PACS and Activated Carbon Services Inc. will host the International Activated Carbon Conferences (IACC-35 and -36) in Orlando, Florida, Feb. 26-27, 2015, and Pittsburgh, Pennsylvania, Sept. 17-18, 2015. Both events offer short courses in conjunction with each conference. You may take the courses without attending the conferences. You may also add your marketing documents without attending.

Table 1, which can be found at https://www.watertechonline.com/ext/resources/magazine-article-images/PDFs/Table_1.pdf, provides a preliminary technical program for the conference taking place in Orlando in February 2015. This carbon conference has three types of technical presentations: Oral, poster and abstract only. It is never too late to participate. It is all-inclusive for carbon users and manufacturers.

Table 2, which can be found at https://www.watertechonline.com/ext/resources/magazine-article-images/PDFs/Table-2.pdf, provides short course descriptions for three popular courses offered during conference week. Additional course offerings are at www.pacslabs.com. These courses can also be provided at the client's time and place.

Here we want to highlight three Orlando technical presentations: Mike Jones, president of Atlas Carbon, will provide an update on a new potential process to manufacture activated carbons (ACs); Bill Purves, CEO of Purves Environmental, will discuss the EPA position on mercury emissions leaving U.S. dental offices; and Henry Nowicki, president of Activated Carbon Services, will present a talk titled, "GAED Advanced Test Method Solves Activated Carbon Problems."

 

New method for production of AC abstract

Atlas Carbon LLC (Atlas) is a new AC manufacturer in Wyoming. Atlas has licensed an AC production technology from Diversified Industrial Minerals LLC (Diversified) and is currently constructing its first market scale facility in the heart of the Powder River Basin coal region. Diversified specializes in high temperature thermal treatment technologies for industrial minerals processing. Diversified’s core technology is Pneumatic Flash Calciner, or PFC, which is a patented new approach to AC production.

The PFC utilizes a co-current flow reactor design unique to the industry to activate carbonaceous feedstock at sizes generally finer than 10 mesh. The material to be activated is fully suspended in a controllable high temperature gas flow, ensuring uniform gas-to-particulate contact. Due to the small particle size and the effective gas contact inherent to co-current flow design of the PFC, activation is quickly accomplished. Overall product retention time in the system is five to 30 seconds — thus facilitating high throughput rates and thereby reducing equipment size and cost. The PFC can produce AC in a fast and tightly controlled manner, utilizing a wide variety of carbonaceous feedstock.

In addition to virgin AC production, the PFC can be utilized for spent PAC or GAC carbon reactivation. AC regeneration bears similarities to virgin AC production. Reaction conditions must be carefully controlled to properly restore spent AC to near original adsorption capacity. The short residence time characteristic of the PFC is favorable for the removal of adsorbates and restoration of the AC pore structure to near original performance standards. The PFC allows high rates of production with uniform and adjustable process control conditions. Significant cost savings versus virgin AC can be realized with proper reactivation.

The PFC technology is faster and requires less capital investment than some other AC thermal technologies. Other methods can require hours of thermal process retention time compared to seconds for the PFC to achieve the same level of activation. This enables the PFC technology to be installed at a lower capital cost per annual pound of AC production than some other competing technologies. Operationally, the PFC is a lower-cost AC production method and requires a small footprint, short warm-up time and lower maintenance costs.

Reaction kinetics play an important role in porosity development during AC and/or reactivation. Many traditional AC production methods rely on maintaining a large inventory or “beds” of hot carbon throughout the furnace or kiln and therefore, the bulk of the hot carbon’s external surface area is in limited contact with the activation gases during much of the carbon’s furnace retention time. Within a traditional rotary kiln or multihearth furnace, the greatest degree of activation occurs during the carbon bed’s free fall, agitation or mixing with the hot activating gases. The PFC design takes advantage of that known solid-gas contact characteristic value, and its total suspended particulate flow regime allows for continuous rapid and uniform activation conditions without maintaining any significant hot carbon inventory in the process. Such optimal process control allows the PFC to generate a tighter pore size distribution during virgin carbon activation or to reactivate spent carbon under tighter parameters than various traditional production methods.

 

Background GAED information

The Gravimetric Adsorption Energy Distribution (GAED) test method has solved refractory vapor, aqueous and solvent AC problems. It has been applied to powder, granular, pellet, fabric and composite forms of AC and other materials.

