By Henry Nowicki, George Nowicki, Wayne Schuliger, Shib Mookherjea and Barbara Sherman

New test methods can facilitate scientific discoveries and lead to new commercial granular activated carbon (GAC) products. Also, a new or modified paradigm can result when advanced data acquisition is available to base decisions on.

Before new models based on improved data acquisition can be provided, it is critical that we have a complete understanding of the state-of-the-art and history. New working concepts typically build on prior work.

Two historical recommended readings provide an understanding of how activated carbons work.^1,2 Dr. Milton Manes also connected this early work and brought it up to the present in his writings. ³

Advanced modern test methods
Two advanced test methods are improving decisions made by activated carbon users and manufacturers. These test methods have been coined Gravimetric Rapid Pore Size Distribution (GRPD) and Trace Capacity Test Method (TCTM). If you are using or plan to apply activated carbon to solve water or air problems, you need to know about these two advanced test methods.

GRPD has been previously covered in additional writings ^4-17 providing examples of the usefulness of GRPD. On several occasions five to 12 different vendor activated carbon samples were analyzed by GRPD and American Society Testing Materials (ASTM) activated carbon test methods to determine the best product for client applications.

Typically the different vendor samples had similar ASTM test method results for iodine and butane activity and other standardized tests. But, upon GRPD advanced testing, significant and relevant differences were revealed, allowing carbon users to select the best GAC for their applications.

GRPD has shown that it is capable of differentiating activated carbons with the same ASTM iodine numbers for drinking water applications. GRPD provides differentiation of these same iodine number samples and a full-characterization of the test samples.

GRPD also provides a full- characterization of performance and physical properties for the sorbent sample: characteristic and differential adsorption and desorption curves; aqueous- and vapor-phase isotherms; third-degree polynomial equation for adsorption pore volume as a function of specific adsorption potential energies; pore size distribution; total pore volume; cleanliness of tested sample; and mid- and high-capacity adsorption values and surface area in meters squared per gram. The process has been run on a wide variety of sorbent types and forms, thus a new sample can be run and quickly determine its market strengths and weaknesses based on comparison with the prior run collective database.

Trace capacity test method applications
The TCTM process compliments GRPD by providing more detailed information for the tested sample about the high adsorption energy sites in the GRPD test method.¹⁸ The following information will further outline this needed new test method and help set-up and/or use the test method to evaluate sorbent materials to solve some pressing real commercial opportunities.

Often test methods are the difference makers in commercial product development efforts. Some problems the TCTM are expected to help are: presently difficult to remove small adsorbates at trace levels from water and air streams, endocrine disrupter chemicals, carbon dioxide and methane capture and release and many more.

It is obvious to look at the use of tetrafluoromethane (TFM) as the sorbent challenge gas based on prior use of 1,1,1,2-tetrafloromethane (TFE) as the challenge gas for the GRPD test method ^4-17 . These many GRPD applications for a full-characterization of sorbent materials will continue to grow as more is learned about the benefits of GRPD .

Use of TFM for the TCTM is a natural extension of TFE, because TFM requires higher energy binding sites to efficiently capture it compared to TFE. Choosing TFM as the challenge gas provides a lower boiling point and lower polarizability of the path to characterize the highest potential adsorption energy sites in a sorbent test sample.

Localized vs. mobile graphitic surface binding
Molecules that hit the activated carbon surface (from the vapor-, liquid- or melt-phases) are pictured to glide or hop along the graphitic surface ². With activated carbon’s heterogenous adsorption energy distribution, the adsorbate speed on the surface and its ability to hold upon the adsorbate and keep it from going back into the bulk phase depend largely on the adsorbent localized adsorption energy.

By designing and manufacturing more high-energy adsorption sites with targeted specificity into the adsorbent, it makes sense that present molecules which are refractory to activated carbon adsorption may be adsorbable at low, partial pressures and concentrations relative to their saturation concentrations. This is a worthy future goal. A significant trace capacity test method to evaluate present and future emerging sorbents for this market is needed by users and manufacturers.

In order to help solve some real-world problems, this new trace capacity test method will improve capture and release of low-concentration, hard-to-remove organics from water, carbon dioxide, hydrogen, methyl bromide, ethylene, endocrine disrupters. Other applications are also beneficiaries of this trace capacity test method. This TCTM provides a way to better determine the high energy binding site total pore volume per mass or volume of the tested sorbent.

New application for ASTM butane activity apparatus
The test apparatus for the TCTM can be the standard ASTM butane activity test apparatus. The test method number is D 5742-95 and is titled Standard Test Method for Determination of Butane Activity of Activated Carbon.

