will flow. If the same signal is applied to a non-conductor (i.e. a

dielectric material) then electromagnetic waves are propagated. If the electromagnetic energy

is absorbed by the dielectric, the temperature of the material rises in proportion to the energy

absorbed. The most common embodiment of microwave heating is the microwave oven in

URC 80647 - 2 -

which 2.45 GHz microwaves couple primarily with the rotational transitions of dipolar water

molecules. Different dipole-dipole loss phenomena occur in solids such as silicon carbide (SIC)

and barium titanate (BaTiO3) which couple very effectively with microwaves. In these

materials the frictional losses which result in the generation of heat are manifested through

oscillatorily induced polarizations (Maxwell-Wagner effect, etc.) rather than by rotationally

induced internal friction2-L

In concept, microwave powered thermal regeneration of a loaded adsorbent can occur

via three possible mechanisms: 1) the adsorbent only couples with the microwaves; 2) both

adsorbent and sorbate couple; and 3) the sorbate only couples. From an energy efficiency

perspective, the latter mechanism offers the greatest potential savings in comparison to

conventional thermal regeneration methods. Similar mechanisms apply to sorbents such as

lithium hydroxide (LiOH) and silver oxide (Ag20) in which the contaminant is chemically

bound, i.e., as Li2CO 3 and Ag2CO3, respectively. Regeneration of chemisorbed materials will,

in general, require higher temperatures, longer regeneration times, or both. The ability of

microwave heating to achieve extremely rapid heat-up to very high temperatures may be a

particular advantage when applied to the regeneration of these sorbents, and may make

possible the regeneration of sorbents which otherwise would not be practical.

For the purposes of the initial investigation, a representative variety of candidate

sorbent materials which are potentially useful in the removal of airborne water vapor, CO2, and

trace organics were screened for susceptibility to thermal regeneration using microwave

power. These experiments were conducted at 2.45 GHz. In addition, because the

susceptibilities of materials to microwave heating vary with the frequency of incident radiation,

a variety of sorbent materials were also screened for their dielectric loss characteristics over a

range of frequencies between 1.37 - 2.6 GHz. In these experiments, bulk properties were

measured, with contributions arising from both the sorbent and the gas phase filling the pores

and intergranular spaces 4-9.

URC 80647 - 3 -

IL EXPERIMENTAL SECTION.

Experimental Approach. To explore the usefulness of microwave power for the thermal

regeneration of sorbents, the Phase I research effort focused on two primary areas of

experimentation: 1) characterization of the susceptibility of a typical range of sorbents loaded

with common airborne contaminants toward microwave powered thermal regeneration using

2.45 GHz microwaves; and 2) investigation of the spectral responses of sorbents over a range

of incident microwave frequencies to determine if particular regions of the microwave

spectrum exist which may be especially well suited for use with a particular sorbent.

Sorption-Desorption Studies. A variety of sorbents were selected for study, including:

activated carbon, carbon based molecular sieves, lithium hydroxide, silica gel, silver oxide, and

zeolite molecular sieves. Acetone, carbon dioxide, trichloroethylene, and water vapor were

selected as challenge contaminants. Small packed sorbent beds were exposed to humidified air

streams containing the appropriate contaminants and the relationships between cumulative flow

and breakthrough of the sorbates were monitored. Once breakthrough occurred, the sorbents

were exposed to microwave energy and the bed temperatures and effluent gas concentrations

were monitored. For the cases in which successful thermal regeneration was indicated, this

was confirmed by a subsequent re-loading of the sorbent with the contaminant to ensure that

substantial sorption capacity had been regained.

Microwave Spectral Studieg Low power studies were conducted to examine the dielectric

loss characteristics of a selection of typical sorbent materials over a range of frequencies. The

dielectric loss properties determine a material's susceptibility to microwave heating. These

properties are functions of both frequency of the incident microwave radiation and of the

temperature of the medium. Owing to the time and monetary constraints inherent to the Phase

I effort, room temperature experiments were conducted over the relatively narrow range of

frequencies between 1.3 - 2.7 GHz. A vector network analyzer based system was assembled

URC 80647 -4-

to monitor three properties of each test specimen: relative reflected power, relative transmitted

power, and the phase shitt of the transmitted power.

Materials and Apparatus.

Microwave Powered Thermal Desorption Apparatus. The microwave transmission and

irradiation testbed is illustrated in Figure 1. The apparatus is composed of a series of WR 430

rectangular waveguide elements, and includes a magnetron, shorting plate, waveguides,

directional coupler, solid state microwave detector, RF power meter, and a water load. An

800 W magnetron, emitting at 2.45 GHz, is located in the launcher waveguide section. The

launcher section is terminated at one end by a shorting plate located at a distance of IA

wavelength from the magnetron antenna. At the opposite end of the launcher section

microwaves are transmitted in the transverse electric (TE) mode into the test chamber

waveguide section where packed sorbent beds are placed in the microwave field. The launcher

waveguide section is connected to a 60 dB directional coupler instrumented with a Hewlett-

Packard (HP) 478A solid state microwave transducer and Ht ) 432A power meter. Any

microwave energy which has not been absorbed passes into a water load which serves as a sink

for excess energy to prevent the reflection of microwaves backward through the waveguide

components toward the magnetron. Water circulates through the load at a flow rate of _ 1

L/rain under the action ofa Micropump (Concorde, CA) #120-000 pump with #7144-00 gear

drive. Microwave power output is controlled by a variable transformer which controls the

voltage to the magnetron power supply. The relationship between variable transformer

settings and output power is illustrated in Figure 2.

The packed sorbent beds are held in place within the test chamber using the mechanism

illustrated schematically in Figure 3. The device is mounted vertically through the center of the

test chamber waveguide section. The packed sorbent bed is confined within length of quartz

tubing with an internal diameter of 1.07 cra, and held in place using glass wool end plugs. The

sorbent bed is positioned so that the mid-point of the packed bed is in the exact center of

URC 80647 - 5 -

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URC 80647 - 6 -

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Figure 3. Device for Mounting Sorbent Beds in the Rectangular Waveguide.

URC 80647 - 7 -

thewaveguide. Gas enters from the bottom and flows upward through the sorbent bed. A J-

type thermocouple is mounted inside.

Challenge gases were fed into the apparatus from compressed gas cylinders, with initial

pressures ranging from 15.5 - 20.7 MPa (2250 - 3000 psi). The gas stream passed through

primary and second stage pressure regulators, to an Aalburg Instruments #052-04gG variable

area flow meter (Cole-Parmer, Chicago, IL), and then through the sparging chamber illustrated

in Figure 4, in which the stream was saturated with water vapor. In the case of CO2 sorptions,

the liquid within the sparging vessel was maintained at an acidic pH and was pre-saturated with

the contaminant before flow into the packed sorbent bed was initiated. In the case of the

organic contaminants, the aqueous phase consisted of a solution with an amount of dissolved

organic compound sufficient for equilibrium to exist between the gas phase and the liquid

phase, according to Henry's Law,

kH = pC2"

where kn is the Henry's Law constant, pC is the atmospheric partial pressure of the

contaminant in atmospheres, and Z is the mole fraction of the dissolved contaminant.

Figure 4.

Gas InletGas Outlet

Sparging Apparatus for Humidifying the Contaminated Gas Stream.

URC 80647 - 8 -

Multi.frequency Microwave Transmission and Reflection Apparatus. A network analyzer

based system was assembled to measure the dielectric loss characteristics of candidate sorbents

over the frequency range between 1.3 - 2.7 GHz. The apparatus is illustrated schematically in

Figure 5. Variable frequency microwaves are output via coaxial cable from the Hewlett-

Packard (I-IP) Model 8754A Vector Network Analyzer sequentially to: 1) a frequency doubler

(MA-COM D-6-4), 2) an HP Model 778D dual directional coupler, and 3) a coaxial cable to

WR 430 rectangular waveguide adapter. Attenuated signals representing both incident and

reflected power levels are routed back to the network analyzer from the directional coupler.