GAED advanced instrumentation applies the Polanyi physical adsorption model.1 The Polanyi model connects vapor- and aqueous-phase physical adsorption. This enables the use of a GAED vapor-phase test method for aqueous applications.

GAED samples are run as a received form; a few grams are fully characterized for its adsorption energy distribution and corresponding pore volume for physical adsorption capabilities in one day. All carbons are not the same. They have heterogeneous adsorption sites and the distribution varies with the type of carbon.

GAED samples are dried to remove water and determine dry apparent density with the ASTM D-2854-96 oven test. The amount of water is reported. This allows for GAED testing comparative dry basis and volume basis.

 

A summary of the GAED test method is provided

The ASTM dry sample is placed into the GAED sample compartment, which can be heated to 240o C in argon and cooled to -20o C. Once the sample (powder, granular, pellet, fabric or composite material) is in the GAED sample compartment, a temperature program, which can be tailored to specific samples, runs automatically. The sample is heated from room temperature to 240o C and held for 25 minutes to clean it. The weight loss is reported. The cleaned sample is challenged with 1,1,1,2-tetrafluoroethane (TFE) because only the high adsorption energy sites are capable of adsorption of TFE at a high temperature. Then the sample temperature program is lowered to -20o C to reveal the pore volumes for weaker adsorption energy sites. After the adsorption curve is obtained, the temperature program is reversed to provide the desorption curve. For well-prepared ACs, the adsorption and desorption curves are the sample. Polanyi calls this the “Characteristic Curve,” adsorption energy density (cal/cc) versus adsorption space or pore volume. GAED runs cover seven orders of TFE concentration and three orders of carbon loading capacity.

The Characteristic Curve can be fitted to a polynomial equation to provide pore volume (cc/100 g) at specific adsorption energies.2 These equations are used to provide isotherms, which enable the calculation of the amount of carbon needed for an application, and determine the best carbon to be used.

GAED provides sorbent optimization through computerized routines. This avoids “designer's intuition” and arrives at a true and often non-intuitive result.

Further reading and examples of the GAED test method can be found at www.pacslabs.com. GAED details are covered in a two-day course hosted by Nowicki, provided three to four times each year.

 

Some problems solved with GAED

PACS Laboratories has provided around 4,500 GAED sample runs. Some refractory problems solved with GAED are:

  • GAED enables determination of isotherms for specific organic compounds at a client-specified temperature on specific AC samples.
  • GAED can shed light on the position of chemical impregnants added to AC. A GAED comparison of the impregnated and starting AC has provided this information. Location of impregnants can make a big difference on performance.
  • GAED can best define the micropore volumes of AC samples. These high adsorption energy sites are needed for physical adsorption of trihalomethanes (THMs) disinfection byproducts and other trace water soluble organics. Its measure is called a trace capacity number (TCN) and is obtained during the GAED.

 

Interpretation of acetoxime TCN test values

The best TCN numbers determined by GAED are 14 to 18 mg/cc. Good numbers for well-made bituminous coal-based products and ordinary coconut-based products range from 11 to 14 mg/cc. Ordinary numbers for ordinary coal-based products, subbituminous and well-made lignite products are 7 to 11 mg/cc. Ordinary lignite and wood-base products are 4 to 7 mg/cc. For a TCN less than 4 mg/cc, the carbons generally have a very low apparent density (less than 0.30 g/cc).

Each reactivation of a spent carbon reduces the TCN value. Carbons after multiple reactivations can have half the TCN of the virgin starting carbon that was spent.

  • GAED can be used to define what type of AC is best for an application and to help define the feedstock (wood, coconut shell or coal) in an unknown, questioned AC.
  • GAED can define the change in pore structure before and after thermal reactivations.
  • It can determine the pore volume loss in AC after powdered carbon has been made into pellets or carbon blocks.

 

Emerging mercury emission problems at dental offices

The next serious threat to the environment is mercury from dental amalgams. For many wastewater treatment plants, mercury is still an issue when meeting National Pollutant Discharge Elimination System (NPDES) discharge limits for mercury. The national discharge limit suggested by EPA is 12 ng/l. The limit established for the Great Lakes is 1.3 ng/l. Many states have established limits lower than the 12 ng/l (5 ng/l in many), which causes concern for treatment plants in those states. A significant part of the problem today is mercury being released by dental offices into the municipal treatment plant influent. To resolve the problem, EPA is proposing a rule to require dental offices to place amalgam separators in their offices to reduce the mercury discharge into the waste stream.