The above sample tube has 16.7 ml (plus or minus 0.05 ml) of volume for the sample. The sample packing density in the sample tube, carbon weight in grams/16.7 ml, must be equal to at least 94 percent of its dry apparent density obtained in ASTM method D 2854: Test Method for Apparent Density of Activated Carbon.

Butane gas is passed through the sample at 25^o C (77^o F), the butane is thermostated in a water bath before it is sent through the sample tube, containing the sample, in a water bath at 25^oC. The sample tube is weighed until constant weight for butane capacity is obtained. The result is presented in grams of butane per 100 grams of sorbent tested or 100-ml of sorbent volume.

Using this ASTM butane test stand, TCTM total pore volume can be obtained by using TFM in place of butane gas. TCTM is done like a butane number, but TFM gas is used in place of butane.

Since TFM is a much more difficult challenge for the sorbent, only high- adsorption potential energy binding sites adsorb TFM. Again, test results can be expressed in grams of TFM adsorbed per 100 grams of sorbent or per 100 ml of sorbent volume, just like is done with the standard butane test.

Unused and used GAC
Granular activated carbons (GAC) have a determinable limit on how much pollutants they can hold before breakthrough. You need to know that all activated carbons are not the same and will have different pollutant capacities before breakthrough.

GRPD is being used to determine what GAC pore size adsorption spaces are needed for different applications. This needed adsorption space is based on a comparison of GRPD runs with the unused and used GAC for the application. The difference in the used and unused GRPD runs provides the pore structure needed for specific application.¹⁹

It is important to clearly understand the relatively recent ASTM recommended terms unused- and used-GAC. ²⁰ The ASTM recommends (via personal discussions with Dr. Amos Turk) use of these words in place of virgin (unused) and spent or exhausted (used) carbon. The starting carbon in your application is the unused-GAC and the used-GAC is what you change out to start a new treatment.

Completely used-GAC occurs when influent and effluent through a GAC column is the same. We suspect that we will continue to see virgin, fresh, spent, exhausted and other terms to describe the status of GAC; but we should all try to use the ASTM recommended glossary of terms in order to understand each other better and be more productive.

ASTM method approval process
Getting GRPD formally through the ASTM process as a listed method will not happen in the near future. There are only a few instruments available to provide this

sample-specific, full characterization for adsorption information package; the ASTM process takes years.

One way around the small number of GRPD type instruments is to apply the ASTM butane activity test equipment. There are many laboratories with butane activity test stands and well qualified equipment operators. By selecting a suite of challenge gases and applying the butane activity test stand, it is possible to approach the GRPD test package of information.

Recent comparison of ASTM butane activity method and working capacity and butane working capacity determined by GRPD indicates both GRPD and ASTM butane activity test D 5742-95 and ASTM D 5228-96, Test Method for Determination of the Butane Working Capacity of Activated Carbon, yield the same results.²¹ This is another testimonial to the power and ruggedness of GRPD testing.

The trace capacity method is designed to compliment the GRPD full characterization test method by focusing on the binding sites with the highest adsorption forces. All adsorption binding sites in activated carbons are not the same.

Selecting the best activated carbon for a specific application depends on determination of the sorbent’s pore structure. The TCTM and GRPD test methods are powerful aids in pore structure determinations. Being able to better measure the distribution of high-energy adsorption sites with TCTM is expected to help facilitate development of new emerging sorbents designed to help solve some important problems.