Microwaves are transmitted through the WR 430 rectangular waveguide in the transverse

electric (TE) mode. The microwaves pass through a WR 430 to WR 650 waveguide transition

and into the Specimen Confinement Chamber. The Specimen Chamber consists of a hollow

rectangular box (18 x 12.9 x 3 cm) with an internal volume of 414 cm 3, constructed from 0.48

cm thickness polycarbonate sheets. The path length for microwave travel through the chamber

is 2.05 cm. Microwaves reflected by the specimen travel in the reverse direction via the

directional coupler to the network analyzer. Microwaves transmitted through the Specimen

Confinement Chamber pass through a WR 650 to WR 430 transition into a WR 430 to coaxial

cable adapter, and then by coaxial cable to the network analyzer. The network analyzer

sweeps through the entire frequency range at a pre-determined sweep rate. Output power,

reflected power, and transmitted power levels are monitored by the network analyzer and

analog signals are output to a Hewlett-Packard Model 75900 X-Y plotter and also, via analog

to digital converter (DATAQ DI180), to an IBM Compatible 80486 personal computer for

data storage. In essence the waveguide sections form two symmetrical 'horn antennas' which

surround the specimen and present the microwaves as a plane wavefront to the specimen.

Dielectric loss characteristics are determined from a comparison of transmitted and reflected

power, and from the related phase relationships, in comparison to the incident power.

URC 80647 - 9 -

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URC 80647 -10-

Sorbents. Type 830IMC activated carbon was acquired from CECA, Inc. (Tulsa, OK).

Coconut Shell Charcoal, #5769, was purchased from Alltech (Deerfield, IL). Carbosieve S-III

carbon based molecular sieve was acquired from Supelco (Belefonte, PA). A second carbon

based molecular sieve was prepared by Dr. Pramad Sharma at the Jet Propulsion Laboratory

using the methods of Foley l°. Lithium hydroxide was purchased from Cyprus Foote Mineral

Company (Kings Mountain, NC). Molecular sieves 5A and 13X were donated by UOP (Des

Plaines, IL). Silica gel was acquired from EM Science (Gibbstown, NJ). Silver carbonate was

purchased from Aldrich (Milwaukee, WI). Zeolite ZSM-5 catalyst was donated by Mobil

Corporation (Paulsboro, NJ). Pelletized silver oxide was prepared using a sodium silicate

binder.

Contaminants. Compressed gas cylinders containing 0.5% carbon dioxide in air were obtained

from Pacific Airgas (Portland, OR). Acetone and trichloroethylene were obtained from

Aldrich (Milwaukee, WI). Separate contaminated air feed streams containing 300 ppm

acetone and 50 ppm trichloroethylene (TCE) were prepared by addition of the appropriate

volume of contaminant into evacuated high pressure gas cylinders, followed by pressurization

with breathing quality air to 15.5 MPa (2250 psi) for steel cylinders and to 20.7 MPa (3000

psi) for aluminum cylinders.

Analytical Instruments. Carbon dioxide concentrations were determined using an ASTRO

Model 2001 TIC/TOC analyzer (League City, TX) and an ASTRO 5600AT continuous on-line

non-dispersive infrared (NDIR) CO 2 monitor. Trichloroethylene and acetone were determined

using an HP-5710A gas chromatograph with a packed SP-1000 column (Supelco, Belefonte,

PA) and flame ionization detection. Water vapor was monitored using an EG&G Model 880

Dew Point Hygrometer. Continuous hydrocarbon monitoring was performed using a Beckman

Model 400 Hydrocarbon Analyzer.

URC 80647 - 11 -

HI. RESULTS AND DISCUSSION.

Microwave Powered Thermal Regeneration of Sorbents.

The sorption and microwave powered thermal desorption characteristics of carbon

dioxide, water vapor, acetone and trichloroethylene (TCE) were studied using a range of

typical sorbent materials. Because of the diversity of the chemical properties of the

contaminants, no individual sorbent was appropriate for the removal of all airborne species.

The single-sorbent/single-contaminant experiments conducted are summarized in the matrix

presented in Table I.

Table I - Summary of Individual Sorption/Regeneration Experiments.

Acetone C02 TCE Water

Activated Carbon + +

Carbosieve S-Ill + + -

Lithium Hydroxide - + - -

Molecular Sieve 5A - + +

Molecular Sieve 13X - + +

Silica Gel - - +

Silver Oxide - + - -

Zeolite ZSM-5 + - + -

Initial regeneration experiments using the waveguide based microwave irradiation

apparatus were terminated prematurely due to the destruction of the thermocouple.

Apparently, the grounded thermocouple positioned within the low loss material became an

efficient absorber (antenna) and heated rapidly. This was confimaed when temperatures >1000

°C were indicated Within a few seconds of full power irradiation ofa LiOH bed confined within

URC 80647 - 12 -

a quartz tube. In this case, it was evident that the temperature was that of the thermocouple,

and not that of the packed bed. For this reason, in subsequent experiments the thermocouple

was positioned in the exit gas stream. In this location, a few centimeters away from the

sorbent bed and the microwave field, the temperature of the effluent gas emanating from the

packed bed during regeneration was indicated. The experiments utilizing activated carbon

were the single exception. Activated carbon was found to couple so strongly with the

microwave radiation, that an embedded thermocouple was shielded and thus not affected.

Sorption and Thermal Desorption of Aceton_ Activated carbon, Carbosieve S-III, and ZSM-

5 were investigated as candidate thermally regenerable acetone sorbents for use with

microwave powered heating systems. Based upon previous work, activated carbon and

Carbosieve were known to sorb acetone strongly_m, m2. Further, Carbosieve S-III had been

identified as a selective sorbent for low molecular weight species such as acetone and methyl-

ethyl-ketone. In addition, the performance of ZSM-5, a high silica synthetic zeolite was also

studied. ZSM-5 is commonly used as an industrial catalyst for a variety of synthetic reactions.

A 4.95 cm 3 packed bed of activated carbon (2.13 g) was prepared using #5769 coconut

shell charcoal. In the initial sorption experiment, 300 ppm of acetone in air saturated with

water vapor was fed to the sorbent bed at a flow rate of 1 L/min. Effluent acetone levels were

monitored by an on-line hydrocarbon analyzer and confirmed by gas chromatography. Initial

breakthrough was noted after 99 liters of flow. Fifty percent breakthrough occurred at 120 L.

Complete breakthrough was observed after 150 L of cumulative flow. The loaded activated

carbon bed was thermally regenerated using an initial power level of 23 W under a dry nitrogen

flow at 0.1 L/min. At this relatively low level of incident radiation, bed temperatures of 180°C

were attained. Upon increasing the power to 35 W, maximum bed temperatures of 380°C

were observed. The adequacy of thermal regeneration was confirmed by a repeat sorption.

Equivalent performance was attained prior to and after thermal regeneration. The results of

sorption and regeneration experiments are presented in Figures 6 and 7, respectively.

URC 80647 - 13 -

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URC 80647 - 14 -

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Figure 7. Thermal Regeneration of Acetone Loaded Activated Carbon.

URC 80647 - 15 -

A 1.9 cm 3 bed containing 1.36 g of Carbosieve S-HI was challenged with humidified

air containing _ 300 ppm acetone at 1 L/min. Initial breakthrough occurred after 90 liters of

cumulative flow. Fifty percent breakthrough and total breakthrough were observed at 150

liters and 240 liters, respectively. The acetone loaded bed was thermally regenerated using

stepwise increasing applied microwave power levels between 86 - 600 W, corresponding to

exit gas temperatures between 90 - 230°C. The bulk of the acetone was desorbed at the 86 W

power level. A subsequent sorption experiment confirmed the adequacy of the microwave

powered thermal regeneration. Sorption and desorption experimental results are shown in

Figures 8 and 9, respectively.