The amalgam separator (with the exception of one) is nothing more than a settling chamber where the mercury amalgam separates from the liquid stream by simply precipitating to the bottom of the chamber. This approach removes 95 percent or more of the amalgam (based upon the ISO 11143 standard) in the waste stream depending upon design. In all separator designs currently used, the amalgam remains at the bottom of the separator or in a chamber filled with water. It is assumed all of the mercury remains in the chamber and very little is discharged into the environment to sewers. This assumption is incorrect.

The American Dental Association (ADA) and most dentists claim the mercury in the amalgam is permanently bonded and is not a hazard. This assumption is incorrect. The mercury in the amalgam not only slowly dissolves in water, but becomes a significant water hazard. The water discharging from an amalgam separator contains three basic types of mercury: Organically bound mercury in biologicals such as blood and tissue, elemental mercury as suspended molecules and dissolved mercury in ionic form. The ADA and EPA are not aware of this issue and assume the one to five percent of the discharge into a waste stream is not significant. This is a false assumption.

If one examines the remaining one percent being discharged into a waste stream, 90 percent may be removed by simple filtration. That still leaves 0.1 percent of the waste stream containing nonfilterable particulate and dissolved and suspended mercury. This represents 1 billion ng/l, and this quantity is diluted by the water used in the dental office; however, readings as high as 1.6 million ng/l of dissolved mercury have been detected at manholes in the street where dilution has occurred. Dissolved mercury is a major hazard entering a wastewater treatment plant and is the most difficult to remove from a waste stream. Purves Environmental and Mercury One LTD have analyzed the discharges from dental offices since 2003 and found that the contribution of dissolved mercury by dental offices to the wastewater treatment plant in a small city is over 100 times greater than residential and industrial influent and is the major contributor of dissolved mercury into the plant. Though separators are considered the solution to the problem, they may be contributors. Design changes have to be made to adequately solve this recognized problem.

Purves Environmental evaluated the discharges from many separators in use in dental offices. All separators in the study were in use for six or more months. The results of the study found elemental and dissolved mercury exiting the separators were in concentrations of 480,000 ng/l or more (up to 7.5 million ng/l). Only one type of separator had consistent quantities below that number: The M.A.R.S.

A bio-med unit consistently had concentrations at 65,000ng/l or lower. When examining the operations of the separators, this was the only unit that had true treatment for dissolved and element mercury built into it. The units contain sulfurized AC filtration as a final step that effectively removed both elemental and dissolved mercury. Comparing the average discharge from a M.A.R.S system to the average of all of the other separators (M.A.R.S. 36,000ng/l versus 484,000ng/l), the M.A.R.S. system demonstrates that particulate, dissolved and elemental mercury removal can be achieved in one separator. Though separators are welcomed as a means to reduce particulate mercury from the environment, the designs must be changed to include removal of dissolved and elemental mercury. If such changes are not implemented, the burden on the wastewater treatment plant will continue to increase and meeting NPDES discharge limits for mercury will become more difficult.

Much more information and training will be provided at the International Activated Carbon Conference and Courses week, Feb. 23-28, 2015. See www.pacslabs.com for details.

 

Editor’s note: Due to space constraints, we have published the Tables mentioned in this article in full online. 

 

 

References

  1. Polanyi, M. Verh. deut. physik. Ges 16, 1012 (1914), 18, 55.
  2. Greenbank, M. Hall of Fame Lecture. Pittsburgh, PA 1999.

Henry Nowicki, Ph.D./M.B.A., is president and senior scientist for Activated Carbon Services, which provides independent routine and advanced laboratory testing, consulting, expert witness, R&D, new product development and marketing and technical short training courses, as well as sponsors the International Activated Carbon Conference and Courses. Nowicki is the conference chairperson. He has been awarded SBIR awards as Principal Scientist on activated carbon projects. He may be contacted by phone at (412) 334-0459 or email at Henry@pacslabs.com.

Barbara Sherman, MS, directs the conference registration and logistics. She may be reached by emailing Barb@pacslabs.com.