References

1. Polanyi, M. Verh. Dent physik. Ges 16, p. 1012. 1914 and 18 p 55, 1916
2. DeBoer, J.H. The Dynamical Character of Adsorption. 2^nd ed. Oxford at the Clarendon Press 1968
3. Manes, Milton. Encyclopedia of Environmental Analysis and Remediation. Meyers, Robert, Editor. John Wiley & Sons, Inc. TSBN 0-471-1708-0, 1998
4. Nowicki, H. and Greenbank, M. Advanced Instruments for Sorbent Adsorbate(s) Determination and Sorbent Adsorption and Desorption Evaluation. Presented at 23^rd Army Science Conference. Orlando FL Dec. 2-5, 2002
5. Nowicki, H. and Greenbank, M. New Differential Heat-of-Adsorption Instrument. Presented at 23^rd Army Science Conference. Orlando FL Dec. 2-5, 2002
6. Nowicki, Henry et. al. GRPD instrument reveals sorbent materials critical information. Pittsburgh Conference (PittCon) New Analytical Instruments 230-12P, March 2, 2008
7. Nowicki, Henry et. al. GRPD determination of activated carbons in coal fired electric power plants fly ash samples. PittCon Analysis for Energy Production 1570-8P, March 4, 2008
8. Nowicki, Henry et.al. GRPD location of positional placement of chemical impregnant into Activated Carbons. PittCon Material Sciences, 2740-5P, March 5, 2008
9. Nowicki, Henry; Sherman, Barbara; and Nowicki, George. “GRPD Modern Activated Carbon Testing.” Filtration News August/September 2007 p 28-33.
10. Nowicki, Henry; Carr, Bud; and Nowicki, George. “GRPD Comparison of Two Activated Carbon Felts.” Water Conditioning and Purification. p 28-33. June 2007
11. Nowicki, Henry et. al. “Modern GRPD Test Differentiates Activated Carbons.” Water Conditioning and Purification. p. 62-64. February 2007
12. Nowicki, Henry and Sherman, Barbara. “Activated Carbon: Advanced Test Method.” Filtration News. July/August p. 14-21, 2006
13. Nowicki, Henry and Sherman, Barbara. “Activated Carbon: Advanced Test Method.” Water Conditioning and Purification. P. 32-36. March 2006 at https://wcponline.com/PDF/Nowickietal0306.pdf
14. Nowicki, Henry and Sherman, Barbara. “Activated Carbon: Comparison of Classical and Advanced GRPD Test Methods.” Water Conditioning and Purification. P. 28-35 April 2006
15. Nowicki, Henry. Determination of Adsorption Energy Distributions in Activated Carbons and other Sorbents. 200-20P. Pittsburgh Conference. 2006
16. 16. Nowicki, Henry. “Selecting the Best Activated Carbon for the Process -Application.” Filtration News. Page 18-22. July/August 2005
17. Nowicki, Henry. GRPD Helps to Select the Best GAC for a Municipal Drinking Water Plant. 22^nd International Activated Carbon Conference. Pittsburgh PA Oct 7-8, 2008
18. Greenbank, Mick. Using a Gas-phase Test to Predict Liquid-phase Activated Carbon Performance at Trace Concentrations. 24^th International Activated Carbon Conference and Courses Program. Pittsburgh, PA. October 6-10, 2009
19. Nowicki, Henry. “GRPD Comparison of Unused and Used Drinking Water Granular Activated Carbons.” Water Conditioning & Purification p 32-27 April 2009.
20. Nowicki, George et. al. “The Importance of Activated Carbon Terminology: A Glossary of Terms.” Water Conditioning & Purification. (WC&P) February 2008 page 88-94
21. Nowicki, Henry et.al. Comparison of GRPD method with ASTM Butane Activity and Butane Working Capacity Test Methods. International Activated Carbon Conference. Pittsburgh, PA. October 6-10, 2009

About the Authors
Henry Nowicki, Ph.D./MBA, is President for PACS, develops new products and business and directs the day-to-day products and services developments and delivery. Nowicki has provided technical assistance to legal professional in over 40 prior cases and provides the introductory class for the Activated Carbon School. He can be reached at [email protected] or by phone (724) 457-6576.

George Nowicki, BA/BS, is Laboratory Manager for PACS and is a senior activated carbon specialist. He is an instructor in the Activated Carbon School, and may be contacted by email at [email protected] or by phone at (724) 457-6576.

Wayne Schuliger, PE, is Technical Director for PACS and a leading engineer consultant for activated carbon adsorption systems. Schuliger is an instructor in the PACS Activated Carbon School and can be reached by email at [email protected].

Shib Mookherji, Ph.D., is Director of Quality Assurance for PACS. He is also a teacher for the PACS short course “Development and Validation of Analytical Methods.”

Barbara Sherman, BS/MBA, is Director of Short Courses and Conferences for PACS. She coordinates the bi-annual International Activated Carbon Conference and Courses program. and can be contacted by email at [email protected] or by phone at (724) 457-6576.

About PACS and Activated Carbon Services
Professional Analytical and Consulting Services, Inc. (PACS) is celebrating its 26^th year of business and its major division, Activated Carbon Services, is in its 25^th year of business. The firm provides products and services to enhance its clients’ position in their market places. Products and services are described at www.pacslabs.com.

If you would like to hear the inventor’s talk about the new Trace Capacity Test Method, plan to attend their session in Pittsburgh, PA on October 6 at 9:15 am at IACC-24. If you know of other new test methods capable of aiding better sorbent selection decisions, let us know through [email protected].