A 2.87 g packed bed containing 4.95 cm 3 of ZSM-5 catalyst in the hydrogen form was

challenged with _ 240 ppm acetone in humidified air at 1 L/rain. Breakthrough began after 20

L of flow. Fifty percent breakthrough was observed at 83 L, and total breakthrough occurred

after 160 L of cumulative flow. The bed was thermally regenerated at full microwave power

(780 W). The thermocouple was located in the exit gas stream, and indicated a maximum

temperature of_ 80°C. A repeat sorption experiment was conducted using 236 ppm acetone

in humidified air. The breakthrough characteristics observed during the second run indicated

that the ZSM-5 bed had been adequately regenerated. The results of the sorption and

regeneration experiments are presented in Figures 10 and 11, respectively.

Sorption and Thermal Desorption of Carbon Dioxide. CO 2 sorption experiments were

conducted using lithium hydroxide, Molecular Sieve 5A, the carbogenic molecular sieve

prepared at JPL, silver carbonate, and silver oxide.

A lithium hydroxide bed containing 1.62 g was challenged with 0.5% CO 2 in dry air at

1 L/min. Effluent CO 2 levels were determined on individual samples using a TICfrOC

analyzer. A thermal regeneration was attempted for 15 minutes at 780 W microwave power

using dry nitrogen. In this experiment maximum effluent gas temperatures reached 5 I°C after

eight minutes and remained steady thereafter. The total effluent was collected

URC 80647 - 16 -

00 .... I .... I .... I .... ! .... I .... I .... I .... i .... i .... i ....

250

--_ 200EQ.Q.

• 150t-O

loo

50

0

3OO

0

f

''''f''''i .... I''''f''''l .... I .... f .... I''''i''''l''''

25 50 75 100 125 150 175 200 225 250 275

Cumulative Flow (L)

''''1''''1''''1 .... I''''1''''1''''1 .... I .... I''''1''''

25O

200E

O.v

• 1501--0

_100

50

0

J

f

''''l''''i''''l''''l''''l''''l''''l''''l''''l''''l''''

0 25 50 75 100 125 150 175 200 225 250 275

Cumulative Flow (L)

Figure 8. Sorption of Acetone on Carbosieve S-III: Top Imti_, Bottom After Regeneration.

URC 80647 -17-

25000

EO.O.

v

¢-O

8<C:(l)

EIii

20000

15000

10000

5O00

0

0 1 2 3 4 5 6 7 8 9 10 11 12

Cumulative Flow (L)

250 .... , .... , .... , .... , .... , .... , .... , .... , .... , .... , .... , .... 800

.--. 200oq...

(_ 150O

E

100(/)

(.9

50

i

700

..................................................................................................................................................600 _.

Temperature.................Power

.... I .... ! .... I .... [ .... I .... I .... I .... I .... I .... I .... [ ....

1 2 3 4 5 6 7 8 9 10 11

40o>

300.D

200 :_

100

0

2

Cumulative Flow (L)

Figure 9. Thermal Regeneration of Acetone Loaded Carbosieve S-III.

URC 80647 -18-

250

200

A

E150

e'sV

tDr-

_ 100

50

0

' ' ' I ' ' ' I ' ' ' I ' ' ' I ' ' ' I ' ' ' I " " 1 l ' I ' I ' ' I i ' I '

0' ' I ' ' ' I ' ' ' I " ' ' I ' ' ' I ' ' ' I ' ' ' I ' ' ' I ' ' ' I ' ' '

20 40 60 80 100 120 140 160 180 200

Cumulative Flow (L)

250

200

E 150

c

8 100<

50

0

0 20 40 60 80 100 120 140 160 180 200

Cumulative Flow (L)

Figure 10. Sorption of Acetone on Zeolite ZSM-5: Top Initial, Bottom After Regeneration.

URC 80647 -19-

A

EO.Q.

v

Q)c-

O

8<t-O

EUJ

25000

20000

15000

10000

5OOO

'1 I ......... I

_ Saturated FID Response

0 1 2 3 4 5 6

Cumulative Flow (L)

100

90

.-. 800o._.

70

co 60O

E 50

40

0 30

10

0

TemperaturePower

1 2 3 4 5 6

Cumulative Flow (L)

7

8O0

7OO

600500 _

0

400 _>

300o_

200 _

100

0

]Figure 11. Thermal Regeneration of Acetone Loaded ZSM-5.

URC 80647 -20-

in a gas-tight bag which yielded a CO 2 concentration of 0.04%. Following this regeneration

attempt, the bed was challenged with 0.5% CO 2 in air saturated with water vapor. Under these

conditions additional CO 2 was adsorbed. This is believed to be due to the facilitation of the

chemisorption reaction by the presence of water. For this reason, the sorption from humidified

air was repeated using a fresh LiOH bed. The results of the dry and wet air sorptions are

presented in Figure 12. This was followed by a second attempted thermal desorption using

nitrogen saturated with water vapor. The effluent gas reached a maximum temperature of 55 °

C. The effluent gas yielded an average CO 2 concentration of 0.06%. While the LiOH bed

coupled with the microwave field to a minor extent, temperatures achieved were not sufficient

to reverse the chemisorption of CO 2.

In order to achieve the higher temperatures required for reversal of the reactions

responsible for chemisorption of CO 2 by LiOH, a composite bed was prepared consisting of

90% LiOH and 10% activated carbon by weight. This bed was exposed to the full microwave

power of the waveguide irradiation system (780 W). Under these conditions, the quartz tube

melted after an exposure of less than one minute, indicating that bed temperatures in excess of

1470°C had been attained. Clearly, very high temperatures can be achieved using a composite

bed. However, owing to the constraints of time, this line of investigation was discontinued.

A packed bed containing 2.81 g of Molecular Sieve 5A was challenged with dry air

containing 0.5% CO 2 at a flow rate of 1 L/min. The initial breakthrough occurred almost

immediately. Fifty percent breakthrough occurred at approximately 6 liters of cumulative flow.

Total breakthrough was observed after 50 liters. Regeneration was conducted using full

microwave power and dry nitrogen at 0.1 L/min. Gases were collected in impermeable bags

for analysis. During thermal desorption the effluent gas temperature rose to a maximum of 55 °

C. The results of sorption and regeneration experiments are shown in Figure 13. Integration

of the breakthrough curve yielded a total mass loading of 56 mg CO2, corresponding to 2% of

the initial sorbent bed weight. The microwave powered thermal desorption yielded 75 mg

CO 2. The discrepancy is believed due to the sorption of CO 2 by the sorbent bed during

URC 80647 -21-

0.50 . . . , . . . , .... , , , , . . , ' I ' " ' ' I

0.45

0.40

"-" 0.35

-_ 0.:30,m

X

.o 0.25aCo 0.20f,,,..

(j 0.15

0.10

0.05

0.00

/

, , , , , , , , .... , , , , , , .I I

0 50 100 150 200 250

Cumulative Flow (L)

f

I ' ' I ' '

300 350

.50 .... I ' ' ' I ' ' ' I ' I _ ' ' ' I I .... l ' "

0.45

0.40

0.35(l)

"o 0.30.DX

.o 0.25DCo 0.20-e

o 0.15

0.10

0.05

0.00

f

J

' ' ! ' ' ' I ' ' I ' ' I ' ' ' I ' ' I ' ' ' ' I '

0 50 100 150 200 250 300 350

CumulaUve Flow (L)

Figure 12. Chemisorption of COa by LiOH: Top-dry sorption, Bottom-wet sorption

URC 80647 - 22 -

,6 '''''''''l'''''''''l'''''''''l'''''''''l' ...... ''1'''''''''

0.5

o_ 0.4(1)

X0i:5 o.3e-o

m 0.2rO

0.1

0.0

tJ

f

0IJ;llrlllllllllll=l|ll=lllllrllllJl_r_llllllllWlrlllllllllj

10 20 30 40 50 60

Cumulative Flow (L)

3.0 6O

02 ,.-'"' ....................................................................

o_2.5 .......... .................Temperature

•o_ 2.0_3

1.5

_ 0.5

0.0

0 1 2 3 4 5 6

Cumulative Flow (L)

m

40 ._

a0 _I--

20 _

0

Figure 13. Sorption of CO2 by Molecular Sieve 5A (top), and Regeneration (bottom).

URC 80647 -23-

exposure to the atmosphere prior to initiation of the experiment. The carbon dioxide levels

recovered upon heating indicated a complete regeneration &the Molecular Sieve 5A.

A 1.8 cm 3 packed bed containing the total supply of carbogenic molecular sieve

prepared for us by JPL (0.52 g) was challenged with humidified air containing 0.5% CO 2 at 1

L/rain. The first sample of effluent was collected after 2 L of cumulative flow and indicated

total breakthrough of CO 2. The subsequent thermal desorption experiment was invalidated

because the glass wool plug at the outflow face of the bed melted, and the packed bed was

pushed beyond the microwave radiation field inside the waveguide. It is noteworthy that the

softening point for borosilicate glass is _ 700°C. This temperature was apparently achieved

inside the packed bed, while the indicated exit gas temperature never exceeded 92°C. This

result suggests strong coupling between the earbogenie molecular sieve and the incident 2.45

GHz radiation. The bed was repacked and the glass wool plugs were repositioned so that they

did not make physical contact with the sorbent bed, and also were located outside the

microwave field. Preliminary tests indicated that the repacked bed was neither moved nor

fluidized by the 1 L/min air flow.

The sorption experiment was repeated with identical results; atter 2 minutes (the time

of the first sample collection) total breakthrough of CO 2 was evident. The subsequent

regeneration was conducted under reduced power (_, 390 W) to avoid the extreme

temperatures encountered previously. Thermal desorption was conducted under dry nitrogen

flowing at 0.1 L/min. A maximum outlet gas temperature of 57°C was observed. The effluent

gas was collected in 1 L gas-tight bags at 10 minute intervals. The analysis of the first sample

indicated 0.13% CO 2. Subsequent samples contained no carbon dioxide. Assuming ideality

and a temperature of 20°C inside the gas bag, this corresponds to 2.38 mg of CO 2 (0.5% of

bed weight).

Following this, a third sorption was conducted. This time total breakthrough was not

achieved until 7 minutes into the experiment. The subsequent thermal desorption yielded 5.49

mg CO2, corresponding to approximately 1% of the sorbent bed's weight. Performance of the

URC 80647 -24-

sorbentwas apparently improving over subsequent regenerations. It is not known whether the

performance of this material was adversely affected by the temperatures > 700°C achieved

during the first series of experiments. Also, considering the very small volume of sorbent

available, the very high face velocity, and the highly unfavorable ratio of bed length to volume

under which these tests were conducted, that any CO 2 sorption was observed must be taken as

a preliminary positive result for this material. Further work with sufficient quantities of

material of known pore size distribution should be conducted.

As an initial evaluation of the potential for microwave powered regeneration of silver

oxide based CO 2 sorbents, a packed bed containing 0.68 g of powdered reagent grade Ag2CO 3

was irradiated at full power (780 W) under a dry nitrogen flow of 0.1 L/min. No increase in

the exit gas temperature above ambient was observed after 5 minutes. Following this

experiment a bed containing 2.00 g of Ag20 pellets prepared using a sodium silicate binder

was irradiated for four minutes under similar conditions. The exit gas temperature stabilized at

43°C. The bed was quickly opened and a surface temperature of 159°C was indicated by an

IR thermometer. Grain boundary effects are know to be important in dielectric loss

mechanisms. This may explain the difference in behavior between the powder and the pellets.

While the heating achieved in the silver oxide pellets under microwave irradiation was

significant, the temperatures achieved were still less than the typical 220°C at which silver

oxide sorbents are regenerated. To explore the possibility of attaining higher temperatures, a

3.60 cm 3 composite bed containing 1.14 g of silver carbonate and 0.76 g of activated carbon

was prepared. This bed was irradiated using a stepwise increase in microwave power under

dry nitrogen flowing at 0.1 L/min. The effluent was collected in gas-tight bags and analyzed.

Considerable carbon dioxide was produced. The experimental results are shown in Figure 14.

Maximum exit gas temperatures of 183°C were recorded at full power. Inspection of the bed

after irradiation indicated that the silver carbonate had been reduced to metallic silver. This

was most probably because decomposition temperatures (300°C) were achieved within the

bed. The reducing activity of the activated carbon may have been a contributing factor.

URC 80647 -25-

11 200

10

,-,, 9v

"u°_

x 7.o_E3,.. 6o-2 5¢o

4c(D= 3

EuJ 2

1

0

...""

//

/

i

CO2

.................Temperature

0 1 2 3 4 5 6

Cumulative Flow (L)

175

0150 °v

,¢

125 "_

(:2.loo E

I--75 _

50 _Xu.I

25

0

Figure 14. Microwave Powered Thermal Decomposition of Silver Carbonate.

A 2.97 cm3composite bed was prepared containing 2.00 g of Ag20 pellets and 2.27 g

of powdered (t-silicon carbide. The initial brownish coloration of the Ag20 indicated that the

sorbent was at least partially loaded with CO 2. The Ag20-SiC composite bed was irradiated at

245 W with water saturated nitrogen flowing at 0.1 L/min and effluent CO 2 levels were

monitored continuously. Immediately upon application of power, effluent CO 2 levels rose

above the 5,000 ppm upper limit of the NDIR detector and remained off scale for sixteen

minutes. An effluent carbon dioxide concentration of_ 24,500 ppm was determined for a gas

sample collected during this period. Exit gas temperature reached a maximum of _ 72°C.

Following regeneration, a bed temperature of 269°C was measured using an IR thermometer.

This indicated that temperatures were probably not high enough within the bed to promote

decomposition of the silver oxide during the thermal desorption. The regenerated Ag20-SiC

bed was challenged with 0.5% CO 2 in humidified air at 0.32 L/min. Fifty percent breakthrough

URC 80647 - 26 -

occurred in 1.5 minutes. Seventy five percent breakthrough was seen at 16 minutes, and

complete breakthrough was evident at 50 minutes.

To investigate the compatibility of a molecular sieve CO 2 sorbent and a strong

microwave susceptor, a composite bed containing 1.05 g Molecular Sieve 5A and 0.87 g

activated carbon was challenged with 0.5% carbon dioxide in dry air at a flow rate of 320

mL/min. Effluent CO 2 levels were tracked continuously using an on-line NDIR analyzer.

Following sorption, the bed was thermally regenerated using microwave power levels ranging

from 39 - 210 W. The adequacy of thermal regeneration was confirmed by a second sorption,

yielding virtually identical results. The sorption and regeneration experimental results are

illustrated in Figures 15 and 16, respectively.

Sorption and Thermal Desorption of Trichloroethylene (TCE). The sorption and microwave

powered thermal desorption characteristics of trichloroethylene (TCE) were studied using

activated carbon, Carbosieve S-III, and ZSM-5.

A 4.95 cm 3 activated carbon bed weighing 2.21 g was challenged with _. 50 ppm TCE

in humidified air at a flow rate of 1 L/min. In this experiment, sorption was limited by kinetics.

Initial steady-state effluent TCE concentrations were _. 6 ppm and began rising to higher levels

between 400 - 500 L of cumulative flow. The TCE loaded activated carbon bed was

regenerated under nitrogen at 0.1 L/min. During regeneration a maximum sorbent bed

temperature of 525°C was observed at a microwave power level of 38 W. Following thermal

regeneration, a second sorption was conducted, yielding results similar to that of the first

sorption, indicating that a complete reactivation of the bed had been achieved. The two

sorption events are depicted in Figure 17. Concentration, temperature and power profiles for

the microwave powered thermal desorption are illustrated in Figure 18.

An attempt was made to load a 5 cm 3 bed containing 3.46 g of Carbosieve S-III.

Challenged with 50 ppm TCE, breakthrough had not begun after 1255 L of cumulative flow.

URC 80647 -27-

0.50

0.45

0.40

o_ 0.35

(1.)"o 0.30.m

X

.o_ 0.25at-O 0.20

o 0.15

0.10

0.05

0.00i ......... I ......... I ......... I ......... I ......... I .........

0 1 2 3 4 5 6

Cumulative Flow (L)

V

.9DC0

,.Qf,,.,,=

o

0.50

0.45

0.40

0.35

0.30

0.25

0.20

0.15

0.10

0.05

0.00

......... I ......... I ......... i ii... - i ......... I .........

0, 1 . . . . . . . I ...... . • . I ......... | . ....... , i , . ....... I . ...... . ,

1 2 3 4 5 6

CumulaUve Flow (L)

Figure 15. Sorption of CO 2 on Composite MS-SA: Top - Initial, Bottom -After Regeneration.

URC 80647 -28-

0.4 I I I I i

V

0"oX.o_ac0

f,...

0

c

q_W

0.3

0.2

0.1

0.0

0.0

I

0.5

I I I

1.0 1.5 2.0

Cumulative Flow (L)

I

2.5 3.0

250 I I I I I 2OO

225

200

175

150n

12s100

50

_ ....,.... .........

/

.....o"

Power

..................Temperature25

0 , , , , , 0

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Cumulative Flow (L)

175

0150 °v

125 "_0

100 E

1-75 _

050 _

25

Figure 16. Thermal Regeneration of CO 2 Loaded MS 5A Composite Bed.

URC 80647 - 29 -

55

50

45

E 40O.v 35¢::

30.C:g 25£_ 20e-u•_ 15F--

10

0

0

.... I .... I .... I I .... I .... I .... I .... I ....

100 200 300 400 500 600 700 800 900

Cumulative Flow (L)

55.... I .... I .... I .... I .... I .... I .... I .... | ....

50

45A

E 40Q.Q.

35C__ 30

t'-"g 25£

_ 20t-O"_ 15I---

10

5

0

TCE Feed Tank Depleted

\

0

' ' ' ' I ' ' ' ' I ' ' ' ' I ' ' ' ' I ' ' ' ' I ° ' ' ' I ' ' ' ' I l , , , I ' ' ' '

100 200 300 400 500 600 700 800 900

CumulatNe Flow (L)

Figure 17. Sorpti0n of TCE on Activated Carbon: Top Initial, Bottom After Regeneration.

URC 80647 -30-

8000

7000

6000

EQ.a. 5000

LUL) 4000t--

3000EUJ

2000

1000

0

0 2 4 6 8

Cumulative Flow (L)

I

10 12

A

oo

E

I--"10

130

550

5O0

450

400

350

300

250

200

150

100

50

0

............................. i

-- Temperature.................Power

2 4 6 8 10

Cumulative Flow (L)

Figure 18. Regeneration of TCE Loaded Activated Carbon.

60

5O

40 vL..

30 n°=>

20 .__

10

0

12

URC 80647 -31-

low. Due to the apparently extremely high capacity of this sorbent for TCE, a smaller bed

containing only 0.33 g was prepared. Breakthrough for this bed began at approximately 30 L

of cumulative flow. Thermal desorption was conducted at a constant 490 W power level,

during which a maximum effluent gas temperature of63°C was observed. The repeat sorption

experiment (40 ppm TCE) confirmed that the bed had been adequately regenerated. The

results ofsorption and thermal regeneration experiments are presented in Figures 19 and 20.

A 2.77 g bed of hydrogen form ZSM-5 was challenged with 550 ppm TCE in

humidified air at 1 L/min. Owing to a calculational error, the contaminated air for this

experiment was prepared at a much higher concentration than intended. Complete

breakthrough occurred immediately upon initiation of flow. The loaded bed was thermally

desorbed under full microwave power using dry nitrogen at 0.1 L/min. The exhaust gas

temperature rapidly heated to 90°C, and then slowly fell to 35°C. The initially high

temperature can be attributed to the direct coupling of the incident microwaves with both

adsorbed water and TCE. Virtually all TCE was desorbed in the first 800 cm 3 of effluent gas.

The results of the thermal desorption are illustrated in Figure 21.

Sorption and Thermal Desorption of Water Vapor. Water loaded silica gel, Molecular Sieve

13X, and Molecular Sieve 5A were evaluated for compatibility with microwave powered

thermal regeneration.

A packed bed containing _ 5 cm 3 of silica gel was installed in the waveguide. Breathing

quality air flowed through the sparging apparatus and into the packed bed at a flow rate of 1

L/min. Effluent water vapor was tracked using an on-line dew point monitor. Measurements

taken with the air flow by-passing the sorbent bed indicated that the gas stream was fully

saturated with water vapor. The initial sorption of water vapor on silica gel is illustrated in

Figure 22. The sorption was strongly exothermic, yielding a maximum exit air temperature of

42°C. Following sorption, air flow was terminated and a flow of dry nitrogen was initiated at

URC 80647 -32-

50

45

E 40

O.

¢_ 35e-

_ 30e-

o_ 25t-O

_- 2O

15

10

40

0

''''|''''l''''l''''l''''l''''l''''l''''l''''l''''

25 50 75 100 125 150 175 200 225 250

Cumulative Flow (L)

.... | .... I .... I .... I .... I .... ! .... I .... I .... l ....

35

E 300.0.

"- 25_.v

2O=o0

i--

15

10

5 ''''1''''1''''1''''1''''1''''1''''1''''1''''1''''

0 25 50 75 100 125 150 175 200 225 250

Cumulative Flow (L)

Figure 19. Sorption of TCE on Carbosieve S-1TI: Top Initial, Bottom After Regeneration.

URC 80647 - 33 -

EO.O.

v

LU0I--,4=#

c--

ELU

6000

5000

4OO0

3000

2000

1000

0

I I | I I

0I I I I I

1 2 3 4 5

Cumulative Flow (L)

6

70 800

60A

00

v 500

3

40

E

3O

..-.20

10

0

Temperature

Power

1 2 3 4 5 6

Cumulative Flow (L)

700

6o0Im

500 •

400 •>

300 _

200 _

100

0

Figure 20. Regeneration of TCE Loaded Carbosieve S-IZI.

URC 80647 - 34 -

14000

12000 /\...\

8000

6000

ELU 4000

2000

0

"-...

-- TCE

.................Temperature

I. .,, .... --_ ......... , ......... , ......... , .........

0 1 2 3 4 5

Throughput (Liters)

Figure 21. Thermal Regeneration of TCE Loaded ZSM-5.

100

90

8O

70

60

5O

40

30

20

10

0

OOv

-.I

t_L

(DCL

E_DI-t0}

(.9

XLU

1 L/min. At the same time :full microwave power was applied. Maximum temperatures

achieved were 90°C at 3 minutes into the regeneration. AtIerward the temperature slowly

decreased. These data are consistent with the interpretation that water molecules were the

primary agent for absorption of microwaves. Once the water was removed from the system,

temperature began to fall. To confirm that the silica gel bed was, adequately regenerated, a

second sorpfion was conducted. The results, illustrated in Figure 23, indicated a complete

restoration of the bed's sorption capacity.

Similar experiments were performed using a packed bed containing 3.47 cm 3 ( 2.12 g)

of Molecular Sieve 13X. During sorptiort, exit gas temperatures of 62°C were attained. A

four minute thermal desorption was performed under full microwave power. Exit gas

URC 80647 - 35 -

¢,.)q_,

t-O

13.

E3

25

20

15

10

5

0

-5

-10

-15

-20

50

I I I I I

0

/

I I I

5 10 15

Cumulative Flow (L)

I I

20 25

I I I I I

ff

3O

.--. 45

40

CZ.

E 35I-

<•*-' 30¢-

EELI 25

2O

0

I

5

Figure 22.

I I I I

10 15 20 25

Cumulative Flow (L)

Initial Sorption of Water Vapor on Silica Gel.

3O

URC 80647 -36-

9....

¢-°_

013_

E3

25

2O

15

10

5

0

-5

-10

-15

5O

I I I I I

' ' ' ' I ' I I

0 5 10 15

Cumulative Flow (L)

I I '

20 25 30

I ! I I I

45

0v

= 40

Ille_

E 35

I---

<30

e'-ID

Eu.I 25

2O

½

I I

0 5 10

Figure 23.

I I I

15 20 25

Cumulative Flow (L)

Sorption of Water Vapor on Silica Gel Following Regeneration.

30

URC 80647 -37-

temperaturerosesteadilythroughoutthe regeneration, reaching 240°C after four minutes. The

second sorption of water vapor indicated complete regeneration of the molecular sieve 13X.

The initial sorption and second sorption are shown in Figures 24 and 25, respectively. The

temperatures achieved during regeneration indicate fairly strong coupling of the molecular

sieve with the microwave field. The experimental results obtained using a 5 cm 3 packed bed of

Molecular Sieve 5A are given in Figures 26-28. During sorption maximum exit gas

temperatures of 52°C were observed. Under full microwave power during desorption, exit gas

temperatures rose to 118°C until irradiation was terminated 14 minutes into the regeneration.

Based upon these data, it appears that silica gel couples only very weakly with the

incident microwave energy, and that regeneration is in large part attributable to the direct

uptake of energy by adsorbed water molecules. On the other hand, Molecular Sieve 13X

appears to be quite susceptible to microwave heating. An intermediate case is presented by

Molecular Sieve 5A, for which significant microwave absorption by the solid medium and by

adsorbed water appears to occur.

Sorption and Regeneration of Layered Media for CO2, Water Vapor and TraceOrganics.

A layered composite sorbent bed consisting of 0.56 g Molecular Sieve 13X, 0.17 g

Carbosieve S-IH, and 2.27 g Molecular Sieve 5A, in sequence fi'om inflow face to outlet, was

prepared for a challenge with an air stream saturated with water vapor and containing 0.5%

CO2, 628 ppm acetone, and 105 ppm TCE. Sorption was conducted at a flow rate of 100

mL/min. Effluent levels of CO2, total hydrocarbon, and dew point were monitored

continuously. Carbon dioxide began initial breakthrough at 5.2 liters of cumulative

throughput. Fifty percent breakthrough occurred at approximately 9.5 liters, and total

breakthrough was observed at 14 liters. Hydrocarbon breakthrough began after 9.2 liters of

cumulative flow and never reached 50%. Water adsorption as indicated by dew point was

anomalous. The dew point fell steadily until the 9 liter mark had been reached, after which it

URC 80647 -38-

L)9,..,

t-°_

0Q.

a

25

20

15

10

5

o

-5

-10

-15

-2O

7O

I

0 5

I I !

10 15 20

Cumulative Flow (L)

I I I

I

25 30

I I I I I

60o

soE

•'= 40<

C

Z_

E 30uJ

20.... I ' ' ' ' I ' ' ' I I I

0 5 10 15 20 25 30

Cumulative Flow (L)

Figure 24. Initial Sorption of Water Vapor on Molecular Sieve 13X.

URC 80647 -39-

0o.,..,,

t.-o_

0Q.

O)E3

25

20

15

10

5

0

-5

-10

-15

-20

7O

0 5 10 15 20 25

Cumulative Flow (L)

I I I I I

3O

0 609,_,

_ 50

e_EIDI-•'=- 40<

C

IE 30LU

20

0

Figure 25.

f I I

5 10 15 20 25 30

Cumulative Flow (L)

Sorption of Water Vapor on Molecular Sieve 13X Following Regeneration.

URC 80647 - 40 -

C°_

0(3.

D

25

20

15

10

5

0

-5

-10

-15

-20

50

.... I .... I .... I .... | .... I .... I .... I ....

' ' ' ' i ' ' ' ' I ' ' ' ' I ' ' ' ' I i , , , I ' ' ' ' ! ' ' ' ' ! ' ' " '

0 5 10 15 20 25 30 35 40

Cumulative Flow (L)

.... I .... I .... I ' " ' ' I ' ' ' " I .... I .... I ....

..--.,45

:_ 40

E 35

I.--

<_ 30e-

Eul 25

2O ........ , , , , , , ,

0 5 10 15 20 25 30 35 40

Cumulative Flow (L)

Figure 26. Initial Sorption of Water Vapor on Molecular Sieve 5A.

URC 80647 - 41 -

cJo,..,

e-o

13-

a

25

20

15

10

5

0

-5

-10

-15

-20

150

I I ' I

0 2 4 6

I I I I I I I I

I I I _ I I I

8 10 12 14 16 18

Cumulative Flow (L)

2O

125_J9,...

100

L_

-- 50e-

Eu.l 25

00 2

Figure 27.

4 6 8 10 12 14 16 18 20 22 24

Cumulative Flow (L)

Thermal Regeneration of Water Loaded Molecular Sieve 5A.

URC 80647 - 42 -

25

2O

15

--- 10

o,_.5¢-

°_

0

0

0.)

a -5

-10

-15

-2O

6O

• ' ' I .... ! .... I .... I .... ! .... I .... I ....

0

' ' ' I ' ' ' ' I ' ' ' ' I ' ' ' ' l ' ' ' ' I ' ' ' ' I ' ' ' ' I ' ' ' '

5 10 15 20 25 30 35 40

Cumulative Flow (L)

.... I ' ' ' ' 1 ' " v---, I " ' ' ' I " ' ' ' I ' ' ' " I .... I ' ' '

55

0

v 50

45<1.)

E 4OI--._-< 35

¢-

::= 30

LM

25

20

0

• ' ' I .... I .... I .... I .... I .... I .... ! ....

5 10 15 20 25 30 35 40

Cumulative Flow (L)

Figure 28. Sorption of Water Vapor on Molecular Sieve 5A Following Regeneration.

URC 80647 - 43 -

began to rise. Because the dew point never exceeded -10°C, adequate removal of water vapor

by the layered composite bed was indicated.

Based upon 100% breakthrough of CO 2, regeneration was initiated after 14 liters of

flow. Maximum effluent gas temperatures of approximately 45°C were observed during

regeneration. Following regeneration, a second sorption was conducted, yielding results which

were essentially identical with those obtained initially. This confirmed the adequacy of the

microwave powered thermal regeneration. The results of the initial and second sorption

experiments are shown in Figures 29, and 30 respectively.

Microwave Reflection and Transmission Spectra.

All of the microwave powered thermal regenerations attempted in the current study

utilized 2.45 GI-Iz as the frequency of irradiation. To evaluate the potential for more favorable

microwave heating of sorbent materials using other frequencies, a spectral study of microwave

transmission, reflection, and phase shift over the frequency range between 1.3 - 2.7 GHz was

conducted using the vector network analyzer based multifi'equency microwave transmission

and reflection apparatus.

decibels (riB), defined as,

Transmitted and reflected power levels were measured in terms of

PdB = 10 log:-_-

where P,,, is the measured power level and P, is a reference power level, in this case a 20 dB

sample of the network analyzer RF output.

Transmission and reflection spectra are presented for the empty sample chamber,

830IMC activated carbon, #5769 activated carbon, lithium hydroxide, Molecular Sieve 5A,

Molecular Sieve 13X, dry silica gel, wet silica gel, and silver carbonate in Figures 31-39

respectively. The phase shifts of transmitted power for these materials as a function of

frequency are presented in Figures 40-44.

URC 80647 - 44 -

0._ .... I .... I''''i''''l .... 1 .... ! .... I .... I .... I .... I .... I .... I .... I .... I ....

V

X.o_0

0

0.5

0.4

0.3

0.2

0.1

0.0

170

165

E 160O.

t-O-e 155

2_, 150"r

145

140

0

J

.... I''''I .... I''''I .... I_''' l'''f l''''l''''l''''l''''l''''l ''''

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Cumulative Flow (L)

-"

Dew Point

Hydrocarbon

...,..+.+•+ ...•,'•"•'+•'++•'•••'•_•'""'_+•

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Cumulative Flow (L)

15

Figure 29. Composite Bed: Initial Sorption of CO 2, Water Vapor, Acetone and TCE.

URC 80647 - 45 -

0.6 .... I .... I .... I .... I .... I .... I .... I .... T'''' I .... 1 .... I .... ! .... I .... I ....

0.5

o_ 0.4v

Q)

X

.o_ 0.3r"t

0.1

0.0.... I'''' I''''|''''|''''| '' I .... I'' '

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Cumulative Flow (L)

160 .... , .... , .... , .... , .... , .... , .... , .... , .... , .... , .... , .... , .... , .... , ..... 20

155

150

E 145

Q.v 140e-o

13582 130

-1- 125

120

115

110

.................Dew Point

Hydrocarbon

...'•

.•.•"

..."

.r, •

,.,.•.,-'•

'''l .... I .... I .... I .... I''''1''''! .... |'''' I':'' I' '' '1 '"'' I .... ! .... I ....

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Cumulative Flow (L)

-19

-18

-17

0-16 o....

-15 "5EL

-14a

-13

-12

-11

-10

Figure 30. Composite Bed: Repeat Sorption after Microwave Powered Regeneration..

URC 80647 - 46 -

(1)20

E(/)_- 10I,..

I--(1).-> 0

iv'-10

1200

/

1400 1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)

133"OV

OD.."O(1)"6(l)

n,,(D._>

O

3O

20

10

0

-10

-20

-30 ,

1200

L

, i i

I

' r

""k #'_ ;i.

!

1400 1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)Figure 31. Kelative Transmitted and Reflected Power for Empty Sample Chamber.

URC 80647 - 47 -

3O¢n"13V

,- 20(1)

On 10'13(D

E 0t,/)E:

,- -10I--"

_ -20

rY-30

v i

A.//v

' r , r i i , 'l i ,

1200 1400 1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)

3O

133"Ov 20

o 10Q_"0

0

rr -10G).___ -20(1)n,'

-30

1200

L w

1400 1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)Figure 32. Relative Transmitted and Reflected Power: CECA-830IMC Activated Carbon.

URC 80647 -48-

133"10V

L_

O13_"O(D

E(/)E:

i--(D

tm

(_n,"

133'10V

I...

O13..

"6(D

¢i:=

n,"(D

.>_

G)n,"

30

20

10

0

-10

-20

-3O

1200 1400

0 , i i |

1600 1800 2000 2200

Frequency (MHz)

2400 2600 2800

20

10

0

-10

-20

-30

1200

Figure 33.

I

1400 1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)Relative Transmitted and Reflected Power: Alltech 5769 Activated Carbon.

URC 80647 - 49 -

_, 30 ...........133"10v , .

13_ 10

-10I-

° i_ -20

r_-30

1200 1400 1600 1800 2000 2200 2400 2600

Frequency (MHz)

28OO

30

133"10v 20

o 100_

(I)

_6 0

r_ -lO

-20(D

-,,--[-

| , =

1i , |-30 ......

1200 1400 1600 1800 2000 2200 2400 2600

Frequency (MHz)Figure 34. Relative Transmitted and Reflected Power: Lithium Hydroxide

2800

URC 80647 - 50 -

30133"OV

20

a.. lO"0

"_ 0e-

i--

m_

m

n,

-lO

-20

-3O

1200 1400

• I

1600 1800 2000 2200

Frequency (MHz)

2400 2600 2800

30

m"Ov 20

10

"O(1)"6 0cD

_-10

(1).>..,I,-I

-20(1)

° |

III

i i i i i i

/

-30 ......

1200 1400 1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)Figure 35. Relative Transmitted and Reflected Power: Molecular Sieve 5A.

URC 80647 - 51 -

,_ 30 .......133"0V

20 ! '

a.. 10 I

p •

" /•_=,_._o L __ -lO

F--

"_ -20m

n_-30

1200 1400 1600 1800 2000 2200

Frequency (MHz)

2400 2600 2800

133"10v 20t._

no I0

o

_-I0

._.m-20

n,'

30 ¸

o

:,,,..-

-30 . , ,

I

f , , , , ,

1200 1400 1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)Figure 36. Relative Transmitted and Reflected Power: Molecular Sieve 13X.

URC 80647 - 52 -

_, 30133"(3V

,- 20(D

On 10"O(D

"g: 0E

-10I--

0

-20I

-30

1200 1400 1600 1800 2000 2200 2400 2600

Frequency (MHz)

2800

30

ED

v 20L_

(1)

o 1013.

"0(1)_ o

_ -10

iI

-20

n,"

-30

1200 1400 1600 1800 2000 2200 2400 2600

Frequency (MHz)Figure 37. Relative Transmitted and Reflected Power: Silica Gel.

2800

URC 80647 - 53 -

30m"10V

0Q.. 10'10

E 0

e-

-10I--

-20

n,"-30

1200 1400 1600 1800 2000 2200

Frequency (MHz)

2400 2600 2800

rn"0V

I,..

(D

013_

"0

rY

.>_

(_rY

30

20

10

0

-10

-20

-30

• tl

"._ ._

i 1 f i i

fV

i

1200 1400 1600 1800 2000 2200 2400 2600 2800

Figure 38.

Frequency (MHz)Relative Transmitted and Reflected Power: Silica Gel with Adsorbed Water.

LrKc 80647 - 54 -

,_ 30

10V

, 20(D

O10

"0

"_ 0l-

-10I--

>=i

n,'

20 i

30 ....

1200 1400

Yv

i i i i i TVl r== I1!

1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)

£OOV

I,=

O13_O

"5¢)

n,

=l

n,'

30

2O

10

0

10

20

30

1200

411 •

y

i v i v =

UI V V

i i | i = i i

1400 1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)Figure 39. Relative Transmitted and Reflected Power: Silver Carbonate.

URC 80647 - 55 -

¢D(D(DL_

(DE3V

c-co(D

¢U..CZ13..

180

90

0

-90

-180

1200

t!I'/11 i

• ',I l I /: I • " .

' / /1400 1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)

180 , .

90

° i121

.__ 0 '

co

,-- -90

-180 i

1200

\ ,

1400 1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)Figure 40. Transmitted Power Phase ShiR:Top-Empty Cell, Bottom-CECA-830IMC.

URC 80647 - 56 -

o0

E3

t-O9

o0

¢-Q_

180

90

0

-90

-180

1200 1400 1600

/./

i ,

!

• (I

1800 2000 2200 2400 2600 2800

Frequency (MHz)

U)O

¢3)

E3v

l--co

(/)

(...Q.

180

90

0

-90

-180

1200

Figure 41.

t

|

.i 1

1400 1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)TransmittedPower PhaseShL_:Top-5769 Activated Carbon, Bottom:LiOH.

URC 80647 - 57 -

t.=

aV

om

t-OO

oo

t-13.

180

90

0

-90

-180

1200

180

I

1400

I

!|=,

! I

//• /

/1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)

I,.=

O)

av

gi

t-O9

¢/}

¢-13..

90

0

-90

-180

1200

i

1400 1600 1800 2000 2200 2400 2600

Frequency (MHz)Figure 42. Transmitted Power Phase Shift: Top - MS 5A, Bottom - MS I3X.

28OO

URC 80647 - 58 -

180

90

O)

D

0gm

t.-

03

.= -90Q.

-180

1200 1400 1600 1800 2000 2200 2400 2600

Frequency(MHz)

2800

03

O)(_r'tv

¢:t=m

r-

(_03

t-EL

180

90

0

-9O

-180

1200

Figure 43.

, I[ _ °

1400 1600 1800 2000 2200 2400 2600 2800

Frequency (MHz)TransmittedPower Phase Shift: Top-Dry Silica Gel, Bottom-Wet Silica Gel.

URC 80647 - 59 -

09tDot2_qDDV

e"03(1)09

e--13.

180 • •

0

-9O

-180

1200 1400

Figure 44.

l'l'' t1600 1800 2000 2200 2400 2600

Frequency (MHz)Transmitted Power Phase Shift: Silver Carbonate.

28O0

As a basis for comparison, these materials were also heated at 2.45 GHz in a

rectangular waveguide system for 20 seconds. The samples were enclosed within glass Petri

dishes. At the end of the microwave exposure, the waveguide was opened and the temperature

of the media were determined using an IR thermometer. The results are presented in Table II.

Table IL Waveguide Microwave Heating Tests Results at 2.45 GHz.

Sorbent Mass (g) AT (°C)

Empty Petri Dish 1

Activated Carbon - IMC830 4.34 > 204 (offscale)

Activated Carbon - 5769 4.22 218

Lithium Hydroxide 5.98 0

Molecular Sieve 5A 5.90 5

Molecular Sieve 13X 9.26 38

Silica Gel 5.6 17

Silver Carbonate 5.13 2

Water 10.47 45

URC 80647 - 60 -

Several interesting features are evident in this assemblage of microwave spectra relative

to the 2.45 GHz frequency at which the heating experiments were conducted. Both activated

carbons show a much stronger absorption at 1.46 GHz and at frequencies between 1.80-1.85

GHz. LiOH absorbs more strongly in the 1.85-1.9 GHz region. A relatively broad band of

enhanced susceptibility is seen for Molecular Sieve 13X between 1.825-1.910 GHz. The

differences in transmission spectra between the wet and dry silica gel is particularly

pronounced at 1.5, 1.75, and 1.81-1.87 GHz. By contrast, the presence of water results in

little or no difference in silica gel spectra at 1.725, and between 1.95-2.6 GHz.

The above is only a cursory interpretation of the vast body of information contained

within the reflection, transmission, and phase lag spectra. Unfortunately, the time constraints

of the Phase I performance period did not permit a more thorough and thoughtful analysis.

IV. CONCLUSIONS.

Feasibility of the use of microwave heating for the fast and efficient thermal

regeneration of sorbents for the removal of carbon dioxide, water vapor, and trace organics

from contaminated air streams has been conclusively demonstrated. Microwave powered

thermal regeneration of single sorbents and composite sorbent beds loaded with acetone,

triehloroethylene (TCE), carbon dioxide, and water vapor has been achieved using a

rectangular waveguide based test apparatus emitting at a frequency of 2.45 GHz. Both

activated carbon and Carbosieve S-IH were identified as excellent microwave regenerable

sorbents for use in the removal of airborne organics. Water loaded silica gel, Molecular Sieve

13X, and Molecular Sieve 5A were also effectively regenerated under microwave irradiation at

this frequency. Molecular Sieve 5A and a carbogenic molecular sieve prepared at NASA's Jet

Propulsion Laboratory were identified as viable microwave regenerable CO 2 sorbents. A

sorbent bed containing multiple media was challenged with air containing 0.5% CO2, 300 ppm

acetone, 50 ppm TCE, and saturated with water vapor. The composite bed was shown to

URC 80647 - 61 -

effectively purify the contaminated air stream and to be completely regenerated by microwave

induced heating.

Spectral studies of the reflection, transmission and phase shifts of microwaves

irradiating a variety of sorbents over the frequency range between 1.37 - 2.6 GI-Iz have

indicated that significant differences in the dielectric loss characteristics (which are responsible

for a material's susceptibility to microwave heating) occur between sorbents as a function of

frequency. Frequencies have been identified with potential for more effective microwave

heating of specific sorbents. Based upon these results, further development of this highly

promising technology is highly recommended.

Currently, expendable cartridges containing activated carbon and lithium hydroxide are

used for the removal of trace contaminants, CO 2, and water vapor inside the suit during EVA.

A regenerable system is in the final stages of development for deployment during assembly of

the future International Space Station Alpha (ISSA). This system will use metal oxide CO2

sorbents in conjunction with other thermally regenerable media. Regeneration of these devices

will take place within the cabin of the shuttle or space station and will operate using

conventional resistive heating elements and will rely on conduction and convection of heat to

the thermally regenerable media.

Based upon the successful microwave powered regenerations of sorbents for water

vapor, carbon dioxide, and trace organics separately and in combination, it is highly probable

that a more efficient and more convenient regenerable air purification system for EVA can be

designed based upon this technology. For example, rather than removing expended sorbents

from the EMU for regeneration, microwave power could be delivered directly to the EMU via

coaxial cable, allowing regeneration to take place in situ. This would provide substantial

savings in crew time. Additionally, significant improvements in size, weight, power

consumption, regeneration efficiency, and regeneration times can be gained.

In addition to the obvious applicability to EVA and Advanced Life Support, two

specific systems with strong potential for commercial application have also been identified.

URC 80647 -62-

These are the acetone-Carbosieve S-III and TCE-ZSM-5 combinations. The first system

represents an environmentally benign method for the recovery of waste solvents in a variety of

industrial chemical processes. Using the highly selective carbon based molecular sieve, and the

extremely rapid thermal desorption capabilities inherent to microwave heating, acetone (or

similar solvents) can be recovered from waste gas streams by sorption and then concentrated

by flash thermal desorption for collection by condensation. The second commercial application

exploits the fact that ZSM-5 is not only a sorbent for removal of airborne trichloroethylene, it

is also an effective catalyst for the deep oxidation of this contaminant, particularly in the

chromium form. Thus, the TCE-ZSM-5 system forms the basis for a combined environmental

remediation process to achieve both the separation and the ultimate destruction of TCE.

V. REFERENCES.

1. Carslaw, H.S., and Jaeger, J.C., Conduction of Heat in Solids, 2nd Ed., Clarendon Press,

Oxford, 1959.

2. von Hippel, A., Dielectrics and Waves, Wiley, New York, 1954

3. von Hippel, A., Ed., Dielectric Materials and Applications, Technology Press of MIT,

Cambridge, 1954.

4. Tsang, L., and Kong, J.A., Scattering of Electromagnetic Waves from Random Media with

Strong Permittivity Fluctuations, Radio Sci., 16 (3), 303-320, 1981.

5. Bergman, D.J., The Dielectric Constant of a Composite Material - A Problem in Classic

Physics, Phys. Lett. C, 43 (9), 377-407, 1978.

Polder, D., and Van Santert, J.H., The Effective Permeability of Mixtures of Solids,

Physica, 12 (5), 257-271, 1946.

Taylor, L.S., Dielectric Properties of Mixtures, 1EEE Trans. Antennas Propagat., AP-13

(6), 943-947, 1965.

.

.

URC 80647 - 63 -

8. Stogryn, A., The Bilocal Approximation for the Effective Dielectric Constant of an

Isotropic Random Medium, IEEE Trans. Antennas Propagat., AP-32 (5), 517-520,

1984.

9. N_st, B., Hansen, B.D., and Haslund, E., Dielectric Dispersion of Composite Material,

Physica Scripta, T44, 67-70, 1992.

10. Foley, H.C., Carbogenic Molecular Sieves: Synthesis, Properties, and Applications,

MicroporousMater., 4, 407-433, 1995..

11. Atwater, J.E., and Holtsnider, J.T., Airborne Trace Organic Contaminant Removal Using

Thermally Regenerable Multi-Media Layered Sorbents, SAE Trans. ,I. Aerosp., 100,

1726, 1991.

12. Atwater, J.E., and Holtsnider, J.T., Simple Models for the Breakthrough of Humidified

Acetone and Ethyl Acetate on a Carbon Based Molecular Sieve, Carbon, 34 (6), 824-

825, 1996.

URC 80647 - 64 -